Pediatric neurosurgery : tricks of the trade 9781604068696, 1604068698

Table of contents :
Pediatric Neurosurgery: Tricks of the Trade
Media Center Information
Title Page
Copyright
Dedication
Contents
Video Table of Contents
Foreword
Preface
Acknowledgments
Contributors
Section I Introduction
1 Basic Surgical Technique
2 Diagnostic Procedures
3 Neuroanesthesia
4 Pre- and Postoperative Management of the Neurosurgical Patient
5 Pediatric Neurosurgical Positioning
6 Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures
7 Surgical Safety
Section II Neurology
8 Neonatal Neurologic Examination
9 Neurologic Examination of the Child and Adolescent
Section III Congenital Malformations
Section III.A Malformations of the Scalp and Skull
10 Congenital Defects of the Scalp and Skull
11 Deformational Plagiocephaly
12 Nonsyndromic Synostosis: Overview
13 Sagittal Synostosis Repair Surgery
14 Operative Techniques in Cranial Vault Reconstruction: Nonsyndromic Coronal Craniosynostosis
15 The Surgical Repair of Unilateral Coronal Synostosis
16 The Surgical Repair of Metopic Synostosis
17 Syndromic Craniosynostosis
18 Minimally Invasive Craniosynostosis Surgery
19 External Distraction for Frontofacial Advancement
20 The Surgical Management of Craniopagus Twins
Section III.B Malformations of the Brain
21 Malformations of the Cerebral Hemispheres
22 Occipital Encephalocele
23 Surgical Approach to Sphenoethmoidal Encephaloceles
24 The Chiari I Malformation
25 The Chiari II Malformation
Section III.C Malformations of the Spine
26 Craniocervical Junction Abnormalities in Children
27 Disorders of the Vertebral Column
28 Spinal Deformity/Kyphosis
29 Scoliosis
Section III.D Malformations of the Spinal Cord
30 Myelomeningocele
31 Tight Filum Terminale
32 Spinal Tethering Tracts
33 Spinal Lipomas
34 Split Cord Malformation: From Gastrulation to Operation
35 Congenital Spinal Cysts
Section IV Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation
36 The Pathophysiology and Classification of Hydrocephalus
37 Ventricular Shunting for Hydrocephalus
38 Endoscopic Treatment of Hydrocephalus
39 Congenital Intracranial Cysts
40 The Dandy-Walker Malformation
41 Idiopathic Intracranial Hypertension
Section V Trauma
42 Management of Pediatric Scalp Injuries
43 Skull Fractures
44 Traumatic Brain Injury
45 Penetrating Head Injuries
46 Vascular Injuries
47 Abusive Head Injuries
48 Cranioplasty
49 Neurointensive Care of Head Injuries
50 Pediatric Vertebral Column and Spinal Cord Injuries
51 Brachial Plexus Birth Injuries
Section VI Neoplasms
52 Molecular and Genetic Advances in the Treatment of Brain Tumors
Section VI.A Supratentorial Neoplasms
52 Molecular and Genetic Advances in the Treatment of Brain Tumors
54 Pineal Region Tumors
55 Cerebral Hemispheric Tumors
56 Intraventricular Tumors
57 Tumors of the Optic Pathway and Hypothalamus
58 Pituitary Tumors
Section VI.B Infratentorial Neoplasms
59 Cerebellar Astrocytoma
60 Medulloblastoma
61 Infratentorial Ependymomas
62 Pediatric Brainstem Gliomas
63 Intracranial Epidermoids
Section VI.C Scalp, Skull, and Skull Base Neoplasms
64 Tumors of the Scalp and Skull
65 Tumors of the Skull Base and Orbit
Section VI.D Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves
66 Tumors of the Vertebral Column
67 Extramedullary Spinal Cord Tumors
68 Intramedullary Spinal Cord Tumors
69 The Surgical Management of Pediatric Brachial Plexus Tumors
Section VI.E Other
70 The Neurocutaneous Syndromes
71 Adjuvant Chemotherapy and the Role of Neurosurgery for Pediatric Central Nervous System Tumors
72 Adjuvant Radiation Therapy for Pediatric Tumors
Section VII Infections
Section VII.A Cranial
73 Meningitis and Encephalitis
74 Cranial Epidural Abscess and Subdural Empyema
75 Cerebral Abscess
76 Tuberculous, Fungal, and Parasitic Infections
77 Cysticercosis
Section VII.B Spinal
78 Evaluation and Management of Pediatric Spinal Infections
Section VIII Epilepsy and Functional Disorders
79 Epilepsy Classification, Evaluation, and Imaging
80 The Surgical Treatment of Epilepsy: Overview
81 Invasive Monitoring in Pediatric Neurosurgery
82 The Surgical Treatment of Temporal Lobe Epilepsy
83 The Surgical Treatment of Extratemporal Epilepsy
84 The Surgical Treatment of Rolandic Epilepsy in Children
85 Hemispherotomy and Hemispherectomy
86 Palliative Surgical Procedures for Epilepsy
87 The Evaluation and Treatment of Spasticity
88 Intrathecal Therapy for Movement Disorders
89 Microelectrode- Guided Deep Brain Stimulation in Children
90 Interventions for Acute and Chronic Pain in Children
Section IX Vascular Disorders
91 Stroke in Children
92 Pediatric Aneurysms
93 Pediatric Arteriovenous Malformations
94 Cavernous Malformations and Venous Malformations
95 Vein of Galen Aneurysmal Malformations
96 Moyamoya Syndrome/ Pial Synangiosis
97 Surgical Management of Spinal Arteriovenous Malformations
Section X New and Emerging Techniques
98 Advances in Neuroimaging
99 Intraoperative Imaging
100 Interventional Neuroradiology
101 Image- Guided Surgery
102 Advances in Neuroendoscopy
103 Endoscope- Assisted Microsurgery
104 Laser Ablation of Deep Lesions
105 Techniques for Limiting Blood Loss and Blood Transfusions in Pediatric Neurosurgery
Index

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Pediatric Neurosurgery Tricks of the Trade

Alan R. Cohen, MD, FACS, FAAP, FAANS Neurosurgeon-in-Chief Chairman Department of Neurosurgery Boston Children’s Hospital Franc D. Ingraham Professor of Neurosurgery Harvard Medical School Boston, Massachusetts

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Executive Editor: Timothy Hiscock Managing Editor: Elizabeth Palumbo Director, Editorial Services: Mary Jo Casey Editorial Assistant: Nikole Connors Production Editor: Kenneth L. Chumbley International Production Director: Andreas Schabert Vice President, Editorial and E-Product Development: â•…â•…Vera Spillner International Marketing Director: Fiona Henderson International Sales Director: Louisa Turrell Director of Sales, North America: Mike Roseman Senior Vice President and Chief Operating Officer: Sarah Vanderbilt President: Brian D. Scanlan Illustrations by Thomson Press and Emily Ciosek Cover Illustration by Jennifer Pryll Library of Congress Cataloging-in-Publication Data Pediatric neurosurgery (Cohen) Pediatric neurosurgery : tricks of the trade / [edited by] Alan R. Cohen. p. ; cm. ISBN 978-1-60406-869-6 -- ISBN 978-1-60406-870-2 (eISBN) I. Cohen, Alan, 1946- , editor. II. Title. [DNLM: 1. Child. 2. Neurosurgical Procedures—methods. 3. Nervous System Diseases—surgery. WS 340] RD593 617.4’80083—dc23 2015019388

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Contents

Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi Section Iâ•… Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Section Editor: Tae Sung Park

1 Basic Surgical Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Alan R. Cohen 2 Diagnostic Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Chad A. Glenn, Naina L. Gross, and Timothy B. Mapstone 3 Neuroanesthesia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulpicio G. Soriano and Craig D. McClain 4 Pre- and Postoperative Management of the Neurosurgical Patient. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Robert C. Tasker 5 Pediatric Neurosurgical Positioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jonathan A. Pindrik, Sheng-fu Larry Lo, Edward S. Ahn 6 Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Daniel M. Schwartz, Andrew Paul Warrington, Anthony K. Sestokas, and Ann-Christine Duhaime 7 Surgical Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thomas G. Luerssen Section IIâ•… Neurology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section Editor: Scott L. Pomeroy

25 30 51 58 83

89

8 Neonatal Neurologic Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Charles C. Duncan and Laura R. Ment 9 Neurologic Examination of the Child and Adolescent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Jessica H. R. Goldstein and Nancy Bass Section IIIâ•… Congenital Malformations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Section Editor: Concezio Di Rocco

Section III.Aâ•… Malformations of the Scalp and Skull. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 10 Congenital Defects of the Scalp and Skull. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Daniel James Guillaume 11 Deformational Plagiocephaly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mark R. Proctor 12 Nonsyndromic Synostosis: Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . David H. Harter and David A. Staffenberg 13 Sagittal Synostosis Repair Surgery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Douglas Cochrane and Peter Albert Woerdeman 14 Operative Techniques in Cranial Vault Reconstruction: Nonsyndromic Coronal Craniosynostosis . . . . . . . . . . . . . . . . . . . . . . . . . . Christopher C. Chang, Derek M. Steinbacher, Charles C. Duncan, and John A. Persing

105 109 113 119 125

15 The Surgical Repair of Unilateral Coronal Synostosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Jodi L. Smith, Laurie L. Ackerman, and Robert J. Havlik 16 The Surgical Repair of Metopic Synostosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Philipp R. Aldana and Nathan J. Ranalli 17 Syndromic Craniosynostosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Concezio Di Rocco, Paolo Frassanito, Sandro Pelo, and Gianpiero Tamburrini

vii

viii Contents 18 Minimally Invasive Craniosynostosis Surgery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . David F. Jimenez and Constance M. Barone 19 External Distraction for Frontofacial Advancement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Richard D. Hayward and David J. Dunaway 20 The Surgical Management of Craniopagus Twins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . James Tait Goodrich and David A. Staffenberg Section III.Bâ•… Malformations of the Brain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Malformations of the Cerebral Hemispheres. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael D. Partington and Debbie K. Song 22 Occipital Encephalocele. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . James Ayokunle Balogun and James M. Drake 23 Surgical Approach to Sphenoethmoidal Encephaloceles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Robert F. Keating and Derek A. Bruce 24 The Chiari I Malformation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zachary L. Hickman and Neil Feldstein 25 The Chiari II Malformation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hugh J. L. Garton Section III.C Malformations of the Spine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Craniocervical Junction Abnormalities in Children. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arnold H. Menezes 27 Disorders of the Vertebral Column. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Luigi Bassani and Douglas Brockmeyer 28 Spinal Deformity/Kyphosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steven W. Hwang 29 Scoliosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kaine C. Onwuzulike and George H. Thompson Section III.Dâ•… Malformations of the Spinal Cord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Myelomeningocele. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Benjamin C. Warf 31 Tight Filum Terminale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thomas J. Wilson and Karin Muraszko 32 Spinal Tethering Tracts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Casey Madura and Bermans J. Iskandar 33 Spinal Lipomas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tarik Ibrahim, Robin M. Bowman, and David G. McLone

151 158 171

191 193 197 203 210 222

231 233 240 246 252

267 269 274 280 287

34 Split Cord Malformation: From Gastrulation to Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Dachling Pang 35 Congenital Spinal Cysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 Elias Boulos Rizk, R. Shane Tubbs, and W. Jerry Oakes Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Section Editor: John Kestle

36 The Pathophysiology and Classification of Hydrocephalus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . David M. Frim and Ashley Ralston 37 Ventricular Shunting for Hydrocephalus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Walavan Sivakumar, Jay Riva-Cambrin, Vijay M. Ravindra, and John Kestle 38 Endoscopic Treatment of Hydrocephalus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alexandra D. Beier and Abhaya V. Kulkarni 39 Congenital Intracranial Cysts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spyridon Sgouros and Vassilios Tsitouras 40 The Dandy-Walker Malformation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conor Mallucci and Christopher Parks 41 Idiopathic Intracranial Hypertension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sarah J. Gaskill and Arthur E. Marlin

313 316 321 325 330 335

Contents Section Vâ•…

Trauma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Section Editor: George I. Jallo

42 Management of Pediatric Scalp Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arthur Wang, Jordan M. S. Jacobs, and Avinash Mohan 43 Skull Fractures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elizabeth C. Tyler-Kabara 44 Traumatic Brain Injury. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brian T. Farrell and Nathan R. Selden 45 Penetrating Head Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kyle G. Halvorson and Gerald A. Grant 46 Vascular Injuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jeffrey C. Mai, Kyle M. Fargen, Spiros Blackburn, and David W. Pincus 47 Abusive Head Injuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shenandoah Robinson 48 Cranioplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jordan P. Steinberg and Arun K. Gosain 49 Neurointensive Care of Head Injuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ash Singhal and Alexander Ross Hengel 50 Pediatric Vertebral Column and Spinal Cord Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dachling Pang and Sui-To Wong 51 Brachial Plexus Birth Injuries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nathan J. Ranalli and T. S. Park

341 348 355 363 374 379 385 395 399 412

Section VIâ•… Neoplasms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 Section Editor: Frederick A. Boop 52 Molecular and Genetic Advances in the Treatment of Brain Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423 Vijay Ramaswamy, Marc Remke, and Michael D. Taylor Section VI.Aâ•… Supratentorial Neoplasms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429 53 Craniopharyngioma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jeffrey H. Wisoff 54 Pineal Region Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Gordon McComb and Laurence Davidson 55 Cerebral Hemispheric Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Robert P. Naftel, Elizabeth C. Tyler-Kabara, and Ian F. Pollack 56 Intraventricular Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Renee M. Reynolds and Richard G. Ellenbogen 57 Tumors of the Optic Pathway and Hypothalamus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liliana C. Goumnerova 58 Pituitary Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gautam U. Mehta and John A. Jane Jr. Section VI.Bâ•… Infratentorial Neoplasms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

431

59 Cerebellar Astrocytoma. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stephanie L. Da Silva and Mark D. Krieger 60 Medulloblastoma. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lauren Ostling and Corey Raffel 61 Infratentorial Ependymomas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael DeCuypere and Frederick A. Boop 62 Pediatric Brainstem Gliomas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

481

Jonathan Roth and Shlomi Constantini

437 450 457 466 473

479

488 496 502

63 Intracranial Epidermoids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509 Henry W. S. Schroeder Section VI.Câ•… Scalp, Skull, and Skull Base Neoplasms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 64 Tumors of the Scalp and Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523 Nalin Gupta and William Y. Hoffman 65 Tumors of the Skull Base and Orbit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529 Kaisorn L. Chaichana, Ignacio Jusue-Torres, and George I. Jallo

ix

x Contents Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 66 Tumors of the Vertebral Column. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sudhakar Vadivelu and Andrew Jea 67 Extramedullary Spinal Cord Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Timothy W. Vogel and Jeffrey R. Leonard 68 Intramedullary Spinal Cord Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael Weicker and Rick Abbott 69 The Surgical Management of Pediatric Brachial Plexus Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Elias Boulos Rizk and John “Jay” C. Wellons III Section VI.Eâ•… Other. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

537 547 556 563

571

70 The Neurocutaneous Syndromes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573 Herbert E. Fuchs 71 Adjuvant Chemotherapy and the Role of Neurosurgery for Pediatric Central Nervous System Tumors. . . . . . . . . . . . . . . . . . . . . . 584 Mark W. Kieran 72 Adjuvant Radiation Therapy for Pediatric Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589 Thomas E. Merchant

Section VIIâ•… Infections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 Section Editor: A. Graham Fieggen

Section VII.A Cranial. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 73 Meningitis and Encephalitis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dhruve Jeevan and Michael E. Tobias 74 Cranial Epidural Abscess and Subdural Empyema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . William E. Whitehead 75 Cerebral Abscess. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Justin Davis and Thomas A. Pittman 76 Tuberculous, Fungal, and Parasitic Infections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Graham Fieggen and Anthony A. Figaji 77 Cysticercosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tenoch Herrada-Pineda, Juan Antonio Ponce-Gomez, Salvador Manrique-Guzman, and Francisco Revilla-Pacheco

599 605 612 616 630

Section VII.Bâ•… Spinal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641 78 Evaluation and Management of Pediatric Spinal Infections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643 Jonathan Yun, Brian J. A. Gill, and Richard C. E. Anderson Section VIIIâ•… Epilepsy and Functional Disorders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649 Section Editor: Matthew D. Smyth 79 Epilepsy Classification, Evaluation, and Imaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iván Sánchez Fernández and Tobias Loddenkemper 80 The Surgical Treatment of Epilepsy: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hai Sun, Sergey Abeshaus, and Jeffrey G. Ojemann 81 Invasive Monitoring in Pediatric Neurosurgery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jean-Pierre Farmer and Jeffrey Atkinson 82 The Surgical Treatment of Temporal Lobe Epilepsy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Benjamin A. Rubin and Howard L. Weiner 83 The Surgical Treatment of Extratemporal Epilepsy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alexander G. Weil and Sanjiv Bhatia 84 The Surgical Treatment of Rolandic Epilepsy in Children. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christian J. Cantillano Malone and James T. Rutka 85 Hemispherotomy and Hemispherectomy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael H. Handler and Brent O’Neill 86 Palliative Surgical Procedures for Epilepsy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matthew D. Smyth and Aimen S. Kasasbeh 87 The Evaluation and Treatment of Spasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shenandoah Robinson 88 Intrathecal Therapy for Movement Disorders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bruce A. Kaufman

651 662 665 674 684 695 703 712 723 731

Contents 89 Microelectrode-Guided Deep Brain Stimulation in Children. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737 Ron L. Alterman and Irene P. Osborn 90 Interventions for Acute and Chronic Pain in Children. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742 Charles Berde Section IXâ•… Vascular Disorders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753 Section Editor: R. Michael Scott 91 Stroke in Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cormac O. Maher 92 Pediatric Aneurysms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allyson Alexander and Michael S. B. Edwards 93 Pediatric Arteriovenous Malformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Graciela Zuccaro and Javier González Ramos 94 Cavernous Malformations and Venous Malformations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christopher David Kelly and Raphael Guzman 95 Vein of Galen Aneurysmal Malformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alejandro Berenstein and Srinivasan Paramasivam 96 Moyamoya Syndrome/Pial Synangiosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Edward R. Smith and R. Michael Scott 97 Surgical Management of Spinal Arteriovenous Malformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shakeel A. Chowdhry and Robert F. Spetzler Section Xâ•… New and Emerging Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section Editor: James M. Drake 98 Advances in Neuroimaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Edward Yang and Caroline D. Robson 99 Intraoperative Imaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paul Klimo Jr., David J. Daniels, and Asim F. Choudhri 100 Interventional Neuroradiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bradley A. Gross, Michael J. Ellis, and Darren Orbach 101 Image-Guided Surgery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yair M. Gozal and Timothy W. Vogel 102 Advances in Neuroendoscopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Robert P. Naftel and John “Jay” C. Wellons III 103 Endoscope-Assisted Microsurgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Henry W. S. Schroeder 104 Laser Ablation of Deep Lesions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joseph R. Madsen 105 Techniques for Limiting Blood Loss and Blood Transfusions in Pediatric Neurosurgery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paul Steinbok

755 759 768 779 788 799 805

815 817 827 834 841 846 853 860 867

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875

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Video Table of Contents

Video Editor: Timothy W. Vogel



1 Basic Surgical Technique



9 Neurological Examination of the Child and Adolescent

Alan R. Cohen

Jessica H. R. Goldstein and Nancy Bass

13 Sagittal Synostosis Repair Surgery Limited Vertex Craniectomy and Postoperative Helmetting Sagittal Synostosis: Open Technique D. Douglas Cochrane and Peter Albert Woerdeman

15 The Surgical Repair of Coronal Synostosis Jodi L. Smith

16 Metopic Synostosis: Bifrontal Craniotomy and Supraorbital Advancement Philipp R. Aldana and Nathan J. Ranalli

18 Minimally Invasive Endoscopic Treatment of Sagittal Synostosis David F. Jimenez and Constance M. Barone

24 The Chiari I Malformation Neil Feldstein

27 Anterior Cervical Discectomy and Fusion Douglas Brockmeyer

28 Spinal Osteotomies Steven W. Hwang

31 Tight Filum Terminale Karin Muraszko

33 Surgical Management of Spinal Lipomas

Tarik Ibrahim, Robin M. Bowman, and David G. McLone

37 Ventriculoperitoneal Shunt Placement

Jay Riva-Cambrin, John Kestle, Vijay M. Ravindra, and Walavan Sivakumar

38 Endoscopic Third Ventriculostomy: Tectal Glioma with Hydrocephalus Abhaya V. Kulkarni

39 Suprasellar Arachnoid Cyst Spyridon Sgouros

41 Idiopathic Intracranial Hypertension Sarah J. Gaskill

44 External Ventricular Drain Insertion in an Infant Lissa C. Baird and Nathan R. Selden

51 Brachial Plexus Repair Surgery T. S. Park

55 Cerebral Hemispheric Tumors Ian F. Pollack and Robert P. Naftel

59 Cerebellar Astrocyotoma Mark D. Krieger

60 Medulloblastoma

Lauren Ostling and Corey Raffel

61 Posterior Fossa Ependymoma Frederick A. Boop

63 Intracranial Epidermoids Henry W. S. Schroeder

65 Tumors of the Skull Base and Orbit George I. Jallo

77 Neurocysticercosis: Endoscopic Treatment Tenoch Herrada-Pineda

82 The Surgical Treatment of Temporal Lobe Epilepsy Benjamin A. Rubin and Howard L. Weiner

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Video Table of Contents 86 Palliative Surgical Procedures for Epilepsy Matthew D. Smyth

89 Deep Brain Stimulation for Movement Disorders Ron L. Alterman

93 Arteriovenous Malformations Graciela Zuccaro

94 Cavernous Malformations and Venous Malformations Raphael Guzman

95 Vein of Galen Malformations

Alejandro Berenstein and Srinivasan Paramasivam

97 Compact Intramedullary Spinal Arteriovenous Malformation Shakeel A. Chowdhry and Robert F. Spetzler

102 Advances in Neuroendoscopy

Robert P. Naftel and John “Jay” C. Wellons III

103 Endoscope-Assisted Microsurgery Henry W. S. Schroeder

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Foreword Most neurosurgeons are familiar with the quote Ars longa, vita brevis—the art is long, life is short. Although written in Latin, this quote is ascribed to the ancient Greek physician Hippocrates, from his work entitled Aphorismi. Perhaps unlike any other neurosurgical subspecialty, pediatric neurosurgery is a discipline of nuances in which the subtleties of practice are brought to bear over the course of one’s professional career. Even then, a lifetime is insufficient to learn everything. Of course, I speak of both the cognitive and the procedural sides of pediatric neurosurgery. Our practice of pediatric neurosurgery is, after all, an amalgam of time-honored methods that have been passed on to us from our mentors, who learned in a similar manner from their mentors, in a cycle dating back to the origins of pediatric neurosurgery with Franc Ingraham at the Children’s Hospital in Boston, who himself was a disciple of the founding father of organized neurosurgery, Harvey Cushing. What better way is there for us to appreciate and learn the wisdom of the ages in pediatric neurosurgery than to adapt the teachings of experts who have imparted their knowledge to us in this unique and accessible textbook. In Pediatric Neurosurgery: Tricks of the Trade, residents, fellows, and neurosurgeons alike will find an up-to-date compendium of Pearls and Pitfalls involving approaches to pediatric neurosurgical conditions that will help improve the delivery of patient care and satisfy best practices. From patient positioning, to neuroanesthetic considerations, to optimum postoperative management, it is clear that this textbook transcends the typical multiauthored textbook on the technical aspects of pediatric neurosurgery. I was thus pleased to see the attention paid to neurosurgical judgment throughout all chapters, as it is just as important to know when to operate as to know when not to. In addition, care was taken to ensure that the content of the textbook was comprehensive, innovative, and timely. As examples, chapters on the management of scoliosis, external distraction for frontofacial advancement, intrathecal therapy for movement disorders, and laser ablation for deep brain lesions would not have existed in textbooks written for pediatric neurosurgeons a decade ago.

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Pediatric Neurosurgery: Tricks of the Trade is also replete with superior video content that demonstrates, step-by-step, critical aspects of the various neurosurgical procedures, from patient positioning, to the skin incision, to the craniotomy, to the intradural phase of the operation. Tricks of the trade are liberally provided throughout the voice-over comments from the videos. You will see and learn how to bevel your scissors while opening the dura in order to avoid cortical venous lacerations; to open the blades of an endoscopic forceps in the coronal plane when performing an endoscopic third ventriculostomy to avoid injuring the basilar artery; and to preserve the ependyma beneath the corpus callosum to avoid a cerebrospinal fluid disturbance postoperatively during corpus callosotomy, among many, many other pearls and tricks. The videos are a major strength of the textbook and are edited at a perfect length for learners, being set at 3 to 5 minutes to capture the neurosurgical essence of each procedure. Benjamin Franklin once wrote: “Tell me and I forget; teach me, and I may remember; involve me, and I learn.” This quote is particularly applicable to the present textbook, as the charge to the authors for each chapter was to write the definitive work on the subject area and to provide caveats and experiential knowledge so that readers could not only have the best academic resource at their fingertips on a given pediatric neurosurgical condition, but could also practice complication avoidance by carefully observing the advice that has been handed down to us by our sage predecessors. To return to Franklin’s quote in closing, Pediatric Neurosurgery: Tricks of the Trade is an example of the ultimate method of teaching as it involves all of us in an exercise in learning that is unlikely to be duplicated for years to come. We owe Alan Cohen, editor, and the authors of each chapter a big debt of gratitude for providing us with a tome that will help all of us better look after our patients and achieve the best outcomes possible, though the art is long. James T. Rutka, MD, PhD, FRCS(C), FACS, FAAP, FAANS R. S. McLaughlin Professor and Chair Department of Surgery Division of Neurosurgery The Hospital for Sick Children University of Toronto Toronto, Ontario, Canada

Preface “Simplicity is the ultimate sophistication.” Leonardo da Vinci

The practice of pediatric neurosurgery is one of the most remarkable and rewarding endeavors in all of medicine. The ability to help alleviate suffering and restore health to an ailing, sometimes gravely stricken child, is an extraordinary privilege granted to a limited few. It is this special privilege that makes the many arduous years of training in pediatric neurosurgery bearable. By and large, pediatric neurosurgery is a difficult field. Surgical disorders of the developing nervous system are often complex and present exceptional challenges to the pediatric neurosurgeon, who must learn to master a broad field in great depth over a limited time. It is essential for the pediatric neurosurgeon to acquire a detailed understanding of a vast amount of specialized anatomy, pathology, and pathophysiology that is constantly changing throughout childhood. The explosion of knowledge in the last decade about the molecular and genetic bases for neurosurgical disorders is a bit overwhelming and will form the basis for more effective, tailored treatments for our patients. At the same time, advances in neurodiagnostic imaging and improvements in surgical instrumentation are occurring at a rapid pace. The field is becoming so complex that it is sometimes difficult to comprehend. This book is an attempt to simplify some of these complexities. Its purpose is twofold: (1) to present a concise overview of the current state-of-the-art of pediatric neurosurgery as elaborated by expert colleagues from around the world; and (2) to provide the reader with a blueprint for enhancing performance and achieving excellence in the operating room. Great surgeons, like great musicians, possess an elusive skill set that is easy to recognize but harder to define. The consistent features appear to be a unique combination of inherent technical ability that has been refined by meticulous, painstaking practice—a combination that has ultimately brought these per-

formers to a state of seasoned wisdom. Just as there are many ways to play the same tune, there are many ways to carry out the same operation. And some clearly work out better than others. Why is that? What is it that makes certain surgeons exceptional and others only good or average at best? What are the factors necessary to deliver a virtuoso performance? What measures can we take to improve our proficiency in the operating room? Surely, nature plays an important role, as some surgeons seem to operate with innate, effortless dexterity right from the get go. But inborn ability is only part of the picture, and it’s not worth focusing on this too much since there’s little we can do to alter our genetic heritage. Fortunately, there’s much that can be done to perfect our technique, enhance our performance, and improve our outcomes. We can learn a lot from the experience of others. One major key to success, I believe, is using the actions of others, both good and bad, to improve our own abilities. Surgical judgment develops over time. Astute practitioners learn much from their own mistakes and from the mistakes of others. Elite performance is the result of patience, practice, and perseverance. Elite performers demonstrate an economy of movement in the OR. They are deeply focused on the problem at hand and the paramount goal of getting the patient safely through the procedure, whether it is the removal of a small dermoid cyst from the skull or a large cavernous malformation from the medulla. They come to the OR well prepared. They are organized. They use checklists. They have learned to remain methodical and calm, even in the presence of crisis. They respect their colleagues and inspire the OR staff to work together as a team. My hope is that this book will provide pediatric neurosurgeons with a strategy for becoming elite performers. This is a book about the art of pediatric neurosurgery. It is intended to fill a void. There are xv

xvi Preface numerous publications about the details of pediatric neurosurgical disorders, including journal articles, didactic texts, and atlases of anatomy and surgery. What is missing is a personal account of the journey, a compilation of the wisdom of the masters, a tricks of the trade of pediatric neurosurgery in which experts share what they have learned from past experiences, both their successes and their mistakes. Much of what separates a great neurosurgeon from a good neurosurgeon is nuance. Many times a subtle operative maneuver here or there can simplify a difficult procedure or prevent a dangerous or catastrophic event later on. This book is a collection of pedia-

tric neurosurgical operations written by masters from around the world who share their personal surgical pearls, operative nuances, procedural refinements, and techniques for avoiding pitfalls and for dealing with them should they occur. I hope that these nuances from the masters will inspire readers to improve their skill sets and to set higher expectations for themselves. I hope this will lead them to pursue intense, focused, deliberate practice in an effort to achieve excellence in the operating room.

Alan R. Cohen, MD Boston, Massachusetts

Acknowledgments He who studies medicine without books sails an uncharted sea, but he who studies medicine without patients does not go to sea at all. Sir William Osler

I wish to extend my heartfelt thanks to the parents of my patients for entrusting me with the care of those whom they hold most dear in the world. It is a great privilege to be a pediatric neurosurgeon and to share the lives and dreams of these courageous young resil� ient heroes, who have taught me more about neurosurgery than I could have ever imagined. I am also most grateful to Thieme Publishers for helping me bring this book to fruition. I was fortu�nate

to be guided by an expert editorial and production team who brought a passion to the project that I cannot repay. In particular, I would like to thank Kay Conerly, Judith Tomat, Sara D’Emic, Liz Palumbo, Nikole Connors, Kenny Chumbley, and Tim Hiscock. Finally, I thank Jennifer Pryll, whose beautiful artwork graces the book’s cover. Alan R. Cohen, MD

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Contributors Rick Abbott, MD Professor, Clinical Neurosurgery Department of Neurosurgery Albert Einstein College of Medicine Bronx, New York Sergey Abeshaus,€MD Attending Neurosurgeon Department of Neurological Surgery Pediatric Neurosurgery Unit Rambam Health Care Campus Haifa, Israel Laurie L. Ackerman, MD, FAANS Assistant Professor Department of Neurosurgery Riley Hospital for Children at Indiana University Health Goodman Campbell Brain and Spine Indianapolis, Indiana Edward S. Ahn, MD Associate Professor of Neurosurgery, Pediatrics, and Plastic Surgery Division of Pediatric Neurosurgery The Johns Hopkins University School of Medicine Baltimore, Maryland Philipp R. Aldana, MD Associate Professor and Chief€€€€€ Department of Neurosurgery University of Florida College of Medicine–Jacksonville€€€€€€€€€€€ Jacksonville, Florida Allyson Alexander, MD, PhD Neurosurgery Division of Pediatric Neurosurgery Lucile Packard Children’s Hospital Stanford University School of Medicine Stanford, California Ron L. Alterman, MD Professor of Neurosurgery Harvard Medical School Chief, Division of Neurosurgery Beth Israel Deaconess Medical Center Boston, Massachusetts

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Richard C. E. Anderson, MD, FACS, FAAP Associate Professor, Division of Pediatric Neurosurgery Department of Neurological Surgery Columbia University Morgan Stanley Children’s Hospital of New York Presbyterian New York, New York Jeffrey Atkinson, MD, FRCS(c) Paediatric Neurosurgeon€ McGill University Health Centre Assistant Professor Departments of Neurology, Neurosurgery, and Paediatric Surgery McGill University Montreal, Quebec, Canada€ Lissa C. Baird, MD Pediatric Neurosurgeon Medical Director of Pediatric Neuro-oncology Oregon Health & Science University Portland, Oregon James Ayokunle Balogun, MBBS, FWACS Division of Pediatric Neurosurgery The Hospital for Sick Children Toronto, Ontario, Canada Constance M. Barone, MD, FACS Professor of Neurosurgery Department of Neurosurgery University of Texas Health Science Center San Antonio, Texas Nancy Bass, MD Associate Professor Department of Pediatrics and Neurology Case Western Reserve University School of Medicine Rainbow Babies and Children’s Hospital Case Western Reserve University Cleveland, Ohio

Contributors╅ Luigi Bassani, MD Assistant Professor Director of Pediatric Neurosurgery Rutgers New Jersey Medical School Newark, New Jersey Alexandra D. Beier, DO, FACOS Assistant Professor of Neurosurgery and Pediatrics Division of Pediatric Neurosurgery University of Florida Health–Jacksonville Jacksonville, Florida Charles Berde, MD, PhD Sara Page Mayo Chair Chief, Division of Pain Medicine Department of Anesthesiology, Perioperative, and Pain Medicine Boston Children’s Hospital Professor Department of Anaesthesia (Pediatrics) Harvard Medical School Boston, Massachusetts Alejandro Berenstein, MD Site Chair Senior Faculty Neurosurgery, Radiology, Pediatrics Institute of Neurology and Neurosurgery Mount Sinai Roosevelt Mount Sinai St. Luke’s New York, New York Sanjiv Bhatia, MD, FACS Pediatric Neurosurgery Miami Children’s Hospital Associate Professor Department of Neurosurgery University of Miami Miller School of Medicine Miami, Florida

Robin M. Bowman, MD Associate Professor Department of Neurological Surgery Northwestern University Feinberg School of Medicine Evanston, Illinois Douglas Brockmeyer, MD Professor of Neurosurgery Chief of Pediatric Neurosurgery Department of Neurosurgery University of Utah Salt Lake City, Utah Derek A. Bruce, MB, ChB Professor of Neurosurgery and Pediatrics Center for Neuroscience and Behavioral Medicine Children’s National Medical Center Washington, DC Christopher C. Chang, MD Craniofacial Surgery Department of Plastic Surgery The Johns Hopkins Hospital University of Maryland Shock Trauma Center Baltimore, Maryland Kaisorn L. Chaichana, MD Assistant Professor of Neurosurgery, Oncology, and Otolaryngology Department of Neurosurgery Johns Hopkins Hospital€ Baltimore, Maryland

Spiros Blackburn, MD Assistant Professor Department of Neurosurgery University of Florida Gainesville, Florida

Asim F. Choudhri, MD Associate Chair–Research Affairs Department of Radiology Associate Professor of Radiology, Ophthalmology, and Neurosurgery University of Tennessee Health Science Center Director of Neuroradiology Le Bonheur Neuroscience Institute Le Bonheur Children’s Hospital Memphis, Tennessee

Frederick A. Boop, MD Professor and Chairman Department of Neurosurgery University of Tennessee Health Sciences Center Semmes-Murphey Clinic Memphis, Tennessee

Shakeel A. Chowdhry, MD Department of Neurosurgery Northshore University Health System Assistant Professor University of Chicago Pritzker School of Medicine Chicago, Illinois

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xx Contributors D. Douglas Cochrane, MD, FRCS(C) Head, Division of Neurosurgery Professor of Surgery Department of Pediatric Surgery Department of €Surgery British Columbia Children’s Hospital University€of€British Columbia Vancouver, British Columbia, Canada Alan R. Cohen, MD, FACS, FAAP, FAANS Neurosurgeon-in-Chief Chairman Department of Neurosurgery Boston Children’s Hospital Franc D. Ingraham Professor of Neurosurgery Harvard Medical School Boston, Massachusetts€ Shlomi Constantini, MD, MSc Professor and Director Department of Pediatric Neurosurgery The Israeli Neurofibromatosis Center Dana Children’s Hospital Tel-Aviv Medical Center Tel Aviv University Tel Aviv, Israel David J. Daniels, MD, PhD Assistant Professor of Neurosurgery Pediatric Neurosurgery Mayo Clinic Rochester, Minnesota Stephanie L. Da Silva, BA Clinical Research Coordinator€ Division of Neurosurgery Children’s Hospital Los Angeles Los Angeles, California Laurence Davidson, MD, FAANS Director, Pediatric Neurosurgery Division of Neurosurgery Walter Reed National Military Medical Center Assistant Professor of Surgery and Pediatrics Uniformed Services University of the Health Sciences Bethesda, Maryland Justin Davis, MD Department of Neurological Surgery Neuroscience Associates of Kansas City Overland Park, Kansas Michael DeCuypere, MD, PhD Department of Neurosurgery University of Tennessee Health Science Center Memphis, Tennessee

Concezio Di Rocco, MD Professor Director of Pediatric Neurosurgery International Neuroscience Institute Hannover, Germany James M. Drake, BSE, MBBCh, MSc, FRCS(C), FACS Division Head, Pediatric Neurosurgery Professor of Surgery University of Toronto Shoppers Drug Mart Harold Hoffman Chair Pediatric Neurosurgery Director, Centre for Image Guided Innovation and Therapeutic Intervention The Hospital for Sick Children Toronto, Ontario, Canada Ann-Christine Duhaime, MD Director, Pediatric Neurosurgery Massachusetts General Hospital Professor Department of Neurosurgery Harvard Medical School Boston, Massachusetts David J. Dunaway, FDSRCS, FRCS Specialty Lead for Craniofacial Surgery Great Ormond Street Hospital London, England Charles C. Duncan, MD Professor of Neurosurgery and Pediatrics Department of Neurosurgery Yale School of Medicine New Haven, Connecticut Michael S. B. Edwards, MD, FAANS, FACS, FAAP Lucile Packard Endowed Professor of Neurosurgery and Pediatrics Co-Director, Center for Children’s Brain Tumors at Stanford Department of Neurosurgery Stanford University Lucile Packard Children’s Hospital Stanford Stanford, California Richard G. Ellenbogen, MD, FACS Professor and Chairman Department of Neurological Surgery Theodore S. Roberts Endowed Chair Director, Neurosciences Institute University of Washington School of Medicine Seattle Children’s Hospital Seattle, Washington

Contributors Michael J. Ellis, MD, FRCS(C) € €€ Medical Director Pan Am Concussion Program Department of Surgery and Pediatrics Section of Neurosurgery University of Manitoba € Co-Director, Canada North Concussion Network Scientist, Children’s Hospital Research Institute of Manitoba€ Winnipeg, Manitoba, Canada Kyle M. Fargen, MD, MPH Faculty Department of Neurosurgery University of Florida Gainesville, Florida Jean-Pierre Farmer, MD, CM, FRCS(C) Dorothy Williams Professor and Chair Department of Pediatric Surgery Professor of Neurosurgery, Pediatric Surgery, Oncology, and Surgery€ McGill University Surgeon-in-Chief and Director Neurosurgery Division The Montreal Children’s Hospital McGill University Health Centre Montreal, Quebec, Canada Brian T. Farrell, MD, PhD Department of €Neurological Surgery Oregon Health€& Science University€ Portland, Oregon Neil Feldstein, MD, FACS Associate Professor Neurological Surgery Department of Neurological Surgery New York Presbyterian Hospital Columbia University Medical Center Director, Pediatric Neurological€Surgery Morgan Stanley Children’s Hospital€ New York, New York Iván Sánchez Fernández, MD Division of Epilepsy and Clinical Neurophysiology Department of Neurology Boston Children’s Hospital Harvard Medical School Boston, Massachusetts A. Graham Fieggen, MSc, MD, FC Neurosurg(SA) Helen and Morris Mauerberger Professor and Head Division of Neurosurgery University of Cape Town Cape Town, South Africa

Anthony A. Figaji, MMed, PhD, FC Neurosurg(SA) SARChI Professor of Clinical Neuroscience Division of Neurosurgery University of Cape Town Cape Town, South Africa Paolo Frassanito, MD Consultant Pediatric Neurosurgery Catholic University Medical School Rome, Italy David M. Frim, MD, PhD Ralph Cannon Professor and Chief Section of Neurosurgery University of Chicago Chicago, Illinois Herbert E. Fuchs, MD, PhD, FAANS, FAAP, FACS Associate Professor of Surgery Division of Neurosurgery Chief of Pediatric Neurosurgical Services Department of Surgery Duke University Medical Center Durham, North Carolina Hugh J. L. Garton, MD, MHSc Associate Professor Department of Neurosurgery University of Michigan Ann Arbor, Michigan Sarah J. Gaskill, MD Professor Department of Neurosurgery and Brain Repair Division of Pediatric Neurosurgery University of South Florida Tampa, Florida Brian J. A. Gill, MD Department of Neurological Surgery Columbia-New York Presbyterian Hospital€ New York, New York Chad A. Glenn, MD Department of Neurosurgery University of Oklahoma Health Sciences Center Oklahoma City, Oklahoma Jessica H. R. Goldstein, MD Assistant Professor of Pediatrics Department of Pediatric Neurology Case Western Reserve University School of Medicine Rainbow Babies and Children’s Hospital Cleveland, Ohio

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xxii Contributors James Tait Goodrich, MD, PhD, DSci (Hon) Director, Division of Pediatric Neurosurgery Children’s Hospital at Montefiore Professor of Clinical Neurosurgery, Pediatrics, Surgery (Plastic and Reconstructive Surgery) Leo Davidoff Department of Neurological Surgery Albert Einstein College of Medicine Bronx, New York Arun K. Gosain, MD, FACS, FAAP Professor and Chief Division of Pediatric Plastic Surgery Lurie Children’s Hospital Northwestern University Feinberg School of Medicine Chicago, Illinois Yair M. Gozal, MD, PhD Department of Neurosurgery University of Cincinnati College of Medicine Cincinnati, Ohio Liliana C. Goumnerova, MD, FRCS(C), FAANS Director, Pediatric Neurosurgical Oncology Boston Children’s Hospital/Dana Farber Cancer Institute Associate Professor of Neurosurgery Harvard Medical School Department of Neurosurgery Boston Children’s Hospital Boston, Massachusetts Gerald A. Grant, MD, FACS€ Associate Professor Department of Neurosurgery€ Chief of Pediatric Neurosurgery Lucile Packard Children’s Hospital Stanford University Stanford, California Bradley A. Gross, MD Department of Neurosurgery Brigham and Women’s Hospital and Harvard Medical School Boston, Massachusetts Naina L. Gross, MD Assistant Professor Department of Neurosurgery University of Oklahoma Oklahoma City, Oklahoma Daniel James Guillaume, MD Associate Professor Department of Neurosurgery University of Minnesota Minneapolis, Minnesota

Nalin Gupta, MD, PhD Benioff UCSF Professor in Children’s Health Departments of Neurological Surgery and Pediatrics University of California–San Francisco Chief, Division of Pediatric Neurosurgery UCSF Benioff Children’s Hospital San Francisco, California Raphael Guzman, MD Professor of Neurosurgery Vice Chair and Chief, Pediatric Neurosurgery Department€of Neurosurgery Division of Pediatric Neurosurgery University Children’s Hospital of Basel Basel, Switzerland Kyle G. Halvorson, MD Department of Surgery Duke University Medical Center Durham, North Carolina Michael H. Handler, MD, FACS, FAAP McMurry Seebaum Chair and Chief of Pediatric Neurosurgery Professor University of Colorado School of Medicine Denver, Colorado David H. Harter, MD Assistant Professor of Neurosurgery Division of Pediatric Neurosurgery New York University New York, New York Robert J. Havlik, MD Chairman Department of Plastic Surgery Medical College of Wisconsin Milwaukee, Wisconsin Richard D. Hayward, MBBS, FRCS(Eng) Professor Department€of Pediatric Neurosurgery Great Ormond Street Hospital for Children NHS Trust London, England Alexander Ross Hengel, BSc Clinical Research Coordinator Department of Surgery Division of Pediatric Neurosurgery University of British Columbia Vancouver, British Columbia, Canada Tenoch Herrada-Pineda, MD Department of Pediatric Neurosurgery ABC Medical Center Mexico City, Mexico

Contributors Zachary L. Hickman, MD Department of Neurological Surgery New York-Presbyterian Hospital Columbia University Medical Center Department of Neurological Surgery Morgan Stanley Children’s Hospital Columbia University Medical Center New York, New York William Y. Hoffman, MD, FAAP Professor and Chief University of California–San Francisco Plastic Surgery Stephen J. Mathes Endowed Chair Vice Chair, Department of Surgery University of California–San Francisco San Francisco, California Steven W. Hwang, MD Assistant Professor€ Department of Neurosurgey Tufts Medical Center Chief of Pediatric Neurosurgery Floating Hospital for Children Boston, Massachusetts Tarik Ibrahim, MD Department of Neurological Surgery Loyola University Chicago, Illinois Bermans J. Iskandar, MD Professor of Neurosurgery and Pediatrics Director, Pediatric Neurosurgery Department of Neurological Surgery University of Wisconsin Hospital and Clinics Madison, Wisconsin Jordan M. S. Jacobs, MD Assistant Professor of Plastic Surgery Department of Surgery Mount Sinai Health System Director Westchester Cleft and Craniofacial Teams New York, New York George I. Jallo, MD Professor of Neurosurgery, Pediatrics and Oncology Director, Pediatric Neurosurgery Department of Neurosurgery The Johns Hopkins University Baltimore, Maryland

John A. Jane Jr., MD Professor of Neurosurgery and Pediatrics Department of Neurosurgery University of Virginia Health System Charlottesville, Virginia Andrew Jea, MD Associate Professor Department of Neurosurgery Baylor College of Medicine Staff Neurosurgeon Director, Neuro-Spine Program Director, Educational Programs Texas Children’s Hospital Houston, Texas€ Dhruve Jeevan, MD, MA Department of Neurosurgery The Hospital for Sick Children University of Toronto Toronto, Ontario, Canada David F. Jimenez, MD, FACS Professor and Chairman Department of Neurosurgery University of Texas Health Science Center San Antonio, Texas Ignacio Jusue-Torres, MD Salisbury Fellow Department of Neurosurgery The Johns Hopkins University School of Medicine Baltimore, Maryland Aimen S. Kasasbeh, MD, PhD Neural Engineering Laboratory Mayo Clinic Rochester, Minnesota Bruce A. Kaufman, MD Professor Department of Neurosurgery Medical College of Wisconsin Chief, Pediatric Neurosurgery Children’s Hospital of Wisconsin Milwaukee, Wisconsin Robert F. Keating, MD Professor and Chief Division of Neurosurgery Children’s National Medical Center George Washington University School of Medicine Washington, DC€

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xxiv Contributors Christopher David Kelly, MD Department of Neurosurgery University Hospital Basel Basel, Switzerland John Kestle, MD Professor and Vice Chair, Clinical Research Department of Neurosurgery University of Utah Salt Lake City, Utah Mark W. Kieran, MD, PhD€€€€€€€€€€ Director, Pediatric Medical Neuro-Oncology€€€€€€ Department of Pediatric Hematology/Oncology Dana-Farber Cancer Institute Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Paul Klimo Jr., MD, MPH Chief, Pediatric Neurosurgery Le Bonheur Children’s Hospital Department of Neurosurgery Semmes-Murphey Neurologic and Spine Institute Memphis, Tennessee Mark D. Krieger, MD Billy and Audrey Wilder Chair Division of Neurosurgery Children’s Hospital Los Angeles Professor, Department of Neurological Surgery Keck School of Medicine University of Southern California Los Angeles, California Abhaya V. Kulkarni, MD, PhD, FRCS(C) Professor and Neurosurgeon Division of Neurosurgery The Hospital for Sick Children University of Toronto Toronto, Ontario, Canada Jeffrey R. Leonard, MD, FAANS Neurosurgeon-in Chief Department of Pediatric Neurosurgery Nationwide Children’s Hospital Professor Department of Neurological Surgery The Ohio State Medical School Columbus, Ohio Sheng-fu Larry Lo, MD, MHS Department of Neurosurgery The Johns Hopkins University Baltimore, Maryland

Tobias Loddenkemper, MD Director of Clinical Epilepsy Research Division of Epilepsy and Clinical Neurophysiology Associate Professor Department of Neurology Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Thomas G. Luerssen, MD, FACS, FAAP Chief, Pediatric Neurological Surgery Chief Quality Officer–Surgery Texas Children’s Hospital Professor of Neurological Surgery Department of Neurological Surgery Baylor College of Medicine Houston, Texas Joseph R. Madsen, MD Director, Epilepsy Surgery Program Associate Professor of Neurosurgery Department of Neurosurgery Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Casey Madura, MD Department of Neurosurgery University of Wisconsin Hospital and Clinics Madison, Wisconsin Cormac O. Maher, MD Associate Professor Department of Neurosurgery University of Michigan Ann Arbor, Michigan Jeffrey C. Mai, MD, PhD Neurosurgeon Inova Medical Group Neurosurgery Fairfax, Virginia Conor Mallucci, MBBS, FRCS Consultant Paediatric Neurosurgeon€ Department of Neurosurgery Alder Hey Children’s NHS Foundation Trust€ Liverpool, England Christian J. Cantillano Malone, MD Paediatric Neurosurgery and Epilepsy Departamento de Neurocirugía€ Pontificia Universidad Católica de Chile Hospital Sotero del Rio Santiago, Chile€

Contributors Salvador Manrique-Guzman, MD,€MSc Neurosurgeon Department of€Neurosurgery€ ABC Medical Center Mexico City, Mexico

Laura R. Ment, MD Associate Dean and Professor Departments of Pediatrics and Neurology Yale School of Medicine New Haven, Connecticut

Timothy B. Mapstone, MD Wilkins Professor and Chairman Department of Neurological Surgery The University of Oklahoma Health Sciences Center Oklahoma City, Oklahoma

Thomas E. Merchant, DO, PhD Member and Chairman Department of Radiation Oncology Baddia J. Rashid Endowed Chair in Radiation Oncology St. Jude Children’s Research Hospital Memphis, Tennessee

Arthur E. Marlin, MD, MHA Professor of Neurosurgery Division of Pediatric Neurosurgery University of South Florida Tampa, Florida Craig D. McClain, MD, MPH Senior Associate in Perioperative Anesthesia Assistant Professor of Anaesthesia Boston Children’s Hospital Harvard Medical School Boston, Massachusetts J. Gordon McComb, MD Chief Emeritus Division of Neurosurgery Children’s Hospital of Los Angeles Professor Department of Neurological Surgery University of Southern California Keck School of Medicine Los Angeles, California David G. McLone, MD, PhD Chief Emeritus of Pediatric Neurosurgery Children’s Memorial Hospital Professor Northwestern University Feinberg School of Medicine Ann and Robert H. Lurie Children’s Hospital of Chicago Chicago, Illinois Gautam U. Mehta, MD Department of Neurosurgery University of Virginia Health System Charlottesville, Virginia Arnold H. Menezes, MD Professor and Vice Chairman Department of Neurosurgery University of Iowa Hospitals and Clinics Iowa City, Iowa

Avinash Mohan, MD Assistant Professor of Neurosurgery and Pediatrics Department of Neurosurgery New York Medical College Valhalla, New York Karin Muraszko, MD Chair and Julian T. Hoff, MD, Professor, Neurological Surgery Professor, Pediatrics and Communicable Diseases Professor, Plastic Surgery University of Michigan Ann Arbor, Michigan Robert P. Naftel, MD Assistant Professor Department of Neurosurgery Vanderbilt University Nashville, Tennessee W. Jerry Oakes, MD€€€€€€€€€€€€€€€€€€€€€€€€€€ Professor of Neurosurgery and Pediatrics Surgeon-in-Chief Department of Neurosurgery Children’s of Alabama Birmingham, Alabama Jeffrey G. Ojemann, MD Professor of Neurological Surgery Richard G. Ellenbogen Chair in Pediatric Neurosurgery Seattle Children’s Hospital Seattle, Washington Brent O’Neill, MD Assistant Professor Department of Neurosurgery University of Colorado School of Medicine Children’s Hospital Colorado Aurora, Colorado

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xxvi Contributors Kaine C. Onwuzulike, MD, PhD Department of Neurosurgery University of Utah School of Medicine Salt Lake City, Utah Darren Orbach, MD, PhD Division Chief Interventional and Neurointerventional Radiology Boston Children’s Hospital Boston, Massachusetts Irene P. Osborn, MD Associate Professor of Anesthesiology Albert Einstein College of Medicine Director, Division of Neuroanesthesia Mountefiore Medical Center Bronx, New York Lauren Ostling, MD Clinical Instructor Department of Neurological Surgery University of California–San Francisco School of Medicine San Francisco, California Dachling Pang, MD, FRCS(C), FRCS(Eng), FACS Professor of Paediatric Neurosurgery University€of€California–Davis Chief, Regional Centre for Paediatric Neurosurgery Kaiser Permanente Hospitals Northern California Oakland, California Srinivasan Paramasivam, MD, MRCS Ed Assistant Professor Department of Neurosurgery–Cerebrovascular Program Mount Sinai Health System New York, New York T. S. Park, MD Neurosurgeon-in-Chief St. Louis Children’s Hospital Shi H, Huang Professor or Neurological Surgery Washington University St. Louis, Missouri Christopher Parks, BSc, MBBS, FRCS(SN) Consultant Paediatric Neurosurgeon Department of Paediatric Neurosurgery Alder Hey Children’s NHS Foundation Trust Liverpool, England Michael D. Partington, MD Pediatric Neurosurgeon Gillette Children’s Specialty Healthcare St. Paul, Minnesota

Sandro Pelo, MD, PhD Professor Chief, Department of Maxillo-Facial Surgery Catholic University Medical School Rome, Italy John A. Persing, MD€€€ Professor of Plastic Surgery Professor of Neurosurgery Chief, Section€of Plastic Surgery Department of Surgery Yale University School of Medicine€ New Haven, Connecticut David W. Pincus, MD, PhD L. D. Hupp Professor of Pediatric Neurosurgery Department of Neurosurgery University of Florida Gainesville, Florida Jonathan A. Pindrik, MD Assistant Professor Department of Neurosurgery Nationwide Children’s Hospital The Ohio State University Columbus, Ohio Thomas A. Pittman, MD Professor Department of Neurosurgery University of Kentucky Lexington, Kentucky Ian F. Pollack, MD, FACS, FAAP€ Chief, Pediatric Neurosurgery€ Children’s Hospital of Pittsburgh€ Leland Albright Professor of Neurological Surgery€ Vice Chairman for Academic Affairs Department of Neurological Surgery€ Co-Director, UPCI Brain Tumor Program€ University of Pittsburgh School of Medicine€ Pittsburgh, Pennsylvania Scott L. Pomeroy, MD, PhD Chair, Department of Neurology Neurologist-in-Chief Boston Children’s Hospital Bronson Crothers Professor of Neurology Director, Intellectual and Developmental Disabilities Research Center Harvard Medical School Boston, Massachusetts

Contributors Juan Antonio Ponce-Gómez, MD Department of Neurosurgery Lic. Adolfo López Mateos Hospital Institute of Security and Social Services of State Workers Mexico City, Mexico Mark R. Proctor, MD, FAAP, FAANS Associate Professor of Neurosurgery Director of Craniofacial Surgery Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Corey Raffel, MD, PhD Professor of Clinical Neurosurgery and Pediatrics Department of Neurological Surgery University of California–San Francisco San Francisco, California Ashley Ralston, MD Department of Neurosurgery University of Chicago Pritzker School of Medicine Chicago, Illinois Vijay Ramaswamy, MD, PhD, FRCP(C) Attending Neuro-Oncologist Division of Hematology/Oncology The Hospital for Sick Children Toronto, Ontario, Canada Javier González Ramos, MD Neurosurgeon Department of Neurosurgery Hospital de Pediatría Prof. Dr. Juan P. Garrahan Buenos Aires, Argentina Nathan J. Ranalli, MD Assistant Professor of Neurosurgery and Pediatrics Division of Pediatric Neurological Surgery University of Florida Health Science Center– Jacksonville Wolfson Children’s Hospital Jacksonville, Florida Vijay M. Ravindra, MD Department of Neurosurgery Clinical Neurosciences Center University of Utah Salt Lake City, Utah

Marc Remke, MD Department of Pediatric Neuro-Oncogenomics Department of Pediatric Oncology, Hematology, and Clinical Immunology University Children’s’ Clinic, and Department of Neuropathology Medical Faculty Heinrich-Heine-University Düsseldorf, Germany German Cancer Consortium and German Cancer Research Center Heidelberg, Germany Francisco Revilla-Pacheco, MD, MBA, FACS Neurosurgeon Department of Neurosurgery€ The American British Cowdray Medical Center Mexico City, Mexico Renee M. Reynolds, MD Assistant Professor of Neurosurgery University at Buffalo Neurosurgery Pediatric Neurosurgery Women and Children’s Hospital of Buffalo Buffalo, New York Jay Riva-Cambrin, MD, MSc Associate Professor Department of Neurosurgery University of Utah Salt Lake City, Utah Elias Boulos Rizk, MD, MSc Assistant Professor of Pediatric Neurosurgery Department of Neurosurgery Penn State University Hershey Medical Center Hershey, Pennsylvania Shenandoah Robinson, MD, FACS, FAAP Director of Functional Neurosurgery Associate Professor of Neurosurgery and Neurology Department of Neurosurgery Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Caroline D. Robson, MB, ChB Operations Vice Chair, Radiology Division Chief, Neuroradiology Department of€Radiology Boston Children’s Hospital Boston, Massachusetts

xxvii

xxviii Contributors Jonathan Roth, MD Pediatric Neurosurgeon Department of Pediatric Neurosurgery Dana Children’s Hospital Tel Aviv Medical Center Tel Aviv, Israel

Spyridon Sgouros, MD, FRCS(SN) Head of Department Mitera Children’s Hospital Professor University of Athens Medical School Athens, Greece

Benjamin A. Rubin, MD Department of Neurosurgery New York University Langone Medical Center New York, New York

Ash Singhal, MD, FRCS(C) Clinical Assistant Professor Pediatric Neurosurgeon Division of Neurosurgery British Columbia Children’s Hospital Vancouver, British Columbia, Canada

James T. Rutka, MD, PhD, FRCS(C), FACS, FAAP, FAANS R. S. McLaughlin Professor and Chair Department of Surgery Division of Neurosurgery The Hospital for Sick Children University of Toronto Toronto, Ontario, Canada Henry W. S. Schroeder, MD, PhD Professor and Chairman Department of Neurosurgery University Medicine Greifswald Greifswald, Germany Daniel M. Schwartz, PhD Teaneck, New Jersey R. Michael Scott, MD Professor of Neurosurgery Harvard Medical School Fellows Family Chair in Pediatric Neurosurgery Neurosurgeon-in-Chief, Emeritus Department of Neurosurgery Boston Children’s Hospital Boston, Massachusetts€ Nathan R. Selden, MD, PhD Campagna Chair of Pediatric Neurological Surgery Director, OHSU Neurological Surgery Residency Program Department of Neurological Surgery Oregon Health & Science University President, Congress of Neurological Surgeons Chair, Committee on Resident Education Society of Neurological Surgeons Portland, Oregon Anthony K. Sestokas, PhD, DABNM, FASNM Chief Clinical Officer Department of Intraoperative Neuromonitoring SpecialtyCare Nashville, Tennessee

Walavan Sivakumar, MD Department of Neurosurgery Clinical Neurosciences Center University of Utah Salt Lake City, Utah Edward R. Smith, MD Co-Director Cerebrovascular Surgery and Interventions Center Director Pediatric Cerebrovascular Surgery Department of Neurosurgery, Vascular Biology Program Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Jodi L. Smith, PhD, MD, FAANS John E. Kalsbeck Professor and Director of Pediatric Neurosurgery Riley Hospital for Children at Indiana University Health Goodman Campbell Brain and Spine Associate Professor of Neurological Surgery Indiana University School of Medicine Indianapolis, Indiana€ Matthew D. Smyth, MD, FAANS, FACS, FAAP Professor of Neurosurgery and Pediatrics Director, Pediatric Epilepsy Surgery Program Department of Neurosurgery Washington University St. Louis Children’s Hospital St. Louis, Missouri Debbie K. Song, MD Pediatric Neurosurgeon€ Department of Neurosurgery Gillette Children’s Specialty Healthcare St. Paul, Minnesota

Contributors Sulpicio G. Soriano, MD, FAAP BCH Endowed Chair in Pediatric Neuroanesthesia Professor of Anaesthesia Departments of Anesthesiology, Perioperative and Pain Medicine€ Boston Children’s Hospital Harvard Medical School Boston, Massachusetts Robert F. Spetzler, MD Director, Barrow Neurological Institute J. N. Harber Chairman and Professor of Neurological Surgery Division of Neurological Surgery Barrow Neurological Institute Phoenix, Arizona David A. Staffenberg, MD, DSci (Hon), FACS Vice Chair, Department of Plastic Surgery Chief, Division of Pediatric Plastic Surgery Professor of Plastic Surgery, Neurosurgery, and Pediatrics Department of Plastic Surgery New York University Langone Medical Center New York, New York Derek M. Steinbacher, DMD, MD, FACS, FAAP Associate Professor Director of Craniofacial Program Plastic and Maxillofacial Surgery Yale University School of Medicine New Haven, Connecticut Jordan P. Steinberg, MD, PhD Pediatric Craniofacial Surgery Children’s Healthcare of Atlanta Atlanta, Georgia Paul Steinbok, MBBS, FRCS(C) Professor Department of Surgery British Columbia Children’s Hospital University of British Columbia Vancouver, British Columbia, Canada Hai Sun, MD, PhD Assistant Professor Department of Neurological Surgery Louisiana State University Health Sciences Center–Shreveport Shreveport, Louisiana

Gianpiero Tamburrini, MD Professor Department of Pediatric Neurosurgery Institute of Neurosurgery Catholic University Medical School Rome, Italy Robert C. Tasker, MA, MD (Cantab); MBBS (Lond); DCH, FRCPCH,€FRCP,€FHEA (UK); AM (Harvard) Professor of Neurology Professor of Anaesthesia (Pediatrics) Chair in Neurocritical Care Boston Children’s Hospital Senior Associate Staff Physician Department of Neurology Department of Anesthesiology, Perioperative and Pain Medicine Division of Critical Care Medicine Harvard Medical School Boston, Massachusetts Michael D. Taylor, MD, PhD, FRCS(C) Garron Family Chair in Childhood Cancer Research The Hospital for Sick Children Professor of Surgery Division of Neurosurgery University of Toronto School of Medicine Toronto, Ontario, Canada George H. Thompson, MD Director, Pediatric Orthopaedic Surgery Rainbow Babies and Children’s Hospital University Hospitals Case Medical Center Professor, Orthopaedic Surgery and Pediatrics Case Western Reserve University Cleveland, Ohio Michael E. Tobias, MD Co-Chief of Pediatric Neurosurgery Maria Fareri Children’s Hospital Valhalla, New York Assistant Professor of Neurosurgery New York Medical Center Hawthorne, New York Vassilios Tsitouras, MD Neurosurgeon Department of Pediatric Neurosurgery€ Mitera Children’s Hospital€ Athens, Greece R. Shane Tubbs, PhD Professor Division of Pediatric Neurosurgery Children’s Hospital of Alabama Birmingham, Alabama

xxix

xxx Contributors Elizabeth C. Tyler-Kabara, MD, PhD Associate Professor Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania Sudhakar Vadivelu, DO Co-Director, Cerebrovascular Program Assistant Professor of Neurosurgery and Radiology Division of Pediatric Neurosurgery Cincinnati Children’s Hospital Medical Center Cincinnati, Ohio Timothy W. Vogel, MD Assistant Professor Division of Pediatric Neurosurgery€ Division€of Developmental Biology Cincinnati Children’s Hospital€ University of Cincinnati Cincinnati, Ohio

John “Jay” C. Wellons III, MD, MSPH Chief of Pediatric Neurosurgery Professor of Neurosurgery and Pediatrics Department of Neurosurgery Vanderbilt University Medical Center Monroe Carell Jr. Children’s Hospital at Vanderbilt Nashville, Tennessee William E. Whitehead, MD Associate Professor Department of Neurosurgery Baylor College of Medicine Texas Children’s Hospital Houston, Texas Thomas J. Wilson, MD Department of Neurosurgery University of Michigan Ann Arbor, Michigan

Arthur Wang, MD Department of Neurosurgery New York Medical College Westchester, New York

Jeffrey H. Wisoff, MD Professor of Neurosurgery and Pediatrics Director, Division of Pediatric Neurosurgery New York University Langone Medical Center New York, New York

Benjamin C. Warf, MD Hydrocephalus and Spina Bifida Chair Boston Children’s Hospital Associate Professor of Neurosurgery Harvard Medical School Boston, Massachusetts

Peter Albert Woerdeman, MD, PhD Pediatric Neurosurgeon Department of Neurosurgery University Medical Center Utrecht Wilhelmina Children’s Hospital Utrecht, The Netherlands€

Andrew Paul Warrington, ECNE Senior International Clinical Specialist Intraoperative Neurophysiology Medtronic Rochester, New York

Sui-To Wong, MBBS, MMedSc, FHKAM, FRCSEd Consultant Neurosurgeon Department of Neurosurgery Tuen Mun Hospital Hong Kong, China

Michael Weicker, MD Four Corners Spine and Pain Farmington, New Mexico

Edward Yang, MD, PhD Staff Neuroradiologist Department of Radiology Boston Children’s Hospital Boston, Massachusetts

Alexander G. Weil, MD, FRCS(C) Assistant Professor Department of Surgery Division of Pediatric Neurosurgery Sainte-Justine University Hospital Center University of Montreal Montreal, Quebec, Canada Howard L. Weiner, MD Professor of Neurosurgery and Pediatrics Division of Pediatric Neurosurgery Department of Neurosurgery New York University Langone Medical Center New York, New York

Jonathan Yun, MD Department of Neurological Surgery Columbia-New York Presbyterian Hospital New York, New York Graciela Zuccaro, MD, PhD Head Department of Neurosurgery Children’s Hospital Juan P. Garrahan Professor of Neurosurgery Buenos Aires University Buenos Aires, Argentina

Section I Introduction

Section Editor: Tae Sung Park

This section covers a wide range of fundamental issues in pediatric neurosurgery and contains seven chapters. Chapter 1, “Basic Surgical Technique,” provides steps of preoperative and operative planning and execution of surgery in the operating room. Dr. Cohen, the editor of this textbook, emphasizes the importance of sound surgical judgment, setting the tone in the operating room, and the goal of getting the patient safely and expeditiously through the surgery and out of the operating room. Other operative details of neurosurgery are also provided. Chapter 2 addresses common diagnostic and therapeutic procedures: assessment of shunts, lumbar puncture, external ventricular catheter placement, and subdural taps. In addition to operative detail and preoperative planning, the authors describe the equipment needed and provide expert suggestions. Chapter 3 covers important areas of pediatric neuroanesthesia, such as special equipment, vascular access and positioning, management of fluids, and blood loss. The authors also address the anesthetic considerations for specific neurosurgical procedures. Chapter 4, “Pre- and Postoperative Management of the Neurosurgical Patient,” starts with a review of cerebrovascular and CSF physiology. It ends with a review of common clinical problems in the periop-

erative period, such as causes of delayed emergence from anesthesia, choice of intravenous fluids for different age groups, and management of hyponatremia and hypernatremia. Chapter 5 is devoted to the positioning of children during surgery. It includes descriptions of special cautions in rigid cranial immobilization, supine positioning for specific common operative procedures, prone positioning for tumor surgery, and lateral positioning for lumboperitoneal shunt and baclofen pump insertion. Chapter 6 addresses intraoperative neurophysiological monitoring in children. It not only provides details of various monitoring techniques, but also discusses tailored monitoring for specific procedures. Chapter 7 addresses surgical safety. The chapter focuses on three major and related strategies derived from highly reliable organizations, which have gained widespread acceptance: the development of a culture of safety, the creation of effective surgical teams, and the use of communication support tools—specifically, checklists and handoff scripts in patient care. This section, then, provides the reader with a comprehensive overview of basic principles that should be followed for the practice of safe and successful pediatric neurosurgery.

1

Basic Surgical Technique Alan R. Cohen

If an operation is difficult, you are not doing it properly. Robert E. Gross, MD (1905–1988) Surgeon-in-Chief, Boston Children’s Hospital

1.1╇ Introduction and Background

1.1.2╇ Setting the Tone

1.1.1╇Overview

The operating room (OR) is a theater, and the stage should be set before the patient enters the room. The patient is the focus of all activity, and the OR staff and equipment should be positioned to maximize efficiency and flow. Once the patient has been anesthetized, meticulous attention is paid to positioning. Pressure points are padded, and the region of interest is generally placed at the highest point in the field. Overhead lighting is adjusted, and the operator will often put on a headlight and loupes. The operating microscope is balanced, and ancillary equipment is readied for use. The tension is often high in the operating room, and the surgeon should attempt to set the tone and relax the room. The surgical team will function better when the members are calm and know what is expected of them. The attitude of the surgeon will set the tone for the entire team. The more a surgical procedure can be standardized, the better. Standardization improves efficiency and reduces the chance for error. Immediately before incision is made, a “time-out” is performed by the entire operative team according to predetermined checklists (Fig. 1.1). Checklists help the surgeon ensure the safety of a procedure, much as they help the airline pilot ensure the safety of a flight. A preprocedure timeout entails correct identification of the patient, the procedure, and the operative site. For lateralized procedures, the operative site is marked unambiguously before the patient enters the OR. If possible, the patient or family should participate in the preoperative site marking. A standardized checklist is used and should include information about relevant history, physical findings, lab results, and imaging studies. Confirmation is made that there is a signed consent. Medication allergies should be noted. Anticipated risks are discussed, along with whether blood is available if a transfusion is expected. Special equipment for the procedure should be reviewed, and medications,

Attention to basic surgical technique is of paramount importance to the success of the simplest of procedures as well as the most complex. A cavalier surgeon can turn a beautiful operation into a disastrous misadventure in a split second. The proper use of instruments and the careful, meticulous handling of tissue during dissection are essential skills that must be mastered by all successful surgeons. But the real key to successful surgery is preoperative planning, which, by definition, begins well before the patient enters the operating room. Preoperative planning mandates sound surgical judgment, which can be an elusive skill. Simply because an operation is feasible doesn’t necessarily mean it should be done. According to an old Hebrew proverb, the art of surgery is the ability to use superior judgment to avoid having to use superior skills. Is surgery necessary in the first place? What is the purpose of the operation? Are there alternative measures that could avoid surgery and its attendant risks? These are all issues of surgical judgment. The surgeon planning an operation is like the general preparing for combat. Sometimes the greatest warrior is one who can manage a conflict without fighting. This chapter focuses on the basic surgical techniques involved in carrying out a craniotomy in a child. Some technical considerations are unique, such as the rich vascularity of the scalp. Other principles can be generalized to other neurosurgical procedures, such as those performed on the spine, spinal cord, and peripheral nerves.

3

4 Section Iâ•… Introduction

Fig. 1.1â•… The entire operative team participates in the preprocedural timeout, which is performed according to a standard checklist protocol.

such as antibiotics, antiepileptics, and steroids, should be discussed. The names of individuals on the procedure team are recited, including the surgeon, assistant surgeon, anesthesiologist and assistant, scrub nurse, circulating nurse, OR technicians, and others who will be participating in the case. The names of those participating in the case are also written on a board viewable to all in the room. The act of having individuals recite their names out loud may seem childlike, but it actually enables team members to identify one another and develop a rapport. In a time of crisis, it is much easier for members of the team to speak up if they know one another’s names. A second timeout is performed before final closure of the wound.

1.1.3╇Goals

out the entire case. Placing the head in a dependent position, for example, can increase venous pressure and bleeding. Awkward twisting of the neck can lead to jugular vein compression and increase the risk of bleeding. The head is supported on a doughnut or padded horseshoe or carefully fixed in a pinion head holder. Positioning also applies to the surgical team. The assistant surgeon and scrub nurse should be placed where they can be of maximal benefit. There should be adequate space for equipment, such as the operating microscope, image guidance systems, and neurophysiologic monitoring. If endoscopy is used, the video screen should be placed such that the key members of the team can see it without straining their necks. The overhead lighting is brought in at different angles to maximize brightness on the operative field. The surgeon will often wear a headlight and loupes.

Flow A great operation is like a carefully orchestrated ballet. The surgeon choreographs the procedure and must pay scrupulous attention to the flow of the case. Smooth flow is a hallmark of a successful operation. The surgeon should always be thinking two or three steps ahead, anticipating which instruments will be needed. The best operations are not ones in which the surgeon acts in a rushed fashion, but ones that flow smoothly from one step to the next. Members of a team who have worked together for some time get to know each other’s style. A good surgeon will always have an instrument in each hand and will rarely take his eyes off the operative field. When asking for an instrument, the surgeon holds up a hand without looking away (Fig. 1.3). A good assistant will

From the moment the patient is wheeled into the OR, every action of every individual on the team should be directed toward getting the patient safely and expeditiously through the procedure and out of the OR.

1.2╇ Operative Detail and Preparation 1.2.1╇ Preoperative Planning Positioning The importance of patient positioning cannot be overstated (Fig. 1.2). Improper positioning can cause the surgeon and the surgical team to struggle through-

Fig. 1.2â•… The “military tuck” position for a posterior fossa craniotomy. The head of the bed is elevated, and the child is carefully fixed in the pinion head holder such that the neck is flexed but lifted somewhat so that it is parallel to the floor.

1â•… Basic Surgical Technique facilitate lining up the incision properly for closure. The incision is then walled off with cloth towels and covered by an iodoform-impregnated adherent drape. The scalp is then infiltrated with a dilute solution of bupivacaine or xylocaine with epinephrine (1:200,000 dilution) to help minimize blood loss.

1.2.2╇ Key Steps and Operative Nuances Scalp Incision

Fig. 1.3â•… Economy of movement. The surgeon’s eyes are fixed on the operative field as the scrub nurse passes instruments to the surgeon’s raised hands.

anticipate the surgeon’s needs and have complementary instruments in the field. A good scrub nurse can foresee which instrument the surgeon will need next and will often have it ready without ever having been asked. The finest surgeons practice economy of movement. One action gently blends into the next, and nothing appears hurried. Every action has a purpose that was thought out in advance, and there are no unnecessary maneuvers. With each step, the surgeon anticipates the worst-case scenario. What could go wrong? What pitfalls might appear? What operative catastrophes must be avoided? This frame of mind allows the surgeon to stay on course but also to act calmly and confidently should a crisis occur.

The incision should be designed to avoid interrupting the major arterial supply to the scalp. If future surgery is considered, the incision should be planned so that it could be extended to form a new incision if necessary (e.g., conversion of a burr hole to a craniotomy). Whenever possible, the incision should be designed so as not to sit directly over subcutaneous hardware, such as shunt valves and reservoirs. The rich vascularity of a child’s scalp facilitates wound healing but can also lead to significant blood loss during surgery. The operator takes advantage of the fact that the scalp sits directly over the firm skull. The operator’s nondominant hand is placed firmly on one side of the incision with the fingers spread. The assistant’s hand is placed on the opposite side. Because the scalp overlies the firm skull, this pressure serves to control bleeding. This pressure minimizes bleeding from the scalp during incision. The operator holds the knife as if it were a pen, with the index finger on top to permit graduated downward pressure on the blade (Fig. 1.5). The inci-

Preparation and Draping There are various methods for preparing the skin prior to incision. I prefer to clean the skin with isopropyl alcohol and prep with povidone-iodine scrub and solution. I mark the incision with a sterile felt pen after the field is dry but before the drapes are placed (Fig. 1.4). This allows me to see available anatomical landmarks. Cross-hatch marks are drawn to

Fig. 1.4â•… The incision is marked after the skin is prepped but before the drapes are placed so that anatomical landmarks can be seen clearly. The area is surrounded by towels and covered with an iodoform-impregnated band.

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6 Section Iâ•… Introduction

Fig. 1.5â•… The scalp is incised with a no. 15 blade knife. The knife is held like a pen in the dominant hand. The incision is made smoothly with the belly of the knife. To minimize bleeding, pressure is applied to either side of the proposed incision by the nondominant hand of the surgeon on one side and the assistant on the other.

sion is made smoothly with the belly of the blade. The scalp is opened only as far as the region that can be compressed by the fingers of the operator and assistant. Once the subcutaneous tissue is mobilized slightly, it is grasped with toothed forceps and everted for application of spring clips (Fig. 1.6). I prefer low-profile clips, such as baby Raney clips. I apply the Raney clips such that the superficial (external) lip of the clip is placed first, and then the deep (internal) lip is rolled into place to incorporate the full thickness of the scalp in the clip. Placing the superficial lip of the clip first prevents the clip from causing the iodoform-impregnated drape to slide off the scalp. Such spring clips are used sparingly in young infants because they can exert significant pressure on the scalp. Alternatively, a monopolar coagulator can be used to divide the subcutaneous tissue. Excessive suctioning of the soft tissues should be avoided as it can stir up more bleeding. Scalp bleeding is controlled by bipolar or monopolar coagulation. The bleeding site can often be identified by applying and removing a gauze sponge with the nondominant hand. Suction can be used if excess bleeding pools up in the wound. Suction is essential to keep the field dry when using the monopolar coagulator, as this device will not work in a wet field. For a pterional flap, I generally divide the temporalis fascia sharply with a knife and use monopolar cautery to go through the muscle. Excessive cauterization of the temporalis muscle can lead to atrophy, but in a young child the paramount focus is prevention of blood loss. A myocutaneous flap can be held under tension with fish hooks.

It is a good practice to leave the pericranium attached to the skull to minimize blood loss. For frontal craniotomies that may traverse the frontal sinuses, a vascularized pericranial flap can be harvested for later mobilization (Fig. 1.7). This flap is based on the supraorbital arteries. Alternatively, a vascularized temporalis fascial flap can be mobilized. For closure, the frontal sinus is exenterated and filled with a graft of abdominal fat and fibrin glue before being covered by the vascularized pericranial graft. For a midline posterior fossa exposure, it is essential to identify the avascular ligamentum nuchae. Veering off to one side can lead to significant blood loss from the vascular strap muscles of the neck. One trick to keep on the midline is to use a hemostat forceps to spread the tissue, looking for the slight angulation of the muscle fibers on either side of the midline. Dissection through the ligamentum nuchae can be performed with virtually no blood loss.

Craniotomy In the modern era of power tools, some may not be familiar with the old-fashioned manual technique for performing a craniotomy. Hand-driven tools still have a role in neurosurgery, particularly for making burr

Fig. 1.6â•… Scalp clips can be applied to control bleeding. The scalp edge is held up with toothed forceps, and the clip is applied from the outside first to prevent dislodging the iodoform-impregnated drape from the skin. In young infants, Raney clips should be used judiciously and protected by a gauze sponge to prevent pressure necrosis of the scalp.

1â•… Basic Surgical Technique a

b

Fig. 1.7â•… The scalp can be mobilized in the supra-pericranial plane to minimize bleeding from the skull. In selected cases, a vascularized pericranial flap can be mobilized and covered with a moistened gauze sponge for later use in covering an exposed frontal sinus. (a) Before mobilization. (b) After mobilization.

holes in the young child. The skull of a young child or infant can be quite thin, and use of a power perforator must be done with care to avoid the risk of plunging. A hand-driven McKenzie perforator can be used to make burr holes in a young child, and it is an acceptable way to make burr holes in an older child if power instruments are not available (Fig. 1.8a). The McKenzie perforator is attached to a Hudson a

brace, and the operator applies pressure on the brace handle while turning the perforator in a clockwise fashion. Care must be taken not to plunge. When the tip of the perforator penetrates the inner table of the skull, it generates a resistance, causing the perforator to “catch.” The perforator is removed and a round or pineapple-shaped burr is fixed in the Hudson brace in order to widen the burr hole (Fig. 1.8b). Unlike b

Fig. 1.8â•… Drilling the burr hole with hand instruments. (a) The initial hole is made with a McKenzie perforator attached to a Hudson brace. (b) The hole is widened with a burr attached to a Hudson brace.

7

8 Section Iâ•… Introduction the perforator, this burr does not catch. To prevent plunging, the operator should lift the instrument after several turns to assess the progress of the opening. The site is irrigated by the assistant. Bone bleeding during the burr hole creation can be controlled by administering bone wax and drilling through it. Bone wax can be used sparingly to stop bleeding after the hole has been made. In young infants, extra care must be taken because the McKenzie perforator may penetrate the skull during a single turn of the brace. A small opening made by the perforator can be expanded using curettes and a Kerrison punch. More commonly, the burr hole is made with power instruments. An acorn bit can be used with a Midas Rex drill (Medtronic, Minneapolis, MN, USA). Care must be exercised to prevent laceration of the dura, because the acorn can sometimes jump due to “chatter” created by the power drilling process. A power perforator is effective in creating a nice round burr hole. The power perforator has a clutch that should stop the drill from spinning once the inner table has been violated. This safety measure cannot be guaranteed, so the operator uses the nondominant hand as a brace to prevent plunging (Fig. 1.9). Smaller power perforators are available for use in infants. Once the holes are made, the dura can be gently stripped from the undersurface of the bone with a

dissector, such as a dental tool, Penfield no. 3 dissector, or Gigli saw guide. To prevent excess dural bleeding, the operator should strip sparingly, and only in areas overlying proposed cuts. In many cases, dural stripping is not necessary. If the dura is penetrated during stripping at one burr hole, the bone cut should be made from another burr hole toward the site that was torn. The bone cuts to connect the burr holes are made with a power drill and footplate (e.g., Midas Rex B-1 bit). The bone cuts are beveled slightly outward to help prevent sinking of the flap when it is replaced, though this is less of a concern with the current use of plates and screws to resecure the bone. Cuts should be made from the outer edge of one burr hole to the outer edge of the next in order to maximize the size of the craniotomy. The drill is held with two hands, and a gentle forward pressure is applied to cut the bone (Fig.€1.10). Depressing the dura a millimeter or so helps engage the bit properly to make a smooth cut. If the drill gets stuck, the operator can gently angle the instrument forward and backward to help get back on track. It is important to keep the drill properly aligned to prevent it from getting stuck. The assistant irrigates the field, and the bone dust is collected and placed in a moistened

Fig. 1.9â•… The burr hole is commonly made using a power perforator that has a clutch to help prevent plunging. The surgeon’s nondominant hand is used to provide tactile feedback and serve as a counterbrace in the event the instrument plunges. The bone dust is collected in a moist cup for replacement during closure.

Fig. 1.10â•… The craniotomy is elevated using a high-speed drill and footplate. Depressing the footplate about a millimeter helps make the cut smoother. Rocking the drill forward and backward can help prevent it from getting stuck. The cuts are made to allow maximal exposure of the craniotomy. The cuts can be beveled to prevent sinking of the bone flap, though this is less of a problem when the bone is resecured with plates and screws.

1â•… Basic Surgical Technique

a

b

is raised, centered on the pterion (Fig. 1.12). If more frontal exposure is indicated, the bone flap can be tailored and extended more anteriorly. The inferior cut is made last, as the thickened bone over the lateral sphenoid wing can be difficult to cut across and sometimes needs to be cracked. Epidural bleeding is controlled with the bipolar forceps. Bone bleeding is controlled with wax. The lateral edge of the sphenoid wing can be removed with rongeurs and shaved down with a drill to enhance the exposure. In selected cases, the orbital roof can be removed or an orbitozygomatic approach can be fashioned to gain lower exposure. Such exposures can be particularly helpful for approaching lesions that extend superiorly, such as a craniopharyngioma going up high to the third ventricle. The lower bone removal allows the operator a more direct approach to high lesions with less retraction of brain.

Interhemispheric Transcallosal Craniotomy

Fig. 1.11â•… Hand instruments can be used to elevate the craniotomy. (a) A Gigli saw guide is carefully passed beneath the bone in the epidural space from one burr hole to another. (b) The Gigli saw is attached to the guide, and the operator sweeps the saw back and forth at a shallow angle of about 30 degrees above the skull on each side until each cut is completed.

cup for replacement during closure. Examples of several craniotomies are listed below. Bone cuts can also be made with hand-held tools. A Gigli saw guide is passed gently under the bone from one burr hole to another. The Gigli saw is a twisted wire with an eyelet that can be attached to a hook on the guide, facilitating passage of the saw under the bone. The saw is then held with handles or clamps in the surgeon’s two hands, and the bone is cut from inside out with back-and-forth movements while the guide is left in place to protect the dura (Fig. 1.11a,b).

The interhemispheric approach to the anterior ventricular system can be performed through a variety of scalp incisions. I prefer a bicoronal incision and use a quadrilateral bone flap whose medial extent is directly on the midline (Fig. 1.13). For such a midline approach, I place the most posterior midline burr hole about 1 cm behind the bregma and the most anterior hole about 5 or 6 cm in front of the bregma. Lateral holes are made 4 to 5 cm off the midline. A useful anatomical guide is that a line drawn from the

Pterional Craniotomy The pterional craniotomy is fashioned using a curvilinear scalp incision beginning in front of the tragus and extending to the midline, just behind the hairline. A myocutaneous flap is reflected forward and held in place with fish hooks. The bone flap is made with two burr holes. The posterior hole is positioned over the low squamous temporal bone just above the posterior margin of the zygoma. The anterior hole is placed in the keyhole region. An elliptical craniotomy

Fig. 1.12â•… Pterional craniotomy. The bone flap is fashioned with two burr holes: one at the squamous temporal bone above the posterior zygoma and the other in the keyhole region.

9

10 Section Iâ•… Introduction Midline Posterior Fossa Craniotomy

Fig. 1.13â•… Craniotomy for a midline interhemispheric transcallosal approach. The medial burr holes are placed last, directly on the midline. Bone cuts are made going away from the midline. The midline is carefully stripped, and midline cuts are made last. The dura is reflected medially to protect the sinus.

bregma to the external auditory meatus will bisect the foramen of Monro. For the transcallosal approach, the midline burr holes over the superior sagittal sinus are placed last, and the midline is stripped last. The thinking behind this is that the operator must always anticipate the worst-case scenario (e.g., sagittal sinus tear) and prepare for it. Drilling is always performed in a direction away from the venous sinuses. If the sinus is injured, the bone flap can be elevated rapidly if the other cuts have already been made. Sinus injury can result in torrential bleeding. The bleeding site must be properly exposed. The head of the bed should be elevated. Sometimes bleeding can be controlled with thrombin-soaked gelfoam and pressure. Larger tears may need to be covered with muscle and oversewn with a dural reflection. Some surgeons expose the superior sagittal sinus by placing burr holes on either side of it. I place burr holes directly over the sinus and strip gently with a dental tool, followed by a Penfield no. 3, followed by a Gigli saw guide. If stripping is not easy, I will add more burr holes over the midline. Once the bone flap is off, visualization of midline structures can be facilitated by using an acorn bit to bevel the native bone along the midline and to permit a more medial reflection of the dura. In reflecting the dura medially, care must be taken to avoid occluding the superior sagittal sinus.

The midline posterior fossa craniotomy is a standard workhorse in pediatric neurosurgery. The occipital bone is exposed through a vertical midline incision that is kept open with automatic retractors. The foramen magnum is identified and cleared of soft tissue with curettes. For low approaches that require removal of the posterior arch of C1, I expose the rostral posterior arch of C2 and work toward the region of the foramen magnum and C1 going from above downward and from below upward, trying to prevent premature entry into the atlanto-occipital membrane and dura. One must exercise caution working laterally at C1 to avoid injuring the vertebral arteries and the paravertebral venous plexus. The craniotomy is fashioned using two burr holes. The burr holes are placed just inferior to the transverse sinus, with each hole placed 1 to 2 cm on either side of the midline (Fig. 1.14). The lateral cuts are made first and extend inferiorly into the foramen magnum. The bone is thick at the lateral margins of the foramen magnum, so the drill is brought more medially to enter the foramen. Exposure at the foramen magnum can be widened with rongeurs and Kerrison punches after the bone flap has

Fig. 1.14â•… Midline posterior fossa craniotomy. The foramen magnum is cleared with curettes. Two burr holes are made just inferior to the transverse sinus, each just lateral to the midline. Bone cuts are made from the burr holes extending laterally and inferiorly to the foramen magnum. The midline cut connecting the two burr holes is made last. Rostral to the left.

1â•… Basic Surgical Technique been removed. If the operator has difficulty reaching the foramen magnum from above, the drill can be removed and cuts can be made starting from the foramen magnum going upward. The final cut across the midline is made last. The dura is stripped from the undersurface of the bone with dissectors. The operator uses the drill to go partway from one side and then completes the cut going from the other side. The bone over the midline has a keel that can be quite thick, and frequently there are underlying emissary veins that need to be controlled. Bone bleeding is controlled with wax. The craniotomy can be widened as necessary with rongeurs. If superior exposure is necessary (e.g., for an infratentorial supracerebellar approach), the operator uses an acorn drill bit to bevel the bone overlying the transverse sinuses. This maneuver permits a little more rostral reflection of the rostral dural leaflets, which can aid significantly in the exposure over the top of the cerebellum.

Dural Opening Epidural bleeding can be controlled by tenting the dura to drill holes placed around the margins of the craniotomy with 4–0 Nurolon sutures (Ethicon, Somerville, NJ, USA; Fig. 1.15). Tenting sutures should be applied prior to durotomy, because if a cortical vessel were to be injured by the needle, the

Fig. 1.15â•… The dura is tented to the margins of the craniotomy with 4–0 Nurolon sutures. Tenting is done prior to durotomy. The tenting sutures are applied close to the bone to minimize shrinkage of the dura.

bleeding site could be identified and controlled once the dura is opened. Dural tenting sutures should be used sparingly because they can shrink the dural surface available for closure. In some cases, such as a craniotomy for epidural hematoma, multiple dural tenting sutures are a very effective way of obtaining hemostasis and obliterating the epidural space. In selected cases, such as an epidural hematoma, a central dural tack-up suture can be used to fasten the dura to drill holes placed in the center of the bone flap, helping to obliterate the epidural space. Several steps are taken before the dura is incised. Appropriate instruments are organized. Microsuction devices are hooked up. If a retraction system is to be used, it is set in place. For a vascular case, such as an aneurysm or arteriovenous malformation, clips are brought out and loaded. The dura is opened with a no. 15 blade knife on a long handle, using gentle, repetitive cuts about a centimeter in length to deepen the durotomy until the arachnoid is visible. The dura can be held up with a fine-toothed forceps or a fine hook. The dural opening is extended by cutting along the groove of a dental instrument placed underneath the dura by the assistant surgeon. Alternatively, the dural opening is extended using Metzenbaum scissors (Fig. 1.16). The operator looks underneath the dura to ensure that there are no bridging veins in the way. If the brain

Fig. 1.16â•… The dura is opened initially with a no. 15 blade knife. The dural incision can be extended by using the blade to cut over a dental instrument or with Metzenbaum scissors. The scissors are beveled to prevent excess pressure on the brain. The dural flap can be held under tension with 4–0 Nurolon sutures and covered with a moist collagen sponge to minimize shrinkage.

11

12 Section Iâ•… Introduction is tight, the scissors are held at a flat angle, nearly parallel to the dura, in order to prevent the internal blade of the scissors from injuring the brain. The durotomy is planned to maximize exposure and minimize bleeding. In the posterior fossa midline, the dura is opened in a Y shape to help control bleeding from the occipital sinus (Fig. 1.17). Such bleeding can be troublesome, particularly in young children, who may have large venous lakes in the central portion of the posterior fossa dura. Bleeding can be effectively controlled using silver clips, with care taken to include both the inner and outer layers of dura in the clips (Fig. 1.17). Occipital sinus bleeding can also be sealed with bipolar coagulation. Other dural openings are tailored to the specific site. U-shaped openings can be reflected toward the location of venous sinuses. This reduces the chance of lacerating bridging veins during durotomy and can also help to tamponade sinus bleeding should it occur. The dural incision should be at least a centimeter away from the adjacent bone edge to allow the operator enough room for dural closure. I make the turns in the U at right angles to help me find the appropriate landmarks for closing the dura. Linear or cruciate openings are used in selected cases. The dura is held open with retraction sutures of 4–0 Nurolon. The dural flap is covered with a moist

microfibrillar collagen film, such as Bicol (Codman Neuro, Raynham, MA, USA), or a wet gauze sponge.

Brain Manipulation and Dissection If the brain is to be retracted, it is retracted gently. Automatic brain retractors should be placed in a low profile so that the operator’s hands can be as close to the wound as possible. If the brain is to be entered, it is also done gently. For a sulcal approach, the pia mater is opened sharply and gentle dissection is carried out under microsurgical guidance. For a gyral approach, the corticectomy can be made in a linear or circular fashion. The surgeon tries to find the shortest route to the lesion, but plans may need to be modified to avoid traversing eloquent structures. The portion of exposed brain that is not part of the operative trajectory is covered with a moist collagen sponge and kept moist with irrigation throughout the procedure. Microsurgery is best performed with the surgeon sitting in a comfortable position. Arm rests help prevent fatigue and facilitate fine microsurgical manipulation. When available, a mouthpiece attached to the microscope enables the surgeon to make fine adjustments during the procedure without slowing the flow. The operative field is kept dry with suction and bipolar coagulation. The suction tip is used gently to clear the field and identify bleeding sites, which are coagulated with the bipolar forceps. Some bleeding can be controlled with pressure from a Cottonoid (Codman Neuro, Raynham, MA, USA) patty placed over the torn vessel with the bipolar forceps. The patty is gently slid off the bleeder by the bipolar forceps, and the suction tip exposes the bleeder, which is then coagulated using the bipolar forceps. Persistent oozing from an edematous brain can be covered with a piece of thrombin-soaked Gelfoam (Pfizer, New York, NY). Use of warmed irrigating solution helps to promote hemostasis.

Managing the Lesion Fig. 1.17â•… The posterior fossa dura is opened in a Y shape with silver clips utilized to control bleeding from the occipital sinus. It is important to include both the inner and outer dural leaflets in the clips. Note ependymoma in the vallecula. Rostral at the top.

Strategies for removing a tumor differ depending on its location, its consistency, and its vascularity. Nevertheless, some general principles apply. Whenever possible, the tumor should be devascularized early in the procedure. Access to feeding vessels, such as

1â•… Basic Surgical Technique the anterior choroidal artery supply to a choroid plexus papilloma, should be part of the preoperative planning. Deep feeders, such as posterior choroidal vessels, can sometimes be embolized through an endovascular approach prior to surgery. Some tumors are best debulked in a piecemeal fashion to prevent excessive retraction of the brain. Others, such as hypervascular hemangioblastomas, should be circumferentially stripped of their blood supply and removed as a single specimen to prevent major blood loss. In separating a tumor from normal brain, it is preferable to retract the tumor, when possible, rather than the brain. Usually, both the tumor and the brain require some manipulation. Some very vascular tumors, such as primitive neuroectodermal tumors or malignant gliomas, can bleed profusely. These tumors are best handled by rapid gutting. Dividing the mass into quadrants and moving from one to another can be helpful. After debulking of the tumor in one quadrant, hemostasis is achieved with bipolar coagulation or packing with Gelfoam and a Cottonoid, while attention is directed toward another quadrant.

bleeding from the occipital sinus, they are removed. Often this can be done without stirring up more bleeding. If bleeding occurs, the exposed dural edges can be sealed with bipolar coagulation or oversewn with a running suture of 4–0 Nurolon. A pericranial autograft can be sutured in place to facilitate a watertight dural closure, or an allograft (e.g., cadaveric AlloDerm) can be used. The operative bed is filled with irrigation prior to placement of the final suture. After the dura has been closed, the anesthesiologist performs a Valsalva maneuver to test the integrity of the closure.

Bone The bone flap is replaced with titanium plates and screws (Fig. 1.18). In young infants, absorbable plates and screws or suture material is preferable to prevent migration of metallic hardware deep through the dura or superficially though the scalp. Sutures or wire can also be used to secure the bone in older children. The bone dust collected from the opening is applied to cover gaps between the craniotomy and skull.

Closing Brain A closing timeout is performed to ensure that all sponges and Cottonoid patties are accounted for. The surgeon must be fastidious in achieving hemostasis before closing the dura. The operative cavity is filled with warmed Ringer solution, and bleeding sites are identified and coagulated with the bipolar. If Cottonoid patties have been used, they are irrigated and gently removed.

Dura The dura is closed primarily with interrupted or running sutures of 4–0 Nurolon. Smaller sutures are used in young infants. If the dura is tense, it is best approximated beginning in a region of lesser tension and working toward the tighter area. Often this technique will permit successful closure of even recalcitrant dura. The posterior fossa dura usually requires placement of a graft. If silver clips were used to control

Fig. 1.18â•… The bone flap is secured using titanium plates and screws. In young infants, titanium should be avoided because the plates can sit “proud” and penetrate the scalp, or the screws can go deep and penetrate the dura and brain. In young infants, the bone flap can be replaced using absorbable plates and screws or suture material. Rostral at the bottom.

13

14 Section Iâ•… Introduction Scalp The scalp is closed in layers with absorbable sutures. If scalp clips have been used, only a few are removed at a time in order to prevent bleeding while the scalp is reapproximated. An inverted suture is used to close the galea. When working in tight areas, it is helpful to apply the inverted suture at a slight angle on one side and a mirror image angle on the other (Fig. 1.19). The suture is tied parallel to the incision, and the lower arm of the suture is pulled preferentially on the first throw in order to effectively bury the knot and evert the scalp edges for final closure of the skin. A square knot is tied with a total of 4

throws. The skin is closed with a simple running 4–0 or 5–0 absorbable suture.

1.3╇ Outcomes and Postoperative Course 1.3.1╇ Postoperative Considerations The importance of basic technique in pediatric neurosurgery cannot be overemphasized. Detailed attention must be paid to both the nontechnical and the technical aspects of an operation. Procedures are often carried out to treat life-threatening conditions, and even a small technical error can lead to catastrophic consequences.

1.3.2╇Complications

Fig. 1.19â•… The galea is reapproximated with inverted absorbable sutures. If the working area available is tight, the sutures can be placed in an angled fashion. The suture is tied parallel to the incision, and the lower arm of the suture is pulled preferentially on the first throw in order to effectively bury the knot and evert the scalp edges.

Careful attention to basic surgical technique will help the operator minimize the risk of complications as well as provide guidelines for managing complications, should they occur. A major pitfall associated with pediatric neurosurgical procedures is blood loss. It is my hope that the techniques described in this chapter will offer the surgeon strategies to minimize bleeding and to handle it should it occur. Other complications to be avoided are wrong-side surgery, infection, and cerebrospinal fluid (CSF) fistulas. Wrong-side surgery can be prevented by paying dutiful attention to the checklist during a timeout. The risk of infection can be reduced by gentle handling of tissue. CSF fistulas can be avoided by performing a watertight dural closure whenever possible and using measures to divert CSF, such as ventricular drainage, when necessary. The wise surgeon will remember that in any operative procedure, very small mistakes can lead to very big problems.

2

Diagnostic Procedures Chad A. Glenn, Naina L. Gross, and Timothy B. Mapstone

2.1╇ Bedside Functional Assessment of Ventricular Shunt: Introduction and Background 2.1.1╇Indications 1. Need for functional assessment of ventricular catheter 2. Need for evaluation of intracranial pressure (ICP) 3. Need for emergent drainage of cerebrospinal fluid (CSF) 4. Need for injection of pharmacologic agents for therapeutic or diagnostic purposes

2.1.2╇Goals 1. Determination of ventricular catheter function 2. Measurement of ICP 3. Drainage of CSF 4. Administration of pharmacologic agents

2.1.3╇ Alternate Procedures 1. Evaluation of ventricular shunt in the operating room

2.1.4╇Advantages 1. Safety and ease of procedure 2. Performed at bedside for emergent CSF drainage 3. Rapid interpretation of findings

2.1.5╇Contraindications 1. Local infection near puncture site, or systemic infection 2. Exposed ventricular shunt tubing, reservoir, or valve 3. Need for subarachnoid CSF (e.g., to diagnose meningitis)

2.2╇ Operative Detail and Preparation 2.2.1╇ Preoperative Planning and Special Equipment The location of the CSF reservoir may be palpated directly. Review of skull X-ray images aids in further localization. The reservoir usually consists of a protruding convex bulb. It may be located over a burr hole or in line with the ventricular catheter (Fig. 2.1).

Equipment Needed 1. Hair clippers 2. Standard surgical site preparation materials and drapes 3. Sterile gloves, surgical hat, and facemask 4. Small-bore or winged needles, 25 gauge 5. 3- to 5-milliliter (mL) syringes 6. Sterile saline-filled syringes 7. 3-way stopcock and manometer 8. Sterile specimen containers

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16 Section Iâ•… Introduction

Fig. 2.1â•… Bedside functional assessment of ventricular shunt. A winged needle is inserted into the cerebrospinal fluid (CSF) reservoir at a perpendicular angle to assess for spontaneous flow of CSF. The reservoir should always be proximal to the valve mechanism with respect to the ventricular catheter.

2.2.2╇ Key Steps of the Procedure and Operative Nuances After the reservoir is palpated, hair clippers may be used to trim a small patch of hair. The site is prepped and draped in the standard and sterile fashion. The needle is inserted perpendicular to the reservoir. Immediately after, spontaneous flow of CSF may be observed. A syringe should not be attached during initial needle placement, as this may create an air lock, blocking CSF flow. If spontaneous flow is noted, a manometer is attached to measure opening pressure and the pressure response to a Valsalva maneuver if the patient is able. The opening pressure is most accurate when the patient is calm and the base of the manometer is level with the external auditory meatus. If spontaneous flow is absent, a syringe may be attached and gentle suction applied to initiate flow. A syringe may also be used to withdraw CSF for diagnostic studies or to administer pharmacologic or radiographic agents. The needle is then removed at the same angle at which it was inserted, minimizing reservoir damage and skin bleeding.

mating opening pressure (Fig. 2.1). Because the tubing is typically not marked and the location of the reservoir may be above or below the external auditory meatus, only gross observations can be made.

Absence of Spontaneous Flow Absence of spontaneous flow may be due to low ICP, an air lock, or an occluded ventricular catheter. Attachment of a syringe with gentle negative pressure may facilitate CSF flow. If this is ineffective, 1 to 2 mL of sterile saline may be flushed into the reservoir to try to flush out any occlusion. Do not flush additional saline if there is no return. If only the volume of fluid flushed returns, it may indicate that the ventricular system is collapsed or that the catheter tip is not located in the ventricular system. If a larger volume returns, it may indicate that the ventricular catheter occlusion was dislodged. If flushing does not generate CSF flow, either the proximal catheter is not functioning properly or the reservoir was not accessed.

Volume of CSF to Remove

2.2.3╇ Expert Suggestions Winged Needles Winged needles are preferred because low-resistance tubing is attached to the needle base with a threaded attachment at the opposite end, allowing attachment of a manometer or syringe as well as easy visualization of CSF column height when esti-

The volume of CSF that is appropriate to remove depends upon the clinical scenario. A sample of 3 to 4 mL of CSF is typically sent for routine studies. If there is concern about elevated ICP, a larger volume is commonly removed. In the case of a firm fontanelle or concerning radiographic findings, 20–30 mL of CSF may be drained. Indications that enough fluid has been drained include neurologic improvement, fontanelle

2â•… Diagnostic Procedures softening, and lowering of ICP measurement. Excessive drainage may result in catheter occlusion or neurologic decline secondary to hematoma development. Clinical considerations as well as diagnostic imaging serve to aid in determining how much CSF to drain.

Assessing the Distal Catheter If the reservoir is not located over a burr hole, one may consider applying local pressure to the ventricular catheter proximally after a CSF column has been obtained to evaluate for decreasing column height, serving as an indicator of distal catheter and valve function. However, applying pressure does not ensure that the proximal portion of the catheter has been entirely occluded, limiting interpretation.

2.2.4╇ How to Avoid Pitfalls

2.3╇ Outcomes and Postoperative Course 2.3.1╇ Postoperative Considerations 1. Proper technique and interpretation of ventricular shunt puncture 2. Laboratory evaluation of CSF

2.3.2╇Complications 1. Irreparable damage to ventricular shunt system 2. Infection 3. Proximal catheter occlusion from repeated attempts to withdraw CSF 4. Introduction of air into the vascular system in the patient with a ventriculoatrial shunt

Locate the Reservoir Do not attempt puncture until the location of the reservoir is known with relative certainty. If the valve has an integrated reservoir, the reservoir will be proximal to the valve mechanism. Improper needle introduction may result in catheter laceration or damage to the valve mechanism, requiring replacement.

Do Not Use Large-Volume Syringes or Large-Gauge Needles Large-volume syringes are capable of generating excessive negative pressure at the catheter tip, which may damage adjacent neurovascular structures or pull choroid plexus into the catheter lumen. Largegauge needles may increase the risk of developing a persistent CSF leak from the reservoir or damaging the adjacent catheter or valve mechanism.

2.2.5╇ Salvage and Rescue Development of CSF Collection under the Scalp Reservoir puncture may result in CSF leakage despite proper technique, though this is uncommon. This may occur when larger-gauge needles are used or the subgaleal pocket created for valve placement has not yet sealed. CSF may be drained by needle aspiration with careful avoidance of underlying shunt components. An occlusive dressing can then be applied. Persistent or enlarging CSF collections require further investigation in the operating room.

2.4╇ Lumbar Puncture: Introduction and Background 2.4.1╇Indications 1. Need for subarachnoid cerebrospinal fluid (CSF) for diagnostic or therapeutic purposes 2. Need for administration of intrathecal therapeutic or radiographic agents 3. Need to evaluate intracranial pressure (ICP)

2.4.2╇Goals 1. Laboratory evaluation of CSF 2. Relief of elevated ICP through therapeutic drainage of CSF 3. Administration of intrathecal therapeutic or radiographic agents

2.4.3╇ Alternate Procedures 1. Cervical spinal puncture

2.4.4╇Advantages 1. Absence of spinal cord 2. Familiar technique

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18 Section Iâ•… Introduction

2.4.5╇Contraindications 1. 2. 3. 4. 5.

Spinal defect or associated mass Obstructive hydrocephalus Nonfunctioning ventricular shunt Local skin infection Bleeding diathesis

2.5╇ Operative Detail and Preparation 2.5.1╇ Preoperative Planning and Special Equipment Equipment Needed 1. Standard surgical site preparation materials and drapes 2. Sterile gloves, surgical hat, and facemask 3. Lumbar puncture kit to include local anesthetic, specimen collection tubes, spinal needle (21–22 gauge), manometer

2.5.2╇ Key Steps of the Procedure and Operative Nuances With the help of an assistant, the patient is placed in the left lateral decubitus position (for a right-handed individual) and curled into the fetal position. The back should be perpendicular to the ground. The iliac crest is palpated to localize the L4–L5 interspinous space. The site is then marked, prepped, and draped. A small amount of local anesthetic is used. It is important to ensure that all needed equipment is readily available prior to attempting puncture. The spinal needle is introduced through the L3–L4 or L4–L5 interspace, with the bevel facing upward at an angle that is aiming toward the umbilicus and parallel to the ground (Fig. 2.2). Resistance will be met as the needle passes through the supraspinous and interspinous ligaments. A “pop” or sudden decrease in resistance may be felt as the needle pierces the thecal sac. Next, the bevel is rotated toward the patient’s head, and the stylet is removed to check for spontaneous CSF flow. Opening pressure may be measured in the calm patient with legs straightened. CSF is then drained into the collection tubes to send for desired studies. The stylet is replaced, and the needle is withdrawn. If no leakage of CSF is noted at puncture site, a small dressing is applied.

Fig. 2.2â•… Lumbar puncture. The spinal needle is introduced into the L3–L4 or L4–L5 interspace. Resistance will be met as the needle advances through the supraspinous and interspinous ligaments until a “pop” or sudden decrease in resistance occurs as the needle pierces the thecal sac.

2.5.3╇ Expert Suggestions Proper Positioning Proper positioning is vital. An assistant should be available to assist with maintaining the desired position.

Measuring Opening Pressure Be sure to use local anesthetic. Opening pressure measurements are useless in the agitated patient. The legs should also be straightened, as fetal positioning may increase intraabdominal or intratho-

2â•… Diagnostic Procedures racic pressure, which may translate to an artificially elevated measurement.

2.6╇ Outcomes and Postoperative Course

Obtaining CSF

2.6.1╇ Postoperative Considerations

Always use a spinal needle that contains a stylet. Use of a needle without a stylet may introduce epithelial tissue into the spinal canal and result in an epidermoid. Never attempt to instill or aspirate the spinal needle until CSF flow has been established, as this may result in subarachnoid hemorrhage and epidural or subdural hematoma.

2.5.4╇ How to Avoid Pitfalls Avoid Overpositioning Though the fetal position opens the spinal interspaces, facilitating needle passage, excessive kneeto-chest pressure may result in hypoxia in the infant.

1. Flat positioning for a few hours after a large volume of CSF is drained 2. Laboratory evaluation of CSF

2.6.2╇Complications 1. Herniation syndrome or hematoma (may develop acutely or in a delayed fashion secondary to sudden decompression of CSF in the setting of elevated ICP) 2. Infection secondary to poor technique or systemic infection 3. Development of parasthesias secondary to nerve root injury 4. Spinal headache 5. Subcutaneous CSF leak

Do Not Overdrain Avoid free flow of CSF between collections. Always replace the stylet when not obtaining specimen. Overdrainage may precipitate herniation or hematoma development.

Check Puncture Site Do not initiate lumbar puncture above L2, as this may result in puncture of the spinal cord.

2.5.5╇ Salvage and Rescue Neurologic Changes If the patient develops altered mental status, weakness, or severe parasthesias, the spinal needle should be carefully removed and the procedure aborted. Additional imaging may be warranted if the cause of the symptoms cannot readily be explained.

Leakage of CSF Repeated puncture of the dura mater and arachnoid may result in persistent CSF leakage. Leakage may improve with flat positioning for 24 to 48 hours but, if persistent, may indicate the need for a blood patch.

2.7╇ External Ventricular Catheter Placement: Introduction and Background 2.7.1╇Indications • Therapeutic need for ventricular decompression through cerebrospinal fluid (CSF) drainage • Therapeutic need for administration of chemotherapeutic or other pharmacologic agents • Diagnostic need for ventricular CSF for laboratory analysis • Diagnostic need for injection of radiographic agents to facilitate ventricular imaging • Diagnostic need for intracranial pressure (ICP) measurement

2.7.2╇Goals 1. Measurement of ICP 2. Therapeutic ventricular decompression 3. Collection of ventricular CSF for laboratory analysis 4. Injection of radiographic contrast agents for ventricular imaging 5. Administration of chemotherapeutic or other pharmacologic agents

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20 Section Iâ•… Introduction

2.7.3╇ Alternate Procedures 1. Placement of ICP monitor 2. Lumbar puncture

2.7.4╇Advantages 1. Rapid assessment of ICP 2. Potential for therapeutic drainage of CSF to lower ICP 3. Repeated ventricular CSF sampling as needed 4. Administration of chemotherapeutic, pharmacologic, or radiographic agents into the ventricular space

2.7.5╇Contraindications 1. Bleeding diathesis 2. Need for subarachnoid CSF (e.g., to diagnose meningitis)

2.8╇ Operative Detail and Preparation 2.8.1╇ Preoperative Planning and Special Equipment Prior to consideration of ventricular catheter placement, intracranial imaging should be obtained to evaluate the ventricular anatomy and for surgical planning. Several cranial sites have been described for ventricular puncture. The approaches most commonly utilized at our institution are coronal (the Kocher point), posterior parietal (the Keen point), and occipital. A method employed at our institution to identify the coronal entry site in the pediatric population is described here.

Equipment Needed 1. Hair clippers 2. Standard surgical site preparation materials and drapes 3. Sterile gloves, surgical gown, surgical hat, and facemask 4. Cranial access kit to include local anesthetic, marking pen, scalpel with handle, twist drill, spinal needle, 10 mL of sterile saline, trocar, basic instruments, collection tubes, and nylon suture 5. Ventricular catheter with stylet

6. External CSF collection system with pressure transducer 7. Cardiac and apnea monitors

2.8.2╇ Key Steps of the Procedure and Operative Nuances Cranial imaging is reviewed to choose the appropriate side and approach for ventricular catheter placement. The patient is positioned in a recumbent position with the head of bed elevated at 20 to 30°. An assistant is preferred for maintenance of proper patient positioning. A coronal site on the nondominant hemisphere is preferred. The coronal suture is palpated, and the midpupillary line is marked. A marking pen is then used to plan an incision that is approximately 1 cm anterior to the coronal suture. The hair surrounding the planned incision site as well as the tunneling site is trimmed. The area is prepped and draped in sterile fashion. Local anesthetic is injected at the incision and tunneling site. The incision is carried to the cranium with the scalpel blade used to scrape away adjacent pericranium. The twist drill is used to make a hole 1 cm anterior to the coronal suture in the midpupillary line without penetrating the dura mater. Forceps are used to remove any bone dust, and this process is enhanced with gentle irrigation of saline. A spinal needle or scalpel is used to fenestrate the dura mater. The premeasured catheter is aimed in the coronal plane perpendicular to the skull surface and toward the ipsilateral medial canthus (Fig. 2.3). A gentle “pop” is often felt as the ventricular space is entered. The stylet should be removed once the ventricular space is entered before the catheter is advanced further. It is at this point that the opening pressure may be determined, as drainage of even a small amount of CSF may result in an artificially low measurement. After the opening pressure check, the catheter may be advanced an additional centimeter after the stylet is removed. The ending depth of the catheter will vary depending upon ventricular anatomy, skull thickness, and patient age, but with standard approaches in the pediatric population this depth should not exceed 4.5 to 5 cm at the skull. The trocar is attached to the catheter and tunneled under the scalp 3 to 5 cm away from the incision while catheter depth is maintained. CSF flow is confirmed after the trocar is removed. The threaded cap is attached to the end of the catheter to prevent excess CSF drainage as the catheter is secured to the scalp. Nylon suture is employed to close the scalp incision and to secure the catheter to the scalp. The catheter is laid in a curvilinear or circular line and sutured to the scalp at multiple points. A U-shaped stay stitch may also be placed where the catheter

2â•… Diagnostic Procedures a

b

Fig. 2.3â•… (a,b) External ventricular catheter placement. An incision is planned, preferably on the nondominant hemisphere, that allows a twist drill hole to be made approximately 1 cm anterior to the coronal suture along the midpupillary line. The ventricular catheter is advanced in a perpendicular fashion to enter the ventricular space.

exits the scalp so that the site may be easily closed after the drain is removed. The catheter is then attached to the collection system, which is set to the desired height relative to the external auditory meatus and is attached to the pressure transducer. Once the catheter is attached, the ICP and waveform may be assessed.

2.8.3╇ Expert Suggestions Sedation Sedatives may be employed to ensure that patients are calm, as rapid head movements in an agitated patient may result in damage to neurovascular structures or anomalous catheter placement.

Skull Thickness Skull thickness will vary with patient age. Extra care must be taken to avoid plunging through the dura mater when using the twist drill on the younger patient with a softer and thinner cranium.

2.8.4╇ How to Avoid Pitfalls Check Blood Clotting Parameters Ensure that basic coagulation parameters and platelet counts are normal. The pediatric population is less commonly taking anticoagulants or antiplatelet agents, but this simple step should not be disregarded.

Place Catheters at the Correct Depth and Within CSF Pathways The ventricular catheter depth should never be greater than 6 cm at the skull surface using standard approaches. Imaging should be obtained to ensure that all catheter fenestrations are located within CSF pathways if radiographic or other pharmacologic agents are to be given. Administration of these agents intraparenchymally may result in neurologic injury.

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22 Section Iâ•… Introduction Prevent Pressure Damage in Posterior Fossa Mass and Hydrocephalus In patients with obstructive hydrocephalus secondary to a posterior fossa mass lesion, rapid drainage of CSF, and the concomitant decrease in supratentorial pressure, may be sufficient to widen the pressure differential between the infratentorial and supratentorial compartments, facilitating upward herniation of the cerebellum through the incisura. Instead, the ICP should be allowed to decrease gradually to the upper limits of normal through CSF drainage. The ICP is approximated by the height of the CSF column on the vertically raised premeasured ventricular catheter.

2.8.5╇ Salvage and Rescue Catheter Debris Catheter debris from choroid plexus, blood clot, or infection may result in a nonfunctioning ventricular catheter. Gentle flushing, first distally and then proximally, with sterile saline may dislodge any debris. If resistance is met or bright red blood is noted in the catheter, imaging should rapidly be obtained.

2.9╇ Outcomes and Postoperative Course 2.9.1╇ Postoperative Considerations 1. Postoperative imaging to ensure proper catheter placement (should absolutely be obtained if pharmacologic or radiographic agents are to be administered)

2.9.2╇Complications 1. CSF infection 2. Intracranial hemorrhage secondary to direct vascular damage or rapid ventricular drainage 3. Seizure 4. Development of catheter track from the ventricular system to the scalp 5. Upward herniation

2.10╇ Percutaneous Subdural Tap: Introduction and Background 2.10.1╇Indications 1. Need for physical or laboratory evaluation of extra-axial fluid collection 2. Signs or symptoms of elevated intracranial pressure (ICP) or mass effect

2.10.2╇Goals 1. Physical and laboratory assessment of extraaxial collection, including culture or cytology when indicated 2. Therapeutic drainage of fluid to reduce elevated intracranial pressure or mass effect

2.10.3╇ Alternate Procedures 1. Burr hole craniotomy 2. Subdural catheter placement

2.10.4╇Advantages 1. Bedside procedure 2. Rapid physical and laboratory analysis of extra-axial fluid collection 3. Therapeutic drainage of extra-axial fluid collection when associated with elevated ICP

2.10.5╇Contraindications 1. Local scalp infection 2. Minimal extra-axial collections in an asymptomatic patient 3. Bleeding diathesis

2.11╇ Operative Detail and Preparation 2.11.1╇ Preoperative Planning and Special Equipment This procedure is most often performed in infants with an open or fibrosed fontanelle, but it may also be performed in patients with splayed coronal sutures. In addition, it may be performed bilaterally when clinically indicated.

2â•… Diagnostic Procedures

Equipment Needed 1. Hair clippers 2. Standard surgical site preparation materials and drape 3. Sterile gloves, surgical hat, and facemask 4. Local anesthetic 5. Subdural or winged needles, 23 to 25 gauge 6. Sterile 10-mL threaded syringes 7. Sterile specimen containers 8. Hemostat (optional) 9. Small dressing 10. Cardiac and apnea monitors

2.11.2╇ Key Steps of the Procedure and Operative Nuances Cranial imaging is reviewed to identify the optimal location of puncture. With the help of an assistant, the patient is positioned supine with his or her head slightly elevated. The anterior fontanelle is palpated, identifying the lateral, anterior, and posterior boundaries (Fig. 2.4). The lateralmost aspect of the anterior fontanelle is prepped and draped in sterile fashion after the hair is trimmed. Sedation or local anesthetic may be utilized in an agitated patient. The boundary of the skull and the fontanelle is identified. The skin overlying the skull at the boundary is pushed forward and held in position. The needle is introduced at a 15° from perpendicular angle just beyond the edge of the skull into the subdural space (Fig. 2.4). The depth of needle placement is closely monitored. A rapid decrease in resistance may be felt as the subdural space is entered. Fluid may flow spontaneously in those with elevated ICP or may require gentle aspiration. Once the flow is established, a hemostat may be placed onto the needle at the scalp edge to maintain depth. Once the desired volume of fluid is removed and collected into specimen containers, the needle is carefully removed. If the skin has been pulled as described above, there should be only minimal drainage. Brief, simple pressure is applied if needed. A sterile bandage may be placed at the needle puncture site.

2.11.3╇ Expert Suggestions Scalp Manipulation Pulling the scalp at the skull edge over the fontanelle for needle placement enables an occluded tract once the needle is removed and the adjacent skin is allowed to return to its resting position. This greatly reduces the likelihood of postprocedural drainage.

Fig. 2.4â•… Percutaneous subdural tap. After the lateral boundary of the anterior fontanelle is palpated, the overlying scalp is gently pushed forward. The spinal needle is introduced at an angle 15° from perpendicular and advanced into the subdural space.

Imaging It is advisable to obtain cranial imaging prior to subdural puncture to discern whether the procedure will likely be beneficial and, if so, to localize the optimal site for needle placement.

Fluid Drainage Depending upon the clinical scenario, varying volumes of drainage are appropriate. In the patient with large collections thought to be contributing to elevated ICP, drainage may continue until neurologic status improves or the fontanelle softens. Initially, this volume should be just enough to relieve significant pressure, minimizing the risk for iatrogenic injury and decline secondary to a rapid decrease in ICP. Patients requiring repeated tap may be drained more aggressively on subsequent taps.

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24 Section Iâ•… Introduction

2.11.4╇ How to Avoid Pitfalls Use Correct Needle Depth In most situations, the needle depth should not exceed 1.5 to 2 cm. Advancing the needle farther increases the likelihood of damaging cortical structures.

Use a Lateral Approach If Possible If acceptable, lateralizing the puncture site as much as possible minimizes the risk of venous sinus damage. The midpupil line marks the optimal medial boundary.

2.11.5╇ Salvage and Rescue When to Seek Additional Imaging If the fluid being drained changes as volume is removed to resemble bright red blood, or if there is a neurologic change noted after the procedure,

urgent cranial imaging should be obtained for further evaluation.

2.12╇ Outcomes and Postoperative Course 2.12.1╇ Postoperative Considerations 1. Infectious versus hemorrhagic nature of fluid to direct further work-up 2. Improvement in neurologic exam (may indicate symptomatic elevated ICP)

2.12.2╇Complications 1. Hematoma development from improper technique or excessive drainage 2. Infection

3

Neuroanesthesia Sulpicio G. Soriano and Craig D. McClain

3.1╇ Introduction and Background 3.1.1╇Goals The anesthetic management of infants and children undergoing neurosurgical procedures should be based on the developmental stage of the patient. The evolving maturational changes of the various organ systems have a significant impact on the selection of drugs and techniques for the safe conduct of anesthesia. Age-dependent differences in cranial bone development, cerebrovascular physiology, and neurologic lesions distinguish neonates, infants, and children from their adult counterparts. In particular, the central nervous system (CNS) undergoes a tremendous amount of structural and physiological change during the first 2 years of life. The goal of this chapter is to highlight these age-dependent differences and their effect on the anesthetic management of the pediatric neurosurgical patient.

3.2╇ Operative Detail and Preparation 3.2.1╇ Preoperative Planning and Special Equipment Neonates and infants have the highest risk of any age group for perioperative respiratory and cardiovascular morbidity and mortality. The systemic effects of general anesthesia and the physiological stress of surgery have an important impact on this vulnerable group. Therefore, a thorough review of the patient’s history can reveal conditions that may increase the risk of adverse reactions to anesthesia and identify patients who require more extensive evaluation or whose medical condition needs to be optimized before surgery. If a cardiac defect is suspected (loud

cardiac murmur, low room-air oxygen saturation, cyanosis, or respiratory distress), it is necessary to obtain echocardiography and an assessment by a pediatric cardiologist in order to optimize cardiac function prior to surgery. There are also specific perioperative concerns in pediatric patients (Table 3.1). Preoperative fasting guidelines have evolved and are frequently dictated by regional practices (Table 3.2). The purpose of limiting oral intake is to minimize the risk of aspiration of gastric contents on induction. However, prolonged fasting periods and vomiting may induce hypovolemia and hypoglycemia, which can exacerbate hemodynamic and metabolic instability under anesthesia.

3.2.2╇ Key Steps of the Procedure and Operative Nuances Induction of Anesthesia A smooth transition into the operating suite depends on the level of anxiety and the cognitive development and age of the child. Children between the ages of 9 to 12 months and 6 years may have separation anxiety. Midazolam, administered orally or intravenously, is effective in relieving anxiety and producing amnesia. Parental involvement during induction of anesthesia is common in pediatric operating rooms and requires full engagement of the surgical team. Obtunded and lethargic patients do not require premedication with sedatives and should have an anesthetic induction performed in an expeditious manner. Induction of anesthesia is dictated by the patient’s comorbidities and neurologic status. If the patient does not have intravenous access, anesthesia can be induced with sevoflurane, nitrous oxide, and oxygen by mask. Intracranial hypertension may be exacerbated by hypercarbia and hypoxia, which may occur if the airway becomes obstructed during induction, and vigilant maintenance of a patent airway with

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26 Section Iâ•… Introduction Table 3.1â•… Coexisting conditions that affect anesthetic management Condition

Anesthetic implications

Congenital heart disease

Hypoxia Arrhythmias Cardiovascular instability Paradoxical air emboli

Prematurity

Postoperative apnea

Gastrointestinal reflux

Aspiration pneumonia

Upper respiratory tract infection

Laryngospasm, bronchospasm, hypoxia, pneumonia

Craniofacial abnormality

Difficult tracheal intubation

Denervation injuries

Hyperkalemia after succinylcholine Resistance to nondepolarizing muscle relaxants Abnormal response to nerve stimulation

Epilepsy

Hepatic and hematological abnormalities Increased metabolism of anesthetic agents Ketogenic diet

Arteriovenous malformation

Congestive heart failure

Neuromuscular disease

Malignant hyperthermia Respiratory failure Sudden cardiac death

Chiari malformation

Apnea Aspiration pneumonia

Hypothalamic/pituitary lesions

Diabetes insipidus Hypothyroidism Adrenal insufficiency

mild hyperventilation will alleviate this problem. In patients with intravenous access, anesthesia can be induced with propofol. Some patients presenting for neurosurgical procedures may be at particular risk for aspiration of gastric contents, and a rapidsequence induction of anesthesia with succinylcholine is required to intubate the trachea expeditiously. Contraindications to the use of succinylcholine include malignant hyperthermia susceptibility, muscular dystrophies, and recent denervation injuries.

Table 3.2â•… Preoperative fasting guidelines Substance

Fasting period

Clear liquids

2 hours

Breast milk

4 hours

Formula or fortified breast milk

6 hours

Solid food

Midnight

Vascular Access and Positioning Limited access to the patient during neurosurgical procedures requires secure intravenous access prior to the start of surgery. Large peripheral venous cannulae are sufficient for most craniotomies. Should initial attempts fail, central venous cannulation may be necessary. Femoral vein catheterization avoids the risk of pneumothorax and does not interfere with cerebral venous return. Furthermore, femoral catheters are more easily accessible to the anesthesiolo-

gist. Cannulation of the radial artery provides direct blood pressure monitoring and sampling for blood gas analysis. Other useful arterial sites in infants and children include the dorsalis pedis and posterior tibial artery. Patient positioning requires careful preoperative planning to allow adequate access to the patient for both the neurosurgeon and the anesthesiologist. Furthermore, various surgical positions affect the physi-

3â•…Neuroanesthesia Table 3.3â•… Physiologic effects of patient positioning Position

Physiological effect

Head-up/sitting

Increased cerebral venous drainage Decreased cerebral blood flow Increased venous pooling in lower extremities Postural hypotension

Head-down

Increased cerebral venous and intracranial pressure Decreased functional residual capacity (lung function) Decreased lung compliance

Prone

Venous congestion of face, tongue, and neck Decreased lung compliance Venocaval compression

Lateral decubitus

Decreased compliance of downside lung

ologic status of the patient (Table 3.3). The prone position can increase intraabdominal pressure and lead to impaired ventilation, venocaval compression, and bleeding due to increased epidural venous pressure. Soft rolls are generally used to elevate and support the lateral chest wall and hips in order to minimize abdominal and thoracic pressure. Performing neurosurgical procedures with the patient’s head slightly elevated facilitates venous and CSF drainage from the surgical site. However, this increases the likelihood of venous air emboli (VAE). Significant rotation of the head can also impede venous return via compression of the jugular veins and can lead to impaired cerebral perfusion, increased ICP, and venous bleeding. Obese patients may be difficult to ventilate in the prone position and may benefit from the sitting position. In addition to the physiological sequelae of the sitting position, a whole spectrum of neurovascular compression and stretch injuries can occur.

Maintenance of Anesthesia The most frequently used technique during neurosurgery consists of an opioid (fentanyl, sufentanil, or remifentanil) and low-dose isoflurane or sevoflurane. Dexmedetomidine can be used as an adjunct; it does not significantly affect most intraoperative neurophysiologic monitoring and reduces opioid requirements. Patients on chronic anticonvulsant therapy usually require a larger dose of neuromuscular blocking agents and opioids because of induced enzymatic metabolism of these agents. The use of neuromuscular blocking agents should be discussed with the surgical and monitoring teams if assessment of motor function during seizure and spinal cord surgery is planned.

Management of Fluids and Blood Loss Meticulous fluid and blood administration is essential in order to minimize hemodynamic instability, especially in the pediatric patient. Stroke volume is relatively fixed in the neonate and infant, so the patient should be kept euvolemic. Normal saline is generally chosen because it is mildly hyperosmolar and should minimize cerebral edema, but rapid infusion of more than 60 mL/kg of normal saline may cause hyperchloremic acidosis. The routine administration of glucose-containing solutions is generally avoided during neurosurgical procedures, except in patients who are at risk for hypoglycemia. Patients with diabetes mellitus or total parenteral alimentation, as well as premature and small newborn infants, may require glucose-containing intravenous fluids. Premature neonates have a circulating blood volume of approximately 100 mL/kg total body weight; full-term newborns have a volume of 90 mL/kg; and infants have a blood volume of 80 mL/kg. Maximal allowable blood loss (MABL) can be estimated using a simple formula: MABL = Estimated circulating blood volume × (Starting hematocrit – Minimum acceptable hematocrit)/Starting hematocrit. Transfusion of 10 mL/kg of packed red blood cells increases hemoglobin concentration by 2 g/dL. Pediatric patients are susceptible to dilutional thrombocytopenia in the setting of massive blood loss and multiple red blood cell transfusions. Administration of 5 to 10 mL/kg of platelets increases the platelet count by 50,000 to 100,000/mm3. The routine use of the antifibrinolytic tranexemic acid in surgical procedures with excessive blood loss, such as posterior spine fusions, cardiac surgery, and craniofacial reconstructive procedures, has been shown to decrease blood loss in pediatric patients.

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28 Section Iâ•… Introduction Anesthetic Management of Specific Neurosurgical Procedures Congenital Disorders Myelomeningocele/Encephalocele Tracheal intubation of a neonate with a myelomeningocele or encephalocele can be challenging depending on the size and location of the defect. The supine patient may be elevated on rolled-up towels in order to minimize direct pressure on the lesion. Blood and fluid loss depends upon the size of the lesion and the amount of tissue dissection required to repair the defect.

Hydrocephalus The anesthetic technique depends on the patient’s symptoms. In a patient with intact mental status or one in whom intravenous access cannot be established, an inhalation induction with sevoflurane and gentle cricoid pressure may be used. If, however, the patient is obtunded, is at risk for herniation, or has a full stomach, intravenous access should be established in order to perform a rapid-sequence induction followed by tracheal intubation. VAE may occur during placement of the distal end of a ventriculoatrial shunt if the operative site is above the heart. Acute obstruction of a ventricular shunt requires urgent treatment because an acute increase in intracranial pressure in the relatively small cranial vault of the infant or child can have devastating consequences.

Neoplasms Posterior Fossa Tumors Posterior tumors may impinge upon brainstem structures vital to the control of respiration, heart rate, and blood pressure, complicating the intraoperative management of these patients. Respiratory control centers can be damaged during surgical dissection. Stimulation of the nucleus of cranial nerve V can cause hypertension and tachycardia. Irritation of the nucleus of the vagus nerve may result in bradycardia or postoperative vocal cord paralysis. Continuous observation of the blood pressure and electrocardiography (ECG) are essential to detect encroachment upon these vital structures. Inadvertent entry into the straight and transverse sinus can precipitate massive VAEs.

Supratentorial Tumors Craniopharyngiomas may be associated with hypothalamic and pituitary dysfunction. Steroid replacement therapy with either dexamethasone or hydrocortisone may be required because the integrity of the hypothalamic-pituitary-adrenal axis may

be uncertain. Perioperative diabetes insipidus (DI) can lead to electrolyte and hemodynamic derangements. Laboratory studies should therefore include serum electrolytes and osmolality, urine specific gravity, and urine output. DI is marked by sudden polyuria (> 4 mL/kg/hr), hypernatremia, and hyperosmolarity. Initial management consists of infusion of aqueous vasopressin (1 to 10 mU/kg/hr) and judicious fluid administration that matches urine output and estimated insensible losses.

Epilepsy Epilepsy surgery poses several anesthetic management issues. General anesthetics can compromise the effectiveness of intraoperative neurophysiologic monitors that guide the resection of the epileptogenic focus. High levels of volatile anesthetics and neuromuscular blockade may also suppress cortical stimulation. Nitrous oxide can precipitate pneumocephalus after a recent craniotomy (3 weeks) and should be avoided until after the dura is opened. A variety of techniques have been advocated to facilitate intraoperative assessment of motorsensory function and speech. In the “sleep-awakeasleep” technique, the patient undergoes general anesthesia for the surgical exposure. The patient is then awakened for functional testing, and general anesthesia is reinstituted when patient cooperation is no longer needed. Most cooperative patients will tolerate sedation with propofol or dexmedetomidine. Propofol does not interfere with electrocorticography (ECoG) if it is discontinued 20 minutes before monitoring in children undergoing an awake craniotomy. Supplemental opioids are administered to provide analgesia. It is, however, imperative that candidates for craniotomy under local anesthesia or sedation be mature and psychologically prepared to participate in this procedure.

Cerebrovascular Disease The primary goal of the anesthesiologist during cerebrovascular surgery is to optimize cerebral perfusion while minimizing the risk of bleeding. A large arteriovenous malformation (AVM) in neonates may be associated with high-output congestive heart failure requiring vasoactive support. Hypertensive crisis after embolization or surgical resection of the AVM should be rapidly treated with vasodilators. The goal of anesthetic management of patients with moyamoya disease is to optimize cerebral perfusion with aggressive preoperative hydration and to maintain normotension or mild hypertension during surgery and the postoperative period. Intraoperative normocapnia is essential, because both hyper- and hypocapnia can lead to steal phenomenon from the ischemic region. Intraoperative EEG monitoring may be utilized during surgery to detect cerebral isch-

3â•…Neuroanesthesia emia. Optimization of cerebral perfusion should be extended into the postoperative period to maintain euvolemia and, using sedatives and opioids, to prevent hyperventilation induced by pain and crying.

Neuroendoscopy Technological advances in endoscopic surgery have provided less-invasive approaches to the surgical management of CNS lesions. Despite the relative safety of this procedure, hypertension, arrhythmias, and neurogenic pulmonary edema have been reported in conjunction with acute intracranial hypertension due to lack of egress of irrigation fluids and/or manipulation of the floor of the third ventricle.

3.2.3╇ Salvage and Rescue Hemodynamic collapse due to massive blood loss or venous air embolism looms as a catastrophic complication for any major craniotomy. Large-bore intravenous access and arterial blood pressure monitoring are therefore essential for these procedures. Massive blood loss should be aggressively treated with crystalloid and blood replacement and vasopressor therapy (e.g., dopamine, epinephrine, norepinephrine). Venous air embolism commonly occurs during the surgery. Maintaining normovolemia minimizes this risk. Early detection of a VAE with continuous precordial Doppler ultrasound may allow treatment to be instituted before large amounts of air are entrained. Should a VAE produce hemodynamic instability, the operating table must be placed in the Trendelenburg position in order to improve cerebral perfusion and prevent further entrainment of intravascular air. Special risks exist in neonates and young infants because right-to-left cardiac mixing lesions can result in paradoxical emboli. In the case of severe cardiovascular collapse, some pediatric centers have rapid-response extracorporeal membrane oxygenation (ECMO) teams, which can provide cardiopulmonary support when the crisis is refractory to standard cardiopulmonary resuscitation algorithms.

3.3╇ Outcomes and Postoperative Course 3.3.1╇ Postoperative Care Hemodynamic and Respiratory Support The severity of the intraoperative course dictates the need for admission to an intensive care unit. Factors like massive blood loss, hemodynamic instability, neurological deficits, seizures, and prolonged surgical time necessitate close observation and immediate treatment. The acuity of the intensive care setting is essential for early detection and treatment of evolving postoperative events. These include bleeding, neurological deficits, electrolyte abnormalities, respiratory distress, and fluid shifts. The immediate availability of magnetic resonance imaging (MRI) or computed tomography (CT) is mandatory in order to assess evolving neurological deficits.

Sedation and Pain Management Postoperative neurosurgical patients should be comfortable, awake, and cooperative to complete serial neurological examinations. In pediatrics, these goals can be difficult to maintain because of the cognitive level of the patient. The mainstay of sedation in the pediatric intensive care unit remains a combination of an opioid and a benzodiazepine. Opioids like morphine and fentanyl should be carefully titrated to minimize postcraniotomy pain while maintaining consciousness. Propofol is a potent, ultrashort-acting sedative-hypnotic but has only limited utility in pediatrics because it is associated with a fatal syndrome of bradycardia, rhabdomyolysis, metabolic acidosis, and multiple organ failure when used over extended periods in small children. Dexmedetomidine has analgesic properties and is a useful agent for reversible sedation.

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4

Pre- and Postoperative Management of the Neurosurgical Patient Robert C. Tasker

4.1╇ Introduction and Background Perioperative management of pediatric neurosurgical patients presents many challenges. Many conditions and complications are unique to small children, and a basic understanding of age-related physiology and pharmacology is essential in minimizing perioperative morbidity. The “pediatric” age range is from newborn through to adult; thought of in another way, this is a mass range of 1 to 100 kg—a difference in mass of two orders of magnitude. In terms of the changing brain, the pediatric range spans a sixfold increase in brain weight from birth to maturity, with most of the change occurring by the age of 2 years.

4.1.1╇ Goal of Perioperative Care The overall goal of perioperative care is to prepare the patient for the right surgery, at the right time, under the right circumstances of physiology and pharmacology, all with the best expected outcomes for the child’s underlying condition. In order to achieve these objectives, there must be clear documentation in the patient’s medical record and good communication between all team members. All hospitals will have their own policy and procedures manuals that cover the details of what is expected of medical practitioners and what is considered best care practices in preparing a child for a neurosurgical procedure. Table€4.1 outlines the checklist for the general preoperative case review. After the operation, those caring for the child will also need information in a systematic manner. We use the formula one hand-off technique. The basis of this technique is that there is limited time to transfer information and the right details need to be conveyed to the next team caring for the child, be it in the neurosurgical ward or in the surgical intensive care unit (ICU). Table 4.2 outlines the checklist for the postop-

30

erative transition of care. The neurosurgeon and anesthesiologist need to convey succinctly what happened in the operating room and what they want to happen in the immediate postoperative period. The postoperative attendants need to be cognizant of any concerns about bleeding, compromised tissue, derangements in homeostasis, and requirements for postoperative antibiotics, steroids, etc. We find that this process is best served by attending-to-attending signout. Also, it is my view that, if the postoperative attendant is not familiar with the procedures that have occurred in the operating room, then that attendant should take the time to observe what actually happens (e.g., craniotomy for resection of tumor, craniosynostosis repair, Chiari decompression, craniotomy and resection for epilepsy, bypass procedure for vascular insufficiency, and resection of arteriovenous malformation would be a good start). This chapter is a review of basic information and understanding that are required by those involved in perioperative care. The format of this chapter differs from others in this book in that it is about “what are you thinking,” “what information needs to be conveyed between attendants,” and why. Please note that, at a number of points in this chapter, recommendations are made concerning drugs and drug doses. Many of these drugs are not licensed for use in children or for the indications described. Readers should check usage with their own national drug regulatory, hospital pharmaceutical, and professional bodies.

Clinical Pearl 1 Have a checklist of information that should be signed out at the transitions of patient care (preoperative to operative, operative to postoperative, postoperative to discharge).

4â•… Pre- and Postoperative Management of the Neurosurgical Patient Table 4.1â•… Elective neurosurgical admissions Activity

Details

Action

Clerking

• Presenting complaint • Previous medical history • Developmental level • Previous anesthetics • Medications • Allergies • Seizures

• Documented

Examination

•C  entral and peripheral nervous systems • Raised ICP • Cardiopulmonary • General level of hydration

• Documentation of neurologic deficits • May need preoperative resuscitation and treatment

Comorbidities

• Intercurrent illness • Any cardiopulmonary disease • Any gastroesophageal reflux • Endocrinopathy

• Discuss with anesthesiologist

Blood testing

• Hemoglobin • Urea and electrolytes • Blood cross-matched

Fasting period

• Solid food • Formula • Breast milk • Clear fluids

• 6 hours • 6 hours • 4 hours • 2 hours

Preoperative anesthesia review

• IV access • Premedication

Special preoperative interventions required

• Cerebrovascular cases

• Intravascular euvolemia

• Endocrine-risk cases

• Stress hormone and other HPA-axis assessment

Medications

• All medications, including route

• Discussion of route of administration and whether medications can be withheld

Seizure plan

• Current AEDs, if any

• Review AEDs with pediatric epilepsy/ neurology

Abbreviations: AEDs, antiepileptic drugs; HPA, hypothalamic-pituitary-adrenal; ICP, intracranial pressure.

4.2╇ Brain Hydrodynamic Physiology There are general principles of brain hydrodynamic physiology that will be known to all practitioners of neurosurgery. However, to the novice in pediatric neurosurgery, there are nuances that are also worth knowing, particularly as they relate to some of the problems that may become evident postoperatively, and these are discussed in later sections.

4.2.1╇ Cerebrospinal Fluid Eighty percent of cerebrospinal fluid (CSF) is produced in the choroid plexus of the lateral and fourth ventricles. The remainder is produced in the interstitial space and ependymal lining. In the adult, normal CSF volume is 150 mL (50% intracranial and the rest intraspinal). In the neonate, CSF volume is 50 mL. The rate of CSF production across all ages is 0.15 to 0.30 mL/min (up to ≈ 450 mL/day).

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32 Section Iâ•… Introduction Table 4.2â•… Postoperative signout using “formula one” Item

Details

Operation

• Procedure •C  omplicated or uncomplicated • Concerns •W  ound drains • E xternal ventricular drain (e.g., where and what head of pressure being used)

Anesthesia

•P  remedication used • L aryngoscopy and whether the airway is difficult • Anesthesia • Emergence •P  ostoperative pain management  hether sedation is required (e.g., neurovascular child needing dexmedetomidine for deep •W sedation to prevent early postoperative agitation, crying, and hypocapnia)

Intraoperative fluids

• Intravenous fluids used • Estimated blood loss and use of blood products; final hematocrit • Urine output • Any intraoperative laboratory tests

Surgical plan

• Head-of-bed positioning required • Blood pressure targets • Perioperative antibiotics • Use of antiemetics and steroids • Laboratory tests • In those who return with an endotracheal tube in situ, the plan for extubation • Frequency of neurologic observations and special instructions on signs to watch for • Seizure plan • Postoperative imaging plan • What has been discussed with the family and any other consultants required (e.g., infectious disease, neuro-oncology)

Postoperative fluids

• Volume required (maintenance or more) • Serum sodium target • Strategy for cerebral edema, if required

Organ system review

• Special concerns, particularly in regard to cormorbidities and when other therapies are required (e.g., asthma treatment) • When feeding can be restarted

There are two pathways for CSF circulation: a major, adult, pathway with CSF absorption through arachnoid villi (arachnoid granulation) into the venous sinuses, and a minor, infantile, pathway with CSF drainage through the ventricular ependyma, the interstitial and perivascular space, and perineural lymphatics. The need for CSF circulation begins early during intrauterine development because the choroid plexus is formed during the first trimester. Because arachnoid granulations do not appear until just before birth, it is unlikely that CSF reabsorption via the adult route of circulation is the major pathway during infancy. In fact, there is some evidence that arachnoid granulations continue to develop well into the second decade, and so the “infantile” route of circulation may be significant in childhood as well.

Clinical Pearl 2 Large CSF losses in young children with an external ventricular drain in situ may represent a significant wasting of sodium. Pay attention to perioperative CSF drainage volume and serum sodium concentration.

4.2.2╇ Intracranial Pressure Intracranial pressure (ICP) is the pressure of CSF inside the cerebral ventricles, which is often approximated with cerebral intraparenchymal pressure

4â•… Pre- and Postoperative Management of the Neurosurgical Patient measured using a fiber-tipped microsensor. In health, ICP is determined by cerebral blood flow (CBF) and CSF circulation. The Davson equation describes this relationship and states that ICP is the sum of sagittal sinus pressure and the product of CSF formation rate and resistance to CSF outflow. Normal values for sagittal sinus pressure, CSF formation rate, and resistance to CSF outflow are 5 to 8 mm Hg, 0.3 mL/min, and 6 to 10 mm Hg/mL/min, respectively. In most clinical situations, sagittal sinus pressure stays constant or is coupled to central venous pressure. In practice, measured ICP is often greater than the value calculated using the equation. The difference is due to a vascular component, which is probably a result of pulsation in the arterial bed and is determined by the interaction between pulsatile arterial inflow and venous outflow curves, cardiac function, and cerebral vasomotor tone. Under usual conditions, ICP remains less than 15 mm Hg and reflects the volume of three compartments: brain parenchyma (1,200–1,600 mL in the adult human), extracellular or CSF (100–150 mL), and cerebral blood volume (CBV) (100–150 mL). Since the intracranial vault is fixed in volume in the developed cranium, increases in the size of one component of the intracranial contents must be compensated by removal of an equivalent amount of another intracranial component, or ICP will increase. The point at which perfusion-compromising ICP elevation occurs is dependent on brain elastance and potential displacement of intracranial contents. Normal values of ICP are less in newborns (2–6 mm Hg) and children (< 15 mm Hg) than in adults. The impact of the cranial vault on intracranial hydrodynamics is also different in children. The infant’s cranium has the potential for growth, with open fontanelles and sutures, so that there is greater total compliance of the system. For example, a slow-growing tumor will not have an acute mass effect because compensatory increase in intracranial volume occurs with expansion (widening of sutures and fontanelles) and growth. As a result, infants and young children may have advanced intracranial pathology at the time of presentation, with little reserve.

4.2.3╇ Cerebral Metabolism The brain is one of the most metabolically active organs of the body, and it requires a constant supply of oxygen (O2) and nutrient, mainly glucose. In the adult, the brain consumes about one-fifth of total body O2 utilization. Cerebral metabolic rate for oxygen (CMRO2) in normal, conscious young men is approximately 3.5 mL O2 per 100 g brain mass per minute. The CMRO2 of an entire adult brain of average weight (i.e., 1.4 kg) is therefore about 50 mL O2/min.

Clinical Pearl 3 The zero reference point for ICP is the level of the third ventricle, using the external auditory meatus (EOM) as the marker. However, there are circumstances when this reference point may be important to consider, for example: • When calculating the cerebral perfusion pressure (i.e., difference between mean blood pressure and mean ICP), remember that blood pressure is calibrated to the level of the right atrium (RA). • When the head of the patient’s bed is elevated, the EOM and RA are not at the same level, and the cerebral perfusion number reported to you as a simple automated calculation will have a systematic error. • In the operating room, you will be used to having both the arterial pressure and the ICP calibrated to the same level. However, in the ICU, you will not be able to convince colleagues to recalibrate the arterial line to the EOM.

A 70-kg adult consumes about 250 mL O2/min in the basal resting state. Therefore the brain, which represents only about 2% of total body weight, accounts for 20% of the resting total body O2 consumption. The functions of nervous tissues are mainly excitation and conduction of nerve impulses, and these are reflected in the increasing activity of the brain. Electrical energy, ultimately, is derived from chemical processes, and it is likely that most of the energy consumption of the brain is used for active transport of ions. Oxygen is used in the brain almost entirely for the oxidation of carbohydrate. The energy equivalent of the total cerebral metabolic rate is, therefore, approximately 20 W, or 0.25 kcal/min. Let us assume that this energy is used mainly for the synthesis of high-energy phosphate bonds, that the efficiency of the energy conservation is approximately 20%, and that the free energy from hydrolysis of the terminal phosphate of adenosine triphosphate (ATP) is 7 kcal/mol. This energy expenditure supports the steady turnover of close to 7 millimoles, or approximately 4 × 1021 molecules, of ATP per minute in the entire brain. In the normal, in vivo state, glucose is the only significant substrate for energy metabolism in the brain. The stoichiometry of glucose utilization and CMRO2 is as follows. The normal, conscious human brain produces carbon dioxide (CO2) at about the same rate of CMRO2 of 156 µmol/100 g tissue/min, leading to a respiratory exchange ratio of 1:1. CMRO 2 and CO2 production are equivalent

33

34 Section Iâ•… Introduction to a rate of glucose utilization of 26 µmol/100 g tissue/min, assuming 6 µmol of O 2 consumed and CO2 produced for each micromole of glucose completely oxidized to CO 2 and water. (The actual glucose utilization is, however, 31 µmol/100g/min. For complete oxidation of glucose, the theoretical ratio of O 2:glucose utilization is 6; the excess glucose utilization is responsible for a measured ratio of only 5.5 µmol O 2/µmol glucose. The fate of the excess glucose is unknown, but it is probably distributed in lactate, pyruvate, and other intermediary metabolites.)

Development and Cerebral Glucose Metabolism Cerebral glucose utilization in 5-week-old infants is three-quarters that of the adult brain. The developing brain also metabolizes lactate, ketone bodies, amino acids, and free fatty acids. Adult rates of glucose utilization are first achieved by the age of 2 years; after this age, there is a further increase through to the age of 8 years, followed by a decline in metabolic rate through to the age of 20 years. This crescendo-decrescendo pattern of change likely represents the consequence of brain development and the subsequent “pruning” of neurons, synapses, and pathways that occurs with maturation.

Cerebral Oxygen Equations Equations describing the pathway for blood and oxygen in the brain (see text for details): CMRO2 = (CBF × CaO2) – (CBF × CvO2) – CiO2

Q = ∆P/R



Q = (Π × r4 × ∆P)/(8 Ŋ × L)



Q = CBV/t`



CBV = 1.09 × CBV0.29



OEF = (SaO2 – SjvO2)/SaO2



OEF = CMRO2/(CBF × 1.34 × [Hb] × SaO2 where CaO2 is the oxygen content of arterial blood; CBF is the cerebral blood flow; CBV is the cerebral blood volume; CiO2 is the oxygen content of brain tissue; CMRO2 is the cerebral metabolic rate for oxygen; CvO2 is the oxygen content of venous blood; [Hb] is the hemoglobin concentration; Ŋ is blood viscosity; L is vessel length; OEF is oxygen extraction fraction of brain; ∆P is the pressure gradient between inflow and outflow; Q is flow; R is resistance to flow; r is vessel radius; SaO2 is oxyhemoglobin saturation of arterial blood; SjvO2 is oxyhemoglobin saturation of jugular venous blood; and t` is mean transit time of blood.

Cerebral Oxygen Kinetics Human brain maturation is incomplete at birth and continues to progress during the first years of life. As already discussed, brain development is associated with regional changes in glucose metabolism. Given that O2 needs to be delivered to the tissue at a rate that is biochemically proportionate to metabolic needs, it should come as no surprise that regional cerebral blood flow (CBF) also changes with development. CMRO2 must be equal to the total amount of O2 delivered to cerebral tissue per unit time minus the amount left in the venous circulation per unit time and the amount that accumulates in the cerebral tissue per unit time (see box Cerebral Oxygen Equations). The extraction of O2 from cerebral tissue is so closely matched to the brain’s metabolic needs that O2 content of brain tissue is small. The vast majority of the arteriovenous O2 content difference (AVDO2) is made up of O2 offloaded from hemoglobin, and the amount of O2 offloaded from hemoglobin in the cerebral circulation is tightly regulated by many physiologic factors, including brain pH, brain temperature, concentration of cerebral metabolites, and amount of adult hemoglobin.

4.2.4╇ Cerebral Blood Flow CBF is coupled to CMRO2, and both increase proportionately after birth. Whole-brain CBF at birth is, on average, 50 mL/100 g/min. CBF increases after birth, peaks between the ages of 5 and 8 years (≈€70 mL/100 g/min), and then declines to the adult level (≈€50 mL/100 g/min) in early teenage. Despite these changes, oxygen extraction fraction (OEF) is constant even in early childhood. CBF responsiveness or reactivity to changes in CO2, O2, and cerebral perfusion pressure (CPP, as defined by difference in mean blood pressure [BP] and mean ICP) clearly occurs in the developing brain. Under anesthesia, CBF decreases by about 20%; under deep general anesthesia, it decreases by up to 50%. In white matter, blood flow is about 25% of that of the cortex in the awake state, but it is not markedly influenced by anesthesia; differences between white and gray matter diminish when subjects are deeply anesthetized. The physical laws that describe steady laminar flow of uniform fluids through nondistensible tubes are helpful in understanding in vivo cerebrovascular

4â•… Pre- and Postoperative Management of the Neurosurgical Patient

Cerebral Blood Flow and Vasospasm

Fig. 4.1â•… Mean blood pressure by age, showing the mean and 5th and 95th percentiles for average-sized children at each age.

hemodynamics. Ohm’s law predicts that flow is proportional to the pressure gradient between inflow and outflow divided by the resistance to flow (see box Cerebral Oxygen Equations). In brain, CPP is taken as the driving pressure for CBF. Critical questions like “How low can perfusion pressure go?” are very difficult to address. The answer is different in adults; but when should we be concerned? Fig. 4.1 summarizes normal mean BP in children aged 1 to 17 years (boys and girls), and this, at least, is a starting point for tight control of the driving pressure to CBF. In the perioperative patient, we often use both intra-arterial lines and noninvasive cuff measurements, and it is important to know what to do with these measurements. For example, what number is the “real” number when there is a difference in the two measurements? (See Clinical Pearl 4.) Vascular resistance is determined principally by vessel radius (see box Cerebral Oxygen Equations), and an estimate of cerebrovascular resistance (CVR) can be made for any vascular segment of interest in which flow and upstream and downstream pressure gradients are known. Poiseuille’s law shows that the major determinants of CBF are perfusion pressure, blood viscosity, and vessel radius (see box Cerebral Oxygen Equations). Vessel length is an unchanging parameter.

Clinical Pearl 4 Invasive arterial line BP is usually measured from the radial artery. Noninvasive BP is measured with a pressure-sensitive cuff around the upper limb (i.e., brachial artery BP). When there is a difference in the measurements, consider: • Brachial pressure may be a better measure of central pressure when monitoring indicates apparent hypotension. • In young, healthy individuals with good “elastic” tissue, pulse pressure amplification occurs in peripheral arteries and may cause radial artery BP (particularly systolic pressures) to be higher than more central pressures.

Vasospasm is extremely rare in children; whether this is because we do not look for it or because we do not have good age-specific normative data from trans� cranial Doppler (TCD) is unknown. However, from the preceding discussion we can see how a reduction in vessel radius will lead to risk of ischemia. In clinical practice, the highest risk of pediatric aneurysmal subarachnoid hemorrhage is during postoperative days 4 to 14.

4.2.5╇ Cerebral Blood Volume CBV is determined by two factors: CBF and capacitance vessel diameter (i.e., small veins and venules). CBV increases with vasodilation and decreases with vasoconstriction. Although CBF frequently changes in the same direction as CBV, these variables are inversely related under normal situations (e.g., autoregulation) or in pathological situations. Further, blood volume is not equally distributed throughout the brain; blood volume per unit weight is greater in gray matter than in white, with further variation among the various nuclei. Average CBV in humans is 3 to 4 mL/100 g tissue. Pathology, which affects either CBF or cerebral venous capacitance, may modulate CBV with subsequent effects on ICP. More quantitatively, the central volume principle relates the volume that intravascular blood occupies within brain (CBV in mL) and the volume of blood that moves through the brain per unit time (CBF in mL/min) (see box Cerebral Oxygen Equations). For example, although CBV is increased during vasodilation, CBF may not change if blood flow velocity is correspondingly reduced. Surplus blood volume accumulates primarily within cerebral veins, known to receive sympathetic innervation and to respond to sympathetic stimulation, and within capillaries to a smaller degree. Normally, increases in CBV can be physiologically controlled by two maneuvers: increased blood outflow to the extracranial venous circulation and restricted inflow via constriction of the major feeding arteries.

4.2.6╇ Cerebrovascular Autoregulation Cerebral resistance arteries dilate during reductions in CPP and constrict during increases in pressure (Fig.€4.2). As a result, CBF remains relatively constant over a fairly broad range of arterial pressure defined as the autoregulatory plateau. The lower and upper limits of the autoregulatory plateau in adults have been determined as approximately 50 to 60 mm Hg and 150 to 160 mm Hg, respectively. The lower limit of autoregulation refers to the point at which CBF starts to decrease and not to the point at which cerebral resistance arteries are fully

35

36 Section Iâ•… Introduction Clinical Pearl 5 In regard to cerebral autoregulation and development, be conservative and assume that there is a very narrow autoregulatory range around baseline blood pressure.

4.2.7╇ Cerebrovascular Response to Carbon Dioxide

Fig. 4.2â•… Cerebral blood flow as a function of perfusion pressure: the autoregulatory curve can be shifted to the right by increased sympathetic nervous system (SNS) stimulation or chronic hypertension (HTN). The circles denote the change in vessel diameter and, therefore, change in vascular resistance.

vasodilated. Cerebral resistance arteries may continue to dilate to some degree even after the lower limit of CBF autoregulation is exceeded. Passive reductions in diameter occur only at very low levels of CPP. Thus, the lower limit of cerebral vasodilation does not match precisely the lower limit of CBF autoregulation. Reductions of CPP below the lower limit of autoregulation result in hypoperfusion in the brain. In an attempt to compensate for reductions in CBF, the extraction coefficient of O2 from the blood increases. No clinical symptoms are observed until reductions in CPP exceed the ability of increased O2 extraction to satisfy metabolic demands of cerebral tissues. The mechanisms responsible for CBF autoregulation are not yet clearly understood. Possibilities that have been considered include neurogenic, myogenic, metabolic, and endothelial factors.

Under steady-state conditions, over a period of 10 minutes, inhalation of 5 to 7% CO2 results in a 75% increase in CBF. Inhalation of gas containing only 10% O2 increases CBF by 35%. Both hypercapnia and hypoxia lead to a decrease in cerebral vascular resistance (CVR), indicating that the increase in CBF is a consequence of vasodilation. In 1948, Kety and Schmidt described a curvilinear relationship between arterial partial pressure of CO2 (PaCO2) and CBF. A reduction of PaCO2 from 40 to 20 mm Hg decreased CBF, but not to the same extent as the increase in CBF when PaCO2 is increased from 40 to 60 mm Hg. In these studies, CMRO2 did not change during this degree of hypercapnia or hypoxia. The increase in CBF without any increase in CMRO2 resulted in a decrease in AVDO2 (i.e., reduced O2 extraction). The hypercapnia-induced increase in CBF is ≈ 6% per mm Hg change in PaCO2, and hypocapnia decreases CBF by ≈ 3% per mm Hg change in PaCO2 (Fig. 4.3). The relation between CBF and CBV (including arterial, capillary, and venous blood volume) during changes in PaCO2 has also been investigated in humans. The increase in CBV during

Cerebrovascular Regulation in Development In normal term infants, several days are required for the maturation of vascular responses. Studies in preterm babies have shown that CBF increases over the first 3 postnatal days. The lower limit of cerebral autoregulation of 29 mm Hg has been described in nonanesthetized preterm infants less than 30 weeks gestational age. There are no available data on which to determine whether the cerebral autoregulation curve for ex-premature infants mimics that of term infants. There is also evidence that autoregulatory reserve is less in older infants than in children and adults and that the physical state of the patient matters. For example, in cases of craniosynostosis, very low CPPs have been recorded.

Fig. 4.3â•… Cerebral blood flow as a function of partial pressure of carbon dioxide or oxygen. See how the oxygen curve shifts to the right in the presence of anemia ([Hb] low). PaCO2, partial pressure of carbon dioxide in arterial blood; PaO2, partial pressure of oxygen in arterial blood.

4â•… Pre- and Postoperative Management of the Neurosurgical Patient hypercapnia is less than that in CBF, and the degree of decrease in CBV during hypocapnia is less than that in CBF (see box Cerebral Oxygen Equations). According to Poiseuille’s law, CBV increases proportionally to the square of the diameter, yielding the relation CBV = c × CBF0.5, which is in good agreement with the relation during changes in PaCO2. The question of whether alteration in PaCO2 changes CBF equally in all brain regions is somewhat controversial, as is the question of whether both gray and white matter behave in the same way. There appears to be a developmental difference in CBF response to CO2, although in all age groups, CBF increases with increasing PaCO2. In both the fetus and the newborn, gray matter CBF increases at PaCO2 greater than 40 mm Hg but changes little at lower PaCO2 levels. Also, the change in CBF per mm Hg change in PaCO2 is higher in the newborn than in the fetus, which suggests that the cerebrovascular response to CO2 is not complete at birth. This depressed CO2 response in the fetus may be correlated to a difference in CMRO2 (i.e., when CBF responses are normalized for CMRO2, the increase in CBF is greatest in newborns, smaller in adults, and even smaller in fetuses). Hypocapnia does not alter the lower limit of cerebral autoregulation in mature animals but does lead to lower CBF per unit change in CPP. At lower BP, below the level of cerebral autoregulation, there is an attenuation of the slope of the CBF/CPP graph, suggesting that the cerebral vascular response is attenuated with hypotension. CBF in preterm infants is dependent on PaCO2. The cerebral vascular response to PaCO2 is less in the first day after birth and increases with gestational age. It is also attenuated, but not eliminated, in hypotensive infants. This reactivity is present even in preterms; it is estimated to be about 4% per mm Hg PCO2. Intraoperatively, it is also preserved in children (18 months to 7 years of age) anesthetized with sevoflurane (see later section on drug effects on CBF). Hypocapnia may, therefore, result in cerebrovascular vasoconstriction and reduction of CBF.

Clinical Pearl 6 Acute change in PaCO2 has an acute effect on CBF: • Hypercapnia increases CBF by 6% per mm Hg increase in PaCO2 above 40 mm Hg. Be concerned about this possibility in the patient with obstructed breathing or sleep apnea. • Hypocapnia decreases CBF by 3% per mm Hg decrease in PaCO2 below 40 mm Hg. Be concerned about this possibility in the patient who is in pain and crying or is hyperventilating.

4.2.8╇ Cerebrovascular Response to Oxygen Hypoxia elevates CBF. CBF does not change in response to small deviations of the PaO2 around normal levels. Rather, when PaO2 falls to ≈ 50 mm Hg, regional CBF begins to rise. As PaO2 is further reduced below this threshold, CBF increases exponentially. It may reach over 400% of basal flow at lowered PaO2 in an attempt to maintain O2 delivery. There is no significant change in CMRO2 over the range of PaO2 from 23 to 100 mm Hg. The responses of the cerebral circulation to hypoxia relate to hemoglobin oxygen saturation (SaO2). At a PaO2 > 70 mm Hg, the SaO2 is 100%. However, when the PaO2 reaches about 50 mm Hg, the SaO2 is 85%. Under conditions of reduced availability of O2 (e.g., anemia), the regional CBF/PaO2 curve is shifted to the right (Fig. 4.3). Hypoxic elevations in regional CBF are not associated with changes in metabolic rates. However, the vasodilation is additive with that produced by metabolic signals, particularly acidosis and hypercapnia.

4.3╇ Anesthetics Influencing Postoperative Care One should not manage a child in the postoperative period without knowing what has gone on before. Considering the pathway from preoperative treatments to induction of anesthesia and the surgical procedure to recovery room care, and then admission to the ICU, as a continuum is absolutely essential. Postoperative neurosurgical children will have been exposed to a number of therapies before and during surgery. As discussed already, at the time of handoff, a formal assessment should be made of pre-, intra-, and postoperative issues (Table 4.2). An essential component of the handoff assessment is medicines, anesthetics, and fluid therapy. For example, the patient may have been hyperhydrated in preparation for a cerebrovascular procedure (as

Clinical Pearl 7 Acute change on PaO2 has an acute effect on CBF: • Hypoxia (PaO2 ≤ 50 mm Hg) increases CBF. • SaO2 < 85% increases CBF. • The effect of SaO2 and PaO2 on CBF is exacerbated by the presence of anemia. That is, the homeostatic threshold for hypoxic drive to increase CBF is raised. The hypotensive or hypocapnic infant will not be able to mount this protective response; thus, they are at risk.

37

38 Section Iâ•… Introduction described later). They will have received anesthetics that have been specifically used because they depress cerebral metabolism. However, it is the other unwanted cerebrovascular effects that may be of concern postoperatively.

or remifentanyl) along with nitrous oxide (70%) and low-dose (0.2–0.5%) isoflurane is a frequently used technique, and when it comes to postoperative considerations, those caring for such patients should be aware of cumulative dosing and timings. For example, nitrous oxide may contribute to postoperative nausea and vomiting and dose-dependent increase in CBF. Clearly, we do not want a postoperative infant, following a procedure on an arteriovenous malformation, to be vomiting such that episodic rises in intrathoracic pressure are transmitted to intracranial vessels (see Clinical Pearl 8).

4.3.1╇ Intraoperative Anesthetic Drugs and Agents Volatile anesthetics act as potent vasodilators in the cerebral circulation. They are capable of uncoupling the usual relationship between CBF and CMRO2 (described previously). Such uncoupling increases CBV and, in consequence, raises ICP or worsens intracranial hypertension. Desflurane and isoflurane blunt the autoregulatory response of maintaining CBF with change in CPP. Nitrous oxide has vasodilatory effects. Both isoflurane and sevoflurane decrease CMRO2, but flow-metabolism coupling is maintained (Table 4.3). Intravenous anesthetics, sedative/hypnotic drugs, and opioids also have effects, but they do not cause cerebrovascular vasodilatation. For example, barbiturates and propofol maintain autoregulation and flow-metabolism coupling while reducing absolute level in CBF, CBV, and CMRO2. Propofol maintains cerebrovascular reactivity to CO2 when the latter is above 30 mm Hg. However, propofol at high doses induces hypotension. Maintenance of anesthesia during neurosurgery with an opioid (fentanyl or other related synthetic opioids, such as sufentanil

Clinical Pearl 8 The cerebral circulation can be modeled as a Starling resistor, where the important “downstream” pressure is ICP or cerebral venous pressure, whichever is higher. Cerebral venous pressure may be raised acutely by several causes of obstruction to venous outflow from the cranium: • Kinking of neck vessels by head position, or neck vessels obstructed by central venous catheter • Neck collar that is too tight, or tight circumferential neck ties for securing tracheostomy • Periodic rise in intrathoracic pressure—coughing, crying, Valsalva maneuver, mechanical ventilation with high mean airway pressure or high end-expiratory pressure (typically > 8 cm H2O)

Table 4.3â•… Effects of anesthetics, benzodiazepines, and opioids on cerebral metabolism, circulation, and intracranial pressure Agent

CMRO2

CBF

Pressure autoregulation

ICP

Inhaled anesthetic • Sevoflurane • Isoflurane • Desflurane

↓↓

Â�↑

Absent

Â�Â�↑

Inhaled nitrous oxide

↑ or no change

Â�Â�↑

Present

Â�↑Â�

Intravenous anesthetic • Propofol • Thiopental

↓↓

↓↓

Present

↓↓

Dissociative anesthesia • Ketamine

No change

Â�Â�Â�↑Â�Â�↑Â�

?

Â�Â�Â� ↑Â� ↑Â�Â�

Sedative benzodiazepines

↓↓

↓

Present

↓

Analgesic opioids

No change

No change

Present

No change

The direction of arrows indicates increase or decrease, and the number of arrows indicates the strength of the derangement above “no change” qualitatively. Abbreviations: CBF, cerebral blood flow; CMRO2, cerebral metabolic rate for oxygen; ICP, intracranial pressure.

4â•… Pre- and Postoperative Management of the Neurosurgical Patient

4.3.2╇ Emergence from Anesthesia At the end of the operative procedure, in the neurosurgical patient, careful planning is required to balance the need for early endotracheal extubation and awakening so as to obtain a clinical examination versus the risk of profound hemodynamic instability on cerebral hydrodynamics. There are, potentially, two interlocking vicious cycles in pathophysiology that ultimately lead to hemodynamic instability, cerebral edema, and intracranial hemorrhage (Fig.€4.4), and these should be considered in the context of what is required in the postoperative period. Hence, in some high-risk children there might be a plan for postoperative mechanical ventilation or deep sedation (see box Emerging from Anesthesia). Emergence agitation may be due to pain, a full bladder, dysnatremia (described later), drug reaction (e.g., paradoxical reaction to midazolam or diphenhydramine), or emergence delirium (e.g., reaction to sevoflurane). The treatable causes should be identified and dealt with or even anticipated. For example, pain and agitation can be anticipated and treated with bolus doses of opioids, propofol, clonidine, or dexmedetomidine. The stress response with emergence hypertension can be treated with low-dose fentanyl infusion (1.5 µg/kg/hr) and an antihypertensive. In regard to the antihypertensive, the choice is between a beta-blocker (labetalol or esmolol) and a calcium channel antagonist (nicardipine). There is no ideal drug: beta-blockers have the risk of bradycardia and cardiac conduction delays, whereas the calcium channel antagonists cause cerebral vasodilation, impaired autoregulation, and risk of hypotension. Use what you are familiar with and what has been

approved in your institution—the authors’ choice is labetalol since it is readily titratable. Dexmedetomidine infusion is being used increasingly in pediatric neurosurgery; there are no data, but its use is gaining popularity because it acts as a sedative, sympatholytic, and analgesic.

Emerging from Anesthesia Cases for Consideration of Delaying Extubation and Emergence from Anesthesia • Preoperative altered level of consciousness • Surgery lasting > 6 hours • Large tumor resection with preoperative midline shift • Injury to cranial nerves IX, X, XI • Complications during surgery (see Table 4.5) • Intraoperative brain swelling • Hypothermia • Coagulopathy • Acid-base abnormality • Dysnatremia (see text for details)

4.3.3╇ Failure to Awaken Occasionally, a patient may unexpectedly fail to awaken at the end of surgery. A number of factors should be considered and corrected (Table 4.4) and, if necessary, emergency imaging should be done.

Fig. 4.4â•… Stress-induced pathophysiology during emergence from anesthesia. CBF, cerebral blood flow; CMRO2, cerebral metabolic rate for oxygen; ICP, intracranial pressure; mBP, mean blood pressure.

39

40 Section Iâ•… Introduction Table 4.4â•… Factors to consider in the patient failing to wake up at the end of surgery Factor

Intervention

Hypothermia

Warm patient

Hypoglycemia

Check blood glucose and treat accordingly

Hypercapnia

Check blood gas and supportive ventilation

Hypoosmolality

Check serum electrolytes and treat accordingly

Hypothyroid

Thyroid hormone required for benzodiazepine metabolism; support patient until patient awakens and thyroid function tests available

Neuromuscular blockade

Impaired hepatic and/or renal metabolism may prolong the effect

Altered drug metabolism

See thyroid above; also consider drug dosing and drug clearance of continuous infusions used

Seizure

Assess and treat accordingly

Intracranial bleeding

Imaging required and surgery

Intracranial pressure/ ischemia

Imaging required

4.4╇ Surgery-Related Perioperative Crisis Management In common with many forms of surgery, in neurosurgery there is the general risk of infection, bleeding, and deep vein thrombosis. In infants and small children there is also the risk of postoperative hypothermia, which may affect the postoperative course if there is significant vasoconstriction. For example, shivering related to hypothermia or volatile anesthetics can double the body’s oxygen consumption and increase mean arterial blood pressure by 35%. Both of these responses may be counterproductive in the child undergoing arterial bypass surgery for moyamoya and should therefore be avoided. In regard to the general principles for brain resuscitation that may be required, children can be considered the same as adults. That is, hypotension, hypoxia, and hypercapnia all have the potential for

worsening intraoperative cerebral hydrodynamics (as described previously) and may lead to brain injury. Seizures, hyperpyrexia, and hypoglycemia may also require management. The anesthesiologist will attend to these and notify the operating neurosurgeon of the occurrence. Table 4.5 provides an overview of specific problems that may also occur during and after surgery. (Hemorrhage, “brain relaxation,” and cerebral edema are considered in later sections.)

4.5╇ Perioperative Intravenous Fluids The prescription of intravenous maintenance fluids for children unable to tolerate oral therapy is fundamental in perioperative care. What we want to know is how much and what type of fluid we should give postoperatively. The main aims of fluid therapy are, first, to have a hemodynamically stable patient; second, to avoid electrolyte abnormalities; and third, to ensure adequate glucose control. The first aim requires careful maintenance of intravascular volume. Preoperative fluid restriction or use of mannitol, hypertonic saline, or diuretics may lead to BP instability and even cardiovascular collapse intraoperatively, with problems carrying over into the postoperative phase. It is therefore important to know what has happened intraoperatively, the estimated blood loss as a proportion of blood volume, as well as fluid inputs and outputs before ward or ICU admission. Normal saline is the preferred intravenous fluid for neurosurgery cases because its osmolality (308 mOsm/L) should minimize occurrence of hyponatremia (serum sodium < 135 mmol/L) and cerebral edema. In pediatric practice, we calculate rate of maintenance fluid administration scaled to weight of the patient using the classic Holliday and Segar formula for daily fluids: 100 mL/kg for the first 10 kg in body weight; add 50 mL/kg to 1,000 mL for the next 10 kg in body weight (i.e., weight 10 to 20 kg); add 20 mL/kg to 1,500 mL for weight above 20 kg. These rates are based on normal conditions in health and they may not reflect what is needed in the operating room. The following are examples of the issues that need to be considered. How long was the procedure? How much maintenance fluid has been given? It is not unusual for long procedures to necessitate maintenance fluid up to 10 mL/kg/hr. Were any saline boluses given? When more than 60 mL/kg has been used, there is the risk of hyperchloremic metabolic acidosis, which may not be appreciated unless serum chloride is measured.

4â•… Pre- and Postoperative Management of the Neurosurgical Patient Table 4.5â•… Surgery-related perioperative complications and their management Complication

Risk

Treatment

Aspiration of gastric contents

•P  atients with full stomach •P  atients with raised ICP and vomiting in the presence of altered level of consciousness

At the time of endotracheal intubation: •S  uction airway before mechanical ventilation (MV) •M  V with 100% oxygen (FiO2 1.0) and positive end expiratory pressure (PEEP) •P  ostoperative MV should be anticipated

Intrathoracic trauma

•H  eart, lung, and great vessel injury from procedure to tunnel sheath for VPS

Evaluate for signs of cardiorespiratoryabdominal instability and treat accordingly

Latex allergy

•P  atients with myelomeningocele •P  atients with sensitization to latex

A type 1 IgE-mediated reaction with urticaria, angioedema, bronchospasm, and anaphylactic shock:  revent further exposure by removing all •P triggering agents •A  ssess airway, breathing, and circulation (ABC) and treat with full cardiorespiratory support if needed  urvey of the skin for urticaria •S  educe or discontinue volatile anesthetics •R •T  reat, if needed, with airway, oxygen, fluid bolus, epinephrine, steroids, and antihistamines  end off serum tryptase levels once the •S patient is stable

SDH or upward herniation

Rapid lowering of open EVD or decompression of hydrocephalus:  emorrhage: rupture of cortical bridging •H veins •U  pward herniation: brain stem signs with bradycardia, EKG changes, and irregular breathing

Evaluate neurologic status for signs of raised ICP: •A  BCs and support if required • Imaging •S  urgical intervention as required

Venous air embolism (VAE)

 uring placement of ventriculoatrial shunt •D •D  uring craniosynostosis repair •S  urgical site higher than heart  ir in intravenous tubing •A •P  ersistence of patent foramen ovale, which increases the potential for paradoxical air embolism

VAE is recognized by an abrupt fall in EtCO2, hypoxia, hypotension, bradyarrhythmia, and “mill wheel” murmur. Avoid the use of nitrous oxide because of its low blood-gas partition coefficient and its ability to increase the size of any air embolus that occurs. Treatment of VAE should be immediate: •C  onsider compressing jugular veins •S  urgeon to flood the operative field or pack wound/bone; lower surgical site to below heart level •M  V with FiO2 1.0 and zero PEEP; discontinue volatile anesthetic, Valsalva maneuver and prevent negative ITP •A  spirate air in central line in situ •A  BCs and full cardiorespiratory support if needed

Hemodynamic instability during ETV

•S  timulation of floor of third ventricle with arrhythmia, bradycardia, asystole; or, hypertension from catecholamine release •R  aised ICP

General evaluation for causes of hemodynamic instability, such as hypoxia, hypercapnia, distended bladder, awareness, and raised ICP. In addition:  BCs and support if required •A • In case of procedure-related stimulus, treat if it does not resolve spontaneously when stimulation has stopped

(Continued on page 42)

41

42 Section Iâ•… Introduction Table 4.5 (Continued)â•… Surgery-related perioperative complications and their management Complication

Risk

Treatment

Postoperative aSAH vasospasm

Rare in children but can occur postoperative day 4 to 14

Evaluate with serial TCD and ad hoc use of adult therapies: •T  riple-H therapy, including: hydration, hemodilution, and hypertension •N  imodipine, angioplasty

Normal perfusion pressure breakthrough

High-flow AVM with postoperative parenchymal hemorrhage or cerebral edema

Should be anticipated in high-flow AVM cases: •S  taged embolization to surgical procedure •M  aintenance of normal to slightly low BP postoperatively

AV fistulas and vein of Galen malformation

High-output cardiac failure

May need hemodynamic support and MV

Moyamoya

Bypass surgery with risk of stroke related to perioperative events or natural history

Postoperative risk of stroke should be anticipated and limited: •A  void dehydration, hyperventilation, and hypotension  ggressive analgesia to minimize BP •A fluctuations and hyperventilation

Abbreviations: aSAH, aneurysmal subarachnoid hemorrhage; AV, arteriovenous; AVM, arteriovenous malformation; BP, blood pressure; BPS, ventriculoperitoneal shunt; EKG, electrocardiogram; EtCO2, end-tidal carbon dioxide; ETV, endoscopic third ventriculostomy; EVD, external ventricular drain; FiO2, fraction of inspired oxygen; ICP, intracranial pressure; IgE, immunoglobulin E; ITP, intrathoracic pressure; SDH, subdural hematoma; TCD, transcranial Doppler; VPS, ventriculoperitoneal shunt.

Clinical Pearl 9 Calculation of weight-based maintenance fluid requirement in a child: Administer • • • •

100 mL/kg for the first 10 kg (0–10 kg) 50 mL/kg for the next 10 kg (11–20 kg) 20 mL/kg for the next 10 kg (21–30 kg) 10 mL/kg for the next 10 kg (≥ 31 kg)

A 35-kg child should therefore receive 1,000 mL + 500 mL + 200 mL + 50 mL = 1,750 mL/day or 73 mL/hr as maintenance therapy. In general, it is good to limit the maximum calculated maintenance at an adult level of 2,500 mL/day. If, however, the intention is to give 1.5 times maintenance, then the volumes would be 2,625 mL/day or 109 mL/hr.

4.6╇ Postoperative Dysnatremia (Hyponatremia and Hypernatremia) Disorders of salt and water homeostasis are common in postoperative neurosurgical patients. The four main renal salt and water-handling problems that occur in such children are inappropriate intravenous fluid administration, euvolemic state of antidiuretic hormone excess (i.e., syndrome of inappropriate ADH excess [SIADH]), cerebral salt wasting (CSW), and diabetes insipidus (DI).

Before embarking on detailed analysis of salt and water balance, when an abnormally low serum sodium level is received from the laboratory, first make some assessment of salt losses, for example, salt loss via CSF drainage. Second, consider whether the hyponatremia is actually pseudohyponatremia due to the use of perioperative radiologic nonionic hyperosmolar contrast medium.

Clinical Pearl 10 Salt loss via CSF drainage. For a child weighing 35 kg, we estimate the following: • Usual sodium maintenance is 2 to 4 mmol/kg/ day (70 to 140 mMol/day) • CSF drainage up to 400 mL/day is equivalent to 60 mmol sodium/day • In this instance, the child could require up to 200 mmol sodium/day (≈ 6 mmol/kg/day), and we have not yet accounted for urinary losses. Therefore, making an assumption that hyponatremia is due to SIADH and therefore volumerestricting the child, without first checking that adequate sodium replacement has occurred, is the wrong course of action.

4â•… Pre- and Postoperative Management of the Neurosurgical Patient

4.6.1╇ Inappropriate Intravenous Fluids Postoperatively, there is significant risk of hospitalacquired hyponatremia (serum sodium concentration < 135 mmol/L). In this setting, postoperative pain, stress, nausea, vomiting, narcotics, and volume depletion may all have the potential to stimulate vasopressin production and to induce a state of euvolemic hyponatremia not dissimilar to SIADH. However, what is also clear is that hypotonic fluids or restricted fluids may all result in hyponatremia. There have been few trials of intravenous fluids in postoperative neurosurgical patients in the pediatric ICU, but those carried out to date indicate that urine tonicity is almost always fixed in the postoperative period (e.g., in those receiving normal saline at maintenance, urine tonicity is ~ 200 mOsm/L, whereas in those receiving any other prescription, urine tonicity is lower, ~ 160 mOsm/L), and urine output is constant at ~ 1 mL/kg/hr. What this indicates is that isotonic fluids prevent postoperative falls in serum sodium concentration, but hypotonic fluids may result in falls in serum sodium concentration because of renal desalination. In none of these studies was fluid overload or significant hypernatremia a complication. Another important consideration when assessing salt and water balance is to review what has happened to the child throughout the perioperative period. By nature, our physiology is geared toward surviving a salt-poor dietary environment. Humans are not very good at dealing with salt excess. So, for example, take an average 4- to 8-year-old child who weighs between 16 and 26 kg. The recommended salt intake per day in normal 4- to 8-year-olds is 1.2 g/day (20 mMol/day). Actual upper limit of intake by 4- to 8-year-olds from observational studies in 2004 is ~ 2.6 g/day (44 mMol/day). In perioperative neurosurgical practice, we commonly place patients on 1.5 times fluid maintenance using normal saline, which in a 26-kg child is equivalent to a salt intake of 21.8 g/day (374 mMol/day). We then often reduce intake, abruptly, to maintenance fluids of 14.5 g/day (249 mMol/day). So, we have taken a child with a normal salt intake—albeit likely higher than what public health would recommend—and increased this intake by a factor of 8 perioperatively and then reduced this intake to a sixfold increase from baseline. During these interventions we sometimes see unexpected hypernatremia or hyponatremia. Let us consider the “threat” to homeostasis that has occurred in the perioperative period and the physiologic attempts to rectify this change. High salt intake is a powerful physiologic stimulus and results in renal and hormonal changes to excrete sodium. The stimulus to sodium excretion is an expanded arterial volume. The mechanism of renal loss of the salt load occurs in the proximal tubule. (The luminal sodium transport system and the basolateral sodium

pump are removed from the membranes of individual proximal tubular cells, leading to reduced ability to reabsorb filtered sodium ions.) Studies from the 1950s to the 1990s in healthy adults looked at transitioning from low to high salt intake (0.6 g/day to 20.5 g/day) and the reverse. Similar studies have been carried out using saline solutions. A change to a high salt intake leads to a new steady state in hormone secretion, with high ADH, low renin, and low aldosterone. If there is a decrease in rate of infusion of saline, the patient continues to excrete sodium because of secondary renal salt wasting due to the prevailing endocrine environment—high ADH, low renin, low aldosterone. There is at least a 2-day delay in restoring hormone physiology back to baseline when salt intake is reduced back to normal levels; the body is generally much better at “switching on” rather than “switching off” mechanisms.

Clinical Pearl 11 Perioperative care with intravenous fluids is an assault to homeostasis, even when using isotonic fluids. Consider the following when assessing salt and water balance: • Always assess intake and output and measure the tonicity balance. • Patients are at risk of hyponatremia when there are abrupt decreases in intake of normal saline since we have induced a high-ADH, lowrenin, and low-aldosterone state with the high salt intake. • Not all hyponatremia is SIADH; it may be “appropriate” for the patient. • So called “salt wasting” in patients receiving high volumes of saline is not necessarily “cerebral salt wasting,” as it may represent the new steady state of output matching input. • In the patient with hypothalamic-pituitary abnormality, remember two things and act upon the laboratory results when available: thyroid hormone is needed to excrete a water load, and cortisol is also needed.

4.6.2╇ Syndrome of Inappropriate Antidiuretic Hormone Secretion Postoperative hyponatremia, euvolemia, and ADH excess defines the SIADH. As a screening approach, we often use the following parameters: serum sodium concentration 20 mmol/L), and

43

44 Section Iâ•… Introduction variable urine osmolarity. Therefore, regular monitoring of intravascular volume, urine output and tonicity, and serum electrolytes is needed during the period of administering intravenous fluids. The other causes of hyponatremia that need to be excluded are volume depletion, edematous states (congestive heart failure, cirrhosis, and nephrosis), renal dysfunction, adrenal insufficiency, and hypothyroidism. If the cause is perioperative SIADH, it has occurred because of free water retention at the same time as natriuresis, which maintains fluid balance at the expense of serum osmolality. The ADH excess leads to increased water permeability in the collecting duct, water retention, and subclinical volume expansion, with an increase in total body water of 7 to 10%. Volume expansion also triggers hemodynamic regulatory mechanisms to maintain plasma volume at the expense of sodium, which is in part due to a pressure natriuresis and a secondary release of natriuretic peptides. Because of the risk of hyponatremia in the perioperative period, many clinicians choose to avoid using hypotonic solutions altogether. It should be noted that Ringer’s lactate sodium (130 mmol/L) might also result in a fall in serum sodium (see preceding discussion). This fluid is often used intraoperatively, as it is a balanced solution with a physiologic amount of base, calcium, and potassium and will limit the hyperchloremic acidosis that occurs with large volumes of normal saline. The treatment of SIADH is to reduce free water excess by fluid restriction and diuretics. If a hyponatremic seizure occurs, then hypertonic saline should be used to correct serum sodium; the level to be targeted is that at which the seizure comes under control,

often >€130 mmol/L. Taking 0.6 L/kg body weight as the apparent volume of distribution for sodium, one should anticipate an immediate increase of 3 to 5 mmol/L in serum sodium concentration with a rapid intravenous bolus of 4 to 6 mL/kg body weight of 3% saline.

Clinical Pearl 12 Serum uric acid is a useful corroborating test in diagnosing SIADH: • Serum uric acid is < 4.0 mg/dL. • Increased urate clearance with fractional excretion of urate > 12% (normal < 10%) at time of hyponatremia, which improves on correction of hyponatremia.

4.6.3╇ Cerebral Salt Wasting CSW is a diagnosis of exclusion based on clinical criteria, and it is overdiagnosed in my experience. The essential features of the syndrome are renal sodium and chloride wasting in a patient with a contracted effective arterial blood volume, where other causes of excess sodium excretion have been excluded. Volume contraction is likely to be present when there is a deficit of sodium that exceeds 2 mmol/kg. Hyponatremia is a nonspecific clue. The literature suggests that this condition is common in children after all types of neurosurgical procedures and that it results from excessively high atrial or brain natriuretic peptide levels. The box Cerebral Salt Wasting lists some of the

Cerebral Salt Wasting Diagnosis of cerebral salt wasting in a patient with excretion of sodium and chloride without obvious cause

Exclude: • A physiologic cause for the excretion of sodium chloride (e.g., an expanded extracellular fluid volume from hyperhydration with 1.5 times maintenance followed by abrupt decreases in intake) • A noncerebral cause for natriuresis: • Diuretics • States with low aldosterone (a stimulator for reabsorption of sodium) • Adrenocortical insufficiency • Congenital salt-losing renal tubular disorders (Bartter or Gitelman syndrome)

• Presence of an inhibitor of renal reabsorption of sodium, such as osmotic agents or high concentration of ligands for the calcium receptor in the loop of Henle (e.g., hypercalcemia, gentamicin) • Obligatory excretion of sodium by the excretion of anions other than chloride • High-output renal failure (renal tubular damage, such as obstructive uropathy, interstitial nephritis, and acute tubular necrosis) • Sodium wasting from CSF or drainage Other explanations for salt wasting: • Natriuretic agents of cerebral origin • Downregulation of renal sodium transport by chronic hypervolemia • Pressure natriuresis from adrenergic agents • Suppression of the release of aldosterone

4╅ Pre- and Postoperative Management of the Neurosurgical Patient diagnoses that should be excluded before concluding that the patient has CSW. (It should be noted that atrial natriuretic peptide level is high in the patient who has been managed with hypervolemic fluid management. In this instance, natriuresis as a response to volume control is part of homeostasis, and not CSW.) The incidence of CSW is apparently on the order of 1 to 5% of neurosurgical procedures, and it has been reported in association with calvarial remodeling, tumor resection, and hydrocephalus. A screening approach, when there is concern about possible CSW, is hyponatremia (€3 mL/kg/hr) and elevated urine sodium (>€120 mmol/L) when available, or elevated urinary osmolarity (>€300 mOsm/L water). The physiology involves inappropriate and excessive release of natriuretic peptides that leads to a primary natriuresis and volume depletion. A secondary hormonal response occurs with an increase in the renin-angiotensin system and arginine vasopressin production. The median onset of CSW is on postoperative day 3, lasting a median of 3 days. In contrast to hyponatremia due to SIADH, the fractional excretion of urate is elevated but does not improve when hyponatremia is corrected (see Clinical Pearl 12). Patients with CSW are more likely to have suffered postoperative stroke, to have chiasmatic or hypothalamic tumors, and to be younger than patients with normal postoperative sodium concentration. Almost half of the patients with CSW have postoperative hyponatremic seizures (serum sodium < 130 mmol/L). The treatment of CSW involves sodium administration to match urinary losses and correction of intravascular volume contraction. In some instances, more rapid resolution of hyponatremia after volume expansion has been achieved with fludrocortisone.

4.6.4╇ Diabetes Insipidus DI results from a deficiency of vasopressin, and it is an expected complication of surgical procedures near the pituitary or hypothalamus. It is most frequently seen in association with craniopharyngioma, where it can be a presenting symptom in 40% of cases. In most patients, DI is transient, but ~ 6% develop permanent DI. The diagnosis should be suspected when serum sodium rises above 145 mmol/L in association with urine output above 2.5 mL/kg/ hr for 3 consecutive hours, or more than 4 mL/kg/ hr in any one hour. The urine osmolality should be hypotonic (€300 mOsm/L) in the absence of glycosuria, mannitol use, and renal failure. Important consequences of this condition are severe dehydration and hypovolemia, since urine output is driven by lack of vasopressin.

Knowledge of the patterns of DI that can occur following surgery in the hypothalamic-pituitary area is important. The most common is that associated with local edema as a result of traction or manipulation of the pituitary stalk. This lesion usually results in transient polyuria that begins 2 to 6 hours after surgery and resolves as edema diminishes in 1 to 7 days. A “triphasic pattern” has also been described (see Clinical Pearl 13). Transection of the pituitary stalk or destruction of the hypothalamic median eminence will result in permanent DI. Frequently, permanent DI, either partial or complete, develops without interphase changes.

Clinical Pearl 13 The triphasic pattern in postoperative electrolyte disturbance and DI, with the following phases: • Initial: polyuria in the first postoperative days • Second: normal urinary output or SIADH resulting from release of previously stored ADH from damaged neurons • Depletion of vasopressin stores with polyuria There are a variety of successful approaches to treating DI. It is useful to have a neuroendocrine assessment preoperatively, with a perioperative care plan, since deficiencies of thyroid and/or adrenocortical hormones can coexist. In the child with known DI, preoperatively, some endocrinologists prefer not to replace vasopressin and to restrict total fluid intake to approximately twice-normal maintenance (scaling to body surface area rather than weight, i.e., 3 L/m2/day), recognizing that this can result in mild hypernatremia and thirst but minimizing the more dangerous risk of water intoxication with vasopressin administration. Others prefer to withhold long-acting DDAVP (desmopressin acetate, the synthetic analog of ADH) in the perioperative period and instead manage DI with intermittent injections of intramuscular vasopressin. Administration of excessive fluids in this setting, as with the perioperative maintenance of DDAVP, can result in hyponatremic seizures. When new-onset, postoperative DI is recognized, the following strategy should lead to serum sodium concentrations between 130 and 150 mmol/L. These patients respond to an infusion of aqueous vasopressin (20 units/500 mL). Aqueous vasopressin is used because of its rapid onset of action and brief duration of effect. However, its potential vascular effects (i.e., hypertension) mean that close observation in a monitored setting is required. The infusion is started at 0.5 mΥ/kg/hr and titrated upward in 0.5 mU/kg/ hr increments every 5 to 10 minutes until urine out-

45

46 Section Iâ•… Introduction put decreases to less than 2 mL/kg/hr. It is rare to require more than 10 mU/kg/hr. Once urine output is less than 2 mL/kg/hr, the vasopressin infusion is not adjusted downward. Neither is fluid administration adjusted according to urine output. Antidiuresis with vasopressin is essentially an “all-or-none” phenomenon, and the aqueous infusion is used to produce a “functional SIADH” state. This strategy recognizes that renal blood flow remains normal in the normovolemic, but maximally antidiuresed, child. Because urine output is then minimal (0.5 mL/kg/hr), other clinical markers of volume status must be followed closely. For example, anuria together with increased heart rate or decreased BP may be evidence of hypovolemia. Vasopressin infusion does not induce acute tubular necrosis, and severe oliguria or anuria is an indication for additional fluid and not for decreasing or discontinuing the infusion. When vasopressin is used, infusion fluids should be carefully restricted because in the presence of full antidiuresis, excessive fluids (oral or intravenous) can lead to intravascular volume overload. In addition, administration of hypotonic fluids (oral or intravenous) can result in dangerous hyponatremia. Restricting fluids to replacement of insensible losses, which is generally considered to be about two-thirds usual maintenance rates, may prevent this complication. In children at risk of developing permanent DI, in whom adequate oral intake has been established, intravenous fluids and the vasopressin infusion can be discontinued while free oral intake is permitted. Subsequent treatment of DI is withheld until the child demonstrates polyuria. At this time, treatment with DDAVP, rather than restarting a vasopressin infusion, is recommended. DDAVP is a synthetic vasopressin with duration of action of 12 to 24 hours. It is usually administered intranasally at a dose of 5 to 10 micrograms. Oral DDAVP can be used at 10 to 20 times the nasal dose. Antidiuresis generally begins within 1 hour. In children with known DI, DDAVP treatment can be resumed once an intact thirst mechanism has returned and oral intake occurs without vomiting.

4.6.5╇ Glucose or No Glucose in Perioperative Intravenous Fluids Intraoperatively, the stress response is generally able to maintain normal serum glucose levels without exogenous glucose administration. However, in postoperative infants and small children, particularly if there has been an effective fast of 6 to 12 hours, there is the risk of perioperative hypoglycemia. It is therefore advisable to use glucose-containing fluids to meet baseline demands. Infants require continuous infusions of glucose at 5 to 6 mg/kg/min in order to maintain serum levels. Hence, normal saline in 2.5 to 5% dextrose is often used. In general, older children

and adolescents can tolerate 18 to 24 hours of fasting. One risk of giving exogenous glucose is that, with the stress of critical illness (and resulting insulin resistance), hyperglycemia may be induced and, in turn, may be associated with neurologic injury and poor outcome. However, while it is known that hyperglycemia may worsen ischemia, it remains unclear that the opposite—tight glycemic control—offers significant benefits to children. Therefore we follow a conservative approach that maintains the random serum glucose level in the normal range, below 180 mg/dL.

4.7╇ Brain Relaxation and Treatment of Cerebral Edema Cerebral edema may occur intraoperatively in the patient with open dura and visible brain swelling. It may also occur postoperatively. Table 4.6 summarizes the treatments used to prevent and treat cerebral edema. There is no evidence base for using these therapies in general neurosurgery, and it should be noted that Table 4.6 is merely guidance on what people report that they use, often borrowed from traumatic brain injury (TBI) care. For the most upto-date guidance on the management of raised ICP in the context of severe TBI in infants, children, and adolescents, the reader should look at the searchable guidelines on the Brain Trauma Foundation website (see http://braintrauma.org/coma-guidelines/). The second edition of the pediatric guidelines was published in 2012 and is available as open access.

4.7.1╇ Rescue Hyperosmolar Therapy in Suspected Cerebral Edema Two intravenous hyperosmolar agents are used for the treatment of cerebral edema: mannitol and 3% hypertonic saline (3% HS). Increasingly, 3% HS is the preferred osmotherapy agent rather than mannitol. There are no randomized controlled trials supporting this practice, so it is important to understand the advantages and disadvantages of these therapies.

Mannitol Mannitol has the potential to fail in treating cerebral edema. An intravenous bolus dose is distributed throughout the extracellular fluid within 3 minutes, except in areas protected by the intact blood-brain barrier (BBB). There is an acute rise in extracellular osmolality in body tissues because mannitol (molecular weight 182) causes an influx of water from the intracellular compartment; this restores osmotic equilibrium between the intracellular and extracel-

4â•… Pre- and Postoperative Management of the Neurosurgical Patient Table 4.6â•… Interventions for limiting and treating cerebral edema Factor or agent

Intervention

Cerebral venous drainage

• Head elevation: increased risk of venous air embolism if craniotomy is underway (see Table 4.5) • Head midline • Minimize intrathoracic pressure

CPP optimization

• No guidelines as to level (see text for details) • Target normal mean arterial blood pressure (see Fig. 4.1)

PaCO2 optimization

• Target the normal range of 35 to 40 mm Hg • Mild hyperventilation (30 to 35 mm Hg) can be used for short periods

Intravenous hyperosmolar therapy (see text for details)

• Mannitol: 0.25 to 1 g/kg raises serum osmolarity by 10 to 20 mOsm/L

Anesthetic agents (see Table 4.3)

• Barbiturate bolus: induced cerebral vasoconstriction and reduces CMRO2 • Propofol bolus (see Table 4.3)

Dexamethasone

• Used in vasogenic edema around tumor or abscess • Complications include stress hyperglycemia, hypertension, and septic shock

Hypothermia

• Reduces CMRO2, but of no proven value in TBI • Avoidance of hyperthermia may be just as effective

CSF drainage

• May be used if there is access to the lateral ventricles

Abbreviations: CMRO2, cerebral metabolic rate for oxygen; CPP, cerebral perfusion pressure; CSF, cerebrospinal fluid; ICP, intracranial pressure; PaCO2, partial pressure of carbon dioxide in arterial blood; TBI, traumatic brain injury.

lular compartments, at a higher volume than before the drug was given. This water shift dilutes and lowers serum sodium concentration. Subsequent renal clearance of mannitol from the circulation produces an osmotic diuresis and elimination of free water, further raising total body osmolality and serum sodium concentration. The net effect of the initial, single dose of mannitol is no change or a small net rise in total body osmolality. However, repeated dosing of mannitol over 48 hours, with coadministration of isotonic saline, will lead to a consistent rise in serum osmolality and serum sodium concentration.

Clinical Pearl 14 Nonresponse to intravenous mannitol is well recognized after a single bolus dose: • Hyponatremia is well described in the neurology/neurosurgery intensive care literature. • “Nonresponse” with failure to elevate serum sodium concentration by ≥ 1 mmol/L over 48 hours of treatment is seen in at least 22% of neurocritical care adult cases receiving mannitol for cerebral edema and raised intracranial pressure. • In practice, it makes sense to use 3% hypertonic saline first, and then mannitol.

3% Hypertonic Saline As noted already in the discussion of SIADH, taking 0.6 L/kg body weight as the apparent volume of distribution for sodium, one should anticipate an immediate increase of 3 to 5 mmol/L in serum sodium concentration with a rapid intravenous bolus of 4 to 6 mL/kg body weight of 3% HS. Table 4.7 summarizes the data that better explain the effect of changes in serum sodium concentration during the course of treatment for cerebral edema. What is important is the state in serum–BBB–extracellular space kinetics. For example, the half-life for equilibration of sodium across the intact BBB is 1 hour, but less if the barrier is disrupted. This means that change in serum sodium concentration as a strategy for treating cerebral edema will, theoretically, become less effective the longer one adopts this strategy—unless, of course, one is prepared to continue to escalate serum level to very high values. We should also note from Table 4.7 that the choroid plexus behaves more like the peripheral circulation, since it has a reflection coefficient to sodium of zero. Hence, changing serum sodium concentration will have no effect on limiting water flow across the endothelium within the choroid plexus, but mannitol would have such an effect. Similarly, as vasogenic cerebral edema worsens, one would expect a fall in the reflection coefficient for sodium (decrease from 1 to 0.93 to zero). Therefore,

47

48 Section Iâ•… Introduction Table 4.7â•… Blood–brain barrier (BBB) physiologic function based on the Starling equation Reflection coefficient

Permeabilitysurface product (mL [g × min]–1)

Half times (t1/2)

1.00

2.4 × 10–4

1 hour

0.90



> 0.53

1.0 × 10–3

2.3 hours

1,026

1.00

1.00

2.4 × 10–4

1 hour

—

1.00

1.5 × 10–6

—

Intravenous solution

Effective mOsm/L

Saline 0.9%

285

1.00

Mannitol 20%

1,100

3%-HS Albumin

BBB

CP

—

According to the Starling equation: Jcap = Lcap [(Pplasma – Ptissue) – σprotein(πprotein,plasma – πprotein,tissue) – σsalt(πsalt,plasma – πsalt,tissue)] Driving pressure = (Pplasma – Ptissue) – σprotein(πprotein,plasma – πprotein,tissue) – σsalt(πsalt,plasma – πsalt,tissue) where Pplasma – Ptissue is the hydrostatic pressure difference between plasma and tissue; πprotein,plasma – πprotein,tissue is the difference in protein osmotic pressure between plasma and tissue; Lcap is capillary hydraulic conductivity; Jcap is capillary water flow; σ is the osmotic reflection coefficient; R is the universal gas constant (0.082 L×atm/mol×K); T is the absolute temperature (kelvins); Csolute is the concentration of impermeant solute, and πsolute,plasma is the solute osmotic pressure in plasma; BBB, blood–brain barrier; CP, choroid plexus; permeability-surface product the capillary hydraulic conductivity; half times, approximate exchange half times of the intact BBB for various substances; 3%-HS, 3% hypertonic saline. See text for details.

prolonged and repeated dosing of intravenous 3%-HS is not without risk—it will have limited effect and may even worsen the edema as the BBB fails. Taken together, in patients with acute onset of cerebral edema, it seems reasonable to start with 3%-HS to gain acute control, but mannitol should also be introduced (molecular weight 182, reflection coefficient of 0.9 at BBB).

4.8╇ Blood Loss Intraoperatively, neurosurgical trauma may lead to uncontrollable bleeding because of the technique being used. For example, during endoscopic ventriculostomy, there is risk of trauma to the basilar artery or its branches, which will result in bleeding and hemodynamic instability. In this instance, emergency craniotomy is likely to be needed as well as other rescue therapies (e.g., intravenous fluids, vasopressors, blood and blood products, mechanical ventilation with 100% oxygen, and ICP-directed therapies). In surgeries involving craniotomy, there may be some degree of accumulated blood loss during the procedure, and blood should be replaced.

4.8.1╇ Massive Blood Loss Massive blood loss may occur in young infants undergoing intracranial tumor surgery or in infants undergoing craniosynostosis repair, for example. When blood loss reaches 50 to 75% of the preoperative blood volume (or 40 to 60 mL/kg), some derangement in

coagulation is likely. At this level, serum prothrombin and partial thromboplastin times should be obtained and fresh frozen plasma given if necessary. The derangements in the balance between coagulation and anticoagulation may be complex (e.g., some degree of hypercoagulability, which may be related to hemodilution, or as hemorrhage approaches 100% of blood volume, coagulopathy due to factor depletion) and advice from the blood bank and transfusion service is often required. Your hospital should have a Massive Transfusion Protocol, and for certain procedures blood loss should be anticipated and a special protocol used. This strategy may include anticipatory use of tranexamic acid, fresh frozen plasma, platelets, cryoprecipitate, and calcium gluconate. In the postoperative period, blood loss via drains should be followed closely, and signs of significant blood loss (tachycardia, hypotension, hypocapnia, and respiratory variation in systolic blood pressure) should be recognized and acted upon.

4.9╇ Postoperative Pain and Sedation Management Ideally, postoperative neurosurgical patients are comfortable, awake, and sufficiently cooperative so as to complete serial neurological examinations and not be at risk of hyperventilation and its consequent effects on cerebral hydrodynamics. In pediatrics, these goals can be difficult to maintain because of differences in development and understanding of the patient.

4â•… Pre- and Postoperative Management of the Neurosurgical Patient

4.9.1╇Analgesia

4.9.2╇ Nausea and Vomiting

Each patient should have an age-appropriate assessment of pain. Various scales are used, and you should be familiar with the protocol in your own institution, such as the Modified Infant Pain Scale in infants or the Visual Analog Scale in older children. Even the most minimal scalp incision can cause postoperative pain. Surgery around the neck may result in significant nuchal spasm, and regular muscle relaxants are required. The postoperative strategy for muscle relaxation and analgesia should be discussed during the formula one signoff (Table 4.2), since what has occurred intraoperatively influences what is optimal postoperatively. For example, short-acting intravenous opioids (e.g., fentanyl, remifentanil) may have been used along with longer-acting agents (e.g., morphine). Prior remifentanil usage is associated with subsequent tolerance to opiates and a high postoperative opiate requirement. All hospitals will have a pain service, and a planned postoperative protocol will be in place (which includes use of patient- or nurse-controlled analgesia, monitoring for respiratory depression and somnolence, and indications for narcotic reversal with naloxone), which should be followed. Although intravenous opiates are frequently used, other agents, such as acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs), may be a useful addition to lessen the total dose of opiate and to reduce the risk of respiratory depression and compromised neurologic examination. Table 4.8 lists pediatric dosages that may be used in the postoperative period.

Postoperative nausea and vomiting are horrible and can lead to changes in cerebral hydrodynamics that are counterproductive to good recovery and healing after operations requiring craniotomy. They are frequent in infants and children and should be prevented with prophylactic antiemetic drugs. It is common practice to start administering these agents intraoperatively (Table 4.8). Again, use the agent your hospital prefers for infants and children. Some agents may be better at preventing vomiting but have no effect on nausea.

4.9.3╇ Intensive Care Unit Sedation and Analgesia For some patients on extended management in the ICU, a low level of sedation with analgesia is required using a combination of opioid and benzodiazepine via continuous infusion. The ideal sedation includes short-acting or reversible agents that can be withdrawn intermittently to permit assessment. Some agents suitable for adults are unsuitable in children, and some agents used widely in pediatrics are less useful in adults. In the mechanically ventilated child, the most commonly used sedative agent is midazolam. Titration to a validated sedation score is recommended, and regular “drug holidays” help prevent excessive sedation and tolerance. Infants and children receiving sedative infusion for more than 5 days are at risk of withdrawal when infusions are

Table 4.8â•… Pediatric dosages of analgesics and antiemetics used in the postoperative period Agent

Dosage

Effect

Acetaminophen

•O  ral: 10–15 mg/kg q4h •R  ectal in children: initial dose 30 mg/kg, then subsequent dosage 20 mg/kg q6h •R  ectal in neonates: initial dose 30 mg/kg, then subsequent dosage 20 mg/kg q12h

Analgesia •M  aximum dose in children is 100 mg/kg or 4 g/day, whichever is lower •M  aximum dose in neonates and infants is 75 mg/kg/day

Oxycodone

Oral: 0.05–0.15 mg/kg

Analgesia

Morphine

• Intravenous in infants (> 2 months) and children: incremental dosages of 0.025–0.1 mg/kg  CA: 10–20 µg/kg/dose, lockout 8 to 15 min, •P basal 0–30 µg/kg/hour

Analgesia •D  osing interval will be affected by half-life (2 hours after 2 months) • PCA 4-hour limit of 250–400 µg/kg

Ondansetron

• Intravenous: 0.15 mg/kg

Antiemetic

Dexamethasone

• Intravenous: 0.0625–1.0 mg/kg

Antiemetic

Abbreviations: PCA, patient-controlled analgesia; q4h, every 4 hours; q6h, every 6 hours; q12h, every 12 hours.

49

50 Section Iâ•… Introduction discontinued abruptly. In regard to analgesia, opioids like morphine and fentanyl should be carefully titrated to minimize postcraniotomy pain yet maintain consciousness. Patient-controlled analgesia may be helpful. Propofol is a potent, ultrashort-acting sedative-hypnotic that is extremely useful in adult neurocritical care but has only limited utility in pediatrics. This is because of its association with the propofol infusion syndrome— a fatal syndrome of bradycardia, rhabdomyolysis, metabolic acidosis, and multiple organ failure—when used over extended periods. While the mechanism of the syndrome remains unclear, it appears related to both the duration of therapy and the cumulative dose. These difficulties are much less common in adults. Some centers have advocated propofol use in children under strict controls, but propofol is generally limited to operative anesthesia, procedural sedation, and continuous infusions of limited duration ( 60 mm Hg, from a baseline of 40 mm Hg) is conducted last. In order to establish irreversibility, age-related observation periods are necessary. An observation period of 24 hours is required for infants up to the age of 30 days of age, and 12 hours for infants and children older than 30 days and younger than 18 years. The first examination determines whether the child has met the accepted neurologic examination criteria for brain death. The second examination confirms brain death based on an unchanged and irreversible condition. It is recommended that assessment of neurologic function after cardiopulmonary arrest or other severe acute brain injuries should be deferred for 24 hours, or longer if there are concerns or inconsistency in the examination. Ancillary studies, such as electroencephalography and radionuclide cerebral blood flow studies, are not required to establish the diagnosis of brain death, nor are they a substitute for the clinical examination. These studies are used when components of the clinical examination or apnea testing cannot be completed safely because of the patient’s medical instability, if there is uncertainty about the results of the neurologic examination, or if a medication or metabolic effect is present. Attendants who are familiar with practice in adults will recognize an immediate difference between the pediatric and adult criteria for brain death: in children, we continue to use two examinations, whereas in adults the guidelines indicate that a single examination suffices. You should be familiar with the protocol for determination of brain death in your own institution—all centers in the United States have their own checklists and policy documents.

5

Pediatric Neurosurgical Positioning Jonathan A. Pindrik, Sheng-fu Larry Lo, and Edward S. Ahn

5.1╇ Introduction and Background Positioning represents a significant component of operative planning in all neurosurgical subspecialties, including pediatric neurosurgery. Appropriate alignment of the head, neck, and spine for specific operative approaches requires careful deliberation to optimize target exposure, patient safety, and surgeon comfort. Nuances in the anatomy of infants, children, and adolescents require special consideration to optimize patient safety. Key factors include anterior fontanelle patency, fusion of skeletal sutures, calvarial vault thickness, strength and bulk of cervical paraspinal musculature, and overall torso or extremity size. Careful consideration of these factors, combined with open communication among the surgical, nursing, and anesthetic teams, allows safe positioning and optimal operative exposure in pediatric neurosurgery.

centers (including the authors’ institution) implement rigid pin fixation in children aged 3 years and above with incremented force starting at 30 to 40 lb (Fig. 5.1).1,3 The pin force may be increased toward adult levels (60 lb, using adult pins) in older children and adolescents with normal cranial development.1 Although skull thickness generally increases with age, a high degree of variability exists among different age groups and patients.1 The calvaria within infants below age 1 year often ranges between 2 and 3 mm in thickness. Additional factors, such as chronic hydrocephalus, cause cranial vault thinning in younger children.3,4 Therefore, rigid cranial fixation requires a carefully planned and tailored approach for individual patients. To decrease the risks of cranial fixation in children, alternative strategies have been suggested to achieve

5.2╇ Positioning Detail and Preparation 5.2.1╇ Rigid Cranial Immobilization Attaining rigid cranial fixation in infants and young children presents challenges due to immaturity of the cranial vault. Standardized recommendations regarding cranial fixation in pediatric patients do not exist, despite its common usage and frequent reports of related complications. Skull thickness variability within different age groups complicates the adoption of uniform guidelines for cranial immobilization. Some pediatric neurosurgical centers implement rigid pin fixation in children aged 1 to 2 years, with forces below 30 lb (often 20 lb or lower for young infants).1 However, forces below 30 lb carry risks of pin slippage as a result of inadequate seating of the pin upon the calvaria.2 Most pediatric neurosurgical

Fig. 5.1â•… Rigid cranial fixation. For midline prone positioning, rigid cranial fixation with the Mayfield skull clamp at a pin force of 40 lb (in younger children) provides adequate stability and support of the head.

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52 Section Iâ•… Introduction safe cranial immobilization. Assessing the skull thickness on preoperative head computed tomography (CT) verifies the feasibility of applying rigid pin fixation.3 Furthermore, avoidance of the temporal squamosa (if possible) during pinning may decrease the risks of skull fracture.3 Pediatric pins offer shorter, duller, and blunter tips to help prevent skull perforation. Below age 3, other strategies include three-point skull clamps reinforced with rubber plugs or disks over the cranial pins, combinations of the standard horseshoe headrest and cranial fixation systems, or joint usage of the horseshoe headrest and adhesive U-drapes to achieve cranial immobilization.1–3,5 Incorporating a horseshoe headrest or suctioned beanbag to support the weight of the head allows the cranial pins or adhesive drapes to solely address immobilization.1,3,5

5.2.2╇ Supine Position Supine positioning involves the patient lying with his or her back and torso dependently on the operating table. This straightforward style of positioning accommodates various neurosurgical procedures (Table 5.1). Transmitting the patient’s mass to a proportionately large surface area with adequate soft tissue and musculature, supine positioning generally avoids many of

the potential risks and complications associated with other positioning styles (prone, lateral, sitting).

Ventricular Shunt Insertion or Revision Frontal, parietal, and occipital approaches to ventricular shunt insertion or revision can be accomplished safely and effectively with supine positioning. While frontal shunt manipulation favors neutral or nearneutral head positioning, parietal or occipital shunt placement generally requires generous head rotation contralaterally. The supple nature of most pediatric necks (barring torticollis, contractures, or prior occipitocervical fusion) typically allows adequate head rotation. A small to moderate-sized bump (sheet or gel roll) placed under the ipsilateral torso may aid surgical site exposure in addition to head turning. The patient’s torso can remain in a neutral position with the upper extremities tucked and padded by the side. This supine, neutral position of the torso accommodates distal shunt insertion into multiple termini (ventriculoatrial, ventriculopleural, and ventriculoperitoneal shunts). Proximal shunt revision or insertion into noncomplicated, dilated ventricles typically can be performed without cranial fixation. In this context, the head may rest on circular foam padding or

Table 5.1â•… Examples of neurosurgical operations for different positions Supine

Prone

Lateral

Sitting/Concorde

Ventricular shunt insertion or revision ETV Endoscopic supratentorial arachnoid cyst fenestration Supratentorial tumor biopsy or resection Endoscopic endonasal approaches to skull base lesions Seizure focus phase II monitoring or resection Vagal nerve stimulator insertion or revision Brachial plexus exploration and repair Supratentorial SDH or EDH evacuation Frontal, temporal, or parietal skull fracture correction Hemicraniectomy Open craniosynostosis repair Cranial reduction or expansion

Chiari malformation (I, II) decompression Infratentorial tumor or lesion resection Occipital tumor or lesion resection Myelomeningocele repair Suboccipital decompression for cerebellar hemorrhage or edema (infarct, etc.) Posterior cervical, thoracic, or lumbar surgery Extended posterior cranial vault reconstructions (prone with head in seal position)

Lumboperitoneal shunting Intrathecal baclofen pump insertion or revision Retrosigmoid approach for lesions within lateral posterior fossa or cerebellopontine angle cistern

Posterior fossa tumor or lesion resection Pineal region tumor resection Occipital region tumor or lesion resection

Abbreviations: EDH, epidural hematoma; ETV, endoscopic third ventriculostomy; SDH, subdural hematoma.

5â•… Pediatric Neurosurgical Positioning

Fig. 5.2â•… Supine positioning for ventricular shunt insertion. Standard supine positioning with the head turned contralaterally and resting upon a horseshoe headrest allows access to the cranial ventricular shunt and distal peritoneal shunt insertion sites.

a cerebellar (horseshoe) headrest reinforced with soft cotton wrapping (Fig. 5.2). Complex hydrocephalus or diminutive ventricular caliber (slit ventricle syndrome) may require cranial fixation to allow intraoperative frameless stereotactic navigation.

Tumor Resection in the Frontal, Temporal, Parietal, or Skull Base Regions Depending on location, most lesions within the frontal, temporal, and parietal regions or arising from the skull base can be approached with supine positioning. While bicoronal approaches for midline pathology typically employ neutral head positioning with slight neck flexion, unilateral lesions usually require head rotation contralaterally. Placement of a small to moderate-sized bump under the ipsilateral scapula or torso may aid head rotation. Slight head tilting and neck extension allow the ipsilateral frontal lobe to fall away from the anterior cranial fossa, as needed for skull base lesions. Neck manipulation (including rotation, flexion, and extension) should be performed carefully given the weak cervical paraspinal musculature. Excessive flexion or “kinking” of the neck may result in internal jugular vein (IJV) occlusion, impairing intracranial venous outflow and raising intracranial pressure (ICP). Rigid cranial fixation allows intraoperative neuronavigation and prevents slight head movement during key portions of the procedure (craniotomy, dural opening, tumor resection) (Fig. 5.3).

Fig. 5.3â•… Cranial fixation and frameless stereotactic navigation. Rigid cranial fixation allows reference registration of an intraoperative navigation system and provides immobility necessary for critical steps in intracranial, neuro-oncologic surgery.

Endoscopic Approaches to the Lateral and Third Ventricles Endoscopic approaches to the third and lateral ventricles via a precoronal burr hole typically employ supine positioning with neutral head location (Fig.€5.4). Endoscopic third ventriculostomy (ETV) can be performed usually without cranial fixation and with the head resting upon a cerebellar (horseshoe) headrest reinforced with soft cotton wrapping. Endoscopic

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54 Section Iâ•… Introduction

Fig. 5.4â•… Supine position for endoscopic third ventriculostomy (ETV). Standard positioning for stereotactic-assisted ETV via a precoronal burr hole involves supine neutral orientation with slight neck flexion and attachment of the neuronavigation reference marker.

fenestration of arachnoid cysts may require different head positioning and angling depending on cyst location. For instance, temporal or middle fossa arachnoid cysts might employ contralateral head rotation to optimize cyst entry through minimal cortex and to foster cyst fenestration into the nearest cistern or ventricle.

Brachial Plexus Exploration and Repair Exploration and/or repair of the brachial plexus introduce additional variables to consider for positioning. Nerve stimulation to test for upper-extremity movement usually requires sterile preparation of the involved arm, forearm, and hand into the surgical field, or usage of partially transparent surgical drapes. Furthermore, harvest of unilateral or bilateral sural nerve grafts for autologous graft reconstruction will require sterile preparation of one or both lower extremities and an apparatus to raise the lower extremity in a fixed position for patients beyond infancy (alternatively, sural nerve grafts can be obtained with the patient in prone position as the first stage of the operation). Supine positioning with contralateral head rotation upon a circular foam headrest offers optimal exposure of the brachial plexus. Supra- and infraclavicular approaches to the brachial plexus incorporate similar positioning. Distal exploration of the peripheral nerve branches in the arm require elbow extension and shoulder abduction of the sterilely prepared upper extremity lying upon an arm rest (Fig. 5.5).

Fig. 5.5â•… Positioning for brachial plexus exploration and repair. Brachial plexus exploration and repair often require supraclavicular and brachial approaches depending on the extent of injury. The outstretched, sterilely prepared extremity may be placed on a draped arm rest.

5.2.3╇ Prone Position Prone positioning involves dependency of the face, ventral torso, and extremities on the operating table. Entailing more risks than standard supine positioning, prone positioning requires careful deliberation to minimize pressure on dependent structures. Anatomic regions at risk include the face and ocular globes, breasts in adolescent girls, abdomen in overweight or obese patients, hips, male external genitalia, and other structures under pressure or compression. Padding helps minimize these risks by cushioning firm regions (chest, hips) and allowing softer structures (breasts, abdomen, male external genitalia) to hang freely. Rolled-up sheets or surgical towels aligned transversely under the chest and hips accommodate prone positioning in neonates and infants. Gel rolls (reinforced with soft cotton wrapping) aligned longitudinally along the bilateral aspects of the patient’s torso can be used for older patients (children, adolescents). Upper extremities should be tucked at the sides (thumbs down) and cushioned with foam padding for cranial and cervical operations or directed superiorly on arm rests (90° abduction at the shoulder and 90° flexion at the elbow) for thoracic and lumbar operations. If not secured with rigid cranial fixation, the cranial vault should be placed face down on a cerebellar (horseshoe) headrest or special foam padding with clearings for the eyes, nose, mouth, and endotracheal tube. Both surgeons and anesthesiologists should check pressure around the orbit to minimize pressure transmitted to the ocular globes. Members of the surgical and nursing team also should check all dependent regions for appropriate padding and all

5â•… Pediatric Neurosurgical Positioning freely hanging soft tissue structures (breasts, abdomen, external genitalia). Potential disadvantages of prone positioning include decreased drainage of cerebrospinal fluid (CSF) and blood and increased airway pressures.6

Infratentorial Operations Positioning for infratentorial or craniocervical operations (Chiari decompression, posterior fossa lesion resection, suboccipital craniectomy) generally follows standard principles. Patients below the age of 3 years may be positioned without rigid cranial fixation, as described previously. However, rigid cranial fixation should be considered for older patients (children and adolescents) (Fig. 5.6). Bringing the torso superiorly along the operating table with the shoulders lying just beyond the table’s edge allows appropriate head positioning and guards against chin compression. Generous neck flexion and posterior translation of the head place the suboccipital region into a prominent and accessible location. Furthermore, these maneuvers enhance exposure of the craniocervical junction and upper cervical spine. Excessive neck flexion and obstructed venous outflow can be avoided by checking for two-fingerbreadth spacing between the chin and neck or sternal notch. Positioning for posteriorly located (occipital) lesions above the tentorium can proceed similarly, without the need for substantial neck flexion.

5.2.4╇ Lateral Position Lateral positioning places the sides of the patient’s torso and lower extremities dependently to support body weight. The lateral decubitus and park bench

Fig. 5.6â•… Midline prone positioning. Rigid cranial fixation with midline prone positioning and cervical flexion provides adequate exposure of the suboccipital region and craniocervical junction.

positions apply to lumboperitoneal shunting, insertion or revision of an intrathecal baclofen pump, and retrosigmoid approach for lesions within the lateral posterior fossa or cerebellopontine angle. Several guiding principles can simplify the challenging nature of lateral positioning. Extension of the dependent lower extremity and flexion of the above lower extremity (this orientation may vary depending on surgeon preference) with an interposed pillow helps stabilize the lower body and relax the ipsilateral iliopsoas muscle. Suctionassisted molding of a beanbag conformed to the body contour helps stabilize the torso. However, the beanbag should be contorted appropriately to maintain access to the lumbar posterior midline and lateral abdominal region for lumboperitoneal shunting and intrathecal baclofen pump insertion. An axillary roll or gel cushion inserted below the dependent axilla provides cushion and support for this region. The park bench position additionally employs rigid cranial fixation with head rotation contralaterally toward the ground to expose the suboccipital retrosigmoid region (Fig. 5.7). Placing the patient’s torso and surrounding beanbag superiorly on the operating table, with the level of the shoulder beyond the upper edge of the table, allows the dependent upper extremity to rest comfortably on foam padding and sheets supported by the Mayfield attachment (Integra, Plainsboro, NJ, USA). The nondependent upper extremity should be cushioned with a pillow and secured with foam padding and tape wrapped circumferentially around the torso and beanbag (after suction-assisted molding). As with other positions, all pressure points and anatomic regions abutting rigid structures should be checked to avoid excessive compression.

Fig. 5.7â•… Park bench positioning. Park bench positioning employs rigid cranial fixation, beanbag stabilization, copious padding, and generous amounts of cloth tape to achieve safe immobilization and adequate exposure of the lateral suboccipital, retrosigmoid region.

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56 Section Iâ•… Introduction

5.2.5╇ Sitting Position More frequently used abroad, the sitting position entails perioperative risks that limit its usage in most American centers. This orientation involves upper torso elevation to 90 to 100°, with gentle cervical flexion to tilt the head forward approximately 20 to 30° (Fig. 5.8).7,8 As in prone positioning, excessive cervical flexion should be avoided by checking for two-fingerbreadth spacing between the chin and neck or sternal notch.7,8 Advantages of the sitting position include natural anatomic orientation and enhanced surgical exposure, improved drainage of CSF and blood, decreased intracranial pressure as a result of enhanced venous drainage, decreased airway pressures and improved ventilation, and the ability to observe facial reflections of cranial nerve stimulation.6–9 Significant disadvantages include risks of venous air embolism (VAE), paradoxical air embolus (PAE) with cardiac or end organ ischemia, hemodynamic instability or hypotension, pneumocephalus or tension pneumocephalus, postoperative infratentorial hemorrhage, upper airway and tongue edema, spinal cord injury, and compression or traction peripheral neuropathies (including brachial plexus injuries).6–9 Furthermore, awkward or strained surgeon hand orientation contributes to the undesirable nature of this position.

Intraoperative techniques to detect VAE include transesophageal echocardiography (TEE) or precordial Doppler ultrasound (pcDUS), measurement of end-tidal pressures of carbon dioxide (PECO2), and arterial line placement with continuous monitoring of mean arterial pressure (MAP).6–9 Preoperative TEE can help diagnose patent foramen ovale (PFO), a recognized contraindication to the sitting position due to elevated risk of PAE.8,9 Precipitous decline in PECO2 and/or MAP (with elevated heart rate), along with pcDUS or TEE positive findings, suggest clinically relevant VAE.6,8,9 Additional monitoring techniques to optimize patient safety for the seated position include somatosensory and motor evoked potentials (SSEPs, MEPs). Methods to reduce the risk of VAE include fluid administration, antigravity or antishock suits in older patients, elastic banding of the lower extremities in younger children, and lower-extremity elevation.6–9 These measures help maintain adequate total and cerebral venous pressure while preventing venous pooling in the lower extremities. Mechanical ventilation with normocapnia and normal positive end-expiratory pressure (PEEP; 5 to 10 cm H2O) and central venous line insertion represent other techniques to help prevent or prepare for VAE.6–9 Additionally, craniotomy edges should be waxed or covered with hemostatic agents to occlude diploic vein sites.7–9 In the event of confirmed VAE, methods to prevent adverse sequelae include covering exposed sinuses with saline-soaked cotton material or gelatin foam while flooding the surgical field with saline.7–9 The operating table may be tilted to lower the patient’s head.7,8 Jugular venous compression may help identify sites of dural venous sinus entry that can be repaired with suturing, muscle or fascia plugging, or occlusion with hemostatic clips.7–9 In the event of hemodynamic instability or collapse, the operating table may be tilted to bring the right side of the heart up while the anesthetic team may attempt to aspirate the VAE from the right atrium via the central venous catheter.7,8 Constant communication between the neurosurgical and anesthetic teams helps reduce the risks and prevent adverse sequelae of VAE.

5.3╇ Outcomes and Postoperative Course

Fig. 5.8â•… Sitting position. The sitting position aids surgical exposure of posterior fossa, occipital, and pineal region lesions but entails multiple significant risks that limit its usage in most American pediatric neurosurgical centers.

Successful positioning for pediatric neurosurgery involves establishing an orientation comfortable for both the patient and the surgeon that allows successful completion of the operation without position-related complications. Although infrequent, adverse events related to positioning require careful review and scrutiny to prevent

5â•… Pediatric Neurosurgical Positioning their recurrence. Contact between hard or rigid surfaces and the skin, especially over bony surfaces or those with minimal subcutaneous soft tissue, may lead to pressure ulcers and skin irritation or breakdown.10 Many of these complications can be prevented with adequate padding and vigilant attention to compressed surfaces. Dependent body surfaces supporting moderate weight may exhibit myonecrosis, especially during prolonged surgery.10 Cranial pin fixation carries risks of scalp laceration, depressed skull fracture, epidural hematoma, dural laceration, subdural hematoma, cortical lacerations or contusions, CSF leak, and perforation of shunt hardware.1,3 Depending on their extent, depressed skull fractures or epidural hematomas may require emergent operative intervention. Despite their proposed safety, pediatric pins carry risks of local skin pressure or necrosis, especially during prolonged operations.3 Patient orientation and body arrangement contribute substantially to position-related complications. Excessive head rotation combined with flexion or extension may lead to postoperative neck discomfort or infrequent cases of upper cervical destabilization.11 If identified early, upper cervical rotary subluxation can be treated conservatively with reduction and external immobilization.11 Significant neck flexion may also cause intraoperative intracranial hypertension due to venous outflow obstruction. Prone positioning with the head lying on a horseshoe headrest requires careful attention to orbital pressure to avoid ocular complications (ischemic optic neuropathy).1,10 Traction or compression of the extremities during prolonged cases may cause temporary or permanent postoperative peripheral nerve deficits (brachial plexus injuries, ulnar nerve compressive neuropathy, radial nerve palsy).10 Additional position-related complications include facial or bodily burns from pooling of preparatory solutions on the headrest or operating table.

References ╇1.

╇2.

╇3.

╇4.

╇5.

╇6.

╇7.

╇8.

╇9.

10. 11.

Berry C, Sandberg DI, Hoh DJ, Krieger MD, McComb JG. Use of cranial fixation pins in pediatric neurosurgery. Neurosurgery 2008;62(4):913–918, discussion 918–919 Agrawal D, Steinbok P. Simple technique of head fixation for image-guided neurosurgery in infants. Childs Nerv Syst 2006;22(11):1473–1474 Vitali AM, Steinbok P. Depressed skull fracture and epidural hematoma from head fixation with pins for craniotomy in children. Childs Nerv Syst 2008;24(8): 917–923, discussion 925 Wong WB, Haynes RJ. Osteology of the pediatric skull. Considerations of halo pin placement. Spine 1994;19(13):1451–1454 Sgouros S, Grainger MC, McCallin S. Adaptation of skull clamp for use in image-guided surgery of children in the first 2 years of life. Childs Nerv Syst 2005;21(2):148–149 Orliaguet GA, Hanafi M, Meyer PG, et al. Is the sitting or the prone position best for surgery for posterior fossa tumours in children? Paediatr Anaesth 2001;11(5):541–547 Lindroos AC, Niiya T, Randell T, Romani R, Hernesniemi J, Niemi T. Sitting position for removal of pineal region lesions: the Helsinki experience. World Neurosurg 2010;74(4-5):505–513 Jadik S, Wissing H, Friedrich K, Beck J, Seifert V, Raabe A. A standardized protocol for the prevention of clinically relevant venous air embolism during neurosurgical interventions in the semisitting position. Neurosurgery 2009;64(3):533–538, discussion 538–539 Dilmen OK, Akcil EF, Tureci E, et al. Neurosurgery in the sitting position: retrospective analysis of 692 adult and pediatric cases. Turk Neurosurg 2011;21(4):634–640 Harrop JS. Patient positioning: is it really a big deal? World Neurosurg 2012;78(5):440–441 Heary RF, Reid P, Carmel PW. Atlantoaxial rotatory fixation after ventriculoperitoneal shunting. Neuropediatrics 2011;42(5):197–199

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6

Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures Daniel M. Schwartz, Andrew Paul Warrington, Anthony K. Sestokas, and Ann-Christine Duhaime

6.1╇ Introduction and Background The goal of pediatric neurosurgery is to cure or meliorate disease of the nervous system using surgical methods that maximize benefit to the child while minimizing risk. Intraoperative neurophysiological monitoring is one of the most important modalities used to achieve these goals. The history of what can be done, how it can be done, and its utility for the surgeon has evolved along with other technical and conceptual advances in the procedural specialties. Intraoperative monitoring is a relatively young field, and neurosurgeons in general, and pediatric neurosurgeons in particular, may have varying experiences with different sorts of monitoring modalities and practitioners. One of the earliest uses of intraoperative monitoring, which had as its aim minimizing potentially preventable damage to neural structures, was cranial nerve monitoring during cerebellopontine angle and otologic surgery. The professionals involved in this aspect of the emerging field often came from backgrounds in audiology. Another early use of monitoring in the general sense was intraoperative corticography to assess epileptogenic tissue during seizure surgery, most often performed by neurologists or neurophysiologists specializing in epilepsy. As somatosensory and later motor evoked potentials came into use in scoliosis and spine tumor surgery, the field of intraoperative monitoring began to expand, becoming an independent specialty, arising from these various lineages. As its use in children may encompass differences in maturational physiology, disease processes, and anesthetic considerations, additional experience has been gained and further subspecialization has occurred. At present, the practice models, training, credentialing processes, and oversight of intraoperative monitoring vary among organizations, specialties, and institutions. This chapter provides an overview of the modalities most commonly utilized in children, anesthetic implications, typical pediatric neurosurgical scenarios encountered, role and limitations of monitoring, and

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surgical perspective. These observations have arisen from a great deal of pediatric intraoperative monitoring experience and study, but it should be kept in mind that different practitioners may approach these goals in different ways, and that the field continues to grow and to benefit from careful study and technologic advancement.

6.2╇ Overview and Goals of Neuromonitoring Multimodality (evoked potentials, electromyography, electroencephalography, cerebral blood flow) intraoperative neurophysiology (ION) has become commonplace in pediatric neurosurgery. The underlying premise of ION in pediatric neurosurgery is multifaceted: • To assess continuously the functional integrity of central and peripheral nervous system anatomical structures, pathways, and vascular supplies at risk for iatrogenic injury • To identify, verify presence of, and determine proximity of specific neural structures and landmarks that either are obscure from, or outside of, the surgeon’s immediate visual field or have abnormal or distorted anatomical features • To help guide placement of indwelling therapeutic neurostimulators or recording electrodes used to treat neurologic disease (e.g., epilepsy, dystonia) • To provide an intraoperative diagnostic tool for lesion identification prior to surgical intervention (e.g., neurolysis) These different goals can be met by techniques that monitor function as well as those that locate, or map, functional areas or structures. This chapter focuses on the application of multimodality ION across the broad spectrum of pediatric neurosurgical procedures.

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

6.3╇Intraoperative Neurophysiological Monitoring Modalities in Children 6.3.1╇ Somatosensory Evoked Potentials (SSEPs) Since the seminal work of Nash and coworkers1 describing the continuous recording of lowerextremity somatosensory evoked potentials to assess spinal cord function during surgical correction of spinal deformity in children, SSEPs have become a mainstay neuromonitoring modality used to detect disruption of transmission along a peripheral sensory nerve, nerve plexus, and the entire neuraxis from the spinal cord to the sensory cortex. Briefly, SSEPs are elicited by stimulating a peripheral nerve, typically the posterior tibial or peroneal nerve in the lower extremities or the ulnar or median nerve in the upper extremities. Lowerextremity SSEPs permit assessment of dorsal column–medial lemniscal system (DC-MLS) function along the entire length of the neuraxis (i.e., spinal cord, brainstem, and cerebral hemispheres), whereas upper-extremity SSEPs provide functional DC-MLS assessment from the cervical segment of the spinal cord and cephalad. The ascending sensory volley triggered by posterior tibial or peroneal nerve stimulation enters the spinal cord through dorsal sacral and lumbar nerve roots at several segmental levels (S1–L4) and may ascend the spinal cord via multiple pathways. The general consensus is that the dorsal or posterior column spinal pathways are the primary sites of mediation for the SSEP.2–4 Other pathways, such as the dorsal spinocerebellar and anterolateral tracts, may also contribute to the early somatosensory evoked responses that are used for monitoring spinal cord function.5–7 Upon ascending the spinal cord, the neural signal enters the medullary nuclei in the brainstem. Because there are no afferent pathway synapses prior to this subcortical entry point, SSEPs recorded up to the level of the lower brainstem reflect the integrity predominantly of peripheral nerve fibers and spinal cord white matter. Beyond the medullary nuclei, the neural pathway mediating the SSEP continues as the internal arcuate fiber system, which crosses the brainstem and ascends as the medial lemniscal pathway, projecting to the thalamus; there is another synaptic junction in the thalamus that in turn projects to the sensorimotor cortex, where additional synaptic interaction may occur. Neural maturation plays a dominant role in determining success of SSEP recordings in infants, particularly those less than 3 months of age. Compared to adults, shorter limb length and smaller-diameter peripheral nerve fibers, as well as incomplete central

myelination, result in paradoxical SSEP latencies at subcortical and cortical levels. Subcortical responses recorded from an electrode positioned over the proximal cervical spine, for example, have shorter latencies, whereas responses from electrodes placed over the somatosensory cortex are prolonged relative to those of a normal adult. By 6 to 8 years of age, neuromaturation of the somatosensory pathway has progressed such that central conduction velocity is comparable to that of a normal adult. As a result of neural immaturity, cortical SSEPs to lower-extremity (posterior tibial nerve) stimulation are often markedly labile and of inadequate amplitude to permit reliable and valid neuromonitoring in infants under the age of 6 months. Conversely, cortical SSEPs to upper-extremity (median and ulnar nerve) stimulation are usually present and more reliable. Decreasing the stimulus repetition rate can help overcome the compromising effect of central myelin immaturity when ulnar nerve SSEPs need to be recorded in infants less than 6 months of age, as depicted in Fig. 6.1a–c. Observe that, had a standard stimulus repetition rate of 4.1 to 5.1 Hz been used to monitor cortical SSEPs in this patient, the neuromonitoring clinician would have been led to conclude that responses simply were too labile and attenuated to permit reliable and valid detection of emerging injury. The application of recording electrodes for SSEP monitoring in children is the same as that for adults; however, the neuromonitoring clinician must be cognizant of the cranial suture lines and fontanelles that may be open. Hence, careful attention should be paid to directing subdermal needle electrodes away from these areas so as not to cause a transdural puncture wound.

6.3.2╇ Transcranial Electrical Motor Evoked Potentials (tceMEPs) TceMEPs are neuroelectrical events recorded from descending motor pathways, including the corticospinal tract (CST), spinal cord interneurons, anterior horn cells, spinal nerve roots, and skeletal muscles after transcranial application of a high-voltage anodal electrical stimulus. CST axons project from cortex through the internal capsule to the caudal medulla. Here, the fibers decussate and descend into the lateral and anterior funiculi of the spinal cord. In contrast with ascending spinal cord axons, which mediate SSEPs, descending CST axons that mediate tceMEPs enter the spinal cord gray matter, where they interact with spinal interneurons. There are both direct and indirect axonal projections to alpha motor neurons, which in turn innervate peripheral muscle.8 Lateral CST fibers that synapse in the cervical segment of the spinal cord are arranged medially, followed laterally by fibers that synapse in the thoracic, lumbar, and sacral regions, respectively.

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60 Section Iâ•… Introduction

Fig. 6.1â•… Subcortical and cortical somatosensory evoked potentials to interleaved stimulation of the left (columns 1 and 2, respectively) and right (columns 3 and 4, respectively) ulnar nerves in a 5-month-old infant at three stimulation rates: (A) 4.1 Hz, (B) 3.1 Hz, (C) 2.1Hz. Subcortical responses were recorded between conventional electrode position Fpz and the upper cervical spine (Cs2). Cortical responses were recorded between Fpz and Cp4 (left ulnar nerve stimulation) and between Fpz and Cp3 (right ulnar nerve stimulation).

TceMEPs mediated by the CST can be recorded from the spinal epidural or subdural space via a catheter-type electrode or from peripheral musculature using subdermal needle electrodes. Responses recorded from the epidural space are led by a D-wave triggered by depolarization of motor neurons that project directly into the CST. In awake or lightly anesthetized patients, the D-wave is followed by a series of I-waves elicited indirectly via cortical synapses.9 Descending cortical volleys then summate temporally and spatially to excite spinal motor neurons that project to skeletal muscles, triggering compound muscle action potentials. The intraoperative monitoring of D-waves has particular value during excision of intramedullary spinal cord tumors10; however, it requires a recording electrode to be placed directly over dura, either percutaneously or through a laminotomy, precluding routine use of this technique in most corrective spine surgeries. It is both easier and preferable to record myogenic motor responses from upper- and lower-extremity peripheral muscle for most spine procedures. Unlike D-waves, which provide information only about the spinal cord, myogenic motor evoked potentials can also assess and identify functionally significant changes in individual spinal nerve roots or peripheral nerves.11–13 Anodal current stimulation is more effective at activating the corticomotor neurons than cathodal stimulation; the active electrode is positive.14 Optimal stimulation sites for motor cortex activation are interpolated from standard scalp electrode positions defined by the International 10/20 system, as illustrated in Fig. 6.2.

Fig. 6.2â•… Schematic showing typical sites for anodal transcranial electrical stimulation (M1-4, Mz) in relation to conventional electrode positions Cp1–Cp4, Cpz, Pz, Fpz (International 10-20 System of Electrode Placement).

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures In the pediatric population, prebent stainless steel beveled needle electrodes are preferable to corkscrewtype electrodes, especially in infants, where unclosed fontanelles and sutures can be at risk for invasive electrode placement. Routinely, anodal stimulation is applied to the electrode site of M1 and M2 for activation of right and left contralateral limbs, respectively; unilateral activation is facilitated by placing the cathode at Cz. Lower-extremity tceMEPs are elicited more prominently with anodal stimulation at Mz and the cathode placed a few centimeters anterior. Transcranial electrical stimulation for myotomal motor evoked potentials usually consists of constantvoltage rectangular pulse trains (N = 3 to 9 stimuli) having durations (pulse width) of 50 to 75 µsec and interstimulus intervals (ISIs) that range from 1 to 5 msec. Use of longer pulse durations and ISIs can improve the acquisition of reliable tceMEPs in infants under 12 months, as shown in Fig. 6.3a–d. Note that with stimulation using 5 pulses at a pulse width (PW) of 50 µsec and ISI equal to 1 msec, no tceMEPs could be recorded in a 3-month-old infant, thereby rendering the case unmonitorable. Increasing the number of pulses to 6, PW to 75 µsec, and ISI to 2 msec produced

a

minimal response emergence at select myotomes. At the longest ISI (3.3 msec), however, large-amplitude myotomal tceMEPs were readily apparent at all recording sites, suitable for consistent neuromonitoring of corticospinal tract integrity (Fig. 6.3d). Triggering of tceMEPs can be challenging in some pediatric patients, particularly those with congenital abnormalities or pre-existing motor deficits. Facilitation of tceMEPs using preconditioning techniques has been shown to enhance responses that would otherwise not be monitorable. Journée et al reported that delivery of two stimulus trains closely spaced in time increased motor evoked potential amplitudes by a mean factor of over 15 times in a group of patients whose responses to a single train were smaller than 100 microvolts.15 In general, facilitation is most beneficial in children with pre-existing motor deficits who present with unreliable, labile, small-amplitude responses at baseline and who otherwise would be deemed unmonitorable. On occasion, however, facilitation can help improve amplitude resolution and, hence, interpretation of meaningful intraoperative tceMEP change in neurologically normal pediatric patients

Fig. 6.3â•… Effect of adjusting stimulus train parameters on triggering of tceMEPs from left upper and lower extremities in a 3-month-old infant.Constant-voltage stimulation set at 300 V. Muscle abbreviations: AS, external anal sphincter; FD, first dorsal interosseous; GA, gastrocnemius; IO, iliopsoas; QD, quadriceps; TA, tibialis anterior. (a)â•… N, 5 stimulus pulses delivered using an interstimulus interval (ISI) of 1 msec and pulse width (PW) of 50 µsec. (Continued on page 62)

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62 Section Iâ•… Introduction

b

c

Fig. 6.3 (Continued)â•… (b) N, 5 pulses; ISI, 1 msec; PW, 75 µsec. (c) N, 6 pulses; ISI, 2 msec; PW, 75 µsec.

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

d Fig. 6.3 (Continued)â•… (d) N, 6 pulses; ISI, 3.3 msec; PW, 75 µsec.

with small responses to single-train stimulation, as exhibited in Fig. 6.4. We have not seen any false-negative results even with extremely high-risk children using tceMEP facilitation (Fig. 6.4). Despite the proven value of tceMEP mapping and monitoring in pediatric spine and intracranial surgery, there continues to be concern among some

surgeons and neuromonitoring providers regarding potential untoward effects, particularly seizure onset, following repetitive transcranial electrical stimulation (RTES) for tceMEP monitoring. Other expressed safety concerns include the possibility of tongue bite injury, other movement-induced injury, arrhythmia, and adverse interactions with implants.

Fig. 6.4â•… TceMEP facilitation in a 13-year-old boy with a history of quadriplegic cerebral palsy. Upper row of traces shows motor evoked potentials from right upper- and lower-extremity muscles recorded after presentation of a single stimulus train consisting of five pulses spaced 1 msec apart. Note that while there are visible potentials from first dorsal interosseous and abductor hallucis muscles, there are no monitorable responses from quadriceps and tibialis anterior muscles. Lower row of traces shows facilitated motor evoked potentials to a second identical stimulus train delivered immediately after the first. Responses from quadriceps and tibialis anterior muscles are now clearly visible after facilitation by the first stimulus train, and there is amplitude enhancement of responses from first dorsal interosseous and abductor hallucis muscles.

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64 Section Iâ•… Introduction In a large series (N = 18,862) investigating the safety of RTES for tceMEP monitoring in pediatric and adult patients ranging in age from 70 years, however, Schwartz et al reported no evidence of seizure provocation, neuronal damage, or cardiovascular effects.16 The rare complication noted, across all age categories, was self-limiting tongue bite, which can be mitigated easily using a soft bite block inserted by the anesthesiologist following intubation. A follow-up study by Shah and coworkers evaluated the safety of RTES for tceMEP monitoring in 45 children with severe spastic cerebral palsy and an active history of seizure disorder.17 Here again, no child showed signs of RTES-provoked seizure onset during or immediately after tceMEP-monitored surgical correction of neuromuscular scoliosis. Our experience in neuromonitoring of tceMEPs in adult and pediatric spine surgery over more than two decades has shown it to be extremely safe and highly sensitive and specific for detection of emerging spinal cord injury.16–19 We have found that reluctance to attempt tceMEP monitoring in infants and young children ≤ 1 year of age is often associated with an incorrect assumption that there will be no monitorable signals or that it is unsafe. Neuromonitoring personnel who are inexperienced in pediatrics also may fall back on a standardized approach, failing to alter stimulation and recording parameters (PW, ISI, voltage, number of pulses in train, use of facilitation, etc.), which can convert an otherwise unmonitorable case into one with well-defined and stable tceMEP amplitudes. In our experience, when there is preoperative clinical evidence of intact motor function, upperextremity myotomal tceMEP monitoring is feasible

in approximately 95% of pediatric patients less than 12 months old and in 100% more than 1 year old. By comparison, lower-extremity tceMEPs are recordable in about 85% of children less than 12 months old, in 95% of those between 12 and 24 months old, and in 100% of children more than 2 years old. To be sure, tceMEP recording may be less successful in children with severe pre-existing neurologic compromise, such as those with spastic cerebral palsy; however, even in this population we have been able to record acceptable tceMEPs for valid neuromonitoring interpretation at least 50% of the time.18

6.3.3╇ Stimulated Electromyography Stimulated (i.e., evoked, triggered) electromyography (stEMG) is used to: • Confirm functional integrity of a neural element (e.g., cranial nerve, spinal nerve root, peripheral nerve) • Map the anatomical course and proximity of specific neural elements in the presence of pathology or other cause of obscurity within the surgeon’s field of view • Differentiate between neural and nonneural tissue Unlike SSEPs and tceMEPs, which are categorized as neuromonitoring modalities, stEMG is commonly used as a neurophysiological mapping technique. Moreover, in contrast to its neuromonitoring counterparts, the quality, reliability, and validity of stEMG results are not age dependent, as illustrated in Fig. 6.5.

Fig. 6.5â•… Compound action muscle potentials triggered during facial nerve mapping in a 6-day-old infant undergoing resection of teratoma located in the neck and extending into the skull base. The left, middle, and right columns show triggered responses from orbicularis oculi, orbicularis oris, and mentalis muscles, respectively. Single-pulse constant-current stimuli (50 µsec duration), ranging in intensity from 1.2 mA (top row) to 0.49 mA (bottom row), were presented at a rate of 2.7 Hz.

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

Flush tip Monopolar electrode spreads controlled stimulation to a return electrode placed in nearby tissue.

a

EMG discharge activity. Moreover, perhaps because the perineural sheath protects peripheral segments of cranial nerves (e.g., VII, X, XII), spinal nerve roots, or peripheral nerves of the extremities, spEMG is not particularly sensitive for detecting mechanical irritation, compression, or other insult during surgical procedures wherein the nerve is not exposed directly. In such situations, tceMEPs may serve as a more valuable adjunctive neuromonitoring modality for assessing signal transmission through a nerve.13,20–22

Inner cathode and outer anode electrodes minimize stimulus spread

6.4╇ Optimal Anesthetic Techniques for ION in the Pediatric Population b Fig. 6.6╅ Examples of (a) disposable monopolar and (b) concentric bipolar electrical stimulators commonly used for stEMG mapping and testing.

Because of broad current spread, monopolar electrical stimulation (Fig. 6.6a) is used to survey proximity of a specific neural element when the neurosurgeon’s ability to identify the structure visually is incomplete or unreliable, such as when mapping the surface of a large acoustic (cerebellopontine angle) tumor to search for presence of facial nerve or splayed nerve fascicles. Conversely, concentric bipolar stimulation (Fig. 6.6b) introduces direct focal stimulation with minimal current spread; therefore, it is better suited to achieve the following goals: • To differentiate between neural and nonneural tissue • To differentiate between cranial nerves (e.g., V vs. VII, IX vs. X, etc.) or spinal nerve roots (e.g., L4 vs. L5 vs. S1, etc.) • To assess neural functional integrity

6.3.4╇ Spontaneous Electromyography (spEMG) Intraoperative spontaneous (free-running) electromyography involves the recording of electrical activity produced by skeletal muscle to identify acute irritation of cranial, spinal, or peripheral nerves secondary to mechanical contact, direct tractional pull, heat dispersion from electrocautery, or other noxious stimuli that can excite the nerve to depolarize. While in many cases early awareness of nerve irritation can prevent overmanipulation and subsequent injury, it is possible to injure a nerve by sharp transection, ischemia, or gradual stretch without intraoperative

The success of intraoperative neuromonitoring is highly dependent on anesthetic management. Essentially, all anesthetic agents depress synaptic function in both brain and spinal cord gray matter. As a result, neurophysiological signals that traverse or are generated at synaptic junctions are also depressed. Any anesthetic that depresses signal amplitude excessively will produce increased signal variability, interpretive ambiguity, and clinical uncertainty.23 The underlying goal for anesthesia, therefore, is to obtain and maintain an anesthetic state that not only is appropriate for achieving hypnosis, amnesia, akinesis, and analgesia, but also allows for continuous, reliable evaluation of neurophysiological signals for optimal neuromonitoring. Signal variability resulting from alterations in anesthetic depth may result in interpretive error, as well as unnecessary performance of a wake-up test, increased surgeon anxiety, and, ultimately, mistrust of ION data and personnel. In general, all inhalational agents (isoflurane, desflurane, sevoflurane) produce a dose-related increase in latency and reduction in amplitude of the cortical SSEP.24 Although the exact sites of action for these potent agents remain unclear, the gases appear to dissolve in the neuronal plasma membrane. The resulting effect is inhibition of ion channel function with significant alteration in synaptic and axonal transmission. Neurophysiological signals that rely on synaptic function are influenced to a far greater extent by inhalational agents than are those not dependent on synapses. Even at steady-state low end-tidal concentrations (0.25 to 0.5 minimum alveolar concentration [MAC]) of inhalational agent, neurophysiological response amplitude can become highly unstable and variable, causing signals to be either too obscure to detect significant change or completely obliterated. The effect of potent anesthetics is much less pronounced on the subcortical SSEP recorded over cervical spine than on its cortical counterpart and is minimal on spinal epidural or peripheral responses. In the past, when the only available neuromonitor-

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66 Section Iâ•… Introduction ing modality was the SSEP, it was possible to avoid the adverse effects of inhalational anesthesia simply by recording a subcortical potential in the presence of muscle relaxation. Given the ascendant role of tceMEPs for intraoperative monitoring of corticospinal tract function, the depressive effects of volatile anesthetics on the excitability of motor pathways that mediate tceMEPs is of particular significance. As was the case historically with SSEP monitoring, there continues to be considerable controversy about the degree to which volatile agents depress myogenic tceMEP amplitudes. In contrast to ongoing controversies about the effects of volatile anesthetic gases on SSEPs and myogenic tceMEPs, there seems to be general consensus that the effect of nitrous oxide on cortical SSEP and tceMEP amplitudes is sufficiently great to recommend avoiding its use entirely in monitored cases.24–29 This is particularly important if it is used in combination with a volatile agent, because the introduction of nitrous oxide lowers the MAC, thereby having an additive effect on suppression of evoked potential amplitudes. In light of the difficulties encountered with volatile agents and nitrous oxide, we have advocated, since 1992, use of a total intravenous anesthetic (TIVA) regimen in both pediatric and adult surgical procedures to facilitate uncompromised ION signal amplitudes. If TIVA is precluded or denied for any reason, a team approach involving the surgeon, anesthesiologist, and neuromonitoring professional is needed to discuss the risks, benefits, and interpretive ambiguity that may result from using inhalational agents or nitrous oxide. Prior to the advent of multimodality monitoring of spinal motor tract and nerve root function, it was commonplace to keep the patient relaxed pharmacologically during surgery. Neuromuscular blocking (NMB) agents have no adverse effect on SSEPs and may in fact improve the quality of recordings by eliminating myogenic interference. In contrast, NMB agents compromise all responses that are recorded from muscle (tceMEP, spEMG, stEMG, etc.), which depend on reliable transmission of neural signals across the neuromuscular junction. Although there has been some suggestion that myogenic tceMEP and EMG monitoring can be conducted in the presence of partial NMB, this practice should be avoided if at all possible.30–32 The effects of NMB can vary between the upper and lower extremities, between the left and right sides of the body, and between muscles within single limbs, thereby making it difficult, if not impossible, to maintain a homogeneous state of partial equilibrated NMB. When combined with the difficulty of maintaining a constant state of partial NMB across time, as well as the interactive effects that volatile and intravenous anesthetics have on the pharmacodynamics and pharmacokinetics of nondepolarizing relaxants,

the uncertainty introduced to decision making when using partial NMB can be significant for intraoperative neurophysiological monitoring.33

6.5╇ ION Application During Pediatric Neurosurgical Procedures 6.5.1╇Intracranial Supratentorial Procedures The primary role for ION in supratentorial procedures is evaluation of primary motor and somatosensory cortices and associated subcortical pathways. These regions are at risk of injury when they are within the immediate vicinity of pathology like tumors and vascular abnormalities. Multimodality ION provides several tools for ongoing assessment of these cortical and subcortical regions. The monitoring clinician must be able to evaluate the neural risk factors specific to the surgical procedure and implement appropriate test modalities so as to provide the surgeon with accurate and timely feedback about the integrity of monitored structures. Motor and somatosensory evoked potentials provide sensitive and specific coverage of pre- and postcentral cortical gyri, respectively. If the procedure poses risk of vascular compromise, the addition of multichannel electroencephalography (EEG) can extend monitoring coverage beyond these regions. The EEG can also help guide the surgeon and anesthesiologist during titrated infusion of neural protective agents, such as etomidate, that may be required to reduce metabolic demand of the brain during periods of reduced blood flow. The supratentorial approach to tumor resection often involves an incision site and scalp reflection that displace scalp electrodes from their optimal locations, more notably in infants. In these situations, it is helpful to obtain baseline tceMEP and SSEP recordings using an undisturbed scalp electrode setup prior to prepping of the surgical site. This allows for documentation of any pre-existing signal abnormalities that might otherwise be attributed to suboptimal placement of cephalic electrodes. Triggering of tceMEPs can be compromised if the stimulating electrodes are moved away from the primary motor cortex. While increasing stimulation intensity to compensate for electrode displacement may ultimately trigger a motor evoked potential, that strategy can be counterproductive. Increasing stimulation voltage may shunt current below the region of desired resection and thus increase the likelihood of a false-negative outcome, as illustrated in Fig. 6.7. The increased stimulation intensity can also increase patient movement, putting the patient

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

Fig. 6.7â•… Coronal section of the brain showing location of tumor (highlighted) and hypothetical paths of current flow during transcranial electrical stimulation at near-threshold (solid line) and suprathreshold (dashed line) intensities. The former path traverses the region of tumor, allowing for monitoring of involved corticospinal tract fibers. In contrast, the latter path undercuts the lower margins of the lesion and may activate distal motor tract fibers even in the presence of proximal damage, leading to a false-negative finding.

at risk for injury from unintended migration of a surgical instrument. A preferable strategy is to activate corticomotor neurons using a sterile electrode placed directly over motor cortex, as illustrated in Fig. 6.8. This technique lowers the stimulation intensity needed for primary motor cortex activation, which in turn reduces the risk of current shunting below the resection site. It also minimizes or eliminates the effect of patient movement, thereby limiting interference with surgical resection, and allows near-continuous monitoring and mapping during dissection (Fig. 6.8). Functional mapping of eloquent cortex also can facilitate safer resection of cortical and subcortical lesions in the frontoparietal regions. SSEP phase reversal testing can be performed to identify the central sulcus (Fig. 6.9), while low-intensity focal anodal

Fig. 6.8â•… Arrow points to sterile 4-contact electrode strip placed over cortex to facilitate direct stimulation of motor cortex. Diameter of each contact exposure is 5 mm.

stimulation aids in mapping the motor homunculus (Fig. 6.10a–c). Use of a flexible monopolar stimulating probe (see Fig. 6.10) facilitates motor mapping from within tumor capsule or adjacent to other lesions, such as cortical dysplasia, and aids in localization of internal capsule fibers when the lesion extends subcortically. Unlike mapping of motor cortex, which requires anodal monopolar stimulation, cathodal monopolar stimulation should be used to map the internal capsule. It is recommended that, when the lesion is in close proximity to primary motor areas, mapping/testing should be performed repeatedly during resection to confirm that stimulation thresholds remain unchanged (Fig. 6.9 and Fig. 6.10).

Fig. 6.9â•… Intraoperative neurophysiological mapping of the central sulcus in a 17-year-old female patient prior to resection of epileptogenic focus in right frontal cortex. Recording electrode was similar to that shown in Fig. 6.8. Ulnar nerve SSEP phase reversal localized the central sulcus between electrodes 3 (EL3) and 4 (EL4).

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68 Section Iâ•… Introduction

a

b

c

Fig. 6.10â•… Motor cortex mapping in a 17-year-old male patient prior to resection of epileptogenic zones in the left frontotemporal region. Motor cortex was mapped under total intravenous anesthesia (propofol/opioid) without muscle relaxation by triggering motor evoked potentials with anodal pulse trains (3 pulses, 1.1-msec interpulse interval, 50-µsec pulse duration). A cathode was placed in the contralateral scalp. Muscle abbreviations: DLT, deltoid; ECR, extensor carpi radialis; FDI, first dorsal interosseous; TA, tibialis anterior; TNG, tongue. (a) Upper panel shows stimulation probe over site A, which triggered low-threshold responses from the right wrist extensor and hand intrinsic muscles, as illustrated by adjacent traces. (b) Middle panel shows stimulation probe over site B, which triggered low-threshold responses from the tongue, as illustrated. (c) Lower panel shows sites A and B prior to (left) and following (right) resection of epileptogenic zones. This patient did not show any motor deficits postoperatively.

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

Awake Speech Mapping: An Intraoperative Neurophysiological Approach The application of ION is integral during procedures requiring resection of epileptogenic foci or lesions that are proximate to areas involved in language function. These procedures often require the patient to remain awake, when this is feasible, so that neurologic status can be observed directly during functional neurophysiological testing. The primary role for the pediatric surgical neurophysiologist in these cases is to provide scaled, pre-

cisely timed electrical stimulation for the surgeon to survey cortical tissue while the patient performs language-oriented tasks. Disruption of the patient’s behavior during performance of these tasks implicates the stimulated tissue in language function. A complementary interpretive role for the pediatric surgical neurophysiologist or pediatric neurologist is to identify EEG after-discharges (ADs) associated with cortical stimulation, as noted in Fig. 6.11a,b. These ADs are key to identifying the upper limit of applied stimulation. The most common approach for mapping language function is to implement the Penfield stimulation

a

b Fig. 6.11â•… Electrocorticography during and immediately following bipolar train stimulation to establish cortical after-discharge threshold. (a) 3-mA biphasic pulse stimulation at 50 Hz. No after-discharges noted on any of three EEG channels following stimulation. (b) 4-mA biphasic pulse stimulation at 50 Hz. After-discharges are noted on the second and third EEG channels following stimulation.

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70 Section Iâ•… Introduction technique.34,35 Our adaptation of the technique involves delivery of biphasic pulses at 50 Hz for durations of 3 to 5 seconds. The period of each biphasic pulse is 1 msec. Initially, we stimulate the facial representation of primary motor cortex, increasing intensity until we observe or the patient reports facial twitches. These stimulation thresholds can range from 1 to 3 mA and are considered the “floor” threshold. We then stimulate cortex outside the primary motor representation, increasing current intensity gradually until after-discharge is noted, as represented in Fig. 6.11b. This latter intensity is deemed the “ceiling” threshold, which defines the upper limit of applied stimulation during functional testing. Once effective and safe threshold boundary values have been defined, subsequent stimulation of target cortical tissue takes place while the child performs various tasks that probe language function. These tasks range from simple counting to more complex sentence and image or word recognition. When stimulation of a cortical region provokes speech arrest or hesitation, the eloquent tissue is usually spared. Because absence of hesitation does not rule out presence of eloquent cortical tissue, communication with

the child is maintained throughout the resection phase in order to monitor language function.36

Infratentorial Procedures Historically, the applied intraoperative neurophysiological monitoring for infratentorial or brainstem operations focused predominantly on identification and functional preservation of cranial nerves VII and VIII. As an outgrowth, multimodality neuromonitoring has expanded infratentorial surveillance to include all motor cranial nerves and select cranial nerve nuclei, as well as extended regions of the brainstem that may be at surgical risk. For example, transcranial electrical motor evoked potentials, such as those displayed in Fig. 6.12a, can be used to assess descending corticospinal motor fibers in the area of the pons and medulla, while somatosensory evoked potentials (Fig. 6.12b,c) survey long sensory tracts ascending through the regions of the medulla, pons, and midbrain to the thalamus. Brainstem auditory evoked potentials (BAEPs), shown in Fig. 6.12e, are used not only for functional assessment of cranial

Fig. 6.12â•… Example of multimodality monitoring during resection of a posterior fossa ependymoma in a 5-year-old boy. (A) Transcranial electrical motor evoked potentials recorded from bilateral first dorsal interosseous (FD) and tibialis anterior (TA) muscles. (B) Cervical/brainstem and cortical somatosensory evoked potentials to sequential stimulation of the left and right ulnar nerves. (C) Cortical somatosensory evoked potentials to sequential stimulation of the left and right posterior tibial nerves. (D) Compound muscle action potentials recorded from bilateral FD muscles to train-of-four stimulation of the left and right ulnar nerves (neuromuscular junction testing). (E) Brainstem auditory evoked potentials to sequential click stimulation of the left and right ears. (F) Single-channel electroencephalography (to facilitate monitoring of anesthetic depth).

