Imaging Anatomy. Ultrasound [2 ed.] 9780323548007

Table of contents :
Front Cover
Imaging Anatomy: Ultrasound
Copyright Page
Dedication
Contributing Authors
Preface
Acknowledgments
Sections
Table of Contents
SECTION 1:
Brain and Spine
Chapter
1. Scalp and Calvarial Vault
TERMINOLOGY
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
EMBRYOLOGY
Chapter
2. Brain
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
3. Orbit
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
4. Transcranial Doppler
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
5. Vertebral Column and Spinal Cord
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
SECTION 2:
Head and Neck
Chapter
6. Neck Overview
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
7. Sublingual/Submental Region
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
8. Submandibular Region
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
9. Parotid Region
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
EMBRYOLOGY
Chapter
10. Upper Cervical Level
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
11. Midcervical Level
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
12. Lower Cervical Level and Supraclavicular Fossa
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
13. Posterior Triangle
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
14. Thyroid Gland
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
EMBRYOLOGY
Chapter
15. Parathyroid Glands
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
EMBRYOLOGY
Chapter
16. Larynx and Hypopharynx
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
17. Trachea and Esophagus
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
18. Vagus Nerve
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
19. Carotid Arteries
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
20. Vertebral Arteries
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
EMBRYOLOGY
Chapter
21. Neck Veins
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
22. Cervical Lymph Nodes
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
SECTION 3:
Thorax
Chapter
23. Thoracic Outlet
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
24. Pleura
GROSS ANATOMY
ANATOMY-BASED IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
25. Diaphragm
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
26. Chest Wall
GENERAL ANATOMY AND FUNCTION
SKELETAL STRUCTURES
MUSCLES
VESSELS AND NERVES
IMAGING
Chapter
27. Breast
TERMINOLOGY
LOBE/SEGMENT
DUCTAL SYSTEM
TERMINAL DUCT LOBULAR UNIT
ZONAL ANATOMY
INNERVATION
VASCULAR SUPPLY
LYMPHATICS AND LYMPH NODES
IMAGING ISSUES
SECTION 4:
Abdomen
Chapter
28. Liver
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
29. Biliary System
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
30. Spleen
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
EMBRYOLOGY
Chapter
31. Pancreas
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
32. Kidneys
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
EMBRYOLOGY
Chapter
33. Adrenal Glands
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
34. Bowel
GROSS ANATOMY
IMAGING ANATOMY
Chapter
35. Abdominal Lymph Nodes
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
36. Aorta and Inferior Vena Cava
TERMINOLOGY
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
37. Peritoneal Cavity
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
38. Abdominal Wall
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
SECTION 5: Pelvis
Chapter
39. Iliac Arteries and Veins
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
40. Ureters and Bladder
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
41. Prostate and Seminal Vesicles
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
42. Testes and Scrotum
GROSS ANATOMY
EMBRYOLOGY
ANATOMY-BASED IMAGING ISSUES
IMAGING ANATOMY
CLINICAL IMPLICATIONS
Chapter
43. Penis and Urethra
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
44. Uterus
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
EMBRYOLOGY
Chapter
45. Cervix
GROSS ANATOMY
IMAGING ANATOMY
Chapter
46. Vagina
TERMINOLOGY
GROSS ANATOMY
IMAGING ANATOMY
EMBRYOLOGY
CLINICAL IMPLICATIONS
Chapter
47. Ovaries
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
48. Pelvic Floor
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL APPLICATIONS
SECTION 6:
Upper Extremity
Chapter
49. Sternoclavicular and Acromioclavicular Joints
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
50. Shoulder
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
51. Axilla
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
52. Arm
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
53. Arm Vessels
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
54. Elbow
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
55. Forearm
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
56. Forearm Vessels
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
57. Wrist
TERMINOLOGY
IMAGING ANATOMY
Chapter
58. Hand
EXTRINSIC FLEXOR MUSCLES: DIGITS 2-5
INTRINSIC MUSCLES: HYPOTHENAR AREA
INTRINSIC MUSCLES: THENAR AREA
INTRINSIC MUSCLES: PALMAR AREA
TENDONS
Chapter
59. Hand Vessels
TERMINOLOGY
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
60. Thumb
TERMINOLOGY
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
61. Fingers
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
62. Brachial Plexus
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
63. Radial Nerve
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
64. Median Nerve
TERMINOLOGY
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
65. Ulnar Nerve
GROSS ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
SECTION 7:
Lower Extremity
Chapter
66. Gluteal Muscles
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
67. Groin
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
68. Hip
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
69. Thigh Muscles
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
70. Femoral Vessels and Nerves
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
71. Knee
TERMINOLOGY
GROSS ANATOMY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
72. Leg Muscles
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
73. Leg Vessels
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
74. Leg Nerves
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
75. Ankle
GROSS ANATOMY
ANATOMY IMAGING ISSUES
Chapter
76. Tarsus
TERMINOLOGY
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
Chapter
77. Foot Vessels
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
Chapter
78. Metatarsals and Toes
IMAGING ANATOMY
ANATOMY IMAGING ISSUES
CLINICAL IMPLICATIONS
SECTION 8:
Obstetrics and Developmental Anatomy
Chapter
79. Embryology and Anatomy of 1st Trimester
TERMINOLOGY
EMBRYOLOGY
ANATOMY IMAGING ISSUES
Chapter
80. Embryology and Anatomy of Brain
TERMINOLOGY
MAJOR EMBRYOLOGIC EVENTS
CEREBRUM, CEREBELLUM, AND VENTRICLES
IMAGING ISSUES
Chapter
81. Embryology and Anatomy of Spine
SPINAL CORD DEVELOPMENT
VERTEBRAL BODY DEVELOPMENT
FAILURE OF NEURAL TUBE CLOSURE
Chapter
82. Embryology and Anatomy of Face and Neck
GENERAL CONCEPTS
NOSE, LIPS, AND PALATE
MANDIBLE AND EARS
EYES
LYMPHATICS
EMBRYOLOGY OF COMMON ANOMALIES
Chapter
83. Embryology and Anatomy of Chest
GENERAL CONCEPTS
EMBRYONIC STAGE (26 DAYS TO 6 WEEKS)
PSEUDOGLANDULAR STAGE (6-16 WEEKS)
CANALICULAR STAGE (16-28 WEEKS)
SACCULAR STAGE (28-36 WEEKS)
ALVEOLAR STAGE (36 WEEKS TO 8 YEARS)
OTHER DEVELOPMENTAL REQUIREMENTS
NEONATAL LUNG
Chapter
84. Embryology and Anatomy of Cardiovascular System
EMBRYOLOGY OVERVIEW
ARTERIAL EMBRYOLOGY
VENOUS EMBRYOLOGY
CARDIAC ANATOMY
CIRCULATION
Chapter
85. Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract
EARLY EMBRYOLOGIC EVENTS
ABDOMINAL VESSELS
ABDOMINAL ORGANS
SELECTED DEFECTS IN DEVELOPMENT
Chapter
86. Embryology and Anatomy of Genitourinary Tract
DEVELOPMENT OF URINARY TRACT
DEVELOPMENT OF ADRENAL GLANDS
DEVELOPMENT OF MALE GENITAL TRACT
DEVELOPMENT OF FEMALE GENITAL TRACT
INDEX

Citation preview

SECOND EDITION

WOODWARD GRIFFITH | ANTONIO | AHUJA WONG | KAMAYA | WONG-YOU-CHEONG

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SECOND EDITION

Paula J. Woodward, MD Professor of Radiology David G. Bragg, MD and Marcia R. Bragg Presidential Endowed Chair in Oncologic Imaging Adjunct Professor of Obstetrics and Gynecology University of Utah School of Medicine Salt Lake City, Utah

James F. Griffith, MD, MRCP, FRCR Professor Department of Imaging and Interventional Radiology The Chinese University of Hong Kong Hong Kong (SAR), China

Gregory E. Antonio, MD, DRANZCR, FHKCR Honorary Professor Department of Imaging and Interventional Radiology The Chinese University of Hong Kong Consultant Radiologist Scanning Department St. Teresa’s Hospital Hong Kong (SAR), China

Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Professor of Diagnostic Radiology & Organ Imaging Faculty of Medicine The Chinese University of Hong Kong Prince of Wales Hospital Hong Kong (SAR), China

K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology) Consultant & Clinical Associate Professor (Honorary) Department of Imaging and Interventional Radiology Prince of Wales Hospital Faculty of Medicine The Chinese University of Hong Kong Hong Kong (SAR), China

Aya Kamaya, MD, FSRU, FSAR Associate Professor of Radiology Director, Stanford Body Imaging Fellowship Stanford University School of Medicine Stanford, California

Jade Wong-You-Cheong, MBChB, MRCP, FRCR Professor Department of Diagnostic Radiology and Nuclear Medicine University of Maryland School of Medicine Director of Ultrasound University of Maryland Medical Center Baltimore, Maryland

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1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899

IMAGING ANATOMY: ULTRASOUND, SECOND EDITION

ISBN: 978-0-323-54800-7

Copyright © 2018 by Elsevier. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Publisher Cataloging-in-Publication Data Names: Woodward, Paula J. Title: Imaging anatomy. Ultrasound / [edited by] Paula J. Woodward. Other titles: Ultrasound. Description: Second edition. | Salt Lake City, UT : Elsevier, Inc., [2017] | Includes bibliographical references and index. Identifiers: ISBN 978-0-323-54800-7 Subjects: LCSH: Human anatomy--Handbooks, manuals, etc. | Ultrasonic imaging--Handbooks, manuals, etc. | MESH: Ultrasonography--methods--Atlases. | Anatomy, Cross-Sectional--Atlases. Classification: LCC QM25.I43 2017 | NLM WN 17 | DDC 616.07’543--dc23 International Standard Book Number: 978-0-323-54800-7 Cover Designer: Tom M. Olson, BA Cover Art: Richard Coombs, MS Printed in Canada by Friesens, Altona, Manitoba, Canada Last digit is the print number: 9 8 7 6 5 4 3 2 1

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Dedication

To Anthony Why? You know why! But may you keep asking why (and why not) throughout your life. In those questions, you’ll find a marvelous adventure. Love, Lala PJW

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Contributing Authors Jill M. Abrigo, MD, DPBR

Anne Kennedy, MD

Clinical Tutor Department of Diagnostic Radiology and Organ Imaging The Chinese University of Hong Kong Hong Kong (SAR), China

Professor of Radiology Adjunct Professor of Obstetrics and Gynecology Executive Vice Chair of Radiology Codirector of Maternal Fetal Diagnostic Center University of Utah School of Medicine Salt Lake City, Utah

Shweta Bhatt, MD Associate Professor Department of Imaging Sciences University of Rochester Medical Center Rochester, New York

Winnie C. W. Chu, MBChB, FRCR Professor Department of Diagnostic Radiology and Organ Imaging The Chinese University of Hong Kong Hong Kong (SAR), China

Richard E. Fan, PhD Engineering Research Associate Department of Urology Stanford University School of Medicine Stanford, California

Bryan R. Foster, MD

Assistant Professor Department of Radiology Oregon Health & Science University Portland, Oregon

Simon S. M. Ho, MBBS, FRCR Assistant Professor Department of Diagnostic Radiology and Organ Imaging The Chinese University of Hong Kong Hong Kong (SAR), China

Stella Sin Yee Ho, RDMS, RVT, PhD Adjunct Associate Professor Department of Imaging & Interventional Radiology Prince of Wales Hospital Faculty of Medicine The Chinese University of Hong Kong Hong Kong (SAR), China

Barton F. Lane, MD Assistant Professor Clinical Director of CT Department of Diagnostic Radiology and Nuclear Medicine University of Maryland School of Medicine Baltimore, Maryland

Ryan K. L. Lee, MBChB, FRCR, FHKAM (Radiology) Associate Consultant and Clinical Assistant Professor (Honorary) Department of Imaging and Interventional Radiology Prince of Wales Hospital Faculty of Medicine The Chinese University of Hong Kong Hong Kong (SAR), China

Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology) Associate Consultant and Clinical Associate Professor (Honorary) Department of Imaging and Interventional Radiology Prince of Wales Hospital Faculty of Medicine The Chinese University of Hong Kong Hong Kong (SAR), China

Vivian Y. F. Leung, PhD, RDMS Adjunct Assistant Professor Department of Diagnostic Radiology and Organ Imaging The Chinese University of Hong Kong Hong Kong (SAR), China

Eric K. H. Liu, PhD, RDMS Adjunct Associate Professor Department of Imaging and Interventional Radiology The Chinese University of Hong Kong Hong Kong (SAR), China

Chander Lulla, MD, DMRD Consultant Sonologist RIA Clinic Mumbai, India

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Thomas A. Miller, DO

Sathi A. Sukumar, MBBS, FRCP (UK), FRCR

Assistant Professor of Pediatrics Division of Pediatric Cardiology University of Utah Salt Lake City, Utah

Consultant Radiologist University Hospital of South Manchester Manchester, United Kingdom

L. Nayeli Morimoto, MD

Staff Radiologist VA Palo Alto Healthcare System Palo Alto, California Clinical Instructor (Affiliated) Department of Radiology Stanford University School of Medicine Stanford, California

Clinical Instructor Department of Radiology Stanford University School of Medicine Stanford, California

Alex W. H. Ng, MBChB, FRCR, FHKCR, FHKAM (Radiology) Consultant and Clinical Associate Professor (Honorary) Department of Imaging and Interventional Radiology Prince of Wales Hospital Faculty of Medicine The Chinese University of Hong Kong Hong Kong (SAR), China

Bhawan K. Paunipagar, MBBS, MD, DNB Senior Consultant Radiologist, Head of MRI/CT Division Department of Radiology Wockhardt Hospitals, South Mumbai Mumbai, Maharashtra, India

Michael D. Puchalski, MD Professor of Pediatrics Adjunct Professor of Radiology Associate Director of Pediatric Cardiology Director of Non-Invasive Imaging University of Utah/Primary Children’s Hospital Salt Lake City, Utah

Ali M. Tahvildari, MD

Katherine To’o, MD Staff Radiologist Veterans Affairs Palo Alto Health Care System Palo Alto, California

Ashish P. Wasnik, MD Assistant Professor Department of Radiology Division of Abdominal Imaging University of Michigan Health System Ann Arbor, Michigan

Nicole S. Winkler, MD Assistant Professor of Radiology University of Utah Salt Lake City, Utah

Deyond Y. W. Siu, MBChB, FRCR Honorary Clinical Tutor Department of Diagnostic Radiology and Organ Imaging The Chinese University of Hong Kong Hong Kong (SAR), China

Roya Sohaey, MD Professor of Radiology Adjunct Professor of Obstetrics and Gynecology Director of Fetal Imaging Oregon Health & Science University Portland, Oregon

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Preface Anatomy is the fundamental infrastructure upon which all comprehension of the human body builds, in both health and disease. It is essential to everyone who practices medicine but is critical to those of us who perform and interpret ultrasound. You cannot understand what is abnormal without a thorough understanding of what is normal. That is why we wrote this book. This second edition of Imaging Anatomy: Ultrasound is the single most detailed and inclusive ultrasound anatomy text available on the market. I have always found studying anatomy a bit like reading the dictionary—there is a lot of fantastic information, but there isn’t much of a plot. Such a necessary topic is often difficult to approach. We have taken it as our mission, however, to break down those barriers and create an accessible anatomy text. Here is our story:

• The Characters: Each anatomic area (Brain & Spine, Head & Neck, Thorax, Abdomen, Pelvis,

Extremities, and Developmental Anatomy) has its own complete cast of fascinating characters (organs). There is no hero in this book though; each is as important as the next, from the Parotid Gland to the Pelvic Floor to the Metatarsals and Toes. They all have their vital role to play.

• The Story Line: Every chapter begins with Gross Anatomy, followed by Imaging Anatomy, which

includes best imaging techniques, helpful tips, and potential pitfalls. The tale is presented in an engaging, reader-friendly style. Convoluted descriptions are abandoned as key anatomic principles are outlined in a succinct, bulleted format for quick reference.

• The Illustrations: Never before has there been such a beautifully illustrated ultrasound anatomy

text. The graphics, created by our own very talented group of medical illustrators, are of extraordinary quality. Those alone would make this book worth the read. But then following the graphics are extended galleries of detailed, extensively labeled, high-quality ultrasound images. A page turner for certain.

• The Authors: Given the expansive scope of this book, it required experts in all the various anatomic regions. I am quite fortunate to have some brilliant sonologists leading and editing their areas: Drs. James Griffith (Musculoskeletal), Anil Ahuja (Head & Neck), and Aya Kamaya & Jade WongYou-Cheong (Abdomen & Pelvis). In addition to the physicians, I must acknowledge the talented sonographers whose fine work is highlighted throughout this book.

• The Editorial Staff: To publish any book (especially one of this complexity) takes an incredible

group of individuals working behind the scenes to make it happen. I would like to thank the wonderful Elsevier Salt Lake City editorial and production staff, medical illustrators, and image editors—with a special shout out to Matt Hoecherl, who helped me immeasurably. I’m extremely lucky to work with you guys.

It is with a great deal of pride that we present to you the second edition of Imaging Anatomy: Ultrasound. While it might not be an epic thriller, it does have a compelling narrative to keep the reader engaged and informed throughout.

Paula J. Woodward, MD Professor of Radiology David G. Bragg, MD and Marcia R. Bragg Presidential Endowed Chair in Oncologic Imaging Adjunct Professor of Obstetrics and Gynecology University of Utah School of Medicine Salt Lake City, Utah

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x

Acknowledgments

Lead Editor Matt W. Hoecherl, BS

Text Editors Arthur G. Gelsinger, MA Nina I. Bennett, BA Terry W. Ferrell, MS Lisa A. Gervais, BS Karen E. Concannon, MA, PhD Megg Morin, BA

Image Editors Jeffrey J. Marmorstone, BS Lisa A. M. Steadman, BS

Illustrations Richard Coombs, MS Lane R. Bennion, MS Laura C. Wissler, MA

Art Direction and Design Tom M. Olson, BA Laura C. Wissler, MA

Production Coordinators Rebecca L. Bluth, BA Angela M. G. Terry, BA Emily C. Fassett, BA

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Sections

SECTION 1: Brain and Spine SECTION 2: Head and Neck SECTION 3: Thorax SECTION 4: Abdomen SECTION 5: Pelvis SECTION 6: Upper Extremity SECTION 7: Lower Extremity SECTION 8: Obstetrics and Developmental Anatomy

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TABLE OF CONTENTS

SECTION 1: BRAIN AND SPINE 4

8 38

50

74

Scalp and Calvarial Vault Winnie C. W. Chu, MBChB, FRCR and Vivian Y. F. Leung, PhD, RDMS Brain Paula J. Woodward, MD Orbit Paula J. Woodward, MD, Stella Sin Yee Ho, RDMS, RVT, PhD, and Deyond Y. W. Siu, MBChB, FRCR Transcranial Doppler Stella Sin Yee Ho, RDMS, RVT, PhD, Deyond Y. W. Siu, MBChB, FRCR, and Paula J. Woodward, MD Vertebral Column and Spinal Cord Paula J. Woodward, MD

124

130

136

144

SECTION 2: HEAD AND NECK 86

92

98

104

112

118

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Neck Overview K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Sublingual/Submental Region K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Submandibular Region K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Parotid Region K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Upper Cervical Level K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Midcervical Level K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology)

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158

164

170

184

190

Lower Cervical Level and Supraclavicular Fossa K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Posterior Triangle K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Thyroid Gland Paula J. Woodward, MD, K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Parathyroid Glands Paula J. Woodward, MD, K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Larynx and Hypopharynx K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Trachea and Esophagus K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology), and Paula J. Woodward, MD Vagus Nerve K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Carotid Arteries K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Vertebral Arteries K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology) Neck Veins K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology)

TABLE OF CONTENTS 198

208

218

224

228

234

Cervical Lymph Nodes K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), Yolanda Y. P. Lee, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Anil T. Ahuja, MBBS (Bom), MD (Bom), FRCR, FHKCR, FHKAM (Radiology)

458

SECTION 3: THORAX

488

Thoracic Outlet Gregory E. Antonio, MD, DRANZCR, FHKCR, Eric K. H. Liu, PhD, RDMS, and Paula J. Woodward, MD Pleura Paula J. Woodward, MD, Gregory E. Antonio, MD, DRANZCR, FHKCR, and Eric K. H. Liu, PhD, RDMS Diaphragm Gregory E. Antonio, MD, DRANZCR, FHKCR, Eric K. H. Liu, PhD, RDMS, and Paula J. Woodward, MD Chest Wall Gregory E. Antonio, MD, DRANZCR, FHKCR, Eric K. H. Liu, PhD, RDMS, and Paula J. Woodward, MD Breast Nicole S. Winkler, MD

468 482

494 504

SECTION 6: UPPER EXTREMITY 530

536

554

SECTION 4: ABDOMEN 248 272 284 292 302 330 336 352 356

386 394

Liver Aya Kamaya, MD, FSRU, FSAR Biliary System L. Nayeli Morimoto, MD Spleen Ali M. Tahvildari, MD and Paula J. Woodward, MD Pancreas Barton F. Lane, MD Kidneys Jade Wong-You-Cheong, MBChB, MRCP, FRCR Adrenal Glands Paula J. Woodward, MD Bowel Sathi A. Sukumar, MBBS, FRCP (UK), FRCR Abdominal Lymph Nodes Jade Wong-You-Cheong, MBChB, MRCP, FRCR Aorta and Inferior Vena Cava Simon S. M. Ho, MBBS, FRCR, Jill M. Abrigo, MD, DPBR, and Chander Lulla, MD, DMRD Peritoneal Cavity Jade Wong-You-Cheong, MBChB, MRCP, FRCR Abdominal Wall Jade Wong-You-Cheong, MBChB, MRCP, FRCR

562

570

578

598

606

614

628

640

SECTION 5: PELVIS 408

424 434

446

Iliac Arteries and Veins Simon S. M. Ho, MBBS, FRCR, Jill M. Abrigo, MD, DPBR, and Chander Lulla, MD, DMRD Ureters and Bladder Ashish P. Wasnik, MD and Paula J. Woodward, MD Prostate and Seminal Vesicles Katherine To'o, MD, Richard E. Fan, PhD, and Paula J. Woodward, MD Testes and Scrotum Shweta Bhatt, MD and Paula J. Woodward, MD

Penis and Urethra Paula J. Woodward, MD Uterus Barton F. Lane, MD and Paula J. Woodward, MD Cervix Barton F. Lane, MD Vagina Barton F. Lane, MD Ovaries Bryan R. Foster, MD Pelvic Floor Stella Sin Yee Ho, RDMS, RVT, PhD, Deyond Y. W. Siu, MBChB, FRCR, and Paula J. Woodward, MD

646

656

668

Sternoclavicular and Acromioclavicular Joints James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Shoulder James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Axilla James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Arm James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Arm Vessels James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Elbow James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Forearm James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Forearm Vessels James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Wrist James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Hand James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Hand Vessels James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Thumb James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Fingers James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Brachial Plexus James F. Griffith, MD, MRCP, FRCR, K. T. Wong, MBChB, FRCR, FHKCR, FHKAM (Radiology), and Paula J. Woodward, MD

xv

TABLE OF CONTENTS 676

684

694

706

716

726

736

748

762

780

792

810

814

832

846

852

Radial Nerve James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Median Nerve James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB Ulnar Nerve James F. Griffith, MD, MRCP, FRCR and Bhawan K. Paunipagar, MBBS, MD, DNB

872

SECTION 7: LOWER EXTREMITY

924

Gluteal Muscles Ryan K. L. Lee, MBChB, FRCR, FHKAM (Radiology), Gregory E. Antonio, MD, DRANZCR, FHKCR, and Eric K. H. Liu, PhD, RDMS Groin Alex W. H. Ng, MBChB, FRCR, FHKCR, FHKAM (Radiology), Gregory E. Antonio, MD, DRANZCR, FHKCR, and Eric K. H. Liu, PhD, RDMS Hip Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Thigh Muscles Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Femoral Vessels and Nerves Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Knee Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Leg Muscles Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Leg Vessels Gregory E. Antonio, MD, DRANZCR, FHKCR, Eric K. H. Liu, PhD, RDMS, and Paula J. Woodward, MD Leg Nerves Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Ankle Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Tarsus Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Foot Vessels Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS Metatarsals and Toes Gregory E. Antonio, MD, DRANZCR, FHKCR and Eric K. H. Liu, PhD, RDMS

SECTION 8: OBSTETRICS AND DEVELOPMENTAL ANATOMY 860

xvi

Embryology and Anatomy of 1st Trimester Anne Kennedy, MD

888 894 906 914

934

Embryology and Anatomy of Brain Anne Kennedy, MD Embryology and Anatomy of Spine Paula J. Woodward, MD Embryology and Anatomy of Face and Neck Roya Sohaey, MD Embryology and Anatomy of Chest Paula J. Woodward, MD Embryology and Anatomy of Cardiovascular System Thomas A. Miller, DO and Michael D. Puchalski, MD Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract Paula J. Woodward, MD Embryology and Anatomy of Genitourinary Tract Paula J. Woodward, MD

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SECOND EDITION

WOODWARD GRIFFITH | ANTONIO | AHUJA WONG | KAMAYA | WONG-YOU-CHEONG

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SECTION 1

Brain and Spine

Scalp and Calvarial Vault Brain Orbit Transcranial Doppler Vertebral Column and Spinal Cord

4 8 38 50 74

Brain and Spine

Scalp and Calvarial Vault

TERMINOLOGY Definitions • Fontanelle: Broad areas of connective tissue at junction of major sutures

GROSS ANATOMY Overview • Scalp ○ Scalp has 5 layers – Skin (epidermis, dermis, hair, sebaceous glands) – Subcutaneous tissue (very vascular fibroadipose tissue) – Epicranial tissue (scalp muscles, galea aponeurotica) – Subaponeurotic tissue (loose areolar connective tissue) – Pericranium (periosteum of skull) • Skull (28 separate bones, mostly connected by fibrous sutures) ○ Cranium has several parts – Calvarial vault – Cranial base – Facial skeleton ○ Calvarial vault composed of several bones – 2 frontal bones separated by metopic suture – Paired parietal bones – Squamous occipital bone – Paired squamous temporal bones ○ 3 major serrated fibrous joints (sutures) connect bones of vault – Coronal suture – Sagittal suture – Lambdoid suture ○ Outer, inner tables – 2 thin plates of compact cortical bone – Separated by diploic space (cancellous bone containing marrow) ○ Endocranial surface – Lined by outer (periosteal) layer of dura – Grooved by vascular furrows – May have areas of focal thinning (arachnoid granulations), foramina (emissary veins)

IMAGING ANATOMY Overview • Scalp: Hypoechoic, 5 layers cannot be further separately resolved • Calvarium echogenic outer/inner tables; diploic space filled with fatty marrow and appears hypoechoic, suture appears as gap between echogenic calvarium • Frontal bones ○ Frontal sinuses show wide variation in aeration ○ Frontal bones often appear thickened, hyperostotic (especially in older females) • Parietal bones ○ Areas of parietal thinning, granular foveolae (for arachnoid granulations) common adjacent to sagittal suture 4

○ Inner tables often slightly irregular (convolutional markings caused by gyri), grooved by paired middle meningeal arteries + vein • Occipital bone ○ Deeply grooved by superior sagittal, transverse sinuses ○ Internal occipital protuberance marks sinus confluence (torcular Herophili) • Temporal bones ○ Thin, inner surface grooved by middle meningeal vessels ○ Outer surface grooved by superficial temporal artery • Fontanelle: Provide acoustic window for US examination of underlying brain parenchyma ○ Anterior fontanelle ○ Between 2 frontal and 2 parietal bones, usually disappears by age 2 ○ When fused, corresponds to bregma: Meeting of sagittal, coronal sutures ○ Posterior fontanelle ○ Small, usually closes between 3-6 months of age ○ When fused, corresponds to lambda: Meeting of sagittal, lambdoid sutures ○ Pterion – Anterolateral fontanelle; closes between 3-6 months of age – H-shaped junction between frontal, parietal bones + greater sphenoid wing, squamous temporal bone ○ Asterion – Posterolateral fontanelle, persists until 2 years of age ○ Mastoid fontanelle ○ Located at junction of temporosquamous and lambdoid sutures ○ Persists until 2 years

ANATOMY IMAGING ISSUES Imaging Recommendations • High-frequency linear array transducers provide superb resolution of near-field structures • Good skin-to-transducer coupling achieved by copious use of acoustic coupling gel • Superficial standoff pad can be used to increase depth of focal zone • US can be used to evaluate cranial sutures and assists diagnosis of craniosynostosis (premature fusion of sutures)

EMBRYOLOGY Embryologic Events • Skull base formed from endochondral ossification • Calvarial vault forms via membranous ossification ○ Curved mesenchymal plates appear at day 30 ○ Extend toward each other, skull base ○ As paired bones meet in midline, metopic and sagittal sutures are induced (coronal suture is present from onset of ossification) ○ Unossified centers at edges of parietal bone form fontanelles ○ Vault grows rapidly in 1st postnatal year

Scalp and Calvarial Vault

Sagittal suture Anterior fontanelle

Brain and Spine

SCALP AND CALVARIAL VAULT

Coronal suture

Metopic suture Frontonasal suture

Anterior fontanelle Temporosquamosal suture Coronal suture Anterolateral fontanelle (pterion)

Posterior fontanelle Lambdoid suture

Posterolateral/mastoid fontanelle (asterion)

Mendosal suture

Sweat gland and duct Epidermis Sebaceous gland Hair follicle Subcutaneous fibroadipose tissue

Dermis Superficial, deep vascular plexi Epicranial aponeurosis Subaponeurotic areolar tissue

Pericranium Diploic space

Outer table, calvarium Inner table, calvarium Venous "lake"

(Top) Graphic depiction of an infant cranium, frontal view, is shown. The anterior fontanelle is present between 2 frontal and 2 parietal bones, which usually close by 2 years of age. When fused, this site corresponds to bregma: The meeting point of sagittal and coronal sutures. (Middle) Lateral view of an infant calvarial vault is shown. The posterior fontanelle is small and usually closes by 3-6 months of age. When fused, this corresponds to lambda: The meeting of sagittal and lambdoid sutures. The anterolateral fontanelle (pterion) closes at ~ 3 months of age. The posterolateral fontanelle (asterion) often persists until 2 years of age. (Bottom) Scalp and calvarium are depicted in cross section. The 5 scalp layers are depicted. Skin consists of epidermis and dermis. Hair follicles and a sebaceous gland, the subcutaneous fibroadipose tissue, and sweat glands and ducts as well as superficial and deep cutaneous vascular plexi are shown.

5

Brain and Spine

Scalp and Calvarial Vault US AND T2WI MR, SCALP US gel Scalp Outer table of calvarium Periosteum covering calvarium Inner table of calvarium Cortical v. in subarachnoid space

Superior sagittal sinus

Subarachnoid space Cerebral cortex

US gel Scalp Outer table of calvarium Inner table of calvarium

Cortical v. in subarachnoid space Subarachnoid space

Cerebral cortex

Cerebral sulcus

Scalp

Outer table of calvarium Diploic space

Superior sagittal sinus

Inner table of calvarium

Subarachnoid space Cerebral hemisphere

(Top) Anterior coronal US scan through the anterior fontanelle shows the scalp covering the frontal bone of the calvarial vault. The 5 layers of the scalp are as follows: Skin, connective tissue consisting of lobules of fat, artery and emissary vein, aponeurosis, loose connective tissue, which accounts for mobility of the scalp on the underlying bone and periosteum adhering to the outer table of skull. These 5 layers, however, cannot be resolved by US. (Middle) Midsagittal scan through the anterior fontanelle shows the scalp covering the frontal bone of the calvarial vault. Beneath the inner table of the calvarial vault is the anechoic subarachnoid space. (Bottom) Coronal T2 MR shows the hypointense outer and inner table of calvarium. The scalp and diploic space are hyperintense. The superior sagittal sinus appears as signal void structure below the inner table of calvarium.

6

Scalp and Calvarial Vault Brain and Spine

US AND T2WI MR CALVARIUM

Scalp Calvarium

Suture

Scalp Calvarium Suture

Scalp

Suture

Outer table of calvarium

Cortical vv. in subarachnoid space Inner table of calvarium Cerebral cortex

(Top) Coronal US through the anterior fontanelle shows the scalp and calvarium. There is discontinuity in a hypoechoic band extending from the outer to inner table of the calvarial vault. This represents a normal suture. The scalp appears hypoechoic compared to the echogenic outer and inner tables of the calvarium. The 5 layers of the scalp cannot be resolved by US. (Middle) Coronal US through the anterior fontanelle shows another suture of the calvarial vault. The width and curvature of sutures is variable and should not be mistaken for a bony fracture. (Bottom) Sagittal T2 MR of the scalp and calvarium is shown. The suture line appears with the same signal intensity as the outer and inner table of calvarium. Cortical veins can be seen within the hyperintense subarachnoid space, which is immediately under the inner table.

7

Brain and Spine

Brain

8

GROSS ANATOMY Supratentorial Structures • Gyri: Complex convolutions of brain cortex; hypoechoic on ultrasound (US) • Sulci (fissure): CSF-filled grooves or clefts that separate gyri; echogenic on US ○ Sulci separate gyri, fissures separate hemispheres/lobes • Frontal lobe ○ Central sulcus separates frontal, parietal lobes ○ Precentral gyrus contains primary motor cortex ○ Premotor cortex: Within gyrus just anterior to precentral gyrus (motor cortex) ○ 3 additional major gyri: Superior frontal gyrus, middle frontal gyrus, & inferior frontal gyrus – Superior sulcus separates superior & middle gyri – Inferior sulcus separates middle & inferior gyri ○ Orbital gyri cover base of frontal lobe; gyrus rectus medially • Parietal lobe ○ Posterior to central sulcus ○ Separated from occipital lobe by parietooccipital sulcus (medial surface) ○ Postcentral gyrus: Primary somatosensory cortex ○ Superior & inferior parietal lobules lie posterior to postcentral gyrus ○ Supramarginal gyrus lies at end of sylvian fissure ○ Angular gyrus lies ventral to supramarginal gyrus ○ Medial surface of parietal lobe is precuneus, in front of parietooccipital sulcus • Occipital lobe ○ Posterior to parietooccipital sulcus ○ Primary visual cortex on medial occipital lobe ○ Cuneus on medial surface • Temporal lobe ○ Inferior to sylvian fissure ○ Superior temporal gyrus: Primary auditory cortex ○ Middle temporal gyrus: Connects with auditory, somatosensory, visual association pathways ○ Inferior temporal gyrus: Higher visual association area ○ Includes major subdivisions of limbic system • Insula ○ Lies deep in floor of sylvian fissure, overlapped by frontal, temporal, parietal opercula • Limbic system ○ Includes amygdala, hippocampus, thalamus, hypothalamus, basal ganglia, & cingulate gyrus – Cingulate gyrus extends around corpus callosum ○ Important role in emotion, behavior, & long-term memory • White matter tracts: 3 major types of fibers ○ Association fibers: Interconnect different cortical regions in same hemisphere ○ Commissural fibers: Interconnect similar cortical regions of opposite hemispheres – Corpus callosum is largest commissural fiber, links cerebral hemispheres ○ Projection fibers: Connect cerebral cortex with deep nuclei, brainstem, cerebellum, spinal cord – Internal capsule is major projection fiber

• Basal ganglia ○ Paired deep gray matter nuclei ○ Caudate nucleus, lentiform nucleus (including putamen, globus pallidus) • Thalamus ○ Paired nuclear complexes, serve as relay station for most sensory pathways

Posterior Fossa (Infratentorial) Structures • Protected space surrounded by calvarium & bounded by tentorium cerebelli superiorly & foramen magnum inferiorly • Posterior fossa contents ○ Brainstem (midbrain, pons, & medulla oblongata) anteriorly, cerebellum posteriorly ○ Cerebral aqueduct & 4th ventricle ○ CSF cisterns containing cranial nerves, vertebrobasilar arterial system & veins • Cerebellum ○ Integrates coordination & fine-tuning of movement, & regulation of muscle tone ○ 3 surfaces: Superior (tentorial), inferior (suboccipital), anterior (petrosal) ○ 2 hemispheres & midline vermis – Divided into lobes & lobules by transverse fissures – Major fissures: Primary (tentorial), horizontal (petrosal), prebiventral/prepyramidal (suboccipital) cerebellar fissures ○ Connected to brainstem by 3 paired peduncles – Superior cerebellar peduncle (brachium conjunctivum) connects cerebellum to cerebrum via midbrain – Middle cerebellar peduncle (brachium pontis) connects to pons – Inferior cerebellar peduncle (restiform body) connects to medulla • Brainstem ○ 3 anatomic divisions – Midbrain (mesencephalon): Upper brainstem, connects pons & cerebellum with forebrain – Pons: Bulbous midportion of brainstem, relays information from brain to cerebellum – Medulla: Caudal (inferior) brainstem, relays information from spinal cord to brain ○ Functional divisions – Ventral part: Large descending white matter tracts; contains midbrain cerebral peduncles, pontine bulb, medullary pyramids – Dorsal part: Tegmentum, common to midbrain, pons & medulla; contains cranial nerve nuclei & reticular formation

Ventricular System & Subarachnoid Space • Cerebral ventricles consist of paired lateral, midline 3rd, & 4th ventricles • Communicate with each other as well as central canal of spinal cord & subarachnoid space • Direction of CSF flow ○ Lateral ventricles → foramen of Monro → 3rd ventricle → cerebral aqueduct → 4th ventricle → foramina of Luschka & Magendie → subarachnoid space ○ Bulk of CSF resorption through arachnoid granulations in superior sagittal sinus

Brain – Posterior extension of cavum septi pellucidi – Begins to close from posterior to anterior from 6month gestation; 97% closed by full term ○ Cavum velum interpositum: Potential space above choroid in roof of 3rd ventricle & below fornices – Typically seen in premature infants

Brain and Spine

• Lateral ventricles ○ Paired, C-shaped, curve posteriorly from temporal horns, arch around/above thalami ○ Each has body, atrium, 3 horns (frontal, temporal, & occipital) – Occipital horn typically largest – Asymmetry is common, often L > R – Sizes change with maturity, more prominent in preterm infants ○ Atrium/trigone: Confluence of horns – Contains glomus of choroid plexus ○ Lateral ventricles communicate with each other & 3rd ventricle via Y-shaped foramen of Monro • 3rd ventricle ○ Thin, usually slit-like, between thalami – May not see fluid, just bright echogenic line on US ○ 80% have central adhesion between thalami (massa intermedia) ○ Communicates with 4th ventricle via cerebral aqueduct (of Sylvius), passing through dorsal midbrain • 4th ventricle ○ Infratentorial, diamond-shaped cavity (rhomboid fossa) along dorsal pons & upper medulla ○ Fastigium: Blind ending, dorsally pointed midline outpouching from body of 4th ventricle – Important marker for true midline vermian plane on US ○ Communicates with subarachnoid space via foramina of Magendie & Luschka ○ Terminates inferiorly at obex, which communicates with central canal of spinal cord • Choroid plexus ○ Produces CSF ○ Glomus (enlargement of choroid plexus in atrium) thickest area ○ Tapers & extends anteriorly to foramen of Monro & roof of 3rd ventricle ○ Tapers laterally into roof of temporal horns ○ Present in roof of 4th ventricle but never extends into frontal or occipital horns • Subarachnoid space/cisterns ○ CSF spaces between pia & arachnoid ○ Numerous trabeculae, septa, membranes cross subarachnoid space & create smaller compartments termed cisterns – Supratentorial/peritentorial cisterns: Suprasellar, interpeduncular, ambient (perimesencephalic), quadrigeminal cistern, & cistern of velum interpositum – Infratentorial (posterior fossa) cisterns: Prepontine, premedullary, superior cerebellar, cisterna magna, & cerebellopontine ○ All cisterns communicate with each other & with ventricular system • Midline cystic structures (normal variants) ○ Cavum septi pellucidi: Anterior to foramen of Monro, between anterior horns of lateral ventricles – 85% closed by 3-6 months after birth, some remain open into adulthood □ Once closed called septum pellucidum ○ Cavum vergae: Posterior to foramen of Monro, interposed between bodies of lateral ventricles

ANATOMY IMAGING ISSUES Imaging Approaches • Anterior fontanelle most commonly used approach ○ Sagittal scans – Midline scan: Best view for corpus callosum, cerebellar vermis – Sweep side-to-side from this position documenting key areas □ Caudothalamic groove: Most common site of germinal matrix hemorrhage □ Size of lateral ventricle □ Far lateral to assess degree of sulcal development ○ Coronal scans – Important to maintain symmetrical imaging of each 1/2 of brain – Symmetrical structures (from anterior to posterior) include: Frontal horns, bodies & trigones of lateral ventricles; caudate nuclei, putamen, internal capsule, & thalami – Midline structures (from anterior to posterior) include: Interhemispheric fissure, genu & anterior body of corpus callosum, cavum septi pellucidi, 3rd ventricle, brainstem • Posterior fontanelle ○ Best view to evaluate occipital horns for intraventricular hemorrhage – Can misinterpret clot adherent to choroid plexus from anterior fontanelle approach alone • Mastoid fontanelle ○ Located at junction of squamosal, lambdoidal, occipital sutures ○ Transducer placed about 1 cm behind helix of ear & 1 cm above tragus ○ Allows assessment of brainstem & posterior fossa ○ Best view for 4th ventricle, posterior cerebellar vermis, cerebellar hemispheres, & cisterna magna • Transtemporal ○ Temporal bone anterior to ear is thin, allowing imaging of brainstem even after sutural closure ○ Best view for cerebral peduncles & 3rd ventricle

Imaging Pitfalls • Need to know changing appearance with gestational age at birth; normal gyral pattern in 26-week preterm infant would be abnormal in term infant • Slit-like lateral ventricles common in infants, not to be mistaken for cerebral edema • Glomus of choroid plexus can be bulbous & irregular, not to be mistaken for blood clot ○ Evaluate with color Doppler & posterior fontanelle view • Echogenic material in frontal or occipital horns is clot; choroid does not extend into these horns

9

Brain and Spine

Brain GYRI AND SULCI

Central sulcus

Precentral gyrus

Postcentral gyrus

Superior frontal gyrus Supramarginal gyrus Middle frontal gyrus

Angular gyrus

Inferior frontal gyrus Superior temporal gyrus

Sylvian fissure Occipital pole

Middle temporal gyrus Inferior temporal gyrus

Cerebellum Brainstem

Superior frontal gyrus Middle frontal gyrus

Superior frontal sulcus

Inferior frontal gyrus Precentral sulcus Precentral gyrus Central sulcus Postcentral gyrus Postcentral sulcus Superior parietal lobule Inferior parietal lobule

Occipital lobe

(Top) Lateral surface of the brain depicts the major gyri and sulci. The frontal lobe extends from the frontal pole to the central sulcus. The supramarginal and angular gyri are part of the parietal lobe. The superior temporal gyrus contains the primary auditory cortex, and also forms the temporal operculum. The insular cortex lies within the sylvian fissure beneath the frontal, temporal, and parietal opercula. (Bottom) Surface anatomy of the cerebral hemisphere, seen from above, shows the gyri and lobules on the left, and the sulci on the right. The central (Rolandic) sulcus separates the anterior frontal lobe from the posterior parietal lobe. The precentral gyrus of the frontal lobe is the primary motor cortex while the postcentral gyrus of the parietal lobe is the primary sensory cortex. On ultrasound, the sulci appear echogenic while the adjacent gyri are hypoechoic.

10

Brain Brain and Spine

MIDLINE, SUBARACHNOID SPACE

Medial frontal gyrus Central sulcus Cingulate sulcus Precuneus Cingulate gyrus Parietooccipital sulcus Genu of corpus callosum Fornix

Septum pellucidum Calcarine sulcus

Anterior commissure Splenium of corpus callosum Uncus Parahippocampal gyrus

Central sulcus Pericallosal cistern Parietooccipital sulcus Cistern of velum interpositum Interpeduncular cistern Suprasellar cistern

Superior cerebellar cistern Quadrigeminal cistern

Prepontine cistern

Premedullary (medullary) cistern Cisterna magna

(Top) This midline sagittal graphic shows a medial view of the cerebral hemisphere. The corpus callosum represents the major commissural fiber. The fornix and cingulate gyrus are important in the limbic system. The cingulate gyrus is involved with emotion formation and processing, learning, and memory. (Bottom) Sagittal midline graphic through the interhemispheric fissure depicts subarachnoid spaces with CSF (blue) between the arachnoid (purple) & pia (orange). The central sulcus separates the frontal lobe (anterior) from the parietal lobe (posterior). The pia mater is closely applied to the brain surface, whereas the arachnoid is adherent to the dura. The ventricles communicate with the cisterns and subarachnoid space via the foramina of Luschka and Magendie. The cisterns normally communicate freely with each other.

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Brain and Spine

Brain VENTRICULAR SYSTEM

Body of lateral ventricle

Foramen of Monro 3rd ventricle

Frontal horns

Suprapineal recess Occipital horns

Location of massa intermedia Optic (chiasmatic) recess, 3rd ventricle Infundibular recess, 3rd ventricle

Atrium Pineal recess Cerebral aqueduct (of Sylvius) 4th ventricle

Temporal horn Foramen of Magendie Paired foramina of Luschka

Obex

Schematic 3D representation of the ventricular system, viewed in the sagittal plane, demonstrates the normal appearance and communicating pathways of the cerebral ventricles. CSF flows from the lateral ventricles through the foramen of Monro into the 3rd ventricle, and from there through the cerebral aqueduct into the 4th ventricle. CSF exits the 4th ventricle through the foramina of Luschka and Magendie to the subarachnoid space.

12

Brain Brain and Spine

STANDARD US PLANES VIA ANTERIOR FONTANELLE

(Top) Graphic shows the common coronal planes used in ultrasound brain scanning: Plane A to F from front to back. Cerebral cortex (CC); body of lateral ventricle (BV); frontal horn (FH); occipital horn (OH); massa intermedia (M); pineal recess (PR); 3rd ventricle (3); temporal horn (TH); supraoptic recess (SR); infundibular recess (IR); 4th ventricle (4); cerebellum (CB). (Bottom) Graphic shows the common sagittal planes used in ultrasound brain scanning: Plane A to C from midline to lateral. Cerebellum (CB); cerebral cortex (CC); corpus callosum (Coc); cavum septi pellucidi (CSP); frontal horn (FH); foramen of Monro (FM); occipital horn (OH); temporal horn (T); 3rd ventricle (3); 4th ventricle (4).

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Brain and Spine

Brain CORONAL US VIA ANTERIOR FONTANELLE Superior frontal gyrus Interhemispheric fissure

Frontal lobes Cortical sulcus Orbital roof Eye

Falx cerebri

Centrum semiovale

Anterior clinoid Sella turcica

Interhemispheric fissure Genu, corpus callosum Frontal horn Caudate nucleus (head) Cingulate sulcus Sylvian fissure

Insula

Internal capsule

Temporal lobe

Middle cranial fossa

(Top) The 1st of 9 coronal ultrasounds of the brain through the anterior fontanelle in a term infant shows the frontal lobes lie in the anterior cranial fossa with orbital cavities deep to the floor of the skull base. (Middle) An image centered more posteriorly demonstrates a slightly more echogenic white matter region of the brain parenchyma known as the centrum semiovale. Parts of the skull base, including the sella turcica and anterior clinoid, can be seen. (Bottom) Image acquired just anterior to the foramen of Monro. The frontal horns of lateral ventricles are now seen. No choroid plexus should be present in the frontal horns. Any intraventricular echogenic material seen at this level should raise the suspicion of blood clot. The head of the caudate nucleus is inferior and lateral to the frontal horn and is separated from the lentiform nucleus by the internal capsule.

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Brain

Interhemispheric fissure

Falx

Brain and Spine

CORONAL T1 MR

Superior frontal gyrus Middle frontal gyrus

Superior frontal sulcus Inferior frontal gyrus Inferior frontal sulcus

Straight gyrus/gyrus rectus

Orbital roof

Eye

Superior frontal gyrus Middle frontal gyrus Inferior frontal gyrus

Interhemispheric fissure

Centrum semiovale

Straight gyrus Optic n.

Medial rectus muscle

Superior frontal gyrus Middle frontal gyrus Inferior frontal gyrus Genu, corpus callosum Caudate head

Cingulate gyrus Frontal horn Internal capsule

Sylvian fissure

Temporal lobe Middle cranial fossa

(Top) The 1st of 9 coronal T1 MR images through the cerebral hemispheres from anterior to posterior is shown. The images are taken through planes/levels corresponding to those commonly used for ultrasound scans through the anterior fontanelle. The 3 major frontal gyri are shown: Superior frontal gyrus, middle frontal gyrus, and inferior frontal gyrus, separated by the superior and inferior frontal sulci. The straight gyrus (gyrus rectus) is the most medial, covering the base of the frontal lobe. (Middle) Slightly more posteriorly, the major white matter tracts, the centrum semiovale, are seen. (Bottom) This image shows the frontal horns. Immediately below each frontal horn is the caudate head, separated from the lentiform nucleus by the internal capsule.

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Brain and Spine

Brain CORONAL US VIA ANTERIOR FONTANELLE Cingulate gyrus Corpus callosum, body Lateral ventricle Cavum septi pellucidi Caudate Lateral ventricle

Foramen of Monro

Foramen of Monro

3rd ventricle

Cavum septi pellucidi Corpus callosum Lateral ventricle Choroid plexus in foramen of Monro Choroid plexus in roof of 3rd ventricle Choroid plexus in foramen of Monro

Falx Frontal lobe Body of lateral ventricle Choroid plexus Thalamus Sylvian fissure Quadrigeminal cistern

Vermis

Choroidal fissure Temporal lobe Tentorium cerebelli Cerebellar hemisphere

(Top) The 4th of 9 coronal ultrasounds through the anterior fontanelle in a term infant is shown. This image is taken at the level of the foramen of Monro. The lateral ventricles are seen with the body of the caudate nucleus and anterior portions of the thalami below. It is not uncommon that the ventricles are asymmetric. (Middle) Just slightly more posterior, the choroid plexus is present on the floor of the lateral ventricles and roof of the 3rd ventricle. The 3 echogenic foci of the choroid plexus, 1 on the roof of the 3rd ventricle and 2 located bilaterally on the floor of the lateral ventricles, are known as the 3-dot sign. (Bottom) A more posterior coronal image at the level of the quadrigeminal cistern is shown. Another ultrasound landmark, known as the echogenic star, is seen, which comprises the choroidal fissures as the upper limbs and tentorium cerebelli as the lower limbs. Inferiorly, the vermis appears echogenic, while the cerebellar hemispheres on both sides are hypoechoic.

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Brain

Body, corpus callosum

Brain and Spine

CORONAL T1 MR

Foramen of Monro Lateral ventricle Caudate 3rd ventricle

Inferior frontal gyrus Superior temporal gyrus

Ambient cistern

Middle temporal gyrus Inferior temporal gyrus Occipitotemporal gyrus

Brainstem

Body, corpus callosum Insula Lateral ventricle 3rd ventricle Temporal horn

Sylvian fissure Thalamus Choroidal fissure

Temporal lobe Brainstem

Falx cerebri

Cerebellar hemisphere

Body, corpus callosum

Sylvian fissure Body of lateral ventricle Quadrigeminal cistern Thalamus Temporal horn Tentorium cerebelli

Choroidal fissure

Cerebellar vermis Cerebellar hemisphere

(Top) The 4th of 9 coronal T1 MR images through the cerebral hemispheres from anterior to posterior is shown. The images are taken through planes/levels corresponding to those commonly used for ultrasound through the anterior fontanelle. This image is taken at the level of the foramen of Monro where both lateral ventricles unite, becoming the 3rd ventricle in the midline. (Middle) This image shows the thalami on either side of the 3rd ventricle. (Bottom) This image slightly more posterior shows the quadrigeminal cistern in the midline. Together with choroidal fissures and tentorium cerebelli on both sides, it gives rise to the characteristic echogenic star appearance on coronal ultrasound scanning.

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Brain and Spine

Brain CORONAL US VIA ANTERIOR FONTANELLE Interhemispheric fissure

Parietal lobe Sylvian fissure Glomus of choroid plexus Splenium, corpus callosum Occipital horn

Falx

Parietal lobe

Periventricular halo

Occipital lobe

Falx

White matter

Occipital lobe

(Top) The 7th of 9 coronal ultrasounds obtained through the anterior fontanelle in a term infant is shown. This image is taken at the trigone of the lateral ventricles. The glomus of the choroid plexus appears highly echogenic, nearly occupying the whole trigone. (Middle) This image, slightly posterior to the trigone, shows mildly echogenic white matter regions within the corona radiata, lateral and parallel to both trigones of the lateral ventricles. These regions are known as the periventricular halo, a normal finding, present in almost all normal mature and premature neonates. The echogenicity of the halo should be less than that of the choroid plexus and symmetrical in appearance. (Bottom) The most posterior coronal image shows the cortex of the occipital lobe with multiple echogenic sulci extending medially from the lateral margin of the brain. The falx is in midline.

