Photo Atlas of Skull Base Dissection 9781588905215, 2008029454

Table of contents :
Contents
I
Anterior Skull Base
1 Craniofacial Anatomy
2 Transmaxilloethmoidal Approach
3 Transfacial Transmaxillary Approach
4 Bifrontal Transbasal Approach
5 Endonasal Paraseptal Transsphenoidal
Approach
6 Transoral Approach
7 Orbital Approach
II
Anterolateral Skull Base
8 Anatomy for Anterolateral Skull Base
Surgery
9 Frontotemporal Orbitozygomatic
Transcavernous Approach
III
Lateral Skull Base
10 Anatomy for Lateral Skull Base Surgery
11 Preauricular Transzygomatic Approach
to the Anterior Infratemporal Fossa and
Middle Infratemporal Fossa
12 Middle Fossa
IV
Posterolateral Skull Base
13 Anatomy for Posterolateral Skull
Base Surgery
14 Transmastoid Approach:
Retrolabyrinthine, Translabyrinthine,
and Transcochlear Approaches
15 Combined Petrosal Approach
16 Postauricular Transmastoid Posterior
Infratemporal Fossa Transjugular
Approach
17 Total Petrosectomy with Partial
Clivectomy
V
Posterior Skull Base
18 Anatomy for Posterior Skull
Base Surgery
19 Transcondylar Transtubercular Approach
20 Lateral Suboccipital Approach: Superior,
Middle, and Inferior Cerebellopontine
Angle Approach
Index

Citation preview

Photo Atlas of Skull Base Dissection

Photo Atlas of Skull Base Dissection Techniques and Operative Approaches Masahiko Wanibuchi, MD, PhD Instructor Department of Neurosurgery Sapporo Medical University School of Medicine Skull Base Fellow Duke University Medical Center Allan H. Friedman, MD Guy L. Odom Professor of Neurological Surgery Neurosurgeon-in-Chief Program Director Duke University Medical Center Division of Neurosurgery/Department of Surgery Takanori Fukushima, MD Director Carolina Neuroscience Institute and Skull Base Surgery Center Professor of Neurosurgery Duke University Medical Center, Duke Raleigh Community Hospital, and West Virginia University Medical Center

Thieme New York • Stuttgart

Thieme Medical Publishers, Inc. 333 Seventh Avenue New York, NY 10001 Executive Editor: Kalen D. Conerly Associate Editor: Ivy Ip Vice President, Production and Electronic Publishing: Anne T. Vinnicombe Production Editor: Martha Wetherill Vice President, International Marketing and Sales: Cornelia Schulze Sales Director: Ross Lumpkin Chief Financial Officer: Peter van Woerden President: Brian D. Scanlan Compositor: Macmillan Solutions Printer: Everbest Printing Company, Ltd Library of Congress Cataloging-in-Publication Data Wanibuchi, Masahiko. Photo atlas of skull base dissection / Masahiko Wanibuchi, Allan H. Friedman, Takanori Fukushima. p. ; cm. Includes index. ISBN 978-1-58890-521-5 1. Skull base—Dissection—Atlases. 2. Skull base—Surgery—Atlases. I. Friedman, Allan H. (Allan Howard), 1949- II. Fukushima, Takanori. III. Title. [DNLM: 1. Skull Base—anatomy & histology—Atlases. 2. Dissection—methods—Atlases. 3. Skull Base— surgery—Atlases. WE 17 W247p 2009] RD529.W26 2009 617.5'1400222—dc22 2008029454 Copyright © 2009 by Thieme Medical Publishers, Inc. This book, including all parts thereof, is legally protected by copyright. Any use, exploitation, or commercialization outside the narrow limits set by copyright legislation, without the publisher’s consent, is illegal and liable to prosecution. This applies in particular to photostat reproduction, copying, mimeographing or duplication of any kind, translating, preparation of microfilms, and electronic data processing and storage. Important note: Medical knowledge is ever-changing. As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy may be required. The authors and editors of the material herein have consulted sources believed to be reliable in their efforts to provide information that is complete and in accord with the standards accepted at the time of publication. However, in view of the possibility of human error by the authors, editors, or publisher of the work herein, or changes in medical knowledge, neither the authors, editors, or publisher, nor any other party who has been involved in the preparation of this work, warrants that the information contained herein is in every respect accurate or complete, and they are not responsible for any errors or omissions or for the results obtained from use of such information. Readers are encouraged to confirm the information contained herein with other sources. For example, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this publication is accurate and that changes have not been made in the recommended dose or in the contraindications for administration. This recommendation is of particular importance in connection with new or infrequently used drugs. Some of the product names, patents, and registered designs referred to in this book are in fact registered trademarks or proprietary names even though specific reference to this fact is not always made in the text. Therefore, the appearance of a name without designation as proprietary is not to be construed as a representation by the publisher that it is in the public domain. Printed in China 54321 ISBN 978-1-58890-521-5

To all of my family: my wife, Masako; my son, Sora; and my daughter, Momoko. And to my teachers: Drs. Kazuo Hashi, Kiyohiro Houkin, Allan H. Friedman, and Takanori Fukushima. —Masahiko Wanibuchi, MD, PhD

To my teachers: Drs. Odom, Wilkins, Yasargil, Drake, and Fukushima. —Allan H. Friedman, MD

To my patients with skull base tumors. —Takanori Fukushima, MD, DMSc

Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi I Anterior Skull Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 1

Craniofacial Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Chapter 2

Transmaxilloethmoidal Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Chapter 3

Transfacial Transmaxillary Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Chapter 4

Bifrontal Transbasal Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Chapter 5

Endonasal Paraseptal Transsphenoidal Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Chapter 6

Transoral Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Chapter 7

Orbital Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 7.1 Transcranial Orbital Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 7.2 Lateral Orbital Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

II Anterolateral Skull Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Chapter 8 Chapter 9

Anatomy for Anterolateral Skull Base Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Frontotemporal Orbitozygomatic Transcavernous Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

III Lateral Skull Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Chapter 10 Anatomy for Lateral Skull Base Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 10.1 Anatomy and Exploration of the Infratemporal Fossa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 10.2 Anatomy and Exploration of the Facial Nerve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Chapter 11 Preauricular Transzygomatic Approach to the Anterior Infratemporal Fossa and Middle Infratemporal Fossa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach. . . . . . . . . . . . . . . . . . 166 11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach . . . . . . . . . . . . . . . . . . . 193 Chapter 12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 IV Posterolateral Skull Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Chapter 13 Anatomy for Posterolateral Skull Base Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .241 13.1 Superior Petrosa (Middle Fossa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 13.2 Lateral Petrosa (Mastoid) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 13.3 Posterior Petrosa (Inner Petrosa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256

viii

Contents

Chapter 14 Transmastoid Approach: Retrolabyrinthine, Translabyrinthine, and Transcochlear Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.1 Retrolabyrinthine Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.2 Translabyrinthine Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.3 Transcochlear Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

267 267 281 286

Chapter 15 Combined Petrosal Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Chapter 16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach . . . . . . . . . . 311 Chapter 17 Total Petrosectomy with Partial Clivectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 V Posterior Skull Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 Chapter 18 Anatomy for Posterior Skull Base Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 Chapter 19 Transcondylar Transtubercular Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 Chapter 20 Lateral Suboccipital Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.1 Superior Cerebellopontine Angle Approach for Trigeminal Neuralgia and Paratrigeminal Lesions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.2 Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors . . . . . . . . . . . . 20.3 Inferior Cerebellopontine Angle Approach for Hemifacial Spasm and Jugular Foramen Lesions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

402 402 409 421

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

Foreword

Like other subspecialties of neurosurgery, skull base surgery has continuously developed over the past three decades. In spite of many alternative modalities to microsurgery, specific skull base techniques are still frequently required to treat complex lesions involving the base of the skull. Teaching such techniques to the younger generation of neurosurgeons has become a major task of those who have pioneered developing and mastering these techniques. Thus, several centers around the world provide excellent hands-on courses of skull base anatomy and surgery. These complex techniques require not only profound theoretical knowledge but also practical laboratory work on anatomical specimens before the techniques can be routinely applied in the operating room. With its detailed figures and legends as visual and textual guides, Photo Atlas of Skull Base Dissection perfectly fulfills the prerequisites to learning a broad spectrum of skull base approaches and dissection techniques in the anatomical lab. The more than 1,200 high-quality color photographs are impressive and unique. As all of the images were obtained from the authors’ personal dissections, they demonstrate skill and meticulous technique, and reflect Professor Takanori Fukushima’s vast experience with all aspects of skull base surgery. Moreover, the photographs reveal the authors’ special sense for important anatomical and surgical details necessary for such demanding work. The photographs are arranged throughout the atlas in a uniform fashion. Each page contains figures on the right

side of the page corresponding to figure legends on the left side of the page. Altogether, these figure legends form a comprehensive body of explanations related to a certain approach or anatomical description—without additional text—making it very easy for the reader to understand each surgical step. A few anatomical drawings are added in Chapters 10, 13, and 18 in order to stress anatomical highlights, such as the mastoid portion of the facial nerve or the lateral craniocervical junction. The systematic arrangement of the photographs in a strictly consecutive fashion allows for quick, step-by-step learning of each surgical approach. Due to the excellent quality of dissections, the great variety of surgical approaches, the precise anatomical descriptions covering the entire skull base, and, in particular, the superb didactic value of the atlas, Photo Atlas of Skull Base Dissection is one of the best manuals that can be recommended to young neurosurgeons who wish to learn advanced skull base techniques or to those who wish to improve their skills in skull base surgery.

Helmut Bertalanffy, MD Professor and Chairman Department of Neurosurgery University Hospital of Zurich Editor-in-Chief Neurosurgical Review

Preface

Innovations in skull base surgery have extended the reach of the neurosurgeon. Skull base approaches not only facilitate the resection of tumors, but also facilitate exposure for the safe treatment of vascular abnormalities and intrinsic brainstem lesions. Skull base surgery is dependent on a solid knowledge of anatomy. A firm grasp of anatomy not only allows the surgeon to safely perform technically demanding skull base approaches, but also allows the surgeon to modify standard approaches to optimize exposure needed in a particular case. This book reviews standard skull base approaches in a step-by-step fashion. The relevant anatomy encountered by the surgeon is illustrated by a large number of photographs taken of cadaver specimens. These photographs show not only the anatomy that would be seen at the time of surgery but also the relevant structures adjacent to the exposure. In between the steps of the standard operative exposure, dissections of the adjacent tissue are performed to demonstrate important structures. The goal is to provide the surgeon with a mental picture of the operative region so that the surgeon will understand the consequences of extending the exposure. The relationship of the operative corridor to the adjacent anatomy is stressed. This helps the surgeon understand when the dissection is taking place close to a critical structure and when entering the adjacent tissue can be done without endangering the patient. The book’s twenty chapters are divided into five sections reflecting five trajectories for approaching the skull

base: anterior, anterolateral, lateral, posterolateral, and posterior skull base. At the beginning of each section, relevant anatomy for the trajectory that is not usually dissected at the time of surgery is shown. Each chapter covers either the surgical anatomy of a specific region or a special skull base approach. Extensions of the approach are shown. Chapters begin with a short introduction and list of key steps to help the reader quickly obtain an overview of each dissection. At the end of the chapter, several photos are included to define the arteries, nerves, and neural tissue visible through the exposure and the limits of that particular exposure. The goal of this book is to assist neurosurgeons, otolaryngologists, and head and neck surgeons to better understand the limits and possibilities of skull base approaches. It is our hope that this volume will lead to improved surgical techniques, innovative skull base approaches, and better care for patients.

Acknowledgments We express our deep appreciation for the assistance of Karen S. Koenig, Administrative Manager, Division of Neurosurgery in Duke University Medical Center; and Lori Radcliffe, Manager in the Carolina Neuroscience Institute. This book would not have been completed without their hard work and dedication.

I

Anterior Skull Base

1 Craniofacial Anatomy Anterior skull base approaches often give the most direct access to midline skull base lesions. An understanding of the anatomy is important for transnasal, transsphenoidal, and transoral approaches and for approaching the medial cavernous sinus.

Key Steps Step 1. Nose and nasal cavity, paranasal sinuses (Fig. 1.1) Step 2. Cavernous sinus from the medial direction (Fig. 1.36) Step 3. Anatomy for a transoral approach (Fig. 1.52)

Illustrated Steps with Commentary

SNC GAC

LC

Fig. 1.1 (Step 1) Cartilaginous framework of the

nose.

The major or greater alar cartilage is the thin flexible lattice that forms the anterior, medial, and lateral walls of the nares. The septal cartilage separates the two nares. (GAC, greater alar cartilage; LC, lateral crus of the greater alar cartilage; MC, medial crus of the greater alar cartilage; SNC, septal nasal cartilage)

MC

SNC LNC

GAC

Fig. 1.2 Lateral nasal cartilage. The lateral nasal cartilage is the flat extension of the nasal bone that bridges the gap between the nasal bone and the lesser and greater alar cartilages. The septal cartilage separates the left and right lateral nasal cartilages, and the left and right greater alar cartilages. (GAC, greater alar cartilage; LNC, lateral nasal cartilage; SNC, septal nasal cartilage)

GAC

4

I Anterior Skull Base

GAC

GAC

Fig. 1.3 Depressor septi nasi muscle.

DSNM

The depressor septi nasi muscle originates from the incisive fossa of the1.1 maxilla and 1) inserts into posterior ala and septal cartilage. Fig. (Step Cartilaginous framework of the The lateral nasal cartilage is the flat extension of the nasal bone nose. that bridges gap between the nasal thelattice lesser that and The major orthe greater alar cartilage is thebone thin fland exible greater alar cartilages. The and septal cartilage theThe leftsepand forms the anterior, medial, lateral walls separates of the nares. right lateral separates nasal cartilages, the(GAC, left and rightalar greater alar tal cartilage the twoand nares. greater cartilage; cartilages. (DSNM, depressor septi nasi muscle; GAC, greater LC, lateral crus of the greater alar cartilage; MC, medial crus of alar the cartilage) greater alar cartilage; SNC, septal nasal cartilage)

FNS

MPL NMS

Fig. 1.4 1.1 Medial (Step 1)palpebral Cartilaginous ligament. framework of the nose. The medial palpebral ligament originates from the frontal process

FPMx

of the maxilla, dividesalar in half, and inserts upperlattice and lower The major or greater cartilage is theinto thinthe flexible that tarsus. Injury to thismedial, ligament result in aofcosmetically signifi forms the anterior, andcan lateral walls the nares. The sep-cant asymmetry of thethe palpebral fissure. (FNS, frontonasal suture; tal cartilage separates two nares. (GAC, greater alar cartilage; FPMx, frontal of the alar maxilla; MPL, MC, medial palpebral LC, lateral crusprocess of the greater cartilage; medial crus ofligathe ment; nasomaxillary greaterNMS, alar cartilage; SNC,suture) septal nasal cartilage)

MPL

SNC

Fig. 1.5 Subperichondrial dissection plane

PC

between the septal nasal cartilage and the perichondrium. Fig. 1.1 (Step 1) Cartilaginous framework of the nose. In the transseptal approach to the sphenoid sinus the mucosa is separated thealar septal nasal cartilage, vomer, andthat the The major orfrom greater cartilage is the thinthe flexible lattice perpendicular platemedial, of the and ethmoid. is raised forms the anterior, lateralThe wallsmucosa of the nares. Thefrom sepanterior to posterior. anterior spine; M, mucosa; MPL, tal cartilage separates(ANS, the two nares.nasal (GAC, greater alar cartilage; medial palpebral ligament; SNC, septal nasal LC, lateral crus of the greaterPC, alarperichondrium; cartilage; MC, medial crus of the cartilage) greater alar cartilage; SNC, septal nasal cartilage)

ANS

M

1 Craniofacial Anatomy

M Fig. 1.6 Incisive foramen. The Fig.nasopalatine 1.1 (Stepartery 1) Cartilaginous (a branch of the framework sphenopalatineof artery) the

runs in a groove in the vomer along with the nasopalatine nerve nose. and thealar incisive canalisinthe thethin maxilla to anastomose The exits majorthrough or greater cartilage flexible lattice that with Thewalls nasopalatine nerve formsthe thegreater anterior,palatine medial, artery. and lateral of the nares. Thecomsepmunicates the greater palatine (ANS, anterior nasal tal cartilagewith separates the two nares. nerves. (GAC, greater alar cartilage; spine; IF, incisive foramen; mucosa; PC,MC, perichondrium; LC, lateral crus of the greaterM,alar cartilage; medial crus ofSNC, the septal cartilage) SNC, septal nasal cartilage) greaternasal alar cartilage;

SNC

IF

PC ANS

SNC IF Fig. 1.1 (Step 1) Cartilaginous framework of the nose.1.7 The nasopalatine artery and nerve are Fig.

surrounded by mucosa as they exit the that The major or greater alar cartilage is the thinthrough flexible lattice forms the foramen. anterior, medial, and lateral walls of the nares. The sepincisive

ANS

tal cartilage two nares. (GAC, cartilage; The incisive separates foramen the is demonstrated at greater the tip alar of the blunt LC, lateral crusanterior of the greater alar cartilage; medialSNC, crus septal of the probe. (ANS, nasal spine; IF, incisiveMC, foramen; greater alar cartilage; SNC, septal nasal cartilage) nasal cartilage)

SNC

Fig. 1.8 1.1 The (Step septal 1) Cartilaginous cartilage articulates framework withof the the palatine nose. process of the maxilla. The major articulation or greater between alar cartilage the septal is the cartilage thin flexible and the lattice palatine that process forms the ofanterior, the maxilla medial, is dislocated and lateral to the walls contralateral of the nares. side Theinsepthe microscopic tal cartilage separates transnasalthe approach two nares. to the (GAC, sphenoid greater sinus. alar In cartilage; the endoscopic LC, lateralapproach crus of thethe greater nasalalar septum cartilage; can be MC,left medial in place. crus of (ANS, the anterior greater alar nasal cartilage; spine; SNC, SNC,septal septalnasal nasalcartilage) cartilage)

ANS

5

S

I Anterior Skull Base

BN

6

SNC

Fig. 1.9 Bony nasal septum. The anterior edges of the vomer and perpendicular plate of the ethmoid are seen after the nasal septal cartilage is detached. (BNS, bony nasal septum; SNC, septal nasal cartilage)

MT

MT

Fig. 1.10 Inferior and middle turbinates (nasal concha) and nasal septum.

The middle and inferior turbinates differ in shape. The inferior turbinate is comma shaped and the middle turbinate is teardrop shaped. The safest method for the operating surgeon to find the middle turbinate is to begin at the nasal floor and identify each more superior turbinate in succession. (ANS, anterior nasal spine; IT, inferior turbinate; MT, middle turbinate)

IT

IT

ANS

SON

FLS

Orb

FPMx

Fig. 1.11 Fossa for the lacrimal sac. The fossa for the lacrimal sac sits over the suture between the lacrimal bone and the frontal process of the maxilla. (FLS, fossa for the lacrimal sac; FPMx, frontal process of the maxilla; M, mucosa; Orb, orbit; SON, supraorbital notch [foramen]; ZFF, zygomaticofacial foramen)

M ZFF

1 Craniofacial Anatomy

FS

ES

Fig. 1.12 Nasal septum covered by the peri-

SS

M

chondrium, periosteum, and mucosa.

A groove on the nasal septum marks the location of our initial mucosal incision when performing an endonasal transsphenoidal procedure. This is a modified transseptal approach in which mucosal flaps are raised over the posterior 1 cm of the nasal septum. After the incision is made, a posterior mucosal flap is stripped from the medial bony septum in the subperiosteal plane. When the body of the sphenoid bone is reached, the dissection is continued laterally across the face of the sphenoid bone to the sphenoid ostia. This flap is used to cover the sphenoid sinus opening at the end of the case. (ES, ethmoid sinus; FS, frontal sinus; M, mucosa; SS, sphenoid sinus)

M

PC

Fig. 1.13 Mucosa and perichondrium. The mucosa and perichondrium form distinct layers over the septal nasal cartilage. (M, mucosa; PC, perichondrium)

PerE

Fig. 1.14 Variation of the nasal septum:

protrusion of the upper edge of the vomer.

The nasal septum may be irregular or fenestrated. These irregularities may obstruct the surgeon’s view of the posterior nasal septum. (PerE, perpendicular plate of the ethmoid; SS, sphenoid sinus)

SS

7

8

I Anterior Skull Base

FS ES

SS Fig. 1.15 Filaments of the olfactory nerve.

M

Filaments of the olfactory nerve (arrow) penetrate the ethmoid bone through the cribriform plate. These filaments can be damaged by stripping the mucosa off the roof of the nasal cavity. (ES, ethmoid sinus; FS, frontal sinus; M, mucosa; SS, sphenoid sinus)

M

Fig. 1.16 Nasopalatine nerve passing into the incisive foramen (canal).

ANS

The nasopalatine nerve (arrows) is a distal branch of the maxillary nerve. The posterior superior nasal branches enter the nasal cavity through the sphenopalatine foramen. (ANS, anterior nasal spine; IF, incisive foramen; M, mucosa)

IF

FS ES

SS

PerE Vo CVo SNC

Fig. 1.17 Nasal septum. The nasal septum is formed by the vomer, the septal nasal cartilage, and the perpendicular plate of the ethmoid. (ANS, anterior nasal spine; CVo, cuneiform part of the vomer; ES, ethmoid sinus; FS, frontal sinus; PerE, perpendicular plate of the ethmoid; PPM, palatine process of the maxilla; SNC, septal nasal cartilage; SS, sphenoid sinus; Vo, vomer)

PPM ANS

1 Craniofacial Anatomy

FS ES

PerE

Fig. 1.18 Surgical trajectory for the transnasal transsphenoidal approach to the sella turcica.

The speculum is advanced between the nasal septum and middle turbinate. The mucosa of the nasal septum is incised 1 cm anterior to the body of the sphenoid bone. As noted in Figure 1.12, this mucosal flap covers the sphenoid sinus after the operation is completed. Once the nasal septum is displaced contralateral to the surgical approach, the nasal mucosa is stripped from the contralateral posterior 1 cm of the nasal septum and anterior body of the sphenoid. (ANS, anterior nasal spine; ES, ethmoid sinus; FS, frontal sinus; PerE, perpendicular plate of the ethmoid; PPM, palatine process of the maxilla; SNC, septal nasal cartilage; SS, sphenoid sinus; Vo, vomer)

SS SNC

Vo

PPM ANS

ES

ST SS Vo

MT

OSS

Fig. 1.19 Natural ostium of the sphenoid sinus. The natural ostium of the sphenoid sinus is seen to enter the nasal cavity at the level of the superior half of the middle turbinate. (Ch, choana; ES, ethmoid sinus; IT, inferior turbinate; MT, middle turbinate; OSS, ostium of the sphenoid sinus; PPM, palatine process of the maxilla; SS, sphenoid sinus; ST, superior turbinate; Vo, vomer)

Ch

IT PPM

ES

MT

Fig. 1.20 Communication of the anterior

ethmoidal cells, frontal, and maxillary sinuses.

The maxillary sinus drains under the middle turbinate into the hiatus semilunaris. At the anterior end of the hiatus is a canal, which drains the frontal sinus. (Ch, choana; ES, ethmoid sinus; IT, inferior turbinate; MT, middle turbinate; PPM, palatine process of the maxilla; SS, sphenoid sinus; Vo, vomer)

SS Vo

Ch

IT PPM

9

10

I Anterior Skull Base

ES

OSS

ST

SS SpC

MT

Fig. 1.21 Location of the sphenopalatine foramen.

SPF

The sphenopalatine foramen is a canal through the edge of the palatine bone that articulates with the body of the sphenoid bone. The posterior superior nasal branches of the maxillary nerve and the sphenopalatine artery enter the nasal cavity through that foramen. Bleeding from the sphenopalatine artery is easily controlled if the surgeon knows the anatomy of that vessel. (Ch, choana; ES, ethmoid sinus; ET, eustachian tube; MT, middle turbinate; OSS, ostium of the sphenoid sinus; SpC, sphenoidal crest; SPF, sphenopalatine foramen; SS, sphenoid sinus; ST, superior turbinate)

ET

IT

ST

OSS

SpC SPF

MT

Fig. 1.22 Magnification of Fig. 1.21. Magnified view of the natural ostium to the sphenoid sinus and the sphenopalatine foramen. (MT, middle turbinate; OSS, ostium of the sphenoid sinus; SpC, sphenoidal crest; SPF, sphenopalatine foramen; ST, superior turbinate)

ST

SS

SPA

MT

Fig. 1.23 Sphenopalatine artery. The sphenopalatine artery and the posterior superior nasal branches of the maxillary nerve enter the nasal cavity through the sphenopalatine foramen. (MT, middle turbinate; SPA, sphenopalatine artery; SS, sphenoid sinus; ST, superior turbinate)

Ch

1 Craniofacial Anatomy

ST

TT

Fig. 1.24 Pharyngeal opening of the eustachian

ET

MT

tube.

The pharyngeal ostium of the eustachian tube is bound posteriorly by the torus tubarius, a protrusion in the mucosa overlying the cartilaginous auditory canal and the salpingopharyngeal fold overlying the salpingopharyngeus muscle. (ET, eustachian tube; MT, middle turbinate; ST, superior turbinate; TT, torus tubarius)

IT Fig. 1.25 Inferior turbinate (inferior nasal concha).

The inferior turbinate is a separate bone, which articulates from anterior to posterior with the maxilla, lacrimal, ethmoid, and palatine bones. When looking into the nares, the surgeon becomes oriented by locating the inferior turbinate as the closest turbinate to the nasal floor. (IT, inferior turbinate)

MT

Fig. 1.26 Middle turbinate (middle nasal concha). The middle turbinate is the termination of the lateral mass of the ethmoid bone. The surgeon finds this important landmark by angling the nasal speculum up from the inferior turbinate. (MT, middle turbinate)

11

12

I Anterior Skull Base

ST

MT Fig. 1.27 Superior turbinate (superior nasal concha).

A junction of the superior turbinate and middle turbinate is a landmark for the anterior border of the sphenoid sinus. (MT, middle turbinate; ST, superior turbinate)

OSS Fig. 1.28 Natural ostium of the sphenoid sinus. The natural ostium of the sphenoid sinus, which communicates the nasal cavity with the sphenoid sinus in the sphenoethmoidal recess, can be seen by retracting the middle concha laterally. The natural ostium enters the sphenoid sinus halfway between the sinus roof and floor. (OSS, ostium of the sphenoid sinus)

Fig. 1.29 Upper arch of the choana (posterior nasal aperture).

Behind the inferior turbinate within the nasal cavity the choana or opening to the pharynx is seen. A characteristic fold in the mucosa lying under the attachment of the ala vomer to the body of the sphenoid bone marks the upper end of the choana. The ala vomer underlies the medial portion of the upper arch of the posterior nasal aperture and the medial pterygoid process underlies the lateral arch. (UAC, upper arch of the choana)

UAC

1 Craniofacial Anatomy

CVo

Fig. 1.30 Cuneiform part of the vomer. The ala is the horizontal portion of the vomer bone, which articulates with the sphenoid bone, the sphenoid process of the palatine bone, and the vaginal process of the medial pterygoid. The ala is evident as a thickening in the posterior inferior aspect of the bony septum. (CVo, cuneiform part of the vomer)

S

Fig. 1.31 Suture between the body of the

AVo

AVo

sphenoid and the vomer.

During a transsphenoidal procedure, the vomer is broken anterior to its articulation with the sphenoid bone and dislocated away from the surgeon to enlarge the surgical corridor. The spine of the sphenoid bone and the overlying ala vomer form an excellent landmark for the midline, should the surgeon become disoriented during the procedure. (AVo, ala of vomer; S, sphenoid bone)

S

S

AVo

AVo Fig. 1.32 The ala of the vomer and the ostia of the sphenoid sinus.

The relationship of the natural ostia of the sphenoid sinus to the articulation between the vomer and the sphenoid bone is demonstrated. (AVo, ala of vomer; CVo, cuneiform part of the vomer; S, sphenoid bone)

CVo

13

14

I Anterior Skull Base

OSS

Fig. 1.33 Sphenopalatine foramen. The sphenopalatine foramen transmits the nasopalatine nerve, one of the branches of the maxillary division of the trigeminal nerve and the sphenopalatine artery. In this figure, the surgeon is shown the relationship between the sphenopalatine fissure, the sphenopalatine foramen, the nasal cavity, and the sphenoid sinus. (AVo, ala of vomer; Ch, choana; CVo, cuneiform part of the vomer; ION, infraorbital nerve; NPN, nasopalatine nerve; OSS, ostium of the sphenoid sinus; PN, greater and lesser palatine nerves; PPF, pterygopalatine fossa; PPG, pterygopalatine ganglion; PSA, posterior superior alveolar branch; S, sphenoid bone; SPF, sphenopalatine foramen; UAC, upper arch of the choana; V2, maxillary nerve [third division of the trigeminal nerve])

PPF

AVo

PSA

NPN

CVo PN

UAC

UAC

Ch

Ch

PPG

PSA

PPF

NPN PN

Fig. 1.34 Pharyngeal branches emerging from the pterygopalatine ganglion.

The nerves within the pterygopalatine fissure are demonstrated. The superior nasal branch enters the sphenopalatine foramen. The greater and lesser palatine nerves travel inferiorly to the greater and lesser palatine foramena. The posterior superior alveolar nerve enters the posterior alveolar canal. The pharyngeal branch of the maxillary nerve passes through the pharyngeal canal along with a branch of the maxillary artery. (NPN, nasopalatine nerve; PN, greater and lesser palatine nerves; PPF, pterygopalatine fossa; PPG, pterygopalatine ganglion; PSA, posterior superior alveolar branch; UAC, upper arch of the choana)

UAC

TS CP(3)

Fig. 1.35 Opening of the sphenoid sinus. The anterior wall of the sphenoid sinus is opened revealing the anterior wall of the sella turcica. The surgeon should note the pattern of the intrasinus septa on preoperative imaging and identify those septa as the sinus is opened. This will avoid an incomplete view of the sella turcica. The surgeon should also keep in mind that the nasal speculum points across the sphenoid sinus instead of straight posteriorly. Thus, if the approach is through the left nostril, the surgeon will be looking toward the right side of the sella turcica. (CL, clivus; CP(3), carotid prominence formed by the C3 portion of the internal carotid artery; CP(5), carotid prominence formed by the C5 portion of the internal carotid artery; SF, sella floor; TS, tuberculum sellae)

ION

PPG

AVo

SPF

V2

S

S

SF CP(5)

CL

1 Craniofacial Anatomy

C3

C3

DSF

Fig. 1.36 (Step 2) Basilar venous plexus. Removing the posterior wall of the sphenoid sinus reveals the basilar venous complex, the C3 portion of the carotid artery, the dura of the sella turcica, and the medial cavernous sinus. There is usually an intercavernous dural sinus within the superior aspect of the dura and a large intracavernous sinus inferiorly. Bleeding from these sinuses can be controlled by packing the venous sinuses with small pieces of oxidized cellulose and bipolar cautery. Raising the head of the bed lowers the venous pressure. (BP, basilar plexus; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DCL, dura of the clivus; DSF, dura of the sella floor)

BP

C5 DCL

ON OA

ON

OA

C2

C2

St

C3

C3 PG

C4

Fig. 1.37 Removal of the dura from the anterior pituitary fossa and anterior cavernous sinus.

This overview shows the relationship of the C3 segment of the carotid artery to the pituitary gland. (C2, C2 [axis]; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; OA, ophthalmic artery; ON, optic nerve; PG, pituitary gland; St, stalk)

C5

ES Orb

SOF

ES SOF

ON C2

C2

C3 C3

IOF

Fig. 1.38 The C5 segment of the carotid arteries

C3

St C4

PPF

C5

PG

C4 C5

CL

V2

are seen inferior to the cavernous carotid arteries.

The C5 segment of the carotid artery frequently indents the lateral walls of the sphenoid sinus. (C2, C2 [axis]; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; Ch, choana; CL, clivus; ES, ethmoid sinus; IOF, infraorbital fissure; ION, infraorbital nerve; MxS, maxillary sinus; ON, optic nerve; Orb, orbit; PG, pituitary gland; PN, greater and lesser palatine nerves; PPF, pterygopalatine fossa; SOF, superior orbital fissure; SPF, sphenopalatine foramen; St, stalk; V2, maxillary nerve [third division of the trigeminal nerve])

Orb

ON

IOF

ION

PPF

SPF

MxS

PN

Ch

Ch

MxS

15

16

I Anterior Skull Base

ON

ST

Fig. 1.39 Right internal carotid artery passing into the cavernous sinus.

The C5 portion of the carotid artery lies adjacent to the wall of the sphenoid sinus before passing into the cavernous sinus. The lateral wall of the nasal cavity, the nasopharynx, and the medial cavernous sinus are exposed. An anatomical relationship of these structures is well documented. (C2, C2 [axis]; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; ET, eustachian tube; IT, inferior turbinate; MT, middle turbinate; ON, optic nerve; PG, pituitary gland; ST, superior turbinate; V2, maxillary nerve [third division of the trigeminal nerve]; VI, abducens nerve)

MT

C3

C2

C5

V2

PG

C4

VI

IT ET

ST

SS

MT Fig. 1.40 Opening of the posterior ethmoid cells into the nasal cavity.

The posterior ethmoid air cells communicate with the nasal cavity above the superior turbinate. (MT, middle turbinate; SS, sphenoid sinus; ST, superior turbinate)

CP(3)

Fig. 1.41 Right carotid prominence. A bulge of bone, the carotid prominence, is seen on the lateral wall of the sphenoid sinus. Above the prominence is a bulge marking the optic canal. In individual cases there may be a dehiscence of this bone over these structures. (CP(3), carotid prominence formed by C3 portion of the internal carotid artery; SF, sella floor; ST, superior turbinate)

ST

SF

1 Craniofacial Anatomy

ON DSF

C3

Fig. 1.42 Medial wall of the cavernous sinus on the right side.

Removal of the lateral wall of the sphenoid sinus reveals the cavernous sinus. The medial wall of the cavernous sinus and the C5 portion of the carotid artery can be seen once the lateral wall of the sphenoid sinus is removed. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DSF, dura of the sella floor; ON, optic nerve; VI, abducens nerve)

VI

C5

DCL

VI C5 Fig. 1.43 Extradural portion of the abducens nerve.

The abducens nerve is seen after it exits Dorello’s canal and enters the cavernous sinus. (C5, C5 portion of the internal carotid artery; DCL, dura of the clivus; VI, abducens nerve)

ON

C3

Fig. 1.44 An intercavernous sinus running

between the osteal dura and dura propria on the sella floor.

The interconnections (arrows) that run between the leaves of dura in front and under the pituitary gland can cause troublesome bleeding during transsphenoidal surgery. Pushing small bits of oxidized cellulose into these venous channels will help clear the surgical field of blood. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; ON, optic nerve)

C5

17

18

I Anterior Skull Base

ON

DDR

PG

C3

IOV Fig. 1.45 Right cavernous sinus.

V2

Removing bone with a diamond drill anterior to the carotid artery will open the bony canals containing V2 and the optic nerve. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DDR, distal dural ring; IOV, infraorbital vein; ON, optic nerve; PG, pituitary gland; V2, maxillary nerve [third division of the trigeminal nerve]; VI, abducens nerve)

VI

C5

ON OA

MR

C3

CTR

Fig. 1.46 Common tendinous ring (common

IOV

annular tendon).

Further bony removal above V2 will open the apex of the orbit. The annular tendon gives origin to the muscles of the ocular cone. (C3, C3 portion of the internal carotid artery; CTR, common tendinous ring; IOV, infraorbital vein; MR, medial rectus muscle; OA, ophthalmic artery; ON, optic nerve)

ON

DR

OA

C3

CTR

C4 VI

Fig. 1.47 Internal carotid sympathetic plexus. The carotid sympathetic plexus emanates from the superior cervical sympathetic ganglion and ascends with the internal carotid artery. Several communicating branches from the plexus exist. A communicating branch to the abducens nerve is exposed in this figure. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; CTR, common tendinous ring; DR, dural ring; OA, ophthalmic artery; ON, optic nerve; PG, pituitary gland; SpP, sympathetic plexus; V2, maxillary nerve [second division of the trigeminal nerve]; VI, abducens nerve)

PG

V2

C5 SpP

VI

1 Craniofacial Anatomy

C3 C4 MHT

Fig. 1.48 Meningohypophyseal trunk. The meningohypophyseal trunk originates from the junction of C5 and C4. It generally gives off an arterial branch to the clivus, the tentorium, and the posterior pituitary. The dorsal meningeal and tentorial arteries are seen in this dissection. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; MHT, meningohypophyseal trunk; V2, maxillary nerve [third division of the trigeminal nerve]; VI, abducens nerve)

V2

VI

C5

ON

PG C3 C4

SPS PS

Fig. 1.49 Superior and inferior petrosal sinuses. The inferior and superior petrosal sinuses enter the cavernous sinus. The abducens nerve passes through the inferior petrosal sinus. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DCL, dura of the clivus; IPS, inferior petrosal sinus; ON, optic nerve; PG, pituitary gland; PSL, petrosphenoidal ligament; SPS, superior petrosal sinus; V2, maxillary nerve [third division of the trigeminal nerve]; VI, abducens nerve)

DCL

L

IPS

VI

C5 V2

ON

DDR OA

PG MR

C3

CTR

Fig. 1.50 Distal and proximal dural rings. The intraclinoidal portion of the carotid artery passes through the proximal and distal dural rings. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; CTR, common tendinous ring; DDR, distal dural ring; MR, medial rectus muscle; OA, ophthalmic artery; ON, optic nerve; PDR, proximal dural ring; PG, pituitary gland; VI, abducens nerve)

PDR

VI

C4

19

20

I Anterior Skull Base

ON OA

C3

III

CTR

IV

SOV

Fig. 1.51 Lateral wall of the cavernous sinus

V1

viewed from the medial direction.

The oculomotor, trochlear, abducens, and ophthalmic nerves pass lateral to the carotid artery in the oculocarotid membrane. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; CTR, common tendinous ring; III, oculomotor nerve; IPS, inferior petrosal sinus; IV, trochlear nerve; OA, ophthalmic artery; ON, optic nerve; PSL, petrosphenoidal ligament; SOV, superior orbital vein; SpP, sympathetic plexus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [third division of the trigeminal nerve]; VI, abducens nerve)

PSL VI SpP

V2

HP

SP UV

Fig. 1.52 (Step 3) Posterior and superior walls of

OPx

the oral cavity.

In the transoral approach, the surgeon depresses the tongue and views the posterior mucosa of the oropharynx. (HP, hard palate; OPx, oropharynx; SP, soft palate; UV, uvula)

HP

NPx

Fig. 1.53 Mucosa of the nasopharnyx and oropharynx.

The mucosa of naso- and oropharynx is exposed after removal of the soft palate. In surgery, a midline incision is made and thick flaps, including the mucosa and underlying muscle, are retracted laterally. The mucosa and soft palate have been removed in this cadaver dissection. At the time of surgery, the soft palate is usually retracted superiorly. Future superior exposure can be obtained by splitting the soft palate in the midline. This maneuver usually results in some incomplete separation of the oropharnyx and nasal pharynx at the time of swallowing. (ET, eustachian tube; HP, hard palate; NPx, nasopharynx; OPx, oropharynx)

ET ET

OPx

C5

IPS VI

1 Craniofacial Anatomy

HP

NPx ET

Fig. 1.54 Eustachian tube on the right side. The pharyngeal ostium of the eustacian tube is demonstrated. This landmark allows the exposure of the pharynx seen from a transoral approach to be compared with the exposure of the pharynx seen from a transnasal approach. (ET, eustachian tube; HP, hard palate; NPx, nasopharynx; OPx, oropharynx)

OPx

LCpM

LCpM

Fig. 1.55 Longus capitis and longus colli muscle. The longus capiti are paired muscles that run from the inferior occipital bone to the anterior tubercle of the transverse processes of C3-6. They overlie the longus colli at this level, which runs from the anterior tubercle of the anterior arch of C1 to the anterior tubercle of the lateral masses of C3-5. (LClM, longus colli muscle; LCpM, longus capitis muscle)

LClM

LClM

Vo

CL

RCAM

LCpM

ICA

ICA

Fig. 1.56 Removal of the right longus capitis muscle.

Removing the longus capitis muscle on the right reveals the right longus colli muscle and the C1-C2 facet. (C1F, C1 facet; C2F, C2 facet; CL, clivus; ICA, internal carotid artery; LClM, longus colli muscle; LCpM, longus capitis muscle; RCAM, rectus capitis anterior muscle; Vo, vomer)

C1F C2F LClM

LClM

21

22

I Anterior Skull Base

CL

RCAM

Fig. 1.57 Rectus capitis anterior muscle. The rectus capitis anterior muscle lies under the longus capitis muscle. It is a short muscle that arises from the anterior tubercle of the transverse process of C1 and inserts into the inferior margin of the occipital bone. (CL, clivus; RCAM, rectus capitis anterior muscle)

CL OcC ICA

C1C aC1

Fig. 1.58 Occipital condyle, C1 condyle, and condylar emissary vein on the right side.

Laterally we see an emissary vein coming from the condyle and the vertebral arteries passing from the transverse process of C1 behind the condyle. The high cervical internal carotid artery, just proximal to the carotid canal, is also seen in front of the condyle. (aC1, anterior arch of the C1 [atlas]; C1C, C1 condyle; C1F, C1 facet; C2F, C2 facet; CL, clivus; ICA, internal carotid artery; LClM, longus colli muscle; OcC, occipital condyle)

C1F C2F

CL

ICA

Fig. 1.59 Anterior atlanto-occipital membrane. The anterior atlanto-occipital membrane attaches the anterior arch of the atlas to the occipital bone. (CL, clivus)

LClM

1 Craniofacial Anatomy

CL

ICA

Fig. 1.60 Exposure of pars basilaris of the occipital

C1C

ICA

aC1

C1F

bone, atlas, and axis.

The anterior muscles are removed from the base of the occiput through C2. The right vertebral artery is seen passing between the transverse processes of C2 and C3 and between the transverse process of C1 and the atlanto-occipital membrane. The artery may take a serpiginous course between the transverse process of C1 and the atlanto-occipital membrane. (aC1, anterior arch of the C1 [atlas]; C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; Ds, dens; ICA, internal carotid artery; VA, vertebral artery)

C1F

Ds

C2F C2 C2F VA

Vo

CL

aC1

Fig. 1.61 Drilling of the anterior arch of the atlas.

C1F

The anterior arch of C1 can be removed using a Kerrison rongeur. The authors prefer to use a drill to remove the anterior arch of C1 in layers. (aC1, anterior arch of the C1 [atlas]; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; Ds, dens; Vo, vomer)

Ds

C2F

C2

CL

ApL

AlL

Fig. 1.62 Dens and related ligaments. The dens is attached to the occipital bone by the apical and alar ligaments. Behind the dens lies the cruciate ligament. The apical ligament makes removal of the tip of the dens problematic. The authors prefer to drill the dens from the top down. Once the dens is detached from the body of C2 it is difficult to grasp or drill. (AlL, alar ligament; ApL, apical ligament; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; Ds, dens)

Ds

C1F C2F C2

AlL

23

24

I Anterior Skull Base

CL

OcC OcC C1C

Fig. 1.63 Tectorial membrane and cruciate

C1C CrL

C1F

C1F

ligament.

C2F

The dens is removed to reveal the cruciate ligament and tectorial membrane, which lie anterior to the dura mater. (C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; CrL, cruciate ligament; OcC, occipital condyle)

C2F

C2

CL

OcC

OcC

C1C

ICA

C1C

TcM

TL

Fig. 1.64 Venous plexus anterior to the tectorial

C1F

membrane.

C2F

Removal of the cruciate ligament reveals a venous plexus anterior to the tectorial membrane. (C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; ICA, internal carotid artery; OcC, occipital condyle; TcM, tectorial membrane; TL, transverse ligament)

C1F

C2

C2F

CL

OcC OcC C1C

C1C TcM

C1F

Fig. 1.65 Tectorial membrane. The tectorial membrane is just anterior to the dura of the upper spinal canal. (C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; OcC, occipital condyle; TcM, tectorial membrane)

C2F

C1F C2

C2F

1 Craniofacial Anatomy

CL

D

OcC

OcC

C1C

TcM

C1C

C1F

C1F

C2F

C2F

C2

Fig. 1.66 Tectorial membrane and dura mater. Opening the tectorial membrane reveals the dura matter. (C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; D, dura mater; OcC, occipital condyle; TcM, tectorial membrane)

CL

OcC C1C

OcC

C1C

D

Fig. 1.67 Dura mater. The dura mater is exposed over the axis after the anterior arch of the atlas, the dens, the apical, alar, and cruciate ligaments, and the tectorial membrane are removed. (C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; D, dura mater; OcC, occipital condyle)

C1F C2F

C1F C2F

C2

CL

OcC

OcC

C1C

C1C Sp

C1F

Fig. 1.68 Upper spinal cord. The upper spinal cord and anterior spinal artery are seen once the upper spinal dura is opened. (C1C, C1 condyle; C1F, C1 facet; C2, C2 [axis]; C2F, C2 facet; CL, clivus; OcC, occipital condyle; Sp, spinal cord)

C1F

C2F C2

C2F

25

2 Transmaxilloethmoidal Approach The transmaxilloethmoidal approach affords the surgeon a view of the sellar and parasellar regions. The approach can be used for clival chordomas, chondrosarcomas, or pituitary tumors with a large cavernous sinus or clival extension, for encephaloceles, and for medial orbital pathology.

Key Steps Position: Supine Step 1. Incise the paranasal skin incision (Fig. 2.1) Step 2. Expose the maxilla and identify the infraorbital nerve (Fig. 2.2) Step 3. Identify the lacrimal sac (Fig. 2.3) Step 4. Identify the anterior ethmoidal artery and nerve (Fig. 2.6) Step 5. Perform a maxillostomy and ethmoidectomy (Fig. 2.7) Step 6. Remove the nasal turbinates (Fig. 2.9) Step 7. Perform a sphenoidectomy (Fig. 2.15) Step 8. Expose the pituitary gland and bilateral cavernous wall (Fig. 2.18) Step 9. Expose the midclivus (Fig. 2.25)

Illustrated Steps with Commentary

Fig. 2.1 (Step 1) Incise the paranasal skin. A skin incision is made lateral to the nasal border.

2 Transmaxilloethmoidal Approach

LS

Mx IO

Fig. 1.1 (Step 1) Cartilaginous framework of the

N

nose.

Fig. The major 2.2 or (Step greater 2) alar Expose cartilage theis maxilla the thin fland exibleidentify lattice that formsinfraorbital the anterior, medial, the nerve.and lateral walls of the nares. The septal cartilage separates nares. (GAC, greater alar cartilage; The infraorbital surfacethe of two the maxillary bone is exposed. The inLC, lateral nerve crus ofisthe greater alar MC,limit medial crus of the fraorbital a landmark forcartilage; the lateral of dissection. greater alar cartilage; SNC, nasal (ION, infraorbital nerve; LS,septal lacrimal sac;cartilage) Mx, maxilla)

LS

NMS

Fig. 1.1 (Step 1) Cartilaginous framework of the nose.2.3 (Step 3) Identify the lacrimal sac. Fig. IO N

After The major exposing or greater the infraorbital alar cartilage nerve, is the thethin lacrimal flexible sac lattice in the that medial forms orbital the anterior, wall should medial, be and identifi lateral ed. walls The lacrimal of the nares. duct The extends sepfrom tal cartilage the medial separates palpebral the two commissure nares. (GAC, to the greater lacrimal alarsac. cartilage; (ION, infraorbital LC, lateral crus nerve; of the LS,greater lacrimal alar sac; cartilage; Mx, maxilla; MC, medial NMS, nasomaxilcrus of the lary greater suture) alar cartilage; SNC, septal nasal cartilage)

Mx

LF

NMS Mx

Fig. 1.1 (Step 1) Cartilaginous framework of the

nose.

The major or greater alar cartilage is the thin flexible lattice that forms2.4 the anterior, and lateral walls Fig. Cut themedial, nasolacrimal duct.of the nares. The septal cartilage separates two (GAC, greater The nasolacrimal duct the is cut sonares. that the lacrimal sacalar cancartilage; be sepaLC, lateral the greater(ION, alar cartilage; MC,nerve; medialLF, crus of the rated fromcrus theofperiorbita. infraorbital lacrimal greaterMx, alarmaxilla; cartilage; SNC, septal nasalsuture) cartilage) fossa; NMS, nasomaxillary

ION

27

28

I Anterior Skull Base

LF

Fig. 2.5 Expose the lacrimal fossa.

Mx

The fossa for the lacrimal sac is found anterior to the posterior lacrimal crest. The lacrimal fossa overlies the anterior lacrimal bone and posterior frontal process of the maxillary bone. (LF, lacrimal fossa; Mx, maxilla)

AEA&N

LF

Fig. 2.6 (Step 4) Identify the anterior ethmoidal artery and nerve. Peeling off the periorbita from the medial orbital wall exposes the anterior ethmoidal artery, which passes through the anterior ethmoidal foramen in the suture between the ethmoid and frontal bones. (AEA&N, anterior ethmoidal artery and nerve; LF, lacrimal fossa)

NLD

MxS

N

Bone is removed from the anterior wall of the maxillary sinus to preserve the mucosa of that sinus. (ION, infraorbital nerve; MxS, maxillary sinus; NLD, nasolacrimal duct)

IO

Fig. 2.7 (Step 5) Perform a maxillostomy and ethmoidectomy.

2 Transmaxilloethmoidal Approach

Et

MxS NLD

Fig. 2.8 Maxillostomy and ethmoidotomy

exposing the medial maxillary and anterior ethmoid sinuses. IO

The maxillary and anterior ethmoid sinuses are exposed. The extent of the bone removed defines the limits of the surgical exposure. (Et, ethmoid sinus; ION, infraorbital nerve; MxS, maxillary sinus; NLD, nasolacrimal duct)

N

EB MT MxS NLD

Fig. 2.9 (Step 6) Remove the lateral wall of the

nasal cavity.

IT

IO N

The wall between the maxillary sinus and the nasal cavity is opened. The middle and superior nasal conchae are parts of the ethmoid bone. The inferior concha is a separate bone that lies adjacent to the maxillary sinus. (EB, ethmoid bulla; ION, infraorbital nerve; IT, inferior turbinate; MT, middle turbinate; MxS, maxillary sinus; NLD, nasolacrimal duct)

Et MT

MxS

NLD IT

Fig. 2.10 Completion of the ethmoidectomy. IO N

An ethmoidectomy with removal of the middle turbinate is performed. (Et, ethmoid sinus; ION, infraorbital nerve; IT, inferior turbinate; MT, middle turbinate; MxS, maxillary sinus; NLD, nasolacrimal duct)

29

30

I Anterior Skull Base

Ch

NS

NPx Fig. 2.11 Exposure of the choana after removal of the nasal turbinates.

The removal of the nasal turbinates exposes the nasal septum and choana. The choanae are the posterior openings of the nasal cavity. This opening is outlined by the medial pterygoid plate, the sphenoid bone, the vomer, and the palatine bones. (Ch, choana; NPx, nasopharynx; NS, nasal septum)

Ch ET

NPx

Fig. 2.12 Identification of the orifice of the eustachian tube.

The eustachian tube enters the pharynx behind the inferior turbinate. The orifice of the eustachian tube is seen in the lateral wall of the nasopharynx. The posterior wall is marked by a ridge produced by the posterior edge of the eustachian tube pushing out the mucosa and the torus. (Ch, choana; ET, eustachian tube; NPx, nasopharynx)

ET NS

Fig. 2.13 Relationship between the ethmoid sinus, the choana, and the nasal septum.

Removal of the maxillary sinus, the nasal turbinates, and the ethmoid sinus opens a broad surgical corridor. The origin of the superior turbinate emanates from the roof of the ethmoid sinus. (Ch, choana; ET, eustachian tube; NS, nasal septum)

Ch

2 Transmaxilloethmoidal Approach

Et OSS

NS

Fig. 2.14 Identification of the natural ostium of the sphenoid sinus. Removal of the superior turbinate reveals the ostium of the sphenoid sinus. The ostium of the sphenoid sinus lies above the middle turbinate and behind the posterior edge of the superior turbinate. (Et, ethmoid sinus; OSS, ostium of the sphenoid sinus; NS, nasal septum)

SF

NS

SS

Fig. 2.15 (Step 7) Perform a sphenoidostomy. Opening the sphenoid sinus exposes the anterior wall of the sella turcica. (NS, nasal septum; SF, sella floor; SS, sphenoid sinus)

NS CP3

SF SS

Fig. 2.16 Overview at this stage. The sella turcica and the prominence over the right carotid artery are well seen. (CP3, carotid prominence formed by the C3 portion of the internal carotid artery; NS, nasal septum; SF, sella floor; SS, sphenoid sinus)

31

32

I Anterior Skull Base

SF NS

SS CP5

Fig. 2.17 Identification of the C5 carotid prominence. The carotid prominence covering the C5 portion of the internal carotid artery that lies on the lateral wall of the sphenoid sinus is observed above the choana. (Ch, choana; CP5, carotid prominence formed by the C5 portion of the internal carotid artery; NS, nasal septum; SF, sella floor; SS, sphenoid sinus)

Ch

PG NS CL Fig. 2.18 (Step 8) Expose the pituitary gland and bilateral cavernous wall.

Removal of the anterior wall of the sella turcica reveals the dura covering the pituitary gland. The pituitary gland is seen from the paramedial oblique view. (CL, clivus; PG, pituitary gland; NS, nasal septum)

PG

CL

Fig. 2.19 Exposure of the medial cavernous wall on the left side.

The bulging of the C5 portion of the left internal carotid artery is seen below the medial cavernous sinus. (C5, C5 portion of the internal carotid artery; CL, clivus; PG, pituitary gland)

C5

2 Transmaxilloethmoidal Approach

PG

C4

CL

C5

Fig. 2.20 Opening of the cavernous sinus on the left side.

The removal of the medial cavernous sinus wall exposes the C4 portion of the internal carotid artery. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; CL, clivus; PG, pituitary gland)

C3

PG

C4

C5

Fig. 2.21 Exposure of the internal carotid artery on the left side.

The C3 to C5 portion of the internal carotid artery on the left side is well demonstrated. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; PG, pituitary gland; NS, nasal septum)

C3

PG

C4

Fig. 2.22 Exposure of the medial cavernous wall on the right side.

Exposure of the medial cavernous wall on the right side (approach side) is more difficult because the line of the surgeon’s view is tangential. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; CL, clivus; PG, pituitary gland)

C5

CL

NS

33

34

I Anterior Skull Base

ON

Chi

Fig. 2.23 Anatomical relationship between the

optic nerve, pituitary gland, pituitary stalk, and internal carotid artery on the left side.

St

C3

PG

The tuberculum sella is removed and the dura above the pituitary gland is opened. The anatomical relationship between the left optic nerve, pituitary gland, and left carotid artery is well demonstrated with minimum retraction of the nasal septum. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; Chi, chiasm; NS, nasal septum; ON, optic nerve; PG, pituitary gland; SpP, sympathetic nerve; St, stalk)

NS

C4 C5

SpP

Chi

St

PG

C3

Fig. 2.24 Anatomical relationship between the

CL

optic nerve, pituitary gland, pituitary stalk, and internal carotid artery on the right side.

The ipsilateral structures are more difficult to see. (C3, C3 portion of the internal carotid artery; Chi, chiasm; CL, clivus; PG, pituitary gland; St, stalk)

PG NS

CL

Ch

Fig. 2.25 (Step 9) Expose the midclivus. By extending our opening in the anterior wall of the sphenoid sinus, the midclivus can be seen. (Ch, choana; CL, clivus; NPx, nasopharynx; NS, nasal septum; PG, pituitary gland)

NPx

2 Transmaxilloethmoidal Approach

St C3

PG CL

Fig. 2.26 Overview of the final exposure. A low magnification view demonstrates the surgical exposure in the context of the patient's face. (C3, C3 portion of the internal carotid artery; CL, clivus; NS, nasal septum; PG, pituitary gland; St, stalk)

NS

35

3 Transfacial Transmaxillary Approach The transfacial transmaxillary approach is a radical approach that affords the surgeon exposure from the anterior skull base to the clivus.

Key Steps Position: Supine   Step 1. Incise the skin and elevate the flap (Fig. 3.1)   Step 2. Perform orbito-zygomatic-maxillary osteotomies (Fig. 3.4)   Step 3. Reflect the temporalis muscle (Fig. 3.7)   Step 4. Expose the infratemporal fossa (Fig. 3.10)   Step 5. Perform a frontotemporal craniotomy (Fig. 3.12)   Step 6. Expose the nasal cavity (Fig. 3.13)   Step 7. Expose the parapharyngeal space and the tensor veli palatini muscle (Fig. 3.14)   Step 8. Expose the clivus and posterior fossa dura (Fig. 3.24)   Step 9. Remove the ramus of the mandible (Fig. 3.33) Step 10. Expose the high cervical and paraclival regions (Fig. 3.34)

Illustrated Steps with Commentary

Fig. 3.1 (Step 1) Incise the skin and elevate the

flap.

A preauricular skin incision is made extending a standard fron­ tal skin incision inferiorly along the mandible. A second incision extends from the inferior orbital rim back along the top of the zygoma. Thus, the skin incision includes a hemicoronal incision, a preauricular incision, a high cervical incision, a temporal incision, a conjunctival incision, and a paranasal incision.

3 Transfacial Transmaxillary Approach

F

Fig. 3.2 Reflection of the skin flap. A reflection of the skin flap exposes the frontal bone, the tempo­ ralis and masseteric muscles, the zygoma, and the maxilla. As part of the temporal incision, the frontal branch of the facial nerve is transected and tagged. The nerve is reanastamosed at the time of the closure. The preauricular dissection must be deep to the superficial layer of the parotid gland and lateral to the main trunk of the facial nerve to avoid facial nerve injury. The facial nerve and its branches in the parotid gland are elevated with the facial flap. trunk facial nerve should be preserved Fig.The 1.1main (Step 1)of the Cartilaginous framework ofwhen the possible; nose. however, if a high cervical incision is required, the facial nerve can be and repaired during wound clo­ The major or transected, greater alartagged, cartilage is the thin flexible lattice that sure. this specimen, the facial nervewalls is transected. TheThe parotid formsInthe anterior, medial, and lateral of the nares. sep­ gland, including the facial is raised with the facial (DTF, tal cartilage separates thenerve, two nares. (GAC, greater alarflap. cartilage; deep temporal fascia; F, frontal bone; MM, masseteric LC, lateral crus of the greater alar cartilage; MC, medialmuscle; crus of Mx, the maxilla; Or, orbit; Zy, zygomatic greater alar cartilage; SNC, septalarch) nasal cartilage)

DTF

Or Zy Mx MM

F

DTF

Or Zy Mx

Fig. 1.1 (Step 1) Cartilaginous framework of the

nose.

RM

Fig. The major 3.3 or Reflection greater alarof cartilage the masseteric is the thin flexible muscle. lattice that forms the anterior,of medial, and lateralmuscle walls ofexposes the nares. The sep­ Inferior reflection the masseteric the ramus talthe cartilage separates two nares. (GAC, alarbone; cartilage; of mandible. (DTF,the deep temporal fascia;greater F, frontal Mx, LC, lateralOr, crus of the greater alar MC, medial crus of the maxilla; orbit; RM, ramus ofcartilage; the mandibule; Zy, zygomatic greater alar cartilage; SNC, septal nasal cartilage) arch)

F

DTF

Or Zy

Mx

Fig. 1.1 (Step 1) Cartilaginous framework of the nose.3.4 (Step 2) Perform orbito-zygomaticFig.

maxillary The major orosteotomies. greater alar cartilage is the thin flexible lattice that forms the anterior, and lateral walls The zygomatic archmedial, and the anterior wall of the nares. maxillaThe aresep­ re­ tal cartilage separates the two nares. (GAC,fascia; greater cartilage; moved in one piece. (DTF, deep temporal F, alar frontal bone; LC, lateral crus the greater alar of cartilage; MC, medial crus of the Mx, maxilla; Or,oforbit; RM, ramus the mandibule; Zy, zygomatic greater alar cartilage; SNC, septal nasal cartilage) arch)

RM

37

38

I Anterior Skull Base

Fig. 3.5 Exposure after the osteotomy. An osteotomy of the zygoma and the maxilla exposes the coro­ noid process of the mandibule, the fat tissue in the pterygopala­ tine fossa, and the maxillary sinus. The lateral wall of the orbit has also been removed. (DTF, deep temporal fascia; F, frontal bone; Fat, fat tissue; MxS, maxillary sinus; Or, orbit; RM, ramus of the mandibule)

F

TM Or

MxS

Fig. 3.6 Removal of adipose tissue exposing the

contents of the pterygopalatine fossa.

RM

The removal of the adipose tissue behind the posterior wall of the maxillary sinus exposes the pterygopalatine fossa. The deep temporal fascia is removed to show the relationship between the insertion of the temporalis muscle and the coronoid process. (F, frontal bone; MxS, maxillary sinus; Or, orbit; RM, ramus of the mandibule; TM, temporalis muscle)

F

T Or

MxS

Fig. 3.7 (Step 3) Reflect the temporalis muscle. An inferior reflection of the temporalis muscle exposes the base of the middle fossa. The temporalis muscle with the coronoid process is detached with a drill and reflected. (F, frontal bone; MxS, maxillary sinus; Or, orbit; T, temporal bone; TM, temporalis muscle)

TM

3 Transfacial Transmaxillary Approach

F

T Or

DTA MA

MxS

Fig. 3.8 Reflection of the temporalis muscle with

the coronoid process to preserve the posterior deep temporal artery.

TM

The coronoid process is fractured obliquely and left attached to the temporalis muscle to preserve the blood supply to the muscle through the posterior deep temporal artery. (DTA, deep temporal artery; F, frontal bone; MA, maxillary artery; MxS, maxillary sinus; Or, orbit; T, temporal bone; TM, temporalis muscle)

F

T iLPM

sLPM

Or

MxS

Fig. 3.9 Exposure of the lateral pterygoid muscle.

DTA

Removal of a main trunk of the internal maxillary artery and the pterygoid venous plexus exposes the superior and inferior heads of the lateral pterygoid muscle. (DTA, deep temporal artery; F, frontal bone; iLPM, inferior head of the lateral pterygoid muscle; MxS, maxillary sinus; Or, orbit; sLPM, superior head of the lateral pterygoid muscle; T, temporal bone; TM, temporalis muscle)

TM

T V3

Or

MxS

Fig. 3.10 (Step 4) Remove the lateral pterygoid muscle.

Removal of the superior and inferior heads of the lateral pterygoid muscle exposes the infratemporal and pterygopalatine fossae. The branches of the mandibular nerve are exposed. (DTA, deep temporal artery; MxS, maxillary sinus; Or, orbit; T, temporal bone; TM, temporalis muscle; V3, mandibular nerve [third division of the trigeminal nerve])

DTA

TM

39

40

I Anterior Skull Base

F

T Or

V3 LL

MxS

Fig. 3.11 Removal of the posterior wall of the maxillary sinus.

DTA

TM

The infratemporal and pterygopalatine fossae and the maxillary sinus that become a corridor to the anterior and anterolateral skull base are well exposed. (DTA, deep temporal artery; F, frontal bone; LL, lateral lamina of the pterygoid process; MxS, maxillary sinus; Or, orbit; T, temporal bone; TM, temporalis muscle; V3, mandibular nerve [third division of the trigeminal nerve])

FD

TD Or V3

Fig. 3.12 (Step 5) Perform a frontotemporal craniotomy.

A frontotemporal craniotomy is elevated. (DTA, deep temporal ar­ tery; FD, frontal dura; LL, lateral lamina of the pterygoid process; MxS, maxillary sinus; Or, orbit; TD, temporal dura; TM, tempora­ lis muscle; V3, mandibular nerve [third division of the trigeminal nerve])

LL

MxS DTA

TM

FD

TD Or SS V3

Fig. 3.13 (Step 6) Flattening the floor of the

middle fossa and removal of the medial wall of the maxillary sinus to expose the nasal cavity.

Flattening the floor of the middle fossa with a diamond drill ex­ poses the mandibular (V3), maxillary (V2), and vidian nerves, and the sphenoid sinus. A medial wall of the maxillary sinus is also re­ moved. (FD, frontal dura; Or, orbit; SS, sphenoid sinus; TD, tem­ poral dura; TM, temporalis muscle; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

Vi

TM

3 Transfacial Transmaxillary Approach

TD V2 SS

Or

Vi

V3

Fig. 3.14 (Step 7) Expose the parapharyngeal

TVPM

space and the tensor veli palatini muscle.

The tensor velli palatini muscle arises from the scaphoid fossa at the top of the pterygoid process and posteriorly from the medial aspect of the spine of the sphenoid bone. This thin and triangular shaped muscle is attached to the anterolateral membranous wall of the eustachian tube lateral to the levator veli palatine muscle. The tendon passes around the pterygoid hamulus. (Or, orbit; SS, sphenoid sinus; TD, temporal dura; TM, temporalis muscle; TVPM, tensor veli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

TM

TD V2

Or

SS Vi V3

ET

TM

Fig. 3.15 Exposure of the eustachian tube (auditory or pterygotympanic tube).

Removal of the tensor velli palatini muscle exposes the eustachian tube. (ET, eustachian tube; Or, orbit; SS, sphenoid sinus; TD, tem­ poral dura; TM, temporalis muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third divi­ sion of the trigeminal nerve]; Vi, vidian nerve)

TD V2 Or

SS Vi

Fig. 3.16 Enlargement of Fig. 3.15. The superior constrictor muscle of the pharynx is well seen. The fibrous layer that supports the pharyngeal mucosa is thickened above the superior constrictor to form the pharyngobasilar fascia. The fascia is attached to the basilar part of the occipital bone and the petrous part of the temporal bone medial to the eustachian tube, and to the posterior border of the medial pterygoid plate and pterygomandibular raphe. (DTA, deep temporal artery; ET, eustachian tube; LVPM, levator velli palatini muscle; Or, orbit; PhxBF, pharyngobasilar fascia; SCPhx, superior constrictor muscle of the pharynx; SS, sphenoid sinus; TD, temporal dura; V2, maxil­ lary nerve [second division of the trigeminal nerve]; V3, mandibu­ lar nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

PhxBF

V3 ET

LVPM

DTA SCPhx

41

42

I Anterior Skull Base

FD

TD

Or

V2 SS

V3

ET

Vi

TM

Fig. 3.17 Overview of the exposure. (ET, eustachian tube; FD, frontal dura; Or, orbit; SS, sphenoid sinus; TD, temporal dura; TM, temporalis muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

Or V3 ET Fig. 3.18 Identification of the longus capitis and rectus capitis anterior muscles.

RCAM

The longus capitis and rectus capitis anterior muscles are seen through the retropharyngeal space. The rectus capitis is a short muscle originating from the anterior mass and transverse pro­ cesses of the atlas. The longus capitis originates from the anterior tubercle of C3­6. Both insert into the occipital bone anterior to the foramen magnum. (DTA, deep temporal artery; ET, eustachian tube; ICA, internal carotid artery; LCpM, longus capitis muscle; Or, orbit; RCAM, rectus capitis anterior muscle; RM, ramus of the mandibule; SCPhx, superior constrictor muscle of the pharynx; SPhM, stylopharyngeal muscle; V3, mandibular nerve [third divi­ sion of the trigeminal nerve])

ICA

LCpM SCPhx SPhM

DTA

RM

Or

V3 ET RCAM

LCpM

IX ICA

Fig. 3.19 Identification of the glossopharyngeal nerve.

The glossopharyngeal nerve is observed passing over the stylo­ pharyngeal muscle. The nerve passes lateral to the internal ca­ rotid artery. (ET, eustachian tube; ICA, internal carotid artery; IX, glossopharyngeal nerve; LCpM, longus capitis muscle; Or, orbit; RCAM, rectus capitis anterior muscle; SCPhx, superior constrictor muscle of the pharynx; SPhM, stylopharyngeal muscle)

SPhM

SCPhx

3 Transfacial Transmaxillary Approach

ET

RCAM LCpM

IX

IC A

Fig. 3.20 Review of anatomical relationships in the retropharyngeal space.

SCPhx

SPhM

The rectus capitis anterior muscle lies posterior and medial to the longus capitis muscle and under the internal carotid artery, the glossopharyngeal nerve, and the stylopharyngeal muscle in the retropharyngeal space. (ET, eustachian tube; ICA, internal carotid artery; IX, glossopharyngeal nerve; LCpM, longus capitis muscle; RCAM, rectus capitis anterior muscle; SCPhx, superior constrictor muscle of the pharynx; SPhM, stylopharyngeal muscle)

TD

V2 SS Vi

V3

PhxBF

ET Fig. 3.21 The course of the eustachian tube. A metal bar is inserted into the eustachian tube that connects the middle ear to the nasopharynx. (ET, eustachian tube; LCpM, lon­ gus capitis muscle; PhxBF, pharyngobasilar fascia; SCPhx, superior constrictor muscle of the pharynx; SS, sphenoid sinus; TD, tem­ poral dura; V2, maxillary nerve [second division of the trigemi­ nal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

LCpM SCPhx

V3 Fig. 3.22 After removal of the eustachian tube. The longus capitis muscle originates from the anterior tubercles of the third, fourth, fifth, and sixth cervical vertebrae and be­ comes broad and thick above, where it is inserted into the infe­ rior surface of the basilar part of the occipital bone. The rectus capitis anterior is a short, flat muscle situated behind the upper part of longus capitis. It arises from the anterior surface of the lateral mass of the atlas and the root of its transverse process, and ascends almost vertically to the inferior surface of the basilar part of the occipital bone immediately anterior to the occipital con­ dyle. (DTA, deep temporal artery; LCpM, longus capitis muscle; RCAM, rectus capitis anterior muscle; SCPhx, superior constrictor muscle of the pharynx; V3, mandibular nerve [third division of the trigeminal nerve])

RCAM

LCpM

DTA

SCPhx

43

44

I Anterior Skull Base

Or

TD

RCAM

Fig. 3.23 Division of the mandibular nerve. A spine of the sphenoid bone is well seen after the mandibular nerve is divided. The spine is the inferior lateral corner of the greater wing of the sphenoid bone. The spine fits into the groove between the petrous and squamosal portions of the temporal bone and lies just behind the foramen spinosum. (DTA, deep tem­ poral artery; IX, glossopharyngeal nerve; LCpM, longus capitis muscle; Or, orbit; RCAM, rectus capitis anterior muscle; SCPhx, superior constrictor muscle of the pharynx; SSph, spine of the sphenoid bone; TD, temporal dura)

SSph

LCpM

IX

SCPhx

DTA

V2

TD

SS

Or

Vi

V3

CL Fig. 3.24 (Step 8) Exposure of the basilar

part of the occipital bone (clivus) through the retropharyngeal space.

LCpM

RCAM

An upper part of the basilar part of the occipital bone is exposed compressing the pharyngobasilar fascia and the superior con­ strictor muscle anteriorly. (CL, clivus; DTA, deep temporal artery; LCpM, longus capitis muscle; Or, orbit; RCAM, rectus capitis an­ terior muscle; SCPhx, superior constrictor muscle of the pharynx; SS, sphenoid sinus; TD, temporal dura; V2, maxillary nerve [sec­ ond division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

SCPhx DTA

TD

SS V3

RC

AM

Vi

CL

Fig. 3.25 Removal of the longus capitis muscle. The rectus capitis anterior muscle is well exposed after the longus capitis muscle is removed. (CL, clivus; DTA, deep temporal artery; Or, orbit; RCAM, rectus capitis anterior muscle; SCPhx, superior constrictor muscle of the pharynx; SS, sphenoid sinus; TD, tem­ poral dura; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

DTA

SCPhx

Or

3 Transfacial Transmaxillary Approach

V2 SS

TD V3

Or

Vi

OcC

CL

Fig. 3.26 Removal of the rectus capitis anterior muscle.

SCPhx

DTA

TD

Fig. 3.27 Exposure of the occipital and C1 condyles.

The occipital, C1 condyle, and facet lie behind the rectus capitis anterior muscle. The anatomical relationship between the internal carotid artery that enters into the carotid canal, the spine of the sphenoid bone, the facet, and the anterior arch of the atlas is well seen from an anterolateral direction. (aC1, anterior arch of the C1 [atlas]; C1C, C1 condyle; CL, clivus; DTA, deep temporal artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; OcC, oc­ cipital condyle; Or, orbit; SCPhx, superior constrictor muscle of the pharynx; SPhM, stylopharyngeal muscle; TD, temporal dura)

Or

ICA

OcC

IX

C1C SPh

CL

aC1 M

SC Ph x

Removal of the rectus capitis anterior muscle exposes the basilar part of the occipital bone. (CL, clivus; DTA, deep temporal artery; OcC, occipital condyle; Or, orbit; SCPhx, superior constrictor muscle of the pharynx; SS, sphenoid sinus; TD, temporal dura; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve; V2, maxillary nerve [second division of the trigemi­ nal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

DTA

TD C5

Or

Fig. 3.28 Elevation of the temporal base with the

SSph

dura mater.

Elevation of the basal temporal dura exposes the C5 portion of the internal carotid artery as it exits the carotid canal in the mid­ dle fossa. (C1C, C1 condyle; C5, C5 portion of the internal carotid artery; CL, clivus; ICA, internal carotid artery; OcC, occipital con­ dyle; Or, orbit; SSph, spine of the sphenoid bone; TD, temporal dura)

ICA

OcC C1C

CL

45

46

I Anterior Skull Base

TD C5 Or

C6

CL

Fig. 3.29 Exposure of the intracranial extradural portion of the internal carotid artery.

The C5 and C6 segments of the internal carotid artery can be ex­ posed by opening the intrapetrous carotid canal. The canal can be opened from a lateral direction by drilling through the bony eustachian canal and the canal that houses the tensor tympani muscle. (C5, C5 portion of the internal carotid artery; C6, C6 por­ tion of the internal carotid artery; CL, clivus; DTA, deep temporal artery; OcC, occipital condyle; Or, orbit; SCPhx, superior constric­ tor muscle of the pharynx; TD, temporal dura)

OcC

DTA

SCPhx

TD C5 Or

C6 PD

CL

Fig. 3.30 Drilling of the basilar part of the occipital bone (clivectomy).