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

Fig. 6.13â•… Cranial nerve mapping using stimulated electromyography during resection of a posterior fossa ependymoma in a 5-year-old boy. Cranial nerves IX and XI are identified using concentric bipolar stimulation at < 1 mA. LMA, left masseter muscle, LMN, left mentalis muscle; LOC, left orbicularis oculi muscle; LOR, left orbicularis oris muscle; LTN, left tongue; LTR, left trapezius muscle; PA, soft palate.

nerve VIII but also for the ipsilateral and contralateral brainstem pathway between the auditory nuclei and rostral lateral lemnisci (Fig. 6.12). In conjunction with multimodality evoked potentials, both free-running (spontaneous) and stimulated electromyography (EMG) can be performed to monitor motor function of cranial nerves III–VII and IX–XII, as well as to map the floor of the fourth ventricle via identification of select cranial nerve nuclei. Precise localization of these cranial nerves and their respective nuclei is facilitated by use of a sterile hand-held concentric bipolar electrical stimulator that limits current spread (see Fig. 6.6). Fig.€6.13 presents an illustrative example of cranial nerve mapping identifying the glossopharyngeal and spinal accessory nerves.

Chiari Malformation Chiari malformations consist of caudal displacement of the cerebellar tonsils, and sometimes medulla, through the foramen magnum. Types I and II are the most common and, when indicated, are usually treated with surgical intervention that includes a suboccipital decompressive craniectomy and possible duraplasty. Multimodality ION, including cortical SSEP, tceMEP, BAEP, and EMG, can be used to assess the integrity of the spinal cord, brainstem, and lower cranial nerves as well as for identifying preexisting neurophysiological deficits and for detecting presence of evolving injury during positioning, bony decompression, and intradural exposure. This may be particularly useful in reoperations or cases thought to be accompanied by significant adhesions, anterior compression, instability, or other high-risk factors.37

6.5.2╇ Spine Surgery Spinal Dysraphism Spinal dysraphism consists of congenital spinal or spinal cord defects secondary to failed closure of the neural tube or fusion of bony elements during early development. There are several pathologies associated with spinal dysraphism, including but not limited to various forms of spina bifida, Chiari malformation, tethered spinal cord, syringomyelia, lumbosacral lipoma, diastematomyelia, and dermal sinus tracts. Each of these pathologies may require neurosurgical intervention with application of ION.38 Neurosurgical intervention for release of the various forms of tethered spinal cord usually involves precise lumbar or lumbosacral laminectomy near the site of intended release. The general principle is to begin dissection in normal anatomy and move systematically toward the area of abnormality. In cases of simple filum section, the dura is opened over the desired location of section followed by careful dissection of lumbosacral spinal nerve roots and subsequent identification and sectioning of the isolated filum terminale. In cases where there are other congenital anomalies, such as lipoma or meningocele, the risk of iatrogenic neurologic injury can be increased. Here again, in general, the dura is opened over an area of normal anatomy. As dissection continues toward the area of abnormality, ION can aid in distinguishing neural from nonneural tissue and provides constant feedback about the functional integrity of neural structures at risk. The primary role of ION during untethering procedures is to facilitate identification and sparing of spinal nerve roots or fascicles that may be adher-

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72 Section Iâ•… Introduction ent to the filum, sinus tract, fatty mass, or scar tissue. Once the dura is opened, it is important for the neurosurgeon to establish a positive neural control by stimulating a clearly visualized nerve root prior to stimulation of the filum, as exemplified in Fig. 6.14. Here again, a bipolar (preferably concentric) stimulator is used to probe individual lumbar and sacral roots directly, which typically have depolarization thresholds ≤ 3 mA (pulse duration 100 µsec). Higher thresholds may be indicative of current spread through cerebrospinal fluid, which should be suctioned from the site. If subsequent circumferential stimulation of the filum at intensities up to 7 mA triggers a compound muscle action potential, the filum should be examined carefully for presence of nerve fascicles. Detailed attention should be paid to the presence of small compound muscle action potentials with thresholds < 3 mA. These stimulus-

evoked EMG responses are usually elicited by depolarization of adherent low sacral nerve fascicles that can be freed prior to sectioning of the filum to reduce the risk of postoperative bladder or bowel dysfunction. Restimulation of the filum circumferentially following fascicular dissection should result in absence of any recordable stimulated EMG responses even at high intensities (Fig. 6.14b). Minimizing or eliminating current spread is essential to reliable identification of isolated spinal nerve roots and nerve fascicles. Accordingly, use of monopolar stimulation at durations used typically for detecting pedicle screw violation of the medial wall is inappropriate for intradural nerve root mapping. Again, we recommend concentric bipolar stimulation with pulse durations of 50 to 100 µsec (usually 100 µsec) determined by the presence and magnitude of response spread across multiple myotomes. While there often is

a Fig. 6.14â•… Stimulus-triggered EMG testing prior to sectioning of filum terminale during a spinal cord untethering procedure in a 4-month-old boy. Muscle abbreviations: AS, external anal sphincter; GA, gastrocnemius; IO, iliopsoas; QD, quadriceps; TA, tibialis anterior. (a) Concentric bipolar stimulation at intensities between 0.2 and 1.8 mA (100-µsec pulse duration, 2.1-Hz stimulation rate) used to identify lower sacral nerve root fascicle.

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

b Fig. 6.14 (Continued)â•… (b) Stimulation of filum at intensities up to 9.5 mA prior to sectioning reveals no compound muscle action potentials, consistent with absence of adherent neural elements.

some spread to an adjacent myotome, such as simultaneous EMG responses from both the anterior tibialis and gastrocnemius muscles on stimulation of the L5 nerve root, in most instances the depolarizing nerve can be identified readily based on the response amplitude, defined morphology, and temporal resolution. An additional practice that should be avoided is “muscle linking”; that is, combining two muscles into one recording channel (e.g., quadriceps and anterior tibialis). This oft-noted practice among less experienced ION personnel defeats the ability to determine the innervating nerve root and can lead to erroneous interpretation communicated to the surgeon (Fig. 6.14). In addition to surveillance of the filum terminale, ION contributes to overall patient safety by monitoring nerve root function. Spontaneous EMG, lowerextremity tceMEPs, and posterior tibial nerve SSEPs are monitored both during the laminectomy/laminotomy phase as well as during opening of dura and exploration of exposed lumbosacral roots, to identify acute nerve root stretch or compression. TceMEPs should be supported with both spEMG and stEMG

from multiple myotomes. Some spEMG discharges coincide with tceMEP decrements, while others do not; therefore, it is important for the pediatric surgical neurophysiologist to pay close attention to the spEMG throughout the procedure and to provide immediate feedback to the surgeon during episodes of vigorous neurotonic discharge activity.

Diastematomyelia Diastematomyelia is a congenital disorder in which the presence of an osseous or fibrous septum in the central portion of the spinal canal causes “splitting” of the spinal cord into two hemicords. This usually occurs between the low thoracic region and the sacrum, with the most common locale being in the upper lumbar region. Due to the nature of the surgical exposure and the need for removal of the abnormal bony septum and/or dural sheath, the spinal cord and its component hemicords may be at risk for injury from retraction, as illustrated in Fig. 6.15.

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74 Section Iâ•… Introduction

a

b

Fig. 6.15â•… TceMEP monitoring results from a 14-year-old with diastematomyelia during procedure to remove osseous septum. Posterior tibial nerve somatosensory evoked potentials (not shown) were absent at baseline. Muscle abbreviations: AD, adductor; AS, external anal sphincter; FD, first dorsal interosseous (upper extremity control); GA, gastrocnemius; QD, quadriceps; TA, tibialis anterior. (a) Baseline left (upper panel) and right (lower panel) tceMEPs from multiple myotomes. (b) Loss of right-side lower-extremity tceMEPs with sparing of the upper-extremity control and external anal sphincter responses following retraction of right hemicord, prompting surgical alert, hemodynamic intervention, and subsequent closure.

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

c Fig. 6.15 (Continued)â•… (c) No return of right-side lower-extremity tceMEPs following 40 minutes of pharmacologically induced hypertension. Postoperatively, this patient was noted to have new-onset right lower-extremity paresis, which showed partial recovery after 10 days.

Monitoring the cord and the adjacent roots on each side can help the surgeon proceed with safe dissection and removal of the midline tether, as well as sectioning the distal fila.

Intradural and Extradural Spine Tumors Glial tumors are the most common intramedullary spinal cord tumors. Children who present with these lesions usually have pre-exisiting neurological compromise, exhibiting symptoms of myelopathy and/ or radiculopathy.39 Consequently, they are at heightened risk for additional neurologic compromise during tumor resection and can benefit from multimodality intraoperative monitoring of spinal cord and spinal nerve root function with D-waves, myogenic tceMEPs, and SSEPs. The D-wave is a direct corticospinal tract (CT) volley generated following single-pulse electrical stimulation applied to the cortex. This descending volley is recorded over the spinal cord either epidurally or intradurally using a catheter-type bipolar electrode.10,40 D-waves complement myotomal tceMEP monitoring and provide valuable information that can

facilitate safe maximal resection of intramedullary tumor tissue. Whereas sustained intraoperative loss of tceMEPs is consistent with compromise of corticospinal tract conduction that may manifest as paresis or paralysis in the immediate postoperative period, simultaneous preservation of D-wave amplitudes at or above 50% of baseline is a positive long-term prognostic indicator (Fig.€6.16a–c). These patients generally recover preoperative motor strength over the course of a few hours to a few days.40 This feedback can be extremely helpful to the surgeon during dissection, allowing for necessary tissue manipulation to effect appropriate tumor removal within a likely recoverable range. SSEPs can serve two distinct neurosurveillance purposes during intramedullary spinal cord tumor resection. The primary role is to assess the functional integrity of the dorsal column tracts. Alternatively, SSEPs can also be used to map the location of the dorsal median sulcus prior to myelotomy. One such mapping technique makes use of SSEP phase reversal to identify the physiologic midline. SSEPs are recorded from the scalp to bipolar stimulation along the longitudinal axis of the dorsal column. The site of stimulation is moved systematically from left

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76 Section Iâ•… Introduction

a

Fig. 6.16╅ Left and right myotomal tceMEPs and D-waves recorded during resection of a T2 intramedullary tumor in a 16-year-old female patient. Muscle abbreviations: AD, adductor longus; AH, abductor hallucis; FD, first dorsal interosseous; GA, gastrocnemius; QD, quadriceps; TA, tibialis anterior. (a) Progressive tceMEP attenuation on the left side (arrow) evolving to complete response loss from the left adductor, quadriceps, and tibialis anterior muscles and significant (>€65%) response amplitude attenuation from the left gastrocnemius and abductor hallucis muscles. (b) Significant (> 65%) amplitude depression of right lower-extremity myotomal tceMEPs (arrow) correlative to signal changes on the left side. b

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures

c Fig. 6.16 (Continued)â•… (c) Preservation of D-wave recordings in the presence of significant deterioration of myotomal responses. Slight changes in D-wave latency and amplitude are secondary to repositioning of the recording electrode to midline. This patient awoke with new-onset left lower-extremity paresis that resolved within 24 hours.

to right until SSEP polarity inverts as the midline is crossed. Alternatively, differential antidromic activation of the left and right posterior tibial nerves can be used to localize the dorsal median sulcus using the same stimulation paradigm, as illustrated in Fig. 6.17. A third strategy involves recording SSEPs directly from the spinal cord during stimulation of the left and right posterior tibial nerves and localizing the midline to the region of maximal response amplitude.

6.5.3╇ Peripheral Nerve ION ION during peripheral nerve surgery has been performed since the 1960s. In 1968, Kline and DeJonge first reported on the use of direct nerve stimulation and recording of compound nerve action potentials (CNAPs) to evaluate peripheral nerve injuries.41 This technique remains the gold standard for establishing evidence of conduction in the presence of peripheral

nerve pathology, and it finds application in procedures like peripheral nerve transposition, exploration and resection of neuroma in continuity, and intraoperative treatment of traumatic nerve injury, as shown in Fig. 6.18. We have found that the optimal approach to successful stimulation of surgically exposed peripheral nerve and recording of CNAPs is to use tripolar stimulation and bipolar recording.42,43 The tripolar/ bipolar electrodes are bent like a shepherd’s crook and are used to support or suspend the nerve away from other conductive elements within the surgical field. The tripolar electrode is designed with both outer electrodes linked together as the anode, with the middle electrode serving as the cathode. This tripolar arrangement limits the spread of stimulus artifact and is particularly helpful in cases where distances between the stimulation and recording sites are less than 10 cm. The placement of a ground electrode between stimulating and recording electrodes also aids in reduction of stimulus artifact.

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78 Section Iâ•… Introduction

Fig. 6.17â•… Differential antidromic activation of the left and right posterior tibial nerves (PTN) during dorsal column stimulation used to localize dorsal median sulcus prior to myelotomy. Left and right columns show evoked responses from left and right PTNs, respectively, during stimulation at various sites over the dorsal spinal cord. Evoked responses recorded using paired subdermal needles at the level of the medial malleolus. Lateralized bipolar stimulation (6 mA pulses, 200 µsec duration) along the longitudinal axis of the spinal cord differentially activates the left or right PTN. Stimulation over the midline triggers smaller responses bilaterally.

6.6╇ What the Pediatric Neurosurgeon Should Understand about the Role of Neuromonitoring Despite the increased use of ION in pediatric neurosurgery over the past decade, its role sometimes continues to be misunderstood. In general, the principal goals of intraoperative neurophysiological monitoring are as follows44:

• To identify evolving disruption of biochemical, metabolic, or hemodynamic processes that predispose a neural pathway or anatomical structure to injury • To provide functional identification and mapping of neural structures (e.g., cranial nerves, spinal nerve roots, peripheral nerves, eloquent cortical tissue) to help define safe boundaries for entry, dissection, or resection • To assess functional integrity of anatomical structures and pathways

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures Secondarily, ION can also aid in assessing the effects of rescue intervention (such as elevation of blood pressure or removal of compressive or distracting hardware) as well as adequacy of anesthetic depth.44,45 The underlying basis for ION, therefore, is to minimize the overall incidence and severity of iatrogenic neurologic injury, thereby improving surgical safety and outcome. Contrary to the belief of some neurosurgeons, neuromonitoring should not be viewed in the perspective solely of injury prediction, but rather of injury prevention, as illustrated in Fig. 6.19. The three cardinal rules for neuromonitoring success in pediatric surgery are the following:

Fig. 6.18â•… Compound nerve action potentials (CNAPs) recorded from left median nerve in a 10-year-old child following traumatic injury. Recordings were made using a bipolar hook electrode placed under the nerve distal to the site of injury. Constant voltage stimulation was delivered proximally using a tripolar electrode. CNAPs with a latency of 2 msec were triggered at threshold stimulus intensity less than 2 V, confirming conduction through the site of injury.

• View neuromonitoring manifestations of “emerging” injury as early warning indicators of impending functional neural compromise if the situation is left unattended. • Foster effective communication of ION alerts to provoke increased surgical vigilance and/ or rescue interventions depending upon the type, pattern, and context of ION change. • Act promptly in the face of neuromonitoring change to stem continued evolution of compromising conditions. The prevailing question then relates to when a given change in neural transmission is deemed clinically significant, warranting a surgical alert and intervention. To understand this better, the surgeon must recognize that interpretation of intraoperative neuromonitoring

Fig. 6.19â•… Graphic hypothetical illustration to show that the purpose of ION is to identify early changes in neurophysiological conduction to enable timely intervention and prevention, not prediction of permanent neurologic deficit.

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80 Section Iâ•… Introduction data most often takes place in the presence of uncertainty or ambiguity. The role of the responsible ION provider, therefore, is to minimize those variables that can have a negative effect on interpretive decisions. The first step toward reducing interpretive ambiguity for injury prevention is for the ION provider to have a clear understanding of why he or she is involved in the surgery. Just as the surgeon develops a surgical plan before engaging in surgery, so too must the responsible ION professional. All too often ION is based on a standardized, “one size fits all” approach, rather than a risk-analysis algorithm centered on answering a set of patient- and procedurespecific questions, outlined as follows: • Which neural structures, pathways, or vascular supplies, both within and outside of the immediate surgical field, might be at risk for neural injury? • Which neuromonitoring modalities should be combined to provide the broadest surveillance of those neural structures, pathways, or vascular supplies potentially at risk for neural injury? • What anesthetic techniques will have the least compromising effect on clinical interpretation of significant signal change? • What nonsurgical, physiological, or anesthetic factors (e.g., patient positioning, hypotension, volume depletion, hypocapnia, use of inhalational anesthetics, partial neuromuscular blockade) or medical comorbidities (e.g., diabetes, pre-existing neurologic compromise) can account for signal changes that can affect clinical interpretation and decision making? • What surgical maneuvers are associated with risk of neural injury? • What rescue intervention strategies (e.g., elevation of blood pressure, release of retractors, temporary cessation from surgery, etc.) will help restore neural homeostasis in the unlikely event of significant signal change? Failure to formulate a rational neuromonitoring plan based on answers to the foregoing six questions not only can lead to inappropriate selection or inadequate number of monitoring modalities but also can increase the likelihood of miscommunication between neuromonitoring personnel and the surgeon and anesthesiologist as well as increase potential interpretive error. Successful implementation of the neuromonitoring plan depends critically on a coordinated team approach that begins with preoperative discussion of surgical, anesthesia, and neuromonitoring priorities. It is important that the ION provider be able to communicate effectively with the surgeon and anesthesiologist about the most effec-

tive approach to monitoring at-risk structures, as well as be able to articulate any limitations imposed by the patient’s baseline neurologic status, by technical limitations in the ability to interrogate specific structures at risk (such as cerebellum or visual pathways), or by suboptimal selection of monitoring modalities or anesthetic technique. Adding complexity to the questions of what to monitor and how best to interpret the data is that there are few highly educated and experienced neuromonitoring personnel with specialized knowledge and training, particularly in pediatric neurophysiological monitoring. Few would argue about the need for a fellowship-trained pediatric neurosurgeon and anesthesiologist; however, there has been a general lack of that same appreciation for pediatric neuromonitoring as a subspecialty requiring highly knowledgeable and skilled professional personnel for maximum benefit. If neuromonitoring is to be effective in general, and in pediatric neurosurgery in particular, then the ION provider must be viewed as an integral member of the surgical team, and both the surgeon and anesthesiologist must trust that the monitoring professional has the following attributes: • General and specialized fund of knowledge in neuromonitoring as a specialty • Competence and experience in formulating an appropriate monitoring plan • Ability to make instantaneous decisions regarding neurophysiological change or for anatomical mapping • Ability to communicate changes effectively in the context of the surgery, anesthesia, and physiology • Ability to develop a plausible explanation for neuromonitoring change so as to facilitate an interventional strategy

6.7╇ Perspective of a Pediatric Neurosurgeon It is often assumed that the main goal of intraoperative monitoring is to detect changes and thereby avoid injury. In fact, while this is a critical role of monitoring, it is also true that the absence of change allows the surgeon working with an experienced monitoring team to have the courage to continue a surgical intervention to the point of completion. This is true in tumor removal, in which the continued maintenance of signals from the motor or sensory pathways or lack of irritation of cranial nerves, spinal nerve roots, peripheral nerves, and so forth reassures the surgeon that dangerous territory has not been traversed. It is also true in resection of epi-

6â•… Intraoperative Neurophysiological Monitoring During Pediatric Neurosurgical Procedures leptogenic tissue, which often looks grossly identical to adjacent eloquent cortex or subcortical tracts; the steady maintenance of signals during resection enables more complete elimination of the epileptogenic zone. It is likewise true in complex tethered cord surgery, in which complete untethering often can be accomplished because the surgeon does not lose heart in a sea of fat and scar tissue for fear of transecting vital nerves and causing weakness or incontinence. In the ideal situation, the surgeon relies on teamwork with the anesthesiologist and the monitoring professional, working together to accomplish the surgical goal safely and completely. Despite ION’s status as an extraordinarily useful adjunct, there are still “blind spots” in ION. These include mapping and monitoring of cerebellar pathways, including the dentate nuclei; reliable mapping and monitoring of language, memory, and other neurocognitive areas in the anesthetized patient; and visual pathway mapping and monitoring. Monitoring in very young infants is possible but requires specialized techniques from an experienced team. Pediatric neurosurgeons can, and should, be willing to collaborate with monitoring professionals, scientists, and engineers to continue to develop the field to meet the needs of the children we treat.

6.8╇Conclusions Like most elements of modern surgical practice, successful use of intraoperative neuromonitoring requires teamwork, communication, and a combination of science and experience. Advances in monitoring over the past several decades have led to an increasingly important role for neuromonitoring during pediatric neurosurgical interventions. While more work needs to be done to expand the scope of ION for children and to address some areas of controversy, the present state of the art clearly improves the safety and increases the scope of what surgeons can accomplish. ION is a relatively young field, and surgeons can promote its evolution by working closely with ION professionals to expand its use to optimize the care of children with disorders of the nervous system.

References ╇1. Nash

CL Jr, Lorig RA, Schatzinger LA, Brown RH. Spinal cord monitoring during operative treatment of the spine. Clin Orthop Relat Res 1977; (126):100–105 ╇2. Cohen AR, Young W, Ransohoff J. Intraspinal localization of the somatosensory evoked potential. Neurosurgery 1981;9(2):157–162 ╇3. Cusick JF, Myklebust J, Larsn SJ, Sances A Jr. Spinal evoked potentials in the primate: neural substrate. J Neurosurg 1978;49(4):551–557

╇4. Larson SJ, Sances A Jr, Christenson PC. Evoked somatosen-

sory potentials in man. Arch Neurol 1966;15(1):88–93 DH. Somatosensory evoked potentials in man: differentiation of spinal pathways responsible for conduction from the forelimb vs hindlimb. Prog Neurobiol 1985;25(1):1–25 ╇6. Powers SK, Bolger CA, Edwards MS. Spinal cord pathways mediating somatosensory evoked potentials. J Neurosurg 1982;57(4):472–482 ╇7. Simpson RK Jr, Blackburn JG, Martin HF III, Katz S. Peripheral nerve fiber and spinal cord pathway contributions to the somatosensory evoked potential. Exp Neurol 1981;73(3):700–715 ╇8. Amassian VE, Stewart M, Quirk GJ, Rosenthal JL. Physiological basis of motor effects of a transient stimulus to cerebral cortex. Neurosurgery 1987;20(1):74–93 ╇9. Amassian VE. Animal and human motor system neurophysiology related to intraoperative monitoring. In: Deletis V, Shils JL, eds. Neurophysiology in Neurosurgery. San Diego, CA: Academic Press; 2002: 3–24 10. Deletis V. Intraoperative neurophysiology and methodologies used to monitor the functional integrity of the motor system. In: Deletis V, Shils JL, eds. Neurophysiology in Neurosurgery. San Diego, CA: Academic Press; 2002: 25–51 11. Schwartz DM, Sestokas AK, Hilibrand AS, et al. Neurophysiological identification of position-induced neurologic injury during anterior cervical spine surgery. J Clin Monit Comput 2006;20(6):437–444 12. Bhalodia VM, Sestokas AK, Tomak PR, Schwartz DM. Transcranial electric motor evoked potential detection of compressional peroneal nerve injury in the lateral decubitus position. J Clin Monit Comput 2008;22(4):319–326 13. Lyon R, Lieberman JA, Feiner J, Burch S. Relative efficacy of transcranial motor evoked potentials, mechanicallyelicited electromyography, and evoked EMG to assess nerve root function during sustained retraction in a porcine model. Spine 2009;34(16):E558–E564 14. Amassian VE, Quirk GJ, Stewart M. A comparison of corticospinal activation by magnetic coil and electrical stimulation of monkey motor cortex. Electroencephalogr Clin Neurophysiol 1990;77(5):390–401 15. Journée HL, Polak HE, de Kleuver M, Langeloo DD, Postma AA. Improved neuromonitoring during spinal surgery using double-train transcranial electrical stimulation. Med Biol Eng Comput 2004;42(1):110–113 16. Schwartz DM, Sestokas AK, Dormans JP, et al. Transcranial electric motor evoked potential monitoring duing spine surgery: is it safe? Spine 2011;36(13):1046–1049 17. Shah SA, Wiggins CR, Schwartz DM, et al. Spinal cord monitoring during scoliosis surgery in children with spastic cerebral palsy: is it feasible and safe even with an active seizure disorder? Presented at the Scoliosis Research Society (SRS) 46th Annual Meeting and Course, Louisville, KY, September 14–17, 2011 18. DiCindio S, Theroux M, Shah S, et al. Multimodality monitoring of transcranial electric motor and somatosensory-evoked potentials during surgical correction of spinal deformity in patients with cerebral palsy and other neuromuscular disorders. Spine 2003;28(16):1851-1855 ╇5. York

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DM, Auerbach JD, Dormans JP, et al. Neurophysiological detection of impending spinal cord injury during scoliosis surgery. J Bone Joint Surg Am 2007;89(11):2440–2449 20. Fan D, Schwartz DM, Vaccaro AR, Hilibrand AS, Albert TJ. Intraoperative neurophysiologic detection of iatrogenic C5 nerve root injury during laminectomy for cervical compression myelopathy. Spine 2002;27(22):2499–2502 21. Bose B, Sestokas AK, Schwartz DM. Neurophysiological detection of iatrogenic C-5 nerve deficit during anterior cervical spinal surgery. J Neurosurg Spine 2007;6(5):381–385 22. Bhalodia VM, Schwartz DM, Sestokas AK, et al. Efficacy of intraoperative monitoring of transcranial electrical stimulation–induced motor evoked potentials and spontaneous electromyography activity to identify acute-versus delayed-onset C-5 nerve root palsy during cervical spine surgery: clinical article. J Neurosurg Spine 2013;19(4):395–402 23. Schwartz D, Sestokas A. The use of neuromonitoring for neurological injury detection and implant accuracy. In: Vaccaro A, Regan J, Crawford A, Benzel E, Anderson D, eds. Complications of Pediatric and Adult Spinal Surgery. New York, NY: Marcel Dekker; 2004: 159–172 24. Sebel PS, Flynn PJ, Ingram DA. Effect of nitrous oxide on visual, auditory and somatosensory evoked potentials. Br J Anaesth 1984;56(12):1403–1407 25. Schwartz DM, Schwartz JA, Pratt RE Jr, Wierzbowski LR, Sestokas AK. Influence of nitrous oxide on posterior tibial nerve cortical somatosensory evoked potentials. J Spinal Disord 1997;10(1):80–86 26. Sloan TB, Heyer EJ. Anesthesia for intraoperative neurophysiologic monitoring of the spinal cord. J Clin Neurophysiol 2002;19(5):430–443 27. DiCindio S, Schwartz DM. Anesthesia implications for spinal cord monitoring in children. Anesthesiol Clin North America 2005;23:765–787 28. Sloan TB, Koht A. Depression of cortical somatosensory evoked potentials by nitrous oxide. Br J Anaesth 1985;57(9):849–852 29. Jellinek D, Platt M, Jewkes D, Symon L. Effects of nitrous oxide on motor evoked potentials recorded from skeletal muscle in patients under total anesthesia with intravenously administered propofol. Neurosurgery 1991;29(4):558–562 30. Kalkman CJ, Drummond JC, Kennelly NA, Patel PM, Partridge BL. Intraoperative monitoring of tibialis anterior muscle motor evoked responses to transcranial electrical stimulation during partial neuromuscular blockade. Anesth Analg 1992;75(4):584–589 31. Lang EW, Beutler AS, Chesnut RM, et al. Myogenic motor-evoked potential monitoring using partial neuromuscular blockade in surgery of the spine. Spine 1996;21(14):1676–1686

32. Minahan RE, Riley LH III, Lukaczyk T, Cohen DB, Kostuik JP.

The effect of neuromuscular blockade on pedicle screw stimulation thresholds. Spine 2000;25(19):2526–2530 33. Schwartz DM, Bhalodia BM, Vaccaro A. Neurophysiologic detection of medial pedicle wall violation in the lumbar and thoracic spine. In: Loftus CM, Traynelis VC, eds. Intraoperative Monitoring Techniques in Neurosurgery, 2nd ed. New York, NY: McGraw-Hill Professional, in press. 34. Penfield W, Boldrey E. Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation. Brain 1937;60:389–443 35. Ojemann SG, Berger MS, Lettich E, Ojemann GA. Localization of language function in children: results of electrical stimulation mapping. J Neurosurg 2003;98(3):465–470 36. Sahjpaul RL. Awake craniotomy: controversies, indications and techniques in the surgical treatment of temporal lobe epilepsy. Can J Neurol Sci 2000;27(Suppl 1):S55–S63, discussion S92–S96 37. Anderson RC, Dowling KC, Feldstein NA, Emerson RG. Chiari I malformation: potential role for intraoperative electrophysiologic monitoring. J Clin Neurophysiol 2003;20(1):65–72 38. Sutton L, Schwartz D. Congenital anomalies of the spinal cord. In: Simeon F, Rothman R, eds. The Spine, 4th ed. Philadelphia, PA: WB Saunders; 1999: 267–302 39. Tsulee J, Benzel E. Primary tumors of the spine. Contemporary Neurosurgery 2006;28(6):1–8 40. Yanni DS, Ulkatan S, Deletis V, Barrenechea IJ, Sen C, Perin NI. Utility of neurophysiological monitoring using dorsal column mapping in intramedullary spinal cord surgery. J Neurosurg Spine 2010;12(6):623–628 41. Kline DG, DeJonge BR. Evoked potentials to evaluate peripheral nerve injuries. Surg Gynecol Obstet 1968;127(6):1239–1248 42. Tiel RL, Happel LT Jr, Kline DG. Nerve action potential recording method and equipment. Neurosurgery 1996;39(1):103–108, discussion 108–109 43. Robert EG, Happel LT, Kline DG. Intraoperative nerve action potential recordings: technical considerations, problems, and pitfalls. Neurosurgery 2009;65(4, Suppl): A97–A104 44. Schwartz DM, Sestokas AK. A systems-based algorithmic approach to intraoperative neurophysiological monitoring during spinal surgery. Semin Spine Surg 2002;14(2):136–145 45. Schwartz DM, Sestokas AK. Facilitated assessment of unconsciousness from morphologic changes in the bilateral posterior tibial nerve cortical somatosensory evoked potential under total intravenous propofol anesthesia during spine surgery. J Clin Monit Comput 2004;18(3):201–206

7

Surgical Safety Thomas G. Luerssen

The same motives always produce the same actions; the same events follow from the same causes. David Hume An Enquiry Concerning Human Understanding (1748)

7.1╇Introduction Medicine is delivered by human beings in order to try to help other humans. Regardless of intellect, motivation, training, and practice, human beings make errors. Studies from the airline industry indicate that, even for routine tasks in low-stress situations, humans will make an error of some sort about every 30 minutes. For complex tasks at high stress levels, this time drops to about 30 seconds.1 Fortunately, humans have the capability of adapting and can correct many errors immediately. However, because humans are fallible, many errors either are not recognized or cannot be corrected, and therefore result in harm and sometimes catastrophe. The surgical patient is at particularly high risk for adverse events in a hospital. The World Health Organization estimates that, in industrialized countries, major complications occur in upward of 20% of inpatient surgical patients, with a death rate of roughly 0.5%.2 Half of these complications are thought to be preventable. Even the most straightforward procedures have numerous complex steps that provide opportunity for process failure and attendant patient injury. Consequently, efforts at improving patient safety must assume major importance in a health care system. Safety is a crucial element in what are called highreliability organizations (HROs). Examples of HROs include the airline industry, nuclear power plants, electrical power grid systems, and military systems controlling operations on submarines or aircraft carriers. These organizations are routinely exposed to high-risk situations but reliably achieve exceedingly low rates of failure or accidents. These HROs developed systematic approaches to error prevention many years ago and continuously refine their safety systems in order to approach zero defects. The lessons learned from HROs are only recently being applied in health care, and adoption of proven safety strategies in modern health care has been agonizingly slow despite ample evidence of effectiveness. A notable exception to this statement comes from our colleagues in anesthesia. That specialty’s focus on detecting adverse events and

preventing patient harm resulted in a reduction of anesthesia-related deaths from 3.7/10,000 anesthetics to 1 to 2/200,000 in ASA I or II patients.3 Entire texts have been written about patient safety strategies and processes. Opportunities to prevent harm exist at every point of a surgical patient’s management, from first encounter to admission to discharge and beyond. One common element in error causation is seen throughout the patient care experience and proves to be at the root of the vast majority of adverse events that result in patient harm. This common element is absent or ineffective communication.4 This chapter focuses on three major and related strategies derived from HROs that have gained widespread acceptance and have delivered improved outcomes, mostly by improving communication. These are: • The development of a culture of safety • The creation of effective surgical teams • The use of communication support tools— specifically, checklists and handoff scripts— in patient care

7.2╇ A Culture of Safety Without an institutional commitment to patient safety, processes that are implemented, even if mandatory, have little chance of being effective or being sustained. On the other hand, if a culture of safety is established and nurtured, safety microsystems arise almost spontaneously, with substantial and measurable improvements in outcomes and reductions in adverse events. HROs have several important characteristics that are diametrically opposite to the historical approaches used in health care. First, HROs have a preoccupation with failure. Health care organizations historically focused on successes and positive outcomes, referring failed processes, serious safety events, and adverse outcomes to “risk management.” Organizations preoccupied with failure measure and

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84 Section Iâ•… Introduction study all identifiable events, even if they do not result in harm, and correct processes prior to an adverse event occurring. Repeat failures almost never occur. HROs avoid oversimplification. The delivery of health care is one of the most complex of all human endeavors. Complex systems are not amenable to simplification strategies, which may seem to work well for an organization most of the time, but when these strategies fail, the outcomes can be disastrous. HROs constantly survey and improve their operations. The culture promotes thorough understanding of operations from the frontline staff to the management and encourages communication of issues so that problems are corrected as they are discovered and before they reach a patient. In line with that, HROs listen to the institutional experts. Most of the time the true experts are not in positions of authority but are right at the point of contact or point of care. In a culture of safety, these people are empowered and even encouraged and rewarded to bring problems forward and to participate in developing effective solutions. Finally, HROs are nimble and resilient. The culture allows rapid responses to unanticipated events and rapid recovery using innovative solutions. Managers are empowered to respond with innovative approaches when the standardized procedures are not working. Simply put, a culture of safety encourages transparent reporting, uses internal metrics much more than external benchmarks, and is focused on continuous improvement in care delivery processes small and large. Potential problems are addressed prior to real problems occurring. Unexpected events are reported and dealt with immediately. Solutions are developed both “top down” and “bottom up,” and everyone at every level in the organization is invested in error prevention as a core value.

7.3╇ Formation of Effective Teams From this point on, the focus of this chapter is the operating room (OR). Gawande and coworkers have shown that, for surgical patients, most patient harm events occur in the OR.5 However, the concepts discussed—team formation and function, communication, and the use of checklists and structured communication—apply universally throughout the surgical patient’s care continuum, from first contact with a health care system to well after discharge. Pronovost and Freischlag, in a recent editorial, provided a succinct description of the culture of the modern-day OR: “Operating rooms are among the most complex, political, social and cultural structures that exist, full of ritual, drama, hierarchy, and too often conflict.”6 This culture provides an ideal environment for miscommunication or failed communication, which, as discussed earlier, are the most common

cause of adverse events in health care.4 Effective teamwork provides a framework for preventing communication errors, by empowering and encouraging each member of the surgical team (surgeons, anesthesiologists, nurses, technicians, etc.) to monitor not only themselves in their own roles but also each other and clearly communicate concerns, or even stop a process that is unclear until all members agree that it is safe to proceed. Formation of effective teams is not just naming individuals and assigning roles. It takes training and practice and continuous improvement, as well as “after action” analysis of performance, especially in the case of process failure. Effective team communication is horizontal. This means that all members are considered equally important in their observations and expressing concerns, while recognizing that each member of the team has different knowledge, skill, and expertise. The major characteristics of effective teams are team leadership, mutual performance monitoring, backup behaviors, adaptability, communication, team orientation. and, perhaps most importantly, mutual trust.7 The airline industry developed a program generally referred to as Crew Resource Management (CRM), which has now been successfully applied in health care.8 There are now several training programs developed using the CRM methodology that teach effective teamwork and communication in health care. There is strong evidence that the investment in time and resources in team training reduces major adverse events in surgery.9 Lastly, regarding team performance in the OR—also based on lessons learned from the aviation industry— the author strongly believes that the idea of a “sterile cockpit” should be applied in the operating theater. Although evidence of effectiveness is limited and probably impossible to prove, I have not allowed music and have stringently limited idle conversations, phone interruptions, and pagers in the operating room. Not only are they distractions, but also the message they confer to the team (and others) is that the team’s focus is not entirely on the patient and the procedure at hand.

7.4╇ Checklists and Structured Communication Checklists are structured communication and recording of processes that are designed to increase standardization and to avoid reliance on memory in order to reduce errors and omissions. Safety checks have been shown to be effective in high-risk areas like aviation and nuclear power. In the seminal report by the Institute of Medicine in 1999, it was recommended that verification processes like checklists be implemented in medical practice.10 In response to that suggestion, the Joint Commission mandated the use of what was called the “Universal Protocol” (UP) in 2004. This was a rudimentary preop-

7â•… Surgical Safety erative checklist. Most reports indicated that the UP had minimal if any effect on reducing serious harm events in the OR. We studied the UP prior to implementing a more robust checklist at Texas Children’s Hospital (TCH) and found that, although the UP was reported as completed for every operation, it was led by the nurses, while other members of the OR personnel were disengaged and frequently not even in the room. A trained independent observer of the UP during that study scored it as complete and correct less than half the time. In 2009, the World Health Organization’s (WHO) Safe Surgery Saves Lives Study Group published the results of a robust surgery safety checklist (SSCL) used in eight hospitals worldwide.11 They showed a positive beneficial effect for this SSCL. Even prior to that publication, many institutions, including ours, were implementing a WHO-based SSCL. Using quality improvement methodology, we developed an SSCL for our patient population and implemented it beginning in January 2009. We learned that, very much like forming effective teams, the implementation of an SSCL requires specific training and

practice as well as measurement and reporting of performance. It took about one year to achieve our goal of greater than 95% compliance. However, when we studied the effect of the SSCL on patient outcomes, we noted a major reduction in patient safety events in the OR and improved efficiency in the OR. Even more interesting, as the SSCL was adopted, a safety microsystem appeared in which the users began expanding and improving the TCH SSCL. After regular and multiple iterations, TCH now has six SSCLs in five geographic OR environments, along with additional service-specific, casespecific, and intraoperative emergency procedure checklists (Fig. 7.1). WHO-based checklists are tripartite and are meant to address the three major steps in a surgical patient’s journey through the OR. The three parts include a preoperative “briefing,” which occurs just before the patient is transferred from the preoperative holding area (or hospital floor, intensive care unit, or emergency room) to the OR suite. This is meant to be an opportunity for the surgeon and

Fig. 7.1â•… Current Texas Children’s Hospital surgery safety checklist for the main campus operating rooms. Courtesy of Texas Children’s Hospital.

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86 Section Iâ•… Introduction anesthesiologist and the OR team to review the plans and concerns for the upcoming procedure; to identify the patient; to confirm the procedure site and side; and to confirm that all the necessary equipment, implants, blood products, drugs, and irrigation fluids are available. We try to have the family participate in the preoperative briefing. There is also a postoperative “debriefing,” which occurs before the patient leaves the OR suite. This is the opportunity to ensure that all specimens and laboratory tests are checked and rechecked, that the receiving patient care area is ready for the patient with staff and equipment, and that there is agreement between surgeon and anesthesiologist about the postoperative care issues. It is also the time for “after action analysis,” where problems are discussed and referred for solution, equipment issues are identified and referred for repair, and opportunities for improvement are brought forward. Highly effective OR teams use the briefing and debriefing opportunities and structure to their fullest potential, expanding the information transfer far beyond the minimums requested. The cornerstone of an SSCL is the “timeout” or surgical pause. This occurs immediately before invasion of the patient. Most of the time this means prior to the surgical incision, but we have interpreted this more broadly and do timeouts prior to pin fixation, injections of anesthetic, placement of lumbar drains, and so forth. If anesthesia personnel are placing deep lines or placing blocks, they perform a timeout prior to their procedures. The timeout is a “system reset”— the last chance to confirm all the important elements of the procedure. This is a true checklist, meant to be read point by point—not memorized or altered—and listened to by every member of the team. Any concerns are voiced, and all members of the team must confirm agreement that they are ready to proceed. There is no reason to forgo performing a timeout, including emergencies. A timeout usually takes less than 90 seconds, and complications are reduced in urgent operations when a preprocedure checklist is used.12 Checklists are living documents. Our SSCLs are revised about every 6 months, using input from the OR staff and surgeons and from analysis of safety reports. Each revision has been immediately accepted by the users, and compliance remains extremely high.

7.5╇ Handoffs Clear communication is essential when transferring patient care from location to location and/or from caregiver to caregiver. In a progressively more complex medical environment, these transitions

occur frequently and are the points where critical information is omitted or misunderstood. Structured handoffs are one of several ways being developed to transfer important information efficiently and accurately. Two common and well-developed handoff strategies are SBAR (for Situation—Background—Assessment—Recommendation) and P5 (for Patient—Problems—Pertinent History—Plans or Procedure—Precautions or Pitfalls). Whatever structured communication process is adopted by an institution, it takes training and practice among users in order to become effective. Most important, it should become an expectation for the transmitter and the receiver of information, with specific ways of clarifying and confirming understanding of the information.

7.6╇Conclusion Patient safety, error prevention, and structured processes to prevent adverse outcomes are assuming a primary position in health care. It is likely that most institutions and health care systems will move toward mandatory training in error prevention. Furthermore, credentialing and recredentialing of medical privileges will include analysis of adverse events and participation in institutional safety and error prevention programs. Considering that almost half of adverse events occurring in a hospital arise in the OR, surgeons and OR staff should embrace patient safety and error prevention efforts. Considering the impact that safer surgery can have on an institution, the OR can become the innovation laboratory for safety program development in the future.

References ╇1.

╇2.

╇3.

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╇5.

╇6.

Müller M. Increasing safety by implementing optimized structures of team communication and the mandatory use of checklists. Eur J Cardiothorac Surg 2012;41(5):988–992 World Health Organization. WHO Guidelines for Safe Surgery 2009. Geneva, Switzerland: World Health Organization; 2009. http://whqlibdoc.who.int/publications/2009/9789241598552_eng.pdf Pierce EC Jr. The 34th Rovenstine Lecture. 40 years behind the mask: safety revisited. Anesthesiology 1996;84(4):965–975 The Joint Commission. The Joint Commission: four key root causes loom large in sentinel event data. ED Manag 2012;24(6):S3–S4 Gawande AA, Thomas EJ, Zinner MJ, Brennan TA. The incidence and nature of surgical adverse events in Colorado and Utah in 1992. Surgery 1999;126(1):66–75 Pronovost PJ, Freischlag JA. Improving teamwork to reduce surgical mortality. JAMA 2010;304(15):1721–1722

7â•… Surgical Safety Baker DP, Day R, Salas E. Teamwork as an essential component of high-reliability organizations. Health Serv Res 2006;41(4 Pt 2):1576–1598 ╇8. Dunn EJ, Mills PD, Neily J, Crittenden MD, Carmack AL, Bagian JP. Medical team training: applying crew resource management in the Veterans Health Administration. Jt Comm J Qual Patient Saf 2007;33(6):317–325 ╇9. Neily J, Mills PD, Young-Xu Y, et al. Association between implementation of a medical team training program and surgical mortality. JAMA 2010;304(15):1693–1700 10. Kohn LT, Corrigan JM, Donaldson MS, Committee on Quality of Health Care in America, Institute of Medi╇7.

cine. To Err is Human: Building a Safer Health System. Washington, DC: National Academy Press; 2000 11. Haynes AB, Weiser TG, Berry WR, et al; Safe Surgery Saves Lives Study Group. A surgical safety checklist to reduce morbidity and mortality in a global population. N Engl J Med 2009;360(5):491–499 12. Weiser TG, Haynes AB, Dziekan G, Berry WR, Lipsitz SR, Gawande AA; Safe Surgery Saves Lives Investigators and Study Group. Effect of a 19-item surgical safety checklist during urgent operations in a global patient population. Ann Surg 2010;251(5):976–980

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Section II Neurology

Section Editor: Scott L. Pomeroy In this era, with an ever-increasing number of advanced diagnostic modalities, the neurologic examination remains the essential first step in assessing an infant or child with nervous system disease. Through skilled examination, the locus of disease can be established and, combined with history and general examination, the cause of disease can often be inferred and priorities set as to whether urgent intervention is needed. The chapters in this section describe the steps and procedures needed for neurologic examination

of infants, children, and adolescents. The authors describe the need for careful observation to assess overall function, followed by a step-by-step, detailed examination to determine whether individual components of the nervous system are impaired. Each of the authors of this section has extensive experience in neurologic assessment. The content of each chapter reflects a careful and systematic approach. The chapters describe important observations and examination tips, pointers and “pearls,” which are truly the tricks of the trade.

8

Neonatal Neurologic Examination Charles C. Duncan and Laura R. Ment

8.1╇ Introduction and Background Despite the development of sophisticated perinatal assessment strategies, the examination of the newborn infant remains a key step in the neonatal neurologic evaluation. The neonatal neurologic examination is gestational age- and state-dependent and may provide important information about both central and peripheral neurologic problems. While much has been written on this topic, the fundamentals of the neurologic examination of the neonate are simple and easy to perform and may offer critical information about urgent neurologic and neurosurgical problems. They are dependent on observation, the infant’s response to external stimulation, evidence of appropriate neuromaturation, and an assessment of tone and reflexes.

8.2╇ Observation of the Neonate A hallmark of the neonatal neurologic examination is observation of the resting infant. This inspection should include observations about tone and spontaneous movements, respiratory pattern, and level of alertness. Although tone and posture are related to postmenstrual age (i.e., weeks from conception) at the time of assessment, it is important to note both the infant’s posture and spontaneous movements. Preterm neonates of 28 weeks or less will lie with arms and legs fully extended, and term infants will assume a posture of full flexion, but in infants of all postmenstrual ages, spontaneous movements should be symmetric and nonstereotypic. An infant with a hemiparesis will have decreased spontaneous movement of the affected arm and leg, while a neonate with a plexus injury may show a flaccid arm with weak shoulder, wrist, or hand. Similarly, the neonate with repetitive, stereotypic, rhythmic movements of a single extremity is worri-

some for neonatal seizures and an underlying focal lesion, while the infant with irregular respirations or periods of spontaneous apnea may harbor a serious posterior fossa lesion or be experiencing seizures. Finally, the baby with no spontaneous movements but a normal pattern of respiration may be simply sleeping, but those who appear “hyperalert” with darting eye movements and spontaneous clonus may be suffering from hypoxic, toxic, or metabolic encephalopathy.

8.3╇ The Infant’s Response to External Stimulation Following a quiet period of observation, the infant should be stimulated with a bright light, bell, and noxious stimulation. The eyelids are fused in preterm neonates until the 26th week of gestation, but all neurologically intact infants will blink to light, even through closed eyelids. Failure to blink to light may reflect an altered level of consciousness or a structural lesion. Similarly, ringing of the bell should result in change of state. Sleeping infants will arouse, while active babies may quiet. Movements should be symmetric and nonstereotypic, as myoclonic jerks may be stimulus-, and particularly noise-, dependent. As with the response to photic stimulation, the failure to respond to a bell may reflect encephalopathy, but it may also be indicative of structural or toxic disorders. Neonates with auditory neuropathies or structural malformations may be awake and active but unresponsive to sound. Similarly, those with toxic exposures, such as hyperbilirubinemia and emerging kernicterus, may also not respond to auditory stimulation. Finally, a gentle sternal rub (i.e., “noxious stimulation”) should evoke symmetric movement of all four extremities. Failure of one arm and leg to mirror the other strongly suggests a focal lesion, while

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92 Section IIâ•… Neurology a flaccid arm may be indicative of a brachial plexus lesion. Importantly, evidence of myoclonic activity, tonic posturing, or apneic respirations are all consistent with significant neurologic impairment requiring immediate attention. Likewise, infants with little or no response to sternal rub should be immediately evaluated for intracranial, cervical, and metabolic life-threatening conditions. Nonsedated infants with no response to photic, auditory, and tactile stimulation need urgent evaluation for coma, while those with atypical or focal responses should be evaluated for infectious, structural, or metabolic causes of encephalopathy.

8.3.1╇ Evidence for Neuromaturation The increasing survival of extremely low gestational neonates demands a working knowledge of neuromaturation, and serial examinations of the prematurely born should optimally demonstrate progressive acquisition of the neurologic parameters that characterize term neonates.

Visual System Eyelids are fused in preterm neonates through the 26th week of gestation, and the pupils are dilated and nonreactive to light until gestational week 28. Eye movements should always be full and equal but are frequently difficult to assess in the critically ill neonate. Notably, although one does not expect the newborn infant to fix and follow reliably on a bright light or multicolored large object, healthy term neonates whose mothers have not received sedation or pain medication will fix and follow on the day of birth. Similarly, healthy preterm neonates (i.e., “feeders and growers”) will also fix and follow beginning at 34 weeks of gestation. When assessing visual function, it is important to remember both that the focal length of the term neonate is approximately 6 to 8 inches and that neonates will make random horizontal eye movements. Thus, when one is certain that the baby is fixing on the target object, it is key to ensure that she will track not only horizontally but also up and down. Finally, although it is possible to perform a neurologic examination on a sleeping infant, newborns are unlikely to “fix and follow” when awoken from a sound sleep and may require a second assessment.

Acquisition of Tone and Motor Skills While much has been written about the developmental progression of both passive and active tone in the preterm neonate and the conditions that alter tone in the term infant, it is important to remem-

ber a few key facts. First, tone and emerging motor skills must always be symmetric; second, intercurrent infectious or metabolic etiologies may cause the infant to appear severely encephalopathic and thus obscure neurologic findings; and finally, a mismatch in tone and motor skills suggests a central disorder. In the preterm neonate, the developmental emergence of tone begins in the lower extremities. Thus the infant of 28 weeks postmenstrual age will independently lie with legs fully extended, the neonate of 30 to 32 weeks will begin to flex the hips and knees, and a 34-week infant will begin to demonstrate the “frog-leg” posture of a term neonate. There is similar progression of tone in the upper extremities such that the arms are fully extended in the infants of 28 weeks gestation, beginning to flex at 30 to 32 weeks and fully flexed by 34 to 36 weeks of gestation. Two signs common to the emergence of tone in the preterm neonate are the “scarf sign” and assessment of the popliteal angle. To perform the scarf sign, the examiner gently pulls the infant’s arm across his chest and measures the position of the elbow. The elbow will not reach the midline in the term infant, while in a hypotonic neonate or one of lower gestational age the elbow will extend across the midline to the opposite thorax. Similarly, to perform an assessment of the popliteal angle, the examiner uses one hand to flex the infant’s thigh upon her abdomen. Putting gentle pressure on the back of the thigh with the other hand, the examiner extends the leg and assesses the angle formed by the thigh and lower leg. In term infants, this angle is approximately 90°, while those of younger gestational age or hypotonia will extend their legs 120° or greater. Likewise, the emergence of head control (demonstrated by holding the upper extremities and raising the infant from the examination table) does not begin until 34 weeks and is not fully present until 36 to 40 weeks postmenstrual age. Notably, the healthy preterm infant will also begin to bear weight when placed in an upright position at approximately 34 weeks, and a final hallmark of typically developing infants at postmenstrual age is the emergence of shoulder strength, best demonstrated by the ability to not “slip through” when held gently under the arms in an upright position.

Primitive Reflexes Finally, several of the primitive reflexes, such as the Moro, sucking, and swallowing responses, are also gestational age–dependent. Thus, although we have never seen a surviving neonate who lacked a Moro response, infants of less than 36 weeks gestation demonstrate the incomplete Moro, in which the arms are extended but there is no secondary flex-

8â•… Neonatal Neurologic Examination ion to the midline. Similarly, the sucking response emerges between 30 and 32 weeks postmenstrual age, but the neonate cannot reliably suck and swallow until 33 to 34 weeks of gestation.

8.3.2╇ Assessment of Tone and Reflexes The assessment of tone, reflexes, and motor skills (also called “active tone” by many observers) can provide important information not only about neurodevelopment during the third trimester of gestation but also about the pattern and localization of injury in critically ill neonates of any gestational age. As previously described, the infant’s tone and motor skills should be both consistent with his gestational age and at all times symmetric. It is easiest to obtain reflexes at the biceps, patella, and Achilles tendons in preterm and term infants. While the biceps and patellar reflexes are performed in similar fashion for both neonates and older children and adults, it may be easier to obtain the Achilles reflex by flexing the infant’s ankle and tapping on the plantar surface. Neonates are not yet well peripherally myelinated, and reflexes should be at most 1+ symmetrically present in infants of all postmenstrual ages. If one notes “brisk reflexes,” such as ankle clonus or the spread of one knee jerk to the opposite extremity, the examiner should confirm such hyperreflexia with both crossed-adductor and patellar reflexes. Thus, one expects the extremely low gestational age infant to be profoundly floppy with no head control or shoulder strength. The 34-week gestational age infant should demonstrate emerging head control and tone within both the lower and upper extremities, while the term neonate should have good (but not excessive) passive tone, which permits the full range of movements, as well as appropriate head control, shoulder strength, and the ability to bear weight.

Focal Neurologic Findings Focal lesions include those characterized by hemiparesis or monoparesis. Infants with evidence for a hemiparesis—and particularly those with hyperreflexia—should be urgently assessed for a focal lesion. Notably, approximately 75% of infants with perinatal stroke present with hemiparesis and focal seizures in the newborn period, while those with acute subdural hemorrhages are obtunded in association with a spastic hemiparesis. The latter group of infants will demonstrate split cranial sutures, full fontanelles, and abnormal eye movements on complete examination. In contrast, monoparesis may reflect either a central or a peripheral lesion. These are best differ-

entiated by an assessment of tone and reflexes. The infant with a central lesion will exhibit an altered level of arousal, focal increased tone, and brisk reflexes, while the neonate with a brachial plexus injury will be wide awake and eating well but have a flaccid, areflexic extremity and the possibility of a clavicular fracture.

Symmetric Changes in Tone and Reflexes Infants with symmetric changes in tone and reflexes may harbor neurologic disease at any point in the neuraxis, and the careful neurologic examination will help to localize this for the clinician. Infants with obtundation, peripheral hypertonia, poor active tone (i.e., “mismatch” in active and passive tone examinations), and marked hyperreflexia should be evaluated for a central lesion, while flaccid infants with obtundation and absent reflexes require immediate evaluation for spinal injury. Notably, the former group of infants, in whom an intracranial lesion is suspected, may exhibit two additional signs of “hypertonia.” The first is the “hypertonic Moro,” in which there is no first phase of abduction of the upper extremities; instead, the infant whose head has been gently dropped onto the mat shoots his arms forward in response to this stimulus. The second finding is the “hypertonic suck” or “chomp,” a well-known hallmark of the infant with a central lesion. In contrast, neonates with altered levels of arousal but gestational age appropriate or somewhat depressed tone and strength are more likely to demonstrate structural, chromosomal, or metabolic lesions. Additional aspects of the physical examination, such as dysmorphic features, cardiac murmurs, or organomegaly, as well as imaging studies, may provide evidence of chromosomal disorders. Finally, alert infants with feeding difficulties, poor central and peripheral tone, and absent reflexes should be evaluated for spinal muscular atrophy, neuropathy, or congenital myopathy. Notably, the neurologic characteristics of the infant with spinal muscular atrophy include tongue fasciculations, micrognathia, arthrogryposis (i.e., congenital contractures), congenital hip dislocation, and spontaneous fine movements of the fingers and toes consistent with peripheral fasciculations. In addition, their mothers also report decreased fetal movement and polyhydramnios. Infants with myotonic dystrophy will be similarly hypotonic and areflexic but exhibit none of the signs of anterior horn cell dysfunction. Notably, myotonia is not elicitable in neonates until the end of the first year of life, but it can be easily tested by tapping on the thenar eminence of affected mothers. Finally, although rare, infants with congenital myopathies/dystrophies, neuropathies, or mitochondrial disorders may present with hypotonia and hyporeflexia.

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94 Section IIâ•… Neurology

8.3.3╇ Elements of the Traditional Neurologic Examination Following the observation, stimulation, and assessment of both neuromaturation and tone/reflexes portions of the neonatal neurologic assessment, the examiner is encouraged to perform the more traditional aspects of the pediatric neurologic examination. These include assessment of growth parameters, assessment of cranial nerve function, and the general physical examination.

Growth Parameters Critical to the neurologic examination of the neonate is assessing not only the infant’s growth status (i.e., appropriate for gestational age [AGA], small for gestational age [SGA], or large for gestational age [LGA]) but also the orbitofrontal circumference (OFC). SGA infants may have experienced maternal placental dysfunction, suffered congenital infections, or harbor genetic abnormalities (and subsequent CNS malformations). Further, although LGA status may be the result of genetic variants, such as BeckwithWiedemann syndrome, it may reflect abnormalities in maternal glucose. As with weight and length, OFC should be plotted on gestation-age-appropriate curves to assess relative micro- and macrocephaly. Microcephaly may be attributable to congenital infections, chromosomal variants, congenital CNS malformations, or maternal toxic exposure. In contrast, macrocephaly is found both in infants with acute disorders and those with congenital disorders. The emergent causes of macrocephaly include hydrocephalus, acute intracranial hemorrhages (intraparenchymal, subdural, or epidural), and tumor. These neonates have split sutures, full fontanelles, and intermittent or fixed downgaze with sixth nerve palsies, as well as emesis and apnea, and should be evaluated with emergency magnetic resonance imaging (MRI) of the brain. Macrocephaly is also found in neonates with the following disorders: congenital hydrocephalus (secondary to fetal hemorrhagic stroke, congenital infection, or structural malformation); neurocutaneous disorders, such as neurofibromatosis and tuberous sclerosis; chromosomal abnormalities; and familial “big head.” Notably, benign enlargement of the subarachnoid spaces, or “external hydrocephalus,” is not commonly diagnosed in the newborn period but rather occurs across the first postnatal year.

Cranial Nerve Assessment Although the pupillary response to light is present in neonates beginning at the 28th week of gestation, in infants with fixed and dilated pupils one must always check that the pupils have not been pharmacologically dilated in preparation for a retinal exam. Although it has often been written that “infants do not herniate,” exceptions to the rule do occur, and encephalopathic infants with the new onset of either unilateral or bilateral fixed and dilated pupils should be emergently evaluated for intracranial hemorrhage or the acute onset of hydrocephalus or edema. If the imaging study is unremarkable, the fixed and dilated pupil(s) should raise concern for a postictal phenomenon, and an electroencephalogram (EEG) should be performed. As a final word, it is important to check the infant’s pupillary responses but not to evoke periorbital ecchymoses and edema; having the nonobtunded infant of 32 weeks gestation onward suck on a pacifier almost always results in the eyeopening reflex. In contrast to the pupillary response, eye movements—both horizontal and vertical—are present in infants of all gestational ages. Since sleeping, obtunded, or otherwise critically ill neonates will not typically fix and follow on a bright object, it is important to note that the doll’s head maneuver, in which the infant’s head is moved slowly from side to side, can be used to elicit horizontal eye movements in infants until the 46th postmenstrual week. This technique should never be employed, however, in an infant in whom there is a question of spinal injury. In addition, if eye movements appear to be absent and cold-water caloric stimulation is to be performed, one must first check the intactness of the tympanic membranes. Corneal responses may be easily obtained in sleeping infants by gently applying a sterile swab to the corneal membrane; an alternative strategy is the simple use of a puff of air directed at the cornea. Similarly, spontaneous facial movements are common in sleeping infants, and thus the assessment of cranial nerve VII may be done in either the sleeping or awake infant. In the encephalopathic neonate, a gentle sternal rub almost always results in facial movement, although the eyelids may not necessarily open. As described previously, hearing can be checked by auditory stimulation. Finally, checking the gag reflex can be challenging in neonates of all gestational ages; gently stroking the infant’s palms will almost always result in mouth-opening (the palmo-omental reflex), permitting the gag to be checked with a soft swab. In critically ill neonates, the gag reflex is occasionally

8â•… Neonatal Neurologic Examination followed by a secondary period of apnea, suggesting that the examiner should be particularly vigilant.

Elements of the General Physical Examination The neonatal neurologic examination would not be complete without a check for dysmorphic and atypical features. Colobomata, or keyhole-shaped defects in the iris, retina, choroid, or optic disk, may be a component of syndromes like CHARGE (coloboma, heart defects, atresia of the nasal choanae, retardation of growth, genital abnormalities, and ear abnormalities or deafness) or may be found in typically developing neonates. They are generally unilateral. Similarly, congenital cataracts accompany a wide variety of disorders ranging from congenital infections, including toxoplasmosis and cytomegalovirus (CMV), to genetic and metabolic causes, including Down syndrome and galactosemia. Facial dysmorphisms may be associated with genetic syndromes; sacral dimples and midline spinal hairy patches are markers of spinal deformities; and peripheral abnormalities, such as rocker bottom feet, may be markers of trisomy 13 or 18. Skin lesions (both hyperpigmented and hypopigmented) are found in neurocutaneous disorders, and hepatomegaly accompanies both congenital infections (CMV) and metabolic/ genetic disorders ranging from Zellweger syndrome to galactosemia.

Examining the Parents The final portion of the examination involves not only interviewing but on occasion examining the parents. Macrocephaly is commonly familial, atypical features are not always dysmorphic, and neuromuscular disorders frequently run in families. Thus the parent of an infant with megalencephaly may have multiple café au lait spots, while that of a floppy and hyporeflexic neonate may exhibit myotonia.

8.3.4╇ Strategies for Examining the Neurologic System of the Neonate Electroencephalography Seizures occur in up to 5% of infants in newborn intensive care units, and the seizures of neonates do not necessarily mirror those of the older infant and child. Generally, neonatal seizures are manifest in

five different ways, characterized as follows: multifocal tonic-clonic activity (one arm followed by a leg “waving” in stereotypic fashion across the warming table); focal clonic or tonic-clonic events (the hallmark of an underlying structural lesion); myoclonus, or repetitive “Moro”-like events; intermittent tonic activity worrisome for herniation; and apnea. Suspicion for seizure should be followed by immediate assessment for hypoglycemia and meningitis followed by EEG. Since neonates may not reliably perform the given activity during a routine 50-minute tracing, a video-EEG is preferable whenever possible.

CNS Imaging The advent of cranial ultrasonography and MRI has greatly improved our understanding of neonatal neurologic emergencies, and the imaging strategy of choice depends upon the infant’s gestation and symptoms. Cranial ultrasound (cUS) provides the opportunity to evaluate neonates rapidly for intraventricular hemorrhage, ventricular size, and periventricular anomalies at the bedside. Pitfalls include peripheral and posterior fossa issues. Serial cUS can demonstrate important trends in ventricular size in posthemorrhagic hydrocephalus in the premature infant, for example. MRI ordinarily involves infant transport except for the few very fortunate nurseries with such machines within them or adjacent. Ordinarily, contrast is not needed unless detailed MR angiography is needed or parenchymal infection or tumor is of concern. Quickbrain MRI (qbMRI) or fast-spin T2 imaging can provide more rapid imaging but limits the information available for parenchymal lesions. Finally, infants may not show diffusion changes for a week or more. Computed tomography (CT) is rarely utilized at present except in emergency situations with rapid neurologic progression, as with acute epidural, subdural, or parenchymal hemorrhages. Exceptions can occur with depressed fractures and nonaccidental trauma. Short T1 inversion recovery (STIR) MRI of the spine has been the most useful in the evaluation of spinal trauma. In infants, the entire spine can ordinarily be imaged within the coil; hence, obtaining this imaging well repays the effort. In nonaccidental trauma, injuries can be found across the entire spine. Serial imaging in infants, whether by cUS, MRI, or a combination, like serial neurologic examinations, can be critical to their care.

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9

Neurologic Examination of the Child and Adolescent Jessica H. R. Goldstein and Nancy Bass

9.1╇Introduction The neurologic examination of the child and adolescent is very similar to that of the adult patient, with one very important exception: it is much harder! Often, pediatric patients are unable to explain what their problem is or follow the instructions for a neurologic exam. The neurologic examination begins from the moment you first walk into the room. Observing the child informally while taking a history can provide valuable information and guide the more formal examination. Is there an asymmetry in movement? How does the child play and interact with family and surroundings? Are there dysmorphic features, unusual head shape, or birthmarks? Many important physical findings are uncovered before the formal neurologic exam begins. The aim of this chapter is to provide a concise and complete guide to the pediatric neurologic examination, with emphasis on strategies for examining young, uncooperative, or cognitively impaired children.

9.2╇ The Pediatric Neurologic Examination The purpose of the neurologic exam is to localize an area of dysfunction based on a chief complaint. In the pediatric population, this requires assessing a patient’s neurologic function in the context of his or her development, which may be normal or abnormal. A friendly demeanor, keen observation of the child, and flexibility with the order in which the exam is performed will help maximize the information to be gained. For example, many children are apprehensive about having their reflexes tested or funduscopic examination but enjoy the “less invasive” strength or gait exams. Starting with the “least invasive” exam elements may help the child relax and allow you to

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build a rapport before tackling the more challenging parts of the exam. The neurologic examination always begins with a thorough history and general physical exam. A comprehensive history should be obtained and should include birth history as well as developmental history. Sometimes, the only symptom of hydrocephalus in a school-age child is worsening school performance. Even in the older child, growth parameters, particularly head circumference, should be obtained and compared to previous values to obtain a trajectory of growth. The neurologic exam itself can then be broken down into seven broad categories: mental status, cranial nerves, motor, reflexes, sensation, coordination, and gait.

9.2.1╇ Mental Status The mental status test of the young child relies on the physician’s ability to engage the child in conversation.1 The age and developmental level of the patient must be taken into consideration. The complete mental status examination encompasses the following modalities: level of consciousness, orientation, speech/language, memory, fund of knowledge, insight/judgment, abstract thought, and calculations. The power of observation allows the clinician to assess the structure and function of the child’s language, the quality and content of play, as well as affect, eye contact, and behavior.2

9.2.2╇ Cranial Nerves The cranial nerve examination is the most difficult portion of the neurologic exam in an uncooperative or young child. A colorful toy can be your most important tool. Cranial nerve I: Sense of smell can be difficult to test in a young child. Absence of sense of smell can be

9â•… Neurologic Examination of the Child and Adolescent seen in patients following a head injury, with frontal lobe tumors, or with congenital brain malformations. Cranial nerve II (optic nerve): Funduscopic examination begins with identifying the red reflex from afar. This is vital to ensure there is no “white pupil,” which could suggest a retinoblastoma or congenital cataract. To check visual fields in a child, show the child a toy in central vision and slowly bring in another toy from the periphery. Visual acuity in the young child who is not yet able to identify letters confidently can be assessed with a picture chart. Cranial nerves III, IV, and VI: To begin the assessment of the extraocular muscles, first examine the eyes at rest. Look for a “setting-sun” sign, indicating increased intracranial pressure, or a tendency for one eye to drift when covered, suggesting strabismus (Fig. 9.1). Next, check the child’s eye movements in all four quadrants. In a young or uncooperative child, moving a colorful toy can help with this assessment. Note any limitations in movement or dysconjugate gaze. Cranial nerve V: In older children, sensation can be tested with various modalities (usually light touch and pinprick) in the three distributions of the trigeminal nerve with a side-to-side comparison. Cranial nerve VII: Children usually enjoy this portion of the exam because they get to make “funny faces.” In an apprehensive child, this can be a good way to begin the examination. The key feature to focus on is symmetry: smiling, crying, raising of the eyebrows. Cranial nerve VIII: Rubbing the fingers together next to each ear screens for asymmetries in hearing.

Fig. 9.1â•… Sun-setting eyes. Downward deviation of the eyes (“setting-sun sign”) secondary to an upward gaze paresis, seen in patients with increased intracranial pressure.

In addition to its auditory functions, CN VIII carries vestibular information, which can in part be assessed during the Romberg test (described subsequently). Vestibular function can more thoroughly be assessed with caloric testing in symptomatic patients.2 Cranial nerves IX/X: Many children are very resistant to examination of the posterior pharynx. Asking the patient to open the mouth and say “Aaah” and observing for palate symmetry can assess cranial nerves IX/X. To assess cranial nerves IX and X fully, a gag reflex can be elicited with a cotton swab. This maneuver is frequently met with a good deal of resistance from the child and is often best saved until the end of the exam. Cranial nerve XI: To test the strength of the sternocleidomastoid muscle, have the child turn his or her head to each side against your resistance. Shoulder shrugs against resistance provide an assessment of trapezius muscle strength. Cranial nerve XII: “Stick out your tongue!” The tongue should be examined for atrophy, fasciculations, and deviation. Remember that the tongue always deviates toward the side of the lesion!

9.2.3╇Motor The motor examination encompasses four major components: bulk, abnormal movements, tone, and strength (with the mnemonic BATS). In the motor examination, you are looking for patterns suggesting a specific localization of disease. While assessing muscle bulk, you should pay attention to asymmetries, which may suggest a subtle hemiparesis. A child with increased muscle bulk in the calves may have muscular dystrophy. Aligning the thumbs or great toes near each other and seeing whether one is bigger or smaller can suggest an asymmetry in bulk and a hemiparesis. Tone is a measure of the degree of resistance to passive movement. In the arms and legs, grasping the wrist or ankle and gently shaking it back and forth can measure tone. This maneuver can be repeated gently at each joint. Tone can provide a clue to the timing of injury in the central nervous system. Hypotonia usually indicates an acute injury (such as in spinal cord shock), whereas hypertonia is typically seen in a chronic insult. An exception to this occurs with injury to the cerebellum. In this case, the patient may remain hypotonic long-term. When assessing muscle strength, the pattern of weakness can offer clues to etiology. Proximal muscle weakness suggests a myopathy, whereas distal muscle weakness suggests a neuropathy. Muscle strength, graded on a scale from 0 to 5, can be difficult to test formally in the uncooperative child (Table 9.1). Offering a toy and noting the resistance to your pull tests a child’s distal strength. Asking a child to

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98 Section IIâ•… Neurology Table 9.1â•… Grading of muscle strength

Table 9.2â•… Grading of reflexes

0

No muscle movement

0

Absent reflex

1

Minimal movement (a flicker)

1

Hyporeflexia

2

Movement with gravity eliminated

2

Normal

3

Movement against gravity

3

Hyperreflexia, no clonus

4

Able to resist with partial strength

4

Clonus present

5

Able to resist with full strength

9.2.5╇Sensation stand from a supine position on the floor with the arms folded across the chest is a test of proximal muscle strength. If the child uses the hands to “walk up him- or herself,” this is an indication of proximal muscle weakness (Gowers maneuver). In a lethargic or comatose patient, a leg that is laterally deviated can suggest weakness or hemiparesis (Fig. 9.2). Throughout the examination, note should be made of any involuntary or abnormal movements that the patient exhibits. These can range from motor tics to sterotypies, such as hand flapping, to choreoathetotic movements. The presence of muscle fasciculations is a lower motor neuron sign.

9.2.4╇ Reflexes Assessment of reflexes often provides the key clue to localization. Hyperreflexia indicates a process affecting the central nervous system, whereas the presence of hyporeflexia suggests a nerve or muscle problem. Hyperreflexia can be accompanied by clonus or spread of the reflex (e.g., crossed adductor sign). The presence of a mixed hyper/hyporeflexia can suggest a lesion in the spinal cord or a process affecting both the central and peripheral nervous system. Localization to the spine is also suggested in a child with hyporeflexia but bilateral upgoing toes (Babinski sign) (Table 9.2).

Just as in adults, a thorough sensory examination relies heavily on the ability of the patient to report differences in various sensory stimuli. In young children, the power of tickling (and sometimes pinching!) the feet and hands can provide at least a crude assessment of sensation. The sensory examination tests the primary sensory modalities and cortical sensation. Two major ascending pathways carry the primary sensory modalities: the dorsal column–medial lemniscus system (proprioception or joint position and vibration tested with 128-Hz tuning fork) and the anterolateral system (pain, temperature, crude touch). To test each pathway, one sensory component specific to that pathway may be chosen (i.e., pain and vibration). Detection of sensory level using a pin can be important in suspected spinal cord pathology. Compare the same area side to side (Does this feel the same on both sides?) and move from affected to normal regions. The Romberg test is a test of proprioception. The child is first asked to stand with feet together and eyes open. When balance is achieved, the child is asked to close the eyes and maintain balance. Removing the visual stimuli requires the child to rely on proprioception (and to some degree vestibular sensation) to maintain balance. Cortical sensation (integrated sensory modalities) reflects the integration of the primary sensory modalities, typically a function of the parietal lobe. Stereognosis (identification of objects placed in the hand while the eyes are closed), graphesthesia (identification of letters or numbers drawn on the palm), and detection of double simultaneous stimuli are all examples of tests of cortical sensation. Ability to perform these tests is age dependent; often they can be done only in the older child or adolescent.

9.2.6╇Coordination

Fig. 9.2â•… Hemiparesis. In an obtunded or comatose patient, position of the lower extremities with lateral deviation of the leg can suggest a hemiparesis.

Coordination testing includes finger-to-nose and heelto-shin maneuvers as well as tests of rapid alternating movements. To help engage young children, use a toy or a light and ask the child to reach and touch it. Until preschool age, it is common for children to exhibit

9â•… Neurologic Examination of the Child and Adolescent mirror movements of the opposite hand (synkinesis). The location of ataxia follows the anatomy of the cerebellum: truncal and/or gait ataxia suggests a lesion involving the cerebellar vermis, whereas appendicular ataxia (predominantly involving the limbs) localizes to the cerebellar hemispheres.

9.2.7╇Gait The gait examination begins with observation of the normal gait, with attention to arm swing, base of gait, asymmetries in movement, and length of stride. The child should be asked to walk on the toes and heels as well as tandem walk (heel-toe)—a maneuver that cannot be performed well until around 8 years of age. A wide-based gait suggests a problem with balance or ataxia. A “waddling” gait with excessive lumbar lordosis suggests proximal weakness. In the reluctant child, strategic positioning of a parent or loved toy can encourage the child to walk or run for the examination.

9.3╇Conclusion With practice, any clinician can gain comfort with performing a complete neurologic examination in the pediatric population. Finessing the powers of observation, having a friendly demeanor, and approaching the child at the child’s developmental level will help maximize the information that can be gathered.

Tricks of the Trade: Neurologic Exam Pearls • Observation! Much can be learned with close observation from the moment you walk into the room! • Don’t forget the general physical examination. This includes head circumference in all your patients • The fundus should be examined in all patients. • The motor exam is BATS: bulk, abnormal movements, tone, and strength. • A laterally deviated leg in a comatose or lethargic patient suggests a hemiparesis. • Handedness develops at around age 18 months. Always ask parents whether they feel their baby is right or left handed. Early onset handedness suggests a hemiparesis. • All children should be asked to rise from the floor to enable observation of proximal muscle weakness.

References ╇1. Griesemer D. The neurologic examination. In: Maria BL,

ed. Current Management in Child Neurology. Hamilton, Ontario, Canada: BC Decker; 2005: 14–21 ╇2. Swaiman KF. Neurologic examination of the older child. In: Swaiman KF, Ashwal S, Ferriero DM, eds. Swaiman’s Pediatric Neurology: Principles and Practice. 4th ed. Philadelphia, PA: Elsevier; 2006: 17

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Section III

Congenital Malformations Section Editor: Concezio Di Rocco

Identification of the most appropriate management of congenital malformations of the brain, spinal cord, and their envelopes has been the main justification for the field of pediatric neurosurgery to emerge from general neurosurgery. Indeed, it was obvious early on that an understanding of the physiopathogenetic mechanisms underlying these complex malformations, the effects of which may extend throughout life, required the expertise and full engagement of dedicated neurosurgeons. This section of the book demonstrates the impressive progress that has been achieved in the field. It took almost a century for the craniosynostoses to be recognized on the basis of molecular criteria rather than merely morphological features. Such an understanding has had a significant impact, not only on the clinical definition of the individual nosologic entities, but also on the timing and method of their surgical management, as well as on the possibility of predicting specific outcomes for the different types. Further advances in craniosynostosis correction include the recent introduction of techniques developed in other fields of surgery, such as osteodistraction and the use of the endoscope. Nowadays, cerebral malformations and their more common clinical manifestations, namely, seizure disorders, are dealt with during the first months or years of life. An effect of this shift has been a dramatic improvement in functional prognosis. Also, relatively “new” neurosurgical problems have emerged due to

more accurate neuroimaging—for example, the Chiari type I malformation, which is still the subject of scientific debate. At the same time, the management of known malformations, such as the Chiari type II malformation, is currently carried out according to objective criteria rather than subjective interpretation. Moreover, specific preventive measures for this malformation have now been developed, namely, the prenatal management of myelomeningocele. The progress achieved by general neurosurgery in the surgical correction of spinal and craniocervical junction congenital anomalies has been introduced in pediatric neurosurgery with excellent results, as is demonstrated by several chapters in this section. Additionally, the descriptions of the congenital malformations of the spine and spinal cord that have been used since the early development of pediatric neurosurgery have now become more focused, which has aided the accurate delineation of different dysraphic states, each of which requires individualized understanding and management. In summary, this section, devoted to congenital malformations of the CNS and its coverings, exemplifies the impressive improvements, both theoretical and surgical, that have resulted from the strong dedication of pediatric neurosurgeons in the care of congenitally malformed infants and children. The section is also a vivid demonstration of how the management of children born with these malformations continues to be a stimulating field of research.

Section III.A

Malformations of the Scalp and Skull

10

Congenital Defects of the Scalp and Skull Daniel James Guillaume

10.1╇ Introduction and Background 10.1.1╇Indications Congenital malformations of the scalp and skull are encountered regularly in a pediatric neurosurgical practice. The differential diagnosis for such lesions is quite large and includes aplasia cutis congenita (ACC) (Fig. 10.1a) and dermoid and epidermoid tumors (Fig. 10.1b), the Langerhans cell histiocytosis spectrum of disorders, occult meningocele or encephalocele, hemangioma, fibrous dysplasia, osteoma, lipoma (Fig. 10.2a–c), plexiform neurofibroma, growing skull fracture, and malignant tumors.1 In the majority of cases the lesion will be benign. Diagnostic workup and management include a complete and detailed history and exam, and imaging that may a

b

include plain radiographs, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound.1 Many of the lesions can be managed without surgery. Some indications for surgical intervention include: the need for definitive diagnosis, pain, interference with grooming, impending rupture or risk of infection, and risk of bleeding or air embolus.2

10.1.2╇Goals The goals of surgery depend on the type of lesion, location, and presence of symptoms. In general, goals are: • To establish diagnosis if this cannot be made based on history, exam, and imaging • To repair the cranial defect

c

Fig. 10.1â•… This 4-month-old girl was found to have three scalp lesions. (a) Near the vertex were two 6-mm, waxy, round, flat papules with translucent cigarette paper–like membranes through which several hairs could be seen (arrows), consistent with aplasia cutic congenita (ACC). (b) Anterior to these was a 1-cm flesh-colored firm nontender midline nodule (arrow). Both hands and feet demonstrated digital dysplasia with apparent constrictive bands around fingers and syndactyly of several fingers and toes, presumably from amniotic band syndrome. Workup included cranial ultrasound, magnetic resonance imaging (MRI), X-ray imaging of hands and feet, and karyotype studies, all of which were normal except (c) MRI, which demonstrated a cystic lesion. To evaluate for Adams Oliver syndrome, given the cranial and limb abnormalities, a transthoracic echocardiogram was done, which was normal. All three lesions were removed. The posterior lesions were consistent with ACC, while the anterior lesion was a dermoid cyst (arrow).

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106 Section III.Aâ•… Malformations of the Scalp and Skull a

b

c

Fig. 10.2â•… (a) This 12-month-old girl was noted to have a scalp mass shortly after birth. Exam showed a 4 × 2.5-cm soft tissue mass slightly eccentric to the right along the vertex of the scalp that was hairless only over the lesion (arrows), moved with the underlying scalp tissue, and did not increase with Valsalva or position changes. (b) The lesion was mildly homogeneously hyperechoic on ultrasound and identical to fat on MRI, being hyperintense on T1 (arrow) and (c) hypointense on fat-saturation (arrow) MR images, consistent with lipoma.

• To decrease the risk of injury to underlying brain and vascular structures, including the sagittal sinus • To decrease the risk of cerebrospinal fluid (CSF) leak • To improve the cosmetic appearance

10.1.3╇ Alternate Procedures Some congenital skull and scalp malformations, including cephalohematoma and ACC, can be managed nonsurgically.3,4 On rare occasions, certain scalp lesions are best managed with chemotherapy or radiation. For example, some cases of Langerhans cell histiocytosis require chemotherapy and/or low-dose radiation therapy, and radiation has been utilized for treatment of surgically inaccessible hemangiomas, but such cases are infrequent.5

10.1.4╇Advantages The advantages of surgical excision of skull and scalp lesions include the ability to obtain a definitive diagnosis, improvement of cosmetic deformity, and no need to continue following the patient in clinic with occasional imaging studies. Indeed, excision of a lesion can be more cost-effective, efficient, and definitive than following a patient in clinic over several years with serial imaging.

10.1.5╇Contraindications Some relative contraindications to surgical management of malformations of the skull and scalp include medical comorbidities that can increase risk of infection or bleeding or that can lead to other complications. Selected lesions, such as ACC of the scalp, can be effectively treated nonoperatively and will often heal spontaneously with frequent changes of salineand antibiotic-soaked dressings.

10.2╇ Operative Detail and Preparation 10.2.1╇ Preoperative Planning and Special Equipment Preoperative planning includes a carefully obtained history and full physical exam. This usually comprises a full inspection of the scalp, midline back, and skin. A detailed full-body exam may demonstrate associated findings that can require consultation with dermatology, genetics, or other providers. Appropriate imaging studies can aid in diagnosis. Plain radiographs may demonstrate calvarial lucencies. The presence of multiple defects (with the exception of venous lakes) is suggestive of malignancy.1 Expansion of the diploë with bulging of one or both tables

10â•… Congenital Defects of the Scalp and Skull suggests a benign lesion, whereas full-thickness lesions affecting both tables can raise concern for malignancy. The presence of peripheral sclerosis or peripheral vascular channels suggests benign lesion. Hemangiomas classically show a honeycomb, trabecular, or sunburst pattern, while fibrous dysplasia can show well-defined islands of bone or a grossly mottled appearance. Epidermoid lesions typically have a sclerotic edge (Fig. 10.1b).1

10.2.2╇ Expert Suggestions and Comments Much information can be obtained from the physical exam, which should be systematic in a well-lit room. Note the overall appearance and color of the lesion and presence or absence of hair. Measure each lesion. Palpate to note texture and consistency (firm, rubbery, fluctuant, soft) and feel how far the lesion extends below the skin surface. Palpate bony changes surrounding the lesion, such as raised or scalloped borders. Feel whether the lesion is attached to the epidermis, dermis, or bone or is freely movable. Note changes to skin surrounding the lesion. An ultrasound can easily be obtained without sedation on a clinic day and can give valuable information, including fluid within lesion, vascular flow, and sometimes involvement of underlying intracranial space. It is important to take an extra few minutes to perform a full-body exam, including a careful review of the skin and midline back, giving consideration to possible associated anomalies (see Fig. 10.1).

10.2.3╇ Key Steps of the Procedure and Operative Nuances For lesions in which there is concern for malignancy, a biopsy may be indicated. In general, the goals of surgery are as stated earlier. The vast majority of lesions can be localized with palpation alone, but for small nonpalpable lesions, image guidance can be used to keep the scalp scar small. Most lesions can be removed with an elliptical or semicircular incision. The scalp incision should be large enough to expose the entire defect. The adjacent scalp should be widely undermined in the subgaleal plane to allow approximation of the edges without tension following excision of the lesion. The skull defect can be dissected by incising the pericranium along the bony edges down to bone, with curettage of the bony edges. For midline lesions, one should be cautious about vascular attachments to the sagittal sinus. Larger defects may require a rotation flap to be made with assistance from a plastic surgeon.

There are operative nuances associated with particular lesions, as follows: Epidermoid and dermoid tumors are typically treated with excision and curettage of bone margins. One should search for a tract leading to the intracranial cavity; if found, this must followed to obtain excision of the complete lesion. If the lesion is adjacent to the sinus, the surgeon should be prepared for dural sinus repair, although sinus damage would be extremely rare. Eosinophilic granulomas can spontaneously regress, but most are treated with curettage. Multiple lesions are treated with chemotherapy and/or low-dose radiation.5 Grossly, these lesions are pinkgray to purple, protruding from the bone, involving pericranium and sometimes dura, but dural penetration is rare. Patients presenting with eosinophilic granuloma should be seen by oncology, as up to 31% develop additional lesions.5 In the case of an occult cephalocele, the fibrovascular stalk should be circumferentially dissected and transected flush with the dura.2 The skull defect beneath the lesion is usually small and does not require cranioplasty; however, scalp tissue can occasionally scar to the underlying dura, causing pain. A rotational pericranial pedicle flap can add an additional barrier. For larger skull defects, a split calvarial graft can be harvested from adjacent skull and placed into the defect.2 Other surgical treatment options include split-thickness or full-thickness skin graft, scalp rotation flaps, pericranial flaps, rib grafts, latissimus dorsi muscle flap, and tissue expansion.3

10.2.4╇ Hazards, Risks, and Avoidance of Pitfalls Risks include infection, CSF leak, and vascular injury. These can often be avoided by careful planning, vigilant interpretation of preoperative imaging studies, and meticulous surgical technique. After excision of large eosinophilic granulomas with extensive calvarial involvement, there can be an extensive inflammatory reaction. In some cases, the bone defect repair should be delayed following lesion excision to allow the inflammatory reaction to settle down.

10.2.5╇ Salvage and Rescue Surgical excision of most skull and scalp lesions is relatively low-risk. In the rare event that damage to the sagittal sinus occurs, the sinus should be repaired during the procedure, and the patient should undergo appropriate vascular imaging immediately following the procedure.

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10.3╇ Outcomes and Postoperative Course 10.3.1╇ Postoperative Considerations Postoperative care is routine, and most patients can be sent home the same day as surgery. Infants should avoid lying directly on the incision until adequate healing has occurred.

10.4╇Complications Complications that can occur following excision of calvarial or scalp lesions include infection, CSF leak, and injury to underlying sagittal sinus for midline lesions.

References ╇1.

╇2.

╇3.

╇4.

╇5.

Willatt JMG, Quaghebeur G. Calvarial masses of infants and children. A radiological approach. Clin Radiol 2004;59(6):474–486 Piatt JH. Congenital defects of the scalp and skull. In: Albright AL, Pollack IF, Adelson PD, eds. Principles and Practice of Pediatric Neurosurgery, 2nd ed. New York, NY: Thieme Medical Publishers; 2008: 254–264 Santos de Oliveira R, Barros Jucá CE, Lopes Lins-Neto A, Aparecida do Carmo Rego M, Farina J, Machado HR. Aplasia cutis congenita of the scalp: is there a better treatment strategy? Childs Nerv Syst 2006;22(9):1072–1079 Burkhead A, Poindexter G, Morrell DS. A case of extensive aplasia cutis congenita with underlying skull defect and central nervous system malformation: discussion of large skin defects, complications, treatment and outcome. J Perinatol 2009;29(8):582–584 Rawlings CE III, Wilkins RH. Solitary eosinophilic granuloma of the skull. Neurosurgery 1984;15(2):155–161

11

Deformational Plagiocephaly Mark R. Proctor

11.1╇ Introduction and Background Intentional skull molding has long been practiced around the world as a ritual in certain cultures. We are currently in an era where we have introduced unintentional skull molding as a consequence of a program to protect babies. Sudden infant death syndrome, or SIDS, is a somewhat poorly understood but tragic condition in which seemingly healthy infants die in their sleep. It became recognized that prone sleeping seems to predispose children to this condition, which led to the introduction of the Back to Sleep program in 1992 by the American Academy of Pediatrics (AAP). In exchange for the reduction in SIDS, we have created an epidemic of occipital skull flattening.1 Certainly, in balance, exchanging a fatal condition for a primarily cosmetic condition is an excellent trade-off, but for pediatric neurosurgeons and craniofacial surgeons, this has introduced a new disease process that essentially never before existed. The goal of this chapter is to explain my method of diagnosing the condition, establishing when there is a need for treatment, and reviewing the treatment options and results for this relatively benign but high-frequency condition. I would stress that this is primarily a conservative treatment paradigm, and there is no focus on the surgical correction of the disorder, which is almost never indicated.

11.2╇Diagnosis The vast majority of cases of deformational plagiocephaly are easily diagnosed by clinical exam based on the ipsilateral advancement of the occiput, ear, and forehead when the infant’s head is viewed from above (Fig. 11.1). Radiographic confirmation of the diagnosis should very rarely be indicated and certainly should not be part of routine clinical practice. There will be a small percentage of patients in

Fig. 11.1â•… Classic head shape associated with deformational plagiocephaly, with ipsilateral advancement of the occiput, ear, and forehead.

whom the clinical distinction between deformation and craniosynostosis may be difficult, but routine radiology exams should not be considered. Indeed, when I am asked by a pediatrician whether or not to obtain X-ray images or a computed tomography (CT) scan before sending the patient in for evaluation, the answer is unequivocally negative. I think it is more economical, and lower risk, for the child to be sent directly to a specialist if the pediatrician is unsure, and most specialists should be able to establish the diagnosis correctly at least 90% of the time without radiographs.

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11.3╇ Indications for Treatment The indications for treatment of deformational plagiocephaly are one of the more controversial and poorly understood aspects of the condition. Most craniofacial experts believe that it is primarily a cosmetic condition but the relationship to developmental delay is poorly understood. It is quite clear that the conditions rose to epidemic proportions within a few years after the Back to Sleep program was instituted in 1992. It is quite possible that supine sleeping in and of itself has altered developmental milestones to some extent, as babies often prefer supine positioning and have less reason to move about and explore their environment when their faces are pointing upward and they can freely look around.2 It is also fairly clear that children with developmental delay who move about less spontaneously are at higher risk for this condition. However, it is far less clear that the condition causes developmental delay.3 I stress that my indications for treatment rely heavily on the cosmetic issues and theoretical concerns about functional issues related to the head shape itself, such as difficulty in fitting for protective headwear when the children get older. In addition, concerns about ear and jaw issues related to malposition are by and large not being borne out in clinical practice over time. One of the major questions to be answered is when the condition requires treatment. There is no simple answer. The algorithm is truly based on a combination of age, response to conservative therapies, and severity of disease. Even at a young age, a child would be a candidate for repositioning therapy, as well as physical therapy, if there is significant muscular torticollis. In addition, instituting tummy time while the child is awake is always appropriate, although it is not prudent to contradict the recommendation for supine sleeping, which has had a marked effect on the incidence of SIDS. The Back to Sleep program has cut the rate of SIDS in half, albeit from a low rate of 1 in 1,000 children to 1 in 2,000 children. In my practice, I will not institute helmet therapy before 4 months of age. If I see a child before then, I will establish baseline measurements and institute a program of conservative treatment, with repositioning and possibly physical therapy if torticollis exists. I will then plan to see the child back when he or she is at least 4 months old. I do find that anthropometric measurements are extremely helpful, because it is impossible to recall the severity of the head shape subjectively when you are following a large population of patients (Fig. 11.2). Consistent with data in the literature, for asymmetries less than approximately 9 mm, I would generally not institute orthotic treatment. If the asymmetry is greater than 9 mm, I would consider the use of the helmet. The

Fig. 11.2â•… Technique for measuring the cranial vault asymmetry using calipers.

specific nuance here is that younger children have more time to improve, and I would therefore be more tolerant of conservative therapy. For children with brachycephaly, which is a symmetric flattening of the back of the head, the generally accepted criteria for helmet therapy would be a cephalic index (ratio of the width of the head divided by the length of the head) of 0.93 or greater, whereas below 0.93, conservative therapies will likely be successful.

11.4╇ Treatment Options There are several tiers of treatment for deformational plagiocephaly. These include: • • • • •

Repositioning Sleep aids Treatment of underlying muscular torticollis Helmet therapy Surgery

11.4.1╇Repositioning/Education It should be stressed that deformational plagiocephaly is essentially a preventable condition. There is no controversy regarding the fact that the condition blossomed after the Back to Sleep program. Unfortunately, while primary care providers are well versed in the need to reinforce supine treatment, they are much less well versed in the need for education on how to prevent plagiocephaly. Recent data from a

11â•… Deformational Plagiocephaly study in Canada indicate that the incidence of plagiocephaly is even higher than originally suspected, on the order of 46% of children.4 Although this may seem extreme, the fact that it is being recognized in the pediatric literature as a significant issue will likely lead to a higher degree of education, and hopefully a much lower incidence of the condition in the future. There are several easy repositioning techniques. When an infant is very young and still being swaddled, the parent can simply elevate one shoulder for one night and the other shoulder for the next night, or some similar way switching position after each nap, and so forth. As the child reaches 2 to 3 months of age, repositioning becomes more challenging. One simple trick is to move the things that the child likes to play with or look at to one side or the other, so that there is always something to keep the child’s interest. Finally, tummy time while awake is very effective, both at keeping the child off the back of the head and at encouraging strengthening of the neck muscles by having the child raise the head and look around.

11.4.2╇ Sleep Aids The use of specialized pillows or devices in the crib is generally not recommended by the AAP. The concern is that anything soft could somehow impede the baby’s ability to breathe, thereby increasing the potential risk of SIDS. There is the possibility that devices currently under development but not widely available might be acceptable sleep aids. However, for the time being, repositioning without the use of other devices is preferred, and I don’t encourage the use of any particular sleep aid.

underlying philosophy of that field that reinstitution of normal CSF flow will correct bodily ills, the therapy will again be similar to the goals of physical therapy. In summary, I don’t support the use of chiropractic or craniosacral therapy, but I don’t discourage it if the families have pursued it.

11.4.4╇ Helmet Therapy There are fairly extensive data to support the fact that helmets, also referred to as cranial orthoses, are quite effective in treating deformational plagiocephaly. Few craniofacial experts would refute this, but no doubt others would argue whether or not it is more effective than the natural history of conservative therapy and, frankly, whether or not the condition even requires treatment.5 I do advocate the use of helmets for the more severe cases of deformational plagiocephaly that are either not responding to conservative therapies or occurring in children older than 6 to 7 months.6 Whereas I would never suggest to a family that the helmet will lead to a more normal neurocognitive development of the child, it does quite consistently improve the morphology of the head. Helmets are well tolerated and have extraordinarily low complication rates. Because of regulations imposed by the Food and Drug Administration, the cost of helmeting has skyrocketed; on average, the therapy will cost the family or their insurance company $2,000 to $3,000. The average length of treatment is 3 months. In my practice, family satisfaction with helmeting is very high, and the results are very reliable. We can generally expect a 50 to 90% reduction in the degree of asymmetry (Fig. 11.3).

11.4.3╇ Treatment of Underlying Muscular Torticollis A high percentage of children with deformational plagiocephaly will be found to have difficulty in turning the head to the opposite side. Tightness of the sternocleidomastoid muscle will give a classic tilt to the side of the affected muscle and rotation to the contralateral side, since the tight muscle is attaching to the back of the head. A standard part of the evaluation of any child should be assessing the rotation of the head. If the muscle is clearly tight, then therapy, either a home stretching exercise program or formal physical therapy, should be considered. Some families have seen, or wish to see, a chiropractor. In my view this is acceptable, since the chiropractor really would be simply treating the torticollis similarly to a physical therapist. Similarly, some families ask about craniosacral therapy. Whereas I do not support the

Fig. 11.3â•… Laser scan representation of the effects of helmet therapy.

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11.4.5╇Surgery This particular section is quite brief, because in my view there is no significant indication for surgery in this condition. As stated previously, there is no established neurocognitive concern with deformational plagiocephaly. In my view, there is little indication for a major operation for a primarily cosmetic condition, and I have not done surgery for this condition. In some large series of deformational plagiocephaly, a small percentage of patients have undergone surgery, although this has never been my recommendation to a family. The distinction between deformational plagiocephaly and lambdoid synostosis should be discussed. In general, once you have seen a case of true lambdoid synostosis, the distinctions are going to be very clear. The synostosis gives a classic windswept appearance to the skull in the coronal plane, with the skull shifting away from the side of fusion. There is generally significant elongation of the skull along the affected suture, with a prominent mastoid, inferior displacement, and bossing. X-ray images are often unreliable at establishing the diagnosis, and a CT scan would be an essential step before consideration of surgery.

11.5╇Results The results for this condition should be looked at from both cosmetic as well as functional perspectives. When the condition first came to light in the 1990s, there was substantial concern that alterations in ear and jaw position would lead to long-term functional consequences. Largely, this is not been borne out by clinical practice. Similarly, whereas there does seem to be a higher association of developmental delay issues in children with deformational plagiocephaly, no author has suggested that the skull deformity is the cause of the neurocognitive problems. It is easy to imagine that a child with developmental delay, who has delayed gross motor function, will have a higher incidence of skull deformity from lying supine on the soft infant skull. I never counsel patients to pursue treatment because of neurocognitive issues, and though I do discuss the functional consequences of ear and jaw asymmetry, I also stress that it does not seem to be a long-term problem. From a cosmetic perspective, there is no doubt that the appearance issues are more prominent in a baby than in older individuals. Even if there is no objective improvement in the skull shape, four or five factors make it less noticeable over time. One factor is that most people have more hair as they

get older, which hides the deformity. Also, as a child gets bigger, we are less likely to see him or her from a bird’s eye view, which is when the deformation is most noticeable. In addition, the head is 25% of the baby’s mass, whereas it is only approximately 9% of an adult’s mass, and visually there is far less focus on the head of an adult. Finally, the skull shape probably does slowly improve over time in many individuals, and the thickening of the bone and the thickening of the scalp tend to soften any of the deformity. Therefore, it is visually less apparent, and some authors have even suggested the incidence of deformation is lower in older children than it is in adults.7

11.6╇Conclusion Deformational plagiocephaly is an essentially benign condition that is an unintended consequence of the Back to Sleep program. The concerns are primarily cosmetic, and I suggest that the condition be evaluated in this context. Education of primary care physicians and parents should go a long way toward reducing the incidence, and in those children with significant issues, treatment options should include repositioning, physical therapy, and helmets. Surgery should almost never be considered.

References ╇1.

╇2.

╇3.

╇4.

╇5.

╇6.

╇7.

Robinson S, Proctor M. Diagnosis and management of deformational plagiocephaly. J Neurosurg Pediatr 2009;3(4):284–295 Hutchison BL, Stewart AW, Mitchell EA. Characteristics, head shape measurements and developmental delay in 287 consecutive infants attending a plagiocephaly clinic. Acta Paediatr 2009;98(9):1494–1499 Collett BR, Gray KE, Starr JR, Heike CL, Cunningham ML, Speltz ML. Development at age 36 months in children with deformational plagiocephaly. Pediatrics 2013;131(1):e109–e115 Mawji A, Vollman AR, Hatfield J, McNeil DA, Sauvé R. The incidence of positional plagiocephaly: a cohort study. Pediatrics 2013;132(2):298–304 Mortenson P, Steinbok P, Smith D. Deformational plagiocephaly and orthotic treatment: indications and limitations. Childs Nerv Syst 2012;28(9):1407–1412 Kluba S, Kraut W, Reinert S, Krimmel M. What is the optimal time to start helmet therapy in positional plagiocephaly? Plast Reconstr Surg 2011;128(2):492–498 Roby BB, Finkelstein M, Tibesar RJ, Sidman JD. Prevalence of positional plagiocephaly in teens born after the “Back to Sleep” campaign. Otolaryngol Head Neck Surg 2012;146(5):823–828

12

Nonsyndromic Synostosis: Overview David H. Harter and David A. Staffenberg

12.1╇ Introduction and Background

Indications

12.1.1╇ Definition, Pathophysiology, and Epidemiology

Surgery is the only intervention indicated for the correction of craniosynostosis or, in extreme, unusual cases, of uncorrected deformational plagiocephaly. The indication for surgical intervention for nonsyndromic craniosynostoses is largely based on projections of the child’s appearance after completion of craniofacial growth without treatment. Our understanding of cranial vault and skull base development has advanced based on clinical experience and on radiologic and basic laboratory investigations. Most frequently, the decision for surgery is based on knowledge of the natural history of nontreated individuals, parental preference, and input from the surgical team, frequently neurosurgeons and plastic/ craniofacial surgeons. We believe that an important component of the decision for surgery is the specific team’s experience, results, and options—local experience, expertise, and expectations matter. Multiple approaches (endoscopic, endoscope-assisted, suturectomy, and more extensive procedures, such as cranial vault remodeling) are currently used, each with acceptable safety and cosmetic results. Nonsyndromic single-suture synostosis has been correlated with either elevated ICP or developmental disorders in a small proportion of cases, although a considerable range has been reported. Without unequivocal clinical data demonstrating elevated ICP—parenchymal or ventricular measurements, lumbar puncture, or papilledema3—we do not include it as a rationale for surgery. We do not emphasize a prophylactic role for surgery in the “prevention of possible future developmental or neurological problems.”4 Although developmental delay has been noted to occur in patients with synostoses, no causal relationship has been confirmed; neither early nor late surgical intervention has been shown to improve these delays.5

Deformities of the cranium, including abnormal shape and contour, have long attracted the attention of laypeople, shamans, and medical professionals. Premature closure of a cranial suture may cause a noticeable deformity of the cranial vault. Some of these deformities are characterized by craniofacial asymmetry. The estimated incidence of craniosynostosis is 1 in 2,000 births. The contemporary incidence may in fact be higher, as milder cases are identified and evaluated for treatment.1 Nonsyndromic cranial synostoses are unique in neurosurgical practice; the rationale for treatment often stems from aesthetic and social concerns, less frequently from the need to normalize intracranial pressure (ICP) to preserve neurologic function. Secondary synostosis consists of premature closure of one or more sutures with an identifiable risk factor— iatrogenic, metabolic, hematologic, pharmacologic, or structural. Genetic syndromes are identified in 5 to 15% of cases. Syndromic synostoses may involve single or multiple sutures, including the skull base, and are accompanied by identifiable genetic markers and may include developmental central nervous system (CNS), skeletal, facial, or other systemic abnormalities. In sporadic, nonsyndromic cases, the initial premature pathophysiologic suture closure or senescence is usually idiopathic. However, some associated risk factors have been identified; twin and multiple gestation, oligohydramnios, and intrauterine constriction are among the most commonly implicated. Clomiphene citrate for infertility has also been associated with an increased risk of synostosis.2

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114 Section III.Aâ•… Malformations of the Scalp and Skull Clinical Presentation and Diagnosis To understand the clinical presentation of nonsyndromic synostosis, recognizing that cranial growth is driven directly by brain growth is helpful. Head shape resulting from nonsyndromic single-suture synostosis depends upon the specific suture involved. The classic model for cranial growth, based on Virchow’s model, is of growth restriction in the axis perpendicular to the involved suture, with compensatory growth in other directions. In practice, this model is often correct; however, variations may occur by the addition of other variables, such as an accompanying deformational change due to intrauterine restriction or postnatal factors, such as positioning. Most cases of nonsyndromic synostosis may be diagnosed by historical and clinical findings. The initial recognition of abnormal head shape may occur at the time of birth, with less severe cases often incorrectly attributed to cranial molding due to delivery or intrauterine factors. The natural history of synostosis is typically a progressive deformity as brain growth continues. A palpable ridge over the involved suture is a common finding on exam, although not universal. In our experience, the diagnosis of singlesuture synostosis can be made accurately solely on clinical grounds.

Family Counseling Consultation usually includes the pediatric neurosurgeon and plastic surgeon. Frequently, a pediatric ophthalmologist is consulted to evaluate for papilledema. In cases with asymmetry (e.g., unilateral coronal or lambdoid), the ophthalmologist assesses and quantifies strabismus, an ocular cause for torticollis. Undiagnosed strabismus can be a cause of continued head tilt. It is imperative that these cases be evaluated and treated by an experienced craniofacial team working in the same location. While many craniofacial teams believe in the importance of practicing in a multidisciplinary team, we emphasize the need for a true transdisciplinary approach. Members of a transdisciplinary team work together and have a deep understanding of each other’s perspective and skill set. This is much more than a semantic difference. The value of institutional experience, development of processes, and long-term patient follow-up not only promotes better outcomes but also provides fertile ground for education of students, residents, and fellows, as well as the development of institutional volume and memory. Resources on our craniofacial team include nurse practitioners, otolaryngologists, dieticians, social workers, speech therapists, psychologists, geneticists, and craniofacial orthodontists, as well as a full-time medical photographer with 2D and 3D capabilities. Support from parents

who have navigated the choice of procedure, preparation, recovery, and expectations is perhaps the most valuable resource of any craniofacial surgical team. We advocate for communication and connection with families who have been through the process as a component of preoperative decision making and counseling.

Sagittal Synostosis Premature closure of the sagittal suture results in skull growth that is disproportionately in the anterior–posterior dimension. Dolichocephaly (“long head,” cephalic index 74.9 or less) or scaphocephaly (“keel-shaped head”) are the traditionally used terms. Among cases of sagittal synostosis, a spectrum of head shapes may be noted. This variability reflects the severity, timing, and extent of suture closure. Findings are typically more notable at the occiput because of the closure of the suture from posterior to anterior. The initial shape seen is a “cupping” of the occiput that many refer to as an “occipital bullet.” As synostosis progresses anteriorly, brain growth drives increasing cranial volume; frontal bossing and bitemporal pinching will be noted. In principle and practice, frontal bossing and bitemporal pinching are compensatory changes. Surgical correction under 1 year of age allows this compensation to correct itself. Excepting late corrections, we rarely correct the forehead during surgery, obviating an unnecessarily extensive operation. Closure of only the posterior portion of the suture usually results in severe narrowing of the parietal region, an occipital “bullet” or “knob” and significant frontal bossing and widening, called “golf tee” deformity. Closure of the middle portion of the suture may result in a saddle-shaped deformity. In these variants, ridging is usually palpable over the affected portion of the suture. When patients present early, and surgery is feasible before 3 months of age, we offer endoscopic strip craniectomy for milder cases and add barrel-staves for moderate cases.6 However, we use this approach only when parents accept compliance with postoperative cranial orthoses. In our synostosis patients and our deformational plagiocephaly patients, we find that fewer parents are willing to accept helmets and the social stigma that accompanies long-term orthotic use. These families may favor surgery that does not require a helmet postoperatively. For these patients, we perform a calvarial vault remodeling (CVR), which consists of a suture trellis and resorbable fixation (STAR-Fix). This technique has been used successfully with good long-term results.7 The technique eliminates the occipital bullet and does not leave any areas of dura unprotected by bone. For patients who present later in childhood or in their teens, the area of social concern is the forehead, on account of the bifrontal bossing and the bitemporal pinching. The occipital bullet is more easily hid-

12â•… Nonsyndromic Synostosis: Overview den. Because this dynamic is different from that in the typical infant, we will perform a bilateral frontoorbital expansion (FOE). This can be combined with a strip craniectomy when additional growth may lead to further deformity. In teens, cranial growth is almost complete, so the suture may be left in place and ridging can be simply burred flush. The FOE is performed laterally in order to avoid the developing frontal sinus. We have found that patients with mild deformities (those “too mild for surgery”) may go on to develop these late forehead changes, potentially leading to severe psychosocial distress. They are frequently told at that point that there are no options (“now it’s too late to do surgery”). The diagnosis of complete or partial sagittal synostosis can usually be made with confidence on clinical grounds alone. We do not recommend routine preoperative computed tomography (CT) scans.8 Plain radiographs or CT scans are obtained for atypical cases or upon parental request. We prefer protocols for CT that limit radiation exposure. Magnetic resonance imaging (MRI) is indicated for patients with significant developmental disorders or structural brain abnormalities identified on CT.

Unilateral coronal synostosis may cause severe facial and calvarial differences. Differentiating coronal craniosynostosis from deformational plagiocephaly is critical, as the natural histories and treatment options are opposite. Since marked asymmetry is present, the problem is usually identified early by parents or caregivers. Physical findings include a palpable ridge over the affected suture and flattening (plagiocephaly) on the side of the synostotic suture. Contralateral frontal bossing may be seen. The nasal root is deviated toward the affected side; the ipsilateral superior orbital rim is also skewed superiorly and laterally. The ear is usually displaced anteriorly on the side of the involved suture, thereby decreasing the distance between the ear and the lateral canthus as compared with the other side. We have used uni- and bilateral FOA for the treatment of unilateral coronal synostosis9 and offer early ( 8 months of age) with isolated sagittal synostosis, more radical reshaping is recommended and is achieved with an open vertex craniectomy, including releasing biparietal wedge craniectomies with or without bilateral barrel osteotomies and with or without an occipital remodeling craniotomy. We do not do staged or “front-and-back” procedures because forehead reshaping occurs over time, with or without helmeting, as the result of craniofacial growth. Basic craniotomy instrumentation and powered tools for burr holes and osteotomies are all that are needed. A head lamp, surgical loupes, and suction cautery facilitate adequate vision for simple vertex craniectomy done through anterior and posterior coronal incisions. If endoscopes are to be used to assist in the extradural dissection, we have used a 4-mm 30° endoscope (Karl Storz, Tuttlingen, Germany). In minimally invasive procedures, bone is cut with straight or curved Mayo scissors, and Goldman septum scissors are used for thicker bone.

13.3.2╇ Expert Suggestions and Comments The operation type and techniques used to normalize head shape are based on the patients’ specific skull shape and age.

13.3.3╇ Key Steps of the Procedure and Operative Nuances 1. Following anesthetic induction and intubation, one or two IVs and an arterial line are placed; no urinary catheter, central line, or precordial monitoring is used. Prophylactic antibiotics are given. 2. Positioning should be as simple as possible. For a minimal vertex craniectomy, the patient is positioned either lateral on a padded beanbag (Fig. 13.1a–c), in the “sphinx” position (Fig.€13.1d–f), or prone in a padded horseshoe headrest in a near-neutral position (Fig. 13.1g,h). The lateral decubitus position is less complex from an anesthetic perspective. In older infants, or when a more radical open vertex craniectomy is planned, the prone position on a horseshoe headrest is always chosen. The patient is secured to the table with “bum and chest” straps, and the head is fixed to the head-

13â•… Sagittal Synostosis Repair Surgery rest with an adhesive U-drape. This prevents fluids from running onto the face during the operation and avoids pressure and moisture skin breakdown. This technique also stabilizes the head to the headrest. Eyes, forehead, maxillae, and body pressure points are checked to ensure no local pressure,10 and the stability of the patient on the table is checked by putting the table through any movements that will be necessary during the operation, prior to draping. Should the patient shift on the table, adjustments in the securing straps are made and the position retested. 3. Prepping and draping: After minimal hair clipping, we do a double 2% chlorhexidine gluconate solution skin prep, carefully avoiding any dripping of prep solution under the U-drape onto the skin and eyes. The last prep is allowed to dry, and any excess liquid

a

d

b

e

prep in the hair is absorbed with sterile towels prior to draping. 4. Scalp incision (Fig. 13.1): For minimal vertex craniectomy, two 5– to 6-cm-long coronal incisions are made: one just posterior to the anterior fontanelle and one just in front of the posterior fontanelle. Alternatively, a wider coronal incision at the midpoint of the sagittal suture or a “lazy S”-shaped midline incision over the sagittal suture can be used. For an open vertex craniectomy, a bicoronal zigzag incision is made from behind the ear, crossing the midline in the anterior third of the sagittal suture, and to behind the other ear. The lateral zigzags are curved at least twice the width of the eventual scar, and the incision comes straight over the vertex.

g

h

c

f

Fig. 13.1â•… (a) Positioning of the head in sagittal craniosynostosis repair surgery. (b) The lateral head position, with the side of the head resting on a doughnut-shaped gel pad. (c) The head is fixed with adhesive U-drape before sterile draping. (d) A lateral view of the “sphinx” position. (e) The head is placed on a gel-padded beanbag or Doro headrest (PMI, Frieburg, Germany) and fixed with adhesive U-drape. (f) Frontal view of the “sphinx” position after sterile draping. (g) The prone position with the forehead resting on a padded horseshoe head holder before draping. (h) After draping.

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122 Section III.Aâ•… Malformations of the Scalp and Skull After local anesthesia (0.25% xylocaine and 1/400,000 adrenaline) administration, the scalp incision is made with either fine-tip cautery or scalpel. With the pericranium left intact, a subgaleal scalp dissection is done, with attention to meticulous hemostasis. 5. Bone removal: Access to the extradural space at the coronal suture can be achieved with either bilateral burr holes or dissection through the coronal suture. Bilateral burr holes are placed anterior to the lambdoid suture. Burr holes are fashioned with a craniotome using either an acorn (6-mm) or match head (2.2-mm) burr. The holes are placed parasagittally, 1.5 to 2 cm off midline. Ideally, the planned parasagittal osteotomies do not cross the location of the commonly present parietal emissary veins. In the minimal procedure, after the vertex scalp is elevated in the subgaleal plane, only as wide as necessary for the parasagittal osteotomies, anterior and posterior craniectomies are fashioned to include the fused suture under direct vision. This provides access to the extradural space, from anterior and posterior trajectories for the scope or dissector. Using direct visualization with a headlight and loupes (or, less commonly, with the endoscope), the parasagittal osteotomies are made starting with either the craniotome or scissors, depending on access provided by the scalp incision and bone thickness (Fig. 13.2b). The osteotomies continue from either anteriorly or posteriorly, with cuts from the opposite direction made to join at the mid-parietal level. An osteotomy across the midline posteriorly is made with a craniotome, scissors, or blade cut after the dura is freed. If present, any wormian bone or bone present anterior to the lambda can then be removed under direct vision. The scalp is further dissected for anterior and posterior parietal wedge osteotomies made parallel to the coronal and lambdoid sutures. Scissors are adequate for these osteotomies. They do not need to cross the squamosal suture. Hemostasis is achieved under direct vision using bipolar cautery on the dura and subgaleal vessels and with bone wax and/or monopolar cautery on the diploic space. Floseal Matrix (Baxter Healthcare, Deerfield, IL, USA) can be used for fast hemostasis in difficult-to-reach bleeding. Hemostasis must be meticulous. In the older infants and those with prominent occipital prominence, the more radical open vertex craniectomy is performed with the patient in the prone position (Fig. 13.1g,h). The same anesthetic precautions are taken as described for the minimal procedure. A bicoronal incision is used as previously described. Scalp flaps are mobilized to

a

b

Fig. 13.2â•… Oblique, 3D-rendered view with semitransparent scalp showing skin incisions and osteotomies. (a) Open bone work, including circular occipital remodeling of interparietal occipital bone. (b) Minimally invasive bone work.

the coronal sutures and posteriorly to and over the occipital prominence, exposing the coronal, lambdoid, and squamosal sutures laterally. Accessing the extradural space either with burr holes or through the coronal sutures, a vertex craniectomy is performed using a craniotome and the fused, nonadherent sagittal suture and adjacent parietal bone can be elevated from the dura and reflected on the lambdoid sutures. The vertex bone can then be sharply dissected at the lambda. This technique should be avoided if there is a wormian bone at the posterior fontanelle or the lambda is angled in such a way that the vertex bone would cause compression and occlusion of the superior sagittal sinus during the maneuver. In this situation, the posterior parietal osteotomy should be done using a craniotome and the bone at the lambda should be elevated under direct vision. When the occipital bone is deformed, the posterior parietal bones are often concave, creating

13â•… Sagittal Synostosis Repair Surgery the clinical biparietal narrowing. This narrowing can be addressed by excising these depressions (wedge osteotomies) (Fig. 13.2a). If the occipital deformity is to be addressed, the lambdoid sutures must be freed from the dura through their whole length. The bilateral occipital craniotomy is done in a circular fashion, elevating the interparietal portion of the occipital bone. This bone flap can be either left off or remodeled (flattened using radial cuts) and repositioned (sutured to the posterior parietal bones). If there is not spontaneous widening of the vertex craniectomy defect, narrow wedge osteotomies or barrel staves are made parallel to the coronal suture as far as to the squamosal suture and the parietal bones are hinged laterally on the squamosal suture and contoured using the Tessier bone bending forceps. The posterior parietal wedge osteotomies can be “narrowed” with sutures. This causes the parietal bone to buckle and gives an immediate wider biparietal diameter and appearance. Hemostasis is as described previously and must be meticulous. 6. Scalp closure: Closure of the scalp is done in two layers. We use Vicryl (Ethicon, Somerville, NJ, USA) 3–0 interrupted stitches subcutaneously and dissolvable running Vicryl Rapide 4–0 for skin closing. The skin is then sprayed with an adhesive OpSite spray dressing (Smith-Nephew, Mississauga, Ontario, Canada). Postoperatively, the head of the patient is raised 20 to 30°. Average skin-to-skin time for the minimal procedure is about 1 hour, for the more radical open procedure about 1.5 hours. 7. Postoperative helmet therapy: Calvarial growth will conform to the inner shape of a helmet worn postoperatively. By creating a helmet with an optimal inner shape, the posthelmeting clinical results have been made predictable. The goal of helmeting is a cephalic index of approximately 0.8. Ideally, the helmet is worn 23 hours per day unless there is scalp pressure or irritation. Compressive molding, as is done on other forms of calvarial deformity, is not performed. We have experimented with locally fabricated helmets but have had best quality and service from the manufacturer producing bivalved cranial remolding orthoses (Orthomerica, Orlando, FL, USA). Although stereographic imagery from craniofacial surface scanners can be used to define the starting cranial morphology, our orthotic team prefers to base the helmet on a cast mold. The patient has

a mold made at 10 days following surgery, when postoperative swelling has, in most cases, resolved. When the helmet is fitted, shims may be necessary if the anteroposterior (AP) dimension has further decreased as swelling has resolved. Biparietal shims may be needed to achieve a secure fit. Patients are seen every 3 weeks by the orthotist, and as the AP dimension increases, the helmet liner is shaved, the shell is adjusted to accommodate the new size goal, and biparietal shims are removed. Helmeting is maintained for at least 6 months. Only one helmet has been necessary in our patients to date. Since the helmet’s shell is adjustable, it does not need to be remade. The inner foam insert can be carved to address areas of pressure. The weight of the helmet may be a concern for very young patients; however, to the present, a standard helmet has proven adequate.

13.3.4╇ Hazards, Risks, Avoidance of Pitfalls In general, the mortality and morbidity rates of sagittal synostosis repair surgeries are very low.1,11 Nevertheless, great care is always needed during positioning to avoid pressure sores, ocular injury, and slipping as table position changes. Proper exposure of the extradural space and hemostatic control are needed to avoid dural tears, sagittal sinus hemorrhaging, or air embolism. One should anticipate that the dura and sinus will be adherent at nonfused segments of the sagittal, coronal, and lambdoid sutures and at the lambda. Dural dissection from those parts of the bone is more difficult and therefore prone to dural tearing. Such dissection should be done under direct vision. Smoothing the bone edges after osteotomy and craniectomies might lower the risk of impinging the dura or skin postoperatively. To decrease the risk of postoperative bleeding from the scalp, we like to elevate the head 20–30° degrees postoperatively.

13.3.5╇ Salvage and Rescue Massive bleeding is possible in areas where the sagittal sinus is adherent to the sagittal suture or lambda. Such adherence occurs in areas of a patent, normal suture and not in the areas where the suture is fused. Hemorrhage can also occur from the diploic and unrecognized parietal emissary veins. We usually have blood for transfusion available. The secure positioning of the patient on the operating table allows head-up or head-down positioning quickly to address blood loss or air entrainment.

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13.4╇ Outcomes and Postoperative Course 13.4.1╇ Postoperative Considerations During the postoperative period, we elevate the head 20 to 30° upright. Usually, patients who had minimally invasive surgery go home within 24 to 48 hours. Patients who had more extensive surgery are nursed on the ward for 3 to 4 days prior to discharge. Follow-up assessments of wound healing are made at 4 to 6 weeks postoperatively and at the time of helmet fitting and adjustment.

13.4.2╇Complications Patients who have had minimally invasive sagittal synostosis repair surgery have rarely required blood transfusion. In the more extensive procedures, 10 to 15% of patients need a blood transfusion either intraoperatively (rare) or postoperatively.12 The complication types and rates we have seen are similar to those reported by others.1,11 Clinically significant sutural fusion of previously normal coronal or lambdoid sutures after a vertex craniectomy is uncommon. This is usually recognized because of the falloff of head growth in the first 24 months following the initial correction. Papilledema may be present. In most situations, the bone growth cannot keep pace with brain growth, and craniostenosis results. A cranial expansion operation may then be needed. Recurrent dolichocephaly of a degree meriting repeat operation is also rare. In this situation, a radical remodeling with parietal widening is needed. This can be done with a single operation or more gradually with cranial distractors.

References ╇1.

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Lee HQ, Hutson JM, Wray AC, et al. Analysis of morbidity and mortality in surgical management of craniosynostosis. J Craniofac Surg 2012;23(5):1256–1261 Lattanzi W, Bukvic N, Barba M, et al. Genetic basis of single-suture synostoses: genes, chromosomes and clinical implications. Childs Nerv Syst 2012;28(9): 1301–1310 Johnson D, Wilkie AO. Craniosynostosis. Eur J Hum Genet 2011;19(4):369–376 Arnaud E, Renier D, Marchac D. Prognosis for mental function in scaphocephaly. J Neurosurg 1995;83(3):476–479 Da Costa AC, Anderson VA, Holmes AD, et al. Longitudinal study of the neurodevelopmental characteristics of treated and untreated nonsyndromic craniosynostosis in infancy. Childs Nerv Syst 2013;29(6):985–995 Speltz ML, Endriga MC, Mouradian WE. Presurgical and postsurgical mental and psychomotor development of infants with sagittal synostosis. Cleft Palate Craniofac J 1997;34(5):374–379 Sood S, Rozzelle A, Shaqiri B, Sood N, Ham SD. Effect of molding helmet on head shape in nonsurgically treated sagittal craniosynostosis. J Neurosurg Pediatr 2011;7(6):627–632 Agrawal D, Steinbok P, Cochrane DD. Long-term anthropometric outcomes following surgery for isolated sagittal craniosynostosis. J Neurosurg 2006;105(5, Suppl): 357–360 Massimi L, Tamburrini G, Caldarelli M, Di Rocco C. Effectiveness of a limited invasive scalp approach in the correction of sagittal craniosynostosis. Childs Nerv Syst 2007;23(12):1389–1401 Lee J, Crawford MW, Drake J, Buncic JR, Forrest C. Anterior ischemic optic neuropathy complicating cranial vault reconstruction for sagittal synostosis in a child. J Craniofac Surg 2005;16(4):559–562 Alvarez-Garijo JA, Cavadas PC, Vila MM, Alvarez-Llanas A. Sagittal synostosis: results of surgical treatment in 210 patients. Childs Nerv Syst 2001;17(1-2):64–68 Hentschel S, Steinbok P, Cochrane DD, Kestle J. Reduction of transfusion rates in the surgical correction of sagittal synostosis. J Neurosurg 2002;97(3):503–509

14

Operative Techniques in Cranial Vault Reconstruction: Nonsyndromic Coronal Craniosynostosis Christopher C. Chang, Derek M. Steinbacher, Charles C. Duncan, and John A. Persing

14.1╇ Introduction and Background 14.1.1╇Diagnosis Coronal synostosis may occur in one or both halves of the coronal suture. Unilateral fusion results in an asymmetric cranial vault, cranial base, and facial skeleton. Bilateral fusion results in a symmetric brachycephalic skull deformity involving the vault, base, and facial skeleton. Skull deformity is associated with potential for neurodevelopmental anomalies, presumably related to regional compression of brain parenchyma.1,2 Craniosynostosis can occur in combination with a constellation of other dysmorphisms, resulting from genetic mutations in patients with specific syndromes. However, it can also occur in isolation without any clear association in an otherwise normal, healthy child, in which case it is known as nonsyndromic craniosynostosis.3

14.2╇ Unilateral Coronal Synostosis Unilateral coronal synostosis (UCS) is the third most common nonsyndromic form, after sagittal and metopic synostoses. UCS is twice as likely in females as in males and usually presents in early infancy. Coronal malformation can also affect the underlying orbits and midface, which can result in a progressively deforming facial asymmetry.

14.2.1╇ Physical Exam On exam, patients typically present with a flattened half of the forehead. This is descriptively known as frontal synostotic plagiocephaly; however, the malfor-

mation associated with synostosis must be differentiated from deformational plagiocephaly (DP).4 Patients with DP can present with similar physical features in the frontal region, but DP is distinguished from UCS by its characteristic parallelogram skull shape and relative lack of cranial base deformity. This head shape is the result of unequal pressure on the occiput while in utero or when the infant sleeps on his back. UCS is further distinguished from DP by anterior displacement of the pinna ipsilateral to the fused coronal suture, with nasal radix deviation, ipsilateral temporal squamosal bulging, and contralateral chin point deviation due to ipsilateral anterior displacement of the glenoid fossa, and the harlequin orbit when viewed radiographically.

14.2.2╇Imaging Radiographic imaging is performed to confirm the diagnosis and aids in preoperative planning. The current study of choice is low-dose computed tomography (CT), as radiation exposure to infants is minimized. Furthermore, sedation may be needed for young patients to ensure a high-quality study.

14.2.3╇ Treatment Planning Timing of treatment in pediatric craniofacial patients is a balance between the risk of surgery versus the potential for progression of disease, as well as general operative risks. Clinical evidence suggests a link between neurodevelopment and craniosynostosis, and earlier intervention generally results in better neurologic outcomes.5 The optimal timing for surgery is yet to be defined, but depending on the type of craniosynostosis, 3 to 6 months of age appears to be the best blend of safety and efficacy.3

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126 Section III.Aâ•… Malformations of the Scalp and Skull

14.3╇ Operative Detail and Preparation 14.3.1╇ Surgical Treatment: Unilateral Coronal Craniosynostosis The deformity of unilateral coronal craniosynostosis is marked by asymmetric constriction and expansion of the cranial vault.

Approach When the patient has primarily frontoparietal deformity without significant posterior deformity, she can be placed in the supine position using a padded Mayfield horseshoe headrest. The headrest is compressed as narrow as possible to allow visualization of the parietal occiput. Optimal position for the patient is to have the neck flexed at approximately 30° but the face parallel with the floor. If there is significant posterior vault deformity requiring surgical correction, a modified prone position is preferred to allow more complete correction of the occiput. Sterile prep and drape of the scalp and face to the level of the cheeks and anterior portions of the ear allows visualization of the proximal nose, eyelids, and brow region, which are typically asymmetric. To reduce scar visibility, the scalp incision is oriented obliquely and posteriorly in order to have the resultant scar fall perpendicular to the orientation of the majority of hair follicles. The incision line is planned posterior to the whorl of the scalp hair in the occiput. In order to make this incision, one must preserve the ascending branch of the superficial

temporal artery in order to avoid vascular compromise of the scalp flap. The incision is taken down to the level of the galeal-supraperiosteal plane, resulting in anterior and posterior scalp flaps, which are reflected. Flap elevation is continued anteriorly to the level of the orbital rims. Dissection is continued by cutting through the periosteum, and subperiosteal/periorbital dissection is performed in order to preserve the supraorbital nerves and vessels superiorly. Protection of the medial canthal tendon attachment is maintained medially. Laterally, incision is continued to the level of the frontozygomatic suture; however, care is taken to avoid complete separation of the soft tissue at the suture, as the orbital rims will be “hinged” forward later in the procedure based on the soft tissue attachment.

Frontal Bone The goal of frontal bone remodeling is to develop a bifrontal bone graft with a symmetric span equal on both sides. Measurements are taken at the mid-orbit at the supraorbital notch, superiorly and laterally at the level of the lateral orbital rim on the unaffected side. These measurements are then transferred to the affected side to plan appropriate length and contour. Care is also taken to visualize the “breakpoint” at the level of the hairline, which is marked with ink on the bone (Fig. 14.1). A bifrontal bone graft is elevated extending posteriorly through the normal patent suture to the contralateral side. Subsequently, this is mirrored at a point equidistant from the supraorbital rim on the fused side, typically 1.5 to 2 cm posterior to the fused suture. This is done to recruit the addi-

Fig. 14.1â•… After exposure, the pathologic suture is identified along with the contralateral unaffected side. Additional bone is recruited approximately 1 to 1.5 cm posterior to the suture to support the bone graft after advancement. The frontal bone is contoured on the back table and stabilized in place with resorbable plates or sutures.

14â•… Operative Techniques in Cranial Vault Reconstruction: Nonsyndromic Coronal Craniosynostosis tional bone needed to reestablish normal frontal and orbital projection. The orbital rim is cut at a distance approximately 1 cm from the free border of the supraorbital rim to reduce the possibility of fracture with rim advancement. Epidural dissection is begun through the patent anterior fontanelle or adjacent to it via a burr hole. A second burr hole is placed superior to the level of the orbital rim, but in the superior temporal region bilaterally (above the planned excursion of the recessed supraorbital rim). The frontal bone osteotomy line on the fused side is drawn in ink, incorporating additional width and frontal bone length to equal the distance between the orbital rim and the patent coronal suture on the nonfused side. A parietal bone graft strip approximately 1 to 1.5 cm wide is harvested from the contralateral (nonfused) side to accommodate the advanced ipsilateral bone. This may be useful for further augmentation of the supraorbital rim during advancement and will result in near-symmetric bone defects bilaterally with remodeling and repositioning of the fronto-orbital complex. The bifrontal craniotomy also allows access to the parietal regions bilaterally. Once elevated, the bone graft is placed in a moist, blood-soaked sponge on the back table for remodeling. Barrel stave osteotomies, oriented anteroposteriorly, are placed into the parietal bone to address the parietal flattening ipsilateral to the fused suture.6 In select patients older than 1 year, adjunctive bony maneuvers, such as kerfs, may be useful to weaken the bone selectively and improve the contour via controlled fracture patterns.

Orbits Attention is then directed to the orbital rims, where the orbital dimensions have been noted preoperatively on 3D CT scan. Typically, on the fused side, the orbital rim width is narrowed mediolaterally by approximately 2 to 3 mm; on the nonfused side, the height is shortened by a similar amount. Therefore, contouring of the orbital rim will be done to correct the mediolateral dimension on the fused side, and only superiorly on the nonfused side of the skull. The orbital roof osteotomy is performed 5 mm posterior to the internal border of the superior orbital rim with an air-powered drill and a side-cutting burr. The osteotomy extends inferiorly only to the level of the medial canthus medially, and laterally to the frontozygomatic (FZ) suture (Fig. 14.2). At this point, an osteotome is used to pivot forward the supraorbital rim. A greenstick fracture is planned at the FZ suture because the goal of this procedure is not only to advance the orbital rim but also to “procline” or tilt the superior orbital rim forward (Fig. 14.3).7 The incomplete separation at the FZ suture will result in a stable base for the orbital rim advancement. This is done in order to reduce the likelihood of a diminished bony profile of the supraorbital rim and frontal bone, common to many other advancement techniques.8 In our opinion, it is important not to disconnect the FZ suture and fix it anteriorly because of concerns related to growth restriction, even if resorbable plates are used. Remodeling the orbital rim ex vivo also compromises growth potential through devascularization and dehydration of the bone. The deficient orbital rim is

Fig. 14.2â•… The orbital roof osteotomy is performed to reestablish supraorbital projection and symmetry. This is performed 5 mm posterior to the internal border of the rim with an air-powered drill and side-cutting burr. A malleable retractor is used to protect the intraorbital contents, and the bandeau is advanced.

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128 Section III.Aâ•… Malformations of the Scalp and Skull terior fixation (Fig. 14.4). This allows forward support while preventing posterior collapse secondary to external soft tissue compression (Fig. 14.5). Once this is completed, the frontal bone graft is treated by radial osteotomies and wedge resections, then molded using the Tessier rib bender to create a normal form of projection of the two halves of the frontal region. The frontal bone is attached to the advanced supraorbital rims by 3–0 Maxon suture (Medtronic, Minneapolis, MN, USA). The remaining bone chips are used to fill the gaps created by the advancement of the orbital rim. The soft tissue is redraped to assess the advancement, which is positioned to overcorrect the supraorbital rim 2 to 3 mm. Additional augmentation can be achieved using the anterior parietal bone graft harvested from the nonfused side of the skull earlier in the procedure if needed. Once adequate projection is achieved, the wound is irrigated, hemostasis is achieved, and the incision is closed (Fig. 14.6). Fig. 14.3â•… The goal of supraorbital advancement is to reestablish projection without compromising future growth. The supraorbital rim is canted forward while inferior support and attachment to the frontozygomatic suture are maintained.

advanced and tilted forward approximately 1.5 cm; it is pivoted medially on the region of the frontonasal suture. This advancement provides exposure to the greater wing of the sphenoid, which is abnormally oriented obliquely. A rongeur is used to remove the lateral portions of the greater wing of the sphenoid to a point just lateral to the lateral portion of the superior orbital fissure. This will reduce the globe proptosis on the fused side by expanding the potential orbital space, since the intraorbital volume is smaller than that on the contralateral side. Additionally, it also allows reconstruction (flattening) of the temporal fossa (squamous temporal bone), which has a convex lateral profile. In the contralateral (nonfused side) orbit, the orbit is trimmed at the inferior border of the superior orbital rim, accounting typically for approximately 2 mm of downward impingement of the orbital rim on the globe. Care is taken to avoid detachment of the lateral canthus from the frontal process of the zygoma to maintain normal positioning of the palpebral fissure. Following the contouring of the periorbital region, the orbital rim is advanced, but secured in a fashion that does not inhibit further growth. Specifically, using a resorbable U-shaped strut plate (KLS Martin, Mühlheim, Germany) that is secured only to the lateral portion of the orbital rim allows it to be buttressed forward in a tongue-and-groove manner to the squamous temporal bone without direct pos-

Fig. 14.4â•… A U-shaped resorbable plate (KLS Martin, Mühlheim, Germany) is used to buttress the lateral portion of the parietal bone and to stabilize orbital rim advancement while reducing concerns of permanent growth restriction.

Fig. 14.5â•… Once the rim is advanced and fixated, there is compensatory increase in intracranial volume posteriorly.

14â•… Operative Techniques in Cranial Vault Reconstruction: Nonsyndromic Coronal Craniosynostosis

Fig. 14.6â•… Immediate on-table result illustrates a patient with unilateral right-sided coronal synostosis and postoperative resolution after whole-vault cranioplasty.

14.3.2╇ Surgical Treatment: Bilateral Coronal Craniosynostosis Preoperative Considerations Patients with bilateral coronal synostosis frequently present with associated skull deformities typically due to limited skull expansion (anteroposteriorly, i.e., brachycephaly, and superoinferiorly, i.e., oxycephaly). Although these may be addressed by a sequential or staged posterior vault expansion followed by a later fronto-orbital advancement, our preference is to do both procedures simultaneously, at one stage if at all possible, because of a perceived superior end result. In patients who have associated or complicating medical comorbidities, it may be preferable to consider two stages, such as instances of Arnold-Chiari malformation, and/or tracheostomy dependence. Consideration must be given to the postoperative positioning of the patient to prevent relapse of the corrected cranial vault; if the patient cannot be positioned laterally for respiratory reasons, a two-stage approach should be considered, as continuous occipital pressure postoperatively may recreate brachycephaly. Children who have had multiple previous procedures for bilateral coronal synostosis, particularly syndromic patients, may also require a staged approach of posterior vault expansion first, followed by cranial vault remodeling thereafter, especially if a ventriculoperitoneal shunt is involved. The staged approach can be done as early as on the same day; however, frequently it is done with a period of weeks between stages to allow expansion of the occiput posteriorly, either by fixed advancement or distraction techniques.

Approach As access to the entire cranial vault is necessary, the modified prone position is useful. A well-padded cervical collar, beanbag, and positioning rolls are helpful to adequately protect the patient during surgery. A central line and Doppler monitoring should be utilized to monitor for air emboli. All bifrontal craniotomy cases, regardless of position, are associated with increased risk of air embolism, and appropriate monitoring is essential. A posteriorly oriented coronal incision is made into the occiput from the temporal region. Anterior and posterior scalp flaps are developed in the subgaleal/supraperiosteal plane. With bilateral coronal suture fusion, a barrel stave osteotomy is designed as a bifrontal craniotomy with bilateral supraorbital rim advancement and a parieto-occipital osteotomy posteriorly (Fig. 14.7).

Fig. 14.7â•… In bilateral coronal suture fusion, a barrel stave osteotomy is designed as a bifrontal craniotomy with bilateral supraorbital rim advancement and a parieto-occipital osteotomy posteriorly.

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130 Section III.Aâ•… Malformations of the Scalp and Skull The frontal craniotomy extends from the anterior fontanelle to approximately 1 cm above the supraorbital rim. Laterally, the osteotomy is extended to the squamous temporal bone. Parietal bone struts, which are usually 1 to 2 cm wide, are allowed to remain attached to the squamous temporal bone, but the parietal bone posterior to this strut behind the lambdoid suture is marked for craniotomy. The length of posterior extension is dependent on the degree of occipital flattening and oxycephaly. The parietal bones, following craniotomy, are removed and placed as separate bone grafts on the back table with the bifrontal bone for later remodeling. Following this, occipital barrel staves are placed in the remaining occipital bone down to approximately 1 cm above the foramen magnum. This requires elevation of the occipital muscles so as to reach the appropriate level of osteotomy in the posterior aspect of the skull. These bone segments are then “outfractured” posteriorly. The distal portions of the barrel staves are bent with the Tessier bender to give a more inward rotation so as not to create pressure points on the overlying scalp postoperatively. Attention is directed back to the fronto-orbital complex, where osteotomies as described for unilateral coronal synostosis were made. The orbital roof osteotomy is created with a side-cutting burr extending from the anterior cribriform region to the lateral orbital roof followed by an osteotome through the lateral orbital wall down to the level of the FZ suture. The bone is fractured anteriorly, pivoting on the FZ suture soft tissue and the midline from the frontonasal suture. Some splaying of the bone is typically seen at the midline frontal bone, where resorbable Maxon or polydioxanone (PDS) suture is used to maintain the alignment of the medial aspects of the frontal bone. As with unilateral coronal synostosis, care is taken not to detach the orbital rims completely at the FZ suture, as this will needlessly risk hindering bone growth by devascularization. Squamous temporal bones, which are convex, are partially resected using a rongeur anteriorly to the mid-portion of the squamous temporal bone. With the expanded space posteriorly in the barrel-staved occiput, the height of the skull can be reduced anteriorly and inferiorly. By displacing the parietal bar from the vertex of the skull posteriorly approximately 1 to 2 cm, the contour of the frontal region is significantly improved by reducing the abnormal and convex high point of the forehead posteriorly into a more normal skull form (Fig. 14.8). The height of the skull is usually reduced approximately 1 cm using resorbable sutures in this maneuver. Once this is performed, the frontal bone graft undergoes radial osteotomies and wedge resections of bone to enable normal contouring. Sufficient space is left between the parietal bone strut posterolaterally in the posterior border of the frontal bone to simulate a new coronal suture pathway.

Fig. 14.8â•… After removal of the anterior and posterior bone segments, the height of the skull can be reduced anteriorly and inferiorly. By displacing the parietal bar from the vertex of the skull posteriorly approximately 1 to 2 cm, the contour of the frontal region is significantly improved into a more normal skull form.

The parietal bones undergo radial osteotomies and convex bending of the parietal bone segments. These bone grafts are attached to the underlying dura but not to the surrounding bone, leaving an approximately 7- to 8-mm gap in the perimeter to the adjacent bone, particularly in the midline in the paramedian areas in the parietal area (Fig. 14.9). This is done to reduce the likelihood for early reformation of abnormal bone and reduction of the correction of the deformity. The temporalis muscle is elevated and secured with PDS or Maxon suture to the lateral orbital rim and possibly the fixation plate. The wound is then irrigated and made hemostatic and the scalp closed as described for unilateral coronal synostosis.

14.4╇ Outcomes and Postoperative Course 14.4.1╇ Postoperative Care Postoperatively, the patient is placed laterally in the decubitus position so as not to indent the weakened occipital bone and recreate the flattening of the skull that was evident preoperatively. Within 3 to 4 weeks following surgery, a skull-molding helmet is used to

14â•… Operative Techniques in Cranial Vault Reconstruction: Nonsyndromic Coronal Craniosynostosis that many patients benefit socially from early intervention. Early surgical remodeling and intracranial pressure relief are important to reduce the degree of negative neurologic sequelae. Further investigation is needed to clarify this relationship.

References ╇1.

╇2.

╇3.

╇4.

Fig. 14.9â•… In cases of bilateral coronal synostosis repair, anterior and posterior bone flaps are elevated and recontoured on the back table. Barrel stave and radial osteotomies are made posteriorly to allow reshaping and posterior expansion.

avoid pressure on the occiput to further guide reconstruction of the skull, protect the bony framework, and reduce pressure in the midline occiput.

Outcomes Cranial vault remodeling for coronal craniosynostosis has undergone an evolution of techniques and strategies. Aesthetic and social outcomes have improved so

╇5.

╇6.

╇7.

╇8.

Cohen SR, Persing JA. Intracranial pressure in single-suture craniosynostosis. Cleft Palate Craniofac J 1998;35(3):194–196 David LR, Wilson JA, Watson NE, Argenta LC. Cerebral perfusion defects secondary to simple craniosynostosis. J Craniofac Surg 1996;7(3):177–185 Persing JA. MOC-PS(SM) CME article: management considerations in the treatment of craniosynostosis. Plast Reconstr Surg 2008;121(4, Suppl):1–11 Liu Y, Kadlub N, da Silva Freitas R, Persing JA, Duncan C, Shin JH. The misdiagnosis of craniosynostosis as deformational plagiocephaly. J Craniofac Surg 2008;19(1):132–136 Magge SN, Westerveld M, Pruzinsky T, Persing JA. Long-term neuropsychological effects of sagittal craniosynostosis on child development. J Craniofac Surg 2002;13(1):99–104 Persing JA, Mayer PL, Spinelli HM, Miller L, Criscuolo GR. Prevention of “temporal hollowing” after frontoorbital advancement for craniosynostosis. J Craniofac Surg 1994;5(4):271–274 Patel A, Chang CC, Terner JS, Tuggle CT, Persing JA. Improved correction of supraorbital rim deformity in craniosynostosis by the “tilt” procedure. J Craniofac Surg 2012;23(2):370–373 Cornelissen MJ, van der Vlugt JJ, Willemsen JC, van Adrichem LN, Mathijssen IM, van der Meulen JJ. Unilateral versus bilateral correction of unicoronal synostosis: an analysis of long-term results. J Plast Reconstr Aesthet Surg 2013;66(5):704–711

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15

The Surgical Repair of Unilateral Coronal Synostosis Jodi L. Smith, Laurie L. Ackerman, and Robert J. Havlik

15.1╇ Introduction and Background The skull consists of several plates of bone separated by sutures: fibrous joints that function by depositing bone at their margins in response to brain expansion. The skull grows to accommodate brain growth, especially during the first 2 years of life, when brain volume can increase up to three times its size at birth. Sutures must be open for the skull to grow and attain its characteristic normocephalic shape. When one or more cranial sutures close prematurely, the skull stops growing in the direction perpendicular to the closed suture but continues to grow parallel to the closed suture. Craniosynostosis is the term used to describe this condition, and the shape of the skull is altered in a predictable manner with recognizable patterns that depend on which suture is fused. Premature closure of the coronal suture results in frontal or anterior plagiocephaly. Diagnosis is made clinically (Fig. 15.1) and confirmed radiographically, with sclerosis of the fused suture and a harlequin abnormality resulting from relative elevation of the greater wing of the sphenoid bone on the affected side (Fig. 15.2).

15.1.1╇ Key Principles

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• If untreated, coronal synostosis will lead to severe deformity of the forehead, orbit, and nose that worsens with head growth. • Treatment is surgical and is best carried out by a pediatric neurosurgeon and craniofacial surgeon, with a pediatric anesthesiologist administering the anesthesia. • Surgery is usually performed between 4 and 8 months of age because the calvarial bone has developed sufficient thickness to enable fixation and provide structural stability; the bone is malleable, making remodeling easier; rapid brain growth helps bone remodeling; bony defects heal more rapidly; and early correction prevents further compensatory deformities.

Fig. 15.1â•… Six-month-old girl with right frontal plagiocephaly secondary to right coronal synostosis. She presents with ridging along the right coronal suture, retrusion of the right supraorbital bar, compensatory left frontal bossing, and significant asymmetry of the orbits and palpebral fissures, with the right orbit increased in vertical height and the nasal root deviated to the right.

15â•… The Surgical Repair of Unilateral Coronal Synostosis

15.1.3╇ Treatment Goals There are two primary goals of treatment of coronal synostosis: • To release the fused suture(s) to allow the brain to grow and expand normally and to prevent problems associated with increased intracranial pressure • To establish the normal contour of the brow, orbits, forehead, and skull and thereby to minimize psychosocial problems To accomplish these goals, the supraorbital bar is removed, reshaped, and advanced forward and lowered on the affected side and is rigidly fixed in position to the nose and lateral orbits. The reconstructed forehead is reshaped and then secured to the supraorbital bar. If there is excessive height to the skull, total calvarial remodeling is also performed to decrease the height of the skull. Fig. 15.2â•… Plain skull film in infant with right coronal synostosis, showing a harlequin abnormality due to relative elevation of the greater wing of the sphenoid bone on the affected side.

• Overcorrection of the affected side diminishes the need for reoperation.

15.1.2╇Indications The patient with partial or unilateral coronal synostosis exhibits ridging of the prematurely fused half of the coronal suture, flattening of the ipsilateral frontal and parietal bones, bulging of the ipsilateral squamous portion of the temporal bone, deviation of the nasal root to the side of the fused suture, and compensatory bossing of the contralateral frontal and parietal bones. From an en face view, the ipsilateral brow and supraorbital rim are elevated and recessed, making the eye on the affected side seem more open because of the increased vertical height of the orbit, and the nasal root is deviated toward the affected side. Bicoronal synostosis results in a flat, retruded forehead with shortening in the anteroposterior dimension, compensatory bulging in the transverse dimension, and increased skull height. The supraorbital rims are recessed and elevated, with the deformity being symmetric bilaterally. Improvement of the overall skull shape is the main indication for surgical correction. This is accomplished by forward advancement of the recessed forehead, correction of the compensatory bossing of the contralateral forehead in unilateral coronal synostosis, correction of the increased skull height in bicoronal synostosis, and correction of the orbital abnormality.

15.1.4╇ Alternate Procedures Surgical technique is tailored to the severity of the calvarial vault and skull base deformity created by the coronal synostosis. Resection of the affected suture alone will not correct the associated compensatory skull shape changes and fronto-orbital abnormalities that accompany premature fusion of the coronal suture. The best surgical results are achieved with extensive reconstruction and active reshaping of the fronto-orbital deformity by advancement of the supraorbital rim and reshaping of the frontal bone on the affected side.

15.1.5╇Advantages The procedure described in this chapter prevents intracranial hypertension and its associated sequelae, minimizes psychosocial problems related to the associated craniofacial deformity, and optimizes growth potential of the brain in the early perinatal period.

15.1.6╇Contraindications Other congenital problems, such as heart or lung conditions, may pose contraindications to surgical treatment if the child is not suitable to undergo general anesthesia. If a blood dyscrasia is present, appropriate pre-, intra-, and postoperative management is essential to avoid excess blood loss. Moreover, in the face of multiple other congenital anomalies resulting in an overall poor prognosis, surgical correction may not be appropriate.

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134 Section III.Aâ•… Malformations of the Scalp and Skull

15.2╇ Operative Detail and Preparation

15.2.2╇ Expert Suggestions, Comments, Tips, Pearls, Lessons Learned

15.2.1╇ Preoperative Planning and Special Equipment—Special Instructions, Position, Anesthesia

Detection of possible air emboli warrants immediate flooding of the field with irrigation, lowering the head of the bed, and waxing of all bone edges. It is essential to know the amount of blood that is lost during the procedure and to monitor the coagulation status and platelet count. Give blood products when indicated and promptly replace fluid losses to maintain hemodynamic stability. When possible, dissect in a supraperiosteal plane to minimize blood loss from the bone, and wax all bone edges when cut.

A head computed tomography (CT) with 3D bony reconstruction is helpful in preoperative planning to delineate the full extent of the calvarial vault and skull base deformities (Fig. 15.3a,b). Photographs are taken preoperatively and serve as a baseline for postoperative outcome assessments (Fig. 15.1). Preoperative planning must also take into account the potential for intraoperative blood loss and venous air embolism so that a sufficient amount of blood and appropriate monitoring are available for surgery. Special equipment used in the surgical correction of coronal synostosis includes at least two large-bore peripheral intravenous catheters, an arterial line, a Foley catheter, a precordial Doppler and end-tidal CO2 monitor to detect air embolism, corneal protectors, resorbable craniofacial plate-and-screw fixation hardware (e.g., LactoSorb, Walter Lorenz Biomet Microfixation, Jacksonville, FL, USA), a sterile hot water bath to facilitate bending of the plates, bone benders, and high-speed drill and saw systems.

a

15.2.3╇ Key Procedural Steps The patient is placed on the operating table in a supine position. After adequate intravenous access and cardiopulmonary monitoring are established, the patient is intubated and general anesthesia is induced. A Foley catheter, arterial line, precordial Doppler, and bilateral corneal protectors are placed. The head is positioned straight up in a well-padded horseshoe head holder. A 2–0 silk suture is pressed against the scalp along the coronal suture to create a line extending from ear to ear. This is used as a reference line to mark a scalloped-patterned bicoronal

b

Fig. 15.3â•… (a,b) 3D reconstruction of head CT in a 10-month-old girl with left anterior plagiocephaly related to premature fusion of the left coronal suture.

15â•… The Surgical Repair of Unilateral Coronal Synostosis incision, taking care to stay well behind the hairline (Fig. 15.4). The hair is clipped along the incision line (or completely if the parents desire), and the incision is thoroughly prepared with a solution of 2% chlorhexidine gluconate and 70% isopropyl alcohol. Prior to opening the incision, a prophylactic antibiotic is administered (e.g., cefazolin 25 mg/kg). The incision is infiltrated with 0.25% bupivacaine with 1:200,000 units of epinephrine and then opened with a no. 15 scalpel blade beveled in the direction of the hair follicles to avoid cutting across their shafts and to minimize visibility of scarring. The anterior and posterior scalp flaps are elevated in the subgaleal/supraperiosteal plane using Bovie electrocautery to maximize hemostasis. The posterior scalp flap is reflected back to the midparietal region. Approximately 1 cm above the orbital rims, the pericranium is incised parallel to the rim, and periorbital dissection proceeds in a subperiosteal plane using periosteal elevators to preserve the periorbital fascia. An osteotome is used to free the supraorbital nerve from its bony encasement. Periorbital dissection, bilaterally along the superior and lateral aspects of the orbits, mobilizes the globes and exposes the frontozygomatic sutures bilaterally and the nasofrontal suture in the midline. This results in exposure of the entire supraorbital rim. The temporalis muscles and fasciae are opened, and the anterior aspect of muscle and fascia are reflected anteriorly out of the infratemporal fossa with the anterior scalp flap. Next, the craniofacial surgeon marks (1) a bifrontal craniotomy encompassing the fused coronal suture(s) and (2) the supraorbital bar, including an extension behind the sphenoid wing on the affected side and a design to allow an orbital rim osteotomy at its junction with the lateral orbital wall on the side opposite the coronal synostosis.

The bifrontal craniotomy is performed by the neurosurgeon, with the posterior extent of the bone flap extending posterior to the coronal sutures bilaterally and the anterior boundary extending to 1 cm above the supraorbital rims (Fig. 15.5a,b). A high-speed craniotome is used to place burr holes in strategic locations to prevent weakening of the supraorbital bar and to facilitate subsequent elevation of the bone flap. The dura is carefully stripped along the anterior cranial fossae to the level of the crista galli in the midline as well as along the lateral aspects of the greater sphenoid wings and temporal fossae bilaterally using periosteal elevators. On the affected side, the temporal extension of the supraorbital bar is freed up by making osteotomies with the drill. Together, the neurosurgeon and craniofacial surgeon remove the supraorbital bar (Fig. 15.5b), which serves as the foundation of the reconstruction. To do this, osteotomies are carried out across each orbital roof, taking care to protect the brain and contents of the orbit with malleable brain retractors, but not retracting excessively, as the cuts are made. The

a

b

Fig. 15.4â•… Nine-month-old girl with right coronal synostosis positioned supine on the operating table and showing a reference line used to mark a scalloped-patterned bicoronal incision.

Fig. 15.5â•… (a,b) Nine-month-old girl with right coronal synostosis after bifrontal craniotomy and removal of the supraorbital bar.

135

136 Section III.Aâ•… Malformations of the Scalp and Skull orbital osteotomies extend medially just anterior to the cribriform plate and laterally to the frontozygomatic sutures. An osteotomy is also made through the lateral orbital wall on the affected side beginning at the frontozygomatic suture, and this is carried back to join the osteotomy of the temporal extension. On the contralateral side, a vertical osteotomy is performed at the level of the lateral orbital rim. Next, an osteotome is used to make a vertical osteotomy through the ipsilateral pterion, taking care to prevent injury to the temporal and frontal lobes. A reciprocating saw is used to create an osteotomy at the nasion just above the nasofrontal suture. The supraorbital bar is then removed intact and placed on the back table in a saline-soaked sponge. Following this, the aberrant bone in the region of the ipsilateral pterion and junction of the orbital roof, lateral orbital wall, and temporal bone is resected toward the anterior clinoid using a combination of rongeurs. This allows for brain expansion into the previously constricted space. The bone edges are waxed for hemostasis, and the dura is inspected for rents, which, if observed, are repaired primarily with 4–0 nonabsorbable, braided nylon suture. At this point, the craniofacial surgeon commences with the reconstruction portion of the operation. A series of curves is cut on the endocranial surface of the supraorbital bar as needed to allow infolding of the temporal extension. A resorbable plate is placed obliquely at the midline, and an additional triangular plate is placed at the junction of the supraorbital bar with the lateral temporal extension on the affected side to allow for infolding of this extension. The plates are heated in a sterile water bath and then secured to the bar using 4-mm resorbable screws. A second triangular plate is placed on the contralateral side to allow for stable junction of the supraorbital bar with the lateral orbital wall and the lateral forehead (Fig. 15.6).

After reshaping, the supraorbital bar is repositioned in the field and stabilized with a degree of forward advancement that is patient dependent and based on the aesthetic sense of the craniofacial surgeon. Typically, the orbital rim on the affected side is advanced to match the contralateral side using the temporal extension secured to the adjacent temporal bone; the contralateral side is recessed. Overcorrection of the ipsilateral or affected side diminishes the need for reoperation. The frontal bone is reshaped using a combination of bone benders, inner and outer cortex burring, and barrel-stave osteotomies. After remodeling, the native contralateral frontal bone is rotated into position and placed into the advanced ipsilateral frontal area (Fig.€15.7a,b). The bone is then anchored to the supraorbital bar in its new position by securing it to the previously placed plates using 4-mm screws. A series of cuts are made in the native ipsilateral bone, including removal of the bone along the fused coronal suture. The bone is then

a

b

Fig. 15.6â•… Supraorbital bar from patient with right coronal synostosis, showing resorbable plates positioned to create a stable junction of the supraorbital bar with the nasal bone in the midline and with the frontal bones bilaterally.

Fig. 15.7â•… (a) A 6-month-old girl with left coronal synostosis, showing retrusion of the left forehead and supraorbital bar and compensatory right frontal bossing, positioned supine on a horseshoe headholder. (b) Anterior cranial vault reconstruction with left fronto-orbital advancement.

15â•… The Surgical Repair of Unilateral Coronal Synostosis carefully cut to size, rotated, and contoured so that the orientation of the coronal suture closure is horizontal (Fig. 15.7b). This bone is then anchored to the supraorbital bar using the existing plates using 4-mm screws. Following this, the excess bone that was cut off from the caudal aspect of the ipsilateral frontal bone in the region of the fused suture is used to fill the defect on the ipsilateral side between the frontal and parietal bones created by the forward advancement. This is stabilized using a resorbable plate and screws. The wound is extensively irrigated with antibiotic solution, and 0 Prolene (Ethicon, Somerville, NJ, USA) sutures are placed to reapproximate the scalp flaps. The galea is then closed using buried interrupted 3–0 Vicryl (Ethicon, Somerville, NJ, USA) sutures. The scalp is closed using a running, noninterlocking 5–0 Monocryl (Ethicon, Somerville, NJ, USA) suture, and a sterile dressing is applied. The corneal protectors are removed prior to extubation.

15.2.4╇ Hazards, Risks, Avoidance of Pitfalls, and Difficulties Encountered Dural lacerations must be monitored for and repaired to prevent persistent CSF leak. Additional risks include increased blood loss and the need for

blood transfusion intraoperatively, air embolism, infection with the potential for operative management, injury to the brain or globes, pressure sores, and persistent asymmetry requiring further surgery.

15.3╇ Outcomes and Postoperative Course 15.3.1╇ Postoperative Considerations and Complications Immediately postoperatively, patients are managed in the ICU and are given appropriate analgesia to keep them comfortable. As a consequence of periorbital manipulation, the eyelids typically swell shut within 24 hours after surgery; the swelling usually resolves in 3 to 4 days. The patient is discharged from the hospital when eating a regular diet and the eyes are open. Patients are followed until skull growth is complete. In a small percentage of cases, resorbable plates and screws dissolve into a liquid that collects under the skin and sometimes requires reoperation for evacuation.

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16

The Surgical Repair of Metopic Synostosis Philipp R. Aldana and Nathan J. Ranalli

16.1╇ Introduction and Background 16.1.1╇Indications In metopic synostosis, where there is premature fusion of the metopic suture, there is resultant restriction of frontal bone growth laterally, with ridging of the forehead and midline, bitemporal narrowing, and bilateral supraorbital retrusion. This results in a triangular forehead, prominent midline sagittal ridge, and shortening of the anterior cranial fossa1 (Fig. 16.1 and Fig. 16.2). Increased intracranial pressure (ICP) is an absolute indication for surgical repair. The common indication for surgery is defor-

Fig. 16.1â•… Bird’s eye view of cranium with metopic synostosis and trigonocephalic configuration. Patent coronal, sagittal, and lambdoid sutures, anterior and posterior fontanelles, and fused metopic suture are labeled.

138

mity correction. Although cognitive impairment has been associated with craniosynostosis, the pathogenesis of this is unclear, and surgical repair to avert or improve cognitive impairment is currently not an acceptable indication.

16.1.2╇Goal The goal is to achieve the best possible and durable correction of deformity, at the lowest risk for the patient.

Fig. 16.2â•… Anterior view of cranium with metopic synostosis. Patent sagittal and coronal sutures and fused metopic suture with bifrontal narrowing are labeled.

16â•… The Surgical Repair of Metopic Synostosis

16.1.3╇ Alternate Procedures For infants less than 6 months of age, an option is endoscopic synostectomy followed by prolonged application of a molding helmet (further discussed in Chapter 18). For very mild cases, simple observation may be an option. The addition of steel wire springs to distract the midline frontal orbital area to correct hypotelorism has been described by some but is not in widespread use.2

16.1.4╇Advantages The advantage of open repair of metopic synostosis over the endoscopic techniques includes definitive and rapid correction of the deformity in the immediate postoperative period. The techniques can be employed, with minor modifications, at any age of patient. In addition, the open techniques do not require the patient to have a prolonged application of a molding helmet. In patients with ICP, the open approach allows immediate relief of pressure.

16.1.5╇Contraindications The contraindications are identical to those for any patient undergoing a craniotomy.

16.2╇ Operative Detail and Preparation 16.2.1╇ Preoperative Planning and Special Equipment A preoperative, computerized tomographic (CT) scan of the brain with three-dimensional (3D) reconstructions of the skull is performed. This serves to evaluate the anatomy of the frontal bone and orbits as well as a general screen for any intracranial abnormalities. A preoperative surgical plan is generated with the craniofacial surgeon. Ophthalmologic evaluation to rule out papilledema is obtained when increased ICP is suspected clinically or if CT findings are suggestive of increased ICP, such as diffuse copper-beaten pattern, dorsum sella erosion, suture diastasis, or narrowing of the basal cisterns.3 If increased ICP is confirmed, then the need for surgery becomes more urgent and the case is scheduled at the soonest available date. Otherwise, we prefer to time surgery no earlier than 3 months of age so that the infant is physiologically better able to cope with stresses of surgery. Patients are prepared for a blood transfusion, and the family is routinely given the option to donate.

16.2.2╇ Expert Suggestions and Comments These patients are best managed as part of a craniofacial program, which includes an experienced craniofacial surgeon. As part of the informed consent, the surgical goals are discussed with the parents. In cases where the patients present with a prominent metopic ridge without severe trigonocephaly, we encourage conservative treatment and observation, as the bony prominence can improve in appearance over time. In addition, the presence of, or potential for, cognitive delay should not influence surgical decision making, since there is no clear evidence showing that surgical correction of metopic synostosis has any influence on the child’s cognitive ability.

16.2.3╇ Key Steps of the Procedure and Operative Nuances Position and Prep During supine positioning on the horseshoe headrest, the pressure on the patient’s scalp should be distributed evenly to prevent focal alopecia or decubitus ulcers. To prevent the hair from parting down the line of a straight bicoronal incision postoperatively, we instead utilize a wavy or zigzag incision. The preparation of the scalp with antiseptic should extend from behind the bicoronal incision anteriorly and inferiorly to the eyebrows and to the skin of the upper eyelids bilaterally. Betadine Ophthalmic (5% povidone-iodine; Alcon, Fort Worth, TX, USA) is used when prepping near the eyebrows, as are corneal guards. Extending the prep inferiorly will facilitate visualizing the degree of supraorbital advancement at the end of the case, which is an important step in the reconstruction.

Bifrontal Craniotomy The limits of the exposure should include the coronal suture, the nasion and supraorbital rims, and bilaterally, the frontozygomatic suture. Using narrow periosteal elevators, the periorbita is dissected off the supraorbital rim and about 1 cm off the orbital roof bilaterally. Burr holes are placed behind the coronal suture and superior to the pterion as well as approximately 1 cm above the superior orbital rim in the midline. The dura should be stripped carefully in the midline, at the level of the coronal suture, as well as at any areas of the skull that show the copper-beaten inner table. The dura is frequently invaginated in a notch in the metopic suture (metopic notch) at its anterior limit near the nasion, so particular care should be taken when handling the dura during the

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Fig. 16.3â•… Open repair of metopic synostosis illustrating bifrontal craniotomy and removal of supraorbital bar. Burr holes posterior to the coronal sutures, at the keyhole, and in the midline at the inferior aspect of the fused metopic suture, as well as the cut lines for bifrontal craniotomy and supraorbital bar removal, are labeled.

craniotomy in this area.4 Anteriorly, we ensure that about 1 cm of frontal bone is left attached to the superior orbital rim (Fig. 16.3). A sagittal saw is used to create the osteotomy in the orbital roof, proceding from medial to lateral. Gentle retraction is placed on the frontal lobe dura and periorbita for protection. The osteotomy is extended laterally, anterior to the greater wing of the sphenoid. In the midline, the osteotomy is completed anterior to the foramen cecum with a small osteotome. In less severe cases, the supraorbital bar can be left attached to the midline. The temporal lobe dura is protected prior to removal of the lateral aspect of the sphenoid ridge.

Reconstruction The supraorbital bar is molded into a broader shape after drilling some partial-thickness grooves along the inner table to make it more malleable. Alternatively, the supraorbital bar can be split in half at the midline and then reshaped and reattached following placement of rigid fixation. The supraorbital bar is advanced anteriorly by 1 cm and is secured to the skull base using resorbable plate fixation. The frontal bone flap is split down the middle, and each half is rotated and then usually switched sides to obtain a broader forehead. A bone bender is used to shape the frontal bone (radial osteotomies can be made in the bone to facilitate this). The anterior portions of the parietal and temporal bones are also reshaped

to match the edges of the reconstructed frontal bone flap, which is secured with resorbable plates. During the reconstruction phase, we intermittently reflect the scalp flap back over the bony reconstruction to ensure a good cosmetic outcome (Fig. 16.4).

16.2.4╇ Hazards, Risks, Avoidance of Pitfalls Blood Loss The majority of the blood loss occurs during scalp incision and osteotomies. The Bovie with a Colorado tip is used to complete the scalp incision (sparing the pericranium) once the outermost scalp layer is scored with a knife. Electrocautery is also used to help separate the galea from the pericranium. The pericranium is incised with the Bovie along the path of the craniotomy, leaving the pericranium attached to the bone flap. Tranexamic acid can decrease the transfusion rates in craniosynostosis surgery.5

Handling of the Dura Dura should be separated from the inner table as previously described. Dural laceration in the area of the metopic notch must be avoided, as this can result in hemorrhage from the sagittal sinus. Dural coagulation for hemostasis should be judicious, as excessively coagulated dura may inhibit bone regrowth.

16â•… The Surgical Repair of Metopic Synostosis

Fig. 16.4â•… Open repair of metopic synostosis demonstrating reconstruction. Labeled are: frontal bone split down the middle with sides subsequently switched/rotated and radial osteotomies performed to widen the forehead; barrel stave osteotomies cut into the parietal and temporal bones to facilitate reshaping to match the widened frontal bones; and supraorbital bar advanced 1 cm anteriorly.

Optimizing Cosmetic Outcome The degree of advancement of the supraorbital bar and recontouring of the frontal bone as well as the adjacent parietal and temporal bones are all details that require planning with the craniofacial surgeon. The supraorbital bar is advanced at least 1 cm anteriorly.

16.2.5╇ Salvage and Rescue Injury to the superior sagittal sinus anteriorly is addressed first with gentle pressure to control the bleeding. If anterior sagittal sinus injury cannot be controlled with tamponade, then a stick tie around the sagittal sinus with nonabsorbable suture achieves hemostasis easily. Injury to the sagittal sinus more posteriorly is unlikely, as the edges of the anterior fontanelle, although adherent to the dura, are usually not difficult to dissect off the sagittal sinus. Injuries to the sagittal sinus at this level can also be controlled with tamponade; direct repairs of the sinus have been described. Ligation of up to the anterior third of the sagittal sinus can be performed safely, although this should be a maneuver of last resort.

16.3╇ Outcomes and Postoperative Course 16.3.1╇ Postoperative Considerations Blood is drawn for hemoglobin 4 to 6 hours postoperatively and again the following day. Blood transfusions are considered for hemoglobin less than 8 following evaluation of the patient’s physiologic state. Periorbital edema is almost always present between postoperative days 1 and 3 and is usually accompanied by emesis and fever. Fever is the most common postoperative complication following craniosynostosis repair.6 This is rarely infectious in nature and is self-limiting. Since we use absorbable plates for the reconstruction, we uniformly advise the parents to not be alarmed if painless scalp swelling occurs 9 to 12 months following surgery, as this can occur in up to 25% of cases when certain absorbable cranial plating systems are used. This is associated with the period of plate resorption.7

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16.3.2╇Complications

References

Infections

╇1.

Infections can occur rarely following this surgical procedure (less than 2% in one series).6 The management is similar to that of other craniotomy infections. Deep infections may require open débridement and, if osteomyelitis is present, bone flap removal as well as prolonged intravenous antibiotics. In infants, bone flap removal in the face of an infection can result in regrowth of the bone from the native dura. Thus, an adequate period of observation of several months is reasonable prior to planning any secondary reconstructive surgeries.

╇2.

Poor Cosmetic Outcomes Reoperation to correct poor long-term cosmetic outcomes following initial adequate craniofacial reconstruction is uncommon. In one series, 8% of children had regrowth of bony ridge at the metopic suture, requiring a second operation for burring of the metopic ridge.8 Temporal hollowing can also be a reason for reoperation in up to 15% of patients.1

╇3.

╇4.

╇5.

╇6.

╇7.

╇8.

van der Meulen J. Metopic synostosis. Childs Nerv Syst 2012;28(9):1359–1367 Maltese G, Tarnow P, Lauritzen CG. Spring-assisted correction of hypotelorism in metopic synostosis. Plast Reconstr Surg 2007;119(3):977–984 Tuite GF, Evanson J, Chong WK, et al. The beaten copper cranium: a correlation between intracranial pressure, cranial radiographs, and computed tomographic scans in children with craniosynostosis. Neurosurgery 1996;39(4):691–699 Weinzweig J, Kirschner RE, Farley A, et al. Metopic synostosis: Defining the temporal sequence of normal suture fusion and differentiating it from synostosis on the basis of computed tomography images. Plast Reconstr Surg 2003;112(5):1211–1218 Goobie SM, Meier PM, Pereira LM, et al. Efficacy of tranexamic acid in pediatric craniosynostosis surgery: a double-blind, placebo-controlled trial. Anesthesiology 2011;114(4):862–871 Esparza J, Hinojosa J. Complications in the surgical treatment of craniosynostosis and craniofacial syndromes: apropos of 306 transcranial procedures. Childs Nerv Syst 2008;24(12):1421–1430 Aldana PR, Wieder K, Postlethwait RA, James HE, Steinberg B. Ultrasound-aided fixation of biodegradable implants in pediatric craniofacial surgery. Pediatr Neurosurg 2011;47(5):349–353 Aryan HE, Jandial R, Ozgur BM, et al. Surgical correction of metopic synostosis. Childs Nerv Syst 2005;21(5):392–398

17

Syndromic Craniosynostosis Concezio Di Rocco, Paolo Frassanito, Sandro Pelo, and Gianpiero Tamburrini

17.1╇ Introduction and Background Syndromic craniosynostosis (SC) is a heterogeneous group of congenital malformations characterized by morphological and functional anomalies of craniofacial development. SC is estimated to comprise 15% of all craniosynostoses, although its identification is relatively recent. Indeed, the historic classification of craniosynostoses based upon the clinical phenotype was recently refined thanks to advances in molecular genetics, highlighting the crucial role played by the genes encoding for the fibroblast growth factor receptor (FGFR1, FGFR2, and FGFR3). Although this classification is useful for diagnostic purposes, we still have to clarify the impact of these mutations on the development of the brain along with the skull. In fact, “unifying” theories about an integrated development of the skull and the brain are gaining favor.1,2 The management of SC has to deal mainly with: cephalocranial disproportion, intracranial hypertension, impairment of respiratory function (obstructive apnea syndrome), and visual problems. Finally, the midface retrusion, which is the main cause of respiratory problems, also affects maxillofacial development, resulting in dental growth anomalies and cosmetic problems (Fig. 17.1).3 The aims of the surgical treatment are: • To correct the functional and cosmetic anomalies • To restore the normal spatial relationships between the skull and the contained cerebral and vascular structures • To correct the secondary alterations in cerebrospinal fluid (CSF) dynamics and venous circulation • To reorient the abnormal vectors of cranial growth Timing and choice of the surgical procedure result from the complex interpretation of anatomic and functional anomalies and of their variable inter-

reaction in different patients and are essentially dictated by the clinical course of the SC, which is largely unpredictable (Table 17.1). Therefore, the surgical strategy should follow an individually adapted, staged, growth- and age-related, tailormade concept. The surgical treatment consists of: • • • • •

Posterior cranial fossa expansion Treatment of hydrocephalus Frontal advancement Craniofacial advancement Maxillomandibular procedures

17.2╇ Operative Detail and Preparation 17.2.1╇ First Stage: Posterior Expansion According to our protocol, the first stage of cranial vault remodeling is posterior expansion to relieve intracranial hypertension within the first year of life, usually at 2 to 3 months. The young age of the patient contraindicates a complete remodeling of the skull or an anterior expansion, because of the higher rate of relapse at this stage. We recommend performing invasive monitoring of intracranial pressure (ICP) before and immediately after the procedure to confirm the effect of the skull expansion. The relevance of this procedure is variable in different syndromes; in particular, it is more prominent in Crouzon and severe forms of Pfeiffer syndrome. In the absence of intracranial hypertension, cranial vault reconstruction can be postponed to 6 to 8 months of life, with the aim of a more stable surgical result. Thorough neuroimaging evaluation, by means of thin-layer computed tomography (CT) scan and brain magnetic resonance imaging (MRI) with venous angiogram, is mandatory to define the severity of the constriction and to tailor the surgical technique to the patient’s

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144 Section III.Aâ•… Malformations of the Scalp and Skull Table 17.1â•… How syndromic craniosynostosis differs from isolated (nonsyndromic) craniosynostosis Nonsyndromic craniosynostosis

Syndromic craniosynostosis

Genetic anomalies

Rare

About 50% of cases (30% genetic mutations, 16% chromosomal abnormalities)

Clinical phenotype

Constant, well defined

Not ever recognizable, even undefined in the first months of life Consistent risk of diagnostic error and inappropriate surgery

Diagnosis

Clinical

Clinical suspicion + Genetic confirmation

Cerebral anomalies

Rare

Frequent

Natural history

Well known

Unpredictable

Surgery (timing and modalities)

Defined

Undefined

Result of surgery

Predictable

Unpredictable

Prognosis

Excellent

Variable

Follow-up

Very low risk of relapse

Significant risk of relapse; modifications eventually occurring up to the adult age (multidisciplinary follow-up)

condition. When the bone thickness is greater than 1 mm, and the constriction of posterior structures and the compression of major venous sinuses are moderate, we perform a standard posterior cranial vault expansion. A bicoronal stealth incision is used, and the skin flap is dissected away from the periosteal layer in a blunt fashion. The periosteum is left in place in order to minimize the bleeding risk from transosseous vascular channels. Incision of the periosteum is carried out to expose the line of the planned osteotomy. In these cases, craniotomy can be usually performed with a high-speed drill and craniotome. Thereafter, the bone flap is carefully dissected away from the dural layer. A midline suboccipital decompression is performed if Chiari malformation is concomitantly present or if a prominent midline bony ridge impinges on the hindbrain structures (see Special Considerations). The parieto-occipital bone flap is reshaped, if necessary, and any bony ridges or spurs on its internal aspect are shaved off by means of high-speed drill. Finally, it is advanced, exploiting the so-called tongue-and-groove technique, and is fixed in the desired position by means of silk sutures or resorbable plates (Fig. 17.2a–h). In cases of bone thickness less than 1 mm, lattice bone defects, or severe compression of venous sinuses with extensive compensatory venous circulation, we prefer to perform a free-floating occipital flap, thereby avoiding dissecting the bone away from the dura mater. This option enables us to reduce the risk of severe bleeding and of dural tearing and to minimize the opera-

tive time. In such a case, bone rongeurs are preferred for performing the osteotomy.

17.2.2╇ Second Stage: Anterior Advancement The second stage is the anterior advancement, either frontal or frontofacial, to address cosmetic issues and also ocular and respiratory problems. This procedure is usually recommended at 5 to 6 years of age, with the aim of a stable result and reduced risk of relapse because the maxillofacial bone structure growth ends around the seventh year of life, but it can be anticipated in children with severe breathing problems or ocular proptosis, which jeopardizes visual function. We perform a monobloc frontofacial osteotomy (a so-called Le Fort IV osteotomy) along with the placement of internal distractors. We usually harvest a bifrontal bone flap, which is subsequently reshaped. The midface is then mobilized through a Le Fort III osteotomy. Hypertelorism, if present, may be corrected at this stage. Finally, a pair of internal distractors is positioned, fixed posteriorly to the temporal bone and anteriorly to the maxilla. The frontal bone flap is thereafter secured to the orbital bandeau by silk stitches and left “floating” above the midfacial complex (Fig. 17.3a–d). The complex is gradually advanced in order to provide a correct anterocaudal position for the midfacial structures in accordance with the physiological growth pattern.

17â•… Syndromic Craniosynostosis

Fig. 17.1â•… Main problems associated with syndromic craniosynostosis (cranial: red, facial: purple, and mandibular: blue).

17.3╇ Outcomes and Postoperative Course This surgical strategy enables us to deal promptly and effectively with the main issues in SC. The advantages of the posterior expansion are the predictable and stable expansion of the skull, resulting in long-term control of intracranial hypertension, the decompression of the major venous sinuses (though questioned nowadays), and the reestablishment of correct CSF circulation at the craniocervical junction. The main drawbacks are the high blood transfusion rate (80%) and the relatively long operating time (mean 80 minutes). The complications encountered are intraoperative dural tear (10%) and postoperative CSF leak (5%). In our experience, the risk of relapse is 10%, and it is exclusively associated with the presence of a CSF extrathecal shunt device, placed to treat the secondary hydrocephalus (see Special Considerations). Once the excessive ICP is relieved, we can deal with the “anterior” issues. We aim at performing frontal remodeling and midface distraction in a

single procedure, since this approach provides significantly better results in terms of aesthetic and functional outcome than the two-stage procedure.4,5 However, in case of frontal lobe compression or ocular problems, early frontal advancement is indicated. In such a case, the risk of relapse is higher, and a new frontal advancement would be eventually coupled to midface advancement when the patient is older. In case of severe impairment of respiratory function at a young age (under 1 year old), the patient is usually not eligible for midface advancement. In this case, an elective tracheostomy enables us to manage the respiratory issues immediately while awaiting the optimal age for craniofacial advancement. A very young age is a relative contraindication to osteodistraction of the midface. However, an age threshold is not defined, and each case should be examined with a thin-cut CT scan in order to evaluate the thickness of the bony structures. In our experience, the youngest patient receiving frontofacial advancement was 13 months old. Unfortunately, the intraoperative placement of the distractors was complicated by an infraction of the maxilla, which finally evolved into

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146 Section III.Aâ•… Malformations of the Scalp and Skull b

a

d

c

f e

g h

Fig. 17.2â•… (a–h) Surgical steps for posterior cranial expansion.

17â•… Syndromic Craniosynostosis

b

a

c

d

Fig. 17.3â•… (a–d) Surgical steps for frontofacial advancement.

fracture during the distraction phase. A second operation to push back the midfacial complex and stabilize the fracture was required. The distraction was thereafter completed with very good result (Fig. 17.4a–f). To overcome this problem, some authors propose the use of an external device exploiting transfacial pins,6 though burdened by other disadvantages (see Spe-

cial Considerations). In conclusion, the functional and aesthetic benefits of frontofacial distraction are well documented, but these advantages are associated with a significant complication rate, with major morbidity occurring in between 10% and nearly 60% of patients.7 CSF leak remains the most frequent complication, and it is usually managed by external spinal drainage. Some

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148 Section III.Aâ•… Malformations of the Scalp and Skull a

b

c

d

e

f

Fig. 17.4â•… Frontofacial advancement in a baby boy with Crouzon syndrome. (a) Preoperative 3D CT. (b) Postoperative X-ray image. (c,d) Left maxillary fracture. Pictures of the patient (e) before and (f) after osteodistraction.

17â•… Syndromic Craniosynostosis authors propose bringing a pedicle flap of vascularized pericranium under the inferior surface of the frontal lobe to cover the defect of the orbital roof and sealing it with fibrin glue in order to minimize the risk of dural tearing during the distraction period.7

17.3.1╇ Special Considerations Venous Circulation Preoperative radiological workup of SC should include MRI with MR venography to evaluate the venous drainage of the brain. Stenosis of the jugular foramina and subsequent hypertrophy of basal emissary veins are a well-known phenomenon. Other peculiar conditions that might affect the surgical planning should be identified. For example, an association between sinus pericranii and craniosynostoses has been reported, although no formal hypothesis about a common pathogenesis has been formulated. Surgical injury to such a structure during craniofacial reconstruction is potentially lethal, so the preoperative planning should carefully consider this issue.8

Intracranial Hypertension and Hydrocephalus SC is usually characterized by abnormal ICP. This picture results from several factors, in particular cephalocranial disproportion, abnormal venous circulation, and respiratory problems. This issue is usually managed by posterior cranial vault expansion. The concomitant presence of hydrocephalus, which is not necessarily associated, raises concerns about the optimal surgical strategy, as ICP represents the prevalent stimulus to skull growth. Therefore, treatment of hydrocephalus should be reserved for patients showing severe hydrocephalus or active ventricular dilation after cranial vault expansion. If it is not clear that ventricular dilation is progressive and symptomatic, the child should not be treated by extracranial CSF shunting, because shunting can diminish the driving force of the developing brain. Endoscopic third ventriculostomy (ETV) has proven to be a valuable treatment option: it probably will be able to manage the obstructive component secondary to the distortion of the neural structures or crowding of the posterior cranial fossa, without “loss” of intrathecal CSF.9 Consequently, extracranial CSF shunting procedures should be considered as the last treatment option in the event of ETV failure because of their high complication rate (30%) and the associated risk of relapse of the synostosis.

Chiari Malformation (CM) CM in SC is an acquired disorder with a multifactorial pathogenesis,10 mainly resulting from cephalocranial disproportion and abnormal venous circulation. Additionally, intracranial hypertension and hydrocephalus may favor the secondary descent of the cerebellar tonsils into the foramen magnum. Thus, in children with active ventricular dilation, hydrocephalus should be managed as the first step. If CM is evident in the first year of life, it can be managed by coupling a midline suboccipital decompression to the posterior cranial vault expansion. Wide opening of the lateral margins of the foramen magnum is recommended in order to minimize the risk of bone regrowth, whereas the opening of the dura mater is generally not advised because of the risk of severe bleeding from the dural edges secondary to collateral venous circulation. If CM is diagnosed after the cessation of craniofacial growth, a wait-and-see policy can be adopted in asymptomatic cases. If symptoms are present, a classical midline suboccipital decompression with an enlarging duroplasty can be undertaken. In fact, craniocerebral disproportion and venous sinus compression are usually less severe at this stage. Finally, the risk of bone regrowth is lower at this stage.3

Osteodistraction: Devices and Modalities The introduction of osteodistraction techniques, which promote progressive osteogenesis, has overcome the complications resulting from the gap created by conventional monobloc advancement, first described by Ortiz-Monasterio in 1978. The question of the particular type of device (external versus internal) to use for distraction is debated, since the results are similar. The main categories of distraction devices are: internal push-screw type (developed by Cohen et al in 1995), external halo-frame-based pulling type (developed by Polley and Figueroa in 1997), and internal distraction spring or coil (developed by Lauritzen et al in 1998). Each system has its pros and cons, which are beyond the scope of this chapter and are well defined in the literature.11,12 Essentially, external devices offer the advantage of easier application and postoperative management, but they are associated with a poorer quality of life during the distraction period. Thus, they should be reserved for more cooperative patients, namely adolescents and adults. On the other hand, internal devices are better tolerated by younger children. Concerning the distraction modalities, we recommend deferring the start of distraction to approximately 5 to 7 days after

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150 Section III.Aâ•… Malformations of the Scalp and Skull surgery, since protocols starting earlier are associated with a higher risk of complication, in particular CSF leakage. The distraction rate varies from 0.5 to 1 mm per day and is tailored to the particular patient’s condition. At the end of the distraction period, the distractors are left in place for up to 6 months to consolidate the result. Thereafter, a second intervention is required to remove the distractors.

╇5.

References

╇8.

Raybaud C, Di Rocco C. Brain malformation in syndromic craniosynostoses, a primary disorder of white matter: a review. Childs Nerv Syst 2007;23(12):1379–1388 ╇2. Richtsmeier JT, Flaherty K. Hand in glove: brain and skull in development and dysmorphogenesis. Acta Neuropathol 2013;125(4):469–489 ╇3. Tamburrini G, Caldarelli M, Massimi L, Gasparini G, Pelo S, Di Rocco C. Complex craniosynostoses: a review of the prominent clinical features and the related management strategies. Childs Nerv Syst 2012;28(9):1511–1523 ╇4. Adolphs N, Klein M, Haberl EJ, Menneking H, Hoffmeister B. Frontofacial advancement by internal distraction devices. A technical modification for the management of craniofacial dysostosis in early childhood. Int J Oral Maxillofac Surg 2012;41(6):777–782

╇6.

╇7.

╇1.

╇9.

10.

11.

12.

Arnaud E, Di Rocco F. Faciocraniosynostosis: monobloc frontofacial osteotomy replacing the two-stage strategy? Childs Nerv Syst 2012;28(9):1557–1564 Ahmad F, Cobb AR, Mills C, Jones BM, Hayward RD, Dunaway DJ. Frontofacial monobloc distraction in the very young: a review of 12 consecutive cases. Plast Reconstr Surg 2012;129(3):488e–497e Dunaway DJ, Britto JA, Abela C, Evans RD, Jeelani NU. Complications of frontofacial advancement. Childs Nerv Syst 2012;28(9):1571–1576 Frassanito P, Massimi L, Tamburrini G, Caldarelli M, Pedicelli A, Di Rocco C. Occipital sinus pericranii superseding both jugular veins: description of two rare pediatric cases. Neurosurgery 2013;72(6):E1054–E1058 Di Rocco F, Jucá CE, Arnaud E, Renier D, Sainte-Rose C. The role of endoscopic third ventriculostomy in the treatment of hydrocephalus associated with faciocraniosynostosis. J Neurosurg Pediatr 2010;6(1):17–22 Di Rocco C, Frassanito P, Massimi L, Peraio S. Hydrocephalus and Chiari type I malformation. Childs Nerv Syst 2011;27(10):1653–1664 Meling TR, Høgevold HE, Due-Tønnessen BJ, Skjelbred P. Midface distraction osteogenesis: internal vs. external devices. Int J Oral Maxillofac Surg 2011;40(2):139–145 Pelo S, Gasparini G, Di Petrillo A, Tamburrini G, Di Rocco C. Distraction osteogenesis in the surgical treatment of craniostenosis: a comparison of internal and external craniofacial distractor devices. Childs Nerv Syst 2007;23(12):1447–1453

18

Minimally Invasive Craniosynostosis Surgery David F. Jimenez and Constance M. Barone

18.1╇ Introduction and Background 18.1.1╇Indications The management of congenital deformities presents a great challenge to treating surgeons and pediatric teams. The management of craniosynostosis certainly falls into this realm. The surgical treatment of this condition has undergone many changes since its original inception in the 1890s.1 The goal has always been to normalize the cranial and facial shape and the proportions of the patient’s craniofacial skeleton and soft tissues. The introduction of calvarial vault remodeling techniques in the 1970s led to many more patients being treated by craniofacial teams, in a multidisciplinary fashion, with very good results.2–5 However, outcomes remained inconsistent, and these procedures were associated with significant trauma, blood loss, and transfusion rates. Our goals have been to use the concept of a rapidly developing and growing infant brain to correct the congenital deformity ultra-early by using endoscopically assisted, minimally invasive techniques. Careful analysis of our outcomes during the last 17 years indicates that these procedures produce excellent and long-lasting results.6–10 Advantages include short surgical times (an hour or less), significantly less blood loss, and transfusion rates varying between 0% and 7%. Hospitalization stays average one night, and thus costs are markedly decreased. However, most important, correction and normalization of the patient’s deformities occur in a progressive and sustained fashion. Our selection criteria include most infants under the age of 6 months who present with isolated or multiple nonsyndromic craniosynostoses. Contraindications include treatment of children who have previously undergone surgery and those over 9 months of age.

18.2╇ Operative Detail and Preparation Significant preparation and precautions should be taken, as with any other pediatric operation, and are not detailed in this chapter. Nevertheless, competent anesthesiology and surgical staff support are necessary for a successful operation. Sagittal synostosis patients are placed in the sphinx position, taking care to use a precordial Doppler, on an appropriately padded beanbag. Patients with coronal or metopic synostoses are placed on a padded cerebellar horseshoe head rest. Endoscopes used include 0° and 30° rigid rod lens Hopkins (Karl Storz, Tuttingen, Germany) systems. Endoscopic bipolar forceps (Karl Storz) are particularly useful in obtaining adequate coagulation during metopic and sagittal operations. In collaboration with the Storz company, we developed a custom-made hand-held endoscopic dural retractor (J&B Dural Retractor, Karl Storz), which enables adequate coagulation of the bone and diploë following the osteotomies (Fig. 18.1). After surgery, custom-made cranial molding orthoses (Orthoamerica, Orlando, FL) are used to mold the cranial vault appropriately over the ensuing year (Fig. 18.2). Although these orthoses require close and frequent supervision, the ultimate excellent result typically warrants their use.

18.2.1╇ Sagittal Synostosis The patient is placed in the modified prone position and is carefully monitored for venous air embolism (VAE). After appropriate antibiotics are given and the head is properly prepped, two small (2 to 3 cm) incisions are made across the midline, one being immediately in front of the lambda and the

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152 Section III.Aâ•… Malformations of the Scalp and Skull

Fig. 18.1â•… The Endoscopic J&B Dural Retractor has been specifically designed to protect the scalp and dura during osseous coagulation. The insulated blades can be opened at different widths and angles while an endoscope is inserted to enable full visualization of the surgical field.

second behind the anterior fontanelle (Fig. 18.3). In order to minimize blood loss, a needle-tip monopolar Bovie (Valley Lab, Valley Forge, PA) is used at a 15-W blend setting. Using the Bovie, a dissection plane is developed between the galea and the pericranium, a maneuver that ensures minimal blood loss (Fig.€18.4). A rhinoplasty lighted retractor can then be used in conjunction with a 0° endoscope to achieve this maneuver. Anterior and posterior osteotomies are made with 5-mm Kerrison rongeurs at each incision site. A wedge of bone is cut between the anterior incision and the anterior fontanelle. This action allows the placement of a 30° rigid endoscope (aimed at the undersurface of the overlying skull) in order to develop a plane between the dura and the bone, extending from lambda to anterior fontanelle (Fig. 18.5). Once the calvaria is isolated, paramedian osteotomies are made with either Mayo scissors (for thin infant skull) or Storz bone craniosynostosis scissors. The width of the osteotomy is inversely proportional to the age of the infant (ranging between 2 and 6 cm). Wedge osteotomies are made bilaterally at each incision and extend toward the squamosal suture. Care is taken to avoid making the osteotomies too close to the coronal or lambdoid sutures

Fig. 18.2â•… Artistic representation of a child with right coronal craniosynostosis and ipsilateral frontal plagiocephaly. The orthosis prevents further displacement of the bossed left frontal area while allowing the recessed right frontal bone to move forward and inferiorly. This process enables correction of associated vertical dysmorphism and supraorbital rim recession correction.

18â•… Minimally Invasive Craniosynostosis Surgery

Fig. 18.3â•… Diagram showing the location of the scalp incisions for treating sagittal craniosynostosis. A helmet is used postoperatively to help mold the head into a normocephalic shape.

Fig. 18.4â•… Endoscopic view of dissection of the subgaleal plane. A retractor elevates the scalp as the loose areolar tissue plane is developed and carefully dissected using a needle-tip Bovie. Care is taken to develop this plane above the pericranium in order to minimize blood loss.

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154 Section III.Aâ•… Malformations of the Scalp and Skull

Fig. 18.5â•… Endoscopic view of the area of dissection below the stenosed sagittal suture and above the dura. An insulated suction tip is used to dissect the epidural plane, and a 30° endoscope affords excellent visualization of the surgical interface.

and risk creating a durotomy. Bone hemostasis is obtained with the use of a suction/monopolar unit (Valley Lab, Valley Forge, PA) set at 60 W. Further and final hemostasis is achieved with Surgiflo (Johnson & Johnson, New Brunswick, NJ).

18.2.2╇ Coronal Synostosis A small 2 to 3 cm incision is made at the stephanion over the stenosed coronal suture (Fig. 18.6). Subgaleal dissection, using a monopolar with a needle tip, is developed medially toward the anterior fontanelle and laterally to the squamosal suture (posterior to the pterion). A pediatric craniotome is used to create a 7-mm burr hole at the incision. The burr hole is elongated with Kerrison rongeurs, allowing the placement of a 30° rigid endoscope under the bone (Fig. 18.7). The dura is dissected from the overlying bone and a 6-mm osteotomy made with bone-cutting scissors. In a similar fashion, the bone is separated from the dura down to the pterion and squamosal suture. Because the dura is closely adherent to the coronal suture closest to the pterion, the 6-mm osteotomy is directed posteriorly and away from the pterion. Hemostasis is obtained with suction electrocautery and Surgiflo, as previously mentioned.

18.2.3╇ Metopic Synostosis A small 2 to 3 cm incision is made on the scalp behind the hairline and in front of the anterior fontanelle, over the stenosed metopic suture (Fig. 18.8). The subgaleal plane is developed between the anterior fontanelle and the nasion, using a rhinoplasty lighted retractor and needle-tip electrocautery. A 7-mm burr hole is made with a pediatric perforator, and the burr hole is extended longitudinally along the metopic suture. A no. 1 Penfield dissector enables separation of the dura and the bone for the short distance to the anterior fontanelle. A 6-mm osteotomy is made with disk-cutting rongeurs (Acromed 2028-68, Raynham, MA, USA; Fig. 18.9). Attention is directed to developing the epidural space toward the nasion using a 30° angled rigid endoscope for visualization. Typically, a number of bridging perforating veins extending from the sagittal sinus are encountered. These veins can bleed profusely and should be directly cauterized using endoscopic straight bipolar forceps (Karl Storz, Germany). Elevation of the head is useful in controlling bleeding and improving visualization, provided that a careful watch for venous air embolism is kept with a precordial Doppler. The osteotomy is taken all the way down to the nasofrontal suture. As previously described, final hemostasis is obtained with suction monopolar electrocautery and Surgiflo.

18â•… Minimally Invasive Craniosynostosis Surgery

Fig. 18.6â•… Artistic rendition of location of scalp incision and amount of bone removed for the treatment of coronal synostosis. Care must be taken to extend the osteotomy all the way down to the squamosal suture but behind the area of the stenosed coronal suture.

18.3╇ Outcomes and Postoperative Course The majority of patients are kept in hospital overnight and are discharged the following morning. The minimally invasive techniques are not associated with significant bruising or swelling, and pain is controlled with acetaminophen/ibuprofen and intravenous morphine as needed. The patients do not have postoperative fevers, so extensive and invasive work-ups are not necessary. The incisions are closed with galeal 4–0 Monocryl (Ethicon, Somerville, NJ, USA) and Steri-Strips (3M, St. Paul, MN, USA). Orthoamerica’s infrared Star Scanner is used to scan the baby’s head so that a custom-made cranial orthosis can be manufactured to help mold the head into a normal shape. Several orthoses are

needed during the primary postoperative treatment period (6–12 months), given the rapid growth of the infant’s head. Although the helmet is considered burdensome and hard on the patients by some, our team’s experience with over 2,000 helmets proves that the children and parents adapt well to the constant use and wear of the helmets. We believe that the use of helmets following surgery is crucial and paramount in obtaining satisfactory and long-lasting results. Careful anthropometric analysis of our patients, over a 17-year period, indicates that these procedures are associated with excellent results and outcomes. For sagittal synostosis, complete correction of scaphocephaly with long-lasting results is obtained in 87% of the patients. For coronal patients, more than half achieve complete correction of vertical dysmorphism, with the remainder of the patients having minimal asymmetry. Likewise, there

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156 Section III.Aâ•… Malformations of the Scalp and Skull

Fig. 18.7â•… Exposure for endoscopic surgery of a right coronal synostosis using a rhinoplasty lighted retractor via a 2-cm incision placed halfway between the anterior fontanelle and the ipsilateral pterion. A needle-tip Bovie is used to develop the subgaleal plane.

Fig. 18.8â•… Illustration shows location of the scalp incision over the midline and behind the hairline. The osteotomy extends from the anterior fontanelle to the nasion. Postoperatively, the helmet allows lateral and forward expansion of the frontal lobes and bones, while holding the prominent midline in place.

18â•… Minimally Invasive Craniosynostosis Surgery

Fig. 18.9â•… Endoscopic view of the midline craniotomy located between the two frontal bones. A suction/dissection instrument is used to depress the dura and to allow visualization of the epidural space. The osteotomy is extended all the way down to the nasion.

are high correction levels of mid-sagittal imbalance and nasal deviation. We are extremely pleased with the results of treating trigonocephaly associated with metopic synostosis. Most patients obtain complete normalization with no residual evidence of preoperative deformities. Complications have been minimal, with most occurring early in our series. Small ossification defects (N = 8), dural tears (N = 6), and incision infections (N = 4) have occurred in the total cohort of patients (N >€500). The patients who have failed to correct fully or adequately can be traced to an improperly manufactured/fitted helmet or to parental noncompliance. In summary, treating infants with craniosynostosis at a very early age, using the aforementioned minimally invasive endoscopic-assisted techniques, is associated with excellent outcomes and minimal morbidity. This option should be considered by craniofacial teams caring for these patients when they present or are referred at a young age.

╇3. ╇4.

╇5.

╇6.

╇7.

╇8.

╇9.

References Lannelongue M. De la craniectomie dans la microcéphalie. Compte Rendu Acad Sci 1890;110:1382–1385 ╇2. Knoll BI, Shin J, Persing JA. The bowstring canthal advancement: a new technique to correct the flattened supraorbital rim in unilateral coronal synostosis. J Craniofac Surg 2005;16(3):492–497 ╇1.

10.

Marchac D. Radical forehead remodeling for craniostenosis. Plast Reconstr Surg 1978;61(6):823–835 Marchac D, Renier D, Broumand S. Timing of treatment for craniosynostosis and facio-craniosynostosis: a 20-year experience. Br J Plast Surg 1994;47(4):211–222 Persing JA, Jane JA, Delashaw JB. Treatment of bilateral coronal synostosis in infancy: a holistic approach. J Neurosurg 1990;72(2):171–175 Jimenez DF, Barone CM, McGee ME, Cartwright CC, Baker CL. Endoscopy-assisted wide-vertex craniectomy, barrel stave osteotomies, and postoperative helmet molding therapy in the management of sagittal suture craniosynostosis. J Neurosurg 2004;100(5, Suppl Pediatrics):407–417 Jimenez DF, Barone CM. Multiple-suture nonsyndromic craniosynostosis: early and effective management using endoscopic techniques. J Neurosurg Pediatr 2010;5(3):223–231 Jimenez DF, Barone CM. Endoscopic craniectomy for early surgical correction of sagittal craniosynostosis. J Neurosurg 1998;88(1):77–81 Jimenez DF, Barone CM. Early treatment of anterior calvarial craniosynostosis using endoscopic-assisted minimally invasive techniques. Childs Nerv Syst 2007;23(12):1411–1419 Jimenez DF, Barone CM. Early treatment of coronal synostosis with endoscopy-assisted craniectomy and postoperative cranial orthosis therapy: 16-year experience. J Neurosurg Pediatr 2013;12(3):207–219

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19

External Distraction for Frontofacial Advancement Richard D. Hayward and David J. Dunaway

19.1╇ Introduction and Background 19.1.1╇Goals The frontofacial advance (FFA) or monobloc procedure was introduced by Ortiz-Monasterio1 as a method for dealing in one operation with the three most serious problems that can affect those born with a craniosynostosis-associated syndrome (Apert, Crouzon, or Pfeiffer, for example): raised intracranial pressure (ICP), by enlarging the cranial volume; corneal exposure, by advancing the orbital rims; and upper airway obstructions, by advancing the maxilla (Fig. 19.1). Although the frontofacial complex (FFC) is moved as a single entity, its separation from the remainder of the cranium and the skull base usually requires the detachment of the frontal bones from the supraorbital bar. This provides the access necessary to allow the transverse osteotomy cut to be made across the anterior skull base that, together with osteotomies to the vomer, the medial and lateral orbital walls, the anterior orbital floor (along the line of the inferior orbital fissure), and the pterygoids, allows the maxilla, the orbital rims, and the nose to be mobilized in one piece. The reassembled FFC can then be moved to its new position by one of two methods: by immediately advancing it the required distance and maintaining it there with bone grafts and screws and plates (metallic or absorbable), or by using postoperative distraction. Retention of the distraction apparatus once the desired movement has been achieved provides sufficient splintage of what is an essentially unstable situation to allow bony consolidation.2

19.1.2╇Advantages A particular problem with the perioperative advance and stabilization of the FFC is the limitation placed upon the amount it can be moved by the soft tissue

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envelope of facial muscles, skin, and other tissues with which it is surrounded. The gradual advance provided by distraction reduces this problem and also avoids the extra dissection required for access to the various sites needed for rigid fixation. Bradley3 and his colleagues have also described how combining the monobloc with distraction can lead to a decrease in the complication rate (in particular cerebrospinal fluid [CSF] leaks) associated with immediate rigid fixation. The monobloc can be further refined by removing a wedge of bone from the mobilized frontonasal region of the FFC and dividing what remains below in the midline: a facial bipartition.4 Closing the gap this produces by rotating medially both halves of the face reduces both hypertelorism and any lateral downward cant of the orbits while widening the maxilla and bending the face in a way that changes its coronal axis from concave to convex5—all maneuvers particularly useful in correcting the characteristic facial deformity of Apert syndrome6,7 (Fig. 19.2a,b). The distractors used to advance the FFC fall into two broad groups: internal and external. Internal distractors are essentially ram-screw devices whose baseplates are fixed to each side of the bone cuts. When the shaft of the distractor rod connecting them is rotated, the mobilized segment is pushed forward or backward.8 For a monobloc advance, the anterior baseplates are located in the lateral frontal and zygomatic areas, while the posterior plates are fixed to the skull behind the craniotomy. The disadvantage of this system is the tendency (particularly in the younger child) for such laterally positioned distraction forces to push the sides of the face forward at the expense of the center and produce an unwanted degree of central concavity. This can be offset to some extent by attaching the moving part of the system not to the facial bones themselves but to a Steinmann pin passed horizontally through the face so that it can be pushed forward as a whole. External distractors pull, rather than push, the mobilized bone segment using wires attached to

19â•… External Distraction for Frontofacial Advancement a

b

c

d

Fig. 19.1â•… Soft tissue and bone images of a 2-year-old child with Crouzon syndrome (a,b) pre and (c,d) postmonobloc distraction.

plates screwed to whichever part of the (mobilized) FFC the surgeon wishes. A typical combination includes attachment bilaterally to the fronto-orbital ridge and the maxilla; the more midline the placement, the more the tendency to “pull out” any pre-existing central facial concavity. The wires are brought out through the skin and are connected to a frame fixed by metallic or ceramic-tipped pins to the

patient’s head. The frame is so constructed that, by turning a screw on each side, it can be lengthened in the anteroposterior (AP) direction and thus pull the FFC forward. In our practice, we favor external distraction for the FFC using the RED frame (KLS-Martin, Jacksonville, FL, USA; Fig. 19.3); we have described our experience with regard to functional outcomes,9

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160 Section III.Aâ•… Malformations of the Scalp and Skull a

b

Fig. 19.2â•… Facial bipartition: operative photos. (a) Midline wedge of bone removed from between the orbits. (b) The orbits brought together.

separate components (and sometimes in two stages): the fronto-orbital segment as a conventional frontoorbital advance (FOA) and the maxilla as a (subcranial) Le Fort III, again with or without distraction.12–15 There is evidence in the literature to show that this approach has a lower complication rate than monobloc distraction,6 although, as already mentioned, Bradley and coworkers3 reported that combining the monobloc with distraction led to a decrease in their complications. It has been our experience, however, that the cosmetic results of the monobloc are superior. The FOA plus Le Fort III can leave the patient with an unsightly lengthening of the nose due to forward rotation and descent of the Le Fort III segment during distraction. This movement also increases the height of the orbits and can produce unfavorable periocular changes. The monobloc, by keeping the orbital rims intact, avoids these disadvantages. Fig. 19.3â•… A 12-year-old boy with Crouzon syndrome approaching the end of the consolidation period following a monobloc procedure with external distraction using the RED frame.

incidence of relapse,10 and its use in the very young11 and for the management of Apert syndrome.7

19.1.3╇ Alternative Procedures The monobloc, with or without distraction, by definition leaves the patient with a potential communication between the (contaminated) nose and the (sterile) frontal extradural space. It is for this reason that some craniofacial units prefer to advance the FFC as two

19.1.4╇Contraindications The monobloc distraction procedure represents a formidable clinical “journey” for the patient, with periods of up to 6 months with the distraction device in place being recommended by some craniofacial centers. This means that it is suitable only for those who are able to tolerate it, which a child or adolescent with severe learning difficulties may be unable to do. For those with definite functional issues (advancing corneal exposure, for example), for whom some form of surgery is mandatory but who are unable to tolerate the distraction process, alternative operations in which the necessary reconstruction can be achieved as a “one-off” with immediate bony stabilization will need to be considered.

19â•… External Distraction for Frontofacial Advancement

19.2╇ The Monobloc Frontofacial Advance Using External Distraction 19.2.1╇Indications As will become apparent, the overlap between the timing and the indications for monobloc surgery is broad enough for both topics to be considered together. As the majority of craniofacial syndromes result from gene mutations, usually involving the fibroblast growth factor receptor (FGFR) cascade, it should be no surprise that they continue to exert their ill effects for as long as the cranial and facial skeletons are growing. It is this phenomenon that is responsible for the tendency for the results of reconstructive operations to drift over time toward their preoperative state despite what appeared at surgery to have been a satisfactory result. The degree to which this process (which is not to be confused with relapse due to failure of bone grafts or plates and screws or any injurious effects of the procedure itself) occurs is influenced by the severity of the gene’s phenotypic expression and the age at which the surgery is performed. Thus it is seen most in the severely affected child being operated upon at a young age whose craniofacial growth is proceeding rapidly;10 it will be less of an issue in a more mildly affected child whose growth is nearly complete. This has important implications for the timing of surgery. If the result of craniofacial surgery on a child with syndromic synostosis is to be stable into adulthood, it should ideally be postponed until the most active growth phase of the area being operated upon (the fronto-orbital region or the maxilla, for example) has been completed, unless a particular functional complication demands earlier intervention. This means that, in practice, the majority of children with Apert syndrome and the more severe forms of Pfeiffer and Crouzon syndromes may need several procedures during their early years to treat such functional issues as raised ICP, exorbitism, and airway obstruction, as well as the psychological problems related to their appearance (from teasing, for example). This is in contrast to more mildly affected children (with Saethre-Chotzen and Muenke syndromes, for example), for whom reversion is less of an issue even after early surgery. As a general rule, the older the patient, the more likely is cosmesis to be the main indication for surgery. In the very young (less than 3 years old but occasionally as early as 1 year old11), severe corneal exposure (and the desire to avoid the complications of long-term tarsorrhaphies) and upper airway obstruction (in an attempt to avoid long-term tracheotomy) have been our indications for monobloc

surgery. Raised ICP alone is best dealt with (in the absence of hydrocephalus requiring some form of CSF diversion) by a posterior cranial vault expansion using springs.15 Although some units still recommend an early FOA for all patients with syndromic craniosynostosis to control either actual or predicted raised ICP, our policy (in those cases severe enough to be likely to require monobloc surgery at some stage) is to avoid a procedure whose cosmetic results (in this more extreme situation) are unimpressive and that will inevitably complicate the frontal dissection needed for a later monobloc. The logical conclusion to be drawn from this is that to achieve a result that will remain stable over many years, monobloc surgery should be postponed until all cranial and facial growth has been completed: the late teenage years. Clearly such a policy will be unacceptable for many children, particularly those whose already precarious hold on education in mainstream schools may be further weakened by the psychological impact of their unusual appearance. The various components of the craniofacial skeleton each have growth patterns of their own. It has been calculated that the cranio-orbito-zygomatic skeleton reaches more than 85% of its adult size by the age of 5 years.16,17 Our policy, based more on clinical observation than on measurement, is to assume that if the forehead and supraorbital region are in a satisfactory configuration at around 10 years of age, they are unlikely to need further correction, and essentially cosmetic reconstructions after that can focus more on the maxilla and mandible, where growth will continue until secondary dentition is complete: the mid to late teens. In brief, we perform a monobloc with external distraction on very young children only when they present with exorbitism sufficient to threaten the corneas and/or upper airway obstruction severe enough to require tracheotomy, and when they accept the need for further craniofacial procedures (possibly including repeat monobloc distraction) in the years to come. In older children, in whom the indications are more likely to be cosmetic, we often choose a timing that precedes a child’s move to the next rung on the schooling ladder. At age 10 and over, a child who needs both frontal and maxillary correction will benefit from monobloc distraction with (for the younger members of this cohort) acknowledgment that he or she will likely need a Le Fort I (alveolar) advance (with or without mandibular surgery) when they are older in order to achieve satisfactory dental occlusion. Non-hydrocephalus-associated raised ICP occurring at any age and uncomplicated by ophthalmic or airway problems is best treated with a vault expansion that avoids the frontal region.

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19.3╇ Operative Detail and Preparation A detailed description of the basic procedure has been provided by Posnick.18 What follows here are some of the adjustments (anaesthetic, plastic, and neurosurgical) we have made to the basic technique in an attempt to lower morbidity and to improve results. Our emphasis is on those elements of most concern to the neurosurgeon.

19.3.1╇ Preoperative Planning Anesthesia Craniofacial surgery should never be undertaken without the input of pediatric anesthesiologists19 experienced in the pre-, intra-, and postoperative care of children who may already have an obstructed airway, raised ICP, and (because of anomalous cranial venous drainage20,21) an enhanced risk of major hemorrhage during the procedure. An example of their preoperative role is their input to the decision whether a child with an obstructed airway about to undergo frontofacial surgery should have a preliminary tracheotomy (discussed subsequently). General anesthesia for a patient with a severe facial deformity may call for fiberoptic intubation, an essential skill for the craniofacial anesthesiologist. The circulating blood volume of a young child is small, and losses that an older patient can cope with can lead to a swift circulatory collapse. A fail-safe approach is always to be ahead, rather than behind, with blood loss. Large-volume transfusions (one circulating blood volume or more) will interfere with coagulation; immediate access to fresh frozen plasma, platelets, and other clotting factors is essential. We have found that the use of cell salvage has significantly reduced donor exposure of our patients during monobloc surgery. Correct positioning of the patient is particularly vital in craniofacial operations, and the anesthesiologist has an important role in this. A head-up tilt with no obstruction of neck veins is essential to reduce intracranial venous hypertension, although such a position will open the patient to the (in our experience) very small risk of air embolism. During the surgery, there are many opportunities for the endotracheal tube to be damaged or dislodged. To reduce this risk, we use an armored tube held in position by a wire that encircles first the tube and then (intraorally) the mandible.

Tracheotomy versus No Tracheotomy Children having a monobloc distraction predominantly for airway obstruction tend to be very young (< 3 years) in whom a tracheotomy is already indicated (or has already been performed) due to failure of such alternative procedures as adenoidectomy and nasopharyngeal prong insertion. The aim of the monobloc, therefore, is to prevent the need for longterm tracheotomy, with all its attendant problems of possible blockage and interference with speech development and feeding. As a general rule, we avoid tracheotomy wherever possible in the older (> 3 years) child (maintaining airway patency in the immediate postoperative period with bilateral nasopharyngeal stents that are removed after one week—see below), while for the younger child the tracheotomy is performed a week or so before the distraction monobloc, retained until 2 or 3 months have elapsed following removal of the frame, and then the child’s airway patency is assessed by our otorhinolaryngologist (ORL) colleagues with a microlaryngobronchoscopy (MLB). In our study of monoÂ� bloc distraction in the very young,11 it proved possible to remove the tracheotomy in six of nine children in whom it had been needed for severe airway obstruction prior to the operation.

Antibiotics Our present policy is for a weight-appropriate dose of amoxicillin/clavulanic acid to be administered intravenously during induction of anesthesia and continued by the same route for one week.

19.3.2╇ Key Steps of the Procedure Incision Access Access to large areas of the skull and face are often required in craniofacial surgery. A scar on the head is best hidden if the hair lies across it, rather than being parted by it, as with the “classic” neurosurgical incision, which follows the line of the coronal sutures downward into the temporal region. Many units employ a zigzag incision to provide both hair cover for the scar and the degree of skin stretch needed when the skull vault has been expanded. We favor a bicoronal incision that has its center just behind the hairline and that then falls in a gentle curve to behind each ear before angling forward just above the tragus. This provides access to the entire skull and, thanks to the pliant skin of the child, to the tissues of the face as low as the floor of the orbits.

19â•… External Distraction for Frontofacial Advancement The hair of a young child need not be removed. For an older child with thick hair, we take a 1-inch (25-mm) strip only (using clippers rather than a razor in order to avoid infection-encouraging damage to the skin).

Tumescent Solution For many years we have injected a large (“tumescent”) volume of a solution containing a long- and a short-acting local anesthetic, a steroid, epinephrine, and hyalase into the proposed incision, the skin flaps, and the tissues of the face. Not only have we found that this reduces postoperative swelling, but also it has (in children undergoing surgery for unisutural synostosis) shortened hospital stay.22

Technical Differences Between the Very Young and the Older Patient The monobloc procedure is essentially the same in infants and adults, but each age group poses its own difficulties for the surgeon. The relatively small circulating blood volume of infants and young children necessitates meticulous hemostasis at every stage. The calvarial and facial bones of younger children are relatively thin and have much less tensile strength than those of adults and older children. Great care needs to be taken when mobilizing the frontofacial segment in order to avoid inadvertent fractures. Osteotomies must be fixed without tension, and particular care must be taken to find fixation points for the distractor plates strong enough to withstand the forces to which they will be subjected. Despite this, however, the monobloc osteotomies are generally technically more straightforward in young children than in adults. The thinner bones divide easily, and, because facial height in young children is proportionally less, the access needed to perform the osteotomies is also better.

The Facial Dissection All the soft tissue dissection needed for the mono� bloc osteotomy should be performed before any bony cuts are made. The frontal periosteum should be raised as a separate layer to the skin in order to preserve the supraorbital vessels and nerves. It will be used later in the procedure to close off the nasal from the cranial cavities, as discussed subsequently. Laterally, the plane of the coronal flap should be kept deep to the superficial layer of the deep temporal fascia to avoid damage to the frontal branch of the facial nerve. This is particularly important for the exposure of the zygomatic arch. Once the lateral orbital wall has been exposed, the dissection is con-

tinued along the orbital floor and the inferior orbital rim. It is completed by continuing inferiorly along a subperiosteal plane behind the zygoma to reach the posterior maxilla and lateral pterygoid plate. In the midline, the dissection is extended downward to expose the nasal bones and medial orbital walls. The dissection here is taken sufficiently posterior to the lacrimal duct to leave the medial canthal tendon intact and is continued until it joins the previously completed orbital floor dissection. The last phase of soft tissue work is required, not for the monobloc osteotomy itself, but for the subsequent placement of the distractor fixation plates. It is also needed in a facial bipartition for the inferior bone cuts. It starts with an intraoral upper labial sulcus incision, through which the buttress of bone around the nasal pyriform fossa can be exposed.

The Craniotomy The craniotomy component of the monobloc is needed for access to the anterior skull base and must therefore be generous enough to allow this with minimal dural retraction. The frontal bone may also require reshaping as part of the operation, particularly if there has been a previous FOA. When planning the craniotomy, the neurosurgeon must take both these factors into account. It may well be that the anterior parietal region has a more agreeable contour than the frontal and should, therefore, be included in the flap. The superior cut should ideally be at a point on the vertex where the frontal bone has passed from the vertical to the horizontal. Failure to do this will result in an unsightly step appearing in the forehead as the frontofacial segment is pulled forward. In brief, as a general rule, a bone flap that is too small is more likely to interfere with achieving a satisfactory result than one that turns out to be too generous. Cutting the flap itself can be made more difficult by scarring from previous surgery and by the abnormal internal bony contours of the skull, both of which can increase the risk of producing a dural tear.

Guiding the Osteotomies The monobloc procedure cleaves the entire facial skeleton from the skull base. It is essential to make sure that all necessary bone cuts have been successfully completed before trying to mobilize the monobloc segment in order to minimize the risk of fracturing it. Although those around the orbits, zygoma, and anterior skull base are carried out under direct vision, the division of the nasal septum and the pterygomaxillary disjunction are performed blind and rely on the surgeon’s knowledge of anatomy as well as his or her sense of proprioception. Where the anatomy is

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164 Section III.Aâ•… Malformations of the Scalp and Skull known to be more abnormal than usual, neuronavigation techniques can be helpful.23 We perform the osteotomies in the following order. 1. The zygomatic arch is divided close to the body of the zygoma. The arch is wide and thick at this point, and the greater surface area of the osteotomy provides favorable conditions for distraction callus formation and subsequent ossification. 2. Next, the lateral orbital wall is divided with a reciprocating saw. In patients with short lateral orbital walls (often seen in Apert syndrome), care must be taken to keep the osteotomy sufficiently anterior to prevent the saw from drifting into the middle cranial fossa and damaging the temporal lobe. 3. The orbital floor osteotomy is completed with a reciprocating saw and 7-mm straight osteotomes. 4. The orbital and nasal roof/anterior cranial fossa floor osteotomy can now be made. Careful attention to the position and angulation of the reciprocating saw blade is essential. In the midline the blade must pass anterior to the crista galli (the foramen cecum makes a useful aiming point) to prevent tearing the dura, where it is often tightly attached here, while for the medial orbital wall osteotomy it must be angled to pass behind the medial canthal tendon. 5. The medial wall osteotomy is made with a straight osteotome under direct vision. It is import to ensure that this cut connects with the orbital floor osteotomy. 6. The pterygomaxillary osteotomy is now made. This can be undertaken from above by passing an osteotome deep to the zygomatic arch, or from below via an intraoral approach from either a palatal or buccal direction. We now prefer an intraoral buccal approach. An incision is made over the maxillary tuberosity, and a broad, curved pterygoid osteotome is positioned in the palpable groove between the maxillary tuberosity and the hamulus. The surgeon holds the osteotome in one hand and places the index finger of the other palatally so that the groove between the maxilla and hamulus can be felt from the other side. The first assistant then strikes the osteotome with a mallet until the surgeon can feel the blade of the osteotome with the finger in the palate beneath the mucosa. The surgeon is now sure that this blindly performed bone cut is both complete and correctly positioned. 7. The final bony cut cleaves the nasal septum from the skull base. A broad straight

osteotome is placed in the center of the cut across the anterior cranial fossa floor, and to guide it one of the surgical team places an index fingertip at the posterior edge of the hard palate. The osteotome is driven downward toward the fingertip until a change in tone of the sound of the mallet striking the osteotome indicates that the bone cut has reached the hard palate and the nasal septum has therefore been divided. 8. The osteotomized monobloc/frontofacial segment is finally mobilized with Rowe disimpaction forceps. If the bony cuts have all been completed, this should require minimum force.

Closure Prior to closure, the titanium plates needed to secure the distraction wires are placed, usually three in the supraorbital region and two in the lower maxilla adjacent to the pyriform fossa. The plates we use are those supplied by the manufacturers of the KLS Martin RED distractor system.

Bony Closure The lateral (vertical) osteotomy cut for the monobloc procedure lies just behind the lateral orbital margin. When the mobilized fronto-facial complex is pulled forward during the distraction process, it leaves a gap in the anterior temporal region, which can be responsible for an unsightly hollowing in this area that in our experience is not always hidden by re-suspension of the temporalis muscle. A convenient way of preventing this hollowing is to cut out a piece of bone from the anterior temporal region and attach it to the anterior end of the lower border of the (remodeled as necessary) frontal bone. It can also be attached to the lateral orbital wall. In this way no gap is left behind the lateral orbital wall; the area of bone defect is more posterior, where it is better hidden by the body of the temporalis muscle and by hair (Fig. 19.4). Children undergoing the monobloc procedure often have a considerable deformity of their frontal bones, due to both their syndrome and (sometimes) previous fronto-orbital surgery. Also, simple reattachment of the frontal bone flap to the mobilized supraorbital ridge may, as the frontofacial complex is pulled forward, leave it in an unsightly vertical position. A convenient way of allowing it to take on a more appropriate shape is to divide it transversely into three or four segments that are then reattached by absorbable sutures at their lateral ends. Pressure from the skin during the distraction process then bends the forehead armadillo-fashion to give it a more agreeable contour (Fig. 19.1d and Fig. 19.5)

19â•… External Distraction for Frontofacial Advancement

Fig. 19.4â•… Pieces of bone from each temporal region have been reattached to the anterior-inferior edge of the frontal bone flap to reduce temporal hollowing as the frontofacial segment is pulled forward (note the beaten copper appearance of the bone’s inner surface, suggesting previously raised intracranial pressure).

Soft Tissue Closure It is essential to ensure that the facial soft tissues are adequately suspended before wound closure. The two key features to this process are: 1. A strong lateral canthopexy secured to drill holes in the lateral orbital wall to prevent descent of the lateral canthus insertion during distraction 2. Suspensory sutures elevating the malar fat pads and midfacial soft tissues (these can be secured to the temporal fascia) The potential space beneath the coronal flap is drained by two suction drains placed centrally with their exit sites close to the vertex so that their paths do not cross the fixation points of the distractor frame. Suction drainage reduces swelling and hematoma collection in the first 48 hours but can be effective only if the anterior cranial fossa floor repair is robust enough to prevent nasal secretions being sucked into the anterior cranial fossa. The intraoral incisions are closed with absorbable sutures, and the coronal skin incision is closed in two layers, also with absorbable sutures. In order to secure the airway in the early postoperative period, a tightly fitting nasopharyngeal airway is passed down through each nostril, and a nasogastric feeding tube is passed down the lumen of one of them. By occluding the nasopharynx, the nasopharyngeal tubes also help reduce the opportunity for respiratory-driven intranasal pressure changes to drive nasal secretions into the dead space between the frontal bone and frontal dura that the monobloc procedure (with or without distraction) inevitably produces.

Fig. 19.5â•… Recontouring the frontal bone using the “armadillo” technique: the frontal bone has been divided transversely to allow it to take on a more appropriate contour as it is pulled forward during the distraction process.

Applying the Distractor Frame The KLS Martin RED distraction system consists of a three-fourths cranial circumference titanium halo and an anterior framework, to which the distraction wires of 2–0 stainless steel passed through the previously placed fixation plates in the frontal and pyriform fossa regions are attached (Fig. 19.3). The halo is fixed to the skull by a series of ceramic or steel-tipped pins passed through the skin to engage with the underlying bone along the temporoparietal region above each ear. Care must be taken to avoid any ventriculoperitoneal shunt tubing or cranial defects from previous operations. Correct angulation of the frame is important because it determines the direction (vector) of the distraction process. Ideally this should be parallel with the Frankfort plane, a line passing through the lowest point of the inferior orbital rim and the external auditory meatus. However, because there is a tendency for the frame to slip slightly during distraction and the true vector of distraction to rotate downward, we now angle the frame 10 to 15° above the Frankfort plane.

Affixing the Frame in the Very Young The use of a halo in the very young can be complicated not only by failure of the infant skull to provide secure fixation for the distraction process but also by

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b

Fig. 19.6â•… (a) Preventing pin penetration in the very young: a sheet of titanium mesh is placed under the skin, (b) where the pins of the distortion halo can engage with it.

penetration of the pins through the bone and dura and into the brain. Our solution is to insert under the skin (posterior to the craniotomy) a piece of titanium mesh cut to a size that conforms to the area where the pins will be placed. The mesh is anchored to the bone by a couple of short screws. After the skin incision has been closed, the halo is applied, with care taken to ensure that its pins engage (using only finger tightening) with the underlying titanium mesh (Fig. 19.6a,b). Any later loosening of the pins is dealt with by further finger tightening, a process that can lead to some inward displacement of both the mesh and the bone to which it is attached. Our experience, however, is that any such deformity (which is preferable to pin penetration of dura and brain) will, given that these children are by definition very young, “grow itself out” during subsequent skull growth.

A liquid diet is introduced around day 5/6. The NGT is retained to supplement the oral food and liquid intake for as long as necessary. Should it need to be replaced, great care must be taken to ensure that during its reintroduction there is no “blind” upward probing of the defect in the anterior skull base. The distraction process can be painful in its own right, particularly in older patients, but the young tolerate it surprisingly well (Fig. 19.7). We commence the tricyclic antidepressant amitryptyline in appropriate doses on day 2 following the operation and continue it (with supplementary analgesics as necessary) until it is no longer required.

19.4╇ Outcomes and Postoperative Course 19.4.1╇ Postoperative Care Early Postoperative Care A monobloc procedure involves both intra- and perioral bone cuts and causes severe facial swelling that may continue for a week or more. Our policy is to protect the eyes during surgery with temporary tarsorrhaphies that are removed at the end of the operation. During the next few days, obsessional nursing attention to eye and mouth care, in particular, is essential. A nasogastric tube (NGT) is left on free drainage for the first 24 hours and then is used for feeding.

Fig. 19.7â•… A 2-year-old boy with Crouzon syndrome “adjusting” the anterior components of his external distraction frame.

19â•… External Distraction for Frontofacial Advancement

The Distraction Process In the early part of our series, we started distraction on the first postoperative day, but after experiencing a disturbing incidence of CSF leaks, we changed our practice to incorporate a latency period of 1 week. This not only assists consolidation of the anterior cranial fossa floor repair, it also promotes early callus formation at the osteotomy sites. We distract the whole frame at a rate of 1 mm per day (0.5 mm twice a day) by turning the screws at the back of the halo. Fine adjustments to the direction of advance of the monobloc segment, both vertical and horizontal, can be made by using the screws on the anterior part of the frame itself. The endpoint of distraction is a matter of clinical judgment. The aim is to correct retrusion at the orbital level. It is generally not possible to correct the dental occlusion fully without causing an unsightly degree of enophthalmos. Because of the risk of relapse (as described earlier), we try if possible (and particularly in the younger child) to overdistract by 2 to 3€mm. The frame is removed under general anesthesia approximately 6 weeks after the end of distraction.

Pin Site Care We advise hair washing every second day and massage around the screw sites with shampoo to keep them clean. A hand-held shower can be used close to the wound and pin sites to remove debris and keep them clean. If the pin sites become “crusted,” and this is difficult to remove, we recommend massaging in some olive oil, leaving it on overnight and washing it off the following day with regular shampoo. This process can be repeated as necessary until the problem has resolved. The pins should be checked regularly and tightened (finger tightening is usually sufficient even in the older child). Pins that remain loose despite this may have penetrated the bone and should be replaced where possible by pins passed through an adjacent hole in the halo. Dislodging of the whole halo occurs occasionally and requires replacement under general anesthesia.

that any tears that are made be meticulously closed, using a pericranial patch if necessary. An area where the dura is particularly vulnerable is in the midline of the child with a very foreshortened anterior fossa floor. The space available here for the vertical osteotomy cut is severely restricted, and even gentle retraction can tear the dura at its attachments to the crista galli—a site where it is difficult to achieve effective closure. The following maneuvers can reduce this risk. 1. Make the anterior skull base cut through, and certainly no more posterior than, the foramen caecum (Fig. 19.8). 2. Take advantage of a well-developed frontal sinus (in Apert syndrome particularly) to make the transverse osteotomy cut through it and thus avoid having to retract dura from the anterior fossa floor. The posterior wall of the sinus should be removed. Care should be taken to remove all the mucosa within the sinus. We have had troublesome mucoceles arise over the postoperative years on a couple of occasions. 3. At the end of the operation, swing a vascularized flap of pericranium through an orbit and into the cranial cavity and stitch it fore and aft across the gap the osteotomy has produced in the anterior skull base. This “curtain” may also help reduce contamination of the frontal extradural space (Fig. 19.9).

19.4.2╇Complications CSF Leak CSF leakage is a well-recognized risk of any surgery that places the anterior cranial fossa into communication with the nose. It is essential, therefore, that the neurosurgeon take great care to avoid dural tears when raising the craniotomy flap (often difficult when there has been previous frontal surgery) and

Fig. 19.8â•… The foramen caecum, identified by the thin strand of frontal dura that passes into it, is exposed by gentle frontal retraction.

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Fig. 19.10â•… The gap in the anterior fossa floor and the pericranial flap covering it have been reinforced with tissue adhesive.

Management of CSF Leakage

Fig. 19.9â•… A pericranial flap has been passed through the left orbit and stitched to hold it across the defect in the anterior fossa floor of the patient, who has had a facial bipartition. The relatively raised airway pressure below is causing it to balloon upward.

Some craniofacial surgeons stitch this flap to the dura itself in order to prevent CSF leakage from a basal dural tear. 4. Seal the area with tissue adhesive (Fig. 19.10). 5. Lumbar drain: a. Elective diversion of CSF away from the site of any potential leak, by inserting a lumbar drain at the end (or even at the commencement) of the procedure, should be considered when the dural closure appears less sound than the neurosurgeon would like. b. Lumbar drains should, like external ventricular drains, always be tunneled in order to reduce the risk of ascending infection. c. Elective lumbar drainage is unnecessary when the patient already has a functioning ventriculoperitoneal shunt. It also introduces the risk of infecting that system. d. Ideally, elective CSF diversion should cover the start of the distraction process, when there is the greatest chance of disrupting whatever precautionary steps the neurosurgeon has employed to reduce the risk of leakage.

The use of nasal-pharyngeal stents/airways may conceal any CSF rhinorrhea occurring during the first postoperative week. A minor leak is best ignored for a day or two—fortunately, spontaneous cessation is likely. When it persists, however, a lumbar drain should be inserted—“one-off” lumbar punctures have not, in our experience, been particularly helpful in this situation. The drain should be retained for as long as practical, ideally 7 to 10 days, particularly if distraction is continuing during this period. Rarely, it may be necessary to ask an ORL colleague to try and close the leak transnasally using an endoscope. We have not, to date, had to carry out a transcranial repair of the defect in the anterior skull base.

Retraction Damage to the Frontal Lobes Computed tomography (CT) and magnetic resonance (MR) scans of a child with Apert syndrome who had the first of what turned out to be three grand mal seizures several months after a monobloc-facial bipartition with distraction showed areas of altered attenuation/signal in those areas most subjected to dural retraction during the mobilization of the frontofacial complex: at the pterional ends of the greater sphenoid wings and in the midline (Fig. 19.11). A subsequent review of 50 of our monoblocs’ postoperative CTs24 showed that this was not an isolated phenomenon, though it was one of which we had previously been unaware. It was present in about two-thirds of the children, and was usually “mild” but was classified as “severe” in three. Whether such changes are due to retraction alone or are compounded by the transmission of the vibrations from a reciprocating saw via a mal-

19â•… External Distraction for Frontofacial Advancement the patient remains generally well despite a pyrexia (and other indicators of possible infection) but there is no obvious focus (such as a fluid collection that could be tapped), our policy is, if possible, to avoid empirical (or blind) antibiotic therapy. When pyrexia persists, however, or if evidence of a possible focus for the infection becomes apparent, we have a low threshold for reopening the scalp incision and thoroughly washing out the operative site with an antimicrobial solution. Antibiotics appropriate to any bacteria cultured following this procedure are then administered by whatever route and for whatever period our microbiological colleagues advise.

19.5â•… Late Postoperative Considerations

Fig. 19.11â•… Computed tomography bi-pterional and midline attenuation changes following monobloc/bipartition with distraction.

leable retractor to the underlying brain, remains unknown (as, at present, does its incidence in other units performing these and similar procedures). Nevertheless, this incident emphasizes the need for the neurosurgical participant in such operations to ensure that his or her plastics/craniofacial colleague keeps the amount of retraction needed to make the anterior skull base osteotomy cuts as minimal as possible.

Infection The monobloc procedure, whether aided by distraction or not, opens up by definition a communication between the bacterially contaminated nose and the frontal extradural space. The gradual speed of the distraction process gives time for forward expansion of the intracranial contents to reduce the volume of the frontal extradural “dead space” that any frontal advance inevitably produces, but inevitably there will be some such space, and it will fill with a mixture of blood and air.25 Add to this a large area of devascularized bone, and the situation is ripe for infection. Our policy is to continue with our prophylactic antibiotic regime (previously described) for 48 hours postsurgery and then, in the absence of any indicators of obvious infection, to discontinue it. Infection can manifest itself in two particular ways: with or without an obvious infectious focus. If

The monobloc osteotomy with external distraction can produce dramatic improvements in both function and appearance. It is important, however, to emphasize to patients and their families that, even in patients undergoing surgery in late adolescence (when little or no further facial growth is anticipated), further (and lesser) procedures may well be required in order to achieve the finest long-term result. Examples of such “fine tuning” include orthodontics, a LeFort 1 (with or without mandibular surgery) for both aesthetic and occlusal reasons, canthopexies, and rhinoplasty.

19.6╇Conclusion The monobloc frontofacial advance using distraction is a very major operation whose safe performance requires the input of an experienced surgical, anesthetic, and nursing team. While many of the surgical components of the operation are the responsibility of the plastic/maxillofacial surgeon, the most serious postoperative complications (hematomas, CSF leakage, and intracranial infection, for example) all fall within the province of the neurosurgeon. There is no place in surgery of this scale for the “occasional” neurosurgeon—one who is not fully committed to the conduct of the entire procedure from the initial incision to the placement of the distractor frame and then to the patient’s postoperative care.

References ╇1.

Ortiz-Monasterio F, del Campo AF, Carrillo A. Advancement of the orbits and the midface in one piece, combined with frontal repositioning, for the correction of Crouzon’s deformities. Plast Reconstr Surg 1978;61(4):507–516

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Eley KA, Witherow H, Hayward R, et al. The evaluation of bony union after frontofacial distraction. J Craniofac Surg 2009;20(2):275–278 Bradley JP, Gabbay JS, Taub PJ, et al. Monobloc advancement by distraction osteogenesis decreases morbidity and relapse. Plast Reconstr Surg 2006;118(7):1585–1597 van der Meulen JC. Medial faciotomy. Br J Plast Surg 1979;32(4):339–342 Ponniah AJ, Witherow H, Richards R, Evans R, Hayward R, Dunaway D. Three-dimensional image analysis of facial skeletal changes after monobloc and bipartition distraction. Plast Reconstr Surg 2008;122(1):225–231 Dunaway DJ, Britto JA, Abela C, Evans RD, Jeelani NU. Complications of frontofacial advancement. Childs Nerv Syst 2012;28(9):1571–1576 Greig AV, Britto JA, Abela C, et al. Correcting the typical Apert face: combining bipartition with monobloc distraction. Plast Reconstr Surg 2013;131(2): 219e–230e Arnaud E, Marchac D, Renier D. Quadruple internal distraction with early frontal-facial advancement for faciocraniodysostosis [in French]. Rev Stomatol Chir Maxillofac 2004;105(1):13–18 Witherow H, Dunaway D, Evans R, et al. Functional outcomes in monobloc advancement by distraction using the rigid external distractor device. Plast Reconstr Surg 2008;121(4):1311–1322 Witherow H, Thiessen F, Evans R, Jones BM, Hayward R, Dunaway D. Relapse following frontofacial advancement using the rigid external distractor. J Craniofac Surg 2008;19(1):113–120 Ahmad F, Cobb AR, Mills C, Jones BM, Hayward RD, Dunaway DJ. Frontofacial monobloc distraction in the very young: a review of 12 consecutive cases. Plast Reconstr Surg 2012;129(3):488e–497e Fearon JA. Halo distraction of the Le Fort III in syndromic craniosynostosis: a long-term assessment. Plast Reconstr Surg 2005;115(6):1524–1536 Shetye PR, Davidson EH, Sorkin M, Grayson BH, McCarthy JG. Evaluation of three surgical techniques for advancement of the midface in growing children with syndromic craniosynostosis. Plast Reconstr Surg 2010;126(3):982–994

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Shetye PR, Kapadia H, Grayson BH, McCarthy JG. A 10year study of skeletal stability and growth of the midface following Le Fort III advancement in syndromic craniosynostosis. Plast Reconstr Surg 2010;126(3):973–981 de Jong T, van Veelen ML, Mathijssen IM. Spring-assisted posterior vault expansion in multisuture craniosynostosis. Childs Nerv Syst 2013;29(5):815–820 Waitzman AA, Posnick JC, Armstrong DC, Pron GE. Craniofacial skeletal measurements based on computed tomography: Part II. Normal values and growth trends. Cleft Palate Craniofac J 1992;29(2):118–128 Waitzman AA, Posnick JC, Armstrong DC, Pron GE. Craniofacial skeletal measurements based on computed tomography: Part I. Accuracy and reproducibility. Cleft Palate Craniofac J 1992;29(2):112–117 Posnick JC. Monobloc and facial bipartition osteotomies: a step-by-step description of the surgical technique. J Craniofac Surg 1996;7(3):229–250, discussion 251 Mallory S, Bingham R. Anaesthesia for craniosynostosis surgery. In: Hayward R, Jones B, Dunaway D, Evans R, eds. The Clinical Management of Craniosynostosis. London, UK: Mac Keith Press; 2004: 355–373 Hayward R. Venous hypertension and craniosynostosis. Childs Nerv Syst 2005;21(10):880–888 Thompson DN, Hayward RD, Harkness WJ, Bingham RM, Jones BM. Lessons from a case of kleeblattschädel. Case report. J Neurosurg 1995;82(6):1071–1074 Neil-Dwyer JG, Evans RD, Jones BM, Hayward RD. Tumescent steroid infiltration to reduce postoperative swelling after craniofacial surgery. Br J Plast Surg 2001;54(7):565–569 Jeelani NU, Khan MA, Fitzgerald O’Connor EJ, Dunaway D, Hayward R. Frontofacial monobloc distraction using the StealthStation intraoperative navigation system: the ability to see where you are cutting. J Craniofac Surg 2009;20(3):892–894 Cobb AR, Boavida P, Docherty R, et al. Monobloc and bipartition in craniofacial surgery. J Craniofac Surg 2013;24(1):242–246 Posnick JC, al-Qattan MM, Armstrong D. Monobloc and facial bipartition osteotomies for reconstruction of craniofacial malformations: a study of extradural dead space and morbidity. Plast Reconstr Surg 1996;97(6):1118–1128

20

The Surgical Management of Craniopagus Twins James Tait Goodrich and David A. Staffenberg

20.1╇ Introduction and Background 20.1.1╇Indications The indications for the separation of craniopagus twins are mostly based on their family’s wishes. With now a personal involvement in 15 sets of craniopagus twins, it is clear to us that there are far more nonsurgical issues than surgical issues in considering a separation.1–8 Conjoined twins are reported as 1:200,000 births, and 2% are craniopagus, so the incidence of craniopagus appears to be about 1:10,000,000 births. Only one to two sets of craniopagus twins are identified per year around the world. In the vast majority of cases, they occur in less-developed countries with limited medical resources. Another key point is that in many cases there are significant social, ethical, and religious issues that surround the decision to undergo or not to undergo a surgical separation. In some instances, prenatal detection may prompt termination of the pregnancy because, until now, historical outcomes have been so poor. In our experiences, six of the 15 cases never made it to any surgical management as, for cultural and religious reasons, the family wanted no intervention done. The typical reasons, interestingly, hark back to an ancient religious philosophy that such a birth was a monstrum, “a divine omen indicating misfortune, an evil omen, portent,” from monere “to warn,”9 whence we get the word “monster”—an influential ethical concept that may be a significant barrier to acceptance and treatment. This concept has to be seriously considered by the medical team and reviewed with the family before undertaking a surgical separation. The majority of craniopagus twins (approximately 80%) will not survive to the age of 2 because of complications associated with their medical and congenital conjoining. Medical issues encountered

early on are cardiac and renal issues, and these need to be evaluated by the consulting physicians and corrected as quickly as possible. A review of the literature and personal discussions with treating surgeons show that these children commonly present as medical emergencies. The most common medical emergency is high-output cardiac failure in one of the twins. All of this having been said, the indication for separation is as a life-saving measure, as otherwise there is a very high mortality rate in untreated craniopagus twins. Craniopagus twins surviving to adulthood are extremely rare, with fewer than five reported cases.

20.1.2╇Goals A successful surgical separation is one in which there are two surviving twins with the least morbidity possible. In some situations, one twin may be so sick as not to be salvageable, and in that case, the surgical goal would be to preserve the life of the less affected child. We have been involved with one set of twins where, despite a good delivery and early signs of survival, one twin developed a necrotizing enterocolitis and died. An emergency separation was undertaken, but the other twin also died. In conjoined twins sharing significant vascularity, one twin will be physiologically dominant. This finding is often demonstrated as hypertension in one twin, while the other is hypotensive. This finding is interesting, as the “dominant twin” may appear to have failure to thrive due to an elevated metabolic rate. This dominant twin may receive more than his or her fair share of venous return, leading to greater urinary output compared with the other twin. This curious physiology can be incorrectly interpreted as an “emergency.”

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20.1.3╇ Alternative Procedures It is important to note that historically the treatment of craniopagus twins has been the surgical separation done as a single-stage procedure. With the rare exception of the mild “conjoined” twin—meaning that the anatomical connection is only scalp and skull, with no brain or vascular connections—we do not recommend single-stage procedures, for reasons that are discussed under the operative details. A key element to survival of surgical separation is not only to do the separation in stages, but to allow adequate time between stages for healing and adaptation. Our philosophy and the evolution of this approach are reviewed in this chapter.

20.1.4╇Advantages In the twins who have undergone separations as a multistaged procedure, now numbering five sets of twins, we have reduced the previously reported high mortality (greater than 50%) to zero. Equally as important, the staged procedure has reduced morbidity significantly, especially in the case of hydrocephalus, where none of our twins has required ventriculoperitoneal shunt placement. The staged procedure has also enabled us to reduce infection and meningitis, which mostly results from cerebrospinal fluid (CSF) leaks, to zero. Postoperative CSF leaks can be devas-

a

tating to these patients, and it remains best to avoid CSF leaks at all costs. The multistaged approach allows both twins to “equilibrate” their cerebral vasculature so that, at the time of final separation, the cerebral vascular flow dynamics will be nearly equal in the sense of volume flow into and out of each brain.

20.1.5╇Contraindications Nature can provide cases of conjoined brains that are just too complex to separate. As part of the initial workup, it is incumbent on the medical, neurosurgical, and neuroradiology teams to determine the degree of conjoining and how much brain is actually fused. In our experience, this can range from zero to severe, meaning there is an area of conjoined brain greater than 5 to 6 cm in diameter. In one situation, a case of an angular conjoined set of twins, the anatomy was such that there was a diencephalic bridge between the two twins (Fig. 20.1a,b and Fig. 20.2). Separation of the brains and cutting the bridge was felt to entail an unacceptably high risk of severe morbidity and likely death to one or both twins. In another set of twins, the angle of rotation of the conjoined brains was severe, and to do the separation would require removal of the occipital lobe of one child to access the conjoined brain. In addition, one of the twins was born without kidneys and was using the other twin for kidney function, although dialysis and living-related trans-

b

Fig. 20.1â•… (a) A set of total angular craniopagus twins with an extremely complex conjoining of brains and vascular anatomy. (b) A set of craniopagus twins with a complex conjoining of the brain and a diencephalic bridge between the two thalamis of the children. Image courtesy of Doug Cochrane, MD, Vancouver, BC.

20â•… The Surgical Management of Craniopagus Twins a

b

Fig. 20.2â•… (a) An image showing the complex venous anatomy and the lack of a circumferential venous plexus (CVP) to work with as a surgical corridor. This set of twins is a set with total angular connection. We have consistently found this type of conjoining to be the most complex and these twins to be the least likely to be separated and at very high risks. (b) One child from (a) showing the venous vascular anatomy from a posterior view. The complex mixture of the two torculas makes for very complex surgical planning. Image courtesy of Doug Cochrane, MD, Vancouver, BC.

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174 Section III.Aâ•… Malformations of the Scalp and Skull plant may be options if separation is required. In a set of dicephalopagus twins (two conjoined heads on a single body and brainstem), the anatomy was such that one head would have been sacrificed to save the other. For this reason, dicephalopagus twins are rarely candidates for separation. These particular children expired from medical issues before any serious surgical planning could be undertaken. While not often thought of as a contraindication, religious and social issues do count in some cases. We have been involved in six sets of craniopagus twins whose families, for either religious or social reasons, would not consider a surgical separation; these beliefs were respected and no surgery was undertaken. In four sets of twins, death resulted from medical issues before a separation could be undertaken. One set came from a remote rural area of India, and we have not been able to obtain follow-up.

20.2╇ Operative Detail and Preparation 20.2.1╇ Preoperative Planning and Special Equipment In most sets of craniopagus twins, the initial medical emergency is related to the vascular connections of the brain and unequal cardiac outputs. It is not uncommon to see one child in high-output cardiac failure with the second child “parasitic” to the other twin. In our first separation case, one child arrived

Fig. 20.3â•… A set of craniopagus twins in which the physiological differences between the two are clearly demonstrated. Twin A, on the left, arrived in a severe hypertensive state with a blood pressure of 220/110 mm Hg, while Twin B, on the right, was 60/40 mm Hg and oliguric. Twin A was in high-output cardiac failure at the time of arrival for the first separation procedure.

with a blood pressure of 220/110 mm Hg while the other was 60/40 mm Hg and oliguric (Fig. 20.3). The most common life-threatening risk to these twins is the disproportionate cardiac output, so input from cardiology and urology is critical from the beginning. It is a balancing act, because reducing the blood pressure in the hypertensive child too quickly can lead to severe vascular dynamics problems in the other twin. A query that always comes up is how much medication is actually shared between the twins. In other words, if an antihypertensive medication is given to one twin, how will it affect the other? A similar question also has to be asked about anesthetic agents. As it turns out, despite sometimes significant amounts of sharing of cerebral vascularity, there appears to be little vascular exchange of medications. The preoperative work-up for the neurosurgical team revolves around sorting what is conjoined anatomically. Work-up includes cerebral angiography, both venous and arterial phases, to determine the anatomical connections between the twins. In all of our cases, the venous anatomy became critical. Surprisingly, arterial connections are rare, and, when present, they have not been significant issues in the separations. Craniopagus twins almost always have a venous lake between the two brains, referred to as a circumferential venous plexus (CVP; Fig. 20.4 and Fig. 20.5). This is a shared venous lake that cannot be easily separated or bypassed, and the decision has to be made as to which twin will get the majority of the CVP. In the vascular work-up, this plexus is analyzed and typically goes to the dominant twin, meaning the one who receives most of the venous outflow. The other twin develops his or her own venous anatomy as the team completes the staged separations. In true craniopagus twinning there is always a brain connection. Magnetic resonance imaging (MRI) will determine the amount of anatomical connection in some cases. All of that having been said, the MRI can also be misleading in suggesting there is no connection, as a CSF plane can be seen with interdigitating gyri (Fig. 20.6). Based on our experience, we now assume there is a brain connection despite the MR findings. To date, all of the surgically operated cases have had some, if not significant, degrees of brain connection. To assist in the surgical planning, we have been routinely acquiring MRI and computed tomography (CT) imaging studies and had medical models made of the venous anatomy. These models are helpful for the various team members in understanding the complex neuroanatomy (Fig. 20.7 and Fig. 20.8). The models also are very helpful in the preoperative planning and setup of the operating room. As the angulations of the conjoined heads can vary immensely, these models

20â•… The Surgical Management of Craniopagus Twins a

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Fig. 20.4â•… (a,b) Computed tomography (CT) venogram with Twin A superior and Twin B inferior. The central venous pressure (CVP) can be seen as a “lake” of venous blood at the interface of the two brains. Twin A has clear dominance in venous outflow, with a large, prominent torcula and draining sinus. Twin B has a clear paucity of venous flow in the region of the CVP.

Fig. 20.5â•… Medical model reconstructed from CT venogram and detailing the venous anatomy, the CVP at the interface of the brains, and the clear dominance of venous outflow going to Twin A on the right. Image courtesy of Medical Modeling, Golden, CO.

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Fig. 20.6â•… Coronal magnetic resonance imaging (MRI) showing the interdigitating brain. On MRI, the brains appear to be separate, but at the final surgical separation there turned out to be a significant fusion: incomplete anatomical separation of the parietal lobes of the two children.

help the surgeons and nursing team in setting up the operating room and operative positioning. Anesthesiology is involved from the beginning in the assessment and management of the twins. Depending on the angulations of the conjoined brains, which can range from simple to very complex, the anesthesiology team has to work out the details on how to position and orally intubate the children. In two cases, the intensive care team decided to place tracheostomies at the beginning, and these were removed after the final separation. It is now routine to provide each twin with his or her own anesthesia team, and that team remains the same for each of the twins throughout the separations. Each child is treated individually, and each will have his or her own unique medical and anesthetic issues that will be identified early on.10 We involve the pediatric intensive care unit (PICU) team from the beginning, and through each surgery we also keep the same PICU team members. Despite being an identical twin, each twin has proven to have his or her own medical and intensive care issues. The contribution of plastic surgery is critical. Each of the twin sets produces unique problems in skin coverage at the end of the final separation. The common goal is to provide a complete and secure covering of both brains, with the goal of reducing CSF leaks to zero. Oral hygiene needs to be assessed so that dental restorations can be completed in order to minimize infection and bacteremia during the various stages. In the seminal case, this dental evaluation was done under general anesthesia so the anesthesiologists had an opportunity to observe their dynamics under anesthesia.

Fig. 20.7â•…Operative positioning of twins using models constructed from the CT imaging. In this case, the models outline the venous anatomy. Models courtesy of Medical Modeling, Golden, CO.

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Fig. 20.8â•… A plastic model of the topographical anatomy constructed from the CT scans. On the scalps of the twins, the venous systems are outlined in methylene blue. Models courtesy of Medical Modeling, Golden, CO.

20.3╇ Separation of Craniopagus Conjoined Twins 20.3.1╇ The Plastic Surgeon’s Perspective, Including Planning, Pearls, and Pitfalls As with many rare challenges, separation presents initially as a deceptively simple problem requiring only the most basic clinical techniques. As in many reconstructive problems, this paradigm mandates that the neurosurgical team perform the various separations, with the plastic surgeons providing closure at the end of the separation. Historically, these approaches have included, as with the separation of many other types of conjoined twins, the use of tissue expansion prior to the final separation. In the best hands, at the most capable medical centers, the mortality reported in the literature over the past 50 years has been greater than 50%. Craniofacial surgery frequently demands a coordinated effort between plastic surgery and neurosurgery and many other specialties; sepa-

rating craniopagus twins takes this coordination to a stratospheric level. However, this coordination is of paramount importance. Success clearly requires an understanding of the complex interrelationship between the “separation” and the “reconstruction” and an understanding that decisions made for one aspect of the surgery will have a profound impact on another aspect of the surgery; the impact can be disastrous or, if planned well, can be advantageous. The separation of craniopagus conjoined twins is a very rare and complex challenge requiring exquisite coordination between the neurosurgeon and plastic surgeon. Success lies, in part, in the recognition that a successful outcome demands that all recognize that their own component parts of the surgery have significance for the others’ parts. In other words, poor planning by another may mar a superb result by one. It should be clear, for instance, that poorly planned or executed flaps will likely lead to CSF leak, meningitis, and, possibly, brain exposure and death. For the plastic surgeon, it soon becomes clear that unexpected cerebral edema will undo the bestplanned flaps. Herein lies the strength of the staged

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178 Section III.Aâ•… Malformations of the Scalp and Skull technique, as well as the importance of recognizing the nuance of planning. When too many bridging veins from the CVP sinus are interrupted acutely, the alternate venous pathways (venous collaterals) are overwhelmed and cerebral edema occurs, possibly even leading to venous infarcts. Once cerebral edema ensues, successful scalp coverage becomes much more challenging. With a staged approach, the collateral veins are able to dilate gradually to carry the increased demands. Our experience is that at the time of final separation, there is very little cerebral edema. This increases the success rate of closure, allowing the vascularized flaps to heal without CSF leak. Since the first incision of the first stage will be a part of the final flap design, planning is crucial. A variety of flap designs may be considered. One must remember that vascularized free tissue transfer in an infant is far less useful than in an adult because the relative surface area of an infant’s scalp is twice that of an adult, and vascularized free flaps (e.g., latissimus dorsi and rectus abdominis muscles) are comparatively smaller than in adults. Tissue expansion should be used as well to maximize the amount of available vascularized tissue. There are many options for dura replacement. We considered expanded tensor fascia lata from the twins’ thighs, but the fascia lata has a grain and has the potential to leak. In spite of our usual commitment to autolo-

gous tissues, we have chosen Durasis, now referred to as Biodesign Dural Graft (Cook Medical, West Lafayette, IN, USA), because of its watertight properties. Another option is to utilize the pericranium for dura replacement as a pedicled flap, but sometimes the graft lengths might not be enough to provide a full watertight closure. Once the flaps have been completed, they can then receive bone or skin grafts. The planning of the scalp flaps may be counterintuitive. We have found it very helpful to construct a 3D model, such as a RapidView Model (Medical Modeling, Golden, CO, USA), of the skin surface from neck to neck and including the ears. The data for constructing the models come from the CT imaging studies. The plastic surgeon can use this model to design and modify the plans well ahead of the first stage of surgery (Fig. 20.9 and Fig. 20.10). A no. 2 pencil can be used on the model surface as on 3D paper; marks can be measured, erased, and modified. The proposed skin flap designs must be reviewed with other team members so that all understand the implications of the design, coverage, and protection. Proper flap design will avoid suture lines at the vertex, since this is, by definition, the most distal part of the flap and, therefore, the part of the flap most likely to suffer necrosis and the part most difficult to replace. Furthermore, the brain vertex is likely to have a dura graft, which will require time to develop its own vascular supply. If the dura

Fig. 20.9â•… For planning the scalp flaps, it is recommended to use a 3D model, such as a RapidView Model (Medical Modeling, Golden, CO, USA). The model is constructed to provide the skin surface from neck to neck, including the ears, so that the plastic surgeon can use the model to design and modify the plans well ahead of the first stage of surgery. Preliminary no. 2 pencil lines have been placed on these models.

20â•… The Surgical Management of Craniopagus Twins

Fig. 20.10â•… Operating room tables set up reversed so the foot ends of the tables meet. Horseshoe head holders are used to support both twins. The models are helpful in working out the positioning of the patients and also for the plastic surgeon in designing the flap. Models courtesy of Medical Modeling, Golden, CO.

graft (autologous, heterotopic, or alloplastic) is not yet well healed, it will not support an overlying skin graft. Corners and angles should be avoided to keep the best blood supply and to avoid the need for trimming. The flaps should include reliable blood supply. The most suitable design is a sinusoidal pattern, which allows one flap to turn over across the vertex of one twin while the other does the same to cover the other twin. As craniopagus twins present with multiple variations in angles of conjoining, the skin flaps are unique for each case. Steps in design: 1. Consider the interaxial angulations of the twins: As the angle decreases from 180°, the flaps that are designed may be of varying lengths. The next step will determine where the long flap should be designed. The flaps are planned and marked carefully on the twins in the first stage and opened as needed. Previously healed parts of the incision will need to be reopened at the final stage. 2. Consider which twin will be the final recipient of the CVP sinus lake: The twin who will receive the CVP sinus lake will

ultimately have more volume to cover than the twin without the lake (assuming that there will be minimal cerebral edema at the time of separation). This may lead the shortsighted surgeon to design the longer flap for this twin. The twin receiving the CVP sinus lake will, however, require a smaller dura graft because of having a smaller defect in the middle of the sinus lake. The flap must cover that small graft, but any shortfall can be closed with a skin graft or acellular dermal graft (e.g., Alloderm, LifeCell, NJ, USA). The twin who does not receive the lake will have a smaller volume or surface area to cover but will need a larger dura graft, which must be covered successfully with a healthy vascularized scalp flap at the time of separation. It is this twin, therefore, who should receive the larger (or longer) flap. If an acellular dermis graft is used on the native dura initially, it can be grafted later with a thin split-thickness skin graft once healthy granulation tissue is noted. 3. Consider hairline and pattern of hair growth: In examining the flaps, the direction of hair

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growth is an important detail in design and execution. Sinusoidal flaps allow transfer of hair from one twin to the other (like a yin-yang), so a cowlick is avoided. This also allows the scars to be placed within the hair-bearing scalp. Consider tissue expansion: Tissue expansion enables the team to increase the amount of available vascularized scalp. It is more challenging than usual in a staged procedure because of the existing scars, which increase the risk of exposure and infection. It is important to note that the expansions must be available at the time of final separation, so we recommend placing them in a separate procedure 7 weeks before separation. Because the healing scars from earlier stages increase the risk of tissue expander extrusion, the expanders should not be placed at the plane of conjoining but toward the base of each flap; placement through small remote incisions should be considered. The expanders are allowed to heal for 3 weeks, after which 10% of their final volume is instilled sterilely every 3 days. If the expanders are removed at the beginning of the separation surgery, the expanded scalp may shrink, in which case the advantage is lost. So we recommend placing the expanders through small incisions away from the base of the flaps. By placing the expanders away from the plane of conjoining, the expanders can be left in place during the final neurosurgical separation. The skin expanders are removed only at the time of final closure. If necessary, be prepared to remove enough native skull to avoid impinging on the blood supply of the flaps from below. Consider bony fixation: Resorbable fixation is unnecessary. We recommend the use of titanium (metallic) hardware to secure craniotomy at each stages. Titanium fixation provides additional stability, particularly as you complete the third procedure. Plus, the craniotomies previously done can be easily opened at the time of the final separation. Consider autologous split bone grafting at the time of separation. Remember that the addition of nonvascularized bone on top of nonvascularized dura can increase the risk of infection. Bone grafting will not be possible in areas where the scalp flap does not fully cover. When in doubt, do not bone-graft primarily, although grafting at a later stage may be an additional challenge. As these children often arrive with mild to severe nutritional deficits, we make use of the time between stages to provide additional calories through a soft nasogastric tube or a

percutaneous endoscopic gastrostomy (PEG) or gastrostomy tube (G-tube), and provide occupational and physical therapy (OT/PT). We have not required any special equipment in the operating room other than the medical models and our everyday neurosurgical and craniofacial instruments. Some surgical teams have had specially constructed operating tables made for their cases. In our cases, we have used two operating room tables that are reversed and placed end to end. A horseshoestyle head holder is placed on each table to position and hold the heads. As these are staged procedures with various positions needed, we have found this to be the most facile approach. The final separation will require a 360° exposure of each head, and so far we have been able to position and rotate the children without difficulty (Fig. 20.11).

20.3.2╇ Expert Suggestions, Comments The concepts behind the staged separations of these twins are based on a key anatomical point of a gradual equalization of the venous output of each child. A key concept, based on the venous anatomy, is to decide which twin will get the CVP. An anatomical variant unique to craniopagus twins (Fig. 20.12), the CVP is a lake or a pool of venous blood at the intersection of the two brains. The sagittal sinus is typically present only at the outflow points anterior and posterior to the CVP. The CVP and its venous outflow patterns can be extremely variable and related to the angle of attachment. The nondominant twin will have the least amount of deep venous anatomy present and shunts most of his or her venous output to the dominant twin. Gradually separating the CVP from the nondominant twin allows that twin to develop his or her own internal venous anatomy. The physiological changes during the staged separations can be quite dramatic, in particular in twins with extreme differences in blood pressures and urodynamics. In our first set of twins, the dominant twin presented with a blood pressure of 200/120 mm Hg, while his brother was 60/40 mm Hg and oliguric. By the time of the fourth and final separation, both twins had normalized their blood pressures and urinary outputs. At the final separation, a review of the venous anatomy of the nondominant twin revealed an extensive and rich system of venous outflow pathways. An extensive review of the literature looking at cases of surgical craniopagus separation revealed that the degree of angulation of the conjoined brains is extremely important. As the angle of conjoined brain becomes more acute, the surgical risk of separation increases. The location, size, and volume of flow through the torcula of each twin are also critical factors in the separation (Fig. 20.13).

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Fig. 20.11â•… Intraoperative image taken at the completion of the first stage of separation, showing the positioning of the twins.

Fig. 20.12â•… Artistic reconstruction showing the conjoined brains and the interface where the central venous pressure (CVP) lies. The disparity in venous outflow can be appreciated, with Twin A on the right taking most of the outflow from the CVP.

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Fig. 20.13â•… Table outlining the various types of craniopagus conjoining. These images were compiled from an extensive review of the literature. Each type of conjoining has its own unique surgical separation features. The angular total craniopagus tends to be the most complex in the conjoined vascular anatomy. From Stone JL, Goodrich JT. Review article. The craniopagus malformation: classification and implications for surgical separation. Brain 2006;129:1084–1095.

20.3.3╇ Key Steps of the Procedure and Operative Nuances At the very beginning, the plastic surgery team has to outline the flap design for the final scalp coverage. The plastic surgeon is responsible for the opening and closing at each of the stages and is responsible for flap viability. We typically divide the heads into a series of quadrants. The first stage is done away from the major outflows of the CVP. All stages are done as craniotomies, with the flap replaced with metallic fixation plates

at the end of the surgery. In the preoperative planning, the decision has been made as to which twin will get the CVP. The surgical plane for separation will be on the nondominant side of the CVP (Fig. 20.14). A margin of 2 to 3 mm of dura is left on the side of the dominant twin. The plane on the nondominant twin will be subdural, and in this space the bridging veins going into the CVP will be found. This subdural space is followed deep to about 50% of the diameter of the heads. Bleeding from the dural edges is controlled with bipolar electrocautery and small vascular clips. When large veins are encountered, we place a temporary-type aneurysm clip and occlude the ves-

20â•… The Surgical Management of Craniopagus Twins

Fig. 20.14â•… The initial craniotomy and dural incision have been completed. To the left of the dural incision is Twin A with the central venous pressure (CVP) and a 2 to 3-mm marginal end of dura. To the right is Twin B with the arachnoid and underlying brain to be seen. Bridging vessels are slowly occluded and taken at each of the stages. The CVP goes in its entirety to Twin A in this case.

sel. We then look for any significant brain swelling, and in those cases where there is significant swelling, the clips are removed and applied more slowly. Either vascular clips or aneurysm clips are placed on the larger veins and then they are cut in between. The decision on how much separation is done at each stage is based on the condition of the brain and lack of swelling. In cases where there is a large torcula present, it is best to occlude this structure gradually with a series of vascular clips. Rushing this occlusion can lead to significant if not severe brain swelling. At each stage, just before closing, a sheet of Silastic (Dow Corning, Midland, MI, USA) material is placed between the two brains. These Silastic sheets prevent the brains from scarring together and, at the final separation, provide an excellent anatomical plane. At the final separation, the team will have to deal with conjoined brain. The conjoining can be minimal (e.g., 1 to 3 cm) or significant, meaning greater than 5 cm in diameter (Fig.€20.16). The brain separation is done through a sulcus and following around in a circumferential fashion with bipolar electrocautery on a low-current setting. Once separated, the nondominant twin will have a large dural defect through which the brain will tend to herniate, particularly when the child is in a prone or supine position. At this point a critical maneuver needs to be done, and that is to protect the brain from “slumping” out of the skull. The surgeon needs to place a gauze/sponge soaked in a warmed physiological solution over the exposed brain and hold it in position. If this is not properly done, the force of gravity will pull the brain out, leading to potential damage to the brain and brainstem. At the time of the final separa-

Fig. 20.15â•… Intraoperative view of Twin B at the final stage of separation with exposed brain; note the lack of dura, which has gone with the central venous pressure (CVP) to Twin A. This large defect will be repaired with a dura substitute in a watertight fashion.