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Brain

Interhemispheric fissure

Cingulate gyrus

Falx cerebri

Brain and Spine

CORONAL T1 MR

Parietal lobe

Body of lateral ventricle Glomus of choroid plexus

Sylvian fissure Splenium, corpus callosum

Vermis Tentorium cerebelli Cerebellar hemisphere

Superior sagittal sinus Superior parietal lobule Falx cerebri

Corona radiata Calcarine sulcus

Middle occipital gyrus Inferior occipital gyrus

Superior sagittal sinus

Interhemispheric fissure

Occipital lobe

(Top) The 7th of 9 coronal T1 MR images through the cerebral hemispheres from anterior to posterior are shown. The images are taken through planes/levels corresponding to those commonly used for ultrasound scans through the anterior fontanelle. The glomus of the choroid plexus is prominent within the trigones of the lateral ventricles. (Middle) More posterior image shows the posterior parietal lobes and occipital lobes. Cerebral hemispheres are separated by the interhemispheric fissure, which contains the falx cerebri. The ventricular system and cerebellum are no longer seen at this level. The primary visual cortex is on the medial aspect of the occipital lobe. (Bottom) This most posterior image shows gyri of the occipital lobe and a portion of the superior sagittal sinus, which arches posteriorly to the torcular Herophili.

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Brain and Spine

Brain SAGITTAL US VIA ANTERIOR FONTANELLE Frontal lobe Cingulate sulcus Cingulate gyrus Callosal sulcus above corpus callosum Genu, corpus callosum Inferior frontal lobe

Fornix Occipital lobe

3rd ventricle Pons

Medulla

4th ventricle Vermis Cisterna magna

Cingulate sulcus Cingulate gyrus Callosal sulcus above corpus callosum Parietal lobe Thalamus Occipital lobe Midbrain Pons Medulla

4th ventricle

Vermis

Central sulcus Frontal lobe Frontal horn of lateral ventricle Body of lateral ventricle

Caudate nucleus (head) Caudothalamic groove

Thalamus

Temporal lobe Cerebellum

(Top) The 1st of 6 sagittal ultrasounds of the brain through the anterior fontanelle in term infant is shown. This image, obtained in the midline, shows the corpus callosum as a hypoechoic curving line. Callosal and cingulate sulci are parallel to and above the corpus callosum. The midline also allows evaluation of the posterior fossa structures, including the brainstem anteriorly and the vermis posteriorly. The 4th ventricle is well seen in this plane and appears as a triangular fluid-filled structure at the level of the mid vermis. (Middle) Parasagittal image obtained angling slightly lateral to midline: The thalamus and echogenic sulci can now be seen more clearly. (Bottom) Parasagittal image obtained by angling more laterally shows the caudothalamic groove, the junction between the caudate nucleus and the thalamus. This is the area of the vascular germinal matrix, which is vulnerable to hemorrhage in preterm infants.

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Brain

Cingulate sulcus

Superior sagittal sinus

Brain and Spine

SAGITTAL T1 MR

Splenium corpus callosum Cingulate gyrus Genu, corpus callosum Callosal sulcus Fornix Midbrain Pons

3rd ventricle Cerebral aqueduct 4th ventricle

Medulla

Central sulcus Splenium, corpus callosum Thalamus Midbrain Pons Prepontine cistern Premedullary cistern

Frontal lobe Lateral ventricle Caudate head Caudothalamic groove Thalamus Temporal lobe

Tentorium cerebelli 4th ventricle Cerebellar hemisphere

Central sulcus Parietal lobe Parietooccipital sulcus

Occipital lobe Cerebellar hemisphere

(Top) The 1st of 6 sagittal T1 MR images through the cerebral hemispheres from midline to lateral is shown. The images are taken through planes/levels corresponding to those commonly used for ultrasound scans through the anterior fontanelle. The midline sagittal image shows the corpus callosum, the largest commissural fiber connecting both cerebral hemispheres. (Middle) Parasagittal image just off the midline is shown. The tentorium cerebelli is a dural fold separating the brain into supratentorial and infratentorial compartments. (Bottom) More lateral image shows the caudothalamic groove between the caudate head and thalamus. The parietooccipital sulcus is an important landmark, differentiating the parietal from the occipital lobes.

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Brain and Spine

Brain SAGITTAL US VIA ANTERIOR FONTANELLE

Frontal lobe

Body of lateral ventricle

Thalamus Choroid plexus in atrium Sylvian fissure

Occipital horn

Temporal lobe

Cortical sulcus Cortical gyrus

Peritrigonal blush

Sylvian fissure

Occipital lobe

Temporal lobe

Cortical sulcus Cortical gyrus

Sylvian fissure

Temporal lobe

(Top) This parasagittal image shows the glomus of the choroid plexus in the trigone. The glomus tapers anteriorly as it courses along the floor of the lateral ventricle to the foramen of Monro and continues along the roof of the 3rd ventricle. It also tapers posteriorly from the trigone into the temporal horn of each lateral ventricle. Glomus may appear bulbous and irregular at the trigone and should not be mistaken as a blood clot. (Middle) This parasagittal image is obtained just lateral to the lateral ventricle. The echogenic white matter of the brain just posterior and superior to the ventricular trigone is known as the peritrigonal blush or halo, representing radiating white fiber tracts (corona radiata). The peritrigonal blush is more prominent in premature than in term neonates. (Bottom) This is the last and most lateral sagittal image obtained, showing the mature sulcal pattern with hyperechoic sulci and hypoechoic gyri.

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Brain Brain and Spine

SAGITTAL T1 MR

Choroid plexus in atrium of lateral ventricle Choroid plexus in temporal horn of lateral ventricle

Occipital horn

Cerebellar hemisphere

Central sulcus Precentral gyrus

Postcentral gyrus

Superior frontal gyrus

Sylvian fissure Superior temporal gyrus Middle temporal gyrus

Superior frontal gyrus

Central sulcus

Middle frontal gyrus Inferior frontal gyrus Superior temporal gyrus Middle temporal gyrus

Inferior temporal gyrus

(Top) This image shows a prominent choroid plexus within the atrium of the lateral ventricle, which tapers posteriorly and extends into the temporal horn. (Middle) This parasagittal image shows the sylvian fissure bound superiorly by the frontal operculum and inferiorly by the temporal operculum. The central sulcus separates the frontal lobe anteriorly from the parietal lobe posteriorly. (Bottom) This image shows the most lateral portion of the sylvian fissure. The temporal lobe is inferior to the sylvian fissure. The superior temporal gyrus contains the primary auditory cortex. The middle temporal gyrus connects auditory, somatosensory, and visual association pathways. The inferior temporal gyrus is the higher visual association area.

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Brain and Spine

Brain PREMATURE INFANT (23 WEEKS 6 DAYS)

Corpus callosum

Sylvian fissure Opercula Insula

Tips of temporal horns Cavum septi pellucidi

Caudate

Caudothalamic groove Thalamus

Parietooccipital sulcus

Occipital lobe

Cerebellum

Sylvian fissure

Eye Temporal lobe

(Top) This coronal image of a very premature infant, born at 23-weeks 6-days gestational age, shows a very large, square, open sylvian fissure. The opercula have not yet grown to cover the insula. (Middle) Sagittal image through the caudothalamic groove in the same case shows the parietooccipital sulcus. The cortex otherwise appears "flat" without gyri/sulcal formation. (Bottom) Another sagittal image further lateral shows similar findings with no cortical gyri/sulci seen.

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Brain

Parietal operculum

Brain and Spine

SYLVIAN FISSURE AT DIFFERENT AGES

Sylvian fissure Insula Temporal operculum

Thalamus

Temporal lobe Cerebellar vermis Cerebellar hemisphere Cisterna magna

Parietal operculum

Sylvian fissure

Insula

Temporal operculum

Cerebellar hemisphere Tentorium cerebelli Cisternal magna

Choroid in lateral ventricles and roof of 3rd ventricle Sylvian fissure Cortical sulci 3rd ventricle

(Top) A different infant born at 29 weeks 1 day shows more advanced development of the sylvian fissures. The frontal, temporal, and parietal lobes all have opercula, which have grown to cover the insula. (Middle) At 31 weeks 6 days the opercula have grown to cover the insula. (Bottom) Another coronal image through the level of the sylvian fissure in a full-term infant shows multiple gyri and sulci over the convexities of the brain. It is important to understand the developmental anatomic changes; lack of cortical sulci may be normal for preterm infants, depending on the gestational age at delivery, but is very abnormal at term.

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Brain and Spine

Brain SAGITTAL US VIA POSTERIOR FONTANELLE

Posterior fontanelle

Body, corpus callosum

Splenium, corpus callosum

Thalamus Midbrain Pons

Vermis 4th ventricle

Medulla

Thalamus Glomus of choroid

(Top) Although routine scanning is performed via the anterior fontanelle, the posterior fontanelle is another alternative, particularly when it is difficult seeing more posterior structures in the brain. (Middle) This scan through the posterior fontanelle in a 26-week premature infant was performed to better evaluate the corpus callosum. The splenium is particularly well seen in this view. (Bottom) Color Doppler image shows flow within the choroid plexus of the glomus. The posterior fontanelle view can be helpful to differentiate bulky choroid from clot. The occipital horn does not contain choroid plexus, and any echogenic material in the occipital horn should raise the suspicion of intraventricular hemorrhage.

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Brain Brain and Spine

AXIAL US THROUGH TEMPORAL BONE

Anterior fontanelle Temporosquamosal suture Coronal suture

Squamous part of temporal bone

Lambdoid suture Mastoid/posterolateral fontanelle

3rd ventricle (walls coapted)

Interhemispheric fissure Thalamus

Occipital lobe

Insula

Sylvian fissure

Temporal lobe

Midbrain

Interpeduncular cistern Cerebellar vermis Cerebral peduncle Ambient cistern

(Top) Graphic of the transtemporal acoustic window is shown. The transducer is placed more anterior and superior than the mastoid fontanelle approach. The temporal bone anterior to the ear is thin enough to allow imaging of the brainstem even after closure of the temporosquamosal suture. This acoustic window allows the best assessment of cerebral peduncles and the 3rd ventricle. (Middle) Transtemporal axial scan in a 29-week premature infant shows intracranial anatomy in a plane similar to CT or MR. (Bottom) The temporal bone anterior to the ear is thin, allowing imaging of the brainstem even after sutural closing. This is the best view for the cerebral peduncles and midbrain.

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Brain and Spine

Brain CEREBELLUM AND POSTERIOR FOSSA Quadrigeminal plate cistern Superior cerebellar cistern Midbrain (mesencephalon)

Cerebral aqueduct Primary/tentorial fissure

Pons Horizontal/petrosal fissure Basilar artery Medulla

Prepyramidal/suboccipital fissure Cisterna magna

Cervical spinal cord

Thalamus

Midbrain Pons

4th ventricle

Medulla Vermis

Cisterna magna

4th ventricle

Vermis

Cerebellar hemispheres

(Top) Sagittal midline graphic of the posterior fossa shows the anterior brainstem and posterior cerebellum separated by the 4th ventricle. The brainstem consists of midbrain (mesencephalon), pons, and medulla. The cerebellum has superior (tentorial), inferior (suboccipital), and anterior (petrosal) surfaces. The primary (tentorial) fissure and horizontal (petrosal) fissures divide the vermis and cerebellar hemispheres into lobules. (Middle) This midline sagittal view shows the brainstem. The pons is easily identified by its anterior bulge. (Bottom) A coronal image through the anterior fontanelle of a premature infant, born at 29 weeks 1 day, shows symmetric cerebellar hemispheres. The vermis is midline, covers the 4th ventricle, and is more echogenic than the rest of the cerebellum.

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Brain

Anterior fontanelle

Brain and Spine

POSTERIOR FOSSA VIA MASTOID APPROACH

Coronal suture Posterior fontanelle Temporosquamosal suture

Lambdoid suture

Mastoid/posterolateral fontanelle

Occipital lobe

Vermis Cerebral peduncles

Cisterna magna

4th ventricle Cerebellar hemisphere

4th ventricle Vermis Cisterna magna

Cerebellar folia

(Top) The mastoid/posterolateral fontanelle is located at the junction of temporosquamosal, lambdoidal, and occipital sutures. It allows assessment of brainstem and posterior fossa structures, which are not well demonstrated in the standard planes through the anterior fontanelle. The transducer is placed ~ 1 cm behind the helix of ear and 1 cm above the tragus. This acoustic window allows the best visualization of 4th ventricle, posterior cerebellar vermis, cerebellar hemispheres, and cisterna magna. (Middle) The mastoid approach allows for detailed evaluation of the posterior fossa structures. This is a premature infant (27 weeks 5 days), which is evident by the lack of cortical gyri and cerebellar folia. (Bottom) Another mastoid view in an infant born at 37 weeks shows maturation with extensive folia on the surface of the cerebellum.

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Brain and Spine

Brain CAVUM SEPTI PELLUCIDI ET VERGAE Cavum septi pellucidi Frontal horn

Occipital horn

Corpus callosum

Cavum vergae

Frontal horn Cavum septi pellucidi

3rd ventricle

Frontal horn

Cavum septi pellucidi

Corpus callosum Cavum septi pellucidi et vergae

Midbrain Pons

Vermis

Medulla Cisterna magna

(Top) Coronal graphic with an axial insert shows a classic cavum septi pellucidi with a posterior extension, the cavum vergae. It creates a finger-like CSF collection between the lateral ventricles. (Middle) The cavum septi pellucidi can be quite large, especially in premature infants and should not be confused with an elevated 3rd ventricle or intracranial cyst. (Bottom) Midline sagittal image in this 27-week premature infant shows a cavum septi pellucidi continuing posteriorly into the cavum vergae. This is a common finding in premature infants. The cavum vergae is closed in 97% of full-term infants and the cavum septi pellucidi is closed in 85% of infants by 3-6 months of age; however, it can remain open until adulthood.

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Brain

Lateral ventricles

Cavum velum interpositum

Brain and Spine

CAVUM VELUM INTERPOSITUM

Fornices

Cavum velum interpositum

Internal cerebral vv. Roof of 3rd ventricle

Splenium, corpus callosum

Cavum septi pellucidi Fornices Thalami

Cavum velum interpositum

Splenium, corpus callosum

Cavum septi pellucidi et vergae

Cavum velum interpositum

(Top) Sagittal graphic with an axial insert shows a cavum velum interpositum. Note the elevation and splaying of the fornices. Also noted is the inferior displacement of the internal cerebral veins and 3rd ventricle. (Middle) Midline sagittal ultrasound shown a mildly complex cavum velum interpositum. (Bottom) This premature infant has a cavum septi pellucidi, vergae, and interpositum. Like a cavum septi pellucidi and vergae, a cavum velum interpositum is more common in premature infants.

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Brain and Spine

Brain VASCULAR ANATOMY

Superior sagittal sinus

Callosomarginal a.

Pericallosal a.

Anterior cerebral a.

Vein of Galen

Posterior cerebral a. Straight sinus

Superior cerebellar a. Basilar a.

Sinus confluence (torcular Herophili) Anterior inferior cerebellar a.

Posterior inferior cerebellar a.

Vertebral a.

This graphic shows the arteries, sinuses, and veins, which can be seen seen on a routine midline sagittal view. The anterior cerebral artery and its 2 main branches, the pericallosal and callosomarginal arteries, are easily seen on midline color Doppler ultrasound. The basilar artery is also easily identified, running anterior to the brainstem. The middle cerebral and posterior cerebral arteries are better evaluated in an axial plane using a transtemporal or mastoid approach.

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Brain

Pericallosal a.

Brain and Spine

MIDLINE COLOR DOPPLER

Cingulate gyrus

Anterior cerebral a. Corpus callosum

Basilar a.

Cingulate sulcus Callosomarginal a.

Anterior cerebral a. Pericallosal a.

Cortical branches from callosomarginal a.

Callosomarginal a. Anterior cerebral a.

Distal pericallosal a. Flash artifact Vein of Galen Straight sinus Basilar a.

(Top) Midline sagittal color Doppler image, obtained via the anterior fontanelle, shows the pericallosal artery running in the callosal sulcus, just above the corpus callosum. In a normal newborn, the pericallosal artery should be close to the surface of the corpus callosum. While in callosal agenesis, this artery remains far from the 3rd ventricle and takes an upward oblique direction. (Middle) The anterior cerebral artery divides into the pericallosal artery, which continues along the corpus callosum, and the callosomarginal artery, which courses superiorly to travel above the cingulate gyrus within the cingulate sulcus. (Bottom) Multiple cortical branches of the callosomarginal artery are seen traveling within cortical sulci.

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Brain and Spine

Brain CIRCLE OF WILLIS Interhemispheric fissure Olfactory n. (CNI) Optic n. (CNII)

Anterior communicating a. Anterior cerebral a.

Pituitary infundibulum Internal carotid a. Oculomotor n. (CNIII)

Posterior communicating a. Posterior cerebellar a.

Trigeminal n. (CNV) Superior cerebellar a. Basilar a.

Middle cerebral a.

Internal carotid a.

Anterior communicating a.

Horizontal (A1) anterior communicating a. segment

Precommunicating (P1) posterior cerebral a. segment Posterior communicating a.

Middle cerebral a.

Anterior communicating a. Anterior cerebral a. (A2 segment) Horizontal (A1) anterior communicating a. segment

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Internal carotid a. bifurcation Precommunicating (P1) posterior cerebral a. segment Posterior communicating a.

(Top) The circle of Willis illustrated in situ shows its intricate relationship to adjacent structures. It located in the suprasellar cistern just below the diencephalon. The hypothalamus, infundibular stalk, and optic chiasm lie in the middle of the circle. The horizontal (A1) anterior cerebral artery segment passes above the optic nerves (CNII); the posterior communicating artery passes above the oculomotor nerves (CNIII). The anterior communicating artery is near the midline, below the interhemispheric fissure. (Middle) The circle of Willis is shown in isolation and turned 90° counterclockwise to match the plane of the ultrasound. (Bottom) Transtemporal axial color Doppler in a premature infant with ventriculomegaly from an intracranial hemorrhage shows the circle of Willis. The anterior and middle cerebral arteries are the terminal branches of the internal carotid artery. The posterior cerebral artery is the terminal branch of the basilar artery. These 3 crucial arteries communicate via the anterior and posterior communicating arteries in a complete circle of Willis. The transtemporal approach provides the best window for evaluating the circle of Willis.

Brain Brain and Spine

CEREBRAL ARTERIES

Cortical branch of anterior cerebral a.

Middle cerebral a.

Caudate nucleus Anterior thalamostriate a. Posterior thalamostriate a. Thalamus

(Top) Doppler waveform of a cortical branch of the anterior cerebral artery shows a low-resistance waveform with abundant diastolic flow. Velocity of the cerebral artery is a reliable reflection of intracranial pressure. (Middle) Doppler waveform of the middle cerebral artery in the coronal plane is obtained by angling the beam laterally toward the sylvian fissure. A low-resistance arterial waveform is again noted. (Bottom) Color Doppler ultrasound obtained by a parasagittal scan through the anterior fontanelle shows the thalamostriate arteries. Anteriorly, the caudate nucleus is supplied by the anterior thalamostriate artery while the thalamus posteriorly is supplied by the posterior thalamostriate artery. The thalamostriate arteries arise from the middle cerebral artery.

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Brain and Spine

Brain CEREBRAL VEINS AND SINUSES Superior sagittal sinus Vein of Galen

Inferior sagittal sinus Straight sinus

Internal cerebral vv. Sinus confluence (torcular Herophili) Transverse sinus Occipital sinus Basal veins of Rosenthal Sigmoid sinus

Superior sagittal sinus

Superficial cortical v. Subarachnoid space

Superior sagittal sinus

Cortical vein entering superior sagittal sinus

Doppler waveform

(Top) This graphic shows the the connections between the major dural sinuses and deep cerebral veins. The internal cerebral veins and basal veins of Rosenthal drain into the vein of Galen, which in turn drains into the straight sinus. (Middle) Sagittal color Doppler scan through the anterior fontanelle shows a superficial cortical vein traversing the subarachnoid space and draining into the superior sagittal sinus. (Bottom) Spectral Doppler waveform of the superior sagittal sinus shows the waveform of the sinus to be pulsatile, under the effect of transmitted cardiac pulsations.

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Brain Brain and Spine

CEREBRAL VEINS AND SINUSES

Corpus callosum

Vein of Galen

Straight sinus

Straight sinus

Transverse sinus

Superior cerebellar a. 4th ventricle Vermis

(Top) Color Doppler ultrasound obtained by a midline sagittal scan through the anterior fontanelle shows the relationship of the vein of Galen and straight sinus. The vein of Galen is seen under the splenium of the corpus callosum. It receives drainage from the paired internal cerebral veins and basal veins of Rosenthal. The vein of Galen continues inferiorly into the straight sinus. The straight sinus, superior sagittal sinus, and transverse sinuses converge posteriorly, forming the torcular Herophili. (Middle) In the angled coronal plane, the straight sinus is seen in the midline between the lateral ventricles. (Bottom) Other sinuses can be evaluated using different acoustic windows. The transverse sinus can be accessed via a mastoid fontanelle approach, as shown here. The cerebral venous system is valveless, and pulsed Doppler waveforms typically show cardiac pulsations.

37

Brain and Spine

Orbit

GROSS ANATOMY Overview • Eye is embedded in ocular fat, moved by ocular muscles, and surrounded by bony orbit • Anterior segment of globe ○ Cornea: Transparent; covers iris and pupil ○ Anterior chamber: Directly behind cornea; filled with aqueous fluid for maintaining ocular pressure ○ Iris: Colored diaphragm in anterior chamber ○ Pupil: Opening in center of iris ○ Lens: Behind pupil; capable of image focusing • Posterior segment of globe ○ Vitreous body (humor): Clear, jelly-like substance in posterior chamber ○ Retina: Inner wall membrane of globe; receives image and converts it into nerve impulses ○ Macula: Center of retina; daylight and color vision ○ Fovea: Macular center; highest spatial resolution ○ Sclera: Dense, fibrous outer coating of globe ○ Choroid: Vascular layer between retina and sclera • Optic nerve: Transmits nerve impulses from retina to brain ○ Surrounded by dural sheath ○ Extends posteriorly to optic chiasm and tract

IMAGING ANATOMY Internal Contents • Ocular structures ○ Lens: Well-defined, oval, echolucent structure behind iris ○ Vitreous cavity: Echolucent posterior compartment ○ Retina: Layer subjacent to vitreous ○ Macula: Appears as short, bright reflector ○ Sclera: Highly reflective; thickness ↑ with ↓ eye size (anterior: 0.6 mm and posterior: 1.0 mm) ○ Choroid: Normally indistinguishable from overlying retina and underlying sclera; vascular with color Doppler • Extraocular muscles ○ Rectus muscles: Periglobal, hypoechoic structures with origin from annulus of Zinn – Medial rectus: Thickest and easiest to examine – Lateral rectus: Patient's nose may interfere with transducer movement during examination – Inferior rectus: Difficult to examine – Superior rectus and levator palpebrae muscles: Usually depicted as 1 complex ○ Superior and inferior oblique muscles difficult to visualize • Nerves ○ Optic nerve: Cranial nerve II (CNII) – Hypoechoic linear structure exiting globe posteromedially – Easily identified at equator of eye ○ Remainder of intraocular nerves not usually identify by ultrasound unless enlarged – Oculomotor nerve (CNIII): Motor to medial, superior, and inferior recti and levator palpebrae; parasympathetic motor to iris – Trochlear nerve (CNIV): Motor to superior oblique – Trigeminal nerve (CNV): Sensory from orbit and eyelids (V1) – Abducens nerve (CNVI): Motor to lateral rectus 38

• Arteries and veins ○ Ophthalmic artery – Major blood supply to orbit □ Largest ocular artery; fastest Doppler velocity – Enters orbit through optic foramen, below and lateral to optic nerve – Crosses over nerve to nasal side of orbit □ Straight portion easily seen on nasal side orbit □ Often tortuous in posterior orbit – Blood velocities vary with age, systemic blood pressure, smoking, and posture □ High-resistance waveform; resembles that of external carotid artery □ Dicrotic notch is usually present ○ Lacrimal artery – Large branch of ophthalmic artery – Runs along upper border of lateral rectus – Often originates before entering orbit – Sometimes derived from anterior branches of middle meningeal artery ○ Central retinal artery and vein – Most readily detectable orbital vessels – Run parallel to each other within optic nerve – Artery on nasal side and vein on temporal side – Flow unaffected by blood pressure and postural changes but affected by ↑ intraocular pressure ○ Superior ophthalmic vein – Largest vein detected in center of retrobulbar orbit – Runs obliquely and superior to optic nerve – Ends in cavernous sinus via superior orbital fissure – Enhance visualization by Valsalva maneuver ○ Inferior ophthalmic vein – Runs in inferior orbit and has 2 branches – One joins pterygoid venous plexus via inferior orbital fissure – Another frequently drains into superior ophthalmic vein ○ Posterior ciliary arteries – Seen on the nasal and temporal side of optic nerve

ANATOMY IMAGING ISSUES Imaging Recommendations • Insonation power maintained at level of low mechanical index (< 0.23) • Avoid prolonged scanning to ↓ chance of lens damage • Minimal acoustic jelly and gentle transducer pressure applied on closed eyelid during scanning to minimize eye movement due to patient discomfort

CLINICAL IMPLICATIONS Clinical Importance • Assessment of ophthalmic artery: Potential for collateral flow in proximal carotid occlusion • Evaluation of extraocular muscle thickening • Investigation of central retinal artery and vein occlusion; cranial arteritis; nonarteritic ischemic optic neuropathy; diabetic retinopathy; retinal detachment; ocular metastasis

Orbit Brain and Spine

OPTIC NERVE AND EXTRAOCULAR MUSCLES

Optic n. head Medial rectus m. Optic n.

Optic nerve sheath

Lateral rectus m.

Optic chiasm Pituitary infundibulum

Optic tract

Levator palpebrae superioris m. Superior rectus m. Trochlea Superior oblique m. Ophthalmic a.

Medial rectus m. Lateral rectus m.

Optic nerve-sheath complex

Inferior rectus m. Inferior oblique m.

(Top) The eyes are embedded in ocular fat and protected by the surrounding bony orbit. The optic nerve, chiasm, and tract form the afferent visual pathway. The medial and lateral rectus muscles are seen in this plane. The medial rectus muscle is the thickest and most easily evaluated by ultrasound. (Bottom) Frontal graphic of the right orbit is shown. The rectus muscles originate at the annulus of Zinn at the orbital apex and insert at the corneoscleral junction of the eye, forming a muscle cone. The superior oblique muscle courses through the trochlea, providing for the angled pulley motion of this muscle. The inferior oblique inserts at the inferolateral aspect of the eye. The oblique muscles are more difficult to evaluate by ultrasound.

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Brain and Spine

Orbit EXTRAOCULAR MUSCLES Globe

Lacrimal gland

Medial rectus m. Lateral rectus m.

Optic n.

Ophthalmic a.

Vitreous

Lateral rectus m.

Medial rectus m. Medial orbital wall Retrobulbar fat

Lateral orbital wall Optic n.

Vitreous

Retina

Medial rectus m. Retrobulbar fat

(Top) Axial high-resolution T1 MR at the level of the midorbit shows the medial and lateral rectus muscles on either side of the optic nerve. The ophthalmic artery is seen as it is crossing over the optic nerve from the temporal to the nasal side of orbit. (Middle) Axial grayscale ultrasound of the right orbit shows the hypoechoic medial and lateral recti running obliquely within the bony orbit. The optic nerve is surrounded by echogenic retrobulbar fat. (Bottom) This medially angled transverse ultrasound just above the optic nerve better shows the medial rectus muscle. It is the largest and most easily imaged of the recti muscles. Medial transducer angulation to evaluate the lateral rectus is often limited by the patient's nose.

40

Orbit

Superior oblique m.

Levator palpebrae superioris m.

Brain and Spine

EXTRAOCULAR MUSCLES

Superior rectus m.

Lateral rectus m.

Medial rectus m.

Inferior oblique m.

Inferior rectus m.

Levator palpebrae superioris m.

Superior rectus m. Superior ophthalmic v. Optic n.

Upper eyelid

Inferior rectus m. Inferior oblique m.

Superior rectus, levator palpebrae superioris complex

Optic n.

(Top) This graphic of the left orbit demonstrates the extraocular muscles in a sagittal plane. The superior and inferior oblique muscles attach to the sclera posterolaterally and are more difficult to evaluate with ultrasound. The levator palpebrae superioris muscle originates from the annulus of Zinn with the recti muscles. It courses above the superior rectus to insert on the upper eyelid. (Middle) High-resolution oblique sagittal MR of the eye shows the intimate relationship between the superior rectus and levator palpebrae superioris muscles. (Bottom) Sagittal grayscale ultrasound of the right orbit, oriented to match the MR, shows the superior rectus and levator palpebrae muscle complex. Although the superior rectus and levator muscles sometimes can be imaged as distinct structures, these 2 muscles are usually displayed as 1 complex with conventional technique.

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Brain and Spine

Orbit ANTERIOR GLOBE Orbicularis oculi Superior tarsus

Cornea Pupil

Lens

Anterior chamber Iris

Sclera

Cornea

Eyelid

Anterior chamber Iris

Pupil

Anterior chamber

Lens

(Top) This graphic shows the anterior eye, including (from front to back) the transparent avascular cornea, the anterior chamber filled with aqueous fluid, beneath which is the iris, pupil, and lens. (Middle) A midline axial image shows the cornea, anterior chamber, iris, and pupil. (Bottom) Angling the transducer slightly cephalad in the same patient shows the lens. It has a characteristic well-defined, oval shape

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Orbit

Ophthalmic a.

Brain and Spine

VASCULAR SUPPLY

Cavernous internal carotid a.

Petrous internal carotid a.

Extracranial internal carotid a. External carotid a. Common carotid a.

Lacrimal gland

Supraorbital a. Short posterior ciliary aa.

Lacrimal a. Optic n. Ophthalmic a.

Origin from internal carotid a. Supratrochlear v.

Nasofrontal v.

Superior ophthalmic v. Optic n.

Angular v.

Inferior ophthalmic v. Cavernous sinus

Facial v.

Pterygoid plexus Deep facial v. Retromandibular v.

(Top) The ophthalmic artery is the 1st intradural branch of the internal carotid artery and is the major blood supply of the orbit. (Middle) Axial graphic (superior view) shows the relationship of the ophthalmic artery and its branches. The ophthalmic artery crosses over the optic nerve from the temporal to nasal side in the posterior orbit. The lacrimal artery is one of the largest branches, which runs along the upper border of the lateral rectus muscle to supply the lacrimal gland. (Bottom) The superior ophthalmic vein is the largest orbital vein. It begins at the nasofrontal vein, passes through the superior orbital fissure, and ends in the cavernous sinus. The inferior orbital vein runs in the inferior orbit with one branch joining the superior ophthalmic vein and another exiting via the inferior orbital fissure to the pterygoid plexus.

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Brain and Spine

Orbit OPTIC NERVE AND VESSELS Sclera

Optic n.

Retina Central retinal a. and v. Choroid

Retina

Optic n. head

Sclera Optic n.

Choroidal aa.

Central retinal v.

Central retinal a.

(Top) Sagittal graphic of the posterior right eye at the level of the optic nerve head shows the central retinal artery and vein. These are the most easily identifiable orbital vessels. They run parallel to each other in the optic nerve with the artery on the nasal side and vein on the temporal side. (Middle) Axial grayscale ultrasound through the midglobe of the right eye shows the hypoechoic optic nerve. (Bottom) Color Doppler ultrasound in the same patient easily shows the parallel central retinal artery on the medial (nasal) side and the vein on the lateral (temporal) side.

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Orbit Brain and Spine

OPHTHALMIC ARTERY

Ophthalmic a. (nasal side) Lacrimal a. (temporal side) Optic n.

Ophthalmic a.

Dicrotic notch

Ophthalmic a.

Reversed blood flow

(Top) Axial color Doppler ultrasound of the right orbit demonstrates the ophthalmic artery continuing along the nasal side of the orbit. The lacrimal artery is an early, large branch of the ophthalmic artery, which courses along the temporal side of the orbit. The ophthalmic artery is the largest artery in the orbit with the fastest blood flow and is readily detectable on color Doppler examination. It is more tortuous in the posterior orbit but is relatively straight in the nasal orbit. Normal flow direction is directed toward the transducer. (Middle) Axial spectral Doppler ultrasound of normal right ophthalmic artery is shown. The characteristic waveform is antegrade and high resistance with a dicrotic notch. Note the waveform resembles that of the external carotid artery. (Bottom) The ophthalmic artery can provide collateral circulation as shown in this patient with proximal internal carotid artery occlusion. Flow is reversed, flowing away from the transducer (blue) with retrograde flow confirmed on the Doppler tracing. In addition, the flow resistance is lowered with absent dicrotic notch. The resulting waveform is similar to that of the normal internal carotid artery.

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Brain and Spine

Orbit OPHTHALMIC VEINS

Top of globe

Superior ophthalmic v.

Inferior ophthalmic v.

Superior ophthalmic v.

Superior ophthalmic v.

Superior ophthalmic v. waveform

(Top) Axial color Doppler ultrasound of the most superior aspect of the right eye shows the ophthalmic vein as it courses over the globe. (Middle) A more posterior image shows the junction of the superior and inferior ophthalmic veins above the optic nerve. The superior ophthalmic vein runs obliquely in the center of the retrobulbar orbit receiving a branch of the inferior ophthalmic vein before it ends in the cavernous sinus via the superior orbital fissure. Note the flow direction of both veins is away from the transducer. (Bottom) Axial spectral Doppler ultrasound shows a right superior ophthalmic vein waveform, which is continuous and constant on the negative side of the trace. The flow pattern in this vessel is variable, it may be constant or phasic. In addition, flow direction may be reversed during a Valsalva maneuver.

46

Orbit Brain and Spine

3D ULTRASOUND, RIGHT ORBIT

Pupil and lens Iris

Zonular fiber and ciliary process

Nose Zygoma of maxilla

Globe

Optic n.

Bony orbital socket

Superior rectus m.

Globe

Bony orbit

(Top) 3D ultrasound of the right orbit (frontal view) using a high-resolution 12-MHz linear 3D transducer demonstrates the anterior chamber of the eye. The pupil and lens are seen surrounded by the highly reflective iris, zonular fibers, and ciliary processes. (Middle) 3D ultrasound of the right orbit (axial view) shows the optic nerve exiting from the posterior aspect of the eye. This view is useful in the investigation of retrobulbar abnormality of the orbit. (Bottom) 3D ultrasound of the right orbit (coronal view) shows the attachment of the superior rectus muscle to the eye. With proper manipulation of 3D-rendered images in 3 orthogonal planes, different extraocular muscle attachments to the eye can be demonstrated.

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Brain and Spine

Orbit OPTIC NERVE MENINGIOMA

Globe

Optic n. meningioma Medial rectus m.

Lateral rectus m.

Optic n.

Globe

Optic n. meningioma

Optic n.

Globe

Medial rectus m. Optic n.

Optic n. meningioma

(Top) Axial grayscale ultrasound of the left eye shows a histologically proven optic nerve sheath meningioma. The mass is large and moderately echogenic encasing the optic nerve and abutting the medial and lateral rectus muscles. Although the mass is identified by ultrasound, further evaluation with MR is required for complete evaluation. (Middle) Corresponding axial color Doppler ultrasound shows increased vascularity within the mass. (Bottom) Corresponding axial T1 C+ MR of the left eye shows a soft tissue mass with homogeneous contrast enhancement encasing a normal-looking optic nerve. Features are consistent with an optic nerve meningioma.

48

Orbit Brain and Spine

OCULAR MELANOMA

Anterior chamber

Posterior chamber (vitreous) Ocular melanoma Detached retina

Anterior chamber Lens

Ocular melanoma Intratumoral vessels Detached retina

Anterior chamber

Ocular melanoma

Posterior chamber (vitreous)

Detached retina

Medial rectus m.

Lateral rectus m.

(Top) Axial grayscale ultrasound of the left eye shows a histologically proven ocular melanoma. It is arising from the medial wall of the posterior chamber behind the lens. The mass is large, heterogeneous, and occupies nearly 1/3 of the posterior chamber with part of the retina "peeled" off from the underlying sclera. (Middle) Corresponding axial color Doppler ultrasound shows multiple small vessels within the mass. (Bottom) Corresponding axial T1 C+ MR of the left eye with fat saturation shows the ocular melanoma arising from the sclera of the medial wall of the posterior chamber. The mass shows homogeneous enhancement and lifts off part of the retina from the underlying sclera.

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Brain and Spine

Transcranial Doppler

TERMINOLOGY Abbreviations • Carotid arteries ○ Common carotid (CCA); internal carotid (ICA) • Cerebral arteries ○ Anterior (ACA); middle (MCA); posterior (PCA) • Communicating arteries ○ Anterior (ACoA); posterior (PCoA) • Posterior fossa vertebrobasilar arteries ○ Vertebral (VA); basilar (BA); posterior inferior cerebellar artery (PICA); anterior inferior cerebellar artery (AICA); superior cerebellar artery (SCA) • Sinuses ○ Superior sagittal (SSS); sphenoparietal (SPS); straight (SS); transverse (TS); cavernous (CS) • Cerebral veins ○ Basal vein of Rosenthal (BV); internal cerebral (ICV); great vein of Galen (GV); deep middle cerebral (dMCV); anterior cerebral (ACV)

GROSS ANATOMY Intracranial Internal Carotid Artery • Complex course with several vertical/horizontal segments, 3 genus (1 petrous, 2 cavernous) • 6 intracranial segments (cervical ICA = C1) ○ Petrous (C2), lacerum (C3), cavernous (C4), clinoid (C5), ophthalmic (C6), communicating (C7)

Anterior Cerebral Artery • Smaller, more medial terminal branch of ICA with 3 segments • A1: Horizontal or precommunicating segment ○ Extends anteromedially above optic nerve & chiasm, below medial olfactory stria • A2: Vertical or postcommunicating segment ○ From ACoA junction, ascends in interhemispheric fissure, anterior to corpus callosum rostrum • A3: Distal segment ○ Pericallosal artery; begins distal to origin of callosomarginal artery • ACoA: Communicates between A1 segments; completes anterior portion of circle of Willis • Cortical branches supply anterior 2/3 of medial hemispheres ○ Medial orbitofrontal artery (1st cortical branch) ○ Frontopolar artery arises from mid A2 ○ Pericallosal artery begins distal to origin of callosomarginal artery ○ Callosomarginal artery is smaller of 2 distal ACA branches • Perforating branches supply medial basal ganglia, corpus callosum genu, internal capsule anterior limb

Middle Cerebral Artery • Larger, lateral terminal branch of supraclinoid ICA with 4 main segments • M1: Horizontal segment ○ From terminal ICA bifurcation to MCA bifurcation • M2: Extends from MCA bifurcation to periinsular sulci ○ Superior trunk: Prefrontal, precentral, central sulcus (rolandic), anterior parietal, orbitofrontal arteries 50

• • • •

○ Inferior trunk: Posterior parietal, middle temporal, posterior temporal, occipital temporal. angular (terminal) arteries M3: Courses inferolaterally through sylvian fissure M4: Exits sylvian fissure & ramifies over cerebral convexity Cortical branches supply most of lateral surface of cerebral hemispheres; except convexity & inferior temporal gyrus Penetrating lenticulostriate branches arise from M1 & supply basal ganglia, internal & external capsules

Posterior Cerebral Artery • BA terminates into 2 PCAs, with 4 segments • P1: Precommunicating segment; extends laterally from BA to junction with PCoA • P2: Ambient segment; swings posterolaterally around midbrain • P3: Quadrigeminal segment; short segment within lateral aspect of quadrigeminal cistern behind midbrain • P4: Calcarine segment; PCA terminates above tentorium in calcarine fissure • Cortical branches supply posterior 1/3 of medial hemisphere surface, inferior temporal lobe, & occipital lobe (including visual cortex) ○ Anterior temporal artery arises from P2; courses anterolaterally & anastomoses with MCA branches ○ Posterior temporal artery arises from P2; courses posterolaterally along hippocampal gyrus ○ Medial & lateral terminal trunks; major branches include parietooccipital & calcarine arteries • Penetrating branches supply mesencephalon, thalami, posterior limb of internal capsule, optic tract ○ Thalamoperforating arteries arise from P1 ○ Thalamogeniculate arteries arise from P2 • Ventricular/choroidal branches arise from P2 & supply choroid plexus of 3rd/lateral ventricles, thalami, posterior commissure, & cerebral peduncles

Vertebrobasilar System • V3 segment (atlas loop) is extracranial/extraspinal; exits at transverse foramen (atlas) to enter into foramen magnum • V4 segment is intradural/intracranial ○ Perforates dura, enters skull through foramen magnum, courses superomedially behind clivus ○ Branches include anterior & posterior spinal arteries, meningeal branches, perforating branches to medulla & PICA – PICA: Arises from distal VA, curves around/over cerebellar tonsil, gives off perforating medullary, choroid, tonsillar, cerebellar branches • BA large median artery formed by union of VAs ○ It courses superiorly in prepontine cistern & has multiple branches – Pontine, midbrain perforating branches – AICA: Courses inferolaterally, lies ventromedial to CNVII & VIII; often loops into IAC; its size is inversely proportional to size of PICA – SCA: Arise from distal BA, course posterolaterally around mesencephalon below CNIII, tentorium; lie above CNV, often in contact with it – PCA (terminal BA branches)

Transcranial Doppler

• Dural venous sinuses lie between 2 layers of dura mater & drain intracranial veins ○ Posterosuperior sinuses: SSS, inferior sagittal, 2 TS, SS & occipital ○ Anteroinferior sinuses: 2 CS, 2 superior petrosal, 2 interCS, 2 inferior petrosal & basilar plexus • Intracranial veins: Cerebral & cerebellar veins ○ Superficial ("external") cerebral veins: Divided into superior, middle, & inferior divisions ○ Deep ("internal") cerebral veins – Drain deep parts of hemisphere & are in pairs – Run parallel with each other posteriorly beneath splenium of corpus callosum – BV: Receives ACV, dMCV, inferior striate veins – GV: Receives ICVs, BV, pericallosal veins, & veins draining superior aspect of posterior fossa □ Curves backward & upward around splenium of corpus callosum & into SS – Cerebellar veins: Superior & inferior □ Superior cerebellar veins run anteromedially across superior vermis to end in SS & ICVs □ Inferior cerebellar veins (larger) end in TS, superior petrosal, & occipital sinuses

ANATOMY IMAGING ISSUES Imaging Recommendations • Can assess intracranial stenosis & occlusive disease, monitor recanalization after thrombolysis & collateral formation ○ Preoperative compression test to evaluate collateralizing capacity of circle of Willis • Performed using low-frequency transducer (1.8-3.6 MHz) • Grayscale ultrasound: Identify main anatomical structures in correct plane, followed by color Doppler ultrasound • Unless specified, conventional color coding used ○ Red: Flow toward transducer ○ Blue: Flow away from transducer • Vessel identification depends on window used, beam angulation, insonation depth, & flow direction • Basal skull arteries are extremely variable in size, development, & course; supplementary CTA/MRA is useful to enhance its diagnostic accuracy • For difficult cases, compression test is helpful for arterial identification & assessment of collaterals ○ Must be performed by experienced investigator ○ Exclude risk of embolism in extracranial arteries prior to compression ○ For anterior circulation, compress CCA in lower neck by 2 fingers ○ For vertebrobasilar system, compress VA at mastoid slope • Normal adults: Highest velocities in MCA or ACA • Flow velocities in basal cerebral arteries show consistent decrease with increasing age

Transtemporal Approach (Most Common Approach) • Transducer on temporal bone superior to zygomatic arch • Axial mesencephalic plane ○ Identify hypoechoic, butterfly-shaped mesencephalon as landmark

○ Assess C5-C7 segments, A1 segment, M1 & M2 segments, P1 & P2 segments, PCoA ○ Also assess dMCV, BV, GV, SS, & contralateral TS • Axial ventricular plane ○ Tilting of transducer 10° upward from mesencephalic plane ○ Identify hypoechoic 3rd ventricle, echogenic pineal gland, & choroid plexus of trigone ○ Assess A2 segment, M2 & M3 segments, & P3 ○ Assess midline shift due to MCA infarction • Anterior/posterior coronal planes ○ Assess C4-C7 segments, A1 segment, M1-M3 segments, PCA, & distal BA • Normal mean velocities & depth of insonation ○ Terminal ICA: 39 ± 9 cm/sec (60-67 mm) ○ MCA: 62 ± 12 cm/sec (30-67 mm) ○ ACA: 50 ± 11 cm/sec (60-80 mm) ○ PCA: 39 ± 10 cm/sec (55-80 mm)

Brain and Spine

Intracranial Veins

Transfrontal Approach • Insonation depth of 10-16 cm • Paramedian frontal bone window ○ Slightly lateral t midline of forehead ○ Identify echogenic orbital roof, hypoechoic 3rd ventricle, & corpus callosum • Lateral frontal bone window ○ Just above lateral aspect of eyebrow ○ Identify echogenic falx cerebri, sylvian fissure, & hypoechoic mesencephalon • Assess A1 & A2 segments, M1 segment, PCA, PCoA, pericallosal artery • Also assess ICV, GV, SS

Transforaminal/Suboccipital Approach • Transducer placed between squama occipitalis & spinous process of 1st cervical vertebra • Ultrasound beam aimed at nasal bridge • Identify echogenic processus transversus & clivus • Assess VAs & BA, which are visualized as Y • Normal mean velocities & depth of insonation ○ VA: 38 ± 10 cm/sec (40-85 mm) ○ BA: 41 ± 10 cm/sec (> 80 mm)

Transorbital Approach • • • •

Problem of insonation of orbital lens Low mechanical index < 0.23 highly recommended Assess intraocular vessels, C4-C6 segments Normal mean velocities & depth of insonation ○ Ophthalmic artery: 21 ± 5 cm/sec (40-60 mm) ○ Carotid siphon: 47 ± 10 cm/sec (60-80 mm)

Submandibular Approach • Assess distal C1 & C2 segments • Normal mean velocities & depth of insonation ○ Cervical ICA: 37 ± 9 cm/sec (35-70 mm)

Imaging Pitfalls • Extensive variations; incomplete circle of Willis • Variable probe-to-vessel angle • Misdiagnosis: Hyperdynamic collaterals for stenosis; vasospasm for stenosis; displacement of basal vessels by mass lesion for occlusion 51

Brain and Spine

Transcranial Doppler DISTAL INTERNAL CAROTID ARTERY

Anterior cerebral a.

Middle cerebral a. Communicating (C7) segment

Ophthalmic (C6) segment Clinoid (C5) segment Anterior choroidal a. Anterior genu, cavernous internal carotid a.

Posterior communicating a. Cavernous C4 segment

Foramen rotundum (& a.) Lacerum C3 segment Foramen ovale (& a.) Horizontal C2 segment

Vertical C2 segment

Ophthalmic a.

Meningohypophyseal trunk Inferolateral trunk A. of foramen rotundum Vidian a.

C3 (lacerum) internal carotid a. segment

Middle meningeal a. (cut off) Internal maxillary a.

Accessory meningeal a.

(Top) Graphic shows intracranial internal carotid artery (ICA) segments. The C2 segment runs in the carotid canal and continues as the C3 segment after leaving the canal. The C4 segment, an extension of C3, has branches anastomosing extensively with external carotid artery (ECA) branches. The C5 segment ends near the anterior clinoid process and the C6 segment extends to just below the posterior communicating artery (PCoA). The C7 segment, after giving rise to the PCoA, branches into anterior cerebral artery (ACA) and middle cerebral artery (MCA). (Bottom) Graphic shows numerous ICA to ECA anastomoses through cavernous and deep facial branches of the 2 arteries, respectively. These include numerous anastomoses in and around the orbit; the small vidian artery anastomosing between the internal maxillary artery and petrous C2 segment and the accessory meningeal artery, an important branch that may supply part of the trigeminal ganglion, anastomosing with the inferolateral trunk of the cavernous ICA.

52

Transcranial Doppler

Eye

Brain and Spine

DISTAL INTERNAL CAROTID ARTERY

Internal carotid a., C5 segment

Sphenoparietal sinus

Petrous bone

Anterior cerebral a., A1 segment

Anterior choroidal a. Sphenoid bone, lesser wing Posterior communicating a. Internal carotid a., C7 segment

Posterior

Anterior

Middle cerebral a. Sphenoparietal sinus

Petrous bone Anterior choroidal a. Posterior communicating a.

Posterior

Sphenoid bone, lesser wing Anterior cerebral a., A1 segment Internal carotid a., C7 segment

Anterior

(Top) Axial color Doppler ultrasound (transorbital approach) shows the C5 segment of the ICA with flow toward the transducer. C4-C6 segments can be assessed by this approach. (Middle) Axial color Doppler ultrasound (transtemporal approach) at a plane slightly caudad to the standard mesencephalic plane shows the C7 segment of the ICA, ACA, and sphenoparietal sinus. (Bottom) Axial oblique color Doppler ultrasound (transtemporal approach) with slight caudad tilting from the standard axial mesencephalic plane shows the anterior choroidal artery and PCoA branching out from the communicating segment of the ICA.

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Brain and Spine

Transcranial Doppler ANTERIOR CEREBRAL ARTERY

Frontopolar a. branches

Gyrus rectus Interhemispheric fissure

Anterior communicating a.

Trigone, olfactory n.

Horizontal (A1) anterior cerebral a. segment

Vertical (A2) anterior cerebral a. segment Optic n. Supraclinoid internal carotid a.

Pituitary infundibulum Posterior cerebral a.

Cingulate sulcus

Callosomarginal a.

Cingulate gyrus Pericallosal a.

Distal (A3) anterior cerebral a. segment Frontopolar a. Vertical (A2) anterior cerebral a. segment

Splenial branch, anterior cerebral a. Splenial branch, posterior cerebral a.

Orbitofrontal a.

(Top) Submentovertex graphic shows the relationship of the circle of Willis and its components to the cranial nerves. Note that the normal course of the horizontal (A1) segment is over the optic nerves. (Bottom) Sagittal (midline) graphic through the interhemispheric fissure shows the relationship of the ACA and its branches to the underlying brain parenchyma. The A2 segment ascends in front of the 3rd ventricle within the cistern of the lamina terminalis. The A3 segment curves around the corpus callosum genu. The branch point of the distal ACA into the pericallosal and callosomarginal arteries varies. Almost the entire anterior 2/3 of the medial hemisphere surface is supplied by the ACA and its branches. Branches of the posterior and anterior cerebral arteries anastomose around the corpus callosum genu.

54

Transcranial Doppler Brain and Spine

ANTERIOR CEREBRAL ARTERY

Ipsilateral middle cerebral a., M1 segment Ipsilateral posterior cerebral a., P1 segment

Ipsilateral anterior cerebral a., A1 segment

Contralateral posterior cerebral a., P1 segment Posterior

Anterior

Right anterior cerebral a., A2 segment

Sphenoid bone Right anterior cerebral a., A1 segment Left anterior cerebral a., A1 segment Sella turcica

Callosomarginal a.

Pericallosal a. Anterior cerebral a., A2 segment Anterior cerebral a., A1 segment

Frontopolar a. Anterior communicating a.

Middle cerebral a. Toward vertex

Toward base of skull

(Top) Axial color Doppler ultrasound (transtemporal approach) shows the MCA/ACA junction on the mesencephalic plane, which is the most useful plane for showing the circle of Willis. However, it is limited in depicting more distal segments of the ACA, which can be visualized using a transfrontal approach. (Middle) Axial color Doppler ultrasound (paramedian frontal approach) shows the right A2 segment running along the interhemispheric fissure. Echogenic sphenoid bone and sella turcica provide important landmarks for identification of the A2 segment, which starts close to the sella turcica and tip of the sphenoid bone. (Bottom) Sagittal color Doppler ultrasound (paramedian frontal approach) shows the frontopolar artery arising anteriorly from the mid A2 segment and the callosomarginal artery branching out from the distal A2 segment. Note the pericallosal artery (A3 segment) can be seen by this approach.

55

Brain and Spine

Transcranial Doppler ANTERIOR CEREBRAL ARTERY Anterior Frontal lobe, brain Falx cerebri Ipsilateral anterior cerebral a., A2 segment Ipsilateral anterior cerebral a., distal A1 segment Mesencephalon

Contralateral anterior cerebral a., A1 segment

Posterior

Frontal lobe, brain

Anterior cerebral a., A2 segment

A2 segment, waveform

Ipsilateral anterior cerebral a., A2 segment Anterior communicating a.

Contralateral anterior cerebral a., A2 segment

Ipsilateral anterior cerebral a., A1 segment Contralateral anterior cerebral a., A1 segment

(Top) Axial color Doppler ultrasound (lateral frontal approach) shows the A2 segment as seen through the frontal bone at the lateral eyebrow. The ipsilateral A2 segment is often seen as a prominent vessel running along the hyperechoic falx cerebri with flow toward the transducer. Sometimes the contralateral distal A1 or proximal A2 segment can be depicted coursing obliquely toward the ipsilateral A2 segment, mimicking the anterior communicating artery (ACoA), which is infrequently discernible in normal subjects. (Middle) Axial spectral Doppler ultrasound (lateral frontal approach) of the A2 segment shows the typical low-resistance waveform with forward flow. (Bottom) Corresponding oblique axial reformatted CT arteriogram shows the A1 segments becoming A2 segments after the ACoA junction. They then ascend parallel in the interhemispheric fissure.

56

Transcranial Doppler

Callosomarginal a.