The basilar part of the occipital bone is drilled under the internal carotid artery. The posterior fossa dura is exposed. (aC1, anterior arch of the C1 [atlas]; C1C, C1 condyle; C5, C5 portion of the in­ ternal carotid artery; C6, C6 portion of the internal carotid artery; CL, clivus; DTA, deep temporal artery; OcC, occipital condyle; Or, orbit; PD, posterior fossa dura; SCPhx, superior constrictor muscle of the pharynx; TD, temporal dura)

OcC C1C aC1

SCPhx

DTA

TD DS

Or

PD CL

OcC C1C

Fig. 3.31 Partial clivectomy. The bony edge of the dorsum sellae is seen by lifting the internal carotid artery. (aC1, anterior arch of the C1 [atlas]; C1C, C1 con­ dyle; CL, clivus; DS, dorsum sellae; DTA, deep temporal artery; OcC, occipital condyle; Or, orbit; PD, posterior fossa dura; SCPhx, superior constrictor muscle of the pharynx; TD, temporal dura)

aC1 DTA

SCPhx

3 Transfacial Transmaxillary Approach

TD

Or

PD CL

OcC

Fig. 3.32 Exposure of the posterior fossa dura. Removal of the basilar portion of the occipital bone with a diamond drill exposes the posterior fossa dura. (aC1, anterior arch of the C1 [atlas]; C1C, C1 condyle; CL, clivus; DTA, deep temporal artery; OcC, occipital condyle; Or, orbit; PD, posterior fossa dura; SCPhx, superior constrictor muscle of the pharynx; TD, temporal dura)

C1C

SCPhx

aC1

DTA

C5 C6

ICA P Sty

IX

SC

Fig. 3.33 (Step 9) Remove the ramus of the

M

SPhM SGM SHL SHM

mandible.

After the ramus of the mandible is removed, the stylopharyngeal, styloglossus, and the styloid muscles are well exposed. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the inter­ nal carotid artery; ICA, internal carotid artery; IX, glossopharyn­ geal nerve; SCM, sternocleidomastoid muscle; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPhM, stylopharyngeal muscle; StyP, styloid process)

ICA

P Sty

OcC

IX

C1C SP

SG M M L SH SH

The stylopharyngeal, styloglossus, and stylohyoid muscles are well seen. The stylohyoid ligament runs parallel to the stylohy­ oid muscle. The glossopharyngeal nerve and the high cervical portion of the internal carotid artery are seen between the sty­ loglossus and the stylopharyngeal muscles. (aC1, anterior arch of the C1 [atlas]; C1C, C1 condyle; ICA, internal carotid artery; OcC, occipital condyle; IX, glossopharyngeal nerve; SCM, sterno­ cleidomastoid muscle; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPhM, stylopharyngeal mus­ cle; StyP, styloid process)

M

attach to the styloid process (magnification of Fig. 3.33).

SC

Fig. 3.34 (Step 10) Expose the three muscles that

hM

aC1 IC

A

IX

47

48

I Anterior Skull Base

TD Or C5 C6 Vo

CL

PD

NS

ICA

P Sty

Fig. 3.35 Removal of the lateral wall of the nasal M SC

cavity.

The nasal septum is seen after the lateral wall of the nasal cavity is removed. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; CL, clivus; ICA, internal ca­ rotid artery; NS, nasal septum; Or, orbit; PD, posterior fossa dura; SCM, sternocleidomastoid muscle; SMs, muscles that attached to the styloid process; StyP, styloid process; TD, temporal dura; Vo, vomer)

SMs

FD TD

Et C5 C6

NS

ICA

CL

M SC

The orbit is removed and the ethmoid sinus is skeletonized through the medial wall of the orbital cavity. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; CL, clivus; Et, ethmoid sinus; FD, frontal dura; ICA, internal carotid artery; NS, nasal septum; PD, posterior fossa dura; SCM, sternocleidomastoid muscle; SMs, muscles that attach to the sty­ loid process; StyP, styloid process; TD, temporal dura; Vo, vomer)

P Sty

Fig. 3.36 Removal of the orbit.

Vo

PD

SMs

FD TD Et C5 C6 ICA

P Sty

PD

Fig. 3.37 Ethmoidectomy. M SC

After ethmoidectomy the anterior skull base is exposed. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the inter­ nal carotid artery; CL, clivus; Et, ethmoid sinus; FD, frontal dura; ICA, internal carotid artery; NS, nasal septum; PD, posterior fossa dura; SCM, sternocleidomastoid muscle; SMs, muscles that attach to the styloid process; SS, sphenoid sinus; StyP, styloid process; TD, temporal dura; Vo, vomer)

SMs

SS

Vo CL

NS

3 Transfacial Transmaxillary Approach

FD TD Et ST C5

MT

C6 ICA

M SC

After the nasal septum is removed the superior, middle, and in­ ferior turbinates on opposite sides are exposed. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal ca­ rotid artery; CL, clivus; Et, ethmoid sinus; FD, frontal dura; ICA, internal carotid artery; IT, inferior turbinate; MT, middle turbinate; PD, posterior fossa dura; SCM, sternocleidomastoid muscle; SMs, muscles that attach to the styloid process; ST, superior turbinate; StyP, styloid process; TD, temporal dura)

P Sty

Fig. 3.38 Removal of the nasal septum.

PD

SMs

CL

IT

49

4 Bifrontal Transbasal Approach This midline bifrontal transbasal approach has been mostly used for the extradural tumor of the middle anterior skull base. An olfactory nerve is preserved in the unilateral transbasal approach, but olfaction is generally sacrificed when the bifrontal transbasal approach is used. In the extensive transbasal approach, the bifrontal craniotomy is combined with a supraorbital osteotomy to allow the surgeon to perform an ethmoidectomy, sphenoidostomy, and extensive clivectomy. This approach affords the surgeon access to the cavernous sinus and the orbital apex. The surgical angle makes control of hemorrhage from the medial cavernous sinus challenging. Although an extensive intradural exposure is possible, it is generally avoided because of the risk of postoperative infection. The approach is most often used for the resection of midline clival lesions, frontal skull base lesions, medial orbital lesions, and paranasal lesions, including nasopharyngeal tumors, chondrosarcomas, chordomas, and meningiomas.

Key Steps Position: Supine Step 1. Reflection of scalp (Fig. 4.1) Step 2. Craniotomy (Fig. 4.10) Step 3. Closure of the anterior fossa dura (Fig. 4.18) Step 4. Osteotomy of orbital roots (Fig. 4.21) Step 5. Ethmoidectomy (Fig. 4.30) Step 6. Sphenoidostomy (Fig. 4.39) Step 7. Clivectomy (Fig. 4.49) Step 8. Intradural exposure (Fig. 4.53)

Variations of the Transbasal Approach 1. Unilateral transbasal approach 2. Standard bifrontal transbasal approach without removal of the supraorbital bar 3. Limited bifrontal transbasal approach removal of the supraorbital bar between supraorbital foramen or notch 4. Extended bifrontal transbasal approach removal of the whole supraorbital bar 5. Extensive bifrontal transbasal approach removal of the whole supraorbital bar and lateral orbital wall

4 Bifrontal Transbasal Approach

Illustrated Steps with Commentary

A B C Fig. 4.1 (Step 1) Skin incision. A long pericranial graft can be obtained by lifting the posterior scalp flap (A). A more posteriorly placed skin incision facilitates harvesting of a longer pericranial flap (C). A more posteriorly placed skin incision can be hidden behind the patient’s hairline (B).

PC

Fig. 4.2 A long vascularized pericranial or galeal flap is raised and hinged on the orbital arteries. (PC, pericranial flap)

Fat

Fig. 4.3 Elevation of the skin flap with protection of the frontalis branch of the facial nerve. The deep and superficial layers of the temporal fascia are separated by the deep temporal fat pad close to the zygoma. Both layers attach to the lateral aspect of the zygomatic arch. The superficial layer is contiguous with the pericranium, so the superficial layer can be separated from the deep layer by continuing a subperiosteal dissection over the temporalis muscle. (DDTF, deep layer of the deep temporal fascia; Fat, fat tissue; SDTF, superficial layer of the deep temporal fascia)

DDTF SDTF

51

52

I Anterior Skull Base

Fig. 4.4 Supraorbital and supratrochlear nerves

and arteries.

The skin flap should be raised to preserve the supraorbital and supratrochlear nerves and arteries. These nerves and arteries emerge from the notches or foramen in the supraorbital ridge. The supraorbital nerve ascends over the forehead and ends in two branches, a medial and a lateral branch. They are initially situated beneath the frontalis muscle, reaching nearly as far back as the lambdoid suture. The medial branch perforates the frontalis muscle and the lateral branch penetrates the galea aponeurotica. (SOF, superior orbital fissure; SON, supraorbital nerve)

SON

SON

SOF

SOF

(A) Fig. 4.5 Supratrochlear notch (A) and supraorbital foramen (B) on the right side.

(B)

If the bony encasement of the nerve is incomplete, the nerve can be raised out of the notch along with the pericranium. In the case of a complete bony foramen, the nerve and artery can be released by cutting a “V” shaped wedge of bone (A “V” osteotomy) around the foramen with a small drill bit, a sagittal saw, or a small osteotome.

(A)

Fig. 4.6 “V” osteotomy of supraorbital foramen. In this case, the supratrochlear nerve and artery (A) pass over a notch in the supraorbital ridge; the supraorbital nerve and artery (B) pass through a foramen that is opened by a “V” osteotomy in the supraorbital ridge.

(B)

4 Bifrontal Transbasal Approach

Fig. 4.7 Complete release of the supraorbital nerve and the artery with foramen. The “V” osteotomy was begun with a diamond drill. The thinned bone is fractured with an osteotome.

NFS

Fig. 4.8 Craniotomy for a unilateral transbasal approach. Unilateral transbasal approaches afford the surgeon a limited view of the anterior medial skull base that lies medial to the orbit. The further the craniotomy is extended toward the opposite side, the wider that medial corridor will become. (NFS, nasofrontal suture)

NFS

Fig. 4.9 Craniotomy for bilateral transbasal approach. The bilateral frontal craniotomy for the transbasal approach should extend at least between the midposition of the orbital rims. Further lateral exposure, especially to the right for a righthanded surgeon, affords the surgeon a greater degree of freedom for bringing instruments into the operative field. When the dura is thin and adherent to the bone, the craniotomy is performed in two stages. A dura frontal flap is turned within 1.5 cm of the midline. The pericranium overlying the sagittal sinus is freed from the bone and the contralateral frontal bone flap is turned. (NFS, nasofrontal suture)

53

54

I Anterior Skull Base

FS

Fig. 4.10 (Step 2) Bilateral frontal craniotomy for a transbasal approach.

If the frontal sinuses are well developed, the inferior bone cut of the craniotomy passes through the frontal sinuses. The mucosa should be drilled from the frontal sinus cavities that are removed with the frontal bone flap and from the remaining frontal sinus. If the dura is to be opened, opening the anterior ethmoid air cells will provide another path for a CSF leak. (FS, frontal sinus)

NFD NFD

Fig. 4.11 Frontonasal duct. The frontal sinus drains into the nasal cavity under the middle turbinate through the frontonasal duct. The duct originates at the inferior medial corner of the frontal sinus occlusion of the duct and isolates the frontal sinus from the nose. The inner table of the frontal sinus is removed to improve visualization of the skull base. The mucosal rests are removed from the walls of the sinus with a diamond drill to avoid the formation of a mucocele. (NFD, nasofrontal duct)

FB

Fig. 4.12 Dural elevation from the frontal base of the inferior fossa.

The dura is elevated from the base of the anterior fossa to expose the crista galli. (FB, frontal base)

FB

4 Bifrontal Transbasal Approach

FS

FS

FB FB CG Fig. 4.13 Crista galli. The dura is tightly pulled over the crista galli and tethered bilaterally at the olfactory groove. The anterior edge of the crista galli can be exposed, but it is difficult to completely remove the dura covering without tearing the dura. (CG, crista galli; FB, frontal base; FS, frontal sinus)

FB AE A& N

Fig. 4.14 Anterior ethmoid nerve and artery

emerging from the anterior ethmoidal foramen.

The anterior ethmoid artery should be coagulated as the first step in raising the dura from the cribriform plate. (AEA&N, anterior ethmoid artery and nerve; FB, frontal base)

AEA&N

PEA&N

Fig. 4.15 Posterior ethmoid nerve and artery emerging from posterior ethmoidal foramen.

The posterior ethmoid artery is coagulated as the next step. (AEA&N, anterior ethmoid artery and nerve; PEA&N, posterior ethmoid artery and nerve)

55

56

I Anterior Skull Base

CG

CP AE A& N

Fig. 4.16 Cribriform plate. After the anterior and posterior ethmoid arteries are coagulated the dura is sharply dissected from the cribriform plate severing the olfactory nerve. (AEA&N, anterior ethmoid artery and nerve; CG, crista galli; CP, cribriform plate)

CG CP AE

A&

N

Fig. 4.17 Anterior and posterior ethmoid nerves and arteries cut at orifice of the anterior and posterior ethmoidal foramen.

The anterior and posterior ethmoid arteries pass posterior laterally after entering the anterior fossa. The arteries’ impressions can be seen as grooves in the bone. These tributaries of the ophthalmic arteries supply blood to anterior fossa tumors. (AEA&N, anterior ethmoid artery and nerve; CG, crista galli), (CP, cribriform plate; PEA&N, posterior ethmoidal artery and nerve)

PEA

&N

CG CP

Fig. 4.18 (Step 3) Dural holes made by branches of the olfactory nerves.

Holes where the olfactory nerve branches penetrate the dura must be closed. These small holes should be closed in two layers. Simple sutures are used to approximate the dura. A fascial patch is sewn over the disrupted dura. (CG, crista galli; CP, cribriform plate)

CP

4 Bifrontal Transbasal Approach

Fig. 4.19 Stitches of small holes. The small holes resulting from the elevation of the frontal base dura should be stitched closed by plicating the dura on either side of the row of holes.

Fig. 4.20 Fascial patch graft. A patch is sewn over the dural rents to ensure a watertight closure.

Fig. 4.21 (Step 4) Variations in the size of the osteotomy of the supraorbital bar.

The size of the osteotomy of the supraorbital bar will vary depending on the amount of exposure required. Regardless of the lateral extent of the bone to be removed, the inferior bone cut is on the frontonasal suture. A lower bone cut will not increase the exposure. The medial palpebral ligament, which is attached to the frontal process of the maxillary bone, should be preserved. (AA', limited bifrontal transbasal approach; B-B', extended bifrontal transbasal approach)

B

A

A'

B'

57

58

I Anterior Skull Base

A

B C Fig. 4.22 Variations in the lateral extent of a supraorbital bar resection.

(A, limited bifrontal transbasal approach; B, extended bifrontal transbasal approach; C, extensive bifrontal transbasal approach)

Fig. 4.23 Osteotomy for limited bifrontal transbasal approach.

The periorbita is separated from the frontal bone. The periorbita and dura are protected with flat metal retractor blades. The periorbita can also be protected by Gelfoam (Pfizer Inc., NY, NY) or bone wax placed between the periorbita and the frontal bone. A sagittal saw is used to perform an osteotomy through the frontonasal suture and medial to the supraorbital notches. Finally, osteotomies of the orbital roof connect the frontonasal and supraorbital bony cuts using a sagittal saw or a diamond drill.

SON

SON NFD

Fig. 4.24 Exposure achieved after a limited supraorbital osteotomy.

The frontonasal duct is seen after the orbital bar is removed. Further drilling of the frontal sinus exposes the anterior and posterior ethmoid sinuses. (NFD, nasofrontal duct; SON, supraorbital nerve)

NFD

4 Bifrontal Transbasal Approach

SON

SON Or

NFD

NFD

Or

Fig. 4.25 Extended osteotomy for a bifrontal transbasal approach.

For the extended bifrontal osteotomy the orbital rim is cut at the level of the superior temporal line. These incisions are connected to the frontonasal osteotomy by an incision through the orbital roof. These orbital roof cuts are most safely made using a diamond drill. (NFD, nasofrontal duct; Or, orbit; SON, supraorbital nerve)

10 mm

Fig. 4.26 Supraorbital bar. Ten millimeters of orbital roof is removed along with the supraorbital bar in the extended transbasal approach. The remaining orbital roof is removed piecemeal.

SON

SON Or

Fig. 4.27 Osteotomy for an extensive bifrontal transbasal approach.

For the extensive bifrontal transbasal osteotomy the lateral orbital rim osteotomy is made through the frontal process of the zygoma. (NFD, nasofrontal duct; Or, orbit; SON, supraorbital nerve)

NFD

NFD

Or

59

60

I Anterior Skull Base

SON

LG Or

Fig. 4.28 Osteotomy for an extensive bifrontal transbasal approach.

The lateral orbital wall is removed. The lacrimal gland is well seen through the periorbita. (LG, lacrimal gland; Or, orbit; SON, supraorbital nerve)

SON

SON

NFD

Or

NFD

Or

Fig. 4.29 Removal of the orbital roof. The orbital roof is removed. (NFD, nasofrontal duct; Or, orbit; SON, supraorbital nerve)

Et

Et mNC Fig. 4.30 (Step 5) Opening of the ethmoid sinus. Drilling the posterior inferior wall of the frontal sinus exposes the ethmoid sinus. Further resection of the ethmoid sinus exposes the nasal mucosa. If the dura is opened, opening the ethmoid sinuses makes it more difficult to control CSF. The surgeon must meticulously close the dura and fastidiously secure the vascularized pericranial graft over the bony opening. (Et, ethmoid sinus; mNC, mucosa of the nasal cavity)

4 Bifrontal Transbasal Approach

mNC

mNC

SC Fig. 4.31 Nasal mucosa covering. The nasal cavity must be separated from the surgical field to prevent postoperative infection. After the cribriform plate is removed, the nasal mucosa is mobilized from the medial orbit. (mNC, mucosa of the nasal cavity; SC, sphenoidal crest)

mNC

mNC

Vo

SC Fig. 4.32 Separation of the nasal cavity. The mobilized nasal mucosa should be plicated with absorbable sutures covering the nasal cavity. This maneuver helps isolate the nasal cavity from the surgical field. (mNC, mucosa of the nasal cavity; SC, sphenoidal crest; Vo, vomer)

mNC

mNC

OSS

Fig. 4.33 Exposure of the sphenoid sinus. The natural ostia of the sphenoid sinus exit through the sphenoidal concha. The natural ostia exit through the vertical midpoint of the sphenoid sinus. (mNC, mucosa of the nasal cavity; OSS, ostium of the sphenoid sinus; TS, tuberculum sellae)

OSS

TS

61

62

I Anterior Skull Base

mNC

mNC

SC

Fig. 4.34 A less magnified view of the anterior

fossa.

Looking from above, the natural ostia into the sphenoid sinus are seen bilaterally. The nasal mucosa is seen entering the ostium on the right. The perpendicular plate of the ethmoid is seen articulating with the crest of the sphenoid. (mNC, mucosa of the nasal cavity; OSS, ostium of the sphenoid sinus; SC, sphenoidal crest; TS, tuberculum sellae)

OSS

TS

mNC

mNC SC

Fig. 4.35 Exposure of the sphenoid concha. The nasal mucosa is raised bilaterally to expose the sphenoid concha. (mNC, mucosa of the nasal cavity; SC, sphenoidal crest; TS, tuberculum sellae)

TS

PerE Vo

Al SC

Fig. 4.36 The anatomical relationship between

the nasal mucosa, sphenoidal concha, and vomer.

The posterior nasal septum is composed of the perpendicular plate of the ethmoid superiorly and the vomer inferiorly. The perpendicular plate of the ethmoid articulates with the thin sphenoidal crest and the ala of the vomer covers the thicker teardrop shaped rostrum of the sphenoid. (Al, ala of the vomer; SCo, sphenoidal concha; SC, sphenoidal crest; OSS, ostium of the sphenoid sinus; PerE, perpendicular plate of the ethomoid; Vo, vomer)

SCo

SCo OSS

4 Bifrontal Transbasal Approach

MT

MT SC

OSS

Fig. 4.37 The anatomical relationship between the middle turbinate and the sphenoid concha.

The middle turbinate, perpendicular plate, sphenoid concha, and natural ostia of the sphenoid sinus are well seen after the nasal mucosa is cut. (MT, middle turbinate; ON, optic nerve; OSS, ostium of the sphenoid sinus; SC, sphenoidal crest; TS, tuberculum sellae)

TS

ON

ON

SON

SON

Or

Or

MT

MT

Fig. 4.38 Before sphenoidostomy. The anterior wall of the sphenoid is exposed by removing the last remnants of the ethmoid sinuses. This picture should be compared with the next photo (Fig. 4.39). (MT, middle turbinate; ON, optic nerve; Or, orbit; SON, supraorbital nerve; TS, tuberculum sellae)

TS

ON

ON

SON

SON

Fig. 4.39 (Step 6) After sphenoidostomy. The anterior and superior walls of the sphenoid sinus are removed. The optic canals should not be opened to avoid the risk of injury to the optic nerves. The medial wall of the orbit should also be kept intact. Meningitis can be avoided by establishing multiple barriers between the CSF and the nasal cavity. The dura should be kept closed to protect against postoperative intracranial infection. The dura on the planum sphenoidale between the optic nerves can be used to anchor sutures by holding the vascularized free flap to the anterior skull base after surgery. The nasal mucosa may be sutured to separate the nasal cavity from the neurocranium. (MT, middle turbinate; ON, optic nerve; Or, orbit; SON, supraorbital nerve; SS, sphenoid sinus)

Or

Or

MT

MT

SS ON

ON

63

I Anterior Skull Base

Or

CP5

Or

SS 3

CP3

Fig. 4.40 Sella floor and carotid prominence.

SF

ON

The sella floor, carotid prominence, and optic canals are seen. In some patients the bony covering of the carotid arteries and optic nerves is incomplete, making the carotid vulnerable to injury. (CP3, carotid prominence formed by C3 portion of the internal carotid artery; CP5, carotid prominence formed by C5 portion of the internal carotid artery; ON, optic nerve; Or, orbit; SF, sella floor; SS, sphenoid sinus)

CP

64

ON

ICS

CP 3

SF

ON

CP3

ON

Fig. 4.41 Sella floor and intercavernous sinus. The intercavernous sinus is skeletonized through the thin sella floor. The bilateral carotid prominences overlying the C3 portion (anterior bend) of the internal carotid arteries are observed. (CP3, carotid prominence formed by C3 portion of the internal carotid artery; ICS, intercavernous sinus; ON, optic nerve; SF, sella floor)

CP5

Or CL

Fig. 4.42 Carotid prominences overlying the C3 CP

and C5 on the left side.

3

Two prominences on the lateral wall of the sphenoid sinus overlie the carotid artery. The superior prominence under the optic canal overlies C3 and the inferior posterior prominence overlies C5. (CL, clivus; CP3, carotid prominence formed by C3 portion of the internal carotid artery; CP5, carotid prominence formed by C5 portion of the internal carotid artery; ON, optic nerve; Or, orbit; SF, sella floor)

ON

SF

CP

3

ON

4 Bifrontal Transbasal Approach

CP3

SF

Fig. 4.43 Carotid prominences overlying C3.

ON

This magnified view demonstrates the carotid prominence overlying the C3 portion of the internal carotid artery. The carotid sheath and orbitocarotid recess can be seen in this view. (CP3, carotid prominence formed by C3 portion of the internal carotid artery; OCR, opticocarotid recess; ON, optic nerve; SF, sella floor)

OCR

TP

CP5 Fig. 4.44 Trigeminal prominence. The trigeminal prominence covering the maxillary nerve, second division (V2) of the trigeminal nerve can be seen on the lateral wall of the sphenoid sinus just below the carotid prominence. (C3, C3 portion of the internal carotid artery; CP5, carotid prominence formed by C5 portion of the internal carotid artery; ON, optic nerve; TP, trigeminal prominence)

C3 ON

C5

Fig. 4.45 Internal carotid artery from C5 to

C3

C3 portion skeletonized through the medial cavernous wall.

Removing the bone from the lateral wall of the sphenoid sinus demonstrates the course of the carotid artery through the cavernous sinus. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DSF, dura of the sella floor; ON, optic nerve)

DSF ON

65

66

I Anterior Skull Base

FOEV Vi TP

Fig. 4.46 Exposure of the vidian canal.

C5

Further drilling of the lateral wall of the sphenoid sinus results in exposes of the vidian canal lateral to the C5 portion of the internal carotid artery. (FOEV, foramen ovule emissary vein; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; ON, Optic nerve; TP, trigeminal prominence; Vi, vidian nerve)

C3 ON

FOEV V3 Vi

Fig. 4.47 Exposure of the vidian nerve,

mandibular nerve, and foramen ovale emissary vein.

The vidian nerve lies lateral to the C5 portion of the internal carotid artery. The mandibular nerve, the third division (V3) of the trigeminal nerve, and the foramen ovale emissary vein that constitutes a prominent connection between the posterior cavernous sinus, and the pterygoid plexus are observed lateral to the vidian nerve. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; FOEV, foramen ovale emissary vein; ON, optic nerve; TP, trigeminal prominence; V2, maxillary nerve; V3, mandibular nerve; Vi, vidian nerve)

V2 TP ON

C5

C3

FOEV V2

Fig. 4.48 Maxillary nerve. The maxillary nerve (V2) is found between the C5 segment of the carotid artery and the vidian canal. As the microscope has been tilted laterally, the vidian nerve is not well seen in this photograph. Below the maxillary nerve we see the medial edge of V3 accompanied by a prominent emissary vein. (C3, C3 portion of the internal carotid artery; FOEV, foramen ovale emissary vein; ON, optic nerve; V2, maxillary nerve [second division of the trigeminal nerve])

C3 ON

4 Bifrontal Transbasal Approach

aFM CL

Fig. 4.49 (Step 7) Clivectomy. Moving back to the midline, the clivus is removed behind and under the sphenoid sinus. (aFM, anterior portion of the foramen magnum; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; CL, clivus; DSF, dura of the sella floor; ON, optic nerve)

C5

C5 C3 ON

DSF

ON

aFM CL C5

C5

Fig. 4.50 Extension of the clivectomy to the foramen magnum.

The clivectomy can be extended to the anterior wall of the foramen magnum. (aFM, anterior portion of the foramen magnum; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; CL, clivus; DSF, dura of the sella floor; ON, optic nerve)

C3

C3 DSF

ON

ON

aFM

Fig. 4.51 Dural exposure. Complete clivectomy exposes the anterior aspect of the posterior fossa dura. The blue dye that indicates the basilar plexus is seen on the dura. Although these veins can cause troublesome bleeding, hemostasis can usually be accomplished with hemostatic agents and patience. (aFM, anterior portion of the foramen magnum; DSF, dura of the sella floor; ON, optic nerve; PD, posterior fossa dura)

PD

ON

DSF

ON

67

68

I Anterior Skull Base

aFM

CP5

JT

PD

Fig. 4.52 Jugular tubercle on the left side. The jugular tubercle on the left side is seen as an upward pointing bony protrusion. Because of the limited surgical corridor, it is difficult to demonstrate the jugular tubercle and the anterior foramen magnum in the same picture. (aFM, anterior portion of the foramen magnum; CP5, carotid prominence formed by C5 portion of the internal carotid artery; JT, jugular tubercle; PD, posterior fossa dura)

VA VA

Fig. 4.53 (Step 8) Dural opening. Most often the transbasal approach is used for extradural lesions. In such cases every effort should be made to maintain the integrity of the dura as a barrier against infection. If the surgeon intends to open the dura, the intradural dissections demonstrated in Figs. 1.56–1.60 will afford the reader the intradural anatomy as seen from the transbasilar approach. Should the surgeon elect to open the dura, plans must be made to close off the cavity with vascularized tissue. (BA, basilar artery; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DSF, dura of the sella floor; ON, optic nerve; VA, vertebral artery)

C5

C5

BA C3

C3 DSF

ON

ON

ASA Md Fig. 4.54 Medulla oblongata and upper cervical spine.

Opening the dura at the inferior end of the clivectomy demonstrates the upper cervical spinal cord, the medulla oblongata, the basilar artery, and the vertebral arteries. The anterior spinal artery and the spinal rootlets are also seen. (ASA, anterior spinal artery; BA, basilar artery; Md, medulla oblongata; VA, vertebral artery)

VA

VA BA

4 Bifrontal Transbasal Approach

ASA Md VA PICA Fig. 4.55 Exposure of the vertebrobasilar junction.

VA

AICA

BA

The vertebrobasilar junction and left anterior inferior cerebellar artery are observed. (AICA, anterior inferior cerebellar artery; ASA, anterior spinal artery; BA, basilar artery; Md, medulla oblongata; PICA, posterior inferior cerebellar artery; VA, vertebral artery)

XII

XI PICA

Fig. 4.56 Exposure of lower cranial nerves over

X

the abducens nerve on the left side.

The lower cranial nerves over the abducens nerve and posterior inferior cerebellar artery on the left side are seen by translocating the left vertebral artery. The lower cranial nerves are seen passing over the jugular tubercle. (IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; VI, abducens nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

IX

VI

JT VA X IX

Fig. 4.57 Exposure of the glossopharyngeal and vagus nerves on the left side.

The glossopharyngeal and vagus nerves are observed on the left side passing over the jugular tubercle. (IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; X, vagus nerve)

AICA

69

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I Anterior Skull Base

XII VA XI X

Fig. 4.58 Exposure of the hypoglossal and accessory nerves on the left side.

The accessory and hypoglossal nerves are seen on the left side. (VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

SpP C5 C3

Fig. 4.59 Exposure of the left internal carotid artery after removal of the medial wall of the cavernous sinus on the left side.

ON

PG

Removal of the medial wall of the cavernous sinus demonstrates the internal carotid artery from C3 to C5. Sympathetic nerve fibers travel along the wall of the artery. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; ON, optic nerve; PG, pituitary gland; SpP, sympathetic plexus)

FOE V

Vi

Fig. 4.60 Exposure of the vidian nerve. The deep petrosal nerve is a branch of the sympathetic plexus that surrounds the carotid artery. It joins the greater superficial petrosal nerve to form the vidian nerve. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; FOEV, foramen ovale emissary vein; SpP, sympathetic plexus; Vi, vidian nerve)

SpP

C3

C5

4 Bifrontal Transbasal Approach

C6 SpP

Fig. 4.61 Passing of the dissector through the triangle formed by V2 and V3.

To understand the relationship of the branches of the trigeminal nerve as seen from a transbasal approach, compared with the more familiar relationship appreciated from a middle fossa approach, a dissector is passed through the triangle formed by V2 and V3 in the middle fossa. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; ON, optic nerve; SpP, sympathetic plexus)

C5

C3

C4

ON

Vi

Fig. 4.62 Identification of the foramen ovale. To appreciate the anatomical relationships seen through the transbasal approach, the probe is placed through the foramen ovale. (C5, C5 portion of the internal carotid artery; SpP, sympathetic plexus; Vi, vidian nerve)

SpP

ET Vi

Fig. 4.63 The position of the eustachian tube. The dissector is inserted in the eustachian tube that connects the middle ear to the nasopharynx. (ET, eustachian tube; Vi, vidian nerve)

C5

71

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I Anterior Skull Base

PG

ON

St

ON

Fig. 4.64 Exposure of the optic chiasm and the pituitary stalk.

The chiasm, bilateral optic nerves, and stalk are observed in this view. (ON, optic nerve; PG, pituiraty gland; St, stalk)

Or

VA

C5 VA

C3

Fig. 4.65 Exposure of the anterior circulation and

ON

St

C1

DS

ON

C1 M1

M1

Chi

A1

Acom A2 A2

Heu

C5

C3 OA

ON

III

PG

and adjacent structures on the right side.

Removal of the cavernous sinus reveals the third cranial nerve and the free margin of the tentorium. The optic nerve and the C2 segment of the carotid artery are also seen. (C1, C1 [atlas]; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; III, oculomotor nerve; OA, occipital artery; ON, optic nerve; PG, pituitary gland; St, stalk)

Or

C3

optic chiasm.

Cutting the dura along the sphenoid wings and elevating the frontal lobes demonstrates the carotid bifurcations above the optic chiasm inferiorly, and we see the vertebrobasilar junction. (A1, A1 [horizontal] portion of the anterior cerebral artery; A2, A2 portion of the anterior cerebral artery; Acom, anterior communicating artery; BA, basilar artery; C1, C1 [atlas]; C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; Chi, chiasm; DS, dorsum sellae; Heu, Heubner's artery; M1, M1 portion of the middle cerebral artery; M2, M2 portion of the middle cerebral artery; ON, optic nerve; Or, orbit; St, stalk; VA, vertebral artery)

Fig. 4.66 Observation of the oculomotor nerve

C5

BA

C1 St

A1

M2

4 Bifrontal Transbasal Approach

C3

III

ON

IV

C1 Fig. 4.67 Identification of the trochlear nerve. The trochlear nerve is covered by a thin dural membrane. (C1, C1 [atlas]; C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve)

C3

III

ON C1 Fig. 4.68 Trochlear nerve. The thin dural membrane is peeled off so the trochlear nerve is well seen. The tentorium is raised with a forceps. (C1, C1 [atlas]; C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve)

IV

73

5 Endonasal Paraseptal Transsphenoidal Approach

The endonasal paraseptal approach is most often used to remove pathology within the sella turcica. The technique has been used to remove intradural pathology extending anterior to the tuberculum sellae and above the sellar turcica.

Key Steps Position: Supine with neck slightly extended Step 1. Identify the middle turbinate (Fig. 5.2) Step 2. Creation of a paraseptal mucosal flap (Fig. 5.5 ) Step 3. Remove the anterior wall of the sphenoid sinus (Fig. 5.11 ) Step 4. Open the sella floor (Fig. 5.16 ) Step 5. Dural incision (Fig. 5.17) Step 6. Repair the paraseptal mucosal flap (Fig. 5.22)

Surgical Tips As the surgeon is operating in a deep narrow hole, hemostasis should be established at each step. Bleeding can be controlled with oxidized cellulose and bipolar cautery. The key instruments for tumor removal are curettes of various sizes and angles. A plane should be established between the tumor and the normal flattened pituitary gland. The tumor is then systematically removed by first gutting the tumor and then dissecting the walls of the tumor toward the midline. Brisk venous cavernous sinus bleeding is controlled by elevation of the head, oxidized cellulose, and gentle pressure. It is not uncommon for a lip of arachnoid to protrude in front of the superior edge of the pituitary tumor. This is a possible site for cerebral spinal fluid leaks.

Illustrated Steps with Commentary

IT Fig. 5.1 Approach through the left nostril. The right-handed surgeon is more comfortable operating through the left nostril. The surgeon’s view is oblique to the right. For lesions extending to the left cavernous sinus, the surgeon’s view of the lesion is improved by operating through the right nostril. (IT, inferior turbinate)

5 Endonasal Paraseptal Transsphenoidal Approach

MT Fig. 5.2 (Step 1) Identify the middle turbinate through the left nostril. The floor of the nasal cavity is first identified. The inferior nasal turbinate is found and the middle nasal turbinate is seen above the inferior nasal turbinate. This methodical technique will avoid erroneous identification of this important landmark. (MT, middle turbinate)

NS MT

IT

Fig. 5.3 Identification of the middle turbinate. (IT, inferior turbinate; MT, middle turbinate; NS, nasal septum)

NS MT

Fig. 5.4 Nasal septum opposite to the middle turbinate. A microscope is tilted toward the nasal septum to start a mucosal incision. (MT, middle turbinate; NS, nasal septum)

75

76

I Anterior Skull Base

NS

MT NM

Fig. 5.5 (Step 2) Paraseptal mucosal incision. An incision is made in the mucosa of the nasal septum with a cautery approximately 1 cm anterior to the sphenoid sinus. This will create a mucosal flap that can be reapproximated to the nasal septum at the end of the case. (MT, middle turbinate; NM, nasal mucosa; NS, nasal septum)

NS

MT

NM

Fig. 5.6 Paranasal mucosal elevation. The mucosal flap is raised from the vomer, perpendicular plate of the ethmoid, and anterior wall of the sphenoid sinus. (MT, middle turbinate; NM, nasal mucosa; NS, nasal septum)

NS NM Fig. 5.7 Creation of the paranasal mucosal pocket. The vomer is cracked anterior to the ala vomer, and the vomer and perpendicular plate of the ethmoid are pushed to the right. The mucosa over the right side of the anterior sphenoidal wall is stripped from that bone. The mucosa is held laterally by a nasal speculum. (NM, nasal mucosa; NS, nasal septum)

5 Endonasal Paraseptal Transsphenoidal Approach

OSS

Fig. 5.8 Identification of the bilateral natural ostia of the sphenoid sinus bilaterally.

fVo

The ostia of the sphenoid sinus are identified bilaterally. (fVo, fractured vomer; OSS, ostium of the sphenoid sinus)

OSS

aVo

aVo

Fig. 5.9 Exposure of the ala vomer remnant (keel

bone).

fVo

The ala vomer covers the spine of the sphenoid bone. When the medial nasal septum is dislocated laterally, the ala vomer remains attached to the sphenoid bone and produces a characteristic teardrop shaped landmark. (aVo, ala of the vomer; fVo, fractured vomer; OSS, ostium of the sphenoid sinus)

aVo

aVo

Fig. 5.10 Downward tilting of the microscope. As a surgical trajectory viewing the ostium of the sphenoid sinus is slightly high for the approach to the sella floor, the microscope should be tilted downward, putting the tip of the keel bone in the center of the surgeon’s field. Stripping mucosa high off the ethmoid sinus risks injury to the bundles of the olfactory nerve. (aVo, ala of the vomer; fVo, fractured vomer)

fVo

77

78

I Anterior Skull Base

mSS

Fig. 5.11 (Step 3) Exposure of the mucosa of the sphenoid sinus.

The ala vomer and the anterior wall of the sphenoid sinus are removed with a diamond drill. The opening is made as wide as possible. (mSS, mucosa of the sphenoid sinus)

SF CP3 Fig. 5.12 Opening of the sphenoid sinus. The mucosa within the sphenoid sinus is removed. Troublesome bleeding from the mucosa can be controlled with bipolar cautery or temporary compression with Gelfoam (Pfizer Inc., NY, NY). The surgeon should note the position of the intrasinus septa on the preoperative imaging studies and match them to the anatomy found at the time of surgery. (CP3, carotid prominence formed by the C3 portion of the internal carotid artery; SF, sella floor; SS, sphenoid sinus)

SS

SF CP3

Fig. 5.13 Identification of the left C3 and C5 carotid prominences.

The C3 portion of the carotid artery makes an impression that protrudes into the sphenoid sinus lateral to the pituitary gland. The C3 segment protrudes lateral to the medial clivus. (CP3, carotid prominence formed by the C3 portion of the internal carotid artery; CP5, carotid prominence formed by the C5 portion of the internal carotid artery; CL, clivus; SF, sella floor)

CL

CP5

5 Endonasal Paraseptal Transsphenoidal Approach

SF

CP3 Fig. 5.14 Identification of the right C3 and C5 carotid prominence.

The prominence of the C5 carotid artery can be seen below the sella turcica. The C3 carotid artery lies under the protuberance of bone over the optic nerve. The perisellar protuberance is the outpouching of bone over C3. (CP3, carotid prominence formed by the C3 portion of the internal carotid artery; CP5, carotid prominence formed by the C5 portion of the internal carotid artery; CL, clivus; SF, sella floor)

CL CP5

SF

Fig. 5.15 Viewing of the sella turcica. The anterior sella protrudes into the sphenoid sinus in most cases. In the concha type sella (3%) cancellous bone covers the sella turcica. In these cases, the sella is not obvious when looking through the sphenoid sinus. (SF, sella floor)

SF

Fig. 5.16 (Step 4) Drilling of the sella floor with an endonasal drill.

The anterior wall of the sella turcica is removed with a diamond drill or Kerrison rongeur. Care is taken not to injure the carotid arteries , the venous channels that run in the dura, or the cavernous sinuses. Opening of the intercavernous sinuses in the underlying dura leads to annoying bleeding that can be controlled with oxidized cellulose and bipolar cautery. (SF, sella floor)

79

80

I Anterior Skull Base

DSF Fig. 5.17 (Step 5) Exposure of the dura of the pituitary gland.

A large intercavernous sinus frequently runs through the inferior anterior aspect of the sella dura. Bleeding from this sinus can be avoided by cauterizing the walls of the sinus before cutting through the sinus. (DSF, dura of the sella floor; ICS, intercavernous sinus)

ICS

DSF

C3

ICS

Fig. 5.18 Obtaining maximal exposure of the dura of the pituitary gland on the right side.

The dura should be exposed until the cavernous sinus is seen bilaterally. The cavernous sinus is identified by its blue color. It usually protrudes anterior to the dura covering the pituitary gland and covers C3. (C3, C3 portion of the internal carotid artery; DSF, dura of the sella floor; ICS, intercavernous sinus)

C3 PG ICS Fig. 5.19 Exposure of the medial cavernous sinus wall on the left side.

The anatomical relationship between the pituitary gland, the intercavernous sinus, and the C3 and C5 portions of the internal carotid artery is demonstrated. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; ICS, intercavernous sinus; PG, pituitary gland)

C5

5 Endonasal Paraseptal Transsphenoidal Approach

C3 PG ICS Fig. 5.20 Separation of the dura of the pituitary gland from the true medial cavernous wall.

C5

The normal pituitary gland can be separated from the true medial cavernous wall that is very thin. (C3, C3 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; ICS, intercavernous sinus; PG, pituitary gland)

PG Fig. 5.21 Opening of the right cavernous sinus for an extended transsphenoidal approach.

C3

C4

The covering of the cavernous sinus can be opened to expose the C3 carotid artery. Venous bleeding can be controlled with a hemostatic agent such as oxidized cellulose. There are no neural structures between the carotid artery and the pituitary gland. Care should be taken not to injure the fine branches of the carotid artery. (C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; PG, pituitary gland)

MT

Fig. 5.22 (Step 6) Renovation of the paraseptal mucosal flap.

If a CSF fistula develops, fat is placed into the sella turcica. It is held in place with fibrin glue and an absorbable cranial fixation plate. In the case of a large CSF fistula, a piece of fascia is used to reconstruct the anterior sellar wall. Once the speculum is removed, the medial nasal septum is pushed back to the midline. The ipsilateral mucosal flap is approximated to the nasal septa. (MT, middle turbinate; NM, nasal mucosa)

NM

81

82

I Anterior Skull Base

AHA

Fig. 5.23 Renovation of the paraseptal mucosal flap.

A pledget of absorbable hemostatic agent approximates the mucosal flap to the midline septum. The flap is held against the midline with fibrin glue. (AHA, absorbable hemostatic agent)

6 Transoral Approach The transoral approach affords the surgeon exposure for midline lesions located from the lower third of the clivus to the upper cervical spine. This procedure is most often used for extradural midline lesions. The surgical corridor is tightly confined with limited ability for lateral extension. It can be used for intradural lesions that are tightly confined to the midline. The mobility of the mandible must be assessed before the surgery unless the surgeon is planning to split the mandible and the tongue.

Key Steps Position: Supine Step 1. Mouth opening and tongue retraction (Fig. 6.4) Step 2. Uvula elevation (Fig. 6.7) Step 3. Incision of the posterior wall of the oropharynx (Fig. 6.8) Step 4. Exposure of the longus colli and capitis muscles (Fig. 6.10) Step 5. Retraction of the longus capitis muscle (Fig. 6.11) Step 6. Exposure of the clivus, atlas, and axis (Fig. 6.13) Step 7. Drilling of the clivus and atlas (Fig. 6.14) Step 8. Exposure of the tectorial membrane and dura (Fig. 6.14) Step 9. Dural opening (Fig. 6.16)

Surgical Tips The transoral approach is usually used to treat extradural lesions. Opening the dura risks spinal fluid leak and postoperative meningitis. This approach has been used to treat intradural lesions such as basilovertebral junction aneurysms, but in general, opening the dura is avoided.

Illustrated Steps with Commentary

Fig. 6.1 Preparation for a transoral approach in a

cadaver.

Because most cadaver preparations are rigid, the mandible is retracted laterally after an osteotomy has been performed and the tongue is removed. Obviously this is not done as part of a standard surgical approach. If the surgeon needs to extend the approach more superiorly, the soft palate can be split and the tongue and mandible can be split in the midline. Splitting the soft palate results in liquids refluxing into the nasal cavity. Before splitting the soft palate, the surgeon should assess the exposure afforded by retracting the soft palate.

84

I Anterior Skull Base

Fig. 6.2 Preparation for a transoral approach in a cadaver: skin removal. In the cadaver the skin and the soft tissue are removed from the mandible.

Fig. 6.3 Preparation for a transoral approach in a cadaver: mandibular osteotomy. In the cadaver an osteotomy of the mandible is performed bilaterally. This allows the front of the jaw to be displaced and the oral cavity is exposed.

Fig. 6.4 (Step 1) Preparation for a transoral approach in a cadaver: opening the mouth. The mandible is retracted from the maxilla.

6 Transoral Approach

Fig. 6.5 Preparation for a transoral approach in a cadaver: tongue removal. The tongue is removed to expose the oral pharynx.

HP SP Uv OPhx

Fig. 6.6 Setting of the mouth gag. In surgery a mouth gag is used to depress the tongue and hold the mouth open. Releasing the tongue depressor every 30 minutes will reduce the chance of tongue ischemia. (HP, hard palate; OPhx, oropharynx; SP, soft palate; Uv, uvula)

HP SP OPhx

Fig. 6.7 (Step 2) Elevation of the uvula toward the nasopharynx. The uvula is retracted upward. Further superior exposure can be achieved by splitting the soft palate in the midline. Soft palate flaps have been described that are hinged on the palatine blood vessels. (HP, hard palate; OPhx, oropharynx; SP, soft palate)

85

I Anterior Skull Base

Fig. 6.8 (Step 3) Mucosal incision of the posterior wall of the oropharynx. The mucosa covering the posterior wall of the oropharynx is incised.

SP

CM

LCp M

Fig. 6.9 Identification of superior pharyngeal constrictor muscles.

LClM

86

The superior pharyngeal constrictor muscle is exposed behind the mucosa. The longus capitis and the longus colli muscles are seen deep to the superior pharyngeal constrictor muscle. (LClM, longus colli muscle; LCpM, longus capitis muscle; SPCM, superior pharyngeal constrictor muscle)

LCpM

Fig. 6.10 (Step 4) Identification of the longus colli and longus capitis muscles. The longus capitis muscles lie lateral to the longus colli muscles. (LClM, longus colli muscle; LCpM, longus capitis muscle)

LClM

6 Transoral Approach

LCpM

LCpM

Fig. 6.11 (Step 5) Lateral retraction of the longus capitis muscle.

For teaching purposes the mucosa, constrictor muscles, longus muscles, and anterior longitudinal ligament were raised in layers in this dissection. In surgery all four layers are dissected laterally as a single unit to provide a strong well-vascularized flap of tissue. (LClM, longus colli muscle; LCpM, longus capitis muscle)

LClM

LClM

CL

C1 C2 Fig. 6.12 Removal of the anterior longitudinal ligament.

The anterior longitudinal ligament connects the body of the axis with the anterior arch of the atlas. (C1, C1 [atlas]; C2, C2 [axis]; CL, clivus)

CL

C1 Fig. 6.13 (Step 6) Exposure of the clivus, atlas,

C2

and axis.

The clivus, the anterior arch of the atlas, and the axis are exposed. (C1, C1 [atlas]; C2, C2 [axis]; CL, clivus; LClM, longus colli muscle)

LClM

LClM

87

88

I Anterior Skull Base

CL

TM Fig. 6.14 (Steps 7 and 8) Drilling of the clivus and atlas with exposure of the tectorial membrane.

The top of the odontoid is attached to the skull base by the paired alar ligaments and the apical ligament. The apical ligament makes removal of the tip of the odontoid difficult. These ligaments are best cut sharply. (C2, C2 [axis]; CL, clivus; TM, tectorial membrane)

C2

CL

TM

PD

Fig. 6.15 Exposure of the dura mater. The tectorial membrane, a cephalad extension of the posterior longitudinal ligament, is opened to reveal the dura. (C2, C2 [axis]; CL, clivus; PD, posterior fossa dura; TM, tectorial membrane)

C2 CL PD

VA

VA

Fig. 6.16 (Step 9) Dural opening. The two vertebral arteries are seen anterior to the medulla. (CL, clivus; PD, posterior fossa dura; VA, vertebral artery)

7 Orbital Approach Lesions behind the equator of the globe are best approached through a lateral orbit (modified Krönlein) approach or a transcranial approach. The lateral orbit approach provides adequate exposure for most lesions lateral to the optic nerve. Lateral lesions originating in the orbit apex can be difficult to remove using this approach. Lesions of the optic nerve, orbital apex, or medial orbit are best exposed through a transcranial approach. The contents within the orbit can be approached between the superior oblique and levator palpebrae muscles, between the levator and superior rectus muscles, or between the superior rectus and lateral rectus muscles depending on the location of the pathology. The transcranial approach can be extended into the subdural compartment for lesions such as optic gliomas.

7.1 Transcranial Orbital Approach Key Steps Position: Supine, head lateral Step 1. Semilunar skin incision (Fig. 7.1) Step 2. Scalp elevation in one layer with release of the supraorbital nerve (Fig. 7.2) Step 3. Frontal craniotomy (Fig. 7.4) Step 4. Removal of the supraorbital bar (Fig. 7.8) Step 5. Opening of the periorbita (Fig. 7.11) Step 6. Dissection in the orbital cavity through the roof of the orbit (Fig. 7.13)

Illustrated Steps with Commentary

Fig. 7.1 (Step 1) Positioning and scalp incision. The head is rotated approximately 15 degrees away from the side of the surgery with the patient placed in a supine position. A semilunar skin incision is made behind the hairline.

90

I Anterior Skull Base

TM SON

Fig. 7.2 (Step 2) Scalp and temporalis muscle elevation in one layer. The scalp and temporalis muscle are reflected in one layer. The zygomatic process of the frontal bone is completely exposed to identify the frontozygomatic suture. The supraorbital nerve should be carefully preserved. (SON, supraorbital nerve; TM, temporalis muscle)

TM SON

Fig. 7.3 “V” osteotomy of supraorbital foramen (see Figs. 4.6, 4.7, 4.8).

The supraorbital foramen is opened with a fine osteotome, sagittal saw, or small diamond burr. A “V” shaped osteotomy frees the nerve and accompanying artery. (SON, supraorbital nerve; TM, temporalis muscle)

SON

Fig. 7.4 (Step 3) Frontal craniotomy. A frontal craniotomy is performed. Although some surgeons remove the orbital rim along with the frontal craniotomy, we prefer to remove these two structures separately. (SON, supraorbital nerve)

7.1 Orbital Approach: Transcranial Orbital Approach

SON G

Fig. 7.5 Separation of periorbita from the orbital roof using a sharp edge raspatory. The periorbita is separated from the orbital roof with a sharp curved periosteal elevator. (G, gelatin sponge; SON, supraorbital nerve)

SON G

Fig. 7.6 Releasing the periorbita. The periorbita is peeled off the bony orbital wall with a curved raspatory that has a sharp edge. Absorbable gelatin sponge or bone wax is gradually inserted between the bony wall and the periorbita. The Gelfoam (Pfizer Inc., NY, NY) or bone wax acts as a spacer to protect the periorbita from the drill or osteotome. (G, gelatin sponge; SON, supraorbital nerve)

SON

Fig. 7.7 Dural elevation. The dura of the frontal base is peeled off the floor of the anterior fossa. The supraorbital bar is cut using a sagittal saw, fine drill, or osteotome. Injury of the periorbita should be avoided. (SON, supraorbital nerve)

91

92

I Anterior Skull Base

10mm

FS

Fig. 7.8 (Step 4) Releasing of supraorbital bar. The superior orbital wall is cut or fractured between the two previously made cuts, approximately 10 mm back from the orbital rim, using a fine osteotome, sagittal saw, or drill (FS, frontal sinus)

SON FS

Fig. 7.9 Removal of supraorbital bar. The supraorbital bar is removed protecting the periorbita. (FS, frontal sinus; SON, supraorbital nerve)

SON

Et

Fig. 7.10 Removal of the orbital roof. The supraorbital bone is removed using a sharp rongeur. Care is taken not to injure the periorbita or compress the optic nerve in the apex of the orbit. (Et, ethmoid sinus; SON, supraorbital nerve)

Orbit

7.1 Orbital Approach: Transcranial Orbital Approach

LG

SON

Fig. 7.11 (Step 5) Opening of periorbita. The periorbita is opened (it is removed in this dissection). (LG, lacrimal gland; SON, supraorbital nerve)

LG

STN

Or

Et

N

LPSM

SRM

SOM

SO

LRM

FN

Fig. 7.12 Removal of intraorbital fat.

IV

In the cadaver the intraorbital fat tissue is removed in order to show a surgical anatomy of this approach. During surgery the intraorbital fat is mobilized using blunt dissection. (Et, ethmoid sinus; FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LRM, lateral rectus muscle; Or, orbit; SOM, superior oblique muscle; SON, supraorbital nerve; SRM, superior rectus muscle; STN, supratrochlear nerve)

LG

STN NCN

Or SO N

MRM

LPSM SRM

Fig. 7.13 (Step 6) Anatomy of the superior orbital contents.

The supraorbital nerve, levator palpebrae superioris muscle, and superior rectus muscle are seen to occupy the midline in this transcranial approach. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; SOA, supraorbital artery; SOM, superior oblique muscle; SON, supraorbital nerve; SRM, superior rectus muscle; STN, supratrochlear nerve)

SOA

SO

ON

M FN

IV

LRM

93

94

I Anterior Skull Base

LG Or

STN

SO

N

SOA

LPSM

N

LRM

SRM

M

ON FN

LN

VI

SO V

The optic nerve enters the orbit through the annulus of Zinn and lies below the superior rectus muscle. The ophthalmic artery crosses over the optic nerve from lateral to medial. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; SOA, supraorbital artery; SOM, superior oblique muscle; SON, supraorbital nerve; SOV, superior ophthalmic vein; SRM, superior rectus muscle; STN, supratrochlear nerve; VI, abducens nerve)

SO

levator palpebrae superioris muscle.

NC

Fig. 7.14 Exposure of the optic nerve deep to the

IV

Fig. 7.15 Medial approach to the orbit. LG STN

Or

SOA

NC N

SO

MRM

LPSM

N

LRM PEtA

SO

III(MRM)

M

The levator palpebrae superioris and superior rectus muscles are shifted laterally away from the superior oblique muscle to expose the optic nerve and medial structures. The nasociliary nerve and the distal ophthalmic artery are seen coursing over the optic nerve toward the medial wall of the orbit. At the apex the optic nerve is crossed by the trochlear nerve. The ophthalmic artery is seen passing over the optic nerve. The branch of the nasociliary nerve providing sensation to the ocular globe leaves the nasociliary nerve prior to the nerve crossing the optic nerve. The nasociliary nerve crosses over the optic nerve and branches into the infratrochlear nerve, and ethmoidal nerves on the medial side of the orbit. (CTR, common tendinous ring; FN, frontal nerve; III(MRM), oculomotor nerve branch to the medial rectus muscle; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; PEtA, posterior ethmoidal artery; SOA, supraorbital artery; SOM, superior oblique muscle; SON, supraorbital nerve; STN, supratrochlear nerve)

ON

FN IV

CTR

LG Or NC N

MRM

PEtA

M

The optic nerve is exposed between the levator palpebrae superioris muscle and superior rectus muscle. The frontal nerve can be displaced laterally or medially. Care should be taken not to injure the branch of the oculomotor nerve to the levator muscle. (CTR, common tendinous ring; FN, frontal nerve; III(MRM), oculomotor nerve branch to the medial rectus muscle; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle; SOV, superior ophthalmic vein; SRM, superior rectus muscle)

SRM

SO

Fig. 7.16 Midline approach.

LPSM

ON

III(MRM)

SO F IV N

CTR

V

LRM

7.1 Orbital Approach: Transcranial Orbital Approach

LG Or NCN

Fig. 7.17 Lateral approach.

LRM

SRM

SO

PEtA

M

The levator palpebrae superioris and superior rectus muscles are shifted medially away from the lateral rectus muscle to expose the optic nerve and ophthalmic artery, nasociliary nerve, and other lateral structures. This approach shifts the frontal and trochlear nerve medially out of the surgical exposure. (CTR, common tendinous ring; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; NCN, nasociliary nerve; OA, ophthalmic artery; ON, optic nerve; Or, orbit; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle; SOV, superior ophthalmic vein; SRM, superior rectus muscle; VI, abducens nerve)

LPSM

ON

LN

VI

LA

OA IV

SO

FN

V

CTR

LRM ON VI

SOM

LN LA

FN

IV

CTR

Fig. 7.18 Exposure of the common tendinous ring (common annular tendon or annulus of Zinn).

The origin of the medial, lateral, superior, and inferior rectus muscles is the common tendinous ring. (CTR, common tendinous ring; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LN, lacrimal nerve; LRM, lateral rectus muscle; ON, optic nerve; SOM, superior oblique muscle; VI, abducens nerve)

LG LRM

SO

VI

M

LN FN

LA

Fig. 7.19 Trochlear nerve. The trochlear nerve innervates to the superior oblique muscle. This nerve does not pass through the annulus of Zinn, but passes above the muscular cone. (CTR, common tendinous ring; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LRM, lateral rectus muscle; SOM, superior oblique muscle; VI, abducens nerve)

IV CTR

95

96

I Anterior Skull Base

LG ST N

LRM

SO M

VI

nerves.

PEtA

FN

Fig. 7.20 The trochlear and posterior ethmoidal The trochlear and posterior ethmoidal nerves are seen in this view. The posterior ethmoidal nerve is a branch of the nasociliary nerve. The nasociliary nerve is a branch of V1, which enters the orbit through the annulus of Zinn between the two heads of the lateral rectus muscle. The nasociliary nerve passes over the optic nerve, giving off the long cilliary nerves, the infratrochlear nerve, the anterior and posterior ethmoidal nerves, and the external nasal nerve, and innervates the lateral wall of the nasal cavity. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LRM, lateral rectus muscle; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle; STN, supratrochlear nerve; VI, abducens nerve)

IV

SOM

Et

FN

PEtA

IV Fig. 7.21 Posterior ethmoidal nerve and artery. The posterior ethmoidal nerve and artery that pass into the posterior ethmoidal foramen are well seen. The posterior ethmoidal artery is a branch of the ophthalmic artery. (Et, ethmoid sinus; FN, frontal nerve; IV, trochlear nerve; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle)

LG

Fig. 7.22 Exposure of the superior ophthalmic

LRM

MRM

vein and the nasociliary nerve.

SO V NCN

ON

FN

EtA M

SO

The superior ophthalmic vein (not colored) is seen below the superior rectus muscle. The nasociliary nerve that proximally gives origin to the long ciliary nerves and distally divides into the infratrochlear, the anterior ethmoidal, and the posterior ethmoidal nerves. It is exposed medial to the superior ophthalmic vein. (EtA, ethmoidal artery; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; SOM, superior oblique muscle; SOV, superior ophthalmic vein; SRM, superior rectus muscle)

LN

SRM LPSM

IV

LA

7.1 Orbital Approach: Transcranial Orbital Approach

LG

MRM EtA

SO

III(

SRM M

M

RM

)

ON

Fig. 7.23 Exposure of the medial rectus muscle.

LPSM

The medial rectus muscle and the branch of the inferior division of the oculomotor nerve that innervates the muscle are well seen. (EtA, ethmoidal artery; III(MRM), oculomotor nerve branch to the medial rectus muscle; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; MRM, medial rectus muscle; ON, optic nerve; SOM, superior oblique muscle; SRM, superior rectus muscle)

IV

LG

Tr MRM

LPSM

SO

superior oblique muscle.

M

The superior oblique muscle originates from the lesser wing of the sphenoid bone. Its tendon bends at right angles as it passes through a pulley that originates from the trochlear fovea of the frontal bone. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; MRM, medial rectus muscle; SOM, superior oblique muscle; SRM, superior rectus muscle; Tr, trochlea of the superior oblique muscle)

IV

LG

LRM STN

SON

Fig. 7.25 Identification of the lateral rectus

muscle.

VI

SOV LPSM

FN

The lateral rectus muscle and the abducens nerve are seen deep to the lacrimal gland. The lateral rectus muscle originates from the fibrous ring as two heads. The nasociliary nerve, abducens nerve, and oculomotor nerves pass through the annulus of Zinn medial to the interval between the two heads of the lateral rectus muscle. (FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; SON, supraorbital nerve; SOV, superior ophthalmic vein; SRM, superior rectus muscle; STN, supratrochlear nerve; VI, abducens nerve)

IV

SRM

SRM FN

Fig. 7.24 Identification of the trochlea of the

LN LA

97

98

I Anterior Skull Base

LG Or

SO

STN

SO

N

LPSM

LRM

SRM

M

ON OA

FN

Fig. 7.26 Optic nerve. The optic nerve is exposed through the lateral approach. The nasociliary nerve and branches of the ophthalmic artery cross the dorsal aspect of the nerve from lateral to medial. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; OA, ophthalmic artery; ON, optic nerve; Or, orbit; SOM, superior oblique muscle; SON, supraorbital nerve; SRM, superior rectus muscle; STN, supratrochlear nerve)

IV

IV

LG Or ST N

LPSM

N

IRM

NCN

III(IOM)

LRM

III(IRM)

SO M

VI

LN LA

OA SO V

FN

The inferior rectus muscle and the inferior oblique muscle are innervated by the inferior division of the oculomotor nerve. The branch to the inferior oblique muscle also provides parasympathetic innervation of the ciliary ganglion. (CTR, common tendinous ring; FN, frontal nerve; III(IOM), oculomotor nerve branch to the inferior oblique muscle; III(IRM), oculomotor nerve branch to the inferior rectus muscle; IRM, inferior rectus muscle; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; NCN, nasociliary nerve; OA, ophthalmic artery; Or, orbit; SOM, superior oblique muscle; SON, supraorbital nerve; SOV, superior ophthalmic vein; STN, supratrochlear nerve; VI, abducens nerve)

SO

Fig. 7.27 Identification of the inferior rectus muscle and nerve for inferior oblique muscle.

IV CTR

7.2 Orbital Approach: Lateral Orbital Approach

7.2 Lateral Orbital Approach Key Steps Position: Supine or lateral position Step 1. Slightly curved skin incision at the lateral canthus (Fig. 7.28) Step 2. Exposure of the lateral orbital bar (frontal process of the zygoma) (Fig. 7.29) Step 3. Removal of the lateral orbital bar and opening of the lateral wall of the orbit (Fig. 7.31) Step 4. Opening of the periorbita (Fig. 7.35) Step 5. Dissection in the orbital cavity from the lateral side (Fig. 7.38)

Illustrated Steps with Commentary

Zy

Fig. 7.28 (Step 1) Skin incision. A small semilunar skin incision is made behind the lateral canthus. The inferior edge of the incision should be straight to avoid facial nerve injury. There is a risk of facial nerve injury if the incision line is extended posteriorly along the zygomatic arch. (Zy, zygoma)

Zy

LOR

Fig. 7.29 (Step 2) Exposure of the frontal process of the zygoma.

The skin flap is raised anteriorly exposing the frontal processes of the zygoma. (LOR, lateral orbital rim; Zy, zygoma)

99

100

I Anterior Skull Base

LOB

FZS

Fig. 7.30 Exposure of the lateral orbital wall. The temporalis muscle is detached and posteriorly retracted to expose the lateral wall of the orbit and the posterior face of the zygomatic process. (FZS, frontozygomatic suture; LOB, lateral orbital bar; MT, marginal tubercle)

Fig. 7.31 (Step 3) Removal of the lateral orbital bar.

The lateral orbital bar and the frontal process of the zygomatic bone are removed.

Fig. 7.32 Removal of the lateral orbital bar. The superior and inferior edges of the lateral orbital bar are cut with a fine osteotome or sagittal saw.

MT

7.2 Orbital Approach: Lateral Orbital Approach

PO

Fig. 7.33 Removal of the lateral orbital wall. The lateral wall of the orbit is removed with a drill or rongeur to expose the periorbita. (PO, periorbita)

TD PO

CTR

FD Fig. 7.34 Common tendinous ring (annulus of Zinn).

The annulus of Zinn, frontal, and temporal dura are exposed. (CTR, common tendinous ring; FD, frontal dura; PO, periorbita; TD, temporal dura)

LRM F

Fig. 7.35 (Step 4) Opening of the periorbita. The periorbita is opened. The lateral rectus muscle and lacrimal gland are seen along with the intraorbital fat tissue. (F, fat tissue in the orbit; LRM, lateral rectus muscle)

101

102

I Anterior Skull Base

LRM

LG Fig. 7.36 Lacrimal gland. The lacrimal gland is seen. The intraorbital fat has been removed to better demonstrate the surgical anatomy. During surgery the fat is not removed but retracted out of the way. (LG, lacrimal gland; LRM, lateral rectus muscle)

IRM

III(

IO

M

)

LRM OA SOV

SRM

Fig. 7.37 Lateral rectus muscle. The lateral rectus muscle is seen in the center of the surgical field. (III(IOM), oculomotor nerve branch to the inferior oblique muscle; IRM, inferior rectus muscle; LRM, lateral rectus muscle; OA, ophthalmic artery; SOV, superior ophthalmic vein; SRM, superior rectus muscle)

IRM

III(

IO

M

)

LRM ON

Fig. 7.38 (Step 5) Approach above the lateral rectus muscle.

The lateral rectus muscle is retracted inferiorly. The frontal nerve, the superior rectus muscle, the optic nerve, and the branches of the ophthalmic artery are seen. (FN, frontal nerve; III(IOM), oculomotor nerve branch to the inferior oblique muscle; IRM, inferior rectus muscle; LRM, lateral rectus muscle; OA, ophthalmic artery; ON, optic nerve; SRM, superior rectus muscle)

SRM

FN

OA

7.2 Orbital Approach: Lateral Orbital Approach

IRM

III(

IO

M

)

OA ON LRM

Fig. 7.39 Approach below the lateral rectus muscle.

The lateral rectus muscle retracted toward the roof of the orbit. This exposes the inferior rectus muscle, the optic nerve, and branches of the inferior division of the oculomotor nerve. (III(IOM), oculomotor nerve branch to the inferior oblique muscle; IRM, inferior rectus muscle; LRM, lateral rectus muscle; OA, ophthalmic artery; ON, optic nerve;, SRM, superior rectus muscle)

SRM

IRM

III(

IO

M

)

IOV

MRM LRM

Fig. 7.40 Inferior ophthalmic vein. The inferior ophthalmic vein (not injected in this specimen) is seen crossing over the inferior rectus muscle and the medial rectus muscle. (III(IOM), oculomotor nerve branch to the inferior oblique muscle; IOV, inferior ophthalmic vein; IRM, inferior rectus muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; SRM, superior rectus muscle)

SRM

IRM III(IRM)

III(IOM)

LRM Fig. 7.41 Inferior rectus muscle. The inferior rectus muscle and the nerve that innervates that muscle are well seen. The branch of the inferior division of the oculomotor nerve that innervates the inferior oblique muscle is retracted by the dissector. (III(IOM), oculomotor nerve branch to the inferior oblique muscle; III(IRM), oculomotor nerve branch to the inferior rectus muscle; IRM, inferior rectus muscle; LRM, lateral rectus muscle; SRM, superior rectus muscle)

SRM

103

104

I Anterior Skull Base

IOM IRM

Or

LRM LG

LN

Fig. 7.42 Inferior oblique muscle. The inferior oblique muscle and its attachment to the ocular globe appear in the middle of the field. (IOM, inferior oblique muscle; IRM, inferior rectus muscle; LG, lacrimal gland; LN, lacrimal nerve; LRM, lateral rectus muscle; Or, orbit; SRM, superior rectus muscle)

SRM

LRM

VI ON NCN

Fig. 7.43 The abducens nerve. The abducens nerve is seen entering the lateral rectus muscle on the medial side of that muscle. (LRM, lateral rectus muscle; NCN, nasociliary nerve; ON, optic nerve; SRM, superior rectus muscle; VI, abducens nerve)

SRM

IRM

III(

IO

M

)

LRM ON NCN

Fig. 7.44 Trochlear nerve. The trochlear nerve passes outside the annulus of Zinn to innervate the superior oblique muscle. (III(IOM), oculomotor nerve branch to the inferior oblique muscle; IRM, inferior rectus muscle; IV, trochlear nerve; LRM, lateral rectus muscle; NCN, nasociliary nerve; OA, ophthalmic artery; ON, optic nerve; SOM, superior oblique muscle; SRM, superior rectus muscle)

SOM

SRM

IV

OA

7.2 Orbital Approach: Lateral Orbital Approach

LRM VI

ON

OA SOV

Fig. 7.45 Superior oblique muscle, superior ophthalmic vein, and optic nerve.

The superior ophthalmic vein (not injected) leaves the muscular cone by passing between the lateral and the superior rectus muscles. (LRM, lateral rectus muscle; OA, ophthalmic artery; ON, optic nerve; SOV, superior ophthalmic vein; SRM, superior rectus muscle; VI, abducens nerve)

SRM

LRM ON

VI OA

NCN

Fig. 7.46 Nasociliary nerve. The nasociliary nerve is seen passing over the optic nerve along with the distal portion of the ophthalmic artery. The nasociliary nerve, ophthalmic artery, and superior ophthalmic vein all pass over the optic nerve from anterior medial to posterior lateral. (LRM, lateral rectus muscle; NCN, nasociliary nerve; OA, ophthalmic artery; ON, optic nerve; SOV, superior ophthalmic vein; SRM, superior rectus muscle; VI, abducens nerve)

SOV SRM

105

II

Anterolateral Skull Base

8 Anatomy for Anterolateral Skull Base Surgery

In this chapter, the anatomy of the anterolateral skull base, including the lateral wall of the cavernous sinus, is explored. An understanding of this anatomy is essential for planning surgeries in and around the cavernous sinus. In this chapter, the left cavernous sinus is dissected.

Key Steps Step 1. Separation of dura propria from lateral wall of cavernous sinus (Fig. 8.2) Step 2. Separation of dura propria from the lateral loop (Fig. 8.6) Step 3. Opening of oculomotor foramen (Fig. 8.10) Step 4. Exposure of the gasserian ganglion (Fig. 8.15) Step 5. Opening of Parkinson’s triangle (Fig. 8.17) Step 6. Identification of abducens nerve (Fig. 8.19)

Illustrated Steps with Commentary V2 V1 GG

IV III

Fig. 8.1 Superolateral wall of the cavernous sinus. This exposure of the left cavernous sinus begins with an extradural dissection of the dura from the superior orbital fissure and the floor of the middle fossa. The anterior clinoid process has already been removed (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion). (COM, carotico-oculomotor membrane; GG, gasserian ganglion; ON, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

C4/5

COM

ON

110

II Anterolateral Skull Base

V1 IV

II

COM

III Fig. 8.2 (Step 1) Carotico-oculomotor membrane. The dura propria is separated from the lateral wall of the cavernous sinus. The oculomotor nerve, trochlear nerve, and V1 are encased in the lateral wall of the cavernous sinus. The C3 portion of the internal carotid artery is covered by the carotico-oculomotor membrane. (COM, carotico-oculomotor membrane; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve])

MSR Fig. 8.3 Bony protrusion over lateral loop (midsubtemporal tubercle).

AE

GSP

N

The dura is dissected from the anterior tip of the bony middle fossa. A bony protrusion of the middle cranial fossa wall is usually seen lateral to the lateral loop. This mid-subtemporal tubercle is a useful landmark for finding the lateral loop at the time of surgery. The lateral loop is the web between the V3 and the V2 fibers. (AE, arcuate eminence; GSPN, greater superior petrosal nerve; LL, lateral loop; MSR, mid-subtemporal ridge; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

MMA

V2

V1

MSR LL

Fig. 8.4 Bony protrusion over lateral loop. The bony protrusion, the mid-subtemporal tubercle, is seen anterior and between the foramen rotundum and foramen ovale. The other landmark useful for finding the foramen ovale is the foramen spinosum. Practically, the middle meningeal artery can be followed to the foramen spinosum, and the foramen spinosum guides the surgeon to the foramen ovale. (GSPN, greater superior petrosal nerve; LL, lateral loop; MMA, middle meningeal artery; MSR, mid-subtemporal ridge; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

LL

GSPN

V3

V2

V1

8 Anatomy for Anterolateral Skull Base Surgery

MMA LL V3

SS

V2

Fig. 8.5 Skeletonized sphenoid sinus. The sphenoid sinus can be entered medial to the second division of the trigeminal nerve (V2). The surgeon must be careful when drilling the bone from around V2 as an opening in the sphenoid sinus can result in a troublesome CSF leak. A light has been placed in the sphenoid sinus to illuminate that sinus in this photo. (LL, lateral loop; MMA, middle meningeal artery; SS, sphenoid sinus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V1

MSR

Fig. 8.6 (Step 2) Lateral loop medial to bony

protrusion.

V3

MMA

V2

V3

Fig. 8.7 The dura propria is separated from V2 and

V3.

The initial separation of the dura propria from the trigeminal nerve is done with a sharp knife. The dissection can usually be continued with a blunt dissector. Usually the dura attachment on the lateral side of V3 will need to be cut with a knife. (C4, C4 portion of the internal carotid artery; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2

LL

As the dura propria is separated from V2, V3, and the lateral loop of the trigeminal nerve. Venous bleeding will invariably be encountered. The bleeding channels are a part of the rich anastamosis between the pterygoid plexus and the cavernous veins. Cauterizing these channels may result in facial paresthesias. It is best to pack these channels with oxidized cellulose, apply gentle pressure, and wait. Recalcitrant bleeding can be stopped with oxidized cellulose and fibrin glue. (LL, lateral loop; MSR, mid-subtemporal ridge; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V1

GG IV C4

III

II

111

112

II Anterolateral Skull Base

MMA V3

Fig. 8.8 The dura propria is separated from

V2

GSPN

V1

the branches of the trigeminal nerve and the trigeminal ganglion.