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Fig. 20.16â•… Intraoperative view showing the conjoined brain in a set of craniopagus twins. The Cottonoid patty is going under the conjoined brain. The suction tip in the upper surgeon’s hand shows the area where the two brains failed to separate.

tion, the nondominant twin will be left with a large dural defect. With the CVP now given to the dominant twin, the surface of the nondominant twin’s brain will be more fully exposed. The dural defect needs to be covered with a dural substitute in a watertight fashion. The dominant twin will also have a dural defect at the point of the conjoined brain, and this also needs to be repaired in the same watertight fashion. Two sepa-

rate neurosurgical and plastic surgery teams will be needed at the time of the final separation (Fig. 20.17, Fig. 20.18, Fig. 20.19, and Fig.€20.20). Before the final stage, the tissue expanders have to be placed. As discussed previously, the tissue expanders should not be placed until the final stage, as earlier placement can lead to infection and potential CSF leaks. A key concept is that the plastic surgery

20â•… The Surgical Management of Craniopagus Twins

Fig. 20.17â•… Magnified view of Fig. 20.16 showing the conjoined brains. The right parietal lobe of Twin B is conjoined with the left parietal lobe of Twin A. These types of conjoined brain are a common operative finding in craniopagus twins.

team cannot tissue-expand too much! Because the healing scars on the scalp from earlier stages make extrusion of the tissue expanders more likely, the expanders should be placed away from the plane of conjoining, perhaps through small remote incisions. Tissue expansion should proceed cautiously under careful supervision of the plastic surgery team. Full scalp coverage is absolutely critical at the final stage of separation. During the final stage, the neurosurgeons should make every effort to leave the expanders in situ as long as possible, as this helps to prevent the natural scalp shrinkage from taking place when the expanders are removed. Often asked is how many surgical stages are required to separate craniopagus twins. The minimum number of stages appears to be three, and the typical number to date has been four procedures. Timing between each of the stages has been on average 6 to 10 weeks.

20.3.4╇ Hazards/Risks/Avoidance of Pitfalls One of the significant advantages of doing a staged separation in craniopagus twins is the ability to stop the surgery when critical issues, such as excessive blood loss or venous swelling of the brain, occur. The length of each stage is determined by how well the separation is going at the time—that is, based on how well each twin is doing. The most significant surgical errors include1: • Trying to get too much done in each stage, leading to more edema and wound healing complications2 • Not allowing enough time between stages for healing and softening of the indurated scalp The timing between stages cannot necessarily be determined in advance and is best judged by the

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Fig. 20.18â•… At the time of separation with Twin A to the left and Twin B to the right. Note how the surgeon is carefully holding the exposed brain while maneuvering the twin to a new position. This is a key maneuver to keep in mind, as otherwise the brain will slump out of the calvarial defect, potentially leading to severe stretch injury to the brain.

plastic surgeons based on their examination of the patients’ healing, nutrition, and progress with occupational or physical therapy. In assessing a set of craniopagus twins, the key factor comes down to amount of conjoined brain and vascular anatomy. Single-stage separations should be reserved only for those cases of minimal conjoining (e.g., scalp and skull only). A very thorough understanding of the vascular anatomy is key to reduction of risks to each twin. The decision as to which twin will get the CVP is key, and typically it is the dominant twin. In a review of the literature and our own experience, the risks and pitfalls occur mainly in two areas. The first is a too rapid separation that does not allow the nondominant twin a chance to develop his or her own collateral circulation within the deep venous system. The other hazard is failure to develop an adequate closure of both the dura and the scalp/skin, and thereby fail-

ing to prevent CSF leaks and potential meningitis (Fig.€20.21). It is critical for the anesthesia team to have a full understanding of the cardiac, renal, and respiratory issues in each twin. Cardiac issues are common and high-output cardiac failure is a real issue in the dominant twin. There is a fine line between the amount of cardiac output regulation (i.e., its reduction) in the dominant twin and the collateral effect on perfusion in the nondominant twin. Because of the disparity that is often present, renal issues also have to be monitored in the sense of urinary output. It appears craniopagus twins do not necessarily “share” anesthetic drugs, but the team needs to be prepared to deal with this intraoperatively. During the separations, due to the large veins encountered, the risk of pulmonary air embolism is real, and the anesthesia teams need to be prepared to deal with these events.

20â•… The Surgical Management of Craniopagus Twins

Fig. 20.19â•… Cortical surface of Twin A. The central venous pressure is just above the surgeon’s right hand. Just above the surgeon’s right thumb is the dural defect from the conjoined brain that was separated.

20.4╇ Salvage and Rescue Salvage and possible rescue are real issues in craniopagus twins. Cardiac issues are at the top of the list, as failure to manage cardiac output can lead the dominant twin into fulminant cardiac failure. The most common cause for rushing craniopagus twins into a rapid-sequence surgery is cardiac failure. Two other situations we have encountered are examples

of emergent salvage situations. In a set of full-term craniopagus twins, one twin developed necrotizing enterocolitis, became septic, and went into shock. A rapid, single-stage separation was attempted, but both twins died. In another set of twins, born prematurely at 27 weeks gestational age, one twin had multiple congenital anomalies, including lumbar myelomeningocele, facial clefting, and hand duplications. Due to prematurity and sepsis, that twin died

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Fig. 20.20â•… Set of models constructed from a set of craniopagus twins using CT imaging. The pattern of the brain interface can be clearly appreciated when the two models are juxtaposed. This type of modeling is helpful in giving a 3D understanding on how the two brains interface.

shortly after birth. An emergency separation was done, and at surgery only the scalp and skull were conjoined. The duras between the brains were intact, and as a result the separation was completed successfully and the dominant twin survived.

20.5╇ Outcomes and Postoperative Course 20.5.1╇ Postoperative Considerations Among the postoperative considerations is the length of intubation. With the exception of the final separation, virtually all children have been extubated at the end of each of the staging procedures. At the final surgery, the intubation has lasted longer, mainly to keep the children sedated and to reduce stress against the scalp closures. The timing has ranged from 2 to 4 days maximum. Historically, a real concern has been the development of hydrocephalus after separation. This condition is much more common in the singlestage approach and is likely to be due to the sudden changes in the venous outflow dynamics. In the staged procedures, the development of hydroceph-

alus has not occurred in any of the twins, but this should always be considered a high risk and monitored for. As previously discussed, the development of untreated hydrocephalus and a subsequent CSF leak can lead to a disastrous infection and significantly worsens outcomes in the studies we have reviewed. Due to unequal sharing of vascular flow, it is not uncommon for one of the twins to be oliguric, with minimal urine output. The dominant twin does the vast majority of the dialysis. As the staged surgeries advance, it is common to see the oliguric twin pick up on urinary output and normalize. We have also been involved in a set of twins where one of the twins had no kidneys and would have needed a transplant or dialysis if the separation had proceeded. In one set of twins, due to an equally shared vascularity, both twins had normal urinary output. Wound management is critical in the postoperative period to provide both good scalp coverage and prevention of CSF leakage and infection. Here the skin expansion is key, so that there is both adequate coverage and skin edges that are not under significant tension. We have been routinely using perioperative anticonvulsant drugs (ACD). While there has been no set length of time, the average postoperative therapy

20â•… The Surgical Management of Craniopagus Twins

Fig. 20.21â•… This graphic reconstruction illustrates the important key concept in the staged separation of craniopagus twins. The concept is that staging the procedure allows the nondominant twin to develop his or her own deep venous outflow circulation. The image at the left is before surgery with Twin A, the dominant twin, below. The image at the right, taken from the CT venogram done just before the final separation, shows the rich collateral circulation that has developed in Twin B.

duration for these children has been in the range of 4 to 6 months.

20.5.2╇Complications Postoperative complications come down to several key issues. As discussed, CSF leaks and infections are critical to avoid. Prevention of these issues is related to a secure wound closure and adequate tissue coverage at the final separation. While hydrocephalus is not necessarily a complication, failure to recognize

it early on and treat it can increase the risks of CSF leakage. Good nutritional support is key during the various separations, and it is typical that the dominant twin will have been the cardiac and renal engine driving both twins. Physical therapy and rehabilitation are provided throughout the hospital stay to help build up muscle tone and stamina. Not often appreciated in the literature, there appears to be a time frame in which these surgeries should be considered. Due to the increasing vascular conjoining that occurs with aging of these twins, if a separation is being considered, it is best to do

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190 Section III.A╅ Malformations of the Scalp and Skull References ╇1.

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╇9.

10.

Fig. 20.22â•… Christmas card from the patients’ family 9 years postseparation, with both twins in the sixth grade.

it before the twins are 2 to 3 years old, and ideally between 6 months and 2 years. It has become very clear from our series of cases that the staging of these operations versus a single-stage approach has significantly reduced postoperative issues and complications. The surgical and medical teams also have to be aware of other possible congenital anomalies of the various organ systems. Failure to uncover these issues at the beginning will only increase the risks of further complications and reduce the chances for such a happy ending as that shown in Fig. 20.22.

Goodrich JT, Staffenberg DA. Craniopagus twins: clinical and surgical management. Childs Nerv Syst 2004;20(8-9):618–624 Staffenberg DA, Goodrich JT. Separation of craniopagus conjoined twins: an evolution in thought. Clin Plast Surg 2005;32(1):25–34, viii Stone JL, Goodrich JT. The craniopagus malformation: classification and implications for surgical separation. Brain 2006;129(Pt 5):1084–1095 Browd SR, Goodrich JT, Walker ML. Craniopagus twins. J Neurosurg Pediatr 2008;1(1):1–20 Staffenberg DA, Goodrich JT. Craniopagus conjoined twins: an evolution in thought. In: David DJ, ed. Craniofacial Surgery 11. Proceedings of the Eleventh International Congress of the International Society of Craniofacial Surgery. Pianoro, Italy: Medimond; 2005: 69–76 Staffenberg DA, Goodrich JT. Successful separation of craniopagus conjoined twins using a staged approach: an evolution in thought. In: Thaller S, Bradley J, Garri J, eds. Craniofacial Surgery. New York, NY: Informa; 2008: 127–142 Staffenberg DA, Goodrich JT. Craniopagus twins. In: Weinzweig J, ed. Plastic Surgery Secrets. 2nd ed. Philadelphia, PA: Mosby-Elsevier; 2010: 268–271 Browd S, Goodrich JT, Walker M. Craniopagus. In: Winn HR, ed. Youmans Textbook of Neurological Surgery, vol. 2. 6th ed. Philadelphia, PA: Elsevier-Saunders; 2011: 1928–1936 Lewis CT, Short C. A Latin Dictionary. Oxford, UK: Clarendon Press; 1879. http://www.perseus.tufts.edu/ hopper/text?doc=Perseus%3Atext%3A1999.04.0059%3 Aentry%3Dmonstrum Girshin M, Broderick C, Patel D, et al. Anesthetic management of staged separation of craniopagus conjoined twins. Paediatr Anaesth 2006;16(3):347–351

Section III.B

Malformations of the Brain

21

Malformations of the Cerebral Hemispheres Michael D. Partington and Debbie K. Song

21.1╇ Introduction and Background Cerebral malformations affect 1% of all births and result from derangements in normal neuroembryological development.1 Congenital malformations can thus be categorized according to their putative relationship to the stages of normal brain development: neurulation, neuronal proliferation, migration, organization, and myelination. This chapter provides an overview of the major congenital malformations of the cerebral hemispheres in the context of the neurodevelopmental process. The role of neurosurgical management in the conditions presented is discussed, with the recognition that not all such lesions require surgical intervention. A brief overview of neuroembryology follows, to furnish a framework of organization when considering malformations of the cerebral hemispheres. Central nervous system formation begins with gastrulation, during which the bilaminar blastocyst transforms into a trilaminar embryo. The notochord develops and then induces formation of the neural plate (a focally thickened area of ectoderm). The neural plate then invaginates to form the neural groove, whose lateral edges then thicken and proliferate to form the neural folds. Closing of the neural groove forms the neural tube, which starts at the hindbrain– cervical junction and proceeds in both the rostral and caudal directions. Following this closure, disjunction occurs and the superficial ectoderm adjacent to the neural tube separates from and closes over the underlying neuroectoderm. The rostral end of the neural tube forms three fluid-filled brain vesicles: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). Subsequent remodeling of the neural tube leads to the formation of the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon, as well as the midbrain, pontine, and cerebral flexures. Following completion of neurulation, development of the brain neocortex involves a complex sequence of cellular proliferation and cell death, neuronal migration,

organization, and myelination. Most brain development therefore occurs after neurulation, and so it follows that many of the malformations of the cerebral hemispheres are postneurulation in origin. The malformations discussed in this chapter are listed in the box Cerebral Hemisphere Malformations.

Cerebral Hemisphere Malformations Neurulation Malformations • Anencephaly • Dermoid/dermal sinus tract Malformations of Prosencephalon Development • Holoprosencephaly • Septo-optic dysplasia Postneurulation Malformations • Disorders of neuronal proliferation • Microcephaly • Hemimegalencephaly Disorders of Neuronal Migration • Lissencephaly (agyria, pachygyria) • Heterotopias • Schizencephaly

21.2╇ Neurulation Malformations Anencephaly is the most severe cerebral neurulation malformation and is due to failure of neural tube closure starting from the anterior neuropore. The malformation is characterized by a large skull defect with exposed abnormal brain. Anencephaly affects 0.5 to 2 per 1,000 live births and is four times more com-

193

194 Section III.Bâ•… Malformations of the Brain mon in females.2,3 Maternal α-fetoprotein screening is abnormal, and the lesion is visible on ultrasound. The lesion is incompatible with prolonged survival. A focal failure of disjunction, in which there is a persistent epithelial-lined communication between the cutaneous ectoderm and the neuroectoderm, results in a dermal sinus tract; when a mass of intracranial ectodermal tissue is present, a dermoid tumor results. Dermal sinus tracts are lined by keratinized squamous epithelium (to a varying extent) and can be found along the midline from the columella of the nose down to the sacrum.3 Cranial dermal sinus tracts are most commonly found in the midline occiput, where they can be associated with posterior fossa dermoid tumors, or in the nasal region, where they can also be associated with dermoids. The clinical presentation is variable. A dermal sinus tract may appear as a small cutaneous pit, often with fine hair at its base. Dermoids and dermal sinus tracts have the potential to become infected, resulting in meningitis or intracranial abscess. Intermittent extrusion of keratin from a sinus tract or recurrent local infections (usually due to skin flora) may also be noted. Larger lesions can produce mass effect, either in the posterior fossa or in the anterior skull base, where dermoid tumors may produce hypertelorism and other skull base anomalies. Magnetic resonance (MR) imaging of dermal sinus tracts is required to assess for intracranial extension and the presence of a dermoid tumor. CT imaging may also be helpful in clarifying bone anatomy.

21.3╇ Disorders of Prosencephalon Development The spectrum of holoprosencephalies is due to a failure of cleavage of the developing prosencephalon. The prechordal mesoderm is responsible for ventral induction signals that lead to the division of the prosencephalon into the telencephalon and diencephalon and into distinct cerebral hemispheres. The adjacent mesenchymal tissue is also involved in the formation of midline facial structures. Hence, midface anomalies of varying severity are often associated with holoprosencephaly. Holoprosencephaly has been associated with a variety of chromosomal abnormalities and genetic syndromes (trisomies 13 and 18, Smith-Lemli-Optiz syndrome), genetic mutations (Sonic hedgehog, ZIC2, SIX3, TGIF), and several teratogens.4 Holoprosencephaly can be further categorized into three subtypes based on the degree of brain cleavage: alobar, semilobar, or lobar. Alobar holoprosencephaly is the most severe form of holoprosencephaly, characterized by a single, midline forebrain monoventricle with an almost complete lack of hemispheric cleavage. The thalami are fused,

and the interhemispheric structures are absent. Alobar holoprosencephaly is associated with severe midface abnormalities including proboscis, cyclopia, ethmocephaly, and cebocephaly. In semilobar holoprosencephaly, there is an incompletely formed interhemispheric fissure posteriorly, with separation of the occipital lobes but fused anterior hemispheres. An H-shaped monoventricle with partially separated occipital and temporal horns results.5 Lobar holoprosencephaly is the least severe form of holoprosencephaly, characterized by cerebral hemispheres that are nearly completely developed with normal sulcation, but with fusion of the frontal poles and orbital surfaces. In the rarest subtype of holoprosencephaly (the middle interhemispheric variant), the posterior frontal and parietal regions are fused but the inferior frontal lobes are separated. Most children with holoprosencephaly will have some form of developmental disability, the severity of which relates to the extent of the brain malformation. Symptomatic epilepsy develops in 40% of children with holoprosencephaly.4 Other manifestations of holoprosencephaly include endocrinopathies, hypothalamic dysfunction, limb defects, cleft lip and/or palate, a single maxillary central incisor, and hypotelorism. Other structural brain malformations can be seen, such as schizencephaly. Septo-optic dysplasia (de Morsier syndrome) is a disorder characterized by varying degrees of optic nerve hypoplasia, pituitary dysfunction, and midline structural defects, such as agenesis of the septum pellucidum and/or dysgenesis of the corpus callosum. Septo-optic dysplasia is thought to represent an abnormality of midline prosencephalon development.6 The disorder can be associated with other brain malformations, such as schizencephaly, cortical dysplasia, aqueductal stenosis, encephaloceles, porencephaly, and hydranencephaly. Clinical findings in children with septo-optic dysplasia include visual impairment, hypopituitarism, developmental delay, seizures, cerebral palsy, and spastic motor deficits.6 The etiology of septo-optic dysplasia is unclear, but exposure to teratogens, in utero vascular events and infections, and mutations of the HESX1 homeobox gene have been all been implicated in this disorder.3

21.4╇ Proliferation Disorders Abnormalities in neuronal proliferation can result in either microcephaly or macrocephaly. Impaired proliferation—due to either a decreased number of neuronal progenitors, reduced proliferation of neurons, or excessive cell death—results in microcephaly. In microcephaly vera, there is a diminished size of the proliferative units, but the brain has a normal gyral

21â•… Malformations of the Cerebral Hemispheres pattern. In radial microbrain, the number of proliferative units is diminished. There is no indication for neurosurgical intervention in microcephaly. In hemimegalencephaly, hamartomatous overgrowth results in an enlarged cerebral hemisphere that is grossly abnormal. The affected hemisphere is commonly lissencephalic, with gray matter heterotopias, polymicrogyria, focal cortical dysplasias, and white matter abnormalities. Imaging demonstrates ventriculomegaly with midline shift. Clinically, hemimegalencephaly is associated with early-onset intractable epilepsy, cranial asymmetry, hemiplegia, and mental retardation. Intractable seizures associated with hemimegalencephaly are amenable to surgical management by hemispherectomy.

21.5╇ Migrational Disorders Following a phase of neuronal proliferation, cellular migration occurs along glial fibers that extend radially from the germinal zone to the brain surface. Disruption in neuronal migration can give rise to a spectrum of brain malformations of varying clinical severity. Many of the following disorders are characterized by epilepsy, and neurosurgical management (to ameliorate seizures) may be considered in select cases. Lissencephaly is characterized by a brain with a smooth surface with absent or poor sulcation (agyria). In pachygyria, a few shallow sulci with a small number of broad gyri are present. Mutations in the LIS1 and DCX genes, which normally regulate microtubule activity during neuronal migration, have been implicated in the development of lissencephaly.3 Type I lissencephaly is associated with a thickened cortex with broad, flat gyri, shallow sylvian fissures, a smooth gray–white matter interface, and colpocephaly.5 Affected children have developmental delay, early-onset seizures, and spastic quadriparesis.7 Type I lissencephaly can occur in isolation or as part of Miller-Dieker syndrome.2 Type II lissencephaly is characterized by a thickened, unlayered cerebral cortex with no recognizable organization. Type II lissencephaly is associated with Walker-Warburg syndrome and Fukuyama’s congenital muscular dystrophy.2 Children with Walker-Warburg syndrome have ocular malformations, congenital hypotonia, and, commonly, hydrocephalus. Gray matter heterotopias consist of normal neurons in abnormal locations due to abnormal neuronal migration along radial glial fibers. While heterotopias may be present in normal individuals, they can also cause intractable epilepsy and may thus be a surgical target for seizure control. Schizencephaly is the most severe of the brain malformations associated with abnormal neuronal

migration. It represents a complete agenesis of part of the germinative zones and results in cerebrospinal fluid-filled clefts in which no neuronal migration has taken place. Such clefts are lined with heterotopic gray matter and extend from the cerebral cortex to the ependymal surface of the ventricle. The cleft walls are incompletely divided in closed-lip schizencephaly; in open-lip schizencephaly, the cleft walls are separated. Schizencephalic clefts can be unilateral or bilateral, symmetric or asymmetric.

21.6╇ Operative Detail and Preparation Surgical excision is the treatment of dermal sinus tracts and dermoid tumors. Treatment is recommended given the potential for serious infections and possibility of growth. Surgical preparation for an anterior lesion should include planning for a possible combined procedure with a craniofacial surgeon. For an anterior dermal sinus tract with intracranial extension, the tract should be traced back in its entirety from the nasal region, and the extradural and intradural compartments should be explored. If present, a dermoid tumor should be completely excised. Occipital dermal sinus tracts should be followed down through a craniectomy. An intradural exploration should be planned in order to trace and completely excise the stalk and any associated mass, with great care taken to avoid injury to nearby venous sinuses. A preoperative MR venogram is essential, particularly since venous sinus anatomy can be aberrant. Intraoperative pathology consultation can be helpful in identifying the transition from epithelial to glial tissue in the sinus: glial tissue can be safely left in place in neural structures, as it does not give rise to dermoids. The remaining surgical options for patients with hemispheric malformations are described in greater detail elsewhere in this text, but are identified in the following paragraphs. Neurosurgical management of holoprosencephaly involves treating hydrocephalus, which develops in fewer than a third of patients.3,4 Additionally, most children with holoprosencephaly have some degree of motor impairment that may include spasticity and/or dystonia, for which intrathecal baclofen therapy may be indicated. Neurosurgical interventions in septo-optic dysplasia and type II lissencephaly are limited to shunting for hydrocephalus. There are no specific technical features to consider. The remaining group of malformations listed may result in epilepsy with focal features, and directed surgical epilepsy procedures may be a consideration.

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21.7╇ Outcomes and Postoperative Course In surgery for dermal sinus tracts and dermoids, a risk of chemical meningitis exists perioperatively. Dermoids can recur on a very slow basis, even decades after initial resection. Outcomes and complications of treatment of hydrocephalus and epilepsy are considered elsewhere in this text.

References De Catte L, De Keersmaeker B, Claus F. Prenatal neurologic anomalies: sonographic diagnosis and treatment. Paediatr Drugs 2012;14(3):143–155 ╇2. Partington MD, Petronio JA. Malformations of the cerebral hemispheres. In: McLone DG, Marlin AE, Reigel ╇1.

DH, et al, eds. Pediatric Neurosurgery. Philadelphia, PA: WB Saunders; 2001: 202–208 ╇3. Stiner E, Bruderlin-Nelson C, Nguyen T. Congenital intracranial malformations. In: Albright AL, Pollack IF, Adelson PD, eds. Principles and Practice of Pediatric Neurosurgery. New York, NY: Thieme; 2008: 197–216 ╇4. Kauvar EF, Muenke M. Holoprosencephaly: recommendations for diagnosis and management. Curr Opin Pediatr 2010;22(6):687–695 â•…5. Osborn AG. Diagnostic Neuroradiology. St. Louis, MO: Mosby; 1994 ╇6. Fard MA, Wu-Chen WY, Man BL, Miller NR. Septooptic dysplasia. Pediatr Endocrinol Rev 2010;8(1): 18–24 ╇7. Spalice A, Parisi P, Nicita F, Pizzardi G, Del Balzo F, Iannetti P. Neuronal migration disorders: clinical, neuroradiologic and genetics aspects. Acta Paediatr 2009;98(3):421–433

22

Occipital Encephalocele James Ayokunle Balogun and James M. Drake

22.1╇ Introduction and Background Occipital encephaloceles are presently regarded as postneurulation disorders1,2 and are usually confined to the midline between the lambdoid suture and foramen magnum. They are classified based on their relationship to the torcular herophili as either supratorcular or infratorcular.3 The neck of the sac is closely related to the venous sinuses, particularly the superior sagittal sinus, torcular herophili, and the occipital sinus, but rarely to the transverse sinuses. They vary in size and consistency as outlined in the figures, from large containing potentially viable brain and en passage vessels (Fig. 22.1a–c) and large containing primarily cerebrospinal fluid (CSF), to small with CSF only (Fig. 22.2), and they can also be detected in utero (Fig. 22.3). Children with relatively large encephaloceles may be relatively microcephalic and have major brain malformations.1 A detailed delineation of the vascular anatomy using magnetic resonance

a

(MR) angiography and venography may be necessary, especially in large encephaloceles (Fig. 22.4a–e), and may determine the limits of surgery.2 The contents of the sac vary from the usual dysplastic neural tissue to, rarely, functional occipital lobe, brainstem, or cerebellum.1,2,4,5 Patients with occipital encephalocele may also have associated anomalies, such as beaking of the brainstem; ventral vermis; and abnormalities of the corpus callosum, including agenesis, cortical dysgenesis, and myelomeningocele.6,7 Hydrocephalus occurs more frequently in these patients than in patients with anterior encephaloceles.8

22.2╇Indications The primary goals of surgery include removal of the sac, reduction of viable herniated brain, and watertight dural closure with adequate healthy skin cover.5 In some b

Fig. 22.1â•… Partially cystic occipital encephalocele, with herniation of dysplastic occipital lobe, but also cerebellum and possibly brainstem, seen on (a,b) sagittal imaging. In (b) it appears that some of the distal arterial and venous vascular structures are herniating with the dysplastic brain. (Continued on page 198)

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198 Section III.Bâ•… Malformations of the Brain c

a

b

Fig. 22.1 (Continued)â•… (c) Partially cystic occipital encephalocele, with herniation of dysplastic occipital lobe, but also cerebellum and possibly brainstem, seen on axial imaging.

patients, where the sac is primarily CSF-filled and vascular involvement, usually venous, precludes excision, a CSF shunt may result in adequate decompression (Fig. 22.4a–e). While conservative management is an option, a patient with a large encephalocele may be difficult to nurse and subsequently manage, herniating brain may be traumatized, and the abnormality is quite disfiguring. Very small or atretic encephaloceles, by contrast, are probably better left alone unless there are compelling reasons for excision. Occipital encephaloceles detected early in utero (Fig. 22.3) often result in neurosurgical consultation regarding potential outcomes.

22.3╇ Operative Detail and Preparation Surgery proceeds under general anesthesia, and it is important to have the services of an experienced neuroanesthetist because of the challenge

Fig. 22.2â•… (a,b) Small occipital encephalocele with overlying vascularized skin. There is also extensive cortical gyral dysgenesis on the left side.

sometimes encountered with the intubation of the patient related to the occipital mass. Various modifications have been proposed, such as intubating the patient with the encephalocele in a head ring, intubating the patient in the lateral position, and occasionally decompressing a large encephalocele to facilitate intubation. 9,10 Volume replacement is important, necessitating adequate vascular access and preemptive preparation for acute hemorrhage, which is a major operative hazard. Adequate attention must be paid to preserving body temperature using a warming blanket. The child is positioned prone with the head flexed and supported on a horseshoe headrest. The chest is supported on a bolster. Perioperative antibiotic is administered.

22â•… Occipital Encephalocele a

b

Fig. 22.3â•… Small occipital encephalocele seen on intrauterine magnetic resonance imaging (MRI).

22.4╇ Key Steps of the Procedure The steps of the surgical procedure are outlined in Fig. 22.5a–e. It may be necessary to grasp a large encephalocele at the dome of its sac, where there is healthy skin, and elevate it with tissue forceps so as to facilitate skin preparation. Care must be taken with this manipulation to avoid interfering with basal brainstem function (Fig. 22.5b). A transverse skin incision is made, usually extending elliptically around the lesion to facilitate skin closure (Fig. 22.5b). A vertical incision might be preferred in low-lying lesions extending across the foramen magnum to the cervical spine. A dissection plane is developed bluntly or by using monopolar cautery with tips such as the Colorado tip, taking care not to enter into the sac. This is continued until the neck of the sac and the bone defect are clearly delineated. The pericranium should be preserved and the skin retracted while adequate hemostasis is secured. The dome of the dural sac is incised and decompressed by releasing CSF and specimen sent for culture. The content of the sac is then assessed to determine presence of viable neural tissue (Fig.€22.5c). Three scenarios may be encountered at this point. The lesion might be a simple meningo-

c

Fig. 22.4â•… (a) Predominantly cystic high parietal/occipital encephalocele seen on sagittal T2-weighted image. (b,c) Magnetic resonance (MR) venography showing significant abnormality of the venous drainage, with extension of vascular structures into the extracranial cyst. (Continued on page 200)

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200 Section III.Bâ•… Malformations of the Brain d

e

Fig. 22.4 (Continued)â•… (d) Following a ventriculopertioneal shunt the cyst has collapsed, demonstrating a very small extracranial nubbin of tissue. (e) Repeat magnetic resonance venography (MRV) imaging, showing only a small venous herniation into residual pouch.

cele, allowing the redundant dura to be amputated, leaving enough cuff at the base for a watertight dural closure. The second scenario is that the dura sac contains gliotic or malformed brain, as often encountered. This extracranial mass of tissue should be amputated at its base after it is bluntly dissected off the dura, maintaining hemostasis with bipolar

a

coagulation, taking cognizance of the neurovascular structures within the sac (Fig. 22.5d). Finally, the sac content may be viable neural tissue, necessitating reduction into the cranial space, which might be facilitated by enlarging the skull defect using rongeurs. Minimizing blood entry into the ventricles is important.

b

Dyplastic neural tissue Fig. 22.5â•… Illustrated steps in repair of an occipital encephalocele. From Drake JM, MacFarlane R. Encephalocele. In: Cheek W, ed. Atlas of Pediatric Neurosurgery. Philadelphia, PA: WB Saunders; 1996, with permission. (a) Positioning and prepping. (b) Circumferential skin incision with preservation of dura.

22â•… Occipital Encephalocele c

Dural sac

d

Neural tissue

Dural sac

Bipolar forceps

Suction Neural tissue

Cotton patty

e

Edge of bone defect

The dura is then closed primarily and augmented if necessary with fibrin glue and/or dura substitute/ pericranial patch (Fig. 22.5e). Usually the bony defect is small and will diminish in size with growth of the child, thus making repair unnecessary. The redundant skin is trimmed and tension-free two-layered scalp closure performed. The wound edges may need to be undermined in the subgaleal plane if they are devoid of subcutaneous tissue to allow excision to normal skin. Dressing is then applied to the wound.

22.5╇ Complications and Outcome

Dura mater

Fig. 22.5 (Continued)â•… (c) Opening of dura and mobilization of dysplastic cortex. (d) Amputation of dysplastic cortex. (e) Dural repair.

Patients are carefully observed for CSF leak and healthy perfused skin edges. A CSF leak is the most common complication. Encephaloceles involving the brainstem should be monitored for brainstem dysfunction, including apnea, feeding problems, and aspiration. Postoperative hydrocephalus may occur in up to 30 to 60% of cases,11–13 which may require a CSF shunt or potentially an endoscopic third ventriculostomy (ETV). Patients with significant brain abnormalities may have severe developmental delay. Patients with atretic encephaloceles may be completely normal, with the lesion being an incidental finding.

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202 Section III.B╅ Malformations of the Brain References ╇ 1.

╇ 2.

╇ 3.

╇ 4.

╇ 5.

╇ 6.

Chapman PH, Swearingen B, Caviness VS. Subtorcular occipital encephaloceles. Anatomical considerations relevant to operative management. J Neurosurg 1989;71(3):375–381 Sather MD, Livingston AD, Puccioni MJ, Thorell WE. Large supra- and infra-tentorial occipital encephalocele encompassing posterior sagittal sinus and torcular herophili. Childs Nerv Syst 2009;25(7):903–906 Ghatan S. Encephalocele. In: Winn HR, ed. Youmans Neurological Surgery, 6th ed. Philadelphia, PA: Elsevier Saunders; 2011: 1898–1905 Shokunbi T, Adeloye A, Olumide A. Occipital encephalocoeles in 57 Nigerian children: a retrospective analysis. Childs Nerv Syst 1990;6(2):99–102 Alexiou GA, Sfakianos G, Prodromou N. Diagnosis and management of cephaloceles. J Craniofac Surg 2010;21(5):1581–1582 Baradaran N, Nejat F, Baradaran N, El Khashab M. Cephalocele: report of 55 cases over 8 years. Pediatr Neurosurg 2009;45(6):461–466

╇ 7.

╇ 8.

╇ 9.

10.

11.

12.

13.

Martínez-Lage JF, Poza M, Sola J, et al. The child with a cephalocele: etiology, neuroimaging, and outcome. Childs Nerv Syst 1996;12(9):540–550 Bui CJ, Tubbs RS, Shannon CN, et al. Institutional experience with cranial vault encephaloceles. J Neurosurg 2007; 107(1, Suppl):22–25 Singh N, Rao PB, Ambesh SP, Gupta D. Anaesthetic management of a giant encephalocele: size does matter. Pediatr Neurosurg 2012;48(4):249–252 Vasudevan A, Kundra P, Priya G, Nagalakshmi P. Giant occipital encephalocele: a new paradigm. Paediatr Anaesth 2012;22(6):586–588 Hoving E, Blaser S, Kelly E, Rutka JT. Anatomical and embryological considerations in the repair of a large vertex cephalocele. Case report. J Neurosurg 1999;90(3):537–541 Kiymaz N, Yilmaz N, Demir I, Keskin S. Prognostic factors in patients with occipital encephalocele. Pediatr Neurosurg 2010;46(1):6–11 Lo BW, Kulkarni AV, Rutka JT, et al. Clinical predictors of developmental outcome in patients with cephaloceles. J Neurosurg Pediatr 2008;2(4):254–257

23

Surgical Approach to Sphenoethmoidal Encephaloceles Robert F. Keating and Derek A. Bruce

23.1╇ Introduction and Background Although it is unlikely that the average neurosurgeon will be presented with a child harboring a sphenoethmoidal encephalocele, the inherent craniofacial issues pose surgical challenges common to a number of other complex skull base anomalies and thus warrant a detailed overview of the diagnostic and therapeutic approach. Despite the relative paucity of published reports, there is an ongoing debate regarding the best approach to repairing this variable skull base defect, revolving around an extracranial vs intracranial (or combination) line of attack. Not surprisingly, the best approach will often depend upon the extent of defect as well as other coexisting morbidities. Smaller defects appear to do well with a more limited transpalatal (transoral) exposure, whereas larger deficiencies often require a transcranial repair (or combination) to deal effectively with reconstructive efforts involving calvarial reinforcement of the floor. In this condition, reported to have an incidence of 1 to 2 per 700,000 live births, the degree and extent of the midline anomalies can be quite variable. This is the rarest of all encephaloceles and principally involves a defect in the skull base in the region of the sella turcica (Fig. 23.1). The patient may present with recurrent meningitis, CSF leak, breathing difficulties, and/or pituitary dysfunction. Concomitant craniofacial disorders include hypertelorism; ocular entities, such as coloboma, anophthalmia, and dysplastic optic discs; cleft lip/palate; and other midline defects, such as dysgenesis of the corpus callosum or facial/nasal clefts1–5 (Fig. 23.2). The etiology and embryological parameters remain unclear at present but are presumed to occur at an early embryonic stage. The timing of diagnosis is often predicated by the presence of a nasopharyngeal mass, which, if large enough, may obstruct respiration at any early age. The more extensive lesions will permit larger herniation of cerebral contents and, in turn, may present in the newborn. Consequently, larger lesions also manifest a greater

a

b

Fig. 23.1â•… Midline defect in skull base with herniation of brain and cerebrospinal fluid (CSF). The location of the pituitary gland and size of defect are critical in the scope of repair. (a) Sagittal view. (b) Coronal view.

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204 Section III.Bâ•… Malformations of the Brain a

Fig. 23.2â•… The bony defect may be limited to a small area of the sella region or be larger, to include part of the planum sphenoidale.

likelihood of pituitary dysfunction and even the potential for visual disturbances (Fig. 23.3). A not uncommon association has been seen with morning glory syndrome6–8; while often presenting with uni-ocular visual changes, it may occasionally be present in a bilateral fashion. These patients manifest with a distinct “morning glory” pattern to their optic disc and may have concomitant pituitary dysfunction of variable severity as well as dysgenesis of the corpus callosum, frontonasal dysplasia, and hypertelorism. It is not uncommon for these individuals to have progressive pituitary and visual loss and thus the need for long-term surveillance.

23.2╇ Operative Detail and Preparation 23.2.1╇ Surgical Approaches • • • • • •

Transoral/palatal Transcranial Intradural Extradural Extended subfrontal with olfactory sparing Endoscopic transnasal

Despite the rarity of sphenoethmoidal encephalocele, there are a number of reports in the literature that document approaches to it from extracranial as well as intracranial avenues. One can even consider endoscopic approaches, although this may be limited for the larger and more involved lesions. The first surgical report was published by Michael Lewin; he commented on the successful, transpalatal approach to repair of sphenoethmoidal encephalocele in two children, at ages 3 months and 4 years, which in turn was facilitated by the presence of a cleft palate.9

b

Fig. 23.3â•… (a) The pituitary gland may be at the base of the sac and attached to the nasal mucosa, or (b) higher in the sac and within the bony canal.

Transoral/Transpalatal Advantages • Able to do repair for simple lesions in up to 50% of patients with cleft palate

Disadvantages • Difficult to obtain adequate soft tissue for repair • Poor exposure for extracranial pituitary glands, extensive calvarial defects • Higher rate of pituitary injury • Higher recurrence rate Lewin points out that transcranial repair of the defect, particularly involving access to the bony defect, is challenging because of the frequently friable nature of the dural sac as well as “distorted cerebral anatomy and abnormal vasculature.” It is

23â•… Surgical Approach to Sphenoethmoidal Encephaloceles interesting to observe that there was no neurosurgical involvement in these cases, and this may have contributed a plastic surgery bias in choosing the surgical route.

Transcranial-Intradural Advantages • Direct visualization of optic chiasm, pituitary gland/stalk

Disadvantages • Difficult to see bottom of sac • Usually impossible to dissect pituitary gland free • Pituitary/hypothalamic injury More recent reports present combined experiences with both transoral as well as transcranial surgical methods. In a report from UCLA,10 Lesavoy et al present a patient repaired at 4 weeks via an extra- as well as intradural repair with a delayed closure of the cleft palate at 15 months of age and a hypertelorism reconstruction at 6 years. The patient was followed for 25 years and has demonstrated excellent maintenance of correction. The authors recommend early repair and cite the need for longterm craniofacial reconstructive efforts. The most recent report,11 in 2013 from Tokyo, relates Ogiwara and Morota’s experience with seven patients over 8 years, treated by either a transpalatal or a combined extra- and intracranial exposure. Four patients with a limited bony defect, confined to the sphenoid bone, were successfully treated by a transpalatal approach. In three other patients, with more pronounced calvarial deficiencies, two patients required multiple surgeries for recurrent encephalocele prolapse after a single approach, but the other patient was doing well after 3.5 years following a combined extra- and intracranial repair at the outset.

encephalocele in 11 patients, with an average age at time of surgery of 4.08 years (0.9–12.6) and a nearequal distribution of sex (6 female patients, 5 males). Fifty-five percent of the patients had an associated cleft lip or palate, and 27% had evidence of corpus callosum dysplasia. The majority of repairs (9) were done by an extended subfrontal, olfactory-sparing, extradural approach with separate dissection of the cribriform plate (thus olfactory-sparing). One case was done via a transoral technique and resulted in worsened pituitary dysfunction as well as the need for reoperation after 2 years. Another individual remains without surgery 11 years out because of the extracranial location of the pituitary gland (normal function) and significant reservations about preservation of pituitary function in the surgical setting. The patient currently is doing well with normal pituitary function. Outcomes were generally excellent for the extended subfrontal approach. In all but one, olfaction was preserved. No individuals had deterioration

a

b

Extended Subfrontal/Olfactory-Sparing Advantages • • • •

Preserves smell Extradural simplicity/safety Protects pituitary gland Minimizes risk to optic chiasm/hypothalamus/ pituitary gland • Good visualization for soft tissue closure and bone graft The first author’s personal experience over a 26-year period has involved repair of sphenoethmoidal

Fig. 23.4â•… (a) Contrast computed tomography (CT) scan taken 1.5 years after the operation shows the bone graft. This was unchanged from an immediate postoperative scan. The graft is not directed toward the clivus and is too inferior to the skull base. (b) Magnetic resonance imaging (MRI) showing an appropriately placed bone graft as a thin black line.

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206 Section III.Bâ•… Malformations of the Brain in pituitary or visual function. One patient had a bone infection, which was treated successfully with antibiotics and débridement. Another patient developed delayed fever and stiff neck after 2 weeks. There was no growth in the CSF, but the child was treated for 1 week for possible meningitis. Another patient had an inappropriately placed skull base bone graft that did not obliterate the encephalocele sac completely but has not required any additional surgery (Fig. 23.4). An additional patient presented with a delayed CSF leak after 2 years, which resolved after placement of a ventriculoperitoneal (VP) shunt. Late complications have included the development of moyamoya disease after 15 years (possibly a result of repeated meningitis as an infant) as well as a cavernous angioma in the pericallosal white matter 3 years after surgery. Overall, there was a 22% incidence of early complications, with recurrence of the encephalocele in one case requiring reoperation (transoral case). All patients undergoing preservation of the cribriform plate retained their sense of smell, and there were no children with permanent worsening of pituitary, neurological, or visual function.

23.2.2╇ Preoperative Considerations • Endocrine and visual field work-up • Thorough genetics and plastic surgery evaluation

a

• Radiographic evaluation with both computed tomography (CT) (bone windows) and magnetic resonance imaging (MRI) • Need to know where pituitary gland resides (intra- vs extracranial) • Need to define location and extent of bony defect • Location of the carotid siphons within the sphenoid bone and distance apart from each other • Location of the optic chiasm

23.3╇ Illustrative Surgical Case Example A 3.8-year-old girl with hypertelorism (no cleft palate/lip) is seen to have a frontal skull base defect with herniated pituitary gland (Fig. 23.5). The patient is placed in a supine position and undergoes a standard bicoronal incision after administration of preoperative antibiotics (cefazolin). Care is taken to preserve a large area of the pericranium for subsequent use as a vascularized graft for the reconstruction of the floor. The bone graft is harvested from the initial frontal craniotomy flap in a split-calvarial fashion. A bifrontal bone flap is removed, allowing access to the subfrontal area as well as exposure for removal of the nasal bone. The olfactory grooves, with intact olfactory nerves, as well as the bony septum are preserved. A midline bandeau of the medial orbital rims and nasal bone down to the nasal bone–cartilage junction is removed through the foramen cecum, exposing the anterior aspect of the cribriform plate and upper nasal septum. The medial canthi are left attached to the nasal bone, and the cuts are made anterior to them to avoid postoperative enophthalmos. This also spares the lacrimal ducts (Fig. 23.6).

b

Fig. 23.5â•… (a) CT and (b) MRI demonstrating defect in frontal floor with herniated pituitary gland lying within the defect.

23â•… Surgical Approach to Sphenoethmoidal Encephaloceles

Fig. 23.6â•… Removal of frontal bone and nasal bone to the level of the crista galli (arrows). Free the olfactory grooves and upper nasal septum to preserve the olfactory nerves intact through the cribriform plate.

The cribriform plate is freed from the skull base with the use of small osteotomes, taking care to protect and preserve the olfactory nerves and not injure the dura at the posterior margin of the cribriform plate. After successful dissection, the nasal septum and mucosa are divided several millimeters below the bone of the skull base to ensure that the olfactory rootlets are intact in the mucosa. Next, the olfactory nerves and residual septum, mucosa, and cribriform plate are mobilized and retracted in a superior direction to allow access to the remaining planum sphenoidale (Fig. 23.7). The approach is now under the planum sphenoidale. Sometimes the sphenoid bone is dysplastic and the sphenoid sinus is not formed. The sphenoid bone is drilled away to expose the dural sac and its attachment to the nasal mucosa. (The carotid siphon is quite close in a small child, and the distance between the two siphons should be measured on the preoperative films to establish exactly how wide the drilling can be.) The dural sac is dissected circumferentially

Fig. 23.8â•… After drilling of the sphenoid bone, the pituitary can now be visualized and dissected from the nasal mucosa (arrow). The dural stalk must be freed 360°, and then the pituitary can be freed from the nasal mucosa. Usually, the pituitary is not enveloped by dura on the inferior surface.

Fig. 23.7â•… Upper nasal septum attached to the bone of the olfactory grooves (arrows). This area is retracted to allow extradural access to the remainder of the anterior skull base. If the planum sphenoidale is normal, it can be removed, but usually this is unnecessary.

360° to be able to mobilize it before placing the bone graft from the floor of the frontal fossa to the clivus. It is usual for the pituitary gland to have a deficient dural membrane at its base. This cannot be sutured, but once the gland is freed from the nasal mucosa and elevated, the excess dura can be invaginated to seal the dural sac temporarily. The frontal pericranial flap is then brought in to surround the bone graft, and tissue glue is placed between the bone graft and the dura to create a seal (Fig. 23.8). The cribriform plate and pituitary gland are elevated sufficiently to enable placement of the bone graft at the skull base (Fig. 23.9). The bone graft is placed with the vascularized pericranial graft to enhance the success of fusion (Fig. 23.10). This graft serves to keep the pituitary gland within the intracranial compartment as well as to reduce the likelihood of a CSF leak. When possible,

Fig. 23.9â•… Freeing of the base of the sac and/or pituitary gland from the nasal mucosa and elevation just high enough to get a bone graft in contact with the clivus.

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208 Section III.Bâ•… Malformations of the Brain

Fig. 23.10â•… Making a sandwich of pericranium around the bone graft (arrow).

the graft is fixed to the skull base with a lag screw, wire, or suture. After successful placement of the bone/pericranial graft, the nasofrontal bone flap is returned to its anatomical position and secured with rigid fixation (Fig. 23.11). Postoperatively, antibiotics are administered for 24 to 48 hours and steroids may be used for 48 hours (tapering dose) to mitigate periorbital/flap swelling. A postoperative CT and MRI are undertaken to confirm location of the bone flap as well as the pituitary gland. A lumbar drain may be utilized for a persistent CSF leak. One needs to remain vigilant for any signs of meningitis.

23.4╇Conclusion Although there has been long-standing debate about the efficacy of intracranial vs extracranial approaches to the repair of sphenoethmoidal encephaloceles, the limited clinical experience to date has failed to establish a definitive answer. Nonetheless, it has been our experience that an extended subfrontal extradural approach is effective for the majority of our patients, while offering the opportunity to spare the olfactory apparatus as well as pituitary and visual function, with limited acute and chronic morbidity.

23.5╇ Pearls and Pitfalls It is important to evaluate for concomitant morbidity, looking for endocrine, visual, or radiographic (head CT and MRI) abnormalities at the outset to

Fig. 23.11â•… Final replacement of the nasofrontal bone flap (arrow).

appreciate the patient’s baseline. Genetic and plastic surgery evaluations are also important. Surgical approach will be directed by extent of pituitary dysraphism and calvarial defect. The larger defects as well as pituitary displacement (from its normal intracranial position) will warrant an extra/ transcranial approach. A transoral/palatal approach may be combined with an intracranial approach to offer greater visualization of extensive pharyngeal lesions. Remaining extradural with an expanded subfrontal approach allows sparing of the olfactory apparatus (smell) and enhances visualization of the skull floor defect and encephalocele (with associated pituitary stalk). Follow up closely for any evidence of delayed CSF leak, hydrocephalus, or meningitis in postoperative period. Preservation of an intact vascularized pedicle of pericranium at the outset is critical for later use when securing the bone graft. Removal of the nasofrontal bone should be undertaken with medial orbital osteotomies made anterior to medial canthus/lacrimal duct. Dissection and mobilization of the cribriform plate and associated olfactory nerves are best served by the use of small osteotomes. Power tools in this tight and limited space are too unpredictable. When dissecting the olfactory nerves for mobilization of the cribriform, it is best to dissect below the level of mucosa, to ensure that the olfactory rootlets are left intact. In the young child, the sphenoid sinus is not developed and the surrounding sphenoid bone is often dysplastic, and it may be difficult to localize the pituitary stalk as well as carotid siphons accurately.

23â•… Surgical Approach to Sphenoethmoidal Encephaloceles Preoperative measurement of the distance between the carotid siphons is important to guide the extent of eventual bony drilling. Intraoperative imaging as well as the use of frameless stereotactic localization may be of value here. It is important to mobilize the dural sac 360° before retraction superiorly (prior to placement of the bone graft). The dural sleeve may be attenuated in places and is frequently deficient at its base. Redundant dura in the area may be invaginated at this location to help seal off any CSF leaks. The pericranial graft and tissue glue significantly contribute as well to closing off this defect. Successful placement of the skull base bone graft entails the use of a vascularized pericranial graft in contact with the bone as well as fixation of the bone to the skull base (lag screw, wire, etc.) A lumbar drain may be used in the setting of a persistent CSF leak in addition to acetazolamide therapy. If the leak persists, it may be necessary to consider a VP shunt.

References Tada M, Nakamura N. Sphenoethmoidal encephalomeningocele and midline anomalies of face and brain. Hokkaido Igaku Zasshi 1985;60(1):48–56 ╇2. Sakoda K, Ishikawa S, Uozumi T, Hirakawa K, Okazaki H, Harada Y. Sphenoethmoidal meningoencephalocele associated with agenesis of corpus callosum and median cleft lip and palate. Case report. J Neurosurg 1979;51(3):397–401

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Modesti LM, Glasauer FE, Terplan KL. Sphenoethmoidal encephalocele: a case report with review of the literature. Childs Brain 1977;3(3):140–153 Koral K, Geffner ME, Curran JG. Trans-sphenoidal and sphenoethmoidal encephalocele: report of two cases and review of the literature. Australas Radiol 2000;44(2):220–224 Acherman DS, Bosman DK, van der Horst CM. Sphenoethmoidal encephalocele: a case report. Cleft Palate Craniofac J 2003;40(3):329–333 Morioka M, Marubayashi T, Masumitsu T, Miura M, Ushio Y. Basal encephaloceles with morning glory syndrome, and progressive hormonal and visual disturbances: case report and review of the literature. Brain Dev 1995;17(3):196–201 Leitch RJ, Winter RM. Midline craniofacial defects and morning glory disc anomaly. A distinct clinical entity. Acta Ophthalmol Scand Suppl 1996; (219):16–19 Hope-Ross M, Johnston SS. The morning glory syndrome associated with sphenoethmoidal encephalocele. Ophthalmic Paediatr Genet 1990;11(2):147–153 Lewin ML. Sphenoethmoidal cephalocele with cleft palate: transpalatal versus transcranial repair. Report of two cases. J Neurosurg 1983;58(6):924–931 Lesavoy MA, Nguyen DT, Yospur G, Dickinson BP. Nasopharyngeal encephalocele: report of transcranial and transpalatal repair with a 25-year follow-up. J Craniofac Surg 2009;20(6):2251–2256 Ogiwara H, Morota N. Surgical treatment of transsphenoidal encephaloceles: transpalatal versus combined transpalatal and transcranial approach. J Neurosurg Pediatr 2013;11(5):505–510

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24

The Chiari I Malformation Zachary L. Hickman and Neil Feldstein

24.1╇ Introduction and Background 24.1.1╇Indications Hans Chiari first described the Chiari I malformation in 1891 based on anatomical observations during autopsy of caudal displacement of the cerebellar tonsils through the foramen magnum without medullary abnormalities.1 Once thought to be rare in the pediatric population, Chiari I has been increasingly diagnosed in children over the past several decades with the advent of magnetic resonance imaging (MRI).2–4 The main indication for the surgical treatment of Chiari I in children is imaging demonstrating unilateral or bilateral cerebellar tonsil herniation through the foramen magnum with loss of cerebrospinal fluid (CSF) signal at the craniocervical junction, in the presence of attributable symptoms that are refractory to medical management, including recurrent occipital headache, nuchal pain, vertigo, parasthesias, extremity paresis, hyperreflexia, ataxia, or nystagmus (Fig. 24.1). Severe cases may result in ventral brainstem compression and associated respiratory and lower cranial nerve dysfunction. Russell and Donald first reported on the association between Chiari malformations and hydrosyrÂ� ingomyelia (syrinx) formation in 1935 (Fig. 24.2).5 Depending on the series, the incidence of syrinx in patients with Chiari I ranges from 20 to 75%.6–10 Current accepted theory implicates compression of the posterior fossa and impairment of CSF flow at the level of the craniocervical junction as the causative process resulting in symptoms and syrinx formation.10–12 Syrinx formation is often associated with myelopathic symptoms in a distribution dependent on the spinal cord level involved; however, even in the absence of associated symptoms, syrinx formation is regarded by the majority of neurosurgeons as an indication for the surgical treatment of Chiari I given the high risk for eventual spinal cord dysfunction.13

210

Fig. 24.1â•… Sagittal T2-weighted MR image of a child with Chiari I malformation demonstrating herniation of the cerebellar tonsils through the foramen magnum with loss of cerebrospinal fluid (CSF) signal at the craniocervical junction.

24â•… The Chiari I Malformation concomitant resolution of the syrinx over time.16 In cases where Chiari I presents in combination with syrinx formation and scoliosis, syrinx resolution often results in cessation of scoliosis curve progression and in regression depending on the severity of the curvature at the time of operative intervention.

24.1.3╇ Alternative Procedures

Fig. 24.2â•… Sagittal T2-weighted MR image of a child with Chiari I malformation and an associated large cervicothoracic syrinx.

Scoliosis has also been associated with Chiari I malformation, generally when presenting in combination with syrinx formation.14 In these cases, primary treatment of the Chiari I malformation is the currently accepted rule, often resulting in resolution of the syrinx and cessation of scoliosis curve progression. However, there is insufficient evidence to put forth recommendations for or against the surgical treatment of asymptomatic Chiari I malformations that present with scoliosis in the absence of syrinx. In these cases, operative management should be based on the clinical judgment of the treating neurosurgeon.

24.1.2╇Goals The primary goal of surgical intervention for Chiari I malformation is to decompress the craniocervical junction, thereby increasing the size of the cisterna magna and restoring normal CSF flow dynamics.15 The majority of patients with Chiari I have an improvement in symptoms following surgical treatment, and for those with associated syrinx there is often

There is no alternative to surgery for children with symptomatic Chiari I malformation that is refractory to medical management. Rather, alternative treatments are related to the specific type of operative procedure to be performed. Historically, a myriad of surgical techniques have been advocated, including suboccipital decompression (SOD) with an appropriate number of cervical laminectomies, dural opening with patch grafting (duraplasty), and various intradural procedures, including lysis of arachnoid adhesions, obex plugging, and cauterization or resection of the cerebellar tonsils.4,6,17–23 Additionally, patients with syrinx have been treated with syringocisternostomy and placement of syringosubarachnoid, syringopleural, syringoperitoneal, thecoperitoneal, and fourth ventricular shunts and stents with varying degrees of success.21,23–34 The mainstay of surgical treatment has been SOD with duraplasty, with or without concomitant intradural procedures.13,35,36 Recently, many authors have advocated for a more conservative surgical approach in children that avoids duraplasty in an effort to prevent complications associated with dural opening.37–44 These complications most commonly include pseudomeningocele, CSF leak, and meningitis; more rarely, hydrocephalus, postoperative apnea, hygroma formation, and subdural and epidural hematoma have been reported.4,7,41,45,46

24.1.4╇ Advantages and Disadvantages The advantages of SOD without duraplasty compared to a more traditional SOD with duraplasty include the following: • Avoidance of the common complications associated with duraplasty and intradural techniques • Decreased operative time • Shorter hospital stay • A quicker return to normal activity Disadvantages of this more conservative technique are largely related to the possibility that the craniocervical junction will be inadequately decompressed, which may lead to continued symptoms postoperatively and the need for a second-look operation. In our institutional experience, how-

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212 Section III.Bâ•… Malformations of the Brain ever, over 90% of children who present with Chiari I malformation, with or without syrinx, can be successfully treated by SOD without duraplasty, having durable resolution of associated symptoms and syrinx resolution. Conversely, the potential advantages of SOD with duraplasty include: • More prompt re-establishment of normal CSF dynamics at the craniocervical junction • Faster or more thorough resolution of an associated syrinx • Faster or more thorough resolution of associated scoliosis Additionally, SOD with duraplasty helps minimize the number of cervical laminectomies required if tonsillar reduction is to be performed. In cases where tonsillar herniation extends to the level of C2 or lower, the senior author typically prefers to pursue SOD with duraplasty and tonsillar reduction rather than forgo duraplasty and perform a multilevel cervical laminectomy. The main disadvantage of SOD with duraplasty is again related to complications commonly associated with dural opening, including pseudomeningocele, CSF leak, and meningitis.

24.1.5╇Contraindications Contraindications to the primary surgical treatment of children with Chiari I malformation via SOD, with or without duraplasty, include: • Significant untreated hydrocephalus • Significant ventral brainstem compression • Significant craniocervical instability In addition, in the setting of rapid loss of neurologic function, rapid progression of syrinx or scoliosis, or likely need for occipital-cervical fusion, we recommend initial treatment with a dural opening procedure rather than the more conservative SOD without duraplasty.

24.2╇ Operative Detail and Preparation 24.2.1╇ Preoperative Planning and Special Equipment In addition to routine preoperative planning, appropriate imaging (typically MRI), demonstrating unilateral or bilateral cerebellar tonsil herniation through the foramen magnum with loss of CSF signal at the craniocervical junction, is necessary. The most caudal cervical level of tonsillar herniation should

be assessed to aid in determining the appropriate number of laminectomies required for adequate decompression. MRI of the entire neuraxis should be obtained to evaluate for associated cervicothoracic syrinx. If scoliosis is present, standard long-cassette radiographs should be used to determine the baseline degree of curvature. Neuroelectrophysiological monitoring may be considered during the surgical treatment of children with Chiari I malformation. Since patients with Chiari I have a tight craniocervical junction, somatosensory evoked potentials (SSEPs) are used to ensure that no injury occurs from hyperflexion of the neck during patient positioning.47,48 Intraoperative recording of brainstem auditory evoked potentials (BAEPs) can be performed using standard techniques as previously described and can be used as a guide to assess the adequacy of the decompression (Fig. 24.3).49,50 These should be set up after the induction of general anesthesia and before positioning to obtain baseline data. The use of intraoperative ultrasonography (USG) is particularly recommended when performing SOD without duraplasty to ensure that the osseous decompression is adequate and extends below the level of the herniated cerebellar tonsils. In our experience, we find intraoperative USG to be less clinically useful when dural opening techniques are utilized. Optimal patient positioning is prone with the head immobilized in an age-appropriate fixation device and the neck flexed, allowing for two finger widths of space between the chin and anterior neck/sternum. Appropriate postpositioning airway pressures and unchanged SSEPs should be confirmed with the anesthesiology and monitoring teams, respectively. If SOD with duraplasty is to be performed, a dural substitute is needed to augment the closure in a relaxed and watertight fashion. Three types of dural substitutes are commonly utilized: autograft, biologic allograft, or synthetic allograft. A common option for autograft is pericranium harvested from the surrounding suboccipital exposure. Another option is lumbodorsal fascia or fascia lata obtained through a separate incision. The advantage of the pericranium graft is that it does not require a separate incision. The downside is that it generally requires extending the incision rostrally to obtain sufficient pericranium for the graft. Biologic allografts are typically bovine pericardium, while synthetic allografts include any of the various manufactured dural substitutes. It is beyond the scope of this chapter to argue the merits or deficiencies of these various allograft materials. Most neurosurgeons are comfortable with one and generally stick with it for all of their duraplasties. The senior author has utilized all of the various graft materials and generally prefers bovine pericardium as a dural substitute when performing SOD with duraplasty.

24â•… The Chiari I Malformation

Fig. 24.3â•… Tracings of BAEPs from a child with Chiari I malformation obtained (1) at baseline with the patient supine (before positioning); (2) following suboccipital decompression (SOD) with division of the atlanto-occipital membrane; and (3) after duraplasty. The recordings demonstrate a reduction in the wave I to V interpeak latency following SOD but no further reduction after opening and patching of the dura.

24.2.2╇ Expert Suggestions and Comments The number of cervical laminectomies should be minimized, but it is necessary to ensure that the osseous decompression is below the final level of the cerebellar tonsils once the surgery is complete. When the level of tonsillar herniation is at, or caudal to, the C2 lamina, the senior author often prefers to pursue an SOD with duraplasty and concomitant tonsillar reduction to avoid more than one cervical laminectomy. It is also important to minimize lateral subperiosteal dissection during exposure to avoid disturbing the joint capsules. This reduces the risk of postoperative “swan neck” deformity.

24.2.3╇ Operative Nuances Suboccipital Decompression Without Duraplasty Technique Following induction of general anesthesia, SSEP and BAEP monitoring are set up and baseline recordings obtained, and proper patient positioning achieved as just described. An appropriately sized midline linear skin incision over the craniocervical junction

is made, and the soft tissue and muscle layers dissected with a minimum of electrocautery. These are then retracted to expose the inferior aspect of the occipital bone, foramen magnum, and the posterior arch of C1, as needed. Posterior fossa decompression is then carried out via a small suboccipital craniectomy, with particular focus on the foramen magnum, using a combination of pneumatic drill and rongeurs. The final dimensions of the craniectomy are variable depending on the individual patient. An appropriate laminectomy is performed to the level of the lowest caudal descent of the cerebellar tonsils. For most patients, only a C1 laminectomy is required. Intraoperative USG is used at this point to demonstrate that the osseous decompression is sufficient to extend below the herniated cerebellar tonsils. The atlantooccipital membrane, which is in large part responsible for the compression at the foramen magnum, is then incised on either side of the midline to avoid unnecessary bleeding. In the senior author’s technique, further decompression is then obtained via dural scoring, in which a series of parallel vertical partial-thickness durotomies are created in the cervical dura (Fig. 24.4). The cervical dura is thicker than the suboccipital dura and more resistant to tearing and unintended durotomy during this procedure. Therefore, we refrain from

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214 Section III.Bâ•… Malformations of the Brain

Fig. 24.4â•… Schematic demonstrating the senior author’s suboccipital decompression (SOD) without duraplasty technique for the treatment of Chiari I malformation in pediatric patients using a standard suboccipital craniectomy, C1 cervical laminectomy, resection of the atlanto-occipital membrane (arrows), and scoring of the outer layer of cervical dura (dashed lines).

extending our durotomies rostral to the foramen magnum. The sharp end of a standard double-ender probe is used to pierce the outer layer of dura at the foramen magnum and is extended caudally via blunt dissection to the limit of the osseous decompression. Care is taken to preserve the integrity of the inner dural layer during this step. As many parallel vertical partial-thickness durotomies are performed as are allowed by the osseous decompression, typically four to eight. Adequacy of the final SOD is assessed at this point by intraoperative USG, demonstrating an increase in the CSF space dorsal to the brainstem and spinal cord as well as a cessation of abnormal pistonlike tonsillar motion and a return of normal, nonpathologic cerebellar pulsation.43,51 Meticulous hemostasis is then achieved through a combination of gentle tamponade and the use of standard hemostatic agents. Bipolar electrocautery of the dura is avoided in order to prevent dural shrinkage and subsequent reduction in the extent of decompression obtained. As a general rule, we refrain from suturing the muscle closed in order to avoid increasing pressure at the site of the osseous decompression, which could theoretically lead to recur-

rent compression at that site. Approximation of the muscle fascia and subcutaneous tissues is attained in layers with interrupted absorbable sutures, followed by final skin closure with a 5–0 running absorbable suture. A standard dressing is applied, and the patient is taken out of fixation and positioned supine for extubation. The surgeon should be prepared for bleeding from the scalp at the sites of head fixation; if gentle tamponade does not stop the bleeding, then a single stitch or staple should suffice.

Suboccipital Decompression with Duraplasty Technique For SOD with duraplasty, an initial osseous decompression is performed as detailed in the preceding section. A common approach to open the dura is in a Y-shaped fashion. In this method, the dura is opened first over the cerebellar hemispheres, with the short limbs of the letter Y meeting in the middle and then extending caudally as a single incision into the cervical dura. To minimize excessive bleeding from midline venous sinuses during dural opening,

24â•… The Chiari I Malformation it is advisable initially to bring the two short limbs of the Y close, but not completely, to the midline. Once both limbs are present, a pair of hemostats is placed from either side across the midline for a total of four hemostats, occluding the venous sinus (Fig. 24.5). Sharp incision with a blade or a pair of fine scissors allows for the completion of the dural opening across the midline. Once this is complete, the upper portion of the dural opening between the two short limbs of the letter Y can then be elevated and secured with temporary stitches. The sinus is tied off with a single 4–0 silk suture, which will remain after dural closure. The dural incision is next extended caudally in the midline into the cervical dura, completing the Y incision and exposing the cerebellar tonsils and upper cervical spinal cord. To minimize bleeding, it is generally helpful to tack the dural edges back, either by sutures hung on hemostats or tied to muscle, depending on surgeon preference. It is advisable to wall off the exposed dura with moist material, such as Cottonoid (DePuy Synthes, West Chester, PA, USA), to prevent the dural edges from desiccating and ultimately to help with the dural closure. If one elects to open the dura without incising the underlying arachnoid, an option at this point is to proceed with dural grafting to avoid the increased risk of CSF leak that accompanies any of the further intradural techniques. Many neurosurgeons feel that

the arachnoid needs to be opened to explore outflow from the fourth ventricle and to lyse any obstructing arachnoid adhesions. This can be done with loupe magnification and sharp dissection; alternatively, an operating microscope may be used. With all the intradural techniques, care must be taken to avoid injury to any blood vessels or cranial nerves, which are visualized in the lateral aspects of the opening. In addition, direct cauterization or manipulation to the surface of the lower brainstem and upper cervical spinal cord are to be avoided at all costs to prevent postoperative complications. If no further surgery is to be performed on the cerebellar tonsils, then duraplasty is undertaken at this point in the procedure. This is discussed in detail later in this chapter. If the operating neurosurgeon elects to decrease the volume of the herniated cerebellar tonsils, there are many techniques available. The safest recommendation is the use of gentle bipolar electrocauterization of the cerebellar tonsil surface (Fig. 24.6a,b). Bipolar electrocautery should be utilized at a low setting in an attempt to keep the pia intact and to avoid entering into the cerebellar tonsils’ parenchyma, which may lead to increased bleeding or potential scarring. This technique is facilitated by the use of an operating microscope, but loupe magnification and a good headlight are also sufficient. Microsurgical techniques are used initially to lyse any arachnoid adhesions

Fig. 24.5â•… Schematic demonstrating the senior author’s technique for occlusion of the midline occipital venous sinus with two pairs of hemostats during initial opening of the posterior fossa dura when suboccipital decompression (SOD) with duraplasty is performed.

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216 Section III.Bâ•… Malformations of the Brain a

b

Fig. 24.6â•… (a) Intraoperative photograph demonstrating significantly herniated right (RT) and left (LT) cerebellar tonsils in a child with Chiari I malformation prior to tonsillar reduction with gentle electrocautery. (b) Intraoperative photograph from the same patient following tonsillar reduction demonstrating markedly decreased size of the right (RT) and left (LT) cerebellar tonsils. The dorsal spinal cord (SC) and caudal aspect of the fourth ventricle (arrow) are now easily visible.

sharply to prevent inadvertent injury to surrounding blood vessels, nerve roots, or the lower brainstem or upper cervical spinal cord. Once the tonsils are freed, they can be individually reduced in volume by applying gentle bipolar electrocautery to the tonsillar surface (Video 24.1). This can be applied dorsally as well as laterally and inferiorly, but as one approaches the undersurface of the cerebellar tonsil, more care needs to be utilized to prevent accidental cauterization of the surface of the lower brainstem or upper spinal cord. A general practice is to continue tonsillar cauterization until the caudal aspect of the fourth ventricle is visualized (Fig. 24.6b). This is easily identified by the presence of choroid plexus at the bottom of the fourth ventricle at the level of the foramen of Magendie. One of the advantages of tonsillar resection or reduction procedures is that they allow for a smaller dural opening. It is possible to deliver the tonsils safely up out of the spinal canal by gently dissecting and lifting, then applying gentle cauterization. This technique prevents the need for extending the incision and dural opening caudal to the initial level of herniation. This is especially helpful if there is significant herniation of the cerebellar tonsils and the treating neurosurgeon is attempting to avoid excessive laminectomies. Other intradural options that are largely historical footnotes at this point include various methods

of obex plugging and stenting of the fourth ventricle. Interested readers can find extensive reviews of these techniques through literature searches. Once the intradural portion of the surgery is complete, the next step is to close the dura. A few centers have advocated leaving the dura open to maximize decompression, but we believe this adds unnecessary risk postoperatively. All readers should realize that in treating Chiari I with dural opening techniques, the dura should not be closed primarily, as it would negate the benefit of having opened the dura in the first place. Duraplasty is performed by use of an appropriate dural substitute to augment the closure in a relaxed and watertight fashion. The available types of dural substitute are discussed previously in this chapter. Regardless of the dural substitute used, the general rule is to obtain as watertight a closure as possible, given that the majority of complications related to Chiari I surgery are related to a CSF issue, specifically pseudomeningocele formation, CSF leak, or meningitis. These can often be avoided with a meticulous dural closure. The senior author has found that the “parachute” technique, which involves both interrupted and running braided nylon monofilament stitching, attains the most dependable closure (Fig. 24.7). After the dural sub-

24â•… The Chiari I Malformation

Fig. 24.7â•… Intraoperative photograph demonstrating the “parachute” technique for duraplasty that is preferred by the senior author. One midline and two immediate paramedian stitches are used in an interrupted fashion to secure the caudal aspect of the dural graft in place. Two lateral paramedian sutures are then used in a running fashion up both limbs of the closure and across the rostral end of the graft.

stitute is cut to the appropriate dimensions, a series of stitches are placed at the caudal end of the graft and, under direct vision, are then attached to the recipient site at the caudal end of the dural opening. The senior author generally uses one midline stitch and two paramedian stitches on either side of the midline. The midline and immediate paramedian stitches are used in an interrupted fashion to secure the graft. The needles are left on the two lateral paramedian stitches and are used in a running fashion up both limbs of the closure and ultimately across the rostral end of the graft (Fig.€24.8). It is important when closing the dura

to get a full-thickness closure of the dural leaves. If not, there is a risk for intradural bleeding. This risk is greatest at the level of the occipital/marginal sinus, and one should take special care to visualize the inner layer of dura and include it in the running stitch. The dural closure should be tested by intradural injection of sterile saline solution before the final dural stitch is applied. The final stitch is then secured and a Valsalva maneuver performed. Any sign of leak can be primarily addressed with single interrupted sutures. One option at this point is the use of various dural sealants that are available, to be applied along the suture line circumferentially.

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218 Section III.Bâ•… Malformations of the Brain disruption of the cervical spine joint capsules and injury to the vertebral arteries. Likewise, the number of cervical laminectomies should be minimized to mitigate the risk of eventual spinal instability. Care should be taken to recognize asymmetry in bone thickness from side to side, which can lead to dural tears during the osseous decompression. Direct electrocautery on the occipital bone should be used with caution, given the unpredictable bone thickness and propensity for bony defects, especially in the very young pediatric population. Excessive electrocautery may result in dural tears or cerebellar injury in these instances. In younger children, particularly, one should avoid excessive bleeding from the midline occipital venous sinus during dural opening. The senior author’s technique for opening the posterior fossa dura, described previously in this chapter, is very useful in this regard.

24.2.4╇ Salvage and Rescue

Fig. 24.8â•… Intraoperative photograph demonstrating the final appearance of the watertight duraplasty.

The remainder of the procedure, including hemostasis, soft tissue closure, and the final dressing, is undertaken in a similar fashion as for SOD without duraplasty, with particular attention paid to obtaining a watertight closure of the muscle fascia with interrupted absorbable sutures. The method of skin closure, via subcuticular stitch, interrupted or running nylon stitch, or staples, is at the discretion of the treating neurosurgeon. The senior author generally prefers a loose, wide-based running nylon stitch when dural opening is performed.

24.2.3╇ Avoidance of Pitfalls The operating neurosurgeon should take care to avoid hyperflexion of the neck when positioning the patient for surgery. The optimal amount of flexion is such that there are two finger widths of space between the chin and anterior neck/sternum. Appropriate airway pressures and stable SSEPs should be confirmed after positioning is complete. It is also important to coordinate the use of appropriate anesthetic agents with the monitoring team so that SSEPs and BAEPs may be continuously recorded throughout the procedure. Excessive lateral subperiosteal dissection during exposure should be avoided to prevent

As discussed previously, meticulous dural and muscle fascia closure is essential when SOD with duraplasty is performed. Persistent CSF leaks that are noted intraoperatively following dural patch grafting can be managed through the use of additional interrupted sutures, different graft sizes or materials, or various dural sealants. Active hydrocephalus should be treated prior to any dura-opening Chiari procedure to mitigate the risk of pseudomeningocele, CSF leak, and meningitis. Toddlers and young children often have less soft tissue for closure than older children and may be at greater risk for CSF leak postoperatively. In these cases, placement of a spinal drain after the induction of general anesthesia can be considered to aid in the prevention of CSF leaks and related complications. Failure of improvement in symptoms or syrinx resolution postoperatively should be assessed and managed on a case-by-case basis. In toddlers and young children, there is a higher potential for osseous overgrowth of the decompression. These cases may be managed by repeat SOD without duraplasty to remove only the new bone growth. In general, however, if a repeat operation is deemed necessary, a more invasive intervention should be considered during the second surgery: if SOD without duraplasty was initially undertaken, reoperation should likely include duraplasty; if SOD with duraplasty was initially undertaken, reoperation should likely include more extensive intradural manipulations, and so forth. In the case of syrinx, if symptoms continue and there is no appreciable resolution following SOD with duraplasty and tonsillar reduction/ resection, then direct shunting of the syrinx may be considered.

24â•… The Chiari I Malformation

24.3╇ Outcomes and Postoperative Course 24.3.1╇ Postoperative Considerations Postoperative care is standardized in most institutions for pediatric suboccipital craniectomies. Choices for the initial management of pain include patient-controlled analgesia (PCA) versus a combination of intravenous narcotics, muscle relaxants, and anti-inflammatory medications. Patients are transitioned to oral medications prior to discharge from the hospital. It is important to mobilize the patient as soon as possible, with the child sitting up and out of bed hopefully within the first 12 to 24 hours. In addition to the avoidance of CSF-related complications, one of the main advantages of SOD without duraplasty is that the treating neurosurgeon can be more liberal in allowing the patient to return to normal activity. In these cases, discharge to home is generally on postoperative day 2, with a full return to sports after 3 or 4 weeks or as tolerated. For SOD with duraplasty, there should be increased vigilance to detect any evidence of CSF-related complications. These patients are generally discharged to home on postoperative day 3, with a full return to normal activity after 1 to 3 months. If postoperative recovery is proceeding as expected, then reimaging is deferred until approximately 1 year after surgery. At that time, MRI of the cervical and thoracic spine, as appropriate, is obtained to assess for resolution of any associated syrinx. Routine imaging to screen for the development of spinal instability in asymptomatic patients is not recommended. However, should a patient develop symptoms that may be attributed to spinal instability (e.g., persistent neck pain, new radicular or myelopathic symptoms), then this should be assessed with upright cervical plain radiographs with flexion-extension views. Computed tomography (CT) imaging of the cervical spine may also be obtained at the discretion of the treating neurosurgeon. Patients with Chiari I malformation who present with scoliosis should be routinely evaluated for cessation of curve progression by their orthopedic surgeon or neurosurgeon, as appropriate.

24.3.2╇Complications The most common complications associated with SOD without duraplasty are those for any routine pediatric suboccipital craniectomy. The main advantage of this technique is that it avoids the most common complications associated with dural opening, including pseudomeningocele, CSF leak, and meningitis. Inadequate decompression is avoided by routine use of intraoperative USG and BAEP record-

ings. For SOD with duraplasty, the risk of CSF-related complications can be mitigated by ensuring that active hydrocephalus is treated prior to surgery; through the occasional use of spinal drains in toddlers and young children who have less robust soft tissues for closure; through the use of appropriate dural graft sizes and materials; and by ensuring a meticulous, watertight dural and muscle fascia closure. These complications should be managed in the usual fashion, and reoperation for persistent pseudomeningocele and CSF leaks seriously considered. It is important to consider that persistent CSF leaks may be secondary to occult infection or aseptic meningitis. Failure of postoperative improvement may rarely be due to osseous overgrowth of the decompression, particularly in SOD without duraplasty. If preoperative symptoms fail to improve or an associated syrinx fails to involute adequately following Chiari I surgery, a second-look operation with a more invasive intervention may be necessary.

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Chiari H. Über Veränderungen des Kleinhirns infolge von Hydrocephalie des Grosshirns. Dtsch Med Wochenschr 1891;17(42):1172–1175 Klekamp J, Batzdorf U, Samii M, Bothe HW. The surgical treatment of Chiari I malformation. Acta Neurochir (Wien) 1996;138(7):788–801 Krieger MD, McComb JG, Levy ML. Toward a simpler surgical management of Chiari I malformation in a pediatric population. Pediatr Neurosurg 1999;30(3):113–121 Park JK, Gleason PL, Madsen JR, Goumnerova LC, Scott RM. Presentation and management of Chiari I malformation in children. Pediatr Neurosurg 1997;26(4): 190–196 Russell DS, Donald C. Mechanism of internal hydrocephalus in spina bifida. Brain 1935;58(2):203–215 Levy WJ, Mason L, Hahn JF. Chiari malformation presenting in adults: a surgical experience in 127 cases. Neurosurgery 1983;12(4):377–390 Paul KS, Lye RH, Strang FA, Dutton J. Arnold-Chiari malformation. Review of 71 cases. J Neurosurg 1983;58(2):183–187 10.3171/jns.1983.58.2.0183 Saez RJ, Onofrio BM, Yanagihara T. Experience with Arnold-Chiari malformation, 1960 to 1970. J Neurosurg 1976;45(4):416–422 10.3171/jns.1976.45.4.0416 Williams B. The distending force in the production of “communicating syringomyelia.” Lancet 1969;2(7613): 189–193 Williams B. A critical appraisal of posterior fossa surgery for communicating syringomyelia. Brain 1978;101(2): 223–250 Williams B. On the pathogenesis of syringomyelia: a review. J R Soc Med 1980;73(11):798–806 Oldfield EH, Muraszko K, Shawker TH, Patronas NJ. Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications

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for diagnosis and treatment. J Neurosurg 1994;80(1):3– 15 10.3171/jns.1994.80.1.0003 Rocque BG, George TM, Kestle J, Iskandar BJ. Treatment practices for Chiari malformation type I with syringomyelia: results of a survey of the American Society of Pediatric Neurosurgeons. J Neurosurg Pediatr 2011;8(5):430–437 10.3171/2011.8.PEDS10427 Krieger MD, Falkinstein Y, Bowen IE, Tolo VT, McComb JG. Scoliosis and Chiari malformation Type I in children. J Neurosurg Pediatr 2011;7(1):25–29 10.3171/2010.10.PEDS10154 Batzdorf U. Chiari I malformation with syringomyelia. Evaluation of surgical therapy by magnetic resonance imaging. J Neurosurg 1988;68(5):726–730 Feldstein NA, Choudhri TF. Management of Chiari I malformations with holocord syringohydromyelia. Pediatr Neurosurg 1999;31(3):143–149 Gardner WJ. Hydrodynamic mechanism of syringomyelia: its relationship to myelocele. J Neurol Neurosurg Psychiatry 1965;28:247–259 Hoffman HJ, Neill J, Crone KR, Hendrick EB, Humphreys RP. Hydrosyringomyelia and its management in childhood. Neurosurgery 1987;21(3):347–351 Logue V, Edwards MR. Syringomyelia and its surgical treatment—an analysis of 75 patients. J Neurol Neurosurg Psychiatry 1981;44(4):273–284 Bidziński J. Late results of the surgical treatment of syringomyelia. Acta Neurochir Suppl (Wien) 1988;43: 29–31 Bidziński J. Pathological findings in suboccipital decompression in 63 patients with syringomyelia. Acta Neurochir Suppl (Wien) 1988;43:26–28 Garcìa-Uria J, Leunda G, Carrillo R, Bravo G. Syringomyelia: long-term results after posterior fossa decompression. J Neurosurg 1981;54(3):380–383 10.3171/ jns.1981.54.3.0380 Peerless SJ, Durward QJ. Management of syringomyelia: a pathophysiological approach. Clin Neurosurg 1983;30:531–576 Fujii K, Natori Y, Nakagaki H, Fukui M. Management of syringomyelia associated with Chiari malformation: comparative study of syrinx size and symptoms by magnetic resonance imaging. Surg Neurol 1991;36(4):281–285 Isu T, Iwasaki Y, Akino M, Abe H. Syringo-subarachnoid shunt for syringomyelia associated with Chiari malformation (type 1). Acta Neurochir (Wien) 1990;107(3-4): 152–160 Padovani R, Cavallo M, Gaist G. Surgical treatment of syringomyelia: favorable results with syringosubarachnoid shunting. Surg Neurol 1989;32(3):173–180 Rhoton AL Jr. Microsurgery of Arnold-Chiari malformation in adults with and without hydromyelia. J Neurosurg 1976;45(5):473–483 10.3171/jns.1976.45.5.0473 Tator CH, Meguro K, Rowed DW. Favorable results with syringosubarachnoid shunts for treatment of syringomyelia. J Neurosurg 1982;56(4):517–523 10.3171/ jns.1982.56.4.0517 Barbaro NM, Wilson CB, Gutin PH, Edwards MS. Surgical treatment of syringomyelia. Favorable results with sy-

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ringoperitoneal shunting. J Neurosurg 1984;61(3):531– 538 10.3171/jns.1984.61.3.0531 Van Calenbergh F, Hoorens G, Van den Bergh R. Syringomyelia: a retrospective study Part II: Diagnostic and therapeutic approach. Acta Neurol Belg 1990;90(2):100–110 Philippon J, Sangla S, Lara-Morales J, Gazengel J, Rivierez M, Horn YE. Treatment of syringomyelia by syringo-peritoneal shunt. Acta Neurochir Suppl (Wien) 1988;43:32–34 Vassilouthis J, Papandreou A, Anagnostaras S, Pappas J. Thecoperitoneal shunt for syringomyelia: report of three cases. Neurosurgery 1993;33(2):324–327, discussion 327–328 Vengsarkar US, Panchal VG, Tripathi PD, et al. Percutaneous thecoperitoneal shunt for syringomyelia. Report of three cases. J Neurosurg 1991;74(5):827–831 10.3171/jns.1991.74.5.0827 Milhorat TH, Johnson WD, Miller JI. Syrinx shunt to posterior fossa cisterns (syringocisternostomy) for bypassing obstructions of upper cervical theca. J Neurosurg 1992;77(6):871–874 10.3171/jns.1992.77.6.0871 Haines SJ, Berger M. Current treatment of Chiari malformations types I and II: A survey of the Pediatric Section of the American Association of Neurological Surgeons. Neurosurgery 1991;28(3):353–357 Haroun RI, Guarnieri M, Meadow JJ, Kraut M, Carson BS. Current opinions for the treatment of syringomyelia and Chiari malformations: survey of the Pediatric Section of the American Association of Neurological Surgeons. Pediatr Neurosurg 2000;33(6):311–317 Isu T, Sasaki H, Takamura H, Kobayashi N. Foramen magnum decompression with removal of the outer layer of the dura as treatment for syringomyelia occurring with Chiari I malformation. Neurosurgery 1993;33(5):845–850 Hida K, Iwasaki Y, Koyanagi I, Sawamura Y, Abe H. Surgical indication and results of foramen magnum decompression versus syringosubarachnoid shunting for syringomyelia associated with Chiari I malformation. Neurosurgery 1995;37(4):673–679 Gambardella G, Caruso G, Caffo M, Germanò A, La Rosa G, Tomasello F. Transverse microincisions of the outer layer of the dura mater combined with foramen magnum decompression as treatment for syringomyelia with Chiari I malformation. Acta Neurochir (Wien) 1998;140(2):134–139 Genitori L, Peretta P, Nurisso C, Macinante L, Mussa F. Chiari type I anomalies in children and adolescents: minimally invasive management in a series of 53 cases. Childs Nerv Syst 2000;16(10-11):707–718 Munshi I, Frim D, Stine-Reyes R, Weir BK, Hekmatpanah J, Brown F. Effects of posterior fossa decompression with and without duraplasty on Chiari malformation-associated hydromyelia. Neurosurgery 2000;46(6):1384–1389, discussion 1389–1390 Navarro R, Olavarria G, Seshadri R, Gonzales-Portillo G, McLone DG, Tomita T. Surgical results of posterior fossa decompression for patients with Chiari I malformation. Childs Nerv Syst 2004;20(5):349–356 10.1007/s00381-003-0883-1

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Yeh DD, Koch B, Crone KR. Intraoperative ultrasonography used to determine the extent of surgery necessary during posterior fossa decompression in children with Chiari malformation type I. J Neurosurg 2006; 105(1, Suppl):26–32 10.3171/ped.2006.105.1.26 Caldarelli M, Novegno F, Vassimi L, Romani R, Tamburrini G, Di Rocco C. The role of limited posterior fossa craniectomy in the surgical treatment of Chiari malformation type I: experience with a pediatric series. J Neurosurg 2007; 106(3, Suppl):187–195 10.3171/ped.2007.106.3.187 Depreitere B, Van Calenbergh F, van Loon J, Goffin J, Plets C. Posterior fossa decompression in syringomyelia associated with a Chiari malformation: a retrospective analysis of 22 patients. Clin Neurol Neurosurg 2000;102(2):91–96 Cristante L, Westphal M, Herrmann HD. Craniocervical decompression for Chiari I malformation. A retrospective evaluation of functional outcome with particular attention to the motor deficits. Acta Neurochir (Wien) 1994;130(1-4):94–100 Anderson RC, Emerson RG, Dowling KC, Feldstein NA. Attenuation of somatosensory evoked potentials dur-

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ing positioning in a patient undergoing suboccipital craniectomy for Chiari I malformation with syringomyelia. J Child Neurol 2001;16(12):936–939 Anderson RCE, Dowling KC, Feldstein NA, Emerson RG. Chiari I malformation: potential role for intraoperative electrophysiologic monitoring. J Clin Neurophysiol 2003;20(1):65–72 Friedman WA, Kaplan BJ, Gravenstein D, Rhoton AL Jr. Intraoperative brain-stem auditory evoked potentials during posterior fossa microvascular decompression. J Neurosurg 1985;62(4):552–557 10.3171/jns.1985.62.4.0552 Anderson RCE, Emerson RG, Dowling KC, Feldstein NA. Improvement in brainstem auditory evoked potentials after suboccipital decompression in patients with Chiari I malformations. J Neurosurg 2003;98(3):459–464 10.3171/jns.2003.98.3.0459 McGirt MJ, Attenello FJ, Datoo G, et al. Intraoperative ultrasonography as a guide to patient selection for duraplasty after suboccipital decompression in children with Chiari malformation type I. J Neurosurg Pediatr 2008;2(1):52–57 10.3171/PED/2008/2/7/052

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25

The Chiari II Malformation Hugh J. L. Garton

25.1╇ Introduction and Background 25.1.1╇ Definition, Pathophysiology, and Epidemiology In his original paper of 1891, describing the hindbrain herniations in postmortem specimens of infants, Chiari described three variations.1 The second of these, type II, featured caudal displacement of the cerebellar vermis, fourth ventricle, and caudal medulla into the upper cervical spine. He distinguished this from the type I variation, in which only the cerebellar tonsils were positioned caudally with the spine. He observed the association between the type II malformation and myelomeningocele (MMC), as did Arnold, his contemporary.2 Today, the term “Chiari II malformation” (CMII) is often used broadly to describe the constellation of intracranial anatomical abnormalities that are seen in MMC. Table 25.1 lists common spinal and intracranial abnormalities seen as part of, or in association with the Chiari II complex.3 The posterior fossa itself is small, and, critically for the surgeon, the tentorium is often markedly down-sloping, with the torcula near to the foramen magnum. The fourth ventricle is elongated, often extending into the upper cervical spine. The choroid plexus can remain in the subarachnoid space, at or below the foramen of Magendi, and could be confused for an enhancing mass lesion.4 The herniated vermian tissue, when seen clinically at surgery, is scarred and distorted and often difficult to separate from the adjacent brainstem. A medullary kink is seen in upward of two-thirds of patients with CMII.5 With the inferior displacement of the lower brainstem into the upper cervical spinal canal, the kinking occurs as the upper cervical spinal cord, just below the gracile and cuneate nuclei, is held by the dentate ligaments, with the medullary segment folded dorsally.6,7 Cranial nerves exiting the lower medulla must ascend back up into the cranial vault

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to exit their respective foramina. The medullary kink is often seen near the inferiormost aspect of the ectopic cerebellar vermis, and it must be recognized as distinct to avoid surgical trauma. Syringomyelia is present in the majority of patients.8 Spinal arachnoid cysts, often quite large, either can be seen at birth or develop during early childhood.9–11 Dysplasia of the brainstem nuclei has been noted in half of patients coming to autopsy, including the olivary nuclei and basal pontine nuclei (derivatives, along with the cerebellum itself, of the alar plate of the rhombencephalon).12 Similarly, abnormal brainstem auditory evoked potentials have been noted to correlate with clinical symptoms thought to be due to the CMII malformation.13 Rostrally, the tectum is frequently shaped into a bird’s beak by the partial or complete fusion of the collicular plates (Fig. 25.1).3 The incisura is generally enlarged, and when the cerebellar volume is normal, in the face of a small posterior fossa, the superior aspect of the cerebellum is seen to “tower” through it. Similarly, the small posterior fossa may force the cerebellum to wrap around the brainstem, sometimes termed “cerebellar inversion.”14 In the midbrain and diencephalon, the massa intermedia is enlarged and the floor of the third ventricle is often thickened, which increases the difficulty in performing endoscopic third ventriculostomy. Despite the hydrocephalus that is present in most patients with CMII and MMC, the third ventricle is typically not overly enlarged. The aqueduct of Sylvius, studied at autopsy, has been noted to be foreshortened, tortuous, and dorsally migrated.5 The hydrocephalic child with CMII/MMC very commonly has a colpocephalic lateral ventricular appearance with a dilated atrium and occipital horn, with the frontal horn typically more normal in size. The etiology of hydrocephalus in these patients is not clear. In classical terms, both obstructive and communicating mechanisms have been demonstrated in individual patients. Infection, exposure of the arachnoid to the potentially

25â•… The Chiari II Malformation Table 25.1â•… Common manifestations associated with the Chiari II malformation in myelodysplasia Brainstem and cerebellar abnormalities

Cerebellar vermis, fourth ventricle displaced inferiorly into cervical spine, vermis often attached to, and difficult to separate from, underlying brainstem Choroid plexus displaced inferiorly, often remaining outside the ventricle Cervicomedullary kink Cerebellum may be small and entirely within the cervical spine in some cases Tectum is “beaked” related to fusion of the colliculi3

Cervical spine abnormalities

Syringomyelia Spinal arachnoid cysts Bony C1 arch incomplete, but with persistence of periosteal fibrous band

Skull and cranial dura

Small posterior fossa, enlarged foramen magnum Fenestrated falx cerebri Low-lying tentorium and torcula Lückenschädel

Ventricles/midbrain

Hydrocephalus, with prominence of the atria and occipital horns Enlarged massa intermedia Thickened third ventricular floor

Cerebral cortex

Heterotopias Medial occipital lobe interdigitation Corpus callosum dysgenesis

toxic effects of amniotic fluid, lack of CSF pressure to drive CSF pathway development, and obstruction of CSF outflow are all among proposed mechanisms. Obstruction, if present, is theorized to arise from a tightly compacted posterior fossa at the aqueduct, fourth ventricular outflow obstruction, and/or inadequate posterior fossa subarachnoid spaces, among others.15–17 Malformations of cortical development, such as periventricular nodular heterotopias, are quite frequent, as is callosal dysgenesis, along with abnormalities of the falx cerebri, leading to interdigitation of the right and left medial occipital cortical gyri. The pathophysiological mechanism by which Chiari II develops and leads to the variety of abnormalities just iterated is uncertain. The leading hypothesis, advanced by McLone and Knepper, 16 is that the open neural tube present in utero in children with MMC allows leakage of CSF during the normal period of neural tube closure and thereafter. This deprives the embryo of a normal period of transient CSF outflow obstruction that would ordinarily cause distention of the developing ventricles. The result is a lack of

normal cell–cell interaction between the developing brain and surrounding mesenchyme, leading to an overly small posterior fossa, which then cannot accommodate the developing cerebellum, producing either upward or downward herniation or both. In this theory, the intimate relationship between the germinal matrix and unpressurized ventricles also accounts for the cortical migration disorders seen. Hydrocephalus, secondary to mesenchymal crowding just described, is the consequence of the CMII malformation, not a cause.15 The results of the Management of Myelomeningocele Study (MOMS) trial of in utero myelomeningocele closure appear to be at least partially consistent with this theory. Prenatal closure was associated with a significant reduction in both the incidence and severity of the posterior fossa abnormalities in comparison to postnatal closure. Thirty-six percent of prenatally closed patients had no hindbrain herniation present, compared to just 4% of postnatally closed infants, while 67% of postnatally closed patients had moderate to severe herniation vs. only 25% in the prenatal closure group.8 Cerebellar tonsil position has been noted to ascend after postna-

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224 Section III.Bâ•… Malformations of the Brain

25.2╇ Clinical Presentation

Fig. 25.1â•… T1-weighted sagittal MRI of the Chiari II malformation. The posterior fossa is crowded with an elongated brainstem and the cerebellar tonsils and vermis are herniated below the foramen magnum. There is dysgenesis of the copus callosum and hypoplasia of the falx with stenogyria (multiple small compacted gyri separated by shallow sulci). The massa intermedia is enlarged and the tectum is beaked.

tal closure also, although this was not correlated with avoidance of CMII-related symptoms.18 Alternative, less well-developed hypotheses have been proposed. For example, Williams has proposed that posterior fossa hypoplasia is the primary event, leading secondarily to hydrocephalus, which results in spinal cord injury and/or anencephaly.19 However, this ignores or fails to explain a large body of evidence demonstrating the pathophysiology of neural tube closure failure and is contradicted by the observation that the CMII malformation is present in utero prior to the development of hydrocephalus. Traction on the brainstem from a tethering malformation has also been considered, with the idea that the malformation is pulled inferiorly. However, it has been argued that, in anatomical studies, the dentate ligaments prevent distal traction from exerting significant force on distant, rostral spinal cord segments.20 The overall incidence of CMII follows the incidence of MMC closely, as seen in the MOMS prenatal closure trial. In the United States, despite the fortification of cereals and breads with folate, about 3.4 per 10,000 children are born with MMC, and over 90% will have CMII.21 The rate at which children become specifically symptomatic varies between 15 and 30%.22–25 Symptomatic CMII is the major source of mortality in infancy among children with MMC, usually related to respiratory insufficiency or aspiration.8,23,26

There are three age-dependent presentations of CMII. At birth, a small number of neonates will fail to breathe properly at or immediately following birth.8,25 Older infants become symptomatic over weeks to months, with swallowing dysfunction and poor feeding, aspiration, stridor, and apneic spells. Associated physical findings include those expected from dysfunction of the lower cranial nerves, namely, a weak cry, horseness, and stridor. Arm weakness is also frequently reported.25 Opisthotonus can sometimes be present. In older children, it is more common to see spinal and cerebellar dysfunction, with myelopathic features, such as progressive arm weakness, loss of muscle mass, spasticity, and occasionally ataxia and suboccipital neck pain. Often patients report deterioration of handwriting or self-catheterization skills. These symptoms typically come on slowly. Cranial nerve dysfunction can certainly be present but is less dramatic than in younger patients.27 Progressive scoliosis may occur. Since syringomyelia is often coincidentally present, such symptoms in older patients are difficult to assign exclusively to either pathology, and the pathologies themselves are closely intertwined.

25.3╇Imaging 25.3.1╇Ultrasound Prenatal ultrasound (US) of patients with potential neural tube defects includes an evaluation of the posterior fossa. A banana sign is the curved appearance of the cerebellar hemispheres in the absence of a visible cisterna magna.28 This is a US equivalent of cerebellar inversion, noted previously, and relates to the small volume of the posterior fossa displacing the cerebellar hemispheres around the brainstem. This sign has a reported sensitivity of 100% and specificity of 96% in a high-risk population at 16 to 23 weeks gestation, and similar rates of accuracy via transvaginal US prior to 12 weeks.29,30 A second common prenatal cranial US finding in MMC is the lemon sign. This relates to the appearance of the frontal bones and is unrelated to the CMII malformation. Postnatal US has also been used both pre- and intraoperatively, demonstrating both the nature of the CMII malformation and the frequently associated syringomyelia.9

25.3.2╇ Magnetic Resonance Imaging Postnatal magnetic resonance imaging (MRI) is the standard evaluative tool for patients with symptoms potentially related to CMII. It demonstrates the presence and severity of the anatomical features of the

25â•… The Chiari II Malformation malformation described. With reference to diagnostic and operative decision making, MRI also provides an assessment of ventricles, the relative compression of the brainstem and cerebellum in the upper cervical spine, and the degree of syringomyelia present. In autopsy studies, syringomyelia is present in over 80% of patients with MMC/CMII. MRI studies of living patients note its presence in more like 20 to 40% of patients.31,32 In the highly selected group of children in the MOMS trial, at approximately 1 year of age, 39% of prenatally closed patients had syringomyelia vs. 58% for those closed postnatally.8 The incidence at birth is not well reported, but is likely in the 20 to 30% range also. Prenatal MRI is essential in the evaluation of children for prenatal closure of myelomeningocele. In situations where prenatal closure is not contemplated, prenatal MRI can be helpful with respect to the possibility of CMII symptoms postnatally but is not mandatory.33

25.4╇ Treatment Options and Alternatives The surgical management of CMII is based on case series and expert opinion. There are few if any comparative trials. All statements about management should be regarded in this light. Nevertheless, patients with symptoms require care, albeit with imperfect clinical decision support. Any child with symptoms presumed to be from CMII should be evaluated and treated for hydrocephalus and/or shunt failure before a CMII decompression is considered. This is true for both the infant and child presentations. What constitutes an adequate evaluation of the shunt in this setting is not established. Imaging alone was used as the sole modality in 31 of 33 patients in one recent series.34 Others have argued for a more aggressive approach, given the possibility of shunt failure without overt ventricular size change, using modalities such as intracranial pressure (ICP) monitoring and direct shunt exploration.35 In a child not already shunted, shunt placement should precede CMII decompression, but how long one should wait before proceeding to shunt placement is unclear. In many case series, it is apparent that infants with bilateral vocal cord paralysis and/ or severe periodic apnea are treated quite urgently, with only a short interval (1 to 7 days) between shunt placement and CMII decompression.25,27,34 While there is some debate about the utility of CMII decompression, clear-cut brainstem dysfunction in the absence of shunt failure or untreated hydrocephalus is usually considered an indication for surgical decompression. The two most convincing symptoms attributed to brainstem dysfunction are stridor and swallowing dysfunction. In neonates

and infants, where the presentation is generally more rapid, inspiratory stridor is the classic physical finding of vagus nerve dysfunction. Direct laryngoscopic assessment will confirm the diagnosis and should be performed in suspected cases. Ocal et al reported that bilateral complete cord paralysis was associated with a very poor prognosis when present at birth, rather than when occurring in later infancy.26 Other series quote a higher survival rate, but with frequent need for tracheostomy.25,34 Swallowing dysfunction, with associated chronic aspiration, is seen in both infants and older children. Indirect evidence by history may include repeated pneumonias and poor weight gain and growth. Barium swallow studies with impregnated foods demonstrate the diagnosis. Esophageal manometry and pH studies have also been used.27 Alternative treatments, often needed even in the face of a completed CMII decompression, include tracheostomy and gastrostomy tube (G-tube) placement. There is some evidence that, for patients suffering from significant swallowing or respiratory distress, earlier rather than delayed CMII decompression is associated with an improved outcome.25,27 Sleep apnea is a more complicated symptom to sort out. Some patients will have severe prolonged apneas with cyanosis, and these have been reported to have high mortality rates despite decompression.36 However, such patients are fortunately rare. Waters and colleagues performed polysomnograms on about 80% of patients in a single-institution myelomeningocele clinic. Results were classified as mildly abnormal in 42% and moderate or severely abnormal in 17%. In this latter group, 12 patients were found to have central obstruction, and five had an obstructive pattern. Of note, a history of CMII decompression was strongly predictive of moderate to severe apnea, perhaps demonstrating that the procedure is not highly likely to correct the problem. In addition, following diagnosis, two patients in this series who had not previously undergone decompression, subsequently were decompressed, neither with notable improvement. Also of note, one-third of patients treated surgically for obstructive sleep apnea failed to improve, suggesting perhaps a lack of pharyngeal muscle control. Nevertheless, the authors argued for surgical treatment of the obstruction where observed.37 Thus, it is the authors’ opinion that, in patients with sleepdisordered breathing, particularly in the absence of other compelling features of brainstem compression, due consideration should be given to management with positive-pressure support techniques, such as continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP). In older patients, as mentioned previously, the symptoms of CMII often include myelopathic features. Because syringomyelia is very common, it becomes relevant to sort out whether symptoms are due to the CMII, the syringomyelia, or both. Usually, secondary

225

226 Section III.Bâ•… Malformations of the Brain spinal cord tethering enters the differential diagnosis also. La Marca et al, reporting on the Chicago experience, noted that among 45/231 patients who had significant syringes, one-third had typical CMII symptoms, such as difficulty swallowing, and just under a third had a mixed clinical picture. All were evaluated for CSF shunt failure. The former group underwent decompression alone, despite the syrinx, while the latter underwent both decompression and syrinx shunt placement among other procedures. The authors argued that the generally positive outcome supported this clinically driven approach.32 Mehta and colleagues, reviewing the experience at Johns Hopkins, studied the impact of tethered cord release (TCR) on CMII symptoms.38 As noted previously, traction on the brainstem has been one of the longstanding hypotheses to explain the dysfunction seen, particularly when it occurs later in childhood. In 29 of 86 cases, the authors catalogued 44 symptom complaints related to upper extremity motor/sensory function and bulbar features, including swallowing dysfunction, three-fourths of which improved after TCR. Nystagmus and apnea improved in only about half the patients who complained of them. No patient experienced complete relief. Follow-up MRI demonstrated no change in the configuration of the posterior fossa. The authors concluded that mild and moderate symptoms traditionally attributed to CMII could be treated with TCR but that severe symptoms should be treated with CMII decompression.38

MRI assessment of the severity of the CMII has been examined for prognostic significance. Wolpert et al evaluated features including the caudal displacement of the pons, various cervicomedullary deformities, and the presence of CSF anterior to the cervical spinal cord. None of these related to the clinical condition of the patient.39 Most authorities caution against using the level of cerebellar descent as a predictive marker for surgical treatment. Imaging nevertheless almost certainly plays a role in treatment decisions. A patient with a capacious foramen magnum and upper cervical spine with ample CSF around the herniated vermis and brainstem is not as likely to receive a posterior fossa decompression, especially for less than clear symptoms, as is a patient with a paucity of CSF around the brainstem or with cystic dilation of neural structures in the region. Imaging features have been reported to guide surgical decisions in the type of decompression performed. In the St Louis series, although not explicitly stated in the text, a patient with an expanded fourth ventricle extending into the upper cervical spine is described as being typical of a group treated with bony decompression and duraplasty, by the study authors, while an otherwise similar patient with a relative paucity of CSF around the brainstem but no other remarkable features is described as typical of a patient receiving a bone-only decompression.34 Fig. 25.2 provides the author’s preoperative decision-making algorithm.

Fig. 25.2â•… Management algorithm. CMII, Chiari II malformation; MRI, magnetic resonance imaging; UE, upper extremity.

25â•… The Chiari II Malformation

25.5╇ Operative Details and Preparation

25.6╇ Key Steps, Operative Nuances, Pitfalls to Avoid

25.5.1╇ Preoperative Planning, Positioning, and Perioperative Monitoring

Soft tissue exposure is from the suboccipital region to the lowest extent of the cerebellum and medullary kink. The author prefers to use occipital periosteum as a dural graft when necessary, and the incision is sized to allow this also. Exposure of the suboccipital bone can be limited, as the bony removal at the foramen magnum is either modest or not necessary at all. The spinous processes and lamina of the cervical spine are exposed down to the needed level, with care taken to avoid injury in the midline in the typically bifid C1 and to avoid excessive dissection around the cervical facet complex. Cervical laminectomies of the affected levels can then be performed. If needed, a modest suboccipital craniectomy can be performed. Because the operation is performed for decompression, the author prefers to remove the lamina with a high-speed drill, avoiding placing instruments into the epidural space while the lamina remains intact. Although midline posterior bone at C1 is often absent, a fibrous band including the periosteum of C1 is almost always present and must be excised. Whether a durotomy should be performed is the subject of current debate, as it is with patients undergoing decompression for CMI. The debate is reviewed in a subsequent section. If a durotomy is to be performed, as is the author’s general practice, intraoperative US is used to confirm the intradural anatomy prior to durotomy. A midline durotomy is then made. The inferior extent of the dissection should be the normal cervical spinal cord, below the most caudal extent of the cerebellar vermis and medullary kink, which should be included in the decompression. The dissection should be carried superiorly sufficient to expose the floor of the fourth ventricle. The rostral dissection must stop short of the torcula, obviously, but smaller dural venous sinuses are frequently encountered in the rostral dural opening and can produce vigorous bleeding. The key to controlling this is to ensure that either a clip or bipolar cautery is applied to the full thickness of the dural opening, including both inner and outer leaves. Persistent bleeding almost always indicates that only the outer layer has been included in the attempt at hemostasis. Under magnification, an intradural dissection is performed to lyse arachnoid adhesions and to dissect the intradural structures until the fourth ventricular outflow is freed. Several pitfalls must be avoided:

Assuming one has made the decision to proceed with surgical correction of the CMII, the most important preoperative step has already been mentioned, but bears repeating: Be sure that there is clear evidence of adequate treatment of hydrocephalus. The author prefers, in the absence of an examinable fontanelle, to perform either ICP monitoring or direct surgical exploration of a CSF shunt to ensure its function before proceeding with a CMII decompression. Shunt taps, although advocated for this purpose also, provide only transient information about ICP and can be inaccurate in the face of partial catheter obstruction. Additional issues that deserve consideration include assessment of the bony stability of the craniocervical junction. Bony abnormalities of the craniocervical junction are common, and flexion-extension films are desirable in older patients to demonstrate the stability of the bony articulations in the flexed position in which the patient will be operated on.40 Somatosensory evoked potentials (SSEP) and motor evoked potentials (MEP) are used in perioperative monitoring by some authors but not others.22,25,34,35 I prefer to use them; however, it is common that no usable information can be obtained in very young patients or older patients with significant disabilities. It is known that latencies of several of the observed peaks are prolonged in patients with CMII but decrease closer to normal with increasing age.41,42 Because the brainstem is directly in the operative field and potentially subject to manipulation, it has been standard practice in our institution to place a pad for pacing/defibrillation in the unlikely event of sudden cardiac arrhythmia (usually bradyarrythmia) during the procedure. This has been observed very infrequently. It has been our practice to monitor arterial pressure by catheter during CMII decompression. Preoperative review of the neuroanatomy should focus on the position of the torcula, which, as previously noted, is very low-lying, sometimes just above the bony lip of the foramen magnum. Patients are positioned prone, on chest rolls with the head flexed. Generally, only modest flexion is needed. The pathology is at the foramen magnum and below, so there is no need to be able to reach high up into the posterior fossa. The head can be supported with either a horseshoe head holder or a pin fixation device depending on the child’s age.

1. The medullary kink is usually positioned at the same level as the inferior vermis. These two structures can be mistaken for each

227

228 Section III.Bâ•… Malformations of the Brain other. It is best to identify the normal spinal cord below the kink as an aid. Intraoperative ultrasound may also be very helpful in this regard. 2. As noted previously, the choroid plexus is often present at the outflow of the fourth ventricle rather than in it. Once this is recognized, it can be used to guide the surgeon to the fourth ventricle. Several anatomical variations have been described, including intramedullary choroid plexus, glial and arachnoid cysts, and subependymoma.43,44 Once the free movement of CSF from the fourth ventricle is noted, closure is then performed with copious irrigation and attention to hemostasis to minimize intradural blood. A dural patch graft is then sewn into position in a watertight fashion, and superficial closure is performed in anatomical layers.

25.6.1╇ Intraoperative Alternatives Whether the dura should be opened in patients undergoing CMII is now a matter of debate. James and Brant reported on 18 patients with CMII undergoing bone-only decompression. Pain, arm weakness, and spasticity improved reliably, swallowing difficulties in about half, and respiratory difficulties in four of six patients.45 The St. Louis group reported on 33 patients, 26 of whom underwent bone-only decompression. The results of these patients were compared with the remaining seven patients who underwent duraplasty. Importantly, the criteria by which patients were allocated to the treatment choices are not specified. Patients undergoing boneonly decompression were younger. Operative time and blood loss were less, as was length of stay, but the differences were modest. Outcomes between the two groups were similar, with the exception that syringomyelia, when present, was less likely to improve in the bone-only group. Four of five reoperations performed in bone-only decompression group were for asymptomatic increase in syrinx size, and bony regrowth was observed in one of these patients.34

25.6.2╇Complications Typical complications to be anticipated following the procedure are those seen with any central nervous system (CNS) procedure, including bleeding, infection, neurological injury, and CSF leak or pseudomeningocele. Additionally, improvement of

preoperative symptoms of stridor and dysphagia, while not strictly a complication, can take weeks or even months, so patients with these symptoms preoperatively will need careful postoperative management to avoid additional sequelae, such as respiratory arrest and aspiration. Some patients will be best served by tracheostomy and G-tube placement if recovery appears delayed. Vigilance for shunt failure, particularly in those undergoing duraplasty, is essential. In one clinical series, where reported, shunt failure rates were as high as 76% over 3 years.35 Spine instability following cervical laminectomy in pediatric patients is well reported in the literature generally. Specifically, in patients with CMII, 19 of 20 patients who had undergone decompression had an average of 4 mm of anterolisthesis of C2 on C3 (vs. 1 mm in a control CMII group that had not undergone decompression).46 However, McLaughlin et al reported only one of 32 patients required treatment for instability at a mean followup of 3.7 years.47

25.7╇ Outcomes and Postoperative Course Historically, mortality with or without surgical intervention for neonates with severe symptoms from CMII was 50 to 75%.24,48 More recent studies have a much lower reported mortality of 4 to 20%.22,25,34 However, the mortality reported in these series appears to be related to the failure of preoperative symptoms to improve rather than operative misadventure. For example, patients with preoperative bilateral vocal cord paralysis are unlikely to improve in the early postoperative period. Even if eventual recovery is possible, tracheostomy is required in the short term in most patients. Less severe forms of vocal cord dysfunction, including apneic spells and stridor not associated with bilateral vocal cord paralysis, have a better chance of recovery, and tracheostomy may be avoidable. Similarly, G-tube placement can be predicted to be needed in patients with more severe swallowing dysfunction preoperatively but, like tracheostomy, may not be permanent. Older patients with motor and sensory symptoms attributed to CMII appear to fare much better. Table 25.2 details abstracted outcomes from several case series of CMII decompressions. As with most surgical diseases, as much diligence should be placed on deciding who can be helped as on the technical performance of the procedure.

25â•… The Chiari II Malformation Table 25.2â•… Tabulation of outcome events in selected series of CMII decompression Study

Number, age, follow-up

Mortality

Improved stridor (avoided trach)

Improved GI

Improved motor

7/12

10/10

Vandertop et al25

N = 17, < 1 mo, FU 65 mo

2/17

8/13

Talamonti and Zella22

N = 24, 0–14 yr, FU 11 yr

2/9 (< 1 yr) 0/15 (> 1 yr)

Transitory tracheostomy and G-tube in all young patients, all recovered eventually

3/3

Pollack et al27

N = 25 (13: < 2 mo; 12: 6 mo–10 yr), FU 38 mo

3/13

1/6 with bilateral VCP; 8/8 with stridor but no VCP

5/10

8/8

Messing-Jünger and Röhrig35

N = 14, mean 7.1 yr, FU 2 yr

0/14

na

na

na

Akbari et al34

N = 33 (26: mean 2 yr; 7: mean 8 yr), FU 5 yr

1/33

12/18

11/19

2/3

Abbreviations: FU, follow-up; GI, gastrointestinal; mo, month; na, not available; VCP, vocal cord paralysis; yr, year.

References ╇1.

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Chiari H. Über Veränderungen des Kleinhirns infolge von Hydrocephalie des Grosshirms. Dtsch Med Wochenschr 1891;17(42):1172–1175 Koehler PJ. Chiari’s description of cerebellar ectopy (1891). With a summary of Cleland’s and Arnold’s contributions and some early observations on neuraltube defects. J Neurosurg 1991;75(5):823–826 Naidich TP, Pudlowski RM, Naidich JB. Computed tomographic signs of Chiari II malformation. II: Midbrain and cerebellum. Radiology 1980;134(2):391–398 Stark JE, Glasier CM. MR demonstration of ectopic fourth ventricular choroid plexus in Chiari II malformation. AJNR Am J Neuroradiol 1993;14(3):618–621 el Gammal T, Mark EK, Brooks BS. MR imaging of Chiari II malformation. AJR Am J Roentgenol 1988;150(1): 163–170 Daniel PM, Strich SJ. Some observations on the congenital deformity of the central nervous system known as the Arnold-Chiari malformation. J Neuropathol Exp Neurol 1958;17(2):255–266 Peach B. Arnold-Chiari malformation: anatomic features of 20 cases. Arch Neurol 1965;12:613–621 Adzick NS, Thom EA, Spong CY, et al; MOMS Investigators. A randomized trial of prenatal versus postnatal repair of myelomeningocele. N Engl J Med 2011;364(11):993–1004 DiPietro MA, Venes JL, Rubin JM. Arnold-Chiari II malformation: intraoperative real-time US. Radiology 1987;164(3):799–804 Rabb CH, McComb JG, Raffel C, Kennedy JG. Spinal arachnoid cysts in the pediatric age group: an association with neural tube defects. J Neurosurg 1992;77(3):369–372

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Heinz R, Curnes J, Friedman A, Oakes J. Exophytic syrinx, an extreme form of syringomyelia: CT, myelographic, and MR imaging features. Radiology 1992;183(1): 243–246 Gilbert JN, Jones KL, Rorke LB, Chernoff GF, James HE. Central nervous system anomalies associated with meningomyelocele, hydrocephalus, and the ArnoldChiari malformation: reappraisal of theories regarding the pathogenesis of posterior neural tube closure defects. Neurosurgery 1986;18(5):559–564 Koehler J, Schwarz M, Boor R, et al. Assessment of brainstem function in Chiari II malformation utilizing brainstem auditory evoked potentials (BAEP), blink reflex and masseter reflex. Brain Dev 2000;22(7):417–420 Schmitt HP. “Inverse Chiari type II syndrome” in untreated hydrocephalus and its relationship to typical Arnold-Chiari syndrome. Brain Dev 1981;3(3): 271–275 McLone DG, Dias MS. The Chiari II malformation: cause and impact. Childs Nerv Syst 2003;19(7-8):540–550 McLone DG, Knepper PA. The cause of Chiari II malformation: a unified theory. Pediatr Neurosci 1989;15(1): 1–12 Walsh DS, Adzick NS, Sutton LN, Johnson MP. The rationale for in utero repair of myelomeningocele. Fetal Diagn Ther 2001;16(5):312–322 Morota N, Ihara S. Postnatal ascent of the cerebellar tonsils in Chiari malformation type II following surgical repair of myelomeningocele. J Neurosurg Pediatr 2008;2(3):188–193 Williams H. A unifying hypothesis for hydrocephalus, Chiari malformation, syringomyelia, anencephaly and spina bifida. Cerebrospinal Fluid Res 2008;5:7 Stevenson KL. Chiari type II malformation: past, present, and future. Neurosurg Focus 2004;16(2):E5

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Boulet SL, Yang Q, Mai C, et al; National Birth Defects Prevention Network. Trends in the postfortification prevalence of spina bifida and anencephaly in the United States. Birth Defects Res A Clin Mol Teratol 2008;82(7):527–532 Talamonti G, Zella S. Surgical treatment of CM2 and syringomyelia in a series of 231 myelomeningocele patients. Neurol Sci 2011;32(Suppl 3):S331–S333 McLone DG. Results of treatment of children born with a myelomeningocele. Clin Neurosurg 1983;30:407–412 Park TS, Hoffman HJ, Hendrick EB, Humphreys RP. Experience with surgical decompression of the Arnold-Chiari malformation in young infants with myelomeningocele. Neurosurgery 1983;13(2):147–152 Vandertop WP, Asai A, Hoffman HJ, et al. Surgical decompression for symptomatic Chiari II malformation in neonates with myelomeningocele. J Neurosurg 1992;77(4):541–544 Ocal E, Irwin B, Cochrane D, Singhal A, Steinbok P. Stridor at birth predicts poor outcome in neonates with myelomeningocele. Childs Nerv Syst 2012;28(2): 265–271 Pollack IF, Pang D, Albright AL, Krieger D. Outcome following hindbrain decompression of symptomatic Chiari malformations in children previously treated with myelomeningocele closure and shunts. J Neurosurg 1992;77(6):881–888 Nicolaides KH, Campbell S, Gabbe SG, Guidetti R. Ultrasound screening for spina bifida: cranial and cerebellar signs. Lancet 1986;2(8498):72–74 Blumenfeld Z, Siegler E, Bronshtein M. The early diagnosis of neural tube defects. Prenat Diagn 1993;13(9):863–871 Campbell J, Gilbert WM, Nicolaides KH, Campbell S. Ultrasound screening for spina bifida: cranial and cerebellar signs in a high-risk population. Obstet Gynecol 1987;70(2):247–250 Piatt JH Jr. Syringomyelia complicating myelomeningocele: review of the evidence. J Neurosurg 2004;100(2 Suppl Pediatrics):101–109 La Marca F, Herman M, Grant JA, McLone DG. Presentation and management of hydromyelia in children with Chiari type-II malformation. Pediatr Neurosurg 1997;26(2):57–67 Chao TT, Dashe JS, Adams RC, Keefover-Hicks A, McIntire DD, Twickler DM. Fetal spine findings on MRI and associated outcomes in children with open neural tube defects. AJR Am J Roentgenol 2011;197(5):W956–961 Akbari SH, Limbrick DD Jr, Kim DH, et al. Surgical management of symptomatic Chiari II malformation in infants and children. Childs Nerv Syst 2013 Messing-Jünger M, Röhrig A. Primary and secondary management of the Chiari II malformation in

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Section III.C

Malformations of the Spine

26

Craniocervical Junction Abnormalities in Children Arnold H. Menezes

26.1╇ Introduction and Background The treatment of pathological states associated with the craniovertebral junction (CVJ) in children is uniquely challenging because of the underlying complex anatomy, embryology, and biomechanics of this region.1 The author’s experience started with a “decision tree” for management of such pathology in 1977 and still has held true in managing more than 6,000 patients symptomatic with CVJ abnormalities. The pathology encountered is myriad. The application of surgical techniques in children has grown out of the understanding of managing problems in adults, including the surgical approaches and fusion techniques.1,2 Factors taken into consideration are: (1) reducibility, which implies ability to restore anatomical alignment, thereby relieving compression on the neural structures; (2) direction of encroachment on the cervicomedullary neural structures, and the mechanics

of compression; (3) presence of abnormal ossification centers; and (4) etiology of the underlying process and the presence of secondary neural abnormalities, such as hindbrain herniation syndrome, hydrocephalus, syringomyelia, and vascular compression. The primary goal is to relieve compression at the cervicomedullary border, and, in reducible lesions, stabilization is paramount to maintain the neural decompression.3 In irreducible lesions, decompression is mandated at the site of encroachment―whether with a ventral, posterolateral, or posterior approach. In any circumstance, if instability is present or expected, a posterior fixation is critical for stability (Fig. 26.1). In the older individual, traction is utilized in the decision making. The application of traction is age dependent. In the very young, traction is done after the child is asleep in the operating room. Otherwise, preoperative “halo” traction is applied and the effects are documented (Fig. 26.2a–c). Decision making follows Fig. 26.1.

Fig. 26.1â•… “Decision tree” for management of craniovertebral abnormalities.

233

234 Section III.Câ•… Malformations of the Spine a

b

c

Fig. 26.2â•… A 14-year-old adolescent boy with traumatic atlantoaxial instability with ruptured cruciate ligament. (a) Awake fiberoptic intubation in a collar (left) prior to crown “halo” application. After anesthesia for arthrodesis (right). (b) (A) Preoperative measurements of atlas lateral mass screw length and C2 translaminar screw lengths. (B) Operative view of right C1 lateral mass screw and C2 pars screw in place. (c) (L) Intraoperative view of bilateral interlaminar rib grafts supplementing fusion. (R) Postoperative lateral cervical radiograph visualizing the fusion construct.

26â•… Craniocervical Junction Abnormalities in Children Imaging consists of plain radiographs, magnetic resonance imaging (MRI) in dynamic mode with the flexed and extended position in the sagittal plane, and computed tomography (CT), including twodimensional (2D) and three-dimensional (3D) reconstructions for diagnosis and preoperative planning. Pediatric patients afflicted with CVJ abnormalities have been recognized from early infancy. Hence one has to choose the most appropriate time for surgical intervention and, in the interim, conservative

management using stabilization techniques, such as molded bracing. Problems include distortion of the craniocervical border and cervicomedullary compression, distortion, and dislocation. The presence of a Chiari I malformation or hindbrain herniation in CVJ abnormalities is always secondary to a small posterior fossa. This includes the appearance of syringohydromyelia.4,5 Hence the primary problem first needs to be tackled, unlike the case of the child in Fig. 26.3a–c.

a

b

Fig. 26.3â•… An 11-year-old child who underwent posterior fossa decompression for Chiari I abnormality 1 year earlier. The patient returned with increasing quadriparesis and decreased sensation to pain in hands. (a) Note ventral pontomedullary compression by abnormal clivus-odontoid articulation. There is now a cervical syringomyelia present. A primary ventral decompression is needed. (b) Composite of photomicrographs during transoral odontoid resection. (L) The odontoid tip is being freed. (R) Cruciate ligament seen after odontoid removal. (Continued on page 236)

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236 Section III.Câ•… Malformations of the Spine

c Fig. 26.3 (Continued)â•… (c) (L) Intraoperative view of dorsal occipitocervical fusion construct in patient 2A and 2B. (R) Postoperative cervical radiograph of the occipitocervical fusion.

26.2╇ Operative Detail and Preparation 26.2.1╇ Craniovertebral Junction Fusions Before the age of 4 years, the author prefers to use autologous rib graft for either occipitocervical or atlantoaxial arthrodesis. The reader is referred to appropriate references for details.5,6 Instrumented fusion is now possible with an older child, above the age of 5 years, who has adequate size of midline occipital keel and axis pedicle, and pars size of more than 4 mm (Fig. 26.2a–c). It is also possible to do a lateral mass fusion at the atlas if the anatomy accepts this. Hence imaging is critical. In light of the length limitations of this chapter, the ways to avoid complications are provided in Table 26.1 and Table 26.2.

26.2.2╇ Transoral Craniovertebral Decompression This procedure can be divided into the open variety and the endoscopic procedures carried out through the nose as well as through the mouth. The open transoral procedures that are most used are the transoral-transpalatopharyngeal approach, the Le Fort I

dropdown maxillotomy, the midline glossotomy, and the mandibular split. The latter are rarely used at the author’s institution. The endoscopic procedures are very limited in their usefulness due to the inability to provide closure of the posterior pharyngeal space, as well as the fact that most of these children have hypoplastic occipital condyles and a near horizontal clivus. This means that the approach has to be through the mouth and is limited. However, it can be combined with the open procedure. Complications associated with the transoral procedures and the means to avoid them are listed in Table 26.3 and Table 26.4.

26.3╇Conclusion It is critical to avoid fusion in situ without trying to restore anatomical alignment (Fig. 26.4). Decompressive procedures as well as fusion procedures in children must be followed into adulthood because of the forward growth of the ventral craniocervical junction, such as the clivus and odontoid process. Hence posterior fixation alone may require a ventral procedure at a later stage (Fig. 26.4). There are significant complications that are associated with instrumentation in a very young child and the author shares his experience in the hopes of preventing complications.

26â•… Craniocervical Junction Abnormalities in Children Table 26.1â•… Perioperative complications and avoidance with transoral-transpalatopharyngeal craniovertebral junction surgery Complication

Prevention/management

1. Unnecessary ventral procedure

Preoperative reduction if possible.

2. Oral aperture too small

Distance between incisors must be > 25 mm. May improve with administration of intravenous paralyzing agents. May need mandible and/or tongue split or another approach.

3. Inability to reach clivus for resection due to platybasia

Divide soft palate and possibly hard palate. Intraoperative fluoroscopy.

4. Lost, cannot reach distal dens or epidural masses

Fluoroscopy. Novice may use frameless stereotaxy. Resection of dens starts at rostral end.

5. Damage to eustachian tubes and hypoglossal nerves

Lateral exposure limited to 2 cm from midline.

6. Persistent bleeding at clivus

Bleeding from circular sinus needs fibrillar collagen/oxidized cellulose; otherwise, both dural leaves clipped. Pannus and arterial bleeding must be coagulated.

7. Intra-arachnoid lodgement, cerebrospinal fluid (CSF) leakage

Preoperative lumbar drain. Attempt dural closure. Fascia + fat + plasma glue. CSF drainage. 1 week antibiotics.

Table 26.2â•… Delayed complications of transoropharyngeal craniovertebral junction surgery Complication

Prevention/management

1. Severe tongue swelling

IV Decadron; intermittent release of tongue depressor. Retain dental guards in children.

2. Meningitis

Cerebrospinal fluid (CSF) exam. Lumbar drainage. No oral intake. Antibiotics. Close CSF leak.

3. Palatal dehiscence

Inadequate closure. Must be reclosed.

4. Neurological worsening

Check alignment → traction. Reassess meningitis? Abscess? Retained lesion? Vascular compromise? Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA).

5. Pharyngeal dehiscence

< 1 week―reclosure > 1 week―hyperalimentation, antibiotics

6. Retropharyngeal abscess

Check for osteomyelitis and meningitis. Extrapharyngeal drainage.

7. Delayed pharyngeal bleeding

Secondary infection. Exclude osteomyelitis and vertebral artery erosion and false aneurysm. MRI, computed tomography (CT), and angiography necessary!

8. Persistent hoarseness of voice

Appears 4–6 weeks after surgery. Granulomas on vocal cords must be visualized. Vocal cord rest and proton pump inhibitors needed.

9. Velopalatine incompetence

Usually appears 4–6 months after surgery. Pharyngeal retraining/prosthesis. Retropharyngeal fat injection. May need pharyngeal flap.

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238 Section III.Câ•… Malformations of the Spine Table 26.3â•… Perioperative complications and avoidance with dorsal craniocervical fusions Complication

Prevention/management

1. Difficult intubation

Preoperative airway evaluation Awake or through mask fiberoptic intubation while maintaining cervical alignment using external orthosis

 ystemic hypotension and spinal 2. S cord infarction

Avoiding systemic hypotension during intubation and judicious use of vasopressors to maintain physiological mean arterial pressure

3. G  ross instability at craniovertebral junction

Interim stabilization of C1 and C2 with a dorsal approach with towel clips during subperiosteal exposure

4. Inability to stabilize

Selection of appropriate fusion technique with recourse to salvage instrumentation and noninstrumentation techniques

5. Inability to achieve transarticular Need to use low T1 insertion site trajectory 6. Inadequate bony purchase in C1 lateral mass

In children, must point to medial aspect of C1 lateral mass because of shape

7. D  ecline in neurological status or worsening of intraoperative neurophysiological monitoring

Verification of physiological cardiorespiratory status Maintenance of dynamic traction Operative positioning and fixation under fluoroscopic guidance Awake positioning in older children when compliant

8. N  eurological worsening in immediate postoperative period

Postoperative epidural hemorrhage or seroma If due to use of bone morphogenic protein, drain should be used at surgery Surgical exploration and débridement

9. C  erebrospinal fluid egress from unintended durotomy

Use hemostatic agents and place screw when encountered during occipital screw placement Identification and primary repair of spinal dural tear

10. E xcessive venous bleeding with C1 lateral mass exposure

Careful subperiosteal dissection behind C1 posterior arch with bipolar cauterization as needed Last resort is C2 ganglionectomy to visualize the dorsal rostral C1 lateral mass

11. A  rterial bleeding from within C1–C2 foramen

Visible with cannulated transarticular screw; place screw and leave in situ Contralateral instrumentation is contraindicated Postoperative angiogram evaluation

12. V  enous bleeding during occipital Preoperative identification of occipital keel and transverse sinus with measurement of screw placement occipital diploë on imaging studies enables accurate determination of screw length and placement site Placement of hemostatic agents (oxidized cellulose or surgical) and use of flat-head screws

a

b

c

Fig. 26.4â•… (a) Midsagittal T1-weighted magnetic resonance imaging (MRI) of brain and C-spine at age 3 years. Child underwent dorsal O-C1–C2 bone fusion without reduction. (b) MRI at age 9 years. Note the invaginated odontoid and new holocord syrinx. (c) Reconstructed three-dimensional (3D) computed tomography (CT) of craniovertebral junction (CVJ) at age 9 years and the solid osseous dorsal fusion. Patient needed reduction prior to initial fusion.

26â•… Craniocervical Junction Abnormalities in Children Table 26.4â•… Delayed complications and their management with craniovertebral junction dorsal fusions Complication

Prevention/management

1. Hypoglossal nerve injury and pharyngeal penetration

Accurate determination of C1 screw length on preoperative computed tomography (CT) studies Verification on postoperative CT study Operative revision as needed

2. Neurological decline

Surgical site infection Loss of anatomical alignment with neural compromise Vascular injury or delayed arteriovenous (AV) fistula. Obtain angiogram. Violation of spinal canal by screw. Operative revision is mandated.

3. Wound infection

Careful hemostasis Perioperative antibiotics May need débridement and closure with drain. Instrumentation and grafts can be salvaged successfully following surgical débridement and appropriate antibiotic regimen.

4. Loss of anatomical alignment

Construct failure with screw fracture or pull out. Redo procedure. If no instrumentation done, place in traction and “halo” vest.

5. Nonunion, pseudoarthrosis

External orthosis for 4–5 months in instrumented fusions with bone grafts and 6 months for noninstrumented cases Revision surgery is mandated in face of persistent instability.

6. Delayed onset of pain after bracing removed

Neuropathic pain if screws violate neural foramen Pseudofusion with persistent instability. CT examination may document “halo” around screws.

7. Upper airway obstruction and dysphagia

Fusion in flexion alignment with oropharyngeal space compromise. Operative revision is needed to restore neutral alignment.

References ╇1. Menezes

AH. Decision making for management of craniovertebral junction pathology. Oper Tech Neurosurg 2005;8:125–130 ╇2. Menezes AH. Surgical approaches: postoperative care and complications “transoral-transpalatopharyngeal approach to the craniocervical junction.” Childs Nerv Syst 2008;24(10):1187–1193 ╇3. Menezes AH, Fenoy KA. Remnants of occipital vertebrae: proatlas segmentation abnormalities. Neurosurgery 2009;64(5):945–953, discussion 954

╇4. Menezes

AH. Craniovertebral junction abnormalities with hindbrain herniation and syringomyelia: regression of syringomyelia after removal of ventral craniovertebral junction compression. J Neurosurg 2012;116(2):301–309 ╇5. Menezes AH. Craniocervical fusions in children. J Neurosurg Pediatr 2012;9(6):573–585 ╇6. Ahmed R, Menezes AH. Management of operative complications related to occipitocervical instrumentation. Neurosurgery 2013; 72(2, Suppl Operative)ons214– ons228, discussion ons228

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27

Disorders of the Vertebral Column Luigi Bassani and Douglas Brockmeyer

27.1╇ Introduction and Background Surgical stabilization of the pediatric cervical spine is necessary when a patient’s bony and/or ligamentous structures provide insufficient structural support and protection for the spinal column and spinal cord. There are relatively few indications for stabilizing the cervical spine, which is generally achieved through either an anterior or a posterior approach. This chapter focuses primarily on anterior cervical approaches in pediatric patients. It discusses the general principles regarding anterior cervical procedures, along with the nuances that ensure operative success.

27.1.1╇ Indications for Cervical Stabilization The anterior spinal column provides much of the structural stability of the pediatric cervical spine. It is susceptible to abnormalities caused by congenital deformity, neoplasia, and traumatic injury. Children may be born with congenital anomalies, such as Klippel-Feil syndrome, Larsen syndrome, achondroplasia, or spinal segmental dysgenesis, which can all destabilize the cervical spine. Spinal stenosis and postlaminectomy/postradiation “swan neck” deformities may also require anterior cervical stabilization. Neoplastic growths within the vertebral body, such as Langerhans cell histiocytosis, osteoid osteomas/osteoblastomas, osteochondromas, and aneurysmal bone cysts (Fig. 27.1), can cause destruction and collapse of the vertebral column, with subsequent kyphosis and spinal canal compromise. Finally, trauma can inflict flexion/distraction injuries resulting in anterior wedge compression fractures, fracture dislocations, jumped facets, and unstable posterior ligamentous injuries (Fig. 27.2).

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Patients with congenital anomalies, neoplasia, or traumatic injury present with typical clinical syndromes. Neck pain, especially with motion, is the most common presenting complaint. Neurological deficits, such as radiculomyelopathic findings, may also be present but are uncommon in a nontraumatic setting. Bowel and bladder symptoms are uncommon. Children with significant cervical pain and/or progressive neurological deficits should be considered for early, perhaps urgent, surgical intervention. Children with congenital anomalies and progressive deformity are also candidates for surgical intervention―but on a more elective basis. As a general rule, anterior cervical procedures should be undertaken by those experienced in dealing with spinal pathology in children.

27.1.2╇Goals The primary goals of anterior cervical spine surgery are to restore cervical spine alignment and provide structural stability. In the process, successful rigid fixation should alleviate neck pain as well as prevent progressive neurological compromise. Other goals include motion and growth preservation, which are both accomplished by fusing the minimum number of levels necessary to achieve stability.

27.1.3╇ Alternate Procedures There are two main alternate ways in which nonoperative cervical support can be accomplished. The simplest form is a cervical collar, which can be used in children for minor to moderate injuries, such as unilateral facet fractures, Jefferson fractures, and hangman’s fractures. More complex cervical spine traumas, such as combined Jefferson and hangman’s fractures, may require more rigid external fixation,

27â•… Disorders of the Vertebral Column a

b

c

d

Fig. 27.1â•… A 14-year-old adolescent girl presented with 9 months of neck pain and 2 weeks of right C6 radicular pain and signs and symptoms of myelopathy. (a) Coronal and (b) axial magnetic resonance images (MRIs) of the cervical spine revealed loss of height, abnormal T2 hyperintensity, and vivid T1 enhancement in the right C6 vertebral body, pedicle, and posterior elements with extension into the right C5–C6 neural foramen. After embolization of the tumor and sacrifice of the right vertebral artery, an anterior C6 corpectomy with tumor resection and reconstruction with allograft and C4–C6 fusion was performed. (c) Postoperative X-rays and (d) sagittal computed tomography (CT) of the cervical spine at 3 months revealed good alignment and a solid fusion from C4–C6.

such as a “halo” vest. A halo can provide enough long-term, rigid fixation that long segment fusions and adjacent segment breakdown can be avoided in certain circumstances. The disadvantages of a halo are the need to wear a large external brace for approximately 12 weeks, and the risks of halo pin site infections and scarring.

27.1.4╇Advantages Cervical spine instrumentation and fusion, whether anterior or posterior, can be used as a stand-alone construct for stabilization and reconstruction, avoiding an external halo orthosis. Internal fixation maintains long-term cervical growth by avoiding disruption of

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242 Section III.Câ•… Malformations of the Spine a

b

c

d

Fig. 27.2â•… A 16-year-old adolescent boy playing on a trampoline flipped and landed on his head with his neck in the flexed position. (a) Initial computed tomography (CT) scans of the cervical spine revealed a C5–C6 flexion distraction injury with focal kyphosis and splayed facet joints at C5–C6. (b) A magnetic resonance imaging (MRI) and short T1 inversion recovery (STIR) sequence of the cervical spine revealed significant posterior interspinous ligamentous injury. Together, these findings supported C5–C6 instability requiring surgical stabilization. (c) Preoperative and (d) postoperative cervical spine plain films revealed improvement in cervical alignment, restoration of disk height, and reduction of facet splaying after surgery.

axial growth plates at adjacent levels. Furthermore, internal fixation preserves motion segments at the level above and below the construct. The theoretical disadvantage is that it may ultimately lead to adjacent segment degeneration over time; however, this has not been seen in the senior author’s 20 years of experience.

27.2╇ Operative Detail and Preparation 27.2.1╇ Preoperative Evaluation Children with suspected cervical spine abnormalities require appropriate imaging to properly determine the surgical care plan. The first step is to obtain

anterior-posterior and lateral cervical spine plain X-rays (Fig. 27.2c). These films provide information about vertebral body height, spinal alignment, and the presence or absence of block vertebrae. Obtaining a thin-cut cervical spine computed tomography (CT) scan with sagittal (Fig. 27.2a) and coronal reconstruction is the next step, giving the surgeon detailed bony anatomy of the cervical spine. This is imperative before planning any cervical procedure; however, it is especially necessary when planning anterior vertebral column reconstruction for congenital deformities and neoplastic destruction and for stabilization of flexion-distraction injuries. Magnetic resonance imaging (MRI) of the cervical spine is useful in examining the spinal cord and nerve roots (Fig. 27.1a,b) and in determining the status of the posterior ligamentous complex (Fig. 27.2b). Finally,

27â•… Disorders of the Vertebral Column dynamic flexion-extension X-rays may be important to determine whether a given anterior vertebral column pathology is unstable. Dynamic films often allow a surgeon to determine the necessity and the extent of the fusion and reconstruction. The multimodal use of these images allows the surgeon to choose appropriate operative interventions. For instance, in the presence of congenital vertebral anomalies, dynamic imaging may uncover unsuspected instability that would lead a surgeon to undertake treatment for a patient. Similarly, with traumatic flexion-distraction injuries of the cervical spine, minimal bony kyphosis may be seen on plain films and CT; nevertheless, significant posterior ligamentous injury visible on MRI would lead the surgeon to stabilize and fuse the appropriate levels.

27.2.2╇ Intraoperative Procedure Anterior cervical spine surgery begins with proper airway management and patient positioning. Cervical alignment should be maintained while endotracheal intubation is accomplished. This may be done in a variety of ways, including in-line axial traction during intubation, maintenance of a hard cervical collar during intubation, awake fiberoptic intubation, or nasotracheal intubation. Once intubated, the child is positioned for surgery. If a patient is in cervical traction because of a traumatic injury, the head is placed on a horseshoe head holder and traction is applied in the standard fashion. If a hard cervical collar has been used for stabilization, the patient is placed in halter traction at 5 pounds, the head is positioned on a doughnut cushion, and the collar removed. A small gel roll is gently fitted between the shoulder blades and sometimes under the neck to provide support. Electrophysiological monitoring may be used but is not strictly necessary unless significant intraoperative reduction is planned. Cervical levels are then confirmed with fluoroscopy, and an anterior cervical incision site is marked. A typical anterior cervical approach is used, with the incision marked over the level of the pathology. Once the platysma is divided, a dissection plane between the omohyoid and sternocleidomastoid muscles is created. The longus colli is identified, and a midline incision is made over the appropriate vertebral bodies. These levels are confirmed with fluoroscopy, and self-retaining retractors are placed. Distraction pins are placed in the midline of the vertebral body above and below the level of the discectomy or corpectomy, with care taken to place the pins in the middle of the body in the cephalad/caudad direction. Fluoroscopy is used to place the pins in a convergent fashion so that, once the vertebral bodies are distracted, intraoperative reduction may occur.

Each diskectomy needed is carried out in the standard fashion using the operating microscope, curettes, drills, and microinstruments. Removal of the entire cartilaginous endplate generates the boniest surface area available for graft-on-bone contact, thus increasing the fusion rate. The diskectomy should be extended laterally to the uncovertebral joint. In the setting of trauma or congenital anomalies, there is no need to open the posterior longitudinal ligament. When performing a corpectomy for neoplastic involvement, the disk spaces above and below the body are removed, as previously described, and the vertebral body is subsequently drilled away.

27.2.3╇ Interbody Grafts and Biologics Once the disk space is prepared, the distance between the inferior and superior endplates is measured to determine the size of the interbody graft. The grafting options for standard diskectomies include autologous tricortical iliac crest, iliac crest allograft, and polyetheretherketone (PEEK) implants. Given our high rate of cervical fusion, the authors’ customary practice is to use iliac crest allograft. This can be supplemented with demineralized bone matrix, placed within the graft and smeared along the edges of the implant. Larger grafts are required if a corpectomy is performed. In these cases, there are many options available for anterior reconstruction. A single-level corpectomy can be reconstructed using a large piece of tricortical iliac crest allograft. Other options include fibular strut graft, titanium or carbon-fiber cages that can be filled with cancellous bone and demineralized bone matrix, and PEEK stackable cages. After placing the graft, the surgeon must make sure that the graft fits snugly between the two vertebral bodies. This will prevent graft settling, migration, and kick out.

27.2.4╇Instrumentation After interbody graft placement, anterior cervical instrumentation is used to secure the construct while the arthrodesis matures over the next 2 to 3 months. An anterior cervical plate increases fusion rates from 90% to more than 96% when compared with fusion without plating.1 Static plates feature small, constraining screw holes and have no translational ability. Dynamic plating systems allow for controlled settling, by allowing either the screws to translate through elongated holes or the plate to translate across an internal track. Either way, dynamic plates allow for load sharing across the construct and graft subsidence. Studies have shown no significant difference in clinical outcomes or fusion rates between static and dynamic plates in singlelevel constructs2; however, some data suggest that

243

244 Section III.Câ•… Malformations of the Spine multilevel constructs using static plates have a higher rate of failure compared with those using dynamic plating systems, probably because of stress shielding.3,4 In our practice, the authors have adopted the dynamic transitional plating system for both singlelevel and multilevel reconstructions. The anterior plate is placed under live lateral fluoroscopy. The smallest plate that extends over the endplates is utilized. Screws are placed in a rostralmedial trajectory in the vertebral body above the graft and a caudal-medial trajectory in the vertebral body below the graft. This type of screw placement increases pull-out strength of the screws, thus reducing risks for instrumentation failure. Immediate revision is recommended if poor purchase or trajectory is noted during screw placement. New screws can be placed in a different trajectory, or rescue screws can be placed in the same drill hole for better purchase. If the desired level cannot be instrumented because of complications, there should be little hesitancy to extend the plating system to the next level to achieve the desired screw purchase.

27.2.5╇ Wound Closure After the anterior cervical spine is reconstructed, wound closure is of great importance. The wound should be copiously irrigated with bacitracin. Meticulous hemostasis should be obtained to prevent oozing and potential cervical hematoma. Once the self-retaining retractors are removed, the sternocleidomastoid muscle should fall back into place, and a multilevel closure is performed. The authors routinely place sterile strips on the wound. We recommend the use of a cervical hard collar for approximately 4 to 6 weeks postoperatively.

27.2.6╇ Hazards, Risks, and Avoidance of Pitfalls 1. During the surgical approach, injury to the carotid artery, esophagus, or trachea can occur. Proper technique, correct identification of tissue planes, and gentle handling of the tissues will avoid most of these problems. 2. Misidentification of vertebral body levels can be avoided by the proper use of intraoperative fluoroscopy. If any doubt exists as to the proper level, do not hesitate to check the level using fluoroscopy! 3. Nothing must be placed in the canal blindly to avoid causing spinal cord injury. This also means avoiding placing a spinal needle into the disk space for identification of levels. Use a safe, radiopaque instrument, such as a Bovie

tip, for localization purposes. Doing so also moves the procedure along faster. 4. Avoid over-drilling of the vertebral body to ensure that enough bone is available for proper screw purchase. The structural integrity of the anchor vertebral bodies must be preserved at all costs.

27.3╇ Outcomes and Postoperative Course 27.3.1╇ Postoperative Considerations Children undergoing anterior cervical spine fusion typically experience an uncomplicated postoperative course. Unless there are significant comorbidities, such as spinal cord injury or potential airway issues, children at the authors’ institution usually do not spend time in the intensive care unit after surgery. Patients with the aforementioned risk factors are monitored at least overnight in the intensive care unit. The postoperative care plan involves pain control, neurological and airway monitoring, and wound management. The postoperative pain associated with anterior cervical neck dissections is typically minimal. Patients generally do well with acetaminophen and nonsteroidal anti-inflammatory medications. There is rarely a need for significant narcotic use after a straightforward anterior diskectomy/ vertebrectomy/fusion.

27.3.2╇Complications Complications from anterior cervical spine approaches are also rare. Children may have immediate postoperative dysphagia caused by the endotracheal tube or retraction on the esophagus. This typically resolves itself in a few days and, at most, within 2 weeks. Children are usually started on a mechanical soft diet immediately after surgery as long as they are able to swallow without significant discomfort. A hoarse voice is another potential complication; it may be secondary to injury to the recurrent laryngeal nerve, but it may also occur secondary to simple retraction. This is self-limited in the vast majority of cases and resolves over a couple of days. Wound infections occur in less than 1% of anterior cervical spine surgeries. Superficial infections can be treated with wound care and oral antibiotics. Deep cervical wound infections require more aggressive treatment with wound exploration– washout and concomitant long-term antibiotics tailored to the specific pathogen. Graft and hardware failure can also occur, with an incidence of less than

27â•… Disorders of the Vertebral Column 2%. Graft failure can occur in the setting of stressshielding from a static cervical plate or loosening of the hardware. Hardware failure can entail screw pull-out, screw fracture, and plate fracture, the latter being extremely rare. Screw pull-out or fracture can lead to plate migration and impingement on the esophagus. This may present with pain and swallowing difficulties in children. Over time, this can lead to erosion through the esophagus and fistula formation. Although rare, these complications need to be considered in children presenting with postoperative pain, swallowing difficulties, or progressive neurological symptoms. Depending on the situation, management involves revision of the graft and/or hardware.

27.3.3╇Follow-up After uncomplicated anterior cervical spine surgery, children routinely undergo anterior-posterior and lateral (Fig. 27.2d) cervical spine X-rays on the first postoperative day. They are seen for follow-up in clinic at 1 and 3 months if there are no postoperative surgical issues. A lateral cervical spine X-ray is obtained during both of these visits, with the

3-month postoperative film typically showing a successful arthrodesis (Fig. 27.1c). Graft settling on the postoperative X-ray is expected if the surgeon has used a dynamic plate. Unless there are other issues, after the 3-month follow-up, patients can be monitored by their pediatricians with referral for any recurrent symptoms or changes.

References ╇1. Kaiser

MG, Haid RW Jr, Subach BR, Barnes B, Rodts GE Jr. Anterior cervical plating enhances arthrodesis after discectomy and fusion with cortical allograft. Neurosurgery 2002;50(2):229–236, discussion 236–238 ╇2. Goldberg G, Albert TJ, Vaccaro AR, Hilibrand AS, Anderson DG, Wharton N. Short-term comparison of cervical fusion with static and dynamic plating using computerized motion analysis. Spine 2007;32(13):E371–E375 ╇3. DuBois CM, Bolt PM, Todd AG, Gupta P, Wetzel FT, Phillips FM. Static versus dynamic plating for multilevel anterior cervical discectomy and fusion. Spine J 2007;7(2):188–193 ╇4. Li H, Min J, Zhang Q, Yuan Y, Wang D. Dynamic cervical plate versus static cervical plate in the anterior cervical discectomy and fusion: a systematic review. Eur J Orthop Surg Traumatol 2013;23(1, Suppl 1):S41–S46

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28

Spinal Deformity/Kyphosis Steven W. Hwang

28.1╇ Introduction and Background 28.1.1╇Indication This chapter primarily focuses on surgical correction of kyphosis, although often it is not an isolated entity and may reflect a combination of kyphoscoliosis. The techniques described can be performed asymmetrically to also address the coronal and axial plane deformity. The most common pediatric surgical etiologies related to kyphosis include Scheuermann kyphosis, congenital kyphosis, and less frequent etiologies, such as iatrogenic, myelomeningocele-related, traumatic, or oncologic kyphosis. The indications for surgical correction are often myelopathy, kyphosis > 70 degrees, progressive kyphosis with significant growth potential/skeletal immaturity (i.e., subtypes of congenital scoliosis), or nonhealing skin ulcerations.

is mostly complete. Similarly, growing systems may help slightly but do not primarily address sagittal balance and are mostly targeted at coronal improvement. Alternative surgical approaches can be very powerful but require lengthening, as opposed to shortening, of the spinal column for correction and can incur additional risk. A posterior approach shortens the spine and also minimizes the respiratory impairment associated with a transthoracic approach.

28.1.5╇Contraindications The risks and benefits of surgery should always be weighed and factors like significant osteoporosis or potential for loss of significant growth should be considered, as well as conditions associated with high rates of pseudarthrosis or surgical complications (i.e., syndromic conditions, neurofibromatosis type 1 [NF1], etc.).

28.1.2╇Goals The primary goals should be to correct the deformity and restore sagittal and coronal balance (Fig. 28.1). These can be achieved through careful planning and application of corrective maneuvers to achieve an osseous fusion.

28.2╇ Operative Detail and Preparation

28.1.3╇Alternatives

Standard spinal instrumentation is required for exposure and implantation of hardware and should include a deformity set. A Jackson 4 post bed can be used for patients of a sufficient size; alternatively, gel rolls are used in smaller children. Particular attention should be paid to ensuring the pressure points are well padded and the abdomen is free. Preoperative computed tomography (CT) and magnetic resonance imaging (MRI) sequences are routinely obtained to better plan for screw size and to avoid unexpected anatomical variations. Preoperative radiographs are important to evaluate flexibility of the curve and to anticipate what type of osteotomies will be required.

Alternate procedures include bracing, a growing system (i.e., growing rods or vertical expandable prosthetic titanium ribs), or a vertebrectomy from an anterior or lateral approach.

28.1.4╇Advantages Bracing can be useful to temporize or possibly improve curvature in an immature spine, but it has a limited role in severe kyphosis or after spinal growth

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28.2.1╇ Preoperative Planning and Special Equipment

28â•… Spinal Deformity/Kyphosis a

b

Fig. 28.1â•… (a) Illustration of an anteroposterior (AP) image of the spine highlighting a goal of coronal balance < 4 cm, with a level pelvis and level shoulders. (b) A lateral spine image showing a goal of sagittal balance < 5 cm, normal thoracic curvature (T2–T12; 20–40 degrees), and normal lumbar lordosis (may vary dependent on pelvic parameters).

Typically, closure of 1 mm of a Ponte osteotomy will gain 1 degree of correction; a pedicle subtraction osteotomy will gain 15 to 25 degrees, depending on the level, extent, and size of the vertebral body; and a vertebral column resection will often provide 30 to 40 degrees of correction. Specific angles and distances can be premeasured using mathematical formulae, or software programming (Surgimap, New York, NY) is available to anticipate the amount of correction intraoperatively. Significant blood loss should be anticipated, and therefore large-bore IV access as well as an arterial line should be placed. An antifibrinolytic should be considered and a cell saver should be used throughout the case. Neuromonitoring with a bite block should be planned with clear

communication among the anesthesiologist, surgeon, and neurophysiologist.

28.2.2╇ Expert Suggestions During the case, serial labs should be drawn and transfusions administered as necessary. Antibiotics should be re-dosed serially and motor evoked potentials should be tested frequently and after any significant intervention. The mean arterial pressure is typically maintained near 60 mm Hg during the procedure and elevated to 80 mm Hg during corrective maneuvers, provided the patient is normotensive at baseline.

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248 Section III.Câ•… Malformations of the Spine

28.2.3╇ Key Steps of the Procedure/ Operative Nuances After adequate exposure, the screws should be placed first because the osteotomies will lead to greater blood loss and should be reserved for the end.

Ponte Osteotomies The caudal aspect of the spinous process can be removed with a Leksell rongeur until the midline epidural fat can be visualized (this can also be drilled) (Fig. 28.2a). A ½-inch osteotome can be used

and aligned parallel to the lamina angling rostrally and laterally (Fig. 28.2b). A mallet is used to advance the osteotome to a line drawn extending from the inferior border of the transverse process. A second cut can then be made over the imaginary line pointing slightly laterally to avoid plunging medially inadvertently, thus disconnecting the inferior articulating process (Fig. 28.2c). A 2 or 3 Kerrison punch can then be used starting in the midline where the epidural fat is visible and extended laterally and rostrally to remove the superior articulating process of the inferior level (Fig. 28.2d). Early and plentiful use of hemostatic agents like thrombin mixed foam can be useful to control and minimize epidural bleeding.

a

b

c

d

e

f

Fig. 28.2â•… Ponte osteotomy. (a) Sawbone demonstration removing the spinous process and exposing the midline epidural fat. (b) First cut of the osteotomy removing the inferior articulating process; the osteotomy should be angled laterally and parallel to the lamina to minimize a downward trajectory (the dotted line highlights the rostral extent of the osteotomy). (c) The second osteotomy cut should disconnect the inferior articulating process and should also be aimed slightly laterally. (d) A Kerrison punch can then be used to remove the superior articulating process, proceeding laterally. (e) Lateral view of a completed osteotomy. (f) Lateral view highlighting the correction obtained with closure of the osteotomy (approximately 1 degree/1 mm).

28â•… Spinal Deformity/Kyphosis Alternatively, the M8 drill bit can be used to perform any component of the facetectomy. The pedicles can be easily palpated through the osteotomy to assist in pedicle screw trajectories as well.

Pedicle Subtraction Osteotomy (PSO) If additional correction is required, a PSO can be performed. After facetectomies above and below the desired level are completed, a laminectomy is performed. The pedicles should then be isolated and removed. A drill or curette can be used to core the pedicle into the vertebral body. A curette can be used

to save the cancellous bone for graft material. Caution should be taken to avoid injury to the adjacent nerve roots, when removing the rostral and caudal portion of the pedicle. Typically, the pedicle is drilled until it is egg-shell thin and then the fragments of bone are fractured away from neural structures (Fig. 28.3a). The rib head will need to be removed (by drill or rongeur) or disarticulated and depressed. Once a wedge of the vertebral body has been appropriately removed, the lateral walls of the body can be fractured in a V-shaped cut using an osteotome or drill (Fig. 28.3b). A plane can then be developed between the vertebral body and anterior longitudinal ligament using a Penfield 1 or microcurette. A Kerrison punch or drill

a

b

c

d

e

f

Fig. 28.3â•… Pedicle subtraction osteotomy. (a) A drill or curette can be used to core the pedicle and leave an egg-shell thin layer of bone. (b,c) A wedge of the vertebral body can then be removed to the anterior wall of the vertebral body. (d) Finally, with temporary rods in place, the posterior wall of the vertebral body should be removed. (e,f) The osteotomy should then be closed, in apposition to the edges of bone.

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250 Section III.Câ•… Malformations of the Spine can be used to disconnect the anterior wall. Only the width of the drill or Kerrison need be removed to release the anterior border. A head light or microscope is useful to adequately visualize surgical anatomy. Finally, the posterior wall should be thinned using a drill or curette (a curved drill can facilitate thinning the more midline bone). A dental dissector should be used to ensure that the dura does not adhere to the PLL. The contralateral assistant should protect and gently retract the dura using a Penfield while the posterior wall is drilled. During this final step, a temporary rod should be placed on the contralateral side to avoid a sudden release. After the posterior wall is thinned, a no. 11 blade or microscissors can be used to cut the PLL as far across as possible while gently retracting the dura. By alternating sides, the surgeon should almost be able to connect cuts from both sides. A down-pushing curette can then be gently used to depress and disconnect the remaining posterior vertebral wall. Often, difficulty with this step is due to a greater amount of residual bone than expected. This can be addressed by gentle traction of the dura and removal of the rib head to allow for a more medial exposure. A distractor can then be placed between screw heads (or between a screw and vice-grip, if the

a

distance is too great) and the temporary rod can be released allowing for gentle reduction (Fig. 28.3c). Attention should be paid to monitoring the dura for excessive buckling. If the vertebral body does not collapse, most likely one of the walls remains continuous and requires more attention.

Vertebral Column Resection (VCR) This technique is similar to a PSO but involves the complete removal of the vertebral body (Fig. 28.4a). Once the pedicle is removed, the drill can be used to rapidly delineate the extent of resection by drilling rostrally and caudally into the disk space. A large curette can then be used to remove the disk material and prepare the endplate of the adjacent level. Caution should be taken to avoid violation of the endplate that may lead to graft subsidence. The lateral walls, anterior wall, and posterior wall are similarly removed in a more complete fashion. To obtain adequate exposure for cage implantation, a nerve root will often need to be sacrificed (Fig. 28.4b). A temporary clip should be applied to the nerve root prior to transection with neuromonitoring for several min-

b

Fig. 28.4â•… Vertebral column resection (VCR). A graft should be placed ventrally but not distracted fully and the posterior elements compressed for correction; a lordotic graft can be placed to increase correction. (a) Precorrection lateral image with the graft in place. (b) Postcorrection lateral view.

28â•… Spinal Deformity/Kyphosis utes to ensure that a radicular branch does not supply the anterior spinal artery primarily at this level. A variation of this has been described as a spineshortening osteotomy for recurrent tethered cord patients. Typically, the caudal one-third to one-half of the vertebral body below the pedicle is left intact and collapsed into the caudal endplate of the superior level, resecting approximately 2 cm of height.

28.2.4╇ Hazards/Risks/Avoidance of Pitfalls During Ponte osteotomies, the spinal cord is located on the concave side and may increase risk when removing the superior articulating process; a drill may be safer if significant scoliosis is present. With small pedicles or poor bone integrity, avoidance of excess stress at a single level is important. A longer construct with a longer temporary rod to redistribute forces is essential. Often a complete removal of the rib head is not necessary; it can be drilled thin enough to be malleable and/or depressed, thereby minimizing the risk of pleurotomy. Generally, a pleurotomy does not require treatment but a drain can be placed with large defects. Temporary clipping with neuromonitoring may be useful to avoid sacrifice of an important segmental vessel, and these vessels can be preserved by sacrificing the contralateral root instead. During deformity correction, excessive reduction may lead to dural buckling that can cause spinal cord compression. Reduction of correction should be adopted to correct this or a duraplasty can also be performed. If this occurs secondary to excessive shortening, a graft can be placed anteriorly to provide a pivot point and to augment height.

28.2.5╇ Salvage and Rescue Screw Salvage If there is difficulty with placement of a pedicle screw, several approaches can be tried: (1) An “inout-in” trajectory going through the transverse process through the rib head–vertebral body junction and back into the vertebral body can be adopted. (2) The pedicle can be palpated through a laminotomy or the Ponte osteotomy. However, at the apex on the concave side, the spinal cord may abut upon the pedicle and prohibit palpation. Instead, palpation from laterally or superiorly can be used. (3) A medial trajectory palpating the deep, cortical laminar bone can be adopted and a sequentially more lateral trajectory can be trialed until the cancellous pedicle is identified. (4) A hook can be placed instead. (5) The screw can be skipped if sufficient other points of fixation exist. Screws with questionable purchase can also be supplemented with wiring under the lamina.

Neuromonitoring Changes If changes are present, technical problems should first be assessed. Simultaneously, a discussion with anesthesiology should be initiated to ensure no changes in sedatives were administered, to verify temperature, to elevate the mean arterial pressure (MAP) over 80 mm Hg (assuming normal baseline MAPs), and to verify the most recent hematocrit. While the anesthesiologist and neurophysiologist are addressing these issues, the surgical team should investigate the most recent surgical interventions and reverse any if appropriate (i.e., reduce reduction, verify screw position, etc.). If the neuromonitoring changes persist, while correcting any aberrant findings, the patient should be weaned toward a Stagnara wake-up test.

Dural Issues If a durotomy occurs and is visible, it should be primarily repaired with consideration of reinforcement using a glue substitute. A ventral durotomy may be repaired by wrapping a layer of dural substitute circumferentially around the cord and suturing it dorsally. Dural buckling, if symptomatic, can be addressed by reducing the amount of focal correction achieved or by performing a duraplasty.

28.3╇ Outcomes and Postoperative Course Postoperative considerations: Patients should be closely monitored in the intensive care unit (ICU) overnight and have serial labs drawn. Their MAPs should be normalized, and hypotension should be avoided. The author otherwise encourages early mobilization, incentive spirometry, and routine posoperative care. The author routinely places patients on prophylactic antibiotics while drains are in place.

28.3.1╇Complications Complications encountered include: infection, wound dehiscence, neurological impairment, blood loss, ileus, superior mesenteric artery syndrome, respiratory issues (atelectasis, pneumonia), malposition or breakage of instrumentation, pain, pseudarthrosis, cerebrospinal fluid (CSF) leak, and loss of correction. Any postoperative neurological impairment should be investigated with an emergent MRI and CT.

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29

Scoliosis Kaine C. Onwuzulike and George H. Thompson

29.1╇ Introduction and Background Scoliosis is a complex, three-dimensional rotational deformity of the spine. It is most common during late childhood and adolescence, particularly in girls. There is typically one major curve, usually a rightside thoracic (viewed on the posterior-anterior [PA] radiograph), with compensatory curves proximally and/or distally in the cervicodorsal, lumbosacral, or lumbar regions (Fig. 29.1). The classification of scoliosis is divided into four major categories: idiopathic (unknown causation, subclassified as infantile, juvenile, and adolescent); congenital (failure of formation [hemivertebrae], failure of segmentation [unilateral bars], or mixed); neuromuscular (myopathic and neurogenic disorders); and syndromic (associated with a syndrome). Idiopathic scoliosis, especially the adolescent form, is the most common. It affects 2 to 3% of the general population. The female:male ratio is relatively equal in small curves, but increases to 3 to 4:1 in larger curves.1,2 The cosmetic implications for scoliosis are far-reaching, especially in the pediatric and adolescent populations. Patients with severe deformities often have lower self-esteem that can profoundly impact their social interaction and professional development. Untreated severe deformities can result in pulmonary compromise and gastrointestinal crowding.3 They can result in degenerative spinal arthritis, chronic back pain, and increased mortality. Thoracic curves are more likely to cause abnormal pulmonary functions. Physical findings of scoliosis can include: uneven or elevated musculature on one side of the spine; a rib prominence or a prominent shoulder blade (rib hump), caused by rotation of the ribs in thoracic scoliosis; and the appearance of lower extremity length inequality (lumbar curve). Symptoms of scoliosis are usually none to mild. However, they may become progressive in severe cases and lead to several complications. Asymmetrical loading of the facets and disk spaces can lead to

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Fig. 29.1â•… Adolescent idiopathic scoliosis with a structural right thoracic curve and left upper thoracic and left thoracolumbar compensatory curves. This patient is Risser 3, based on ossification of the iliac apophysis.

accelerated degenerative changes resulting in symptomatic spinal stenosis, spondylolisthesis, and disk degeneration. Severe scoliosis (i.e., > 90 degrees) can further result in cardiopulmonary dysfunction via diminished intrathoracic volume, mechanical chest wall dysfunction, decreased vital capacity, and cor pulmonale, leading to premature death.1 Neurological deficit from direct spinal cord or nerve root compression is rare. Kyphoscoliosis, especially when

29 â•… Scoliosis associated with a significant gibbus deformity, is particularly prone to causing spinal cord compromise.

29.1.1╇Indications Studies of adolescent-onset scoliosis have demonstrated that patients with scoliosis show minimal progression in the magnitude of the curve in adulthood, if the curve is less than 40 degrees at skeletal maturity. Although curves in different regions of the spine progress differently, curves measuring 40 to 50 degrees at skeletal maturity progress an average of 10 to 15 degrees during a normal lifetime; curves measuring greater than 50 degrees at skeletal maturity progress at a rate of approximately 1 to 2 degrees per year on average.2,3 The most common means for measuring the degree of curvature in the scoliotic spine is by the Cobb technique (Fig. 29.2). This is obtained by measuring the intersection of a perpendicular

line through the superior endplate of the curve’s uppermost tilted vertebrae with that of a perpendicular line through the inferior endplate of the curve’s lowermost tilted vertebrae. Full-length, standing PA spine plain films are the standard technique for evaluating the severity and progression of the scoliotic spine. These measurements should ideally be obtained with the patient in the upright position, head straight, the importance of which is paramount to consistent and accurate curve measurements. Estimation of skeletal maturity can be assessed by evaluating the epiphyseal status of the left-hand wrist radiographs (bone age), Tanner stages, progressive sitting and standing height measurements, age at menarche, and the Risser sign (Fig.€29.3), which is defined by the amount of ossification present in the iliac apophysis and measures its progressive ossification from anterolaterally to posteromedially. Most surgeons depend primarily on the Risser stage and menarchal status in determining skeletal maturity. Magnetic resonance imaging (MRI) is reserved for patients with an early onset of scoliosis (i.e., before age 8 years); rapid curve progression of more than 1 degree per month; an unusual curve pattern, such as left thoracic curve; and neurological signs, symptoms, or findings.

29.1.2╇Goals The primary goal of treating scoliosis, irrespective of etiology, is preventing further progression of the curve magnitude. Several treatment options exist for the management of scoliosis in the pediatric population―observation, spinal orthosis, and surgery.1–3 Observation, although not an active

Fig. 29.2â•… Demonstration of Cobb angle measurement (white vertebrae = apex of curve).

Fig. 29.3â•… Risser sign determination. The iliac apophysis is divided into four equal segments on the posterior-anterior (PA) radiograph. The medial extent of the ossification is used to determine the sign. The last feature is Risser 5, when the area beneath the ossification fuses to the crest. This signifies complete skeletal maturity.

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254 Section III.Câ•… Malformations of the Spine intervention, should not imply neglect, but rather a systematic surgeon and family-oriented surveillance of the effects of the disease process on growth and development. Curves 25 degrees or less in immature patients require observation for possible progression. This entails regularly scheduled followup and assessment of the aforementioned dynamic processes affecting disease progression. The frequency is based on curve magnitude and estimated remaining growth (Risser sign, menarchal status). It is usually every 4 months for 1 to 2 years, depending on age and maturity and any curve progression. If no significant progression is observed, then transition to every 6 months for the last 2 years of growth, and then annually for an additional 2 years, and perhaps every other year thereafter for the more severe curves. Spinal orthosis is used to minimize further curve progression in young children and those with curve progression. The indications for the use of an orthosis include: age 10 years or older when prescribed, Risser 0 to 2, primary curve 25 to 40 degrees, no prior treatment, and, if female, either premenarchal or less than 1 year postmenarchal crowding.4 The best response to spinal orthosis is seen in idiopathic scoliosis, whereas congenital, neuromuscular, and syndromic scoliosis respond poorly to bracing in most instances. It has been the authors’ practice to use a night-bending orthosis, such as a custom-fit Providence orthosis.5 This is worn 8 to 10 hours per night. A major advantage is that it is under the direct supervision of the parents. The main problem with any orthosis is compliance with the protocol. Possible complications from prolonged bracing include cutaneous irritation and excessive heat formation, which may be uncomfortable. More serious complications may include compression of abdominal viscera resulting in gastroesophageal reflux, restriction of chest excursion, and trunk muscle deconditioning.

29.1.3╇ Alternate Procedures There are limited alternate procedures when surgical indications have been met. Unfortunately, these have very specific indications. For children with earlyonset scoliosis of all etiologies, the use of serial Risser casts and nonfusion surgical techniques (growing rods, vertically expandable prosthetic titanium ribs [VEPTR], and growth modulation procedures) can be considered.6,7 These typically will delay the need for a final fusion but will not prevent it. This can be very advantageous in children who still have a considerable amount of remaining spinal growth. The one exception is the use of growth modulation, in which growth is inhibited over the convexity of the curve and encouraged over the concavity. The indications for these procedures are the same as for orthotic

management. If successful, they may prevent the need for a final fusion and allow the adolescent to have a mobile spine at the end of growth.

29.1.4╇Advantages Major advantages of the alternate surgical procedures are that they prevent further curve progression and in some cases help restore spinal alignment prior to final fusion.7 Above all, they help to allow for further spine and truncal growth, which enhances the space available for the lungs and stabilizes pulmonary functions. This is critically important in an adult. This is a major goal of this type of treatment in very young children.

29.1.5╇Contraindications The contraindications to alternate procedures are basically based on the age of the patient and the severity of the deformity. They offer little advantage to the older patient who has already met surgical criteria for a posterior spinal fusion and segmental spinal instrumentation. Older children or adolescents would be best managed by the latter procedure. Those with severe spinal deformities may also not be suitable candidates. Certainly, growing rods or VEPTR can be considered in this age group, particularly if the patient is quite young. These devices require periodic lengthening (usually every 6 months). However, when the patient has reached a satisfactory age, a final fusion will need to be performed. This will finalize the procedure and eliminate the need for periodic lengthening of the growing devices.

29.2╇ Operative Detail and Preparation Operative preparation begins with an experienced team. During preadmission testing, appropriate nasal cultures are obtained for possible methicillin-resistant Staphylococcus aureus. Standard blood work is also performed. Prior to surgery, PA and lateral standing as well as anteroposterior (AP) supine maximum bending radiographs are obtained. Appropriate measurements are made to determine flexibility, which will be an aid in determining the proximal and distal end vertebrae of the fusion. At the time of surgery, intravenous and intra-arterial lines are inserted. Most patients will receive intrathecal morphine as an adjuvant to postoperative pain management.8 The spinal cord monitoring lines are inserted at this time. The patient is then positioned in the prone position on a Jackson table. This allows for proper truncal

29 â•… Scoliosis and extremity support and avoidance of pressure on the abdomen that will increase venous pressure and postoperative bleeding. Patients receive intraoperative antibiotics as well as an antifibrinolytic to help minimize blood loss.9,10 It is important that fluoroscopy or an intraoperative computed tomography (CT) scanner be available to assist during the procedure. Bipolar sealer device has recently been shown to be very effective to further decrease intraoperative blood loss.11 Following appropriate prepping and draping, the skin is marked for the incision. A Bovie cord is used as a guide to create a straight line incision. The subcutaneous tissues are infiltrated with a 1 to 500,000 saline and epinephrine solution. This helps constrict the superficial vessels and minimize blood loss. The fascia is exposed and split over the spinous processes of the vertebrae to be instrumented. Further infusion of the saline and epinephrine solution is performed down to the lamina. Subperiosteal dissection is then carried out. Intraoperative radiography or fluoroscopy is used to identify the planned end vertebrae for instrumentation. The spine has been completely cleared of muscle and soft tissues. Facetectomies are performed and the underlying cartilage removed. This will enhance fusion. Once the facetectomies have been completed, instrumentation can be performed. There are a variety

of instrumentation techniques. These include all-pedicle screw constructs (Fig. 29.4a–g), hybrid constructs with thoracic hooks and lumbar pedicle screws (Fig.€29.5a–g), and all-hook constructs. The two former techniques are the most widely used today. When pedicle screws are used, the posterior entrance to the pedicle is exposed by removing all overlying cortical bone. The pedicle is then probed and the site felt with the ball-tipped probe. Preoperative radiographs are utilized to determine the approximate diameter of the screws. This is also helpful in determining the length of the screws. The site is then tapped if nontapping screws are to be used. If self-tapping screws are utilized, then tapping is not necessary. Once the desired pattern of implants on both the right and left sides of the spine has been performed, fluoroscopy is used to check the screws’ alignment, particularly their direction and length. If acceptable, then electromyographic (EMG) stimulation of all pedicle screws is performed. There is typically stimulation up to 30 milliamperes (mA). Transmission of signals of less than 10 mA is of concern for a medial breach of the pedicle. Higher amplitude usually is not significant. The concavity rod is inserted first. This can be a 5.0, 5.5, or 6.35 titanium or cobalt chrome rod depending on the size of the patient. Stainless steel can also be considered but is less common due to the associated

a

Fig. 29.4â•… A 15-year-old male Jehovah’s Witness with progressive adolescent idiopathic scoliosis. (a) A standing posterior-anterior (PA) preoperative radiograph demonstrates an 85-degree right thoracic major curve between T6 and T12. (Continued on page 256)

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256 Section III.Câ•… Malformations of the Spine b

c

Fig. 29.4 (Continued)â•… (b) Physiological thoracic kyphosis and lumbar lordosis are shown. (c) An anteroposterior (AP) supine right maximum-bending radiograph. The right thoracic major curve reduces to 38 degrees.

29 â•… Scoliosis d

e

Fig. 29.4 (Continued)â•… (d) The AP left maximum-bending radiograph shows the flexibility of the left upper thoracic and left lumbar curves. (e) The intraoperative traction radiograph under general anesthesia. There was slightly more correction than on the sidebending radiograph. (Continued on page 258)

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258 Section III.Câ•… Malformations of the Spine f

g

Fig. 29.4 (Continued)â•… (f) A PA standing radiograph obtained 2.5 years postoperatively demonstrates correction to 36 degrees using a hybrid construct (thoracic hooks and lumbar pedicle screws). Observe the improved truncal balance. (g) Physiological sagittal alignment with 31 degrees of thoracic kyphosis and 59 degrees of lumbar lordosis.

29 â•… Scoliosis nickel allergy. Once it is properly aligned, the rod is then rotated away from the concavity until it appears entirely straight when viewed from a posterior aspect. Beginning with a proximal or distal approach, the first set screw is tightened and compression or distraction is applied between the screws. The convex of the rod is inserted next and the opposite compressiondistraction mode performed. The spine will typically look completely straight at the end of the procedures. A final check with either fluoroscopy or CT is then performed. If the alignment is satisfactory and spinal cord monitoring normal, the wound is irrigated. The

exposed bone is then decorticated and this bone plus an additional 90 to 120 mm from homologous cancellous bone cubes are applied throughout the spine. The wound is closed in layers. This usually consists of the fascia and subcutaneous tissues. A single drain is placed on the top fascia and brought out over one of the iliac crests. This helps remove any postoperative blood. The skin is closed with a running subcuticular closure. Steri-Strips (3M Healthcare Products, St. Paul, MN) and sterile dressings are then applied. The patient is then returned to bed and final radiographs are obtained. Particular attention is paid to the chest

a

Fig. 29.5â•… A 13-year-old girl with severe progressive juvenile idiopathic scoliosis. (a) Preoperative posterior-anterior (PA) standing radiograph demonstrates a 93-degree right thoracic curve between T4 and T11. (Continued on page 260)

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260 Section III.Câ•… Malformations of the Spine b

c

Fig. 29.5â•… (Continued) (b) Physiological thoracic kyphosis and lumbar lordosis. (c) The major curve reduces only to 75 degrees on the supine anteroposterior (AP) right maximum-bending radiograph.

29 â•… Scoliosis d

e

Fig. 29.5â•… (Continued) (d) The left upper thoracic and left lumbar curves are less flexible owing to the severity of the major curve. (e) Intraoperative traction radiograph under general anesthesia illustrates more flexibility than expected with reduction of the major curve to 48 degrees, as well as the corresponding curves. (Continued on page 262)

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262 Section III.Câ•… Malformations of the Spine f

g

Fig. 29.5 (Continued)â•… (f) A postoperative PA standing radiograph obtained 6 months later identifies correction to 26 degrees using an all-pedicle screw construct. She also has achieved excellent truncal balance. (g) Detailing 33 degrees of thoracic kyphosis and 35 degrees of lumbar lordosis.

29 â•… Scoliosis to be certain that a pneumothorax has not occurred. If the final radiographs are satisfactory, the patient is awakened, the neurological status is checked, and the patient is sent to the postanesthesia care unit (PACU).

29.2.1╇ Operative Planning and Special Equipment Preoperative planning begins when the patient has met the appropriate criteria for surgical intervention. This is based on the measurements on the preoperative PA standing radiograph of the entire spine. Once this decision has been made, then additional studies are necessary. The flexibility of the spine is assessed by preoperative AP supine maximum right- and leftbending radiographs of the entire spine. The angles are measured using the same levels as were obtained from the standing radiographs. Flexibility helps determine the upper and lower vertebrae to be instrumented. The final flexibility assessment is made intraoperatively with a traction radiograph. In this technique, the anesthesiologist applies traction to the patient’s head and a resident, fellow, or clinical nurse applies traction to the feet. Gentle but maximum traction is applied and a repeat AP radiograph of the entire spine is obtained. Again, the same measurement levels are utilized. The end vertebrae are determined by the most horizontal vertebrae from proximal and distal aspects and by using the center sacral line. This line should pass between the pedicles and be relatively centered. Bending radiographs are also useful because they demonstrate the motion in the disk space. The disk space that reverses its alignment on the sidebending films is usually quite flexible and can also be utilized to help determine the end vertebrae. A considerable amount of special equipment is necessary in performing spinal deformity surgery in addition to the appropriate implants. This includes the use of intraoperative fluoroscopy and/or CT scanner. Intrathecal morphine and antifibrinolytic are administered to help in management of pain postoperatively and perioperative blood loss.8–11 A bipolar sealing device will be very effective in further decreasing intraoperative blood loss. Of course, all patients require antibiotics to minimize the risk for postoperative infection―one of the more serious complications of this type of surgery.

29.2.2╇ Expert Suggestions/Comments One of the most difficult decisions in pediatric spinal deformity surgery is determining the lower end vertebra for instrumentation. Maintaining mobility in the lumbar spine is critically important to function as an adult. It is important not to go too low because this will sacrifice motion and increase the risk for degenerative changes in the few remaining mobile seg-

ments. If the lower instrumented vertebrae are too high, this will predispose to an add-on deformity in the lumbar spine. The Lenke et al classification offers suggestions on when to choose a selective thoracic fusion and when to extend into the lumbar spine.12 This classification has three components: curve type (1 to 6), lumbar modifier (A, B, or C), and a sagittal thoracic modifier (–, N, or +). It has good interobserver and intraobserver reliability. An accurate classification and determination of flexibility can be very helpful in making the appropriate treatment selection. Another important decision is accurately identifying the upper and lower end vertebrae intraoperatively. This is best accomplished using fluoroscopy and/or plain radiographs. Although it may seem simple, sometimes it can be difficult.

29.2.3╇ Key Steps of the Procedure/ Operative Nuances All the steps in the procedure of spinal deformity correction are critically important. The reader can probably tell by now that there are several key points. These include antibiotic administration to decrease the risk of an acute postoperative infection; the administration of intrathecal morphine to aid in postoperative pain management8; the use of antifibrinolytic medications, such as tranexamic acid and epsilon aminocaproic acid, to decrease intraoperative blood loss9,10; the use of a bipolar sealing device to further enhance the control of intraoperative and postoperative blood loss11; intraoperative spinal cord monitoring, including transcranial motor and somatosensory evoked potentials; and a detailed knowledge of spinal anatomy. Decreasing blood loss results in better exposure of the spine intraoperatively, has less of a physiological impact postoperatively, helps speed overall recovery, and lowers costs. Intrathecal morphine will result in decreased pain and fewer pain medication-related complications and helps speed the patient’s overall recovery.8 Perhaps the most important operative nuance is understanding the spinal anatomy, particularly that of the pedicles. They become more oblique in the upper thoracic spine and more vertical in the lumbar spine. Awareness of this anatomical change allows more accurate probing and insertion of pedicle screws. This results in fewer medial breaches and reduces the possibility of neurological injury.

29.2.4╇ Hazards/Risks/Avoidance of Pitfalls The greatest risk in pediatric spinal deformity surgery occurs intraoperatively, when nerve root and spinal cord injury are most likely to occur. This is usu-

263

264 Section III.Câ•… Malformations of the Spine ally an iatrogenic complication. A thorough knowledge of anatomy as well as experience performing this type of surgery are critically important to help minimize complications. The highest risk for neurological injury occurs in children who have idiopathic scoliosis. These children are essentially neurologically normal and the deformity is based on inherited factors. Neurological injury can occur from a medial breach from the pedicles or inserting pedicle screws, and from using too large a hook in the thoracic spine, in which the blade of the hook comes in contact with the dura and possibly the spinal cord. Knowledge of spinal anatomy and experience will help the surgeon minimize the risk for these complications. If spinal osteotomies are being performed concomitantly to increase flexibility, this would be another potential risk for neurological injury. Many times, these complications can be minimized or prevented entirely by intraoperative spinal cord monitoring. An experienced monitoring technician is mandatory in this type of surgery. Other risk factors include hypotension, which can affect blood flow to the spinal cord and results in neurological injury. It is essential that hypotensive anesthesia, commonly performed in this type of surgery, be maintained with a pressure of approximately 70 mm of mercury. If neurological changes are seen, raising the blood pressure is the first step―and many times the most crucial step―in reversing any potential monitoring changes.

29.2.5╇ Salvage and Rescue This section deals primarily with the onset of intraoperative spinal cord monitoring changes. This is a very critical change and one that must be managed appropriately to prevent any impending spinal cord or neurological problem. The first steps when intraoperative spinal cord monitoring changes have occurred are to stop the procedure, raise the blood pressure back to physiological levels, and be certain the patient is hemodynamically stable by giving blood replacement, if necessary. If these actions do not result in improvement in spinal cord monitoring over a 5- to 10-minute interval, then a wake-up test must be performed. This consists of reversing the anesthesia and having somebody at the patient’s feet to assess for movement when the patient is asked to move the feet by the anesthesiologist. The surgeon’s role is to be certain the patient does not shift on the Jackson table because there is a potential for a fall. If the spinal cord monitoring changes reverse and the patient’s wake-up test shows voluntary motion in the feet, anesthesia is reintroduced even though the mean arterial blood pressure may be higher. The

procedure can then resume. However, if there are recurrent spinal cord monitoring changes, it is best to abort the procedure, close the wound, and come back in 1 to 2 weeks to complete the process. The patient then undergoes an urgent evaluation to be certain that there are no other abnormalities, such as an extradural or intradural hematoma, that may be applying pressure on the spinal cord or nerve roots. This is best assessed by postoperative MRI.

29.3╇ Outcomes and Postoperative Course The authors assess outcomes of pediatric spinal deformity surgery on several factors. First and foremost is the avoidance of complications, safe deformity correction, restoration of physiological frontal and sagittal plane alignment and balance, and no need for further surgery. These are achieved by detailed preoperative assessment of the patient, appropriate determination of the end vertebrae, and meticulous surgical procedure and appropriate postoperative management.

29.3.1╇ Postoperative Considerations The postoperative management of patients following spinal deformity surgery is vital. For most patients, it is important that no postoperative orthosis be required. This can be variable depending on the patient’s diagnosis. Generally, children and adolescents with idiopathic scoliosis do not want to wear an orthosis. However, it may be necessary for some patients with neuromuscular disorders to use an orthosis because it will help their sitting alignment and function. Children and adolescents with idiopathic scoliosis are placed on protected activities for 5 months postoperatively. This means no organized sports or gym. Nevertheless, they are allowed to engage in individual activities, such as swimming, jogging, or bicycle riding. They are more than capable of doing routine household chores. The main goal is to avoid activities in which the patient is subject to falls or injuries until the spine has had adequate time for initial healing. Patients with neuromuscular scoliosis may return to physical therapy when they are comfortable. The therapist should avoid any truncal activities. Patients with syndromic scoliosis are more variable, depending on their preoperative functional level. Some will be managed like patients with idiopathic scoliosis, whereas others will need to be managed like those with a neuromuscular deformity.

29 â•… Scoliosis

29.3.2╇Complications Complications in spinal deformity surgery in children and adolescents are relatively uncommon but are based on the preoperative etiology.12,13 The risks for neurological injury, which is the most severe complication of this type of surgery, can vary from 0.5 to 1.0% in idiopathic scoliosis and may be higher in other forms. Postoperative infection occurs in 1 to 2% of patients with idiopathic scoliosis but may be higher with neuromuscular scoliosis because of associated comorbidities and decreased nutritional status. The risk for bone implant and metal failure in the immediate postoperative period is rare but is increased with neuromuscular scoliosis due to underlying osteoporosis and osteopenia. Late pseudarthrosis is also uncommon and is usually manifested by a broken rod. Late infection, in the authors’ experience, is more likely―especially an acute postoperative infection. Whether this represents a slow, small re-infection from the immediate postoperative period or one that has been recently acquired is uncertain. Medical complications do occur; these are predominantly gastrointestinal, cardiac, and pulmonary conditions. They can be both acute and chronic. It is important that these be considered during the preoperative evaluation and appropriate consultations obtained to minimize the risk of these problems.

References ╇1. Weinstein SL, Ponseti IV. Curve progression in idiopath-

ic scoliosis. J Bone Joint Surg Am 1983;65(4):447–455 SL. Natural history. Spine 1999;24(24):2592– 2600 ╇3. Weinstein SL, Zavala DC, Ponseti IV. Idiopathic scoliosis: long-term follow-up and prognosis in untreated patients. J Bone Joint Surg Am 1981;63(5):702–712 ╇2. Weinstein

╇4. Richards

BS, Bernstein RM, D’Amato CR, Thompson GH; SRS Committee on Bracing and Nonoperative Management. Standardization of criteria for adolescent idiopathic scoliosis brace studies: SRS Committee on Bracing and Nonoperative Management. Spine 2005;30(18):2068– 2075, discussion 2076–2077 ╇5. Janicki JA, Poe-Kochert C, Armstrong DG, Thompson GH. A comparison of the thoracolumbosacral orthoses and Providence orthosis in the treatment of adolescent idiopathic scoliosis: results using the new SRS inclusion and assessment criteria for bracing studies. J Pediatr Orthop 2007;27(4):369–374 ╇6. Waldron SR, Poe-Kochert C, Son-Hing JP, Thompson GH. Early onset scoliosis: the value of serial Risser casts. J Pediatr Orthop 2013;33(8):775–780 ╇7. Tis JE, Karlin LI, Akbarnia BA, et al; Growing Spine Committee of the Scoliosis Research Society. Early onset scoliosis: modern treatment and results. J Pediatr Orthop 2012;32(7):647–657 ╇8. Tripi PA, Poe-Kochert C, Potzman J, Son-Hing JP, Thompson GH. Intrathecal morphine for postoperative analgesia in patients with idiopathic scoliosis undergoing posterior spinal fusion. Spine 2008;33(20):2248–2251 ╇9. Thompson GH, Florentino-Pineda I, Poe-Kochert C, Armstrong DG, Son-Hing JP. The role of Amicar in sameday anterior and posterior spinal fusion for idiopathic scoliosis. Spine 2008;33(20):2237–2242 10. Thompson GH, Florentino-Pineda I, Poe-Kochert C, Armstrong DG, Son-Hing J. Role of Amicar in surgery for neuromuscular scoliosis. Spine 2008;33(24):2623–2629 11. Gordon ZL, Son-Hing JP, Poe-Kochert C, Thompson GH. Bipolar sealer device reduces blood loss and transfusion requirements in posterior spinal fusion for adolescent idiopathic scoliosis. J Pediatr Orthop 2013;33(7):700–706 12. Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Joint Surg Am 2001;83-A(8):1169–1181 13. Fu KM, Smith JS, Polly DW, et al; Scoliosis Research Society Morbidity and Mortality Committee. Morbidity and mortality associated with spinal surgery in children: a review of the Scoliosis Research Society morbidity and mortality database. J Neurosurg Pediatr 2011;7(1):37–41

265

Section III.D

Malformations of the Spinal Cord

30

Myelomeningocele Benjamin C. Warf

30.1╇ Introduction and Background

a

The process of primary neurulation occurs in the first month of gestation. Neural tube defects occur when a segment of the nascent neural tube fails to fuse in the dorsal aspect, leading to abnormally formed and exposed neural elements at that level. Myelomeningocele (Fig. 30.1a,b) is a neural tube defect in which the tube fails to close at one point along the developing spinal cord, leading to a domino effect of failed posterior closure of the dura, posterior spinal elements (the spina bifida defect), muscle, fascia, and skin. The non-neurulated segment of spinal cord (the placode) is open like a book, with posterior nerve roots exiting from a lateral aspect and motor roots exiting from a ventral aspect. The edges of the ditchlike, opened-out dura are fused laterally to the margins of the fascia and skin defects. The lateral margins b

Fig. 30.1â•… Lumbar myelomeningocele with cerebrospinal fluid (CSF) leak. (a) Note midline placode and surrounding epithelial membrane elevated in a dorsal fashion into a sac by underlying CSF. (b) Axial cross-section of myelomeningocele.

269

270 Section III.Dâ•… Malformations of the Spinal Cord of the placode are connected to the encircling edges of the skin defect by a thin epithelial bridge. There is typically an accompanying meningocele sac elevating the placode and epithelium from a dorsal aspect, which may be ruptured at the time of presentation. Occasionally, there is no sac but the lesion is flat and flush with the surrounding skin (sometimes referred to as myeloschisis). These malformed neural elements lead to varying levels of motor and sensory dysfunction. The infant born with myelomeningocele presents an urgent problem from the perspective of infection risk. Exposed neural elements and active or threatened cerebrospinal fluid (CSF) leak pose a high risk of meningitis and/or ventriculitis, which can be fatal or cause significant morbidity. Thus, closure of the defect is imperative. In developing countries, some patients who have not been treated and avoid death from central nervous system (CNS) infection may epithelialize the skin defect, effectively sealing over the exposed neural elements and eliminating CSF leak. However, this method of “closure” is not cosmetically optimal and may complicate the future management of these patients in the case of symptomatic spinal cord tethering. In the developed world, most infants have been prenatally diagnosed and their delivery, typically by cesarean section, has already been anticipated by the consulting neurosurgeon. At the time of delivery, a sterile, moist, occlusive dressing is applied to the lesion and the infant is placed on intravenous antibiotics by the neonatology staff. Closure is ideally accomplished within 24 to 48 hours if the infant is otherwise sufficiently stable. With active CSF leak, closure should proceed as soon as possible. Prenatal closure of the myelomeningocele has recently demonstrated some benefits to the child and is becoming an increasingly available option. It should be noted that more than half of these infants develop hydrocephalus, either present at birth or―more often―becoming obvious after the back is closed. Although this is typically treated by placement of a ventriculoperitoneal shunt, the author has been able to avoid shunt placement in the majority. In the author’s current practice, about two-thirds of these infants require treatment for hydrocephalus, and three-fourths of those requiring treatment are successfully managed by combined endoscopic third ventriculostomy and bilateral endoscopic choroid plexus cauterization (ETV/CPC).1,2

30.2╇ Operative Detail and Preparation The main purpose of the closure is to prevent infection. The key elements are a watertight reconstruction of the dura and a viable skin closure. After the

induction of general anesthesia, the infant is positioned prone on small chest rolls with all pressure points adequately padded. The skin surrounding the defect can be washed with Betadine scrub; however, the myelomeningocele lesion itself is only gingerly prepped with Betadine paint that is also used on the skin. A generous field is prepped and draped from well above the defect to the buttocks and with a lateral approach as far as is practical in case relaxing incisions or rotation flaps are needed. The sac is incised sharply and entered in the midline at its caudal margin. A dissection guide, such as a hemostat, is passed in superior and lateral approaches to protect underlying nerve roots as a surgical assistant incises the epithelial membrane sharply. In this way the placode is circumscribed to separate it from its attachment to the surrounding epithelial tissue. At the cephalad margin of the placode, extra care needs to be taken to identify and protect the underlying spinal cord as it exits the spinal canal. After this, any small pieces of epithelium still attached to the placode are trimmed with a no. 11 blade or microscissor to prevent the future development of an intraspinal dermoid cyst. Many pediatric neurosurgeons at this point will bring the lateral margins of the placode together medially with a few interrupted stitches through the pia near the dorsal root entry zone (Fig. 30.2). This surgical neurulation recapitulates the neural tube closure, restoring more normal local anatomy, and helps facilitate future operations for spinal cord untethering. There are occasions in which the placode is bulky and does not fit easily within the reconstructed dural sac. It is often helpful to examine the ventral surface of the placode to identify the most caudal exiting nerve roots from a caudal aspect. These are typically nonfunctional but the author prefers to give them the “benefit of the doubt” as much as possible. Placode tissue caudal to the most caudal exiting nerve roots from a caudal aspect can be resected to reduce the bulk. In the case of an infant with a thoracic level myelomeningocele and complete paraplegia, placode resection can be more liberal if necessary to achieve a good closure. The use of dural grafts most likely increases the risk of CSF leak and infection as well as the operative time, and is not recommended here. Typically, even a fairly restricted thecal sac expands with growth and development of the child, as can be seen on subsequent spine magnetic resonance imaging (MRI) studies. Dissection of the dura to reconstruct the sac can be challenging and is a crucial part of the procedure. At the cephalad margin of the spina bifida skin defect, a small midline vertical incision is made and blunt dissection is extended down to the epidural space. This can usually be identified by the epidural fat overlying the normal dura and immediately caudal to the last intact lamina at the cephalad margin of the

30 â•… Myelomeningocele

Fig. 30.2â•… Cross-section of myelomeningocele placode showing pial suture placement for operative recapitulation of neurulation after excision of epithelial membrane.

spina bifida defect. The author finds this more reliable than trying to initially identify the plane of dissection between the dura and the lumbodorsal fascia at the lateral edge of the defect. Dissection proceeds bluntly within this epidural space with lateral and caudal approaches to elevate the dura off the underlying lumbodorsal fascia; the dura is then incised as far in a lateral aspect as possible near its lateral line of fusion with the skin and underlying fascia. This is done in a bilateral fashion. Then the entire sheet of dural tissue is dissected from lateral to medial off the lumbodorsal fascia until the epidural fat is exposed within the spinal canal. This sometimes requires sharp disconnection of the inferior-lateral dural sac from the medial margin of the fascial defect. Complete disconnection of the dura from its fascial attachment and hinging the dural flaps in a medial fashion within the canal are essential to a tensionfree dural closure (Fig. 30.3). After the dural flaps are mobilized, their edges are approximated in the midline with a running suture (such as 4–0 Nurolon or Vicryl, or 5–0 Prolene) on a small noncutting needle. Once this is accomplished, the anesthetist provides a

Valsalva maneuver as the surgeon checks the integrity of the closure and looks for points of CSF leakage. Pinpoint leaks can be closed with a single figure-ofeight dural stitch. Some surgeons advocate mobilizing fascial flaps to close in a medial fashion over the dural reconstruction. This does provide an additional layer, but it also adds time, tissue trauma, and blood loss. In the face of a technically satisfactory and watertight dural closure, the author has not found this to be necessary. However, in cases for which the soft tissue defect is sufficiently large for its closure to be technically challenging, the author has previously described a closure technique that does incorporate the fascia.3 Finally, the skin must be closed in a way that avoids tension and ischemia along the suture line. The skin is bluntly undermined by spreading with a hemostat circumferentially around the defect. Care should be taken to preserve the surrounding columns of tissue that may contain its blood supply. As much skin as is possible should be mobilized with lateral undermining. The skin edges are then brought

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272 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 30.3â•… Cross-section of myelomeningocele demonstrating the dural flaps reflected in a medial aspect after their detachment from the fascia. “Neurulated” placode now rests in a ventral position.

together with interrupted 3–0 or 4–0 Vicryl stitches through the relatively tough layer at which the dura, fascia, and skin had been congenitally fused. A small, round Jackson Pratt (JP) drain can be placed subcutaneously with an exit through a distant stab incision for connection to bulb suction. This prevents fluid accumulation beneath the flap that can compromise wound healing, and the author has not found this to encourage spinal fluid leakage. After the skin edges are approximated, redundant (and especially abnormal) skin and “dog ears” are trimmed in such a way that the edges lie flat and even. The skin is closed with a 4–0 monofilament on a cutting needle. I use interrupted vertical mattress stitches with an absorptive suture, such as Monocryl. The wound is covered with a dry dressing and the infant is kept prone or on the side for several days in the postoperative period to avoid pressure on the closure that could compromise its vascular supply. A suture line that is under too much tension is doomed to dehiscence. If primary skin closure is technically impossible, which is rarely the case, other techniques may be required. This can be accomplished with cutaneous or myocutaneous flap rotations, typically in conjunction with a plastic surgery colleague. As a last resort, relaxing incisions in the flank regions lateral to the defect can be created. This allows closure of the defect over the dura. The relaxing incisions can then heal in by secondary intention with wet-to-dry dressing changes or can be covered

by skin grafts. Although it is reassuring to have this as a rescue procedure, the author has never found it necessary. In developing countries, infants presenting late may have an infected myelomeningocele (Fig. 30.4). These should be mechanically debrided and thoroughly irrigated with antibiotic solution until all inflammatory and purulent material is eliminated. The closure can then proceed as described above, although the tissue planes are often compromised and thickened. These wounds are more likely to dehisce in the days following closure. In the event

Fig. 30.4â•… Grossly infected lumbar myelomeningocele with purulent drainage in a Ugandan infant.

30â•…Myelomeningocele of wound dehiscence in the context of a limitedresource environment, and as long as there is no CSF leak, the author has found dressing changes that employ raw (unprocessed) honey to be particularly effective in stimulating granulation tissue. Standard wet-to-dry dressing changes with sterile saline are an alternative. Postoperatively, a course of intravenous antibiotic treatment for meningitis should be completed.

30.3╇ Outcomes and Postoperative Course To prevent stool and urine from settling on the incision, a plastic adhesive drape can be used as a barrier between the buttocks and the operative site. However, meticulous nursing care is crucial to keeping the suture line clean and dry. The site must be observed for any early sign of wound dehiscence or CSF leak, and it must be managed aggressively. The JP drain should be removed within a day or two, once its output is minimal. The development of progressive hydrocephalus should be watched for with daily head circumference measurements, physical examination, and weekly cranial ultrasound. The team also needs to watch for signs of symptomatic brainstem dysfunction, such as stridor or dysphagia. Prior to discharge from the hospital, it is helpful to obtain an MRI of the brain and spine to get a baseline of the ventricular configuration and anatomical anomalies related to the Chiari II malformation, and to look for hydromyelia,

which can act as a “fifth ventricle” in these children, expanding in response to hydrocephalus or failure of its treatment. The entire multidisciplinary team of our Spina Bifida Center also assesses the infant. Mortality should be very low in developed countries with centers accustomed to caring for these children. But the author has found that in the context of low-income countries, mortality from unrelated and treatable medical conditions may be much higher for these children than for their unaffected peers. This was likely from decreased access to routine health care for these disabled children, and the author showed that 5-year survival was significantly enhanced with simple, community-based monitoring programs.4

References ╇1. Warf

BC, Campbell JW. Combined endoscopic third ventriculostomy and choroid plexus cauterization as primary treatment of hydrocephalus for infants with myelomeningocele: long-term results of a prospective intent-to-treat study in 115 East African infants. J Neurosurg Pediatr 2008;2(5):310–316 ╇2. Warf BC. Hydrocephalus associated with neural tube defects: characteristics, management, and outcome in sub-Saharan Africa child’s nervous system, special annual issue. Hydrocephalus (Oi S, ed.) 2011;27:1589–1594 ╇3. Patel KB, Taghinia AH, Proctor MR, Warf BC, Greene AK. Extradural myelomeningocele reconstruction using local turnover fascial flaps and midline linear skin closure. J Plast Reconstr Aesthet Surg 2012;65(11):1569–1572 ╇4. Warf BC, Wright EJ, Kulkarni AV. Factors affecting survival of infants with myelomeningocele in southeastern Uganda. J Neurosurg Pediatr 2011;7(2):127–133

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31

Tight Filum Terminale Thomas J. Wilson and Karin Muraszko

31.1╇ Introduction and Background Although various forms of spinal dysraphism have long been described, Garceau was likely the first to describe surgical correction of a tight filum terminale when in 1953 he described three patients presenting with progressive paresthesias, gait disturbance, difficulty with micturition, and kyphoscoliosis who underwent lumbar laminectomy and sectioning of thickened filum terminales. The symptoms present preoperatively significantly abated in each of the three patients.1 In 1956, Jones and Love described six additional cases of tight filum terminale who underwent what they called an intradural lumbosacral exploration with resection of the filum terminale. Similar to Garceau, they were pleased with the outcomes of the operations, saying: “Severance of this structure (the filum terminale) corrects what seems to be a hopeless neurologic deficit.”2 Anatomically, the filum terminale interna extends off the tip of the conus medullaris and continues free-floating to the tip of the thecal sac, where it continues as the filum terminale externa or coccygeal ligament, eventually attaching to the coccyx (Fig. 31.1). The filum terminale under normal circumstances anchors the conus medullaris, but its elastic properties allow slight movement of the conus medullaris during flexion and extension of the spine. Loss of the elasticity of the filum terminale can place abnormal tension on the conus medullaris, particularly during flexion and extension of the spine, resulting in dysfunction.3

274

Fig. 31.1â•… The filum terminale interna extends from the tip of the conus medullaris to the distal end of the thecal sac. It then continues from the distal end of the thecal sac as the filum terminale externa and attaches to the coccyx.

31â•… Tight Filum Terminale

31.2╇ Operative Detail and Preparation 31.2.1╇ Preoperative Planning Clinical Presentation Little is known about the true incidence or prevalence of tight filum terminale, and the clinical manifestations of a tight filum terminale or tethered cord are widely varying. The most common presenting symptoms include urologic problems, neurological problems, including pain, and orthopedic abnormalities. Urologic symptoms include incontinence, urinary frequency, urinary urgency, and recurrent urinary tract infections. Often the urologic symptoms are very subtle and are only detected with urodynamic testing. The neurological deficits seen with a tight filum terminale are often a combination of upper and lower motor neuron dysfunction, with motor deficits being more common than sensory deficits.3 Delayed development of gait, spasticity, and atrophy are common findings. Although less frequent, when sensory deficits are present, the most typically involved areas are the perineum and the feet, which may lead to unrecognized injuries to a

the feet, such as ulcers.3 Pain is a typical presentation in adults but in children is either less common or less commonly recognized. Orthopedic abnormalities seen include scoliosis, foot deformities or foot asymmetries, limb-length discrepancies, and gluteal asymmetry. Finally, an increasing number of cases of tight filum terminale are discovered incidentally during imaging studies.

Diagnosis and Preoperative Evaluation A wide variety of diagnostic testing modalities are utilized in the diagnosis and evaluation of tight filum terminale, including plain X-rays, magnetic resonance imaging (MRI), computed tomography (CT), and urodynamic testing. Plain X-rays are not utilized specifically for the diagnosis of tight filum terminale but can aid in evaluation of any scoliotic deformity that may be present as a result and can assist in preoperative planning to identify any occult vertebral abnormalities that may exist. The authors’ preoperative evaluation generally consists of an MRI of the lumbosacral spine, scoliosis X-rays, and urodynamic studies. MRI is the imaging modality most often leading to the identification of tight filum terminale (Fig.€31.2). b

Fig. 31.2â•… (a) Sagittal T2-weighted MRI. (b) Axial T2-weighted MRI showing a fat-infiltrated thickened filum terminale. (Continued on page 276)

275

276 Section III.Dâ•… Malformations of the Spinal Cord c

d

Fig. 31.2 (Continued)â•… (c) Sagittal T2-weighted MRI. (d) Axial T2-weighted MRI showing a fat-infiltrated, thickened filum terminale.

This imaging modality can be used to determine the level of the conus medullaris, to measure the thickness of the filum, and to identify a fatty filum if present. Sagittal T1- and T2-weighted images can be used to show the level of the conus medullaris. Whereas a low-lying conus medullaris (Fig. 31.3) is frequently associated with a tight filum terminale and tethered cord, and the identification of a low-lying conus medullaris may be suggestive of the diagnosis, a normally positioned conus does not exclude the diagnosis. Axial T1 images are often useful in determining the diameter of the filum terminale as well as for identification of a fatty filum.3 The normal filum terminale is 2 mm or less in diameter at the level of the L5–S1 disk space. Anything larger than 2 mm is considered abnormally large.4 In pediatric patients, determining the extent of bladder dysfunction based on clinical history and physical examination can be difficult, and following change postoperatively can be problematic without an objective measure to follow. Subclinical urologic symptoms are often present in patients with tight filum terminale even when the primary presenting feature is nonurologic. The most common finding with urodynamic testing is hypertonic autonomous neurogenic bladder.5 The majority of patients have an incomplete neurogenic bladder, and a completely denervated (atonic) bladder is rare.5 Preoperative urodynamic studies provide a useful baseline for comparison postoperatively if there are any urologic issues and the authors generally acquire these studies in all patients with tight filum terminale.

Fig. 31.3â•… Sagittal T1-weighted magnetic resonance imaging (MRI) showing a low-lying conus medullaris.

31â•… Tight Filum Terminale filum but normal conus medullaris, and asymptomatic patients with a low-lying conus medullaris but normal filum terminale. Further data are needed in order to generate consensus about managing these patients.

31.2.2╇ Expert Suggestions for Management For some patients, the decision to recommend operative intervention is based on consensus. Patients who are symptomatic with a low-lying conus medullaris, particularly when a fatty filum terminale is present, should be surgically treated. However, there are a host of patients not fitting these criteria for whom the decision to recommend operative intervention is less clear. Patients can be broadly thought of based on three characteristics—symptomatic versus asymptomatic, normal versus low-lying conus medullaris, and normal versus fatty filum. Most would agree that symptomatic patients with an abnormal filum terminale but a conus medullaris in normal position should also be treated surgically. For symptomatic patients with both a normally positioned conus medullaris and normal appearing filum terminale, search for other causes is generally undertaken. Several groups remain for which no consensus exists and these patients must be evaluated on an individual basis. These groups include symptomatic patients with a low-lying conus medullaris but normal filum, asymptomatic patients with an abnormal

31.2.3╇ Key Steps of the Procedure and Operative Nuances The surgical approach to management of a tight filum terminale is straightforward in concept. The patient is positioned in the prone position with all pressure points padded and monitoring electrodes for intraoperative electrophysiological monitoring are placed, including monitoring of the anal sphincter. The authors monitor somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) for every case. An incision is made exposing from approximately L5 to past the midsacrum. Next, an L5 laminoplasty is carried out. Occasionally, the filum can be accessed between L5 and S1 without any bone removal. In order to achieve this, the patient must be flexed at the hips. The dura and arachnoid are then opened and the filum terminale is identified (Fig. 31.4). The filum can be shown

a

b

c

d

Fig. 31.4â•… (a,b) Intraoperative photographs showing a thickened filum terminale isolated from the cauda equina with a blue vascular loop encircling the filum. (c,d) Intraoperative photos showing cut ends of the thickened filum terminale.

277

278 Section III.Dâ•… Malformations of the Spinal Cord by a number of characteristics including the presence of infiltrating fat, a distinctive coloration that is bluish, and the lack of nodes of Ranvier. Anatomically, the filum terminale is generally in a posterior midline position. Once the filum is identified, all nerve roots are dissected free from the filum and care is taken to ensure the filum is free circumferentially from the nerve roots. A vascular loop is placed around the filum at this point. The authors then carry out electrical stimulation of the filum terminale prior to sectioning. The filum terminale is then bipolar cauterized and divided, first in a proximal approach and then in a distal approach. The dura is then closed in a watertight fashion using a 4–0 nylon suture. The closure is supplemented with patient-derived fibrin glue. If any sculpting is necessary or there is a significant lipoma, plastic surgery colleagues assist in closure. Great fascial closure is necessary to achieve low rates of cerebrospinal fluid (CSF) leak. A fast-absorbing gut suture is then used to close the skin in a running fashion.

31.3╇ Outcomes and Postoperative Course 31.3.1╇ Postoperative Considerations Postoperatively, patients are maintained on flat bed rest to minimize stress on the dural repair. The optimal period for flat bed rest is not clear. With good dural closure, the authors have generally kept patients flat for 24 hours postoperatively and then allowed them to be upright prior to discharge home. When dural closure is more tenuous, generally patients are kept flat for longer periods of time, but they are evaluated on a case-by-case basis. Controversy still exists regarding management of patients with suspected occult tight filum terminale syndrome. However, in patients with occult tight filum terminale syndrome, defined as patients having symptoms of tight filum terminale with nondiagnostic imaging (both the conus medullaris at a normal level and a normal diameter of the filum terminale), roughly 75% of patients show subjective or objective improvement following surgical untethering.6 One recent smaller series reported that improvement following untethering may be even higher, reporting that 100% of patients with suspected occult tight filum terminale improved in at least one domain and 88% of patients improved in all domains that were affected preoperatively.7 Of patients with urologic abnormalities, roughly 50% show objective improvement on urodynamic studies after untethering.6,8 These patients may present with any combination of dermatological, urologic, neurological, and orthopedic signs and symptoms. Patients presenting with involvement in two or more catego-

ries are the most likely to show some improvement postoperatively.6 Neurological symptoms, including pain, sensory abnormalities, and weakness, seem to be the most likely symptoms to respond to surgical untethering.8 In patients with tight filum terminale, there does not seem to be a relationship between duration of symptoms and the likelihood of responding to surgical untethering for spasticity and pain. However, there does seem to be an inverse relationship between the duration of symptoms and the likelihood of responding for sensorimotor function and bladder function.9,10 Surgical success rates have varied in the reported literature. Most of the literature reports an approximately 50% improvement rate for bladder symptoms.9,11,12 Improvement in bladder symptoms is more likely to occur in younger children than in older children and adults.13 One recent series reported that 88% of patients showed stabilization or improvement in neurological symptoms following untethering.14 Coronal balance is an important preoperative and postoperative consideration relative to surgical untethering for tight filum terminale. A significant number of patients presenting with signs and symptoms of tight filum terminale and tethered cord syndrome have a scoliotic deformity at the time of presentation. It is important to consider this when counseling patients on the operative outcomes of surgical untethering and what is likely to occur relative to the scoliotic deformity. In the only series to date focusing on tight filum terminale, 20% of patients had worsened coronal alignment following surgical untethering. Over 50% of the patients with worsened alignment progressed to the point of needing surgical fusion.15 It has been hypothesized that surgical untethering may halt or even reverse the process of progressive scoliotic deformity. This seems to be true in patients with less severe curves. However, surgical untethering is a significant risk factor for progression in those patients presenting with a significant curve. In this series, patients presenting with a Cobb angle ≥ 35 degrees were the most likely to progress postoperatively.15 This should be considered when counseling patients with tight filum terminale who are considering surgical untethering.

31.3.2╇Complications The most common complications associated with surgical untethering are CSF leak/pseudomeningocele, wound infections, and retethering. In the most recent series for surgical untethering of a tight filum terminale, the overall complication rate was 12%. The CSF leak/pseudomeningocele rate was 5%, wound infection rate was 4%, and retethering rate was 5%.14 The most common reason for retethering is

31â•… Tight Filum Terminale arachnoid adhesions, and retethering is likely more common than was initially recognized. Retethering can occur years after the initial untethering. Yong and colleagues reported an overall retethering rate of 8.6% following sectioning of a tight filum terminale. The median time to symptomatic retethering was 23.4 months. Older patients, patients with a higher conus medullaris, and patients with more arachnoiditis (from either an infection or CSF leak) at the time of the initial operation were more likely to retether earlier.1 People have proposed using implants to reduce retethering but to date nothing has been successful.16,17 The authors believe that cooperation between neurosurgery and plastic surgery for closure of these cases can help minimize the risk of wound dehiscence and CSF leak. The authors’ plastic surgery colleagues most commonly employ a pantsover-vest multilayered repair using paraspinous musculature followed by medially based lumbosacral fascia flaps, although other techniques are used when this is not feasible. Using this methodology, our CSF leak rate is approximately 1%.18 The authors believe the cooperative effort significantly decreases this complication. By placing an additional layer of vascularized tissue between the skin and the repaired dura, both wound complications and CSF leak can be minimized.

References ╇1. Yong

RL, Habrock-Bach T, Vaughan M, Kestle JR, Steinbok P. Symptomatic retethering of the spinal cord after section of a tight filum terminale. Neurosurgery 2011;68(6):1594–1601, discussion 1601–1602 ╇2. Kusske JA, Turner PT, Ojemann GA, Harris AB. Ventriculostomy for the treatment of acute hydrocephalus following subarachnoid hemorrhage. J Neurosurg 1973;38(5):591–595 ╇3. Dóczi T, Szerdahelyi P, Gulya K, Kiss J. Brain water accumulation after the central administration of vasopressin. Neurosurgery 1982;11(3):402–407 ╇4. Unsinn KM, Geley T, Freund MC, Gassner I. US of the spinal cord in newborns: spectrum of normal findings, variants, congenital anomalies, and acquired diseases. Radiographics 2000;20(4):923–938

╇5. Fukui

J, Kakizaki T. Urodynamic evaluation of tethered cord syndrome including tight filum terminale: prolonged follow-up observation after intraspinal operation. Urology 1980;16(5):539–552 ╇6. Fabiano AJ, Khan MF, Rozzelle CJ, Li V. Preoperative predictors for improvement after surgical untethering in occult tight filum terminale syndrome. Pediatr Neurosurg 2009;45(4):256–261 ╇7. Cornips EM, Vereijken IM, Beuls EA, et al. Clinical characteristics and surgical outcome in 25 cases of childhood tight filum syndrome. Eur J Paediatr Neurol 2012;16(2):103–117 ╇8. Wehby MC, O’Hollaren PS, Abtin K, Hume JL, Richards BJ. Occult tight filum terminale syndrome: results of surgical untethering. Pediatr Neurosurg 2004;40(2):51–57, discussion 58 ╇9. Bui CJ, Tubbs RS, Oakes WJ. Tethered cord syndrome in children: a review. Neurosurg Focus 2007;23(2):E2 10. Hüttmann S, Krauss J, Collmann H, Sörensen N, Roosen K. Surgical management of tethered spinal cord in adults: report of 54 cases. J Neurosurg 2001;95(2, Suppl):173–178 11. Guerra LA, Pike J, Milks J, Barrowman N, Leonard M. Outcome in patients who underwent tethered cord release for occult spinal dysraphism. J Urol 2006;176(4 Pt 2):1729–1732 12. Lee GY, Paradiso G, Tator CH, Gentili F, Massicotte EM, Fehlings MG. Surgical management of tethered cord syndrome in adults: indications, techniques, and long-term outcomes in 60 patients. J Neurosurg Spine 2006;4(2):123–131 13. Lapsiwala SB, Iskandar BJ. The tethered cord syndrome in adults with spina bifida occulta. Neurol Res 2004;26(7):735–740 14. Ostling LR, Bierbrauer KS, Kuntz C IV. Outcome, reoperation, and complications in 99 consecutive children operated for tight or fatty filum. World Neurosurg 2012;77(1):187–191 15. Chern JJ, Dauser RC, Whitehead WE, Curry DJ, Luerssen TG, Jea A. The effect of tethered cord release on coronal spinal balance in tight filum terminale. Spine 2011;36(14):E944–E949 16. Boop FA, Chadduck WM. Silastic duraplasty in pediatric patients. Neurosurgery 1991;29(5):785–787, discussion 788 17. Colak A, Pollack IF, Albright AL. Recurrent tethering: a common long-term problem after lipomyelomeningocele repair. Pediatr Neurosurg 1998;29(4):184–190 18. Levi B, Sugg KB, Lien SC, et al. Outcomes of tethered cord repair with a layered soft tissue closure. Ann Plast Surg 2013;70(1):74–78

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32

Spinal Tethering Tracts Casey Madura and Bermans J. Iskandar

32.1╇ Introduction and Background The term tethering tract was proposed in the 1970s by James and Lassman1 in their classic treatise on spina bifida occulta, and a tethering tract consists of a persistent embryological channel that extends variably between the spinal cord and skin. The different tracts were named according to histological characteristics (dermal sinus tract, meningocele manqué), and were best understood in the context of their specific embryology. The tracts typically extend from spinal cord to skin, but they have variable lengths and may begin or end in any of the intervening tissues (dura, muscle, and bone). Dermal sinus tracts are, as the name implies, epithelium-lined channels that arise in areas of focal nondisjunction of the neural ectoderm from the cutaneous ectoderm.2,3 A typical dermal sinus tract may end in a cutaneous opening at the skin (dermal sinus) and is occasionally associated with an intradural inclusion tumor or cyst (dermoid, epidermoid, or teratoma).2,4 Based on their histological observation that certain tethering tracts possess meningeal elements, James and Lassman coined the term meningocele manqué and hypothesized that these channels represent embryological meningoceles that failed to form completely.1

32.1.1╇ Expert Suggestions and Comments Based on recent microscopic analyses of tethering tracts obtained from a series of 20 patients, the authors found that none of the tracts studied had evidence of meningocele elements or epithelial membrane antigen (EMA) staining, and that only a minority possessed epithelial elements or associ-

280

ated inclusion tumors. Accordingly, the authors have moved away from histological classification schemes. Instead, they have found it useful to categorize these embryological connections into “long tracts” that extend from spinal cord to fascia or skin and are usually detected on magnetic resonance imaging (MRI), and “short tracts” that are confined to the dural sac attaching to the cord on one end and the inside of the dura on the other, are often associated with split cord malformations, and are typically multiple.5 The authors observed that, whereas the short tracts are virtually always fibrous with occasional neural tissue and are removed surgically for the sole purpose of untethering, long tracts may contain epithelial elements and accordingly should be entirely removed to prevent postoperative dermoid/epidermoid tumors. Tethering tracts are often associated with cutaneous stigmata that give away the presence of an otherwise occult spinal lesion. These can occur singly or in combination, usually in the midline lumbosacral region, and include skin dimple/sinus opening (Fig.€32.1 and Fig. 32.2), hypertrichosis, midline hemangioma, subcutaneous lipoma, caudal appendage, and scarred/ atretic meningocele. Presenting symptoms include lower-limb weakness, back pain, leg pain, foot/leglength discrepancy, scoliosis, and bowel and/or bladder dysfunction.1 When a cutaneous opening with communication with the spinal canal is present, early surgery is recommended to eliminate the tangible risk of spinal abscess and/or meningitis. A tethering tract without cutaneous opening may be dealt with surgically in a semielective fashion. The “gold standard” diagnostic study when a tethering tract is suspected is a lumbosacral MRI with and without gadolinium, which will outline the tract, identify dermal inclusion elements and other tethering spinal lesions, and show the position of the conus medullaris.

32â•… Spinal Tethering Tracts

Fig. 32.1â•… Sagittal view schematic of a dermal sinus tract that starts in a skin dimple and ends on the dorsal aspect of the spinal cord. Note a dermoid tumor at the cord attachment site.

32.2╇ Operative Details and Preparation

Fig. 32.2â•… Pathological sinus opening in the midline lumbosacral region.

When planning surgery on tethering spinal tracts, the authors recommend adherence to the following guidelines: (1) Removal of the entire tract from skin to cord because residual epithelial tissue may produce late postoperative dermoid/epidermoid tumors. (2) Removal of epithelial inclusion tumors in their entirety because residual tissue may create a chemical meningitis and/or recurrence of the tumor, making future surgical attempts challenging; however, removing inclusion tumors that are heavily calcified or adherent to neural elements may be challenging and hazardous in its own right. In such situations, surgeon experience and judgment play an important role in determining the extent of resection. (3) Careful search for other tethering lesions

281

282 Section III.Dâ•… Malformations of the Spinal Cord (e.g., thick filum terminale, split cord malformation), which may or may not be evident on preoperative imaging. Other than MRI, a baseline preoperative urodynamic study is suggested. The patient is placed prone on the operating table with roll pads under chest and hips, allowing flexion of the lumbar spine. Electromyelogram (EMG) and somatosensory evoked potential (SSEP) monitoring are used per surgeon preference. A linear incision with an ellipsoid portion surrounding the projection of the tethering tract onto the skin (if present) is planned (Fig. 32.3). The goal of the initial exposure is to follow the tract, using it as a guide for dissection. The incision is carried down to the dermis, then directed along the tethering tract through the superficial layers to the lumbar fascia, skeletonizing the tract along the way (Fig. 32.4). Once the fascia is opened, the paraspinous musculature is dissected away from bone and a laminectomy is performed, preserving the entry point of the tract. Because these cases frequently occur in very young patients, scissors will often suffice to perform the laminectomy. The operating microscope is brought into the field and the tract is followed until the connection with the dura is identified (Fig. 32.5 and Fig. 32.6). The dura is opened beginning caudally and progress-

Fig. 32.3â•… Skin incision that ellipses around the dermal sinus.

ing cephalad, again creating an ellipse around the tract entry site (Fig. 32.7). The tract is followed to its insertion into the cord (Fig. 32.8), at which point it is divided hemostatically, allowing en bloc resection of the entire tract from skin to spinal canal (Fig. 32.9). Inclusion tumors must be removed with great care to prevent rupture of their potentially inflammatory contents into the spinal canal. Subsequently, close inspection and repair of other tethering anomalies are performed, and the filum terminale is sectioned per routine. A typical multilayer closure ensues.

32.2.1╇ Expert Suggestions and Comments While resecting a tethering tract, attention should be directed at the following: (1) Meticulous tract dissection and resection eliminate the possibility of epithelial remnants and future growth of inclusion tumors. (2) When a cutaneous opening is present, early surgery minimizes the possibility of abscess and meningitis, and the related late complications of adhesions and retethering. (3) Division of the filum terminale and repair of other potentially tethering lesions minimize the chance of future neurourologi-

32â•… Spinal Tethering Tracts

Fig. 32.4â•… Note the sinus tract as it enters the dura. Dermal sinus tract is skeletonized in the subcutaneous tissues and fascia.

Fig. 32.5â•… Note the sinus tract as it enters the dura.

283

284 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 32.6â•… Sinus tract attaching to the skin on one end, with the other end entering the dura.

Fig. 32.7â•… Dural opening caudal to the tract.

32â•… Spinal Tethering Tracts

Fig. 32.8â•… Dura ellipsed around the tract exposing the conus and cauda equina. Note tract attachment to spinal cord.

cal deterioration and the need for repeat tethered cord release surgery. (4) Rarely, one encounters an unexpected abscess or dermoid mass in the conus or cauda equina. In such cases, significant effort should be spent in safely debriding the inflammatory tissues and removing epithelial membranes to minimize the possibility of future adhesions and recurrences. (5) Tethering tracts occasionally attach to the under aspect or side of the bone; when removing the lamina, one must avoid undue “pulling” to minimize further traction on the spinal cord.

32.3╇ Outcomes and Postoperative Course

Fig. 32.9â•… Completely resected sinus tract including attached subcutaneous adipose tissue and skin.

Postoperatively, the patient is kept in a flat position for approximately 24 hours. Discharge from the hospital occurs when pain is controlled, food and drink are tolerated, and bladder function is restored to baseline. Physical therapy (PT) and occupational therapy (OT) evaluations are conducted when appropriate. Postoperatively, attention should be directed at the possibility of (1) aseptic meningitis, (2) urinary retention, (3) cerebrospinal fluid (CSF) leak or pseudomeningocele, (4) infection, and (5) lower extremity neuropathic pain that can be treated with

285

286 Section III.Dâ•… Malformations of the Spinal Cord a limited course of gabapentin or similar agents. Long-term, serial MRI should be considered to rule out new inclusion tumors or cysts.

32.4╇Conclusions With close attention to detail and the pitfalls outlined herein, surgery on tethering spinal tracts can be performed safely with very few complications. When early diagnosis is made, surgery allows baseline neurourological status to be maintained.

References ╇1. James

CCM, Lassman LP. Spina bifida occulta. Orthopedic, radiological and neurosurgical aspects. London, England: Academic Press; 1981 ╇2. Kanev PM, Park TS. Dermoids and dermal sinus tracts of the spine. Neurosurg Clin N Am 1995;6(2):359–366 ╇3. Jindal A, Mahapatra AK. Spinal congenital dermal sinus: an experience of 23 cases over 7 years. Neurol India 2001;49(3):243–246 ╇4. Ackerman LL, Menezes AH. Spinal congenital dermal sinuses: a 30-year experience. Pediatrics 2003;112(3 Pt 1):641–647 ╇5. Rajpal S, Salamat MS, Tubbs RS, Kelly DR, Oakes WJ, Iskandar BJ. Tethering tracts in spina bifida occulta: revisiting an established nomenclature. J Neurosurg Spine 2007;7(3):315–322

33

Spinal Lipomas Tarik Ibrahim, Robin M. Bowman, and David G. McLone

33.1╇ Introduction and Background Lipomyelomeningocele (LMM) is the most common type of occult spinal dysraphism. In LMMs, the lipoma attaches to the spinal cord, usually through a defect in the fascia/lamina, with the spinal cord commonly being low lying. Rarely, a child may have an intradural lipoma with no associated spina bifida. Many surgeons generally classify LMMs into different subtypes based upon the intricate relationship between the lipoma and neural elements, as suspected from the preoperative imaging and further defined at the time of surgery. The different subtypes―transitional, terminal, and dorsal―were originally described by Chapman in 1982.1 Pang and associates recently proposed a possible fourth subtype, classified as chaotic, although not all surgeons support this additional classification.2 LMMs are commonly suspected based upon the changes in the skin and subcutaneous tissues overlying this tethering lesion (Fig. 33.1). Some children are asymptomatic at the time of presentation; other children may present with orthopedic, urological, and/or neurological changes secondary to tethering or compression of the spinal cord. Unfortunately, for the child with a lipoma that is intimately intertwined with neural elements, such as in a transitional LMM, complete surgical untethering is often unattainable. The difficulty facing neurosurgeons is being able to ascertain from only the preoperative imaging the relationship between the lipoma and the surrounding nervous structures. The authors recommend safely debulking the lipoma; however, if the resection reaches a point where new or increased neurological deficits are likely, then the procedure should be terminated.

Fig. 33.1â•… Lipomyelomeningoceles (LMMs) are commonly suspected based upon the changes in the skin and subcutaneous tissues overlying this tethering lesion.

287

288 Section III.Dâ•… Malformations of the Spinal Cord

33.2╇ Operative Preparation and Detail Total spine magnetic resonance imaging (MRI) is obtained on all children preoperatively, which allows for better characterization of the LMM and its surrounding anatomy. A T1-weighted sequence commonly delineates the LMM, its level of entrance through the fascia, and its point of attachment to the spinal cord. A T2-weighted image allows the surgeon to better visualize cerebrospinal fluid (CSF) spaces and any associated myelocystocele-appearing changes, syringomyelia, or meningocele, such as an anterior meningocele, which is commonly associated with Currarino triad. Preoperative MRIs are instrumental in determining the location and extent of the surgical incision. In cases of suspected retethering following LMM resection, it is important to interpret MRIs with the understanding that a persistently low-lying conus on sagittal images does not confirm the diagnosis because it is an expected finding. The diagnosis of a retether relies upon the neurological, urological, and orthopedic evaluations. The preoperative MRI, however, is very helpful at the time of surgery. Neurological function is documented preoperatively. All patients undergo a baseline bladder function evaluation by urology. The lower extremities are evaluated by orthopedics for deformity and strength. A manual muscle test is performed by physical therapy. Indications for intraoperative monitoring are controversial in LMM surgery. An electromyelogram (EMG) may be helpful in identifying motor roots and functional neural tissue when there is any ambiguity. Stimulation of structures before transecting them has been of little value and should not give the surgeon confidence that sectioning of a nervous structure is safe. Approach the operation with the goal of complete untethering, realizing that you will not always be able to accomplish this goal depending upon the attachment of the lipoma to the nervous tissue. Partial untethering, however, does not necessarily imply that the child will not improve postoperatively, because if the tension on the spinal cord can be improved, neurological function can improve. In preparation for the procedure, the child is administered a general anesthetic and then positioned prone on the operative table after all pressure points are well padded and a bladder catheter is placed. Older children have lower extremity compression stockings applied, and all children are kept warm with a heating blanket. Prophylactic antibiotics are administered. The authors do not routinely administer prophylactic steroids. An incision is created in the midline overlying the subcutaneous lipoma and carried superiorly to the level of normal anatomy as defined by the preoperative MRI. A subdermal component of the lipoma, if

present, is not removed because this can create a poor cosmetic result, and/or seroma or pseudomeningocele formation, which can lead to poor wound healing. The interface between the lipoma and overlying soft tissue is developed. Once the lipoma has been completely separated from the overlying skin, the plane between the lipoma rostrally and the loose areolar tissue above the fascia is dissected, moving caudally until the point at which the lipoma penetrates the fascia is identified (Fig.€33.2). The dissection is then extended circumferentially in this plane around the lipoma. A midsagittal incision is made in the fascia over the posterior spinous processes for one to several levels superiorly, depending upon the superior extent of the lipoma as determined by the preoperative MRI. The paraspinous muscles are then dissected off the posterior spinous process and lamina bilaterally. If, as is typically the case, the immediately superior lamina is bifid, and enough dura mater is exposed to allow an incision, no laminectomy is needed. If the lamina is not bifid or if the lipoma extends much more rostral as demonstrated on the MRI, the superior laminas are removed. A laminoplasty is a good option in all cases, especially for younger children. It is important to note how the lipoma attaches to the spinal cord on the preoperative MRI, and if any neural tissue extends out into the soft tissue, as is often the case in a myelocystocele. Once the dura over the more normal cord is visible, the dura is opened with a scalpel. The incision is carried inferiorly toward the lipoma, with care taken to identify the underlying neural structures as the dissection continues. Once the incision approaches the point at which the lipoma penetrates the dura, it is essential to stay in the subdural space and to reflect the arachnoid away from the dura at the point of the incision. This is crucial because the dorsal roots enter the cord at almost exactly the point at which the dura, lipoma, and spinal cord join (Fig. 33.3). Should the incision in

Fig. 33.2â•… A longitudinal view of a dorsal lipoma and the surrounding tissues.

33â•… Spinal Lipomas

Fig. 33.3â•… A cross-sectional view of a dorsal lipoma is seen in the inset. Care must be taken during dural opening, given the proximity of the dorsal roots to the dural attachment and lipoma.

the dura be carried dangerously close to the point of the dural insertion into the lipoma, the dorsal roots could be transected. The dorsal roots are invariably within the subarachnoid space, so that operating in the subdural plane automatically sweeps the nerves medially and allows safe incision of the dura. Retention sutures are used to reflect the dura laterally and to allow vision into the thecal space to evaluate the relationship among the nerves, spinal cord, and lipoma (Fig. 33.4). It is occasionally necessary to begin the resection of the lipoma before the dissection around the periphery of the mass. When the lipoma is extremely large and compresses the neural elements laterally against the edges of the bone, it may be impossible to get into that space without unduly compressing the neural tissues, and therefore some resection of the lipoma is carried out. The laser is used in the vaporizing mode, under magnification, staying in the midline and within fatty tissue. Once significant midline decompression is accomplished, the spinal cord can be retracted from the edges of the bone and the dorsal nerve roots can be identified. The goal is to circumscribe the lipoma in the subdural space so that it is completely freed from the

Fig. 33.4â•… The relationship of the dorsal lipoma to the dorsal roots and spinal cord is apparent here.

289

290 Section III.Dâ•… Malformations of the Spinal Cord dural edges. At that point, the interface between the lipoma and the cord with its dorsal roots becomes apparent and the main mass of the lipoma can simply be transected and removed with the laser (Fig.€33.5). Often, a large intramedullary portion of the lipoma remains, and it is debulked down to the interface between the lipoma and glial fibrous layer (Fig.€33.6). It has been the authors’ experience that any nerve exiting dorsally through the lipoma or any blood vessel entering or leaving dorsally through the lipoma and passing through the lipoma and passing out of the thecal canal above the lamina is nonfunctional and can be transected. Any nerve passing inferiorly toward the vertebral foramina is likely to be functional and is preserved.

Once the lipoma has been transected and debulked, it is important to check distally for a thickened filum. If the filum is thickened, and/or the cord is low lying, the authors transect the filum (Fig.€33.7). When possible, pia-to-pia sutures are used to close the midline placode (prior attachment of the lipoma). This decreases the amount of raw tissue available to scar up to the dura, and may prevent future tethering. The dura should be closed in a watertight fashion. Often, if there is a large amount of intradural lipoma, there is adequate dura available to reconstruct the caudal sac. Where it is not possible, a dural patch is utilized. If a watertight closure is not possible, a lumbar subarachnoid drain is placed and is tunneled superiorly through the soft tissues to exit the skin

Fig. 33.5â•… The interface between the lipoma and the cord with its dorsal roots becomes apparent and the main mass of the lipoma can simply be transected and removed with the laser.

33â•… Spinal Lipomas

Fig. 33.6â•… A cross-sectional view of the spinal cord after resection of a majority of the dorsal lipoma, exposing the fibrotic interface.

Fig. 33.7â•… Exposure of the spinal cord after resection of the dorsal lipoma. The fibrotic interface is apparent. The distal filum is transected.

291

292 Section III.Dâ•… Malformations of the Spinal Cord superior-lateral to the incision. The drain is used for CSF diversion until wound healing occurs. The wound is closed in a layered fashion. With wound closure, it is important not to impinge on, or constrict, the underlying neural elements. It makes little sense to do a delicate dissection of neural tissues only to compress them and interfere with their blood supply in an attempt to prevent CSF from getting into the subcutaneous tissues. Any excess subcutaneous space should be closed, because this allows for seroma or pseudomeningocele formation.

33.3 Outcomes and Postoperative Course

drain is placed. Postoperatively, the child is maintained on flat bed rest for 4 days and then slowly mobilized. Neurological decline following a total/near-total resection is more common in children who were symptomatic before surgery. Pang and his group found that, overall, 5.9% of their symptomatic patients were worse in some regard after their surgery.4 This included 8.2% of children who presented preoperatively with pain, paresthesias, or dysesthesias; 5.9% of children with neurogenic bladder/bowel; and 2.1% with weakness and/or gait changes. Wound dehiscence is typically the result of poor postoperative care if the closure was appropriate. The authors take great care in training their ancillary staff to avoid this preventable complication.

33.3.1╇ Postoperative Considerations

References

Retethering rates following the initial surgical procedure have been documented in the literature as between 10 and 50%, and retethering manifest with neurological, orthopedic, and/or urological decline.3 Retethering is reported in most series as occurring between ages 3 and 8 years, although it is known to occur sooner or in more delayed fashion. Surgery for a retether is often complicated by numerous adhesions and a thickened arachnoid. Neuromonitoring is again useful to help identify nerve roots, which may not be obvious due to the degree of scarring. In these cases, finding the subdural plane, and untethering there, is quite helpful.

33.3.2╇Complications CSF leak may occur, but the authors try to avoid it with a watertight dural closure. A Valsalva maneuver is performed and if there is any leakage, a lumbar

╇1. Chapman

PH. Congenital intraspinal lipomas: anatomic considerations and surgical treatment. Childs Brain 1982;9(1):37–47 ╇2. Pang D, Zovickian J, Oviedo A. Long-term outcome of total and near-total resection of spinal cord lipomas and radical reconstruction of the neural placode: part I— surgical technique. Neurosurgery 2009;65(3):511–528, discussion 528–529 ╇3. Bowman RM, Mohan A, Ito J, Seibly JM, McLone DG. Tethered cord release: a long-term study in 114 patients. J Neurosurg Pediatr 2009;3(3):181–187 ╇4. Pang D, Zovickian J, Oviedo A. Long-term outcome of total and near-total resection of spinal cord lipomas and radical reconstruction of the neural placode, part II: outcome analysis and preoperative profiling. Neurosurgery 2010;66(2):253–272, discussion 272–273

34

Split Cord Malformation: From Gastrulation to Operation Dachling Pang

It is not birth, marriage, or death, but gastrulation which is truly the important event in your life. Lewis Wolpert1 1929– , CBE, FRS, FRSL, FMedSci developmental biologist, author, broadcaster

34.1╇ Introduction and Background Split cord malformation (SCM) is rare. In the registry of the author and his associates there are more than 3,000 complex spinal cord malformations. Of these, 185 cases of SCM of mixed types reflect the author’s unusual referral pattern. SCM is sui generis as a gastrulation malformation―different from both primary and secondary neurulation malformations, but, like all the others, SCM is a tethering lesion.

34.2╇ Embryogenesis: Basic Error in Gastrulation In 1992, the author and his colleagues proposed that the basic error of all double spinal cord malformations occurs early in gastrulation, specifically during formation of the notochord.2 The notochord grows rearward as new prenotochordal cells are added to its back end. These prenotochordal cells come from the primitive knot (called the Hensen node in chick embryos); they stream past the primitive pit and wedge themselves between the ectoderm and the endoderm in the midline. Cells from each bank of the Hensen node must therefore achieve midline integration at the caudal end of the growing notochord to become a solid cord (Fig. 34.1a). This midline integration must involve a cell adhesion molecule, probably fibronectin.3 The basic error in SCM is very possibly a failure of midline integration of the newly forming notochordal cell columns (Fig. 34.1b), perhaps due to defective fibronectin or mistiming of its appearance.4 If this interruption of midline integration occurs only briefly, there will remain a small area of persistent

ectoderm-to-endoderm adhesion flanked by the two unfused heminotochords (Fig.€34.1b). This dorsoventral ecto-endodermal adhesion tract henceforth maintains the contiguity between the embryonic surface (ectodermal) and the yolk sac (endodermal) (Fig. 34.2). Mesenchymal cells from the ubiquitous cell pool now form close alliance to this tract to supply the mesodermal constituents, converting them into the ecto-endomesenchymal tract. Slightly later, around postovulation day (POD) 28, a fourth group of progenitor cells derived from the meninx primitiva, newly gelating between the notochord and the neural plate, become involved with the endomesenchymal tract.2 The final shaping of the mature double cord malformation depends on four developmental variables: (1) differentiation of the four progenitor cell components; (2) persistence of the endomesenchymal tract; (3) anomalous interaction between the hemineural plates and the heminotochords during neurulation; and (4) midline healing of the split neural plate and notochord.

34.2.1╇ Progenitor Cell Differentiation and Classification of Split Cord Malformation The fate of the primitive meninx cells probably has the most cataclysmic consequences because, by virtue of their destiny to form dura and bone, they determine the definitive arrangements of the hemicords that feature in SCM classification. If the meninx cells become incorporated into the midline endomesenchymal tract, a median dural layer forms next to the medial aspect of the hemicord to complete

293

294 Section III.Dâ•… Malformations of the Spinal Cord a

b

Fig. 34.1â•… Basic error in split cord malformation (SCM). (a) Prenotochordal cells from each dorsal lip of the Hensen node must undergo midline integration under the ectoderm to form the solid midline notochord. (b) In SCM, midline integration of these cells is temporarily interrupted, leaving behind a midline space where the ectoderm is still adherent to endoderm, allowing an ectoendodermal fistula to form.

a separate dural tube for each hemicord. Additionally, in accordance with their sclerogenic function, the meninx cells within the tract but not directly adjacent to the hemicords form a midline bone spur between the two median dural walls, continuous with the bone of the developing vertebral centrum. This configuration, designated type I SCM, therefore consists of two hemicords each contained within its own dural tube, separated by a dura-sheathed rigid osseocartilaginous median septum (Fig. 34.3). The spinal cord is transfixed solidly to the spinal canal by the bony and dural septa. The sclerogenic effect of the meninx primitiva cells when they admix with cells of the developing neural arches accounts for the often massively hypertrophic fusion of several adjacent laminae at the level of a type I SCM. In contrast to type I, meninx cells are excluded from the endomesenchymal tract of type II SCM, and a thin fibrous

septum instead of dura or bone spur will form from the “ordinary” mesenchyme between the hemicords. Both hemicords will lie within a single dural tube inside a noncompartmentalized spinal canal, separated by a fibrous rather than an osseocartilaginous median septum (Fig. 34.4). However, this fibrous septum is always adherent to the medial aspect of the hemicords, and by virtue of its firm peripheral attachment to the dorsal and/or ventral dural wall, it is as real a tethering lesion as the bone spur of a type I SCM (Fig. 34.5). The reason some endomesenchymal tracts entrap meninx cells, whereas other tracts exclude them, may well be timing. Since gastrulation and therefore formation of the endomesenchymal tract occur around POD 18 to 22 in a rostrocaudal direction, an early tract would have completed its development long before the appearance of the meninx

34â•… Split Cord Malformation: From Gastrulation to Operation

Fig. 34.2â•… Basic split cord malformation (SCM) model: formation of the endomesenchymal tract. An ecto-endodermal adhesion (fistula) begins where the two germ layers are in direct contact in the midline, flanked by two heminotochords. The midline neuroectoderm is thus bisected into two hemineural plates (upper left). Each hemineural plate neurulates independently in relation to its own heminotochord (upper right). Condensation of mesenchyme around the midline fistula forms the endomesenchymal tract. Evolution of the elements of this tract determines the midline components of the SCM (lower left). Cells from meninx primitiva appearing between heminotochord and hemineural tube around postovulation day (POD) 29 (lower right).

cells (POD 27–29), whereas a later tract might be more likely to ensnare meninx cells during its evolution. This is consistent with the fact that the earlier cervical and high thoracic SCMs are almost exclusively type II SCMs, whereas type I SCMs are mostly located in the lower thoracic and lumbar regions5 (Fig. 34.3 and Fig. 34.4). As the mesodermal progenitor within the midline tract, the mesenchymal cells differentiate into exuberant blood vessels, skeletal muscles, fibrous bands, and lipoma within the median cleft in both SCM types―becoming either embedded in a type II fibrous septum or tightly bound to the median dural sleeve of a type I bony septum. If neural crest cells located at the neural folds are also entrapped by the endomesenchymal tract, paramedian dorsal nerve roots (being the central processes of dorsal gan-

glion cells) and ganglion cells will run between the dorsal medial aspect of the hemicords and midline structures. Sometimes, these paramedian dorsal roots are accompanied by stout fibrous bands and median arteries in a leash that penetrates the dorsal dura and becomes anchored in extradural fibrofatty tissues, adding to the tethering effect. These are the myelomeningocele manqués found in about 70% of the author’s cases, more commonly in type II lesions. Derivatives of the yolk sac endoderm, such as neurenteric cysts, are rare, perhaps because of the fastidious nature of endodermal induction in unaccustomed locations, such as the median cleft. Neurenteric cysts can be intracleft but extramedullary, intramedullary within one hemicord, or in the subcutaneous layer, outside the dura, even in the prevertebral fascia (Fig. 34.6).

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296 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 34.3â•… Timing of the meninx primitiva-endomesenchymal tract interaction: formation of type I split cord malformation (SCM). Normal bipotential meninx cells appear between notochord and neural tube around postovulation day (POD) 29, and migrate around the latter to form the dural tube and help form the bony neural arches. Meninx primitiva cells become admixed with the endomesenchymal tract, where they migrate around each hemicord and form two complete dural sacs. The sclerogenic potential of these cells enables them also to form the median bony (or cartilage) septum between the medial dural sleeve as well as the hypertrophic neural arch (upper left). Endomesenchymal tracts of the lower thoracic and lumbar cord, neurulating much later than POD 18 (beginning of gastrulation), are more likely than higher levels to incorporate the meninx cells (lower left). Fully formed type I SCM, with double dural tubes, bony septum, and hypertrophic neural arches (lower right).

34.2.2╇ Ectodermal Derivatives and Persistence of the Dorsal Endomesenchymal Tract

cause cord compression. The entire intradural sinus tract and cyst must be excised to prevent recurrence (Fig. 34.7, lower tier).

Rarely, a dermal sinus tract derived from ectodermal progenitor cells is formed when the original connection between the endomesenchymal tract and the dorsal surface of the embryonic plate is retained. For a type I lesion, the dermal sinus tract can be traced from the skin pit through defects in the myofascial layers and neural arches to the bone spur. Thus, the tract is always extradural and does not directly contribute to the tethering. In a type II SCM, however, the dermal sinus tract is of necessity intradural, where it retains connection with the median fibrous septum (Fig. 34.7). The tract is often densely adherent to the hemicords, and many will develop an intradural, dermoid cyst large enough to

34.2.3╇ Persistence of the Ventral Endomesenchymal Tract, Ventral Tethering, and Associated Intestinal Anomalies Persistence of the ventral endomesenchymal tract causes tethering on the ventral surface of the hemicords. Four categories of ventral tethering in type II SCM have been recorded in the author’s series.6 1. A purely ventral fibrous septum may be tightly adherent to the underside of the reunited hemicords at variable distances

34â•… Split Cord Malformation: From Gastrulation to Operation

Fig. 34.4â•… Formation of type II split cord malformation (SCM). Meninx primitiva cells are uninvolved in the endomesenchymal tract and enclose only the outer aspects of each hemicord to form a single dural sac that surrounds both hemicords. The absence of meninx cells in the median cleft explains the absence of the sagittal bone septum, its investing dural sleeve, and possibly also the low incidence of hypertrophic neural arches in type II SCM. The mesenchyme from the endomesenchymal tract persists to form a sagittal fibrous septum, which is always adherent to the medial wall of the hemicords (upper left). Fully formed type II SCM with single dural sac, median fibrous septum, and the adhesions between septum and medial surface of the hemicords, responsible for the tethering in type II lesions (lower right).

rostral to its ventral anchor point on the midline dura (Fig. 34.8). 2. A through-and-through fibrous septum or band may attach to both the ventral and dorsal dura, thereby doubly tethering the hemicords. 3. Rarely, a complete intradural fibrous septum is continuous with a dorsal dermal sinus tract that may expand into a large intradural dermoid cyst sporting a deep fibrous link with the median septum, which in turn goes through the ventral dura into the vertebral body (Fig. 34.7). 4. In the exceedingly rare case in which the entire endomesenchymal tract remains as a

patent primitive canal connecting the yolk sac (future gut) with the amniotic sac, part of the small bowel may herniate through this conduit and appear on the back of the embryo as an intestinal fistula. Or, less rare, a nonpatent link with the yolk sac is retained, the pulling effect of which produces an intestinal diverticulum that can reach enormous size within the thorax, where it remains attached at its upper end to the neural stalk of an anterior hemimyelomeningocele. Alternatively, the retained ventral endomesenchymal tract acts as a tethering band on the proximal intestine and prevents normal clockwise rotation of the primitive midgut, causing intestinal malrotation.

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298 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 34.5â•… Type II split cord malformation (SCM). Sharp triangular-shaped fibrous septum attached to dorsal dura and hemicords (upper left). Computed tomographic myelography (CTM) shows the hemicords but not the septum (upper right). Pulling on the extradural fibrofatty tissue also tugs on the subjacent fibrous septum and tents up both hemicords, illustrating the treacherous tethering nature of the septum (lower left). Median cleft shown after fibrous septum has been resected flush with the hemicords. Hemicords are untethered (lower right).

34.2.4╇ Composite Split Cord Malformations and Multiple Split Cord Malformations A composite malformation consists of two or more SCMs of differing types occurring in tandem, with no normal cord in between. The most common constituent of a composite SCM is a type I-type II-type I combination.5 The three median elements are continuous, suggesting that the entire lesion results from a single (but very large) endomesenchymal tract in which meninx primitiva precursor cells have been included at both ends to cause the type I lesion, but not in the middle where the median septum remains fibrous. If two or more SCMs occur in the same patient but are separated by an inter-

val of normal spinal cord, they are true multiple SCMs. These are rare because they result from multiple endomesenchymal tracts (i.e., from multiple embryological errors in the same neural tube). The individual SCMs may be all type I or type II, or of mixed types.

34.2.5╇ Anomalous Interaction between Hemineural Plates and Heminotochord: Associated Myelomeningocele and Hemimyelocele Approximately 25 to 35% of SCMs have an associated open neural tube defect (ONTD).5,7 Depending on whether one or both hemicords are

34â•… Split Cord Malformation: From Gastrulation to Operation

a

d

b

c

e

f

Fig. 34.6â•… Intracleft neurenteric cyst in a 76-year-old man with a type I split cord malformation (SCM). (a) Documented sites of endodermal derivatives (neurenteric cysts) within the embryonic footprint of the endomesenchymal tract in SCM. Subcutaneous, intracleft, ventral extradural, and prevertebral cysts have all been seen. (b) Sagittal magnetic resonance imaging (MRI) shows the sagittal bone spur traversing the spinal canal. (c) Computed tomographic myelography (CTM) shows hemicords within their individual dural tubes, and a midline filling defect. (d,e) Intraoperative pictures. (d) Median bony septum still within its dural sleeve. (e) Intracleft neurenteric cyst just rostral to the bone spur. (f) Histology of the neurenteric cyst shows ciliated epithelial lining with mucin-secreting goblet cells, both of endodermal ancestry.

involved in the dysraphic sac, the lesion may contain a hemimyelomeningocele8 or a full-blown myelomeningocele.5,9–13 Normal neurulation begins with formation of the floor plate,14-17 which in turn is dependent solely on inductive influences of the sonic hedgehog gene expressed by the adjacent notochord.18 Such interactions are spatially and directionally programmed and may be profoundly disturbed if the hemineural plate is too far removed from its companion heminotochord.19 In SCM, abnormal movements of the hemineural plate, because it is hinged to the cutaneous

ectoderm only on one side and receiving mechanical and inductive influence from only one set of lateral paraxial mesoderm, must at times place it at an untenable distance from the heminotochord. The end result may be a misshaped hemicord with variable number of gray horns, or a full-fledged myelomeningocele or hemimyelomeningocele. The cases of hemimyelomeningocele in the author’s series all had complete dorsoventral septa that were steeply oblique, and it was always the dorsally displaced (by the oblique septum) hemineuroplate that failed to neurulate.5,12

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300 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 34.7â•… Type II split cord malformation (SCM) and associated dermal sinus tract from persistence of the dorsal ecto-endomesenchymal tract. Drawings depict encystment of the intradural portion of this tract resulting in large intradural dermoid cyst dorsal to the hemicords, continuous with the median fibrous septum. Computed tomographic myelography (CTM) shows the dermoid cyst dorsal to a large left hemicord and a much smaller right hemicord, the two separated by a dorsal median fibrous septum (upper tier, left). Skin pit (middle). Probe placed inside the outer portion of the subcutaneous sinus tract (right). Intraoperative drawing of the relationship between dermoid cyst, median fibrous septum, and hemicords (lower tier, upper left). Deep tract of the dermoid cyst joining the median fibrous septum (upper right). Median fibrous septum being cauterized (lower left). Emphasis on the conjoint nature of the median septum and the deeper tract of the dermoid cyst (lower right).

34.3╇ Clinical Features and Indications for Surgery There is no doubt both types of SCM are tethering lesions. Of patients with type I SCM in the author’s series, 72% are symptomatic compared to 64% with type II SCM, with no statistical difference. The clinical picture is also very similar between the two types, with three noted exceptions: (1) type I patients are more prone to have prominent dysesthetic pain in the legs and perineum and pain at the split cord site; (2) the incidence of progressive scoliosis is significantly higher in type I; and (3) signs of chronic sympathetic dystrophy, such as nonhealing ulcer, thin hairless skin, anhydrosis, dependent rubor, koil-

onychia, and recurrent osteomyelitis of the toes, are much more common in type I patients.5 As with other tethering lesions, the probability of neurological injury increases with longitudinal growth of the spine and with time. When the neurological grade of patients with type I SCM is correlated with age by linear regression, the R2 coefficient is 0.768, suggesting a strong tendency for type I patients to deteriorate with age. When the same linear regression is performed on type II SCM patients, the R2 coefficient is 0.613, also implying a moderately strong likelihood for type II patients to deteriorate with age. These simple statistical exercises argue strongly for prophylactic surgery to be performed for both types of SCM in children.

34â•… Split Cord Malformation: From Gastrulation to Operation

Fig. 34.8â•… Pure ventral fibrous septum in type II split cord malformation (SCM). Computed tomographic myelography (CTM) shows ventral septum (upper left). Stiff ventral fibrous septum attached to the caudal reunion site of the hemicords, the septum assuming an oblique slant pointing rostrally. Note median blood vessel skirting its rostral free edge (upper right). Exposure of the ventral septum by gently lifting the reunited cord upward (lower left). Cutting the ventral septum (lower right).

Of the 96 type II SCMs the author’s group explored, some significant tethering element was found in every case, in spite of an unimpressive preoperative magnetic resonance imaging (MRI). Of note is that only 40% of the ventral pathology was picked up by preoperative imaging, and in half of the patients, the ventral tethering lesions were not recognized on first glance at surgery until specific search maneuvers were undertaken.6 Clinically, 100% of patients with ventral tethering experienced neurological progression, compared to only 60% of patients with purely dorsal septa, and many displayed myelopathic signs. It appears ventral traction on the hemicords is more deleterious to the corticospinal tracts than pure dorsal tethering.

34.4╇ Preoperative Neuroimaging MRI is an excellent screening test, especially for localization of the split cord and for recording associated non-SCM malformations11; however, it will miss the

details of structures within the median cleft. Computed tomographic myelography (CTM) with iohexol is more sensitive than MRI for displaying fine soft tissue bands and myelomeningocele manqué, and it also shows the bony anatomy well. It is superior to MRI in precisely characterizing the fibrous septum, especially its obliquity and relationships with the hemicords.

34.5╇ Operative Detail and Preparation 34.5.1╇ Operative Technique In a type I SCM, the bony septum is always extradural, the medial walls of the double dural tubes forming a complete sleeve for the bone in the sagittal midline. The septum itself is frequently fused with, and hidden under, the neural arches. The hypertrophic laminae are rongeured away piecemeal around

301

302 Section III.Dâ•… Malformations of the Spinal Cord the attachment of the bony septum so that the latter’s dural attachment can be safely dissected off the bone deep within the cleft. A Woodson dental elevator with a thin, angulated, sharp edge is well suited to peel off the dura with minimal lateral wedging motions. For most type I septa, their ventral junction with the vertebral body is usually flimsy; they could thus be easily avulsed from the dural cleft. Removal of the bone spur greatly facilitates later resection of the dural sleeve. Embedded in the septum is a fairly constant central artery that can bleed briskly on avulsion. A deft plunge deep into the cleft with some bone wax on a cotton patty should handle the bleeding.20

The dura is opened on both sides of the now empty dural cleft to isolate the median dural sleeve (Fig. 34.9a). The medial aspect of each hemicord is often tightly adherent to the dural sleeve by fibrous bands that must be taken down (Fig. 34.9b). Paramedian dorsal nerve roots between the hemicords and the median dural sleeve must be cut prior to resection of the dural sleeve (Fig. 34.9c). The dural sleeve is always wedged tightly against the caudal reunion of the hemicords, and the median cleft rostral to the septum is therefore a safe, spacious area to begin resection of the dural sleeve. Proceeding caudally from the rostral edge of the sleeve where the hemicords are least adherent, the surgeon cau-

a

b

c

d

Fig. 34.9â•… Operative sequence of type I septum resection. (a) Dura being opened along the medial edge of the median dural sleeve; right hemicord and a glimpse of the median cleft exposed. (b) Median dural sleeve completely isolated. Note small intracleft neurenteric cyst and abundant adhesion between dural sleeve and right hemicord. (c) Taut paramedian dorsal roots and median vessel attached to rostral end of dural sleeve. (d) All median cleft contents removed; hemicords untethered.

34â•… Split Cord Malformation: From Gastrulation to Operation terizes the ventral attachment of the sleeve to seal the central vessels and then cuts it flush with the ventral dural wall. Any remaining bony stump must now be trimmed down until it is no longer in contact with the ventral surface of the hemicords, to avoid retethering (Fig. 34.9d). Closure of the anterior dural defect is unnecessary because the abundant adhesions between the ventral dura and the posterior longitudinal ligament preclude cerebrospinal fluid (CSF) leakage. Anterior dural closure is actually undesirable because the anterior suture line can potentially tether the hemicords. Frequently, a myelomeningocele manqué containing paramedian dorsal nerve roots, fibrous bands, and large blood vessels tautly tethers the hemicords to the dorsal dura. These bands always penetrate the dura at a level more caudal than their origin from the hemicords, and they often form an exuberant tuft of fibroadipose tissue that, unlike ordinary loose extradural fat, clings tenaciously to the dura and marks the underlying myelomeningocele manqué. These bands must be cut flush with the hemicords to complete the untethering. In 5 to 10% of type I SCMs, the bony septum is diagonal and divides the spinal canal into a large and a small compartment, which correspondingly house a larger (major) hemicord and a smaller (minor) hemicord, respectively. The minor hemicord is partly sheltered by the overhanging oblique bone spur and is also ventrally rotated from view, thus it is particularly prone to injury during bone spur removal. In all cases of type II SCM, some form of fibrous (mesenchymal) septum or band is found within the midline cleft―either a pure dorsal septum, the most common, or a ventral or dorsoventral septum. Hypertrophic and fused laminae, common in type I lesions, are seldom found in type II SCMs, and laminectomy is technically easy and safe. A midline dural opening immediately exposes a dorsal or complete septum but a purely ventral septum has to be sought for by gently rotating the hemicords to one side. All type II fibrous septa are found near the caudal end of the split. Paramedian dorsal roots and myelomeningocele manqués coursing dorsally from the hemicords are cut flush with the hemicords.

34.5.2╇ Ventral Tethering and Associated Intestinal Anomalies Ventral exploration of a type II SCM should be conducted by gently lifting and rotating one hemicord toward the midline, made easier by wide bony exposure. If a dorsal fibrous septum and myelomeningocele manqués are present, they should first be cut to free the hemicords.

In cases of associated intestinal malrotation, the prevertebral band to the duodenum or ileocecal junction must be cut to release the bowel obstruction, and the cord tethering is handled via a separate operation to section the ventral band. In cases of true intestinal diverticulum, the site of bowel duplication is usually the duodenum or proximal jejunum because the original attachment of the ventral endomesenchymal tract tends to be at the foregut region of the yolk sac. The diverticulum needs to be first surgically detached from the bowel, and the spinal cord surgery for excision of the ventral band planned secondarily. In a rare case of a duodenal diverticulum and massive intrathoracic enterogenous cyst (Fig. 34.10), the bowel surgery was done first, followed in a few months with a thoracotomy and resection of the cyst. The anterior hemimyelomeningocele was excised last.

34.5.3╇ Associated Myelomeningocele and Hemimyelocele In most myelomeningoceles, the open unneurulated neural placode is terminal and thus is caudal to the SCM. Less commonly, the open placode is segmental and may therefore be rostral to the SCM. If the SCM is diagnosed long after the initial neural tube repair, the original neural placode would have to be taken sharply down from the dura at the time of definitive surgery for the SCM. By definition, a hemimyelocele represents a segmental dysraphic lesion. A common scenario is when the median septum is horizontally oblique so that the one hemineural plate that is thus dorsally displaced sits too far from its companion heminotochord and fails to neurulate. The resultant open neural tube defect, made up of this one hemiplacode, was often mistaken to be the whole lesion, whereas in fact the other successfully neurulated hemicord had been hidden from view by the oblique septum. The SCM is usually revealed months later by a routine surveillance MRI or because of increasing left-right discrepancy in leg function. At surgery, the initial repair site is taken down carefully and the repaired hemiplacode is detached from the dura. The median septum is removed in the fashion described above. Some hemimyeloceles the author and his group have treated are in fact saccular limited dorsal myeloschisis,21 where a robust neural stalk consisting of central and peripheral nervous tissues extends from one hemicord into the base of a skin-covered sac and forms a neural nodule or a segmental myelocystocele. The hemicord is in essence tethered at its connection with the CSF sac. At surgery, the sac is opened from the top; the nonfunctional neural stalk is resected flush with the surface of the involved hemicord, and the adjacent

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304 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 34.10â•… Large intrathoracic intestinal diverticulum in a 3-year-old girl with an anteroposterior type II split cord malformation (SCM). Sagittal T2 magnetic resonance imaging (MRI) shows the large intrathoracic cystic intestinal diverticulum whose upper end is connected to the hemimyelocele neural stalk of a type II SCM that had extended into the mediastinum through an anterior body defect (left). Computed tomographic myelography (CTM) shows the details of the hemimyelocele (right). The left column shows the successive upper axial cuts and the start of the anteroposterior split cord. A stout hemimyelocele stalk emerges from the front of the anterior hemicord (third image down). The hemicords rejoin immediately caudal to the hemimyelocele (fourth image down). The right column shows the anterior hemimyelocele stalk “straddles” the anterior vertebral defect and “steps into” the superior mediastinum, bringing with it a sleeve of cerebrospinal fluid- (CSF) filled dura, the lowest stump of which is connected to the intestinal diverticulum.

median septum of bone, cartilage, or fibrous tissue is excised to release both hemicords.

References

34.5.4╇ Retethering in Split Cord Malformation

╇2. Pang

Retethering in type II SCM is exceedingly uncommon if cases with unrevealed ventral septum are excluded. The recurrence rate for type I SCM is almost always related to ventral tethering by the stump of an inadequately resected bone spur sticking to the overlying hemicords. This stump will have to be shaved off until the ventral bony canal is smooth and flush. Another rare scenario dates back to the group’s early attempts to close the ventral dural defect for fear of CSF leak, with the ventral sutures ironically becoming the focus of dense adhesions to the hemicords. The author now strongly recommends against closing the ventral dura after resection of a type I spur.

╇1. Wolpert L. The Triumph of the Embryo. Dover ed. Mine-

ola, NY: Dover Publications; 2008 D, Dias MS, Ahab-Barmada M. Split cord malformation: part I: a unified theory of embryogenesis for double spinal cord malformations. Neurosurgery 1992;31(3):451–480 ╇3. Krolo M, Vilović K, Sapunar D, Vrdoljak E, SaragaBabic M. Fibronectin expression in the developing human spinal cord, nerves, and ganglia. Croat Med J 1998;39(4):386–391 ╇4. Dias MS, Pang D. Split cord malformations. Neurosurg Clin N Am 1995;6(2):339–358 ╇5. Pang D. Split cord malformation: part II: clinical syndrome. Neurosurgery 1992;31(3):481–500 ╇6. Pang D. Ventral tethering in split cord malformation. Neurosurg Focus 2001;10(1):e6 ╇7. Mahapatra AK. Split cord malformation—a study of 300 cases at AIIMS 1990–2006. J Pediatr Neurosci 2011;6(Suppl 1):S41–S45

34╅ Split Cord Malformation: From Gastrulation to Operation ╇8. Jans

L, Vlummens P, Van Damme S, Verstraete K, Abernethy L. Hemimyelomeningocele: a rare and complex spinal dysraphism. JBR-BTR 2008;91(5):198–199 ╇9. Iskandar BJ, McLaughlin C, Oakes WJ. Split cord malformations in myelomeningocele patients. Br J Neurosurg 2000;14(3):200–203 10. Kumar R, Bansal KK, Chhabra DK. Occurrence of split cord malformation in meningomyelocele: complex spina bifida. Pediatr Neurosurg 2002;36(3):119–127 11. Ozturk E, Sonmez G, Mutlu H, et al. Split-cord malformation and accompanying anomalies [in French]. J Neuroradiol 2008;35(3):150–156 12. Pang D. Split cord malformation. In: Pang D, ed. Disorders of the Pediatric Spine. New York, NY: Raven Press; 1995: 253–264 13. Pang D. Spinal cord lipoma. In: Batjer H, Loftus C, eds. Textbook of Neurological Surgery. New Jersey: Lippincott Williams & Wilkins; 2002 14. Schoenwolf GC, Desmond ME. Descriptive studies of occlusion and reopening of the spinal canal of the early chick embryo. Anat Rec 1984;209(2):251–263 15. Schoenwolf GC, Franks MV. Quantitative analyses of changes in cell shapes during bending of the avian neural plate. Dev Biol 1984;105(2):257–272

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Straaten HWM, Hekking JWM, Thors F, WiertzHoessels EL, Drukker J. Induction of an additional floor plate in the neural tube. Acta Morphol Neerl Scand 1985;23(2):91–97 17. Youn BW, Malacinski GM. Axial structure development in ultraviolet-irradiated (notochord-defective) amphibian embryos. Dev Biol 1981;83(2):339–352 18. Kirillova I, Novikova I, Augé J, et al. Expression of the sonic hedgehog gene in human embryos with neural tube defects. Teratology 2000;61(5):347–354 19. Saraga-Babić M, Stefanović V, Wartiovaara J, Lehtonen E. Spinal cord-notochord relationship in normal human embryos and in a human embryo with double spinal cord. Acta Neuropathol 1993;86(5):509–514 20. Pang D. Surgical management of split cord malformations. In: Wilkins RH, Rengachary SS, eds. Neurosurgical Operative Atlas. Vol 3. Baltimore, MD: Williams & Wilkins; 1993: 135–149 21. Pang D, Zovickian J, Oviedo A, Moes GS. Limited dorsal myeloschisis: a distinctive clinicopathological entity. Neurosurgery 2010;67(6):1555–1579, discussion 1579–1580

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35

Congenital Spinal Cysts Elias Boulos Rizk, R. Shane Tubbs, and W. Jerry Oakes

35.1╇ Introduction and Background

35.1.2╇ Enterogenous Cysts

Congenital spinal cysts are relatively unusual lesions. They include arachnoid, enterogenous, teratomatous, neurenteric, foregut, bronchogenic, epithelial, ependymal, dermoid, and epidermoid cysts. Presentation and symptoms are reflected by location and rate of growth, with compression of the spinal cord, nerve roots, or both. Symptoms include pain, weakness, ataxia, and/or bladder incontinence. Furthermore, many of these lesions are discovered incidentally on imaging.