Brain and Spine

ANTERIOR CEREBRAL ARTERY

Distal A2 segment

Proximal A2 segment Anterior communicating a. Distal A1 segment Middle cerebral a. Posterior cerebral a. Toward vertex

Toward base of skull

Callosomarginal a. Anterior cerebral a. A2 segment

Callosomarginal a., waveform

Callosomarginal a. Pericallosal a. (A3 segment)

Anterior cerebral a., A2 segment

Anterior cerebral a., A1 segment

(Top) Sagittal color Doppler ultrasound (paramedian frontal approach) illustrates the A2 segment giving off the callosomarginal artery, which is the smaller branch of the distal ACA. It runs posterosuperiorly in cingulate sulcus and on the superior surface of the cingulate gyrus. Its flow is directed toward the transducer. (Middle) Sagittal spectral Doppler ultrasound (paramedian frontal approach) shows the antegrade, low-resistance waveform of callosomarginal artery of the A2 segment. (Bottom) Corresponding oblique sagittal reformatted CT arteriogram shows the A2 segment giving off the callosomarginal artery and becoming the A3 segment (pericallosal artery). A similar branching pattern is seen on the opposite side.

57

Brain and Spine

Transcranial Doppler MIDDLE CEREBRAL ARTERY

Orbitofrontal (lateral frontobasal) a. M1 (horizontal) middle cerebral a. segment Supraclinoid internal cerebral a.

Anterior temporal a.

Cortical (M4) branches

Cortical (M4) middle cerebral a. branches Sylvian (lateral cerebral) fissure Lenticulostriate a. Top loops of M2 segments delineate apex of sylvian fissure Opercular (M3) middle cerebral a. segments Insular (M2) middle cerebral a. segments Anterior cerebral a. (cut off)

Internal carotid a.

Middle cerebral a. bifurcation (genu) M1 (horizontal) middle cerebral a. segment Anterior temporal a.

(Top) The MCA and its relationship to adjacent structures is depicted on these graphics. The submentovertex graphic shows the left temporal lobe sectioned through the temporal horn of the lateral ventricle. The MCA supplies much of the lateral surface of the brain and is the larger of the 2 terminal branches of the ICA. (Bottom) AP graphic shows the MCA and its relationship to the adjacent brain. The MCA courses through the sylvian fissure, and the M1-M4 segments are well delineated. A few medial and numerous lateral lenticulostriate arteries arise from the top of the horizontal (M1) MCA segment, course superiorly through the anterior perforated substance, and supply the lateral basal ganglia and external capsule.

58

Transcranial Doppler

Middle cerebral a., M2 segment

Brain and Spine

MIDDLE CEREBRAL ARTERY

Middle cerebral a., M1 segment Posterior cerebral a.

Anterior cerebral a. Anterior communicating a.

Posterior

Anterior

Middle cerebral a., M1 segment Posterior cerebral a.

Internal carotid a., C7 segment

Posterior communicating a.

Posterior

Anterior

Prefrontal a.

M2 segment, superior trunk M2 segment, inferior trunk Middle cerebral a., M1 segment

Lateral orbitofrontal a.

(Top) Axial color Doppler ultrasound (transtemporal approach) on the mesencephalic plane illustrates the MCA appearing in the anterior aspect of the circle of Willis. The origin of the M1 segment can be determined accurately with identification of the MCA/ACA junction. (Middle) Axial color Doppler ultrasound (transtemporal approach) on the standard mesencephalic plane depicts the M1 segment arising from the communicating segment of the ICA with flow direction toward the transducer. (Bottom) Axial oblique color Doppler ultrasound of the MCA bifurcation (transtemporal approach) shows the superior and inferior trunks of the M2 segments. Note the MCA bifurcates in ~ 75% of normal subjects, and the rest trifurcate with an individual anterior temporal artery.

59

Brain and Spine

Transcranial Doppler MIDDLE CEREBRAL ARTERY

Ipsilateral middle cerebral a., M2 segment (superior trunk) Ipsilateral middle cerebral a., M2 segment (inferior trunk) Ipsilateral middle cerebral a., horizontal M1 segment Ipsilateral anterior cerebral a., A1 segment Mesencephalon Contralateral anterior cerebral a., A1 segment Posterior

Anterior

Small cortical branch

Middle cerebral a., M2 (insular) segment Middle cerebral a, distal M1 segment

Posterior

Ipsilateral M2 insula segment

Ipsilateral middle cerebral a., M1 segment Sphenoid bone, lesser wing Posterior cerebral a.

Ipsilateral internal carotid a. C7 segment Posterior communicating a.

Mesencephalon Contralateral internal carotid a., C7 segment

Posterior

(Top) Axial color Doppler ultrasound (transtemporal approach) of a young adult shows the M1 segment of the MCA on the standard mesencephalic plane where it starts from the ICA termination to MCA bi-/trifurcations. In young adults, the M1 usually bows dorsally. (Middle) Oblique coronal color Doppler ultrasound (transtemporal approach) of the same adult shows the M2 segment in the insula. Note that the flow direction in the M2 segment is directed toward the transducer in the proximal segment and away from the transducer as it ascends within the sylvian fissure. (Bottom) Axial color Doppler ultrasound (transtemporal approach) of the MCA in an elderly patient shows a tortuous M1 segment. Its distal portion bows ventrally, bringing the entire segment closer to sphenoid bone. The M1 segment originates near the medial aspect of the lesser wing of the sphenoid and traverses laterally and horizontally to end in the limen insulae.

60

Transcranial Doppler Brain and Spine

MIDDLE CEREBRAL ARTERY

Middle cerebral a., M1segment

M1 segment, waveform

Middle cerebral artery, M2 segment

Cortical branch, waveform M2 segment, waveform

Middle cerebral a., M1 segment

M1 segment, waveform

(Top) Axial spectral Doppler ultrasound (transtemporal approach) of the MCA in a young adult shows that the waveform pattern is of low resistance, and the mean velocity is within normal range of 62 ± 12 cm/sec. The clinical importance of assessing the MCA is its high association with stroke in diseased arteries. (Middle) Oblique, coronal, spectral Doppler ultrasound (transtemporal approach) of a young adult shows a waveform of the M2 segment, which is away from the transducer. The waveform is inseparable from that of a small neighboring cortical branch with flow toward the transducer. (Bottom) Axial spectral Doppler ultrasound (transtemporal approach) of an elderly patient shows Doppler waveform of the M1 segment. Note that accurate flow velocity measurement in an elderly patient may be difficult due to uncertainty in angle correction in a tortuous vessel.

61

Brain and Spine

Transcranial Doppler POSTERIOR CEREBRAL ARTERY

Callosal marginal a.

Pericallosal a. Splenial a.

Choroidal a. Parietooccipital a. Posterior cerebral a. Posterior communicating a.

Calcarine a.

Oculomotor n. (CNIII) Basilar artery

Posterior communicating a.

Superior cerebellar a.

Supraclinoid internal carotid a.

Anterior temporal a. Oculomotor n. (CNIII)

Precommunicating (P1) posterior cerebral a. segment Ambient (P2) posterior cerebral a. segment

Posterior temporal a.

Calcarine (P4) posterior cerebral a. segment

Quadrigeminal (P3) posterior cerebral a. segment

Parietooccipital a.

Calcarine a. and branches

(Top) Lateral graphic shows the posterior cerebral artery (PCA) and its branches. The PCA has central (perforating), choroidal, and cortical branches as well as a small branch to the corpus callosum splenium. The tentorium and CNIII lie between the PCA above and the superior cerebellar artery below. (Bottom) Submentovertex graphic shows the PCA and the relationship of its segments to the midbrain. The PCA supplies the occipital lobe and almost all of the inferior surface of the temporal lobe (except for its tip). The precommunicating (P1) PCA segment extends from the basilar bifurcation to the PCoA junction. The ambient (P2) segment swings posterolaterally around the midbrain. The quadrigeminal segment (P3) lies behind the midbrain. The PCA terminal segment is the calcarine (P4) segment.

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Transcranial Doppler

Middle cerebral a.

Brain and Spine

POSTERIOR CEREBRAL ARTERY

Ipsilateral posterior cerebral a., P2 segment (posterior)

Ipsilateral posterior cerebral a., P2 segment (anterior) Internal carotid a., C7 segment Ipsilateral posterior cerebral a., P1 segment

Posterior communicating a.

Contralateral posterior cerebral a.

Posterior

Anterior

Middle cerebral a.

Posterior cerebral a., P2 segment

Ipsilateral internal carotid a., C7 segment

Posterior communicating a. Contralateral middle cerebral a. Posterior

Anterior

Posterior cerebral a., P2 segment (posterior)

Mesencephalon Posterior cerebral a., P2 segment (anterior)

Posterior

Anterior

(Top) Axial color Doppler ultrasound (transtemporal approach) on the mesencephalic plane shows the P1 segment extending laterally from the basilar artery to its junction with the PCoA and continuing as the P2 segment around the mesencephalon. The flow direction of P1 and anterior P2 segments is toward the transducer, whereas the posterior P2 segment is away from the transducer. (Middle) Axial color Doppler ultrasound (transtemporal approach) shows the PCoA is identified as a vascular structure connecting the ICA C7 segment to the PCA with flow away from the transducer. The clinical importance of investigation of PCoA is due to the prevalence of aneurysm formation and effectiveness of collateralization. (Bottom) Axial color Doppler ultrasound (transtemporal approach) shows the P2 segment curving posteriorly around mesencephalon with change in flow direction around the curvature.

63

Brain and Spine

Transcranial Doppler POSTERIOR CEREBRAL ARTERY

Middle cerebral a., M2 segment

Middle cerebral a., M1 segment Ipsilateral posterior cerebral a., P2 segment (posterior) Ipsilateral posterior cerebral a, P2 segment (anterior) Ipsilateral posterior cerebral a, P1 segment Mesencephalon

Ipsilateral internal carotid a., communicating segment Posterior communicating a. Contralateral internal carotid a.

Contralateral P1 segment Posterior

Ipsilateral posterior cerebral a., P2 segment

Anterior

Middle cerebral a., M1 segment Ipsilateral internal carotid a., communicating segment

Ipsilateral posterior cererbal a., P1 segment Distal basilar a. Contralateral posterior cerebral a., P1 segment Ipsilateral posterior cerebral a., P3 segment Contralateral posterior cerebral a., P2 segment

Ipsilateral posterior communicating a. Contralateral posterior communicating a. Contralateral internal carotid a.

Internal carotid a. Posterior communicating a.

Posterior cerebral a.

Posterior communicating a. waveform

(Top) Axial color Doppler ultrasound (transtemporal approach) on the mesencephalic plane shows the P1 segment emerging in the interpeduncular cistern with the P2 segment encircling the mesencephalon with flow toward transducer in P1 and P2 segments. A short P3 segment is also noted with flow away from the transducer. With adequate acoustic penetration, the contralateral arterial segments can be visualized with flow direction opposite to the ipsilateral arteries. (Middle) Corresponding MR arteriogram in a similar projection plane shows the bilateral PCAs and PCoAs in the circle of Willis. (Bottom) Axial spectral Doppler ultrasound (transtemporal approach) of the PCoA on standard the mesencephalic plane shows normal backward flow from the ICA to the PCA in this artery. Note only 75% of the PCoA is discernible transcranially.

64

Transcranial Doppler

Posterior communicating a., P2 segment (posterior)

Brain and Spine

POSTERIOR CEREBRAL ARTERY

Posterior communicating a., P2 segment (anterior) Posterior communicating a. P1 segment

Posterior communicating a.

Posterior communicating a. P2 segment (anterior)

P2 segment, waveform

Posterior communicating a., P2 segment (posterior)

P3 segment, waveform

(Top) Axial spectral Doppler ultrasound (transtemporal approach) of the P1 segment shows the waveform of P1 flow is of low resistance and on the positive side of the trace. Note that the P1 segment is short and often hypoplastic or absent, making its visualization difficult. (Middle) Axial spectral Doppler ultrasound (transtemporal approach) of the anterior P2 segment on the axial mesencephalic plane shows normal antegrade low-resistance flow with a waveform pattern similar to the P1 segment. (Bottom) Axial spectral Doppler ultrasound (transtemporal approach) of the posterior P2 segment on the axial ventricular plane shows the waveform of this segment is of low resistance and on the negative side of the trace, denoting flow away from transducer.

65

Brain and Spine

Transcranial Doppler VERTEBROBASILAR SYSTEM

Posterior cerebral a. Superior cerebellar a. Basilar a.

Right anterior inferior cerebellar a.

Pontine perforating branches Common anterior inferior cerebellar a.- posterior inferior cerebellar a. trunk (common variant)

Right posterior inferior cerebellar a. Intradural (V4) VA segment V3 segment, atlas loop

Anterior spinal a.

Lateral posterior choroidal a. Posterior cerebral a. Medial posterior choroidal a. Superior hemispheric branches

Superior vermian a. Superior cerebellar a. Basilar a. with pontine perforating a.

Anterior medullary segment, posterior inferior cerebellar a. Caudal loop, lateral medullary segment, posterior inferior cerebellar a.

Great horizontal fissure, cerebellum Supratonsillar segment, posterior inferior cerebellar a., with choroidal branches Inferior vermian a. (posterior inferior cerebellar a.) Inferior hemispheric branches (posterior inferior cerebellar a.) Posterior meningeal a. V3 segment (atlas loop)

(Top) Frontal graphic depicts the vertebrobasilar system. The V3 is the short extraspinal vertebral artery (VA) segment that extends from the top of the C1 to the foramen magnum. The V4 is the intradural (intracranial) segment. A right posterior inferior cerebellar artery (PICA) is shown originating from the VA, while the right anterior inferior cerebellar artery (AICA) is from the basilar artery. A combined AICA-PICA trunk is a common normal variant and is shown on the left side. (Bottom) Lateral graphic depicts the vertebrobasilar system. Note the relationship of the PICA loops to the medulla, cerebellar tonsil. Watershed between the SCA, PICA is often near the great horizontal fissure of the cerebellum.

66

Transcranial Doppler Brain and Spine

VERTEBROBASILAR SYSTEM

Right vertebral a. V4 segment

Left vertebral a., V4 segment Proximal basilar a.

Left vertebral a., V4 segment Right vertebral a., V4 segment Proximal basilar a.

Posterior cerebral a., P2 segment Posterior cerebral a., P3 segment

Posterior cerebral a. P1 segment Basilar a.

Mesencephalon

Posterior

Anterior

(Top) Axial color Doppler ultrasound (suboccipital approach) through the foramen magnum shows the right V4 segment of the VA and proximal basilar artery with flow directed away from the transducer. Note that reversed basilar artery flow toward the transducer would signify severe intracranial subclavian steal. (Middle) Axial color Doppler ultrasound (suboccipital approach) through the foramen magnum shows the left V4 segment of the VA with flow directed away from the transducer. The convergence of 2 V4 segments forming the basilar artery should give rise to a Y configuration. However, the Y configuration may not be always obtainable because the 3 vessels are not always on the same plane. (Bottom) Axial color Doppler ultrasound (transtemporal approach) on the standard mesencephalic plane shows the distal portion of basilar artery, which terminates into the PCAs in the interpeduncular/suprasellar cistern.

67

Brain and Spine

Transcranial Doppler VERTEBROBASILAR SYSTEM

Atlas, posterior arch

Bilateral vertebral a. V3 segments

Right vertebral a., V3 segment

Left vertebral a., V3 segment

Right V3 segment, waveform Right vertebral v., waveform

Right vertebral a., V3 segment

Left vertebral a., V3 segment

Left V3 segment, waveform Left vertebral v., waveform

(Top) Axial color Doppler ultrasound (suboccipital approach) at a level just above the atlas shows the 2 short extraspinal V3 segments exiting from the transverse foramina of the atlas and running posteromedially at the horizontal groove on the posterior arch (atlas). The flow direction of these vessels is toward the transducer. (Middle) Corresponding spectral Doppler ultrasound of the right V3 segment demonstrates the characteristic antegrade low-resistance flow pattern of this vessel. Note the Doppler signal from the ipsilateral vertebral vein is frequently inseparable from the arterial signal and is detected on the opposite side of the trace. (Bottom) Corresponding spectral Doppler ultrasound of the left V3 segment shows similar waveform as the contralateral artery.

68

Transcranial Doppler Brain and Spine

VERTEBRAL ARTERY V4 SEGMENT

Vertebral v.

Bilateral vertebral a., V4 segments

Right V4 segment

Right V4 segment, waveform

Left V4 segment

V4 segment, waveform

(Top) Axial color Doppler ultrasound (suboccipital approach) through the foramen magnum shows the 2 intradural V4 segments of the VA with flow directed away from the transducer. The 2 vertebral veins formed in the suboccipital triangle from numerous small tributaries are also visualized with flow toward the transducer. (Middle) Corresponding spectral Doppler waveform of the right V4 segment shows the normal antegrade low-resistance flow pattern similar to the V3 segment, but with opposite flow direction, as evident by the negative tracing. (Bottom) A spectral Doppler waveform of the left V4 segment shows a similar tracing.

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Brain and Spine

Transcranial Doppler INTRACRANIAL VEINS AND SINUSES Superior sagittal sinus V. of Galen Inferior sagittal sinus Thalamostriate v. Septal v.

Falx cerebri

Straight sinus

Internal cerebral v. Sinus confluence (torcular Herophili) Transverse sinus Occipital sinus

Basal v. of Rosenthal Sigmoid sinus

Anterior cerebral v. Superficial middle cerebral v.

Optic chiasm

Deep middle cerebral v.

Basal v. of Rosenthal

Galen v.

Sphenoparietal sinus

Cavernous sinus Superior petrosal sinus

Anterior and posterior intercavernous sinuses Basilar (clival) venous plexus

Inferior petrosal sinus Sigmoid sinus and jugular v.

Transverse sinus

Straight sinus

Sinus confluence (torcular Herophili)

(Top) This 3D rendering of the falx cerebri with major dural sinuses and deep veins shows the interconnections between these 2 venous systems. (Middle) Graphic shows an inferior intracranial view of the deep venous structures. Intracranial veins are valveless veins, which pierce the arachnoid membrane and meningeal layer of dura mater and drain into the cranial venous sinuses. (Bottom) Graphic shows the superior intracranial view of the dural venous sinuses. The cerebral hemispheres, midbrain, and pons as well as the left 1/2 of the tentorium cerebelli have been removed. Note the numerous interconnections between both halves of the cavernous sinus, the basilar venous plexus, and the petrosal sinuses.

70

Transcranial Doppler Brain and Spine

INTRACRANIAL VEINS

Posterior cerebral a., P3 segment Basal v. (of Rosenthal)

Middle cerebral a. Deep middle cerebral v. Mesencephalon

Posterior

Anterior

Basal v. (of Rosenthal) Posterior cerebral a. P2 segment Mesencephalon Great v. of Galen Pineal body and quadrigeminal cistern Posterior

Anterior

Lateral mesencephalic v.

Basal v., posterior segment Middle cerebral a. Basal v., anterior segment

Deep middle cerebral v.

Mesencephalon Anterior cerebral v.

Posterior

Anterior

(Top) Axial color Doppler ultrasound (transtemporal approach) illustrates the basal vein of Rosenthal (BV) running posteriorly along the mesencephalon with flow signal away from the transducer. The ipsilateral PCA is often seen closely related to it with opposite flow direction. (Middle) Axial color Doppler ultrasound (transtemporal approach) demonstrates the great vein of Galen (GV). The vein is identified in the midline posterior to mesencephalon in the hyperechoic triangular region of the pineal body and quadrigeminal cistern. (Bottom) Axial color Doppler ultrasound (transtemporal approach) shows the 2 tributaries of the BV: The anterior cerebral vein (ACV) and deep middle cerebral vein (dMCV). The ACV courses posteriorly along the base of the brain and joins the dMCV, which runs in the sylvian fissure to form the BV just anterior to the mesencephalon. Note that both the ACV and MCV are accompanied by their respective arteries.

71

Brain and Spine

Transcranial Doppler INTRACRANIAL VEINS

Posterior cerebral a. P2 segment

Basal v., posterior segment

Mesencephalon

Posterior

Anterior

Middle cerebral a.

Deep middle cerebral v. Basal v., posterior segment Basal v., anterior segment

Anterior cerebral v.

Mesencephalon

Posterior

Anterior

Anterior

Interhemispheric fissure Anterior cerebral v.

Mesencephalon

Color noise, artifact

Posterior

(Top) Axial color Doppler ultrasound (transtemporal approach) shows the posterior segment of the BV. The vein is seen surrounding the mesencephalon and runs almost parallel to the PCA. The blue color coding of the vessel indicates flow directed away from the transducer. (Middle) Axial color Doppler ultrasound (transtemporal approach) with a more anterior tilting approach is shown. The ACV is seen running posteriorly to join the dMCV before draining into the anterior segment of BV. The flow in the ACV and anterior segment of BV is directed toward the transducer, as denoted by the red color coding. (Bottom) Axial color Doppler ultrasound (paramedian frontal approach) shows the ACV, which courses posteriorly within the interhemispheric fissure; this small vein, after joining the dMCV, forms the BV. Identification of this vessel is difficult due to its slow flow.

72

Transcranial Doppler Brain and Spine

INTRACRANIAL VEINS

Basal v., posterior segment

Posterior cerebral a., P2 segment

Posterior segment of basal v., waveform

Basal v. Anterior cerebral v. Middle cerebral a. Deep middle cerebral v.

Anterior cerebral v., waveform

Anterior cerebral v.

Anterior cerebral v., waveform

(Top) Axial spectral Doppler ultrasound (transtemporal approach) shows the BV waveform (posterior segment) with typical respiratory phasicity. (Middle) Axial spectral Doppler ultrasound (transtemporal approach) shows the Doppler waveform of the ACV. Note the waveform is on the positive scale, representing flow toward the transducer. (Bottom) Axial spectral Doppler ultrasound shows the ACV waveform obtained from the paramedian frontal approach with the flow away from the transducer. Note the flow direction of a vessel depends on the scanning approach used, and the ACV flow is toward the transducer using transtemporal approach but away from the transducer using the transfrontal approach.

73

Brain and Spine

Vertebral Column and Spinal Cord

GROSS ANATOMY Vertebral Bodies • Vary in size, shape depending on region • Cervical: Upper 7 vertebrae ○ C1 (atlas): No body, spinous process; circular shape ○ C2 (axis): Body with bony peg (dens/odontoid process) ○ C3-C6 similar in size, shape; C7 marked by longest spinous process • Thoracic: Bodies heart-shaped, central canal round, short pedicles, broad laminae ○ Costal articular facets on body/transverse processes • Lumbar: Large body, thick pedicles, broad laminae • Sacrum: Fusion of 5 segments • Coccyx: Fusion of 3-5 segments

Spinal Cord • Suspended within thecal sac • Anchored to dura by denticulate ligaments • 2 widened segments: Cervical enlargement (C3-T2) and lumbar enlargement (T9-T12) • Cord tapers to diamond-shaped point (conus medullaris), normally ends at T12 to L2-L3, most common at T12-L1 • In contrast to brain, gray matter is on inside with white matter on periphery of cord ○ Central gray matter, formed by columns ("horns") of neuronal cell bodies, is roughly H-shaped • Filum terminale: Connective tissue extension of pia mater extending inferiorly from conus ○ Fuses distally into dura, attaches to dorsal coccyx • Cauda equina: "Horse's tail" of lumbar, sacral, coccygeal nerve roots below conus • Nerve roots ○ Cervical spine: 8 nerves, which exit above vertebral body – C8 nerve root exits above T1 ○ Remainder of nerve roots exit below vertebral body ○ Paired dorsal, ventral roots exit from their respective hemicords – Unite in/near intervertebral foramen to form ganglion

IMAGING ANATOMY Vertebral Bodies • Ossified vertebral body appears echogenic ○ Cartilaginous tip at spinous process appears hypoechoic • Cartilaginous coccyx is hypoechoic ○ Ossified coccygeal vertebral bodies have rounded central nucleus rather than square contour as in sacrum

Spinal Cord • Cord is predominately hypoechoic ○ Central echogenic complex: Interface between myelinated ventral white matter commissure and CSF within ventral median fissure ○ Central spinal canal (ependymal canal): CSF-containing space throughout length of cord; contiguous with ventricular system – Typically do not see fluid in canal unless dilated ○ Conus medullaris: Terminal part of cord, should taper gradually • Cauda equina: Multiple, linear, diverging nerve roots 74

○ Drape dependently within thecal sac, undulate with each CSF pulsation • Filum terminale should be < 2 mm in diameter ○ Hypoechoic center with more echogenic outer margin ○ Dorsal extension toward coccyx

ANATOMY IMAGING ISSUES Imaging Recommendations • Nonossified posterior-median intraneural synchondrosis provides ample acoustic window in newborns • Spinal cord is best visualized by US within 1st month after birth for term infants • Transverse scan of cord possible in older infant as cartilaginous gap in vertebral ring allows penetration of US beam • Determination of position of tip of conus medullaris should always be included in neonatal spine US

Imaging Approaches • Infants are preferably scanned in prone position • Decubitus position is adopted to calm struggling baby by bottle or breast feeding • Scan both longitudinally and transversely using highfrequency linear US transducer • Ways to define vertebral levels where conus ends ○ Count downward from 12th rib ○ Count upward after defining lumbosacral junction – For more clear delineation of L5-S1, accentuate lumbar lordosis by elevation of shoulders • Craniocervical junction can be assessed by scanning base of skull through foramen magnum

Imaging Pitfalls • Counting of vertebral level upward from last ossified vertebral body can be misleading due to variability in ossification of coccygeal vertebral bodies • In older infants, ossification may preclude an adequate examination

CLINICAL IMPLICATIONS Clinical Importance • Tethered cord ○ Conus terminates at or above inferior L2 vertebra in ≥ 98% of normal population – Conus at normal position by 0-2 months of age ○ Conus terminating below L2-L3 disc is abnormal at any postnatal age but significance questionable in absence of signs/symptoms – Important to evaluate appearance of nerve roots and filum terminale as well as conus level – Follow-up scan for borderline cases ○ Conus located over mid L3 or lower, or with lack of normal nerve-root pulsations, requires further evaluation with MR ○ Filum terminale thickened (> 2 mm at L5-S1 on axial/transverse images) ○ Cord may appear taut or directly apposed to dorsal thecal sac – Lack of conus motion with CSF pulsations – Lack of dependent ventral shift of conus when prone

Vertebral Column and Spinal Cord

Cervicomedullary junction

Cerebellar tonsil

Basion

Brain and Spine

CERVICAL SPINE

Opisthion Anterior arch of C1 Odontoid process of C2

Ligamentum nuchae

Body of C2

Interspinous l.

Vertebral body of C5

C5 spinous process

C5-C6 intervertebral disc Central spinal canal

C1 nerve

Rootlets

Spinal ganglion

C8 n. T1 n.

(Top) Sagittal midline graphic of the cervical spine and cord shows a gentle lordotic curve and smooth alignment of the adjacent vertebrae. The cerebellar tonsils are normally above the line between the basion and opisthion. There is smooth transit of the cervicomedullary junction without kinking. (Bottom) Graphic of the cervical spine, with key vertebral bodies highlighted, shows the nerve rootlets coalescing; after forming ventral and dorsal nerve roots, they will unite in the intervertebral foramen to form a spinal ganglion. The cervical nerves are unique as they exit above their respective vertebral body. C8 nerve root exits above T1; below this, the nerve root exits below its vertebral body.

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Brain and Spine

Vertebral Column and Spinal Cord SPINAL CORD

Gray matter

Central spinal canal

Subdural (potential) space Pia mater (on spinal cord)

Subarachnoid space Arachnoid

Anterior spinal a. Dura mater

Epidural fat

Dural nerve root sleeve

Ventral median fissure Ventral nerve root Ventral horn/gray matter column Denticulate l.

Spinal ganglion

Dorsal horn/gray matter column Dorsal nerve root

Dorsal median sulcus

(Top) Cutaway graphic of the spinal cord and its coverings demonstrates the meningeal layers and their relationship to adjacent regional structures. (Bottom) Axial graphic shows the internal anatomy of the distal thoracic spinal cord. In contrast to the brain, the gray mater is on the inside, while the white matter is along the periphery. The gray matter forms columns that are roughly H-shaped in cross section. The deep ventral median fissure divides the ventral hemicords, while the smaller dorsal median sulcus divides the dorsal hemicords. The dorsal and ventral nerve roots arise from the dorsolateral and ventrolateral sulci, respectively, and unite in the intervertebral foramen to form the spinal ganglion.

76

Vertebral Column and Spinal Cord Brain and Spine

CAUDA EQUINA

Dura

Anterior spinal l.

Conus Posterior spinal l.

Cauda equina Filum terminale

Conus medullaris

Nerve roots of cauda equina

Filum terminale

(Top) Sagittal graphic of the thoracolumbar junction demonstrates a normal conus and cauda equina anatomy. The filum terminale lies among the cauda equina roots and affixes the conus dorsally to the terminal thecal sac. (Bottom) Coronal graphic through the middle of the spinal canal shows the distal spinal cord and nerve roots of the cauda equina. Note the cord ends in a diamond-shaped point, the conus medullaris. Lumbar nerve roots exit the thecal sac just under the pedicles of their same-numbered vertebral segments. The filum terminale is a strand of connective tissue that extends inferiorly from the conus to the dorsal coccyx. It typically contains no functional neural tissue and no fat. A normal conus should end above the inferior margin of L2. Extension below the the L2-L3 disc space is concerning for possible tethered cord.

77

Brain and Spine

Vertebral Column and Spinal Cord CERVICAL SPINE

Posterior arch of C1 Opisthion

Spinous process of C2 Spinal cord

Foramen magnum Cervicomedullary junction Odontoid process (dens) of C2 Basion Anterior arch of C1

Body of C2 (axis) Fused synchondrosis

Posterior neck mm. Cartilaginous tips of spinous processes

C1

Ossified portions of spinous processes

Cervical cord

Lower cervical spine

(Top) Sagittal T2 MR of the cervical spine is displayed in the prone position to match the spinal ultrasound. High-signal CSF is seen within the foramen magnum and surrounding the spinal cord. There is a smooth transition of the cervicomedullary junction. The cerebellar tonsils should be normally above the line between basion and opisthion. (Middle) The spinous processes of the cervical spine are longer and overlap more than in the lower spine making visualization of the cord more difficult, particularly in the transverse plane. Note the cartilaginous portion of the spinous processes appears hypoechoic, while the ossified portion of the vertebral body is echogenic and shadowing. The upper cervical cord is seen by scanning laterally through the neck and angling toward the spinal canal. (Bottom) Slightly lower and angled medially, the lower portion of the cervical cord can be seen.

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Vertebral Column and Spinal Cord

Supraspinous l.

Interspinous l. Ligamentum flavum Subarachnoid space Posterior longitudinal l.

Brain and Spine

THORACIC SPINE

Spinous process Epidural fat Posterior dural margin Spinal cord

Anterior longitudinal l.

Dural

Subarachnoid space

Intervertebral disc Ossified thoracic vertebral body

Spinal cord

Cartilaginous spinous process Lamina

Central echogenic complex Spinal cord

Nerve roots

(Top) This image at mid thoracic level shows this segment of the spinal cord is more narrow when compared with the higher level (C3 to T2) and lower level (T9 to T12). (Middle) Longitudinal ultrasound at the mid thoracic level of the spinal cord shows the narrowest portion of the cord. The cord should lie dependently within the thecal sac. (Bottom) This transverse scan is taken at T12. At this point, the cord has started to widen again. The spinal cord is predominately hypoechoic with a central echogenic complex. Nerve roots are seen around the cord as it is approaching the conus medullaris.

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Brain and Spine

Vertebral Column and Spinal Cord LONGITUDINAL US, CONUS Conus medullaris

Cauda equina

Central echogenic complex

L2-L3 disc L2 vertebral body

Dorsal nerve roots

Filum terminale

Ventral nerve roots

Filum terminale

Nerve roots

(Top) The caudal portion of the cord tapers gradually forming the conus medullaris and should terminate above the L2-L3 disc space as in this case. Contrary to popular misunderstanding, this central echogenic complex is predominately a reflection of echoes from the interface between the ventral white commissure and CSF within the ventral median fissure rather than from the central canal. The nerve roots surrounding the conus tail form the cauda equina (horse's tail). (Middle) The filum terminale is connective tissue continuation of the pia mater extending inferiorly from the conus. It extends dorsally through the thecal sac to insert on the dura of the dorsal coccyx. The nerve roots and filum should should move freely and undulate with CSF pulsations. The dorsal nerve roots are seen as they move to exit the canal, while the ventral nerve roots lie dependently within the thecal sac. (Bottom) More distally, the filum terminale is seen moving dorsally to insert on the dura at the level of the coccyx.

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Vertebral Column and Spinal Cord

Unossified spinous process

Subarachnoid space

Brain and Spine

AXIAL US, CONUS

Spinal cord

Dura mater

Dorsal nerve roots

Lamina

Tip of conus medullaris

Ventral nerve roots

Filum terminale

Nerve roots

(Top) Axial ultrasound in the upper lumbar spine at the level of the conus medullaris shows the normal hypoechoic cord with central echogenic complex. The spinal cord lies within the subarachnoid space, which is bound by the dura mater and filled with CSF. Echogenic nerve rootlets are seen draped around the cord. (Middle) Axial ultrasound scanning between L2 and L3 shows the tip of the conus. It is surrounded by free-floating nerve roots, collectively known as cauda equina. The conus normally should be above the L2-L3 disc space. (Bottom) Axial ultrasound at L4 level shows the filum terminale and nerve rootlets of cauda equina, all of which should float freely within the thecal sac. The filum terminale is the prolongation of the pia mater and attaches dorsally at the level of the coccyx. The filum terminale can be clearly distinguished from the nerve roots of the cauda equina and should be < 2 mm in diameter.

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Brain and Spine

Vertebral Column and Spinal Cord SACRUM AND COCCYX Filum terminale

Conus medullaris

S4 vertebral body S5 vertebral body

Coccyx

Hyperechoic ossification center

Hypoechoic cartilaginous portion Gluteal m.

(Top) This extended field of view shows the filum terminale extending dorsally within the thecal sac to insert on the dura at the level of the coccyx. One of the most difficult and crucial things in spinal sonography is accurately numbering the vertebral bodies. The angle at L5-S1 can be accentuated by raising up the shoulders; confirm your impression by counting down from the last rib. Only after confirming in both directions can you be confident in your determination of the conus level. (Middle) The coccygeal segments are the last vertebral bodies to ossify so they often appear partially or completely hypoechoic by ultrasound. (Bottom) The ossification center of a coccygeal vertebral body is rounded, helping to distinguish it from a sacral vertebral body, which has a square ossification center.

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Vertebral Column and Spinal Cord

Conus medullaris

Brain and Spine

ABNORMAL CORD

Nerve roots

Split cord

Nerve roots Epidural hematoma Conus medullaris

(Top) In this case of tethered cord, the conus is ending very low at the level of S3. Also note the cord appears stuck to the dorsal surface of the sac and not lying dependently as would normally be seen. No free-floating nerve roots were seen during the real-time examination and are shown here in a conglomerate mass. (Middle) In the axial plane, not only is the position abnormal, but there is a cleft seen within the cord. A split cord was confirmed by MR. (Bottom) This scan was performed after a failed attempt at a lumbar puncture. The scan shows the thecal sac is surrounded by a hyperechoic epidural hematoma. The nerve roots are compressed to the middle of the sac.

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SECTION 2

Head and Neck

Neck Overview Sublingual/Submental Region Submandibular Region Parotid Region Upper Cervical Level Midcervical Level Lower Cervical Level and Supraclavicular Fossa Posterior Triangle Thyroid Gland Parathyroid Glands Larynx and Hypopharynx Trachea and Esophagus Vagus Nerve Carotid Arteries Vertebral Arteries Neck Veins Cervical Lymph Nodes

86 92 98 104 112 118 124 130 136 144 150 158 164 170 184 190 198

Head and Neck

Neck Overview

TERMINOLOGY Abbreviations • Infrahyoid neck (IHN)

Definitions • Suprahyoid neck (SHN): Spaces from skull base to hyoid bone (excluding orbits, paranasal sinuses, and oral cavity) including parapharyngeal, pharyngeal mucosal, masticator, parotid, carotid (CS), buccal, retropharyngeal (RPS), and perivertebral (PVS) spaces • Infrahyoid neck (IHN): Spaces below hyoid bone to thoracic inlet, including visceral space (VS), posterior cervical space (PCS), anterior cervical space (ACS), CS, RPS, and PVS

IMAGING ANATOMY Overview • Fascial spaces of SHN and IHN are key for cross-sectional imaging ○ Concept is difficult to apply with ultrasound • Ultrasound anatomy is based on division of neck into anterior and posterior triangles ○ Anterior triangle: Bounded anteriorly by midline and posteriorly by posterior margin of sternomastoid muscle – Further divided into suprahyoid and infrahyoid portions – Suprahyoid portion: Divided by anterior belly of digastric muscle into submental and submandibular triangles – Infrahyoid portion: Divided by superior belly of omohyoid muscle into muscular and carotid triangles ○ Posterior triangle: Bound anteriorly by posterior margin of sternomastoid muscle and posteriorly by anterior border of trapezius muscle – Apex formed by mastoid process, base of triangle formed by clavicle – Subdivided by posterior belly of omohyoid muscle into occipital triangle (superior) and supraclavicular triangle (inferior) • Submental region ○ Key structures include anterior belly of digastric muscle, mylohyoid, genioglossus and geniohyoid muscles, sublingual glands, and lingual artery • Submandibular region ○ Key structures include submandibular gland, mylohyoid muscle, hyoglossus muscle, anterior and posterior bellies of digastric muscle, facial vein, and anterior division of retromandibular vein (RMV) • Parotid region ○ Key structures include parotid gland, masseter and buccinator muscles, RMV, and external carotid artery (ECA) • Cervical region ○ Upper cervical region: Skull base to hyoid bone/carotid bifurcation – Key structures include internal jugular vein (IJV), carotid bifurcation, jugulodigastric node, and posterior belly of digastric muscle ○ Midcervical region: Hyoid bone to cricoid cartilage – Key structures include IJV, common carotid artery (CCA), vagus nerve, and lymph nodes 86

○ Lower cervical region: Cricoid cartilage to clavicle – Key structures include IJV, CCA, superior belly of omohyoid, and lymph nodes • Supraclavicular fossa ○ Key structures include trapezius, sternomastoid, omohyoid muscles, brachial plexus elements, and transverse cervical nodes • Posterior triangle ○ Bordered anteriorly by sternomastoid muscle and posteriorly by trapezius muscle ○ Floor formed by scalene muscles, levator scapulae, and splenius capitis muscles • Midline ○ Key structures include hyoid bone, strap muscles, thyroid, larynx, and tracheal rings

ANATOMY IMAGING ISSUES Imaging Recommendations • Use of high-resolution transducers is essential • Color/power Doppler examination provides useful supplementary information to grayscale ultrasound • US is very sensitive in identifying abnormalities (and in characterizing many head and neck soft tissue lesions) ○ Combination with fine-needle aspiration cytology (FNAC) provides specificity and increased diagnostic accuracy • US + FNAC usually provides adequate information for patient management • Cross-sectional imaging (CT, MR) may be required for ○ Large mass, when detailed anatomical extent is not fully examined by US ○ Deep-seated lesion with suboptimal US visualization and evaluation ○ Preoperative assessment of relevant adjacent structures (e.g., bone involvement)

Imaging Approaches • Ultrasound imaging protocol ○ Start in submental region by scanning in transverse plane ○ Next, scan submandibular region in transverse and longitudinal/oblique planes ○ Then scan parotid region in transverse and longitudinal planes ○ Then examine upper cervical, midcervical, and lower cervical regions in transverse plane ○ Then examine supraclavicular fossa with transducer held transversely ○ Then scan posterior triangle transversely along a line drawn from mastoid process to ipsilateral acromion ○ Finally, scan midline and thyroid gland in both transverse and longitudinal planes • This protocol is robust and can be tailored to suit individual clinical conditions • Transverse scans quickly identify normal anatomy and detect abnormalities • Any abnormality identified is further examined in longitudinal/oblique planes (grayscale and Doppler) • In restless children, it may not be possible to follow above protocol ○ It would therefore be best to evaluate primary area of interest first, before child becomes uncooperative

Neck Overview Head and Neck

SCANNING AREAS AND LYMPH NODE GROUPS

Parotid gland

Sternocleidomastoid m.

Hyoid bone Thyroid cartilage Trapezius m. Cricoid cartilage

Omohyoid m.

High internal jugular lymph nodes Jugulodigastric lymph node

Submandibular lymph nodes Submental lymph nodes

Cricoid cartilage

High spinal accessory lymph nodes Middle internal jugular lymph nodes

Low internal jugular lymph nodes

Visceral space nodes Low spinal accessory lymph nodes Superior mediastinal nodes

(Top) Schematic diagram shows the protocol for ultrasound examination of the neck with 8 regions scanned in order: (1) Submental region, (2) submandibular region, (3) parotid region, (4) upper cervical region, (5) midcervical region, (6) lower cervical region, (7) supraclavicular fossa, and (8) posterior triangle. The above protocol is robust and helps to adequately evaluate the neck for common clinical conditions. Note that deep structures cannot be adequately assessed by ultrasound. (Bottom) Lateral oblique graphic of the neck shows the anatomic locations of the major nodal groups of the neck. Division of the internal jugular nodal chain into high, middle, and low regions is defined by the level of the hyoid bone and cricoid cartilage. Similarly, the spinal accessory nodal chain is divided into high & low regions by the level of the cricoid cartilage.

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Head and Neck

Neck Overview NECK SPACES

Submandibular space Pharyngeal mucosal space/surface Retropharyngeal space

Masticator space Posterior belly, digastric m.

Danger space Parapharyngeal space Alar fascia Perivertebral space, prevertebral component

Parotid space Carotid space Posterior cervical space

Perivertebral space, paraspinal component

Middle layer, deep cervical fascia Anterior cervical space

Visceral space

Retropharyngeal space

Carotid sheath

Danger space Perivertebral space, prevertebral component Deep layer, deep cervical fascia touches transverse process Perivertebral space, paraspinal component

Carotid space Superficial layer, deep cervical fascia

Posterior cervical space

Deep layer, deep cervical fascia

(Top) Axial graphic shows the suprahyoid neck spaces at the level of the oropharynx. The superficial (yellow line), middle (pink line), and deep (turquoise line) layers of deep cervical fascia (DCF) outline the suprahyoid neck spaces. Notice that the lateral borders of the retropharyngeal and danger spaces are called the alar fascia and represent a slip of the deep layer of DCF. (Bottom) Axial graphic depicts the fascia and spaces of the infrahyoid neck. The 3 layers of DCF are present in the suprahyoid and infrahyoid neck. The carotid sheath is made up of all 3 layers of DCF (tricolor line around carotid space). Notice the deep layer completely circles the perivertebral space, diving in laterally to divide it into prevertebral and paraspinal components. Although the spaces are not adequately demonstrated by US, it is important to be familiar with the concept in order to understand neck anatomy.

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Neck Overview

Subcutaneous tissue Platysma m.

Head and Neck

TRANSVERSE ULTRASOUND

Anterior belly of digastric m. Mylohyoid m. Geniohyoid m. Sublingual gland Branch of lingual a.

Genioglossus m.

Subcutaneous tissue Platysma Submandibular gland Posterior belly of digastric m. Deep "process" of submandibular gland

Facial a.

Anterior belly of digastric m. Mylohyoid m.

Hyoglossus m.

Subcutaneous tissue Tip of mastoid process Parotid gland, superficial lobe

Ramus of mandible

Retromandibular v.

(Top) Standard transverse grayscale ultrasound shows the submental region. The mylohyoid muscle is an important landmark for the division of the sublingual (deep to mylohyoid muscle) and submandibular (superficial to mylohyoid muscle) spaces. Part of the extrinsic muscles of the tongue, including the geniohyoid and genioglossus, are visualized. (Middle) Standard transverse grayscale ultrasound shows the submandibular region. The submandibular gland is the key structure with its homogeneous echotexture. The gland sits astride the mylohyoid and posterior belly of the digastric muscles. (Bottom) Standard transverse grayscale ultrasound shows the parotid region. Note that the deep lobe is obscured by shadowing from the mandible and cannot be evaluated. The retromandibular vein serves as a landmark for the intraparotid facial nerve.

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Head and Neck

Neck Overview TRANSVERSE ULTRASOUND Subcutaneous tissue Submandibular gland Jugulodigastric lymph node

Sternocleidomastoid m.

Facial v. Branches of external carotid a. External carotid a.

Internal jugular v. Internal carotid a.

Sternohyoid m. Sternothyroid m. Sternocleidomastoid m. Internal jugular v. Vagus n. Scalenus anterior m.

Common carotid a. Thyroid gland

Longus coli

Vertebral vessel

Subcutaneous tissue Sternocleidomastoid m. Sternohyoid m. Sternothyroid m.

Internal jugular v. Superior belly of omohyoid m. Longus coli

Thyroid gland Common carotid a. Esophagus

(Top) Standard transverse grayscale ultrasound shows the upper cervical level. Key structures include the internal jugular vein, the proximal internal and external carotid arteries, and the jugular chain lymph nodes. The jugulodigastric node is the most prominent and consistently seen on ultrasound. (Middle) Standard grayscale ultrasound shows the midcervical level. Note the vagus nerve is clearly seen on ultrasound. (Bottom) Standard grayscale ultrasound shows the lower cervical level. The thyroid gland is related to the common carotid and internal jugular vein laterally. The anterior strap muscles (including the sternohyoid and sternothyroid muscles) and the superior belly of the omohyoid are clearly visualized.

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Neck Overview

Sternocleidomastoid m.

Head and Neck

TRANSVERSE ULTRASOUND

Brachial plexus elements Scalenus medius Scalenus anterior Vertebral transverse process

Sternocleidomastoid m. Intermuscular fat plane Levator scapulae m.

Semispinalis capitis m.

Vertebral transverse process

Isthmus of thyroid Subcutaneous tissue Sternohyoid m. Sternothyroid m. Thyroid gland (right lobe) Thyroid gland (left lobe) Cervical trachea

Longus coli

(Top) Standard grayscale ultrasound shows the supraclavicular fossa. Note that the trunks of the brachial plexus are consistently seen on high-resolution ultrasound at this site. (Middle) Standard transverse grayscale ultrasound shows the posterior triangle. Note that the intermuscular fat plane is visible. The spinal accessory nerve and lymph nodes are important contents of the posterior triangle. (Bottom) Standard transverse grayscale ultrasound shows the midline of the lower anterior neck. The isthmus of the thyroid gland, the trachea, and the longus coli are key structures to be identified.

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Head and Neck

Sublingual/Submental Region

TERMINOLOGY Synonyms • Sublingual space (SLS), submental triangle

Definitions • Sublingual region: Paired nonfascial-lined spaces of oral cavity in deep oral tongue, above floor of mouth, superomedial to mylohyoid muscle

IMAGING ANATOMY Overview • Borders of submental triangle are readily defined on ultrasound ○ Floor is formed by mylohyoid muscle ○ Apex is limited anteriorly by symphysis menti ○ Base is bounded posteriorly by hyoid bone ○ Anterior belly of digastric muscle represents sides of triangle • SLS is deep space of oral cavity superomedial to mylohyoid muscles ○ Contains key neurovascular structures of oral cavity ○ Includes glossopharyngeal nerve (CNIX), hypoglossal nerve (CNXII), lingual nerve (branch of V3), lingual artery and vein

Anatomy Relationships • SLS relationships ○ SLS in deep oral tongue superomedial to mylohyoid muscle and lateral to genioglossus-geniohyoid muscles ○ Communication between SLSs occurs in midline anteriorly as narrow isthmus beneath frenulum ○ SLS communicates with submandibular space (SMS) and inferior parapharyngeal space (PPS) at posterior margin of mylohyoid muscle – There is no fascia dividing posterior SLS from adjacent SMS – Therefore, there is direct communication with SMS and PPS in this location

Internal Contents • Major muscles forming borders of submental triangle ○ Anterior belly of digastric muscle – Marks lateral border of submental triangle ○ Mylohyoid muscle – Muscle of floor of mouth – Muscular sling between medial aspect of mandibular bodies – Anterior attachment to mandible inferior to origins of genial muscles – Separates SLS (deep to mylohyoid muscle plane) from SMS (superficial to mylohyoid muscle) ○ Genioglossus and geniohyoid muscles – Form root of tongue – Together with hyoglossus muscle, they make up major extrinsic muscles of tongue • Posterior aspect of SLS is divided into medial and lateral compartments by hyoglossus muscle • Lateral compartment contents ○ Hypoglossal nerve – Motor to intrinsic and extrinsic muscles of tongue 92

– Intrinsic muscles of tongue include inferior lingual, vertical, and transverse muscles ○ Lingual nerve: Branch of mandibular division of trigeminal nerve (CNV3) combined with chorda tympani branch of facial nerve – Lingual nerve branch of CNV3: Sensation to anterior 2/3 of oral tongue – Chorda tympani branch of facial nerve: Anterior 2/3 of tongue taste and parasympathetic secretomotor fibers to submandibular ganglion/gland ○ Sublingual glands and ducts – Lie in anterior SLS bilaterally – ~ 5 small ducts open under oral tongue into oral cavity – With age, sublingual glands atrophy, becoming difficult to see on imaging ○ Submandibular glands and submandibular ducts – Submandibular gland deep margin extends into posterior opening of SLS – Submandibular duct runs anteriorly to papillae in anteromedial subfrenular mucosa • Medial compartment contents ○ Glossopharyngeal nerve (CNIX) – Provides sensation to posterior 1/3 of tongue – Carries taste input from posterior 1/3 of tongue – Located more cephalad in medial compartment compared to lingual artery and vein ○ Lingual artery and vein – Vascular supply to oral tongue – Seen running just lateral to genioglossus muscle

ANATOMY IMAGING ISSUES Imaging Recommendations • High-resolution ultrasound is ideal imaging tool for evaluating submental masses • Major structures are best seen on transverse scans with patient's neck in slight hyperextension • For more deep-seated lesions (e.g., deep to root of tongue), MR is necessary for better anatomical assessment ○ Ultrasound may help in directing needle for guided biopsy of such lesions

Key Concepts • What defines mass as primary to SLS ○ Center of lesion is superomedial to mylohyoid muscle and lateral to genioglossus muscle • Common lesions in submental region include ○ Congenital lesions: Epidermoid/dermoid cyst ○ Enlarged lymph node: Reactive, inflammatory or neoplastic (metastatic/lymphomatous nodes) ○ Inflammatory conditions: Ranula, abscess ○ Sublingual gland lesions: Sialadenitis, calculus, benign/malignant salivary gland tumor

Sublingual/Submental Region Head and Neck

SUBLINGUAL SPACE

Sublingual gland Submandibular duct

Mylohyoid m.

Genioglossus m. Submandibular space Hyoglossus m. Lingual a.

Sublingual space Masticator space

Intrinsic tongue mm.

Oral mucosal space/surface Hyoglossus m. Submandibular duct Sublingual gland Lingual n. Hypoglossal n. Glossopharyngeal n./lingual a. Genioglossus/geniohyoid mm.

Sublingual space Mylohyoid m. Submandibular space Root of tongue

(Top) Axial graphic through the body of the mandible shows the sublingual space (on patient's left, shaded in green) situated superomedial to the mylohyoid muscle and lateral to the genioglossus muscle. Notice the absence of fascia surrounding the sublingual space. The yellow line represents the superficial layer of deep cervical fascia. (Bottom) Coronal graphic through the oral cavity shows position of the mylohyoid muscle, which is the landmark in this area. The sublingual space is shaded in green. The medial sublingual space compartment contains the glossopharyngeal nerve (CNIX) and lingual artery/vein, and the lateral sublingual space compartment contains the submandibular duct, sublingual gland, lingual nerve, and hypoglossal nerve (CNXII). The fascia-lined (yellow line) submandibular space is inferolateral to the mylohyoid muscle.

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Head and Neck

Sublingual/Submental Region TRANSVERSE ULTRASOUND

Platysma m. Anterior belly of digastric m. Geniohyoid m. Sublingual gland

Mylohyoid m. Genioglossus m. Branch of lingual a.

Subcutaneous tissue Anterior belly of digastric m. Mylohyoid m. Geniohyoid m. Genioglossus m. Sublingual gland Branch of lingual a.

Platysma m. Anterior belly of digastric m. Mylohyoid m. Geniohyoid m. Sublingual gland

Branch of lingual a.

(Top) Anterior transverse grayscale ultrasound of the submental and sublingual region is shown. The mylohyoid muscle is the landmark for division of the sublingual space (deep to the mylohyoid plane) and submandibular space (superficial to the muscle plane). The sublingual gland appears as homogeneous, hyperechoic structures lateral to the geniohyoid/genioglossus muscle. Branches of lingual artery can be easily picked up on transverse plane. The submandibular duct sits alongside the lingual vessels, and a submandibular calculus may impact at this site. (Middle) More posterior transverse grayscale ultrasound allows the clear depiction of extrinsic muscles of the tongue at the root. (Bottom) Transverse grayscale ultrasound shows the submental region in a more posterior location.

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Sublingual/Submental Region

Anterior belly of digastric m.

Head and Neck

POWER DOPPLER ULTRASOUND AND CORONAL MR

Geniohyoid/genioglossus mm. Mylohyoid m. Branch of lingual a. Sublingual gland

Nasal septum Inferior nasal turbinate Zygomatic arch Maxilla Oral mucosal space/surface Buccinator m. Branch of lingual a. Mylohyoid m.