GG

A blue latex injected into the veins and cavernous sinus has been removed to better demonstrate the anatomy. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superior petrosal nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

C4

C5

IV III

PSL

II

MMA V3

Fig. 8.9 Relationship with posterior clinoid

V2

GSPN

process and intradural oculomotor nerve.

The posterior loop of the carotid artery, the posterior clinoid, and the intradural oculomotor nerve are all seen rostral to V1. The oculomotor nerve will enter its intradural tunnel by piercing a triangular region of dura that is anchored by the anterior clinoid, posterior clinoid, and petrous bone tip. (C2, C2 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superior petrosal nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

GG

V1 C4 IV

C5

VI

PSL

III

PCP

C4/5 IV

Fig. 8.10 (Step 3) Opening of the oculomotor foramen.

The oculomotor foramen leads into a canal. The oculomotor nerve runs through this canal, which can be opened to free the nerve. Freeing the oculomotor nerve is a useful maneuver when approaching basilar tip aneurysms, via either a subtemporal or a pterional route. The length of the canal that can be opened is limited by the crossing of the trochlear nerve over the oculomotor nerve. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve)

III

III C2

II

8 Anatomy for Anterolateral Skull Base Surgery

IV C4/5

Fig. 8.11 Division of the oculomotor nerve in the oculomotor canal.

The oculomotor nerve has already divided into its superior and inferior portions in the oculomotor canal. The two divisions are separated by a thin membranous structure. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve)

III

V1

C4/5

IV

Fig. 8.12 Skeletonization of the posterior genu of the internal carotid artery.

The posterior genu of the internal carotid artery connecting the C5 and C4 portions of the carotid artery can be seen between the trochlear nerve and V1 through the outer membrane of the cavernous sinus. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve])

III

SOV

V1 Fig. 8.13 Superior orbital fissure. The oculomotor nerve, the trochlear nerve, V1, and the abducens nerve pass through the superior orbital fissure. The oculomotor nerve runs medial to the tip of the anterior clinoid process. The trochlear nerve runs lateral to the oculomotor nerve. It passes over the top of CN III as it enters the orbit. The abducens nerve and V1 can be seen passing over the oculomotor nerve. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; III, oculomotor nerve; IV, trochlear nerve; SOV, superior ophthalmic vein ; V1, ophthalmic nerve [first division of the trigeminal nerve])

IV C4/5

III

113

114

II Anterolateral Skull Base

MMA

V2

V3

GG

V1

Fig. 8.14 Complete cavernous sinus exposure. The oculomotor, the trochlear, the trigeminal nerve and its divisions, and the posterior bend of the internal carotid artery are seen through the true cavernous membrane that covers the cavernous sinus. (C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

C4/5 IV

III

V2 V1

GG

Fig. 8.15 (Step 4) Exposure of the gasserian ganglion.

The gasserian ganglion lies in the dural pocket commonly called Meckel’s cave. Meckel’s cave is filled with cerebrospinal fluid. The gasserian ganglion lies on the trigeminal impression of the petrous apex. (GG, gasserian ganglion; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

V2

V3

V1

Fig. 8.16 Exposure of nerves lying in the lateral wall of the cavernous sinus.

After removal of the dura propria, all nerves lying on the lateral wall of the cavernous sinus and the internal carotid artery can be seen. (C2, C2 portion of the internal carotid artery), (C4, C4 portion of the internal carotid artery), (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

C4

GG

C5

IV

III

C2

II

8 Anatomy for Anterolateral Skull Base Surgery

V3 V2

Fig. 8.17 (Step 5) Opening of Parkinson’s triangle.

The meningohypophyseal trunk, the abducens nerve, and Grüber’s ligament (petrosphenoidal ligament) can be seen through Parkinson’s triangle. This exposure can also be achieved by working between the trochlear and the oculomotor nerve and the paramedian triangle. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

V1

GG C5

VI PSL

C4 IV III

PCL

Fig. 8.18 Meningohypophyseal trunk. Branching of the meningohypophyseal trunk is visible. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; III, oculomotor nerve; IPS, inferior petrosal sinus; IV, trochlear nerve; MHT, meningohypophyseal trunk; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; VI, abducens nerve)

GG V1 PA VI

Fig. 8.19 (Step 6) Abducens nerve passing under the petrosphenoidal (Grüber’s) ligament.

The abducens nerve passes under the petrosphenoidal (Grüber’s) ligament. This marks the exit of the abducens nerve from the intradural sleeve (Dorello’s canal) through which the nerve passes. The nerve is covered with a venous plexus as it travels through this canal. (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; IPS, inferior petrosal sinus; PA, petrosal apex; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; VI, abducens nerve)

IPS

PSL PCL

C5

115

116

II Anterolateral Skull Base

GG

V1 PA

VI

C5

IPS

PSL

Fig. 8.20 Identifying the petroclinoidal fold. The petroclinoidal fold passes from the petrous tip to the posterior clinoid. The oculomotor nerve passes over the fold of the dura to enter the oculomotor canal. (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; IPS, inferior petrosal sinus; PA, petrosal apex; PCL, petroclival ligament; PSL, petrosphenoidal ligament; V1, ophthalmic nerve [first division of the trigeminal nerve]; VI, abducens nerve)

PCL

V2 V1

C4 Fig. 8.21 C4 portion of the internal carotid artery. The C4 carotid artery is seen between the trochlear nerve and V1. (C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

IV

C5

III

MMA

V3

V2

Fig. 8.22 Complete exposure of the cavernous sinus from a lateral direction.

Exposure of the cranial nerves in their respective sheaths is technically not difficult. Bleeding from the cavernous sinus or the venous confluence at the petrous tip can be controlled by packing the venous channels with small pieces of oxidized cellulose, and applying gentle pressure and patience. (C2, C2 portion of the internal carotid artery; C4/5, posterior genu of the internal carotid artery connecting C4 and C5 portion; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PCP, posterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V1

GG C4/5

IV

III PCP

C2

II

8 Anatomy for Anterolateral Skull Base Surgery

MMA

V3 V2

Fig. 8.23 Removal of the lateral wall of the

GG

cavernous sinus.

V1

The blue silicone fills the rich venous plexus that surrounds the carotid artery, communicates with the pterygoid plexus over the trigeminal nerve, and passes posterior to the dorsum sellae and the clivus. (GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

MMA

V3

Fig. 8.24 View after removal of the blue silicone

V2

GG

(venous space).

A relationship of the nerves and the arteries is demonstrated. At the time of surgery dissection through the venous plexus is not insurmountable. Packing the bleeding points with small pieces of oxidized cellulose and suctioning through a cotton sponge will usually control the venous hemorrhage. (C2, C2 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DR, distal dural ring; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

III

IV

SPS

C5 IV

V1 III DR

C2

II

III

SCA

MMA

V3 GG Fig. 8.25 Abducens nerve. The abducens nerve is well seen medial to the first division of the trigeminal nerve (V1) through Parkinson’s triangle (lateral triangle). (BA, basilar artery; C2, C2 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; DR, distal dural ring; GG, gasserian ganglion; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus; V1, ophthalmic nerve [first division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

SPS

VI C5 PSL

V1 IV

III C2

SCA

III BA

DR

II

117

118

II Anterolateral Skull Base

C6

Fig. 8.26 View after the removal of the trigeminal nerve.

Removal of the trigeminal nerve demonstrates not only the abducens nerve but also the C5 portion of the internal carotid artery. This segment lies under the junction of V2, V3, and the gasserian ganglia. (BA, basilar artery; C2, C2 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; COM, carotico-oculomotor membrane; DR, distal dural ring; III, oculomotor nerve; IV, trochlear nerve; PA, petrosal apex; PCA, posterior cerebral artery; PSL, petrosphenoidal ligament; PV, petrosal vein; SCA, superior cerebellar artery; SPS, superior petrosal sinus; VI, abducens nerve)

VI

PA

SPS

C5

PSL

DR

PV

COM

C2

III

SCA PCA

BA

SpP

PA

VI C5

PSL

Fig. 8.27 Dorello’s canal. The abducens nerve travels through Dorello’s canal, which is formed by the pyramidal apex and the petrosphenoidal ligant (Grüber’s ligament) and sphenoid bone. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; PA, petrosal apex; PCA, posterior cerebral artery; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SpP, sympathetic plexus; VI, abducens nerve)

IV III

C4

IV III C3 SCA

III

C2

PCA

II

MMA

SpP

PA

Fig. 8.28 Internal carotid artery. The wall of the carotid artery is removed, leaving behind the red latex that filled the carotid lumen. (BA, basilar artery; C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PA, petrosal apex; PCA, posterior cerebral artery; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SpP, sympathetic plexus; SPS, superior petrosal sinus; VI, abducens nerve)

VI C4

C5

SPS

PSL

IV

C3

III C2

III

IV SCA PCA

BA

II

8 Anatomy for Anterolateral Skull Base Surgery

PLL C6

SpP

Fig. 8.29 Anatomy of the paraclinoid and

cavernous portion of the internal carotid artery.

VI

PA

The carotid artery is seen traveling from the subarachnoid space into the clinoid space between the inner and outer carotid rings. Proximal to the carotid space, the carotid artery enters the cavernous sinus. It exits from the cavernous sinus at the level of the petrolingual ligament, where it is frequently ensheathed in veins well into the petrous canal. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; PA, petrosal apex; PLL, petrolingual ligament; PSL, petrosphenoidal ligament; SpP, sympathetic plexus; VI, abducens nerve)

C5

C4 IV

III

PSL

C3 C2

III

MMA

GSPN

C6 PLL

Fig. 8.30 Exposure of the horizontal C6 portion of the internal carotid artery.

The C6 portion of the carotid artery is found by drilling the petrous tip under the greater superficial petrosal nerve. Lateral to the carotid canal lies the eustachian tube and the tensor tympani muscle. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; C4, C4 portion of the internal carotid artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; GSPN, greater superior petrosal nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; MMA, middle meningeal artery; PLL, petrolingual ligament; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus; TFR, trigeminal fibrous ring; TI, trigeminal impression; VI, abducens nerve)

VI

TI

SPS

C5

TFR

PSL

IV

C4 III

C3 C2

II

III

SCA

MMA

PLL

PA

Fig. 8.31 Exposure after removal of the internal carotid artery and the nerves.

The anatomical relationship between the underlying bones and ligaments is demonstrated. (II, optic nerve; III, oculomotor nerve; MMA, middle meningeal artery; PA, petrosal apex; PCL, petroclival ligament; PCP, posterior clinoid process; PLL, petrolingual ligament; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus)

SPS

PSL

PCL

II PCP SCA

III

119

120

II Anterolateral Skull Base

MMA

PLL

Fig. 8.32 The petrosphenoidal ligament and the

PA

SPS

IPS

petroclival dural fold.

The petrous ridge is exposed after the tentorium is removed. (BA, basilar artery; II, optic nerve; III, oculomotor nerve; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PA, petrosal apex; PCA, posterior cerebral artery; PCL, petroclival ligament; PCP, posterior clinoid process; PLL, petrolingual ligament; PICA, posterior inferior cerebellar artery; Po, pons; PSL, petrosphenoidal ligament; SCA, superior cerebellar artery; SPS, superior petrosal sinus)

PSL

PIC

Po

A

BA

PCL

II PCP SCA III

PCA

PA IPS

PSL

PICA

BA

L

An anatomical relationship of the petrosphenoidal ligament, petroclinoidal fold and the inferior petrosal sinus is demonstrated. (BA, basilar artery; IPS, inferior petrosal sinus; PA, petrosal apex; PCL, petroclival ligament; PCP, posterior clinoid process; PICA, posterior inferior cerebellar artery; PSL, petrosphenoidal ligament)

PC

Fig. 8.33 Magnified view of Fig. 8.32.

PCP

PA

Fig. 8.34 View after the removal of the dura of the middle cranial base and the clivus.

The boney anatomy underlying the structures of the medial middle fossa is seen. (BA, basilar artery; III, oculomotor nerve; PA, petrosal apex; PCA, posterior cerebral artery; PCP, posterior clinoid process; SCA, superior cerebellar artery)

BA SCA PCA III

PCP

8 Anatomy for Anterolateral Skull Base Surgery

Fig. 8.35 Cavernous sinus triangles (see Figs. 8.9 and 8.36).

5 AE

11

Co 6

10

8

IAC

9

4

Fig. 8.36 Cavernous sinus triangles (1, Anteromedial triangle [Dolenc]; 2, Medial triangle [Dolenc, Hakuba]; 3, Superior triangle [Fukushima]; 4, Lateral triangle [Parkinson]; 5, Posterolateral triangle [Glasscock, Paullus]; 6, Posteromedial triangle [Kanzaki, Kawase]; 7, Posteroinferior triangle [Fukushima]; 8, Premeatal triangle [Day, Fukushima]; 9, Postmeatal triangle [Day, Fukushima]; 10, Anterolateral triangle [Mullan]; 11, Far lateral triangle [Lateral Loop] [Dolenc]; AE, arcuate eminence; Co, cochlea; IAC, internal auditory canal)

3

7 2

1

121

9 Frontotemporal Orbitozygomatic Transcavernous Approach

The transcavernous approach widens the exposure afforded by a standard pterional craniotomy. This procedure is not only useful in approaching lesions within the cavernous sinus, but is useful in approaching the interpeduncular and the prepontine cisterns.

Key Steps Position: Supine with head turned 45 degrees away from the side of the surgery Step 1. Skin incision, question mark shape (Fig. 9.1) Step 2. Scalp elevation (one, one and a half, or two layers) (Fig. 9.3) Step 3. Frontoorbital detatchment (Fig. 9.9) Step 4. Frontotemporal craniotomy (Fig. 9.13) Step 5. Orbitozygomatic osteotomy (Fig. 9.17) Step 6. Anterior clinoidectomy A. Exposure of the anterior clinoid process (Fig. 9.35) B. Coring of the anterior clinoid process and removal of lateral half of the process (Figs. 9.36 and 9.37) C. Removal of medial half of the clinoid process and partial removal of the optic strut (Figs. 9.39 and 9.40) D. Removal of the tip of the clinoid process (Fig. 9.42) Step 7. Exposure of cavernous sinus (Fig. 9.46) Step 8. Intradural procedure (Fig. 9.48)

Variations of Orbitozygomatic Craniotomy 1. Limited supraorbital bar osteotomy 2. Extended orbitozygomatic osteotomy 3. Transzygomatic osteotomy

Illustrated Steps with Commentary

A B Fig. 9.1 (Step 1) Skin incision. (A, routine incision for a pterional approach; B, incision for a large frontotemporal exposure; C, extended incision for frontotemporal, orbitobasal, and middle fossa exposure)

C

9 Frontotemporal Orbitozygomatic Transcavernous Approach

DTF LAT TPM

Fig. 9.2 Layers to be elevated. The surgeon cuts through the subcutaneous fat and the temporoparietal fascia before reaching the muscle fibers of the temporalis muscle. (DTF, deep temporal fascia; LAT, loose areolar tissue; TPM, temporoparietal muscle)

Fig. 9.3 (Step 2) One layer scalp and temporalis muscle elevation. The zygomatic arch only should be removed when the surgeon will be looking under the temporal lobe. Removing the orbital rim facilitates the surgeon looking up under the frontal lobe. When an orbital, but not orbitozygomatic, osteotomy is planned, the muscle does not need to be separated from the scalp. Care is taken to separate the origin of the temporalis muscle from the frontal zygomatic process and adjacent greater wing of the sphenoid.

IFF dDTF Fig. 9.4 One and a half layer scalp elevation. The skin, galea, periosteum, temporoparietal fascia, and superficial layer of the deep temporal fascia are elevated together when an orbitozygomatic osteotomy is planned. The temporalis muscle and true temporal fascia (deep layer of the deep temporal fascia) is left in place. The deep and superficial layers of the deep temporal fascia are separated by the deep temporal fat pad. The superficial layer is contiguous with the periosteum on the lateral surface of the zygoma. (dDTF, deep layer of the deep temporal fascia; IFF, interfascial fat pad; sDTF, superficial layer of the deep temporal fascia)

sDTF

123

124

II Anterolateral Skull Base

dDTF

Fig. 9.5 One and a half layer scalp elevation (orbitozygomatic exposure).

sDTF

The superficial layer of the temporal fascia and the pericranium are raised along with the skin flap to expose the supraorbital bar and the contiguous zygomatic arch. The frontalis branch of the facial nerve is thus protected. The muscle and fascia are elevated as a second layer. This procedure is indicated for an extended orbitozygomatic craniotomy. Care is taken not to injure the supraorbital nerve. (dDTF, deep layer of the deep temporal fascia; sDTF, superficial layer of the deep temporal fascia)

G FM

Fig. 9.6 Two layer scalp elevation. This two layer method is used when a large vascularized pericranial flap will be needed for closure. The skin galea, temporoparietal fascia, and superficial layer of the deep temporal fascia are elevated. The periosteum, temporalis muscle, and true temporal fascia (deep layer of the deep temporal fascia) are left attached to the bone. The posterior skin edge should be separated from the periosteum to expose a large pericranial flap. This procedure results in a vascularized pericranial flap that can be used to close the wound. If the pericranial flap is thin, a myofascial or galeal flap can be used. In cases where the galea is separated from the skin, care should be taken to protect the vasculature that runs in the subcutaneous fat. (dDTF, deep layer of the deep temporal fascia; FM, frontalis muscle), (G, galea aponeurotica; IFF, interfascial fat pad; PO, periosteum; sDTF, superficial layer of the deep temporal fascia)

IFF

dDTF PO sDTF

PO

Fig. 9.7 Two layer scalp elevation (pericranial flap

dDTF

elevation).

The periosteum should be separated from under the posterior scalp edge to enlarge the periosteal flap. The loose connective tissue under the galea should be left attached to the periosteum to thicken the periosteal flap. However, the loose connective tissue on the deep temporal fascia can be elevated with parietotemporal fascia toward the skin flap. The pericranial flap is elevated with its blood supply intact. (dDTF, deep layer of the deep temporal fascia; PO, periosteum; sDTF, superficial layer of the deep temporal fascia)

sDTF

9 Frontotemporal Orbitozygomatic Transcavernous Approach

FM G

dDTF

sDTF Fig. 9.8 Two layer scalp elevation (elongation of the pericranial flap).

PO

The pericranial flap can be elongated by back cutting the pericranium. The pedicle of the flap must be kept broad enough to maintain an adequate blood supply to the tip of the flap. The flap should be kept moist during the surgery. (dDTF, deep layer of the deep temporal fascia; FM, frontalis muscle; G, galea aponeurotica; PO, periosteum; sDTF, superficial layer of the deep temporal fascia)

MP

FZS

LOW TD

Fig. 9.9 (Step 3) “Golf club” drilling (frontoorbital detachment). A bur hole is drilled crossing the lateral surface of the greater wing of the sphenoid bone as close to the frontal process as possible. This key bur hole, called the “golf club head,” exposes the lateral dura of the anterior and middle fossae on the sides of the sphenoid wing. (FZS, frontozygomatic suture; LOW, lateral orbital wall; MP, marginal process; TD, temporal dura)

LOW TD Fig. 9.10 “Golf club” drilling (frontoorbital detachment).

The cortical bone of the lateral orbital wall and the dura of the frontal base and temporal tip are exposed by drilling across the greater wing of the sphenoid bone. The meningoorbital band, which marks the lateral edge of the superior orbital fissure, can be seen through this key hole. (FD, frontal dura; LOW, lateral orbital wall; TD, temporal dura)

FD

125

126

II Anterolateral Skull Base

FZS LOW

Shaft

Fig. 9.11 “Golf club” drilling (drilling the subtemporal groove).

Because it is difficult to use a craniotome under the temporalis muscle, a groove is drilled into the bone of the middle fossa as anterior and inferior as possible. This groove connects with our “golf club head.” (FZS, frontozygomatic suture; LOW, lateral orbital wall)

Fig. 9.12 Frontotemporal craniotomy. Additional holes are made along the route of the proposed bone flap. The number of holes made depends on how attached the dura is to the bone. The bony flap is outlined with a craniotome.

Fig. 9.13 (Step 4) Frontotemporal craniotomy The craniotomy is raised.

Club Head

9 Frontotemporal Orbitozygomatic Transcavernous Approach

Fig. 9.14 Separation of periorbita. A curved sharp dissector is used to separate the periorbita from the orbital roof. The lacrimal gland is encountered laterally. This gland is dissected down with the periorbita.

GS

Fig. 9.15 Separation of periorbita. Gelfoam (Pfizer Inc., NY, NY) is placed between the periorbita and the bony orbit to avoid injury of the periorbita at the time of the osteotomy. (GS, gelatin sponge)

SON

Fig. 9.16 Separation of periorbita. The periorbita is kept intact by placing the Gelfoam between the periorbita and the superior orbital wall. The supraorbital nerve is protected. (SON, supraorbital nerve)

127

128

II Anterolateral Skull Base

FZS Fig. 9.17 (Step 5) Limited supraorbital bar

5 mm

osteotomy.

The osteotomy on the medial side of the orbit is made lateral to the supraorbital foramen or notch. Usually there is no advantage to carrying the osteotomy medial to the supraorbital notch. The lateral side of the osteotomy is made just lateral to the frontozygomatic suture. This limited orbital osteotomy allows the surgeon to look up under the frontal lobe. With a standard pterional approach, the orbital roof forces the surgeon’s line of sight inferiorly. (FZS, frontozygomatic suture)

10mm

Fig. 9.18 Limited supraorbital bar osteotomy. The osteotomy is completed by drilling the lateral and superior orbital walls 10 mm deep to the inner table of the craniotomy edge with a diamond drill.

Fig. 9.19 Limited supraorbital bar osteotomy. If the periorbita is injured, the intraorbital fat is exposed. Because the fat obstructs the surgeon’s view, the torn periorbita should be sutured with a 6-0 suture to hold the fat out of the surgeon’s line of sight.

9 Frontotemporal Orbitozygomatic Transcavernous Approach

10mm

Fig. 9.20 Supraorbital bar and superior wall of the orbit are removed.

Zy

TM Fig. 9.21 Extended orbitozygomatic osteotomy. The supraorbital bar, the frontal process of the zygoma, and the zygomatic arch are removed as one piece. The three black lines indicate the location of the osteotomies. (TM, temporalis muscle; Zy, zygomatic arch)

TM

Fig. 9.22 Extended orbitozygomatic osteotomy. The extended orbitozygomatic osteotomy is completed by drilling the superior and lateral orbital walls 10 mm deep to the inner table of the craniotomy edge with a diamond drill. (TM, temporalis muscle)

129

130

II Anterolateral Skull Base

TM

Fig. 9.23 Extended orbitozygomatic osteotomy. After the supraorbital bar and the zygomatic arch are removed as one piece, the orbit and the insertion of the temporalis muscle are exposed. (TM, temporalis muscle)

Fig. 9.24 Raising the temporalis muscle. Raising the temporalis muscle exposes the temporal base.

Fig. 9.25 Midsubtemporal ridge over lateral loop. There is a characteristic protrusion of bone between the mandibular and maxillary branches of the trigeminal nerve. This bony protrusion is usually seen over the lateral loop, which is another name for the dural bridge between V2 and V3. We named this bony protrusion the mid-subtemporal ridge. The ridge serves as a landmark for the identification of V2 and V3 (See Figs. 8.3–8.6 and Figs. 11.1–11.24, and 11.26).

9 Frontotemporal Orbitozygomatic Transcavernous Approach

Fig. 9.26 Drilling the inner bony table. Bony protrusions including the mid-subtemporal ridge emanating from the inner plate of the middle fossa should be removed with a diamond drill to flatten the base of the middle fossa. Removal of the bony protrusions and the inner plate allows the surgeon to view the base of the middle fossa without obstruction.

MOB

Fig. 9.27 Meningoorbital band. The meningoorbital band marks the lateral edge of the superior orbital fissure. (MOB, meningoorbital band)

MOB

Fig. 9.28 Superior orbital fissure. A recurrent branch of the lacrimal artery may pass back through the superior orbital fissure to anastomose with the middle meningeal artery. (MOB, meningoorbital band)

131

132

II Anterolateral Skull Base

Fig. 9.29 Division of the meningoorbital band. The lateral edge of the meningoorbital band can be divided 5–7 mm medially without risking injury to the oculomotor nerve. The division of the band frees the dura propria from the inner layer of the cavernous sinus dura, which houses the cranial nerves.

Fig. 9.30 Beginning the osteal dura elevation from the superior orbital fissure.

SOF

After the meningoorbital band is cut, the dural covering the temporal lobe can be separated from the inner layer of the cavernous sinus. (SOF, superior orbital fissure)

TCM

Fig. 9.31 Osteal dura elevation from the superior orbital fissure.

A sharp dissector is used to dissect the osteal dura from the dura propria. There is a loose connection in between these two layers. This plane may be obliterated by an infiltrating process such as a meningioma. (TCM, true cavernous membrane = osteal dura covering the lateral cavernous wall)

9 Frontotemporal Orbitozygomatic Transcavernous Approach

V2 V1 Fig. 9.32 Skeletonization of cranial nerves III, IV,

IV

III

V1, V2, and the superior orbital vein.

Elevation of the dura propria reveals cranial nerve III, IV, V1 and V2. (III, oculomotor nerve; IV, trochlear nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

EB

Fig. 9.33 Elevation of the dura from the floor of

the anterior fossa to the ethmoidal band (posterior ethmoidal nerve and artery).

The ethmoidal band marks the medial border of the anterior fossa dural elevation. (EB, ethmoidal band = posterior ethmoidal artery and nerve)

EB

Fig. 9.34 Magnified view of the ethmoidal band. The posterior ethmoidal nerve and artery form the ethmoidal band. (EB, ethmoidal band = posterior ethmoidal artery and nerve)

133

134

II Anterolateral Skull Base

V2 V1 Fig. 9.35 (Step 6A) Exposure of the base of the

IV

anterior clinoid process.

III

ON

The dura medial to the superior orbital fissure is often thin, but with a sharp dissector it can usually be elevated from the lesser wing of the sphenoid until the shadow of the optic nerve can be seen through the thin bone of the orbital apex and the falciform ligament. (III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

Fig. 9.36 (Step 6B) First step of removing of the anterior clinoid process.

V2

Coring of the anterior clinoid process. The anterior clinoid is removed in steps. First, the anterior clinoid is freed from the lesser wing of the sphenoid anteriorly. The optic strut attachment to the anterior clinoid is preserved, as it will secure the anterior clinoid during the remainder of the drilling. The third nerve runs in the fibrous tissue lateral to the anterior clinoid. Thus, the lateral wall of the clinoid is thinned and peeled off the fibrous tissue with a thin dissector. All drilling of the optic strut and optic canal is done under copious irrigation to avoid heat damage. This photo shows the first step. The anterior clinoid is hollowed in the beginning. (III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

V1 IV

ON

III

V2 COM

V1 Fig. 9.37 (Step 6B) Removing the lateral half of the anterior clinoid process.

The second step is to remove the lateral half of the anterior clinoid process preserving the medial half of the clinoid and its attachment to the optic strut. The microscope is tilted laterally. The oculomotor nerve runs just under the lateral half of the process. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

IV

III

T ON

9 Frontotemporal Orbitozygomatic Transcavernous Approach

V2

COM OC

V1 III

IV

T

ON

Fig. 9.38 Tilting the microscope medially. The microscope is tilted medially in preparation for removing the medial anterior clinoid. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; OC, optic canal; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

V2

COM

ON

V1 IV

Fig. 9.39 (Step 6C) Removal of medial half of the

III

T

anterior clinoid process.

The bone over the optic canal is thinned and lifted off the nerve with a dissector. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

OS

V2

ON

V1 Fig. 9.40 (Step 6C) Partial removal of the optic strut.

The optic strut is partially removed with a diamond drill. The surgeon should be aware that the sphenoid sinus may extend into the optic strut. (III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; OS, optic strut; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

IV

III

T

135

136

II Anterolateral Skull Base

Fig. 9.41 Observation of carotico-oculomotor

V2

membrane.

COM

V1

A microscope is returned to a neutral position. The base of the anterior clinoid process has been removed. The carotico-oculomotor membrane that covers the C3 portion of the internal carotid artery is observed after the base is detached. When this membrane is completely preserved, venous bleeding from the medial triangle of the cavernous sinus is not encountered. More frequently, cavernous sinus bleeding is controlled with small bits of oxidized cellulose. (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

IV

III

ON

T

V2 COM

V1 IV

III

ON

T

Fig. 9.42 (Step 6D) Removal of the tip of the anterior clinoid process.

The anterior clinoid tip is held in a forceps and freed from the interclinoid attachment with a sharp dissector. (COM, caroticooculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; T, tip of the anterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

EB

V2 COM

V1 Fig. 9.43 Completion of removal of the anterior clinoid process.

The anterior clinoid process is completely removed. An anatomical relationship of the cavity created by removing the anterior clinoid process and adjacent structures is well demonstrated. (COM, carotico-oculomotor membrane; EB, ethmoidal band = posterior ethmoidal artery and nerve; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

IV

III

ON

9 Frontotemporal Orbitozygomatic Transcavernous Approach

Fig. 9.44 Removal of the orbital roof. The remainder of the roof and the lateral wall of the orbit are partially removed. The purpose of the removal of this roof is to make the anterior skull base flat.

ON COM

Fig. 9.45 Identifying the C3 portion of the internal carotid artery covered by the carotico-oculomotor membrane.

The C3 portion of the internal carotid artery is exposed when the anterior clinoid is removed. The artery is covered by the carotico-oculomotor membrane (true cavernous membrane). (COM, carotico-oculomotor membrane; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve])

V1 IV

III

ON C3

V2 Fig. 9.46 (Step 7) Mobilization of the membrane covering the oculomotor nerve.

The relationship between V2, V1, CN III, CN IV, and the carotid artery is demonstrated. The caritico-oculomotor membrane has been removed from the carotid artery. The oculomotor nerve is covered by a thin membrane. (C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve])

III V1 IV

137

138

II Anterolateral Skull Base

ON

V2 Fig. 9.47 Removing the true cavernous membrane.

The membrane has been removed to expose the nerves that reside in the lateral wall of the cavernous sinus. In clinical cases, the true cavernous membrane is not removed. (C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; SOV, superior ophthalmic vein; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; VI, abducens nerve)

Fig. 9.48 (Step 8) Opening the dura. The dura is incised in a semilunar fashion at first.

Fig. 9.49 Opening the dura. The dura’s opening is extended in a “crossbow” fashion. A cuff of the dura, including the external carotid ring, is preserved. This cuff serves as an anchor for dural sutures at the time of closure.

V SO VI

C3 V1 IV

III

9 Frontotemporal Orbitozygomatic Transcavernous Approach

C2 ON

C1 A1 M1

Fig. 9.50 Opening the sylvian fissure. The sylvian fissure is opened to expose the internal carotid, middle cerebral, and anterior cerebral arteries. (A1, A1 segment of the anterior cerebral artery; C1, C1 portion of the internal carotid artery; C2, C2 portion of the internal carotid artery; M1, M1 segment of the middle cerebral artery; ON, optic nerve)

COM

ON

C2

DR

Fig. 9.51 Opening the dura. The dural opening is continued laterally and medially at the base. (C2, C2 portion of the internal carotid artery; COM, caroticooculomotor membrane; DR, dural ring; ON, optic nerve)

COM DR

C2 PCP

Fig. 9.52 Magnified view. The external and internal carotid dural rings and the intervening clinoid space are well demonstrated. (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; DR, dural ring; ON, optic nerve; PCP, posterior clinoid process)

ON

139

140

II Anterolateral Skull Base

COM ON

DR C2 PCP

Fig. 9.53 Initial incision of the dural ring. The medial side of the dural ring is incised at first. (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; DR, dural ring; ON, optic nerve; PCP, posterior clinoid process)

COM ON

III C2

Fig. 9.54 Releasing the internal carotid artery from the dural ring.

The dural ring is dissected from the inside out. The oculomotor canal is opened. A blunt hook tents up the dural cuff that surrounds the oculomotor nerve and the dura is cut with a pointed knife. Bothersome bleeding from the medial triangle of the cavernous sinus may be encountered (arrowheads). (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)

COM

III Fig. 9.55 Removing the carotico-oculomotor

C2

membrane.

The carotico-oculomotor membrane is held in a forceps or by a blunt hook. (C2, C2 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)

ON

III

9 Frontotemporal Orbitozygomatic Transcavernous Approach

COM

III

C3 ON

Fig. 9.56 Opening the carotico-oculomotor

C2

membrane.

The membrane is incised by scissors or a sharp knife. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)

III

Fig. 9.57 Opening the carotico-oculomotor membrane.

C3 III

COM

Bleeding from the dural venous complex, which drains into the posterior cavernous sinus and the connection of the posterior cavernous sinus with the basal sinus, is controlled by packing the bleeding points with small pieces of a oxidized cellulose held in place by gentle pressure. Large slabs of hemostatic agents will only obstruct the surgeon’s view and are no more effective in stopping hemorrhage from discrete bleeding points. The carotico-oculomotor membrane is raised laterally and pushed into the cavernous sinus with a piece of oxidized cellulose. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; COM, carotico-oculomotor membrane; III, oculomotor nerve; ON, optic nerve)

ON C2

III

V1 C3 IV Fig. 9.58 Exposing the C3 portion of the internal

ON III C2

carotid artery.

After the carotico-oculomotor membrane has been removed, the relationship between V1, CN II, CN III, CN IV, and the intra- and extradural carotid arteries is demonstrated. (C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; PCP, posterior clinoid process; V1, ophthalmic nerve [first division of the trigeminal nerve])

PCP

141

142

II Anterolateral Skull Base

V1 ON

IV

C2

III

BA

Fig. 9.59 Viewing the top of the basilar artery.

PC

The anterior inferior portion of the sylvian fissure is opened and the internal carotid artery is followed to its bifurcation. The opening between the oculomotor nerve and the carotid artery makes a corridor to the distal basilar artery. The posterior communicating artery is divided in this specimen. (BA, basilar artery; C2, C2 portion of the internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; ON, optic nerve; P1, P1 segment of the posterior cerebral artery; PC, posterior communicating artery; V1, ophthalmic nerve [first division of the trigeminal nerve])

P1

ON

C2 BA

III

P1

SCA

P1 Fig. 9.60 Viewing the top of the basilar artery. The two proximal posterior cerebral arteries (P1) segments and the left superior cerebellar artery are clearly seen. (BA, basilar artery), (C2, C2 portion of the internal carotid artery; III, oculomotor nerve; ON, optic nerve; P1, P1 segment of the posterior cerebral artery; SCA, superior cerebral artery)

C3 III ON PCP

C2 BA

SCA

Fig. 9.61 Viewing the top of the basilar artery. The basilar artery proximal to the superior cerebellar artery can be occluded with a temporary clip. A well-developed posterior clinoid process may disturb surgical access to the mid-basilar artery. (BA, basilar artery; C2, C2 portion of the internal carotid artery; C3, C3 portion of the internal carotid artery; III, oculomotor nerve; ON, optic nerve; P1, P1 segment of the posterior cerebral artery; PCP, posterior clinoid process; SCA, superior cerebral artery)

P1

9 Frontotemporal Orbitozygomatic Transcavernous Approach

III

PCP PC

III

P2 Fig. 9.62 Viewing the ipsilateral posterior communication artery.

The ipsilateral posterior communicating artery is seen anastomosing with the left posterior cerebral artery. (III, oculomotor nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; PC, posterior communicating artery; PCP, posterior clinoid process)

P1

143

III

Lateral Skull Base

10 Anatomy for Lateral Skull Base Surgery In this chapter, we review the anatomy of the extracranial lateral skull base and the course of the facial nerve. It is important that the surgeon knows this anatomy before approaching lesions of the infratemporal fossa.

10.1 Anatomy and Exploration of the Infratemporal Fossa Key Steps Step 1. Exposure of facial nerve (Fig. 10.3) Step 2. Identification of digastric trunk of facial nerve (Fig. 10.6) Step 3. Exposure of masseter muscle (Fig. 10.10) Step 4. Exposure of pterygoid plexus (Fig. 10.14) Step 5. Removal of ramus of mandible (Fig. 10.16) Step 6. Exposure of middle meningeal artery (Fig. 10.20) Step 7. Dissection of pterygoid muscles (Fig. 10.21) Step 8. Identification of styloid muscles (Fig. 10.28)

Illustrated Steps with Commentary

pSTA

FM

TPM fSTA

ZMjM

GAN

Fig. 10.1 Anatomy of the infratemporal skull base. SCM

The skin is raised and the subcutaneous layers are demonstrated. The superficial temporal artery runs lateral to the temporoparietal muscle. (FM, frontal muscle; fSTA, frontal branch of the superficial temporal artery; GAN, great auricular nerve; Pl, platysma; pSTA, parietal branch of the superficial temporal artery; SCM, sternocleidomastoid muscle; TPM, temporoparietal muscle; ZMjM, zygomaticus major muscle)

Pl

148

III Lateral Skull Base

G FM

pSTA

TPM

fSTA

Fig. 10.2 Superficial temporal artery. The superficial temporal artery runs lateral to the temporoparietal muscle that continues into the galea aponeurotica. The anterior part of the galea aponeurotica, the frontal muscle, is seen at the forehead. The auriculotemporal nerve, a branch of the trigeminal nerve, is also seen. The nerve runs parallel to the superficial temporal artery around the root of the zygoma. (ATN, auriculotemporal nerve; FM, frontal muscle; fSTA, frontal branch of the superficial temporal artery; G, galea aponeurotica; pSTA, parietal branch of the superficial temporal artery; TPM, temporoparietal muscle)

ATN

TB ZB ZM

BB

Fig. 10.3 (Step 1) Exposure of the facial nerve and the superficial layer of the parotid gland.

After removing the temporoparietal muscle and the fascia of the masseteric muscle, the branches of the facial nerve, the masseteric muscle, and the superficial lobe of the parotid gland are seen. (BB, buccal branch of the facial nerve; GAN, great auricular nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; SCM, sternocleidomastoid muscle; sPG, superficial layer of the parotid gland; TB, temporal branch of the facial nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)

sPG

MM

GAN MMB SCM TB ZB ZMjM

BB dPG

Fig. 10.4 Deep lobe of the parotid gland. After removing the superficial lobe of the parotid gland, the deep layer of the parotid gland is seen. The facial nerve runs between the superficial and deep layer of the parotid gland. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; dPG, deep layer of the parotid gland; GAN, great auricular nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; SCM, sternocleidomastoid muscle; TB, temporal branch of the facial nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)

MM GAN

MMB CB

SCM

jM

10.1 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Infratemporal Fossa

TB ZB

SMF

Fig. 10.5 Five branches of the facial nerve. Once the superficial lobe of the parotid gland is removed, the major branches of the facial nerve are exposed. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; dPG, deep layer of the parotid gland; FN, facial nerve; IJV, internal jugular vein; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; MsT, mastoid tip; OA, ophthalmic artery; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; TB, temporal branch of the facial nerve; XI, accessory nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)

FN PA

ZM

jM

MsT DB

BB

dPG OA

DM

XI

IJV

MM

SCM CB

MMB

SMF

MsT

FN

PA

dPG Fig. 10.6 (Step 2) The digastric branch of the

DB

The first branch of the facial nerve, the digastric branch, originates from the proximal portion of the extracranial facial nerve, just distal to the stylomastoid foramen. It can be found by rotating the superior margin of the digastric muscle. This is an easy way to locate the facial nerve at the time of surgery. (DB, digastric branch; DM, digastric muscle; dPG, deep layer of the parotid gland; FN, facial nerve; IJV, internal jugular vein; IX, glossopharyngeal nerve; MsT, mastoid tip; OA, ophthalmic artery; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen)

OA

facial nerve.

SCM

DM

IX

SMF MsT

IJV

TB FN PA

ZB BB

DB Fig. 10.7 The digastric branch of the facial nerve. The relationship between the digastric branch of the facial nerve and the posterior belly of the digastric muscle is more fully demonstrated after the occipital artery is divided. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; dPG, deep layer of the parotid gland; FN, facial nerve; IJV, internal jugular vein; IX, glossopharyngeal nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; MsT, mastoid tip; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; TB, temporal branch of the facial nerve)

dPG DM

IX

SCM

IJV CB

MMB

MM

149

150

III Lateral Skull Base

TB SMF

PA

FN

MsT

ZB

BB

DB

Fig. 10.8 Exposure of the distal external carotid artery.

DM

The neck of the mandible and the external carotid artery are seen after the deep layer of the parotid gland is removed. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; FN, facial nerve; IJV, internal jugular vein; IX, glossopharyngeal nerve; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; MsT, mastoid tip; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; TB, temporal branch of the facial nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)

IX

IJV

MM

SCM

CB

MMB

LOR Zy Fig. 10.9 Anterior dissection exposing the zygomaticus major muscle.

ZM FN

RM

ECA

The zygomaticus major muscle originates from the lateral surface of the zygomatic bone and inserts into the angle of the mouth. The zygomaticus minor muscle lies just medial to the zygomaticus major muscle. The zygomaticofacial nerve, a branch of the maxillary nerve (the second division of the trigeminal nerve) is also seen exiting from the zygomaticofacial foramen. This nerve, along with the zygomaticotemporal nerve, can be injured during a zygomatic osteotomy. (DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; LOR, lateral orbital rim; MM, masseteric muscle; RM, ramus of the mandible; ZFF, zygomaticofacial foramen; ZMjM, zygomaticus major muscle; Zy, zygoma)

DM

MM

Zy MN FN

RM Fig. 10.10 (Step 3) Exposing the masseteric The masseteric nerve is seen just posterior to the masseteric muscle. The nerve that passes through the mandibular notch is a branch of the mandibular nerve (the third division of the trigeminal nerve). (DB, digastric branch; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; IJV, internal jugular vein; MM, masseteric muscle; MN, masseteric nerve; RM, ramus of the mandible; SCM, sternocleidomastoid muscle; XI, accessory nerve; Zy, zygoma)

EC A

DB muscle.

ZFF

DM XI

IJV SCM

MM

jM

ZM

jM

10.1 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Infratemporal Fossa

Zy

Fig. 10.11 Layers of the masseteric muscle. The masseteric muscle consists of three layers: the superficial, the middle, and the deep layers. The superficial layer (peeled off in this photo) is the largest and arises from a thick aponeurosis originating from the maxillary process of the zygomatic bone and from the anterior two-thirds of the inferior border of the zygomatic arch. The middle layer arises from the medial aspect of the anterior two thirds of the zygomatic arch and from the lower border of the posterior third of this arch. The deep layer arises from the medial surface of the zygomatic arch. The muscle inserts into the lateral ramus and coronoid process of the mandible. (DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; IJV, internal jugular vein; mMM, middle layer of the masseteric muscle; RM, ramus of the mandible; sMM, superficial layer of the masseteric muscle; XI, accessory nerve; Zy, zygoma)

RM

sMM

EC

FN

mMM

A

DM XI IJV

DTA

CrP

CnP MN FN

EC A

Fig. 10.12 Insertion of the temporalis muscle. The coronoid process of the mandible where the temporalis muscle inserts is exposed after the masseteric muscle has been removed. (BM, buccal muscle; CnP, condylar process; CrP, coronoid process; DM, digastric muscle; DTA, deep temporal artery; ECA, external carotid artery; FN, facial nerve; MN, masseteric nerve; RM, ramus of the mandible)

BM

RM

DM

TM

A DT T D N

CnP Fig. 10.13 Exposure of the deep temporal nerve and the masseteric nerve. With the masseteric muscle removed, the posterior deep temporal nerve to the temporalis muscle and the nerve to the masseter muscle are clearly seen along with the deep temporal artery. Cauterizing the undersurface of the temporalis muscle risks injury to the deep temporal nerves and deep temporal artery. (CnP, condylar process; CrP, coronoid process; DTA, deep temporal artery; DTN, deep temporal nerve; FN, facial nerve; MN, masseteric nerve; RM, ramus of the mandible; TM, temporalis muscle)

FN

CrP MN

RM

151

152

III Lateral Skull Base

DTA

LOR

DTN PVP

Fig. 10.14 (Step 4) Pterygoid venous plexus.

MN

FN

EC A

The rich pterygoid venous plexus surrounds the lateral pterygoid muscles. This plexus communicates with numerous skull base, orbital, and dural veins, including the cavernous sinus. (BM, buccal muscle; BN, buccal nerve; CnP, condylar process; CrP, coronoid process; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; LOR, lateral orbital rim; MN, masseteric nerve; PVP, pterygoid venous plexus; RM, ramus of the mandible; SCM, sternocleidomastoid muscle)

CrP

CnP

RM

DM

BN BM

SCM

DTA DTN

LPM

Fig. 10.15 Magnified view of Fig. 10.14.

PVP

CnP MA

CrP

MN

EC A

This figure demonstrates some of the branches of the internal maxillary artery, deep temporal artery, and nerve. (CnP, condylar process; CrP, coronoid process; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; LOR, lateral orbital rim; LPM, lateral pterygoid muscle; MA, maxillary artery; MN, masseteric nerve; PVP, pterygoid venous plexus; RM, ramus of the mandible)

LOR

RM

DTN

DTA

LPM PVP

Fig. 10.16 (Step 5) Removal of the central portion of the ramus of the mandible.

MA

MN

FN

BN

EC A

Anatomical structures behind the mandible are exposed. The inferior alveolar artery is seen branching from the maxillary artery, and accompanied by the inferior alveolar nerve. The lingual nerve runs parallel to the inferior alveolar nerve, passing from the medial surface of the lateral pterygoid muscle to the lateral surface of the medial pterygoid muscle. (BM, buccal muscle; BN, buccal nerve; CnP, condylar process; CrP, coronoid process; DB, digastric branch; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; LN, lingual nerve; LPM, lateral pterygoid muscle; MA, maxillary artery; MN, masseteric nerve; PVP, pterygoid venous plexus; SCM, sternocleidomastoid muscle)

CrP CnP

DB

BM

DM IAN SCM

IJV

LN

10.1 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Infratemporal Fossa

DTN DTA sLPM MA

Fig. 10.17 The buccal nerve and the maxillary

MN

FN

MPM

DB

BN

EC A

LN

DM

BM

IA N N MH

After the pterygoid venous plexus is removed, the superior and inferior heads of the lateral pterygoid muscle are well seen. The buccal nerve lies in between these two heads to provide sensation to the cheek. (BM, buccal muscle; BN, buccal nerve; CnP, condylar process; DB, digastric branch; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MHN, mylohyoid nerve; MN, masseteric nerve; MPM, medial pterygoid muscle; SCM, sternocleidomastoid muscle; sLPM, superior head of the lateral pterygoid muscle)

iLPM

CnP

artery.

IJV SCM

DTN A DT PM sL

MN

MA iLPM

Fig. 10.18 Exposure of the maxillary artery, the

inferior alveolar nerve, and the lingual nerve.

FN DB

MPM

MT

IA

BN

DM

EC A MH

BM

LN

N N

IJV SCM

M A

The buccal nerve passes between the two heads of the lateral pterygoid muscle and the lingual nerve passes beneath the inferior head of the lateral pterygoid muscle. The mylohyoid nerve branches from the inferior alveolar nerve. (BM, buccal muscle; BN, buccal nerve; DB, digastric branch; DM, digastric muscle; DTA, deep temporal artery; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MHN, mylohyoid nerve; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; SCM, sternocleidomastoid muscle; sLPM, superior head of the lateral pterygoid muscle)

FN

MT

DB

ECA BN

DM

SML

Fig. 10.19 The sphenomandibular ligament. SH M

The sphenomandibular ligament descends from the sphenoidal spine to the lingular of the mandible. It is separated from the mandible by the maxillary artery and the inferior alveolar artery and nerve. (BN, buccal nerve; DB, digastric branch; DM, digastric muscle; ECA, external carotid artery; FA, facial artery; FN, facial nerve; IJV, internal jugular vein; MA, maxillary artery; MT, maxillary tuberosity; SHM, stylohyoid muscle; SML, sphenomandibular ligament)

IJV

FA

153

154

III Lateral Skull Base

sLPM DTN

STA MMA

MN

Fig. 10.20 (Step 6) The middle meningeal artery.

FN

The middle meningeal artery emerges from the maxillary artery and passes deep to the lateral pterygoid muscles to enter the foramen spinosum. (BN, buccal nerve; DB, digastric branch; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MHN, mylohyoid nerve; MMA, middle meningeal artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)

MT

A M

ECA

DB

BN LN

IA N

DM

MH

MN

DTN

N

MPM

Fig. 10.21 (Step 7) The lateral and medial pterygoid muscles.

sLPM

MMA iLPM

STA

MT

FN EC

LN

A

DM

BM

N

M

IJV

BN

IA

M MP

The two distinct heads of the lateral pterygoid muscle originate from the greater wing of the sphenoid bone and the lateral surface of the lateral pterygoid plate and insert into the neck of the condyle of the mandible. The larger deep head of the medial pterygoid muscle arises from the medial surface of the lateral pterygoid process and inserts into the medial surface of the ramus of the mandible. The smaller superficial head arises from the tuberosity of the maxilla. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MHN, mylohyoid nerve; MMA, middle meningeal artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; SCM, sternocleidomastoid muscle; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)

iLPM

HN

SCM

sLPM BN

DTN MN

Fig. 10.22 Relationship between the lateral and

FN

A

The medial pterygoid muscle is seen inferior to the lateral pterygoid muscle. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MN, masseteric nerve; MPM, medial pterygoid muscle; sLPM, superior head of the lateral pterygoid muscle)

EC

medial pterygoid muscles.

iLPM

LN IAN

BM

DM

MPM IJV

10.1 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Infratemporal Fossa

M sLP

MA

FN

EC

Fig. 10.23 The deep and superficial heads of the medial pterygoid muscle.

MT

IAN LN

BM

A

DM

The superficial head of the medial pterygoid muscle has been raised. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; IJV, internal jugular vein; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)

BN

iLPM

STA

MPM

IJV

sLPM DTN

STA MA

Fig. 10.24 The lateral pterygoid muscle. FN

MT

EC A

IAN

DM

M

LN

BM

PM

sL

PM

The buccal nerve emerges between the superior and inferior heads of the lateral pterygoid muscle. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; iLPM, inferior head of the lateral pterygoid muscle; LN, lingual nerve; MA, maxillary artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)

BN

iLPM

MN

MN

Fig. 10.25 The lateral lamina of the pterygoid

process.

BN

LPP

STA

MT

MA FN

EC A

The inferior head of the lateral pterygoid muscle arises from lateral surface of the lateral pterygoid process. That muscle has been removed to reveal the lateral pterygoid process. (BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; DTN, deep temporal nerve; ECA, external carotid artery; FN, facial nerve; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MN, masseteric nerve; MPM, medial pterygoid muscle; MT, maxillary tuberosity; sLPM, superior head of the lateral pterygoid muscle; STA, superior temporal artery)

DTN

DM

IAN M

LN

PM

BM

155

III Lateral Skull Base

FO

ATN

STA

FN

LPP

MT

DM

BM

FO

ATN

STA

Fig. 10.27 The chorda tympani.

M MP

A

IAN

IAN

CT

SH

M

BN

MA

FN

LPP

MMA

MT LN

EC

M MP

A

The inferior alveolar nerve has been detached and elevated. The chorda tympani, a branch of the facial nerve, joins the lingual nerve coursing to the tongue. The chorda tympani exits the skull on the medial surface of the spine of the sphenoid bone. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; FO, foramen ovale; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MMA, middle meningeal artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; SHM, stylohyoid muscle; STA, superior temporal artery)

CT

LN

EC

The relationship between the lingual nerve and the inferior alveolar nerve is demonstrated. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DM, digastric muscle; ECA, external carotid artery; FN, facial nerve; FO, foramen ovale; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MMA, middle meningeal artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; STA, superior temporal artery)

MA

BN

Fig. 10.26 The lingual and inferior alveolar nerve.

MM A

156

DM

BM

FO y St P

LPP

IJV

PM

The neck and condyle of the mandible and the external carotid artery have been removed. Three muscles, the stylohyoid, the styloglossus, and the stylopharyngeal muscles that attach to the styloid process are seen. The internal carotid artery runs medial to these muscles. (BM, buccal muscle; DM, digastric muscle; FA, facial artery; FO, foramen ovale; IJV, internal jugular vein; LPP, lateral lamina of the pterygoid process; MT, maxillary tuberosity; OA, ophthalmic artery; SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process; TVPM, tensor velli palatini muscle)

TV

OA

Fig. 10.28 (Step 8) The styloid muscles.

MT

SPM SGM SHM

DM

FA

BM

10.1 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Infratemporal Fossa

C6 C6

ICA P Sty

IX

SC

M SPM SGM SHL SHM

Fig. 10.29 The styloid muscles. The styloid muscles and stylohyoid ligament are exposed in another specimen. The mandible and external carotid artery have been removed. (C6, C6 portion of the internal cerebral artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; SCM, sternocleidomastoid muscle; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process)

Fig. 10.30 The foramen ovale from the lateral

side.

ATN

FO BN

P Sty

DB

LPP

MMA

FN

MT

LN

IJV

IAN

DM

CT

SPM SGM

OA

SHM

The pterygoid muscles, the mandible, and the external carotid artery have been removed. This view gives the surgeon a sense of the relationship between the foramen ovale and the lateral pterygoid plate. This relationship is important to keep in mind when drilling through the middle fossa. The pterygoid plates will be encountered when drilling anterior to the line connecting the foramen ovale and foramen rotundum. We clearly see the middle meningeal artery entering the foramen spinosum and the distal branches of the internal maxillary artery in the pterygopalatine fossa. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DB, digastric branch; DM, digastric muscle; FA, facial artery; FN, facial nerve; FO, foramen ovale; IAN, inferior alveolar nerve; IJV, internal jugular vein; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MMA, middle meningeal artery; MT, maxillary tuberosity; OA, ophthalmic artery; SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process)

BM

FA

ATN

FO

Fig. 10.31 Anatomical structures in the

MMA

BN

LPP MT

ICA TVPM

OA

IJV DM

SConsM

SG SHM

Medial to the pterygoid muscles, we see the pharyngeal muscles. Demonstrated are the superior constrictor muscle, tensor velli palatini muscle, buccinator muscle, and maxillary tuberosity. The maxillary tuberosity and the adjacent palatine bone give rise to the superficial head of the medial pterygoid muscle. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; DM, digastric muscle; FO, foramen ovale; ICA, internal carotid artery; IJV, internal jugular vein; LPP, lateral lamina of the pterygoid process; MMA, middle meningeal artery; MT, maxillary tuberosity; OA, ophthalmic artery; SConsM, superior constrictor muscle; SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; StyP, styloid process; TVPM, tensor velli palatini muscle)

P Sty

parapharyngeal space.

SP M M

BM

157

158

III Lateral Skull Base

10.2 Anatomy and Exploration of the Facial Nerve Key Steps Step 1. Extracranial Portion (Fig. 10.32) Step 2. Infratemporal Fossa (Fig. 10.37) Step 3. Posterior Petrosa (Inner Petrosa) (Fig. 10.39) Step 4. Lateral Petrosa (Mastoid) (Fig. 10.44) Step 5. Superior Petrosa (Middle Fossa) (Fig. 10.52) TPF

Fig. 10.32 (Step 1) The extracranial portion. The superficial lobe of the parotid gland has been removed so that branches of the facial nerve can be seen. There are usually five main motor branches of the facial nerve within the parotid gland, but the numerous interconnections between these branches result in a highly variable anatomy. (BB, buccal branch of the facial nerve; CB, cervical branch of the facial nerve; DB, digastric branch; DM, digastric muscle; IJV, internal jugular vein; MM, masseteric muscle; MMB, marginal mandibular branch of the facial nerve; PA, pes anserinus; SCM, sternocleidomastoid muscle; SMF, stylomastoid foramen; STA, superior temporal artery; TB, temporal branch of the facial nerve; TPF, temporoparietal fascia; XI, accessory nerve; ZB, zygomatic branch of the facial nerve; ZMjM, zygomaticus major muscle)

STA

TB

ZMjM

ZB

PA SMF DB

BB MM DM IJV

XI

MMB CB

SCM

GSPN

MsT

P

DB DM

Fig. 10.33 The digastric branch of the facial nerve. Although the facial nerve may give off an auriculotemporal branch to the occipital muscle at the stylomastoid foramen, the branch to the digastric muscle is a fairly constant landmark that will lead the surgeon to the facial nerve. (DB, digastric branch; DM, digastric muscle; GSPN, greater superficial petrosal nerve; MsT, mastoid tip; OA, ophthalmic artery; OSCM, obliquus capitis superior muscle; P, parotid gland)

OSCM

OA

10.2 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Facial Nerve

P

SMA

MsT Fig. 10.34 Detailed view of Fig. 10.33.

FN

A close-up view demonstrates the digastric branch leaving the facial nerve. In this specimen the digastric muscle has been retracted posteriorly. The facial nerve is seen heading for the stylomastoid foramen medial to the styloid process. The occipital artery is seen under the digastric branch of the facial nerve. The posterior auricular artery may give rise to the stylomastoid artery, which passes through the stylomastoid foramen. (DB, digastric branch; DM, digastric muscle; FN, facial nerve; MsT, mastoid tip; OA, ophthalmic artery; P, parotid gland; SMA, stylomastoid artery)

DB DM

OA

P

SHM

FN Fig. 10.35 The digastric branch and the proximal portion of the extracranial facial nerve.

DB

The posterior belly of the digastric muscle is returned to the original position. The digastric branch of the facial nerve is best found between the anterior border of the posterior belly of the digastric muscle and the posterior border of the stylohyoid muscle. These relationships are important for the surgeon who is trying to find the proximal extracranial end of a nonfunctioning facial nerve. (DB, digastric branch; DM, digastric muscle; FN, facial nerve; IJV, internal jugular vein; OA, ophthalmic artery; OSCM, obliquus capitis superior muscle; P, parotid gland; SHM, stylohyoid muscle; XI, accessory nerve)

OSC

IJV

DM

XI

M OA

FN

FO STA

LPP MT

EC A DM

CT

IAN

LN

BM

M MP

The chorda tympani joins to the lingual nerve in the infratemporal fossa deep to the lateral pterygoid muscle. (ATN, auriculotemporal nerve; BM, buccal muscle; BN, buccal nerve; CT, chorda tympani; DM, digastric muscle; ECA, external carotid artery; FO, foramen ovale; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid process; MA, maxillary artery; MMA, middle meningeal artery; MPM, medial pterygoid muscle; MT, maxillary tuberosity; STA, superior temporal artery)

BN

MA

Fig. 10.36 The chorda tympani.

MM A

ATN

159

160

III Lateral Skull Base

FO SSph Fig. 10.37 (Step 2) The infratemporal fossa. The chorda tympani is better seen once the inferior alveolar nerve is retracted superiorly. The chorda tympani is seen traveling along the inferior border of the lateral pterygoid muscle. The nerve carries special sensory taste fibers from the anterior two-thirds of the tongue and preganglionic parasympathetic fibers from the facial to the submandibular ganglion. (BM, buccal muscle; CT, chorda tympani; FO, foramen ovale; IAN, inferior alveolar nerve; ICA, internal carotid artery; IJV, internal jugular vein; LN, lingual nerve; MT, maxillary tuberosity; OA, ophthalmic artery; SSph, spine of the sphenoid bone; TVPM, tensor velli palatini muscle)

IAN

CT

ICA

TVPM

IJV

MT

LN

OA

BM V3

BN CT

Fig. 10.38 The chorda tympani via an

infratemporal fossa approach.

The chorda tympani as viewed from a surgical view (infratemporal fossa approach). The chorda tympani is seen anastomosing with the lingual nerve. The mandibular nerve (V3) is seen to divide into its multiple branches soon after passing through the foramen ovale. (BN, buccal nerve; CT, chorda tympani; IAN, inferior alveolar nerve; LN, lingual nerve; MA, maxillary artery; V3, mandibular nerve [third division of the trigeminal nerve])

MA LN

IAN

SF

TC BB SV

Fig. 10.39 (Step 3) Drilling of the internal

The transverse crest separates the superior and inferior vestibular nerves. The cochlear nerve exits anterior to the inferior vestibular nerve. The facial nerve and the nervus intermedius exit the internal auditory canal anterior to the superior vestibular nerve. (BB, buccal branch of the facial nerve; IV, inferior vestibular nerve; M-VII, meatal segment of the facial nerve; SF, singular foramen; SV, superior vestibular nerve; TC, transverse crest)

M-VII

auditory canal to demonstrate the intrameatal facial nerve.

IV

10.2 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Facial Nerve

V

SF

TC Fig. 10.40 Anatomy at the fundus.

BB SV

M-VII

The vestibule (which connects the cochlea to the semicircular canals) is 2 mm posterior to the transverse crest. If the vestibule is opened, hearing will be lost. (BB, buccal branch of the facial nerve; IV, inferior vestibular nerve; M-VII, meatal segment of the facial nerve; SF, singular foramen; SV, superior vestibular nerve; TC, transverse crest; V, vestibule)

IV

V 2 mm TC

BB

Fig. 10.41 The posterior petrosal segment. The vestibule is about 2 mm posterior to the transverse crest that lies between the superior and inferior vestibular nerves. To demonstrate the hazards of drilling the fundus of the internal auditory canal, a 2 mm diamond bur is shown in the operative field. (BB, buccal branch of the facial nerve; IV, inferior vestibular nerve; M-VII, meatal segment of the facial nerve; SV, superior vestibular nerve; TC, transverse crest; V, vestibule)

SV M-VII

IV

CT

SMF

I

Fig. 10.42 The intramastoid facial nerve. The tympanic segment facial nerve is most constantly found along the anterior wall of the lateral semicircular canal. The nerve can take a variable course between the lateral semicircular canal and the stylomastoid foramen. (CT, chorda tympani; DR, dural ring; ES, emdolymphatic sac; I, incus; JB, jugular bulb; LSC, lateral semicircular canal; PD, posterior fossa dura; PSC, posterior semicircular canal; SMF, stylomastoid foramen; SS, sigmoid sinus; SSC, superior semicircular canal; TT, temporal tegmen; V-VII, vertical segment of the facial nerve)

I V-VI

LSC

TT SSC

PSC ES

PD SS

JB

DR

161

162

III Lateral Skull Base

IB

I

LC(I) SSC

S

Fig. 10.43 The facial recess.

LSC

The facial recess is opened anterior to the facial nerve, leading the surgeon into the middle ear. Care must be taken not to open the annulus of the tympanic membrane, as the thin skin deep in the external auditory canal cannot be sutured. Opening the annulus will expose the operative field to the external auditory canal. (CT, chorda tympani; Gn, genu [second turn or external genu] of the facial nerve; I, incus; IB, incus buttress; LC(I), long crus of the incus; LSC, lateral semicircular canal; P, parotid gland; PSC, posterior semicircular canal; S, stapes; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

T-V I

P I

CT

Gn

PSC

M

V-VII

I SC

T-V I

Fig. 10.44 (Step 4) The lateral petrosal segment.

SSC

Proximal to the lateral semicircular canal, the nerve turns anteriorly to join the geniculate ganglion. (I, incus; LSC, lateral semicircular canal; M, malleus; SC(I), short crus of the incus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve)

(I)

I

LSC

CT

Fig. 10.45 The whole course of the intramastoid

facial nerve.

The semicircular canals have been removed so that the surgeon can see the vertical (mastoid), tympanic, labyrinthine, and meatal segments of the facial nerve as would be seen during a translabyrinthine approach to a cerebellopontine angle tumor. (CT, chorda tympani; DR, dural ring; GG, geniculate ganglion; Gn, genu [second turn or external genu] of the facial nerve; I, incus; IV, inferior vestibular nerve; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SMF, stylomastoid foramen; SS, sigmoid sinus; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; TT, temporal tegmen; V-VII, vertical segment of the facial nerve)

TT

I

GG

T-VII

I V-VI

L-VII

DR

JB

M-VII SV

SMF

Gn IV

SS

10.2 Anatomy for Lateral Skull Base Surgery: Anatomy and Exploration of the Facial Nerve

I

Fig. 10.46 The whole course of the intramastoid facial nerve.

TT

CT

T-VII

GG L-VII

In this approach the facial nerve is separated from the superior vestibular nerve as it enters the internal auditory canal by a spicule of bone called Bill’s bar. The facial nerve is anterior superior in the internal auditory canal. If the surgeon is planning to transpose the facial nerve, the greater superficial petrosal nerve must be cut anterior to the geniculate ganglia. (bCo, basal turn of the cochlea; CN, cochlear nerve; CT, chorda tympani; GG, geniculate ganglion; Gn, genu [second turn or external genu] of the facial nerve; I, incus; IV, inferior vestibular nerve; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; Mo, modiolus; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; TT, temporal tegmen; V-VII, vertical segment of the facial nerve)

M-V

CN

II

GSPN

Gn

bCo

Mo

SV

IV

M

C6

TMm

I

CT C7

GG

intramastoid facial nerve.

G

Co

JB CA

M-V

PSC

II

SPS

ES SS

V3 dPN

internal auditory canal.

The facial nerve and superior vestibular nerves are seen exiting the fundus of the internal auditory canal separated by Bill’s bar. The surgeon can see how the fundus of the canal is wedged between the cochlea and the superior semicircular canal. The labyrinthine segment of the facial nerve joins the greater superficial petrosal nerve at the geniculate ganglion, making a sharp turn posteriorly. (AE, arcuate eminence; C6, C6 portion of the internal cerebral artery; Co, cochlea; dPN, deep petrosal nerve; GG, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

II V-V

R

SSC

(C6, C6 portion of the internal cerebral artery; C7, C7 portion of the internal cerebral artery; CA, cochlear aqueduct; Co, cochlea; CT, chorda tympani; ES, emdolymphatic sac; G, galea aponeurotica; GG, geniculate ganglion; GSPN, greater superficial petrosal nerve; I, incus; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; LSC, lateral semicircular canal; M, malleus; M-VII, meatal segment of the facial nerve; P, parotid gland; PSC, posterior semicircular canal; R, round window; S, stapes; SPS, superior petrosal sinus; SS, sigmoid sinus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; TMm, tympanic membrane; V-VII, vertical segment of the facial nerve)

Fig. 10.48 The facial nerve at the fundus of the

P

I

LSC

Fig. 10.47 Diagram of the whole course of the

I

S

I T-V

LVI

I V-VI

GSPN

T-VII GG

C6

L-VII

SV

Co AE IAC

163

III Lateral Skull Base

T-VII FB

GG Fig. 10.49 Magnified view of Fig. 10.48. The surgeon can see the difficulty in dislodging the geniculate ganglion from its bony canal when attempting a translocation of the facial nerve. (AE, arcuate eminence; BB, buccal branch of the facial nerve; Co, cochlea; FB, Fukushima's bar (geniculate notch); GG, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

L-VII

GSPN

Co

(C6, C6 portion of the internal cerebral artery; C7, C7 portion of the internal cerebral artery; Co, cochlea; CT, chorda tympani; G, galea aponeurotica; GG, geniculate ganglion; I, incus; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; LSC, lateral semicircular canal; M, malleus; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

M

AE

V-VII

CT

C6

SV

IAC

C7

Fig. 10.50 Semicircular canals as seen from the middle fossa.

BB

G

I

LSC

T-VII GG L-VII SV

Co IAC

PSC

SSC

TMJ

CT

CT

The chorda tympani enters the middle ear posteriorly through the posterior canaliculus and passes medial to the handle of the malleus to exit through the anterior canaliculus. (CP, cochleariform process; CT, chorda tympani; ET, eustachian tube; GG, geniculate ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; TMJ, temporomandibular joint)

CT

I M

ET

CP

LSC

I

Fig. 10.51 The chorda tympani in the middle ear.

TVI

164

GSPN

GG

SSC IAC

10.2 Anatomy for Lateral Skull Base Surgery: Anatomy of the Facial Nerve

TMJ

CT CT

I

ET

M

Fig. 10.52 (Step ) he superior petrosal

CP

segment.

Fig. 10.53

middle fossa.

er ie

TVI

I

The chorda tympani runs medial to the temporomandibular joint along the petrotympanic ssure to exit just medial to the spine of the sphenoid bone. (CP, cochleariform process; CT, chorda tympani; ET, eustachian tube; , geniculate ganglion; SPN, greater super cial petrosal nerve; I, incus; M, malleus; T-VII, tympanic segment of the facial nerve; TMJ, temporomandibular joint)

GG

GSPN

of the facial ner e from the

The whole course of the chorda tympani is seen. (C , C portion of the internal cerebral artery; Co, cochlea; CT, chorda tympani; ET, eustachian tube; , galea aponeurotica; , geniculate ganglion; SPN, greater super cial petrosal nerve; I, incus; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; LSC, lateral semicircular canal; M, malleus; PSC, posterior semicircular canal; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; V-VII, vertical segment of the facial nerve; V , mandibular nerve third division of the trigeminal nerve )

LN

IAN

TMJ

Fig. 10.54

iagram of the facial ner e as seen through the middle fossa. (C , C portion of the internal cerebral artery; C , C portion of the internal cerebral artery; Co, cochlea; CT, chorda tympani; ET, eustachian tube; , galea aponeurotica; , geniculate ganglion; SPN, greater super cial petrosal nerve; I, incus; IAC, internal auditory canal; IAN, inferior alveolar nerve; IPS, inferior petrosal sinus; L-VII, labyrinthine segment of the facial nerve; LN, lingual nerve; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; PSC, posterior semicircular canal; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; V-VII, vertical segment of the facial nerve; V , mandibular nerve third division of the trigeminal nerve ; VI, abducens nerve)

V-VII

CT

V3

s

MMA M

ET

II T-V

TTM

C'7 C6

GSPN

IPS VI

GG

CO

L-V I

G

I

LSC PSC

I

SV

IAC

SSC

165

11

Preauricular Transzygomatic Approach to the Anterior Infratemporal Fossa and Middle Infratemporal Fossa

The preauricular transzygomatic anterior infratemporal fossa approach affords the surgeon access to the infratemporal and pterygoid fossae through the middle fossa. This is particularly useful for treating tumors involving the bones at the base of the middle fossa, such as trigeminal schwannomas with an extracranial component, maxillary tumors, nasopharyngeal carcinomas, meningiomas with infratemporal invasion, juvenile nasopharyngeal angiofibromas, and chondroblastomas. The preauricular transzygomatic middle infratemporal fossa approach affords the surgeon access to the retropharyngeal space, middle and lower clivus, and anterior arch of the atlas. The main corridor of this approach is between V3 and the styloid process. This approach provides access to the lesions of clivus and the infratemporal internal carotid artery from a superiolateral approach. A condylectomy can result in postoperative ankylosis, and should be avoided if possible.

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach Key Steps Position: Supine with head rotated 60 degrees to the opposite side or lateral Step 1. Sickle shaped skin incision (Fig. 11.1) Step 2. Raising the skin flap (Fig. 11.6) Step 3. Performing zygomatic osteotomy (Fig. 11.12) Step 4. Outlining a craniotomy (Fig. 11.18) Step 5. Flattening the floor of the middle fossa (Fig. 11.23) Step 6. Separation of the dura propria (Fig. 11.27) Step 7. Cutting the middle meningeal artery (Fig. 11.28) Step 8. Exposing the vidian canal (Fig. 11.31) Step 9. Unroofing the mandibular and maxillary branches of the trigeminal nerve (Fig. 11.34) Step 10. Removing the pterygoid process (Fig. 11.52) Step 11. Identifying the eustachian tube (Fig. 11.70)

Illustrated Steps with Commentary

Zy

Fig. 11.1 (Step 1) Skin incision. A sickle shaped incision is made beginning 5 mm below the inferior border of the root of the zygomatic arch. A. This incision, the less invasive approach, is in most cases adequate to access the infratemporal fossa and adjacent regions. It preserves the pterygoid muscles. B. This incision, the extended approach, allows the skin flap to be retracted more anteriorly for removal of the lateral and medial pterygoid muscles to access the parapharyngeal region and the nasopharynx. This approach also allows the infratemporal approach to be combined with a transorbital or transcavernous approach. The wider approach allows the trajectory of the surgeon’s vision to pass more inferiorly. (Zy, zygoma)

A B

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

sDTF TPM

Fig. 11.2 Temporoparietal muscle and fascia. The skin, temporoparietal muscle, temporoparietal fascia, and galea are incised, preserving the deep temporal fascia. (sDTF, superflcial layer of the deep temporal fascia; TPM, temporoparietal muscle)

TPM LAT

Fig. 11.3 Auricularis anterior muscle and fascia. Cutting through the temporoparietal fascial over the ear, the surgeon will note a thin muscle that takes origin from the fascia and inserts in front of the helix. This is the auricularis anterior muscle, more commonly called the anterior portion of the temporoparietal muscle. The temporoparietal fascia is separated from the superflcial layer of the deep temporal fascia. (LAT, loose areolar tissue; sDTF, superflcial layer of the deep temporal fascia; TPM, temporoparietal muscle)

sDTF

Fig. 11.4 Deep temporal (interfascial) fat pad. The deep temporal fat pad is seen splitting the temporalis fascia into a deep and a superflcial layer. The yellow fat pad can be seen under the superflcial layer of the temporal fascia. The superflcial layer is contiguous with the superflcial periosteum of the zygoma. The superflcial layer of the temporalis fascia can be separated by raising the periosteum from the origin of the zygomatic process of the frontal or temporal bones. Following this plane over the muscle will separate the superflcial from the deep layer of the fascia. (sDTF, superflcial layer of the deep temporal fascia)

sDTF

167

168

III Lateral Skull Base

dDTF IFF

Fig. 11.5 An incision is made in the superficial

layer of deep temporal fascia to expose the deep temporal fat pad.

The superflcial layer of the temporal fascia is separated from the deep layer and the superflcial layer is raised along with the scalp ap to protect the frontal branch of the facial nerve. (dDTF, deep layer of the deep temporal fascia; IFF, interfascial fat pad; sDTF, superflcial layer of the deep temporal fascia)

sDTF

dDTF

sDTF

Fig. 11.6 (Step 2) Raising skin ap. The skin ap is raised with the superflcial layer of deep temporal fascia and deep temporal fat pad to protect the frontal branch of facial nerve. The deep layer is left attached to the muscle. (dDTF, deep layer of the deep temporal fascia; sDTF, superflcial layer of the deep temporal fascia)

Zy dDTF Fig. 11.7 Exposing the lateral orbital rim and zygomatic arch.