Enterogenous cysts are rare congenital lesions with an unknown etiology.3 They have been reported in all age groups. The lesions result from an error in development during the 3rd and 4th weeks of neurogenesis.4 Cysts are usually the result of the lack of separation between neural and enteric tubes by the notochord.5 The thoracic spine is the most common location of these lesions, followed by the cervical and then lumbar regions (Fig. 35.1 and Fig. 35.2). Cysts are usually associated with a defect in the anterior spinal elements, although these defects can also be located dorsally (Fig. 35.3, Fig. 35.4, and Fig. 35.5). Furthermore, occult spinal dysraphism can be present in up to 60% of patients.6 Microscopically, the cysts have a layer of columnar, pseudostratified, or stratified cuboidal epithelium cells on a basement membrane layer with a supporting connective tissue layer. On CT scan, enterogenous cysts appear as hypodense, isodense, or hyperdense lesions. On MRI, enterogenous cysts may appear as hypointense or hyperintense lesions on T1-weighted images and may appear hyperintense on T2-weighted images.

35.1.1╇ Arachnoid Cysts Spinal arachnoid cysts in pediatric patients are rare. Pathogenesis could be secondary to spontaneous herniation of arachnoid material into the epidural space through a defect in the dura mater, or due to an anomalous splitting of the arachnoid.1 Nabors et al classified arachnoid cysts into three main categories2: (1) type I, extradural meningeal cysts without nerve root fibers; (2) type II, extradural meningeal cysts with nerve root fibers; and (3) type III, intradural meningeal cysts/intradural arachnoid cysts. The cyst membrane is usually thin and transparent. With hematoxylin and eosin staining, the walls are typically seen as made of fibrous connective tissue and are lined by arachnoid meningothelial cells. Plain radiographs offer little benefit in the diagnosis of arachnoid cysts. On computed tomography (CT), arachnoid cysts appear hypodense and do not take up contrast. Magnetic resonance imaging (MRI) remains the procedure of choice, with signal characteristics similar to cerebrospinal fluid (CSF). Arachnoid cysts are hypointense on T1 images and hyperintense on T2 images and do not restrict on diffusion-weighted images. They also do not enhance with contrast.

306

35.1.3╇ Ependymal Cysts Ependymal cysts are also a rare entity. They are hypothesized to originate secondary to the evagination of the floor plate, which becomes entrapped to form an ependymal cyst. Microscopically, the cyst wall consists of cuboidal cells seen on hematoxylin, eosin, and periodic acid–Schiff (PAS) staining. They are more often found in an intramedullary location.7 Ependymal cysts can be located anywhere along the craniospinal axis. MRI is the modality of choice to evaluate ependymal cysts. They usually present as isointense on T1 and T2 images, with no contrast enhancement.

35â•… Congenital Spinal Cysts

Fig. 35.2â•… Clinical photo of the back of a neonate with three cutaneous signatures of occult spinal dysraphism (focal hirsutism, subcutaneous mass [neurenteric cyst], and dermal sinus).

Fig. 35.1â•… Sagittal magnetic resonance imaging (MRI) of a 19-year-old patient imaged for Klippel-Feil anomaly. Incidentally found complex lipoma combined with neurenteric cyst of the conus.

Fig. 35.3â•… Computed tomography (CT) axial image of patient with subcutaneous mass (neurenteric cyst), dorsal spinal defect, and intraspinal fat.

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308 Section III.Dâ•… Malformations of the Spinal Cord

Fig. 35.5â•… Material aspirated from the cyst, composed of mucin.

lary space of the lumbosacral region.9 Macroscopically, the lesion is well circumscribed. The capsule usually has a pearly sheen. The interior of the capsule is filled with soft, white material in concentric lamellar layers. Dermoids are rounded, smooth, and well-defined lesions. Inside the lesion, the contents are usually thickened, cheesy, and yellowish, with calcium deposits and hair integuments. Dermoid cysts, and less frequently epidermoid cysts, can be associated with a dermal sinus tract.10 CT can show a heterogeneously dense structure in the spinal canal. On MRI, epidermoid cysts can display a variety of signals on T1- and T2-weighted images.

35.2╇ Operative Detail and Preparation

Fig. 35.4â•… Intraoperative view of neurenteric cyst of the conus.

35.1.4╇ Dermoid and Epidermoid Cysts Dermoid and epidermoid cysts are thought to be secondary to an anomalous implantation of ectodermal cells between the 3rd and 5th week of embryonic life.8 Dermoids are slightly more common in the spinal canal than epidermoids. Epidermoids are frequently located in the subdural extramedul-

• In general, congenital spinal cysts are tackled in a similar fashion. Access to the spinal canal is performed in the usual fashion while the patient is positioned prone on gel rolls. Following localization of the operative level, bone removal is performed. The preferred practice of the authors is laminoplasty; however, a laminectomy is also a feasible option. Required instruments following dural opening include the surgical microscope and appropriate microinstruments. Neuromonitoring is an adjunct modality that could be beneficial when intramedullary lesions are encountered. • The goal is to remove neurenteric, dermoid, or epidermoid cysts. However, the risks of complete excision should be weighed with each case. The recurrence rate for neurenteric cysts when not completely resected is 27%

35â•… Congenital Spinal Cysts

•

•

•

•

in the case series of the authors.6 Ultimately, surgical cure is the goal; however, many cases are associated with considerable risks, especially neurenteric cysts. If there is a suspicion that the lesion could be a neurenteric cyst, a glass syringe with a 20-gauge needle is used to aspirate the cyst material. Mucous aspiration is pathognomonic for neurenteric cysts (Fig. 35.5). Neurenteric cysts are very difficult to completely excise due to microscopic residual that could be left attached around the wall of the lesion. It is not unusual that patients re-present later with recurrence of symptoms and recurrence of the disease process. Therefore, long-term follow-up is recommended due to recurrence. The higher the lesion in the spinal column, the more the patient is at risk of neurological compromise. Therefore, judicious resection or manipulation of the cord should be performed when attempting to resect the lesion. Arachnoid cysts can be observed, fenestrated, percutaneously drained, or shunted. The recurrence rate is 5.3% following surgical treatment of arachnoid cysts.11 Open microsurgical fenestration is the treatment of choice. The cyst wall is resected by pulling the edges into the midline. An attempt is made to find the dural communication into the spinal canal and closure of the defect. In the case of cyst fenestration, restoration of CSF flow is achieved by creating multiple defects in the cyst wall.

35.3╇ Outcomes and Postoperative Care The goal of treatment, when deemed appropriate, is safe surgical resection. The alternative is partial resection, decompression, or continued observation of the cyst when risk of injury outweighs the benefits of complete resection. After surgical intervention, the authors tend to keep patients flat in bed for at least 24 hours postoperatively. Bladder catheterization is ceased as soon as possible to decrease the risk

of urinary tract infections. Patients are encouraged to ambulate and get out of bed early when deemed appropriate. This varies significantly among surgeons. Follow-up is scheduled in a regular fashion, with imaging performed on a yearly basis afterward, especially in the case of neurenteric cysts, to document any recurrence. CSF leakage should be addressed immediately either with resuturing at the bedside or with wound exploration in the operating room and lumbar drain placement, with gradual weaning to allow for adequate skin healing.

References ╇1. Bright

R. Serous cysts in the arachnoid. In: Reports of Medical Cases Selected with a View of Illustrating the Symptoms and Cure of Diseases by a Reference to Morbid Anatomy. London, England: Longman; 1831 ╇2. Nabors MW, Pait TG, Byrd EB, et al. Updated assessment and current classification of spinal meningeal cysts. J Neurosurg 1988;68(3):366–377 ╇3. Gao P, Osborn AG, Smirniotopoulrs JG, Boyer RS. Neuroenteric cyst—pathology, imaging spectrum and differential diagnosis. Int J Neuroradiol 1995;1:17–27 ╇4. Gimeno A, Lopez F, Figuera D, Rodrigo L. Neuroenteric cyst. Neuroradiology 1972;3(3):167–172 ╇5. Sharma RR, Ravi RR, Gurusinghe NT, et al. Cranio-spinal enterogenous cysts: clinico-radiological analysis in a series of ten cases. J Clin Neurosci 2001;8(2):133–139 ╇6. Rauzzino MJ, Tubbs RS, Alexander E III, Grabb PA, Oakes WJ. Spinal neurenteric cysts and their relation to more common aspects of occult spinal dysraphism. Neurosurg Focus 2001;10(1):e2 ╇7. Chhabra R, Bansal S, Radotra BD, Mathuriya SN. Recurrent intramedullary cervical ependymal cyst. Neurol India 2003;51(1):111–113 ╇8. McLone D. Pediatric Neurosurgery: Surgery of the Developing Nervous System. Philadelphia, PA: W.B. Saunders; 2001 ╇9. Scarrow AM, Levy EI, Gerszten PC, Kulich SM, Chu CT, Welch WC. Epidermoid cyst of the thoracic spine: case history. Clin Neurol Neurosurg 2001;103(4):220–222 10. Radmanesh F, Nejat F, El Khashab M. Dermal sinus tract of the spine. Childs Nerv Syst 2010;26(3):349–357 11. Evangelou P, Meixensberger J, Bernhard M, et al. Operative management of idiopathic spinal intradural arachnoid cysts in children: a systematic review. Childs Nerv Syst 2013;29(4):657–664

309

Section IV

Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation Section Editor: John Kestle

The management of hydrocephalus is the most common task facing the pediatric neurosurgeon. Although insertion of a ventriculoperitoneal shunt may not be the most elegant of neurosurgical procedures, it is one of the most effective. After decades of similar treatment options, without much in the way of provocative research, a number of new developments are reinvigorating the field of hydrocephalus. There has been increased basic-science activity and recently some evidence that ciliopathy may play a role. The “dishevelled” gene has been described, which localizes to cilia of ependymal cells. Loss of dishevelled genes in mice resulted in abnormal alignment of ependymal cilia and hydrocephalus.1 Large clinical trials with specific study questions and appropriate sample sizes are now seeking answers to relevant clinical research questions.2,3 Advanced imaging techniques are being used to assess disease severity and prognosis.4 And some results suggest that diffusion tensor imaging (DTI) might be more informative than ventricle size alone.5 Surgical innovation in third ventriculostomy (with choroid plexus coagulation) has expanded the role of third ventriculostomy to infants who previously would have been shunted.6 Despite all of these exciting advances, we still face, on a daily basis, children in need of urgent surgical care for their hydrocephalus. We are therefore fortunate to read the “tricks of the trade” used by experts in the field today.

╇1. Ohata

S, Nakatani J, Herranz-Perez V, Cheng J, Belinson H, Inubushi T, et al. Loss of dishevelleds disrupts planar polarity in ependymal motile cilia and results in hydrocephalus. Neuron 2014;83:558–571 ╇2. Adzick NS, Thom EA, Spong CY, Brock III JW, Burrows PK, Johnson MP, et al. A randomized trial of prenatal versus postnatal repair of myelomeningocele. MOMS Investigators. N Engl J Med 2011;364(11):993–1004 ╇3. Whitelaw A, Jary S, Kmita G, Wroblewska J, MusialikSwietlinska E, Mandera M, et al. Randomized trial of drainage, irrigation and fibrinolytic therapy for premature infants with posthemorrhagic ventricular dilatation: developmental outcome at 2 years. Pediatrics 2010;125:e852–e858 ╇4. Air E, Yuan W, Holland S, Jones B, Bierbrauer K, Altaye M, et al. Longitudinal comparison of pre- and postoperative diffusion tensor imaging parameters in young children with hydrocephalus. J Neurosurg Pediatr 2010;5:385–391 ╇5. Buckley RT, Yuan W, Mangano FT, Phillips JM, Powell S, McKinstry RC. Longitudinal comparison of diffusion tensor imaging parameters and neuropsychological measures following endoscopic third ventriculostomy for hydrocephalus. J Neurosurg Pediatr 2012;9:630–635 ╇6. Warf B. Comparison of endoscopic third ventriculostomy alone and combined with choroid plexus cauterization in infants younger than 1 year of age: a prospective study in 550 African children. J Neurosurg 2005;103(6):475–481

36

The Pathophysiology and Classification of Hydrocephalus David M. Frim and Ashley Ralston

36.1╇ Introduction and Background In a “tricks of the trade” volume, a chapter on pathophysiology and classification may seem, a priori, a bit out of place. However, for a complicated disease entity like hydrocephalus, which takes up as much as 40% of most pediatric neurosurgery practices,1 facility with the disorder’s causes and its various manifestations is a necessity. The discussion in this chapter is not presented in the standard model of other chapters in this volume that set forth perioperative “tricks” to reduce operative complications or pearls of wisdom that make clear why a certain surgical approach will work best. Rather, the pearl of this chapter is a framework of understanding of the various pathophysiological types of hydrocephalus; the trick is learning to use that understanding to design an evaluative and treatment approach for each specific child with hydrocephalus. The authors hope this approach will be of some value—perhaps representing an alternative way to place another pearl into our pediatric neurosurgical bag of tricks.

36.1.1╇ Definition There are several published definitions of hydrocephalus.2 Practically speaking, the authors have used a relatively simple definition that describes hydrocephalus as an accumulation of cerebrospinal fluid (CSF) within the ventricular space at an inappropriate pressure. Although somewhat simplistic, this definition has proved durable over many years of practice because it correctly identifies ventriculomegalic high-pressure situations as hydrocephalus but also includes other entities, such as the syndrome of normal-pressure hydrocephalus of the older population, within the definition. Some situations, such as the slit ventricle syndrome in shunted hydrocephalus, are also included, as pressures within the ventricles in that situation are inappropriately elevated and can be further elevated by infusion of small volumes

into the ventricles. Certain other entities, such as pseudotumor cerebri, are excluded from the family of hydrocephalic disorders by this definition because pseudotumor, although not completely understood, can be modeled as an accumulation of CSF outside the brain in the subarachnoid space. Arachnoid cyst, although clearly a CSF-filled space that is often under inappropriate pressure, is also excluded by this definition because the fluid pressure is not within a ventricle.

36.2╇Pathophysiology The ventricular system consists of two lateral ventricles, a third ventricle, and a fourth ventricle. CSF is actively secreted in all four ventricles by choroid plexus through complex mechanisms that involve active secretion of water and control of a variety of solubilized electrolytes and proteins. A first-pass model assigns bulk flow of CSF from the lateral ventricles through the foramina of Monro into the third ventricle, along the aqueduct of Sylvius into the fourth ventricle, and finally out the foramina of Luschka and Magendie into the craniocervical junction subarachnoid space. The function of CSF has not yet been fully defined, nor have the nuances of its production and reabsorption. The CSF reabsorption surface is often, and practically so, defined as the subarachnoid space arachnoid granulations, although exactly how much CSF is truly reabsorbed into those structures as opposed to draining into the skull base lymphatic system3 or being reabsorbed along the cranial and spinal nerve roots4 has not yet been fully determined. Ventriculomegaly denotes large ventricles. This can represent a pathological state or a variant of normal, and, as with so many other descriptive definitions related to hydrocephalus, it is of little use in determining the nature of a CSF problem. In simplistic terms, hydrocephalus arises from an obstruction

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314 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation to bulk CSF flow or inability to absorb the CSF being produced. The obstruction can occur at any point along the CSF pathways from secretion to absorption, as described above. Due to the obstruction (where malabsorption and CSF overproduction are considered forms of obstruction), CSF accumulates in the ventricles and other fluid-filled spaces “upstream” to the obstruction and eventually causes progressive elevation in intracranial pressure, stretching of the periventricular white matter with attendant neurological symptoms, compression of periventricular structures, and, more ominously, brainstem compression, downward herniation of the brainstem, and eventual death. The pace of these changes can be urgent or can be spread out over years. Treatment of hydrocephalus is designed to prevent these steps from occurring. There are many other factors and nuances to the dynamics of CSF that are neglected in this approach5: the pulsatile nature of CSF flow, the flow-altering effects of the foramina and the aqueduct, and the presence of a viscoelastic brain that contains a pulsatile vasculature with a variable phase relationship to CSF pulsatility. Although fascinating in many ways, these issues are immaterial to the basic clinical management of hydrocephalus. Only in approaching very complicated hydrocephalic situations, such as the slit ventricle syndrome,1 do these other conceptual models play a role. The pathophysiology and treatment of hydrocephalus then become a simple matter: determine the cause of CSF flow obstruction, malabsorption, or overproduction and correct it either by removing the obstruction (i.e., a foraminal tumor), creating a bypass around the obstruction (i.e., third ventriculocisternostomy for primary aqueductal stenosis), diverting the CSF to an extracranial absorptive surface for hydrocephalus of malabsorption (i.e., ventriculoperitoneal shunting for posthemorrhagic hydrocephalus), or removing the entity that is hyperproducing CSF (i.e., choroid plexus papilloma).

36.3╇ Classification Within the framework described, subtypes of hydrocephalus have been classified since the early 20th century for practical clinical approaches.6 The terms communicating and noncommunicating hydrocephalus are archaic and are based in an era when recoverable dye and air ventriculography were our primary imaging modalities. They suggest both a hydrocephalus that affects all four ventricles (allowing the dye or air ventriculogram to communicate between all the ventricles), which can only be caused by obstruction to CSF reabsorption, and a hydrocephalus where the air ventriculogram does not communicate across all

ventricles—which can only be caused by an obstructing lesion between ventricles with “upstream” CSF accumulation.6 The authors have favored a more fruitful rendition of this nomenclature7: absorptive and obstructive hydrocephalus, which describe the pathophysiological mechanisms. As per the earlier discussion, obstructive hydrocephalus is generally treated by removal of the obstruction if possible, absorptive hydrocephalus by delivery of the produced CSF to an alternative absorptive site. Other approaches to these two classes of hydrocephalus can also be entertained: CSF overproduction causing absorptive hydrocephalus is treated by the removal of the secreting entity (almost always choroid plexus papilloma) or the reduction of CSF secretion either via medical means (acetazolamide) or via cauterization/ablation of the choroid plexus.2 In another axis, hydrocephalus can be classified by its symptomatology as either compensated or noncompensated. This classification provides a clinical dichotomy between hydrocephalus that requires intervention (noncompensated) and that which does not. The helpful concept here is that not all hydrocephalus causes symptoms and not all hydrocephalus requires intervention. This tenet is central to the treatment of hydrocephalus because the aphorism regarding surgery, “there is no surgery like no surgery,” can now be adapted to a neurosurgical aphorism, “there is no shunt like no shunt.” A third axis for hydrocephalus classification is based on its chronicity: acute versus chronic hydrocephalus. This classification provides additional clinical insight into the pace of the disease with an internal recommendation for or against treatment. Acute hydrocephalus can be a neurosurgical emergency when neurological deficits progress rapidly as intracranial pressure (ICP) rises. Chronic hydrocephalus in many ways approximates compensated hydrocephalus, where progression is slow, if present at all, and intervention is pursued with a deliberate approach. A fourth axis for hydrocephalus classification is congenital versus acquired. This classification scheme has less distinct clinical benefit for decision making than those discussed earlier. However, this dichotomous classification does place hydrocephalus within the patient’s totality by defining whether the hydrocephalus, as an intrinsic part of a patient’s genetic nature, is associated with additional syndromes, is a manifestation of an inborn genetic error that is causing hydrocephalus as a bystander, or should affect an individual’s family planning. Acquired hydrocephalus has none of those concerns and defines the hydrocephalus as secondary to another process that may have much more impact on the patient (i.e., severe head trauma), and may be self-limited in time.

36  The Pathophysiology and Classification of Hydrocephalus

36.4╇Conclusions Hydrocephalus is a complicated manifestation of obstruction of CSF flow causing an accumulation of fluid within the brain ventricles at an inappropriate pressure. For purposes of current clinical care, its pathophysiology is simple and in many ways the nomenclature used to classify the disease predicts and directs treatment options. The concepts of the several dichotomous classification systems presented in this chapter highlight the many ways that we think about hydrocephalus and the diverse ways that it is approached. These concepts should be kept in mind when reading and reviewing clinical recommendations for hydrocephalus treatment. Such recommendations should always conform to the straightforward physiological concepts of CSF flow and obstruction.

References ╇1. Frim

DM, Gupta N. Hydrocephalus. In: Frim DM, Gupta N, eds. Pediatric Neurosurgery. Georgetown, TX: Landes Biosciences; 2006: 117–129 ╇2. Rekate HL. A contemporary definition and classification of hydrocephalus. Semin Pediatr Neurol 2009;16(1):9–15 ╇3. Johnston M. The importance of lymphatics in cerebrospinal fluid transport. Lymphat Res Biol 2003;1(1):41– 44, discussion 45 ╇4. Zakharov A, Papaiconomou C, Djenic J, Midha R, Johnston M. Lymphatic cerebrospinal fluid absorption pathways in neonatal sheep revealed by subarachnoid injection of Microfil. Neuropathol Appl Neurobiol 2003;29(6):563–573 ╇5. Penn RD, Linninger A. The physics of hydrocephalus. Pediatr Neurosurg 2009;45(3):161–174 ╇6. Pudenz RH. The surgical treatment of hydrocephalus—an historical review. Surg Neurol 1981;15(1):15–26 ╇7. Beni-Adani L, Biani N, Ben-Sirah L, Constantini S. The occurrence of obstructive vs absorptive hydrocephalus in newborns and infants: relevance to treatment choices. Childs Nerv Syst 2006;22(12):1543–1563

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37

Ventricular Shunting for Hydrocephalus Walavan Sivakumar, Jay Riva-Cambrin, Vijay M. Ravindra, and John Kestle

37.1╇ Introduction and Background The management of hydrocephalus remains the most common problem encountered by pediatric neurosurgeons and is a significant burden to the pediatric health care system.1 Despite promising advances in endoscopy,2 ventricular peritoneal shunting remains the workhorse for this condition. The decision to treat a child with possible hydrocephalus should be based on findings that are progressive over time. It is uncommon to treat a child with ventriculomegaly on the first encounter, unless it is severe. The authors’ indications to treat are progressive enlargement of the ventricular system and/ or worsening clinical manifestations over time. These clinical manifestations may be developmental delay, head circumference crossing percentiles, or progressive symptoms of raised intracranial pressure.3 Once a decision to treat has been made, a number of options are available. If there is an obvious lesion causing the hydrocephalus, such as posterior fossa cyst or cerebellar hematoma, the management of the hydrocephalus may first consist of removing the causative lesion. Next, consideration should be given to endoscopic approaches. Endoscopic third ventriculostomy with/without choroid plexus coagulation should be considered, and the Endoscopic Third Ventriculostomy Success Score4 is a very useful tool in the clinic. It allows an assessment of the likely success rate so that appropriate discussions can be held with the family. Other endoscopic approaches may be considered with loculated fluid compartments or intraventricular septations. In the absence of those options, ventriculoperitoneal shunting will be required. The only other consideration is whether the hydrocephalus is due to a reversible cause, such as hemorrhage. If so, the use of a temporizing measure, such as an external ventricular drain, subgaleal shunt, or reservoir, may be appropriate first.5 Of course, shunting should be avoided or delayed in the context of infection of the central nervous system or significant systemic infection.

316

37.2╇ Operative Detail and Preparation 37.2.1╇ Preoperative Planning The child’s skin should be wiped with a chlorhexidine sponge before being brought to the operating room. The operating room personnel should be notified of the necessary equipment, including ultrasound. At the time of initial shunt placement, stereotactic systems are not typically necessary, although they are used routinely by some surgeons.6 The choice of shunt equipment receives a lot of attention in the literature. The preference of the authors is a two-piece system. The first piece is the ventricular catheter, and the second piece consists of a burr-hole reservoir, which snaps onto the ventricular catheter, a valve, and peritoneal tubing. The authors typically use a differential pressure valve for the initial shunt since they have not seen advantages to adjustable valves7 or valves that are designed to address overdrainage.8 Siphon-limiting valves are occasionally used in older children with fused sutures and very large ventricles. The authors currently use antibioticimpregnated catheters at the ventricular and peritoneal ends as part of an ongoing assessment of these products at their center. The evidence in the literature for these catheters suggests a reduced infection rate,9 although a well-designed, high-powered randomized trial has not been conducted.

37.2.2╇ Intraoperative Issues The patient is positioned supine with the head on a horseshoe headrest. The head is rotated to the left, and the head and neck are positioned so that the neck is straightened to facilitate passing of the shunt from the peritoneal end to the head (Fig.€37.1a). The child is given preoperative antibiotics, and the incisions are planned and infiltrated

37â•… Ventricular Shunting for Hydrocephalus a

b

Fig. 37.1â•… Preoperative patient positioning. (a) Patient supine with head rotated to left. Anatomical landmarks: anterior fontanelle, incision, and midline are marked. (b) Scalp incision showing dura overlying anterior fontanelle.

with local anesthetic. A little bit of hair is clipped along the planned incisions, and then the tract of the shunt is prepped with a chlorhexidine sponge. The hair in between the planned incisions, which is allowed to dry for 3 minutes, is included in the prep, the skin is covered with an iodophor-impregnated adhesive, and the field is draped. All participants in the surgery should perform a full surgical scrub rather than using antiseptic cream10 and should wear double gloves. After prepping and draping, the authors change their outer gloves.

Three incisions are used. In the coronal region, a C-shaped incision is made in line with the pupil in the lateral corner of the anterior fontanelle (Fig. 37.1b). With an open fontanelle, the entry site into the dura is planned to be just in front of the parietal bone so that the reservoir from the shunt is sitting partially on bone. In children without an open fontanelle, a burr hole is placed in the same location. The second incision is retroauricular. This should be placed far enough behind the ear so that the shunt tubing will not be underneath the pinna. The abdominal incision

317

318 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation is generally made to the right of the umbilicus or in the midline subxiphoid region. Ultrasound is used to visualize the ventricular system through the anterior fontanelle or the burr hole. The distance from the dura to the frontal horn of the ventricle is measured so that the ventricular catheter length can be selected. The target for the ventricular catheter is the frontal horn just in front of the foramen of Monro, away from the choroid plexus. The tip of the catheter should be above the floor of the frontal horn so that it will be in cerebrospinal fluid as the ventricle decreases in size. The shunt system is then passed subcutaneously. This is done with an attempt to minimize subgaleal

tissue dissection. Excessive dissection causes bleeding and creates a pocket in which the shunt can move and fluid and blood can accumulate. The first step is to use the plastic sheath from the shunt passer by itself. The tapered end is inserted into the coronal incision, and it is then passed, in the subgaleal space, to the retroauricular incision (Fig. 37.2a). Without the shunt passer in the sheath, the sheath is able to make the curve around the head and excessive dissection is not necessary. The distal end of the shunt tubing is then placed into the sheath until it is visualized coming out the retroauricular incision. The sheath is then pulled out through the retroauricular incision (Fig. 37.2b). To pass the tubing from the retroauricular incision

a

b

Fig. 37.2â•… Tunneling between coronal and retroauricular incision. (a) Coagulation of the soft tissues performed to facilitate passage of the plastic sheath. (b) Hemostat used to pull plastic sheath through incision to avoid excessive dissection.

37â•… Ventricular Shunting for Hydrocephalus Fig. 37.3â•… Illustration of the minilaparotomy technique for distal peritoneal tube placement. Hemostat forceps are used to localize individual layers of the abdominal cavity until the peritoneum is reached. A small incision is made in the peritoneum until bowel or omentum is visualized.

down to the abdomen, the shunt passer is placed inside the plastic sheath. The shunt passer and sheath are then tunneled from the abdominal incision to the retroauricular incision, and the tubing is pulled down through the sheath to the abdomen. The shunt system should be pulled all the way down into its final position to make sure that there is an adequate pocket for the valve and reservoir at the top end. This pocket does not need to be very large and, again, excessive dissection should be avoided. The system is then irrigated so that there are no air pockets. At the coronal entry site, the dura is then opened. This is done using monopolar cautery on a brain needle. This results in a small hole in the dura that is just big enough to permit the ventricular catheter. This snug fit of the dura around the ventricular catheter minimizes the risk of cerebrospinal fluid leak. The catheter is placed with ultrasound guidance, and the target is the frontal horn in front of the choroid plexus. The shunt insertion endoscope is not used because it has not been shown to improve ventricular catheter position or shunt survival.11 Once the catheter is in place, fluid should flow spontaneously, and then the reservoir is snapped onto the ventricular catheter. At the peritoneal end, there should be spontaneous flow of fluid. Aspiration from the distal end is discouraged and is rarely necessary. The tubing should be checked so that there are no kinks and to make sure

that it has a smooth course from the coronal incision down to the abdomen. The distal end in the peritoneal space can be placed with an abdominal trocar or through a minilaparotomy. If the trocar is used, it is placed in the wound until the abdominal wall fascia is palpated. The abdominal wall can be lifted through the drapes, and the trocar can then be inserted at an angle of approximately 45 degrees to the floor. It should be directed away from the umbilicus. Once the trocar pops through into the peritoneal space, there is a natural tendency for the surgeon to pull back. This can result in the trocar coming out partially and therefore should be avoided. Care should be taken when the trocar is removed because the edge of the trocar can cut the shunt tubing. The shunt tubing, therefore, must be in line with the opening in the trocar during removal. For surgeons who prefer to use a minilaparotomy, it can be performed in the midline through a subxiphoid incision or through a muscle-splitting approach on either side (Fig. 37.3). Once the peritoneal end is in place, all wounds should be irrigated with bacitracin solution. The layers are sequentially closed in each wound. At the coronal end, a two-layer closure should be performed, including the galea and the skin. The authors prefer to use absorbable sutures in the skin. A dressing is applied to each wound.

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37.3╇ Outcomes and Postoperative Course Postoperative care includes elevation of the head of the bed 30 degrees and administration of one dose of cefazolin 8 hours after the surgery. The next day, prior to discharge, an imaging study of the ventricular system is obtained as a baseline for early follow-up. Although the insertion of a new ventriculoperitoneal shunt is a straightforward procedure, it should not be delegated to the most junior members of the team. Attention to detail and standardized protocols may help to reduce complications and allow a rapid and uneventful recovery from the procedure.

References ╇1. Simon TD, Riva-Cambrin J, Srivastava R, Bratton SL, Dean

JM, Kestle JR; Hydrocephalus Clinical Research Network. Hospital care for children with hydrocephalus in the United States: utilization, charges, comorbidities, and deaths. J Neurosurg Pediatr 2008;1(2):131–137 ╇2. Warf BC, Campbell JW. Combined endoscopic third ventriculostomy and choroid plexus cauterization as primary treatment of hydrocephalus for infants with myelomeningocele: long-term results of a prospective intent-to-treat study in 115 East African infants. J Neurosurg Pediatr 2008;2(5):310–316 ╇3. Kestle J. Hydrocephalus in children: approach to the patient. In: Youmans JR, Winn HR, Ralph Erskine Conrad Memorial Fund, eds. Youmans Neurological Surgery. 6th ed. Philadelphia, PA: Elsevier/Saunders; 2011 ╇4. Kulkarni AV, Drake JM, Kestle JR, Mallucci CL, Sgouros S, Constantini S; Canadian Pediatric Neurosurgery Study

Group. Predicting who will benefit from endoscopic third ventriculostomy compared with shunt insertion in childhood hydrocephalus using the ETV Success Score. J Neurosurg Pediatr 2010;6(4):310–315 ╇5. Wellons JC, Shannon CN, Kulkarni AV, et al; Hydrocephalus Clinical Research Network. A multicenter retrospective comparison of conversion from temporary to permanent cerebrospinal fluid diversion in very low birth weight infants with posthemorrhagic hydrocephalus. J Neurosurg Pediatr 2009;4(1):50–55 ╇6. Levitt MR, O’Neill BR, Ishak GE, et al. Image-guided cerebrospinal fluid shunting in children: catheter accuracy and shunt survival. J Neurosurg Pediatr 2012;10(2):112–117 ╇7. Kestle JR, Walker ML; Strata Investigators. A multicenter prospective cohort study of the Strata valve for the management of hydrocephalus in pediatric patients. J Neurosurg 2005;102(2 Suppl):141–145 ╇8. Kestle J, Drake J, Milner R, et al. Long-term follow-up data from the Shunt Design Trial. Pediatr Neurosurg 2000;33(5):230–236 ╇9. Klimo P Jr, Thompson CJ, Ragel BT, Boop FA. Antibioticimpregnated shunt systems versus standard shunt systems: a meta- and cost-savings analysis. J Neurosurg Pediatr 2011;8(6):600–612 10. Kestle JR, Riva-Cambrin J, Wellons JC III, et al; Hydrocephalus Clinical Research Network. A standardized protocol to reduce cerebrospinal fluid shunt infection: the Hydrocephalus Clinical Research Network Quality Improvement Initiative. J Neurosurg Pediatr 2011;8(1):22–29 11. Kestle JR, Drake JM, Cochrane DD, et al; Endoscopic Shunt Insertion Trial participants. Lack of benefit of endoscopic ventriculoperitoneal shunt insertion: a multicenter randomized trial. J Neurosurg 2003;98(2):284–290

38

Endoscopic Treatment of Hydrocephalus Alexandra D. Beier and Abhaya V. Kulkarni

38.1╇ Introduction and Background

38.1.3╇ Alternate Procedures

The number of etiologies for hydrocephalus is vast; however, the overall treatment goal is the same―cerebrospinal fluid diversion. A distinction is typically made between communicating hydrocephalus and obstructive hydrocephalus. Although more endoscopic procedures are being utilized for communicating hydrocephalus, this chapter focuses on endoscopic techniques for obstructive hydrocephalus. More specifically, this chapter discusses how the endoscope is utilized in performing an endoscopic third ventriculostomy (ETV), as well as how it is used in treating complex hydrocephalus.

• Cerebrospinal fluid shunting

38.1.1╇Indications • Etiology-specific indications include: triventricular hydrocephalus, fourth ventricular outlet obstruction, isolated ventricle, multiloculated hydrocephalus, retrocerebellar cysts (including Dandy-Walker malformation and variant, Blake pouch cyst, posterior fossa arachnoid cysts). • Anatomy-specific indications include: • ETV: enlarged lateral and third ventricles, downward deviation for third ventricular floor, sizeable retroclival cistern, and identification of basilar artery • Cyst fenestration/septostomy: thinned cyst/ septal wall • The above are all relative indications and not absolutely necessary, but generally preferable.

38.1.2╇Goal • Restoration of normal cerebrospinal fluid dynamics with normalization of intracranial pressure and neurocognitive functioning

38.1.4╇Advantages • Allows cerebrospinal fluid diversion utilizing a more homeostatic pathway that is theoretically more physiological • No physical hardware to malfunction, to become infected, or to need replacement • Avoids the need for transgression of another body cavity (usually peritoneum)

38.1.5╇Contraindications • Etiology-specific contraindications relative to communicating hydrocephalus: young age • Anatomy-specific contraindications relative to: • ETV: slit/small ventricles, tight retroclival cistern, inability to visualize basilar artery, previous history of subarachnoid scarring, especially prepontine scarring on CISS/ FIESTA magnetic resonance imaging (MRI) • Cyst fenestration/septostomy: unfavorable venous anatomy

38.2╇ Operative Detail and Preparation 38.2.1╇ Preoperative Planning and Special Equipment • Review of preoperative imaging to ensure adequate trajectory and size of

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322 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation foramen of Monro to allow passage of the ventriculoscope • Ventriculoscope • Ultrasound

38.2.2╇ Expert Suggestions/Comments • Prior to the procedure, a careful preoperative inspection of equipment is essential. • High-quality MRI is imperative in deciding the appropriate intervention. • Neuronavigation can be beneficial with small ventricles and in localizing an ideal trajectory for a septostomy or cyst fenestration.

38.2.3╇ Key Steps of the Procedure/ Operative Nuances Positioning • For standard ETV or septostomy, the patient is positioned supine with the head in a slightly flexed position on a well-padded horseshoe. • Alternatively, rigid fixation with pins or a DORO headrest system if neuronavigation is utilized. • A precoronal incision is outlined: • For a standard ETV, the incision is made in line with the midpupillary line. • For septostomy, it may be best to make the incision approximately 1 to 2 cm lateral to midpupillary line to obtain a trajectory that is more perpendicular to the septum. • For cyst fenestration procedures, the patient position and incision must be individualized, using the following principles: • Attempt to find the shortest route to the thinnest, most easily traversed part of the cyst. • Use of neuronavigation is often helpful in landmarking the entry point and in intraoperative guidance, especially if the endoscope is registered and tracked by the neuronavigation system.

•

• •

• • • •

Procedure • A curvilinear incision is made with scalpel and cautery, keeping in mind that the incision might later be used for a shunt, should the endoscopy fail. • Two “kissing” burr holes are made with a perforator bit from a high-speed drill for

•

a burr hole large enough to allow for the simultaneous use of ultrasound for real-time guidance. In infants, a small bone flap can be lifted, preferably hinged on the coronal suture, to be replaced with suture at the completion of the case. The dura is opened in a linear fashion, with minimal cauterization (to allow for watertight primary closure at completion of procedure). Ultrasound is utilized to plan an ideal trajectory to the lateral ventricle through the enlarged burr hole (alternatively, one can use an open fontanelle for the ultrasound; however, guidance is somewhat more difficult since it is not directly in line with the surgical trajectory). A brain needle is placed into the lateral ventricle under ultrasound guidance. The brain needle is withdrawn and a ventriculoscope is then inserted into the lateral ventricle. Entry into the ipsilateral ventricle is confirmed using anatomical landmarks (Fig. 38.1). For an ETV: • The ventriculoscope is advanced through the foramen of Monro into the third ventricle (Fig. 38.2). • After identifying an ideal site (anterior to the mammillary bodies and basilar artery, posterior to dorsum sella), a blunt instrument (e.g., stylet from an external ventricular drainage catheter or closed forceps) is inserted and, utilizing a twisting motion, is used to pierce the third ventricular floor. • Next, the hole is expanded (e.g., using a balloon-dilating catheter or spreading grasping forceps in a coronal plane). • This is repeated until the hole is at least 1€cm. • The third ventricular floor should balloon up and the ventriculoscope can be driven through the ETV hole to examine the prepontine cistern for any residual membranes. • Complete fenestration of all membranes requires visualization of clival dura and a “naked” basilar artery. For cyst fenestration/septostomy: • Advance the ventriculoscope to the membrane in need of fenestration. • Utilizing bipolar coagulation, cauterize in the region of the future septostomy site,

38â•… Endoscopic Treatment of Hydrocephalus

Fig. 38.1â•… Endoscopic view of right lateral ventricle.

Fig. 38.2â•… Endoscopic view of third ventricular floor.

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324 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation

• • • • •

looking for an anatomical safe area that is relatively avascular. • If the membrane is thick and not translucent, traverse the membrane in a slow, layer-by-layer fashion, intermittently examining the site for vessels to avoid. • Next, use the grasping forceps to create a fenestration in the membrane. Then spread forceps (or use a balloon-dilating catheter) to enlarge the hole until it is at least 1 cm. • The ventriculoscope can be advanced through the hole to ensure that the expected anatomy is seen and to confirm true fenestration. • Cautery and scissors can then be used to further enlarge the fenestration as needed. After the procedure has been completed, irrigation is allowed to run to clear debris and assist in hemostasis. Inspection of the fornix and ventricular walls is performed prior to removal of ventriculoscope. After the ventriculoscope is withdrawn, a Duragen plug is placed in the superficial portion of the tract and cortical surface. The dura is re-approximated with suture (watertight, if possible) and a meticulous skin closure is performed. An external ventricular drain may be left in the ventricular cavity to monitor pressure postoperatively.

38.2.4╇ Hazards/Risks/Avoidance of Pitfalls • If thickened third ventricular floor and abnormal anatomy are encountered, the procedure may need to be aborted. • To avoid forniceal injury, maintain cognizance of where the ventriculoscope is located in the ventricle and avoid rostral pressure when through the foramen of Monro. • The most common cause of intraventricular hemorrhage is venous bleeding that will clear with irrigation and time.

• Increase in intracranial pressure can ensue if there is not adequate irrigant outflow. • Risks associated with endoscopic procedures include: basilar artery injury, endocrinological disturbances, forniceal injury, and intraventricular hemorrhage.

38.2.5╇ Salvage and Rescue • Ventriculoperitoneal or cystoperitoneal shunting can be an acceptable alternative and salvage procedure. • In the advent of nonclearing hemorrhage, an external ventricular drain can be left. • If severe hemorrhage is encountered from major arterial injury (e.g., basilar artery), immediate postoperative angiography is indicated.

38.3╇ Outcomes and Postoperative Course 38.3.1╇ Postoperative Considerations Unlike the case with ventriculoperitoneal shunting, the ventricles do not decrease in size dramatically postoperatively. It can take several months to see noticeable changes. If an external ventricular drain is left for nonclearing ventricular hemorrhage, it should be drained low to clear the blood and then rapidly weaned, to facilitate usage of the fenestration.

38.3.2╇Complications • Minor • Cerebrospinal fluid leak, pneumocephalus, subdural hygromas, intraventricular hemorrhage, and seizures • Major • Arterial injury; forniceal injury; endocrinological dysfunction; and damage to the hypothalamus, thalamus, or midbrain

39

Congenital Intracranial Cysts Spyridon Sgouros and Vassilios Tsitouras

39.1╇ Introduction and Background 39.1.1╇Indications

Controversial (Most Neurosurgeons Avoid Treatment) • Nonspecific headaches • Epilepsy • Developmental delay

Absolute • Presence of neurological signs and symptoms that can be clearly attributed anatomically to the presence of the cyst (Table 39.1) • Documented increased intracranial pressure (ICP), expressed with symptoms (headaches, vomiting, papilledema) or invasive recording • Coexisting hydrocephalus

The threshold for surgical intervention usually is lower in children than in adults, according to AlHolou et al.1 A “treating the scans” approach should be avoided. Nonspecific issues, such as developmental delay or seizures without clear localization, usually persist even after a successful reduction in cyst size.

39.1.2╇Goals

Relative • A cyst that increases in size, as seen in serial imaging, in the absence of new or progressive symptoms • Evidence of previous bleeding into, or in proximity with, the cyst

• The main goal is improvement of clinical status or prevention of further deterioration without additional morbidity. • Radiological reduction of the cyst is desirable and considered a form of treatment success. The objective is to decrease the mass effect

Table 39.1â•… Clinical presentation of intracranial arachnoid cysts Hydrocephalus and increased ICP

Macrocephaly, bulging fontanelle, splayed sutures (neonates and toddlers)

Middle fossa cysts (sylvian fissure)

Bulging and thinning of adjacent bone, seizures, developmental delay, mild proptosis, visual loss

Suprasellar cysts

Endocrine abnormalities (precocious puberty, GH insufficiency), eating disturbances, visual field loss, bobble-head doll syndrome

Posterior fossa cysts

Ataxia, long tract signs, hearing loss, facial weakness, swallowing difficulties

Quadrigeminal cysts

Parinaud sign

Nonspecific signs and symptoms

Failure to thrive, behavioral disorders, poor school performance

Headache, vomiting, dizziness, lethargy, papilledema, VI nerve palsy (older children)

Abbreviations: GH, growth hormone; ICP, intracranial pressure.

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326 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation of the cyst and to treat the concomitant hydrocephalus. Neuroendoscopic fenestration is regarded as the first line of surgical treatment today. The goal is a wide communication of the cyst with the basal cisterns and/or the ventricles, to minimize risk for recurrence and to avoid shunt insertion.

39.1.3╇ Alternate Procedures Microsurgery for Cyst Fenestration― Marsupialization This remains a reliable option in experienced hands. Some surgeons prefer a small cortical fenestration to leave less space for subdural collections. The previously practiced complete excision of cyst wall is not widely employed any more.

Cystoperitoneal Shunt For many neurosurgeons today, shunting is the last option for recurrences after craniotomy or neuroendoscopy. It is a good first-line option for very large middle fossa arachnoid cysts that extend over the convexity of the hemisphere. Many neurosurgeons would use an adjustable valve to avoid rapid cyst decompression.

39.1.4╇Advantages The biggest advantage of neuroendoscopic management is minimal invasiveness, associated with good chance of permanent cyst reduction and avoidance of shunt. Technological advancements and increased experience have made this approach safe and versatile, with an improved success rate. Even multiple neuroendoscopic attempts are a reasonable option for recurrent cases.

39.1.5╇Contraindications • If the cyst wall is tough and/or adherent to the surrounding neurovascular structures, the endoscopic procedure should be abandoned and switched to a microsurgical or endoscope-assisted microsurgical approach. • Some huge posterior fossa cysts with significant mass effect over the brainstem should not be drained aggressively. Rapid brainstem transposition can be hazardous. Cystoperitoneal

shunting with a high opening pressure initially is a viable option, although catheters in the posterior fossa should not lie in proximity with the brainstem. Overall, catheters in the posterior fossa are best avoided because they end up penetrating into the brainstem, with consequent neurological defects.

39.2╇ Operative Detail and Preparation 39.2.1╇ Preoperative Planning and Special Equipment Cinalli and colleagues state that neuronavigation is an excellent tool and is becoming a necessity. A second option would be a detailed study of the patient’s magnetic resonance imaging (MRI) and planning according to the findings. Special sequences that reveal thin walls or septations (e.g., CISS, FIESTA) are of paramount importance.2 Laser-assisted neuroendoscopy has proven safe so far and decreases the procedure time. The laser has the advantage over monopolar coagulation that it does not shrink the cyst wall when performing the fenestration, thus ensuring a bigger diameter of fenestration. Additional use of balloon dilatation and division of arachnoid strands with endoscopic scissors is often required (Fig. 39.1). The goal is a wide communication of the cyst with the basal cisterns (cystocisternostomy [CC]) or the ventricular system (ventriculocystostomy [VC]) with effective management of hydrocephalus (ventriculocystocisternostomy [VCC]) if present.

39.2.2╇ Expert Suggestions/Comments • Detailed informed consent of the parents is needed. In cases of developmental delay or epilepsy, the outcome expectations should be clear and understood. • In cases of posterior fossa cyst and hydrocephalus, Karabatsou and associates suggest that an endoscopic third ventriculostomy (ETV) should be performed first and after that the cyst fenestration.3 • In suprasellar cysts causing obstructive hydrocephalus, a septostomy should be considered after the appropriate fenestrations. The patency of the aqueduct is also examined before the withdrawal of the endoscope. Often, an ETV is necessary.

39 â•… Congenital Intracranial Cysts a

b

d

c

e

Fig. 39.1â•… Midsagittal image T2W-FIESTA sequence of a 12-month-old girl who presented with increasing head circumference, widened cranial sutures, tense fontanelle, and recent episodes of vomiting. (a) There is a large suprasellar arachnoid cyst filling the region of the third ventricle and hydrocephalus. (b) Intraoperative image obtained through the endoscope at the beginning of the operation. The endoscope is in the right lateral ventricle looking at the region of the foramen of Monro. The superolateral wall of the arachnoid cyst is seen through the foramen of Monro. (c) Intraoperative image obtained through the endoscope immediately after completion of the fenestration on the superolateral wall of the cyst. The fenestration was performed with the monopolar diathermy and enlarged with balloon dilatation and division with scissors. (d) Image obtained through the endoscope just after performing fenestration on the inferior wall of the cyst and before balloon dilatation. The floor of the third ventricle has thinned out and become transparent, and the operator can see the basilar artery and the structures of the prepontine cistern. At completion of the fenestration, in effect, a third ventriculostomy was performed as well. (e) Midsagittal image T2W-FIESTA sequence obtained a few days after endoscopic fenestration of the suprasellar arachnoid cyst and third ventriculostomy. There are flow voids in the areas of the fenestrations at the superior and inferior walls of the cysts that are produced by the flow of cerebrospinal fluid (CSF) through the fenestrations.

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328 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation

39.2.3╇ Key Steps of the Procedure/ Operative Nuances • The endoscopic trajectories are chosen with neuronavigation, aiming for the creation of as many areas of communication as possible. If there is a previous ventricular peritoneal (VP) or cyst-peritoneal (CP) shunt, removal during the procedure should be considered. • The burr hole is placed in a location that, if needed, it can be easily converted to a minicraniotomy. • The burr hole is made at the highest possible point so that minimal cerebrospinal fluid (CSF) is lost. For the same reason, a small incision is performed on the cortical surface and the endoscopic sheath is quickly and carefully introduced. If much CSF is lost, the danger for subdural collections increases, the cyst walls interfere with the endoscopic view, and the accuracy of the neuronavigation further decreases. • The fenestration on the basal cisterns should be done with great care. The optimal instruments for a more “atraumatic” opening are, in order of smoothness: the balloon catheter, a blunt probe, the scissors, the laser (if applicable), and lastly the monopolar diathermy. Diathermy use should be kept at a minimum close to the hypothalamus. • Tailored irrigation (Ringer’s solution at body temperature) is necessary for the removal of blood products and air. The outlet channel of the endoscope is connected to a collection bag, to avoid spillage of irrigation fluid in the operative field and risk of electrocution from accidentally deficient application of the grounding pad.

39.2.4╇ Hazards/Risks/Avoidance of Pitfalls • Careful coagulation of the cyst wall before the initial opening minimizes bleeding during the procedure. • In order to avoid subdural collections postoperatively, it’s important to prevent separation of the cyst wall from the overlying dura. If that occurs, care should be taken to “restore” the attachment using fine sutures or controlled coagulation. • In CCs for Sylvian cysts, all the membranes should be opened down to the prepontine cistern. The basilar artery must be clearly

visualized. Pulsations of the walls verify CSF flow. The opening must be of sufficient size (preferably, at least 1 cm). The floating remnants over the fenestration are removed (cut or coagulated) to prevent reclosure. Insertion of a catheter with multiple holes through the opening can further prevent the obstruction, although it is not recommended (catheter may migrate with time). If the cyst wall is thick, the cisternal landmarks are not visible, and the surgeon doesn’t feel confident, then the fenestration should be abandoned. • CSF leakage can be avoided with careful closure. In children, the dural opening is sutured. More important is the tight closure of the galea over the burr hole. If persistent leakage or subgaleal collections occur, the options are redo endoscopy or shunting with wound resuturing. • Children with bilateral Sylvian cysts are likely to suffer from glutaric aciduria type 1 (GAT1). • Insertion of a VP shunt for hydrocephalus due to an arachnoid cyst can increase the cyst size if the cyst is left untreated.

39.2.5╇ Salvage and Rescue • Most bleeding can be controlled with a combination of irrigation, pressure (with the balloon), and coagulation. In case of major bleeding, the endoscopic procedure is rapidly converted to an open one.

39.3╇ Outcomes and Postoperative Course 39.3.1╇ Postoperative Considerations • MRI scans with CSF flow studies are performed soon after the endoscopic or microsurgical procedures. Reduction of cyst size is not accomplished immediately; however, a scan performed within 6 weeks of surgery should show some difference in cyst size. The reduction is more evident in children than in adults. Single-photon emission computed tomography (SPECT) studies have shown that perfusion defects disappear even though the size of the cysts is not completely reduced, according to Sgouros and Chapman.4 • Children < 2 years old are more likely to end up with a shunt.

39 â•… Congenital Intracranial Cysts • Gangemi et al state that the success rate of neuroendoscopy for suprasellar, quadrigeminal, and posterior fossa cysts is more than 83%. For Sylvian and interhemispheric cysts, the success rate is less than 75%.5

39.3.2╇Complications According to El-Ghandour, immediate complications are hemorrhage and nerve damage. Most oculomotor nerve palsies are transient, in the absence of obvious surgical nerve damage. Later complications are CSF leaks with meningitis (5 to 7%) and subdural hematomas/hygromas (9 to 15%). The incidence of complications was found to be higher in VCCs than in VCs.6

References ╇1. Al-Holou

WN, Yew AY, Boomsaad ZE, Garton HJL, Muraszko KM, Maher CO. Prevalence and natural history of arachnoid cysts in children. J Neurosurg Pediatr 2010;5(6):578–585 ╇2. Cinalli G, Peretta P, Spennato P, et al. Neuroendoscopic management of interhemispheric cysts in children. J Neurosurg 2006;105(3 Suppl):194–202 ╇3. Karabatsou K, Hayhurst C, Buxton N, O’Brien DF, Mallucci CL. Endoscopic management of arachnoid cysts: an advancing technique. J Neurosurg 2007;106(6 Suppl):455–462 ╇4. Sgouros S, Chapman S. Congenital middle fossa arachnoid cysts may cause global brain ischaemia: a study with 99Tc-hexamethylpropyleneamineoxime single photon emission computerised tomography scans. Pediatr Neurosurg 2001;35(4):188–194 ╇5. Gangemi M, Seneca V, Colella G, Cioffi V, Imperato A, Maiuri F. Endoscopy versus microsurgical cyst excision and shunting for treating intracranial arachnoid cysts. J Neurosurg Pediatr 2011;8(2):158–164 ╇6. El-Ghandour NMF. Endoscopic treatment of middle cranial fossa arachnoid cysts in children. J Neurosurg Pediatr 2012;9(3):231–238

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40

The Dandy-Walker Malformation Conor Mallucci and Christopher Parks

40.1╇ Introduction and Background There is much discussion in the literature about correct diagnosis of Dandy-Walker malformation, and ever since it was first described there has been debate about the criteria required to distinguish it from other cystic posterior fossa conditions. The protracted development of the cerebellum exposes it to malformation at many stages of its embryology that can be influenced by teratogenic substances and genetic conditions. This leads to the variety in conditions affecting this part of the central nervous system. Terminology like Dandy-Walker variant, Dandy-Walker continuum, and Dandy-Walker complex has been introduced in order to distinguish “true” Dandy-Walker malformation from other, similar conditions. These classifications, the grading systems within them, and the slight variance among them often seem to further confuse the diagnostic process. Making the correct diagnosis is important in estimating prognosis and in understanding the embryology of the condition in any particular patient. The diagnostic criteria for true Dandy-Walker malformation proposed by Klein et al1 and modified by Spennato et al2 are given in the box Diagnostic Criteria for Dandy-Walker Malformation. The potential outcome is predominantly influenced by any associated central nervous system anomalies and the early treatment of hydrocephalus, which develops in around 80% of patients. Knowledge of the anatomical malformations, such as the degree of vermian hypoplasia, will aid in counseling the families of affected patients.

40.1.1╇ Evolution of Management Strategies Surgical management can do little to influence the outcome of the part of the condition related to primary central nervous system malformation and so is directed at control of the associated hydrocephalus

330

Diagnostic Criteria for Dandy-Walker Malformation These criteria, visible on thin-section midsagittal T2 images of the brain, are sufficient and necessary to diagnose “true Dandy-Walker malformation.” They are taken from a review article by Spennato et al.2 1. Large median posterior fossa cyst widely communicating with the fourth ventricle 2. Absence of the lower portion of the vermis at different degrees (lower three quarters, lower half, lower quarter) 3. Hypoplasia, anterior rotation, and upward displacement of the remnant of the vermis 4. Absence or flattening of the angle of the fastigium 5. Large, bossing posterior fossa with elevation of the torcular 6. Anterolateral displacement of normal or hypoplastic cerebellar hemispheres and of the posterior fossa cyst. In order to simplify the decision-making process, the authors propose stratification based on treatment strategy. This groups all of the conditions together and divides them based on the need to treat hydrocephalus, a posterior fossa cyst, or both. True Dandy-Walker malformation has free communication with the supratentorial ventricular system via a patent aqueduct, but this is not always the case in related conditions. Early management of posterior fossa cystic dilation involved craniotomy and cyst-wall excision. This was performed in the premicrosurgical era and was associated with a high failure rate and significant mortality. It is now reserved for only a very limited number of cases resistant to other procedures. With current techniques, one would not expect to find the reported mortality rates associated with this early surgery.

40 â•… The Dandy-Walker Malformation With the improvement in shunt technology, it became the mainstay of treatment. True DandyWalker has free communication between the posterior fossa cyst and the supratentorial ventricles, and so should be able to be managed with a shunt from the lateral ventricle. Unfortunately, due to the significant variability in related conditions, this is not always the case, and herniation through the tentorium is a risk. For this reason, many opted for a cystoperitoneal shunt in the first instance. The improvement in magnetic resonance imaging (MRI) scanning and its increased availability mean that we are no longer left guessing about the anatomy, and thus patients should be appropriately investigated with high-resolution imaging prior to any surgical intervention. This should remove a concern about upward herniation from the decision-making process. More recently, there has been a significant shift to the use of endoscopic cerebrospinal fluid (CSF) diversion in order to avoid shunting. The authors encourage this, but also frequently utilize endoscopy for placement of stents in this condition in order to avoid needing more than one shunt. The technique and considerations with endoscopic placement of stents are discussed later in the chapter.

40.1.2╇ Current Management Strategies The decision-making process involved in the management of hydrocephalus with a cystic dilation of the fourth ventricle is outlined in a flow diagram in Fig. 40.1. This encompasses Dandy-Walker and all of the related conditions. The premise is to manage the hydrocephalus and posterior fossa cyst with endoscopy only, if possible, and, if not possible, to avoid multiple shunts by communicating the cyst with the ventricular system. This approach has similar advantages to the use of endoscopic third ventriculostomy (ETV) over shunts, which include reduction in infection rate due to the avoidance of foreign bodies and a more physiological management of CSF. The use of complex endoscopy should, however, only be undertaken with significant experience. It is, of course, contraindicated if the anatomy of the third ventricle is not favorable, or if communicating the cyst with the supratentorial ventricular system is impossible, usually due to the vascular anatomy in the pineal region. As with all shunt procedures, the peritoneal status needs to be satisfactory and the patient should be clear of infection.

Fig. 40.1â•… Treatment strategy for hydrocephalus with cystic dilation of fourth ventricle. CPS, cystoperitoneal shunt; ETV, endoscopic third ventriculostomy; VPS, ventriculoperitoneal shunt.

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332 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation

40.2╇ Operative Detail and Preparation 40.2.1╇ Preoperative Planning and Special Equipment During the planning phase, patients need a highresolution MRI of the brain in order to establish the patency of the aqueduct allowing communication between the fourth ventricular cystic dilation and the supratentorial ventricular system. In the authors’ institution, CISS (constructive interference in a steady state) and CSF flow imaging sequences are used; however, if these are not available, ventriculography would be satisfactory. It is also important to evaluate the third ventricular anatomy with regard to suitability for endoscopic third ventriculostomy. Patients with a thick or steeply angled third ventricular floor may not be suitable, depending on the equipment available and the experience of the surgeon. Near effacement of the prepontine cistern or the presence of a high ectatic basilar termination similarly may preclude ETV. It is essential to include a fine-cut volume T1 sequence in the MRI protocol for use with a neuronavigation system. The system used by the authors is a StealthStation with AxiEM (Medtronic) that enables accurate navigation of the neuroendoscope in real time without the requirement for rigid fixation of the patient’s skull. This is especially beneficial in patients under age 1 year.3 Surgical trajectory planning can be performed on the image guidance software preoperatively to locate the entry point in the best trajectory to avoid major vessels and have a straight path to the cyst. If an ETV is to be performed as well as a stent, evaluation should be made as to whether one entry point is feasible for both procedures or if a second burr hole would be safer. Patients should be prepared for surgery in the standard way. In the authors’ unit, antimicrobial wash (Octenisan, Schülke & Mayr) is used on the preoperative day and the morning of surgery. Crossmatch of blood is not routinely requested. Prior to induction of anesthesia, it is crucial to check that the endoscope camera is functioning adequately and that the relevant instruments are immediately available and sterile. The authors’ preference is to use a 3-mm rigid endoscope (B. Braun Melsungen AG) with a light source, a high-definition camera, and Ringer lactate solution for irrigation. Neuronavigation is used with a stylet that fits down the endoscope working channel and that can even be used as an instrument for perforation of membranes. Due to the thickness of the cyst membrane, fenestration can be challenging. For this reason it is important to have a variety of endoscopic instruments available prior to commencing the proce-

dure. The authors suggest having a bilobed balloon catheter4 (Neuroballoon, Integra Life Sciences Corp.), some Decq forceps (Karl Storz GmbH & Co., Tuttlingen, Germany), and either a monopolar microendoscopic electrode instrument (MEII, Codman, Johnson and Johnson) or a laser as a minimum; however, the availability of endoscopic forceps and scissors is recommended, too. Planning and preparation are of paramount importance because once the endoscopy is started, the surgeon should be able to focus on the procedure and not need to be instructing supporting staff on where to locate the instruments or how to adjust the navigation system, for example. The trajectories for ETV and for stent placement, if required, should be planned and the length of the catheter required should be measured. The catheter can then have extra holes cut along its length allowing communication between the cyst and the ventricular system. If an ETV is required as well as a stent, the ventriculostomy should be performed first in order that the stent is not disturbed following placement and in the event that any bleeding caused during stent placement does not make ETV more difficult due to poor visualization. ETV is performed in the standard way.

40.2.2╇ Using Stents with Endoscope If a stent is required in the fourth ventricular cyst, there are two steps: first, endoscopic fenestration and second, placement of the stent under endoscopic vision. It is suggested that a “figure of eight” burr hole (i.e., two burr holes touching) be performed with a match-head drill. One burr hole is for the endoscope and the other for the stent. Using image guidance, ventricular cannulation is performed in the correct trajectory. There is no place for arrogance in this maneuver, such as judging that image guidance is superfluous for an “experienced” surgeon. Performing this part of the process optimally is often what decides the outcome of the procedure. If the correct trajectory has been selected, the surgeon should find it easy to navigate through the ventricular system to the site selected for fenestration. When the appropriate membrane is found, a suitable area with no visible vessels should be selected. There is highly likely to be a thick, double membrane. This second membrane should be expected and, unless there is a clear view into a capacious cyst following puncture of the first membrane encountered, it should be assumed that there will be a second membrane that should be actively sought out and fenestrated. Once a satisfactory fenestration into the cyst has been performed and a clear view into the cyst is possible, the stent should be placed under endoscopic vision. The catheter, with precut extra holes, is

40 â•… The Dandy-Walker Malformation placed through the burr hole next to the endoscope using the image guidance stylet in place of the supplied stylet. The catheter is advanced to the fenestration and inserted using image guidance to confirm placement. It is vital in infants to pass the catheter a significant distance into the cyst in order to allow for calvarial growth that can act to withdraw the stent. The stent is then attached and secured to a burr hole reservoir that prevents movement of the stent and can be used to connect a shunt if required.

a

40.2.3╇ Fenestration Tips Generally, an attempt is made to fenestrate using a blunt-tipped instrument, such as the balloon or the electromagnetic (EM) guidance stylet. If, however, the membrane is tough or very floppy, then a blunttipped instrument slides off or pushes the membrane without making a hole. In cases like this, it can be useful to use a sharp monopolar electrode (MEII, Codman, Johnson and Johnson) with a retractable tip in order to make a tiny beginning of a fenestration. This is often enough to allow fenestration to be completed safely with a blunt-tipped instrument. It is rare to need to use the monopolar with current or scissors; however, again, rather than making a significant window, a tiny hole that should then be enlarged with the bilobed balloon will suffice. These measures are to avoid damage to vessels that may be unseen on the other side of the membrane.

b

40.2.4╇ Dealing with Bleeding On puncture of the double membrane it is possible to encounter some bleeding. It is important to keep the endoscope pointing at the origin of the bleeding and to irrigate with Ringer lactate solution at body temperature. Often this is enough, but another strategy is to inflate the balloon enough to permit gentle tamponade of the bleeding for a minute, allowing the coagulation mechanisms to work. Damage to a major vein could be catastrophic and thus is avoided by careful planning, cautious technique, and experience.

40.2.5╇ Other Considerations and Salvage Procedures As outlined in the flow diagram of decision making (Fig. 40.1), it is possible that intraoperative factors prevent the intended surgery from being performed or, if ETV has been performed, that the CSF absorptive capacity is reduced such that an alternative procedure is required (Fig. 40.2). This strategy should be in place prior to the commencement of the initial procedure. If ventriculoperitoneal and separate cystoperitoneal shunts are required, they should be

c

Fig. 40.2â•… Patient was born prematurely at 33 weeks gestation with antenatal diagnosis of Dandy-Walker malformation. Endoscopic third ventriculostomy (ETV) was attempted at approximately age 4 weeks with ventricular cystic stent but did not control the hydrocephalus. Shunt to peritoneum was attached to stent 5 days later. (a) T2 sagittal magnetic resonance imaging (MRI) showing large posterior fossa cystic dilation with vermian hypoplasia. (b) T1 axial view of same patient showing the membrane fenestrated endoscopically. (c) Postoperative appearance.

333

334 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation connected through a Y-connector, allowing the use of a single distal shunt system. Postoperatively, patients should be monitored with regular neurological observations, as they would be following any endoscopic procedure. In the days following surgery, baseline measurement of head circumference should be made in young children. Postoperative imaging should be performed within a reasonable time period in order to document catheter position and to assess the ventricular and cystic size. The authors recommend that MRI be performed between 2 weeks and 3 months after the procedure.

40.3╇ Outcomes and Postoperative Course Dandy-Walker malformation and its variants should be an obstructive etiology of hydrocephalus; however, there appears to be a spectrum of etiology in congenital malformations in which some cases also have reduced CSF absorption.5 It has been widely acknowledged that ETV in infants has a lower success rate than in older children.6 There are few case series giving specific success rates in patients with Dandy-Walker malformations, and even those that discuss this topic may not give specific age breakdown or report several pathologies. The authors’ own experience is that approximately 50% of infants with Dandy-Walker malformation can be successfully treated with ETV alone, but the success rate climbs with age. The neurological outcome is predominantly due to the severity of the neurological malformation but can be further influenced by the hydrocephalus management. The early reported high mortality has significantly improved in the modern era. More recently published series report mortality as around 20%, predominantly due to infection, uncontrolled hydrocephalus, and shunt complications.7,8 It is likely that the mortality would be significantly lower in a current and heterogeneous group of patients with posterior fossa cystic abnormalities because the true Dandy-Walker patients tend to be at the more severely affected end of the spectrum, and the authors do not feel that these reported mortality rates reflect their experience.

40.3.1╇Conclusion Surgical management of Dandy-Walker syndrome and related conditions can be very challenging. The procedures are technically difficult and should not be undertaken lightly by inexperienced surgeons. The use of ETV in children under age 1 year is controversial due to a significant failure rate. Perhaps the very young would be most likely to have successful treatment with a shunt or a shunt connected to a stent. Older children and those presenting with blockage of a previously placed shunt should certainly be considered for endoscopic treatment. The verticality of the third ventricular floor in Dandy-Walker patients makes the procedure more difficult than in other obstructive pathologies. For this reason, it is of paramount importance to have a secondary treatment strategy planned before embarking on treatment.

References ╇1. Klein

O, Pierre-Kahn A, Boddaert N, Parisot D, Brunelle F. Dandy-Walker malformation: prenatal diagnosis and prognosis. Childs Nerv Syst 2003;19(7-8):484–489 ╇2. Spennato P, Mirone G, Nastro A, et al. Hydrocephalus in Dandy-Walker malformation. Childs Nerv Syst 2011;27(10):1665–1681 ╇3. Sangra M, Clark S, Hayhurst C, Mallucci C. Electromagnetic-guided neuroendoscopy in the pediatric population. J Neurosurg Pediatr 2009;3(4):325–330 ╇4. Guzman R, Pendharkar AV, Zerah M, Sainte-Rose C. Use of the NeuroBalloon catheter for endoscopic third ventriculostomy. J Neurosurg Pediatr 2013;11(3):302–306 ╇5. Beni-Adani L, Biani N, Ben-Sirah L, Constantini S. The occurrence of obstructive vs absorptive hydrocephalus in newborns and infants: relevance to treatment choices. Childs Nerv Syst 2006;22(12):1543–1563 ╇6. Kulkarni AV, Drake JM, Kestle JRW, Mallucci CL, Sgouros S, Constantini S; Canadian Pediatric Neurosurgery Study Group. Predicting who will benefit from endoscopic third ventriculostomy compared with shunt insertion in childhood hydrocephalus using the ETV Success Score. J Neurosurg Pediatr 2010;6(4):310–315 ╇7. Marinov M, Gabrovsky S, Undjian S. The Dandy-Walker syndrome: diagnostic and surgical considerations. Br J Neurosurg 1991;5(5):475–483 ╇8. Asai A, Hoffman HJ, Hendrick EB, Humphreys RP. DandyWalker syndrome: experience at the Hospital for Sick Children, Toronto. Pediatr Neurosci 1989;15(2):66–73

41

Idiopathic Intracranial Hypertension Sarah J. Gaskill and Arthur E. Marlin

41.1╇ Introduction and Background Idiopathic intracranial hypertension (IIH) is a condition in which there is increased intracranial pressure without an identifiable etiology. Importantly, it is a diagnosis of exclusion. In particular, infections, mass lesions, hydrocephalus and vascular abnormalities must be ruled out by obtaining magnetic resonance imaging (MRI) and magnetic resonance venography (MRV) of the brain. Other considerations for etiology in the pediatric population include endocrine abnormalities, acquired anemias, and some medications― most notably tetracycline and vitamin A—and some chemotherapy agents. The first series of patients with IIH was published by Dandy in 1937. He treated many of these patients with a subtemporal craniectomy with excellent results.1 Although the stereotypical patient with this condition is an obese woman in the third or fourth decade of life, IIH is seen with increasing frequency in the pediatric population, likely in part due to increased obesity in children. As reported by Genizi et al, in a series of 244 children with IIH, the pediatric population falls into two categories―prepubertal (up to age 11 years) and pubertal (ages 12–17 years). Obesity is far more common in the pubertal patients (64%) versus the prepubertal patients (26%) and females are more frequently afflicted in the pubertal patients, 70% of which were female.2 IIH typically presents with headaches and papilledema. Other signs and symptoms of increased intracranial pressure may be present, such as sixth nerve palsy, as well as visual loss and pulsatile tinnitus. In the patient with documented papilledema and no other etiology, a diagnosis of IIH can be made by performing a lumbar puncture (LP) to measure the opening pressure. The pressure must be greater than 28 cm H2O to qualify for a diagnosis of IIH.3 In the pediatric population, the performance of an LP with seda-

tion can cause an artificially high measurement and this must be taken into consideration. The LP can serve as both a diagnostic and a therapeutic measure if a large volume of cerebrospinal fluid (CSF) is drained to alleviate symptoms. Indeed, LPs can be performed serially as a management technique. Once the diagnosis is made, the goal of treatment first and foremost is the preservation of vision. Treatment begins with a medical approach. In those patients who are obese, weight loss is recommended. Additionally, medical therapy with acetazolamide or furosemide can be initiated. In patients with sustained symptoms and papilledema, CSF shunt placement has been the mainstay of treatment even prior to optic nerve sheath decompression. Lumboperitoneal shunts (LPS) have often been used because the ventricles in IIH are typically small. In the pediatric population, LPS have been associated with a high incidence of acquired Chiari malformations4 and it is now more common that ventriculoperitoneal shunts are placed with the aid of neuronavigation protocols. It has been the observation of the authors that shunt placement results in a long series of emergency room evaluations, admissions, and frequent shunt revisions because of recurrent headaches. This has led to the authors’ treatment paradigm, which proceeds from medical intervention, serial LPs, optic nerve sheath decompression, and finally, if headaches persist, to the performance of a subtemporal decompression, which is the subject of this chapter. The advantage of this approach is that the subtemporal window provides a ready assessment of intracranial pressure without the need for any invasive procedures or even diagnostic evaluations. Because IIH patients frequently present with persistent headaches, a simple palpation of the window will clarify that the headache is not related to increased intracranial pressure.

335

336 Section IVâ•… Hydrocephalus and Disorders of Cerebrospinal Fluid Circulation

41.2╇ Operative Detail and Preparation Under general anesthesia, the patient is positioned supine with the head in a horseshoe head holder with a roll under the shoulder to extend the neck. The right temporal region is shaved, prepped, and draped. A frontotemporal curvilinear incision is made extending from the root of the zygomatic arch, behind the hairline and extending up to the frontotemporal junction to expose the temporalis muscle (Fig. 41.1). The temporalis muscle is divided at the fascial attachment to the skull, leaving a cuff for later re-approximation. The muscle is then elevated with the scalp flap and retracted anteriorly to expose the temporal bone. A craniectomy is then performed using a combination of a high-speed drill and rongeurs to create a cranial defect at the base of the temporal fossa extending as far anterior as can be achieved and measuring approximately 5

Fig. 41.1â•… Incision made for subtemporal decompression.

cm in height by 6 cm in length (Fig. 41.2). The dura is opened in a large cruciate fashion and should be widely opened to avoid injury to the temporal lobe. Usually there is an increased subarachnoid space and, upon opening the dura, a significant evacuation of CSF is expected. The entire dural opening is covered with a dural substitute that is not sutured in place but rather placed over the temporal lobe prior to closing the incision. Closure is achieved in separate layers of muscle, galea, and finally skin. Postoperatively there will be some swelling at the site. This typically resolves in 4 to 6 weeks and the defect becomes unnoticeable (Fig. 41.3). Once this operation has been performed, any evaluation for headache or other symptoms related to intracranial pressure can be a simple clinical evaluation of the subtemporal craniectomy site. In the experience of the authors, this has been 100% effective in the management of IIH patients. Patients who have persistent headaches are managed medically. No patient has gone on to require shunt placement after subtemporal craniectomy. One patient, who relocated to another city, underwent repair of the subtemporal craniectomy defect with a cranioplasty. He had recurrence of the symptoms and the cranioplasty had to be removed.

Fig. 41.2â•… Intraoperative view of the bony defect to create a subtemporal window measuring approximately 5 × 6 cm.

41â•… Idiopathic Intracranial Hypertension

Fig. 41.3â•… Patient 1 week after a subtemporal decompression. It is not at all cosmetically apparent.

References ╇1. Dandy WE. Intracranial pressure without brain tumor: di-

agnosis and treatment. Ann Surg 1937;106(4):492–513 J, Lahat E, Zelnik N, Mahajnah M, Ravid S, Shahar E. Childhood-onset idiopathic intracranial hypertension: relation of sex and obesity. Pediatr Neurol 2007;36(4):247–249

╇2. Genizi

╇3. Avery

RA, Licht DJ, Shah SS, et al. CSF opening pressure in children with optic nerve head edema. Neurology 2011;76(19):1658–1661 ╇4. Chumas PD, Armstrong DC, Drake JM, et al. Tonsillar herniation: the rule rather than the exception after lumboperitoneal shunting in the pediatric population. J Neurosurg 1993;78(4):568–573

337

Section V Trauma

Section Editor: George I. Jallo

In this section of the book, the authors focus on care of the child or adolescent with brain or spinal cord injuries. The section starts with the simple management of scalp injuries and skull fractures, as well as closed-head injuries. The management of penetrating injury is controversial, as the pediatric literature is based on accidental injuries in the play environment, rather than gunshot wounds as in the adult population. Following chapters discuss the management of less common vascular injuries and nonaccidental injuries in the infant. These vascular injuries, albeit rare, are potentially life threatening, as they may result in

ischemic injury to the brain. The authors proceed to discuss cranioplasty or craniofacial reconstruction following the intracranial injury. The section concludes with chapters on spinal cord injury and management of brachial plexus injury. The authors also discuss the critical-care management of the child with and without closed-head injury or traumatic brain injury. The indications for intracranial pressure or external ventricular drain are discussed, as well as key steps for the care of the injured child. At the completion of this section, the reader should have a solid foundation for managing traumatic injuries in children.

42

Management of Pediatric Scalp Injuries Arthur Wang, Jordan M. S. Jacobs, and Avinash Mohan

42.1╇Background Our understanding of the human scalp dates back to 3000 bc when the Egyptians first studied the natural history and severity of scalp injuries.1 Later, around 200 bc, ancient tribesmen armed with this knowledge would inflict scalp injuries on their enemies as a form of punishment and slow death.1 It was not until 1917 that Cushing, while serving in the U.S. Army Base Hospital–British Expeditionary Force, offered a series of 250 head/scalp injuries that proved the pitfalls involved in closing complex scalp wounds.2 Since then, there have been many advances, especially in the field of plastic surgery, that have complemented neurosurgical procedures. The advances range from the repair of traumatic scalp injuries to reconstruction of complex scalp defects following cancer resection to cranial vault remodeling to correct craniosynostosis. The goals of repairing scalp injuries in modern times are no different from those that guided Cushing in the 1900s3: debride nonviable tissue, obtain hemostasis, and close the wound. Because the scalp offers a layer of protection to the cranium and adds aesthetic features to an individual, the management of scalp injuries deserves its own chapter. The authors review the anatomy of the scalp and discuss current techniques in both neurosurgery and plastic surgery that have advanced the management of scalp injuries.

42.2╇ Scalp Anatomy and Neurovascular Supply The scalp spans the cranium from the superior orbital rim anteriorly to the superior nuchal line posteriorly and ranges from 3.0 to 8.0 mm thick.3 There are five anatomical layers of the scalp that can be remembered by the mnemonic SCALP (Table€42.1 and Fig. 42.1)3:

S―Skin C―Subcutaneous tissue A―Aponeurosis L―Loose connective tissue P―Pericranium The scalp has a rich vascular supply with numerous anastomoses connecting the main vascular pedicles. This extensive vascular network allows the scalp to be mobilized and closed using local tissue in many cases; however, it also can result in substantial and potentially life-threatening hemorrhage if scalp injuries are not controlled quickly. A detailed understanding of this vascular system is necessary for any successful flap design and rotation or primary repair of scalp lacerations. The arterial supply of the scalp originates predominantly from the external carotid artery and to a lesser degree from branches of the internal carotid artery―ophthalmic artery branch (Fig. 42.2). The scalp is supplied3:

Table 42.1â•… Layers of the scalp Layer

Clinical relevance

Skin

Donor site for split-thickness skin grafts

Cutaneous tissue

Contains blood vessels, lymphatics, nerves

Aponeurosis (galea aponeurotica)

Tensile strength, connection between frontalis and occipitalis muscles

Loose connective tissue

Avascular plane for flap elevation, offers scalp mobility over the cranium, site where scalp abscesses, avulsions, hematomas occur

Pericranium

Adheres to the cranium, vascular foundation for skin grafts

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342 Section Vâ•… Trauma

Fig. 42.1â•… Anatomical layers of the skin, subcutaneous tissue, aponeurosis, loose connective tissue, and pericranium (SCALP).

Fig. 42.2â•… Vascular supply and innervation of the skin, subcutaneous tissue, aponeurosis, loose connective tissue, and pericranium (SCALP).

42 â•… Management of Pediatric Scalp Injuries Table 42.2â•… Innervation of the scalp Sensory nerve

Scalp region innervated

C2–C4

Posterior scalp

Zygomaticotemporal nerve

Temporal region of scalp

Auriculotemporal nerve

Temporal region of scalp

Greater and lesser occipital nerves

Posterior scalp

1. Anteriorly, by the supraorbital and supratrochlear arteries 2. Laterally, by the superficial temporal artery (STA) with frontal and parietal divisions 3. Posteriorly, by the posterior auricular and occipital arteries Venous drainage of the scalp follows a similar pattern as the arterial supply and further includes transcranial drainage into venous sinuses via emissary veins.3 The scalp has many sensory nerves traversing it. Sensory nerves that supply the scalp are branches of the trigeminal nerve and the dorsal rami of cervical C2–C4 nerves. They include (Table 42.2 and Fig.€42.2)3: 1. Anteriorly, by the supratrochlear and supraorbital nerves 2. Laterally, by the auriculotemporal and zygomaticotemporal nerves 3. Posteriorly, by the greater and lesser occipital nerves The temporal and posterior auricular branches of the facial nerve provide motor innervation of the scalp, controlling forehead movement.

42.3╇ Operative Detail and Preparation 42.3.1╇ General Management of Scalp Injuries The majority of scalp injuries are secondary to blunt trauma sustained in motor vehicle accidents, high altitude falls, and industrial accidents. Scalp injuries may be closed (i.e., contusions, localized hematomas) or open (i.e., abrasions, punctures, lacerations, degloving injuries, avulsions) and can result in loss of tissue. The goals of scalp injury management include4: • Promote wound healing by closing an open wound

• Protect the underlying cranium and neurovascular structures • Reduce risk of infection by débridement of a contaminated wound • Restore cosmesis, including contour and hairlines Regardless of the severity, the management of scalp injuries begins with adhering to the basic guidelines of wound care as described by Goodrich and Blum3: • • • • • •

Examination Hemostasis Débridement Skin closure Antibiotics Tetanus prophylaxis

An initial examination of the wound should be thoroughly conducted to categorize the scalp injury and its characteristics (see box Types of Scalp Injuries).5,6

Types of Scalp Injuries • • • • • • • • • •

Abrasions Contusions (bruises) Laceration Avulsion Hematoma Thermal Electrical burns Chemical burns Radiation environment of injury Wound characteristics (size, depth, margins, foreign body, necrosis) • Vascularity of surrounding tissue • Underlying cranial defect • Character of local tissue Imaging studies are important to identify underlying fractures and intracranial injuries. Often, scalp injuries can be masked by the patient’s hair, scalp swelling/hematoma, or extensive scalp hemorrhage, as seen in lacerations, avulsions, and degloving injuries. Control of scalp bleeding must be done promptly, especially in pediatric patients, who have limited blood volume and who are more susceptible to hypovolemic shock. At the authors’ institution, the total blood volume in a child is roughly estimated by multiplying the child’s weight by 80 mL blood/kg. The authors routinely have the blood bank prepare

343

344 Section Vâ•… Trauma packed red blood cells in case they need to transfuse blood. Hemostasis can be obtained through firm, continuous pressure to the scalp edge and can be facilitated by use of vasoconstricting agents, such as 0.05% lidocaine with epinephrine 1:100,000 and a compression bandage. Once hemostasis is achieved, the wound should be probed in a sterile manner to feel for underlying skull fractures and foreign debris, such as dirt, glass, and rocks. Copious irrigation should be used to clean the wound to prevent subsequent wound infection or potential meningitis. Antibiotics and tetanus prophylaxis should also be given at the time. The topic of tissue closure is addressed in the following text.

42.3.2╇ Repair of Common Scalp Injuries with Intact Tissue Repair of scalp injuries requires a careful assessment of the nature of the injury, the condition of the local/ surrounding tissue, and the underlying cranium (see box Types of Scalp Injuries). Closed scalp injuries, such as contusions and abrasions, do not require surgical intervention if the dermis is intact. Such injuries are usually cared for by emergency department staff and require simple cleaning and local wound care. Similarly, small scalp hematomas with no compromise of the overlying skin perfusion will resolve without the need for surgical evacuation. Simple scalp lacerations are very common and are usually caused by sharp objects. Once again, hemostasis is first obtained, followed by débridement, and then closure. In such injuries, primary closure is often able to be achieved. After débridement to create fresh skin edges, the galeal layer is reapproximated using Vicryl (Ethicon, Somerville, NJ, USA) suture in a buried, interrupted fashion. The skin edges are then brought into anatomical alignment with a simple, continuous layer using a monofila-

ment, such as nylon. The patient is brought back to the office for suture removal at least 2 weeks later to ensure sufficient wound tensile strength has developed. In the authors’ pediatric patients, with thinner skin and less subcutaneous fat, undyed Vicryl sutures are used to avoid visibility. Perhaps even more so in children, careful re-approximation of the skin edges makes for better anatomical alignment and ideal scarring, as well as lower rates of infection.

42.3.3╇ Repair of Scalp Injuries with Loss of Tissue When the scalp injury is severe enough to involve tissue loss, reconstructive techniques with the help of plastic surgeons may be required. Such injuries include scalp avulsions, thermal injury, electrical and chemical burns, and radiation injury. Consider the nature of the injury, the surrounding tissue, and its vascular supply. Management should begin with the simplest approach first and can be summarized below in the reconstructive ladder: • • • •

Primary closure Skin grafts: full thickness or split thickness Local flaps Regional flaps (trapezius, latissimus dorsi, temporalis, pectoralis major) • Free tissue transfer (microvascular free flaps)

42.3.4╇ Skin Grafts If the wound cannot be primarily closed, skin grafts are the next simplest option. The surgeon should ensure that the wound is first debrided, is free of infection, and has a vascularized wound bed to support the skin graft. Skin grafts can be either split thickness (STSG) or full thickness (FTSG). An FTSG is

Table 42.3â•… Comparison of split-thickness and full-thickness grafts Split thickness

Full thickness

Contents

Epidermis + portion of dermis

Epidermis + entire dermis

Donor site

Thigh or lateral buttock

Retroauricular or supraclavicular areas, groin, abdomen

Advantages

Easier to stretch and conform over larger surface areas

Better aesthetic outcomes, remains softer, less contraction

Disadvantages

Undergoes greater amount of contracture―less aesthetically pleasing

Bulky, more difficult to revascularize

Healing ability

Heals secondarily by epithelialization

Heals by primary closure

42 â•… Management of Pediatric Scalp Injuries 4. Preservation of the pericranium as a vascularized bed for the graft

42.3.5╇Flaps When a scalp wound is not amenable to primary closure or skin grafting, healthy, vascularized tissue in the form of a flap is the next rung on the reconstructive ladder. A flap should be used when no vascular bed is available to support a graft (i.e., a scalp defect in which the periosteum has been stripped). The goals of flap design are to provide sufficient tissue for tension-free closure, to preserve the integrity of the transferred tissue with its blood supply, and to allow closure of the donor site. A flap can be defined either by the donor tissue or by its blood supply pattern (Table 42.4).1,3,7

42.3.6╇ Local Flaps

Fig. 42.3â•… Healed split-thickness skin graft.

harvested to include the epidermis and the full thickness of the dermis (including the sebaceous glands and hair follicles), whereas an STSG includes only a portion of the dermis (Table 42.3 and Fig 42.3).1 A few principles govern the selection of graft type: 1. Inverse relationship between the amount of dermis and the degree of subsequent skingraft contracture 2. Inverse relationship between the thickness of the graft and successful adherence and healing (“take”) 3. The donor graft retains properties of the donor site

The basic principle of a local flap is moving tissue with laxity or redundancy from one area to another while preserving its vascular supply. In the scalp, the donor sites are most commonly the lateral temporal and posterior scalp, where there is the greatest amount of excess tissue available without tremendously distorting the anatomy. There are three local flap techniques. In all three, it is important to widely undermine the scalp in the subgaleal layer in order to reduce tension along the suture line. Refer to figures.1,3 • Rotation flap―semicircular flap rotated around a pivot point (Fig. 42.4, Fig. 42.5, and Fig. 42.6) • Transposition flap―square/rectangular flap rotated around a pivot point into adjacent defect. The design of this flap should ensure that the flap is longer than the defect area. A commonly used technique is the Gillies tripod technique.

Table 42.4â•… Types of donor flaps Flap by donor tissue

Flaps by blood-supply pattern

Cutaneous (skin only) Muscle (muscle only) Myocutaneous (muscle and overlying skin) Osteocutaneous (bone and skin) Fasciocutaneous (fascia and skin) Omental

Random Axial pattern (types I–V)7

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346 Section Vâ•… Trauma

Fig. 42.5â•… Intraoperative design of advancement rotation flap. Fig. 42.4â•… Full-thickness scalp defect.

• Advancement flap―The flap is moved directly into the defect without rotation or transposition.

42.3.7╇ Regional (Distant Pedicle) and Free Flaps

Fig. 42.6â•… Postoperative advancement rotation flap.

Transfer of more distant tissue to reconstruct larger, complex scalp defects can be achieved with either pedicle flaps, in which the vascular supply remains intact, or free flaps, in which the vascular pedicle is disconnected and then reconnected using microsurgery. Many different donor sites have been used, and the flaps are designed in conjunction with a plastic surgeon with a detailed understanding of the vascular anatomy and expertise in microsurgical techniques. The most superficial of all flaps is the cutaneous flap, a full-thickness skin and subcutaneous tissue flap with an attached vascular pedicle. Many times the underlying fascia is included in order to increase the reliability of the blood supply (fasciocutaneous flap). A myocutaneous flap includes the full-thickness skin and subcutaneous tissue as well as the underly-

42 â•… Management of Pediatric Scalp Injuries ing fascia and muscle. Muscle flaps that have been used with success in scalp reconstruction include the pectoralis major, latissimus dorsi, and trapezius.3,4,8–10 These flaps provide a large volume of tissue and have consistent, reliable vascular anatomy. A pedicle latissimus flap is tunneled through the axilla with care taken not to injure the brachial plexus and axillary vessels.3,4,6 It can be used to cover temporal, parietal, and occipital scalp defects. The pectoralis flap can be used to cover frontal and temporal defects; however, it is bulky and can leave significant distortion of the donor site, which is an especially important consideration in women. An osteocutaneous flap is indicated when composite tissue is needed to reconstruct both skin and bony defects. Examples include: the fibula flap, the deep circumflex iliac artery (DCIA) flap with iliac crest, the parascapular flap with scapula, and the radial forearm flap.4,6 Omental flaps were once used with great success because of the ease of being harvested, large surface area, and robust vasculature. The necessity of a laparotomy and availability of less invasive flaps make this option less common today.1,4,6

42.3.8╇ Tissue Expansion The idea of tissue expansion stems from the fact that skin is capable of significant stretching (e.g., abdominal skin in pregnancy and obesity). Tissue expansion, first described by Radovan in 1978, involves implanting a tissue expander (Silastic device with a port through which saline can be infused) adjacent to the defect.1 Initial expansion is deferred for 2 to 3 weeks postinjury. In the office setting, sterile saline is then infused into the expander weekly to gradually stretch the overlying skin. Once adequate expansion has taken place, the expander is removed and a local flap is designed to reconstruct the scalp with the redundant tissue. The main advantage of this technique is aesthetically pleasing results since the tone, color, and texture of the adjacent tissue are well matched. It also enables restoration of hairlines and hair-bearing skin. The disadvantages are the risk of infection, the long duration of treatment, and the need for at least two surgeries.1,3,5

42.4╇ Outcomes and Postoperative Course Complications of scalp injuries and reconstruction include infection, tissue loss, injury to the underlying cranium and neurovascular structures, secondary wound contracture, graft or flap failure, and poor aesthetic outcomes. Avoiding these complications begins in the operating room with proper surgical planning between the neurosurgeon and plastic surgeon. Care must be taken to avoid excess tension on any flaps and their pedicles. Postoperatively, monitoring of flap viability is very important. Flap assessment includes color, turgor, and capillary refill. In certain cases, the authors use a handheld Doppler to monitor arterial and venous flow. Any sign of compromised perfusion warrants a return to the operating room.

References ╇1. Reddy

K. Scalp injuries. In: Tandon PN, ed. Ramamurthi & Tandon’s Textbook of Neurosurgery. New Delhi, India: Jaypee Brothers Medical Publishers; 2012: 422–431 ╇2. Cushing HA. A study of a series of wounds involving the brain and its enveloping structures. Br J Surg 1917;5:555–684 ╇3. Goodrich JT, Blum KS. Management of scalp injuries. In: McLone DG, ed. Pediatric Neurosurgery: Surgery of the Developing Nervous System. 4th ed. Philadelphia, PA: W.B. Saunders; 2001: 565–573 ╇4. Hodges A, ed. A-Z of Plastic Surgery. Oxford, England: Oxford University Press; 2008: 250–251 ╇5. Moodambidana K. Scalp and skull injuries. In: Thamburaj VA, ed. Textbook of Contemporary Neurosurgery. New Delhi, India: Jaypee Brothers Medical Publishers; 2012: 569–584 ╇6. Mueller RV. Facial trauma: soft tissue injuries. In: Neligan PC, ed. Plastic Surgery. 3rd ed. London: Elsevier Saunders; 2013: 23–49 ╇7. Rousso DE, Sule S, Stough D, Whitworth JM. Hair replacement techniques. In: Papel ID, ed. Facial Plastic and Reconstructive Surgery. 3rd ed. New York, NY: Thieme Medical Publishers; 2009: 409–421 ╇8. Brenner MJ. Scalp reconstruction. In: Branham G, ed. Thomas Procedures in Facial Plastic Surgery: Facial Soft Tissue Reconstruction. Shelton, CT: People’s Medical Publishing House; 2011: 117–135 ╇9. Linton PC, Leitner DW. Surgery of the Scalp. Operative Neurosurgical Techniques. New York, NY: Grune & Stratton; 1988 10. Mathes SJ, Nahai F. Classification of the vascular anatomy of muscles: experimental and clinical correlation. Plast Reconstr Surg 1981;67(2):177–187

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43

Skull Fractures Elizabeth C. Tyler-Kabara

43.1╇Background 43.1.1╇Indications Many skull fractures do not require surgical management. The initial assessment and follow-up are essential in determining which fractures require surgical intervention. In general, linear skull fractures do not require any intervention. Observation is important to identify rare, growing skull fractures, which are more likely to occur in the very young and are typically associated with more severe injuries that include laceration of the dura.1 Depressed skull fractures are more likely to require surgical intervention. Traditional teaching has been that all depressed skull fractures greater than the thickness of the skull or with a neurological deficit should undergo surgical repair. Neurological deficit is usually secondary to the underlying contusion and rarely improves with surgical intervention. Additionally, even some depressed fractures that are depressed the full thickness do not present a problem with cosmesis. Since many depressed skull fractures can be managed conservatively,2,3 the author has sought a more individualized approach to management of these fractures. If there is evidence of a dural laceration, elevation is strongly recommended, as it is when there is an underlying contusion or neurological deficit (Fig.€43.1 and Fig. 43.2). Comminuted depressed fractures are associated with a higher incidence of dural laceration.4 In the intact child with concerns for long-term cosmesis, surgical elevation is also recommended. In the intact child with no concerns regarding cosmesis, the risk and benefits are reviewed and observation is considered.

348

Fig. 43.1â•… A 15-year-old adolescent male pitcher struck in the head by batted ball. He presented with brief loss of consciousness and left arm weakness.

All open skull fractures with dural laceration require surgical exploration.2 This is discussed with penetrating head injuries in Chapter 45. In the setting of frontal sinus fractures with persistent rhinorrhea or increasing pneumocephalus, craniotomy for repair of the cerebrospinal fluid (CSF) leak is recommended.

43 â•… Skull Fractures

Fig. 43.2â•… Three-dimensional (3D) reconstruction of the fracture seen in Fig. 43.1. Note, the shape matches that of the baseball.

43.1.2╇Goals The goals of surgery include repair of any underlying dural injury and cosmetic repair of the depressed fracture. The surgical incision should be cosmetic. If the skull fracture is behind the hairline, the incision should be designed to maximize cosmesis. If the fracture is on the face, a bicoronal incision or other incision hidden in the hairline may be preferred.

up, delayed surgery for repair of the fracture and the dural defect would be indicated.

43.1.4╇Advantages Surgical elevation at the time of injury may be technically easier than a delayed repair. This is certainly true in the setting of a growing skull fracture.

43.1.3╇ Alternate Procedures

43.1.5╇Contraindications

The alternative to surgical elevation would be observation. Delayed surgery can be performed for cosmetic reasons if a family or child decides later that the cosmetic effects are undesirable. Similarly, if an enlarging leptomeningeal cyst is identified at follow-

In the patient with a severe traumatic brain injury, early repair of depressed skull fracture would be contraindicated unless it was thought to be contributing to increased intracranial pressure. A depressed skull fracture overlying a dural sinus in an asymptomatic patient should also be observed rather than elevated.

349

350 Section Vâ•… Trauma

43.2╇ Operative Detail and Preparation 43.2.1╇ Preoperative Planning and Special Equipment Preoperative planning should include computed tomography (CT) imaging and standard instruments for a craniotomy. The imaging should be reviewed to identify any potential dural sinus injuries. A threedimensional (3D) reconstruction may provide some benefit when contouring an elevated fracture but is not necessary. This author prefers to use titanium

plates in children more than 10 years old and absorbable plates in children less than 10 years old. The appropriate plating system is obtained prior to the start of the procedure. In addition, anticonvulsants may be initiated preoperatively or intraoperatively, if there is a contusion or brain laceration. If there is concern about increased intracranial pressure and it has been determined that it is necessary to elevate the fracture, mannitol up to 1 g/kg can be given intravenously (IV). Anesthesia should also be asked to maintain an end-tidal carbon dioxide (CO2) of 25 to 35 mm Hg. Elevation of the head of the bed may also be helpful.

Fig. 43.3â•… An incision marked to allow access to the full extent of the fracture. The area is prepped and draped using sterile technique.

43 â•… Skull Fractures

Fig. 43.4â•… The incision is opened and the full extent of the fracture is visualized.

43.2.2╇ Expert Suggestions/Comments • Fractures are typically greenstick in nature and can sometimes be reshaped on the back table. • The bone should be rigidly fixed with good approximation to the surrounding bone to maximize bone healing. • In very young children with ping-pong fractures, the fracture can be elevated with an instrument placed under the depression via an adjacent burr hole.

43.2.3╇ Key Steps of the Procedure/ Operative Nuances • The head is placed on a padded horseshoe and the hair is clipped over the fracture site. The incision is planned to fully expose the fracture (Fig. 43.3 and Fig. 43.4). • A burr hole is placed adjacent to the fracture and if necessary a craniotomy is created around the fracture site (Fig. 43.5).

351

352 Section Vâ•… Trauma

Fig. 43.5â•… Burr hole (arrow). A craniotomy has been performed around the fracture site. The bone flap has not yet been elevated.

• The bone fragments are then recontoured and rigidly fixed with plates (Fig. 43.6 and Fig.€43.7).

43.2.4╇ Hazards/Risks/Avoidance of Pitfalls • Closely review preoperative imaging to assess possible involvement of dural sinuses. • Any dural lacerations should be closed primarily.

• Dural tack-ups can be placed if the dura has been stripped from the surrounding bone to reduce the risk of a postoperative epidural hematoma.

43.2.5╇ Salvage and Rescue Severe complications during elevation of a depressed skull fracture are infrequent but usually occur when encountering an unexpected injury to a dural sinus. This may be at the site of the depressed fragments

43 â•… Skull Fractures

Fig. 43.6â•… The greenstick fracture is reduced on the back table.

but may be at the edge of the fracture. Sinus bleeding can typically be tamponaded with a cottonoid patty or Gelfoam. Injecting particulate hemostatic agents into a sinus is not suggested because it can have unintended sequelae if the sinus becomes occluded or the material embolizes. The best strategy is to fully expose the sinus tear and to repair it by sewing muscle or fascia over the tear. Fascia can typically be taken from the exposed galea or pericranium. Muscle can be taken from the temporalis or occipital musculature. If no fascia or muscle is available, a piece of Gelfoam can be used.

43.3╇ Outcomes and Postoperative Course 43.3.1╇ Postoperative Considerations • Patient should be observed for posttraumatic seizures and, if seizures are identified, antiepileptics should be considered. • Patients should be prohibited from contact sports postoperatively, even in the absence of postconcussive symptoms.

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354 Section Vâ•… Trauma

Fig. 43.7â•… The recontoured bone flap is rigidly fixed with good bony approximation.

43.3.2╇Complications Complications include resorption of the elevated bone fragments, painful hardware, and settling of the bone flap leaving a cosmetic defect. Resorption is uncommon but can be minimized by rigidly fixing the bone flap against healthy bone to improve bone healing. This can also help reduce settling of the flap. Painful hardware can often be removed, thus alleviating the discomfort.

References ╇1. Muhonen

MG, Piper JG, Menezes AH. Pathogenesis and treatment of growing skull fractures. Surg Neurol 1995;43(4):367–372, discussion 372–373 ╇2. Bullock MR, Chesnut R, Ghajar J, et al; Surgical Management of Traumatic Brain Injury Author Group. Surgical management of depressed cranial fractures. Neurosurgery 2006;58(3 Suppl):S56–S60, discussion Si–iv ╇3. Steinbok P, Flodmark O, Martens D, Germann ET. Management of simple depressed skull fractures in children. J Neurosurg 1987;66(4):506–510 ╇4. Erşahin Y, Mutluer S, Mirzai H, Palali I. Pediatric depressed skull fractures: analysis of 530 cases. Childs Nerv Syst 1996;12(6):323–331

44

Traumatic Brain Injury Brian T. Farrell and Nathan R. Selden

44.1╇Background This chapter focuses on the neurosurgeon’s role in optimal management of pediatric traumatic brain injury (TBI), highlighting decision making in both the operating room and the intensive care unit (ICU). The chapter is divided into two sections focusing on the critical care and operative management of pediatric TBI. The critical care section also includes techniques for intracranial pressure (ICP) monitoring and external ventricular drain (EVD) placement, whereas the operative section focuses on unilateral hemispheric and bilateral frontotemporal decompressive craniectomy.

44.1.1╇Indications In children with severe TBI, the first steps in management should be establishment of optimal oxygenation, ventilation, and circulation (Fig. 44.1). In numerous studies, hypoxia and hypotension are harbingers of poor neurological outcome.2 Braindirected critical care after TBI depends on careful neurological monitoring or, in the case of severe TBI, measurement of ICP with or without additional physiological parameters, such as oxygenation, cerebral blood flow, and compliance.3 ICP may be determined using a parenchymal monitor or an EVD. As reviewed in the TBI guidelines, indications for ICP monitoring or EVD placement in children may include: 1. Glasgow Coma Scale (GCS) score ≤ 8 2. Computed tomography (CT) findings suggesting a risk for neurological deterioration 3. Need for ongoing sedation or prolonged anesthetic

In essence, any child who has suffered a major TBI and who does not have a reliable neurological examination is a potential candidate for ICP monitoring. In the judgment of the treating neurosurgeon, for example, a child with a moderate TBI scheduled for a major orthopedic or abdominal procedure under general anesthesia may benefit from ICP monitoring. Ventricular drains allow both monitoring and cerebrospinal fluid (CSF) drainage as therapy for intracranial hypertension, but they result in slightly more procedurally related morbidity than parenchymal ICP monitors. The cardinal principle of effective critical care for severe TBI in children is maintenance of physiological homeostasis. Historically, efforts to substantially alter homeostatic parameters, such as the induction of profound hyperventilation in an effort to lower ICP, led to worsened outcomes.4 Current protocols, as reflected in the pediatric TBI guidelines, instead argue for maintenance of physiological homeostasis, including a normal range for blood oxygenation and glucose, normal to slight hypocapnia, and normothermia. Provision of enteral nutrition appropriate to the overall state of patients and their injuries, if possible, should be instituted early. Patients should be positioned to protect them from exacerbation of occult spinal injuries and to optimize cerebral venous outflow (neck neutral, reverse Trendelenburg position). Where required to control ICP, prevent injury, or facilitate ventilator management, patients may be sedated and pharmacologically paralyzed. The goal of ICP management, and specifically the avoidance of intracranial hypertension, is twofold: first, protection of cerebral perfusion and therefore avoidance of secondary ischemic injury, and second, the prevention of brain herniation and catastrophic sudden deterioration or death. The upper limits of safe ICP in infants and children vary at different ages

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356 Section Vâ•… Trauma

Fig. 44.1â•… Treatment algorithm.1 Modified from Guidelines for the Acute Medical Management of Severe Traumatic Brain Injury in Infants, Children, and Adolescents, 2003, first edition. CPP, cerebral perfusion pressure; CSF, cerebral spinal fluid; GCS, Glasgow Coma Score; ICP, intracranial pressure; MAP, mean-arterial pressure.

and are less well established than in adults. Although data to support specific thresholds are preliminary, a lower ICP treatment threshold in infants may improve outcome. Prolonged ICP elevations are clearly associated with poor neurological outcome and death.5 Many practitioners have adopted cerebral perfusion pressure (CPP), rather than ICP, as the primary target of TBI critical care therapies. Like ICP, CPP, which is equal to the mean arterial blood pressure

(MAP) minus the ICP, has variable lower safe limits depending on age. Importantly, CPP management is actually composed of three entirely different strategies: (1) avoidance of hypotension (for which there is excellent evidence); (2) permissive systemic hypertension in the face of raised ICP; and (3) induced systemic hypertension in response to high ICP and low CPP. The first two of these are homeostatic mechanisms of therapy. By contrast, induced systemic

44 â•… Traumatic Brain Injury hypertension is a nonhomeostatic intervention for which there is limited evidence. Furthermore, a subset of children with severe TBI, in whom cerebral vascular dysregulation causes hyperemia,6 may respond poorly to induced systemic hypertension. In children with truly refractory intracranial hypertension despite optimal medical therapy, surgical intervention may be an effective salvage method, although this remains unproven.7 Decompressive surgery is an option for children with closed head injury under the following conditions: 1. Refractory intracranial hypertension (as defined by the guidelines) despite maximal nonsurgical therapy, including hyperosmolar therapy, hyperventilation, deep sedation, CSF diversion, and chemical paralysis 2. Early signs of neurological deterioration and/ or brain herniation 3. Cerebral edema with significant mass effect, including at the time of surgery for evacuation of a hematoma.

44.1.2╇Goals When treating severe TBI, the neurosurgeon should focus on the prevention of ongoing or secondary brain injury. The measurement and optimal management of ICP, oxygenation, and circulation are cardinal features of this approach. Early and aggressive application of protocol-driven care pathways should streamline decision making and improve outcomes. An example of such a protocol is shown in Fig. 44.1.

44.1.3╇Advantages Despite preventive measures, TBI remains a leading cause of death and disability in the pediatric population. In 2012, updated evidence-based guidelines for pediatric closed head injury were released, further advancing the concept that rigorous protocol-based multidisciplinary treatment algorithms that incorporate ICU care, invasive monitoring, and surgical intervention improve outcomes.8,9

44.1.4╇Contraindications Hemodynamic or respiratory instability and coagulopathy should be corrected prior to undertaking invasive intracranial procedures to monitor or treat severe TBI.

44.2╇ Operative Detail and Preparation 44.2.1╇ Preoperative Planning and Special Equipment Nonsurgical Management of TBI (ICP Monitor and External Ventricular Drain Placement) ICP monitoring requires several pieces of special equipment, including a digital monitoring station and a sterile prepackaged kit that contains the pressure-transducing catheter, protective plastic sheath, matching twist-drill bit, and a threaded bolt for securing the monitor in the skull. For EVD placement, a sterile EVD catheter and collection system are required, as well as suture for securing the drain to the scalp. For both the ICP monitor and EVD procedures, a sterile kit containing a twist drill, draping materials, scalpel, and sharp spinal needle is also required. ICP monitor and EVD placement can be performed at the bedside in the ICU under sedation with local anesthesia; however, they can also be performed in the operating room based on surgeon and/or institutional preference. In all cases, formal and complete sterile preparation, draping, gown, and gloving are necessary. Recently, antibiotic-impregnated EVD catheters have been used in an attempt to reduce the risk of EVD infection (which is particularly elevated in patients with frontal skull base fractures).

Expert Suggestions/Comments In the event of unilateral or asymmetric injury, the authors favor placement of the monitor or drain on the side that is more severely injured, both to reflect what is likely the area of highest ICP and to avoid the potential for complication-related injury to the relatively spared hemisphere. In cases of global injury, the nondominant side is usually chosen. For EVD placement in children with slit or shifted ventricles, frameless stereotaxy may be utilized. EM-emitting navigation systems are available for children too young for rigid cranial fixation.

Key Steps of the Procedure/Operative Nuances Kocher’s point (approximately 1 cm anterior to the coronal suture in the midpupillary line and 3 cm from midline) is a useful entry point for both ICP monitor

357

358 Section Vâ•… Trauma and EVD placement. For ICP monitor placement, after sterile prep and infiltration of local anesthetic, a stab incision is made with a no. 11 or no. 15 blade. The twist-drill bit sized to the bolt device is used to create a tiny trephine. The bit will catch at the inner table, at which point forward rotation should continue while withdrawing the entire drill, to avoid plunging and to remove bone bits from the hole. The threaded bolt is then screwed into the twist-drill hole and the plastic end cap is loosened. The dura should be opened sharply by passing an 18-g spinal needle through the shaft of the bolt. This maneuver is made safer by first bending the needle shaft, prior to placing the bolt, at a location that allows only 3 to 5 mm of protrusion past the bolt tip. The pressure-transducing catheter is then connected to the monitoring station and zeroed. The catheter tip is threaded through the bolt, such that the red indicator line on the plastic sheath aligns with a pair of hash marks on the catheter at the appropriate depth. The plastic screw cap is then tightened to the bolt to secure the catheter in place and the protective sheath is secured to the plastic cap on the end of the bolt. Once the catheter is in place, the monitoring station should display the ICP and waveform. The left side of Fig. 44.2 diagrams the optimal placement of an ICP monitor.

In order to place an EVD, a larger sterile field is prepared to accommodate tunneling of the EVD catheter at least 5 cm from the burr hole to the skin exit site, and a small linear incision in the sagittal plane is created at Kocher’s point. Alternatively, if placement of a shunt is anticipated, it is best to use a 90-degree hockey stick incision open to the posterior and lateral directions, so the shunt hardware implanted at a subsequent procedure will not cross under any incision line. To avoid extra-axial hematoma formation, hemostasis should be obtained with bone wax after creating a burr hole and again after opening the dura, using bipolar cautery. The EVD catheter should be aimed in the sagittal plane toward the ipsilateral tragus and in the coronal plane toward the medial canthus, which should correspond to an angle orthogonal to the skull in all directions. The catheter is passed gently through the brain until an ependymal “pop” indicates that the ventricle has been entered, generally at a depth of about 4 cm from the outer table of the skull in older children and adolescents (although a specific depth in each patient may be measured from imaging studies). Once CSF return is seen, the catheter should be advanced forward off the end of the rigid stylet to an appropriate depth (about 6 cm in larger children and adolescents). The catheter should then be carefully tunneled under hair-bearing skin in a direction that avoids the future potential tract of a distal shunt, in case this becomes necessary, and which does not transgress any natural or iatrogenic fontanelle. The catheter should be carefully secured to the scalp, for example, using a modified roman sandal technique.10 The scalp is closed in layers and the catheter is connected to a sterile enclosed CSF collection system and a transducer is used to record ICP. The right side of Fig. 44.2 demonstrates ideal placement and securing of the EVD. A video for a demonstration of the EVD placement procedure is provided as an online supplement to this chapter.

Hazards/Risks/Avoidance of Pitfalls Especially in younger children, careful drilling technique (low pressure and high rotational velocity) should be employed to avoid plunging through the inner table of the skull and injuring the underlying brain. The dura and then the pia should be opened sharply to avoid creating a potentially life-threatening hematoma by dissecting the dura from the inner table of the skull or by stretching and tearing subdural bridging veins.

Fig. 44.2â•… Anatomical landmarks for intracranial pressure (ICP) monitor (left) and external ventricular drain (EVD) (right) placement, also demonstrating a method for tunneling and securing EVD catheters. (By Andy Rekito. Used with permission from Oregon Health & Science University.)

Salvage and Rescue If an ICP monitor cannot be zeroed, or gives unreliable ICP readings, a new fiberoptic catheter should be placed using sterile technique. Alternatively, a

44 â•… Traumatic Brain Injury ventriculostomy can be placed to allow ICP measurement as well as CSF diversion to better control ICP. For EVD placement, if the ventricle cannot be immediately cannulated, alternate strategies should be employed, such as the assistance of an additional surgeon, the use of frameless stereotaxy or transburr hole ultrasound, or by obtaining a brain CT scan with the catheter left in place to determine the catheter position relative to the ventricle. Currently, many surgeons use ultrasound or stereotaxy prospectively in all cases of small and/or shifted ventricles.

After local infiltration, a large myocutaneous flap is elevated, using Raney clips to control bleeding. Fig.€44.3 illustrates the burr hole placement, craniectomy, and dural opening used during a typical decompression. Multiple burr holes should be evenly spaced around the planned craniotomy, with attention to placement at the anatomical keyhole, the root of the zygoma, and the parietal boss. Convexity burr holes should be placed ≥ 1.5 cm lateral to the midline to

Surgical Management of Closed Head Injury (Decompressive Craniectomy) Decompressive craniectomy is performed under emergency circumstances, in response to early signs of neurological deterioration or herniation, and/or refractory or worsening intracranial hypertension despite maximal medical management, in the setting of a salvageable neurological examination.5 As such, pediatric neurosurgical hospitals should maintain the proper equipment and staffing to allow immediate surgery. Transient preoperative hyperventilation, bolus mannitol, and hypertonic saline may be initiated to treat dangerously elevated ICP until decompression is accomplished.

Expert Suggestions/Comments The appropriate decompressive procedure should be chosen in each case based on careful review of the clinical course and imaging. Patients with unilateral injury or hematoma generally require a panhemispheric frontotemporoparietal decompressive craniectomy, whereas patients with evidence of bilateral injury may benefit more from either bilateral hemispheric or bifrontal decompression. Failure to open the dura or to create a wide enough osseous and dural decompression may result in brain incarceration at the bone edges, stroke, and worsened outcome.

Key Steps of the Procedure/Operative Nuances Frontotemporoparietal Decompressive Craniectomy The patient is positioned supine on a horseshoe or gel headrest with the head horizontal, parallel to the floor, and a large gel roll under the ipsilateral shoulder. The bed is placed in gentle reverse Trendelenburg position to facilitate venous return and lower ICP. Generally, a cervical collar should remain in place for positioning unless the spine has been cleared. A large reverse question-mark incision provides access to most of the hemicranium.

Fig. 44.3â•… Anatomical landmarks for decompressive hemicraniectomy, illustrating burr hole placement, craniectomy, and dural opening. (By Andy Rekito. Used with permission from Oregon Health & Science University.)

359

360 Section Vâ•… Trauma avoid injury to the superior sagittal sinus. The bone flap can then be stored either in a sterile tissue bank or in the abdominal subcutaneous space. The inferior aspects of the squamous temporal bone and lateral sphenoid wing may be removed with rongeurs until the craniectomy is nearly flush with the floor of the middle fossa, in order to ensure adequate temporal lobe decompression and prevent uncal herniation. Any exposed air cells should be thoroughly waxed and/or plugged with muscle tissue to prevent CSF leak. The dura should be widely opened to allow brain expansion. After evacuation of any intracranial hematoma, a loose expansion duraplasty is created with onlay dural substitute. An epidural suction drain is placed

prior to wound closure. The myocutaneous flap is then re-approximated in layers in standard fashion. For the bifrontal (Kjellberg and Prieto) decompressive craniectomy,11 the same preoperative considerations apply. Bifrontal decompressive craniectomy is performed with the patient supine with the nose toward the ceiling and the neck in the neutral position. A bicoronal incision extends to the root of the zygoma bilaterally. A myocutaneous flap is opened and mobilized anteriorly to the supraorbital rim, exposing the bilateral frontal convexity and anterior temporal fossae. Fig. 44.4 shows the burr hole sites, craniectomy, and dural cuts used during a typical

Fig. 44.4â•… Anatomical landmarks for bifrontal decompressive craniectomy, illustrating burr hole placement, craniectomy, and dural opening. (By Andy Rekito. Used with permission from Oregon Health & Science University.)

44 â•… Traumatic Brain Injury decompression. Posteriorly, parasagittal burr holes are created to dissect the dura free over the sagittal sinus. The dura should be opened horizontally in the inferior frontal region bilaterally, allowing ligation of the inferior sagittal sinus and complete transection of the falx cerebri. Finally, this large “fish mouth” durotomy should be extended into the anterior temporal region to promote maximal brain relaxation. Any intracranial hematoma may be evacuated. An onlay dural substitute should be applied prior to epidural drain placement and layered closure.

Hazards/Risks/Avoidance of Pitfalls In children, excessive blood loss is a significant hazard. Surgeons should maintain close communication with anesthesia providers regarding ongoing blood loss, hemodynamic stability, and transfusion needs. The patient’s coagulation profile and body temperature should also be monitored during surgery.

Salvage and Rescue Intraoperative ultrasound may be used to investigate any focal or unexplained cerebral herniation during surgery, in order to identify and assist in removal of occult intraparenchymal or distant subdural hematoma. Life-threatening bleeding may occur during surgery as the result of traumatic injury to dural venous sinuses (and may present upon elevation of the craniectomy bone flap). Circumferential control of a lacerated sinus is necessary to control bleeding. If a venous sinus laceration cannot be directly sutured, then the laceration may be occluded with large Gelfoam pledgets and the surrounding dura permanently tacked to an adjacent bone edge in order to maintain hemostasis.

44.3╇ Outcomes and Postoperative Course 44.3.1╇ Postoperative Considerations Children generally require ICP monitor or EVD placement to guide medical treatment after surgical decompression. After surgery, nursing staff should maintain precautions to protect the site of a decompressive craniectomy, using special care when turning, repositioning, and transferring the patient. A soft orthotic helmet should be fit to the patient to permit early mobilization and should be worn until cranioplasty can be performed. Autologous cranioplasty for

reconstruction after trauma craniectomy is, itself, a hazardous procedure associated with high risks of postoperative infection, bone resorption, and late posttraumatic hydrocephalus. Although the optimal timing for reconstruction is uncertain, recent reports suggest that bone reimplantation a few weeks after decompression, after ensuring the resolution of traumatic cerebral edema using preoperative magnetic resonance imaging (MRI), may reduce complication rates.12

44.3.2╇Complications Several unique complications may arise during treatment of severe TBI in children. Posttraumatic hydrocephalus may require ventriculostomy conversion to, or primary placement of, a ventriculoperitoneal shunt. Decompressive craniectomy is occasionally associated with “syndrome of the trephined,” in which headaches, lethargy, or delayed neurological deterioration can occur associated with a sunken craniectomy flap; these symptoms are frequently reversed by cranioplasty.

References ╇1. Adelson

PD, Bratton SL, Carney NA, et al; American Association for Surgery of Trauma; Child Neurology Society; International Society for Pediatric Neurosurgery; International Trauma Anesthesia and Critical Care Society; Society of Critical Care Medicine; World Federation of Pediatric Intensive and Critical Care Societies. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents. Chapter 17. Critical pathway for the treatment of established intracranial hypertension in pediatric traumatic brain injury. Pediatr Crit Care Med 2003;4(3 Suppl):S65–S67 ╇2. Chesnut RM, Marshall SB, Piek J, Blunt BA, Klauber MR, Marshall LF. Early and late systemic hypotension as a frequent and fundamental source of cerebral ischemia following severe brain injury in the Traumatic Coma Data Bank. Acta Neurochir Suppl (Wien) 1993;59:121–125 ╇3. Tisdall MM, Smith M. Multimodal monitoring in traumatic brain injury: current status and future directions. Br J Anaesth 2007;99(1):61–67 ╇4. Muizelaar JP, Marmarou A, Ward JD, et al. Adverse effects of prolonged hyperventilation in patients with severe head injury: a randomized clinical trial. J Neurosurg 1991;75(5):731–739 ╇5. Kochanek PM, Carney N, Adelson PD, et al. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents—second edition. Pediatr Crit Care Med 2012;13(Suppl 1): S18–S23 ╇6. Bruce DA, Alavi A, Bilaniuk L, Dolinskas C, Obrist W, Uzzell B. Diffuse cerebral swelling following head injuries in children: the syndrome of “malignant brain edema.” J Neurosurg 1981;54(2):170–178

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362 Section V╅ Trauma ╇7. Kochanek

PM, Carney N, Adelson PD, et al. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents—second edition. Pediatr Crit Care Med 2012;13(Suppl 1): S53–S57 ╇8. Kochanek PM, Carney N, Adelson PD, et al; American Academy of Pediatrics-Section on Neurological Surgery; American Association of Neurological Surgeons/ Congress of Neurological Surgeons; Child Neurology Society; European Society of Pediatric and Neonatal Intensive Care; Neurocritical Care Society; Pediatric Neurocritical Care Research Group; Society of Critical Care Medicine; Paediatric Intensive Care Society UK; Society for Neuroscience in Anesthesiology and Critical Care; World Federation of Pediatric Intensive and Critical Care Societies. Guidelines for the acute medical

management of severe traumatic brain injury in infants, children, and adolescents—second edition. Pediatr Crit Care Med 2012;13(Suppl 1):S1–S82 ╇9. Kochanek PM, Carney N, Adelson PD, et al. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents—second edition. Pediatr Crit Care Med 2012;13:S1–S2 10. Whitney NL, Selden NR. Pullout-proofing external ventricular drains. J Neurosurg Pediatr 2012;10(4):320–323 11. Kjellberg RN, Prieto A Jr. Bifrontal decompressive craniotomy for massive cerebral edema. J Neurosurg 1971;34(4):488–493 12. Piedra MP, Thompson EM, Selden NR, Ragel BT, Guillaume DJ. Optimal timing of autologous cranioplasty after decompressive craniectomy in children. J Neurosurg Pediatr 2012;10(4):268–272

45

Penetrating Head Injuries Kyle G. Halvorson and Gerald A. Grant

45.1╇Background Neurosurgical experience with pediatric penetrating head trauma has developed largely as a result of war-related injuries.1 Harvey Cushing’s addition of peri-injury antibiotics significantly decreased morbidity for patients suffering penetrating trauma during WWI.2,3 Korean War patients provided operative data on the importance of early surgical evacuation of hematomas, whereas the Vietnam War provided education for surgeons on the risk of a negative outcome when attempting full retrieval of deep-seated intraparenchymal bone fragments.4,5 The Gulf wars and the war in Afghanistan taught combat trauma teams how to treat intracranial blast injuries secondary to improvised explosive devices.6 Much of the current pediatric literature surrounding penetrating injuries is built upon accidental injuries occurring in the course of normal childhood play. However, multiple case reports exist describing penetrating trauma secondary to self-inflicted gunshot wounds. The focus of this chapter is the operative management of penetrating head trauma in children.

45.1.1╇Indications The decision to proceed with neurosurgical operative intervention is based on physical examination and imaging findings. Risk factors for poor outcome include an initial poor Glasgow Coma Scale (GCS) of 3 to 5, fixed and dilated pupils, lack of brainstem reflexes, autonomic instability, posterior fossa penetration, and polytrauma.7 With a pediatric patient, there is a profound emotional drive in parents and family members to proceed with extraordinary measures. Neurosurgeons are often asked by families for advice and guidance when making quick decisions in a very short period of time. It is therefore important that an objective, realistic conversation regarding the morbidity of trauma takes place prior to consideration of operative intervention.

In a child with a reassuring initial neurological examination and a retained foreign body or significantly depressed bone fragment on radiological imaging, neurosurgical intervention should be considered. Additionally, evacuation of lesions causing mass effect, vascular injury, and open scalp lesions with intracranial communication, cosmetic deformities, and cerebrospinal fluid (CSF) leakage should warrant operative management. The St. Louis Scale for Pediatric Gunshot Wounds to the Head was proposed to help guide decision making for neurosurgeons with respect to these injuries. The scale takes into account three levels of predictive criteria. Primary predictive criteria were pupil reactivity, deep nuclei or third ventricular involvement, and elevated intracranial pressure (> 30 mm Hg), with each of these factors given 3 points. Additionally, posterior fossa penetration, projectile trajectory, and greater than three lobes injured were deemed secondary predictive criteria and given 2 points each. Finally, bilateral hemispheric injury, hypotension on presentation, and midline shift were tertiary predictive criteria and given a score of 1 point each. Scores less than or equal to 4 are associated with a good outcome.8

45.1.2╇Goals The goal of neurosurgical intervention is to minimize additional intracerebral trauma. Early surgical intervention, when warranted, and only after a patient has met advanced trauma life-support goals, should proceed quickly and efficiently in order to reduce secondary injury. Easily decompressible bone fragments, hair, debris, bullet fragments, or other foreign bodies should be removed. Dural tears should be repaired primarily or with a graft, unless doing so would secondarily increase intracranial pressure or the child is so sick that there is a need to abort surgery. Injured vasculature should also be repaired if possible. Finally, the benefits and risks of replacing the bone flap must be considered. Even if the intra-

363

364 Section Vâ•… Trauma cranial portion of the procedure has been successful, subsequent injury may result from lack of bony coverage of the brain, difficult intracranial pressure (ICP) management, and infection due to contamination of the previously open wound.

45.2╇ Operative Detail and Preparation

45.1.3╇ Alternative Procedures

Initial evaluation and workup in the field and upon arrival at a trauma center are similar to those for other cranial injuries. First priority must be given to stabilizing the patient’s airway, breathing, and circulation, the ABCs of trauma management. Neurological assessment should follow as quickly as possible after initial stabilization of the patient. A neurosurgeon must account for other significant injuries that may alter the surgical management plan and triage. Consideration of patient age, approximate time of injury, initial GCS, and type or mechanism of penetrating injury are the initial factors that must be reviewed. Physical examination data, including pupillary and subsequent brainstem reflexes, are then reviewed. Finally, laboratory data, including coagulation studies and platelet count, in combination with additional comorbidities, are taken into account because they may make operative management more challenging, if not contraindicated. The neurosurgeon has a critical role in the initial trauma assessment and triage. In the event that the patient has not already had an airway secured, the neurosurgeon would prefer an oral airway, due to the risk of inadvertent intracranial injury from nasal intubation in cases where facial fractures have occurred. Short-acting neuromuscular blocking agents of the nondepolarizing class are also preferred in order to limit long-term depression of the neurological examination. These agents also briefly minimize spikes in ICP secondary to coughing due to the cough reflex. Once an airway has been obtained, some neurosurgeons recommend hyperventilation; however, its role in penetrating head injury management has not yet been fully established. Also of critical importance is the management of hypotension. In the setting of increased ICP or low systolic blood pressure, cerebral perfusion suffers dramatically. Many studies have suggested that cerebral perfusion pressure (CPP) lower than 40 mm Hg portends a higher mortality rate.10 Hypertension may also result as a manifestation of the Cushing response. In this setting, as well as with most intracranial injuries, the following therapies may yield clinical benefit: osmotic therapy with mannitol (0.5–1 g/kg) to a target serum osmolality of 320 to 340 mOsm/L; hypertonic saline (3 or 23% boluses) to a target serum sodium of greater than 150 mEq/L; furosemide boluses (0.5–1 g/kg), or vasopressors, such as dopamine or vasopressin, may be required given the clinical parameters.

Invasive neurosurgical procedures are not warranted in all penetrating head trauma cases. Penetrating injuries that cross the midline, brainstem injuries, major vascular injuries, and retained foreign bodies in close proximity to, or in direct communication with, the ventricular system may not be amenable to operative intervention. Hydrocephalus secondary to edema may require cerebral spinal fluid (CSF) diversion for ICP monitoring. Anticipated quality of life without surgical intervention must be considered for pediatric patients with profound penetrating injury. The focus should be shifted toward supportive care and organ donation in these patients.

45.1.4╇Advantages Early surgical intervention in the pediatric patient can improve long-term functional outcome. Some older literature suggests that postinjury infection rates are decreased.9 Early definitive neurosurgical management also allows for earlier surgical intervention by other pediatric specialties. It is important to note, however, that early surgical intervention may not always negate significant long-term neurological injury. Children may have difficulties with activities of daily living (ADLs), vision loss, short- or long-term memory loss, or personality disturbances. Although these deficits may improve with time, the possibility of permanent cognitive devastation or persistent vegetative state also exists.

45.1.5╇Contraindications Pediatric neurosurgeons need to delineate between surgical and supportive management of children with penetrating head injuries. As previously mentioned, patients with low GCS (3 to 5) and multiple neurological deficits at time of presentation are more likely to have a poor chance of full neurological recovery.7 Contraindications to neurosurgical intervention are not firmly accepted; however, they include large intraparenchymal hematomas in eloquent brain, bullet, or other foreign body crossing midline or through the center of the brain, and path of travel through the ventricles.7

45.2.1╇ Preoperative Planning and Special Equipment

45 â•… Penetrating Head Injuries Even after the initial trauma stabilization and primary survey, the neurosurgeon has a role in the secondary survey. Communication between the neurosurgeon and the trauma team should encourage placement of a Foley catheter (not condom catheter) for bladder decompression and to monitor fluid status, an orogastric tube for stomach decompression, and spinal precautions, including placement and maintenance of a Miami J cervical collar, reverse Trendelenburg bed positioning, and head elevation to 30 degrees. Trauma and emergency medical services (EMS) personnel should be instructed not to remove retained foreign bodies in the field or in the trauma bay, even with neurosurgical evaluation pending. Removal of retained objects may lead to uncontrollable hemorrhage outside of the operating room. Intracranial injury patients are routinely treated with antiepileptic therapy at time of presentation. Levetiracetam (20 mg/kg) is commonly chosen as first line given the relatively benign side-effect profile and the lack of need for routine serum plasma levels. Phenytoin and fosphenytoin are other common alternatives in the trauma setting, although their teratogenicity and hepatic induction effects must be considered. Identification of a coagulopathy and anemia in the initial trauma assessment is important when considering invasive neurosurgical management. Penetrating head injury patients are at significant risk of developing disseminated intravascular coagulation (DIC). If abnormal coagulation studies or a low platelet count are discovered on laboratory analysis, they need to be aggressively corrected to prevent intraoperative and perioperative bleeding. This is of

a

b

special consideration in infants and very young children because this population is very susceptible to subgaleal hematomas, which result in a decrease in intravascular volume leading to subsequent hypotension and overall worse prognosis. Once a pediatric patient is stable with respect to the initial evaluation and surveys, imaging must be obtained. The gold standard to evaluate intracranial processes is a noncontrast computed tomography (CT) of the head and cervical spine. From these images, information about missile trajectory, disbursement of intracranial fragments, ventricle penetration, and resultant hematoma formation can be ascertained (Fig. 45.1). Additionally, the injury epicenter can be located with respect to the major cerebral vessels, allowing better prediction of potential motor and sensory areas that may be ultimately affected. Early information regarding the stability of the cervical spine is also evaluated, a key consideration should the patient require operative management. Angiographic evaluation and possible intervention may be required in cases where missiles travel near the proximal middle cerebral, anterior cerebral, vertebral, or basilar arteries. This also holds true of the major intracranial venous structures, including the cavernous, superior sagittal, transverse, and sigmoid sinuses. The goal of angiographic evaluation is to determine the degree of injury to major vascular structures in relation to the spatial orientation of the penetrating object. These studies can provide useful information for operative planning and about the potential need for major vessel repair at the time of surgery. If there is time before operative management, a CT angiogram (CTA) can be helpful if the bul-

c

Fig. 45.1â•… Penetrating gunshot wound to the head in a child. Initial emergency department presentation. (a) Note stellate entrance wound superior to the left orbital rim with scalp debris and herniated devitalized brain tissue. (b) Note the large outwardly displaced frontal bone plate with disruption of the coronal suture, significant comminution, and a retained bullet fragment in the left parietal region. (c) Further inferior image of intracranial debris and superficial shrapnel.

365

366 Section Vâ•… Trauma let fragments or trajectory is in close proximity to the sylvian fissure or circle of Willis. The pericallosal artery should be carefully looked at with a trajectory in the frontal region that crosses the interhemispheric fissure. Penetrating traumatic cranial injuries are commonly contaminated, either from the missile on impact or by surrounding debris at the site of penetration. Routine use of perioperative antibiotics decreases morbidity associated with neurosurgical interventions. Weight-based dosing of vancomycin provides broad coverage antibiotic therapy as well as defense against methicillin-resistant Staphylococcus aureus (MRSA). This is combined with a third-generation cephalosporin, providing both gram-negative and gram-positive coverage, as well as metronidazole for anaerobe coverage. If wound cultures do in fact grow specific organisms, speciation with susceptibilities may be obtained for targeted antibiotic therapy. Additionally, antibiotic therapies may be tailored based on a patient’s fever curves. Without the proper antibiotic prophylaxis, patients are at risk of meningitis, abscess formation, or wound infection. Thus the benefit of short-term antibiotic use appears to outweigh the risk of broad coverage. However, the optimal duration of antibiotic therapy is unknown, but generally it is given for 3 to 5 days from the time of injury.

45.2.2╇ Expert Suggestions/Comments In cases of penetrating intracranial injuries in children, evaluation and imaging must be obtained immediately after resuscitation. Once a decision for surgical management has been made, operative management must follow as quickly and efficiently as possible. Intraoperatively, the pediatric neurosurgeon should communicate closely with the anesthesia and nursing teams. Particular attention should be paid to end-tidal carbon dioxide (CO2), hematocrit, and need for intraoperative blood transfusion, in addition to fresh frozen plasma and platelets. There also may be a need for activated Factor VIIa if the child develops DIC due to the brain injury. Minimizing delays and goal-oriented progress through the operation are critical for optimizing postoperative outcome.

45.2.3╇ Key Steps of the Procedure/ Operative Nuances Once the patient enters the operating room and general anesthesia is induced, the next critical step is patient positioning. In cases of penetrating injury with severe intracranial trauma, a horseshoe Mayfield head frame with padding is generally used to avoid pins into a skull fracture, to protect the

extracranial vasculature that later may be used for a bypass, and to allow for extensive undermining of the subgaleal space for primary closure in children with a large scalp defect. Often a shoulder roll or bump is required to achieve optimal positioning and the neck is maintained in the neutral position due to the risk of a possible concomitant cervical spine injury and to maximize venous drainage. The patient’s scalp is then prepared by shaving an area large enough to assess the orientation of the wound from the missile, as well as the need for tunneling to an exit point of an intraoperative drain placement. After sterilely prepping and draping the patient, an incision is made, attempting to incorporate the often-stellate entry point laceration, with plans for a wide scalp flap. This affords broad scalp mobilization with improved access to depressed bone fragments and better hemorrhage control. In the case of frontal injuries, special attention is paid to the possibility of frontal sinus involvement. If the frontal sinuses have pneumatized and injury is apparent, operative exenteration and vascularized pericranial flap isolation are needed. These lesions are typically packed with abdominal fat harvested through a periumbilical incision. If there is no pericranium available due to the severity of the blast injury, fascia lata can be harvested from the thigh and laid into the anterior cranial fossa. Because penetrating injuries are open contaminated wounds, we do not use a lot of synthetic material due to the potential risk for infection. However, if there is a large bony defect along the floor, it is prudent to lay some titanium mesh below the pericranial flap to buttress the frontal lobe. Additional consideration must also be given to bony skeletal involvement in frontal injuries, specifically the orbit and orbital roofs. It is helpful to lay in some additional mesh or Medpor orbital reconstruction (Stryker) implant to reconstruct the orbital roof, which will make any later reconstruction much easier. Once the devitalized brain tissue, debris, and foreign objects have been debrided and removed from the trauma site, evaluation of the dural defect is quickly accomplished. If a pericranial graft is not readily available, an appropriately sized dural substitute is requested for delayed closure as an onlay graft. Often the graft does not need to be sewn to the native dura since time is of the essence. The longer the surgery, the higher the cumulative risk for blood loss and hypotension. If there is brain swelling and shift on the CT scan, a larger craniectomy is required for ICP control (Fig.€45.2). Often the swelling will continue to progress after a blast injury and should be anticipated. When elevating the bone flap, the dural attachments are freed with delicate technique so as to avoid further dural laceration. Tack-up sutures are placed around the periphery of the operative site and the

45 â•… Penetrating Head Injuries a

b

c

Fig. 45.2â•… (a) Preoperative planning for cranioplasty. Initial computed tomography (CT) demonstrating trajectory and intracranial injury of left frontal gunshot wound to the head in a 4-year-old right-handed child. (b) Same 4-year-old child 6 months’ status postdecompression and evacuation of superficial fragments. (c) Preprosthesis manufacture three-dimensional (3D) CT at same 6-month time point after initial surgery.

edges are packed with Surgicel Fibrillar. If the dura is not opened to the extent necessary to decompress the injured brain, a stellate incisional extension is made toward the major venous sinuses. Any injury to the venous sinuses can lead to further swelling and can be lethal. If there is excessive bleeding intraoperatively, fresh frozen plasma (FFP) should be administered early and before the coagulation parameters return from the laboratory. The time it takes for the coagulation studies to come back from the laboratory is often too long to make a difference intraoperatively. If there is persistent bleeding despite FFP, the authors would consider infusing activated Factor VIIa to control the bleeding. FLOSEAL (Baxter Healthcare Corp., Deerfield, IL) or other hemostatic adjuncts can be very helpful in the extradural and intradural compartments for hemostasis. Maximal medical management intraoperatively is critical. Gentle hyperventilation should be used throughout the case. Since heavy use of mannitol can be risky in young children due to the risk of hypovolemia secondary to the diuresis, hypertonic saline (3%) can be very effective intraoperatively and postoperatively to maintain an elevated osmolarity. However, it is frequently necessary to debride devitalized brain tissue or quickly evacuate intraparenchymal hematomas to expeditiously reduce cerebral edema. In cases of dominant hemisphere surgery, care is taken to avoid white matter violation or deep exploration into the ventricle because this results in poor functional outcome postoperatively.7,11 Once the surgical field is dry, an ICP monitor should be placed for postoperative management in

children with GCS < 8 preoperatively or with intraoperative brain swelling. If feasible to place intraoperatively, a ventriculostomy is placed both to monitor ICP as well as to divert CSF to decrease the risk for a postoperative CSF leak. A layer of Surgicel is applied over the friable dura and exposed brain, as well as a layer of dural substitute. In addition, a subgaleal drain is placed. It is generally left in place until the postoperative drainage has declined to less than 20 mL over 24 hours. Attention is then turned to closure of the galea. In cases where postoperative infection is likely, interrupted stitches using a monofilament suture are used. If optimal galeal closure is not possible secondary to a large scalp defect, galeal advancement procedures are often needed and consultation with a plastic surgeon should be anticipated as early as possible in the case to assist with a rotational flap closure. Often with extensive undermining of the subgaleal space in children, a primary closure can be achieved (Fig. 45.3). In cases where a decision is made to leave the bone flap off for ICP management, the bone can often be frozen and banked for possible later insertion. If there is a high degree of comminution of the fragment, clear contamination, likely poor cosmetic result, or no clear salvage plan during the initial surgery, the edges of the remaining bone are beveled for delayed prosthetic cranioplasty. Should the patient need a prosthetic flap, a three-dimensional (3D) CT scan is obtained at a later date to manufacture a precise-fit implant. In general, the time from decompression to cranioplasty has shortened due to the potential for plateau or decline in neurological function with the sag of the cerebral hemisphere with gravity.

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368 Section Vâ•… Trauma a

b

Fig. 45.3â•… Operative management of penetrating head injury secondary to suicide attempt. Operative positioning. In this case a Mayfield skull clamp was used; however, we often use a horseshoe Mayfield attachment. (a) A wide area of hair is shaved and prepped and the incision is planned based on the extent of bony injury on preoperative computed tomography (CT) imaging, as well as anticipated need for scalp mobilization.

45 â•… Penetrating Head Injuries c

d

Fig. 45.3 (Continued)â•… (b) Once the scalp is elevated, a vascularized pericranial graft is secured for later obliteration of the frontal sinus. (c) Assessment of the bony comminution and plan for craniotomy. (d) Elevation of the bone flap in standard two-piece fashion over the superior sagittal sinus. (Continued on page 370)

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370 Section Vâ•… Trauma e

f

Fig. 45.3 (Continued)â•… (e) Exenteration of the frontal sinus and packing with abdominal fat, tissue glue, and mesh plating along the anterior skull base. (f) Final bony reconstruction using a variety of mesh and cranial plates with good cosmetic results.

45 â•… Penetrating Head Injuries g

h

Fig. 45.3 (Continued)â•… (g) Note the intraoperative placement of an extraventricular drainage catheter on the right side of the image, and also a small subgaleal drain for postoperative subgaleal hematoma evacuation. (h) Postoperative three-dimensional (3D) CT to evaluate intraoperative reconstruction.

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372 Section Vâ•… Trauma

45.2.4╇ Hazards/Risks/Avoidance of Pitfalls Vertex penetrating injuries are high risk due to the likelihood of injury to the sagittal sinus and should be approached with extreme caution. If one has to sacrifice the sinus, there may be lethal consequences due to the impact on ICP with less venous return. It is also imperative to involve ophthalmology if there is an orbital injury, in case it is possible to restore vision or if an enucleation and placement of a temporary implant are required at the time of the craniotomy.

45.2.5╇ Salvage and Rescue The early use of activated Factor VIIa in the military setting has been a tremendous asset in the management of penetrating injuries, and it should be considered for children undergoing surgical intervention with an ensuing coagulopathy. If hemostasis cannot be achieved, the bone should be left off and a subgaleal drain placed prior to scalp closure.

45.3╇ Outcomes and Postoperative Course 45.3.1╇ Postoperative Considerations Typically, all patients undergoing exploration for penetrating intracranial injuries are monitored postoperatively in the pediatric intensive care unit (PICU). Close communication with the PICU team is essential in the initial hours to days after neurosurgical intervention. Hypotension, elevated ICP, respiratory distress, coagulopathy, seizures, fevers or other systemic indications of sepsis or infection, venous sinus thrombosis, sudden change in neurological examination, or decreased serum osmolarity require urgent and thorough evaluation by the neurosurgical team with subsequent correction accordingly. Once a reassuring and stable neurological examination develops, the authors aggressively initiate physical, occupational, and speech therapy as appropriate.

45.3.2╇Complications Complications after penetrating head injuries occur both due to the injuries themselves and secondary to surgery. CSF leaks are common after the initial penetrating injury. Intraoperatively, they should be managed with a watertight dural closure when possible. However, if a postoperative leak occurs, definitive surgical closure with autologous graft should be considered. If this is not possible, CSF diversion

should be accomplished with either a permanent shunt or temporary ventriculostomy catheter. If the ICP is normal and there are no signs of downward herniation, a temporary lumbar drain may yield clinical resolution of the leak. Vascular complications often occur secondary to penetrating head injuries. These include vasospasm, delayed hemorrhage from pseudoaneurysm rupture, subarachnoid hemorrhage (SAH), and traumatic arteriovenous fistula formation. A high index of suspicion must be maintained postoperatively for these complications because they can be life threatening and must be managed aggressively and quickly. Retained foreign bodies pose a risk of postoperative infection or abscess formation and possibly fragment migration. Immediate intracranial imaging should be obtained with significant late neurological examination changes because operative management may be indicated for retrieval. These children therefore require long-term follow-up.1,6,8,11–24

References ╇1. Ambrosi

PB, Valença MM, Azevedo-Filho H. Prognostic factors in civilian gunshot wounds to the head: a series of 110 surgical patients and brief literature review. Neurosurg Rev 2012;35(3):429–435, discussion 435–436 ╇2. Winn HR. Penetrating head injuries. Youmans Neurological Surgery. Philadelphia, PA: W.B. Saunders; 2011 ╇3. Cushing H. A series of wounds involving the brain and its enveloping structures. Br J Surg 1917;5:558–684 ╇4. Meirowsky A. Penetrating wounds of the brain. In: Costes J, ed. Neurological Surgery of Trauma. Washington, DC: Office of the Surgeon General, Department of the Army; 1965: 103–136 ╇5. Carey ME, Young H, Mathis JL, Forsythe J. A bacteriological study of craniocerebral missile wounds from Vietnam. J Neurosurg 1971;34(2 Pt 1):145–154 ╇6. Klimo P Jr, Ragel BT, Scott WH Jr, McCafferty R. Pediatric neurosurgery during Operation Enduring Freedom. J Neurosurg Pediatr 2010;6(2):107–114 ╇7. Kazim SF, Shamim MS, Tahir MZ, Enam SA, Waheed S. Management of penetrating brain injury. J Emerg Trauma Shock 2011;4(3):395–402 ╇8. Bandt SK, Greenberg JK, Yarbrough CK, Schechtman KB, Limbrick DD, Leonard JR. Management of pediatric intracranial gunshot wounds: predictors of favorable clinical outcome and a new proposed treatment paradigm. J Neurosurg Pediatr 2012;10(6):511–517 ╇9. Arendall RE, Meirowsky AM. Air sinus wounds: an analysis of 163 consecutive cases incurred in the Korean War, 1950–1952. Neurosurgery 1983;13(4):377–380 10. Adelson PD, Bratton SL, Carney NA, et al; American Association for Surgery of Trauma; Child Neurology Society; International Society for Pediatric Neurosurgery; International Trauma Anesthesia and Critical Care Society; Society of Critical Care Medicine; World Federation of Pediatric Intensive and Critical Care Societies. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents.

45 â•… Penetrating Head Injuries Chapter 4. Resuscitation of blood pressure and oxygenation and prehospital brain-specific therapies for the severe pediatric traumatic brain injury patient. Pediatr Crit Care Med 2003;4(3 Suppl):S12–S18 11. Surgical management of penetrating brain injury. J Trauma 2001; 51(2 Suppl): S16–S25 12. Brain Trauma Foundation, American Association of Neurological Surgeons, Joint Section on Neurotrauma and Critical Care. Guidelines for the management of severe head injury. J Neurotrauma 1996;13(11):641–734 13. Guidelines for the management of severe head injury. Introduction. J Neurotrauma 1996;13(11):643–645 14. Bauer R, Fritz H. Pathophysiology of traumatic injury in the developing brain: an introduction and short update. Exp Toxicol Pathol 2004;56(1-2):65–73 15. Bell RS, Mossop CM, Dirks MS, et al. Early decompressive craniectomy for severe penetrating and closed head injury during wartime. Neurosurg Focus 2010;28(5):E1 16. Fischer BR, Yasin Y, Holling M, Hesselmann V. Good clinical practice in dubious head trauma—the problem of retained intracranial foreign bodies. Int J Gen Med 2012;5:899–902 17. Grant GA. Management of penetrating head injuries: lessons learned. World Neurosurg 2014;82(1-2):25–26 18. Khan MB, Kumar R, Irfan FB, Irfan AB, Bari ME. Civilian craniocerebral gunshot injuries in a developing country:

presentation, injury characteristics, prognostic indicators, and complications. World Neurosurg 2014;82(1-2):14–19 19. Mackerle Z, Gal P. Unusual penetrating head injury in children: personal experience and review of the literature. Childs Nerv Syst 2009;25(8):909–913 20. Mathew P, Gibbons AJ, Christie M, Eisenburg MF. Operative treatment of paediatric penetrating head injuries in southern Afghanistan. Br J Neurosurg 2013;27(4):489–496 21. Murakami Y, Wei G, Yang X, et al. Brain oxygen tension monitoring following penetrating ballistic-like brain injury in rats. J Neurosci Methods 2012;203(1):115–121 22. Plantman S, Ng KC, Lu J, Davidsson J, Risling M. Characterization of a novel rat model of penetrating traumatic brain injury. J Neurotrauma 2012;29(6):1219–1232 23. Robles LA. High-velocity gunshot to the head presenting as initial minor head injury: things are not what they seem. Am J Emerg Med 2012;30(9):2089.e5–2089.e7 24. Zaaroor M, Soustiel JF, Brenner B, Bar-Lavie Y, Martinowitz U, Levi L. Administration off label of recombinant factor-VIIa (rFVIIa) to patients with blunt or penetrating brain injury without coagulopathy. Acta Neurochir (Wien) 2008;150(7):663–668

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46

Vascular Injuries Jeffrey C. Mai, Kyle M. Fargen, Spiros Blackburn, and David W. Pincus

46.1╇Background Evidence supporting best practices for pediatric cerebrovascular injuries is unfortunately scant owing to their relative rarity. Vascular injuries encompassing the neck or head can be generated by either penetrating or blunt mechanisms. Traumatic injuries can lead to either intracranial or extracranial injuries involving the carotid or vertebral arteries that may result in ischemic stroke or life-threatening hemorrhage. In addition, either penetrating or blunt trauma can lead to the delayed formation of intracranial pseudoaneurysms. In adults, carotid artery injuries occur in 20% or less of penetrating neck injuries and in 0.4% or less of blunt neck injuries.1 Although major vascular injuries are uncommon, timely diagnosis and treatment are important to ensure adequate cerebral perfusion and prevent hypovolemic shock. At times, rapid diagnosis of a cervical vascular injury may be difficult due to the concomitant presence of traumatic brain injury or poor neurological examination secondary to cerebral hypoperfusion or sedation, multitrauma to the chest or abdomen and alternative sources of hemorrhage, and the presence of significant extremity injuries. Fortunately, when identified, the majority of pediatric intracranial and extracranial vascular injuries are managed nonoperatively.

46.2╇ Extracranial Arterial Injuries in Children 46.2.1╇ Penetrating Vascular Injuries Penetrating injuries of the neck are generally a result of animal bites in younger patients, and secondary to gunshot wounds in the older pediatric cohort

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(Fig.€46.1). For the purposes of categorizing and triaging such injuries, the neck has been divided into three zones to account for the important vascular, pulmonary, or gastrointestinal structures requiring attention after traumatic injury (Fig. 46.2). In adults, zone 2 is the most frequent site of injury of the carotid artery. Although pediatric data are limited, penetrating neck injuries in children appear to have a similar incidence, with zone 2 being the most common. Furthermore, injuries to this zone can be the most complicated due to the presence of the carotid and vertebral arteries, jugular vein, esophagus, trachea and larynx, thoracic duct, branches of the vagus nerve, and the thyroid gland. In one study of 157,000 pediatric emergency department or trauma center visits over a 5-year period, only 32 instances of penetrating neck injuries (PNIs) were identified in individuals spanning ages 10 months through 16 years. Zone 2 of the neck was involved in 84% of these cases (between the cricoid cartilage and the angle of the mandible).2 Only one-fourth of these patients were treated surgically; of the 8 patients who underwent surgical exploration, none revealed vascular injuries and no cerebral angiograms were required. A second large retrospective review of 19,363 pediatric trauma patients uncovered 39 instances of PNIs. Six patients underwent surgical exploration, with only one-third of the procedures being therapeutic.3 Avoiding exploration because of imaging findings were 15 patients. In adults, immediate surgical exploration is recommended after PNI when certain examination findings are present. These include hypotensive shock or refractory hypotension, pulsatile cervical bleeding, enlarging neck hematoma, carotid bruit, or the loss of pulses with evolving neurological deficit. Whereas the absence of such “hard signs” after zone 2 injuries does not definitively rule out a vascular injury, an adult study from 1994 demonstrated that only 1% of

46 â•… Vascular Injuries a

b

c

Fig. 46.1╅ An 11-year-old boy sustained a gunshot wound to the right neck requiring resuscitation in the field and intubation. (a)€Following computed tomography (CT) imaging, he was taken emergently to the operating room where a transected right common carotid artery bifurcation was identified (trajectory marked with white dots). The right common, internal, and external carotid arteries were ligated. Further exploration also revealed a right vertebral dissection and bleeding. The vertebral artery was packed. (b) Angiography was performed following surgery to evaluate for residual bleeding and collateral flow and showed complete occlusion of the right carotid and vertebral arteries (catheter angiogram). (c) As shown, the left carotid and left magnetic resonance imaging (MRI) of the brain revealed right hemisphere and posterior cerebral artery territory infarctions. The patient eventually died.

Fig. 46.2â•… The neck has been divided into three zones to account for the important vascular, pulmonary, or gastrointestinal structures requiring attention after penetrating injury.

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376 Section Vâ•… Trauma patients had vascular injuries in the absence of such findings.4 One study of children, published in 1991, identified seven indications for mandatory surgical exploration after PNI in zone 2: (1) expanding and/ or pulsatile hematoma; (2) shock; (3) subcutaneous air on imaging; (4) carotid bruit, thrill, or neck crepitus/dysphagia; (5) blood in the oropharynx; (6) need for anesthesia to close the wound due to the young patient’s inability to tolerate wound repair under local anesthetic; and (7) inability to study the patient’s neck injuries due to the presence of other severe injuries.5 Although the data in children are limited, a retrospective review of 31 patients argued that observation is an acceptable management strategy, in the absence of hard signs, as long as the child remains hemodynamically stable.2 Neck imaging is recommended in patients with PNI who are hemodynamically stable to evaluate the extent of the injuries radiographically. Catheter angiography remains the gold standard imaging technique to evaluate injury to the carotid or vertebral arteries after PNI, with sensitivity and specificity of detecting an operative injury approximately 100 and 95%, respectively. Magnetic resonance imaging (MRI), although excellent at evaluating soft tissue, is limited by the time required to obtain imaging and cannot be used after gunshot wounds where fragments are retained. Ultrasound imaging has also been studied but lacks acceptable sensitivity. Computed tomography angiography (CTA) has emerged as a rapid means of assessing the spine, soft tissue, and aerodigestive tract while also visualizing the carotid and vertebral arteries. Although data on the usefulness of CTA in children are limited, one small pediatric study of 28 patients indicated that CTA had a sensitivity of 100% and a specificity of 96% in detecting vascular injury after PNI.6 Collectively, these data suggest that obligatory neck exploration or angiography after PNI may not be necessary in the pediatric population. Rather, rapid CTA imaging is the preference to evaluate the region of interest. When vascular injuries are discovered, as in the adult population, open surgical repair of common carotid or cervical internal carotid injury is recommended when feasible. In select cases, an external carotid artery to internal carotid artery transposition, or reversed saphenous vein or radial artery bypass of the involved segments can be considered, provided that the clamp time will not prove to be excessive. Injuries to the carotid artery in zone 3 or foraminal injuries to the vertebral artery may prove difficult to obtain adequate exposure to perform successful arterial repair. Furthermore, severe injuries to the extracranial carotid or vertebral arteries may not allow open surgical repair, necessitating ligation of the artery. Direct repair is recommended, if it can be performed, because many patients will improve neurologically following arterial repair and

restoration of cerebral perfusion. On the other hand, procedural mortality associated with arterial ligation is high, at 45% in one study, although those that did not expire did not have a change in neurological status, indicating that ligation was tolerated.7 However, other studies have suggested a higher risk of stroke with ligation. In some cases, emergent angiography with embolization and vessel sacrifice is necessary to prevent exsanguination. Injury to the external carotid artery branches may be successfully managed by vessel embolization proximal (and distal, if possible) to the site of injury with liquid embolic agents or detachable coils. However, extensive external carotid collaterals, and the presence of external-internal carotid anastomoses, can complicate this strategy. In a similar fashion, proximal vertebral artery embolization after vertebral artery injuries can be performed more safely if a contralateral vertebral artery remains intact. Internal jugular vein injury can be managed conservatively or with ligation or repair if accessible. The majority of traumatic pseudoaneurysms of the common or extracranial internal carotid arteries are asymptomatic and can be treated conservatively with observation or a single antiplatelet agent. In the absence of flow limitation from an associated dissection, antiplatelet agents, anticoagulation, or both should be initiated to reduce the risk of thromboembolism. Follow-up imaging with magnetic resonance angiography (MRA), CTA, or angiography in 4 to 6 weeks, and then again at 6 months, is preferred to confirm stability. Occasionally, large cervical pseudoaneurysms may develop and require treatment. When this occurs, the options include vessel sacrifice, surgical reconstruction, or endovascular reconstruction.

46.2.2╇ Nonpenetrating Vascular Injuries Vascular injuries are much more common in the adult population after gunshot wound or blast injuries to the neck than after stabbing or blunt injuries. The most common mechanisms of blunt carotid injuries include: (1) hyperextension and rotation, occurring frequently in the upper cervical spine during motor vehicle accidents where the carotid is injured along the lateral masses of the upper cervical spinal segments; (2) direct blow to the artery from a blunt force; and (3) vessel laceration secondary to trauma from adjacent bony fractures. Because vascular injuries are much less common after blunt injuries than with penetrating injuries, occurring in less than one half of 1% of patients, the diagnosis of vascular injuries after blunt trauma is often more difficult and warrants a high degree of clinical suspicion. As expected, hard signs are only rarely present, so such injuries are usually only discovered

46 â•… Vascular Injuries after neck imaging is obtained or when neurological symptoms develop. Blunt trauma to the major cervical arteries may result in dissection or pseudoaneurysm formation, which puts the child at risk for acute ischemic stroke secondary to thromboembolism or cerebral hypoperfusion if the intimal flap is occlusive.

46.3╇ Intracranial Vascular Injuries in Children 46.3.1╇ Dissection and Stroke The best evidence for pediatric vascular trauma relating to stroke is derived from the International Pediatric Stroke Study Group, which surveyed 1,187 children and adults ages 28 days through 19 years who sustained arterial ischemic stroke (AIS) or cerebral sinovenous thrombosis. Approximately 11% of pediatric AIS cases were associated with head and neck trauma.8 AIS resulted in significant morbidity, with persistent neurological deficit at the time of discharge observed in more than 70% of patients. Dissection in the setting of AIS was associated with a 2% risk of death and a 3% risk of intracranial mortality. In a separate study of 14,991 pediatric patients with blunt trauma, 45 cases of blunt cerebrovascular injuries (BCVIs) were identified (0.3% of traumas) and 10 of the patients manifested stroke symptoms within 72 hours of injury.9 Screening imaging to evaluate for arterial dissection should be performed in patients with cervical spine fractures, carotid canal skull base fractures, traumatic brain injuries, diffuse axonal injuries, Le€Fort II/III injuries, or high mechanism of injury, as per criteria used in adult patients.9 However, the index of suspicion should be expanded in pediatric patients to include those with nonbasilar skull fractures, chest trauma, or direct neck trauma as well. The choice of CTA versus MRA to screen asymptomatic patients for dissection remains contentious because some studies suggest a lower sensitivity and specificity of MRA in comparison to CTA. On the other hand, in children, the long-term risk of ionizing radiation exposure still needs to be considered and MRI clearly has the advantage of detecting subtle ischemic events. For patients with ischemic stroke symptoms in the setting of trauma, an MRI with MRA including fat saturation is recommended. If the MRA is normal, in the setting of AIS, digital subtraction angiography (DSA) should be performed to exclude the presence of an otherwise occult lesion. Owing to the absence of pediatric randomized controlled trials, the optimal antithrombotic

strategy to employ in pediatric arterial dissection remains unclear. Data in adults strongly support the use of either anticoagulation or antiplatelet administration in the setting of asymptomatic BCVI, with a stroke rate of 0.5% in the treated patients versus 21.5% in the untreated patients. In children, anticoagulation with unfractionated heparin is preferred when imaging discloses the presence of intraluminal thrombus, flow-limiting dissection, occlusion, or infarct involving the carotid or vertebral artery territories. In cases where the dissection is not flow limiting, with only minimal stenosis, then a single antiplatelet is sufficient. Traumatic dissections of the intracranial arteries are more difficult to treat and are associated with greater morbidity and mortality than extracranial arterial dissections. In fact, one study demonstrated a mortality rate approximating 50% for intracranial carotid artery dissections in children.10 Similar to extracranial dissections, the mainstay of therapy for intracranial lesions is antiplatelet agents. Anticoagulation, in contrast, is not recommended in intracranial dissection due to the risk of subarachnoid hemorrhage.11 Open surgical or endovascular techniques are recommended in those who remain symptomatic after appropriate medical therapies have been initiated.11 Whereas open vascular repair with limited morbidity is possible for extracranial dissections, open surgical techniques for intracranial pathology are associated with significant procedural morbidity. Angioplasty and stenting is an additional treatment option for extracranial or intracranial dissection. The authors will occasionally employ stents in the setting of ischemic strokes or traumatic intracranial aneurysms (TIAs) associated with a severe, flow-limiting extracranial stenosis. In adults, two meta-analyses have demonstrated that emergency extracranial carotid stenting for dissection is safe and effective, with excellent 1-year patency. In fact, the Society of Vascular Surgery recommends endovascular management of extracranial dissection if the patient remains symptomatic after appropriate antithrombotic agents have been administered.12 However, this technique remains unstudied in children and the risks and benefits of stenting are not yet understood in this patient population. In addition, the treatment of intracranial dissection with angioplasty and stenting is poorly evidenced and limited to case series only at this time. Follow-up imaging is recommended in cases of dissection to document healing of the endothelium. The authors typically perform this at 4 to 6 weeks and again at 6 months. Depending on the initial treatment regimen, at 6 months either anticoagulation can be stopped and transitioned to a single antiplatelet, or the antiplatelet can be stopped.

377

378 Section Vâ•… Trauma

46.3.2╇ Traumatic Intracranial Aneurysms TIAs, accounting for less than 1% of all cerebral aneurysms, are observed with higher frequency in the pediatric population, and can arise from either penetrating or nonpenetrating injuries. Typically, they manifest as an aneurysmal hemorrhage within 3 weeks of initial injury, resulting in 50% mortality.13 These aneurysms can form in the context of what would appear to be minor trauma, but, more frequently, penetrating trauma precedes their formation. They tend to involve the supraclinoid carotid artery or the anterior cerebral artery, including the pericallosal or callosomarginal locations; however, infraclinoid and basilar aneurysms can form when skull base fractures are present. The relative rarity of traumatic aneurysm formation weighed against the risks of radiation exposure from screening CTAs in the pediatric population or the difficulties of obtaining MRAs in these patients (requiring general anesthesia in order to achieve adequate imaging quality) has complicated their detection. In most cases of closed head injury, there is no role for vascular imaging and it is the preference of the authors to reserve this type of imaging for penetrating injury only. If initial imaging at the time of evaluation is concerning for a vascular injury or pseudoaneurysm, cerebral angiography is indicated to determine optimal treatment, either surgical or endovascular. The index of suspicion should be accordingly higher in pediatric patients who have sustained basilar skull fractures or penetrating injuries. Aggressive treatment of traumatic aneurysms is warranted when they are discovered because surgical intervention more than halves the overall rate of mortality. Either open microsurgery or endovascular methods are appropriate, dependent upon the comfort level of the surgeon. The authors’ preference has been open microsurgery for these lesions in order to definitively treat the aneurysm, particularly if mass effect from an intracerebral hematoma is present as well. When employed, endovascular interventions require close long-term follow-up in the pediatric population.

46.3.3╇Vasospasm Cerebral vasospasm occurs frequently in both the anterior and posterior circulation following pediatric traumatic brain injury. In patients up to age 14 years, vasospasm was measured by transcranial Doppler ultrasound in 45% of patients in the middle cerebral

artery (MCA) territory and 18% in the basilar territory following trauma.14 Onset occurs between days 0 and 11 following injury. When symptomatic, vasospasm may be treated with intra-arterial verapamil or balloon angioplasty to restore cerebral perfusion.

References ╇1. Martinakis

VG, Dalainas I, Katsikas VC, Xiromeritis K. Endovascular treatment of carotid injury. Eur Rev Med Pharmacol Sci 2013;17(5):673–688 ╇2. Abujamra L, Joseph MM. Penetrating neck injuries in children: a retrospective review. Pediatr Emerg Care 2003;19(5):308–313 ╇3. Vick LR, Islam S. Adding insult to injury: neck exploration for penetrating pediatric neck trauma. Am Surg 2008;74(11):1104–1106 ╇4. Beitsch P, Weigelt JA, Flynn E, Easley S. Physical examination and arteriography in patients with penetrating zone II neck wounds. Arch Surg 1994;129(6):577–581 ╇5. Hall JR, Reyes HM, Meller JL. Penetrating zone-II neck injuries in children. J Trauma 1991;31(12):1614–1617 ╇6. Hogan AR, Lineen EB, Perez EA, Neville HL, Thompson WR, Sola JE. Value of computed tomographic angiography in neck and extremity pediatric vascular trauma. J Pediatr Surg 2009;44(6):1236–1241, discussion 1241 ╇7. du Toit DF, van Schalkwyk GD, Wadee SA, Warren BL. Neurologic outcome after penetrating extracranial arterial trauma. J Vasc Surg 2003;38(2):257–262 ╇8. Mackay MT, Wiznitzer M, Benedict SL, Lee KJ, Deveber GA, Ganesan V; International Pediatric Stroke Study Group. Arterial ischemic stroke risk factors: the International Pediatric Stroke Study. Ann Neurol 2011;69(1):130–140 ╇9. Jones TS, Burlew CC, Kornblith LZ, et al. Blunt cerebrovascular injuries in the child. Am J Surg 2012;204(1):7–10 10. Fullerton HJ, Johnston SC, Smith WS. Arterial dissection and stroke in children. Neurology 2001;57(7):1155–1160 11. Roach ES, Golomb MR, Adams R, et al; American Heart Association Stroke Council; Council on Cardiovascular Disease in the Young. Management of stroke in infants and children: a scientific statement from a Special Writing Group of the American Heart Association Stroke Council and the Council on Cardiovascular Disease in the Young. Stroke 2008;39(9):2644–2691 12. Ricotta JJ, Aburahma A, Ascher E, Eskandari M, Faries P, Lal BK; Society for Vascular Surgery. Updated Society for Vascular Surgery guidelines for management of extracranial carotid disease: executive summary. J Vasc Surg 2011;54(3):832–836 13. Larson PS, Reisner A, Morassutti DJ, Abdulhadi B, Harpring JE. Traumatic intracranial aneurysms. Neurosurg Focus 2000;8(1):e4 14. O’Brien NF, Reuter-Rice KE, Khanna S, Peterson BM, Quinto KB. Vasospasm in children with traumatic brain injury. Intensive Care Med 2010;36(4):680–687

47

Abusive Head Injuries Shenandoah Robinson

47.1╇Background

47.1.2╇ Initial Evaluation

In developed countries, trauma is the leading cause of death for infants and children who were born healthy. Improved safety measures, such as the use of helmets with sports, and improved car safety have promulgated the decline in traumatic brain injuries (TBI) among children and young teens. Mortality and serious morbidity from TBI have failed to decline as rapidly among infants and toddlers, in large part due to the sustained incidence of abusive head trauma (AHT). AHT knows no social, religious, ethnic, or geographic bounds. In the United States, wide differences in the incidence and patterns of AHT exist,1 and a recent increase in the incidence of AHT occurred during the most recent recession.2 A single-institution study found that one-third of head injuries in children younger than age 2 years were inflicted.3 Thus, for all infants with altered mental status or traumatic injuries, AHT should be included in the differential diagnosis.

The description of any precipitating event should be elicited by multiple providers over time to assess consistency, and to correlate the mechanism provided with the injuries sustained. Red flags for further investigation include: changing stories, a mechanism incompatible with the infant’s developmental stage (a 2-month-old infant generally is not able to roll itself off a couch or bed), presentation of the infant for medical care by someone who was not present at the time of injury, a delay in presentation for care, evaluations at multiple different hospitals within a few months, multiple injuries, and siblings who have been placed in protective custody. It is not unusual for descriptions of fever, intercurrent illness, difficulty breathing or other non–central nervous system (CNS)-related symptoms to be offered.

47.1.1╇Screening In general, all children younger than age 2 years who present with altered mental status of unknown etiology, and all who experienced reported traumatic events, should have a baseline screening evaluation by a social worker or other provider who is familiar with recognizing AHT and related concerns. Although the infant may not have suffered direct inflicted trauma, the child may have suffered injuries unnecessarily due to poor supervision or lack of knowledge, substance abuse, or domestic violence. By screening all infants, any suggestion of bias in the diagnostic process is diminished.

47.1.3╇Examination On examination, external signs of injury may or may not be present. Any scars, bruises, burns, or other worrisome lesions should be documented by hospital security services using their established protocols for the appropriate chain for collection of evidence. Altered mental status, irregular respiration, or a worrisome cry may be present. Seizures, often subclinical, may occur in 50% of infants over the acute and subacute period. Seizures may manifest in infants as a fluctuating mental status. The head circumference should be measured and compared to prior measurements obtained from the primary care physician during well-child visits. The fontanel may be full and tense, and cranial sutures may be splayed. Scalp veins may be engorged secondary to elevated intracranial pressure. Dilated pupils, setting-sun, or sixth

379

380 Section Vâ•… Trauma nerve palsies may be present. Any focal neurological deficits, such as significant hand preference or gaze deviation, are noted. Hand preference should not be apparent in infants younger than age 1 year. A full dilated funduscopic examination by an ophthalmologist is necessary to document any retinal hemorrhages, detachments, or other abnormalities. The examination can be useful to aid in establishment of the diagnosis but does not need to be done urgently. In the acute period, pharmacological dilatation of the pupils can potentially obscure serial neurological examinations. Evidence of retinal hemorrhages typically persists for up to 2 weeks, and the examination can thus be delayed for 1 to 2 days if needed to preserve the pupil examination. If trauma is suspected, consultation with the trauma service is warranted. Some infants with inflicted trauma suffer additional injuries to the chest or abdomen, in addition to skeletal injuries.

47.1.4╇Imaging Depending on the acuity and availability, either computed tomography (CT) or magnetic resonance imaging (MRI) of the brain can be obtained for the initial imaging. Emergent imaging is warranted as soon as traumatic injury is added to the list of differential diagnoses. If the child is already receiving medical care, it is important to image early to prevent any abnormalities from being attributed to the medical care rather than the precipitating trauma. At many centers, a CT can be obtained most expeditiously to determine whether urgent operative intervention is needed (Fig 47.1). Other neurosurgical emergencies in the differential diagnosis for an infant with a tense fontanel and poor neurological status include acute hydrocephalus and subdural empyema or abscess. When the patient has been stabilized, an MRI of the brain and spine is warranted to document potential additional injuries, and the progression of any initial abnormalities observed on the CT scan. MR angiography (MRA) is useful to identify vessel injury in the neck or head. Additionally, MR venography (MRV) is useful to identify venous thrombi. Many infants experience a prolonged period of poor oral intake or emesis prior to receiving medical care and can develop intracranial venous thrombi due to dehydration. Head ultrasound (US) is not recommended because extra-axial collections of different ages are difficult to visualize well on US, and other lesions,

such as stroke, can be more challenging to detect. It cannot be emphasized enough that information from the clinical presentation and CNS imaging need to be integrated to achieve an accurate diagnosis, and this is usually done by a team that includes neurosurgeons, neurologists, critical care physicians, child protection pediatricians, and neuroradiologists. A skeletal survey is performed to identify any acute or chronic bone injuries. Only about 20% of children with inflicted intracranial injuries have injuries identified on the skeletal survey. Even if the prognosis is quite grave, the skeletal survey can be helpful in establishing the time course and extent of injuries.

47.1.5╇ Additional Laboratory Studies Depending on the situation, additional laboratory studies are warranted. If intracranial hemorrhage is present, a hematological evaluation should be undertaken to demonstrate that platelets and clotting are normal. A few infants may have vitamin K deficiency. Metabolic diseases that predispose to subdural hematomas or hygromas, such as glutaric acidosis, are rare. Most infants with such metabolic diseases are diagnosed with the disorder by presenting with seizures and developmental delay, and the subdural collections are diagnosed as the encephalomalacia progresses. It is exceedingly unlikely that a previously healthy infant will present with subdural collections from such a metabolic disease; however, the testing may be warranted to help establish the diagnosis of AHT. Similarly, although infection like bacterial meningoencephalitis causes subdural hygromas, it is rare for the infant to present with symptoms from the hygromas without a serious precipitating illness. Blood product administration will complicate obtaining these tests. Ideally, blood samples are drawn prior to any blood product administration, but this is not always possible in a critically ill infant.

47.1.6╇Documentation Clear, consistent documentation is best for every patient, but it is especially important for potential prosecution of AHT cases. Unless a perpetrator confesses, successful prosecution can be quite challenging and is typically under 20%. The medical team’s

47 â•… Abusive Head Injuries

a

b

c

d

e

f

g

h

i

j

k

l

Fig. 47.1â•… Computed tomography (CT) images from three infants illustrate the differences between (a–d) a normal infant, (e–h) an infant who was inadvertently dropped and suffered an isolated nondisplaced occipital skull fracture, and (i–l) an infant who suffered abusive head trauma (AHT) and expired. Images from the level of the skull base show patent cisterns in the normal infant and the infant with skull fracture, whereas the infant with AHT has no subarachnoid cisterns present, but has scalp edema, acute hemorrhage over the tentorium, (j) a right suboccipital skull fracture that extends superiorly, (i, j) and areas of supratentorial and infratentorial hypodensities consistent with stroke. Images from the level of the frontal horns and the top of the brain show patent subarachnoid spaces and no parenchymal abnormalities in the normal infant (b,c) and the infant with a skull fracture (f,g), with very minimal scalp edema overlying the fracture (f). By contrast, the infant with AHT has almost no subarachnoid space, acute hemorrhage along the falx, (j) bilateral loss of the gray/white junction in the cortex, and (k) significant bilateral scalp edema with a left fracture near the vertex. Bone windows from the normal infant (d) and infant with an isolated skull fracture (h) show patent but opposed cranial sutures. The occipital skull fracture with overlying scalp edema is shown (h). Bone window image from the infant with AHT shows splayed coronal and lambdoid sutures (l) plus a left parietal skull fracture, and bilateral scalp edema.

role is to provide accurate, nonjudgmental documentation that will withstand cross-examination by a defense attorney. Any discrepancy or perceived error or lapse in the evaluation will be capitalized on to bring into question the entirety of the infant’s medical care, particularly the diagnosis. A structured protocol for the evaluation of these children can be quite helpful.

47.1.7╇ Operative Interventions A small subset of infants will present with a large epidural or subdural hematoma with mass effect that warrants emergent evacuation via a craniotomy (Fig 47.2). Most will have subdural collections of various ages that may or may not require drainage to relieve pressure on the brain. There are several tech-

381

382 Section Vâ•… Trauma a

b

d

e

c

f

Fig. 47.2â•… A previously healthy, developmentally normal 20-month-old boy was reportedly found unresponsive by his mother midmorning and was brought immediately to the hospital by ambulance. He had been observed to be alert and playing an hour before. Upon presentation to medical care, he was hypothermic, hypertensive, intubated, and unresponsive to painful stimuli, with the left pupil 7 mm and the right pupil 5 mm, both unreactive to light. (a–f) An emergently obtained computed tomography (CT) scan demonstrated a left acute subdural hematoma both over the convexity and along the falx, (b) effaced cisterns, (c,d) midline shift, and bilateral supratentorial ischemia relative to the cerebellum (b). The patient died from his abusive head trauma (AHT).

niques for managing subacute and chronic subdural hematomas or hygromas. Many will resolve eventually without operative intervention, once the infant is no longer experiencing recurrent episodes of head injury.

future shunt in case permanent diversion of subdural hygroma fluid or ventricular cerebrospinal fluid (CSF) is needed.

Preoperative Planning

A craniotomy of an epidural or subdural hematoma is performed using the standard techniques applicable to older patients. Significant care is taken throughout to minimize blood loss and to adequately replace estimated losses. Many of these infants have suffered hypoxic-ischemic or vascular injury in addition

The infant should be stabilized as best as possible and may need blood products. Incisions for either a craniotomy or burr hole drainage of subdural hematomas should be planned to accommodate a

Key Steps

47 â•… Abusive Head Injuries to hemorrhage, and secondary insult due to anemia should be minimized. In younger infants, burr holes for subdural hematoma drainage or as a starting point for a craniotomy can be made from the open cranial sutures. Craniotomies can be fashioned with a craniotome or heavy scissors. Significant craniocerebral disproportion may exist, and thus dural tack-up sutures may be needed. A watertight dural closure is desired because these infants are at risk for later development of a leptomeningeal cyst. Bone flaps can be secured in place with sutures. If the brain is quite swollen, one option may be to secure the bone flap with a suture at one point. This will allow room for swelling and avoid some of the long-term challenges of a cranioplasty in a growing infant. Most surviving infants will be neurologically devastated, and many will need supplemental nutrition with a gastrostomy tube. There are several techniques for managing subdural hematomas or hygromas. Some prefer to initially drain the fluid with a tap at the lateral aspect of the fontanel using a needle. The authors have typically placed a drain unilateral to the largest collection. Care is taken to plan incisions to facilitate later placement of a permanent shunt if needed. Placing the drain in the operating room (OR) provides optimal management of these often critically ill infants and allows a better chance of draining collections of multiple ages. In many cases, even if bilateral collections are present, a single drain may be adequate. The color of the fluid drained, especially any differences among collections of multiple ages, can provide useful information. For the drain, a ventricular catheter is soft and pliable and is perhaps least likely to inadvertently penetrate the underlying brain. Other types of catheters are also routinely used. The catheter should be positioned with the tip pointing posteriorly to improve the drainage of residual fluid when the child is lying supine. The authors typically drain the fluid with the bag set at the tragus, and then, once the fluid starts to clear, gradually wean the drainage by raising the height of the drainage bag. In the majority of infants, temporary drainage will suffice. Due to the extensive parenchymal injury, many infants will experience significant encephalomalacia that exacerbates the existing craniocerebral disproportion. The decision to insert a permanent shunt should be made after careful review. A few children may require permanent subdural to peritoneal shunting. If available, a 4-cm Leroy catheter is useful because it provides a reservoir to tap and collect specimens if needed, and the catheter is at a slight angle from the reservoir, which allows it to remain in the extra-axial space.

Hazards Children who suffer AHT often present for medical care hours to days after the injury, and thus may be severely dehydrated, anemic, or suffering from additional undiagnosed injuries. When emergency procedures are needed without the luxury of time for a thorough preoperative evaluation, extra vigilance must be exercised to minimize additional complications.

Salvage and Rescue Complications from drainage of subdural hematomas are rare but do occur. Subacute and chronic subdural hematomas may be associated with encephalomalacia and increase the risk of inadvertent conversion to an acute subdural hematoma. Also, care must be taken when fractures are in close proximity to the sagittal or transverse sinuses.

47.2╇ Outcomes and Postoperative Course Infants and children with AHT are vulnerable to numerous complications of critical illness and typically benefit from multidisciplinary care from neurologists, intensivists, child protection specialists, trauma surgeons, and neurosurgeons. Infants with AHT are at high risk for seizures, which can be subclinical.4 Seizures and their treatment can complicate observation of the neurological examination, for example, during attempted weaning of a subdural drain. Completion of the full evaluation for inflicted injuries, such as documentation of the presence or absence of retinal hemorrhages, often occurs in the postoperative period. The entire team should be aware of any pharmacological manipulation of the pupils for a funduscopic examination. Thus, care for these infants requires thorough and frequent communication among the teams. If unilateral drainage of a subdural hematoma fails to adequately drain the contralateral side, then additional surgery is indicated in a timely fashion. Similarly, if weaning of the subdural drain fails, the drain will need to be converted to a subdural peritoneal shunt.

47.2.1╇ Long-Term Outcome Many children with AHT suffer chronic neurological deficits, including developmental delay, cerebral palsy, and epilepsy. Ideally, these children are followed in a multidisciplinary clinic throughout

383

384 Section Vâ•… Trauma childhood. The risk of epilepsy is proportional to the degree of head injury and will increase with time.

References ╇1. Berger

RP, Fromkin JB, Stutz H, et al. Abusive head trauma during a time of increased unemployment: a multicenter analysis. Pediatrics 2011;128(4):637–643 ╇2. Huang MI, O’Riordan MA, Fitzenrider E, McDavid L, Cohen AR, Robinson S. Increased incidence of nonacciden-

tal head trauma in infants associated with the economic recession. J Neurosurg Pediatr 2011;8(2):171–176 ╇3. Dashti SR, Decker DD, Razzaq A, Cohen AR. Current patterns of inflicted head injury in children. Pediatr Neurosurg 1999;31(6):302–306 ╇4. Arndt DH, Lerner JT, Matsumoto JH, et al. Subclinical early posttraumatic seizures detected by continuous EEG monitoring in a consecutive pediatric cohort. Epilepsia 2013;54(10):1780–1788

48

Cranioplasty Jordan P. Steinberg and Arun K. Gosain

48.1╇Background 48.1.1╇Indications Cranioplasty refers to the surgical repair of skull defects. Acquired defects may arise directly from trauma, or secondarily from surgery to treat trauma, intracranial vascular events, or tumors. In the latter situation, a portion of the skull may be removed to permit swelling of the brain (decompressive craniectomy). Although large sections of calvaria may subsequently be replaced, infection or tumor infiltration may preclude this strategy and necessitate more complex reconstruction. Cranial contour abnormalities may result directly from trauma or secondary repair of traumatic defects. Moreover, contour abnormalities may be seen in congenital deformities, including craniosynostosis, or as secondary effects from the surgical correction of such deformities. Undercorrection of craniosynostosis, relapse of the original deformity, or new deformities induced by surgery may require delayed cranioplasty.

48.1.2╇Goals The goals of cranioplasty include the restoration of an aesthetically pleasing cranial shape and contour as well as the provision of adequate protection for the underlying brain. Autogenous bone graft, obtained from sites like calvaria, iliac crest, rib, and tibia, has long served as the standard working material for reconstruction. Wolfe and colleagues have demonstrated complication rates of less than 1% with harvests from each of the aforementioned sites and continue to advocate for both the safety and superiority of bone grafts with proper training and technique.1 It is clear today, however, that long-term results of cranioplasty with autogenous bone are

often plagued by unpredictable maintenance of volume and/or shape. In addition, donor-site limitations must be taken into account, particularly in the pediatric population where adequate autogenous bone may not be available for reconstruction. These factors have contributed to a tremendous expansion in the development and utilization of alloplastic materials in cranioplasty over the past 25 years. A discussion of these materials, as well as tips and caveats regarding their use, is the focus of this chapter.

48.1.3╇ Alternate Procedures A variety of alloplastic materials, ranging from inert titanium metal to more recently characterized “biomaterials,” are commercially available for cranioplasty. The latter derive their name from a purported ability to augment or replace native tissue functions. For the reasons previously stated, cranioplasty with the use of biomaterials has become a popular alternative to reconstruction with autogenous bone graft. Broadly, biomaterials may be grouped into three categories: calcium phosphate cement pastes, osteoactive biomaterials, and prefabricated polymers (Table 48.1).2 Calcium phosphate preparations, predominantly in the form of hydroxyapatite, have been used in ceramic forms dating back to 1970. Despite a macroporous architecture allowing bony ingrowth, these forms are brittle, difficult to mold, and structurally unstable. Hydroxyapatite or carbonated apatite cement pastes, available since 1992, are much more easily shaped intraoperatively, have fast setting times, and show enhanced stability and strength. As a result, cement pastes have become the most common preparations of calcium phosphate in use today. Osteoactive biomaterials include bioactive glass, demineralized bone matrix (DBM), and novel agents, such as recombinant human bone morpho-

385

386 Section Vâ•… Trauma Table 48.1â•… Biomaterials for cranioplasty Biomaterial

Composition

Unique features

Manufacturer

BoneSource

Hydroxyapatite

Thick granular paste

Stryker

HydroSet

Hydroxyapatite

Injectable; useful for sealing cervices

Stryker

Mimix

Hydroxyapatite

Larger pore size; fast curing times

Biomet

Norian

Carbonated apatite/dahllite

Injectable paste of fast-set putty

Synthes

NovaBone

Bioactive glass

Production of interface apatite layer and direct bond to host bone as well as bone replacement

Porex/Stryker

Demineralized bone matrix

Processed human bone tissue (including bone morphogenetic protein)

Porous and easily molded paste; scaffold for bone replacement but lacking structural support until mineralization occurs

Synthes

Infuse bone graft

Recombinant human bone morphogenetic protein-2 (rhBMP-2)

May result in thinner bone production; lack of initial structural support; uncertain safety profile

Medtronic

Adipose-derived stem cells

–

Experimental at this time

–

PMMA

Polymethylmethacrylate

Inexpensive, strong, stable; can be quickly prepared; risk of infection

–

Medpor

Porous polyethylene

Permits fibrovascular, bone ingrowth; risk of infection, extrusion

Porex/Stryker

Hard tissue replacement polymer (HTRP)

PMMA/polyhydroxyethylmethacrylate

Permits fibrovascular ingrowth; negative surface charge to deter bacteria

Biomet

PEEK

Polyetheretherketone

Inert, lightweight, stiff; heat/ radiation resistant; easily modified/ drilled/fixated; excellent orbitofronto-temporal reconstruction

Synthes

Calcium phosphate cements

Bioactive materials

Prefabricated polymers

genetic protein-2 (rhBMP-2). These materials allow bony ingrowth and replacement via osteoconductive, osteoinductive, and/or osteogenic properties. Finally, prefabricated polymers include materials like polymethylmethacrylate (PMMA), porous polyethylene, hard tissue replacement polymer (HTRP), and polyetheretherketone (PEEK). Polymeric materials provide structural integrity, are nonresorbable, and may be prefabricated with computer-aided design/computeraided manufacturing (CAD/CAM) technology using the unaffected side in a mirrored fashion.3

48.1.4╇Advantages The ideal alloplastic material for cranioplasty has been described as: (1) capable of inducing tissue ingrowth; (2) strong enough to protect the underlying brain; (3) easily shaped to fill a calvarial defect or restore contour; (4) stable over the patient’s lifetime or, if resorbed, replaced by structurally stable bone; (5) biocompatible without inducing a significant inflammatory or reactive tissue response; (6) radiolucent; and (7) nonallergenic, noncarcinogenic, and

48 â•… Cranioplasty non–disease-transmitting.4 Numerous case series and reviews have highlighted the advantages and disadvantages of cranioplasty with titanium, calcium phosphate cements, bioactive materials, and prefabricated polymers with respect to the alreadymentioned criteria. However, general guidelines governing the selection of particular materials for particular applications have heretofore been lacking. Also lacking is a delineation of which specific cases may be best reconstructed by means of autogenous bone grafting, using either traditional means as reviewed by Wolfe and colleagues5 or particulate grafting as described by Greene et al.6 Clinical and translational research over the past decade on the use of alloplastic materials have led us to the algorithm depicted in Fig. 48.1. As discussed in detail, well-characterized shortcomings of various materials govern flow in this empirically derived scheme. Decision points focus hierarchically on: (1) the degree to which skeletal growth is complete at the time of cranioplasty; (2) whether inlay or onlay reconstruction is required; and (3) the forces to be borne by the reconstructed area (i.e., load-bearing vs. non–load-bearing).2

48.1.5╇Contraindications Absolute contraindications to cranioplasty are few and typically just necessitate a delay in reconstruction. Active intracranial infection or osteomyelitis of replaced calvarial bone often requires at least a 6-month period for clearance of the infection after washout and/or bone removal. Large cerebrospinal fluid leaks may also mandate a staged reconstruction until the appropriate interventions have been taken to control the leak. Conditions associated with increased intracranial pressure may likewise demand a staged approach. Finally, in cases of malignancy involving calvarial bone, final reconstruction should await confirmation of negative margins. Relative contraindications to the use of specific alloplastic materials in cranioplasty deserve mention. Of particular focus are calcium phosphate cement pastes, which have been extensively used for a variety of craniofacial applications. Although early animal studies suggested significant bone replacement in these products, subsequent reports failed to confirm evidence of bony ingrowth into

Fig. 48.1â•… Algorithm to guide the choice of alloplastic materials for use in cranioplasty. (Used with permission from Gosain et al.2)

387

388 Section Vâ•… Trauma the microporous architecture of many commercially available preparations. Whereas osteoconduction and osteoinduction may be seen with pastes engineered to contain tricalcium phosphate, a rapidly resorbing component leading to macropore formation and therefore bony ingrowth, pure hydroxyapatite cement pastes show bone growth only around the periphery of the material.7 This has now been confirmed clinically by a number of groups using a variety of commercially available products.2,8 It is the contention of the authors that, with a lack of evidence of bone replacement, calcium phosphate cement pastes should be used with caution in the cranial vault before age 3 years, while growth is still occurring. This relative contraindication also pertains to polymers, since these implants also do not allow bony ingrowth to any significant extent. In addition to growth considerations, communication with the paranasal sinuses should be regarded as a relative contraindication to the use of calcium phosphate cements and polymers. Higher rates of infection have been shown with both alloplasts in this setting. Limited tissue integration in the presence of a contaminated environment likely explains this association.8

48.2╇ Operative Detail and Preparation 48.2.1╇ Preoperative Planning and Special Equipment Planning, execution, and risks/pitfalls of autogenous bone grafting, in particular split calvarial grafting, have been well described by Wolfe and colleagues5 and are therefore not discussed here. In accordance with the algorithm shown in Fig. 48.1, the authors focus here on the use of calcium phosphate cements for onlay augmentation in skeletally mature children, the use of bioactive material for inlay calvarial reconstruction in variably aged children, and the use of prefabricated polymers for onlay or inlay applications in older children. Selection is guided by the algorithm, with complexity of the defect as an added consideration when multiple materials are appropriate. Complex orbito-fronto-temporal defects are notoriously difficult to reconstruct accurately with

manual molding of materials and are good candidates for CAD/CAM-prefabricated implants in skeletally mature patients. A high-resolution computed tomography (CT) scan is required for this process and is sent to the manufacturer, who then develops a model and custom implant based on the existing/anticipated defect and the contralateral normal anatomy.3 A CT scan is useful in all cases to precisely delineate areas of deficiency to be reconstructed. No particular equipment is needed for the application of calcium phosphate cement paste as an onlay. For inlay reconstruction with bioactive glass or DBM, the authors advocate the placement of a resorbable plate (or, in skeletally mature patients, titanium mesh) to support the material until mineralization occurs. For polymeric implants, the ability to drill through the material and secure it to surrounding bone with titanium miniplates and screws gives the most stable fixation.

48.2.2╇ Expert Suggestions/Comments A few points regarding exposure are noteworthy: 1. The authors’ favored initial approach to the cranial vault involves a subgaleal plane of dissection. This allows preservation of the pericranium, which may serve as an additional layer for revascularization (Fig.€48.2). Moreover, it enables the raising of a pericranial flap that can be useful for covering the final reconstruction or to obliterate the frontal sinus or its associated outflow tract. 2. A cuff of temporalis muscle should be left at the superior temporal crest before transitioning to a subpericranial plane of dissection over the temporal fossa and forehead. This aids in resuspension of the temporalis at the end of the case (Fig. 48.2). This resuspension, along with care taken to avoid simultaneous dissection on both superficial and deep sides of the temporalis muscle, helps to avoid temporal atrophy and hollowing that may otherwise require revision surgery in the future. This alone is often an indication for secondary cranioplasty in children following craniosynostosis correction.

48 â•… Cranioplasty

Fig. 48.2â•… Approach to the cranium in a case of bicoronal synostosis. Note the subgaleal plane of dissection up to the forehead region (large yellow arrows), with preservation of the pericranium down on the bone to enable a pericranial flap to be raised later if needed. Also note the cuff of temporalis muscle left behind at the transition to a subpericranial plane in the temporal fossa for later resuspension of the temporalis muscle (black arrows).

48.2.3╇ Key Steps of the Procedure/ Operative Nuances The whole scalp is shaved to accurately mark a sinusoidal incision for the coronal approach, with posterior flares above the ears to avoid the superficial temporal vessels and at the crown to avoid visibility in the event of male pattern alopecia (Fig. 48.3). Exposure proceeds as described in the previous section. Onlay application of calcium phosphate cement paste begins with preparation of the paste according to the manufacturer’s instructions. BoneSource (Stryker, Kalamazoo, MI, USA), for example, is prepared by mixing tetracalcium phosphate powder and anhydrous dicalcium phosphate powder in a sodium phosphate solution, yielding a paste with a setting time of 5 to 8 minutes. The paste can then be molded by hand to areas of temporal hollowing

or frontal depression. For inlay application of bioactive glass or DBM, resorbable plates are placed as support over the dura, as noted previously. NovaBone (Stryker, Kalamazoo, MI, USA) bioactive glass is mixed in a 1:1 fashion with particulate bone material obtained from cranial burr holes, then developed into a paste consistency by mixing with autologous whole blood. Application of NovaBone (Stryker) is shown in Fig.€48.4 and Fig.€48.5. Inlay reconstruction with polymeric implants is performed by burring down prefabricated implants as necessary to obtain optimal fit, then fixating as previously mentioned with the use of titanium miniplates and screws. A fluted Blake drain is placed out of contact with the alloplastic material and left in place for 48 hours postoperatively. The dressing is removed on the 3rd postoperative day. A postoperative baseline CT scan is generally obtained before the patient leaves the hospital, and again at 6 months to 1 year.

389

390 Section Vâ•… Trauma a

b

c

Fig. 48.3â•… Coronal incision pattern. A sinusoidal incision is marked equidistant from a line established from ear to ear with the use of a heavy silk suture. The incision flares posteriorly above the ears to avoid the superficial temporal vessels, and posteriorly at the crown to minimize visibility where hairline recession may occur in later ages. (a) Crown view. (b) Left side. (c) Right side.

48.2.4╇ Hazards/Risks/Avoidance of Pitfalls Although other authors have described inlay reconstruction with calcium phosphate cement pastes, the authors of this chapter have generally avoided this application for the following reasons: (1) lack of bony ingrowth as previously stated, making this a potentially unstable reconstruction in the long term; and (2) an increased incidence of complications, par-

ticularly with full-thickness defects greater than 5 cm (or 25 cm2).8 With regard to the latter, the authors have adopted this general size criterion even for the use of bioactive glass/DBM because they have noted variable mineralization with larger defects. Previous radiation or thinning of the scalp tissues should be noted preoperatively. These factors increase the risk for wound complications. If necessary, soft tissue augmentation should be addressed prior to cranioplasty to minimize the chances of breakdown.

48 â•… Cranioplasty a

b

c

d

e

f

Fig. 48.4â•… Use of bioactive glass as an inlay in 40-year-old patient with Crouzon syndrome requiring cranial vault remodeling. (a) Thumb printing of the frontal bone is evident from pressure of the underlying brain. (b) NovaBone (Stryker, Kalamazoo, MI, USA) is prepared in a 1:1 mixture with particulate bone material obtained from cranial burr holes and autologous whole blood. (c) The supraorbital bandeau and frontal bone flap are repositioned to allow a more normal forehead contour. (d) Bone gaps are spanned with resorbable plates over exposed dura to establish a scaffold for NovaBone (Stryker). (e,f) NovaBone (Stryker) is placed into the bony gaps that would otherwise not be expected to ossify in this adult patient.

391

392 Section Vâ•… Trauma a

b

c

d

Fig. 48.5â•… Photographic and tomographic images of 40-year-old patient with Crouzon syndrome after cranial vault remodeling and use of bioactive glass for inlay cranioplasty. (a) Preoperative frontal photograph. (b) A 6-month postoperative frontal view. (c) Preoperative lateral photo. (d) A 6-month postoperative lateral image showing marked improvement in forehead flattening.

48 â•… Cranioplasty e

f

Fig. 48.5 (Continued)â•… (e) A 1-week postoperative computed tomography (CT) scan. (f) A 6-month postoperative CT scan demonstrating conversion of the majority of the reconstructed defect to bone density and a stable reconstruction with no need for reoperation.

393

394 Section Vâ•… Trauma

48.2.5╇ Salvage and Rescue Salvage and rescue of alloplastic cranioplasty hinges on the nature of the specific complication (see last section). In general, fluid collections or infections may first be treated with aspiration and culturespecific antibiotics. Failure to resolve with antibiotics necessitates operative exploration, débridement of any inciting agents, such as fragmented material or sinus mucosa, and, in chronic cases, complete removal of the alloplast with delayed cranioplasty using a distinct approach. Although failure of one alloplastic reconstruction (e.g., PMMA) does not necessarily portend failure with another method (e.g., PEEK), the authors recommend switching to another category of implant if possible at the time of secondary reconstruction (exchanging nonporous PEEK for porous polyethylene or autogenous bone graft).

48.3╇ Outcomes and Postoperative Course 48.3.1╇ Postoperative Considerations As noted earlier, a baseline CT scan is useful to obtain in the immediate postoperative period, particularly with osteoactive materials through which bone growth is later expected. Patients should be followed closely in the first few months to assess symmetry and contour as edema resolves. Grading systems, such as those described by Marchac and Greensmith,9 may be used to more objectively evaluate appearance. For tumors, follow-up imaging should be performed according to protocol, in which case a radiolucent alloplastic material is desirable.

48.3.2╇Complications In contrast to the marked resorption often seen with autogenous bone graft, alloplastic materials have more long-term stability. Unfortunately, this stability is often at the expense of significant bony ingrowth, as has been noted for microporous calcium phosphate cements. The lack of complete replacement by, and integration

with, native bone increases the risk for complications with these materials even years after surgery. Microfragmentation and associated seroma or chronic lowgrade infection requiring reoperation have been seen with calcium phosphate cements.8 Late infections have also been noted with polymeric implants, in most cases due to occult sinus communication.9

References ╇1. Tessier

P, Kawamoto H, Posnick J, Raulo Y, Tulasne JF, Wolfe SA. Complications of harvesting autogenous bone grafts: a group experience of 20,000 cases. Plast Reconstr Surg 2005;116(5 Suppl):72S–73S, discussion 92S–94S ╇2. Gosain AK, Chim H, Arneja JS. Application-specific selection of biomaterials for pediatric craniofacial reconstruction: developing a rational approach to guide clinical use. Plast Reconstr Surg 2009;123(1):319–330 ╇3. Rudman K, Hoekzema C, Rhee J. Computer-assisted innovations in craniofacial surgery. Facial Plast Surg 2011;27(4):358–365 ╇4. Magee WP Jr, Ajkay N, Freda N, Rosenblum RS. Use of fast-setting hydroxyapatite cement for secondary craniofacial contouring. Plast Reconstr Surg 2004;114(2):289–297 ╇5. Tessier P, Kawamoto H, Posnick J, Raulo Y, Tulasne JF, Wolfe SA. Taking calvarial grafts, either split in situ or splitting of the parietal bone flap ex vivo—tools and techniques: V. A 9650-case experience in craniofacial and maxillofacial surgery. Plast Reconstr Surg 2005; 116(5 Suppl):54S–71S, discussion 92S–94S ╇6. Greene AK, Mulliken JB, Proctor MR, Rogers GF. Pediatric cranioplasty using particulate calvarial bone graft. Plast Reconstr Surg 2008;122(2):563–571 ╇7. Gosain AK, Riordan PA, Song L, et al. A 1-year study of osteoinduction in hydroxyapatite-derived biomaterials in an adult sheep model: part II. Bioengineering implants to optimize bone replacement in reconstruction of cranial defects. Plast Reconstr Surg 2004;114(5):1155– 1163, discussion 1164–1165 ╇8. Afifi AM, Gordon CR, Pryor LS, Sweeney W, Papay FA, Zins JE. Calcium phosphate cements in skull reconstruction: a meta-analysis. Plast Reconstr Surg 2010;126(4): 1300–1309 ╇9. Marchac D, Greensmith A. Long-term experience with methylmethacrylate cranioplasty in craniofacial surgery. J Plast Reconstr Aesthet Surg 2008;61(7):744–752, discussion 753

49

Neurointensive Care of Head Injuries Ash Singhal and Alexander Ross Hengel

49.1╇Background Head injuries are one of the leading causes of death and disability in children and young adults between ages 1 and 18 years.1,2 Despite representing a modest proportion of all head injuries, severe traumatic brain injuries (TBIs) are associated with a high risk of mortality and neurological morbidity in children and young adults.2 Apart from primary prevention efforts and organized trauma systems, the principal ways in which severe TBI outcomes can be improved are by adequate physiological resuscitation, avoidance of secondary neurological injury, and prompt diagnosis and treatment of raised intracranial pressure (ICP). Thus it is important to manage TBI in children in a systematic and evidence-based manner to improve short- and long-term neurological outcomes. The American Association of Neurological Surgeons (AANS) and the Congress of Neurological Surgeons (CNS), together with the American Academy of Pediatrics and Neurocritical Care Society (as well as many other groups), have recently endorsed a set of guidelines for the acute medical management of severe tbi in infants, children, and adolescents.3 This chapter incorporates many of these evidencebased guidelines, to form the basis for consistent and outcomes-oriented best practices for neurointensive care of head injuries.

in children with severe TBI.3–5 However, it should be cautioned that this represents a level III recommendation (formerly “option”) and there is recent evidence in adult TBI that ICP monitoring is not necessarily associated with better outcomes.6

49.1.2╇ Intracranial Hypertension Thresholds Multiple studies have suggested that sustained elevations in ICP above a threshold of 20 mm of mercury (mm Hg) can lead to detrimental neurological outcomes in the pediatric population.3,5 However, ICP and blood pressure are age-dependent in children―the ICP threshold of 20 mm Hg should not be considered as a uniform threshold across all age groups, with infants having a lower ICP threshold, and teenagers having a threshold close to 20 mm Hg. Maintaining ICP thresholds, and using a threshold of 20 mm Hg, is a level III recommendation.3,5 However, a recent prospective randomized study in adult TBI demonstrated that target ICP-based therapies were not superior to other forms of care for adult TBI.6 Nevertheless, sustained elevations of ICP should be aggressively medically managed, and measures to achieve “normal” ICP are discussed below.

49.1.1╇ ICP Monitoring

49.1.3╇ Cerebral Perfusion Pressure (CPP) Thresholds

There are multiple lines of evidence supporting the use of ICP monitors in children. Clinically severe TBI has a high incidence of raised ICP.3 There is a widely reported association between high ICP and poor outcomes. Furthermore, the best published outcomes (in severe TBI) are in the context of systematic approaches to identify and normalize high ICP; successful ICP lowering measures are associated with better clinical outcomes. Intensive monitoring of ICP is recommended

CPP is equal to mean arterial pressure minus mean ICP. Multiple studies have suggested that in the days after TBI, CPP is typically higher in survivors compared to nonsurvivors. However, the causality of this association has never been conclusively determined. Maintaining a minimum CPP of 40 mm Hg in pediatric TBI victims could reduce mortality and poor neurological outcomes and is considered a level III recommendation.3,7 Nevertheless, precise mini-

395

396 Section Vâ•… Trauma mum CPP thresholds have yet to be determined in the pediatric population. Level III evidence also supports maintaining a CPP threshold range in children between 40 and 50 mm Hg.3 In comparison, adult guidelines call for a CPP range between 50 and 60 mm Hg. Because of the discrepancy in CPP thresholds between adults and children, CPP thresholds are likely age-dependent. Maintaining a CPP above a minimum level could allay potential secondary complications; however, there is general agreement in the literature that avoidance of intravascular hypovolemia, volume expansion, and ICP lowering measures are safer and likely more effective measures than improving CPP levels via commencement of inotrope therapy.

saline for the treatment of severe pediatric TBI range between 0.1 and 1 mL/kg of body weight per hour. The minimum dose of continuous 3% saline that achieves and maintains an ICP < 20 mm Hg should be used. There is insufficient evidence supporting the use of mannitol, hypertonic saline that is more concentrated than 3%, and other hyperosmolar agents in the clinical management of severe pediatric TBI. In the case of mannitol, which has not been shown to be detrimental or ineffective but rather is less well studied than 3% saline, clinicians must weigh their comfort with mannitol infusions and dosing against the more robust evidence supporting the use of 3% saline.

49.1.4╇Neuroimaging

Hypothermia therapy has been postulated to reduce mechanisms of secondary injury after severe TBI, by slowing cerebral metabolic demands and by a reduction in ICP. With the results of the HypHIT study, and the lack of any other studies demonstrating beneficial outcomes with refined cooling protocols, therapeutic hypothermia in pediatric TBI remains at best an investigational treatment.9 However, hyperthermia is potentially harmful for the injured brain, causing increased cerebral metabolism and should therefore be avoided.

Neuroimaging is obviously essential in pediatric TBI management because it allows assessment of the intracranial extent and severity of TBI. Computed tomography (CT) can rapidly detect intracranial injury (hemorrhage as well as hypodensity) and bony and soft tissue pathology, making it an ideal imaging technique for head trauma. Although magnetic resonance imaging (MRI) poses less radiation risk to children, it is more difficult to employ acutely after a TBI, owing to access issues, refinement of imaging protocols, and challenges of adequately resuscitating children while in the magnet. It might be that with the current interest in reducing radiation from imaging studies (particularly in children) and fast MRI techniques, MRI will one day supplant CT usage in trauma. Although indications for initial CT scans in TBI are increasingly refined, there is little evidence supporting routine repeat or follow-up imaging.8 Followup imaging has potential risks (radiation, transport of the critically ill child) as well as significant cost. Whereas repeat scanning is necessary where clinical deterioration is present (level of consciousness, ICP issues), there is sufficient evidence to recommend against the use of routine repeat CT scans after pediatric TBI (level III evidence).

49.1.5╇ Hyperosmolar Therapy The use of hypertonic saline (3%) for the acute management of intracranial hypertension in severe pediatric TBI is supported as a level II recommendation (formally known as a “guideline”).3 Acute use of 3% hypotonic saline should be in the range of 6.5 to 10 mL/kg, although many pediatric intensive care practitioners counsel more judicious initial infusions (3 to 5 mL/kg). In addition, there is support for the continuous infusion of hypertonic saline (3%), while the patient is in intensive care for severe TBI (level III recommendation).3 Effective continuous doses of 3%

49.1.6╇Temperature

49.1.7╇ Cerebral Spinal Fluid Drainage The therapeutic drainage of cerebral spinal fluid (CSF) is an option to reduce ICP in severe TBI patients. Level III evidence supports CSF drainage to reduce ICP through the use of an external ventricular drain (EVD), which in practice suggests that EVD is superior to parenchymal ICP monitors, given its potential therapeutic use.3,4 Another option supported by level III evidence is lumbar drainage (provided there is no intracranial mass lesion/shift, and the basal cisterns are open).3

49.1.8╇Hyperventilation Despite a lack of solid scientific evidence supporting its efficacy, hyperventilation therapy has been traditionally used to rapidly reduce raised ICP in pediatric TBI patients, and perhaps its use is justified as a temporizing method in the acute raised ICP situation, such as a herniation syndrome. Level III evidence suggests that prophylactic hyperventilation to an arterial carbon dioxide tension (PaCO2) less than 30 mm Hg should be avoided within the first 48 hours following severe TBI.3,10 When hyperventilation is used to reduce ICP, surgeons and physicians should be mindful of evaluation for cerebral ischemia caused by chronic or aggressive hyperventilation.

49 â•… Neurointensive Care of Head Injuries

49.1.9╇ Antiseizure Prophylaxis Severe pediatric TBI is associated with posttraumatic seizures (PTS), with approximately 10% of pediatric TBI patients developing PTS in the postinjury period.3 To negate the potential issues associated with early PTS (increased oxygen demand, increased cerebral metabolism, and ICP), level III evidence supports the use of phenytoin for prophylactic antiepileptic therapy (7 days postinjury) in the pediatric population. This practice is supported both in the pediatric and adult literature.3 It is important to note that prophylactic phenytoin use in children has no demonstrated impact on improved long-term outcome, and does not diminish the incidence of late posttraumatic epilepsy.

49.1.10╇Corticosteroids Although corticosteroids are useful in the treatment of many pediatric neurological illnesses, evidence from multiple pediatric and adult studies supports a level II guideline recommending that corticosteroids not be used in the treatment of raised ICP in severe pediatric TBI.3 There is no scientific evidence that corticosteroids are correlated with improved neurological outcome, reduced ICP, or decreased mortality in pediatric TBI; and corticosteroids are associated with increased complication rates.

49.1.11╇ Decompressive Craniectomy Decompressive craniectomy (DC) is a surgical modality that is increasingly being utilized in both pediatric and adult TBI, but without clearly defined indications or outcomes. DC is recommended to control medically refractory raised ICP and decreased CPP, persistent neurological deterioration, and cerebral herniation early in the postinjury period (level III recommendation). However, this recommendation is largely based on adult TBI literature. Although the techniques of wide bony decompression and wide duraplasty are now accepted, the authors still await the results of ongoing randomized trials to more clearly characterize patient populations that might benefit from this procedure, as well as the outcomes that can reasonably be expected. When the procedure is offered, the literature suggests that bony decompressions should be large and duraplasty extensive (e.g., bifrontal or unilateral frontotemporoparietal), and the bone should be completely removed instead of left free-floating in place.3 This necessitates an institutional protocol for the banking/freezing of bone (or insertion into a separate patient site, such as the abdominal fat). In children, the resorption rate of reinserted craniotomy flaps is

as high as 50%, and efforts should be taken to reinsert the bone flap as early as possible. Once the acute period of brain swelling has resolved, which is often apparent once the DC site becomes sunken, the bone flap can be safely reinserted―typically within 2 weeks of the DC. Although there remains a relative lack of quality research on DC in the pediatric population, there is a moderate body of research on the use of DC for the treatment of TBI in the adult population. A recent randomized controlled trial demonstrated that early bifrontotemporoparietal DC effectively decreased refractory raised ICP and time spent in the intensive care unit compared to patients undergoing only medical management; however, the results were complicated by the fact that DC patients had a higher risk of unfavorable long-term outcomes compared to patients with medical management only.11 Level III research suggests that the use of DC is associated with improved neurologic outcomes in severe pediatric TBI.3,12 Nevertheless, there is insufficient evidence characterizing factors that optimize the patient selection for DC in children, and ongoing randomized trials might shed further light on the beneficial effects of DC surgery.

49.2╇Conclusion The popularly endorsed guidelines for the acute medical management of severe TBI in infants, children, and adolescents provides neurosurgeons with recent and evidence-based recommendations on how to manage severe TBI in the pediatric population. Stronger levels of evidence (level II) support using 3% saline for the treatment of acute raised ICP, not using corticosteroids, and avoiding 24-hour courses of moderate hypothermia to treat severe pediatric TBI. In addition, level III evidence supports several different pediatric TBI clinical management techniques: (1) maintaining an ICP threshold under 20 mm Hg; (2) maintaining a CPP threshold of 40 mm Hg (range 40–50 mm Hg is age dependent); (3) using DC for intractable raised ICP; (4) using 3% saline as continuous infusion; (5) the use of EVD and lumbar drainage to drain chronically high ICP; (6) the use of barbiturates, thiopental, and etomidate as sedation medications; (7) short-course phenytoin treatment to prevent early post-TBI seizures; (8) avoiding prolonged hyperventilation; and (9) avoiding routine repeat CT imaging. With this set of recommendations, physicians can effectively employ current evidence-based and systematically supported neurointensive management techniques to improve the outcome of severe pediatric TBI.

397

398 Section V╅ Trauma References ╇1. Bowman

SM, Bird TM, Aitken ME, Tilford JM. Trends in hospitalizations associated with pediatric traumatic brain injuries. Pediatrics 2008;122(5):988–993 ╇2. Ducrocq SC, Meyer PG, Orliaguet GA, et al. Epidemiology and early predictive factors of mortality and outcome in children with traumatic severe brain injury: experience of a French pediatric trauma center. Pediatr Crit Care Med 2006;7(5):461–467 ╇3. Kochanek PM, Carney N, Adelson PD, et al; American Academy of Pediatrics-Section on Neurological Surgery; American Association of Neurological Surgeons/ Congress of Neurological Surgeons; Child Neurology Society; European Society of Pediatric and Neonatal Intensive Care; Neurocritical Care Society; Pediatric Neurocritical Care Research Group; Society of Critical Care Medicine; Paediatric Intensive Care Society UK; Society for Neuroscience in Anesthesiology and Critical Care; World Federation of Pediatric Intensive and Critical Care Societies. Guidelines for the acute medical management of severe traumatic brain injury in infants, children, and adolescents—second edition. Pediatr Crit Care Med 2012;13(Suppl 1):S1–S82 ╇4. Jagannathan J, Okonkwo DO, Yeoh HK, et al. Long-term outcomes and prognostic factors in pediatric patients with severe traumatic brain injury and elevated intracranial pressure. J Neurosurg Pediatr 2008;2(4):240–249 ╇5. White JR, Farukhi Z, Bull C, et al. Predictors of outcome in severely head-injured children. Crit Care Med 2001;29(3):534–540

╇6. Chesnut

RM, Temkin N, Carney N, et al; Global Neurotrauma Research Group. A trial of intracranial-pressure monitoring in traumatic brain injury. N Engl J Med 2012;367(26):2471–2481 ╇7. Figaji AA, Zwane E, Thompson C, et al. Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 2: relationship with clinical, physiological, and treatment factors. Childs Nerv Syst 2009;25(10):1335–1343 ╇8. Natale JE, Joseph JG, Rogers AJ, et al; PECARN (Pediatric Emergency Care Applied Research Network). Cranial computed tomography use among children with minor blunt head trauma: association with race/ethnicity. Arch Pediatr Adolesc Med 2012;166(8):732–737 ╇9. Hutchison JS, Ward RE, Lacroix J, et al; Hypothermia Pediatric Head Injury Trial Investigators and the Canadian Critical Care Trials Group. Hypothermia therapy after traumatic brain injury in children. N Engl J Med 2008;358(23):2447–2456 10. Curry R, Hollingworth W, Ellenbogen RG, Vavilala MS. Incidence of hypo- and hypercarbia in severe traumatic brain injury before and after 2003 pediatric guidelines. Pediatr Crit Care Med 2008;9(2):141–146 11. Cooper DJ, Rosenfeld JV, Murray L, et al; DECRA Trial Investigators; Australian and New Zealand Intensive Care Society Clinical Trials Group. Decompressive craniectomy in diffuse traumatic brain injury. N Engl J Med 2011;364(16):1493–1502 12. Weintraub D, Williams BJ, Jane J Jr. Decompressive craniectomy in pediatric traumatic brain injury: a review of the literature. NeuroRehabilitation 2012;30(3):219–223

50

Pediatric Vertebral Column and Spinal Cord Injuries Dachling Pang and Sui-To Wong

50.1╇Background Injuries to the spinal cord and vertebral column are relatively uncommon in children from birth to age 17 years, with incidence of 1 to 10% of all spinal injuries. Data from major pediatric spinal trauma centers indicate that injury to the juvenile spine differs from its adult counterpart in anatomical and biomechanical foundations, mechanism of injury, response to deformation, injury pattern, and outcome.1,2

50.2╇Biomechanical Considerations In contrast to the adult spine, the juvenile vertebral column is inherently more malleable to deforming forces. This physiological hypermobility allows considerable movement between vertebral segments without damage, but at the expense of providing less protection to the underlying spinal cord. Several unique features of the juvenile spine account for this physiological hypermobility. First, the ligaments and joint capsules are elastic and stretchable. Second, owing to their high water content, the intervertebral disks in children are also exceedingly yielding to longitudinal forces, allowing the vertebral column of neonates to lengthen by as much as 2 inches without rupture when distracted. Third, the facet joints are shallow and oriented more horizontally than in adults, permitting translational as well as flexion and extension movements. Fourth, the immature vertebral bodies are wedged anteriorly, which encourages forward slippage. Fifth, the uncinate processes that normally restrict lateral and rotational movements are absent in children younger than age 10 years. Sixth, the biologically active and hypervascular growth zone in the end plate is a potential

site of shifting by splitting readily from the centrum with even moderate shearing. Last, the proportionally large size of the infant’s head and delicate nuchal musculature predispose the neck to wide flip-flop swings when subjected to flexion and extension. Moreover, the upper cervical segments in infants and young children are especially hypermobile in flexion and thus most susceptible to flexion injuries, mainly because the horizontal orientation of the facets and the anterior wedging of the vertebral bodies are more prominent in the upper four cervical segments in this age group. Many of the features of the juvenile spine transform into “adult states” around age 8 or 9 years. In particular, the vertebral bodies become less wedged and more rectangular, the facet joints deepen and become more vertical, the uncinate processes enlarge, and the ligaments gain in tensile strength. With increasing age, the head also assumes a smaller proportion of the body and thus lessens its own lever effect. This biomechanical maturation takes place much more abruptly and successfully in the upper cervical segments, so that the upper neck becomes much more resistant to injury around age 8 years. The lower cervical spine, in contrast, seems to mature more gradually.3,4 The preceding biomechanical data predict the following: (1) in the younger age group (birth to age 8 years), there are fewer fractures and subluxations and more spinal cord injury without radiographic abnormality (SCIWORA); (2) spinal cord injury (SCI) in young children is more severe than in older children (ages 9 to 17 years); (3) there are more upper cervical injuries and more severe cord damage in the very young; (4) there are more fractures and subluxations than SCIWORA but less severe cord injury in older children; and (5) there is a preponderance of lower cervical injuries in older children resembling the adult pattern.5

399

400 Section Vâ•… Trauma

50.3╇ Special Injury Types 50.3.1╇SCIWORA Mechanisms of Spinal Cord Injury The pathogenetic concept of SCIWORA is based on the premise that the inherently elastic juvenile spine can accommodate considerable intersegmental displacement without fracture or ligamentous rupture, but at the expense of the underlying spinal cord. This implies that the stabilizing ligaments and fibrocartilaginous structures, although sufficiently elastic to stretch and recoil without rupturing, are severely sprained or even partially torn to render the spine “occultly unstable” and vulnerable to repeated stress. Four mechanisms may be involved in the pathogenesis: hyperextension, flexion, distraction, and spinal cord ischemia. During violent hyperextension of the juvenile spine, the anterior longitudinal ligament (ALL) ruptures, the intervertebral disk shears from the brittle growth zone of the end plates, and the upper vertebra displaces backward onto the spinal cord (Fig. 50.1). Elastic recoil of the displaced segment enables perfect spontaneous

reduction to give a normal X-ray. Similar conditions as well as the horizontal facets likewise predispose to hyperflexion myelopathy. In addition, the extremely malleable infantile spinal column can stretch up to 2 inches without breakage, but the inelastic spinal cord ruptures if stretched more than 0.25 inches; this undoubtedly accounts for most obstetrical cord injury. In nonobstetrical SCIWORA, the best evidence of distraction is found in cases when the thoracic spine is forcefully distracted in lap-belt injuries. Finally, the precarious architecture of the neonatal atlanto-occipital articulations predisposes the upper cervical cord to ischemic necrosis from vertebral artery occlusion.

Magnetic Resonance Imaging Findings The extraneural soft tissue injury demonstrated on magnetic resonance imaging (MRI) is well correlated with the mechanism of injury.6 For example, rupture of the ALL, widening of the anterior intervertebral space, and anterior disk herniation are found in cases of hyperextension. Rupture of the posterior longitudinal ligament (PLL), posterior disk herniation, intradiskal hemorrhages, and hemorrhages in the

Fig. 50.1â•… Extreme hyperextension mechanism in spinal cord injury without radiographic abnormality (SCIWORA). Rupture of the anterior longitudinal ligament (ALL) (red arrow), posterior listhesis of the upper spinal segments, and impact on the subjacent spinal cord (black arrow). Inset shows split in the vulnerable growth zone of the vertebral end plate secondary to shearing (lower left). Sagittal T2 magnetic resonance imaging (MRI) shows split in the end plate and slight posterior shift of the upper segments that could snap back into place to give a normal X-ray, due to natural recoil of the juvenile spine (right).

50 â•… Pediatric Vertebral Column and Spinal Cord Injuries

Fig. 50.2â•… Magnetic resonance imaging (MRI) of major cord hemorrhage in spinal cord injury without radiographic abnormality (SCIWORA). T1 and T2 axial images in the acute stage show deoxyhemoglobin (isointense on T1; dark on T2 [red arrows]) within more than 50% of the cord (upper). T1 MRI 2 days postinjury showing massive intramedullary bleeding (lower left). T1 MRI 6 months later displays severe atrophy of the cervicothoracic cord (lower right).

interspinous and interlaminar soft tissues are seen with flexion, translational, and distraction injuries. Five patterns of cord findings are seen on the post-SCIWORA MRI: • Complete disruption of the spinal cord is seen in severe distraction injuries in very young children. • Major cord hemorrhage occurs when more than 50% of the cord on axial MRI shows evidence of extravasated hemoglobin (Fig.€50.2). Major hemorrhage is associated with severe deficits and a dismal prognosis. • Minor cord hemorrhage occurs when less than 50% of the cord shows evidence of hemorrhage. It is associated with moderately severe initial deficits but a decent chance for recovery. • Edema only, without hemorrhage, is predictive of a good outcome. • Approximately 35% of patients with clinically proven SCIWORA do not have

MRI abnormalities in their spinal cords. These patients have an excellent prognosis for complete recovery. If the initial MRI is abnormal, a chronic study at 3 to 6 months is obtained to detect syrinx formation and marked atrophy of the cord.

Management and Outcome Patients with SCI but without abnormalities on plain films undergo thin-section, axial computed tomography (CT) with bone algorithms to rule out an occult fracture, followed by MRI. Flexion and extension X-rays of the spine are obtained to rule out overt ligamentous instability. In many patients, severe spasm of the paraspinal muscles precludes adequate immediate dynamic study, which must be repeated a few days later. Patients with cervical cord injuries are immobilized in a Guilford brace (G.A. Guilford and Sons Orthotic Laboratory Ltd., Cleveland, OH, USA) or other cervical-thoracic brace for 3 months. Mid- to

401

402 Section Vâ•… Trauma low-thoracic lesions are treated with a thoracolumbar orthosis (TLSO), and upper thoracic lesions are fitted with a TLSO with added chin and occiput supports. Both contact and noncontact sports are strictly prohibited for at least 3 months. In general, the presenting neurologic status predicts the long-term outcome, in that severe and complete cord lesions do not improve with time, and only early good-grade patients have recovery potentials. However, when the five post-SCIWORA MRI findings are correlated with the four grades of neurologic deficits (complete, severe, mild, and normal) at presentation and at 6 months, cord edema and normal MRI are associated with excellent improvement in spite of poor initial grades, and minor cord hemorrhage falls somewhere in between dire and good outcomes.1

50.3.2╇ Atlanto-Occipital Dislocation (AOD) Anatomy and Pathophysiology The occipitoatlantoaxial (O-C1-C2) articulations function as a single unit. The atlas works as a biconcave washer between two spheres of motion. The upper articulations, between the occipital condyles and the atlas, are cup-shaped in the sagittal plane and medially tilted in the coronal plane. This orientation allows flexion, extension, and some lateral bending, but minimal rotation. In contrast, the biconvex and laterally tilted facet articulations between the atlas and axis allow a large degree of rotation centered about the dens. Stability of the O-C1-C2 unit is provided by the strong tectorial membrane, a well-developed continuation of the PLL that straps the body of C2 to the clivus, the paired alar ligaments that connect the dens to the occipital condyles, and the cruciate ligament. Flexion of the basion beyond the tip of the dens is limited by the tectorial membrane, whereas extension is checked by the tectorial membrane and by bony contact between the opisthion and the arch of C1. Lateral bending and rotation are controlled by the alar ligaments. When both the alar ligaments and tectorial membrane are cut in cadaver experiments, complete occipitoaxial dissociation occurs.7 Traumatic AOD results from high-energy impacts that cause rupture of the tectorial membrane and alar ligaments. The most common force vector involved is hyperextension; only about 25% of AOD cases are from hyperflexion. More than 70% of AOD had either rupture or dehiscence of the tectorial membrane. Because the alar ligaments are also ruptured in AOD, the distraction forces must be directed obliquely to the head, such as with an oblique hit to one side of

the chin, or a hyperflexion-distraction blow to the occiput.

Clinical Presentation and Diagnosis Children with traumatic AOD present with signs of brainstem, upper spinal cord, and cranial nerve injuries. Of the children who survive AOD, 30% are apneic or in full cardiorespiratory arrest at the scene. Other brainstem findings include pupillary abnormalities, nystagmus, ocular bobbing, decerebrate posturing, and alterations in consciousness. The motor deficits include quadriparesis, cruciate paralysis, crossed hemiplegia, or hemiparesis. Brainstem injury is due to a combination of actual tissues’ disruption from compression and shearing, and ischemia secondary to vertebral artery spasm or thrombosis. The caudal six pairs of cranial nerves may also be injured from downward traction of the medulla against the fixed points at their exit foramina. The diagnosis of AOD is contingent on a high level of suspicion in trauma victims, especially those with mandibular and facial fractures or with instantaneous cardiorespiratory instability. Casting of the brainstem with subarachnoid blood should immediately suggest a distraction injury at the atlantooccipital junction, and tectorial membrane rupture on MRI in this setting is also highly associated with AOD (Fig. 50.3). Gross separation of the occiput and atlas is seldom obvious on plain X-ray; however, the radiographic “chase” for the diagnosis in the face of the above clues should be relentless because survival depends on early recognition.

Radiographic Diagnostic Criterion― Condyle-C1 Interval Almost all of the older radiographic criteria for AOD utilize bony landmarks that do not actually participate in the atlanto-occipital articulation, and all are plagued with high incidences of false-negatives. The much more reliable condyle-C1 interval (CCI) is based on a direct measurement of the O-C1 joint interval and reflects a more precise indicator of O-C1 integrity. A normative study using both coronal and sagittal reformatted CT images through the condyle– C1 joints of 89 normal children in 20077 shows that the normal occipital condyle–C1 joint in children is tightly held together by strong ligaments, with a mean CCI of 1.28 mm (Fig. 50.4). No individual gap measurement in any projection exceeds 2.5 mm. Also, there is strong left-right joint symmetry in both the CCI and conformational anatomy. Linear regression analysis between age and CCI shows that the

50 â•… Pediatric Vertebral Column and Spinal Cord Injuries

a

b

Fig. 50.3╅ Sagittal magnetic resonance imaging (MRI) in tectorial membrane injuries in atlanto-occipital dislocation (AOD). (a)€Rupture of tectorial membrane; arrow points to the free end. (b) Rupture of the tectorial membrane (right arrow) off clivus (left arrow).

a

b

c

Fig. 50.4â•… Occipital condyle–C1 interval (CCI). (a) Drawing of CCI (in red) and the four points (arrowheads) of measurement. (b)€Coronal and (c) sagittal reformatted computed tomography (CT) images showing normal CCI and points of measurement (arrowheads). Mean CCI incorporates both coronal and sagittal measurements.

403

404 Section Vâ•… Trauma mean CCI value is extremely stable from birth to age 18 years and, furthermore, the left-right symmetry is also age conserved.7 Based on these findings, the authors set a new diagnostic criterion for AOD if the observed mean CCI in a patient is equal to or greater than 4 mm, or if the two joints are grossly asymmetric.8 On testing this new criterion in a series of 24 patients with AOD, the authors found that 22 patients had bilateral widened CCI from 7 to 20 mm (Fig. 50.5), and 2 patients had unilateral joint widening qualifying for unilateral AOD. Gross left-right asymmetry was seen in 10 patients, including complete bilateral joint dissociation (Fig. 50.5) and lateral shifting of both condyles on C1. Furthermore, five cases in which all four “standard” published tests (Wholey’s, Powers’, Harris’, and Sun’s criteria) gave manifestly normal readings had CCIs that were emphatically positive for AOD (Fig. 50.5, lower). Besides having a high diagnostic sensitivity, CCI also has by far the highest specificity score among all the other tests. Since the normal O–C1 joint is tightly held together by ligaments to a very narrow joint gap, sudden rupture of these ligaments instantly releases this tight hold, similar to unfastening a compressed

coil, and the joint surfaces spring apart, resulting in a widened gap, and because the normal myoligamentous hold on the joint is “active” or tonic, it would be impossible for the joint surfaces to resume tight apposition once the ligaments are disrupted. Thus a widened CCI can only be made wider but not narrower by postinjury shifting of the head and neck, thereby eliminating false-negative readings. By converse reasoning, any injury not directly affecting the stability of the O–C1 joint will not cause a widened CCI to give a false-positive reading. Finally, because the normal CCI does not significantly change from birth to age 18 years, the validity of the test is not limited by age.

50.3.3╇ Operative Detail and Preparation Management of Atlanto-Occipital Dislocation Once the suspicion of AOD is entertained, however tentatively, traction should be avoided for fear of increasing the occiput-C1 distraction. Preliminary stabilization can be maintained with a stiff cervical collar and side sand bags while obtaining CT and

a

b

Fig. 50.5â•… Two cases of atlanto-occipital dislocation (AOD). (a) Coronal, left parasagittal (middle), and right parasagittal (right) computed tomography (CT) showing widely separated condyle–C1 intervals (CCIs) (upper). CT of another case (lower). Sagittal CT shows all four conventional radiographic criteria (left). (b) Wholey’s basion-dens interval (BDI), Powers’ ratio BC/AC, Harris’ basionaxis interval (BAI), and Sun’s interspinous ratio (C1C2/C2C3) are all normal, but the CCIs are widely separated.

50 â•… Pediatric Vertebral Column and Spinal Cord Injuries MRI scans. After AOD is confirmed by CT and MRI, a “halo” vest should be fitted to maintain temporary stability while other life-threatening injuries can be dealt with. As soon as the patient’s general condition is stabilized, internal fixation of the occiput to C2 is necessary. The type of OC-C1-C2 fixation depends on the patient’s age and the corresponding anatomy of the region relevant to screw purchase, including the thickness of the occipital bone, the size and strength of the lateral mass of C1 and the pars interarticularis (isthmus) of C2, and the adjacency of the vertebral artery to the projected screw-paths. Anatomy permitting, screw-plate fixation is biomechanically superior to wire-loop techniques, and its more solid fixation often dispenses with the postoperative halo. Thus in older children, the authors prefer occipital screw-plate fixation using C1-C2 transarticular screw, C2 isthmus screw, or the adapted Goel-Harms technique of C1 lateral mass screw and C2 isthmus screws. Although the authors usually select children over age 6 years for intra-axial screws, the age limit should be flexible to suit the morphology of the prospective screw-paths, which should be planned using triplane CT reconstruction through the C2 isthmus and C1 lateral mass. In children, the thickest occipital bone buttress for screw anchorage is usually the midline keel and sometimes near the base of the mastoid. In young children, the authors prefer sublaminar wiring, and if the C1 and C2 laminae are exceedingly delicate, as in children younger than 3 years, the fusion is extended to C3 or even C4 to distribute the stress on the uprights, with minimal additional loss of combined segmental motion. When the occipital squama is too thin for regular screw purchase, the authors have recently used the “inside-outside” screw technique (see following). Postoperative halo is necessary if sublaminar wiring is used.

Neurologic Outcome Despite previous reports of very high mortality for AOD, recent advances in diagnostic efficacy have significantly improved survival. There is no doubt the prognosis for AOD depends on the severity of the initial neurologic injury. Patients with complete high cord transection or severe head injuries generally do poorly. The authors’ series documents 19% early and delayed deaths, 12% complete or severe residual quadriplegia, but 69% excellent neurologic recovery, considerably better than historical data. There is no difference between the authors’ series and the literature in the prognosis of the poor-grade patients, who tend to fare poorly. The better overall outcome of the authors’ series owes instead to a larger proportion of AOD patients initially admitted with moderate-togood neurologic grades. The aggressive and expect-

ant search by the authors for the diagnosis using CCI on every traumatized child fitting the clinical and mechanistic profiles of AOD probably succeeded in making early diagnosis and thus avoided secondary injury to the cord.

50.3.4╇ Atlantoaxial Rotatory Fixation In normal individuals, the C1-C2 joint is responsible for up to 60% of the total axial rotation at the craniocervical region, the atlanto-occipital articulation is responsible for another 3 to 8°, and the rest is shared by the subaxial segments in diminishing measures. Patients with atlantoaxial rotatory fixation (AARF) typically present with painful torticollis, with the head in the “cock-robin” position, with the chin turned toward one side, and the neck laterally flexed to the opposite side in a position reminiscent of a robin listening for worms. AARF is most commonly encountered after upper respiratory infections, trauma, and surgery of the head and neck; however, up to 24% of cases have no obvious cause. There is no such thing as a “diagnostic” separation angle between C1 and C2 because pathological rotatory fixation typically occurs well within the physiological range of rotation, explaining why AARF cannot be distinguished from normal rotation in a static X-ray. One also cannot pin down a fixed C1–C2 separation angle in AARF with motion X-rays because true C1 and C2 interlock is exceedingly rare, and symptomatic patients often show preservation of some interbody movements although having variable degrees of pathological “stickiness” between C1 and C2 in rotation. Here, AARF is defined as gross departures from the normal rotational relationship between the atlas and axis.

Motion Analysis of C1-C2 Rotation: Normal Composite Motion Curve A unique feature of the atlanto-axial articulation is that the facets are oriented more horizontally than all the other facet joints of the cervical spine, which that have much steeper angles. This nearly horizontal orientation of the C1C2 articulation enables the atlas to rotate on the axis with minimum bony impediment. Furthermore, the padding of joint cartilage converts the actual articulating surfaces to biconvex disks. Rotation of the atlas pivots about the odontoid process, to which are attached the alar ligaments that function as the check ligaments against excessive rotation of the atlas on the axis. The alar ligaments connect the tip of the dens to the occipital condyles and the lateral mass of C1, which explains the yoking between C1 and C2 in rotation. To study the normal dynamics of C1–C2 rotation, thin-cut, nonoverlapping axial CT scans were used to

405

406 Section Vâ•… Trauma determine the C1 and C2 angles (C1° and C2° in relation to the vertical axis (0°) during a full rotational sweep of the head.9 The separation angle between C1 and C2, the C1C2°, is the algebraic difference between the two angles, or C1° minus C2°. Seven to eight sets of C1° and C1C2° are obtained with the head turned to different positions from 0° to one side and then turned fully to the opposite side. Plotting the C1° on the x-axis―which denotes the head positions―against the C1C2° on the y-axis―which represents the C1–C2 separation angles―into a motion curve thus displays the instantaneous relationship between C1 and C2 in all head positions during a full head swing (i.e., the curve accurately defines the rotational dynamics between C1 and C2 for the entire physiological range of head rotation [to both sides]). Combining the individual motion curves of multiple subjects into a composite curve using the sixth degree “best fit” polynomial function on the total pool of C1 and C1–C2 separation angles, therefore, formulates an accurate mathematical and graphical prediction of the entire spectrum of C1 and C2 relationship during normal axial rotation (Fig. 50.6). The composite curve very nearly passes through the 0 point, which means that the crossover between C1 and C2 when turning from one

side to the other occurs with the head (C1) almost exactly at vertical 0° (i.e., with the nose straight forward [below 0° in the y-axis C1C2°þ becomes negative, meaning C1 is on the other side of C2]). This indicates that the vertical 0° position is the null point of normal rotation. In addition, the portion of the curve within one quadrant describing motion on one side appears to be the exact mirror image of the curve in the diagonal quadrant depicting motion to the opposite side (Fig. 50.6).

Normal and Abnormal Dynamics of C1–C2 Rotation There are three distinct regions on the composite motion curve reflecting three distinct phases of C1-C2 rotation. With initial head rotation to the right, C1 is “cranked” rightward by the tight, bony structures of the roller-in-groove condyle-C1 joint. In contrast, the lax capsular ligaments and the oblique orientation of the alar ligaments allow C2 to be unperturbed for the first 23° or so of head movement. During this first or single motion phase when C2 remains immobile and only C1 moves, the C1 and C1–C2 separation angles are identical and the curve is perfectly linear, with a

Fig. 50.6â•… Composite motion curve of C1–C2 rotation derived from 29 normal children. Single motion phase when only C1 moves (phase 1). Double motion phase when C2 is being dragged along with C1 by the alar ligaments (phase 2). Unison motion phase when C1 and C2 move in perfect unison because their separation angle is fixed (phase 3). The curve cuts through the 0° null point, meaning C1 crosses over C2 when both are at 0°. Right and left rotation paths are identical mirror images.

50 â•… Pediatric Vertebral Column and Spinal Cord Injuries gradient of exactly 1 (Fig. 50.6, phase 1). Beyond 23°, the left alar ligament begins to tighten and spins the odontoid process in the same direction as C1, thus commencing the second or double-motion phase, where the C1–C2 separation angle is always less than the C1 angle. The curve begins to arc downward (Fig. 50.6, phase 2). With continued head turning, the ligaments become progressively more taut. Further C1C2 separation is increasingly impeded, and C2 is pulled more forcefully and faster toward C1; thus even though the C1–C2 separation angle continues to widen, its rate of change is progressively less with each additional degree of C1 rotation. The gradient of the motion curve becomes accordingly less steep as the arc of the curve flattens to a plateau. As the C1 angle approaches 65°, the ligaments and capsular membranes become maximally stretched and the bony contours in the joint surfaces of the axis and atlas also reach contact limits; further widening between C1 and C2 ceases, commencing the plateau or unison motion phase of the curve (Fig. 50.6, phase 3). The two bones now turn as a couple with a fixed separation angle of about 43° as the head continues to rotate as far as 90° from vertical 0°. Head turning from 65° onward is carried out by subaxial motion only. In AARF, the defining pathological state is therefore not any absolute angle of separation between C1 and C2, but the abnormal way in which C1 and C2 interrelate during axial rotation; and it is the fluidity and freedom of movement that characterize the severity.9

Diagnostic Motion Study and Classification of Atlantoaxial Rotatory Fixation Patients with painful torticollis are given three sets of CT scans: (1) with the head in the presenting position (P position); (2) with the head turned to the 0 position (P0 position); and (3) with the head turned to the side opposite to the presenting position as far as the patient can tolerate (P- or “corrected” position). The corresponding C1 and C1–C2 separation angles are obtained for the three positions. By convention, the side toward which the chin is initially pointing is assigned the positive sign. The diagnostic motion curve is constructed as for the normal motion curve, except that the three data points from the P, P0, P- scan sequences are joined with straight lines. The diagnostic curve is analyzed in the context of normal C1-C2 rotation by superimposing it on the physiological composite motion curve, made into a normal template by adding 8° to each side of the mean to account for variance distribution due to physiological hypermobility.10 In type I AARF, the reduction of the C1–C2 separation angle at maximum tolerated correction (P-) is minimal; the C1C2 separation angles are virtually unchanged even when the head is forcibly rotated way past the midline. All type I motion curves are thus almost straight lines across the right and left upper quadrants of the normal template (Fig. 50.7). It signifies virtual bony interlock and represents the most extreme form of AARF. In type II AARF, the

Fig. 50.7â•… Classification of atlantoaxial rotary fixation (AARF). All three types of AARF curves are superimposed on the normal motion curve template. The mean normal rotation pattern is displayed as the blue band (refer to text).

407

408 Section Vâ•… Trauma maximum reduction of the C1–C2 separation angle (at P-) is greater than 20% of the presenting C1–C2 separation angle (at P0) but C1 cannot be made to cross over C2. Their motion curves slope downward from right to left, but never traverse the x-axis where crossover normally takes place (Fig. 50.7). Type II AARF patients thus have slightly less severe “stickiness” than type I patients. In type III patients, the C1– C2 separation angle narrows with correction and C1 can be forced to cross C2, but always at very abnormal head positions. Their motion curves traverse the x-axis at points where the C1 angle is less than –20°, far left of normal crossover near 0° (Fig. 50.7). Type III AARF patients thus show less stickiness than the other two types because C1 can be forced to cross C2, but only if the head (or C1) is cranked way past the expected null point at 0°. For instant diagnosis and classification of AARF, the user superimposes a patient’s motion curve on the diagnostic domain diagram (Fig. 50.8), whose three diagnostic domains correspond roughly to the areas on the template occupied by the three respective types of abnormal curves. Patients with muscular torticollis have no actual injuries to the C1C2 joints and therefore display motion curves in the normal zone. Some patients have stickier rotation than normal, and their motion curves cross the x-axis at the ambiguous zone of –8° to –20° yet do not fulfill the authors’ AARF criteria (Fig. 50.8). They are put in the diagnostic gray zone (DGZ), and are given cervical collars and analgesics only. Many “gray” patients

revert to normal curves on re-study in 2 weeks, but some will stay symptomatic and progress to type III AARF.

Consequences of Untreated Chronic Atlantoaxial Rotatory Fixation Neurologic deficits are uncommon in acute AARF. Chronic untreated AARF, however, frequently leads to persistent painful spasm of the sternomastoid and nuchal muscles, fixed head tilt, and facial asymmetry due to unrelenting, asymmetric muscle pull on the developing maxillofacial structures. Three other more sinister complications are associated with chronic AARF. (1) Delay of treatment longer than 2 to 3 months often leads to a more severe form of AARF, which therefore forebodes a more prolonged and troublesome course requiring C1-C2 fusion. (2) Because children have a strong instinctive need to maintain a forward-pointing visual axis, prolonged side turning of the torticollic head may lead to dangerous occiput-C1 laxity resulting from overstretching of muscles and ligaments around the atlantocondylar joints after repeated straining and cranking of the head to the midline to regain forward vision. (3) With chronic anterior displacement of the ipsilateral C1 facet on C2, the center of mass of the head is also carried forward, gradually increasing the bending movement that encourages further flexion and translation of the head. This causes progres-

Fig. 50.8â•… Diagnostic domain diagram for the three types of atlantoaxial rotary fixation (AARF), the diagnostic gray zone (DGZ), and the normal motion corridor in the blue band. A 3-point test curve from a patient can be drawn on this diagram to sort out the AARF type, or whether the C1–C2 rotation is normal or in the DGZ. The dark-yellow zone is the overlap area between types II and III domains.

50 â•… Pediatric Vertebral Column and Spinal Cord Injuries sive stretching of the transverse atlantal ligament to accommodate for the backward-migrating odontoid, ultimately rendering the ligament permanently redundant and ineffective, and thus endangering the spinal cord.11

Treatment Protocol and Outcome Treatment of AARF is rendered in two phases: reduction and stabilization. Halter traction is set up to reduce acute and subacute subluxations. Skull-calipers traction is used on chronic patients. Following reduction, all acute (treatment delay less than 1 month) and subacute (treatment delay from 1 to 3 months) patients are immobilized with a Guilford brace for 3 months. The first recurrences are treated with repeat traction, but second recurrences are treated with the halo device for 3 months. Third recurrences and recurrence while in halo are treated with posterior C1–C2 fusion. Chronic patients (treatment delay longer than 3 months) who are successfully reduced by traction are immobilized by the halo device for 3 months. Failure to reduce, or failure to maintain reduction while in halo, is treated with C1–C2 fusion. Acute patients generally reduce with halter traction regardless of AARF types, but acute type I and type II patients are more likely than acute type III patients to show slippage. Subacute type III patients fared only slightly worse. Only chronic type III patients have hope of preserving normal dynamics. The chronic types I and II patients almost never achieve reduction or stay in reduction in spite of repeated efforts, and most will require fusion.11

50.3.5╇ Atlantoaxial Fusion Any fusion technique for this extremely mobile joint must withstand all four planes of motion—flexion, extension, rotation, and translation. In young children with a widened space between the C1 and C2 arches, the Brooks fusion uses bilateral sublaminar cables around a well-fitting corticocancellous bone graft compressed against the C1 and C2 rings. With this construct, there is stability in both flexion and extension, and the buttressing bone graft also serves as a friction block between the two bony arches and offers stability against rotation and translation. Occasionally, continued micromotions at the fusion site promote graft resorption and retard bone formation, ultimately leading to graft shrinkage and disintegration of the Brooks construct. Thus, in children younger than 3 or 4 years, the authors prefer using bilateral C1-C2 sublaminar soft cables and then tightening them until the two arches touch (“kiss-

ing” fusion). The conjoined bony rings offer stability in flexion and extension, as well as serving as an effective friction block. In older children, the authors prefer intra-axial screw constructs. Magerl’s C1-C2 transarticular screw fixation reports a 95 to 98% fusion rate but does necessitate an interposing graft between the arches of C1 and C2 to eliminate flexion and extension.12 A better alternative is the Goel-Harms technique of C1 pedicle and C2 isthmus screws linked by bilateral side plates. In some children, the pars interarticularis (isthmus) may be too narrow for safe passage of a 3.5-mm screw. The absolute dimension of the isthmus must be premeasured and the screw path preplanned on a virtual image.

50.3.6╇ Occipital-Cervical Fusion with Instrumentation In young children, bone thickness of the occiput is of great concern for providing adequate screw purchase. Occipital midline screw plate capitalizing on the thick midline keel has been successful in achieving rigid skull fixation in children as young as 3 years. The occipital cruciate “mountaineer plate” (DePuy, DePuy Synthes Spine, Inc., Raynham, MA, USA) is equipped with adjustable bilateral contoured rods that are either linked via cable connectors to C1 and C2 sublaminar cables (Fig. 50.9), or interlocked with C2 transarticular screws or isthmus screws. On-laid iliac crest cortical and cancellous bone grafts are applied. In children younger than 3 years or with thin occipital skulls, the authors use the “inside-outside” screw technique,13 which utilizes a contoured plate affixed to the occiput by means of a flat-headed screw placed through a burr hole in the calvaria so that the head of the screw is in the epidural space and the threaded stem faces outward (hence inside-outside). The entrance burr hole is cut into a keyhole extending toward the thicker mastoid prominence, into which the out-pointing screw stem is guided. A modified Axis plate with a custom-tapered, perforated vertical stem (Sofamor Danek, Memphis, TN, USA) designed especially for sublaminar wiring to small delicate laminae is placed through the out-pointing screw stem, and a nut is semitightened on the exposed screw threads with a socket wrench. After the C1–C2 sublaminar cables have been inserted and tightened on the plate, the occipital screw is firmly tightened against the nut with the socket wrench and a counter-torque screw fixator (Fig. 50.10). Alternatively, the inside-outside occipital plate with a contoured lower rod stem can be linked to C1 and C2 intra-axial screws.

409

410 Section Vâ•… Trauma

Fig. 50.9â•… Occipital-C2-C3 fusion with “mountaineer” occipital cruciate plates and sublaminar cables in a 2½-year-old boy. Cruciate plate fixed to occipital keel via three screws, bilateral rods, and C2-C3 sublaminar soft cables linked to rods via cable connectors (left). Immediate postoperative X-ray and good callus on computed tomography (CT) 4 months later (right).

Fig. 50.10â•… Occipital-C1 to C4 fusion with “inside-outside” screw-plate system in an 11-month-old boy. Keyholes (black arrows) with larger entry zone for the screw heads, and the narrower keys for the protruding screw stems. The screw with an out-pointing stem and an offset head is held to be inserted (left). Both plates and screws have been tightened against the occiput, and the slimmer lower plate tightened against the delicate laminae by soft cables threaded through the small holes (middle). Immediate postoperative X-ray and callus 6 months later (right).

50 â•… Pediatric Vertebral Column and Spinal Cord Injuries

References ╇1. Pang

D. Spinal cord injury without radiographic abnormality in children, 2 decades later. Neurosurgery 2004;55(6):1325–1342, discussion 1342–1343 ╇2. Hamilton MG, Myles ST. Pediatric spinal injury: review of 174 hospital admissions. J Neurosurg 1992; 77(5):700–704 ╇3. Pang D, Wilberger JE Jr. Spinal cord injury without radiographic abnormalities in children. J Neurosurg 1982;57(1):114–129 ╇4. Pang D, Pollack IF. Spinal cord injury without radiographic abnormality in children—the SCIWORA syndrome. J Trauma 1989;29(5):654–664 ╇5. Pang D. Pediatric spinal cord injuries. In: McLone DG, ed. Paediatric Neurosurgery. 4th ed. Philadelphia, PA: W.B. Saunders; 2001: 660–694 ╇6. Grabb PA, Pang D. Magnetic resonance imaging in the evaluation of spinal cord injury without radiographic abnormality in children. Neurosurgery 1994;35(3): 406–414, discussion 414 ╇7. Pang D, Nemzek WR, Zovickian J. Atlanto-occipital dislocation: part 1—normal occipital condyle-C1 interval in 89 children. Neurosurgery 2007;61(3):514–521, discussion 521

╇8. Pang

D, Nemzek WR, Zovickian J. Atlanto-occipital dislocation—part 2: The clinical use of (occipital) condyleC1 interval, comparison with other diagnostic methods, and the manifestation, management, and outcome of atlanto-occipital dislocation in children. Neurosurgery 2007;61(5):995–1015, discussion 1015 ╇9. Pang D, Li V. Atlantoaxial rotatory fixation: Part 1—Biomechanics of normal rotation at the atlantoaxial joint in children. Neurosurgery 2004;55(3):614–625, discussion 625–626 10. Pang D, Li V. Atlantoaxial rotatory fixation: part 2—new diagnostic paradigm and a new classification based on motion analysis using computed tomographic imaging. Neurosurgery 2005;57(5):941–953, discussion 941–953 11. Pang D, Li V. Atlantoaxial rotatory fixation: part 3—a prospective study of the clinical manifestation, diagnosis, management, and outcome of children with alantoaxial rotatory fixation. Neurosurgery 2005;57(5):954–972, discussion 954–972 12. Gluf WM, Brockmeyer DL. Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 67 pediatric patients. J Neurosurg Spine 2005;2(2):164–169 13. Pang D, Zovickian JG. Vertebral column and spinal cord injuries in children. In: Winn HR, ed. Neurological Surgery. 6th ed. Philadelphia, PA: W.B. Saunders; 2011: 2293–2332

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51

Brachial Plexus Birth Injuries Nathan J. Ranalli and T. S. Park

51.1╇Background 51.1.1╇Indications Pediatric brachial plexus birth injuries (BPBI) arise from excessive lateral traction forces applied to one or more of the plexal elements during birth. Despite increased attention to risk factors like fetal macrosomia and shoulder dystocia, BPBI occur in 5,400 children born in the United States each year.1 Whereas many cases are mild and transient, recent reports suggest that previously published rates of spontaneous recovery are overly optimistic and highlight the advantages of primary surgical repair in select patients.2,3 Infants diagnosed with BPBI should be evaluated in a comprehensive multidisciplinary brachial plexus clinic. The authors grade strength using the modified British Medical Research Council scale (BMRC 0 to 5). Many palsies resolve in the first few weeks, signifying a neuropraxic insult, while axonotmetic and neurotmetic lesions fall into one of four patterns of injury: 1. C5–C6 (Erb palsy)―internal rotation of the arm, adduction at the shoulder, extension at the elbow, and pronation of the forearm; most common 2. C5–C7―Erb plus flexion at the wrist with fingers extended (waiter’s tip posture) 3. C5–T1―varying degrees of weakness to flaccid, insensate paralysis of the entire arm and hand with pale or mottled skin, with or without Horner syndrome 4. C8–T1 (Klumpke palsy)―claw hand posture and Horner’s syndrome; very rare

412

Patients are reexamined 1 month after birth following the initiation of physical therapy (PT). For children with total BPBI, the poor prognosis is explained to the parents and the authors recommend microsurgical reconstruction by age 3 months.4–6 If the patient has improving hand function without shoulder or biceps recovery, PT is continued and he is seen on a monthly basis. By age 3 months, infants with antigravity strength in the biceps, triceps, or deltoid muscles may be followed expectantly; children with less than antigravity strength undergo imaging and electrophysiological studies in preparation for likely surgical intervention. If, at age 6 months, the muscles still have not recovered antigravity strength, exploration and repair are recommended.3

51.1.2╇Goals The aim is to perform microsurgical brachial plexus exploration and repair in infants who will not attain antigravity strength through conservative management. The goal is to achieve excellent functional outcomes, including reduced rates of joint contractures and permanent muscle atrophy, while minimizing unnecessary surgical intervention in children destined to recover spontaneously.

51.1.3╇ Alternate Procedures Previous reports suggested that most patients with BPBI make a complete spontaneous recovery with PT alone. Although more recent publications have demonstrated much lower rates of satisfactory spontaneous recovery, many children with BPBI will never be offered primary surgical intervention. In addition,

51 â•… Brachial Plexus Birth Injuries as many as 35% of infants and children with BPBI will experience chronic joint deformities, including contractures at the shoulder, elbow, and wrist. Secondary reconstruction procedures are performed by orthopedic surgeons when such patients attain a rehabilitation plateau. These include muscle or tendon transfers, rotational osteotomies, and, later, shoulder arthrodesis.

51.1.4╇Advantages Primary exploration and repair of BPBI with grafting or nerve transfer is a safe and effective approach that can be applied as early as age 3 months. Direct visualization of the plexal elements afforded by this technique is the only way to accurately diagnose the extent of the injury. Blood loss and postoperative pain are minimal, hospital stays are short, and functional outcomes are excellent when microsurgical repair is undertaken.

51.1.5╇Contraindications If components of the patient’s birth history or physical examination do not fully support the diagnosis of BPBI, further work-up is indicated to eliminate other etiologies of upper extremity weakness, including stroke or spinal cord pathology. Evidence that the patient is likely to achieve complete recovery with PT alone also precludes surgery. General surgical contraindications, including active systemic or skin infection, anemia, coagulopathy, or inability to tolerate general anesthesia, are the same for this surgery.

51.2╇ Operative Detail and Preparation 51.2.1╇ Preoperative Planning and Special Equipment Patients with concern for phrenic nerve injury on examination should undergo a chest X-ray to look for an elevated hemidiaphragm; those with fractures of the ribs, clavicle, spine, or humerus should have radiographs of the specific site of suspected injury. At some institutions, an electromyelogram (EMG) and nerve conduction studies are done at 3 months. Several papers state that because denervation disappears early in newborn trauma and extensive collateral sprouting occurs rapidly, EMG may not accurately portray the severity of the clinical condition.7 The authors have not found EMG to be helpful in their own practice. They use fast spin-echo cer-

vical magnetic resonance imaging (MRI) to look for both pseudomeningoceles (Fig. 51.1) and any sign of spinal cord injury; however, 15% of radiographic pseudomeningoceles are not associated with complete nerve root avulsion. Computed tomography (CT) myelography is an invasive alternative to MRI that provides better delineation of nerve roots and intervertebral foramina but requires general anesthesia, lumbar puncture, intrathecal contrast, and radiation exposure.

51.2.2╇ Expert Suggestions/Comments The primary clinical dilemma is to determine when BPBI warrants surgical exploration and reconstruction, and the absence of motor recovery is the main indication for operative intervention. The authors found that patients in their own series who had less than antigravity biceps strength by age 6 months had unsatisfactory outcomes with nonsurgical management and have used this to guide the timing of surgical treatment.3 Management of expectations is important, and the authors counsel parents from the beginning that the goal of surgery is to improve the functional capabilities of the arm, that it may never be completely normal, and that recognizable benefits may not appear for 6 months.

51.2.3╇ Key Steps of the Procedure/ Operative Nuances Position and Prep Surgery is performed under general anesthesia with a short-acting neuromuscular agent to permit intraoperative electrical stimulation. The patient is positioned supine with a gel roll placed to elevate the clavicular region and the head rotated to the contralateral side. The entire neck, chest, affected upper extremity, and both lower limbs are prepared in a sterile manner to allow for visual inspection of the muscles of the affected arm during surgery and to accommodate the potential need for bilateral sural nerve harvesting; this last point has been modified at the authors’ own institution because they are using the AxoGen Avance peripheral nerve allograft in lieu of sural nerve autografts (AxoGen, Inc., Alachu, FL, USA).

Supraclavicular and Infraclavicular Exploration For an upper trunk palsy, a standard supraclavicular approach is used (Fig. 51.1, Fig. 51.2, Fig. 51.3, Fig.€51.4, Fig. 51.5, Fig. 51.6, and Fig. 51.7); treatment of the lower plexus sometimes requires an infraclavic-

413

414 Section Vâ•… Trauma

Fig. 51.1â•… Pseudomeningocele along the left C8 spinal nerve root.

Fig. 51.2â•… Right-sided upper trunk injury. Enlarged upper trunk with a neuroma (1); enlarged suprascapular nerve (2); phrenic nerve (3); anterior division of the upper trunk (4); and enlarged C5 spinal nerve root (5).

51 â•… Brachial Plexus Birth Injuries

Fig. 51.3â•… Transfer of C4 nerve to the suprascapular nerve (arrow). The abnormal upper trunk has been removed.

ular exposure. The incision begins under microscopic visualization two finger breadths beneath the mastoid tip and follows the posterior border of the sternocleidomastoid muscle to the midpoint of the clavicle; for a combined approach, the incision is extended laterally along the superior border of the clavicle to the deltopectoral groove and curved inferiorly to the anterior axillary fold. The platysma muscle is incised and a layer of fibrofatty tissue overlying the brachial plexus is elevated. The omohyoid is divided and the transverse cervical vessels are retracted or cauterized. The subclavius muscle and clavicular periosteum are divided at the clavicle. The first goal is to identify the phrenic nerve along the anterior scalene muscle. Direct electrical stimulation and observation of responses are used throughout and aid in the labeling of nerves. The upper trunk neuroma will be apparent, and the C5 root is located by following the most superficial portion of the upper

trunk toward the neural foramen. The anterior scalene muscle is partially resected to provide access to the C6–T1 roots; care must be taken when exposing the T1 root given its proximity to the pleura and subclavian vessels. Soft Silastic vessel loops are used to designate and retract the roots, while the three trunks are identified close to the clavicle and are freed from surrounding fibrotic tissue. The dorsal scapular and suprascapular nerves are located arising from C5 and the upper trunk, respectively; the long thoracic nerve is found under the upper trunk above the middle scalene muscle. Infraclavicular exposure is achieved by dissecting along the deltopectoral groove and dividing the pectoralis major at its insertion into the humerus and at the midpoint of the pectoralis minor; the cephalic vein is preserved and marking sutures in the pectoralis major facilitates closure. The three cords as well as the median, ulnar, musculocutaneous, and axillary nerves are visualized.

415

416 Section Vâ•… Trauma

Fig. 51.4â•… Nerve grafts are placed between the C5–C6 nerve roots and anterior and posterior divisions.

Graft Harvesting

Repair Procedures

Traditionally, the authors harvested autologous sural nerve grafts through bilateral, open, posterior lower leg stepladder incisions; endoscopic harvest of the sural nerves has also been described. Because the sensory sural nerves are smaller than the mixed nerves of the brachial plexus, multiple segments of sural nerve are needed to create an adequate graft spanning the distance from nerve root to trunk. This requires a second or third incision, increases the risk of wound infection, and may cause postoperative pain or paresthesias in the patient. The authors now use a decellularized and sterile extracellular matrix (Avance, AxoGen) processed from donor human peripheral nerve tissue. Alternative donor sites include nerves taken from areas of the patient’s own plexus where reinnervation is unlikely to occur, such as the medial cutaneous nerve of the forearm.

Resection of conducting neuromas-in-continuity has been shown to have better results than performing external neurolysis alone.8 The authors combine a semiquantitative evaluation of muscle contraction in response to electrical stimulation of the nerve root proximal to the neuroma with intraoperative inspection of the neuroma, awareness of preoperative muscle strength, and knowledge of MRI findings to determine which elements to graft. If the root or trunk is ruptured and electrical stimulation up to 10 mA (milliamperes) generates no or minimal muscle contraction, the neuroma is resected and a repair is performed. The primary objective of surgery for an upper trunk palsy is to restore shoulder and biceps muscle functions through a variety of grafting and neurotization procedures. These include using the stumps of the C5 and/or C6 roots, the C7 root, or the spinal

51 â•… Brachial Plexus Birth Injuries

Fig. 51.5â•… A few nerve grafts are sutured with 9–0 nylon to the brachial plexus.

accessory nerve for grafting to all or part of the upper trunk or suprascapular nerve. For a total plexus injury, multiple nerve grafts must be employed. If several nerve root stumps are identified, these are divided and used for grafting all trunks and cords of the brachial plexus. If only a single nerve root stump is accessible, it is grafted to the upper trunk and lower trunk. All nerve grafts should be prepared 10 to 15% longer than the measured defect length and combined to match the diameter of the host nerves. Neurorrhaphy is performed with 9–0 Prolene epineurial sutures combined with fibrin glue.

Nerve root avulsions require neurotization. This is accomplished via nerve crossover or transfer between an uninjured neighboring donor nerve and a distal segment of nonfunctioning nerve directly or with grafts. Transferring fascicles of the ulnar nerve that supply the flexor carpi ulnaris to the motor branches of the biceps is the Oberlin procedure. The authors use this and radial-nerve-to-axillary-nerve transfers during the primary repair or 6 to 12 months later in the setting of partial neurologic recovery to augment biceps and deltoid function, respectively. Intercostal, medial pectoral, median, thoracodorsal, long thoracic, and subscapular nerves have been utilized by

417

418 Section Vâ•… Trauma

Fig. 51.6â•… Nerve grafts placed between C5–C6 spinal nerve roots and anterior and posterior divisions of the brachial plexus.

others for neurotization; the long-term efficacy of these transfers in babies is unknown. The phrenic nerve transfer is not recommended in infants in light of their immature respiratory systems.

Closure Wound closure is performed in layers, including reapproximation of the pectoralis major and platysma muscles, in a routine manner. The shoulder is maintained in adduction over the trunk with an elastic bandage and sling, and a soft collar is applied to the neck.

51.2.4╇ Hazards/Risks/Avoidance of Pitfalls Risks of the surgery include loss of preoperative muscle strength, injury to the phrenic nerve with diaphragmatic paralysis, cerebrospinal fluid leak, pneumothorax, thoracic duct injury (left-sided approach only), injury to the carotid and subclavian arteries or jugular and subclavian veins, pseud� arthrosis of the clavicle in the setting of clavicular osteotomy, and wound infection. Rarely, a wound hematoma or airway edema may result in respira-

51 â•… Brachial Plexus Birth Injuries

Fig. 51.7â•… Fibrin glue around the nerve grafts.

419

420 Section Vâ•… Trauma tory compromise and the patient must be monitored closely for evidence of airway insufficiency and swallowing dysfunction. When using the spinal accessory transfer to the suprascapular nerve to reinnervate the infraspinatus and supraspinatus muscles, care must be taken to section the nerve distal to the first branch of the trapezius muscle in order to avoid a significant motor deficit.

Salvage and Rescue The authors perform Oberlin and/or radial to axillary nerve transfer procedures when either the primary repair did not result in adequate biceps or deltoid function or the primary exploration reveals avulsions or severely traumatized roots and trunks that make grafting impossible. They also believe the Oberlin transfer could be considered at the primary operation in a patient who achieved spontaneous recovery of shoulder function without satisfactory recovery of biceps function by the 6-month time point.

51.3╇ Outcomes and Postoperative Course 51.3.1╇ Postoperative Considerations Most patients are discharged on postoperative day 1 or 2. The arm is immobilized in a sling for 3 weeks, at which point PT is initiated to prevent contractures. The patient is seen every 3 months in clinic and pain is managed with acetaminophen or ibuprofen. Other authors advocate prolonged use of a cast placed in the operating room with subsequent use of a sling for several months prior to starting PT.