Hard palate Intrinsic m. of tongue Genioglossus m. Alveolar process of mandible Sublingual gland

Submandibular gland Platysma m. Submental lymph node

Geniohyoid m.

Middle concha and middle meatus

Maxillary sinus

Anterior belly of digastric m. Subcutaneous tissue

Nasal septum Maxilla Molar tooth Hyoglossus m. Median raphe of tongue Body of mandible

Hard palate Facial v.

Genioglossus m. Inferior alveolar n. and a. Geniohyoid m.

Mylohyoid m.

Submandibular lymph node

Platysma m.

Anterior belly of digastric m.

(Top) Power Doppler ultrasound of the submental region shows the presence of color flow within the branches of the lingual artery. The use of Doppler examination aids in differentiation from the dilated submandibular duct. (Middle) Correlative coronal T1WI MR shows the floor of the mouth and tongue. The mylohyoid muscle is the landmark separating the sublingual and submandibular spaces. (Bottom) Correlative coronal T1WI MR shows the floor of the mouth and tongue in a location more posterior. For optimal use of ultrasound, the operator must also be familiar with the correlative anatomy on other imaging modalities.

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Head and Neck

Sublingual/Submental Region LONGITUDINAL AND TRANSVERSE ULTRASOUND Subcutaneous tissue Platysma m. Mylohyoid m. Geniohyoid m. Mandible

Genioglossus m.

Subcutaneous tissue Platysma m. Anterior belly of digastric m. Mylohyoid m. Sublingual gland

Subcutaneous tissue Platysma m. Anterior belly of digastric m. Mylohyoid m. Sublingual space

Ranula

(Top) Longitudinal grayscale ultrasound of the submental region shows the relationship of the mylohyoid, geniohyoid, and genioglossus muscles. Note that scanning just off the midline will show more of the anterior belly of the digastric muscle rather than the mylohyoid muscle anteriorly. (Middle) Parasagittal longitudinal grayscale ultrasound shows the submental region. The sublingual gland is visualized within the sublingual space (deep to the mylohyoid muscle) underneath the anterior belly of the digastric and mylohyoid muscles. (Bottom) Transverse grayscale ultrasound shows a well-circumscribed, anechoic, cystic lesion in the left sublingual space (i.e., deep to the mylohyoid muscle plane). The appearance is suggestive of a ranula; relationship to the mylohyoid determines whether it is a simple or diving ranula.

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Sublingual/Submental Region

Pituitary gland

Medulla oblongata and cerebellum Sphenoid sinus

Nasal septum

Head and Neck

SAGITTAL MR AND TRANSVERSE ULTRASOUND

Clivus

Hard palate Soft palate Superior longitudinal m. Genioglossus m. Geniohyoid m. Mylohyoid m. Hyoid bone

Ethmoid air cells

Anterior arch of atlas and odontoid process Lingual follicles Epiglottis Hypopharynx Spinal cord Tracheal ring

Cavernous portion of internal carotid a.

Middle meatus Inferior nasal concha

Longus capitis

Superior longitudinal m. Oropharynx Genioglossus m. Geniohyoid m. Sublingual gland Mandible

Hyoid bone Piriform fossa

Anterior belly of digastric m. Thyroid cartilage

Anterior belly of digastric m. Mylohyoid m. Geniohyoid/genioglossus mm. Epidermoid cyst

(Top) Sagittal T1WI MR shows the floor of the mouth close to the midline. Note the positions of the mylohyoid and geniohyoid muscles between the mandible anteriorly and hyoid bone posteriorly. (Middle) Sagittal T1WI MR shows the floor of the mouth in the paramedian plane. Note that the anterior belly of the digastric muscle is now seen as it extends anteromedially to insert on the inner cortex of the mandible. (Bottom) Transverse grayscale ultrasound of the submental region shows a well-circumscribed, homogeneous, hyperechoic, midline mass deep to the mylohyoid, geniohyoid, and genioglossus muscles. The appearances and anatomical location of the lesion are suggestive of an epidermoid cyst. Congenital lesions in the neck are site specific, and familiarity with the correlative anatomy is often the best clue to their diagnosis.

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Head and Neck

Submandibular Region

TERMINOLOGY Abbreviations Definitions • Fascial-lined space inferolateral to mylohyoid muscle ○ Contains submandibular gland, lymph nodes, and anterior belly of digastric muscles

IMAGING ANATOMY Overview • One of the distinct locations within oral cavity that may be used to develop location-specific differential diagnoses ○ Other locations include oral mucosal space/surface, sublingual space, and root of tongue

Anatomy Relationships • • • •

Inferolateral to mylohyoid muscle Deep to platysma muscle Cephalad to hyoid bone Communicates posteriorly with sublingual space and inferior parapharyngeal space at posterior margin of mylohyoid muscle • Continues inferiorly into infrahyoid neck as anterior cervical space

Internal Contents • Submandibular gland ○ 1 of 3 major salivary glands ○ Divided anatomically into superficial and deep lobes by mylohyoid muscle ○ Superficial lobe is larger and in SMS itself – Superficial layer, deep cervical fascia forms submandibular gland capsule – Crossed by facial vein and cervical branches of facial nerve (marginal mandibular branch) ○ Smaller deep lobe, often called deep "process" – Tongue-like extension of gland that wraps around posterior aspect of mylohyoid muscle – Projects into posterior aspect of sublingual space – Submandibular duct projects off deep lobe into sublingual space ○ Submandibular gland innervation – Parasympathetic secretomotor supply from chorda tympani branch of facial nerve – Comes via lingual branch of CNV3 • Submental (level IA) and submandibular (level IB) nodal groups ○ Receive lymphatic drainage from anterior facial region – Including oral cavity, anterior sinonasal, and orbital areas ○ Few elliptical lymph nodes with preserved internal architecture is constant normal finding • Anterior belly of digastric muscle ○ Divides suprahyoid portion into submental and submandibular triangles • Hyoglossus muscle ○ Deep to mylohyoid muscle ○ Marks anterior margin of submandibular gland 98

•

• Submandibular space (SMS) • •

•

○ Submandibular duct runs between hyoglossus muscle and mylohyoid muscle Facial vein and artery pass through SMS ○ Facial vein courses anteriorly and superiorly to submandibular gland Anterior division of retromandibular vein ○ Outlines posterior border of submandibular gland Caudal loop of CNXII ○ Passes through SMS before looping anteriorly and cephalad into tongue muscle Tail of parotid gland may "hang down" into posterior SMS

ANATOMY IMAGING ISSUES Questions • Major clinical-radiological question when mass is present in SMS: Is lesion nodal or submandibular gland in origin ○ If "beaking" of submandibular gland tissue around lesion margin is present, and lesion is completely surrounded by glandular parenchyma, lesion origin is in submandibular gland ○ Fatty cleavage plane between mass and submandibular gland identifies lesion as nodal in origin ○ Internal architecture (e.g., presence of echogenic hilum) helps to identify lymph node • Consider major differential diagnoses for mass in submandibular region ○ Congenital lesion: Epidermoid cyst, cystic hygroma ○ Inflammatory condition: Submandibular gland sialadenitis/abscess, diving ranula, chronic sclerosing sialadenitis (Kuttner tumor), Sjögren syndrome ○ Lymph node enlargement: Reactive, inflammatory, or neoplastic (secondary or lymphomatous) ○ Benign salivary gland tumor, lipoma ○ Malignant salivary gland tumor

Imaging Recommendations • Scan submandibular region in transverse and longitudinal/oblique planes, as these best demonstrate floor of submandibular region, hyoglossus, and mylohyoid muscles • Always establish origin of mass (i.e., submandibular glandular or extraglandular mass), as this will help to narrow differential diagnosis • Remember to evaluate glandular/extraglandular ductal dilatation and lymph nodes at this location

Imaging Pitfalls • Distinction between submandibular glandular mass and enlarged lymph node can be difficult, especially if mass is large • Lesions of parotid tail may appear in posterior submandibular region clinically • Coronal MR helps to evaluate and localize large masses at this site

Submandibular Region Head and Neck

SUBMANDIBULAR SPACE

Platysma m. Sublingual space Mylohyoid m. Submandibular node (level I) Submandibular gland, superficial portion Masseter m.

Masticator space

Submandibular space

Medial pterygoid m. Submandibular gland, deep portion

Oropharyngeal mucosal space/surface

Oral mucosal space/surface Mylohyoid ridge of mandible Inferior alveolar n. Submandibular gland, superficial portion Facial v. Submandibular node (level I) Platysma m.

Sublingual space Mylohyoid m. Submandibular space

Root of tongue

Anterior belly of digastric m.

(Top) Axial graphic shows the oral cavity with emphasis on the submandibular space (SMS), shaded in light blue on the patient's left. The SMS is inferolateral to the mylohyoid muscle. Note that the principal structures of the SMS are the submandibular gland and lymph nodes. (Bottom) In this coronal graphic through the oral cavity, the SMS is shaded in light blue. The superficial layer of the deep cervical fascia (yellow line) is seen lining the vertical horseshoe-shaped SMS inferolateral to the mylohyoid muscle. The contents of the SMS are the anterior belly of the digastric muscle, submandibular nodes, submandibular gland, and facial vein. Note that the platysma muscle forms the superficial margin of the SMS.

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Head and Neck

Submandibular Region TRANSVERSE ULTRASOUND Subcutaneous tissue Platysma m. Submandibular gland Anterior belly of digastric m. Posterior belly of digastric m.

Mylohyoid m.

Facial a. Hyoglossus m.

Subcutaneous tissue Platysma m. Angle of mandible Submandibular gland Mylohyoid m. Facial a.

Hyoglossus m.

Subcutaneous tissue Platysma m. Superficial lobe of submandibular gland

Normal lymph node Facial a.

Mylohyoid m.

Deep process of submandibular gland

(Top) Transverse grayscale ultrasound shows the submandibular region. The submandibular gland sits astride the posterior belly of the digastric and mylohyoid muscles. The hyoglossus muscle is seen deep to the submandibular gland. (Middle) Transverse grayscale ultrasound of the submandibular region (slightly more posterior scan) shows the consistent relationship of the submandibular gland superficial to the mylohyoid and hyoglossus muscles. The submandibular duct runs between these 2 muscles. (Bottom) Transverse grayscale ultrasound shows the submandibular gland. The gland is divided into superficial and deep lobes, demarcated by the free posterior edge of the mylohyoid muscle. Normal lymph nodes are a constant finding in this region.

100

Submandibular Region

Mentalis m. Platysma m.

Genioglossus m. Sublingual gland

Submandibular duct Submandibular gland, superficial portion Submandibular gland, deep portion External and internal jugular v. Internal jugular v. and branches Sternocleidomastoid m. Platysma m.

Subcutaneous tissue Mental foramen

Head and Neck

AXIAL MR AND POWER DOPPLER ULTRASOUND

Inferior alveolar n. Mylohyoid m. Hyoglossus m. Masseter m. Medial pterygoid m. Posterior belly of digastric m. Longus coli Vertebral a. Subcutaneous tissue Body of mandible

Mylohyoid cleft

Genioglossus Lymph node

Mylohyoid m.

Lingual septum Hyoglossus m.

Facial v.

Posterior belly of digastric m.

Jugulodigastric node Intervertebral disc

Subcutaneous tissue Platysma m. Hilar vascularity of lymph node

Facial a.

Submandibular gland

Mylohyoid m.

(Top) Axial T2WI MR shows the floor of the mouth. The SMS contains submandibular glands, fat, and lymph nodes. Note the high-signal submandibular ducts entering the posterior aspect of sublingual spaces bilaterally. (Middle) In a more inferior image, both submandibular glands are seen wrapping around the posterior margins of the mylohyoid muscles. The neurovascular pedicle to each side of the tongue is closely related to the hyoglossus muscle. (Bottom) Transverse power Doppler ultrasound of submandibular gland shows vascular flow within the facial artery. Note the presence of normal hilar vascularity within the lymph node.

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Head and Neck

Submandibular Region TRANSVERSE ULTRASOUND Subcutaneous tissue Platysma m. Facial v. Submandibular gland Mylohyoid m. Tail of parotid gland Retromandibular v.

Facial a.

Subcutaneous tissue Platysma m. Submandibular gland Mylohyoid m. Angle of mandible Facial a. Normal lymph node

Submandibular gland Dilated intraglandular ducts Anterior belly of digastric m. Calculus Mylohyoid m. Posterior belly of digastric m.

(Top) Transverse grayscale ultrasound shows the posterior submandibular region. Note the close proximity of the submandibular gland to the tail of the parotid gland. On ultrasound, it may be difficult to localize the origin of large lesions at this site. Displacement of vessels often provides the clue. (Middle) Longitudinal grayscale ultrasound shows the submandibular region. The submandibular gland is located inferior and posterior to the mandible and superficial to the mylohyoid muscle. (Bottom) Transverse grayscale ultrasound of the left submandibular gland shows a large obstructing calculus with intraglandular ductal dilatation. Note the glandular parenchyma appears heterogeneous and hypoechoic, compatible with sialadenitis secondary to obstruction.

102

Submandibular Region

Facial v.

Head and Neck

POWER DOPPLER ULTRASOUND AND PATHOLOGY

Retromandibular v. Facial a.

Mandible Facial a. Hilar vascularity in normal lymph node Facial a. branch supplying submandibular gland

Submandibular gland Mylohyoid m.

Submandibular gland Prominent intraglandular vessels Anterior belly of digastric m. Mylohyoid m.

(Top) Transverse color Doppler ultrasound helps to identify and confirm important vascular landmarks in the posterior submandibular region, including the retromandibular vein and facial artery. (Middle) Longitudinal power Doppler ultrasound of the submandibular region shows the relationship of the facial artery to the superficial portion of the submandibular gland. The hilar vascularity of a normal lymph node and the vessels supplying the submandibular gland are seen. (Bottom) Transverse power Doppler ultrasound of the left submandibular gland shows an enlarged, heterogeneous submandibular gland with patchy hypoechoic "nodular" areas. Note prominent intraglandular vessels running through "nodules" with no mass effect/displacement. No ductal dilatation or calculus is seen. These changes are also present in the contralateral gland (not shown), suggesting chronic sclerosing sialadenitis (Kuttner tumor).

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Head and Neck

Parotid Region

TERMINOLOGY Abbreviations

Questions

• Parotid space (PS)

• Extends from external auditory canal (EAC) and mastoid tip superiorly to below angle of mandible (parotid tail)

• Is deep lobe of parotid gland involved ○ For parotid mass, it is important to determine location and extent of involvement in relation to extracranial facial nerve (i.e., superficial/deep lobe involvement) – Difference in surgical approach and risk of perioperative facial nerve injury ○ Intraparotid facial nerve is not visible with USG, CT, or MR, except proximally with high-resolution MR ○ On US, RMV is used as marker for division of parotid gland into superficial and deep lobes (due to close proximity to CNVII)

Internal Contents

Imaging Approaches

• Parotid gland ○ Divided anatomically into superficial lobe and deep lobe by extracranial facial nerve – Superficial lobe: Constitutes ~ 2/3 of parotid glandular parenchyma – Deep lobe: Smaller component, projects into lateral parapharyngeal space • Extracranial facial nerve (CNVII) ○ Exits stylomastoid foramen as single trunk; ramifies within PS lateral to retromandibular vein (RMV) ○ Ramifying intraparotid facial nerve creates surgical plane between superficial and deep lobes • External carotid artery (ECA) ○ Medial and smaller of 2 vessels seen just behind mandibular ramus in PS • RMV ○ Lateral and larger of 2 vessels seen just behind mandibular ramus in parotid ○ Formed by union of superficial temporal vein and maxillary vein ○ Intraparotid facial nerve branches course just lateral to RMV • Intraparotid lymph nodes ○ ~ 20 lymph nodes found in each parotid gland ○ Parotid nodes are 1st-order drainage for EAC, pinna, and surrounding scalp • Parotid duct ○ Emerges from anterior PS, runs along surface of masseter muscle ○ Duct then arches through buccal space to pierce buccinator muscle at level of upper 2nd molar • Accessory parotid glands ○ Project over surface of masseter muscle ○ Present in ~ 20% of normal anatomic dissections • Masseter muscle ○ Muscle of mastication related to outer surface of mandibular ramus ○ Parotid duct runs anteriorly on its surface • Buccinator muscle ○ Deep muscle of buccal space, extends anteriorly and just medially to anterior margin of masseter muscle – Parotid duct pierces to enter buccal mucosa at upper 2nd molar level

• Scan in both transverse and longitudinal planes ○ Transverse scans define anatomic location of salivary gland masses in relation to ECA and RMV ○ Longitudinal scans help to better evaluate lesions in parotid tail and for Doppler examination • USG cannot evaluate deep lobe mass or deep extension of superficial masses ○ Lower frequency transducer (e.g., 5 MHz) with gel block/standoff pad helps to evaluate large parotid mass with suspicious deep lobe extension ○ MR/CT is required for full anatomical delineation ○ US helps to direct needle for guided biopsy • Always evaluate masseter muscle as its lesions clinically mimic parotid pathology • Normal intraglandular ducts are seen as echogenic streaks within parotid parenchyma ○ When dilated, seen as 2 bright lines separated by fluid within ○ Extraglandular portion of duct is seen on US only if it is dilated

Definitions • Paired lateral suprahyoid neck spaces enclosed by superficial layer of deep cervical fascia containing parotid glands, nodes, and extracranial facial nerve branches

IMAGING ANATOMY Extent

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ANATOMY IMAGING ISSUES

CLINICAL IMPLICATIONS Clinical Importance • Although US cannot visualize parotid deep lobe, it is still ideal initial imaging modality to evaluate parotid masses, as most are located in superficial lobe ○ US characterizes common salivary masses and safely guides fine-needle aspiration cytology/biopsy for confirmation

EMBRYOLOGY Embryologic Events • PS undergoes late encapsulation in embryogenesis

Practical Implications • Late encapsulation results in intraparotid lymph nodes • Warthin tumor arises within this lymphoid tissue (intraparotid > > periparotid > upper cervical) • Parotid nodes are 1st-order drainage for malignancies of adjacent scalp, EAC, pinna, and deep face • No such nodes in submandibular gland due to early encapsulation; therefore, no Warthin tumor or nodal metastases in submandibular gland

Parotid Region

Parotid gland

Head and Neck

PAROTID GLAND AND SPACE

Temporal branches of facial n.

Zygomatic branches of facial n. External auditory meatus Posterior auricular n.

Parotid duct Masseter m.

Main trunk of facial n. (from stylomastoid foramen)

Buccal branches of facial n. Marginal mandibular branch of facial n.

Cervical branch of facial n.

Masticator space

Parapharyngeal space External carotid a. Deep lobe parotid gland Retromandibular v. Intraparotid facial n. Styloid process Intraparotid lymph node Posterior belly of digastric m. Superficial layer, deep cervical fascia Mastoid tip

(Top) Lateral schematic diagram shows the parotid region. The parotid gland is situated in front of the external auditory meatus and below the zygomatic arch. The parotid duct emerges from the anterior margin and passes superficial to the masseter muscle. The facial nerve, after emerging from the stylomastoid foramen, enters the parotid gland and divides into terminal branches to supply muscles of facial expression. (Bottom) Axial graphic shows the parotid space (PS) at the level of C1 vertebral body. The intraparotid course of the facial nerve extends from just medial to the mastoid tip to a position just lateral to the retromandibular vein, dividing the parotid gland into superficial and deep lobes.

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Head and Neck

Parotid Region TRANSVERSE US Subcutaneous tissue Parotid gland, superficial lobe Ramus of mandible

Retromandibular v. Tip of mastoid process

Subcutaneous tissue Platysma m. Ramus of mandible Masseter m.

Sternocleidomastoid m. Tail of parotid gland

Retromandibular v. External carotid a.

Posterior belly of digastric m.

Subcutaneous tissue Masseter m. Ramus of mandible

Retromandibular v. Sternocleidomastoid m.

External carotid a.

Superficial lobe, parotid gland

(Top) Transverse grayscale US shows the parotid region. Note its relationship to the mastoid process and the mandibular ramus. The glandular parenchyma shows a homogeneous, hyperechoic pattern. The retromandibular vein is visualized as a round, anechoic structure within the parotid gland. (Middle) Transverse grayscale US shows the parotid tail region. The sternocleidomastoid muscle and the posterior belly of the digastric muscle are related to the posterior margin of the parotid tail. The retromandibular vein and external carotid artery serve as markers to infer the location of CNVII. (Bottom) Transverse grayscale US shows the parotid gland. The retromandibular vein is usually larger and lateral to the external carotid artery within the parotid gland. Note that the deep lobe is obscured by shadowing from the mandibular ramus.

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Parotid Region

Buccinator m.

Head and Neck

AXIAL T1 MR AND POWER DOPPLER US

Parotid duct Parapharyngeal space Ramus of mandible Intraparotid facial nerve course Retromandibular v. Internal jugular v. and internal carotid a.

Masseter m.

Masseter m. Parotid space Parotid gland Posterior belly of digastric m.

Masticator space

Medial pterygoid m. Parapharyngeal space External carotid a.

Carotid space

Retromandibular v. Parotid gland Sternocleidomastoid m.

Posterior belly of digastric m.

Parotid gland, superficial lobe Sternocleidomastoid m. Retromandibular v. External carotid a.

(Top) Axial T1-weighted MR at the oral pharyngeal level shows the parotid gland as a homogeneous T1-hyperintense structure posterolateral to the mandibular ramus and masseter muscle. Note the projected intraparotid facial nerve course drawn on the right. (Middle) Axial T1-weighted MR shows a more inferior level of the parotid glands. The PS relates anteriorly to the masticator space, medially to the parapharyngeal space, and is separated medially by the posterior belly of digastric muscle from the carotid space. (Bottom) Power Doppler US helps to depict the retromandibular vein and external carotid artery, which are sometimes difficult to see in patients with bright fatty parotid glands. The retromandibular vein and external carotid artery help to infer location of CNVII.

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Head and Neck

Parotid Region LONGITUDINAL US

Subcutaneous tissue Intraparotid duct Parotid gland

Ramus of mandible

Subcutaneous tissue Echogenic hilum in intraparotid lymph node Intraparotid lymph node

Parotid gland

Subcutaneous tissue Parotid gland, superficial lobe Retromandibular v. Ramus of mandible

Posterior belly of digastric m. External carotid a.

(Top) This is the 1st image in a series of longitudinal grayscale US scans of the parotid gland. The parotid gland is superficial to the ramus of the mandible. (Middle) Second image shows a normal intraparotid lymph node in the superficial lobe of the parotid gland. On high-resolution US, normal nodes are invariably seen in the parotid tail and in the pretragal parotid gland. The elliptical shape and normal internal architecture with echogenic hilum suggest its benign nature. (Bottom) Third image at the plane of the retromandibular vein is shown. Such anatomy is best seen in children and young adults where there is not much fat deposition in the gland.

108

Parotid Region

Cavernous portion of internal carotid a. Meckel cave Mandible Parapharyngeal space Parotid gland, superficial lobe Retromandibular v. Parotid gland, deep lobe

Head and Neck

CORONAL T1 MR AND POWER DOPPLER US

Clivus Foramen lacerum Body of mandible Body of C2

Jugulodigastric lymph node Common carotid a. Longus coli m.

Sternocleidomastoid m.

Subcutaneous tissue Parotid gland Hilar vascularity in normal intraparotid lymph node

Subcutaneous tissue Parotid gland, superficial lobe Retromandibular v.

(Top) Coronal T1-weighted MR shows the parotid glands. The retromandibular vein is seen as a signal-void tubular structure traversing the parotid gland vertically, helping to suggest the location of CNVII. (Middle) Longitudinal power Doppler US of the parotid gland shows the presence of hilar vascularity within a normal intraparotid lymph node. On high-resolution US, more nodes are seen in children compared to adults. (Bottom) Longitudinal power Doppler US of the parotid gland clearly delineates the retromandibular vein.

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Head and Neck

Parotid Region TRANSVERSE US

Subcutaneous tissue

Masseter m.

Parotid gland, superficial lobe

Ramus of mandible

Subcutaneous tissue Buccinator m.

Fat-filled buccal space Masseter m.

Gas/buccal mucosa interface

Mandible

Parotid gland Benign mixed tumor Tip of mastoid process

Posterior acoustic enhancement

(Top) Transverse grayscale US of the anterior parotid region shows the masseter muscle superficial to the ramus of the mandible and closely related to the parotid gland. Note that masseter muscle lesions can mimic parotid pathology clinically. (Middle) Transverse grayscale US of the anterior parotid region/facial region shows the buccinator muscle as a thin, hypoechoic structure extending anteriorly and just medial to the anterior margin of the masseter muscle. The buccal space, which lies lateral to the buccinator muscle, is fat filled and contains the facial nerve, vein, artery, and the parotid duct. (Bottom) Transverse grayscale US of the right parotid gland shows a well-defined, solid, heterogeneous, hypoechoic mass with a lobulated margin in the superficial lobe. Despite the solid nature of the tumor, there is intense posterior acoustic enhancement, often seen in benign mixed tumors. Pathology confirmed benign mixed tumor.

110

Parotid Region

Intrinsic muscles of tongue Lingual septum

Head and Neck

AXIAL T1 MR AND TRANSVERSE US

Masseter m. Ramus of mandible

Medial pterygoid m. Parapharyngeal space

Superficial lobe of parotid gland

Stylopharyngeus m.

External carotid a.

Internal carotid a.

Retromandibular v.

Internal jugular v.

Posterior belly of digastric m. Sternocleidomastoid m.

Inferior oblique m.

Splenius capitis m.

Subcutaneous tissue Buccinator m. Zygomaticus m. Buccal fat space Course of parotid duct Tongue Masseter m. Soft palate Pharyngeal constrictor m. Oropharynx

Ramus of mandible Parotid gland, superficial lobe Medial pterygoid m. Retromandibular v.

Dilated parotid duct Parotid gland Ramus of mandible Masseter m.

(Top) Axial T1-weighted MR of the right parotid region shows the relationship of the parotid gland to the masseter muscle and the ramus of the mandible, the parapharyngeal space and the posterior belly of the digastric muscle, and the upper sternocleidomastoid muscle. (Middle) Axial T1-weighted MR shows the anterior parotid region. The parotid duct courses anteromedially within the buccal fat space and pierces the buccinator muscle at the level of the upper 2nd molar into the buccal mucosa. (Bottom) Transverse grayscale US of the right parotid gland shows a grossly dilated parotid duct superficial to the ramus of the mandible and masseter muscles. The ductal dilatation is due to distal parotid ductal stricture close to the orificial opening. Note that the parotid gland itself is atrophic and heterogeneous, secondary to chronic infection.

111

Head and Neck

Upper Cervical Level

TERMINOLOGY Abbreviations • • • •

Internal carotid artery (ICA) External carotid artery (ECA) Internal jugular vein (IJV) Jugulodigastric (JD) lymph node

Synonyms • Carotid triangle • Suprahyoid anterior triangle

Definitions • Portion of anterior triangle adjacent to major vessels of carotid sheath • Extends from skull base superiorly to hyoid bone inferiorly

IMAGING ANATOMY Overview • Cervical region is divided into upper, mid, and lower cervical levels in order to identify relevant groups of jugular cervical lymph nodes • On ultrasound, upper cervical region is best scanned transversely from submandibular/parotid tail region to carotid bifurcation • Major structures of upper cervical level: Cervical portion of ICA, ECA with origins of major branches, carotid bifurcation, IJV, posterior belly of digastric muscle, and JD lymph node

Internal Contents • Cervical portion of ICA ○ 1 of 2 branches from common carotid artery – Runs lateral or posterolateral to ECA – Usually of larger caliber than ECA – Low-resistance arterial flow waveform on Doppler ultrasound ○ Supplies anterior part of brain, eye, and its appendages ○ Divided into bulbous, cervical, petrous, cavernous, and cerebral portions ○ Only first 2 portions lie extracranially and are accessible by ultrasound ○ No branch in extracranial portions • ECA ○ Runs medial to cervical ICA ○ Smaller than ICA ○ High-resistance arterial flow waveform on Doppler ultrasound ○ Plays pivotal role in collateral circulation if arterial occlusion of ICA/vertebral artery ○ 1st branch: Superior thyroid artery – Readily detected by grayscale and Doppler examination • Carotid bifurcation ○ ~ at level of hyoid bone (i.e., division between upper and midcervical levels) ○ Bulbous dilatation of proximal ICA beyond carotid bifurcation: Carotid bulb ○ Carotid body is located at carotid bifurcation • IJV ○ Inferior continuation of sigmoid sinus from level of jugular foramen at skull base 112

○ Right usually of larger caliber than left ○ Lateral/posterolateral to ICA ○ Acts as landmark for jugular cervical lymph nodes • Posterior belly of digastric muscle ○ Key structure in separating parotid region superiorly from upper cervical level inferiorly ○ Runs anteroinferiorly from mastoid process to hyoid bone ○ Emerges deep to sternocleidomastoid muscle to abut tail of parotid gland ○ Major vessels run deep to muscle – From posterior to anterior: IJV, ICA, and ECA • JD lymph node ○ Largest and most superior lymph node of deep jugular chain, a.k.a. "sentinel" node of internal jugular chain ○ Resides close to carotid bifurcation/IJV ○ Orientated along line of digastric muscle ○ Commonly involved in head and neck cancer • Vagus nerve ○ Descends from skull base within carotid sheath ○ Sandwiched between ICA medially and IJV ○ More difficult to see than in mid and lower cervical levels

ANATOMY IMAGING ISSUES Questions • What are common differential diagnoses for mass in upper cervical level ○ Enlarged lymph nodes: Reactive, inflammatory, and neoplasm (metastases/lymphoma) ○ Congenital lesion: 2nd branchial cleft cyst ○ Vascular lesion: IJV varix, IJV thrombosis ○ Neoplasm: Vagal schwannoma, carotid body tumor • What are common sites ○ JD lymph node is common site of nodal metastases from head and neck cancer ○ Common sites of primary include oral cavity (including tonsils and tongue), nasopharyngeal carcinoma ○ JD node also commonly involved in lymphoma – Multiple, often bilateral nodal involvement, pseudocystic/reticulated internal architecture on ultrasound

Imaging Recommendations • Scan in transverse plane from submandibular region/parotid tail down to carotid bifurcation ○ Longitudinal scanning for more detailed assessment of internal architecture of lesion and evaluation of intralesional vascularity on Doppler • Color flow imaging helps to identify major vessels and their anatomic relation to node/mass ○ Also provides flow information of cervical masses to characterize their nature • US provides safe real-time guidance for fine-needle aspiration cytology (FNAC)/biopsy to further enhance diagnostic yield ○ FNAC/biopsy is not recommended for suspected carotid body tumor due to risk of uncontrolled bleeding

Upper Cervical Level Head and Neck

UPPER CERVICAL ANATOMY

Parotid gland

Posterior belly of digastric muscle Submandibular gland Internal jugular v. External carotid a.

Hyoid bone

Cervical portion of internal carotid a. Carotid bifurcation Vagus n.

Submandibular space Pharyngeal mucosal space/surface Retropharyngeal space

Masticator space Posterior belly, digastric m.

Danger space Parapharyngeal space Alar fascia Perivertebral space, prevertebral component

Parotid space Carotid space Posterior cervical space

Perivertebral space, paraspinal component

(Top) Schematic diagram shows the key structures in the upper cervical level. The hyoid bone and the carotid bifurcation are 2 anatomical landmarks for the inferior margin of the upper cervical level. With high-resolution ultrasound, the jugulodigastric lymph node will be consistently seen at this site and should not be mistaken for pathology. Visualization of a similar node on the opposite side helps. (Bottom) Axial graphic shows the suprahyoid neck spaces at the level of the oropharynx. The superficial (yellow line), middle (pink line), and deep (turquoise line) layers of the deep cervical fascia outline the suprahyoid neck spaces. Ultrasound assessment of the upper cervical level involves scanning transversely along the major vessels of the carotid sheath (i.e., the internal carotid artery and internal jugular vein).

113

Head and Neck

Upper Cervical Level TRANSVERSE ULTRASOUND Subcutaneous tissue Jugulodigastric lymph node Submandibular gland Facial v. Sternocleidomastoid m. Internal jugular v. Internal carotid a.

Branches of external carotid a. External carotid a. Gas within supraglottic larynx

Subcutaneous tissue Platysma m. Jugulodigastric lymph node Posterior belly of digastric m. Internal carotid a. Sternocleidomastoid m. Internal jugular v. Scalenus anterior

External carotid a. Gas within supraglottic larynx

Longus coli

Transverse process

Subcutaneous tissue Sternocleidomastoid m. Common carotid a. Vagus n. Internal jugular v.

Gas within supraglottic larynx

Scalenus anterior Tip of transverse process of cervical vertebra Longus coli m.

(Top) First image in a series of consecutive transverse grayscale ultrasound images of the upper cervical level clearly identifies key vascular landmarks, including the internal and external carotid arteries and the internal jugular vein. The uppermost and largest deep cervical lymph node (i.e., the jugulodigastric lymph node) is consistently seen on ultrasounds in the upper cervical level anterior to the carotid arteries. It is usually elliptical, hypoechoic, and with echogenic hilum. (Middle) Second image shows the carotid bifurcation in the transverse plane. The external carotid artery is usually more medial and smaller than the internal carotid artery. (Bottom) Third image below the level of carotid bifurcation clearly shows the common carotid artery, internal jugular vein, and vagus nerve to be major structures within the carotid sheath.

114

Upper Cervical Level

Base of tongue

Facial v. Retromandibular v.

Head and Neck

AXIAL CECT

Vallecula Epiglottis

External carotid a. Carotid space Sternocleidomastoid m. Posterior triangle lymph node with normal hilar architecture

Posterior cervical space Vagus n.

Scalenus anterior Semispinalis capitis and semispinalis cervicis

Submandibular lymph nodes

Submandibular gland

Platysma m. Pyriform fossa Facial v. External jugular v. Jugulodigastric lymph node

External carotid a. Internal carotid a.

Internal jugular v. Longus coli Sternocleidomastoid m.

Vertebral a. and v. Vertebral body

Hyoid bone Submandibular gland Platysma m. External jugular v. Common carotid a. Internal jugular v.

Pre-epiglottic space Aryepiglottic fold Pyriform fossa Posterior cervical space

Vagus n. Prevertebral m. Sternocleidomastoid m. Levator scapulae m.

(Top) At the level just above the hyoid bone, the carotid bifurcation can be seen. The vagus nerve is seen within the carotid sheath. (Middle) CECT image shows the suprahyoid neck at the level of the free margin of epiglottis. The jugulodigastric lymph node is commonly seen; however, the internal architecture is better assessed on ultrasound than CECT. (Bottom) At the level of the hyoid bone, the carotid space now contains the common carotid artery, internal jugular vein, and vagus nerve only. The submandibular space is seen anteriorly and is predominantly fat filled at this level. Familiarity with cross-sectional anatomy is key to optimal ultrasound examination of the neck, as lesions at this level are site specific.

115

Head and Neck

Upper Cervical Level TRANSVERSE ULTRASOUND Subcutaneous tissue Platysma m. Submandibular gland Normal echogenic hilus in jugulodigastric node Jugulodigastric node Sternocleidomastoid m.

Branches of external carotid a.

Internal jugular v. External carotid a. Internal carotid a. Scalenus anterior

Internal carotid a. External carotid a.

Carotid body paraganglioma

Submandibular gland Sternocleidomastoid m. 2nd branchial cleft cyst Carotid bifurcation

(Top) Transverse grayscale ultrasound shows the upper cervical level. The normal jugulodigastric lymph node is elliptical in shape with preserved echogenic hilum. Its anatomical relationship with the major neck vessels is better appreciated on power Doppler ultrasound. (Middle) Transverse grayscale ultrasound of the left upper cervical level shows a large, heterogeneous, hypoechoic mass centered at the carotid bifurcation, splaying the internal and external carotid arteries. Appearances and location are strongly indicative of carotid body paraganglioma. (Bottom) Transverse grayscale ultrasound of the right upper cervical level shows a well-circumscribed cystic mass with a pseudosolid appearance along the medial edge of the sternomastoid muscle, posterior to the submandibular gland and superficial to major vessels within the carotid sheath. Location and appearances are suggestive of 2nd branchial cleft cyst. This pseudosolid appearance is commonly seen in congenital neck cysts, including thyroglossal duct cysts.

116

Upper Cervical Level

Subcutaneous tissue Sternocleidomastoid m.

Head and Neck

POWER DOPPLER ULTRASOUND

Jugulodigastric lymph node Hilar vascularity of jugulodigastric lymph node Internal jugular v. Internal carotid a.

Facial v. Branches of external carotid a.

External carotid a.

Carotid body paraganglioma External carotid a. Internal carotid a. Intratumoral vascularity

Submandibular gland

2nd branchial cleft cyst Carotid bifurcation

Sternocleidomastoid m.

(Top) Transverse power Doppler ultrasound shows the upper cervical level. The major vessels, including the internal and external carotid arteries and the internal jugular vein, show color flow. Note the presence of normal hilar vascularity within the echogenic hilum of the jugulodigastric lymph node. (Middle) Transverse power Doppler ultrasound shows marked intratumoral vessels in carotid body paraganglioma. Note the characteristic splaying of internal and external carotid arteries. (Bottom) Axial T1WI MR shows a lobulated right upper neck lesion with well-circumscribed margins located posterior to the submandibular gland, along the medial edge of the sternocleidomastoid muscle and superficial to major arteries of the carotid sheath. Location of lesion is typical for 2nd branchial cleft cyst. Note T1-hyperintense signal within the 2nd branchial cleft cyst due to proteinaceous intracystic content.

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Head and Neck

Midcervical Level

TERMINOLOGY Definitions • Portion of anterior triangle adjacent to major vessels of carotid sheath • Extends from hyoid bone superiorly to cricoid cartilage inferiorly

IMAGING ANATOMY Overview • Major lymphatic drainage of head and neck region is via deep jugular cervical lymph nodes, which are distributed along upper, mid, and lower cervical levels • Key structures at midcervical level ○ Common carotid artery (CCA), internal jugular vein (IJV), vagus nerve, lymph nodes, omohyoid muscle, and esophagus

Internal Contents • CCA ○ Arises from aortic arch directly on left from brachiocephalic trunk on right ○ Ascends neck within carotid sheath – Medial to IJV – Vagus nerve sandwiched between CCA and IJV ○ No named branches in midcervical level ○ Bifurcates into internal carotid artery and external carotid artery at level of hyoid bone ○ Low-resistance arterial flow pattern • IJV ○ Inferior continuation of sigmoid sinus from jugular foramen at skull base ○ Major deep venous drainage from brain and neck ○ Descends within carotid sheath – Lateral to CCA at midcervical level ○ Joins subclavian vein to form brachiocephalic vein ○ Ultrasound appearance – Occasionally presence of slow venous flow may mimic IJV thrombus □ Real-time visualization of layering and sharp linear interface help to distinguish it from thrombus □ Make sure IJV is compressible and has respiratory phasicity • Vagus nerve (CNX) ○ Extracranial segment starts superiorly from jugular foramen at skull base ○ Descends along posterolateral aspect of carotid artery within carotid sheath – Passes anterior to aortic arch on left and subclavian artery on right ○ Major autonomic nerve supply to visceral organs in thorax and abdomen ○ Ultrasound appearance – On transverse scan, appears as round, hypoechoic structure with central echogenicity □ Close relation to CCA, IJV is clue to its identification – On longitudinal scan, seen as long tubular hypoechoic structure with fibrillar pattern • Lymph nodes

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○ Numerous lymph nodes are seen along deep jugular chain in midcervical level ○ Receive lymphatic drainage from upper jugular chain and directly from adjacent structures, including larynx, hypopharynx, and thyroid gland – Commonly involved in nodal metastases from common head and neck cancers ○ Usually located anterior to vessels of carotid sheath ○ Ultrasound appearance – Small, elliptical in shape, presence of echogenic hilus, preserved hilar vascularity on Doppler imaging • Omohyoid muscle ○ Arises from anterior portion of body of hyoid bone ○ Runs obliquely to cross anterior to CCA and deep to sternocleidomastoid muscle ○ Intermediate tendon overlies IJV – Occasionally mistaken for lymph node ○ Then runs obliquely across inferior posterior triangle to attach to posterior aspect of lateral clavicle • Cervical esophagus ○ Junction of cricopharyngeus muscle and proximal cervical esophagus is located in midcervical level ○ Lies posterior/posterolateral to trachea and medial to CCA – More commonly slightly off midline to left – Asking patient to swallow during real-time sonography helps to accurately identify esophagus ○ Ultrasound appearance – May be mistaken for parathyroid adenoma or paratracheal lymph node – Have patient swallow to confirm if any question

ANATOMY IMAGING ISSUES Imaging Approaches • Scan in transverse plane along major vessels of carotid sheath (keep CCA and IJV in center of image) ○ From carotid bifurcation down to level of cricoid cartilage • Longitudinal/oblique plane for better assessment of internal architecture and vascularity of any lesion detected on scanning in transverse plane • Color flow imaging helps to identify major vessels and characterize lesions in this region • Ultrasound also provides safe real-time guidance for fineneedle aspiration cytology or biopsy

CLINICAL IMPLICATIONS Clinical Importance • Common differential diagnoses for mass at midcervical level ○ Enlarged lymph nodes: Reactive, inflammatory, or neoplastic (metastases/lymphoma) disease ○ Inflammatory: Abscess ○ Congenital lesion: Lymphatic malformation, off-midline thyroglossal duct cyst ○ Neoplasm: Vagal schwannoma, esophageal lesion

Midcervical Level

Hyoid bone

Head and Neck

MIDCERVICAL ANATOMY

Internal jugular v.

Vagus n.

Omohyoid m.

Common carotid a.

Cricoid cartilage

Anterior strap mm.

Platysma m. Superficial layer, deep cervical fascia Middle layer, deep cervical fascia Recurrent laryngeal n.

Thyroid gland

Anterior cervical space

Common carotid a. Internal jugular v. Vagus n. (CNX) Deep layer, deep cervical fascia Sympathetic trunk

Carotid space

Retropharyngeal space Danger space

(Top) Schematic diagram shows the midcervical level, which contains key structures, including the common carotid artery, internal jugular vein, and vagus nerve within the carotid sheath. The hyoid bone and the cricoid cartilage are the anatomical landmarks for the superior and inferior borders of the midcervical level, respectively. With high-resolution ultrasound, normal small jugular chain lymph nodes may be seen at this site and should not be mistaken for pathology. (Bottom) Axial graphic shows the midcervical level in the infrahyoid neck. Note that the carotid sheath contains all 3 layers of the deep cervical fascia (tricolor line). In the infrahyoid neck, the carotid sheath is tenacious throughout its length. The infrahyoid carotid space contains the common carotid artery, internal jugular vein, and vagus cranial nerve.

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Head and Neck

Midcervical Level TRANSVERSE ULTRASOUND Subcutaneous tissue Sternocleidomastoid m. Lymph node Common carotid a.

Internal jugular v.

Thyroid lamina

Vagus n. Anterior scalene m.

Platysma m. Sternocleidomastoid m. Lymph node

Internal jugular v. Tip of transverse process of cervical vertebra

Common carotid a. Thyroid lamina Gas within supraglottic larynx

Vagus n. Scalenus anterior m. Transverse process of cervical vertebra

Subcutaneous tissue Sternohyoid m. Sternothyroid m.

Superior pole of right thyroid gland Sternocleidomastoid m. Internal jugular v. Common carotid a.

Transverse process of cervical vertebra

(Top) First image shows consecutive transverse grayscale ultrasound of midcervical level. Deep cervical lymph nodes are commonly found along and anterior to the major vessels of the carotid sheath. These are commonly hypoechoic and elliptical with a normal echogenic hilum and hilar vascularity. (Middle) Second image shows midcervical level in transverse plane. At this level, the common carotid artery, internal jugular vein, and vagus nerve are the main structures within the carotid sheath. The vagus nerve is usually located between the common carotid artery and the internal jugular vein and appears as a small, round, hypoechoic nodule with a central echogenic dot. (Bottom) Third image shows the midcervical level. The cricoid cartilage may not be routinely seen on ultrasound, and visualization of the superior pole of the thyroid gland ~ coincides with this level.

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Midcervical Level

Platysma Infrahyoid strap m. Sternocleidomastoid m. Common carotid a. Internal jugular v. Longus coli

Thyroid cartilage

Head and Neck

AXIAL CECT

Paraglottic space Aryepiglottic fold Posterior pharyngeal wall Pharyngeal constrictor m. Posterior cervical space

Levator scapulae m. Semispinalis capitis Semispinalis cervicis

Infrahyoid strap m. Thyroid cartilage Vocal cord Superior thyroid a. External jugular v.

Arytenoid Cricoid cartilage Paraspinal m. Vertebral body/intervertebral disc

Levator scapulae m.

Anterior jugular v.

Transverse process

Infra-hyoid strap m. Trachea

Sternocleidomastoid m. Thyroid gland External jugular v.

Cricoid cartilage Thyroid cartilage Esophagus Longus coli m. Vertebral a.

Levator scapulae m.

(Top) CECT shows the upper thyroid cartilage level. Major structures of the midcervical level, including the common carotid artery, internal jugular vein, and sternocleidomastoid muscle, are well demonstrated. Small lymph nodes are commonly seen adjacent to major vessels of the carotid sheath. (Middle) CECT shows the level of the lower thyroid lamina. Apart from the common carotid artery and internal jugular vein, branches of the external carotid artery, such as the superior thyroid artery, can be demonstrated. (Bottom) CECT shows the level of the cricoid cartilage. The upper pole of the thyroid gland begins to be included in cross section. Note the presence of calcification/ossification in the thyroid lamina and cricoid cartilages, which is a normal age-related change.

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Head and Neck

Midcervical Level TRANSVERSE GRAYSCALE ULTRASOUND

Sternocleidomastoid m. Internal jugular v. tumor thrombus Thyroid carcinoma in right lobe Internal jugular v.

Common carotid a.

Sternocleidomastoid m.

Metastatic lymph node

Internal jugular v.

Common carotid a.

Sternocleidomastoid m.

Metastatic lymph nodes from papillary thyroid carcinoma

Papillary thyroid carcinoma Right common carotid a.

Right internal jugular v.

(Top) Transverse grayscale ultrasound of the right midcervical level shows an eccentric, hypoechoic thrombus in the anteromedial wall of the right internal jugular vein. Note the presence of an adjacent thyroid carcinoma in the right lobe. (Middle) Transverse grayscale ultrasound of the left midcervical level shows an enlarged, round, solid, hypoechoic, deep cervical lymph node with loss of echogenic hilum. The adjacent left internal jugular vein is compressed. Pathology showed metastatic squamous cell carcinoma. (Bottom) Transverse grayscale ultrasound of the right midcervical level shows multiple enlarged, round, solid, slightly hyperechoic lymph nodes with punctate calcification suggesting metastases from primary papillary thyroid carcinoma. Note thyroid papillary carcinoma seen as an ill-defined, solid, hypoechoic nodule with punctate and coarse calcification in the right lobe of the thyroid gland. The right internal jugular vein is compressed by enlarged lymph nodes but remains patent.

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Midcervical Level

Sternocleidomastoid m.

Head and Neck

TRANSVERSE COLOR, DOPPLER, AND GRAYSCALE ULTRASOUND

Vascularity within tumor thrombus Thyroid gland (right lobe)

Common carotid a.

Metastatic lymph node

Peripheral/subcapsular intranodal vascularity Internal jugular v.

Subcutaneous tissue thickening

Abscess Gas within abscess cavity

Common carotid a.

(Top) Transverse color Doppler ultrasound in a patient with occlusive internal jugular vein thrombus shows the presence of vascularity within the internal jugular vein thrombus, suggesting it is a tumor thrombus rather than a bland venous thrombus. (Middle) Transverse power Doppler ultrasound shows the presence of peripheral/subcapsular intranodal vessels in a metastatic lymph node from head and neck squamous cell carcinoma. The vascularity is completely different from the hilar pattern of a normal cervical lymph node. (Bottom) Transverse grayscale ultrasound shows a neck abscess with fluid and gas within. The adjacent soft tissue is edematous and thickened. Note its close proximity to the common carotid artery, putting it at a risk of rupture.

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Head and Neck

Lower Cervical Level and Supraclavicular Fossa

TERMINOLOGY Definitions • Portion of lower anterior neck adjacent to carotid sheath, below level of cricoid cartilage and above level of clavicle

IMAGING ANATOMY Overview • Key structures in lower cervical level ○ Vessels: Common carotid artery (CCA), internal jugular vein (IJV), subclavian artery ○ Vagus nerve ○ Scalenus anterior muscle ○ Lymph nodes • Key structures in supraclavicular fossa ○ Trapezius, sternocleidomastoid, omohyoid muscles ○ Brachial plexus (BP) elements ○ Transverse cervical chain lymph nodes

Internal Contents • Subclavian artery ○ Arises from brachiocephalic trunk on right and aortic arch on left ○ Major arterial supply to upper limb ○ Contributes to arterial supply to neck structures and brain via vertebral artery ○ Junction of subclavian artery and CCA is readily identified on scanning in transverse plane in lower cervical level – Location marks root of neck ○ Origin of subclavian artery can be seen by angling transducer inferiorly behind medial head of clavicle • Scalenus anterior muscle ○ Runs inferiorly from transverse processes of cervical spine ○ Passes posterior to IJV to dip behind clavicle ○ Lies between 2nd part of subclavian artery posteriorly and subclavian vein anteriorly ○ Related posteriorly to scalenus medius muscle – BP roots/rami lie between scalenus anterior muscle and scalenus medius muscle in supraclavicular fossa – Scanning inferiorly in transverse plane, BP roots/rami appear as small, round, hypoechoic structures emerging from behind lateral border of scalenus anterior muscle • BP ○ Formed from ventral rami of C5-T1 ± minor branches from C4, T2 ○ Divided into roots/rami, trunks, division, cords, and branches – Roots/rami: Originate from spinal cord levels C5-T1 enter posterior triangle by emerging between scalenus anterior and medius muscle – Trunks: Upper (C5-C6), middle (C7), lower (C8-T1) – Divisions: Formed by each trunk, dividing into anterior and posterior branches in supraclavicular fossa – Cords: Lateral, medial, posterior cords descend behind clavicle to leave posterior triangle and enter axilla – Branches: In axilla • Trapezius muscle

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○ Anterior border marks posterior margin of posterior triangle and supraclavicular fossa and is easily recognized ○ Distal portion is attached to lateral clavicle • Inferior belly of omohyoid muscle ○ Runs obliquely from intermediate tendon to traverse inferior portion of supraclavicular fossa ○ Divides occipital triangle superiorly from supraclavicular triangle inferiorly • Transverse cervical chain lymph nodes ○ Seen adjacent to transverse cervical artery and vein, which arise from thyrocervical trunk and IJV ○ Related to and just superior to inferior belly of omohyoid muscle

ANATOMY IMAGING ISSUES Imaging Approaches • From midcervical level, proceed to scan in transverse plane along carotid sheath until medial head of clavicle (keep CCA and IJV in center of image) • Then sweep laterally in transverse plane above mid-/lateral portion of clavicle to assess supraclavicular fossa

Consider • Enlarged lymph node is most common cause of mass in lower cervical level and supraclavicular fossa ○ Terminology – Omohyoid node: Deep cervical chain node just superior to omohyoid (where omohyoid crosses IJV) – Virchow node: Signal node; lowest node of deep cervical chain nodes – Troisier node: Most medial node of transverse cervical chain nodes ○ Reactive nodes – Enlarged, cortical hypertrophy, preserved echogenic hilum and hilar vascularity ○ Metastatic nodes – Round, hypoechoic, peripheral/subcapsular vascularity, may have central necrosis ○ Lymphomatous nodes – Large, heterogeneous, reticulated/pseudocystic appearance, increased peripheral and central vascularity, bilateral involvement ○ Tuberculous lymphadenitis – Matted, necrotic, enlarged nodes with soft tissue edema and hypovascular/displaced hilar vascularity on power Doppler ultrasound • Isolated metastatic lymph node in supraclavicular fossa is unusual from primary in head and neck region ○ Careful search for infraclavicular primary is indicated ○ Common primary from lung, breast, esophagus, and colorectal cancers • Differential diagnoses ○ BP schwannoma ○ Lipoma ○ Venous malformation ○ Lymphatic malformation

Lower Cervical Level and Supraclavicular Fossa Head and Neck

LOWER CERVICAL AND SUPRACLAVICULAR ANATOMY

Hyoid bone Internal jugular v. Scalenus anterior m. Thyroid cartilage Trapezius m. Thyroid gland Vagus n. Recurrent laryngeal n. Common carotid a.

Phrenic n. Transverse cervical a. Brachial plexus Subclavian a.

Trachea Clavicle

Thyroid gland

Subclavian v.

Thyroid cartilage

Phrenic n. Scalenus anterior m.

Vagus n.

Brachial plexus Common carotid a. Thyrocervical trunk Subclavian a.

Internal jugular v.

Clavicle Trachea Left brachiocephalic v.

(Top) Graphic in lateral projection shows the anatomical relationship of major structures in the lower cervical level and supraclavicular fossa, including the common carotid artery, internal jugular vein, subclavian vessels, and brachial plexus. In assessing the supraclavicular fossa on ultrasound, adequate visualization is achieved by sweeping the transducer laterally in the transverse plane from the medial head of the clavicle. (Bottom) Graphic in frontal projection shows the lower cervical level and medial portion of the supraclavicular fossa. The major lymph nodes in these regions are mainly located close to the major vessels of the carotid sheath, including the Virchow node and the Troisier node. Presence of isolated malignant nodes at this site usually points to an infraclavicular primary. Proximity of these nodes to adjacent pulsatile vessels makes Doppler examination at this site suboptimal/difficult.