The superflcial layer of the temporalis fascia is raised along with the contiguous periosteum of the zygomatic process of the frontal bone and the zygomatic arch. (dDTF, deep layer of the deep temporal fascia; sDTF, superflcial layer of the deep temporal fascia; Zy, zygoma)

sDTF

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

Zy

dDTF sDTF PO

Fig. 11.8 Vascularized pericranial fiap. The vascularized pericranial flap can be used to seal off an opening into a lateral extension of the frontal sinus should that sinus be opened. (dDTF, deep layer of the deep temporal fascia; PO, periosteum; sDTF, super cial layer of the deep temporal fascia; Zy, zygoma)

PO

Fig. 11.9 Elongated pericranial fiap. The pericranial flap can be made quite large by raising the surrounding skin through the subgaleal plane. The flap can be elongated with a back cut so as to reach openings in the skull base. A well-developed sphenoid sinus may be opened when drilling through the bone anterior to the lateral loop of the trigeminal nerve. The eustachian tube may be opened when drilling lateral to the intrapetrous segment of the carotid artery. (PO, periosteum)

Zy

dDTF sDTF Fig. 11.10 Exposure of lateral orbital rim, zygomatic arch, and masseter muscle. Following the plane of the super cial temporal fascia will lead to a subosteal dissection of the zygoma. This dissection plane is continued over the orbital rim. (dDTF, deep layer of the deep temporal fascia; sDTF, super cial layer of the deep temporal fascia; Zy, zygoma)

169

170

III Lateral Skull Base

ZFF

Fig. 11.11 Zygomaticofacial foramen. The zygomaticofacial nerve, one of the two branches of the zygomatic nerve, passes through the zygomaticofacial foramen. Injury to this nerve results in numbness of the scalp lateral to the orbit. (ZFF, zygomaticofacial foramen)

Fig. 11.12 (Step 3) Landmarks for the osteotomy of the zygomatic arch. A limited zygomatic osteotomy allows the temporalis muscle to be raised anteriorly and inferiorly. This allows the surgeon to see parallel to the floor at the pole of the anterior middle fossa with minimal temporal lobe retraction. The posterior osteotomy is made obliquely through the root of the zygoma tangential to the glenoid fossa. The anterior osteotomy is made parallel to the orbit. The osteotomy begins at the marginal tubercle and should avoid the zygomaticofacial foramen. (MP, marginal process)

MP

MP

Fig. 11.13 Freeing the marginal tubercle. The deep layer of the temporal fascia is separated from the undersurface of the zygomatic arch. (MP, marginal process)

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

Fig. 11.14 Detaching the zygomatic arch. Osteotomies through the zygoma free a bone that resembles the bone of a T-bone steak. This bone is referred to as the “T” bone. The anterior cut is made parallel with the bony orbit and the posterior cut is made obliquely, parallel to the zygomatic root. A cut through the maxillary process frees the bone.

Fig. 11.15 Raising the “T” bone The "T" bone cut from the zygomatic arch is reflected inferiorly and left attached to the masseteric muscle. Leaving the bone attached to the masseteric muscle diminishes postoperative pain and provides the bone with a blood supply.

TM Fig. 11.16 Inferior refiection of the temporalis

muscle.

The muscle is reflected through the opening created by the osteotomy. The muscle remains attached to its insertion onto the mandible. The muscle belly is not cut. The temporalis muscle is simply detached from the lateral skull. Care is taken not to injure the innervation and vasculature that lies on the undersurface of the muscle. Thus we raise the muscle with a sharp elevator and minimize cautery to the undersurface of the muscle. Oblique holes are drilled along the temporal line to reattach the muscle at the end of the case. (TM, temporalis muscle)

171

172

III Lateral Skull Base

TM

Fig. 11.17 Deep temporal arteries and nerve. The deep temporal arteries and nerve that supply vasculature and innervation to the temporalis muscle are seen on the undersurface of the muscle. Damage to these structures can result in atrophy of the temporalis muscle. (aDTA, anterior deep temporal artery; pDTA, posterior deep temporal artery; TM, temporalis muscle)

aDTA

pDTA

TD Fig. 11.18 (Step 4) Orbitotemporal detachment

(beginning of a “golf-club” drilling).

A hole is made in the greater wing of the sphenoid bone parallel to the roof of the orbit exposing the temporal and frontal dura with a coarse or extra coarse diamond drill,. The site of this hole is located at the depression between the middle and anterior fossa. Removing this bone exposes the lateral orbital wall and the frontal and temporal dura. This hole resembles the head of a golf club. This hole allows the surgeon to separate the frontal and temporal dura from the bone flap. It is dif cult to cut through the greater wing of the sphenoid with a craniotome. (FD, frontal dura; LOW, lateral orbital wall; TD, temporal dura)

LOW

FD

LOW TD

Fig. 11.19 Identification of the anterior division of the middle meningeal artery. The anterior division of the middle meningeal artery is seen passing under the greater wing of the sphenoid. (FD, frontal dura; LOW, lateral orbital wall; TD, temporal dura)

FD

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

Shaft Fig. 11.20 Subtemporal groove drilling (completion of the “golf-club” drilling). Beginning at the hole made in the lateral greater wing of the sphenoid bone, a groove is drilled through the lateral wall and floor of the middle fossa. By drilling this groove the surgeon is able to reach the margins of the middle fossa, which cannot be easily reached with a craniotome. The shape of the keyhole (a head) and this subtemporal groove (a shaft) resembles a bent golf club.

Fig. 11.21 Frontotemporal craniotomy. A frontotemporal craniotomy is turned using a craniotome connecting the two ends of the “golf club.” Additional bur holes are made if the dura is tenaciously adherent to the bone.

Fig. 11.22 Refiecting the craniotomy. The root of the zygoma will serve as a guide to the middle fossa. The anterior margin of the root of the zygoma is directly lateral to the foramen ovale; the midpoint of the root of the zygoma is lateral to the foramen spinosum; the posterior root is lateral to the geniculate ganglion (see Figs. 12.10 and 12.11).

Club Head

173

174

III Lateral Skull Base

MSR Fig. 11.23 (Step 5) Bony protrusion of temporal base (landmark for the lateral loop). Characteristically a bony protrusion is found lateral to the lateral loop of the trigeminal nerve. This protrusion should be burred flat. Furthermore, the bony ridges coming from the floor of the middle fossa should be removed with a diamond drill so as not to obstruct the surgeon’s line of sight. (MSR, mid-subtemporal ridge)

MSR V2

Fig. 11.24 Foramen rotundum (V2). The foramen rotundum is seen anterior to the tip of the temporal dura and just lateral to the inferior end of the superior orbital ssure. (MSR, mid-subtemporal ridge; V2, maxillary nerve [second division of the trigeminal nerve])

MMA

Fig. 11.25 Middle meningeal artery. The middle meningeal artery can be followed to the foramen spinosum. (MMA, middle meningeal artery)

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

MMA

Fig. 11.26 Foramina ovale (V3) and spinosum

V3

(MMA).

The foramen spinosum is frequently hidden under the protuberance of bone. It is found below the midzygomatic root. This foramen can always be localized by following the middle meningeal artery inferiorly along the dura. The foramen ovale lies anterior and medial to the foramen spinosum. (MMA, middle meningeal artery; V3, mandibular nerve [third division of the trigeminal nerve])

Fig. 11.27 (Step 6) Lateral loop formed by the

MSR

MMA

maxillary and mandibular nerves.

The dura propria is dissected from the maxillary nerve, the mandibular nerve, and the gasserian ganglion. Lifting the dura that covers the temporal lobe from the dura that covers the maxillary and mandibular nerves reveals the lateral loop, which connects those two nerves. Numerous veins connecting the pterygoid venous plexus and the cavernous sinus pass along those nerves. Venous bleeding is controlled by pushing hemostatic oxidized cellulose into the venous channels. Coagulation is limited to avoid facial paresthesia. (MMA, middle meningeal artery; MSR, mid-subtemporal ridge; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

V2

MMA

Fig. 11.28 (Step 7) Sacrifice of middle meningeal

artery.

The middle meningeal artery is ligated to allow the dura over the temporal lobe to be mobilized from the floor of the middle fossa. (MMA, middle meningeal artery; V3, mandibular nerve [third division of the trigeminal nerve])

V3

175

176

III Lateral Skull Base

MMA

MSR LL V2

V3

Fig. 11.29 Elevating the dura propria. The dura propria is elevated from the lateral loop of the trigeminal nerve. (MMA, middle meningeal artery; MSR, mid-subtemporal ridge; LL, lateral loop; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

FO Fig. 11.30 Skeletonizing the foramen rotundum

and ovale.

This maneuver frees the maxillary and mandibular nerves. The foramen rotundum and ovale are enlarged following the maxillary and mandibular nerves through the skull. These nerves appear to be coming up toward the surgeon as the canal is elongated. Drilling through the lateral loop leads to the pterygoid process of the sphenoid bone. Care should be taken not to enter the sphenoid sinus when drilling along the maxillary nerve. (FO, foramen ovale; FR, foramen rotundum; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

FR V2

FO VC Fig. 11.31 (Step 8) Vidian canal (in the case of a

poorly developed sphenoid sinus).

The vidian canal is found by drilling into the bone outlined by the lateral loop. The vidian canal is seen inferior to the maxillary nerve. It passes through the body of the sphenoid bone superior to the medial and lateral pterygoid plate. It passes into the pterygopalatine space. If the sphenoid sinus is well developed, drilling toward the vidian canal can open the sphenoid sinus. (FO, foramen ovale; FR, foramen rotundum; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VC, vidian canal)

FR

V3 V2

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

FO

VC Fig. 11.32 Vidian canal (in the case of a moderately developed sphenoid sinus). When the sphenoid sinus is better developed, the vidian canal is pushed laterally. (FO, foramen ovale; FR, foramen rotundum; V2, maxillary nerve [second division of the trigeminal nerve]; VC, vidian canal)

FR

V2

V3

Fig. 11.33 Vidian canal after shrinkage of

sphenoid sinus mucosa (in the case of a welldeveloped sphenoid sinus). The mucosa of the sphenoid sinus is seen below the maxillary nerve in this picture. The vidian canal is obscured by the redundant sphenoid mucosa. The canal travels lateral to the sphenoid sinus to enter the pterygopalatine fossa. The internal maxillary artery terminates in the pterygopalatine fossa. The nerve of the vidian canal innervates the pterygopalatine ganglion and communicates with branches of the maxillary nerve in that fossa. (mSS, mucosa of the sphenoid sinus; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VC, vidian canal)

VC

V2

mSS

PPF Fig. 11.34 (Step 9) Unroofing the foramen

rotundum.

The foramen rotundum is unroofed following the maxillary nerve to the pterygopalatine fossa. Medial to the maxillary nerve we see the confluence of the superior and inferior ophthalmic veins as they enter the cavernous sinus. (FR, foramen rotundum; PPF, pterygopalatine fossa; V2, maxillary nerve [second division of the trigeminal nerve]; VN, vidian nerve)

VN

FR V2

177

178

III Lateral Skull Base

MMA

FO V3 V2

Fig. 11.35 Unroofing the foramen ovale. The foramen ovale is unroofed following V3 into the infratemporal fossa. (FO, foramen ovale; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

VC

V3

mSS FOEV Fig. 11.36 Foramen ovale emissary vein. Several veins are found traveling along the mandibular nerve through the foramen ovale. These veins connect the rich pterygoid venous system with the cavernous sinus. Bleeding from these veins can usually be controlled by packing their lumen with hemostatic agents, then patiently applying gentle pressure. (FOEV, foramen ovale emissary vein; mSS, mucosa of the sphenoid sinus; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VC, vidian canal)

V2

PPF

VN

FO

FR Fig. 11.37 Unroofing the vidian canal. The vidian canal and the maxillary nerve are followed distally into the pterygopalatine flssure. (FO, foramen ovale; FR, foramen rotundum; PPF, pterygopalatine fossa; V2, maxillary nerve [second division of the trigeminal nerve]; VN, vidian nerve)

V2

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

sLPM IO N

Fig. 11.38 Exposing the distal branches of the maxillary and mandibular nerves.

V3

The maxillary nerve is followed distally into the pterygopalatine fossa and the mandibular nerve is followed distally into the infratemporal fossa. The vidian nerve is seen just below the maxillary nerve. This specimen had a poorly developed sphenoid sinus. (ION, infraorbital nerve; sLPM, superior head of the lateral pterygoid muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2

DTN MN

sLPM Fig. 11.39 Exposing the branches of the mandibular nerve without removing the lateral pterygoid muscle.

ATN

BN

The mandibular nerve divides into an anterior and a posterior trunk. The anterior trunk supplies most of the motor branches of the mandibular nerve plus the buccal nerve (the only sensory nerve from this trunk, which provides sensation to the inner and outer cheeks. The posterior trunk supplies most of the sensory branches plus the mylohyoid nerve, the only motor branch of that trunk. (AT(V3), anterior trunk of the mandibular nerve; ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; MN, masseteric nerve; sLPM, superior head of the lateral pterygoid muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

AT(V3) V3 V2

MN DTN

Fig. 11.40 Beginning of the cartilaginous portion of the eustachian tube medial to the foramen spinosum. Drilling medial to the foramen spinosum and posterior to the foramen ovale and preserving the temporomandibular joint, the surgeon will encounter the eustachian tube. The carotid artery, which travels medial to the eustachian tube, turns medially toward the cavernous sinus under the lateral loop. (ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; MN, masseteric nerve; V3, mandibular nerve [third division of the trigeminal nerve])

ATN

BN

ET

V3

179

180

III Lateral Skull Base

sLPM DTN

N AT

BN

ET V3 Fig. 11.41 Exposing the middle part of the cartilaginous eustachian tube. The cartilaginous portion of the eustachian tube is seen medial to the mandibular nerve under the lateral loop. (ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; sLPM, superior head of the lateral pterygoid muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2

sLPM IO

BN

N

Fig. 11.42 Exposing the branches of the maxillary and mandibular nerves. The maxillary and mandibular nerves are followed until they branch within the pterygopalatine flssure and infratemporal fossa, respectively. (ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ION, infraorbital nerve; MN, masseteric nerve; sLPM, superior head of the lateral pterygoid muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; ZN, zygomatic nerve)

Fig. 11.43 Identifying the branches of the maxillary nerve. The zygomatic branch, which enters the infraorbital flssure to innervate the temporal area behind the zygomaticofrontal process via in the zygomaticotemporal and zygomaticofacial nerves, branches off the maxillary nerve. The posterior superior alveolar nerve, which innervates the maxillary sinus and the molar teeth, branches from the maxillary nerve in the pterygopalatine fossa and runs in a slightly curved “S” shape toward the infraorbital sulcus or canal. The infraorbital nerve enters the inferior orbital flssure. (ION, infraorbital nerve; V2, maxillary nerve [second division of the trigeminal nerve]; ZN, zygomatic nerve)

DTN MN N AT

V3 ZN

V2

ION

ZN

V2

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

GPN & LPN

PPG Fig. 11.44 Identifying the nerves in the

pterygopalatine fossa.

ION

The pterygopalatine ganglion receives parasympathetic innervation from the vidian nerve and provides postganglionic flbers to the lacrimal gland and nasal mucosa. It is seen on the undersurface of V2. (GPN, greater palatine nerve; ION, infraorbital nerve; LPN, lesser palatine nerve; PPG, pterygopalatine ganglion; V2, maxillary nerve [second division of the trigeminal nerve]; ZN, zygomatic nerve)

V2

ZN

GPN & LPN

Fig. 11.45 Demonstrating the greater and lesser palatine nerves. The greater and lesser palatine nerves pass through the pterygopalatine ganglion to innervate the hard palate, adjacent gums, soft palate, and uvula. (GPN, greater palatine nerve; ION, infraorbital nerve; LPN, lesser palatine nerve; PPG, pterygopalatine ganglion; V2, maxillary nerve [second division of the trigeminal nerve]; VN, vidian nerve)

IO

N

PPG

VN

V2

AFR

ION

IOA Fig. 11.46 Artery of the foramen rotundum. The artery of the foramen rotundum is a branch of the internal maxillary artery. This artery may be an important blood supply for meningiomas of the middle fossa. (AFR, artery of the foramen rotundum; IOA, infraorbital artery; ION, infraorbital nerve; V2, maxillary nerve [second division of the trigeminal nerve]; ZN, zygomatic nerve)

ZN

V2

181

182

III Lateral Skull Base

IOA

ION

V2

ZN

Fig. 11.47 Identifying the branches of the

maxillary nerve.

The posterior inferior nasal branches leave the pterygopalatine ganglion and pass through the palatine bone to innervate the inferior nasal concha. (IOA, infraorbital artery; ION, infraorbital nerve; V2, maxillary nerve [second division of the trigeminal nerve]; ZN, zygomatic nerve)

ION

ZN Fig. 11.48 Identifying the branches of the maxillary nerve.

VN

PPG

NPN

A closeup view reveals branches of the maxillary nerve that innervate the pharynx and the nasal mucosa, the posterior nasal branches, the pharyngeal branches, and the pterygopalatine ganglion. (ION, infraorbital nerve; NPN, nasopalatine nerve; PPG, pterygopalatine ganglion; V2, maxillary nerve [second division of the trigeminal nerve]; VN, vidian nerve; ZN, zygomatic nerve)

GPN & LPN IO

N

PPG

ZN Fig. 11.49 Identifying the branches of the maxillary nerve. An overview of the maxillary nerve demonstrates the vidian nerve innervating the pterygopalatine ganglion, the greater and lesser palatine nerves, and posterior nasal branches. (GPN, greater palatine nerve; ION, infraorbital nerve; LPN, lesser palatine nerve; NPN, nasopalatine nerve; PPG, pterygopalatine ganglion; V2, maxillary nerve [second division of the trigeminal nerve]; VN, vidian nerve; ZN, zygomatic nerve)

NPN

VN V2

V2

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

DTN & MN

sLPM

Fig. 11.50 Identifying the branches. A closeup view of the mandibular nerve demonstrates the anterior and posterior divisions. The deep temporal, masseteric, buccal, lateral pterygoid, auriculotemporal, inferior alveolar, and lingual nerves are deflned. The nerve to the masseter passes over the lateral pterygoid muscle to innervate the masseter through the mandibular notch. The deep temporal nerve takes a similar course. The lateral pterygoid nerve enters the deep surface of that muscle. The buccal nerve passes between the superior and inferior heads of the lateral pterygoid muscle. The auriculotemporal nerve runs deep to the lateral pterygoid muscle and exits posterior to the mandible. Similarly, the lingual and the inferior alveolar nerves run deep to the lateral pterygoid and lateral to the medial pterygoid muscles. (AT(V3), anterior trunk of the mandibular nerve; ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; MN, masseteric nerve; NLPM, nerve to the lateral pterygoid muscle; sLPM, superior head of the lateral pterygoid muscle; TMJ, temporomandibular joint)

TMJ AT N

NLPM BN

ET

AT(V3)

sLPM

LN

TMJ N AT

& MN

Looking inferiorly we see the auriculotemporal, inferior alveolar, and lingual nerves. (AT(V3), anterior trunk of the mandibular nerve; ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; IAN, inferior alveolar nerve; LN, lingual nerve; MN, masseteric nerve; sLPM, superior head of the lateral pterygoid muscle; TMJ, temporomandibular joint)

N DT

Fig. 11.51 Identifying the branches of the mandibular nerve.

BN

IAN

ET

AT(V3)

sLPM BN LPP MPP Fig. 11.52 (Step 10) Lateral and medial laminae of pterygoid process. Drilling into the pterygoid process, we can see the lateral and medial wings of the pterygoid process. (BN, buccal nerve; LPP, lateral lamina of the pterygoid plate; MPP, medial lamina of the pterygoid plate; (sLPM, superior head of the lateral pterygoid muscle; (V2, maxillary nerve [second division of the trigeminal nerve])

V2

183

III Lateral Skull Base

Fig. 11.53 Superior head of lateral pterygoid

MN

sLPM

MA

DTN &

184

BN

muscle.

The superior head of the lateral pterygoid muscle originates from the inferior lateral greater wing of the sphenoid bone and adjacent posterior maxilla. It inserts into the medial neck of the condyle of the mandible. (ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; MA, maxillary artery; MN, masseteric nerve; sLPM, superior head of the lateral pterygoid muscle; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve])

TMJ

ATN

ET V3

NLPM

sLPM iLPM

BN Fig. 11.54 Branching of the mandibular nerve. The buccal nerve is seen in the interval between the superior and inferior heads of the lateral pterygoid muscle. The inferior head originates from the lateral surface of the lateral pterygoid plate and inserts into the neck of the mandible. (BN, buccal nerve; iLPM, inferior head of the lateral pterygoid muscle; NLPM, nerve to the lateral pterygoid muscle; sLPM, superior head of the lateral pterygoid muscle; V3, mandibular nerve [third division of the trigeminal nerve])

V3

DTN & MN NLPM Fig. 11.55 Detaching the superior head of the

lateral pterygoid muscle.

The superior head of the lateral pterygoid muscle is detached from the greater wing of the sphenoid bone to provide a better view of the buccal nerve heading toward the buccinator. It mediates sensation of the mucosal surface of the cheek. (BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; iLPM, inferior head of the lateral pterygoid muscle; MA, maxillary artery; MN, masseteric nerve; NLPM, nerve to the lateral pterygoid muscle; sLPM, superior head of the lateral pterygoid muscle; TMJ, temporomandibular joint; V2, maxillary nerve [second division of the trigeminal nerve])

iLPM

MA

TMJ

BN ET sLPM V2

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

MPM LPP

MA

LN

BN

Fig. 11.56 Identifying the lateral lamina of pterygoid process, medial pterygoid muscle, and maxillary artery.

IO

The superior and inferior heads of the lateral pterygoid muscles have been removed to demonstrate the medial and lateral plates of the pterygoid process and the internal maxillary artery. (BN, buccal nerve; ION, infraorbital nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid plate; MA, maxillary artery; MPM, medial pterygoid muscle; MPP, medial lamina of the pterygoid plate; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

MPP N

V3 V2

MPM MA

Fig. 11.57 Maxillary artery and mandibular nerve

branches.

Looking inferiorly we see the inferior alveolar nerve and the lingual nerve. (BN, buccal nerve; ET, eustachian tube; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid plate; MA, maxillary artery; MPM, medial pterygoid muscle; MPP, medial lamina of the pterygoid plate; V3, mandibular nerve [third division of the trigeminal nerve])

LPP

LN

ET

BN

MPP

V3

MA

CT IAN LN

Fig. 11.58 Identifing the chorda tympani joining the lingual nerve. The chorda tympani, which has exited the skull adjacent to the spine of the sphenoid bone, is seen joining the lingual nerve. CT, chorda tympani; IAN, inferior alveolar nerve; LN, lingual nerve; MA, maxillary artery)

IAN

185

III Lateral Skull Base

LN

IAN

MA CT

Fig. 11.59 Chorda tympani joining the lingual

nerve.

The chorda tympani runs medial to the inferior alveolar nerve. (CT, chorda tympani; IAN, inferior alveolar nerve; LN, lingual nerve; MA, maxillary artery)

IAN

LN DTN & MN

Fig. 11.60 The otic ganglion.

N AT OG

MMA

ET

BN

The otic ganglia receives innervation from the lesser petrosal nerve (branch of cranial nerve IX) and supplies parasympathetic innervation to the parotid gland via the auriculotemporal nerve. (AT(V3), anterior trunk of the mandibular nerve; ATN, auriculotemporal nerve; BN, buccal nerve; DTN, deep temporal nerve; ET, eustachian tube; IAN, inferior alveolar nerve; LN, lingual nerve; MMA, middle meningeal artery; MN, masseteric nerve; OG, otic ganglion)

AT(V3)

MA LN

IAN

AT N

186

BN

NMPM

Fig. 11.61 The medial pterygoid nerve. The medial pterygoid nerve branches very proximally off the main trunk of the mandibular nerve. It innervates the tensor velli palatini and tensor tympani muscles. (AT(V3), anterior trunk of the mandibular nerve; ATN, auriculotemporal nerve; BN, buccal nerve; IAN, inferior alveolar nerve; LN, lingual nerve; MA, maxillary artery; NMPM, nerve to the medial pterygoid muscle)

AT(V3)

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

MPM LPP

LN

MA BN

Fig. 11.62 Lateral loop, maxillary and mandibular

nerve branches, and maxillary artery.

ET

Branches of the mandibular nerve and adjacent structures in the infratemporal fossa are shown. (BN, buccal nerve; ET, eustachian tube; LN, lingual nerve; LPP, lateral lamina of the pterygoid plate; MA, maxillary artery; MPM, medial pterygoid muscle; PBF, pharyngobasilar fascia; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

PBF V2 NMPM LN

MPM

IAN

LPP Fig. 11.63 Removing the maxillary artery and

exposing the tensor velli palatine.

The tensor velli palatini muscle lies medial to the medial pterygoid muscle. It originates from the upper medial pterygoid plate and spine of the sphenoid bone. (AT(V3), anterior trunk of the mandibular nerve; BN, buccal nerve; ET, eustachian tube; IAN, inferior alveolar nerve; LN, lingual nerve; LPP, lateral lamina of the pterygoid plate; MPM, medial pterygoid muscle; NMPM, nerve to the medial pterygoid muscle; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve])

TVPM

BN

ET PBF V2

MPM

Fig. 11.64 Removing the lateral lamina of the pterygoid process. Removing the lateral plate of the pterygoid process demonstrates the deep head of the medial pterygoid muscle, which originates from the medial surface of the lateral pterygoid plate, and the origin of the tensor velli palatini muscle from the base of the pterygoid plate. (ET, eustachian tube; LN, lingual nerve; MPM, medial pterygoid muscle; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

AT(V3)

LN

TVPM ET PBF V2

V3

187

188

III Lateral Skull Base

TVPM Fig. 11.65 Partially removing the medial pterygoid muscle.

MPP ET

Partially removing the medial pterygoid muscle exposes the medial lamina of the pterygoid process and the tensor velli palatini muscle. The eustachian tube enters the pharynx adjacent to that muscle. (ET, eustachian tube; MPP, medial lamina of the pterygoid plate; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

PBF V2

TVPM MPP V3

Fig. 11.66 Medial lamina of pterygoid process.

IO N

The medial lamina of the pterygoid process is dissected from the eustachian tube. (ION, infraorbital nerve; MPP, medial lamina of the pterygoid plate; TVPM, tensor velli palatini muscle; V3, mandibular nerve [third division of the trigeminal nerve])

TVPM ET

Fig. 11.67 Removing the medial lamina of the pterygoid process. Removing the medial lamina of the pterygoid process exposes the cartilaginous portion of the eustachian tube and its entrance into the nasopharynx. (ET, eustachian tube; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3 PBF V2

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

TVPM ET

Fig. 11.68 (Step 11) Direction of eustachian tube. The cartilaginous portion of the eustachian tube originates at the junction between the squamous and petrous portions of the temporal bone and ends in the nasal portion of the pharynx under the tensor velli palatini muscle. (ET, eustachian tube; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3 PBF V2

TVPM

ET Fig. 11.69 The eustachian tube and the tensor velli palatini muscle. The eustachian tube enters the pharynx under the tensor velli palatini muscle. (ET, eustachian tube; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

PBF V2

TVPM ET Fig. 11.70 (Step 11) Posterior translocation of V3. The tensor velli palatini muscle and the cartilaginous portion of the eustachian tube are exposed after the mandibular nerve is posteriorly translocated. (ET, eustachian tube; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle)

PBF

189

190

III Lateral Skull Base

TVPM ET Fig. 11.71 Beginning removal of the tensor velli palatini muscle.

PBF

The tensor velli palatini is removed in a stepwise fashion. (ET, eustachian tube; PBF, pharyngobasilar fascia; TVPM, tensor velli palatini muscle)

SPCM LVPM

ET Fig. 11.72 Removing the tensor velli palatini

muscle.

This exposes the eustachian tube and the superior constrictor of the pharynx. (ET, eustachian tube; LVPM, levator velli palatini muscle; PBF, pharyngobasilar fascia; SPCM, superior pharyngeal constrictor muscle)

PBF

LVPM

Fig. 11.73 The levator velli palatini muscle. The levator velli palatini muscle originates from the petrous portion of the temporal bone and passes deep into the entrance of the eustachian tube into the pharynx. (ET, eustachian tube; LVPM, levator velli palatini muscle)

ET

11.1 Preauricular Transzygomatic Anterior Infratemporal Fossa Approach

SPCM LVPM

NP

ET Fig. 11.74 Opening the eustachian tube into the nasopharynx.

PBF

The eustachian tube is opened so that the anatomical relationship of the nasopharynx and the infratemporal fossa can be demonstrated. (ET, eustachian tube; LVPM, levator velli palatini muscle; NP, nasopharynx; PBF, pharyngobasilar fascia; SPCM, superior pharyngeal constrictor muscle)

SPCM LVPM

NP

ET Fig. 11.75 Direction of the eustachian tube. The dissector is inserted so that a course of the eustachian tube is indicated. (ET, eustachian tube; LVPM, levator velli palatini muscle; NP, nasopharynx; PBF, pharyngobasilar fascia; SPCM, superior pharyngeal constrictor muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V3

PBF V2

PH SPCM Fig. 11.76 The pterygoid hamulus. The pterygoid hamulus serves as a pulley for the tendon of the tensor velli palatini muscle. (ET, eustachian tube; NP, nasopharynx; PH, pterygoid hamulus; SPCM, superior pharyngeal constrictor muscle)

NP ET

191

192

III Lateral Skull Base

TM

SPCM NP

LOW

ET

PBF V2

V3

Fig. 11.77 Exposing the infratemporal and pterygoid fossae. The infratemporal and pterygoid fossae are completely exposed. (ET, eustachian tube; LOW, lateral orbital wall; NP, nasopharynx; PBF, pharyngobasilar fascia; SPCM, superior pharyngeal constrictor muscle; TM, temporalis muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

MT MS

NP

Fig. 11.78 The maxillary sinus.

ET

IO

A bony opening on the opposite side of the pterygopalatine flssure takes the surgeon into the maxillary sinus. (ET, eustachian tube; ION, infraorbital nerve; MS, maxillary sinus; MT, maxillary tuberosity; NP, nasopharynx; PBF, pharyngobasilar fascia; V3, mandibular nerve [third division of the trigeminal nerve])

N PBF

MT

SPCM LVPM

MS NP

ET

Fig. 11.79 Magnified view of the anterior infratemporal fossa approach.

V3

IO N

Magnifled view of the infratemporal fossa and adjacent structures. (ET, eustachian tube; ION, infraorbital nerve; LVPM, levator velli palatini muscle; MS, maxillary sinus; MT, maxillary tuberosity; NP, nasopharynx; PBF, pharyngobasilar fascia; SPCM, superior pharyngeal constrictor muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

PBF V2

V3

11.1 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

TM

ITF

MS

SPCM

PBF

fossa approach.

The flnal view of the anterior infratemporal fossa approach exposes the infratemporal and pterygoid fossae. (ET, eustachian tube; ION, infraorbital nerve; ITF, infratemporal fossa; LOW, lateral orbital wall; MS, maxillary sinus; NP, nasopharynx; PBF, pharyngobasilar fascia; PPF, pterygopalatine fossa; SPCM, superior pharyngeal constrictor muscle; TM, temporalis muscle; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

NP

ION

Fig. 11.80 Final view of the anterior infratemporal

LOW

ET

V3

V2

PPF

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach Key Steps Position: Lateral position Step 1. Skin incision: sickle shaped (Fig. 11.81) Step 2. Zygomatic osteotomy (Fig. 11.84) Step 3. Anteroinferior refiection of temporalis muscle (Fig. 11.86) Step 4. Temporal craniotomy (Fig. 11.87) Step 5. Drilling of the base of the middle fossa with exposure of the mandibular nerve (V3) (Fig. 11.90) Step 6. Exposure of C6 (horizontal portion) of ICA by opening Glasscock’s triangle (Fig. 11.93) Step 7. Condylectomy (Fig. 11.96) Step 8. Identiflcation of vaginal plate and styloid diaphragm in the retrocondylar pouch and anterior translocation of V3 (Fig. 11.103) Step 9. Identiflcation of styloid and glossopharyngeal nerve (muscles) (Figs. 11.106 and 11.107) A. Stylohyoid muscle (Fig. 11.106) B. Glossopharyngeal nerve and carotid sheath (Fig. 11.107) Step 10. Exposure of high cervical portion of ICA (Fig. 11.109) Step 11. Identiflcation of longus capitis muscle on clivus (Fig. 11.110) Step 12. Exposure of high cervical, C7 (vertical) and C6 (horizontal) carotid artery (Fig. 11.112) Step 13. Exposure of clivus with or without anterior translocation of ICA (Fig. 11.114) Step 14. Identiflcation of rectus capitis anterior muscle, anterior atlantoaxial membrane and anterior arch of C1 (Fig. 11.117)

193

194

III Lateral Skull Base

Illustrated Steps with Commentary 5 mm

Fig. 11.81 (Step 1) Incising the skin in a sickle shaped fashion. The patient is placed in the lateral position. A sickle shaped skin incision is made extending 5-10 mm below the zygomatic arch.

Zy

dDTF

sDTF Fig. 11.82 Splitting the deep temporal fascia to expose its deep layer and zygomatic arch. The superflcial layer of the deep temporal fascia is incised. The superflcial layer of the temporal fascia is continuous with the periosteum covering the zygomatic arch. By raising the periosteum, the surgeon will be able to flnd the plane between the layers of the temporal fascia. (dDTF, deep layer of the deep temporal fascia; sDTF, superflcial layer of the deep temporal fascia; Zy, zygoma)

Zy

Fig. 11.83 Exposing the temporomandibular joint.

The temporomandibular joint is found at the root of the zygoma. (dDTF, deep layer of the deep temporal fascia; sDTF, superflcial layer of the deep temporal fascia; Zy, zygoma)

sDTF

dDTF

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

Zy

Fig. 11.84 (Step 2) Zygomatic osteotomy. An osteotomy of the zygoma is performed between the lateral orbit and the root of the zygoma. This limited osteotomy frees the temporalis muscle, which can then be retracted further anteriorly. The mandibular fossa can be removed with the zygomatic arch. In our hands this often results in postoperative pain. (dDTF, deep layer of the deep temporal fascia; sDTF, super cial layer of the deep temporal fascia; Zy, zygoma)

sDTF

dDTF

Fig. 11.85 Inferior refiection of the zygomatic

arch.

The freed zygoma is reflected inferiorly attached to the masseter muscle. This decreases postoperative pain and provides the osteotomy with a blood supply. (dDTF, deep layer of the deep temporal fascia; sDTF, super cial layer of the deep temporal fascia)

sDTF

dDTF

TM

Fig. 11.86 (Step 3) Anteroinferior refiection of the temporalis muscle. The origin of the temporalis muscle is freed and the muscle is reflected through the gap left by the zygomatic osteotomy. (TM, temporalis muscle)

195

196

III Lateral Skull Base

TD

FD

Fig. 11.87 (Step 4) Temporal craniotomy. The temporal craniotomy is performed in the fashion described in Part I. The lateral wall of the middle fossa is cut with a drill as far anteriorly and inferiorly as is possible. (FD, frontal dura; TD, temporal dura)

Fig. 11.88 Identifying the middle meningeal artery, the mandibular nerve, and the maxillary nerve by elevating the dura mater. The temporal dura is separated from the temporal base, and the bony base is flattened with a diamond drill. The foramen spinosum can be identi ed by tracing the middle meningeal artery inferiorly. That foramen lies deep to the mid-anterior root of the zygoma.

GSPN V3 Fig. 11.89 The mandibular nerve. The middle meningeal artery is divided. The foramen ovale is seen deep and anterior to the foramen spinosum. The dura propria is separated from the mandibular nerve (anteriorly and inferiorly) with a sharp blade. The dissection is continued posteriorly with a sharp dissector. (GSPN, greater super cial petrosal nerve; V3, mandibular nerve [third division of the trigeminal nerve])

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

FO

Fig. 11.90 (Step 5) Drilling of the temporal base

with opening of foramen ovale and exposure of lateral loop formed by V3 and V2.

V3

The foramen ovale is opened with a diamond drill. The vidian nerve is exposed in the body of the sphenoid bone between the mandibular and the maxillary nerves. The sphenoid sinus lies medial to the vidian nerve. (FO, foramen ovale; FR, foramen rotundum; GG, gasserian ganglion; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve)

Vi V2

GG

FR

V3 GG

V2

Fig. 11.91 Identifying the extracranial mandibular nerve. As soon as the mandibular nerve exits from the skull it divides into multiple sensory and motor nerves. (GG, gasserian ganglion; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

TMJ

MMA

FO Fig. 11.92 Defining Glasscock’s triangle. Glasscock’s triangle is deflned by the greater superflcial petrosal nerve medially, a line contiguous with the posterior border of the mandibular nerve, and a line between the foramen spinosum and the arcuate eminence. (FO, foramen ovale; MMA, middle meningeal artery; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve])

V3

197

198

III Lateral Skull Base

TMJ ET

FO

T TM Fig. 11.93 (Step 6) Drilling of Glasscock’s

C6

V3

triangle.

The tensor tympani muscle is seen superflcial to the eustachian tube. These two structures lie lateral to the C6 portion of the carotid artery and medial to the glenoid fossa. The surgeon should be careful drilling medial to the C6-C7 junction of the carotid artery as that is the location of the cochlea. (C6, C6 portion of the internal carotid artery; ET, eustachian tube; FO, foramen ovale; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; V3, mandibular nerve [third division of the trigeminal nerve])

TMJ FO C6

V3

Fig. 11.94 Exposing the C6 horizontal portion of the internal carotid artery. The C6 portion of the carotid artery lies under and slightly medial to the greater superflcial petrosal nerve. (C6, C6 portion of the internal carotid artery; FO, foramen ovale; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve])

CP

Fig. 11.95 Exposing the temporomandibular

joint.

The condylar process of the mandible is seen within the glenoid fossa (mandibular fossa). (CP, condylar process)

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

CP Fig. 11.96 (Step 7) Cutting of condylar process of mandible and root of zygoma. The temporomandibular joint is removed by cutting the condylar process of the mandible. The temporal bone posterior to the glenoid process and lateral to the tensor tympani muscle is incised to remove the glenoid fossa. Again, the glenoid fossa should not be removed unless a condylectomy is planned. (CP, condylar process; GG, gasserian ganglion; TMJ, temporomandibular joint; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

TMJ

V3 V2

GG

TMJ

C6 Fig. 11.97 Identifying the C6-C7 junction. The horizontal portion of internal carotid artery (C6) lies medial to the glenoid fossa. (C6, C6 portion of the internal carotid artery; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve])

EAC

VP

C6

Fig. 11.98 Removing the condyle of the mandible. The lateral pterygoid muscle has been detached and we see the branching of the mandibular nerve. The vaginal plate is exposed. (C6, C6 portion of the internal carotid artery; EAC, external auditory canal; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VP, vaginal plate)

V3 V2

V3

199

200

III Lateral Skull Base

TVPM

Fig. 11.99 The retrocondylar pouch.

VP

Deep to mandibular nerve we see the tensor velli palatini muscle, which takes it origin from the root of the medial pterygoid plate. The levator velli palatine takes its origin posterior from the vaginal process of the tympanic bone just anterior to the carotid artery and passes medial to the tensor muscle. (C6, C6 portion of the internal carotid artery; ET, eustachian tube; TVPM, tensor velli palatine muscle; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve; VP, vaginal plate)

ET V3

C6

Vi

TVPM VP ET

Fig. 11.100 Tensor velli palatini muscle after the anterior translocation of the mandibular nerve. The tensor velli palatini muscle and the vaginal plate are well seen after anterior translocation of the mandibular nerve. (C6, C6 portion of the internal carotid artery; ET, eustachian tube; TVPM, tensor velli palatine muscle; V3, mandibular nerve [third division of the trigeminal nerve]; Vi, vidian nerve; VP, vaginal plate)

C6

Vi

V3

SPCM

Fig. 11.101 The superior pharyngeal constrictor

muscle.

The superior pharyngeal constrictor muscle is seen medial to the tensor velli and levator velli palatine muscles. (SPCM, superior pharyngeal constrictor muscle; TVPM, tensor velli palatine muscle)

TVPM

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

VP ET C6

V3

Fig. 11.102 The boundary of the C7 vertical and C6 horizontal portions of the internal carotid artery and the tensor tympani muscle. The tensor tympani muscle lies lateral to the C6 portion of the carotid artery. (C6, C6 portion of the internal carotid artery; ET, eustachian tube; V3, mandibular nerve [third division of the trigeminal nerve]; VP, vaginal plate)

SD VP Fig. 11.103 (Step 8) Vaginal plate and styloid

diaphragm.

The styloid process lies lateral to the cervical carotid artery. In this photo, we see the vaginal plate and the styloid diaphragm, which lies just lateral to the styloid process and the styloid muscles. (C6, C6 portion of the internal carotid artery; SD, styloid diaphragm; V3, mandibular nerve [third division of the trigeminal nerve]; VP, vaginal plate)

C6

V3

SGM SPM

Fig. 11.104 Removing the styloid diaphragm. The styloglossus and stylopharyngeal muscles can be identifled after removing the styloid diaphragm. (SGM, styloglossus muscle; SPM, stylopharyngeal muscle; V3, mandibular nerve [third division of the trigeminal nerve])

V3

201

202

III Lateral Skull Base

SHM

SGM SPM

Fig. 11.105 Three muscles originating from the styloid process. The stylopharyngeal, styloglossus, and stylohyoid muscles originate from the styloid process. (SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; V3, mandibular nerve [third division of the trigeminal nerve])

V3

SHM SGM Fig. 11.106 (Step 9A) Stylohyoid muscle. The stylohyoid muscle can be seen well after retracting the styloglossus and stylopharyngeal muscles. (SGM, styloglossus muscle; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle)

SPM

IX CS Fig. 11.107 (Step 9B) Glossopharyngeal nerve and carotid sheath. The glossopharyngeal nerve is seen crossing the internal carotid artery. This nerve is adjacent and sometimes under the posterior edge of the stylopharyngeal muscle. (CS, carotid sheath; IX, glossopharyngeal nerve)

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

APA IX ICA

Fig. 11.108 The ascending pharyngeal artery. The carotid sheath is opened. The ascending pharyngeal artery is seen anterior to the internal carotid artery. (APA, ascending pharyngeal artery; ICA, internal carotid artery; IX, glossopharyngeal nerve)

SG

M

SPM

IX ICA Fig. 11.109 (Step 10) High cervical ICA and

glossopharyngeal nerve.

The anatomical relationship between the high cervical internal carotid artery, the glossopharyngeal nerve, the styloglossus muscle, and the stylopharyngeal muscle is demonstrated. (ICA, internal carotid artery; IX, glossopharyngeal nerve; SGM, styloglossus muscle; SPM, stylopharyngeal muscle; V3, mandibular nerve [third division of the trigeminal nerve])

V3

SPM

IX

Fig. 11.110 (Step 11) Longus capitis muscle on

basilar part of occipital bone (clivus).

Anterior to the carotid artery the longus capitis muscle comes into view. This muscle originates from the anterior transverse processes of the upper cervical vertebra and inserts into the basilar part of the occipital bone. (ICA, internal carotid artery; IX, glossopharyngeal nerve; LCpM, longissimus capitis muscle; SPM, stylopharyngeal muscle; V3, mandibular nerve [third division of the trigeminal nerve])

ICA

LCpM V3

203

204

III Lateral Skull Base

SGM SPM

IX ICA Fig. 11.111 The relationship between the structures in the retrocondylar pouch.

LCpM

VP

The stylopharyngeal muscle, the styloglossus muscle, and the glossopharyngeal nerves are seen crossing the internal carotid artery. (ICA, internal carotid artery; IX, glossopharyngeal nerve; LCpM, longissimus capitis muscle; SGM, styloglossus muscle; SPM, stylopharyngeal muscle; V3, mandibular nerve [third division of the trigeminal nerve]; VP, vaginal plate)

V3

IX ICA C7

Fig. 11.112 (Step 12) Drilling the vaginal plate to

expose high cervical, C7 vertical, and C6 horizontal ICA.

C6

V3 V2

The high cervical, C7 vertical, and C6 horizontal portions of the internal carotid artery can be seen after the vaginal plate is drilled away. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

IX ICA

C7 Fig. 11.113 Enlarged view of the high cervical ICA

C6-C7.

The center of Fig. 11.112 is enlarged. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; V3, mandibular nerve [third division of the trigeminal nerve])

C6

V3

11.2 Preauricular Transzygomatic Middle Infratemporal Fossa Approach

C7

CL

Fig. 11.114 (Step 13) Exposure of basilar part of occipital bone (middle clivus). Removing the petrous tip medial and anterior to the carotid artery leads to the clivus. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; V3, mandibular nerve [third division of the trigeminal nerve])

V3

C6 IX ICA

C7 Fig. 11.115 Anterior translocation of the internal carotid artery and mandibular nerve. Figure 11.114 demonstrates the mid clivus. To reach the lower clivus, the internal carotid artery must be translocated anteriorly. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; V3, mandibular nerve [third division of the trigeminal nerve])

C6

V3

SPM

IX ICA

C7 C6

Fig. 11.116 Nonmagnified view of Fig. 11.115. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; SPM, stylopharyngeal muscle; TD, temporal dura; V3, mandibular nerve [third division of the trigeminal nerve])

TD

V3

205

206

III Lateral Skull Base

RC

Fig. 11.117 (Step 14) Anterior refiection of rectus capitis anterior muscle to further expose the clivus and anterior arch of C1. The lower clivus is exposed further by translocating the rectus capitis anterior muscle that lies just medial to the longus capitis muscle. (CL, clivus; RCAM, rectus capitus anterior muscle)

AM

CL

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

The anterior petrosectomy is a versatile exposure. It is often combined with a subtemporal exposure to increase the surgical corridor. Variations of the anterior petrous approach are used to approach small acoustic neuromas or lesions of the petrous apex such as a cholesterol granuloma. This approach can open a corridor into the posterior fossa when operating a trigeminal schwannoma or an epidermoid tumor lying lateral to the midbrain. The exposure can be used for small high-riding petrous apex meningiomas. The exposure affords a face-on view of the anterior lateral pons for removing cavernomas. The anterior petrosectomy may be combined with a posterior petrosectomy for lesions that lie below the seventh and eighth cranial nerves.

Key Steps Position: Supine with head turned or lateral position with head laterally flexed   Step 1. Skin incision: sickle shaped (Fig. 12.1)   Step 2. Temporal craniotomy (Fig. 12.12)   Step 3. Dura propria elevation to identify the lateral loop (Fig. 12.21)   Step 4. Exposure of the middle fossa rhomboid with anterior translocation of V3 (Fig. 12.24)   Step 5. Drilling of the foramen ovale to shift the mandibular nerve (V3) anteriorly (Fig. 12.27)   Step 6. Drilling of the middle fossa rhomboid (anterior petrosectomy) (Fig. 12.30)   Step 7. Identification of the inferior petrosal sinus and the abducens nerve (Fig. 12.36)   Step 8. Exposure of the facial nerve at the fundus of the internal auditory canal (Fig. 12.40)   Step 9. Inferior translocation of the internal carotid artery and drilling of the clivus (Fig. 12.55) Step 10. Opening of dura and division of the tentorium (Fig. 12.56) Step 11. Identification of the intradural structures (Fig. 12.58)

Illustrated Steps with Commentary

PZP Zy

Fig. 12.1 (Step 1) Skin incision. The head is placed in the lateral position with the neck laterally flexed toward the floor. (The patient is in the lateral or supine position with the head in the lateral position.) A. This sickle shaped skin incision is made for the treatment of a small tumor such as a vestibular schwannoma. B. This question mark shaped skin incision is for an expansive subtemporal middle fossa rhomboid approach. C. This large question mark shaped skin incision is made for extended subtemporal middle fossa rhomboid approach and for harvesting a vascularized galeofascial pericranial flap. The skin incision should start at the preauricular zygomatic point that is located 10 mm anterior to the tragus on the root of the zygoma. The incision extends along the posterior border of the sideburn. If possible, the incision extending below the hairline follows a skin crease. (PZP, posterior zygomatic point; STL, superior temporal line; Zy, zygoma)

A B C

STL

208

III Lateral Skull Base

DTF

Fig. 12.2 Soft tissue opening. Basic: When employing a one-layer exposure, the incision is made through the skin and temporalis muscle. The pericranium, galea, temporoparietal fascia, or deep temporal fascia can be used for dural plasty at the end of the case. (DTF, deep temporal fascia)

Sq

Fig. 12.3 Mid-temporal bone exposure using the one-layer exposure.

The muscle is retracted along with the skin. The roots of the zygoma and squamosal suture are exposed. (Sq, squamosal suture)

DTF

Fig. 12.4 Two-layer exposure with preparation of a vascularized graft.

To prepare a vascularized flap for closure, a two-layer exposure is needed. The periosteal-fascial pericranial flap is used to reinforce the dural closure to avoid a postoperative cerebrospinal fluid leak and infection. (DTF, deep temporal fascia; PO, periosteum)

PO

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

DTF

PO Fig. 12.5 Preparing the vascularized flap. To harvest as much tissue as is possible, the skin and galea are undermined around the circumference of the flap. (DTF, deep temporal fascia; PO, periosteum)

Fig. 12.6 Periosteal-fascial flap. The edges of the skin are undermined so the vascularized flap is larger than the area exposed by the skin incision.

Fig. 12.7 Preparing the vascularized galeaofascial pericranial flap.

The vascularized flap can be back cut lengthwise so that the tip of the flap can reach the petrous apex.

209

210

III Lateral Skull Base

Fig. 12.8 Elongation of the vascularized galeaofascial pericranial flap.

The pedicle of the flap must be wide enough to maintain the flap’s blood supply. The temporalis muscle must be left intact to avoid a cosmetic deformity.

Zy

Sq

Fig. 12.9 Exposure of the root of zygoma. The zygomatic root has an inclination of 20 degrees and is 20 mm in length. (Sq, squamosal suture; Zy, zygoma)

Z Root of

Fig. 12.10 Relationship between the zygomatic root and structures in the middle fossa. The foramen ovale is medial to the anterior edge of the zygomatic root, the foramen spinosum is medial to the midpoint of the zygomatic root, and the geniculate ganglion is medial to the posterior edge of the zygomatic root.

Posterior Point

ygoma

Midpoint

Anterior Point

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

40%

MMA

V3 V2

GG

Fig. 12.11 Relationship between the middle cranial base structures and the root of zygoma. The boundary between the foramen ovale and the spinosum corresponds to the point just anterior to the midpoint of the root of the zygomatic artery. (GG, gasserian ganglion; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of trigeminal nerve])

Midpoint of Root of Zygoma

1/3

2/3

Fig. 12.12 (Step 2) Craniotomy for approaching the internal auditory canal. The trajectory for surgery centered in the vicinity of the internal auditory canal is optimal when the surgeon is viewing anterior to posterior. Starting from the midpoint of the zygomatic root, the bone flap should extend twice as far anteriorly as it does posteriorly to facilitate this view.

Midpoint of Root of Zygoma

2/3 (1/2) Fig. 12.13 Craniotomy for approaching the posterior cavernous sinus, gasserian ganglion, and petrous apex. On the other hand, because the surgical trajectory is posterior to anterior for operations approaching the posterior cavernous sinus, gasserian ganglion, or petrous apex, the posterior portion of the craniotomy should be made equal to or larger than the anterior portion. The ratio of the anterior to the posterior is 1:1–1:2.

1/3 (1/2)

211

212

III Lateral Skull Base

Fig. 12.14 Drilling the subtemporal groove. A groove (arrowheads) is drilled through the bone above the root of the zygoma so that the craniotomy will extend down to the floor of the middle fossa. A second bur hole is placed approximately 10 to 15 mm above the squamosal suture. If the dura is tenaciously adherent to the bone, additional holes are made to facilitate stripping the dura from the bone before turning the craniotomy flap. (Sq, squamosal suture)

Fig. 12.15 Outlining the craniotomy. The subtemporal groove and the bur hole are connected using an osteotome.

Fig. 12.16 Elevation of the craniotomy. A craniotomy is elevated.

Sq

10-15 mm

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

Fig. 12.17 Dural elevation. The dura is elevated from the floor of the middle fossa toward the middle meningeal artery and the foramen spinosum.

Fig. 12.18 Flattening of the floor of the middle

fossa.

The inner plate of the floor of the middle fossa should be drilled flat so that the surgeon’s line of vision is unobstructed by bony protrusions. Care must be taken not to flatten the arcuate eminence and open into the superior semicircular canal. The geniculate ganglion can be localized by stimulating the adjacent facial nerve through the bone.

MMA

Fig. 12.19 Identifying the middle meningeal

artery.

The middle meningeal artery should be followed proximally to identify the foramen spinosum. (MMA, middle meningeal artery)

213

214

III Lateral Skull Base

FS FO

Fig. 12.20 Identifying the foramen spinosum.

MMA

The foramen spinosum can be found by following the middle meningeal artery to its exit from the cranium. The foramen is often obscured by a bony overhang that can be removed with a diamond drill. The foramen ovale is seen medial and anterior to the foramen spinosum. (FO, foramen ovale; FS, foramen spinosum; MMA, middle meningeal artery)

MMA

FO

Fig. 12.21 (Step 3) Dura propria elevation. The middle meningeal artery is coagulated by bipolar coagulation and interrupted using a No. 11 or 15 blade knife. The dura propria elevation is begun by making an incision between the dura covering the temporal lobe and the fibrous tissue covering V3. (FO, foramen ovale; MMA, middle meningeal artery)

Fig. 12.22 Identifying the mandibular nerve and greater superficial petrosal nerve. The dura propria is gradually elevated over the mandibular branch of the trigeminal nerve. The greater superficial petrosal nerve (GSPN) is frequently found in its groove along with a branch of the middle meningeal artery, which passes medial to the foramen spinosum and under the mandibular nerve into the vidian canal. The GSPN is sharply separated from the temporal dura. Traction on the nerve can injure the geniculate ganglion and the facial nerve. The foramen ovale emissary vein connecting the pterygoid plexus with the cavernous sinus is seen passing through the foramen ovale. Bleeding from this vein should be controlled using an absorbable hemostatic agent. Bipolar coagulation should be kept to a minimum. (AE, arcuate eminence; FOEV, foramen ovale emissary vein; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V3, mandibular nerve [third division of the trigeminal nerve])

MMA FOEV AE

GSPN

V3

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

MMA GSPN V3

AE GG

Fig. 12.23 Identifying the lateral loop.

V2

The foramen rotundum can be found by following the dura anteriorly from the foramen ovale toward the superior orbital fissure. The lateral loop formed by the anterior border of the mandibular nerve and the inferior border of the maxillary nerve should be identified. (GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

MMA GSPN

V3

Fig. 12.24 (Step 4) Rhomboid exposure. Working down along the petrous ridge from lateral to medial, the arcuate eminence (AE) is encountered on the superior surface of the petrous bone. The medial edge of the AE lies approximately at the level of the geniculate ganglia. The rhomboid space is delineated by the petrous ridge, the AE, the greater superficial petrosal nerve, and the posterior border of the mandibular nerve. This includes Kawase’s and Glasscock’s triangles. (AE, arcuate eminence; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; Rbd, rhomboid; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2 AE

GG

Rbd

GSPN V3

AE

Fig. 12.25 Identifying the two petrosal ridges. The petrous ridge is notched by a groove that cradles the superior petrosal sinus. The surgeon needs to strip the dura over two humps to completely expose the petrous ridge. (1st R, first ridge of the petrous bone; 2nd R, second ridge of the petrous bone; AE, arcuate eminence; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; Rbd, rhomboid; V3, mandibular nerve [third division of the trigeminal nerve])

Rbd 1st R

GG 2nd R

215

216

III Lateral Skull Base

MMA FO Fig. 12.26 Opening the foramen ovale.

V3

GSPN

The foramen ovale should be opened so that V3 can be translocated anteriorly without kinking the nerve. The tip of the petrous bone lies under the Gasserian ganglion. Compare with Fig. 12.27. (FO, foramen ovale; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2 GG

MMA V3 Fig. 12.27 (Step 5) Opening the foramen ovale. The foramen ovale is unroofed using a diamond drill. The drill is constantly cooled to avoid heat injury to the mandibular nerve. Opening the foramen ovale allows the mandibular nerve to be mobilized anteriorly to expose the tip of the petrous bone. (GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

GSP

N GG

ET(C

Fig. 12.28 Exposing the eustachian tube. Drilling through the bone posterior to the foramen ovale and medial to the foramen spinosum results in the exposure of the cartigenous portion of the eustachian tube. This is not done in a standard approach. The eustachian tube can be viewed as running deep to the tensor tympani muscle and lateral to the carotid artery. If the eustachian tube is opened at the time of surgery, it must be closed to avoid a CSF leak. If the eustachian tube is closed, the patient’s tympanic membrane may need to be opened to drain the middle ear and mastoid sinus. (ET(C), cartilaginous part of the eustachian tube; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; V3, mandibular nerve [third division of the trigeminal nerve])

V2

V3

)

GSPN GG

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

MMA GSPN

Fig. 12.29 Anterior Translocation of the

mandibular nerve and gasserian ganglion. Anterior translocation of the freed mandibular nerve allows the petrous tip and the trigeminal impression (Meckel’s cave) to be exposed. Two spatulas are usually used to expose the anterior petrous bone. One is wedged under the petrous ridge. The other holds the anteriorly translocated trigeminal nerve. (1st R, first ridge of the petrous bone; 2nd R, second ridge of the petrous bone; AE, arcuate eminence; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; Rbd, rhomboid; TI, trigeminal impression; V3, mandibular nerve [third division of the trigeminal nerve])

V3

AE

Rbd

TI

1st R 2nd R

MMA

V3 GSPN

Co Fig. 12.30 (Step 6) Drilling in the rhomboid

space.

AE

Drilling along the petrous ridge between the arcuate eminence and the mandibular nerve will expose the dura lining the porus acousticus. It is safest to expose the internal auditory canal medially away from the cochlea and the superior semicircular canal. (AE, arcuate eminence; Co, cochlea; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; V3, mandibular nerve [third division of the trigeminal nerve])

MMA GSPN

Fig. 12.31 Skeletonizing the internal auditory

canal.

The internal auditory canal (IAC) is found by bisecting the angle between the greater superficial petrosal nerve and the arcuate eminence. The cortex and the cancellous bone over the rhomboid are removed. Laterally the internal carotid artery is found inferior to the greater superficial petrosal nerve. The hard bone surrounding the cochlea is found medial to the gena of the carotid artery. The IAC is most extensively drilled at the meatus where it can be exposed 270 degrees circumferentially. As we drill laterally the bony opening must lie directly over the IAC as the semicircular canal lays posterior and the cochlea lies anterior to the IAC. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; MMA, middle meningeal artery; V3, mandibular nerve [third division of the trigeminal nerve]

Co AE

IAC

V3 C6

217

218

III Lateral Skull Base

ET(C)

Fig. 12.32 Exposing the posterior fossa dura and inferior petrosal sinus. Drilling anterior to the internal auditory canal will expose the posterior fossa dura up to the inferior petrosal sinus. The inferior petrosal sinus marks the junction of the petrous bone and the clivus. Medially the abducens nerve passes through the inferior petrosal sinus into Dorello’s tube. The cochlea lies 5 mm medial to the geniculate ganglion, 9 mm medial to the malleus head, and 1–2 mm medial to the genu of the internal carotid artery at the boundary between the vertical C7 and horizontal C6 portion of the artery. Because no defined bony landmarks identify the cochlea, the surgeon should imagine its location based on the surrounding structures. An average length of the bony canal that contains the GSPN from the geniculate ganglion to the facial hiatus is approximately 9 mm. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; ET(C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; PD, posterior fossa dura; V3, mandibular nerve [third division of the trigeminal nerve])

GSPN C6 Co

IPS

IAC

AE

PD

MMA V3

GSPN C6

Co AE

T

PD

Fig. 12.33 Exposing the petrous tip. The tip of the petrous bone (T) lies under the gasserian ganglion. Anterior translocation of the mandibular nerve is necessary to expose the petrous apex. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery; PD, posterior fossa dura; T, tip of the petrous bone; V3, mandibular nerve [third division of the trigeminal nerve])

GSPN

V3

C6

Fig. 12.34 Removing the petrous tip. The tip of the petrous bone is hard to remove because the petroclival and petrosphenoidal ligaments hold it firmly in place. Similar to removing the tip of the anterior clinoid, the tip is drilled until it is a small sliver of bone that can be stripped from its ligamentous attachments. (C6, C6 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; PD, posterior fossa dura; T, tip of the petrous bone; V3, mandibular nerve [third division of the trigeminal nerve])

PD

T

GG

V3

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

MMA

V3

GSPN C6 Fig. 12.35 Complete removal of the rhomboid.

IP

Co

The greater superficial petrosal nerve (GSPN) lies over the horizontal C6 portion of the internal carotid artery (C6 ICA). Retraction of the GSPN can damage the facial nerve. If the GSPN cannot be easily preserved, it should be cut. Drilling under the GSPN will expose the C6 ICA. The eustachian tube lies lateral to the C6 ICA. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PD, posterior fossa dura; V3, mandibular nerve [third division of the trigeminal nerve]

S

PD

AE IAC

MMA V3 GSPN C6 Co

Fig. 12.36 (Step 7) Identification of abducens nerve on floor of inferior petrosal sinus.

AE

The abducens nerve exits the posterior fossa passing through the inferior petrosal sinus (IPS). At the time of surgery, the IPS is opened and packed with absorbable hemostatic agent lateral to the nerve. The nerve is found on the floor of the IPS. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PD, posterior fossa dura; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

IAC

PD

The abducens nerve is covered by the fibrous capsule (Dorello’s tube) inside the inferior petrosal sinus. (IAC, internal auditory canal; PD, posterior fossa dura; VI, abducens nerve)

VI

PD

IAC

Fig. 12.37 Identifying the fibrous membrane (Dorello’s tube) around abducens nerve.

IPS

VI

219

220

III Lateral Skull Base

MMA GSPN

nerve on the floor of the inferior petrosal sinus and surrounding structures.

Co AE

IAC

IPS

Fig. 12.38 Relationship between the abducens

V3

C6 PD

VI

An overview demonstrates the relationship between the abducens nerve and the surrounding structures. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; PD, posterior fossa dura; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

Gen C6 AE IAC

SA

Fig. 12.39 Identifying the subarcuate artery.

Co

GSPN

Looking posteriorly the relationship between the IAC, superior semicircular canal, and cochlea is demonstrated. The subarcuate artery is seen passing through the center of the superior semicircular canal. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; SA, subarcuate artery)

AmpS

T-V II

Fig. 12.40 (Step 8) Exposure of the fundus of

internal auditory canal.

II L-V

SV SSC

SA

M-VII

The fundus of the internal auditory canal (IAC) is wedged between the superior semicircular canal (SSC) and the cochlea. When the surgeon drills the fundus of the canal, it is important to only drill directly above the nerves in the fundus or the cochlea or the SSC will be disrupted. The geniculate isthmus (dotted triangle) is defined by the ampulla of the SSC, the cochlea, and the geniculate ganglion. It lies lateral to the fundus of the IAC. (AmpS, ampulla of the superior semicircular canal; Co, cochlea; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SA, subarcuate artery; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

Gen

IAC

GSPN

Co

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

T-VI I Fig. 12.41 Identifying Bill’s bar and the geniculate notch (Fukushima’s bar). The bony notch between the superior vestibular and facial nerve is Bill’s bar. Another bony notch lies between the labyrinthine segment and tympanic segment of the facial nerve, the geniculate notch (Fukushima’s bar). The tympanic segment of the facial nerve enters the fallopian canal. The greater superficial petrosal nerve is seen joining the facial nerve at the geniculate ganglion. (BB, Bill’s bar; Co, cochlea; FB, Fukushima’s bar [geniculate notch]; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

FB

SV BB

Gen

II L-V

SSC

Co

IAC

Fig. 12.42 Identifying the deep petrosal nerve and greater superficial petrosal nerve. The greater superficial petrosal nerve (GSPN) is seen above and parallel to the internal carotid artery. The GSPN is seen to join the deep petrosal nerve to form the nerve of the vidian canal (vidian nerve) that innervates the pterygopalatine ganglion. The origin of the vidian canal is the anterior wall of the foramen lacerum. The GSPN carries sensory and preganglionic parasympathetic fibers from the facial nerve. The deep petrosal nerve (DPN) carries postganglionic sympathetic fibers that enter the skull along with the internal carotid artery. (C6, C6 portion of the internal carotid artery; Co, cochlea; DPN, deep petrosal nerve; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; SA, subarcuate artery; SSC, superior semicircular canal; V3, mandibular nerve [third division of the trigeminal nerve])

Gen

GSPN

C6

Co

SSC

IAC SA

GSPN

VII AE An overview of the extradural exposure obtained by the middle fossa rhomboid approach is demonstrated. (AE, arcuate eminence; C6, C6 portion of the internal carotid artery; Co, cochlea; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; IPS, inferior petrosal sinus; MMA, middle meningeal artery; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

V3

DPN

MMA

Fig. 12.43 Overview at this stage.

GSPN

IAC

Co

PD

IP

S

C6

V3

221

222

III Lateral Skull Base

CT CP

I

Fig. 12.44 Exposure of tympanic cavity.

M

LSC

The tympanic cavity is usually not opened during the rhomboid approach. The dissection is continued to demonstrate the regional anatomy. The tympanic cavity is exposed by removing the tegmen tympani, which is the roof of the middle ear. (C6, C6 portion of the internal carotid artery; Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET(B), bony part of the eustachian tube; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; PD, posterior fossa dura; SSC, superior semicircular canal; SV, superior vestibular nerve; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve)

MMA

ET(B) TTM

T-V II

GSPN

SSC

Co

SV

C6

IAC

CT

PD

TMJ

Fig. 12.45 Identifying the chorda tympani and

MMA

eustachian tube.

LSC

IM CP

V3

GSPN

Co

IAC

ET(C)

TTM

I

SSC

E T(B)

I T-V

The chorda tympani enters the tympanum (middle ear) through the posterior wall of the tympanum. It passes medial to the malleus to leave the tympanum through a hole in the anterior wall of the middle ear. (C6, C6 portion of the internal carotid artery; Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET(B), bony part of the eustachian tube; ET(C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; SSC, superior semicircular canal; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

C6

CT TMJ

I

Fig. 12.46 Relationship between the incus,

malleus, and chorda tympani.

M

ET(B)

CP VI T-

TTM

I

The chorda tympani exits anteriorly passing through a canal in the petrotympanic fissure. (Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET(B), bony part of the eustachian tube; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve)

LSC

Gen

SSC IAC

GSPN Co

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

Fig. 12.47 Exposing the chorda tympani into the infratemporal fossa toward the lingual nerve (branch of posterior trunk of the mandibular nerve).

TMJ

The chorda tympani exits the cranium just medial to the spine of the sphenoid bone and joins with the lingual nerve, a branch of the posterior trunk of the mandibular nerve (V3), in the infratemporal fossa. The connection of the chorda tympani and the lingual nerve is shown in chapter 11 describing the anterior infratemporal fossa approach (Figs. 11.1–11.58 and 11.1–11.59). (CT, chorda tympani; ET(B), bony part of the eustachian tube; ET(C), cartilaginous part of the eustachian tube; ITF, infratemporal fossa; MMA, middle meningeal artery; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; V3, mandibular nerve [third division of the trigeminal nerve])

ITF MMA

CT

ET(C)

ET(B)

TTM

V3

TMJ

MMA

Fig. 12.48 Identification of tensor tympani

muscle.

The tensor tympani muscle is seen to arise from the cartilaginous portion of the eustachian tube and the adjacent sphenoid bone. It passes above and medial to the eustachian tube before entering the tympanum. The tendon of the muscle turns approximately 90 degrees at the cochleariform process toward the manubrium of the malleus. (C6, C6 portion of the internal carotid artery; Co, cochlea; CP, cochleariform process; CT, chorda tympani; ET(B), bony part of the eustachian tube; ET(C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; MMA, middle meningeal artery; SSC, superior semicircular canal; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

CT

I M LSC

CP

T-V II

V3

TTM

GSPN

SSC IAC

ET(C)

ET(B)

Co C6

CT

Cut End of CT MM I

Fig. 12.49 Identifying the stapes and the tensor

tympani tendon.

The tensor tympani tendon makes a sharp turn at the cochleariform process around the edge of the septum of the muscular canal and inserts into the manubrium of the malleus. (AmpS, ampulla of the superior semicircular canal; C7, C7 portion of the carotid artery; CP, cochleariform process; CT, chorda tympani; FB, Fukushima’s bar [geniculate notch]; Gen, geniculate ganglion; I, incus; LSC, lateral semicircular canal; MH, malleus head; MM, manibrium of the malleus; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

LSC

MH

S

C7

CP AmpS SSC

T-V I

SV

I

FB

Gen

223

224

III Lateral Skull Base

Cut End of CT

CT V-VII G

Fig. 12.50 Exposing the vertical (mastoid) segment of the facial nerve. The facial nerve passes between the incus and the lateral semicircular canal and then is referred to the vertical segment of the facial nerve. (AmpS, ampulla of the superior semicircular canal; C7, C7 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; Gen, geniculate ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; PSC, posterior semicircular canal; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

I LSC AmpS

PSC

SSC

Gen I I L-V

Cut End of GSPN Co

IAC

V-VII

TMJ

CT

nerve, the greater superficial petrosal nerve, and the chorda tympani.

C7

T-VI I

SV

Fig. 12.51 Exposing the main trunk of the facial

ITF G PSC

IM LSC T-VII Gen

ET(C)

ET(B)

V3

TTM GSPN

SSC

Co

L-VII SV

C6

IAC

The relationship between the facial nerve, chorda tympani, and greater superficial petrosal nerve are demonstrated. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET(B), bony part of the eustachian tube; ET(C), cartilaginous part of the eustachian tube; G, genu [second turn or external genu] of the facial nerve; Gen, geniculate ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; ITF, infratemporal fossa; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; TVII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve]; V-VII, vertical segment of the facial nerve)

M

S

M-VII

TMJ I

ET(B)

I

Fig. 12.52 Overview at this step.

SSC

IAC

V3

GSPN

Co PD

C6

IPS

The anatomical relationship at this step of the dissection is shown. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET(B), bony part of the eustachian tube; ET(C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; IPS, inferior petrosal sinus; LSC, lateral semicircular canal; M, malleus; PD, posterior fossa dura; SSC, superior semicircular canal; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve; V-VII, vertical segment of the facial nerve)

ET(C)

VI V-

LSC

CT

M

VI

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

Orifice of ET

Fig. 12.53 Exposing the vertical C7 portion of

internal carotid artery.

The vertical C7 portion of the internal carotid artery is exposed by drilling through the eustachian tube. Knowledge of this relationship is helpful when performing a temporal bone resection for carcinoma of the middle ear. Drilling through the temporal bone from lateral to medial at the level of the posterior root of the zygoma, the carotid artery will lie medial to the eustachian tube. (C6, C6 portion of the carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; orifice of ET, orifice of eustachian tube; ET(C), cartilaginous part of the eustachian tube; Gen, geniculate ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

I

M

LSC

ET(C) C7

T-V II

SV L-VI

SSC

TMJ

V3

I Gen

C6

Co

IAC Orifice of ET I

LSC AmpS

I T-V

Fig. 12.54 Exposing the vertical C7 portion of the

internal carotid artery.

I

A more anterior trajectory demonstrates the relationship of the genu of the internal carotid artery and the cochlea. The cochlea lies medial and very close to the artery. (AmpS, ampulla of the superior semicircular canal; C6, C6 portion of the carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; orifice of ET, orifice of eustachian tube; ET(C), cartilaginous part of the eustachian tube; Gen, geniculate ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; SA, subarcuate artery; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

SSC

SV -VII Gen L

SA

IAC

ET(C

) V3

Co

II T-V

IAC

The mid-clivus can be exposed more extensively by the anterior translocation of the carotid artery. (C6, C6 portion of the carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; Co, cochlea; Gen, geniculate ganglion; GG, gasserian ganglion; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

C7

C6

SV

Fig. 12.55 (Step 9) Inferior translocation of internal carotid artery.

TMJ

M

C7

L-VII Gen

Co

CL C6

V3 GG

225

226

III Lateral Skull Base

C6

Co

IAC

VI

Fig. 12.56 (Step 10) Posterior fossa dural incision. The dura of the posterior fossa is incised in an inversed “T” fashion. (C6, C6 portion of the carotid artery; Co, cochlea; IAC, internal auditory canal; VI, abducens nerve)

C7

LSC

T-V II

SV Fig. 12.57 Dural opening of the internal auditory

canal.

SSC

Po Fig. 12.58 (Step 11) Identification of intradural abducens nerve. The middle fossa rhomboid approach is ideal for viewing the anterolateral surface of the pons. The abducens nerve is demonstrated at the anterior margin of the intradural exposure. The nerve enters into the inferior petrosal sinus, penetrating the posterior fossa dura medial to the trigeminal nerve. The exit of the nerve into Dorello’s canal is often hidden by the anterior arachnoid of the prepontine cistern. (Po, pons; VI, abducens nerve)

M-VII

When opening the dura surrounding the internal auditory canal (IAC), care must be taken not to injure the nerves within. In the surgeon’s mind the IAC is like a funnel. The fundus is shallow and the porus acousticus is deep, so the nerves are most likely to fall away from the dura at the meatus. (C7, C7 portion of the carotid artery; Co, cochlea; Gen, geniculate ganglion; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; MVII, meatal segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

VI

II L-V

Gen Co

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

Co VI BA

Po

Fig. 12.59 Identifying the mid-basilar artery. The abducens nerve appears to cross the mid-portion of the basilar artery from the lateral view. (BA, basilar artery; Co, cochlea; Po, pons; VI, abducens nerve)

Co

BA VI

Fig. 12.60 Identifying the lower basilar artery. By angling the microscope inferiorly the lower portion of the basilar artery can be seen. (BA, basilar artery; Co, cochlea; VI, abducens nerve)

Co VA VA BA Fig. 12.61 Identifying the vertebrobasilar artery

junction.