51.3.2╇Outcomes The results of surgery depend on the severity of the injury. Recovery typically begins within 2 to 10 months after surgical intervention and may continue until the patient is age 5 years. Because the goal of surgery is not only to restore function but to prevent permanent changes in the denervated muscle that could result in long-term orthopedic deformities, the objectives include: stabilization of the shoulder through reinnervation of the supraspinatus and deltoid muscles, restoration of elbow flexion with reactivation of the biceps, and improvement of median sensory nerve function in cases of total palsies for

future secondary reconstruction procedures. Multiple authors have demonstrated that neurologic improvement occurs in 75 to 95% of patients undergoing surgical reconstruction, with most achieving antigravity strength in the shoulder and/or elbow.5,9 Boome and Kaye published results including antigravity strength in 95% of the deltoid and 80% of the biceps muscles in patients following surgery; Laurent and Lee found 85 to 95% of patients recovered antigravity strength above the elbow and a 50 to 70% recovery rate distal to the elbow.10,11 In the authors’ own series, patients undergoing exploration and repair for upper plexus lesions achieved better results than those having surgery for lower plexus injuries.12

References ╇1. Benjamin

K. Part 1. Injuries to the brachial plexus: mechanisms of injury and identification of risk factors. Adv Neonatal Care 2005;5(4):181–189 ╇2. Hoeksma AF, ter Steeg AM, Nelissen RG, van Ouwerkerk WJ, Lankhorst GJ, de Jong BA. Neurological recovery in obstetric brachial plexus injuries: an historical cohort study. Dev Med Child Neurol 2004;46(2):76–83 ╇3. Noetzel MJ, Park TS, Robinson S, Kaufman B. Prospective study of recovery following neonatal brachial plexus injury. J Child Neurol 2001;16(7):488–492 ╇4. Waters PM. Obstetric brachial plexus injuries: evaluation and management. J Am Acad Orthop Surg 1997;5(4):205–214 ╇5. Gilbert A, Tassin JL. Surgical repair of the brachial plexus in obstetric paralysis [in French]. Chirurgie 1984;110(1):70–75 ╇6. Bain JR, Dematteo C, Gjertsen D, Hollenberg RD. Navigating the gray zone: a guideline for surgical decision making in obstetrical brachial plexus injuries. J Neurosurg Pediatr 2009;3(3):173–180 ╇7. Vredeveld JW. Clinical neurophysiological investigations. In: Gilbert A, ed. Brachial Plexus Injuries. London, England: Martin-Dunitz; 2001: 42 ╇8. Capek L, Clarke HM, Curtis CG. Neuroma-in-continuity resection: early outcome in obstetrical brachial plexus palsy. Plast Reconstr Surg 1998;102(5):1555–1562, discussion 1563–1564 ╇9. Terzis JK, Liberson WT, Levine R. Obstetric brachial plexus palsy. Hand Clin 1986;2(4):773–786 10. Boome RS, Kaye JC. Obstetric traction injuries of the brachial plexus. Natural history, indications for surgical repair and results. J Bone Joint Surg Br 1988;70(4):571–576 11. Laurent JP, Lee RT. Birth-related upper brachial plexus injuries in infants: operative and nonoperative approaches. J Child Neurol 1994;9(2):111–117, discussion 118 12. Sherburn EW, Kaplan SS, Kaufman BA, Noetzel MJ, Park TS. Outcome of surgically treated birth-related brachial plexus injuries in twenty cases. Pediatr Neurosurg 1997;27(1):19–27

Section VI Neoplasms

Section Editor: Frederick A. Boop

In writing of childhood brain tumors in their 1954 book Neurosurgery of Infancy and Childhood, Franc Ingraham and Donald Matson, two of the fathers of pediatric neurosurgery in North America, noted that “the paucity of localizing neurological symptoms and signs . . . and the inability of infants and young children to define complaints accurately all serve to make early detection of brain tumors in this age group difficult.”€Since that time, the ready availability of CT and MRI has shortened the interval between the onset of symptoms and diagnosis; however, it is still not uncommon for€children to see three or four primary care or subspecialty physicians prior to diagnosis.€ That said, in the hands of an experienced pediatric neuroradiologist, the diagnosis of tumor type can now be made prior to surgery in over 90% of cases.€At present, for most pediatric brain tumors, we are still at a point where the extent of surgical resection is the most important determinant of outcome. Whereas a decade ago the number of children enrolled in prospective clinical trials who had a gross total resection was half, it now appears to be over 70%, suggesting that fellowship-trained pediatric neurosurgeons now€understand the importance of€approaching these children with curative intent.€

The understanding of tumor biology and the molecular pathways leading to tumorigenesis is currently changing by the month. Newer targeted molecular therapies are offering exciting new opportunities for treatment. The molecular subtypes have also proven, in many instances, to better predict response to therapy and prognosis than what is seen under the microscope by the pathologist.€ As such, reductions in the toxicity of the treatment for these children seems to be creating more functional cancer survivors than were seen twenty years ago.€ Advances in noninvasive functional neuroimaging, such as DTI and tractography,€coupled with more accurate intraoperative image guidance, have allowed for more aggressive surgery to be performed with fewer deficits.€ This is an exciting era for those of us who care for children with cancer.€Certainly, challenges remain, as will be outlined in the chapters that follow, but for the contemporary pediatric neurosurgeon, we can now anticipate a cure for the majority of the children referred to us with cancer. In this section of the book, experts in all aspects of childhood tumor treatment offer lessons learned that will benefit the reader. Keeping in mind the ancient Chinese proverb, “a wise man learns from others’ mistakes, while a fool learns from his own,” Tricks of the Trade should make us all wise.

52

Molecular and Genetic Advances in the Treatment of Brain Tumors Vijay Ramaswamy, Marc Remke, and Michael D. Taylor

52.1╇Background Our understanding of the biology of pediatric brain tumors has increased dramatically in the past decade. Specifically, advances in integrated genomics and the advent of next-generation sequencing have allowed us to gain profound insights into the molecular genetics underlying primary brain tumors, and have revealed unexpected intertumor heterogeneity. Specifically, tumors that appear identical under the light microscope can have remarkably different biological behaviors. These advances in our understanding of the molecular genetics of pediatric brain tumors may help to improve risk stratification, thereby making therapy more effective, and at the same time opening the door to the discovery of novel therapies in pathways previously unknown to be implicated in tumorigenesis. There is currently an ongoing effort to characterize molecularly a vast array of pediatric brain tumor entities. Recent reports have put a particular focus on medulloblastoma and ependymoma plus highgrade and low-grade gliomas. Our fundamental understanding of these tumor entities has changed dramatically as a result of large multi-institutional collaborations, where previously unattainable numbers of tumors are analyzed on a genome-wide scale, and clustered in an unbiased manner. Herein, the authors attempt to summarize some of the major breakthroughs in our understanding of the molecular biology and genetics of pediatric brain tumors― specifically medulloblastoma, ependymoma, and glioma―over the past few years.

52.2╇Medulloblastoma Current risk stratification has been primarily clinical and to some extent morphological; however, neither classification is adequate for accurate risk stratification. As a result, many children remain

either overtreated or undertreated without much improvement in outcome over the past 10 years. Initial genomic studies of medulloblastoma revealed that it is a distinct tumor entity from other round, small, cell tumors of the central nervous system, but also suggested that molecular signatures can be used to predict outcome.1 Subsequent studies went on to reveal that medulloblastoma actually comprises four distinct subgroups displaying unique demographics, genetics, transcriptomes, and outcomes. These four subgroups are termed the subgroup for activation of the canonical wnt/wingless (WNT) pathway; the subgroup for activation of the sonic hedgehog (SHH) pathway; group 3, characterized by focal amplifications of the MYC oncogene; and group 4, which is the most common subgroup.2–5 Patients with WNT-activated tumors have an excellent prognosis, exceeding 95% 5-year overall survival, whereas group 3 patients have a dismal prognosis of approximately 50% 5-year overall survival.5 Most importantly, risk stratification based on molecular subgrouping offers a more precise prediction of outcome compared to either clinical or pathological classification alone. Next-generation sequencing has also revealed that each subgroup has specific single nucleotide variations, fusions, and somatic copy number aberrations (Table 52.1).6 This suggests that the next generation of clinical trials will have to take into account the underlying genetic differences among the four principal subgroups. A clear example of how molecular stratification is changing therapies is seen in the next generation of clinical trials for the WNT and SHH subgroups. Patients with WNT-activated tumors have an excellent prognosis using current multimodal therapies. Thus, upcoming trials will de-escalate therapies, specifically for WNT pathway tumors, in both North America and Europe, and will involve de-escalation of either craniospinal irradiation or chemotherapy. Patients with SHH pathway tumors are ideal candidates for therapy with the smoothened inhibitors, such as vismodegib (GDC-0449) and LDE-0445.7 More

423

424 Section VIâ•… Neoplasms Table 52.1â•… Molecular characteristics of the four medulloblastoma subgroups Molecular feature

WNT

SHH

Group 3

Group 4

Broad gain

n/a

3q (27%)

17q (62%), 7 (55%), 1q (35%), 18 (26%), 8q (22%), 12q (17%)

17q (73%), 7 (47%), 12q (20%), 18 (16%)

Broad loss

6 (85%)

9q (47%), 10q (26%), 17p (25%)

16q (50%), 10q (49%), 17p (42%), 9q (21%)

17p (63%), 8p (41%), 10q (15%)

Recurrent somatic mutations/focal SCNAs/gene fusions

CTNNB1 (91%), DDX3X (50%), SMARCA4 (26%), MYC (17%), MLL2 (13%), TP53 (13%)

PTCH1 (28%), TP53 (14%), MLL2 (13%), DDX3X (12%), MYCN (8%), BCOR (8%), LDB1 (7%), TCF4 (6%), GLI2 (5%)

MYC (17%), PVT1-MYC (12%), SMARCA4 (11%), OTX2 (8%), CTDNEP1 (5%), LRP1B (5%), MLL2 (4%)

KDM6A (13%), SNCAIP (10%), MYCN (6%), MLL3 (5%), CDK6 (5%), ZMYM3 (4%)

Expression signature

WNT signaling

SHH signaling

Retinal/GABAergic

Neuronal/ glutamatergic

MYC/MYCN expression

MYC +

MYCN +

MYC +++

Both low

Cell of origin

Progenitor cells in lower rhombic lip

CGNPs of the EGL/ cochlear nucleus; NSCs of the SVZ

Prominin1+, lineage NSCs; CGNPs of the EGL

Unknown

Abbreviations: CGNP, cerebellar granule neuron precursor; EGL, external granule layer; n/a, non-applicable; NSC, neural stem cell; SCNA, somatic copy number alteration; SHH, sonic hedgehog; SVZ, subventricular zone; WNT, wingless.

importantly, the identification of a distinct subgroup of medulloblastoma that is driven by SHH activation allows identification of those patients who are most likely to respond. Moreover, integrated genomics allows identification of patients with SHH-activated tumors with downstream events, such as GLI2 amplification or SMO mutations, that could predispose to developing resistance to SHH pathway inhibition. The search for subgroup-specific therapies for group 3 and group 4 patients is currently underway. Several pathways, such as inhibition of MYC or transforming growth factor-beta (TGF-β), are promising candidates for group 3 subgroup-specific treatment intervention. Several techniques currently exist to identify subgroups, including gene expression analysis, DNA methylation analysis, and immunohistochemistry, particularly for identification of WNT (nuclear beta-catenin), and SHH (SFRP1 and GAB1 expression).5 One limitation of all studies on medulloblastoma to date has been the paucity of research examining genomic events in the metastatic compartment. Cross species genomics has also revealed that metastatic medulloblastomas are highly divergent from their matched primaries, in both mouse and human tumors. Moving forward, it may become necessary to biopsy the metastatic compartment to properly stratify patients into appropriate clinical trials of novel agents.

52.3╇Ependymoma Ependymoma is the third most common children’s brain tumor arising in any location along the craniospinal axis. Radial glial cells are considered the cell of origin for all ependymomas independent of tumor location.8 Although ependymomas from different parts of the craniospinal axis appear morphologically identical, integrated genomic studies have revealed the presence of distinct entities of ependymoma.8,9 This strongly suggests that although morphologically identical, ependymomas from different parts of the brain have distinct molecular signatures (including somatic copy number aberrations and transcriptomes) and clinical outcomes. A recent consensus meeting in Heidelberg, Germany, describes distinct subgroups of ependymoma in each of the anatomical compartments (supratentorial, posterior fossa, and spinal). Posterior fossa ependymoma has been studied the most extensively, with two distinct subgroups, termed groups A and B (Table 52.2), occurring primarily in younger and older children, respectively. More importantly, there appears to be significant clinical relevance to these subgroups because group A has a much poorer prognosis independent of gross total resection, which currently is the single

52 â•… Molecular and Genetic Advances in the Treatment of Brain Tumors Table 52.2â•… Molecular characteristics of ependymoma subgroups Molecular feature

PF-A

PF-B

Broad gain

1q (20%)

18 (59%), 9 (56%), 15q (50%), 20 (48%), 12 (44%), 4 (37%), 7 (37%), 11 (33%), 21q (22%), 5 (19%)

Broad loss

22q (13%), 6 (11%)

6 (56%), 22q (41%), 3 (37%), 10 (37%), 17q (33%), 14q (22%), 1 (19%), 8 (19%), 2 (15%)

Recurrent somatic mutations/ focal SCNAs/gene fusions

Unknown

Unknown

Dysregulated pathways

PDGF, angiogenesis, RAS/GTPase, integrin, ECM assembly, tyrosine kinase signaling, MAPK, TGF-beta

Ciliogenesis, microtubule assembly, mitochondrial/oxidative metabolism

Cell of origin

Radial glial cells

Radial glial cells

Abbreviations: ECM, extracellular matrix; MAPK, mitogen-activated protein kinase; PDGF, platelet-derived growth factor; PF-A/-B, posterior fossa ependymoma Group A/B, respectively; SCNA, somatic copy number alteration; TGF-beta, transforming growth factor-beta.

most predictive factor in ependymoma. Indeed, it is likely that group A tumors have a higher incidence of brainstem invasion, thus precluding gross total resection.9 This suggests that molecular subgroups rather than clinical factors (e.g., extent of surgical resection) comprise the most prognostic factor in posterior fossa ependymomas.

52.4╇ Pilocytic Astrocytoma Pilocytic astrocytomas are the most common brain tumors of childhood and are diagnosed primarily on the basis of morphological characteristics. A subset of pilocytic astrocytomas, particularly those of the optic pathway, has been associated with neurofibromatosis type I, and generally these tumors have a more favorable prognosis. However, recent studies, particularly next-generation sequencing of a large number of pilocytic astrocytomas, have revealed lesions to be associated almost exclusively with the mitogen-activated protein kinase (MAPK) pathway, mostly mediated by rearrangements affecting BRAF.10 Specifically, the most common genetic aberrations are BRAF fusions followed by point mutations in BRAF or KRAS, FGFR1, PTON11 and NTRK2 fusions.11,12 This strong association between genetic lesions in the MAPK pathway and pilocytic astrocytomas suggests that MAPK inhibition, particularly with BRAF inhibitors, such as PLX4032, and the MEK inhibitor AZD6244, both of which are being evaluated in early clinical trials for low-grade gliomas.

52.5╇ High-Grade Gliomas Pediatric high-grade gliomas comprise both hemispheric high-grade gliomas and the diffuse intrinsic pontine gliomas. Integrated genomic studies, particularly next-generation sequencing, have revealed that pediatric high-grade gliomas harbor a mutational spectrum distinct from that of their adult counterparts (Table 52.3). Specifically, recurrent mutations in histone modifiers have been identified in both hemispheric glioblastoma and in diffuse intrinsic pontine glioma.13 The histone 3 variant H3.3 is affected by single amino acid substitutions in lysine 27 (K27) mostly in pontine and thalamic highgrade gliomas, whereas single amino acid substitutions in glycine 34 (G34) affect pediatric high-grade gliomas and are mutually exclusive of IDH1 mutations.14,15 Other recurrent mutations closely associated with incorporation of H3.3 into chromatin have been identified, including ATRX and DAXX, strongly suggesting that dysregulation of proper chromatin architecture assembly underlies the pathogenesis of at least a subset of pediatric high-grade gliomas. Mutations affecting TP53 are largely associated with IDH1 mutations and H3F3A mutations. The frequency of TERT promoter mutations and alternative lengthening of telomeres increases with age in glioblastomas. The finding of H3.3 K27M substitution in pediatric diffuse intrinsic pontine gliomas (DIPGs) is of particular diagnostic interest because current diagnosis of DIPGs is based upon a characteristic magnetic resonance imaging (MRI) appearance;

425

426 Section VIâ•… Neoplasms Table 52.3â•… Molecular characteristics of low-grade and high-grade gliomas Histopathological entity

Hallmark feature

Methylation pattern

Additional alterations

Pilocytic astrocytoma

MAPK activation (mostly due to BRAF-KIAA1549 fusions)

–

–

Diffuse intrinsic pontine glioma

H3F3A K27 mutation HIST1H3B K27 mutation

–

PDGFR amplification

Glioblastoma (GBM)

–

–

–

GBM―children

H3F3A K27 mutation

–

–

GBM―adolescents

H3F3A G34 mutation

G-CHOP (hypomethylation)

–

GBM―young adults

IDH1 mutation

G-CIMP (hypermethylation)

–

Abbreviations: G-CHOP, CpG hypomethylator phenotype; G-CIMP, glioma-CpG-island methylator phenotype; MAPK, mitogen-activated protein kinase.

however, this particular single amino acid substitution appears to be a much more sensitive marker of DIPGs than clinical and radiological factors alone. This offers the opportunity to accurately delineate patients with true high-grade gliomas of the pons and therefore identify those patients as candidates for phase I studies, while identifying those patients with atypical disease who would be expected to have a more indolent disease course. Taken together, the identification of a distinct mutational spectrum in pediatric high-grade gliomas suggests that current approaches to adult high-grade gliomas may not be directly applied to pediatric disease, and future therapies should target these mutations in chromatin architecture. Previous studies of structural aberrations in DIPGs have shown that focal amplification of PDGFRA is a recurrent event. To this extent, several ongoing studies are underway evaluating the use of receptor tyrosine kinase inhibition, specifically PDGFR inhibition, in the treatment of diffuse intrinsic pontine gliomas.16,17 Integrated genomics has thus revealed several new insights into pediatric high-grade gliomas specifically, allowing for more precise, molecular-based diagnosis but also opening up new pathways for drug discovery.

identified several novel pathways that can be targeted more effectively―specifically the use of SHH pathway inhibitors in medulloblastoma and the use of MAPK inhibition in pilocytic astrocytomas. These studies would certainly fail without proper patient selection. In the years to come, we should expect the next generation of clinical trials to integrate clinical and biological stratification of patients to improve patient classification and to identify novel molecular-based therapeutic strategies.

52.6╇Conclusion

References

The advent of integrated genomics has led to tremendous new insights into the pathogenesis and biology of various pediatric brain tumors. Although currently the contribution of integrated genomics has been to subdivide tumors that are morphologically identical into distinct entities, this in itself allows for more robust clinical trial design and allows more robust identification of clinical associations. However, despite its infancy, integrated genomics has

Pearl/Pitfall Future discoveries depend on the availability of high-quality tumor material. Thus, one paramount contribution of neurosurgical teams is the collection and storage of tumor tissue at –70°C. Fresh-frozen tissue is not only becoming increasingly mandated as inclusion criteria for upcoming clinical trials, but might also help to inform alternative treatment strategies in case of resistance to conventional treatment protocols.

╇1. Ramaswamy

V, Northcott PA, Taylor MD. FISH and chips: the recipe for improved prognostication and outcomes for children with medulloblastoma. Cancer Genet 2011;204(11):577–588 ╇2. Remke M, Hielscher T, Korshunov A, et al. FSTL5 is a marker of poor prognosis in non-WNT/non-SHH medulloblastoma. J Clin Oncol 2011;29(29):3852–3861 ╇3. Remke M, Hielscher T, Northcott PA, et al. Adult medulloblastoma comprises three major molecular variants. J Clin Oncol 2011;29(19):2717–2723

52 ╅ Molecular and Genetic Advances in the Treatment of Brain Tumors ╇4. Northcott

PA, Korshunov A, Witt H, et al. Medulloblastoma comprises four distinct molecular variants. J Clin Oncol 2011;29(11):1408–1414 ╇5. Taylor MD, Northcott PA, Korshunov A, et al. Molecular subgroups of medulloblastoma: the current consensus. Acta Neuropathol 2012;123(4):465–472 ╇6. Northcott PA, Jones DT, Kool M, et al. Medulloblastomics: the end of the beginning. Nat Rev Cancer 2012;12(12):818–834 ╇7. Rudin CM, Hann CL, Laterra J, et al. Treatment of medulloblastoma with hedgehog pathway inhibitor GDC0449. N Engl J Med 2009;361(12):1173–1178 ╇8. Taylor MD, Poppleton H, Fuller C, et al. Radial glia cells are candidate stem cells of ependymoma. Cancer Cell 2005;8(4):323–335 ╇9. Witt H, Mack SC, Ryzhova M, et al. Delineation of two clinically and molecularly distinct subgroups of posterior fossa ependymoma. Cancer Cell 2011;20(2):143–157 10. Pfister S, Janzarik WG, Remke M, et al. BRAF gene duplication constitutes a mechanism of MAPK pathway activation in low-grade astrocytomas. J Clin Invest 2008;118(5):1739–1749 11. Jones DT, Hutter B, Jäger N, et al; International Cancer Genome Consortium PedBrain Tumor Project. Recurrent somatic alterations of FGFR1 and NTRK2 in pilocytic astrocytoma. Nat Genet 2013;45(8):927–932 12. Zhang J, Wu G, Miller CP, et al; St. Jude Children’s Research Hospital–Washington University Pediatric Cancer

Genome Project. Whole-genome sequencing identifies genetic alterations in pediatric low-grade gliomas. Nat Genet 2013;45(6):602–612 13. Wu G, Broniscer A, McEachron TA, et al; St. Jude Children’s Research Hospital–Washington University Pediatric Cancer Genome Project. Somatic histone H3 alterations in pediatric diffuse intrinsic pontine gliomas and non-brainstem glioblastomas. Nat Genet 2012;44(3):251–253 14. Sturm D, Witt H, Hovestadt V, et al. Hotspot mutations in H3F3A and IDH1 define distinct epigenetic and biological subgroups of glioblastoma. Cancer Cell 2012;22(4):425–437 15. Schwartzentruber J, Korshunov A, Liu XY, et al. Driver mutations in histone H3.3 and chromatin remodelling genes in paediatric glioblastoma. Nature 2012;482(7384):226–231 16. Paugh BS, Broniscer A, Qu C, et al. Genome-wide analyses identify recurrent amplifications of receptor tyrosine kinases and cell-cycle regulatory genes in diffuse intrinsic pontine glioma. J Clin Oncol 2011;29(30): 3999–4006 17. Zarghooni M, Bartels U, Lee E, et al. Whole-genome profiling of pediatric diffuse intrinsic pontine gliomas highlights platelet-derived growth factor receptor α and poly (ADP-ribose) polymerase as potential therapeutic targets. J Clin Oncol 2010;28(8):1337–1344

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Section VI.A

Supratentorial Neoplasms

53

Craniopharyngioma Jeffrey H. Wisoff

53.1╇Background Debate persists regarding the optimal management of craniopharyngiomas. Regardless of selected management strategy, however, definitive tumor control or cure should be the goal of any treatment for pediatric craniopharyngiomas. The relative scarcity of craniopharyngiomas, the persistent lack of consensus regarding optimal treatment, and the potential morbidity of all forms of treatment combine to make evaluations of the optimal management strategy difficult, if not impossible. Given similar rates of disease control and survival with the two main treatment strategies, total resection versus partial resection and irradiation, the focus of outcome assessment has shifted to quality-of-life metrics. In this chapter, the author describes the technical aspects of surgery where the goal is obtaining a gross total resection with cure of pediatric craniopharyngioma while maximizing the overall quality of a child’s life for the decades to come. Categorization of the pattern and extent of growth assists in evaluating treatment options, potential surgical approach, and predicting outcome. Several different clinical-radiological classification systems have been proposed; all attempt to describe the degree of vertical and horizontal extension, displacement of the optic nerves and chiasm, the number of anatomical regions involved by tumor, and overall size. The size is graded as small (2 cm), medium (2 to 4 cm), large (4 to 6 cm), and giant (> 6 cm). Attention must be paid to the relationship of the dorsal aspect of the tumor and the hypothalamus. Increased involvement and deformation of the hypothalamus have been shown to predict the level of preoperative hypothalamic dysfunction as well as the operative morbidity of resection. As craniopharyngiomas enlarge, they can form multilobulated

cysts that extend along the pathways of least resistance and invade nearby anatomical spaces in the anterior, middle, and posterior fossae. These extensions must be recognized in order to optimize the surgical approach and to minimize retraction injury to normal brain parenchyma. Giant tumors may extend into multiple or all compartments, extending from the medulla to the foramen of Monro. A variety of operative approaches has been described and championed by different surgeons, including the subfrontal, pterional, bifrontal interhemispheric, subtemporal, transcallosal, and sphenoidal. Surgical adjuncts, including the trans� ultrasonic aspirator, frameless stereotaxy, and rigid and flexible neuroendoscopes, should be available and utilized when appropriate. The author prefers a modification of the pterional craniotomy with the additional removal of the supraorbital rim, anterior orbital roof, and zygomatic process of the frontal bone. This approach offers the shortest, most direct route to the suprasellar region and minimizes or eliminates retraction of normal brain. Tumors extending from the pontomedullary junction to above the foramen of Monro can be removed through this approach. In no patient is a cortical resection or sacrifice of the olfactory nerve necessary.

53.2╇ Operative Detail and Preparation 53.2.1╇ Preoperative Evaluation Depending on the clinical status and age of the patient prior to surgery, the author prefers a complete evaluation by various specialists that includes ophthal-

431

432 Section VI.Aâ•… Supratentorial Neoplasms mological, endocrinological, and neuropsychological testing. Parents and families are counseled about the expected short- and long-term postoperative course. The author’s preoperative imaging protocol consists of magnetic resonance imaging (MRI) with frameless stereotactic image acquisition and computed tomography (CT) (Fig. 53.1). CT provides detailed information about the extent and location of tumor calcification. Careful evaluation of multiplanar MRI is essential to understand the often complex relationship that craniopharyngiomas have to the visual apparatus, hypothalamus, and surrounding vasculature and will lead to improved outcomes.

fixation in young children; (2) there are shallow pediatric pins that avoid penetration of the thin skull in children < age 4 years; (3) pin tension is manually adjusted and is far more sensitive and uses less pressure than the Mayfield headholder; and (4) the head may be rotated approximately 30 degrees to either side in the frame, allowing a variety of trajectories to the suprasellar region. Infants and children < age 18 months are secured in a horseshoe headrest with extensive taping. For a right-sided approach, the head is first rotated 60 to 75 degrees to the left (more rotation for anteriorly displaced “prefixed” optic chiasm with retrochiasmatic tumors, and less rotation for posteriorly displaced “postfixed” optic chiasm seen with prechiasmatic tumors), and then the vertex is extended toward the ground with slight forward flexion toward the chin (Fig. 53.2). This allows the sphenoid ridge and Sylvian fissure to be directly along the trajectory to the suprasellar region. Frameless stereotaxy is used in all cases.

53.2.2╇ Preparation and Positioning Dexamethasone (0.1 mg/kg), levetiracetam (7 to 20 mg/kg), and cephalexin (25 mg/kg) are administered after induction and intubation. Mannitol (0.25 g/kg) is then given at the time of skin incision to help maximize brain relaxation. The diuretic effect is maximal within the first hour of surgery, long before manipulation of the pituitary stalk and hypothalamus may produce diabetes insipidus that complicates fluid and electrolyte management. Hyperventilation to a pH carbon dioxide (CO2) of 26 to 28 is maintained during the craniotomy and initial dural opening. Rigid fixation in the head frame is used for all patients > age 18 months. The author prefers the Sugita system for four reasons: (1) it allows six-pin

a

53.2.3╇Craniotomy The author utilizes a zigzag or Stealth incision beginning directly at the tragus just above the zygoma, hugging the contour of the anterior pinna, and then continuing 2 to 3 cm posterior to the hairline to the opposite midpupillary line (Fig. 53.3). Keeping the incision as close as possible to the ear, similar to a facelift procedure, minimizes the cosmetic impact of a facial scar.

b

Fig. 53.1â•… (a) Magnetic resonance imaging (MRI) and (b) computed tomography (CT) of craniopharyngiomas.

53 â•… Craniopharyngioma

Fig. 53.3â•… Stealth incision.

Fig. 53.2â•… Positioning.

Fig. 53.4â•… Craniotomy.

The temporalis fascia and muscle are cut with a no. 15 blade, not electrocautery, to minimize tissue damage and subsequent atrophy as well as retraction of the fascia. Since the temporalis muscle of a child and adolescent is substantially less bulky than that of an adult, the author bluntly dissects off the underlying calvaria with a periosteal elevator to allow for excellent reapproximation at the end of the case and to minimize temporalis muscle atrophy. The muscle is reflected anteriorly with the scalp flap, exposing the orbital rim to the supratrochlear notch, the zygomatic process of the frontal bone, and the temporal

433

434 Section VI.Aâ•… Supratentorial Neoplasms bone to just above the root of the zygoma. Spring hooks attached to the Sugita frame aid in retraction of the muscle and scalp. A one-piece, modified pterional craniotomy with removal of the anterior orbital roof, supraorbital rim, and zygomatic process of the frontal bone is now performed (Fig. 53.4). The periorbita is dissected free of the roof and lateral orbital wall. Two burr holes are placed: one in the low temporal region just above the zygoma, and the other at the “keyhole.” A handheld drill, such as the Hudson brace and perforator, allows the bone dust from the burr hole to be collected and saved for part of the reconstruction of the cranial contour at closure. For most children younger than age 12 years, the author uses the Midas Rex and B5 craniotome to create the anterior, posterior, and medial cuts of the craniotomy. Held at a 45-degree angle, the initial cut is from the temporal burr hole anteriorly to the sphenoid ridge. Then in a standard fashion the craniotome goes posteriorly from the temporal burr hole until approximately the midpupillary line, when it gently curves anteriorly to the supratrochlear notch. Using the craniotome like a jigsaw, the zygomatic process of the frontal bone is divided just beyond the suture to the keyhole. Guarded osteotomes 1 cm wide are used to create the medial cut from the orbital rim 1 cm posteriorly along the roof of the orbit and then a cut along the orbital roof from the keyhole to join with the medial orbital roof osteotomy. The entire frontal-orbitalzygomatic-temporal construct is then elevated, with fracturing of the sphenoid ridge. The craniotomy flap is typically 7 to 8 cm in length and 4 to 5 cm in width, with generous exposure of the frontal and temporal lobes on either side of the Sylvian fissure. The middle meningeal artery is frequently severed as the bone is elevated, and it needs immediate coagulation with the bipolar cautery. The sphenoid ridge is then removed with either small rongeurs or a 3- to 4-mm cutting burr. This author always places Gelfoam strips beneath the margins of the craniotomy and tents the dura to the bone. If severe hydrocephalus is present or if there is a significant solid tumor component superiorly within the third ventricle, a 4-mm endoscope is placed into the lateral ventricle under stereotactic guidance and held in place with a rigid retractor. This maneuver allows for alternation of visualization and dissection of tumor from either the endoscopic, intraventricular, or microscopic trans-sylvian routes.

53.2.4╇ Intracranial Dissection The dura is opened in a rectangular fashion and reflected anteriorly. The author prefers squared corners on his dural opening to allow exact approximation when closing. Hemoclips are used for dural

bleeding, and bipolar cautery is avoided to prevent shrinkage of the dura. The operating microscope is then introduced and is used for all further dissection. Throughout the surgery, retraction of the brain is minimized. Mannitol, hyperventilation, and gradual drainage of cerebrospinal fluid (CSF) through the opened sylvian fissure and basal cisterns will usually provide excellent relaxation, even in the presence of moderate degrees of hydrocephalus. Ventricular drainage is reserved for cases refractory to these maneuvers or when the use of an intraventricular endoscope is anticipated (vide infra). Although hydrocephalus is present in up to two-thirds of patients, preoperative shunting is reserved for patients with severe symptoms of increased intracranial pressure that are unresponsive to medical management. Since these tumors often extend diffusely throughout the suprasellar cisterns, displacing and distorting normal structures, identification of the vascular anatomy provides essential landmarks. Starting laterally, the sylvian fissure is widely split and the distal branches of the middle cerebral artery are identified. The arachnoidal dissection proceeds medially to the main trunk of the middle cerebral artery, which is followed proximally to the ipsilateral carotid bifurcation, anterior cerebral artery, and internal carotid artery. As the carotid is followed proximally to the clinoid, the optic nerve, chiasm, and/or tracts are identified in relation to the tumor. Sharp dissection is used to open the arachnoid above the optic nerves and chiasm; however, the author prefers blunt dissection with the bipolar or microdissectors when working along the anterior, medial, or lateral aspects of the optic nerves and chiasm to avoid cutting the small perforating vessels running from the carotid to the optic pathways Premature decompression of craniopharyngiomas, especially cystic tumors, causes the tumor capsule and arachnoid to become redundant, obscuring the planes of dissection. Working in the prechiasmatic, opticocarotid, and carotidotentorial triangles, an arachnoidal plane is developed and maintained between the intact tumor and the branches of the ipsilateral carotid and vessels of the circle of Willis, preserving all of the vessels and their perforating branches. This plane is developed posteriorly until the basilar artery is identified. In primary tumors, the membrane of Liliequist invariably separates the tumor from the basilar artery. The choice of instruments and method of dissection are critical. If the microbipolar is used for dissection, care must be taken to avoid overstretching the vessels. Some bipolars, such as the Yasargil, which the author prefers, have a relatively high opening force or spread. Particularly in reoperations, where the vessels may be less elastic or even fibrotic due to previous surgical manipulation or irradiation, exces-

53 â•… Craniopharyngioma sive stretch by the bipolar may cause an iatrogenic laceration, often at a branching vessel distant from the area of direct dissection. Although it is invariably quicker to use the bipolar for dissection, if there is scarring, difficulty identifying normal perforating vessels, or simply limited experience by the surgeon, slower and more focused separation of the tumor, optic apparatus, and vessels in arachnoidal planes using a variety of microdissectors is preferable. The Rhoton 6, 7, 8 and the large Yasargil microdissectors are the author’s workhorses for these situations. Once the vascular anatomy has been identified and separated from the tumor, the cyst is aspirated and the solid internal component is debulked. Care is taken to preserve the capsule of the tumor. Again working in the parachiasmal spaces and maintaining arachnoidal planes, the tumor is progressively dissected free from the optic nerves, the contralateral carotid and its branches, and the inferior aspect of the optic chiasm. An attempt is always made to identify and preserve the pituitary stalk; this can be accomplished in 30% of patients. When the stalk cannot be separated free from the tumor, it is sectioned as distal as possible and relatively early to prevent undue traction on the hypothalamus. After the tumor is dissected free from the entire circle of Willis, the pituitary stalk, and the optic apparatus, the capsule is grasped with micro-ring forceps and, with alternating traction and blunt dissection, the gliotic plane is developed that allows the tumor to be delivered from its attachment to the hypothalamus in the region of the tuber cinereum. After the tumor is removed, the entire bed must be inspected for inadvertent residual disease. A micromirror or 30-degree angled endoscope is used to view the undersurface of the chiasm and hypothalamus to confirm a complete resection. When the tumor extends into the third ventricle or has a significant retrochiasmatic component, the lamina terminalis is fenestrated. The previous placement of the neuroendoscope into the lateral or third ventricle at the start of the operation assists in monitoring the delivery of the intraventricular component of the tumor as well as providing additional CSF drainage for relaxation. Additional endoscopic dissection can be performed, eliminating the need for simultaneous or sequential transcallosal exposure of the intraventricular tumor. The lamina terminalis is easily distinguished from the chiasm, appearing pale, avascular, and often distended by tumor. There is usually a small vessel running from the middle of the anterior optic chiasm posteriorly toward the lamina terminalis. This helps to keep the surgeon oriented to the true midline. The microdissectors are particularly useful in this area. Care must be taken to remain on the wall of the tumor and not to dissect into the white matter of the medial optic tracts. Once the third ventricle

is entered and the tumor has been freed from the walls of the floor of the ventricle, the intraventricular tumor can be relatively easily delivered, often simultaneously through the lamina terminalis as well as from below the chiasm. With cystic tumors, gentle, continuous traction in a hand-over-hand fashion with small micro-ring forceps is necessary to prevent tearing of the cyst capsule, which can at times be diaphanous in consistency. As retrochiasmatic tumor is removed, the prechiasmatic space may widen, allowing an additional avenue for dissection. Dissection of the intrasellar tumor begins with sharp dissection along the posterior diaphragma sellae followed by separation of the tumor capsule from the dura of the posterior sella. If the tumor involves the dura or there are tears in the dura during dissection, there can be brisk venous bleeding from the circular and cavernous sinuses. Attempts to use bipolar coagulation are usually futile. Gentle pressure with a cottonoid or micropatty followed by packing with small pledgets of Surgicel gauze or Floseal should quickly control the hemorrhage. Dissection continues from posterior to lateral on the left, taking care to understand the relationship between the tumor and cavernous internal carotid artery. As dissection continues anteriorly, removal of the posterior planum sphenoidale and tuberculum sellae may be required to gain adequate intrasellar exposure. A micromirror or the 30-degree angled endoscope may provide adequate visualization of the anterior sella. The last area of dissection is the ipsilateral lateral wall of the sella. There is always a relative blind spot directly under the right optic nerve and internal carotid artery. Again micromirrors and the angled endoscope are a substantial aid to visualization. The standard transsphenoidal pituitary ring curettes and dissectors are a tremendous adjunct for removal of tumor along the anterior and right lateral walls of the sella. After removal of tumor, the floor of the sella must be thoroughly inspected. Rarely, there are defects communicating with the sphenoid sinus that must be obliterated with fat and pericranial grafts. Following tumor removal, the entire tumor bed must be inspected for residual disease with either a micromirror or an angled endoscope. Papaverinesoaked Gelfoam pledgets are then placed around the arteries of the circle of Willis to help ameliorate vasospasm and are removed prior to dural closure.

53.2.5╇Closure The dura is closed using interrupted 5–0 absorbable PDS sutures to approximate the corners, followed by a continuous running locking suture of 5–0 PDS. Any hemoclips that were placed during the dural opening are removed; the locking suture is both hemostatic and watertight. Prior to the final sutures, the intra-

435

436 Section VI.Aâ•… Supratentorial Neoplasms dural space is filled with warm, saline irrigation to eliminate as much intracranial air as possible. Fibrin glue is usually applied to buttress the dural closure. Additional Floseal is placed in the epidural space. The bone is replaced using absorbable microplates and screws. For a good cosmetic appearance, it is critical to have a plate bridge the zygomatic cut as well as just above the medial supraorbital rim. The bone dust that was harvested during the burr holes is used to fill the defect in the region of the keyhole. If the defect is extensive, then one of the commercially available calcium phosphate bone pastes can be used to re-create the normal bony contour. The author believes that closing the temporalis muscle and fascia in individual layers improves the cosmetic appearance and lessens the postoperative pain with jaw movement. Avoiding electrocautery to cut the muscle and fascia initially, further assists a low-tension closure. If an intraventricular endoscope was utilized, a ventricular drain is passed through the endoscope tract into the third ventricle and is attached to straight drainage at 10 cm above ear level.

53.3╇ Outcomes and Postoperative Course 53.3.1╇ Postoperative Care Following surgery and neurological examination, all children are transferred immediately to the pediatric intensive care unit. A multidisciplinary team of pediatric endocrinologists, neuro-oncologists, and intensivists collaborate in the postoperative care. Frequent urine and electrolyte analyses are performed to monitor for, and aggressively treat, electrolyte disturbances, namely DI. All children are placed on nimodipine for 10 days to prevent vasospasm secondary to manipulation and exposure of the circle of Willis to blood and the craniopharyngioma cyst fluid. Dexamethasone is tapered over the course of 1 week. Anticonvulsants are stopped after 2 weeks unless postoperative seizures occur that are not attributable to electrolyte disturbances. Postoperative MRI and CT are performed within 48 hours of surgery to ensure complete resection. Surveillance MRI and clinical follow-up occur every 3 months during the first year, every 4 months during the second year, every 6 months for the next 3 years, and every year for the next 5 years. Frequent imaging allows for early detection of recurrence

while tumors are small and preferably asymptomatic. However, long-term imaging and follow-up are important because late recurrences have been reported. Regular evaluations by dedicated pediatric endocrinologists, ophthalmologists, and neurooncologists are essential in managing these children long term.

53.3.2╇Outcome In the MRI era, radiographically confirmed complete resection is possible in 80 to 100% of patients. In the author’s series of 101 children who underwent radical resection of craniopharyngiomas, gross total resection was accomplished in all 66 (100%) of primary tumors and in 20 of 35 (57%) recurrent tumors with acceptably low morbidity. Perioperative mortality following aggressive surgery has also declined substantially over the past two decades, secondary to advances in neuroimaging and microsurgical techniques, from more than 10% down to 0 to 4% in most current series. Surgeon experience with craniopharyngiomas has a significant impact on the likelihood of achieving complete resection and good functional outcomes. Surgeons performing more than two operations per year for radical resection had good outcomes in 87% of children, compared to only 52% in those performing fewer operations. Good and excellent functional outcomes were achieved in 80% of children and more than 60% of college-age patients either attending or graduating from college—a clear indication of the high functionality of the majority of these children. New hypothalamic morbidity occurred in 25% of children; however, it was mild or moderate in all but two cases. Less than 20% of the author’s patients developed obesity and only two patients developed severe or morbid obesity. The author continues to believe that children with craniopharyngiomas should be treated with curative intent at presentation and that, in experienced hands, radical resection of pediatric craniopharyngioma at both presentation and recurrence offers the best chance of durable disease control and potential cure. Given that most recurrences happen in the first few years following resection and the lower morbidity of reoperation on smaller tumors, frequent surveillance imaging in the early postoperative period is necessary to identify recurrence early and immediately treat it while it’s small. Late recurrences, however, do happen and require continued long-term follow-up and imaging.

54

Pineal Region Tumors J. Gordon McComb and Laurence Davidson

54.1╇Background The pineal region contains a number of important anatomical structures and can harbor a variety of histologies, most notably numerous types of neoplastic lesions. For many tumors, both benign and malignant, surgical resection is indicated; however, access to the pineal region is hindered by many important surrounding anatomical structures. There has been an evolution in surgical approaches to the pineal region that, along with the implementation of the operating microscope and refinement of microsurgical techniques, has dramatically improved the safety and efficacy of surgery in this region. Since some tumors, such as germinomas, do not require excision, a minimally invasive endoscopic biopsy may be indicated in certain situations in order to obtain a histological diagnosis prior to making the decision to perform a larger surgery with the goal of resection. Over the last century, many surgical approaches have been proposed to address the diverse histologies in this complex area. No attempt is made here to critique the various approaches. The infratentorial supracerebellar approach, favored by some, is not discussed here. This chapter details the posterior interhemispheric retrocallosal and transcallosal approaches to the pineal region, the authors’ choice for addressing lesions in this area because these approaches provide the best access with the least complications.

54.2╇ Operative Detail and Preparation 54.2.1╇ Cerebrospinal Fluid Drainage The majority of patients with tumors in the pineal region have hydrocephalus. One way to deal with this is the placement of a preoperative cerebrospinal fluid

(CSF) diverting shunt. However, this results in marked diminution in the size of the ventricles, the dilatation of which is very helpful because removal of CSF at the time of the operation provides significant exposure to the pineal region. More recently, some authors are advocating endoscopic third ventriculostomy (ETV) preoperatively to address the hydrocephalus. The presence of a functioning ETV does not reduce ventricular size to the same degree as a CSF-diverting shunt; however, it is an additional operative procedure. At the time of surgery, one can usually drain CSF from the interhemispheric fissure and, upon reaching the pineal region, the opening of the surrounding arachnoid leads to increased amounts of CSF being drained and progressively more exposure. If it is not possible to adequately drain CSF in order to reach the inferior region of the interhemispheric fissure, it is always possible to place a ventriculostomy via the exposed cortex at the time of surgery. It is unusual for the authors having to resort to that maneuver, however. In many cases with tumor removal, it is possible to reestablish CSF circulation without having to resort to an ETV or to CSF diversion. If the patient shows rapid neurologic decline because of raised intracranial pressure (ICP) secondary to the hydrocephalus before an operative procedure can be undertaken, an alternative is either to do an ETV or to place a ventriculostomy. If a ventriculostomy is placed, the ventricles are kept moderately dilated by draining CSF only if the ICP exceeds 20 Torr. This allows for further decompression of the ventricles at the time of surgery and permits the inferior hemisphere to fall away from the falx cerebri, resulting in better exposure to the retrocallosal region or the corpus callosum. In the postoperative period, the presence of a ventriculostomy will accept monitoring of ICP and indicate whether CSF circulation has been adequately reestablished. Even if the ventricles are of normal size at the beginning of the procedure, enough CSF can be drained to provide adequate exposure. If need be, osmotic and nonosmotic dehydrating agents can be used.

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438 Section VI.Aâ•… Supratentorial Neoplasms

54.2.2╇ Patient Position The patient is placed in a lateral decubitus position with the operative side down (Fig. 54.1). The hips and knees are flexed to approximately 90 degrees. This provides a very stable platform for the patient. Tape is used to secure the patient to the table in order to allow for considerable rotation, elevation, or depression so as to be able to change the angle to the operative corridor, providing better visualization to the deep midline structures. Tape is applied to the hips and shoulder after placing padding within the axilla of the down shoulder. The extremities are also secured to prevent them from moving during changes in table position. The head is fixed using a Mayfield clamp or compatible device in older children, while a horseshoe headholder is used in infants and toddlers (Fig. 54.2). If the tumor is in the midline region, the patient can be positioned with either side down; however, if the lesion is eccentric to one side, the mass is placed superiorly so as to allow gravity to deliver it into the operative field. Lesions with extension to the posterior fossa need to be approached from the ipsilateral side of the brainstem, and therefore the patient is positioned with the tumor side down. With patients who require reoperation for tumor recurrence, the craniotomy can be performed on the contralateral side, without increased risk, to avoid the postoperative scarring from the initial procedure.

The patient’s head is elevated 30 degrees above the horizontal. If a retrocallosal approach is needed, the head is rotated to bring the posterior portion of the calvarium approximately 30 degrees above a line parallel to the floor. In the transcallosal approach, the superior sagittal sinus is kept parallel to the floor (Fig. 54.3). With the patient in the lateral decubitus position, the falx cerebri supports the superior hemisphere, while gravity, aided by CSF drainage, produces excellent exposure of the deep midline structures with minimal or no retraction of the dependent hemisphere (Fig. 54.4). Compared to a sitting position, the lateral decubitus position allows the surgeon to enjoy a closer working distance to the pineal region. The surgeon experiences less fatigue because the surgeon’s hands and arms are placed at waist or chest level and are not extended. Another important advantage is that the hands can most often be placed side by side rather than one above the other, as is usually the case with the patient in the sitting position. An additional advantage with the patient in the lateral decubitus position is that the incidence of the operating microscope to the pineal region can be varied widely, thereby gaining more exposure to the deep midline area even though the corridor is narrow (Fig. 54.5). The raising and lowering of the patient allows further exposure of the deep midline structures (Fig. 54.6). Additional flexibility in the vertical plane is provided by altering the height and angulation of the microscope.

Fig. 54.1â•… Schematic view of a patient in the lateral decubitus position. The hips and knees are flexed 90 degrees to provide stability. Padding is placed in the axilla and adhesive tape is used to fix the patient to the table. Not shown is tape applied to the superior shoulder. (Used with permission from McComb and Apuzzo.2)

54 â•… Pineal Region Tumors a

b

Fig. 54.2â•… The patient is in the left lateral decubitus position. A horseshoe headholder, rotatable in the horizontal and vertical planes, was used instead of Mayfield pins given his young age. A horseshoe provides good stability in young children. (a) The superior sagittal and transverse sinuses (solid lines) and scalp flap (dashed line) are drawn. (b) A frontal ventriculostomy is in place.

a

b

c

Fig. 54.3â•… Patient’s head position. (a) The head is angulated 30 degrees above the horizontal plane. (b) With a retrocallosal approach, the vertex of the head is also rotated approximately 30 degrees above the horizontal plane. (c) With a transcallosal approach, the corpus callosum is kept parallel to the horizontal plane. (Used with permission from McComb and Apuzzo.2)

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440 Section VI.Aâ•… Supratentorial Neoplasms a

a

b

c b

Fig. 54.5â•… (a–c) Altering the height and angulation of the microscope in addition to changing the level of the operating table provides for greater flexibility in the vertical plane. (Used with permission from McComb and Apuzzo.2)

Fig. 54.4â•… (a) Angulation of the head 30 degrees from the horizontal plane (b) provides gravity retraction of the inferior hemisphere to assist in development of the parafalcine corridor. (Used with permission from McComb and Apuzzo.2)

Other advantages of the lateral decubitus position compared to the sitting position include less set-up time (especially if placement of a right atrial catheter is eliminated), reduction of postural hypotension, decreased cardiovascular instability, and negligible risk of air embolism. In fact, the authors have had no instances of air emboli when using the lateral decubitus position. A major advantage, the degree of maneuverability with the lateral decubitus position, is lost when using the prone position. Gravity in the prone position is not as much an ally in providing exposure

without retraction. There is always the possibility of compromised ventilation, access to the airway, or pressure injury to the face. If given a choice, anesthesiologists much prefer the use of the lateral decubitus position over either the sitting or prone position.1

54.2.3╇Craniotomy An 8- to 10-cm long U-shaped incision is made with the length and width nearly equal and the incision extending just across the midline, the inferior segment being slightly above the level of the inion (Fig.€54.2a).2,3 For a retrocallosal approach, two midline burr holes separated approximately 6 to 8 cm are placed, with the inferior one being in the region of the torcula (Fig. 54.7). By placing the midline burr holes through the sagittal suture, it is easier to dissect the

54 â•… Pineal Region Tumors

Fig. 54.6â•… Raising and lowering the operating table greatly increases visualization of the pineal region, while minimizing the width of the bone flap required and the degree of hemispheric retraction. (Used with permission from McComb and Apuzzo.2)

dura mater from either side of the overlying bone, rather than trying to cross the suture line at a distance because one is more likely to cause a dural laceration. A third burr hole is placed 3 to 4 cm lateral to midline, midway between the other two burr holes. After separating the dura mater from the overlying bone, a craniotome is used to cut a free bone flap. Usually, the bone flap extends slightly past the midline because this obviates the possibility of lacerating the superior sagittal sinus when connecting the two burr holes. Also, it allows displacement of the falx cerebri slightly, if needed. The dura mater is opened following the edges of the bone flap, leaving enough exposed dura mater for easy postoperative closure. The dura mater is hinged on the superior sagittal sinus and is kept in place with retention sutures. If bridging veins are encountered that would compromise exposure or are at risk of being avulsed, they are coagulated and divided. With a retrocallosal approach, the bridging veins are few and small (Fig. 54.8). If a transcallosal approach is needed, the head is still elevated at 30 degrees from the horizon-

Fig. 54.7â•… The head is angled up 30 degrees and the nose is turned downward toward the floor at a 30-degree angle from horizontal. Two burr holes are placed in the midline, and one is placed 3 to 4 cm lateral to the midline on the dependent side. The bone flap needs to extend to the midline, and inferiorly to just above the level of the torcula and transverse sinus. A 6- to 8-cm long and 3- to 4-cm wide bone flap is usually sufficient. (Used with permission from McComb et al.3)

tal, but the corpus callosum is kept parallel to the floor. The draining veins encountered in a more anterior transcallosal approach tend to be larger and more frequent. We have found that one can sacrifice these bridging veins without any risk of venous infarction if one does not produce any significant retraction pressure on the hemisphere (Fig. 54.9). At the end of the procedure, the dura mater is approximated without trying to make a watertight closure. A piece of oxidized cellulose the size of the cranial defect is placed over the dura mater and bone flap secured. Other dissolvable dural closure material can be used but often is more expensive. The likelihood of a CSF leak is diminished by attempting to open the normal CSF pathways with the tumor removal, the presence of a ventriculostomy, or having done an ETV.

441

442 Section VI.Aâ•… Supratentorial Neoplasms a

b

Fig. 54.8â•… The dura mater has just been opened, hinged on the superior sagittal sinus (SSS) and held in place with retention sutures. The falx is visible and the dependent left hemisphere is just beginning to fall away from the midline. (a) It was necessary to divide the two bridging veins that became joint just before entering the SSS. (b) Intraoperative photograph showing the large amount of gravity-assisted retraction possible without the use of a fixed retractor. The splenium of the corpus callosum is visible to the left of the cavity created by excising the tumor.

54 â•… Pineal Region Tumors a

b

Fig. 54.9â•… Intraoperative photograph obtained after opening of the dura mater. The dura is being reflected onto the superior sagittal sinus (SSS). In the middle of the operative field is a single but complex draining vein. (a) The patient was placed in a lateral decubitus position, left side down, with the head angled 30 degrees upward and the corpus callosum parallel to the floor. (b) Intraoperative photograph showing the corpus callosum. The vein has been coagulated and divided. With additional removal of cerebrospinal fluid (CSF), the hemisphere has fallen further from the midline without mechanical retraction in spite of the fact that the ventricles were not dilated. (Used with permission from McNatt et al.4)

443

444 Section VI.Aâ•… Supratentorial Neoplasms

54.2.4╇ Sacrifice of Either Superficial or Deep Cerebral Bridging Veins The most direct route to many midline cerebral lesions is often barred by the presence of superficial or deep bridging veins. Because of a perceived consequence of surgically occluding and dividing these veins, imaging studies are frequently obtained to map a corridor that may be less direct and/or restricted, in order to avoid these veins and reach the desired destination. This can result in a less than optimal exposure and reduce the ability to achieve the ideal outcome, be it greater or complete tumor resection or reduced collateral involvement of structures adjacent to the target location. Conventional wisdom predicts venous infarction is likely to occur with obstruction to either the superficial or deep draining veins. Extensive connections exist between the superficial and deep venous system, with a significant degree of overlap and bidirectional flow because the cerebral veins have no valves. The extensive anastomotic nature of the cerebral venous system allows venous drainage to be altered as needed through the numerous collateral pathways. The authors have reported on their own experience in 63 pediatric patients of occluding one or more of the middle third superior sagittal sinus cortical bridging veins as the initial intracranial step in a transcallosal approach to deep midline tumors, without a single incidence of venous infarction.4 This study was followed by a second publication investigating a retrocallosal approach to pineal lesions wherein superficial bridging veins were sacrificed in 7 patients and deep bridging veins (basal vein of Rosenthal, internal cerebral vein, and precentral cerebellar vein), in another 3 patients, again with no evidence of venous infarction.5 In a third publication, the authors reviewed the clinical and experimental literature regarding the effects of sacrificing the deep cerebral veins and did not find evidence of the dire consequences of venous infarction that conventional wisdom predicts.6,7 Using the most direct approach to the region of interest without regard to location of the bridging veins is of significant advantage. It is highly suspected that the sequelae attributed to occluding the superficial and deep bridging cerebral veins result from brain retraction, especially against gravity, and can be avoided by positioning the patient and using an approach wherein gravity is an ally and not an enemy (Fig. 54.10).8,9

54.2.5╇ The Retrocallosal Approach The majority of masses in the pineal region can be partially or completely excised using a retrocallosal approach, avoiding retraction or incision of the splenium of the corpus callosum (Fig. 54.11). This

eliminates the possibility of producing a splenial disconnection deficit. The medial edge of the bone flap is centered on the midline, with the posterior margin at the level of the torcula and the transverse sinus. If the lesion is small, a narrow operative corridor is adequate, and the length of the bone flap can be correspondingly smaller. The midline, torcula, and transverse sinus can be marked on the skin prior to draping, so as to properly identify the pertinent anatomical landmarks (Fig. 54.2a). Drainage of CSF from the interhemispheric fissure or via a ventriculostomy while gently pressing on the medial surface of the hemisphere will almost always provide excellent exposure to the deep midline structures. Self-retaining retractors are not used. Handheld retractors allow for constant repositioning of the retractors and reduce the chance of injury to a given area of the cortex. Depending upon the size and the posterior extent of the pineal mass, it may or may not be seen through the dense arachnoid normally present at the tentorial notch. Generally, it is not necessary to expose the splenium of the corpus callosum, although one needs to be cognizant of its location. The internal cerebral veins, basal vein of Rosenthal, posterior pericallosal veins, internal occipital veins, posterior mesencephalic veins, precentral cerebellar veins, and the superior vermian veins may be encountered. Frequently, the tumor mass will displace some of these veins, making it possible to work between them; however, sometimes it is necessary to coagulate and divide one or more of these vessels. Further exposure can be obtained by dividing either the falx cerebri or the tentorium, as shown in Fig. 54.12. Tumor removal and dividing the falx cerebri will permit gravity to bring that portion of the tumor superior to the midline more readily into the operative field. Tumor removal can be accomplished with a variety of techniques, including aspiration, bipolar coagulation, ultrasonic aspiration, and so on, depending on the consistency of the mass and preference of the surgeon (Fig. 54.13). Depending on the location of the lesion and the degree of resection, the third ventricle may have been entered. If the third ventricle is entered, it is more likely that normal CSF circulation will be reestablished.

54.2.6╇ The Transcallosal Approach If the mass originates and is confined to the posterior portion of the third ventricle or extends well anterior to the splenium of the corpus callosum from a pineal location, a transcallosal approach is indicated (Fig.€54.14). Because the transcallosal approach is more anterior than the retrocallosal approach, the calvarial opening is shifted forward to a corresponding degree. Whereas the bridging veins from the posterior

54 â•… Pineal Region Tumors a

b

Fig. 54.10â•… In this diagram Dandy placed the patient’s head in a lateral position and drained cerebrospinal fluid (CSF) to transcallosally approach a third ventricular tumor. (a) The superior hemisphere is being retracted against gravity. (b) Head position rotated 180 degrees. The right hemisphere is dependent and falls away from the midline. Gravity is now an ally rather than an enemy, and less pressure is required to retract the hemisphere. (Used with permission from Dandy.8)

445

446 Section VI.Aâ•… Supratentorial Neoplasms

Fig. 54.12â•… Combined incision of tentorium (A) and falx (D) to optimize regional parapineal exposure. Fig. 54.11â•… With a retrocallosal interhemispheric approach, the tumor can be viewed from above through a relatively narrow corridor that allows increased visibility by moving the patient and microscope. Dividing the tentorium or falx adds to the extent of the exposure.

parietal and occipital lobes to the superior sinus are few and small, the veins are larger and more numerous from the midparietal portion of the hemisphere and assume more importance in venous drainage. The splenium of the corpus should be left intact because dividing it results in a left hemialexia. If combined with a left occipital lobe injury or any other lesion that results in a right hemianopsia, the patient experiences the disabling effect of alexia without agraphia. The deficit produced by a small midcallosal section has not been well studied but appears to be inconsequential. Even large lesions of the pineal region that extend well rostral to the splenium can be removed by a combination of a retrocallosal and midtranscallosal approach leaving the splenium intact. The falx cerebri width varies considerably, as does the degree of adhesions between the two hemispheres beneath the falx. It is best to identify both pericallosal arteries, thereby ensuring

that the dissection is between the two and not on the lateral side of one before the corpus callosum is reached. A 2- to 2.5-cm incision is made with a microsucker in the body of the corpus callosum 2.5 to 3 cm anterior to the tip of the splenium. A narrow-bladed, handheld retractor can be placed through the incision to aid visualization. Dissection is simplified if the tumor mass or hydrocephalus has thinned the corpus callosum and the posterior fornix. Just beneath the corpus callosum, the connective tissue of the tela choroidea, containing the internal cerebral veins and the choroid plexus, are encountered. It is often possible to coagulate and divide the connective tissue between the internal cerebral veins, allowing these veins to be displaced laterally in order to enter the third ventricle. However, if necessary, either one or both of these veins may be occluded and divided with little or no risk. Entry into the third ventricle is appreciated by noting the smooth ependymal lining and presence of CSF. Tumor removal is accomplished in a manner similar to that in the retrocallosal location. If a more anterior exposure is present, one can divide the choroidal fissure to gain access to the third ventricle, rather than going through the tela choroidea.

54 â•… Pineal Region Tumors a

b

c

Fig. 54.13â•… Preoperative T1-weighted (a) axial, (b) sagittal, and (c) coronal magnetic resonance images (MRIs) obtained after addition of contrast material showing a large, heterogeneously enhancing, atypical teratoid/rhabdoid tumor in the pineal region and posterior fossa. (Continued on page 448)

447

448 Section VI.Aâ•… Supratentorial Neoplasms d

e

Fig. 54.13 (Continued)â•… Intraoperative photograph demonstrating gravity-assisted retraction of the left occipital lobe, bringing the underlying tentorium into view. (d) Tumor is seen growing through the tentorium with the cerebellum visible at right and the splenium of the corpus callosum on the left side of the image. (e) The tentorium has been widely opened.

54.3╇ Outcomes and Postoperative Course Access to tumors of the pineal region can be challenging because of the deep location and important surrounding anatomical structures. In this chapter,

the authors describe their experience with the posterior interhemispheric retrocallosal and transcallosal approaches. With careful attention to patient positioning and surgical technique, these approaches provide excellent direct access to the pineal region with minimal trauma to the brain and a low risk of complications.

54 â•… Pineal Region Tumors f

g

Fig. 54.13 (Continued)â•… Postoperative T1-weighted (f) axial and (g) sagittal MRIs obtained after addition of contrast showing gross total resection of the tumor. (Used with permission from Davidson et al.5)

References ╇1. McComb JG, Barky K. Lateral decubitus position for pos-

terior fossa surgery in children. In: Humphreys RP, ed. Concepts in Pediatric Neurosurgery. Basel, Switzerland: Karger; 1985: 207–213 ╇2. McComb JG, Apuzzo MLJ. The lateral decubitus position for the surgical approach to pineal location tumors. In: Marlin AE, ed. Concepts in Pediatric Neurosurgery. Basel, Switzerland: Karger; 1988: 186–199 ╇3. McComb JG, Levy ML, Apuzzo MLJ. The posterior interhemispheric retrocallosal and transcallosal approaches to the third ventricle region. In: Apuzzo MLJ, ed. Surgery of the Third Ventricle. 2nd ed. Baltimore, MD: Williams & Wilkins; 1998: 743–747 ╇4. McNatt SA, Sosa IJ, Krieger MD, McComb JG. Incidence of venous infarction after sacrificing middle-third superior sagittal sinus cortical bridging veins in a pediatric population. J Neurosurg Pediatr 2011;7(3):224–228 ╇5. Davidson L, Krieger MD, McComb JG. Posterior interhemispheric retrocallosal approach to pineal region and posterior fossa lesions in a pediatric population. J Neurosurg Pediatr 2011;7(5):527–533 ╇6. McComb JG. Is there of risk to occlusion of the deep cerebral veins when removing pineal location tumors? In: Marlin AE, ed. Concepts of Pediatric Neurosurgery. Basel, Switzerland: Karger; 1987: 72–80 ╇7. Davidson L, McComb JG. The safety of the intraoperative sacrifice of the deep cerebral veins. Childs Nerv Syst 2013;29(2):199–207

Fig. 54.14â•… The pineal tumor depicted in this drawing extends into the posterior third ventricle and is best approached transcallosally. (Used with permission from McComb et al.3)

╇8. Dandy

W. An operation for the removal of pineal tumors. Surg Gynecol Obstet 1921;33:113–119 ╇ 9. Chi JH, Lawton MT. Posterior interhemispheric approach: surgical technique, application to vascular lesions, and benefits of gravity retraction. Neurosurgery 2006;59(1 Suppl 1):ONS41–ONS49

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55

Cerebral Hemispheric Tumors Robert P. Naftel, Elizabeth C. Tyler-Kabara, and Ian F. Pollack

55.1╇Background 55.1.1╇Indications Cerebral hemispheric brain tumors are operated upon for oncological and/or epilepsy-related reasons. Oncological indications include the need for relief of clinical and radiological evidence of mass effect from the tumor and the need for pathological diagnosis. In children, the major predictor of survival for both indolent and malignant tumors is the extent of resection.1–3 The most common hemispheric tumors are gliomas; however, unlike in adults, most pediatric gliomas are low grade.4 Often, medically refractory epilepsy is the presenting symptom in children with cerebral hemispheric tumors, particularly with glioneuronal tumors (Fig. 55.1).5 When the intractable epilepsy is localized to the lesion and associated epileptogenic cortex, surgery is indicated.6

55.1.2╇Goals The goals of therapy are individualized to each patient depending on location and histology of the tumor. Patients are evaluated and treated to achieve oncological and epilepsy-related goals, including pathological diagnosis of the tumor, maximum safe cytoreduction of the tumor, and treatment of associated epilepsy by either lesionectomy or in many cases resection of the associated epileptogenic cortex. For well-circumscribed superficial lesions, gross total resection is often the operative goal if it can be achieved without inordinate risk. Radiographic complete resection is feasible for most superficial pilo-

450

Fig. 55.1â•… A 14-year-old boy with medically intractable complex partial epilepsy. Coronal T1 sequence with contrast magnetic resonance imaging (MRI) revealed a right insular tumor. He underwent a grid-based resection of the right insular ganglioglioma and surrounding epileptogenic cortex.

cytic astrocytomas, many superficial nonpilocytic astrocytomas, and some superficial high-grade gliomas (Fig. 55.2 and Fig. 55.3). No matter the histology, there appears to be a major prognostic advantage to obtaining a gross total or near-total resection. Conversely, for some infiltrative, poorly circumscribed high-grade gliomas and nonpilocytic low-grade gliomas that invade critical brain regions, deep nuclei, or cross midline, extensive resection may not be feasible without unacceptable morbidity. In these cases, a biopsy may be a better option.

55 â•… Cerebral Hemispheric Tumors

Fig. 55.2â•… A 13-year-old girl presented to the emergency department after a first-time seizure complaining of a severe headache. Axial T1 with contrast magnetic resonance imaging (MRI) revealed a hemorrhagic right parietal tumor. Because of its superficial location, operative goal was complete radiological resection of the glioblastoma multiforme.

Fig. 55.3â•… A 13-month-old boy presented to the emergency department with lethargy. Axial T1 with contrast magnetic resonance imaging (MRI) revealed this large right frontal tumor. Because it was well circumscribed, the operative goal was a complete radiological resection of the primitive neuroectodermal tumor. If significant bleeding had been encountered, the procedure would not have been staged.

55.1.3╇ Alternate Procedures The alternatives to resection of hemispheric tumors include continued clinical observation, especially for smaller tumors with slow or unknown growth kinetics. For tumors that are in deep-seated or eloquent locations where the surgical morbidity of attempted resection would be unacceptable, biopsy is a reasonable alternative to achieve diagnosis. Chemotherapy and radiotherapy are adjuvant therapies for some tumor types, but surgery is generally recommended as first-line therapy.

55.1.4╇Advantages Surgical resection is advantageous because progression-free survival is most closely linked to extent of resection. Patients with indolent tumors who undergo complete resection can achieve a cure.

55.1.5╇Contraindications Resection of tumors in eloquent cortex or deep-seated locations may be problematic because of the risk of serious neurological deficit. Also, occasionally germ cell tumors can form in the cerebral hemispheres and are preferentially treated with radiotherapy and/ or chemotherapy rather than resection.

55.2╇ Operative Detail and Preparation 55.2.1╇ Preoperative Planning and Special Equipment Preoperative planning is assisted by multiple surgical adjuncts including stereotactic neuronavigation and functional imaging. The surgeon must confirm that all necessary equipment is available and functioning. Using stereotactic image guidance, an operative approach that minimizes damage to eloquent brain and optimizes the extent of maximum safe resection can be planned. Functional magnetic resonance imaging (MRI) and diffusion tensor imaging can localize critical cortical and subcortical loci and pathways to assist with surgical planning. These functional studies can be fused with the stereotactic guidance images to establish anatomical relationships between these functional pathways and the tumor. Depending on availability, other useful tools include intraoperative MRI and ultrasound, which provide real-time feedback on the location of the lesion and extent of resection. An ultrasonic aspirator can be helpful for debulking, but its use should be anticipated because setup can be slow.

451

452 Section VI.Aâ•… Supratentorial Neoplasms In addition to functional imaging studies, cortical stimulation techniques, which may be applied extraoperatively, using previously inserted grid or strip electrodes, or intraoperatively, at the time of the planned tumor resection, are helpful in directly localizing speech and motor areas.7 Somatosensoryevoked potential (SSEP) monitoring, defining the site of phase reversal, can also help to delineate sensorimotor cortex. In patients with intractable epilepsy in association with cortical lesions, electrocorticography (ECOG) can discriminate whether the seizures originate from the lesion alone or if there is additional epileptogenic cortex. If any of these monitoring or stimulation techniques will be used, the anesthesiologist must be informed preoperatively so that the appropriate anesthetics are used. In view of the growing trend to minimize or avoid hair shaving for neurosurgical procedures, an antibacterial shampoo on the night before surgery and on the morning of surgery is often employed to decrease skin and hair flora. In patients with significant mass effect from the tumor, corticosteroids may be initiated preoperatively and, if an extensive resection is achieved, tapered in the postoperative period. In addition, anticonvulsants may be initiated preoperatively or intraoperatively and, depending on the clinical history in terms of seizures, may be discontinued several days after surgery.

55.2.2╇ Expert Suggestions/Comments • In patients with long-standing epilepsy associated with a tumor (lesional epilepsy), surgery is planned from an epileptogenic perspective with subdural grid insertion. The grid allows localization of the epileptogenic cortex as well as mapping of motor and speech cortex using external stimulus (Fig. 55.4). • In patients with epilepsy for less than 6 months associated with the tumor, lesionectomy is performed with intraoperative ECOG. • The risk of bleeding and the estimated blood volume of the child should be considered before surgery and discussed with anesthesiology. A type and cross should be performed on all patients and typically the blood is in the room and available for transfusion.

Fig. 55.4â•… In this illustration, subdural electrodes have been inserted in a patient with intractable lesional epilepsy. Extraoperatively, the peritumoral epileptogenic cortex as well as speech and motor cortex can be mapped. Therefore, both oncology and epilepsy surgical indications can be appropriately treated.

55.2.3╇ Key Steps of the Procedure/ Operative Nuances • The head is secured in three-point fixation, and children with thin skulls (generally younger than 4 years) are supported with the Mayfield infinity support system headrest (Integra, Plainsboro, NJ, USA) or a padded horseshoe (Fig. 55.5). • Stereotactic navigation is a useful operative adjunct for many cerebral hemispheric tumors. It assists the surgeon in planning the incision, craniotomy, and dural opening. • Neurophysiological monitoring is used for tumor resections involving, or adjacent to, the sensorimotor cortex. SSEPs can be helpful in alerting the surgeon to any significant neurophysiological changes and in identifying the central sulcus through phase reversal. • In patients who will require subdural grid electrode insertion or intraoperative stimulation for mapping, plans must be made for the craniotomy to be large enough to expose the appropriate cortex.

55 â•… Cerebral Hemispheric Tumors • For superficial cortical tumors and subcortical lesions that are not immediately beneath functionally essential cortex, the most direct trajectory to the lesion is usually selected. However, for lesions adjacent to or involving critical brain regions, stereotactic and/or functional mapping techniques are useful for selecting the safest approach to the tumor. • Functional mapping, stereotactic navigation, and incorporation of tractography are valuable for deep lesions near the thalamus and basal ganglia. The approach to these deep, subcortical lesions is influenced by the predominant direction of tumor growth. Lesions that grow medially and encroach on or expand within the lateral ventricle can be approached transcallosally or from a transfrontal aspect, whereas tumors that extend laterally in the nondominant hemisphere may be approached through the insula after the Sylvian fissure has been opened. Laterally extending lesions within the dominant hemisphere and tumors that arise more posteriorly within the thalamus may be reached using a posterior parietal approach situated behind the sensorimotor cortex and above the angular gyrus. Selected lesions can also be reached via an occipital trajectory or via an incision in the middle temporal gyrus. Finally, tumors that project anterolaterally can be reached from a paramedian frontal trajectory, provided that care is taken to avoid injury to the motor pathways. These approaches are depicted in Fig. 55.6a–d and Fig. 55.7a–c.

Fig. 55.5â•… Positioning young children can be difficult, especially if neuronavigation is desired. Traditional three-point pinning fixation may not be safe because of their thin skulls and pressure needed to rigidly fixate the head. Using the combination of horseshoe headrest and three-point pin fixation is possible utilizing the Mayfield infinity support system headrest (Integra, Plainsboro, NJ, USA); the head can be rigidly fixated and reduce this risk of penetrating the skull.

a

b

Fig. 55.6â•… Skin incisions (dashed lines) and operative approaches for supratentorial hemispheric lesions in various locations. (a) Temporal lesion. (b) Low frontal lesion. (Continued on page 454)

453

454 Section VI.Aâ•… Supratentorial Neoplasms c

d

Fig. 55.6 (Continued)â•… (c) Intraventricular lesion. (d) Occipital lesion. (These images are provided courtesy of Thieme Medical Publishers, Albright, Pollack, Aldeson, Operative Techniques in Pediatric Neurosurgery, Stuttgart: Thieme, 2000.)

a

b

c

Fig 55.7â•… Craniotomies and dural openings for supratentorial hemispheric lesions in various locations. (a) Temporal lesion. (b) Low frontal lesion. (c) Intraventricular lesion. (This image is provided courtesy of Thieme Medical Publishers, Albright, Pollack, Aldeson, Operative Techniques in Pediatric Neurosurgery, Stuttgart: Thieme, 2000.)

55 â•… Cerebral Hemispheric Tumors • In most cases, a frozen section is obtained because subsequent intraoperative management may be influenced by the diagnosis. For example, for certain diagnoses, particularly ependymoma, extent of resection has such an overwhelming impact on prognosis that risking a minor neurologic deficit is more acceptable if it will permit a complete resection. Conversely, for a malignant glioma, a concerted effort to remove the central tumor mass is made without pursuing the lesion into surrounding infiltrated brain tissue. • After obtaining an adequate biopsy specimen and sending it for a frozen section, a resection technique involving central debulking and extracapsular dissection proceeds. Tumor resection is usually initiated using ultrasonic aspiration to centrally debulk the lesion. Whereas some low-grade gliomas have a well-defined tumor margin or capsule, in many others, including high-grade gliomas, no such plane is observed, and the resection must proceed from the inside outward until a boundary between tumor and normal brain is reached. • For cystic, benign astrocytomas with a welldefined nodule in which the cyst lining is nonenhancing and translucent, resection of the wall is unnecessary.8 • In cases when a dural graft is needed, pericranium is the preferred substrate, although there are also a variety of adequate nonautologous options. • In older children, metal plates, absorbable plates, or sutures may be used to re-secure the bone flap. In younger patients, absorbable plates or sutures are preferred. • An absorbable suture is used for the skin closure to avoid the difficulty of suture removal in a child.

55.2.4╇ Hazards/Risks/Avoidance of Pitfalls • In infants with large tumors, such as desmoplastic infantile gangliogliomas (Fig. 55.8), special attention should be paid to carefully monitoring and treating blood loss and ensuring adequate replacement of platelets and clotting factors because of the risk of life-threatening blood loss during tumor resection. On some occasions, surgery may need to be staged to accomplish complete resection.9

Fig 55.8â•… A 12-month-old boy presented with macrocephaly. Coronal T1 sequence with contrast magnetic resonance imaging (MRI) revealed a large, cystic tumor. He underwent resection of the desmoplastic infantile ganglioglioma. Preoperatively, preparations were made for transfusion of blood products as well as thresholds to stop surgery and return later for a second stage of resection.

• Neuronavigation can lose accuracy after dural opening and tumor manipulation due to brain shift. Ultrasound and intraoperative MRI can help to provide real-time feedback.

55.2.5╇ Salvage and Rescue Surgeons should be prepared for changes in intracranial pressure due to edema or bleeding. Standard techniques for lowering intracranial pressure are used in emergency situations: the head of the bed is elevated; hyperventilation to a PaCO2 between 25 and 30 is achieved; and mannitol is dosed in a range of 0.25 to 1 g/kg. An external ventricular drain can be inserted to drain spinal fluid or, if the tumor is cystic, the cyst can be cannulated and drained. If there is concern for hematoma formation but localization of the hematoma is not apparent, ultrasound can be used to quickly localize and evacuate the hematoma.

455

456 Section VI.Aâ•… Supratentorial Neoplasms

55.3╇ Outcomes and Postoperative Course 55.3.1╇ Postoperative Considerations • When warranted, corticosteroids are typically tapered over 3 to 7 days if significant tumor debulking has been achieved. • Postoperative MRI is obtained in the first 48 hours to determine extent of resection.

55.3.2╇Complications Complications and morbidity depend on the location of the tumor; however, various deficits―motor, sensory, speech/language, visual/ocular, memory, or endocrine dysfunction―could occur. The location of the tumor and goals of treatment determine the potential morbidity, which should be discussed with the family during the informed consent process.

References ╇1. Pollack IF, Claassen D, al-Shboul Q, Janosky JE, Deutsch M.

Low-grade gliomas of the cerebral hemispheres in children: an analysis of 71 cases. J Neurosurg 1995;82(4): 536–547 ╇2. Wisoff JH, Sanford RA, Heier LA, et al. Primary neurosurgery for pediatric low-grade gliomas: a prospective multi-institutional study from the Children’s Oncology Group. Neurosurgery 2011;68(6):1548–1554, discussion 1554–1555 ╇3. Finlay JL, Boyett JM, Yates AJ, et al; Childrens Cancer Group. Randomized phase III trial in childhood highgrade astrocytoma comparing vincristine, lomustine, and prednisone with the eight-drugs-in-1-day regimen. J Clin Oncol 1995;13(1):112–123 ╇4. Louis DN, Ohgaki H, Wiestler OD, et al. The 2007 WHO classification of tumours of the central nervous system. Acta Neuropathol 2007;114(2):97–109 ╇5. Haddad SF, Moore SA, Menezes AH, VanGilder JC. Ganglioglioma: 13 years of experience. Neurosurgery 1992;31(2):171–178 ╇6. Englot DJ, Berger MS, Barbaro NM, Chang EF. Factors associated with seizure freedom in the surgical resection of glioneuronal tumors. Epilepsia 2012;53(1):51–57 ╇7. Berger MS, Kincaid J, Ojemann GA, Lettich E. Brain mapping techniques to maximize resection, safety, and seizure control in children with brain tumors. Neurosurgery 1989;25(5):786–792 ╇8. Beni-Adani L, Gomori M, Spektor S, Constantini S. Cyst wall enhancement in pilocytic astrocytoma: neoplastic or reactive phenomena. Pediatr Neurosurg 2000;32(5):234–239 ╇9. Duffner PK, Burger PC, Cohen ME, et al. Desmoplastic infantile gangliogliomas: an approach to therapy. Neurosurgery 1994;34(4):583–589, discussion 589

56

Intraventricular Tumors Renee M. Reynolds and Richard G. Ellenbogen

56.1╇Background 56.1.1╇Indications/Goals/ Alternate Procedures/Advantages/ Contraindications Microsurgery plays a vital role in the management of pediatric intraventricular tumors. The extent of surgical resection, pathology, and associated neurologic morbidity has implications for both the child’s prognosis and outcome. These tumors are generally slow growing and become extremely large before engendering symptoms. Symptoms usually only occur after ventricular enlargement, compression of eloquent cortex, intratumor hemorrhage, or seizures. Intraventricular tumors can be surgically formidable due to their deep-seated location in cerebrospinal fluid (CSF) spaces, surrounding eloquent structures, robust vascular supply/drainage, and relative rarity. Regardless of the approach, all surgical options require the surgeon to breach a cortical structure. The primary goal in the treatment of most ventricular tumors is to achieve gross total resection while preserving function and limiting morbidity. Surgical options for complete resection are primarily microsurgical, although in select patients endoscopic techniques are part of the armamentarium. Although endoscopic techniques are mostly used as an adjuvant to microsurgery in the authors’ practice, each technique has unique indications and advantages. The initial considerations for selecting a surgical approach when reviewing the magnetic resonance imaging (MRI) of a patient with an intraventricular tumor are as follows: (1) indications for surgery (biopsy or resection versus observation), (2) anatomy, (3) pathological differential diagnosis, (4) vascular supply/venous drainage, and (5) brain topography/eloquent cortex. In the authors’ practice, posterior third ventricle/pineal region tumors with associated obstructive noncommunicating hydrocephalus are initially

treated with an endoscopic biopsy and third ventriculostomy. An endoscopic biopsy may be used to determine the management of an asymptomatic or incidentally discovered intraventricular mass suspicious for malignancy. Endoscopic techniques combined with experienced neuropathology achieve accurate diagnosis with minimal brain retraction, less disruption of cortical tracts, and a shorter hospital course. The authors use both endoscopes and/ or microsurgical mirrors in nearly every open microsurgical intraventricular tumor resection, especially when a tumor may be adherent to structures outside their field of vision. The combination of the two tools provides better visualization and access than either one alone. However, endoscopic coagulation and resection technology has not yet evolved to the point where a large vascular tumor can be easily removed solely with this technique. The authors utilize either a transcortical or transcallosal microsurgical approach in each patient with a ventricular tumor in whom a radical resection would be advantageous. The neurologic surgeon can enter at almost any topographic “safe” region of the cerebral cortex or corpus callosum and remove a large intraventricular tumor through either of these two approaches. The decision of which of the two approaches is superior depends on an analysis of the best trajectory, most generous line of sight/field of vision, and safest working corridor for the specific intraventricular tumor based on its anatomical relationships. Early control of the vascular supply is optimal; however, many approaches that are designed to avoid eloquent structures often do not secure control of the tumor vessels until most of the mass is removed. Each approach has inherent advantages and risks1 (Fig. 56.1). Often, but not always, the best trajectory with the least perturbation to the brain is the shortest distance to the lesion or through the thinnest portion of the cortex or corpus callosum. The authors have no particular preference between transcortical versus transcallosal routes and use both with equal

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458 Section VI.Aâ•… Supratentorial Neoplasms

Fig. 56.1â•… This diagram illustrates the spectrum of potential transcortical approaches for removing masses in the lateral or third ventricle.

comfort. There is much written on the subject of one approach being superior to the other, but the decision depends on the specific tumor anatomy and the surgeon’s experience and preference.2 The transcortical approach is simple and attractive, especially with a tumor’s significant dilatation of the lateral ventricles. The risks of a skillful transcortical microsurgical operation through thinned cortex using a small corticectomy are often minimal and the surgeon’s field of vision is expansive. This approach will facilitate splitting the choroidal fissure, identifying the medial or lateral choroidal branches, and sacrifice of the tumor supply. A mobile, malleable retractor or speculum device through a modest corticectomy (< 20 mm) is often adequate to circumnavigate and remove a very large lesion. The transcallosal approach is an elegant, direct route to the lateral and third ventricles and preserves the cortical anatomy, theoretically lowering the incidence of postoperative seizures. The anterior two-thirds of the callosum for anterior approaches, or the splenium for posterior approaches, can be divided without significant neuropsychological effect in most patients. Notable exceptions are patients with crossed language dominance or previous corpus callosum resections in which there was a risk of aphasia. The risks of venous infarct and

retraction-related deficits in the interhemispheric approach are fortunately uncommon but not trivial, even when retractors are used judiciously. The interhemispheric approach also requires study of the venous anatomy to ensure the surgeon chooses a trajectory and hemisphere that contain the fewest cortical vessels draining into the sagittal sinus. There is less concern for venous infarct in posterior interhemispheric approaches in which there are fewer bridging veins.

56.2╇ Operative Detail and Preparation 56.2.1╇ Preoperative Planning and Special Equipment/Expert Suggestions/ Comments Computed tomography (CT) will often reveal the mass lesion as well as associated ventriculomegaly, calcification, or intratumoral hemorrhage. All patients require high-resolution MRI with T1- and T2-weighted triplanar, fluid-attenuated inversion recovery (FLAIR), and gadolinium-enhanced images.

56 â•… Intraventricular Tumors In these tumors, magnetic resonance angiography (MRA) and magnetic resonance venography (MRV) sequences are invaluable for both surgical planning and assessing vascular supply prior to consideration of cerebral angiography. More sophisticated MRI sequences, including functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), can also be acquired to delineate the eloquent cortex or large fiber tracts, respectively. These MRI tools help the surgeon define the safest surgical corridor. Almost all patients receive tumor blood supply from the posterior lateral choroidal arteries (lateral ventricles) or posterior medial choroidal arteries (third ventricle). Patients found to have highly vascular lesions with large flow voids on MRI should undergo selective cerebral angiography and embolization when feasible. Successful embolization significantly minimizes blood loss and thus facilitates safe radical resection The authors’ cerebrovascular interventional team performs embolization in children as young as a few months old, when technically possible. Historically, massive blood loss was the cause of intraoperative catastrophe and death. Even small blood losses impact the hemodynamic stability of children, and in adults embolization usually obviates the need for blood transfusion. Key equipment required for a successful and safe microsurgical resection are a frameless stereotactic guidance system, an ultrasonic aspirator, straight and angled endoscopes, microsurgical mirrors, a retraction system (tubular or spatula), irrigating nonstick bipolar cautery, and an array of neuromicrosurgery tools. Adjuncts that we have used and that are helpful but not necessary include intraoperative ultrasound, intraoperative CT, OmniGuide laser (OmniGuide, Inc., Cambridge, MA, USA), and intraoperative cortical mapping when resecting a dominant-hemisphere lesion.

56.2.2╇ Key Steps of the Procedure/ Operative Nuances Transcortical Approaches to the Lateral and Third Ventricles There are a variety of scalp incisions suitable for transcortical trajectories. Regardless of the surgeon’s choice, the goals should be to provide adequate exposure to the lesion while maintaining a healthy blood supply to the scalp. All incisions should be positioned behind the patient’s hairline for cosmetic reasons. The authors utilize a zigzag-style incision for a bicoronal approach, and simple “linear” incision or “serpentine” incisions for other locations because they achieve the best cosmetic result and the most expansive bone exposure.3 Hair clipping is minimal.

Frontal horn/lateral ventricular approaches, in which the bone flap will be adjacent to the midline, can be addressed with a modified unicoronal or bicoronal incision. Occipital approaches necessitate a bone flap bordering the sagittal and/or transverse sinuses and are best achieved with linear, serpentine, or horseshoe-shaped incisions. Temporal ventricular lesions can be adequately exposed through a linear/zigzag, serpentine, or question-mark incision that facilitates visualization of all three temporal gyri. The craniotomy is performed based on the frameless stereotactic trajectory that maximizes the visualization of the tumor through a corticectomy or corpus callosotomy centered in the middle of the bone flap to permit maximal maneuverability. In general, for lesions in the anterior horn or anterior body of the lateral ventricle or third ventricle, an approach through the middle frontal gyrus or associated sulci is optimal. With the patient positioned supine and the head slightly flexed (15–30 degrees), a bone flap is fashioned based on the navigation, saddling the coronal suture, thus always avoiding the motor strip. For temporal lesions, options include entry through a middle temporal gyrus corticectomy or a transtemporal horn, occipitotemporal corticectomy. The head of the supine patient is rotated approximately 45 to 90 degrees to the contralateral side, with the vertex slightly down to permit venous drainage and gravity-assisted retraction. The craniotomy should be performed to allow visualization of all three temporal gyri over the mass. When utilizing the middle temporal gyrus approach on the dominant hemisphere, it is often best to preserve the superior temporal gyrus because some language may be encoded there. In dominant hemisphere tumors, language mapping may be used to avoid postoperative language deficits but is rarely needed if the corticectomy is within 4 cm of the temporal tip. A lesion located in the ventricular atrium and occipital horn is best approached through the high parieto-occipital junction, utilizing a corticectomy between the postcentral sulcus and the parieto-occipital sulcus to avoid the visual tracts. The trajectory is often the same one or slightly above the path one would take for placing a parietal-occipital ventricular catheter. These operations can be performed with the patient in the prone or lateral position. However, using this approach for very large tumors, the vascular supply is secured only after most of the tumor bulk is removed. Stereotactic guidance is often helpful to take a path that is above the visual tracts and a trajectory through the thinnest cortex. Alternatively, for a large tumor with thinned cortex in this location, a corticectomy through Keen’s point (3 cm above and 3 cm posterior to the pinna of the ear) in the nondominant hemisphere is often safe when combined with

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460 Section VI.Aâ•… Supratentorial Neoplasms DTI. The surgeon can avoid the motor strip and secure the vascular supply early with meticulous planning. Once the craniotomy is performed, the authors perform a cruciate dural opening to make maximum use of the bone opening, protecting the brain with a moist Telfa. The corticectomy is chosen based on the underlying tumor location via the least disruptive pathway to eloquent cortex. Although the authors have performed exposures through a sulcus, they prefer entrance through a gyrus, thereby avoiding retracting or avulsing a branch artery. Their preferred method is to plan a trajectory into the ventricle with stereotactic guidance. The pia/arachnoid undergoes bipolar cautery and is incised with an arachnoid knife. A ventriculostomy catheter is then passed down the planned trajectory into the ventricular system and confirmed with CSF return. The corticectomy is opened approximately 10 to 20 mm utilizing bipolar cautery and microsuction, exposing the catheter by following it through the subcortical white matter and through the ependymal surface of the ventricle. This maneuver necessitates very little subcortical dissection and allows the placement of malleable or speculum retractors to increase visibility. If the lesion is large (> 5 cm) and the patient is at significant risk of retraction injury, the authors lengthen the cortical incision and release retraction tension often. Almost all ventricular tumors can be microsurgically resected through no more than a 20-mm corticectomy.

Transcallosal Approaches to the Lateral and Third Ventricles Transcallosal approaches should be entertained in cases where the patient: (1) has small ventricles, (2) the tumor extends bilaterally, (3) the tumor is located in the third ventricle, or (4) the tumor is more posterior in the body of the lateral ventricle. Optimal patient positioning is supine, with the head midline, flexed 15 degrees. Although either side is acceptable for placement of the craniotomy, the authors prefer nondominant hemisphere approaches in anterior lesions to avoid language deficits. A craniotomy crossing the midline is then fashioned above the lesion, in part based on the cortical venous anatomy. The craniotomy also bridges the coronal suture. Breach of the sinus is carefully avoided during the craniotomy with burr holes on each side of the midline. The dura is gently reflected to the midline, developing a working corridor and line-of-sight approach adjacent to the falx, medial to the cingulate gyrus, and through the corpus callosum. The surgical

corridor chosen is one that sacrifices the fewest (and preferably no) bridging veins. The pericallosal arteries are visualized and protected with a cottonoid. A 10- to 20-mm longitudinal callosotomy is performed until the ependyma and ventricular systems are identified. A single retractor is placed, and the lateral ventricular anatomy is inspected. Lesions in the lateral ventricle should be visible upon entrance to the ventricular system. All third ventricular lesions that do not dilate a foramen require a subchoroidal or interforniceal, transvelum interpositum approach. The authors prefer the subchoroidal approach, which entails opening the choroidal fissure between the fornix and the thalamus by dividing the tenia between the fornix and choroid plexus to avoid damage to the thalamostriate vein and the thalamus. Posterior interhemispheric approaches are excellent for pineal region/posterior third ventricle tumors, especially when the tentorium is too steep to approach the tumor from the supracerebellar, infratentorial approach. The authors perform the posterior interhemispheric operation with the patient in the prone position, with all dependent body parts protected. The craniotomy, as in the anterior approach, is placed on the vertex across the midline so the shortest, most direct trajectory through the splenium is achieved. Whereas the splenium may be thicker than the body of the callosum, there are fewer bridging veins on the cortical surface of the posterior part of the brain than on the anterior portion. In addition, once the splenium is opened, the surgeon will visualize the velum interpositum containing the paired internal cerebral veins and posterior medial choroidal arteries. Care must be taken to avoid sacrificing the deep veins. Often, the surgeons can either work between the internal cerebral veins or gently retract both of them to one side while they are still embedded in the velum interpositum. The tumor resection proceeds; the surgical working corridor can be as far posterior as the tectum and as far forward as the anterior third ventricle. Regardless of approach, the tumor is resected with multiple microsurgical techniques based on its consistency and adherence to surrounding structures. The authors religiously place cottonoids around the tumor to protect normal structures and to form a barrier against blood and tumor spillage. The basic principles for successful tumor dissection include early identification of the interface between the surrounding normal anatomy and the tumor margins. Internal debulking is required with ultrasonic aspirator, laser, microsurgical suction, and bipolar coagulation. Two illustrative cases are reviewed in Fig. 56.2 and Fig. 56.3.

56 â•… Intraventricular Tumors a

b

d c

Fig. 56.2â•… (a) T2 axial and (b) T1 coronal with gadolinium. Preoperative magnetic resonance imaging (MRI) on patient with a large biventricular (L > R) subependymoma. The patient presented with partial complex seizures, papilledema, and cognitive decline. She underwent a left frontal transcortical approach to the tumor. (c) T2 axial and (d) T1 coronal with gadolinium. The patient had a gross total resection with return of her cognitive function to baseline (1 month) and resolution of her increased pressure; she is shunt free. The transcortical trajectory can be seen in the coronal image and she is seizure free.

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462 Section VI.Aâ•… Supratentorial Neoplasms a

c

e

b

d

f

Fig. 56.3â•… (a) T1 axial with gadolinium, (b) T1 sagittal with gadolinium, and (c) coronal with gadolinium. This 20-year-old woman presented with slow cognitive decline, confusion, lethargy, and memory loss, which caused her to lose her job. She had a spindle cell meningioma involving both her lateral and third ventricles. (d) Axial with gadolinium, (e) sagittal with gadolinium, and (f) coronal with gadolinium showed gross total resection of tumor through a right parasagittal craniotomy and interhemispheric transcallosal approach. Tumor was removed from the third ventricle via a right choroidal fissure split. The patient returned to school and work 1 year later. She required a shunt but returned to her premorbid neurologic condition.

56 â•… Intraventricular Tumors

56.2.3╇ Hazards/Risks/Avoidance of Pitfalls Complication avoidance begins even before incisions are made with proper positioning of the patient. The patient should be secured to the operating table to avoid movement and all pressure points should be adequately padded to avoid compression injuries. Measures to prevent deep vein thrombosis should be in place, including compression stockings and sequential compression devices in older children. If positioning requires the patient’s head to be elevated, increasing the risk of symptomatic air embolism, proper anesthetic preparation should be secured, including continuous Doppler recording and preoperative evaluation for a probe-patent foramen ovale (PPFO). Patients are pretreated with corticosteroids and mannitol and end-tidal carbon dioxide (CO2) levels are reduced to facilitate brain relaxation and resection. The dura is opened and based along the sinuses to avoid venous injury and provide maximal exposure. Tack-up sutures are placed along the periphery of the craniotomy to prevent postoperative epidural formation. Although the authors have sacrificed superficial veins obstructing their vision, excessive coagulation can cause edema or venous infarct. Although they have compromised the integrity of a deep vein on rare occasions when removing large tumors, sacrificing the veins in the deep venous system has more potential for a poor outcome. Additionally, once the cortical trajectory has been developed, excessive retraction should be avoided with periodic release of retracted cortex. Retraction of vascular structures should be monitored closely to avoid alterations in perfusion. Given the small working corridors, it is vital to inspect all aspects of the ventricular chamber to ensure complete resection prior to closure. Endoscopes and dental mirrors are utilized to gain visualization of any areas in question. In particular, the authors have needed these tools to find residual tumor stuck to the undersurface of the corpus callosum, the far end of the frontal, occipital, and temporal horns, and especially the contralateral ventricle. Ventricular communication is an essential goal of surgery and numerous moves can be undertaken intraoperatively to promote this, from frequent irrigation and inspection of the ventricles. Fenestration of the septum should be performed to allow direct ventricular communication between the lateral ventricles. Prior to closing, the authors “tour” both lateral and third ventricles with an endoscope, removing blood clots, debris, and fragments of potential tumor. An external ventricular drain (EVD) is placed within the ventricle and tunneled subcutaneously to a site adjacent to the incision. External drainage of debris, including proteinaceous material

and residual blood, facilitates the removal of these inflammatory products. Such interventions theoretically reduce both the effects of chemical meningitis and the development of shunt-dependent hydrocephalus. If the cortex collapses after an enormous intraventricular tumor is removed, the authors often place a subdural catheter over the cortex after sealing the corticectomy to avoid a subdural hygroma. Placing the patient in bed with the affected cortex down helps prevent the decompressed cortex from pulling further away from the dura.

56.3╇ Outcomes and Postoperative Course 56.3.1╇ Postoperative Considerations Patients are monitored in an intensive care setting for a minimum of 24 hours following surgery. A postoperative CT scan or Haste sequence MRI is performed immediately following surgery to identify blood products, ventricular size, and the presence and extent of edema. Additional MRI imaging is recommended within 72 hours to evaluate the extent of resection. Patients who undergo transcortical resection are placed on anticonvulsants during surgery and maintained for 1 week postoperatively, unless the patient presented with a seizure, necessitating a more long-term evaluation. Most patients suffer symptoms of chemical meningitis, such as headache and irritability, following intraventricular surgery. In an effort to reduce these symptoms, the authors place the patient on a tapering dose of intravenous steroids (often started preoperatively) as well as analgesic medications until the symptoms dissipate. EVD facilitates removal of inflammatory cells, blood, and tumor debris circulating in the CSF.

56.3.2╇Complications Neurologic deficits are often dependent on the specific approach (Table 56.1). Visual field deficits, both temporary and partial, can be appreciated in some patients who have undergone a posterior transcortical or middle fossa approach to their tumors. Postoperative weakness or sensory loss can occur after an interhemispheric transcallosal as well as a transcortical approach, and it is often secondary to retraction or venous compromise. Removal of retractors during the operation at timed intervals and careful planning of the approach to avoid sacrificing veins can be helpful. Preoperative evaluation of the internal cerebral veins on coronal and sagittal images often helps identify not only the shift in the deep venous drain-

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464 Section VI.Aâ•… Supratentorial Neoplasms Table 56.1â•… Intraventricular tumor approaches: indications and risks Approach

Indication(s)

Potential risks

Middle frontal gyrus

Lesion in bilateral frontal horns, body of lateral ventricle, third ventricle

Seizures, abulia, subdural hygroma

Anterior transcallosal approach

Lesion in bilateral frontal horns, body of lateral ventricle, third ventricle

Venous infarct, hemiparesis, sensory deficits

Middle temporal gyrus and transtemporal horn-occipitotemporal gyrus incision

Lesions in temporal horn, ambient and crural cisterns, atrium/trigone

Language deficits on dominant hemisphere, hemiparesis, visual field deficit

Superior parietal corticectomy

Lesion in atrium, posterior lateral ventricle, trigone

Visual field deficit, intraoperative hemorrhage

Posterior transcallosal approach

Lesion in pineal region, posterior third ventricle

Venous infarct, hemiparesis, injury to upward gaze center

Lateral temporal parietal corticectomy

Lesion in atrium, posterior temporal horn

Gerstmann syndrome in dominant hemisphere, visual field deficit

age but also the location of the body of the fornices. The neurologic deficit that can occur from sacrifice of a cortical vein is typically temporary and resolves with the edema; however, permanent motor deficits do occur. Language deficits can occur in patients with dominant temporal horn lesions and can be avoided with preoperative fMRI, DTI, or intraoperative language mapping. Memory and cognitive deficits can occur secondary to frontal lobe or limbic system manipulation in either transcortical or transcallosal approaches. This risk is significant and may have long-term implications for quality of life. To avoid this complication, the authors identify the body/pillars of the fornices and fimbria on the MRI preoperatively and early during resection. This is not always possible, especially when removing very large tumors. In addition, the authors consider simply shaving off tumor adherent to the limbic system, thalamus, and deep white matter and not attempting a microscopic cure, particularly in benign pathologies. Ventriculomegaly is improved but may be mildly persistent in patients following intraventricular tumor removal. The ventricular chambers may be permanently or transiently enlarged secondary to preoperative hydrocephalus or volume loss following resection of a large tumor. An EVD and followup imaging should be used judiciously and patiently. The EVD is slowly raised in order to drain all the ventricular debris and to determine if the patient has long-term shunting needs. Hydrocephalus requiring permanent CSF diversion occurs in less than 20% of the patients in the authors’ series. The need for permanent CSF diversion occurs more often with more malignant tumors and in those who do not receive a gross total resection.

Subdural hygromas are also a well-documented complication of intraventricular tumor removal. Patients with extremely large tumors with associated thinned cortical mantle are at greatest risk. The cortical surface falls away from the dura with successful resection of the tumor. Complication avoidance with irrigation into the ventricles prior to closure, closure of the pial surface, placement of a subdural drain in high-risk patients, and encouraging the patient to lie with the surgical side down for several days postoperatively can help. However, up to one-fourth of patients will be found to have such collections on postoperative imaging. Some hygromas are symptomatic, and not self-limiting, and thus will need temporary drainage or shunting of this space.

56.4╇Conclusions Surgery for intraventricular tumors in children is both elegant and complex because there is a wide spectrum of microsurgical approaches to achieve the goal of gross total resection with minimal neurologic sequelae. However, they all require the surgeon to traverse a cerebral structure. The most advantageous approach is not always readily apparent or limited to one solution. Well-planned microsurgical approaches can achieve safe and complete resection of many benign tumors. The neurosurgeon must undertake meticulous preoperative evaluation of such technical issues as line of sight, field of view, safe working corridor, extent of tumor, surrounding eloquent cortex, and precise anatomy of vascular supply, venous drainage, and CSF spaces. The endo-

56 â•… Intraventricular Tumors scope has been a valuable adjuvant to microsurgical techniques in terms of intraoperative visualization, biopsy, and treatment of hydrocephalus. The endoscopic technology will hopefully evolve so that it can play a larger role in resection of intraventricular tumors in the future.

References ╇1. Ellenbogen RG. Transcortical surgery for lateral ventric-

ular tumors. Neurosurg Focus 2001;10(6):E2

╇2. Rhoton AL Jr. The lateral and third ventricles. Neurosur-

gery 2002;51(4 Suppl):S207–S271 TH, Ellenbogen RG. Microsurgical approaches to the ventricular system. In: Ellenbogen RG, Abdulrauf SI, eds. Principles of Neurosurgery. 3rd ed. Elsevier; 2010

╇3. Lucas

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57

Tumors of the Optic Pathway and Hypothalamus Liliana C. Goumnerova

57.1╇Background Tumors of the optic pathway and hypothalamus are a unique subset of tumors seen in the pediatric population. They can occur as isolated neoplasms but are also commonly seen in neurofibromatosis 1 (NF1), and their management (surgical and adjuvant) is influenced by the presence or absence of NF1.

57.1.1╇Indications The basic and most common indications for surgery are for diagnostic purposes, for tumor debulking or resection, for control of hydrocephalus, and, on rare occasions, for control of seizures or for decompression of the optic nerves and chiasm without significant tumor resection. Tumors of the optic pathways and chiasm are seen not infrequently in the NF1 population and if there is a diagnosis or there are features of NF1, and the radiographic and clinical presentations are typical, then there is no indication for surgery for diagnosis― treatment up front is usually chemotherapy. In patients who do not have known NF1 (or a diagnosis cannot be made on clinical grounds at presentation) and who present with a tumor in this location, there are options for either proceeding with surgery or adjuvant therapy depending on the clinical presentation. Patients who present with visual deterioration alone or with hypothalamic or pituitary dysfunction, and who do not have evidence of hydrocephalus, may be treated up front with chemotherapy alone without surgery or tissue for diagnostic purposes. However, for patients who present with hydrocephalus or who have a significant cystic component of the tumor that is causing pressure on the surrounding structures and/or visual apparatus, surgery may be an option up front. Surgery in this patient population needs to be undertaken with very clearly established goals and

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expectations because these tumors are rarely completely excised and there is significant morbidity associated both with the primary disease and with all of the various surgical and nonsurgical treatments that the tumors ultimately require.

57.1.2╇Goals The goals of surgery are dependent on the background of the patient. Generally speaking, the primary goal is to obtain tissue for diagnostic purposes, and the additional goals of surgery depend on the indications: (1) need for decompression of the visual apparatus, (2) decompression of cyst, (3) debulking of tumor, (4) treatment of hydrocephalus, and (5) attempt at overall resection of tumor.

Treatment of Hydrocephalus Hydrocephalus is often the presentation in very young children with large optic pathway/hypothalamic/third ventricular tumors. This is usually due to a large mass filling the third ventricle and obstructing the foramen of Monro or the aqueduct. In situations where debulking is not being performed up front, placement of a shunt combined with an endoscopic biopsy is performed. The author performs an endoscopic biopsy followed by a septostomy and then placement of a ventriculoperitoneal (VP) shunt with a frontal ventricular catheter. An important consideration is the incision for the biopsy/shunt placement. A curvilinear or semilunar incision that can be incorporated into a bicoronal or other incision for a subsequent possible craniotomy should be performed. Because the tumor involves the floor of the third ventricle, an endoscopic third ventriculostomy (ETV) is not possible and should not be attempted.

57 â•… Tumors of the Optic Pathway and Hypothalamus

Tumor-Directed Surgery Craniotomy―Approach from Skull Base This approach is primarily for tumors that do not have significant extension into the third ventricle and is usually reserved for debulking of the optic nerve or chiasm from mass effect either due to a cyst or a large exophytic component.

Craniotomy―Approach via Third Ventricle The author’s preferred route for tumors involving the hypothalamus/third ventricle/optic pathways is an interhemispheric transcallosal corridor through the third ventricle. This allows excellent visualization of the tumor, accepts decompression of the ventricular system, and permits debulking of the tumor. However, it does not afford the ability to deal with the tumor at the skull base.

Endoscopy Endoscopic biopsy of these tumors can be relatively easily performed and tissue obtained for diagnostic purposes. With the improvement in endoscopic techniques, instrumentation, and stereotactic navigation, these biopsies, if necessary, can be performed in the absence of hydrocephalus with minimal morbidity. Although pathologically most of these tumors are low-grade gliomas, there are now ample data showing that different pathological subtypes have different biological behavior. In addition, with the development of drugs directed toward the identified genetic abnormalities in these tumors, it is even more important to know the exact pathological and genetic diagnosis because adjuvant treatment is clearly impacted by that.1 Hence, even though resection may not be an upfront operative and therapeutic option, an endoscopic biopsy is a relatively safe and easy technique that can provide a sufficient amount of tissue for the aforementioned purposes.

57.2╇ Operative Detail and Preparation 57.2.1╇ Preoperative Planning and Special Equipment Tractography and mapping of the visual pathways in these tumors have been recently reported. The author does not routinely perform these studies preoperatively and it is unclear how reliable these

studies are in patients who frequently are significantly visually compromised.2 Nevertheless, it is essential to attempt and obtain complete visual assessment with formal visual field testing prior to undertaking any operation for these tumors. Visual field assessment can be accomplished relatively reliably in young children by experienced ophthalmologists; it is essential to have such a colleague on the team because this associate is also very important in the follow-up of these patients and the subsequent decision making in their management. In children in whom visual field assessment cannot be performed, one should obtain visual acuity and evoked potential testing. Formal endocrinological assessment via blood work is also critical prior to undertaking any operative procedure in these patients. Imaging consists of magnetic resonance imaging (MRI) of the brain with and without contrast administration, diffusion, and thin cuts through the pituitary sella and suprasellar areas in three planes (coronal, axial, and sagittal), so that one can get the best evaluation of the anatomy and relationship of the tumor to the vessels, sellar anatomy, and optic apparatus. This is critical in the decision making as far as approach, assessment of surgical goals and expectations, and complications. The author and her team also routinely obtain an MRI of the entire spine because dissemination can be present, especially in very young children with optic pathway and hypothalamic gliomas. The author has not found angiography necessary and does not obtain it preoperatively. Similarly, magnetic resonance angiography/magnetic resonance venography (MRA/MRV) are not of additional benefit and the thin-cut imaging provides sufficient anatomical detail. In my institution we work in a multidisciplinary program, and it is very helpful, and our usual practice, to obtain the input of the neurology and oncology teams prior to surgery to discuss the goals and objectives of the surgical intervention.

Endoscopic Procedures The author’s preferred approach is via a right frontal burr hole unless there is asymmetric dilatation of the lateral ventricle, in which case she then uses the larger of the two ventricles. The equipment is a rigid endoscope with capability of utilizing either a 0- or 30-degree endoscope with instruments for cauterization, biopsy, and resection. The Nico Myriad device is a handheld apparatus that allows tissue aspiration and cutting and can be utilized via an endoscope, making it a very useful tool for some resections and biopsies.

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468 Section VI.Aâ•… Supratentorial Neoplasms

57.2.2╇ Expert Suggestions and Comments Key Steps of the Procedure Endoscopic Procedure The patient is positioned supine with the head maintained in the midline position and slightly flexed, nose pointing upward. It is not necessary to use rigid fixation and the author will position the patient on a gel donut. It is essential to discuss this position with the anesthesiologist and to ensure that there is no migration of the endotracheal tube because the patient’s neck is flexed. A standard right frontal approach to the ventricle is utilized, since the lesion is usually at the foramen of Monro and one does not have to be concerned about posteriorly located lesions in the third ventricle. Since these patients may need to undergo a subsequent procedure, the skin incision should not be a linear incision that is parallel to the sagittal suture. The author prefers to use a curvilinear incision that can be incorporated in the future into a bicoronal variant of pterional incision, or an incision for a right frontal craniotomy, if the patient were to need a subsequent interhemispheric procedure. Once the burr hole is made, she cannulates the ventricle with the endoscopic sheath and trocar and then advances the 30-degree endoscope. The bone chips from the burr hole are preserved (for this reason she frequently uses a handheld Hudson brace and Mackenzie perforator unless the skull thickness is extreme) and at the end of the process are placed back in the defect. The 30-degree endoscope is preferable for use in biopsies because it allows better visualization of the instruments as the biopsy is performed. Monopolar and bipolar cautery is utilized and samples from the tumor are obtained that should be of adequate amount for both diagnostic and molecular studies. The author always obtains a frozen tissue diagnosis to ensure that there is both diagnostic tissue and sufficient tissue that can be used for all of the relevant biological research. Once sufficient tissue is obtained, the area of biopsy is inspected to make sure that there is no bleeding, and the endoscope is removed. The dura is not closed and a small piece of Gelfoam is placed on top of the dural defect (not as a plug in the cortex) and the preserved bone chips are placed on top and the skin incision is closed in layers. This allows for the skull to “fill in” and there is no, or very minimal, cosmetic defect and obviates the need to place a burr hole cover―many of these children are very young and often the metal plates and screws can be irritating and cause wound disruption.3

Craniotomy All patients should have an arterial line and Foley catheter as well as adequate intravenous access. The author does not routinely administer steroids or mannitol but will often treat with prophylactic antiepileptic drugs (AEDs) for a short course of 5 days if there is evidence of retraction injury to the frontal cortex. In the absence of that, it is not necessary to administer AEDs.

Skull Base Approach from Below This approach is utilized for decompression of a large tumor and drainage of cysts associated with the tumor; however, it is not particularly useful if a significant component of the tumor extends into the third ventricle. Since many, if not all, of these tumors are chemosensitive, surgical involvement up front is limited to situations where there is need for acute decompression of mass effect―be it from solid or cystic components of the tumor. The author’s preferred route here is via a pterional approach and the side depends on the involvement of the optic nerves and quality of vision. She usually approaches these tumors from either the side of the more significantly affected eye, or from the side where, for example, a large cyst is causing compression. A modified pterional incision is utilized that can be extended into a bicoronal incision if one needs to approach the third ventricular component of the tumor at a later date. The patient is placed in rigid immobilization with the head rotated to the contralateral side and slightly extended, allowing for the frontal lobe to fall back. The author does not feel that it is necessary to remove the supraorbital bar or to perform an orbitozygomatic approach. A slightly extended frontal component of the craniotomy is lifted so that one can have adequate visualization anteriorly. It is not necessary to routinely split the Sylvian fissure, but it is very helpful to drill down the sphenoid wing so that there is access to the skull base. The path should be personalized to each case, the relevant anatomy, and the goals of surgery. Once the frontal lobe is retracted, the author places a Greenberg retractor because she does not feel that handheld retraction is adequate. The most crucial component here is to identify the normal anatomy, if possible, and that can be quite challenging with very large tumors. The optic nerves may be completely distorted and flattened, so prior to any biopsies it is vital to identify the normal structures in the area. In these cases, intraoperative navigation may be helpful but following the normal vascular and bony anatomy is the most favorable guide. Once the optic nerve is identified, then a biopsy and debulking of the tumor can be performed. Large cysts are relatively easily identified and intraoperative naviga-

57 â•… Tumors of the Optic Pathway and Hypothalamus tion is very useful in those situations to identify their locations so that they can be treated. Although there have been papers discussing the complete or radical resection of these tumors, since they arise from the optic nerves, the author does not believe they can ever be 100% completely removed, and the goal of surgery is to decompress, obtain tis-

a

c

sue diagnosis, and avoid causing additional neurologic or endocrinological injury. The tumors can be quite extensive and extend into the frontal lobes, thalamic areas, hypothalamus, and third ventricle. If one addresses the third ventricular component via an approach from below, the surgeon has to go through the floor of the third ventricle and hypothalamic

b

d

Fig. 57.1â•… Preoperative contrast-enhanced T1-weighted images in (a) sagittal and (b) axial planes of a large optic pathway/hypothalamic/third ventricular tumor causing compression of the brainstem. (c) Sagittal MRI demonstrates resection of tumor with layer left on floor of third ventricle (left arrow) and no obstruction of the aqueduct with clearing of the posterior third ventricle (right arrow). (d) Panel shows extent of resection and no evidence of tumor in aqueduct when compared to (b).

469

470 Section VI.Aâ•… Supratentorial Neoplasms area, and this is a cause of significant morbidity that could be avoided by a less aggressive resection and treatment with adjuvant chemotherapy. The consistency of the tumor often varies from being very avascular and watery to tumors that are loose but have multiple vessels coursing through them with significant bleeding or firm and rubbery consistency. An ultrasonic aspirator is useful for those tumors but it has to be used very carefully to avoid inadvertently entering into areas of concern and to control bleeding. Since many patients are small, young children, blood loss is a significant consideration and surgical resection needs to be tempered. As with any surgery in the sellar/suprasellar area, care must be taken to identify the major blood vessels of the circle of Willis and their multiple branches. Whereas identifying the internal carotid artery (ICA) and its major branches is fairly straightforward, the perforator branches may be completely engulfed by the tumor and inadvertently taken, assuming they are tumor vessels. Therefore, cautery of vessels needs to be performed very carefully and judiciously.

Approach via the Third Ventricle This approach is primarily for tumors that have large intraventricular components and is reserved for situations where there is significant mass effect and hydrocephalus. The goal here is not only to provide tissue for diagnosis but also to debulk the tumor, decompress the brainstem, and prevent the need for subsequent shunting (Fig. 57.1). The patient is positioned supine with the head in a midline position and slightly flexed so that one can have access to the third ventricle. The head is rigidly immobilized and, for infants younger than 12 months, the author will sometimes use a modified clamp with multiple pins to distribute the pressure over the skull. However, if this is performed in very young infants or the skull is very thin upon preoperative evaluation (physical examination and imaging), then she will utilize a gel ring and flexion on that. A right frontal craniotomy is performed to access the foramen of Monro and the third ventricle. The author prefers to make the skin incision so that the bone flap crosses over to the contralateral side and straddles the sagittal and coronal sutures. Intraoperative navigation is beneficial in planning the craniotomy flap, although standard landmarks are equally useful. The bone flap is extended laterally enough in case one needs to leave a frontal catheter. Again, no steroids or mannitol is administered routinely, although the author will use prophylactic AEDs. The dura is opened in a U shape, based on

the sagittal sinus and reflected to the contralateral side. The frontal lobe is retracted and a standard interhemispheric transcallosal strategy is used. The tumors are almost always immediately visible at the level of the foramen of Monro, and once the lateral ventricle is entered, a retractor is placed on the falx and frontal lobe with care taken to avoid pressure on the pericallosal artery. Once in the lateral ventricle, it is very important to orient one’s self because some tumors will cause distortion of the fornix and foramen of Monro. The author identifies the choroid plexus, cauterizes it, and also performs a subchoroidal dissection for entry into the posterior third ventricle to permit adequate access to the tumor. The thalamostriate and septal veins are identified. The next step is to perform a septostomy between the two lateral ventricles because that is essential in the management of the accompanying hydrocephalus. Once both of these have been done, attention is given to the tumor. Biopsy and debulking are performed utilizing the same principles as mentioned earlier. As the tumor is debulked, it is critical to identify the lateral walls of the third ventricle, although in some very large tumors that may not be possible until a significant debulking has been accomplished. Care must be taken to identify where the perforator and other branches of the anterior cerebral artery (ACA) and middle cerebral artery (MCA) are coursing through the tumor. The goals of surgery are to debulk the tumor and open up the aqueduct; therefore, the direction of resection needs to be geared toward the posterior aspect of the tumor/third ventricle (Fig. 57.2). Here it is very helpful to have intraoperative navigation because these tumors are very large and the anatomy can be somewhat distorted. Not infrequently, although the floor of the third ventricle has not been injured, there can be intraoperative development of diabetes insipidus (DI), and this needs to be discussed preoperatively with the anesthesia team so they are prepared for it and treat it appropriately. The goal is not to perform a complete resection because that is not possible via this path, with the exception of a few selected cases. Consequently, one should avoid going deep into the floor of the third ventricle and the author usually aims to leave a layer of tumor there. An intraoperative ultrasonic aspirator, navigation, and endoscopy to look into the ventricle are useful adjuncts, although the author believes that navigation and identifying normal anatomical landmarks are most imperative. In very large tumors, there may be significant extension laterally into the thalami and it is vital to frequently check anatomical landmarks. Perforating branches,

57 â•… Tumors of the Optic Pathway and Hypothalamus a

b

Fig. 57.2â•… (a) Intraoperative microscope view of right foramen of Monro with the fornix splayed and distended over a loose, grayish tumor filling the third ventricle. (b) Mobilization of tumor bulk away from ventricular wall and the open aqueduct at the bottom of the instrument.

as well as some of the larger branches coming off the ACAs and MCAs, are often engulfed by these massive tumors and extreme care needs to be taken to avoid injury to these vessels. Cautery is used sparingly for bleeding, although on occasions they can be fairly bloody. Intraoperative MRI is also very valuable in giving more accurate estimation of the extent of resection and anatomical orientation.

Hazards, Risks, and Avoidance of Pitfalls The major risks or hazards of operating on these tumors are vascular injury, visual loss, multiple endocrinopathies, and hypothalamic injury. The complication of hypothalamic obesity that is seen with aggressive resections involving the floor of the third ventricle is extremely disabling, without any good treatment available for it; all efforts need to be made not to injure and/or involve resection extending into the hypothalamus. For that reason, surgical goals need to be very clear prior to the operation and intraoperative attention needs to be directed toward the anatomical landmarks. Here, navigation is very useful.

57.3╇ Outcomes and Postoperative Course The majority of patients will have transient change in their electrolyte balance (hyponatremia or hypernatremia), and this needs to be managed with great attention in conjunction with the endocrinology and intensive care unit (ICU) teams. All patients are cared for in the ICU overnight and frequently will need

more than an overnight stay. It is crucial to monitor and manage hyponatremia very closely so as to avoid changes in level of consciousness and seizures. Rarely, some patients will have so-called “hypothalamic storms” consisting of episodes of tachycardia, some systolic hypertension, and significant temperature elevations in the absence of an infection. These will subside and require symptomatic treatment once infection has been excluded. Neurologic deficits such as new-onset weakness, sensory deficits, and blindness, can all occur postoperatively and should be treated appropriately. It is critical to have a multidisciplinary team involved in the overall management of these patients. They have multiple issues related to the tumors, and they will often require multiple therapies over the course of many years. In rare circumstances, a second operation may be necessary for another debulking; however, the risks of neurologic and endocrinological deficits increase in this instance, and repeat surgery is usually reserved for after there has been failure of multiple regimens of chemotherapy. On occasion, repeat surgery may need to be performed for cyst decompression. However, the cysts will refill unless the tumor is adequately treated with subsequent adjuvant therapy and, therefore, any surgery should be followed by adjuvant therapy. This author has not found the instillation of radioactive isotopes or chemotherapeutic agents particularly beneficial, although these modalities have been utilized, as a rarity, in very carefully selected patients. The author reserves radiation therapy as a last resort, and only after there has been failure of multiple surgical and chemotherapeutic approaches. Approximately 50% of these tumors fail one of the

471

472 Section VI.Aâ•… Supratentorial Neoplasms first modalities of treatment and require an operation in addition to first- or second-line chemotherapy and/or a second surgical resection. However, emerging data show that once patients survive into their late teens and early twenties, these gliomas―like most low-grade gliomas―become quiescent, and the biggest risk of mortality is associated with radiation therapy.4 Therefore, an aggressive, multidisciplinary approach is very important in the overall management of optic pathway tumors. Hydrocephalus can be difficult to manage, especially in very young infants who present with massive hydrocephalus and large tumors. In this particular patient population, there is frequently the development of extra-axial fluid collections. These need to be treated conservatively but will, on occasion, require placement of a subdural shunt and, at times, these will need to be connected to a VP shunt. This author tries to avoid complex shunt systems with multiple catheters, although that is preferable to multiple independent shunt systems. Due to the large tumors in the ventricular system and the elevated protein content in the cerebrospinal fluid (CSF), there are frequently recurrent shunt malfunctions caused by ventricular catheter occlusion or valve problems; this is a significant morbidity for these patients. Thus it is best to place shunts only when absolutely necessary. Long-term complications of tumors in this location include moyamoya disease, which is addressed in a separate chapter. The relevant point is to ensure that one preserves the superior temporal artery (STA) branch while performing the initial craniotomy

because a fair number of children will ultimately need a revascularization procedure. In summary, tumors in the optic pathway/hypothalamus and third ventricle are complex tumors that require a multidisciplinary approach from the time of diagnosis until the child enters adulthood. This includes making the appropriate decision up front to proceed with surgery or chemotherapy and then at each step of the course of the disease. Surgery will be undertaken on multiple occasions for a number of indications; however, the goals of surgery need to be very clearly identified because there are significant risks associated with surgery and the postoperative care is difficult and long. Nevertheless, ultimately, surgery can be very beneficial if utilized in conjunction with adjuvant therapies.

References ╇1. Chen

YH, Gutmann DH. The molecular and cell biology of pediatric low-grade gliomas. Oncogene 2014;33(16):2019–2026 ╇2. Lober RM, Guzman R, Cheshier SH, Fredrick DR, Edwards MS, Yeom KW. Application of diffusion tensor tractography in pediatric optic pathway glioma. J Neurosurg Pediatr 2012;10(4):273–280 ╇3. Ahn ES, Goumnerova L. Endoscopic biopsy of brain tumors in children: diagnostic success and utility in guiding treatment strategies. J Neurosurg Pediatr 2010;5(3):255–262 ╇4. Bandopadhayay P, Bergthold G, London WB, et al. Longterm outcome of 4,040 children diagnosed with pediatric low-grade gliomas: an analysis of the Surveillance Epidemiology and End Results (SEER) database. Pediatr Blood Cancer 2014;61(7):1173–1179

58

Pituitary Tumors Gautam U. Mehta and John A. Jane Jr.

58.1╇Background

58.1.5╇Contraindications

58.1.1╇Indications

Most prolactinomas should undergo a trial of medical therapy before surgery is considered. Small, asymptomatic adenomas should be followed with serial imaging.

Transsphenoidal pituitary surgery is indicated for nonfunctioning pituitary macroadenomas and endocrineactive pituitary adenomas, including prolactinomas resistant to medical therapy. Tumors compressing the optic chiasm and associated with progressive visual decline are an indication for more urgent surgery.

58.1.2╇Goals For lesions causing visual deficits, the primary goal of surgery is decompression of the optic chiasm. For all other tumors, the goals of surgery are maximal, safe resection and confirmation of diagnosis. A secondary goal for invasive lesions that cannot be completely resected is debulking to provide a radiation target that minimizes exposure of the optic apparatus.

58.2╇ Operative Detail and Preparation 58.2.1╇ Preoperative Planning and Special Equipment • Right-handed surgeons should operate on the patient’s right side so that their dominant hand is over the operative field (Fig. 58.1). The patient should be semirecumbent with

58.1.3╇ Alternate Procedures Transcranial approaches may be indicated for large tumors with significant extrasellar extension. Combined transsphenoidal and transcranial approaches may be beneficial for large tumors that cross neurovascular planes.

58.1.4╇Advantages The transsphenoidal approach offers a direct route to the sella and the anterior pituitary. The route has a favorable risk profile compared to transcranial methods. This often results in a reduction in operative time and hospital stay.

Fig. 58.1â•… Recommended operating room setup.

473

474 Section VI.Aâ•… Supratentorial Neoplasms

•

•

• •

•

the dorsum of the nose parallel to the floor to decrease venous pressure and to promote drainage of blood out of the field. The neck is laterally flexed, with the left ear toward the left shoulder, and the head rotated toward the surgeon. The bed is rotated away from the surgeon while the axis of the head is maintained neutral to the room to minimize the working distance. The site of an abdominal fat graft should be prepped and draped for every case. Oxymetazoline sprays are used by the patient in preanesthesia holding. Once intubated, cottonoids soaked in oxymetazoline are placed in the nose to promote vasoconstriction. Neuronavigation should be considered for all pediatric patients, particularly with abnormal carotid anatomy, repeat transsphenoidal surgeries, or in cases in which the sphenoid sinus is not pneumatized, incompletely pneumatized, or has a presellar or conchal conformation. Angled endoscopes should be available, particularly for cases with extrasellar extension. With abnormal nasal anatomy, such as septal deviation or concha bullosa, and with reoperations, the authors typically work with an otolaryngologist with sinonasal specialization. An orogastric (OG) tube can be placed preoperatively to suction blood and irrigation, which can cause postoperative discomfort. An OG tube should not be placed (unless under direct visualization) postoperatively or for reoperations because the sella and brain are no longer protected by bone.

58.2.2╇ Expert Suggestions/Comments A review of the nasal corridor on preoperative imaging may reveal abnormal nasal anatomy. Additionally, intersphenoid sinus septae should be marked because they may drive the surgeon laterally during surgery if they are not recognized. Finally, carotid anatomy should be reviewed because variation is frequent and may require the use of neuronavigation.

58.2.3╇ Key Steps of the Procedure/ Operative Nuances A binasal approach is used with an 18-cm, 0-degree endoscope. The middle turbinate is injected with local anesthetic with 1:200,000 epinephrine. The

Fig. 58.2â•… Lateralization of the middle turbinate and view of the superior turbinate, sphenoid os, choana, and septum indicating the cut (dashed line) that should be made to preserve the mucosa and its vascular supply before the posterior septectomy.

inferior and middle turbinates are then lateralized to visualize the superior turbinate (Fig. 58.2). When possible, the sphenoid os is identified medial to the inferior third of the superior turbinate or 1.5 cm above the choana. The superior turbinate and posterior septum are then injected. The inferior two-thirds of the superior turbinate are resected using through-biting instruments and a soft tissue shaver, opening into the posterior ethmoids. The sphenoid ostium is then opened and the sphenoidotomy is widened superiorly until the opticocarotid recess and tuberculum sellae are visualized. This is repeated in the contralateral naris. The mucosa of the posterior septum is sharply incised along its superior margin and anteriorly at the level of the posterior aspect of the middle turbinate (Fig. 58.2). This mucosa is dissected off the bony septum toward the floor of the nasal cavity for a potential vascularized flap. The downward dissection of mucosa is continued posterolaterally along the sphenoid rostrum, allowing for removal of bone without injury to mucosa or the vasculature it invests. The posterior septum is then resected using rongeurs and back-biting instruments. A bone punch or high-speed, self-irrigating drill is used to level the floor of the anterior sphenoidotomy until instruments can pass freely below the level of the tumor and remove any septations in the sphenoid sinus. If the sphenoid sinus is nonpneumatized, the drill should be used to carefully create a wide corridor to the sella. Neuronavigation should

58 â•… Pituitary Tumors be checked frequently to localize the carotid arteries. If the sphenoid sinus is aerated, the opticocarotid recesses (OCR) and paraclival carotid protuberances will mark the course of the carotids (Fig. 58.3). At this point, the authors change to a binasal three- or four-hand approach with a 30-cm, 0-degree endoscope, and the suction in the right nostril and working instrument in the left. When removing the anterior wall of the sella, the ideal initial opening is in the inferior, right corner. This allows ergonomic removal of the remainder of the sellar floor with Kerrison rongeurs for the right-handed surgeon. However, this requires certainty regarding the location of the carotid artery. Opening the sella in its center provides a reliably safe entry. The sellar bone should be removed laterally until the cavernous sinus is visualized bilaterally and superiorly until the superior intercavernous sinus is visible. In cases in which the superior intercavernous sinus has been obliterated by the tumor, the bony opening should proceed up to, and often include, the tuberculum sellae. Inferiorly, the floor of the sella is completely removed. The authors typically remove a large rectangle of dura to maximize exposure; however, a cruciate incision is equally acceptable. When the location of the carotids is not certain, a Doppler is useful prior to incising the dura. On opening, care should also be taken to not

enter the pituitary or tumor pseudocapsule. A subdural plane should be dissected centrifugally. For macroadenomas, tumor resection is often performed in a sequential piecemeal fashion. The center of the tumor capsule is sharply incised and cup forceps are used to remove samples for pathology. This opening is then used to insert ring curettes and suctions into the tumor to resect it. These tumors are often soft and typically can be removed using the suction. The bottom of the tumor against the floor of the sella is resected first to prevent early descent of the diaphragma sellae, which would tend to obstruct the operative field. Tumor resection is then carried to the back of the sella and to the walls of the cavernous sinus. A large ring curette can be helpful to elevate the remaining tumor as the inferior resection is completed. The superior tumor is resected in a similar fashion. Again, a large ring can be used to elevate the diaphragm. If tumor remains superiorly that cannot be visualized, a Valsalva maneuver can be used to push the tumor and diaphragm down into the field. Moderate, controlled elevation of end-tidal carbon dioxide (CO2), temporary jugular compression, and injection of air or saline in a lumbar drain can also be used. Folds in the diaphragm should be carefully inspected for residual tumor.

Fig. 58.3â•… View of the sellar floor (SF) demonstrating the clivus (C), planum sphenoidale (PS), opticocarotid recesses (OCR), and the optic (OP) and carotid protuberances (CP). The bony opening (dashed line) is taken up to the tuberculum sellae (TS).

475

476 Section VI.Aâ•… Supratentorial Neoplasms For microadenomas that present to pituitary capsule, circumferential dissection using the tumor pseudocapsule as a surgical dissection plane is possible. If the tumor is entered, it may still be removed in piecemeal fashion. Deep tumors may be accessed by making a vertical incision in the gland to reach the tumor. If the magnetic resonance imaging (MRI) is negative for the tumor, gland exploration can be performed by making a series of vertical incisions taken progressively deeper within the gland. A variety of acceptable methods may be used to repair the sella. If there is no evidence of an intraoperative cerebrospinal fluid (CSF) leak and the diaphragma sellae is not overly thin, an absorbable gelatin sponge or a cellulose polymer may be placed within the tumor bed with or without an extradural rigid buttress. If there is an intraoperative CSF leak, one should consider placing an autologous graft material (fat or fascia lata) and/or collagen matrix material within the tumor cavity and a rigid buttress to reconstruct the sellar opening. A vascularized nasoseptal flap is useful for large defects in the diaphragma sellae, particularly if there is complete destruction of the sellar floor preventing placement of a rigid buttress. The nose is then irrigated thoroughly and the middle turbinates are medialized. The authors do not routinely pack the nose or place lumbar drains.

58.2.4╇ Hazards/Risks/Avoidance of Pitfalls • Injury of the nasal mucosa can lead to adhesions or synechiae and should be minimized. Further, the septal mucosa may be required for a vascularized flap. It may be necessary to remove and insert the endoscope with instruments to change them under direct visualization. • Care should be taken not to unnecessarily cauterize or damage the posterior septal branches of the sphenopalatine artery (Fig. 58.2). This can lead to significant bleeding, postoperative epistaxis, and/or pseudoaneurysm formation or injury to vascular supply of the mucosal flap. • Inferior landmarks, such as the choana and the sphenoid ostium, should be identified early to establish a vertical orientation and to avoid unnecessary dissection superiorly, which carries risk of injury to the anterior cranial fossa and subsequent CSF leak. Care should also be taken with any manipulation of the turbinates, bony septum, or intersphenoid sinus septae that may transmit force to the anterior cranial base.

• During tumor resection, the pituitary gland and tumor should not be pulled down excessively because CSF leaks and stalk injury may occur from this maneuver.

58.2.5╇ Salvage and Rescue • For large intraoperative CSF leaks, the authors often reconstruct the diaphragma sellae using a collagen matrix, followed by a carefully sized abdominal fat graft within the surgical cavity, a layer of collagen matrix to reconstruct the anterior dura, a rigid buttress in an extradural plane beneath the remaining edges of sellar bone, and a fibrin glue. Transmitted brain pulsations through the reconstruction confirm that the sella has not been overly packed. • Bleeding from the cavernous sinus or intracavernous sinus is low flow and can typically be controlled easily with a gelatin sponge soaked in thrombin or a hemostatic matrix. • If carotid injury is encountered, 1 × 1-inch cottonoids should be used to rapidly pack the sphenoid sinus and nose. These should be ready at the start of every case. Bleeding may drain into the mouth, which may also need to be packed. A Foley catheter can be placed within the sphenoid sinus for compression. The patient then should be taken to angiography emergently.

58.3╇ Outcomes and Postoperative Course • An intensive care unit (ICU) admission should be considered for patients with significant sleep apnea risk, particularly if a CSF leak is encountered and continuous positive airway pressure (CPAP) cannot be used. • Visual acuity should be tested as soon as possible after all cases, particularly when a fat graft is used, because the graft can compress the optic apparatus. New visual deficits in this case are an indication for immediate reoperation. • For persistent postoperative leaks, the authors use lumbar drainage or reoperation with a nasoseptal flap. If a nasoseptal flap is not available, they obliterate the sphenoid sinus with a large fat graft after removal of the native mucosa. • Sodium levels should be checked regularly postoperatively for diabetes insipidus (DI)

58 â•… Pituitary Tumors and syndrome of inappropriate antidiuretic hormone (SIADH). Desmopressin can be administered as needed for DI; however, a standing order is not indicated initially because most DI is transient. SIADH can be treated with fluid restriction. The authors check patients’ serum sodium 1 week after surgery to screen for delayed SIADH. • am cortisol levels should also be checked for 2 days postoperatively to screen for adrenal insufficiency (AI). For levels less than 8 µg/dL, patients are placed on cortisol replacement. • Patients should be discharged with rescue doses of hydrocortisone and desmopressin

in case they experience AI or DI at home. These medications should be taken after consultation with the surgeon or endocrinologist, ideally after a serum chemistry and cortisol level are drawn. • Epistaxis can occur after pituitary surgery and is typically self-limited. Sustained bleeding is often from branches of the sphenopalatine artery and can be controlled by direct bedside cauterization under endoscopic guidance or packing. If the source is unclear and the epistaxis is sustained, angiography should be strongly considered.

477

Section VI.B

Infratentorial Neoplasms

59

Cerebellar Astrocytoma Stephanie L. Da Silva and Mark D. Krieger

59.1╇Background Cerebellar astrocytomas are the most common brain tumors encountered in children, accounting for about 40% of all brain tumors of the posterior fossa in childhood.1–3 Patients usually present toward the end of their first decade, with a median age around 8 years.4 These lesions are almost never anaplastic or malignant. The most common variety is the pilocytic astrocytoma. These are World Health Organization (WHO) grade I and are typically either microcystic or consist of a mural nodule with a large associated cyst. They usually are not invasive into surrounding brain. Less commonly seen are plain astrocytomas that are WHO grade II and are locally invasive to varying degrees. Both types may be seen with neurofibromatosis. Despite the histological heterogeneity, both types of tumors are potentially curable with surgical resection. However, invasion of critical brain structures may limit the degree of surgical resection. Presentation is relatively nonspecific for a posterior fossa mass. Acute symptoms are typically seen when obstruction of the fourth ventricle or aqueduct of Sylvius results in hydrocephalus and concomitant intracranial hypertension. This may take the form of headache, nausea/vomiting, or, in infants, increasing head circumference. A more indolent presentation may be seen in the absence of hydrocephalus when there is cerebellar dysfunction, resulting in ataxia, gait abnormalities, and nystagmus. Involvement of the floor of the fourth ventricle may result in progressive emesis. Brainstem involvement may cause progressive cranial neuropathies.5,6

59.1.1╇Indications Symptomatic lesions always require treatment. In many circumstances, a computed tomography (CT) scan may be obtained initially. However, in most

cases, magnetic resonance imaging (MRI) with and without contrast should be obtained to identify the lesion and its involvement with associated brain structures. An MRI of the spine should also be obtained to evaluate for multicentric or disseminated tumors. Magnetic resonance spectroscopy and diffusion-weighted images (DWIs) may aid in the differential diagnosis and can better delineate invasiveness. The patient should be evaluated for neurofibromatosis where appropriate. On MRI, pilocytic astrocytomas generally appear well circumscribed, with only narrow areas of infiltration. The tumors may be solid, cystic with a mural nodule and a nonenhancing cyst wall (Fig. 59.1), cystic within an enhancing cyst wall (Fig. 59.2), or mixed solid and cystic.7 It has also been noted that midline vermian tumors tend to be predominately solid and enhancing, whereas hemispheric tumors are more cystic.6 Careful observation should be made if the tumor is located within the fourth ventricle or arises from the floor of the fourth ventricle. DWI may help in this regard. Determining the tumor’s location and origin will allow for better protection against injury to the brainstem at the time of surgery. As more and more children undergo MRIs for a variety of causes, asymptomatic cerebellar lesions are being detected with increasing frequency. Obvious tumors are treated the same as symptomatic lesions. However, many of these lesions are ambiguous, diffuse, invasive, and not readily surgically accessible. These are typically followed conservatively with successive scans and are treated if/when they progress. With the exception of incidentally discovered deep and invasive lesions, surgery is indicated to make a diagnosis and, where feasible, to attempt gross total resection. Surgical intervention may be urgent or emergent if progressive hydrocephalus is present and causing significant symptoms.

481

482 Section VI.Bâ•… Infratentorial Neoplasms a

b

Fig. 59.1â•… (a) Preoperative and (b) postoperative T1-postcontrast magnetic resonance imaging (MRI) scan of a 3-year-old child with hydrocephalus and a solid/cystic pilocytic astrocytoma.

59.1.2╇Goals A clear delineation of the goals of surgical intervention always serves the surgeon and the patient best. In a stepwise fashion, the first goal should be to alleviate the hydrocephalus. The second goal should be to obtain a tissue diagnosis. The third goal is to not harm the patient; these are typically slow-growing and indolent lesions that may respond to alternative therapies. The ultimate goal is to effect a gross total resection of the lesion, where appropriate.

The art and science of the treatment of these lesions is to know when gross total resection is appropriate. Disseminated/multicentric lesions, by definition, can never be completely resected; whereas debulking may be beneficial, aggressive resection causing neurologic deficits should be avoided in these cases. Tumors that arise from, or secondarily invade, the brainstem typically cannot be completely resected without causing unacceptable deficits; in these cases, a subtotal resection with a trial of chemotherapy should be considered. Preoperative MRI,

59 â•… Cerebellar Astrocytoma a

b

Fig. 59.2â•… An 11-year-old boy who presented with nearly 2 weeks of difficulty walking and persistent vomiting is shown (a) in preoperative and (b) postoperative T1-postcontrast magnetic resonance imaging (MRI). Imaging appeared to be consistent with a cystic mass; intraoperatively, he was found to have a solid microcystic tumor.

with utilization of spectroscopy and DWI, can help determine invasiveness. However, in many cases, the degree of resectability can only be determined intraoperatively, through direct microscopic visualization and brainstem monitoring during resection. The authors had many cases where the tumor appeared to be discrete on imaging but was found to be invasive intraoperatively. Alternatively, some pilocytic astrocytomas appear to invade the brainstem but are in fact separable and safely resected (Fig. 59.3).

Not to be underestimated is the role of the family in this decision and their acceptance of risk. Many families will “want it out,” to avoid the need for adjuvant therapy and the long-term uncertainty of the outcome of a subtotal resection. These families need to understand the risks of aggressive surgery and that, even with a documented gross total resection, delayed recurrences have happened, and thus vigilant follow-up is required. Other families will have a low tolerance for surgical risk and wish

483

484 Section VI.Bâ•… Infratentorial Neoplasms a

b

to try chemotherapy after a biopsy. They need to comprehend the risks of alternative therapies and the possibility of tumor growth and progression, necessitating a delayed surgical approach under possibly less ideal circumstances. Most families will put their trust in the neurosurgeon and the neurooncology team, establishing a reciprocal therapeutic relationship to tailor the best approach to the individual situation. The degree of surgical resection is determined by the surgeon’s intraoperative estimate combined with a contrast-enhanced MRI done within 72 hours of the surgery. Gross total resection is characterized by complete resection of the enhancing solid portion of the tumor along with nonenhancing T2 tumor. Exogenous perioperative steroids may decrease the avidity of the enhancement; this should be kept in mind when evaluating the postoperative scans. In most circumstances, the cyst wall, even when it enhances, does not progress to tumor growth, and thus does not need to be resected. However, many of these tumors appear on MRI to be cystic but in fact turn out to be solid tumors with microcystic change; these “cysts” need to be resected in their entirety.

59.1.3╇ Alternate Procedures Biopsy followed by adjuvant therapy is an option for tumors that cannot be resected due to their involvement with critical brain structures, for cases that have disseminated, or in cases where the family cannot accept the risks of aggressive surgical resection. Chemotherapy, typically consisting of carboplatin and vincristine, has been shown to have some efficacy. Radiation therapy, including proton beam therapy and stereotactic radiosurgery, is an alternative for older children. However, these therapies have mixed results and may lead to adverse consequences.8

59.1.4╇Advantages Fig. 59.3╅ Patient, a 12-year-old boy, presented with symptoms of dizziness and imbalance. (a) Preoperative and (b) postoperative T1-postcontrast magnetic resonance imaging (MRI) was performed. Magnetic resonance spectroscopy (MRS) suggested a pilocytic astrocytoma and an aggressive surgical resection was undertaken.

Gross total removal is considered curative, with longterm, event-free survival for these children exceeding 90%.4,8 Moreover, radiologically confirmed complete resection has been reported to result in recurrence in less than 10% of patients.4 Long-term outcomes are still excellent when only subtotal resection is achieved.9

59.1.5╇Contraindications Surgical resection is limited if the tumor involves critical brain structures. Aggressive surgical resection should also be tempered in cases of disseminated disease. In this case, where the only possibility is to perform a subtotal or partial

59 â•… Cerebellar Astrocytoma resection, patients should be followed with serial MRI scans, given the tendency of these tumors to remain quiescent.8

59.2╇ Operative Detail and Preparation 59.2.1╇ Preoperative Planning and Special Equipment The timing of the surgery deserves primary consideration. In most cases, patients present with indolent symptoms, and there is no need to rush to surgery. However, some patients present with rapidly progressive elevations of intracranial pressure, either due to cyst expansion or, more commonly, obstructive hydrocephalus. Such patients may deteriorate rapidly, and expedited surgery is indicated to alleviate the elevated intracranial pressure. In some cases, urgent cerebrospinal fluid (CSF) diversion is needed prior to tumor surgery. External ventricular drains are placed for patients who have decreased levels of consciousness. However, this is done only after careful consideration because these patients are subsequently more likely to need permanent CSF diversion. There is some thought that endoscopic third ventriculostomy, performed prior to and separate from tumor resection, may alleviate the hydrocephalus and decrease the need for permanent CSF diversion. Some of these tumors have a significant blood supply. Intraoperative blood loss should be anticipated, and it may be a particular issue in infants. Coagulation status should be addressed, and blood for transfusion should be available. Standard neurosurgical equipment should be available for the procedure. The authors have not found particular utility in frameless stereotaxy for posterior fossa tumors because there can be significant error, given the distance from facial fiducial points and difficulty in coregistration for the back of the head. The authors have found considerable benefit to advanced intraoperative ultrasound, which can localize tumors (particularly when there is a large cyst) and determine the extent of residual tumor intraoperatively. Intraoperative MRI would serve a similar purpose, but it is obviously more cumbersome. The authors use both the ultrasonic aspirator and the aspirating tissue shaver to resect tumors. The ultrasonic aspirator is somewhat better for large-volume tumors that are soft, whereas the tissue shaver has some advantages for fibrous tumors. Brainstem, somatosensory, and motor-evoked potential monitoring should be arranged if there is any question of brainstem involvement.

59.2.2╇ Expert Suggestions/Comments Patient positioning and surgical approach should be considered together to give the best surgical view of the tumor while minimizing the risk to surrounding brain structures. In general, a route should yield the shortest path to the tumor. Rare tumors involve the lateral brainstem or come to the surface in the cerebellopontine angle. A retrosigmoid approach is usually best for these tumors. Some tumors come closest to the tentorial surface. Here, a supracerebellar infratentorial path may be used. If the tentorial facing tumors are close to midline, the authors have had good success using an occipital interhemispheric transtentorial approach. The vast majority of tumors are either in the fourth ventricle or come closest to the surface in the cerebellar hemispheres. In these cases, a wide midline occipital craniotomy is best. Most surgeons would use the prone position, because it is relatively easy to do, allowing two surgeons to work across from each other, and offering easy identification of the midline. The authors have preferred the lateral decubitus position: it gives the anesthesiologist ready access to the endotracheal tube, prevents chest/abdominal compression that can impair venous return, and prevents blood and CSF from pooling in the operative field. If the affected side is positioned up, retraction is minimized. Unfortunately, this position makes it more difficult for the assistant surgeon.

59.2.3╇ Key Steps of the Procedure/ Operative Nuances Prior to the start of the procedure, the surgeon should discuss with the anesthesiologist methods of controlling intracranial pressure and maintaining an adequate blood volume. The authors use rigid skull fixation in all children older than 2 years, unless there has been longstanding intracranial hypertension and the bone is exceptionally thin. A midline incision is delineated from the inion to the spinous process of C2. Wide bony exposure is the goal; the posterior arch of C1 is removed if the cerebellar tonsils are low lying. To avoid injury, the dura should not be opened if it appears tense. The anesthesiologist should use medical means to lower the intracranial hypertension, including mannitol, furosemide, carbon dioxide (CO2) management, and possibly barbiturates. If a ventriculostomy was placed preoperatively, it can be drained at this time. If there is considerable hydrocephalus and a ventriculostomy wasn’t placed preoperatively, a burr hole can be placed intraoperatively and the ventricle cannulated. If the tumor is associated with a large cyst, the cyst can be aspirated with ultrasound guidance prior to opening the dura.

485

486 Section VI.Bâ•… Infratentorial Neoplasms Once the dura is opened, ultrasound can be used to give a picture of the tumor for comparison after resection and to direct a path to the tumor. Hemispheric tumors are accessed through a transverse corticotomy in a cerebellar folia; this is better tolerated than an incision in the vermis. In the experience of the authors, higher (more cephalad) corticotomies minimize cerebellar retraction. If the tumor is associated with a large cyst, the cyst can be opened distal to the mural nodule, giving a wider exposure. Fourth ventricular tumors can be accessed by elevating the cerebellar tonsils and opening the telovelar region. Vermian retraction should be minimized. The tumor is biopsied and then debulked using microsurgical dissection techniques, the ultrasonic aspirator, and the tissue shaver as appropriate. A tumor can be aggressively resected from the cerebellar hemispheres; vermian dissection should be more judicious (Fig. 59.4).

a

b

Resection of a tumor that is invasive into the floor of the fourth ventricle and the periaqueductal region should be avoided; vital sign changes and changes in the evoked potential monitoring are useful adjuvants to the surgeon’s direct view. The tumor should be cleared out of the aqueduct of Sylvius where possible, to give the patient the best chance of avoiding the need for permanent CSF diversion. The authors typically place a cottonoid over the aqueduct to prevent blood products from seeping into the third ventricle. The extent of tumor resection is checked with the intraoperative ultrasound. When resection is completed, the authors will often place a ventriculostomy catheter on the floor of the fourth ventricle to drain any residual blood products and to ameliorate the effects of hydrocephalus on the healing wound. Care should be taken to prevent this ventriculostomy from traversing the aqueduct of Sylvius, where it can cause local pressure.

59.2.4╇ Hazards/Risks/Avoidance of Pitfalls The biggest surgical risks are due to aggressive surgical retraction and aggressive resection of a tumor that is invasive into the brainstem. In most cases, situational awareness can minimize these risks. The authors minimize the use of fixed retractors, try to avoid retraction of the cerebellar vermis, and ensure they are not retracting the cerebellum against the bony confines of the posterior fossa. If the tumor is in the cerebellar hemisphere, suitable positioning of the patient and appropriate placement of the corticotomy will minimize retraction. The brainstem is best protected by suitable neuromonitoring and vigilance for vital sign changes. If there is not excessive mass effect limiting retraction, the authors place a cottonoid on the floor of the fourth ventricle early in the procedure for protection. Identification of the normal anatomy helps to limit surgical misadventures in this regard.

59.2.5╇ Salvage and Rescue These tumors may be well vascularized, but they are rarely fed by large blood vessels. Meticulous surgical technique, with coagulation of the small tumor vessels, will minimize blood loss. Diligent tumor resection will hasten the end of the blood loss. Blood is kept available to transfuse patients who lose a significant amount of blood relative to their body mass. Fig 59.4╅ (a) Large solid pilocytic astrocytoma of the right cerebellar hemisphere exposed through a lateral craniotomy. (b) Gross total resection of the tumor.

59 â•… Cerebellar Astrocytoma

59.3╇ Outcomes and Postoperative Course 59.3.1╇ Postoperative Considerations Following surgical resection, patients should have a postoperative MRI within 72 hours to radiologically confirm the extent of surgical resection.10 Repeat resection should be considered for gross residual disease that is resectable. Hydrocephalus may present with neurologic changes, wound leakage, or a pseudomeningocele. It should be properly treated.

59.3.2╇Complications Cerebellar mutism is defined as a transient mood disorder with partial or complete loss of motor movements for speech production. It can be a severe complication that occurs in as many as 29% of children following posterior fossa surgery.11 Cerebellar mutism is uniquely characterized by delayed onset (1 to 6 d) and limited duration (1 d–1 y) followed by a period of recovery in which speech is marked by dysarthria.12 There is no established treatment for cerebellar mutism, although a patient may recover spontaneously and speech therapy may be useful in monitoring speech impairment.12 Mood stabilizers may be of some benefit.

References ╇1. Loh

JK, Lieu AS, Chai CY, et al. Arrested growth and spontaneous tumor regression of partially resected low-grade cerebellar astrocytomas in children. Childs Nerv Syst 2013;29(11):2051–2055 ╇2. Gunny RS, Hayward RD, Phipps KP, Harding BN, Saunders DE. Spontaneous regression of residual low-grade

cerebellar pilocytic astrocytomas in children. Pediatr Radiol 2005;35(11):1086–1091 ╇3. Vassilyadi M, Shamji MF, Tataryn Z, Keene D, Ventureyra E. Postoperative surveillance magnetic resonance imaging for cerebellar astrocytoma. Can J Neurol Sci 2009;36(6):707–712 ╇4. Due-Tønnessen BJ, Lundar T, Egge A, Scheie D. Neurosurgical treatment of low-grade cerebellar astrocytoma in children and adolescents: a single consecutive institutional series of 100 patients. J Neurosurg Pediatr 2013;11(3):245–249 ╇5. Ilgren EB, Stiller CA. Cerebellar astrocytomas. Clinical characteristics and prognostic indices. J Neurooncol 1987;4(3): 293–308 ╇6. Desai KI, Nadkarni TD, Muzumdar DP, Goel A. Prognostic factors for cerebellar astrocytomas in children: a study of 102 cases. Pediatr Neurosurg 2001;35(6):311–317 ╇7. Ogiwara H, Bowman RM, Tomita T. Long-term follow-up of pediatric benign cerebellar astrocytomas. Neurosurgery 2012;70(1):40–47, discussion 47–48 ╇8. Krieger MD, Gonzalez-Gomez I, Levy ML, McComb JG. Recurrence patterns and anaplastic change in a longterm study of pilocytic astrocytomas. Pediatr Neurosurg 1997;27(1):1–11 ╇9. Steinbok P, Mangat JS, Kerr JM, et al. Neurological morbidity of surgical resection of pediatric cerebellar astrocytomas. Childs Nerv Syst 2013;29(8):1269–1275 10. Morreale VM, Ebersold MJ, Quast LM, Parisi JE. Cerebellar astrocytoma: experience with 54 cases surgically treated at the Mayo Clinic, Rochester, Minnesota, from 1978 to 1990. J Neurosurg 1997;87(2):257–261 11. Robertson PL, Muraszko KM, Holmes EJ, et al; Children’s Oncology Group. Incidence and severity of postoperative cerebellar mutism syndrome in children with medulloblastoma: a prospective study by the Children’s Oncology Group. J Neurosurg 2006;105(6 Suppl):444–451 12. Gudrunardottir T, Sehested A, Juhler M, Schmiegelow K. Cerebellar mutism: review of the literature. Childs Nerv Syst 2011;27(3):355–363

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60

Medulloblastoma Lauren Ostling and Corey Raffel

60.1╇Background Medulloblastoma is the most common malignant brain tumor in children, accounting for 20% of all pediatric central nervous system (CNS) tumors. Although persons of any age can develop medulloblastoma, the peak age of occurrence is from ages 4 to 6 years.1 These tumors most commonly arise in the midline within the vicinity of the fourth ventricle. They com-

a

monly arise from the inferior medullary velum in the roof of the fourth ventricle and enhance brightly on magnetic resonance imaging (MRI). Medulloblastomas are small, round, blue-cell tumors with a high nuclear to cytoplasmic ratio that makes them appear hypointense on a T2-weighted MRI (Fig. 60.1). Ventricular occlusion with associated hydrocephalus is typical, and involvement of the brainstem can occur if the tumor invades the floor of the fourth ventricle.

b

Fig. 60.1â•… Medulloblastoma appearance on magnetic resonance imaging (MRI). (a) T1-weighted gadolinium-enhanced sagittal image showing the tumor arising from the inferior medullary velum and filling the fourth ventricle. In this case there was dissemination of tumor in the subarachnoid space, as seen by the contrast enhancement within the cerebellar folia. (b) T2-weighted axial image showing the same tumor arising from the inferior medullary velum.

488

60â•…Medulloblastoma Medulloblastomas are also known for their propensity to disseminate through the subarachnoid space within the cerebrospinal fluid (CSF), allowing them to metastasize to distant sites in the lateral and third ventricles, in the intracranial subarachnoid space, and down the spinal canal.

60.1.1╇Indications The goals for operative intervention are straightforward. They include: (1) relief of mass effect to alleviate symptoms, (2) obtaining tissue for diagnosis, and (3) safely reducing tumor burden, with the understanding that extent of resection affects overall survival.

60.2╇Goals Children with medulloblastoma are stratified into “average” and “high-risk” groups based on their age at diagnosis, presence of CSF dissemination, and amount of residual tumor postoperatively. Specifically, greater residual tumor (more than 1.5 cm2 on the image slice showing the maximal residual tumor) will place children in the high-risk category.1 Gross total resection of the primary tumor is the main objective; however, if this cannot be achieved safely, near-total resection (≤€1.5 cm2 residual) remains beneficial.2 Residual tumor burden greater than 1.5 cm2 may need to be left, when significant neurologic compromise would result from a more aggressive resection. Given that these tumors are often located within the fourth ventricle, the telovelar and transvermian approaches are generally utilized.

60.2.1╇ Alternate Procedures For more laterally located tumors, often of the desmoplastic subtype, a direct, transcortical approach into the affected cerebellar hemisphere can be used. In addition, some advocate a horizontal split of the vermis rather than the more frequently used vertical incision for midline tumors.

60.2.2╇Advantages Cadaveric studies have been performed in an attempt to quantify the amount of exposure gained from a telovelar versus transvermian approach. The transvermian path may provide a small advantage in gaining access to the rostral fourth ventricle, whereas the telovelar route allows easier access to the lateral recesses and foramen of Luschka.3–5 However, the telovelar is preferred over the transvermian approach by many surgeons, given the proposed relationship

between splitting the vermis and the development of cerebellar mutism.6,7 This relationship, however, is by no means certain. Additionally, combining a C1 laminectomy with the telovelar path may allow improved access to the most rostral portion of the fourth ventricle, making ventricular exposure equal to the transvermian route.4

60.2.3╇Contraindications At the time of initial diagnosis, gross total resection of the primary tumor remains the standard of care. In the face of subarachnoid dissemination at presentation, a somewhat less aggressive approach is justified. Surgery is recommended for local recurrence without dissemination proven by both MRI and cytology, but it is contraindicated in the case of recurrent, disseminated disease that is present in up to 75% of patients at the time of recurrence. In these cases, children are typically treated with high-dose chemotherapy and autologous stem cell transplant.

60.3╇ Operative Detail and Preparation 60.3.1╇ Preoperative Planning/Special Equipment Prior to operation for tumor resection, an MRI scan of the entire neuraxis with and without administration of gadolinium contrast enhancement should be performed. At the surgeon’s discretion, fiducials can be placed for the MRI scan to allow the use of intraoperative magnetic resonance imaging (iMRI). Several studies have proven the relationship between residual tumor burden and outcome for children with medulloblastomas.2 iMRI may be used to assess for residual tumor, rather than scanning postoperatively with a potential for return to the operating room. If the preoperative scan shows evidence of CSF dissemination, then a less aggressive approach to resection of the posterior fossa mass is warranted. If MRI of the spine is not obtained preoperatively, a scan of the spine should be delayed at least 2 weeks postoperatively to allow for clearance of blood products from the subarachnoid space that may obscure metastases that are present. The presence of severe hydrocephalus, with its associated alteration in level of consciousness, occasionally may require emergent treatment with an external ventricular drain (EVD). Some surgeons advocate the initial treatment of hydrocephalus, regardless of severity, with an endoscopic third ventriculostomy, followed by subsequent tumor resection.8 When hydrocephalus is not severe, other

489

490 Section VI.Bâ•… Infratentorial Neoplasms surgeons suggest the placement of a frontal EVD following induction of anesthesia just prior to the posterior fossa approach for tumor removal. Neuromonitoring, including somatosensory evoked potentials (SSEPs) and cranial nerve monitoring, may be used in cases where the tumor directly abuts or invades the brainstem in order to prevent persistent neurologic deficits. Finally, standard preoperative steroids and antibiotics should be given.

From a vascular standpoint, these tumors may have large draining veins located inferiorly. Preservation of these veins until near the end of the procedure will help prevent significant bleeding. If bleeding is encountered that cannot be easily coagulated, packing with Gelfoam and Neuro Patties can often aid in hemostasis. It is important to remain patient; move to a new area of tumor, and come back to the original site of bleeding once sufficient time has passed.

60.3.2╇ Expert Suggestions/Comments

60.3.3╇ Key Steps

Identification of the normal floor of the fourth ventricle above and below the tumor is essential for preventing accidental entry into the brainstem during tumor resection. The floor must be determined both superiorly and inferiorly to the tumor. Superiorly, a “cap” of CSF is often present due to ventricular obstruction and can help define the rostral aspect of the tumor. In addition, a keen understanding of the anatomy of the floor will help to serve as a roadmap during resection.

The patient is placed in the prone position (Fig.€60.2), head fixed within a skull fixation device, and a midline incision from the inion to approximately C2 is made. A suboccipital craniotomy centered on the midline, remaining just below the transverse sinus and including the foramen magnum, is then performed (Fig. 60.3). The inferior opening should be as wide as the foramen magnum but rarely needs to be extended into the medial third of the condyle. If the tonsils extend inferiorly or if tumor extends to the

Fig. 60.2â•… Operative positioning. The patient is prone with the neck flexed in a “military tuck” to open the foramen magnum. The head is carefully supported in a pin headholder and the bony surfaces are well padded.

60â•…Medulloblastoma

Fig. 60.3â•… Posterior fossa craniotomy. The rostral extent of bone removal is just below the transverse sinuses. Caudally, the craniotomy extends into the foramen magnum.

rostral portion of the fourth ventricle, the posterior arch of C1 can be removed to gain exposure. Next, the dura is opened in either a linear, y shape, or slightly curved fashion depending on surgeon preference (Fig. 60.4). Dural retention sutures are then placed and the arachnoid of the cisterna magna is opened with sharp dissection. At this point, the surgeon is left with a view of the cerebellar tonsils, the vallecula, and the cervicomedullary junction (Fig. 60.5).

Telovelar Approach The cerebellomedullary fissure is defined as the cleft that exists between the anterior surface of the tonsils and the posterior aspect of the caudal medulla. For smaller fourth-ventricular tumors, this anatomy will be preserved and entry into the ventricle can be achieved by incising the tela choroidea and the inferior medullary velum, which make up the inferior portion of the roof of the fourth ventricle. No

known functional neural tissue exists within these structures, making this approach the choice of many surgeons. In order to reach the telovelar junction, dissection of the arachnoid in the uvulotonsillar and medullotonsillar space is performed, followed by elevation of the tonsil superolaterally and retraction of the uvula toward the contralateral hemisphere. The tela is incised near the foramen of Magendie. The incision is extended superiorly through the inferior medullary velum to the level of the fastigium, where it joins the superior medullary velum. The tumor should come into view at this point and resection can commence.3,5 For larger tumors, extension through the foramen of Magendie occurs and thinning of the vermis and cerebellar peduncles may be present (Fig. 60.6). The tela and inferior medullary velum may be indistinguishable as well. In these cases, the tumor should be initially debulked. This may allow for partial restoration of normal anatomy and the surgical corridor discussed earlier can then be used.9

491

492 Section VI.Bâ•… Infratentorial Neoplasms

Fig. 60.4â•… “Y-shaped” durotomy helps the operator manage bleeding from the occipital and marginal sinuses. Here bleeding was controlled with silver clips. The pink tumor can be seen in the vallecula through the arachnoid overlying the cerebellar tonsils.

Transvermian Approach

Tumor Resection―Both Approaches

For the transvermian approach, the same opening down to the level of the tonsils is performed. However, instead of completing the arachnoid dissection around the tonsils to access the cerebellomedullary fissure, the inferior vermis (uvula) is identified in the midline between the cerebellar hemispheres and tonsils and split vertically. The nodule lies beneath the uvula and will also require splitting. Both sides of the vermis are then retracted laterally to expose the roof of the fourth ventricle. The tela and inferior medullary velum should then be incised for entry into the ventricle. Similar to the telovelar approach, the superior medullary velum should remain intact as decussating fibers from the superior cerebellar peduncle lie beneath this structure.3

During tumor resection, for both small and large tumors, an attempt to locate a plane between the tumor and surrounding tissue should be made. This allows for circumferential resection without damage to underlying structures. In addition, feeding vessels should be coagulated early on to prevent excessive bleeding during resection. These tumors are often soft and can be removed with gentle suction. If a plane has not been identified, caution must be taken not to enter the floor of the fourth ventricle or adjacent cerebellar peduncles. Neuronavigation and neuromonitoring may be helpful in guiding resection around eloquent areas. Once maximal, safe tumor resection is completed, the dura is closed in primary fashion with a dural graft as necessary. A Valsalva maneuver should be per-

60â•…Medulloblastoma

Fig. 60.5â•… Exposure of the fourth ventricle, in another patient. Here, rostral is to the left. The cerebellar tonsils are gently moved laterally and rostrally exposing the caudal fourth ventricle. The right posterior inferior cerebellar artery is clearly seen.

formed to assess for any CSF leakage. The bone is then put back and fixed in place with titanium plates and screws and the muscles are approximated in layered fashion. The fascia must be closed tightly, followed by closure of the subcutaneous tissue and skin.

Hazards/Risks/Avoidance of Pitfalls Careful attention should be paid to the dural opening because a persistent occipital sinus may exist. This can be present in up to 10% of adults; however, it is more frequently encountered in infants who have not yet begun to ambulate.10 In addition, the marginal sinus surrounds the cervicomedullary junction at the foramen magnum. The marginal sinus can sometimes be coagulated. However, coagulation of the dura will inevitably cause it to shrink, making

primary closure more difficult. When a large sinus or venous lake is encountered, the two leaves of the dura forming the walls of the sinus can be sutured together, effectively obliterating the sinus. Small surgical or aneurysm clips should be available because they can be used for both the marginal and occipital sinus. Occasionally, the occipital sinus may need to be ligated and divided. Moving forward to the arachnoid dissection around the tonsils, care must be taken in preserving both the medial and lateral trunks of the posterior inferior cerebellar artery (PICA). In addition, placement of a retractor blade along the tonsil can cause damage to the cerebellar tissue itself if it is too taut, or cause vascular compromise of the telovelotonsillar branch of PICA, found between the tonsil and the inferior roof of the fourth ventricle. During resection, it may become clear that the tumor is adherent

493

494 Section VI.Bâ•… Infratentorial Neoplasms

Fig. 60.6â•… Exposure of a large tumor, in another patient. Here again, rostral is to the left. Note the soft, pink vascular tumor projecting from the fourth ventricle into the vallecula. The cerebellar tonsils are retracted laterally and the vermis is retracted rostrally, allowing visualization of the caudal pole of the tumor. A cottonoid patty is slid anterior to the tumor to protect the floor of the fourth ventricle.

to, or infiltrates, the brainstem. If the tumor cannot easily be lifted away from the brainstem, a layer of tumor a few millimeters thick must be left behind because the tumor is invasive into the parenchyma of the brainstem; its resection there invariable leads to damage to the nuclei and tracts located just below the floor. Similarly, aggressive pulling on the tumor can result in damage to the brainstem and/or cranial nerves, leaving the patient with permanent neurologic sequela. As mentioned previously, knowledge of the floor anatomy and identification of areas of normal floor are essential in avoiding entry into the brainstem.

60.4╇ Outcomes and Postoperative Course 60.4.1╇ Postoperative Considerations Postoperatively, the patient will need to be monitored for the development of hydrocephalus. In most cases, an EVD will be present and a weaning trial will assess the need for permanent CSF diversion. An MRI should be performed in the immediate (within 72 h) postoperative period to assess for residual tumor burden. If that burden exceeds 1.5 cm2, then further resection should be considered if the surgeon feels this can be done safely.

60.4.2╇Complications The most dreaded complication following resection of large, midline posterior fossa tumors, especially medulloblastomas, is the development of cerebellar mutism or posterior fossa syndrome.6 These terms are often used interchangeably to describe a syndrome of delayed-onset oropharyngeal apraxia, including lack of speech, hypotonia, ataxia, emotional lability, and sometimes cranial nerve deficits. The syndrome, once thought to be quite rare, has been reported to occur in as many as 30% of patients undergoing resection of a medulloblastoma. Multiple theories have been proposed in an attempt to provide an anatomical explanation for this syndrome; however, none has been proven. One popular theory suggests that splitting of the inferior vermis plays a role in development of mutism.6,7 However, studies that have utilized the newer telovelar approach have failed to find a decline in mutism.11 The dentatothalamic pathway is thought to play a role but, again, is not the sole determinant in development of the syndrome. Additional studies have found that brainstem invasion correlates with a higher risk of developing mutism. Unfortunately, this syndrome does not always resolve as initially proposed. Instead, most patients improve, but they can be left with speech and neurocognitive deficits.6,12 This becomes very important when defining the risks of surgery to the parents. Brain-

60â•…Medulloblastoma stem dysfunction, which is sometimes included in descriptions of posterior fossa syndrome, is an obvious risk when tumor infiltrates the brainstem and removal is attempted. However, this can also occur when the floor of the fourth ventricle is not properly identified. Finally, there are the postoperative complications common to most procedures within the posterior fossa, including infection, pseudomeningocele, and overt CSF leak. Standard precautions, such as preoperative antibiotics, tight dural and fascial closure, and wound care, should all be taken.

References ╇1. Gottardo NG, Gajjar A. Current therapy for medulloblas-

toma. Curr Treat Options Neurol 2006;8(4):319–334 PM, Boyett JM, Finlay JL, et al. Metastasis stage, adjuvant treatment, and residual tumor are prognostic factors for medulloblastoma in children: conclusions from the Children’s Cancer Group 921 randomized phase III study. J Clin Oncol 1999;17(3):832–845 ╇3. Tanriover N, Ulm AJ, Rhoton AL Jr, Yasuda A. Comparison of the transvermian and telovelar approaches to the fourth ventricle. J Neurosurg 2004;101(3):484–498 ╇4. Deshmukh VR, Figueiredo EG, Deshmukh P, Crawford NR, Preul MC, Spetzler RF. Quantification and comparison of telovelar and transvermian approaches to ╇2. Zeltzer

the fourth ventricle. Neurosurgery 2006;58(4 Suppl 2):ONS-202–ONS-206, discussion ONS-206–ONS-207 ╇5. Jean WC, Abdel Aziz KM, Keller JT, van Loveren HR. Subtonsillar approach to the foramen of Luschka: an anatomic and clinical study. Neurosurgery 2003;52(4):860–866, discussion 866 ╇6. Gudrunardottir T, Sehested A, Juhler M, Schmiegelow K. Cerebellar mutism: review of the literature. Childs Nerv Syst 2011;27(3):355–363 ╇7. Rekate HL, Grubb RL, Aram DM, Hahn JF, Ratcheson RA. Muteness of cerebellar origin. Arch Neurol 1985;42(7): 697–698 ╇8. Bhatia R, Tahir M, Chandler CL. The management of hydrocephalus in children with posterior fossa tumours: the role of pre-resectional endoscopic third ventriculostomy. Pediatr Neurosurg 2009;45(3):186–191 ╇9. Rajesh BJ, Rao BR, Menon G, Abraham M, Easwer HV, Nair S. Telovelar approach: technical issues for large fourth ventricle tumors. Childs Nerv Syst 2007;23(5):555–558 10. Ayanzen RH, Bird CR, Keller PJ, McCully FJ, Theobald MR, Heiserman JE. Cerebral MR venography: normal anatomy and potential diagnostic pitfalls. AJNR Am J Neuroradiol 2000;21(1):74–78 11. Zaheer SN, Wood M. Experiences with the telovelar approach to fourth ventricular tumors in children. Pediatr Neurosurg 2010;46(5):340–343 12. Palmer SL, Hassall T, Evankovich K, et al. Neurocognitive outcome 12 months following cerebellar mutism syndrome in pediatric patients with medulloblastoma. Neuro-oncol 2010;12(12):1311–1317

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61

Infratentorial Ependymomas Michael DeCuypere and Frederick A. Boop

61.1╇Background First described as a unique neoplasm by Cushing and Bailey in 1926, posterior fossa ependymomas continue to represent a management challenge, not only to the neurosurgeon but also to the multidisciplinary team. Ependymomas are the third most common brain tumor in children followed by medulloblastomas and astrocytomas. More than 90% of the time, the tumor is localized at diagnosis. Posterior fossa ependymomas typically occur within the first decade of life, with half occurring at age 3 years or younger.1 Given the young presentation, the clinical picture is often unclear and the child has often been seen by several physicians prior to diagnosis. Infants may be quite ill from chronically raised intracranial pressure at presentation. The initial management by the surgeon is paramount to the child’s survival and future quality of life.

61.2╇ Conceptual Issues Except for rare instances, ependymomas tend to be confluent tumors that displace or encase surrounding structures. Although they may be locally invasive, they tend not to be infiltrative neoplasms. Given that numerous published series, both retrospective and prospective, have demonstrated that the extent of surgical resection is currently the most significant factor influencing survival, the importance of neurosurgery is unequaled both for survival and for quality of life. When the neurosurgeon stops in the middle of ependymoma resection and says or thinks “primum non nocere,” he is generally delivering a death sentence to the child. Conventional chemotherapy has yet to show extension of overall survival for ependymoma. Whereas radiotherapy is effective in preventing a completely resected ependymoma from growing back, it is much less effective in controlling

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future growth of a significant portion of residual tumor. In fact, most studies have shown a nearly twofold difference in survival between a totally resected ependymoma and anything less. That being understood, if a surgeon finds himself uncomfortable with further resection of a difficult ependymoma, there is nothing wrong with stopping surgery with plans to either come back another day or refer the infant to a center with more experience in dealing with these difficult neoplasms. Although the minority of children with ependymomas have disseminated disease at presentation, if the child is stable enough to tolerate the study, a preoperative contrasted magnetic resonance imaging (MRI) of the entire neuraxis is worthwhile. Obtaining spinal imaging following surgery always confounds the situation because blood products and postoperative changes in spinal imaging confuse the picture of metastatic disease. If the child is too unstable for a spine MRI prior to surgery, it is best to wait 2 to 3 weeks after surgery to obtain imaging. Similarly, staging children with ependymoma by lumbar cerebrospinal fluid cytology is of very low yield and is often negative even in the face of metastases seen on imaging.

61.3╇ Operative Detail and Preparation Infratentorial ependymomas generally fall into two broad categories: the midline fourth ventricular tumors (Fig. 61.1) and the cerebellopontine angle (CPA) ependymomas (Fig. 61.2). The epidemiology, surgical positioning, molecular profile, risks, and outcome with these two types of ependymomas are distinct and worthy of comment. Both ependymomas have a propensity to interweave themselves into potential space, with fourth ventricular tumors often growing out of the foramen of Magendie or the

61 â•… Infratentorial Ependymomas a

b

Fig. 61.1â•… (a) T2-weighted axial and (b) T1-weighted sagittal magnetic resonance imaging (MRIs) of a classic fourth ventricular ependymoma in a 19-year-old presenting with a several-month history of vomiting. Note the invasion of the floor of the fourth ventricle at the obex and extension of tumor through both the left foramen of Luschka and the foramen of Magendie.

foramina of Luschka, whereas the CPA ependymomas will grow out of skull base foramina and along the lateral gutters of the spinal canal. The positioning of the child with a fourth ventricular ependymoma is prone, with the neck flexed in preparation for a typical midline suboccipital craniotomy. Should the tumor extend down the spinal canal, either a hemilaminectomy or a replacement laminoplasty is preferred. Since the facets will often

fuse at any spinal level in which the periosteum is stripped, it is worthwhile to limit the exposure only to the spinal levels involved with the tumor. Two-thirds of fourth ventricular ependymomas will invade the floor of the fourth ventricle. Hence, once the exposure is made, one should inspect the floor of the ventricle early. If the tumor invades the floor of the ventricle, one should limit the manipulation of the tumor during resection, lest the patient

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498 Section VI.Bâ•… Infratentorial Neoplasms

Fig. 61.2â•… T2-weighted axial image of a 2-year-old infant with a typical cerebellopontine angle (CPA) ependymoma. Note tumor filling the fourth ventricle and CPA. The brainstem is rotated by tumor. The child presented after a midline suboccipital craniotomy and incomplete resection at another institution. The tumor in the CPA and ventral to the pons cannot be safely reached from a midline approach.

develop a “floor of the fourth syndrome.” Careful review of the preoperative MRI will often give insight into where the tumor is invasive. For most fourth ventricular ependymomas with invasion, the obex and hypoglossal trigones will be most commonly involved. Too aggressive of a resection in this area can lead to inability to swallow, with aspiration, postoperatively. Fourth ventricular tumors generally derive most of their blood supply from the vermian branches of the posterior inferior cerebellar artery (PICA). As such, identifying the tonsillar loops of PICA early on and following them into the ventricle provide proximal control of the vascular supply. By identifying and sacrificing tumor vessels early as they leave the vermian branches of PICA, one can significantly devascularize these tumors before breaching them. If one tonsillar loop of PICA is seen to be enlarged compared to the other, this is often the side contributing the dominant blood supply to the tumor. Before opening the tumor capsule, it is important to place absorbable gelatin sponges over the spinal subarachnoid space and over the lateral gutters of the spinal canal. Limiting the iatrogenic spread of cancer cells and blood along the spinal canal or into the third and lateral ventricles is critical because metastatic progression of ependymomas is often iatrogenic.

Once the fourth ventricular ependymoma has been dissected and debulked, the last area to be addressed should be the component invading the floor of the fourth ventricle. At this juncture, the goal is to thin down the remaining carpet of tumor without damaging the floor of the ventricle. The tumor will have caused numerous small neoplastic vessels to grow up through the floor of the ventricle to supply the tumor. Overzealous bipolar coagulation in this location can be devastating. If the vessels are oozing in the floor of the ventricle, they are much better handled with gelatin coagulant sponges, gentle irrigation, and patience. Alternatively, tearing these small neoplastic vessels by manipulation of the tumor can cause them to retract into the brainstem and bleed beneath the surface of the ventricular floor. If one were to show most neurosurgeons an acoustic neuroma and ask how they would approach it, most would say from a retrosigmoid craniotomy. The CPA ependymomas arise in the cerebellopontine angle presumably from ependymal rests at the lateral aspect of the foramen of Luschka and along the lateral pons, allowing them to grow around the vessels and cranial nerves lateral to the brainstem as well as into the fourth ventricle (Fig. 61.3). As they enlarge, they rotate the brainstem, further distorting the anatomy. Whereas a midline suboccipital approach may allow

61 â•… Infratentorial Ependymomas

Fig. 61.3â•… This diagram details the cerebellopontine angle (CPA) ependymoma that takes its origin from the foramen of Luschka and the lateral pons just above the pontomedullary junction. As it grows, it fills the CPA and fourth ventricle, rotating the brainstem and encasing both cranial nerves and vessels.

for resection of the fourth ventricular component of these tumors, it is not adequate to safely address the lateral aspect of the tumor or that portion ventral to the pons. For this reason, significant tumor is often left ventrolaterally. Given that the CPA ependymomas are more likely to occur in younger children and are more likely to recur, to metastasize, and to cause death than their midline counterparts, the management of these tumors is particularly challenging.2 The authors have found that placing these children prone with the neck flexed and chin turned to the

shoulder ipsilateral to the tumor will allow one to airplane the operating table maximally from side to side (Fig. 61.4). With a hockey-stick incision that extends to the top of the ipsilateral ear and a bone exposure that crosses the midline but extends over to the transverse-sigmoid sinus junction, one can remove the fourth ventricular component of the tumor, then use a telovelar approach and rotate the table to visualize and remove the lateral component of the tumor.3 Ependymomas will often grow around nerves and vessels but can usually be separated

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500 Section VI.Bâ•… Infratentorial Neoplasms

Fig. 61.4â•… Positioning of the patient for resection of the cerebellopontine angle (CPA) ependymoma is prone and flexed, in pins for older children or horseshoe headrest for younger children, with the chin turned to the ipsilateral shoulder. By strapping the patient to the operating table, the table can be rotated in one direction for resection of the midline fourth ventricular portion of the tumor or the opposite direction for a retrosigmoid resection of the lateral portion of the tumor.

safely. These tumors have a propensity to grow out of the jugular foramen and the porus acusticus, but these portions can be retrieved with gentle microsuction. It is important to remember to dissect the tumor from the cranial nerves and not the reverse. Even with minimal manipulation of the ninth and tenth cranial nerves, the majority of infants will have transient swallowing difficulties postoperatively and are at high risk for aspiration in the first few weeks postoperatively. It is worthwhile to have an otolaryngologist involved in the evaluation and management of these children as they are extubated and until they are able to pass a formal swallowing study after surgery.4 Finally, it is important to try to remove all solid coagulant or other foreign materials from the resection cavity before closing. There have been several instances in which such materials cause enhancement on delayed postoperative imaging that can be confusing for recurrence of disease.

61.4╇ Outcomes and Postoperative Course As mentioned, if there has been significant dissection along the inferior portion of the fourth ventricular floor or manipulation of the lower cranial nerves, the patient is at risk for aspiration in the early postoperative period. If the surgery has been long, it may be prudent to keep the patient intubated and sedated overnight to allow for formal evaluation of swallowing at the time of extubation. Since the extent of resection is the major determinant of survival, parents are counseled preoperatively that an early postoperative MRI (postoperative computed tomography [CT] scanning is not adequate to stage residual tumor) will be performed and that if significant residual tumor is identified, the recommendation will be made to return to surgery to attempt further removal. Anaplastic tumors in young infants may be

61 â•… Infratentorial Ependymomas highly vascular and associated with significant blood loss. In such cases, delaying second-look surgery to give chemotherapy can significantly devascularize the tumor, making repeat resection elective and safer. If return to surgery is anticipated, it is easier to keep the childr intubated and sedated overnight and until the MRIs have been reviewed than it is to extubate and re-intubate later. The acquisition of intraoperative MRI (iMRI) has significantly impacted this situation. At the authors’ institution, the year prior to obtaining iMRI, there was a 7% rate of repeat craniotomy for unanticipated residual tumor. With iMRI, the rate of return to surgery for residual tumor has now dropped to 1%. With CPA ependymomas, a word of caution regarding hearing is worthwhile. If there is much manipulation of the eighth cranial nerve during surgery, the child may lose hearing in the ear ipsilateral to the tumor. Likewise, if a child receives platinum-based chemotherapy, which can predispose to sensorineural hearing loss, followed by high-dose radiation to the posterior fossa and cochlea, the child may be at high risk for hearing impairment following treatment. As such, shielding of the cochlea during radiation therapy is important in the treatment plan of these children.

61.4.1╇ Management of Recurrent Disease Histological grade of ependymomas has been of controversial value in older studies. Indeed, if extent of resection is evaluated by postoperative noncontrast CT scans or in institutions where the rate of grosstotal resection of ependymomas is 50% or less, histology may not be predictive because children with grade II tumors and those with grade III tumors will do equally poorly. In well-controlled prospective studies with high-definition surveillance MRI, histology is a major predictor of outcome. Given that ependymomas are not chemosensitive tumors, the salvage rate for recurrent ependymomas has been on the order of 15 to 20%.5 Given that most recurrences are local, most institutions have been hesitant to consider re-irradiation to the brainstem. In the last several years, the authors’ approach to recurrent ependymomas has been to aggressively

resect all residual disease and to treat with re-irradiation. If the interval between first irradiation and re-treatment is more than 18 months, most children have tolerated re-treatment well, and the authors’ survival rate for this group of children has been nearly 50%.6

61.4.2╇Conclusions The understanding of the cancer stem cell of origin of ependymoma and the molecular events leading to the development of these neoplasms is proceeding rapidly. However, at present, the only cure for children with this disease is aggressive surgical resection of their tumors followed by focal conformal irradiation. The development of specialty centers with concentrated experience and surgical adjuncts like iMRI seems to afford improved outcome with fewer longterm sequelae of treatment. In the future, targeted biological therapies will hopefully make the current approach no longer necessary.

References ╇1. Gurney JG, Smith MA, Bunin GR. CNS and miscellaneous

intracranial and intraspinal neoplasms. In: Ries LA, Smith MA, Gurney JG, eds. Cancer Incidence and Survival Among Children and Adolescents: United States SEER Program 1975–1995. Bethesda, MD: National Cancer Institute, SEER Program; 1999: 51–63 ╇2. Witt H, Mack SC, Ryzhova M, et al. Delineation of two clinically and molecularly distinct subgroups of posterior fossa ependymoma. Cancer Cell 2011;20(2):143–157 ╇3. Sanford RA, Merchant TE, Zwienenberg-Lee M, Kun LE, Boop FA. Advances in surgical techniques for resection of childhood cerebellopontine angle ependymomas are key to survival. Childs Nerv Syst 2009;25(10):1229–1240 ╇4. Thompson JW, Newman L, Boop FA, Sanford RA. Management of postoperative swallowing dysfunction after ependymoma surgery. Childs Nerv Syst 2009;25(10): 1249–1252 ╇5. Bouffet E, Capra M, Bartels U. Salvage chemotherapy for metastatic and recurrent ependymoma of childhood. Childs Nerv Syst 2009;25(10):1293–1301 ╇6. Merchant TE, Boop FA, Kun LE, Sanford RA. A retrospective study of surgery and reirradiation for recurrent ependymoma. Int J Radiat Oncol Biol Phys 2008;71(1):87–97

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62

Pediatric Brainstem Gliomas Jonathan Roth and Shlomi Constantini

62.1╇Background Brainstem gliomas (BSG) in children include a diverse group of tumors with different presenting symptoms and tumor configurations that lead to a plethora of biological behaviors and variable prognoses. BSG represent 10 to 20% of all pediatric brain tumors, and about 20 to 30% of infratentorial tumors. BSG are diagnosed at all ages. However, they are rarely diagnosed before age 5 years, and their occurrence peaks at around age 10 years. Males and females are more or less equally affected. As opposed to cerebellar and many supratentorial tumors, BSG involve super-eloquent neural tissue, and thus were previously considered inoperable. However, as has been shown by Epstein and others, in selected subgroups of tumors, and with the integration of intraoperative mapping and monitoring, resection is feasible, with reasonable neurologic and oncological outcomes.1–3 With the addition of gentle chemotherapy and modern radiation techniques, decision making on the combination of treatment options has become more complex. Currently, there is no unified approach for BSG. Treatment is dictated by tumor location, configuration, and biological behavior. In this chapter, the authors review the various tumors and propose a schematic treatment paradigm.

62.1.1╇ Classification With the improvement of neuroimaging, diagnosis and classification of BSG has been refined, depending mainly on location and tumor configuration (e.g., whether the tumor is focal, cystic, or diffuse), as follows: 1. Configuration: Generally speaking, focal and cystic tumors tend to be low grade and behave in a more indolent manner, whereas diffuse

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tumors tend to be high grade and behave aggressively. This concept is true for all brainstem locations. 2. Location: BSG may be located in the midbrain, pons, or medulla, with some overlap depending on the extent of the tumor. a. Midbrain tumors include: i. Tectal tumors (with or without exophytic components) (Fig. 62.1) ii. Aqueductal tumors (Fig. 62.2) iii. Tegmental tumors b. Pontine tumors include: i. Focal (isolated) pontine tumors, or pontine tumors with extension to the brachium pontis (middle cerebellar peduncle) (Fig. 62.3) ii. Diffuse (intrinsic) pontine gliomas (DPG, DIPG) (Fig. 62.4) c. Medullary tumors include: i. Dorsal exophytic tumors (Fig. 62.3) ii. Cervicomedullary tumors iii. Focal intrinsic medullary tumors iv. Diffuse medullary tumors

62.1.2╇Symptoms BSG may produce several types of symptoms: 1. Elevated intracranial pressure (ICP): BSG may cause hydrocephalus by obstructing the aqueduct, fourth ventricle, or fourth ventricular outlet. Hydrocephalus may develop gradually or acutely, leading to headaches, vomiting, and drowsiness. 2. Cranial nerve (CN) deficits: These may occur in any location and are related to CN nuclei involvement by the tumors, or from injuries to the CN themselves.

62 â•… Pediatric Brainstem Gliomas a

b

Fig. 62.1â•… (a) Axial and (b) sagittal T2-weighted magnetic resonance images (MRIs) showing a tectal glioma. Note the flow artifact on the sagittal view (arrow, following an endoscopic third ventriculostomy), and the extension to the left thalamus/pulvinar (arrowhead).

a

b

Fig. 62.2â•… Aqueductal tumor―ependymoma. (a) Preoperative and (b) postoperative scan. Tumor was resected through a transfourth ventricular approach.

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504 Section VI.Bâ•… Infratentorial Neoplasms a

b

c

d

Fig. 62.3â•… (a) Exophytic medullary, (b,c) focal medullary, (d) and focal pontine glioma. All pathologies were pilocytic astrocytomas.

Upper brainstem tumors may cause pseudobulbar palsy. Midbrain region tumors may cause Parinaud syndrome (secondary to pressure on the upper tectal region and hydrocephalus), and third or fourth CN palsies. Oculomotor nerve palsy may include pupil dilation if the Edinger-Westphal nucleus is involved. Pontine tumors may cause facial or abducens nerve palsy. Cochlear and trigeminal nerve symptoms are rare. Medullary tumors may cause lower cranial nerve deficits, manifesting with hoarseness and difficulties swallowing as well as recurrent aspiration. Failure to thrive may occur in infants. Torticollis is a common finding with cervicomedullary tumors, causing impaction of the foramen magnum and compression of the spinal accessory nerve. 3. Long-tract symptoms: These include general weakness and pyramidal signs. Sensory symptoms are relatively rare, most probably because they are less overt. 4. Cerebellar symptoms: These are more common with pontine tumors, especially those involving the brachium pontis. 5. Other symptoms, such as respiratory decline and abnormal respiratory patterns. These occur secondary to involvement of the medullary and lower pontine respiratory centers, and secondary to generalized decreased respiratory muscle innervation. Vomiting is a common symptom of tumors involving the obex. Vomiting may be a sole presenting symptom. Thus brain magnetic resonance imaging (MRI) needs to be part of the evaluation of children with recurrent vomiting, even in the absence of other symptoms or signs.

Symptoms may evolve slowly, over the course of a few months, or in an accelerated fashion, within days to weeks. Fast symptom eruption is associated with high-grade tumors, such as DPG.

62.1.3╇ Diagnosis and Imaging The diagnostic gold standard is brain MRI, including T1- and T2-weighted images both with and without contrast, and fluid-attenuated inversion recovery (FLAIR). These images will accurately outline the location of the tumor; relationship of the tumor to neighboring structures, such as the aqueduct, fourth ventricle, and blood vessels; enhancing components; ventricular size and orientation; and leptomeningeal spread. Most BSG are hypointense on T1 and hyperintense on T2 and FLAIR and may have an enhancing component. Importantly, enhancing tumors are not necessarily high grade. WHO grade I lesions often have an enhancing component. T1–T2 overlap is an important sign of focal BSG. When the T1 hypointensity overlaps the T2 hyperintense signal, these suggest a noninfiltrative or lowgrade tumor. However, DPG typically present with a diffuse T1 hypointensity of the pons that overlaps the T2 hyperintensity. Thus the T1–T2 overlap must be assessed in the wider context of other radiological findings. DPG typically show a generalized swelling of the pons, with engulfment of the basilar artery anteriorly (Fig. 62.4). Diffusion-weighted imaging (DWI) is important when assessing pontine tumors because primitive neuroectodermal tumors (PNET) may mimic DPG4 and are associated with a restricted signal on DWI (Fig. 62.5). Tectal tumors have a typical radiological appearance. They are epicentered in the tectum (posterior to the aqueduct), although they may extend to the medial aspect of the pulvinar (Fig. 62.1). They are hypo-isointense on T1, hyperintense on T2, and usually do not enhance. Tectal tumors typically compress

62 â•… Pediatric Brainstem Gliomas a

b

Fig. 62.4â•… (a) Axial and (b) sagittal T2-weighted magnetic resonance images (MRIs) showing classic appearance of a diffuse brainstem glioma.

a

b

Fig. 62.5â•… (a) Brainstem primitive neuroectodermal tumor (PNET). On the axial T2 image, the lesion may be mistaken for a diffuse pontine glioma. (b) However, the lesion is eccentric. On diffusion, the lesion is restricted.

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506 Section VI.Bâ•… Infratentorial Neoplasms the aqueduct, leading to obstructed hydrocephalus. Enhancing tectal tumors tend to have a more aggressive behavior because they tend to grow. Magnetic resonance spectroscopy (MRS) has been proposed as part of the evaluation of BSG to distinguish between low- and high-grade tumors. However, there is currently no consensus regarding the role of MRS. Note that some BSG (such as DPG) may have a low-grade histological and MRS appearance but have an aggressive biological behavior, similar to high-grade tumors. Thus MRS may be part of the diagnostic work-up, but only as a complementary tool. Although BSG rarely metastasize, it is good policy to perform spinal MRI as part of the primary screening, especially if there are symptoms suggesting spinal seeding, or in the presence of brain leptomeningeal spread.

62.1.4╇Pathology BSG include all WHO grades I to IV astrocytomas. Grade I tumors (mainly, pilocytic astrocytomas) usually present as discrete lesions, often with a cystic component; however, they may present as dorsally exophytic tectal or medullary (and cervicomedullary) tumors. They usually enhance following gadolinium and may be associated with significant edema (e.g., in the cervical spine). Often, the tumor includes nonenhancing components a well. WHO grade II tumors (diffuse low-grade astrocytomas) may present in any location along the brainstem. Their biological behavior is very diverse. Tectal and exophytic tumors usually have a very indolent course. On the other hand, DPG may also have the histological appearance of WHO II but behave aggressively. WHO grade II tumors usually do not enhance and are hypointense on T1 and hyperintense on T2 and FLAIR. WHO grades III and IV tumors (anaplastic astrocytomas and glioblastoma multiforme) may arise in any location, more commonly in the pons (as a DPG). They are often associated with ill-defined enhancement (grade III) or a necrotic, ring-enhancing component (grade IV). Other glial pathologies may rarely arise in the brainstem, including gangliogliomas, oligodendrogliomas, and pilomyxoid astrocytomas.

62.1.5╇ Differential Diagnosis Other types of lesions that may mimic BSG include: 1. Inflammatory changes (such as multiple sclerosis, acute demyelinating encephalitis)

2. Other oncological pathologies (such as brainstem PNET) 3. Nonspecific benign findings (such as NF hamartomas-neurofibromatosis spots) 4. Vascular lesions (such as cavernomas, vasculitis) Thus, diagnosis depends on the specific clinical and radiological aspects.

62.2╇ Operative Detail and Preparation 62.2.1╇ Biopsy Considerations Both tectal tumors and DPG are usually diagnosed radiologically, with no need for a biopsy. Regarding DPG (and, rarely, diffuse medullary tumors), some authors have suggested performing a biopsy as part of the treatment paradigm.5 However, most agree that typical radiological appearance will suffice for diagnosis, and that biopsy should only be performed in atypical lesions (e.g., eccentric pontine lesions, or lesions that are restricted on DWI), or as part of trial protocols. Needle biopsies of DPG may have an important role in the future for the identification of biomarkers and individualized treatment planning. Aqueductal tumors may be of various pathologies, including low- and high-grade astrocytomas or ependymomas, and thus we recommend performing an endoscopic biopsy as part of the surgery to treat the related hydrocephalus with an endoscopic third ventriculostomy (ETV). (See text following for technical considerations.) Regarding other BSG, such as focal intrinsic or exophytic tumors, these tumors usually require resection, and therefore there is no reason for a primary biopsy as part of the treatment process.

62.2.2╇ Surgical Treatment Surgical treatment for BSG must address two aspects: alleviating secondary hydrocephalus and treating the tumor.

62.2.3╇ Treatment of Hydrocephalus Because the hydrocephalus is obstructive, often an ETV is the preferred treatment. Tectal gliomas are an example of BSG that typically favor ETV and, as explained previously, there is no need to perform a biopsy of the lesion. Long-term success rates are about 80 to 95%.6

62 â•… Pediatric Brainstem Gliomas As opposed to typical tectal gliomas, aqueductal tumors are rare and may include other pathologies, such as high-grade gliomas and ependymomas. The authors therefore recommend performing an endoscopic biopsy as part of the ETV procedure. Various techniques may be used to combine an ETV with an endoscopic biopsy, such as using a rigid endoscope for the ETV and a flexible endoscope for the biopsy. The advantage of this approach is that the entry point planned for the ETV can be used for the biopsy as well. Another option is to perform two entry holes, one for the ETV and another one, more anteriorly, for the biopsy. The disadvantage of such an approach is the need for two openings and two trajectories through the tissue. A third option is to create a compromise opening midway between the ideal entry point for the ETV and the ideal entry point for the biopsy. The downside of this approach is the fact that this route is not optimal for either procedure; the surgeon is actually compromising on the ideal trajectories for both tasks. With secondary hydrocephalus caused by other BSG, such as midbrain or pontine tumors, the tumors may severely distort the anatomy, anteriorly pushing the basilar artery and diminishing the brainstemclival distance. This may increase the risk of vascular injury during an ETV, and thus in most of these BSG, the authors recommend inserting a shunt if the hydrocephalus is not expected to improve following tumor resection.

62.2.4╇ Tumor Resection Before discussing the technical aspects of BSG surgery, it is important to stress the multimodality approach necessary for such tumors. Over recent years, radiation and chemotherapy have proven to be efficient treatments for focal and low-grade tumors. Thus careful decision making regarding the role of surgery as well as additional treatments is paramount. Tectal gliomas and diffuse brainstem tumors are not amenable to resection. The role of resection is for treatment of focal tumors, especially for tumors exhibiting an exophytic component. It is generally accepted that, similar to low-grade astrocytomas located elsewhere in the central nervous system (CNS), aggressive resection of focal BSG (which are often low grade) may increase progression-free survival (PFS) and overall survival (OS). When possible, removal of a focal tumor (which often is the enhancing part of the lesion), or the exophytic component of the tumor, is considered the surgical goal.7,8 Often, gross total resection may not be performed safely, and thus an extensive resection (even if subtotal) is done. Most focal tumors are exophytic medullary or cervicomedullary tumors; however, they may be located at any part of the brainstem.

Successful BSG resection relies on intraoperative monitoring (IOM) and mapping.1–3 These include long-tract monitoring (such as motor evoked potentials and somatosensory evoked potentials), as well as electromyelogram (EMG) monitoring of cranial nerves (including CN VII, IX, X, XI, and XII). Mapping includes direct monopolar or bipolar stimulation of brainstem regions to identify the CN nuclei location and continuity of the CN. Diffusion tensor imaging (DTI) is important when operating on tegmental lesions (in the midbrain or pons). DTI outlines the location of the pyramidal tracts and assists in surgical planning. DTI should not replace IOM because the accuracy of DTI is limited. Anesthesia protocols must enable electrophysiological monitoring, and thus include mainly total IV anesthesia (TIVA) with propofol and remifentanil. Volatile anesthesia may negatively affect the accuracy of the monitoring. Surgical approaches include midline suboccipital telovelar approaches (for paraventricular pontine and medullary tumors, cervicomedullary tumors, and tumors located in the lower part of the aqueduct). Paramedian routes are useful for laterally located exophytic medullary BSG. Trans- and subtemporal paths are used for focal laterally extending midbrain tumors. Supracerebellar infratentorial, occipital-transtentorial, or interparietal-transsplenial approaches are used for dorsal exophytic tectal gliomas. For cervicomedullary tumors, upper cervical laminectomies or laminotomies are performed. Regardless of the surgical approach, careful and judicious resection should be performed, focusing only on clearly pathological tissue.8

62.3╇ Outcomes and Postoperative Course 62.3.1╇ Postoperative Complications Resection of BSG may lead to specific neurologic complications, including cranial neuropathy, sensory deficits (deep, superficial, and pain), and motor deficits. Other complications, depending on the surgical region, may include a decline in consciousness (upper brainstem), respiratory insufficiency (lower brainstem), and vomiting (obex). Thus extubation should be performed only once the patient is awake and able to demonstrate a positive gag reflex and cough. Over the first few hours and days following surgery, the patient should be monitored for gag reflex, cough, aspiration, and apnea.

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508 Section VI.Bâ•… Infratentorial Neoplasms

62.3.2╇ Adjuvant Oncological Treatments DPG Chemotherapy has failed to show any advantage in treating DPG.9–11 Currently, focal radiation combined with steroids is the sole treatment for DPG. Usually these tumors initially respond to radiation, achieving a few months of clinical improvement, followed by a grave prognosis. Several other treatments have been tried, such as convection-enhanced delivery (CED) of various chemotherapeutics, but with limited results.12

Tectal Gliomas Tectal tumors do not require treatment and should be followed radiologically. If a tectal tumor shows a clear change in configuration or enhancement, a biopsy should be considered (either endoscopic or open, depending on the size of the ventricles and the exact anatomical configuration of the tumor). However, radiation may be a valid treatment choice even in the absence of a tissue diagnosis. In case of clear exophytic tectal tumors, a resection may be performed; the main risk of surgery is vertical and disconjugate horizontal eye movements.

Focal BSG These lesions may have an unpredictable course. Following a subtotal resection, some lesions remain stable for years, and may even spontaneously regress. Thus careful radiological and clinical follow-up are crucial. If clear growth has been documented, chemotherapy (such as vincristine-carboplatin) or focal radiation may be applied. Generally, radiation is precluded for younger patients due to secondary brain injury and the potential to induce secondary tumors. Thus, in children younger than about 10 years, chemotherapy will usually be the primary adjuvant treatment.

Follow-up Modalities The standard follow-up method is MRI. However, in recent years, more accurate techniques, such as volumetrics, have been applied to measure tumor size. This enables a better sense of the true rate of growth and may aid in decision making regarding treatment timing.

References ╇1. Constantini

S, Epstein F. Surgical indication and technical considerations in the management of benign brain stem gliomas. J Neurooncol 1996;28(2-3):193–205 ╇2. Epstein F, Constantini S. Practical decisions in the treatment of pediatric brain stem tumors. Pediatr Neurosurg 1996;24(1):24–34 ╇3. Morota N, Deletis V, Lee M, Epstein FJ. Functional anatomic relationship between brain-stem tumors and cranial motor nuclei. Neurosurgery 1996;39(4):787–793, discussion 793–794 ╇4. Zagzag D, Miller DC, Knopp E, et al. Primitive neuroectodermal tumors of the brainstem: investigation of seven cases. Pediatrics 2000;106(5):1045–1053 ╇5. Sanai N, Wachhorst SP, Gupta NM, McDermott MW. Transcerebellar stereotactic biopsy for lesions of the brainstem and peduncles under local anesthesia. Neurosurgery 2008;63(3):460–466, discussion 466–468 ╇6. Li KW, Roonprapunt C, Lawson HC, et al. Endoscopic third ventriculostomy for hydrocephalus associated with tectal gliomas. Neurosurg Focus 2005;18(6A):E2 ╇7. Teo C, Siu TL. Radical resection of focal brainstem gliomas: is it worth doing? Childs Nerv Syst 2008;24(11): 1307–1314 ╇8. Klimo P Jr, Pai Panandiker AS, Thompson CJ, et al. Management and outcome of focal low-grade brainstem tumors in pediatric patients: the St. Jude experience. J Neurosurg Pediatr 2013;11(3):274–281 ╇9. Pollack IF, Stewart CF, Kocak M, et al. A phase II study of gefitinib and irradiation in children with newly diagnosed brainstem gliomas: a report from the Pediatric Brain Tumor Consortium. Neuro-oncol 2011;13(3):290–297 10. Korones DN, Fisher PG, Kretschmar C, et al. Treatment of children with diffuse intrinsic brain stem glioma with radiotherapy, vincristine and oral VP-16: a Children’s Oncology Group phase II study. Pediatr Blood Cancer 2008;50(2):227–230 11. Chassot A, Canale S, Varlet P, et al. Radiotherapy with concurrent and adjuvant temozolomide in children with newly diagnosed diffuse intrinsic pontine glioma. J Neurooncol 2012;106(2):399–407 12. Anderson RC, Kennedy B, Yanes CL, et al. Convectionenhanced delivery of topotecan into diffuse intrinsic brainstem tumors in children. J Neurosurg Pediatr 2013;11(3):289–295

63

Intracranial Epidermoids Henry W. S. Schroeder

63.1╇Background Epidermoids are rare congenital lesions that may spread widely along the subarachnoid spaces, mostly at the base of the skull. Because of their pearl-like shine and the irregular nodular surface, they were referred to as the “pearly tumor” by Cruveilhier in 1828. Epidermoids arise from ectodermal cells that are misplaced during neural tube closure in embryonic life.1 Epidermoids consist of a thin capsule filled with soft, white material that is the result of progressive desquamation from the epithelial lining and breakdown of keratin. This material is rich in cholesterol, has a waxy consistency, and forms concentric lamellae.2 Removal of the cyst contents is easy because of their consistency and avascular nature. Epidermoids grow very slowly, at a linear rate resembling the growth of the human epidermis. Because of this slow progression, they often reach a considerable size before causing symptoms. Epidermoids frequently extend along the basal cisterns through the tentorial notch from the posterior to the middle cranial fossa or vice versa. They often grow around important neurovascular structures and adhere to them densely. Nevertheless, gross total resection is the therapy of choice.3

63.2╇ Preoperative Considerations 63.2.1╇ Clinical Symptoms Headaches are a common complaint. Other symptoms depend on the location of the lesion. Infratentorial epidermoids often present with dizziness, balance problems, or cranial nerve dysfunction. Located in the temporomesial region, they can become symptomatic with seizures. Lesions located in the ventricles may cause occlusive hydrocephalus. Epidermoids in the pineal region may cause Parinaud syndrome or diplopia. Visual problems may occur

with epidermoids located along the visual pathways. Hemiparesis is a finding with epidermoids compressing the corticospinal tract.

63.2.2╇Imaging Magnetic resonance imaging (MRI) is the imaging modality of choice. In general, epidermoids appear almost isointense to cerebrospinal fluid (CSF) in T1and T2-weighted sequences, although they can be slightly hyperintense in T1 and hypointense in T2 (Fig. 63.1a,b). They are nonenhancing lesions. Standard axial, coronal, and sagittal planes are usually obtained. Diffusion-weighted imaging (DWI) can be used for an accurate diagnosis. On DWI, epidermoids show a hyperintense signal in contrast to the brain and CSF, whereas arachnoid cysts are hypointense (Fig. 63.1c). In order to differentiate epidermoids from arachnoid cysts, the author and his team prefer highresolution constructive interference in steady state (CISS) sequences. These images show nicely the solid content of the lesions and the relation to important neurovascular structures (Fig. 63.1d). In CISS images, epidermoids usually appear as inhomogeneous lowintensity structures with irregular borders.

63.2.3╇ Indications for Surgery Symptomatic epidermoids are an indication for surgery if no contraindications exist. Symptomatic lesions usually show a mass effect on MRI, with indentation of the adjacent brain, midline shift, and/or ventricular compression. The surgical indication for asymptomatic lesions remains controversial. In the author’s opinion, surgery for asymptomatic small lesions is not justified. However, if the lesion is large with considerable mass effect, the author usually recommends surgery before symptoms occur, especially in younger patients. Of course, the alternative of wait and scan is offered to the patients and relatives as well.

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510 Section VI.Bâ•… Infratentorial Neoplasms a

b

c

d

Fig. 63.1â•… (a) Appearance of epidermoids in magnetic resonance imaging (MRI). T1-weighted axial image showing a hypointense nonenhancing cerebellar lesion with mass effect. (b) T2-weighted axial image showing a hyperintense cerebellar lesion with mass effect. (c) Diffusion-weighted image (DWI) showing a hyperintense signal of the cerebellar lesion. (d) Constructive interference in steady state (CISS) axial image showing an irregular hypointense lesion in front of the brainstem.

63 â•… Intracranial Epidermoids

63.3╇ Operative Detail and Preparation 63.3.1╇Surgery Goal of Surgery The goal of surgery in epidermoids is the evacuation of the lesions and the total resection of the capsule that represents the vital part of the lesion. This ideal goal is frequently not achievable because of the adherence of some part of the capsule to important neurovascular structures. When the capsule adheres densely to the cranial nerves or brain, even meticulous bimanual microsurgical dissection will result in disruption of the vascular supply and subsequent neurologic deficit that has to be avoided. Therefore, the amount of capsule resection must be tailored to the individual situation. Sometimes, gross total resection is possible although the imaging shows severe encasement of the neurovascular structures, simply because a good plane is present between the lesion and nerves as well as vessels. That is why the amount of resection cannot be predicted before surgery, but has to be determined during the dissection. What can accurately be predicted is that the chance of total resection exists only in virgin cases. In recurrent lesions, at least in the author’s experience, there is mostly a thick and sticking capsule that covers the structures like sugar icing and leaves no chance for a total-capsule resection.

Approach Planning According to the findings of the MRI, the approach is selected. For cerebellopontine angle lesions, the author and his team usually take a simple retrosigmoid approach even if the epidermoid has a significant extension into Meckel’s cave or the middle cranial fossa. The subtemporal or pterional route is mainly selected when the major tumor part is supratentorial. Since large epidermoids significantly displace the brain that provides space for the surgery, standard paths are sufficient to reach the lesion in any location. The author and his team have never used extensive skull base approaches, such as transpetrosal or orbitozygomatic routes, for epidermoid lesions. Use of endoscopes compensates for the limited exposure.4 All the epidermoids resected by the author and his team involving both posterior and middle cranial fossa were removed via a single small craniotomy. Combined approaches are not necessary when endoscopes are applied.

Surgical Technique The positioning of the patient on the operating table depends on the location of the epidermoid. For most

approaches, including pterional, subtemporal, and retrosigmoid, the patient is positioned supine. After general anesthesia has been induced, the head is placed in three-pin fixation. Single-shot antibiotic prophylaxis (1.5 g cefuroxime) is administered intravenously. Multimodal neuromonitoring is used routinely when cranial nerves or brainstem are involved. Neuronavigation has not been considered to be helpful in the author’s series so far. The operating field is prepared and draped. After craniotomy and dural opening have been performed, the arachnoid cisterns are opened widely to allow egress of CSF. This step relaxes the brain and provides sufficient space for the microsurgical manipulation without using self-retaining retractors. At first the epidermoid surface is exposed and the overlying arachnoid is dissected. After adjacent cranial nerves and vessels have been identified, the tumor capsule is incised. The content is evacuated with the aid of suction, curettes, and forceps. After decreasing the mass effect of the lesion, the capsule is dissected from the neurovascular structures in a bimanual technique (Video 63.1). The author uses one tumor forceps to hold the capsule and an anatomical microforceps to dissect the capsule away from the nerves, vessels, and brain surface (traction and countertraction technique). Utmost care has to be taken to avoid devascularization of the cranial nerves or injury to the small perforators. Ideally, a total resection of the capsule is performed. However, if the capsule is very sticky to the neurovascular structures, it makes no sense to push for a total resection because the resection may result in surgical damage to nerves, vessels, and pial surface of the brain. Even when a sticky capsule can be pulled from a cranial nerve with anatomical preservation of the nerve, at least devascularization of the nerve will probably occur with subsequent neurologic deficits. In these scenarios, it is advisable to leave the sticky capsule part in place. Certainly, the risk for recurrence is increased under these circumstances; nevertheless, since the growth of epidermoids is very slow, it is better to accept a recurrence many years after surgery than to cause a permanent neurologic deficit that decreases the quality of life of the patient. However, in general, only small parts of the capsule cannot safely be removed in primary cases. If the epidermoid can be visualized in a straight line, the whole procedure is performed with the operating microscope (Fig. 63.2). However, if some parts of the tumor cannot be seen in a straight line, endoscopes are very useful to remove the hidden tumor parts (Fig. 63.3). The endoscope-assisted microsurgical technique has been applied in epidermoids that extend in two or more compartments (e.g., cerebellopontine angle lesion with extension into Meckel’s cave or middle cranial fossa). Usually, 30- and 45-degree endoscopes are used to visualize and resect the hid-

511

512 Section VI.Bâ•… Infratentorial Neoplasms a

b

c

d

Fig. 63.2â•… (a,b) Microsurgical resection of an epidermoid of the fourth ventricle in a 27-year-old man presenting with headache, balance problems, and dizziness. T1-weighted axial magnetic resonance imaging (MRI) showing a hypointense nonenhancing lesion within the fourth ventricle. Note the brainstem impression (arrow). (c) T1-weighted and (d) T2-weighted sagittal MRI showing a nonenhancing lesion within the fourth ventricle.

63 â•… Intracranial Epidermoids e

f

g

h

Fig. 63.2 (Continued)â•… (e) Microsurgical visualization of the tumor between the cerebellar tonsils. (f) Debulking of the lesion. (g) Dissection of the tumor capsule from the rhomboid fossa. (h) Intact floor of the fourth ventricle after total tumor resection. (Continued on page 514)

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514 Section VI.Bâ•… Infratentorial Neoplasms i

j

k

l

Fig. 63.2 (Continued)â•… T1-weighted axial MRIs obtained 4 years after surgery showing no remnant or recurrence. (i,j) The brainstem impression completely disappeared. (k) T1-weighted and (l) T2-weighted sagittal MRIs obtained 4 years after surgery confirmed no recurrence. The patient was doing fine without any neurologic deficit.

63 â•… Intracranial Epidermoids a

b

c

d

Fig. 63.3â•… (a–c) Endoscope-assisted microsurgical resection of an epidermoid of the ambient cistern in a 32-year-old woman presenting with a recurrent epidermoid after two microsurgical tumor resections 15 and 4 years earlier. T2-weighted axial magnetic resonance imaging (MRI) showing a hyperintense lesion within the ambient cistern with brainstem impression. T1-weighted (d) sagittal and (Continued on page 516)

515

516 Section VI.Bâ•… Infratentorial Neoplasms e

f

h

g

i

Fig. 63.3 (Continued)â•… (e) coronal MRIs showing a hypointense nonenhancing lesion deeply indenting the cerebellar peduncle. (f) Microsurgical visualization of the tumor under the tentorium. (g) Endoscopic visualization of the course of the trochlear nerve (arrows) at the frontal aspect of the tumor. (h) Microsurgical resection of the pearly tumor. (i) Identification of the trochlear nerve (arrow) after removal of the dorsal tumor part.

63 â•… Intracranial Epidermoids j

k

l

m

Fig. 63.3 (Continued)â•… (j) Endoscopic removal of the tumor extending into the cerebellar peduncle with curved curettes under view of a 45-degree endoscope. (k) Final endoscopic inspection after tumor removal. (l) Final microsurgical inspection after tumor removal. (m) T2-weighted axial MRIs were obtained 1 year after surgery and showed no tumor remnant. (Continued on page 518)

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518 Section VI.Bâ•… Infratentorial Neoplasms n

o

p

q

Fig. 63.3 (Continued)â•… The brainstem compression completely disappeared. (n–o) T2-weighted axial MRIs were obtained 1 year after surgery and showed no tumor remnant. (p) T1-weighted sagittal and (q) coronal MRIs obtained 1 year after surgery confirmed gross total tumor resection. The patient was doing fine with no new neurologic deficit.

63 â•… Intracranial Epidermoids den tumor parts.5 Only once, a 70-degree endoscope had to be used. But it is very difficult to handle the instruments under view of a 70-degree optic. The jet irrigation technique performed with the aid of a syringe is used to mobilize remote tumor parts that cannot be reached with the instruments. Details of the endoscope-assisted technique and its pitfalls are described in Chapter 103. Once the tumor has been removed, the tumor cavity and subarachnoid spaces are vigorously irrigated to remove any tumor remnants and avoid chemical meningitis. The dura is closed in a watertight fashion and the bone flap is fixed with microplates or craniofix. The wound is closed in layers. The patient is observed for 1 night in the intensive care unit.

63.4╇ Outcomes and Postoperative Course 63.4.1╇ Complications and Results Fortunately, mortality and permanent morbidity are rare in surgery for epidermoids. In the author’s series of 18 patients, there was no mortality and only 1 patient with permanent morbidity. The author and his team experienced one thalamic hemorrhage after resection of a giant epidermoid involving the supratentorial and infratentorial subarachnoid spaces on the left side. The thalamic part of the lesion was only debulked and no attempt was made to dissect the capsule from the thalamic surface. There was no intraoperative hemorrhage. The patient woke up with aphasia and severe hemiparesis. Computed tomography (CT) obtained immediately after surgery showed a thalamic hemorrhage adjacent to the tumor capsule that was left in place, but there was no hemorrhage into the resection cavity. Probably the manipulation of the thalamic surface underlying the capsule while debulking the epidermoid caused the bleeding. Fortunately, the aphasia was only temporary and the hemiparesis improved to a very mild permanent deficit. Temporary morbidity included cranial nerve deficits in 3 patients. Aseptic meningitis has been reported to be the most common cause of postoperative morbidity.3 In the author’s series, aseptic meningitis was not a problem. In 2 patients, a moderately increased body temperature was noted 2 and 5 days after surgery, respectively. No other signs of meningitis were observed. The absence of aseptic meningitis in this small series is probably attributed to abundant irrigation during and after tumor removal. The tumor was completely evacuated in 15 patients (83%). In 3 patients, a near-total resection

(less than 5% tumor) was identified on the postoperative MRIs. In 3 patients, two surgeries were performed because of the tumor extension. In only 4 patients, the capsule was totally removed. In most patients, small parts of the capsule that were adherent to nerves and vessels were left in place. The endoscope-assisted technique was used in 16 patients and was considered to be helpful in all cases. In all patients, tumor remnants that were not visible with the operating microscope could be identified and removed with the aid of endoscopes with angulated view. There was no obvious complication related to the application of the endoscopes. The preoperative symptoms improved in 16 patients. In 2 patients presenting with hearing loss, the tumor resection resulted in a marked improvement of hearing. Trigeminal neuralgia, which was the initial symptom in 1 patient, disappeared after surgery. The author’s protocol for surveillance after surgery is neurologic examination and MRI after 3 months, 1 year, and then every 2 to 3 years. The mean follow-up is 6 years, ranging from 1 to 12 years. To date, one recurrence has been observed 10 years after resection of a large recurrent lesion in which a thick and sticky capsule covering all the neighboring neurovascular structures remained in place. The third surgery was uneventful and the patient was doing fine without new neurologic deficits. Furthermore, the team operated on two recurrent tumors 15 and 19 years after the initial surgery, respectively. These lesions were removed without causing new morbidity, confirming the literature that suggests an excellent functional prognosis even after a second or third operation.6

63.5╇Conclusion Gross total or near-total resection is the therapy of choice for intracranial epidermoids. The endoscopeassisted microsurgical technique is extremely helpful in most lesions that spread along the subarachnoid spaces. It enables safe tumor removal even when tumor parts are not visible in a straight line. Tumor extensions into adjacent cranial compartments can be removed via the same approach without the need for retracting neurovascular structures or enlarging the craniotomy.

63.5.1╇Disclosure The author is a consultant to Karl Storz GmbH & Co. KG, Tuttlingen, Germany.

519

520 Section VI.B╅ Infratentorial Neoplasms References ╇1. Toglia

JU, Netsky MG, Alexander E Jr. Epithelial (epidermoid) tumors of the cranium. Their common nature and pathogenesis. J Neurosurg 1965;23(4):384–393 ╇2. Russell DS, Rubinstein LJ. Pathology of Tumours of the Nervous System. 5th ed. London, England: Edward Arnold; 1990 ╇3. Yaşargil MG, Abernathey CD, Sarioglu AC. Microneurosurgical treatment of intracranial dermoid and epidermoid tumors. Neurosurgery 1989;24(4):561–567

╇4. Schroeder

HW, Hickmann AK, Baldauf J. Endoscope-assisted microsurgical resection of skull base meningiomas. Neurosurg Rev 2011;34(4):441–455 ╇5. Schroeder HW, Oertel J, Gaab MR. Endoscope-assisted microsurgical resection of epidermoid tumors of the cerebellopontine angle. J Neurosurg 2004;101(2):227–232 ╇6. Yamakawa K, Shitara N, Genka S, Manaka S, Takakura K. Clinical course and surgical prognosis of 33 cases of intracranial epidermoid tumors. Neurosurgery 1989;24(4):568–573

Section VI.C

Scalp, Skull, and Skull Base Neoplasms

64

Tumors of the Scalp and Skull Nalin Gupta and William Y. Hoffman

64.1╇Background 64.1.1╇Indications An enormous diversity of tumors arises from the tissues of the scalp and skull. However, children, as opposed to adults, rarely develop primary solid epithelial malignancies and for this reason metastatic tumors are rare. The most common metastatic tumor to the calvaria in children occurs in the setting of disseminated neuroblastoma, and these tumors usually respond to the primary treatment modality. Fortunately, most of the neoplasms encountered in children are either benign (dermoid, osteoma) or represent unusual proliferative lesions (e.g., fibrous dysplasia, aneurysmal bone cyst). For lesions that demonstrate progressive growth or those where tissue is required to confirm the diagnosis, surgical resection is usually indicated―resulting in a visible deformity. With the exception of dermoid cysts, primary scalp tumors in children are rare. The most common true neoplasm is a peripheral neurofibroma in patients with neurofibromatosis type 1 (NF1), although most do not require excision.

64.1.2╇Goals The two primary goals are complete excision of the neoplasm and restoration of normal anatomical structures to protect the brain and provide skin coverage. Since excision often results in a bony or soft tissue defect, reconstruction is an important part of the preoperative planning.

64.1.3╇ Alternate Procedures In general, the decision to perform surgery is determined by the natural history of the tumor or mass and the underlying effect on cosmesis. A stable, but

visible, osteoma located on the forehead may require excision for cosmetic reasons; however, a similar lesion in the occipital area can be observed. Some vascular lesions, such as hemangiomas or arteriovenous malformations, may benefit from embolization prior to surgery.

64.1.4╇Contraindications The primary contraindication to surgery is if the tumor is best treated with systemic therapy. This is usually true with malignant tumors, such as neuroblastoma and lymphoma.

64.2╇ Operative Detail and Preparation 64.2.1╇ Preoperative Planning and Special Equipment In general, the scalp and skull (with the exception of the skull base) are readily accessible, and positioning of the patient is straightforward; thus the lesion in question is directly approachable. The exact reconstruction technique (e.g., rotation flap, skin graft, or free flap) will determine if any other part of the patient’s body is to be prepared for an additional procedure. Typically, removal of a skull lesion will be determined by a preoperative decision whether to remove the lesion along with the surrounding calvaria, or piecemeal. The extent of the involved calvaria is important to define, particularly in terms of the size of the defect that must be repaired. A thin-cut computed tomography (CT) scan is very helpful, especially for lesions that involve the skull base. Standard power equipment used for craniotomies is usually sufficient to accomplish these goals.

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524 Section VI.Câ•… Scalp, Skull and Skull Base Neoplasms

64.2.2╇ Expert Suggestions/Comments Primary excision of skull tumors usually requires adequate exposure around the perimeter of the lesion. In general, the margins of lesions located on the convexity are more easily defined and can be removed en bloc. This is usually straightforward since the normal bone around the lesion can be cut using the same techniques as performing a craniotomy. Rarely, for some vascular lesions, embolization is very helpful to reduce bleeding during removal of the lesion. In general, autologous bone graft is preferred for the repair of cranial defects in children. Although synthetic grafts are an excellent option, their durability over decades is unclear. The advantage of autologous bone graft is that usually it will become incorporated into the calvaria and will not be subject to failure or change over time. In very young children, autologous bone will probably allow some degree of expansion as the head grows―a property that a synthetic material will not have.

Anticipating the technique used for the skull repair will sometimes dictate the extent and shape of the initial resection. For example, a lesion involving the calvaria under the forehead may be best repaired with an autologous bone graft taken from the parietal area, a region that mimics the natural curve of the forehead. A larger skull resection may facilitate the final cosmetic appearance.

64.2.3╇ Key Steps of the Procedure/ Operative Nuances Small scalp tumors can be removed en bloc and the scalp closed primarily. This is easier for tumors that are oval or narrow. Round lesions that exceed 2 to 3 cm in size will require some form of rotation flap or scalp expansion for optimal closure. For very large lesions, rotation flaps will need to be correspondingly large. Particular care must be taken to plan the vascular supply of the flaps to prevent necrosis of the edges or corners (Fig. 64.1).

Fig. 64.1â•… A postoperative view of a child with a large melanocytic nevus. The nevus has been excised, leaving a small margin at the midline. The incisions for the rotation flaps along the hairline and occiput were planned to preserve the blood supply to the scalp.

64 â•… Tumors of the Scalp and Skull For small, focal calvarial lesions, removal of the actual lesion and curettage of the surrounding bony edge are sufficient to prepare the site for the final repair. Very small defects can be adequately repaired using only hydroxyapatite cement. This material is inherently brittle; therefore, if larger defects require repair, the cement should be supplemented with some sort of “scaffolding.” This can be either absorbable mesh or titanium mesh. The latter, obviously, is much more durable and a better choice for very large defects where greater strength and stability are required. The most common technique for obtaining autologous bone is to split a full-thickness segment of calvaria obtained from another site. This will require exposure of a larger portion of the calvaria; this is not a concern when a bicoronal incision is used, but may increase the scope of the procedure if only a small incision is planned. Although it depends on the thickness of the bone, split-thickness grafts are difficult to obtain in children younger than 5 years. If a full-thickness bone graft is obtained, then the donor

site can be repaired with demineralized bone substitute (Fig. 64.2). In young children, the donor site, which has normal dura and periosteum, will have a very high likelihood of reconstituting normal bone. The size of the donor site should be overestimated by 2 to 3 mm in all directions. Frequently, the edges require further fine removal of bone to obtain an exact fit. For cosmetically important areas like the forehead, preparing the recipient site with a “shelf” at the deep edge will prevent settling of the bone graft and facilitate a smooth and tight junction with the existing calvaria. Obviously, if no autologous material is available, then there are synthetic alternatives that include a preformed graft derived from a preoperative CT scan (Fig. 64.3), a combination metallic mesh with either hydroxyapatite cement or methyl methacrylate, or an absorbable mesh plate with hydroxyapatite cement. The authors tend to favor the latter for young children with smaller defects. The mesh can be used as a scaffolding to “carry” the cement that is placed after the mesh is secured in place.

Fig. 64.2â•… Excision of an occipital skull mass and repair. Intraoperatively, the patient is placed in the prone position. A large occipital mass was removed, resulting in a large calvarial defect. An autologous bone graft was obtained from the right parietal region and then used to repair the defect. The graft is held in place with an absorbable plate. The large donor site was bridged using a bone graft from the left parietal area and the gaps were filled in with demineralized bone matrix (not shown).

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526 Section VI.Câ•… Scalp, Skull and Skull Base Neoplasms

Fig. 64.3â•… Placement of a custom synthetic implant. The advantage of this technique is that the exposure is limited to the area of the defect and the implant requires minimal adjustment prior to final placement.

Skull base lesions can be very challenging, depending on the location. For slow-growing, asymptomatic lesions, such as fibrous dysplasia, observation may be the best option. If resection is performed, careful consideration should be taken to anticipate the subsequent repair (Fig. 64.4).

64.2.4╇ Hazards/Risks/Avoidance of Pitfalls Benign tumors of the skull generally respect tissue planes and do not invade the overlying scalp or underlying dura. Direct invasion of the dura and brain, or adjacent scalp, will greatly alter the scope and nature of the procedure and must be determined prior to surgery. If a tumor is noted to invade the dura, then a decision should be made to excise and repair the dura. If it is unknown whether the tumor extends into the brain, the procedure should be completed, and then more detailed imaging should be obtained prior to removing the intradural portion of the tumor.

64.2.5╇ Salvage and Rescue Most problems encountered in these procedures arise from an inability to repair the resulting bony or scalp defect. With respect to the skull, there are

many synthetic options available (e.g., titanium mesh, hydroxyapatite cement) that will allow repair of the defect if autologous bone graft is unavailable. In a worst-case scenario, a portion of the cranial defect can be left open and then repaired secondarily with synthetic material at a second procedure. Scalp defects that cannot be closed primarily are a challenge. If a sufficient portion of the scalp has been prepped, then usually extension of the incision and rotation flaps can cover most defects. If a very large defect is left that cannot be closed, then the only solution is a free flap. If this is at all a possibility, a preoperative consultation with a microvascular plastic surgeon is mandatory.

64.3╇ Outcomes and Postoperative Course 64.3.1╇ Postoperative Considerations In general, the primary postoperative considerations are ensuring adequate viability of the scalp, especially if a rotation or advancement procedure has been done, and reducing the likelihood of infection. Typically, the authors do not use routine postoperative antibiotics unless there is a certainty of contamination. A surgical drain is usually used to prevent

64 â•… Tumors of the Scalp and Skull a

b

Fig. 64.4â•… (a) An expanding region of fibrous dysplasia involving the forehead in a young adult. The exposure preserved the periosteum, which will be important for cosmesis. (b) The orbital roof and supraorbital ridge have been removed, and the orbital roof repaired using titanium mesh. (Continued on page 528)

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528 Section VI.Câ•… Scalp, Skull and Skull Base Neoplasms c

Fig. 64.4 (Continued)â•… (c) The final appearance with a segment of parietal bone used to repair the forehead, and a titanium mesh used to repair the donor site posteriorly.

accumulation of a large fluid collection under the scalp. In children, the authors rarely use nonabsorbable sutures; thus wound care is tailored to keep the incision clean and dry.

64.3.2╇Complications The primary complication to be avoided is infection, particularly one that involves the material used for the cranioplasty. In infants, in whom the bone

becomes revascularized rapidly, the authors have successfully treated postoperative infections with aggressive débridement and irrigation but have not removed the actual bone graft. Long-term antibiotics are required but are usually successful. In older patients, particularly those who may have had other treatment, such as radiation, the presence of an infection involving the bone graft will require removal of the material and subsequent replacement, once a sufficient course of antibiotic therapy is complete.

65

Tumors of the Skull Base and Orbit Kaisorn L. Chaichana, Ignacio Jusue-Torres, and George I. Jallo

65.1╇Background Skull base tumors account for less than 5% of cranial lesions in children (Fig. 65.1).1,2 These tumors occur in fewer children than in adults and are more common in boys than girls.1,2 The tumors can be especially challenging because of the constraints of the developing brain and cranium, the small size of infants and their limited physiological reserves, and distinct histologies. As a result, there has been reluctance to widely adopt skull base approaches in children.1–3 However, advances in surgical technology as well as a working knowledge of skull base anatomy have allowed the implementation of skull base approaches in children.4–8

Until recently, skull base surgery has been primarily limited to adults.4–8 Skull base surgery in children has certain advantages and disadvantages as compared to surgery in adult patients. The advantages in children are that children have a higher proportion of histologically benign lesions, better long-term outcomes, typically better tissue planes, and lack of frontal sinus development and shorter anterior fossa for anterior cranial approaches.1–3 The disadvantages of these procedures include the presence of primary growth plates that hinder certain approaches and reconstruction, lack of aerated sinus development that could provide corridors to the skull base, and more sensitivity to retraction-induced edema, among others.1–3 Regardless, with advancements in surgical

Fig. 65.1â•… Schematics of an endonasal transphenoidal resection of a pituitary adenoma in a pediatric patient.

529

530 Section VI.Câ•… Scalp, Skull and Skull Base Neoplasms equipment and techniques, tumors of the skull base and orbit are becoming more amenable to safe resection in children.4–6 In this chapter, the authors discuss some of the more common approaches to skull base tumors in children, operative planning, technical nuances, and postoperative considerations.

65.2╇ Operative Detail and Preparation 65.2.1╇ Preoperative Planning In general, both computed tomography (CT) and magnetic resonance imaging (MRI) are obtained prior to surgery. CT scans are used to delineate bony anatomy, including presence and/or absence of aerated sinuses. When surgery is planned in close proximity to major vessels (e.g., internal carotid artery), CT angiography (CTA) is often used to better understand the relationship of key vessels with the tumor and bony anatomy. MRI with and without gadolinium is also obtained to characterize the tumor. In the majority of cases, surgical navigation is used with both CT and MRI. Additionally, a pediatrician and an anesthesiologist should evaluate patients prior to surgery. This is important because many of these children have syndromic conditions that may affect other organ systems (e.g., cardiovascular system), have limited physiological reserves, and can be obligate nasal breathers, which may lead to respiratory distress because of their lesion or surgery. Furthermore, many of these procedures are done in conjunction with an otolaryngologist and/or plastic surgeon. Typical instrumentation that should be available includes surgical navigation, intraoperative monitoring (motor evoked and somatosensory evoked potentials), endoscopy with a variety of different angled scopes, and a surgical microscope.

65.2.2╇ Operative Approaches This chapter mainly focuses on the transsphenoidal approach for sellar and clival lesions. A list of common skull approaches is shown in Table 65.1.

Transsphenoidal/Extended Transsphenoidal This approach, often done in conjunction with an otolaryngologist, involves the use of an endoscope and/ or microscope4 (Video 65.1). In the past, a sublabial approach was used, but now a transnasal path is pre-

ferred by most. This provides excellent access to midline skull base structures, including cribriform plate, sella, and clivus. The use of an extended transsphenoidal approach, which involves removal of the medial and/or posterior wall of the maxillary sinus and/or ethmoid sinuses, can widen the exposure and provide more lateral exposure for lesions in the cavernous sinus, infratemporal fossa, and middle fossa. Disadvantages of this approach include difficulty of dural repair, lack of development of aerated sinuses, especially sphenoid and maxillary sinus, making access difficult, and small nares in children. The authors typically avoid using this route for intradural lesions. A key to this approach in children is to use both intraoperative CT and MRI navigation to facilitate navigating the small aerated sinuses. Additionally, varying scopes, including 30- , 45- , and 70-degree scopes, should be readily available in order to provide different views of the sphenoid sinus and facilitate tumor resection. Complications include endocrine abnormalities, internal carotid artery injury, cerebrospinal fluid (CSF) leak, and sinusitis. A key is to make sure the surgeon is in the midline to avoid injury to the cavernous carotid artery. This is facilitated by using the rostrum as a midline landmark, in addition to surgical navigation.

Orbitozygomatic/Modified Orbitozygomatic/ Supraorbital Craniotomy The orbitozygomatic (OZ) craniotomy can be done in one or two pieces, but the authors often prefer two pieces. The first piece is a frontal pterional craniotomy and the second piece combines the orbital rim, orbital roof, and zygoma.5,6,8 The modified orbitozygomatic (MOZ) craniotomy is similar to the OZ craniotomy, except only the orbital roof and rim are removed. The supraorbital craniotomy can be done via a transpalpebral or supraciliary incision.5,6,8 For the supraorbital craniotomy, more lateral exposure can be done by extending the eyebrow incision in a curvilinear fashion lateral to the eyebrow. These approaches provide good access to lesions near the cavernous sinus and suprasellar region. Medial access is easier in children because of the lack of development of the frontal sinus. The position of the optic chiasm in relation to the sella is important because a prefixed chiasm may preclude the use of a supraorbital approach to retrochiasmatic lesions. The use of an ultrasonic bone scalpel can minimize the gaps in the craniotomy, which is especially critical on the anterior surface of the face. Additionally, the use of bone cement can help with the reconstruction. Complications include frontalis nerve paresis, poor cosmetic result, cheek hypesthesia, and trismus.

65 â•… Tumors of the Skull Base and Orbit Table 65.1â•… List of possible skull base lesions in children Orbit Hemangioma Fibrous dysplasia Schwannoma Dermoid Neurofibroma Lymphatic malformation Anterior cranial fossa Intracranial: Meningioma Esthesioneuroblastoma

Developmental/Other: Nasal glioma Nasal dermoid Encephaloceles/meningoceles

Sinonasal: Inverted papilloma Mucocele Nasal polyposis Olfactory neuroblastoma Rhabdomyosarcoma

Bone: Fibrous dysplasia Chondrosarcoma Osteoblastoma Aneursymal bone cyst

Clivus: Chordoma Chondrosarcoma Ewing’s Sarcoma Osteosarcoma Lymphoma Rhabdomyosarcoma

Developmental/other: Teratoma Meningioma

Middle cranial fossa Sellar: Pituitary adenoma Craniopharyngioma

Temporal bone Benign: Otitis externa Cholesteatoma Eosinophilic granuloma Osteoma Paraganglioma

Intermediate/malignant: Langerhans’ histiocytosis Rhabdomyosarcoma Lymphoma

Posterior fossa Jugular foramen: Paraganglioma Schwannoma Neurofibroma

Petroclival: Meningioma Schwannoma Chordoma Chondrosarcoma

Transpetrosal/Anterior Petrosectomy This approach involves removing bone of the petrous apex anterior to the facial nerve and medial to the internal carotid artery and trigeminal nerve. This route is best for lesions at the petrous apex. It can be combined with intradural opening of the tentorium, thus allowing access to both the supratentorial and infratentorial compartments. This approach can be used for lesions with moderate supratento-

rial and infratentorial extension. This technique can be combined with a temporal craniotomy and/ or zygomatic osteotomy, which is referred to as an extended transpetrosal path. Complications of the technique include damage to the facial nerve, injury to the trochlear nerve during tentorial opening, CSF leakage, injury to the vein of Labbé, and conductive hearing loss. Due to the lack of malleability of the pediatric brain, the endaural approach is usually accompanied with measures to reduce brain vol-

531

532 Section VI.Câ•… Scalp, Skull and Skull Base Neoplasms ume, including administering mannitol and utilizing hyperventilation.

Transfacial/Anterior Craniofacial These approaches are usually done in conjunction with a head and neck surgeon and/or plastic surgeon. The transfacial route can be categorized into transoral, transpalatal, lateral rhinotomy, Le Fort I osteotomy, and midfacial degloving. Transoral and transpalatal paths provide access to sphenoidal and upper clival lesions. Le Fort I osteotomy and midfacial degloving, especially when combined with ethmoidectomy and medial maxillectomy, provide access to the paranasal sinuses, pterygoid fossa, and central skull base. Anterior craniofacial approaches combine a bifrontal craniotomy with a transfacial approach, which provides access to the anterior cranial fossa and sinonasal cavities. These techniques are often used in adults, but can be used in children with necessary modifications. A key to this approach is to avoid the children’s central incisors in order to spare their tooth buds. Complications of these methods include poor cosmetic outcomes, loss of tooth buds, palatal fistula, and wound dehiscence.

Retrosigmoid/Extended Retrosigmoid/ Presigmoid These paths are among the most commonly used approaches for posterior fossa lesions, especially for lesions in the cerebellopontine angle.7 A retrosigmoid route involves removing bone posterior to the sigmoid sinus, whereas an extended retrosigmoid involves removing bone overlying the sinus to increase exposure with the dural opening. A presigmoid approach involves a mastoidectomy in combination with an extended retrosigmoid approach. The addition of removing the labyrinth makes it a translabyrinthine technique. A key to this approach is to make sure to drop the vertex of the head in order to provide wider access to the lateral brainstem and cranial nerves. Surgical navigation also facilitates localization of the venous sinuses. Complications of these approaches include venous sinus injury, cranial nerve injury, and CSF leaks.

Transcondylar/Far Lateral This method involves combining a retrosigmoid approach with additional inferior and anterior bone removal of up to 50% of the occipital condyle. This provides additional lateral exposure that allows access to the lower clivus, foramen magnum, and ventral portion of the upper cervical spine. A key to

this approach is early identification of the vertebral artery in order to avoid inadvertent injury. This system can be combined with ligation of the sigmoid sinus, otherwise known as a transcondylar transsigmoid approach. Complications of the technique include vertebral artery injury, venous sinus injury, and cervical instability.

65.3╇ Outcomes and Postoperative Course Postoperative care is dependent on the lesion treated and the skull base approach used. Following surgery, the patient is typically observed overnight in the intensive care unit with serial neurologic examinations. For lesions in close proximity to the optic apparatus, patients also undergo serial ophthalmological examinations. Patients who undergo a supraorbital or orbitozygomatic approaches often require ice to the eye to minimize swelling. Patients who undergo transnasal procedure often require nasal saline to minimize congestion. Patients are typically administered antibiotics for 24 hours postoperatively. For patients with nasal packing or stents, antibiotics are typically administered until the stents are removed. For the majority of intracranial lesions, steroids are administered for approximately 3 days postoperatively to help with pain control as well as chemical meningitis. For lesions in close proximity to the pituitary gland, serial serum sodium and urine-specific gravity checks are done to monitor for potential diabetes insipidus. A pediatric endocrinologist usually assists with the postoperative care of these patients. An MRI with gadolinium is typically done within 48 hours of surgery to assess extent of resection and potential postoperative complications, including intracranial bleeding, stroke, hydrocephalus, and pneumocephalus, among others. The patient is usually mobilized with the assistance of physical therapy on postoperative day 1. Prophylactic subcutaneous heparin is not generally administered unless the patient is at high risk of a deep vein thrombosis/pulmonary embolism (i.e., prolonged intubation, nonmobile, hypercoagulable state). Skull base surgery, especially in children, is high risk; immediate complications have been as high as 57% in some case series.3 However, skull base lesions have better long-term outcomes than in adult patients, most likely due to a higher proportion of benign lesions.1–3 Complete tumor removal has been greater than 90% in several series, with greater than 80% tumor-free survival after 2 years.1–3 These outcomes, nevertheless, are dependent on tumor pathology, surgical approach, and experience of the surgeon and institution, among others.

65 â•… Tumors of the Skull Base and Orbit

References ╇1. Manning SC, Bloom DC, Perkins JA, Gruss JS, Inglis A. Di-

agnostic and surgical challenges in the pediatric skull base [case reports review]. Otolaryngol Clin North Am 2005;38(4):773–794 ╇2. Tsai EC, Santoreneos S, Rutka JT. Tumors of the skull base in children: review of tumor types and management strategies [review]. Neurosurg Focus 2002;12(5):e1 ╇3. Teo C, Dornhoffer J, Hanna E, Bower C. Application of skull base techniques to pediatric neurosurgery [case reports review]. Childs Nerv Syst 1999;15(2–3):103–109 ╇4. Frazier JL, Chaichana K, Jallo GI, Quiñones-Hinojosa A. Combined endoscopic and microscopic management of pediatric pituitary region tumors through one nostril: technical note with case illustrations [case reports]. Childs Nerv Syst 2008;24(12):1469–1478

╇5. Jallo

GI, Bognár L. Eyebrow surgery: the supraciliary craniotomy: technical note. Neurosurgery 2006;59(1 Suppl 1):E157–E158 ╇6. Jallo GI, Suk I, Bognár L. A superciliary approach for anterior cranial fossa lesions in children. Technical note. J Neurosurg 2005;103(1 Suppl):88–93 ╇7. Raza SM, Quinones-Hinojosa A. The extended retrosigmoid approach for neoplastic lesions in the posterior fossa: technique modification [case reports]. Neurosurg Rev 2011;34(1):123–129 ╇8. Raza SM, Quinones-Hinojosa A, Lim M, Boahene KD. The transconjunctival transorbital approach: a keyhole approach to the midline anterior skull base. World Neurosurg 2013;80(6):864–871

533

Section VI.D

Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves

66

Tumors of the Vertebral Column Sudhakar Vadivelu and Andrew Jea

66.1╇Background Spinal column tumors in the growing spine, from atlas to coccyx, are rare and diverse lesions (Table€66.1). In the evaluation of a child with persistent back pain, a tumor should be considered in the differential diagnosis and investigated. If a tumor is identified, common goals of treatment are removal of the lesion, preservation of neurologic function, and maintenance of spinal column stability.

66.1.1╇ Surgical Treatment Excision is a piecemeal removal of a tumor (curettage); this is an intralesional procedure. Resection is an attempt to remove the tumor en bloc. Based

Table 66.1â•… Common pediatric spinal column tumors Benign

Osteoid osteoma Osteoblastoma Giant cell tumor Aneurysmal bone cyst Eosinophilic granuloma Nerve sheath tumors Sacral coccygeal teratoma

Malignant

Osteosarcoma Ewing sarcoma Chordoma Chondrosarcoma

Metastatic

Rhabdomyosarcoma Neuroblastoma Retinoblastoma Wilms tumor Teratoma–teratocarcinoma Leukemia Ewing sarcoma

on the surgical margins, a pathologist should classify the resection as intralesional, marginal, or wide. Radical resection is the en bloc removal of the tumor together with the complete compartment of origin. This is not possible in the spinal column without taking spinal cord and nerve roots. It is unclear whether en bloc resection with higher attendant morbidity portends better long-term outcomes than with piecemeal removal. Palliative procedures are all surgical procedures that are directed at a functional response (e.g., cord decompression and fracture stabilization) with or without partial removal of the tumor. Palliative procedures are done to make a diagnosis, decrease pain, and improve function.

66.2╇ Operative Detail and Preparation The management of spinal column tumors has evolved significantly over the last 15 years. Advances in spinal instrumentation and single-stage, posterior-only surgical approaches and techniques in children have enabled surgeons to treat these lesions more radically and to reconstruct the spinal column more effectively. The use of spinal stabilization in conjunction with the surgical treatment of these neoplasms has resulted in significant improvement in outcomes. Fusion techniques derived from adult spinal instrumentation techniques are applicable, except in the youngest patients (< age 1 y). Occipitocervical screw fixation has been used in children as young as 1.5 years, obviating the need for external fixation devices such as the “halo” vest or cast immobilization, which may be poorly tolerated by children. Pedicle screw fixation is feasible in children as young as 4 years. For children ≥ age 8 years, the spinal anatomy and configuration do not differ from

537

538 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves the adult spine in terms of sensitivity or response to instrumentation. Preoperative thin-cut computed tomography (CT) through the area of interest should help the surgeon decide if the bony anatomy can accept instrumentation. Screw length and trajectory should be estimated based on preoperative CT. Titanium alloy implants should be used in cases of neoplasm where frequent magnetic resonance imaging (MRI) is anticipated to follow tumor residual or recurrence. The decreased ferromagnetic properties of titanium alloy compared to stainless steel result in less scatter distortion of the image, permitting better tumor follow-up. Segmental implants, such as cross-link members, should be omitted directly over or opposite the tumor site because this may cause an unnecessary degradation in postoperative imaging. Children past the infantile period can be successfully instrumented for spinal stability without increased risk of complications in the immediate postoperative period. However, follow-up studies are needed to determine the long-term effects in terms of spinal alignment and growth in the immature pediatric spine.

66.2.1╇ Occipital Screw Technique Prior to drilling, anatomical landmarks are identified. Four bony landmarks on the outer occipital cortex should be visible: the posterior rim of the foramen magnum, the superior nuchal line, the inferior nuchal line, and the external occipital protuberance. Safe placement of occipital instrumentation is between the inferior and superior nuchal line. Occipital screws 4.0 to 4.5 mm in diameter may be placed in a bicortical fashion using the stop drill or stepwise drill technique in 2-mm increments (Fig.€66.1). Drill and screw trajectories should be angled medially toward the thick midline keel. Left and right occipital screws are staggered to avoid intersection of screw paths.

66.2.2╇ C1 Lateral Mass Screw Procedure The posterior arch of C1 is identified and followed laterally to visualize the lateral masses. Notably, there is a step-off between the medial aspect of the C1 lamina and the medial surface of the C1 lateral mass; this anatomical feature is different from in adults, where the medial C1 lamina is flush with the medial C1 lateral mass. Subperiosteal dissection of the C2 nerve roots and associated venous plexi from the junction between the posterior arch of C1 and lateral masses is performed to minimize bleeding. Alternatively, the C2

nerve roots and venous plexi can be coagulated with bipolar electrocautery and divided with little clinical significance. After palpating the medial and lateral surfaces of the lateral mass, a pilot hole may be drilled in the center of the lateral mass, usually no more than 2 to 3 mm from the medial surface. The rest of the placement of the C1 lateral mass screws (Fig. 66.2) proceeds utilizing the technique described by Harms and Melcher, using either 3.5- or 4.0-mm diameter polyaxial screws. The drill and screw trajectories are angled 0 to 5 degrees medially and are aimed at the superior half of the anterior arch of C1 on fluoroscopy. Bicortical purchase is usually achieved about 4 mm from the anterior cortex of the anterior arch.

66.2.3╇ C1–C2 Transarticular Screw Method A midline incision is made to expose the posterior elements from C1 to C3, with particular attention paid to the C2–C3 facet joints. The superior and medial aspects of the C2 pars are exposed. There is no reason to expose the lateral aspect of the C2 pars; in fact, this may be a dangerous maneuver due to the proximity of the vertebral artery. The roof of the C2 pedicle is followed to the C1–C2 facet joint. The C2 entry point may be identified by first locating the medial edge of the C2–C3 facet joint. The C2 entry site is just lateral and rostral to this point, and may be estimated by visualizing the course of the medial pars (approximately 3 mm up and 3 mm out). The drill or Kirschner wire (K-wire), either through a stab incision lateral to the T1 spinous process or through an extended incision, is typically directed 15 degrees medially, with the superior angle visualized by fluoroscopy. The drill or K-wire is directed down the C2 pedicle and across the C1–C2 joint, aiming at the anterior tubercle of C1. The tip of the drill or K-wire is advanced to a point 4 mm short of the anterior C1 tubercle, attaining purchase of the anterior cortex of C1. After tapping, a fully threaded 3.5- or 4.0-mm diameter cortical screw is used (Fig. 66.3). The necessary screw length can be measured directly from the drill or the K-wire. Screws are typically 34 to 44 mm in length. The procedure is repeated on the contralateral side.

66.2.4╇ C2 Pars/Pedicle Screw Process The entry point of a C2 pars/pedicle screw (Fig. 66.4) is similar to that of C1–C2 transarticular screw placement. The medial, superior, and roof of the C2 pars/

66 â•… Tumors of the Vertebral Column

Fig. 66.1â•… Occipital screw placement. (Art by Kathy Relyea. Printed with permission.)

pedicle should be exposed, dividing the C2 nerve root and venous plexus, if necessary. The medial trajectory of the C2 pars/pedicle screw parallels the medial border of the C2 pars/pedicle, and the superior trajectory is guided by fluoroscopy, aiming for the anterior tubercle of C1; however, the C2 pars/pedicle screw stops short of the C1–C2 joint. Screw length is typically one-half of the screw length for a C1–C2 transarticular screw, measuring 16 to 22 mm in length.

66.2.5╇ Translaminar Screw Approach A high-speed drill is used to open a small “entry” cortical window at the junction of the spinous process and lamina, close to the rostral margin of the lamina. Similarly, a high-speed drill is used to open a small “exit” cortical window at the junction of the facet and lamina, close to the rostral margin of the lamina. Using a hand drill as described by Wright,

539

540 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves

Fig. 66.2â•… Placement of C1 lateral mass screws. (Art by Kathy Relyea. Printed with permission.)

the contralateral lamina is carefully drilled along its length, with the drill visually aligned along the angle of the exposed contralateral laminar surface, aiming for the exit point. The drill tip should then be observed at the exit window. This gives confirmation that the drill did not violate the inner cortex of the lamina, allows bicortical screw purchase, and enables accurate measure of the appropriate screw length. Typically, a screw 20 to 30 mm in length and 3.5 or 4.0 mm in diameter could be placed. A small entry cortical window is then made at the junction of the spinous process and lamina, close to the caudal aspect of the lamina on the opposite side. The earlier described process is then repeated for this crossing translaminar screw (Fig. 66.5). Fluoroscopy is not used during this technique. It neither guides screw trajectory nor confirms screw placement because it is difficult to interpret on anteroposterior (AP) and lateral views where the screw lies in relation to the spinal canal.

66.2.6╇ C3–C7 Lateral Mass Screw Technique The entire lateral mass of the subaxial cervical spine is exposed from its medial junction with the lamina to the lateral step-off. The entry point is identified approximately 1 mm inferior and 1 mm medial to the center of the two-dimensional (2D) “square” posterior surface of the lateral mass. The drill and screw trajectories are superior and lateral (approximately 20 degrees up and 20 degrees out) to avoid the nerve root and vertebral artery, respectively, aiming for the superolateral “deep” corner of the three-dimensional (3D) “cube” of the lateral mass in the mind’s eye of the surgeon. Unicortical purchase is safe, but bicortical purchase may afford a biomechanical advantage. Fluoroscopy may be used but is unnecessary. Boys usually tolerate 12- to 16-mm × 3.5-mm screws, and girls tolerate 10- to 14-mm × 3.5-mm screws (Fig.€66.6).

66 â•… Tumors of the Vertebral Column

Fig. 66.3â•… C1–C2 transarticular screw placement. (Art by Kathy Relyea. Printed with permission.)

66.2.7╇ Sublaminar Wire/Band Strategy Passing a metal wire or polyester band under the lamina does require a learning curve. The malleable metal end of the wire or polyester band is shaped into a gentle curve for passage around the lamina. The wire or band is always passed in a caudal-to-rostral direction. The tip of the wire or band is gripped with hemostats or forceps, and the rest of the passage follows a push-pull technique―being mindful to keep tension so that a loop of band does not compress the thecal sac. After all the sublaminar wires or bands have been passed, each of the wires or clamps is closed over the rods. The loop around the lamina is tightened with a tensioner. The final tension is primarily evaluated by the surgeon, taking into account the strength of the bone of the patient. Important points to consider when using this technique include: (1) the radius of curvature of the malleable metal tip should be at least equal to the length

of the lamina; (2) the bend of the tip should not be greater than 45 degrees; (3) lateral passage of sublaminar metal wires or polyester bands should be avoided; (4) removal of additional bony lamina is not necessary because it does not significantly decrease the depth of band penetration but potentially weakens the lamina and increases the risk of instrumentation failure; (5) removal of the spinous process is recommended before direct midline passage of the sublaminar band; and (6) maintaining tension on the band throughout passage by using a push-pull technique prevents bowing of the band into the spinal canal.

66.2.8╇ Thoracic and Lumbar Pedicle Screw Procedure The entry point for pedicle screw placement may be consistently found at the confluence between the pars interarticularis and transverse process. A thorough

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542 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves

Fig. 66.4â•… C2 pars/pedicle screw placement. (Art by Kathy Relyea. Printed with permission.)

knowledge of pedicle anatomy and the sagittal and axial angulation of the individual pedicles is mandatory for safe screw placement. Angles for the pedicle finder, tap, and screw are best judged using preoperative CT or MRI of the thoracic or lumbar region. Intraoperative real-time guidance with fluoroscopy or direct palpation of the pedicle through a laminotomy may aid in screw placement, as an alternative to freehand placement.

66.2.9╇Sacrectomy Briefly, the first stage includes a midline laparotomy, mobilization of the visceral and neural structures, and ligation of the internal iliac vessels. A colostomy is performed, and a right vertical rectus abdominus myocutaneous flap fed by the inferior epigastric vessels is mobilized, wrapped in a bowel bag, and placed in the

pelvis. The second stage is performed the next day and includes L5 and S1 laminectomies; bilateral osteotomies and disarticulation of the sacrum from the ilium at the sacroiliac joints; ligation of the thecal sac inferior to the takeoff of the L5 nerve roots; complete L5–S1 diskectomy; and transection of the S1–S5 nerve roots. The entire sacrum along with the tumor is removed. After placement of bilateral L3–L5 pedicle screws (Fig. 66.7), a transverse 5.5-mm rod (transiliac bar) is placed with the ends outside of the iliac cortical surfaces and is secured using O-shaped clamps (modified from lateral connectors intended for iliac screws), and then connected to a midline L5 inferior end plate screw. Two iliac bolts are inserted. The longitudinal pedicle screw rods are then secured to the rod attached to the iliac screws with lateral and domino connectors. Cross-connectors are placed in two places: from one lumbar rod to another and from the rod attached to the iliac screws to the transiliac bar. A titanium mesh

66 â•… Tumors of the Vertebral Column

Fig. 66.5â•… Placement of C2 translaminar screws. (Art by Kathy Relyea. Printed with permission.)

Fig. 66.6â•… Lateral mass screws in the cervical spine. (Art by Kathy Relyea. Printed with permission.)

543

544 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves

Fig. 66.7â•… Thoracic and lumbar pedicle screw placement. (Art by Kathy Relyea. Printed with permission.)

66 â•… Tumors of the Vertebral Column

Fig. 66.8â•… Lateral extracavitary approach to allow placement of anterior instrumentation. (Art by Kathy Relyea. Printed with permission.)

cage is then cut to fit the defect between the two ilia. This is secured in place using two titanium wires. The previously mobilized rectus abdominis myocutaneous pedicle flap is advanced through the pelvis and is used to reconstruct the sacral defect.

66.2.10╇ Anterior Spinal Instrumentation Anterior spinal instrumentation is used far less commonly than posterior spinal instrumentation. The principal disadvantage of anterior approaches to the pediatric spine for placement of anterior hardware is that they may frequently require a second procedure

for decompression of posterior pathology or placement of posterior spinal instrumentation. However, today many pediatric spine surgeons feel comfortable placing anterior spinal instrumentation (Fig. 66.8) through a posterior or posterolateral approach, gaining both anterior and posterior exposure of the spinal column through a single route. A costotransversectomy or lateral extracavitary approach for the thoracic and lumbar spine will allow simultaneous placement of anterior spinal instrumentation with the installation of posterior spinal instrumentation. As with posterior instrumentation, standard spinal instrumentation, such as titanium or polyetheretherketone (PEEK) cages, may have too large

545

546 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves a profile for general pediatric use; careful study of preoperative CT is mandatory to determine if the patient’s anatomy will be able to accept anterior instrumentation. Other potential complications include nerve root injury; implant loosening and migration; injury to critical vascular structures, such as the carotid artery, aorta, or inferior vena cava; injury to the spinal cord or its covering; visceral injury; adjacent level disease, especially in the mobile cervical spine; stenosis; and possible instability resulting from rigidity of the construct.

66.3╇ Outcomes and Postoperative Course Children past the infantile period can be successfully instrumented for spinal stability without increased risk of complications in the immediate postoperative period. However, follow-up studies are needed to determine the long-term effects in terms of spinal alignment and growth in the immature pediatric spine. Some reports studying the upper cervical spine after instrumented fusion have found minimal effect on alignment and growth; however, effects on the pediatric spine below the C2 level have yet to be determined.

67

Extramedullary Spinal Cord Tumors Timothy W. Vogel and Jeffrey R. Leonard

67.1╇Background Primary lesions of the intradural extramedullary space are rare spinal tumors in children and are most frequently associated with leptomeningeal metastases from primary brain tumors. Extramedullary spinal tumors account for approximately 30% of all intradural lesions1 and have a wide diversity in their histological presentation.2 Tumors in this region include nerve sheath tumors, such as schwannomas and neurofibromas; myxopapillary ependymoma; meningiomas, especially in children with a history of neurofibromatosis type 2 (NF2); atypical teratoid rhabdoid tumors (ATRT); primitive neuroectodermal tumors (PNETs); and nonneoplastic lesions, including epidermoids, dermoids, arachnoid cysts, and neurenteric cysts (Table 67.1). There is currently no class I evidence regarding the surgical management of extramedullary spinal cord tumors because the frequency of each histological type of tumor varies from series to series depending upon an institution’s referrals.3 Table 67.1â•… Differential diagnosis for intradural extramedullary lesions of the spine Neoplastic lesions

Nonneoplastic lesions

Neurofibroma

Epidermoid

Schwannoma

Dermoid

Myxopapillary ependymoma

Arachnoid cyst

Atypical teratoid rhabdoid tumor (ATRT)

Neurenteric cyst

Primitive neuroectodermal tumor (PNET)

Clinical presentation in children with spinal lesions may often be delayed as a result of slow tumor growth, and diagnosis can be challenging in light of vague complaints of back, flank, or segmental pain depending upon spinal cord or nerve root compression4 (Fig. 67.1). The most common complaints are back pain, expressed verbally or nonverbally, limb weakness, sphincter dysfunction, and sensory disturbance.1 Lesions may be diagnosed only during work-up for scoliosis or if an unrelated trauma occurs. Radicular pain and sensorimotor deficits tend to be late presentations in children with extramedullary tumors.5 Any child with significant back or leg pain or who has lower extremity weakness with delayed motor developmental milestones should be investigated thoroughly. Magnetic resonance imaging (MRI) is the modality of choice for defining intradural extramedullary lesions. Computed tomography (CT) is used to investigate surrounding bone for remodeling or calcification within the lesion; however, MRI with contrast defines the plane between the lesion and the spinal cord and the soft tissue planes surrounding the lesions. It may be difficult to differentiate meningioma from schwannoma with MRI because T1 and T2 signal characteristics are comparable. Schwannomas usually demonstrate more heterogeneous T2 signal and cause vertebral scalloping and widening of the neural foramen. Tumors that possess a dural tail or contain calcification may predict meningioma.5

67.1.1╇Indications Surgical indications can be divided into emergent and urgent depending upon the clinical presentation. Emergent intervention is warranted for children showing evidence of spinal instability on neuroradiologic imaging or bowel/bladder dysfunction. Urgent indications for surgical intervention include altered neurologic examination, progressive

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548 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves

Fig. 67.1â•… An axial image of the spine with overlying spinous processes, spinal cord, ventral and dorsal nerve roots, and dura reveals compression of the spinal cord by the intradural extramedullary lesion. The tumor shown here has preserved a clear dissection plane that can be utilized during resection. The tumor may also involve the spinal roots or may have an intramedullary component.

spinal deformity, or persistent pain that is refractory to medication or conservative treatments. Whereas the definitions of urgent and emergent are not consistent, the authors believe that emergent surgical indications, as defined by progressive spinal deformity and/or neurologic deficits, should be addressed within hours of completing workup, especially if the loss of function is less than 48 hours old.

67.1.2╇Goals The idealized goal for an operative procedure for extramedullary spinal lesions is gross total resection when possible. With invasive or infiltrative lesions, such as neurofibromas in patients with

neurofibromatosis type 1 (NF1), complete resection of a lesion may be difficult or impossible without imposing a neurologic deficit with resection of the involved nerve segment or creating spinal instability6 (Fig. 67.2). Accurate fluoroscopic localization avoids excessive laminectomies, and preservation of facet joints helps limit the risk of kyphotic deformities.7 Clinical studies on pediatric patients with cervical intradural lesions reveal that approximately 33% of children undergoing laminectomy or laminoplasty develop kyphotic deformity.8 This incidence increases if radiotherapy is added.9 Risk factors for progressive kyphotic deformity in the cervical spine include patient age less than 3 years, pre-existing spinal deformity, myelopathic symptoms, and three or more laminectomies or resection of facet joints.8

67 â•… Extramedullary Spinal Cord Tumors

Fig. 67.2â•… Dorsal view of the spine with spinous processes removed and dura opened to reveal the underlying lesion involving the dorsal (sensory) spinal nerve roots. Tumors such as neurofibromas and schwannomas may involve the nerve roots and are amenable for surgical resection. Note how the involved nerve root travels out through the neural foramen, making surgical exposure of the involved segment essential for total resection.

67.1.3╇ Alternate Procedures Alternatives to invasive surgical interventions have been described by various groups. Monitoring growth of an otherwise asymptomatic lesion may be warranted with serial MRI in select pediatric patients. In addition, some lesions may be treated with adjuvant therapies,10 including chemotherapy and stereotactic radiosurgery,11 if the diagnosis is certain or if tissue has been acquired. Schwannomas may be amenable to radiosurgery; however, the authors believe that

these tumors are amenable to surgical resection if they involve dorsal (sensory) roots.

67.1.4╇Advantages The advantages of surgical resection of an extramedullary spinal tumor include obtaining surgical specimens to make a diagnosis and removal of the lesion, which may prevent additional growth of the lesion and additional neurologic dysfunction. Bowel

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550 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves and bladder dysfunction may also be prevented with surgical extirpation of an offending lesion.

67.1.5╇Contraindications Absolute contraindications to surgical intervention in children with extramedullary spinal tumors include untreated systemic infection that may lead to meningitis, or current treatment with anticoagulation that may lead to subdural hemorrhage. Some centers also perform resection of metastatic extramedullary medulloblastoma in the presence of systemic control, although no data exist that show this has any effect on prognosis.

67.2╇ Operative Detail and Preparation This section details some insights from the authors’ experience resecting extramedullary spinal lesions. Common tenets that apply to all such tumors are adequate localization and exposure of the involved region. These principles help to avoid intraoperative delay and complications that can arise from surgical resection. Discussions with the family on the potential operative risks should be held, outlining the potential for postoperative sensorimotor and bowel and bladder dysfunction. There also exist the common surgical risks of hemorrhage, infection, and potential need for instrumentation in certain cases where instability is present or suspected. Finally, because patients will be in the prone position for surgery, discussions may be warranted on the risk of rare postoperative visual loss.

67.2.1╇ Preoperative Planning and Special Equipment Preoperative planning begins with a thorough clinical history and physical examination paired with diagnostic neuroradiologic imaging. Establishing baseline neurologic function is essential for following in a patient’s postoperative clinical course and to ensure that future symptoms are not associated with a possible recurrence. MRI is the modality of choice for determining the location and extent of tumors, and axial T1- and T2-weighted sequences can aid in

the diagnosis (Fig. 67.3). Preoperative imaging warrants an MRI of the entire neuralaxis, including the brain, to evaluate for spinal metastasis that originated from a primary brain tumor. Preoperative plain radiographs with flexion and extension views may also be warranted if there is concern about spinal instability or deformity and if the lesion involves the pedicles or vertebral bodies. In these instances, CT images of the spine to assess pedicle size may be necessary. Spinal cord monitoring with somatosensory evoked potentials (SSEPs) and motor evoked potentials12 (MEPs) may aid in surgical resection to monitor spinal tract and neurologic function during a planned operative procedure. Discussions should be held among the anesthesiology, surgical, and electrophysiology staffs to ensure that the appropriate general anesthetic agents are provided and adequate mean arterial pressures are maintained, if there is concern about spinal cord compression or manipulation. Endoscopic and minimally invasive spinal surgical techniques may be employed during surgical resection. Tube-assisted microsurgical access may limit damage to surrounding ligaments but may limit exposure of intradural lesions.

67.2.2╇ Expert Suggestions/Comments During surgery, the authors recommend a thorough localization of the lesion using intraoperative fluoroscopic imaging confirmed with ultrasound images. These modalities, when paired with preoperative MRI, will limit the size of the incision and exposure of the neural elements to those critical for the resection of the lesion. In addition, limited laminectomy may help prevent future kyphotic deformity by maintaining the posterior osteoligamentous tension band. We also take great care to avoid exposure or disruption of the facet joints, limiting the risk for spinal destabilization. The principles especially apply to the cervical spine, where there are more vertically oriented facet joints that are prone to progressive kyphosis if damaged.