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Head and Neck

Lower Cervical Level and Supraclavicular Fossa TRANSVERSE ULTRASOUND

Subcutaneous tissue Sternohyoid m. Sternothyroid m.

Sternocleidomastoid m.

Right lobe of thyroid gland

Internal jugular v. Common carotid a.

Cervical esophagus

Longus colli m.

Subcutaneous tissue Sternocleidomastoid m. Internal jugular v. Valve within proximal internal jugular v. Valve in proximal subclavian v. Subclavian v.

Subcutaneous tissue Sternocleidomastoid m. Brachial plexus elements Internal jugular v. Scalenus anterior m. Scalenus medius m.

Common carotid a.

Transverse process

(Top) First image in a series of transverse grayscale ultrasound images shows the lower cervical level. Major structures at this level include the common carotid artery, internal jugular vein, thyroid gland, and overlying muscles of the anterior neck. (Middle) Second image shows the level of the medial supraclavicular fossa. Note the proximity of the proximal internal jugular vein to the subclavian vein at this site, which join to form the brachiocephalic vein. Supraclavicular lymph nodes are commonly found adjacent to these major vessels. (Bottom) Third image shows the lateral supraclavicular fossa. The scalenus anterior and medius muscles are clearly visualized with the trunks of the brachial plexus between them. Ultrasound is often used to guide brachial plexus blocks. Ultrasound also helps to exclude brachial plexus involvement by metastases at this site.

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Lower Cervical Level and Supraclavicular Fossa

Sternohyoid m. Sternocleidomastoid m. Internal jugular v. Common carotid a.

Head and Neck

AXIAL CECT AND POWER DOPPLER ULTRASOUND

Sternothyroid m. Trachea Thyroid gland, right lobe

Anterior scalene m.

Esophagus

External jugular v. Brachial plexus root

Inferior thyroid a. Prevertebral mm.

Middle scalene m.

Posterior scalene m.

Sternocleidomastoid m. Internal jugular v.

Subclavian v. Common carotid a.

Subcutaneous tissue Sternocleidomastoid m. Internal jugular v. Common carotid a.

Sternohyoid m. Sternothyroid m. Thyroid gland

(Top) Axial CECT shows the lower cervical level. The relationship of the thyroid gland with the adjacent structures, including the carotid sheath, strap muscles, trachea, and esophagus is demonstrated. (Middle) Transverse power Doppler ultrasound in the supraclavicular fossa helps to delineate vascular structures in this region, including the confluence of the internal jugular vein and the subclavian vein. The proximal portion of the common carotid artery from the brachiocephalic trunk is also seen at this level. (Bottom) Transverse power Doppler ultrasound of the lower cervical level allows the clear depiction of the color-filled common carotid artery and internal jugular vein. Nodes are often seen at this site and are readily evaluated by ultrasound and, if needed, biopsied using ultrasound guidance.

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Head and Neck

Lower Cervical Level and Supraclavicular Fossa LONGITUDINAL ULTRASOUND AND PATHOLOGY Subcutaneous tissue Clavicle Sternocleidomastoid m. Internal jugular v.

Brachiocephalic v. Subclavian v.

Subcutaneous and soft tissue thickening

Gas locule within abscess

Trachea Abscess cavity with pus Common carotid a.

Intranodal cystic necrosis

Metastatic supraclavicular lymph nodes

(Top) Longitudinal grayscale ultrasound of the supraclavicular fossa shows the confluence of the internal jugular vein and the subclavian vein to form the brachiocephalic vein just above the medial portion of the clavicle. Nodes often nestle under these vessels, making biopsy access difficult. Pulsation from the vessels also makes Doppler evaluation of nodes at this level suboptimal. (Middle) Transverse grayscale ultrasound of the left lower cervical level shows abscess formation in the left lobe and perithyroidal soft tissue due to acute suppurative thyroiditis. Note the presence of pus and echogenic foci due to gas bubbles. (Bottom) Transverse grayscale ultrasound of the right supraclavicular fossa shows multiple enlarged, round, predominantly solid, hypoechoic lymph nodes with intranodal cystic necrosis and no adjacent soft tissue edema. Appearances are highly suspicious of metastatic lymph nodes. Isolated metastatic nodes at this site point to an infraclavicular primary, commonly from lung, breast, or esophagus.

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Lower Cervical Level and Supraclavicular Fossa Head and Neck

CECT AND PATHOLOGY

Sternocleidomastoid m. Internal jugular v. Right lobe of thyroid gland

Subclavian v.

Clavicle

Brachiocephalic v.

Left lobe of thyroid gland Right lobe of thyroid gland

Abscess

Internal jugular v. Internal jugular v. Common carotid a. Common carotid a.

Brachial plexus schwannoma Contiguous n.

(Top) Coronal reformatted CECT of the lower neck and the supraclavicular fossa illustrates the venous anatomy. (Middle) Axial CECT of acute suppurative thyroiditis shows a large heterogeneous abscess with thick peripheral enhancement involving the left lobe of the thyroid gland and perithyroidal soft tissue. Note the presence of fluid and gas within the abscess cavity and marked subcutaneous thickening in left lower neck. (Bottom) Longitudinal grayscale ultrasound of the right supraclavicular fossa shows a solid, hypoechoic, lobulated mass contiguous with a thickened nerve. The appearances suggest a brachial plexus schwannoma. The continuation with a nerve is the clue to its diagnosis.

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Head and Neck

Posterior Triangle

TERMINOLOGY Abbreviations • Posterior cervical space (PCS)

Definitions • Posterolateral fat-containing space in neck with complex fascial boundaries that extends from posterior mastoid tip to clavicle behind sternocleidomastoid muscle

IMAGING ANATOMY Overview • Posterolateral fat-filled space just deep and posterior to sternomastoid muscle • Posterior border bound by anterior edge of trapezius muscle

Extent • PCS extends from small superior component near mastoid tip to broader base at level of clavicle • When viewed from side, appears as tilting tent

Anatomy Relationships • Superficial space lies superficial to PCS • Deep to PCS is perivertebral space ○ Anterior PCS is superficial to prevertebral component of perivertebral space ○ Posterior PCS is superficial to paraspinal component of perivertebral space

Internal Contents • Fat is primary component of PCS • Floor is formed by muscles running obliquely: Scalene muscles, levator scapulae, and splenius capitis muscles (from anterior to posterior) ○ Subdivided by inferior belly of omohyoid muscle into occipital and subclavian triangles • Muscular floor is covered by superficial and deep layers of deep cervical fascia • Spinal accessory nerve (CNXI) ○ Arises from nerve cells in anterior gray column of upper 5 segments of spinal cord ○ Ascends alongside spinal cord and enters skull through foramen magnum ○ Unites with cranial root to exit through jugular foramen ○ Spinal portion then separates from cranial root ○ Motor supply to soft palate, pharynx, larynx, sternocleidomastoid, and trapezius muscles • Spinal accessory lymph node chain ○ Level 5 spinal accessory nodes (SAN) further subdivide into A and B levels at hyoid bone – Level 5A: SAN above cricoid cartilage level – Level 5B: SAN below cricoid cartilage level • Preaxillary brachial plexus ○ Segment of brachial plexus emerging from anterior and middle scalene gap passes through PCS ○ Leaves PCS with axillary artery into axillary fat • Dorsal scapular nerve ○ Arises from brachial plexus (spinal nerves C4 and C5) ○ Motor innervation to rhomboid and levator scapulae muscles 130

• Transverse cervical artery and vein ○ Arises from thyrocervical trunk of subclavian artery and internal jugular vein respectively ○ Course in inferior posterior triangle and parallel to clavicle

ANATOMY IMAGING ISSUES Imaging Approaches • Scanning is usually undertaken in transverse plane • From mastoid tip superiorly to acromion process inferiorly ○ Spinal accessory chain lymph nodes run from point midway between mastoid process and angle of mandible to outer 1/3 of clavicle

Imaging Pitfalls • On transverse scan, tips of transverse process of cervical vertebrae may be seen as echogenic structures with posterior acoustic shadowing ○ Do not mistake these for calcified lymph nodes ○ Longitudinal scan helps to clarify

Consider • On ultrasound, normal-looking nodes are routinely found in posterior triangle of healthy individuals • Most lesions in posterior triangle arise from spinal accessory chain lymph nodes ○ Reactive lymphadenopathy – Elliptical, preserved internal architecture and hilar vascularity ○ Infective lymphadenitis, such as tuberculous lymphadenitis – Enlarged hypoechoic necrotic nodes with matting and soft tissue edema, avascular or displaced hilar vascularity ○ Metastatic lymph nodes – Primary from nasopharyngeal carcinoma and squamous cell carcinoma (SCC) from other H&N sites – Enlarged, round, hypoechoic nodes with intranodal necrosis and peripheral vascularity ○ Lymphomatous nodes – Usually bilateral neck involvement – Enlarged, heterogeneous, reticulated/pseudocystic appearance, increased hilar and peripheral vascularity, hilar > > peripheral • Other diseases that may occur in posterior triangle include ○ Congenital lesion: Lymphangioma, usually transspatial ○ Benign tumor: Lipoma, nerve sheath tumor

CLINICAL IMPLICATIONS Clinical Importance • CNXI runs in floor of posterior triangle ○ Accessory cranial neuropathy results when CNXI is injured ○ Most commonly injured during neck dissection for malignant SCC nodes ○ Less commonly injured by extranodal spread of SCC • SAN are main normal occupants of PCS

Posterior Triangle Head and Neck

POSTERIOR CERVICAL SPACE

Mastoid tip

Sternocleidomastoid m.

External jugular v.

Accessory n. (CNXI)

Spinal accessory nodal chain

Dorsal scapular n. Trapezius m. Inferior belly omohyoid m.

Clavicle

Tricolor carotid sheath Carotid space Sternocleidomastoid m. Prevertebral component, perivertebral space Brachial plexus root Omohyoid m.

Posterior cervical space

Paraspinal mm.

Paraspinal component, perivertebral space

Trapezius m.

Superficial layer, deep cervical fascia Deep layer, deep cervical fascia

(Top) Lateral graphic of the neck shows the posterior triangle as a "tilting tent" with its superior margin at the level of the mastoid tip and its inferior border at the clavicle. Note that it has 2 main nerves in its floor, the accessory nerve (CNXI) and the dorsal scapular nerve. The spinal accessory nodal chain is its key occupant with regards to the kind of lesions found in the posterior triangle. (Bottom) Axial graphic through the thyroid bed of the infrahyoid neck depicts the posterior cervical space (PCS) with its complex fascial borders. The superficial layer of the deep cervical fascia is its superficial border, while the deep layer of the deep cervical fascia is its deep border. Note the tricolor carotid sheath is its anteromedial border. The brachial plexus roots travel through the PCS on their way to the axillary apex.

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Head and Neck

Posterior Triangle TRANSVERSE ULTRASOUND Subcutaneous tissue Sternocleidomastoid m. Intermuscular fat plane

Tip of transverse process of cervical vertebra Levator scapulae Semispinalis m.

Sternocleidomastoid m. Intermuscular fat plane

Levator scapulae

Semispinalis m.

Subcutaneous t. External jugular v. tributaries Scalenus anterior m. Brachial plexus elements Scalenus medius Levator scapulae m. Trapezius m.

(Top) First of 3 transverse grayscale ultrasound images shows the posterior triangle. The sternocleidomastoid muscle marks the anterior border of the posterior triangle. Muscles form the floor of the posterior triangle. Note the accessory nerve and nodes lie in the intermuscular fat plane. (Middle) Standard transverse grayscale ultrasound of the posterior triangle shows the intermuscular fat plane, which is best screened in this plane. Once pathology is detected, further examination, particularly Doppler, is best done longitudinally. (Bottom) Lower level of the posterior triangle is shown. The trapezius muscle marks the posterior margin of the posterior triangle. The main bulk of the levator scapulae muscle forms the muscular floor.

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Posterior Triangle

Subcutaneous t. Sternohyoid and sternothyroid Thyroid lamina

Head and Neck

AXIAL MR

Platysma Vocal cord Arytenoid

Common carotid a. Internal jugular v.

Sternocleidomastoid m.

Scalenus anterior m.

External jugular v.

Levator scapulae m.

Semispinalis cervicis m.

Splenius capitis m. Trapezius m.

Semispinalis capitis m. Semispinalis m.

Tracheal ring Thyroid gland, right lobe Scalenus anterior m. Longus coli m. Vertebral body

Multifidus m. Semispinalis capitis and cervicis mm.

Trunk of brachial plexus Scalenus medius and posterior Levator scapulae m. Semispinalis m.

Trapezius m.

Infrahyoid strap m. Thyroid gland, right lobe

T1 vertebral body 1st rib Transverse process Vertebral lamina

Sternocleidomastoid m. Scalenus anterior m. Trunk of brachial plexus Scalenus medius Supraclavicular fossa Levator scapulae m. Semispinalis mm. Trapezius m.

Investing fascia

Subcutaneous t.

(Top) Axial PD MR of the neck at the level of the vocal cord shows the largely fat-filled posterior triangle with muscular floor. (Middle) Axial PD MR of the neck at the level of thyroid gland shows the scalenus medius muscle begins at the midcervical level. The nerve roots and the trunk of the brachial plexus is seen emerging between the scalenus anterior and medius muscles. (Bottom) Axial PD MR of the lower posterior triangle shows the trunks of the brachial plexus between the scalenus anterior and the medius muscles diverging posterior to the clavicle to the axillary region. Note the content of the posterior triangle is predominantly fat with large muscles forming its boundaries.

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Head and Neck

Posterior Triangle POSTERIOR TRIANGLE PATHOLOGY

Tips of transverse process Reactive nodes

Sternocleidomastoid m. pseudotumor

Common carotid a. Left lobe of thyroid gland Trachea

Sternocleidomastoid m. pseudotumor

Lymph node in posterior triangle

(Top) Longitudinal grayscale ultrasound of the posterior triangle shows a chain of reactive accessory nodes. Note their location in the intermuscular fat plane. Do not mistake the tips of the transverse processes with calcified nodes. (Middle) Transverse grayscale ultrasound in an infant with torticollis shows a heterogeneously enlarged left sternocleidomastoid muscle. The appearance is compatible with a sternocleidomastoid pseudotumor. (Bottom) Longitudinal grayscale ultrasound of the left posterior triangle confirms sternocleidomastoid muscle hypertrophy. Part of the normal muscular striations are preserved.

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Posterior Triangle

Subcutaneous soft tissue thickening

Head and Neck

POSTERIOR TRIANGLE PATHOLOGY

Tuberculous lymph node Displaced hilar vascularity

Lymphatic malformation

Septations

Sternocleidomastoid m.

Lymphovascular malformation Levator scapulae m.

(Top) Longitudinal color Doppler ultrasound in the posterior triangle shows multiple enlarged, hypoechoic lymph nodes with displaced hilar vascularity. Pathology showed tuberculous lymphadenitis. Once pathology is detected in transverse scans, it is better evaluated on a longitudinal scan, particularly if performing a Doppler examination. (Middle) Transverse grayscale ultrasound shows a large, multiseptated, cystic mass occupying the left posterior triangle in a child. The appearance is suggestive of a lymphatic malformation. These lesions are transspatial and frequently extend into other neck spaces. (Bottom) Oblique transverse grayscale ultrasound shows a child who underwent 2 treatments of ultrasound-guided sclerotherapy for a large, multiloculated lymphatic malformation. Note that small cystic locules persist; however, much of the lymphatic malformation has been replaced by fatty tissue. Ultrasound safely guides intralesional sclerosant and readily monitors posttreatment change in size and appearance.

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Head and Neck

Thyroid Gland

IMAGING ANATOMY Overview • H- or U-shaped gland in anterior cervical neck formed from 2 elongated lateral lobes with superior and inferior poles connected by median isthmus

Anatomy Relationships • Thyroid gland lies anterior and lateral to trachea in visceral space of infrahyoid neck • Extends from level of 5th cervical vertebra to 1st thoracic vertebra • Posteromedially are tracheoesophageal grooves ○ Contains paratracheal lymph nodes, recurrent laryngeal nerve, parathyroid glands • Posterolaterally are carotid spaces ○ Contains common carotid artery, internal jugular vein, vagus nerve • Anteriorly are infrahyoid strap muscles • Anterolaterally are sternocleidomastoid muscles

Internal Contents • Thyroid gland ○ 2 lateral lobes (i.e., right and left lobes) – Measure ~ 4 cm in height – Each lobe has upper and lower poles – Lateral lobes are commonly asymmetric in size ○ Lateral lobes are joined by midline isthmus ○ Pyramidal lobe present in 30-50% of cases – Extends superiorly from isthmus toward hyoid bone – More common on left • Arterial supply ○ Superior thyroid arteries – 1st anterior branch of external carotid artery □ Runs superficially on anterior border of lateral lobe □ Sends branch deep into gland before curving toward isthmus where it anastomoses with contralateral artery – Proximal course closely associated with superior laryngeal nerve ○ Inferior thyroid arteries – Arise from thyrocervical trunk, branch of subclavian artery – Ascend vertically, then curve medially to enter tracheoesophageal groove – Most branches penetrate posterior aspect of lateral thyroid lobe – Closely associated with recurrent laryngeal nerve ○ Thyroidea ima occasionally present (3%) – Single vessel originating from aortic arch or brachiocephalic artery – Enters thyroid gland at inferior border of isthmus • Venous drainage ○ 3 pairs of veins arise from venous plexus on surface of thyroid gland ○ Superior and middle thyroid veins drain into internal jugular veins ○ Inferior thyroid veins drain into brachiocephalic veins • Lymphatic drainage ○ Lymphatic drainage is extensive and multidirectional ○ Initial lymphatic drainage courses to periglandular nodes 136

– Prelaryngeal, pretracheal (Delphian), and paratracheal nodes along recurrent laryngeal nerve – Paratracheal nodes drain along recurrent laryngeal nerve into mediastinum – Regional drainage occurs laterally into internal jugular chain (levels 2-4) and spinal accessory chain (level 5), higher in neck along internal jugular vein

ANATOMY IMAGING ISSUES Imaging Approaches • Ultrasound appearance ○ Normal thyroid parenchyma has fine, uniform echoes and is hyperechoic compared to adjacent muscles ○ Echogenic thyroid capsule is clearly visualized and helps to differentiate thyroid lesions from extrathyroidal masses • Both longitudinal and transverse scans are required for comprehensive ultrasound assessment of thyroid gland ○ Transverse scan helps to locate thyroid nodules, their relationship to trachea, major vessels in carotid sheath, and to evaluate internal architecture and extrathyroid extension ○ Longitudinal scan helps to evaluate internal architecture, vascularity on Doppler, and extrathyroidal extension • Examination of thyroid nodules includes ○ Ultrasound features of thyroid nodule ○ Assessment of adjacent structures (including trachea, esophagus, strap muscles, carotid artery, and internal jugular vein) and cervical lymph nodes

EMBRYOLOGY Embryologic Events • Thyroid gland originates from 1st and 2nd pharyngeal pouches (medial anlage) • Originates as proliferation of endodermal epithelial cells on median surface of developing pharyngeal floor termed foramen cecum • Bilobed thyroid gland descends anterior to pharyngeal gut along thyroglossal duct • Inferior descent of thyroid gland anterior to hyoid bone and laryngeal cartilages

Practical Implications • Thyroglossal duct cyst: Results from failure of involution of portion of thyroglossal duct • Thyroid tissue remnants: From sequestration of thyroid tissue along thyroglossal duct ○ Seen anywhere along course of thyroglossal duct from foramen cecum to superior mediastinum • Ectopic thyroid gland: From incomplete descent of thyroid into low neck ○ Seen anywhere along course from foramen cecum in tongue base to superior mediastinum ○ Most common location is just deep to foramen cecum in tongue base (i.e., lingual thyroid)

Thyroid Gland

External carotid a.

Head and Neck

THYROID GLAND, VASCULAR SUPPLY

Internal carotid a. Superior thyroid a. Superior thyroid a. Common carotid a.

Inferior thyroid a. Inferior thyroid a.

Costocervical trunk Thyrocervical trunk Vertebral a. Thyroidea ima Subclavian a. Brachiocephalic a.

Internal mammary a.

Superior thyroid a. Hypopharynx

Vagus n.

Superior parathyroid gland Thyroid gland

Right recurrent laryngeal n.

Inferior thyroid a. Common carotid a. Inferior thyroid v.

Cervical esophagus Thyrocervical trunk

(Top) Anterior graphic shows the arterial supply to the thyroid. The superior thyroid artery is the 1st branch of the external carotid artery. The inferior thyroid artery arises from the thyrocervical trunk, a branch of the subclavian artery. The thyroidea ima is a variant branch, which arises from the aortic arch or brachiocephalic artery, and enters the inferior border of the isthmus. (Bottom) Coronal graphic from behind shows both the arterial and venous vascular supply. Note the close proximity of the recurrent laryngeal artery, which runs in the tracheoesophageal groove along the posterior border of the thyroid gland.

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Head and Neck

Thyroid Gland TRANSVERSE ULTRASOUND

Subcutaneous tissue Sternocleidomastoid m. Sternohyoid m. Sternothyroid m. Internal jugular v. Common carotid a.

Right lobe of thyroid gland Trachea

Esophagus

Subcutaneous tissue Sternocleidomastoid m. Sternohyoid m. Sternothyroid m. Omohyoid m. Lower pole of right thyroid gland Internal jugular v.

Trachea Inferior thyroid a.

Common carotid a.

Esophagus Longus colli m.

Subcutaneous tissue Strap m. Thyroid capsule Tracheal ring Left lobe of thyroid gland Thyroid isthmus Right lobe of thyroid gland

Longus colli m.

(Top) Transverse grayscale ultrasound of the right lobe of the thyroid gland shows the homogeneous, hyperechoic echo pattern of the glandular parenchyma. Note its close anatomical relationship with the major vessels of the carotid sheath (internal jugular vein and common carotid artery) laterally, the trachea medially, and the cervical esophagus posteromedially. (Middle) Transverse grayscale ultrasound shows the level of the inferior pole of the thyroid gland. The inferior thyroid artery is a consistent finding related to and supplying the inferior pole. (Bottom) Midline transverse grayscale ultrasound shows the thyroid isthmus connecting the 2 lobes. The isthmus lies on the anterior surface of the trachea. In view of the intimate anatomical relationship between the thyroid gland and the trachea, a local tumor invasion to the trachea from malignant thyroid carcinoma is commonly seen, rendering surgical excision more extensive than total thyroidectomy.

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Thyroid Gland

Sternocleidomastoid m. Sternohyoid and sternothyroid mm.

Infrahyoid strap mm.

Head and Neck

AXIAL CECT

Tracheal ring

Inferior thyroid v. Trachea Thyroid gland, right lobe Internal jugular v. Common carotid a.

Tracheoesophageal groove Esophagus

Inferior thyroid a.

Longus coli m.

Scalenus anterior m. Vertebral a.

Anterior jugular v.

Vertebral body

Infrahyoid strap mm.

Sternocleidomastoid m. Thyroid gland, right lobe

Trachea

Internal jugular v. Common carotid a. Inferior thyroid a.

Esophagus Longus coli m.

Thyroid gland isthmus

Anterior jugular v.

Sternocleidomastoid m. Infrahyoid strap mm. Inferior thyroid v. Thyroid gland, right lobe

Trachea

Common carotid a. Tracheoesophageal groove

Prevertebral m.

Inferior thyroid a.

Esophagus

Vertebral a.

(Top) Correlative CECT shows the right thyroid gland. The thyroid gland is seen as a triangular, homogeneously enhancing structure embracing the anterior aspect of the cervical trachea. The inferior thyroid artery seen on this CT is the main trunk, while that seen on the ultrasound is a branch. (Middle) Axial CECT shows the lower pole of the thyroid gland. (Bottom) Axial CECT shows the neck at midline, indicating the tracheoesophageal groove. Remember that the recurrent laryngeal nerve, paratracheal nodes, and parathyroid glands may be seen on ultrasound in this location, but they normally cannot be well demonstrated on routine CT images. Always evaluate extensions of the tumor into the trachea, tracheoesophageal groove, nodes, strap muscles, common carotid artery, and internal jugular vein.

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Head and Neck

Thyroid Gland LONGITUDINAL ULTRASOUND Subcutaneous tissue Anterior portion of sternocleidomastoid m. Sternohyoid m. Sternothyroid m. Inferior pole of thyroid gland Superior pole of thyroid gland

Inferior thyroid a. Longus colli m.

Cervical vertebrae

Subcutaneous tissue Sternocleidomastoid m. Sternohyoid m. Sternothyroid m. Inferior thyroid a. Thyroid gland Esophagus

Cervical vertebra

Subcutaneous tissue Sternohyoid m. Sternothyroid m.

Thyroid gland Superior thyroid a.

(Top) Parasagittal longitudinal grayscale ultrasound shows the thyroid gland. The homogeneous, hyperechoic echo pattern of the glandular parenchyma is better assessed on longitudinal scans. Part of the tortuous course of the inferior thyroid artery is seen in relation to the lower pole. (Middle) Parasagittal longitudinal grayscale ultrasound shows the inferior thyroid artery coursing superiorly from the inferior pole within the glandular parenchyma. (Bottom) Parasagittal longitudinal grayscale ultrasound shows the superior thyroid artery, the 1st anterior branch of the external carotid artery, running inferiorly within and supplying the upper pole of the thyroid gland. Longitudinal scans best evaluate the glandular parenchyma and vascularity.

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Thyroid Gland

Larynx

Head and Neck

LONGITUDINAL ULTRASOUND

Thyroid cartilage Cricoid cartilage

Internal jugular v.

Thyroid gland lobe, left Trachea

Common carotid a. Right subclavian a. Superior mediastinum

Strap mm.

Thyroid gland

Esophagus Longus colli m.

Cervical vertebral bodies

Inferior thyroid v.

Inferior thyroid a.

(Top) In this image, the H- or U-shaped lobes of the thyroid gland are particularly well seen. Note the intimate relationship between the superomedial thyroid gland and the larynx. Remember that for thyroid malignancies the 1st-order nodes are the paratracheal nodes, which drain inferiorly into the superior mediastinum. (Middle) The thyroid gland is also immediately related to the esophagus as shown in this longitudinal scan taken from the lateral neck. (Bottom) This longitudinal color Doppler ultrasound shows both the inferior thyroid artery and vein. The thyroid gland is a very vascular organ. Three pairs of veins arise from a venous plexus on the surface of the gland. The superior and middle veins drain to the internal jugular vein and the inferior thyroid vein drains into the brachiocephalic vein.

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Head and Neck

Thyroid Gland PYRAMIDAL LOBE

Pyramidal lobe Strap m.

Right lobe of thyroid

Left lobe of thyroid

Isthmus

Pyramidal lobe

Strap m.

Thyroid isthmus

Common carotid a. Trachea

Thyroid gland (right lobe)

Pyramidal lobe

Strap m.

Right lobe of thyroid

(Top) There are many variants in the size and shape of the thyroid gland. This graphic shows the most common, a pyramidal lobe, which formed along the thyroglossal duct, and is present to some degree in 30-50% of the population. They more commonly project to the left but can be in the midline or to the right. Note that it is anterior to the strap muscles, while the main thyroid lobe is posterior. (Middle) Transverse grayscale ultrasound shows the pyramidal lobe of the thyroid gland. The echo pattern is identical to the normal right thyroid lobe (i.e., homogeneous, hyperechoic). It is located anterior to the anterior strap muscle. This should not be mistaken for a mass. Careful scanning will show it connects to the isthmus of the thyroid. (Bottom) A longitudinal ultrasound in the same patient shows the pyramidal lobe anterior to the strap muscle.

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Thyroid Gland Head and Neck

THYROGLOSSAL DUCT CYST

Foramen cecum Epiglottis Hyoid bone

Thyroglossal duct tract

Thyroid gland isthmus

Thyroid cartilage

Thyroid gland lobe

Thyroglossal duct cyst

Hyoid bone

Posterior acoustic enhancement

Infrahyoid thyroglossal duct cyst Suprahyoid thyroglossal duct cyst Hyoid bone

(Top) Sagittal oblique graphic displays the thyroglossal duct tract as it traverses the cervical neck from its origin at the foramen cecum to its termination in the anterior and lateral visceral space of the infrahyoid neck. Failure of complete involution results in persistent secretion of the epithelial cells, which line the duct and the formation of a cyst. (Middle) Longitudinal grayscale ultrasound shows a well-defined, suprahyoid thyroglossal duct cyst with uniform internal echoes and posterior enhancement (pseudosolid appearance). This homogeneous appearance is due to intracystic proteinaceous content. (Bottom) Longitudinal grayscale ultrasound shows multiple thyroglossal duct cysts both above (suprahyoid) and below (infrahyoid) the hyoid bone. These may be found midline/paramidline between foramen cecum at the tongue base and the thyroid bed.

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Head and Neck

Parathyroid Glands

TERMINOLOGY Abbreviations • Parathyroid gland (PTG)

Definitions • Endocrine glands that control calcium metabolism by producing parathormone

IMAGING ANATOMY Anatomy Relationships • Small lentiform glands posterior to thyroid gland in visceral space ○ Extracapsular in most cases but can be located within thyroid gland • Located in region of tracheoesophageal groove • Normal measurements ○ ~ 6 mm in length, 3- to 4-mm transverse, and 1-2 mm in anteroposterior diameter • Normal glands are often not seen on imaging (US/CT/MR) ○ If specifically targeted, normal PTG may be seen by using high-frequency transducer ○ Appear as small, well-circumscribed, hypoechoic nodules posterior to thyroid gland separated by echogenic thyroid capsule • Variable number, but typically 4 ○ 2 superior and 2 inferior PTGs ○ May be as many as 12 • Superior PTGs ○ More constant in position as compared with lower PTGs ○ Lie on posterior border of middle 1/3 of thyroid in 75% ○ 25% found behind upper or lower 1/3 of thyroid ○ 7% found below inferior thyroidal artery ○ Rarely found behind pharynx or esophagus • Inferior PTGs ○ More variable in location ○ 50% of inferior glands lie lateral to lower pole of thyroid gland ○ 15% lie within 1 cm of inferior thyroid poles ○ 35% position is variable, residing anywhere from angle of mandible to lower anterior mediastinum ○ Intrathyroidal PTG are rare • Arterial supply ○ Superior PTG supplied by superior thyroid artery ○ Inferior PTG supplied by inferior thyroid artery

ANATOMY IMAGING ISSUES

144

○ Angulate transducer at clavicle to see any obvious lesion in mediastinum ○ PTAs demonstrate hypervascularity on color flow imaging ○ Color flow imaging best done in longitudinal plane • Nuclear scintigraphy ○ Tc-99m sestamibi concentrates in PTA ○ Useful for detection of ectopic PTA (most common site below inferior thyroid pole)

Imaging Pitfalls • Parathyroid lesion may be confused with other lesions or normal anatomical structures ○ Paratracheal lymph nodes – Look for echogenic hilum and typical color Doppler pattern with central vessel ○ Thyroid nodules in subcapsular location ○ Longus colli muscle, esophagus, blood vessels also potential mimics – Scan in multiple planes and use color Doppler • Detection of parathyroid lesion is limited in ○ Obese patients with short neck ○ Ectopic PTG (e.g., in mediastinum) ○ Postoperative neck

Consider • Main indication for imaging of PTGs is localization of PTA causing hyperparathyroidism with hypercalcemia

CLINICAL IMPLICATIONS Clinical Importance • PTA is most common cause of primary hyperparathyroidism • US localization facilitates minimally invasive parathyroidectomy • US safely guides percutaneous injection of absolute alcohol in PTA

EMBRYOLOGY Embryologic Events • Superior PTGs develop from 4th branchial pouch along with primordium of thyroid gland • Inferior PTGs develop from 3rd branchial pouch along with anlage of thymus ○ Descend variable distance with thymic anlage in thymopharyngeal duct tract ○ May descend into anterior mediastinum as far as pericardium

Imaging Approaches

Practical Implications

• Usually targeted exam looking for parathyroid adenoma (PTA) • US technique ○ Best 1st examination for localizing most PTA ○ Use high-resolution linear array transducer (7.5-10 MHz) ○ Identifies 95% of PTA weighing > 1 gram ○ Easier to start scanning in transverse plane with patient's neck hyperextended ○ Start above thyroid at angle of mandible and move downward, scanning through thyroid to level of clavicle

• Abnormal PTG descent may cause inferior PTG to occupy "ectopic" sites ○ May be of critical importance when searching for PTA – In cases where surgical exploration for PTA is done without imaging, no PTA may be found if PTG is ectopic

Parathyroid Glands Head and Neck

PARATHYROID GLANDS

Thyroid isthmus

Middle layer, deep cervical fascia Thyroid gland Trachea

Tracheoesophageal groove

Parathyroid gland Paratracheal lymph node Recurrent laryngeal n.

Esophagus

Esophagus Superior thyroid a.

Superior parathyroid gland

Thyroid

Inferior parathyroid gland

Superior parathyroid gland

Recurrent laryngeal n.

Inferior thyroidal a.

Common carotid a.

Inferior parathyroid gland

Inferior thyroidal v.

Vagus n.

(Top) Axial graphic at the thyroid level depicts the superior parathyroid glands in the visceral space just posterior to the thyroid gland. Note that there are 3 key structures found in the area of the tracheoesophageal groove: The recurrent laryngeal nerve, paratracheal lymph node chain, and parathyroid glands. (Bottom) Coronal graphic illustrates the esophagus, parathyroid glands, and thyroid gland from behind. The drawing depicts the typical anatomic relationships of the paired superior and inferior parathyroid glands in the visceral space. Note the arterial supply to superior and inferior parathyroid glands is from the superior and inferior thyroid arteries, respectively.

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Head and Neck

Parathyroid Glands NORMAL PARATHYROID Sternohyoid Anterior jugular v.

Platysma Sternocleidomastoid m.

Trachea

Sternothyroid m. Lower pole of left lobe of thyroid

Tracheoesophageal groove

Internal jugular v. Common carotid a.

Esophagus Vertebral body

Scalenus anterior m. Scalenus medius m.

Trachea

Trachea

Tracheoesophageal groove

Parathyroid gland Esophagus

Strap mm.

Right lobe thyroid Parathyroid gland

(Top) Axial CECT of the neck shows the region of the lower pole of the thyroid's left lobe. A normal parathyroid gland is normally not seen. The anatomical location is commonly at the tracheoesophageal groove, posterior to the thyroid gland. (Middle) Transverse color Doppler US at a similar level shows a small, ovoid, hypoechoic area of soft tissue in the tracheoesophageal groove. Although it is difficult to tell with certainty, this is likely a normal parathyroid gland. (Bottom) Longitudinal scan of the right thyroid shows a larger, hypoechoic nodule in the expected location of the parathyroid gland, posterior the middle 1/3 of the thyroid gland. This is the typical location of the superior parathyroid glands. Careful analysis during a real-time scan should be done to prove they are outside the thyroid capsule and not a thyroid nodule. A parathyroid gland may also sometimes be confused with a small lymph node, but a normal lymph node should have an echogenic hilum.

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Parathyroid Glands Head and Neck

PARATHYROID ADENOMA

Isthmus of thyroid gland

Thyroid gland Parathyroid gland

Trachea Parathyroid adenoma Recurrent laryngeal n.

Esophagus

Trachea Sternocleidomastoid m. Thyroid Internal jugular v. Parathyroid adenoma Common carotid a.

Esophagus

Right lobe of thyroid

Common carotid a.

Trachea

Calcification within adenoma Esophagus

(Top) Axial graphic shows a well-circumscribed mass in the left tracheoesophageal groove causing mass effect on the recurrent laryngeal nerve, esophagus, trachea, and left thyroid lobe. This is typical of a parathyroid adenoma, but a recurrent laryngeal nerve schwannoma or nodal disease in the paratracheal nodal chain could also cause such an appearance. (Middle) Axial CECT in a patient with acute hoarseness shows a well-defined, round mass in left tracheoesophageal groove. The mass is distinct from the posterior aspect of the left thyroid lobe and appears slightly less enhancing than the thyroid, typical of a parathyroid adenoma. The hoarseness was from impingement of the recurrent laryngeal nerve, which improved after surgery. (Bottom) Transverse grayscale US shows a wellcircumscribed, solid, round, hypoechoic parathyroid adenoma posterior to the right thyroid lobe in the region of the tracheoesophageal groove. This patient had biochemical evidence of primary hyperparathyroidism. Note that the presence of calcification within an adenoma is uncommon; it is more commonly seen with carcinoma.

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Head and Neck

Parathyroid Glands PARATHYROID ADENOMA Strap mm.

Thyroid Thyroid capsule

Parathyroid adenoma

Parathyroid adenoma

Parathyroid adenoma Thyroid nodules

(Top) Longitudinal US of the left lobe of the thyroid in a patient with hypercalcemia shows a well-defined, ovoid, hypoechoic mass. Note the distinct thyroid capsule, confirming this is posterior to the thyroid and therefore likely a parathyroid gland rather than a thyroid nodule. (Middle) Color Doppler US in the same patient shows increased vascularity, typical of a parathyroid adenoma. (Bottom) Longitudinal grayscale US shows a hypoechoic mass below the lower pole of the thyroid gland in a patient with hypercalcemia. Multiple thyroid nodules are also seen.

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Parathyroid Glands Head and Neck

PARATHYROID ADENOMA

Trachea

Left common carotid a. Right common carotid a.

Bilateral parathyroid adenomas

Parathyroid adenoma Thyroid gland

Normal tracer uptake in major salivary gland

Faint uptake in thyroid gland Uptake in parathyroid adenoma

(Top) Transverse grayscale US shows multiple parathyroid adenomas on either side of the trachea. Of patients with primary hyperparathyroidism, 2-3% may have multiple parathyroid adenomas. (Middle) Longitudinal grayscale US shows a well-circumscribed parathyroid adenoma inferoposterior to the lower pole of left lobe of the thyroid gland. The echotexture of the adenoma is heterogeneous. (Bottom) Planar sestamibi scintigraphy in the same patient shows a solitary focus of increased tracer uptake superimposed on the lower pole of the left thyroid gland. The scintigraphic features are suggestive of solitary hyperfunctioning parathyroid adenoma.

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Head and Neck

Larynx and Hypopharynx

IMAGING ANATOMY Overview • Larynx: Cartilaginous skeleton bounded by ligaments and muscles at junction of upper and lower airway ○ Cranial margin at level of glossoepiglottic and pharyngoepiglottic folds with caudal margin defined by lower edge of cricoid – Superior connection: Oropharynx – Inferior connection: Trachea • Hypopharynx: Caudal continuation of pharyngeal mucosal space, located between oropharynx and esophagus ○ Extends from level of glossoepiglottic and pharyngoepiglottic folds superiorly to inferior border of cricoid cartilage (cricopharyngeus muscle) – Superior connection: Oropharynx – Inferior connection: Cervical esophagus

Internal Contents • Laryngeal cartilages ○ Thyroid cartilage: Largest laryngeal cartilage – "Shields" larynx – 2 anterior laminae meet anteriorly at acute angle – Superior thyroid notch at anterosuperior aspect – Superior cornua are elongated and narrow, and they attach to thyrohyoid ligament – Inferior cornua are short and thick, articulating medially with sides of cricoid cartilage ○ Cricoid cartilage: Only complete ring in endolarynx – Provides structural integrity – 2 portions: Posterior lamina and anterior arch – Lower border of cricoid cartilage is junction between larynx above and trachea below ○ Arytenoid cartilage: Paired pyramidal cartilages that sit on top posterior aspect of cricoid cartilage – Vocal and muscular processes are at level of true vocal cord (TVC) – Vocal processes: Anterior projections of arytenoids where posterior margins of TVC attach ○ Corniculate cartilage: Rests on top of superior process of arytenoid cartilage within aryepiglottic (AE) fold • Supraglottic larynx ○ Extends from tip of epiglottis above to laryngeal ventricle below ○ Contains vestibule, epiglottis, preepiglottic fat, AE folds, false vocal cord (FVC), paraglottic space, and arytenoid cartilages ○ Epiglottis: Leaf-shaped cartilage, larynx lid with free margin (suprahyoid), fixed portion (infrahyoid) – Petiole is "stem" of leaf that attaches epiglottis to thyroid lamina via thyroepiglottic ligament – Hyoepiglottic ligament attaches epiglottis to hyoid – Glossoepiglottic fold is midline mucous membrane covering hyoepiglottic ligament ○ Preepiglottic space: Fat-filled space between hyoid bone anteriorly and epiglottis posteriorly ○ AE folds: Projects from cephalad tip of arytenoid cartilages to inferolateral margin of epiglottis – Represents superolateral margin of supraglottis, dividing it from pyriform sinus (hypopharynx) 150

○ FVC: Mucosal surfaces of laryngeal vestibule of supraglottis ○ Paraglottic spaces: Paired fatty regions beneath FVC and TVC – Superiorly, they merge into preepiglottic space, which terminates inferiorly at under surface of TVC • Glottic larynx ○ TVC and anterior and posterior commissures – Composed of thyroarytenoid muscle (medial fibers are "vocalis muscle") covered by mucosa – Anterior commissure: Midline, anterior meeting point of TVC • Subglottic larynx ○ Subglottis extends from under surface of TVC to inferior surface of cricoid cartilage ○ Mucosal surface of subglottic area is closely applied to cricoid cartilage • Hypopharynx: Consists of 3 regions ○ Piriform sinus: Anterolateral recess of hypopharynx – Between inner surface of thyrohyoid membrane (above), thyroid cartilage (below), and AE folds (laterally) – Pyriform sinus apex (inferior tip) at level of TVC – Anteromedial margin of pyriform sinus is posterolateral wall of AE fold (marginal supraglottis) ○ Posterior hypopharyngeal wall: Inferior continuation of posterior oropharynx wall ○ Post cricoid region: Anterior wall of lower hypopharynx – Interface between hypopharynx and larynx – Extends from cricoarytenoid joints to lower edge of cricoid cartilage

ANATOMY IMAGING ISSUES Imaging Recommendations • Role of US in laryngeal cancer is limited, particularly in era of MDCT and MR • US may serve supplementary role to clinical examination and CT/MR in assessing superficial extent of laryngeal tumor • US combined with fine-needle aspiration cytology is useful for nodal staging of laryngeal tumor • Although role of US in imaging of larynx is very limited, sonologist doing neck US should be familiar with its anatomy in order not to mistake its appearances for abnormalities

Imaging Sweet Spots • Real-time US is well suited to quickly evaluate vocal cord mobility in children presenting with hoarseness and stridor • US also guides safe percutaneous vocal cord injection for patients with cord palsy, provided degree of cartilaginous calcification does not obscure US visualization of vocal cord

Imaging Pitfalls • Presence of motion and calcification/ossification within laryngeal cartilage (common in adult) restricts detailed sonographic assessment of internal laryngeal structures

Larynx and Hypopharynx Head and Neck

SUPRAGLOTTIC STRUCTURES

Hyoid bone Preepiglottic space Vallecula

Glossoepiglottic fold Pharyngoepiglottic fold Epiglottis, free edge

Pharyngeal constrictor m.

Thyroid cartilage

Posterior pharyngeal wall

Preepiglottic space

Hyoepiglottic l. Paraglottic space Epiglottis, fixed portion Aryepiglottic fold Pyriform sinus Pharyngeal constrictor m.

Posterior pharyngeal wall

Thyroid cartilage False vocal cord

Paraglottic space

True vocal cord Aryepiglottic fold Pharyngeal constrictor m.

Arytenoid superior process Pyriform sinus Posterior pharyngeal wall

(Top) Axial graphic of the larynx and hypopharynx shows the roof of hypopharynx at the hyoid bone level and the high supraglottic structures. The free edge of the epiglottis is attached to the hyoid bone via the hyoepiglottic ligament, which is covered by the glossoepiglottic fold. (Middle) Graphic at the midsupraglottic level shows the hyoepiglottic ligament dividing the lower preepiglottic space. No fascia separates the preepiglottic space from the paraglottic space. These 2 endolaryngeal spaces are submucosal in locations where tumors can hide from clinical detection. The aryepiglottic fold represents the junction between the larynx and hypopharynx. (Bottom) Graphic at the low supraglottic level shows false vocal cords formed by mucosal surfaces of laryngeal vestibule. The paraglottic space is beneath the false vocal cords, a common location for submucosal tumor spread.

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Head and Neck

Larynx and Hypopharynx GLOTTIC AND SUBGLOTTIC STRUCTURES

Anterior commissure Thyroid cartilage

Vocal l.

Vocalis m. Thyroarytenoid m. Pyriform sinus apex Cricoid cartilage

Vocal process, arytenoid cartilage Arytenoid cartilage Thyroarytenoid gap Posterior cricoarytenoid m.

Postcricoid hypopharynx

Thyroid cartilage Undersurface of true vocal cord

Cricoid cartilage

Cricothyroid space Posterior cricoarytenoid m.

Pharyngeal constrictor m. Longus capitis m.

Postcricoid hypopharynx Posterior wall, hypopharynx

Cricothyroid membrane

Cricoid cartilage Thyroid gland Cricothyroid joint Inferior cornu, thyroid cartilage

Recurrent laryngeal n. Cervical esophagus

(Top) Graphic at the glottic, true vocal cord level shows the thyroarytenoid muscle, which makes up the bulk of the true vocal cord. The medial fibers of the thyroarytenoid muscle are known as the vocalis muscle. Pyriform sinus apex is seen at the glottic level. (Middle) Graphic at the level of the undersurface of the true vocal cord shows the posterior lamina of the cricoid cartilage. Postcricoid hypopharynx represents the anterior wall of the lower hypopharynx and extends from the cricoarytenoid joints to the lower edge of the cricoid cartilage at the cricopharyngeus muscle. The posterior wall of the hypopharynx represents the inferior continuation of the posterior oropharyngeal wall and extends to the cervical esophagus. (Bottom) Graphic at the subglottic level shows the cricothyroid joint immediately adjacent to the recurrent laryngeal nerve, which is located in the tracheoesophageal groove.

152

Larynx and Hypopharynx

Epiglottis, free margin Hyoid bone Aperture for internal branch of superior laryngeal n. Thyrohyoid membrane

Head and Neck

LARYNX

Thyroid cartilage, superior cornu

Thyroid notch Thyroid cartilage, anterior lamina

Cricothyroid membrane

Thyroid cartilage, inferior cornu Cricoid cartilage, anterior ring

1st tracheal ring

Epiglottis, free edge

Hyoid bone Hyoepiglottic l. Preepiglottic space

Laryngeal ventricle

Thyrohyoid membrane Aperture for internal branch of superior laryngeal n. Aryepiglottic fold Arytenoid cartilage False vocal cord True vocal cord

Vocal l. Cricoid cartilage

Epiglottis

Paraglottic space Hyoid bone

Thyrohyoid membrane Quadrangular membrane

Thyroid cartilage False vocal cord

Laryngeal ventricle

True vocal cord

Vocalis m.

Thyroarytenoid m.

Conus elasticus

Cricoid cartilage

(Top) Anterior graphic depicts the laryngeal cartilage, which provides the structural framework for the soft tissues of the larynx. Note that 2 large anterior laminae "shield" the larynx. The thyrohyoid membrane contains an aperture through which the internal branch of the superior laryngeal nerve and associated vessels course. (Middle) Sagittal graphic of the midline larynx shows the laryngeal ventricle air space, which separates false vocal cords above from true vocal cords below. (Bottom) Coronal graphic (posterior view) shows the false and true vocal cords separated by the laryngeal ventricle. The quadrangular membrane is a fibrous membrane that extends from the upper arytenoid and corniculate cartilages to the lateral epiglottis. The conus elasticus is a fibroelastic membrane that extends from the vocal ligament of the true vocal cord to the cricoid.

153

Head and Neck

Larynx and Hypopharynx TRANSVERSE ULTRASOUND Subcutaneous tissue Strap mm. Preepiglottic space Thyroid lamina Paraglottic space

Subcutaneous tissue Strap mm. Preepiglottic space Thyroid lamina Intrinsic mm. of larynx at supraglottic level

Paraglottic space False vocal cord

Subcutaneous tissue Strap mm.

Intrinsic mm. of larynx at glottic larynx level

Thyroid cartilage Paraglottic space True vocal cord

Arytenoid cartilage

(Top) Axial grayscale ultrasound of the larynx at the supraglottic larynx level shows that the thyroid laminae are the largest cartilaginous structures of the larynx and appear as thin, hypoechoic bands that join at the midline anteriorly. The hyperechoic, fatfilled paraglottic and preepiglottic spaces are important surgical landmarks for the staging of laryngeal carcinoma. (Middle) Transverse grayscale ultrasound of the larynx at the level of the false vocal cords shows abundant fat in the paraglottic spaces. The echo-poor intrinsic muscles of the larynx are embedded within the echogenic paraglottic fat. (Bottom) Transverse grayscale ultrasound of the larynx at the level of the true vocal cords shows that the arytenoid cartilage appears as echogenic foci posteriorly with attachments to the true vocal cords, which have distinct echo-poor appearances.

154

Larynx and Hypopharynx Head and Neck

AXIAL CECT

Thyroid notch Thyroid cartilage Epiglottis Pyriform sinus

Preepiglottic space Paraglottic space Aryepiglottic fold Hypopharynx, posterior wall

Thyroid cartilage Strap mm.

Paraglottic space False vocal cord Hypopharynx, posterior wall

Anterior commissure True vocal cord Thyroid cartilage Posterior commissure Thyroarytenoid gap Hypopharynx

Vocal process, arytenoid Arytenoid cartilage Cricoid cartilage

(Top) Axial CECT of the high supraglottic level shows that the preepiglottic and paraglottic spaces are continuous. This allows tumors to spread submucosally in these locations. The aryepiglottic fold, part of the larynx, represents a transition between the larynx and hypopharynx. (Middle) Axial CECT shows the low supraglottic level at the false vocal cord level. The paraglottic space represents the deep fatty space beneath the false vocal cords. Tumors that cross the laryngeal ventricle and involve false and true vocal cords are considered transglottic. (Bottom) Axial CECT at the glottic level shows the true vocal cords in abduction during quiet respiration. True vocal cord level is identified on CT when the arytenoid and cricoid cartilages are seen and muscle fills the inferior paraglottic space. The anterior and posterior commissures of the true vocal cords should be < 1 mm in normal patients. The postcricoid hypopharynx is typically collapsed.

155

Head and Neck

Larynx and Hypopharynx LONGITUDINAL ULTRASOUND Medial edge of strap m. Subcutaneous tissue Thyrohyoid l. Isthmus of thyroid cartilage Preepiglottic space Hyoid bone

Strap m Thyroid cartilage Cricoid cartilage Intrinsic mm. of larynx Paraglottic space

Subcutaneous tissue Strap m. Cricoid cartilage Intrinsic m. of larynx Thyroid cartilage Paraglottic space

(Top) Midline sagittal longitudinal grayscale ultrasound of the supraglottic larynx shows the fat-filled, echogenic, preepiglottic space underneath the thyrohyoid membrane. Tumor spread at this location is readily assessed by ultrasound. (Middle) Parasagittal longitudinal grayscale ultrasound of the larynx shows sonolucent thyroid and cricoid cartilages with no laryngeal calcification/ossification in a young adult. The paraglottic space is fat filled and appears echogenic. The intrinsic muscles of the larynx are embedded within the paraglottic space and are hypoechoic on ultrasound. (Bottom) Parasagittal longitudinal grayscale ultrasound shows the larynx further lateral. Gas within the laryngeal lumen appears highly echogenic, casting posterior acoustic shadowing.

156

Larynx and Hypopharynx

Vallecula

Head and Neck

SAGITTAL AND CORONAL REFORMATTED NECT

Epiglottis

Hyoid bone Preepiglottic space

Posterior wall, hypopharynx

Thyroid cartilage Laryngeal ventricle Cricoid cartilage Cricoid cartilage

Epiglottis Hyoid bone Aryepiglottic fold Thyroid cartilage Arytenoid cartilage

Pyriform sinus

Cricoid cartilage Thyroid gland

Hyoid bone Thyroid cartilage False vocal cord True vocal cord

Paraglottic space Laryngeal ventricle

Cricoid cartilage

(Top) Parasagittal reformatted NECT shows the laryngeal ventricle air space that separates the false vocal cords above from the true vocal cords below. (Middle) In this coronal reformatted NECT, aryepiglottic folds are well seen as they extend from the lateral epiglottis to the arytenoid cartilage. The pyriform sinus is the most common location for tumors of the hypopharynx. (Bottom) In this coronal reformatted NECT, the laryngeal ventricle is visible as an air space between false vocal cords above and true vocal cords below. When a tumor crosses the laryngeal ventricle to involve the true and false cords, it is transglottic, which has important treatment implications. Coronal imaging is particularly useful for evaluation of transglottic disease. Note that ultrasound is unable to demonstrate such detailed anatomy, particularly of deeper structures.