By angling the microscope more inferiorly the vertebrobasilar artery junction can be seen. (BA, basilar artery; (Co, cochlea; VA, vertebral artery)

227

228

III Lateral Skull Base

Tent IV Fig. 12.62 Identifying the posterior cerebral and

SC A SC A

superior cerebellar arteries.

The middle fossa dura is opened by a linear incision parallel with the superior petrosal sinus. Above the tentorium cerebelli the surgeon is afforded a lateral view of the pons and the midbrain. The trochlear nerve, the posterior cerebral artery, and the superior cerebellar artery can be seen in the ambient cister. (IV, trochlear nerve; MB, midbrain; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery; Tent, tentorium)

P2 MB

SPS Tent III

Pcom

A SC Fig. 12.63 Identifying the oculomotor nerve. Tilting the microscope anteriorly affords the surgeon a view of the dorsum sellae and the proximal oculomotor nerve that runs between the superior cerebellar artery and the posterior cerebral artery. (III, oculomotor nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus; Tent, tentorium)

SC A

P2 P1

SPS Fig. 12.64 Cutting the tentorium and superior petrosal sinus. In most cases the exposure achieved with an anterior petrosectomy is enlarged by simultaneously opening the dura of the middle fossa. Usually the posterior and middle fossa opening are connecting by ligating the superior petrosal sinus. The superior petrosal sinus is ligated between two silk sutures that occlude the sinus. (SPS, superior petrosal sinus; Tent, tentorium)

Tent

om Pc P1

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

Tent

IV Fig. 12.65 Identifying the trochlear nerve. The trochlear nerve is seen running into the caudal surface of a free margin of the tentorium cerebelli. (IV, trochlear nerve; Tent, tentorium)

Tent

10 mm

IV

Fig. 12.66 Opening the tentorial tunnel of the trochlear nerve. The superficial tentorium cerebelli is obliquely cut approximately 10 mm over the trochlear nerve. This exposes the extracavernous portion of the nerve that runs through a tunnel within the tentorium. (IV, trochlear nerve; Tent, tentorium)

TFR

2 1 Fig. 12.67 Second tentorial incision toward the trigeminal fibrous ring. The fibrous ring around the trigeminal nerve is opened. The tentorium is cut from the fibrous ring surrounding the trigeminal nerve to the dural incision made over the trochlear nerve. Opening the trigeminal fibrous ring frees the trigeminal nerve from the dura. The incision in the tentorium is usually made from lateral to medial to facilitate the coagulation of venous channels and tentorial arteries. (TFR, trigeminal fibrous ring)

229

230

III Lateral Skull Base

SPS

IV

SC

A

Fig. 12.68 Identifying the superior petrosal sinus. The superior petrosal sinus is often ligated with 4-0 silk sutures before the tentorium is cut. In this dissection it was left intact to demonstrate its relationship to the surrounding structures. (IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus)

P2

IV

Fig. 12.69 Packing oxidized cellulose into the superior petrosal sinus.

P2

Venous bleeding can be controlled by packing oxidized cellulose into the superior petrosal sinus or posterior cavernous sinus, or both. (IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery)

GG V Fig. 12.70 Complete tentorial division. The tentorium cerebelli is completely divided. The arrow demonstrates the entrance into the posterior cavernous sinus. This posterior cut will deprive a meningioma of feeding arteries coming from the intracavernous carotid artery and passing through the tentorium. (GG, gasserian ganglion; IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery; V, trigeminal nerve)

IV

SC A

P2

SC

A

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

GG

V Po IV

Fig. 12.71 Tacking the tentorial edge. To expand the surgical field, the edge of the tentorium cerebelli should be tacked up posteriorly. (GG, gasserian ganglion; IV, trochlear nerve; P2, P2 segment of the posterior cerebral artery; Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve)

SC A

P2

V3

Po V SCA

GG

Fig. 12.72 Exposing the trigeminal nerve. The opening between the middle and posterior fossa is enlarged by opening the trigeminal fibrous ring that marks the entrance at the trigeminal nerve into Meckel’s cave. (GG, gasserian ganglion; IV, trochlear nerve; MB, midbrain; Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve; V3, mandibular nerve [third division of the trigeminal nerve])

MB

IV

V3 S-V

M-V Fig. 12.73 Identifying the motor root of the trigeminal nerve. The motor root of the trigeminal nerve runs along the medial edge of the nerve as the nerve emerges from the pons. (GG, gasserian ganglion; IV, trochlear nerve; M-V, motor root of the trigeminal nerve; SCA, superior cerebellar artery; S-V, sensory root of the trigeminal nerve; V3, mandibular nerve [third division of the trigeminal nerve])

SCA IV

GG

231

232

III Lateral Skull Base

V3

Po VI Fig. 12.74 Identifying the abducens nerve under the trigeminal nerve. After the tentorium is divided, the abducens nerve can be seen under the root of the trigeminal nerve. (Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve; VI, abducens nerve; V3, mandibular nerve [third division of the trigeminal nerve])

V SCA C6 Co VI VI

Po

BA

Fig. 12.75 Identifying the basilar artery. The exposure affords the surgeon a view of the middle and lower portions of the basilar artery, the lateral pons, the trigeminal nerve, and the abducens nerve. (BA, basilar artery; C6, C6 portion of the internal carotid artery; Co, cochlea; Po, pons; V, trigeminal nerve; VI, abducens nerve)

V

SCA

IV

SC A

Fig. 12.76 Identifying the oculomotor nerve, the posterior cerebral artery, and the superior cerebellar artery. Superiorly we see the upper basilar artery, posterior cerebral artery, superior cerebellar artery, and oculomotor nerve. The anterolateral surface of the midbrain is also seen. (III, oculomotor nerve; IV, trochlear nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery)

P2

P1

III m Pco

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

BA

SC A

IV

SC A

III

III

Fig. 12.77 Exposing the proximal oculomotor nerve by retracting the posterior cerebellar artery. The oculomotor nerve is demonstrated exiting the midbrain between the posterior cerebral artery and the superior cerebellar artery. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve; SCA, superior cerebellar artery)

BA

SC

A

III

A

P1

III

Pco m

SC

IV

P1 Fig. 12.78 Exposing the upper portion of the basilar artery.

TPA

The upper basilar artery and the thalamoperforating arteries are demonstrated. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve; P1, P1 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebellar artery; TPA, thalamoperforating arteries)

III

Pcom

III Pco m

IV

Fig. 12.79 Identifying the oculomotor and trochlear nerves on opposite sides. Looking across the front of the midbrain, the oculomotor and trochlear nerves on the side contralateral to the exposure can be seen. (III, oculomotor nerve; IV, trochlear nerve; Pcom, posterior communicating artery)

233

234

III Lateral Skull Base

ICA

III

m Pco

Fig. 12.80 Identifying the posterior communicating and anterior choroidal arteries.

AntCho

II

Tilting the microscope more anteriorly improves the surgeon’s view of the oculomotor nerve, the internal carotid artery, and the posterior communicating and anterior choroidal arteries. The optic nerve can be seen over the arteries. (AntCho, anterior choroidal artery; ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve; Pcom, posterior communicating artery)

ICA

III II

II

Fig. 12.81 Exposing the optic chiasm. The inferior surface of the optic nerves and the optic chiasm are visible by retracting the posterior communicating and internal carotid arteries. (ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve)

III PCP III Pcom Fig. 12.82 Exposing the internal carotid artery and oculomotor nerve on opposite sides. The internal carotid artery and the oculomotor nerve on the opposite sides can be seen. (ICA, internal carotid artery; III, oculomotor nerve; Pcom, posterior communicating artery; PCP, posterior clinoid process)

ICA

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

TMJ

CT Fig. 12.83 Exposing the eustachian tube to

demonstrate the relevant anatomy.

The lateral wall of the eustachian tube is opened to demonstrate its course. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET(C), cartilaginous part of the eustachian tube; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

LSC

ET(C

I M VII IAC

SSC

Fig. 12.84 Opening the eustachian tube to

demonstrate the relevant anatomy.

The metal bar is passed inside the eustachian tube toward the nasopharynx. (C6, C6 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; SSC, superior semicircular canal; TMJ, temporomandibular joint; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

TMJ

I LSC SSC

VI

I

IAC

Fig. 12.85 Opening the cochlea, semicircular

The dissector is put inside the basal turn of the cochlea. The middle turn lies right under the geniculate ganglion. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CT, chorda tympani; ET(C), cartilaginous part of the eustachian tube; I, incus; LSC, lateral semicircular canal; M, malleus; MT, middle turn of the cochlea; SSC, superior semicircular canal; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve]; Ve, vestibule; V-VII, vertical segment of the facial nerve)

C6

Co

Co

V-VII

canals, and vestibule to demonstrate the relevant anatomy.

V3

GSPN

CT

)

LSC

V3

GSPN

CT

I M T-V I Ve I

C6

TMJ MT ET(C)

C7

SSC BT

V3

235

236

III Lateral Skull Base

TMJ V-VII

CT I

LSC Fig. 12.86 Opening the cochlea, semicircular

canals, and vestibule to demonstrate the relevant anatomy.

Ve

PSC

Magnified view of Fig. 12.85. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CT, chorda tympani; Gen, geniculate ganglion; I, incus; LSC, lateral semicircular canal; M, malleus; MT, middle turn of the cochlea; PSC, posterior semicircular canal; SSC, superior semicircular canal; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; Ve, vestibule; V-VII, vertical segment of the facial nerve)

M

T-V II

C7

MT

Gen

BT

SSC

V-VII

TMJ

G LSC

Fig. 12.87 The promontory is shown indenting

the middle ear to demonstrate the relevant anatomy.

PSC

The promontory can be seen easily after the incus, the malleus, the stapes, and the chorda tympani are removed. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; G, genu [second turn or external genu] of the facial nerve; Gen, geniculate ganglion; LSC, lateral semicircular canal; MT, middle turn of the cochlea; P, pons; PSC, posterior semicircular canal; SSC, superior semicircular canal; TMJ, temporomandibular joint; T-VII, tympanic segment of the facial nerve; Ve, vestibule; V-VII, vertical segment of the facial nerve)

T-V P II

Ve

M T Gen

C7

BT

SSC

TMJ

Cut End of VII Fig. 12.88 The anatomical dissection demonstrates the relationship between the cochlea, the vestibule, and the semicircular canals. The relationship of the cochlea, the vestibule, and the semicircular canals are outlined in this picture. The relationship of the vestibule to the internal auditory canal (IAC) is relevant to the retrosigmoid and translabyrinth approaches. That relationship is nicely demonstrated in this dissection. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; LSC, lateral semicircular canal; MT, middle turn of the cochlea; P, pons; SSC, superior semicircular canal; TMJ, temporomandibular joint; Ve, vestibule; VII, facial nerve)

P

LSC Ve SSC

MT BT

C7

12 Middle Fossa Rhomboid Approach (Anterior Petrosectomy)

Cut End LSC of VII demonstrates the relationship of the promontory (basilar turn of the cochlea) to the vestibule.

SSC

The relationship of the vestibule, the promontory, and the cochlea can be easily understood from this dissection. The promontory is opened to demonstrate the relationship between the basal turn of the cochlea and the vestibule. (AT, apical turn of the cochlea; BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; LSC, lateral semicircular canal; Mo, modiolus; MT, middle turn of the cochlea; SSC, superior semicircular canal; Ve, vestibule; VII, facial nerve)

C7

AT

Ve

Fig. 12.89 The anatomical dissection

MT Mo

BT

C7 LSC Ve Fig. 12.90 The anatomical dissection

demonstrates the relationship of the vestibule to the cochlea. The basal turn of the cochlea connects with the vestibule and is also very close to the internal carotid artery. (BT, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; LSC, lateral semicircular canal; SSC, superior semicircular canal; Ve, vestibule)

BT SSC

237

IV

Posterolateral Skull Base

13 Anatomy for Posterolateral Skull Base Surgery

Before operating on the petrous bone, the surgeon should have mastered the three dimensional anatomy of the temporal bone. In this chapter, the anatomy encountered during surgery is demonstrated from a middle fossa, mastoid, and posterior fossa approach.

13.1 Superior Petrosa (Middle Fossa) Key Steps Step 1. Anterior petrosectomy (Fig. 13.1) Step 2. Note anatomy of semicircular canals (Fig. 13.3)

Illustrated Steps with Commentary

V3 DPN

Fig. 13.1 (Step 1) Anatomy of the middle cranial base.

An anterior petrosectomy has been performed. The greater superficial petrosal nerve runs above the carotid artery. The hard bony capsule of the cochlea is medial to the genu of the carotid artery. The fundus of the internal auditory canal is wedged between the cochlea and the superior semicircular canal. The posterior fossa dura along the petrous face is exposed. (AE, arcuate eminence; (C6, C6 portion of the internal carotid artery; Co, cochlea; DPN, deep petrosal nerve; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

GSPN

T-VII GG

C6

L-VII

SV

Co AE IAC

IV Posterolateral Skull Base

T-VII

Fig. 13.2 Magnified view of the fundus of the internal auditory canal exposed through the superior petrosa.

The bony capsules of the superior, posterior, and lateral semicircular canals have been dissected from mastoid air cells. The facial nerve passes between the middle ear and the lateral semicircular canal. The head of the malleus is seen articulating with the bony body of the incus. The tensor tympani articulates with the neck of the malleus. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; I, incus; IAC, internal auditory canal; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

BB

Co

M

AE

V-VII

CT

C6

SV

IAC

C7

Fig. 13.3 (Step 2) Anatomical relationship of the

semicircular canals and the middle ear.

L-VII

GSPN

G

I

LSC

T-VII GG L-VII SV

Co IAC

PSC

SSC

TMJ V-VII

G CT

M

ET

V3

I LSC

I

Bill’s bar separates the superior vestibular from the facial nerve. The labyrinthine segment of the facial nerve passes from the internal auditory canal to the geniculate ganglion. The tympanic segment of the facial nerve passes posterior and the greater superficial petrosal nerve passes anterior from the geniculate ganglion. (AE, arcuate eminence; BB, Bill’s bar; Co, cochlea; FB, Fukushima’s bar [geniculate notch]; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; L-VII, labyrinthine segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

FB

GG

TVI

242

TTM

GG I L-V

GSPN

I

Co C6

IAC

SSC

PSC

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

LN

IAN

TMJ

Fig. 13.5 Schema of Fig. 13.4. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; Co, cochlea; CT, chorda tympani; ET, eustachian tube; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; I, incus; IAC, internal auditory canal; IAN, inferior alveolar nerve; IPS, inferior petrosal sinus; LN, lingual nerve; LSC, lateral semicircular canal; L-VII, labyrinthine segment of the facial nerve; M, malleus; MMA, middle meningeal artery; PSC, posterior semicircular canal; S, stapes; SSC, superior semicircular canal; SV, superior vestibular nerve; TMJ, temporomandibular joint; TTM, tensor tympanic muscle; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve; V-VII, vertical segment of the facial nerve)

V-VII

CT

V3

s

MMA M

ET

II T-V

TTM

C'7 C6

GSPN

GG

Co

IPS

IAC

VI

Key Steps Step 1. Superficial mastoidectomy (Fig. 13.6) Step 2. Note anatomy of the middle ear (Fig. 13.8) Step 3. Note cochlear aqueduct (Fig. 13.16) Step 4. Blue line the semicircular canals (Fig. 13.17)

Illustrated Steps with Commentary

M I T-V II

Fig. 13.6 (Step 1) Tympanic portion of the facial nerve.

SSC

LSC

LSC PSC

I

SV

13.2 Lateral Petrosa (Mastoid)

A superficial mastoidectomy has been performed. The body of the incus is seen in the atrium of the mastoid. The tympanic segment of the facial nerve is seen over the lateral semicircular canal. (I, incus; LSC, lateral semicircular canal; M, malleus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve)

L-V I

G

I

SSC

243

244

IV Posterolateral Skull Base

I

I)

Fig. 13.7 Facial recess. The bone over the genu of the facial nerve has been exposed anterior to the lateral semicircular canal by removing the lateral wall of the facial canal. The long crus of the incus, the stapes, and the promontory are seen through the facial recess framed by the short process of the incus, the chorda tympani, and the vertical portion of the facial nerve. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; LC(I), long crus of the incus; LSC, lateral semicircular canal; P, promontory; PSC, posterior semicircular canal; S, stapes; SM, stapedial muscle; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

FR

S

LSC

P

T-V I

CT

I

G

PSC

Fig. 13.8 (Step 2) Fibrocartilaginous ring.

V-VI I

SM

I

The articulation of the incus with the stapes, the chorda tympani, the tympanic membrane, and the fibrocartilaginous ring are seen. Care should be taken not to disrupt the fibrocartilaginous ring, which marks the circumference of the tympanic membrane. Disruption of the thin skin of the external auditory canal, the fibrocartilaginous ring, or the tympanic membrane contaminates the wound and serves as a conduit for cerebrospinal fluid to enter the external auditory canal. (CP, cochleariform process; CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; LC(I), long crus of the incus; LSC, lateral semicircular canal; M, malleus; Man(M), manibrium of the malleus; S, stapes; SC(I), short crus of the incus; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

SC

M

(I)

Ma

LC (I CP

n(M

)

FR

CT

)

S T-VII

LSC

G

M

Fig. 13.9 The tympanic membrane. The tympanic membrane articulates circumferentially with the fibrocartilaginous ring and the manibrium of the malleus attaches to the tympanic membrane. The short crus of the incus is disarticulated from the epitympanic recess. The long crus articulates with the stapes. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; LC(I), long crus of the incus; LSC, lateral semicircular canal; M, malleus; Man(M), manibrium of the malleus; PSC, posterior semicircular canal; S, stapes; SC(I), short crus of the incus; SSC, superior semicircular canal; TM, tympanic membrane; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

( LC

IB SSC

I

SC(I)

CT

LC( I)

M

an

TM (M

V-VII

FR

)

S

SSC

T-VII

LSC

PSC

G

V-VII

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

M

I SC

(I) LC (

Fig. 13.10 Jacobson’s nerve on the promontory. The tympanic branch of the glossopharyngeal nerve (Jacobson’s nerve) courses along the promontory. This nerve provides sensory innervation to the mucous membrane of the middle ear. Its fibers are joined by sympathetic fibers to form the tympanic plexus. Fibers coalesce to form the lesser petrosal nerve, which exits through a small hole in the tegmen tympani lateral to the greater superficial petrosal nerve. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; I, incus; LC(I), long crus of the incus; LSC, lateral semicircular canal; M, malleus; P, promontory; R, round window; S,stapes; SC(I), short crus of the incus; TN, tympanic nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

I)

CT S

FR

P R TN

T-VII

LSC

G

LC (I

)

CT

S

P R TN

Fig. 13.11 Enlarged view of Jacobson’s nerve, Fig.

13.10.

(CT, chorda tympani; LC(I), long crus of the incus; P, promontory; R, round window; S,stapes; TN, tympanic nerve)

CT V-VII C7 TN Fig. 13.12 Jacobson’s nerve. Jacobson’s nerve emerges from the glossopharyngeal nerve into the infralabyrinthine and suprajugular spaces. (C7, C7 portion of the internal carotid artery; CT, chorda tympani; IX, glossopharyngeal nerve; JB, jugular bulb; PSC, posterior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)

PSC

IX

JB

V-VII

245

246

IV Posterolateral Skull Base

Ex-VII

V-VII C7 IX

TN

Fig. 13.13 Jacobson’s nerve. Jacobson’s nerve runs between the internal carotid artery and the jugular bulb. (C7, C7 portion of the internal carotid artery; ExVII, extracranial portion of the facial nerve; IX, glossopharyngeal nerve; JB, jugular bulb; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)

JB

I IB M

CT

an (M )

Fig. 13.14 The stapedial muscle.

SSC

The tiny tendon of the stapedial muscle exists under the proximal vertical portion of the facial nerve, very close to the external genu of the facial nerve. The tendon attaches to the neck of the stapes. (CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; Man(M), manibrium of the malleus; PSC, posterior semicircular canal; SM, stapedial muscle; SSC, superior semicircular canal; ,TM, tympanic membrane; V-VII, vertical segment of the facial nerve)

TM

G

LSC

V-VII

SM

PSC JB ES

I IB CT

S

G

LSC SSC Fig. 13.15 The stapedial muscle. The facial nerve is raised to show the stapedial muscle. (CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; S, stapes; SM, stapedial muscle; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

V-VII

SM

PSC JB ES

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

Fig. 13.16 (Step 3) The cochlear aqueduct. The cochlear aqueduct passes from the base of the cochlea close to the vestibule and communicates with the jugular foramen close to the exit of the glossopharyngeal nerve. Drilling in front of the superior aspect of this structure risks injury to the cochlea. Drilling close to the inferior end of the cochlear aqueduct risks injury of the glossopharyngeal nerve. The cochlear aqueduct divides the bone into an infralabyrinthine and a suprajugular triangle. The infralabyrinthine triangle is delineated by the cochlear aqueduct, posterior fossa dura, and posterior semicircular canal. Extension of the superior leg of the infralabyrinthine triangle leads to the basal turn of the cochlea. Drilling cranial to the superior line of this triangle can lead to cochlear injury. The suprajugular triangle is defined by the cochlear aqueduct, jugular bulb, and C7 vertical portion of the internal carotid artery. An extension of the inferior leg of the suprajugular triangle leads to the ninth nerve canal. Drilling caudal to the inferior leg of this triangle can lead to glossopharyngeal nerve injury. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; IB, incus buttress; ILT, infralabyrinthine triangle; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SJT, suprajugular triangle; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)

IB

TT

CT

LSC

V-VII

G

SSC

PSC

SS

TT

CT

V-VII

G

LSC

JB CA

SSC

canals.

PSC

The hard bone around the semicircular canals can be thinned under constant irrigation until the canals are seen through the thinned bone. This maneuver is performed during a middle fossa or presigmoid approach to maximize the size of the operative field. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)

ES

SS

I

IB

LSC

TT

CT G

SSC

PSC

Fig. 13.18 Opening the bony labyrinth.

SS

V-VII CA

ES

The orientations of the three semicircular canals are demonstrated. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; VVII, vertical segment of the facial nerve)

JB

ES

IB

Fig. 13.17 (Step 4) Blue line of the semicircular

SJT

CA

ILT

JB

247

248

IV Posterolateral Skull Base

I

CT

IB G

TT

JB V

SSC

Fig. 13.19 The vestibular aqueduct.

CA

ES

VA

The vestibular aqueduct opens into the vestibule close to the opening of the common crus. The position of the posterior semicircular canal can be estimated by following the endolymphatic sac to the vestibular aqueduct. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V, vestibule; VA, vertebral artery; V-VII, vertical segment of the facial nerve)

SS

I

CT

IB P

TT

VII M-

Fig. 13.20 Opening the internal auditory canal.

V-VII

SV

The facial, the cochlear, and the superior and inferior vestibular nerves travel in the internal auditory canal. The superior and inferior nerves are elevated to show the underlying facial and the cochlear nerves, respectively. (C, cochlear nerve; CA, cochlear aqueduct; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; I, incus; IB, incus buttress; IV, inferior vestibular nerve; JB, jugular bulb; M-VII, meatal segment of the facial nerve; P, promontory; SS, sphenoid sinus; SV, superior vestibular nerve; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)

C IV

G

V-VII

JB

CA

SS

CT

T-VII

GG L-VII

Fig. 13.21 Opening the basal turn of the cochlea. The vestibule connects the semicircular canals with the cochlea. Drilling anterior to the posterior semicircular canal under the facial nerve exposes the vestibule and the basal turn of the cochlea. (bCo, basal turn of the cochlea; C, cochlear nerve; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; IV, inferior vestibular nerve; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

bCO

M-VII

SV

C

IV

G

V-VII

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

M CT

CP

Fig. 13.22 The oval and round windows.

P R

LSC

To show the relationship between the internal auditory canal and semicircular canals, the posterior semicircular canal and a part of the superior semicircular canal are drilled away. The oval window is the seat of the head of the stapes bone. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; PSC, posterior semicircular canal; R, round window; SS, sphenoid sinus; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)

I V-VI

G

TN CA

SSC

JB PSC

SS

M CT

CP

P R

LSC

I V-VI

G

SSC

CA

TN

JB

Fig. 13.23 The cochlear aqueduct. The focus is on the cochlear aqueduct, which connects the basal turn of the cochlea with the jugular foramen. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; PSC, posterior semicircular canal; R, round window; SS, sphenoid sinus; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)

PSC

SS

M

CP CT LSC SSC Fig. 13.24 The oval window. The dissector is inserted through the oval window. The tip of the dissector can be seen in the vestibule. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; R, round window; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)

P

R

V-VII

G

TN CA

JB

249

250

IV Posterolateral Skull Base

M

CP

CT

LSC

P

SSC

V-VII G

Fig. 13.25 The round window. The dissector is inserted through the round window. The tip of the dissector can be seen in the vestibule. (CA, cochlear aqueduct; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; SSC, superior semicircular canal; TN, tympanic nerve; V-VII, vertical segment of the facial nerve)

CA

TN

JB

M CP

Fig. 13.26 The cochleariform process. The cochleariform process serves as a pulley for the tensor tympani muscle. The malleus and the incus have been removed. (CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; LSC, lateral semicircular canal; M, malleus; P, promontory; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

CT

LSC

P

SSC

V-VII

G

M CP CT P R Fig. 13.27 The vestibule. The vestibule is opened. A white or yellow dot (Mike’s dot) marks the superior division of the vestibular nerve, which exits to innervate the lateral and superior semicircular canals. (CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; M, malleus; P, promontory; R, round window; SSC, superior semicircular canal; V, vestibule; VVII, vertical segment of the facial nerve)

SSC

V

G

V-VII

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

M CP

bCo

SSC

Fig. 13.28 White or yellow dot in the vestibule. The superior vestibular nerve is seen as a skeletonized white or yellow point. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; CP, cochleariform process; M, malleus; SSC, superior semicircular canal; TN, tympanic nerve)

CA

TN

M Fig. 13.29 The basal turn of the cochlea and facial

nerve.

GG

CP

T-VII

L-VII

SSC

CT bCo G

V-VII

M-VII

The vestibule opens into the basal turn of the cochlea anteriorly. Removing the roof of the vestibule opens the fundus of the internal auditory canal. The facial nerve is on the opposite side of Bill’s bar. The cochleariform process is a landmark of the geniculate ganglion of the facial nerve when the translabyrinthine approach is performed. (bCo, basal turn of the cochlea; CP, cochleariform process; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

JB

M CP T-V II

GG

L-VII

Fig. 13.30 The basal turn of the cochlea.

bCo

TP

SSC M-VII

The relationship between the fundus of the internal auditory canal and the basal turn of the cochlea is demonstrated. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; CP, cochleariform process; GG, gasserian ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; TP, transverse process; T-VII, tympanic segment of the facial nerve)

bCo

CA

JB

251

252

IV Posterolateral Skull Base

M CP bCo

bCo

Mo

TP

Fig. 13.31 The basal turn of the cochlea.

SSC

The facial nerve has been translocated inferiorly to expose the length of the basal turn of the cochlea. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; CP, cochleariform process; M, malleus; Mo, modiolus; SSC, superior semicircular canal; TP, transverse process)

CA

M

M

an

(M

)

FR

TM

C6

Fig. 13.32 The internal carotid artery.

SSC

bCo

Mo

bCo

C7

The genu of the carotid artery between carotid segments C6 and C7 is located anterior to the cochlea. (bCo, basal turn of the cochlea; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; FR, fibrocartilaginous ring; JB, jugular bulb; M, malleus; Man(M), manibrium of the malleus; Mo, modiolus; SSC, superior semicircular canal; TM, tympanic membrane)

JB

M FR

SSC Fig. 13.33 The auditory tube (eustachian tube). The eustachian tube is lateral to the C6 segment of the carotid artery. (bCo, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; FR, fibrocartilaginous ring; JB, jugular bulb; M, malleus; Mo, modiolus; SSC, superior semicircular canal)

Mo

bCo

C7

JB

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

M

II V-V Fig. 13.34 The auditory tube (eustachian tube).

SSC

JB

M-VII

The facial nerve is returned to its normal position to demonstrate the relationship between the eustachian tube and the nerve. (C7, C7 portion of the internal carotid artery; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; M, malleus; MVII, meatal segment of the facial nerve; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

C7

G

M

aCo

C7

mCo Mo

Fig. 13.35 Exposing the cochlea via the transmastoid approach.

SSC

bCo

TC

CA

Drilling the posterior wall, the three turns of the cochlea are seen. (aCo, apical turn of the cochlea; bCo, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; JB, jugular bulb; M, malleus; mCo, middle turn of the cochlea; Mo, modiolus; SSC, superior semicircular canal; TC, transverse crest)

M

aCo

SSC

Mo

bCo

I V-VI G CA

The facial nerve is returned to its normal position to demonstrate the relationship between the cochlea and the facial nerve. (aCo, apical turn of the cochlea; bCo, basal turn of the cochlea; CA, cochlear aqueduct; G, genu [second turn or external turn] of the facial nerve; M, malleus; Mo, modiolus; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

II T-V

Fig. 13.36 The relationship between the cochlea and the facial nerve.

JB

253

IV Posterolateral Skull Base

CT V-VII

C7 IX IPS

CA

IX

Fig. 13.37 The anatomy of the pars nervosa of the

X XII XI

jugular foramen.

XI

X,

The picture from Chapter 16 (transjugular approach) demonstrates the ninth cranial nerve separated from the tenth and eleventh cranial nerves by the inferior petrosal sinus. The condyle has been opened to demonstrate the hypoglossal nerve and the jugular vein. The sigmoid sinus has been removed. (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; CT, chorda tympani; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; V-VII, vertical segment of the facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XII

JT

VA

M C6

I

CT C7

SS

TT

P

II V-V

R

LSC

G

JB

SSC

CA

Fig. 13.38 Schema of the intramastoid-1.

PSC

Overview after the standard mastoidectomy. The facial nerve is skeletonized. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external turn] of the facial nerve; I, incus; JB, jugular bulb; LSC, lateral semicircular canal; M, malleus; P, promontory; PSC, posterior semicircular canal; R, round window; SPS, superior petrosal sinus; SS, sphenoid sinus; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)

SPS

ES SS

GSPN

254

TM CT

GG

Co

Co

M-V II

Fig. 13.39 Schema of the intramastoid-2. The mastoid portion of the facial nerve is seen overlying the cochlea. (Co, cochlea; CT, chorda tympani; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; TM, tympanic membrane; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

II V-V

I

I

I T-V

LVI

G

13.1 Anatomy for Posterolateral Skull Base Surgery: Superior Petrosa (Middle Fossa)

C6 C7

SPS

CL

JB

VI IPS

Fig. 13.40 Schema of the intramastoid-3.

VII

A partial clivectomy is done after drilling of the semicircular canals and the cochlea. The inferior petrosal sinus is seen. The abducens nerve exists in the inferior petrosal sinus. The facial nerve has been posteriorly translocated. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; SPS, superior petrosal sinus; VI, abducens nerve; VII, facial nerve)

C6 C7

SPS

CL VI IPS

BA AICA

Fig. 13.41 Schema of the intramastoid-4. After opening the dura, the abducens nerve is well seen. The nerve penetrates the clival dura and runs in the inferior petrosal sinus toward Dollero’s canal. (BA, basilar artery; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; SPS, superior petrosal sinus; VI, abducens nerve; VII, facial nerve)

JB

VI

VII

255

256

IV Posterolateral Skull Base

13.3 Posterior Petrosa (Inner Petrosa) Key Steps Step 1. Preparation of dura for opening of IAC (Fig. 13.42) Step 2. Opening of IAC (Fig. 13.44) Step 3. Identification of transverse crest (Fig. 13.48)

Illustrated Steps with Commentary

Fo

Fig. 13.42 (Step 1) Inner petrosa anatomy, important for a retrosigmoid C-P angle approach to a transmeatal exposure.

JF

IAC

The fovea marks the apex of the endolymphatic sac. To open the internal auditory canal a dural flap is turned in the shape of an inverted “U.” The base of the “U” is just beyond the fovea. Opening the dura further laterally risks opening into the sigmoid sinus. The arms of the “U” are 2 mm above and below the internal auditory canal. (Fo, fovea; IAC, internal auditory canal; JF, jugular foramen)

6-7 mm

2 mm

2m

Fig. 13.43 Inverted "U" shaped dural reflection for unroofing the internal auditory canal for vestibular schwannoma surgery. Dural feeding vessels traveling to an acoustic schwannoma can be cut and coagulated when the dural flap is raised.

m

13.3 Anatomy for Posterolateral Skull Base Surgery: Posterior Petrosa (Inner Petrosa)

Fig. 13.44 (Step 2) Internal auditory canal. The opening of the internal auditory canal (IAC) is initiated using a 4 mm extra coarse diamond bur. The IAC is roughly defined exposing the apex of its posterior curve. The gutters are defined to expose the posterior 180 degrees of the IAC dura using progressively smaller burs. The bone over the IAC is “eggshelled” and chipped away. To avoid opening the vestibule, approximately 6-8 mm of IAC is exposed. The exact length of the opening is defined for each patient from the preoperative magnetic resonance image or computed tomography scan. The vestibule runs behind the fundus of the IAC when the patient is in the lateral position. (IAC, internal auditory canal; SA, subarcuate artery)

IAC

SA

d-IAC Fig. 13.45 Dura mater of the internal auditory

canal.

The dural covering of the internal auditory canal (IAC) can be very thin. Thus, the surgeon is safest using an “eggshell” approach; i.e., thinning the bone overlying the IAC and lifting the thinned bone off of the dura. (d-IAC, dura of the internal auditory canal; SA, subarcuate artery)

SA

SF

TC

Fig. 13.46 Maximum exposure of the fundus to save hearing without opening the vestibule. The facial nerve is seen exiting the internal auditory canal (IAC) superior and deep. The cochlear nerve and two vestibular nerves are inferior to the facial nerve in this specimen. The dura is trimmed close to the walls of the bony opening so that the overhanging dura doses not obstruct the surgeon’s view. The fundus of the IAC is opened by obliquely drilling the bone that lies between the vestibule and the IAC. (IV, inferior vestibular nerve; SF, singular foramen; SV, superior vestibular nerve; TC, transverse crest; VII, facial nerve)

SV

VII IV

257

258

IV Posterolateral Skull Base

V

TC

Fig. 13.47 Opening the vestibule. If hearing is to be preserved, the vestibule should not be opened. This dissection demonstrates the relationship between the vestibule and the fundus of the internal auditory canal. (TC, transverse crest; V, vestibule)

V

2 mm TC

Fig. 13.48 (Step 3) Distance of vestibule from transverse crest. The vestibule lies 2 mm posterior-lateral to the transverse crest at the fundus. Further drilling will be done to define the relationship of the middle and inner ear structures to the retrosigmoid approach. Although these structures are not exposed during the retrosigmoid approach, these dissections will further enhance the reader’s understanding of the anatomy in the region. (TC, transverse crest; V, vestibule)

ES

Fig. 13.49 The endolymphatic sac. The endolymphatic sac lies in a triangular shaped bony depression situated between the fovea and the sigmoid sinus. (ES, endoymphatic sac)

13.3 Anatomy for Posterolateral Skull Base Surgery: Posterior Petrosa (Inner Petrosa)

PSC

V-VII

SSC V

Fig. 13.50 The semicircular canals viewed from the inner petrosa.

JB TC

Further bony removal defines the relationship of the vestibule, semicircular canals, and internal auditory canal. The posterior semicircular canal and the connection of the common crus with the superior semicircular canal are demonstrated. (IV, inferior vestibular nerve; M-VII, meatal segment of the facial nerve; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; V, vestibule; V-VII, vertical segment of the facial nerve)

SV M-VII IV

V-VII

G

PSC R

JB

Fig. 13.51 The jugular bulb. In this case the jugular bulb lies far inferior the internal auditory canal (IAC). In other cases the jugular bulb lies very close to the IAC. If the jugular bulb interferes with the exposure of the IAC, the bulb can be shrunk with the aid of a bipolar cautery and pushed inferiorly with bone wax. (G, genu [second turn or external turn] of the facial nerve; IV, inferior vestibular nerve; JB, jugular bulb; PSC, posterior semicircular canal; R, round window; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; V, vestibule; V-VII, vertical segment of the facial nerve)

SSC

V TC SV IV

PSC

SSC

CC

V JB

TC

Fig. 13.52 The common crus. The common crus connects the posterior and superior semicircular canals. The subarcuate artery enters through the posterior face of the petrous bone and passes through the center of the superior semicircular canal. (CA, cochlear aqueduct; CC, common crus; IV, inferior vestibular nerve; JB, jugular bulb; M-VII, meatal segment of the facial nerve; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; V, vestibule)

CA

SV

M-VII

IV

259

260

IV Posterolateral Skull Base

PSC

SSC

CC

V TC

Fig. 13.53 The operative angle.

CA

SV

The semicircular canals and surrounding structures viewed from the operative angle of a surgeon exploring a vestibular schwannoma from a retrosigmoid approach. (CA, cochlear aqueduct; CC, common crus; IV, inferior vestibular nerve; JB, jugular bulb; JF, jugular foramen; M-VII, meatal segment of the facial nerve; PSC, posterior semicircular canal; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; V, vestibule)

IV

M-VII

JF

G

LSC

Fig. 13.54 After the posterior semicircular canal is

removed.

JB

V-VII

TM

SSC

V

The lateral semicircular canal is seen behind the posterior semicircular canal. The cochlear aqueduct is seen passing to the pars nervosa of the jugular foramen. Jacobson’s nerve passes from the jugular foramen to the middle ear. (CA, cochlear aqueduct; G, genu [second turn or external turn] of the facial nerve; IV, inferior vestibular nerve; JB, jugular bulb; JF, jugular foramen; LSC, lateral semicircular canal; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; V, vestibule; V-VII, vertical segment of the facial nerve)

JB TC

CA

SV IV

M-VII

JF

V-VII G

LSC TM

Fig. 13.55 The tympanic ring and internal carotid

artery.

The genu of the carotid artery lies lateral to the cochlea. The posterior superior margin of the tympanic ring is separated from the lateral semicircular canal by the facial recess. (C7, C7 portion of the internal carotid artery; FR, fibrocartilaginous ring; G, genu [second turn or external turn] of the facial nerve; JB, jugular bulb; JF, jugular foramen; LSC, lateral semicircular canal; SSC, superior semicircular canal; TM, tympanic membrane; V, vestibule; V-VII, vertical segment of the facial nerve)

SSC

FR

V

JB C7

JF

13.3 Anatomy for Posterolateral Skull Base Surgery: Posterior Petrosa (Inner Petrosa)

V-VII G

LSC TM

Fig. 13.56 Connection from the oval window.

R JB

SSC

The oval window connects the middle ear with the cochlea close to the vestibule. The oval window is covered by the head of the stapes bone. (G, genu [second turn or external turn] of the facial nerve; IV, inferior vestibular nerve; JB, jugular bulb; JF, jugular foramen; LSC, lateral semicircular canal; M-VII, meatal segment of the facial nerve; R, round window; SSC, superior semicircular canal; SV, superior vestibular nerve; TM, tympanic membrane; V-VII, vertical segment of the facial nerve)

SV IV

JF

M-VII

V-VII G

LSC TM

Fig. 13.57 Connection of the round window with the middle ear.

R JB

SSC

The round window on the promontory connects the middle ear with the basal turn of the cochlea close to the vestibule. (G, genu [second turn or external turn] of the facial nerve; IV, inferior vestibular nerve; JB, jugular bulb; JF, jugular foramen; LSC, lateral semicircular canal; M-VII, meatal segment of the facial nerve; R, round window; SSC, superior semicircular canal; SV, superior vestibular nerve; TM, tympanic membrane; V-VII, vertical segment of the facial nerve)

SV IV

JF

M-VII

LSC P

JB

R

SV

SSC Fig. 13.58 The skeletonized superior vestibular

nerve.

The superior vestibular nerve passes to the ampulla of the superior semicircular canal. We are used to seeing this relationship from a middle fossa approach. (CA, cochlear aqueduct; IV, inferior vestibular nerve; LSC, lateral semicircular canal; M-VII, meatal segment of the facial nerve; P, promontory; R, round window; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest)

TC

CA

SV IV M-VII

261

IV Posterolateral Skull Base

LSC bCo

SV

Fig. 13.59 Beginning of the basal turn of the

SSC JB

cochlea.

TC

The promontory is seen within the middle ear over the basal turn of the cochlea. The connection between the basal turn of the cochlea and the vestibule is demonstrated. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; IV, inferior vestibular nerve; JB, jugular bulb; LSC, lateral semicircular canal; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest)

CA

SV IV M-VII

M

Ma

TVI

I

G

n(M )

SSC

SV

bCo

Fig. 13.60 The facial nerve. The facial nerve passes anterior lateral to the lateral semicircular canal. This dissection demonstrates the labyrinthine and tympanic segments of the facial nerve viewed from the inner petrosa approach. (bCo, basal turn of the cochlea; CA, cochlear aqueduct; G, genu [second turn or external turn] of the facial nerve; IV, inferior vestibular nerve; JB, jugular bulb; M, malleus; Man(M), manibrium of the malleus; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve)

JB SV

CA IV

M-VII

I

M TVI

262

GG bCo

SSC

L-VII

Mo bCo

Fig. 13.61 The basal turn of the cochlea. The basal turn of the cochlea is opened. The modiolus that is the central bony pillar of the cochlea is seen. (All but the facial nerve have been removed). (bCo, basal turn of the cochlea; CA, cochlear aqueduct; GG, gasserian ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M, malleus; Mo, modiolus; M-VII, meatal segment of the facial nerve; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve)

JB CA

M-VII

13.3 Anatomy for Posterolateral Skull Base Surgery: Posterior Petrosa (Inner Petrosa)

M Ma n(M

TM

)

lateral half of Co

SSC

JB bCo Mo

CA

C7

Fig. 13.62 Drilled cochlea. After the lateral half of the cochlea is removed, the manibrium of the malleus and the tympanic membrane can be seen. (bCo, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; Co, cochlea; JB, jugular bulb; M, malleus; Man(M), manibrium of the malleus; Mo, modiolus; SSC, superior semicircular canal; TM, tympanic membrane)

ES Fo

Fig. 13.63 Schematic of the retrosigmoid approach to the internal auditory canal and schema of the inner petrosa-1. The inverted “U” shaped dural opening is outlined. The base of the “U” is at the apex of the endolymphatic sac and the arms of the “U” bracket the meatus of the internal auditory canal. (AICA, anterior inferior cerebellar artery; ES, endolymphatic sac; Fo, fovea; IX, glossopharyngeal nerve; JF, jugular foramen; Po, pons; SCA, superior cerebellar artery; Tri, trigeminal nerve; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

JF SCA

VI

Tri

VIII

VII

AICA

Po

IX

X

XI

LSC

PSC

SSC TC

V

IAA

SV IV

Fig. 13.64 Schema of the inner petrosa-2. The internal auditory canal has been opened posteriorly. The position of the semicircular canal and vestibule are demonstrated. (AICA, anterior inferior cerebellar artery; IAA, internal auditory artery; IV, inferior vestibular nerve; IX, glossopharyngeal nerve; JF, jugular foramen; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; Tri, trigeminal nerve; V, vestibule; VI, abducens nerve; VII, facial nerve; X, vagus nerve; XI, accessory nerve)

JF SCA

VI

Tri Po

VII

IX AICA

X

XI

263

264

IV Posterolateral Skull Base

LSC

PSC

SSC

V

Co IAA

SV IV TC

Fig. 13.65 Schema of the inner petrosa-3. The position of the cochlea is demonstrated. (AICA, anterior inferior cerebellar artery; Co, cochlea; IAA, internal auditory artery; IV, inferior vestibular nerve; IX, glossopharyngeal nerve; JF, jugular foramen; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; Tri, trigeminal nerve; V, vestibule; VI, abducens nerve; VII, facial nerve; X, vagus nerve; XI, accessory nerve)

SCA

VI

Tri

JF VII

IX AICA

Po

X

XI

LSC

PSC

SSC

V SA

Co

TC

CA

SV IV

IAA

Fig. 13.66 Schema of the inner petrosa-4. The cochlear aqueduct and the subarcuate artery are demonstrated. (AICA, anterior inferior cerebellar artery; CA, cochlear aqueduct; Co, cochlea; IAA, internal auditory artery; IV, inferior vestibular nerve; IX, glossopharyngeal nerve; JF, jugular foramen; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SA, subarcuate artery; SCA, superior cerebellar artery; SSC, superior semicircular canal; SV, superior vestibular nerve; TC, transverse crest; Tri, trigeminal nerve; V, vestibule; VI, abducens nerve; VII, facial nerve; X, vagus nerve; XI, accessory nerve)

JF SCA

VI

Tri

VII

IX AICA

Po

X

XI

LSC

PSC SSC

V SA

Co

C7 JB CA

SV IV

Fig. 13.67 Schema of the inner petrosa-5. The jugular bulb and the internal carotid artery are demonstrated. (AICA, anterior inferior cerebellar artery; (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; Co, cochlea; IV, inferior vestibular nerve; IX, glossopharyngeal nerve; JB, jugular bulb; JF, jugular foramen; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SA, subarcuate artery; SCA, superior cerebellar artery; SSC, superior semicircular canal; SV, superior vestibular nerve; Tri, trigeminal nerve; V, vestibule; VI, abducens nerve; VII, facial nerve; X, vagus nerve; XI, accessory nerve)

JF SCA

VI

Tri Po

VII

IX AICA

X

XI

13.3 Anatomy for Posterolateral Skull Base Surgery: Posterior Petrosa (Inner Petrosa)

T-VII PSC

GG

II L-V

SSC

V

G

Co

C7 JB

SA SV IV

Fig. 13.68 Schema of the inner petrosa-6. The course of the facial nerve is demonstrated. (AICA, anterior inferior cerebellar artery; C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; Co, cochlea; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; IV, inferior vestibular nerve; IX, glossopharyngeal nerve; JB, jugular bulb; JF, jugular foramen; L-VII, labyrinthine segment of the facial nerve; Po, pons; PSC, posterior semicircular canal; SA, subarcuate artery; SCA, superior cerebellar artery; SSC, superior semicircular canal; SV, superior vestibular nerve; Tri, trigeminal nerve; T-VII, tympanic segment of the facial nerve; V, vestibule; VI, abducens nerve; VII, facial nerve; X, vagus nerve; XI, accessory nerve)

JF

CA SCA

VI

Tri

IX

VII

AICA

Po

X

LSC

PSC

SSC V

IAA

TC

Fig. 13.69 Schema of the inner petrosa-7.

SCA

The dura and the nerves are removed. The semicircular canals and the vestibule are demonstrated. (AICA, anterior inferior cerebellar artery; IAA, internal auditory artery; JF, jugular foramen; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; TC, transverse crest; V, vestibule; VI, abducens nerve)

JF

AICA

VI

Po

LSC

PSC

SSC

V TC

Fig. 13.70 Schema of the inner petrosa-8. The cochlea is demonstrated. (AICA, anterior inferior cerebellar artery; Co, cochlea; IAA, internal auditory artery; JF, jugular foramen; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; TC, transverse crest; V, vestibule; VI, abducens nerve)

VI

SCA

Po

Co IAA

AICA

JF

XI

265

266

IV Posterolateral Skull Base

GG

II L-V

SSC

T-VII PSC

V

Fig. 13.71 Schema of the inner petrosa-9. The facial nerve, the internal auditory canal, and the jugular bulb are demonstrated. (AICA, anterior inferior cerebellar artery; C7, C7 portion of the internal carotid artery; Co, cochlea; G, genu [second turn or external turn] of the facial nerve; GG, gasserian ganglion; IAA, internal auditory artery; JB, jugular bulb; JF, jugular foramen; L-VII, labyrinthine segment of the facial nerve; Po, pons; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; TC, transverse crest; T-VII, tympanic segment of the facial nerve; V, vestibule; VI, abducens nerve)

G

TC

Co

C7

JB

IAA

VI

SCA

Po

JF AICA

14

Transmastoid Approach: Retrolabyrinthine, Translabyrinthine, and Transcochlear Approaches

The retrolabyrinthine, translabyrinthine, and transcochlear approaches offer the surgeon progressively flatter trajectories to the clivus. These approaches are usually combined with a temporal craniotomy and incision of the tentorium cerebelli to increase the scope of the surgery and the surgeon’s working room. Even the retrolabyrinthine approach, which preserves the patient’s hearing, affords the surgeon a very nice view of the lateral brainstem limited by the seventh and eighth cranial nerves. This approach is used to expose extra-axial tumors and small to moderate sized aneurysms of the basilar artery. Larger lesions and lesions that significantly cross the midline are exposed by the translabyrinthine and transcochlear exposures.

14.1 Retrolabyrinthine Approach Key Steps Position: Lateral Step 1. Skin incision retroauricular c-shaped (Fig. 14.1) Step 2. Scalp elevation in two layers (galeocutaneous and myofascial layers) (Fig. 14.2) Step 3. Exposure of the body of the mastoid (Fig. 14.7) Step 4. Drilling of the outer triangle of the mastoid (Fig. 14.11) Step 5. Identification of the sigmoid sinus plate (Fig. 14.13) Step 6. Identification of the lateral semicircular canal in the mastoid antrum (Fig. 14.14) Step 7. Exposure of the semicircular canals (Fig. 14.22) Step 8. Exposure of the facial nerve (Fig. 14.25) Step 9. Exposure of the jugular bulb (Fig. 14.28)

Illustrated Steps with Commentary

MT

Fig. 14.1 (Step 1) Skin incision retroauricular "C" shaped.

The mastoid tip is palpated and outlined on the skin, the internal auditory canal lies along a plane drawn through the external auditory canal. (MT, mastoid tip)

268

IV Posterolateral Skull Base

Fig. 14.2 (Step 2) Elevating the scalp flap. The scalp flap should be elevated in two layers. The skin, subcutaneous fat, and a thin layer of fibrous tissue are elevated. Twothirds the thickness of fibrous tissue is left behind.

GFFM

Fig. 14.3 Harvesting the galeofascial patch. The galeofascial fibrous membrane (epicranium aponeurotica) should be harvested to facilitate closing the dura at the end of the surgery. (GFFM, galeofascial fibrous membrane)

PAM

Fig. 14.4 Harvesting a galeofascial fibrous membrane.

(PAM, posterior auricular muscle)

14.1 Transmastoid Approach: Retrolabyrinthine Approach

PAM

SCM

Fig. 14.5 Identifying the postauricular and sternocleidomastoid muscles.

After the galeofascial fibrous tissue is harvested, the postauricular and sternocleidomastoid muscles are exposed. (PAM, posterior auricular muscle; SCM, sternocleidomastoid muscle)

Fig. 14.6 Elevating the myofascial layer to expose the mastoid.

The myofascial layer can be incised in a “T” shaped fashion, but incising the fascia in a “C” shape makes for better exposure. The underlying muscle is elevated from the occipital bone.

SMC

MacT

SqS

Fig. 14.7 (Step 3) Identification of superficial bony landmarks.

The squamosal, parietomastoid, occipitomastoid, and lambdoid sutures and the asterion are identified. Macewen’s triangle is 15 mm superficial to the mastoid antrum and the spine of Henle is 15 mm superficial to the external genu of the facial nerve. The supramastoid crest or ridge that corresponds to the temporal tegmen is identified. (As, asterion; LS, lambdoid suture; MacT, Macewen’s triangle; OMS, occipitomastoid suture; PMS, parietomastoid suture; SMC, supramastoid crest; SqS, squamosal suture)

PMS

As LS

OMS

269

270

IV Posterolateral Skull Base

PMS As OMS

Fig. 14.8 Identifying the asterion.

LS

The asterion, the intersection of the parietomastoid, occipitomastoid, and lambdoid sutures, is identified. The asterion is an approximate landmark for the inferior corner of the transverse sinus–sigmoid sinus junction. (As, asterion; LS, lambdoid suture; OMS, occipitomastoid suture; PMS, parietomastoid suture)

SH

Fig. 14.9 Identifying Macewen’s triangle and the spine of Henle.

Macewen’s triangle is detected as a depressed, triangular area in the mastoid bone posterior and superior to the external auditory canal. The spine of Henle is a bony protrusion on the superoposterior edge of the external auditory canal. In some cases this bony protrusion is not well developed. (MacT, Macewen’s triangle; SH, spine of Henle; SMC, supramastoid crest)

Fig. 14.10 Identifying the three corners of the outer triangle. The posterior point of the root of the zygoma, the mastoid tip, and a point just medial to the asterion are the landmarks of the outer triangle. This triangle makes the superficial landmarks for beginning the mastoidectomy.

SMC

MacT

14.1 Transmastoid Approach: Retrolabyrinthine Approach

Fig. 14.11 (Step 4) Incising the outer triangle. The sides of the outer triangle are incised with a cutting bur.

Fig. 14.12 Drilling the cortical bone and mastoid

air cells.

The cortical bone within the outer triangle is removed with a cutting bur. The mastoid air cells are drilled away evenly in a planar fashion. The surgeon must avoid digging a hole into the air cells. Another option is a cosmetic mastoidectomy. The cortical bone over the mastoid is removed as a single piece to be replaced at the end of the case. This technique has a greater risk of injuring the sigmoid sinus. The value of the cosmetic mastoidectomy is diminished because the bony defect of a standard mastoidectomy can be restored with titanium plates and hydroxy appetite.

SSP

Fig. 14.13 (Step 5) Identification of sigmoid sinus

plate.

With even planar drilling of the posterior temporal bone, the cortical bone over the sigmoid sinus will transmit the blue of the sigmoid sinus. The sigmoid sinus may run very anteriorly when the mastoid sinus is small. In such cases the bone over and behind the sigmoid sinus should be removed so that the sigmoid sinus can be retracted posteriorly. (SSP, sigmoid sinus plate)

271

272

IV Posterolateral Skull Base

MA

SSP Fig. 14.14 (Step 6) Identification of the mastoid

antrum.

The first deep landmark is the mastoid antrum. This lies 15 mm deep to Macewen’s triangle. The antrum is a large air cell. The hard bone of the lateral semicircular canal is seen protruding posteriorly into the mastoid antrum. In addition, the short crus of the incus protrudes inferiorly into the antrum. (MA, mastoid antrum; SSP, sigmoid sinus plate)

MA LSC Fig. 14.15 Identifying the bony protrusion of the lateral semicircular canal. The hard yellow cortical bone of the lateral semicircular canal can be seen bulging into the mastoid antrum. All the important anatomical structures except the sigmoid sinus lie medial to the level of the lateral apex of the lateral semicircular canal. This means that drilling lateral to the lateral semicircular canal is safe. (LSC, lateral semicircular canal; MA, mastoid antrum; SSP, sigmoid sinus plate)

SSP

MA LSC

SSP

Fig. 14.16 Saucerizing the mastoid cavity. The remaining air cells lateral to the lateral semicircular canal are removed. The posterior fossa dura is found medial to the sigmoid sinus. The dura can be exposed without risk to the level of the lateral semicircular canal. Medial to this level the surgeon will encounter the posterior semicircular canal. (LSC, lateral semicircular canal; MA, mastoid antrum; SSP, sigmoid sinus plate)

14.1 Transmastoid Approach: Retrolabyrinthine Approach

I LSC

SSP Fig. 14.17 Identifying the incus. The body and short crus of the incus can be seen protruding into the inferior antrum. This important landmark distinguishes the antrum from other air cells. (I, incus; LSC, lateral semicircular canal; SSP, sigmoid sinus plate)

I LSC

SS Fig. 14.18 Exposing the temporal tegmen and sigmoid sinus. To access to the presigmoid area, the bone covering the lateral and the sigmoid sinuses should be removed completely. The bone is drilled until it is paper thin and then dissected from the venous sinus with a flat sharp dissector. The freed sinus can be retracted posteriorly out of the surgeon’s line of sight. (I, incus; LSC, lateral semicircular canal; SS, sphenoid sinus)

I LSC

SS

Fig. 14.19 Exposing the digastric ridge. The fallopian canal exits the temporal bone through the medial edge of the anterior digastric ridge, making the ridge an important landmark. (DR, dural ring; I, incus; LSC, lateral semicircular canal; SS, sphenoid sinus)

DR

273

274

IV Posterolateral Skull Base

I

Fig. 14.20 Removing the anterior portion of the temporal tegmen.

LSC

Great care should be taken to avoid perforating the thin dura above the anterior portion of the temporal tegmen that is near the aditus. The midportion of the temporal base slopes inferiorly into the mastoid, making it easy for the surgeon to drill through the underlying dura. A good technique is to use Gelfoam (Pfizer Inc., NY, NY) as a spacer between the middle fossa dura and the temporal bone. ((I, incus; LSC, lateral semicircular canal)

I

LSC

Fig. 14.21 Exposing the lateral semicircular canal. The hard bone of the lateral semicircular canal is followed posterior laterally from the antrum. The lateral semicircular canal shares its anterior wall with the fallopian canal. (I, incus; LSC, lateral semicircular canal)

Fig. 14.22 (Step 7) Exposure of semicircular

canals.

The posterior semicircular canal runs perpendicular to the lateral semicircular canal. The endolymphatic sac, which can be seen on the posterior fossa dura, points to the inferior half of the posterior semicircular canal. The superior semicircular canal protrudes into the temporal tegmentum. The common crus connects the superior semicircular canal with the posterior canal. The center of the superior semicircular canal is marked by the subarcuate artery. (LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal)

LSC SSC PSC

14.1 Transmastoid Approach: Retrolabyrinthine Approach

LSC SSC Fig. 14.23 Removing the opercular bone medial to the posterior semicircular canal.

PSC

The bone over the posterior fossa dura up to the posterior semicircular canal should be removed. Removing the opercular bone medial to the posterior semicircular canal improves the surgeon’s vision of the lateral cerebellopontine angle. (LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal)

I

SSC

LSC

Fig. 14.24 Thinning the bone of the semicircular canals (bony labyrinth). The hard bone overlying the semicircular canals can be gradually thinned until the blue of the underlying membranous canals is seen using a diamond drill and profuse irrigation. Irrigation is important to mitigate the heat generated by the drill and to wash away the dull bone dust, which improves the surgeon’s view. (I, incus; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal)

PSC

I T-V II

Fig. 14.25 (Step 8) Identification of tympanic segment of the facial nerve anterior to the lateral semicircular canal. The bone overlying the tympanic segment of the facial nerve lies immediately anterior to the lateral semicircular canal. This is the most anatomically constant position of the nerve, which can meander through the mastoid. (I, incus; LSC, lateral semicircular canal; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve)

SSC

LSC

275

276

IV Posterolateral Skull Base

I

Fig. 14.26 Skeletonizing the mastoid segment of

the facial nerve.

SSC

LSC

V-VII

PSC

The most anatomically constant location of the facial nerve is its external genu, which lies anterior to the lateral semicircular canal. The course of the nerve is then charted to the stylomastoid foramen starting from this point. The nerve is exposed by removing bone first from its lateral and then its posterior surface. It is possible to find the nerve at the stylomastoid foramen by following the digastric groove anteriorly, but at the stylomastoid foramen the nerve is covered by fibrous tissue and the nerve is not distinct. (DR, dural ring; I, incus; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

DR

SS

SSC

LSC

JB PSC

Fig. 14.27 Exposing the inferior segment of the sigmoid sinus.

SS

As the sigmoid sinus is followed inferiorly, the wall of the sinus becomes thinner and more fragile. A thin malleable layer of bone may be left in place over the inferior loop of the sigmoid sinus. Sigmoid sinus bleeding is best controlled by Gelfoam. (JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal)

V-VII

LSC SSC

JB

PSC Fig. 14.28 (Step 9) Exposure of jugular bulb. In this specimen, the jugular bulb is prominent. The jugular bulb lies anterior to the sigmoid sinus. In this specimen the bulb rises almost to the posterior semicircular canal. Drilling anterior to the posterior semicircular canal risks injury to the cochlea. (JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

SS

14.1 Transmastoid Approach: Retrolabyrinthine Approach

I IB Fig. 14.29 Exposing the facial recess. The external genu and mastoid segments of the facial nerve and the chorda tympani are exposed. The facial recess is defined by the incus buttress, the chorda tympani, and the mastoid segment of the facial nerve. The stapes with the long crus of the incus and the promontory with the round window can be observed through the facial recess. (CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; I, incus; IB, incus buttress; JB, jugular bulb; LSC, lateral semicircular canal; P, promontory; PSC, posterior semicircular canal; S, stapes; V-VII, vertical segment of the facial nerve)

S

CT

P

LSC

V-VII

G

JB PSC LC(I) FR

Fig. 14.30 Skeletonizing the annulus tympanicus. The lateral portion of the annulus tympanicus can be skeletonized. It is seen as a white band ventral to the chorda tympani. Disrupting the annulus of the tympanic membrane or the skin of the external auditory canal lateral to the membrane risks the formation of a cerebrospinal fluid fistula. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external genu] of the facial nerve; LC(I), long crus of the incus; LSC, lateral semicircular canal; P, promontory; PSC, posterior semicircular canal; S, stapes; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

S

LSC

T-V I

CT

P I

G PSC

V-VII

SC (I) LC (

Fig. 14.31 Examining the middle ear. The annulus tympanicus is exposed. The chorda tympani runs between the malleus and the incus. The manibrium of the malleus can be seen attaching to the tympanic membrane. The cochleariform process is seen between the incus and the lateral semicircular canal after the buttress of the incus is removed. The cochleariform process marks the location of the geniculate ganglion. (CP, cochleariform process; CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external genu] of the facial nerve; LC(I), long crus of the incus; LSC, lateral semicircular canal; S, stapes; SC(I), short crus of the incus; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

CP

CT

I)

FR

S

LSC

T-VII

G

V-VII

277

278

IV Posterolateral Skull Base

SC(I) CT

LC( I)

Fig. 14.32 Demonstrating the middle ear

anatomy.

The chorda tympani has been removed to better demonstrate the relationship between the annulus tympanicus, the tympanic membrane, and the manibrium of the malleus. (CT, chorda tympani; FR, fibrocartilaginous ring; G, genu [second turn or external genu] of the facial nerve; LC(I), long crus of the incus; LSC, lateral semicircular canal; Man(M), manibrium of the malleus; SC(I), short crus of the incus; TM, tympanic membrane; V-VII, vertical segment of the facial nerve)

FR

TM M

an

(M

)

LSC

G

V-VII

SC (I) ( LC I)

CT

Fig. 14.33 Identifying Jacobson’s nerve on the

S

promontory.

Jacobson’s nerve (the tympanic nerve), a branch of the glossopharyngeal nerve, can be seen passing over the promontorium. The nerve passes through the middle ear to the otic ganglion innervating the parotid gland. Jacobson’s nerve on the promontory can give rise to glomus tympanicum tumors. (CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; LC(I), long crus of the incus; LSC, lateral semicircular canal; P, promontory; RW, round window; S, stapes; SC(I), short crus of the incus; TN, tympanic nerve [Jacobson’s nerve]; T-VII, tympanic segment of the facial nerve)

LSC

RW

P

TN

T-VII G

CT

V-VII

C7 Fig. 14.34 Identifying Jacobson’s nerve in front of the jugular bulb. Jacobson’s nerve (the tympanic nerve) is identified by drilling the bone anterior to the jugular bulb. The nerve runs in the bony canal between the jugular bulb and the carotid canal. Jacobson’s nerve in this location can be the origin of a glomus jugulare tumor. (C7, C7 portion of the internal carotid artery; CT, chorda tympani; IX, glossopharyngeal nerve; SS, sphenoid sinus; TN, tympanic nerve [Jacobson’s nerve]; V-VII, vertical segment of the facial nerve)

TN

IX SS

14.1 Transmastoid Approach: Retrolabyrinthine Approach

C7 TN

IX

Fig. 14.35 Identifying the origin of Jacobson’s

nerve.

SS

Jacobson’s nerve (the tympanic nerve) originates from the glossopharyngeal nerve. (C7, C7 portion of the internal carotid artery; IX, glossopharyngeal nerve; SS, sphenoid sinus; TN, tympanic nerve [Jacobson’s nerve])

I

Fig. 14.36 Identifying the stapedius muscle. The stapedius muscle, which is innervated by the facial nerve, can be exposed medial to the external genu of the facial nerve in the temporal bone. The short tendon of the stapedius muscle emerges from the pyramidal eminence of the temporal bone and inserts onto the neck of the stapes close to its articulation with the incus. This muscle tilts the head of the stapes away from the oval window, protecting the cochlea from loud noises. (CT, chorda tympani; G, genu [second turn or external guru] of the facial nerve; I, incus; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; S, stapes; SM, stapedial muscle; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

CT

S LSC

G

V-VII

SSC PSC

SM JB

LSC SSC Fig. 14.37 Establishing the blue lines of the semicircular canals. The blue lines (arrowheads) of the semicircular canals can be seen by gradually shaving the cortical bone. The blue line of each semicircular canal corresponds to the membranous labyrinth. In the cadaver the lines appear brown. (LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal)

PSC

279

280

IV Posterolateral Skull Base

Fig. 14.38 Exposing the cochlear aqueduct (final view of retrolabyrinthine petrosectomy). The cochlear aqueduct, which connects the cerebrospinal fluid with the perilymph, can be seen between the bony labyrinth and the pyramidal fossa of the jugular foramen. The cochlear aqueduct separates the infralabyrinthine triangle and the suprajugular triangle. The infralabyrinthine triangle is defined by the inferior point of the posterior semicircular canal, the cochlear aqueduct, and the posterior fossa dura. An extension of the superior leg of this triangle leads to the basal turn of the cochlea. Great care should be taken not to drill anterior to this line when preserving hearing. The suprajugular triangle is defined by the superior point of the jugular bulb, the cochlear aqueduct, and the carotid canal. An inferior extension of the anterior side of the triangle leads to the glossopharyngeal nerve. (CA, cochlear aqueduct; CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external guru] of the facial nerve; ILT, infralabyrinthine triangle; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SJT, suprajugular triangle; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)

Fig. 14.39 Viewing the course of the cochlear

CT TT

V-VII

G

LSC

SJT

SSC PSC

ILT

CA

ES

PSC

aqueduct.

The cochlear aqueduct (ductus perilymphaticus) connects the perilymphatic spaces of the cochlea (scala tympani) with the subarachnoid space of the posterior fossa. The cochlear aqueduct permits the free flow of cerebrospinal fluid into the labyrinth. It passes under the ampullary arm of the posterior semicircular canal and runs toward the top of the hairpin curve of the ninth nerve canal. The cochlear aqueduct arises on the posterior wall of the scala tympani through a small orifice. The aqueduct originates from the inferomedial edge of the round window and proceeds under the spiral lamina. From there, it is directed backward and inferiorly toward the top of the hairpin curve of the ninth nerve canal. It empties into the posterior fossa at the level of the inferior border of the petrosa by the pyramidal fossa, a wide orifice that is found 4 to 5 mm below the internal auditory meatus. The cochlear aqueduct is 10 to 12 mm long and transmits a small vein. (CA, cochlear aqueduct; IX, glossopharyngeal nerve; PSC, posterior semicircular canal)

CA

IX

14.2 Transmastoid Approach: Translabyrinthine Approach

14.2 Translabyrinthine Approach Key Steps Step 10. Removal of the semicircular canals (Fig. 14.40) Step 11. Exposure of the internal auditory canal (Fig. 14.48)

Illustrated Steps with Commentary

I CT

S

TT LSC

V-VII

G

SSC

Fig. 14.40 (Step 10) Opening of membranous

labyrinth.

SM

The membranous labyrinth of the three semicircular canals has been opened to demonstrate their course. The stapedius muscle is seen just under the genu of the facial nerve. (CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external guru] of the facial nerve; I, incus; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; S, stapes; SM, stapedial muscle; SSC, superior semicircular canal; TT, tegmen tympani; V-VII, vertical segment of the facial nerve)

PSC

AmS

I

ES

AmL S

CT

P

V-VII

G

Fig. 14.41 Opening the ampulla of each semicircular canal. A diamond drill is used to remove to the remainder of the bony labyrinth to expose the ampullae. (AmL, ampulla of the lateral semicircular canal; AmP, ampulla of the posterior semicircular canal; AmS, ampulla of the superior semicircular canal; CC, common crus; CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; I, incus; JB, jugular bulb; P, promontory; S, stapes; SM, stapedial muscle; V-VII, vertical segment of the facial nerve)

JB SM

CC

AmP

JB

281

282

IV Posterolateral Skull Base

I

AmL AmS

CT S

P V-VII

Fig. 14.42 Exposing the round window and

promontory

The facial nerve is retracted posteriorly to expose the round window. The foot of the stapedius is seen covering the oval window. The oval window opens into the vestibule, which connects the labyrinth with the cochlea. (AmL, ampulla of the lateral semicircular canal; AmP, ampulla of the posterior semicircular canal; AmS, ampulla of the superior semicircular canal; CC, common crus; CT, chorda tympani; I, incus; JB, jugular bulb; P, promontory; S, stapes; V-VII, vertical segment of the facial nerve)

JB CC

AmP

AmL

I

AmS RW

P Fig. 14.43 Demonstrating the round window and promontory. The round window is located in the basal turn of the cochlea. It lies between the genu of the facial nerve and the promontory of the cochlea. (AmL, ampulla of the lateral semicircular canal; AmP, ampulla of the posterior semicircular canal; AmS, ampulla of the superior semicircular canal; CC, common crus; I, incus; JB, jugular bulb; P, promontory; RW, round window)

JB CC

AmP

I

CT S G

JB

V

Fig. 14.44 Opening the vestibule. The vestibule connects the cochlea and the labyrinth. It lies lateral to the fundus of the internal auditory canal. (CT, chorda tympani; ES, endolymphatic sac; G, genu [second turn or external genu] of the facial nerve; I, incus; JB, jugular bulb; S, stapes; V, trigeminal nerve; V-VII, vertical segment of the facial nerve)

I V-VI

ES

14.2 Transmastoid Approach: Translabyrinthine Approach

I V-VII

RW

JB

V

ES

Fig. 14.45 Demonstrating the relationship between the vestibule and the round window. The round window is seen at the junction of the vestibule and the basal turn of the cochlea. (ES, endolymphatic sac; I, incus; JB, jugular bulb; RW, round window; V, trigeminal nerve; V-VII, vertical segment of the facial nerve)

I S

P

L-V II

G

V

Fig. 14.46 The vestibule. The lateral and posterior semicircular canals have been removed. The vestibule is medial to the genu of the facial nerve and inferior and slightly lateral to the fundus of the internal auditory canal. The vestibule can serve as a landmark for finding the facial nerve. (ES, endolymphatic sac; G, genu [second turn or external genu] of the facial nerve; I, incus; L-VII, labyrinthine segment of the facial nerve; P, promontory; S, stapes; V, trigeminal nerve; V-VII, vertical segment of the facial nerve)

ES

L-V I

P I

G Fig. 14.47 Identifying the vestibular aqueduct. The vestibular aqueduct perforates the posterior wall of the vestibule a little below the orifice of the common crus of the superior and posterior semicircular canals. The ductus endolymphaticus traverses the petrosal cortex, enlarging like an estuary forming a bony cleft called the endolymphatic meatus (apertura external aqueductus vestibuli or fossette ungueale). This depression in the petrous portion of the temporal bone houses the endolymphatic sac. Thus, the endolymphatic sac is a good landmark for finding the common crus of the labyrinth. (ES, endolymphatic sac; G, genu [second turn or external genu] of the facial nerve; L-VII, labyrinthine segment of the facial nerve; P, promontory; V, trigeminal nerve; VA, vertebral artery; V-VII, vertical segment of the facial nerve)

V-VII

V VA

ES

V-VII

283

284

IV Posterolateral Skull Base

GG

I

T-VII

Fig. 14.48 (Step 11) Exposing the internal auditory canal. The labyrinth (semicircular canals) and vestibule are drilled away. As the bone is thinned over the internal auditory canal (IAC), it appears blue. The thinned bone on the IAC should be removed with a sharp dissector. In the case of vestibular schwannoma, the IAC may appear to be yellow or ruby red, depending on the vascularity of the tumor. (CT, chorda tympani; G, genu (second turn or external genu) of the facial nerve; GG, geniculate ganglion; I, incus; IAC, internal auditory canal; IV, inferior vestibular nerve; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SV, superior vestibular nerve; TP, transverse process; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

CT V-VII

L-V II

G

M-VII

TP

JB

IV SV

IAC

GG L -V II I T-VI

V-VII

G TP

vertical crest (Bill’s bar).

M-VII

BB

Fig. 14.49 Identifying the transverse crest and the The transverse crest between the superior and inferior vestibular nerves can be seen. The vertical crest, well known as Bill’s bar, can also be seen between the facial and superior vestibular nerves. (BB, Bill’s bar; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; IAC, internal auditory canal; IV, inferior vestibular nerve; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; SV, superior vestibular nerve; TP, transverse process; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

SV

IV

JB IAC

LC(I) GG

S

L-V II

G

II T-V

Fig. 14.50 Magnified view of the transverse crest (BB, Bill’s bar; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; IAC, internal auditory canal; IV, inferior vestibular nerve; LC(I), long crus of the incus; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; P, promontory; S, stapes; SV, superior vestibular nerve; TP, transverse process; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

SV

TP

M-VII

and the vertical crest (Bill’s bar).

BB

P

IAC

IV

V-VII

14.2 Transmastoid Approach: Translabyrinthine Approach

I

CT

GG I L-V I

P

V-VII

G

SV

IV

M-VII

The superior and inferior vestibular nerves and the facial nerve can be seen. The meatal loop of the anterior inferior cerebellar artery is seen in the porus acousticus. The meatal segment, labyrinthine segment, first turn, tympanic segment, external genu, and mastoid segment of the facial nerve and the chorda tympani are also seen. The mastoid segment of the facial nerve joins the tympanic segment anterior to the lateral semicircular canal. The nerve makes a sharp turn at the geniculate ganglion where the tympanic and labyrinthine segments meet. (AICA, anterior inferior cerebellar artery; CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; I, incus; IV, inferior vestibular nerve; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; P, promontory; S, stapes; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

T-VII

Fig. 14.51 Opening the dura of the internal auditory canal.