67.2.3╇ Key Steps of the Procedure/ Operative Nuances A key step following the exposure of the dura is to verify the adequate exposure of the lesion in the rostral and caudal directions. The authors suggest intra-

67 â•… Extramedullary Spinal Cord Tumors a

b

c

d

Fig. 67.3â•… Preoperative imaging. (a) T1 with contrast and (b) T2-weighted magnetic resonance images (MRIs) of an intradural extramedullary schwannoma in a patient with a history of neurofibromatosis type 2 (NF2). Note the severe spinal cord compression with presence of a cerebrospinal fluid (CSF) plane between the tumor and the compressed spinal cord. (c,d) Postoperative. T1 with contrast and T2-weighted images revealing extirpation of the tumor and decompression of the spinal cord.

operative ultrasound to confirm that the dura has been exposed above and below the lesion to facilitate and expedite its removal under microscopic guidance. Additional laminectomy and bone work under the microscope can be time-consuming and may lead to additional paraspinal hemorrhage that may obscure the operative field. The dura is opened, taking care to ensure that the extramedullary lesion does not adhere to the dura.

The whole process is also easier if the tumor capsule is maintained on opening. Dural retention sutures are placed to help “tent open” the dura and ensure adequate visualization of the tumor. With the dural opening extending above and below the lesion, the tumor is gently manipulated to identify the plane with the spinal cord. Microsurgical instruments are used to develop the plane and to avoid damage to the underlying spinal cord, with all movements away from the cord.

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b

c

d

Fig. 67.4â•… 1-year postoperative radiographic images in the (a) lateral and (b) anterior-posterior views from the neurofibromatosis type 2 (NF2) patient in Fig. 67.3 who underwent concurrent posterior cervical fusion with tumor removal. Note the presence of a cross-linking plate in (b). Radiographs in (c) flexion and (d) extension reveal the postoperative stability of the cervical fusion at 1 year.

67 â•… Extramedullary Spinal Cord Tumors

67.2.4╇ Hazards/Risks/Avoidance of Pitfalls There are a number of inherent risks associated with the resection of extramedullary lesions. Damage to the spinal cord may occur during exposure of the tumor or on its resection. Manipulation of the tumor should not be so extensive as to distort the adjacent spinal cord. Alternatively, if there is severe spinal canal stenosis from tumor compression, the spinal cord may have lost any residual compliance for manipulation or disturbance. Ensuring that the patient has adequate mean arterial pressure maintenance during anesthesia, induction through the postoperative period, with normotensive to slight hypertensive parameters, may ensure that perfusion to the microcirculation of the normal spinal cord is maintained. Some also advocate performance of laminoplasties because they prevent spinal deformities. In the experience of the authors, however, this has not been the case. Interspinous ligaments are severed above and below the levels that were removed, thus weakening the posterior tension band. The authors do believe that laminoplasties make it easier to perform repeat operations by creating a definitive layer between the subcutaneous tissues and the dura. In most cases, tumor debulking with an ultrasonic aspirating device is necessary prior to extensive surgical resection. Intraoperative SSEP and electromyelogram (EMG) monitoring may aid in determining the limits to aggressive surgical resection and exposure. If changes in SSEP or MEP studies are seen during the procedure, care must be taken to assess if surgical resection should proceed. These decisions should be made on a case-by-case basis with the anesthesiology, surgical, and electrophysiology staffs. If monitoring is lost, the authors will sometimes close to obtain the diagnosis and return another day to complete the resection. This allows for appraisal of neurologic function, a discussion of pathology, and in some instances technically easier resection of the tumor (i.e., blood supply has been interrupted making the tumor easier to remove).

67.2.5╇ Salvage and Rescue Surgeons may encounter hemorrhagic lesions that may be difficult to control with a limited exposure. Should there be an area where hemorrhage persists despite conventional control methods, additional exposure of the region may be required. Tumors may also be encountered where no clear plane exists between the lesion and spinal cord. In these cases, circumferential dissection may be limited and attention should be turned to working in areas of the tumor border where a clear demarcation or plane can be developed. Locations where adherent or intra-

medullary tumor exists can thereby be isolated. Care must be taken on resection of these intramedullary components and subtotal resection may be required to avoid neurologic compromise, if the corticospinal or other essential tracts are involved. If spinal destabilization is encountered as a result of tumor involvement or surgical resection, surgeons should be prepared for instrumentation of the involved spinal levels (Fig. 67.4).

67.3╇ Outcomes and Postoperative Course 67.3.1╇ Postoperative Considerations Following surgery, patients are routinely admitted to the pediatric intensive care unit for observation and careful monitoring of neurologic function and maintenance of cardiovascular parameters, such as mean arterial pressure parameters, if applicable. Cervical collars or lumbar orthoses may be necessary if spinal instrumentation is placed or if there is concern for progressive spinal deformity.7 During the immediate postoperative period, patients remain in a prone position to help prevent cerebrospinal fluid (CSF) leak and to promote healing of the dura for a 24- to 72-hour period. Following this postoperative restriction, patients may be mobilized with the aid of physical therapy. Involvement of the posterior spinal cord may have impaired function in the dorsal columns and patients may have impaired proprioception, initially limiting their ability to ambulate independently. Comprehensive therapeutic teams of therapists, intensivists, and surgeons will help to facilitate early mobilization and recovery following surgery. Postoperative MRI in the 24 to 48 hours following surgery will aid in establishing a baseline image for later comparison and to ensure gross total or extent of subtotal resection. Serial MRI may be required to follow the affected spinal level and to ensure that there is no additional tumor growth. Children must be followed postoperatively by a neurosurgeon because they are at risk for delayed and progressive spinal deformity13 (Fig. 67.5). In cases where multilevel laminectomies have been performed, the authors often follow patients with standing long-cassette X-rays to assess for development of deformity.

67.3.2╇Complications Complications arising from surgical resection of extramedullary spinal tumors include meningitis and local skin infection, CSF leak, subdural hemorrhage necessitating additional surgery for evacuation, weakness and sensory changes in levels below the lesion, and

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b

c

d

Fig. 67.5â•… (a) Preoperative and (b) postoperative T2-weighted magnetic resonance images (MRIs) of an intradural extramedullary plexiform neurofibroma in a patient with a history of neurofibromatosis type 1 (NF1). Note the severe bilateral spinal cord compression in (a) and the subsequent decompression in (b). (c) The patient had a three-level laminectomy at C2–C4 and, despite use of a rigid cervical collar, 6 months postoperatively developed a cervical kyphotic deformity seen in plain radiographs. (d) The progressive deformity was isolated to the C4–C5 level and the patient underwent correction with an anterior cervical diskectomy and fusion seen in the plain radiographs at this level. At 1 year postoperatively, the deformity remains corrected.

67 â•… Extramedullary Spinal Cord Tumors proprioception impairment leading to difficulty in ambulation. Often this neurologic change is more pronounced when the lesion covers multiple levels, and the families should be told to expect this postoperatively even if the surgery is technically without problem. This can be especially distressing for patients who present solely with back pain. More severe and uncommon risks include paralysis, blindness, persistent neuropathic pain, and permanent neurologic impairment in sensorimotor function. These potential occurrences are covered in the initial family discussions so that appropriate expectations are set.

References ╇1. Kumar

R, Singh V. Benign intradural extramedullary masses in children of northern India. Pediatr Neurosurg 2005;41(1):22–28 ╇2. Menezes AH. Craniovertebral junction neoplasms in the pediatric population. Childs Nerv Syst 2008;24(10): 1173–1186 ╇3. Binning M, Klimo P Jr, Gluf W, Goumnerova L. Spinal tumors in children. Neurosurg Clin N Am 2007;18(4): 631–658 ╇4. Rossi A, Gandolfo C, Morana G, Tortori-Donati P. Tumors of the spine in children. Neuroimaging Clin N Am 2007;17(1):17–35 ╇5. Wald JT. Imaging of spine neoplasm. Radiol Clin North Am 2012;50(4):749–776 ╇6. Leonard JR, Ferner RE, Thomas N, Gutmann DH. Cervical cord compression from plexiform neurofibromas in neurofibromatosis 1. J Neurol Neurosurg Psychiatry 2007; 78(12):1404–1406

╇7. Sciubba

DM, Chaichana KL, Woodworth GF, McGirt MJ, Gokaslan ZL, Jallo GI. Factors associated with cervical instability requiring fusion after cervical laminectomy for intradural tumor resection. J Neurosurg Spine 2008;8(5):413–419 ╇8. Furtado SV, Murthy GK, Hegde AS. Cervical spine instability following resection of benign intradural extramedullary tumours in children. Pediatr Neurosurg 2011;47(1):38–44 ╇9. McGirt MJ, Garcés-Ambrossi GL, Parker SL, et al. Shortterm progressive spinal deformity following laminoplasty versus laminectomy for resection of intradural spinal tumors: analysis of 238 patients. Neurosurgery 2010;66(5):1005–1012 10. Dodd RL, Ryu MR, Kamnerdsupaphon P, Gibbs IC, Chang SD Jr, Adler JR Jr. CyberKnife radiosurgery for benign intradural extramedullary spinal tumors. Neurosurgery 2006;58(4):674–685 11. Sachdev S, Dodd RL, Chang SD, et al. Stereotactic radiosurgery yields long-term control for benign intradural, extramedullary spinal tumors. Neurosurgery 2011;69(3):533–539, discussion 539 12. Rajshekhar V, Velayutham P, Joseph M, Babu KS. Factors predicting the feasibility of monitoring lower-limb muscle motor evoked potentials in patients undergoing excision of spinal cord tumors. J Neurosurg Spine 2011;14(6):748–753 13. Kelley BJ, Johnson MH, Vortmeyer AO, Smith BG, Abbed KM. Two-level thoracic pedicle subtraction osteotomy for progressive post-laminectomy kyphotic deformity following resection of an unusual thoracolumbar intradural extramedullary tumor. J Neurosurg Pediatr 2012;10(4):334–339

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68

Intramedullary Spinal Cord Tumors Michael Weicker and Rick Abbott

68.1╇Background 68.1.1╇ Indications and Goals In childhood, intramedullary spinal cord tumors are a rare entity, with < 200 newly diagnosed per year. In contrast to adults, astrocytomas, as opposed to ependymomas, are more common in children. The majority of these are low-grade tumors, with anaplastic astrocytomas and glioblastomas comprising only ~€10%. Ependymomas (12%), hemangioblastomas (5%), and cavernomas (1.7%) are also infrequently encountered. Surgery is indicated for any newly diagnosed intramedullary tumor in a child―the goals of which are to obtain a histological diagnosis and to remove a significant portion of tumor. When surgical resection can remove > 80% of a tumor, long-term, progressionfree survival is equivalent to complete removal.1

68.1.2╇ Alternative Procedures Whereas radiation therapy and, to a lesser extent, chemotherapy may have an adjuvant role in the treatment of spinal cord tumors, surgical removal remains the mainstay of treatment. Most reports on the use of radiation to treat spinal cord tumors contain populations of mixed ages who are predominantly adults. These studies cite 5-year survival rates of 54 to 100% (majority reporting 55–59%) when surgery followed by radiation was used.2 Survival for patients with low-grade tumors was 75 to 85%. This experience, when compared with that of the authors, who saw an 88% 5-year survival in patients with similar tumors treated with surgery alone, shows that surgery is as effective as radiation in controlling these tumors. The known side effects of using radiation in a growing child are avoided with surgery.

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68.2╇ Operative Detail and Preparation 68.2.1╇ Preoperative Planning and Special Equipment Preoperative evaluation of a spinal cord tumor routinely requires a contrast-enhanced magnetic resonance imaging (MRI). Note should be taken of the eccentricity of the tumor within the cord, the presence of cysts capping the rostral and caudal poles of the tumor, and the presence of cysts within the tumor. Ependymomas usually enhance brightly and homogeneously. They typically have rostral and caudal cysts with a hemosiderin cap at their poles. They are usually located in the center of the cord. Astrocytomas and gangliogliomas enhance less frequently and heterogeneously. These neoplasms are more frequently eccentric in the cord. They also generally cause asymmetric enlargement of the cord, something that is almost never seen with ependymomas. Angiography is generally reserved for vascular lesions, such as hemangioblastomas. If scoliosis has developed, 36-in plain films or even computed tomography (CT) may be necessary. Prior to surgery, a discussion with the anesthesiology team is necessary. The authors recommend the use of intraoperative neurophysiological monitoring, including somatosensory evoked potentials (SSEPs), muscle motor evoked potentials (MEPs), and epidural MEPs (D-waves) on all intramedullary tumor resections. The utility of monitoring is significantly decreased by the use of volatile anesthetics, paralytics, and muscle relaxants.

68 â•… Intramedullary Spinal Cord Tumors

68.2.2╇ Keys Steps/Operative Nuances Surgery is performed with the patient in the prone position, with the patient supported on chest rolls. For cervical or cervicothoracic tumors, the head is further stabilized in a headholder. A laminectomy or laminoplasty is performed with a combination of high-speed drill and round burr; the craniotome and/or the Kerrison punch bone removal should expose solid tumor but does not need to extend to the rostral or caudal cysts unless they are considered intratumoral. Intraoperative ultrasonography can aid in visualizing the adequacy of bone exposure. The dura is opened and the median raphe is identified. The spinal cord is often asymmetrically expanded, which can make identification of midline difficult (Fig. 68.1 and Fig. 68.2). Sensory evoked potentials can assist in mapping the dorsal columns. The pia is then opened at the raphe along the length of the tumor with a scalpel or beaver blade (Fig. 68.3). An neodymium:yttrium aluminum garnet (Nd:YAG) laser is used to spot-

cauterize crossing vessels. The laser causes less heat injury to surrounding parenchyma than traditional cautery (Fig. 68.4). The authors prefer to open the raphe with sharp dissection to confine heat injury to the cord to only those points requiring vessel cauterization. Plated bayonets are then used to spread the dorsal columns to the depth of the tumor. Vertically oriented vessels along the median raphe can assist in maintaining a midline dissection (Fig. 68.5). The authors have found it best to avoid excess exposure of the dorsal and lateral surfaces of the tumor until the myelotomy has been carried to its rostral and caudal extent because this may result in unnecessary traction on the dorsal columns and concomitant sensory deficits (Fig. 68.6). Resection of glial tumors is started at the midportion, where the tumor typically has the largest volume, and is carried to the poles. The tumor is initially debulked internally with a combination of bipolar cautery and sonic aspiration (Fig. 68.7). Resection is carried laterally until more normal-appearing tissue is encountered or

Fig. 68.1â•… Focal discoloration of the dorsal surface of this spinal cord marks the level of the intramedullary tumor. Arrows point to vessels that disappear into the median raphe. At a distance from the level of involvement, darkening of the midline highlights the indentation of the surface by the median raphe.

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Fig. 68.2â•… In this case, the cord’s surface is somewhat swollen but the median raphe can be seen. Close inspection at the points shown by arrows identifies vessels plunging into the raphe.

Fig. 68.3â•… The pia is sharply incised. Frequently there can be small pial bands that hold the raphe together 1 to 2 mm deep to the surface. These can be visualized under high magnification and cut sharply (arrow).

68 â•… Intramedullary Spinal Cord Tumors

Fig. 68.4â•… Vessels can cross the midline dorsal to the pial surface that overlays the raphe. Point cautery can be used for these. Shown here is a contact laser with a 0.8-mm tip cauterizing such a vessel.

Fig. 68.5â•… After the pia has been cut, gentle spreading can be used to open up the raphe. The arrows point to vertical vessels that typically line the walls of the raphe on either side (left two arrows; right arrow points to darkening tissue signaling dorsal surface of tumor). Seeing these vertical vessels gives one confidence that the dissection is confined to the raphe. The instrument being used here is a pair of plated bayonets designed by Fred Epstein, MD.

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Fig. 68.6â•… As the raphe is spread open, the darkened surface of the tumor begins to emerge (arrow). It will typically also appear somewhat gelatinous. The myelotomy should extend pole to pole of the tumor prior to beginning the resection so as to decompress the cord; this will allow any tumor swelling to be directed into the myelotomy and not cause additional cord compression.

Fig. 68.7â•… After the entire dorsal surface has been unroofed by opening the raphe, an ultrasonic aspirator or plan aspiration is used to centrally debulk the tumor. Care should be taken in the use of cautery, especially at the margins of the tumor and at its ventral aspects, because vascular cauterization can extend into surrounding normal parenchyma resulting in functional loss.

68 â•… Intramedullary Spinal Cord Tumors decreases in MEPs portend impending catastrophic neurologic injury. Ependymomas may be approached in a somewhat different manner from glial tumors. Compared to the infiltrating nature of astrocytomas, ependymomas will have a tumor–cord interface that is only several cell layers thick. This interface allows the separation of the ependymoma from the spinal cord with minimal disruption of fiber tracts and may allow for total en bloc resection. Initially, a cleavage plane is developed at one of the poles of the tumor with the use of the plated bayonets or the laser. This plane is then carried along the rostral-caudal axis of the tumor by gentle spreading with the bayonets. The blood supply to ependymomas is typically on the ventral surface from branches of the anterior spinal artery. Great care must be taken to cauterize only feeding vessels as they enter into the tumor and not to disrupt the longitudinally running anterior spinal artery. The authors use fine-tipped bipolar forceps or spot-laser cautery to do this. Final hemostasis is obtained with irrigation and local application of microfibrillar collagen or Gelfoam. Excessive use of cautery should be avoided at the tumor margins because this risks cauterization of vessels perfusing the corticospinal tracts and other normal tissue (Fig. 68.8).

The dura is closed primarily in a watertight fashion. If a laminoplasty was performed, the segments of bone are secured with nonabsorbable suture or, alternately, resorbable plates may be used.3 Paraspinal muscle is closed in a tension-free fashion. Cutting the fascia laterally to create in situ myofascial flaps can facilitate this. The paraspinal muscle fascia is then closed in a watertight fashion. Approximation of all muscle layers, with elimination of dead space, and a watertight fascial closure will greatly assist in preventing cerebrospinal fluid (CSF) leaks and subsequent pseudomeningocele formation.

68.2.3╇ Hazards/Risks/Avoidance of Pitfalls A decrease in motor D-wave amplitude (upper motor neuron potentials) of < 50% and/or a loss in the evoked electromyograms (EMGS) are predictive of temporary postoperative motor deficits, whereas a decrease in D-wave amplitude of > 50% is associated with complete and permanent loss of motor function. A precipitous drop in both potentials is most commonly from vascular injury. Elevation of the blood pressure can assist in perfusion of the spinal

Fig. 68.8â•… When the resection is complete, bleeding will typically stop spontaneously or with tamponade using cottonoids. Occasionally, there can be persistent bleeding along the ventral midline of the resection cavity. This may be coming from small branches of the anterior spinal artery; therefore, cautery should be avoided in all but the most resistant bleeding. If tamponade using cottonoids does not work, then thrombin-soaked gelatin sponges can be used. The sponges are left in place for 10 or more minutes before a bleeding source needs cautery in this location.

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562 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves cord and may help preserve postoperative function when a worrisome decrease in potentials does occur.

68.3╇ Outcomes and Postoperative Course 68.3.1╇ Postoperative Considerations Approximately one-third of patients develop a clinically significant spinal deformity that requires operative instrumentation. Given the high incidence of progressive scoliosis in children who have undergone surgery of spinal cord tumors, there should be a lower threshold for surgical intervention than for children with idiopathic scoliosis. Risk of postoperative scoliosis is higher in younger children and occurs most frequently in the cervical, followed by the thoracic, spine. Development of a deformity is rare in the lumbar spine. Laminoplasties may help reduce the incidence of deformity, particularly in children. Additionally, a progressive deformity following tumor resection may indicate tumor recurrence, which would require treatment prior to any surgery to correct the scoliosis. Although not directly related to surgery, approximately 15% of children with intramedullary tumors will develop hydrocephalus at some point in the course of their disease. The pathophysiology is not entirely clear; however, it may be related to increased protein in the CSF, tumor dissemination, or obstruction of CSF outflow at the level of the medulla in the case of cervical tumors.

68.3.2╇Complications Generally, postoperative motor deficits are related to the patient’s preoperative functional status: Patients with a significant motor deficit before surgery are more likely to deteriorate postoperatively. Consequently, the authors advocate early surgical intervention prior to the development of motor deficits. Impaired joint position sense may be a serious functional disability and is more commonly seen after ependymoma than astrocytoma removal. This seems to occur less commonly in children than in adults and, when it does occur, it is better tolerated because children seem better able to compensate for this disability. Persistent CSF leak is relatively rare in patients who have not had prior surgery or received radiation therapy. However, after radiation therapy or prior surgery, there is a significant risk for wound dehiscence and subsequent CSF leak. Consequently, greater care must be taken during wound closure.

References ╇1. Constantini S, Miller DC, Allen JC, Rorke LB, Freed D, Ep-

stein FJ. Radical excision of intramedullary spinal cord tumors: surgical morbidity and long-term follow-up evaluation in 164 children and young adults. J Neurosurg 2000;93(2 Suppl):183–193 ╇2. O’Sullivan C, Jenkin RD, Doherty MA, Hoffman HJ, Greenberg ML. Spinal cord tumors in children: longterm results of combined surgical and radiation treatment. J Neurosurg 1994;81(4):507–512 ╇3. Abbott R, Feldstein N, Wisoff JH, Epstein FJ. Osteoplastic laminotomy in children. Pediatr Neurosurg 1992;18(3): 153–156

69

The Surgical Management of Pediatric Brachial Plexus Tumors Elias Boulos Rizk and John “Jay” C. Wellons III

69.1╇Background Tumors of the pediatric brachial plexus encompass a spectrum of well-defined clinicopathological entities ranging from reactive, inflammatory, infectious, hamartomatous, benign tumors, to high-grade malignant neoplasms, to metastatic neoplasms. An understanding of gross and microscopic anatomy is essential to the comprehension and treatment of pathology involving the peripheral nervous system. The reader is referred to well-known texts in the field for a detailed list of pathological entities and histopathological discussion because these are outside the scope of this chapter. The chapter discusses the surgical management and operative nuances of the more common intrinsic or extrinsic lesions of the brachial plexus.

69.2╇ Pathological Subtypes 69.2.1╇ Intrinsic Tumors Schwannoma Schwannomas are the most common benign tumor of peripheral nerves. The majority occur sporadically. They affect patients of all ages, with a peak between ages 20 to 50 years.1 Schwannomas do not occur with neurofibromatosis type 1 (NF1) but occur as part of NF2, Carney complex, syndrome with nevi, and vaginal leiomyomas.2 Histologically, these are usually encapsulated tumors made up entirely of benign neoplastic Schwann cells.1,3 The tumors grow in an eccentric fashion. Schwannomas show a typical architecture. The cells are arranged in a compact form called Antoni A, or in a less compact form called Antoni B.3 Some of the cells may also palisade to form Verocay bodies. Other pathological variants include plexiform, melanotic, and cellular types. The melanotic type can become malignant. Schwannomas are hypodense on computed tomography (CT)

scan, with intermediate signal on T1-weighted magnetic resonance images (MRI) and hyperintense on T2-weighted images. Schwannomas enhance uniformly with contrast supplementation.

Neurofibroma Neurofibromas are pathologically and genetically different from schwannomas. The presence of intratumor nerve fibers helps distinguish neurofibromas from schwannomas.3 There are two groups of neurofibromas. The solitary type, or non-NF1 neurofibroma, comprises 90% of neurofibromas.4 This type of tumor tends to taper at each end. The solitary type can also be subdivided into dermal and intraneural types. Dermal tumors usually present with nodular tumors of the skin and the subcutaneous tissues. Intraneural neurofibromas are located deeper in nerve roots, trunks, plexus, or peripheral nerves. The second group is the plexiform type, seen almost exclusively with NF1. Usually, these lesions are pathognomonic of NF1 and rarely are malignant.1 They are nondiscrete and exhibit multiple nodular growth along a nerve segment, giving it the typical appearance of a “bag of worms.”3 Histologically, neurofibromas are composed of a mix of Schwann cells, perineurial-like cells, and fibroblasts, interspersed with nerve fibers, wirelike strands of collagen, and myxoid matrix.1,3 They are hypodense on CT, whereas on MRI they present as hypointense on T1-weighted images and hyperintense on T2-weighted images with increased contrast uptake. A target sign can be identified on T2 MRI that represents a dense collagen core.

Malignant Peripheral Nerve Sheath Tumor (MPNST) MPNSTs are a malignant form of neural sheath tumors. The incidence of these tumors is low, accounting for 10 to 15% of soft tissue sarcomas.5 NF1 patients account

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564 Section VI.D╅ Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves for more than half of all the MPNSTs.6 The lifetime risk for an individual with NF1 to develop MPNST is about 8 to 13%.7 Most sporadic and all NF1-associated MPNSTs carry the NF1 deletion; however, further genetic hits are required to undergo malignant transformation.8 Deletions in tumor suppressor genes, including TP53 and CDKN2A, and receptor tyrosine kinase amplification (EGFR) are seen in MPNSTs.9 Patients usually present with a growing mass with associated neurologic manifestation of the involved nervous structure (e.g., paresthesias, pain, weakness, or decreased reflexes).10 Histological characteristics of MPNST include high cellularity, nuclear atypia, mitotically active spindle cells, abrupt variation in cellularity, and increased perivascular cellularity.3 Mitotic figures are more than 4 per 10 high-power fields. Furthermore, MPNSTs can have divergent differentiation into mesenchymal-derived cells, including cartilage, bone, fat, and so on. MRI has little value in terms of distinguishing MPNSTs from schwannomas (Fig.€69.1). Positron emission tomography (PET) has been advocated as an adjunct study to establish increased metabolic activity. However, there is no consensus on the use of PET scan in the preoperative work-up.

Tumors of Neural Origin Neuroblastomas involving the brachial plexus are an extremely rare entity but should be part of the differential diagnosis. Ganglioneuromas are benign

Fig. 69.1â•… Computed tomography (CT) of a malignant peripheral nerve sheath tumor (MPNST).

mature tumors composed of well-differentiated neoplastic ganglion cells and axons. Interspersed among the cells are Schwann cells and fibrous stromal background. The cell of origin is hypothesized to be a neuroblastoma. Grossly, ganglion cells appear as a well-circumscribed, smooth tumor cell. Microscopically, ganglion cells are eosinophilic, large, with large vesicular nuclei and prominent nucleoli.3 Ganglion cells emanate multiple long axons. Interspersed among the axons are Schwann cells.3

69.2.2╇ Extrinsic Tumors Cystic Hygroma A subtype of lymphatic malformation, cystic hygromas can also involve nerves of the brachial plexus. Compression of the brachial plexus could be secondary to a mass effect from a growing lesion within the plexus. Cystic hygromas are thought to be due to a failure of lymphatics to connect with the venous system, dissecting a path along fascial planes and slowly growing in size. Microscopically, they form loose areolar tissue with dispersed vascular channels that encapsulate secretions made up of granular and proteinaceous lymphatic precipitate. Imaging reveals a heterogenous mass with increased signal intensity on T1- and T2-weighted MRIs (Fig. 69.2).

Fig. 69.2â•… T2-weighted magnetic resonance imaging (MRI) of a cystic hygroma involving the left brachial plexus.

69 â•… The Surgical Management of Pediatric Brachial Plexus Tumors

Lipoma There are three types of fatty tumors involving peripheral nerves, as described by Terzis et al: (1) well-encapsulated intraneural lipomas, (2) diffusely infiltrating fibrofatty tumors (lipofibromatous hamartomas), and (3) macrodystrophia lipomatosa (an infiltrating fibrofatty lesion with associated focal macrodactyly). 11 Intraneural lipomas are usually painless and can cause compressive symptoms. Lipofibromatous hamartomas present as a diffuse enlargement of the involved nerve and associated soft tissue. In macrodystrophia lipomatosa, the lesion causes an overgrowth of the hand or finger. Lipomas are composed of fat, which can be entirely composed within a capsule or infiltrated within the nervous structure.

Lipoblastoma Lipoblastomas may be clinically challenging from a diagnostic standpoint, since they are virtually indistinguishable from lipomas and liposarcomas radiologically. They are usually an encapsulated mass that encases mature adipose tissue centrally, surrounded with lipoblasts peripherally. Imaging studies can be beneficial to localize the extent of the disease process; on the other hand, there are no pathognomic signs on CT or MRI to differentiate these lesions from lipomas or liposarcomas (Fig. 69.3).

69.3╇ Operative Detail and Preparation 69.3.1╇ Goals and Expectations Once the decision has been made to pursue surgical treatment for a lesion involving the brachial plexus, it is imperative to have an up-front discussion with the patient, parent, or caregiver on the risks and benefits of surgical biopsy, subtotal debulking, resection, or need for postexcisional reanimation of the affected limb, be it through grafting or neurotization. In general, treatment strategies are dependent on the pathological entity, and it is well within the norm to obtain tissue, confirm diagnosis, and return for a second, more aggressive surgery, if necessary. More benign-type pathological entities, such as neurofibromas, schwannomas, or tumors of neural origin, can be debulked with minimal neurologic sequelae, either through excision of grossly exophytic lesion or through fascicular dissection, identification of involved fascicles, nerve action potential testing, or direct motor stimulation of said fascicles, and selective resection. In settings of fusiform neurofibromas, this is rarely done due to the diffuse nature of the disease process. In suspected higher grade tumors, such as MPNST, it is not uncommon to obtain tissue through needle biopsy or open subtotal debulking, and then discuss the potential benefit imparted by gross total resection and the likely resultant neuro-

Fig. 69.3â•… T2-weighted magnetic resonance imaging (MRI) of a lipoblastoma.

565

566 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves logic deficits from another return to the operating room in a separate setting for larger exposure and more aggressive resection. Due to the need for adjuvant treatment following surgery, it has not been a common practice to perform grafting or neurotization in the same setting. One could certainly imagine clinical scenarios where benign tumors continue to grow despite nonsurgical therapy, and aggressive non–plexus-sparing operations would be necessary. In that setting, earlier reanimation would not be unreasonable. Specific mention needs to be made of the need for collaborative work with other surgical subspecialist colleagues. Specifically, pediatric surgeons skilled at operating in the apex of the lung, the chest wall, and the relevant vascular anatomy are often part of a team surgical approach. In addition, otolaryngologists skilled in the region around the larynx and trachea may be extremely helpful as well. It is the opinion of

the authors that these tumors are best approached in a multidisciplinary manner and that preoperative planning and definition of roles are critical.

69.3.2╇ Anesthetic, Positioning, Prepping, and Monitoring Short-acting paralytics may be useful to the anesthesia team for securing the airway, but the ability to directly stimulate the plexus and nerves is extremely important to the ability to perform the procedure. Therefore, the patient is maintained on anesthesia without paralytics during the procedure. A roll is placed between the shoulder blades, and the head is partially turned away from the operative side in order to better expose the supraclavicular and infraclavicular regions. A wide preparation is made of the ipsilateral arm, chest, shoulder, and neck (Fig. 69.4).

Fig. 69.4â•… Note that the patient’s arm and chest wall are prepped into the surgical field. In addition, the EMG leads are placed by the surgeon in the relevant muscles by the surgical team in conjunction with the electrodiagnostics team. This supraclavicular incision shows the Upper Trunk tagged by the blue loop and the omohyoid muscle split, tied off, and retracted by the heavy silk suture. The tumor itself is being held up by an Allis clamp.

69 â•… The Surgical Management of Pediatric Brachial Plexus Tumors In particular, extremity rolls and drapes are used for the hand and arm because multiple recording needles are placed for monitoring after the field is draped, and it is useful to be able to directly observe muscle movement (in lieu of guessing what is moving under the drapes). The ipsilateral leg is also prepared in case long-segment grafting is needed, however rare. Short-segment grafting could also be obtained using cutaneous nerves of the neck that ramify over the sternocleidomastoid muscle. Monitoring and communication between the technician and the surgeon are critical. Most commonly, electromyelogram (EMG) and nerve action potentials (NAP) are utilized, but certainly tailored for each specific patient.

69.3.3╇Exposure The brachial plexus may be approached from an anterior, posterior, or transaxillary exposure. Exposures for tumor resection are in general best done from the anterior route because it affords the ability to identify the plexus with a broader exposure. With very rare exception (perhaps a small incision just above the clavicle to resect a symptomatic cervical rib in a teenaged girl), the surgical exposure of the brachial plexus is not considered minimal. It is imperative to have a mature understanding of the involved anatomical structures of the region gained through reading and time spent in an anatomical dissection laboratory. The anterior exposure of the plexus has two main components that may be used separately or together: supraclavicular or infraclavicular, and it is important to recognize the limits of each exposure. In terms of nervous structures, the supraclavicular exposure affords the ability to reliably identify the upper, middle, and lower trunks as well as the involved roots more proximally and the nerves that arise from these structures. The divisions tend to be underneath the clavicle but the presence of a mass lesion in the area can displace normal anatomy either superiorly or inferiorly. The infraclavicular exposure allows the surgeon to typically identify the M of the plexus underneath the pectoralis minor muscle and then do work more proximal to the cords and more distal to the terminal nerves of the plexus. It is here that the brachial plexus surgeon is reminded of why the cords are named lateral, medial, and posterior because the brachial artery overlies the posterior cord. It is rare to need to remove the clavicle because a standard laparotomy towel can be wrapped around

the clavicle and can be used to either retract the bone upward or downward (Fig. 69.5). When the clavicle does need to be removed, it is best to have an orthopedic surgeon involved because often a plate may need to be used for replacement. The union rate of the clavicle can be low, particularly when a segment has been completely removed, and therefore is void of blood supply. In the setting of a malignant tumor that may require radiation to the field, the plate may also need to be explanted.

69.3.4╇ Surgical Points Specific to Intrinsic Tumors Exophytic tumors are rare, and tend to be either neurofibromas or schwannomas pathologically. In general, the surgical goal is to excise the portion lying outside of the normal neural structure and, if a single fascicle is involved, to dissect the abnormal away from the normal, stimulate, and excise. More commonly seen are lesions (such as MPNST) that expand the normal neural structure. In addition, these tend to be malignant and surgical excision is often part of the overall care plan. This author has found it useful to make a smaller approach for open biopsy (or via needle in certain cases) so that pathology can be reviewed in a multidisciplinary oncology tumor board-type setting and agreement can be reached about the order of surgery and adjuvant therapy. Resection causes neurologic dysfunction that will very often not improve, and it is important to have each member of the care team and the family aware of the risks. The authors have not made a standard practice of nerve grafting at the time of resection because the chemotherapy and/ or radiation therapy to follow are not conducive to the fragile growth of axons.

69.3.5╇ Surgical Points Specific to Extrinsic Tumors Tumors of the lateral neck, thoracic outlet, or lateral chest wall will often compress or encompass the brachial plexus. As mentioned, monitoring is useful, as are standard nerve dissection and retraction techniques. Because the anatomy of the region is quite complex, the back-and-forth team approach is very useful here to achieve a safe surgical resection while protecting critical involved structures (i.e., thoracic duct, subclavian artery and vein, parietal pleura).

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568 Section VI.Dâ•… Neoplasms of the Spine, Spinal Cord, and Peripheral Nerves

Fig. 69.5â•… An infraclavicular exposure has been added in order to obtain access both above and below the clavicle (wrapped in the blue loop of a laparotomy sponge). Relevant plexus anatomy is protected, tagged, and looped both proximally (XI, suprascapular nerve, upper trunk, middle trunk) and distally (musculocutaneous nerve, median nerve, ulnar nerve, medial cord contribution to the median nerve). Note the cavity below the clavicle where the tumor once resided.

The typically benign nature of extrinsic lesions dictates a less aggressive position in terms of sectioning of the nerve and makes careful identification and protection of critical nervous structures paramount. A small amount of residual cystic hygroma or lipoma, for example, can be followed expectantly. For other, more aggressive lesions, such as lipoblastoma, a more definitive resection may be needed to prevent recurrence. If a portion of the plexus is sectioned during tumor removal, then consideration is given at that time to direct repair (if the ends oppose), jump graft (if the ends do not oppose), or neurotization if proximal innervation is no longer available.

69.3.6╇Closure The authors have found it useful to perform a multilayered closure ending in a subcuticular stitch over a small drain in the tumor bed because the lymphatic tissue that is often transected can “weep” into the cavity. The drain can usually be removed on postoperative day 1 or 2. A persistent high volume of output, particularly of cloudy fluid that becomes more so with fatty foods, should be evaluated for injury of the thoracic duct (on the left side). Postoperative care mainly involves pain control and only brief immobilization in a sling. Range-of-motion is started after 48 hours and formal occupational therapy is started at 2 weeks.

69 â•… The Surgical Management of Pediatric Brachial Plexus Tumors

69.4╇Summary Intrinsic brachial plexus tumors, as well as tumors of the lateral neck, thoracic outlet, lateral chest wall, and axilla involving the structures of the brachial plexus, are rare. When encountered, they are often best approached in a multidisciplinary fashion, including both surgical and oncological colleagues if necessary. In planning for surgery, it is important to discuss surgical goals and risks with the patient and family. Monitoring is essential, as is knowledge of both the standard anatomy and the variations that may be encountered. Surgeons embarking on tumor resection in the region should not hesitate to ask for assistance and/or advice from surgeons with experience in the field.

References ╇1. Pilavaki

M, Chourmouzi D, Kiziridou A, Skordalaki A, Zarampoukas T, Drevelengas A. Imaging of peripheral nerve sheath tumors with pathologic correlation: pictorial review. Eur J Radiol 2004;52(3):229–239 ╇2. MacCollin M, Chiocca EA, Evans DG, et al. Diagnostic criteria for schwannomatosis. Neurology 2005;64(11): 1838–1845 ╇3. Skovronsky DM, Oberholtzer JC. Pathologic classification of peripheral nerve tumors. Neurosurg Clin N Am 2004;15(2):157–166

╇4. Cutler

EC, Gross R. Neurofibroma and neurofibrosarcoma of peripheral nerves. Arch Surg 1936;33:733–779 ╇5. Stark AM, Buhl R, Hugo HH, Mehdorn HM. Malignant peripheral nerve sheath tumours—report of 8 cases and review of the literature. Acta Neurochir (Wien) 2001;143(4):357–363, discussion 363–364 ╇6. Woodruff JM. Pathology of tumors of the peripheral nerve sheath in type 1 neurofibromatosis. Am J Med Genet 1999;89(1):23–30 ╇7. Sørensen SA, Mulvihill JJ, Nielsen A. Long-term followup of von Recklinghausen neurofibromatosis. Survival and malignant neoplasms. N Engl J Med 1986;314(16): 1010–1015 ╇8. Birindelli S, Perrone F, Oggionni M, et al. Rb and TP53 pathway alterations in sporadic and NF1-related malignant peripheral nerve sheath tumors. Lab Invest 2001;81(6):833–844 ╇9. Perry A, Kunz SN, Fuller CE, et al. Differential NF1, p16, and EGFR patterns by interphase cytogenetics (FISH) in malignant peripheral nerve sheath tumor (MPNST) and morphologically similar spindle cell neoplasms. J Neuropathol Exp Neurol 2002;61(8):702–709 10. Hruban RH, Shiu MH, Senie RT, Woodruff JM. Malignant peripheral nerve sheath tumors of the buttock and lower extremity. A study of 43 cases. Cancer 1990;66(6):1253–1265 11. Terzis JK, Daniel RK, Williams HB, Spencer PS. Benign fatty tumors of the peripheral nerves. Ann Plast Surg 1978;1(2):193–216

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Section VI.E Other

70

The Neurocutaneous Syndromes Herbert E. Fuchs

70.1╇Background Neurocutaneous syndromes are a group of varied disorders that have in common involvement of the nervous system and skin. Tumors may be found in the brain, spinal cord, peripheral nervous system, internal organs, skeletal system, and skin. The three most common neurocutaneous syndromes are neurofibromatosis (NF, including type 1, type 2, and schwannomatosis), tuberous sclerosis complex (TSC), and Sturge–Weber syndrome (SWS). All of these conditions are congenital, although they may not manifest immediately at birth, and NF and TSC have known genetic causes. Clinical criteria for the diagnosis of each of these entities have been developed, and specific genetic mutations have been described for several.

70.1.1╇Syndromes Neurofibromatosis Clinical criteria for the diagnosis of NF1 and NF2 were originally described in 1987,1 with further refinement for NF2 in 20022 (see box National Institutes of Health (NIH) Diagnostic Criteria for NF1 and box 2002 Update of NIH Criteria for NF2). NF1, with a prevalence of 1 in 2,500 to 3,000 live births globally, is more common. NF2 occurs in 1 in 25,000 to 40,000 live births globally.2 NF1 is an autosomal dominant condition, caused by germline mutation in the gene on chromosome 17 that encodes neurofibromin. Half of the cases are inherited from a parent with the disorder, and half are from new mutations. An affected parent has a 50% chance of having an affected child. NF2 results from germline mutation in the gene on chromosome 22 that encodes merlin (or schwannomin). NF2 is also autosomal dominant, but some individuals with NF2 may be mosaic for the NF2 mutation, and therefore

National Institutes of Health (NIH) Diagnostic Criteria for NF1 At least two of the following: • Six or more café au lait spots > 5 mm in diameter in prepubertal patients; > 15 mm in postpubertal patients • Two or more neurofibromas of any type, or one plexiform neurofibroma • Axillary or inguinal freckling • Optic nerve glioma • Two or more Lisch nodules (iris hamartomas) • Osseous lesion, such as sphenoid wing dysplasia or tibial pseudoarthrosis • First-degree relative (parent, sibling, or offspring) with NF1

2002 Update of NIH Criteria for NF2 Main criteria Bilateral vestibular schwannoma (VS) or family history of NF2, plus either: 1. Unilateral VS, or 2. Any two of: meningioma, glioma, neurofibroma, schwannoma, and posterior subcapsular lenticular opacities Additional criteria 1. Unilateral VS plus any two of: meningioma, glioma, neurofibroma, schwannoma, and posterior subscapular lenticular opacities, or 2. Multiple meningiomas (two or more) plus unilateral VS or any two of: glioma, neurofibroma, schwannoma, and cataract

573

574 Section VI.Eâ•… Other have a less than 50% chance of transmitting the disorder to offspring.2 Schwannomatosis occurs more rarely, is genetically distinct from NF1 and NF2, and only 15% of cases are inherited.

Neurofibromatosis Type 1 Patients with NF1 may be diagnosed on the basis of cutaneous café au lait spots, along with the presence of a variety of different tumor types (see box National Institutes of Health (NIH) Diagnostic Criteria for NF1). Patients with NF1 may have a wide variety of tumors, including neurofibromas and malignant nerve sheath tumors, optic pathway gliomas, malignant gliomas, leukemia, pheochromocytoma, gastrointestinal tumors, rhabdomyosarcoma, and breast cancer. Cutaneous neurofibromas are the hallmark of NF1, and may be quite extensive. These benign peripheral nerve sheath tumors, arising from Schwann cell precursors, may occur along nerves anywhere in the body and may be nodular, peduncular, or diffuse. The tumors frequently begin to develop during adolescence and increase in number through adulthood. Plexiform neurofibromas involve more diffuse expansion of nerves, often arising along spinal nerve roots and extending down branches. These tumors may cause spinal cord compression, weakness, disfigurement, and pain, and may also undergo malignant transformation. The malignant tumors may metastasize to the lungs, soft tissues, and bone, and are often fatal. Patients with NF1 may also develop gliomas, often pilocytic astrocytomas. Most commonly, these tumors involve the optic pathways, and are predominantly seen in children less than 7 years old. These tumors may involve any portion of the optic apparatus and are often bilateral. Although 15 to 20% of NF1 patients may have optic pathway tumors, less than half produce symptoms. In addition to optic pathway tumors, gliomas may occur in the brainstem, particularly in the medulla, and occasionally in the cerebellum―again, often pilocytic astrocytomas. They are distinct from the areas of increased signal on T2-weighted magnetic resonance imaging (MRI) without mass effect or enhancement on T1-weighted images, known as unidentified bright objects (UBOs), seen in 60 to 80% of NF1 patients. Since these lesions are rarely biopsied, they are presumed to be hamartomas, heterotopias, areas of abnormal myelination, or even low-grade tumors. They have been shown to increase in size and number in early childhood and later regress, suggesting that they may represent changes in myelination patterns with age. These lesions are usually followed with serial imaging. Brainstem gliomas in patients with NF1 are usually more indolent than similar

tumors in non-NF1 patients. They are generally followed with serial imaging unless significant growth suggests a less benign histology. Tectal plate gliomas with obstructive hydrocephalus behave similarly to lesions seen in non-NF1 patients and are treated similarly. Although the majority of gliomas in NF1 patients are low-grade tumors occurring in the first decade of life, patients with NF1 are at increased risk of developing higher grade tumors, with NF1 patients being 50 to 100 times more likely than the general population to develop a symptomatic non– optic pathway brain tumor. Other less common cancers in patients with NF1 include chronic myelogenous leukemia (1%), rhabdomyosarcoma (5%), gastrointestinal stromal tumors (5 to 30%), and pheochromocytoma, with potential for marked hypertension, in up to 13% of NF1 patients.

Neurofibromatosis Type 2 Patients with NF2 have distinctly different tumors from patients with NF1. VS are the hallmark of NF2 and are present in more than 95% of patients with NF2. Schwannomas of other cranial nerves occur in 24 to 51% of patients with NF2. Schwannomas may also occur along peripheral nerves in patients with NF2. Meningiomas occur in 45 to 58% of NF2 patients, and tend to occur at a younger age than sporadic meningiomas. Meningiomas in NF2 patients are often multiple. Ependymomas may occur in 33 to 53% of patients with NF2, often involving the cervical spinal cord, and may extend throughout the cord.

Schwannomatosis Patients with schwannomatosis often have schwannomas occurring along peripheral nerves, similar to patients with NF2, but do not share the NF2 gene mutation or other associated tumors.

Tuberous Sclerosis Complex TSC is a multisystem genetic disorder with variable phenotypic expression. The incidence of TSC is estimated at around 1 in 6,000 live births. Autosomal dominant mutations occur in either the TSC1 gene on chromosome 9, which codes for hamartin, or in the TSC2 gene on chromosome 16, which codes for tuberin.3–5 In two-thirds of patients, TSC occurs as a result of a spontaneous mutation, with only onethird of cases inherited. The diagnosis of TSC is classified as definite, probable, or possible, based on presence of major and minor criteria (Table 70.1). Patients with TSC have

70 â•… The Neurocutaneous Syndromes multiple lesions, including cortical tubers, subependymal glial nodules, subependymal giant cell astrocytomas, retinal phakomas, cardiac rhabdomyomas, renal angiomyolipomas, periungual fibromas, and adenoma sebaceum. TSC patients commonly present with seizures beginning early in childhood, and the seizures often become refractory to medical treatment.

Criteria for Sturge–Weber Syndrome Diagnosis • Leptomeningeal angiomatosis―most commonly occipital and posterior parietal lobes; may be bilateral • Ipsilateral facial cutaneous vascular malformation―usually affects first division of trigeminal nerve distribution

Sturge–Weber Syndrome The cause of SWS is a somatic mutation in the gene GNAQ on chromosome 21, which increases activity in pathways transmitting signals from a subset of G protein coupled receptors.6,7 How this over-activation results in the port-wine stain birthmark and SWS is unknown, and the disorder is considered to be sporadic. Table 70.1â•… Diagnostic criteria for tuberous sclerosis complex (TSC) Major features of TSC

Minor features of TSC

Facial angiofibromas or forehead plaque Nontraumatic ungual or periungual fibromas Hypomelanotic macules (3 or more) Shagreen patch (connective tissue nevus) Multiple retinal nodular hamartomas Cortical tubers Subependymal nodule Subependymal giant cell astrocytoma (SEGA) Cardiac rhabdomyoma, single or multiple Lymphangiomyomatosis Renal angiomyolipoma

Multiple randomly distributed pits in dental enamel Hamartomatous rectal polyps Bone cysts Cerebral white matter “migration tracts” Gingival fibromas Nonrenal hamartoma Retinal achromic patch “Confetti” skin lesions Multiple renal cysts

Definite TSC: Two major features or one major plus two minor features. Probable TSC: One major feature plus one minor feature. Possible TSC: One major feature or two or more minor features.

Characteristic lesions of SWS (see box Criteria for Sturge-Weber Syndrome Diagnosis) include the typical facial cutaneous vascular malformation that may be noted at birth. Most infants with facial cutaneous vascular malformations do not have SWS; however, when there is unilateral or bilateral involvement of the ophthalmic division of the trigeminal nerve, the likelihood of SWS increases. The intracranial leptomeningeal angiomatosis is the key diagnostic feature of SWS. Skull X-ray shows the classic tram-track calcification. Of note, the leptomeningeal angiomatosis may not be seen in infancy but may develop at a later age. Of patients with SWS, 75 to 90% develop partial seizures by age 3 years. Some patients progress to intractable epilepsy, permanent weakness, hemiatrophy, and visual field cuts, along with mental retardation. It is believed that both seizures and neurologic deficits are caused by cerebral hypoxia and microcirculatory stasis.

70.1.2╇Indications Indications for treatment of neurocutaneous syndromes vary with each disorder. Once a diagnosis of a neurocutaneous syndrome is made based on clinical presentation, physical examination, and imaging studies, genetic consultation and testing can be performed to confirm the diagnosis. This is particularly important in younger patients, in whom the physical manifestations of the disorders may not be fully present at birth. Close clinical follow-up with imaging studies is critical for patients with neurocutaneous syndromes, and any clinical deterioration or progression of tumors on imaging should be an indication for further treatment. Specific examples follow.

NF1 Recommended screening studies for patients with NF1 are shown in the box Recommended Screening Studies for Children with Proven or Presumptive NF1.

575

576 Section VI.Eâ•… Other Recommended Screening Studies for Children with Proven or Presumptive NF1 • Annual clinical examination, including detailed neurologic assessment and dermatological evaluation • Annual ophthalmological examination • Brain MRI scan with and without contrast: • Children diagnosed at < age 5 years • Children with new neurologic deficits, visual loss, or endocrinopathy • Spine X-rays and MRI scans: • Children with scoliosis • Children with back pain, radiculopathy, or spinal cord signs • Neuropsychological and developmental testing: • Children with learning, speech, or socialization difficulties, or with impaired fine motor skills • Genetic counseling: offered at diagnosis and as needed thereafter Based on these examinations, clinical and radiographic progression are potential indications for intervention. Cutaneous neurofibromas that are cosmetically significant may be resected. Plexiform neurofibromas that have enlarged or become painful may be surgically debulked, with careful pathological examination for evidence of malignant transformation. The treatment of optic pathway gliomas (OPGs) has been somewhat controversial. The majority of OPGs are asymptomatic. Annual ophthalmological examinations should be performed for evidence of visual loss. Since children younger than 5 years may be unreliable on visual testing, screening MRI scan should be performed in these patients. If a patient exhibits visual loss, endocrinopathy, or new neurologic deficits, further imaging is warranted. The natural history of OPGs appears to be of longterm stability or very slow growth, and therefore patients without significant visual impairment are usually followed closely for signs of progression. In patients with clinical or imaging evidence of tumor progression, treatment is usually initiated with chemotherapy, most commonly with carboplatin and vincristine. Radiation therapy, once a standard therapy in these patients, is no longer recommended due to the threefold increased risk of a radiation-induced secondary central nervous system (CNS) malignancy or moyamoya syndrome. Surgery is usually reserved for resection of a unilateral optic nerve tumor without chiasmatic involvement, in a blind eye. Some authors have favored aggressive surgical debulking of OPGs; however, this procedure has great risk of

causing new neurologic, endocrine, and visual deficits, and is not generally recommended.

NF2 The treatment of NF2 tumors is predominantly focused on close monitoring and, when appropriate, surgery. The recommended screening studies for patients with NF2 are shown in the box Recommended Screening Studies for Children with Proven or Presumptive NF2.

Recommended Screening Studies for Children with Proven or Presumptive NF2 • • • • •

Neurologic examination Ophthalmological examination Audiogram Brain MRI scan with and without contrast Genetic counseling at time of diagnosis, and as indicated

The frequency of these examinations should be determined by the extent of abnormalities found on prior examinations. At a minimum, patients with NF2 should be evaluated as listed every 3 to 5 years. Annual examinations should be performed in children with known lesions.

The treatment of VS in NF2 patients has been controversial. In patients with large tumors and brainstem compression, the decision for surgical resection is obvious. The management of patients with smaller, asymptomatic tumors has been more problematic. Some authors have advocated early surgery for resection of smaller tumors, which have theoretical improved chances for hearing preservation. However, if hearing is not preserved, the immediate loss of functional hearing in the operated ear, coupled with the long-term risk of contralateral deafness, is significant. Some authors have urged, for this reason, initial resection of the smaller tumor to improve chances for hearing preservation, whereas other authors have proposed initial resection of the larger tumor, which poses the most immediate threat to functional hearing. Neither approach has proven more successful, with some evidence for decreased chances of hearing preservation overall in patients with VS tumors and NF2. Tumor resection is often combined with placement of either a brainstem auditory implant or a cochlear implant for improved chances of at least some functional hearing preservation. Because of the difficulties in hearing preservation, many authors currently suggest a more

70 â•… The Neurocutaneous Syndromes conservative approach, deferring surgery until objective evidence of tumor progression either clinically or radiographically. These are complex decisions and should be made in the context of a multidisciplinary team, including neurosurgeons, otologists, and neurologists, and after careful discussions with patients and their families. Options for treatment include stereotactic radiosurgery and, more recently, bevacizumab, a vascular endothelial growth factor (VEGF) monoclonal antibody discussed later. Surgery is the only current therapy for progressively enlarging, symptomatic NF2-associated ependymomas, meningiomas, and schwannomas. Surgery for these tumors is similar to the procedures used for the same tumors in patients without NF2, although morbidity and mortality may be higher, particularly for meningioma surgery, because the NF2 patients tend to have larger tumors at the time of surgery. Alternatives to surgery include stereotactic radiosurgery, as well as the biological agents described later.

Tuberous Sclerosis Complex Patients with TSC come to neurosurgical attention for treatment of subependymal giant cell astrocytoma (SEGA) tumors, with the potential for hydrocephalus or for intractable epilepsy, and for possible resection of cortical tubers, with the goal of improving seizure control. Once diagnosed with TSC, patients are followed with MRI scans for progression of subependymal nodules, with particular attention paid to the region of the foramen of Monro, and the potential for development of hydrocephalus. Progressive enlargement of subependymal nodules and/ or the development of hydrocephalus are indications for treatment. In patients with seizures that have become intractable to medical therapy, comprehensive epilepsy team work-up should be considered to determine if resection of one or more cortical tubers may be beneficial. This work-up should include an electroencephalogram (EEG), magnetoencephalography (MEG) if available, and/or subdural strip and grid electrodes for localization of seizure foci.

Sturge–Weber Syndrome Patients with SWS should be monitored for development of seizures, headache, strokelike episodes, and glaucoma. The management of seizures in patients with SWS is similar to patients with other causes of seizures; anticonvulsant therapy is initiated with a single drug, with additional medications added as needed. In patients with intractable debilitating seizures, hemispherectomy may be of benefit. Thorough evaluation by an epilepsy center may be helpful in selecting operative candidates. Transient neurologic deficits, such as hemiparesis or visual

field deficits, not related to seizures are felt to be due to microcirculatory stasis and are treated with prophylactic aspirin at doses of 3 to 5 mg/kg/day. Children on aspirin therapy should receive varicella immunization and yearly influenza vaccinations, due to the association of these illnesses with Reye syndrome. Patients with SWS may develop glaucoma either early (in infancy), due to resistance to outflow of aqueous humor and raised intraocular pressure, or late (in childhood or early adulthood), as a result of increased episcleral venous pressure caused by arteriovenous shunting. Treatment of glaucoma involves alpha and beta adrenergic eye drops, as well as carbonic anhydrase inhibitors. Surgical treatment may include trabeculectomy and goniotomy.

70.1.3╇Goals NF1 Since many of the tumors associated with NF1 are indolent, with long-term stability or very slow progression, the goals of treatment of NF1-associated tumors are to preserve function and to prevent deformity. Any tumor that shows clinical or radiographic evidence of progression should be considered for treatment. Plexiform neurofibromas that show rapid growth or become painful should be considered for debulking and pathological examination for evidence of malignant progression. If malignant degeneration has occurred, further treatment with radiation and chemotherapy is indicated. Malignant degeneration of plexiform neurofibromas is a leading cause of death in patients with NF1. Evidence of progressive back pain, scoliosis, or new neurologic deficits should lead to MRI scans of the spine; evidence of cord compression by spinal tumors may be treated with surgical debulking. Several of the newer biological agents may also be considered for treatment of extensive disease. Patients should be closely monitored for visual deterioration, as discussed earlier, with the goal of preserving functional vision.

NF2 As is the case for the treatment of NF1-associated tumors, the treatment of NF2 tumors is largely expectant, with treatment reserved for obvious progression, either clinically or radiographically. For VS tumors, in patients with functional hearing, the risk of hearing loss with surgical resection is immediate and permanent; such patients are likely best served with deferring surgery until progressive hearing loss. During this time, patients may also learn sign language, preparing themselves for eventual hearing loss. Similarly, NF2-associated ependymomas, meningiomas, and schwannomas are also monitored

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578 Section VI.Eâ•… Other closely, with treatment reserved for disease progression with impairment of neurologic function.

TSC The goal of surgery for patients with TSC depends on the lesion being treated. SEGAs are low-grade tumors, and resection provides tumor control, as well as prevention or treatment of hydrocephalus. It should be noted that despite resection of a SEGA causing obstructive hydrocephalus and restoration of cerebrospinal fluid (CSF) pathways, some patients will still require shunt placement. Surgery for resection of cortical tubers is generally reserved for treatment of intractable seizures.

SWS The goal of neurosurgical treatment of SWS is to prevent seizures and to halt the cognitive deterioration seen in patients with intractable seizures.

70.1.4╇ Alternate Procedures (Treatments) In addition to the aforementioned surgical approaches, there are several other treatment options available to patients with neurocutaneous syndromes. Recent advances in the understanding of molecular and cellular mechanisms involved with these tumor syndromes have led to the biological therapies that are described below.

NF1 Recent development of genetically engineered mouse models has led to the emergence and preclinical trials of a number of new agents for the treatment of NF1-associated tumors, including cutaneous neurofibromas, plexiform neurofibromas, optic gliomas, malignant nerve sheath tumors, and leukemia.8 These new models allow rapid advancement and testing of new agents, with the ability to proceed to human trials quickly. Encouraging results have been obtained with several of these agents, with the potential to provide targeted therapies in the future. In addition, agents like thalidomide, interferons, and cis-retinoic acid have been used in clinical trials for plexiform neurofibromas, along with several monoclonal antibody-based biological therapies as well. Optic pathway gliomas are now treated with chemotherapy on progression, utilizing primarily carboplatin and vincristine; radiation therapy is not used due to the risk of development of secondary

CNS malignancies or moyamoya syndrome. Surgery for very young patients with huge tumors causing obstructive hydrocephalus has been advocated as an alternative to shunting and chemotherapy, but carries significant risk of new neurologic, visual, or endocrine deficits.

NF2 A number of authors have urged treatment of NF2-associated VS with stereotactic radiosurgery. Smaller tumors may be targeted with minimal radiation dose to surrounding critical structures, and the risk of treatment-induced hearing loss is not immediate―but rather gradual, allowing the patient to learn sign language prior to becoming completely deaf. Hearing preservation has been reported in approximately 40% of NF2 patients at 3 years following radiosurgery. One potential drawback to this approach is that if future surgery is required for either tumor resection or brainstem auditory implant placement, radiation-induced scar tissue may make surgery more difficult. There have been several recent studies of the use of bevacizumab, an anti-VEGF monoclonal antibody, in the treatment of VS.8,9 Encouraging results include 57% of patients with improved hearing, and 55% of patients with greater than 20% tumor reduction on MRI scans following bevacizumab treatment. The response appears durable because 3-year follow-up indicates 61% stable or improved hearing and 54% stable or decreased tumor size. These results have led to a phase 2 trial of bevacizumab in VS patients. Recent studies in patients with progressive VS tumors using lapatinib, an inhibitor of both VEGF and human epidermal growth factor receptor-2 (HER2), indicate some preliminary success. Genetically engineered mouse strains have also been developed for NF2-associated schwannoma and meningioma. These strains are being used to evaluate newer biological therapies for NF2-associated tumors.

TSC The management of patients with TSC primarily involves medical management of seizures, and clinical and radiographic follow-up of subependymal nodules for evidence of SEGA progression or development of hydrocephalus. The management of enlarging SEGAs has been surgical, but recent studies with everolimus, an inhibitor of the mammalian target of rapamycin (m-TOR), have shown durable reductions in size of SEGAs of at least 30% in 75% of patients with TSC, and at least 50% reduction in 30%. The genetic defects in TSC involve the m-TOR com-

70 â•… The Neurocutaneous Syndromes plex; therefore, therapy with everolimus, which can correct the defect, is very encouraging. In addition, a decrease in seizure frequency was also seen in a number of TSC patients treated with everolimus.10

SWS The goal of treatment for patients with SWS is to control seizures and to prevent progressive neurologic deficits and cognitive decline. Patients with SWS who develop intractable seizures despite polytherapy should be considered for surgery. Initially, anatomical hemispherectomy to resect involved cerebral tissue was performed with good early results. Long-term complications, including superficial hemosiderosis, led to preference for functional hemispherectomy, with disconnection preventing generalization of seizures, and focal resections of active cortical and deep lesions. Patients with SWS and episodic neurologic deficits are treated medically with aspirin, as noted earlier.

70.1.5╇Advantages NF1 Close multidisciplinary follow-up of patients with NF1 should help to preserve neurologic function and to prevent progressive deformity. Since the tumors associated with NF1 may be very indolent, aggressive surgical approaches may not yield improved longterm results but may result in further complications. The emerging availability of biological therapeutics for patients with NF1 is encouraging.

NF2 Similar to NF1, close multidisciplinary follow-up of patients with NF2 to monitor progression of NF2associated tumors should result in better preservation of function. A thoughtful approach to the timing of surgery for NF2-associated tumors may result in improved neurologic function and better quality of life for these patients. The emerging use of biological therapeutics for patients with NF2 provides hope for improved future treatments for these patients.

reestablish CSF pathways, including opening of the foramen of Monro and fenestration of the septum pellucidum, so that if future shunting is needed, a unilateral shunt is usually sufficient. In patients with intractable epilepsy, resection of seizure foci associated with cortical tubers may provide significant decrease in seizure frequency, but it also may result in neurologic deficit. The potential use of m–TORbased therapeutics provides hope for improved outcomes for TSC patients.

SWS Early hemispherectomy for control of intractable seizures may help to prevent or delay progressive mental retardation and hemiplegia in patients with SWS.

70.1.6╇Contraindications NF1 Radiation therapy in the treatment of NF1-associated tumors should be avoided if at all possible, due to the increased risk of secondary malignancies in these patients.

NF2 Great care should be taken in considering treatment, either surgical or radiosurgical, for patients with bilateral VS tumors with functional hearing and smaller tumors. The future availability of more biological treatments may change the way NF2 patients are treated.

TSC Patients with stable SEGA tumors without hydrocephalus should be closely monitored but not considered for surgery until progression. Since these tumors are slow-growing, surgery to prevent development of hydrocephalus is probably not warranted in most cases. The availability of biological agents for treatment of SEGA tumors may also change future treatment of these patients.

TSC

SWS

Surgery for resection of SEGA tumors provides immediate tumor control and restores CSF pathways. Risks of surgery include standard craniotomy risks, as well as potential injury to one or both fornices or to deep veins. Surgery provides the opportunity to

Bilateral cerebral involvement with bilateral seizure foci would be a contraindication for hemispherectomy surgery for SWS patients with intractable seizures.

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580 Section VI.Eâ•… Other

70.2╇ Operative Detail and Preparation Surgery for tumors associated with neurocutaneous syndromes is similar to surgery for the same tumor occurring sporadically. In addition, several of the neurocutaneous syndromes may present opportunities for surgical treatment of nontumorous lesions that may also be symptomatic.

70.2.1╇ Preoperative Planning and Special Equipment NF1 Surgery for cutaneous neurofibromas or plexiform neurofibromas is conventional. Surgery for plexiform neurofibromas with spinal cord compression should be performed with intraoperative somatosensory evoked potentials (SSEP) and motor evoked potentials (MEP) monitoring, with tumor debulking the goal. In patients undergoing surgery for OPGs, there should be thorough preoperative evaluation with ophthalmology examination, including visual fields and endocrine testing, and hormone replacement as needed. Generally, surgical resection of large OPG tumors with obstructive hydrocephalus and significant visual impairment should be undertaken as a last option, with an attempt to resect sufficient tumor to allow restoration of CSF pathways, but no attempt should be made at total resection.

toward localization, but typically either MEG (if available) or subcortical grid and strip electrodes for prolonged monitoring help to correlate seizure focus activity with tubers seen on MRI scan. Functional cortical mapping will also provide localization of eloquent cortex and assist in determining resectability of more electrographically active tubers.

SWS Preoperative preparation of patients for hemispherectomy should include cessation of aspirin therapy, due to the increased risk of bleeding in these patients. Blood products should be available because there is significant potential for bleeding just in the process of turning the scalp and bone flaps, due to the cutaneous angioma and aberrant venous networks.

70.2.2╇ Expert Suggestions/Comments NF1 Surgical treatment of NF1-associated tumors should be reserved for clinical or radiographic progression. Surgery and/or chemotherapy may be useful in the treatment of NF1-associated tumors. Radiation therapy should be avoided due to increased risk of radiation-induced secondary malignancies in the patients. Biological therapeutics, developed with the aid of new genetically engineered mouse models, may provide the basis of future therapies for these patients.

NF2

NF2

Preoperative evaluation of patients with VS should include auditory testing and thorough examination of facial nerve function. Intraoperatively, use of brainstem auditory evoked responses (BAERs) and facial nerve monitoring are essential. Hearing preservation approaches are crucial in patients with useful hearing.

When considering surgery for VS, the same considerations that are used in treating VS in non-NF2 patients also apply. Minimizing risk of hearing loss is even more important in NF2 patients, due to the presence of a contralateral tumor. Surgery for meningiomas has potential for increased morbidity and mortality because of the larger size of tumors at time of surgery in NF2 patients. Preoperative embolization may provide significant decrease in intraoperative blood loss and may help to soften the tumor prior to resection. Surgical resection of spinal ependymomas is conventional, and should be performed with the operating microscope and intraoperative SSEP and MEP monitoring.

TSC For resection of SEGA tumors, open or endoscopic approaches may be used. Open approaches to the foramen of Monro may be either transcortical or transcallosal. In either case, enlarged ventricles due to hydrocephalus facilitate the approach. In the case of an enlarging SEGA without hydrocephalus, the transcallosal approach is preferred. For patients with intractable seizures being considered for resective surgery, scalp EEG may provide some guidance

TSC Surgical approaches for SEGA tumors may be open or endoscopic and may be utilized with neuronavigation. Resection of tumor and reestablishment of CSF

70 â•… The Neurocutaneous Syndromes pathways are the primary goals of surgery. Overly aggressive surgical resection of these benign tumors poses the risk of significant neurologic complications. The goals of surgery should be to resect the tumors and to reestablish CSF pathways.

SWS Functional hemispherectomy with potential limited resection of seizure foci based on EEG mapping should be performed in patients with SWS.

70.2.3╇ Key Steps of the Procedure/ Operative Nuances NF1 Peripheral nerve tumors in patients with NF1 are neurofibromas, and therefore diffusely involve the nerve. Plexiform neurofibromas may be debulked but cannot be totally resected. Great care should be taken in the debulking of spinal tumors to avoid damage to the spinal cord or total disconnection of the cord from involved roots.

NF2 The resection of VS tumors in patients with NF2 is similar to the same procedure in patients without NF2. Of note, the surgeon should be vigilant for tumors involving other lower cranial nerves. Resection of meningiomas and ependymomas is also similar to procedures in patients without NF2.

TSC The approach to intraventricular SEGA tumors is conventional, utilizing the endoscope or the operating microscope. If desired, neuronavigation may be used. The trajectory of the approach should be to the foramen of Monro, where most SEGA tumors are located. Once the tumor is visualized, great care is taken to avoid injury to the fornix or thalamostriate veins. As with any intraventricular procedure, the septum pellucidum should be fenestrated to ensure ventricular communication. Patients with hydrocephalus should have an external ventricular drain placed for postoperative monitoring of intracranial pressure (ICP) and CSF drainage requirements. Children with intractable seizures undergoing multistage procedures for monitoring and resection may require further subdural grid and strip electrode monitoring after initial resection, and a subsequent secondary resection, to maximize resection of active tubers.

SWS Hemispherectomy in patients with SWS is similar to other hemispherectomy procedures. The initial elevation of scalp, muscle, and bone flaps is often bloody because of the alteration of venous drainage due to the angiomas. Meticulous attempts at hemostasis are critical because these patients are often very young, with correspondingly low blood volumes.

70.2.4╇ Hazards/Risks/Avoidance of Pitfalls NF1 Resection of plexiform neurofibromas is by definition subtotal, and pursuit of more complete resection may result in neurologic deficits. Resection of OPG tumors in infants with hydrocephalus and poor response to chemotherapy may be considered; however, great care should be taken in the subtotal resection performed to minimize potential for new visual, neurologic, or endocrine deficits.

NF2 Resection of VS tumors should be undertaken with extreme caution to avoid damage to adjacent cranial nerves or the brainstem. Surgery-induced deficits are immediate and may be disabling in patients who otherwise may have had a very indolent course, with deficits developing over many years. Similar strategies for NF-2 associated meningiomas and ependymomas are warranted because overly aggressive surgical resection may result in neurologic deficits that are much more disabling to the patient than those caused by the original tumor.

TSC The surgeon should avoid the temptation to resect multiple subependymal nodules during the resection of a SEGA tumor. The subependymal nodules may never enlarge or cause symptoms; thus their resection is of no benefit to the patient, who may be exposed to unnecessary risk. Careful cortical mapping is vital to avoiding complications in resection of cortical tubers.

SWS Meticulous hemostasis is essential during hemispherectomy in these young children with small circulating blood volumes.

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70.2.5╇ Salvage and Rescue

70.3.2╇Complications

Salvage and rescue techniques for tumor resections in patients with neurocutaneous syndromes are similar to those utilized in patients without neurocutaneous syndromes undergoing similar procedures.

NF1

70.3╇ Outcomes and Postoperative Course 70.3.1╇ Postoperative Considerations NF1 Although the tumors associated with NF1 are often indolent, continued vigilance with multidisciplinary follow-up is critical to the care of patients with NF1. Overall life expectancy of patients with NF1 is 71.5 years, compared to 80 years for the general population.

NF2 Similar to NF1, patients with NF2 must be closely monitored throughout their lifetimes for evidence of tumor progression. Overall life expectancy for patients with NF2 is 69 years.

TSC Patients should be monitored with external ventricular drainage post-SEGA resection, and shunted as needed. In patients undergoing cortical tuber resections for intractable seizures, postoperative monitoring for ongoing seizures or neurologic deficits is indicated.

SWS Postoperatively, an external ventricular drain is used to help clear blood products from the hemispherectomy. Physical and occupational therapy evaluations and treatment are essential for optimal recovery. Approximately one-third of patients will require a CSF shunt.

Complications of surgical procedures for NF1-associated tumors are similar to those in surgery patients without NF1. Radiation therapy for NF1-associated tumors should be avoided, as discussed earlier.

NF2 NF2-associated tumors have surgical procedure complications similar to those in operated patients without NF2. Hearing loss in VS resections is particularly devastating in NF2 patients because of potential for contralateral hearing impairment due to bilateral VS.

TSC Complications of surgery for TSC include hydrocephalus, neurologic deficit, and continued seizures.

SWS Complications of hemispherectomy complications for SWS include superficial hemiparesis, cognitive deterioration, and hydrocephalus.

70.3.3╇Summary The neurocutaneous syndromes comprise a diverse group of disorders that have in common involvement of the nervous system and skin. Because the genetic conditions underlying these ailments are now known, a better understanding of the molecular and cellular mechanisms causing the associated tumors is emerging. As newer biological agents, targeted at the specific defects, are developed, the therapies for these disorders are undergoing a rapid evolution. The role of neurosurgical therapy in these conditions may change significantly in the coming years.

70â•… The Neurocutaneous Syndromes

References ╇1. Stumpf

DA, et al; National Institutes of Health Consensus Development Conference. Neurofibromatosis. Conference statement. Arch Neurol 1988;45(5):575–578 ╇2. Baser ME, Friedman JM, Wallace AJ, Ramsden RT, Joe H, Evans DG. Evaluation of clinical diagnostic criteria for neurofibromatosis 2. Neurology 2002;59(11):1759–1765 ╇3. Merwick A, O’Brien M, Delanty N. Complex single gene disorders and epilepsy. Epilepsia 2012;53(Suppl 4):81–91 ╇4. Connolly MB, Hendson G, Steinbok P. Tuberous sclerosis complex: a review of the management of epilepsy with emphasis on surgical aspects. Childs Nerv Syst 2006;22(8):896–908

╇5. Kassiri

J, Snyder TJ, Bhargava R, Wheatley BM, Sinclair DB. Cortical tubers, cognition, and epilepsy in tuberous sclerosis. Pediatr Neurol 2011;44(5):328–332 ╇6. Thomas-Sohl KA, Vaslow DF, Maria BL. Sturge-Weber syndrome: a review. Pediatr Neurol 2004;30(5):303–310 ╇7. Bachur CD, Comi AM. Sturge-Weber syndrome. Curr Treat Options Neurol 2013;15(5):607–617 ╇8. Lin AL, Gutmann DH. Advances in the treatment of neurofibromatosis-associated tumours. Nat Rev Clin Oncol 2013;10(11):616–624 ╇9. Evans DGR. Neurofibromatosis type 2 (NF2): a clinical and molecular review. Orphanet J Rare Dis 2009;4:16 10. Krueger DA, Care MM, Holland K, et al. Everolimus for subependymal giant-cell astrocytomas in tuberous sclerosis. N Engl J Med 2010;363(19):1801–1811

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71

Adjuvant Chemotherapy and the Role of Neurosurgery for Pediatric Central Nervous System Tumors Mark W. Kieran

71.1╇Background Cancer remains the most common cause of diseaserelated death in children, and brain tumors account for the majority of these events. As part of a multidisciplinary team of neurosurgeons, radiation therapists, and neuro-oncologists, significant advances are being made in certain tumor types that require a level of cooperation among these services to a degree not previously needed. This chapter focuses on tumor types where multidisciplinary involvement is of particular importance today.

Pediatric brain tumors can typically be broken down into five categories (Table 71.1). Whereas exciting advances have occurred across the spectrum of tumor types and grades, a number of new initiatives with those of astrocytic and neural lineages are discussed in detail in this chapter. Astrocytomas account for approximately 50% of all pediatric brain tumors and are typically divided into high-grade gliomas (HGGs; World Health Organization [WHO] grades 3 and 4) and low-grade gliomas (LGGs; grades 1 and 2). As in adults, HGGs continue to have a poor prognosis after maximal

Table 71.1â•… Five common pediatric central nervous system (CNS) tumor types

584

Cell of origin

Tumor name (World Health Organization [WHO] grade)

Spread

Glial

• Astrocytoma – Pilocytic astrocytoma (1) – Fibrillary/diffuse astrocytoma (2) – Anaplastic astrocytoma (3) – Glioblastoma multiforme (GBM) (4) • Ependymoma – Myxopapillary, subependymoma (1) – Classic ependymoma (2) – Anaplastic ependymoma (3) • Oligodendroglioma – Classic oligodendroglioma (2) – Anaplastic oligodendroglioma (3)

Direct

Neural

• Medulloblastoma (4) • Pineoblastoma (4) • Primitive neuroectodermal tumors (PNET) (4)

Seeding

Choroid plexus

• Choroid plexus carcinoma (1) • Atypical choroid plexus papilloma (2–3) • Choroid plexus papilloma (4)

Seeding

Germ cell

• Germinoma (4) • Nongerminoma (4)

Seeding

Rathke pouch

• Craniopharyngioma (1)

Direct

71 â•… Adjuvant Chemotherapy and the Role of Neurosurgery for Pediatric Central Nervous System Tumors surgical resection, focal radiation therapy, and chemotherapy (most often temozolomide).1 One interesting exception to this are infants younger than 1 to 2 years with glioblastoma multiforme (GBM), in which approximately 30% will be long-term survivors after resection (often subtotal) and a limited number of cycles of relatively well-tolerated, average-dose chemotherapy.2 These patients do not need overly aggressive surgery or radiation therapy, which would be functionally and neurocognitively devastating in their age group. Although infant GBM is an example of a possible good outcome for a highly malignant tumor, diffuse intrinsic pontine gliomas (DIPG) provide the opposite experience. Over the last 30 years, DIPG have been diagnosed by clinical and radiographic criteria. This was based on the futility and morbidity associated with biopsy of the pons in studies from the 1960s through 1980s. With dramatic improvement in imaging and neurosurgical techniques, safely biopsying these tumors is now feasible.3 The histopathology of these tumors reveals up to 50% of the lesions are WHO grade 2 or grade 3 gliomas and yet their outcome is as dismal as it is for WHO grade 4 tumors. Biopsy is therefore not indicated if the goal is to grade the tumors. Rather, small biopsies of DIPG allow us to understand the biology of the tumors using advances in molecular biology that permit ever-increasing

amounts of data from smaller and smaller samples.4 For the first time, we now recognize that malignant gliomas in children are molecularly distinct from those in adults, and that DIPGs are molecularly distinct from supratentorial malignant gliomas in children.5 In some way, this important finding has been the first major “advance” in the treatment of these tumors in the last five decades. Discussion of upfront biopsy in the context of an appropriate clinical trial should now be considered in centers with appropriate equipment, expertise, and institutional review board (IRB)-approved studies.3 In contrast to high-grade tumors, pediatric LGGs have a comparatively excellent prognosis when compared to adults, with the majority of patients being long-term survivors. The mutational profile of pediatric LGGs has been well delineated and the majority of patients have defects in the Ras/Raf pathway (Fig.€71.1).6 Whereas traditional treatment of gliomas includes maximal surgical resection and focal radiation therapy, the excellent long-term prognosis of these patients had led to the avoidance of aggressive surgery and radiation therapy and their associated long-term morbidity (cognitive impact, secondary tumors, endocrine defects, vasculopathy). This has led to the use of weekly doses of chemotherapy and, more recently, targeted biological approaches (details further on).

Fig. 71.1â•… Pediatric low-grade gliomas (LGGs) are predominantly a Ras/Raf pathway disease. A small number of targeted mutations or chromosomal defects account for the majority of pediatric LGGs, as noted by the X. BRAF, proto-oncogene B-Raf; FGFR1, fibroblast growth factor receptor 1; NF1, neurobromin; PTPN11, protein-tyrosine-phosphatase-Shp2; TSC 1,2, tuberous sclerosis complex 1 and 2.

585

586 Section VI.Eâ•… Other Parallel to the changes that have happened in treatment of pediatric gliomas, similar advances have also occurred in treatment of medulloblastoma, a common malignant brain tumor of children. All neural tumors were once considered to be a single entity called PNETs (medulloblastoma in the posterior fossa, pineoblastoma in the pineal region, and central nervous system [CNS] PNET for neural tumors elsewhere in the brain and spine). Molecular analysis of medulloblastoma has demonstrated four distinct profiles, suggesting these tumors arise from either different cell lineages, different differentiation stages, and/or different development pathways.7 The ability to predict outcome based on molecular rather than clinical phenotype is leading to a reevaluation of treatment options that are discussed in this chapter. Nonmedulloblastoma CNS PNETs have behaved as a very heterogeneous class of tumors and molecular approaches have suggested that these tumors may represent a mixture of different histologies, which differ from medulloblastoma.

71.2╇ Treatment Details and Considerations 71.2.1╇ Pediatric High-Grade Gliomas When approaching pediatric patients with malignant gliomas, there are two circumstances that require reevaluation of the typical dogma. First, infants with malignant gliomas may survive long term with minimal therapy, and the degree of surgical aggressivity should take this into account.2 Protocols that target infant GBM are now available and should therefore be considered in these patients. For those who respond (approximately 30%), long-term survival is probable. In those with rapid disease progression, switching to standard malignant glioma therapy (focal radiation therapy with or without temozolomide) is reasonable. Since malignant glioma therapy is palliative therapy, the delay in definitive HGG therapy does not alter the long-term prognosis, while giving children with survival potential an opportunity to receive a therapy that does not cause cognitive damage. To date, no clear biological or histological feature has accounted for the difference in outcome in infants with GBM. Second, diffuse pontine glioma treatment is in rapid evolution. Although the outcome for DIPG has not as yet changed, new treatment options offer significant opportunity to make an impact on this disease. Empiric treatment has been a failure and nowhere is the need to better understand the biology greater than in DIPG. The new approach starts with an up-front biopsy of the pons so that therapy can be targeted to the specific molecular characteristics of the tumor, a better understanding of the tumor can

be achieved, and the rare misdiagnosis avoided. In variations on this up-front biopsy approach, patients can undergo insertion of catheters for convectionenhanced delivery of agents into the pons. This overcomes the blood–brain barrier and directly assesses the distribution and activity of both new and old agents in DIPG.

71.2.2╇ Pediatric Low-Grade Gliomas Treatment options for children with LGGs have focused on frequent administration of chemotherapy that matches the low proliferative activity of these tumors. The two standard regimens are vincristine and carboplatin (VC) or thioguanine, procarbazine, CCNU, and vincristine (TPCV).8 Whereas recurrences after chemotherapy are common and occur with a median of approximately 3 years, most pediatric LGG patients will survive their disease. With transition to adulthood, there seems to be a quiescence of the tumors, resulting in both the lack of transformation to a more malignant phenotype and absence of continued progression of the low-grade tumor. Because frequent recurrences of pediatric LGGs can occur before this quiescence happens, a number of “chemotherapy”-based approaches may be needed. With our growing understanding of the genomic abnormalities that give rise to these tumors, most of which signal along the Ras/Raf pathway, biologically based approaches are becoming more commonly used. In patients with progression after VC and TPCV, or in those with neurofibromatosis type 1 (NF1), where alkylators are contraindicated, treatments including bevacizumab ± irinotecan,9 metronomic chemotherapy (weekly intravenous vinblastine10 or daily oral antiangiogenic chemotherapy11), pathway inhibitors (mTOR inhibition,12 BRAF V600E inhibitors, MEK inhibitors), and immune modulatory agents (lenolidomide13) can be used. Limiting surgical damage in patients with LGGs can therefore significantly improve the long-term function of this patient population by allowing less effective but less long-term toxic therapy to keep the tumor under control until tumor stabilization occurs.

71.2.3╇ Malignant Neural Tumors The incorporation of the biology of medulloblastoma into up-front therapy is just beginning. This is of paramount importance to neurosurgeons because they are often the gatekeepers of pathological material coming out of the operating room, usually in conjunction with neuropathologists. Ensuring that samples are prepared in a manner that supports biological assessment will be critical for moving this information into the clinic. Treatment of medulloblastoma

71 â•… Adjuvant Chemotherapy and the Role of Neurosurgery for Pediatric Central Nervous System Tumors was previously risk-adapted based on surgical resection and imaging. For the first time, stratification for therapy will include the results of up-front molecular profiling. WNT-positive medulloblastoma has an excellent prognosis, even when the usual clinical features of high-risk disease are present. For example, WNT-positive medulloblastoma with bulk metastases at diagnosis would be expected to have a poor prognosis and yet survival rates approach 100%.14 Based on molecular profiling (which requires sufficient material and proper handling at the time of surgery), a new international clinical trial of therapy reduction in WNT-positive medulloblastoma has been initiated. Another example is sonic hedgehogactivated medulloblastoma, in which dramatic and durable responses to smoothen inhibitors have been observed in relapsed disease.15 Although determining how to move these inhibitors up front prior to relapse will require more study, this response is a clear demonstration of the power of molecularly defined tumor subgroups and targeted approaches. A third large subgroup of medulloblastoma, which typically contains MYC amplification, has the worst prognosis of the four subtypes of this disease, even when other aspects of the work-up suggest the patient fits within the good-risk category. The recognition that these patients need different therapy is just now reaching protocol design. The development of targeted MYC pathway inhibitors, such as the bromodomain inhibitors, offers a real chance to more effectively target this specific subgroup.16 Unlike medulloblastoma―which has gone from what was initially thought to be one uniform disease to four different subgroups that require different pathway inhibitors―CNS PNETs are a very different story. These tumors appear to be made up from a large number of different histologies, many of which require different therapeutic approaches. For example, tumors originally diagnosed as PNETs, when analyzed by gene expression, had patterns that were identical to ependymomas, choroid plexus carcinoma, atypical teratoid rhabdoid tumor (ATRT), or medulloblastoma, even though their histological appearance appeared consistent with PNET. A CNS PNET that is shown to have loss of INI1 staining is readily accepted as being constituent with an ATRT and is treated as such. When a CNS PNET tumor has the identical gene expression pattern of an ependymoma, for example, it is more difficult to decide whether to change treatment from PNET therapy (craniospinal radiation therapy and multiÂ� agent chemotherapy) to ependymoma therapy (focal radiation). This is not meant to imply that molecular analysis should always trump classic histopathology. These results do show how critical the neurosurgeon, neuropathologist, and molecular biologist are becoming in the determination of the treatment of children with CNS tumors.

71.3╇Summary Although chemotherapy remains an important but very disease-specific treatment option for children with CNS tumors, the increasing ability to molecularly define tumors has begun to change our focus to targeted agents directed at specific mutations rather than nonspecific treatment with cytotoxic drugs. Fulfillment of the promise of molecularly based treatments will require an important interaction among neurosurgeon, neuropathologist, and neurooncologist, not just to obtain the material on which the decisions will be made, but increasingly on the administration of agents that would not normally penetrate the CNS.

References ╇1. Cohen

KJ, Pollack IF, Zhou T, et al. Temozolomide in the treatment of high-grade gliomas in children: a report from the Children’s Oncology Group. Neuro-oncol 2011;13(3):317–323 ╇2. Dufour C, Grill J, Lellouch-Tubiana A, et al. High-grade glioma in children under 5 years of age: a chemotherapy only approach with the BBSFOP protocol. Eur J Cancer 2006;42(17):2939–2945 ╇3. Walker DA, Liu J, Kieran M, et al; CPN Paris 2011 Conference Consensus Group. A multi-disciplinary consensus statement concerning surgical approaches to low-grade, high-grade astrocytomas and diffuse intrinsic pontine gliomas in childhood (CPN Paris 2011) using the Delphi method. Neuro-oncol 2013;15(4):462–468 ╇4. Roujeau T, Machado G, Garnett MR, et al. Stereotactic biopsy of diffuse pontine lesions in children. J Neurosurg 2007;107(1 Suppl):1–4 ╇5. Schwartzentruber J, Korshunov A, Liu XY, et al. Driver mutations in histone H3.3 and chromatin remodelling genes in paediatric glioblastoma. Nature 2012;482(7384): 226–231 ╇6. Jones DT, Hutter B, Jäger N, et al; International Cancer Genome Consortium PedBrain Tumor Project. Recurrent somatic alterations of FGFR1 and NTRK2 in pilocytic astrocytoma. Nat Genet 2013;45(8):927–932 ╇7. Jones DT, Jäger N, Kool M, et al. Dissecting the genomic complexity underlying medulloblastoma. Nature 2012;488(7409):100–105 ╇8. Ater JL, Zhou T, Holmes E, et al. Randomized study of two chemotherapy regimens for treatment of low-grade glioma in young children: a report from the Children’s Oncology Group. J Clin Oncol 2012;30(21):2641–2647 ╇9. Packer RJ, Jakacki R, Horn M, et al. Objective response of multiple recurrent low-grade gliomas to bevacizuÂ� mab and irinotecan. Pediatr Blood Cancer 2009;52(7): 791–795 10. Lafay-Cousin L, Holm S, Qaddoumi I, et al. Weekly vinblastine in pediatric low-grade glioma patients with carboplatin allergic reaction. Cancer 2005;103(12): 2636–2642

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588 Section VI.Eâ•… Other 11. Kieran

MW, Turner CD, Rubin JB, et al. A feasibility trial of antiangiogenic (metronomic) chemotherapy in pediatric patients with recurrent or progressive cancer. J Pediatr Hematol Oncol 2005;27(11):573–581 12. Józwiak S, Stein K, Kotulska K. Everolimus (RAD001): first systemic treatment for subependymal giant cell astrocytoma associated with tuberous sclerosis complex. Future Oncol 2012;8(12):1515–1523 13. Warren KE, Goldman S, Pollack IF, et al. Phase I trial of lenalidomide in pediatric patients with recurrent, refractory, or progressive primary CNS tumors: Pediatric Brain Tumor Consortium study PBTC-018. J Clin Oncol 2011;29(3):324–329

14. Kool

M, Korshunov A, Remke M, et al. Molecular subgroups of medulloblastoma: an international metaanalysis of transcriptome, genetic aberrations, and clinical data of WNT, SHH, Group 3, and Group 4 medulloblastomas. Acta Neuropathol 2012;123(4):473–484 15. Rudin CM, Hann CL, Laterra J, et al. Treatment of medulloblastoma with hedgehog pathway inhibitor GDC0449. N Engl J Med 2009;361(12):1173–1178 16. Filippakopoulos P, Qi J, Picaud S, et al. Selective inhibition of BET bromodomains. Nature 2010;468(7327): 1067–1073

72

Adjuvant Radiation Therapy for Pediatric Tumors Thomas E. Merchant

72.1╇Background Conventional fractionated radiation therapy for childhood brain tumors utilizes high-energy accelerator systems to deliver treatment Monday through Friday, 5 days per week, for a period of 6 to 6.5 weeks (30–33 fractions) using photons or protons. Exceptions include central nervous system (CNS) germinoma, which may be successfully treated using fewer fractions, and the use of radiosurgery, which is meant to obliterate tissue using one or five or fewer high-dose treatments to shorten the overall treatment time. Few indications exist for the use of radiosurgery in children. For fractionated irradiation, the traditional dose per fraction is

1.8 Gy, with some standard allowances for lower (1.5 Gy) or higher (2.0–2.5 Gy) doses depending on the patient, tumor type, and goal of treatment. The volume of irradiation in the treatment of childhood CNS tumors is chosen based on tumor type. Known seeding tumors require craniospinal irradiation (CSI), a classic treatment volume that encompasses the entire subarachnoid space of the brain and spine. CSI may be prophylactically administered based on risk for disease dissemination or may be required in the setting of metastatic disease, as detected by magnetic resonance imaging (MRI) of the brain and spine or cerebrospinal fluid (CSF) cytology (Table 72.1). CSI is the treatment volume

Table 72.1â•… Tumors, extent of disease, and craniospinal irradiation guidelines for radiation therapy administered with curative intent* Diagnosis

Extent of disease

Craniospinal dose

Medulloblastoma

M0

15–23.4 Gy*

Medulloblastoma

M+

36–39.6 Gy

Primitive neuroectodermal tumor (PNET) (supratentorial)

M0

23.4 Gy†

PNET (supratentorial)

M+

36–39.6 Gy

ATRT (atypical teratoid rhabdoid tumor)

M0

23.4 Gy‡

ATRT

M+

36–39.6 Gy

Malignant germ cell tumor

M+

36–39.6 Gy

Germinoma

M+

24 Gy**

Ependymoma

M+

36–39.6 Gy

Low-grade glioma

M+

36–39.6 Gy

Abbreviations: M0, nonmetastatic; M+, metastatic. *Patients ≥ age 3 years based on age and tumor biology (i.e., wingless (WNT) subgroup). **1.5 Gy per fraction. †Standard of care has been 36 Gy; institutional preference 23.4 Gy. ‡CSI (craniospinal irradiation) is controversial for nonmetastatic ATRT.

589

590 Section VI.Eâ•… Other most feared for its contribution to long-term side effects. When administered, CSI is always supplemented by additional treatment to the primary site. Metastatic deposits are irradiated when indicated. The treatment volume for the primary site has been defined according to the tumor type, treatment era, and a variety of clinical factors. Treatment of the primary site for medulloblastoma and ependymoma has changed the most during the past 20 years. In the case of medulloblastoma, treatment of the anatomical posterior fossa has given way to a reduced volume, now including only a 0.5-cm margin surrounding the postoperative tumor bed in some institutional series. Similarly small margins are now used for ependymoma after successive clinical trials. In 1993, an international nomenclature was introduced for three-dimensional (3D) targeting in radiation therapy. Guidelines were adopted for the treatment of pediatric CNS tumors with some modifications. In general, the gross tumor volume (GTV) was defined as the postoperative tumor bed and/or residual disease. The clinical target volume (CTV) was defined by a margin surrounding the GTV and meant to encompass subclinical microscopic disease not detectable by neuroimaging. The CTV was meant to be anatomically confined, meaning that the margin was not geometric; rather it was modified at nonneural interfaces where tumor invasion was unlikely. The planning target volume (PTV) was defined by a geometric margin surrounding the CTV and was meant to account for variability in patient localization associated with interfractional positioning and intrafractional movement. The evolution of treatment volumes and targeting guidelines is defined and discussed for medulloblastoma and ependymoma in the sections that follow. Medulloblastoma is the best example of a disease that requires CSI, and ependymoma is the best example of a disease that requires only focal irradiation.

72.2╇Medulloblastoma Medulloblastoma is the most common malignant brain tumor in children and is prone to metastatic dissemination at diagnosis and at the time of tumor progression. During the past 20 years, significant gains have been achieved in the treatment of this disease owing to well-designed clinical trials balancing the requirement to increase disease control and the need to reduce complications. From a radiation oncology standpoint, the treatment for this tumor is subdivided according to age: children younger than 3 years are treated using regimens that omit CSI.

72.2.1╇ Medulloblastoma in Children Older than 3 Years Standard risk defines patients with no evidence of metastasis at the time of diagnosis. Three important clinical trials that involve modifications of radiation therapy have been conducted by the investigators of the North American pediatric cooperative groups during the past 20 years. Prior to that time, and regardless of extent of disease, all children were treated with 36-Gy CSI and supplemental “boost” irradiation of the anatomical posterior fossa to ≥ 54 Gy. The Children’s Cancer Group (CCG)-9892 study1 was the first to show that the craniospinal dose could be safely lowered to 23.4 Gy, provided that chemotherapy was administered as a component of the overall treatment regimen. Prior attempts to reduce the craniospinal dose were unsuccessful and resulted in an excess of neuraxis relapses.2 There were 85 patients registered on the CCG-9892 protocol and 65 were enrolled as “eligible.” Treatment included weekly vincristine during radiotherapy, and lomustine, cisplatin, and vincristine every 6 weeks, for a total of eight courses. The reported progressionfree survival (PFS) at 5 years was 79%. The concept of reduced-dose CSI with chemotherapy was further tested in the A9961 randomized trial comparing two different chemotherapy regimens with the 23.4-Gy CSI and 55.8-Gy posterior fossa boost regimen.3 For this trial, the chemotherapy also included weekly vincristine during irradiation, and the postirradiation chemotherapy consisted of lomustine, cisplatin, and vincristine, or cyclophosphamide, cisplatin, and vincristine, depending on randomization. Chemotherapy was administered every 6 weeks for eight cycles. The 5-year, event-free survival (EFS) rate was similar for the two treatment arms, 81 ± 2.1% and 86 ± 9%; and the outcome of this trial set the benchmark of 80%, 5-year EFS rate for this disease based on the 23.4-Gy CSI regimen in properly staged patients. Nearly a decade ago, the Children’s Oncology Group (COG) ACNS0331 protocol was activated to enroll children with standardrisk medulloblastoma and to randomize those younger than 8 years to 18-Gy or 23.4-Gy CSI followed by a second randomization to standard posterior fossa boost (54 Gy) or tumor bed boost (54 Gy) using a 1.5-cm CTV.4 Children older than age 8 years at diagnosis were treated using 23.4-Gy CSI and were then randomized to the two different boost regimens. The postirradiation chemotherapy was the same for all treatment arms and included a combination of all agents used in the prior A9961 study. The ACNS0331 study was completed in 2014 and should help to confirm that irradiation of the anatomical posterior fossa is no longer necessary, and that primary-site irradiation should be limited to the postoperative tumor bed with appropriate margin. The study may also address the feasibility and safety of administering 18-Gy CSI in properly staged patients.

72 â•… Adjuvant Radiation Therapy for Pediatric Tumors Similar radiation dose and volume reduction goals were included in the objectives for two successive medulloblastoma studies performed at St. Jude Children’s Research Hospital, Memphis, Tennessee, from 1996 to 20035 and 2003 to 2013.6 Both protocols used intense cyclophosphamide-based postirradiation chemotherapy regimens. The difference in the two protocols was the radiation therapy regimen. Until 2003, average-risk patients received 23.4-Gy CSI, posterior fossa irradiation to 36 Gy, and primary-site irradiation to 55.8 Gy using a 2-cm CTV margin. After 2003, average-risk patients received 23.4-Gy CSI and primary-site irradiation to 55.8 Gy using a 1-cm CTV. There has been an explosion of information about the biology of medulloblastoma. This information, combined with other clinical-pathological information, has yielded new risk stratification and options for the design of radiation therapy regimens. There are now four groups, known as the WNT, SHH, group 3, and group 4.7 The WNT subgroup represents a very low-risk cohort, the SHH subgroup represents a cohort for which agents are available to target the SHH signaling pathway, and the latter groups often represent biologically unfavorable patients for whom increasing treatment intensity may be required. Based on the molecular and clinical classification, there are new opportunities to reduce or to increase the intensity of radiation therapy and chemotherapy. The St. Jude group has settled on modest reductions in chemotherapy for low- and standard-risk patients. Those with low-risk medulloblastoma (WNT subgroup and no evidence of metastatic disease) may be treated with a novel regimen including 15-Gy CSI and 51-Gy (cumulative) primary-site irradiation. Other patients are treated using CSI doses of 23.4 Gy or 36 to 39.6 Gy as appropriate, and the primary-site dose is limited to 54 Gy. The CTV margin for primary-site irradiation in all cases is 0.5 cm.8

72.2.2╇ Medulloblastoma in Children Younger than 3 Years Nearly two decades ago, children younger than 3 years old with medulloblastoma were treated with postoperative chemotherapy in an effort to delay or avoid irradiation. In comparison to the stellar 80%, 5-year EFS rate observed in older, irradiated patients, the Pediatric Oncology Group (POG)-8633 reported a 5-year EFS rate of less than 32%.9 Subsequent studies meant to further intensify chemotherapy did not produce better results. Finally, in 2000, the A9934 study was activated to include focal primary-site irradiation in the frontline management of nonmetastatic patients and after four cycles of postoperative chemotherapy.10 Radiation therapy in this study was limited sequentially to the posterior fossa (18 or 23.4 Gy) and primary site (50.4–54 Gy) based on age and residual disease at the time of irradiation. This regi-

men was successful, resulting in a 4-year, PFS exceeding 50%. Progressions were observed at the primary site prior to radiation therapy and in the neuraxis after radiation therapy, supporting the importance of primary-site irradiation and the need to consider better means to treat the neuraxis. Although the number of patients included in this study was relatively small, among the 74 eligible patients the following points were observed: neuraxis progression in regions that received collateral doses < 12 to 15 Gy (Fig. 72.1); a high rate of primary-site control with 50.4 Gy; and functional outcome preservation based on the protocol-embedded psychology assessment. In summary, the treatment of medulloblastoma continues to evolve and to include efforts to reduce radiation dose and volume. Future efforts to increase intensity to improve disease control in cohorts where gains are needed may combine novel agents concurrently with irradiation in selected patients or consideration of very low doses of CSI in younger patients. Regimens for medulloblastoma that include radiation therapy are presented in Table 72.2.

72.3╇Ependymoma The treatment of ependymoma with radiation therapy is an excellent example of cooperation between neurosurgery and radiation oncology. Local failure, the predominant mode of failure after conventional treatment,11 has been reduced considerably for these patients based on improvements in both surgery and radiation therapy. Children with ependymoma were among the first to benefit from advancements in radiation therapy planning and delivery associated with the conformal treatment era. Protocols involving children with ependymoma have used successively smaller margins to irradiate the preoperative or postoperative tumor bed (Table 72.3). The POG-9132 protocol12 included patients with posterior fossa ependymoma who received hyperfractionated irradiation to 69.6 Gy (1.2 Gy twice daily). This study involved 19 patients. The 4-year EFS rate was 70 ± 25% and 50 ± 36% for patients with gross total resection and subtotal resection, respectively. The CCG-9942 study13 followed as a phase II study of pre-irradiation chemotherapy (vincristine, cisplatin, cyclophosphamide, etoposide) for patients with imaging evidence of residual disease. Pre-irradiation chemotherapy was administered to 41 of the 84 study patients. The 5-year EFS rate was 57 ± 6% for the entire group and 55 ± 8% versus 58.9% comparing irradiated to combined modality patients. Following the significant gains made through the systematic attempt to achieve gross total resection and followed with high-dose, postoperative radiation therapy at St. Jude Children’s Research Hospital,14 COG has since conducted two trials for ependymoma,

591

592 Section VI.Eâ•… Other

Fig. 72.1â•… Pattern of metastatic failure demonstration for a case of medulloblastoma (age < 3 years) treated with focal irradiation after induction chemotherapy. Metastases to the frontal region in volume irradiated with < 15 Gy.

Table 72.2â•… Craniospinal and primary-site regimens for standard-risk medulloblastoma by treatment protocol Protocol

Year

CSI dose

Primary-site CTV

Primary-site dose

SJMB96

1996

23.4 Gy

2.0 cm†

55.8 Gy

COG A9961

1999

23.4 Gy

PF

55.8 Gy

COG A9934

2000

–

1.0 cm‡

54 Gy

SJMB03

2003

23.4 Gy

1.0 cm

55.8 Gy

ACNS0331

2003

23.4 vs. 18.0 Gy

1.5 cm vs. PF

54 Gy

SJYC07

2007

–

0.5 cm

54 Gy

SJMB12

2013

15.0* or 23.4 Gy

0.5 cm

51* or 54 Gy

Abbreviations: CSI, craniospinal irradiation; CTV, clinical target volume/margin; PF, posterior fossa. †36-Gy posterior fossa irradiation. ‡18-Gy (age < 2 years) or 23.4-Gy (age > 2 years) posterior fossa irradiation; low-risk classified according to molecular (WNT subtype) and standard-risk clinical factors. *Low-risk patients (WNT subgroup without metastatic disease)

72 â•… Adjuvant Radiation Therapy for Pediatric Tumors Table 72.3â•… North American protocols for ependymoma, including radiation therapy Protocol

Years

Ages

Volume

No. of patients

POG-9132

Dec. 1991–Dec. 1994

> 36 mo

Focal 2.0 cm†

19

CCG-9942

Feb. 1995–Oct. 1999

> 36 mo

Focal 1.5 cm†

84

ACNS0121

Aug. 2003–Nov. 2007

> 12 mo

Focal 1.0 cm‡

378

ACNS0831

Mar. 2010–present

> 12 mo

Focal 0.5 cm‡

284*

*As of June 19, 2015. †Preoperative tumor bed. ‡Postoperative tumor bed.

ACNS012115 and ACNS0831.16 Both studies have included the strategy of observing children with differentiated supratentorial ependymoma after microscopic complete resection, pre-irradiation chemotherapy and second surgery in initially incompletely resected ependymoma, and immediate postoperative irradiation for all other patients. The difference between the COG ACNS0121 protocol and COG ACNS0831 protocol, in addition to the CTV margins, is the randomization to post-irradiation chemotherapy versus observation for those treated with immediate postoperative irradiation. The results from these studies, as yet unknown,

are expected to be similar to those observed in the St. Jude protocol. Irradiation of ependymoma in young children and the lack of significant treatment-related complications have provided evidence that newer methods of irradiation may improve functional outcomes.17–19 These observations have motivated parents and caregivers to pursue newer methods of irradiation, including proton therapy. Although in many instances the differences in dose distribution appear to be small (Fig. 72.2), there is no known benefit to the collateral irradiation of normal tissues and minor

Fig. 72.2â•… Three-dimensional (3D) proton therapy plan using double scattering (upper images) and intensity-modulated photon therapy plan (lower images) for a case of localized infratentorial ependymoma. The dose distributions are overlaid on a treatment planning computed tomography (CT) in the axial (left), sagittal (center), and coronal (right) planes.

593

594 Section VI.Eâ•… Other differences in dose might contribute to major differences in long-term complications.20 Investigators continue to improve photon external beam radiation therapy for ependymoma using advanced methods of highly conformal, intensity-modulated radiation therapy that restrict the high-dose volume to the target.

References ╇1. Packer

RJ, Goldwein J, Nicholson HS, et al. Treatment of children with medulloblastomas with reduced-dose craniospinal radiation therapy and adjuvant chemotherapy: a Children’s Cancer Group study. J Clin Oncol 1999;17(7):2127–2136 ╇2. Thomas PR, Deutsch M, Kepner JL, et al. Low-stage medulloblastoma: final analysis of trial comparing standard-dose with reduced-dose neuraxis irradiation. J Clin Oncol 2000;18(16):3004–3011 ╇3. Packer RJ, Gajjar A, Vezina G, et al. Phase III study of craniospinal radiation therapy followed by adjuvant chemotherapy for newly diagnosed average-risk medulloblastoma. J Clin Oncol 2006;24(25):4202–4208 ╇4. Michalski JM. A study evaluating limited target volume boost irradiation and reduced dose craniospinal radiotherapy (18.00 Gy) and chemotherapy in children with newly diagnosed standard risk medulloblastoma: a phase III double randomized trial. NCT00085735. ClinicalTrials gov 2013. Available at: http://clinicaltrials.gov/ ct2/show/NCT00085735?term=acns0331&rank=1 ╇5. Merchant TE, Kun LE, Krasin MJ, et al. Multi-institution prospective trial of reduced-dose craniospinal irradiation (23.4 Gy) followed by conformal posterior fossa (36 Gy) and primary site irradiation (55.8 Gy) and dose-intensive chemotherapy for average-risk medulloblastoma. Int J Radiat Oncol Biol Phys 2008;70(3):782–787 ╇6. Gajjar A. Treatment of patients with newly diagnosed medulloblastoma, supratentorial primitive neuroectodermal tumor, or atypical teratoid rhabdoid tumor. NCT00085202. ClinicalTrials gov 2013. Available at: http://clinicaltrials.gov/ct2/show/NCT00085202?term =sjmb03&rank=2 ╇7. Northcott PA, Korshunov A, Pfister SM, Taylor MD. The clinical implications of medulloblastoma subgroups. Nat Rev Neurol 2012;8(6):340–351 ╇8. Gajjar A. A clinical and molecular risk-directed therapy for newly diagnosed medulloblastoma. NCT01878617. ClinicalTrials gov 2013. Available at: http://clinicaltrials. gov/ct2/show/NCT01878617?term=sjmb12&rank=1 ╇9. Duffner PK, Horowitz ME, Krischer JP, et al. The treatment of malignant brain tumors in infants and very young chil-

dren: an update of the Pediatric Oncology Group experience. Neuro-oncol 1999;1(2):152–161 10. Ashley DM, Merchant TE, Strother D, et al. Induction chemotherapy and conformal radiation therapy for very young children with nonmetastatic medulloblastoma: Children’s Oncology Group study P9934. J Clin Oncol 2012;30(26):3181–3186 11. Evans AE, Anderson JR, Lefkowitz-Boudreaux IB, Finlay JL. Adjuvant chemotherapy of childhood posterior fossa ependymoma: cranio-spinal irradiation with or without adjuvant CCNU, vincristine, and prednisone: a Children’s Cancer Group study. Med Pediatr Oncol 1996;27(1):8–14 12. Kovnar E, Curran W, Tomita T. Hyper-fractionated irradiation for childhood ependymoma: improved local control in sub-totally resected tumors. Childs Nerv Syst 1998;14(9):489 13. Garvin JH Jr, Selch MT, Holmes E, et al; Children’s Oncology Group. Phase II study of pre-irradiation chemotherapy for childhood intracranial ependymoma. Children’s Cancer Group protocol 9942: a report from the Children’s Oncology Group. Pediatr Blood Cancer 2012;59(7):1183–1189 14. Merchant TE, Li C, Xiong X, Kun LE, Boop FA, Sanford RA. Conformal radiotherapy after surgery for paediatric ependymoma: a prospective study. Lancet Oncol 2009;10(3):258–266 15. Merchant TE. Observation or radiation therapy and/ or chemotherapy and second surgery in treating children who have undergone surgery for ependymoma. NCT00027846. ClinicalTrials gov 2013. Available at: http://clinicaltrials.gov/ct2/show/NCT00027846?term= nct00027846&rank=1 16. Smith A. Phase III randomized trial of post-radiation chemotherapy in patients with newly diagnosed ependymoma ages 1 to 21 years. NCT1096368. ClinicalTrials gov 2013. Available at: http://clinicaltrials.gov/ct2/ show/NCT01096368?term=acns0831&rank=1 17. Conklin HM, Li C, Xiong X, Ogg RJ, Merchant TE. Predicting change in academic abilities after conformal radiation therapy for localized ependymoma. J Clin Oncol 2008;26(24):3965–3970 18. Di Pinto M, Conklin HM, Li C, Xiong X, Merchant TE. Investigating verbal and visual auditory learning after conformal radiation therapy for childhood ependymoma. Int J Radiat Oncol Biol Phys 2010;77(4):1002–1008 19. Netson KL, Conklin HM, Wu S, Xiong X, Merchant TE. A 5-year investigation of children’s adaptive functioning following conformal radiation therapy for localized ependymoma. Int J Radiat Oncol Biol Phys 2012;84(1):217–223.e1 20. Merchant TE. Clinical controversies: proton therapy for pediatric tumors. Semin Radiat Oncol 2013;23(2):97–108

Section VII Infections

Section Editor: A. Graham Fieggen

Neurosurgeons have an ambiguous relationship with infectious disease. While postoperative infection remains one of our most dreaded complications, successfully treating primary infections, such as brain abscesses and empyemas, can be one of our most rewarding tasks. Although most of the conditions described in this section have diminished in incidence in the developed world, they have experienced a resurgence in importance due to the increased use of immunosuppression, as well as global travel and migration. Diagnosis and treatment of meningitis usually fall within the remit of other specialties, but neurosurgeons may be called on to manage patients who present with recurrent meningitis, where astute clinical assessment may be required before choosing from a wide range of possible investigations. We may also be called upon to manage complications, such as subdural effusions and hydrocephalus, which in this setting may become multiloculated and immensely difficult to control. Improved primary care treatment of sinusitis, otitis media, and endocarditis has led to a marked reduction in intracranial sepsis in developed countries, but these complications remain common in the developing world. Surgical options for empyema range from burr holes, with or without craniectomy, to craniotomy. In the patient presenting with a brain abscess, a presumptive diagnosis may be made in a given clinical setting, but a neurosurgical procedure

is often required to establish a microbiological diagnosis to guide antimicrobial therapy. Although only a single procedure for freehand drainage may be required, stereotactic guidance may be invaluable. Clinical judgment is called for in determining which patient will require repeat drainage or a more complex procedure, such as excision of the abscess. It is important to emphasize the potential to achieve a very good outcome in patients with intracranial sepsis, even in those presenting with poor neurologic status. Effective management also requires identifying and treating the source of infection. One of the most marked changes in neurosurgical epidemiology over the past century has been the worldwide fall in the incidence of tuberculous intracranial mass lesions. However, hydrocephalus as a complication of tuberculous meningitis remains a challenging condition for pediatric neurosurgeons in the developing world. Unusual causes of intracranial infection, such as fungi and parasites, must be borne in mind in the immunocompromised patient. Although parasitic infestations, such as hydatid disease and neurocysticercosis, have typical geographic distributions, it is important to remember them in the differential diagnosis of cystic lesions of the CNS. There are few conditions where neuroendoscopy has widened our therapeutic options to the extent that it has in neurocysticercosis.

596 Section VIIâ•… Infections When considering infections of the CNS, it is important not to overlook the spine, as a delayed diagnosis may compromise outcome. The chapters that follow offer a comprehensive review of all these conditions with many expert insights and tips. As

treatment of these patients may be prolonged, it is important to limit radiation exposure by the sensible use of follow-up imaging. Finally, all physicians share responsibility for using antimicrobial agents wisely in order to reduce the threat of widening resistance.

Section VII.A Cranial

73

Meningitis and Encephalitis Dhruve Jeevan and Michael E. Tobias

73.1╇Background Meningitis most commonly refers to the infection of the leptomeninges and subarachnoid space, whereas encephalitis refers to the nonfocal inflammation of the brain parenchyma. Encephalitis is often associated with inflammation of the meninges, meningoencephalitis, but it can affect other elements of the central nervous system (CNS; myelitis, radiculitis, and optic neuritis). The discussion of encephalitis and meningitis is a broad topic; in this chapter the authors provide an overview, with particular emphasis on the management role of the pediatric neurosurgeon.

73.2╇Meningitis Meningitis can be caused by a variety of infectious agents, including bacteria, viruses, fungi, mycobacteria, and parasites. Although it most commonly presents acutely with symptoms developing within a few hours or days, it can occur more chronically over a few weeks or it can be recurrent, with two or more episodes separated by weeks or months of full recovery. The incidence of meningitis is highest among neonates, and lumbar puncture should be considered in all neonates presenting with fever. In this age group the most common agents are Streptococcus agalactiae (group B streptococcus [GBS]), gramnegative enteric bacteria, principally Escherichia coli and Klebsiella/Enterobacter species, and Listeria monocytogenes.1 In otherwise healthy older children, the three most common organisms causing acute bacterial meningitis worldwide are Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b.2 Overall, the incidence of these acute bacterial meningitides has been decreasing as a result of the introduction of vaccination in the United States.2

The most common route by which pathogenic organisms gain access to the subarachnoid space, resulting in meningitis, is by hematogenous spread with invasion of the choroid plexus. Less typically, bacteria can gain direct access by introduction through trauma, congenital abnormalities, such as a dermal sinus tract, or spread from a contiguous site of infection, such as a paranasal sinusitis. Penetrating head trauma or neurosurgical procedures are commonly associated with Staphylococcus aureus, coagulase-negative staphylococci, streptococci, and gram-negative infection (especially Escherichia coli, Klebsiella, and Pseudomonas aeruginosa).1 The presence of a ventricular shunt is an independent risk factor for meningitis; this is often related to shunt contamination by skin organisms at the time of surgery.1 Important pathophysiological alterations occur in the setting of meningitis that must be understood to allow for its management. Organisms multiply and disseminate quickly throughout the subarachnoid space because of the lack of host defenses within the cerebrospinal fluid (CSF). The inflammatory response to organisms leads to many alterations in CSF function. Proinflammatory mediators play a direct role in injury to neurons, alteration in blood–brain barrier permeability, induction of apoptosis, and induction of cerebral anaerobic metabolism.3 In addition to the role of these cytokines, brain edema, intracranial hypertension, and loss of cerebrovascular autoregulation may contribute to ischemia and neuronal injury. The brain and spinal cord become covered in purulent subarachnoid exudates that infiltrate through the perivascular spaces, causing vascular inflammation and narrowing.4 The foramina of Magendie and Luschka can become obstructed, resulting in obstructive hydrocephalus, although communicating hydrocephalus is more common from blockage at the level of arachnoid villi. The rich exudates can also traverse the cochlear duct to involve the auditory tissue. The clinical symptoms of bacterial meningitis are dependent on both the age of the patient and

599

600 Section VII.Aâ•… Cranial the organism. Interestingly, neonates present with hyperthermia or hypothermia and either irritability or decreased level of consciousness. They may also have a spectrum of constitutional, nonspecific symptoms, such as poor feeding, vomiting, diarrhea, and/or subtle changes in behavior. After age 2 years the classical clinical triad of fever, headache, and stiff neck is more often seen in bacterial meningitis. An altered level of consciousness is seen in more than 90% of patients, and Kernig and Brudzinski signs may be present as well. Meningococcal meningitis may be accompanied by petechial or purpuric rash, although these findings are not always present. Unlike bacterial and viral meningitis, tuberculous meningitis is often associated with papilledema or decreased venous pulsations on funduscopic examination. The diagnosis of meningitis among most children with febrile illness requires expertise and careful examination. A lumbar puncture is necessary when the diagnosis of bacterial meningitis is considered. Although the CSF white blood cell (WBC) counts in bacterial meningitis are > 1,000 cells/mm3, few or no WBCs can be seen in the early phases. The protein concentration is elevated, and glucose concentration is usually depressed. The Gram stain smear is positive in up to 80% of patients with untreated bacterial meningitis. Table 73.1 lists some of the CSF findings based on various meningeal pathogens. Computed tomography (CT) should be performed in all children with bacterial meningitis to determine ventricular size. Early on there may be mild ventricular dilation, although with time CSF spaces can become effaced, with progressive cerebral edema and raised intracranial pressure (ICP). CT may also

demonstrate extra-axial fluid collections, with a sterile effusion being present in about 30% of children with meningitis, often bilaterally. Less often this fluid may represent a subdural empyema, which is most commonly associated with meningitis due to S. pneumoniae. Brain abscess is a rare complication of meningitis, except in the setting of Citrobacter meningitis in the neonate, where it can be seen in up to 80% of cases.5 In cases where infectious abscess or collections are suspected, contrast-enhanced imaging may be necessary. Magnetic resonance imaging (MRI) is useful for demonstrating intraparenchymal abnormalities, such as cerebral edema, infarct, or areas of hypoperfusion. MRI is indicated if there is focality to the neurologic examination that suggests stroke or unilateral fluid collection. Therapy for meningitis is mostly supportive, alongside empirical antimicrobials for specific organisms. Mental status can be severely depressed, requiring endotracheal intubation and mechanical ventilation for airway protection. Septic shock may coexist with meningitis, along with salt and water deficits from fever, tachypnea, poor oral intake, vomiting, and diarrhea. Some patients may also develop the syndrome of inappropriate antidiuretic hormone secretion (SIADH), and/or cerebral salt wasting, further complicating fluid management.6 Intracranial hypertension is extremely common in meningitis. Simple interventions for reducing ICP should be instituted, including: elevation of the head to 30 degrees, maintaining midline positioning, mild hyperventilation, euvolemia, avoiding hyponatremia and hyperthermia, and careful administration of small doses of mannitol may be useful. In select

Table 73.1â•… Common cerebrospinal fluid findings in meningitis

Pathogen

WBC (/mm3)

WBC differential (% PMN)

CSF glucose

CSF/serum glucose ratio (%)

Protein (mg/dL)

Intracranial pressure

Bacterial

100–> 10,000

> 80

< 50

< 50

100–500

Increased

Viral

20–500

< 50

> 50

> 50

50–100

Normal

Lyme

< 500

< 10

> 50

> 50

50–100

Normal

Fungal

20–200

< 10–20

< 50

< 50

50–100

Increased

TB

10–200

< 20

< 50

< 50

100–> 500

Increased

Abbreviations: CSF, cerebrospinal fluid; PMN, polymorphonuclear neutrophil; TB, tuberculosis; WBC, white blood cell.

73 â•… Meningitis and Encephalitis cases this may require invasive ICP monitoring in an intensive care unit.7 If bacterial meningitis is suspected, antibiotic therapy is given empirically based on the age of the patient and is then modified based on CSF cultures. The initial empiric therapy usually consists of a combination of cefotaxime or ceftriaxone plus vancomycin. The duration of antibiotic therapy for meningitis varies with the organism, but on average for uncomplicated cases treatment is usually for 7 to 14 days. E. coli and Klebsiella spp. are the most common gram-negative enteric organisms that cause bacterial meningitis in children other than neonates. A combination of an extended-spectrum cephalosporin or ampicillin, plus an aminoglycoside, administered intravenously, is reasonable empiric therapy for suspected gram-negative meningitis. Dexamethasone has been shown to improve outcome in children with meningitis due to H. influenzae and S. pneumoniae. It has also been shown to reduce mortality and improve neurologic outcome in adults with meningitis due to S. pneumoniae.8 Many recommend its use in children with meningitis who are older than 6 weeks. The dose is 0.6 mg/kg/day for 4 days, with the first dose given 15 to 20 minutes before, or concurrent with, antibiotics. Outcome for meningitis varies with the type of infection, the specific pathogen, and for some infections, the duration of illness before diagnosis and institution of treatment. Despite prompt institution of antibiotic therapy, bacterial meningitis continues to have significant mortality and frequent neurologic sequelae in survivors. In neonatal meningitis, mortality ranges from approximately 10% for infections due to GBS, to as much as 50% in extremely premature infants with gram-negative bacterial meningitis.9 In older infants and children, the mortality ranges from 10 to 30% dependent on the organism.9 Neurologic sequelae occur in approximately 30% of survivors and range from mild cognitive impairment to global psychomotor retardation. Obstructive hydrocephalus occurs in approximately 10% of survivors, and focal injuries, such as cranial nerve palsy or paresis, may occur.9 The most typical neurologic injury is hearing impairment, which occurs in approximately 15 to 20% of survivors. Seizure disorder occurs in about 10% of survivors.9 Aseptic meningitis is a term often used in the setting of CNS inflammation when no bacterial cause is identified. Although the most common cause of aseptic meningitis is viral infection, other causes must be considered in every patient, including tuberculosis

and parameningeal infections (e.g., epidural abscess, sinusitis, and brain abscess), herpes encephalitis in the newborn, Lyme disease, and medication-induced meningitis (e.g., nonsteroidal anti-inflammatory agents). Viral meningitis is caused most often by enteroviruses, which typically have a biphasic pattern of infection.1 Viral meningitis is often preceded by a prodrome of several days of low-grade fever and malaise that progress to severe headaches, photophobia, and neck or back pain. Patients may then report increased sleepiness or confusion. There is no specific treatment for viral meningitis, and recovery without neurologic sequelae is the normal outcome. Recurrent meningitis is defined as two or more separate episodes of meningitis weeks to months apart, with full recovery between events. The most usual predisposing condition to recurrent meningitis is a communication between the subarachnoid space and the base of the skull (CSF leak or fistula) resulting from head trauma, surgery, or a congenital defect. Mondini dysplasia (a developmental arrest in the 7th week of gestation characterized by hypoplasia of the cochlear labyrinth, resulting in 1 to 1.5 turns instead of the normal 2.5 turns) is frequently cited as contributing to recurrent meningitis1 (Fig. 73.1). Epidermoid and dermoid cysts with dermal sinus tract are well-known causes of recurrent meningitis (Fig. 73.2). As a result, occult CNS abnormalities should be suspected in any patient who has recurrent meningitis but does not have predisposing CNS abnormalities or underlying immunological defects. In this category, clearly the meningitis must be treated effectively first, then the associated CNS disease defined and treated. Prophylactic surgery in a patient with a dermal sinus tract or neurenteric cyst is recommended not only for prevention of recurrent meningitis but also because the lesion may be easily corrected before meningitis produces an adhesive inflammatory reaction in the area.10 The role of the pediatric neurosurgeon in the management of meningitis is often limited to those cases with complicated courses10 (Table 73.2). However, it is important to recognize and treat appropriately due to its devastating consequences.

73.3╇Encephalitis Encephalitis involves inflammation of the brain parenchyma and clinically presents with alteration in consciousness. This helps distinguish it from the

601

602 Section VII.Aâ•… Cranial

Fig. 73.1â•… Common congenital lesions associated with recurrent meningitis. Computed tomography (CT) temporal bone demonstrating Mondini dysplasia (arrows) in a child presenting with congenital deafness and recurrent episodes of meningitis.

Fig. 73.2â•… Congenital lesions typically associated with recurrent meningitis. Untreated lumbosacral dermal sinus tract leading to severe meningitis and intradural abscess formation.

73 â•… Meningitis and Encephalitis Table 73.2â•… Indications for neurosurgical management in meningitis/encephalitis Supportive care

Failure of effective penetration of drug therapy into the CSF Occlusion of CSF pathways or hydrocephalus Intracranial hypertension

Management of complications

Subdural effusion Hydrocephalus Intraventricular septation/porencephaly

Recurrent meningitis―manifestation of occult disease

Congenital defects (dermal sinus tract, neurenteric cyst)

Complications of surgical disease

Ventricular shunt-associated infection Cerebral abscess Paranasal sinus infection Encephalocele/spina bifida Traumatic injury

Abbreviation: CSF, cerebrospinal fluid.

more common entity of uncomplicated meningitis, which lacks focal or global neurologic dysfunction. Encephalitis poses a clinical challenge because of the vast number of potential etiologies and the ineffective treatment options in many cases. Without the identification of a causative agent or analysis of brain tissue, the diagnosis is often presumptive and is based on clinical features. The pathophysiology of encephalitis can be the result of direct viral damage to the brain, as is seen in herpes or rabies, or can result from inflammation resulting from aberrant immune responses. Measles, Epstein-Barr virus (EBV), and rubella are examples of viruses that can trigger an autoimmune reaction with resultant postinfectious encephalitis, acute disseminated encephalomyelitis (ADEM), in which the white matter of the brain is involved predominantly.11 Infants may develop encephalitis after intrauterine exposure to cytomegalovirus (CMV) or after prenatal exposure to herpes simplex virus (HSV).12 In older children, encephalitis may occur in association with community-acquired viral infection, vaccination, or after exposure to mosquito-borne viruses.11 Common presentation of encephalitis is with fever, headaches, mental status changes, and seizures. Specific signs and symptoms can vary depending on the area of the brain most affected. Lumbar puncture should be performed for examination and culture to exclude the possibility of bacterial meningitis. A lymphocytic pleocytosis is often seen, with an elevation of protein and normal or mildly lowered glucose. Fluid should be sent for viral culture and polymerase chain reaction (PCR) for detection of herpes and enteroviruses. Electroencephalography (EEG) may provide evidence of focality before lesions are present on imaging, and may even indicate specific etiologies. Imaging is often limited to excluding mass lesions or

brain abscess and to identifying focal lesions typical of herpes encephalitis―characterized by hemorrhagic and necrotizing lesions that are characteristically located in the temporal lobes, orbital frontal cortex, and limbic structures12 (Fig. 73.3a). ADEM is an inflammatory disorder that may follow respiratory infections and also may occur after vaccinations.13 The hallmark of ADEM is focal demyelination seen on MRI, and the illness resembles acute monophasic multiple sclerosis (Fig. 73.3b). Acyclovir is usually given to all patients presenting with suspected encephalitis until herpes virus infection has been excluded. If the diagnosis is confirmed or strongly suspected, therapy is usually continued for 3 weeks. Despite treatment, herpes encephalitis is often devastating―the majority of survivors having long-term neurologic deficits.12 ADEM often responds to corticosteroids, with only one-third of patients going on to develop multiple sclerosis as adults.13 Treatment for the majority of cases of viral encephalitis is supportive, with airway protection, control of ICP, and management of seizures. Brain biopsy should not be routinely used in patients with encephalitis; however, it should be considered in patients with encephalitis of unknown etiology whose condition deteriorates despite treatment with acyclovir.14 Histological examination and viral culture of brain tissue provide the most definitive diagnosis.14

73.4╇Summary Infections of the CNS remain a significant clinical challenge, despite improvement in antibiotic therapy and vaccination. The early identification of the

603

604 Section VII.Aâ•… Cranial a

b

Fig. 73.3â•… Magnetic resonance imaging (MRI) demonstrating classic T2 fluid-attenuated inversion recovery (FLAIR) changes of (a) herpes encephalitis, and (b) acute disseminated encephalomyelitis (ADEM). Temporal lobe and cingulate involvement is typical of herpes encephalitis, whereas in ADEM the lesions are often large and symmetrical, with basal ganglia and thalamic involvement.

infectious agent and aggressive treatment are critical to obtaining the best outcomes. The neurosurgeon’s role in the management of most of these patients is in providing tissue and CSF for diagnosis and for the treatment and surgical management of increased ICP. Although there remain no clear indications about the timing of ICP monitoring in patients with meningitis/encephalitis, severe neurologic impairment with clinical signs suggesting high ICP may be a demonstration of a situation where ICP monitoring can be a significant factor in improving patient outcome, particularly for optimizing brain perfusion.

References ╇1. Long SS, Pickering LK, Prober CG. Principles and Practice

of Pediatric Infectious Diseases: Expert Consult—Online. Elsevier Health Sciences; 2012 ╇2. Schuchat A, Robinson K, Wenger JD, et al; Active Surveillance Team. Bacterial meningitis in the United States in 1995. N Engl J Med 1997;337(14):970–976 ╇3. Sáez-Llorens X, Ramilo O, Mustafa MM, Mertsola J, McCracken GH Jr. Molecular pathophysiology of bacterial meningitis: current concepts and therapeutic implications. J Pediatr 1990;116(5):671–684 ╇4. Quagliarello V, Scheld WM. Bacterial meningitis: pathogenesis, pathophysiology, and progress. N Engl J Med 1992;327(12):864–872

╇5. Sáez-Llorens X, McCracken GH Jr. Bacterial meningitis in

children. Lancet 2003;361(9375):2139–2148 VJ, Scheld WM. Treatment of bacterial meningitis. N Engl J Med 1997;336(10):708–716 ╇7. Sala F, Abbruzzese C, Galli D, et al. Intracranial pressure monitoring in pediatric bacterial meningitis: a fancy or useful tool? A case report. Minerva Anestesiol 2009; 75(12):746–749 ╇8. Odio CM, Faingezicht I, Paris M, et al. The beneficial effects of early dexamethasone administration in infants and children with bacterial meningitis. N Engl J Med 1991;324(22):1525–1531 ╇9. Pomeroy SL, Holmes SJ, Dodge PR, Feigin RD. Seizures and other neurologic sequelae of bacterial meningitis in children. N Engl J Med 1990;323(24):1651–1657 10. Humphreys RP. Surgical management of bacterial meningitis. Can Med Assoc J 1975;113(6):536–538 11. Whitley RJ, Gnann JW. Viral encephalitis: familiar infections and emerging pathogens. Lancet 2002;359(9305): 507–513 12. Kimberlin DW. Herpes simplex virus infections in neonates and early childhood. Semin Pediatr Infect Dis 2005;16(4):271–281 13. Davis LE, Booss J. Acute disseminated encephalomyelitis in children: a changing picture. Pediatr Infect Dis J 2003;22(9):829–831 14. Tunkel AR, Glaser CA, Bloch KC, et al; Infectious Diseases Society of America. The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis 2008;47(3):303–327 ╇6. Quagliarello

74

Cranial Epidural Abscess and Subdural Empyema William E. Whitehead

74.1╇Background If untreated or managed improperly, intracranial infections are fatal. Despite a steady fall in the incidence and mortality of intracranial suppurative disease since the early half of the 20th century, the war on pestilence is not over, and all neurosurgeons must be adept in the diagnosis and management of cranial epidural abcess (CEA) and subdural empyema (SDE). Otorhinogenic infections involving the paranasal sinuses, middle ear, or mastoid process are a common cause; however, infection should also be suspected after penetrating head injury, compound skull fractures, intracranial surgery, and immunosuppression.

74.1.1╇Indications Surgical drainage of a CEA or SDE is indicated in all patients with signs/symptoms of infection, mass effect, or raised intracranial pressure (ICP). Patients with SDEs can decline extremely rapidly, usually from acute hydrocephalus or status epilepticus, and almost always require urgent intervention. Occasionally, otorhinogenic infections will be associated with a small, less than 1-cm thick epidural abscess with minimal mass effect. These epidural empyemas, frequently a complication of sinus disease, usually do not require a neurosurgical procedure as long as the primary site of infection is drained, the organism is identified, and intravenous (IV) antibiotics are initiated.1

74.1.2╇Goals First, and one of the most important goals in the treatment of intracranial infection, is identification of the infecting organism. Intraoperative specimens should be expeditiously sent for aerobic and anaerobic bacterial cultures, fungal stain and culture, and

acid-fast bacteria stain and culture. Consultation concerning infectious disease should occur early so that flora endemic to the region/hospital are considered and covered with an empiric antibiotic regimen. Second, neurosurgical intervention is performed to remove as much pus as possible to eradicate the infection and normalize ICP. This goal, however, is always checked by the need to minimize trauma to important neural and vascular structures. For a CEA, this can usually be accomplished by the placement of one or multiple burr holes. For SDE, a large craniotomy is usually required. Third, at the time of diagnosis, the primary source of the infection (e.g., paranasal sinuses) should be identified. Treatment for the primary source of infection should take place concurrent with neurosurgical intervention. This may require preoperative consultation with ear, nose, and throat (ENT) surgeons for drainage of the nasal sinuses, middle ear, or mastoid process. Simultaneous surgical treatment is associated with a decreased rate of reoperations both intracranially and at the site of infection.2 Failure to address the primary site of infection at the time of intracranial surgery may result in reseeding of the infection through the same pathways.

74.1.3╇ Alternative Procedures For patients in septic shock or otherwise too unstable for craniotomy or general anesthesia, drainage can be performed and cultures obtained via a limited procedure (burr hole or a small craniectomy) and empiric antimicrobials can be started. An ICP monitor and/ or external ventricular drain (EVD) can be inserted for the monitoring and treatment of raised ICP. Once hemodynamically stable, the patient can be taken for a more definitive drainage procedure, if needed. A limited procedure for SDE can also be considered in patients believed to have a nonloculated collection without significant brain edema. This is

605

606 Section VII.Aâ•… Cranial commonly seen in infants with SDE secondary to meningitis and is generally the case in posttraumatic and postoperative SDEs.3

74.1.4╇Advantages Early surgical drainage to identify infecting organisms and relieve mass effect reduces morbidity and mortality and results in a tailored antimicrobial regimen of shorter duration.4

74.1.5╇Contraindications Surgical drainage of a symptomatic CEA or SDE is very rarely contraindicated.

74.2╇ Operative Detail and Preparation 74.2.1╇ Preoperative Planning and Special Equipment General preoperative screening labs are necessary (complete blood count [CBC] with platelets, basic chemistry, coagulation profile); patients with intracranial empyema can be anemic, thrombocytopenic, and coagulopathic, requiring correction of these parameters in preparation for surgery. Baseline erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) should be obtained as well as a type and cross for packed red blood. To aid in the identification of the infecting organism, blood, urine, sputum, and/or wound cultures should be sent. Ideally, preparations for surgery include meticulous review of a brain magnetic resonance imaging (MRI) with and without contrast for localization of the infection, for examination of the sinuses and temporal bone, and to identify associated brain abscess, venous thrombosis, cerebral edema, or a foreign body.5 If a patient is too unstable to undergo an MRI, computed tomography (CT) with and without contrast, with fine cuts through the temporal bones and nasal sinuses, is more than adequate for operative planning. In the case of SDE, antiepileptic medication for seizure prophylaxis should be started; however, this is not necessary in the setting of isolated CEA.6 Preoperative antimicrobials are traditionally held until a specimen is obtained to improve the chances of identifying the infecting organism; however, any sig-

nificant delays in bringing the patient to the operating room (>€1 h), or a clinical deterioration in the patient’s condition (e.g., decline in mental status, seizure) should immediately prompt the initiation of broad-spectrum antimicrobials. The most significant predictor of outcome is the patient’s level of consciousness and the rapidity of disease progression prior to treatment initiation. Therefore, the early initiation of antimicrobials prior to obtaining cultures, especially when the patient’s condition is deteriorating, is easily justified.7

74.2.2╇ Expert Suggestions/Comments Most CEAs are in the frontal region and can extend into the orbit.5 When they are associated with SDE or intraparenchymal brain abscess, the prognosis is worse and treatment is dictated by the presence of these other lesions. When CEAs are entirely in the epidural space, they are usually not associated with significant cerebral edema and tend to be liquid without loculations (Fig. 74.1). Isolated CEAs can be drained using a burr hole or multiple burr holes.8 When draining a CEA and doubt arises as to whether or not there is extension of the infection into the subdural space, one can use intraoperative imaging, such as ultrasound, to look for evidence of SDE after the CEA is removed. A sterile ultrasound transducer is placed directly on the dura. SDEs are typically hypoechoic and will displace the cortical surface away from the dura. If doubt persists, a small (< 1 cm) opening can be made in the dura to inspect for pus. It is better to open the dura than to risk missing a potentially fatal SDE. If the exploration is negative, the durotomy is closed. The risk of the infection spreading into the subdural space is low after adequate drainage of the CEA and the initiation of antimicrobials. If the exploration is positive, a larger craniotomy is performed and the dura is opened widely to drain the subdural space.8 In cases of SDE, it is common for pus to be layered over the entire convexity, along the falx, and over the tentorium (Fig. 74.2). Expect the empyema to be thickest near the primary source of the infection. SDEs can be loculated, tenacious, and extensive, which make them difficult to drain through a limited exposure. Additionally, imaging does not always reveal the full extent of purulent material, especially in cases with significant cerebral edema. Therefore, a large craniotomy is recommended for convexity SDE so that inspection of the convexity, tentorium, and interhemispheric fissure can easily occur with minimal trauma to the cerebral hemisphere. Infratentorial CEAs and SDEs are rare and have a worse prognosis. SDEs in the posterior fossa are com-

74 â•… Cranial Epidural Abscess and Subdural Empyema

Fig. 74.1â•… Cranial epidural abscess with mass effect.

monly associated with hydrocephalus (77%).9 These infections are usually otogenic and can be associated with a cerebellar abscess. Management principles are similar, with burr hole drainage for most CEAs and a wide posterior fossa craniectomy, along with removal of the posterior foramen magnum rim, and mastoidectomy for SDEs. Hydrocephalus should be treated acutely with an EVD.

74.2.3╇ Key Steps of the Procedure/ Operative Nuances Anesthesia should be notified of patients with elevated ICP prior to induction. The partial pressure exerted by carbon dioxide (pCO2) should be kept between 35 and

40 mm Hg to minimize cerebral edema. Empiric antimicrobials should be prepared and given intraoperatively as soon as cultures are obtained. The surgeon should consider wearing a headlight to maximize illumination when inspecting and draining the epidural or subdural space under edges of the craniotomy. For most supratentorial infections the patient is positioned supine with the head straight or rotated to best expose the affected area. Turning the head, a shoulder role is placed parallel to the spine under the ipsilateral shoulder (i.e., right shoulder elevated for right-sided empyema). This minimizes cervical rotation and facilitates venous drainage (Fig. 74.3). Even though burr holes may be all that are required for the drainage of most CEAs, the patient

607

608 Section VII.Aâ•… Cranial

Fig. 74.2â•… Subdural empyema around the convexity, over the tentorium, and within the interhemispheric fissure.

Fig. 74.3â•… Patient positioned for surgery to evacuate a right-sided subdural empyema (SDE). A shoulder roll under the right shoulder limits rotation of the head, and the head of the bed is elevated to maximize venous drainage. The surgical incision comes to midline to facilitate access to the interhemispheric fissure if needed.

74 â•… Cranial Epidural Abscess and Subdural Empyema

Fig. 74.4â•… Intraoperative illustration of a large craniotomy and durotomy for a convexity subdural empyema (SDE).

should be prepped and draped so that the procedure can be converted to a craniotomy using the burr hole incisions if possible. For a unilateral convexity SDE, a question-marktype skin incision extended to the midline will allow for access to the interhemispheric fissure, the majority of the convexity, and the tentorium (as shown in Fig. 74.3). Following skin incision, a myocutaneous flap is mobilized with the pericranium. The pericranium can remain on the skin flap and can be harvested if duraplasty becomes necessary for closure. Perform a large frontotemporoparietal craniotomy. Expand the bony opening as needed with a rongeur to improve access to the empyema. The dura is opened with a C-shaped incision over the frontal lobe (middle frontal gyrus), to the temporal lobe (middle or inferior temporal gyrus) avoiding and preserving the Sylvian veins. Multiple cuts are then made perpendicular to the edges of the durotomy so that the dura can be opened widely (Fig. 74.4). Copious amounts of irrigation and gentle aspiration are used to remove pus from the subdural space. Specimens are sent for culture. The thin, exudative membrane firmly attached to the hyperemic cortex should not be removed; this will lead to damage of the underly-

ing cortex that can result in neurologic deficit, bleeding, and seizures.4 Pus in the interhemispheric fissure and over the tentorium should be washed out under direct visualization. Visualizing the interhemispheric fissure requires expanding the craniotomy over the midline anterior to the coronal suture. The dura is stripped from the overlying bone, taking care not to injure the superior sagittal sinus. A small 3 × 3-cm craniotomy extending over the midline is performed with a craniotome. The dura is opened to the edge of the superior sagittal sinus (SSS) and retracted medially. With illumination and gentle retraction, the majority of the interhemispheric fissure can be visualized and drained (Fig. 74.5). Care is taken not to injure cortical veins during this maneuver. To inspect the tentorium, a rongeur is used to remove bone down to the floor of the middle cranial fossa. The tentorium is inspected by gently retracting the temporal lobe with good illumination. Care is taken not to injure the vein of Labbé. The dura is closed primarily if possible; duraplasty is performed using pericranium or a dural substitute when required. Replace the bone unless there is significant cerebral edema. Infected areas of

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610 Section VII.Aâ•… Cranial

Fig. 74.5â•… Shown intraoperatively is surgical access to the interhemispheric fissure via a small craniotomy anterior to the coronal suture.

bone can be debrided with a drill and then washed in Betadine (Purdue Pharma, Stamford, CT, USA) solution prior to replacement.10

74.2.4╇ Hazards/Risks/Avoidance of Pitfalls Brain swelling may occur after evacuation of the empyema. This can occur quickly and make closure difficult; prior to opening the dura, have irrigation, dural sutures, and duraplasty material readily available. Malignant cerebral edema is commonly associated with otorhinogenic infections and can occur even with very thin collections. There is no known correlation between thickness of SDE and degree of cerebral edema.4 Convexity SDEs with significant interhemispheric collections (> 1 cm) are associated with rapid herniation of the edematous brain, bleeding, and infarction when the dura over the convexity is opened. When a large parafalcine empyema is recognized on preoperative imaging and the dura is tense after craniotomy, it is beneficial to perform the 3 × 3-cm parasagittal craniotomy described earlier with a small durotomy to expose the interhemispheric fissure prior to opening the dura over the convexity. Decompress the interhemispheric fissure first, and then perform the larger opening of the dura.4 Removing as much pus as possible is desirable, but not essential; removal of pus should not come at the expense of injury to a cerebral vein, a dural sinus, or the cerebral cortex. The sacrifice of one cerebral vein increases the risk for cerebral ischemia and infarction. Care should be exercised when designing the bone flap and opening the dura to minimize the risk of injury to these structures. In the event of bleeding from a dural sinus or a cerebral vein, the

use of Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA) and a Cottonoid (Codman & Shurtleff, Raynham, MA, USA) to tamponade the bleeding is preferable to sacrificing these vessels with bipolar cautery. For similar reasons, blindly introducing instruments, irrigation catheters, or drains into the subdural space in an effort to remove additional pus is not recommended, especially in the setting of cerebral edema. This can result in damage to neural and vascular structures, and lead to bleeding, neurologic deficit, and an increased risk for seizures. All operative maneuvers should occur under direct visualization with uncompromised illumination. If there is any evidence of ventricular dilatation, an EVD should be placed, because deterioration from hydrocephalus can be rapid in this group of patients, and a drain will assist in the postoperative management of elevated ICP.9

74.2.5╇ Salvage and Rescue Expect that some patients will require multiple procedures to eradicate the infection. Even on appropriate antibiotic therapy, empyemas can recur and can be seen in new locations (~ 10%).5 It is possible for SDE to spread to the contralateral hemisphere, or across the tentorium after surgical drainage.3 Approximately 25% of patients with CEA may require a second or third surgery to drain accumulating pus.8 About one-third of patients require a second surgery after treatment for SDE.5 There is a low threshold to reoperate in a patient with a symptomatic reaccumulation. If surveillance imaging shows a significant increase in the size of the empyema or new areas of infection, repeat drainage is warranted.

74.3╇ Outcomes and Postoperative Course 74.3.1╇ Postoperative Considerations Postoperatively, broad-spectrum antimicrobials are given until the infecting organism is known. Always consider covering anaerobic organisms.11 ESR and CRP levels can help determine the length of antibiotic therapy.12 In general, IV antibiotics are given for 2 to 4 weeks, followed by 4 weeks of oral antibiotics for an uncomplicated patient.5,8 Immediate postoperative imaging is useful. All patients should be followed closely and repeat scans obtained for any new neurologic deficit or elevation in ESR/CRP. Reaccumulation of empyema or empyema in a new location may require repeat surgery. A final scan should be done near the end of therapy to ensure the empyema has resolved.

74 â•… Cranial Epidural Abscess and Subdural Empyema CEAs occur less frequently than SDEs and have a much better prognosis, with a mortality rate of 1%.8 For SDE, if diagnosis is early and major tenets of treatment are followed, outcomes can be good, with mortality rates of 10 to 15%.5 Significant improvements in preoperative neurologic deficits tend to occur with treatment.5,6 Known risk factors for poor outcome include associated chest infection at presentation, hematological failure, cerebral infarction, and ventriculitis.

74.3.2╇Complications Patients with SDE are at risk for epilepsy. Approximately 60% of patients will have seizures acutely and 30 to 50% will have chronic seizures.6 These patients will require antiepileptic drugs acutely. Attempts to wean seizure medication should not occur until there has been at least 6 months of no seizure activity.5 Dural sinus thrombosis and cerebral venous thrombosis occur commonly with SDE and should be screened for on preoperative and postoperative imaging. If allowed to progress, thrombosis can result in ischemia and stroke, with or without hemorrhage. Maintaining good hydration in the perioperative period is important in preventing and limiting progression of this complication. Anticoagulation is generally withheld in the perioperative period. Hydrocephalus can occur in the setting of SDE and is usually transient. Placement of an EVD allows for continuous drainage of cerebrospinal fluid (CSF). Ventriculoperitoneal shunts are required in approximately 5% of patients.5 After cerebral edema has subsided and CSF is sterile, the EVD can be slowly weaned over 3 to 5 days. If the patient fails due to symptoms or signs of elevated ICP, the EVD should be lowered to 10 cm H2O and drained for an additional 48 to 72 hours. A second wean is then attempted. If the patient fails, placement of a shunt is necessary. CSF should be sterile prior to placement of the shunt and the shunt entry site should be away from the empyema site if possible. Bone flap infections are uncommon. If a bone flap is required, it can be replaced with a very low likelihood of recurrence (1 to 7%).5,8 However, consider

removing the bone flap in patients who require more than two reoperations to clear the infection, and in patients who have completed antimicrobial therapy and have a recurrence. Perform cranioplasty in these patients at least 6 months after completion of therapy.

References ╇1. Heran NS, Steinbok P, Cochrane DD. Conservative neuro-

surgical management of intracranial epidural abscesses in children. Neurosurgery 2003;53(4):893–897, discussion 897–898 ╇2. Hoyt DJ, Fisher SR. Otolaryngologic management of patients with subdural empyema. Laryngoscope 1991; 101(1 Pt 1):20–24 ╇3. Nathoo N, Nadvi SS, Van Dellen JR. Traumatic cranial empyemas: a review of 55 patients. Br J Neurosurg 2000;14(4):326–330 ╇4. Nathoo N, Nadvi SS, Gouws E, van Dellen JR. Craniotomy improves outcomes for cranial subdural empyemas: computed tomography-era experience with 699 patients. Neurosurgery 2001;49(4):872–877, discussion 877–878 ╇5. Nathoo N, Nadvi SS, van Dellen JR, Gouws E. Intracranial subdural empyemas in the era of computed tomography: a review of 699 cases. Neurosurgery 1999;44(3): 529–535, discussion 535–536 ╇6. Cowie R, Williams B. Late seizures and morbidity after subdural empyema. J Neurosurg 1983;58(4):569–573 ╇7. Levy RM. Brain abscess and subdural empyema. Curr Opin Neurol 1994;7(3):223–228 ╇8. Nathoo N, Nadvi SS, van Dellen JR. Cranial extradural empyema in the era of computed tomography: a review of 82 cases. Neurosurgery 1999;44(4):748–753, discussion 753–754 ╇9. Nathoo N, Nadvi SS, van Dellen JR. Infratentorial empyema: analysis of 22 cases. Neurosurgery 1997;41(6):1263– 1268, discussion 1268–1269 10. Widdel L, Winston KR. Pus and free bone flaps. J Neurosurg Pediatr 2009;4(4):378–382 11. Bair-Merritt MH, Shah SS, Zaoutis TE, Bell LM, Feudtner C. Suppurative intracranial complications of sinusitis in previously healthy children. Pediatr Infect Dis J 2005;24(4):384–386 12. Jamjoom AB. Short course antimicrobial therapy in intracranial abscess. Acta Neurochir (Wien) 1996;138(7): 835–839

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75

Cerebral Abscess Justin Davis and Thomas A. Pittman

75.1╇Background

75.1.3╇ Alternate Procedures

75.1.1╇Indications

Small abscesses can be treated with antibiotics if the pathological organism has been identified. Larger lesions require drainage. Three techniques are widely used: stereotactic drainage, open drainage, and open drainage with wall excision. No useful studies comparing the techniques exist but there seems to be a general agreement on their relative merits. Abscess wall excision, except in fungal lesions, is rarely required. Open drainage is useful in cases with a retained foreign body, in situations in which communication with a sinus or open fracture is suspected, and possibly in children with posterior fossa lesions.3,4 In general, however, most lesions, and certainly those that are deep in the brain, are best managed with stereotactic drainage.

A patient who has normal immune function with a known or suspected cerebral abscess should undergo a comprehensive work-up to determine the size, location, and number of lesions and to define the possible source of infection. The work-up should include imaging of the central nervous system (CNS), preferably magnetic resonance imaging (MRI) with and without contrast (Fig. 75.1), blood cultures, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), echocardiogram, radiographs of the chest, teeth, and sinuses and other labs or images as indicated by the clinical presentation. If the infecting organism can be isolated from blood cultures, or from the likely primary site of infection, operative intervention may not be necessary. Cerebral abscesses that are smaller than 2 cm and are caused by a known pathogen(s) can be treated with antibiotics and the patient followed with serial imaging. Even if the pathogen has been identified, abscesses larger than 2 cm should be surgically drained.1 Drainage is also recommended if a lesion enlarges during therapy, fails to respond to therapy, or causes symptoms because of its size or associated edema.2

75.1.2╇Goals There are several reasons to drain a cerebral abscess. Abscess drainage can relieve mass effect and often reduces edema surrounding the lesion. In addition, cultures sent from the abscess generally allow identification of pathogens and the determination of their antibiotic susceptibility. And, if the size of the abscess is reduced, the administered antibiotic may be more effective. Finally, for periventricular abscesses, surgical drainage may decrease the risk of intraventricular rupture.

612

75.1.4╇Advantages There are three major advantages to stereotactic biopsy: it is safe, relatively quick, and can be used to treat an abscess in nearly any intracranial location. In addition, multiple lesions can be treated during the same operation and lesions can be drained repeatedly if necessary. As practical issues, the equipment required is widely available and most neurosurgeons are able to perform the procedure.

75.1.5╇Contraindications There are few contraindications to stereotactic abscess drainage. In some settings, other procedures may be preferred. For instance, as previously discussed, an open procedure is used if a foreign body is present or a fungal source is likely. If a stereotactic drainage has been attempted and the abscess contents could not be aspirated, an open procedure might be necessary. For the most part, nevertheless,

75 â•… Cerebral Abscess a

b

c

d

Fig. 75.1â•… (a) T1 without contrast, (b) T1 with contrast, and (c,d) diffusion-weighted magnetic resonance imaging (MRI) of an abscess.

613

614 Section VII.Aâ•… Cranial unless a patient is too ill to tolerate essentially any procedure, even one done using a local anesthetic, stereotactic drainage is possible.

75.2╇ Operative Detail and Preparation

it is crucial to irrigate until the fluid runs clear and there is no purulent or bloody drainage. With the open approach, care must be taken not to let the contents of the abscess spill out around the surrounding cortex or into the cerebrospinal fluid (CSF) spaces. If this does occur, the area should be copiously irrigated, but the problem is best avoided.

75.2.1╇ Preoperative Planning and Special Equipment

75.2.4╇ Hazards/Risks/Avoidance of Pitfalls

Stereotactic drainage can be performed with or without a frame. Although a frame-based system may be marginally more accurate, the difference is rarely of clinical significance. Frameless systems are usually easier to use, quicker to use, and more readily available. In either case, the abscess should be approached through a trajectory that avoids sulci, visible vessels, and the ventricles. Some form of image guidance can also be helpful if an open procedure is performed. A frameless system is often used; however, ultrasound can serve as a primary means of localizing the lesion or as an adjunct to a frameless system.

Stereotactic abscess drainage is relatively safe but problems can occur if the trajectory is poorly planned. More typical than a complication is ineffective drainage of the lesion. If the abscess contents are thick or septated, it can be difficult, even with vigorous drainage, to empty the cavity. In many cases, however, even incomplete drainage is sufficient. If it is not, a second needle biopsy or perhaps an open approach may be required. Open drainage carries the risk of dissemination of the infection. If care is taken with the contents of the abscess and the ventricle is not violated, the risk of dissemination is very low.

75.2.2╇ Expert Suggestions/Comments

75.2.5╇ Salvage and Rescue

It is important to remember that the goal of surgical abscess drainage is diagnosis and decompression. It is rarely necessary, or advisable, to try to remove the abscess in its entirety. Even in patients who might benefit from total excision, for example those with fungal abscesses, the complications caused by an overly aggressive attempt to remove the capsule may outweigh the advantages of total resection.

A patient can deteriorate rapidly after intraventricular rupture of an abscess. If this occurs, drainage of the abscess should be completed and then a ventriculostomy placed. The ventriculostomy has several functions. It allows measurement and treatment of intracranial pressure while providing ready access to CSF for sampling. The drain also provides a route for administering intraventricular antibiotics if that is thought useful. At present, there is no consensus as to the value of intraventricular antibiotic therapy.

75.2.3╇ Key Steps/Operative Nuances Once the patient is positioned, pinned, and registered in a frameless system, the incision is marked. If an open craniotomy is planned, the pointer is used to determine the best incision site, hair is clipped, and skin is prepped and draped appropriately. Since the goal of surgery is simply drainage of the abscess and not complete resection of the capsule, a small incision, craniotomy, and corticotomy can be used. If the abscess is to be treated by needle drainage, the same procedure is used to mark the incision site, based on the planned entry point. The incision need only be large enough to accommodate the drill that will make the burr hole. Most frameless systems provide proprietary hardware and/or software for performing stereotactic biopsy. Whereas each has its advantages, any system with which the surgeon is familiar can be used. Once the abscess has been penetrated,

75.3╇ Outcomes and Postoperative Course 75.3.1╇ Postoperative Considerations Patients with an intracerebral abscess generally receive antibiotics for at least 8 weeks. An MRI is obtained about every 2 weeks during therapy. The lesions should become smaller over time but imaging improvement can lag behind clinical changes. Images should also be obtained occasionally over the several months following therapy to rule out recurrence of the infection.5 If, either during or after treatment, a lesion becomes significantly larger, repeat drainage should be considered.

75â•… Cerebral Abscess Even with therapy, an intracranial abscess may have significant sequelae. In the modern era, mortality rates have ranged from 8 to 25% for unruptured abscesses and they increase to 27 to 85% in cases complicated by intraventricular rupture.6,7 Among all patients with an intracranial abscess, the rate of long-term neurologic disabilities remains high (20– 70%) and epilepsy is common (30–50%).8

75.3.2╇Complications Abscess drainage is generally safe. Although specific information relating to abscess drainage is not available, the rate of hemorrhage after stereotactic biopsy for other indications is about 8%, with fewer than 2% of patients suffering clinically significant hemorrhage.9 Infections after stereotactic biopsy are apparently very rare.10,11 Whereas the infection rate after open drainage has not been well characterized, it is likely only marginally higher than in other open procedures. Recurrence rates for abscesses range from 0 to 24% but are less than 10% in those treated with antibiotics for at least 6 weeks.7,8

References ╇1. Brook

I. Brain abscess in children: microbiology and management. J Child Neurol 1995;10(4):283–288 ╇2. Erdoğan E, Cansever T. Pyogenic brain abscess. Neurosurg Focus 2008;24(6):E2

╇3. Pandey

P, Umesh S, Bhat D, et al. Cerebellar abscesses in children: excision or aspiration? J Neurosurg Pediatr 2008;1(1):31–34 ╇4. Ciurea AV, Stoica F, Vasilescu G, Nuteanu L. Neurosurgical management of brain abscesses in children. Childs Nerv Syst 1999;15(6-7):309–317 ╇5. Frazier JL, Ahn ES, Jallo GI. Management of brain abscesses in children. Neurosurg Focus 2008;24(6):E8 ╇6. Lee TH, Chang WN, Su TM, et al. Clinical features and predictive factors of intraventricular rupture in patients who have bacterial brain abscesses. J Neurol Neurosurg Psychiatry 2007;78(3):303–309 ╇7. Hakan T. Management of bacterial brain abscesses. Neurosurg Focus 2008;24(6):E4 ╇8. Cavuşoglu H, Kaya RA, Türkmenoglu ON, Colak I, Aydin Y. Brain abscess: analysis of results in a series of 51 patients with a combined surgical and medical approach during an 11-year period. Neurosurg Focus 2008;24(6):E9 ╇9. Field M, Witham TF, Flickinger JC, Kondziolka D, Lunsford LD. Comprehensive assessment of hemorrhage risks and outcomes after stereotactic brain biopsy. J Neurosurg 2001;94(4):545–551 10. Bekelis K, Radwan TA, Desai A, Roberts DW. Frameless robotically targeted stereotactic brain biopsy: feasibility, diagnostic yield, and safety. J Neurosurg 2012;116(5):1002–1006 11. Bernays RL, Kollias SS, Khan N, Brandner S, Meier S, Yonekawa Y. Histological yield, complications, and technological considerations in 114 consecutive frameless stereotactic biopsy procedures aided by open intraoperative magnetic resonance imaging. J Neurosurg 2002;97(2):354–362

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76

Tuberculous, Fungal, and Parasitic Infections A. Graham Fieggen and Anthony A. Figaji

76.1╇Background Tuberculous infection may involve any component of the neuraxis or its coverings, including the vertebral column and skull. The cornerstone of management of central nervous system (CNS) tuberculosis (TB) is adequate antituberculous drug therapy from the outset. For non–drug-resistant TB, this usually entails four drugs: isoniazid, rifampicin, pyrazinamide, and one of streptomycin, ethambutol, or ethionamide, as well as pyridoxine. Treatment should follow local guidelines and advice should be sought from an infectious diseases specialist, especially in cases of drug-resistant TB.

76.2╇ Tuberculous Meningitis 76.2.1╇Indications • A series of more than 500 children with tuberculous meningitis (TBM) reported hydrocephalus in 70%, of whom the majority had communicating hydrocephalus as demonstrated by limited air encephalography.1 The majority of these patients may be managed medically. • Hydrocephalus may occur either in the acute phase of the infection or later due to scarring of the basal cisterns (Fig. 76.1). • Patients with noncommunicating hydrocephalus, or those with communicating hydrocephalus not responding to medical treatment, require cerebrospinal fluid (CSF) diversion. This may be: — Shunt • Usually a ventriculoperitoneal shunt (VPS) • Ventriculopleural shunt avoided if pulmonary disease

616

• Ventriculoatrial shunt may be used if abdomen involved (tuberculous peritonitis). — Endoscopic third ventriculostomy (ETV) — Other neuroendoscopic procedures may be indicated in the patient with tuberculous hydrocephalus, such as septostomy or retrieval of a shunt catheter.

Goals • Control of raised intracranial pressure (ICP) • Patients who undergo successful endoscopic treatment experience conversion of their noncommunicating hydrocephalus to communicating hydrocephalus and usually require ongoing medical management, such as diuretics

Alternate Procedures • Medical management of proven communicating hydrocephalus: — Diuretics • Acetazolamide • Furosemide — Regular lumbar punctures, measuring the opening and closing pressures — Prednisone 2 to 3 mg/kg/daily for one month • Insertion of a shunt is the default treatment option for patients with tubercular hydrocephalus and, in the view of the authors, should be the first choice for patients with: — Reduced level of consciousness or other evidence of critically raised ICP — Proven communicating hydrocephalus

76 â•… Tuberculous, Fungal, and Parasitic Infections a

b

Fig. 76.1â•… Early imaging features of tuberculous meningitis. (a) Computed tomography (CT) scan following contrast administration showing enhancement throughout the basal cisterns and hydrocephalus. (b) Magnetic resonance imaging (MRI) scan (T1-weighted [T1W] following gadolinium) demonstrating hydrocephalus and basal enhancement with numerous small tuberculomas.

Advantages • Carefully selected patients who undergo a successful ETV may avoid the need for a permanently implanted shunt. This is of value because patients with tuberculous meningitis (TBM) appear to have a high rate of shunt complications.

• In the event that the mAEG demonstrates noncommunicating hydrocephalus, it is mandatory that the patient undergoes surgery within 3 hours due to risk of herniation following the lumbar procedure. • Most patients with TBM have significant hyponatremia, and this should be corrected slowly to 130 mmol/L. • Chest X-ray to assess for pulmonary disease

Disadvantages • In the early preoperative phase following ETV, there is less certainty that ICP has been adequately controlled and use of a temporary external ventricular drain (EVD) or CSF reservoir may increase safety.

76.2.2╇ Operative Detail and Preparation Preoperative Planning and Special Equipment • The authors’ practice is to reserve ETV for patients who do not have a reduced level of consciousness and have noncommunicating hydrocephalus, as shown on a modified air encephalogram (mAEG) (see algorithm in Fig. 76.2).

Expert Suggestions/Comments • This procedure should only be performed by an expert in neuroendoscopy due to the grossly abnormal anatomy encountered.

Key Steps of the Procedure/Operative Nuances • Anesthetic precautions if pulmonary TB • Endoscopic set-up routine • Use of a rigid endoscope in TBM cases due to difficulty in sterilizing flexible endoscope • A disposable figure-of-eight balloon is used to perforate the floor.

617

618 Section VII.Aâ•… Cranial Institutional  Protocol  for  the  Management  of  Hydrocephalus  in  Tuberculous  Meningitis    

Suspected  TBM  

 

 

 

 

 

 

 

 

 

 

 

        Hydrocephalus    

    Head  CT  scan    

 

 

 

 

 

 

 

 

 

 

 

 

No  Hydrocephalus  

Proceed  to  diagnostic  LP  if   considered  safe  

Patient  clinically  compromised/   acute  deterioration  of   consciousness?  

No   Yes  

Inform  neurosurgeon  before  proceeding  

Refer  to  neurosurgeon   Emergency   insertion  of  EVD  

Proceed  to  lumbar  AEG  with   measurement  of  opening  pressure    

SXR:  No  air  visible  –   consider  repeat  or  clinical   decision  without  AEG    

SXR:  Air  in  the  basal   cisterns  only  

SXR:  Air  in  the   ventricles   Likely  CommHC  

Likely  Non-­‐CommHC   Trial  of  medical   treatment  (see   text)  

Surgery:  ETV  or  VPS   depending  on  age  of   patient,  resources   and  expertise  

Follow-­‐up  patient   clinically  and   radiologically  for   functioning  ETV  or   VPS  

HCP  resolves  on  CT;   LP  opening  pressure   normalizes  

Head  CT  scan  at  1   and  3  weeks  (+/-­‐   later  CT).  Repeated   LPs  to  monitor   pressure   HCP  fails  to  resolve  or  increases,   opening  pressure  fails  to  normalise  

VPS   Fig. 76.2â•… Algorithm showing decision making in initial management of tuberculous hydrocephalus. (Reprinted with permission of Elsevier.) AEG, air encephalogram; CommHC, communicating hydrocephalus; ETV, endoscopic third ventriculostomy; EVD, external ventricular drain; HCP, hydrocephalus; LP, lumbar puncture; SXR, skull X-ray; TBM, tuberculous menigitis; VPS, ventriculoperitoneal shunt.2

76 â•… Tuberculous, Fungal, and Parasitic Infections

Hazards/Risks/Avoidance of Pitfalls • The major hazards of the procedure relate to the pathological anatomy encountered in acute TBM: — CSF is usually clear―if turbid, consider another diagnosis. — Ventricular wall is studded with tubercles (Fig. 76.3). — The floor is thickened and opaque, obscuring landmarks, such as the mammillary bodies and basilar artery. — Exudate fills the cisternal space. • In chronic TBM, the floor may be thinner and more amenable to perforation, but the cisterns are typically scarred and may be occluded.

Salvage and Rescue • It must never be forgotten that there is an alternative in placing a VPS. • An EVD is always left in place at the end of the procedure to confirm control of hydrocephalus in the short term.

76.2.3╇ Outcomes and Postoperative Course Postoperative Considerations • Patient admitted to ICU postoperatively • Confirmation of communication by performing column test

• EVD removed if communication confirmed and clinical improvement noted • Repeat brain computed tomography (CT) within 48 hours of surgery • Regular lumbar punctures, measuring the opening and closing pressures • Schedule of two weekly imaging sessions for first 2 months • The major long-term complications of TBM include problems of vasculitis, such as infarcts; ependymal enhancement may lead to multilocular hydrocephalus (Fig. 76.4).

Complications • Relatively high failure rate (10/17)3 • Delayed hydrocephalus • Continue TB drugs

76.3╇ Tuberculous Masses A striking aspect of the epidemiology of CNS TB is the dramatic decrease in the incidence of solid tuberculous space-occupying lesions, commonly referred to as tuberculomas. They may still be encountered, with or without accompanying TBM. They need to be distinguished from tuberculous abscesses, which appear to reflect a different immunological response to the infection. Although tuberculomas may occur in the spinal cord, this is rare. A common dilemma is distinguishing a small cerebral tuberculous granuloma from a cysticercus granuloma―seldom do either need specific therapy except anticonvulsants if there is accompanying epilepsy.

76.3.1╇Background Indications

Fig. 76.3â•… Neuroendoscopic view of the floor of the third ventricle, showing numerous ependymal tubercles.2

• Most tuberculomas can be diagnosed on imaging (Fig. 76.5) and managed medically. • Surgery is indicated in the event of: — Diagnostic uncertainty―not uncommon due to the phenomenon of “paradoxical expansion”; this refers to the commonly seen situation where a tuberculoma initially enlarges following commencement of antituberculous therapy, followed by a response within 2 to 3 months. — Mass effect compromising vital neural structures

619

620 Section VII.Aâ•… Cranial a

b

c

Fig. 76.4╅ Complications of tuberculous meningitis (TBM). (a) Magnetic resonance imaging (MRI) scan (T2-weighted [T2W]) demonstrating hydrocephalus and numerous infarcts in the basal ganglia. (b) MR angiogram demonstrating the vasculo�pathy characteristic of TBM. (c) Ependymal enhancement leading to multiloculated hydrocephalus.

76 â•… Tuberculous, Fungal, and Parasitic Infections a

b

Fig 76.5â•… Typical imaging of a tuberculoma. (a) T1-weighted MRI following gadolinium showing enhancement around the margins of the mass. (b) T2-weighted MRI showing the characteristic hypointensity of a tuberculoma.

Goals • Surgery may either be: — Resection of the lesion — Stereotactic biopsy if deep-seated — CSF diversion if hydrocephalus due to focal distortion of CSF pathways (ETV may be highly successful in such cases.)

Alternate Procedures • Medical management

on the surface (prior to CT scanning they were often mistaken for meningiomas) and can be removed intact but, if too large, may have to be removed piecemeal.

76.3.2╇ Operative Detail and Preparation Preoperative Planning and Special Equipment • Antituberculous treatment will almost invariably have been commenced. • Steroids • Navigation or ultrasound may facilitate location of the lesion.

Advantages • Microbiological diagnosis with culture

Expert Suggestions/Comments • Avoid spillage of contents.

Disadvantages • If a tuberculoma is resected, great care must be taken to avoid spilling the contents because this may lead to fulminant tuberculous meningitis (TBM). These lesions often present

Key Steps of the Procedure/Operative Nuances • Anesthetic considerations: — Intravenous (IV) antibiotics at induction

621

622 Section VII.Aâ•… Cranial — Consider use of mannitol and steroids if raised ICP. • Lesion usually firm and avascular, easily separated from brain

Hazards/Risks/Avoidance of Pitfalls • Spillage of contents and contamination of subarachnoid space

fungal masses or meningitis; whereas candidiasis is seen worldwide, blastomycosis, coccidioidomycosis, and histoplasmosis have more specific geographic distribution. Although rare, these should be considered in a patient presenting with low-grade chronic meningitis and hydrocephalus complicated by recurrent shunt failure. Although cryptococcal meningitis is common in adults with HIV, it rarely presents in children.

76.6╇ Fungal Abscess Salvage and Rescue • Piecemeal removal if too large to remove intact • Tuberculous abscesses often recur and may need excision; consideration may also be given to the use of thalidomide.

76.3.3╇ Outcomes and Postoperative Course Postoperative Considerations • Continue antituberculous therapy depending on operative findings, culture, and evidence of TB elsewhere.

Complications • TBM • Recurrence

76.4╇ Other Tuberculous Lesions Although a Cochrane review4 found no evidence for the role of surgery in tuberculous spondylitis, many surgeons believe operative management leads to better control of pain, quicker resolution of neurologic deficits, and improved correction of deformity. Patients co-infected with human immunodeficiency virus (HIV) may develop new lesions when commenced on antituberculous therapy and antiretroviral drugs, a phenomenon termed the immune reconstitution inflammatory syndrome (IRIS).

76.5╇ Fungal Infection Fungi are ubiquitous environmental pathogens but seldom cause disease in immunocompetent individuals. Fungal infections may present with intracranial

76.6.1╇Background Indications • Most commonly caused by Aspergillus in immunocompromised child (typically during the induction phase of chemotherapy for leukemia) • Presents with pyrexia and focal seizure or new onset neurological deficit • Early phase (cerebritis) easy to mistake for an infarct on initial scan (Fig. 76.6)

Goals • Excision of the abscess is required for control. (Fungi invade vessels, causing arteritis, mycotic aneurysms, and further dissemination.)

Alternate Procedures • Excision may not be possible if abscess is deep-seated and inaccessible, in which case stereotactic aspiration may be indicated. • Implantation of an Ommaya reservoir for continual intracavitary administration of amphotericin B has been reported.

Advantages • Cure is possible. • Removal of the abscess with adequate antifungal therapy allows continuation of chemotherapy.

Disadvantages • Excision is more invasive than aspiration. • There may be multiple abscesses, each requiring a craniotomy.

76 â•… Tuberculous, Fungal, and Parasitic Infections a

b

Fig. 76.6â•… Aspergillus brain abscess. (a) Contrast-enhanced CT showing ring-enhancing mass in a young boy receiving chemotherapy for leukemia. (b) Histology following excision confirmed aspergillosis, with evidence of vascular invasion on silver stain.

623

624 Section VII.Aâ•… Cranial

76.6.2╇ Operative Detail and Preparation Preoperative Planning and Special Equipment • Discussion with multidisciplinary team to determine treatment goals • Chest radiograph may show pulmonary lesion. • Correct any hematological and metabolic abnormalities. • Navigation/ultrasound may facilitate surgery.

Expert Suggestions/Comments • Excision facilitated by working around capsule

Key Steps of the Procedure/Operative Nuances • Anesthetic considerations: — IV antibiotics at induction — Consider use of steroids and mannitol. • Pus typically surrounded by a firm, rubbery wall with a soft capsule5 easily separated from brain by gentle suction and judicious use of bipolar5 • Avoid spillage of abscess contents.

Hazards/Risks/Avoidance of Pitfalls • Avoid spillage of abscess contents.

Salvage and Rescue • If abscess location or the patient’s condition doesn’t permit radical excision, aspiration may be warranted to establish diagnosis and reduce mass effect.

76.6.3╇ Outcomes and Postoperative Course Postoperative Considerations • Managed in intensive care unit (ICU) • Postoperative CT scan • Antifungal therapy: — This must be planned in consultation with the pediatric oncologist. — IV amphotericin B is the mainstay of treatment.

— Liposomal amphotericin B has fewer side effects. — Treatment may be converted to oral voriconazole.

Complications • Exacerbation of preoperative neurologic deficit that subsequently improves • Drug side effects

76.7╇ Parasitic Infestations Parasitic infestations can be broadly classified as protozoan (single-celled organisms) or metazoan/ helminthic (complex organisms). Examples of the former include: • Toxoplasmosis — Antenatal infection may lead to hydrocephalus secondary to aqueduct stenosis, which is readily amenable to ETV. — Acquired infection commonly manifests in HIV-infected adults. — Treatment is with sulfadiazine, trimethoprim, and folinic acid. • Amebic abscess — Either meningoencephalitis or brain abscess • Malaria — Raised ICP Helminths include trematodes, such as Schistosoma, causing bilharziasis, or cestodes, such as Taenia (cysticercosis) and Echinococcus (hydatidosis). Schistosomiasis granulomas may present with seizures or myelopathy. Neurocysticercosis is covered in Chapter 77.

76.8╇ Hydatid Cyst Infection is caused by ingestion of food contaminated with eggs of Echinococcus granulosus tapeworm (occasionally other species may infest humans). Whereas hematogenous dissemination to the lung or liver is common, spread to the brain, spinal cord, orbit, skull, or vertebrae may require neurosurgical intervention in 1 to 2% of all cases of hydatidosis. Hydatid cysts consist of an inner germinal layer that gives rise to innumerable protoscolices referred to as hydatid sand (for obvious reasons, when one inspects the contents). This is surrounded by an acellular parasite-derived laminated membrane, cleavage plane in the brain (Fig. 76.7).7

76 â•… Tuberculous, Fungal, and Parasitic Infections a

b

Fig. 76.7â•… Typical imaging appearance of a large unilocular hydatid cyst on (a) computed tomography (CT) and (b) magnetic resonance imaging (MRI). It is vitally important that this diagnosis be considered prior to inadvertenly inserting a shunt!

625

626 Section VII.Aâ•… Cranial

76.8.1╇Background Indications • Typically, a very large unilocular cyst may present with a focal seizure or subtle motor deficit in a disproportionately well-looking child who often has macrocrania and skull asymmetry on closer inspection. • The first challenge is to recognize the condition and not mistake it for an arachnoid cyst (Fig. 76.8). • The second challenge is not to delay treatment for too long because patients have critically raised ICP and sudden decompensation is well described.

Goals • Intact removal without spillage of the contents

Alternate Procedures • If intact removal is NOT considered possible, some authors advocate gentle aspiration of the cyst contents, irrigation with scolicidal agent (hypertonic saline), followed by careful removal of the collapsed cyst wall. This technique is frequently used in removing liver hydatids.

Advantages • Intact removal almost invariably leads to cure of the disease and resolution of the neurologic deficit.

Disadvantages • Large exposure required

76.8.2╇ Operative Detail and Preparation Preoperative Planning and Special Equipment • Medical management of raised ICP, if emergent presentation prior to urgent surgery • If stable, start antihelminthics and schedule for next available operating list: — Albendazole 15 mg/kg/day in two divided doses, to a maximum of 800 mg/day — Praziquantel 40/mg/kg every eight hours • Anticonvulsants • Serology often negative

Expert Suggestions/Comments • Gravity and your anesthetist are indispensable allies in delivering the cyst intact. • Careful review of preoperative imaging for atypical features (Fig. 76.8), which suggest an increased risk of rupture6: — Calcification — Enhancement — Multiple cysts • If multiple intracranial cysts, may need to plan more than one craniotomy

Key Steps of the Procedure/Operative Nuances

Fig. 76.8â•… Coronal magnetic resonance imaging (MRI) following contrast administration, demonstrating an irregular cyst wall with enhancement, suggesting an increased risk of intraoperative rupture.

• The approach to cyst removal is based on the Dowling technique. • Anesthetic considerations: — IV antibiotics at induction — Steroids — Avoid mannitol because there is usually a very large space after evacuation of the cyst. — Anesthetist must be prepared to manage anaphylaxis in the event of cyst rupture. • Each step of the operation must be planned with a view to facilitating removal of the cyst (Fig 76.9).

76 â•… Tuberculous, Fungal, and Parasitic Infections a

b

c

Fig. 76.9â•… Operative steps in removal of a hydatid cyst intact. (a) Careful corticectomy revealing the cyst wall. (b) The cyst is almost ready for delivery. (c) Demonstration of the typical large cavity following cyst removal.

• Position on horseshoe with the head raised 30 degrees, such that the dome of the cyst points to the roof (i.e., the highest area of anticipated corticectomy). • When securing the drapes, make sure you will be able to drop and possibly also turn the head. • Large scalp flap and craniotomy, taking care to place burr holes as far from the cyst as possible • U-shaped dural opening may be preferable because the thin rim of cortex may be adherent to the dura. • Plan the corticectomy to allow cyst removal without lacerating the brain or tearing bridging veins. • Careful corticectomy under loupe magnification, finding the avascular interface between the brain and cyst wall • Bipolar coagulation (while avoiding use of monopolar coagulation) may be used cautiously and Cottonoid (Codman & Shurtleff, Raynham, MA, USA) patties are used to protect the brain as the corticectomy proceeds. • Corticectomy will need to be around threefourths of the diameter of the cyst (Fig. 76.10).

• Cyst removal is accomplished through a combination of: — Using gravity by changing the position of the head — Floating the cyst out by instilling saline through a soft catheter passed behind the cyst — Increasing ICP at the key moment using a Valsalva maneuver • The cyst must be caught intact in a receptacle. • Irrigate the cavity with saline to ensure all lamellae have been removed.

Hazards/Risks/Avoidance of Pitfalls • Intraoperative rupture may cause anaphylaxis and disease recurrence.

Salvage and Rescue • Have large suckers and hypertonic salinesoaked swabs available in case of cyst rupture. In which case: — Place a large-bore sucker in the cyst, aspirate all the contents, and cover the

627

628 Section VII.Aâ•… Cranial a

b

Fig. 76.10â•… Atypical hydatid cysts. (a) Preoperative coronal T1-weighted image demonstrating a multicystic mass with innumerable daughter cysts and marked midline shift. Despite this, the patient was fully conscious with a very subtle left hemiparesis. (b) Intraoperative photograph showing the appearance of multiple hydatid cysts. In such a case, it is likely that previous rupture has occurred and intact removal is highly improbable.

76 â•… Tuberculous, Fungal, and Parasitic Infections

•

• • •

surrounding brain before removing the collapsed cyst intact. — If the cyst wall ruptures and piecemeal removal is necessary, consider irrigating the cavity with hypertonic saline, without spilling into the subarachnoid space. — ALL contaminated instruments, drapes, and gloves must be removed from the surgical field. In reality, the concentration of hypertonic saline and the duration of exposure required for scolicidal effect make this unlikely to add much in a neurosurgical setting. Some authors advocate use of other scolicidal agents such as formalin but we have avoided this in the CNS. It is imperative to prevent spillage into the subarachnoid space or ventricle. Anesthetist to respond to any signs of anaphylaxis

76.9╇ Outcomes and Postoperative Course 76.9.1╇ Postoperative Consideration • Patient must lie in a flat position for a few days. • Check serum sodium if hypertonic saline has been used. • Continue oral albendazole until work-up has been completed. • Image the lungs and liver (CT or ultrasound); lesions elsewhere may require surgery or albendazole. • Prolonged albendazole use is not recommended by the manufacturer but the authors have done so in a limited number of cases with no adverse effects noted. It is, however, important to have a 2-week drug holiday after every 4 weeks of treatment and monitor for adverse effects, including regularly checking liver function tests and complete blood counts. This is particularly helpful in multicystic disease where surgical cure is unlikely (Fig. 76.10).

76.8.2╇Complication • Sudden death from critically raised ICP preoperatively • Rupture into the subarachnoid space leads to widespread dissemination and multiple recurrences. • Postoperative hypernatremia • Seizures • Development of mass effect from subdural hygroma or hydrocephalus is unusual in the experience of the authors. It is essential for neurosurgeons to support public health strategies aimed at reducing the incidence of parasitic diseases.

References ╇1. van

Well GTJ, Paes BF, Terwee CB, et al. Twenty years of tuberculous meningitis: a retrospective cohort study in the Western Cape of South Africa. Pediatrics 2009;123 (1):e1–e8 ╇2. Figaji AA, Fieggen AG. The neurosurgical and acute care management of tuberculous meningitis: evidence and current practice. Tuberculosis (Edinb) 2010; 90:393–400 ╇3. Figaji AA, Fieggen AG. Endoscopic challenges and applications in tuberculous meningitis. World Neurosurg 2013;70(5):1220–1230 ╇4. Jutte PC, van Loenhout-Rooyackers JH. Routine surgery in addition to chemotherapy for treating spinal tuberculosis. Cochrane Database Syst Rev ╇5. Middelhof CA, Loudon WG, Muhonen MD, et al. Improved survival in central nervous system aspergillosis: a series of immunocompromised children with leukaemia undergoing stereotactic resection of aspergillomas. Report of four cases. J Neurosurg 2005;103(4 Suppl):374–378 ╇6. Peter JC, Domingo Z, Sinclair-Smith C, de Villiers JC. Hydatid infestation of the brain: difficulties with computed tomography and the surgical treatment. Pediatr Neurosurg 1994;20(1): 78–83 ╇7. Carrea R, Dowling E Jr, Guevara JA, Surgical treatment of hydatid cysts of the central nervous system in the pediatric age (Dowling’s technique). Childs Brain 1975;1(1): 4–21

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77

Cysticercosis Tenoch Herrada-Pineda, Juan Antonio Ponce-Gomez, Salvador Manrique-Guzman, and Francisco Revilla-Pacheco

77.1╇Background Neurocysticercosis (NCC) is the most common helminthic disease of the central nervous system (CNS) caused by helminths in humans and by the larvae of the Taenia solium parasite. NCC is an endemic disease in developing countries, especially Central and South America, Africa, and East and South Asia, where a combination of warm weather, severe poverty, and illiteracy facilitate parasite transmission. In endemic areas it accounts for more than 12% of admissions at neurologic hospitals and is the main cause of newonset seizure in adults. More than 50,000 deaths per year are linked to NCC, and many more working-age patients develop serious neurologic sequelae. Although NCC is typically considered a public health problem in populations of developing countries, the progressive increase in immigration from

Fig. 77.1â•… World map showing where cysticercosis is endemic.

630

endemic to nonendemic regions has contributed to a substantial increase in its incidence in developed countries. Almost 90% of NCC cases diagnosed in the United States and Europe are in Latin American immigrants (Fig. 77.1).1,2 The unpredictable host reaction to the cysticercoid, as well as the wide range of nervous system (NS) injuries it can cause, makes NCC an intriguing disease that currently accounts for much research, especially in developing countries.2

77.1.1╇Etiopathogenesis Taenia solium has a complex life cycle that involves two hosts. Humans are the only definitive hosts for the adult cestode (worm), whereas pigs and humans are intermediate hosts for the larval or

77 â•… Cysticercosis cysticercoid stage. The adult T. solium dwells in the small intestine of humans, where it adheres to the intestinal wall. Each day, T. solium adults discard a small amount of fertilized proglottids into human feces. Each proglottid contains thousands of eggs that are capable of infecting their hosts and can survive in harsh environments. In places where there is deficient disposal of human feces, pigs feed on and ingest T. solium eggs. Once the eggs reach the intestine, pancreatic enzymes and bile degrade the eggs’ outer layer, releasing oncospheres that can cross the intestinal wall and reach the bloodstream. The oncospheres are then able to reach different host tissues, where the embryos develop into the larval stage (cysticercoids). In these cases, pigs act as the intermediate hosts.1 Human consumption of infected pork that has been inappropriately cooked results in the transmission of the cysticercoid into the small intestine. There, bile and digestive enzymes cause the intussusception of the cysticercoid scolex and its adhesion to the intestinal wall. Afterward, the proglottids begin to multiply and develop into cestodes. After approximately 4 months, the cestodes can pass to the feces as a mature proglottid. Humans can also act as intermediate hosts for T. solium after direct con-

sumption of its eggs, resulting in the development of cysticercoids. Thus, the two main ways in which humans can acquire cysticercosis are the consumption of food contaminated with T. solium eggs and the fecal– oral route in individuals with the intestinal cestode (Fig.€77.2).1 Recent epidemiological studies conclude that human cysticercosis must be considered a disease that is mostly transmitted in a person-to-person fashion, with the infected pig playing a role in perpetuating the infection.2,3 The cysticercoid has two main parts: the vesicular wall and the scolex. After the cysticercoid comes into the NS, it enters a vesicular (viable) stage, where it has a translucent membrane, clear vesicular fluid, and a scolex. The cysticercoid can remain viable for many years, or it can be either degraded or calcified as a result of an immunological attack by the host. During the first stage of the involution, also known as the colloidal stage, the vesicular fluid turns cloudy, and the scolex shows signs of vitreous degradation. Afterward, the cyst wall thickens, and the scolex turns into mineralized granules. The cysticercoid is no longer viable during this granular stage. Finally, the parasite remnants appear as a mineralized nodule (calcified stage).2,4

Fig. 77.2â•… Life cycle of Taenia solium showing the normal cycle of transmission―in which humans act as definitive hosts and pigs act as intermediate hosts―and the aberrant cycle of transmission, in which humans become intermediate hosts and develop cysticercosis.

631

632 Section VII.Aâ•… Cranial The vesicular cysticercoid causes minimal inflammation to the surrounding tissues, as opposed to the colloidal cysticercoid, which is commonly surrounded by a collagenous capsule that causes a monocytic inflammatory response. The surrounding cerebral parenchyma exhibits signs of gliosis, microglia proliferation, edema, neuronal degeneration, and perivascular infiltration of lymphocytes. The edema decreases when the parasite enters the granular and calcified stages. However, the changes in the surrounding tissues due to astrocytic activity become more intense, and multinucleated giant cells appear.2 The meningeal cysticercoid precipitates a severe inflammatory response in the subarachnoid space, forming an exudate consisting of collagen fibers, lymphocytes, multinucleated giant cells, eosinophils, and a hyalinized parasite membrane, which leads to abnormal thickening of the leptomeninges. This inflammation can disseminate and cause damage to the optic chiasm and cranial nerves as well as occlude the arteries of the circle of Willis, thus causing cerebral infarctions.5 The Luschka and Magendie foramina can also be occluded, resulting in obstructive hydrocephalus. The ependymal epithelium damaged by inflammation can protrude into the ventricular cavities and block the flow of cerebrospinal fluid (CSF), especially in the foramen of Monro or the cerebral aqueduct.2 The cysticercoid has several antigens that stimulate the production of specific antibodies. Some of these antigens play an important role in the mechanisms by which the cysticercoid evades the immune response. The most important of these antigens seems to be the B antigen, which is composed of collagen and can bind to C1q, thus inhibiting the classical pathway of complement activation. Similarly, several studies suggest that patients with NCC present with cellular dysfunction of the immune system.1,6

Focal neurologic signs, which vary depending on the number and localization of lesions, have been observed in more than 20% of NCC patients. The most common perturbations occur in the pyramidal tracts. However, signs like sensitivity alteration, involuntary movements, speech alterations, and brainstem functions have also been described.2 Disease progression is usually subacute or chronic with these manifestations, often resembling the progression of a brain tumor. Frequently, the symptoms are observed in patients with large subarachnoid cysts that compress the cerebral parenchyma. Ischemic syndromes occur in approximately 3% of NCC patients and usually affect the posterior limb of the internal capsule, the radiate crown, or the brainstem.2,5 Some NCC patients develop intracranial hypertension that may be associated with convulsive crises or focal deficits. Intracranial hypertension is usually caused by hydrocephalus, which in turn is caused by arachnoiditis, granular ependymitis, or ventricular cysts. Intracranial hypertension can also be caused by cysticercoid encephalitis, a severe form of NCC that is caused by a massive infection of the cerebral parenchyma and leads to a severe immune reaction. This is more common in children and young women and is characterized by a decrease in conscious state, convulsive crises, a decrease in visual acuity, cluster headaches, vomiting, and papilledema.2 Other clinical manifestations are psychiatric alterations, including dementias. Patients with intrasellar lesions can present with visual or endocrinological alterations. Spinal arachnoiditis is characterized by radicular pain, subacute onset of limb weakness, spinal cord cysts, and sensory and motor deficits according to the level of the lesion.2,8 Intraocular cysticercoids cause progressive deficit of visual acuity and/or visual field defects.1

77.1.2╇ Clinical Manifestations

Throughout the years, several diagnostic tools have been used to detect cysticercoids, including fecal, serum, and CSF tests. The frequency with which T. solium eggs are detected in the feces of NCC patients varies according to the severity of the infection. The eggs are not easily detected and can go unnoticed if only a stool test is conducted. Thus it is advisable to conduct serial passages of the patient’s stool, as well as of family members, to identify hosts. Two recent assays have aided in the detection of human taeniasis: ELISA for the detection of coproantigens and DNA hybridization for the detection of eggs.1 Abnormal cytochemistry results in the CSF have been detected in more than 80% of NCC patients.

The pleomorphic clinical manifestations of NCC are linked to the individual differences in each patient, the number and localization of CNS lesions, and the variable disease severity. Seizure (tonic-clonic) is the most common clinical manifestation, occurring in more than 70% of cases. However, on occasion, some patients present with complex partial crises.1,7 The convulsive crises are more common in patients with parenchymal NCC than in patients with subarachnoid or ventricular lesions. The calcifications that were previously considered inert lesions have now been shown to also cause convulsive crises.2

77.1.3╇Diagnosis

77 â•… Cysticercosis However, a normal CSF does not exclude the possibility of NCC. The most consistent finding is mononuclear pleocytosis, which rarely exceeds 300/mm3 and commonly exhibits elevated protein levels. Usually, the glucose levels in the CSF are normal, although low glucose levels have been associated with a negative prognosis.1 The complement fixation test in the CSF is positive in up to 83% of patients with inflammatory changes. However, it is only positive in 22% of patients with parenchymal cysticercosis with normal CSF cytochemistry. Similarly, this method is also less sensitive in ventricular NCC than in subarachnoid NCC.1 ELISA is more reliable when performed in the CSF than in the serum. In the CSF, the test has 87% sensitivity and 95% specificity, although its performance depends on the presence of disease activity.1 In the last few years, the emergence of neuroimaging has aided in more precise diagnoses of NCC, with computed tomography (CT) and magnetic resonance imaging (MRI) studies shedding more light on the number and topography of lesions. CT and MRI can identify a vesicular cysticercoid as a small, round cyst that is well defined from the surrounding parenchyma. The internal scolex is usually visible without any edema or contrast enhancement. Colloidal and granular cysticercoids appear as ill-defined lesions surrounded by edema and contrast ring enhancement. A calcified cysticercoid normally appears as a small, hyperdense nodule without any perilesional edema or contrast enhancement. The most common finding in patients with subarachnoid NCC is the presence of hydrocephalus and, occasionally, abnormal leptomeningeal enhancement. The cystic lesions in the CSF cisterns usually have a multilobular appearance when imaged with CT. Ventricular cysts appear as hypodense lesions distorting the ventricular system. These lesions cause asymmetric hydrocephalus. In contrast, MRI enables better visualization of intraventricular cysts and can detect several internal cysts due to the different signal properties of the cyst liquid and the CSF.2 Retrospective observations by Citow et al reported superiority of MRI over CT scans for the diagnosis of intraventricular NCC.9 Intramedullary cysticercoids appear as rounded lesions with MRI and can have a hyperintense eccentric nodule that represents the scolex. Usually, the cyst has peripheral contrast reinforcement.2 MRI is superior to CT for identifying skull base lesions, as well as for intraventricular, brainstem, or spinal cysts. However, a CT scan is better to distinguish calcifications. For inconclusive cases, MRI must be done when the CT fails to provide enough information.1

77.1.4╇ Medical Treatment Treatment options depend on cyst morphology, host immune response against the parasite, and lesions’ localization. Treatment includes a combination of antiparasitic and nonantiparasitic drugs, as well as surgery.1 Praziquantel has been used for almost two decades for the treatment of NCC. Authors of different studies have reported that praziquantel effectively eliminates 70% of parenchymal NCC after a 15-day treatment with 50 mg/kg/daily administered every 8 hours. It has been suggested that exposure of the cysticercoid to high doses of the drug for more than 6 hours, by administering individual doses of 25 to 30 mg/kg at 2-hour intervals, can be enough to destroy the parasite. However, this treatment option is recommended for cases where only one parenchymal cyst exists.1,2,10 Albendazole is another antiparasitic drug that is used to treat NCC. Originally, 30-day treatments with 15 mg/kg/day were administered. However, it has been shown that treatment with the same dose for only 1 week is equally effective. Albendazole destroys 75 to 90% of parenchymal NCC and has been demonstrated in several comparative studies to be superior to praziquantel. Furthermore, it also destroys subarachnoid and ventricular cysts, given its superior penetration into the CSF.1,11 The antiparasitic treatment not only destroys the cysticercoid but has also been determined to improve the symptomatology. A recent meta-analysis of randomized studies assessed the effect of antiparasitic drugs on the clinical course and neuroimaging studies of NCC patients. The main conclusion was that antiparasitic therapy improves cysticercoid clearance during its vesicular and colloidal stages. Antiparasitic therapy also decreases the risk of recurring convulsive crises in patients with colloidal cysticercoids and generalized crises in patients with ventricular cysticercoids.2,12 Some types of NCC must not be treated with antiparasitic drugs because they can worsen the intracranial hypertension symptoms in patients with cysticercoid encephalitis. Patients with hydrocephalus and parenchymal cysts must use antiparasitic drugs until the hydrocephalus is resolved, with further shunting to avoid an increase in intracranial pressure. Antiparasitic drugs must be used with caution in patients with giant subarachnoid cysts. As a result of the destruction of the parasite, the inflammatory response of the host can occlude the leptomeningeal vessels surrounding the cyst. Therefore, the simultaneous use of corticosteroids is necessary to avoid cerebral infarctions. The most commonly used corticosteroid is intravenous (IV) dexamethasone at a 30-mg/day dose. Dexamethasone can be subsequently replaced by prednisone

633

634 Section VII.Aâ•… Cranial at a 50-mg/day dose. Patients presenting exclusively with calcifications must not receive antiparasitic drugs because these calcifications represent parasites that are already dead.1,2 In general, first-line antiepileptic drugs are sufficient for controlling convulsive crises secondary to NCC. However, there is evidence for relapse in convulsive crises in up to 50% of patients who had been successfully treated for parenchymal cysts but were subsequently removed from antiepileptic drugs.2,13 At medical centers with ample experience in NCC treatment, excision of the cysticercoid is reserved for cases where medical treatment has failed. Hydrocephalus secondary to arachnoiditis is treated with a permanent ventricular shunt. However, there is a high incidence of secondary dysfunction due to the high cell and protein concentrations in the CSF. The ventricular cysts must be either excised or endo-

scopically aspirated. There is a possibility that the cyst could migrate between the diagnosis and treatment times. Thus a new imaging study (CT or MRI) must be conducted prior to any surgical procedure.1 A permanent shunt may not be necessary in the absence of ependymitis. Citow and associates suggested that a permanent shunt system is necessary if intraventricular lesions are present in imaging studies with a contrast-enhancing cyst. Craniotomy must be reserved for only patients with mass effect.9 In a study that included 160 surgically treated NCC patients, Benedicto et al concluded that the longterm prognosis for patients who underwent surgery was poor. Furthermore, age younger than 40 years was a poor prognostic indicator when the cysts were localized in the basal cisterns. A treatment guide for the management of NCC has been proposed (Fig.€77.3).14

a

b

Fig. 77.3â•… (a) Treatment algorithm of patients with parenchymal and cisternal neurocysticercosis (NCC), (b) as well as intraventricular cysticercosis and hydrocephalus. CT, computed tomography; ICP, intracranial pressure; VPS, ventriculoperitoneal shunt.

77 â•… Cysticercosis

77.2╇ Operative Detail and Preparation 77.2.1╇ Endoscopic Treatment of Neurocysticercosis Endoscopic treatment of NCC is reserved for the intraventricular cyst, as well as some subarachnoid forms. Planning of the procedure begins once the cyst location has been identified, utilizing preoperative MRI and, if available, the neuronavigation systems. In the authors’ practice, NCC is divided according to its localization, either in the lateral ventricles, the third ventricle, or the fourth ventricle. For subarachnoid NCC, lesions can be localized to the quadrigeminal cistern (and can protrude into the third ventricle), the interpeduncular cistern, and the sylvian cisterns. The procedures for each of these sites follow.

Surgical Equipment The treatment is performed using a rigid endoscope (Richard Wolf GmbH, Knittlingen, Germany) with an optical channel, work channel, and two irrigationsuction channels (Fig. 77.4). It can also be used to introduce a second instrument. Additional instruments include biopsy tweezers, a bipolar electrode, and a no. 3 Fogarty catheter. Continuous irrigation is used with warm (patient temperature) isotonic solution with antibiotic.

Lateral Ventricles Typically, cysts are localized to the anterior horn of the lateral ventricle. Patients lie on their backs, with their heads in a neutral position on the Mayfield headrest. A neuronavigation system is used and a conventional frontal burr hole is performed. This burr hole is usually 5 cm in front of the coronal suture and 3 cm outside of the median line. The rigid endoscope is introduced until the lateral ventricle is reached. Once inside the ventricle and when regular anatomical landmarks have been localized, irrigation with isotonic solution is started and navigation inside the ventricle begins. When the cyst or multiple cysts are localized, it is very important to determine whether they are freely floating inside the ventricle or whether they are attached to the ventricular wall. If they are floating in the ventricle, biopsy tweezers are introduced, and the cysts are grabbed by the scolex to extract them. It is possible that the cyst might break during this procedure, which is why constant irrigation with isotonic solution is necessary to reduce inflammatory reaction due to spillage of the cyst contents into the ependyma. If the cysts are attached to the ventricular wall, it is crucial to very carefully detach them using the bipolar electrode because the cysts are sometimes intimately related to either vascular structures or the choroid plexus, and heavy bleeding can occur upon extraction in these cases. Once the cyst has been detached from the ventricular wall, it can be extracted in the aforementioned fashion. It is essential to note that, depending on the patient’s position, the cyst can migrate all the way to the occipital branch of the lateral ventricle. Thus it is important to endoscopically inspect the entire ventricular body to detect any cyst migration. Once hemostasis has been verified and no active hemorrhages are evident, the endoscope is removed, and a Surgicel (Johnson & Johnson, New Brunswick, NJ, USA) plug is placed in the corticotomy (Fig. 77.5).

Third Ventricle

Fig. 77.4â•… Rigid endoscope (Richard Wolf GmbH, Knittlingen, Germany) with an optical channel, a working channel, and two irrigation-suction channels.

The cysts are accessible with a precoronal burr hole, similar to a ventriculostomy. Again, patients lie on their backs, with their heads in a neutral position on the Mayfield headrest. A burr hole is created 1 cm in front of the coronal suture and 3 cm outside of the median line. The endoscope is introduced until the ventricle is reached. Once this

635

636 Section VII.Aâ•… Cranial a

c

b

Fig. 77.5â•… (a) Sagittal view of a contrast magnetic resonance imaging (MRI) with the presence of intraventricular cysts in the frontal horn. (b) Axial view of a fluid-attenuated inversion recovery (FLAIR) MRI with the presence of an intraventricular cyst in the frontal horn. (c) Postoperative sagittal view of a T1 FLAIR MRI with the absence of an intraventricular cyst in the frontal horn.

is achieved, irrigation is connected, and the endoscope is moved further into the third ventricle via the foramen of Monro. After the cyst is localized, it must be verified whether it is floating or adheres to the wall of the third ventricle. The cysts are removed by grabbing them with biopsy tweezers, following the same principle used for lateral ventricle cysts (Fig. 77.6).

Fourth Ventricle Treatment of these cysts requires an experienced surgeon. The lesions are approached by creating a burr hole 5 cm in front of the coronal suture and 2 cm outside of the median line. The endoscope is introduced until the lateral ventricle is reached. Once inside the ventricle, the foramen of Monro is localized, and the route proceeds toward the third ventricle. The planned trajectory allows visualization of the sylvian aqueduct, and it is usually possible to visualize the cyst through the aqueduct. The biopsy tweezers are initially introduced

Fig. 77.6â•… Axial view of a fluid-attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) with the presence of multiple intraventricular cysts, with a large cyst in the third ventricle (arrow).

77 â•… Cysticercosis

Fig. 77.7â•… Sagittal view of T1 magnetic resonance imaging (MRI) with fourth ventricular entrapment by cysts and compression of brainstem.

through the aqueduct, and the cyst is removed. However, if this is not possible, the endoscope is carefully introduced all the way to the fourth ventricle without damaging the aqueduct walls. Generally, the lesions break, and it is necessary to remove all fragments and perform continuous irrigation to avoid inflammation of the ependyma due to spilling of the cyst contents. Once the procedure is completed, the endoscope is removed, and a Surgicel (Johnson & Johnson) plug is placed in the corticotomy (Fig. 77.7).

Interpeduncular Cistern Cysts in the interpeduncular cistern are removed by creating a burr hole 1 cm in front of the coronal suture and 1.5 cm outside of the median line. The endoscope is introduced until the anterior horn is reached (Fig. 77.8). Once there, the endoscope is advanced all the way to the anterior third of the third ventricle, and the bottom of the premammillary membrane is identified. A third ventriculostomy is performed in the usual fashion. During the ventriculostomy, the cysticercoid cysts begin to protrude through the stoma and are extracted using biopsy tweezers. After this is done, the endoscope is introduced through the stoma, and the interpeduncular and prepontine cisterns are inspected. If cysts remain, they are extracted using biopsy tweezers. Prior to their extraction, it is important to verify that the cysts do not adhere to the neurovascular structures of the cisterns.

Fig. 77.8â•… Axial view of a fluid-attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) with the presence of multiple interpeduncular cysts.

If they do, the cysts must be carefully detached using a bipolar coagulator. Some membranes can remain attached without causing a recurrence of the cysts. When the task is completed, the endoscope is removed, and the corticotomy is sealed in the usual fashion.

Sylvian Fissure Patients lie on their stomachs under skeletal anchoring. Their heads are extended 15 degrees, rotated 15 degrees toward the side opposite the lesion, and flexed laterally by 10 degrees. The initial incision is made lateral to the superior orbital fissure, above the eyebrow, and following the orbital rim. The subcutaneous tissue is dissected upward toward the frontal region, the skin flap is retracted, and the aponeurosis of the occipitofrontal, orbicular, and temporal muscles is exposed. The frontoparallel muscle to the glabellar muscle is cut using a monopolar electrode, and the temporal muscle is detached and laterally moved to expose the temporal line.

637

638 Section VII.Aâ•… Cranial The temporal and frontal muscles are retracted to expose the superior orbital bone surface. The frontal and orbital muscles need to be gently retracted toward the orbital rim to avoid periorbital hematomas. A frontobasal burr hole, parallel to the temporal line and the frontal base level, is made using high-speed milling. The dura mater is detached, and a craniotome is used to perform a linear cut that goes from the lateral to medial burr hole until the glabella, always careful to avoid opening the frontal paranasal sinus. Afterward, a C-shaped cut is made from the burr hole up to the medial edge of the previously generated linear cut, leaving a 15- to 20-mm medialto-lateral bone flap and a 10- to 15-mm rostrocaudal bone flap. It is imperative to mill the inside fissure of the brow bone to enable a better visualization angle. It is important to drill a portion of the orbital roof. The dural opening is performed afterward in a curved-line fashion, with the base toward the orbit, and is then retracted. Subsequently, it is essential to drain the CSF by opening the carotid and chiasmatic cisterns. Then, the no. 0 endoscope is introduced to continue with the dissection of the arachnoid membranes, and the supraclinoid carotid artery and ipsilateral optical nerve are visualized. Dissection of the carotid bifurcation is continued under endoscopic visualization by following the path of the middle cerebral artery. The sylvian fissure is dissected until the cysticercoid cyst is localized. Subsequently, the fissure is punctured, and the liquid is drained before the cyst is removed using tweezers. The cerebral parenchyma is dissected, and attempts are made to remove it in one piece. Endoscopic visualization is used to verify that there is no residual cyst and that there is adequate hemostasis. Afterward, the endoscope is removed, and the region is irrigated with a solution at body temperature to replace the drained CSF. The dura mater is closed using a continuous suture. The bone flap is replanted using absorbable cranial fixers to cover the burr hole for better aesthetic results. The muscle and subcutaneous cellular tissues are closed using separate stitching, and the skin is closed using a subcuticular suture. It is not necessary to leave a drainage tube (Fig. 77.9).

Fig. 77.9â•… Axial view of a fluid-attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) with the presence of multiple cysts, with particular interest in the sylvian fissure (black arrow).

77.3╇ Outcome and Postoperative Course Neuroendoscopy has proven to be a safe and useful tool to provide relief for intraventricular lesions, particularly NCC. With neuronavigation, most lesions can be localized with high precision and therefore completely removed. The mortality rate for this surgical technique is nearly 0%. When an NCC cyst breaks during extraction, mild cerebritis will occur; nevertheless, it can be buffered with abundant irrigation and a brief course of high-dose corticosteroids.

77 â•… Cysticercosis

References ╇1. Sotelo

J, Del Brutto OH. Review of neurocysticercosis. Neurosurg Focus 2002;12(6):e1 ╇2. Del Brutto OH. Neurocysticercosis: a review. ScientificWorldJournal 2012;2012:159821 ╇3. Gonzalez AE, Lopez-Urbina T, Tsang B, et al; Cysticercosis Working Group in Peru. Transmission dynamics of Taenia solium and potential for pig-to-pig transmission. Parasitol Int 2006;55(Suppl):S131–S135 ╇4. Escobar A, Weidenheim KM. The pathology of neurocysticercosis. In: Singh G, Prabhakar S, eds. Taenia solium Cysticercosis. From Basic to Clinical Science. Oxon, UK: CAB International; 2002: 289–305 ╇5. Del Brutto OH. Stroke and vasculitis in patients with cysticercosis. In: Caplan LR, ed. Uncommon Causes of Stroke. New York, NY: Cambridge University Press; 2008: 53–58 ╇6. Del Brutto OH, Sotelo J, Román GC. Neurocysticercosis: A Clinical Handbook. Lisse, the Netherlands: Swets & Zeitlinger; 1998 ╇7. Del Brutto OH, Santibañez R, Noboa CA, Aguirre R, Díaz E, Alarcón TA. Epilepsy due to neurocysticercosis: analysis of 203 patients. Neurology 1992;42(2):389–392

╇8. Alsina GA, Johnson JP, McBride DQ, Rhoten PR, Mehring-

er CM, Stokes JK. Spinal neurocysticercosis. Neurosurg Focus 2002;12(6):e8 ╇9. Citow SJ, Johnson J, McBride DQ, Ammirati M. Imaging features and surgery-related outcomes in intraventricular neurocysticercosis. Neurosurg Focus 2002;12(6):1–8 10. Del Brutto OH, Campos X, Sánchez J, Mosquera A. Single-day praziquantel versus 1-week albendazole for neurocysticercosis. Neurology 1999;52(5):1079–1081 11. Sotelo J, del Brutto OH, Penagos P, et al. Comparison of therapeutic regimen of anticysticercal drugs for parenchymal brain cysticercosis. J Neurol 1990;237(2):69–72 12. Del Brutto OH, Roos KL, Coffey CS, García HH. Meta-analysis: cysticidal drugs for neurocysticercosis: albendazole and praziquantel. Ann Intern Med 2006;145(1):43–51 13. Del Brutto OH. Prognostic factors for seizure recurrence after withdrawal of antiepileptic drugs in patients with neurocysticercosis. Neurology 1994;44(9):1706–1709 14. Colli BO, Carlotti CG Jr, Assirati JA Jr, Machado HR, Valença M, Amato MC. Surgical treatment of cerebral cysticercosis: long-term results and prognostic factors. Neurosurg Focus 2002;12(6):e3

639

Section VII.B Spinal

78

Evaluation and Management of Pediatric Spinal Infections Jonathan Yun, Brian J. A. Gill, and Richard C. E. Anderson

78.1╇Background

78.1.1╇Indications/Goals

Infections of the pediatric spine are uncommon disorders that frequently present the physician with a diagnostic challenge, due to their often ambiguous clinical presentation. Historically, these infections were associated with high morbidity and mortality. However, as diagnostic and management capabilities have improved, prognosis has improved as well. Regardless, it is still critical to achieve rapid diagnosis and institution of appropriate antimicrobial agents, as well as surgical intervention if indicated. The clinical work-up must begin with a high degree of suspicion in order to achieve a prompt diagnosis and to prevent any of the disastrous sequelae of this disorder. The many ways to classify spinal infections include routes of infection―hematogenous spread, direct inoculation, or contiguous spread―and host response to the offending organism―typically either a pyogenic or granulomatous response. Most bacterial infections result in a pyogenic response. In the spine, pyogenic infections tend to involve either the intervertebral disk space (diskitis) or the vertebral body itself (vertebral osteomyelitis) and are often preceded by an extraspinal infection. Age-related differences in the vascular anatomy of the spine likely influence the type of pathology present. Granulomatous infections arise from fungi, certain bacteria, and, most commonly, tuberculosis. The accurate classification of the infectious agent, as well as location of the infectious process, allows for the best determination of therapeutic course. Regardless of the etiology or location of the disease, the goals of therapy in the setting of pediatric spinal infections should be eradicating the infection, relieving pain, preserving or restoring neurological function, minimizing deformity, and maintaining spinal stability.1 Nonoperative optimal antimicrobial therapy should be first-line, and surgical intervention reserved for failure of conservative treatment.

In all patients, the early initiation of optimal medical management of spinal infections with empiric antimicrobial administration is critical; this begins with an appropriate level of suspicion with the initial examination. Children with pyogenic diskitis between ages 3 to 5 years typically present with an irritable disposition, a limp, or refusal to bear weight on the lower extremities. These symptoms can progress and ultimately the patient becomes uncomfortable in all positions, with some relief when lying supine. Older children with isolated diskitis typically present with back pain, abdominal pain, and occasionally they may experience buttock and leg pain secondary to nerve root irritation.2 Physical examination may reveal focal tenderness to palpation over the involved region, paravertebral spasms, decreased range of motion in the spine, and hamstring tightness. A positive straight leg–raise test may be present.2,3 Vertebral osteomyelitis is rarely seen in children under age 3 years, with afflicted patients typically ranging from ages 6 to 12 years at the time of diagnosis. They often complain of a dull, constant back pain, are febrile, and appear more systemically ill on presentation. Involvement of the upper cervical spine commonly results in torticollis.2,3 Tuberculous spondylitis is a more indolent process. Presenting features include back pain, kyphotic deformation of the spine, and constitutional symptoms such as fever, night sweats, and weight loss. Given the subjective nature of the constitutional symptoms, most cases of spinal tuberculosis are diagnosed late in the disease course, with pronounced kyphotic deformity. Unfortunately, neurological deficits such as lower limb weakness and numbness (Pott paraplegia) are more frequent.4 Acute neurological compromise in patients with pediatric spinal infections may be secondary to vascular thrombosis, mechanical instability, or spinal cord compression caused by an epidural abscess,

643

644 Section VII.Bâ•… Spinal granulation, or other inflammatory tissue. Several years after the initial lesion has healed, late-onset paraplegia may occur due to stretching of the spinal cord over a resultant progressive deformity.4,5 Surgery is generally reserved for the settings of antimicrobial treatment failure and acute neurological decline. The indications or goals of surgical intervention for spinal infections are threefold: (1) identification of unknown causative organism, (2) decompression of neural elements, and/or (3) stabilization of the spine.

78.1.1╇ Alternate Procedures When treatment fails despite empiric antibiotic administration, identification of the unknown causative organism through direct sampling can help guide more effective antibiotic therapy. In some cases, a computed tomography (CT)-guided biopsy may be obtained to determine a definitive diagnosis and sensitivities before initiating medical management. However, biopsies are most commonly reserved for cases of pyogenic diskitis or vertebral osteomyelitis that are unresponsive to empiric intravenous (IV) antibiotics. If the sample obtained proves to be nondiagnostic, then open surgical biopsy may be pursued in order to isolate and appropriately treat the pathogen responsible for the underlying infection, and rule out other neoplastic, fungal, or granulomatous disease.2 Reported positive rates of culture following disk biopsy for suspected pyogenic spinal infection range from 0 to 91%. Due to the inconsistent success rate, the increased risk associated with the procedure, as well as a need for sedation, biopsy is not routinely recommended in the evaluation of pediatric patients with suspected uncomplicated spinal infections.6 Although culturing of Mycobacterium tuberculosis is slow and only yields positive results in 50% of cases, polymerase chain reaction (PCR) analysis may facilitate rapid and accurate diagnosis. Also, pathological examination may reveal the presence of caseating granulomas or acid-fast bacilli, which are highly suggestive of tuberculous infection.

78.2╇ Operative Detail and Preparation 78.2.1╇ Preoperative Planning and Special Equipment Imaging Prior to any interventional procedure, it is critical to obtain adequate imaging to determine the location, extent of bony involvement, and associated deformi-

ties of the infectious process. Plain anteroposterior and lateral radiographs are the best initial imaging study because they allow for visualization of gross vertebral abnormalities, bony destruction, and spinal alignment. However, abnormalities may not appear for many types of infections, which makes plain radiographs an unreliable tool. Magnetic resonance imaging (MRI) is the imaging modality of choice for the evaluation of patients with suspected spinal infections. Typical findings on MRI include loss of disk height, abnormal disk signal, and increased signal in the vertebral end plates on T2-weighted imaging. T1-weighted MRI sequences with administration of contrast may demonstrate abnormal enhancement of the infectious nidus (Fig.€78.1 and Fig.€78.2).2,3,7 Although minimized due to radiation concerns in pediatric patients, CT scans are often indicated to assess bony involvement and for surgical planning if instrumentation is planned.2,3,7 Technetium 99m bone scintigraphy has a sensitivity of up to 90%, and increased marker uptake in the involved motion segment may be apparent as early as 3 to 5 days following the onset of symptoms, making it a good option for patients with high clinical suspicion of spinal infection in the setting of normal radiographs. However, the specificity of this procedure is too low for definitive diagnoses and surgical planning.2

78.2.2╇ Expert Suggestions/Comments There is no consensus regarding the best surgical approach for spinal infections in the pediatric population. The majority of initial interventions for infections of the pediatric spine are from the posterior approach. Simple posterior decompression and débridement are the most commonly used approaches for isolated pyogenic or epidural collections that cause acute neurologic compromise. Posterior instrumentation and fusion may be required if spinal instability or deformity is present. In cases with significant involvement of the vertebral body or anterior structures of the spinal column, anterior approaches with instrumentation and fusion may be necessary. The use of instrumentation in the setting of spinal infection has been controversial, due to the thought that the metallic surfaces would act as an infectious nidus. However, single-stage operative débridement and instrumentation have been increasingly utilized, with minimal recurrence of infection or reoperations after prolonged follow-up.8,9

78.2.3╇ Key Steps of the Procedure/ Operative Nuances • Most débridement, decompression, and stabilization procedures for infections of the pediatric thoracolumbar spine can be done via the posterior approach.

78 â•… Evaluation and Management of Pediatric Spinal Infections a

b

c

Fig. 78.1â•… Pyogenic spondylitis. (a) Increased vertebral body and disk T2-weighted (T2W) signal with epidural extension and destruction of the cortical margins evidence of infection. (b) Signal of the infected vertebral bodies becomes almost similar to the normal ones after (c) enhancement on postcontrast T1-weighted (T1W) image. The borders of the vertebral bodies and the disk with epidural extension are clearly defined on postcontrast image. (From Tali ET. Spinal infections. Eur J Radiol 2004;50(2): 120–133. Reprinted with permission.)

a

b

c

Fig. 78.2â•… Tuberculous spondylitis. (a) Precontrast T1-weighted (T1W) image in the sagittal plane, (b) postcontrast T1W imaging in the sagittal plane, and (c) in the coronal planes shows vertebral body height reduction in L1 vertebra, irregularity and destruction of vertebral end plates, irregular contrast enhancement, and paravertebral and epidural extension of the infectious process. (From Tali ET. Spinal infections. Eur J Radiol 2004;50(2): 120–133. Reprinted with permission.)

645

646 Section VII.Bâ•… Spinal

78.3╇ Outcomes and Postoperative Course

• Complex infections of the cervical spine with significant bone destruction and deformity may require circumferential decompression and fusion. • Meticulous culturing should be undertaken of all suspicious collections, including stains and cultures for anaerobes, aerobes, fungi, and acid-fast bacilli. • In children with extensive epidural collections, skip laminectomies, and sublaminar irrigation, a red, rubber catheter may be used to minimize the chances of spinal instability (Fig. 78.3). • In cases of infection and spinal instability, it is better to have a stable infected spine than an unstable infected spine.

78.3.1╇ Postoperative Considerations Postoperatively, patients should be continued on a course of broad-spectrum antimicrobials until intraoperative cultures allow for tailored selection. This should be done in conjunction with pediatric infectious disease specialists, who also help manage the antibiotic course and help determine adequate response to therapies. These typically include measurement of serial blood inflammatory markers (e.g., white blood cells [WBC], erythrocyte sedimentation rate [ESR], and C-reactive protein [CRP]) and followup imaging studies.

a

b

c

Fig. 78.3â•… (a) Axial T1-weighted (T1W) sequence with contrast. (b) Sagittal T1W sequence with contrast of cervicothoracic spine. (c) Sagittal T1W sequence with contrast of lumbar-sacral spine. In this case, a red, rubber catheter was used between skip laminectomies to irrigate and clear the epidural space.

78 â•… Evaluation and Management of Pediatric Spinal Infections

References ╇1. Tay BK, Deckey J, Hu SS. Spinal infections. J Am Acad Or-

thop Surg 2002;10(3):188–197 M, Carrol CL, Baker CJ. Discitis and vertebral osteomyelitis in children: an 18-year review. Pediatrics 2000;105(6):1299–1304 ╇3. Early SD, Kay RM, Tolo VT. Childhood diskitis. J Am Acad Orthop Surg 2003;11(6):413–420 ╇4. Eisen S, Honywood L, Shingadia D, Novelli V. Spinal tuberculosis in children. Arch Dis Child 2012;97(8):724–729 ╇5. Bailey HL, Gabriel M, Hodgson AR, Shin JS. Tuberculosis of the spine in children. Operative findings and results in one hundred consecutive patients treated by removal ╇2. Fernandez

of the lesion and anterior grafting. J Bone Joint Surg Am 1972;54(8):1633–1657 ╇6. Kayser R, Mahlfeld K, Greulich M, Grasshoff H. Spondylodiscitis in childhood: results of a long-term study. Spine 2005;30(3):318–323 ╇7. Mahboubi S, Morris MC. Imaging of spinal infections in children. Radiol Clin North Am 2001;39(2):215–222 ╇8. Lan X, Xu JZ, Luo F, Liu XM, Ge BF. [One-stage débridement and bone grafting with internal fixation via posterior approach for treatment of children thoracic spine tuberculosis]. Zhongguo Gu Shang 2013;26(4):320–323 ╇9. Rezai AR, Woo HH, Errico TJ, Cooper PR. Contemporary management of spinal osteomyelitis. Neurosurgery 1999;44(5):1018–1025, discussion 1025–1026

647

Section VIII

Epilepsy and Functional Disorders Section Editor: Matthew D. Smyth

Functional neurosurgical procedures have potentially, and significantly, greater impact on children than adults. Earlier interventions can substantially alter developmental trajectory, including positive influences on cognitive function, emotional wellbeing, and physical development. When combined with longer residual life spans of younger patients, the total quality-adjusted-life years make invasive neurosurgical procedures in children more accepted by the medical community and families. As long as our neurosurgical community continues to refine procedures to minimize morbidity, maximize function, and clearly document outcomes, the field of pediatric functional neurosurgery will continue to evolve and expand for the betterment of these children. The chapters in this section address the majority of commonly performed procedures used for the management of epilepsy and movement disorders in children. Introductory chapters for classification and evaluation of epilepsy and movement disorders are followed by up-to-date chapters that emphasize surgical technique and outcomes, with highly instructive videos by recognized masters in the field. Advances in functional imaging and seizure localization that are combined with newer, safer techniques are opening doors for many children

and families previously not considered for intervention. It remains to be seen whether the expanding utilization of recently introduced techniques—such as stereo-EEG, robotics, intraoperative MRI, neuromodulation and responsive neurostimulation, and laser-ablation—will improve outcomes and minimize morbidity beyond the more traditional techniques described in this section. Future editions of this textbook may very well include more expanded descriptions of these newer techniques. But it certainly seems true now that a larger number of children could benefit from more, and earlier, functional neurosurgical procedures than are currently being referred to epilepsy centers and multidisciplinary movement disorders clinics. Each of the authors in this section brings substantial experience, insights, and wisdom to his or her subject. The structure of each chapter provides something for everyone, from the casually interested student, to the experienced senior neurosurgeon already performing these procedures. The authors’ approaches to preoperative planning, operative setup, key steps and pearls, and hazards and pitfalls are followed by a discussion of postoperative management and complications, with the goal of imparting practical, applicable knowledge to improve the clinical practice of the reader.

79

Epilepsy Classification, Evaluation, and Imaging Iván Sánchez Fernández and Tobias Loddenkemper

79.1╇Background Approximately 60% of all patients with epilepsy suffer from focal epilepsy syndromes, and in up to 30% of these patients the condition is not adequately controlled with antiepileptic drugs.1 Approximately 0.9 per 1,000 persons in the general population have uncontrolled epilepsy and these patients could potentially benefit from epilepsy surgery.2 Epilepsy surgery is effective in controlling seizures, and this effectiveness persists over time, with rates of longterm seizure freedom ranging from approximately 25% in frontal lobe epilepsy, to 65% in temporal lobe epilepsy,3 and up to 80% seizure reduction in patients undergoing hemispherectomy. Regarding the underlying pathology, patients with tumors and hippocampal sclerosis tend to do better than those with malformations of cortical development.4 Improved outcomes have been noted in patients with mesial temporal sclerosis, presence of structural abnormalities on magnetic resonance imaging (MRI), concordant MRI and electroencephalogram (EEG) findings, and complete resection of the epileptogenic lesion― particularly when there is a malformation of cortical development.4 The overall mortality of epilepsy surgery is approximately 1%,4 and this must be weighed against the risk of sudden death in epilepsy, with rates up to 9 in 1,000 per year in patients with uncontrolled seizures.5 In children, earlier surgery may also provide a prolonged window of developmental plasticity after epilepsy resolution, and may therefore improve cognitive outcome in epilepsy surgery candidates.6 In addition, epilepsy surgery is more costeffective than not performing surgery because it is less expensive than antiepileptic drug management and improves survival and quality of life.7 Despite the fact that epilepsy surgery for refractory epilepsy is one of the most effective interventions in medicine, it is largely underutilized, with marked delays from

onset of refractoriness until referral for presurgical evaluation.7 The consideration of an epileptic patient for resective surgery begins with a stepwise series of questions that are typically addressed before any therapeutic decision is made: 1. Are the events epileptic seizures? 2. Are seizures refractory to antiepileptic drug management? 3. Where do the seizures originate? 4. What is the etiology of the seizures?4

79.2╇ The Differential Diagnosis of Epileptic Seizures versus Nonepileptic Paroxysmal Events Nonepileptic paroxysmal events are more frequent than epileptic seizures, and ruling nonepileptic events out is critical prior to considering epilepsy surgery. A detailed history is often all that is needed to differentiate nonepileptic paroxysmal events, such as syncope, tics, or migraines, from epileptic seizures. Individual signs or symptoms can be shared between nonepileptic paroxysmal events and epileptic seizures; however, the constellation of clinical features as a whole and their evolution over time help differentiate epileptic and nonepileptic events in most cases (Table 79.1).4 Psychogenic nonepileptic seizures can be difficult to differentiate from epileptic seizures and are very frequently evaluated in reference epilepsy centers. In one large series of 251 patients, 61 patients (24%) undergoing video-EEG monitoring had psychogenic nonepileptic seizures; this group was larger than the group of 58 patients (23%) who were identified as epilepsy surgery candidates.8 The

651

652 Section VIIIâ•… Epilepsy and Functional Disorders Table 79.1â•… Main clinical features that differentiate epileptic seizures from nonepileptic paroxysmal events Symptoms

Epileptic seizures

Syncope

Tics

Migraines

Abrupt onset of the episode

++

++

–

–

Aura consisting of unusual taste in mouth, or unusual smell, or warmth in stomach

+++

–

–

+

Aura consisting of lightheadedness, or dizziness, or visual loss

+

+++

–

+

Stereotyped motor activity

+++

–

++

–

Motor activity that is unresponsive to environmental stimuli

+++

+

–

–

Motor activity that can be modulated by environmental activity

–

–

+++

–

Drowsiness, or motor deficits, or amnesia postevent

+++

+

–

+

Headache

+

+

–

+++

Photophobia or sonophobia

–

–

–

+++

Exacerbation with anxiety

+

+

+++

+

co-occurrence of epileptic seizures in at least 5% of subjects with psychogenic nonepileptic seizures9 may further complicate presurgical evaluation in these patients.

79.3╇ Refractoriness to Medical Therapy The key goals of epilepsy treatment are: (1) seizure control, (2) no adverse events, and (3) the best possible improvement in development and quality of life.4 A prerequisite for epilepsy surgery is pharmacological intractability of seizures. Epilepsy surgery goals are defined on an individual basis, and there are no universally applicable indications for epilepsy surgical evaluation or epilepsy surgery.7 However, when there is failure to control seizures with medications, or when seizure control is achieved at the cost of intolerable side effects that compromise quality of life, epilepsy surgery should be strongly considered.

79.3.1╇ When Are Seizures Pharmacologically Intractable? The chances of controlling seizures drastically drop after failure of the first two antiepileptic drugs. In a large series of 470 patients with previously untreated epilepsy, 47% responded to the first antiepileptic

drug, 13% responded to a second antiepileptic drug (in monotherapy in most cases), and 4% responded to a third or multiple antiepileptic drugs.10 Adding a second antiepileptic drug to a patient on monotherapy is much more likely to control epilepsy (in approximately 65% of patients) than adding a third antiepileptic drug to a patient who is already on two antiepileptic drugs (in approximately 17% of cases).11 As a consequence, refractoriness to medical management is usually considered when there is failure of adequate trials of two tolerated and appropriately chosen and used antiepileptic drugs.12

79.3.2╇ When to Refer for Epilepsy Surgery? All patients with refractory epilepsy should be referred for consideration of surgical treatment unless there are absolute medical contraindications to surgery, seizures are secondary to an intractable and progressive degenerative or metabolic central nervous system (CNS) disease, or the patient refuses to take medication properly.13 Frequently, referral and initiation of presurgical work-up may commence while pharmacological intractability is tested simultaneously,14 in particular if patients have a well-delineated or progressive structural lesion. The progressive improvement in localization techniques and the increased understanding of the mechanisms of seizure generation, networks, and

79   Epilepsy Classification, Evaluation, and Imaging Table 79.2â•… Different interpretations of the dichotomy focal versus generalized across the different classification schemes Classification scheme

Main features of the classification system

Proposals for classification of the epilepsies20,21

The localization dichotomy between partial versus generalized epilepsy was introduced, and it was based on clinical characteristics, EEG features, and etiology. The etiological dichotomy was introduced as primary versus secondary.

ILAE 198122

This classification focused on individual seizures. Localization dichotomy. Partial seizures included simple partial, complex partial, and secondarily generalized. Generalized seizures included absence, myoclonic, atonic, tonic, and tonic-clonic. Etiology. Did not provide a scheme for seizure etiology because the anatomical substrate, etiology, and age factors of seizures were largely based on historical or speculative information rather than information from direct observation.

ILAE 198919

Localization dichotomy. Classified epilepsies and syndromes as localization-related, generalized, undetermined as whether focal or generalized, and special syndromes. Etiology. Divided etiologies into idiopathic, symptomatic, and cryptogenic (presumed to be symptomatic but the etiology was unknown).

Multidimensional approach23,24

This classification emphasizes focal epilepsies and is particularly useful for surgical patients. This approach describes the specific features of the epilepsies in a multidimensional approach. The five axes are: (1) Localization of the epileptogenic zone, (2) Seizure semiology, (3) Etiology, (4) Seizure frequency, and (5) Related medical conditions.

ILAE 2001 and ILAE 200625,26

Introduction of the multiaxial approach with five axes: (1) Seizure semiology, (2) Electroclinical seizure type, (3) Epilepsy syndrome, (4) Etiology, and (5) Degree of disability and impairment. Return to an exclusively syndromic classification of epilepsy with particular attention to the age of onset of the syndrome. Semiology and etiology not well represented.

ILAE 201027

Localization. Individual seizures are classified into focal versus generalized. Epilepsies and syndromes are not classified into this dichotomy. Etiology. Divided into genetic, structural/metabolic, and unknown. Introduction of the multidimensional approach into the ILAE classifications.

Abbreviations: EEG, electroencephalogram; ILAE, International League against Epilepsy.

spread also permit consideration of a wider range of patients, including the very young, the very old, patients with multiple lesions or EEG foci, and patients without a structural abnormality on MRI.7,15 Additionally, generalized interictal epileptiform discharges and seizures are not contraindications to surgery; outcomes in these patients have been very similar to those in other traditionally good candidates when presenting in conjunction with an early developmental lesion, such as a stroke or malformation of cortical development.16,17 The general rule of thumb is that, when in doubt, a referral to an epileptologist or a level IV epilepsy center is warranted. Referral, work-up, and treatment rather sooner than later may have developmental benefits and may prevent sudden unexplained death in epilepsy (SUDEP; Table 79.2, Table 79.3).6,18

79.4╇ Classifications and Approach to Epilepsy Patients 79.4.1╇ Classical Classifications of Seizures and Epilepsies The dichotomy between partial and generalized seizures was introduced by Jackson and since then has been implemented into the current International League Against Epilepsy (ILAE) classification. This current classification of epilepsies and epileptic syndromes applies the dichotomy localization-related/ generalized to the epileptic syndromes (Table 79.2).19 In addition, this classification divides the etiologies of epilepsies into idiopathic, symptomatic, and cryptogenic―presumed symptomatic (Table 79.2).19

653

654 Section VIIIâ•… Epilepsy and Functional Disorders

79.4.2╇ Multidimensional Classification Classical classifications essentially relied on the information collected from two diagnostic modalities: study of the semiological features of seizures and study of the EEG characteristics. Therefore, a descriptive epilepsy classification with four independent dimensions was introduced to allow for inclusion of variable technological progress. This approach is based on a general neurologic assessment, including epilepsy localization (where is the lesion?), seizure semiology description and frequency (what are the seizure types and how frequently do they occur?), etiology (what is the cause for seizures?), and related medical conditions (additional related findings that may be significant).23,24 This approach has advantages during the presurgical assessment29 because it mirrors the information acquisition process in clinical practice and allows for updating of the different dimensions as more data become available. Additionally, the different dimensions are essentially independent from each other, so there is no redundancy, and, more importantly, they can be applied to every individual patient because they only describe objective features (as opposed to classical categories where the individual patient had to be fitted into preset categories or syndromes).24

79.4.3╇ Current Proposal for the Organization of Seizures Based on these and other suggestions, revisions of the ILAE classifications were suggested and the most recent changes now also consider this epilepsy surgery approach to epilepsy including a multidimensional approach. In 2010, a revised terminology and concepts for organization of seizures and epilepsies were proposed by the ILAE commission on classification and terminology.27 In this classification, the etiological categories of idiopathic, symptomatic, and cryptogenic have been replaced by genetic, structural-metabolic, and unknown (Table 79.2).27 Furthermore, several relevant dimensions can now be selected as outlined to describe a patient, in particular with focal epilepsy, to better reflect the approach to epilepsy surgery.

79.5╇ Operative Detail and Preparation Concepts in Epilepsy Surgery Epilepsy surgery assumes a focal location of a “generator” of seizures. Once this generator is completely resected, the patient becomes seizure free. This sei-

zure generator has been termed the epileptogenic zone, “the area of cortex that is indispensable for the generation of seizures.” The objective of epilepsy surgery is the complete resection or disconnection of the epileptogenic zone with preservation of eloquent cortex.28 Currently, there is no single test that allows delineation of the epileptogenic zone prior to resection. Therefore, only when epilepsy surgery leads to seizure freedom can it be established that the resected area was indispensable for seizure generation, and it can be concluded that the epileptogenic zone was included in the resected area or that it was disconnected by surgery.2 Because the epileptogenic zone cannot be delineated with any present study or test, there are a series of surrogate zones that provide an estimation of the epileptogenic zone. Each of the surrogate zones provides different data, and combined analysis and interpretation of this information leads to an estimation of the epileptogenic zone (Table 79.3, Table 79.4, Fig.€79.1).2 Based on growing knowledge about neuronal networks and seizure thresholds in different brain areas, the dichotomy between focal and generalized epilepsy is an obsolete oversimplification. However, it is still maintained because it is very useful for seizure management purposes and plays a central role in the work-up for epilepsy surgery. Patients with focal seizures are frequently better candidates for epilepsy surgery than patients with generalized seizures.30 Different regions of the brain have different levels of epileptogenicity or predisposition to generate epileptic seizures.23,30 In the majority of generalized epilepsy cases, the level of epileptogenicity is high in most or all brain areas (Fig. 79.2a).30 Thus epilepsy surgery will usually not achieve seizure freedom because there will always be remaining brain areas with a low seizure threshold (with the exception being early developmental lesions). In contrast, in focal epilepsy the level of epileptogenicity is low in most brain areas (similar to the seizure threshold of nonepileptic subjects) but high in a specific region: the epileptogenic zone (Fig. 79.2b).30 Hence, resection of this zone in these patients frequently leads to seizure freedom. Often, epileptic patients present with intermediate features between those of focal and generalized seizures (Fig. 79.2c).30 In this case, resection of the brain area with the highest level of epileptogenicity may not lead to seizure freedom but may only unmask other areas with low epileptogenicity that were initially not detected. Consequently, the concept of the epileptogenic zone can be divided into two: the actual epileptogenic zone that is the area of the brain generating seizures during the presurgical evaluation, and the potential epileptogenic zone (or zones) that is the area (or areas) of the brain able to generate seizures after resection or disconnection of the actual epileptogenic zone. Areas

79   Epilepsy Classification, Evaluation, and Imaging Table 79.3â•… Definitions of the cortical zones relevant for epilepsy surgery Usefulness for the delineation of the epileptogenic zone

Zone

Definition

Best evaluated with

Symptomatogenic zone

Area of cortex that, when activated by epileptiform discharges, produces symptoms during a seizure

Seizure semiology Video-EEG Functional imaging Cortical stimulation

There is frequently no overlap between the symptomatogenic zone and the epileptogenic zone. Often the initial ictal symptoms are due to spread of the discharge from an epileptogenic zone located in a symptomatically silent area to a distant area of eloquent cortex that is outside the epileptogenic zone.

Irritative zone

Area of cortex that generates interictal epileptiform discharges

Scalp EEG Invasive EEG MEG fMRI Source analysis of EEG or MEG

Generally, the irritative zone is much bigger than the actual epileptogenic zone. The irritative zone outside the actual epileptogenic zone may or may not be marking potential epileptogenic zones.

Seizure onset zone

Area of the cortex that is involved during the EEG seizure onset

Scalp EEG Invasive EEG Ictal SPECT MEG

Frequently the best marker of the actual epileptogenic zone. However, the seizure onset zone does not delineate the potential epileptogenic zones.

Epileptogenic lesion

Structural brain abnormality that is etiologically related to the epilepsy

MRI PET Scalp EEG Invasive EEG

Complete resection of the epileptogenic lesion does not necessarily lead to seizure freedom. Whereas total resection of cavernous angiomas and well-delineated brain tumors tend to produce epileptogenicity only in the MRI-visible lesion and immediate surroundings, cortical dysplasia and posttraumatic epilepsy typically require more extensive resection for a successful outcome.

Functional deficit zone

Area of cortex that is functionally abnormal in the interictal period

Neurological exam Neuropsychological test EEG MEG Evoked potentials Functional imaging fMRI Wada test Cortical stimulation PET Interictal SPECT

The functional deficit may be related to interictal epileptiform discharges or to an underlying structural lesion and may or may not be correlated with the epileptogenic zone.

Eloquent cortex

Area of cortex that is indispensable for a specific cortical function

Electrical cortical stimulation Evoked potentials MEG fMRI PET

The eloquent cortex does not delineate the epileptogenic zone. The eloquent cortex delineates areas involved in a particular function (e.g., language) that, when resected, would lead to functional deficits. If the epileptogenic zone overlaps with eloquent cortex, a decision should be made on whether complete resection of the epileptogenic zone is worth the loss of function or the function is more important than complete resection of the epileptogenic zone.

Abbreviations: EEG, electroencephalogram; fMRI, functional magnetic resonance imaging; MEG, magnetoencephalography; MRI, magnetic resonance imaging; PET, positron emission tomography; SPECT, single-photon emission computerized tomography. Note: The epileptogenic zone is defined as the area of cortex that is indispensable for the generation of seizures. This is a theoretical construct that cannot be delineated with any present (and possibly future) study. The surrogate cortical zones defined in this table provide an estimation of the epileptogenic zone.2,28

655

656 Section VIIIâ•… Epilepsy and Functional Disorders

Fig. 79.1â•… Scheme of the brain areas relevant for epilepsy surgery. Note that the location and extent of the epileptogenic zone cannot be directly evaluated. The illustrated zones provide an approximation of the epileptogenic zone (see also Table 79.3). (Modified with permission of Loddenkemper.14)

do not have to be adjacent; they can be connected with each other through neuronal networks, and may include subcortical areas.

79.6╇ The Process of Presurgical Evaluation Once a patient is considered for epilepsy surgery, a multistep process with continuous interdisciplinary discussion leads to the eventual decision of whether to proceed with epilepsy surgery and, if that is the case, which surgery best meets the needs of the individual patient (Fig. 79.3 and Fig. 79.4). Discussion during an interdisciplinary epilepsy surgery patient management conference evaluates candidacy for surgery and the need for invasive monitoring and mapping, which may provide additional information on seizure onset, interictal spiking, and function (Fig. 79.5).4

79.7╇ Specific Contribution of Each Diagnostic Test Seizure semiology, neurologic examination, and EEG features usually provide the basis for a lateralizing and localizing hypothesis. MRI localizes the epileptogenic lesion, if present, and based on MRI findings, a high-resolution MRI to evaluate structural lesions may be performed. If clinically indicated, additional techniques, including positron emission tomography (PET) for assessing areas of hypometabolism and single-photon emission computed tomography (SPECT) (interictal and ictal subtraction images determining areas of hyperperfusion during the seizure), as well as magnetoencephalography (MEG) for interictal spike mapping, may be pursued. Functional work-up entails neuropsychological testing and functional MRI (fMRI) or, if clinically indicated, intracarotid amobarbital testing (Wada test) (Table 79.4, Fig. 79.3, and Fig.€79.4).

79   Epilepsy Classification, Evaluation, and Imaging a

b

c

Fig. 79.2â•… Different areas of the brain have different levels of epileptogenicity. Seizures occur more frequently in brain areas that are above the seizure threshold. (a) A patient with generalized seizures has several areas of the brain above the seizure threshold. Therefore, seizures originate from different points and spread easily throughout the brain. (b) A patient with focal seizures has only one area of the brain with a level of epileptogenicity above the seizure threshold. Thus seizures originate only from that area and rarely spread in the brain. In this example, the patient has a temporal focus. (c) Frequently, patients are in the middle of the spectrum between focal and generalized seizures. Although there is a predominant focus for the seizures and seizures may arise only or predominantly from that area (actual seizure-onset zone), there are other brain areas that can give rise to seizures and that may become the primary seizure focus once the actual seizure zone is resected (potential epileptogenic zone). In this instance, the leading focus is frontal but the temporal lobe is also above the seizure threshold. (Modified with permission of Loddenkemper.14)

657

658 Section VIIIâ•… Epilepsy and Functional Disorders

Fig. 79.3â•… Stepwise approach to presurgical evaluation. ECoG, electrocorticography; EEG, electroencephalogram; MEG, magnetoencephalography; MRI, magnetic resonance imaging; PET, positron emission tomagraphy; SPECT, single photon emission computed tomography. (Modified with permission of Glauser and Loddenkemper.4)

Fig. 79.4â•… General overview of the management of refractory epilepsy. AED, antiepileptic drugs; CC, corpus callosotomy; DBS, deep brain stimulation; FDG-PET, fluorodeoxyglusose; KD, ketogenic diet; SDG, subdural grids; VNS, vagal nerve stimulation. (Modified with permission of Glauser and Loddenkemper.4)

79   Epilepsy Classification, Evaluation, and Imaging a

b

Fig. 79.5â•… Variability in the distribution of the electrode arrays based on individual epilepsy presentation. (a) Coverage of the left temporal lobe. (b) Coverage of the right frontal area. (Modified with permission of Sánchez Fernández and Loddenkemper.32)

Interictal fluorodeoxyglucose (FDG) PET may localize the seizure onset zone and the propagating cortex by demonstrating relative glucose hypometabolism compared with the normal brain. Typically, the area of hypometabolism on PET is larger than any focal abnormality on structural MRI (the abnormality on structural MRI is usually associated with the point of greatest hypometabolism on PET).31 Ictal SPECT using 99mTc-HMPAO may detect areas of hyperperfusion during a seizure that might indicate the seizure onset zone. This study is technically challenging because reliable results require radioisotope injection within a few seconds of seizure onset, and the subtraction of the ictal images

from the SPECT images collected during an interictal period.31

79.8╇Conclusion The evaluation of patients for epilepsy surgery aims to localize the cerebral generator(s) that, when resected, render(s) the patient seizure free. The localization of these generators is conceptualized through different cortical zones. Epilepsy surgery is a very effective and safe yet underutilized treatment for refractory epilepsy.

659

660 Section VIIIâ•… Epilepsy and Functional Disorders Table 79.4â•… Specific contribution of the different diagnostic tests Test

Area(s) evaluated

Routine evaluation of epilepsy History

Symptomatogenic zone and functional deficit zone

EEG

Irritative zone and ictal onset zone

Video-EEG

Symptomatogenic, irritative, ictal onset zone

Neuropsychological/psychosocial assessment

Eloquent areas and functional deficit zone

MRI brain

Epileptic lesion

Phase I presurgical evaluation MEG

Irritative zone and ictal onset zone, eloquent areas

SPECT

Ictal onset zone

PET

Epileptic lesion and functional deficit zone

fMRI

Eloquent areas and functional deficit zone

Consideration of Wada test in selected patients

Eloquent areas

TMS

Eloquent areas

Phase II presurgical evaluation Subdural and depth electrode recordings

Irritative zone and ictal onset zone

Cortical stimulation and mapping

Eloquent areas and functional deficit zone

Evoked potentials

Eloquent areas

Intraoperative monitoring Intraoperative recordings, stimulation, and evoked potentials

Irritative zone and eloquent areas

Abbreviations: EEG, electroencephalogram; fMRI, functional magnetic resonance imaging; MEG, magnetoencephalography; MRI, magnetic resonance imaging; PET, positron emission tomography; SPECT, single-photon emission computerized tomography; TMS, transcranial magnetic stimulation. Source: Modified with permission of Loddenkemper.14

Tobias Loddenkemper serves on the Laboratory Accreditation Board for Long-Term (epilepsy and ICU) Monitoring (ABRET); is a member of the American Clinical Neurophysiology Council (ACNS); serves on the American Board of Clinical Neurophysiology; works as an associate editor of Seizure; performs video-EEG long-term monitoring, EEGs, and other electrophysiological studies at Children’s Hospital Boston and bills for these procedures. Tobias Loddenkemper serves on the Laboratory Accreditation Board for Long Term (Epilepsy and Intensive Care Unit) Monitoring, on the Council of the American Clinical Neurophysiology Society, on the American Board of Clinical Neurophysiology, as an Associate Editor for Seizure, as Contributing Editor for Epilepsy Currents, and as an Associate Editor for Wyllie’s Treatment of Epilepsy

6th edition. He is part of pending patent applications to detect seizures and to diagnose epilepsy. He receives research support from the American Epilepsy Society, the Epilepsy Foundation of America, the Epilepsy Therapy Project, PCORI, the Pediatric Epilepsy Research Foundation, Cure, Danny-Did Foundation, HHV-6 Foundation, and investigator initiated grants from Lundbeck, Eisai and Upsher-Smith. He performs video electroencephalogram long-term monitoring, electroencephalograms, and other electrophysiological studies at Boston Children’s Hospital and bills for these procedures and he evaluates pediatric neurology patients and bills for clinical care. He has received speaker honorariums from national societies including the AAN, AES and ACNS, and for grand rounds at various academic centers.

79   Epilepsy Classification, Evaluation, and Imaging References ╇1. Picot

MC, Baldy-Moulinier M, Daurès JP, Dujols P, Crespel A. The prevalence of epilepsy and pharmacoresistant epilepsy in adults: a population-based study in a Western European country. Epilepsia 2008;49(7):1230–1238 ╇2. Rosenow F, Lüders H. Presurgical evaluation of epilepsy. Brain 2001;124(Pt 9):1683–1700 ╇3. Téllez-Zenteno JF, Dhar R, Wiebe S. Long-term seizure outcomes following epilepsy surgery: a systematic review and meta-analysis. Brain 2005;128(Pt 5): 1188–1198 ╇4. Glauser TA, Loddenkemper T. Management of childhood epilepsy. Continuum (Minneap Minn) 2013;19(3 Epilepsy):656–681 ╇5. Surges R, Sander JW. Sudden unexpected death in epilepsy: mechanisms, prevalence, and prevention. Curr Opin Neurol 2012;25(2):201–207 ╇6. Loddenkemper T, Holland KD, Stanford LD, Kotagal P, Bingaman W, Wyllie E. Developmental outcome after epilepsy surgery in infancy. Pediatrics 2007;119(5): 930–935 ╇7. Wiebe S, Jetté N. Epilepsy surgery utilization: who, when, where, and why? Curr Opin Neurol 2012;25(2):187–193 ╇8. Benbadis SR, O’Neill E, Tatum WO, Heriaud L. Outcome of prolonged video-EEG monitoring at a typical referral epilepsy center. Epilepsia 2004;45(9):1150–1153 ╇9. Martin R, Burneo JG, Prasad A, et al. Frequency of epilepsy in patients with psychogenic seizures monitored by video-EEG. Neurology 2003;61(12):1791–1792 10. Kwan P, Brodie MJ. Early identification of refractory epilepsy. N Engl J Med 2000;342(5):314–319 11. Desai J, Mitchell WG. Does one more medication help? Effect of adding another anticonvulsant in childhood epilepsy. J Child Neurol 2011;26(3):329–333 12. Kwan P, Arzimanoglou A, Berg AT, et al. Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia 2010;51(6):1069–1077 13. Engel J Jr. Update on surgical treatment of the epilepsies. Summary of the Second International Palm Desert Conference on the Surgical Treatment of the Epilepsies (1992). Neurology 1993;43(8):1612–1617 14. Loddenkemper T. Diagnosis/treatment: criteria for referral to epilepsy surgery. In: Panayiotopoulos C, Benbadis S, Beran R, et al, eds. Atlas of Epilepsies. London, England: Springer-Verlag; 2010: 1627–1634 15. Chugani HT, Shields WD, Shewmon DA, Olson DM, Phelps ME, Peacock WJ. Infantile spasms: I. PET identifies focal cortical dysgenesis in cryptogenic cases for surgical treatment. Ann Neurol 1990;27(4):406–413 16. Kramer U, Sue WC, Mikati MA. Focal features in West syndrome indicating candidacy for surgery. Pediatr Neurol 1997;16(3):213–217

17. Wyllie

E, Lachhwani DK, Gupta A, et al. Successful surgery for epilepsy due to early brain lesions despite generalized EEG findings. Neurology 2007;69(4):389–397 18. Wiebe S, Blume WT, Girvin JP, Eliasziw M; Effectiveness and Efficiency of Surgery for Temporal Lobe Epilepsy Study Group. A randomized, controlled trial of surgery for temporal-lobe epilepsy. N Engl J Med 2001;345(5):311–318 19. Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia 1989;30(4):389–399 20. Gastaut H. Classification of the epilepsies. Proposal for an international classification. Epilepsia 1969;10(Suppl): 14–21 21. Merlis JK. Proposal for an international classification of the epilepsies. Epilepsia 1970;11(1):114–119 22. From the Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised clinical and electroencephalographic classification of epileptic seizures. Epilepsia 1981;22(4):489–501 23. Loddenkemper T, Kellinghaus C, Wyllie E, et al. A proposal for a five-dimensional patient-oriented epilepsy classification. Epileptic Disord 2005;7(4):308–316 24. Lüders HO, Amina S, Baumgartner C, et al. Modern technology calls for a modern approach to classification of epileptic seizures and the epilepsies. Epilepsia 2012;53(3):405–411 25. Engel J Jr. Classification of epileptic disorders. Epilepsia 2001;42(3):316 26. Engel J Jr. Report of the ILAE classification core group. Epilepsia 2006;47(9):1558–1568 27. Berg AT, Berkovic SF, Brodie MJ, et al. Revised terminology and concepts for organization of seizures and epilepsies: report of the ILAE Commission on Classification and Terminology, 2005-2009. Epilepsia 2010;51(4): 676–685 28. Datta A, Loddenkemper T. The epileptogenic zone. In: Wyllie E, Cascino G, Gidal B, Goodkin H, eds. Treatment of Epilepsy. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2011: 818–827 29. Loddenkemper T. Classification of the epilepsies. In: Wyllie E, Cascino G, Gidal B, Goodkin H, eds. Treatment of Epilepsy. 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2011: 229–242 30. Lüders HO, Turnbull J, Kaffashi F. Are the dichotomies generalized versus focal epilepsies and idiopathic versus symptomatic epilepsies still valid in modern epileptology? Epilepsia 2009;50(6):1336–1343 31. Likeman M. Imaging in epilepsy. Pract Neurol 2013; 13(4):210–218 32. Sánchez Fernández I, Loddenkemper T. Electrocorticography for seizure foci mapping in epilepsy surgery. J Clin Neurophysiol 2013;30(6): 554-570

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80

The Surgical Treatment of Epilepsy: Overview Hai Sun, Sergey Abeshaus, and Jeffrey G. Ojemann

80.1╇Background It is estimated that epilepsy affects about 1% of the general population. The disease incidence has a bimodal distribution, with children and older adults preferentially affected. The urgency of stopping seizures in the developing brain is paramount, since it can prevent a lifetime of disability. Pharmacotherapy becomes ineffective in controlling seizures in approximately 30 to 40% of epilepsy patients.1 Although medical treatment for seizure control has largely remained stagnant, advances have been made in epilepsy surgery over the past few decades. Innovations in technology, in particular imaging and functional brain mapping, have allowed for safer and more efficacious surgery. For a child with epilepsy, successful surgical intervention offers the hope of reversing long-standing medical and psychosocial disability and the potential for a more productive and independent life. Currently, surgery is recommended after the epilepsy has been deemed medically intractable, and the average age of children undergoing epilepsy surgery has progressively fallen.

80.2╇ Pathologies and Etiologies Epidemiological studies have shown that the propensity of a young brain to develop seizures is much greater than that of an adult brain. Whereas some seizures are idiopathic and often remit during adolescence or early adulthood, a significant portion of epileptic seizures can become more frequent and more severe despite ongoing medical treatment, and etiology for the most part remains unknown. Leading causes include hypoxic-ischemic injuries and stroke, focal cortical dysplasia, and benign or low-grade tumors related to neuronal development. To help define long-term prognosis and facilitate surgical referral, the International League Against Epilepsy (ILAE) has classified several epileptic syndromes.2

662

These include tuberous sclerosis, Sturge–Weber syndrome, Rasmussen encephalitis, hemimegalencephaly, and West syndrome. Other lesions that can cause epilepsy include vascular malformations and hypothalamic hamartoma. Mesial temporal sclerosis (MTS) also affects children; however, patients with MTS are generally older, and children with MTS have a higher incidence of dual pathology than adults.3

80.3╇Indications Consensus recommends that children with medically intractable seizures or disabling medication side effects should be referred for consideration of surgical intervention.4 Two criteria should be met before proceeding: intractability and focal onset. Over the years, medical therapy duration before establishment of medical intractability has decreased. Kwan and Brodie demonstrated that 47% of patients with newly diagnosed epilepsy were fully controlled with one antiepileptic medication (AED), and 13% experienced seizure control with a second medication; however, only 4% were seizure free with a third or multiple AEDs. In their cohort, 36% of patients remained medically intractable.1 This study highlighted the fact that multiple additional medications predict a gradually diminishing probability of seizure control. Today, seizures are considered medically intractable after two or three AEDs have been attempted over 1 year. Another study showed that, in image-positive patients, once adequate trials of two to three AEDs failed to control seizures, the chance of becoming seizure free with continued medications was < 5%.5 Based on these findings, if a preoperative evaluation reveals a clear lesion remediable by epilepsy surgery, a more rapid decision to proceed with surgery can be made. Additionally, evidence suggesting that a localizable brain abnormality is the site where seizure originates should be available. Successful surgical

80 â•… The Surgical Treatment of Epilepsy: Overview outcome depends on the removal of the abnormal seizure focus while preserving the normal and eloquent brain. This rule can be relaxed when the goal of the surgery is palliative to prevent catastrophic consequences of seizures, as seen with hemispherectomy and callosotomy. Finally, informed consent has to be obtained from the patient and/or patient’s family before a presurgical evaluation. The risks, benefits, costs, and possible complications have to be discussed for the patient and family to make an informed decision. For some patients, rare seizures are acceptable, whereas one or two events per year can be life-changing for other individuals.

80.4╇ Presurgical Evaluation The aim of presurgical evaluation is to identify the “epileptogenic zone” (EZ), defined as the area of brain necessary and sufficient for generating spontaneous seizures. The removal of the EZ renders seizure freedom. In successful centers, the presurgical evaluation is multidisciplinary, involving health care providers in different fields and utilizing a combination of techniques. Information used to identify the EZ includes history, seizure semiology, neuropsychological testing, clinical neurophysiology evidence, and structural and functional neuroimaging studies. In general, patients with structural lesions on neuroimaging have much better chances of being seizure free after epilepsy surgery. The degree of congruence among seizure semiology, interictal and ictal electroencephalography (EEG) findings, and findings on functional imaging techniques, such as positron emission tomography (PET) and singlephoton emission computed tomography (SPECT), become important. In the event that there is incongruence among these findings, invasive monitoring with subdural or depth electrodes may be used to further define the EZ. Once the EZ is approximately defined, its relationship with eloquent cortical areas is then assessed in order to predict or prevent a possible postoperative deficit. This relationship can be derived from functional testing, such as visual field and neuropsychological tests, and intracarotid amobarbital testing. Functional magnetic resonance imaging (MRI) for language, sensory, and visual function and event-related potentials is often used. In patients with a subdural grid and/or strip electrodes, functional mapping can be obtained from direct cortical stimulation. Combining the information obtained from presurgical evaluation, the risks and benefits of surgery are discussed in a multidisciplinary conference

involving epileptologists, neurosurgeons, neuroradiologists, and neuropsychologists. A final decision must be tailored to each individual patient.

80.4.1╇ Surgery Types A 2004 ILAE survey revealed that 81% of epilepsy surgeries performed on pediatric patients were resective procedures aiming for seizure control by removing portions of the brain, and 19% were palliative operations (vagal nerve stimulators and corpus callosotomy).6 Unlike epilepsy surgery for adults, the type of epilepsy procedure performed for pediatric patients is highly age-dependent. Infants and younger patients (age < 4 y) tend to undergo larger extemporal, multilobar, hemispheric resection (90%), whereas older patients undergo temporal and more focal resections (70%).7 Also differing from adult patients,8 a much higher proportion (70%) of pediatric patients undergo extratemporal resection. In patients with a visible structural lesion, lesion� ectomy usually renders seizure freedom. In these cases, electrocorticography, either through intraoperative or long-term recordings, improves the seizure freedom rate, since the brain adjacent to the lesion may be involved. If seizures can be lateralized but not localized within a given hemisphere, hemispherectomy may be considered. This procedure is ideal if the patient has already suffered dysfunction from the same hemisphere, often seen in perinatal hypoxic injury. Several variations of the traditional hemispherectomy technique have been developed by using more disconnections and increasingly smaller incisions, which lead to less blood loss and potentially fewer postsurgical complications.9 In patients with drop attacks, division of the corpus callosum may offer symptom relief and prevent seizure-related injuries. Generally, the anterior twothirds of the corpus callosum are divided through an interhemispheric approach. Another procedure aiming at palliation is vagus nerve stimulation, which often gives a 50 to 75% reduction in seizure frequency, making it particularly attractive to patients who are not candidates for resective surgery. Open cranial resective surgery can pose special challenges in smaller children. The perioperative blood loss relative to total vascular volume can be significant. Waiting for the child to grow larger before performing epilepsy surgery does not reduce operative risks over the first 3 years of life and can increase the probability for poorer cognitive outcomes.10 Hence, although operating in young children presents greater risk, the increased operative risks are justified in order to prevent permanent seizure-related developmental deficits.11

663

664 Section VIIIâ•… Epilepsy and Functional Disorders MRI-guided, laser-induced thermal ablation for epilepsy is an exciting new minimally invasive technology with an emerging use for lesionectomy of a variety of epileptogenic foci (hypothalamic hamartomas, cortical dysplasias, cortical malformations, tumors) or as a disconnection tool.12 Treating seizures with brain stimulation, either via deep brain structures such as anterior nucleus of the thalamus (ANT), or a closed-loop, responsive cortical stimulation of seizure foci, has shown promising results.13

80.5╇ Outcomes and Postoperative Course The first randomized controlled trial of epilepsy surgery in adults demonstrated superiority of temporal lobe resection over medical management for patients with MTS. No similar randomized controlled trials have been conducted among pediatric patients with epilepsy. Many retrospective cohorts report similar seizure control rates as seen in adults. Similar to adults, pediatric patients with tumors or hippocampal sclerosis tend to do better than patients with malformation of cortical development. Overall mortality from pediatric epilepsy surgery is 1.3% in well-established centers. Predictors of favorable outcomes include history of febrile seizure, MTS, lesions on MRI, congruent EEG and MRI findings, and larger resections. Invasive monitoring and postoperative interictal discharges were associated with persistent seizures.7,10

80.6╇Conclusion Surgical treatment for children with epilepsy is important because there is a higher probability of successfully controlling seizures, with the potential to prevent and sometimes reverse the damage caused by seizures. Surgical techniques and tools continue to evolve rapidly, which may lead to better outcomes.

References ╇1. Kwan P, Brodie MJ. Early identification of refractory epi-

lepsy. N Engl J Med 2000;342(5):314–319 on Classification and Terminology of the International League Against Epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia 1989;30(4):389–399 ╇3. Mohamed A, Wyllie E, Ruggieri P, et al. Temporal lobe epilepsy due to hippocampal sclerosis in pediatric candidates for epilepsy surgery. Neurology 2001;56(12):1643–1649 ╇4. Cross JH, Jayakar P, Nordli D, et al; International League against Epilepsy, Subcommission for Paediatric Epilepsy Surgery; Commissions of Neurosurgery and Paediatrics. Proposed criteria for referral and evaluation of children for epilepsy surgery: recommendations of the Subcommission for Pediatric Epilepsy Surgery. Epilepsia 2006;47(6):952–959 ╇5. Berg AT, Mathern GW, Bronen RA, et al. Frequency, prognosis and surgical treatment of structural abnormalities seen with magnetic resonance imaging in childhood epilepsy. Brain 2009;132(Pt 10):2785–2797 ╇6. Harvey AS, Cross JH, Shinnar S, Mathern GW; ILAE Pediatric Epilepsy Surgery Survey Taskforce. Defining the spectrum of international practice in pediatric epilepsy surgery patients. Epilepsia 2008;49(1):146–155 ╇7. Gilliam F, Wyllie E, Kashden J, et al. Epilepsy surgery outcome: comprehensive assessment in children. Neurology 1997;48(5):1368–1374 ╇8. Wiebe S, Blume WT, Girvin JP, Eliasziw M; Effectiveness and Efficiency of Surgery for Temporal Lobe Epilepsy Study Group. A randomized, controlled trial of surgery for temporal-lobe epilepsy. N Engl J Med 2001;345(5):311–318 ╇9. Schramm J. Hemispherectomy techniques. Neurosurg Clin N Am 2002;13(1):113–134, ix 10. Sugimoto T, Otsubo H, Hwang PA, Hoffman HJ, Jay V, Snead OC III. Outcome of epilepsy surgery in the first three years of life. Epilepsia 1999;40(5):560–565 11. Bittar RG, Rosenfeld JV, Klug GL, Hopkins IJ, Harvey AS. Resective surgery in infants and young children with intractable epilepsy. J Clin Neurosci 2002;9(2):142–146 12. Tovar-Spinoza Z, Carter D, Ferrone D, Eksioglu Y, Huckins S. The use of MRI-guided laser-induced thermal ablation for epilepsy. Childs Nerv Syst 2013;29(11):2089–2094 13. Fridley J, Thomas JG, Navarro JC, Yoshor D. Brain stimulation for the treatment of epilepsy. Neurosurg Focus 2012;32(3):E13 ╇2. Commission

81

Invasive Monitoring in Pediatric Neurosurgery Jean-Pierre Farmer and Jeffrey Atkinson

81.1╇Background 81.1.1╇Indications Invasive monitoring in pediatric neurosurgery is indicated in surgical interventions located near eloquent areas of the cortex, in the brainstem, in the spinal cord, and in the cauda equina. Brainstem and spinal cord monitoring may be required predominantly for the resection of tumors or the treatment of syringomyelia or syringobulbia, as well as for complex craniovertebral surgeries, such as in the treatment of basilar invagination related to osteogenesis imperfecta. Monitoring at the level of the cauda equina is used in untethering procedures1 and in selective dorsal rhizotomies,2,3 as well as in the resection of cauda equina tumors. Invasive monitoring can become necessary for the investigation of intractable, nonlesional epilepsy where mapping of the seizure onset, epileptic zone, and/or the motor and sensory area may be obtainable in the preoperative phase.4,5

81.1.2╇Goals The goals of preoperative monitoring for intractable epilepsy are to clearly delineate the seizure onset and the epileptic zone, as well as the proximity of functional zones to be preserved. With grids and strips it is possible to stimulate the brain4,5 as well, and to identify speech zones (through speech interference) or hand, face, or leg areas. The goal of intraoperative monitoring is to facilitate the safe resection of as much of a tumor as possible without interference with function―whether in the brain, brainstem, spinal cord, or cauda equina. Monitoring for untethering procedures helps preserve sphincteric function, in particular, as well as foot function in cases of complex tethered cord procedures.1 It is also

through monitoring of evoked electromyography (EMG) activity and physiotherapy palpated contractions that the lesioning pattern is established during rhizotomies.2

81.1.3╇ Alternate Procedures There are no alternate procedures that enhance the safety for brainstem surgery, spinal cord surgery, or cauda equina surgery. However, alternate procedures do exist for cortical surgery. Even in very young children placed under light anesthesia, passive movements of the toe or finger may help localize the central sulcus through functional magnetic resonance imaging (fMRI).6 In older children, a verbal memory task, such as the generation of synonyms, can help identify the speech centers. This is more readily done with a 3T (Tesla) magnet (optimal signal/noise ratio) and good collaboration with the anesthetist. In addition, based on fMRI localization of primary cortical eloquent regions, and based on the known anatomical projections toward the peduncle, for instance (or from the optic chiasm to the primary visual cortex in cases of visual activation), fiber tractography is a very helpful adjunct in mapping out the surgery.7 All this information can then be placed in a preoperative plan and be available for surgical navigation. For seizure localization in nonlesional cases, surface telemetry and foramen ovale electrode placement can be alternatives to grid placement in localizing the seizure focus when coupled to corticography during surgery.5 Corticography can be enhanced by the use of remifentanil to enhance brain activation and can be helpful in determining the extent of the resection, particularly if spiking occurs proximal to the cavity of resection. However, there are a number of cases, perhaps on the order of 10 to 20%, where preoperative invasive monitoring with grids and strips is inevitable.