157

Head and Neck

Trachea and Esophagus

IMAGING ANATOMY Overview • Trachea and esophagus pass through visceral space of neck • Trachea ○ 10- to 13-cm flexible tube made of cartilage and fibromuscular membrane – Extends in midline from inferior larynx at ~ 6th cervical vertebral body to carina at upper margin of 5th thoracic vertebral body • Esophagus ○ ~ 25-cm muscular tube of longitudinal and circular smooth muscle – Extends in midline from inferior hypopharynx at ~ 6th cervical vertebral body to 11th thoracic vertebral body ○ Descends behind trachea and thyroid, lying in front of lower cervical vertebrae – Inclines slightly to left in lower cervical neck and upper mediastinum, returning to midline at T5 vertebral body level

Cervical Trachea • Boundaries ○ Anterior – Infrahyoid strap muscles, isthmus of thyroid gland ○ Lateral – Lobes of thyroid gland – Tracheoesophageal groove: Contains recurrent laryngeal nerve, paratracheal nodes, parathyroid glands ○ Posterior – Cervical esophagus • Tracheal cartilages ○ Each cartilage is imperfect ring of cartilage surrounding anterior 2/3 of trachea ○ Flat deficient posterior portion is completed with fibromuscular membrane ○ Cross-sectional shape of trachea is that of letter D with flat posterior side ○ Smooth muscle fibers in posterior membrane (trachealis muscle) attach to free ends of tracheal cartilages and provide alteration in tracheal cross-sectional area ○ Hyaline cartilage calcifies with age ○ Minor salivary glands are sporadically distributed in tracheal mucosa • Blood supply ○ Inferior thyroid arteries and veins • Lymphatic drainage ○ Level VI pretracheal and paratracheal nodes • US appearance ○ Hypoechoic tracheal ring composed of hyaline cartilage that is incomplete posteriorly ○ Ring-down artifacts from air in tracheal lumen ○ Midline behind thyroid isthmus

Cervical Esophagus • Begins at lower border of cricoid cartilage as continuation of hypopharynx ○ Upper limit is defined by cricopharyngeus muscle, which encircles it from front to back • Boundaries 158

• • • • •

○ Anterior – Cervical trachea ○ Anterolateral – Tracheoesophageal groove structures ○ Lateral – Common carotid artery, internal jugular vein, vagus nerve ○ Posterior – Retropharyngeal fascia/muscle Usually in slightly off-midline position to left in cervical portion Active peristalsis in antegrade (i.e., downward) direction Blood supply ○ Inferior thyroid arteries and veins Lymphatic drainage ○ Level VI paratracheal nodes US appearance ○ Thick-walled tubular structure with alternating concentric echogenic/hypoechoic rings (gut signature) – Alternating echogenic/hypoechoic layers representing mucosal, submucosal, muscular, and serosal layers on longitudinal scan ○ Presence of air in lumen; moves on swallowing

ANATOMY IMAGING ISSUES Imaging Recommendations • US is best done with patient's head slightly hyperextended • Ask patient not to swallow during US • Transverse and longitudinal scans are necessary for comprehensive US examination • Assess adjacent structures and regional neck nodes

Imaging Pitfalls • Tracheal ring calcification and intraluminal air render complete assessment of trachea difficult • Intraluminal gas may obscure posterior esophageal wall • Esophagus is mobile tube and slips side to side in neck depending on direction head is turned ○ On US, esophagus may be on right when head is turned to left

CLINICAL IMPLICATIONS Clinical Importance • Recurrent laryngeal nerve is located in tracheoesophageal groove ○ Though nerve itself is not usually visible on US, its expected course should be carefully examined in patients with vocal cord palsy • Often invaded/compressed/displaced by extrinsic neck mass, particularly thyroid ○ Carefully evaluate both trachea and esophagus when neck mass is seen • Primary tracheal tumors are rare

Trachea and Esophagus Head and Neck

TRACHEA AND ESOPHAGUS

Hyoid bone Thyrohyoid membrane

Thyroid cartilage Cricothyroid m.

Inferior pharyngeal constrictor m.

Cricopharyngeus m.

Cricoid cartilage 1st tracheal ring

Longitudinal esophageal m.

Trachea

Thyroid gland Recurrent laryngeal n.

Visceral space

Parathyroid gland Paratracheal lymph node

Tracheoesophageal groove

Cervical esophagus Carotid space

Retropharyngeal space

(Top) Lateral graphic shows junction of larynx and hypopharynx with the trachea and esophagus. The cricopharyngeus muscle is a constrictor muscle and separates the hypopharynx from the cervical esophagus. The esophagus is composed of outer longitudinal muscles and an inner circular muscle layer. The 1st tracheal ring is broadest of all tracheal cartilages and is often merged to cricoid cartilage or 2nd tracheal ring. The rings are incomplete, and the posterior fibromuscular membrane is directly juxtaposed to the esophagus. (Bottom) Axial graphic shows the anteroposterior relationship of the trachea and esophagus in the lower neck. Important components of the tracheoesophageal groove include the recurrent laryngeal nerve, paratracheal nodes, and parathyroid glands.

159

Head and Neck

Trachea and Esophagus TRANSVERSE ULTRASOUND

Sternocleidomastoid m. Trachea

Air and fluid in esophageal lumen

Strap mm.

Esophagus

Thyroid isthmus Subcutaneous tissue

Tracheal ring cartilage

Sternohyoid m. Sternothyroid m. Trachea Left lobe of thyroid gland

Right lobe of thyroid gland

Subcutaneous tissue in suprasternal region Sternocleidomastoid m. Sternothyroid m. Trachea Internal jugular v.

(Top) Transverse grayscale US of the left lower cervical level shows the location of the cervical esophagus posterior to the left lobe of the thyroid gland and posterolateral to the trachea. It is easily recognized by the alternating hypo-/hyperechoic rings (gut signature). If there is any question, have the patient swallow. The recurrent laryngeal nerve is located in the tracheoesophageal groove. The nerve is not visualized on US. (Middle) Transverse grayscale US of the midline anterior neck at the level of thyroid gland shows the trachea as a midline structure underneath the isthmus of the thyroid gland and related laterally to the thyroid lobes. Note the hypoechoic tracheal ring composed of hyaline cartilage that is incomplete posteriorly. (Bottom) Transverse grayscale US of the suprasternal region shows the lower cervical trachea underneath the insertion sites of the strap muscles.

160

Trachea and Esophagus

Anterior jugular v.

Sternohyoid and sternothyroid mm.

Subcutaneous tissue

Head and Neck

AXIAL CECT

Sternocleidomastoid m.

Left lobe of thyroid gland Trachea Internal jugular v. Tracheoesophageal groove Common carotid a. Esophagus Longus coli m. Vertebral body

Subcutaneous tissue Sternocleidomastoid m.

Strap mm.

Scalenus anterior m. Vertebral a.

Anterior jugular v. Thyroid isthmus Left lobe of thyroid gland Trachea

Internal jugular v. Internal carotid a. Inferior thyroid a. Esophagus Vertebral a.

Sternocleidomastoid, sternal head, and clavicular head Internal jugular v.

Common carotid a.

Subclavian a.

Longus coli m.

Subcutaneous tissue in suprasternal region Strap mm.

Trachea

Esophagus Prevertebral m.

Vertebral body

(Top) Axial CECT of the lower cervical level shows the close anatomical relationship of the trachea and the esophagus with adjacent structures, such as the thyroid gland. (Middle) Axial CECT of the lower cervical level shows the trachea surrounded by thyroid lobes and the isthmus and esophagus posterior to the trachea. (Bottom) Axial CECT at the level of the suprasternal region shows that the esophagus at this level is usually slightly off midline to the left in relation to the trachea. The esophagus and trachea are surrounded by mediastinal fat and related to the major vessels in the superior mediastinum. Although US is able to detect the spread of a thyroid tumor to the trachea and esophagus (and vice versa), CT and MR delineate the involvement much better.

161

Head and Neck

Trachea and Esophagus LONGITUDINAL ULTRASOUND AND CT

Epiglottis Hyoid bone

Hypopharynx

Larynx Thyroid cartilage

Cricopharyngeus m. Retropharyngeal space Esophagus

Tracheal rings Trachea

Subcutaneous tissue 4th tracheal ring 3rd tracheal ring 2nd tracheal ring 1st tracheal ring Cricoid cartilage Artifact from tracheal air and calcification

Strap mm.

Left lobe of thyroid

Esophagus

Cervical vertebrae

(Top) Sagittal NECT reformation of the midline infrahyoid neck shows noncalcified tracheal rings anteriorly. These rings form an arch around the trachea and are incomplete posteriorly. The posterior wall is composed of a thick fibromuscular membrane and is immediately adjacent to the esophagus. (Middle) Longitudinal grayscale US of the midline anterior neck shows the presence of hypoechoic tracheal rings along the cervical portion of the trachea. Note the hypoechoic, noncalcified, cricoid cartilage above the tracheal rings. (Bottom) Longitudinal grayscale US of the lower left neck at the thyroid gland level shows the cervical esophagus posterior to the left lobe of the thyroid gland. It is a long tubular structure with alternating echogenic/hypoechoic layers representing the mucosal, submucosal, muscular, and serosal layers.

162

Trachea and Esophagus Head and Neck

PATHOLOGY

Metastasis

Trachea Esophagus

Normal thyroid tissue

Invading tumor

Nasogastric tube in esophageal lumen Common carotid a.

Common carotid a. Left lobe of thyroid gland Metastatic left lower jugular lymph node

Air in esophageal lumen Esophageal tumor

(Top) Transverse grayscale US in a patient with uterine leiomyosarcoma shows large metastasis to the thyroid. The trachea and esophagus are displaced but not invaded. Always evaluate both of these structures when a neck mass, particularly one involving the thyroid, is identified. (Middle) Transverse grayscale US shows a diffusely enlarged, hypoechoic right thyroid lobe due to infiltration by a tumor arising from the esophagus. Note the encasement of the right common carotid artery. (Bottom) Transverse grayscale US of the left lower cervical level shows a large heterogeneous mass posterior to and invading the lower pole of the left thyroid gland, compatible with known locally extensive esophageal carcinoma. Note the presence of left lower jugular lymph node metastases.

163

Head and Neck

Vagus Nerve

164

IMAGING ANATOMY Overview • 10th cranial nerve (CNX) is mixed (sensory, taste, motor, parasympathetic) ○ Parasympathetic nerve supplying regions of head and neck and thoracic and abdominal viscera ○ Additional vagus nerve (CNX) components – Motor to soft palate (except tensor veli palatini muscle), pharyngeal constrictor muscles, larynx, and palatoglossus muscle of tongue – Visceral sensation from larynx, esophagus, trachea, and thoracic and abdominal viscera – Sensory nerve to external tympanic membrane, external auditory canal (EAC), and external ear • 4 major segments: Intraaxial, cisternal, skull base, and extracranial • Intraaxial segment ○ Vagal nuclei are in upper and middle medulla – Contain motor, sensory (including taste from epiglottis), and parasympathetic fibers ○ Fibers to and from these nuclei exit lateral medulla in postolivary sulcus inferior to glossopharyngeal nerve (CNIX) and superior to bulbar portion of accessory nerve (CNXI) • Cisternal segment ○ Exits lateral medulla in postolivary sulcus between CNIX and bulbar portion of CNXI ○ Travels anterolaterally through basal cistern together with CNIX and bulbar portion of CNXI • Skull base segment ○ Passes through posterior pars vascularis portion of jugular foramen (JF) – Accompanied by CNXI and jugular bulb – Superior vagal ganglion is found within JF • Extracranial segment ○ Exits JF into nasopharyngeal carotid space ○ Inferior vagal ganglion lies just below skull base ○ Descends along posterolateral aspect of internal carotid artery (ICA) into thorax – Passes anterior to aortic arch on left and subclavian artery on right ○ Forms plexus around esophagus and major blood vessels to heart and lungs ○ Gastric nerves emerge from esophageal plexus and provide parasympathetic innervation to stomach ○ Innervation to intestines and visceral organs follows arterial blood supply to that organ • Extracranial branches in head and neck ○ Auricular branch (Arnold nerve) – Sensation from external surface of tympanic membrane, EAC, and external ear – Passes through mastoid canaliculus extending from posterolateral JF to mastoid segment of facial nerve (CNVII) canal ○ Pharyngeal branches – Pharyngeal plexus exits just below skull base – Sensory to epiglottis, trachea, and esophagus – Motor to soft palate and pharyngeal constrictor muscles ○ Superior laryngeal nerve

– Motor to cricothyroid muscle – Sensory to mucosa of supraglottis • Recurrent laryngeal nerve ○ On right, recurs at cervicothoracic junction, passing posteriorly around subclavian artery ○ On left, recurs in mediastinum, passing posteriorly under aorta at aortopulmonary window ○ Nerves recur in tracheoesophageal grooves ○ Motor to all laryngeal muscles except cricothyroid muscle ○ Sensory to mucosa of infraglottis

ANATOMY IMAGING ISSUES Imaging Recommendations • Extracranial segment is only portion accessible for USG evaluation (upper, mid, lower cervical regions) ○ Lies between ICA/common carotid artery (CCA) and internal jugular vein (IJV) on transverse scans ○ Linear hypoechoic structure with central echogenic fibrillar pattern on longitudinal scan ○ On axial scans, seen as round, hypoechoic structure with central echogenic focus ○ Best seen from level of carotid bifurcation down to lower cervical region ○ Color/power Doppler helps to distinguish it from small vessels in vicinity of major vessels of carotid sheath • More easily visualized on USG in patients with previous radiotherapy ○ Appears diffusely thickened with smooth contour • USG readily identifies CNX schwannoma in upper, mid, or lower cervical region ○ Appears as round/ovoid solid hypoechoic mass ○ Related to ICA/CCA and IJV – No splaying of carotid bifurcation, which occurs in carotid body tumor ○ CNX is contiguous with mass ○ Increased intranodular vascularity on power Doppler ○ USG features obviate need for fine-needle aspiration/biopsy • Recurrent laryngeal nerve cannot be confidently visualized on USG ○ In patient with vocal cord palsy, USG may help to detect abnormality in tracheoesophageal groove

Imaging Pitfalls • USG cannot assess intrathoracic portion of CNX ○ CT is imaging modality of choice if CNX lesion in mediastinum is suspected

CLINICAL IMPLICATIONS Clinical Importance • CNX dysfunction ○ Proximal symptom complex (lesion between medulla and hyoid bone) – Multiple cranial nerves involved (CNIX-CNXII) with oropharyngeal and laryngeal dysfunction ○ Distal symptom complex (lesion below hyoid bone) – Isolated CNX involvement with laryngeal dysfunction only

Vagus Nerve Head and Neck

VAGUS NERVE

Hypoglossal n. Glossopharyngeal n. Accessory n.

Vagus n.

Internal carotid a.

Carotid sheath with 3 layers of deep cervical fascia Sympathetic chain

Internal jugular v.

Recurrent laryngeal n. Parathyroid gland Tracheoesophageal groove

Internal jugular v.

Paratracheal node

Vagus n. trunk

Common carotid a. Sympathetic chain Carotid sheath with 3 layers of deep cervical fascia

Brachial plexus

(Top) Axial graphic of nasopharyngeal carotid spaces shows the extracranial vagus nerve situated posteriorly in the gap between the internal carotid artery and the internal jugular vein. Note that at this level the glossopharyngeal nerve (CNIX), accessory nerve (CNXI), and hypoglossal nerve (CNXII) are all still within the carotid space. This site is not accessible on ultrasound. (Bottom) Axial graphic through the infrahyoid carotid spaces at the level of the thyroid gland demonstrates that the vagus trunk is the only remaining cranial nerve within the carotid space. It remains in the posterior gap between the common carotid artery and the internal jugular vein. Note the recurrent laryngeal nerve in the tracheoesophageal groove within the visceral space. Remember that the left recurrent laryngeal nerve turns cephalad in the aortopulmonary window in the mediastinum, whereas the right recurrent nerve turns at the cervicothoracic junction around the subclavian artery.

165

Head and Neck

Vagus Nerve TRANSVERSE, POWER DOPPLER, AND LONGITUDINAL ULTRASOUNDS

Subcutaneous tissue Sternocleidomastoid m.

Internal jugular v.

Right lobe of thyroid gland Common carotid a.

Vagus n. Scalenus anterior

Subcutaneous tissue Sternocleidomastoid m. Lymph node Hilar vascularity in lymph node Internal jugular v.

Common carotid a.

Vagus n.

Subcutaneous tissue Sternocleidomastoid m.

Vagus n. Common carotid a.

Transverse process of cervical vertebra

(Top) Transverse grayscale ultrasound of the lower cervical level at the thyroid gland level shows the vagus nerve as a small, round, hypoechoic structure that exhibits central echogenicity within the carotid sheath and is located between the common carotid artery and the internal jugular vein. (Middle) Power Doppler ultrasound of the midcervical level in the transverse plane demonstrates the avascular nature of the vagus nerve adjacent to the common carotid artery and internal jugular vein. Note the presence of hilar vascularity in the adjacent normal deep cervical lymph node. (Bottom) Longitudinal grayscale ultrasound shows the vagus nerve, which appears as a long, thin, tubular, hypoechoic structure with a central echogenic fibrillary pattern within. On ultrasound, the vagus nerve is readily seen from the carotid bifurcation to the lower cervical region.

166

Vagus Nerve

Infrahyoid strap mm.

Anterior jugular v. Sternocleidomastoid m.

Head and Neck

AXIAL AND CORONAL CECT

Trachea Thyroid gland, right lobe

Internal jugular v. Common carotid a. Vagus n. Scalenus anterior External jugular v.

Esophagus Prevertebral m. Inferior thyroid aa. Vertebral a.

Scalenus medius m.

Strap mm. Platysma Thyroid cartilage Sternocleidomastoid m. Vocal cord Common carotid a.

Arytenoid

Internal jugular v. Vagus n.

Prevertebral m.

Vertebral a. and v.

Internal jugular v.

Internal carotid a. External carotid a. Submandibular gland Platysma m.

Carotid bulb Vagus n.

Common carotid a.

Sternocleidomastoid m.

(Top) Axial CECT of the neck at the midcervical level shows the vagus nerve as an isodense dot in the posterior aspect of the carotid sheath. The inferior thyroid arteries are seen as contrast-enhanced dots in its proximity. (Middle) Axial CECT of the neck in a different patient also shows the vagus nerve as an isodense dot in the posterior aspect of the carotid space. (Bottom) Oblique sagittal reformatted CECT of the neck shows the course of the vagus nerve. It is closely related to the posterior aspect of the common carotid artery. Although CT demonstrates the vagus nerve in the neck, high-resolution ultrasound clearly evaluates its internal architecture.

167

Head and Neck

Vagus Nerve PATHOLOGY

Sternocleidomastoid m.

Internal jugular v. Strap mm.

Vagal schwannoma

Common carotid a.

Sternocleidomastoid m. Vagal schwannoma Vagus n.

Sternocleidomastoid m.

Lower pole of right thyroid gland Internal jugular v. Thickened vagus n.

Common carotid a.

Vertebral a.

(Top) Transverse grayscale ultrasound of left midcervical level shows a well-circumscribed, hypoechoic mass closely related to the left internal jugular vein and common carotid artery. The anatomical location helps to identify the mass as originating from the vagus nerve. (Middle) Longitudinal grayscale ultrasound shows a oblong, solid, hypoechoic masses contiguous with the vagus nerve inferiorly. Scanning in a longitudinal plane is best for proving a mass is arising from the nerve. (Bottom) Transverse grayscale ultrasound of the lower cervical level in a patient with previous neck irradiation for head and neck cancer shows that the vagus nerve is diffusely thickened with smooth contour as a result of postirradiation change.

168

Vagus Nerve Head and Neck

PATHOLOGY

Sternocleidomastoid m.

Intratumoral vascularities

Vagal schwannoma

Vagal schwannoma

Sternocleidomastoid m.

Internal jugular v. Transverse process of cervical vertebra Thickened vagus n.

(Top) Longitudinal power Doppler ultrasound of a vagal schwannoma reveals marked increased intratumoral vascularity. Ultrasound readily identifies a vagal nerve schwannoma and obviates the need for fine-needle aspiration cytology or biopsy. (Middle) Coronal fatsuppressed T2WI MR shows marked T2 hyperintensity of vagal schwannoma. (Bottom) Longitudinal grayscale ultrasound shows the diffusely thickened vagus nerve in relation to the internal jugular vein.

169

Head and Neck

Carotid Arteries

GROSS ANATOMY Overview • Common carotid artery (CCA) divides into external carotid artery (ECA) and internal carotid artery (ICA) • ECA is smaller of 2 terminal branches ○ Supplies most of head and neck (except eye, brain) ○ Numerous anastomoses with ICA and vertebral artery; important source of collateral blood flow • ICA has no normal extracranial branches

IMAGING ANATOMY Common Carotid Artery • Right CCA originates from brachiocephalic trunk; left CCA originates from aortic arch • Courses superiorly in carotid space, anteromedial to internal jugular vein • Divides into ECA and ICA at ~ C3-C4 level

Cervical Internal Carotid Artery • 90% posterolateral to ECA • Carotid bulb ○ Focal dilatation of ICA at its origin from CCA ○ Flow reversal occurs in carotid bulb • Ascending cervical segment ○ Courses superiorly within carotid space ○ Enters carotid canal of skull base (petrous temporal bone) ○ No named branch in neck

External Carotid Artery • Smaller and medial compared with ICA • Has 8 major branches in neck • Superior thyroid artery ○ 1st ECA branch (may arise from CCA bifurcation) ○ Arises anteriorly and courses inferiorly to apex of thyroid ○ Supplies superior thyroid and larynx ○ Anastomoses with inferior thyroid artery (branch of thyrocervical trunk) • Ascending pharyngeal artery ○ Arises from posterior ECA (or CCA bifurcation) ○ Courses superiorly between ECA and ICA ○ Visceral branches, muscular branches, and neuromeningeal branches • Lingual artery ○ 2nd anterior ECA branch ○ Loops anteroinferiorly, then superiorly to tongue ○ Major vascular supply to tongue, oral cavity, and submandibular gland • Facial artery ○ Originates just above lingual artery ○ Curves around mandible, then passes anterosuperiorly across cheek, closely related to submandibular gland ○ Supplies face, palate, lip, and cheek • Occipital artery ○ Originates from posterior aspect of ECA ○ Courses posterosuperiorly between occiput and C1 ○ Supplies scalp, upper cervical musculature, and posterior fossa meninges • Posterior auricular artery 170

○ Arises from posterior ECA above occipital artery ○ Courses superiorly to supply pinna, scalp, external auditory canal, and chorda tympani • Superficial temporal artery ○ Smaller of 2 terminal ECA branches ○ Runs superiorly behind mandibular condyle, across zygoma ○ Supplies scalp and gives off transverse facial artery • Maxillary artery ○ Larger of 2 terminal ECA branches ○ Arises within parotid gland, behind mandibular neck ○ Gives off middle meningeal artery (supplies cranial meninges)

ANATOMY IMAGING ISSUES Imaging Recommendations • Normal US appearances of carotid arteries ○ CCA diameter: 6.3 ± 0.9 mm, smooth and thin intima, antegrade low-resistance arterial flow ○ ICA diameter: 4.8 ± 0.7 mm, smooth and thin intima, antegrade low-resistance flow ○ ECA diameter: 4.1 ± 0.6 mm, smooth and thin intima, antegrade high-resistance flow • In assessing carotid arteries on US, following parameters should be examined ○ Intimal-medial thickness – Distance between leading edges of lumen-intima interface and media-adventitia interface at far edge – 0.5 - 1.0 mm in healthy adults ○ Presence of atherosclerotic plaques – Eccentric/concentric, noncircumferential/circumferential – Calcified plaque/soft plaque ○ Luminal diameter/area reduction – Should be measured on true cross-sectional view of affected artery – Color flow imaging helps to detect residual lumen in tight stenosis or in assessing indeterminate total occlusion ○ Spectral Doppler analysis – Arterial flow pattern: Low-resistance/high-resistance flow, antegrade/retrograde flow, special waveform (e.g., damped waveform, preocclusive "thump") – Peak systolic velocity measurement – Systolic velocity ratio measurement

Imaging Pitfalls • Scanning technique must be meticulous to produce reliable Doppler US results • Obliquity of imaging plane in relation to cross section of artery may wrongly estimate degree of stenosis

CLINICAL IMPLICATIONS Clinical Importance • Doppler parameters give physiologic assessment of degree of stenosis • Consider acute idiopathic carotidynia for tender mass around distal carotid, near bifurcation ○ Vessel wall thickening, no luminal narrowing or velocity elevation

Carotid Arteries Head and Neck

NORMAL ARTERIAL ANATOMY

Facial a.

External carotid a. Carotid bulb, internal carotid a. Superior thyroid a.

Internal jugular v.

Common carotid a.

Thyrocervical trunk

Costocervical trunk Subclavian a.

Vertebral a.

Internal mammary a. Brachiocephalic a.

Anterior graphic of the neck, with the veins ghosted, shows the normal arterial anatomy. The right common carotid artery (CCA) arises from the brachiocephalic artery, while the left common carotid artery arises from the aorta. They ascend medial to the jugular veins and bifurcate into the internal (ICA) and external (ECA) carotid arteries at the level of the upper thyroid cartilage. The ECAs supply most of the head and neck, while the ICAs supply the brain and eye. The ICAs have no extracranial branches.

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Head and Neck

Carotid Arteries AORTIC ARCH

Right common carotid a.

Left vertebral a.

Vertebral a.

Right subclavian a.

Brachiocephalic a.

Ascending aorta

Left subclavian a.

Left common carotid a.

Descending aorta

Right subclavian a. Left common carotid a.

Left subclavian a. Right common carotid a. Brachiocephalic a.

Proximal aortic arch

Ascending aorta

Descending aorta

(Top) Graphic shows the classic branching pattern of the 3 great arteries from the aortic arch: The brachiocephalic, left common carotid, and left subclavian arteries. This is seen in ~ 80% of cases. The brachiocephalic and the left CCA may have a common origin (1020% of cases). (Bottom) Left anterior oblique thoracic aortogram demonstrates the anatomy of the aortic arch and its branches. Contrast injected into the distal ascending aorta opacifies the aortic arch and its branches. The 1st branch is the brachiocephalic artery followed by the left common carotid and left subclavian arteries. The irregular contour of the descending aorta and the luminal narrowing of the left subclavian artery are secondary to atherosclerosis.

172

Carotid Arteries

Middle meningeal a.

Head and Neck

COMMON CAROTID ARTERY

Sphenopalatine a. Superficial temporal a.

Infraorbital a. Pterygopalatine fossa

Posterior auricular a.

Maxillary (internal maxillary) a. Occipital a. Superior alveolar a. Ascending pharyngeal a. Lingual a. Carotid bulb, internal carotid a. Inferior alveolar a. Facial a. Superior thyroid a. Common carotid a.

Occipital a.

Posterior auricular a. External carotid a. Ascending pharyngeal a.

Internal carotid a.

Facial a. Lingual a. Superior thyroid a.

(Top) Lateral graphic depicts the CCA and its 2 terminal branches, the ECA and internal ICA. The scalp and the superficial facial structures are removed to show the deep ECA branches. The ECA terminates by dividing into the superficial temporal and internal maxillary arteries (IMA). Within the pterygopalatine fossa, the IMA divides into numerous deep branches. Its distal termination is the sphenopalatine artery, which passes medially into the nasal cavity. Numerous anastomoses between the ECA branches (e.g., between the facial and maxillary arteries) and between the ECA and the orbital and cavernous branches of the ICA provide potential sources for collateral blood flow. (Bottom) The early arterial phase of CCA angiogram is shown with bony structures subtracted. The major ECA branches are opacified.

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Head and Neck

Carotid Arteries CAROTID BIFURCATION Subcutaneous tissue Sternocleidomastoid m. Jugulodigastric lymph node

Internal jugular v. Internal carotid a.

Branches of external carotid a. External carotid a.

Internal carotid a. Common carotid a. Carotid bulb External carotid a.

Subcutaneous tissue Sternocleidomastoid m. Branches of external carotid a. Internal jugular v. Internal carotid a.

External carotid a.

(Top) Transverse grayscale ultrasound shows the upper cervical level at the carotid bifurcation. The CCA bifurcates into the ICA and ECA. The former is usually of larger caliber, laterally located, and has no branches in the neck. (Middle) Longitudinal grayscale ultrasound in coronal orientation demonstrates the carotid bifurcation. The proximal portion of the ICA is usually mildly dilated and is termed carotid bulb. At this site, the color/spectral Doppler study is more complex due to a disturbance of laminar flow and should not be misinterpreted as an abnormality. (Bottom) Color Doppler ultrasound of carotid bifurcation in a transverse plane demonstrates turbulent flow in the carotid bulb. Branches of ECA are easier to depict than on grayscale examination.

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Carotid Arteries

Hyoid bone Hypopharynx

Head and Neck

CAROTID BIFURCATION

Aryepiglottic fold Submandibular gland Facial a. External carotid a. Internal jugular v.

Internal carotid a.

External jugular v. Vertebral a. Sternocleidomastoid m. Levator scapulae m.

Facial a.

External carotid a.

Internal carotid a. Carotid bulb

Hyoid bone Superior thyroid a.

Internal jugular v.

Carotid bulb

Spectral Doppler waveform in carotid bulb Flow reversal in separation zone

(Top) Axial CECT shows the upper neck just beyond the carotid bifurcation. The ICA is larger and more posterolateral in position than the ECA. (Middle) Maximum-intensity projection in the sagittal plane demonstrates carotid bifurcation into the ECA and ICA at the level of the hyoid bone. Note the branching nature of the ECA in contrast to the ICA. (Bottom) Spectral Doppler ultrasound shows the carotid bulb, which has a different flow pattern than the rest of the ICA. In early systole, blood flow is accelerated in a forward direction. As the peak systole is approached, a large separation zone with flow reversal develops. Flow separation should be seen in normal individuals, and its absence should raise the suspicion of plaque formation.

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Head and Neck

Carotid Arteries INTERNAL CAROTID ARTERY Subcutaneous tissue Sternocleidomastoid m. Jugulodigastric lymph node Submandibular gland Internal jugular v. Internal carotid a.

Branches of external carotid a. External carotid a.

Sternocleidomastoid m.

Internal jugular v.

Internal carotid a.

Subcutaneous tissue Sternocleidomastoid m.

Internal jugular v.

Internal carotid a.

(Top) Transverse grayscale ultrasound of the upper neck, just beyond the carotid bifurcation, shows the close anatomical relationship of the upper neck with the internal jugular vein, ECA, and jugulodigastric lymph node. (Middle) Longitudinal grayscale ultrasound shows the ICA. Note its smooth wall with no intimal thickening; it is free of atherosclerotic plaque in a normal individual. No branch is seen in the cervical region. (Bottom) Color Doppler ultrasound shows the ICA and the internal jugular vein in the longitudinal plane. Note that the normal antegrade flow is toward the cranial direction of the ICA and opposite the caudal direction of flow in the adjacent internal jugular vein.

176

Carotid Arteries

Subcutaneous tissue Platysma

Head and Neck

INTERNAL CAROTID ARTERY

Hypopharynx Submandibular gland Jugulodigastric lymph node

Branches of external carotid a. External carotid a.

External jugular v. Internal jugular v.

Vertebral body

Internal carotid a.

Vertebral a.

Sternocleidomastoid m. Levator scapulae m.

Transverse process

Cervical vertebra Internal carotid a.

Facial a. Internal jugular v. External carotid a.

Carotid bulb

Internal jugular v. Internal carotid a.

Spectral Doppler waveform of ICA

(Top) Axial CECT of the upper neck shows the anatomical relation of the ICA with the internal jugular vein and branches of the ECA. (Middle) Maximum-intensity projection CECT in the sagittal plane shows the normal configuration and contour of the cervical portion of the ICA. Note the lack of an arterial branch from the cervical ICA in the neck in contrast to the ECA. Note the mild dilatation of the ICA at its origin (carotid bulb). (Bottom) Spectral Doppler ultrasound in the longitudinal plane shows the cervical portion of the ICA, which has a low-resistance flow pattern with antegrade flow in the diastolic phase. The waveform is different from that of the carotid bulb.

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Head and Neck

Carotid Arteries EXTERNAL CAROTID ARTERY Subcutaneous tissue Sternocleidomastoid m. Submandibular gland Jugulodigastric lymph node Branches of external carotid a. Internal jugular v. Internal carotid a.

External carotid a. Gas in supraglottic larynx

Internal jugular v.

External carotid a.

Superior thyroid a.

Facial a.

Internal jugular v. External carotid a. Superior thyroid a. Facial a.

(Top) Transverse grayscale ultrasound shows the upper neck above the carotid bifurcation. The position of the ECA medial to the ICA and internal jugular vein, posterior to the jugulodigastric lymph node, is well demonstrated. (Middle) Longitudinal grayscale ultrasound shows the ECA. Two anterior branches, the superior thyroid artery and the facial artery, are seen arising from the proximal portion of the ECA. They course inferiorly to the upper pole of the thyroid and superiorly to the facial region. (Bottom) Color Doppler ultrasound shows the ECA in the longitudinal plane. The antegrade flow in the cranial direction of the ECA is demonstrated. Note the opposite flow direction of the adjacent internal jugular vein.

178

Carotid Arteries Head and Neck

EXTERNAL CAROTID ARTERY

Submandibular gland

External jugular v. Internal jugular v. Internal carotid a. Sternocleidomastoid m.

External carotid a.

Vertebral a. Cervical vertebra

Facial a.

Internal carotid a.

Lingual a. External carotid a. Hyoid bone Carotid bulb Superior thyroid a. Internal jugular v.

Internal jugular v. External carotid a.

Spectral Doppler waveform of external carotid a.

(Top) Axial CECT of the upper neck at the hyoid bone level shows the relationship of the ECA with the adjacent ICA and the internal jugular vein. (Middle) Maximum-intensity projection CECT in the sagittal plane shows the normal contour and configuration of the ECA. Note some of its major branches, including the superior thyroid artery, lingual artery, and facial artery, in its proximal portion. (Bottom) Spectral Doppler ultrasound of the ECA in longitudinal plane shows a high-resistance flow pattern with a low diastolic component. Contrarily, the CCA and ICA are of a low-resistance pattern with a high diastolic component.

179

Head and Neck

Carotid Arteries GRAYSCALE AND DOPPLER ULTRASOUND

Sternocleidomastoid m. Internal jugular v.

Atherosclerotic plaque

Internal carotid a.

Stenotic segment, internal carotid a.

Internal carotid a.

Stenotic segment

Spectral waveform of stenotic internal carotid a.

(Top) Longitudinal grayscale ultrasound of the cervical portion of the ICA shows hypoechoic atherosclerotic plaque with marked luminal narrowing. (Middle) Longitudinal color Doppler ultrasound in the same patient helps to demonstrate the turbulent arterial flow through the severe stenotic segment in the proximal ICA. Color flow imaging is a useful tool to distinguish severe stenosis from complete occlusion. (Bottom) Spectral Doppler ultrasound of the proximal ICA demonstrates markedly elevated peak systolic and peak diastolic velocity, indicating severe stenosis.

180

Carotid Arteries Head and Neck

GRAYSCALE AND DOPPLER ULTRASOUND

Internal jugular v. Internal carotid a.

Atherosclerotic plaque

Internal jugular v. Internal carotid a.

Atherosclerotic plaque

Carotid bulb Common carotid a.

(Top) Longitudinal grayscale ultrasound of the cervical portion of the ICA shows a slightly hyperechoic atherosclerotic plaque causing complete arterial occlusion. (Middle) Color Doppler ultrasound in the same patient reveals an absence of arterial flow in the occluded segment of the ICA. (Bottom) Spectral Doppler ultrasound at the carotid bifurcation shows no detectable signal within the occluded segment and preocclusive "thump" proximal to the occluded segment. The carotid bulb was occluded on grayscale imaging (not shown).

181

Head and Neck

Carotid Arteries COMMON CAROTID ARTERY

Subcutaneous tissue Sternocleidomastoid m. Sternohyoid m. Sternothyroid m. Omohyoid m. Internal jugular v.

Right lobe of thyroid gland

Common carotid a.

Cervical esophagus

Sternocleidomastoid m.

Internal jugular v.

Common carotid a.

Thyroid gland

Sternocleidomastoid m.

Common carotid a. Brachiocephalic a. Subclavian a.

(Top) Transverse grayscale ultrasound shows the distal CCA at the level of the upper pole of the thyroid gland. Note that the wall in a normal individual is smooth with no intimal thickening or atherosclerotic plaque. The lumen is circular in cross section. There is no major named branch in the neck apart from the termination into ECA and ICA at the level of the hyoid bone. (Middle) Longitudinal grayscale ultrasound of the CCA shows the smooth outline of the intimal layer. (Bottom) Color Doppler ultrasound of the proximal CCA at the root of the neck in the longitudinal plane demonstrates the normal antegrade arterial flow in the cranial direction. Its origin along with the subclavian artery from the right brachiocephalic artery is also well demonstrated.

182

Carotid Arteries Head and Neck

COMMON CAROTID ARTERY

Trachea Right lobe of thyroid gland Sternocleidomastoid m. Internal jugular v.

Common carotid a.

Cervical vertebra Vertebral a.

Internal jugular v.

Cervical vertebra

Common carotid a. (right) Common carotid a. (left)

Subclavian a.

Brachiocephalic a.

Common carotid a.

Spectral Doppler waveform of common carotid a.

(Top) Axial CECT of the lower neck shows contrast-filled CCA related anteriorly and medially to the right lobe of the thyroid gland and laterally to the internal jugular vein. (Middle) Coronal reformatted CECT shows the normal contour and vertical course of the CCA. It originates from the brachiocephalic artery on the right at the root of the neck with the right subclavian artery. (Bottom) Spectral Doppler ultrasound of the CCA shows low-resistance arterial flow with a forward diastolic component. The scanning technique must be meticulous to produce a reliable Doppler assessment.

183

Head and Neck

Vertebral Arteries

184

IMAGING ANATOMY Overview • Vertebral artery (VA): 4 segments ○ V1 segment (extraosseous segment) – Arises from 1st part of subclavian artery – Courses posterosuperiorly to enter C6 transverse foramen – Branches: Segmental cervical muscular, spinal branches ○ V2 segment (foraminal segment) – Ascends through C6-C3 transverse foramina – Turns superolaterally through inverted L-shaped transverse foramen of axis (C2) – Courses short distance superiorly through C1 transverse foramen – Branches: Anterior meningeal artery, unnamed muscular/spinal branches ○ V3 segment (extraspinal segment) – Exits top of atlas (C1) transverse foramen – Lies on top of C1 ring, curving posteromedially around atlantooccipital joint – As it passes around back of atlantooccipital joint, turns sharply anterosuperiorly to pierce dura at foramen magnum – Branches: Posterior meningeal artery ○ V4 segment (intradural/intracranial segment) – After VA enters skull through foramen magnum, courses superomedially behind clivus – Unites with contralateral VA at or near pontomedullary junction to form basilar artery (BA) – Branches: Anterior, posterior spinal arteries, perforating branches to medulla, posterior inferior cerebellar artery (PICA) – Arises from distal VA, curves around/over tonsil, gives off perforating medullary, choroid, tonsillar, cerebellar branches • BA ○ Courses superiorly in prepontine cistern (in front of pons, behind clivus) ○ Bifurcates into its terminal branches, posterior cerebral arteries (PCAs), in interpeduncular or suprasellar cistern at or slightly above dorsum sellae ○ Branches: Pontine, midbrain perforating branches (numerous), anterior inferior cerebellar artery (AICA), superior cerebellar arteries (SCAs), PCAs (terminal branches)

○ AICA: Internal auditory canal, CNVII and VIII, anterolateral cerebellum ○ SCA: Superior vermis, superior cerebellar peduncle, dentate nucleus, brachium pontis, superomedial surface of cerebellum, upper vermis

Normal Variants, Anomalies • Normal variants ○ VA: Variation in size from right to left, dominance common; origin from aortic arch in 5% • Anomalies ○ VA/BA may be fenestrated or duplicated (may have increased prevalence of aneurysms) ○ Embryonic carotid-basilar anastomoses (e.g., persistent trigeminal artery)

ANATOMY IMAGING ISSUES Imaging Recommendations • V1 and V2 segments are amenable to USG examination • Examination usually starts in V2 segment and proceeds downward to V1 segment, then to its origin • Examination of V2 segment ○ Transducer oriented longitudinally in midcervical region between trachea and sternocleidomastoid muscle ○ Angle transducer laterally from common carotid artery (CCA) and locate V2 segment posterior to acoustic shadowing of transverse processes • Examination of V1 segment ○ Trace caudally from V2 to its origin ○ Left VA more difficult to visualize than right VA ○ Do not confuse with vertebral vein lying adjacent to VA, which can appear pulsatile – Color flow imaging helps to differentiate • Normal waveform of VA on spectral Doppler analysis ○ Low-resistance flow ○ Similar to that of CCA but with lower amplitude ○ Peak systolic velocity: 59 ± 17 cm/sec; end-diastolic velocity: 19 ± 8 cm/sec ○ Flow velocity asymmetry is common and related to caliber of VA

Imaging Pitfalls • VA distal to V2 cannot be properly assessed by USG ○ Abnormalities in spectral Doppler waveform of VA at V1/V2 segment provide clue for disease beyond V2

EMBRYOLOGY

Vascular Territory

Embryologic Events

• VA ○ Anterior spinal arteries: Upper cervical spinal cord, inferior medulla ○ Posterior spinal arteries: Dorsal spinal cord to conus medullaris ○ Penetrating branches: Olives, inferior cerebellar peduncle, part of medulla ○ PICA: Lateral medulla, choroid plexus of 4th ventricle, tonsil, inferior vermis/cerebellum • BA ○ Pontine perforating branches: Central medulla, pons, midbrain

• Plexiform longitudinal anastomoses between cervical intersegmental arteries → VA precursors • Paired plexiform dorsal longitudinal neural arteries (LNAs) develop, form precursors of BA • Transient anastomoses between dorsal LNAs develop and internal carotid arteries (ICAs) appear (primitive trigeminal/hypoglossal arteries, etc.) • Definitive VAs arise from 7th cervical intersegmental arteries, anastomose with LNAs • LNAs fuse as temporary connections with ICAs regress → definitive BA, vertebrobasilar circulation formed

Vertebral Arteries Head and Neck

GRAPHIC AND VOLUME-RENDERED CTA

Foraminal (V2) segment, right vertebral a.

Right common carotid a.

Extraosseous (V1) segment, left vertebral a.

Right subclavian a. Left subclavian a. Brachiocephalic a.

Left common carotid a.

Foramen magnum V3 (extraspinal) vertebral a. segment C1 transverse foramen

V4 (intradural) vertebral a. segment

L-shaped C2 transverse foramen

V2 (foraminal) vertebral a. segment C6 transverse process/foramen

V1 (extraosseous) vertebral a. segment

Right subclavian a.

Left subclavian a.

(Top) AP graphic shows 2 of the 3 extracranial segments of the vertebral arteries (VAs) and their relationship to the cervical spine. The extraosseous (V1) VA segments extend from the superior aspect of the subclavian arteries to the C6 transverse foramina. The V2 (foraminal) segment extends from C6 to the VA exit from the C1 transverse foramina. (Bottom) 3D-VRT CTA shows the extracranial VAs, which originate from the superior aspect of the subclavian arteries. The VAs typically enter the transverse foramina of C6 and ascend almost vertically to C2, where they make a 90° turn laterally in the L-shaped C2 transverse foramina before ascending vertically again to C1.

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Head and Neck

Vertebral Arteries TRANSVERSE, LONGITUDINAL GRAYSCALE AND COLOR DOPPLER Subcutaneous tissue Sternocleidomastoid m.

Common carotid a. Longus colli m. Transverse process of cervical vertebra Body of cervical vertebra Vertebral a.

Subcutaneous tissue Sternocleidomastoid m. Lymph nodes in posterior triangle

Vertebral a.

Vertebral v.

Transverse process of cervical vertebra

Body of cervical vertebra

Sternocleidomastoid m.

Transverse process of cervical vertebra

Vertebral a. Vertebral v.

(Top) Transverse grayscale ultrasound of the lower neck shows the proximal V1 segment of the VA, which arises from the 1st part of the subclavian artery and courses superiorly to enter the transverse foramina of the lower cervical vertebra. Note its posterior relationship to the longus colli at this level. (Middle) Longitudinal grayscale ultrasound of the posterior neck demonstrates the V2 segment of the VA within the transverse foramina of cervical vertebrae. Note the presence of dense posterior acoustic shadowing from the transverse processes, obscuring a clear view of the underlying vertebral vessels. (Bottom) Color Doppler ultrasound shows the V2 segment of the VA in the longitudinal plane. Note the opposite flow direction of the vertebral vein (i.e., craniocaudal direction) as compared with that of the VA (caudocranial direction).

186

Vertebral Arteries

Hyoid bone Vallecula Piriform sinus

Head and Neck

AXIAL AND CORONAL CECT, SPECTRAL DOPPLER ULTRASOUND

External carotid a. Internal carotid a. Internal jugular v. Vertebral a.

Longus colli m. Body of cervical vertebra

Transverse process of cervical vertebra

Lymph nodes in posterior triangle Transverse process of cervical vertebra

Sternocleidomastoid m.

Body of cervical vertebra Vertebral a.

Vertebral a.

Spectral Doppler waveform of vertebral a.

(Top) Axial CECT of the neck at the level of the hyoid bone shows the VA running in a caudocranial direction within the foramen transversarium of the cervical vertebrae. This portion is amenable for ultrasound examination. (Middle) Coronal reformatted CECT of the neck shows the vertical course of the VAs through the transverse foramina of C6-C2 vertebrae. Note its close anatomical relationship with the transverse processes and bodies of the cervical vertebrae. (Bottom) Spectral Doppler ultrasound of the V2 segment of the VA is of low resistance, similar to that of the common carotid artery but with lower amplitude. Spectral analysis of the V2 segment provides a clue to stenosis/occlusion proximally and distally. For example, a high-resistance flow pattern without a diastolic flow component is often associated with a distal flow obstruction.

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Head and Neck

Vertebral Arteries GRAYSCALE AND DOPPLER ULTRASOUND

Transverse process of cervical vertebra

Vertebral a.

Near occlusive segment

Vertebral a. Near occlusive segment

Vertebral a.

(Top) Longitudinal grayscale ultrasound of the V2 segment of the VA shows the presence of hypoechoic atherosclerotic plaque, causing near complete occlusion. (Middle) Color Doppler ultrasound of the VA in the same patient shows a lack of arterial color flow within the nearly occluded segment. (Bottom) Spectral Doppler ultrasound in the same patient shows a high-resistance flow pattern with elevated peak systolic and diastolic velocities.

188

Vertebral Arteries Head and Neck

GRAYSCALE AND DOPPLER ULTRASOUND

Systolic deceleration Small diastolic flow reversal

Systolic deceleration

Larger diastolic flow reversal

Complete flow reversal

(Top) Spectral Doppler ultrasound shows a mild degree of subclavian steal syndrome. There is systolic deceleration of the vertebral flow in an antegrade direction with small diastolic flow reversal. (Middle) Spectral Doppler ultrasound shows a moderate degree of subclavian steal syndrome. The degree of systolic deceleration and diastolic flow reversal is more pronounced with alternating vertebral flow demonstrated. (Bottom) Spectral Doppler ultrasound shows severe subclavian steal syndrome. There is near complete reversal of flow in the VA with relative absent antegrade systolic flow. This pattern is commonly associated with the occurrence of vertebrobasilar symptoms.

189

Head and Neck

Neck Veins

190

GROSS ANATOMY

IMAGING ANATOMY

Overview

Overview

• Major extracranial venous system composed of facial veins, neck veins, scalp, skull (diploic), and orbital veins • Facial veins ○ Facial vein – Begins at angle between eye, nose – Descends across masseter, curves around mandible – Joins internal jugular vein (IJV) at hyoid level – Tributaries from orbit (supraorbital, superior ophthalmic veins), lips, jaw, facial muscles ○ Deep facial vein – Receives tributaries from deep face, connects facial vein with pterygoid plexus ○ Pterygoid plexus – Network of vascular channels in masticator space between temporalis/lateral pterygoid muscles – Connects cavernous sinuses and clival venous plexus to face/orbit tributaries – Drains into maxillary vein ○ Retromandibular vein (RMV) – Formed from union of maxillary and superficial temporal veins – Lies within parotid space – Passes between external carotid artery and CNVII to empty into IJV • Neck veins ○ External jugular vein (EJV) – From union of retromandibular and posterior auricular veins – Courses inferiorly on surface of sternocleidomastoid muscle – Drains into subclavian vein in supraclavicular fossa – Receives tributaries from scalp, ear, and face – Size, extent highly variable ○ IJV – Caudal continuation of sigmoid sinus from jugular foramen at skull base – Jugular bulb = dilatation at origin – Courses inferiorly in carotid space posterolateral to internal/common carotid arteries underneath sternocleidomastoid muscle – Unites with subclavian vein to form brachiocephalic vein – Size highly variable; significant side-to-side asymmetry common; right usually larger than left ○ Subclavian vein – Proximal continuation of axillary vein in thoracic inlet – EJV drains into subclavian vein – Subclavian vein joins IJV to form brachiocephalic vein ○ Vertebral venous plexus – Suboccipital venous plexus – Tributaries from basilar (clival) plexus, cervical musculature – Interconnects with sigmoid sinuses, cervical epidural venous plexus – Terminates in brachiocephalic vein

• Low pressure inside; easily compressible ○ Light probe pressure with good surface contact between transducer and skin to ensure optimal visualization ○ Use of Valsalva maneuver helps to distend major neck veins • IJV ○ Largest vein of neck ○ Deep cervical chain lymph nodes commonly found along its course ○ Beware of thrombosis in patients with previous central venous catheterization or adjacent tumors ○ Always check for compressibility and phasicity on respiration ○ Presence of vascularity in IJV thrombosis is usually seen with tumor thrombus rather than bland venous thrombus • Subclavian vein ○ Accessible on USG by inferior tilting of transducer in supraclavicular fossa ○ Venous valves are present in most patients ○ Thrombosis/stenosis commonly seen in patients on chronic hemodialysis or with previous subclavian venous catheterization • RMV ○ Serves as landmark on USG to infer position of intraparotid portion of facial nerve ○ Anterior division of RMV sandwiched between submandibular gland anteriorly and parotid tail posteriorly – Its displacement helps to determine origin of mass in posterior submandibular region

ANATOMY IMAGING ISSUES Imaging Pitfalls • Neck veins are often overlooked, as most sonologists pay more attention to arteries than veins in neck • Not all neck veins are readily assessed by ultrasound ○ Only large and superficial veins are clearly seen • Asymmetric IJVs are common; 1 IJV may be many times size of contralateral IJV ○ IJV venous varix: Extreme dilatation of IJV upon Valsalva maneuver with clinically palpable neck lump • Slow flow within IJV may appear as low-level hyperechoic intraluminal "mass" ○ May mimic IJV thrombus ○ Moving nature of echoes on real-time ultrasound and sharp linear near-field interface help to distinguish artifacts from slow flow and IJV thrombus

CLINICAL IMPLICATIONS Clinical Importance • Ultrasound safely guides needle for venous access • Absence of respiratory phasicity is strong indicator of abnormality

Neck Veins Head and Neck

FACE AND NECK VEINS

Superior ophthalmic v. Inferior ophthalmic v. Cavernous sinus Angular branch, facial v.

Superior petrosal sinus

Pterygoid venous plexus

Common facial v.

External jugular v.

Internal jugular v.

Anterior jugular v.

Subclavian v.

Brachiocephalic v.

Superior vena cava

Anteroposterior view of the extracranial venous system depicts the major neck veins, their drainage into the mediastinum, and their numerous interconnections with the intracranial venous system. The pterygoid venous plexus receives tributaries from the cavernous sinus and provides an important potential source of collateral venous drainage if the transverse or sigmoid sinuses become occluded.

191

Head and Neck

Neck Veins GRAYSCALE AND COLOR DOPPLER ULTRASOUND (IJV)

Sternocleidomastoid m. Sternohyoid m. Sternothyroid m. Internal jugular v. Vagus n.

Common carotid a. Right lobe of thyroid gland

Anterior scalene m.

Sternocleidomastoid m.

Internal jugular v.

Transverse process of cervical vertebra Anterior scalene m.

Sternocleidomastoid m. Internal jugular v.

(Top) Transverse grayscale ultrasound of the lower cervical level shows the normal anatomical relationship between the internal jugular vein and the adjacent structures. It is underneath the sternocleidomastoid muscle and lateral to the common carotid artery and vagus nerve within the carotid sheath. (Middle) Longitudinal grayscale ultrasound shows the internal jugular vein in the midcervical level. The internal jugular vein appears as a tubular anechoic structure coursing in a vertical direction. It should be examined with light probe pressure and with compression to exclude a venous thrombosis. (Bottom) Corresponding color Doppler ultrasound in the longitudinal plane shows color flow filling the entire lumen of the internal jugular vein. The use of color Doppler helps to identify and evaluate the presence and nature of an internal jugular vein thrombus.

192

Neck Veins

Infrahyoid strap m.

Head and Neck

CECT AND SPECTRAL DOPPLER ULTRASOUND (IJV)

Anterior jugular v. Sternocleidomastoid m. Internal jugular v.

Trachea Right lobe of thyroid gland Esophagus

External jugular v. Common carotid a. Scalenus anterior Scalenus medius Transverse process

Longus coli Vertebral body

Lateral mass

Internal jugular v. Common carotid a. Right lobe of thyroid gland Clavicle

Right brachiocephalic a. Right brachiocephalic v.

External jugular v. Subclavian v. Internal jugular v.