S

JB

AICA

I GG

VI L-

G

M-VII

The superior and inferior vestibular nerves are cut and reflected superiorly and inferiorly respectively. The singular nerve, the small branch of the inferior vestibular nerve that supplies the posterior semicircular canal, is also seen. (Co, cochlear nerve; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; I, incus; IV, inferior vestibular nerve; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; P, promontory; S, stapes; SN, singular nerve; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

p

I

T-VII

Fig. 14.52 Exposing the cochlear nerve.

S

Co

SV

V-VII

JB

IV SN

M CP

GG

I G

M-VII

After the incus is removed, the cochleariform process, where the tendon of the tensor tympani muscle turns 90 degrees toward the manibrium, of the malleus can be seen. This process is a landmark for the first turn and geniculate ganglion of the facial nerve when looking from a posterior approach. (AICA, anterior inferior cerebellar artery; Co, cochlear nerve; CP, cochleariform process; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; IV, inferior vestibular nerve; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M, malleus; M-VII, meatal segment of the facial nerve; P, promontory; SV, superior vestibular nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

VI L-

(final view of translabyrinthine approach).

p

T-VII

Fig. 14.53 Identifying the cochleariform process

Co

SV

IV

AIC

A

V-VII

JB

285

286

IV Posterolateral Skull Base

14.3 Transcochlear Approach Key Steps Step 12. Posterior rerouting of the facial nerve (Fig. 14.55) Step 13. Removal of the cochlea (Fig. 14.65) Step 14. Exposure of the internal carotid artery (Fig. 14.66) Step 15. Petrosectomy and partial clivectomy (Fig. 14.65) Step 16. Identification of the inferior petrosal sinus (Fig. 14.67) Step 17. Identification of the abducens nerve on the bottom of the inferior petrosal sinus (Fig. 14.68) Step 18. Intradural exploration (Fig. 14.69)

Illustrated Steps with Commentary

CP

GG

VI L-

p

I

II V-V

T-VII

G

JB M-V

Fig. 14.54 Exposing the facial nerve from the

II

styloid foramen to the meatus of the internal auditory canal

The whole course of the intramastoid facial nerve is well seen. (CP, cochleariform process; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; P, promontory; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

GSPN

CT CP

P RW

JB Fig. 14.55 (Step 12) Posterior rerouting of facial

nerve.

After the greater superficial petrosal nerve is cut, the facial nerve can be translocated posteriorly. (CP, cochleariform process; CT, chorda tympani; GSPN, greater superficial petrosal nerve; JB, jugular bulb; P, promontory; RW, round window)

14.3 Transmastoid Approach: Transcochlear Approach

GSPN

CT

CP P RW TC

Fig. 14.56 Posterior rerouting of the facial nerve (continued). (CP, cochleariform process; CT, chorda tympani; GSPN, greater superficial petrosal nerve; P, promontory; RW, round window; TC, transverse crest)

CT

CP P RW TC JB

Fig. 14.57 Posterior rerouting of the facial nerve. To maximize exposure of the tympanic cavity, the chorda tympani can be sacrificed. In this specimen the nerve has not been cut. (CP, cochleariform process; CT, chorda tympani; JB, jugular bulb; P, promontory; RW, round window; TC, transverse crest)

CP

bCo Fig. 14.58 Removing the bone surrounding the round window. Drilling the bone at the round window exposes the basal turn of the cochlea. (bCo, basal turn of the cochlea; CP, cochleariform process; JB, jugular bulb)

JB

287

288

IV Posterolateral Skull Base

CP Mo JB

bCo Fig. 14.59 Exposure of basal turn of the cochlea. The basal turn with the modiolus of the cochlea is seen. The basal turn abuts the fundus of the internal auditory canal. The modiolus is the central core of the cochlea. (bCo, basal turn of the cochlea; CP, cochleariform process; JB, jugular bulb; Mo, modiolus)

mCo CP

Mo JB bCo Fig. 14.60 Magnified view of the basal turn of the

cochlea.

The basal turn of the cochlea and the beginning of the middle turn with the modiolus can be seen. (bCo, basal turn of the cochlea; CP, cochleariform process; JB, jugular bulb; mCo, middle turn of the cochlea; Mo, modiolus)

aCo

mCo Fig. 14.61 Demonstrating the basal and middle turns of cochlea. Continued removal of anterior bone with a diamond drill demonstrates the middle turn of the cochlea. (aCo, apical turn of the cochlea; bCo, basal turn of the cochlea; JB, jugular bulb; mCo, middle turn of the cochlea)

bCo

JB

14.3 Transmastoid Approach: Transcochlear Approach

CT

GG

L-V I

T-VII

Fig. 14.62 Basal and middle turns of the cochlea

I

II V-V

bCo

G

with the facial nerve.

JB M-VII

The facial nerve has been returned to its original position to show the anatomical relationship of the facial nerve with the basal and middle turns of the cochlea. (bCo, basal turn of the cochlea; CT, chorda tympani; G, genu [second turn or external genu] of the facial nerve; GG, geniculate ganglion; JB, jugular bulb; L-VII, labyrinthine segment of the facial nerve; M-VII, meatal segment of the facial nerve; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

CT

aCo mCo

Mo

JB bCo

Fig. 14.63 Demonstrating the basal, middle, and

apical turns of the cochlea with the facial nerve transposed.

Further drilling of the otic capsule exposes a cross section of the cochlea. (aCo, apical turn of the cochlea; bCo, basal turn of the cochlea; CT, chorda tympani; JB, jugular bulb; mCo, middle turn of the cochlea; Mo, modiolus)

M

FR

bCo

C7

Fig. 14.64 Probing the eustachian tube. A straight dissector indicates the direction of the eustachian tube. The eustachian canal leaves the middle ear anteriorly. (bCo, basal turn of the cochlea; C7, C7 portion of the internal carotid artery; FR, fibrocartilaginous ring; JB, jugular bulb; M, malleus)

JB

289

IV Posterolateral Skull Base

C7

IPS

JB Fig. 14.65 (Steps 13 and 15) Removal of the cochlea and partial removal of the petrous apex and clivus.

V-VII

CL

The cochlea and petrous apex and the adjacent clivus are drilled away. The genu of the carotid artery is seen anterior to where the cochlea had been. (C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; V-VII, vertical segment of the facial nerve)

SPS

C7 C6 JB Fig. 14.66 (Step 14) Exposure of the vertical C7

and horizontal C6 portion of internal carotid artery After the cochlea, petrous bone, and a part of the clivus are removed the vertical C7 and horizontal C6 portions of the internal carotid artery are exposed. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; SPS, superior petrosal sinus; V-VII, vertical segment of the facial nerve)

CL IPS

C7

IPS Fig. 14.67 (Step 16) Exposure of inferior petrosal

sinus.

The inferior petrosal sinus seen in the center of this picture marks the junction between the petrous bone and the clivus. The vertical (C7) portion of the internal carotid artery is exposed anterior to the jugular bulb. (C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb)

CL

JB

V-VII

290

14.3 Transmastoid Approach: Transcochlear Approach

IPS

CL

VI

JB

PD Fig. 14.68 (Step 17) Identifying the abducens

nerve.

The abducens nerve can be identified toward the anterior end of the inferior petrosal sinus. (CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; PD, posterior fossa dura; VI, abducens nerve)

VI

JB

JT LCN

Fig. 14.69 (Step 18) Identification of jugular tubercle and lower cranial nerves After the posterior fossa dura is opened, the jugular tubercle and lower cranial nerves can be seen. A portion of the clivus has been removed along with the posterior fossa dura. (JB, jugular bulb; JT, jugular tubercle; LCN, lower cranial nerves; VI, abducens nerve)

IPS CL VI

Fig. 14.70 Identifying the intradural abducens

nerve.

The intradural and extradural portions of the abducens nerve are seen. (CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; VI, abducens nerve)

JB

291

292

IV Posterolateral Skull Base

IPS

JB

VI JT

Fig. 14.71 Demonstrating the exit zone of the abducens nerve. The exit zone where the abducens nerve leaves the pons can be seen. (IPS, inferior petrosal sinus; JB, jugular bulb; JT, jugular tubercle; VI, abducens nerve)

CL

VI

JB

IPS BA

Fig. 14.72 Identifying the basilar artery. The basilar artery can be seen from the anterolateral direction without any retraction of the cerebellum or brainstem (pons). This photo demonstrates the exposure seen from the trasotic approach. This approach is helpful for tumors displacing the pons posteriorly such as a large chordoma or a meningioma. (BA, basilar artery; CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; JT, jugular tubercle; VI, abducens nerve)

JT

VI CL

JB

IPS Fig. 14.73 Final view of the standard transcochlear approach. This specimen demonstrates the exposure obtained from a transcochlear approach done in conjunction with an intratemporal or transjugular approach. Frequently the external auditory canal is removed to increase the exposure. (CL, clivus; IPS, inferior petrosal sinus; JB, jugular bulb; JT, jugular tubercle; VI, abducens nerve)

JT

15 Combined Petrosal Approach The combined petrosal approach affords the surgeon a view of the petroclival region extending from the posterior cavernous sinus to the lower cranial nerves, and preserves the patient’s hearing. Preserving the cochlea and semicircular canals limits the surgeon’s access across the midline. The view of the anterior brainstem is at a steeper angle with the preservation of the neuro-otologic structures. This view affords an excellent view of unilateral extensive posterior fossa lesions without significant retraction of the cerebellum. The amount of bone resected is customized for each case. This procedure is useful for approaching petroclival meningiomas, giant and partially thrombosed basilar artery aneurysms, chordomas, and chondrosarcomas. This approach affords the surgeon a lateral view of the posterior fossa and preserves hearing. A key part of this procedure is the removal of the operculum of the temporal bone medial to the posterior and superior semicircular canals.

Key Steps Position: Lateral (Fig. 15.1) Step 1. Skin incision: modified “U” around the ear (Fig. 15.2) Step 2. Scalp elevation in two layers with preparation of a vascularized fasciopericranial flap (Fig. 15.4) Step 3. Superficial mastoidectomy (Fig. 15.10) Step 4. Creating a subtemporal groove (Fig. 15.13) Step 5. Creating a suboccipital groove (Fig. 15.14) Step 6. Craniotomy (Fig. 15.16) Step 7. Flattening the inner plate of the temporal base (Fig. 15.19) Step 8. Opening of the middle fossa rhomboid (Fig. 15.21) Step 9. Dural incision (temporal base and presigmoid posterior fossa dura) (Fig. 15.24) Step 10. Ligation and cutting of the superior petrosal sinus (Fig. 15.33) Step 11. Resection of the tentorium (Fig. 15.34) Step 12. Identification of the cranial nerves and arteries and opening of the Meckel’s cave (Fig. 15.35)

Illustrated Steps with Commentary

MT

Zy

Fig. 15.1 Positioning the patient. The patient is put in a lateral position. A lumbar drain is placed. The pelvis is tilted posteriorly to facilitate the harvesting of abdominal fat and fascia. The neck is laterally flexed so the vertex is positioned closer to the opposite shoulder. The mastoid tip and zygomatic arch are identi ed. (MT, mastoid tip; Zy, zygoma)

294

IV Posterolateral Skull Base

MT Zy As

*

2-2.5cm 6-7cm

Fig. 15.2 (Step 1) Incising the scalp. A modifled “U” shaped incision is made around the ear. The incision starts over the zygomatic root 10 mm anterior to the tragus and travels superiorly behind the hairline for 6-7 cm. It continues posteriorly parallel to the temporal line and turns inferiorly to pass through a point 2-2.5 cm dorsal to the asterion (asterisk). The incision terminates just below the level of the mastoid tip. (As, asterion; MT, mastoid tip; Zy, zygoma)

MT Zy

Fig. 15.3 “C” or “L” shaped skin incision (can be used if a less anterior exposure is needed).

A “C” or “L” shaped skin incision is used for tumors in the posterior cavernous sinus or dumbbell shaped tumors that reside mostly in the posterior fossa. This skin incision is useful when a second stage frontotemporal craniotomy is planned. (MT, mastoid tip; Zy, zygoma)

SCM

DTF

Fig. 15.4 (Step 2) Elevating the fiap in two layers. The skin ap is raised with the galea and parietotemporal fascia. When the patient’s pericranium is thin, the subgaleal loose areolar tissue is left attached to the pericranium to add to the thickness of the vascularized pericranial ap. (DTF, deep temporal fascia; PC, pericranium; SCM, sternocleidomastoid muscle)

PC

15 Combined Petrosal Approach

SCM

DTF

PC Fig. 15.5 Enlarging the pericranial fiap. The galeal layer should be separated from the pericranium along the periphery of the flap to enlarge the size of the pericranial graft. (DTF, deep temporal fascia; PC, pericranium; SCM, sternocleidomastoid muscle)

DTF Fig. 15.6 Elevating the myofascial pericranial fiap.

PC

To provide vascularized tissue to ll the cranial defect and to protect against infection postoperatively, the deep temporal fascia, the pericranium, and the upper part of the sternocleidomastoid muscle should be harvested in a "U" shape fashion, maintaining a wide vascularized pedicle. (DTF, deep temporal fascia; PC, pericranium)

SpM

TM Fig. 15.7 Refiecting the vascularized myofascial pericranial fiap.

The vascularized pericranial flap has a wide pedicle. (SpM, splenius capitis muscle; TM, tympanic membrane)

295

296

IV Posterolateral Skull Base

SpM EAC about 5 cm Fig. 15.8 Elevating the temporalis muscle.

Sq

The temporalis muscle is retracted anteriorly exposing the squamosal portion of the temporal bone, the root of the zygomatic arch, and the pterion. The zygomatic process of the frontal bone does not need to be exposed in this approach. The splenius capitis muscle comes into view when the sternocleidomastoid muscle is partially removed with the myofascial pericranial flap. (EAC, external auditory canal; P, parietal bone; SpM, splenius capitis muscle; Sq, squamosal suture)

P

MEV

O

EAC

Fig. 15.9 Exposing the body of the mastoid and

adjacent occipital bone by refiecting the posterior neck muscles.

Sq

The splenius capitis, semispinalis capitis, and the upper part of the superior oblique muscles are reflected posteriorly to expose the body of the mastoid and the lateral occipital bone. A monopolar coagulator should be used to separate the posterior neck muscles from the occipital bone. (EAC, external auditory canal; MEV, mastoid emissary brain; O, occipital bone; P, parietal bone; Sq, squamosal suture)

P

MEV

SS Fig. 15.10 (Step 3) Performing a super cial

mastoidectomy.

A cosmetic mastoidectomy in which the cortical bone overlying the mastoid is removed along with the craniotomy flap is an option. This option has a greater risk of injuring the sigmoid sinus. The cosmetic defect produced by a standard mastoidectomy can be hidden with a titanium plate. The thin shell of bone that is left covering the sigmoid sinus after a standard piecemeal super cial mastoidectomy should be carefully removed. The free sinus can be compressed posteriorly to improve the surgeon’s view of the posterior fossa. (JB, jugular bulb; MEV, mastoid emissary brain; SCs, semicircular canals; SS, sphenoid sinus)

JB

SCs

15 Combined Petrosal Approach

V-VII Fig. 15.11 Operculum medial to the posterior semicircular canal.

JB

The bone that lies medial to the posterior semicircular canal limits the surgeon’s view of the posterior fossa. This is referred to as the operculum (arrowheads) and should be thinned to improve the exposure. The sharp bone notch that lies between the inferoanterior border of the sigmoid sinus and the posterior border of the jugular bulb should be thinned, but if stuck should not be removed. The surgeon may encounter remarkable bleeding from tears in the wall of the sinus adjacent to this bone’s ridge. (JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

LSC SSC PSC

SS

V-VII

JB

LSC SSC

PSC

Fig. 15.12 Drilling the operculum. The operculum can be removed medial to the yellow bone of the posterior semicircular canal with an extra coarse diamond drill under a constant stream of irrigation. The endolymphatic sac is cut to free the posterior fossa dura from the posterior semicircular canal. The mastoidectomy exposes the posterior fossa dura inferior to the posterior semicircular canal, extending down to the jugular bulb. (JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

Fig. 15.13 (Step 4) Drilling a groove in the inferior temporal bone. After the mastoidectomy is complete, a groove (arrowheads) is drilled along the floor of the middle fossa in line with the root of the zygoma using a 4 mm diamond bur. This helps to minimize bone loss when turning a craniotomy. This groove is extended superiorly along the temporalis muscle to the pterion. After a groove is made in the bone, bone wax is inserted between the bone and the dura. This will protect the dura during drilling of the overlying bone.

SS

297

298

IV Posterolateral Skull Base

Fig. 15.14 (Step 5) Drilling a suboccipital groove. It is difflcult to use a craniotome at the base of the skull. Drilling a groove (arrowheads) along the under surface of the occipital bone maximizes the size of the suboccipital bone ap. A 4 mm diamond bur is used to “eggshell” the bone over the dura. This thin shell of bone is removed with a small bone curette.

2 cm 5 cm Fig. 15.15 Creating bur holes. At least two bur holes should be made with a 4 mm diamond bur. One is made 1-1.5 cm above the highest point of the squamosal suture. The other is made 2 cm behind the asterion over the transverse sinus to avoid injury to the sinus during the craniotomy. If the dura is tightly adherent to the bone, additional holes should be made, and the dura is separated from the bone between the bur holes.

Fig. 15.16 (Step 6) Cutting the craniotomy. A craniotome is used to connect the ends of the subtemporal and suboccipital grooves and the bur holes. The occipital side of the bone ap is short and the temporoparietal side is long.

1-1.5 cm

15 Combined Petrosal Approach

SS TS

SCs

Fig. 15.17 Exposing the dura. A craniotomy is turned with caution to avoid injury to the dural and venous sinuses. To control the dural venous bleeding the surgeon coagulates the dura through an overlying layer of absorbable hemostatic agent. Epidural venous bleeding from the dural edges is controlled by placing absorbable hemostatic agent under dural tacking sutures. (SCs, semicircular canals; SS, sphenoid sinus; TS, transverse sinus)

SCs SS TS

Fig. 15.18 Placing self-retaining retractors. Two self-retaining retractors are used to expose the petrous apex. (SCs, semicircular canals; SS, sphenoid sinus; TS, transverse sinus)

EAC

SCs Fig. 15.19 (Step 7) Removal of irregularities in the bony fioor of the middle fossa. The bony protrusions (arrowheads) from the floor of the middle fossa that impede the surgeon’s line of sight are removed. (EAC, external auditory canal; SCs, semicircular canals)

299

300

IV Posterolateral Skull Base

EAC

Fig. 15.20 Drilling the inner plate of the middle

fossa.

SCs

The bulging of the temporomandibular joint (arrowheads) into the operative fleld should not be drilled to avoid the postoperative ankylosis of this joint. Similarly, care should be taken not to enter the middle ear through the tegmen tympani or open the superior semicircular canal. The two retractors are just posterior to the mid-subtemporal ridge. (EAC, external auditory canal; SCs, semicircular canals)

Fig. 15.21 (Step 8) Identification of middle fossa

rhomboid.

The rhomboid is deflned by the medial edge of the petrous bone, posterior edge of the third division of the trigeminal nerve, the eminentia arcuata (superior semicircular canal), and the greater superflcial petrosal nerve. The superior semicircular canal has already been identifled through the mastoidectomy. The dura propria is separated from the maxillary nerve and the mandibular nerve to expose the flbrous ring through which the trigeminal nerve enters the posterior fossa. The foramen ovale does not need to be opened to translocate the mandibular nerve anteriorly with the combined petrosectomy approach. The flbrous ring around the trigeminal nerve and the tentorial attachment of Meckel’s cave is opened to allow the surgeon to shift the mandibular nerve anteriorly without opening the foramen ovale. (GSPN, greater superflcial petrosal nerve; LSC, lateral semicircular canal; PE, petrosal edge; SSC, superior semicircular canal; V3, mandibular nerve [third division of the trigeminal nerve])

LSC

GSPN V3

SSC PE

T-VII MMA PSC

GSPN

LSC

V3

Fig. 15.22 Drilling the rhomboid portion of the petrous bone. The rhomboid portion of the petrous bone is removed as demonstrated in Chapter 12. The middle meningeal artery is coagulated and cut. Absorbable hemostatic flber is packed into the foramen spinosum as added protection against bleeding from the middle meningeal artery. (Co, cochlea; GSPN, greater superflcial petrosal nerve; IAC, internal auditory canal; LSC, lateral semicircular canal; MMA, middle meningeal artery; PSC, posterior semicircular canal; SSC, superior semicircular canal; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

Co SSC

IAC

15 Combined Petrosal Approach

Fig. 15.23 Exposing the presigmoid and basal temporal dura. Two self-retaining retractors are used to support the dura. One retractor supports the infratemporal dura and a second supports the presigmoid dura.

JB

SCs

Fig. 15.24 (Step 9) Dural incision at the base of

the middle fossa.

An incision is made parallel and just lateral to the tentorium (arrowheads). The dural flap protects the temporal lobe. A careful search is made for veins that drain the lateral and inferior temporal lobe and enter the sigmoid sinus. These veins are carefully protected. The veins may be adherent to the dura before they enter the sinus. (JB, jugular bulb; SCs, semicircular canals; SS, sphenoid sinus; TS, transverse sinus)

SS

TS

JB

SS Fig. 15.25 Exposing the inferior temporal lobe. Once the dura is incised (arrowheads) the inferior temporal lobe is exposed. (JB, jugular bulb; SCs, semicircular canals; SS, sphenoid sinus)

SCs

301

302

IV Posterolateral Skull Base

SCs

Fig. 15.26 Incising the presigmoid dura.

SS

The presigmoid posterior fossa dura is incised between the endolymphatic sac and the sigmoid sinus (arrowheads). This provides a substantial dural flap that will aid in the postoperative dural closure. By opening the dura in this fashion the endolymphatic sac is preserved. The literature is unclear as to the bene ts of preserving the sac. (SCs, semicircular canals; SS, sphenoid sinus)

SPS Fig. 15.27 Identifying the tentorium and the superior petrosal sinus. In most cases the exposure obtained with an anterior petrosectomy is enlarged by simultaneously opening the tentorium, which constitutes the posterior floor of the middle fossa. Usually the posterior and middle fossa openings are connected by ligating the superior petrosal sinus. (SPS, superior petrosal sinus; TE, tentorial edge)

TE

IV

Fig. 15.28 Identifying the trochlear nerve. The trochlear nerve pierces the inferior surface of a free margin of the tentorium cerebelli. (IV, trochlear nerve; TE, tentorial edge)

TE

15 Combined Petrosal Approach

IV

TE

Fig. 15.29 Incising the tentorium along the trochlear nerve. The tentorium cerebelli is obliquely cut about 10 mm along the trochlear nerve to expose the extracavernous portion of the nerve. (IV, trochlear nerve; TE, tentorial edge)

IV TE Fig. 15.30 Incising the tentorium toward the trigeminal fibrous ring. The tentorial incision is extended laterally to reach the trigeminal flbrous ring. Opening the trigeminal flbrous ring allows for maximal exposure of the trigeminal nerve and frees the nerve completely. (IV, trochlear nerve; TE, tentorial edge)

SPS

IV TE

Fig. 15.31 Identifying the superior petrosal sinus. Opening the superior petrosal sinus causes profuse bleeding. (IV, trochlear nerve; PCA, posterior cerebral artery; SCA, superior cerebellar artery; SPS, superior petrosal sinus; TE, tentorial edge)

SC

PCA

A

303

304

IV Posterolateral Skull Base

IV TE

SC

A

Fig. 15.32 Controlling bleeding from the superior petrosal sinus. Venous bleeding from the superior petrosal sinus is controlled by packing absorbable hemostatic flbers into the sinus or the posterior cavernous sinus, or both. (IV, trochlear nerve; PCA, posterior cerebral artery; SCA, superior cerebellar artery; TE, tentorial edge)

PCA

LSC

Fig. 15.33 (Step 10) Completing the tentorial

division.

The superior petrosal sinus is ligated, coagulated, and cut. A 4-0 suture passes around the tentorium and through the presigmoid posterior fossa dura to ligate the superior petrosal sinus. The stitch is passed around the sinus twice to secure ligation of the venous sinus. The tentorium cerebelli is completely divided. An arrow demonstrates an entrance of the posterior cavernous sinus. In the case of petroclival or petrotentorial meningioma, this technique of detaching the posterior cavernous sinus results in the ligation of the feeding arteries from the internal carotid artery to the tumor. (IV, trochlear nerve; LSC, lateral semicircular canal; PCA, posterior cerebral artery; Po, pons; SCA, superior cerebellar artery; SSC, superior semicircular canal; TE, tentorial edge; V, trigeminal nerve)

SSC

V Po

IV SCA

TE

PCA

LSC

SSC

V Po

IV

Fig. 15.34 (Step 11) Tacking up the tentorial

edge.

The cut edge of the tentorium cerebelli is sutured posteriorly to expand the surgical fleld. (IV, trochlear nerve; LSC, lateral semicircular canal; PCA, posterior cerebral artery; Po, pons; SCA, superior cerebellar artery; SSC, superior semicircular canal; V, trigeminal nerve)

SCA

PCA

15 Combined Petrosal Approach

Vm

Vs

IV

SCA Fig. 15.35 (Step 12) Identification of fourth and fifth cranial nerves. After incising the arachnoid of the lateral potomesencephalic cistern, the trochlear nerve and the trigeminal nerve root are freed. (IV, trochlear nerve; SCA, superior cerebellar artery; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)

XI VII X IX

AI

CA

XII

VIII

Fig. 15.36 Identifying cranial nerves VII, VIII, IX, X,

XI, and XII.

Incising the arachnoid of the lateral pontine and medullary cistern frees the facial, cochlear, and lower cranial nerves along with the vertebral artery and the anterior inferior cerebellar artery. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XI

X VII

XII A Fig. 15.37 Identifying cranial nerve XII. When the microscope is angled inferiorly, the hypoglossal nerves can be seen behind the vagus nerve rootlets. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

IC A

IX

VIII

305

306

IV Posterolateral Skull Base

Fig. 15.38 Opening Meckel’s cave and cutting the trigeminal fibrous ring (posterior cavernous detachment). The tentorium is removed from the roof of Meckel’s cave to expose the trigeminal nerve root and gasserian ganglion. Bleeding from the superior petrosal sinus and veins within the roof of Meckel’s cave is controlled with absorbable hemostatic flbers and sutures. The petrosal vein cannot be preserved. The cautery is used sparingly to minimize the risk of postoperative dysesthesias in the trigeminal distribution. The trochlear nerve should be freed from its canal within the tentorium to maximize the resection of a meningioma. The canal can be opened approximately 1 cm. An incision between the flbrous ring of the trigeminal nerve and the posterior edge of the freed trochlear nerve will remove additional tumor flltrated into the tentorium. Extending the trochlear canal opening more than 1 cm risks considerable venous bleeding. From our experience the risks of following the tumor into the cavernous sinus outweigh the beneflts. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; SSC, superior semicircular canal; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)

GG

LSC

IV SSC Vs

Vm

GG LSC Fig. 15.39 Following the course of the trigeminal

nerve.

After Meckel’s cave is opened the tentorium is resected. The trigeminal nerve can be followed from the gasserian ganglion to its entrance into the pons. The motor division of the trigeminal nerve (arrowheads) runs along the medial border of the sensory nerve root. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; SSC, superior semicircular canal; VII, facial nerve; VIII, cochlear nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)

VIII

SSC VII

IV Vs

Vm

GG LSC SSC Fig. 15.40 Finding cranial nerve VI. The distal end of abducens nerve may be buried in a meningioma arising from the nerve’s entrance into Dorello's canal. It is usually easiest to flnd the abducens nerve on the underside of the pons close to the branching of anterior inferior cerebellar artery from the basilar artery. (GG, gasserian ganglion; LSC, lateral semicircular canal; SSC, superior semicircular canal; VI, abducens nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)

VI

Vs

Vm

15 Combined Petrosal Approach

III IV Fig. 15.41 Following cranial nerve IV. The trochlear nerve enters into the tentorium medial to Meckel’s cave. The trochlear nerve will continue in the lateral wall of the cavernous sinus passing over the oculomotor nerve. (III, oculomotor nerve; IV, trochlear nerve)

III

IV

BA

Fig. 15.42 Finding cranial nerve III. The oculomotor nerve can be seen passing between the superior cerebellar artery and the P1 segment of the posterior cerebral artery. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve)

II I

ICA

Fig. 15.43 Viewing the olfactory nerve. The olfactory nerve is seen on the undersurface of the frontal lobe. (AntChol, anterior choroidal artery; I, incus; ICA, internal carotid artery; II, optic nerve; Pcom, posterior communicating artery; St, stalk)

om Pc

AntChol

St II

307

308

IV Posterolateral Skull Base

II

I ICA m Pco

AntChol

St

II

Fig. 15.44 Identifying the internal carotid artery. The internal carotid, anterior choroidal, and posterior communicating arteries and the perforators can be seen easily with minimal retraction of the temporal lobe. (AntChol, anterior choroidal artery; BA, basilar artery; I, incus; ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve; Pcom, posterior communicating artery; St, stalk)

BA

III ICA m Pco

tCh An

ol

II

St

Fig. 15.45 Viewing the optic nerve and pituitary

BA

stalk.

The caudal optic nerve contiguous with the optic tract and the stalk to the pituitary gland entering the diaphragm sellae just anterior to the dorsum sellae can be seen well. (AntChol, anterior choroidal artery; BA, basilar artery; ICA, internal carotid artery; II, optic nerve; Pcom, posterior communicating artery; St, stalk)

m Pco

GG Fig. 15.46 Identifying the superior cerebellar and posterior cerebral arteries.

III V

SCA

In the lateral pontomesencephalic and premesencephalic cistern, the upper portion of the basilar artery and the superior cerebellar and posterior cerebral arteries can be identifled. The oculomotor nerve can be followed into its tentorial canal for a distance of 6-7 mm. The tentorium can be cut between the liberated third and fourth nerves to further detach the tumor from the posterior cavernous sinus. (BA, basilar artery; GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; MB, midbrain; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; Po, pons; SCA, superior cerebellar artery; V, trigeminal nerve)

P2

Po

IV MB

BA

15 Combined Petrosal Approach

BA

III Fig. 15.47 Viewing the basilar tip and P1 segment of the posterior cerebral artery.

P1

P2

The basilar tip and the hypoplastic P1 segment can be identifled under the temporal lobe. (BA, basilar artery; III, oculomotor nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery)

SCA

P2 IV

Fig. 15.48 Viewing the mesencephalon and pons.

BA

III

MB

The upper portion of the brainstem can be seen from an anteromedial trajectory. Intramedullary cavernomas of the anterolateral pons are ideally exposed from this trajectory. (BA, basilar artery; III, oculomotor nerve; IV, trochlear nerve; MB, midbrain; P2, P2 segment of the posterior cerebral artery; SCA, superior cerebellar artery)

GG LSC PSC

Fig. 15.49 An overview of intradural structures

SSC

seen by viewing over the petrous bone.

XII

X

BA

BA

A

XI

AIC

Cranial nerves V through XII in the posterior fossa can be seen. By tipping the microscope the surgeon will see completely different perspectives of the posterior fossa structures. (AICA, anterior inferior cerebellar artery; BA, basilar artery; GG, gasserian ganglion; IX, glossopharyngeal nerve; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

VI

Vs

IX

Vm VIII

VII

309

IV Posterolateral Skull Base

GG LSC PSC SSC

The cranial nerves within the posterior fossa can be seen. (AICA, anterior inferior cerebellar artery; BA, basilar artery; GG, gasserian ganglion; IV, trochlear nerve; IX, glossopharyngeal nerve; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve; X, vagus nerve)

X

IV

BA

A

seen posteriorly by looking over the petrous bone.

SCA

VI

Fig. 15.50 An overview of intradural exposure

AIC

310

IX

Vs VIII

Vm VII

V3

PSC

LSC GG

SSC

VI

Fig. 15.51 An overview of intradural structures seen viewing anteriorly along the petrous bone.

Vs

The trochlear, trigeminal, and abducens nerves can be identifled over the petrous bone. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; Po, pons; PSC, posterior semicircular canal; SSC, superior semicircular canal; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)

Po Vm IV

LSC Fig. 15.52 Motor root of the trigeminal nerve from the subtemporal view. The motor root (arrowheads) of the trigeminal nerve can be identifled at the medial border of the nerve. The dura should be repaired by incorporating a fascial graft if an edge of dura under the temporal lobe is hard to flnd after the meningioma is removed. To obtain a reasonable dural closure, the graft is sewn along the lateral edge of the middle fossa dura. If there is no place to sew the graft along the base of the middle fossa, the graft is secured to the temporal bone with titanium plates and screws. It is not possible to get a perfectly watertight closure, as the trigeminal nerve must pass under the graft. The fascial closure is reinforced with a free fat graft. After the bone ap is secured, the mastoid area is covered with a triangular titanium plate. (GG, gasserian ganglion; IV, trochlear nerve; LSC, lateral semicircular canal; SCA, superior cerebellar artery; SSC, superior semicircular canal; V3, mandibular nerve [third division of the trigeminal nerve]; Vm, motor division of the trigeminal nerve; Vs, sensory division of the trigeminal nerve)

V3 SSC GG

Vs Vm SCA

IV

16

Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

The transjugular approach is ideal for the resection of glomus jugulare tumors and schwannomas of the lower cranial nerves that extend through the cranium, chordomas, chondrosarcomas, and meningiomas. This approach is a combination of infravestibular transmastoid, suprajugular, transjugular, infrajugular, and high-cervical approaches from an anterolateral trajectory. The surgeon begins by defining the anatomy above and below the skull base and following the normal anatomy into the region of the pathology. Most glomus jugulare tumors reside in the sigmoid sinus and high internal jugular vein; thus, the sigmoid sinus juxtaposed with the lower cranial nerves is not disturbed. Access to the lower clivus is facilitated by anterior translocation of the lower cranial nerves and internal carotid artery.

Key Steps Position: Lateral Step 1. “C” shaped skin incision (Fig. 16.1) Step 2. Elevation of scalp in two layers and harvesting of myofascial pericranial flap (Figs. 16.2 and 16.3) A. Elevation of scalp flap (Fig. 16.2) B. Harvesting of myofascial pericranial flap (Fig. 16.3) Step 3. Elevation of posterior neck muscles (Fig. 16.7) Step 4. Extracranial high cervical dissection with identification of (Figs. 16.15–16.36) 1. Transverse process of C1 2. Internal jugular vein 3. CN XI (accessory nerve) under transverse process of C1 4. CN XII (hypoglossal nerve) over internal jugular vein 5. Internal carotid artery 6. CN X (vagus nerve) 7. Stylohyoid muscle 8. CN IX (glossopharyngeal nerve) 9. Vertebral artery Step 5. Mastoidectomy (Fig. 16.40) Step 6. Exposure of jugular bulb and jugular isthmus (Fig. 16.43) Step 7. Exploration of facial recess (Fig. 16.45) Step 8. Anterior translocation of facial nerve to expose internal carotid artery (Fig. 16.49) Step 9. Condylectomy (Fig. 16.54) Step 10. Exposure of the lower cranial nerves with removal of jugular bulb (Fig. 16.64) Step 11. Dural incision (Fig. 16.80) Step 12. Partial removal of inferior clivus with anterior translocation of internal carotid artery (Fig. 16.87)

312

IV Posterolateral Skull Base

Illustrated Steps with Commentary

MA MT

Fig. 16.1 (Step 1) Skin incision. With the patient in the lateral position, a “C” shaped incision is made that begins above and behind the ear and extends below the angle of the mandible. The skin incision extends posterior to the asterion to expose the mastoid portion of the occipital bone and inferiorly below the angle of the mandible to expose the internal jugular vein. (MA, mandibular angle; MT, mastoid tip)

GAN

Fig. 16.2 (Step 2A) Refiection of skin fiap identifying the greater auricular nerve. The greater auricular nerve can usually be identifled 2–3 mm below the mastoid tip. The superflcial fascial layer is split when raising the skin ap. (GAN, greater auricular nerve)

PAM

SCM

Fig. 16.3 (Step 2B) Harvesting of galeofascial graft.

The layer of fascia that lies superflcial to the muscle layers is harvested and can be used to close the dura at the end of the case. Inferiorly this layer merges with the fascia covering the sternocleidomastoid muscle. (PAM, posterior auricular muscle; SCM, sternocleidomastoid muscle)

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

PAM

SCM

Fig. 16.4 Exposing the superficial nuchal muscles. The posterior auricular and the sternocleidomastoid muscles are exposed after the galeofascial graft is harvested. (PAM, posterior auricular muscle; SCM, sternocleidomastoid muscle)

GAN

SCM Fig. 16.5 The greater auricular nerve. The greater auricular nerve, which can be found approximately 2–3 mm caudal to the mastoid tip at an anterior margin of the sternocleidomastoid muscle, should be dissected free at the time that the skin flap is raised. The nerve can be used for the interpositional nerve graft if the facial nerve is injured or involved in the tumor. (GAN, greater auricular nerve; SCM, sternocleidomastoid muscle)

SCM

Fig. 16.6 Cutting the greater auricular nerve. The greater auricular nerve is cut and preserved under a wet cottonoid in preparation for its use in reconstructing the facial nerve at the end of the surgery. (SCM, sternocleidomastoid muscle)

313

314

IV Posterolateral Skull Base

SCM

Fig. 16.7 (Step 3) Cutting of posterior neck muscles using a monopolar coagulator.

The occipital muscle and the sternocleidomastoid muscle are cut in a “C” shape. The suboccipital muscles are retracted as a group anteriorly. (SCM, sternocleidomastoid muscle)

SCM SpC

M

Fig. 16.8 Identifying the splenius capitis. Reflecting the sternocleidomastoid muscle anteriorly we nd the thick splenius capitis muscle inserting just below the superior nuchal line and the longissimus capitis, which inserts into the mastoid process. (SCM, sternocleidomastoid muscle; SpCM, splenius capitis muscle)

M LC

Fig. 16.9 Identifying the longissimus capitis muscle.

The longissimus capitis muscle is seen below the splenius capitis muscle. The semispinalis capitis muscle originates from the transverse processes of the cervical vertebrae and inserts between the superior and inferior nuchal lines under the splenius capitis muscle. (LCM, longissimus capitis muscle)

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

Fig. 16.10 Identifying the styloid diaphragm. The posterior belly of the digastric muscle originates from the digastric groove and is held against the greater cornu of the styloid bone by a flbrous loop. The styloid diaphragm begins at the styloid process and encircles the muscles originating from that process. Retracting the splenius capitis muscle and longissimus capitis muscle reveals a deep fascial layer that is contiguous with the styloid diaphragm. (OA, occipital artery)

OA

Fig. 16.11 Identifying the occipital artery. A deep fascial layer lays under the splenius capitis muscle. This fascia layer covers the occipital artery after the artery passes under the digastric muscle. The flbers of the splenius capitis muscle can be separated with a blunt dissector to reveal the deep fascial layer. The fascia can then be sharply opened. This allows the surgeon to flnd and ligate the occipital artery in a controlled fashion. (OA, occipital artery; OCSM, obliquus capitis superior muscle)

OC

SM

OA

MT

Fig. 16.12 Retracting the superficial suboccipital muscles anteriorly. The sternocleidomastoid and the lateral portion of the middle layer of suboccipital muscles are dissected anteriorly to expose the body of the mastoid. (MT, mastoid tip; OA, occipital artery; OCSM, obliquus capitis superior muscle)

OC

OA

SM

315

IV Posterolateral Skull Base

DM

MT SM

Fig. 16.13 Posterior retraction of the suboccipital

TC1

muscles.

OC

316

The superior oblique and posterior suboccipital muscles are retracted posteriorly to expose the lateral occipital bone and the transverse process of the C1. (DM, digastric muscle; MT, mastoid tip; OCSM, obliquus capitis superior muscle; TC1, transverse process of the C1)

PG Fig. 16.14 Exposing the obliquus capitis superior

DM

muscle.

The superior oblique muscle is seen under the occipital artery originating from the inferior nuchal line. The posterior aspect of the parotid gland can be coagulated when it obstructs the surgeon’s view. Because the marginal branch of the facial nerve passes through the posterior margin of the parotid gland, care should be taken when coagulating this portion of the gland. The facial vein appearing behind the parotid gland should be cut after coagulation with a bipolar forceps. (DM, digastric muscle; OA, occipital artery; OCSM, obliquus capitis superior muscle; PG, parotid gland)

OC

SM

OA

SHM DM MT

IJV TC1 XI OA

Fig. 16.15 (Step 4) Exposure of the accessory

nerve.

The spinal accessory nerve passes under the transverse process of C1. It has a variable relationship with the jugular vein. The nerve lies on top of the internal jugular vein in 70–85% of patients and emerges from behind the vein in 15–30% of patients. (DM, digastric muscle; IJV, internal jugular vein; MT, mastoid tip; OA, occipital artery; OCSM, obliquus capitis superior muscle; SHM, stylohyoid muscle; TC1, transverse process of the C1; XI, accessory nerve)

OSC

M

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

DM

IJV

MT RCLM

Fig. 16.16 (Step 4) Anterior refiection of the

posterior belly of the digastric muscle.

TC1

LSM XI

OA

The rectus capitis lateralis, obliquus capitis superior, obliquus capitis inferior, and levator scapulae muscles attach into the transverse process of C1. The posterior belly of the digastric muscle is reflected anteriorly to protect the facial nerve. (DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OA, occipital artery; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; XI, accessory nerve)

O

OCIM

CSM

DM

IJV

MT RCLM

TC1

LSM S OC

Fig. 16.17 (Step 4) Resection of the occipital

artery.

M

XI

OCIM

The four muscles attached to the transverse process of C1 are better seen after the occipital artery is removed. (DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; XI, accessory nerve)

PG

Fig. 16.18 (Step 4) Identi cation of the hypoglossal nerve. The hypoglossal nerve passes lateral to the greater cornu of the hyoid bone. It is the most posterior lateral of the cranial nerves that accompany the carotid artery. Proximally the nerve is found lateral to the vagus nerve. The vagus and hypoglossal nerves frequently have interconnections. The hypoglossal nerve passes over the hyoid bone deep to the posterior belly of the digastric muscle and the stylohyoid muscle. (IJV, internal jugular vein; LSM, levator scapulae muscle; PG, parotid gland; XI, accessory nerve; XII, hypoglossal nerve)

XII IJV LSM

XI

317

IV Posterolateral Skull Base

XII

ICA

TC1

RCLM

M

SM

IJV

IC

nerve.

RCLM

XII

A

IJV

TC1

X

F

OA

ST ECA

ICA Fig. 16.21 (Step 4) Hypoglossal and vagus

nerves.

The vagus nerve is seen medial to the hypoglossal nerve. (ansa, ansa cervicalis; ECA, external carotid artery; F, facial artery; ICA, internal carotid artery; IJV, internal jugular vein; OA, occipital artery; ST, superior thyroid artery; X, vagus nerve; XII, hypoglossal nerve)

IJV

ansa

LSM

OCIM

The vagus nerve is found traveling between the internal jugular vein and under the internal carotid artery. (ansa, ansa cervicalis; ICA, internal carotid artery; IJV, internal jugular vein; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; X, vagus nerve; XII, hypoglossal nerve)

SM

Fig. 16.20 (Step 4) Identification of the vagus

ansa

LSM

OCI

The descending ramus of the hypoglossal nerve communicates with branches C1-C3 to form the ansa hypoglossi. (ansa, ansa cervicalis; ICA, internal carotid artery; IJV, internal jugular vein; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; XII, hypoglossal nerve)

OC

Fig. 16.19 (Step 4) Ansa hypoglossi

OC

318

XII X

ansa

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

PG

DM SGM SHM

Fig. 16.22 (Step 4) Anatomical relationship of

ECA

structures in the high cervical region.

XII

IJV

The internal jugular vein is larger in this specimen than is usually seen at the time of surgery. (DM, digastric muscle; ECA, external carotid artery; IJV, internal jugular vein; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PG, parotid gland; RCLM, rectus capitis lateralis muscle; SGM, styloglossus muscle; SHM, stylohyoid muscle; TC1, transverse process of the C1; XI, accessory nerve; XII, hypoglossal nerve)

RCLM

TC1

XI OC

SM

LSM

OCIM

PG DM

ICA

IX

SM

RCLM

OC

The glossopharyngeal nerve travels between the stylohyoid muscle and the internal carotid artery. (ansa, ansa cervicalis; DM, digastric muscle; ECA, external carotid artery; ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PG, parotid gland; RCLM, rectus capitis lateralis muscle; SHM, stylohyoid muscle; TC1, transverse process of the C1; XI, accessory nerve; XII, hypoglossal nerve)

TC1

OCIM

A

Fig. 16.23 (Step 4) The glossopharyngeal nerve.

EC

SHM

XII

ansa

IJV

LSM

XI

SHM IX Fig. 16.24 (Step 4) Identification of the stylohyoid muscle and the glossopharyngeal nerve. The glossopharyngeal nerve is seen passing under the stylohyoid muscle. (IJV, internal jugular vein; IX, glossopharyngeal nerve; SHM, stylohyoid muscle)

IJV

319

320

IV Posterolateral Skull Base

PG DM SPM SHL SHM

Fig. 16.25 (Step 4) Identification of the high

cervical ICA by depressing the internal jugular vein. The musculature stemming from the styloid process deflnes the anterior extent of the dissection. (DM, digastric muscle; ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PG, parotid gland; RCLM, rectus capitis lateralis muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; TC1, transverse process of the C1; XI, accessory nerve; XII, hypoglossal nerve)

ICA

TC1

RCLM

IX

XII

IJV OC

SM

OSIM

LSM

XI

PG DM

SPM SGM

SHL SHM

MT

Fig. 16.26 (Step 4) Identification of the muscles stemming from the styloid process.

RCLM

The stylopharyngeal muscle is anterior (ventral) and medial to the styloglossus muscle. The glossopharyngeal nerve passes over this muscle before penetrating into the pharyngeal wall. (DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PG, parotid gland; RCLM, rectus capitis lateralis muscle; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPM, stylopharyngeal muscle; TC1, transverse process of the C1; XI, accessory nerve; XII, hypoglossal nerve)

OC

SM

XII

IJV

TC1

XI

LSM

OCIM

PG Fig. 16.27 (Step 4) Overview of the lower cranial

nerves.

SGM SHM SHL IX IC

RCLM

A

The hypoglossal nerve is seen passing under the greater horn of the hyoid bone. The vagus nerve is seen between the internal carotid artery and internal jugular vein. The glossopharyngeal nerve is seen under the stylohyoid muscle and the spinal accessory nerve is seen under the lateral process of C1. (DM, digastric muscle; ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PG, parotid gland; RCLM, rectus capitis lateralis muscle; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; TC1, transverse process of the C1; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

DM

MT

TC1

IJV OC

SM

OCIM

LSM XI

X

XII

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IJV

MT

TC1

RCLM

DM Fig. 16.28 (Step 4) Identifying the suboccipital

Clearing the veins in the suboccipital triangle reveals the vertebral artery. This venous plexus communicating with the sigmoid sinus, epidural venous plexus, and paravertebral plexus surround the artery. The vertebral artery is seen in the window framed by the obliquus capitis superior muscle, obliquus capitis inferior muscle, and rectus capitis major muscle. At the time of surgery this space is fllled with fat and veins that obscure the artery. The groove in the top of the C1 lamina, the J-groove, can be palpated to localize the vertebral artery. (C1, C1 [atlas]; DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCLM, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

OC

RCM

jM

IJV

MT TC1

RCLM

XI

DM

LSM VA OCIM

SM

Fig. 16.29 (Step 4) Identifying the vertebral artery over the posterior arch of C1.

OCIM

OC

The suboccipital triangle formed by the obliquus capitis superior muscle, obliquus capitis inferior muscle, and rectus capitis major muscle is identifled. (DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCLM, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; TC1, transverse process of the C1; XI, accessory nerve)

SM

triangle.

RC

Mj

C1 M

MT TC1

DM

RCLM

The obliquus capitis superior muscle is re ected posteriorly. (C1, C1 [atlas]; DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; RCLM, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

OCIM RC

Mj

M

IJV XI

VA

Fig. 16.30 (Step 4) Posterior refiection of the obliquus capitis superior muscle.

XI

LSM

C1

LSM

321

322

IV Posterolateral Skull Base

TC1

RCLM

DM

XI

VA OCIM

C1

PAOM

Fig. 16.31 (Step 4) Posterior refiection of the rectus capitis posterior major muscle.

LSM

RCMjM

Reflection of the rectus capitis major reveals the rectus capitis minor muscle. (C1, C1 [atlas]; DM, digastric muscle; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; POAM, posterior occipito-atlantal membrane; RCLM, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

MT RCLM

XI

DM

Fig. 16.32 (Step 4) Exposure of the posterior

LSM

VA

atlanto-occipital membrane.

OCIM

Reflection of the obliquus capitis superior muscle and the rectus capitis major and minor muscles reveals the posterior occipitoatlantal membrane. (C1, C1 [atlas]; DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; POAM, posterior occipito-atlantal membrane; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

POAM C1

MT RCLM

Fig. 16.33 (Step 4) Condylar emissary vein. The posterior condylar emissary vein connects the sigmoid sinus and paravertebral venous plexuses. The occipital condyle and C1 lateral mass are covered by the joint capsule. The posterior occipito-atlantal membrane is seen medial to the joint being pierced by the vertebral artery. (CEV, condylar emissary vein; DM, digastric muscle; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

IJV

TC1

TC1

XI

DM

LSM

VA OCIM CEV

IJV

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IJV RCLM

Fig. 16.34 (Step 4) Anterior refiection of the

posterior belly of the digastric muscle.

The posterior belly of the digastric muscle is reflected anteriorly to protect the facial nerve as it exits the stylomastoid foramen. Reflecting the posterior belly of the digastric muscle forward protects the facial nerve. (C1C, C1 condyle; CEV, condylar emissary vein; IJV, internal jugular vein; LSM, levator scapulae muscle; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

TC1

XI

OC C1C

VA

LSM

OCIM

CEV

MT

IJV RCLM

TC1 XI

OC Fig. 16.35 (Step 4) Removal of the posterior

occipito-atlantal membrane uncovers the dura surrounding the upper most spinal canal. The posterior occipito-atlantal membrane has been removed to expose the dura. The vertebral artery lies within a groove in the top of the lamina of C1, the J-groove. (C1, C1 [atlas]; C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

LSM

VA

C1C

OCIM

CEV

D

C1

IJV RCLM

TC1

XI

LSM C1C VA

CEV Fig. 16.36 (Step 4) Exposure of the C1 condyle. The C1 condyle and the vertebral artery that penetrates the dura are exposed. (C1, C1 [atlas]; C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; RCLM, rectus capitis lateralis muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

D

C1

OCIM

323

324

IV Posterolateral Skull Base

RCLM OC C1C

OCIM

VA CEV Fig. 16.37 Enlarged view of Figs. 16.16–16.36. The occipital condyle, the C1 condyle, and adjacent structures are exposed. (C1C, C1 condyle; CEV, condylar emissary vein; D, dura; JG, J-groove for the vertebral artery; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; PA, posterior arch of the C1; RCLM, rectus capitis lateralis muscle; VA, vertebral artery)

JG

D

PA

MT

IJV TC1 XI

OC C1C

LSM

VA

OCIM CEV

Fig. 16.38 Removing the rectus capitis lateralis

muscle.

D

The rectus capitis lateralis muscle is removed to further expose the occipital and C1 condyles. (C1, C1 [atlas]; C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; TC1, transverse process of the C1; VA, vertebral artery; XI, accessory nerve)

C1

SGM

MT

IJV

OC Fig. 16.39 The foramen transversarium. Resecting the posterior wall of the transverse process of C1 opens the foramen transversarium and allows for posterior displacement of the vertebral artery. The artery may be tethered by the periosteum of the canal and the retroglenoid ligament. (C1, C1 [atlas]; C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; SGM, styloglossus muscle; VA, vertebral artery; XI, accessory nerve)

C1C CEV

VA

D

C1 OCIM

XI

LSM

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

PRZ MT

As

Fig. 16.40 (Step 5) Outlining the mastoidectomy. The outer triangle marked by the posterior point of the root of the zygoma, the mastoid tip, and a point posterior to the asterion is outlined using a 5–6 mm cutting bur. (As, asterion; MT, mastoid tip; PRZ, posterior point of the root of the zygoma)

MA LSC SSP

Fig. 16.41 Identifying the lateral semicircular

canal in the mastoid antrum.

SSC

Fig. 16.42 Exposing the semicircular canals. The position of the superior and posterior semicircular canals can be extrapolated from the lateral semicircular canal. The tip of the lateral semicircular canal is identifled in the antrum; the remainder of that canal can be deflned by following the hard yellow bone posteriorly. The posterior canal is found behind the lateral canal at the level of the endolymphatic sac. In the transjugular approach, complete exposure of the superior semicircular canal is not needed. Decompression of the sigmoid sinus and the exposure of the lateral and posterior semicircular canal are important. (DR, dural ring; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; TT, temporal tegmen)

LSC

The mastoid air cells are aggressively removed lateral to the antrum. The antrum lies 15–17 mm deep to where the posterior root of the zygoma meets the spine of Henle. The tip of the lateral semicircular canal can be seen poking into the antrum. The anterior wall of the lateral semicircular canal is also the posterior wall of the fallopian canal. (LSC, lateral semicircular canal; MA, mandibular angle; SSP, sigmoid sinus plate)

PSC

TT SS

DR

325

IV Posterolateral Skull Base

Fig. 16.43 (Step 6) Exposing the jugular bulb.

LSC

CT SSC

326

The facial nerve is dissected from the surrounding bone as is the chorda tympani. The facial nerve is flrst deflned anterior to the lateral semicircular canal. The nerve is then followed inferiorly to the styloid foramen. The jugular bulb is found inferior and deep to the semicircular canals. Its size is variable. Facial nerve decompression should be performed slowly and carefully. This procedure should not be hurried. The sharp bony notch between the inferoanterior border of the sigmoid sinus and the posterior border of the jugular bulb may be very adherent to the vein. It is often best to thin this bone and leave the pliable thin bone in place. (CT, chorda tympani; DR, dural ring; ES, endolymphatic sac; JB, jugular bulb; LSC, lateral semicircular canal; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; TT, temporal tegmen; V-VII, vertical segment of the facial nerve)

V-VII

PSC

TT

JB

DR

ES

SS

I P

CT

LSC

SSC

V-VII

PSC

Fig. 16.44 Closeup view of the semicircular

JB

canals.

The superior canal pushes upward into the oor of the middle fossa. Care is taken not to drill anterior to the posterior semicircular canal to preserve the cochlea. (See details in Chapter 14.) (CT, chorda tympani; ES, endolymphatic sac; JB, jugular bulb; I, incus; LSC, lateral semicircular canal; P, promontory; PSC, posterior semicircular canal; SS, sphenoid sinus; SSC, superior semicircular canal; V-VII, vertical segment of the facial nerve)

ES SS

S

LSC

CT V-VII TN

Fig. 16.45 (Step 7) Viewing Jacobson’s nerve on the promontory of the cochlea. The middle ear is opened anterior to the facial nerve. Care is taken not to disrupt the annulus of the tympanic membrane. (CT, chorda tympani; JB, jugular bulb; LSC, lateral semicircular canal; S, stapes; SS, sphenoid sinus; TN, tympanic nerve [Jacobson’s nerve]; V-VII, vertical segment of the facial nerve)

SS

JB

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

SGM

TT

SCs VII

IJV

SS

Fig. 16.46 An overview of the extracranial exposure and mastoidectomy. An overview of the dissection at this point shows the relationship between the neck dissection and the mastoidectomy. (C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; LSM, levator scapulae muscle; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; SCs, semicircular canals; SGM, styloglossus muscle; SS, sphenoid sinus; TT, temporal tegmen; VA, vertebral artery; VII, facial nerve; XI, accessory nerve)

CEV

SCs

SS

Fig. 16.47 Drilling off the mastoid tip. Removing the mastoid tip completes exposure of the sigmoid sinus. When the facial nerve is transposed anteriorly, the mastoid tip can be completely removed to connect the mastoidectomy with the cervical dissection. (C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; JB, jugular bulb; LSM, levator scapulae muscle; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; SCs, semicircular canals; SGM, styloglossus muscle; SMF, stylomastoid foramen; SS, sphenoid sinus; TT, temporal tegmen; VA, vertebral artery; VII, facial nerve; XI, accessory nerve)

The seventh nerve is covered by a sheath of flbrous tissue at the stylomastoid foramen. This tissue should be kept intact to avoid injury to the seventh nerve. Because of the dense connective tissue, the seventh nerve is not seen as clearly as it is in the mastoid canal. (CT, chorda tympani; E-VII, extracranial segment of the facial nerve; SMF, stylomastoid foramen; V-VII, vertical segment of the facial nerve)

VA

D

LSM OCIM

SMF

TT

Fig. 16.48 Opening the stylomastoid foramen.

XI

OC C1C

SGM

VII

IJV

JB

XI

OC

VA

C1C CEV

LSM OCIM

D

CT V-VII

E-VII SMF

327

328

IV Posterolateral Skull Base

CT

E-VII

V-VII SP

Fig. 16.49 (Step 8) Translocation of the facial nerve anteriorly. The facial nerve is transposed anteriorly to facilitate dissection into the petrous bone. (CT, chorda tympani; E-VII, extracranial segment of the facial nerve; IJV, internal jugular vein; JB, jugular bulb; SP, styloid process; V-VII, vertical segment of the facial nerve)

IJV

JB

E-VII

CT V-VII Fig. 16.50 Exposing the styloid process. The styloid process lies medial to the stylomastoid foramen. Transposing the nerve anteriorly exposes the styloid process, which in turn lies lateral to the jugular canal. In this photo the styloid process is seen under the anteriorly transposed facial nerve. (CT, chorda tympani; E-VII, extracranial segment of the facial nerve; IJV, internal jugular vein; JB, jugular bulb; SP, styloid process; V-VII, vertical segment of the facial nerve)

SP IJV

JB

E-VII

V-VII

JB

Sp IJV

SS Fig. 16.51 Magnified view of the jugular isthmus. The jugular isthmus and adjacent structures are identifled. (E-VII, extracranial segment of the facial nerve; IJV, internal jugular vein; JB, jugular bulb; SP, styloid process; SS, sphenoid sinus; VA, vertebral artery; V-VII, vertical segment of the facial nerve)

VA

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

TT

SCs

SMF SP

VII

IJV

JB

SS

Fig. 16.52 Overview of the exposure of the sigmoid sinus, jugular bulb, and internal jugular vein.

SHM

SGM

SHL

OC C1C

XI

(C1C, C1 condyle; CEV, condylar emissary vein; D, dura; IJV, internal jugular vein; JB, jugular bulb; LSM, levator scapulae muscle; OC, occipital condyle; OCIM, obliquus capitis inferior muscle; SCs, semicircular canals; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SMF, stylomastoid foramen; SS, sphenoid sinus; TT, temporal tegmen; VA, vertebral artery; VII, facial nerve; XI, accessory nerve)

CEV

LSM

VA

OCIM D

CEV

SP

IJV

JB XI

Fig. 16.53 Exposing the occipital condyle.

C1C

OC

SS

VA

CEV

The occipital condyle and the facet are exposed. (C1C, C1 condyle; CEV, condylar emissary vein; IJV, internal jugular vein; JB, jugular bulb; OC, occipital condyle; SP, styloid process; SS, sphenoid sinus; VA, vertebral artery; XI, accessory nerve)

IJV

JB

XI

SS

Fig. 16.54 (Step 9) Partial condylectomy. The posterior aspect of the occipital condyle above its joint with C1 is removed. Bleeding from the condylar vein when encountered during the drilling is controlled with bone wax and oxidized cellulose. The oxidized cellulose is packed into the lumen of the vein. Bone wax protects the vein from the drill and holds the packing in place. Once the vein is deflned it can be coagulated closed and divided. (C1C, C1 condyle; CEV, condylar emissary vein; IJV, internal jugular vein; JB, jugular bulb; OC, occipital condyle; SS, sphenoid sinus; VA, vertebral artery; XI, accessory nerve)

OC

CEV

C1C

VA

329

330

IV Posterolateral Skull Base

JB SS OC C1C CEV

VA

Fig. 16.55 The closed stump of the vein entering the jugular foramen. The condylar emissary vein runs in the occipital condyle in this specimen. (C1C, C1 condyle; CEV, condylar emissary vein; JB, jugular bulb; OC, occipital condyle; SS, sphenoid sinus; VA, vertebral artery)

SS

OC

CEV

HC VA

Fig. 16.56 Skeletonizing the hypoglossal canal. The hard cortical bone of the hypoglossal canal lies in the cancellous bone of the occipital condyle. The hypoglossal nerve covered by the dura runs in this canal. The rich venous plexus is seen as a blue or purple color through the thinned cortical bone of the hypoglossal canal. (CEV, condylar emissary vein; HC, hypoglossal canal; OC, occipital condyle; SS, sphenoid sinus; VA, vertebral artery)

JB

XII

XI

SS OC

CEV Fig. 16.57 Exposing the hypoglossal canal. The hypoglossal canal runs parallel to the joint the occipital condyle makes with C1. (CEV, condylar emissary vein; JB, jugular bulb; HC, hypoglossal canal; OC, occipital condyle; SS, sphenoid sinus; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

HC

VA

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IJV

JB XII

XI

SS OC JT HEV

Fig. 16.58 Exposing the hypoglossal emissary vein or anterior condylar emissary vein.

VA

The hypoglossal canal is opened. The hypoglossal canal contains the anterior condylar emissary veins and a branch of the ascending pharyngeal artery (not shown). The anterior condylar emissary vein communicates with the suboccipital venous plexus. (HEV, hypoglossal emissary vein; IJV, internal jugular vein; JB, jugular bulb; JT, jugular tubercle; OC, occipital condyle; SS, sphenoid sinus; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

IJV JB

XI

XII

Fig. 16.59 Further exposure of the hypoglossal nerve and the hypoglossal emissary vein.

SS

Note the sharp turn the hypoglossal nerve makes as it exits the hypoglossal canal. (HEV, hypoglossal emissary vein; IJV, internal jugular vein; JB, jugular bulb; SS, sphenoid sinus; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

HEV

VA

XII

XII Fig. 16.60 Exposing the hypoglossal nerve covered by the dura. The hypoglossal nerve covered by the dura is identifled after the hypoglossal venous plexus is removed (or controlled in actual surgery). (VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

XI

VA

331

332

IV Posterolateral Skull Base

V-VII

SP

IJV

JB XII

SS

XII

XI

VA

Fig. 16.61 Overview of the open jugular foramen. The hypoglossal canal and its adjacent structures are seen. (D, dura; IJV, internal jugular vein; JB, jugular bulb; SP, styloid process; SS, sphenoid sinus; VA, vertebral artery; V-VII, vertical segment of the facial nerve; XI, accessory nerve; XII, hypoglossal nerve)

D IJV

XI XII

Fig. 16.62 Identifying the hypoglossal nerve under the internal jugular vein. The hypoglossal nerve makes an acute bend after it exits the condyle medial to the jugular foramen. (IJV, internal jugular vein; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

VA

IX ICA

XII

JB X

Fig. 16.63 Identifying the nerves in the high

IJV

cervical area.

The glossopharyngeal nerve provides a branch as it leaves the jugular foramen, which communicates with a branch of the vagus nerve to innervate the carotid sinus. (ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; JB, jugular bulb; SS, sphenoid sinus; VA, vertebral artery; X, vagus nerve; XII, hypoglossal nerve)

SS VA

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IX X XII

Fig. 16.64 (Step 10) Inspection of the lower cranial nerves. The interconnections between the lower cranial nerves and their branching often makes it difflcult to identify the individual nerves below the jugular foramen. The better deflned distal nerves are traced back to deflne the nerves in the jugular foramen. (ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; X, vagus nerve; XII, hypoglossal nerve)

IJV

ICA

IX

Fig. 16.65 The glossopharyngeal nerve. The glossopharyngeal nerve is seen passing over the internal carotid artery. The hypoglossal nerve also passes over the artery more distally. (ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

ICA

X, XI XII

IJV

CT V-VII C7 Fig. 16.66 Jacobson’s nerve between the carotid canal and the internal jugular vein. Jacobson’s nerve (the tympanic nerve) can be found anterior to the jugular bulb in the bone between the jugular foramen and the carotid canal. Drilling above the jugular bulb, Jacobson’s nerve is found traveling toward the middle ear. (C7, C7 portion of the internal carotid artery; CT, chorda tympani; IX, glossopharyngeal nerve; JB, jugular bulb; TN, tympanic nerve [Jacobson’s nerve]; V-VII, vertical segment of the facial nerve)

TN IX JB

333

334

IV Posterolateral Skull Base

E-VII

V-VII C7 TN

IX

Fig. 16.67 Jacobson’s nerve originating from the

glossopharyngeal nerve.

This closeup view shows Jacobson’s nerve originating from the glossopharyngeal nerve passing into the tympanic canaliculus. (C7, C7 portion of the internal carotid artery; E-VII, extracranial segment of the facial nerve; ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; JB, jugular bulb; TN, tympanic nerve [Jacobson’s nerve]; V-VII, vertical segment of the facial nerve)

ICA

IX JB

IJV

V-VII

C7

IJV

Fig. 16.68 Exposing the C7 vertical portion of the internal carotid artery.

JB

The C7 vertical portion of the internal carotid artery is exposed anterior to the jugular bulb. (C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; JB, jugular bulb; V-VII, vertical segment of the facial nerve)

TT

Fig. 16.69 Overview of the anatomy around the

SCs SS

V-VII

E-VII

C7

IJV

JB

jugular foramen.

(C7, C7 portion of the internal carotid artery; E-VII, extracranial segment of the facial nerve; IJV, internal jugular vein; JB, jugular bulb; SCs, semicircular canals; SS, sphenoid sinus; TT, temporal tegmen; VA, vertebral artery; V-VII, vertical segment of the facial nerve; XI, accessory nerve)

XI VA

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

TT

IX ICA

VII

SCs

JB

XII

X

IJV

SS VA

Fig. 16.70 Overview of the high cervical

XI

dissection.

ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; JB, jugular bulb; SCs, semicircular canals; SS, sphenoid sinus; TT, temporal tegmen; VA, vertebral artery; VII, facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

VII

SCs

TT Fig. 16.71 Removing the lateral sigmoid sinus and internal jugular vein.

IX C7

IX X, XI

SS

XII

ICA

X

XII

XI VA

Most glomus jugulare tumors are extradural and reside in venous structures. This allows the surgeon to remove the lateral portion of the sigmoid sinus, leaving the medial wall, which abuts the cranial nerves intact. (C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; SCs, semicircular canals; SS, sphenoid sinus; TT, temporal tegmen; VA, vertebral artery; VII, facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

C7 IX IPS Fig. 16.72 Exposing the pars nervosa of the jugular foramen. The sigmoid sinus, jugular bulb, and internal jugular veins are removed to reveal the extradural course of the lower cranial nerves. Note the course of the internal carotid artery as it enters the petrous bone. Just inferior to the cochlea the internal carotid artery will turn anteriorly and travel through the petrous bone. (C7, C7 portion of the internal carotid artery; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JT, jugular tubercle; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

X

IX

XI

X, XI JT

XII

335

336

IV Posterolateral Skull Base

IX IPS

X XII XI

IX X, XI

Fig. 16.73 The jugular tubercle and adjacent

JT

structures.

The inferior petrosal sinus enters the sigmoid sinus between the glossopharyngeal and vagus nerves. Bleeding from this oriflce can be controlled by backing oxidized cellulose into the vein. (IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XII VA

C7 IX CA IX

X XII

X, XI

XI JT

Fig. 16.74 Exposing the cochlear aqueduct. The cochlear aqueduct is seen emerging at the cranial bend of the ninth nerve canal. (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; ,IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XII VA

C7

CA

IX

IPS XI

Fig. 16.75 The cochlear aqueduct and the ninth nerve canal. This dissection shows why the cochlear aqueduct is an excellent guide to the position of the glossopharyngeal nerve during a transmastoid dissection. (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XII

X

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IX ICA XII X XI

C7

X, X

IX

I

CA

SS Fig. 16.76 Overview of pars nervosa of the jugular

JT XII

foramen.

The cochlear aqueduct travels between the cochlea and the jugular foramen. It enters the jugular foramen at the level of the glossopharyngeal nerve. (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; ,ICA, internal carotid artery; IX, glossopharyngeal nerve; JT, jugular tubercle; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; SS, sphenoid sinus; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

LSM

VA OCIM

C7 IX X

IPS

CA

XII XI

Fig. 16.77 Drilling of the jugular tubercle. Great care is taken to avoid injury to the lower cranial nerves when removing the jugular tubercle. Bleeding from the adjacent dura must be patiently controlled during the drilling procedure. The cochlear aqueduct marks the glossopharyngeal nerve. (C7, C7 portion of the internal carotid artery; CA, cochlear aqueduct; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

JT VA

II V-V

IX

tubercle.

The jugular tubercle and the cochlear aqueduct have been partially removed with a diamond drill. The lower cranial nerves exit the posterior fossa and pass over the jugular tubercle. (C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; JT, jugular tubercle; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; PSC, posterior semicircular canal; SS, sphenoid sinus; VA, vertebral artery; V-VII, vertical segment of the facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

SS

XII

XI

IX

X, XI

Fig. 16.78 Partial resection of the jugular

ICA

C7

PSC

JT XII

X

LSM

VA OCIM

337

IV Posterolateral Skull Base

C7

IX X

IPS

IX

XII XI

X, XI

338

JT XII

Fig. 16.79 Magnified view of the jugular tubercle. The tubercle lies between the hypoglossal canal and the lower cranial nerves. (C7, C7 portion of the internal carotid artery; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

VA

V-VII

PSC

C7

IX ICA XII

SS JT IX

Fig. 16.80 (Step 11) Intradural exposure.

X

The dura is opened above the jugular foramen. (C7, C7 portion of the internal carotid artery; ICA, internal carotid artery; IX, glossopharyngeal nerve; JT, jugular tubercle; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; PSC, posterior semicircular canal; SS, sphenoid sinus; VA, vertebral artery; V-VII, vertical segment of the facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XI XII

LSM

VA XI

OCIM

C7

JT

IX Fig. 16.81 Intradural exposure of the jugular

foramen.

Note the right angle turn the hypoglossal nerve makes as it exits the hypoglossal canal. (C7, C7 portion of the internal carotid artery; IX, glossopharyngeal nerve; JT, jugular tubercle; VA, vertebral artery; C7, vertical; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

X

VA XI XII

X

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IX X XI

XII

Fig. 16.82 The accessory nerve. The spinal accessory nerve lies most inferiorly on the jugular tubercle. It is not uncommon to stimulate that nerve when drilling the jugular tubercle. (IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XII XI

Fig. 16.83 Right angle turn of the hypoglossal

PIC

nerve.

The intradural hypoglossal nerve makes a right angle turn as it leaves the hypoglossal canal. (PICA, posterior inferior cerebellar artery; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

A VA C7

Fig. 16.84 Partial resection of the jugular

tubercle.

The jugular tubercle is removed below the lower cranial nerves. In most cases the transjugular approach is used to remove tumors in and around the jugular bulb. If the surgeon needs to see across the front of the medulla (as is the case in some anterior foramen meningiomas), the view will be improved by drilling the jugular tubercle under the lower cranial nerves. (C7, C7 portion of the internal carotid artery; IX, glossopharyngeal nerve; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

IX X

VA XI XII

339

340

IV Posterolateral Skull Base

C7 IX X

XI XII

IX Fig. 16.85 Posterior translocation of the

VA

X

hypoglossal nerve.

XI

This procedure improves the surgeon’s view anterior to the occipital condyle. (C7, C7 portion of the internal carotid artery; IX, glossopharyngeal nerve; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

XII C7

IPS

IX

CL

X

, XI

XII Fig. 16.86 Posterior translocation of the lower cranial nerves.

Manipulation of the lower cranial nerves is usually avoided, as the patient will experience at least transient swallowing problems following this maneuver. This translocation does improve the view across the clivus. (C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

VA

IX, X XI XII

C7

IPS

CL

VA Fig. 16.87 (Step 12) Beginning of partial clivectomy. The inferior petrosal sinus is identifled during a partial clivectomy. (C7, C7 portion of the internal carotid artery; CL, clivus; IPS, inferior petrosal sinus; VA, vertebral artery)

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

IX ICA

SCs Fig. 16.88 Overview at this stage. The dura is closed with the aid of a fascia graft. The defect in the mastoid is fllled with a fat graft and covered by titanium mesh or a titanium plate. The posterior belly of the digastric muscle is stitched to deep layer muscles. The flrst and second layer muscles are stitched to the bone. (CL, clivus; ICA, internal carotid artery; IX, glossopharyngeal nerve; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; SCs, semicircular canals; SS, sphenoid sinus; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

CL

SS

XI VA

IPS

LSM OCIM

CL

Fig. 16.89 Petrosectomy with partial clivectomy. Removing the lateral lip of the clivus improves the surgeon’s view to the opposite side. The clivus is not at but cupped, impeding the surgeon’s view to the opposite side. (CL, clivus; IPS, inferior petrosal sinus)

C7

IAC

CL IPS

Fig. 16.90 The inferior petrosal sinus and the internal auditory canal. Cranial nerves VII and VIII can be seen passing from the brainstem to the IAC. (C7, C7 portion of the internal carotid artery; CL, clivus; ICA, internal carotid artery; IPS, inferior petrosal sinus; VII, facial nerve; VIII, vestibulocochlear nerve)

VII, VIII

XII X

341

342

IV Posterolateral Skull Base

AICA VI

Fig. 16.91 The abducens nerve. The abducens nerve is seen exiting the brainstem at the pontomedullary junction. (AICA, anterior inferior cerebellar artery; VI, abducens nerve)

AICA VI Fig. 16.92 Entrance of the abducens nerve into Dorello’s canal. Looking superiorly, the abducens nerve is seen entering Dorello’s canal. (AICA, anterior inferior cerebellar artery; VI, abducens nerve)

VI

BA VA VA

Fig. 16.93 Viewing the vertebrobasilar junction. The junction of the vertebral and basilar arteries is easily seen through this exposure. (BA, basilar artery; VA, vertebral artery; VI, abducens nerve)

16 Postauricular Transmastoid Posterior Infratemporal Fossa Transjugular Approach

VI

BA VA

Fig. 16.94 Viewing the vertebrobasilar junction. This exposure provides the surgeon with an excellent view of the vertebrobasilar junction without any retraction. (BA, basilar artery; VA, vertebral artery; VI, abducens nerve)

343

17 Total Petrosectomy with Partial Clivectomy

The total petrosectomy is the ultimate procedure for viewing the front of the brainstem. Unlike anterior approaches through the face, this exposure affords the surgeon a view of the structures lateral to the midline. By necessity, the patient will loose hearing on the side of the exposure. Although the procedure is most often used to treat large petroclival meningiomas, it also can be employed to treat chordomas.