665

666 Section VIIIâ•… Epilepsy and Functional Disorders young children or very uncooperative older children because of the risk of complications, such as hemorrhage, infection, and leakage of cerebrospinal fluid (CSF), which are all reported with depth electrodes.

81.1.4╇Advantages Invasive monitoring allows the surgeon to push the limits of surgical resection by providing anatomical functional and neurophysiological guidance relating to the integrity of the pathway(s) at risk.

81.2╇ Operative Detail and Preparation

81.1.5╇Contraindications The only relative contraindication to using motor evoked potentials (MEPs) is the presence of an active epileptic disorder. A patient who has a very active seizure disorder and needs monitoring of MEPs during surgery might be pushed into status by the transcranial motor stimulation. The pros and cons of performing MEPs need to be balanced in that circumstance. The other relative contraindication to using evoked potentials intraoperatively is when they are absent preoperatively and therefore even less likely to be present under general anesthesia. Finally, there may be relative contraindication to using grids or strips in the investigation of epilepsy in very

a

c

81.2.1╇ Preoperative Planning and Special Equipment Preoperative somatosensory evoked potentials (SSEPs) are obtained as a baseline for any surgery located in the central area of the brain, brainstem, or spinal cord. In central surgery, the adequacy of preoperative SSEPs allows one (through placement of electrode strips or rows of electrodes from an array perpendicular to the hand or foot area of the central region) to map out, through phase reversal (Fig. 81.1), the central sutures (wave reversal from primary sensory to primary motor function).

b

d

Fig. 81.1â•… (a) Preresection of cortical electrodes placed for somatosensory evoked potential (SSEP) median nerve recording; numbers 6 and 7 in the presumed postcentral and precentral location. (b) SSEP median nerve recording showing phase reversal between electrodes 6 and 7, confirming the location of the central region. (c) Postresection of precentral lesion. (d) Neuronavigation view of cortical surface with functional magnetic resonance imaging (fMRI) of leg activation, diffusion tensor imaging (DTI) fiber tracts for leg area (blue), and segmented lesion in pink.

81 â•… Invasive Monitoring in Pediatric Neurosurgery Auditory brainstem responses (ABRs) are obtained preoperatively in brainstem surgery as an additional modality to monitor neural integrity during entry into the brainstem. MEPs are not obtained preoperatively because they are quite intolerable to children and adolescents. However, an electroencephalogram (EEG) may be necessary to ensure that there is no significant underlying epileptogenic abnormality in patients, who will then undergo transcranial motor stimulation intraoperatively. In cauda equina surgery, the sphincteric activity as well as the foot musculature spontaneous EMG activity can be monitored. Implantation of grids does not occur as a first step in the investigation of patients with seizure disorder. After interpreting seizure semiology, careful assessment of the magnetic resonance imaging (MRI) to determine whether or not subtle lesions such as discrete cortical dysplasia are present or whether there is enlargement of the temporal horn or subtle fluidattenuated inversion recovery (FLAIR) signal changes in the hippocampus, can be beneficial starting points. Surface telemetry (including foramen ovale electrodes for temporal lobe epilepsy) then follows. However, if the hypothesis as to seizure origin is not clear enough to proceed with corticography-guided surgery, grids may be needed. These may allow mapping out of the epileptogenic zone and also establishing the relationship of the epileptic zone with eloquent regions of the brain. Patients undergo computed tomography (CT)

for precise localization of the electrode array. This image is then fused to the MRI scan obtained at the onset of the investigation. This permits transposing localization on the MRI to create a preoperative surgical map for the surgeon that can then be fused onto the navigational scan (Fig. 81.2). fMRI and fiber tractography can help even in younger or less cooperative children to localize specific eloquent areas of the brain. Under light general anesthesia the authors have been able to map the primary visual cortex (visual stimuli, closed eyes) (Fig.€81.3) and the primary sensory/motor region (passive toe/finger movement) of toddlers (Fig. 81.4). The signal localizes to the central sulcus because the response may be partly proprioceptive, partly motor. For older children, we use fMRI technology and a trained clinician able to coach the older child into synonym generation or words starting with a given letter, as well as doing fine motor tasks without actually moving the head in the 3T magnet (Fig. 81.5). When coupled to fiber tractography, this becomes a powerful tool to localize deep projections with accuracy because the voxels used for tractography are placed with added precision. If one is certain of the localization of the primary leg motor area, fiber tracts to the cerebral peduncle can then be mapped with accuracy. These fibers would be different obviously from those originating in the hand area (Fig. 81.4). Furthermore, in epilepsy cases it is possible to coregister positron emission tomography (PET) information or SISCOM (an advanced diagnostic imaging tool)

Fig. 81.2â•… Three-dimensional (3D) representation of cortical surface of magnetic resonance imaging (MRI) fused to postimplantation computed tomography (CT) with 3D segmentation of subdural grid electrodes.

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668 Section VIIIâ•… Epilepsy and Functional Disorders

Fig. 81.3â•… Neuronavigation view of three-dimensional (3D) and multiplanar view of lesion and functional information. Lesion is light blue; proposed surgical corridor is yellow; functional magnetic resonance imaging (fMRI) visual responses are purple; diffusion tensor imaging (DTI) determination of optic radiations is green; and leg motor area and motor fibers are dark blue.

data to the MRI.8 The surgeon or his trainee is then equipped to virtually perform the surgery in advance with anatomical, physiological, metabolic, and functional information―all of which are rapidly transferrable to the navigational MRI during surgery (Fig. 81.6).

81.2.2╇ Expert Suggestions/Comments The availability of phase-reversal central area localization (late 1980s) has allowed the authors to do all of their seizure surgery with patients under general anesthesia. They also try to restrict invasive monitoring to cases of truly intractable epilepsy by coupling extensive preoperative/intraoperative electrophysiological assessment of motor modalities to preserve long-tract motor function or focal motor function, such as tongue, facial nerve, sphincter monitoring, through spontaneous EMG responses. Since the authors have intraoperative magnetic resonance imaging (iMRI) capabilities (2009) for cranial surgery, this is coupled to extensive preoperative 3T imaging information, PET/CT data for metabolic mapping, and fMRI. The accuracy of navigation has been enhanced by the fact that the navigational iMRI is obtained in

the same position as they are operating, making the surgeries as thorough and as safe as possible. The authors feel that, with increased experience with seizure disorders, the need for grid placement to successfully treat epileptic children is probably reduced to about 10 to 15% of all cases presenting to their epilepsy unit. Imaging plays a pivotal role in this paradigm shift.

81.2.3╇ Key Steps of the Procedure/ Operative Nuances Cortical Surgery The importance of preserving navigational precision is critical. With the authors’ 5-pin headholder/ coil, they have been able to immobilize the skulls of children as young as age 11 months, placing the pins in a configuration that would avoid the temporal squama. The torque ceramic pin holder allows up to 60 N (newtons; 13 lbs) of pressure, and this has been enough for children younger than 4 to 6 years. The authors have benefitted tremendously from the accuracy of their navigational information, which is

81 â•… Invasive Monitoring in Pediatric Neurosurgery

Fig. 81.4â•… Three-dimensional (3D) representation of cortical surface, passive (sedated) functional magnetic resonance imaging (fMRI) identification of hand (blue) and leg (green) function with diffusion tensor imaging (DTI) tracts from each motor region. Cortical dysplasia represented in pink. Positron emission tomography (PET) (3 plane views) fused to magnetic resonance imaging (MRI) with hypometabolic region represented in violet.

Fig. 81.5â•… Tumor represented in blue. Functional magnetic resonance imaging (fMRI) of posterior and anterior speech areas (green), with diffusion tensor imaging (DTI) identification of arcuate fasciculus in yellow. Hand motor area and corresponding fiber tract are pink.

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670 Section VIIIâ•… Epilepsy and Functional Disorders

Fig. 81.6â•… Utilizing the preoperative planning of functional, metabolic, diffusion tensor imaging (DTI) and anatomical data to plan the surgery and teach trainees.

then fused to their preoperative multimodality plan. For babies, a horseshoe with a fishnet and fiducial markers placed at the time of obtaining the preoperative MRI scan allows for relatively good accuracy. This accuracy, even if slightly “off” at the surface, can remain quite reliable in depth, even in hemispherotomy cases.

Operations with Grids Images of the grid position as well as the electrophysiological mapping of the epileptic zone are developed preoperatively. The grid must, however, be removed prior to proceeding to the navigational MRI. By fusing the preoperative CT with a preoperative MRI, the fused images can then be transposed to the navigational scan when the patient returns from the iMRI suite.

Brainstem Surgery In brainstem surgery, where information from SSEPs and MEPs as well as ABRs and EMG-induced spontaneous activity of the tongue or the face is critical, anesthetic conditions have to be optimal. These cases are done with total intravenous anesthesia (TIVA) using fentanyl and propofol. The responses can also be altered by a lower body temperature, a lower mean arterial blood pressure, or too deep anesthetic conditions. Communication among anesthesia/electrophysiology, surgeon, and patient is crucial.

Spinal Cord Surgery TIVA is also essential. Again, when a response dampens, the reflex should be to verify as per the authors’ algorithm whether the anesthetic conditions, the blood pressure, or the body temperature of the patient has changed. The anesthetists often use a bispectral index (BIS) monitor to estimate the level of awareness of the patient in such procedures.

Cauda Equina Surgery Selective Dorsal Rhizotomies Again, TIVA conditions have to be used. Furthermore, a “steady state” is needed during the stimulations. Often it is better to get a slightly weaker but clearly visible and reproducible threshold response so that when a supramaximal train is applied, the patient does not develop hemodynamic changes or refractoriness to repeated stimulation. Responses have been shown to be very reliable under those conditions.

Tethered Cord Surgery The most effective technique for tethered cord surgery is sphincteric or foot muscle spontaneous EMG coupled to a portable stimulator that has an amplitude range of 0.5 to 2.0 mA (milliamperes).

81 â•… Invasive Monitoring in Pediatric Neurosurgery

81.2.4╇ Hazards/Risks/Avoidance of Pitfalls Cortical Surgery Inaccuracies introduced by brain shift can have significance. However, the multimodality plan once fused to the first intraoperative scan is available to the surgeon even at the step of planning the craniotomy and can be verified again once the dura is open and the surface anatomy is exposed. In situations of hemispherotomy with large, middle cerebral artery porencephaly, certainly surface brain shift occurs, but remarkably the accuracy at the level of midline structures to be disconnected remains relatively reliable. The pericallosal arteries and their cistern, which are landmarks that guide the intraventricular callosotomy, can be tracked accurately despite superficial brain shift. Phase-reversal localization of the central area is of proven reliability under TIVA conditions. The authors have taken the strategy of correlating their central localization obtained with fMRI preoperatively to

that obtained with phase-reversal techniques intraoperatively (Fig. 81.6). Thus far, the intermodality reliability is quite good. The use of grids or evoked potential electrodes placed on the patient precludes placing the patient in a 3T magnetic field. The majority of suppliers have not yet proven the safety of such metallic electrodes for the 3T magnetic field (although for a 1.5T field this has been confirmed in most cases). Therefore, the operating strategy of going to the magnet for update of information has to be adjusted when a grid is present, as described, or when reference electrodes are present either in the case of corticography or evoked potentials, because the electrodes need to be removed prior to obtaining updated imaging information.

Brainstem and Spinal Cord Surgery The biggest hazard of using monitoring in these cases comes from their false-positive rate. If, during spinal cord or brainstem surgery, some sensory modality function decreases significantly and if the algorithm (Fig. 81.7) check does not reveal any change in condi-

Baseline Preop SSEP

Patient not a candidate for monitoring—discussion with family

Patient is candidate Intraoperative baseline MEP and SSEP after induction Surgical time out •â•‡ EP technician •â•‡Anesthesiologist* •â•‡Neurosurgeon •â•‡Neurologist*

Monitoring baseline maintained during resection 15–20 minutes of pause

Systematic monitoring and documentation by technician and review by anesthetist and orthopedist Surgical time out Re: contributory factors

Return of waveform Yes Resume surgery

No Close and consider returning at another time

Signing of preliminary technical report by all 3 team members

* Individuals specifically trained in MEP/SSEP interpretation

Surgical factors

Technical factors

Modify

Modify

Return to baseline

Change in baseline toward loss of signal meeting international criteria ** Anesthesia and physiological factors Modify

Persistence of loss of signal

** •â•‡ > 50% sensory changes •â•‡ ↑in 10% of latency •â•‡ >80% motor evoked potential loss

Fig. 81.7â•… Algorithm for intraoperative monitoring for neurosurgical procedures at the Montreal Children’s Hospital. MEP, motor evoked potentials; EP, electrophysiology; SSEP, somatosensory evoked potentials.

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672 Section VIIIâ•… Epilepsy and Functional Disorders tions, one can be misled by the decreased signal into not being as aggressive as needed to fully resect the lesion.9 The sensory modality can be reduced at the time of performing the myelotomy or the entry into the cervicomedullary region, and this should not in itself preclude discontinuation of the procedure, particularly if the decline in response is 50% or less. It often returns with time. The cavitron that is used to resect tumoral lesions in those regions can, through its vibration, adversely affect MEPs. This becomes a greater concern for the neurosurgeon. More recently, the authors have used the “tissue select” adjustment to reduce the vibratory interference with MEPs and have had less of such declines in activity. If the activity declines significantly, then it is advisable to pause or to work on the other side so as to allow more time for the waveform to recover. Transient declines of up to 50% in the intensity of the signal have not correlated with loss of function postoperatively, but declines of greater magnitude have.10,11 Frequently, however, the authors can see some decline during the surgery, and at the time of closure a return of amplitudes that is even occasionally greater than the baseline, suggesting that a fiber tract has been decompressed.

Selective Dorsal Rhizotomies If the responses are very good, it is important to use clinical discretion in an attempt to try to balance the elimination of spasticity and the preservation of tone and strength. The most abnormally responding rootlets should be sectioned; however, not all rootlets responding abnormally need to be sectioned to obtain a good result. In the patients where the responses are dampened, such as in cases of refractoriness, then patience is indicated. Adjustments of the propofol infusion rate or the sufentanil infusion rate are needed. Usually by taking a 15- to 20-minute pause to establish a new steady state, responses return. The correlation between physiotherapy and EMG responses and between EMG stimulation of the same root at the authors’ center is well over 90%.2 It is vital to not section more than 50% of S2 dorsal rootlets (both sides combined) to avoid neurogenic bladder issues and to be conservative at L4 to preserve quadriceps’ tone. In cases where the patient responds with hemodynamic changes, it is better not to adjust the anesthetic conditions, but to take frequent pauses after doing the rootlets of one or two roots so as to maintain steady-state conditions.

Untethering Surgery Spontaneous EMG is quite beneficial. Using a portable stimulator set at 0.5 to up to 2 mA can be helpful, when a patient is fully reversed, to clearly identify neural elements in the presence of spontaneous EMG technology.

81.3╇ Salvaging and Rescue When electrophysiological monitoring is dampened during surgery or difficult to obtain at times, it is imperative to be tolerant and to let the operative site recover prior to advancing surgery. If the response does not return or remains dampened, despite the desire to avoid reoperation, it may be advisable in those circumstances to terminate the procedure and let the child recover, even if this means that there could be a second surgery in weeks or months to come. Families like the operations to be successful, preferably with one surgical event; nevertheless, they definitely prefer a staged approach to a significant, permanent motor deficit. This eventuality needs to be discussed preoperatively with families, to allow the surgeon to proceed according to the preoperative plan that has been established jointly with the family. Navigational inaccuracies: If a good deal of the surgery relies on a fused preoperative functional plan that includes fMRI, fiber tractography, PET, or SISCOM data, or an elaborate trajectory through difficult vascular anatomy―all planned virtually―and if inaccuracies set in, it is possible to regain the accuracies through an iMRI with the cranium open and the dura simply reapproximated. At that point, the information can be upgraded and the navigational accuracy will be restored. In approximately 20 to 25% of the authors’ resections, this step allows them to complete a resection safely, avoiding the need for a second surgery. The interpretation of iMRI material, given the presence of air and hemostatic material artifacts, requires a dedicated radiologist with growing experience and is associated with a steep learning curve. In those conditions, correlations between the intraoperative images and the postoperative data obtained 3 months later have been excellent at the authors’ center.

81.4╇ Outcomes and Postoperative Course 81.4.1╇ Postoperative Considerations Invasive monitoring and associated multimodality imaging information render surgeries safer, yet more thorough. It is important to remember, however, that if the modality being monitored has been preserved intraoperatively, such as in cases of brainstem surgery, intensive care unit (ICU) postoperative conditions still need to be optimized. Brainstem vascularity is of the “end vessel” variety and postoperative hypoxia from respiratory compromise in brainstem surgery has been known to extend deficits significantly and often irremediably.

81 â•… Invasive Monitoring in Pediatric Neurosurgery The use of imaging during the operative event toward the end of the procedure, either as an iMRI or postoperative MRI, does not preclude the risk of a complication from pin placement or from significant retraction shift when the patient is moved from a prone to supine position. For patients with grid placement, there are a number of “postgrid placement considerations.” The child has to be accompanied at all times (reliable parent or health care worker) to avoid any grid-related injury. CSF leaks through lead skin tunnels and through the incomplete dural closure, and dressings often need to be reinforced. Patients can develop granulation tissue at electrode sites if the grids are left in place too long. This can further compound the seizure problem if it occurs in areas that are not part of the “future resected epileptic zone.”

81.4.2╇Complications The biggest complication of invasive monitoring is the false sense of security or insecurity that it can bring to the surgeon. In the era preceding reliable MEP responses, the preservation of sensory signal in spinal cord surgery created a false sense of security, particularly for the ventral-most portions of the resection of lesions. The vascular anatomy of the spinal cord is such that ventral coagulation could lead to motor deficits that would not be detected by dorsal column monitoring. Today, techniques like MEPs and spontaneous EMG can help guide motor preservation. The false-positive rate, however, can be high if the team is not trained to follow an algorithm every time there is dampening of a wave or if the threshold to stop the surgery is low. It is essential to go through a “checklist” when waves dampen to ensure that this is not artifactual. It is important also to work elsewhere in the tumor bed until waves return. It is vital to be understanding in selective dorsal rhizotomies if the conditions are not adequate, because if the procedure advances with inadequate monitoring, then it becomes identical to a procedure done without monitoring. The authors have had occasional skin bruising and superficial abrasions at electrode contact sites but these have always been minor.

81.5╇Conclusion Multimodality monitoring, preoperative planning, and judicious use of navigational and electrophysiological information by the pediatric neurosurgeon allow contemporary practitioners to proceed with

safer yet more thorough resections. This is all to the benefit of the child and the family, both short term with respect to hospital length of stay and long term with respect to avoidance of permanent sequelae or recurrences.

References ╇1. Khealani

B, Husain AM. Neurophysiologic intraoperative monitoring during surgery for tethered cord syndrome. J Clin Neurophysiol 2009;26(2):76–81 ╇2. Mittal S, Farmer JP, Poulin C, Silver K. Reliability of intraoperative electrophysiological monitoring in selective posterior rhizotomy. J Neurosurg 2001;95(1):67–75 ╇3. Turner RP. Neurophysiologic intraoperative monitoring during selective dorsal rhizotomy. J Clin Neurophysiol 2009;26(2):82–84 ╇4. Ng WH, Mukhida K, Rutka JT. Image guidance and neuromonitoring in neurosurgery. Childs Nerv Syst 2010;26(4):491–502 ╇5. Gallentine WB, Mikati MA. Intraoperative electrocorticography and cortical stimulation in children. J Clin Neurophysiol 2009;26(2):95–108 ╇6. Ogg RJ, Laningham FH, Clarke D, et al. Passive range of motion functional magnetic resonance imaging localizing sensorimotor cortex in sedated children. J Neurosurg Pediatr 2009;4(4):317–322 ╇7. Yamada K, Sakai K, Akazawa K, Yuen S, Nishimura T. MR tractography: a review of its clinical applications. Magn Reson Med Sci 2009;8(4):165–174 ╇8. O’Brien TJ, So EL, Mullan BP, et al. Subtraction ictal SPECT co-registered to MRI improves clinical usefulness of SPECT in localizing the surgical seizure focus. Neurology 1998;50(2):445–454 ╇9. Sala F, Bricolo A, Faccioli F, Lanteri P, Gerosa M. Surgery for intramedullary spinal cord tumors: the role of intraoperative (neurophysiological) monitoring. Eur Spine J 2007;16(Suppl 2):S130–S139 10. Nuwer MR, Emerson RG, Galloway G, et al; Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology; American Clinical Neurophysiology Society. Evidence-based guideline update: intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology and the American Clinical Neurophysiology Society. Neurology 2012;78(8):585–589 11. Kothbauer KF, Deletis V, Epstein FJ. Motor-evoked potential monitoring for intramedullary spinal cord tumor surgery: correlation of clinical and neurophysiological data in a series of 100 consecutive procedures. Neurosurg Focus 1998;4(5):e1

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The Surgical Treatment of Temporal Lobe Epilepsy Benjamin A. Rubin and Howard L. Weiner

82.1╇Background The temporal lobe and its mesial structures, the amygdala and hippocampus, are particularly epileptogenic regions of the human brain. As such, they are a common source of complex partial seizures (CPS) in both children and adults. Because a high percentage of patients with temporal lobe epilepsy (TLE) are refractory to medical management, TLE is one of the most common surgically treated forms of epilepsy.1 The surgical treatment of TLE is one of the rare examples in neurosurgery in which Level I scientific evidence has shown the benefit of surgical treatment over medical therapy.2 But TLE diagnosis and treatment are not always straightforward. Pathological heterogeneity and variability in a patient’s age, level of development, and neurocognitive abilities represent a unique set of challenges and opportunities for the surgeon. For example, the pathological substrates in adults and children with TLE are discordant. Mesial temporal sclerosis (MTS) is a well-characterized entity and, historically, has been the most usual cause of TLE in adults, but it is a relatively rare cause in children as an isolated finding. In the pediatric population, MTS is usually associated with neocortical pathology, such as tumors or malformations of cortical development.3 This “dual pathology” requires that pediatric patients with TLE receive special preoperative evaluation, surgical planning, and techniques to optimize surgical intervention. Surgeons treating children with TLE should aim to achieve a maximally safe resection and provide durable seizure control with minimal surgical morbidity. This delicate balance can be achieved with a multidisciplinary approach, a comprehensive preoperative work-up, and an understanding of the technical nuances of performing surgery. As with any invasive form of treatment, the risks must be clearly assessed and weighed prior to engaging any surgical plan. However, when pediatric neurosurgeons carefully select patients, surgery can offer children with TLE between a 66 and 80% chance of a favorable outcome.4

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Most will experience a meaningful reduction in seizure frequency, and many can achieve complete seizure freedom. Further, patients and their families can also expect improvements in psychosocial and neurocognitive development.1 Therefore, children with seizure disorders that are refractory to medical management should be referred for surgical evaluation.5

82.2╇ Preoperative Assessment and Indications The preoperative assessment of any patient with a seizure disorder involves a multidisciplinary and multimodal approach, including experts in pediatric neurology, neurosurgery, neuroradiology, critical care, physiatry, and nutrition, as well as expertly trained nursing and social work staff. A thorough, noninvasive workup should include electroencephalography (EEG), structural and functional imaging, and neuropsychological and neuropsychiatric assessments. At the authors’ institution, a multidisciplinary team views the entire workup of all patients being evaluated for epilepsy surgery at a weekly conference, makes a consensus group recommendation, and then presents the recommendation to the family. The most typical indication for epilepsy surgery, for adults and children, is medically intractable epilepsy. This is defined as failure to control seizures with two trials of appropriate antiepileptic drugs (AEDs).6 Nevertheless, medical intractability in children may be more dynamic because the critical window of brain development may mandate more rapid determination of surgical candidacy compared with that of adults. In children who harbor temporal lobe lesions, cortical dysplasia, or tumors, the decision making may be even more complex, especially if the seizures are well controlled on medication. Sometimes, a period of serial imaging may help dictate treatment. Patients harboring temporal lobe lesions that remain stable over time, both clinically

82 â•… The Surgical Treatment of Temporal Lobe Epilepsy and radiographically, present a further challenge. All these decisions need to be made on an individualized basis and depend on patient-specific factors including age, lesion location, and family comfort level with the concept of elective brain surgery.

82.3╇ Goals of Surgery and Alternative Procedures The surgical treatment of TLE ultimately aims for “no seizures, no side effects.” To accomplish this, the preoperative evaluation must first determine the epileptogenic zone and then whether resection of this zone can be performed safely with minimal risk to the patient’s neurological function. In cases where it is not clear that the goals can be achieved in a single-stage resection, surgeons may perform invasive subdural electrode monitoring and stage the resections. When patient risks exceed benefits, practitioners must consider alternative procedures. It is beyond the scope of this chapter; however, alternative surgical procedures, such as vagal nerve stimulation corpus callosotomy and, more recently,

reactive neurostimulation, are generally safe palliative options in select patients.7 Surgery for TLE will likely achieve a successful, seizure-free outcome; but surgeons must remind patients and families that the results may not last. There is a growing recognition that, for unknown reasons, seizures can recur after successful epilepsy surgery and even, in some cases, many years later.8

82.4╇ Operative Detail, Preparation, and Technical Nuances The authors believe a consistent operative approach leads to successful surgery. Whereas each patient is unique, the surgery’s technical details generally should not vary greatly. The basic equipment needed to perform TLE surgery is similar to that of any cranial case. A surgeon’s choice of specific equipment is often based on bias from past experience, style of training, level of comfort, and trends in the field. In general, a cranial fixation device, frameless stereotactic image guidance systems (Fig. 82.1), insu-

Fig. 82.1â•… Brainlab frameless stereotactic neuronavigation device is used to locate and target a lesion in the left posterior mesial temporal lobe on magnetic resonance imaging (MRI). Frameless navigation is a useful adjunct in temporal lobe epilepsy (TLE) surgery to help navigate and target lesions with no visual cues, to target and confirm anatomical landmarks, and for safe and accurate placement of monitoring electrodes.

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676 Section VIIIâ•… Epilepsy and Functional Disorders lated irrigating bipolar forceps, brain retractors, and microdissection equipment are all useful adjuncts in TLE surgery. The authors consider the cavitron ultrasonic surgical aspirator or CUSA (Integra LifeSciences, Plainsboro, NJ, USA) to be a device of the utmost importance. The major portions of cortical resection in TLE are carried out in a subpial manner. Using the CUSA (Integra LifeSciences) on low settings with a “precision tip” is an excellent way of maintaining the pial plane and protecting the vessels on the epipial surface in the subarachnoid space. The exact surgical plan will, of course, depend on the particular patient and the goals of surgery. There is, nonetheless, a basic set of maneuvers that should be mastered including lateral temporal lobe resection, mesial resection of the hippocampus and amygdala, electrode implantation, and lesionectomy. Temporal lobe anatomy is complex, particularly that of the hippocampus and amygdala. As a surgeon gains more experience, the anatomy and the stepwise method of dissection become more intuitive. This chapter is not a surgical atlas; however, the authors have included nuances and “pearls” at each step that will hopefully serve as adjuncts to the basic flow, ease, and safety of the operation.

82.4.1╇Opening The surgeon must take many important pre-incision steps to ensure a successful and smooth operation. Once the patient is anesthetized, the authors administer intravenous (IV) antibiotics, dexamethasone, and a dose of the patient’s typical AED. They then position the patient supine in a Sugita headholder (Mizuho, Union City, CA, USA) and plan an incision. Positioning is a key step for any temporal lobe procedure (Fig. 82.2). After the stereotactic navigation system is registered, the incision is injected with lidocaine and epinephrine, and a rigorous skin cleansing is undertaken. Infection, especially in patients with electrode implants, is a serious risk, but there are techniques to minimize this problem. After the patient is draped, the incision is made taking care to preserve the pericranium, which is always harvested for dural grafting, to obtain a watertight and capacious dural closure. Dural substitutes can be used when necessary, but autologous graft material is preferable in the experience of the authors. Preventing cerebrospinal fluid (CSF) leakage around implanted electrodes protects against infection during seizure monitoring implantation peri-

Fig. 82.2â•… The patient is positioned supine with the head turned about 45 degrees contralateral and a shoulder roll is placed to relax the neck and facilitate venous outflow. An incision is planned from the root of the zygoma with a gentle curve to the frontal region behind the hairline. If electrodes are to be implanted, they can be tunneled posteriorly from the apex of the incision.

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Fig. 82.3â•… Magnetic resonance imaging (MRI) examples of three distinct epileptic lesions involving the dominant temporal lobe and requiring very different surgical exposures. (a) T1 postcontrast axial MRI showing an enhancing tumor situated in the posterior portion of the mesial temporal lobe. (b) T1 postcontrast MRI showing enhancing tumor situated in the posterior portion of the lateral temporal lobe. (c) T1 precontrast MRI showing a cavernous malformation in the anterior lateral portion of the temporal lobe.

ods. Also, when making the incision, care should be taken to preserve the superficial temporal artery to maintain vascularity and promote healing. There is a standard method for dissection and reflection of the temporalis muscle and performing the craniotomy. Notably, these steps can be modified depending on the case at hand (Fig. 82.3). Some cases require smaller, more anterior exposures, whereas others call for larger exposures. Either way, with sound techniques and a good understanding of the anatomy, each case can be tailored to the patient and the pathology being treated.

82.4.2╇ Lateral Temporal Lobe Resection The next procedural goal is to resect the lateral temporal lobe as a single specimen, and to identify and enter the temporal horn of the lateral ventricle (Fig. 82.4). This step varies from patient to patient and depends on whether or not it is the dominant or nondominant hemisphere. Preoperative determination of language localization is imperative (functional magnetic resonance imaging [fMRI], magnetoencephalography [MEG], Wada test, grid mapping, etc.), and the superior temporal gyrus in the dominant temporal lobe should be preserved if possible. Resection size is case-specific―some resections may only include a small tumor in the temporal lobe, whereas in others, malformation of cortical

development may involve the entire lobe (Fig. 82.3). However, the general principle of lateral temporal lobe resection involves two pial incisions: one parallel to the Sylvian fissure and one perpendicular to it at the posterior extent of the planned resection (often dictated by the position of the vein of Labbé). It is helpful to orient yourself by counting the gyri during the perpendicular cut, starting with superior, then middle, then inferior, and finally the fusiform gyrus. The fusiform gyrus is separated from the parahippocampal gyrus at the collateral sulcus. During the lateral resection, the venous anatomy must be respected and preserved until the specimen is ready to be released. This will prevent engorgement of the specimen and protracted bleeding at the resection sites. The pia is coagulated and cut, gradually freeing the lateral temporal lobe. Care must be taken to identify any draining veins from the temporal lobe entering the dura of the middle fossa, and to coagulate and cut these prior to lifting out the specimen. Identifying the temporal horn is the “blow for freedom” moment of the case and the key orientation point for the mesial resection of the amygdala and hippocampus. This is not always as simple as it may seem. It usually can be identified deep to the middle temporal gyrus, at a depth of ~ 3.5 cm, as seen on the magnetic resonance imaging (MRI) scan. It is very important to angle one’s approach to the temporal horn more toward the floor of the middle fossa, especially when starting at the superior temporal

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Fig. 82.4â•… Artist’s rendition of lateral temporal lobe exposure. Keeping in mind the three-dimensional (3D) structure of the mesial temporal anatomy and envisioning these deeper structures’ relationship to the surface anatomy will help the surgeon remain oriented. It also determines the angle of approach because the lateral temporal lobe is resected en route to the mesial structures and the temporal horn of the lateral ventricle. CS, collateral sulcus; FG, fusiform gyrus; ITG, inferior temporal gyrus; MTG, middle temporal gyrus; PHG, parahippocampal gyrus; SF, sylvian fissure; STG, superior temporal gyrus.

gyrus, rather than aiming directly medially, which could result in losing one’s orientation. Frameless stereotaxy can be helpful (Fig. 82.1). Once the ventricle is entered, a cotton strip is placed over the choroid plexus to protect it from blood, to maintain the landmark, and to prevent manipulation of the choroid plexus for the rest of the operation. Never coagulate the choroid plexus, but rather cover it with a cotton strip to avoid injury to the anterior choroidal artery, which could result in hemiplegia. Within the temporal horn, recognition of the anatomy is critical for orientation. The hippocampus is classic in its appearance, just lateral to the choroid plexus within the choroidal fissure. The fimbria lines the medial side of the hippocampus. Just lateral to

the hippocampus is a raised structure, the collateral eminence. The amygdala is a large, bulky, graymatter structure filling the anterior-medial-superior aspect of the operative field (Fig. 82.5).

82.4.3╇ Mesial Resection of the Hippocampus and the Amygdala The next step is to resect the amygdala, which the authors do using the CUSA (Integra LifeSciences). This step represents the steepest part of the learning curve, in their experience. The amygdala is much deeper and more superior than one might envision (Fig. 82.6 and Fig. 82.7). To start, a cut is made from

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Fig 82.5â•… Artist’s rendition of the relationship between the lateral ventricle, choroid plexus (CP), the hippocampus (HC), and amygdala. (a) Always remember that the optic tract (OT) runs in the roof of the lateral ventricle at approximately the level where the CP becomes visible. A cotton strip is used to mark this point and to protect the CP, OT, anterior choroidal artery, and basal vein of Rosenthal (which are just inferior to the OT). PHG, parahippocampal gyrus. (b) The amygdala is removed on a transverse line from the choroidal fissure (CF). (c) The CF is the space between the fimbria of the HC and the CP. Once the amygdala is resected and the HC is retracted and the CF is opened, the posterior cerebral artery (PCA) and optic nerve (ON) can be identified.

the anterior tip of the choroidal fissure to the pia of the anterior-medial temporal lobe, disconnecting the amygdala from the hippocampus. All tissue must be removed to the medial pia, exposing the middle cerebral artery on the other side of the pia superiorly, and the tentorial edge inferiorly. Medial to the tentorial edge, on the other side of the pia (which protects these critical structures), one must visualize the third cranial nerve and posterior cerebral artery. To avoid injury to the optic tract and basal ganglia, one should never resect the amygdala above an imaginary line drawn from the anterior tip of the choroidal fissure to the trunk of the M1 branch of the middle cerebral artery.9

The authors remove the parahippocampal gyrus, separately from the hippocampus, with the CUSA (Integra LifeSciences), again in a subpial fashion. After the amygdala has been resected, exposing the pia medial to the tentorial edge, they work from anterior to posterior with the CUSA (Integra LifeSciences), resecting the parahippocampal gyrus as far posteriorly as the tectal plate. The pia protects the structures in the ambient cistern, including the posterior cerebral artery, the brainstem, and the fourth cranial nerve. Although the authors’ resection of the hippocampus is generally done without fixed brain retractors— a bias of training with Dr. Patrick Kelly, who never

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Fig. 82.6â•… Axial fluid-attenuated inversion recovery (FLAIR) sequence magnetic resonance imaging (MRI) (a) showing evidence of signal abnormality in the left uncus and (b) amygdala suggestive of tumor or malformation of cortical development.

used brain retractors—many surgeons prefer to use them. In that case, one retractor blade is placed medially to expose the medial aspect of the hippocampus, while the second is placed posteriorly within the temporal horn, gently elevating the roof of the posterior aspect of the temporal horn to expose the hippocampal tail. The authors prefer hand-held retractors, with the first assistant gently retracting, as needed. This allows for tactile feedback, is more dynamic, and therefore safer than fixed retraction. The hippocampectomy is carried out microsurgically with the operating microscope (see this chapter’s associated video). The goal is to dissect the hippocampus in a lateral and posterior direction, and to transect it at the tail, as far posteriorly as the tectal plate. The authors use a Penfield 4 dissector and Rhoton 5 suction, and gently peel the fimbria and hippocampus off the pia from medial to lateral. The hippocampus is then rolled medially over a cotton strip to further expose the hippocampal sulcus, in which small branches of the posterior cerebral artery feeding the hippocampus enter through a double fold

of arachnoid. The surgeon needs to dissect free the hippocampus as much as possible, so that these vessels are the only remaining attachment. The vessels are coagulated with the bipolar as close as possible on the body of the hippocampus, and then cut with a curved, bayoneted micro-scissor. The hippocampus is thus mobilized posteriorly and laterally, and transected at the tail with the bipolar. The entire medial aspect of the field is then inspected to ensure that the resection is complete. The authors use the CUSA (Integra LifeSciences) to complete any remaining tissue resection, with great care (Fig. 82.8).

82.4.4╇ Electrode Implantation and Intraoperative Electrocorticography When possible, single-stage operations for TLE are ideal; however, implantation of subdural and depth electrodes often may be necessary to determine the epileptogenic zone, define the epileptic network, and guide the margins of the final resection. There are many

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Fig. 82.7â•… Stepwise microdissection of the lesion seen in Fig. 82.6 in the left mesial temporal lobe. (a) Transcortical dissection down to the lesion at the level of the uncus. (b) After resection of the uncal component of the tumor, the region of the amygdala is identified in a superior medial orientation (blue arrow) and (c) the Cavitron Ultrasonic Surgical Aspirator or CUSA (Integra LifeSciences, Plainsboro, NJ, USA) is used to aspirate it. (d) After complete resection of the lesion, the head of the hippocampus (green arrow) is identified along with the tentorial edge (blue arrow) as the anterior margin of the ambient cistern.

ways to place electrodes for long-term monitoring, and placement is determined on a case-by-case basis. To ensure safety, these electrodes should be inserted under direct vision to avoid tearing veins and causing subdural bleeding. When direct vision is not possible, or when placing depth electrodes, frameless image guidance can help direct a safe trajectory. Because electrodes may remain implanted for a long time, it is crucial to secure them properly. The authors suture implants at the margin of the dura, and at the skin exit sites with 4–0 Nurolon (Ethicon Endo-Surgery, Inc., Somerville, NJ, USA) purse-string

sutures, and then secure them with a 0 Prolene (Ethicon) suture on the scalp. Additionally, performing a watertight dural closure with pericranial graft, placing purse-string sutures where the electrode exits the scalp, and using IV antibiotics are their techniques for minimizing CSF leak and infection. Intraoperative electrocorticography may also help determine the extent of resection. After a lesionectomy or cortical resection, electrodes may be placed at the margins of the resection, looking for epileptiform discharges intraoperatively. When identified as epileptogenic, these regions can be further resected.

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Fig 82.8â•… Artist’s rendition of microsurgical hippocampectomy. The hippocampus is removed in a lateral and posterior direction. (a) Microsurgical instruments can be used to gently peel the fimbria and hippocampus off the pia from medial to lateral. The hippocampus is then rolled medially over a cotton strip to further expose the hippocampal sulcus (HS) between the dentate gyrus (DG) and the subiculum (SB). Small branches of the posterior cerebral artery (PCA) feeding the hippocampus enter the hippocampal sulcus through a double fold of arachnoid. These branches are coagulated with bipolar forceps and cut sharply to prevent bleeding. (b) Line 1 depicts the cut through the SB to the tentorial surface and line 2 represents a cut through the hippocampus and parahippocampal gyrus (PHG) for final detachment. (c) Once detached, the hippocampus and the PHG are removed from the field. The PCA is seen coursing across the cerebral peduncle (CP).

82.5╇Conclusion Surgically treating patients with TLE can be very rewarding. Outcomes tend to be extremely positive, with appropriate patient selection and the support of a comprehensive multidisciplinary team. However, each case represents unique challenges and requires

different strategies to optimize the goals of treatment. The anatomy of the lateral and mesial temporal lobe is complex and there is a sizable learning curve for performing these operations. As in all areas of neurosurgery, a consistent operative approach and cumulative surgical experience are the keys to performing successful and safe surgery.

82â•… The Surgical Treatment of Temporal Lobe Epilepsy

References ╇1. Albright AL, Pollack IF, Adelson PD. Operative Techniques

in Pediatric Neurosurgery. New York, NY: Thieme Medical Publishers; 2001 ╇2. Wiebe S, Blume WT, Girvin JP, Eliasziw M; Effectiveness and Efficiency of Surgery for Temporal Lobe Epilepsy Study Group. A randomized, controlled trial of surgery for temporal-lobe epilepsy. N Engl J Med 2001;345(5):311–318 ╇3. de Ribaupierre S, Wang A, Hayman-Abello S. Language mapping in temporal lobe epilepsy in children: special considerations. Epilepsy Res Treat 2012;2012:837036 ╇4. Spencer S, Huh L. Outcomes of epilepsy surgery in adults and children. Lancet Neurol 2008;7(6):525–537 ╇5. Cross JH, Jayakar P, Nordli D, et al; International League against Epilepsy, Subcommission for Paediatric Epilepsy Surgery; Commissions of Neurosurgery and Paediatrics.

Proposed criteria for referral and evaluation of children for epilepsy surgery: recommendations of the Subcommission for Pediatric Epilepsy Surgery. Epilepsia 2006;47(6):952–959 ╇6. Kwan P, Arzimanoglou A, Berg AT, et al. Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia 2010;51(6):1069–1077 ╇7. Al-Otaibi F, Baeesa SS, Parrent AG, Girvin JP, Steven D. Surgical techniques for the treatment of temporal lobe epilepsy. Epilepsy Res Treat 2012;2012:374848 ╇8. Najm I, Jehi L, Palmini A, Gonzalez-Martinez J, Paglioli E, Bingaman W. Temporal patterns and mechanisms of epilepsy surgery failure. Epilepsia 2013;54(5):772–782 ╇9. Tubbs RS, Miller JH, Cohen-Gadol AA, Spencer DD. Intraoperative anatomic landmarks for resection of the amygdala during medial temporal lobe surgery. Neurosurgery 2010;66(5):974–977

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83

The Surgical Treatment of Extratemporal Epilepsy Alexander G. Weil and Sanjiv Bhatia

83.1╇Background Population-based studies have shown that 5 to 10% of all patients with new-onset seizures will develop refractory epilepsy. The predictors of intractability are seizure onset at a younger age, mental retardation, and a high seizure frequency.1 These children should be evaluated at a comprehensive epilepsy surgery program and considered for candidature for epilepsy surgery.2,3

83.2╇ Indications for Surgical Intervention Extratemporal epilepsy (ETE) is common in children. The clinical semiology in ETE is distinct from seizures originating in the temporal lobe, although frontal or insular lobe seizures can sometimes have a complex symptomatology and resemble temporal lobe epilepsy (TLE). Children have varied pathology, such as malformations of cortical development (e.g., cortical dysplasia [CD]) and seizures are more likely to originate from one or multiple lobes of the extratemporal cortex.1 Refractory ETE may lead to neurocognitive decline, developmental delay, social impairment, and significantly diminished quality of life. Better seizure control may help improve these measures. The neuroplasticity of the immature brain provides greater potential for functional recovery and development following surgery.4 All children with ETE should be evaluated (Fig.€83.1)2,5 by a comprehensive epilepsy center once they are deemed medically intractable.2,3 Presurgical noninvasive tests are used to: (1) localize the epileptogenic zone, and (2) map functional eloquent cortex (sensorimotor, language, vision).

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83.3╇ Preoperative Evaluation 1. Evaluation includes video electroencephalography (EEG), high-quality magnetic resonance imaging (MRI) and physiological imaging with single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetoencephalography (MEG), and functional MRI (fMRI). 2. In nonlesional ETE, interictal and ictal SPECT scanning, PET scanning, and three-dimensional (3D) source imaging, or MEG scanning help localize seizure onset (Fig. 83.2). 3. Image co-registration techniques help in understanding the extent of involved cortex and in planning surgical options (Fig. 83.2 and Fig. 83.3). 4. Neuropsychological testing to evaluate the functional deficits in language, memory, intelligence quotient (IQ), and executive functioning Surgical candidates are divided into three major groups based on MRI findings: lesional ETE has a defined anatomical abnormality on MRI, nonlesional ETE has normal MRI, and dual pathology has two distinct anatomical abnormalities on MRI, such as extratemporal CD plus hippocampal sclerosis (HS).1 In children with ETE, the presence of a lesion that is completely resectable is among the most important prognostic factors for successful treatment of seizures.1,6,7 The surgical approach for ETE is complex and tailored to each individual patient based on the presurgical workup. Patients can be managed with a single- or two-stage approach.1 • Single-stage approach: – Involves cortical resection of the extratemporal epileptogenic zone based

83 â•… The Surgical Treatment of Extratemporal Epilepsy

Fig. 83.1â•… Decision-making algorithm for patients with extratemporal epilepsy (ETE).3 AVM, arteriovenous malformation; ECoG, electrocordicography; FCD, focal cortical dysplasia; fMRI, functional MRI; MEG, magneto encephalography; TS, tuberous sclerosis; vEEG, video electroencephalogram.

on a noninvasive presurgical workup that defines the epileptogenic margins and eloquent cortex. Intraoperative electrocorticography (ECoG) recording is performed in most cases, including all those of CD or dysplastic tumors.7 Invasive electrode implantation with extraoperative recording and stimulation is not necessary in cases where resection will be carried out remote from eloquent areas. When the epileptogenic zone is near eloquent cortex, these functional areas (especially motor) can be mapped noninvasively with fMRI. • Single-stage cortical resective surgery is warranted in children with: 1. Lesional ETE with convergent noninvasive data showing an epileptogenic zone that is remote from eloquent cortex

2. Lesional ETE with convergent noninvasive data showing an epileptogenic zone located in or near eloquent cortex, and noninvasive fMRI showing the epileptogenic zone’s relation to functional area. Intraoperative motor cortex stimulation for motoreloquent or awake craniotomy for language and/or sensorimotor-eloquent resections in cooperative children may be performed in this approach. • Two-stage approach: – When the epileptogenic or eloquent areas cannot be reliably localized noninvasively, a two-stage approach is employed using either subdural grid/depth electrode or stereotactic depth electrode (SEEG) implantation with extraoperative video-EEG monitoring/ stimulation for epileptogenic and functional

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Fig. 83.2â•… (a) A patient with epilepsy related to right parietal gliosis as documented on magnetic resonance imaging (MRI), (b) electroencephalography (EEG) source localization, and (c) MRI-positron emission tomography (PET) co-registration.

mapping, followed by tailored cortical resective surgery. A two-stage approach is often warranted in nonlesional ETE because the epileptogenic area may be diffuse, ill defined, and incorporate or lie adjacent to eloquent areas (language, motor, sensory). This approach is usually indicated in the following scenarios: 1. Lesional ETE and divergent noninvasive data (semiology, interictal or ictal scalp EEG, video-EEG, ictal SPECT, interictal fluorodeoxyglucose [FDG]-PET, MEG) 2. Lesional ETE with convergent noninvasive data showing an epileptogenic zone located in or near eloquent cortex 3. Lesional ETE with multiple lesions (e.g., tuberous sclerosis [TS] or multiple areas of CD) with ambiguous or divergent noninvasive data 4. Lesional ETE with convergent noninvasive data that suggest extent beyond the MRI epileptogenic lesion. Alternatively, a single-stage approach with intraoperative ECOG could be used in this setting.

5. Nonlesional ETE and convergent noninvasive data to define margins of resection

83.4╇Goals The treatment goals of extratemporal resective surgery are to1,6,7: • Eliminate or reduce seizures by removing the epileptogenic area • Achieve palliative reduction of seizure burden in patients with medically intractable seizures in which alternative modalities have failed • Preserve neurological function • Improve quality of life, preserve or improve neurodevelopmental and cognitive outcome

83.5╇ Alternate Procedures Alternate procedures include disconnection and stimulation procedures.

83 â•… The Surgical Treatment of Extratemporal Epilepsy d

Fig. 83.2 (Continued)â•… (d) Surgical planning is performed to delimit the desired resection in relation to the optic radiations. (Continued on page 688)

• Disconnection procedures: – Multiple subpial transection (MST): a. May be used when the seizure focus involves eloquent area (e.g., the sensorimotor cortex or language areas) b. Involves selective interruption of the horizontal intracortical connections required for epileptic synchronicity and propagation, allowing preserving functional vertical pathways subserving function – Anatomical hemispherectomy or functional hemispherotomy: c. Indicated for medically resistant hemispheric epilepsy caused by diffuse hemispheric disorder (e.g., Sturge–Weber, middle cerebral artery [MCA] infarct) resulting in progressive hemispheric syndrome (hemiplegia,

homonymous hemianopsia) when multilobar resection is not feasible – Corpus callosotomy: a. Indicated for medically resistant drop attacks and generalized epilepsy caused by rapid spread from one hemisphere to another – Posterior quadrant disconnection: a. The posterior quadrant refers to the temporo-parieto-occipital area. In subhemispheric multilobar temporoparieto-occipital epilepsy, disconnecting the posterior quadrant can offer a palliative reduction in seizures. • Stimulation procedures: – Implantable stimulation device: a. The NeuroPace RNS, a closed-loop, responsive cortical stimulation device,

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Fig. 83.2 (Continued)â•… (e) Postoperative imaging shows right parietal resection sparing the optic radiations.

has recently been granted premarket approval for use in adults (> age 18 y) with medically refractory partial epilepsy (limited to no more than two epileptogenic foci) by the Food and Drug Administration (FDA). Up to 50% of patients obtain 50% reduction in disabling seizures. – Vagal nerve stimulator (VNS): a. An FDA-approved treatment for medically intractable seizures. In children, VNS is 30 to 50% effective in reducing seizures by 50% in patients who are not candidates for focal resective surgery. – MRI-guided laser thermoablation: a. MRI-guided stereotactic laser thermoablation may be considered as a

treatment option when the epileptogenic area is well localized, deep-seated, adjacent to eloquent cortex, and used in patients being reoperated for residual symptomatic epileptogenic cortex.

83.6╇Advantages • Minimally invasive methods (e.g., laser thermoablation) may be suitable for ablating epileptogenic tissue located in the deep-seated areas, in residual cortex from prior resections, or in patients at risk of multiple surgical interventions throughout life (e.g., TS). Closed-loop, responsive cortical stimulation may help in cases of eloquent ETE.

83 â•… The Surgical Treatment of Extratemporal Epilepsy

83.7╇Contraindications • Hemispherotomy is contraindicated when the function of the epileptogenic hemisphere is intact. • Focal resection and other approaches may be contraindicated when medical condition prohibits general anesthesia (e.g., rhabdomyoma in a TS patient). • VNS may be contraindicated in patients with unilateral vocal cord palsy. • Reoperation after prior extraoperative monitoring must be performed with caution to avoid cortical injury.

83.8╇ Operative Detail and Preparation 83.8.1╇ Preoperative Planning and Special Equipment Detailed discussion with epileptologists should be about the clinical semiology and investigations, and surgical plan (including extent of coverage for subdural grid, strip, depth recordings, and expectations for seizure control), so that adequate exposure can be achieved. In nonlesional cases, it is beneficial to develop a 3D concept about the epileptogenic zone and seizure spread. This helps in planning the placement of sur-

a

b

face grid and insertion of depth electrodes. A number of image manipulation programs can help co-register multimodality imaging modalities to achieve this (Fig. 83.2, Fig. 83.3, and Fig. 83.4). In two-stage procedures, invasive monitoring can be placed using frameless stereotaxy (neuronavigation) or frame-based stereotaxy if SEEG techniques are used. Valproic acid should be weaned for 2 weeks prior to surgery to correct coagulopathy and avoid higher risk of bleeding. Intravenous corticosteroids should be administered at induction to reduce cerebral edema and continued postoperatively. In patients with a history of herpes simplex virus (HSV) encephalitis, the authors advocate the use of prophylactic perioperative intravenous acyclovir to prevent the occurrence of HSV reactivation and fulminant HSV encephalitis following surgery. This may aid in preventing postoperative seizures, neurological decline, and permanent disability related to HSV encephalitis reactivation.8

Special Equipment • Frameless stereotactic system: – Neuronavigation is a particularly useful adjunct in extratemporal resective surgery. It can help plan the craniotomy, identify corresponding cortical areas on MRI, and assess extent of surgical resection. Coregistration of anatomical MRI to functional

c

Fig. 83.3â•… (a) Five-year-old boy with an area of suspected focal cortical dysplasia (FCD) in the right frontal pole on T1-weighted (T1W) magnetic resonance imaging (MRI). (b) Normal interictal positron emission tomography (PET) scan. (c) Area of mismatch in the right frontal lobe between the suspected FCD and the surrounding gray matter on superimposed PET on MRI. The suspected area was removed, and the child was seizure-free at 3-year postoperative follow-up.

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Fig. 83.4â•… The Miami Imaging Pipeline is a conceptual tool used to process imaging data. Multiple data imaging sets (magnetic resonance imaging [MRI], single-photon emission computed tomography [SPECT], and positron emission tomography [PET]) are co-registered using Amide, a software tool for viewing, analyzing, and registering volumetric data imaging sets. These image sets can then be transferred to MeVisLab for three-dimensional (3D) visualization and surgical planning, picture archiving and communication system (PACS) for long-term archiving, and Brainlab (Brainlab, Munich, Germany) for surgical planning and neuronavigation. CT, computed tomography; fMRI, functional magnetic resonance imaging; DTI, diffusion tensor imaging.

mapping (fMRI) and epileptogenic zone (MEG, SISCOM [an advanced diagnostic imaging tool]) can be very valuable in ETE to identify the extent of resection and its relation to eloquent cortex during surgery (Fig. 83.2 and Fig. 83.3). • Intraoperative electrocorticography5: – ECoG is employed intraoperatively in almost all ETE cases to delimit the epileptogenic zone and improve outcome of pediatric epilepsy surgery. It is especially useful in nonlesional cases or lesional cases with CD and dysplastic tumors. • Intraoperative ultrasound (IUS) or intraoperative magnetic resonance imaging (iMRI): – IUS is a feasible, inexpensive tool that can help localize the epileptogenic lesion below the cortical surface and assess extent of resection. It can also aid in electrode

placement in the hippocampus and insula (Fig. 83.5). – iMRI may also be of benefit in cases of CD or low-grade tumors.

83.8.2╇ Expert Suggestions/Comments • Important to interview patient, parents, and other caregivers; assess the details of the seizure semiology to understand the cortex that may be implicated in the origin or spread of the seizure discharge • Discuss the semiology, electrodiagnostic studies, and imaging data with the epilepsy team to understand the location of the putative epileptogenic zone. • Discuss the expectation of seizure control, clinical questions that remain unanswered, and what can be achieved with extraoperative

83 â•… The Surgical Treatment of Extratemporal Epilepsy a

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e

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Fig. 83.5â•… (a) Fluid-attenuated inversion recovery (FLAIR) axial image demonstrates high signal in the subcortical white matter. Transmantle extension is not well seen. (b) T1 axial details abnormal cortex with blurring of the gray-white matter junction and atrophy. (c) Intraoperative ultrasound (IUS) shows increased echogenicity of the subcortical white matter (long arrow) with transmantle extension (short arrow). (d) Ultrasound (US) was utilized to guide electrode placement (short arrow). (e) Computed tomography (CT) confirms correct position of the electrode. (f) Postsurgical FLAIR magnetic resonance imaging (MRI) shows surgical excavation cavity.

monitoring. This assists in planning the extent of coverage for extraoperative monitoring. • At the time of resection, use of microsurgical techniques supplemented by neuronavigation and tractography, whenever needed, to protect eloquent white matter tracts • Precise knowledge of normal and pathological anatomical pathways so that accurate surgical excision of the epileptogenic tissue can be achieved without compromising normal parenchyma

83.8.3╇ Key Steps of the Procedure/ Operative Nuances • Plan for the exposure needed―magnetic resonance venography (MRV) may help avoid major draining veins for interhemispheric exposure.

• Consider an osteoplastic craniotomy bone flap when planning for extraoperative monitoring, reduces risk of bone loss in the event of a wound infection. • Placement of insular depth electrodes may be done stereotactically or advancing them through the limen insula after dissection of Sylvian fissure. Drilling of the lesser wing to obtain a flat access into the insular cortex is effective. • Stimulation of cortical surface for brain mapping may precipitate a seizure―keep icecold Ringer lactate handy to prevent seizure spread and brain swelling. • Use dural substitutes and steroids after electrode placement to prevent postoperative swelling. • At the time of resection, close attention should be given to pathological anatomy and relationship with white matter tracts to avoid

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MRI Left hand sensory

SPECT

Electrical stimulation left corner mouth twitch (44 and 36) Ictal activity

Fig. 83.6â•… Invasive electrode implantation scheme with multimodality work-up. MRI, magnetic resonance imaging; SPECT, singlephoton emission computed tomography.

inadvertent deficits. Co-registration of MRI, tractography, and electrodes can help with 3D conceptualization of anatomical relationships (Fig. 83.6).

Craniotomy If extraoperative monitoring is planned, a large osteoplastic craniotomy is preferred to provide adequate access for placement of subdural and depth electrodes and supply suitable coverage of the area of interest. All the leads are tested prior to closure. The leads are sutured to edges of dura to avoid electrode mobility. Electrodes are tunneled away from the incision and sutured to the skin to avoid displacement. Exit sites are closed over to avoid postoperative cerebrospinal fluid (CSF) leak. Expansive duraplasty using a dural graft may help accommodate postoperative swelling and brain shift due to subdural electrodes. Postoperative computed tomography (CT) is done soon after surgery to facilitate postoperative CT-MRI co-registration to localize the electrodes to the surface gyral anatomy. • Anesthesia considerations: – General anesthesia is preferred; rarely would an awake craniotomy be necessary

for resective surgery of eloquent areas. When intraoperative ECoG or motor cortex stimulation is performed, inhalational anesthetics are reduced. – Anesthetics (e.g., nitrous oxide, inhaled halogenated agents, barbiturates, benzodiazepines) can suppress epileptiform activity and induce confounding burst suppression during intraoperative ECoG. – Sevoflurane at 1.5 MAC, isoflurane less than 0.5% MAC are recommended. • Intraoperative ECoG: – During ECoG, anesthesia is lightened as much as possible to avoid suppressing epileptic activity. Strips and/or grids are placed over cortex of suspected epileptogenicity and a ground and reference are placed in a subgaleal fashion. It is important to evaluate background activity and resting spikes. Focally attenuated background activity or regional burst suppression may suggest focal diseased epileptogenic cortex. The epileptologist will assess for is interictal epileptiform spike activity. The presence of continuous epileptiform discharges is very sensitive and specific for CD.

83 â•… The Surgical Treatment of Extratemporal Epilepsy – Postoperatively the anticonvulsant medications are tapered and monitored for habitual seizures. Once adequate numbers of seizures are obtained and an acceptable hypothesis is formulated about seizure onset, the patient is loaded with anticonvulsants and set up for brain mapping of the eloquent cortex. After the surgical plan is decided upon in conjunction with the epileptologist, a detailed discussion is held with the family about the expectations of seizure control, risks of resection, and postoperative deficits.

Cortical Resective Surgery The suspected area of epileptogenesis, as defined by extraoperative monitoring, is marked out. The cortex is coagulated and corticectomy performed based on anatomical MRI abnormalities and electrophysiological data (SPECT, PET, MEG or MSI) and fMRI data (language, motor), or as based on the plan after extraoperative monitoring (Fig. 83.2). A topectomy (focal corticectomy) is performed by coagulating and incising the pia along the area of planned resection. The gray matter is removed in a subpial manner under magnification, protecting the underlying white matter. Care is taken to avoid coagulating the sulcal vessels. Corticectomy is carried to the depths of the sulcus. This process is often tedious and best performed under magnification. • Frontal corticectomy/lobectomy is usually carried out in a tailored manner. Resection of the orbitofrontal cortex is often carried posteriorly to the anterior insula. The medial resection is carried to the gyrus rectus, where it is important to protect the perforating vessels. When a prefrontal lobectomy is planned, it is essential to identify the central sulcus, either extraoperatively or during surgery, with somatosensory-evoked potential (SSEP) phase reversal. Usually the resection is precoronal. Care is taken to avoid transgressing the interhemispheric fissure. Care should also be taken to avoid skiving posteriorly into the descending motor fibers. • Parietal and occipital corticectomy can be done being careful to avoid the calcarine cortex and the underlying white matter. • Subpial insular corticectomy of short and long gyri can be done either through a transSylvian approach, after opening the Sylvian fissure widely in cases of insulectomy, or

through a trans-opercular approach following a frontoparietal or temporal opercular resection in cases requiring operculoinsulectomy. Caution must be exercised to avoid transgressing the extreme capsule in the depth of the insular resection cavity (Fig.€83.7). Consider using a subgaleal drain to reduce risk of epidural collections, and postoperative CT or MRI to co-register electrodes on surface gyral anatomy.

83.9╇ Outcomes and Postoperative Course Postoperative antibiotics are continued for 48 hours after resection; steroids are continued for a few days following resective surgery and then tapered off. Anticonvulsants are continued postoperatively at a lower dose following phase 1 electrode implantation.

83.9.1╇Complications Transient deficits may relate to region of resection. Patients with resection in the supplementary area may have transient mutism and contralateral weakness (apraxia) that usually resolves in a couple of weeks. Cortical resection in the parietal region may result in hemianopia secondary to ischemic injury to the underlying white matter tracts (optic radiation). This often resolves completely. Insular resection has a high risk of hemiparesis due to vascular injury to the M3 and M4 branches of the MCA. This can be prevented by meticulous microsurgical dissection, preventing vasospasm with postoperative instillation of papaverine locally. Many patients suffer a transient spontaneously resolving hemiparesis related to corona radiate infarct from injury to the long perforators originating from M2. Great care should be taken to avoid entry into the deep white matter, which can result in injury to the arcuate fasciculus. The risk of infection is limited to a rate of 1.5% with one-stage procedures and about 3 to 5% with extraoperative monitoring.

83.9.2╇Outcome Seizure control is achieved in up to 80% of patients with lesional extratemporal epilepsy, whereas in nonlesional extratemporal epilepsy the chance of seizure control is about 60%.7

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Fig. 83.7â•… Two techniques of peri-sylvian operculo-insulectomy. (a) Supial through operculum and (b) trans-Sylvian approach following opening of the sylvian fissure.

References ╇1. Morrison

G, Bhatia S. Surgical management of extratemporal epilepsy in children. In: Principles and Practice of Pediatric Neurosurgery. 2nd ed. ╇2. Jayakar P, Dunoyer C, Dean P, et al. Epilepsy surgery in patients with normal or nonfocal MRI scans: integrative strategies offer long-term seizure relief. Epilepsia 2008;49(5):758–764 ╇3. Jayakar P, Gaillard WD, Tripathi M, Libenson MH, Mathern GW, Cross JH; Task Force for Paediatric Epilepsy Surgery, Commission for Paediatrics, and the Diagnostic Commission of the International League Against Epilepsy. Diagnostic test utilization in evaluation for resective epilepsy surgery in children. Epilepsia 2014;55(4):507–518 ╇4. D’Argenzio L, Colonnelli MC, Harrison S, et al. Cognitive outcome after extratemporal epilepsy surgery in childhood. Epilepsia 2011;52(11):1966–1972

╇5. Awad IA, Rosenfeld J, Ahl J, Hahn JF, Lüders H. Intractable

epilepsy and structural lesions of the brain: mapping, resection strategies, and seizure outcome. Epilepsia 1991;32(2):179–186 ╇6. Ansari SF, Maher CO, Tubbs RS, Terry CL, Cohen-Gadol AA. Surgery for extratemporal nonlesional epilepsy in children: a meta-analysis. Childs Nerv Syst 2010;26(7):945–951 ╇7. Englot DJ, Breshears JD, Sun PP, Chang EF, Auguste KI. Seizure outcomes after resective surgery for extra-temporal lobe epilepsy in pediatric patients. J Neurosurg Pediatr 2013;12(2):126–133 ╇8. Bourgeois M, Vinikoff L, Lellouch-Tubiana A, Sainte-Rose C. Reactivation of herpes virus after surgery for epilepsy in a pediatric patient with mesial temporal sclerosis: case report. Neurosurgery 1999;44(3):633–635, discussion 635–636

84

The Surgical Treatment of Rolandic Epilepsy in Children Christian J. Cantillano Malone and James T. Rutka

84.1╇Background The surgical treatment for epilepsy arising from sensorimotor cortex presents a significant challenge in children because of the difficulty in ictal localization and the risk of injury to eloquent cortex.

84.2╇Indications Children with malignant rolandic epilepsy syndrome suffer from sensorimotor seizures arising from the rolandic region that are refractory to medical intervention. Patients have normal findings on imaging but cognitive difficulties, central epileptic spike wave disturbances on electroencephalography (EEG), and unilateral spike clusters on magnetoencephalography (MEG).1 Many children with malignant rolandic epilepsy syndrome, as well as children with other intractable epilepsy conditions arising from this region, are candidates for resective surgery if feasible.

84.3╇Goals The published rates of seizure freedom after surgery for extratemporal epilepsy vary between 40 and 70%, compared with more than 80% for temporal lobe epilepsy.2 Nevertheless, the goals remain the same: the reduction or elimination of seizures, with minimal morbidity as well as the preservation or improvement of neurocognitive function.3

84.4╇ Alternative Procedures Because of the intractable nature of this form of epilepsy and concern about creating new neurologic deficits if the central epileptogenic zones are resected,

multiple subpial transections (MSTs) through the rolandic region have been attempted previously.1 Theoretically, this technique preserves the vertical functional pathways while eliminating the horizontal seizure-propagating pathways. However, the results are not durable, and seizure outcomes are less than satisfactory over time.

84.5╇Advantages The most important advantages of primary resection of an epileptogenic focus within or near the rolandic cortex are the immediacy of seizure control and the opportunity to completely resect regions of cortical dysplasia or other lesions.

84.6╇Contraindications Important factors that can complicate surgery include multiple seizure foci, nonlesional magnetic resonance imaging (MRI), and proximity of the epileptogenic zone to the eloquent cortex. If the individual patient’s risk:benefit ratio is not favorable, a multistage surgical approach, vagal nerve stimulation (VNS), or corpus callosotomy should be considered.

84.7╇ Operative Detail and Preparation 84.7.1╇ Preoperative Planning and Special Equipment Prior to invasive video-EEG, all children should be assessed with scalp EEG, MRI, functional magnetic resonance imaging (fMRI), and MEG where available. Prolonged video-EEG monitoring is crucial as

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696 Section VIIIâ•… Epilepsy and Functional Disorders an initial approach. Selected patients can undergo fluorodeoxyglucose–positron emission tomography (FDG–PET) scanning and/or single-photon emission computed tomography (SPECT). Formal neuropsychological tests are performed on cooperative patients and those in whom evaluation is possible. A thorough neuropsychological evaluation is essential, not only for supplying a preoperative baseline but also for potentially providing corroborative data for a suspected ictal focus. Wada testing, fMRI, or MEG can also be used to determine hemispheric language lateralization prior to surgery in selected cases.1

Magnetic Resonance Imaging In all cases, brain MRI is performed in a 1.5 to 3.0 T unit. The authors’ epilepsy protocol includes the following sequences: sagittal T1-weighted (T1W) images; axial and coronal dual-echo T2-weighted (T2W) images; coronal fluid-attenuated inversion recovery (FLAIR); and coronal volumetric three-dimensional (3D) fastspoiled gradient recall sequence.1 In children younger than 2 years, longer echo times (50–100 ms) are used on proton density and T2W images to improve evaluation of myelination. If a neoplasm is suspected, Gd (gadolinium)-based contrast is used.1

Magnetoencephalography Studies MEG studies involving a whole-head gradiometer, Omega 151-channel system (VSM Med Tech Ltd.) can also be performed in all patients if available and is highly recommended. In brief, EEG data are collected simultaneously with the MEG recording, which involves 19 electrodes and 2-minute periods, at least 15 in number, of spontaneous data. The epileptic events are visually identified by examining the MEG recordings and cross-referencing them with the simultaneous EEG.4,5 The definition of a clinically significant MEG spike cluster has been previously reported.5

Positron Emission Tomography Scanning To examine cerebral metabolism in selected patients, interictal FDG–PET scans can be used. In children in whom sedation is not required, the interictal FDG– PET scans can be obtained using a GEMS 2048 system (Scanditronix). In younger children who require sedation, interictal FDG–PET scanning is conducted using an ECAT ART system (CTI-Siemens).

84.7.2╇ Expert Comments The ability to operate safely within the rolandic region is dependent on a comprehensive epilepsy work-up as described earlier, and the availability of neurosurgical adjuncts, such as neuronavigation linked to advanced neuroimaging data, and continuous neuromonitoring potential.

84.7.3╇ Key Steps of the Procedure/ Operative Nuances Insertion of Subdural Grids Subdural grids are typically custom-made using data from the semiology of the seizures obtained from the previously described epilepsy work-up. The electrodes are 5 mm in diameter, embedded in a Silastic sheet with center-to-center interelectrode distances ranging from 10 to 13 mm. In several cases, ipsilateral subdural strips and depth electrodes are also placed to capture ictal data from greater regions of the hemisphere. For grid placement, a generous craniotomy is created and a large M-shaped dural opening based on the sagittal sinus is made (Fig. 84.1). The central sulcus is first identified indirectly by determining the inversion polarity (phase reversals) on somatosensory evoked potential recording after median nerve electrical stimulation (Fig. 84.2). Then, confirmation of the precentral (motor) gyrus is achieved using direct cortical stimulation. If seizures are precipitated, irrigating the cortex with ice-cold saline can abort them.1 Following the identification of the central sulcus, as well as elements of the motor cortex, frameless stereotaxy can be used to confirm the location of the SEF, as determined by the preoperative MEG, and to mark the boundaries of a MEG spike cluster as described (Fig. 84.3). For each patient, the subdural grid is placed on the cortical surface and supplemental strip electrodes are positioned as required. Supplemental depth electrodes are arranged, using frameless stereotaxy, in the mesial temporal lobe or into a region of a MEG spike cluster. An image of the final operative field with subdural grid, strips, and depth electrode placements is then captured with a digital camera (Fig. 84.4). To prevent displacement, the grid is sutured to the dura mater at two points. The dura is then closed with large dural grafts, and the bone flap is hinged just superiorly. Individual cables are then tunneled separately through the scalp away from the incision and are secured in place with purse-string sutures.

84 â•… The Surgical Treatment of Rolandic Epilepsy in Children

Fig. 84.1â•… Procedure for invasive subdural grid monitoring. Intraoperative right cerebral hemisphere exposure for intractable rolandic epilepsy. A large craniotomy has been performed to allow grid placement over the right hemisphere centered on the rolandic region. (Courtesy of Ayako Ochi and Hiro Otsubo.)

Fig. 84.2â•… The central sulcus is first identified indirectly by determining the inversion polarity (phase reversals) on somatosensory evoked potential recording after median nerve electrical stimulation. A, Magnetoencephalography somatically evoked field (MEG SEF). B, MEG motor. (Courtesy of Ayako Ochi and Hiro Otsubo.)

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Fig. 84.3â•… Frameless stereotaxy can be used to confirm the location of the somatically evoked field (SEF) as determined by the preoperative magnetoencephalography (MEG), and to mark the boundaries of a MEG spike cluster. (upper left) Three-dimensional reconstruction of right head region showing placement of subdural grid (blue solid areas), and MEG spike cluster (pink solid areas). The subdural grid encompasses the MEG spike cluster in this patient. (Courtesy of Ayako Ochi and Hiro Otsubo.)

84 â•… The Surgical Treatment of Rolandic Epilepsy in Children

Fig. 84.4â•… An image of the final operative field with subdural grid, strips, and depth electrode placements is then captured with a digital camera. D-E-F-G-H magnetoencephalography (MEG) cluster. (Courtesy of Ayako Ochi and Hiro Otsubo.)

Invasive Video-EEG Recording A plain skull radiograph and a head computed tomography (CT) scan are obtained immediately after surgery to verify grid placement. Antiepileptic medications are usually reduced, and a combination of cefotaxime and vancomycin is maintained during the perioperative period. Mapping of motor, sensory, and language functions is performed in one to two sessions on the 3rd or 4th day after grid implantation. EEG activity is recorded simultaneously and monitored by the physician, using a referential montage to detect an after-discharge. After enough ictal events with appropriate semiology have been captured, a seizure map is created to facilitate resection of the ictal onset zone (Fig. 84.5).

Grid Removal and Cortical Resections in the Rolandic Region After sufficient data regarding functional cortex and regions of epileptogenesis have been obtained, the subdural grid is removed and epileptic regions are

resected. A subpial resection method is preferred, preserving the draining veins and arteries en passant wherever possible (Fig. 84.6a,b). It is critical to ensure that the resection is completed all the way to the pial surface and that the gyrus in question has been emptied of all gray matter. In some cases in which the postcentral gyrus is being resected and the premotor cortex is not, a 4 × 1 electrode array is positioned on the motor cortex for continuous (train-of-5) stimulation and monitoring of the corticospinal tract (Fig. 84.7).1 Completeness of resection of the epileptogenic zone is judged based on the intraoperative MEG/neuronavigation data, intracranial video-EEG, and intraoperative ultrasonography findings. All specimens are sent to pathology. Some of the diagnoses to be encountered in the rolandic region include cortical dysplasia, polymicrogyria, gliosis, microdysgenesis, and low-grade brain tumors. Closure of the craniotomy and wound is then performed. Patients are monitored for 1 night in the intensive care unit before being transferred to the neurosurgical ward. To assess the extent of resection, a CT study is performed in the first 24 hours in all patients.

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Fig. 84.5â•… During the following days, after enough ictal events with appropriate semiology, a seizure map can be created to facilitate resection of the ictal onset zone. A, magnetoencephalography somatically evoked field (MEG SEF); B, MEG motor. D-E-F-G-H MEG cluster. Trains of 5: the lowest threshold C, hand (20) B, hand (30). Cortical stimulation elbow (13). Extraoperative evoked potentials can also be included in this map. (Courtesy of Ayako Ochi and Hiro Otsubo.)

84.8╇ Outcomes and Postoperative Course 84.8.1╇ Postoperative Considerations Neurologic Outcome In the authors’ previously published series (22 patients), 90% of the children exhibited an immediate postoperative weakness.1 Dysphasia or word-finding difficulties were identified in 4 children in whom cortical resections were in proximity to known language pathways in the dominant hemisphere. A homonymous hemianopsia was documented in 1 patient.

Functional Recovery In the 6 (27%) children with mild hemiparesis (MRC [Medical Research Council, United Kingdom] grades 4/5) following surgery, all had improved to their preoperative level by the time of their follow-up at 3 to 6 months. In 13 (59%) children with moderate to severe hemiparesis after surgery (MRC grades 2 to

3/5), there was improvement in arm and leg function in all children by the time of their follow-up examination. All children were ambulating independently without assistance. There were 5 (22%) children in whom motor hand function was impaired and did not return to normal. Language disturbances had returned to baseline by the time of the delayed examination in all 4 children in whom it was disturbed postoperatively.1

Seizure Outcome The mean follow-up period in the authors’ series of 22 patients was 4.1 years. Seizure outcome was Engel class I in 14 patients (63%), Engel class II in 4 (18%), Engel class III in 2 (9%), and Engel class IV in 2 (9%).1

84.8.2╇Complications In the authors’ series there were no postoperative deaths. One child developed postresection cerebral edema with delayed reinsertion of the cranial flap. Another child had delayed neurologic deterioration at 5 days postoperatively that was related to edema

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Fig. 84.6â•… (a) Final cortical map before resection. (b) A subpial resection method is preferred, preserving the draining veins and arteries en passant wherever possible. (Courtesy of Ayako Ochi and Hiro Otsubo.)

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Fig. 84.7â•… Train-of-5 strip electrode was placed on the primary motor cortex as shown, and continuous neuromonitoring was performed. The lesion could be safely resected posteriorly without diminution of corticospinal tract activity and electrical conduction. (Courtesy of Ayako Ochi and Hiro Otsubo.)

in the area surrounding the resection area. Two children had wound-healing issues that required débridement. There was one cranial bone flap infection necessitating removal and secondary reconstruction of the calvaria in a delayed manner.1 Surgical complications are minimized by creating the best neurosurgical map at the time of surgery to guide the neurosurgeon, and by preserving critical draining veins and cerebral arteries adjacent to the resections.

References ╇1. Benifla

M, Sala F Jr, Jane J Jr, et al. Neurosurgical management of intractable rolandic epilepsy in children: role of resection in eloquent cortex. Clinical article. J

Neurosurg Pediatr 2009;4(3):199–216 10.3171/2009.3. PEDS08459 ╇2. D’Argenzio L, Colonnelli MC, Harrison S, et al. Seizure outcome after extratemporal epilepsy surgery in childhood. Dev Med Child Neurol 2012;54(11):995–1000 10.1111/j.1469-8749.2012.04381.x ╇3. Schramm J, Kuczaty S, Sassen R, Elger CE, von Lehe M. Pediatric functional hemispherectomy: outcome in 92 patients. Acta Neurochir (Wien) 2012;154(11):2017– 2028 10.1007/s00701-012-1481-3 ╇4. Shiraishi H, Haginoya K, Nakagawa E, et al. Magnetoencephalography localizing spike sources of atypical benign partial epilepsy. Brain Dev 2014, 36(1):21-27 ╇5. Kakisaka Y, Iwasaki M, Alexopoulos AV, et al. Magnetoencephalography in fronto-parietal opercular epilepsy. Epilepsy Res 2012;102(1-2):71–77 10.1016/j. eplepsyres.2012.05.003

85

Hemispherotomy and Hemispherectomy Michael H. Handler and Brent O’Neill

85.1╇Background Hemispherotomy and hemispherectomy are the most extensive epilepsy procedures and among the most effective. Safely accomplishing complete disconnection of a cerebral hemisphere requires extensive knowledge of the surgical anatomy, careful preservation of nearby structures, and attention to the pathological changes in the operated hemisphere.

85.2╇Indications Hemispherotomy is indicated for patients with intractable epilepsy that is well lateralized but poorly localized, or those with epilepsy from diffuse, extensive pathology of a single hemisphere. Typical diagnoses include hemimegalencephaly, multilobar cortical dysplasia, Rasmussen encephalitis, Sturge– Weber syndrome, perinatal stroke, and disorders of gyration. Fig. 85.1 provides some technical nuances to keep in mind with each of these pathologies. Because hemispherotomy disconnects the entire hemisphere, hemiparesis and a visual field defect are inevitable, as is a speech deficit in a dominant hemisphere. Many patients undergoing hemispherotomy already have these deficits, or will predictably incur them as a result of a progressive disease process, such as Rasmussen encephalitis.

85.3╇Goals An anatomical hemispherectomy removes all of the cortical tissue and a good portion of the white matter of the seizure-generating hemisphere. Hemispherotomy, functional hemispherectomy, hemispheric

deafferentation, and hemispheric disconnection all refer to surgical procedures that disrupt all connections between the cerebral cortex of one hemisphere and the remainder of the central nervous system (i.e., thalamus, basal ganglia, and contralateral hemisphere). This is accomplished with some resection of cortex combined with severing all of the white matter pathways from the (sometimes significant) cortical tissue that will be left in place. A properly completed hemispherotomy “functionally” accomplishes the same elimination of all potentially epileptogenic portions of one hemisphere, but with less blood loss, operative time, and complications than an anatomical hemispherectomy. Hemispherotomy is the authors’ procedure of first choice in all appropriate cases. They reserve anatomical hemispherectomy for the rare setting of a failed hemispherotomy (continued seizures from an incompletely disconnected hemisphere).

85.4╇ Alternate Procedures and Advantages A number of different hemispherotomy techniques have been described that involve various amounts of disconnection and resection and different corridors to access the points of disconnection.1–4 Some approaches are graphically depicted in Fig.€85.2. The preferred technique of the authors is the periinsular hemispherotomy.1 They feel that this method provides a sufficiently broad view of all of the relevant anatomy, and the shortest working corridor to the deep structures that must be preserved (thalamus, midbrain, basal ganglia, cerebral arteries, and cranial nerves). The peri-insular route additionally involves a balance of brain resection and disconnection. Procedures with extensive brain resection

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Fig. 85.1â•… Indications for hemispherotomy. (a) Rasmussen encephalitis: an inflammatory condition of unclear etiology that typically presents with explosive, drug-resistant focal motor seizures. In the later stages, functional deficits and peri-sylvian atrophy develop. The right hemisphere in this T2-weighted (T2W) image shows atrophy and some high signal in the white matter. (b) Perinatal stroke: extensive encephalomalacia can distort the normal anatomy. Neuronavigation and careful study of preoperative images help identify surgical landmarks and maintain orientation. (c) Hemimegalencephaly: a hemispheric migration abnormality that manifests with an enlarged, dysplastic hemisphere (the right in this example), often an enlarged ventricle, and explosive epilepsy. Most patients have a hemispherotomy before age 2 years. The small patient size and extensive dysplastic tissue make blood loss a paramount concern. (d) Multilobar cortical dysplasia: images may be normal or may show thickened gray matter (arrow), at times with a tail of abnormally migrated neurons extending toward the ventricle (as in the right frontal lobe on this image). Surgical anatomy is fairly normal. (e) Sturge–Weber: the pial angioma (evidenced by the linear gyriform enhancement on this contrasted T1-weighted magnetic resonance image [T1W MRI]) can be a source of bleeding, requiring additional cautery. Large draining veins, as demonstrated by the dark, periventricular flow void on this T1W-contrasted image and dilated choroid plexus (not shown), must also must be recognized and respected to avoid excessive bleeding.

85 â•… Hemispherotomy and Hemispherectomy are more likely to be complicated by hydrocephalus, whereas minimal brain resection when accompanied by an infarction, particularly of the temporal lobe, can lead to malignant edema, herniation, and even death.2

85.6╇Contraindications Hemispherotomy is the most widely destructive procedure used in the treatment of epilepsy. It should not be undertaken if a smaller area of seizure onset can be defined and resected. Bilateral seizure onset or bilateral pathology on imaging may be a contraindication to hemispherotomy; however, this should not be considered an absolute. Good results have been obtained when the more epileptically active hemisphere has little neurologic function, and the epileptic activity from the opposite hemisphere is minimal.5 Neurologic recovery and brain plasticity are heavily influenced by age. In older patients, particularly those with dominant hemisphere pathology, the functional deficits inflicted by hemispherotomy should be carefully considered in the decision making and may be prohibitive. Hemispherotomy is more risky and technically demanding in young patients, neonates in particular. Such cases should be reserved for surgical teams with more experience.

85.7╇ Operative Detail and Preparation Many approaches to disconnect the cerebral hemisphere have been described. The particular approach of the authors most closely resembles the peri-insular hemispherotomy as originally described by Villemure and Mascott in the 1990s.1

85.8╇ Preoperative Planning The peri-insular hemispherotomy represents a modification of the Rasmussen original description of functional hemispherectomy.6 The operation centers on the lateral aspect of the hemisphere, particularly the sylvian fissure and lateral ventricle. The frontal and temporal operculum are resected, as are the insula, amygdala, and uncus, whereas the majority

of the frontal, parietal, and occipital lobes and a portion of the lateral temporal lobe are disconnected. The operation can be conceptualized in five steps― opening of the lateral ventricle, temporal resection, corpus callosotomy, frontobasal disconnection, and insular resection. Fig. 85.3 provides postoperative images illustrating these steps. A hemispherotomy carries a significant risk of blood loss, especially in the very young, mandating the use of an arterial line and good venous access. Cross-matched blood should be readily available. The authors prefer to use secure fixation of the head in a Mayfield clamp in all patients old enough to accommodate this device. Neuronavigation aids in planning the craniotomy and in maintaining orientation. The operating microscope is always used. Careful study of the preoperative imaging is important because anatomical aberrations frequently occur in the diseased hemisphere. Failure to properly account for aberrant anatomy may be catastrophic. The wide spectrum of pathology will at times mandate modifications in technique and sequence of operative steps (Fig. 85.2).

85.8.1╇ Craniotomy and Opening of the Lateral Ventricle The authors employ a C-shaped skin incision beginning just above the ear. Both the skin incision and craniotomy should extend far enough posterior to allow easy access to the trigone of the lateral ventricle (about 4 cm behind the external auditory canal), superior to permit entry to the corpus callosum, and anterior to allow approach to the sphenoid wing and carotid bifurcation (a few cm anterior to the coronal suture). See Fig. 85.4. Image guidance is extremely useful in planning the approach. Extensive exposure of the lateral ventricle accomplishes disconnection of the outputs of the frontal, parietal, and occipital lobes through the corona radiata and permits access for disconnection of the corpus callosum through the lateral ventricle. The authors begin by creating a corticectomy in line with the body of the ventricle, initially entering near the midbody. The corticectomy should be positioned fairly close to the sylvian fissure (within 3 to 4 cm) because this limits the intervening frontal operculum that will need to be resected later. Image guidance can be quite valuable in initially localizing small ventricles. Once the ventricle is encountered, corticectomy extends anterior, beyond the foramen of Monro, and posterior, around the trigone. Passing middle cerebral artery

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Fig. 85.2â•… A schematic representation of some of the common hemispherotomy techniques. The blue outline indicates the periinsular hemispherotomy described by Villemure and Mascott, and Villemure and Daniel.1,2 The authors will typically resect additional temporal lobe, as outlined in red, to avoid the risk of herniation from brain swelling. The orange outline depicts the trans-sylvian hemispherotomy detailed by Schramm et al.3 The green represents the parasagittal hemispherotomy reported by Delalande et al.4

(MCA) branches supplying the disconnected cortex will be encountered crossing this corticectomy. Many publications advocate careful preservation of these to avoid infarction of the disconnected tissue and resultant brain swelling. The authors have found the preservation of such vessels (and even the MCA trunk) unnecessary and limiting to resection of the insula. This approach mandates more aggressive brain resection, particularly of the temporal lobe, to accommodate the swelling that develops.

85.8.2╇ Temporal Resection The temporal resection begins with extension of the lateral ventricular opening along the length of the temporal horn and beyond to near the temporal tip. This corticectomy, which typically runs through the

middle temporal gyrus, allows access for resection of the mesial temporal structures, namely the uncus, amygdala, and hippocampus. Care must be taken to ensure that the mesial temporal resection is subpial to avoid damage to the structures lying deep in the medial temporal arachnoid plane, namely the lateral midbrain, carotid artery, oculomotor nerve, and posterior communicating artery. The authors accomplish this with a fine, atraumatic suction (usually 5 or 7 F [French]) and judicious bipolar cautery. The inferior temporal and perihippocampal gyri will be disconnected by these maneuvers, but if there is concern for postoperative swelling (in the absence of encephalomalacia or significant atrophy), they are removed. The authors typically leave the superior temporal gyrus and upper portion of the middle temporal gyrus at this stage, and later resect them en bloc with the insula.

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Fig. 85.3â•… (a–c) Postoperative magnetic resonance imaging (MRI) in a patient with Rasmussen encephalitis. Blue arrows highlight the ventricular opening, yellow arrows indicate the temporal resection, white arrows identify the corpus callosotomy, green arrows delineate the frontobasal disconnection, and red arrows point to the insular resection.

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Fig. 85.4â•… A typical incision for peri-insular hemispherotomy is indicated in yellow. Green depicts the typical craniotomy, allowing comfortable access to the lateral ventricle (blue), the corpus callosum (orange), and the insula (red).

85.8.3╇ Corpus Callosotomy The corpus callosum is approached and disconnected entirely from within the lateral ventricle, which at this point has been widely opened. The medial roof of the lateral ventricle is the corpus callosum, and one can usually observe a change in orientation of the ependymal surface as the septum pellucidum meets the corpus callosum. The authors resect through the corpus callosum lateral to this point, into and through the cingulate gyrus, and down to the arachnoid of the interhemispheric fissure―a useful landmark for complete disconnection. If orientation is lost, it is possible to stray across the corpus callosum into the contralateral hemisphere. Disconnection of the corpus callosum begins at the posterior hippocampal margin exposed by the temporal resection. The tail of the hippocampus is

aspirated gently, down to the basal pia-arachnoid, exposing the tentorial edge. The resection follows the tentorial edge (visualized through a veil of arachnoid) posterior then medial, through the transition to the falx cerebri. The falx is then followed anteriorly to complete disconnection of the splenium. As the corpus callosotomy extends anterior to the splenium, the falcine edge deviates away from the corpus callosum. At this point, the pericallosal arteries become visible through the interhemispheric piaarachnoid. Alternatively, the corpus callosotomy can begin at the anterior body. This permits early identification of the pericallosal arteries that will serve as the primary landmark for the surgeon to follow while disconnecting the body and genu of the corpus callosum. The deeper portion of the anterior callosotomy is best accomplished as part of the frontobasal disconnection.

85 â•… Hemispherotomy and Hemispherectomy

Fig. 85.5â•… Operative right peri-insular hemispherotomy for Sturge–Weber syndrome. The vertex is at the bottom of the image, with the temporal fossa exposed by extensive temporal lobe resection at the top of the image (asterisks). The posterior temporal resection connects to the ventricular opening (white arrows) that in turn connects to the basifrontal disconnection (arrowheads), extending down to the sphenoid wing (black arrow). Note: the disconnection encircles the insula and overlying operculum, which have not yet been resected and are distorted by the leptomeningeal angioma of Sturge–Weber.

85.8.4╇ Frontobasal Disconnection In failed hemispherotomy operations, the most common location of a persistent connection is along the frontal base, particularly the medial edge.7 This portion of the operation is the least intuitive and poses the risk of hypothalamic injury. Image guidance is particularly useful. The authors begin the frontobasal disconnection by creating a wide, coronally oriented corticectomy along the lateral frontal lobe. This connects the corticectomy, exposing the frontal horn of the lateral ventricle, to the sphenoid wing. The superior portion of this corticectomy should stay anterior to the foramen of Monro and the caudate, which are visible within the ventricle. The anterior cerebral artery (A1 and A2 segments) serves as the landmark for the deep margin of this disconnection. The A2 has been previously exposed during the anterior corpus callosotomy and will continue to guide the medial part of the frontobasal disconnection. The olfactory tract should be visualized through the pial plane to ensure

that dissection has included the medial, inferiormost portion of the lobe. This exposure is in practice accomplished by working in both a medial to lateral fashion following the A2 laterally from below the genu of the corpus callosum, and a lateral to medial fashion following the A1 origin medially from the carotid apex. As with other disconnecting maneuvers, care must be taken to preserve the pia-arachnoid plane overlying the cerebral vessels and cranial nerves (Fig. 85.5).

85.8.5╇ Insular Resection Upon completion of the corpus callosotomy and frontobasal disconnection, only the insula and opercular tissue remain connected. The authors routinely resect the entire insula after experiencing failed hemispherotomies from an insular-sparing approach. The insular resection begins at the posterior margin of the corticectomy used to open the ventricle. At

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710 Section VIIIâ•… Epilepsy and Functional Disorders this cut surface, the opercular tissue can be identified overlying the sylvian fissure with the insular cortex immediately deep to the sylvian arachnoid. A plane of resection is created by aspirating the insular gray matter. This allows the sylvian arachnoid and overlying operculum to be progressively elevated with a retractor blade. The aspiration of the insular gray matter proceeds anteriorly down to the MCA trunk, accomplishing complete resection of the deep insular cortex. The MCA is then clipped, coagulated, and divided, allowing the operculum, sylvian arachnoid, and any residual superficial insula to be removed as a single block.

85.9╇ Outcomes and Postoperative Course 85.9.1╇ Closure and Postoperative Management Once disconnection is complete, the wound is thoroughly irrigated to flush out as much blood and debris as possible. Particular attention is paid to ensuring that the foramen of Monro is clear and patent. Dural closure, bone flap replacement, and skin closure proceed in a typical fashion. The authors leave a ventriculostomy catheter in the resection cavity and maintain drainage at a low level for 5 days, longer if the cerebrospinal fluid (CSF) remains turbid. Steroids are given postoperatively for a few days. Management is initially in the intensive care unit, typically just overnight. Vomiting, fevers, and some degree of meningismus commonly occur in the early postoperative course. CSF sampling may distinguish among postanesthetic effects, chemical meningitis, and bacterial meningitis. Therapies and rehabilitation services consult early in the postoperative course. (They assess and counsel all hemispherotomy patients preoperatively as well.) All children who do not have preexisting contralateral weakness will develop complete hemiparesis as a result of the procedure. With extensive rehabilitation, significant recovery is expected. The lower limb recovers more completely than the upper, and large proximal musculature recovers better than distal, fine muscles. All children who are ambulatory preoperatively will regain the ability to walk, commonly with a persistent limp. Fine movements of the fingers have the poorest prognosis for recovery, such that the contralateral hand typically functions as a “helper hand.” Improved development and cognition commonly follow hemispherotomy in cases where seizures stop and anticonvulsants can be weaned.8

85.9.2╇ Hazards/Risks/Avoidance of Pitfalls Significant portions of the hemispherotomy involve subpial aspiration of tissue down to an important anatomical structure: hippocampectomy overlies the contents of the ambient cistern and the midbrain farther posterior; the anterior corpus callosotomy follows the pericallosal arteries; and the frontobasal disconnection follows the anterior and middle cerebral arteries. Maintaining the integrity of these arachnoid planes is crucial to avoiding injury to the underlying structures. The authors prefer to use a 7 F suction tip (smaller in infants with flimsier arachnoid) and judicious bipolar cautery to accomplish this. Others use an ultrasonic aspirator at low settings. The only area of resection not bounded by an arachnoid plane is the insula. Care must be taken to identify the depths of the insular sulci and their transition to the white matter of the external capsule in order to avoid inadvertent resection of the putamen and thalamus. The authors have found that elevating the sylvian fissure arachnoid in a posterior to anterior direction by aspirating the insular gray matter accomplishes a thorough insular resection while protecting the underlying basal ganglia. This maneuver does require sectioning of the MCA vessels. Performance of a hemispherotomy will necessarily accomplish the equivalent of an MCA territory infarction, with potential for considerable swelling. It has become the practice of the authors to allow for this by resecting an adequate amount of the temporal lobe, and of the temporal and frontal operculum with the insula. They additionally leave a ventricular drain that allows for monitoring of intracranial pressure if circumstances warrant. Frequently, anatomy can be quite distorted, and typical landmarks are not always apparent. Insular resection and frontobasal disconnection are typically the most disorienting steps, and they risk injury to the hypothalamus. It may be prudent to limit resection in cases of intraoperative confusion, with intent to return if necessary to complete the resection. This is an ideal application for intraoperative magnetic resonance imaging, if available.

85.9.3╇Complications Hemispherotomy is a major intracranial surgery with the potential for any of the typical complications of a craniotomy. In addition to these, hydrocephalus complicates about 25% of hemispherotomy operations.9 Hydrocephalus typically presents weeks after the procedure, mandating continued follow-up. In the authors’ experience over the past 10 years, 12 of 51 hemispherotomy patients developed hydrocepha-

85 â•… Hemispherotomy and Hemispherectomy lus; the latest presented at 5 months postoperatively. Incomplete disconnection occurred in 1 patient of their series (2%) who achieved good seizure control after an anatomical hemispherectomy. Patients numbering 2 (4%) had postoperative endocrinopathy attributed to hypothalamic injury. Both had dramatically abnormal anatomy. Mortality in most series is less than 5%, the authors’ series included.

85.10╇Conclusion Hemispherotomy in appropriate candidates is among the most potent epilepsy surgeries, with published seizure-freedom rates as high as 90%. Thorough understanding of the particular (pathological) anatomy of the operated hemisphere, meticulous technique, and awareness of the potential complications are keys to safely accomplishing this extensive operation.

References ╇1. Villemure

JG, Mascott CR. Peri-insular hemispherotomy: surgical principles and anatomy. Neurosurgery 1995;37(5):975–981

╇2. Villemure

JG, Daniel RT. Peri-insular hemispherotomy in paediatric epilepsy. Childs Nerv Syst 2006;22(8):967–981 ╇3. Schramm J, Kral T, Clusmann H. Transsylvian keyhole functional hemispherectomy. Neurosurgery 2001;49(4): 891–900, discussion 900–901 ╇4. Delalande O, Bulteau C, Dellatolas G, et al. Vertical parasagittal hemispherotomy: surgical procedures and clinical long-term outcomes in a population of 83 children. Neurosurgery 2007;60(2 Suppl 1):ONS19–ONS32 ╇5. Ciliberto MA, Limbrick D, Powers A, Titus JB, Munro R, Smyth MD. Palliative hemispherotomy in children with bilateral seizure onset. J Neurosurg Pediatr 2012;9(4):381–388 ╇6. Rasmussen T. Hemispherectomy for seizures revisited. Can J Neurol Sci 1983;10(2):71–78 ╇7. Vadera S, Moosa AN, Jehi L, et al. Reoperative hemispherectomy for intractable epilepsy: a report of 36 patients. Neurosurgery 2012;71(2):388–392, discussion 392–393 ╇8. Loddenkemper T, Holland KD, Stanford LD, Kotagal P, Bingaman W, Wyllie E. Developmental outcome after epilepsy surgery in infancy. Pediatrics 2007;119(5): 930–935 ╇9. Lew SM, Matthews AE, Hartman AL, Haranhalli N; Post-Hemispherectomy Hydrocephalus Workgroup. Posthemispherectomy hydrocephalus: results of a comprehensive, multiinstitutional review. Epilepsia 2013; 54(2):383–389

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Palliative Surgical Procedures for Epilepsy Matthew D. Smyth and Aimen S. Kasasbeh

86.1╇Background Resective epilepsy surgery procedures aim to achieve seizure freedom and are associated with remission rates as high as 60 to 90%. Palliative epilepsy surgery aims to reduce seizure burden without necessarily rendering the patient seizure-free. In palliative procedures, minimizing seizure burden is the primary objective, and complete resolution of seizures is rarely achieved. Additional objectives of palliative procedures are improving quality of life; minimizing cognitive, behavioral, and developmental impairment; decreasing medication burden and medication side effects; and reducing costs of medical care. For cases where multiple, diffuse, independent epileptogenic foci are detected, when epileptogenic foci overlap with eloquent cortex, or when the epileptogenic zone is poorly localized, palliative surgery may be considered. Such palliative procedures include corpus callosotomy (CC), vagal nerve stimulation (VNS), multiple subpial transections (MSTs), responsive neurostimulation (RNS), and deep brain stimulation (DBS).

86.2╇ Palliative Surgical Procedures 86.2.1╇ Corpus Callosotomy Background CC has been utilized since 1940 for control of seizures, and considerable experience has since accrued. Callosotomy has particular usefulness in cases of diffuse or multifocal epilepsy with atonic seizures, where an epileptogenic focus cannot be identified, in patients with primary generalized seizures, and sometimes in patients with partial seizures with frequency secondary generalization. In higher functioning patients, an anterior callosotomy sparing the splenium is performed in order to pre-

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serve sufficient parietal interhemispheric neuronal connections and minimize neurologic complications and disconnection syndromes. In patients in whom an anterior callosotomy does not result in satisfactory seizure control, a second-stage posterior callosotomy may be attempted, with studies reporting incremental seizure control with this second procedure.1 Accumulating evidence supports the alternative strategy of performing a single-stage complete CC rather than an anterior CC or two-stage complete CC, citing improved seizure control with comparable neurologic complications.2,3 CC is commonly reserved for patients in whom epileptic foci of origin are not amenable to focal resection secondary to their diffuse and multifocal nature. Typical indications are cases where drop attacks, mixed seizure types, and generalized seizures predominate.

Operative Detail and Preparation Some surgeons advocate a lateral position with the head turned parallel to the ground to use gravity to minimize frontal lobe retraction. However, advantages of a supine, head-neutral position include preservation of anatomical orientation and decreased venous and intracranial pressures with head elevation (Fig. 86.1a). Mannitol and intravenous antibiotics are given prior to skin incision. Options for skin incisions include a U-shaped “trap-door” incision, or a linear or gently curving partial bicoronal incision (Fig. 86.1b). A bone flap is created, centered on the right coronal suture, but extending across midline (Fig. 86.1c). A careful dural opening is made and reflected toward the superior sagittal sinus until the interhemispheric fissure is visualized (Fig.€86.1d). Cortical veins posterior to the coronal suture should be carefully preserved. Cotton strips or Telfa may be placed on the mesial frontal lobes to minimize injury over the course of the dissection. The interhemispheric fissure is visualized and arachnoid

86 â•… Palliative Surgical Procedures for Epilepsy a

b

Fig. 86.1â•… (a) Corpus callosotomy (CC) positioning: the patient is positioned supine, in gentle flexion with the head elevated. (b) CC incision: a gentle tranverse sigmoid incision centered near the coronal suture, slightly eccentric to the right, allows adequate bony exposure. A U-shaped “trap-door” incision may also be used. (Continued on page 714)

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714 Section VIIIâ•… Epilepsy and Functional Disorders c

d

Fig. 86.1 (Continued)â•… (c) Bone flap and dural exposure: the superior sagittal sinus (under the Cottonoid [Codman & Shurtleff, Raynham, MA, USA] patty) and 2 to 3 cm of the right frontal lobe dura are exposed via a rectangular craniotomy that crosses the midline. (d) Intradural dissection: the dura is reflected medially, based on the sagittal sinus. Bridging veins may be sacrificed when at or anterior to the coronal suture. Veins posterior to the coronal suture are preserved if possible.

86 â•… Palliative Surgical Procedures for Epilepsy e

f

Fig. 86.1 (Continued)â•… (e) Frontal lobe retraction: the supine position requires frontal lobe retraction, which should be minimized to avoid frontal lobe injury and edema. The interhemispheric fissure is visualized and arachnoid bands are dissected while the retractor blade is advanced. A falcine retractor may be employed, but careful attention is given to avoid compromising the superior sagittal sinus outflow, which increases venous congestion. (f) Callosal exposure: the characteristic white appearance of the corpus callosum is visualized between the pericallosal arteries. The entire length of the callosum should be exposed before proceeding with the transection itself. (Continued on page 716)

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716 Section VIIIâ•… Epilepsy and Functional Disorders g

Fig. 86.1 (Continued)â•… (g) Trajectory for a complete callosotomy: in this patient, a paucity of midline bridging veins allowed good access to the splenium with a fairly direct trajectory, as depicted with the purple and blue lines. In many patients, however, bridging veins limit the posterior exposure. Thus a more anterior corridor may be required, angling posteriorly, to complete the splenial disconnection. (Fig. 86.1a–f from Johnston JM, Smyth MD. Corpus callosotomy. In: Jandial R, McCormick P, Black P, eds. Anterior and Complete. Essential Techniques in Operative Neurosurgery. Reprinted with permission.)

bands are dissected while retractor blades deepen the exposure. Frontal lobe retraction is limited to the minimum necessary to expose the corpus callosum, approximately 10 to 15 mm (Fig. 86.1e). The pericallosal arteries are identified and should be carefully separated to find the avascular midline. The characteristic white appearance of the corpus callosum is visualized between the pericallosal arteries after sharp dissection of adherent arachnoid bands (Fig.€86.1f). It is helpful to completely expose the length of the intended disconnection before beginning callosotomy. The callosotomy may be performed with a combination of low-power bipolar cautery and suction or ultrasonic aspiration. It can be beneficial to confirm midline with the use of frameless neuronavigation before beginning the resection. Dividing the callosum by entering between the midline leaves of the septum and preserving the ependymal lining of the ventricles minimizes postoperative cerebrospinal fluid (CSF) accumulation in the subdural or subgaleal spaces. The posterior callosotomy may be challenging because the

angle of the splenium falls away from the surgeon (Fig. 86.1g). During this final maneuver, the table is placed in a relative Trendelenburg position while the microscope is directed posteriorly, and the intracallosal disconnection is performed from the posterior body to the splenium. During this final maneuver, the pial membrane, protecting the internal cerebral vein and vein of Galen that lies just posterior to the splenial reflection of the callosum, is preserved.

Outcomes and Postoperative Course In addition to drop attacks, seizure types that improve following callosotomy include generalized tonic-clonic, absence, astatic, myoclonic, and complex partial seizures.2 Reported complications of callosotomy include infection (epidural abscess, bone flap osteomyelitis), subgaleal fluid collection, hydrocephalus, epidural hematoma, chronic subdural hematoma, sagittal sinus injury, and venous infarction. Additionally, newly developed seizure types

86 â•… Palliative Surgical Procedures for Epilepsy following CC have been reported. After surgery, baseline anticonvulsant drugs are continued. Following overnight observation in the intensive care unit, the patient is transferred to the neurosurgical ward and mobilized. Most patients are ready for discharge by the third postoperative day, although occasionally a contralateral hemiparesis may be observed; it is usually transient and may be related to a supplementary motor area syndrome or retraction-related edema, and it may prolong the recovery.

86.2.2╇ Vagus Nerve Stimulation Background Although its underlying mechanism of action remains unclear, VNS serves as a valuable palliative therapy for medically refractory epilepsy. Widespread cerebral electrophysiological and neurochemical changes complement the clinical findings of seizure suppression with VNS. Clinical studies, particularly the VNS study group in conjunction with Cyberonics, supported the efficacy of VNS in suppressing medically refractory partial-onset seizures in patients older than age 12 years.4 VNS is currently Food and Drug Administration (FDA)-approved only for this patient population. However, because of the pharmacoresistant nature of epilepsy in children and because children with medically refractory epilepsy are frequently not suitable candidates for resective surgical procedures, VNS is a palliative therapeutic option often used in an “off-label” basis in younger children.

Operative Detail and Preparation After the administration of intravenous antibiotics, the patient is positioned supine with the head gently extended, but not rotated, to open up the anterior cervical region (Fig. 86.2a). A transverse incision is marked midway between the clavicle and the angle of the mandible, ideally within a skin crease. Another incision is marked anterior to the deltopectoral groove (Fig. 86.2b). After sterile skin preparation and draping, the neck dissection is begun. After a transverse incision is made in the skin and platysmal layers, the medial border of the sternocleidomastoid muscle is followed posteriorly to encounter the carotid sheath. Occasionally, the omohyoid muscle is encountered running obliquely across the field, and it can be mobilized inferiorly or superiorly in all cases. The ansa cervicalis may be encountered, and in a similar fashion can be mobilized out of the way of the approach to the carotid sheath. The sheath is opened sharply over the carotid and jugular veins. Careful retraction of

the internal jugular vein laterally while dissecting medially will expose the vagal nerve, which usually lies posteriorly within the carotid sheath. A flexible vessel loop is placed around the nerve; this assists in dissecting the nerve circumferentially of surrounding areolar and connective tissue (Fig. 86.2c). At least 3 cm of nerve should be carefully stripped of soft tissue to allow for wrapping of the electrodes themselves. Once the nerve is identified, dissected, and isolated, the deltopectoral groove incision is made. A subcutaneous pocket is developed medial to the deltopectoral incision, anterior to the pectoralis fascia, allowing for medial placement of the pulse generator away from the incision itself. The VNS leads are then tunneled from the cervical incision to the pulse generator pocket using a shunt tunneler. Next the electrodes are wrapped around the nerve, with the anchor electrode inferior and the anode and cathodes superior. The nerve and electrodes are gently repositioned back within the carotid sheath, and a strain-relief loop is fashioned to eliminate tension on the nerve. At the other incision site, the pulse generator is secured to the electrodes with the provided torque screwdriver, placed into the pocket, and then interrogated for device functionality and electrode integrity as evidenced by normal lead impedance (Fig. 86.2d). The pulse generator is secured to the soft tissue with a nonabsorbable suture, and then each incision is closed in layers with absorbable suture and a layer of skin adhesive.

Outcomes and Postoperative Course With a careful neck dissection and meticulous hemostasis, VNS implantation can safely be performed as an outpatient procedure. Absorbable sutures and a layer of skin adhesive are used for ease of postoperative care and bathing. The device can be activated in the operating room at low settings, or at the initial postoperative visit. The VNS study group demonstrated a median reduction of seizure frequency of 35% at 1 year postoperatively; 44.3% at 2 years; and 44.1% at 3 years. Other studies confirmed long-term benefit of VNS in seizure control. Further studies consistently confirmed the safety and efficacy of VNS, greater seizure control, and improved quality of life in children with medically refractory epilepsy.5 Research has shown improvement in absence, atonic, simple partial, complex partial, and generalized tonic-clonic seizures in addition to significant improvement in seizures in patients with Lennox–Gastaut syndrome. Reports have also documented successful abortion of status epilepticus with VNS. Surgical complications of VNS include implantation site infection and erosion of hardware

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718 Section VIIIâ•… Epilepsy and Functional Disorders a

b

c d

Fig. 86.2â•… (a) Positioning: the patient is positioned supine with a transverse gel roll under the shoulders. The head is in a neutral position, allowing for a dissection directly medial to the sternocleidomastoid muscle in the midcervical region. The pulse generator can be located in the subclavicular region. (b) A transverse cervical incision is marked, midway between the mandible and clavicle, hidden within a skin crease if possible. The authors prefer a separate incision medial to the deltopectoral groove for placement of the pulse generator just in front of the pectoralis fascia. (c) The vagal nerve is exposed within the carotid sheath, and cleared of surrounding soft tissue, thus enabling easy placement of the electrode coils. (d) The pulse generator is positioned within the subclavicular space, and interrogated with the device diagnostics mode to confirm electrode continuity and lead impedance. (Courtesy of Jeffrey P. Blount, MD, UAB.)

through the skin. Lead fracture is also seen. 6 The electrodes were redesigned in 2008 to lower the rate of electrode fracture. Such complications often require explantation of the hardware and/ or hardware revision. Stimulation-related complications of VNS include voice alteration, throat paresthesia, cough, headache, throat pain, dys-

pnea, pharyngitis, lower facial paresis, drooling, dysphagia, aspiration, torticollis, inappropriate laughter, and depression, as well as rare cases of intraoperative cardiac asystole or dysrhythmias. These stimulation-related adverse effects are mild and rarely require modification of stimulation parameters or device explantation.

86 â•… Palliative Surgical Procedures for Epilepsy

86.2.3╇ Multiple Subpial Transections

Operative Detail and Preparation

Background

Usually performed within eloquent cortex adjacent to regions of cortical resection, MSTs are carried out as a series of small subpial incisions made 5 mm apart, perpendicular to the course of the gyrus. After cortical exposure and resection are done, the region for planned MSTs is outlined. Bipolar cautery at 6 to 8 W (watts) is used to gently coagulate the pia at 5-mm spacing along the course of the gyrus to be included in the MST field (Fig. 86.3a). Next, a no. 11 blade or arachnoid knife is used to pierce the pia where the vascularity has been blanched, and then the MST knife (Fig. 86.3b) is introduced, under the pia, to the opposite side of the gyrus. It is then gently drawn back, with the tip of the knife against the undersurface of the pia, to make the subpial incision. This is repeated at 5-mm intervals until the planned field for MSTs is completed. Pial hemorrhage can be controlled with gentle pressure with Cottonoid (Codman & Shurtleff, Raynham, MA, USA) patties and saline irrigation, or judicious use of bipolar cautery if necessary.

In cases where preoperative and intraoperative neurophysiological evaluations converge on seizure foci in the eloquent cortex, precluding focal resection, MSTs are sometimes employed. The use of MSTs followed evidence suggesting that the pathological horizontal spread of seizure activity in the cerebral cortex is largely independent of the physiological, vertically organized function of cortical neuronal columns. Selective disruption of horizontal fibers is, therefore, believed to impair seizure spread while minimizing neurologic compromise.7 Both alone and as an adjunct to surgical resection, MSTs improve seizure control. Syndromes associated with medically refractory epilepsy, such as Rasmussen encephalitis, Landau–Kleffner syndrome, and epilepsia partialis continua, may respond favorably to MST alone.8

a

Fig. 86.3â•… (a) Artist’s depiction of a multiple subpial transection (MST) “knife” performing a subpial transection. (Continued on page 720)

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720 Section VIIIâ•… Epilepsy and Functional Disorders b

c

Fig. 86.3 (Continued)â•… (b) MST spacing: typical spacing of 5 mm between transections along a gyrus. (c) Intraoperative MSTs.

86 â•… Palliative Surgical Procedures for Epilepsy

86.3╇ Outcomes and Postoperative Course Improvements in seizure control have been reported with MST, both independently and as an adjunct to resective surgery. Excellent outcomes (> 95% reduction in seizure frequency) have been reported with MST alone in 71, 62, and 63% of generalized, complex partial, and simple partial seizures, respectively.8 Progress in development and behavior are also seen with MST. In patients with Landau–Kleffner syndrome, where the primary objective is advancement of language rather than seizure control, notable improvement in speech has been reported.9,10 Neurologic complications following MSTs are relatively uncommon, but difficult to distinguish relative to those caused by cortical resection since both are often performed at the same time. The durability of seizure control after MSTs remains controversial.

86.3.1╇ Deep Brain Stimulation and Responsive Neurostimulation DBS has emerged as a viable, reversible, and modifiable surgical strategy employed in adults with Parkinson disease, essential tremor, dystonia, chorea, depression, and pain among other disorders. In children, DBS is under investigation for use in a variety of conditions, including dystonia, Tourette syndrome, juvenile parkinsonism, obsessive-compulsive disorder, obesity, and epilepsy. In children with medically refractory epilepsy, the developing nature of the brain and the evolving character of epilepsy render DBS a particularly suitable strategy where stimulation levels may be continually adjusted. The reversibility of DBS and its preservation of brain anatomy allow the removal of the DBS device once the children outgrow their epilepsy and permit further surgical intervention if necessary. Nevertheless, the novelty of the application of DBS in children with medically refractory epilepsy renders imperative further clinical investigation. Numerous targets have been investigated for DBS in epilepsy, including the anterior thalamic nucleus, hippocampus, mammillary bodies, centromedian nucleus of the thalamus, and subthalamic nucleus, among other regions.11–13 Preclinical and clinical studies implicating the Papez neural circuit in seizure development support targeting this circuit with DBS. Research is predominantly in adult cohorts, with rare pediatric subjects. A multicenter, doubleblinded, randomized trial of DBS of the anterior thalamic nucleus in adults with medically refractory epilepsy (SANTE trial) demonstrated a significantly

greater reduction in seizures with DBS (40.4%) compared with nonstimulated controls (14.5%) 3 months after surgery. At 2 years postoperatively, there was a 56% median reduction in seizure frequency in DBS patients. Reported complications included memory impairment, depression, anxiety, implant site infection, pain, and paresthesias.14 The optimal anatomical target and patient population for DBS in medically refractory epilepsy remain to be identified. The NeuroPace RNS device is a closed-loop system that detects electrographic activity from subdural and depth electrodes and generates bursts of stimulation to abort seizure propagation. The Responsive Neurostimulation Pivotal Trial of the NeuroPace system in patients with medically refractory epilepsy demonstrated a decrease in seizure frequency of 37.9% in stimulated patients, compared with 17.3% in controls at 3 months. At 2 years postoperatively, 46% of patients reported ≥ 50% seizure reduction. Adverse events included headache, memory impairment, dysesthesia, increase in seizures, and depression, in addition to implantation site infection.15

References ╇1. Spencer

SS, Spencer DD, Sass K, Westerveld M, Katz A, Mattson R. Anterior, total, and two-stage corpus callosum section: differential and incremental seizure responses. Epilepsia 1993;34(3):561–567 ╇2. Jalilian L, Limbrick DD, Steger-May K, Johnston J, Powers AK, Smyth MD. Complete versus anterior two-thirds corpus callosotomy in children: analysis of outcome. J Neurosurg Pediatr 2010;6(3):257–266 ╇3. Shim KW, Lee YM, Kim HD, Lee JS, Choi JU, Kim DS. Changing the paradigm of 1-stage total callosotomy for the treatment of pediatric generalized epilepsy. J Neurosurg Pediatr 2008;2(1):29–36 ╇4. Morris GL III, Mueller WM. Long-term treatment with vagus nerve stimulation in patients with refractory epilepsy. The Vagus Nerve Stimulation Study Group E01E05. Neurology 1999;53(8):1731–1735 ╇5. Murphy JV; The Pediatric VNS Study Group. Left vagal nerve stimulation in children with medically refractory epilepsy. J Pediatr 1999;134(5):563–566 ╇6. Smyth MD, Tubbs RS, Bebin EM, Grabb PA, Blount JP. Complications of chronic vagus nerve stimulation for epilepsy in children. J Neurosurg 2003;99(3):500–503 ╇7. Morrell F, Whisler WW, Bleck TP. Multiple subpial transection: a new approach to the surgical treatment of focal epilepsy. J Neurosurg 1989;70(2):231–239 ╇8. Spencer SS, Schramm J, Wyler A, et al. Multiple subpial transection for intractable partial epilepsy: an international meta-analysis. Epilepsia 2002;43(2):141–145 ╇9. Irwin K, Birch V, Lees J, et al. Multiple subpial transection in Landau-Kleffner syndrome. Dev Med Child Neurol 2001;43(4):248–252

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722 Section VIIIâ•… Epilepsy and Functional Disorders 10. Sawhney

IM, Robertson IJ, Polkey CE, Binnie CD, Elwes RD. Multiple subpial transection: a review of 21 cases. J Neurol Neurosurg Psychiatry 1995;58(3):344–349 11. Chabardès S, Kahane P, Minotti L, Koudsie A, Hirsch E, Benabid AL. Deep brain stimulation in epilepsy with particular reference to the subthalamic nucleus. Epileptic Disord 2002;4(Suppl 3):S83–S93 12. Velasco AL, Velasco F, Jiménez F, et al. Neuromodulation of the centromedian thalamic nuclei in the treatment of generalized seizures and the improvement of the quality of life in patients with Lennox-Gastaut syndrome. Epilepsia 2006;47(7):1203–1212

13. Vonck K, Boon P, Achten E, De Reuck J, Caemaert J. Long-

term amygdalohippocampal stimulation for refractory temporal lobe epilepsy. Ann Neurol 2002;52(5):556–565 14. Fisher R, Salanova V, Witt T, et al; SANTE Study Group. Electrical stimulation of the anterior nucleus of thalamus for treatment of refractory epilepsy. Epilepsia 2010;51(5):899–908 15. Morrell MJ; RNS System in Epilepsy Study Group. Responsive cortical stimulation for the treatment of medically intractable partial epilepsy. Neurology 2011;77(13):1295–1304

87

The Evaluation and Treatment of Spasticity Shenandoah Robinson

87.1╇Background

87.2╇ Selective Dorsal Rhizotomy

The two main procedures widely used to treat spasticity in children are selective dorsal rhizotomy (SDR) and intrathecal baclofen (ITB) therapy. The most common classification scale to describe the physical function of children with cerebral palsy is the Gross Motor Function Classification System (GMFCS), which uses levels I to V to describe how the physical impairments in motor function limit mobility. Briefly, children in level I can walk and climb stairs without difficulty but demonstrate impairment with activities like sports that require more coordination and balance, whereas level II children can walk but need to hold onto a rail to climb stairs. Level III children use assistive devices to ambulate short distances but tend to utilize a wheelchair for longer distances. Children with level IV function can use a walker for only short distances and utilize a wheelchair for most of their mobility; and level V children have limitations in all areas of motor function, are wheelchair-bound, and are completely dependent on others for mobility. In general, children with a GMFCS level of I or II and, rarely, III benefit from SDR, whereas most level IIIs and all IVs and Vs have more sustained benefit from ITB therapy. Each procedure has its own strong devotees and detractors, with a relative dearth of well-designed and executed studies to support these allegiances. With both procedures, it is important for families to have realistic expectations, and it often helps for the child and family members to articulate specific goals to reach in the early postoperative period, several months, and years away. Deep brain stimulation (DBS) is indicated for children age 7 years or older with primary dystonia from genetic mutations, most often DYT1. Early reports suggest that DBS may be beneficial in selected children with secondary dystonia. The indications for DBS in secondary dystonia are not yet clear, and publications describing large series of children with reasonable risk:benefit ratios do not yet exist.

87.2.1╇ Indications for Selective Dorsal Rhizotomy The ideal candidate for SDR is a young child who: (1) possesses the cognitive abilities, stamina, and desire to complete the required intensive physical therapy (PT) course after the surgery; (2) has deficits limited to spastic diplegia from preterm birth; (3) has a reasonable chance of maintaining ambulation over time; (4) has adequate trunk and lower extremity strength to stand upright once tone is reduced; and (5) has access to an intensive postprocedure PT program. The postoperative PT program is tailored to each child’s needs and the resources available; however, in general, the child should receive at least approximately 4 to 5 hours per week for at least 6 to 12 weeks, and ideally up to 6 months. Most children do not have sufficient cognition and stamina for the intensive postoperative therapy program until at least age 3 years. Due to the cognitive difficulties commonly associated with prematurity, many may need to be a little older. If there is concern about whether the child or family is capable of the intensive postoperative PT program, a trial of preoperative intensive PT may be warranted. In general, the patient’s primary PT provider can often best assess the child’s and the family’s suitability for an intensive PT program. The goal is to optimize the children’s function as early as feasible to keep them on track in school with their peers. Older, carefully selected children and young adults can also benefit from SDR. Rarely are children who have spastic diplegia from predominantly white-matter injury, such as after a vaccination-induced demyelinating process, good candidates. Most children who were born full term and suffered a hypoxic-ischemic injury, meningitis, or trauma are not good SDR candidates. Close attention should be paid to the assessment of underlying lower extremity strength and trunk strength. Warning signs include a child who has deteriorated

723

724 Section VIIIâ•… Epilepsy and Functional Disorders with temporary tone reduction from botulinum toxin (Botox) injections, or failure due to weakness when trying to graduate from a walker to canes or crutches. Without sufficient strength, the SDR can be debilitating. Arrangements for the postoperative PT program are typically made prior to proceeding with the surgery.

87.2.2╇ Goals of Selective Dorsal Rhizotomy The goals of SDR are to improve ambulation by reducing tone and increasing independent isolated movements in the lower extremities, and to sustain that improvement through at least young adulthood. Typically, children improve one level of devices; however, some children can graduate from primarily using a walker to canes or to ankle-foot orthoses without canes. Although the procedure is termed “selective” because nerve rootlets are chosen for sectioning based on the intraoperative response to stimulation, selective ideally also refers to very careful patient selection.

87.2.3╇ Alternate Procedures For well-selected candidates for SDR, alternate treatments rarely provide as much benefit with the same risk:benefit ratio. It is quite unusual for ITB therapy to be more beneficial than SDR for young children who are likely to ambulate. Other nonneurosurgical procedures are sometimes indicated, including orthopedic procedures. After SDR some children will still benefit from focal botulinum injections, and a subset require orthopedic procedures. The extent of orthopedic surgery required and the recovery time from the orthopedic interventions may be decreased by performing the SDR first.

87.2.4╇Advantages The main advantages of SDR for well-selected patients include its favorable low risk:high benefit ratio, and that it is a one-time procedure with predictable results. Multiple studies have shown improvement in upper extremity and cognitive function following SDR.1,2

87.2.5╇Contraindications Children who do not have sufficient cognitive or emotional development to participate in the intensive postoperative rehabilitation course, and the motivation to continue with therapy and exercise throughout their lives, are unlikely to experience a

sustained benefit from SDR. Similarly, children with too much underlying weakness in the legs or trunk will have difficulty maintaining improvement. SDR is most likely to be of benefit for children born preterm with spastic diplegia; caution is warranted when proceeding with children who have other etiologies of cerebral palsy, or with significant trunk weakness or upper extremity involvement.

87.2.6╇ Operative Detail and Preparation Here the author describes the minimally invasive procedure for SDR.3 These children regress quickly with bed rest and inactivity. With the limited laminectomy, the postoperative recovery is likely shorter, and thus the return to an intense PT program can occur earlier.

Preoperative Planning and Special Equipment Unless recent brain imaging is available, the author obtains a quick, nonsedated magnetic resonance imaging (MRI) of the brain to ensure that there are no unsuspected intracranial lesions, using similar MRI protocols as those utilized for patients undergoing evaluation for ventricular shunt malfunction. Prior to the procedure, the surgeon discusses the perioperative plan with the anesthesia and intraoperative monitoring teams. In addition to intraoperative monitoring, ultrasound (US) with a burr hole probe is necessary, as well as an operative microscope. For the monitoring and sectioning, the author and his team use Peacock electrodes, microinstruments, and a microstraight pick borrowed from otolaryngology colleagues to divide the roots into rootlets.

Key Steps of the Procedure and Operative Nuances After induction of anesthesia, the patient is positioned prone with all pressure points padded, and the patient is then placed in the Trendelenburg position to minimize the risk of intracranial subdural hematoma from excessive cerebrospinal fluid (CSF) drainage. Electrodes are placed for monitoring. After preparing the skin, a midline incision is marked overlying L1/L2. Following opening down to the fascia, the muscle attached to the spinous process and lamina of the lower part of L1 and upper part of L2 is dissected away and a retractor is placed. The interspinous ligament between L1 and L2 is removed, and the US is used to localize the conus and exiting nerve roots (Fig. 87.1). Depending on the conus location, the interspinous

87 â•… The Evaluation and Treatment of Spasticity a

b Fig. 87.2â•… Drawing depicts the steps of the intradural portion of the selective dorsal rhizotomy (SDR) surgery. Patient is positioned prone with the head toward the left, the dura has been opened and retracted with sutures, and the overlying arachnoid has been removed. The conus is protected throughout the surgery.

c

Fig. 87.1â•… Ultrasound (US) is used to localize the conus prior to laminectomy and dural opening. (a) With the patient prone, axial US image shows the conus (yellow arrow) after the L1/L2 interspinous ligament has been removed. (b) US image after the L2/L3 interspinous ligament has been removed shows the remaining conus (yellow arrow) and ventral nerve roots (blue arrow). (c) After the L2 laminectomy has been completed, a sagittal US image shows the triangular conus (yellow arrow) and ventral nerve roots (blue arrow).

ligament at the level above or below is removed. In most children, one level of laminectomy will provide sufficient exposure. The laminectomy is widened and meticulous hemostasis is achieved prior to opening the dura. The dura is opened in the midline and retracted with sutures. Under the microscope, the arachnoid, which can be quite thick in these former preterm infants, is removed (Fig. 87.2). The goal is to test and section the root-

lets from L2 to L5 and S1/half of S2 with the most abnormal response to stimulation. A strip of colored, pliable material (5 × 25 mm), such as from a colored glove or background, is fashioned as a “sling” to hold the nerve roots destined for testing and sectioning. To separate the dorsal from ventral roots as they exit the conus, the dorsal roots are rolled medially to laterally until the division between the dorsal and ventral roots is identified, and a micro-patty is inserted to mark the separation. Medially, the division between half of S2 and the lower sacral roots is maintained with a second micro-patty. Together, the two micro-patties form a shelf, with the roots for testing and sectioning lying above the micro-patties, and the ventral and lower sacral roots for protection located below the sling. The sling is then slipped just above the patties, and the micro-patties are removed. The surgeon inspects laterally and medially to confirm that the desired roots are enclosed in the sling (Fig. 87.3). The roots for testing are divided into five bundles from lateral to medial: L2, L3, L4, L5, and S1/half of S2. Starting with L2, the roots are held in the Peacock electrodes, and stimulation is used to check the localization (Fig. 87.4). This process sets the threshold for testing of the rootlets and confirms that no ventral roots have inadvertently been included. Each root is then divided into multiple rootlets, and each rootlet is stimulated to test how much spread occurs to adjacent muscle groups and the other leg. Rootlets that generate the most spread from stimulation are cut, with approximately 60% of the most affected rootlets cut per root. Uncut rootlets are tucked laterally outside of the sling. The process is then repeated

725

726 Section VIIIâ•… Epilepsy and Functional Disorders Expert Suggestions While stimulation is performed, the electrodes holding the root or rootlets should not contact each other, the sides, or the CSF. To aid in managing the CSF, adjusting the anesthetic can be quite helpful.

Hazards/Risks/Avoidance of Pitfalls

Fig. 87.3â•… A “sling” of pliable material has been inserted to separate the dorsal roots for testing and potential sectioning from the ventral roots and lower sacral roots.

Care must be taken throughout the procedure to remember that the conus lies quite close and is potentially vulnerable. The patient may move with the stimulation, and thus suction while stimulating is generally avoided. Keeping the sling in place during the testing is important. Once the testing and sectioning have begun, it can be difficult to reconstruct the landmarks.

Salvage and Rescue Due to various factors, the intraoperative recordings can be challenging. Although the goal is to select the rootlets with the most abnormal spread for sectioning, one can be reassured that it has been shown that nonselective sectioning of two-thirds of the nerve rootlets is effective in reducing tone.4 Fig. 87.4â•… Right L2 dorsal root held in two electrodes to confirm the localization and to determine the threshold for stimulation of the rootlets.

for the remaining four root groups on that side. If the L1 sensory root can easily be visualized as it exits the foramina, half of it can be cut, with significant care taken to distinguish the whiter, slightly larger dorsal root from the smaller, grayer motor root. The process is repeated on the opposite side. The dura is closed watertight. Just prior to tying the final knot at the completion of the dural closure, the patient is brought out of the Trendelenburg position, and 0.5 µg of fentanyl/kg is infused intrathecally through the remaining dural opening, and the knot is tied. The dural closure is checked with a Valsalva maneuver. The wound is closed in layers, including the muscle, the fascia, and the dermis. Skin is closed with an absorbable, subcuticular suture. The patient is awakened sufficiently to breathe and is maintained on the fentanyl infusion to control postoperative pain from the nerve root stimulation.

8.2.7╇ Postoperative Course Several regimens have been used to manage postoperative pain, which can be quite severe for the first 24 to 36 hours. Consultation with anesthesia, pain, or critical care specialists prior to the surgery is valuable. The author and his team continue the fentanyl infusion from the operating room (OR), decrease it on postoperative day 1, and discontinue it on postoperative day 2. The fentanyl is supplemented by diazepam. Other options include an epidural catheter for pain. The patient is kept lying flat for a few days to minimize headache from CSF loss and leak.

Complications The incidences of CSF leak, postoperative infection, and neurologic injury are exceedingly low. The main postoperative problem can be pain control. Overall, the main complication is poor patient selection and deterioration in the long term. Most patients will experience some regression with growth spurts but this typically improves with additional therapy and Botox injections.

87 â•… The Evaluation and Treatment of Spasticity

Long-Term Outcomes The short-term benefit of SDR with PT compared to PT alone was demonstrated in three small, randomized, controlled prospective trials, and analyzed in a meta-analysis.5 Multiple studies have detailed excellent sustained improvement 10 years and more after SDR.6–9 The selection criteria for SDR and the medical and neurologic outcomes for preterm infants have changed significantly over the past two decades. The selection criteria from a multidisciplinary perspective are still being refined.

87.3╇ Intrathecal Baclofen Therapy 87.3.1╇ Indications for Intrathecal Baclofen Therapy Children and adults with spasticity and other movement disorders, including dystonia arising from almost all etiologies, can benefit from ITB therapy. The minimum weight is typically considered 15 kg, although depending on the body habitus, pumps have been successfully implanted in slightly smaller children. Whereas well over 95% of those with spasticity will achieve excellent relief, approximately 60% with predominantly dystonia can expect excellent relief. Most children with secondary dystonia also have a significant component of spasticity, and the combination of marked improvement in spasticity combined with partial improvement in dystonia can provide significant relief. A test dose administered via a lumbar puncture can be quite useful for all involved to understand what kind of relief may be achieved once the pump is inserted and is delivering the drug.

87.3.2╇ Goals of ITB Therapy Specific goals should be identified preoperatively with the patient, family, and other caregivers. Goals can include increased independence, such as the ability to operate a wheelchair or computer, greater comfort, or improved ease of care.

87.3.3╇ Alternate Procedures ITB is approximately 1,000-fold more potent than enteral baclofen and, with appropriate dosing, does not affect the brain or liver. The response to enteral

baclofen is not predictive of the ITB response. ITB therapy rarely substitutes for orthopedic procedures; however, decreased tone from effective ITB therapy can markedly improve the recovery process for many orthopedic techniques. Because botulinum toxin injections are limited by weight, effective ITB therapy can allow more focal use of botulinum toxin and, in combination with ITB therapy, may provide excellent overall outcome.

87.3.4╇Advantages ITB therapy dosing is quite flexible. For more involved cases, the dosing can be adjusted to accommodate bodily stresses―for example, if a patient has increased tone from an intercurrent illness, fracture, or other surgical procedure. ITB therapy is quite effective across a range of etiologies, from inflicted trauma to neurodegenerative processes, and can offer relief for patients with few other options. Currently, in large-volume centers the complication profile from ITB therapy is lower than that observed with DBS in children.

87.3.5╇Contraindications ITB therapy requires regular maintenance, including refills a few times a year and pump replacement every several years for a new battery. ITB pumps should not be implanted until the managing physician and mechanism for regular maintenance have been established. Very few patients have an adverse reaction to ITB therapy that requires discontinuation of treatment.

87.3.6╇ Operative Detail and Preparation Preoperative Planning and Special Equipment The author and his team obtain a preoperative quick, nonsedated MRI to exclude unsuspected intracranial processes that contraindicate a lumbar puncture. They also employ an infection reduction protocol to minimize the risk of perioperative infections. Currently, two companies manufacture ITB catheters and pumps. Because ITB withdrawal can be potentially life-threatening, components for emergent revision or replacement need to be stocked by a hospital, and a medical and surgical team comfortable with managing baclofen withdrawal and complications must be available.

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728 Section VIIIâ•… Epilepsy and Functional Disorders Key Steps of the Procedure/Operative Nuances Although insertion of the catheter and pump is not one of the most difficult neurosurgical procedures, strict attention to technique is important to minimize technical complications and infections. After the successful induction of anesthesia, the patient is positioned in the lateral decubitus position, with the left side down, on a fluoroscopy-compatible bed. In general, the pump is placed in the right abdomen because many of these patients have or will need a feeding tube at some point. A midline incision is marked in the midline. The author and his team prefer the midline incision because some patients will eventually undergo a spinal fusion. Others prefer to use a paramedian incision. A 10-cm transverse incision is marked in the abdomen at least one fingerbreadth below the costal margin, with care taken to avoid any shunt or feeding tube incisions. The lumbar incision is deepened to the fascia, and sufficient fascia is cleared of adjacent adipose tissue to facilitate suturing the anchor to the fascia well. Using fluoroscopic guidance as little as possible, the thecal sac is accessed with a Tuohy needle to achieve robust flow of CSF. The needle is immediately returned to its position in the sheath to minimize CSF leakage. A three-point, purse-string suture is placed around the sheath and is left tagged to be tied after the catheter is inserted (Fig. 87.5a). The catheter is floated to the desired level using fluoroscopic guidance, with as few exposures as possible to minimize radiation exposure (Fig. 87.5b). The catheter stylet and the needle sheath are removed. The purse-string suture is tied; the anchor is positioned and sutured to the fascia (Fig. 87.5c). Good flow from the catheter is confirmed before and after tunneling the catheter to the abdominal wound. Simultaneously, the abdominal pocket is developed and enlarged caudally just superficial to the fascia. Some prefer to use a subfascial insertion. The pump is also filled with drug during this time. The catheter is trimmed and is attached to the connector, and the connector is attached to the pump, with strict attention to secure connections. The pump is settled into the pocket with all excess tubing tucked deep to the pump. A large permanent suture is used to secure the pump to the posterior fascia using one or two suture loops on the pump. The author and his team use absorbable skin sutures.

Expert Suggestions Care should be taken to minimize excess removal of CSF to reduce the risk of a spinal headache and intracranial subdural hematoma; only one punc-

ture through the fascia should be made with the Tuohy needle. At the same time, brisk flow of CSF is needed to float the catheter well. The purse-string suture in the fascia around the catheter curtails the risk of CSF leak and the catheter backing out of the canal. The anchor should be secured to the fascia as close as possible to where the catheter enters the fascia to lessen the tendency of the catheter to back out.

Hazards/Risks/Avoidance of Pitfalls Determining the source of pump malfunction can be challenging, and care taken during the initial insertion is worth the effort. If acute malfunction is suspected, the patient should be treated with intravenous benzodiazepines and hydration while the pump is assessed. Similar to the treatment of status epilepticus with potent anticonvulsants that may suppress respiration, the patient may require so much medication that airway support, including intubation and ventilation, may be necessary. Enteral baclofen can be used to mitigate some of the symptoms but will not, by itself, safely cover a patient in ITB withdrawal. The most common reasons for acute withdrawal are related to drug refills. If the patient had a refill in the past several days, refilling the pump with fresh drug may resolve the issue. If acute mechanical malfunction is suspected, X-rays are obtained to evaluate for discontinuity, catheter migration, or other structural problems with the catheter. Acute mechanical problems with the pumps, such as a rotor stall, are rare but do occur. Mechanical problems that produce a more subacute presentation include gradual occlusion of the connector or catheter by debris and microleaks. A programmed bolus dose with an effect confirmed about 4 hours after the bolus can clarify whether drug is reaching the CSF. Response to a programmed bolus or dosage increases that dissipate within a few days is suggestive of a catheter microleak. Exploration can often yield an answer more efficiently than an extensive evaluation with computed tomography dye studies.

Salvage and Rescue With infection reduction protocols, current infection rates in the year after insertion typically are below 2%. Late infections can occur years after any surgery, presumably from hematogenous seeding. In approximately 50% of cases, systems can be salvaged by extensive irrigation followed by a prolonged antibiotic course.

87 â•… The Evaluation and Treatment of Spasticity a

b

c

d

Fig. 87.5â•… Insertion of intrathecal baclofen (ITB) catheter in the lumbar spine. (a) Care is taken to insert the Tuohy needle through the fascia only once, to decrease cerebrospinal fluid (CSF) leakage. After the Tuohy needle is inserted into the thecal sac, a pursestring suture is sewn around the sheath of the needle, and tagged for tying after the catheter has been successfully inserted. This minimizes the risk of CSF leaking around the catheter. (b) Intermittent, brief fluoroscopic images are obtained as the catheter is inserted into the desired location, typically the upper thoracic spine. (c) Free flow of CSF is confirmed from the catheter after the stylet is removed, the purse-string suture is tied and the anchor is sutured in place, and the catheter is tunneled to the abdominal pocket. (d) The anchor is sutured in place such that the base of the anchor closely abuts the fascia to minimize any exposed catheter between the fascia and anchor. This curtails the risk of the catheter dislodging out of the spine.

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87.4 Outcomes and Postoperative Course The author and his team provide all patients with a binder to wear to minimize seroma formation. They also obtain a radiograph of the catheter and pump prior to hospital discharge to serve as a baseline, should the patient return for evaluation of pump malfunction.

87.4.1╇Complication The most common complication in the postoperative period is seroma formation. A seroma may appear in the first few days after surgery or in a delayed manner a few weeks after surgery. Use of a binder in the postoperative period reduces, but does not eliminate, seroma formation. As mentioned earlier, infection reduction protocols have markedly decreased the incidence of postoperative infections. If the pump must be removed due to infection, an ITB bolus can be given prior to removal of the pump to ease the acute postoperative withdrawal. A course of intravenous followed by enteral benzodiazepines will still be required. Baclofen withdrawal can be serious and difficult to distinguish from other illnesses in this fragile patient population.

References ╇1. Gigante

P, McDowell MM, Bruce SS, et al. Reduction in upper-extremity tone after lumbar selective dorsal rhizotomy in children with spastic cerebral palsy. J Neurosurg Pediatr 2013;12(6):588–594 ╇2. Craft S, Park TS, White DA, Schatz J, Noetzel M, Arnold S. Changes in cognitive performance in children with spastic diplegic cerebral palsy following selective dorsal rhizotomy. Pediatr Neurosurg 1995;23(2):68–74, discussion 75 ╇3. Park TS, Gaffney PE, Kaufman BA, Molleston MC. Selective lumbosacral dorsal rhizotomy immediately caudal to the conus medullaris for cerebral palsy spasticity. Neurosurgery 1993;33(5):929–933, discussion 933–934 ╇4. Sacco DJ, Tylkowski CM, Warf BC. Nonselective partial dorsal rhizotomy: a clinical experience with 1-year follow-up. Pediatr Neurosurg 2000;32(3):114–118 ╇5. McLaughlin J, Bjornson K, Temkin N, et al. Selective dorsal rhizotomy: meta-analysis of three randomized controlled trials. Dev Med Child Neurol 2002;44(1):17–25 ╇6. Bolster EA, van Schie PE, Becher JG, van Ouwerkerk WJ, Strijers RL, Vermeulen RJ. Long-term effect of selective dorsal rhizotomy on gross motor function in ambulant children with spastic bilateral cerebral palsy, compared with reference centiles. Dev Med Child Neurol 2013;55(7):610–616 ╇7. Josenby AL, Wagner P, Jarnlo GB, Westbom L, Nordmark E. Motor function after selective dorsal rhizotomy: a 10-year practice-based follow-up study. Dev Med Child Neurol 2012;54(5):429–435 ╇8. Langerak NG, Tam N, Vaughan CL, Fieggen AG, Schwartz MH. Gait status 17-26 years after selective dorsal rhizotomy. Gait Posture 2012;35(2):244–249 ╇9. Dudley RW, Parolin M, Gagnon B, et al. Long-term functional benefits of selective dorsal rhizotomy for spastic cerebral palsy. J Neurosurg Pediatr 2013;12(2):142–150

88

Intrathecal Therapy for Movement Disorders Bruce A. Kaufman

88.1╇Background

88.1.3╇ Alternate Procedures

88.1.1╇Indications

Currently, the patients who are tried on intrathecal baclofen are those who have failed the typical oral medications. However, some patients will not respond to intrathecal baclofen and may be better served with deep brain stimulation (DBS).3 The use of DBS in children is currently limited by the lack of knowledge of the best intracerebral target, the appropriate parameters to use, and the long-term benefits. Additionally, there may be a reluctance to place electrodes into a growing child with the unknown longterm effects of both growth and placement.

Pediatric neurosurgeons are exposed to a large number of patients with “movement disorders,” but the majority are secondary movement disorders mixed with spasticity, such as in cerebral palsy, postanoxic brain injury, or posttraumatic brain injury.1,2 The patient’s movement disorder may not be apparent until the spasticity has been alleviated. It was during the treatment of patients with coincident spasticity and dystonia in 1991 that the efficacy of intrathecal baclofen was recognized.2 Since then, intrathecal therapy has been tried and used for a variety of dystonias and movement disorders and is often tried when other therapies have failed to improve the patient―with a majority of patients showing some long-term response.3,4 The uses of intrathecal baclofen for movement disorders seem to be ever increasing because the other options for effective treatment are limited.

88.1.2╇Goals The primary goal of this therapy is to alleviate the most manifest symptoms of the dystonia. This allows for the higher performing patient to achieve normal functions. But even the more dependent and incapacitated patients can be helped by easing the symptoms of their disorders that interfere with their daily care, or even prevent them from participating in their daily activities. In some cases, the dystonic movements are also associated with debilitating pain, and improvement in the symptoms of the movement disorder result in improvement in their pain.

88.1.4╇Advantages The main advantage of intrathecal baclofen is the knowledge acquired over the decades of its use in spasticity. The components for intrathecal delivery of baclofen are widely available, and the techniques and complications of the procedures are well known. The sophistication of the pumps allows for a myriad of different delivery parameters (e.g., bolus vs. continuous, bolus in addition to continuous, stepped delivery) that may have an effect on the symptomatic relief. In addition, once the system is implanted and the appropriate dosing and responses have been achieved, the patients and their caregivers are relieved of any ongoing tasks (except for the needed follow-up and medication refills).

88.1.5╇Contraindications The presence of a cerebrospinal fluid (CSF) shunt is NOT a contraindication, even if the medication is delivered to the ventricular system.4 The diversion of CSF may affect the dosing and the time it takes to define the efficacy of the therapy. It may result in a time of several months to achieve a steady state.

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732 Section VIIIâ•… Epilepsy and Functional Disorders Using intrathecal baclofen for a movement disorder has the same relative contraindication that it has in use for spasticity―that the supervising physician has competence in managing intrathecal baclofen and its complications, and the patient is able to return to that caregiver for assessment and medication refill. In these cases, the treating physician must also have expertise in the evaluation and handling of movement disorders. At this time, it is not clear that intrathecal baclofen can be used as a “first” therapy for movement disorders. In addition, this therapy is an “off-label” use of the medication and the pump and catheters.

88.2╇ Operative Details and Preparation 88.2.1╇ Preoperative Planning and Special Equipment Where to Deliver the Medication There is an ongoing discussion about the best location to deliver the medication into the spinal fluid space. Intrathecal baclofen for spasticity is thought to have its effects at the spinal level, affecting the presynaptic connections of the motor neurons. For the treatment of dystonia, baclofen may work on the cortical surfaces, inhibiting excessively stimulated motor and premotor cortex.3 If that theory is correct, then whatever method delivers the medication in the highest concentration to the cortical surface would work. Thus placement of a spinal catheter in the high cervical region, even to the level of C1, would be expected to work and has been done without complications.1,5 Intraventricular delivery of baclofen has been used when the spinal avenue was not available, the spinal catheter could not be placed in the high cervical region, there were recurring problems with a spinal catheter, or there was no response to the spinal delivery of medication.4,6,7 Many surgeons have aimed to deliver the baclofen into the third ventricle, assuming this will maximize the delivery of medication to the aqueduct and into the fourth ventricle and thus to the convexity, while minimizing dilution of medication within the lateral ventricles. However, the actual dynamics of CSF and drug flow are not known and placement at the foramen of Monro could be just as beneficial. There has not been a comparison of the effects of drug delivery done at the third ventricle versus the lateral ventricle.8 If the goal is placement at or within the third ventricle, then endoscopic assistance will be necessary to ensure accurate placement. Stereotactic guidance may be needed in those patients with altered anat-

omy, such as from trauma, neonatal brain hemorrhage and injury, or with congenital malformations. In those situations, stereotactic guidance can be used to define the best approach to the desired delivery point. If the goal of placement is only at the foramen of Monro, then stereotactic guidance without endoscopy can be used to guide the placement.

Trial of Therapy When intrathecal baclofen was first used for movement disorders, it was felt that the dose required was much higher than that needed to treat spasticity, and the beneficial effects took some time to be seen.2 Together with the need to deliver the medication close to the brain, a single “test dose” administered by a lumbar puncture (as done for spasticity) would not be sufficient to define the usefulness of intrathecal baclofen for a specific patient’s movement disorder. The author and others have used a trial of intrathecal baclofen delivered over days to help define the effect before committing to the placement of the pump. There are several ways to accomplish this; however, all are based on the delivery of baclofen via an external syringe pump, allowing an increase or decrease in dose while under direct observation.

Spinal Insertion to a High Cervical Location Regardless of the best cervical location (C1 or “high cervical”), it is possible to achieve these placements using a lumbar spinal insertion technique.5 The author prefers a spinal catheter as a first choice for either a trial of baclofen therapy or for therapy. The catheter is placed in the same way as is done for routine baclofen pump therapy. A low lumbar midline skin incision is made; the Tuohy needle is inserted into the thecal sac from a paramedian approach, and the catheter is advanced under fluoroscopic guidance to the desired location. On occasion, the catheter will not advance to the desired location, beginning to loop or to hang up on a dentate ligament or an unusual arachnoid septation. In those cases, the author will remove the needle, leaving the catheter with its stylet in place, so that the catheter is not sheared as it is subsequently moved in and out of the canal. The catheter with stylet is pulled back and below the obstruction, and then is rolled between the fingertips as it is advanced into the canal. The retraction/ rolling/advancing can allow the catheter to advance through a different path within the spinal canal to the desired final location. At times, the catheter cannot be advanced. In these cases, the catheter is withdrawn, the wound is closed, and the procedure is abandoned for the time being. If an obstruction is suspected, magnetic resonance imag-

88 â•… Intrathecal Therapy for Movement Disorders ing (MRI) of the spine is obtained to define the anatomy and guide the decision to attempt a spinal catheter again in a few weeks. In the author’s experience, the majority of deferred catheter insertions are completed on the next attempt. The author will obtain an MRI of the spine in advance of the surgery when there is a history of spinal trauma, meningitis with possible arachnoid loculations, or prior intradural spinal surgery. If the catheter cannot be placed through the lumbar spinal insertion, the author will proceed to ventricular access rather than an open cervical insertion. Others have advocated for an open cervical approach to catheter placement when the lumbar access is unavailable or unsuccessful, or there has been a prior spinal fusion in the lumbar region. They would perform an open dissection to the C1–C2 interspace, open the dura under direct vision, and thread the catheter into the subarachnoid space. The author does not feel that the risks of the open cervical approach are justified. The catheters placed by this method are much harder to revise, requiring a repeat of the open technique, and a spinal catheter can be placed even in patients with a well-fused lumbar spine. The reported and relative risks of an intraventricular catheter insertion appear to be about the same as for a spinal catheter.4,7

Lumbar Insertion in the Fused Spine Most patients with a fused spine have a normal intradural compartment that can accommodate a catheter. The few with posttraumatic fusions may not be good candidates for an attempt at spinal catheter placement due to the likely altered intradural anatomy. The patient is placed in the prone position, and fluoroscopy is used to aid in the identification of the insertion site and the catheter positioning once the canal is accessed. A spot in the midline of the lower lumbar spinal fusion is identified that will allow the surgeon to drill a small hole through the fusion mass, between any instrumentation. The author uses a Midas Rex drill with a matchstick bit (M-8, Medtronic) to create a small, round hole through the fusion mass, angled superiorly for easier catheter insertion. The epidural space is identified as the drill or small curette penetrates the bone into the canal. The standard Tuohy needle is used to penetrate the dura and insert the catheter. To minimize CSF leakage, the author will dissect a pedicle of tissue immediately adjacent to the fusion and the hole, place the Tuohy needle (and thus the catheter) through the tissue, and tuck this tissue into the hole once the catheter is in place. Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA) or other tissue sealant of the surgeon’s choice can be used. The catheter is anchored at the dorsal fascia in the typical fashion and is tunneled subcutaneously to a

small flank incision where it is coiled. The catheter can be externalized at the flank for a trial. If immediate pump implantation is planned, the wounds are closed, the patient is repositioned supine and redraped, and the procedure is completed.

Cranial Intraventricular Insertion The author’s technique for catheter placement in the third ventricle uses endoscopy to verify placement. A 12.5 French (F) peel-away introducer is inserted into the lateral ventricle through a coronal burr hole; this sheath can simultaneously accommodate the catheter and a small endoscope (Innervision, Medtronic). Standard stereotactic guidance can be used if needed. The endoscope is placed through the sheath, and the peel-away sheath and endoscope are advanced up to but not through the foramen of Monro under direct vision. The baclofen catheter is passed inside the sheath alongside the endoscope and is advanced into the third ventricle under direct vision. The peelaway sheath is removed, while the surgeon continues to visualize the catheter remaining in place, and then the endoscope is removed. The catheter is passed through the right-angle stent that comes with a small ventricular catheter (#41207 ventricular catheter, Medtronic), using a 2–0 silk tie around the stent and catheter to hold the catheter in place, and sutures to anchor the stent to the pericranium. The Medtronic Ascenda catheter comes with a deployable anchor that is placed around the catheter up to the stent and then is secured to the pericranium with sutures. This anchor is 2 cm long, requiring a longer cranial incision, but most surgeons will also loop the catheter after that anchor for additional strain relief (Fig. 88.1). A commonly used technique to secure the catheter at the burr hole employs the STIMLOC device (Medtronic) designed to anchor DBS leads; this requires a larger burr hole than is needed just for the catheter placement.6 In the past, some surgeons have used a standard or small-diameter CSF shunt ventricular catheter to access the ventricle and deliver the medication. This was connected to the baclofen catheter through a stepped connector. The length of this catheter was recorded, to allow for calculation of the volume inside the tubing. Unfortunately, the new Ascenda (Medtronic) catheter does not allow for the use of a stepped connector, and the supplied connector is not capable of adapting to connect to a ventricular catheter.

Long-Term Trial Insertion Methods A long-term trial of intrathecal baclofen can be accomplished using either an intracranial or intraspinal catheter. The implanted baclofen catheter can

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734 Section VIIIâ•… Epilepsy and Functional Disorders

Fig. 88.1â•… Plain radiograph of an intraventricular baclofen catheter. An extended cranial incision is required to accommodate the catheter as it leaves the burr hole, is secured by a right-angle stent and an anchor, and then is looped for strain relief; the loop is secured by sutures.

be directly externalized but, again, the Ascenda catheter precludes direct connection to a syringe pump. This method has been used with the intent of removing the catheter at the end of the trial and having the patient return for placement of a new complete system. Another variation has the catheter placed using the standard techniques, but terminating at a central venous line-style subcutaneous reservoir. The reservoir is accessed percutaneously in the same fashion as used for central lines. If the trial is successful, the reservoir is removed and the pump is implanted and connected to the existing intrathecal catheter. Again, the Ascenda catheter cannot directly connect to a reservoir. The author’s preferred technique has been to place the intrathecal catheter, anchor it at the fascia or burr hole, and tunnel the catheter to a small, flank incision near the site of a future pump. At that incision the catheter is cut and spliced to a 4.2 F Broviac catheter (#0600524 4.2 F single lumen CV catheter with

SureCuff tissue ingrowth cuff). The Broviac catheter is filled with a baclofen solution and clamped, so that the internal volume of this catheter is not a factor in calculating the bolus needed to fill the baclofen catheter. The Broviac cuff is just inside the externalization site, and the catheter is tunneled and connected to the baclofen catheter. Using a Broviac catheter allows for an easy connection to a syringe pump and, hopefully, limits transcutaneous infection along the externalization site, allowing the intrathecal catheter to remain for permanent use. The author uses a concentration of 20 µg/mL baclofen, purposefully low, so that it would be difficult to have an accidental overdose. The connector supplied with the Ascenda catheter does not easily allow for connection to a Broviac or other reservoir, but a 4.2 F vascular catheter can be connected (Fig. 88.2). The intrathecal catheter is attached to the connector in the standard fashion. The snap-cap on the opposite end of the connector is removed by pulling it off. A 3–0 silk tie is fastened

88 â•… Intrathecal Therapy for Movement Disorders a

b

c

Fig. 88.2â•… Attachment of a Broviac catheter to an Ascenda connector. (a) The Ascenda connector has a cap on each end that, when pressed onto the connector, locks and secures the catheter. The cap can be carefully pulled off. (b) A 3–0 silk tie is attached to the end of the 4.2 French (F) Broviac catheter, and the tie is passed through the hole in the detached cap and is used to pull the Broviac through the cap. The Broviac is cut to an appropriate length, locating the catheter sleeve just under the skin at the externalization site and the connection to the Ascenda catheter at the adjacent flank incision. (c) A small amount of the Broviac is left protruding through the cap; that end is pushed onto the connector, and the cap is pushed into place until it locks. Be careful to align the slots on the cap with the pegs on the connector. The fit is quite tight and care must be taken to ensure the cap is securely locked.

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736 Section VIIIâ•… Epilepsy and Functional Disorders to the very end of the Broviac catheter and is used to pull the catheter through the cap. The Broviac is cut to the appropriate length and is placed over the metal insert of the connector, and the cap is pushed onto the connector and snapped into place, securing the catheter. This connection is sufficient for shortterm use during the trial. If the trial is successful, the patient returns to the operating room for routine implantation of the baclofen pump. The catheter from the pump is tunneled to the flank incision and is connected to the intrathecal catheter using a new connector. If the trial is unsuccessful, the patient returns to the operating room for removal of the catheter. The trial can usually be accomplished in less than 1 week, allowing pump implantation during the same hospitalization.

88.3╇ Outcomes and Postoperative Course 88.3.1╇ Postoperative Considerations The final dose of baclofen that is used to control the movement disorder tends to be similar to, or slightly higher than, that used for spasticity.7 In practice, the managing physician should be less focused on a specific programmed dose and simply and slowly titrate the dose to the desired results or the onset of side effects.4,7 If an externalization trial has been done, there may be some indication of the necessary dose. Patients who do not respond to intrathecal baclofen delivered to one space may show an effect if the medication is delivered to another space (convert a spinal end to an intraventricular end).

88.3.2╇ Complications―Ventricular versus Spinal Catheters In one report, there were fewer problems with intraventricular catheters than with intraspinal catheters, whereas in another, the two techniques had a similar frequency and type of complications.4,7 In both approaches, many of the complications in the past have been due to catheter fractures and failures. This may be obviated by the newly released and redesigned catheter from Medtronic.

88.3.3╇ Complications―High Cervical Catheters The use of baclofen delivered to the high cervical region always raises concerns for respiratory depression or stupor, side effects of baclofen overdose. When baclofen is delivered to the high cervical canal, there have been reports of somnolence and urinary retention, but these immediately reverse with a reduced dose.5 The same authors have noted years of effective treatment at the high cervical level without complications. In another report, there were no side effects of the high cervical delivery of baclofen, even to doses at and above 1,000 µg/day.7

References ╇1. Motta

F, Antonello CE, Stignani C. Upper limb function after intrathecal baclofen therapy in children with secondary dystonia. J Pediatr Orthop 2009;29(7):817–821 ╇2. Panourias IG, Themistocleous M, Sakas DE. Intrathecal baclofen in current neuromodulatory practice: established indications and emerging applications. Acta Neurochir Suppl (Wien) 2007;97(Pt 1):145–154 ╇3. Albright AL, Ferson SS. Intraventricular baclofen for dystonia: techniques and outcomes. Clinical article. J Neurosurg Pediatr 2009;3(1):11–14 ╇4. Turner M, Nguyen HS, Cohen-Gadol AA. Intraventricular baclofen as an alternative to intrathecal baclofen for intractable spasticity or dystonia: outcomes and technical considerations. J Neurosurg Pediatr 2012;10(4):315–319 ╇5. Dykstra DD, Mendez A, Chappuis D, Baxter T, DesLauriers L, Stuckey M. Treatment of cervical dystonia and focal hand dystonia by high cervical continuously infused intrathecal baclofen: a report of 2 cases. Arch Phys Med Rehabil 2005;86(4):830–833 ╇6. Albright AL. Technique for insertion of intraventricular baclofen catheters. J Neurosurg Pediatr 2011;8(4):394–395 ╇7. Rocque BG, Leland Albright A. Intraventricular vs intrathecal baclofen for secondary dystonia: a comparison of complications [ONS supplement]. Neurosurgery 2012; 70(2 Suppl Operative):321–325, discussion 325–326 ╇8. Bollo RJ, Gooch JL, Walker ML. Stereotactic endoscopic placement of third ventricle catheter for long-term infusion of baclofen in patients with secondary generalized dystonia. J Neurosurg Pediatr 2012;10(1):30–33

89

Microelectrode-Guided Deep Brain Stimulation in Children Ron L. Alterman and Irene P. Osborn

89.1╇Background In young patients, deep brain stimulation (DBS) is most commonly used to treat medically refractory primary dystonia, and the globus pallidus internus (GPi) is the site most often targeted.1 Other uses of DBS in children (e.g., secondary dystonia, Tourette syndrome) are currently considered experimental in the United States. Surgery should be considered only in patients with disabling symptoms that are refractory to standard medications; however, younger age, shorter symptom duration, and lack of fixed skeletal deformity at the time of surgery predict better clinical results, arguing for earlier intervention, particularly in patients with the DYT1 gene mutation.2

reotactic frame, the most uncomfortable part of the procedure.

Application of the Stereotactic Frame Stereotactic head frames remain the gold standard for performing DBS lead implants, although “frameless” technologies are gaining in popularity. Application of the frame is the most underappreciated part of the DBS procedure. Applying the frame “square” to the patient’s anatomy (i.e., centered, without rotation in

89.2╇ Operative Detail and Preparation 89.2.1╇ The Deep Brain Stimulation Procedure The DBS device (Fig. 89.1) is implanted in two stages. During the first stage, the DBS lead is implanted into the GPi (unilaterally or bilaterally), employing stereotactic technique. The remaining components (i.e., extension cable[s] and pulse generator[s]) are implanted during the second-stage procedure, which is performed under general anesthesia. Benzodiazepines can be withheld on the morning of the first surgery because they may interfere with intraoperative microelectrode recording (MER); however, baclofen and trihexyphenidyl should be continued, as withholding these medications may induce a dystonic crisis. If severe symptoms make awake surgery difficult for the patient, the first procedure can be performed under conscious sedation with propofol or dexmedetomidine. Small doses of fentanyl may also be administered during application of the ste-

Fig. 89.1â•… The deep brain stimulation (DBS) device. A DBS device consists of a thin DBS lead equipped with four electrode contacts at the tip, a burr hole cap that secures the lead (not shown), an extension cable that is tunneled from the head to the chest pocket, and a programmable pulse generator.

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738 Section VIIIâ•… Epilepsy and Functional Disorders the coronal or axial planes) simplifies the remainder of the targeting process. The frame should be applied so that the base is parallel to the zygoma, thereby yielding axial targeting images that are roughly coplanar to the intercommissural line, the central meridian for stereotactic targeting. Applying the frame on a sedated patient is challenging and requires two assistants, one to hold the head and one to steady the frame until it is fixed to the patient’s skull. The Leksell model G frame is equipped with ear bars that help with this process. Video 89.1 demonstrates frame application on a sedated patient.

Table 89.1â•… Magnetic resonance imaging scanning parameters for fast spin echo/inversion recovery images Excitation time (Te)

120 ms

Relaxation time (Tr)

10,000 ms

Inversion time (Ti)

2,200 ms

Bandwidth

20.83

Field of view (FOV)

24

Slice thickness

3 mm

Image-Based Targeting

Slice spacing

0 mm

The authors employ fast spin echo/inversion recovery (FSE/IR) magnetic resonance imaging (MRI) for initial targeting (Table 89.1 and Fig. 89.2) because the images are acquired rapidly and provide superior resolution of the commissures and deep gray structures. These images are merged with gadolinium-enhanced volumetric T1-weighted (T1W) images (e.g., SPGR) that yield more accurate fiducial registration3 and provide a clear view of the cortical veins, which one is wise to avoid. The imaging data are transferred to an independent workstation equipped with stereotactic targeting software. The commissures are demarcated so the images may be reformatted orthogonal to the intercommissural plane. The preferred target for

Frequency

192 Hz

Phase

160

Number of excitations

1

Frequency direction

Anteroposterior (AP)

Autocontrol frequency

Water

Flow compensation direction

Slice direction

a

Note: Scanning parameters for fast spin echo/inversion recovery (FSE/IR) magnetic resonance imaging (MRI) are demonstrated. A scan of 30 slices can be obtained in 6 to 9 minutes employing these parameters.

b

Fig. 89.2â•… Fast spin echo/inversion recovery (FSE/IR) magnetic resonance imaging (MRI). (a) Axial and (b) coronal FSE/ IR images are employed to target the globus pallidus internus (GPi). (a) The anterior and posterior commissures (AC and PC) are readily visible, as is the GPi. (b) The target is the posteroventral GPi lying 2 to 3 mm superior and lateral to the optic tract (OT).

89â•… Microelectrode-Guided Deep Brain Stimulation in Children treating dystonia is the posteroventral GPi, which lies 19 to 22 mm lateral, 2 to 3 mm anterior, and 4 to 5 mm inferior to the midcommissural point. The authors’ preferred trajectory approaches the target at angles of 60 to 65 degrees superior to the intercommissural plane and 0 to 10 degrees lateral to the vertical axis (Fig. 89.3). The use of this roughly para-

sagittal trajectory simplifies mapping the intraoperative MER data to the parasagittal images depicted in stereotactic atlases.4,5

Room Setup and Anesthetic Technique The patient is positioned supine with the head elevated 30 degrees (Fig. 89.4). Oxygen is delivered via nasal cannula and end tidal carbon dioxide (CO2) is monitored for detection of venous air embolus. The anesthesiologist administers a “scalp block,”6 which maintains patient comfort with minimal sedation and in turn enhances the quality of the MER. The incision and burr hole are centered on the planned trajectory. A sharp corticectomy is performed to ease insertion of the blunt-tipped cannula, minimizing the risk of subcortical and subdural hemorrhage. Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA) or fibrin glue is placed within the burr hole to limit cerebrospinal fluid (CSF) losses and brain shift during MER.

Microelectrode Recording Fig. 89.3â•… Pallidal lead implantation. The authors’ preferred lead position within the globus pallidus internus (GPi) is depicted. A schematic of the model 3387 lead (Medtronic Inc.) is superimposed on a sagittal image, 20 mm lateral of midline, from the Schaltenbrand and Wharen Atlas. GPe, globus pallidus externus.

Fig. 89.4â•… Room setup.

Details of the authors’ MER technique are provided elsewhere.4,5 In brief, MER is used to confirm that the trajectory passes solidly through the GPi, as indicated by a 6- to 8-mm span of clear GPi recordings. The detection of kinesthetic cells within the GPi and/or detection

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740 Section VIIIâ•… Epilepsy and Functional Disorders

Fig. 89.5â•… C-arm fluoroscopy. Lateral fluoroscopic images confirm lead position relative to the frame’s target point.

of the optic tract 2 to 3 mm inferior to the last recorded GPi cell provide additional confirmation of proper targeting but are not requirements for implantation.

Macroelectrode Test Stimulation The DBS lead is inserted along the desired trajectory so that the deepest contact is positioned at the physiologically defined inferior border of the GPi (Fig.€89.3). C-arm fluoroscopy is employed to confirm that the lead is properly targeted (Fig. 89.5). Test stimulation is performed in a bipolar configuration employing the following parameters: pulse width 60 µs; frequency 130 Hz; amplitude 0 to 5 V. Dystonia does not respond to stimulation immediately, so improvement in the operating room (OR) should not be expected. The main purpose of test stimulation is to ensure that no adverse effects are induced with stimulation up to 5 V, well above the typical amplitudes employed for therapy. The lead is secured at the skull with a locking device that also covers the burr hole. Serial fluoroscopy is used to confirm that the lead is not displaced from its desired position during this process. The free end of the lead is encircled around the burr hole cap and left in the subgaleal space. The incision is irrigated with antibiotic saline and closed anatomically. Postoperative MRI is performed to confirm that the leads are well positioned and that there has been no hemorrhage (Fig. 89.6).

Fig. 89.6â•… Postimplantation magnetic resonance imaging (MRI). Axial fast spin echo/inversion reovery (FSE/IR) image immediately after surgery. The deep brain stimulation (DBS) leads are positioned within the posteroventral globus pallidus internus (GPi).

89â•… Microelectrode-Guided Deep Brain Stimulation in Children

Stage Two: Implantation of the Pulse Generator The remaining components of the DBS system(s) are implanted under general anesthesia. This procedure may be performed on the same day, or as an ambulatory process at a later date. The keys to this procedure are: (1) meticulous hemostasis and closure of the chest pocket to minimize the risk of infection (the most common surgical complication in these patients); and (2) placement of the connection between the lead and the extension cable just lateral to the cranial incision, limiting exposure of the lead to potential fracture through movement. (NB: In smaller patients with thin skin, using rechargeable devices that have a lower profile may reduce the risk of pocket infections.)

89.3╇ Outcomes and Postoperative Course 89.3.1╇ Postoperative Care Patients are observed overnight in the intensive care unit (ICU). The preoperative medication regimen is resumed, pain and nausea are controlled, and the patient is closely monitored for dystonic storm. Most patients are discharged on the first postoperative day, once it is established that they are eating and

drinking normally and are neurologically stable. The device(s) are typically activated 2 to 3 weeks after implantation, sooner if the patient is in a dystonic storm. Improvement typically begins after a few weeks of therapy and may not be complete for 1 to 2 years.1

References ╇1. Alterman

RL, Tagliati M. Deep brain stimulation for torsion dystonia in children. Childs Nerv Syst 2007; 23(9):1033–1040 ╇2. Isaias IU, Volkmann J, Kupsch A, et al. Factors predicting protracted improvement after pallidal DBS for primary dystonia: the role of age and disease duration. J Neurol 2011;258(8):1469–1476 ╇3. Ben-Haim S, Gologorsky Y, Monahan A, Weisz D, Alterman RL. Fiducial registration with SPGR MRI enhances the accuracy of STN targeting. Neurosurgery 2011;69:870–875 ╇4. Alterman RL, Shils JL. Pallidal stimulation for dystonia. In: Starr PA, Barbaro N, eds. AANS Neurosurgical Operative Atlas. Vol 5. New York, NY: Thieme Medical Publishers; 2008: 195–203 ╇5. Shils J, Alterman RL. Interventional neurophysiology during movement disorder surgery. In: Deletis V, Shils J, eds. Interventional Neurophysiology. San Diego, CA: Academic Press; 2002: 405–448 ╇6. Osborn I, Sebeo J. “Scalp block” during craniotomy: a classic technique revisited. J Neurosurg Anesthesiol 2010;22(3):187–194

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90

Interventions for Acute and Chronic Pain in Children Charles Berde

90.1╇Background For adults and children, the general approach to acute and chronic pain management should be multidimensional and interdisciplinary.1–6 Approaches to acute pain management in hospitalized infants and children have been summarized previously.1,2 Compared to adults, chronic pain management in children tends to emphasize rehabilitative approaches and less use of interventions. Clinical approaches and outcomes of multidisciplinary pediatric chronic pain programs, rehabilitative treatments, and cognitive behavioral therapy in children have been summarized in recent reviews.4–6 Most literature on interventions for pain in children is based on case reports and case series,7–9 and only rarely on prospective controlled trials.10 In this chapter, the author reviews some clinical impressions and recommendations regarding interventions for acute and chronic pain in children. The emphasis is on similarities and differences between children and adults regarding epidemiology, techniques, pharmacology, risk-benefit considerations, and outcomes. The maturation of pain pathways in developing animals and humans has received intensive study over the past 20 years. Research in this area is well summarized by Fitzgerald and Walker.11 General conclusions from this research are summarized here. Age-related differences in pain responsiveness and pain pathways: 1. Infant animals and infant humans respond to noxious and nonnoxious stimuli with lower thresholds than adults. 2. Receptive fields of spinal dorsal horn neurons in infant animals receive overlapping inputs from larger percentages of body surface than in older animals. 3. Projection of large and small peripheral fibers overlap in the dorsal horn of infant animals; adult-type synaptic organization develops gradually over the first 2 weeks of life in

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infant rats, roughly corresponding to preterm neonates through preschool age in humans. 4. Descending pain inhibitory circuitry develops later than afferent pain transmission in infant animals. 5. Pain is frequently assessed in human neonates by a combination of behavioral measures, especially involving facial expression, withdrawal reflexes, and autonomic changes. Although behavioral and physiological measures are the most practical means available at present for guiding clinical interventions in newborns and preverbal children, it should be recognized that these largely reflect brainstem and diencephalic responses, not cortical responses. For example, infant rats with extensive supracollicular lesions show similar facial and autonomic responses to noxious stimuli as intact rats. 6. The ontogeny of cortical responses to noxious and nonnoxious stimuli in infants is currently being studied by several groups using electrophysiology (EEG and cortical evoked potentials) and imaging (near-infrared spectroscopy [NIRS] and functional magnetic resonance imaging [fMRI]). Cortical electrical and regional blood–flow-related responses to noxious stimuli can be demonstrated in 28week, postmenstrual-age infants. The nature of pain as conscious experience in infants remains a subject of debate.

90.2╇ Acute Pain in Children Treatment of postoperative pain is important both for relieving suffering per se and also for favorably affecting the course of postoperative recovery. Opioids have an important role in postoperative analgesia for adults as well as children. Opioid pharmacology has been studied extensively for children,

90 â•… Interventions for Acute and Chronic Pain in Children and guidelines for dosing are well established. Nevertheless, opioids generate a range of peripheral and central side effects that impose risks and can delay postoperative recovery. A major theme in current perioperative research involves “opioid-sparing” analgesia12 using combinations of non-opioid analgesics (acetaminophen, nonsteroidal anti-inflammatory drugs [NSAIDs], COX-2 inhibitors, gabapentin, and others) as well as regional anesthesia.13–16 Acetaminophen is a useful analgesic in infants and children, including neonates. Rectal absorption is inefficient, slow, and erratic, and much larger rectal than oral doses are required to produce effective blood concentrations. Intravenous acetaminophen is more expensive, but reliable for bioavailability, and has shown effective analgesia in a recent infant analgesic trial.16 NSAIDs have a good track record of safety and efficacy for short-term dosing in children following a wide range of surgeries. Safety and efficacy data are sparse for infants younger than 3 months.14,17,18 Codeine has traditionally been the most widely used opioid for children following neurosurgical procedures. It is a prodrug that works only by metabolic conversion to morphine. This results in unpredictability in dose response. Overall, codeine is a very weak analgesic: ibuprofen routinely outperforms codeine in adult and pediatric analgesic trials. In patients with delayed maturation of CYP 2D6 or with genotypes with slow conversion, codeine is essentially inert. In a study of children of a wide range of ethnic backgrounds undergoing surgery in London, England, even a large intramuscular dose produced undetectable morphine concentrations in 36% of the children.19 Conversely, genotypes associated with ultrarapid metabolism can lead to overdose, and deaths have been reported in children, particularly among those going home after tonsillectomy.20 For these reasons, the Food and Drug Administration (FDA) has strongly discouraged use of codeine in pediatrics. In major U.S. pediatric centers, oxycodone is now used more widely than codeine for oral analgesia. Large case series support safe use of opioid infusions, patient-controlled analgesia, and nurse-controlled analgesia.21–23 Specific patterns of risk have been described. For example, patients with myelomeningocele show impaired ventilator responses to hypoxemia and hypercarbia and generally greater opioid sensitivity than the general population. In neurosurgical patients, effects of opioids on sensorium and respiratory drive are important. Pediatric hospitals should institute hospital-wide protocols for titrated opioid dosing, dose adjustments for known risk factors, nursing observations, and respiratory monitoring as indicated.23,24 Regional anesthesia is used with increasing frequency for postoperative pain management in children of all ages. Local anesthetic pharmacology has been studied in infants and children for several amino amide local anesthetics, including lidocaine, bupivacaine, chloroprocaine,25 and ropivacaine.26 Systemic local anesthetic

toxicity (seizures, cardiac depression) in adults is largely a problem following inadvertent intravascular injection. Only very rarely do adults have systemic toxicity due to an excessive dose injected into an extravascular site. Case reports, case series, and prospective registry studies indicate that systemic toxicity occurs in infants and younger children both from intravascular injections and from excessive dosing in extravascular sites. Safe practice in pediatrics therefore requires routine calculation of maximum safe doses, scaled by body weight. For example, if performing local infiltration in a 5-kg infant using lidocaine 1% (10 mg/mL), a maximum safe dose of 5 mg/kg = 25 mg = 2.5 mL. Using dilute solutions (e.g., 0.5% = 5 mg/mL) permits coverage of a larger area with the same dose. Chloroprocaine is an amino ester local anesthetic that is cleared rapidly by plasma esterases even in young infants.25 For the occasional situation where extensive local infiltration is required for a procedure in an awake infant, chloroprocaine may offer a better safety margin than the amino amides, such as lidocaine or bupivacaine. Chloroprocaine’s duration of action is short, typically less than 20 to 30 minutes following infiltration. Animal models and human infant and adult doseresponse studies and allometric scaling models indicate that therapeutic indices for local and regional anesthesia are narrower in infants than in adults. In general, the dose required to block a nerve or group of nerves scales comparatively weakly with body size. This is true for peripheral blocks as well as for spinal anesthesia. For example, 70-kg adult humans often receive bupivacaine spinal anesthesia in a dose of around 15 mg or roughly 0.2 mg/kg. Similar levels are achieved in a 5-kg neonate by a dose of 4 or 5 mg (i.e., 0.8–1 mg/kg). For spinal anesthesia and for peripheral blocks, even with these larger, weightscaled doses, block durations are shorter than comparable blocks in adults. Conversely, the dose for systemic toxicity scales more directly with body size. Thus the therapeutic index for a single injection of local anesthetics in infants is narrower than that for adults. Hepatic immaturity leads to diminished clearance of amino amide local anesthetics in neonates and young infants. To illustrate, the plasma terminal elimination half-life of bupivacaine is roughly 4 hours in older children. It may be more than 8 hours in neonates. This feature reduces the maximum permissible, weight-scaled hourly dosing for infusions. For instance, bupivacaine infusions for epidural or peripheral blocks can be given safely up to a maximum rate of 0.4 mg/kg/h in older children, but only to 0.2 mg/kg/h in infants < age 3 months. Weightscaled clearances mature over the first 3 to 6 months of life. As with single injections, the diminished clearance of amino amides in the first 6 months of life also leads to a narrower safety margin for prolonged local anesthetic infusions in infants than in older children or adults.

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744 Section VIIIâ•… Epilepsy and Functional Disorders Techniques are available for single-shot peripheral nerve blocks and epidural catheter placements for patients of all ages.27–31 Increasingly, pediatric centers worldwide are using regional anesthesia during and after major operations in infants and children. In adults, regional anesthesia is commonly performed awake or under light sedation. In children, it is generally performed under sedation or general anesthesia, although awake-spinal anesthesia is commonly used to avoid general anesthesia in sick, preterm neonates, especially for inguinal hernia repairs. Performance of injections under general anesthesia therefore requires more indirect methods of proving proper needle placement, both to ensure efficacy and to prevent adverse events from misplacement. In the past 10 years, there has been a dramatic increase in the use of ultrasound guidance for peripheral and neuraxial blocks in infants and children.28,30,32 In the author’s practice, essentially all peripheral nerve and plexus blocks are performed using ultrasound, often combined with nerve stimulation. At Boston Children’s Hospital, on average, 10 to 15 peripheral blocks or peripheral catheter placements are performed daily, aided by dedicated teams of anesthesiologists with additional expertise and training in ultrasound-guided techniques. Ultrasound has the theoretical advantage of increasing the safety of injections in anesthetized children, since the operator can see that needle tips are adjacent to nerves and ensure that injectates spread in a perineural rather than intraneural pattern. In general, the short depth of needle placement and immature bone ossification of infants and toddlers make visualization of structures easier than for many corresponding procedures in adults. For example, among neonates, infants, and toddlers undergoing lumbar puncture, ultrasound using a small, high-frequency “hockey-stick” probe gives good views of the front, back, and sides of the subarachnoid space. (This occasionally may be helpful for lumbar drain placement as well.) For adults, the general outlines of the neuraxis can be seen with ultrasound, but with greatly reduced clarity. For epidural catheter placement in infants, the caudal route is commonly used.29,31 Following needle entry through the sacrococcygeal hiatus, catheters can be advanced cephalad to lumbar or thoracic levels using guidance by ultrasound, fluoroscopy, or nerve stimulation. Nerve stimulation guidance for epidural catheter placement or advancement was described in a series of publications by Tsui and colleagues.31 A wire-wrapped epidural catheter is connected to special adapters for stimulation. As the catheter is advanced, lower leg twitches are seen first. As the catheter tip advances cephalad in the epidural space to around T12–L1, hip flexion predominates. Abdominal twitches and loss of hip flexion twitches imply a catheter tip position above T11. The dermatomal level and sidedness of the twitches

correlate well with tip position seen on fluoroscopy. Animal studies showed that the current required to evoke twitches can also be used to confirm that catheter placement is epidural rather than subarachnoid. The traditional and routine approach to identification of the lumbar or thoracic epidural space in adults, particularly for labor analgesia and postoperative analgesia, involves use of surface landmarks, blind needle advancement, and a loss of resistance to injection of saline or air as a blunt-tipped Tuohy, Weiss, or Crawford needle pops through the ligamentum flavum. For pediatric epidural placement, the author and his team strongly recommend use of saline rather than air for loss of resistance. Early case series on pediatric regional anesthesia reported cases of air embolism, cardiovascular collapse, and neurologic sequelae in infants following needle placement into an epidural vein. In larger, subsequent case series where saline was used universally, this complication has not recurred. In North America and Europe, a major trend in pediatric regional anesthesia is the increasing use of plexus blocks and peripheral nerve blocks. No longer are these restricted to the extremities. For example, pain relief after thoracotomy is increasingly provided by ultrasound-guided paravertebral blocks,32 and catheters and pain relief after abdominal surgery are often provided by transversus abdominis plane (TAP) blocks.33 In general, single-shot block durations last for 6 to 12 hours. Thus for major surgery with an expectation of greater pain and analgesic requirements over several days, placement of catheters for continuous local anesthetic infusion is generally favored to prolong the duration of analgesia. Managing epidural and peripheral catheters postoperatively requires protocols for dosing and dose adjustments, troubleshooting, management of unrelieved pain, proactive management of opioid side effects (e.g., nausea, itching, constipation, etc.), nursing care, monitoring, and a coverage system, such as an acute pain service. At Boston Children’s Hospital, the daily patient census on the acute pain service is typically 30 to 55 patients. With this volume and complexity, coverage involves an attending anesthesiologist/pain physician and fellows and/or nurse practitioners fully dedicated to the service (i.e., with no additional operating room responsibilities). In order to supply prolonged analgesia and avoid the need for tethering patients to catheters and infusion pumps, several groups have developed candidate formulations to provide prolonged-duration, local anesthesia lasting for several days after a single injection. (Disclosure: This is an active area of this author’s research, intellectual property, patents, licenses, and potential future commercial development.) Some approaches have involved controlled release of existing local anesthetics from liposomes, microparticles, or other delivery systems. One of these formulations, Exparel, is currently on the market; however, it is

90 â•… Interventions for Acute and Chronic Pain in Children labeled only for wound infiltration, not for peripheral nerve blockade―and it has not been studied in children. The author’s group has collaborated in the study of a new class of local anesthetics, site-1 sodium channel blockers, both alone and in combination with amino amide local anesthetics and/or vasoconstrictors.34 With allowances for bias, it is the author’s belief that a 2- or 3-day local anesthetic for either wound infiltration or peripheral nerve blockade will be a very convenient way to improve postoperative analgesia, reduce opioid requirements, and thereby reduce postoperative side effects. Whereas a majority of studies of regional anesthesia in pediatrics have involved nonneurosurgical procedures, there are analgesic trials indicating good analgesia (low pain scores and/or reduced opioid requirements) for pediatric cranial procedures with use of either scalp infiltration35 or block of occipital, supraorbital, and supratrochlear nerves with longacting local anesthetics, such as bupivacaine.36

Although most studies of regional anesthesia for acute pain in pediatrics involve elective surgery, there is a role for regional anesthesia in management of acute pain after major injuries to the chest and extremities, particularly once the overall extent of injuries is clarified. In the experience of the author and his group, regional anesthesia has a very important role for children with extensive limb trauma, including amputations, as well as for children with multiple rib fractures.

90.3╇ Chronic Pain in Children 90.3.1╇Epidemiology Some differences in epidemiology3,37,38 of chronic pain between adults and children are cited in the following:

Epidemiology of Chronic Pain in Children versus Adults 1. Episodic pain (days of pain alternating with days of no pain) is very common among children in general pediatric practice. Between 5 and 10% of school-aged children have recurrent headaches, abdominal pains, and limb pains of sufficient severity to seek medical attention. 2. Recurrent headaches and abdominal pains together account for roughly 1 in 5 school days missed in the United States. 3. In a majority of cases, children with recurrent/ episodic pains are medically well, growing, and coping reasonably well. Occasional school absence is common, persistent school absence overall less so. 4. Algorithms for general pediatricians based on structured history, careful physical examination (including neurologic examination), and parsimonious testing have reasonable predictive value in identifying the smaller subset of children who have recurrent pains due to a disease requiring more specific treatment. 5. Identifiable psychosocial risk factors are correlated with increased odds ratio for school absence among children with recurrent pain conditions. 6. Chronic persistent pain is seen commonly in pediatric specialty practice, but is overall less common than for adults. 7. For adults with low back pain, in a population sense, the likelihood of disability is predicted as much by social and psychological variables as by features of the neurologic examination or imaging studies. 8. School avoidance in children can be regarded as a disability syndrome with some analogies to work avoidance in adults.

9. Animal studies and human case series indicate marked age-related differences in responses to nerve injury. For example, brachial plexus injury is commonly painful in adults, only rarely so among infants following perinatal plexus injury. Many forms of neuropathic pain common in adults are rare in childhood. 10. Conversely, animals having undergone surgery or major inflammation in infancy who are then exposed to a repeat episode of inflammation or injury during adolescence show more intense and prolonged pain and hypersensitivity compared to control animals who had not received similar exposures as infants. 11. The common presenting patterns of persistent pain differ according to age, gender, and patterns of activity. For example, complex regional pain syndrome (CRPS), previously known as reflex sympathetic dystrophy (RSD), is very rare before age 6 years, has a peak age of onset in adolescence around ages 11 to 13 years, and has a female:male ratio in different case series ranging from 5:1 to 9:1. In adults, CRPS affects upper and lower extremities with almost equal prevalence. In children, CRPS is at least five times as common in lower extremities compared to upper extremities. 12. For adult pain clinics, especially those staffed by anesthesiologists or physiatrists, more than 50% of patients generally have low back pain or neck pain. Persistent back pain or persistent neck pain is far less common among younger children. Common causes of back pain differ between adolescents and adults.

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746 Section VIIIâ•… Epilepsy and Functional Disorders Some general differences in approach to needle procedures for adults versus children are listed here:

General Differences in Approach to Needle Procedures for Children versus Adults: Implications of Use of Sedation 1. Fear of needles leads to frequent use of sedation or brief general anesthesia for infants and children. 2. It may be difficult to predict which adolescents require sedation for needle procedures. Occasionally, 15 to 16 year olds tolerate an epidural steroid injection with just local anesthesia; many others will find it too scary. 3. Use of sedation requires some specific techniques to optimize interpretation of diagnostic blocks. In general, when there is diagnostic importance in the effects of local anesthetics, the author and his group use long-acting local anesthetics (bupivacaine, ropivacaine) rather than lidocaine. Similarly, they use ultrashortacting sedatives or rapid-offset general anesthetics to accelerate recovery. 4. In some cases with greater diagnostic uncertainty, the team may use repeated local anesthetic injections via an indwelling catheter, rather than single-shot blocks, to give greater confidence in the findings while avoiding the need for repeat needle procedures. 5. If analgesia is required as part of the sedative regimen during diagnostic blocks, the author and his group often use the ultrashort-acting

90.4╇ Specific Chronic Pain Procedures in Children 90.4.1╇ Epidural Steroid Injection for Lumbar Radiculopathy Lumbar radiculopathy in the referral practice of the author and his team is uncommon before age 12 years but is increasingly common through adolescence. A majority of these children have been active in sports, dance, gymnastics, or cheerleading. More than 95% of lumbar radiculopathy cases involve L4–L5 or L5– S1. Most have unilateral radicular symptoms. Obesity is a risk factor for other kinds of musculoskeletal pain in adolescents; however, it has not been a major factor in the population of adolescents with lumbar radiculopathy dealt with by the author and his group. In adults, many pain specialists prefer transforaminal injections over interlaminar approaches. A small number of randomized control trials (RCTs) in adults support this preference. For unilateral radiculopathy, the author also prefers transforami-

opioid remifentanil, which is metabolized by plasma esterases with a half life < 10 minutes. Remifentanil’s short duration of action is useful, but it requires airway expertise and experience in titration to avoid overshoot and hypoventilation. 6. Use of sedation can similarly mask impending complications. For perineural injections, a theoretical benefit of ultrasound guidance is that needles and catheters can be visualized as adjacent to nerves rather than in an intrafascicular location. 7. Risks of medical radiation are highly age-dependent. For an 80 year old, the future lifetime risk from a certain radiation dose is much less than a similar radiation exposure for an infant or child. Whereas the author and his team use fluoroscopy for procedures in children and adolescents, they place great emphasis on limiting radiation exposure as much as feasible by appropriate shielding, distance of the beam from the target, narrowing windows, avoidance of continuous fluoroscopy whenever possible, and minimizing the number of images overall.

nal injections. Fluoroscopy is used in adolescents in anteroposterior (AP), lateral, and tunnel “Scottiedog” views much like with adults. Proper tip placement requires1: needle tip at the 6 o’clock position under the pedicle on an AP view,2 needle tip at the level of the epidural space on the lateral view,3 a pattern of contrast spread that shows some cephalocaudad epidural spread and some tracking along the desired nerve root, and negative aspiration for cerebrospinal fluid (CSF) or blood.4 Many adult pain physicians use a Quincke spinal needle for transforaminal injections. The author’s preference is to use a 22-gauge Tuohy needle with a “hockey-stick” bend. He prefers the blunt tip of the Tuohy needle because of proximity to a nerve root sleeve. For most S1 injections and L5 injections in younger and thinner children, a 3-inch needle is used. For L5 injections in older or heavier adolescents, a 4½-inch needle is often needed for a fairly lateral transforaminal approach. If an injection is for both therapeutic and diagnostic purposes, the author’s general custom is to first give the steroid (traditionally, triamcinolone 40–80

90 â•… Interventions for Acute and Chronic Pain in Children mg) along with 1 mL of lidocaine 1% in this epidural location, and then to give incremental dosing of 2 mL of local anesthetic, as the needle is withdrawn by about 3 to 5 mm, to lie just outside the epidural space in the foramen, so that it can preferentially bathe the affected nerve root. With this technique, the steroid provides the intended therapeutic effect near the disk in the epidural space, and the local anesthetic produces selective nerve root block, while minimizing spillover of local anesthetic to adjacent nerve roots.

90.4.2╇ Medial Branch Blocks and Facet Injections In adults, axial back pain, especially with extension, is commonly ascribed to degenerative arthropathy of the zygapophyseal (facet) joints. The specificity of facetloading maneuvers on physical examination appears low. The sensory innervation of the facet joints was described by Bogduk. Bogduk, Lord, and coworkers studied the predictive value of medial branch local anesthetic injections to predict responses to radiofrequency (RF) denervation procedures in adults. Extension-related axial back pain in children and adolescents is fairly common in referral practice for orthopedic spine specialists. Spondylolysis is generally treated with antilordotic bracing. For a small subgroup of adolescents with persistent extensionrelated axial back pain, the author and his team are consulted for consideration of facet injections of local anesthetic and steroid, medial branch blocks, and―in certain selected cases―RF lesioning. This procedure is usually done for adults in pain clinics. For children and adolescents, there are some additional concerns1: these can theoretically produce temporary denervation of portions of the multifidus muscle, although most of the inputs to this muscle are from midlumbar roots, whereas the levels most commonly addressed for RF lesioning would be from L4–S1.2 There is also anxiety that adolescents who return to sports with denervation of the posterior elements will continue to apply abnormal forces and not be limited by protective sensation.

90.4.3╇ Implanted, Externally Programmable Pumps in Pediatric Palliative Care The use of implanted pumps for administration of baclofen for patients with refractory spasticity is well known to neurosurgeons.9 Technical aspects of pump placement are described in greater detail in Chapter 87. The special case of a technique of intrathecal

catheter placement in the setting of a prior posterior spine fusion and instrumentation is described in Chapter 87. For purposes of this chapter, it is worth mentioning that programmable intraspinal pumps can also be useful for management of refractory spasticity, dystonia, and pain in children with progressive neurologic disorders associated with a shortened life span, including metachromatic leukodystrophy, spinocerebellar ataxia, and a range of other progressive disorders. Experience from a number of pediatric palliative care services indicates that consultations for children with progressive neurologic disorders now are more common than for children with advanced cancer. In some cases, baclofen alone is infused. In highly selected cases, it has been helpful to administer a mixture of baclofen with morphine or another hydrophilic opioid, such as hydromorphone. Although these combinations may be helpful, use of combinations increases the complexity of dose adjustments, since the two medications have different time constants for achieving steady state.

90.4.4╇ Intrathecal or Epidural Ports or Tunneled Catheters for Children with Refractory Pain due to Advanced Cancer The great majority of children and adolescents with advanced cancer can have good analgesia and tolerable side effects with individualized titration of systemic analgesics, especially opioids, and with management of a range of opioid side effects.39 Methadone is a unique synthetic opioid produced as a racemic mixture that is an “accidental combination drug”: the L-isomer is a µ-opioid agonist, whereas the D-isomer is an NMDA-receptor antagonist. Lowdose ketamine infusions can sometimes be titrated to a rate that provides good analgesia, while avoiding dysphoria or other neurocognitive side effects.40 In the practice of the author and his group, trials of methadone and ketamine, due to their technical simplicity, generally precede consideration of an invasive approach. There remains a small subgroup of patients who, despite aggressive opioid dose escalation, side-effect management, and use of adjunctive analgesics, can be made comfortable only at a price of severe somnolence, fatigue, or mental clouding. In some of these cases, neuraxial infusions of mixtures of opioids, local anesthetics, and other analgesics, such as clonidine, may provide improved analgesia and maintained alertness. For many adults, a fully implanted programmable pump is used in this setting. Implantable pumps are ideal for highly potent, generally very

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748 Section VIIIâ•… Epilepsy and Functional Disorders hydrophilic medications like morphine, baclofen, and clonidine. The experience of the author and his team with children in this setting has been that optimal analgesia often required neuraxial infusion of fairly high doses of local anesthetics with catheter tips at optimal dermatomal levels.7,9 Local anesthetics are low-potency drugs

overall, and potency generally correlates with hydrophobicity and low aqueous solubility. The low potency and limited solubility therefore impose a requirement for higher hourly volumes infused for local anesthetic infusions, compared to morphine or baclofen infusions, with the result that an implanted pump could require refills as frequent as every 2 to 4 days.

Technique of Intrathecal Port Placement for Advanced Cancer Below Midthoracic Levels 1. General endotracheal anesthesia, lateral position 2. Very widely prepped field, to include lumbar and lower thoracic spine, flank, lower chest, and abdomen to the midline; removable drape to protect lateral and anterior aspect of the field as the fluoroscopy C-arm is moved around 3. If coagulopathy is present, slow infusion of platelets, fresh frozen plasma (FFP), or other clotting factors as appropriate during the procedure 4. Periprocedural antibiotics, continued for several days postoperatively for children with severe immunosuppression 5. Port pocket incision is made over the lower ribs; 5-mm spinal incision is made at L3–L4 interspace. 6. Tunneling tool is brought around the chest wall and passed through the spinal incision before the spinal puncture. 7. Fluoroscopy in AP view is used to ensure that initial needle direction is aimed to contact dura in the anatomical midline. Lateral view is then used to gauge needle depth. Since Tuohy needles are blunt-tipped and large-beveled, the dura may be indented considerably before it is punctured, so, on some occasions, CSF is obtained when the needle tip appears on fluoroscopy to be slightly anterior/ventral to the middle of the spinal canal. 8. The catheter should be positioned ahead of time and when CSF is obtained, the catheter can be advanced in a continuous motion so that the tip is cephalad to the intended final location. The impression of the author and his group is that if too much CSF leaks out, the odds of catheter catching or curling back are increased. Catheter advancement should be unrestricted. 9. It is crucial to prove that the catheter is advancing in a subarachnoid, rather than subdural or epidural, location. With the wide bevel and narrow space in younger children, these misplacements can occur even when the dural

puncture gives clear flow of CSF. If CSF does not flow back from the catheter, positioning can be confirmed by the pattern of spread of a small volume of an appropriate contrast material, such as iohexol. 10. In order to make optimal use of opioid–local anesthetic mixtures, the proper positioning of the catheter tip is crucial. Location is based on the dorsal root entry levels corresponding to the predominant pain generators. The author’s general recommendations for catheter tip locations are: lumbosacral, T11; lower abdominal, T8; and upper abdominal and lower thoracic, T Intrathecal catheter tips above T5 are generally avoided, since fluctuating levels can result in episodic spread up to T1, with bothersome tingling in the fingers. 11. Catheter tips are advanced to several levels above the intended final level; catheters are brought around through the tunnel and attached to the port connector. Recommendations for securing the catheter to the port vary slightly with different kits. The author and his team have the greatest experience with the Smiths Medical Epidural Port II kit. The port is anchored to the fascia with sutures to maintain its orientation for external access with the Huber needle. 12. Absorbable sutures are used to close the port incision, but the author prefers nylon sutures for the back. Many of these patients are cachectic and immunosuppressed and heal poorly, and CSF may track back along the catheter for several days. 13. For pain arising from below midthoracic levels, the author and group generally prefer intrathecal ports for greatest flexibility and ability to escalate local anesthetic effect. 14. For unilateral pain at cervical or upper thoracic levels, they prefer tunneled catheters or ports directed to the lateral aspect of the epidural space, or occasionally in brachial plexus or paravertebral locations.

90 â•… Interventions for Acute and Chronic Pain in Children

Technique of Epidural Port or Tunneled Catheter Placement for Advanced Cancer at Upper Thoracic or Cervical Levels 1. General endotracheal anesthesia 2. Choice between lateral or prone position depends on intended levels of entry and requirement for cephalad advancement of the catheter in the epidural space. Prone positioning makes the fluoroscopic AP visualization easier, but it can make it more awkward to access the location of the port site on the lower chest wall. Arm positioning can still obscure needle depth on a horizontal lateral view, but this can generally be anticipated and prevented by a “test-drive” view at the level of the epidural needle entry prior to, and again after, prepping and draping. Lateral positioning improves access to the port site, and makes lateral view fluoroscopy with a vertical beam easier, but it makes AP fluoroscopy and arm positioning more challenging. For lateral positioning, arms are generally positioned with shoulder and elbow flexion and kept apart by non–radiopaque supports so that the cervical spine can be viewed in between the arms on a lateral cross-table view. Even with optimal support and a test-drive prior to prepping and draping, the arms can obscure AP views of the spine at upper thoracic and cervical levels. 3. Very widely prepped field, to include thoracic spine, flank, lower chest, and abdomen to the midline; removable drape to protect lateral and anterior aspects of the field as the fluoroscopy C-arm is moved around 4. If coagulopathy is present, slow infusion of platelets, FFP, or other clotting factors as appropriate during the procedure 5. Periprocedural antibiotics, continued for several days postoperatively for children with severe immunosuppression 6. Port pocket incision is made over the lower ribs; 3-mm spinal incision is made at the level of Tuohy needle entry, which is generally between T2 and T5. 7. Tunneling tool is brought around the chest wall and passed through the spinal incision before the Tuohy needle is placed. 8. In order to keep the epidural catheter advancing cephalad at the intended side of the epidural space, a slightly paramedian approach is used. 9. Fluoroscopy in AP view is used to ensure that initial needle direction is aimed ipsilateral to the side of the patient’s pain and at an angle that will permit cephalad catheter advancement.

Initial needle advancement may be directed to just miss the upper border of the spinous process or lamina inferior to the interspace. 10. Lateral view is then used to gauge needle depth. 11. The imaging here is made more difficult by small degrees of obliquity and overlying posterior rib angles. 12. One imaging trick here, useful for both prone and lateral patient positioning: use a fluoroscopy table that permits right-left tilting. Despite efforts to optimize patient positioning beforehand, occasionally some obliquity persists. The C-arm, when positioned in cross-table horizontal view, can move several degrees in one direction from horizontal, but not past horizontal in the other direction. If additional degrees of rotation are required to get an anatomically true lateral view for a patient positioned prone, or an anatomically true AP view for a patient positioned lateral, then tilting of the table can be used to achieve these views without repositioning the patient under the drapes. 13. Once the needle is seated in supraspinous or interspinous ligament, the stylette is removed and a plastic or glass syringe is filled with saline is attached to the needle and advanced with fluoroscopic guidance until a loss of resistance is felt and the needle tip is seen at the posterior aspect of the spinal canal. In younger children, as compared to adults, the loss of resistance can be subtle, with less-pronounced “pop” on crossing the ligamentum flavum. Epidural positioning should be trusted only if there is agreement between the operator’s hands (feeling the change in resistance) and the operator’s eyes (seeing proper location at the dorsal aspect of the spinal canal on lateral fluoroscopic view). A small volume of iohexol is injected to confirm epidural spread. This volume should be limited to 0.5 to 1 mL to avoid obscuring subsequent visualization of the catheter. 14. The epidural catheter is advanced with fluoroscopic guidance to remain ipsilateral to the side of the patient’s pain. The optimal path of the catheter on the AP view should be “lateral enough but not too lateral.” If too close to the midline, the local anesthetic effect will not remain sufficiently unilateral. If the trajectory is too lateral, the chances increase that the catheter will catch and curl back or exit a root foramen.

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90.4.5╇ Neurolytic Blockade in Pediatrics In the experience of the author and his associates, the uses of neurolytic blockade for children, particularly with advanced cancer, have been relatively limited. For a majority of children with severe pain, the distribution of tumor burden and sources of pain is spread over a wider area, making it less feasible to relieve pain by deafferentation of a limited set of peripheral nerves. A second reason for infrequent use of neurolysis is that patients and parents maintain hope even in the setting of advanced cancer. Interventions that produce permanent deficits are difficult to contemplate in conjunction with maintaining these hopes. The most common neurolytic procedure in the author’s practice has been celiac plexus and splanchnic nerve blocks for children with pain predominantly arising from upper abdominal solid viscera, especially liver, spleen, and pancreas. Multiple techniques for celiac neurolysis have been described for adults, and the most extensive outcome literature is for pancreatic cancer. In the practice of the author and his group, this is performed jointly with a pain physician and an interventional radiologist, using an imaging setup known as a Dyna-CT.8 This setup combines many of the advantages of real-time needle advancement using fluoroscopy AP and lateral views with a reconstructed computed tomography (CT) image showing a detailed axial view. The operator draws coordinates on the axial views on the computer screen, and these are projected onto the fluoroscopy images to guide needle trajectories in multiple planes.

90.4.6╇ Continuous Peripheral Nerve Blocks and Epidural Infusions with Local Anesthetics to Facilitate Rehabilitation in Children with Chronic Limb Pain Associated with Complex Regional Pain Syndromes In the author’s practice, a majority of children and adolescents with complex regional pain syndromes receive intensive rehabilitation either as outpatients,4 in same-day hospital treatment,5 or as inpatients without use of regional anesthesia. For a small subset of patients, their severe allodynia, acute limitation of motion, or other factors result in slow progress. In some of these cases, depending on the distribution of their pain, children are admitted as inpatients for a course of continuous regional anesthesia, using either epidural infusions or, increasingly, continuous peripheral perineural or plexus infusions.41 Although the author and his team previously studied lumbar sympathetic blockade as a mechanism-based, ini-

tial double-blind series of injections via indwelling catheters,10 their experience over many years is that selective sympathetic blockade is much more useful than continuous, combined somatic–sympathetic blockade using peripheral, plexus, or epidural infusions. Regional anesthesia in these settings should be used not in isolation but as a component of a multidisciplinary rehabilitation program.

90.5╇Conclusions For children undergoing surgery, wound infiltration and a variety of forms of regional anesthesia can improve postoperative analgesia, reduce side effects, and improve the course of postoperative recovery. Dose adjustments according to age, body dimensions, and disease status are required, and techniques used for adults require some modifications, especially for infants and younger children. Chronic pain management and palliative care in children and adolescents should be approached in multidisciplinary and multimodal fashions, and interventions should be applied selectively with consideration of relative risks and relative benefits. There is a role for implanted pumps for use of baclofen, and sometimes opioids, in children with refractory spasticity and/or dystonia and pain associated with progressive, life-limiting neurologic disorders. Similarly, there is a role for implanted subarachnoid and epidural ports or tunneled catheters for infusions of local anesthetic–opioid mixtures in selected children and adolescents with advanced cancer and pain that cannot be readily managed by aggressive and individualized use of systemic analgesics. Since placement of implantable pumps and ports in pediatric palliative care is a relatively uncommon occurrence, local patterns of expertise will govern who should undertake these procedures. Often, collaboration among specialists can best ensure pooling of expertise to provide optimal care.

References ╇1. Greco

C, Berde CB. Acute pain management in children. In: Ballantyne J, Rathmell J, Fishman S, eds. Bonica’s Management of Pain. 4th ed. Philadelphia, PA: Lippincott, Williams, and Wilkins; 2010: 681–698 ╇2. Greco C, Berde C. Pain management for the hospitalized pediatric patient. Pediatr Clin North Am 2005;52(4):995–1027, vii–viii ╇3. Schechter NL, Palermo T, Walco G, Berde CB. Persistent pain in children. In: Ballantyne J, Rathmell J, Fishman S, eds. Bonica’s Management of Pain. 4th ed. Philadelphia, PA: Lippincott, Williams, and Wilkins; 2010: 767–781 ╇4. Lee BH, Scharff L, Sethna NF, et al. Physical therapy and cognitive-behavioral treatment for complex regional pain syndromes. J Pediatr 2002;141(1):135–140

90 ╅ Interventions for Acute and Chronic Pain in Children ╇5. Logan

DE, Carpino EA, Chiang G, et al. A day-hospital approach to treatment of pediatric complex regional pain syndrome: initial functional outcomes. Clin J Pain 2012;28(9):766–774 ╇6. Robins PM, Smith SM, Glutting JJ, Bishop CT. A randomized controlled trial of a cognitive-behavioral family intervention for pediatric recurrent abdominal pain. J Pediatr Psychol 2005;30(5):397–408 ╇7. Collins JJ, Sethna NF, Wilder RT, Grier HE, Berde CB. Regional analgesia in pediatric terminal malignancy. Pain 1996;65:63–69 ╇8. Berde CB, Sethna NF, Fisher DE, Kahn CH, Chandler P, Grier HE. Celiac plexus blockade for a 3-year-old boy with hepatoblastoma and refractory pain. Pediatrics 1990;86(5):779–781 ╇9. Rork JF, Berde CB, Goldstein RD. Regional anesthesia approaches to pain management in pediatric palliative care: a review of current knowledge. J Pain Symptom Manage 2013;46(6):859–873 10. Meier PM, Zurakowski D, Berde CB, Sethna NF. Lumbar sympathetic blockade in children with complex regional pain syndromes: a double blind placebo-controlled crossover trial. Anesthesiology 2009;111(2):372–380 11. Fitzgerald M, Walker SM. Infant pain management: a developmental neurobiological approach. Nat Clin Pract Neurol 2009;5(1):35–50 12. Kehlet H. Postoperative opioid sparing to hasten recovery: what are the issues? Anesthesiology 2005;102(6):1083–1085 13. Korpela R, Korvenoja P, Meretoja OA. Morphine-sparing effect of acetaminophen in pediatric day-case surgery. Anesthesiology 1999;91(2):442–447 14. Michelet D, Andreu-Gallien J, Bensalah T, et al. A metaanalysis of the use of nonsteroidal antiinflammatory drugs for pediatric postoperative pain. Anesth Analg 2012;114(2):393–406 15. Vetter TR, Heiner EJ. Intravenous ketorolac as an adjuvant to pediatric patient-controlled analgesia with morphine. J Clin Anesth 1994;6(2):110–113 16. Ceelie I, de Wildt SN, van Dijk M, et al. Effect of intravenous paracetamol on postoperative morphine requirements in neonates and infants undergoing major noncardiac surgery: a randomized controlled trial. JAMA 2013;309(2):149–154 10.1001/jama.2012.148050 17. Lesko SM, Mitchell AA. An assessment of the safety of pediatric ibuprofen. A practitioner-based randomized clinical trial. JAMA 1995;273(12):929–933 18. Hiller A, Meretoja OA, Korpela R, Piiparinen S, Taivainen T. The analgesic efficacy of acetaminophen, ketoprofen, or their combination for pediatric surgical patients having soft tissue or orthopedic procedures. Anesth Analg 2006;102(5):1365–1371 19. Williams DG, Patel A, Howard RF. Pharmacogenetics of codeine metabolism in an urban population of children and its implications for analgesic reliability. Br J Anaesth 2002;89(6):839–845 20. Ciszkowski C, Madadi P, Phillips MS, Lauwers AE, Koren G. Codeine, ultrarapid-metabolism genotype, and postoperative death. N Engl J Med 2009;361(8):827–828 21. Howard RF, Lloyd-Thomas A, Thomas M, et al. Nursecontrolled analgesia (NCA) following major surgery in

10,000 patients in a children’s hospital. Paediatr Anaesth 2010;20(2):126–134 22. Morton NS, Errera A. APA national audit of pediatric opioid infusions. Paediatr Anaesth 2010;20(2):119–125 23. Voepel-Lewis T, Marinkovic A, Kostrzewa A, Tait AR, Malviya S. The prevalence of and risk factors for adverse events in children receiving patient-controlled analgesia by proxy or patient-controlled analgesia after surgery. Anesth Analg 2008;107(1):70–75 24. Mazoit JX, Dalens BJ. Pharmacokinetics of local anaesthetics in infants and children. Clin Pharmacokinet 2004;43(1):17–32 25. Henderson K, Sethna NF, Berde CB. Continuous caudal anesthesia for inguinal hernia repair in former preterm infants. J Clin Anesth 1993;5(2):129–133 26. McCann ME, Sethna NF, Mazoit JX, et al. The pharmacokinetics of epidural ropivacaine in infants and young children. Anesth Analg 2001;93(4):893–897 27. Bösenberg AT, Bland BA, Schulte-Steinberg O, Downing JW. Thoracic epidural anesthesia via caudal route in infants. Anesthesiology 1988;69(2):265–269 28. Ganesh A, Rose JB, Wells L, et al. Continuous peripheral nerve blockade for inpatient and outpatient postoperative analgesia in children. Anesth Analg 2007; 105(5):1234–1242 29. Weber T, Mätzl J, Rokitansky A, Klimscha W, Neumann K, Deusch E; Medical Research Society. Superior postoperative pain relief with thoracic epidural analgesia versus intravenous patient-controlled analgesia after minimally invasive pectus excavatum repair. J Thorac Cardiovasc Surg 2007;134(4):865–870 30. Oberndorfer U, Marhofer P, Bösenberg A, et al. Ultrasonographic guidance for sciatic and femoral nerve blocks in children. Br J Anaesth 2007;98(6):797–801 31. Tsui BCH, Wagner A, Cave D, Kearney R. Thoracic and lumbar epidural analgesia via the caudal approach using electrical stimulation guidance in pediatric patients: a review of 289 patients. Anesthesiology 2004;100(3):683–689 32. Qi J, Du B, Gurnaney H, Lu P, Zuo Y. A prospective randomized observer-blinded study to assess postoperative analgesia provided by an ultrasound-guided bilateral thoracic paravertebral block for children undergoing the Nuss procedure. Reg Anesth Pain Med 2014;39(3):208–213 33. Carney J, Finnerty O, Rauf J, Curley G, McDonnell JG, Laffey JG. Ipsilateral transversus abdominis plane block provides effective analgesia after appendectomy in children: a randomized controlled trial. Anesth Analg 2010;111(4):998–1003 34. Rodríguez-Navarro AJ, Berde CB, Wiedmaier G, et al. Comparison of neosaxitoxin versus bupivacaine via port infiltration for postoperative analgesia following laparoscopic cholecystectomy: a randomized, double-blind trial. Reg Anesth Pain Med 2011;36(2):103–109 35. Hartley EJ, Bissonnette B, St-Louis P, Rybczynski J, McLeod ME. Scalp infiltration with bupivacaine in pediatric brain surgery. Anesth Analg 1991;73(1):29–32 36. Suresh S, Voronov P. Head and neck blocks in children: an anatomical and procedural review. Paediatr Anaesth 2006;16(9):910–918

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GT, Macfarlane GJ. Predicting persistent low back pain in schoolchildren: a prospective cohort study. Arthritis Rheum 2009;61(10):1359–1366 38. Huguet A, Miró J. The severity of chronic pediatric pain: an epidemiological study. J Pain 2008;9(3):226–236 39. Collins JJ, Grier HE, Kinney HC, Berde CB. Control of severe pain in terminal pediatric malignancy. J Pediatr 1995;126:653–657

40. Finkel

JC, Pestieau SR, Quezado ZM. Ketamine as an adjuvant for treatment of cancer pain in children and adolescents. J Pain 2007;8(6):515–521 41. Dadure C, Motais F, Ricard C, Raux O, Troncin R, Capdevila X. Continuous peripheral nerve blocks at home for treatment of recurrent complex regional pain syndrome I in children. Anesthesiology 2005;102(2):387–391

Section IX Vascular Disorders Section Editor: R. Michael Scott

If the reader were to peruse a neurosurgical textbook written 30 years ago, he or she would be hardpressed to find a section of the text devoted to the management of pediatric cerebrovascular disorders, perhaps with the exception of vein of Galen malformations. It has become apparent over the past several decades that evolving subspecialization in the area of pediatric cerebrovascular disease has led to many advances in the treatment of children with these disorders. In the process, neurosurgeons have learned much about the epidemiology and presentation of such disorders in children, and surgical management schemes have been designed specifically to treat the pediatric patient. These unique approaches to the pediatric patient have hopefully resulted in improved outcomes, and pari passu, the interest among neurosurgeons in these disorders has flowered. In this section, there are many outstanding examples of this phenomenon. Maher, from the University of Michigan’s C.S. Mott Children’s Hospital, covers the diagnosis and management of stroke in children, reviewing not only the structural problems that may be amenable to surgical treatment but also the metabolic and genetic underpinnings of these conditions. The management of pediatric aneurysms utilizing innovative strategies, such as trapping procedures with cerebral bypass, along with endovascular approaches, is reviewed by Alexander and Edwards from Stanford University, Lucille Packard Children’s Hospital. Zuccaro and Gonzalez Ramos from Buenos Aires, Argentina, give an overview of the manage-

ment of arteriovenous malformations, highlighting a stepwise, disciplined approach to treatment and surgical planning. Guzman, from the University Children’s Hospital in Basel, Switzerland, discusses cavernous malformations in the pediatric population, their typical presentation both clinically and radiographically, and provides management schema for the incidentally discovered and symptomatic lesions. The long-established interventional radiology team at New York University, led by Alejandro Berenstein, in association with his junior colleague Srinivasan Paramasivam, reviews a classification of vein of Galen malformations, along with current concepts regarding treatment of this uncommon disorder, subjects that have become almost exclusively the province of the interventional neuroradiologist. The Boston Children’s Hospital neurosurgical team of Edward R. Smith and myself present recommendations regarding the pre-, peri-, and postoperative management of children with moyamoya disease, and they describe in detail the technique of their surgical revascularization procedure, pial synangiosis. Finally, Chowdhry and Spetzler, from Barrow Neurological Institute in Phoenix, Arizona, present a beautifully illustrated review of spinal arteriovenous malformations and their recommendations for intraoperative management. It is hoped that the reader of this section will gain an increased appreciation for the nuances in the presentation, diagnosis, and treatment of these cerebrovascular conditions in the pediatric population.

91

Stroke in Children Cormac O. Maher

91.1╇Background Strokes in children can result from any one of a number of causes, each of which has its own best treatment. Stroke is one of the top 10 causes of childhood death in developed nations.1,2 Estimates of incidence of pediatric stroke vary between 1.3 and 13.0 per 100,000.2,3 Survivors of childhood stroke often deal with lifelong debility. Following an ischemic stroke, as many as 70% of children will have permanent, lifelong disability.4,5 Furthermore, 25% of children will suffer from a stroke recurrence, highlighting the importance of proper medical and surgical treatment when available.4,5 Strokes are generally divided into ischemic and hemorrhagic categories. Although the ischemic subtype predominates in adults, the incidence of ischemic and hemorrhagic stroke appears to be approximately equal in children, with perhaps only a slight predominance of the ischemic subtype.3,6 Frequent causes of ischemic stroke in infants include cardiomyopathy or congenital cardiac defects, as well as other conditions requiring extracorporeal membrane oxygenation (ECMO). In older children, causative conditions include fibromuscular dysplasia, neurofibromatosis, moyamoya, sickle cell disease, or clotting abnormalities, such as protein C and protein S deficiencies, factor V Leiden disorder, and presence of antiphospholipid or anticardiolipin antibodies.3 The most frequent cause of hemorrhagic stroke in infants is trauma, including hemorrhage during the birthing process, and intraventricular hemorrhage of prematurity. Intracranial hemorrhage in the perinatal period is extremely common on routine screening magnetic resonance imaging (MRI).7 These hemorrhages are usually asymptomatic, remain undetected, and are not included in most reports on intracranial hemorrhage in children. For this reason, most estimates of intracranial hemorrhage incidence in term infants are much lower than those found on screening surveys.3,7 In older children, medical disorders associated with coagulopathy as well as struc-

tural causes, such as arteriovenous malformations (AVMs) and, less commonly, aneurysms and arterial dissections, are the more typical causes of hemorrhagic stroke.

91.2╇ Clinical Presentation As in adults, stroke symptoms in children are usually focal and have sudden onset. Stroke symptoms can be nonspecific in infants and younger children, often leading to diagnostic delays.6 It is not unusual for neonatal strokes to be clinically silent and discovered only on a screening imaging evaluation. In severe cases, both hemorrhagic as well as large ischemic strokes may result in intracranial hypertension. In infants, this usually manifests with a tense fontanelle, splaying of sutures, scalp venous distension, and enlargement of the head circumference. Older children are more likely to have papilledema and extraocular movement abnormalities on examination.

91.3╇Imaging The choice of an appropriate imaging modality depends on patient age and suspected stroke etiology. Ultrasound is a convenient way of imaging the infant brain, especially when serial imaging is required. On the other hand, ultrasound will often miss ischemic strokes and small convexity or posterior fossa hemorrhages.3 Although head computed tomography (CT) is very sensitive for acute hemorrhage, the author and his group prefer to avoid CT and the associated radiation when possible. MRI may be preferred, especially when ischemic stroke is suspected. Cerebral angiography should be obtained only if: (1) a catheter-based intervention is being contemplated; (2) a cerebrovascular lesion, such as

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756 Section IXâ•… Vascular Disorders an aneurysm, AVM, or fistula, is considered possible; or (3) it is part of a diagnostic evaluation for an arteriopathy, such as moyamoya.

91.4╇ Interventional Treatment of Ischemic Stroke Unfortunately, there is little evidence to guide interventional stroke therapy in children, since no clinical trial of intra-arterial thrombolytics or mechanical thrombolysis has included pediatric patients.5 A trial of intravenous tissue plasminogen activator (tPA) administration, the Thrombolysis in Pediatric Stroke (TIPS) trial, is ongoing and may establish the efficacy of this treatment in children.5,8 Pending the results of this and other future trials becoming known, treatment decisions for intra-arterial or mechanical thrombolysis should be made cautiously and only by experienced practitioners until better evidence for efficacy becomes available. More detail on endovascular techniques is provided in Chapter 100.

91.5╇ Surgical Treatment of Moyamoya Moyamoya syndrome may be treated with either direct (superficial temporal artery to middle cerebral artery) or indirect bypass to the middle cerebral artery territory. A variety of indirect techniques have been described, including encephalomyosynangiosis, encephaloduroarteriosynangiosis (EDAS), and pial synangiosis. Each of these operations relies on the ability of the child’s cerebral circulation to parasitize the vascular tissue that is placed in continuity with the brain territory that has inadequate blood supply.9 Many pediatric neurosurgeons have come to favor pial synangiosis, an operation described in more detail in Chapter 96.

91.6╇ Role of Surgery for Ischemic Stroke If a child with a large ischemic stroke continues to deteriorate due to elevated intracranial pressure despite best medical management, surgical treatment may be considered. Relief of pressure by draining cerebrospinal fluid via an external ventricular drain may be an appropriate temporizing measure for some patients. Decompressive craniectomy for stroke is rarely performed in children but may have a role in select cases.10

91.7╇ Surgical Treatment of Intracranial Hemorrhage Surgical treatments of underlying etiologies, such as aneurysms and vascular malformations, are covered elsewhere. Hemorrhages with a significant intraventricular component may benefit from temporary external ventricular drainage. The role of craniotomy for evacuation of intraparenchymal hemorrhage is debated for both children and adults. There is some evidence to suggest that outcomes for children with intraparenchymal hemorrhage may be better than for adults,6 leading some to argue for a more aggressive treatment strategy. In general, neonatal intraparenchymal hemorrhage does not require surgical evacuation. In older children with superficially located cortical hemorrhage and evidence of mass effect, surgical evacuation may be considered in select cases.

91.8╇ Syndromes and Diseases Associated with Pediatric Stroke Pediatric stroke syndromes are often associated with a predilection for cerebral vascular malformations. Syndromes in this category include hereditary hemorrhagic telangiectasia (HHT), PHACE(S), Wyburn-Mason, and Klippel-Trénaunay (syndromes elaborated upon in subsequent paragraphs of this section), and possibly the blue rubber bleb nevus syndrome. Diseases associated with an increased risk for cerebral ischemic disease include MELAS, radiation-induced vasculopathy, and moyamoya (diseases described in greater detail in the next section of this chapter). HHT should be considered in patients with intracranial AVMs, pulmonary arteriovenous fistulae, nosebleeds, gastrointestinal bleeds, or cutaneous telangiectasias.11 HHT follows an autosomal dominant inheritance pattern with high penetrance but variable expressivity. HHT prevalence is approximately 1 or 2 patients per 10,000 individuals. Patients with HHT have a significant lifetime risk of ischemic stroke due to right–left shunting from the associated pulmonary fistulae. For this reason, pulmonary fistulaes in these patients should be repaired, even when the cardiopulmonary status is deemed to be otherwise satisfactory. Since most patients with HHT do not harbor intracranial AVMs, most strokes in individuals with HHT are ischemic strokes resulting from pulmonary fistulae. Hemorrhagic strokes from cerebral AVMs are much less common. Cerebral AVMs in HHT are typically small and multiple. Due to their small size, these AVMs are often best treated with stereotactic radiosurgery.

91â•… Stroke in Children PHACE(S) syndrome is a neurocutaneous disorder that manifests with posterior fossa malformations (P), facial hemangiomas (H), arterial anomalies (A), cardiovascular anomalies (C), eye anomalies (E), and occasionally ventral anomalies of the chest or abdomen, including the sternum (S).12 Most children with PHACE(S) present in infancy with large facial hemangiomas. Patients should be initially screened for cerebrovascular anomalies via noninvasive MRI. Simple hemangiomas are the most frequently reported cerebrovascular anomalies discovered on screening. These lesions have a benign natural history in most cases and may respond to medical therapy if treatment is required. Less often, patients with PHACE(S) may present with more serious cerebrovascular disease, such as aneurysms, major arterial anomalies, or even moyamoya–like progressive vasculopathy. Treatment recommendations for these more severe arteriopathies must be made on an individual basis. Wyburn-Mason syndrome is a rare pattern of abnormal vascular development that affects the face, orbit, and midbrain. Vascular anomalies found in two of the three possible locations are usually considered sufficient to make the diagnosis. Cerebral AVMs associated with this syndrome should be evaluated and treated according to guidelines for nonsyndromic AVMs. Klippel-Trénaunay syndrome is congenital, with an unclear inheritance pattern characterized by hemihypertrophy of one or more extremities, cutaneous nevi, venous varices, and occasionally leptomeningeal vascular dysplasia or arteriovenous malformations. As with Wyburn-Mason, these AVMs should be evaluated and treated according to guidelines for nonsyndromic AVMs.

91.9╇ Familial Cavernous Malformations Although most cavernomas are isolated, sporadic lesions, a significant minority are familial. Most patients with the familial form have multiple lesions; approximately 75% of those with multiple cavernous malformations have the familial form.13 Familial cavernous malformations are inherited in an autosomal dominant pattern with incomplete penetrance. Gradient-echo (GRE) MRI is recommended when screening for very small cavernomas in this population. Cavernomas may arise de novo and older patients with the familial syndrome have a larger number of lesions.14 Cavernomas are covered in more detail in Chapter 94. MELAS is characterized by mitochondrial myopathy (M), encephalopathy (E), lactic (L) acidosis (A), and strokelike episodes (S). MELAS is maternally inherited and usually presents before age 15 years.

Although the strokelike episodes may be clinically indistinguishable from ischemic stroke events, they often do not conform to discrete vascular territories and may, in fact, represent transient capillary permeability leading to focal edema rather than an ischemic event. Treatment with L-arginine has had promising early results for children with this condition.15 Radiation-induced vasculopathy may occur in as many as 10% of children who have been treated with therapeutic radiation for a brain tumor.16 Vascular endothelial cells are actively proliferating and are particularly vulnerable to radiation toxicity. Small arteries are the most likely to be affected. Most affected patients present with ischemic symptoms many years after radiation treatment. Younger age at treatment, higher radiation dose, targeting near the circle of Willis, and a history of neurofibromatosis type 1 are all associated with an increased risk of radiation-induced vasculopathy. Moyamoya is a progressive arteriopathy that usually affects the proximal intracranial anterior circulation cerebral arteries during childhood. The name is derived from the Japanese term for a “puff of smoke,” corresponding to the angiographic appearance of the small collateral arteries that develop in this condition. Although it may result in ischemic or hemorrhagic stroke, ischemic presentations are more common during childhood. Patients with the characteristic cerebrovascular findings in the setting of a systemic condition are said to have moyamoya syndrome, whereas those with only cerebrovascular findings in isolation are diagnosed with moyamoya disease.9

References ╇1. Grunwald IQ, Kühn AL. Current pediatric stroke treatment.

World Neurosurg 2011;76(6 Suppl):S80–S84

╇2. Mallick AA, O’Callaghan FJ. The epidemiology of childhood

stroke. Eur J Paediatr Neurol 2010;14(3):197–205 ES, Golomb MR, Adams R, et al; American Heart Association Stroke Council; Council on Cardiovascular Disease in the Young. Management of stroke in infants and children: a scientific statement from a Special Writing Group of the American Heart Association Stroke Council and the Council on Cardiovascular Disease in the Young. Stroke 2008;39(9):2644–2691 ╇4. deVeber GA, MacGregor D, Curtis R, Mayank S. Neurologic outcome in survivors of childhood arterial ischemic stroke and sinovenous thrombosis. J Child Neurol 2000;15(5):316–324 ╇5. Ellis MJ, Amlie-Lefond C, Orbach DB. Endovascular therapy in children with acute ischemic stroke: review and recommendations. Neurology 2012;79(13 Suppl 1): S158–S164 ╇6. Lo WD. Childhood hemorrhagic stroke: an important but understudied problem. J Child Neurol 2011;26(9): 1174–1185 ╇3. Roach

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CB, Smith JK, Merck LH, et al. Intracranial hemorrhage in asymptomatic neonates: prevalence on MR images and relationship to obstetric and neonatal risk factors. Radiology 2007;242(2):535–541 ╇8. Amlie-Lefond C, Chan AK, Kirton A, et al; Thrombolysis in Pediatric Stroke (TIPS) Investigators. Thrombolysis in acute childhood stroke: design and challenges of the Thrombolysis in Pediatric Stroke clinical trial. Neuroepidemiology 2009;32(4):279–286 ╇9. Smith ER, Scott RM. Spontaneous occlusion of the circle of Willis in children: pediatric moyamoya summary with proposed evidence-based practice guidelines. A review. J Neurosurg Pediatr 2012;9(4):353–360 10. Smith SE, Kirkham FJ, Deveber G, et al. Outcome following decompressive craniectomy for malignant middle cerebral artery infarction in children. Dev Med Child Neurol 2011;53(1):29–33 11. Maher CO, Piepgras DG, Brown RD Jr, Friedman JA, Pollock BE. Cerebrovascular manifestations in 321 cases of hereditary hemorrhagic telangiectasia. Stroke 2001;32(4):877–882

12. Siegel

DH, Tefft KA, Kelly T, et al. Stroke in children with posterior fossa brain malformations, hemangiomas, arterial anomalies, coarctation of the aorta and cardiac defects, and eye abnormalities (PHACE) syndrome: a systematic review of the literature. Stroke 2012;43(6):1672–1674 13. Labauge P, Laberge S, Brunereau L, Levy C, Tournier-Lasserve E. Hereditary cerebral cavernous angiomas: clinical and genetic features in 57 French families. Société Française de Neurochirurgie. Lancet 1998;352(9144):1892–1897 14. Al-Holou WN, O’Lynnger TM, Pandey AS, et al. Natural history and imaging prevalence of cavernous malformations in children and young adults. J Neurosurg Pediatr 2012;9(2):198–205 15. Koga Y, Akita Y, Junko N, et al. Endothelial dysfunction in MELAS improved by L-arginine supplementation. Neurology 2006;66(11):1766–1769 16. Ullrich NJ, Robertson R, Kinnamon DD, et al. Moyamoya following cranial irradiation for primary brain tumors in children. Neurology 2007;68(12):932–938

92

Pediatric Aneurysms Allyson Alexander and Michael S. B. Edwards

92.1╇Background

92.1.1╇Indications

Intracranial aneurysms are much less common in the pediatric population than they are in adults. The largest, long-term retrospective analysis―8,996 consecutive aneurysm patients in Finland―showed that 1.3% of the patients age 18 years or younger suffered from intracranial aneurysms, which is consistent with other studies.1–4 Etiology, size, location, and demographics of aneurysms differ between adult and pediatric patients. The vast majority of intracranial aneurysms in the adult patient are of the saccular or “berry” type in the circle of Willis. This is true in the pediatric population as well. However, aneurysms distal to the circle of Willis are more common―as well as traumatic, dissecting, fusiform, and infectious (mycotic) aneurysms, all of which occur more commonly in children than in adults.5–7 Comorbid conditions, such as coarctation of the aorta, Ehlers–Danlos syndrome, fibromuscular dysplasia, glucose-6-phosphate dehydrogenase deficiency, Kawasaki disease, Marfan syndrome, moyamoya disease, polycystic kidney disease, pseudoxanthoma elasticum, sickle cell anemia, Takayasu arteritis, thalassemia, tuberous sclerosis, and others, have been reported to occur in association with pediatric aneurysms as well.5,6,8–10 Pediatric aneurysms are often found to be more prevalent in boys than girls(1,5,6,10,15,16). The location of pediatric aneurysms is most likely to be at the internal carotid artery or its bifurcation for infectious, traumatic, and saccular aneurysms, and in the posterior circulation for dissecting aneurysms.1,5–7,9 Finally, the incidence of giant aneurysms (> 2.5 cm) is very high in pediatric patients, with various series reporting that 20 to 45% of all pediatric aneurysms are giant.1,4,5,9,11

Pediatric patients with intracranial aneurysms most often present with clinical symptoms of subarachnoid hemorrhage, as is typical of adult patients.5,9 However, these patients may also present with less standard symptoms, such as hydrocephalus, seizures, chronic headache, stroke, tremor, or symptoms of mass effect, including cranial nerve palsies or syndromes of brainstem compression.1,4,5,11,12 Patients with dissecting aneurysms often present with symptoms of stroke or ischemia.7 Additionally, a significant number of pediatric aneurysms, up to 35% in one series, may be incidentally discovered.1 Children presenting with any of these clinical features due to an intracranial aneurysm should undergo definitive treatment of their disease. There are no published reports of the natural history of ruptured aneurysms specifically in the pediatric population. Nevertheless, a large case series of more than 6,000 patients presenting with subarachnoid hemorrhage did contain a small subset of pediatric patients whose ruptured aneurysms were treated with bed rest.3 In that series, 6 of 15 patients had died by 1 year following their subarachnoid hemorrhage, which reinforces the idea that ruptured aneurysms in this population should be treated to prevent mortality.

92.1.2╇Goals The goals of treatment for intracranial aneurysms in the pediatric population are to: 1. Prevent rerupture of a ruptured aneurysm, which could lead to death or permanent disability

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760 Section IXâ•… Vascular Disorders 2. Eliminate the risk of stroke in the case of dissecting or fusiform aneurysm 3. Eradicate symptoms of mass effect, such as cranial nerve palsies, brainstem compression, or hydrocephalus, from a giant aneurysm or clot 4. Avert rupture of unruptured aneurysms

92.1.3╇ Alternate Procedures Aneurysm trapping with or without extracranial-tointracranial bypass is a treatment option for large, complex aneurysms in the pediatric population. As mentioned earlier, a significant fraction of pediatric aneurysms are fusiform or giant in size. Therefore, due to the challenging size, location, and nature of many of these lesions in the pediatric population, various potential techniques must be considered. Indeed, the key to successfully treating these lesions is careful preoperative planning and consideration of nonstandard techniques. Additional options for open surgery include conventional aneurysm clipping, clipping with circulatory arrest, muslin wrapping, clip wrapping, Hunterian ligation, proximal occlusion, bypass without trapping, and excision.9,10,13 Endovascular treatment options must also be carefully considered, such as standard coil embolization, stent-assisted coiling, parent vessel sacrifice, balloon occlusion in combination with parent vessel sacrifice, and flow diversion with the Pipeline or Silk devices.5,10 In truly complex cases, the combination of open surgery and endovascular treatment may need to be considered.14 In some patients with small, distal infectious aneurysms, antibiotic therapy may suffice. In some cases, trapping and bypass may be required to prevent stroke. Finally, conservative treatment with close follow-up may be appropriate in children who have small, incidentally found aneurysms that are unruptured.

92.1.4╇Advantages The advantages of aneurysmal trapping, with or without bypass, are: 1. Complete exclusion of the aneurysm from the circulation greatly decreases the likelihood of recurrence or regrowth, which can be especially important in fusiform, mycotic, or blister aneurysms. 2. In large, multilobed, or giant aneurysms, this may allow for the treatment of the aneurysm

with less need for dissection, which can reduce the risk of intraoperative rupture. 3. Trapping with bypass may be the only way to safely exclude a large aneurysm near the circle of Willis from the circulation without compromising distal perfusion.

92.1.5╇Contraindications Overall, there are few contraindications to treating an intracranial aneurysm that presents with rupture or mass effect. Young age is not a contraindication because even very young infants have been successfully treated for ruptured aneurysms, although at a higher risk. The rare aneurysm that is small and incidentally found may be followed with serial imaging. Contraindications to the use of a bypass graft include young age, due to the small size of the donor and recipient vessels in very young children, which may cause this technique to be technically unfeasible. The smallest appropriate recipient vessel is in the range of 0.8 to 1.0 mm. Absolute contraindications are limited to general contraindications for surgery, such as hemodynamic instability, significant congenital heart disease, or uncorrectable coagulopathy. It may be reasonable to offer only supportive care to patients who have an extremely poor clinical condition at presentation, depending on the wishes of an informed family.

92.2╇ Operative Detail and Preparation 92.2.1╇ Preoperative Planning and Special Equipment Detailed knowledge of the three-dimensional (3D) anatomy of the aneurysm and surrounding vessels is crucial in planning the best treatment strategy. A preoperative computed tomography angiogram (CTA) or magnetic resonance angiogram (MRA) with 3D reconstructions will help in planning the approach. However, with most complex aneurysms, the precision and detailed depiction of vascular anatomy of a digital subtraction catheter angiogram (DSA) are preferable. 3D reconstructions from the DSA should be performed to allow visualization of the aneurysm morphology and associated vessels arising from the wall of the aneurysm. A variety of different sizes and shapes of aneurysm clips must be available, including straight,

92 â•… Pediatric Aneurysms curved, and fenestrated clips. The clip set should also include temporary clips for brief occlusion of major vessels should proximal and distal control be necessary, due to actual or anticipated aneurysm rupture, before permanent clipping or trapping of the aneurysm can be completed. For large and/or complex aneurysms, it is helpful to use intraoperative angiography in order to verify that the aneurysm has been successfully isolated from circulation, that no major vessels or perforators have been compromised, and that the graft is patent if a bypass is performed. This has classically been performed with standard intra-arterial DSA, which has the advantage of excellent detail and the ability to determine aneurysm obliteration without compromise of nearby critical branches. This may not be feasible with infants because an infant radiolucent headholder is not available at this time. Nevertheless, a newer technique utilizing the fluorescent dye indocyanine green (ICG) for intraoperative angiography has the advantages that a femoral catheter is not required, there is only minimal additional operative time, and there is no additional radiation. However,

its accuracy in defining the patency of associated vessel postclipping may not be as good as intra-arterial DSA. Nonetheless, DSA may be performed in the immediate postoperative period at the surgeon’s discretion and remains the standard of care for complete occlusion of the aneurysm and longitudinal follow-up.

92.2.2╇ Expert Suggestions/Comments Obliteration using neurointerventional technique employing coils, balloons, glues, or proximal occlusion should be evaluated as the primary treatment whenever possible based on patient age and the anatomy and morphology of the aneurysm (Fig.€92.1). When a neurointerventional strategy is not technically feasible, direct clipping or trapping (with or without bypass graft) should be the operation of choice. In either circumstance, early intervention to secure the ruptured aneurysm is critical to prevent rerupture and to allow for aggressive treatment of vasospasm with volume enhancement and induced hypertension.

a

Fig. 92.1â•… A complex, unruptured middle cerebral artery (MCA) aneurysm is succesfully treated with direct surgical clipping. (a) The aneurysm is seen upon initial surgical approach at low power. (Continued on page 762)

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c

Fig. 92.1 (Continued)â•… (b) The aneurysm is seen upon initial surgical approach at high power. (c) The aneurysm has been isolated with two temporary clips to allow for safe dissection.

92 â•… Pediatric Aneurysms d

Fig. 92.1 (Continued)â•… (d) The final view of the clipped anueyrsm with the temporary clips removed.

The development of neurohybrid operating suites allows for complex craniotomies and intraoperative catheter angiography using high-resolution DSA without moving the patient to a formal angiography suite. These techniques can now be enhanced by the ability to have image guidance and even intraoperative magnetic resonance imaging (iMRI) scans all in the same operating room (OR) environment. The capacity to have multiple diagnostic modalities available in the same OR suite permits the surgeon and neuroradiologist to obtain all the critical information before leaving the OR. It can also allow for the correction of incomplete clipping or inadvertent perforating vessel stenosis or occlusion, or for the determination of inadequate perfusion to the surrounding brain early enough for correction before there is permanent infarction.

92.2.3╇ Key Steps of the Procedure/ Operative Nuances Induction of anesthesia and prevention of an acute hypertensive event as well as control of blood pressure at the predefined level are critical during the craniotomy, dissection, and exposure of the aneurysm to prevent inadvertent rupture. This is of the utmost importance until the aneurysm and feeding vessel are visualized well enough to emergently place temporary clips.

It is prudent to plan preoperatively for an arterial bypass graft should it be necessary. The superficial temporal artery and the radial artery both are excellent options for grafts except in the youngest of patients. The advantage of the former is that there is only one anastomosis required, and the advantage of the latter is that much more graft length can be harvested. Intraoperative cooling of the core temperature to 35°C can allow for cerebral protection, especially if temporary clips are applied. If the aneurysm has a proximal location, such as at the carotid bifurcation, it is prudent to dissect out and isolate the internal carotid artery in the neck, should immediate intraoperative proximal control be required to allow clipping or in the case of aneurysmal neck rupture. This can be life-saving, especially when the aneurysmal anatomy prevents proximal intracranial control. The neck, perforating branches, and distal outflow must be identified and correlated with the preoperative angiogram. The use of a 3D angiographic reconstruction of the aneurysmal complex should be compared to the intraoperative anatomy. If the anatomy is still unclear, an intraoperative biplane angiogram with a marker placed near the neck of the aneurysm can help ensure that the anatomy is well defined before clipping the aneurysm. In all cases, isolation of the proximal as well as the distal vessel permits temporary clips to be placed,

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764 Section IXâ•… Vascular Disorders allowing better visualization of the aneurysm neck and safer and more accurate placement of the clip on the neck of the aneurysm (Fig. 92.2). This will result in less risk of aneurysmal rupture or neck avulsion during dissection, and more precise clip placement to allow obliteration of the aneurysm from the normal circulation. Transient induced hypotension can aid in the dissection, and may be life-saving if intraoperative rupture occurs. A large selection of aneurysm clips is essential and trialing the clip before attempting placement will assist in defining the right size, shape, and clip angle. After the clip is placed, the use of intravenous ICG can determine if adequate perfusion to surrounding and distal brain has been maintained. If the back side of the aneurysm is difficult to visualize and the surgeon is concerned that a perforating or a proximate vessel is involved within the clip, the use of a small, flexible or rigid endoscope can allow visualization of difficult vessels behind the aneurysm or parent vessel. A biplane intraoperative angiogram is usually performed to ensure that the aneurysm is secured and the parent vessel is patent and not compromised.

a

92.2.4╇ Hazards/Risks/Avoidance of Pitfalls The greatest hazards are not evaluating all the options for treatment and not carefully planning for backup contingencies, if the primary selected modality is not successful. Pediatric neuroanesthesia should be familiar with aneurysm surgical techniques and with the need to carefully control blood pressure on induction to prevent aneurysmal rupture, a situation that may result in morbidity or mortality. Having the necessary intravenous access for drug administration and volume and blood replacement―as well as arterial blood pressure monitoring and central venous access―is important, especially in the instance of intraoperative aneurysmal rupture or planned hypotension, and may be life-saving. The scrub nurse must be familiar with the aneurysm clip systems to be used and should have loaded the most likely to be used clips even before the skin incision is made. There will be no time to search for aneurysm clips and appliers if inadvertent rupture does occur before the neck is isolated and prepared. Surgeons with minimal aneurysm experience should ask for the help of their vascular neurosurgi-

b

Fig. 92.2â•… Endovascular coiling can be a useful treatment for pediatric aneurysms. Demonstrated here is a large basilar tip aneurysm. (a) Three-dimensional (3D) reconstruction from angiography demonstrates the morphology of the aneurysm. (b) Postprocedure anteroposteior (AP) angiogram shows good occlusion of the lesion.

92 â•… Pediatric Aneurysms c

Fig. 92.2 (Continued)â•… (c) Follow-up angiogram details excellent exclusion of the aneurysm from circulation.

cal counterparts and neurointerventionalists to consult and assist. This is particularly beneficial since the frequency of aneurysms in children and adolescents is much lower than in the adult population.

92.2.5╇ Salvage and Rescue The use of the newer endovascular stenting devices has been successful as a salvage strategy, when rupture has occurred during attempted interventional occlusion of an aneurysm using coils or balloon technology. The development of hybrid ORs may allow immediate interventional salvage (temporary proximal occlusion or stent placement) for complex aneurysms that rupture or develop a tear of the parent vessel neck during clip placement.

92.3╇ Outcomes and Postoperative Course 92.3.1╇ Postoperative Considerations Once a ruptured aneurysm has been treated successfully, the patient may still remain at risk for vasospasm. In adults, the standard of care for prevention

and monitoring of vasospasm is nimodipine and transcranial Doppler (TCD) ultrasound, respectively. Pediatric patients do develop vasospasm, although at a much lower rate than adults. One pediatric series reported that 11/57 (19%) patients developed vasospasm after surgical treatment of aneurysm, of which 3 patients developed vasospasm-induced infarction; another series reported that 16% of patients developed clinical vasospasm.9,15 Hence consideration should be given to monitoring for vasospasm using TCDs. Although there is little discussion on the use of this modality in the pediatric population, one case report noted that TCD was successfully used to detect vasospasm in the case of a 13-month-old boy with a ruptured middle cerebral aneurysm.8 Another series reported the adoption of the routine use of TCD to detect vasospasm in pediatric patients since 2003.10 Although many case series and clinical trials of nimodipine use after subarachnoid hemorrhage (SAH) have included a very small percentage of pediatric patients, only one case report specifically addresses the use of nimodipine in an infant. The patient had no adverse reaction to the drug but he did develop vasospasm.8 Another adverse outcome after SAH is the development of hydrocephalus requiring cerebrospinal fluid (CSF) diversion. Patients requiring external ventricular drains (EVDs) for hydrocephalus around the

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766 Section IXâ•… Vascular Disorders time of their SAH should be monitored closely. When possible, the EVD should be slowly weaned and then discontinued as CSF clears itself of blood products, and also depending on the patient’s clinical status. It is prudent to make these decisions clinically in order to minimize the number of computed tomography (CT) scans that any one patient receives. It has been shown, in children, that a dose of radiation equivalent to two to three head CTs can triple the risk of future brain tumors.16

92.3.2╇Complications The complications of surgical treatment of pediatric aneurysms can be divided into intraoperative and postoperative time frames. Intraoperative problems include aneurysm rupture, cerebral edema, and injury or occlusion of arterial vessels, including perforators. These can lead to postoperative difficulties, including cranial nerve palsy, new neurologic deficits, ischemic stroke, and death. Additional postoperative complications include cerebellar hematoma, death,

delayed ischemic strokes (such as from vasospasm or embolization from the lumen of giant aneurysms), epidural hematoma, graft occlusion, hydrocephalus requiring CSF diversion, myocardial infarction, pulmonary embolism, ventilator-associated pneumonia, ventriculitis, and wound infection.1,9 Problems resulting from angiography performed perioperatively may also occur―aneurysm rupture, arterial dissection, groin pseudoaneurysm, or stroke.1,10

92.3.3╇Outcomes Overall, the clinical outcomes are excellent for pediatric patients after treatment of their aneurysms. In Fig.€92.3, the authors have graphically represented the outcomes of patients with at least 1-year follow-up in published series. Please note that these data are presented for illustrative purposes only; a comprehensive review of the literature and all reported outcomes are beyond the scope of this chapter. In one series where details of surgical technique were published, the six patients who were treated with aneurysm trapping

Fig. 92.3â•… Patient outcomes following surgical or endovascular treatment for ruptured aneurysms in the pediatric population are presented graphically. Outcomes are divided into Excellent, Good, Poor, Death, and Lost to Follow-up―color-coded appropriately. Excellent outcome corresponds to Glasgow Outcome Scale (GOS) of 5, or independence; good outcome corresponds to GOS of 4; poor outcome corresponds to GOS of 2 to 3, or dependent. Groups of columns correspond to outcomes divided by published series, initial presenting grade, type of treatment, and overall outcomes. The authors defined good grade as Hunt and Hess grades 1 or 2, or GOS 13 to 15; and poor grade as Hunt and Hess grades 3 to 5 or GOS ≤ 9.

92 â•… Pediatric Aneurysms all had good outcomes.6 Of note, in one series, the two patients who died suffered from rerupture before it was possible to provide surgical treatment.6 Another study17 noted a high rerupture rate and suggested that this rate might be especially high in pediatric patients. Finally, in patients with giant aneurysms, there may be a much higher risk of mortality, because one series of 47 giant aneurysms treated by Peerless and Drake reported an 11% mortality rate.11 Another important consideration is the angiographic outcome. In one series with long-term angiographic follow-up, the annual risk of aneurysm recurrence following surgical clipping was estimated as 2.6%.1

References ╇1. Kakarla

UK, Beres EJ, Ponce FA, et al. Microsurgical treatment of pediatric intracranial aneurysms: longterm angiographic and clinical outcomes. Neurosurgery 2010;67(2):237–249, discussion 250 ╇2. Koroknay-Pál P, Lehto H, Niemelä M, Kivisaari R, Hernesniemi J. Long-term outcome of 114 children with cerebral aneurysms. J Neurosurg Pediatr 2012;9(6):636–645 ╇3. Locksley HB. Natural history of subarachnoid hemorrhage, intracranial aneurysms and arteriovenous malformations. J Neurosurg 1966;25(3):321–368 ╇4. Storrs BB, Humphreys RP, Hendrick EB, Hoffman HJ. Intracranial aneurysms in the pediatric age-group. Childs Brain 1982;9(5):358–361 ╇5. Agid R, Kimchi TJ, Lee SK, Ter Brugge KG. Diagnostic characteristics and management of intracranial aneurysms in children. Neuroimaging Clin N Am 2007;17(2):153–163 ╇6. Fulkerson DH, Voorhies JM, Payner TD, et al. Middle cerebral artery aneurysms in children: case series and review. J Neurosurg Pediatr 2011;8(1):79–89

╇7. Rao

VY, Shah KB, Bollo RJ, et al. Management of ruptured dissecting intracranial aneurysms in infants: report of four cases and review of the literature. Childs Nerv Syst 2013;29(4):685–691 ╇8. Ahn JH, Phi JH, Kang HS, et al. A ruptured middle cerebral artery aneurysm in a 13-month-old boy with Kawasaki disease. J Neurosurg Pediatr 2010;6(2):150–153 ╇9. Aryan HE, Giannotta SL, Fukushima T, Park MS, Ozgur BM, Levy ML. Aneurysms in children: review of 15 years experience. J Clin Neurosci 2006;13(2):188–192 10. Stiefel MF, Heuer GG, Basil AK, et al. Endovascular and surgical treatment of ruptured cerebral aneurysms in pediatric patients. Neurosurgery 2008;63(5):859–865, discussion 865–866 11. Edwards MS, Hoffman HJ, eds. Cerebral Vascular Disease in Children and Adolescents. Baltimore, MD: Williams & Wilkins; 1989 12. Lasjaunias PL, Campi A, Rodesch G, Alvarez H, Kanaan I, Taylor W. Aneurysmal disease in children. Review of 20 cases with intracranial arterial localisations. Interv Neuroradiol 1997;3(3):215–229 13. Bowers C, Riva-Cambrin J, Couldwell WT. Efficacy of clipwrapping in treatment of complex pediatric aneurysms. Childs Nerv Syst 2012;28(12):2121–2127 14. Shin SH, Choi IS, Thomas K, David CA. Combined surgical and endovascular management of a giant fusiform PCA aneurysm in a pediatric patient. A case report. Interv Neuroradiol 2013;19(2):222–227 15. Mehrotra A, Nair AP, Das KK, Srivastava A, Sahu RN, Kumar R. Clinical and radiological profiles and outcomes in pediatric patients with intracranial aneurysms. J Neurosurg Pediatr 2012;10(4):340–346 16. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 2012;380(9840):499–505 17. Proust F, Toussaint P, Garniéri J, et al. Pediatric cerebral aneurysms. J Neurosurg 2001;94(5):733–739

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93

Pediatric Arteriovenous Malformations Graciela Zuccaro and Javier Gonzalez Ramos

93.1╇Background Cerebral arteriovenous malformations (AVMs) are congenital lesions thought to arise during embryogenesis because of failure in the differentiation of vascular channels into mature arteries, capillaries, and veins, resulting in direct arteriovenous shunts without intervening capillary beds.1 There is a structural defect in the formation of the capillary network that is present between arteries and veins, within the substance of the brain, leading to an increase of intraluminal venous pressure producing ectasia and weakness, and possible rupture of the hybrid vessels with both venous and arterial characteristics. It is hypothesized that most malformations occur during the third week of embryogenesis, before the embryo reaches 40 mm in length. However, de novo formation and recurrence of AVMs after treatment have been reported and raise a question about the true epidemiology and natural history of these complicated vascular anomalies. Sonstein et al examined the role of vascular endothelial growth factor (VEGF) as a mediator of angiogenesis in AVM development and found a positive correlation. They also noted an increase in VEGF in children in whom the lesion recurred after obliteration of the AVM by microsurgical resection.2 Most AVMs occur sporadically, although familial cases have been reported and several syndromes, such as Rendu-Osler-Weber syndrome and SturgeWeber syndrome, are associated with vascular malformations. In children, the most frequent clinical presentation of AVMs is intracranial hemorrhage, occurring in 80 to 85% of the cases, followed by seizures in 15%. In the pediatric population, hemorrhagic events from an AVM have been associated with a 25% mortality rate, whereas the mortality rate in adults is 6 to 10%. The annual rate of rebleeding in children is 2 to 4%, compared to 1 to 3% in adults. If the risk of hemorrhage is projected over a 50-year horizon to

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account for a child’s longer life expectancy, the probability of rehemorrhage is about 65%. This may be related to the increased incidence of lesions located in the deep basal ganglia and brainstem in children. Because of the significant risk of rebleeding, high rate of morbidity, and the longer life expectancy of children, aggressive treatment of these lesions is mandatory,3 even in asymptomatic AVMs. The lower incidence of comorbidities and the plasticity of the developing central nervous system (CNS) in children facilitate this aggressive treatment. It has been widely accepted that the goal of treatment should be complete obliteration of the AVM with preservation of neurologic function. The authors agree that with careful planning and adopting a multimodality treatment, complete obliteration can definitely be achieved. Current AVM treatment options include microsurgery, endovascular embolization, and stereotactic radiosurgery―alone or in combination. The use of a balanced multimodality approach reduces procedure-related morbidities and mortalities and at the same time increases treatment efficacy. A common method of grading cerebral AVMs is the Spetzler-Martin system. A Spetzler-Martin grade I AVM is easy to remove without complications. On the other hand, a Spetzler-Martin grade V AVM has a high risk of morbidity and mortality. Between these two extremes there is a wide variety of presentations that should be analyzed individually. Particularly in children, the risk of bleeding and morbidity due to surgery altering the quality of life should be carefully weighed against the long life expectancy.

93.1.1╇ The Role of Surgical Treatment Over the last 25 years, the management of pediatric AVMs has become multidisciplinary, requiring close interaction of neurosurgeons, interventional neuroradiologists, and radiation oncologists. Treatment of the AVM should be tailored to each child.

93 â•… Pediatric Arteriovenous Malformations Microsurgical management is still the treatment of choice for parenchymal AVMs. In the authors’ experience, surgical resection is the first-line and only treatment in Spetzler-Martin grades I (Fig. 93.1 and Fig.€93.2) and II AVMs (Fig. 93.3 and Fig. 93.4). This type of lesion is relatively easy to remove from a technical point of view and is associated with a low risk of morbidity or mortality. Complete microsurgical resection provides the advantage of immediate cure, eliminates the risks of rebleeding, and avoids long-term adverse effects of radiosurgery on the developing brain. In Spetzler-Martin grade III AVMs larger than 6 cm in noneloquent areas and with only a superficial pattern of venous drainage, the authors perform

endovascular therapy in order to reduce the size of the lesion and the intraoperative bleeding before microsurgical treatment (Fig. 93.5). When the grade III AVM is larger than 3 to 6 cm, has superficial drainage, but is located in the eloquent area, management is more complicated. If the lesion has never bled, treatment is conservative, and the patient is closely controlled, taking the long life expectancy in children into account, because a mutilating lesion may affect quality of life. However, if the lesion has bled, stepwise embolization is considered to reduce the AVM flow. The intervention is completed with stereotactic radiosurgery. Outcome is uncertain and often disappointing.

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Fig. 93.1â•… (a) Left carotid angiogram, showing a frontal arteriovenous malformation (AVM) with afferent supply from the pericallosal artery and (b) early drainage to the sagittal sinus and (c) the deep venous system.

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Fig. 93.2â•… (a–c) Left carotid angiogram of the patient in Fig. 93.1 after a total microsurgical removal of the arteriovenous malformation (AVM).

The management of high-grade (SpetzlerMartin grades IV and V) pediatric AVMs is controversial. Because of their great size, deep location, or involvement of the eloquent area, microsurgical resection may be difficult or even impossible without causing severe deficits. Similarly, the large size does not allow a good radiosurgical obliteration rate. High-grade AVMs carry a greater risk of treatment-related complications and some authors believe that partial treatment may worsen outcome in adults. Nevertheless, the poor natural history of this lesion and the ability of the pediatric nervous system to recover support the philosophy of aggressive

management.4 If treatment of a grade IV or V malformation is chosen, risks of the procedure and the possibility of postoperative deficits should be discussed with the patient and family. In the absence of severe or progressive neurologic deficits, grades IV and V AVMs are managed conservatively with observation, unless repeated hemorrhage or progressive neurologic deficit demands intervention. In these cases, the authors perform embolization in a stepwise fashion in order to reduce the high flow and improve the perfusion of the normal surrounding parenchyma. The endovascular techniques also serve as adjuncts to open neurosurgical treatment, radiosurgery treatment, or both.

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Fig. 93.3â•… (a–c) Lateral and (d–f) anteroposterior projections of vertebral angiograms, showing an arteriovenous malformation (AVM). The major feeders of the AVM are the posterior cerebral artery and superior cerebellar arteries.

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Fig. 93.4â•… (a,b) Anteroposterior and (c,d) lateral projections of vertebral angiogram of the patient in Fig. 93.3 after complete microsurgical resection of the arteriovenous malformation (AVM).

In the surgical treatment of these malformations, the risk of complications should be taken into account. Hemorrhage is certainly the most feared complication before, during, and after AVM resection. According to Di Rocco et al,5 surgery as a single procedure allows total removal of the AVM in 70 to 90% of pediatric patients. Of these cases, 52 to 75% do not develop neurologic deficits in the postoperative follow-up. Severe complications have been reported in about 10% of the patients. The reported mortality rate ranges between 0 and 8%. Most authors advise against surgery in adult patients who are admitted in a deep coma; however, in children the good results in similar conditions encourage the treatment of these lesions. As stated by Humphreys et al, “the child’s biological plasticity is

such that the degree of postoperative recovery can be as complete and gratifying as the preoperative deterioration was rapid and dramatic.”

93.1.2╇ The Role of Endovascular Treatment Although in the experience of the authors embolization by itself is unlikely to be a permanent solution to the AVM, it is thought to be very useful as adjuvant therapy to surgical management and radiation treatment. As previously stated, embolization plays an important role in decreasing the volume of the lesion to allow for definitive surgical removal with-

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Fig. 93.5â•… Left carotid angiogram showing a temporomesial arteriovenous malformation (AVM) with afferents from the M1 branch of the middle cerebral artery associated with superficial and deep venous outflow (Spetzler-Martin grade III). (a–c) Preembolization. (d–f) Postembolization.

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774 Section IXâ•… Vascular Disorders out excessive blood loss. Preoperative embolization reduces the intraoperative blood loss, which is of great value in children who have low circulatory blood volume compared to adults. Frizzell and Fisher6 reviewed a series of 1,246 patients who underwent only embolization of their AVMs and found that complete obliteration was achieved in merely 5% of the patients. Wisoff and Berenstein7 demonstrated that although there was clinical improvement, hemorrhage risk did not decrease after embolization alone. At the authors’ center, preoperative embolization is routinely performed in grade III and sometimes in grade II AVMs. In high-grade AVMs, they use the procedure as part of a multimodality therapy or to reduce the size and the flow of the lesion. Various embolic materials are used, including coils, polyvinyl alcohol particles, N-butyl-cyanoacrylate glue, and Onyx. Super-selective arterial catheterization is performed, and if there is an associated aneurysm, it is embolized before the AVM. In cases of large malformations, this therapy is done in multiple stages. Intraoperative angiography is discussed below. The morbidity rate associated with preoperative embolization is 12 to 25% in the literature. All the complications are related to hemodynamics, either hemorrhagic or ischemic, due to normal perfusion pressure breakthrough disturbances of venous drainage or thrombosis of the feeding arteries.

93.1.4╇ AVM Recurrence

93.1.3╇ The Role of Radiosurgery

93.2.1╇ Step One: Understanding the Malformation

Radiosurgery is a treatment option for the management of AVMs in critical cortical locations and for those located in the basal ganglia, thalamus, or brainstem. However, the use of radiation on the developing brain and the late complications, such as neuropsychological impairment, hormonal deficiencies, and the risk of radiation-induced tumors, force the authors to leave this alternative for older children. The annual risk of hemorrhage after radiosurgery is comparable to the risk of hemorrhage in an untreated AVM, and the risk ranges from 1.5 to 4.7% in several recent studies. Therefore, it is advisable that pediatric patients whose AVMs were obliterated using this technique undergo repeated angiographies after they reach adulthood to rule out the possibility of recurrence of the lesion.

Given the longer life expectancy of children, the patient should be followed closely to rule out recurrence of the AVM. In some cases, the authors perform intraoperative angiography to be sure that complete obliteration of the lesion is achieved. Nevertheless, if intraoperative angiography cannot be done, their policy is to perform the procedure before the patient is discharged in order to discover any residual lesion, in which case the patient will undergo reoperation. In the first year and at 5 years after the procedure, a follow-up angiogram is performed. The authors suggest a yearly magnetic resonance angiogram (MRA) because it is an easy and noninvasive procedure. Recurrence of AVMs after angiographic obliteration is low, with reports ranging from 1.5 to 5.5%. There are numerous theories about the possible reasons for recurrence. It has been theorized that growth occurs secondary to hemodynamic stress on the dysplastic vessels of an AVM. It is unclear if the recurrent lesion appears de novo or arises from angiographically occult residual after treatment.

93.2╇ Operative Detail and Preparation

Angiography of the four vessels is the gold standard to study the malformation. Not only the structure (the nidus size, the feeding arteries, and venous drainage), but also the hemodynamic behavior, such as blood flow rate, steal of regional parenchyma, normal arteries in passage, and associated aneurysm should be assessed. The authors always complete the study with magnetic resonance imaging (MRI) to define the exact location and anatomical structure of the lesion, its relation to the surrounding brain, and the bony anatomy, which will help them in planning the surgical approach. At the same time, they use the neuronavigation protocol. If the AVM is close to eloquent brain, the authors order functional magnetic resonance imaging (fMRI).

93 â•… Pediatric Arteriovenous Malformations

93.2.2╇ Step Two: Classification of the Malformation The authors use the Spetzler-Martin grading system to classify the malformation because they believe it is the most reliable method to describe AVM complexity (by size, eloquence of the involved cerebral area, and presence or absence of deep venous drainage).

93.2.3╇ Step Three: Treatment Choice Once the AVM is diagnosed and classified, the surgeon needs to determine if preoperative embolization is indicated.

93.2.4╇ Step Four: Surgical Planning Surgical planning must consider: • Patient position (Fig. 93.6) • Skin and bone flap design • Planning of the corticotomy with neuronavigation in order to approach the feeding vessel before resecting the nidus • If the patient presented with epilepsy, cortical mapping is done in order to allow resection of the epileptic foci as well. • Evaluating the possible intraoperative angiography • Coordination with neuroanesthesia

93.2.5╇ Step Five: Parent Counseling After planning of the surgery, the surgeon must clearly discuss with the parents possible complications and risks with or without surgery. Advantages and disadvantages of the different treatment options should be explained. Parents should sign the informed consent.

93.2.6╇ Step Six: Surgical Treatment The goal of treatment is total removal of the AVM with preservation of neurologic function. Depending on the age and weight of the patient, the authors use a horseshoe headrest for children younger than 2 years and pediatric three-pin head fixation for older children. Frameless navigation cannot be performed in children too young for skull fixation. The head position should be at 30 degrees in order to facilitate venous drainage. The head position and

Fig. 93.6â•… Patient position for surgery on a left frontal arteriovenous malformation (AVM) using neuronavigation and intraoperative angiography.

the skin and bone flap should be according to the location of the AVM. The craniotomy should be as large as possible in order to allow good visualization of the entire AVM, the feeding arteries, and the draining veins. The dura mater may be opened using a standard technique and taking the cortical veins into account. Brain relaxation is achieved by the appropriate positioning of the patient’s head, suitable anesthesia, hypotension, and aspiration of the cerebrospinal fluid (CSF). Once the nidus is exposed, microsurgical dissection of the AVM is performed under the operative microscope and carried out circumferentially around the lesion―looking for the cleavage plane and finally separating the AVM from the normal parenchyma with fluffy cotton. The cotton protects the surrounding brain from injury and allows the surgeon to develop an understanding of the mass of the lesion. Identification of the limbus between the AVM and normal brain is followed by coagulation and section of the opalescent arachnoid along this line. The essential tools for this procedure are the microscope, nonadhering bipolar forceps, different types of scissors, and temporary and

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776 Section IXâ•… Vascular Disorders permanent microclips to occlude large feeding vessels and to test occlusion of the passage vessel. It is very important to identify early the feeding vessels to be coagulated and transected, taking care not to transect the vessels of passage. The feeding vessels are often extremely fragile and subject to hemorrhage with even minor manipulation. The authors recommend intraoperative angiography in the surgical management of AVM because it is very useful in differentiating the feeding arteries from the vessels of passage, and it may obviate the need for reoperation by identifying residual vascular malformation at the time of surgery. Because the surgeon works in a circumferential manner, feeding arteries are sacrificed and the nidus is bipolared, shrinking the lesion and controlling blood loss. The draining veins are not sacrificed until the arterial supply of the AVM has been completely surrounded. Finally, the drainage veins are coagulated and transected to allow removal of the AVM. The entire bed of the malformation should be inspected for any evidence of hemorrhage. At this point, the authors ask the

anesthesiologist to increase the arterial pressure to identify minor hemorrhage. They cover the entire surgical bed with Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA) (Fig. 93.7a,b).