Phasic venous waveform of internal jugular v.

(Top) Axial CECT of the lower neck shows the internal jugular vein, which is usually larger than and lateral to the common carotid artery. The external jugular vein is in a subcutaneous location. (Middle) Coronal reformatted CECT of the lower neck shows the close anatomical relationship of the internal jugular vein and common carotid artery within the carotid sheath. The internal jugular vein continues inferiorly below the clavicle to join the subclavian vein to form the brachiocephalic vein. (Bottom) Transverse spectral Doppler ultrasound shows the internal jugular vein at the level of the supraclavicular fossa at the junction with the subclavian vein. The normal biphasic venous waveform, which varies with respiratory motion, can be easily demonstrated and helps to exclude the presence of obstructing venous thrombus.

193

Head and Neck

Neck Veins GRAYSCALE AND COLOR DOPPLER ULTRASOUND (EJV)

Sternocleidomastoid m. External jugular v.

Internal jugular v. Tributary of subclavian v. Branch of subclavian a.

Subcutaneous tissue Sternocleidomastoid m. Valve

External jugular v.

Internal jugular v.

Subclavian v.

Brachiocephalic v.

Subcutaneous tissue

Sternocleidomastoid m.

External jugular v.

Internal jugular v.

Subclavian v. Brachiocephalic v.

(Top) Transverse grayscale ultrasound of right lower neck shows the location of the external jugular vein in relation to the sternocleidomastoid muscle. It appears as a distended, round, anechoic structure on Valsalva maneuver using light transducer pressure. (Middle) Transverse grayscale ultrasound shows the external jugular vein at the supraclavicular level, at the site of union with the subclavian vein, close to the terminal portion of the internal jugular vein. Valve leaflets are commonly seen within the major veins at the thoracic inlet level. (Bottom) Corresponding transverse color Doppler ultrasound at the supraclavicular level helps to depict the venous drainage of the external jugular vein to the subclavian vein. Note that the subclavian vein joins the internal jugular vein to form the brachiocephalic vein.

194

Neck Veins

Sternocleidomastoid m. Internal jugular v. External jugular v.

Head and Neck

CECT AND SPECTRAL DOPPLER ULTRASOUND (EJV)

Trachea Esophagus Common carotid a.

Branches of subclavian vessels

Sternocleidomastoid m.

Thyroid gland (right lobe) Internal jugular v.

External jugular v.

Subclavian v. Brachiocephalic v. Medial end of right clavicle

Manubrium

External jugular v. Subclavian v.

Internal jugular v.

Normal venous waveform

(Top) Axial CECT shows the right lower neck. Note the superficial anatomical location of the external jugular vein. Thus, light probe pressure is necessary for the assessment of the external jugular vein on ultrasound because with increasing pressure, the vein will be compressed. (Middle) Coronal reformatted CECT shows the right lower neck. Note the drainage of the external jugular vein to the subclavian vein, which joins the internal jugular vein to form the brachiocephalic vein at the thoracic inlet level. (Bottom) Spectral Doppler ultrasound interrogating the terminal portion of the external jugular vein shows a normal, phasic, low-pressure venous waveform, which helps to confirm its patency.

195

Head and Neck

Neck Veins LONGITUDINAL AND TRANSVERSE ULTRASOUND Subcutaneous tissue Clavicle Sternocleidomastoid m. Internal jugular v.

Subclavian v.

Brachiocephalic v.

Internal jugular v.

Pseudothrombus from slow venous flow

Venous vascular malformation

External jugular v.

(Top) Longitudinal grayscale ultrasound at the supraclavicular level shows the union of internal jugular vein and subclavian vein to form the brachiocephalic vein. The more distal portion of the brachiocephalic vein is obscured by the overlying clavicle and is therefore not assessed by ultrasound. (Middle) Longitudinal grayscale ultrasound of the right internal jugular vein shows a pseudothrombus phenomenon due to slow venous flow within the internal jugular vein. Note the layering with a sharp linear border in the internal jugular vein lumen in the near field, which is the clue to distinguish it from venous thrombus. (Bottom) Transverse grayscale ultrasound of the right posterior triangle shows a well-defined hypoechoic mass with multiple internal sinusoidal spaces. The lesion is inseparable from the external jugular vein. Surgery confirmed a venous vascular malformation (VVM) arising from the external jugular vein.

196

Neck Veins Head and Neck

CECT, COLOR AND POWER DOPPLER ULTRASOUND

Internal jugular v. Right lobe of thyroid gland

Subclavian v. Brachiocephalic v. Clavicle

Thrombosed internal jugular v.

Subclavian v.

Common carotid a.

External jugular v.

Sinusoidal space within VVM

(Top) Coronal reformatted CECT of the right supraclavicular fossa shows the formation of the brachiocephalic vein by union of the subclavian vein (dense contrast filling due to injection in ipsilateral antecubital fossa) and internal jugular vein. The brachiocephalic vein can be fully assessed on CECT as compared with ultrasound. (Middle) Transverse color Doppler ultrasound of the right supraclavicular level reveals intraluminal, hypoechoic, avascular echoes causing occlusion of the internal jugular vein. The appearances are of a bland venous thrombus due to prolonged central venous catheterization. (Bottom) Longitudinal power Doppler ultrasound shows the external jugular vein VVM. Note the intimate relationship of the VVM and the external jugular vein. Sinusoidal spaces are usually not color filled due to very slow flow within.

197

Head and Neck

Cervical Lymph Nodes

TERMINOLOGY Synonyms • • • •

Internal jugular chain (IJC): Deep cervical chain Spinal accessory chain (SAC): Posterior triangle chain Transverse cervical chain: Supraclavicular chain Anterior cervical chain: Prelaryngeal, pretracheal, paratracheal nodes • Paratracheal node: Recurrent laryngeal node

Definitions • Jugulodigastric node: "Sentinel" (highest) node, found at apex of IJC at angle of mandible • Virchow node: "Signal" node, lowest node of deep cervical chain • Troisier node: Most medial node of transverse cervical chain • Omohyoid node: Deep cervical chain node superior to omohyoid as it crosses jugular vein • Delphian node: Pretracheal node

IMAGING ANATOMY Overview • In normal adult neck, may be up to 300 lymph nodes ○ Internal structures: Capsule, cortex, medulla, hilum • US appearances of normal cervical lymph node ○ Small, oval/reniform shape with well-defined margin ○ Homogeneous, hypoechoic cortex with echogenic hilum ○ Hilar vascularity on color/power Doppler examination • Imaging-based nodal classification ○ Level I: Submental and submandibular nodes – Level IA: Submental nodes: Found between anterior bellies of digastric muscles – Level IB: Submandibular nodes: Found around submandibular glands in submandibular space ○ Level II: Upper IJC nodes: From posterior belly of digastric muscle to hyoid bone – Level IIA: Level II node anterior, medial, lateral or posterior to IJV; if posterior to IJV, node must be inseparable from IJV; contains jugulodigastric nodal group – Level IIB: Level II node posterior to IJV with fat plane visible between node and IJV ○ Level III: Mid IJC nodes – From hyoid bone to inferior margin of cricoid cartilage ○ Level IV: Lower IJC nodes – From inferior cricoid margin to clavicle ○ Level V: Nodes of posterior cervical space/spinal accessory chain – SAC nodes lie posterior to back margin of sternocleidomastoid muscle – Level VA: Upper SAC nodes from skull base to bottom of cricoid cartilage – Level VB: Lower SAC nodes from cricoid to clavicle ○ Level VI: Nodes of visceral space – Found from hyoid bone above to top of manubrium below – Midline group of cervical lymph nodes – Includes prelaryngeal, pretracheal, and paratracheal subgroups ○ Level VII: Superior mediastinal nodes 198

– Between carotid arteries from top of manubrium above to innominate vein below • Other nodal groups not included in standard imaging-based nodal classification ○ Parotid nodal group: Intraglandular or extraglandular ○ Retropharyngeal (RPS) nodal group: Medial RPS nodes and lateral RPS nodes (Rouvière node) ○ Facial nodal group

ANATOMY IMAGING ISSUES Imaging Approaches • Nodal metastases from primary tumors are site specific; therefore, it is critical to understand usual patterns of lymphatic spread • Equivocal nodes outside usual pattern less suspicious • Likely location of primary tumor can be suspected in patients presenting with nodal mass • Nodal disease outside usual pattern may suggest aggressive tumor or prompt search for 2nd primary

Imaging Pitfalls • Retropharyngeal (RPS) nodes and superior mediastinal nodes cannot be assessed by US

Key Concepts • Useful US features suspicious of malignancy ○ Shape: Round, long:short axis ratio < 2 ○ Loss of echogenic hilum ○ Presence of intranodal necrosis (cystic/coagulation) ○ Presence of extracapsular spread: Ill-defined margin ○ Peripheral/subcapsular flow on color/power Doppler ultrasound ○ Increased intranodal intravascular resistance: Resistive index (RI) > 0.8, pulsatility index (PI) > 1.6 ○ Internal architecture: Punctate calcifications in metastatic node from papillary thyroid carcinoma, reticulated/pseudocystic appearance of lymphomatous node • No single finding sensitive or specific enough; these signs should be used in combination • FNAC helps to improve diagnostic accuracy • Tuberculous nodes mimic metastatic nodes ○ Differentiating features: Intranodal necrosis, nodal matting, soft tissue edema and displaced hilar vascularity/avascularity, calcification (post treatment)

CLINICAL IMPLICATIONS Clinical Importance • Presence of malignant SCCa nodes on staging associated with 50% ↓ in long-term survival ○ If extranodal spread present, further 50% ↓ • Location of metastatic nodes in neck may help predict site of primary tumor ○ RPS and posterior triangle nodes seen in nasopharyngeal carcinoma, and lower cervical nodes in lung cancer ○ When Virchow node found on imaging without upper neck nodes, primary not in neck, and whole-body imaging warranted

Cervical Lymph Nodes Head and Neck

LYMPH NODE GROUPS

Retropharyngeal nodes Submandibular nodes (level IB) Occipital node Mastoid node Parotid node

Submental nodes (level IA)

Jugulodigastric node

Hyoid bone plane Spinal accessory nodal group (VA-VB)

Cricoid cartilage plane

Visceral space nodes Internal jugular nodal group (II-IV)

Transverse cervical nodes

Superior mediastinal nodes

Virchow node

Lateral oblique graphic of the cervical neck depicts an axial slice through the suprahyoid neck. The retropharyngeal nodes behind the pharynx are often clinically occult. The hyoid bone (blue arc) and cricoid cartilage (orange circle) planes are highlighted, as they serve to subdivide the internal jugular and spinal accessory nodal group levels. Regional lymph nodes are staged the same way for almost all head and neck tumors, largely based on size, bilaterality, and number of nodes involved. N stages for most pharyngeal and oral cavity tumors are determined by this generic head and neck nodal classification. Tumors of the nasopharynx, however, have a unique N classification scheme.

199

Head and Neck

Cervical Lymph Nodes FACE AND NECK LYMPH NODES

High internal jugular lymph nodes Jugulodigastric lymph node Submandibular lymph nodes Submental lymph nodes

Cricoid cartilage

High spinal accessory lymph nodes Middle internal jugular lymph nodes

Low internal jugular lymph nodes

Visceral space nodes Low spinal accessory lymph nodes Superior mediastinal nodes

Malar node Infraorbital node

Buccinator node

Retrozygomatic node

Mastoid node

Occipital node Mandibular node

Spinal accessory nodes Parotid nodes Jugulodigastric node

(Top) Lateral oblique graphic of the neck shows the anatomic locations for the major nodal groups of the neck. Division of the internal jugular nodal chain into high, middle, and low regions is defined by the level of the hyoid bone and cricoid cartilage. Similarly, the spinal accessory nodal chain is divided into high and low regions by the level of the cricoid cartilage. (Bottom) Lateral view shows facial nodes plus parotid nodes. None of these nodes bear level numbers but instead must be described by their anatomic location. Note that the internal jugular chain is the final common pathway for all lymphatics of the upper aerodigestive tract and neck.

200

Cervical Lymph Nodes Head and Neck

AXIAL CECT

External carotid a. Internal carotid a. Jugulodigastric node (level II)

Jugulodigastric node (level II)

Internal jugular v. Sternocleidomastoid m.

Spinal accessory node (level VA)

Submandibular node (level IB)

Submandibular node (level IB) Submandibular gland

High internal jugular nodes (level II) Internal jugular v. Parotid nodes (tail area) Sternocleidomastoid m.

Spinal accessory nodes (level VA)

Submental node (level IA) Anterior belly digastric m.

Submandibular node (level IB) Submandibular gland

Sternocleidomastoid m. High internal jugular nodes (level IIA) High internal jugular node (level IIB)

Spinal accessory node (level VA)

(Top) First of 3 axial CECT images of the suprahyoid neck, presented from superior to inferior, demonstrates lymph nodes in the internal jugular (level II) and spinal accessory chains (level V). The jugulodigastric node is the highest or "sentinel" node of the internal jugular chain. (Middle) In this image, the internal jugular & spinal accessory lymph nodes are seen along with submandibular nodes (level IB) anterolateral to the submandibular glands in the submandibular space. Note that the internal jugular nodes are immediately adjacent to the carotid space, whereas the spinal accessory nodes are in the posterior cervical space. (Bottom) In this image just above the hyoid bone, a submental (level IA) node is seen between the anterior bellies of the digastric muscles. Note also the submandibular (level IB), high internal jugular (level IIA & IIB), & spinal accessory (level VA) nodes.

201

Head and Neck

Cervical Lymph Nodes TRANSVERSE AND LONGITUDINAL US AND PATHOLOGY Subcutaneous tissue Platysma m. Sternocleidomastoid m.

Internal jugular v.

Normal jugular lymph node with echogenic hilum Gas in supraglottic larynx

Common carotid a.

Subcutaneous tissue Platysma m. Sternocleidomastoid m.

Lymph node Echogenic hilum of normal lymph node Common carotid a.

Cortical hypertrophy

Internal jugular v.

Preserved echogenic hilum

Common carotid a.

(Top) Transverse grayscale ultrasound of the midcervical level shows the normal appearance of a cervical lymph node (i.e., ovoid shape with echogenic hilum). It is commonly found anterior to the carotid artery/internal jugular vein. (Middle) Longitudinal grayscale ultrasound of the midcervical level shows a normal elliptical hypoechoic lymph node with echogenic hilum anterior to the common carotid artery. (Bottom) Transverse grayscale ultrasound shows a hypoechoic node with cortical hypertrophy and echogenic hilum along the deep cervical/jugular chain. This is the classic appearance of a reactive node. Note its relation to internal jugular vein & common carotid artery. This is a common site of reactive nodes, which are often bilateral & symmetric.

202

Cervical Lymph Nodes

Subcutaneous tissue Platysma m.

Head and Neck

POWER DOPPLER US AND PATHOLOGY

Sternocleidomastoid m.

Normal cervical lymph node

Hilar vascularity within normal lymph node

Internal jugular v. Common carotid a.

Subcutaneous tissue Platysma m. Sternocleidomastoid m.

Hilar vascularity within normal lymph node

Lymph node

Common carotid a.

Sternocleidomastoid m.

Internal jugular v. Hilar vascularity Common carotid a.

(Top) Transverse power Doppler ultrasound shows the presence of hilar vascularity within the echogenic hilum of a normal cervical lymph node. (Middle) Longitudinal power Doppler ultrasound shows hilar vascularity within the echogenic hilum of a normal cervical lymph node. The presence of echogenic hilum and hilar vascularity are good signs of cervical lymph node benignity. (Bottom) Power Doppler ultrasound of a reactive node clearly defines radiating hilar vascularity and relation to IJV and CCA.

203

Head and Neck

Cervical Lymph Nodes PATHOLOGY

Sternocleidomastoid m.

Intranodal cystic necrosis Metastatic lymph nodes

Sternocleidomastoid m.

Lymphomatous lymph node Internal jugular v.

Common carotid a.

Matted tuberculous lymph nodes

Intranodal necrosis

(Top) Transverse grayscale ultrasound of the upper neck shows multiple enlarged, round, predominantly solid, hypoechoic lymph nodes. Patient has known history of H&N cancer. Overall features are consistent with metastatic nodes. Presence of intranodal cystic necrosis in a patient with known primary malignancy is indicative of the metastatic nature of lymph nodes. (Middle) Transverse grayscale ultrasound of a lymphomatous lymph node in mid deep jugular chain demonstrates the typical reticulated echo pattern. (Bottom) Transverse grayscale ultrasound shows multiple matted, enlarged, heterogeneous, hypoechoic lymph nodes in the posterior triangle. Some of them demonstrate intranodal necrosis. A mild degree of edema is noted in the adjacent soft tissue. Features are compatible with tuberculous lymphadenitis.

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Cervical Lymph Nodes Head and Neck

PATHOLOGY

Subcapsular/peripheral nodal vascularity Metastatic lymph nodes

Chaotic peripheral and central intranodal vessels

Displaced hilar vascularity

Lymphomatous lymph nodes

Intranodal necrosis

(Top) Transverse power Doppler ultrasound shows multiple subcapsular/peripheral intranodal vessels in multiple round, hypoechoic, solid lymph nodes at the upper cervical level. Pathology confirmed metastatic squamous cell carcinoma. (Middle) Longitudinal power Doppler ultrasound of multiple lymphomatous lymph nodes shows chaotic peripheral and central intranodal vessels. Note that hilar vascularity is more prominent than peripheral vascularity. (Bottom) Transverse power Doppler ultrasound shows a tuberculous lymph node in posterior triangle that is predominantly hypovascular with displaced hilar vascularity. The hypovascular portion corresponds to intranodal caseating necrosis.

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SECTION 3

Thorax

Thoracic Outlet Pleura Diaphragm Chest Wall Breast

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Thorax

Thoracic Outlet

TERMINOLOGY Synonyms • Terminology is confusing as anatomic and clinical definitions vary • Thoracic outlet is clinical term for junction of head and neck • Anatomically this area is actually referred to as thoracic inlet, with thoracic outlet being opening into abdominal cavity • Superior thoracic aperture also synonym but technically is only bony borders

Definitions • Transition area between cervical/brachial spaces and thoracic cavity • Opening at superior end of rib cage bordered by bony ring ○ Posteriorly: T1 vertebral body ○ Laterally: Right and left 1st ribs and their costal cartilages ○ Anteriorly: Superior border of manubrium

IMAGING ANATOMY Overview • Contents passing through outlet include ○ Trachea ○ Esophagus ○ Great vessels for head and neck and arms ○ Nerves • Thoracic outlet is clinically divided into 3 compartments ○ From medial to lateral: Interscalene triangle, costoclavicular space, retropectoralis minor space

Interscalene Triangle • Boundaries ○ Anterior scalene (anteriorly) ○ Middle and posterior scalene (posteriorly) ○ 1st rib (inferiorly) • Contents ○ Subclavian artery (inferiorly) ○ 3 trunks of brachial plexus (upper and middle trunks in superior part of triangle, inferior trunk behind subclavian artery) • Subclavian vein is anterior to anterior scalene muscle and is thus not within interscalene triangle

Costoclavicular Space • Boundaries ○ Clavicle (superiorly) ○ Subclavius muscle (anterior) ○ 1st rib and middle scalene muscle (posterior) • Contents ○ Subclavian artery and vein ○ 1st part of axillary vein – Axillary artery begins at lateral border of 1st rib as direct continuation of subclavian artery – Axillary artery ends laterally at inferior border of teres major muscle – Posterior to axillary vein ○ 1st part of axillary vein – Anterior to axillary artery 208

○ 2 divisions and 2 cords of brachial plexus form within this space – Posterior cord of brachial plexus is formed by posterior division of upper, middle, and lower trunks – Lateral cord is formed by anterior division of upper and middle trunks – Medial cord is formed by anterior division of lower trunk

Retropectoralis Minor Space • Boundaries ○ Posterior border of pectoralis minor muscle (anteriorly) ○ Subscapularis muscle (posterosuperiorly) ○ Anterior chest wall (posteroinferiorly) • Contents ○ 2nd part of axillary vein and artery ○ 3 cords of brachial plexus: Posterior, lateral, and medial – Names of 3 cords of brachial plexus indicate their relationship with 2nd part of axillary artery – Lateral to pectoralis major muscle, cords divide into 5 terminal branches

Clinical Significance • Thoracic outlet syndrome ○ Compression syndrome of neurovascular structure(s) – Causes arm pain when arm is adducted ○ Typically cervical rib or elongated C7 transverse process present ○ Neurological compression is common in both costoclavicular space and interscalene triangle ○ Arterial compression is most common in costoclavicular space followed by interscalene triangle – Causes narrowing with poststenotic aneurysm ○ Venous compression may cause subclavian vein thrombosis

ANATOMY IMAGING ISSUES Imaging Recommendations • Ultrasound provides distinct advantages in evaluation ○ Allows simultaneous, real-time grayscale (anatomical) and color Doppler (functional) evaluation of vessels to assess compression and flow restriction ○ Can be performed with dynamic maneuvers, which exacerbates thoracic outlet syndrome clinically, allowing simultaneous imaging assessment ○ Allows patients to be scanned in upright position, which frequently exacerbates compression (CT and MR requires patients to be scanned supine)

Imaging Pitfalls • Ultrasound cannot evaluate lungs • Shadowing from lung apices, ribs, and clavicle may make complete evaluation difficult • 8th cervical and 1st thoracic nerve roots are not adequately visualized, especially in patients with short necks

Thoracic Outlet

Apex of axilla, posterior boundary

Thoracic outlet, lateral border

Apex of axilla, medial boundary

Thorax

GRAPHICS, THORACIC OUTLET

T1 vertebral body (thoracic outlet, posterior border) Thoracic outlet, lateral border

Brachial plexus Subclavian a. and v. Axillary a. and v.

Apex of axilla, anterior boundary

Manubrium of sternum (thoracic outlet, anterior border) Body of sternum

Costochondral junction Xiphoid process of sternum

Trachea Left internal jugular v.

Esophagus

1st rib

Manubrium

Left subclavian v.

Left subclavian a.

Aortic arch

(Top) Graphic depicts the thoracic outlet that is bounded by the T1 vertebral body, right and left 1st ribs and their costal cartilages, and the manubrium of sternum. Vascular structures allow blood flow to enter and exit the thorax through this ring. The apex of the adjacent axillary region is also shown, which is bounded by the clavicle, scapula, and outer border of the 1st rib. (Bottom) Lateral graphic of the thoracic outlet shows the subclavian artery and vein as they pass out of the thorax over the 1st rib. At the lateral margin of the 1st rib, they are renamed the axillary artery and vein, and continue as the vascular supply to the arm. The trachea and esophagus are 2 important structures that pass through the thoracic outlet.

209

Thorax

Thoracic Outlet SUPERIOR THORACIC APERTURE

Fat in sternal notch Sternocleidomastoid m.

Sternohyoid m. Sternothyroid m.

Right common carotid a. Left common carotid a. Cartilaginous tracheal ring Lumen of trachea obscured by air

Sternal end of right clavicle

Sternal end of left clavicle Right sternocleidomastoid m.

Fat in sternal notch

Sternohyoid and sternothyroid mm. Trachea

Sternohyoid m.

Sternocleidomastoid m. Anterior scalene m. Common carotid a. Sternothyroid m.

Internal jugular v.

Subclavian a. Apical pleural/lung interface

(Top) Transverse scan of superior thoracic aperture at the sternal notch is shown. The trachea is located in the center of the image, where its cartilaginous ring is well-visualized, but the lumen is obscured by gas. Strap muscles of the neck, which are anterior to the trachea, are well-delineated. (Middle) Transverse scan at sternal notch level with caudal tilting of transducer to better demonstrate the thoracic outlet is shown. The strap muscles appear thinner using this scanning plane. A retrosternal extension of goiter can be demonstrated in this view of the superior thoracic aperture. (Bottom) Transverse scan of left supraclavicular fossa is shown. The lung apex is located deep to the vessels and immediately behind the subclavian vein. This view is good for searching for supraclavicular lymphadenopathy.

210

Thoracic Outlet Thorax

SUPERIOR THORACIC APERTURE

Sternocleidomastoid m. Sternohyoid and sternothyroid mm.

Internal thoracic a.

Brachiocephalic a. Internal jugular v.

Apical pleural/lung interface

Insertion of sternal head of sternocleidomastoid m.

Sternal head of sternocleidomastoid m.

Sternal notch

Sternohyoid and sternothyroid mm. Common carotid a.

Anterior jugular v.

Brachiocephalic a.

Coupling gel filling supraclavicular fossa

Sternocleidomastoid m. Vertebral a.

Subclavian a.

Anterior cortex of clavicle

Internal jugular v.

Apical pleural/lung interface

(Top) Transverse scan of left supraclavicular fossa with caudal tilting of the transducer is shown. The apical pleural/lung interface is visualized immediately behind the brachiocephalic artery, internal jugular vein, and internal thoracic artery. (Middle) Longitudinal scan of superior thoracic aperture at the sternal notch is shown. Insertion of sternocleidomastoid at the sternal notch appears echogenic and tapered compared to the muscle belly. The anterior jugular vein crosses anterior to strap muscles and common carotid artery. (Bottom) Longitudinal scan of supraclavicular fossa along the internal jugular vein is shown. The supraclavicular fossa is filled with coupling gel to provide good transducer contact. The apical pleural/lung interface is visualized immediately behind internal jugular vein and subclavian artery.

211

Thorax

Thoracic Outlet INTERSCALENE TRIANGLE Sternocleidomastoid m.

Middle and posterior scalene mm. 5th cervical nerve root

Anterior scalene m.

6th cervical nerve root 7th cervical nerve root

Omohyoid m.

Brachial plexus elements

Middle and posterior scalene mm.

Anterior scalene m.

Subclavian a.

Apical pleural/lung interface

Sternocleidomastoid m.

Anterior scalene m.

Exiting 5th cervical nerve root Transverse process of 5th cervical vertebra

Exiting 6th cervical nerve root Exiting 7th cervical nerve root

Transverse process of 6th cervical vertebra Transverse process of 7th cervical vertebra

(Top) Oblique coronal scan of upper interscalene triangle is shown. The 5th, 6th, and 7th cervical nerve roots are well-demonstrated in cross section, lying between anterior and middle scalene muscles. The 8th cervical and 1st thoracic nerve roots are usually more difficult to visualize on ultrasound because of their deeper location behind subclavian artery. (Middle) An oblique coronal scan of lower interscalene triangle shows the brachial plexus elements. They appear as a cluster of well-delineated, round, hypoechoic structures that result from the divisions of the nerve trunks. The subclavian artery is seen posterior and medial to the brachial plexus. (Bottom) This oblique coronal scan of interscalene triangle is focused on the nerve roots. The extraforaminal parts of the 5th, 6th, and 7th cervical nerve roots are well-visualized as they exit from the intervertebral foramina in the downward and outward direction.

212

Thoracic Outlet Thorax

COSTOCLAVICULAR SPACE

Acoustic shadow caused by clavicle Subclavius m. Pectoralis major m. Brachial plexus Subclavian a.

Posterior scalene m.

Pectoralis minor m.

Subclavian v.

Clavicle and its posterior acoustic shadow

Trapezius m. Brachial plexus

Subclavian a.

Pectoralis major m.

Subclavius m. Medial end of clavicle and its posterior acoustic shadow Subclavian v.

Subclavian a.

(Top) Sagittal scan of costoclavicular space is shown using an infraclavicular approach. This space is limited superiorly by the clavicle and anteriorly by the subclavius muscle and contains the subclavian vein anteriorly, the subclavian artery immediately posterior to it, and 3 cords of brachial plexus. (Middle) Sagittal scan of costoclavicular space from the supraclavicular approach shows the brachial plexus and subclavian artery. The subclavian vein is obscured by the shadowing posterior to the clavicle. (Bottom) The costoclavicular space is shown in a transverse plane. The long axis of subclavian artery and vein are visualized in this view, but the brachial plexus is difficult to visualize because of its proximity to the clavicle.

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Thorax

Thoracic Outlet RETROPECTORALIS MINOR SPACE

Pectoralis major m. Pectoral branch of thoracoacromial a. Thoracoacromial a. Pectoralis minor m. Brachial plexus elements Axillary v. Axillary a.

Pectoralis major m. Coracobrachialis m. Brachial plexus elements

Pectoralis minor m.

Axillary a. Axillary v.

Pectoralis major m. Pectoralis minor m.

Axillary a. Brachial plexus elements

(Top) A sagittal scan of retropectoralis minor space is shown. This space is bound anteriorly by the pectoralis minor muscle and posteriorly by the anterior chest wall. The axillary artery and vein are well-depicted, and the cords of brachial plexus are visualized above and posterior to the axillary artery. (Middle) Just lateral to the retropectoralis minor space the brachial plexus and axillary artery and vein are moving away from the pectoralis minor muscle, but with a similar configuration as seen in the retropectoralis minor space. (Bottom) A transverse scan of the retropectoralis minor space shows the brachial plexus running parallel to, above, and posterior to the axillary artery. On a longitudinal scan, the axillary vein cannot be visualized together with the axillary artery and brachial plexus in the same image because of their triangular configuration.

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Thoracic Outlet Thorax

DYNAMIC INTERROGATION

Clavicle & its posterior acoustic shadow

Brachial plexus elements Anterior scalene m. Subclavian a.

Clavicle and its posterior acoustic shadow Anterior scalene m. Subclavian a.

Subclavian v. Apical pleural/lung interface

Brachial plexus elements

Pectoralis major m. Clavicle & its posterior acoustic shadow

Subclavius m.

Pectoralis major m. Subclavian v.

Brachial plexus elements Subclavian a.

Subclavius m. Subclavian a. Brachial plexus elements

Subclavian v. Clavicle and its posterior acoustic shadow

Pectoralis major m. Pectoralis minor m.

Pectoralis minor m. Pectoralis major m.

Brachial plexus elements Axillary a. Axillary v.

Axillary v. Axillary a. Brachial plexus elements

(Top) Dual sagittal image of lower interscalene triangle with the arm in neutral position (left image) and 180 degree abduction (right image) is shown. The space in the interscalene triangle decreases with the arm abducted. The brachial plexus and subclavian arterial caliber show no significant change. (Middle) Dual sagittal image of costoclavicular space (from infraclavicular approach) with the arm in a neutral position (left image) and the arm at 180 degrees (right image) is shown. The subclavian vein appears to be compressed by ~ 50%, which is due to the compressive effect of arm abduction in costoclavicular space. (Bottom) Dual sagittal image of retropectoralis minor space with arm in neutral position (left image) and 180 degree abduction (right image) is shown. The axillary artery and brachial plexus show no significant change. The axillary vein is more distended with arm abducted.

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Thorax

Thoracic Outlet SPECTRAL DOPPLER INTERROGATION

Clavicle

Subclavian a. in costoclavicular space

Subclavian v.

Triphasic waveform with peak systolic velocity 92 cm/sec

Clavicle Subclavian a. in costoclavicular space

Subclavian v.

Biphasic waveform with peak systolic velocity 70 cm/sec

Clavicle

Subclavian a. in costoclavicular space

Subclavian v.

Biphasic waveform with peak velocity increased to 350 cm/sec

(Top) Doppler spectrum of the subclavian artery in costoclavicular space is shown with the arm in a neutral position. A normal triphasic waveform is recorded with peak systolic velocity 92 cm/sec. (Middle) Doppler spectrum of subclavian artery in costoclavicular space is shown with the arm in 90 degrees abduction (same subject as previous image). The waveform changes from triphasic to biphasic, with no significant change in peak systolic velocity. (Bottom) Doppler spectrum of subclavian artery is shown with the arm in 180 degrees abduction (same subject as previous image). Biphasic waveform is still present, with the peak systolic velocity markedly increased to 350 cm/sec. Features are indicative of arterial compression in costoclavicular space. The costoclavicular space is the most frequent site of arterial compression.

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Thoracic Outlet Thorax

SPECTRAL DOPPLER INTERROGATION

Subclavian v. in costoclavicular space Clavicle Subclavius m.

Venous waveform with phasic changes and velocity 15 cm/sec

Subclavian v. in costoclavicular space Clavicle Subclavius m.

Venous waveform with phasic changes and velocity 30 cm/sec

Subclavian v. in costoclavicular space Clavicle Subclavius m.

Venous waveform with phasic changes and velocity 40 cm/sec

(Top) Doppler spectrum of the subclavian vein in costoclavicular space is shown with the arm in a neutral position. Normal venous waveform with phasic changes are recorded. (Middle) Doppler spectrum of the subclavian vein in costoclavicular space is shown with the arm in 90 degrees abduction (same subject as previous image). Normal venous waveform with phasic changes is again recorded. The velocity increases from 15-30 cm/sec. (Bottom) Doppler spectrum of subclavian waveform in costoclavicular space is shown with arm 180 degrees abduction (same patient as previous image). The velocity increases to 40 cm/sec while normal venous waveform with phasicity is preserved. This indicates a mild compressive effect of arm abduction on subclavian vein.

217

Thorax

Pleura

GROSS ANATOMY Overview

Ultrasound Technique

• Pleura: Continuous surface epithelium and underlying connective tissue • Visceral pleura adheres to pulmonary surfaces • Parietal pleura is continuation of visceral pleura ○ Lines corresponding 1/2 of thoracic wall ○ Covers ipsilateral diaphragm and ipsilateral mediastinal surface • Visceral and parietal pleurae form right and left pleural cavities ○ Potential spaces containing small amount of serous pleural fluid • Combined thickness of visceral and parietal pleurae and fluid-containing pleural space is < 0.5 mm • Visceral pleura directly apposes and slides freely over parietal pleura during respiration

• Provides detailed imaging of costal surfaces of pleura ○ Use high-frequency linear transducer • Ribs cause posterior acoustic shadowing ○ Scanning in both inspiration and expiration helps examine pleura, which may have been obscured by ribs

Pleural Space • Potential space; normally contains 2-10 mL of fluid • Fluid production capacity: 100 mL/h; fluid absorption capacity: 300 mL/h • Fluid flux normally from parietal pleura capillaries to pleural space; absorbed by microscopic stomata in parietal pleura

Costodiaphragmatic Recesses • Pleura extends caudally beyond inferior lung border • Costal and diaphragmatic pleura separated by narrow slit, costodiaphragmatic recess • Extends ~ 5 cm below inferior border of lung during quiet inspiration • Caudal extent at 12th rib posterolaterally

Visceral Pleura • Covers lung parenchyma surfaces • Blood supply and drainage ○ Supply by systemic bronchial vessels, drainage by pulmonary and bronchial veins ○ Lymphatic drainage to deep pulmonary plexus within interlobar and peribronchial spaces toward hilum • Histology ○ Mesothelial layer, thin connective tissue layer, chief layer of connective tissue, vascular layer, limiting lung membrane (connected to chief layer by collagen and elastic fibers) ○ Single layer of flat mesothelial cells separated by basal lamina from underlying lamina propria of loose connective tissue

Parietal Pleura • Covers nonparenchymal surfaces • Forms lining of thoracic cavities • Blood supply and drainage ○ Supply from adjacent chest wall (intercostal, internal mammary, diaphragmatic arteries) ○ Drainage to bronchial veins (diaphragmatic pleural drainage to inferior vena cava and brachiocephalic trunk) • Histology ○ Single layer of parietal mesothelial cells over loose, fatcontaining areolar connective tissue; bounded externally by endothoracic fascia 218

ANATOMY-BASED IMAGING ISSUES

Clinical Uses • Differentiation of solid pleural masses from fluid • Assessment of echogenicity and morphology of fluid collections • Guide pleural drainage or biopsy

CLINICAL IMPLICATIONS Pleural Effusion • Categorized as transudate- or exudate-based on composition of fluid obtained by thoracentesis ○ Transudate not associated with pleural disease – Systemic abnormalities (cardiac failure, pericardial disease, cirrhosis, pregnancy, hypoalbuminemia, overhydration, renal failure) ○ Exudate indicates presence of pleural disease – Pneumonia, empyema, tuberculosis, neoplasm, pulmonary embolism, collagen vascular disease ○ Split pleura sign: Thickened visceral and parietal pleura encasing abnormal fluid collection – Concerning for empyema in febrile patient – May also occur in noninfected collections, malignant effusion, and hemothorax • Ultrasound ○ Anechoic effusions may be either transudative or exudative ○ Septations suggestive of exudative effusion – Often loculated

Pleural Thickening • Focal thickening ○ Asbestos exposure – Pleural plaques occur 15-20 years after exposure – Focal collections of acellular collagen on parietal pleura (costal, diaphragmatic, and mediastinal pleura) □ Discontinuous areas of pleural thickening, predominantly along 6th-8th ribs and on parietal pleura at domes of diaphragms – May be noncalcified or calcified – There is usually sparing apices and costophrenic sulci ○ Localized fibrous tumor – Solitary lenticular, round, or lobulated neoplasm – Benign (80%) or malignant ○ Bronchogenic carcinoma may focally invade pleura or produce diffuse pleural thickening • Diffuse thickening ○ May be benign (fibrothorax) or malignant (metastases, mesothelioma, lymphoma, invasive thymoma)

Pleura

Ribs

Thorax

PLEURAL SPACES

Airways

Thoracic great vessels Lung Heart

Chest wall m. Chest wall subcutaneous tissue Pleura

Caudal extent of lung

Caudal extent of pleura

Caudal extent of lung

Caudal extent of pleura

(Top) Graphic shows the complex and diverse structures and organs of the thorax, including the primary organs of respiration, thoracic cardiovascular system, and proximal gastrointestinal tract. (Bottom) Graphic shows the anatomy of the pleura with all the other structures removed. The apposed pleural surfaces create a potential space that normally contains a small amount of fluid, which lubricates the pleural surfaces and reduces friction during respiratory motion. The visceral pleura covers the pulmonary surfaces. The parietal pleura covers the nonpulmonary surfaces within the thoracic cavity and extends more caudally than the lungs. The inferior reflection of parietal pleura extends within the costophrenic sulci to the level of the upper kidneys.

219

Thorax

Pleura PLEURAL SPACES

Parietal pleura (green)

Visceral pleura (yellow)

Parietal pleura

Visceral pleura

Incomplete minor fissure Costal pleura

Right major fissure Left major fissure

Caudal extent of lung Costodiaphragmatic recess

Caudal extent of lung

Costodiaphragmatic recess Pleural reflection

Pleural reflection

Diaphragmatic pleura Diaphragmatic pleura

Graphic shows the extent and distribution of the pleura as visualized in the coronal plane. Visceral pleura (yellow) covers the surfaces of both lungs and forms interlobar fissures that may be complete or incomplete in their extension to the hila. Parietal pleura (green) lines both thoracic cavities and may be designated by its location as costal, diaphragmatic, or mediastinal pleurae. Inferiorly, the parietal pleura extends deeply into the costodiaphragmatic recesses where costal and diaphragmatic pleura are in apposition.

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Pleura Thorax

GRAPHIC, PLEURAL SPACES

Parietal pleura

Visceral pleura

Costal pleura

Left major fissure

Anterior costodiaphragmatic recess

Caudal extent of lung

Anterior pleural reflection

Posterior costodiaphragmatic recess Posterior pleural reflection

Diaphragmatic pleura

Graphic shows the extent of parietal (green) and visceral (yellow) pleura as visualized in the sagittal plane in the left midclavicular zone. Notice the depth of the pleural reflections. When evaluating for a pleural effusion by ultrasound, it is best to have the patient in the upright position and scan along the posterior costodiaphragmatic recess.

221

Thorax

Pleura PLEURA, INTERCOSTAL WINDOW

Pectoralis major m. External oblique m.

Subcutaneous fat 4th rib cortex Posterior acoustic shadowing Intercostal space 5th costal cartilage

7th costal cartilage 6th costal cartilage Intercostal mm. Anterior intercostal vessels Reflective surface of visceral pleura/lung interface

Subcutaneous fat

External oblique m. 3rd rib anterior cortex 3rd rib inferior edge Posterior acoustic shadowing

4th rib superior edge Pectoralis major m.

Anterior intercostal vessels Intercostal mm.

Transversus thoracis m.

Reflective surface visceral pleura/lung interface

Subcutaneous fat

Pectoralis major m.

Sternum Internal thoracic v.

Pectoralis minor m.

Internal thoracic a.

Internal intercostal m.

Internal intercostal m. Reflective surface of visceral pleura/lung interface

(Top) Panoramic sagittal scan of the lower anterior chest wall and pleura is shown. The cortex of the ribs produces significant posterior acoustic shadowing, which obscures the underlying pleura; this is less of an issue with costal cartilage (which is relatively sonolucent). By scanning during respiration (and thus pleural movement), all of the pleura can be evaluated with ultrasound. (Middle) Sagittal scan of the anterior pleura is shown. The intercostal muscles run in between the edges of the ribs. The innermost intercostal muscle is separated from the external and internal intercostal muscles by the intercostal vessels and nerve. (Bottom) Oblique transverse scan of the anterior pleura just lateral to the sternum using an intercostal window is shown. Uninterrupted strips of pleura can be demonstrated by placing the transducer obliquely along the intercostal space.

222

Pleura Thorax

PLEURA

Subcutaneous fat

Anterior scalene m.

Subclavian a.

Sternocleidomastoid m. Internal jugular v.

Pleura/lung interface at apex

Brachiocephalic trunk Subclavian v. Internal thoracic a.

Empyema

Liver

Thickened pleura

"Split pleura" encloses fluid collection

Thick and enhancing visceral pleura

Thick and enhancing parietal pleura

(Top) Oblique transverse scan of the apical pleura is shown. The apical pleura is adjacent to important cervical structures. Pathology in the lung apex, such as a Pancoast tumor, can therefore extend readily into the neck. (Middle) Longitudinal ultrasound of the right hemithorax in a patient with pneumonia, persistent fevers, and elevated white count shows a loculated, complex fluid collection. Note the thickened surrounding pleura. Aspiration, using ultrasound guidance, was performed confirming an empyema. (Bottom) Axial CECT (soft tissue window) of a patient with empyema demonstrates the split pleura sign associated with a loculated fluid collection in the posterolateral aspect of the right inferior pleural space. Enhancing, smoothly thickened pleurae "split" to enclose the abnormal fluid collection.

223

Thorax

Diaphragm

IMAGING ANATOMY Overview • Sheet of skeletal muscle that merges centrally to form central aponeurotic tendon • Separates thoracic cavity from abdominal cavity • Descends to increase thoracic volume and decrease intrathoracic pressure ○ Chief muscle of respiration

Muscular Components • Costal/rib contribution ○ Muscle fibers from internal surface of ribs 7-12 ○ Forms left and right hemidiaphragms • Lumbar contribution ○ Originates as diaphragmatic crura and from 3 arcuate ligaments • Sternal contribution ○ Slips of muscle from xiphoid process running posteriorly to insert on central tendon ○ Sternocostal hiatus on each side of these central slips of muscle – Internal thoracic vessels run through hiatus to enter abdomen

Central Tendon • Aponeurosis with interlacing fibers • Peripheral muscular component inserts centrally onto this aponeurosis • Trefoil appearance due to 3 parts ○ Heart rests upon central leaf – Right side of central leaf contains foramen for inferior vena cava ○ Left and right leaves represent domes of hemidiaphragms

Diaphragmatic Crura • Left crus ○ Narrower and shorter than right crus ○ Attached to left side of aorta, left anterolateral surfaces of L1 and L2 vertebral bodies and discs • Right crus ○ Broader and longer than left crus ○ Attached to right side of aorta, right anterolateral surfaces of L1-L3 vertebral bodies and discs ○ Surrounds esophageal hiatus

Arcuate Ligaments • Median arcuate ligament ○ Joins medial aspects of both crura ○ Runs in arch over anterior surface of aorta ○ Contributes fibers to right diaphragmatic crus • Medial arcuate ligament ○ Fibrous thickening of thoracolumbar fascia over proximal aspect of psoas major muscle • Lateral arcuate ligament ○ Fibrous thickening of thoracolumbar fascia over quadratus lumborum muscle ○ Runs in arch from L1 transverse process to ipsilateral 12th rib

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Diaphragmatic Hiatus • Vena caval foramen ○ Located in right posterior margin of central leaf of central tendon ○ At T8/9 intervertebral disc level ○ Inferior vena cava wall adheres to this foramen – Diaphragmatic movement on inspiration dilates inferior vena cava lumen and helps increase flow of blood to right atrium • Esophageal hiatus ○ Located in posterocentral (left of midline) aspect of muscular component of diaphragm ○ At T10 vertebral level ○ Encircled by right crus fibers, which constricts esophagus on inspiration and thus prevents reflux ○ Contains left gastric artery branches, anterior and posterior vagal trunks, and esophagus • Aortic hiatus ○ Located behind median arcuate ligament (thus outside diaphragm) and thus not constricted by respiration ○ At T12 vertebral level ○ Contains aorta, azygos vein, and thoracic duct

Phrenic Nerve (C3-C5 Ventral Rami) • Right phrenic nerve ○ Runs posterolateral to right brachiocephalic vein and superior vena cava ○ Continues between mediastinal pleura and right parietal pericardium, anterior to right lung hilum ○ Finally runs on right side of inferior vena cava to enter right hemidiaphragm lateral to vena caval foramen • Left phrenic nerve ○ Runs between left common carotid artery and left subclavian artery ○ Passes on left side of aortic arch ○ Runs on left parietal pericardium (over left auricle and left ventricle) ○ Enters left hemidiaphragm lateral to left pericardial margin

ANATOMY IMAGING ISSUES Imaging Recommendations • Sonographic imaging of diaphragm is best done using abdominal contents (liver, spleen) as window ○ Gas in lungs precludes using thoracic approach to examine diaphragm (except when there is sizable pleural effusion displacing intervening lung) • US allows real-time evaluation of diaphragmatic movement ○ M-mode can track diaphragmatic excursion ○ Essential for investigating neurological or muscular diaphragmatic abnormalities

Imaging Pitfalls • Diaphragmatic insertions on thoracoabdominal wall may appear as slips of muscle and tendon rather than sheet ○ Can be mistaken for peritoneal nodules

Diaphragm Thorax

DIAPHRAGM

Costomediastinal recess Rib Intercostal mm.

Pericardial sac (on central leaf) Inferior vena cava Esophagus

Sternal part of muscular component Costal part of muscular component Right leaf of central t.

Left leaf of central t. Abdominal aorta

Spine

Lumbar part of muscular component Diaphragmatic pleura

Azygos v. Costal pleura

Xiphoid process (of sternum) Central t. Costal cartilage Inferior vena cava foramen Esophageal hiatus

Right crus of diaphragm

Median arcuate l. Left crus crus of diaphragm Right crus Medial arcuate l. Lateral arcuate l. Quadratus lumborum m. Psoas m.

(Top) Graphic of the diaphragm looking from above is shown. The diaphragm is composed of a central tendon and a peripheral muscular component. The central tendon is made up of 3 leaves: Central leaf (on which rests the pericardium) and left and right leaves form the dome of each hemidiaphragm. (Bottom) Graphic shows the abdominal surface of the diaphragm looking from below. Note the origins of the diaphragm from the sternum, costal cartilages, and lumbar vertebrae and insertion into the trefoil-shaped central tendon, the fibrous aponeurosis of the diaphragmatic muscle fibers. The inferior vena cava hiatus is through the central tendon. The esophageal hiatus is surrounded by the right crus. The median arcuate ligament unites the crura and passes over the aorta just above the celiac axis. The right crus is longer and thicker than the left, and both insert into the anterior longitudinal ligament of the lumbar spine. The psoas passes behind the medial arcuate ligament, and the quadratus lumborum passes behind the lateral arcuate ligament.

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Thorax

Diaphragm DIAPHRAGM

Gallbladder Vena caval foramen

Right lobe of liver

Right leaf of central t. of diaphragm Hepatic v. Costal part of muscular component of diaphragm

Spleen superolateral surface Left pleural effusion Left hemidiaphragm, thoracic surface

Spleen medial surface

Collapsed left lower lobe basal segments

Gallbladder Right lobe of liver

Inferior vena cava Portal v.

Costal part of muscular component of diaphragm

(Top) Oblique sagittal scan of the upper abdomen using a subcostal window is shown. The dome of the diaphragm is well demonstrated with US due to its strong reflection (a result of the gas-containing lung on the other side of the diaphragm). The vena caval foramen is at the right posterior edge of the middle leaf of the central tendon of diaphragm. (Middle) Oblique coronal scan using a left lower intercostal window in a patient with left pleural effusion is shown. The thoracic surface of the diaphragm is outlined by the pleural effusion. Without the effusion, this diaphragmatic surface is difficult to visualize. (Bottom) Oblique transverse scan of the upper abdomen is shown. The costal part of the muscular portion of the diaphragm arises from the internal surface of the inferior 6 ribs. The contraction of this muscular component causes depression of the diaphragm on inspiration.

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Diaphragm Thorax

DIAPHRAGMATIC MOVEMENT Left lobe of liver Portal v. Right lobe of liver Median arcuate l. Inferior vena cava

Stomach with food content Gastric pylorus

Right diaphragmatic crus Cortex of T12 vertebral body

Left diaphragmatic crus

Abdominal aorta Spleen

Slip of lung in right costophrenic recess

Right costophrenic angle Right lobe of liver Ring down artifact Posterior aspect of right hemidiaphragm Posterior aspect of right hemidiaphragm Inferior vena cava

Thoracic cavity Right hemidiaphragm Intersection between cursor line and diaphragm

Liver Cursor line Portal v. appearing intermittently on trace

Position of diaphragm at full inspiration

Position of diaphragm at full expiration

(Top) Transverse scan at the T12 vertebral body level is shown. The aorta emerges under the median arcuate ligament to enter the abdomen. Thus, the aorta is outside the diaphragm and therefore not constricted by it during inspiration. The diaphragmatic crura lie on both sides of the aorta, taking origin from the cortical surface of the lumbar vertebrae. The crura are hypoechoic and should not be mistaken for lymph nodes. (Middle) Oblique transverse scans of the right hemidiaphragm using the same intercostal window during full expiration (left image) and full inspiration (right image) are shown. With inspiration, a slip of lung may enter the costophrenic recess and cause posterior acoustic shadowing (gas ring down). (Bottom) Diaphragmatic tracing obtained in M-mode is shown. The cursor line was placed to cut through the liver and right hemidiaphragm. The respiratory motion of the diaphragm (bright line) can thus be traced.

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Thorax

Chest Wall

GENERAL ANATOMY AND FUNCTION Chest Wall Anatomy • • • • •

Skin, subcutaneous fat Blood vessels, lymphatics, nerves Bone, cartilage Muscles Endothoracic fascia, fibroelastic connective tissue between inner aspect of chest wall and costal pleura

Function • Musculoskeletal cage: Surrounds cardiorespiratory system ○ Effects respiration by expanding and contracting during ventilation

Surface Landmarks • Suprasternal (jugular) notch: At superior manubrium of sternum ○ Between sternal ends of clavicles • Sternal angle: Landmark for internal thoracic anatomy ○ Anterior projection at level of costal cartilage of 2nd rib • Costal margin: Inferior margins of lowest ribs and costal cartilages

SKELETAL STRUCTURES Sternum • Flat, broad bone forms anterior thoracic wall composed of 3 parts (manubrium, body, xiphoid process) • Manubrium forms superior part of sternum • Body articulates with manubrium superiorly, xiphoid process inferiorly, bilateral costal cartilages of 2nd-7th ribs • Xiphoid process variable size, shape, ossification; articulates with body of sternum superiorly

Ribs • 12 pairs, symmetrically arrayed; numbered in accordance with attached vertebral body • True ribs (1-7) attach to sternum by costal cartilages (synovial joints) • False ribs (8-10) articulate by costal cartilages with costal cartilage of 7th rib • Floating ribs (11-12) do not articulate with sternum or rib costal cartilages ○ Short costal cartilages terminate in abdominal wall muscle • Vertebral articulation ○ Head articulates with demifacets of 2 adjacent vertebral bodies ○ Neck located between head and tubercle of each rib ○ Tubercle articulates with vertebral transverse process • Body: Longest part of each rib • Angle: Most posterior part • Costal groove on inner surface of inferior border; accommodates intercostal neurovascular bundle

MUSCLES Pectoral • Pectoralis major: Largest muscle in breast and pectoral region ○ Originates from anterior chest wall, sternum, and clavicle 228

○ Adducts, flexes, and medially rotates arm • Pectoralis minor: Deep to pectoralis major ○ Originates from chest wall, inserts onto coracoid process of scapula ○ Stabilizes scapula

Intercostal • External: Contained within 11 intercostal spaces; extend from tubercle of ribs to costochondral junction • Internal: Middle layer; occupy 11 intercostal spaces; extend from border of sternum to angle of ribs • Innermost: Form inner layer of chest wall muscles with subcostales and transversus thoracis muscles

Serratus Anterior • Thin muscular sheet which overlies lateral thoracic cage and intercostal muscles ○ Arises from upper 8 ribs; wraps around rib cage; inserts along medial border of anterior surface of scapula

VESSELS AND NERVES Arteries • Internal thoracic (internal mammary): Branch of subclavian artery ○ Descends posterior to first 6 costal cartilages supplying intercostal arteries ○ Blood supply for anterior chest wall

Veins • Azygos vein receives drainage from posterior intercostal veins, hemiazygos and accessory hemiazygos veins

Nerves • Anterior rami of thoracic spinal nerves (T1-T11) supply skin, tissues of chest wall; form intercostal nerves • Intercostal nerves run in costal groove, between internal and innermost intercostal muscles • Brachial plexus: Branching network of nerve roots, trunks, divisions, cords, and branches ○ Spinal roots form 3 trunks; behind clavicle, each dividing into anterior and posterior divisions

IMAGING Ultrasound • Allows detailed examination of intercostal spaces and contents • Intercostal muscles are seen as hypoechoic structures • Intercostal membrane is seen as hyperechoic layer ○ However, intercostal structures are often thin, making it difficult to separate them into distinct layers • Only anterior cortex of ribs evaluated (medulla obscured)

Computed Tomography • Helical CT and multiplanar reformations optimal for visualization of osseous lesions

Chest Wall

Sternal notch

Thorax

RIBS AND INTERCOSTAL SPACES

Sternoclavicular joint

Acromioclavicular joint

Glenohumeral joint

Manubrium of sternum

Left clavicle

Sternal angle True ribs (1-7) Body of sternum

False ribs (8-10)

Costal margin Costochondral junction Costal cartilage

Xiphoid process

Skin Subcutaneous fat

Endothoracic fascia

Rib Intercostal v. External intercostal m. Intercostal a. Internal intercostal m. Intercostal n. Innermost intercostal m. Lung Visceral pleura Parietal pleura

Collateral branches

(Top) Graphic depicts the chest wall structures forming a musculoskeletal thoracic cage that surrounds the cardiorespiratory organs and effects respiration by expanding and contracting during ventilation. (Bottom) Graphic demonstrates details of the intercostal region, showing 3 layers of intercostal muscles (external, internal, and innermost) between the ribs. The costal groove along the inferomedial aspect of each rib accommodates the intercostal neurovascular bundle (vein, artery, and nerve). Small collateral branches of the major intercostal vessels and nerves may be present above the body of the subjacent rib. The endothoracic fascia forms a connective tissue layer between the inner aspect of the chest wall and the costal parietal pleura.