Key Steps Position: Lateral   Step 1. “C” shaped skin incision from above the temporal line to below the mastoid tip (Fig. 17.1)   Step 2. Elevation of large vascularized graft (Fig. 17.4)   Step 3. Triple closure of ear canal (Fig. 17.9)   Step 4. Subperiosteal exposure of suboccipital area and V3 segment of the vertebral artery (Figs. 17.15–17.19)   Step 5. Mastoidectomy and labyrinthectomy (Fig. 17.24)   Step 6. Raising of temporal-suboccipital craniotomy (Fig. 17.26)   Step 7. Anterior petrosectomy (Fig. 17.31)   Step 8. Resection of cochlea (Fig. 17.31)   Step 9. Posterior translocation of facial nerve (Fig. 17.34) Step 10. Condylectomy (Fig. 17.41) Step 11. Opening of dura (Fig. 17.53)

Illustrated Steps with Commentary

MA

Fig. 17.1 (Step 1) Skin incision. A large “C” shaped skin incision is made from just above the temporal line to just below the mandibular angle. (MA, mandibular angle)

17 Total Petrosectomy with Partial Clivectomy

Fig. 17.2 Identifying the greater auricular nerve.

GAN

The greater auricular nerve should be identified and preserved. This nerve can serve as a graft if needed. (GAN, greater auricular nerve)

TPM GA

GAN

Fig. 17.3 Raising the skin flap.

OM

The scalp is raised through the loose tissue plane. As much loose tissue as possible is left on the pericranium and fascia so that the vascularized flap will be as thick as possible. (GA, galea aponeurotica; GAN, greater auricular nerve; OM, occipitalis muscle; TPM, temporoparietal muscle)

TPM GA SCM Fig. 17.4 (Step 2) Outlining a vascularized flap. A large vascularized flap is harvested before the craniotomy is performed. This flap is based anteriorly and incorporates the pericranium and the superficial layer of the temporal fascia. The edges of the skin flap are raised to make the vascularized flap as large as possible. (GA, galea aponeurotica; OM, occipitalis muscle; SCM, sternocleidomastoid muscle; TPM, temporoparietal muscle)

OM

345

346

IV Posterolateral Skull Base

GAN

TM

SCM SNL Fig. 17.5 Raising the vascularized flap. (GAN, greater auricular nerve; SCM, sternocleidomastoid muscle; SNL, superior nuchal line; TM, temporalis muscle)

GAN

TM EAC SCM SNL

Fig. 17.6 Dividing the external auditory canal. The external auditory canal is incised. The lateral end of the canal will be closed in three layers. (EAC, external auditory canal; GAN, greater auricular nerve; SCM, sternocleidomastoid muscle; SNL, superior nuchal line; TM, temporalis muscle)

RZy

GAN

SCM Fig. 17.7 Raising the temporalis muscle. The temporalis muscle is elevated from the bone and retracted anteriorly. (GAN, greater auricular nerve; RZy, root of the zygoma; SCM, sternocleidomastoid muscle)

17 Total Petrosectomy with Partial Clivectomy

RZy

SCM Fig. 17.8 Cutting the greater auricular nerve. The greater auricular nerve is cut in a part of the high cervical approach. The nerve is cut in such a way as to preserve a length of nerve for a possible graft. (RZy, root of the zygoma; SCM, sternocleidomastoid muscle)

EAC

Fig. 17.9 (Step 3) Closure of the external auditory canal.

The external auditory canal is divided and closed using a triple closure technique as outlined in Figs. 17.10 to 17.14. (EAC, external auditory canal; SCM, sternocleidomastoid muscle)

Fig. 17.10 Undermining the external auditory

canal.

The skin is dissected from the external canal as deep into the canal as is possible. This will provide a cuff of tissue that will facilitate a watertight closure. If all the squamous epithelium from the ear canal and eardrum is not removed, the patient may develop an epidermoid tumor.

SCM

347

348

IV Posterolateral Skull Base

Fig. 17.11 Inverting the skin of the external auditory canal. The skin edges are inverted so that all squamous epithelium is pushed out into the external ear.

Fig. 17.12 Stitching the external auditory canal. The inverted skin of the external auditory canal is stitched closed from within the ear.

Fig. 17.13 Double closure of the external auditory

canal.

The fascia is pulled together over the external auditory canal with a second layer of sutures.

17 Total Petrosectomy with Partial Clivectomy

Fig. 17.14 Triple closure of the external auditory canal using a vascularized flap. A flap of temporoparietal fascia is rotated back over this suture line as a third layer of closure.

Fig. 17.15 (Step 4) Posterior reflection of the sternocleidomastoid muscle.

Sp

CM

All posterior neck muscles should be elevated from the occipital bone and retracted posteriorly to afford the surgeon an anterolateral view. For this demonstration each muscle layer will be retracted separately. (SpCM, splenius capitis muscle)

LCM OA Fig. 17.16 (Step 4) Posterior reflection of the splenius capitis muscle. (LCM, longissimus capitis muscle; OA, occipital artery)

349

350

IV Posterolateral Skull Base

DM

Fig. 17.17 (Step 4) Posterior reflection of the longissimus capitis muscle exposing the styloid diaphragm. (DM, digastric muscle)

DM

OC SM

Fig. 17.18 (Step 4) Removal of the styloid diaphragm exposing the obliquus capitis superior muscle. (DM, digastric muscle; OCSM, obliquus capitis superior muscle)

EAC

DM

IJV XII Fig. 17.19 (Step 4) Identification of the

LSM

VA OCIM C1

RCMjM

SM

The vertebral artery can be tethered to the lamina of the atlas by a bony or fibrous band. This specimen has an incomplete (fibrous) canal tethering the vertebral artery to the groove of the atlas. (C1, C1 [atlas]; DM, digastric muscle; EAC, external auditory canal; ICA, internal carotid artery; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCMjM, rectus capitis major muscle; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

XI

OC

horizontal portion of the vertebral artery in the suboccipital triangle.

MT

ICA

17 Total Petrosectomy with Partial Clivectomy

VA

OCIM

OCSM

Fig. 17.20 Enlarged view of the suboccipital

triangle.

JG

In this specimen, a fibrous band is seen passing over the V3 segment of the vertebral artery tethering the artery to the “J-groove” of the atlas. A high cervical dissection is only occasionally combined with a total petrosectomy. We include a high cervical dissection in the demonstration for completeness. (JG, J-groove for the vertebral artery; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PA, posterior arch of the C1 [atlas]; RCMjM, rectus capitis major muscle; VA, vertebral artery)

PA

RCM

jM

DM TC1

Fig. 17.21 Anatomical relationships in the high cervical region. The obliquus capitis superior, obliquus capitis inferior, rectus capitis lateralis, splenius cervicalis, and levator scapulae muscles attach to the transverse process of the atlas. The rectus capitis major, obliquus inferior, and obliquus superior outline the superior suboccipital triangle. The obliquus inferior, splenius cervicalis, and semispinalis cervicis muscles outline the inferior suboccipital triangle. (DM, digastric muscle; ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; LSM, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; TC1, transverse process of the C1; XI, accessory nerve; XII, hypoglossal nerve)

IX XII

ICA

XI

IJV

ICA XII

MT XI LSM

capitis superior muscle.

The obliquus capitis superior is detached from the occipital bone. Care should be taken not to disrupt the vertebral artery or the venous plexus that lies inferior to this muscle. (C1, C1 [atlas]; DM, digastric muscle; EAC, external auditory canal; ICA, internal carotid artery; IJV, internal jugular vein; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; RCMjM, rectus capitis major muscle; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

EAC

DM

IJV

Fig. 17.22 Posterior reflection of the obliquus

OCIM

LSM

OCIM

VA C1 RCMjM

351

IV Posterolateral Skull Base

MT

XI

LSM

OCIM

VA

Fig. 17.23 Exposing the occipital condyle and C1

facet.

This specimen has a fibrous canal band that completes the canal over the J-groove of the atlas for the vertebral artery, which must be cut before the artery can be mobilized. The C1 occipital joint lies anterior to the V3 segment of the vertebral artery. (C1, C1 [atlas]; LSM, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; RCMjM, rectus capitis major muscle; VA, vertebral artery; XI, accessory nerve)

C1 RCMjM

SS

Fig. 17.24 (Step 5) Mastoidectomy with labyrinthectomy exposing the vestibule. The technique for performing a mastoidectomy and labyrinthectomy is outlined in Chapter 14. (SS, sigmoid sinus)

T-V II

352

V-VII Fig. 17.25 Labyrinthectomy exposing the internal

auditory canal.

The internal auditory canal is found communicating with the posterior fossa dura. The fundus of the canal is entered by drilling through the superior wall of the vestibule. The facial nerve is on the superior side of Bill’s bar. (G, genu [second turn or external genu] of the facial nerve; IAC, internal auditory canal; T-VII, tympanic segment of the facial nerve; V-VII, vertical segment of the facial nerve)

G IAC

17 Total Petrosectomy with Partial Clivectomy

Fig. 17.26 (Step 6) Outlining the temporal and suboccipital craniotomies. A groove is drilled posterior to the digastric groove connecting to the mastoidectomy. A second groove is drilled above the root of the zygoma connecting to the mastoidectomy posteriorly and extending along the anterior border of the middle fossa to the sphenoid ridge anteriorly. At least two bur holes are placed along the circumference of the proposed flap. If the dura is tenaciously attached to the bone, additional bur holes are made and a groove is drilled across the transverse sinus.

Fig. 17.27 Elevating the craniotomy.

MMA GSPN

AE Fig. 17.28 Identifying the middle meningeal artery passing through the middle fossa cranial base. The middle meningeal artery can be followed to the foramen spinosum. (AE, arcuate eminence; GSPN, greater superficial petrosal nerve; MMA, middle meningeal artery)

353

354

IV Posterolateral Skull Base

V3 Fig. 17.29 Identifying the lateral loop formed by the mandibular and maxillary divisions of the trigeminal nerve. The foramen ovale and rotundum are identified. The exit canals of the mandibular and maxillary branches of the trigeminal nerves are opened. Care is taken to cool the drill with irrigation so as not to burn the nerves. Heating the nerves can lead to postoperative paresthesias. The dura propria is separated from the trigeminal nerve. (GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2

GSPN GG

V3 Fig. 17.30 Identifying the greater superficial petrosal nerve and translocating the mandibular division of the trigeminal nerve anteriorly.

GSPN

The greater superficial petrosal nerve runs into the vidian canal behind the gasserian ganglion and the mandibular division of the trigeminal nerve. The vidian canal leaves the middle fossa through the anterior wall of foramen lacerum. (GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

Fig. 17.31 (Steps 7 and 8) Anterior petrosectomy exposing the horizontal portion of the internal carotid artery. The bone medial to the greater superficial petrosal nerve has been removed to expose the carotid artery. The cochlea, which lies medial to the C6-7 genu, has been drilled away. Because the labyrinth has been opened, removal of the cochlea causes no further neurological deficit. (C6, C6 portion of the internal carotid artery; GG, gasserian ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; T-VII, tympanic segment of the facial nerve; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve])

V2

GG

GSPN

T-V II

V3 IAC

C6

GG

V2

17 Total Petrosectomy with Partial Clivectomy

GSPN T-VII

Fig. 17.32 Dividing the greater superficial

GnG

petrosal nerve from the geniculate ganglion. The facial nerve is freed by dividing the greater superficial petrosal nerve as it branches from the geniculate ganglia. Transposition of the facial nerve almost always results in facial weakness, so the surgeon must determine that exposure afforded by the transposition is necessary. (C6, C6 portion of the internal carotid artery; GnG, geniculate ganglion; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

C6 IAC

GSPN

T-V II Fig. 17.33 Posterior translocation of the facial

C6

nerve

IAC

The facial nerve, released from the greater superficial petrosal nerve, is translocated posteriorly to expose the entire anterior petrous bone. (C6, C6 portion of the internal carotid artery; GSPN, greater superficial petrosal nerve; IAC, internal auditory canal; T-VII, tympanic segment of the facial nerve; V3, mandibular nerve [third division of the trigeminal nerve])

V3

V3

GSPN VII C6 Fig. 17.34 (Step 9) Posterior translocation of the facial nerve. (C6, C6 portion of the internal carotid artery; GSPN, greater superficial petrosal nerve; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

V3

355

356

IV Posterolateral Skull Base

C7 VII

C6

Fig. 17.35 Further petrosectomy exposing the

V3

vertical and horizontal portion of the internal carotid artery.

GG

With the facial nerve transposed, the surgeon is able to resect the bone from the vertical segment of the carotid artery (V7) to the condyle. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; GG, gasserian ganglion; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

JT

SS

C7 VII

C6

V3 GG

LS Fig. 17.36 Overview of the resection at this stage

as viewed from the middle fossa.

(C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; GG, gasserian ganglion; JT, jugular tubercle; LS, lateral sinus; SS, sigmoid sinus; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

V2 V3 C6 VII

JT SS

Fig. 17.37 Overview of the resection at this stage as viewed from the posterior fossa. (C6, C6 portion of the internal carotid artery; GG, gasserian ganglion; JT, jugular tubercle; LS, lateral sinus; SS, sigmoid sinus; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

LS

GG

V2

17 Total Petrosectomy with Partial Clivectomy

V2

VII

V3

GG

OC JB Fig. 17.38 Removing the mastoid tip.

SS

The mastoid tip lateral to the stylomastoid foramen is removed. The stylomastoid foramen lies at the anterior end of the digastric groove. (GG, gasserian ganglion; JB, jugular bulb; LS, lateral sinus; OC, occipital condyle; SS, sigmoid sinus; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VII, facial nerve)

LS

VII

IJV ICA

GG

C7 VA

OC

JB SS

Fig. 17.39 Exposing the jugular foramen. The bone anterior to the occipital condyle is removed to expose the jugular foramen. (C7, C7 portion of the internal carotid artery; GG, gasserian ganglion; ICA, internal carotid artery; IJV, internal jugular vein; JB, jugular bulb; LS, lateral sinus; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve)

LS

VII

IJV C7

XI

JT Fig. 17.40 Identifying the occipital and C1

condyles.

The occipital condyle is located behind the jugular foramen. The vertebral artery overlies the joint between the condyle and the lateral mass of C1. (C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; JB, jugular bulb; JT, jugular tubercle; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve; XI, accessory nerve)

VA

JB

OC SS

357

358

IV Posterolateral Skull Base

VII

C7

IJV

JB

XI

OC XII JT

Fig. 17.41 (Step 10) Condylectomy.

SS

VA

The occipital posterior condyle is removed up to the hypoglossal canal. (C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; JB, jugular bulb; JT, jugular tubercle; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve; XI, accessory nerve; XII, hypoglossal nerve)

C7 IJV

JB

XII XI XII

SS

Fig. 17.42 Identifying the hypoglossal canal.

VA

(C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; JB, jugular bulb; SS, sigmoid sinus; VA, vertebral artery; XI, accessory nerve; XII, hypoglossal nerve)

VII C6 IJV

C7 IX

XII XI Fig. 17.43 Anatomical relationships seen after condylectomy. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; JB, jugular bulb; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve; XI, accessory nerve; XII, hypoglossal nerve)

JB OC VA

SS

17 Total Petrosectomy with Partial Clivectomy

C6 C7

X,

IX

XI

XI

Fig. 17.44 Neural structures in the jugular foramen behind the jugular bulb.

JB

The lower cranial nerves exit the neural foramen medial to the jugular vein. (C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; IX, glossopharyngeal nerve; JB, jugular bulb; SS, sigmoid sinus; X, vagus nerve; XI, accessory nerve)

SS

C7 X

IJV

VII

XII IX

Fig. 17.45 Posterior translocation of the jugular bulb (pars venosa translocation) with anterior translocation of the internal carotid artery.

IPS

XI XII

The inferior petrosal sinus must be detached from the jugular vein before the jugular vein and bulb are transposed posteriorly. Transposing the jugular vein reveals the vagal, glossopharyngeal, and spinal accessory nerves. (C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JB, jugular bulb; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

VA

SS

JB

C7

VII

IJV Fig. 17.46 Posterior translocation of the jugular bulb and lower cranial nerves (pars nervosa and venosa translocation). The pars nervosa is transposed to demonstrate the underlying anatomy. During surgery, such manipulation of the lower cranial nerves would almost certainly result in postoperative swallowing difficulty, and this is rarely done. (C7, C7 portion of the internal carotid artery; IJV, internal jugular vein; IPS, inferior petrosal sinus; IX, glossopharyngeal nerve; JB, jugular bulb; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve; X, vagus nerve; XI, accessory nerve)

X IX

XI VA

JB

IPS

SS

359

360

IV Posterolateral Skull Base

PT

Fig. 17.47 Exposing the jugular tubercle. Transposing the lower cranial nerves exposes the jugular tubercle, which lies under the lower cranial nerves. (PT, petrosal tip)

CL

Fig. 17.48 Partial clivectomy. The lower clivus can be partially resected once the jugular tubercle is removed. (CL, clivus)

Fig. 17.49 Drilling the posterior wall of the lateral mass of the atlas to expose the extracranial vertebral artery. The posterior wall of the transverse process, the posterior costal lamella, is opened with a diamond drill. Care is taken not to injure the veins that surround the vertebral artery. Venous bleeding is meticulously controlled with bipolar cautery to preserve the surgeon’s view through a bloodless field.

17 Total Petrosectomy with Partial Clivectomy

Fig. 17.50 Posterior translocation of the extracranial vertebral artery. Care is taken to assess the quality of the vertebral artery before attempting the transposition. Transposing a calcified atherosclerotic artery can crack the artery or release emboli into the bloodstream.

Fig. 17.51 Anatomical relationship in a high cervical portion after partial removal of the lateral mass of the atlas. Partial removal of the lateral mass of the atlas and the inferior occipital condyle provides the surgeon a flatter trajectory toward the clivus and anterior skull base.

Fig. 17.52 Anterior translocation of the internal carotid artery and posterior translocation of the lower cranial nerves, jugular bulb, and internal jugular vein. A very broad working space is obtained by transposing the arteries, veins, and nerves. The lower cranial nerves should not be manipulated unless they lie in the planned surgical trajectory or are not functioning before the surgery.

361

IV Posterolateral Skull Base

V VII Po

Fig. 17.53 (Step 11) Dural opening. The posterior fossa dura is opened anterior to the sigmoid sinus. The superior petrosal sinus is ligated and cut. Care is taken not to injure the veins draining from the supratentorial compartment toward the sigmoid sinus. (Po, pons; V, trigeminal nerve; VII, facial nerve)

ICA C5

VI

Pcom AntCh

III

A very flat view of the clivus anterior to the pons is obtained. Both vertebral arteries forming the basilar artery are easily reached. (AntCh, anterior choroidal artery; C5, C5 portion of the internal carotid artery; ICA, internal carotid artery; III, oculomotor nerve; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebral artery; V, trigeminal nerve; VI, abducens nerve)

VI

V

P2

A

Fig. 17.54 Exposing the pons and adjacent structures as seen from an anterolateral direction.

SC

362

C7 VII V XII Fig. 17.55 The hypoglossal nerve. The ipsilateral hypoglossal nerve runs under the vertebral artery. (C7, C7 portion of the internal carotid artery; Po, pons; V, trigeminal nerve; VA, vertebral artery; VII, facial nerve; IX, glossopharyngeal nerve; X, vagus nerve; XII, hypoglossal nerve)

Po

VA

IX, X

17 Total Petrosectomy with Partial Clivectomy

C7

VI AICA

VA

VII V

Po

VA IX, X

Fig. 17.56 The vertebrobasilar junction. (AICA, anterior inferior cerebellar artery; C7, C7 portion of the internal carotid artery; IX, glossopharyngeal nerve; Po, pons; V, trigeminal nerve; VA, vertebral artery; VI, abducens nerve; VII, facial nerve; X, vagus nerve)

AICA

BA

VII V Po

VA Fig. 17.57 The lower basilar artery. (AICA, anterior inferior cerebellar artery; BA, basilar artery; IX, glossopharyngeal nerve; Po, pons; V, trigeminal nerve; VA, vertebral artery; VII, facial nerve; X, vagus nerve)

IX, X

BA VI AICA VA Fig. 17.58 The mid-basilar artery. (AICA, anterior inferior cerebellar artery; BA, basilar artery; IX, glossopharyngeal nerve; V, trigeminal nerve; VA, vertebral artery; VI, abducens nerve; VII, facial nerve; X, vagus nerve)

IX,

X

VII V

363

IV Posterolateral Skull Base

V VII

BA

AICA

VA

Fig. 17.59 The third through the twelfth cranial

nerves.

The surgeon has an excellent view of the lateral and anterior pons and the anterior medulla. (AICA, anterior inferior cerebellar artery; BA, basilar artery; V, trigeminal nerve; VA, vertebral artery; VII, facial nerve)

AICA

Fig. 17.60 The oculomotor nerve, supracerebellar, posterior cerebral, posterior communicating, and anterior choroidal arteries.

The oculomotor nerve and trochlear nerves enter the tentorial edge. The posterior tentorium is left intact to protect the inferior temporal lobe. The internal carotid artery gives rise to the posterior communicating artery and the anterior choroidal artery. (AICA, anterior inferior cerebellar artery; III, oculomotor nerve; IV, trochlear nerve; IX, glossopharyngeal nerve; Po, pons; SCA, superior cerebral artery; V, trigeminal nerve; VA, vertebral artery; VI, abducens nerve; VII, facial nerve; X, vagus nerve)

VI VII

VA

V III

Po

IV SCA

IX, X

ICA Pcom

C5 VI

AntCh

III

Fig. 17.61 The internal carotid, posterior

VI

V

P2

(AntCh, anterior choroidal artery; C5, C5 portion of the internal carotid artery; ICA, internal carotid artery; III, oculomotor nerve; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebral artery; V, trigeminal nerve; VI, abducens nerve)

A

communicating, and anterior choroidal arteries.

SC

364

17 Total Petrosectomy with Partial Clivectomy

ICA C5

VI

Pcom AntCh

II III

VI P2

Fig. 17.62 The optic nerve over the internal carotid artery.

SC

A

(AntCh, anterior choroidal artery; C5, C5 portion of the internal carotid artery; ICA, internal carotid artery; II, optic nerve; III, oculomotor nerve; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebral artery; V, trigeminal nerve; VI, abducens nerve)

C6

II

C5

IV

VI

III

V BA

VII Fig. 17.63 The upper basilar artery. (BA, basilar artery; C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve)

ICA Pcom Ant Ch

III IV VI

V

P1

BA

Fig. 17.64 The basilar tip. (AntCh, anterior choroidal artery; BA, basilar artery; ICA, internal carotid artery; III, oculomotor nerve; IV, trochlear nerve; P1, P1 segment of the posterior cerebral artery; P2, P2 segment of the posterior cerebral artery; Pcom, posterior communicating artery; SCA, superior cerebral artery; V, trigeminal nerve; VI, abducens nerve)

SCA

P2

365

366

IV Posterolateral Skull Base

V2

V1

V3 Fig. 17.65 The abducens nerve in the cavernous

sinus.

GG

Opening the cavernous sinus between the trochlear and trigeminal nerves (Parkinson’s triangle) reveals the intracavernous abducens nerve. The carotid artery lies medial to the nerve. Unless the cavernous sinus is packed with tumor, this opening will result in significant venous bleeding. (GG, gasserian ganglion; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

VI III

V

IV

VI GL(PSL)

PCL Fig. 17.66 The petroclinoidal fold. The forceps hold the petroclinoidal fold in the dura, which bridges the petrous bone and the posterior clinoid. (GL(PSL), Gruber’s ligament [petrosphenoid ligament]; PCL, petroclinoid ligament; VI, abducens nerve)

VI

C5

IPS GL(PSL) PCL

Fig. 17.67 The abducens nerve and the petrosphenoidal (Gruber’s) ligament. The abducens nerve bends sharply to pass under the petrosphenoid ligament. (C5, C5 portion of the internal carotid artery; GL(PSL), Gruber’s ligament [petrosphenoid ligament]; IPS, inferior petrosal sinus; PCL, petroclinoid ligament; VI, abducens nerve)

17 Total Petrosectomy with Partial Clivectomy

GL(PSL) IV

VI

C5

C6

III

C7

Fig. 17.68 Opening Dorello’s canal.

V

The tip of a dissector points the petrosphenoid (Gruber’s) ligament. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; GL(PSL), Gruber’s ligament [petrosphenoid ligament]; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; VI, abducens nerve)

VI

Fig. 17.69 Opening the inferior petrosal sinus to expose the abducens nerve. The abducens nerve passes through a fibrous canal between its entrance into the clival dura and its emergence under the petrosphenoid ligament into the cavernous sinus. (VI, abducens nerve)

VI IPS

Fig. 17.70 The abducens nerve. (IPS, inferior petrosal sinus; VI, abducens nerve)

367

368

IV Posterolateral Skull Base

SpP

C5 VI

Fig. 17.71 The abducens nerve and the sympathetic nerve, which travels with the internal carotid artery. (C5, C5 portion of the internal carotid artery; SpP, sympathetic plexus; VI, abducens nerve)

V2

V1

V3 GG VI

Fig. 17.72 Fusing the abducens and the sympathetic nerve. (C5, C5 portion of the internal carotid artery; GG, gasserian ganglion; SpP, sympathetic plexus; V, trigeminal nerve; V1, ophthalmic nerve [first division of the trigeminal nerve]; V2, maxillary nerve [second division of the trigeminal nerve]; V3, mandibular nerve [third division of the trigeminal nerve]; VI, abducens nerve)

Fig. 17.73 The oculomotor nerve into the lateral wall of the cavernous sinus. The oculomotor nerve travels in a canal through the tentorium before reaching the lateral wall of the cavernous sinus. This canal can be opened to increase the surgeon’s working space in front of the midbrain. The trochlear nerve crosses the oculomotor nerve approximately 7 mm anterior to the oculomotor nerve entering the canal, limiting the length of the oculomotor canal that can be safely opened. (III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve)

SpP C5

V

IV V

III IV

17 Total Petrosectomy with Partial Clivectomy

C7

C6

C5

VII

CL VI

V

Fig. 17.74 Further removal of the clivus. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve)

C7

VI

C6 VII

C5

CL V

Fig. 17.75 Skeletonizing the sphenoid sinus. The sphenoid sinus extends a variable distance into the clivus. Opening that sinus creates a problem of closing off the air spaces from the subarachnoid space at the end of the case. The sphenoid sinus should not be opened except to remove a tumor. (C5, C5 portion of the internal carotid artery; C6, C6 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve)

VI VII CL

SpS V

Fig. 17.76 The mucosa of the sphenoid sinus. (CL, clivus; SpS, sphenoid sinus; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve)

369

370

IV Posterolateral Skull Base

C7

VI VII

CL

C5

SpS V

Fig. 17.77 Opening the sphenoid sinus. (C5, C5 portion of the internal carotid artery; C7, C7 portion of the internal carotid artery; CL, clivus; SpS, sphenoid sinus; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve)

Fig. 17.78 Final view of the surgical exposure.

V

Posterior Skull Base

18 Anatomy for Posterior Skull Base Surgery

Surgeons approaching the posterior fossa should be familiar with the extracranial anatomy. The posterior neck muscles can be divided into three overlapping layers. The superficial layer includes the sternocleidomastoid muscle and the splenius capitis muscle. The middle layer includes the longissimus capitis muscle and the semispinalis capitis muscle. A white or yellow soft tissue membrane that lies under the splenius capitis muscle covers the middle layer including the fat tissue, the veins, and the occipital artery. Defining this membrane is helpful in protecting the occipital artery. The deep layer consists of the rectus capitis major muscle, the obliquus superior capitis muscle, and the obliquus inferior capitis muscle. The suboccipital triangle is outlined by the three muscles in the deep layer. The triangle frames the third portion of the vertebral artery.

Key Steps Step 1. Identification of mastoid tip and asterion (Fig. 18.1) Step 2. Identification of splenius capitis muscle (Fig. 18.4) Step 3. Identification of occipital artery (Fig. 18.7) Step 4. Identification of obliquus superior muscle (Fig. 18.18) Step 5. Identification of vertebral artery (Fig. 18.21)

Illustrated Steps with Commentary

EAC

INL

SNL Fig. 18.1 (Step 1) Palpable landmarks. The mastoid tip and posterior body of the mastoid are palpable. A depression can usually be palpated just below the asterion. The inion marks the midline. (EAC, external auditory canal; EOP, external occipital protuberance; INL, inferior nuchal line; SNL, superior nuchal line)

EOP

374

V Posterior Skull Base

PAV

OA Fig. 18.2 The posterior auricular vein. On removing the skin the posterior auricular vein and occipital vein are prominent. The posterior auricular vein passes behind the ear draining into the external jugular vein. (OA, occipital artery; PAV, posterior auricular vein)

P GAN

PAM PAV Fig. 18.3 The occipital belly of the occipitofrontalis muscle and the sternocleidomastoid muscle.

OM

The most superflcial muscles encountered are the sternocleidomastoid and occipital belly of the occipitofrontalis muscle. The trapezius muscle is also superflcial with its lateral edge approximately 2–3 cm medial to the medial edge of the sternocleidomastoid muscle. (GAN, greater auricular nerve; GON, great occipital nerve; OA, occipital artery; OM, occipitalis muscle; P, parotid gland; PAM, posterior auricular muscle; PAV, posterior auricular vein; SCM, sternocleidomastoid muscle)

SCM

GON

OA

P PAM PAV

GAN SCM

OM GON Fig. 18.4 (Step 2) Fascia of the splenius capitis

FSC

muscle.

The splenius capitis attaches to the skull just below the sternocleidomastoid and passes medially to the nuchal ligament. The muscle is seen in the gap between the sternocleidomastoid and the trapezius. (FSC, fascia of splenius capitis; GAN, greater auricular nerve; GON, great occipital nerve; OA, occipital artery; OM, occipitalis muscle; P, parotid gland; PAM, posterior auricular muscle; PAV, posterior auricular vein; SCM, sternocleidomastoid muscle)

OA

18 Anatomy for Posterior Skull Base Surgery

GAN

PAV Fig. 18.5 The superficial layer.

OM

The scalp is removed to reveal the most superflcial layer of muscles. The sternocleidomastoid, trapezius, splenius capitis, levator scapulae, occipital belly of occipitofrontalis muscles, greater auricular nerve, parotid gland, occipital artery, greater occipital nerve, occipital vein, and posterior auricular vein are seen. (GAN, greater auricular nerve; GON, great occipital nerve; LS, levator scapulae muscle; OA, occipital artery; OM, occipitalis muscle; PAV, posterior auricular vein; SCM, sternocleidomastoid muscle; SNL, superior nuchal line; SpC, splenius capitis muscle; Trap, trapezius muscle)

SCM

GON

SNL LS

SpC OA

Trap

P MT PAV

Fig. 18.6 The greater auricular nerve. The greater auricular nerve runs obliquely across the sternocleidomastoid muscle. The nerve crosses the anterior margin of the sternocleidomastoid muscle approximately 3 cm below the mastoid tip. This nerve is available should a graft be needed. (GAN, greater auricular nerve; MT, mastoid tip; P, parotid gland; PAV, posterior auricular vein; SCM, sternocleidomastoid muscle)

SCM

SCM

PAV

Fig. 18.7 (Step 3) The occipital artery and the greater occipital nerve.

The occipital artery passes through the fascia at the corner formed by the posterior edge of the sternocleidomastoid muscle and the superior edge of the splenius capitis muscle. The greater occipital nerve emerges from the corner formed by the superior edge of the splenius capitis muscle, the anterior edge of the trapezius muscle, and the posterior edge of the semispinalis capitis muscle. (GON, great occipital nerve; OA, occipital artery; OM, occipitalis muscle; PAV, posterior auricular vein; SCM, sternocleidomastoid muscle; SpC, splenius capitis muscle)

OM

GO OA

GA

N

SpC

N

375

376

V Posterior Skull Base

P GA

Sq

SCM PMS

Fig. 18.8 The sternocleidomastoid, trapezius,

splenius capitis, levator scapulae, and semispinalis capitis muscles.

Raising the occipitalis muscle we see the asterion and the junction of the squamosal suture with the parietomastoid suture. (GAN, greater auricular nerve; GON, great occipital nerve; Lam, lambdoid suture; LS, levator scapulae muscle; OA, occipital artery; P, parotid gland; PMS, parietomastoid suture; SCM, sternocleidomastoid muscle; SNL, superior nuchal line; SpC, splenius capitis muscle; Sq, squamosal suture; Trap, trapezius muscle)

SNL

N

LS SpC

Lam

GON

Trap

OA

P XI

SCM Fig. 18.9 The accessory nerve. The accessory nerve runs through the two bellies of sternocleidomastoid muscle. (P, parotid gland; SCM, sternocleidomastoid muscle; XI, accessory nerve)

P

SpC

LS

Fig. 18.10 The splenius capitis muscle. The splenius capitis muscle runs under the sternocleidomastoid muscle from the nuchal ligament and upper thoracic spinous processes to an attachment just below the sternocleidomastoid muscle. (LS, levator scapulae muscle; P, parotid gland; SpC, splenius capitis muscle; Trap, trapezius muscle)

Trap

18 Anatomy for Posterior Skull Base Surgery

P DM IJV

XI LS

SpC Fig. 18.11 Removing the sternocleidomastoid

muscle.

After the sternocleidomastoid muscle is removed, the splenius capitis muscle is seen. (DM, digastric muscle; IJV, internal jugular vein; LS, levator scapulae muscle; P, parotid gland; SpC, splenius capitis muscle; Trap, trapezius muscle; XI, accessory nerve)

Trap

P DM IJV

XI Fig. 18.12 Anatomy of the high cervical muscles.

SpC

The semispinalis capitis originates from the transverse processes of the lower cervical and upper thoracic spine and inserts medially between the upper and lower nuchal lines. (DM, digastric muscle; IJV, internal jugular vein; LS, levator scapulae muscle; P, parotid gland; SpC, splenius capitis muscle; XI, accessory nerve)

LS

P DM IJV XI LS Fig. 18.13 The styloid diaphragm. The occipital artery and veins runs within the fatty tissue and connective tissue underneath the thick fascia known as the styloid diaphragm. (DM, digastric muscle; GON, great occipital nerve; IJV, internal jugular vein; LS, levator scapulae muscle; OA, occipital artery; P, parotid gland; Trap, trapezius muscle; XI, accessory nerve)

OA

GON Trap

377

378

V Posterior Skull Base

P DM IJV LgC XI Fig. 18.14 Removing the splenius capitis muscle. Removing the splenius capitis muscle reveals the longissimus capitis muscle, occipital artery, semispinalis capitis muscle, and posterior belly of the digastric muscle. In this case the occipital artery passes over the longissimus capitis muscle. In other cases the artery crosses under this muscle. (DM, digastric muscle; GON, great occipital nerve; IJV, internal jugular vein; LgC, longissimus capitis muscle; LS, levator scapulae muscle; OA, occipital artery; P, parotid gland; SsC, semispinalis capitis muscle; Trap, trapezius muscle; XI, accessory nerve)

LS

OA

GON

SsC

Trap

LgC

OA

LS

SsC

Fig. 18.15 Another variation of the course of the occipital artery. In this case the occipital artery passes under the longissimus capitis muscle. (LgC, longissimus capitis muscle; LS, levator scapulae muscle; OA, occipital artery; SsC, semispinalis capitis muscle)

P

DM IJV

LgC LS Fig. 18.16 The longissimus capitis muscle. The longissimus capitis muscle runs from the transverse processes of the lower cervical and upper thoracic vertebrae to insert under the mastoid process. (DM, digastric muscle; IJV, internal jugular vein; LgC, longissimus capitis muscle; LS, levator scapulae muscle; P, parotid gland; SsC, semispinalis capitis muscle; Trap, trapezius muscle)

SsC

Trap

18 Anatomy for Posterior Skull Base Surgery

P DM IJV

LS

Fig. 18.17 The styloid diaphragm.

SsC

The styloid diaphragm continues forward under the longissimus capitis muscle. The styloid diaphragm covers the deep layer of the posterior neck muscles. (DM, digastric muscle; IJV, internal jugular vein; LS, levator scapulae muscle; P, parotid gland; SsC, semispinalis capitis muscle; Trap, trapezius muscle)

Trap

P DM IJV

RCL OCSM

OCIM LS

Fig. 18.18 (Step 4) Obliquus superior muscle. The obliquus superior muscle originates lateral to the semispinalis capitis muscle between the superior and inferior nuchal lines. It inserts into the upper surface of the transverse process of C1. (DM, digastric muscle; IJV, internal jugular vein; LS, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; P, parotid gland; RCL, rectus capitis lateralis muscle; SsC, semispinalis capitis muscle; Trap, trapezius muscle)

SsC

p Tra

P DM IJV

RCL OCIM OCSM Fig. 18.19 The obliquus superior, the obliquus inferior, and the rectus capitis major muscles. (DM, digastric muscle; IJV, internal jugular vein; LS, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; P, parotid gland; RCL, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; Trap, trapezius muscle)

RCMjM

LS

p Tra

379

V Posterior Skull Base

TP

OC

SOT

RCM j

The suboccipital triangle is formed by the obliquus capitis superior, obliquus capitis inferior, and rectus capitis posterior major. (LS, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCL, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; SOT, suboccipital triangle; TP, transverse process of the C1 [atlas])

TP

LS

M

IJV

XI

VA C1

SM

RCL

IM

Fig. 18.20 The suboccipital triangle.

OC

SM

RCL

OC

OC

380

IM

LS

Fig. 18.21 (Step 5) Horizontal V3 portion of the vertebral artery in the suboccipital triangle. The horizontal segment of the vertebral artery lies in the suboccipital triangle. The rich venous plexus that accompanies this artery has been removed. (C1, C1 nerve; IJV, internal jugular vein; LS, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PA, posterior arch of the C1 [atlas]; RCL, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; TP, transverse process of the C1 [atlas]; VA, vertebral artery; XI, accessory nerve)

RCM

PA

jM

LS

OCSM C1 VA

OCIM

Fig. 18.22 Magnified view of Fig. 18.21. The horizontal segment of the vertebral artery is well seen. The C1 nerve emerges from between the vertebral artery and the posterior arch of the C1 (see Fig. 18.28). (C1, C1 nerve; LS, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; PA, posterior arch of the C1 atlas); RCMjM, rectus capitis major muscle; VA, vertebral artery)

RC

M

jM

PA

18 Anatomy for Posterior Skull Base Surgery

XI

RCL

Fig. 18.23 Muscle attachments to the transverse

TP

LS

OCSM

process.

The rectus capitis lateralis, the obliquus superior, the obliquus inferior, the levator scapulae, and the scalenus medius are attached to the transverse process of C1. The levator scapulae covers the attachment of the splenius cervicalis. (LS, levator scapulae muscle; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; RCL, rectus capitis lateralis muscle; TP, transverse process of the C1 [atlas]; VA, vertebral artery; XI, accessory nerve)

VA

OCIM

P DM

MT RCL

OCSM

IJV

TP

OCIM

VA

Fig. 18.24 Demonstrating the anatomy of the

deep layer of occipital muscles.

LS

PA

(DM, digastric muscle; IJV, internal jugular vein; LS, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; P, parotid gland; PA, posterior arch of the C1 [atlas]; RCL, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

RCM

jM

P DM IJV

MT TP

Sq

SM OC

As Lam

OMS

VA

IM

The gross anatomy of retroauricular and high cervical region is well understood. (As, asterion; DM, digastric muscle; IJV, internal jugular vein; Lam, lambdoid suture; LS, levator scapulae muscle; MT, mastoid tip; OCIM, obliquus capitis inferior muscle; OCSM, obliquus capitis superior muscle; OMS, occipitomastoid suture; P, parotid gland; PMS, parietomastoid suture; RCL, rectus capitis lateralis muscle; RCMjM, rectus capitis major muscle; Sq, squamosal suture; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

PMS

OC

Fig. 18.25 Less magnified view of Fig. 18.24.

RCL

RC

Mj

M

LS

381

382

V Posterior Skull Base

IJV

JB SS

F

JT HC

Fig. 18.26 Schema of the lateral craniocervical

junction.

(C1, C1 nerve; C1C, C1 condyle; C2, C2 nerve; F, facet; HC, hypoglossal canal; IJV, internal jugular vein; JB, jugular bulb; JG, Jgroove for the vertebral artery; JT, jugular tubercle; OC, occipital condyle; PA, posterior arch of the C1 [atlas]; SS, sigmoid sinus; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

TP

VA

C2 C1

OC

C1C

JG PA IJV

JB SS VA

C2 Fig. 18.27 The vertebral artery and the C2 nerve.

PA

The posterior wall of the transverse foramen of the atlas is removed to expose the vertebral artery. (C2, C2 nerve; IJV, internal jugular vein; JB, jugular bulb; PA, posterior arch of the C1 [atlas]; SS, sigmoid sinus; VA, vertebral artery)

VA C1 Fig. 18.28 Variation of the J-groove of the atlas. The horizontal V3 portion of the vertebral artery usually travels over a shallow notch in the superior border of the posterior lamina of the atlas, often referred to as the J-groove. Two variations of the J-groove are a bony canal formation (this Figure) and a flbrous canal formation (Fig. 18.29). (C1, C1 nerve; PA, posterior arch of the C1 [atlas]; VA, vertebral artery)

PA

18 Anatomy for Posterior Skull Base Surgery

VA

OCIM

Fig. 18.29 Variation of the J-groove of the atlas. The vertebral artery is tethered to the J-groove by the posterior atlanto-occipital membrane, which can vary in its thickness. Bone spurs, ponticles, can arise from the edges of the J-groove and on occasion can completely encircle the vertebral artery. In addition, the J-groove is nearly flat in 25% of cases. (OCIM, obliquus capitis inferior muscle; PA, posterior arch of the C1 [atlas]; VA, vertebral artery)

PA

IJV

VII C7 IX

XI

JB VA

Fig. 18.30 Overview of the anatomy of the

SS

posterior skull base following total petrosectomy. (C7, C7 portion of the internal cartoid artery; ICA, internal carotid artery; IJV, internal jugular vein; IX, glossopharyngeal nerve; JB, jugular bulb; PA, posterior arch of the C1 [atlas]; SS, sigmoid sinus; VA, vertebral artery; VII, facial nerve; XI, accessory nerve; XII, hypoglossal nerve)

PA

TP VA PA C2 Fig. 18.31 Overview of the posterior skull base anatomy after condylectomy. (C2, C2 nerve; PA, posterior arch of the C1 [atlas]; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

ICA XII

383

384

V Posterior Skull Base

TP VA OC

C1C C2 JG

Fig. 18.32 Vertebral artery at the craniocervical junction and C1-C2 junction. (C1C, C1 condyle; C2, C2 nerve; JG, J-groove for the vertebral artery; OC, occipital condyle; PA, posterior arch of the C1 [atlas]; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

PA

HC

C1

VA

Fig. 18.33 Opening the transverse foramen of the

atlas.

(C1, C1 nerve; HC, hypoglossal canal; VA, vertebral artery)

HC C1

Fig. 18.34 Posterior translocation of the vertebral

artery.

(C1, C1 nerve; HC, hypoglossal canal; VA, vertebral artery)

VA

19

Transcondylar Transtubercular Approach

The concepts and surgical trajectories of the extreme lateral infrajugular transcondylar-transtubercular exposure (ELITE) and the transjugular approach are totally different. ELITE is a dorsolateral approach to the jugular tubercle that requires an anterior refiection of the posterior neck muscles. The surgical approach is from posterior to anterior exposing the condyle dorsally. On the other hand, the posterior infratemporal fossa transjugular approach is an anterolateral approach for the jugular bulb and infrajugular region that requires a posterior refiection of the posterior neck muscles. The surgical approach is from anterior to the transverse process of the C1 with the surgeon exposing the high cervical region between the C1 and the pharynx. The ELITE approach is useful for vertebral basilar artery junction aneurysms, low clival and ventral foramen magnum lesions, and intradural jugular foramen tumors.

Key Steps Position: Lateral Step 1. Skin incision: lazy "S" shaped (Fig. 19.1) Step 2. Muscular dissection (Fig. 19.4) Step 3. Suboccipital craniectomy (Fig. 19.9) Step 4. Exposure of horizontal portion of vertebral artery (Fig. 19.16) Step 5. Identiflcation of occipital condyle (Fig. 19.18) Step 6. Condylectomy exposing hypoglossal canal (Fig. 19.20) Step 7. Parietal resection of the jugular tubercle (Fig. 19.22) Step 8. Opening of the dura (Fig. 19.25)

Illustrated Steps with Commentary

MT

Fig. 19.1 (Step 1) Positioning and skin incision. The head is placed in a lateral position and the mastoid tip and posterior border of the body of the mastoid are marked. The skin is cut in a lazy "S" shape with the top of the "S" just below the asterion. The center of the opening is the occipital condyle. The condyle lies medial and inferior to the mastoid tip. (As, asterion; MT, mastoid tip)

As

386

V Posterior Skull Base

Fig. 19.2 Exposing the fascia. The fascia on the sternocleidomastoid muscle is exposed.

SCM

SCM Fig. 19.3 Harvesting a fascial graft. An oval of fascia is harvested to achieve a watertight dural closure at the end of the case. (SCM, sternocleidomastoid muscle)

SCM

Fig. 19.4 (Step 2) Exposure of sternocleidomastoid muscle.

The sternocleidomastoid muscle can be seen after the fascia is removed. At the time of surgery the posterior neck muscles on the occipital bone should be cut as a mass using the monopolar coagulator along to the black line drawn in the flgure. In this dissection, each muscle will be exposed to demonstrate the layers of the posterior neck muscles. (SCM, sternocleidomastoid muscle)

19 Transcondylar Transtubercular Approach

SCM

SpCM Fig. 19.5 Exposing the splenius capitis muscle. ELITE is a dorsolateral approach. All the posterior neck muscles on the occipital bone should be reflected anteriorly. After the sternocleidomastoid muscle is cut and reflected anteriorly, the splenius capitis muscle can be seen. (SCM, sternocleidomastoid muscle; SpCM, splenius capitis muscle)

OA

C Lg

M

Fig. 19.6 Exposing the longissimus capitis muscle and the styloid diaphragm.

Anterior reflection of the splenius capitis muscle exposes the longissimus capitis muscle inferiorly. A thick layer of fascia known as the styloid diaphragm will be seen below the splenius muscle. Beneath the fascia the surgeon will nd the occipital artery and several veins embedded in a thin layer of fat. (LgCM, longissimus capitis muscle; OA, occipital artery)

Fig. 19.7 Exposing the semispinalis capitis muscle.

Anterior reflection of the longissimus capitis muscle reveals the styloid diaphragm. The styloid diaphragm covers the middle layer of the posterior neck muscles. The deep muscular layer that consists of the obliquus capitis superior, obliquus capitis inferior, rectus capitis major, and rectus capitis minor muscles lies medial to this styloid diaphragm. (SsCM, semispinalis capitis muscle)

SsCM

387

388

V Posterior Skull Base

Fig. 19.8 Exposing the obliquus capitis superior

OC

SM

muscle.

After posterior reflection of the semispinalis capitis muscle and removal of the styloid diaphragm the obliquus capitis superior muscle that originates between the superior and inferior nuchal lines can be seen. The vertebral artery lies below the inferior border of this muscle, so the surgeon should be careful if a bovie cautery is being used to cut the superior oblique muscle. (OCSM, obliquus capitis superior muscle)

DG

Fig. 19.9 (Step 3) Exposure of occipital bone. After anterior reflection of the obliquus capitis superior muscle the occipital bone is exposed. A lateral suboccipital craniotomy with partial mastoidectomy is performed. (DG, digastric groove)

SS A Fig. 19.10 Identifying the inferior retrosigmoid

point.

To avoid the injury of the vertebral artery the inferior retrosigmoid point (arrow, A) the most caudal (inferior) and posterior edge of the sigmoid sinus should be identi ed. This is the rst landmark in identifying the vertebral artery. (A, inferior retrosigmoid point; SS, sigmoid sinus)

19 Transcondylar Transtubercular Approach

SS

CEV

A

Fig. 19.11 Occluding the condylar emissary vein. The posterior condylar emissary vein is found posterior to the occipital condyle. This vein connects the vertebral venous plexus with the sigmoid sinus passing through a foramen in the condyle. Bleeding is controlled either by cauterizing and dividing this vein or by packing the foramen with oxidized cellulose and bone wax. (A, inferior retrosigmoid point; CEV, condylar emissary vein; SS, sigmoid sinus)

SS A

Fig. 19.12 Opening the foramen magnum. The foramen magnum is opened posterior to the occipital condyle. The foramen magnum is skeletonized back to the posterior point (B; the point that marks the most posterior extent of the foramen magnum). (A, inferior retrosigmoid point; B, foramen magnum posterior point; SS, sigmoid sinus)

B

OC

Fig. 19.13 Relationship between the occipital

condyle and posterior condylar emissary vein.

The posterior condylar emissary vein that drains into the inferior point of the sigmoid sinus originates in the condylar fossa and passes through the condylar canal. Although it is running in the wrong direction, the condylar canal may be mistaken for the hypoglossal canal. (A, inferior retrosigmoid point; B, foramen magnum posterior point; CEV, condylar emissary vein; OC, occipital condyle)

A CEV B

389

390

V Posterior Skull Base

A

Fig. 19.14 Identifying the posterior notch of C1. When the vertebral artery is difflcult to flnd, it can be localized by the following measurements. The posterior point of the foramen magnum (B) lies approximately 30 mm dorsal to the inferior retrosigmoid point (A). The posterior tubercle of C1 (C) lies 10 mm inferior to the posterior point of the foramen magnum (B). The J-groove lies lateral to the posterior tubercle. (A, inferior retrosigmoid point; B, foramen magnum posterior point; C, C1 posterior point)

B C

A D

JG Fig. 19.15 Identifying the J-groove of C1. The surgeon follows the posterior arch of C1 laterally until a depression (J-groove) is found on its superior surface. This groove (point D) marks the location of the vertebral artery. Care should be taken not to damage the venous plexus surrounding the vertebral artery. (A, inferior retrosigmoid point; B, foramen magnum posterior point; C, C1 posterior point; D, J-groove of the C1; JG, J-groove for the vertebral artery; PA, posterior arch of the C1 [atlas])

PA B

C

SS

VA

C1C

Fig. 19.16 (Step 4) Identification of horizontal (V3) segment of vertebral artery. The vertebral artery is identifled at the J-groove of C1 surrounded by the paravertebral venous plexus. Clinically severe venous bleeding can result from injury of this venous sleeve. Absorbable hemostatic agent packing and bipolar cautery are effective for stopping the bleeding. (C1C, C1 condyle; OC, occipital condyle; PA, posterior arch of the C1 [atlas]; SS, sigmoid sinus; VA, vertebral artery)

PA

OC

19 Transcondylar Transtubercular Approach

SS

OC

C1C

A

VA

Fig. 19.17 Overview of landmarks used to identify

D

the vertebral artery and occipital and C1 condyle.

The distances between A and B is 30.5 ± 5.6 mm (21.5, 40.5 mm); B and C, 10.4 ± 2.3 mm (6.0, 14.0 mm); C and D, 19.1 ± 3.8 mm (12.5, 24.5 mm). (A, inferior retrosigmoid point; B, foramen magnum posterior point; C, C1 posterior point; C1C, C1 condyle; D, J-groove of the C1; OC, occipital condyle; PA, posterior arch of the C1 [atlas]; SS, sigmoid sinus; VA, vertebral artery)

PA C

B

SS OC C1C Fig. 19.18 (Step 5) Partial resection of occipital

VA

condyle

The microscope should be tilted laterally to remove the posterior medial corner of the occipital condyle. The occipital C1 joint is left intact and the occipital condyle superior to the joint is removed. (C1C, C1 condyle; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery)

JT

VA Fig. 19.19 The venous plexus in the hypoglossal

canal.

The hypoglossal canal runs above the occipital C1 joint. A thick venous plexus covers the dural sleeve that lies in the bony hypoglossal canal. (HEV, hypoglossal emissary vein; JT, jugular tubercle; VA, vertebral artery)

HEV

391

392

V Posterior Skull Base

SS JT OC Fig. 19.20 (Step 6) Exposure of hypoglossal canal After drilling the cortical bone of the occipital condyle, the cancellous bone is encountered. As the cancellous bone is removed a blue shadow running almost parallel to the joint is encountered. This bony canal inside the cancellous bone is the bony hypoglossal canal. The hypoglossal nerve is covered by the dura and the dura is covered by a venous plexus. This venous plexus around the hypoglossal dural sleeve gives a blue hue seen through the thinned cortical bone. The posterior condylar canal harboring the posterior condylar vein should not be confused with the condylar canal. (HC, hypoglossal canal; JT, jugular tubercle; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery)

HC

VA

SS

JT HC

Fig. 19.21 Locating the jugular tubercle The jugular tubercle is found above the hypoglossal canal. (HC, hypoglossal canal; JT, jugular tubercle; SS, sigmoid sinus; VA, vertebral artery)

VA

SS JT Fig. 19.22 (Step 7) Drilling of jugular tubercle Removing the jugular tubercle affords the surgeon a more anterior view of the medulla and lower pons. Removing the most anterior potion of the jugular tubercle is difflcult because of the overhanging sigmoid sinus. The tubercle should be carefully removed with a diamond drill cooled by irrigation. Rupture or burning of the superior dura can injure the lower cranial nerves. (JT, jugular tubercle; SS, sigmoid sinus; VA, vertebral artery)

VA

19 Transcondylar Transtubercular Approach

SS HC Fig. 19.23 Completion of drilling of the jugular

VA

tubercle.

drilled JT

The jugular tubercle extends anteriorly for about 15 mm. Complete removal of the jugular tubercle is difflcult, but the more tubercle removed the farther anterior the surgeon will see. (HC, hypoglossal canal; JT, jugular tubercle; SS, sigmoid sinus; VA, vertebral artery)

OC

HC

VA

Fig. 19.24 Final view of the extradural exposure. The relationship between the jugular tubercle and the adjacent structures is demonstrated. (HC, hypoglossal canal; JT, jugular tubercle; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery)

Fig. 19.25 (Step 8) Opening the dura. A semilunar incision is made in the dura. The inferior corner of the incision is flrst opened to reach the lateral medullary cistern. Releasing cerebrospinal uid from this cistern allows the cerebellum to fall away from the dura, which reduces the risk of cerebellar injury.

drilled JT

SS

393

394

V Posterior Skull Base

VII, VIII

IX

XI X Fig. 19.26 Surgical view before removing the jugular tubercle. Figures 19.26 and 19.27 are included to demonstrate the advantage the surgeon gains by flattening the jugular tubercle. (IX, glossopharyngeal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

VII,VIII

XI X Fig. 19.27 Surgical view after removing the jugular tubercle. The obstruction created by the jugular tubercle is not observed. The surgical view is improved for operations that involve the region of the anterior pontomedullary junction. (VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

IX

X VA XI Fig. 19.28 Identifying the spinal accessory nerve, posterior inferior cerebellar, and vertebral arteries. The spinal accessory nerve is usually the rst structure seen in the lateral medullary cistern. Opening the cistern exposes the vertebral artery and the posterior inferior cerebellar artery. (IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; VA, vertebral artery; X, vagus nerve; XI, accessory nerve)

PIC

A

19 Transcondylar Transtubercular Approach

IX

X VA XII

XI Fig. 19.29 Identifying the origin of the posterior inferior cerebellar artery. For operations of the vertebral posterior inferior cerebellar artery junction aneurysm, the origin of posterior inferior cerebellar artery (PICA) must be seen. The hypoglossal nerves are frequently close to the origin of PICA. (IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; VA, vertebral artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

PIC

A

IX

X VA Fig. 19.30 Identifying the lower cranial nerves as they exit the jugular foramen.

XI

The glossopharyngeal, vagus, and accessory nerves can be seen passing toward the jugular foramen. The jugular tubercle, which underlies these nerves, has been removed. (IX, glossopharyngeal nerve; VA, vertebral artery; X, vagus nerve; XI, accessory nerve)

AICA

VIII VI X Fig. 19.31 Identifying the vestibulocochlear and facial nerves and the anterior inferior cerebellar artery. The vestibulocochlear and facial nerves are seen rostral to the lower cranial nerves. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

IX XI

VII

395

396

V Posterior Skull Base

V VIII VI Fig. 19.32 Identifying the abducens nerve.

X

The abducens nerve can be seen medial to the vestibulocochlear, facial, and lower cranial nerves. The entrance of Dorello’s canal is seen to be parallel to the internal auditory canal (IAC). The relationship between Dorello’s canal and the IAC will depend on the position of the patient’s head. When operating on clival tumors it is best to identify the abducens nerve at the brainstem. (IX, glossopharyngeal nerve; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve)

VII

IX

VII, VIII IX

BA

X

AICA Fig. 19.33 Identifying the origin of the anterior inferior cerebellar artery.

XI

The abducens nerve frequently exits from the brainstem close to the origin of the anterior inferior cerebellar artery. (AICA, anterior inferior cerebellar artery; BA, basilar artery; IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

PI

CA

X

VA XI

VA

Fig. 19.34 Identifying the vertebrobasilar

junction.

Removing the jugular tubercle gives the surgeon a direct view of the basilar vertebral artery junction. (AICA, anterior inferior cerebellar artery; BA, basilar artery; IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; VA, vertebral artery; VI, abducens nerve; X, vagus nerve; XI, accessory nerve)

PICA

BA AICA

IX

VI

19 Transcondylar Transtubercular Approach

IX BA

AICA

XI

VA

Fig. 19.35 Identifying the opposite vertebral

X

VA

artery.

Both vertebral and anterior inferior cerebellar arteries and the vertebrobasilar junction can be seen once the jugular tubercle has been removed. (AICA, anterior inferior cerebellar artery; BA, basilar artery; IX, glossopharyngeal nerve; VA, vertebral artery; X, vagus nerve; XI, accessory nerve)

TP OC

C2 Fig. 19.36 Expanding the view by additional bony

C1

VA

C1

VA

C1C

N

resection.

The soft tissue extracranial dissection is extended to expose the transverse process of the atlas. The extracranial vertebral artery and the C2 nerve root are well seen. (C1, C1 [atlas]; C1C, C1 condyle; C2N, C2 nerve; OC, occipital condyle; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

TP

C2 Fig. 19.37 After removing the C2 nerve root. The vertebral artery is freed from the vertebral canal in the axis. (C1, C1 [atlas]; C1C, C1 condyle; C2, C2 [axis]; OC, occipital condyle; TP, transverse process of the C1 [atlas]; VA, vertebral artery)

C1C

OC

397

398

V Posterior Skull Base

TP

SS

HC VA C1

Fig. 19.38 Overview of the craniovertebral

junction.

An anatomical relationship around the craniovertebral junction is well demonstrated. (C1, C1 [atlas]; HC, hypoglossal canal; SS, sigmoid sinus; TP, tranverse process of the C1 [atlas]; VA, vertebral artery)

HC

SS

VA

Fig. 19.39 Opening the transverse foramen of the

atlas.

The vertebral artery is freed from the transverse process of the atlas. This is usually done with a diamond drill. Care is taken to avoid opening the perivertebral veins. (HC, hypoglossal canal; SS, sigmoid sinus; VA, vertebral artery)

HC VA Fig. 19.40 Posterior translocation of the vertebral

artery.

The vertebral artery is flrst inspected for severe atherosclerosis. A brittle artery can be a source of emboli, arterial dissection, or rupture when manipulated. If the artery is pliable, it is translocated out of its foramen in the atlas. (HC, hypoglossal canal; SS, sigmoid sinus; VA, vertebral artery)

SS

19 Transcondylar Transtubercular Approach

HC

C1

SS

Fig. 19.41 Exposing the anterior arch of the atlas including the facets. Once the artery is translocated, the surgeon has an unobstructed view of the lateral mass of C1. (C1, C1 [atlas]; HC, hypoglossal canal; SS, sigmoid sinus)

F

C1C

HC

OC

SS

Fig. 19.42 Drilling the anterior arch and the lateral mass of the atlas. The remainder of the inferior condyle, the occipital-C1 joint, the remainder of the transverse process of C1, and the superior lateral mass of C1 are all removed. (C1C, C1 condyle; F, facet; HC, hypoglossal canal; OC, occipital condyle; SS, sigmoid sinus; VA, vertebral artery)

VA

HC

AA AS

Fig. 19.43 After drilling the anterior arch of the

atlas.

The surgeon now has access to the ipsilateral anterior arch of C1. (AA, anterior arch of the C1 [atlas]; AS, articular surface; HC, hypoglossal canal; SS, sigmoid sinus; VA, vertebral artery)

VA

SS

399

400

V Posterior Skull Base

AA

HC

SS

Den

VA

Fig. 19.44 Exposing the dens. The articulation between the anterior arch of C1 and the dens is exposed. (AA, anterior arch of the C1 [atlas]; Den, dens; HC, hypoglossal canal; SS, sigmoid sinus; VA, vertebral artery)

HC

AA Den

Fig. 19.45 Exposing the articulating surface of the

TL

dens.

The dissector is inserted into the posterior articular surface of the dens. The drill can be used to remove the dens from the lateral approach. (AA, anterior arch of the C1 [atlas]; Den, dens; HC, hypoglossal canal; (TL, transverse ligament; VA, vertebral artery)

VA

AA

HC Den

Fig. 19.46 Exposing the articulating surface of the

dens.

The dissector is inserted into the anterior articular surface of the dens. (AA, anterior arch of the C1 [atlas]; Den, dens; HC, hypoglossal canal; VA, vertebral artery)

VA

19 Transcondylar Transtubercular Approach

HC

AA Den

Fig. 19.47 After removing the transverse part of the cruciform ligament. The transverse part of the cruciform ligament is removed to further expose the dens. (AA, anterior arch of the C1 [atlas]; Den, dens; HC, hypoglossal canal; VA, vertebral artery)

VA

HC SS

Fig. 19.48 Drilling the dens. Removing the dens, removing the transverse and superior longitudinal part of the cruciform ligament, and detaching the apical ligament and the alar ligament expose the anterior surface of the dura at the craniocervical junction. (HC, hypoglossal canal; SS, sigmoid sinus)

401

20

Lateral Suboccipital Approach: Superior, Middle, and Inferior Cerebellopontine Angle Approach

The suboccipital craniotomy has been the “standard” approach to lesions within the posterior fossa. This remains an excellent approach to lesions of the cerebellum, posterior and lateral brainstem, and medial face of the petrous bone. In this chapter, we outline a refinement of the retrosigmoid approach. The retrosigmoid is divided into three zones each approached in a slightly different fashion. This refinement makes the surgery less invasive. These approaches can be employed to treat trigeminal neuralgia, hemifacial spasm, trigeminal schwannomas confined to the posterior fossa, vestibular schwannomas, intradural jugular foramen schwannomas and cerebellopontine angle meningiomas.

20.1 Superior Cerebellopontine Angle Approach for Trigeminal Neuralgia and Paratrigeminal Lesions Key Steps Step 1. Skin incision (Fig. 20.1) Step 2. Craniectomy (Fig. 20.7) Step 3. Opening of dura (Fig. 20.8) Step 4. Identification of trochlear nerve (Fig. 20.11) Step 5. Dissection of petrosal vein (Fig. 20.12) Step 6. Dissection around trigeminal nerve root (Fig. 20.15) Step 7. Dislocation of offending artery (Fig. 20.17)

Illustrated Steps with Commentary

MT

Fig. 20.1 (Step 1) Skin incision. An "S" shaped incision is made over the depression that lies behind the body of the mastoid. This depression in the bone is often visible and almost always palpable. The body of the mastoid and the projected inferior edge of the transverse sinus are mapped out on this photo as a dashed line. (EOP, external occipital protuberance; MT, mastoid tip)

EOP

20.1 Lateral Suboccipital Approach: Superior Cerebellopontine Angle Approach for Trigeminal Neuralgia and Paratrigeminal Lesions

Fig. 20.2 Exposing the fibrous soft tissue under the skin.

The superflcial layer of flbrous tissue is split, leaving a small rim of tissue attached to the skin. This rim of tissue is crucial for anchoring sutures during the skin closure.

Fig. 20.3 Harvesting the fibrous tissue graft. The superflcial layer of flbrous tissue is circumscribed. It will be used to obtain a watertight dural closure at the end of the surgery.

Fig. 20.4 Dissecting the fibrous tissue graft. The tissue is harvested as a contiguous graft with a sharp scalpel.

403

404

V Posterior Skull Base

Fig. 20.5 Cutting the sternocleidomastoid and splenius capitus muscles.

The sternocleidomastoid is incised to expose the splenius capitus muscles.

PMS OMS As Lam

Fig. 20.6 Identifying the sutures. The asterion is a most important landmark. It usually lies over the inferior corner of the lateral and sigmoid sinus junction, although there is some variation. (As, asterion; Lam, lambdoid suture; OMS, occipitomastoid suture; PMS, parietomastoid suture)

SS

LS

Fig. 20.7 (Step 2) Performing a craniectomy. A small craniectomy is made exposing the inferior one-third of the lateral sinus and the posterior one-third of the sigmoid sinus. (LS, lateral sinus; SS, sigmoid sinus)

20.1 Lateral Suboccipital Approach: Superior Cerebellopontine Angle Approach for Trigeminal Neuralgia and Paratrigeminal Lesions

SS

LS Fig. 20.8 (Step 3) Dural incision. An inversed "T" shaped dural incision is made to maximize exposure along the transverse and the sigmoid sinuses. (LS, lateral sinus; SS, sigmoid sinus)

Fig. 20.9 Exposing the cerebellar surface. The dural opening will demonstrate the lateral corner of the cerebellar hemisphere. The supracerebellar cistern is opened and cerebrospinal fluid is patiently drained. Pressing on a tense cerebellum will lead to contusion, hemorrhage, and postoperative brain swelling.

T

Fig. 20.10 Inspecting the tentorial surface for bridging veins. Bridging veins are rarely seen over the lateral portion of the cerebellar hemisphere, but the veins do not have an absolute predetermined pattern. Tearing an unexpected vein will obscure the operative eld with blood and can cause a venous infarction. (T, tentorium)

405

406

V Posterior Skull Base

T SC

IV Fig. 20.11 (Step 4) Exploration of the tentorial surface of the cerebellum. At flrst the surgeon explores the upper surface of the cerebellum to identify the trochlear nerve under the edge of the tentorial incisura. (IV, trochlear nerve; SCA, superior cerebellar artery; T, tentorium)

PV

Fig. 20.12 (Step 5) Identification of the petrosal

veins.

Looking laterally over the corner of the cerebellum, the surgeon should expose the petrosal veins entering the superior petrosal sinus. (PV, petrosal vein)

PV Fig. 20.13 Exposing the petrosal veins. The arachnoid membrane that encases the petrosal veins is cut along the veins to release tension from the veins. An attempt should be made to preserve the veins; however, if the veins obstruct the surgeon’s view, a portion of the veins can usually be sacriflced. The entrance of the veins into the superior petrosal sinus can be reinforced with absorbable hemostatic agent and flbrin glue in cases where the veins are under some tension or when a small amount of hemorrhage occurs from the venous– sinus junction. (PV, petrosal vein)

A

20.1 Lateral Suboccipital Approach: Superior Cerebellopontine Angle Approach for Trigeminal Neuralgia and Paratrigeminal Lesions

PV V IV

SCA

Fig. 20.14 Identifying the distal superior

cerebellar artery.

Loops of the superior cerebellar artery are seen to compress the trigeminal nerve. Generally the superior cerebellar artery has bifurcated before reaching the trigeminal nerve. (IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)

PV V IV

SCA

Fig. 20.15 (Step 6) Inspection of the trigeminal

root.

The superior petrosal vein is fed by a confluence of veins draining the petrosal and lateral tentorial surfaces of the cerebellum. Once freed of arachnoid, these veins usually become mobile enough to be retracted out of the surgeon’s line of sight. (IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)

PV SCA Fig. 20.16 Inspecting the trigeminal nerve. The petrosal veins can usually be simply pushed aside when approaching the trigeminal nerve. If the petrosal vein is tethered anteriorly by a trigeminal vein, the trigeminal vein can be coagulated and cut. The offending artery found compressing the trigeminal nerve, a branch of the superior cerebellar artery, is translocated toward the tentorium to separate it from the nerve. Note the difference between Figs. 20.16 and 20.17. (IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)

IV

V

407

408

V Posterior Skull Base

PV V

SCA

Fig. 20.17 (Step 7) Translocation of superior cerebellar artery. A translocation of the superior cerebellar artery has been performed. The artery is displaced toward the tentorium. (PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve)

PV V

Fig. 20.18 Supporting the superior cerebellar artery with Tefion bers and brin glue. In surgery, the superior cerebellar artery is translocated toward the tentorium and is held in place with Teflon bers and brin glue. In this photo, oxidized cellulose was used to hold the artery in place. (PV, petrosal vein; V, trigeminal nerve)

20.2 Lateral Suboccipital Approach: Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors

20.2 Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors Key Steps Step 1. Skin Incision (Fig. 20.19) Step 2. Craniotomy (Fig. 20.25) Step 3. Opening of dura (Fig. 20.30) Step 4. Identification of cranial nerves (Fig. 20.34) Step 5. Meatal drilling (Fig. 20.42) Step 6. Exposure of meatal segment of facial nerve (Fig. 20.51)

Illustrated Steps with Commentary

MT

Fig. 20.19 (Step 1) Skin incision. The seventh and eighth cranial nerves are approached through a craniotomy centered on the mid-sigmoid sinus. Traditionally a "C" shaped incision is made in the skin, although an "S" shaped incision centered 0.5 cm behind the posterior border of the lower body of the mastoid will work. Because this exposure is most often made for tumors, the craniotomy will be larger. (EOP, external occipital protuberance; MT, mastoid tip)

Fig. 20.20 Skin fiap. The skin flap is raised along with a thin layer of brous tissue. Most of the brous tissue is left attached to the suboccipital muscles.

EOP

409

410

V Posterior Skull Base

Fig. 20.21 Dural graft. The remainder of the flbrous tissue is raised as a dural graft. This graft may include some of the covering of the sternocleidomastoid muscle.

PAM SCM

Fig. 20.22 Fibrous dural graft. The flbrous tissue graft allows the dura to be closed in a watertight fashion with autologous tissue at the end of the case. (PAM, posterior auricular muscle; SCM, sternocleidomastoid muscle)

MEV

Fig. 20.23 Raising the muscle fiap. The muscle is raised as a ap. The initial cut through the splenius capitus and sternocleidomastoid reveals the deep fascia overlying the occipital artery. That artery is ligated and then the superior oblique muscle is cut. The full thickness muscle ap is re ected medially. (DG, digastric muscle; MEV, mastoid emissary vein)

DG

20.2 Lateral Suboccipital Approach: Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors

PMS As Fig. 20.24 Planning the craniotomy.

MEV

DG

OMS

Lam

The asterion usually is close to the inferior junction of the transverse and sigmoid sinuses. A prominent emissary vein is usually found 5 mm posterior to the sigmoid sinus. Although opening the bone just above the medial edge of the sigmoid sinus makes anatomical sense, adhesions between a thin-walled sinus and the bone makes this a dangerous practice. (As, asterion; DG, digastric muscle; Lam, lambdoid suture; MEV, mastoid emissary vein; OMS, occipitomastoid suture; PMS, parietomastoid suture)

LS

Fig. 20.25 (Step 2) Performing the craniotomy. The initial perforation of the skull is made through the asterion. It is enlarged until the transverse sinus is localized. (LS, lateral sinus)

SS

LS Fig. 20.26 Making a retrosigmoid groove. A groove is drilled in the bone adjacent to the sigmoid sinus. Especially in older patients, this groove should not be made over the medial edge of the sigmoid sinus, as the sinus may be torn when the bone flap is lifted. An incision just anterior to the exit of the emissary vein will put the surgeon a few millimeters behind the sigmoid sinus. The bone over the posterior edge of the sigmoid sinus can be removed with an extra coarse diamond drill. (LS, lateral sinus; SS, sigmoid sinus)

411

412

V Posterior Skull Base

SS

LS

Fig. 20.27 Making a suboccipital groove. Because it is difflcult to use a craniotomy through the inferior occipital bone, it is easier to extend the retrosigmoid groove along the inferior limb of the craniotomy. (LS, lateral sinus; SS, sigmoid sinus)

SS LS

Fig. 20.28 Performing the craniotomy. If the bone is not absolutely stuck to the dura, the craniotomy can be completed with a craniotome. (LS, lateral sinus; SS, sigmoid sinus)

SS

LS

Fig. 20.29 Exposing the dura. At the end of the craniotomy, additional bone may be removed to expose the inferior edge of the transverse sinus and the posterior edge of the sigmoid sinus. The anterior inferior edge of the craniotomy may be extended to give the surgeon better access to the medullary cistern. (LS, lateral sinus; SS, sigmoid sinus)

20.2 Lateral Suboccipital Approach: Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors

SS

LS

Fig. 20.30 (Step 3) Opening the dura. If a lumbar drain has not been placed, an opening is made in the anterior inferior edge of the dura so that the medullary cistern can be opened. This affords a release of cerebrospinal fluid and lowers the pressure on the cerebellum. The dura is opened in a "C" shaped fashion. (LS, lateral sinus; SS, sigmoid sinus)

Fig. 20.31 Opening the dura. Dural tenting sutures are placed adjacent to the sigmoid sinus to maximize the lateral exposure. If the dura is kept moist, it will contract less and make for an easier dural closure.