93.3╇ Outcomes and Postoperative Course After surgery the patient is sent to the intensive care unit (ICU). In the postoperative period, the authors prescribe antibiotics, steroids, and antiepileptic drugs. Antibiotic therapy is maintained for 48 hours, steroids are tapered and withdrawn after 1 week, and the antiepileptic drugs are continued for 6 months, depending on the electroencephalogram (EEG). If intraoperative angiography was not performed, it is done before the patient is discharged. If residual AVM is discovered, the authors reoperate immediately. The most important complication before, during, and after AVM resection is hemorrhage. Intraoperative blood loss, even if not from uncontrollable hem-

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Fig. 93.7â•… (a) Surgical view of the patient with a frontal arteriovenous malformation (AVM).

93 â•… Pediatric Arteriovenous Malformations b

Fig. 93.7 (Continued)â•… (b) A complete microsurgical resection of the AVM was performed with excellent results.

orrhage, is crucial to limit in small children whose hemodynamic reserves are limited. The anesthesiologist should be aware of blood loss and any other hemodynamic complication that warrants, at any time of the procedure, temporary or permanent cessation of the surgery. Blood loss should be minimized during the entire procedure. Preoperative embolization will help avoid catastrophic hemorrhage. The surgeon should not hesitate to perform an intraoperative angiogram if there is concern about leaving residual AVM that may necessitate further treatment. A hematoma due to poor hemostasis in the surgical bed or from residual AVM is a surgical emergency. In some cases, decompressive craniotomy should be performed because of swelling or hemorrhage in the

surrounding brain due to the redistribution of the vascular flow. When the hyperperfusion of that tissue exceeds the autoregulation mechanism of the vessels, infarct, edema, and hemorrhage may occur over a period of hours to days. It has been calculated that new-onset seizures occur in more than 10% of children after AVM resection, although less than half of them will require chronic drug treatment. According to Rubin et al,3 the postoperative complications will depend almost entirely on the extent of resection and the ability of the brain to compensate for new blood flow dynamics. In the experience of the authors, in agreement with most authors, the strongest prognostic factors for patient outcome are hemorrhagic presentation of the AVM and the neurologic status of the patient

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778 Section IXâ•… Vascular Disorders on admission. Furthermore, the patient who has suffered an intracranial hematoma―but with preserved consciousness or only slight impairment on admission―should have an excellent or good outcome. Over the last years, management of pediatric AVM by multidisciplinary teams has notably improved. To optimize the neurologic outcome, treatment should be tailored to each child presenting with an AVM.

References ╇1. Niazi TN, Klimo P Jr, Anderson RC, Raffel C. Diagnosis and

management of arteriovenous malformations in children. Neurosurg Clin N Am 2010;21(3):443–456 ╇2. Sonstein WJ, Kader A, Michelsen WJ, Llena JF, Hirano A, Casper D. Expression of vascular endothelial growth factor in pediatric and adult cerebral arteriovenous malformations: an immunocytochemical study. J Neurosurg 1996;85(5):838–845

╇3. Rubin

D, Santillan A, Greenfield JP, Souweidane M, Riina HA. Surgical management of pediatric cerebral arteriovenous malformations. Childs Nerv Syst 2010; 26(10):1337–1344 ╇4. Darsaut TE, Guzman R, Marcellus ML, et al. Management of pediatric intracranial arteriovenous malformations: experience with multimodality therapy. Neurosurgery 2011;69(3):540–556, discussion 556 ╇5. Di Rocco C, Tamburrini G, Rollo M. Cerebral arteriovenous malformations in children. Acta Neurochir (Wien) 2000;142(2):145–156, discussion 156–158 ╇6. Frizzell RT, Fisher WS III. Cure, morbidity, and mortality associated with embolization of brain arteriovenous malformations: a review of 1246 patients in 32 series over a 35-year period. Neurosurgery 1995;37(6):1031– 1039, discussion 1039–1040 ╇7. Wisoff JH, Berenstein A. Interventional neuroradiology. In: Edwards MSB, Hoffman HJ, eds. Cerebral Vascular Disease in Children and Adolescents. Baltimore, MD: Williams and Wilkins; 1989: 139–157

94

Cavernous Malformations and Venous Malformations Christopher David Kelly and Raphael Guzman

94.1╇Background 94.1.1╇Indications • Cerebral cavernous malformations (CMs, also called cavernomas, cavernous angiomas, cavernous hemangiomas) are wellcircumscribed, vascular lesions found in the central nervous system (CNS), composed of sinusoidal vascular channels lined by a single layer of endothelium with no intervening normal brain parenchyma. The surrounding tissue is typically gliotic and stained from previous hemorrhage with green, brown, or yellow hemosiderin discoloration.1 Sizes range from 0.1 to 9 cm and are usually larger in children (6.7 cm, on average) than in adults (2 to 3 cm, on average).2 Prevalence of CMs in children is 0.37 to 0.53%, with two peaks of incidence at ages 0 to 3 years and ages2 11 to 16 years, and a male-to-female ratio of 1:1.3 The tendency for overt hemorrhage is higher in children.2 • The most common clinical presentations are seizures (37%), hemorrhage (36%), headache (23%), and focal neurologic deficits (22%). CMs can occur throughout the CNS. The majority of lesions are supratentorial (66%). Seizures are the most common presentation of supratentorial lesions, whereas focal neurologic deficits are the most frequent presentation of infratentorial lesions.3 Brainstem (18%) and cerebellar (6%) lesions typically present with cranial nerve deficits, headache, vertigo, hemiparesis, numbness, or cerebellar symptoms.4,5 CMs can also occur in the basal ganglia, thalamus, hypothalamus, and chiasma (8%), presenting with focal deficits corresponding to their location. Periventricular or intraventricular CMs can cause elevated intracranial pressure and

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hydrocephalus, and present with headaches. Spinal cord CMs are rare (3 to 5% of lesions), and typically exhibit an acute-onset neurologic deficit, motor or sensory loss with signs of myelopathy, followed by rapid decline. Because CMs are low-flow lesions, mortality from hemorrhage is generally lower than that of high-flow lesions. Nevertheless, fatal hemorrhage from a CM can occur, particularly if in a high-risk location, such as the brainstem or posterior fossa. Incidental CMs are thought to have an annual bleeding rate of up to 3%, whereas CMs after hemorrhage have a higher rebleeding rate of 4 to 23%.1 CMs in deep locations have a higher rate of first bleeding (~ 5%/patient per year) and rebleeding (~ 30%/patient per year) than superficial CMs.5 Risk of first-ever seizure in incidental CMs is about 1 to 2.5% per year. After a first-ever seizure, the 5-year risk of epilepsy is, at least in adults, very high (94%).6 Patients with CMs and seizures need to undergo phase I and, if needed, phase II epilepsy evaluation. CMs can be familial (~ 20% of cases; autosomal dominant inheritance with 69% penetrance; mutations in CCM1, CCM2, and/or CCM3 genes), frequently with multiple CMs, or sporadic, usually a single CM.1,2 In the pediatric age group, cranial irradiation is a risk factor for de novo CM formation.7 About one-tenth of patients show apparent associated developmental venous anomalies (DVAs).3 CMs with DVAs are more likely to present with symptomatic hemorrhage.8 Indication for surgery varies among groups: – Asymptomatic CMs are not operated, regardless of location, but are followed by serial magnetic resonance imaging (MRI) and clinical observation.

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780 Section IXâ•… Vascular Disorders – Patients with single CMs in accessible, noneloquent regions or the spinal cord who present with symptoms, documented radiological enlargement, or hemorrhage are almost invariably managed surgically.1 – The optimal treatment of patients with symptomatic CMs in eloquent regions or deep CMs, such as in the brainstem, depends on the perceived risk:reward ratio of surgery. Because the natural history of untreated brainstem, thalamic, and basal ganglia CMs is poor, showing higher hemorrhage and rebleeding rates than CMs that are superficial,4,5 CMs in patients with progressive neurologic deterioration or repeated hemorrhages may be considered for excision. Specifically for brainstem CMs: only if the CM or hemosiderin reaches the pial/ependymal surface as seen in T1weighted (T1W) MRI (most accurate in determining the proximity to the surface, since T2-weighted [T2W] MRI has artifacts due to ferromagnetic properties of the hemosiderin), surgical management is recommended. If the pial/ependymal representation is < 1 mm in distance, access is possible through a brainstem safe entry zone.3 For deep-seated brainstem CMs without pial/ependymal representation, observation is recommended. – In patients with multiple CMs, surgery is aimed at removing the symptomatic and/ or growing lesion. Parents of children with multiple lesions should be informed about the natural course of the untreated CMs and the possibility of familial CMs. Regular follow-ups and referral to genetic services for counseling and mutational testing are recommended in such cases. – CMs causing seizures that are surgically accessible should be resected.

94.1.2╇Goals • The surgical goal is the complete removal of the CM, in order to: – Prevent further hemorrhage – Decrease a possible mass effect and consequent neurologic deficits – Eliminate seizure activity • DVAs should be preserved because they include blood drainage of normal brain parenchyma and the resection of DVAs can lead to venous infarction or hemorrhage.8

94.1.3╇ Alternate Procedures • Observation is recommended for asymptomatic patients and deep-seated lesions without significant bleeding or neurologic deficit. • Medical management is limited to treatment of seizures. • Radiosurgery is not recommended.

94.1.4╇Advantage • The risk for further growth or hemorrhage is eliminated after complete removal of the CM.

94.1.5╇Contraindication • Asymptomatic, mostly incidental CMs are managed expectantly with serial imaging.

94.2╇ Operative Detail and Preparation 94.2.1╇ Preoperative Planning and Special Equipment • Diagnosis is made by MRI using T2W (Fig.€94.1a,b), T2*, or susceptibility-weighted images (SWI) (Fig. 94.1c,d). The best sequence to evaluate pial representation on brainstem CMs is T1W imaging (Fig. 94.1e,f). The DVAs are easily identified on T1W contrast mediaenhanced imaging and SWI. • MRI is not quite pathognomonic; differential diagnosis includes calcified tumors, such as oligodendrogliomas, other low-grade gliomas, thrombosed arteriovenous malformation (AVM), hemorrhagic metastases, granulomas, choriocarcinomas, and infectious and inflammatory nodules. • Computed tomography (CT) is used in the emergency setting to identify hemorrhage. • Digital subtraction angiography does not show CMs and is only used if AVM is in the differential diagnosis. • CMs are often difficult to find during the operation. Precise neuronavigation is essential for CM surgery. • Neuromonitoring―such as motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), and brainstem auditory evoked potentials (BAEP)―should be used for eloquent or near-eloquent lesions.

94 â•… Cavernous Malformations and Venous Malformations

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Fig. 94.1â•… Representative magnetic resonance imaging (MRI): patient with refractory epilepsy and multiple cavernomas (arrows) seen on (a,b) T2-weighted (T2W) image, on (c,d) susceptibility-weighted image (SWI), and on (e,f) T1-weighted (T1W) image. Example of a growing cavernoma (arrow in f compared to the earlier image, e) in the left frontal region and a stable (e,f, arrowhead) right cavernoma.

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782 Section IXâ•… Vascular Disorders • Especially for brainstem lesions, constructive interference in steady state (CISS) and diffusion tensor imaging (DTI) MRI sequences for fiber tracking should be obtained (Fig.€94.2a,b), and the patient’s individual anatomy should be studied. Identify a brainstem safe entry zone (Fig. 94.2c,d), such as the lateral mesencephalic sulcus, the peritrigeminal safe zone, or the inferior olivary nucleus.9 • Intraoperative CT or MRI for image updating and correction of brain shift can be used if available. Centrally located deep lesions are less susceptible to brain shift.

• Intraoperative ultrasound can be used to help find the lesion. • There is no unanimous recommendation for the timing of surgery. In nonacute situations, it is recommended to wait 2 to 4 weeks after hemorrhage for the clot to become liquid.10

94.2.2╇ Expert Suggestions/Comments • Patients who present with seizures should receive antiepileptic drugs. If the CM is in a surgically accessible location and is proven to be the etiology of the seizures, the authors

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Fig. 94.2â•… Case presentation (video): symptomatic cavernous malformation (CM) in the left upper midbrain. Diffusion tensor imaging (DTI) demonstrates (a,b) a lesion dorsal to the fibers of the corticospinal tract, (a) lateral of the superior colliculi. An infratentorial supracerebellar approach left of the midline was chosen, allowing excellent view of the quadrigeminal cistern. (c,d) Branches of the posterior cerebral artery are apparent under the tentorial edge emerging from the ambient cistern.

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Fig. 94.2 (Continued)â•… (e) After dissection of the pial surface, the CM is identified and (f) the laser is used to coagulate and shrink the posterior aspect of the lesion prior to circumferential dissection and removal of the CM. (g) Schematic overview illustrating the presented case. PCA, posterior cranial artery; SCA, superior cerebellar artery.

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Fig. 94.3â•… Illustration of (a) different approaches to deep-seated midbrain and brainstem cavernous malformations (CMs).

recommend early surgery to avoid kindling. Electroencephalography (EEG) is performed 3 months after surgery, and if no epilepsyspecific potentials are seen, the medication should be reduced over a short time period and then stopped. • T2W and T2*W MRI provide a false sense of proximity of the malformation to the surface because of susceptibility artifacts, and hence we rely on T1W images to plan the surgery.

• The individual approach should be chosen to gain best possible access to the CM with minimal damage to healthy brain parenchyma, considering a variety of standard and skull base approaches (Fig. 94.3). • For deep-seated lesions, precise neuronavigation (Fig. 94.2a,b) is essential and intraoperative imaging, such as ultrasound and MRI, can additionally help in locating the lesion.

94 â•… Cavernous Malformations and Venous Malformations b

Fig. 94.4 (Continued)â•… (b) depending on their location. (From Porter RW, Detwiler PW, Spetzler RF. Surgical approaches to the brain stem. Operative Techn Neurosurg 2000;3: 114-123.)

• An added trick for deep-seated lesions is to pull a ventricular catheter over the neuronavigation pointer. The pointer is then advanced to the lesion and the catheter left in place. Dissection can then be performed along the catheter. This prevents losing the lesion if brain shift occurs. • For CMs in eloquent regions, such as the brainstem, the carbon dioxide (CO2) laser can be a beneficial tool (Fig. 94.2f,g). The laser leads to obliteration of the small sinusoidal

vascular channels and hence the lesion will shrink and facilitate removal with less manipulation.

94.2.3╇ Key Steps of the Procedure/ Operative Nuances • Determination of approach and planning of the neuronavigation (identification of critical anatomical structures and safe entry zones

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in brainstem lesions). It is advised to do a trajectory planning using the neuronavigation tools (Fig. 94.2a,b). Preparation of neuronavigation, neuromonitoring, intraoperative ultrasound, and CO2 laser if needed When approaching subpial CMs, brownish or bluish discoloration of brain tissue indicates proximity to the lesion (Fig. 94.2e). Circumferential dissection of the lesion from the adjacent brain is done using standard microsurgical techniques. Remove hemosiderin-stained gliotic brain parenchyma for patients with seizures. Do not attempt to remove the hemosiderin in brainstem CMs. Maintain associated DVAs. To minimize the parenchymal opening, the contents can be removed piecemeal after dissection and devascularization and/or can be shrunk with the CO2 laser (Fig. 94.2f,g). Inspect resection cavity; remove residual to achieve complete removal of the lesion. End this part of the procedure by achieving perfect hemostasis.

94.2.4╇ Hazards/Risks/Avoidance of Pitfalls • Make sure to identify the CM and not to resect only the hemosiderin rim or an old hematoma. • DVAs should be preserved because their resection can lead to venous infarction or hemorrhage.

94.2.5╇ Salvage and Rescue • If brain shift occurred and the lesion cannot be found using neuronavigation, use intraoperative imaging, such as ultrasound.

94.3╇ Outcomes and Postoperative Course 94.3.1╇ Postoperative Considerations • An MRI should be obtained 3 months after surgery to determine complete removal. Partial removal may lead to recurrence of symptoms.11

• In children with supratentorial lobar CMs presenting with seizures, 94% on average are seizure free after surgery. Supratentorial lobar CMs have a high total resection rate (99%) and a low permanent neurologic complication rate after surgery, averaging 4%.11 • Neurologic worsening postoperatively is especially common after brainstem CM resection (45% early morbidity, including 12% requiring tracheostomy and/or gastrostomy) and can be temporary, resolving after several months. The overall, long-term condition is improved or the same in 84% of patients, with worsening in the remaining 16% and an overall mortality of 1.5%.4 Similar to findings in adults,4,5 in a smaller pediatric series of 40 patients, 40% improved; 10% were the same; 48% had new or worsened neurologic deficits; and 1 patient (2.5%) died. Almost half of the patients with new or worsened deficits improved during follow-up, leaving 25% with new permanent deficits and 72.5% improved or the same.12 • In a child with multiple CMs whose symptomatic lesion was resected, the family should be informed about the possibility of new lesions and symptoms in the future.1

94.3.2╇Complications • Incompletely resected lesions have a high rebleeding rate (62%) with 6% mortality.4 • Surgical resection of DVAs, or their thrombosis, is reported to cause catastrophic venous ischemic and hemorrhagic complications, such as venous ischemic infarction, parenchymal hemorrhage, and subarachnoid and intraventricular hemorrhage. Thus, great effort should be made to identify any associated DVAs and avoid their removal.8 • Risk of early neurologic morbidity in brainstem CMs is 45%.4

References ╇1. Smith

ER, Scott RM. Cavernous malformations. Neurosurg Clin N Am 2010;21(3):483–490 ╇2. Mottolese C, Hermier M, Stan H, et al. Central nervous system cavernomas in the pediatric age group. Neurosurg Rev 2001;24(2-3):55–71, discussion 72–73 ╇3. Gross BA, Lin N, Du R, Day AL. The natural history of intracranial cavernous malformations. Neurosurg Focus 2011;30(6):E24

94 ╅ Cavernous Malformations and Venous Malformations ╇4. Gross BA, Batjer HH, Awad IA, Bendok BR, Du R. Brainstem

cavernous malformations: 1390 surgical cases from the literature. World Neurosurg 2013;80(1/2):89–93 ╇5. Pandey P, Westbroek EM, Gooderham PA, Steinberg GK. Cavernous malformation of brainstem, thalamus, and basal ganglia: a series of 176 patients. Neurosurgery 2013;72(4):573–589, discussion 588–589 ╇6. Josephson CB, Leach JP, Duncan R, Roberts RC, Counsell CE, Al-Shahi Salman R; Scottish Audit of Intracranial Vascular Malformations (SAIVMs) steering committee and collaborators. Seizure risk from cavernous or arteriovenous malformations: prospective populationbased study. Neurology 2011;76(18):1548–1554 ╇7. Burn S, Gunny R, Phipps K, Gaze M, Hayward R. Incidence of cavernoma development in children after radiotherapy for brain tumors. J Neurosurg 2007;106(5 Suppl):379–383 ╇8. San Millán Ruíz D, Gailloud P. Cerebral developmental venous anomalies. Childs Nerv Syst 2010;26(10): 1395–1406

╇9. Recalde

RJ, Figueiredo EG, de Oliveira E. Microsurgical anatomy of the safe entry zones on the anterolateral brainstem related to surgical approaches to cavernous malformations. Neurosurgery 2008;62(3 Suppl 1):9–15, discussion 15–17 10. Bruneau M, Bijlenga P, Reverdin A, et al. Early surgery for brainstem cavernomas. Acta Neurochir (Wien) 2006;148(4):405–414 11. Gross BA, Smith ER, Goumnerova L, Proctor MR, Madsen JR, Scott RM. Resection of supratentorial lobar cavernous malformations in children: clinical article. J Neurosurg Pediatr 2013;12(4):367–373 12. Abla AA, Lekovic GP, Garrett M, et al. Cavernous malformations of the brainstem presenting in childhood: surgical experience in 40 patients. Neurosurgery 2010;67(6):1589–1598, discussion 1598–1599

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Vein of Galen Aneurysmal Malformations Alejandro Berenstein and Srinivasan Paramasivam

95.1╇Background Vein of Galen aneurysmal malformations (VGAMs) are primarily formed with arteriovenous (AV) fistulas in the choroidal fissure, supplied by the choroidal arteries and draining to the persistent dilated median vein of the prosencephalon, which is the embryonic drainage of choroidal plexus and precursor of the vein of Galen. The true incidence of vein of Galen malformation is difficult to determine due to significant confusion in the literature that fails to differentiate the VGAM and other vascular malformations that cause dilation of the vein of Galen or its embryonic precursor. The cooperative study of subarachnoid hemorrhage has reported the incidence of VGAM to be less than 1% of all arteriovenous malformations (AVMs).1

95.1.1╇ Classification The embryonic nature of the draining veins of VGAMs was first described by Raybaud and colleagues in 1989,2 followed by Lasjuanias and Berenstein, who subclassified VGAMs into choroidal and mural types. Other vascular disorders that cause dilation of the vein of Galen are designated either as vein of Galen aneurysmal dilatation (VGAD) caused secondarily by pial or dural AV shunts draining into the true vein of Galen or its tributary, or as vein of Galen varix (VGV), which is dilation without associated pial or dural AV shunts.

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tive heart failure (CHF). The lesions consist of multiple fistulas located in the choroidal fissure, usually bilateral, that communicate with the anterior and inferior aspects of the median vein of the prosencephalon via an arterial network. The arterial feeders belong to the limbic system and consist of a variety of bilateral anterior and posterior choroidal arteries, as well as the anterior cerebral arteries. There is often additional supply from the quadrigeminal and thalamoperforating arteries. Among the VGAMs, this type is more challenging to treat (Fig. 95.1 and Fig. 95.2).

Mural Vein of Galen Aneurysmal Malformations Mural VGAMs consist of single or multiple fistulas located in the inferolateral margin of the dilated median vein of the prosencephalon. The quadrigeminal or the posterolateral choroidal arteries (or both) supply the fistulas and may be unilateral or bilateral. In contrast to choroidal VGAM, they have fewer fistulas and typically have outflow restriction, which causes more dilatation of the persistent median vein of the prosencephalon while protecting the heart from high-output cardiac failure. The mural VGAM presents later in infancy as macrocephaly, hydrocephalus, failure to thrive, and, in some, associated with mild-to-moderate cardiac failure or asymptomatic cardiomegaly (Fig. 95.3 and Fig. 95.4).

Vein of Galen Aneurysmal Dilatation

Vein of Galen Aneurysmal Malformation

The ectatic midline vein in VGAD is the well-differentiated true vein of Galen receiving blood from normal brain as well as from the pial and/or dural AVMs.

Choroidal Vein of Galen Aneurysmal Malformations

Pial Arteriovenous Malformation with Vein of Galen Aneurysmal Dilatation

Choroidal VGAM is a primitive type and is the most severe expression of the disease. It usually presents in the newborn period with various degrees of conges-

This type of VGAD is a pial or parenchymal AVM or AV fistula draining into the dilated vein of Galen or its tributary. The dilation of the vein of Galen is

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Fig 95.1â•… Infant presented at birth with respiratory distress and congestive heart failure (CHF). Magnetic resonance imaging (MRI) of brain T2-weighted (T2W) images (a) sagittal and (b) axial sections on day 0 show the vein of Galen aneurysmal malformation (VGAM) with dilated median vein of the prosencephalon draining into embryonic falcine sinus. (c) Magnetic resonance angiography (MRA) details the feeders to the malformation. (d) Magnetic resonance venography (MRV) demonstrates the drainage through the falcine sinus, persistence of occipital sinus, and a patent sigmoid sinus and jugular veins. As the CHF progressed, endovascular embolization was performed in the neonatal period. Left vertebral artery angiograms (e) posteroanterior (PA) and (f) lateral (LAT) views; left internal carotid artery angiogram (i) PA and (j) LAT views; and right common carotid artery angiogram (k) PA and (l) LAT views delineate choroidal-type VGAM with feeders from bilateral posterior choroidal, thalamoperforating arteries, and anterior cerebral arteries. The enlarged median vein of the prosencephalon drains through the falcine sinus with absent straight sinus. (g,h,m–p) The feeders are selectively catheterized using flow-guided microcatheters that are placed close to the fistula and embolized using N-butyl-2-cyanoacrylate (NBCA) under systemic hypotension. NBCA cast is shown for each injection in the inset (1–6). After this embolization procedure, the infant’s CHF improved significantly. The child developed normally both neurologically and psychologically. After a second embolization procedure done at 6 months, the choroidal VGAM was completely treated. (Continued on page 790)

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Fig 95.1 (Continued)â•… The follow-up angiogram was done 5 years later. The left vertebral artery (q) PA and (r) LAT; the right common carotid artery (s) PA and (t) LAT; and left common carotid artery (u) PA and (v) LAT reveal the complete obliteration and persistent occlusion of the fistula. MRI imaging was done at the same time. (w) T2 axial and (x) T1 sagittal images show the complete obliteration of the fistula, with normal development of the brain.

either due to relative obstruction caused by high flow from the malformation or absolute obstruction due to progressive occlusion of the jugular bulb and sigmoid sinus. The etiology of this outflow obstruction is unknown but may be related to underdevelopment of the jugular bulb, abnormal skull base maturation, and high outflow angiopathy of the venous system causing kinking or thrombosis at the tentorial or dural edge of the skull base. VGAD usually presents during childhood or early adulthood due to the primary disease and rarely in young children as highoutput cardiac failure.

Dural Arteriovenous Malformation with Vein of Galen Aneurysmal Dilation Dural AVM with VGAD is an acquired lesion owing to AV shunts located in the dura or in the wall of the vein of Galen secondary to stenosis or thrombosis of the straight sinus, with arterial feeders derived from the falcotentorial dural arteries, and, as a result, cortical venous reflux is frequently noted. Typical clinical presentation is in the fourth or fifth decade of life, as a result of cerebral venous hypertension, seizures, or hemorrhage.

Vein of Galen Varix VGV is dilation of the vein of Galen without the presence of an AV shunt and associated AVM. Two types are encountered in children. One is transient asymptomatic dilation of the vein of Galen in neonates with cardiac failure noticed on an ultrasound study, and it disappears after improvement of the cardiac condition. The other is an anatomical variation where venous drainage of the brain converges toward the deep venous system. It is also asymptomatic, but may predispose to future venous thrombosis and resultant ischemic symptoms because of lack of compliance.

95.1.2╇Embryology The choroid plexus develops while the brain parenchyma is still not penetrated by vessels and is nurtured by diffusion from the surrounding vascularized meninx primitiva. As early as the fifth week of development, the choroidal and quadrigeminal arteries are differentiated; these are the primary arterial supply of the VGAM. Arteries to the choroid plexus

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Fig 95.2â•… (a,b) Antenatally detected vein of Galen aneurysmal malformation (VGAM) with magnetic resonance imaging (MRI). The neonate was born with severe congestive heart failure (CHF), was intubated, and was transferred to the authors’ institution on day 2 of life. During transfer, the child suffered prolonged episodes of decreased oxygen saturation. Left vertebral angiogram (c) posteroanterior (PA) and (d) lateral (LAT); right common carotid artery (e) PA and (f) LAT; left common carotid artery (g) PA and (h) LAT show choroidal VGAM with feeders from anterior and posterior choroidal arteries. The infant was embolized with N-butyl-2-cyanoacrylate (NBCA); the NBCA cast at the end of first procedure is shown (i) in the skull X-ray lateral view. Subsequent embolizations were performed at intervals. During the course, the child developed hydrocephalus due to the thrombosed venous sac forming a third ventricular mass and (j,k) obstructing the foramen of Monro on both sides. (l) Bilateral ventriculoperitoneal shunt was performed. Shunts are usually performed for such exceptional situations and avoided for management of hydrodynamic dysfunction. With subsequent embolizations, the malformation was completely treated. The follow-up angiogram right vertebral artery (m) PA and (n) LAT; right common carotid artery (o) PA; and (p) left common carotid artery detail the complete obliteration of the malformation. In spite of aggressive management, the child had mild developmental delay, possibly due to the initial hypoxic brain damage suffered.

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Fig 95.3â•… A 10-month-old infant presented with progressive macrocephaly. (a) Imaging showed dilated ventricles and a vein of Galen malformation, as shown on a magnetic resonance imaging (MRI) T2-weighted (T2W) image. Left vertebral artery angiogram (b) posteroanterior (PA) and (c) lateral (LAT) displays a mural-type vein of Galen aneurysmal malformation (VGAM). There are two feeding arteries that join before ending in the fistulous malformation. Selective injection using the microcatheter in (d) PA and (e) LAT projections details the single-hole fistula, and the inset (1 and 2) show the embolization with N-butyl-2-cyanoacrylate (NBCA). Both feeders are embolized with one NBCA injection because you see the retrograde filling of the other feeder in the NBCA cast. Postembolization angiogram of left vertebral artery (f) PA and (g) LAT delineates complete obliteration of the malformation with preservation of normal vasculature. Follow-up MRI (h) axial T2W image and (i) sagittal T1-weighted (T1W) image at 1 year show persistent occlusion of the malformation.

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Fig 95.4â•… The infant was born with ventricular septal defect and further evaluation with echocardiogram revealed right ventricular hypertension and patent ductus arteriosus. This led to further exploration with (a) magnetic resonance imaging (MRI) and (b) magnetic resonance angiography (MRA) of the brain that showed a vein of Galen malformation. No treatment was performed at that time. At age 2 months, because the infant developed progressive hydrocephalus, it was decided to treat. Left vertebral artery angiogram (c) posteroanterior (PA) and (d) lateral (LAT) shows the mural-type vein of Galen aneurysmal malformation (VGAM). Super-selective angiogram of the feeders details the fistulous nature of the malformation in (e) PA and (f) LAT projections. (g,h)€N-butyl-2-cyanoacrylate (NBCA) embolization was performed to seal the malformation (insets 1–4). During the second embolization, the NBCA was injected to partially fill the venous sac. (i,j) Postembolization angiogram displays the residual flow to the malformation, now from the right side that was not visible before due to high-flow nature of the fistula. Follow-up angiogram 5 months later of left vertebral artery shows the development of angiogenesis around the partially thrombosed vein of Galen sac that had (k,l) feeders from the parenchymal blood vessels as well as (m–p) from the dural blood vessels (middle meningeal artery) on both sides. (Continued on page 794)

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Fig 95.4 (Continued)â•… Super-selective injection of posterior cerebral artery feeders reveals (q,r) the fine angiogenetic arterial network around the partially thrombosed vein. This network was embolized with NBCA (insets 5 and 6). In inset 6, note the infiltration of NBCA into the draining veins as the authors try to achieve obliteration of the residual venous pouch. The marginal tentorial artery arising from the superior cerebellar artery (s,t) on the right side and (u,v) left side contributed to the fistula and were selectively catheterized and embolized with NBCA (insets 7–10). Follow-up angiogram of left vertebral artery (w) PA and (x) LAT views 6 months later shows the total obliteration of the malformation. The dural feeders to the malformation on the (y,z) right side and (a1,b1) left side regressed with the embolization of the perivenous angiogenetic network of vessels.

include the anterior cerebral artery, anterior choroidal artery, and posterior choroidal artery associated with development of the median vein of the prosencephalon in the roof of the diencephalon. At this developmental stage, the quadrigeminal arteries are numerous and connected by a meningeal capillary network in the meninx primitiva, similar to the pattern seen in VGAMs. Raybaud and colleagues2 estimated that formation of the VGAM probably occurs between the embryonic stage of 21 to 23 mm (6 wk) and 50 mm (11th wk). Thus, with the development of VGAM, the median vein that normally regresses in most parts except the most caudal portion persists as the venous structure draining the high-flow fistulas.

95.1.3╇ Angioarchitecture of Vein of Galen Aneurysmal Malformations VGAMs consist of the feeding arteries that include the anterior and posterior choroidal arteries, the anterior cerebral arteries in the cistern of velum interpositum, the quadrigeminal (collicular) arteries with their dense arterial network in the quadrigeminal cistern, the thalamoperforating arteries, and dural feeders from the falcotentorial arteries draining into the persistent median vein of the prosencephalon, which usually has no communication with the drainage system of the normal brain. The drainage is usually through the embryonic falcine sinus to

95 â•… Vein of Galen Aneurysmal Malformations the posterior third of the superior sagittal sinus with the absence of straight sinus (Fig. 95.1a,e,f). Persistence of other embryological sinuses, such as the occipital and marginal sinuses, is often observed in patients with VGAMs (Fig. 95.1d–f). Persisting arterial anomalies, such as a limbic arterial ring involving the anterior and posterior choroidal arteries and pericallosal arteries, are also frequently present.

95.1.4╇ Clinical Manifestations of Vein of Galen Aneurysmal Malformation The presentation of VGAM is dependent on the severity of the AV shunt and its associated anatomical variation in the draining system, and the presence or absence of venous thrombosis or outflow restriction. VGAM may be detected in utero with routine antenatal ultrasonography, and it may be associated with cardiomegaly. In the neonatal period, the VGAM usually presents with CHF with or without pulmonary hypertension (PHT) due to dramatic change in the circulation pattern from the fetus to a newborn. If severe and not managed adequately, in the acute stage it may lead to hepatomegaly with hepatic dysfunction, prerenal azotemia followed by oliguria, and metabolic and lactic acidosis leading to multiorgan dysfunction. When there is no venous drainage restriction, the CHF is usually worse, and medical treatment may not be able to control it, requiring intervention in the newborn period. Infants usually present with cranial hydrodynamic dysfunction, due to venous hypertension and defective absorption of cerebrospinal fluid (CSF), resulting in ventriculomegaly and macrocrania. Children with long-standing hydrodynamic disorders usually present with developmental delay, seizure, and headache. In a small subset of patients, VGAM may be asymptomatic. Fetuses, neonates, and infants rarely develop an advanced stage of hydrodynamic disorder, with destruction of mainly the white matter of brain parenchyma resulting in ventriculomegaly without elevation of intracranial pressure, a condition termed melting brain syndrome.

95.1.5╇Treatment Endovascular embolization properly timed and performed by a well-trained pediatric neurointerventional team is the treatment of choice and can lead to good clinical outcomes. Medical, surgical, or radiosurgical treatment (or any combination of the three) has only a supporting and limited role.

95.1.6╇ Indications and Timing of Embolization All cases of VGAM need treatment aimed at closure of the shunt. The timing of treatment is determined by the clinical condition of the patient. It is preferable to delay the treatment until age 5 to 6 months. Neonates presenting with CHF that is controlled with medical management are followed up with a plan for embolization at approximately age 5 to 6 months. Indications for urgent treatment in the neonatal period include refractory high-output cardiac failure, PHT, and pulmonary edema resulting from cardiac failure; in infants and older children, symptoms include development of significant macrocrania or hydrocephalus, developmental delay, or venous ischemic changes, such as calcifications, and pial venous hypertension. Contraindications to treatment include neonates with severe cerebral damage and severe multiorgan failure. For children brought to attention late, who already have impaired neurologic function or severe mental retardation, endovascular embolization may be attempted to improve the quality of life, with a clear understanding of the irreversible nature of the delayed treatment. The authors can usually obtain a satisfactory improvement in neurocognitive function and alleviate headache.

95.1.7╇ Goal of Treatment The goal of embolization is complete obliteration of the AV shunt, resulting in normal development without neurologic deficits. For mural VGAM, complete obliteration can usually be achieved in one or two sessions of endovascular treatment. For choroidal VGAM, several sessions of staged embolization may be necessary over a period of several years to achieve complete obliteration; the treatment interval is usually placed at 3 to 6 months but is determined according to the response of the patient to the treatment. In neonates with cardiac failure, the immediate treatment goal is to decrease the flow into the shunt to alleviate heart failure and to enable the neonate to tolerate oral feeds, gain weight, and attain normal developmental milestones. Complete occlusion of the lesion is not the objective at the newborn stage because of the increased risk for complications and limitation in the use of contrast material. Treatment is much safer and easier if the patient is clinically stable and weighs several kilograms more than the birth weight. For infants and children, the immediate goal is to restore the normal hydrovenous equilibrium to avoid ventricular shunting and permit normal development of the patient.

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95.1.8╇ Prenatal Management Prenatally detected VGAM undergoes evaluation by a pediatric cardiologist, including fetal ultrasound and echocardiography to assess the fetal heart size and to determine the presence of associated heart defects. If the fetus has cardiomegaly, the mother is started on digoxin given under cardiac monitoring at doses of 0.5 mg intravenously every 6 hours until a maternal serum digoxin level of close to 2 ng/dL is reached. At that point, the digoxin is switched to an oral maintenance dose, usually about 0.5 mg twice daily, and a digoxin level of approximately 2 ng/dL is maintained until delivery. This seems to better control the digitalis level in the newborn period than if digitalis treatment is started after birth.

95.1.9╇ Neonatal Management Newborns at the authors’ institution are managed in the neonatal intensive care unit, where cardiovascular examination, echocardiogram, and transcranial ultrasound are obtained on day 1 of life. Echocardiogram usually shows persistence of fetal circulation, generalized cardiomegaly, hypercontractility, and PHT, with suprasystemic pressure in the pulmonary artery as measured by tricuspid insufficiency velocity. Presence of dilatation of the ascending aorta and the carotid arteries, with severe diastolic reversal of flow in the descending aorta, are indications of very high-flow shunts. CHF and PHT are managed with mechanical ventilation; nitric oxide; inotropic drugs like digoxin, dobutamine, dopamine, and milrinone; and diuretics. If patients cannot be weaned from ventilatory support or intravenous medications or are progressing toward multiorgan failure, then endovascular intervention to close as much of the fistula as possible and control the CHF is considered. With the experience gained over the years in treating neonates with VGAM and CHF, the authors now tend to intervene earlier than in the past, prior to the neonate’s becoming very sick with worsening cardiopulmonary and multiorgan failure. The cardiac status and the systemic condition of the patient usually improve significantly after embolization, even if complete occlusion of the VGAM cannot be achieved.

95.1.10╇ Pretherapeutic Evaluation Pretherapeutic evaluation of a patient with a VGAM should assess the following: (1) physical parameters, including weight and head circumference and their changes in time; (2) data on the lesions obtained by magnetic resonance imaging (MRI), magnetic reso-

nance angiography (MRA), and magnetic resonance venography (MRV), including feeders, venous dilation, and sinus occlusion (Fig. 95.1a–d, Fig. 95.3a, and 95.4a,b); (3) information about the brain, such as congestion, encephalomalacia, laminar necrosis, atrophy, calcification, and the size of the ventricles, obtained by transfontanelle ultrasound, computed tomography (CT), and/or MRI; (4) cardiac status, including associated cardiac anomalies, determined by clinical assessment and cardiac echocardiography; and (5) renal and liver function and coagulation profile. In view of the limited and challenging arterial access, diagnostic angiography alone is not indicated in neonates and infants and should be performed only when embolization is being considered.

95.1.11╇ Endovascular Treatment Endovascular embolization of VGAM is performed by either transarterial or transvenous occlusion of the fistula. The risk of immediate hemorrhage is significantly less with transarterial embolization. Some centers use a combination of transarterial and transvenous routes for embolization. If a transvenous approach is chosen, one has to be absolutely sure that the vein does not drain the normal brain. In general, even an incomplete venous occlusion of the dilated venous pouch is efficient to control heart failure; however, the authors do not use it in the newborn period. Their earlier experience in three newborns resulted in improved cardiac function but poor brain development in all three cases. At present, the venous approach is used toward the end of treatment, to achieve complete occlusion of the malformation after ascertaining the alternate drainage of the deep venous system. All procedures are done under general anesthesia with arterial pressure monitoring. Femoral arterial puncture is done with a 20-gauge needle with the assistance of Doppler ultrasound to localize and cannulate the femoral artery. A transumbilical artery route is possible for newborn patients and sometimes preferable because of the small size of the femoral artery. In general, particularly in the newborn, the treatment must be efficient. Radiation exposure and fluid load must be minimized in these very sick and friable patients, with particular attention paid to the contrast load. The total contrast used is limited to 6 to 10 mL of pure contrast per kilogram in one session. In neonates with cardiac failure, the first angiographic injection should be for the vessel harboring the largest fistula, which is the first target for embolization, and this vessel is determined on the basis of MRI or MRA. A full angiographic assessment will be done later because of the limited toleration of contrast material by these patients.

95 â•… Vein of Galen Aneurysmal Malformations Transarterial embolization with N-butyl-2-cyanoacrylate (NBCA) in the hands of the authors has been shown to have the best results. NBCA is delivered via a flow-guided microcatheter through a 4Fr-guiding catheter. To close a high-flow fistula, the authors use a high concentration of NBCA, usually greater than 70%, mixed with Lipiodol in various concentrations and tantalum to make it more radioopaque. The embolic agent is usually deposited under systemic hypotension (systolic pressure under 60 mm Hg), within the high-flow fistulous connections at the junction of the vein. Proximal occlusion of feeders will lead to recanalization. The transvenous embolization of a vein of Galen malformation is accomplished from either a percutaneous transfemoral vein or a transtorcular approach. The transtorcular path requires either a surgical exposure or ultrasound-guided percutaneous puncture. Venous occlusion is achieved with coils. The extent of embolization may be monitored during the procedure by injection of contrast material by a transarterial route or directly into the pouch. The transvenous procedure is technically easier; however, it is associated with a higher rate of postprocedure hemorrhage. This technique is contraindicated if the venous channel drains the normal brain. A combined transvenous and transarterial embolization may be beneficial for certain patients in whom complete occlusion of the fistulas cannot he achieved by the transarterial approach alone. In such cases, transvenous embolization is performed at the end, to close small residual fistulas for complete obliteration of the malformation. The embolization is done in sessions at ideally 3to 4-month intervals, or more frequently if needed. On an average, each patient needs about three and a half sessions for a cure. Mural-type malformations are usually closed in one or two sessions, whereas complex choroidal-type malformations require multiple sessions. Following the procedure, children are kept in the pediatric or neonatal intensive care unit. They are given steroids for the first few days and are rapidly tapered. They are monitored closely for the development of hemorrhage, secondary venous sinus thrombosis, and hydrocephalus. Complications with embolization include neurologic complications, such as stroke or focal neurologic deficit, hemorrhage, hemorrhagic infarct, hydrocephalus, and seizures. Nonneurologic problems can include technical difficulty with glue injections like fragmentation of glue cast, venous sinus occlusion or pulmonary infarction, adhesion of the catheter to the artery by glue, and femoral artery occlusion. Hydrocephalus in VGAM is secondary to venous hypertension. If the venous hypertension is reduced early enough by endovascular embolization, hydrocephalus is prevented or treated without placement

of a ventricular shunt. If endovascular treatment is delayed until after the development of hydrocephalus, ventricular shunt placement may be necessary despite endovascular embolization. Third ventriculostomy may be a preferred option in the treatment of hydrocephalus in combination with effective embolization of the VGAM.

95.1.12╇ Surgical Treatment Surgery is no longer indicated as the primary treatment of VGAM because the surgical results are uniformly poor. Surgical craniotomy to allow transtorcular embolization may be considered when the arterial or venous transfemoral route is not possible, although the authors have not needed this approach for the past 15 years.

95.1.13╇ Stereotactic Radiotherapy Stereotactic radiosurgery with either the Gamma Knife or a linear accelerator has no role in newborns, infants, and children. It has a limited role in older patients with relatively slow-flow residual shunts after endovascular treatment.

95.1.14╇Outcomes Prognosis has improved significantly in the past two decades, when treatment for vein of Galen malformation begins prior to the occurrence of neurologic injury. A recent literature review of vein of Galen patients of all ages comparing outcomes from 1983 to 2010 determined that the results from 2001 to 2010 showed a significant improvement.3 In the earlier period, microsurgery was an occasional treatment, with 84.6% mortality. In the later period, embolization was the mainstay of treatment, with good outcomes occurring 60.8% of the time. As expected, when looking at just the neonates in this period, the authors found only a 32.7% rate of good results. In their series of 80 patients with VGAM from 2004 to 2011, they achieved more than 90% occlusion of the malformation in 80.2% of patients, with a mortality rate of 6.2%. In this group, normal neurologic outcome was seen in 61.2% of patients, mild motor delay in 11.2%, and mild cognitive delay in 7.5%, resulting in an overall 80% good outcome rate. In the authors’ series of neonates treated solely with transarterial embolization, normal neurologic outcome was seen in 66.7% of patients and mild developmental delay in 11%, resulting in an overall 77.8% good outcome rate and a low mortality rate of 11%.4

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95.2╇Conclusion Improved understanding of the anatomical, clinical, and pathophysiological features of VGAMs, and the advancement of endovascular embolization as primary therapy have significantly improved the outcome. The majority of children can now survive and have normal neurologic development after proper endovascular treatment. Transarterial embolization has become the primary choice of treatment, and surgery has only a limited adjunctive role for the management of VGAMs. It is important to occlude the fistula sites for effective embolization, and staged embolization should be considered for complicated fistulas to minimize the risk associated with treatment. Ventricular shunting can also be avoided with timely embolization in most cases.

References ╇1. Locksley HB, Sahs AL, Knowler L. Report on the coopera-

tive study of intracranial aneurysms and subarachnoid hemorrhage. Section II. General survey of cases in the central registry and characteristics of the sample population. J Neurosurg 1966;24(5):922–932 ╇2. Raybaud CA, Strother CM, Hald JK. Aneurysms of the vein of Galen: embryonic considerations and anatomical features relating to the pathogenesis of the malformation. Neuroradiology 1989;31(2):109–128 ╇3. Khullar D, Andeejani AM, Bulsara KR. Evolution of treatment options for vein of Galen malformations. J Neurosurg Pediatr 2010;6(5):444–451 ╇4. Berenstein A, Fifi JT, Niimi Y, et al. Vein of Galen malformations in neonates: new management paradigms for improving outcomes. Neurosurgery 2012;70(5):1207– 1213, discussion 1213–1214

96

Moyamoya Syndrome/ Pial Synangiosis Edward R. Smith and R. Michael Scott

96.1╇Background Moyamoya is an arteriopathy of unknown origin that affects the internal carotid arteries (ICA) and their branches, progressively reducing blood flow to the brain and putting patients at risk of stroke. The diagnosis is made by characteristic findings on arteriogram and typically advances over time, following a pattern of luminal occlusion and limited collateral development. It is difficult to predict the rate of advancement in a given patient, which can encompass the spectrum from slow to fulminant. Ultimately, however, the majority of patients with moyamoya experience progression of the disease, with poor

outcomes if untreated. Neurologic status at time of treatment, more than age of the patient, predicts longterm outcome. Up to 66% of patients with moyamoya have progression of the disease with poor outcomes if untreated versus only 2.6% for treated patients. In this chapter, the authors describe a surgical treatment for moyamoya, pial synangiosis (Fig. 96.1).

96.1.1╇Indications Surgical indications include: • Neurologic symptoms suggestive of ischemia coupled with radiographic evidence of moyamoya

Fig. 96.1â•… This schematic shows the general plan for pial synangiosis. The superficial temporal artery (STA) is dissected free, then the bone flap is removed, followed by suturing of the vessel to the brain and subsequent closure, with ingrowth of new collaterals on the last image.

799

800 Section IXâ•… Vascular Disorders • Transient ischemic attacks (TIAs) or loss of cognitive function • Radiographic evidence of diminished cerebral blood flow (stroke, decreased reserve on cerebral blood flow testing)1 Japan’s Ministry of Health and Welfare uses the following guidelines to justify surgery in moyamoya: • Clinically evident symptoms referable to brain ischemia • Imaging studies demonstrating decreased focal cerebral blood flow or perfusion2 Recommendations from the American Heart Association are equally supportive of surgery, stating “progressive ischemic symptoms or evidence of inadequate blood flow or cerebral perfusion reserve in an individual without a contraindication to surgery” should be used as indications to operate.3 It should be noted that recent evidence supports the treatment of asymptomatic patients in select cases, even when moyamoya is incidentally found.4 The timing of surgery is less clear, although most centers offer revascularization once the diagnosis of moyamoya is made. Whereas a delay may be appropriate in some situations (e.g., if the diagnosis is unclear, if the patient needs to recover from a stroke to reduce swelling, or if there are other acute medical issues), the overall goal is to provide treatment as soon as possible. However, this desire to move expeditiously should be balanced with the ability to maximize safety of the operation by electively scheduling cases with experienced staff and availability of all the resources needed to perform the operation.

96.1.2╇Goals The goal of pial synangiosis―and all cerebral revascularization surgery in moyamoya―is to provide new, durable vascular collaterals to the brain that fully supply all ischemic cortex affected by the arteriopathy. Although often achievable by a single operation at one site per hemisphere, there are rare instances in which multiple operations or approaches may be required (such as in cases of isolated anterior or posterior cerebral artery territory ischemia).

96.1.3╇ Alternative Procedures Whereas medical therapy, such as antiplatelet agents and hydration, can be helpful, the primary treatment of moyamoya is surgical revascularization of the brain. Many techniques have been described, but the most common employ healthy branches of the external carotid artery (ECA) as donor vessels.

In general, there are two approaches―indirect, in which a branch of the ECA is used as an onlay graft to grow a robust network of collaterals (with the pial synangiosis described here as representative of one method) or direct, in which a branch of the ECA is anastomosed end to side into a preexisting cortical vessel (such as a superficial temporal artery–middle cerebral artery [STA–MCA] bypass). The advent of endovascular stenting of intracranial vessels has led to attempts to treat moyamoya with this technique. Unfortunately, the results have been uniformly unsuccessful at maintaining durable patency of the vessels.5,6 It has been hypothesized that moyamoya is not amenable to this approach because of its progressive nature (unlike focal atherosclerotic disease), in which the stenotic process continues on either side of the stent.

96.1.4╇Advantages Considerable debate exists over the selection of an individual operative approach. Most U.S. centers will initially revascularize the territory of the MCA, although it is the practice in some Asian hospitals to also include anterior cerebral artery revascularization as part of the initial surgery.7 Direct procedures, such as a STA–MCA bypass, allow immediate restoration of blood flow at the time of surgery, in contrast to indirect procedures that require weeks or months to establish collateral vessels. However, the bypass can be difficult to perform in young children and may increase the risk of reperfusion hemorrhage or edema, making indirect procedures more appealing. The particular choice of pial synangiosis is justified in nearly all pediatric cases, given its efficacy (as reported by multiple centers around the world), its applicability to any age of patient (from infants to adults), and its durability. Long-term follow-up of patients treated with pial synangiosis revealed that although 67% had strokes preoperatively, the stroke rate was only 4.3% after surgery in those patients followed for more than 5 years postoperatively.8 This result mirrors data from other centers, including a meta-analysis of more than 1,100 treated individuals, supporting the premise that surgical treatment of moyamoya confers durable, marked reductions in stroke.1,9 Overall, indirect techniques, such as pial synangiosis, are used in about 75% of all pediatric moyamoya cases.1

96.1.5╇Contraindications Surgery is relatively contraindicated in patients who are a poor operative risk (severe cardiac disease, advanced debilitation from stroke burden or other severe comorbidities).

96 â•… Moyamoya Syndrome/Pial Synangiosis

96.2╇ Operative Detail and Preparation 96.2.1╇ Preoperative Planning and Special Equipment Preoperative management of moyamoya patients is critical to the success of surgery. Strategy is based on the utilization of appropriate imaging for planning and the maintenance of hypervolemia and normocarbia, and prevention of thrombosis and hypotension. A full five- or six-vessel (both ICAs, both ECAs, and one or both vertebrals as indicated) diagnostic angiogram is critical to the planning of the procedure for: 1. Accurate identification of disease status 2. Identification of transdural collaterals so that they may be preserved during surgery 3. Confirmation of the presence of a suitable donor scalp vessel (usually the parietal branch of the STA) Once the decision to operate has been made, the authors follow a standardized perioperative protocol. Dehydration is a significant risk, given the hypoperfused intracranial circulation. To minimize shifts in blood pressure during the induction of anesthesia, the authors routinely admit patients to the hospital on the evening prior to surgery for intravenous hydration. If there are no underlying cardiac or renal limitations, isotonic fluids are run at 1.5 times maintenance rate. Barring medical contraindication, patients are treated with daily aspirin therapy from the time of their diagnosis of moyamoya in order to minimize the risk of thrombosis in the slow-flowing cortical vessels. Dosing is continued up to and including the day prior to surgery (and restarted the day after surgery). Pain and anxiety must be aggressively managed, especially in children, since hyperventilation, as occurs with crying, can induce cerebral vasoconstriction leading to stroke. Steroids, cerebral dehydrating agents, such as mannitol, and anticonvulsants are not administered on a routine basis. Surgical equipment includes intraoperative electroencephalography (EEG) monitoring, an operative microscope, a fine arachnoid knife, and a dedicated set of microinstruments, including jeweler’s forceps, appropriate needle drivers, and tying instruments for 10–0 sutures.

96.2.2╇ Expert Suggestions/Comments • Important aspects of this procedure are nonsurgical, and include preoperative hydration and experienced anesthesia.

• Mapping and dissecting as long a length of STA as possible will increase potential collateral development. • Wide opening of the arachnoid facilitates exposure of the donor vessel to growth factors present in the cerebrospinal fluid (CSF) as well as permitting direct apposition of the donor artery to the pial surface, increasing the likelihood of better collateralization. • Hemostasis at all stages of the operation is critical.

96.2.3╇ Key Steps of the Procedure/ Operative Nuances Positioning EEG electrodes are placed on the patient’s scalp in the preoperative holding area, except for smaller children, in whom the leads are placed after anesthetic induction. The microscope is prepared with opposing oculars enabling binocular vision for the surgical assistant. The scrub nurse is positioned by the patient’s right side with a Mayo stand. Anesthesia is on the patient’s left side. The scalp is shaved over the predicted course of the parietal branch of the STA, which is then mapped out using the Doppler (scratching the skin with a needle to mark its course). The head is placed in pin fixation (except with infants) and the patient is positioned supine with the head turned parallel to the floor, such that the STA site is level. Rolls are used as needed to reduce tension on the neck and the head is translated superior to the torso to facilitate venous drainage.

Vessel Dissection Using high magnification with the microscope, a no. 15 blade is used to score the dermis at the distal end of the STA. A thin, curved hemostat and toothed Adson pickups are used by the surgeon (with suction and a second set of pickups by the assistant) to identify the STA under the skin. Using a repeated technique of subcutaneous dissection with the hemostat over the STA, followed by elevation of the skin by the hemostat and an incision on the hemostat by the assistant, the STA is dissected to the root of the zygoma. Care must be taken to avoid tearing the vessel, particularly if the vessel has tortuous bends or large side branches. Irrigating or nonstick bipolar (with fine tips) is employed for hemostasis of small scalp vessels. A Cottonoid (Codman & Shurtleff, Raynham, MA, USA) is often helpful to cover the distal incision as proximal dissection continues. Dissection

801

802 Section IXâ•… Vascular Disorders often terminates at the takeoff of the frontal branch, near the root of the zygoma. If a long enough segment of STA has been freed, or if the frontal branch provides collateral vessels (based on the preoperative angiogram), the branch is spared. If not, it can be sacrificed. In general, the authors attempt to dissect a 10-cm length of vessel (Fig. 96.2). Colorado tip electrocautery (at low settings) is used in conjunction with the bipolar and microscissors to score the adventitial tissue and galea on either side of the STA down to the temporalis fascia, leaving a 1- to 2-mm cuff on either side of the vessel. Self-retaining retractors are placed―one proximal, one distal. A vessel loop is placed under the distal end of the STA, is clipped with a bulldog, and is used to gently elevate the dissected portion of the vessel from the temporalis. The curved hemostat, in conjunction with the standard electrocautery tip (on a

low setting), is used to complete the release of the vessel from surrounding tissue.

Craniotomy Once the STA is mobilized, the microscope is removed, and the galea is dissected from the temporalis using the electrocautery to develop anterior and posterior scalp flaps. The temporalis is then divided into quarters by two lines―one vertically, along the axis of the vessel, and the other horizontally, perpendicular to the first. The muscle is reflected from the bone (with use of the electrocautery) and held back with multiple hooks to maximize exposure. Two burr holes are made, one near the zygoma and the other near the top of the incision. The footplate is then used to turn a large oval or circular craniotomy flap.

a

b

c

d

Fig. 96.2â•… Operative photographs of pial synangiosis. (a) The mapped course of the superficial temporal artery (STA) (from Doppler ultrasonography), with (b) the open craniotomy, and (c) the dissected vessel below it. (d) Suturing of the vessel to the pia.

96 â•… Moyamoya Syndrome/Pial Synangiosis

Dural Opening

Closure

The dura is opened in a stellate pattern using a no. 15 blade and scissors, with a total of six leaflets, three per side, reflected back with 4–0 sutures over squares of Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA). Care is taken to minimize use of the bipolar on the dura in order to maximize collateral vessel development, although hemostasis is paramount in these patients. Moreover, if preexisting collaterals are identified arising from the middle meningeal branches, then they are preserved at opening (Fig. 96.2).

After the synangiosis is completed, the microscope is removed from the field, and dura is laid on the surface of the brain without suture reapproximation and then is covered with a large piece of salinesoaked Gelfoam (Pfizer). Burr holes are enlarged on the bone flap as needed to facilitate tension-free entry and exit of the donor vessel. The bone flap is then replaced with small titanium plates (not over the burr holes). The temporalis is closed with interrupted Vicryl (Ethicon, Somerville, NJ, USA) sutures in the horizontal plane, leaving the vertical incision open to allow tension-free transit of the STA. Galea is also closed with Vicryl (Ethicon), taking care to avoid suturing the STA, and skin is closed with a running absorbable suture.

Microsurgical Arachnoid Opening and Pial Synangiosis Under the microscope, the arachnoid is widely opened, using the arachnoid blade and jeweler’s forceps. Bleeding is controlled with irrigation or small dots of Gelfoam (Pfizer), and vasospasm, if seen, is treated with papaverine. Once the arachnoid is widely opened, interrupted sutures of 10–0 nylon are placed through the cuff of tissue along the undersurface of the STA and through the outer pial layer, placing three to four knots per suture in order to maintain apposition of the donor vessel to the brain surface. Generally, four sutures are placed (Fig. 96.2).

a

Contralateral Side In bilateral cases, the dominant or most symptomatic side is generally done first, so that if there are intraoperative events that preclude continuing with the second side, the most important hemisphere has been treated. If the EEG and vital signs are stable, the patient is repositioned and the same operation is performed on the contralateral side (Fig. 96.3).

b

Fig. 96.3â•… Angiographic results of pial synangiosis. (a) An anteroposterior [AP] internal carotid injection showing severe moyamoya (arrowhead). (b) An external internal carotid artery (ICA) injection, with abundant surgical collaterals (arrowhead).

803

804 Section IXâ•… Vascular Disorders

96.2.4╇ Hazards/Risks/Avoidance of Pitfalls A number of intraoperative steps can be taken in order to minimize the risk of stroke. These include: • Institution of EEG monitoring, with anesthetic responses (such as addition of neuroprotective agents) utilized when slowing of the baseline waveform occurs • Maintaining normotension during induction; also normothermia (especially with smaller children), normocarbia (avoid hyperventilation to minimize cerebral vasoconstriction, pCO2 > 35 mm Hg), and normal pH • Placement of additional intravenous lines, arterial line, Foley catheter, and pulse oximeter • Positioning of a precordial Doppler to monitor for venous air emboli (relevant with thicker bone resulting from extramedullary hematopoiesis in sickle cell patients)

96.2.5╇ Salvage and Rescue The primary technical complication of this case is injury to the donor vessel. Should the parietal STA be damaged, alternative approaches might include use of an alternative branch (frontal STA, posterior auricular) or application of another pedicle of vascularized tissue (such as a strip of temporalis muscle, periosteum, or dural leaflets).

96.3╇ Outcomes and Postoperative Course 96.3.1╇ Postoperative Considerations and Complications The major risk of this surgery is perioperative stroke. Steps to mitigate this risk include: • Avoiding hyperventilation (relevant with crying in children); pain control is important. • Restarting aspirin therapy on postoperative day 1

• Continuing intravenous hydration at 1.25 to 1.5 × maintenance until child is fully recovered and drinking well (usually 48–72 h) Despite these measures (in addition to careful operative and anesthetic technique), a number of children will still experience strokes. Risk can be minimized through careful administration of the steps outlined and management of affected children at institutions with experienced surgeons, intensivists, anesthesiologists, and nurses.

References ╇1. Fung

LW, Thompson D, Ganesan V. Revascularisation surgery for paediatric moyamoya: a review of the literature. Childs Nerv Syst 2005;21(5):358–364 ╇2. Fukui M. Guidelines for the diagnosis and treatment of spontaneous occlusion of the circle of Willis (‘moyamoya’ disease). Research Committee on Spontaneous Occlusion of the Circle of Willis (Moyamoya Disease) of the Ministry of Health and Welfare, Japan. Clin Neurol Neurosurg 1997;99(Suppl 2):S238–S240 ╇3. Roach ES, Golomb MR, Adams R, et al; American Heart Association Stroke Council; Council on Cardiovascular Disease in the Young. Management of stroke in infants and children: a scientific statement from a Special Writing Group of the American Heart Association Stroke Council and the Council on Cardiovascular Disease in the Young. Stroke 2008;39(9):2644–2691 ╇4. Lin N, Baird L, Koss M, et al. Discovery of asymptomatic moyamoya arteriopathy in pediatric syndromic populations: radiographic and clinical progression. Neurosurg Focus 2011;31(6):E6 ╇5. Drazin D, Calayag M, Gifford E, Dalfino J, Yamamoto J, Boulos AS. Endovascular treatment for moyamoya disease in a Caucasian twin with angioplasty and Wingspan stent. Clin Neurol Neurosurg 2009;111(10):913–917 ╇6. Khan N, Dodd R, Marks MP, Bell-Stephens T, Vavao J, Steinberg GK. Failure of primary percutaneous angioplasty and stenting in the prevention of ischemia in Moyamoya angiopathy. Cerebrovasc Dis 2011;31(2):147–153 ╇7. Kim SK, Wang KC, Kim IO, Lee DS, Cho BK. Combined encephaloduroarteriosynangiosis and bifrontal encephalogaleo (periosteal) synangiosis in pediatric moyamoya disease. Neurosurgery 2008;62(6 Suppl 3):1456–1464 ╇8. Scott RM, Smith JL, Robertson RL, Madsen JR, Soriano SG, Rockoff MA. Long-term outcome in children with moyamoya syndrome after cranial revascularization by pial synangiosis. J Neurosurg 2004;100(2 Suppl Pediatrics):142–149 ╇9. Scott RM, Smith ER. Moyamoya disease and moyamoya syndrome. N Engl J Med 2009;360(12):1226–1237

97

Surgical Management of Spinal Arteriovenous Malformations Shakeel A. Chowdhry and Robert F. Spetzler

97.1╇Background Pediatric spinal vascular malformations are rare, challenging lesions that are a collection of diverse entities. The nomenclature and classification of this myriad of disease entities have evolved as our understanding of the pathophysiology of the various entities has evolved and has been directed by criteria that are critical for determining treatment. Since the first description of a spinal arteriovenous malformation (AVM) by Gaupp in 1888,1 a number of classification schemes for spinal vascular lesions have been proposed. Initial classification systems focused on the pathological characteristics,2 whereas later structures utilized anatomical criteria.3 As the understanding of these lesions grew, many modifications and additions to the classification schemes were proposed, including those by Riche et al,4 Borden et al,5 and Rodesch et al.6 In 2002, the authors proposed a classification system based on the angioarchitecture and pathophysiology of spinal vascular malformations, with slight modifications proposed in 2006, and they use this classification to structure the discussion of pediatric spinal vascular malformations.7,8 Spinal vascular malformations may be grouped into neoplastic lesions (hemangioblastomas and cavernous malformations), arteriovenous fistulas (AVFs), and AVMs. Spinal aneurysms, which when unrelated to AVMs occur due to flow phenomena and arterial dissection, are exceedingly rare and have not been described in the pediatric population. Spinal AVFs are more common in the adult population and typically present with progressive myelopathy.7 They are divided into extradural, dorsal intradural, and ventral intradural AVFs. Extradural AVFs are uncommon (Fig. 97.1a). They represent a direct connection between a branch of the radicular artery and the epidural venous plexus. Symptoms are largely due to venous engorgement and mass effect. These lesions are generally amenable to endovascular therapy. For surgical treatment, midline posterior

exposure of the extradural fistulous point allows for direct obliteration of the fistula and treatment of local compression. Rarely, the dural entry point may be in the ventral dura or may be remote from the level of the supplying radicular artery. Dorsal intradural AVFs are treated with obliteration of the radiculomedullary arterial supply as it enters the dural nerve root sleeve to pathologically arterialize the coronal venous plexus (Fig. 97.1b). These fistulas may present with single (type A) or multiple (type B) feeding arteries. The authors approach these lesions through a midline posterior route and laminoplasty. They may also be treated by endovascular occlusion of the fistulous point. Ventral intradural AVFs are located ventrally and are supplied by the anterior spinal artery (Fig.€97.1c,d). These lesions are subdivided based on the size of the vascular shunt. Increasing fistula size and flow correlate with more pronounced signs of vascular steal and spinal cord compression. An anterior or anterolateral approach may be necessary for adequate exposure, but posterolateral paths are appropriate for ventrolateral lesions. Embolization carries a high risk due to involvement of the anterior spinal artery but may be useful for larger lesions with complex angioarchitecture and multipedicled feeders. AVMs may present with acute myelopathy, progressive myelopathy, radiculopathy, or pain. They are classified as extradural–intradural, intramedullary, and conus medullaris AVMs. Extradural–intradural AVMs are uncommon (Fig. 97.2a). They have been previously described as metameric, juvenile, or type III AVMs. These formidable lesions do not respect tissue boundaries and can involve neural structures, bone, and soft tissue along the affected level. A multidisciplinary approach is necessary, and surgery is reserved for decompression of mass effect along the nerve root and spinal cord. Complete resection is possible but not without significant morbidity (Fig. 97.3). Therefore, the goal of treatment is decompression of neural elements, stabilization, and devascularization through a multidisciplinary approach.

805

806 Section IXâ•… Vascular Disorders a

b

Fig. 97.1â•… Spinal arteriovenous fistulas (AVFs). (a) Posterior view of extradural AVF with marked engorgement of epidural veins resulting in compression of the spinal cord and adjacent nerve roots. (b) Axial view of type A dorsal intradural AVF with abnormal radicular artery along the nerve root sleeve. The network of tiny branches coalesces at the site of the fistula, with marked dilation and arterialization of the intradural veins.

97 â•… Surgical Management of Spinal Arteriovenous Malformations c

d

Fig. 97.1 (Continued)â•… (c) Axial and (d) anterior views of ventral intradural AVF, a midline lesion formed by a fistulous connection between the anterior spinal artery and the coronal venous plexus. (Reprinted with permission from Barrow Neurological Institute.)

807

808 Section IXâ•… Vascular Disorders a

b

Fig. 97.2â•… Spinal arteriovenous malformations (AVMs). (a) Extradural–intradural AVMs cross tissue planes and involve soft tissue, bone, spinal canal, spinal cord, and nerve roots along an entire spinal level or levels. (b) Intramedullary AVM with a compact nidus seen from axial view. Feeding branches from the anterior spinal artery and posterior spinal artery are present. The AVM abuts the pial surface and is amenable to resection. Embolization is selectively utilized.

97 â•… Surgical Management of Spinal Arteriovenous Malformations c

d

Fig. 97.2 (Continued)â•… (c) Intramedullary AVM with a diffuse nidus seen from an oblique posterior view. The diffuse nidus spans normal neural tissue with loops of AVM coursing into and out of the AVM. The pial resection technique is utilized for these lesions. (d) Conus medullaris AVM seen from a posterior view with complex angioarchitecture of feeding vessels from the anterior and posterior spinal arteries as well as radicular arteries. Portions of the AVM may consist of direct arteriovenous (AV) shunts with other region of true AVM nidus that may be partially embedded within the conus. Preservation of en passage vessels is critical during treatment of these lesions. (Reprinted with permission from Barrow Neurological Institute.)

809

810 Section IXâ•… Vascular Disorders a

b

Fig. 97.3â•… Follow-up imaging at 1 year. (a) Sagittal T2-weighted (T2W) magnetic resonance imaging (MRI) of the cervical spine, and (b) lateral cervical plain film of a 10-year-old child with a large extradural–intradural arteriovenous malformation (AVM) spanning C1–C4 with marked neurologic impairment from nerve root and spinal cord compression. Aggressive embolization was followed by bony decompression and intradural and epidural resection of the AVM. (Reprinted with permission from Barrow Neurological Institute.)

Intramedullary AVMs are composed of feeding arteries, draining veins, and a nidus similar to intracranial AVMs. They may be supplied by multiple branches from the anterior spinal and posterior spinal arteries. Associated aneurysms are typical. The nidi may be compact or diffuse (Fig. 97.2b,c). Conus medullaris AVMs possess nidi that are generally extramedullary and pial-based with supply from anterior and posterior spinal arteries, but the nidus may have an intramedullary component (Fig.€97.2d). The authors discuss surgical treatment for spinal AVMs below. Radiosurgery and embolization have been used to treat AVMs; however, longterm results are unclear.

97.2╇ Operative Detail and Preparation Preoperative imaging for spinal AVMs should include magnetic resonance imaging (MRI) and catheter angiography. Gadolinium-enhanced magnetic resonance angiography (MRA) of the spine may permit identifi-

cation of feeding radicular arteries. Involvement of the anterior spinal artery or artery of Adamkiewicz should be noted. For purely intramedullary AVMs, the characteristics of the nidus (compact vs. diffuse) should be mentioned. Intramedullary AVMs have been successfully treated with embolization procedures, but the mainstay of treatment remains surgical extirpation. For extradural–intradural AVMs, the extent of intradural extension and mass effect should be considered. Complex and multipedicled lesions are embolized preoperatively. Embolization is particularly useful for anteriorly located feeding arteries that can complicate resection from a posterior or posterolateral approach; however, it may be limited by the relationship of feeding arteries to the anterior spinal artery. Preoperative embolization should be performed with neurophysiological monitoring, and provocative testing may help to determine the relationship of a feeding pedicle to the spinal cord blood supply. At the authors’ institution, most adjuvant embolization is performed with Onyx or N-butyl-cyanoacrylate (NBCA). The authors routinely use multimodality neurophysiological monitoring with somatosensory evoked and motor evoked potentials and indocyanine green

97 â•… Surgical Management of Spinal Arteriovenous Malformations (ICG) angiography. Prior to the advent of ICG angiography, intraoperative catheter angiography was utilized, and appropriate preparation, including femoral artery catheterization, was made prior to positioning if intraoperative angiography was anticipated. Type and screen are routinely ordered for patients prior to surgery. High-powered magnification and illumination with the surgical microscope, straight and curved microscissors, and nonstick bipolar cauterization are essential. The authors prefer to use the surgical microscope mouthpiece to facilitate visualization and limit the surgical interruption caused by repeated manual repositioning of the microscope. Most AVMs are approached through a posterior midline route with laminoplasty or through a posterolateral path. For ventral intramedullary AVMs, an anterior or anterolateral approach may be used. X-ray or C-arm fluoroscopy may be useful for localization, particularly for thoracic lesions. Generous exposure is obtained to allow easier manipulation of the AVM. The dura is opened in the midline, and the dural edges are elevated with 4–0 Nurolon suture. Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA) is placed along the superior and inferior aspects of the dural opening to limit blood products’ spreading outside of the opera-

a

tive field. ICG angiography is performed after the lesion is exposed to confirm feeding arteries and draining veins as well as en passage vessels. Initially, the arachnoid and pia are dissected to separate vessels along the surface of the spinal cord. For intramedullary lesions with compact nidi that extend to the pial surface, complete resection is feasible. For diffuse lesions with intramedullary extension, the authors utilize a technique of pial resection to devascularize the nidus and limit injury to the spinal cord (Video 97.1).9 Remaining vessels at the pial surface are cauterized (Fig. 97.4). The importance of meticulous sharp dissection and generous use of bipolar cautery cannot be overstated. During dissection of arterial feeders, particularly with the pial resection approach, it is critical to dissect the blood vessel from the pia and spinal cord to allow for controlled bipolar cauterization and sharp division (Fig. 97.5). Failure to obtain complete dissection may limit circumferential cauterization of the vessel and lead to bleeding at the time of vessel division, which may necessitate chasing the vessel into the spinal cord, increasing the likelihood of operative morbidity. Conus medullaris lesions usually present with hugely dilated venous structures. These lesions are

b

Fig. 97.4â•… (a) Sagittal T2-weighted (T2W) magnetic resonance imaging (MRI) of the cervical spine of a 12-year-old boy with sudden onset of dense tetraparesis. (b) Angiography revealed opacification of the anterior spinal artery preventing preoperative embolization. (Continued on page 812)

811

812 Section IXâ•… Vascular Disorders c

Fig. 97.4 (Continued)â•… (c) Postoperative angiogram following resection demonstrating complete obliteration of the arteriovenous malformation (AVM). (Fig. 97.4a reprinted from Velat et al9 with permission from the American Association of Neurological Surgeons. Fig. 97.4b,c reprinted with permission from Barrow Neurological Institute.)

usually treated with combined endovascular and microsurgery, accessed through a midline posterior approach. Care must be taken to preserve critical anterior spinal artery and posterior spinal artery branches because both tend to feed the lesion. For intramedullary lesions within the conus, the pial resection technique described earlier is utilized to reduce operative morbidity. Intraoperative ICG angiography is used after resection to confirm complete resection and patency of en passage vessels. Motor-evoked potentials are checked again following lesion resection. Meticulous hemostasis is obtained, followed by routine watertight dural closure with running 6–0 Prolene (Ethicon, Somerville, NJ, USA) suture.

97.3╇ Outcomes and Postoperative Course Following surgery, spinal angiography is obtained (except in rare cases of intraoperative angiography). Patients are maintained in a flat position overnight

and then are allowed to sit upright on postoperative day 1. Patients are placed under strict blood pressure control for 24 hours. Steroids are not routinely administered in the postoperative period. For patients with symptoms due to compression, vascular steal, or venous hypertension, a slow but steady recovery of function is expected. Immediate postoperative decline in motor function may be due to intraoperative injury to the anterior spinal artery or artery of Adamkiewicz. Injury may not manifest with somatosensory evoked potential changes. Loss of motor evoked potential response due to sacrifice of the anterior spinal artery generally occurs within minutes of sacrifice, and the signals do not return. Acute deterioration in the postoperative period should raise concern for postoperative hemorrhage, and immediate MRI should be obtained to confirm findings, followed by operative evacuation. Patients should be followed postoperatively because there is a risk for recurrence. Recurrence should be suspected in patients with new neurologic deterioration or failure to improve as expected after treatment.

97 â•… Surgical Management of Spinal Arteriovenous Malformations

Fig. 97.5â•… Pial resection technique for intramedullary arteriovenous malformations (AVMs). Meticulous dissection of abnormal vessels at the pial surface is performed, followed by careful coagulation and sharp division, thereby rendering the nidus remaining within the spinal cord parenchyma entirely devascularized. (Reprinted with permission from Barrow Neurological Institute.)

References ╇1. Gaupp J. Hamorrhoiden der pia mater spinalis im gebiet

des lendenmarks. Beitr Pathol 1888;2:516–518 R. The Vascular Abnormalities and Tumors of the Spinal Cord and its Membranes. London, England: Henry Kimpton; 1943 ╇3. Di Chiro G, Doppman JL, Ommaya AK. Radiology of the spinal cord arteriovenous malformations. Prog Neurol Surg 1971;4:329–354 ╇4. Riche MC, Reizine D, Melki JP, Merland JJ. Classification of spinal cord vascular malformations. Radiat Med 1985;3(1):17–24 ╇5. Borden JA, Wu JK, Shucart WA. A proposed classification for spinal and cranial dural arteriovenous fistulous malformations and implications for treatment. J Neurosurg 1995;82(2):166–179 ╇2. Wyburn-Mason

╇6. Rodesch G, Hurth M, Alvarez H, Tadié M, Lasjaunias P. Clas-

sification of spinal cord arteriovenous shunts: proposal for a reappraisal—the Bicêtre experience with 155 consecutive patients treated between 1981 and 1999. Neurosurgery 2002;51(2):374–379, discussion 379–380 ╇7. Spetzler RF, Detwiler PW, Riina HA, Porter RW. Modified classification of spinal cord vascular lesions. J Neurosurg 2002;96(2 Suppl):145–156 ╇8. Kim LJ, Spetzler RF. Classification and surgical management of spinal arteriovenous lesions: arteriovenous fistulae and arteriovenous malformations. Neurosurgery 2006;59(5 Suppl 3):S195–S201, discussion S3–S13 ╇9. Velat GJ, Chang SW, Abla AA, Albuquerque FC, McDougall CG, Spetzler RF. Microsurgical management of glomus spinal arteriovenous malformations: pial resection technique: clinical article. J Neurosurg Spine 2012;16(6):523–531

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Section X

New and Emerging Techniques Section Editor: James M. Drake

It is fitting that this final section, New and Emerging Techniques, is at the end of the book, as it represents in many ways the future of pediatric neurosurgery. Although advanced technology is represented throughout the book in the chapters on the treatment of numerous pediatric surgical disorders, this section concentrates on the technology itself and its applications. It is fair to say that the impact of advanced technology on pediatric neurosurgical care over the past several decades has been phenomenal and is only just beginning. The chapters in this section are written by the leaders of these technological advances and represent a “state-of-the-art” assessment, with a look to the near future. If one were to predict what the future of pediatric neurosurgery will look like (and such predictions are always a little dangerous), image-guided and minimally invasive neurosurgery would be strong trends, in my view. These trends are certainly well represented in the chapters in this section dealing with “Advances in Neuroimaging” and “Intraoperative Imaging.” This latter chapter also refers to the advanced technology in operating room environment, which is only going to be filled with more and more computer systems and imaging devices, with the surgeon orchestrating increasing aspects of the procedure from a console. “Interventional Neuroradiology” includes the percutaneous catheter-based treatments that have revolutionized the management of pediatric vascular disorders, such as vein of

Galen malformations, arteriovenous malformations, and the rare pediatric aneurysms. Pediatric neurosurgeons were early adopters of intraventricular endoscopy, clearly, a minimally invasive technique, and the advances in this field are reflected in the chapters “Image-Guided Surgery,” “Advances in Neuroendoscopy,” and “EndoscopeAssisted Microsurgery.” The “Image-Guided Surgery” chapter also represents another probable trend: the integration of advanced technologies, such as endoscopy and image guidance, to leverage the advantages of both. The chapter on “Laser Ablation for Deep Brain Lesions” is a further example of the integration of technologies. Thermal and laser-ablation technologies for the brain have been available for decades, but the ability to detect temperature change in the brain on MRI changed this from a relatively uncontrolled and imprecise process, to a technique of realtime imaging and monitoring with extraordinary precision, with the applications of this integrated technique only beginning to be realized. The final chapter on “Techniques for Limiting Blood Loss” is perhaps a fitting reminder that in the midst of all the advanced machinery described previously, one should not forget the simpler methodologies and attention to surgical detail that can also have a major impact on positive patient outcomes. Not discussed in this section—as they are still in the experimental stage or on the bench or drawing board—are technologies such as robotics, nano-

816 Section Xâ•… New And Emerging Techniques technology, viral vectors stem cell therapy, . . . and the list goes on. Stay tuned; they are coming and will be exciting. It will also be paramount, as outlined in these chapters, for pediatric neurosurgeons to carefully evaluate new technologies, embrace

them appropriately, be on the lookout for unintended consequences and adverse outcomes, and to advocate for technology that improves the health and quality of pediatric neurosurgical patients worldwide.

98

Advances in Neuroimaging Edward Yang and Caroline D. Robson

98.1╇Background Modern neuroimaging techniques have transformed pediatric neurosurgical practice by making detailed anatomical information routinely available prior to surgery and allowing precise intraoperative navigation. In this chapter, the authors briefly review some of the recent advances that are extending the reach of imaging and equipping neurosurgeons with greater information prior to entering the operating room, in some cases obviating the need for invasive diagnostic procedures. Neuroimaging seeks to answer clinical questions with the greatest possible certainty in the shortest possible time, but this goal involves trade-offs when considering the best imaging modality. Because it depicts brain and spinal cord abnormalities with far greater detail and contrast than computed tomography (CT), magnetic resonance imaging (MRI) is usually the modality of choice for most patients and has the obvious benefit of avoiding ionizing radiation. However, since CT is faster to arrange and perform, it remains the preferred modality for acutely ill patients requiring immediate answers regarding potential mass effect or hemorrhage, particularly in the trauma setting when osseous abnormalities are of concern. CT also remains the mainstay of imaging for patients with implanted hardware or foreign bodies that are not MRI compatible or in some cases have unknown MRI compatibility (e.g., aneurysm clip placed 20 years ago at an outside institution). Nevertheless, it should be noted that many adult institutions have begun defining safety guidelines for MRI with devices such as implantable cardioverter defibrillators,1 and similar guidelines may be anticipated in children’s hospitals, potentially increasing access to MRI for patients with these implants. More recently, CT has become favored over MRI for patients with renal insufficiency requiring a contrast-enhanced examination (e.g., contrast-enhanced angiography). Due to awareness of the potentially fatal complication of nephrogenic systemic fibrosis

in renal failure patients exposed to gadolinium, CT (followed by dialysis) is generally preferable to MRI for this population.

98.2╇ Procedure Detail and Preparation Over the past decade, the number of children requiring sedation/anesthesia for imaging has dramatically decreased due to many advances. In the very young age group (typically, less than 6 months old), it is now often possible to acquire diagnostic images with use of preprocedural feeding and infant immobilizer/swaddling devices. Although some coordination is required between nursing and technologists, it has eliminated the need for sedation in many infants and expanded the range of patients in whom imaging is considered. For older patients, MRI-compatible video and audio equipment allow pleasant distraction by music or movies, increasing the likelihood of a successful examination without sedation. Whereas occasionally MRI interference is experienced from the video goggles, their use does not prevent acquisition of a diagnostic examination. The increasing use of child life specialists has also led to better patient preparation and cooperation for lengthier examinations. Together, these interventions reliably facilitate successful imaging without sedation in cooperative patients as young as age 6 years, particularly when used with new motionreduction MRI pulse sequences.2 Therefore, the primary age group in need of sedation is currently the 6-month to 6-year age group, although selected patients as young as age 4 years can be offered the opportunity to attempt MRI without sedation, and even younger patients to try CT. As one would expect, imaging equipment has dramatically improved over the past decade. Of particular relevance to neurosurgery, 3 Tesla (3T) MRI machines have become available in almost all large

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818 Section Xâ•… New And Emerging Techniques medical centers, in some cases entirely supplanting older 1.5T instruments. When paired with multichannel head coils (e.g., 32 channels), parallel imaging techniques, and new imaging sequences (see following paragraphs), these higher field strength systems provide vastly improved resolution, decreased image noise, and upgraded soft tissue contrast, relative to older hardware.3 Their greater sensitivity also allows use of fewer averaged images to obtain quality studies, potentially shortening examination times. Whereas many newer sequences can be performed on older 1.5T instruments, certain indications mandate use of 3T systems in the authors’ experience: surgical epilepsy evaluations, cranial nerve evaluations, magnetic resonance angiography (MRA), perfusion imaging arterial spin labeling (ASL), and magnetic resonance spectroscopy (MRS). Intraoperative MRI systems allow assessment of resection adequacy prior to closing and feedback on progress of operations with small, exposed surgical fields (e.g., endoscopic surgery). In the authors’ experience, the findings on the intraoperative MRI frequently alter surgical decision making and are well worth the logistical complexities associated with using an MRI in an operating room. Another fundamental change in neuroimaging over the past 10 years is the wide availability of isotropic imaging, for both CT and MRI. Simply stated, with “isotropic” acquisitions, all imaged voxels have nearly the same dimensions in all planes, typically 1

a

mm or less. As a result, the source data can be manipulated in arbitrary directions (coronal, axial, sagittal, and oblique) or viewed as three-dimensional models to better depict abnormalities. Although originally limited to applications like MRA, isotropic data can currently be acquired for a wide variety of MRI sequences, including T1-weighted (spoiled gradient echo [SPGR], magnetization-prepared rapid acquisition gradient echo [MPRAGE]), T2-weighted (T2 SPACE, CUBE, constructive interference steady state [CISS], fast imaging employing steady state acquisition [FIESTA]), and fluid-attenuated inversion recovery (FLAIR) imaging sequences. The isotropic T1-weighted sequences are useful for anatomical depiction of the cortex and gray-white mater junction. The more heavily T2-weighted sequences (e.g., T2 SPACE, FIESTA, or CISS) are utilized chiefly for their myelographic effect. Common applications of the so-called myelographic sequences include detection of tiny nonenhancing tumor implants, delineation of cyst walls and internal septae, and assessment of cranial nerve abnormalities (Fig. 98.1). CT scans are now also typically acquired as isotropic volumes, even for axial brain CTs (including portable CTs), then reconstructed into the desired plane. With the skillful manipulation of isotropic data in a program like Vitrea/TeraRecon/Visage, findings that were previously difficult to see directly become obvious (Fig.€98.2). Given the large number of pediatric neurosurgical patients with shunted hydrocephalus, much atten-

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Fig. 98.1â•… Applications of high-resolution myelographic sequences. (a) A 13-year-old adolescent girl with intermittent headache and vomiting. Sagittal T2 SPACE magnetic resonance imaging (MRI) shows an arachnoid cyst within the inferior fourth ventricle obstructing the foramen of Magendie. (b,c) Pineal region teratoma with disseminated tumor fragments. Whereas (b) the coronal T2 image appears unremarkable, (c) the coronal constructive interference steady state (CISS) images demonstrate subependymal tumor nodules (arrow).

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Fig. 98.2â•… Advantages of postprocessing isotropic imaging data. (a–c) A 15-year-old adolescent boy with endocarditis and acute left-sided weakness. (a) Axial computed tomography (CT) demonstrates hypodensity in the right insula and lentiform nuclei (arrows), (b) indicating acute infarct. (arrows) Thick-section sagittal maximum intensity projection (MIP) images of computed tomography angiography (CTA) data delineate truncation of right middle cerebral artery (MCA) branches (c) not seen on the contralateral side. (d–f) 14-year-old adolescent boy with escalating headache and new right sixth cranial nerve palsy. (d) Noncontrast CT shows a lobulated structure indenting the suprasellar cistern from the right (arrow). (e) Magnetic resonance angiography (MRA) shows flowrelated enhancement in this structure. (f) Surface rendering of the MRA data from superior perspective mirror image demonstrates a giant supraclinoid aneurysm incorporating the posterior communicating artery origin. (Continued on page 820)

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Fig. 98.2 (Continued)â•… (g,h) A 4-month-old with fall. (g) Axial CT shows a combination of sutures and an apparently comminuted left skull fracture (arrows). (h) The three-dimensional (3D) surface rendering documents only a single irregular fracture (arrow) and its relationship to the lambdoid suture.

tion has appropriately focused on reducing cumulative radiation dose in this population.4 Currently, the majority of these patients (and increasing numbers of arachnoid cyst and extra-axial collection patients) in the authors’ center are evaluated with rapid MRI sequences, known as single shot fast spin echo (SSFSE or HASTE, depending on manufacturer), that are priced equivalent to a CT of the head. Unlike a typical MRI, these rapid MRI sequences acquire an entire image slice in approximately 1 second, making it feasible to quickly image all but the most uncooperative children without sedation. Although it is true that most programmable shunts have a certain degree of MRI susceptibility artifact, this artifact usually does not prevent a diagnostic examination. One concern with SSFSE studies is that their relatively poor contrast can obscure findings that require higher image quality, such as parenchymal changes, sinus thrombosis, and small collections.5 Therefore, the authors image selected patients with extended echo train length T2 sequences that provide similar detail to a normal axial T2 sequence with imaging duration between an SSFSE and a conventional T2 study. Whereas “vent check” MRIs cannot be performed as readily as CT, the emergency room is generally willing to wait 1 or 2 hours to obtain an MRI, in order to avoid disrupting the existing schedule. Where MRI is unavailable, very low-dose CT techniques (e.g., with techniques such as

iterative reconstruction or dose modulation) provide a reasonable alternative. Perfusion techniques have become widespread in adult neuroradiology over the last decade,6 but the same cannot be said for pediatric neuroimaging. One practical impediment to pediatric perfusion imaging has been the difficulty of obtaining wide-bore intravenous access (preferably 18 to 20 gauge) necessary for the most widespread contrast perfusion technique, dynamic susceptibility contrast (DSC) perfusion MRI. Nonetheless, the trouble of obtaining DSC data is well worth it in selected cases, for example, suspected radiation necrosis or pseudoprogression (Fig. 98.3). Also, contrast-free perfusion techniques (namely, ASL) are now widely available and have expanded the number of instances where cerebral blood flow can be measured.7 Although not as well studied as DSC, ASL has been reported to correlate well with World Health Organization (WHO) grades in adult tumors.8 Caution is required in extrapolating adult tumor perfusion criteria to pilocytic astrocytomas because the perfusion characteristics can be unpredictable; however, ASL can be helpful in suggesting a higher grade tumor in cases where conventional imaging points away from a pilocytic astrocytoma (Fig. 98.4a–f). ASL also has utility in evaluation of neurovascular pathology, such as acute stroke and moyamoya disease (Fig. 98.4g–h).9

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Fig. 98.3â•… Dynamic susceptibility perfusion imaging applied to pseudoprogression. (a–c) Axial (a) T2 and postcontrast (b) T1 images demonstrate an enhancing left thalamic mass in a 6-year-old child presenting with worsening handwriting. (c) The relative cerebral blood volume (rCBV) map indicated elevated blood volume of more than two times the contralateral thalamus, consistent with a high-grade glioma. Glioblastoma found at biopsy. (d–f) Radiation/Temodar concluded, and 6 weeks later there was increased edema on (d) T2 and a new enhancing mass anterior to (e) the primary lesion, concerning for progression through treatment. However, (f) the rCBV map showed depressed cerebral blood volume in the new site of enhancement (arrow), consistent with pseudoprogression. Area of enhancement anteriorly subsided and area of primary tumor remained stable over the next 6 months.

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Fig. 98.4â•… Applications of arterial spin labeled perfusion imaging. (a,b) Anaplastic astrocytoma (World Health Organization [WHO] grade 3). (a) Axial fluid-attenuated inversion recovery (FLAIR) and (b) arterial spin labeling (ASL) demonstrate markedly elevated cerebral blood flow (CBF) in a bithalamic lesion, favoring high-grade tumor. (c,d) Supratentorial ependymoma (WHO grade II). Mass on axial (c) T2 had depressed (d) CBF, suggesting a lower-grade lesion. (e,f) A cystic cavitated juvenile pilocytic astrocytoma demonstrates peripheral enhancement on the axial (e) T1 postcontrast images but has misleadingly high CBF on (f, arrow) ASL perfusion imaging. (g,h) Moyamoya patient with severe anterior and posterior circulation steno-occlusive disease on an axial (g) magnetic resonance angiography (MRA) maximum intensity projection (MIP) has retained ASL in the basal cisterns and decreased label in (h, arrows) the brain parenchyma on ASL due to delayed transit through proliferative collaterals.

Originally implemented as a tool for detecting infarctions and intracranial abscess, diffusionweighted imaging (DWI) techniques have since evolved into a versatile toolkit for analyzing the microstructural properties of many different tissues. DWI imaging is now routinely used for characterization of new mass lesions based on their diffusion properties. For example, DWI can be used to differentiate a spinal epidermoid from an arachnoid cyst (Fig. 98.5). Additionally, postprocessing techniques can reconstruct brain DWI data acquired with at least six gradient directions into white-matter fiber tracts, “tractography.”10 These tractography techniques can prove very valuable to neurosurgical planning by making explicit the relationship between major

white-matter bundles, a resection site, and a planned surgical tract (Fig. 98.6). Gradient echo (GRE) T2* weighted sequences have long been used to detect local disturbances in magnetic susceptibility from mineralization and blood products (intracellular deoxyhemoglobin and hemosiderin). Over the last 5 to 10 years, an acquisition and postprocessing technique known as susceptibility-weighted imaging (SWI) has been developed that greatly exaggerates this T2* effect.11 As a result, venous anatomy can be seen in great detail without contrast (Fig. 98.7a–c), and sites of hemosiderin deposition become far more obvious than with traditional GRE techniques (Fig. 98.7d–g). Minimum intensity projection (MinIP) views collapse the find-

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Fig. 98.5â•… Tissue characterization using diffusion-weighted imaging (DWI). Young girl with previously excised thoracic dermal sinus and new lower extremity weakness. (a) Sagittal T2-weighted image demonstrates an intramedullary mass with restricted diffusion on (b) DWI and (c) apparent diffusion coefficient (ADC) sequences, consistent with an epidermoid cyst.

ings of several slabs into one and make these abnormalities particularly striking. Over the last 10 years, preoperative functional MRI (fMRI) has been increasingly performed for patients requiring resection of lesions abutting speech centers, motor cortex, or the visual system.12 Whereas acquiring such data is fairly straightforward in a cooperative adult patient, it can be difficult to achieve optimal cooperation in very young patients. In these instances, passive activation protocols can be performed to activate peri-Rolandic cortex. However, the authors’ hospital’s functional MRI service has had success in obtaining awake-fMRI data in patients as young as age 6 years (Fig. 98.8).

98.3╇ Outcomes and Postoperative Course The postprocedural course is expected to be uneventful for a typical imaging examination. However, there are some key steps a pediatric neuroradiologist must take to optimize the value of the imaging study and to ensure the child does not needlessly return to the radiology department, particularly if the patient is under sedation. These steps include protocoling the highest value sequences early in the study (e.g., diffusion first in a possible stroke), monitoring the study for needed protocol modifications (e.g., surgical navigation sequences and postcontrast imaging in the

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Fig. 98.6â•… Diffusion tractography for treatment planning. A 5-year-old boy presented with a left parietal arteriovenous malformation (AVM), here shown using axial (a,b) T2-weighted images. (c) Diffusion tractography was performed with selection of the superior optic radiation (green) and corticospinal tracts (purple). As detailed in the cut-away axial/sagittal composite image, the AVM is located posterior to the corticospinal tract and superomedial to the optic radiations.

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Fig. 98.7â•… Susceptibility-weighted imaging (SWI). (a–c) Use of SWI minimum intensity projection (MinIP) images to visualize venous anatomy. Comparison of axial (a) T2, axial (b) T2* gradient echo (GRE), and (c) MinIP views of the SWI data illustrates the improved visibility of a right frontal developmental venous anomaly (DVA) (arrow) using SWI MinIP images.

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Fig. 98.7 (Continued)â•… (d–g) Improved visibility of small cavernous malformations with SWI compared to T2* imaging. A 3-year-old girl with multiple cavernous malformations (CCM3 mutation) was evaluated by axial (d) T2, axial (e) T2* GRE, (f) SWI, and (g) SWI MinIP sequences. A moderate left temporal, a small left temporo-occipital, and a tiny right temporal (arrow) cavernous malformation are all visible in the SWI images. However, the right temporal lesion is difficult to detect on the T2* image and is not visualized on the T2 image.

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Fig. 98.8â•… Motor and language mapping functional magnetic resonance imaging (fMRI) in a 7-year-old child with enlarging right insular mass. Blood oxygenation-level dependent (BOLD) fMRI maps from an antonym-generation task are superimposed on a sagittal T1-weighted image with crosshairs over the pars opercularis for each hemisphere. The fMRI BOLD maps demonstrate activation of (a) Broca area on the left during the antonym task with no discernible activation on (b) the right side adjacent to insular tumor. Although the patient could not cooperate with instructions during the dedicated motor-activation task, the cephalic motor cortex was activated bilaterally during the antonym task (arrows), delineating relationship to the insular lesion on the right. (Case courtesy of Ralph O. Suarez, PhD, Boston Children’s Computational Radiology Laboratory.)

case of an unexpected brain tumor), and requesting relevant source data when three-dimensional (3D) modeling is anticipated (e.g., thin-section CT data for a complex fracture). Last, but not least, prompt detection of unexpected findings allows the radiologist to facilitate an evaluation in the recovery room by the referring physician, potentially minimizing family distress and waiting once the examination is completed.

References ╇1. Naehle CP, Strach K, Thomas D, et al. Magnetic resonance

imaging at 1.5-T in patients with implantable cardioverter-defibrillators. J Am Coll Cardiol 2009;54(6):549–555 ╇2. Khan JJ, Donnelly LF, Koch BL, et al. A program to decrease the need for pediatric sedation for CT and MRI. Appl Radiol 2007;2007:30–33

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826 Section X╅ New And Emerging Techniques ╇3. Dahmoush

HM, Vossough A, Roberts TP. Pediatric highfield magnetic resonance imaging. Neuroimaging Clin N Am 2012;22(2):297–313, xi ╇4. Pearce MS, Salotti JA, Little MP, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 2012;380(9840):499–505 ╇5. Rozovsky K, Ventureyra EC, Miller E. Fast-brain MRI in children is quick, without sedation, and radiation-free, but beware of limitations. J Clin Neurosci 2013;20(3):400–405 ╇6. Ferré JC, Shiroishi MS, Law M. Advanced techniques using contrast media in neuroimaging. Magn Reson Imaging Clin N Am 2012;20(4):699–713 ╇7. Deibler AR, Pollock JM, Kraft RA, Tan H, Burdette JH, Maldjian JA. Arterial spin-labeling in routine clinical practice, part 1: technique and artifacts. AJNR Am J Neuroradiol 2008;29(7):1228–1234 ╇8. Wolf RL, Wang J, Wang S, et al. Grading of CNS neoplasms using continuous arterial spin labeled perfu-

sion MR imaging at 3 Tesla. J Magn Reson Imaging 2005;22(4):475–482 ╇9. Zaharchuk G, Do HM, Marks MP, Rosenberg J, Moseley ME, Steinberg GK. Arterial spin-labeling MRI can identify the presence and intensity of collateral perfusion in patients with moyamoya disease. Stroke 2011;42(9):2485–2491 10. Yang E, Nucifora PG, Melhem ER. Diffusion MR imaging: basic principles. Neuroimaging Clin N Am 2011;21(1):1–25, vii 11. Haacke EM, Mittal S, Wu Z, Neelavalli J, Cheng YC. Susceptibility-weighted imaging: technical aspects and clinical applications, part 1. AJNR Am J Neuroradiol 2009;30(1):19–30 12. Suarez RO, Whalen S, Nelson AP, et al. Threshold-independent functional MRI determination of language dominance: a validation study against clinical gold standards. Epilepsy Behav 2009;16(2):288–297

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Intraoperative Imaging Paul Klimo Jr., David J. Daniels, and Asim F. Choudhri

99.1╇Background 99.1.1╇ Intraoperative Magnetic Resonance Imaging Because maximal cytoreductive resection is the most important predictor of overall and progression-free survival for many pediatric brain tumors, intraoperative magnetic resonance imaging (iMRI) has become an indispensable asset at numerous children’s hospitals with robust brain tumor programs. The primary advantage of the iMRI is to help children avoid undergoing additional operations.1,2 While the child is under general anesthesia and the wound is open, the surgeon can determine if the tumor has been completely resected or not. If not, the surgeon can then decide whether the remaining tumor can be safely removed. iMRI can identify complications, such as intracranial hemorrhage, that may require evacuation and can predict potential postoperative neurologic changes, such as a stroke or disruption of key tracts, with diffusion tensor imaging. All of this information is helpful when speaking with parents who are anxiously awaiting news of their child’s operation. The intraoperative scan can also replace the postoperative scan that is typically done the day after surgery. iMRI can be beneficial in other operations, such as arteriovenous malformation (AVM) resection and seizure surgery, for the same reasons. There are three main disadvantages of the iMRI: time, potential danger to patient, and cost. The iMRI requires additional operating room time for setup and patient positioning at the beginning of the operation, and then preparing for and conducting each intraoperative scan. Safety, not only for the patient but for all staff in the iMRI suite, is of utmost priority and necessitates close coordination and communication with all members of the iMRI team. Risk to the patient comes from four sources: creation of a projectile, nerve stimulation, acoustic noise, and radio-

frequency burns. Finally, cost is significant and, in some facilities, a prohibitive obstacle. With systems costing between $5 to 10 million US, not including continued maintenance expenses, this is not a technology that is purchased easily, even in high-volume programs.2 At the authors’ facility, they estimated that the savings achieved with the iMRI (i.e., as a result of reduced hospital stay, elimination of postoperative scan, and decreased early reoperation risk) would eclipse the initial capital investment after approximately 900 cases. In states with a certificateof-need (CON) requirement for MRI scanners, assigning a CON to the iMRI has an additional opportunity cost because the scan volume (and resultant clinical revenue) is less than that of an MRI scanner dedicated to diagnostic studies.

99.1.2╇ Computed Tomography One of the most popular intraoperative computed tomography (CT) scanners is the O-arm by Medtronic (Louisville, CO, USA). It is an intraoperative three-dimensional (3D) imaging system that can be used in conjunction with a stereotactic navigation system (Stealth Station S7, Medtronic). The O-arm acquires volumetric CT images with multiplanar and 3D reconstructions that can be automatically registered to the image-guidance system. O-arm technology has been used most commonly in spine surgery, allowing the surgeon to determine the trajectory of the hardware prior to implantation and its final position before closing the wound.3 Spinal instrumentation in children is challenging because the bone has smaller dimensions, may still have cartilaginous components, or may have abnormal congenital anatomy. More recently, the O-arm has found use in stereotactic, functional neurosurgical procedures.4 The authors have also used it in select shunt cases to confirm placement of the proximal catheter during shunt surgery.

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828 Section Xâ•… New And Emerging Techniques The disadvantages of the O-arm are added operative time and radiation exposure. The O-arm requires about 15 minutes per scan, much less than the iMRI. For spinal surgery, typically there are two scans—one prior to placing hardware (if the hardware is to be placed stereotactically) and one after implantation. Radiation exposure is a drawback; however, the O-arm replaces fluoroscopy, and all personnel can step out of the room when the O-arm scan is being done. The O-arm provides multiple predefined imaging protocols, depending upon the anatomical region of interest, the size of the patient, and the desired image quality. Additionally, the radiology technician may choose to increase or decrease imaging parameters, such as kVp (kilovoltage peak) and mAs (milliamperage second), depending upon the clinical requirements. The doses associated with the preset scanning protocols have been found to be well within American College of Radiology (ACR) pass/fail criteria. For techniques that are directly comparable to common diagnostic CT scans, such as abdomen, chest, and head scans done with different scanners (8, 16, 64 slices), the O-arm doses average around 20 to 30% lower than CT doses.3 Another disadvantage is cost, like the iMRI. The O-arm system currently costs approximately $680,000. The Stealth Station S7 cost varies with what software is chosen to operate the machine, which can range from $250,000 to 300,000. Thus, the total price is around $1 million.

99.1.3╇Ultrasound Intraoperative ultrasound (US) has undergone considerable improvements over the past several decades and is now considered commonplace in the operating room. Advancements have included smaller probes; availability of Doppler imaging; and improved resolution, including spatial, contrast, and temporal resolution. Its main function is localizing anatomy or lesions that are either hyperechogenic or hypoechogenic to the surrounding brain parenchyma; guiding the ventricular catheter into the ventricle; finding cystic, calcified, or hemorrhagic lesions in the brain; and in spinal surgery, to confirm the location of a syrinx, spinal cord tumor, or the conus medullaris.5–8 Some have also used it to help them decide whether to perform a bony decompression in patients with Chiari malformations.9,10 Color Doppler imaging can aid in localizing vascular structures, and spectral Doppler can differentiate arteries from veins. US has several advantages.6 First, it provides realtime image acquisition compared with conventional frameless neuronavigation systems that are based on static preoperative images, thereby overcoming tissue shifts that occur with surgical manipulation, resection, or release of cerebrospinal fluid (CSF). Of the technologies discussed here, US is the least

expensive, the easiest and quickest to set up and use, and there is no ionizing radiation. One disadvantage is image resolution: it can be difficult at times to interpret what is being projected on the screen. Therefore, at the authors’ institution they often have their neuroradiologist in the room to help them with image interpretation. Another disadvantage is that a larger burr hole is required to accommodate the probe when using it for catheter placement, if the fontanel is closed over or too small.

99.2╇ Operative Detail and Preparation 99.2.1╇ Intraoperative Magnetic Resonance Imaging The following discusses the authors’ typical iMRI case, which may differ from those in other facilities. The authors use a 3-Tesla, 70-cm bore diameter IMRIS Inc. system (Winnipeg, Manitoba, Canada), in which the scanner is housed in a shielded room adjacent to the operative (OR) suite. For the scan, the doors open and the ceiling-mounted scanner moves to the patient. The first question that the surgeon should answer prior to surgery is: What is the goal of the surgery? Is the goal to have no identifiable tumor on the intraoperative scan, or is a subtotal resection okay because of size or location? Sometimes this question cannot be fully answered preoperatively. Nonetheless, it should be asked, because it will help determine the surgeon’s mindset going into the operation and how the surgeon responds to information provided by the intraoperative scan. For example, the goal of the authors for most medulloblastomas and ependymomas is to have no residual tumor identified on the scan. For other tumors, such as craniopharyngiomas or optic pathway gliomas, the goal is debulking in order to decompress critical structures, such as the optic apparatus, or to reestablish CSF pathways, but rarely complete removal. Next, the surgeon should ask if frameless navigation will be needed. For many midline posterior fossa tumors, neuronavigation is not necessary, but for many other tumors it is beneficial. The neuronavigational (“stealth”) sequence can be done preoperatively or intraoperatively. For elective surgery, the authors often admit the child the day before to have the stealth study done. If it is done intraoperatively, the child may be positioned as if for the surgery and undergo a stealth MRI. This does add time to the case, but it improves registration accuracy because it eliminates skin shift. The child is brought into the OR suite and anesthetized. An MRI-compatible Mayfield three-pin head

99 â•… Intraoperative Imaging holder is carefully applied. All equipment that will be positioned within the magnetic field needs to be MRIcompatible. Wires cannot cross each other and there can be no skin-to-skin contact of the extremities. There are some limitations in body size and positioning. The surgical field needs to be 7 inches from the edge of the bed, so that it can be in the middle of the MRI coils (i.e., the antennae for the MRI scanner). If the surgical field is the cervical spine, the patient will need to be positioned more off the end of the table. The iMRI table has an extension that will provide additional support. If the surgical field is too high (e.g., the head is too flexed), the images will be distorted. Large patients may be too wide to fit in the bore. The bottom coil fits between the arms of the Mayfield so nothing can hang off the end of the bed, such as the patient’s arm, if a park-bench position was contemplated. Although issues with patient body habitus are rarely an insurmountable obstacle in the pediatric population, all members of the iMRI team are needed to ensure proper positioning of the patient. At this time, the authors cannot perform an iMRI-guided resection in patients who cannot tolerate having their heads fixed in pins, namely those who are very young or whose skulls are too thin due to chronic hydrocephalus because there is no way to immobilize the head and have the coil in place. An infant head frame is currently being developed. Once the patient is properly positioned (with or without registration to the neuronavigational system), the safety officer goes through the preoperative checklist. After this, the operation then proceeds as it would in a typical OR suite. The wound is prepped

a

b

and drapes are applied, followed by a “time-out” before the skin is incised. The authors use all of their regular surgical instruments; these do not have to be MRI-compatible because all of the instruments are placed outside the 5 Gauss line during the scan. Once the surgeon is at the point of needing an intraoperative scan, all ferromagnetic objects are removed from the surgical field, such as retractors and hemostats (titanium staples on the drapes are acceptable). The patient is draped with several layers and the safety officer performs another safety check. The MRI is then carefully and slowly advanced to the patient. The primary neurosurgeon and neuroradiologist review the intraoperative scan. The number of sequences performed is dependent on the preoperative lesion characteristics; however, each full intraoperative scan typically adds 1 hour to the case, including safety checks, moving the scanner into and out of the operating room, as well as scan acquisition itself. There are unique challenges when interpreting the intraoperative scan (Fig. 99.1). Air within the resection cavity may distort the image quality of the adjacent tissue, an impact that is most pronounced on gradient echo and diffusion-weighted images. Recently cauterized tissue or blood products will often appear hyperintense and linear on T1-weighted (T1W) images. If this is the second or third intraoperative scan, there may be retained contrast from the previous study. Once the images have been reviewed, the surgeon must decide whether to pursue further resection, inspect an area of concern, or start to close the wound. For cases in which neuronavigation was used, a new stealth scan can be acquired and merged

c

Fig. 99.1â•… (a) Axial T1-weighted (T1W) postgadolinium preoperative imaging through the level of the rostral pons shows a heterogeneously enhancing mixed solid and cystic high-grade lesion in the rostral pons, centered to the right of midline with partial effacement of the fourth ventricle. (b) Axial T1W postgadolinium intraoperative imaging after debulking of the lesion displays reduced lesion volume and decreased mass effect upon the fourth ventricle. (c) Using volumetric images remerged with the stereotactic scan, further resection was performed, and subsequent axial T1W imaging demonstrates evidence of gross total resection; the areas of hyperintense signal along the margins were present prior to gadolinium administration, and were felt to be related to blood products and cautery.

829

830 Section Xâ•… New And Emerging Techniques with the preoperative one in order to improve accuracy that may have been affected by brain shift.

clamped to a vertebral spinous process adjacent to the location where instrumentations are to be placed and directed at the optical camera in such a way that there is an unobstructed line of sight. If the O-arm is to be used for cranial cases, the head needs to be positioned with CT-compatible pins or headboard. At this point, the patient is draped and the O-arm is brought into the field. The O-arm system consists of a 38-inch, bore-motorized gantry attached to a moveable chassis and a digital flat panel detector (Fig. 99.2 and Fig. 99.3). The chassis is moved

99.2.2╇ Computed Tomography For spinal cases, the patient is positioned prone on a Jackson table for thoracic or lumbar cases, or on gel rolls with the head immobilized with a CT-compatible Mayfield head holder for cervical cases. The localizing fiduciary marker (dynamic reference array) is rigidly

a

b

c

d

Fig. 99.2â•… Intraoperative use of the O-arm. (a) After exposure of the desired level(s) through either a standard open or minimally invasive approach, the patient is draped and the reference array is secured in such a way that there is an unobstructed line of sight to the optical camera. The O-arm is brought in and the gantry closed. The images are then acquired and sent to the workstation. (b) The “tracked” (note the reflective balls) instruments are used to precisely place the pedicle screw. With this technology, the surgeon learns to split his focus between the images on the screen and the exposed anatomy in the wound. (c) Case example: the preoperative sagittal T2-weighted (T2W) magnetic resonance imaging (MRI) in this 15-year-old adolescent boy shows an os odontoideum anomaly, pannus behind the odontoid, and a focal area of myelomalacia from repeated microtrauma. (d) A screen shot shows the position of the C1 lateral mass and C2 pars screws in each plane, as well as in a three-dimensional (3D) model.

99 â•… Intraoperative Imaging a

b

c

Fig. 99.3â•… (a) Axial computed tomography (CT) image through the level of the body of the lateral ventricles in a 14-year-old adolescent boy with pseudotumor cerebri. (b) While the O-arm CT scan is optimized for osseous detail, the position of the catheter tip could be identified within the posterior body of the right lateral ventricle. (c) Postoperative CT scan through a similar level confirms the findings from the O-arm scan.

manually, while the motorized gantry opens to a C-position for lateral patient access. The chassis is positioned in line with the surgical field and the gantry is then closed. For a 3D image acquisition, the O-arm rotates 360 degrees, generating 391 images in 13 seconds. The scan data generated are then reconstructed into a 3D image with a resolution of 512 × 512 × 192 pixels, in a 15 × 20-cm cylindrical volume, with 0.83-mm isotropic voxels. The reconstructed image is displayed on the 30-inch digital flat screen. These preimplantation CT scan data are then sent to a navigation guidance computer (Stealth Station S7). Navigation accuracy is assessed by touching bony surface landmarks in the surgical field with the guide probe. Using instruments with reflective spheres, such as gearshifts for lumbar and thoracic pedicle screws or a manual drill for cervical screws, the navigation system generates real-time 3D CT and two-dimensional (2D) fluoroscopic images that allow the surgeon to determine the starting point, trajectory, and length of the tract. A small ball-tip probe is used to palpate the tract to make sure there are no breaches; placement of the screw follows. Once all screws are placed, a postimplantation CT scan is performed and is carefully inspected to ensure that the hardware is in a proper position. For long multilevel fusions, it is important to repeatedly assess the accuracy of the system by touching bony surface landmarks in the area where hardware is to be implanted. The further away one gets from the reference frame, the greater the risk that the accuracy

may “drift,” which may require repositioning of the reference array closer and acquisition of a new scan.

99.2.3╇Ultrasound No specific preoperative planning is necessary. A high-quality 2D US machine with various probe sizes is required. The operative window (craniotomy, burr hole, laminectomy) needs to be large enough to accommodate the US probe. There cannot be an air gap between the probe and the soft tissues being evaluated, which are typically overcome by saline irrigation of the surgical site. Accordingly, the site of parenchymal contact for the probe must be in a position that can be filled with saline. The orientation of the probe should be noted to determine right-left orientation. As previously mentioned, interpretation of the images can be challenging, so it is helpful to have a knowledgeable neuroradiologist in the OR suite for real-time interpretation (Fig.€99.4).

99.3╇ Outcome and Postoperative Course There are no specific postoperative considerations for any of these intraoperative imaging modalities.

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832 Section Xâ•… New And Emerging Techniques a

b

c

d

Fig. 99.4â•… (a) Sagittal T2-weighted (T2W) image in an 8-year-old boy with a mixed solid and cystic intramedullary lesion of the midthoracic cord. (b) Transversely oriented intraoperative ultrasound (US) image was used to localize the lesion, with the walls of the cystic component evident (arrowheads). (c) This was employed to center the dural opening. (d) After collapse of the cyst and resection of portions of the solid tissue, longitudinally oriented US was performed to show the periphery of the tumor (arrowhead) and its relationship to the resection cavity (arrow).

99â•… Intraoperative Imaging

References ╇1. Avula

S, Pettorini B, Abernethy L, Pizer B, Williams D, Mallucci C. High field strength magnetic resonance imaging in paediatric brain tumour surgery—its role in prevention of early repeat resections. Childs Nerv Syst 2013;29(10):1843–1850 ╇2. Shah MN, Leonard JR, Inder G, et al. Intraoperative magnetic resonance imaging to reduce the rate of early reoperation for lesion resection in pediatric neurosurgery. J Neurosurg Pediatr 2012;9(3):259–264 ╇3. Van de Kelft E, Costa F, Van der Planken D, Schils F. A prospective multicenter registry on the accuracy of pedicle screw placement in the thoracic, lumbar, and sacral levels with the use of the O-arm imaging system and StealthStation navigation. Spine 2012;37(25):E1580–E1587 ╇4. Shahlaie K, Larson PS, Starr PA. Intraoperative computed tomography for deep brain stimulation surgery: technique and accuracy assessment. Neurosurgery 2011; 68(1 Suppl Operative):114–124, discussion 124 ╇5. El Beltagy MA, Atteya MM. The benefits of navigated intraoperative ultrasonography during resection of fourth ventricular tumors in children. Childs Nerv Syst 2013

╇6. Padayachy

LC, Fieggen G. Intraoperative ultrasoundguidance in neurosurgery. World Neurosurg 2004; 82(3-4): e409-411 ╇7. Selbekk T, Jakola AS, Solheim O, et al. Ultrasound imaging in neurosurgery: approaches to minimize surgically induced image artefacts for improved resection control. Acta Neurochir (Wien) 2013;155(6):973–980 ╇8. Whitehead WE, Riva-Cambrin J, Wellons JC III, et al; Hydrocephalus Clinical Research Network. No significant improvement in the rate of accurate ventricular catheter location using ultrasound-guided CSF shunt insertion: a prospective, controlled study by the Hydrocephalus Clinical Research Network. J Neurosurg Pediatr 2013;12(6):565–574 ╇9. McGirt MJ, Attenello FJ, Datoo G, et al. Intraoperative ultrasonography as a guide to patient selection for duraplasty after suboccipital decompression in children with Chiari malformation type I. J Neurosurg Pediatr 2008;2(1):52–57 10. Yeh DD, Koch B, Crone KR. Intraoperative ultrasonography used to determine the extent of surgery necessary during posterior fossa decompression in children with Chiari malformation type I. J Neurosurg 2006;105(1 Suppl):26–32

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100

Interventional Neuroradiology Bradley A. Gross, Michael J. Ellis, and Darren Orbach

100.1╇Background 100.1.1╇Indications Diagnostic neuroangiography can be employed to address a panoply of questions regarding cerebrovascular diseases. Most commonly in children, it is used in the work-up of moyamoya/cerebrovascular ischemic disease and in the evaluation of spontaneous intracranial hemorrhage for a suspected arteriovenous lesion or aneurysm. Interventional procedures cover a wide spectrum, as underscored by the case types summarized in Table 100.1―the remainder of this chapter focuses on arteriovenous shunt and aneurysm embolization. Arteriovenous lesions include vein of Galen malformations, arteriovenous fistulae, and arteriovenous malformations (AVMs). Vein of Galen malformations have an aggressive natural history, ranging from cardiac failure in neonates to diffuse bihemispheric brain injury (likely on the basis of sustained Table 100.1â•… A total of 612 consecutive pediatric neurointerventional procedures Case type

No.

Diagnostic angiography

375

Arteriovenous lesion embolization

168

Tumor embolization

21

Aneurysm embolization

16

Retinoblastoma intra-arterial chemotherapy

15

Other case typesa

17

Note: Procedures were performed by the senior author (DBO) at Boston Children’s Hospital, Boston, MA. a Other case types include stroke/venous thrombolysis, spasmolysis, and balloon test occlusion.

834

venous hypertension) in infants and children; therefore, almost all cases in which there has not already been severe irreversible injury should undergo treatment.1 Arteriovenous fistulae causing hemorrhage, venous hypertension, or congestive heart failure or those that have recruited leptomeningeal venous drainage should be treated, in order to avoid the risk of progressive intracranial/venous hypertension or new hemorrhage. Hemorrhagic AVMs or those with associated aneurysms, deep venous drainage, or a deep location merit treatment.2 Endovascular treatment serves as a crucial adjunctive measure prior to surgical resection or radiotherapy of brain AVMs in well-selected cases. Whereas small AVMs in noneloquent territory may be managed at lowest risk with surgery alone, embolization of large AVMs that are poor candidates for subsequent resection or radiosurgery, in the name of palliation alone, remains as yet of unproven benefit. Although a rare entity in children, virtually all symptomatic or ruptured aneurysms require treatment, in order to eliminate symptoms and ameliorate the relatively high risk of short-term rerupture. Unruptured aneurysms more than 7 mm, those in higher-risk locations (posterior circulation, anterior or posterior communicating artery), or those with concerning morphological features (daughter dome, enlargement on serial imaging, dissecting) also generally merit treatment.

100.1.2╇Goals For vein of Galen malformations, the operational goal of endovascular therapy is diminution of flow through the malformation, either to completion or to the extent safely achievable. Depending on clinical presentation, the therapeutic goal is to alleviate or stabilize symptoms or signs that have already accrued (e.g., hydrocephalus, increased intracranial pressure [ICP], cardiac overload) or to prevent neurologic catastrophe (e.g., global parenchymal volume loss with cere-

100â•… Interventional Neuroradiology bral calcifications and profound neurodevelopmental impairment). This is often achieved via staged transarterial embolization. For nidal AVMs, treatment must be individualized and may include targeted exclusion of high-risk features, such as ruptured associated aneurysms of venous pouches, and elimination of AVM fistulous components in preparation for radiosurgery, or the elimination of deep arterial pedicles prior to definitive surgical resection. For aneurysms and arteriovenous fistulae, the goal of endovascular therapy should be radiographic obliteration of the lesion. In the case of arteriovenous fistulae, embolic material should be deposited at/reach the fistula point in order to mitigate the risk of recanalization.3

100.1.3╇ Alternate Procedures Several studies have resulted in class I evidence demonstrating superior clinical outcomes after endovascular coiling of selected cerebral aneurysms, as compared to open microsurgical clipping, in adults.4 Although improved durability of clipping as compared to coiling is a worthwhile consideration in pediatric aneurysm cases, in nearly every case, potential endovascular and open surgical approaches are both discussed by the authors’ group; if a permanent endovascular treatment appears to be achievable, that would usually be the first choice. However, in the case of very wide-necked ruptured aneurysms not amenable to balloon-assisted techniques, or for morphologically complex aneurysms with critical arterial branches involved, the authors usually adopt open microsurgical approaches (Fig. 100.1). Although class I evidence demonstrating the superiority of endovascular embolization of arteriovenous fistulae, as compared to surgical disconnection, does not exist, in accord with the practice at most tertiary adult cerebrovascular centers, the authors also employ an “embolize first” policy for these lesions, with the goal of angiographic cure. However, in cases where the fistulous point may not be reached due to tortuosity or the small size of arterial feeding pedicles, open surgical disconnection may be a viable alternative. On the other hand, in the case of vein of Galen malformations, surgical treatment is generally not considered, owing to prohibitive anticipated microsurgical morbidity in this already medically high-risk population. As mentioned earlier, in the case of AVMs, endovascular therapy is viewed most often as adjunctive to, rather than an alternative to, microsurgical treatment.

100.1.4╇Advantages As compared to potential microsurgical alternatives, endovascular approaches are far less invasive, obviating the need for large incisions, a craniotomy, and

Fig. 100.1â•… This wide-necked, ruptured posterior inferior cerebellar artery (PICA) aneurysm (arrow) was not amenable to endovascular coiling without sacrifice of the parent vessel; it was clipped uneventfully via a far lateral transcondylar approach.

associated blood loss and infectious risks. The vasospastic effects of vessel manipulation are lowered. In addition, with endovascular approaches, the operator has immediate feedback with regard to lesional treatment because a diagnostic angiogram can be, and is typically, performed immediately, to evaluate for obliteration of the lesion or decreased flow. Most importantly, mounting evidence from the adult literature has reinforced clinical outcome benefits of endovascular approaches as compared to microsurgical treatments, particularly in the case of cerebral aneurysms. In the case of AVMs, although embolization is not an advantageous alternative to surgical treatment, it may dramatically lower the risk of potentially lethal intraoperative blood loss. In addition, the glue or Onyx (ev3 Neurovascular, Irvine, CA, USA) cast can provide invaluable intraprocedural angioarchitectural guidance for the neurosurgeon, serving as a visible “road map” to the lesion.

100.1.5╇Contraindications/ Disadvantages Endovascular approaches to cerebrovascular disease may be limited by maximal allowable contrast doses (4 mL/kg for routine cases, up to 7 mL/kg for urgent or emergent procedures), radiation exposure, the caliber or tortuosity of access vessels in young children, and, theoretically, the long-term risk of recanalization after

835

836 Section Xâ•… New And Emerging Techniques coil embolization. The limitations of vascular access in infants and young children are active areas of interest to the authors, as creativity in access methods and the usage of triaxial systems may surmount these previously perceived limitations, as illustrated further on in this chapter.5

100.2╇ Operative Detail and Preparation 100.2.1╇ Preoperative Planning and Special Equipment Preoperative planning begins with a careful history and physical examination of the patient, evaluating not only the neurologic status, but also medical history and family history for pertinent issues, such as coagulopathy or connective tissue disorder. Physical examination should also include evaluation of the femoral artery and peripheral pulses. Infants may undergo a swift preoperative ultrasound to evaluate the diameter of anticipated access vessels. A thorough review of available noninvasive imaging is crucial. If neck/arch imaging is available, the anatomy of the arch and associated vessels should be carefully studied to evaluate for anatomical variants. Given the limitations on acceptable contrast and radiation

a

doses in young children, it behooves the pediatric neurointerventionalist to maximize information accrual from noninvasive vascular imaging, ideally magnetic resonance imaging (MRI). As a means to limit radiation dosages, dedicated pediatric radiation protocols are a valuable adjunct, along with a biplane table on which image-hold techniques can be maximized, such as superimposing new fields of view onto stored images as the table is moved, without requiring live fluoroscopy. Contrast dose may be limited by employing 50% or even 33% contrast in working syringes. The authors employ general endotracheal anesthesia in all cases. All lines are connected to heparinized saline bags that are maintained on continuous drips; a flow regulator is placed on the sheath drip to avoid fluid overload.

100.2.2╇ Expert Suggestions/Comments Infants are generally limited to 4 French (4F) access systems, whereas young children can usually accommodate 5F systems for embolizations. Despite these limitations, the authors have been able to perform both complex coiling and glue embolizations with adjunct devices, such as balloon-catheter assistance, via 4F systems, employing the 4F Vert (Cook Medical, Bloomington, IN, USA) diagnostic catheter as a guide catheter or a 4F shuttle sheath (Cook Medical) (Fig.€100.2 and Fig. 100.3).5

b

c

Fig. 100.2â•… Embolization of a vein of Galen malformation in an ex 28-week-old premature infant with refractory pulmonary hypertension, embolized at 35 weeks’ gestational age. The infant’s femoral arteries measured less than 1.2 mm in diameter and access was thus achieved via the right axillary artery. A 4 French (4F) Vert catheter (Cook Medical, Bloomington, IN, USA) was advanced into the right vertebral artery and an angiographic run was carried out. (a) Frontal view. This demonstrated a choroidal-type vein of Galen malformation. The guide catheter was advanced further to the proximal V3 segment and multiple pedicles were embolized with detachable platinum coils, with significant reduction in flow. (b) Frontal view of super-selective run of a P2 pedicle prior to embolization. (c) Skull X-ray demonstrating deposited coils.

100â•… Interventional Neuroradiology b

a

c

Fig. 100.3â•… Embolization of a pial arteriovenous fistula in a 5-month-old infant. (a) This lateral projection of the right internal carotid artery (ICA) injection via a 4 French (4F) shuttle sheath (Cook Medical, Bloomington, IN, USA) demonstrates rapid arteriovenous shunting through the superior cerebellar arteries bilaterally. An Ascent balloon microcatheter (Codman & Shurtleff, Raynham, MA, USA) was navigated into the left superior cerebellar artery via the right posterior communicating artery, and this super-selective run confirms flow directed into the fistula without parenchymal blush. (b) Lateral view. After balloon-assisted coil embolization, this control run shows markedly reduced flow into the fistula. (c) Lateral view of right ICA injection.

When 5F access is feasible, the authors often use a 5F Envoy guide catheter (Codman & Shurtleff, Raynham, MA, USA) or the 0.058-inch Navien guide catheter (ev3 Neurovascular). Relatively distal access can be achieved with the Navien, originally designed for use in triaxial systems (Fig. 100.4). In young children and infants, the authors have been able to advance inter-

a

mediate catheters over the glidewire over the aortic arch to select vessels without the need for an exchange. An example of balloon-assisted coiling of a basilar sidewall aneurysm using two 0.058 Navien catheters, one in each vertebral artery, is shown in Fig. 100.4. In addition, triaxial systems can be based on a 5F Envoy or Navien guide catheter and are described below.

b

c

Fig. 100.4â•… An 11-year-old child with sickle cell disease and a rapidly enlarging left basilar-superior cerebellar artery aneurysm. Bilateral common femoral artery access was obtained and Navien 0.058-inch intermediate catheters (ev3 Neurovascular, Irvine, CA, USA) were navigated through each sheath into the right and left V4 segments of the vertebral arteries. A dual-lumen Ascent balloon catheter (Codman & Shurtleff, Raynham, MA, USA) was advanced through the 5 French (5F) Navien catheter (ev3 Neurovascular) in the right V4 into the left P1 segment, and a microcatheter was advanced into the aneurysm via the Navien catheter (ev3 Neurovascular) in the left V4. (a) Frontal view of a control angiographic run via the left V4. With balloon assistance, the aneurysm was coiled and occluded. (b) Frontal view of road map image. (c) Frontal view of control angiographic run after coiling.

837

838 Section Xâ•… New And Emerging Techniques nontarget embolization. Very close attention is paid to the course of the embolic material as it is deployed, ensuring that it does not occlude venous outflow in the case of AVM, and also ensuring it is not refluxing into proximal branches. A particular advantage of triaxial systems is that subsequent control angiographic runs may then be swiftly carried out via the intermediate catheter, all the while preserving distal access to allow for swifter super-selective catheterization of a new pedicle with a new microcatheter (Fig. 100.5). Pedicles that are too small for 0.010-inch Onyx-compatible microcatheters may still be amenable to the Magic flow-directed 0.008-inch microcatheter (BALT Extrusion, Montmorency, France) and thus NBCA embolization. Although the authors typically employ standard coiling techniques for cerebral aneurysms, they do perform glue embolization of complex, dissecting aneurysms where parent vessel sacrifice is permissible (Fig. 100.6).

100.2.3╇ Operative Nuances Access is achieved with single-hole puncture using a micropuncture kit. Infants and younger children may pose a challenge due to small vessel caliber― adjunctive ultrasound is thus particularly useful as a means to expedite safe and successful intra-arterial access. Unless absolutely contraindicated, after placement of the sheath, the authors favor heparinizing all infants and young children, prior to cerebral angiography or intervention, to an activated clotting time of 20 to 350. In infants necessitating 4F access, the 4F Vert catheter (Cook Medical) can be advanced over the aortic arch to select the parent vessel of the embolization target (Fig. 100.3). Alternatively, an exchange-length glidewire can be navigated into the external carotid artery for advancement of a 4F shuttle sheath (Cook Medical) into the carotid artery (Fig. 100.2). If a 5F system may be employed, the 0.058inch Navien catheter (ev3 Neurovascular) can serve as an exceptional guide catheter. Aneurysms may then be accessed with a microcatheter for coiling and arteriovenous shunt pedicles may be accessed for Onyx (ev3 Neurovascular) or N-butyl-cyanoacrylate (NBCA) glue embolization (the former assuming the use of a dimethyl sulfoxide [DMSO]-compatible microcatheter). For AVM embolization, the authors often employ triaxial systems to allow for better distal access and support. Through the intermediate catheter, the microcatheter can be advanced into the pedicle of choice and a super-selective angiographic run carried out. This should confirm flow proceeding directly into the arteriovenous shunt prior to the deposition of embolic material to mitigate the risk of

a

100.2.4╇ Avoidance of Pitfalls Of crucial importance during embolization is the careful study of the super-selective pedicle angiogram prior to depositing embolic material, to ensure that functional territory is not placed at risk (Fig.€100.2b and Fig. 100.3b). In the case of arteriovenous shunts, all flow should be directed to the lesion. Anatomical variants must be kept in mind, perhaps best illustrated by the careful analysis of internal maxillary artery injections for the opacification of the ophthalmic artery (Fig. 100.7). In the case of aneurysms, the takeoff of branch vessels should be identified and functional distal vessels should be

b

c

d

Fig. 100.5â•… (a) Lateral view of a right internal carotid artery (ICA) injection demonstrates a choroidal-type vein of Galen malformation, as well as a 180-degree kink in the cervical ICA. (b) The kink was crossed with a 0.044-inch Revive intermediate catheter (Codman & Shurtleff, Raynham, MA, USA). A microcatheter was then advanced through the Revive intermediate catheter (Codman & Shurtleff) into the nidus. (c) Super-selective run via the Echelon microcatheter, lateral view. The malformation was embolized with Onyx (ev3 Neurovascular, Irvine, CA, USA). This control angiographic run via the Revive intermediate catheter (Codman & Shurtleff) after removal of the microcatheter shows reduced flow into the vein of Galen malformation. (d) Lateral view of ICA run.

100â•… Interventional Neuroradiology

a

b

c

Fig. 100.6â•… (a) Lateral view of an external carotid artery (ECA) injection demonstrates a traumatic pseudoaneurysm of a posterior branch of the middle meningeal artery. Given the small caliber and tortuosity of the middle meningeal artery, a 0.008-inch Magic catheter (BALT Extrusion, Montmorency, France) was employed to achieve adequate distal access. (b) Super-selective run via the Magic microcatheter (BALT Extrusion) in the posterior branch of the middle meningeal artery. The aneurysm was embolized with N-butyl-cyanoacrylate (NBCA) and occluded. (c) Lateral view of control ECA angiographic run.

attention should be paid to one-to-one movement of the coil under fluoroscopy, with hand movement at the groin. If this is not observed, coil stretching, although rare, should be suspected and the microcatheter and coil should be removed as a unit.

100.2.5╇ Salvage and Rescue

Fig. 100.7â•… Lateral view of an external carotid artery (ECA) injection demonstrates opacification of the ophthalmic artery via the middle meningeal artery.

very clearly visualized in the working projections (Fig. 100.4). Advancement of the coil into the target should be performed slowly, with attention to the coil’s conformation relative to the aneurysm or target vessel. Coil herniation should prompt withdrawal of the coil and, if persistent, should prompt repositioning of the microcatheter or usage of another coil size or type. Control angiography after coiling must be meticulously inspected for the formation of thrombus in the parent vessels. When coiling, careful

Avoidance of thromboembolic complications is crucial. If clot formation occurs intraprocedurally, a glycoprotein IIb/IIIa inhibitor or, if needed, tissue plasminogen activator (TPA) can be administered. Of course, a misplaced/herniated coil (in the parent vessel) or retained catheter can each be a dangerous source of such complications as well. In cases of a deployed, herniated coil, a micro-retrieval device may be employed to retrieve the coil, or a stent may be deployed to push it against the vessel wall. On the other end of the spectrum of adverse events, hemorrhagic complications, although rare, need to be managed swiftly. Anticoagulation and/ or antiplatelet agents should be reversed. In the event of aneurysm coiling and coil perforation, the coil must be left in place and the aneurysm quickly coiled. Some practitioners keep a deflated balloon ready in the parent vessel to allow for easy adjunctive remodeling or inflation in such an event. The authors do not empirically espouse this approach, particularly in young children, although it is a consideration for “high-risk” or “borderline wide-neck” aneurysms.

839

840 Section Xâ•… New And Emerging Techniques

100.3╇ Outcomes and Postoperative Course 100.3.1╇ Postoperative Considerations At the conclusion of the procedure, the authors typically employ a Safeguard pressure dressing (Maquet, Fairfield, NJ, USA) for 2 hours, after hemostasis has been achieved with manual compression. Patients are monitored in a dedicated postanesthesia care unit with regular groin-site, pulse, and neurologic checks. Although infrequent, groin-site hematomas can often be managed by repeated manual compression; nevertheless, significant hematocrit decrements should be evaluated with appropriate imaging to rule out retroperitoneal hematomas. As of yet, in their pediatric neurointerventional experience (Table 100.1), none has been observed by the authors.

100.3.2╇Complications After a known intraprocedural hemorrhagic event or in the setting of an acute postoperative deficit, an emergent computed tomography (CT) scan is performed. Clot evacuation may be indicated for intraparenchymal hemorrhage; for subarachnoid or intraventricular hemorrhage with hydrocephalus, a ventriculostomy may be placed if hydrocephalus is present. The patient is subsequently carefully monitored in the intensive care unit and standard measures for ICP management are implemented. Although cerebral vasospasm is more rarely symptomatic in children than adults, interval imaging for cerebral vasospasm should be considered, particularly in the setting of subsequent delayed deterioration. If no hemorrhage is seen on the CT scan, an MRI is obtained to better evaluate a suspected ischemic

complication. Patients suffering ischemic complications or at high risk for such events are maintained on antiplatelet agents or even anticoagulants, depending on the vessel at risk and the clinical context. In the authors’ experience with embolization of craniospinal aneurysms and arteriovenous shunts in children, neurologic adverse events have been exceedingly rare, with one single thromboembolic complication and one single hemorrhagic complication. The authors stress that achieving a high safety level in the management of pediatric cerebrovascular diseases, such as those described, is feasible only when the treatment is undertaken by a multidisciplinary team with extensive pediatric experience.

References ╇1. Lasjaunias

PL, Chng SM, Sachet M, Alvarez H, Rodesch G, Garcia-Monaco R. The management of vein of Galen aneurysmal malformations. Neurosurgery 2006;59(5 Suppl 3):S184–S194, discussion S3–S13 ╇2. Ellis MJ, Armstrong D, Vachhrajani S, et al. Angioarchitectural features associated with hemorrhagic presentation in pediatric cerebral arteriovenous malformations. J Neurointerv Surg 2013;5(3):191–195 ╇3. Nelson PK, Russell SM, Woo HH, Alastra AJ, Vidovich DV. Use of a wedged microcatheter for curative transarterial embolization of complex intracranial dural arteriovenous fistulas: indications, endovascular technique, and outcome in 21 patients. J Neurosurg 2003;98(3): 498–506 ╇4. Molyneux A, Kerr R, Stratton I, et al; International Subarachnoid Aneurysm Trial (ISAT) Collaborative Group. International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised trial. Lancet 2002;360(9342):1267–1274 ╇5. Gross BA, Orbach DB. Addressing challenges in 4 F and 5 F arterial access for neurointerventional procedures in infants and young children. J Neurointerv Surg 2014;6: 308-313

101

Image-Guided Surgery Yair M. Gozal and Timothy W. Vogel

101.1╇Background

101.1.2╇Goals

Progress in neurosurgery, perhaps more than any other field, has been closely linked to the rapid development of advanced imaging modalities capable of accurately and rapidly visualizing intracranial and spinal anatomy. The demand in neurosurgical practice for absolute precision in an effort to decrease neurologic morbidity and minimize surgical trauma has driven exponential growth in the application of image-guidance systems. Image-guided surgery, or the real-time correlation of radiographic images to the tissue being manipulated in the operative field, has progressed dramatically since the initial applications of stereotaxy by Spiegel and Wycis in 1947.1 Their ring-based system centered on pneumoencephalographic landmarks has long since given way to frameless navigation in exquisitely detailed magnetic resonance imaging (MRI) (Fig. 101.1), computed tomography (CT) images, and even functional data available today. In the pediatric patient, neuronavigation has become a critical tool for surgeons to improve patient safety and surgical outcomes.

The application of sophisticated imaging technologies to surgical practice has revolutionized the treatment of neurologic diseases.4 These systems enhance the surgeon’s spatial orientation, and thereby maximize surgical accuracy. In turn, improved accuracy helps minimize the surgical “footprint,” reducing invasiveness and driving improvements in patient outcomes.5

101.1.1╇Indications The indications for use of image-guided surgery have expanded tremendously over the past decade and extend into every subspecialty within pediatric neurosurgery. The treatment of hydrocephalus, for example, employs a number of imaging technologies ranging from intraoperative ultrasound to frameless stereotaxy and neuroendoscopy for placement of intraventricular shunt catheters.2 Most commonly, however, image-guided surgical navigation systems have been used to target intracranial lesions that are small are located near eloquent cortex, are associated with abnormal surrounding anatomical landmarks, or require real-time evaluation of the extent of resection.3

101.1.3╇ Alternate Procedures Image guidance in its many forms has become a critical aspect of neurosurgical procedures and is typically considered the standard of care. Occasionally, an image-guidance system on which the surgeon is reliant may be unavailable or otherwise employed in a concurrent case. In these situations, it is important for the surgeon to realize that additional approaches may be available. For example, if neuronavigation based on frameless stereotaxy is unavailable for the resection of a supratentorial tumor or an epileptogenic focus, one may employ other forms of imaging, including intraoperative MRI (iMRI) (Fig. 101.2) or, more practically, ultrasound, to help reorient the surgeon and guide surgical resection. Regardless, it is incumbent on the surgeon to possess an exquisite knowledge of neurosurgical anatomy and to have completed appropriate preoperative planning (Fig. 101.3) so that surgical procedures can be safely completed in the absence of neuronavigation.

101.1.4╇Advantages Apart from preoperative guidance and planning, there are several advantages to incorporating radiologic images and image-guidance systems in surgical practice. First, they provide the surgeon with the capacity to conceptually visualize lesions prior to

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Fig. 101.1â•… An intraoperative image of the sterotactic neuronavigation system used in resection of a supratentorial tumor. The skin registration is included in order to correlate the probe’s movement with the lesion seen on magnetic resonance imaging (MRI). The MRI data can be displayed in the axial, coronal, and sagittal planes in order to plan an appropriate surgical resection and operative approach.

Fig. 101.2â•… A child undergoing positioning for intraoperative magnetic resonance imaging (iMRI). This technology aids in the resection of an intracranial lesion and can be correlated with the stereotaxy in order to verify gross total resection.

101â•… Image-Guided Surgery

Fig. 101.3â•… The preoperative registration process. Using stereotaxy, skin landmarks can be traced with a probe and correlated with preoperative imaging to accurately register the patient’s anatomy. Fiducials are frequently used for preoperative imaging landmarks; however, the use of skin-tracing methods is now more robust, allowing surgeons to avoid the use of fiducials and the difficulties of registering patients who are in a prone position.

surgical incision, allowing for more accurately localized craniotomies and minimizing inadvertent resection of normal brain. Following incision, the surgeon is able to obtain real-time feedback indicating the position of surgical instruments in regard to the lesion of interest. The surgeon may then be guided to the lesion along a prespecified trajectory that protects critical cerebral structures.6 Lesion resection may subsequently be tracked by comparison of the position of the surgical instruments to the preoperative data. In cases where gross total resection is critical, updated intraoperative imaging can be obtained to guide additional resection of residual pathology. Finally, neuronavigation may aid in visualizing important anatomical structures and landmarks in cases requiring implantation of surgical devices, such as multilevel pedicle screw fixation in children with severe scoliotic deformities. Positioning of surgical hardware can be accomplished in a more rapid and precise manner, reducing overall surgical time for complex cases and improving patient recovery.5 Many neuronavigation systems are designed with image-capture capabilities, a feature that is consistent with current efforts to formally document surgical procedures.7

101.1.5╇Contraindications There are no absolute contraindications to using image guidance to improve neurosurgical outcomes. However, these tools are not often used in certain

situations, including trauma or emergency cases, because they require extensive preoperative preparation and may extend total operating time. The system of choice needs to be brought into the operating room and must be set up by individuals who have this expertise. Moreover, if patient registration is required, incision for acute cases may be delayed.

101.2╇ Operative Detail and Preparation The term image guidance has broad application in the field of pediatric neurosurgery. Herein, the authors focus on intraoperative neuronavigation via frameless stereotaxy in neuro-oncologic procedures.

101.2.1╇ Preoperative Planning and Special Equipment Presurgical considerations include patient positioning and appropriate preoperative imaging. Selection of a suitable patient position is highly dependent on the specific procedure, location of the tumor, and the surgeon’s comfort with each potential approach. Final patient positioning is critical because it determines the layout of the operative theater and, in particular, the location of the stereonavigation camera. Furthermore, knowledge of the position of the patient during surgery allows for the appropriate placement of

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844 Section Xâ•… New And Emerging Techniques fiducial markers for patient registration. This is particularly important when the patient is positioned prone and the typical facial landmarks are rendered inaccessible. Preoperative imaging consists of thincut MRI or CT completed with the patient typically wearing adhesive fiducials for subsequent intraoperative reference. If needed, functional imaging data can be merged with preoperative scans showing functional motor or other eloquent tracts to help reduce the risk of their damage during tissue resection and manipulation.

101.2.2╇ Expert Suggestions/Comments Accurate neuronavigation is based entirely on precise registration, the process of aligning the patient in physical space with the exact location of relevant anatomy on preoperative imaging.6 Although surfacematching algorithms are becoming increasingly pervasive, fiducial-based algorithms remain the primary method of registration. Therefore, special attention must be paid during patient positioning and pinning to avoid disruption of previously placed fiducials. For the same reason, preoperative imaging planned for use in navigation should be scheduled as close as possible to the day of surgery to avoid inadvertent movement of the adhesive fiducials prior to surgery. Fiducials should also be carefully placed over bone prominences to avoid their inadvertent movement during registration. In addition to registration, positioning the system camera during surgery is important to ensure that the system can be used easily and effectively throughout the procedure. Infrared cameras employed in most neuronavigation systems are predicated on line of sight for use. Thus the camera should be placed so that direct line of sight is maintained throughout the procedure despite the presence of the surgeon, assistants, surgical instruments, and often the surgical microscope.

101.2.3╇ Key Steps of the Procedure/ Operative Nuances The patient is positioned appropriately with the head fixed with a Mayfield three-pin head clamp. A specialized arm is attached to the head clamp frame that provides a fixed coordinate for the camera to reference in relation to the patient’s head. Careful attention should be paid to avoid any movement of the reference arm independently of the patient’s head within the head clamp because this would necessitate reregistration to maintain accurate neu-

ronavigation. The system camera is positioned with unobstructed line of sight to the patient and reference arm. A specialized tracking device, or pointer, is then used to acquire reference points. This is accomplished by touching the center of each fiducial with the tip of the pointer in view of the camera. When a sufficient number of fiducial reference points have been acquired, the system will match their position in physical space to that in the preoperative imaging. An estimate of registration error is calculated and reported by the system, but accuracy must be manually verified by testing several prominent locations around the head (e.g., tragus, lateral canthus) and correlating their positions to those reported on the neuronavigation monitor. After registration, the skin incision is planned by marking out the borders of the lesion of interest. This process is repeated to establish the boundaries of the craniotomy. Important landmarks within the region of the craniotomy, such as venous sinuses, are also noted and marked. Subsequently, the pointer may be used to direct exposure of the lesion, verify the borders of the tumor within the resection cavity, and protect eloquent tissues from damage. In addition, surgical instruments may be registered and continuously tracked throughout surgical resection.

101.2.4╇ Hazards/Risks/Avoidance of Pitfalls Image-guided surgery is entirely reliant on the accuracy of neuronavigation platforms. In turn, neuronavigation accuracy is driven by the technical aspects of registration and by a phenomenon known as brain shift.4 In pediatric patients, the registration process may be affected when patients unknowingly remove or displace their fiducials prior to arrival in the operating theater. This may be countered either by employing surface-matching algorithms for registration or by obtaining a preoperative localization scan after anesthetic induction. Additional sources of navigation error may occur with movement of the reference arm during surgery. Conveniently, many systems provide the ability to acquire a series of intraoperative reference points that can be used to reregister the patient. These may be as simple as drill holes prepared for dural tack-up sutures. Finally, the occurrence of brain shift is unavoidable and refers to the deformation of the brain as a result of edema, surgical resection, positioning, or cerebrospinal fluid drainage. Intraoperative imaging, whether MRI or ultrasound, has emerged as the primary method of addressing this phenomenon.1

101â•… Image-Guided Surgery

101.3╇ Outcomes and Postoperative Course 101.3.1╇ Postoperative Considerations Whereas image-guidance systems do not typically impact postoperative care, it is worth noting that they do not replace the need for postoperative imaging, both for documentation of the extent of surgical resection and for the monitoring of potential complications.

101.3.2╇Complications Image-guided surgery has revolutionized the practice of neurosurgery, allowing for the development of minimally invasive approaches, improving surgical outcomes, and reducing patient morbidity.5 Although image-guidance systems are designed to increase the level of patient safety, absolute reliance on them can prove catastrophic. The onus remains on the neurosurgeon to possess a thorough knowledge of surgical anatomy and to ensure all neuronavigation feedback is critically evaluated.

References ╇1. Comeau

RM, Sadikot AF, Fenster A, Peters TM. Intraoperative ultrasound for guidance and tissue shift correction in image-guided neurosurgery. Med Phys 2000;27(4):787–800 ╇2. McCallum J. Combined frameless stereotaxy and neuroendoscopy in placement of intracranial shunt catheters. Pediatr Neurosurg 1997;26(3):127–129 ╇3. Schmieder K, Hardenack M, Harders A. Neuronavigation in daily clinical routine of a neurosurgical department. Comput Aided Surg 1998;3(4):159–161 ╇4. Vougioukas VI, Hubbe U, Hochmuth A, Gellrich NC, van Velthoven V. Perspectives and limitations of imageguided neurosurgery in pediatric patients. Childs Nerv Syst 2003;19(12):783–791 ╇5. Pandya S, Motkoski JW, Serrano-Almeida C, Greer AD, Latour I, Sutherland GR. Advancing neurosurgery with image-guided robotics. J Neurosurg 2009;111(6):1141–1149 ╇6. Eggers G, Mühling J, Marmulla R. Image-to-patient registration techniques in head surgery. Int J Oral Maxillofac Surg 2006;35(12):1081–1095 ╇7. Haase J. Neuronavigation. Childs Nerv Syst 1999;15 (11-12):755–757

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102

Advances in Neuroendoscopy Robert P. Naftel and John “Jay” C. Wellons III

102.1╇Background 102.1.1╇Indications • Hydrocephalus―traditionally, endoscopic third ventriculostomy (ETV) has been reserved for a select group of children with a high likelihood of success.1 However, with the addition of choroid plexus coagulation (CPC)2 and the ability to endoscopically fenestrate cystic loculations, patient selection is expanding. • Cyst treatment―colloid cysts were one of the first intraventricular lesions to be resected

a

endoscopically (Fig. 102.1a,b),3 and advances in technique and equipment established this approach as the primary treatment. Additionally, arachnoid, ependymal, and choroidal cysts can be fenestrated (Fig.€102.2a,b). • Tumor management―whereas endoscopic tumor biopsy was first reported by Fukushima in 1973,4 advances in technique and technology allow biopsy of tumors (Fig. 102.3), treatment of concomitant hydrocephalus, and resection for particular tumors or hamartomas,5,6 even in small ventricles.7,8

b

Fig. 102.1â•… A 13-year-old adolescent girl presented with new-onset, intermittent, severe headaches that could not be attributed to another cause. (a) Coronal fluid-attenuated inversion recovery (FLAIR) sequence magnetic resonance imaging (MRI) reveals a 7-mm colloid cyst and small, asymmetric ventricles. (b) The right lateral ventricle has been accessed and insufflated. Via this right frontal approach, the colloid cyst is viewed though the foramen of Monro. The septal vein courses superiorly along the septum, posterior to the fornix. The choroid plexus is obstructing the view of the colloid cyst and would require cauterization and possible resection to better expose the cyst for resection.

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102 â•… Advances in Neuroendoscopy a

b

Fig. 102.2╅ In a patient with obstructive hydrocephalus due to a suprasellar cyst, via a right lateral ventricle approach, the cyst can be visualized through the foramen of Monro. (a) The choroid plexus tracks along the thalamus toward the foramen of Monro. The right thalamostriate vein courses from lateral toward the foramen of Monro. The cyst has dilated the foramen of Monro. This patient underwent a septostomy, fenestration of the cyst into the ventricle, and fenestration of the caudal wall of the cyst into the basal cisterns. (b) The caudal extent of the cyst extends to the prepontine cistern. From this view within the cyst, the basilar artery, left posterior cerebral artery, superior cerebellar artery, oculomotor nerve, and abducens nerve are seen. The caudal wall of the cyst was fenestrated into the basal cisterns.€

102.1.2╇Goals The goal of neuroendoscopy is to provide safe and effective treatment of the underlying pathology, while attempting to minimize morbidity and while respecting patient preferences.

102.1.3╇ Alternate Procedures The primary alternative to endoscopic hydrocephalus treatment is cerebrospinal fluid (CSF) shunting. In cases of loculated hydrocephalus or spinal

fluid cysts, shunting can require multiple ventricular catheters or an open craniotomy to fenestrate loculations. Alternatives for intracranial cyst treatment include craniotomy for resection, stereotactic aspiration, or treatment of the hydrocephalus with shunting and septostomy. Direct cyst shunting is also an option in selected patients. For tumors, biopsy can also be performed stereotactically (frame-based or frameless) or via open craniotomy. For resection of ventricular tumors, a craniotomy could be performed via either a transcallosal or a transcortical approach, depending on location.

Fig. 102.3â•… In a patient with obstructive hydrocephalus due to a pineal region tumor, after an endoscopic third ventriculostomy, the tumor was endoscopically biopsied. The endoscope has been passed through the foramen of Monro to provide this view. The biopsy forceps are passing by the massa intermedia to biopsy the tumor.

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102.1.4╇Advantages For hydrocephalus, successful endoscopic treatment avoids insertion of a shunt and its associated complications. Although acutely the risk of treatment failure is higher with ETV compared to shunt, over the long term, ETVs appear to be more durable. For patients with loculated hydrocephalus or ventricular spinal fluid cysts, neuroendoscopy may not eliminate the need for a shunt but it can make the shunting less complex by reducing the number of ventricular catheters. The majority of neuroendoscopic surgeons believe that endoscopic biopsy has a lower complication profile than stereotactic biopsy because of direct visualization and the ability to achieve hemostasis. For tumor, hamartoma, and colloid cyst resection, experienced surgeons believe that reduced morbidity, avoidance of emptying the ventricle, and patient appeal are important advantages.9

(infection or hemorrhage). However, these contraindications are relative and dependent on surgeon experience. • Cyst treatment―large size is not believed to be a contraindication for endoscopic colloid cyst resection.9 Dense, fibrous cysts have traditionally been more challenging to resect endoscopically; however, with the introduction of an endoscopic tissue shaver (Fig. 102.4) and ultrasonic aspirator, these lesions have become more manageable. • Tumor management―patients with highly vascular tumors are at risk of hemorrhagic complications with biopsy and attempts at resection. Surgeons also agree that, with current techniques, large ventricular tumors are not good candidates for endoscopy.9 • Small ventricles should not be viewed as a contraindication if appropriate steps are taken to ensure ventricular access and navigation (Fig. 102.1a,b).7,8

102.1.5╇Contraindications • Hydrocephalus―contraindications to endoscopic hydrocephalus treatment are relative because likelihood of success is believed to increase with the addition of CPC in certain subgroups of patients.2 Multi-institution prospective trials are needed to evaluate the efficacy of this technique. Relative contraindications include a small or scarred prepontine space and abnormal third ventricular anatomy due to development (spina bifida) or scarring

102.2╇ Operative Detail and Preparation 102.2.1╇ Preoperative Planning and Special Equipment Surgical success and avoidance of morbidity are dependent on thorough, thoughtful preoperative planning. Planning must include:

Fig. 102.4â•… Side-shaving instruments are available that allow debulking or resection of lesions. This tool has a rotating debriding blade and variable suction to control the rate of débridement. The tip can be both extended and rotated. By rotating the tip of the device, it can be used at different angles.

102 â•… Advances in Neuroendoscopy • Prior to cannulation of the lateral ventricle, it is critical to ensure that all instrumentation is working correctly. The authors use a 5-point checklist: orientation, focus, white balance, light source, and irrigation. • Ergonomic arrangement of the room and operative table. Both the stereotactic navigation and the endoscope monitors should be in the surgeons’ direct line of vision (Fig. 102.5). • Using neuronavigation, an entry site and trajectory should be planned that allow safe passage into the ventricles to accomplish the surgical goals without collateral damage. For lesions in the third ventricle, a 3-point plan (burr hole, foramen of Monro, and lesion) is devised (Fig. 102.6). • The surgeon and assistant should discuss the goals of surgery, respective roles, and

common terms for cardinal directional movement. • Potential complications that may require a salvage maneuver should be anticipated.

102.2.2╇ Expert Suggestions/Comments • Neuronavigation is an important preoperative and intraoperative adjunct that should not be overlooked. Besides entry site and trajectory planning, the endoscope can be coregistered to the navigation so that radiologic feedback is available while exploring the ventricles. • Maintaining a clear visual medium is crucial to endoscopic work and, therefore, regulating the irrigation flow rate is helpful. Due to anecdotal and personal experience, lactated Ringers’ irrigation is used instead of normal

Fig. 102.5â•… The room setup must be appropriate for proper ergonomic operating. Two surgeons stand at the head of the bed with the operating room (OR) scrub technician passing instruments. Monitors displaying the endoscopic video and neuronavigation should be comfortably within view at the foot of the bed. The child is positioned in such a way that the scope can be held comfortably for extended periods of time.

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850 Section Xâ•… New And Emerging Techniques making egress from a ventricle controllable through the scope. Using this technique, the ventricular tone can be maintained, balancing the irrigation rate and the amount of egress through the scope. • When endoscopy is being used to treat an obstruction at the foramen of Monro (classically, colloid cysts, but other pathology also applies), a septostomy should be considered as the first step of the procedure to prevent development of loculations.

102.2.3╇ Key Steps of the Procedure/ Operative Nuances

Fig. 102.6â•… For tumors in the third ventricle, a 3-point trajectory should be planned. The trajectory is formulated by projecting a line from the lesion through the foramen of Monro, to the skull. Using this trajectory, risk of injuring the fornix will be minimized.

saline to avoid “washing out” of intravascular sodium. While irrigating, there must be a route for egress from the ventricles or else intracranial pressure (ICP) may exceed safe limits. Increasing the volume of the pulse oximetry is beneficial in listening for bradycardia. • If significant venous bleeding is encountered, it will usually stop after increasing the rate of the irrigation, finding the source of bleeding, and directly irrigating on the source. Great patience is often required. • Operating in small ventricles is possible, but extensive preoperative planning must precede surgery. The ventricles can be gently inflated with irrigation to provide slightly more space, but this must be done with great care so as not to cause a dangerous increase in ICP. This process is not possible when using a split sheath as an avenue of entry to the ventricle because CSF and irrigation will spill out around the endoscope. When operating in small ventricles, it is helpful to operate directly through the brain because the brain provides a seal around the scope,

• Whenever neuronavigation is used, the head is secured in 3-point fixation, and children with thin skulls (generally younger than 4 years) are supported with the Mayfield infinity headrest (Integra, Plainsboro, NJ, USA). • Typically, a curvilinear “shunt incision” is performed to allow for potential shunting in the future, if needed. • In tumor resection cases or when the risk of bleeding is considered to be significant, planning for a potential salvage craniotomy is made and prepped into the surgical field. The operating room (OR) team is notified at the start of the case so that relevant equipment and sterile trays are nearby. • In cases of small ventricles, neuronavigation is always used. Under image guidance with the potential additional adjunct of ultrasound, the ventricle is accessed using a ventricular catheter with a distal slit tip for introduction of the Neuro-PEN endoscope (Medtronic). The anatomy can then be inspected and the ventricle is gradually dilated using irrigation through the endoscope. A modified dilating sheath and trocar can then be introduced under direct endoscopic visual control.10 The trocar and sheath are then removed, and the rigid endoscope is introduced down the tract under direct endoscopic visual control. In the ventricle, the brain provides a seal around the endoscope, and a controlled balance of irrigation inflow and egress maintains the ventricle size. • The foramen of Monro and choroid plexus are immediately identified and any fronds of choroid plexus that are obstructing the view into the third ventricle are carefully coagulated, being careful not to injure the thalamostriate or internal cerebral veins.

102 â•… Advances in Neuroendoscopy • Once the lesion is identified, it is critical to assess the size of the foramen in comparison to the tip of the endoscope. An ideal trajectory would place the lesion directly in front of the endoscope with minimal risk of damage to the ependyma overlying the fornix. However, because of the absence of hydrocephalus and lack of dilation of the foramen, there may be a size mismatch. Often the lesion may be approached with the tip of the endoscope “parked” at the foramen but not through it. Then, relevant instruments can be passed through the foramen for resection. On the occasion that this is not possible and the foramen must be entered, the authors have elected to sacrifice the ependyma overlying the fornix anteriorly in the foramen, rather than risk venous hemorrhage from injury to the vascular structures posteriorly, because that typically requires lengthy irrigation to clear. • Tumor and fibrous colloid cyst resection are challenging because of limited tools available and the inability to use bimanual techniques. Whereas with traditional neuroendoscopy, dissection is for the most part still not bimanual, innovative tools, including the NICO myriad tissue shaver and Cavitron ultrasonic aspirator, have made tumor resection more feasible (Fig. 102.4).11,12 It is critical to recognize the position of the floor of the third ventricle and the relationship of the lesion to the vascular contents in the interpeduncular cistern.

102.2.4╇ Hazards/Risks/Avoidance of Pitfalls • Bleeding―in cases of tumor resection, bleeding can be controlled by selecting patients without highly vascular tumors, coagulating the tumor surface before resecting, and patiently irrigating the source of bleeding when it occurs. • Intracranial hypertension―when this occurs, it is often iatrogenic, due to inattentive control of the irrigation or loculation of fluid. Some surgeons will use ICP monitors.

102.2.5╇ Salvage and Rescue • Preoperative planning for potential conversion to craniotomy should be considered, especially in tumor resection cases. • External ventricular drains may be inserted at the discretion of the surgeon when there has been bleeding or debris.

102.3╇ Outcomes and Postoperative Course 102.3.1╇ Postoperative Considerations • Patients should be monitored for the development of hydrocephalus, any new neurologic deficit, or CSF leak. • After tumor resection, some patients may require short courses of corticosteroids to decrease edema and potential aseptic meningitis.

102.3.2╇Complications • CSF leak after any endoscopic surgery should be considered a possible sign of untreated hydrocephalus. Recurrent CSF leak in the setting of a well-closed wound should be considered diagnostic for untreated hydrocephalus. • Morbidity that could be experienced with an open case, such as motor deficit, sensory deficit, speech-language deficit, visual/ocular deficits, memory deficits, or endocrinological dysfunction, could occur, and even if less likely, should be discussed with the family up front during the preoperative conference. • Patients may be at risk of developing hydrocephalus, including loculated hydrocephalus around the foramen of Monro.

References ╇1. Kulkarni

AV, Drake JM, Mallucci CL, Sgouros S, Roth J, Constantini S; Canadian Pediatric Neurosurgery Study Group. Endoscopic third ventriculostomy in the treatment of childhood hydrocephalus. J Pediatr 2009;155(2): 254–259.e1 ╇2. Warf BC. Comparison of endoscopic third ventriculostomy alone and combined with choroid plexus cauterization in infants younger than 1 year of age: a prospective study in 550 African children. J Neurosurg 2005;103(6 Suppl):475–481 ╇3. Powell MP, Torrens MJ, Thomson JL, Horgan JG. Isodense colloid cysts of the third ventricle: a diagnostic and therapeutic problem resolved by ventriculoscopy. Neurosurgery 1983;13(3):234–237 ╇4. Fukushima T. Endoscopic biopsy of intraventricular tumors with the use of a ventriculofiberscope. Neurosurgery 1978;2(2):110–113 ╇5. Rekate HL, Feiz-Erfan I, Ng YT, Gonzalez LF, Kerrigan JF. Endoscopic surgery for hypothalamic hamartomas causing medically refractory gelastic epilepsy. Childs Nerv Syst 2006;22(8):874–880

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MM, Luther N. Endoscopic resection of solid intraventricular brain tumors. J Neurosurg 2006;105(2):271–278 ╇7. Souweidane MM. Endoscopic surgery for intraventricular brain tumors in patients without hydrocephalus. Neurosurgery 2008;62(6 Suppl 3):1042–1048 ╇8. Naftel RP, Shannon CN, Reed GT, et al. Small-ventricle neuroendoscopy for pediatric brain tumor management. J Neurosurg Pediatr 2011;7(1):104–110 ╇9. Qiao L, Souweidane MM. Purely endoscopic removal of intraventricular brain tumors: a consensus opinion and update. Minim Invasive Neurosurg 2011;54(4):149–154

10. Naftel

RP, Tubbs RS, Reed GT, Wellons JC III. Small ventricular access prior to rigid neuroendoscopy. J Neurosurg Pediatr 2010;6(4):325–328 11. Dlouhy BJ, Dahdaleh NS, Greenlee JD. Emerging technology in intracranial neuroendoscopy: application of the NICO Myriad. Neurosurg Focus 2011;30(4):E6 12. Oertel J, Krauss JK, Gaab MR. Ultrasonic aspiration in neuroendoscopy: first results with a new tool. J Neurosurg 2008;109(5):908–911

103

Endoscope-Assisted Microsurgery Henry W. S. Schroeder

103.1╇Background Endoscope-assisted microsurgery means the use of the microscope and the endoscope in one surgery.1 Usually, the major part of the procedure is performed with the aid of the microscope, a minor part with the endoscope (i.e., the endoscope assists the microscope in obtaining a perfect visualization). Using the operating microscope in neurosurgery has been established for more than 30 years. Microsurgical training is the basic part in any neurosurgical resident training program. However, although becoming more and more popular in the last decade, endoscope-assisted techniques have not yet been well established in many neurosurgical centers. Reasons are many, such as unfamiliarity with the use of endoscopes, lack of proper equipment, unwillingness to have a special endoscopic training, and not being aware of the advantages. This chapter aims to give some insight into the technique and to encourage the reader to use the endoscope in microsurgery.

103.1.1╇ Rationale for Combining the Endoscope with the Operating Microscope The operating microscope is still the preferred visualization tool for most neurosurgical procedures because it provides high resolution, bright illumination, and a stereoscopic view. The resolution is higher than the resolution of the endoscopes used in neuroendoscopy because the diameter of the lens system in the microscope is larger (e.g., 12 mm in the Pentero operating microscope, Carl Zeiss, Oberkochen, Germany). Furthermore, when using the operating

microscope, the surgeon looks directly through the lens system. That means the retina is the primary sensor. Even compared to images generated by highdefinition (HD) cameras that are now routinely used in neuroendoscopy, the resolution of the human eye is still better. Therefore, the operating microscope is the perfect visualization instrument for superficial lesions. However, in deep and narrow surgical corridors, the illumination gets worse. At the entry into the surgical field, the surgeon already loses a great deal of light (Fig. 103.1a). Furthermore, the surgeon must operate with the instruments within the light beam, which further decreases the illumination (Fig. 103.1b). Another major disadvantage of the microscope is the limited depth of focus, especially when using a high magnification. The surgeon frequently has to refocus the microscope during the microsurgical dissection. Finally, with the microscope, only structures that are in a straight line in front of the lens can be seen. The view obtained with endoscopes is completely different. Since the endoscope is inserted deeply into the surgical field, the eye of the surgeon is brought close to the target. State-of-the-art, rod-lens scopes provide a wide angle viewing field, resulting in a panoramic view (Fig. 103.2a). Thus a perfect overview of the surgical field can be obtained even in a deep and narrow surgical field. Because of the wide angle of view, even structures that are not located directly in front of the endoscope tip can be seen. Moreover, when using angulated endoscopes, looking around a corner or behind neurovascular structures is possible (Fig. 103.2b). When rotating the scope, a radarlike overview of the surgical field can be obtained. Furthermore, since the light comes from the tip of the scope, the illumination is not decreased while dissecting with surgical instruments (Fig. 103.2c).

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Fig. 103.1â•… Schematic drawing of microscopic visualization via a supraorbital craniotomy. (a) Microscopic visualization. (b) Dissecting under microscopic view.

This is a major advantage in narrow and deep surgical approaches. The excellent depth of field is striking when using endoscopes for dissection. Refocusing is rarely necessary independently from the zoom. The major disadvantage of the endoscope, in comparison to the microscope, is the lack of stereopsis. Although recently three-dimensional (3D) endoscopes for neurosurgical procedures have been introduced, the resolution and color fidelity are still poor when comparing them to rod-lens endoscopes attached to a HD camera. Consequently, the author still prefers two-dimensional (2D) endoscopes. The lack of true 3D visualization is partially compensated for by the fish-eye effect and motion parallax. The fish-eye effect of the endoscope means that the endoscopic image is distorted. Motion parallax means that closer objects move more than distal objects. Both the fish-eye effect and motion parallax

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contribute to a pseudo-3D impression of an endoscopic image. Therefore, the lack of a stereoscopic view is usually compensated for with some training. Although the microscope still has the better optical resolution, the endoscope frequently provides an image that is superior in terms of information for the surgeon. When using HD cameras that provide images with 1,080 lines and more than 2 million pixels, the image quality is excellent. Because of the size of the displayed image on HD video monitors, neuroanatomical structures are frequently seen better with the endoscope than with the microscope, especially in narrow and deep surgical fields (Fig. 103.3). In conclusion on this subject, because microscope and endoscope have advantages and disadvantages, it seems to be reasonable to combine the advantages of both optical instruments during neurosurgical procedures.

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Fig. 103.2â•… Schematic drawing of endoscopic visualization via a supraorbital craniotomy. (a) Endoscopic 0-degree visualization. (b) Endoscopic 45-degree visualization. (c) Dissecting under endoscopic view.

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Fig. 103.3â•… Visualization of the interpeduncular fossa via an eyebrow approach (supraorbital craniotomy). (a) Microscopic visualization. (b) Endoscopic visualization.

103.1.2╇ Endoscopic Equipment To date, state-of-the-art Hopkins II rod-lens endoscopes attached to HD cameras have provided the best image quality and should be used for endoscope-assisted procedures. Various angles of view are available, including 0, 30, 45, and 70 degrees, for looking around a corner (Fig. 103.4). An angulated eyepiece that brings the camera away from the surgical field is recommended to avoid interference with the surgical instruments. The endoscope’s outer diameter should not exceed 4 mm.

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The author prefers 2.7-mm scopes because they fit into the narrow spaces between the cranial nerves in the cerebellopontine angle. When dissecting under the view of an endoscope with an angulated view, angulated instruments are required to reach the lesion (Fig. 103.5). For illumination, xenon light sources are used because the color temperature of xenon light resembles that of sunlight (6,000 K). This increases the color fidelity. HD video cameras provide a fivefold higher resolution than standard video cameras (NTSC or PAL) and hence should be used whenever possible.2

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Fig. 103.4â•… (a) Endoscopes for endoscope-assisted microsurgery with angulated eyepiece with 0, 30, 45, and 70 degrees of view. (b) Close-up of the endoscope tips.

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Fig. 103.5â•… Instruments for endoscope-assisted surgery with angulated tips.

103.1.3╇Indications The indication for using the endoscope in microsurgical procedures is very simple. If the surgeon cannot see the target area in a straight line with the microscope despite proper microsurgical dissection, use of the endoscope is indicated. Because there are many hidden corners at the skull base, surgery there is the most common indication for endoscope-assisted microsurgery, especially when small craniotomies are being used. Large craniotomies provide many differ-

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ent viewing angles. In small craniotomies, however, a more coaxial view is obtained, which sometimes prevents proper visualization without an endoscope. Endoscope-assisted microsurgery is used, for example, in patients with vestibular schwannomas with tumor extensions deeply into the internal auditory canal who still have useful hearing (Fig. 103.6). When hearing preservation is the aim, the drilling of the posterior wall of the internal auditory canal is limited by the vestibule and the posterior semicircular canal. The viewing angle via the retrosigmoid approach does not allow the direct inspection of the fundus of the internal auditory canal with the microscope, even after extensive drilling of the posterior wall of the internal auditory canal. Endoscopes with angles of 30 or 45 degrees enable a perfect visualization of the tumor remnant in the fundus and a meticulous dissection under direct visualization (Video 103.1). Additionally, the drilled area of the internal auditory canal is finally inspected to find open air cells that might cause cerebrospinal fluid (CSF) leak. Other skull base indications are meningiomas, craniopharyngiomas, and epidermoids/dermoids. Furthermore, the endoscope can be helpful in aneurysm clipping and in microvascular decompression.3–6 Nonetheless, the endoscope is used not only in skull base surgery but also in brain tumor surgery (e.g., in pineal tumor resections via a supracerebellar-infratentorial approach to visualize the entry of the aqueduct or in transcallosal removal of intraventricular tumors to see the lateral tumor parts in the frontal horn).

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Fig. 103.6â•… Endoscope-assisted microsurgical resection of an intrameatal vestibular schwannoma in a 28-year-old man presenting with contralateral hearing loss and normal hearing on the side of the tumor. (a) T1-weighted (T1W) axial and (b) coronal magnetic resonance imaging (MRI) showing a contrast-enhancing lesion (arrow) within the fundus of the internal auditory canal. (c) Axial constructive interference in steady state (CISS) MRI detailing the accurate location of the lesion in the fundus of the internal auditory canal (arrow).

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Fig. 103.6 (Continued)â•… (d) Microsurgical visualization of the lateral part of the tumor (arrow). (e) Endoscopic visualization of the lateral part of the tumor. (f) Endoscopic inspection of the fundus of the internal auditory canal after tumor removal confirming gross total tumor resection with preserved facial and cochlear nerve. (g) Axial bony computed tomography (CT) scan demonstrating the extent of drilling of the posterior wall of the internal auditory canal with preservation of the vestibule and posterior semicircular canal (arrows). (h) Axial and (i) coronal T1W contrast-enhanced MRI obtained 1 year after surgery showing no recurrence within the internal auditory canal (arrow).

103.2╇ Operative Detail and Preparation 103.2.1╇ Technique of EndoscopeAssisted Microsurgery The surgery starts the same as a regular microsurgical procedure. The major part of the operation is done under microscopic view (Fig. 103.7a). Only certain steps of the surgery are performed under endoscopic visualization. The endoscope is mainly used to look behind neurovascular structures and around dural or bony corners, for example, to look into Meckel’s cave or the internal auditory canal via a retrosigmoid approach. Using endoscopes with different angles of view reduces the extent of retraction and the amount of drilling of the skull base in getting

adequate exposure. Especially when using small craniotomies, endoscopes are sometimes indispensable in achieving sufficient visualization, for example, for exploration of the olfactory groove via an eyebrowsupraorbital route. In deep and narrow surgical corridors when the orientation and visualization are poor with the microscope, endoscopes are applied to enhance illumination and viewing field. The endoscope can be inserted into the surgical field under microscopic view. This affords safety when the endoscope has passed nerves or vessels. However, the author prefers to navigate the endoscope under endoscopic view. He does not need to switch his view from the microscope to the endoscope, which might result in unintended movement of the endoscope, with subsequent injury of neurovascular structures. For endoscopic inspection, the endoscope is simply held free hand by the surgeon (Fig. 103.7b). If

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Fig. 103.7â•… Setup in endoscope-assisted microsurgery. (a) Microsurgical dissection with the operating microscope. (b) Free-hand endoscopic inspection. (c) Bimanual endoscopic dissection. The endoscope is fixed to a holding arm. (d) Ergonomic position of the video screen in front of the surgeon.

required, a microsuction device is used in the other hand. Surgical manipulation can be done in this way, too (i.e., the endoscope is held with the left hand and the surgical instrument in the right hand). However, when dissection under endoscopic view is to be performed, in the author’s opinion, the endoscope should be fixed to a holding arm. In this way, the surgeon has both hands free and can perform a bimanual dissection under the microscope (Fig. 103.7c). Of course, the endoscope can be held by the assistant while the surgeon is performing the bimanual dissection. Nevertheless, in the author’s opinion, it is safer when the endoscope is reliably fixed by a mechanical holder to prevent inadvertent movement of the endoscope, especially when dissecting in between cranial nerves. To enable an ergonomic position, the video monitor is placed in front of the surgeon (Fig. 103.7d). Some precautions are necessary to perform a safe endoscope-assisted surgery. The surgeon should keep in mind that the tip of the endoscope may become really hot. Thus the power of the xenon light source should never be 100%; 60 to 80% is sufficient. Also, frequent irrigation is advisable when the scope is fixed in front of nerves and vessels for bimanual dissection. Utmost care must be taken when the endoscope tip has passed neurovascular structures because these structures are then no longer visible. Moving the endoscope and inserting or removing instruments from the surgical field may damage nerves and vessels that are behind the tip of

the endoscope and therefore not under endoscopic view. To prevent fogging of the lens when starting to use the endoscope, the tip is initially placed into the CSF. Warming the tip of the endoscope with saline at body temperature is another way to avoid fogging.

103.2.2╇ Future Developments In the future, high-resolution 3D video camera systems will certainly replace the operating microscope. As chip technology advances more and more, the resolution will become better and better, and finally be even superior to the human eye. Endoscopes will provide high-resolution 3D images too. All information, including optical visualization, preoperative imaging data, navigation, and so on, will be displayed on one large screen.

103.3╇Conclusion Endoscope-assisted microsurgery is a valuable technique that combines the advantages of the operating microscope with those of the endoscope. For dissection of structures that are visible in a straight line, the microscope, with high resolution, excellent color fidelity, and stereoscopic vision, is used. For looking and working “around a corner” and in deep and narrow surgical fields, the endoscope is applied to improve illumination, visualization, and orientation.

103â•… Endoscope-Assisted Microsurgery Although it still has not been proven that endoscope assistance will improve the surgical results, it definitely reduces the surgical trauma. Using endoscopes during microsurgical procedures allows a reduction of the craniotomy size. Looking around bony corners and important neurovascular structures eliminates, or at least diminishes, the need for skull base drilling and retraction.

103.3.1╇Disclosure The author is a consultant to Karl Storz GmbH & Co. KG (Tuttlingen, Germany).

References ╇1. Perneczky

A, Fries G. Endoscope-assisted brain surgery: part 1—evolution, basic concept, and current technique. Neurosurgery 1998;42(2):219–224, discussion 224–225 ╇2. Schroeder HW, Nehlsen M. Value of high-definition imaging in neuroendoscopy. Neurosurg Rev 2009;32(3):303–308, discussion 308 ╇3. Schroeder HW, Oertel J, Gaab MR. Endoscope-assisted microsurgical resection of epidermoid tumors of the cerebellopontine angle. J Neurosurg 2004;101(2):227–232 ╇4. Schroeder HW, Hickmann AK, Baldauf J. Endoscope-assisted microsurgical resection of skull base meningiomas. Neurosurg Rev 2011;34(4):441–455 ╇5. Reisch R, Perneczky A. Ten-year experience with the supraorbital subfrontal approach through an eyebrow skin incision. Neurosurgery 2005;57(4 Suppl):242–255, discussion 242–255 ╇6. Schroeder HW. Transcranial endoscope-assisted skull base surgery—posterior fossa. INS 2013;1(1):5–13

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104

Laser Ablation of Deep Lesions Joseph R. Madsen

104.1╇Background A major goal of neurosurgical management of many deep lesions is to safely destroy, or neutralize the consequences of, a lesion without damage to nearby structures. “Neutralization” here means to render harmless, as in cases where deep lesions cause seizures, such as hypothalamic hamartomas or lesions of the hippocampus. A stereotactic procedure that minimally disrupts other tissue and avoids the longterm effects of ionizing radiation (as with stereotactic radiosurgery [SRS]) may prove to be the strategy of choice. For the technique described in this chapter, laser interstitial thermoablative therapy (LITT), the key additional safety element is the ability to observe the anatomical boundaries and progress of the laser lesion as it is being made.1,2 Since the procedure is performed “closed” through a twist-drill hole, the visualization of the lesion is effected using real-time magnetic resonance imaging (MRI) observation of the target—and automated control of the laser to turn the power off when specific criteria are met. Many of the nuances of the procedure therefore depend on an understanding of the underlying phenomena and on the ability to interact with the stereotactic and laser control software.

104.1.1╇Indications The use of interstitial laser is Food and Drug Administration (FDA)-approved for ablation of a target—but since MRI “visualization” of the lesion and temperature is required, the target (and the implanted laser) must be evident in an MRI field. Practically, targets with a relatively small diameter (up to 3 cm, say) and a spherical or cylindrical overall shape have been most appropriate. A particularly good indication has been ablation of epileptogenic foci, but several types

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of tumors can be debulked in children. Some of the selection criteria would reflect lesions well treated by SRS; however, the thermal technique avoids exposure to ionizing radiation so that it is even possible to re-treat a lesion previously treated by LITT.

104.1.2╇Goals The goal of LITT is to resolve the symptoms (such as seizures or mass effect) resulting from the lesion, without incurring collateral damage.

104.1.3╇ Alternate Procedures Open surgical or stereotactic approaches exist for virtually all lesions treatable by LITT, with different options depending on the anatomy of the specific lesion. For example, hypothalamic hamartomas can be approached endoscopically, with open microsurgery (from within the ventricle or from a skull base approach), or stereotactically with Gamma Knife (Elekta AB, Stockholm, Sweden) or linear accelerator-based radiosurgery. Similarly, mesial temporal lesions can be approached through the sylvian fissure by anterior temporal resection and, again, with ionizing radiation methods. The choice of one approach over another will depend on the surgeon’s experience and availability of the appropriate equipment and software.

104.1.4╇Advantages In general, the desirability of a minimally invasive approach to (potentially) definitively treat a deep lesion, with dramatically less morbidity than from an open craniotomy, and a very short hospital stay, has been very attractive for patients. Shorter operat-

104 â•… Laser Ablation of Deep Lesions ing time might be an advantage as well, but in practice the need to move the patient from one venue (for surgical implantation of the laser) to another (to scan and lesion while in the scanner) has limited this potential advantage.

104.1.5╇Contraindications For the system that is illustrated in this chapter (Visualase, Houston, TX, USA), the laser tip that serves as a point source of energy is directed to the target by a cylindrical, hollow, plastic cranial screw, which is itself placed stereotactically using image guidance. Therefore, if the target does not have the appropriate geometry for laser ablation (spherical or cylindrical), and there is not a safe area of bone for anchorage of the screw system, it may be impractical to perform the laser ablation. In addition, for lesions with a high probability of generating cerebral edema (such as large lesions, lesions in the brainstem, or lesions already causing significant swelling), it should be recognized that the risk of postoperative edema may be high, and the thermal ablation likely does not provide any immediate decompression. A short course of steroids may be indicated, but prospectively optimized guidelines do not yet exist.

104.2╇ Operative Detail and Preparation 104.2.1╇ Preoperative Planning and Special Equipment Laser ablation surgery requires major efforts in planning and equipment preparation—and considering that the actual hands-on surgery involved (drilling a precisely placed hole and threading in a laser guide tube) requires only a short time, it may have one of the highest planning-to-execution ratios in all of neurosurgery. In the preliminary planning, it is useful to rehearse with the entire team (including the operating room [OR] nursing contingent, the anesthesia team, and the radiologists and MRI technologists) the precise order of the steps of the procedure and movements of the patient (if needed). It is possible that, with appropriate and compatible software, the entire procedure could be done in a single MRIenabled operating room (or MROR); however, at this point an appropriate combination of devices has not been assembled in any single operating room in the

United States to permit single-location planning, insertion, and ablation without some movement of the patient. Therefore, planning how and when to move the patient, while maintaining sterility and absence of interference with the probe, is essential. Planning a linear trajectory from twist-drill hole to farthest extent of the target requires only selection of these two points on appropriate planning software (the author and his group currently use the Integra platform with the CRW head frame, although others are available.). In contrast to a stereotactic biopsy through a burr hole, where a small area of cortex might be identified and the insertion point of the probe might be “tweaked” to avoid superficial vessels, in this procedure the point of entry into cortex must be selected before the hole is drilled; indeed, it must be selected before the skin incision is made.

104.2.2╇ Expert Suggestions/Comments The definition of the straight line between the insertion and farthest reach of the target would seem straightforward but in fact there are a number of nuances. Even in the early evaluation of the patient, finding the long axis of the tumor or lesion is important, and careful review of the MRI should convince the surgeon that a good trajectory is possible. Once the surgeon has a good idea of the trajectory from a reasonable entry point to the deepest part of the target, assignment of actual target and entry points will be feasible. Planning software allows study along planes that include the probe and “probe’s eye” views (i.e., planes normal to the probe). The surgeon should select sequences that allow a good visualization of structures it would be desirable to miss: surface veins, any arteries, ventricular surfaces (because of risk of the probe scything and changing trajectory), or sulci (both because of risk of scything and vascular injury). Undoubtedly, software will emerge that evaluates these points automatically. For now, this is a human (surgeon) task.

104.2.3╇ Key Steps of the Procedure/ Operative Nuances A stereotactic head frame with fiducial markings is affixed to the patient, and it is important in these early steps to be aware of the location of the ultimate target and how the imaging and image fusion will allow the target to be reached. The Radionics CRW device has a standard 160-mm distance from the stereotactic frame to the target—but, in fact, the frame often (especially with occipital approaches)

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862 Section Xâ•… New And Emerging Techniques must be farther than this to allow for the cranial fixation screw. This means that there will be a separate “offset” that has a special way of being handled in the software (which was initially designed for biopsies.) The offset procedure is as follows: determine a trajectory from the safe insertion site to the target. Along the determined trajectory (which the software identifies by elevation slider angles, based on traditional spherical polar coordinates), determine a new surrogate target that is 30 mm more superficial along the determined trajectory, and set a new stereotactic target for that. Since the entry point is unchanged, the new line is the correct angle of approach with an artificially altered length. Hence the author and his team can later compensate for this change by adding the 30 mm (or whatever offset was chosen) back in. Software planning packages often contain aids to work with the offset—but it is often useful to write down on paper the coordinates of the original target, the new target, and the angles. The author’s group likes to shave and prep a small region of scalp before actually drilling and placing the probe. It is possible to guess such a location, but they have found that the use of two stereotactic frames (one sterile for the procedure, and one unsterile for identifying precisely the entry point and trajectory) is very helpful when such hardware is available. They

now use such an unsterile stereotactic frame, set to the target and appropriate angles, to determine how to prep and disperse the hair (Fig. 104.1). After prepping and draping (and the customized Apuzzo drapes allow good visualization), they are able to set the CRW frame with entry point and direction (and even offset) as already discussed (Fig. 104.2). Local anesthetic with epinephrine is administered, and a tiny scalp incision (8 mm or less) is made. The 3.2-mm drill guard is inserted, and the hole is drilled (Fig. 104.3). As mentioned earlier, the entire stereotactic placement of the laser depends on the integrity of this hole, so the art is in smoothly drilling the bone with minimal hesitation. In the experience of the author and his team, the drill may or may not open the dura. The 1.9-mm guide probe can be used to determine if the dura is open. If there is still bony obstruction, more drilling is needed. If the bone seems gone but there is still dura, they pass some large-gauge lumbar puncture needles through the guide tube. At any rate, it is critical in the next step that the laser guide pass unimpeded. Once the dura is opened, the skull fixation device is screwed into the twist-drill hole (Fig. 104.4), and then the laser guide tube with the “stiffening stylet” can be inserted (Fig. 104.5). The calculated depth,

Fig. 104.1â•… An unsterile head frame may be used to determine the prospective entry point on the head of the patient, allowing for a minimal scalp preparation and appropriate draping. The optimal entry and target point (defining the trajectory) have already been determined at a workstation.

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Fig. 104.3â•… Drilling the cranial twist-drill hole is constrained by the stereotactic frame, and becomes the critical path guidance for laser placement.

Fig. 104.2â•… The sterile stereotactic frame can subsequently be programmed for delivery of the laser to the target, with the possibility of withdrawal of the laser to reach other points to produce a cylindrical lesion.

according to the stereotactic software, will require the addition of the offset noted before. In passing this guide tube, it is important to use a smooth, continuous motion to ensure a linear trajectory. The laser itself, a diode laser, whose power source will be located outside of the MRI room, is passed into the guide tube. It is also marked with a paper adhesive strip because it may be advanced farther in or back from the target, based on the temperature maps of test laser activations. Depending on the facilities, the patient is now moved to an MRI system with software installed for monitoring thermal laser ablation (Fig. 104.6 and Fig. 104.7). Before the laser is activated with a power sufficient to cause tissue damage, a lower level of heating can be used to show where such heat would go. Typically, the test doses may be at about 4 W (or 29% power), and with the scanner operating continuously, a temperature elevation (indicated by a light blue hue) identifies where the laser energy is

penetrating (Fig. 104.8). If this test heating reaches an appropriate region, the actual ablative lesioning begins by setting the laser at about 10 W (or 68% power). It is possible to advance or retract the actual laser (really, the fiberoptic laser guide within the irrigated guide tube) after seeing the thermography maps made on the basis of this sublethal heating. A software reconstruction of the total region lethally damaged can be displayed to show the union of the regions affected if multiple laser activations at different positions are used (Fig. 104.9).

Fig. 104.4â•… The laser skull fixation device (a plastic screw similar in size to a golf tee) is stereotactically twisted into the drilled hole.

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Fig. 104.5â•… The laser guide tube and then the laser fiber itself are inserted to the correct depth (typically, the deepest lesion).

Fig. 104.7â•… The laser source, attached to the fiberoptic cable, is outside the magnetic resonance imaging (MRI) scanner room.

Fig. 104.6â•… Selection of points of expected ablation (red crosses) and points requiring protection (blue crosses) on the software. The laser will shut off if any of the red crosses reach 90° C, or if any of the blue crosses approach 50°C.

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Fig. 104.8â•… Activation of the laser causes heating, shown in the continuous temperature images and eventually reflected in the damage estimates (in yellow).

Fig. 104.9â•… The estimated combined damage estimate may be examined during lesioning. This is helpful to avoid “skip areas” or “narrow waists” in the overall lesion.

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104.2.4╇ Hazards/Risks/Avoidance of Pitfalls The author and team have experienced one instance of laser placement that was not optimal according to preoperative plan. The laser guide tube had been placed but when the guide tube was removed, a small amount of movement was noted (shown best in the video). In this case, unique in their series, they retreated and planned a different entry and trajectory, and ended with a satisfactory lesion. It is significant to note that this required restarting “from scratch.” Patient movement during the lesioning period is a challenge because if the laser is out of the plane of the surveillance MRI scan, the data will not be correct— and other MRI artifacts can arise from movement. If the response to laser activation is unexpected (e.g., no visible heating despite the laser being on), repeating the anatomical scans is a reasonable first move. The author and his group have had the experience of a laser failure in situ, which could be proved only by removing the laser from the sheath and examining it directly. The laser proved to be damaged at the tip—a rare problem seen with less than 1% of the laser fibers to date, and correctible by replacing with a new laser fiber. This can be done on the MRI table, and the team was able to complete the ablation (with four joined targets) without incident.

104.2.5╇ Salvage and Rescue The two cases just mentioned demonstrate strategies of salvage and rescue from a suboptimal positioning and an actual failure of the laser. The key point is that this is an image-guided therapy, and diagnosis and resolution of problems often require additional imaging. The potential is to continuously check and verify the anatomical accuracy of what

is being done, and, if problems are seen, this option allows for correction.

104.3╇ Outcomes and Postoperative Course 104.3.1╇ Postoperative Considerations To date, the author and his team have observed patients in the intensive care unit, and almost always they are discharged to home on the first postoperative day.

104.3.2╇Complications Whereas complications ranging from death from meningitis to significant neurologic morbidity have been reported, it seems reasonably clear that the complications of the laser-enabled procedure would be far fewer than those with open surgery, and this is hard to dispute. The typical patient experience (overnight observation, then home the next day) is dramatically better than for most open craniotomies—regardless of outcome. The precise indication for LITT in pediatric patients is still in evolution—but likely to be an essential option for the future—and its patient-directedness will attract attention to the surgical treatment of epilepsy and other deep lesions.

References ╇1. Curry

DJ, Gowda A, McNichols RJ, Wilfong AA. MRguided stereotactic laser ablation of epileptogenic foci in children. Epilepsy Behav 2012;24(4):408–414 ╇2. Tovar-Spinoza Z, Carter D, Ferrone D, Eksioglu Y, Huckins S. The use of MRI-guided laser-induced thermal ablation for epilepsy. Childs Nerv Syst 2013;29(11):2089–2094

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Techniques for Limiting Blood Loss and Blood Transfusions in Pediatric Neurosurgery Paul Steinbok

105.1╇Background Blood loss is an integral part of surgery, and since antiquity control of surgical bleeding has been an important concern. Excessive blood loss may lead to transfusion of blood products and the risks attendant on such transfusions, and it may increase the morbidity and even mortality of some surgical procedures. In pediatric patients, especially in infants with their small blood volumes, limiting intraoperative blood loss is particularly essential. In this chapter, the author provides a personal perspective on the various techniques for limiting blood loss in pediatric neurosurgery.

105.1.1╇ Limiting Blood Loss as a Goal If it is felt that limiting blood loss is desirable in any specific patient or operation, it is critical that the surgeon make this a goal of the surgery and communicate this goal. The entire team, including the assistants, nurses, and anesthesiologists, must understand that limiting blood loss and avoiding or limiting blood transfusion are goals of the procedure. The anesthesiologist and the surgeon will need to communicate about the amount of bleeding as the procedure progresses and a decision to transfuse blood products should be made jointly. In the author’s experience, failure to communicate in this way has led to unnecessary blood transfusions. When team procedures are performed, for example, combined neurosurgical and craniofacial operations, it is vital to communicate to the many members of the team that limitation of blood loss is a goal and to remind the team during the procedure about blood loss. Without such communication and reminders, the author and his group have had persistent oozing of blood and unnecessary blood loss from orbital and cranial bone cuts, while bone is being split or a

forehead is being reconstructed at a side table away from the main operative site. Sometimes assistants, such as residents, have experience mainly with adult surgery and fail to recognize the importance of small volumes of blood loss in the young child or infant. Thus they may make little effort to limit what is perceived to be trivial blood loss, which would be inconsequential in the adult but may be important in the young child.

105.2╇ Operative Detail and Preparation 105.2.1╇ Preoperative Preparation In preparation for surgery, medications that may promote intraoperative bleeding should be discontinued in a timely manner, if safe. Aspirin and dipyridamole are the most common medications. For children with epilepsy, the anticonvulsant valproic acid may aggravate intraoperative bleeding and consideration should be given to changing this medication to another anticonvulsant prior to any elective surgery. Optimization of the hematocrit for elective procedures by giving iron or erythropoietin, especially in infants having surgery for craniosynostosis, may allow more blood loss before requiring a blood transfusion, but the author and his group have not done this in their center. For major surgery, where significant blood loss is expected, use of an intravenous antifibrinolytic agent may be considered and discussed with the anesthesiologist. For many of the major procedures done by the author’s team, especially craniofacial procedures, tranexamic acid 10 to 25 mg/kg is given intravenously as a bolus and then run as an infusion of 10 kg/h. In the past, aprotinin had been used, but it has the potential for allergic reactions and has been

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868 Section Xâ•… New And Emerging Techniques superseded in the experience of the author’s team by tranexamic acid. Techniques like hemodilution during the surgery or use of a cell saver for collection and transfusion of the patient’s autologous blood during extradural surgery have been reported; however, these are not techniques that the author and his team have used.

105.2.2╇ Positioning during Surgery Venous hypertension in the operative field will increase blood loss and should be avoided. For lumbar or thoracic spinal surgery, it is important to make sure that the abdomen is free and that the chest can ventilate freely. For cranial surgery, the neck should not be twisted too much, to avoid kinking of the jugular veins. Cranial venous pressure can be reduced by keeping the head slightly above the level of the heart.

105.2.3╇ Cranial Surgery Skin Incision Injection of 0.25% Xylocaine mixed with 1/400,000 epinephrine into the incision line is used routinely as an analgesic and also to reduce bleeding from the incision line. For most smaller incisions or for incisions in older children, where blood loss is less of a concern, the skin is incised with a scalpel. Bipolar cautery is used to control obvious bleeding and, in the scalp, Raney clips are often used to control bleeding from the subcutaneous tissue. However, in a young infant with a long incision, such as a bicoronal incision for craniosynostosis surgery, unipolar cautery with a very fine tip, namely the Colorado tip, is used. The unipolar is set at about 10 to 12 (low) and is used on the cutting mode. Although it is possible to use the Colorado tip to incise the skin directly, the preference of the author and his group is to incise the epidermis with a scalpel and then complete the skin incision with the Colorado tip. Any bleeding from the incision line is stopped with the Colorado tip on a coagulation setting, supplemented by bipolar cautery.

Scalp Flap For most surgery, the scalp flap can be reflected rapidly in either the subgaleal or subperiosteal plane. In young infants with a large scalp flap, where blood loss is more of a concern, more care is exercised to minimize any blood loss during this phase of the operation. For open reconstructive surgery in infants

with sagittal synostosis, scalp dissection is always performed in the subgaleal plane; this is done with the assistance of the unipolar cautery, often changing the Colorado tip to a blade tip at a cautery level of 20 to 25. The assistant uses bipolar cautery to coagulate any vessels prior to cutting, if possible. Subperiosteal dissection across a fused sagittal suture in an infant will result in significant bleeding from the bone close to the midline and unnecessary blood loss. On the other hand, for metopic or coronal synostosis, the amount of blood loss is similar whether the scalp is reflected in the subgaleal or subperiosteal plane. Bleeding from the bone of the calvaria is readily controlled with unipolar cautery supplemented by bone wax, if cautery does not stop the bleeding fully. If a large scalp flap is reflected, once good hemostasis has been obtained with the bipolar cautery, the flap is covered with wet gauze to keep it moist and also to avoid oozing of blood during the procedure. Microfibrillar collagen hemostat (Avitene flour) may be placed in a 50-mL syringe and the bulb of the syringe is used to puff the Avitene (C.R. Bard, Inc., Murray Hill, NJ, USA) onto the exposed scalp flap, prior to covering with the wet gauze (Fig. 105.1). This minimizes any blood loss from the scalp flap, especially when the gauze is removed prior to closure.

Craniotomy Craniotomies, using a high-speed drill like the Midas Rex (Medtronic Inc.), are almost always performed rather than craniectomies with handheld rongeurs. Bleeding from the initial burr holes is easily controlled with bone wax. The cranial cuts are planned so that the ones most likely to be associated with blood loss are done last. If the cuts will traverse a major venous sinus, the cut across the sinus is usually the last one. This permits the bone flap to be removed rapidly if the sinus is opened and then allows for easier control of the venous bleeding. If there is significant bleeding from the cut bone before the craniotomy is complete, bone wax is used in the groove that is the source of the bleeding. Alternatives―if bone wax is unsuccessful and bleeding is excessive―are FloSeal hemostatic matrix (Baxter Healthcare Corp.) or Avitene (C.R. Bard), either of which can be inserted into the groove in the cut bone. Prior to elevating the bone flap, the team should be prepared for bleeding from the region of any exposed venous sinus or from the middle meningeal artery if the bone flap is at the sphenoid wing. On removing the bone flap, any major venous bleeding from the dura or from a venous sinus is covered with a cotton patty that is removed gradually, allowing specific bleeding points to be cauterized with bipolar cautery. If

105 â•… Techniques for Limiting Blood Loss and Blood Transfusions in Pediatric Neurosurgery

Fig. 105.1â•… “Puffing” microfibrillar collagen onto the galea using an Asepto (Aseptosystems, Venice, CA) syringe.

there is bleeding from a venous sinus that is not easily stopped with bipolar cautery, covering this with a piece of Gelfoam (Pfizer Pharmaceuticals, New York, NY, USA) covered with a patty and sometimes elevating the head to reduce venous pressure usually suffice to control the bleeding. At the same time, bone wax can be used to obtain rapid hemostasis from the cut edges of the bone. In infants with thin calvaria, using the unipolar cautery in the coagulation mode can often stop bleeding effectively. For some craniosynostosis procedures, aggressive cauterization of the cut bone with the unipolar set at 60 has avoided even minor oozing of blood from the bone intraoperatively and postoperatively. When using unipolar coagulation on the cut edges of the bone, especially on very high cautery settings, it is safest to protect the dura and/or scalp with insulated retractors. Oozing of blood from the extradural space adjacent to the edge of the cut bone is usually controlled readily with strips of Surgicel (oxidized cellulose; Johnson & Johnson, New Brunswick, NJ, USA) or Gelfoam (absorbable gelatin; Pfizer) placed under the edge of the bone. If that is not successful, the dura can be tacked up with dural sutures to the adjacent

pericranium or to holes drilled into the edge of the bone. These holes can also be used later for replacing the bone flap. Avitene (C.R. Bard) and FloSeal (Baxter Healthcare) are also very effective in stopping bleeding from the bone edges, but they are relatively expensive and the author’s team tends to use these hemostatic agents only when simpler, cheaper methods fail. These products are particularly useful when the edges of the bone are irregular and it is therefore difficult to apply bone wax. FloSeal, in particular, is useful during minimally invasive craniosynostosis procedures, where it is difficult to apply bone wax to parts of the cut bone because of limited exposure. Once hemostasis is achieved, the excess Avitene (Bard) or FloSeal (Baxter) can be irrigated away.

Dural Opening Dural opening should be planned not only to achieve adequate exposure but to limit blood loss. The surgeon should anticipate specific areas where the dural incision is likely to cause bleeding and the team should be prepared to deal rapidly with such

869

870 Section Xâ•… New And Emerging Techniques bleeding. For example, when opening the posterior fossa dura in young children, there may be significant bleeding from the circular sinus and midline occipital sinus. The surgeon should be prepared to use clips to stop bleeding immediately if this occurs and even to place clips and to cut the dura between the clips, thus avoiding additional blood loss (Fig. 105.2). Sometimes it is expedient to place two mosquito clamps across the midline occipital sinus and falx cerebelli and to cut between the clamps. After cutting the falx cerebelli, bleeding can be controlled with sutures along the cut edge while removing the snaps. Bipolar coagulation can also be used, but this will shrink the dura, making it more difficult to close primarily. In general, during dural opening, small bleeders can be controlled readily using a blunt-nosed needle driver to crush the bleeding edge of dura. Bipolar cautery can also be used, but this may cause some shrinking of the dura. Bipolar cautery is generally

reserved for bleeders not stopped simply by crushing. For larger arteries, such as branches of the middle meningeal artery, which are readily apparent, bipolar coagulation may be carried out prior to cutting across the artery. In some areas, such as close to the supratentorial midline, the surgeon needs to be aware that cortical veins may be attached to the dura even 1 cm or more from the eventual entry into the midline sagittal sinus. Care must be taken to avoid cutting these veins inadvertently, not only to prevent blood loss but to avoid potential neurologic deficit. Thus the dura should be opened in such a way that allows the surgeon, when approaching the midline, to look under the dura. Sometimes, despite all precautions, catastrophic dural venous sinus bleeding will occur. The most common situation is probably a tear of the sinus while removing the bone flap. This can often be resolved by elevating the head to reduce venous pressure and

Fig. 105.2â•… Artist’s illustration demonstrating using snaps to prevent venous bleeding when opening the posterior fossa dura.

105 â•… Techniques for Limiting Blood Loss and Blood Transfusions in Pediatric Neurosurgery by covering with Gelfoam (Pfizer) and a patty, with a piece of Avitene sheet (Bard) and a patty, or with Gelfoam followed by some FloSeal (Baxter). FloSeal should not be used directly on an open venous sinus because of the possibility of having some of it enter the venous circulation. If the defect in the sinus is too large, a piece of pericranium can be used to overlap the open sinus superficially. Gentle pressure on this graft by an assistant will stop the bleeding, while the surgeon stitches the periosteal graft to the dura away from the sinus opening. Rarely, an opening into a venous sinus is even more dramatic. For example, the author made a major opening into the transverse sinus when opening the dura to remove a subdural hematoma over the cerebellum and occipital pole in a newborn. The entire dura looked blue and the landmarks for the transverse sinus were not apparent. Assuming that he was over the posterior fossa, the dura was opened lateral to the midline and revealed a solid blood clot, suggesting that this was indeed the subdural space of the posterior fossa. A larger opening in a V fashion was made with the apex in the midline and the dural flap reflected superiorly. When the blood clot was sucked out, there was massive venous bleeding from the opened dura and it became clear that the dural opening was actually into the torcular and adjacent transverse sinuses, which had been occluded and distended by an intraluminal thrombus. The neonate’s blood pressure fell and cardiac arrest rapidly supervened. The situation was salvaged by cardiac massage under the patient, with the patient still prone, and rapid suturing of the dural flap (now recognized to be the external wall of the sinus) closed while transfusing blood.

Intradural Cranial Surgery Intradural bleeding may occur from the surface, away from the major site of surgery; from the brain that is intentionally cut, either for resection or to access a deeper lesion; or from the lesion itself. Surface veins may tear and bleed if stretched during access to the area of surgery or secondary to collapse of the brain as cerebrospinal fluid (CSF) is drained or a large mass lesion is removed. It is crucial to protect the veins that are likely to be at risk. For example―during an interhemispheric approach to the corpus callosum, the veins traversing the interhemispheric fissure to the sagittal sinus and posterior and anterior to the area of dissection are at risk. These can be protected in part by wrapping a thin strip of Gelfoam or placing some Tisseel fibrin sealant (Baxter) around the vein at risk. If the vein tears and bleeds, control using bipolar cautery is usually straightforward.

When a cut is made into the cortex, simple bipolar coagulation of the normal vasculature prior to cutting will prevent most bleeding. Any bleeding that does occur can be stopped similarly with bipolar cautery, if it is coming from significant vessels. If it is more of an ooze, gentle tamponade with cotton patties with or without placement of Gelfoam or Surgicel on the bleeding area usually suffices. Hemostasis is more challenging when the bleeding is coming from abnormal vessels adjacent to a lesion, such as an arteriovenous malformation (AVM) or within a tumor. The mainstay of hemostasis is bipolar cautery and, especially for AVMs, a nonstick bipolar forceps is important. This prevents sticking of friable vessels to the tip of the bipolar, with subsequent tearing of the vessels as one attempts to free up the bipolar tips. There are many such nonstick systems available, and a discussion of the merits of one versus another is outside the scope of this chapter. Whatever system is used, the surgeon should stop periodically and have the bipolar tips cleaned when they start to accumulate debris. In AVMs, gentle dissection around the AVM and gradual disconnection of the feeding arterial supply by cutting after cauterization or after placing clips for larger vessels will reduce the amount of blood loss. Mild hypotension may also be beneficial. When bleeding occurs from the AVM nidus, gentle pressure with a cotton patty usually controls the bleeding and allows the surgery to continue, sometimes in another part of the AVM dissection. For tumors, if possible the major arterial supply should be accessed and disconnected from the tumor early in the procedure. For example, in many midline posterior fossa tumors, especially those in the fourth ventricle, the major feeders enter the tumor inferiorly from branches of the posterior inferior cerebellar artery (PICA). Early identification of the PICAs and following these arteries distally to identify and cauterize feeders to the tumor will reduce blood loss significantly when debulking of the central part of the tumor is performed. Similarly, for presumed choroid plexus tumors, knowledge of the location of the major feeding artery/arteries will allow a plan that permits the surgeon to access the vessels early in the tumor removal. Many large tumors are debulked with a suction device or an ultrasonic aspirator, such as the Cavitron ultrasonic surgical aspirator (CUSA). For vascular tumors, there is an attachment to the CUSA that allows monopolar cautery to be applied to the tip of the aspirator during aspiration of the tumor. The author and his group have employed this adjunct only rarely but it can be useful, especially during the internal debulking phase of a tumor operation.

871

872 Section Xâ•… New And Emerging Techniques More importantly, bleeding is controlled by tamponade with patties, sometimes placed over a piece of Gelfoam. Gentle pressure is applied and the surgeon works on a different part of the tumor, allowing hemostasis to occur in the tamponade area. Later, when the patty is removed with irrigation fluid, the bleeding is usually controlled. It is important to work in one area and tamponade the bleeding before starting up bleeding in another area. Otherwise, the surgeon is faced with having to control multiple areas of bleeding at the same time, with poor visualization because of the bleeding. Other adjuncts to be considered include Avitene and FloSeal. For many years, the author used Avitene as his hemostatic agent of choice during surgery to resect brain tumors. When tamponade with Gelfoam and a patty failed, Avitene could be compressed, placed on a patty and then the patty with Avitene could be placed directly onto the bleeding area and gently compressed. This was often successful in stopping bleeding. Sometimes the Avitene could be broken up and placed in a large syringe with a bulb and then puffed into the surgical field and covered with patties. This was especially useful to stop the oozing that was sometimes present at the end of the tumor resection. The excess Avitene was irrigated out, leaving behind a very thin layer that was not visible― not even through the operating microscope. After patients experienced some significant foreign-body reactions to the Avitene, the author discontinued the use of this product intracerebrally and reserved its use for the extradural space. Instead of Avitene, the author has been using FloSeal when the bleeding during a tumor resection is not controlled by simple tamponade or bipolar cautery. The FloSeal is easy to apply and has been very effective when used in the same situations for which Avitene had been used. Some surgeons prefer to use strips of Surgicel to line a resection cavity to control small amounts of oozing blood; the author has not done this because he prefers not to have residual material left in the surgical site. Avitene and FloSeal have the theoretical advantage that almost all of the material can be washed out after use, leaving no obvious residue. If there is major venous bleeding during intracerebral surgery, the venous pressure can be reduced by tilting the head of the patient upward, taking care to recognize the potential for air embolism as the surgical field is elevated above the level of the heart. Reducing the venous pressure will decrease the volume of blood coming from the open vein and allow better visibility to identify the precise site of the bleeding. This assists the surgeon in correct action, either bipolar cauterization or compression, depending on the situation.

105.2.4╇ Craniospinal and Spinal Surgery Blood loss is generally less of a problem in spinal surgery than in cranial surgery and blood transfusions are much less frequent. The basic techniques outlined previously for cranial neurosurgery apply similarly in spinal neurosurgery. Only a few points need be mentioned. Bleeding may be a problem during dural opening in Chiari I or Chiari II decompressions. Typically, bleeding from the cut dura in the cervical region is easily controlled by placing sutures full-thickness through the dural edges and placing the dural edges under tension. Bleeding from the dura as one goes across the circular sinus at the bottom of the posterior fossa may be an issue, as described previously. One caveat is that in Chiari II decompressions (associated with myelomeningoceles) the transverse sinus may be very low, even at the level of the foramen magnum. In such a case, if the dura is opened superiorly into the region of the foramen magnum, there may be catastrophic bleeding from the cut sinus. During spinal operations, using the monopolar cautery to assist with dissection of the muscles off the spinous processes and laminae reduces blood loss. For multilevel laminectomies, using the bone scalpel or Midas Rex (Medtronic) with a guarded attachment to make the laminar cuts reduces blood loss, compared to laminectomies using handheld rongeurs. Venous bleeding from the epidural space is readily controlled with bipolar cautery and by placing thin strips of Gelfoam in the lateral extradural space under the bone edges. Bony bleeding is usually controlled with bone wax. In surgeries for extradural tumors, there may be significant bleeding when removing the tumor. The techniques used for intracerebral tumors are applicable. In this situation Avitene is sometimes very helpful in limiting blood loss. One needs to anticipate situations where blood loss may be a problem. One of these is the removal of a diastematomyelic bony spur in a neonate. Some of these spurs bleed with every bite of the bone and, if one is not careful, there will be significant blood loss relative to the neonate’s blood volume. This is most critical in newborns and in the author’s experience such blood loss was almost fatal in one newborn having a repair of a hemimyelomeningocele. There was a large bony spur separating the exposed spinal cord from the deeper normal half of the spinal cord. On attempting to remove the spur, there was arterial bleeding with each bite of the spur with a small Kerrison rongeur. The bleeding could be stopped readily with bone wax and the surgery proceeded. How-

105 â•… Techniques for Limiting Blood Loss and Blood Transfusions in Pediatric Neurosurgery ever, the extent of cumulative blood loss was not recognized and the infant suddenly became severely hypotensive before resuscitation with blood products reversed the situation.

105.2.5╇ Indications for Blood Transfusion Even with all the techniques discussed here to limit blood loss during neurosurgery, there will be significant blood loss in some patients. If one of the goals is to avoid blood transfusion, the entire team needs to agree on and understand the indications and threshold for such a transfusion. Clearly, if the patient is unstable hemodynamically from blood loss, a blood transfusion is required. Similarly, if there has been significant blood loss and further bleeding is anticipated during the operation, it is wise to transfuse before hemodynamic changes occur. In some centers, blood is transfused early to allow the anesthesiologist to keep up with the blood loss. This inevitably leads to higher transfusion rates than otherwise might be the case. It is also important that the team

knows what the threshold is for blood transfusion in the postoperative phase. For extracerebral operations, such as cranial reconstructions, if the child, often an infant, is stable hemodynamically and the oxygen (O2) saturations are normal from a finger monitor, the author’s group allows the hemoglobin level to fall to 60 g/L (hematocrit approximately 0.18) before a blood transfusion is given. For intracerebral operations, where patients often have an arterial line and/or central venous line in place in an intensive care unit setting, if the child is stable, blood transfusions are typically withheld unless the mixed venous O2 saturation decreases or the arterial lactate rises.

105.3╇Conclusion There are many maneuvers that may result in less blood loss during neurosurgical procedures. However, to be successful in limiting blood loss and blood transfusions, it is critical that all members of the intraoperative and postoperative management team understand that these are goals of the surgery.

873

Index Note: Page numbers followed by f or t indicate figures or tables, respectively.

A

abscess, cerebral. See cerebral abscess abusive head injuries. See head injuries, abusive acetaminophen, 49t, 743 activated Factor VIIa, 372 acute disseminated encephalomyelitis (ADEM), 603, 604f acyclovir, 603, 689 age-related differences in pain responsiveness and pain pathways, 742 American Academy of Pediatrics (AAP) – 1987 Task Force Recommendation for Guidelines for the Determination of Brain Death in Infants and Children, updated, 50 – Back to Sleep program, 109 American Clinical Neurophysiology Society (ACNS) – 0121 protocol, 593t – 0331 protocol, 590, 592t – 0831 protocol, 593t American Heart Association (AHA) moyamoya guidelines, 800 analgesics, 49 – dosages, 49t anencephaly, 193–194 anesthesia. See neuroanesthesia aneurysms – alternate procedures, 760 – goals of surgery, 759–760 – incidence, 759 – indications for surgery, 759 – outcomes and postoperative course, 765–767 – preoperative planning, 760–763 – rupture, treated with bed rest, 759 – surgical management of, 763–764 – trapping, 760 – traumatic intracranial, 378 angiography, cerebral, 755–756 anterior spinal instrumentation, for spinal column tumors, 545–546 antiepileptic therapy, for penetrating brain injury, 365 antifibrinolytic agents, 867–868 antiparasitic drugs, 633 Apert syndrome, 158 aplasia cutis congenita, 105f arachnoid cysts, 306, 308–309, 325–329 arterial spin labeling (ASL), 820, 822f arteriovenous fistulas, spinal, 805, 806f–807f arteriovenous malformations. See also vein of Galen aneurysmal malformations (VGAMs); arteriovenous malformations, cerebral; arteriovenous malformations, spinal – anesthetic implications, 26t

– anesthetic management, 28 arteriovenous malformations, cerebral, 768–778 – classification, 775 – imaging, 774 – incidence, 768 – outcomes and postoperative course, 776–778 – recurrence, 774 – and Rendu-Osler-Weber syndrome, 768 – role of endovascular treatment, 772, 774 – role of radiosurgery, 774 – role of surgical treatment, 768–772, 773f – Spetzler-Martin grading system, 768 – and Sturge-Weber syndrome, 768 – surgical management of, 775–776, 777f – surgical planning, 775 – and vascular endothelial growth factor (VEGF), 768 arteriovenous malformations, spinal, 805–813 – classification, 805 – imaging, 810 – outcomes and postoperative course, 812 – surgical management of, 810–812, 813f Ascenda catheter, 733, 734, 735f, 736 aspirin therapy, 577 astrocytomas, adjuvant chemotherapy for, 584–587 astrocytoma, pilocytic. See pilocytic astrocytoma atlanto-occipital dislocation (AOD), 402–405 atlantoaxial fusion, 409 atlantoaxial rotatory fixation, 405–409 auditory brainstem responses (ABRs), preoperative, 667 Avitene, 868, 872 awake speech mapping, 69–70

B

Back to Sleep program (AAP), 109 baclofen. See intrathecal baclofen therapy bevacizumab, for treatment of vestibular schwannoma, 578 bilateral coronal synostosis. See synostosis, bilateral coronal bilateral fronto-orbital expansion, 115 biomaterials, for cranioplasty, 385–386 biopsy, for brainstem gliomas, 506 blood flow, cerebral, 34–35 blood loss – perioperative management, 48

– techniques for limiting, 867–873 blood pressure, arterial line, 35 blood pressure, mean, by age, 35f blood transfusions – indications for, 873 – techniques for limiting, 867–873 blood volume, cerebral, 35 bone scintigraphy, technetium 99m, 644 brachial plexus birth injuries, 413–420 – British Medical Research Council scale, 412 – incidence, 412 – outcomes and postoperative course, 420 – surgical management of, 413–420 brachial plexus exploration and repair, supine position for, 54 brachial plexus tumors, 563–569 – goals and expectations, 565–566 – incidence, 563–564 – pathological subtypes, 563–565 – surgical management of, 566–569 brain death, 50 brain manipulation and dissection, general, 12 brain tumors, molecular and genetic advances in the treatment of, 423–426 brainstem auditory evoked potentials (BAEPs), 212, 213f brainstem gliomas, 502–508 – biopsy considerations, 506 – classification, 502 – diagnosis and imaging, 504–506 – differential diagnosis, 506 – oncological treatments, 508 – outcomes and postoperative course, 507 – pathology, 506 – symptoms, 502, 504 – treatment of hydrocephalus from, 506–507 – tumor resection, 507 brainstem surgery, intraoperative monitoring during, 670, 671 British Medical Research Council scale, for brachial plexus injuries, 412

C

C-arm fluoroscopy, 740 C1 lateral mass screw procedure, for spinal column tumors, 538, 539f C1–C2 transarticular screw method, for spinal column tumors, 538, 541f C2 pars/pedicle screw process, for spinal column tumors, 538–539, 542f C3–C7 lateral mass screw technique, for spinal column tumors, 540, 543f

calvarial vault remodeling, 114 carbon dioxide, cerebrovascular response to, 36–37 catheter, Ascenda, 733, 734, 735f, 736 cauda equina surgery, intraoperative monitoring during, 670 cavernomas. See cavernous malformations cavernous angiomas. See cavernous malformations cavernous hemangiomas. See cavernous malformations cavernous malformations, 779–786 – familial, 757 – imaging, 780–782 – incidence, 779 – indications for surgery, 779–780 – outcomes and postoperative course, 786 – preoperative planning, 780–782 – and seizures, 779 – surgical management of, 785–786 – symptoms, 779 cavitron ultrasonic surgical aspirator (CUSA), 871 cerebellar astrocytoma. See pilocytic astrocytoma cerebellar mutism, 487, 494–495 cerebellopontine angle ependymoma. See infratentorial ependymomas cerebral abscess, 612–615 – outcomes and postoperative care, 614–615 – preoperative planning, 614 – surgical management of, 614 cerebral blood flow, 34–35 cerebral blood volume, 35 cerebral edema, 46–48 cerebral hemispheric tumors, 450–456 – goals of therapy, 450–451f – outcomes and postoperative course, 456 – preoperative planning, 451–452 – surgical management of, 452–455 cerebral malformations, 193–196 – disorders of prosencephalon development, 194 – incidence, 193 – migrational disorders, 195 – neuronal proliferation disorders, 194–195 – neurulation malformations, 193–194 cerebral metabolism, 33–34 cerebral oxygen kinetics, 34 cerebral palsy. See spasticity cerebral perfusion pressure (CPP), 356–357, 395–396 cerebral salt wasting, 44–45 – and meningitis, 600 cerebrospinal fluid – general, 31–32

875

876 Index cerebrospinal fluid drainage – in head injuries, 396 – for pineal region tumors, 437–438 cerebrovascular autoregulation, 35–36 cerebrovascular disease, anesthetic management in, 28–29 cerebrovascular response to carbon dioxide, 36–37 cerebrovascular response to oxygen, 37 cervical collar, 240–241 cervical stabilization, indications for, 240 checklists, 84–86 chemotherapy – as adjuvant therapy for CNS tumors, 584–587 – for brainstem gliomas, 508 Chiari I malformation, 210–219 – anesthetic implications of, 26t – and hydrosyringomyelia (syrinx) formation, 210, 211f – and scoliosis, 211 – suboccipital decompression for –– intraoperative neuromonitoring during, 71 –– with duraplasty, technique, 214–218 –– without duraplasty, technique, 213–214 –– preoperative planning and special equipment, 212–213 – in syndromic craniosynostosis, 149 Chiari II malformation, 222–229 – anesthetic implications of, 26t – clinical presentation, 224 – common manifestations, 223 – imaging, 224–225 – incidence, 222 – management algorithm, 226f – and myelomeningocele, 222 – surgical management of, 227–229 –– intraoperative neuromonitoring during, 71 – in syndromic craniosynostosis, 149 – and tethered cord release, 226 – treatment options and alternatives, 225–226 child abuse. See head injuries, abusive child life specialists, 817 Children’s Cancer Group (CCG) – 9892 study, 590 – 9942 study, 591, 593t – A9934 protocol, 592t – A9961 protocol, 592t chloroprocaine, 743 circumferential venous plexus, 174, 175f closing, surgical, general, 13–14 Cobb angle measurement of scoliosis, 253 codeine, 743 complex regional pain syndromes, 750 composite motion curve, 405–406 computed tomography (CT), 95 – advances in, 817–825 – intraoperative, 827–828 –– example operative case, 830–831 – isotropic imaging, 818, 819f congenital heart disease, anesthetic implications of, 26t

conjoined twins. See craniopagus twins constructive interference in steady state (CISS) sequences (MRI), 509, 510f, 782, 818f coordination testing, 98–99 coronal synostosis. See synostosis, coronall corpus callosotomy – for hemispherectomy/ hemispherotomy, 708 – for epilepsy, 663, 687, 712–717 cortical dysplasia, 704f cortical resective surgery – for extratemporal epilepsy, 692–693 – for rolandic epilepsy, 699 cortical surgery, intraoperative neuromonitoring during, 668, 670, 671 corticosteroids, in head injuries, 397 cranial epidural abscess, 605–611 – outcomes and postoperative course, 610–611 – preoperative planning, 606–607 – surgical management of, 607, 608–610 cranial fossa expansion, posterior, 143–144, 145f cranial immobilization, rigid, 51–52 cranial nerves – assessment, 94–95 – examination of, 96–97 cranial resective surgery, for epilepsy, 663 cranial ultrasound (cUS), 95 cranial vault reconstruction, for coronal craniosynostosis, 125–131 craniectomy, decompressive. See decompressive craniectomy craniofacial abnormality, anesthetic implications of, 26t craniopagus twins – incidence, 171 – outcomes and postoperative course, 188–190 – pearls, and pitfalls, 177–182f – preoperative planning and special equipment, 174–177f – surgical management of, 171–190 –– procedure, 182–185 – types, 182f craniopharyngioma, 431–436 – craniotomy for, 432–436 – outcomes and postoperative course, 436 – preoperative evaluation, 431–432 – preparation and positioning, 432, 433f cranioplasty, 385–394 – alternative procedures, 385–386 – biomaterials for, 385–386 – contraindications, 387–388 – goals of, 385 – outcomes and postoperative course, 394 – preoperative planning, 388, 389f – procedure, 389, 390f craniospinal irradiation (CSI), 589–594 craniospinal surgery, reducing bleeding during, 872–873

craniotomy, 7–11 – bifrontal, 139–142 – for craniopharyngioma, 432–436 – for extratemporal epilepsy, 692–693 – for hemispherectomy/ hemispherotomy, 705–706, 708f – interhemispheric transcallosal, 9–10 – midline posterior fossa, 10–11 – for pial synangiosis for moyamoya, 802 – for pineal region tumors, 440–446 – pterional, 9 – reducing bleeding during, 868–869 – skull base approach, 467–471 – third ventricle approach, 467–471 craniovertebral decompression, transoral, 236, 237f craniovertebral junction abnormalities, 233–238 – decision tree for management of, 233f – surgical management of –– craniovertebral junction fusions, 236 –– transoral craniovertebral decompression, 236 craniovertebral junction fusions, 236, 237f, 238f Crouzon syndrome, 143, 148f, 159f, 160f, 166f, 392f–393f CSF. See cerebrospinal fluid CT. See computed tomography (CT) culture of safety, 83–84 Currarino triad, 288 cystic hygroma, brachial plexus, 564–569 cysticercosis. See neurocysticercosis cystoperitoneal shunt, for arachnoid cysts, 326 cysts. See specific cysts

D

Dandy-Walker malformation – diagnostic criteria, 330 – management strategies, 330–331 – surgical management of, 332–334 – outcomes, 334 – treatment strategy, 331f Davson equation, 33 de Morsier syndrome, 194 decompressive craniectomy – for head injuries, 397 – for traumatic brain injury, 359–361 deep brain stimulation, 737–741 – image-based targeting, 738–739 – macroelectrode test stimulation, 740 – microelectrode recording, 739–740 – outcomes and postoperative course, 741 – palliative for epilepsy, 721 – pulse generator implantation, 741 deformational plagiocephaly, 109–112 – diagnosis, 109 – distinct from lambdoid synostosis, 112, 116–117 – helmet therapy for, 111 – incidence, 111 – indications for treatment, 110 – results, 112

– treatment options, 110–112 denervation injuries, anesthetic implications of, 26t dermal sinus tract, 194, 195 dermoid cysts, 308, 309 dermoid tumors, 105f, 194, 195 desmoplastic infantile gangliogliomas, 455 dexamethasone, dosages, 49t DI. See diabetes insipidus (DI) diabetes insipidus (DI), 45–46 diastematomyelia, intraoperative neuromonitoring during, 73–75 diastematomyelic bony spur, 872–873 diffuse intrinsic pontine gliomas (DIPG), 585 diffusion tensor imaging (DTI), 507, 782 diffusion-weighted imaging (DWI), 822, 823f digital subtraction catheter angiogram (DSA), 760 digoxin, 796 diskectomy, 243–244 dissection, and vascular injuries, 377 distraction, external, for frontofacial advancement, 158–169 dolichocephaly. See synostosis, sagittal dorsal rhizotomies. See selective dorsal rhizotomy Dowling technique, 626 dural opening, 11–12 – reducing bleeding during, 869–871 dynamic susceptibility contrast (DSC) perfusion MRI, 820 dysnatremia, postoperative, 42–46

E

edema, cerebral, 46–48 effective team formation, 84 electrode implantation and intraoperative electrocorticography, for temporal lobe epilepsy, 680–681 electroencephalography, 95 electromyography, spontaneous (spEMG), 65 electromyography, stimulated (stEMG), 64–65 ELISA, 632–633 embolization, endovascular, 772, 774, 796–797, 834–840 empyema, subdural. See subdural empyema encephalitis, 601, 603, 604f – herpes, 603, 604f, 689 – indications for surgical management, 603t – pathophysiology, 603 encephalocele, anesthetic management in, 28 encephalocele, occipital, 197–201 – indications for surgery, 197–198 – surgical management of, 198–201 encephalocele, sphenoethmoidal, 203–209 – incidence, 203 – and morning glory syndrome, 204 – surgical approaches, 204–206 –– extended subfrontal/olfactorysparing, 205–206

╅ –– illustrative surgical case, 206–208 –– transcranial-intradural, 205 –– transoral/transpalatal, 204–205 encephalomyelitis, acute disseminated, 603, 604f endoscope-assisted microsurgery, 853–859 – indications for, 856–857f – technique, 857–858 endoscopic approaches to the lateral and third ventricles, supine position for, 53–54 endoscopic stent placement, 332–333 endoscopic third ventriculostomy (ETV) – for hydrocephalus, 321–324 – supine position for, 53–54 Endoscopic Third Ventriculostomy Success Score, 316 endoscopy. See also endoscopeassisted microsurgery – 3D, 854 – advances in, 846–851 – anesthetic management of, 29 – for cyst treatment, 846–851 – equipment, 855, 856f – for hydrocephalus, 846–851 – laser-assisted, 326 – for optic pathway/hypothalamus tumors, 467–471 – for tumor management, 846–851 enterogenous cysts, 306, 307f, 308–309, 308f ependymal cysts, 306, 308–309 ependymoma – adjuvant radiation therapy for, 591–594 – molecular and genetic advances in the treatment of, 424–425 ependymomas, infratentorial, 496–501 – floor of the fourth syndrome, 498 – and hearing, 501 – outcomes and postoperative course, 500–501 – radiation therapy, 501 – re-irradiation, 501 – surgical management of, 496–500 epidermoid cysts, 308, 309 epidermoids, intracranial, 509–519 – clinical symptoms, 509 – imaging, 509, 510f – indications for surgery, 509 – outcomes and postoperative course, 519 – surgical management of, 511–519 epidural abscess, cranial. See cranial epidural abscess epidural catheter placements, 744 epidural steroid injection, for lumbar radiculopathy, 746–747 epilepsy. See also specific types of epilepsy – anesthetic implications of, 26t – anesthetic management of, 28 – classifications, 653–656, 657f, 660t – differential diagnosis, 651–652 – epileptogenic zones, 654–656, 657f, 663 – evaluation and imaging, 654–656, 657f – incidence, 651

– indications, 662–663 – vs nonepileptic paroxysmal events, 651–652 – palliative surgical procedures for, 712–721 –– corpus callosotomy, 712–717 –– deep brain stimulation, 721 –– multiple subpial transections, 719–721 –– vagus nerve stimulation, 717–718 – pathologies and etiologies, 662 – presurgical evaluation, 663 – refractory to medical therapy, 652–653, 655t – surgery types, 663–664 epilepsy, extratemporal – alternate procedures, 686–688 – decision-making algorithm, 685f – indications for surgery, 684↜– preoperative evaluation, 684–689 – preoperative planning, 689–691 – surgical approach, 684–686 –– craniotomy, 692–693 – surgical management of, 691–694 –– cortical resective surgery, 693, 694f epilepsy, rolandic, 695–702 – outcomes and postoperative course, 700, 702 – preoperative planning and imaging, 695–700 epilepsy, temporal lobe – goals of surgery, 675 – preoperative assessment, 674–675 – surgical management of, 675–682 –– electrode implantation and intraoperative electrocorticography, 680–681 –– lateral temporal lobe resection, 677–678, 679f –– mesial resection of the hippocampus and the amygdala, 678–680, 681f, 682f epileptogenic zones, 654–656, 657f, 663 Erb palsy. See brachial plexus birth injuries ETV. See endoscopic third ventriculostomy everolimus, for treatment of subependymal giant cell astrocytoma (SEGA) tumors, 578–579 exparel, 744–745 external ventricular catheter placement, 19–22 external ventricular drain – anatomical landmarks for placement, 358f – in traumatic brain injury, 357–359 extratemporal epilepsy. See epilepsy, extratemporal

F

facet injections, 747 Factor VIIa, activated, 372 fenestration tips, 333 fibrin glue, 419f fibrous dysplasia, 527f filum terminale, tight, 274–279 – clinical presentation, 275 – diagnosis, 275 – outcomes and postoperative course, 278–279

– preoperative evaluation, 275 – surgical management of, 277–278 flaps, skin. See skin flaps floor of the fourth syndrome, 498 fluoroscopy, C-arm, 740 focal neurologic findings, 93 fractures, skull. See skull fractures frontobasal disconnection, for hemispherectomy/ hemispherotomy, 709 frontofacial advancement, external distraction for, 158–169 fronto-orbital expansion, bilateral, 115 frontotemporoparietal decompressive craniectomy, for traumatic brain injury, 359–361 Fukuyama’s congenital muscular dystrophy, 195 functional MRI (fMRI), 656, 823, 825f – preoperative, 667, 668f, 669f fungal abscess, 622–624 fungal infection, 622

G

gait examination, 99 gangliogliomas, desmoplastic infantile, 455 ganglioneuromas, brachial plexus, 564–569 gastrointestinal reflux, anesthetic management of, 26t genetics – ependymoma, 424–425 – high-grade gliomas, 425–426 – holoprosencephaly, 194 – lissencephaly, 195 – medulloblastoma, 423–424 – pilocytic astrocytoma, 425 – septo-optic dysplasia (de Morsier syndrome), 194 – Sturge-Weber syndrome, 575 – syndromic synostosis, 143 Gigli saw, 9 Gillies tripod technique, 245 Glasgow Coma Scale (GCS), 363 glioblastoma multiforme (GBM), 585 gliomas, brainstem. See brainstem gliomas gliomas, diffuse intrinsic pontine (DIPG), 585 gliomas, high-grade. See astrocytomas gliomas, low-grade. See astrocytomas glucose utilization, 33–34 grid implantation, 667 – for rolandic epilepsy, 696–699 Gross Motor Function Classification System (GMFCS), 723 growth parameters, 94 gunshot wounds. See head injuries, penetrating

H

halo vest, 241 handoff checklists, 86 head injuries, abusive, 379–384 – additional lab studies, 380 – documentation, 380–381 – examination, 379–380 – imaging, 380, 381f – incidence, 379 – initial evaluation, 379

Index

– long-term outcome, 383–384 – operative intervention, 381–383 – perioperative care, 383 – screening, 379 – and seizures, 379 head injuries, neurointensive care of, 395–397 – antiseizure prophylaxis, 397 – cerebral perfusion pressure thresholds, 395–396 – corticosteroids, 397 – CSF drainage, 396 – decompressive craniectomy, 397 – hyperosmolar therapy, 396 – hyperventilation, 396 – hypothermia therapy, 396 – imaging, 396 – intracranial hypertension thresholds, 395 – intracranial pressure monitoring, 395 head injuries, penetrating, 363–372 – antiepileptics, 365 – goals of surgery, 363–364 – outcomes and postoperative course, 372 – perioperative antibiotics, 366 – surgical management of, 364–371 – use of activated Factor VIIa, 372 – vertex penetrating injuries, 372 helmet therapy – for deformational plagiocephaly, 111 – after surgery for sagittal synostosis, 123 hemimegalencephaly, 195, 704f hemimyelocele, and split cord malformation, 303–304 hemimyelomeningocele, 872–873 hemispherectomy/hemispherotomy, 703–711 – for epilepsy, 663, 687 – outcomes and postoperative course, 710–711 – preoperative planning, 705, 706f, 707f – procedure –– corpus callosotomy, 708 –– craniotomy and opening of the lateral ventricle, 705–706, 708f –– frontobasal disconnection, 709 –– insular resection, 709–710 –– temporal resection, 706 hemorrhagic telangiectasia (HHT), 756 high-reliability organizations, 83–86 holoprosencephaly, 194 Horner syndrome. See brachial plexus birth injuries hydatid cyst, 624–629 hydatidosis. See hydatid cyst hydrocephalus – after aneurysm surgery, 765–766 – anesthetic management of, 28 – from brainstem gliomas, 506–507 – classification, 314 – definition, 313 – endoscopic third ventriculostomy for, 321–324 – and myelomeningocele, 270 – in optic pathway/hypothalamus tumors, 466 – pathophysiology, 313–314

877

878 Index hydrocephalus (continued) – in syndromic craniosynostosis, 149 – in tuberculous meningitis, 617, 618f – ventriculoperitoneal shunting, 316–320 hydrosyringomyelia (syrinx) formation, and Chiari I malformation, 210, 211f hyperosmolar therapy, in head injuries, 396 hypertonic saline, 3%, 47–48 hyperventilation, in head injuries, 396 hypothalamic lesions, anesthetic implications of, 26t hypothalamus tumors. See optic pathway/hypothalamus tumors hypothermia therapy, in head injuries, 396

I

ICP. See intracranial pressure ictal SPECT using mTc-HMPAO, 659 idiopathic intracranial hypertension, 335–337 – diagnosis, 335 – surgical management of, 336–337 image-guided surgery, 841–845 imaging. See specific modalities immune reconstitution inflammatory syndrome (IRIS), 622 implantable cardioverter defibrillators, and MRI, 817 implantable stimulation device, for extratemporal epilepsy, 687–688 indocyanine green, 761, 810–811 infant’s response to external stimulation, 91–95 infratentorial ependymomas. See ependymomas, infratentorial infratentorial operations, prone position for, 55 infratentorial procedures, intraoperative neuromonitoring during, 70–71 insular resection, for hemispherectomy/ hemispherotomy, 709–710 interbody grafts, 243 International League Against Epilepsy (ILAE) classification, 653–656, 657f, 660t, 662 intracarotid amobarbital testing (Wada test), 656, 657t intracranial aneurysms, traumatic, 378 intracranial cysts, congenital, 325–329 – alternative treatments –– cystoperitoneal shunt, 326 –– marsupialization, 326 – surgical management of, 328–329 intracranial epidermoids. See epidermoids, intracranial intracranial hemorrhage, surgical treatment of, 756 intracranial hypertension, 149 intracranial hypertension thresholds, 395 intracranial hypertension, idiopathic. See idiopathic intracranial hypertension

intracranial pressure (ICP) – Davson equation, 33 – general, 32–33 – in head injuries, 395 – and meningitis, 600–601 – in traumatic brain injury, 355–357 – zero reference point, 33 intradural cranial surgery, reducing bleeding during, 871–872 intraoperative imaging, 827–832 intraoperative magnetic resonance imaging (iMRI), 489, 818 intraoperative neuromonitoring, 58–81, 665–673 – algorithm for, 671f – awake speech mapping, 69–70 – during brainstem surgery, 670, 671 – during cauda equina surgery, 670, 672 – during Chiari I malformation suboccipital decompression, 212–213 – during Chiari malformation procedures, 71 – complications, 673 – during cortical surgery, 668, 670 – during diastematomyelia surgery, 73–75 – during infratentorial procedures, 70–71 – optimal anesthetic techniques for, 65–66 – during peripheral nerve surgery, 77–78f – postoperative considerations, 672–673 – role of, 78–80 – during spinal cord surgery, 670, 671 – during spinal dysraphism surgery, 71–73 – spontaneous electromyography (spEMG), 65 – stimulated electromyography (stEMG), 64–65 – during supratentorial procedures, 66–68 – during surgery for spine tumors, 75–77 – transcranial electrical motor evoked potentials (tceMEPs), 59–64 intrathecal baclofen therapy, 747 – cranial intraventricular insertion, 733, 734f – high cervial spinal insertion, 732–733 – long-term trial insertion methods, 733–734, 735f, 736 – lumbar insertion in the fused spine, 733 – for movement disorders, 731–736 – outcomes and postoperative course, 736 – for spasticity, 727–730 – therapy trial, 732 intrathecal port for cancer pain, 747–749 intrathoracic trauma, 41t intravenous fluids – glucose vs no glucose, 46 – inappropriate, 43 – perioperative, 40, 42 intraventricular tumors, 457–465 – outcomes and postoperative course, 463–464

– preoperative planning, 458–459 – surgical management of –– transcallosal approaches to the lateral and third ventricles, 460–462f –– transcortical approaches to the lateral and third ventricles, 459–460 invasive video-EEG recording, 699, 700f isotropic imaging, 818, 819f

J

Japan’s Ministry of Health and Welfare moyamoya guidelines, 800

K

Klippel-Trenaunay syndrome, and stroke, 757 Klumpke palsy. See brachial plexus birth injuries Kocher’s point, 357–358 kyphosis, 246–251 – preoperative planning, 246–247 – surgical management of –– pedicle subtraction osteotomy, 249–250 –– ponte osteotomies, 248–249 –– vertebral column resection, 250–251

L

lambdoid synostosis. See synostosis, lambdoid lambdoid synostosis, distinct from deformational plagiocephaly, 112 lapatinib, for treatment of vestibular schwannoma, 578 laser interstitial thermoablative therapy (LITT), 860–866 laser-assisted neuroendoscopy, 326 lateral position, 55 lateral temporal lobe resection, for temporal lobe epilepsy, 677–678, 679f latex allergy, 41t leptomeningeal angiomatosis, 575 lesion management, during surgery, general, 12–13 lesionectomy, for epilepsy, 663 lipoblastoma, brachial plexus, 565–569 lipoma, 106f lipoma, brachial plexus, 565–569 lipomas, spinal. See spinal lipomas lipomyelomeningocele. See spinal lipomas lissencephaly, 195 lumbar puncture, 17–19 lumbar radiculopathy, epidural steroid injection for, 746–747

M

magnetic resonance imaging (MRI), 95, 224–225 – 3 Tesla (3T), 817–818 – advances in, 817–825 – constructive interference steady state (CISS) images, 509, 510f, 782, 818f – dynamic susceptibility contrast (DSC) perfusion, 820 – functional (fMRI), 656, 667, 668f, 669f, 823, 825f

– and implantable cardioverter defibrillators, 817 – intraoperative (iMRI), 489, 818, 827 –– example operative case, 828–830 – isotropic imaging, 818, 819f – for rolandic epilepsy, 696 – short T1 inversion recovery (STIR), 95 – for stroke, 755 – vent check, 820 – video goggles for, 817 magnetoencephalography (MEG), 656 – for rolandic epilepsy, 696 malignant peripheral nerve sheath tumors (MPNSTs), 563–569 Management of Myelomeningocele Study trial, 223, 225 mannitol, 46–47 marsupialization, for arachnoid cysts, 326 McKenzie perforator, 7–8 medial branch blocks, 747 medical modeling, 174, 175f, 176f, 177f, 178f, 188f medulloblastoma, 488–495, 586–587 – adjuvant radiation therapy, 590–594 – molecular and genetic advances in the treatment of, 423–424 – outcomes and postoperative course, 494–495 – preoperative planning, 489–490 – surgical management of, 490–494 –– telovelar approach, 491, 494f –– transvermian approach, 492 –– tumor resection, 492–493 melanocytic nevus, 524f MELAS, 757 meningitis, 599–601, 602f, 603t. See also tuberculous meningitis – antibiotic therapy, 601 – clinical symptoms, 599–600 – CSF findings, 600, 600t – indications for surgical management, 603t – therapy for, 600 mesial resection of the hippocampus and the amygdala, for temporal lobe epilepsy, 678–680, 681f, 682f metopic synostosis. See synostosis, metopic Miami Imaging Pipeline, 690f microcephaly, 194–195 microsurgery, endoscope-assisted, 853–957 midline fourth ventricular ependymoma. See ependymomas, infratentorial migrational disorders, 195 Miller-Dieker syndrome, 195 Mondini dysplasia, 601, 602f monobloc distraction procedure, 158–169 morning glory syndrome, and sphenoethmoidal encephalocele, 204 morphine, dosages, 49t motor examination, 97–98 movement disorders, intrathecal baclofen therapy for, 731–736 moyamoya disease/syndrome, 28–29, 757, 799–804 – alternative procedures, 800

╅ – guidelines justifying surgery, 800 – imaging, 801 – outcomes and postoperative course, 804 – pial synangiosis for, 799–804 – surgical treatment of, 756 MRI. See magnetic resonance imaging (MRI) MRI-guided laser-induced thermal ablation, for epilepsy, 664, 688 multiple subpial transection (MST), for epilepsy, 687, 719–721 multisutural synostosis. See synostosis, multisutural muscle bulk, 97 muscle strength, 97, 98t myelographic sequences, 818 myelomeningocele, 269–273 – anesthetic management, 28 – and Chiari II malformation, 222 – and hydrocephalus, 270 – and split cord malformation, 303–304 – surgical management of, 270–273

N

nausea and vomiting, postoperative management, 49 neonate observation, 91 nerve blocks – medial branch, 747 – peripheral, 743 –– continuous, 750 nerves, of the scalp, 343t neuroanesthesia – agents and drugs, 38 – coexisting conditions that affect anesthetic management, 26t – emergence from, 39 – failure to awaken from, 39, 40t – influence on postoperative care, 37–40 – maintenance of, 27 – management of fluids and blood loss, 27 – management of specific disorders, 28–29 – optimal techniques for intraoperative neuromonitoring, 65–66 – preoperative planning for, 25 – regional, 743 – vascular access and positioning, 26–27 neuroblastomas, brachial plexus, 564–569 neurocutaneous syndromes, 573–582 neurocysticercosis, 630–638 – antiparasitic drugs, 633–634 – clinical manifestations, 632 – diagnosis, 632–633 – endoscopic treatment, 635–638 –– in fourth ventricle, 636–637 –– in interpeduncular cistern, 637 –– in lateral ventricles, 635, 636f –– in sylvian fissure, 637–638 –– in third ventricle, 635–636 – etiopathogenesis, 630–632 – incidence, 630 – medical treatment, 633–634 – outcome and postoperative course, 638 – treatment algorithm, 634f

neuroembryology, 193 neurofibromas, brachial plexus, 563–569 neurofibromatosis 1 (NF1), 573–574 – advantages/contraindications, 579 – alternate treatments, 578 – and optic pathway/hypothalamus tumors, 466–472 – outcomes and postoperative course, 582 – preoperative planning, 580 – surgical goals, 577 – surgical management of, 581 – treatment indicators, 575–576 neurofibromatosis 2 (NF2), 573–574 – advantages/contraindications, 579 – alternate treatments, 578 – outcomes and postoperative course, 582 – preoperative planning, 580 – surgical goals, 577–578 – surgical management of, 581 – treatment indications, 576–577 neuroimaging, 396 – advances in, 817–825 neurologic examination – neonatal, 91–95 – pediatric, 96–99 – traditional, 94–95 neurologic findings, focal, 93 neurolytic blockade, 750 neuromaturation, evidence for, 92–93 neuromuscular disease, anesthetic implications, 26t neuronal proliferation disorders, 194–195 neuromonitoring, intraoperative, 58–81 neuroradiology, interventional, 834–840 neurulation malformations of the brain, 193–194 nonepileptic paroxysmal events, vs epilepsy, 651–652 nonsteroidal anti-inflammatory drugs (NSAIDs), 743

O

O-arm, intraoperative CT, 827–828 occipital encephalocele. See encephalocele, occipital occipital screw technique, for spinal column tumors, 538, 539f occipital-cervical fusion with instrumentation, 409–410f Ohm’s law, 35 ondansetron, dosages, 49t operating room setup, general, 3 opioids, 742–743 optic pathway/hypothalamus tumors, 466–472, 576 – hydrocephalus treatment, 466 – outcomes and postoperative course, 471–472 – surgical management of –– craniotomy, skull base approach, 467–471 –– craniotomy, third ventricle approach, 467–471 –– endoscopy, 467–471 orbit tumors. See skull base and orbit tumors

orbitozygomatic approach to skull base tumors, 530 osteodistraction devices and modalities, 149–150 osteomyelitis, vertebral, 643–646 osteotomy, pedicle subtraction, 249–250 oxycodone, 743 – dosages, 49t oxygen kinetics, cerebral, 34 oxygen, cerebrovascular response to, 37

P

pain management, postoperative, 48–50 pain – acute, 742–745 – age-related differences in responsiveness and pathways, 742 – cancer, 747–749 – chronic, 745–750 – epidemiology of chronic in children vs adults, 745 parasitic infestation, 624 park bench position, 55 patient positioning. See positioning, patient Pediatric Oncology Group (POG) – 8633 study, 591 – 9132 study, 591, 593t pedicle subtraction osteotomy, 249–250 penetrating head injuries. See head injuries, penetrating percutaneous subdural tap, 22–24 perfusion imaging, 820 perinatal stroke, 704f perioperative antibiotics, for penetrating brain injuries, 366 perioperative management, 30–48 – of crises, 40, 41t – IV fluids, 40, 42 peripheral nerve blocks, 744 peripheral nerve surgery, intraoperative neuromonitoring, 77–78f Pfeiffer syndrome, 143 PHACES(S) syndrome, and stroke, 756 pial synangiosis – goals of, 800 – for moyamoya syndrome, 799–804 – outcomes and postoperative course, 804 – preoperative planning, 801 – procedure, 801–803 pilocytic astrocytoma, 481–487. See also brainstem gliomas – goals of surgery, 482–484 – molecular and genetic advances in the treatment of, 425 – on MRI, 481, 482f, 483f – outcomes and postoperative course, 487 – preoperative planning, 485 – surgical management of, 485–486 pineal region tumors, 437–448 – craniotomy for, 440–446 –– retrocallosal approach, 444, 446f, 447f –– transcallosal approach, 444, 446, 448f – CSF drainage, 437–438

Index

– outcomes and postoperative course, 448 – patient positioning, 438–440 pituitary adenoma, endonasal transphenoidal resection of, 529f pituitary lesions, anesthetic implications of, 26t pituitary tumors, 473–477 – outcomes and postoperative course, 476–477 – preoperative planning, 473–474 – surgical management of, 474–476 plagiocephaly, deformational. See deformational plagiocephaly ponte osteotomies, 248–249 positioning, patient, 4, 51–57 – anesthetic implications of, 26–27 – lateral position, 55 – for pineal region tumors, 438–440 – physiologic effects of, 27t – prone position, 54–55 – rigid cranial immobilization, 51–52 – sitting position, 56 – supine position, 52–54 positron emission tomography (PET), 656 – for rolandic epilepsy, 696 posterior cranial fossa expansion, 143–144, 145f posterior fossa syndrome, 494–495 posterior fossa tumors, anesthetic management, 28 postoperative care, anesthetics influencing, 37–40 prematurity, anesthetic implications of, 26t preoperative case review checklist, 31t preoperative fasting guidelines, 26t preoperative neuromonitoring, 666–668 preoperative planning, general, 3 primitive reflexes, neuromaturation of, 92–93 prone position, 54–55 – for infratentorial operations, 55 propofol, 50 propofol infusion syndrome, 50 prosencephalon development disorders, 194 pseudomeningocele, 414f pyogenic diskitis, 643–646

R

radial microbrain, 195 radiation therapy – adjuvant, 589–594 – craniospinal irradiation (CSI), 589–594 – focal, for brainstem gliomas, 508 – for infratentorial ependymomas, 501 radiation therapy protocols – American Clinical Neurophysiology Society (ACNS) –– 0121 protocol, 593t –– 0331 protocol, 590, 592t –– 0831 protocol, 593t – Children’s Cancer Group (CCG) –– 9892 study, 590 –– 9942 study, 591, 593t –– A9934 protocol, 592t –– A9961 protocol, 592t

879

880 Index radiation therapy protocols (continued) – Pediatric Oncology Group (POG) –– 8633 study, 591 –– 9132 study, 591, 593t – St. Jude –– SJMB03 protocol, 592t –– SJMB12 protocol, 592t –– SJMB96 protocol, 592t –– SJYC07 protocol, 592t radiation-induced vasculopathy, 757 Rasmussen encephalitis, 704f, 707f reflexes – assessment of, 98 – grading of, 98t – primitive, neuromaturation of, 92–93 relative cerebral blood volume map, 821f Rendu-Osler-Weber syndrome, and cerebral arteriovenous malformations, 768 retrosigmoid/presigmoid approach, to skull base tumors, 532 rigid cranial immobilization, 51–52 Risser sign for scoliosis, 253 rolandic epilepsy. See epilepsy, rolandic

S

sacrectomy, for spinal column tumors, 542, 544f, 545 safety, surgical, 83–87 sagittal synostosis. See synostosis, sagittal salt loss, vs CSF drainage, 42 scalp anatomy, 341–343 scalp flap, reducing bleeding during, 868, 869f scalp incisions, general, 5–7f scalp injuries – flaps, 345–347 – management of, 341–347 – repair with intact tissue, 344 – repair with loss of tissue, 344 – skin grafts, 344–345 – tissue expansion, 347 scalp tumors, 523–528 – outcomes and postoperative course, 526, 528 – surgical management of, 524–527f scalp, congenital defects of, 105–108 scaphocephaly. See synostosis, sagittal schizencephaly, 195 schwannomas, brachial plexus, 563–569 schwannomas, vestibular – and hearing, 576–577, 578 – and treatment with bevacizumab, 578 – and treatment with lapatinib, 578 schwannomatosis, 574 scoliosis, 252–265 – and Chiari I malformation, 211 – incidence, 252 – indications for surgery, 253 – indications for use of orthosis, 254 – measurement –– Cobb angle, 253 –– Risser sign, 253 – outcomes and postoperative course, 264–265

– surgical management of, 254–263 sedation management, postoperative, 48–50 seizures – and abusive head injuries, 379 – antiseizure prophylaxis for head injuries, 397 – and cavernous malformations, 779 – postoperative, 50 selective dorsal rhizotomy – intraoperative monitoring during, 670, 672 – for spasticity, 723–727 sensory examination, 98 septo-optic dypslasia, 194 serum uric acid, 44 short T1 inversion recovery (STIR) MRI, 95 SIADH. See syndrome of inappropriate antidiuretic hormone secretion (SIADH) single shot fast spin echo (SSFSE) imaging, 820 site-1 sodium channel blockers, 745 sitting position, 56 skin flaps – local flaps, 345–346 – regional (distant pedicle) and free flaps, 346–347 – for scalp injuries, 345–347 skin grafts, 344–345 skin incisions, reducing bleeding during, 868 skull base and orbit tumors, 529–532 – outcomes and postoperative course, 532 – surgical management of, 530–532 –– orbitozygomatic/modified orbitozygomatic/supraorbital craniotomy approach, 530 –– retrosigmoid/extended retrosigmoid/presigmoid approach, 532 –– transcondylar/far lateral approach, 532 –– transfacial/anterior craniofacial approach, 532 –– transpetrosal/anterior petrosectomy approach, 531–532 –– transsphenoidal approach, 530 skull fractures, 348–354 – indications for surgery, 348–349 – outcomes and postoperative course, 353–354 – preoperative planning, 350 – surgical management of, 351–353 skull tumors, 523–528 – outcomes and postoperative course, 526, 528 – surgical management of, 524–527f skull, congenital defects of, 105–108 sodium channel blockers, site-1, 745 somatosensory evoked potentials (SSEPs), 59, 60f, 212 – preoperative, 666 spasticity, 723–730 – intrathecal baclofen therapy for, 727–730 – selective dorsal rhizotomy for, 723–727 speech mapping, awake, 69–70 spEMG. See spontaneous electromyography (spEMG)

Spetzler-Martin grading system, for cerebral arteriovenous malformations, 768 spinal column tumors, 537–546 – operative detail and preparation, 537–538 – surgical management of –– anterior spinal instrumentation, 545–546 –– C1 lateral mass screw procedure, 538, 540f –– C1–C2 transarticular screw method, 538, 541f –– C2 pars/pedicle screw process, 538–539, 542f –– C3–C7 lateral mass screw technique, 540, 543f –– occipital screw technique, 538, 539f –– sacrectomy, 542, 544f, 545 –– sublaminar wire/band strategy, 541 –– thoracic and lumbar pedicle screw procedure, 541–542 –– translaminar screw approach, 539–540, 543f spinal cord injuries, 399–410 – atlantoaxial fusion, 409 – atlantoaxial rotatory fixation, 405–409 – atlanto-occipital dislocation (AOD), 402–405 – biomechanical considerations, 399 – occipital-cervical fusion with instrumentation, 409–410f – spinal cord injury with radiographic abnormality (SCIWORA), 400–402 spinal cord injury without radiographic abnormality (SCIWORA), 400–402 spinal cord surgery, intraoperative monitoring during, 670, 671 spinal cord tumors, extramedullary, 547–555 – outcomes and postoperative course, 553–555 – surgical management of, 550–553 spinal cord tumors, intramedullary, 556–562 – incidence, 556 – outcomes and postoperative course, 562 – preoperative planning, 556 – surgery vs radiation, 556 – surgical management of, 557–562 spinal cysts, congenital, 306–309 spinal deformity. See kyphosis; scoliosis spinal dysraphism, intraoperative neuromonitoring, 71–73 spinal infections, 643–646 spinal lipomas, 287–292 – Currarino triad, 288 – surgical management of, 288–292 spinal surgery, reducing bleeding during, 872–873 spinal tethering tracts, 280–286 – outcomes and postoperative course, 285–286 – surgical management of, 281–285 spinal tumors, intraoperative neuromonitoring, 75–77

split cord malformation, 293–304 – associated myelomeningocele and hemimyelocele, 303–304 – associated open neural tube defect, 298–299 – classification of, 293–296 – clinical features, 300–301 – embryogenesis, 293–298 – indications for surgery, 300–301 – preoperative neuroimaging, 301 – and retethering, 304 – surgical management of, 301–304 – ventral tethering and associated intestinal anomalies, 303 spontaneous electromyography (spEMG), 65 SSEPs. See somatosensory evoked potentials (SSEPs) St. Jude – SJMB03 protocol, 592t – SJMB12 protocol, 592t – SJMB96 protocol, 592t – SJYC07 protocol, 592t St. Louis Scale for Pediatric Gunshot Wounds to the Head, 363 Starling equation, 48t Starling resistor model, 38 status epilepticus, postoperative, 50 stEMG. See stimulated electromyography (stEMG) stents, endoscopic use, 332–333 stereotactic neuronavigation system, 842f stereotaxy, 843f stimulated electromyography (stEMG), 64–65 stroke – causes, 755 – clinical presentation, 755 – and hemorrhagic telangiectasia, 756 – imaging, 755–756 – incidence, 755 – ischemic, 756 – and Klippel-Trenaunay syndrome, 757 – and PHACE(S) syndrome, 757 – syndromes and diseases associated with, 756–757 – and vascular injuries, 377 – and Wyburn-Mason syndrome, 757 Sturge-Weber syndrome, 575, 704f – advantages/contraindications, 579 – alternate treatments, 579 – and cerebral arteriovenous malformations, 768 – outcomes and postoperative course, 582 – preoperative planning, 580, 581 – surgical goals, 578 – surgical management of, 581 – treatment indicators, 577 subdural empyema, 605–611 – outcomes and postoperative course, 610–611 – preoperative planning, 606–607 – surgical management of, 607, 608–610 subdural tap, percutaneous, 22–24 subependymal giant cell astrocytoma (SEGA) tumors, 577 – and treatment with everolimus, 578–579

╅ sublaminar wire/band strategy, for spinal column tumors, 541 suboccipital decompression – with duraplasty, technique, 214–218 – without duroplasty, technique, 213–214 – without vs with duroplasty, 211–212 sudden infant death syndrome (SIDS), 109 sun-setting eyes, 97 superficial temporal artery–middle cerebral artery (STA–MCA) bypass, for moyamoya, 800 supine position, 52–54 – for brachial plexus exploration and repair, 54 – for endoscopic approaches to the lateral and third ventricles, 53–54 – for endoscopic third ventriculostomy, 53–54 – for tumor resection, 53 – for ventricular shunt insertion or revision, 52–53 supratentorial procedures, intraoperative neurophysiological monitoring for, 66–68 supratentorial tumors, anesthetic management of, 28 surgical complication rates, 83 surgical preparation and draping, 5 surgical safety, 83–87 – checklist, 85f susceptibility-weighted imaging (SWI), 822, 824f syndrome of inappropriate antidiuretic hormone secretion (SIADH), 43–44 – and meningitis, 600 synostosis, coronal – bilateral, surgical repair of, 129–130 – minimally invasive treatments, 154, 155f, 156f – surgical repair of, 132–137 – unilateral, 115, 125–129f synostosis, lambdoid, 115 – distinct from deformational plagiocephaly, 116–117 synostosis, metopic, 115 – minimally invasive treatments, 154, 157f, 158f – surgical repair of, 138–142 synostosis, multisutural, 115 synostosis, nonsyndromic – incidence, 113 – lambdoid, 115 – metopic, 115 – multisutural, 115 – overview, 113–118 – presentation and diagnosis, 114 – sagittal, 114–115 – vs syndromic synostosis, 144t – unilateral coronal, 115 synostosis, sagittal, 114–115 – incidence, 119 – minimally invasive treatments, 151–154 – postoperative helmet therapy, 123 – surgical repair of, 119–124 – treatment goals, 119 synostosis, syndromic, 143–150 – and Chiari malformation, 149

– frontofacial advancement, 158–169 – genetic causes, 143 – vs nonsyndromic synostosis, 144t syrinx formation (hydrosyringomyelia), and Chiari I malformation, 210, 211f

T

Taenia solium. See neurocysticercosis TBI. See traumatic brain injury (TBI) tceMEPs. See transcranial electrical motor evoked potentials (tceMEPs) technetium 99m bone scintigraphy, 644 telovelar approach, to medulloblastomas, 491, 494f temporal lobe epilepsy. See epilepsy, temporal lobe temporal resection, for hemispherectomy/ hemispherotomy, 706 tethered cord release, and Chiari II malformation, 226 tethered cord surgery, intraoperative monitoring, 670, 672 tethering tracts, spinal. See spinal tethering tracts thermal ablation, MRI-guided laserinduced, 664 thermoablative therapy, laser interstitial, 860–866 thoracic and lumbar pedicle screw procedure, for spinal column tumors, 541–542 tight filum terminale, 274–279 timeout, during surgical procedures, 3–4 tissue expansion, for scalp injuries, 347 tone and motor skill, neuromaturation of, 92 tone and reflexes – assessment of, 93 – symmetric changes in, 93 torticollis, 110, 111 tracheotomy vs no tracheotomy during monobloc distraction, 162 tractography, 467, 822, 824f – preoperative, 667, 668f, 669f transcallosal approaches to the lateral and third ventricles – for intraventricular tumors, 460–462f transcondylar/far lateral approach, to skull base tumors, 532 transcortical approaches to the lateral and third ventricles, for intraventricular tumors, 459–460 transcranial Doppler ultrasound, for vasospasm monitoring, 765 transcranial electrical motor evoked potentials (tceMEPs), 59–64 transfacial/anterior craniofacial approach, to skull base tumors, 532 translaminar screw approach, for spinal column tumors, 539–540, 543f transpetrosal/anterior petrosectomy approach, to skull base tumors, 531–532 transsphenoidal approach, to skull base tumors, 530 transvermian approach, to medulloblastomas, 492

traumatic brain injury (TBI), 355–361 – indications for surgery, 355–357 – management of intracranial pressure, 355–357 – nonsurgical management of, 357–359 – outcomes and postoperative course, 361 – pediatric guidelines, 355 – surgical management of, 359–361 – treatment algorithm, 356 traumatic intracranial aneurysms, 378 trigonocephaly. See synostosis, metopic triphasic pattern (in postoperative electrolyte disturbance and DI), 45 tuberculomas, 619, 621–622 tuberculous meningitis, 616–619, 620f – and HIV, 622 – hydrocephalus during, 617, 618f tuberculous spondylitis, 622, 643–646 tuberous sclerosis complex, 574–575 – advantages/contraindications, 579 – alternative treatments, 578–579 – outcomes and postoperative course, 582 – preoperative planning, 580, 581 – surgical goals, 578 – surgical management of, 581 – treatment indicators, 577 tumescent solution, 163 tumor resection, supine position for, 53

U

ultrasound – cranial, 95 – intraoperative, 212, 828 –– example operative case, 831 – for peripheral and neuraxial blocks, 744 – prenatal, 224 – for stroke, 755 unilateral coronal synostosis. See synostosis, coronal, unilateral universal protocol, 84–85 upper respiratory tract infection – anesthetic implications, 26t uric acid, serum, 44

V

vagus nerve stimulation, for epilepsy, 663, 688, 717–718 vascular endothelial growth factor (VEGF), and cerebral arteriovenous malformations, 768 vascular injuries, 374–378 – and dissection and stroke, 377 – incidence, 374 – nonpenetrating, 376–377 – penetrating, 374–376 – traumatic intracranial aneurysms, 378 – vasospasm, 378 vasospasm, 35, 765 – following vascular injuries, 378 vein of Galen aneurysmal dilatation, 788, 790 – dural, 790 – pial, 788, 790

Index

vein of Galen aneurysmal malformations (VGAMs), 788–798 – angioarchitecture of, 794–795 – choroidal, 788, 789f–790f, 791f – classification, 788 – clinical manifestations, 795 – embolization, 795 – embryology, 790, 794 – endovascular embolization, 796–797 – mural, 788, 792f, 793f–794f – neonatal management, 796 – outcomes, 797 – prenatal management, 796 – treatment, 795 vein of Galen varix, 790 venous air embolism, 41t venous circulation of the brain, 149 venous malformations, 779–786 ventral tethering, and split cord malformation, 303 ventricular catheter, external. See external ventricular catheter ventricular shunt – bedside functional assessment of, 15–17 – insertion or revision, supine position for, 52–53 ventricular system, 313–314 ventriculomegaly, 313–314 ventriculoperitoneal shunting – for hydrocephalus, 316–320 – intraoperative issues, 316–319 vertebral column disorders, 240–245 – alternate procedures, 240–241 – indications for cervical stabilization, 240 – outcomes and postoperative course, 244–245 – preoperative preparation, 242–243 – procedure, 243 – surgical management of –– instrumentation, 243–244 –– interbody grafts and biologics, 243 vertebral column resection, 250–251 vertex penetrating injuries, 372 vestibular schwannoma – endoscope-assisted microsurgery for, 856f–857f – and hearing, 576–577 video goggles, for MRI, 817 visual system, neuromaturation of, 92 vitamin K deficiency, 380 volumetrics, 508 vomiting and nausea, postoperative management of, 49

W

Wada test (intracarotid amobarbital testing), 656, 657t Walker-Warburg syndrome, 195 winged needles, 16 World Health Organization – Safe Surgery Saves Lives Study Group, 85–86 Wyburn-Mason syndrome, and stroke, 757

X

xenon light, for endoscopy, 855 xylocaine, 868

881