Fig. 20.32 Retraction of the petrosal surface of the cerebellum. Cottonoid paddies or other protective pads are placed in a “V” over the petrosal surface of the cerebellum.

413

414

V Posterior Skull Base

Fig. 20.33 Exploring the petrosal surface of the temporal bone.

If the surgeon is trying to preserve hearing, the cerebellar hemisphere is not retracted straight laterally as it is in this photo. In such cases the superior petrosal surface is flrst exposed.

VII, VIII V PV

AICA IX X

Fig. 20.34 (Step 4) Exploring the seventh and

JT

eighth nerve complexes.

A large branch of anterior inferior cerebellar artery is seen below the seventh and eighth nerve complex. The seventh nerve originates ventral to the eighth nerve but then rotates rostrally to assume its position anterior to the superior vestibular nerve. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; JT, jugular tubercle; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve)

VII, VIII V PV

AICA

Fig. 20.35 Exploring the petrosal surface of the temporal bone. The operculum of the temporal bone is seen between the trigeminal and seven-eight complex. The ventral portion of this bone obstructs the surgeon’s view of the trigeminal nerve entering Meckel's cave. (AICA, anterior inferior cerebellar artery; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve)

JT

20.2 Lateral Suboccipital Approach: Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors

V PV

AICA

SC

A

IV

Fig. 20.36 Upper extent of the exposure. The superior cerebellar surface, the petrosal veins, and the superior cerebellar arteries are all seen by tilting the microscope upward. (AICA, anterior inferior cerebellar artery; IV, trochlear nerve; PV, petrosal vein; SCA, superior cerebellar artery; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve)

JT

VIII

XI IX

X

Fig. 20.37 Finding the origin of the eighth nerve. The choroid plexus is a good landmark for the foramen of Luschka. The approximate location of this foramen can also be found by following the ninth nerve to its exit from the brainstem. Because the dorsal cochlear nucleus lies in the floor of the foramen of Luschka, the eighth nerve is seen to exit the brainstem just anterior to the foramen. (CP, choroid plexus; IX, glossopharyngeal nerve; JT, jugular tubercle; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

CP

XI IX

X XII

Fig. 20.38 The lower end of the exposure. Tilting the microscope inferiorly, the spinal accessory nerve is seen at the lower edge of the lower cranial nerve bundle. The hypoglossal nerve is seen to exit below the jugular tubercle close to the posterior inferior cerebellar artery. (CP, choroid plexus; IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

CP

VII, VIII

PICA

415

416

V Posterior Skull Base

IX X

XI

XII

PICA Fig. 20.39 The inferior exposure. The posterior inferior cerebellar artery is seen passing below the three fascicles of the hypoglossal nerve. (IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve)

V PV

VII, VIII IX

AICA JT

Fig. 20.40 Demonstrating the cranial nerves

exposed by this approach.

An anatomical relationship is well demonstrated in this photo. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; JT, jugular tubercle; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

Fo

VII, VIII Fig. 20.41 Identifying the fovea created by the endolymphatic sac. A bony depression (arrow) created by the endolymphatic sac is a good landmark for the lateral extent of the meatal drilling. (Fo, fovea; VII, facial nerve; VIII, cochlear nerve)

X

XI

20.2 Lateral Suboccipital Approach: Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors

Fig. 20.42 (Step 5) Preparing to open the internal auditory canal. Cottonoids, oxidized cellulose, and even Gelfoam (Pflzer Inc., NY, NY) can become caught in the surgeon’s drill. It is safest to protect the brain with a attened strip of bone wax.

Fig. 20.43 Cerebellar protection. The bone wax plate is placed under the retractor blade.

Fig. 20.44 Raising a dural fiap. A dural ap is turned with its apex at the fovea of the temporal bone. This is the approximate apex of the endolymphatic sac and marks the position of the posterior semicircular canal.

417

418

V Posterior Skull Base

Fig. 20.45 Preparing to open the internal auditory

canal.

The dural flap is held under the bone wax to protect the seventh and eighth cranial nerves.

Fig. 20.46 Opening the internal auditory canal. Drilling begins with a 4 mm coarse diamond drill at the porus acusticus. In hearing preserving operations, the depth at which the vestibule lies can be determined from preoperative imaging. The surgeon must be very cautious at depths greater than 6 mm. With the patient in the lateral position, the vestibule lies supercial to the internal auditory canal.

IAC

Fig. 20.47 Opening the internal auditory canal. The bone is rst removed at the porus acusticus. The internal auditory canal is gradually exposed laterally. (IAC, internal auditory canal)

20.2 Lateral Suboccipital Approach: Middle Cerebellopontine Angle Approach for Acoustic Nerve and Tumors

ML Fig. 20.48 Opening the internal auditory canal. The opening should be widened to expose at least 180 degrees of the porus acusticus. The shoulders of the opening are removed using progressively smaller sizes of diamond bits. Care must be taken when drilling caudally of the eighth nerve and rostrally of the seventh cranial nerve. Air cells may be encountered and should be fllled with bone wax. The dome of the jugular bulb may be encountered caudally. The dome can be shrunk using a bipolar cautery. (ML, meatal loop of the anterior inferior cerebellar artery)

ML Fig. 20.49 Identifying the meatal loop of the anterior inferior cerebellar artery.

VII, VIII

V

CA

PV

IX X

AI

The posterior dura of the internal auditory canal is opened using a sharp scissors or hook knife. This dura is usually very thin. A loop of vessel is seen branching from anterior inferior cerebellar artery and entering the internal auditory canal. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; ML, meatal loop of the anterior inferior cerebellar artery; PV, petrosal vein; V, trigeminal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve; XI, accessory nerve)

SV IVN IAA ML Fig. 20.50 Identifying the superior and inferior vestibular nerves. Further opening of the dura reveals the internal auditory artery. The superior and inferior vestibular nerves are seen from this posterior approach. (IAA, internal auditory artery; IVN, inferior vestibular nerve; ML, meatal loop of the anterior inferior cerebellar artery; SV, superior vestibular nerve)

XI

419

420

V Posterior Skull Base

M-VII

IAA

Fig. 20.51 (Step 6) Removing the superior and

inferior vestibular nerves and the cochlear nerve. The internal auditory artery can be seen branching off of a loop of the anterior inferior cerebellar artery after removing the superior and inferior vestibular nerves and the cochlear nerve. In hearing preservation surgery for vestibular schwannomas, preservation of the cochlear nerve and the internal auditory artery is essential. The meatal segment of the facial nerve is demonstrated. (IAA, internal auditory artery; ML, meatal loop of the anterior inferior cerebellar artery; M-VII, meatal segment of the facial nerve)

ML

IAA

M-VII

ML V Fig. 20.52 Final view of this approach after removing the superior and inferior vestibular nerves and the cochlear nerve. The meatal segment of the facial nerve and the internal auditory artery are preserved. (AICA, anterior inferior cerebellar artery; IAA, internal auditory artery; IX, glossopharyngeal nerve; JT, jugular tubercle; ML, meatal loop of the anterior inferior cerebellar artery; M-VII, meatal segment of the facial nerve; PV, petrosal vein; V, trigeminal nerve; X, vagus nerve; XI, accessory nerve)

PV

A

ICA

IX X JT

XI

20.3 Lateral Suboccipital Approach: Inferior Cerebellopontine Angle Approach for Hemifacial Spasm and Jugular Foramen Lesions

20.3 Inferior Cerebellopontine Angle Approach for Hemifacial Spasm and Jugular Foramen Lesions Key Steps Step 1. Skin incision (Fig. 20.53) Step 2. Muscular dissection (Fig. 20.57) Step 3. Craniectomy (Fig. 20.62) Step 4. Opening of dura (Fig. 20.64) Step 5. Identification of lower cranial nerves (Fig. 20.66)

Illustrated Steps with Commentary

MT

Fig. 20.53 (Step 1) Skin incision. An "S" shaped incision is centered behind the mastoid tip approximately 5 mm behind the mastoid body. (MT, mastoid tip)

Fig. 20.54 Skin opening. The skin is opened along with the underlying adipose tissue and a small amount of adjacent flbrous tissue.

421

422

V Posterior Skull Base

Fig. 20.55 Preparing a fascial graft. The remainder of the flbrous tissue along with some of the sternocleidomastoid muscle fascia is harvested for a dural graft to be used at time of closure.

SCM

Fig. 20.56 Harvesting the fascial graft. This graft is used to close the dura in a water tight fashion at the end of the case. The flbers of the sternocleidomastoid muscle are separated. (SCM, sternocleidomastoid muscle)

SpCM

Fig. 20.57 (Step 2) Spreading the splenius capitis

muscle.

The flbers of the splenius capitis muscle are separated. (SpCM, splenius capitis muscle)

20.3 Lateral Suboccipital Approach: Inferior Cerebellopontine Angle Approach for Hemifacial Spasm and Jugular Foramen Lesions

Fig. 20.58 Identifying a thick layer of the fascia. A thick layer of the fascia that includes the occipital artery will be seen below the splenius capitis muscle.

MEV

OA

Fig. 20.59 Exposing the cranium. The middle layer of the posterior neck muscles and the semispinalis capitis and longissimus capitis muscles are divided to expose the cranium. The occipital artery is seen above the superior oblique muscle. (MEV, mastoid emissary vein; OA, occipital artery)

MEV OS Fig. 20.60 Exposing the cranium. The emissary vein is usually encountered approximately 5 mm posterior to the sigmoid sinus. (MEV, mastoid emissary vein; OSCM, obliquus superior capitis muscle)

CM

423

424

V Posterior Skull Base

Fig. 20.61 Exposing the cranium. The superior oblique muscle is retracted to obtain maximal exposure of the cranium inferior to the mastoid.

SS

Fig. 20.62 (Step 3) Opening the cranium. A small craniotomy or craniectomy is performed. Additional bone usually needs to be removed to expose the posterior edge of the sigmoid sinus. The craniotomy is usually enlarged inferiorly toward the foramen magnum. (SS, sigmoid sinus)

SS

Fig. 20.63 Partial condylectomy. After the bone flap is removed, the bony opening is enlarged to expose to medial edge of the sigmoid sinus and posterior edge of the occipital condyle. (SS, sigmoid sinus)

20.3 Lateral Suboccipital Approach: Inferior Cerebellopontine Angle Approach for Hemifacial Spasm and Jugular Foramen Lesions

SS

Fig. 20.64 (Step 4) Opening the dura. If a lumbar drain has not been placed, the dura is flrst opened close to the lateral inferior edge of the craniotomy. (SS, sigmoid sinus)

SS

Fig. 20.65 Releasing the cerebrospinal fiuid. The medullary cistern is opened to release spinal uid. Care is taken not to injure the spinal accessory nerve during this maneuver. (SS, sigmoid sinus)

X

PIC

A

IX

Fig. 20.66 (Step 5) Exposing the lower cranial

nerves.

Once the dura is opened, the lower cranial nerves can be seen by gently retracting the lateral edge of the cerebellar tonsil. (IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; X, vagus nerve; XI, accessory nerve)

XI

425

V Posterior Skull Base

IX

X

CP

PIC

Fig. 20.67 Exposing the lower cranial nerves. The glossopharyngeal nerve is seen entering the brainstem superior to the rootlets of the vagal nerve. The choroid plexus is seen just posterior to the glossopharyngeal nerve. (CP, choroid plexus; IX, glossopharyngeal nerve; PICA, posterior inferior cerebellar artery; X, vagus nerve)

CA

VII, VIII

AI

426

IX

X

Fig. 20.68 Exposing the eighth cranial nerve. The eighth cranial nerve is seen to enter the brainstem anterior to the choroid plexus. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve)

VII, VIII

AICA

REZ

IX Fig. 20.69 Exposing the root entry zone of the

facial nerve.

Only the root entry zone (REZ) of the facial nerve is exposed in microvascular decompression for hemifacial spasm. Exploration of whole course of the facial nerve is not needed. The anterior cerebellar artery runs near the REZ in this photo. (AICA, anterior inferior cerebellar artery; IX, glossopharyngeal nerve; REZ, root entry zone; VII, facial nerve; VIII, cochlear nerve; X, vagus nerve)

X

A

Index

Note: Page numbers followed by f indicate figures. A abducens nerve, 17f–20f, 69f, 94f–98f, 104f–105f, 112f, 116f–119f, 138f, 165f, 219f, 224f, 226f–227f, 243f, 255f, 263f–266f, 292f, 309f–310f, 342f–343f, 362f–365f, 367f–370f, 395f in cavernous sinus, 366f entrance into Dorello’s canal, 342f exit zone, 292f exposure of, 367f extradural portion, 17f fibrous membrane around, identification of, 219f on floor of inferior petrosal sinus identification of, 219f relationship to surrounding structures, 220f identification of, 291f, 306f, 396f intradural, identification of, 226f, 291f passing under petrosphenoidal ligament, 115f under trigeminal nerve, identification of, 232f accessory nerve, 69f, 149f–151f, 158f–159f, 254f, 263f–265f, 309f, 317f, 319f–324f, 327f, 329f–341f, 350f–352f, 357f–359f, 376f–378f, 380f–381f, 383f, 394f–397f, 415f–416f, 419f–420f exposure of, 70f, 316f, 425f identification of, 305f acoustic nerve and tumors, middle cerebellopontine angle approach for, 409–420 alar cartilage, major (greater), 3f alar ligament, 23f ala vomer, 12f–14f remnant, exposure of, 77f anatomy, craniofacial, 3–25 annulus of Zinn, 101f exposure of, 95f annulus tympanicus, skeletonizing of, 277f ansa cervicalis, 318f–319f ansa hypoglossi, 318f anterior atlanto-occipital membrane, 22f anterior cerebral artery A1 portion, 72f, 139f A2 portion, 72f anterior choroidal artery, 307f–308f, 362f, 364f–365f identification of, 234f anterior clinoid process base, exposure of, 134f lateral, removal of, 134f medial, removal of, 135f removal of, 134f tip, 135f–136f removal of, 136f anterior communicating artery, 72f anterior ethmoidal artery, 55f–56f identification of, 28f anterior ethmoidal nerve, 55f–56f identification of, 28f anterior fossa, 62f dural elevation, 133f anterior inferior cerebellar artery, 69f, 263f–266f, 285f, 305f, 309f–310f, 342f, 363f–364f, 397f, 414f–416f, 426f identification of, 395f meatal loop, 419f–420f identification of, 419f

origin, identification of, 396f anterior longitudinal ligament, removal of, 87f anterior nasal spine, 4f–6f, 8f–9f anterior spinal artery, 25f, 68f–69f anterolateral skull base, anatomy, 109–121 apical ligament, 23f arcuate eminence, 110f, 120f, 163f–164f, 214f–215f, 217f–220f, 241f–242f, 353f ascending pharyngeal artery, 203f asterion, 269f, 294f, 325f, 381f, 385f, 404f, 411f identification of, 270f atlanto-occipital membrane, 23f anterior, 22f atlas (C1), 72f–73f, 87f, 321f–324f, 350f–352f, 397f–399f anterior arch, 22f–23f, 45f–47f, 400f–401f drilling of, 23f, 399f exposure of, 206f, 399f condyle, 22f–25f, 46f–47f, 324f, 327f, 329f, 382f, 384f, 390f–391f, 397f, 399f exposure of, 45f, 323f identification of, 357f landmarks for, 391f exposure of, 87f facet, 21f–25f, 399f exposure of, 352f J-groove, 391f identification of, 390f lateral mass drilling of, 399f partial removal of, 361f posterior wall, drilling of, 360f posterior arch, 324f, 351f, 380f, 382f–384f, 390f–391f posterior notch, identification of, 390f posterior point, 390f–391f transverse foramen opening of, 384f, 398f posterior wall, 382f transverse process, 316f–324f, 351f, 380f–384f, 397f–398f exposure of, 397f muscular attachments to, 381f auditory tube. See eustachian tube auricularis anterior muscle, 167f auriculotemporal nerve, 148f, 156f–157f, 159f, 179f–180f, 183f–184f, 186f axis (C2), 15f–16f, 23f–25f, 87f–88f, 397f exposure of, 87f facet, 21f–25f B basilar artery, 68f–69f, 72f, 117f–118f, 120f, 227f, 233f, 255f, 292f, 307f–310f, 342f–343f, 364f–365f, 396f–397f identification of, 232f lower, 363f identification of, 227f mid-, 363f identification of, 227f top, viewing, 142f upper, 365f exposure of, 233f basilar tip, 309f, 365f basilar venous plexus, 15f bifrontal transbasal approach, 50–73 Bill’s bar. See vertical crest (Bill’s bar)

bony labyrinth opening of, 247f thinning of, 275f bony nasal septum, 6f buccal muscle, 151f–152f, 154f–157f, 159f–160f buccal nerve, 152f–157f, 159f, 179f–180f, 183f–187f bur holes, 298f C carotico-oculomotor membrane, 109f–110f, 118f, 135f, 137f, 139f–140f observation of, 136f opening of, 141f removal of, 140f carotid canal, intrapetrous, opening of, 46f carotid prominence(s), 64f C3 [formed by C3 portion of internal carotid artery], 14f, 16f, 31f, 64f–65f, 78f, 80f–81f left, identification of, 78f right, identification of, 79f C5 [formed by C5 portion of internal carotid artery], 14f, 64f–65f, 67f–68f, 80f–81f identification of, 32f left, identification of, 78f right, identification of, 79f right, 16f carotid sheath, 202f carotid sympathetic plexus, 18f cavernous sinus, 19f abducens nerve in, 366f complete exposure of, 114f from lateral direction, 116f internal carotid artery passing into, 16f lateral wall nerves in, exposure of, 114f oculomotor nerve into, 368f osteal dura covering, 132f removal of, 117f viewed from medial direction, 20f medial wall, 17f exposure of, 80f on left side, 32f on right side, 33f removal, 70f separation from dura of pituitary gland, 81f opening of, 33f posterior, approach to, craniotomy for, 211f right, 18f opening of, for extended transsphenoidal approach, 81f superolateral wall, 109f cavernous sinus triangle(s), 120f anterolateral, 120f anteromedial, 120f far lateral, 120f lateral, 120f medial, 120f posteroinferior, 120f posterolateral, 120f posteromedial, 120f postmeatal, 120f premeatal, 120f superior, 120f cerebellum petrosal surface, retraction of, 413f protection of, 417f

428

Index cerebellum (continued) surface, exposure of, 405f cerebrospinal fluid (CSF), in medullary cistern, release of, 425f cervical muscle(s), high, anatomy, 377f cervical region, high anatomical relationship of structures in, 319f dissection, overview of, 335f nerves in, identification of, 332f cervical spine, upper, 68f choana, 9f–10f, 14f–15f, 32f, 34f exposure of, 30f upper arch, 12f, 14f chorda tympani, 156f–157f, 159f, 161f–165f, 235f–236f, 242f–251f, 254f, 277f–282f, 284f–287f, 289f, 326f–328f, 333f exposure of, 223f–224f identification of, 185f, 222f infratemporal fossa approach to, 160f joining lingual nerve, 185f–186f in middle ear, 164f choroid plexus, 415f, 426f clivectomy, 46f, 67f extension to foramen magnum, 67f partial, 46f, 255f, 340f, 360f petrosectomy with, 341f with total petrosectomy, 344–370 clivus, 14f–15f, 21f–25f, 32f–35f, 44f–49f, 64f, 67f, 78f–79f, 87f–88f, 203f, 225f, 255f, 291f–292f, 340f–341f, 370f dura of, 15f, 17f, 19f exposure of, 87f, 206f middle, exposure of, 205f partial removal of, 290f removal of, 369f C1 nerve, 380f, 382f, 384f C2 nerve, 382f–384f, 397f cochlea, 120f, 163f–165f, 217f–227f, 232f, 235f, 241f–243f, 254f, 263f–266f, 300f anatomical dissection of, 236f–237f apical turn, 237f, 253f, 288f–289f basal turn, 163f, 235f–237f, 251f–253f, 262f–263f, 287f–289f exposure of, 288f opening of, 248f drilled, 263f exposure of, via transmastoid approach, 253f and facial nerve, relationship between, 253f middle turn, 235f–237f, 253f, 288f–289f opening of, 235f–236f removal of, 290f cochlear aqueduct, 163f, 247f–254f, 259f–265f, 337f course, 280f exposure of, 280f, 336f cochleariform process, 164f–165f, 222f–223f, 244f, 249f–252f, 286f–288f identification of, 285f cochlear nerve, 163f, 248f, 263f, 306f, 309f–310f, 394f–396f, 414f–416f, 419f, 426f exposure of, 285f identification of, 305f origin, identification of, 415f removal of, 420f cochlear promontory, 326f combined petrosal approach, for posterolateral skull base, 293–310 positioning for, 293f common annular tendon, 18f exposure of, 95f common crus, 259f–260f, 281f–282f common tendinous ring, 18f–20f, 94f–95f, 98f, 101f exposure of, 95f condylar emissary vein, 322f–324f, 327f, 329f–330f anterior, exposure of, 331f occipital condyle and, relationship, 389f occlusion of, 389f condylar process (mandibular), 151f–153f, 198f cutting of, 199f condylectomy, 358f anatomical relationships seen after, 358f

partial, 329f, 424f coronoid process, 38f–39f, 151f–152f cortical bone, drilling of, 271f cranial nerve(s), 364f II. See optic nerve III. See oculomotor nerve IV. See trochlear nerve V. See trigeminal nerve VI. See abducens nerve VII. See facial nerve VIII. See cochlear nerve IX. See glossopharyngeal nerve X. See vagus nerve XI. See accessory nerve XII. See hypoglossal nerve exiting jugular foramen, identification of, 395f lower, 320f identification of, 291f inspection of, 333f over abducens nerve, exposure of, 69f posterior translocation of, 340f, 359f, 361f in posterior fossa, 309f–310f craniectomy, performance of, 404f craniocervical junction lateral, 382f vertebral artery at, 384f craniofacial anatomy, 3–25 craniotomy, 298f for bilateral transbasal approach, 53f–54f centered on mid-sigmoid sinus performance of, 411f–412f planning, 411f for unilateral transbasal approach, 53f craniovertebral junction, 398f cranium exposure of, in inferior cerebellopontine angle approach, 423f–424f opening of, in inferior cerebellopontine angle approach, 424f cribriform plate, 56f crista galli, 56f exposure of, 54f–55f cruciate ligament, 23f–24f cruciform ligament, transverse part, removal of, 401f D deep petrosal nerve, 70f, 163f, 241f identification of, 221f deep temporal artery(ies), 40f–47f, 151f–153f, 172f anterior, 172f posterior, 39f, 172f deep temporal fascia, 37f–38f, 123f, 208f–209f, 294f–295f deep layer, 51f, 123f–125f, 168f–169f, 194f–195f superficial layer, 51f, 123f–125f, 167f–169f, 194f–195f deep temporal (interfascial) fat pad, 167f–168f deep temporal nerve, 152f–155f, 172f, 179f–180f, 183f–184f, 186f exposure of, 151f dens, 23f, 401f articulating surface, exposure of, 400f drilling of, 401f exposure of, 400f depressor septi nasi muscle, 4f digastric groove, 388f digastric muscle, 149f–159f, 316f–317f, 319f–322f, 350f–351f, 377f–379f, 381f, 410f–411f posterior belly, anterior reflection of, 317f, 323f digastric ridge, exposure of, 273f Dorello’s canal, 118f opening of, 367f Dorello’s tube, identification of, 219f dorsum sellae, 46f, 72f dura elevation from frontal base, 54f, 57f, 91f exposure of, 299f, 412f incision of, 405f inverted “U” shaped reflection, 263f for vestibular schwannoma surgery, 256f opening of, 138f–139f, 362f, 393f, 413f, 425f of upper spinal canal, 323f

dural flap, raising of, 417f dural graft, 410f fibrous, 410f dural ring, 18f, 139f, 161f–162f, 273f, 276f, 325f–326f distal, 117f–118f incision of, 140f release of internal carotid artery from, 140f dural ring(s) distal, 18f–19f proximal, 19f dura mater, 25f exposure of, 88f dura propria, elevation of, 176f, 214f E endolymphatic sac, 161f, 163f, 246f–248f, 254f, 258f, 263f, 280f–283f, 326f fovea created by, identification of, 416f endonasal paraseptal transsphenoidal approach, 74–82 ethmoid, perpendicular plate, 7f–9f, 62f–63f ethmoid air cells, posterior, opening into nasal cavity, 16f ethmoidal artery, 96f–97f ethmoidal band, 133f, 136f ethmoidal foramen anterior, 55f–56f posterior, 55f–56f ethmoid bulla, 29f ethmoidectomy, 28f–29f, 48f ethmoid sinus, 7f–10f, 15f, 30f–31f, 48f–49f, 92f–93f, 96f anterior, exposure of, 29f opening of, 60f eustachian tube, 10f, 16f, 20f, 42f–43f, 164f–165f, 183f–188f, 190f, 192f–193f, 198f, 200f–201f, 242f–243f, 252f–253f bony part, 222f–224f cartilaginous portion, 179f–180f, 216f, 218f, 222f–225f, 235f course, 43f direction, 189f, 191f exposure of, 41f, 216f, 235f identification of, 222f opening of, 235f into nasopharynx, 191f orifice, 225f identification of, 30f pharyngeal opening, 11f pharyngeal ostium, 21f position, 71f probing of, 289f right, 21f external auditory canal, 199f, 296f, 299f–300f, 346f, 350f–351f, 373f closure of, 347f double closure of, 348f skin, inverting, 348f stitching of, 348f triple closure of, 349f undermining of, 347f external carotid artery, 151f–156f, 159f, 318f distal, exposure of, 150f external occipital protuberance, 373f, 402f, 409f F facial artery, 153f, 157f, 263f, 318f facial nerve, 151f–157f, 221f, 235f–237f, 255f, 257f, 262f, 264f–265f, 289f, 309f–310f, 327f, 329f, 335f, 341f, 356f–358f, 362f–365f, 369f–370f, 383f, 394f, 396f, 414f–416f, 419f anatomy, 158–165 anterior translocation of, 328f branches, 148f–149f buccal branch, 148f–150f, 158f, 160f–161f, 164f cervical branch, 148f–150f, 158f and cochlea, relationship between, 253f digastric branch, 149f–150f, 152f–154f, 157f–159f exploration of, 158 exposure of, 148f, 426f

Index from styloid foramen to meatus of internal auditory canal, 286f external genu. See facial nerve, genu extracranial portion, 158f, 246f, 327f–328f, 334f proximal, 159f frontal branch, 37f protection of, 51f at fundus of internal auditory canal, 163f genu, 162f–163f, 224f, 236f, 242f–251f, 253f–254f, 259f–262f, 265f–266f, 277f– 286f, 289f, 352f identification of, 305f, 395f intramastoid, 161f–163f intrameatal, 160f intraoperative management of, 37f labyrinthine segment, 162f–165f, 220f–221f, 224f–226f, 241f–243f, 248f, 251f, 254f, 262f, 265f–266f, 283f–286f, 289f lateral petrosal segment, 162f main trunk, exposure of, 224f marginal mandibular branch, 148f–150f, 158f mastoid segment, 254f exposure of, 224f skeletonizing of, 276f meatal segment, 160f–163f, 220f, 224f, 226f, 248f, 251f, 253f–254f, 259f–262f, 284f–286f, 289f, 420f from middle fossa, 165f posterior petrosal segment, 161f posterior rerouting of, 286f–287f posterior translocation of, 355f root entry zone, exposure of, 426f second turn. See facial nerve, genu superior petrosal segment, 165f temporal branch, 148f–150f, 158f tympanic segment, 162f–165f, 220f–226f, 235f–236f, 241f–245f, 248f, 253f–254f, 262f, 265f–266f, 277f, 284f–286f, 289f, 300f, 352f, 354f–355f identification of, 275f vertical segment, 161f–165f, 235f–236f, 242f–251f, 253f–254f, 259f–261f, 276f–286f, 289f–290f, 297f, 326f–328f, 332f–334f, 337f–338f, 352f exposure of, 224f zygomatic branch, 148f–150f, 158f facial recess, 162f, 244f exposure of, 277f fascial graft harvesting of, 386f, 422f preparation of, 422f fascial patch graft, 57f fibrocartilaginous ring, 244f–245f, 252f, 260f, 277f–278f, 289f fibrous soft tissue, exposure of, 403f fibrous tissue graft dissection of, 403f harvesting of, 403f foramen magnum anterior portion, 67f–68f extension of clivectomy to, 67f opening of, 389f foramen magnum posterior point, 389f–391f foramen ovale, 156f, 159f–160f, 175f, 177f, 198f, 214f identification of, 71f from lateral side, 157f opening of, 197f, 216f skeletonizing of, 176f unroofing of, 178f foramen ovale emissary vein, 66f, 70f, 178f, 214f foramen rotundum, 174f, 177f, 197f artery, 181f skeletonizing of, 176f unroofing of, 177f foramen spinosum, 175f identification of, 214f foramen transversarium, 324f fovea, 256f, 263f frontal base, 54f–55f dural elevation from, 54f, 57f, 91f frontal bone, 37f–40f frontal craniotomy, 90f

frontal dura, 40f, 42f, 48f–49f, 101f, 125f, 172f, 196f frontalis muscle, 124f–125f frontal muscle, 147f–148f frontal nerve, 93f–98f, 102f frontal sinus, 7f–9f, 54f–55f, 92f frontonasal duct, 54f frontonasal suture, 4f frontoorbital detachment, 125f frontotemporal craniotomy, 40f, 126f, 173f frontotemporal orbitozygomatic transcavernous approach, 122–143 frontozygomatic suture, 100f, 125f–126f, 128f Fukushima’s bar, 164f, 223f, 242f identification of, 221f G galea aponeurotica, 124f–125f, 148f, 163f–165f, 167f, 345f galeofascial fibrous membrane, 268f harvesting, 268f galeofascial graft, harvesting of, 268f, 312f galeofascial pericranial flap, vascularized elongation of, 210f preparation of, 209f gasserian ganglion, 109f, 111f–112f, 114f–117f, 197f, 199f, 211f, 215f–216f, 218f, 225f, 230f–231f, 241f–243f, 248f, 251f, 254f, 262f, 265f–266f, 306f, 308f–310f, 354f, 356f–357f, 366f, 368f anterior translocation of, 217f approach to, craniotomy for, 211f exposure of, 114f geniculate ganglion, 162f–165f, 220f–226f, 236f, 284f–286f, 289f, 355f geniculate notch, 164f, 223f identification of, 221f Glasscock’s triangle definition of, 197f drilling of, 198f glossopharyngeal nerve, 43f–45f, 47f, 69f, 149f–150f, 157f, 202f–205f, 245f–246f, 254f, 263f–265f, 278f, 280f, 309f–310f, 319f–320f, 332f–341f, 351f, 358f–359f, 362f–364f, 383f, 394f–397f, 414f–416f, 419f–420f exposure of, 69f, 425f–426f identification of, 42f, 305f, 319f tympanic branch. See Jacobson’s nerve “golf club” drilling, 125f–126f, 172f–173f greater alar cartilage, 3f–4f lateral crus, 3f medial crus, 3f greater auricular nerve, 147f–148f, 313f, 346f, 374f–376f cutting of, 313f, 347f identification of, 312f, 345f greater occipital nerve, 374f–378f greater palatine nerve, 14f–15f, 182f demonstration of, 181f greater superficial petrosal nerve, 158f, 163f–165f, 196f, 215f–223f, 235f, 241f–243f, 254f, 286f–287f, 300f, 353f–354f division from geniculate ganglion, 355f exposure of, 224f identification of, 214f, 221f, 354f greater superior petrosal nerve, 110f, 112f, 119f Grüber’s ligament. See petrosphenoidal ligament H hard palate, 20f–21f, 85f hemifacial spasm, inferior cerebellopontine angle approach for, 421–426 Heubner’s artery, 72f hiatus semilunaris, 9f hypoglossal canal, 382f, 384f, 393f, 398f–401f exposure of, 330f, 392f identification of, 358f skeletonizing of, 330f venous plexus in, 391f hypoglossal emissary vein, 391f exposure of, 331f hypoglossal nerve, 69f, 254f, 309f, 318f–320f, 330f–333f, 335f–341f, 350f–351f, 358f–359f, 362f, 383f, 395f, 415f–416f

exposure of, 70f, 331f identification of, 305f, 317f, 332f posterior translocation of, 340f right angle turn, 339f I incision for combined petrosal approach, 294f for craniotomy centered on mid-sigmoid sinus, 409f “C” shaped, 294f dural, 405f of dural ring, 140f extended, for frontotemporal, orbitobasal, and middle fossa exposure, 122 for inferior cerebellopontine angle approach, 421f for large frontotemporal exposure, 122 “L” shaped, 294f for middle fossa rhomboid approach, 207f of paraseptal mucosa, 76f for postauricular transmastoid posterior infratemporal fossa transjugular approach, 312f for pterional approach, 122 retroauricular “C” shaped, 267f scalp semilunar, 89f, 99f for transcranial orbital approach, 89f sickle shaped, 166f for preauricular transzygomatic middle infratemporal fossa approach, 194f for superior cerebellopontine angle approach, 402f for total petrosectomy, 344f for transcondylar transtubercular approach, 385f incision(s) for bifrontal transbasal approach, 51f conjunctival, 36f hemicoronal, 36f high cervical, 36f paranasal, 26f, 36f preauricular, 36f temporal, 36f for transfacial transmaxillary approach, 36f incisive foramen, 5f, 8f incus, 161f–165f, 222f–225f, 235f–236f, 242f–246f, 248f, 254f, 274f–277f, 279f, 281f–285f, 307f–308f, 326f identification of, 273f long crus, 162f, 244f–245f, 277f–278f short crus, 162f, 244f–245f, 277f–278f incus buttress, 162f, 244f, 246f–248f, 277f inferior alveolar nerve, 152f, 154f–157f, 159f–160f, 165f, 183f, 185f–187f, 243f exposure of, 153f inferior cerebellopontine angle approach, for hemifacial spasm and jugular foramen lesions, 421–426 inferior nuchal line, 373f inferior oblique muscle, 98f, 104f inferior ophthalmic vein, 103f inferior petrosal sinus, 19f–20f, 115f–116f, 120f, 165f, 218f–221f, 224f, 243f, 254f–255f, 291f–292f, 335f–338f, 340f–341f, 359f, 366f exposure of, 218f, 290f opening of, 367f inferior rectosigmoid point, 389f–391f identification of, 388f inferior rectus muscle, 102f–104f identification of, 98f innervation, 103f inferior vestibular nerve, 160f–161f, 163f, 248f, 257f, 259f–265f, 284f–285f identification of, 419f removal of, 420f infralabyrinthine triangle, 247f, 280f infraorbital artery, 181f infraorbital fissure, 15f infraorbital nerve, 14f–15f, 29f, 179f–181f, 185f, 188f, 192f–193f

429

430

Index infraorbital nerve (continued) identification of, 27f infraorbital vein, 18f infratemporal dura, exposure of, 301f infratemporal fossa, 39f–40f, 160f, 193f, 223f–224f anatomy, 147–157 exploration of, 147–157 exposure of, 192f infratemporal skull base, anatomy, 147f inion, 373f inner petrosa-1, 263f inner petrosa-2, 263f inner petrosa-3, 264f inner petrosa-4, 264f inner petrosa-5, 264f inner petrosa-6, 265f inner petrosa-7, 265f inner petrosa-8, 265f inner petrosa-9, 266f inner petrosa, anatomy, 256–266 intercavernous sinus, 64f, 80f–81f between osteal dura and dura propria on sella floor, 17f interfascial fat pad, 123f–124f, 168f interior fossa, frontal base, 54f–55f dural elevation from, 54f, 57f internal auditory artery, 263f–266f, 419f–420f opening of, 248f internal auditory canal, 120f, 164f–165f, 218f–219f, 221f–225f, 235f, 241f–243f, 256f–257f, 300f, 341f, 354f–355f approach to, craniotomy for, 211f drilling of, 160f dura, 257f opening of, 226f, 285f exposure of, 284f fundus, 161f, 242f exposure of, 220f facial nerve at, 163f maximum exposure to save hearing without opening vestibule, 257f labyrinthectomy exposing, 352f opening of, 418f–419f preparation for, 417f–418f retrosigmoid approach to, 263f skeletonizing of, 217f internal carotid artery, 21f–24f, 42f–43f, 45f, 47f–49f, 118f, 157f, 160f, 203f–205f, 234f, 252f, 307f–308f, 318f, 320f, 332f–335f, 337f–338f, 341f, 350f–351f, 362f, 364f–365f, 383f anterior translocation of, 205f, 359f, 361f cavernous portion, anatomy, 119f C1 portion, 139f C2 portion, 116f–119f, 139f–142f C3 portion, 15f–20f, 33f–35f, 65f–68f, 70f–73f, 118f–119f, 137f–138f, 141f–142f exposure of, 141f identification of, 137f C4 portion, 15f, 18f–19f, 33f–34f, 71f, 111f–112f, 114f–116f, 118f–119f C5 portion, 15f–20f, 33f–34f, 45f–46f, 48f–49f, 65f–68f, 70f–72f, 112f, 114f–119f, 362f, 364f–370f C6 portion, 46f–49f, 71f, 118f–119f, 157f, 198f–201f, 204f–205f, 217f–223f, 225f–226f, 232f, 235f, 241f–243f, 252f, 254f–255f, 354f–356f, 358f–359f, 365f, 367f, 369f exposure of, 119f, 198f, 290f C7 portion, 201f, 204f–205f, 223f–224f, 226f, 235f–237f, 242f–243f, 245f–246f, 252f–255f, 260f, 263f–266f, 278f, 289f, 333f, 335f–341f, 356f–359f, 362f–363f, 367f, 369f–370f, 383f exposure of, 225f, 290f, 334f exposure of, 33f, 234f high cervical, 203f–204f identification of, 320f horizontal portion, 199f, 201f exposure of, 354f, 356f identification of, 308f inferior translocation of, 225f

intracranial extradural portion, exposure of, 46f left, 34f exposure of, 70f posterior genu, connecting C4 and C5 portions, 109f, 112f–114f, 116f skeletonization of, 113f release from dural ring, 140f removal of, exposure after, 119f right, 34f passing into cavernous sinus, 16f vertical portion, 201f exposure of, 225f, 356f internal carotid sympathetic plexus, 18f internal cerebral artery C6 portion, 163f–165f C7 portion, 163f, 165f internal jugular vein, 149f–151f, 153f, 155f, 157f–158f, 160f, 316f–324f, 327f–329f, 331f–335f, 350f–351f, 357f–359f, 377f–383f exposure of, 329f posterior translocation of, 361f removal of, 335f intramastoid-1, 254f intramastoid-2, 254f intramastoid-3, 255f intramastoid-4, 255f intraorbital fat, removal of, 93f J Jacobson’s nerve, 245f–246f, 326f between carotid canal and internal jugular vein, 333f identification of in front of jugular bulb, 278f on promontory, 278f origin, identification of, 279f originating from glossopharyngeal nerve, 334f on promontory, 245f jugular bulb, 161f–163f, 245f–251f, 253f–255f, 259f–263f, 265f–266f, 277f, 279f, 281f–288f, 290f–292f, 296f–297f, 301f, 327f–335f, 357f–358f, 382f–383f exposure of, 276f, 326f, 329f posterior translocation of, 359f, 361f jugular foramen, 256f, 260f–261f, 263f–266f anatomy, overview of, 334f cranial nerves exiting, identification of, 395f exposure of, 357f intradural exposure of, 338f lesions, inferior cerebellopontine angle approach for, 421–426 neural structures in, 359f open, overview of, 332f pars nervosa exposure of, 335f overview of, 337f jugular isthmus, 328f jugular tubercle, 68f–69f, 254f, 292f, 331f, 335f–336f, 338f, 356f–358f, 382f, 391f–392f, 394f, 414f–416f, 420f drilling of, 337f, 392f–393f exposure of, 360f identification of, 291f, 392f partial resection of, 337f, 339f removal of, surgical view after, 394f K keel bone, 77f L labyrinth, membranous, opening of, 281f labyrinthectomy exposing internal auditory canal, 352f mastoidectomy with, 352f lacrimal artery, 95f–98f lacrimal fossa, 27f exposure of, 28f lacrimal gland, 60f, 93f–98f, 102f, 104f lacrimal nerve, 94f–98f, 104f lacrimal sac fossa for, 6f identification of, 27f

lambdoid suture, 269f–270f, 376f, 381f, 404f, 411f lateral loop, 111f, 130f, 175f–176f, 187f bony protrusion over, 110f exposure of, 197f identification of, 215f, 354f landmark for, 174f medial to bony protrusion, 111f lateral orbital bar, removal of, 100f lateral orbital rim, 99f, 150f, 152f exposure of, 168f–169f lateral petrosa, anatomy, 243–255 lateral pterygoid muscle, 152f, 154f exposure of, 39f inferior head, 39f, 153f–155f, 184f nerve to, 183f–184f removal of, 39f superior head, 39f, 153f–155f, 179f–180f, 183f–184f detachment of, 184f lateral rectus muscle, 93f–96f, 98f, 101f–105f approach below, 103f approach to, 102f identification of, 97f lateral sinus, 356f–357f, 404f–405f, 411f–413f lateral skull base, anatomy, 147–165 lateral suboccipital approach, for posterior skull base surgery, 402–427 lesser palatine nerve, 14f–15f, 181f–182f demonstration of, 181f lesser petrosal nerve, 186f levator palpebrae superioris muscle, 93f–98f levator scapulae muscle, 317f–324f, 327f, 329f, 337f, 341f, 350f–352f, 375f–381f levator veli palatini muscle, 190f–191f lingual nerve, 152f–157f, 159f–160f, 165f, 183f, 185f, 187f, 223f, 243f chorda tympani joining, 185f–186f exposure of, 153f longissimus capitis muscle, 203f–204f, 349f, 378f exposure of, 387f identification of, 314f posterior reflection of, 350f longus capitis muscle, 21f, 43f–44f, 86f identification of, 42f, 86f lateral retraction of, 87f removal of, 44f longus colli muscle, 21f–22f, 86f–87f identification of, 86f loose areolar tissue, 123f, 167f M Macewen’s triangle, 269f identification of, 270f malleus, 162f–165f, 222f, 224f–225f, 235f–236f, 242f–245f, 249f–254f, 262f–263f, 285f, 289f head, 223f manubrium, 223f, 244f, 246f, 252f, 262f–263f, 278f mandible condyle, removal of, 199f coronoid process, 38f ramus, 37f–38f, 42f, 150f–152f central portion, removal of, 152f removal of, 47f mandibular angle, 312f, 325f, 344f mandibular nerve, 40f–45f, 110f–111f, 114f–117f, 160f, 163f, 165f, 175f–178f, 180f–181f, 187f–188f, 191f–193f, 197f–205f, 211f, 215f–216f, 218f–225f, 231f–232f, 235f, 241f–243f, 300f, 310f, 354f–357f, 366f, 368f anterior translocation of, 200f, 205f, 217f, 354f anterior trunk, 179f, 183f, 186f branches, 39f, 184f–185f exposure of, 179f–180f identification of, 183f distal branches, exposure of, 179f division of, 44f dura propria separated from, 111f exposure of, 66f extracranial, identification of, 197f identification of, 196f, 214f

Index lateral trunk, 187f posterior translocation of, 189f mandibular osteotomy, in cadaver, 84f marginal process, 125f, 170f marginal tubercle, 100f freeing of, 170f masseteric muscle, 148f–150f, 158f exposure of, 37f, 150f layers, 151f reflection of, 37f masseteric nerve, 150f–154f, 179f–180f, 183f–184f, 186f exposure of, 151f masseter muscle, exposure of, 169f mastoid anatomy, 243–255 antrum, identification of, 272f body, 373f exposure of, 296f exposure of, 269f mastoid air cells, drilling of, 271f mastoid cavity, saucerizing of, 272f mastoidectomy with labyrinthectomy exposing vestibule, 352f outlining of, 325f overview of, 327f standard, overview after, 254f superficial, 243f, 296f superficial landmarks for, outer triangle, 270f–271f mastoid emissary vein, 296f, 410f–411f, 423f mastoid tip, 149f–150f, 158f–159f, 293f–294f, 312f, 315f–317f, 320f–321f, 323f–325f, 350f–352f, 373f, 381f, 385f, 402f, 409f, 421f drilling of, 327f removal of, 357f maxilla, 28f, 37f exposure of, 27f frontal process, 4f, 6f palatine process, 5f, 8f–9f maxillary artery, 39f, 152f–156f, 159f–160f, 184f–187f exposure of, 153f identification of, 185f maxillary nerve, 14f–16f, 18f, 20f, 40f–45f, 66f, 109f–111f, 114f–117f, 133f–138f, 174f–178f, 180f–181f, 183f–185f, 187f–189f, 191f–193f, 197f, 199f, 204f, 211f, 215f–216f, 354f, 356f–357f, 366f, 368f branches exposure of, 180f identification of, 180f, 182f distal branches, exposure of, 179f dura propria separated from, 111f identification of, 196f maxillary sinus, 9f, 15f, 28f, 38f–40f, 192f–193f medial, exposure of, 29f medial wall, removal of, 40f posterior wall, removal of, 40f maxillary tuberosity, 153f–157f, 159f–160f, 192f maxillostomy, 28f–29f Meckel’s cave, 114f opening of, 306f medial palpebral ligament, 4f medial pterygoid muscle, 153f–154f, 156f, 159f, 187f deep head, 155f identification of, 185f nerve to, 186f–187f partial removal of, 188f superficial head, 155f medial rectus muscle, 18f–19f, 93f–94f, 96f, 103f exposure of, 97f medulla oblongata, 68f–69f meningohypophyseal trunk, 19f, 115f meningoorbital band, 131f division of, 132f mesencephalon, 309f midbrain, 228f, 231f, 308f–309f midclivus, exposure of, 34f middle cerebellopontine angle approach, for acoustic nerve and tumors, 409–420 middle cerebral artery M1 portion, 72f, 139f

M2 portion, 72f middle cranial base anatomy, 241f structures, relationship to zygomatic root, 211f middle cranial fossa, bony protrusion, 110f middle ear anatomy, 242f, 278f examination of, 277f middle fossa anatomy, 241–243 base, 131f dural incision at, 301f bony floor, irregularities, removal of, 299f floor, flattening of, 40f, 213f inner plate, drilling of, 300f rhomboid, identification of, 300f structures in, relationship to zygomatic root, 210f middle fossa rhomboid approach, 207–237 middle meningeal artery, 110f–111f, 114f, 116f–120f, 154f, 156f–157f, 159f, 165f, 174f–176f, 186f, 197f, 211f, 214f–217f, 219f–223f, 243f, 300f anterior division, identification of, 172f identification of, 196f, 213f passing through middle fossa cranial base, identification of, 353f sacrifice of, 175f mid-subtemporal ridge, 110f–111f, 130f–131f, 174f–176f mid-subtemporal tubercle, 110f mid-temporal bone exposure, 208f modiolus (of cochlea), 163f, 237f, 252f–253f, 262f–263f, 288f–289f mouth, opening of, in cadaver, 84f mouth gag, setting, 85f mucosa nasal, 4f–5f, 7f–9f, 76f, 81f nasopharyngeal, 20f oropharyngeal, 20f of posterior wall of oropharynx, incision of, 86f muscle flap, for craniotomy centered on midsigmoid sinus, 410f mylohyoid nerve, 153f–154f N nasal aperture, posterior, upper arch, 12f nasal cartilage greater alar, 3f–4f lateral, 3f septal, 3f–6f, 8f–9f nasal cavity lateral wall, removal of, 29f, 48f mucosa, 60f–62f separation of, 61f nasal concha, 6f. See also turbinate(s) nasal septum, 7f–8f, 30f–35f, 48f, 75f–76f irregular, 7f posterior, 62f removal of, 49f variation, protrusion of upper edge of vomer, 7f nasociliary nerve, 93f–95f, 98f, 104f–105f exposure of, 96f nasofrontal duct, 58f–60f nasofrontal suture, 53f nasolacrimal duct, 28f–29f cutting, 27f nasomaxillary suture, 4f, 27f nasopalatine artery, 5f nasopalatine nerve, 5f, 8f, 14f, 182f nasopharynx, 21f, 30f, 34f, 191f–193f mucosa, 20f neck muscle(s) posterior cutting of, using monopolar coagulator, 314f reflection of, 296f superficial, exposure of, 313f nose, cartilaginous framework, 3f O obliquus capitis inferior muscle, 317f–324f, 327f, 329f, 337f–338f, 341f, 350f–352f, 379f–381f, 383f

obliquus capitis superior muscle, 158f–159f, 315f–320f, 379f–381f, 423f exposure of, 316f, 350f, 388f posterior reflection of, 321f, 351f occipital artery, 72f, 159f, 315f–318f, 349f, 374f–378f, 387f, 423f course, variations, 378f identification of, 315f resection of, 317f occipital bone, 296f basilar part drilling of, 46f exposure of, 44f–45f, 205f exposure of, 296f, 388f pars basilaris, exposure, 23f occipital condyle, 22f, 24f–25f, 45f–47f, 323f–324f, 327f, 330f–331f, 357f–358f, 382f, 384f, 393f, 397f, 399f exposure of, 45f, 329f, 352f identification of, 357f landmarks for, 391f partial resection of, 391f and posterior condylar emissary vein, relationship, 389f occipitalis muscle, 345f, 374f–375f occipital muscle(s), deep layer, anatomy, 381f occipitofrontalis muscle, occipital belly, 374f occipitomastoid suture, 269f–270f, 381f, 404f occipitomental suture, 411f oculomotor foramen, opening of, 112f oculomotor nerve, 20f, 72f–73f, 109f–111f, 114f–120f, 133f–138f, 140f–143f, 234f, 308f–309f, 362f, 364f–367f branch to inferior oblique muscle, 98f, 102f–103f branch to inferior rectus muscle, 98f, 103f branch to medial rectus muscle, 94f, 97f division, in oculomotor canal, 113f exposure of, 234f identification of, 228f, 232f–233f, 307f inferior division, identification of, 98f intradural, 112f membrane covering, mobilization of, 137f proximal, exposure of, 233f olfactory nerve, 307f branches, dural holes made by, 56f filaments, 8f operculum drilling of, 297f medial to posterior semicircular canal, 297f removal of, 275f ophthalmic artery, 15f, 18f–20f, 95f, 98f, 102f–105f, 149f, 156f–160f ophthalmic nerve, 20f, 109f–117f, 133f–138f, 141f–142f, 366f, 368f optic canal, 135f optic chiasm, 34f exposure of, 72f, 234f optic nerve, 15f–20f, 63f–68f, 70f–73f, 93f, 95f–97f, 102f–103f, 105f, 109f–112f, 114f, 116f–120f, 134f–142f, 234f, 307f–308f exposure of, 98f deep to levator palpebrae superioris muscle, 94f left, 34f over internal carotid artery, 365f right, 34f opticocarotid recess, 65f optic strut, partial removal of, 135f oral cavity posterior wall, 20f superior wall, 20f orbit, 6f, 15f, 37f–42f, 44f–48f, 59f–60f, 64f, 72f, 93f–95f, 98f, 104f lateral wall, 125f–126f, 172f, 192f–193f exposure of, 100f removal of, 101f removal of, 48f superior, anatomy of, 93f orbital approach, 89–105 lateral, 89, 98–105 transcranial, 89–98 lateral, 95f

431

432

Index orbital approach (continued) medial, 94f midline, 94f orbital roof, removal of, 60f, 92f, 137f orbitotemporal detachment, 172f orbitozygomatic craniotomy, variations, 122 orbitozygomatic exposure, 124f orbito-zygomatic-maxillary osteotomy, 37f–38f orbitozygomatic osteotomy, extended, 122, 129f–130f oropharynx, 20f–21f, 85f mucosa, 20f posterior wall, mucosal incision of, 86f otic ganglion, 186f outer triangle, 270f–271f oval window, 249f connections from, 261f P paranasal mucosa elevation, 76f pocket, creation of, 76f parapharyngeal space anatomical structures in, 157f exposure of, 41f paraseptal mucosa, incision of, 76f paraseptal mucosal flap, renovation of, 81f–82f paratrigeminal lesions, superior cerebellopontine angle approach for, 402–408 parietal bone, 296f parietomastoid suture, 269f–270f, 376f, 381f, 404f, 411f Parkinson’s triangle, opening of, 115f parotid gland, 158f–159f, 162f–163f, 316f–317f, 319f–320f, 374f, 376f–379f, 381f deep lobe, 148f–149f superficial lobe, exposure of, 148f pars nervosa anatomy, 254f exposure of, 335f overview of, 337f translocation of, 359f partial clivectomy, 255f with total petrosectomy, 344–370 partial condylectomy, 329f perichondrium, 4f–5f, 7f pericranial flap, 51f for combined petrosal approach, 294f–295f elevation of, 124f elongation of, 125f, 169f vascularized, 169f pericranium, 294f periorbita, 101f opening of, 93f, 101f release of, 91f separation from orbital roof, 91f, 127f periosteal-fascial flap, 209f periosteum, 7f, 124f–125f, 169f, 208f–209f pes anserinus, 149f–150f, 158f petroclinoidal fold, 366f identification of, 116f petroclinoid ligament, 366f petroclival dural fold, 120f petroclival ligament, 115f–116f, 119f–120f petrolingual ligament, 119f–120f petrosal apex, 115f–116f, 118f–120f petrosal edge, 300f petrosal ridge(s), identification of, 215f petrosal tip, 360f petrosal vein(s), 118f, 407f, 414f–416f, 419f–420f exposure of, 406f identification of, 406f petrosectomy anterior, 207–237 exposing horizontal portion of internal carotid artery, 354f exposing vertical and horizontal portion of internal carotid artery, 356f with partial clivectomy, 341f total, with partial clivectomy, 344–370 petrosphenoidal ligament, 19f–20f, 112f, 115f–120f, 366f abducens nerve passing under, 115f

petrosphenoid ligament, 367f petrous apex approach to, craniotomy for, 211f partial removal of, 290f petrous bone first ridge, identification of, 215f rhomboid, drilling of, 300f second ridge, identification of, 215f petrous tip exposure of, 218f removal of, 218f pharyngobasilar fascia, 41f, 43f–44f, 187f–193f pharynx exposure of, transoral approach, 21f superior constrictor muscle, 41f–47f pituitary gland, 15f–16f, 18f–19f, 33f–35f, 70f, 72f, 80f dura, exposure of, 80f exposure of, 32f pituitary stalk, 15f, 34f–35f, 307f–308f exposure of, 72f platysma, 147f pons, 120f, 226f–227f, 231f–232f, 236f, 263f–266f, 304f, 308f–309f, 362f–364f exposure of, 362f postauricular transmastoid posterior infratemporal fossa transjugular approach, 311–343 posterior auricular muscle, 268f, 312f–313f, 374f, 410f identification of, 269f posterior auricular vein, 374f–375f posterior cerebellar artery, retraction of, 233f posterior cerebral artery, 118f, 120f, 303f–304f, 364f identification of, 228f, 232f, 308f P1 segment, 142f–143f, 228f, 232f–233f, 309f, 365f P2 segment, 143f, 228f, 230f–232f, 308f–309f, 362f, 364f–365f posterior clinoid process, 112f, 116f, 120f, 139f–143f, 234f posterior communicating artery, 142f, 228f, 232f–233f, 307f–308f, 362f, 364f–365f identification of, 234f viewing, 143f posterior condylar emissary vein occipital condyle and, relationship, 389f occlusion of, 389f posterior deep temporal artery, 39f posterior ethmoidal artery, 96f, 133f, 136f posterior ethmoidal nerve, 96f, 133f, 136f posterior ethmoid artery, 55f–56f, 94f–95f posterior ethmoid nerve, 55f–56f posterior fossa cranial nerves in, 309f–310f dura, 218f–220f, 222f, 224f, 291f exposure of, 218f incision of, 226f posterior fossa dura, 46f–49f, 68f, 88f, 161f exposure of, 47f, 67f posterior inferior cerebellar artery, 69f, 120f, 339f, 396f, 415f–416f, 425f–426f identification of, 394f origin, identification of, 395f posterior occipito-atlantal membrane, 322f exposure of, 322f removal of, 323f posterior petrosa, anatomy, 256–266 posterior skull base surgery anatomy for, 373–384 after condylectomy, overview, 383f after total petrosectomy, overview, 383f lateral suboccipital approach, 402–427 palpable landmarks for, 373f posterior zygomatic point, 207f posterolateral skull base anatomy, 241–266 combined petrosal approach for, 293–310 postauricular transmastoid posterior infratemporal fossa transjugular approach for, 311–343 transmastoid approach, 267–292

preauricular transzygomatic anterior infratemporal fossa approach, 166–193 preauricular transzygomatic middle infratemporal fossa approach, 166, 193–206 extended, 166f less invasive, 166f presigmoid dura exposure of, 301f incising, 302f promontory (cochlear), 244f–245f, 248f–250f, 254f, 261f, 277f–278f, 282f–286f demonstrating, 282f exposure of, 282f pterygoid fossa, exposure of, 192f pterygoid hamulus, 191f pterygoid process lateral lamina, 40f, 155f–157f, 159f, 183f, 187f identification of, 185f removal of, 187f medial lamina, 183f, 185f, 188f removal of, 188f pterygoid venous plexus, 152f pterygopalatine fossa, 14f–15f, 38f–40f, 177f–178f, 193f nerves, identification of, 181f pterygopalatine ganglion, 14f, 181f–182f pharyngeal branches emerging from, 14f R rectus capitis anterior muscle, 21f–22f, 43f–44f anterior reflection of, 206f exposure of, 44f identification of, 42f removal of, 45f rectus capitis lateralis muscle, 317f–324f, 379f–381f removal of, 324f rectus capitis major muscle, 321f, 350f–352f, 379f–381f posterior reflection of, 322f retrocondylar pouch, 200f structures in, relationship between, 204f retrolabyrinthine approach, for posterolateral skull base, 267–280 retropharyngeal space anatomical relationships in, 43f exposure of basilar part of occipital bone (clivus) through, 44f retrosigmoid groove, drilling of, 411f rhomboid, 215f, 217f complete removal of, 219f exposure of, 215f rhomboid space, drilling in, 217f round window, 163f, 245f, 249f–250f, 254f, 259f, 261f, 278f, 283f, 286f–287f bone surrounding, removal of, 287f connection with middle ear, 261f demonstrating, 282f exposure of, 282f S scalp elevation one and a half layer, 123f–124f two layer, 124f–125f and temporalis muscle, reflection in one layer, 90f, 123f sella turcica anterior wall, 14f, 31f floor, 14f, 16f, 31f–32f, 64f–65f, 78f–79f drilling of, 79f dura, 65f, 67f–68f, 80f dura of, 15f, 17f transnasal transsphenoidal approach, surgical trajectory for, 9f viewing of, 79f semicircular canal(s), 259f, 296f, 299f–302f, 326f–327f, 329f, 334f–335f, 341f ampulla, opening of, 281f anatomical dissection of, 236f anatomy, 242f blue lines of, 247f establishing, 279f

Index bone, thinning of, 275f exposure of, 274f, 325f lateral, 161f–165f, 222f–226f, 235f–237f, 242f–247f, 249f–250f, 254f, 260f–265f, 273f, 275f–281f, 297f, 300f, 304f, 306f, 309f–310f, 326f ampulla, 281f–282f bony protrusion, identification of, 272f exposure of, 274f identification of, 325f opening of, 235f–236f posterior, 161f–165f, 224f, 236f, 242f–247f, 249f, 254f, 259f–260f, 263f–266f, 274f–277f, 279f–281f, 297f, 300f, 309f–310f, 325f– 326f, 337f ampulla, 281f–282f operculum medial to, 297f removal of, 260f seen from middle fossa, 164f superior, 161f–165f, 220f–222f, 224f–226f, 235f–237f, 242f–244f, 246f–254f, 259f–266f, 274f–276f, 279f–281f, 297f, 300f, 304f, 306f, 309f–310f, 325f–326f ampulla, 223f–225f, 281f–282f semispinalis capitis muscle, 376f–379f exposure of, 387f septal nasal cartilage, 3f, 5f–6f, 8f–9f and perichondrium, subperichondrial dissection plane between, 4f sigmoid sinus, 161f–163f, 352f, 356f–359f, 362f, 382f–383f, 388f–393f, 398f–401f, 404f–405f, 411f–413f, 424f–425f exposure of, 329f inferior segment, exposure of, 276f lateral, removal of, 335f sigmoid sinus plate, 272f–273f, 325f identification of, 271f singular foramen, 160f–161f, 257f sinus(es), nasal. See also specific sinus communication, 9f skin flap for combined petrosal approach, 294f for craniotomy centered on mid-sigmoid sinus, 409f for retrolabyrinthine approach, elevation of, 268f for total petrosectomy, 345f soft palate, 20f, 85f sphenoidal crest, 10f, 61f–63f sphenoid bone, 13f–14f spine, 44f–45f, 160f sphenoid concha, 63f exposure of, 62f sphenoidostomy, 31f, 63f sphenoid sinus, 7f–10f, 16f, 32f, 41f–45f, 64f, 111f, 247f–249f, 254f, 273f, 276f, 278f, 296f–297f, 299f, 301f–302f, 325f–332f, 334f–335f, 337f–338f, 341f anterior wall, 63f surgical opening, 14f exposure of, 61f mucosa, 177f–178f, 369f exposure of, 78f natural ostia, bilateral, identification of, 77f natural ostium, 9f–10f, 12f–14f, 61f–63f identification of, 31f opening of, 78f, 370f posterior wall, removal, 15f skeletonizing of, 369f superior wall, 63f transnasal approach endoscopic, 5f microscopic, 5f transseptal approach, 4f sphenomandibular ligament, 153f sphenopalatine artery, 10f sphenopalatine foramen, 14f–15f location of, 10f spinal accessory nerve, identification of, 394f spinal cord, upper, 25f, 68f spine of Henle, identification of, 270f splenius capitis muscle, 295f–296f, 349f, 375f–377f

cutting of, 404f exposure of, 387f fascia, 374f identification of, 314f posterior reflection of, 349f removal of, 378f spreading of, 422f squamosal suture, 208f, 210f, 212f, 269f, 296f, 376f, 381f stapedial muscle, 244f, 246f, 281f identification of, 279f stapes, 162f–163f, 165f, 224f, 243f–246f, 277f–279f, 281f–285f identification of, 223f sternocleidomastoid muscle, 47f–49f, 147f–150f, 152f–154f, 157f–158f, 294f–295f, 312f–314f, 345f–347f, 374f–376f, 387f, 410f, 422f cutting of, 404f exposure of, 386f fascia, exposure of, 386f identification of, 269f posterior reflection of, 349f removal of, 377f styloglossus muscle, 156f–157f, 201f–204f, 319f–320f, 324f, 327f, 329f exposure of, 47f stylohyoid ligament, 47f, 157f, 320f, 329f stylohyoid muscle, 153f, 156f–157f, 159f, 202f, 316f, 319f–320f, 329f identification of, 319f styloid diaphragm, 201f, 377f, 379f exposure of, 350f, 387f identification of, 315f, 423f removal of, 201f, 350f styloid muscle, 156f–157f exposure of, 47f styloid process, 47f–49f, 157f, 329f, 332f exposure of, 328f muscles attached to, 47f–49f muscles originating from, 202f muscles stemming from, identification of, 320f stylomastoid artery, 159f stylomastoid foramen, 149f–150f, 158f, 161f–162f, 327f, 329f opening of, 327f stylopharyngeal muscle, 42f–43f, 45f, 156f–157f, 201f–205f, 320f exposure of, 47f subarcuate artery, 221f, 225f, 257f, 265f identification of, 220f suboccipital craniotomy elevation of, 353f outlining of, 353f suboccipital groove, drilling of, 298f, 412f suboccipital muscle(s) posterior retraction of, 316f superficial, anterior retraction of, 314f suboccipital triangle, 351f, 380f horizontal segment of vertebral artery in, identification of, 350f identification of, 321f subtemporal groove, drilling of, 126f, 212f superficial temporal artery, 148f frontal branch, 147f–148f parietal branch, 147f–148f superior cerebellar artery, 117f–120f, 230f–233f, 263f–266f, 303f–305f, 309f–310f, 406f–407f, 415f distal, identification of, 407f identification of, 228f, 232f, 308f supporting, with Teflon fibers and fibrin glue, 408f translocation of, 408f superior cerebellopontine angle approach, for trigeminal neuralgia and paratrigeminal lesions, 402–408 superior cerebral artery, 142f–143f, 362f, 364f–365f superior constrictor muscle, 157f superior nuchal line, 346f, 373f, 375f–376f superior oblique muscle, 93f–98f, 104f–105f trochlea, identification of, 97f

superior ophthalmic vein, 94f–95f, 97f–98f, 102f, 105f, 113f, 138f exposure of, 96f superior orbital fissure, 15f, 52f, 113f, 131f–132f osteal dura elevation from, 132f superior orbital vein, 20f, 133f superior petrosa, anatomy, 241–243 overview of, 242f superior petrosal sinus, 19f, 117f–120f, 163f, 254f–255f, 290f, 303f bleeding from, controlling, 304f cutting of, 228f identification of, 230f, 302f–303f packing oxidized cellulose into, 230f superior pharyngeal constrictor muscles, 190f–193f, 200f identification of, 86f superior rectus muscle, 93f–98f, 102f–105f superior temporal artery, 154f–156f, 158f–159f superior temporal line, 207f superior thyroid artery, 318f superior vestibular nerve, 160f–165f, 221f–226f, 241f–243f, 248f, 257f, 259f–265f, 284f–285f identification of, 419f removal of, 420f skeletonized, 261f supracerebellar artery, 364f suprajugular triangle, 247f, 280f supramastoid crest, 269f–270f supraorbital artery, 52f, 93f–94f supraorbital bar, 59f osteotomy, variations in, 57f release of, 92f removal of, 92f resection, lateral extent, variations in, 58f supraorbital bar osteotomy, 129f limited, 122, 128f supraorbital foramen, 90f supraorbital nerve, 52f, 58f–60f, 63f, 90f–94f, 97f–98f, 127f complete release of, 53f supraorbital notch (foramen), 6f, 52f supraorbital osteotomy, limited, exposure achieved after, 58f supraorbital ridge, 52f supratrochlear artery, 52f supratrochlear nerve, 52f, 93f–94f, 96f–98f sylvian fissure, opening of, 139f sympathetic plexus, 20f, 70f–71f, 118f–119f, 368f T “T” bone, 171f raising of, 171f tectorial membrane, 24f–25f exposure of, 88f venous plexus anterior to, 24f tegmen tympani, 247f–248f, 254f, 280f–281f temporal base bony protrusion, 174f drilling of, 197f temporal bone, 39f–40f inferior, drilling groove in, 297f petrosal surface, exploration of, 414f temporal craniotomy, 196f elevation of, 353f outlining of, 353f temporal dura, 42f–49f, 101f, 125f, 172f, 196f, 205f elevation of, 45f temporal dure, 40f–41f temporal fascia deep layer, 51f superficial layer, 51f temporalis muscle, 38f, 40f–42f, 129f, 172f, 192f–193f, 346f anteroinferior reflection of, 195f elevation of, 130f, 296f, 346f exposure of, 37f inferior reflection of, 171f insertion, 151f reflection of, 38f–39f and scalp, reflection in one layer, 90f, 123f temporal lobe, inferior, exposure of, 301f

433

434

Index temporal tegmen, 161f–163f, 325f–327f, 329f, 334f–335f anterior portion, removal of, 274f exposure of, 273f temporomandibular joint, 164f–165f, 183f–184f, 197f–199f, 222f–225f, 235f–236f, 242f–243f exposure of, 194f, 198f temporoparietal fascia, 158f, 167f temporoparietal muscle, 123f, 147f–148f, 167f, 345f tensor tympanic muscle, 165f, 198f, 222f–224f, 242f–243f identification of, 223f tensor tympani tendon, identification of, 223f tensor veli palatini muscle, 41f, 156f–157f, 160f, 187f–189f, 200f removal of, 190f tentorial edge, 302f–304f tacking up, 231f, 304f tentorium, 229f cutting of, 228f division of, 304f identification of, 302f incising along trochlear nerve, 303f toward trigeminal fibrous ring, 303f surface exploration of, 406f inspection of, for bridging veins, 405f thalamoperforating arteries, 233f tongue, removal of, in cadaver, 85f torus tubarius, 11f total petrosectomy, with partial clivectomy, 344–370 transbasal approach bifrontal, 50–73 extended, 50, 57f–58f extended osteotomy for, 59f extensive, 50, 58f osteotomy for, 59f–60f limited, 50, 57f–58f standard, 50 bilateral, craniotomy for, 53f–54f unilateral, 53f variations, 50 transcochlear approach, for posterolateral skull base, 286–292 transcondylar transtubercular approach incision for, 385f positioning for, 385f for posterior skull base surgery, 385–401 transfacial transmaxillary approach, 36–49 translabyrinthine approach, for posterolateral skull base, 281–285 transmastoid approach, for posterolateral skull base, 267–292 transmaxilloethmoidal approach, 26–35 transoral approach, 83–88 preparation for, in cadaver, 83f–85f transsphenoidal approach endonasal paraseptal, 74–82 transnasal, to sella turcica, surgical trajectory for, 9f transverse crest, 160f–161f, 253f, 257f–266f, 287f identification of, 284f transverse ligament, 24f, 400f transverse process, 251f–252f, 284f transverse sinus, 299f, 301f transzygomatic osteotomy, 122 trapezius muscle, 375f–379f trigeminal fibrous ring, 119f

cutting of, 306f tentorial incision toward, 229f trigeminal ganglion, dura propria separated from, 112f trigeminal impression, 119f, 217f trigeminal nerve, 230f–232f, 263f–265f, 282f–283f, 304f, 308f, 362f–370f, 396f, 407f–408f, 414f–416f, 419f–420f branches, 71f dura propria separated from, 112f course, 306f exposure of, 231f first division. See ophthalmic nerve identification of, 305f inspection of, 407f motor division, 305f–306f, 309f–310f motor root, 231f, 310f identification of, 231f removal of, 118f second division, 18f. See also maxillary nerve sensory division, 305f–306f, 309f–310f sensory root, 231f third division, 19f, 39f–40f. See also mandibular nerve; maxillary nerve trigeminal neuralgia, superior cerebellopontine angle approach for, 402–408 trigeminal prominence, 65f–66f trigeminal root, inspection of, 407f trochlear nerve, 20f, 93f–98f, 104f, 109f–119f, 133f–138f, 141f–142f, 228f, 230f–233f, 304f, 306f, 308f–310f, 364f–367f, 406f– 407f, 415f course, 307f identification of, 73f, 229f, 233f, 302f, 305f incising tentorium along, 303f tentorial tunnel, opening of, 229f true cavernous membrane, 132f removal of, 138f tuberculum sellae, 61f–63f turbinate(s) inferior, 6f, 9f, 11f, 16f, 29f, 49f, 75f middle, 6f, 9f–12f, 16f, 29f, 49f, 63f, 76f, 81f identification of, 75f removal of, 29f–30f superior, 9f–12f, 16f, 30f, 49f tympanic cavity, exposure of, 222f tympanic membrane, 163f, 244f, 246f, 252f, 254f, 260f–261f, 263f, 278f, 295f tympanic nerve, 245f–246f, 249f–251f, 278f–279f, 326f, 333f–334f originating from glossopharyngeal nerve, 334f tympanic ring, 260f U uvula, 20f, 85f elevation of, toward nasopharynx, 85f V V1. See ophthalmic nerve V2. See maxillary nerve V3. See mandibular nerve vaginal plate, 199f–201f, 204f drilling of, 204f vagus nerve, 69f–70f, 254f, 263f–265f, 309f–310f, 319f–320f, 332f–333f, 335f–341f, 359f, 362f–364f, 394f–397f, 414f–416f, 419f–420f exposure of, 69f, 425f–426f identification of, 305f, 318f vascularized flap outlining, 345f preparation of, 209f

raising, 346f in triple closure of external auditory canal, 349f vascularized graft, preparation of, 208f vertebral artery, 23f, 68f–70f, 72f, 88f, 227f, 248f, 254f, 283f, 321f–324f, 327f–332f, 334f–343f, 350f–352f, 357f–359f, 363f–364f, 381f–383f, 392f–393f, 395f–401f at C1-C2 junction, 384f at craniocervical junction, 384f extracranial exposure of, 360f posterior translocation of, 361f identification of, 394f, 397f landmarks for, 391f J-groove for, 324f, 351f, 382f, 384f identification of, 390f variations, 382f–383f over posterior arch of C1, identification of, 321f posterior translocation, 384f, 398f V3 portion (horizontal segment), 380f identification of, 350f, 390f vertebrobasilar junction, 72f, 342f–343f, 363f exposure of, 69f identification of, 227f, 396f vertical crest (Bill’s bar), identification of, 221f, 284f vestibular aqueduct, 248f identification of, 283f vestibular schwannoma, surgery inverted “U” shaped dural reflection for, 256f operative angle for retrosigmoid approach, 260f vestibule, 161f, 235f–236f, 248f, 250f, 259f–260f, 263f–266f, 283f anatomical dissection of, 236f–237f distance from transverse crest, 258f opening of, 235f–236f, 258f, 282f white or yellow point, 251f vestibulocochlear nerve, 341f identification of, 395f vidian canal, 176f–178f exposure of, 66f unroofing of, 178f vidian nerve, 40f–45f, 71f, 177f, 181f–182f, 200f exposure of, 66f, 70f vomer, 8f–9f, 21f, 23f, 48f, 61f–62f, 77f ala, 62f cuneiform part, 8f, 13f–14f “V” osteotomy, 52f–53f, 90f Z zygoma, 150f–151f, 168f–169f, 194f–195f, 207f, 293f–294f frontal process, exposure of, 99f root, 346f–347f exposure of, 210f posterior point, 325f relationship to middle cranial base structures, 211f relationship to structures in middle fossa, 210f zygomatic arch, 37f, 99f, 129f–130f detachment of, 171f exposure of, 168f–169f inferior reflection of, 195f osteotomy, landmarks for, 170f zygomatic nerve, 180f–181f zygomaticofacial foramen, 6f, 150f, 170f zygomaticofacial nerve, 150f zygomatic osteotomy, 195f zygomaticus major muscle, 147f–150f, 158f exposure of, anterior dissection for, 150f