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Thorax

Chest Wall CHEST WALL MUSCULATURE

Skin Subcutaneous fat Costal cartilage

Sternum

Pectoralis major m.

Transverse thoracic m.

Pectoralis minor m.

Internal thoracic v. Innermost intercostal m.

Parasternal lymph node Internal intercostal m. Internal thoracic a. External intercostal m.

Intercostal v., a., and n.

Vertebral body

Latissimus dorsi m. Serratus anterior m.

Facet joint

Teres major m. Scapula

Transverse spinous process

Endothoracic fascia

Subscapularis m. Rhomboid m. Erector spinae mm. Trapezius m.

Graphic depicts the chest wall layers as visualized in the axial plane, including skin, subcutaneous fat, blood vessels, lymphatics, and musculoskeletal structures. The innermost layer, the endothoracic fascia, is a fibroelastic connective tissue layer between the inner aspect of the chest wall and the pleura.

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Chest Wall

Pectoralis major m.

Thorax

MR, CHEST WALL

Sternum

Pectoralis minor m. Latissimus dorsi m.

Serratus anterior m.

Teres major and minor mm. Subscapularis m. Scapula

Rhomboid m.

Infraspinatus m. Trapezius m.

Trapezius m.

Infraspinatus m. Subscapularis m.

Serratus anterior m.

Spinal cord

Latissimus dorsi m.

Trapezius m. Rhomboid m.

Serratus anterior m.

Latissimus dorsi m.

Intercostal neurovascular bundles

(Top) Axial T1 MR at the level of the aorticopulmonary window shows the major muscles of the chest wall. (Middle) Coronal T1 MR of the chest through the level of the thoracic spinal canal is shown. The serratus anterior is a thin muscular sheet that overlies the lateral thoracic cage and intercostal muscles. It wraps around the rib cage and inserts along the medial border of the scapula. (Bottom) Coronal T1 MR through the level of the posterior ribs is shown. The neurovascular bundles run along the inferior aspect of the ribs in the costal groove.

231

Thorax

Chest Wall RIBS AND INTERCOSTAL SPACES

Skin Subcutaneous fat

Pectoralis major m.

Anterior cortex of 4th rib

Posterior acoustic shadowing

Costal cartilage of 4th rib

Pleura and anterior lung interface

Subcutaneous fat

Intercostal mm.

Pectoralis major m.

5th costal cartilage

6th costal cartilage

Pleura and anterior lung interface

Anterior cortex of 8th rib

Anterior cortex of 9th rib Subcutaneous fat

Pleura and lung interface External and internal intercostal mm.

External oblique m. Innermost intercostal m.

(Top) Transverse view of the costochondral junction of the 4th rib is shown.The costal cartilage appears homogeneously hypoechoic and does not produce significant posterior acoustic shadowing, thus allowing the underlying pleural surface to be seen. The cortex of the 4th rib casts a strong posterior shadow, obscuring the underlying pleura. (Middle) Oblique sagittal view of the intercostal space between the costal cartilages in the anterior chest wall is shown. The costal cartilages are well defined and oval-shaped on cross section. Intercostal muscles between costal cartilages and overlying pectoralis muscle can be clearly visualized. (Bottom) More laterally, oblique sagittal view shows intercostal spaces between the ribs. Areas behind the ribs are obscured by acoustic shadowing. The intercostal muscles in here are better differentiated compared to more medially.

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Chest Wall

Pectoralis major m.

Thorax

RIBS AND INTERCOSTAL SPACES

Sternal cortex

Intercostal m. Internal thoracic a.

Pleura and anterior lung interface

Internal thoracic v.

3rd costal cartilage Intercostal m. Internal thoracic a.

4th costal cartilage Pleura and anterior lung interface Pectoralis m.

4th costal cartilage 3rd costal cartilage Anterior intercostal a.

Collateral branch of intercostal v. Collateral branch of intercostal a.

Anterior intercostal v. Pectoralis m.

External intercostal membrane

Innermost intercostal m. Internal intercostal m.

(Top) Transverse view of the anterior intercostal space just lateral to the sternum is shown. The internal thoracic artery and vein next to the sternum are well visualized with this approach, as are the overlying pectoralis muscle and underlying pleura. (Middle) Sagittal view of the anterior intercostal space shows the internal thoracic artery. Long axis of the internal thoracic artery can be well delineated by scanning along the lateral margin of the sternum. (Bottom) Sagittal view of the anterior intercostal space and the anterior intercostal vessels is shown. The anterior intercostal artery and anterior intercostal vein are identified just inferior to rib above. Smaller collateral branches of the intercostal artery and vein can be identified just superior to the rib above. At the anterior intercostal space, the external intercostal muscle is seen as a thin membrane.

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Thorax

Breast

TERMINOLOGY Definitions • Lobe (segment): Drainage territory defined by each major duct • Terminal duct: Main duct for segment extending to nipple ○ 2 parts: Extralobular terminal duct (ELTD) and intralobular terminal duct (ILTD) • Lobule: Composed of ILTD and complex system of tiny ducts terminating in blind-ending acini (alveoli) • Terminal ductal lobular unit (TDLU): Lobule + ELTD • Cooper ligaments: Suspensory ligaments extending from anterior mammary fascia into dermis to support breast tissue

LOBE/SEGMENT Composition

TDLU Regression • Postpartum/postlactation and menopause • Hormone-blocking medications: Estrogen receptor antagonists and aromatase inhibitors

ZONAL ANATOMY Premammary Zone • Between skin and anterior mammary fascia • Contains subcutaneous fat, nerves, lymphatics, blood vessels, and Cooper ligaments

Mammary Zone • Between anterior and posterior mammary fasciae • Contains TDLUs and ducts, stromal fat, stromal connective tissue, nerves, lymphatics, and blood vessels

• Major ducts and branches → ELTDs → ILTDs → acini

Retromammary Zone

Clinical Considerations

• Between posterior mammary fascia and chest wall • Contains fat and posterior suspensory ligaments

• Average of 15-20 lobes per breast • Lobar volume and anatomy variable • Most, but not all, lobes drain to corresponding nipple duct orifice (some share common ducts)

DUCTAL SYSTEM Duct Orifices • • • •

Usually 8-12 per nipple Arranged radially in nipple crevices Some major ducts merge deep to nipple surface Quadrant of duct orifice on nipple surface does not always correspond to quadrant of lobe

Lactiferous Sinus (Ampullary Segment) • Widened duct segment just deep to nipple orifice • Average diameter: 4-5 mm

Major Ducts • Average diameter: 1 mm • Arborize into segmental and subsegmental branches of variable length and number giving rise to terminal ducts • Branches may extend into multiple breast quadrants • Drain 20-40 lobules, each containing 10-100 acini

TERMINAL DUCT LOBULAR UNIT Overview • Functional, glandular unit of breast • Composition ○ ELTD + ILTD + acini surrounded by loose stromal matrix of collagen and reticular fibers – 10-100 acini drain into each ILTD • May arise directly from major ducts or lactiferous sinuses • Multiple rows of TDLUs arise from distal segmental/subsegmental ducts

TDLU Proliferation • Late adolescence • Pregnancy and lactation • Exogenous hormones: Birth control pills and hormone replacement therapy (HRT) 234

• Postovulatory (secretory) phase of menstrual cycle

INNERVATION Overview • Breast innervated by 3 nerve groups arising from intercostal and cervical nerves: Medial, lateral, and superior mammary branches • Sympathetic fibers control vasomotor response • Glandular secretory functions controlled hormonally

Medial Breast Innervation • Anterior cutaneous branches of 2nd-6th intercostal nerves passing through intercostal spaces near sternum • Medial branches innervate skin over parasternal region

Lateral Breast Innervation • Lateral cutaneous branches of 2nd-6th intercostal nerves • Perforate chest wall in mid-axillary line • Deep branch of 4th intercostal nerve courses along anterior pectoralis major fascia and has perforators to nipple-areolar complex • 2nd intercostal (intercostobrachial) nerve innervates axillary tail and may be injured during axillary nodal dissection

Superior Breast Innervation • Cutaneous branches of 2nd and 3rd intercostal nerves • Medial, intermedius, and lateral branches of supraclavicular nerve via cervical plexus

Nipple-Areolar Complex Innervation • Nerve plexus arising from lateral cutaneous branches of 3rd-5th intercostal nerves and anterior cutaneous branches of 2nd-5th intercostal nerves • Greatest contribution by deep branch of lateral cutaneous 4th intercostal nerve • Nerves course along superficial fascia, becoming subdermal at areola

VASCULAR SUPPLY Arteries • Vessels enter via superolateral, superomedial, and deep aspects of breast

Breast

Venous Drainage • Superficial and deep system drainage with intramammary anastomoses • Superficial system usually do not parallel arteries ○ Subareolar plexus of nipple-areolar complex creates circumferential radiating draining veins – Superomedial breast drainage to 2nd and 3rd intercostal spaces into internal thoracic vein – Inferior breast drainage to inframammary fold into 4th and 5th intercostal spaces via perforators into lateral or medial drainage routes • Deep system accompany arteries supplying region of breast ○ Superolateral veins drain into subclavian vein ○ Intercostal veins to internal mammary vein ○ Inferolateral veins drain into lateral thoracic vein (tributary to axillary vein)

LYMPHATICS AND LYMPH NODES Breast Lymphatic Drainage • Deep breast tissues to superficial lymphatics to periareolar lymphatic (Sappey) plexus • 75% drainage to axilla via lateral and medial trunks extending from areola to axilla ○ Axilla drains into subclavian lymphatic trunk • 25% drainage to internal mammary nodes • Anastomotic lymphatic channels may communicate with contralateral skin and breast; aberrant drainage common after mastectomy or reduction

Axillary Lymph Nodes • Surgical lymph node levels ○ Level I nodes: Lateral/inferior to pectoralis minor muscle ○ Level II nodes: Deep/posterior to pectoralis minor muscle ○ Level III nodes: Medial and superior to pectoralis minor muscle

Internal Mammary Lymph Nodes • Located in parasternal intercostal spaces, < 5 mm in diameter • Predominantly drain far medial and deep medial breast

Intramammary Lymph Nodes

• 25-28% of normal women have intramammary nodes visible on mammography • May be difficult to distinguish intramammary node in axillary tail from axillary lymph node

Thorax

• Medial and lateral mammary branches and intramammary anastomoses • Medial mammary arteries ○ Originate from internal thoracic artery (a.k.a. internal mammary artery), branch of subclavian artery ○ Emerge from 2nd-4th intercostal spaces ○ Supply medial and central breast • Lateral mammary arteries ○ Multiple origins; supply lateral breast – Lateral thoracic artery (branch of 2nd portion of axillary artery) provides dominant supply – Pectoral branches of thoracoacromial artery (branch of 2nd portion axillary artery) – Perforators from 2nd-4th posterior intercostal arteries – Superior thoracic artery (branch of 1st portion of axillary artery)

IMAGING ISSUES Ultrasound • Image capture and reporting ○ Standardized reporting according to American College of Radiology BI-RADS Atlas most commonly used to report both normal and abnormal findings and guide management ○ Include location of probe on every image and cine clip including breast laterality (right breast vs. left breast), clockface, centimeters from nipple and probe position (transverse or longitudinal) ○ Include symptom (if applicable) in addition to probe location on captured image (i.e., "palpable" or "pain") ○ Report echogenicity of finding relative to normal breast subcutaneous fat • Technical considerations ○ Use high-frequency linear-array transducer with center frequency of at least 12 MHz (preferably higher) ○ Subcutaneous fat is reference echogenicity for other structures and gain should be set so that fat is mid gray • Normal findings ○ Overall breast tissue composition variable ○ Fat: Hypoechoic echotexture ○ Ducts frequently visible under nipple as linear, branching anechoic or hypo- to isoechoic channels depending on content – Physiologic duct dilatation occurs in menopause, pregnancy, and lactation ○ Cooper ligaments visible as hyperechoic curved lines within subcutaneous fat ○ Interlobular stromal fibrous tissue usually hyperechoic ○ Glandular elements usually iso- or slightly hypoechoic ○ Cysts anechoic, round or oval masses that are common and considered normal finding when patient asymptomatic ○ Normal lymph nodes always visible within axilla if no prior surgery and often visible in breast – Morphology □ Elliptical shape with circumscribed margins □ Thin, C-shaped, hypoechoic cortex (≤ 3 mm thick) and hyperechoic fatty hilum □ Morphology more important than size in determining normal vs. abnormal – Variable size: May be > 2 cm in length, especially if fatty – Doppler often shows normal hilar vascularity ○ Normal internal mammary nodes may be visible in intercostal spaces – Smaller than axillary nodes: Average size 4-6 mm – Size criteria more important than morphology; different from axillary nodes ○ Vessels (arteries and veins) commonly visible – Distinguish arteries from veins by direction of flow, pulsatility, waveform; normal veins compressible

• Most common in far lateral, axillary, and posteromedial aspects of breast 235

Thorax

Breast TANNER STAGES OF BREAST DEVELOPMENT

Tanner phase I

Tanner phase II

Tanner phase III

Tanner phase IV

Tanner phase V

Nipple

Developing breast tissue

Fibrous tissue

Rib

236

(Top) During childhood, main ducts branch and give rise to terminal buds, the precursors of terminal ductal lobular units (TDLU). This diagram demonstrates the 5 Tanner phases of breast development with the left column showing progressive changes in breast appearance as viewed from the front, the middle column representing glandular changes as viewed from the side, and the right column depicting corresponding changes in the ducts and TDLU. (I) Nipple elevation but no palpable glandular elements and minimal duct branching; (II) projection of nipple and breast as mound with small terminal buds projecting from ductal branches; (III) increased glandular and areolar tissue with primitive TDLU; (IV) separate nipple-areolar complex as secondary mound and complete TDLU; (V) final development with smooth breast and areolar contour and proliferation of TDLU. (Bottom) Transverse ultrasound shows the subareolar region of a 10-year-old girl. The developing breast tissue consists of proliferating ducts and periductal stromal fibrous tissue, resulting in a hypoechoic mass with finger-like projections deep to the nipple. Clinically, this is a palpable disc of tissue deep to the nipple.

Breast Thorax

LOBE, SEGMENTAL ANATOMY

Lactiferous sinus

Duct orifices

Lobe (segment): Duct orifice, main duct, and TDLU Main duct

Intralobular stroma

Lobule Intralobular acini (alveoli)

Intralobular terminal duct

Extralobular terminal duct Terminal ductal lobular unit

Distal ductal branch

(Top) Sagittal graphic shows components of a lobe/segment from the duct orifice on the nipple surface to the TDLUs. Breasts average 15-20 lobes, draining into 8-12 duct orifices. Variability the in amount of glandular elements (TDLUs) and interlobular fibrous stromal tissue accounts for differences in ultrasound echotexture and mammographic density. (Bottom) The TDLU arises from branches of distal subsegmental ducts and is composed of the extralobular terminal duct (ELTD), the intralobular terminal duct (ILTD), and multiple acini arranged around the ILTD. The TDLU on the left has been sectioned to demonstrate the relationship between acini and the ILTD. Note that 10-100 acini drain into each ILTD. The intralobular stroma is composed of collagen and reticular fibers.

237

Thorax

Breast LYMPHATIC DRAINAGE AND LYMPH NODES

Left axillary v.

Level II axillary nodes

Supraclavicular nodes

Level I axillary nodes Level III axillary nodes

Rotter nodes Pectoralis minor m.

Internal mammary nodes Intramammary nodes

Sappey plexus

(Top) Each major lymph node group has well-defined anatomy. The axillary vein group is medial and posterior to the axillary vein, the pectoral group projects at the lower margin of the pectoral muscle, the scapular group projects at the intersection of posterior axilla and scapula, the central group projects posterior to pectoralis minor muscle into the axillary fat, the interpectoral group (not labeled) projects between pectoralis major and pectoralis minor, the subclavicular group projects at the apex of the axilla, and the inferior external mammary group is lateral and inferior to the breast and the internal mammary chain in the parasternal intercostal spaces. (Bottom) Surgical lymph node levels are most commonly used to describe the location of axillary nodes using the pectoralis minor muscle as a point of reference. Nodes lateral/inferior to the pectoralis minor are level I. Nodes deep/posterior, including interpectoral (Rotter) nodes, are level II. Nodes medial and superior are level III.

238

Breast Thorax

NEUROVASCULAR SUPPLY

Cervical plexus branches

Brachial plexus branches

Long thoracic n.

Anterior cutaneous branches

Lateral cutaneous branches

Subclavian a. Axillary a. Lateral thoracic a.

Internal thoracic (a.k.a. internal mammary) a. Perforators from intercostal aa. Medial mammary aa.

Lateral mammary aa.

Subclavian v. Axillary v. Lateral thoracic v.

Internal thoracic (a.k.a. internal mammary) v.

(Top) The superior breast is innervated by supraclavicular branches from the cervical plexus and brachial plexus. The remaining breast is innervated by anterior and lateral branches of the 2nd-6th intercostal nerves. The long thoracic nerve does not innervate breast tissue but is important to isolate during axillary surgery to avoid denervation of the serratus anterior muscle. (Middle) The majority of the arterial supply to the medial and central breast is provided by the internal thoracic (a.k.a. internal mammary) artery. The arterial supply to the lateral breast arises from the axillary artery via lateral thoracic, superior thoracic, and thoracoacromialis arteries and intercostal perforators. (Bottom) Superficial draining veins join the deep draining venous system. Superficial superomedial draining veins drain into the internal thoracic (a.k.a. internal mammary) vein. The deep venous system is composed of the lateral thoracic vein, which is a tributary to the axillary vein; the superolateral vein, which is a tributary to the subclavian vein; and the posterior intercostals, which are tributaries to the vertebral plexus.

239

Thorax

Breast BREAST PARENCHYMAL VARIATION Premammary zone fat Anterior mammary fascia

Fibroglandular tissue

Fat in retromammary zone

Chest wall

Fibrous bands

Fibroglandular tissue

Intercostal m.

Ducts

Fibroglandular tissue

Glandular elements Fibrous tissue

Fat

Rib

(Top) Transverse view of the breast shows homogeneous background echotexture (fibroglandular), which fills the mammary zone. Normal fat is seen in the premammary and retromammary zones. Isoechoic and hypoechoic masses are more visible within the echogenic fibrous tissue. (Middle) Transverse view of the breast shows homogeneous background echotexture (fat). The echogenic ligaments and bands of fibrous tissue are easily seen coursing through the fat. Delineating the mammary zones is difficult in predominantly fatty breasts. Isoechoic masses can be difficult to detect in this type of predominantly fatty breast tissue. (Bottom) Transverse view of the breast shows heterogeneous background echotexture in which there is dense fibroglandular tissue composed of a mix of echogenic fibrous tissue, hypoechoic and anechoic ducts, and multiple tiny, hypoechoic masses, which typically represent cysts &/or benign proliferative change of TDLUs. A thin band of fat represents the retromammary zone.

240

Breast Thorax

BREAST PARENCHYMAL VARIATION

Fibroglandular tissue

Fat lobule Normal ducts

Retromammary fat

Cooper ll.

Fat lobule Cyst Interlobular fibrous stroma Pectoralis major m.

Glandular elements Rib

Fat

Interlobular fibrous stroma

Cysts Rib

(Top) Transverse ultrasound shows heterogeneous fibroglandular tissue with intermixed lobules of fat adjacent to ducts in the subareolar region. The areolar skin thickens adjacent to nipple. (Middle) Transverse ultrasound of the breast shows heterogeneous fibroglandular tissue containing hypoechoic areas representing glandular elements as well as a more discrete small cyst. Small cysts are common within fibroglandular tissue and considered a normal finding. (Bottom) Transverse ultrasound of the breast shows multiple anechoic cysts clustered together within fibroglandular tissue. This represents fibrocystic change, which is considered a normal variant. Fibrocystic change often waxes and wanes and may cause chronic or cyclical breast pain.

241

Thorax

Breast NIPPLE, INTRAMAMMARY NODE Nipple Areolar skin Fat

Ducts

Fibroglandular tissue

Chest wall

Fat

Lymph node cortex

Fatty hilum

Hilar blood vessels

(Top) Transverse ultrasound of the nipple areolar complex obtained with gel standoff and minimal transducer pressure shows normal nipple, which is indented by the probe and small, anechoic subareolar ducts. The nipple often shadows intensely, limiting evaluation of the subareolar region. Positional changes of the nipple and probe help to circumvent shadowing to allow visualization of the underlying tissue. (Middle) Longitudinal ultrasound of the upper outer quadrant breast shows a normal-appearing intramammary lymph node characterized by its reniform shape, thin anechoic cortex, and hyperechoic fatty hilum. (Bottom) Longitudinal ultrasound of the same lymph node with power Doppler shows vascular flow in the hilum, which should be visible in superficial lymph nodes. An artery is often seen coursing near the lymph node (not shown).

242

Breast Thorax

BREAST DUCTS Nipple

Duct Fibroglandular tissue

Chest wall

Fat

Ducts

Fibroglandular tissue

Chest wall

Fibroglandular tissue

Ducts

(Top) Radial ultrasound of the nipple areolar complex shows a more sessile (rather than rounded) nipple with a mildly ectatic subareolar duct. Multiple ectatic ducts containing anechoic or mildly echogenic fluid is a common finding; however, a solitary dilated duct should raise concern for an intraductal mass or duct obstruction. (Middle) Radial ultrasound of the periareolar breast tissue shows markedly dilated anechoic ducts. This was due to prior subareolar duct excision with associated chronic fluid within residual ducts. The duct walls are smooth as expected with benign duct ectasia. (Bottom) Transverse ultrasound of upper outer quadrant breast tissue with lactational change shows multiple fluid-filled ducts. Ducts dilated with fluid are not commonly seen so diffusely outside of the subareolar region except in the setting of lactation. Fibroglandular tissue with lactational change is isoechoic rather than hyperechoic in the nonlactating breast.

243

Thorax

Breast LACTATION-RELATED CHANGES Premammary fat

Fibroglandular tissue

Retromammary fat Rib

Fibroglandular tissue

Dilated v.

Dilated v.

(Top) Transverse ultrasound of a breast with lactational change shows isoechoic fibroglandular tissue, which expands the mammary zone. The premammary and retromammary fat are compressed. (Middle) Transverse ultrasound of the same tissue with color Doppler shows hypervascularity of the fibroglandular tissue, which is expected in lactational tissue due to the marked increase in blood flow related to milk production. (Bottom) Longitudinal ultrasound without and with color Doppler of breast tissue with lactation change shows an anechoic tubular structure that could represent a duct or blood vessel. Color Doppler proves the finding is a blood vessel rather than a duct. This is a vein that is more dilated than typical for normal breast tissue, but it is normal in a patient who is breast feeding.

244

Breast Thorax

AXILLARY LYMPH NODES

Subcutaneous fat Cortex

Hilar fat

Subcutaneous fat Thickened node cortex

Effaced fatty hilum

Rounded morphology lymph node

Subcutaneous fat

Pectoralis major m.

Pectoralis minor m.

Abnormal level II lymph nodes

(Top) Longitudinal ultrasound of the axilla shows a normal morphology lymph node with uniformly thin, hypoechoic cortex (which should measure < 3-4 mm), circumscribed margins, and hyperechoic fatty hilum. (Middle) Longitudinal ultrasound of the axilla shows multiple abnormal morphology lymph nodes. The adjacent superficial nodes maintain a reniform shape but have markedly thickened cortex, which effaces the hilar fat. The deeper node shows a more rounded morphology in addition to cortical thickening, which are both abnormal findings. (Bottom) Longitudinal ultrasound of the axillary region shows visible abnormal level II axillary lymph nodes, which are characterized by their location deep to the pectoralis minor muscle. Though lymph nodes exist in this location, they are not usually visible on ultrasound unless abnormal.

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SECTION 4

Abdomen

Liver Biliary System Spleen Pancreas Kidneys Adrenal Glands Bowel Abdominal Lymph Nodes Aorta and Inferior Vena Cava Peritoneal Cavity Abdominal Wall

248 272 284 292 302 330 336 352 356 386 394

Abdomen

Liver

248

GROSS ANATOMY Overview • Liver: Largest gland and largest internal organ (average weight: 1,500 g) ○ Functions – Processes all nutrients (except fats) absorbed from gastrointestinal (GI) tract; conveyed via portal vein – Stores glycogen, secretes bile ○ Relations – Anterior and superior surfaces smooth and convex – Posterior and inferior surfaces indented by colon, stomach, right kidney, duodenum, inferior vena cava (IVC), and gallbladder ○ Covered by peritoneum except along gallbladder fossa, porta hepatis, and bare area – Bare area: Nonperitoneal posterior superior surface where liver abuts diaphragm – Porta hepatis: Portal vein, hepatic artery, and bile duct located within hepatoduodenal ligament ○ Falciform ligament – Extends from liver to anterior abdominal wall – Separates right and left subphrenic peritoneal recesses (between liver and diaphragm) – Marks plane separating medial and lateral segments of left hepatic lobe – Carries round ligament (ligamentum teres), fibrous remnant of umbilical vein ○ Ligamentum venosum – Remnant of ductus venosus – Separates caudate from left hepatic lobe • Vascular anatomy (unique dual afferent blood supply) ○ Portal vein – Carries nutrients from gut and hepatotrophic hormones from pancreas to liver along with oxygen □ Contains 40% more oxygen than systemic venous blood – 75-80% of blood supply to liver ○ Hepatic artery – Supplies 20-25% of blood – Liver less dependent than biliary tree on hepatic arterial blood supply – Usually arises from celiac artery – Variations common, including arteries arising from superior mesenteric artery ○ Hepatic veins – Usually 3 (right, middle, and left) – Many variations and accessory veins – Collect blood from liver and return it to IVC – Confluence of hepatic veins just below diaphragm and entrance of IVC into right atrium ○ Portal triad – At all levels of size and subdivision, branches of hepatic artery, portal vein, and bile ducts travel together – Blood flows into hepatic sinusoids from interlobular branches of hepatic artery and portal vein → hepatocytes, which detoxify blood and produce bile □ Blood collects into central veins → hepatic veins

□ Bile collects into ducts → stored in gallbladder and excreted into duodenum • Segmental anatomy ○ 8 hepatic segments – Each receives secondary or tertiary branch of hepatic artery and portal vein – Each drained by its own bile duct (intrahepatic) and hepatic vein branch ○ Caudate lobe = segment 1 – Has independent portal triads and hepatic venous drainage to IVC ○ Left lobe – Lateral superior = segment 2 – Lateral inferior = segment 3 – Medial superior = segment 4a – Medial inferior = segment 4b ○ Right lobe – Anterior inferior = segment 5 – Posterior inferior = segment 6 – Posterior superior = segment 7 – Anterior superior = segment 8

IMAGING ANATOMY Internal Contents • Capsule ○ Reflective Glisson capsule making borders of liver well defined • Left lobe ○ Contains segments 2, 3, 4a, and 4b ○ Longitudinal scan – Triangular in shape – Rounded upper surface – Sharp inferior border ○ Transverse scan – Wedge-shaped tapering to left ○ Liver parenchyma echoes are mid gray with uniform, sponge-like pattern interrupted by vessels • Right lobe ○ Contains segments 5, 6, 7, and 8 ○ Liver parenchymal echoes similar to left lobe ○ Sections of right lobe show same basic shape, though right lobe usually larger than left • Caudate lobe ○ Longitudinal scan – Almond-shaped structure posterior to left lobe ○ Transverse scan – Seen as extension of right lobe • Portal veins ○ Have thicker reflective walls than hepatic veins; portal veins have fibromuscular walls ○ Wall reflectivity also depends on angle of interrogation; portal veins cut at more oblique angle may have less apparent wall ○ Can be traced back toward porta hepatis ○ Normal portal flow is hepatopetal on color Doppler; absent or reversal of flow may be seen in portal hypertension ○ Normal velocity 13-55 cm/sec

Liver

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer ○ 2.5- to 5.0-MHz curvilinear or vector transducer generally most suitable ○ Higher frequency linear transducer (i.e., 7-9 MHz) useful for evaluation of liver capsule and superficial portions of liver • Left lobe ○ Subcostal window with full inspiration generally most suitable • Right lobe ○ Subcostal window – Cranial and rightward angulation useful for visualization of right lobe below dome of hemidiaphragm – Can sometimes be obscured by bowel gas ○ Intercostal window – Usually gives better resolution for parenchyma without influence from bowel gas – Right lobe just below hemidiaphragm may not be visible due to obscuration from lung bases – Important to tilt transducer parallel to intercostal space to minimize shadowing from ribs

Abdomen

○ Portal waveform has undulating appearance due to variations with cardiac activity and respiration ○ Branches run in transverse plane ○ Hepatic portal vein anatomy is variable • Hepatic veins ○ Appear as echolucent defects within liver parenchyma with no reflective wall: Large sinusoids with thin or absent wall ○ Branches enlarge and can be traced toward IVC ○ Flow pattern has triphasic waveform – Resulting from transmission of right atrial pulsations into veins □ A wave: Atrial contraction □ S wave: Systole (tricuspid valve moves toward apex) □ D wave: Diastole ○ Right hepatic vein – Runs in coronal plane between anterior and posterior segments of right hepatic lobe ○ Middle hepatic vein – Lies in sagittal or parasagittal plane between right and left hepatic lobe ○ Left hepatic vein – Runs between medial and lateral segments of left hepatic lobe – Frequently duplicated ○ 1 of 3 major branches of hepatic veins may be absent – Absent right hepatic vein ~ 6% – Less commonly middle and left hepatic vein • Hepatic artery ○ Flow pattern has low-resistance characteristics with large amount of continuous forward flow throughout diastole – Normal velocity: 30-70 cm/sec – Resistive index ranges 0.5-0.8, increases after meal ○ Common hepatic artery usually arises from celiac axis ○ Classic configuration: 72% – Celiac axis → common hepatic artery → gastroduodenal artery and proper hepatic artery → latter gives rise to right and left hepatic artery ○ Variations from classic configuration – Common hepatic artery arising from superior mesenteric artery (replaced hepatic artery): 4% – Right hepatic artery arising from superior mesenteric artery (replaced right hepatic artery): 11% – Left hepatic artery arising from left gastric artery (replaced left hepatic artery): 10% • Bile ducts ○ Normal peripheral intrahepatic bile ducts too small to be demonstrated ○ Normal right and left hepatic ducts measuring few millimeters usually visible ○ Normal common duct – Most visible in its proximal portion just caudal to porta hepatis: < 5 mm – Distal common duct should typically measure < 6-7 mm – In elderly, generalized loss of tissue elasticity with advancing age leads to increase in bile duct diameter: < 8 mm (somewhat controversial)

Imaging Pitfalls • Because of variations of vascular and biliary branching within liver (common), frequently impossible to designate precise boundaries between hepatic segments on imaging studies

CLINICAL IMPLICATIONS Clinical Importance • Liver US often 1st-line imaging modality in evaluation for elevated liver enzymes ○ Diffuse liver disease, such as hepatic steatosis, cirrhosis, hepatomegaly, hepatitis, and biliary ductal dilatation well visualized on US ○ Documentation of patency of portal vein, hepatic vein waveforms, and hepatic arterial velocities helpful in evaluation for etiologies of elevated liver function tests • Liver metastases common ○ Primary carcinomas of colon, pancreas, and stomach commonly metastasize to liver – Portal venous drainage usually results in liver being initial site of metastatic spread from these tumors ○ Metastases from other non-GI primaries (breast, lung, etc.) commonly spread to liver hematogenously • Primary hepatocellular carcinoma ○ Common worldwide – Risk factors include cirrhosis of any etiology and chronic viral hepatitis B in certain populations – Chronic hepatitis C with stage 3 fibrosis and nonalcoholic steatohepatitis may also have increased risk of HCC – US commonly used for screening and surveillance in patients at risk for development of hepatocellular carcinoma typically at 6-month intervals

249

Abdomen

Liver HEPATIC VISCERAL SURFACE

Coronary l.

Right triangular l.

Diaphragm

Left triangular l.

Falciform l.

Ligamentum teres

Gallbladder

Gallbladder Falciform l.

Porta hepatis Gastric impression Right renal impression

Bare area Fissure for ligamentum venosum IVC

(Top) The anterior surface of the liver is smooth and molds to the diaphragm and anterior abdominal wall. Generally, only the anterior/inferior edge of the liver is palpable on a physical exam. The liver is covered with peritoneum, except for the gallbladder bed, porta hepatis, and the bare area. Peritoneal reflections form various ligaments that connect the liver to the diaphragm and abdominal wall, including the falciform ligament, the inferior edge that contains the ligamentum teres, and the obliterated remnant of the umbilical vein. (Bottom) Graphic shows the liver inverted, which is somewhat similar to the surgeon's view of the upwardly retracted liver. The structures in the porta hepatis include the portal vein (blue), hepatic artery (red), and the bile ducts (green). The visceral surface of the liver is indented by adjacent viscera. The bare area is not easily accessible.

250

Liver Abdomen

HEPATIC ATTACHMENTS AND RELATIONS

Falciform l. Coronary l. Left triangular l.

Adrenal gland

Right triangular l.

Lesser omentum

Falciform l. Coronary l.

Left triangular l.

Ligamentum venosum

Sulcus for IVC

Right triangular l.

Lateral segment (left lobe) Falciform l.

Medial segment (left lobe) Right lobe

(Top) The liver is attached to the posterior abdominal wall and diaphragm by the left and right triangular and coronary ligaments. The falciform ligament attaches the liver to the anterior abdominal wall. The bare area is in direct contact with the right adrenal gland, kidney, and inferior vena cava (IVC). (Bottom) Posterior view of the liver shows the ligamentous attachments. While these may help to fix the liver in position, abdominal pressure alone is sufficient, as evidenced by orthotopic liver transplantation, after which the ligamentous attachments are lost without the liver shifting position. The diaphragmatic peritoneal reflection is the coronary ligament whose lateral extensions are the right and left triangular ligaments. The falciform ligament separates the medial and lateral segments of the left lobe.

251

Abdomen

Liver HEPATIC VESSELS AND BILE DUCTS

Right hepatic v. (separates anterior and posterior segments of right lobe of liver)

Left hepatic v. (separates medial and lateral segments of left lobe of liver)

Right hepatic duct Middle hepatic v. (separates right and left lobes of liver) Right hepatic a.

Left hepatic duct

Left portal v. Right portal v.

Common hepatic duct

Left hepatic a. Proper hepatic a.

Cystic duct IVC

Gallbladder

Main portal v.

Common bile duct

Graphic emphasizes that at every level of branching and subdivision, the portal veins, hepatic arteries, and bile ducts course together, constituting the portal triad. Each segment of the liver is supplied by branches of these vessels. Conversely, hepatic venous branches lie between hepatic segments and interdigitate with the portal triads but never run parallel to them.

252

Liver

Segment 1 (caudate)

Segment 8

Abdomen

HEPATIC ARTERIAL ANATOMY

Segment 4

Segment 2

Left hepatic a. Segment 7 Segment 3

Segment 5

Left gastric a.

Splenic a.

Segment 6

Celiac trunk

Common hepatic a.

Cystic a.

Gastroduodenal a.

Right hepatic a. Right gastroepiploic a. Proper hepatic a.

Graphic demonstrates the conventional hepatic arterial supply to the liver. The celiac artery arises at roughly the T12 level before dividing into the common hepatic artery, left gastric artery, and splenic artery. The common hepatic artery gives off the gastroduodenal artery inferiorly and becomes the proper hepatic artery, which then divides into the right and left hepatic arteries at the liver hilum. The left hepatic artery courses superiorly and slightly to the left before giving off branches to segments 2-4. In some instances, the segment 4 artery may arise directly from the proper hepatic artery and is then termed the middle hepatic artery. The right hepatic artery divides into anterior and posterior branches, which take a upward vertical course and horizontal course, respectively. The anterior branch gives off arteries supplying segments 5 and 8, while the posterior branches supplies segments 6 and 7. Segment 1 (caudate) is typically supplied by small branches of either the right or left hepatic arteries (or both).

253

Abdomen

Liver HEPATIC ARTERIAL VARIANTS

Cystic a.

Left hepatic a.

Left gastric a. Right hepatic a. Gastroduodenal a. Common hepatic a.

Superior mesenteric a.

Accessory left hepatic a. "Conventional" right and left hepatic aa.

Proper hepatic a.

Left gastric a.

(Top) Graphic depicts a separate origin of the left hepatic artery from the celiac trunk. In addition, the right hepatic artery is "replaced," arising from the superior mesenteric artery. The gastroduodenal and cystic arteries arise from the replaced right hepatic, as is common with this variation. (Bottom) Graphic depicts an "accessory" left hepatic artery arising from the left gastric artery. An accessory artery is a vessel in addition to those originating from the conventional depiction. In this case, there is a left hepatic artery arising from the proper hepatic artery as well. All of these variations are common and have major implications for patients undergoing any sort of upper abdominal surgery, especially partial hepatic resection or liver transplantation.

254

Liver Abdomen

HEPATIC ARTERIAL VARIANTS

Inferior phrenic a.

Left gastric a. Left hepatic a. Right hepatic a. Splenic a. Common hepatic a. Gastroduodenal a.

Superior mesenteric a.

Proper hepatic a. Gastroduodenal a. Superior mesenteric a. Common hepatic a.

(Top) In over 40% of individuals, there are variations in the origin and course of the hepatic arteries that differ from the "conventional" depiction. In this graphic, the left hepatic artery arises from the common hepatic artery, proximal to the origin of the gastroduodenal artery. The gallbladder and extrahepatic common bile duct are supplied by the right hepatic artery, as usual. The hepatic artery courses parallel to the portal vein and lies between the vein and the bile duct. (Bottom) Graphic shows a completely replaced hepatic artery arising from the superior mesenteric artery. In this setting, the hepatic artery passes through or behind the head of the pancreas and the portal vein and may be inadvertently ligated during pancreatic surgery if this variant is not recognized.

255

Abdomen

Liver TRANSVERSE LEFT LOBE OF LIVER

Subcutaneous fat Segment 3

Rectus abdominis m. Segment 4b Falciform l. Portal v. IVC

Pancreas Splenic v. Left renal a. Aorta Spine

Ligamentum venosum Rectus abdominis m. Falciform l. Left portal v.

IVC

Pancreas

Aorta

Middle hepatic v.

Rectus abdominis m.

Portal v. branch

Left hepatic v. Middle hepatic v. Right hepatic v.

(Top) Transverse grayscale US of the left lobe of the liver is shown centered at the level of the falciform ligament and pancreas. (Middle) Transverse grayscale US of the left lobe of the liver is shown. (Bottom) Transverse grayscale US of the left lobe of the liver is shown centered at the level of the left hepatic vein.

256

Liver Abdomen

LEFT LOBE OF LIVER: LEFT PORTAL VEIN

Rectus abdominis m.

Left portal v. Middle hepatic v. IVC RIght hepatic v.

Rectus abdominis m.

Left portal v.

IVC

Rectus abdominis

Left portal v. Middle hepatic v. Right portal v. Right hepatic v.

Left lobe lateral segment Ligamentum venosum Caudate lobe

IVC Spectral tracing of left portal v.

(Top) Transverse grayscale US of the left lobe of the liver is shown centered at the left portal vein. (Middle) Transverse color Doppler US of the left lobe of the liver is shown centered at the level of the left portal vein. Flow in the left portal vein is directed toward the transducer, indicating that the flow is hepatopetal and therefore normal. (Bottom) Spectral tracing of the left portal vein on this transverse pulsed Doppler US shows that the flow is monophasic, directed toward the transducer, with a mildly undulating waveform related to slight transmission of the cardiac cycle, which is a normal appearance for the portal vein.

257

Abdomen

Liver LEFT LOBE OF LIVER: LEFT HEPATIC VEIN

Left rectus abdominous m.

Right rectus abdominis m.

Middle hepatic v. Right hepatic v.

Left hepatic v.

Left rectus abdominis m.

Segment 8

Segment 2 Left hepatic v.

Segment 7 Middle hepatic v.

IVC

Left rectus abdominis m.

Left hepatic v. Middle hepatic v. Right hepatic v. A wave

D wave S wave

(Top) Transverse grayscale US of the liver centered at the left hepatic lobe shows the right, middle, and left hepatic veins as they join into the intrahepatic IVC. (Middle) Transverse color Doppler US of the liver, centered at the confluence of the hepatic veins, shows that the flow direction is away from the transducer, directed toward the IVC. (Bottom) Spectral tracing of the left hepatic vein near the confluence with the IVC shows a characteristic triphasic waveform pattern, which represents reflection of cardiac motion.

258

Liver Abdomen

LONGITUDINAL LEFT LOBE OF LIVER

Abdominal m.

Diaphragm Heart

Left lateral liver Stomach

Heart

Superior mesenteric a. Celiac a.

Aorta

Left portal v. Portal v. Heart Hepatic a. Left hepatic v. Falciform l. Junction of IVC and right atrium

(Top) Longitudinal grayscale US of the left lobe of the liver shows a triangular-shaped cross section. The heart is partially visualized above the diaphragm. (Middle) Longitudinal grayscale US view of the left lobe of the liver at the level of the aorta shows the aorta posterior to the liver, the celiac artery, and superior mesenteric artery arising from the aorta. (Bottom) Longitudinal grayscale US of the left lobe of the liver shows the left hepatic vein and left portal vein in cross section.

259

Abdomen

Liver TRANSVERSE RIGHT LOBE OF LIVER

Middle hepatic v.

Anterior branch right portal v.

Left hepatic v.

Right hepatic v. IVC Diaphragm

Middle hepatic v. Anterior right portal v. branch Right hepatic v. branch Right hepatic v. branch

IVC

Diaphragm

Right portal v. Posterior branch of right portal v. IVC Diaphragmatic crus

(Top) Transverse grayscale US at the level of the hepatic vein confluence shows the right, middle, and left hepatic veins as they join with the IVC posteriorly. (Middle) Transverse grayscale US of the liver just below the confluence of the hepatic veins shows the IVC and more peripheral portions of the right and left hepatic veins. (Bottom) Transverse grayscale US of the right lobe of the liver, centered at the right portal vein, shows the posterior branch of the right portal vein, which is typically directed away from the transducer.

260

Liver Abdomen

RIGHT LOBE OF LIVER: RIGHT HEPATIC VEIN

Anterior right portal v.

Middle hepatic v. Right hepatic v.

Diaphragm

Middle hepatic v.

Right hepatic v.

A wave D wave S wave

Middle hepatic v.

Right hepatic v.

Left hepatic v.

A wave

D wave S wave (Top) Transverse color Doppler US of the right lobe of the liver shows that the right and middle hepatic veins are directed away from the transducer and flowing toward the IVC. (Middle) Spectral tracing of the right hepatic vein shows a typical triphasic waveform with A, S, and D waves representing reflection of cardiac motion in the hepatic veins. (Bottom) Spectral tracing of the middle hepatic vein shows a typical triphasic waveform with A, S, and D waves representing reflection of cardiac motion in the hepatic veins.

261

Abdomen

Liver MAIN PORTAL VEIN

Right portal v.

Main portal v. Hepatic v. branch

IVC

Right portal v.

Main portal v.

IVC

Main portal v.

IVC Main portal v. spectral tracing

(Top) Longitudinal oblique grayscale US is shown centered at the level of the main and right portal veins. (Middle) Longitudinal oblique color Doppler US, centered at the level of the main and right portal veins, shows that flow in the portal vein is directed toward the liver (hepatopetal). (Bottom) Longitudinal oblique spectral Doppler US of the main portal vein shows that the flow is hepatopetal, with gentle undulation reflecting the cardiac and respiratory cycle.

262

Liver Abdomen

PORTA HEPATIS

Hepatic a.

Systolic peak

End diastole

Common bile duct

Right hepatic a. Main portal v. IVC

Right hepatic a.

Common bile duct

Main portal v.

IVC

(Top) Longitudinal oblique spectral tracing of the main hepatic artery shows a typical low-resistance waveform with brisk upstroke and forward diastolic flow. In this case, the hepatic artery velocity is 44 cm/sec, which is normal. When measuring velocity, proper angle correction is the key to obtaining accurate velocities. (Middle) Oblique grayscale US of the liver, centered at the porta hepatis, shows the common bile duct anterior to the right hepatic artery and portal vein. The IVC is seen posterior to the portal vein. (Bottom) Oblique color Doppler US of the liver, centered at the porta hepatis, shows the common bile duct is anterior to the portal vein, and the right hepatic artery is between these 2 structures. This is the typical anatomy in this location, although anatomic variants of the right hepatic artery may occur in which the hepatic artery may be located anterior to the common bile duct.

263

Abdomen

Liver LONGITUDINAL LIVER

Left portal v.

Middle hepatic v.

Main portal v.

Heart Left hepatic v.

Middle hepatic v.

IVC

Left hepatic v. IVC

IVC

A wave S wave D wave

(Top) Longitudinal grayscale US of the right lobe of the liver is shown centered at the level of the IVC. (Middle) Longitudinal color Doppler US of the liver is shown at the level of the IVC. (Bottom) Spectral tracing of the IVC shows a typical triphasic waveform with A, S, and D waves representing reflection of cardiac motion in the IVC.

264

Liver Abdomen

OTHER VIEWS OF LIVER

Inferior liver margin

Right kidney

Right lobe of liver Diaphragm

Liver capsule

Hepatic v. branch Portal v. branch

Gallbladder fundus

Gallbladder wall

Gallbladder lumen

Gallbladder wall fold

(Top) Longitudinal grayscale US of the right lobe of the liver shows the liver ends just above the inferior margin of the right kidney. Normal hepatic length should be < 15.0-15.5 cm. Notice that the normal hepatic parenchyma is slightly hyperechoic compared to the normal kidney. (Middle) Transverse high-resolution US of the liver capsule, as seen here, is typically obtained with higher frequencies (79 MHz). Subtle nodularity of the capsule and small subcapsular liver lesions that may not be as well visualized with standard (3-5 MHz) frequencies are best visualized with this view. Note the hepatic veins have no discernible wall, whereas the portal veins have slightly echogenic walls. (Bottom) Longitudinal oblique US shows a normal gallbladder with anechoic fluid within the lumen and normal appearance of the gallbladder wall. Normal gallbladder wall thickness (< 3 mm) should be measured at the interface with the liver. A fold in the gallbladder neck is incidentally seen in this patient.

265

Abdomen

Liver LIVER SEGMENTAL ANATOMY

Segment 8

Segment 4a

Segment 2

Segment 7

Segment 3

Falciform l.

Segment 6 Segment 4b Segment 5

Segment 4b Segment 5

Segment 6 Segment 3

Segment 1

Segment 2 Segment 7 Segment 4a

(Top) 1st of 2 graphics demonstrating the segmental anatomy of the liver in a somewhat idealized fashion is shown. Segments are numbered in a clockwise direction, starting with the caudate lobe (segment 1), which cannot be seen on this frontal view. The falciform ligament divides the lateral (segments 2 and 3) from the medial (segments 4a and 4b) left lobe. The horizontal planes separating the superior from the inferior segments follow the course of the right and left portal veins. An oblique vertical plane through the middle hepatic vein, gallbladder fossa, and IVC divides the right and left lobes. (Bottom) Inferior view of the liver shows that the caudate is entirely posterior, abutting the IVC, ligamentum venosum, and porta hepatis. In this view, a plane through the IVC and gallbladder ~ divides the left and right lobes.

266

Liver Abdomen

LIVER SEGMENTAL ANATOMY

(Top) Illustration demonstrates the division of the Couinaud segments of the liver at 4 different levels of the liver. The Couinaud segments are defined by the hepatic veins (hepatic vein plane) and the portal veins (portal vein plane). (Bottom) Another illustration focuses on the segments at each of the 4 levels shown in the previous graphic, with graphic A the most superior (at the level of the IVChepatic vein confluence) and graphic D the most inferior (at the level of the portal-splenic confluence). The left hepatic vein divides segments 2 and 3 from 4a and 4b, which the plane of the left portal vein divides the superior segments of the left lobe (2 and 4a) from the inferior segments (3 and 4b). The middle hepatic vein divides segments 4a/b from 5 and 8, while the right hepatic vein divides segments 5 and 8 from 6 and 7. The right portal vein divides the superior segments of the right lobe (7 and 8) from the inferior segments (5 and 6).

267

Abdomen

Liver LIVER SEGMENTAL ANATOMY (CT)

Segment 8 Right hepatic v. plane

Segment 7

Left hepatic v. plane Segment 4a

Segment 2

Middle hepatic v. plane Segment 8 Right hepatic v. plane

Segment 7

Left hepatic v. plane Segment 4a/b

Segment 2/3

Middle hepatic v. plane Left portal v. Segment 1 Segment 8

Right hepatic v. plane Segment 6/7

(Top) Axial CECT through the superior liver demonstrates the right hepatic vein coursing through the right lobe, dividing segments 7 and 8. The right hepatic vein plane also divides segments 5 and 6 below the level of the portal veins. (Middle) A slightly more caudal image (still above the portal vein plane) demonstrates the left hepatic vein plane (line extrapolated through the plane of the left hepatic vein) dividing segments 2 and 4a of the liver, the middle hepatic vein plane (line extrapolated through the middle hepatic vein) dividing segments 4a and 8, and the right hepatic vein plane (line extrapolated through the middle hepatic vein) dividing segments 7 and 8. (Bottom) More caudal level now demonstrates the portal veins coming into view, which divide the liver into superior and inferior segments. The portal vein plane demarcates the division between segments 2 and 3, 4a and 4b, 5 and 8, and 6 and 7.

268

Liver

Falciform l. Right hepatic v. plane

Abdomen

LIVER SEGMENTAL ANATOMY (CT)

Segment 3

Segment 4b Middle hepatic v. plane

Fissure of ligamentum venosum

Right portal v. Segment 1 (caudate) Segment 5

Left hepatic v. plane Segment 6

Left hepatic v. plane Segment 3 Segment 4b Middle hepatic v. plane Segment 1 Segment 5

Right hepatic v. plane Segment 6

Segment 4b Middle hepatic v. plane

Segment 5 Right hepatic v. plane Segment 6

(Top) Axial CECT below the portal vein plane now demonstrates segments 3, 4b, 6, and 7. Note the location of the caudate lobe surrounding the IVC and posterior to the fissure of the ligamentum venosum. (Middle) Axial CECT more inferiorly continues to demonstrates the inferior segments of the liver, including 3, 4b, 5, and 6. (Bottom) Final CECT through the inferior liver now shows that most of the left hepatic lobe has gone out of view in this patient, leaving only the inferior segments of the right hepatic lobe (5 and 6) defined by the middle and right hepatic veins.

269

Abdomen

Liver LIVER SEGMENTAL ANATOMY: TRANSVERSE RIGHT LIVER (US)

Plane of middle hepatic v. Segment 4a Left hepatic v. Segment 8

Plane of right hepatic v. Segment 7 Diaphragm

Falciform l. Segment 4b Plane of middle hepatic v.

Segment 5

Plane of right hepatic v. Segment 6

Diaphragm

Plane of middle hepatic v. Segment 4b

Gallbladder Segment 5 Plane of right hepatic v. Segment 6 Right kidney

270

(Top) Transverse US of the upper right lobe of the at the level of the confluence of the hepatic veins shows the right hepatic vein separates segment 7 (superior posterior segment of the right lobe of the liver) from segment 8 (superior anterior segment of the right lobe of the liver), and the middle hepatic vein separates segment 8 from segment 4a (superior medial segment of the left lobe of the liver). (Middle) Transverse US of the right lobe of the liver just below the level of the portal vein shows the right hepatic vein, which demarcates the anterior from posterior segments of the right lobe of the liver. The plane of the middle hepatic vein separates the left lobe from the right lobe of the liver. A horizontal plane in line with the main portal vein demarcates the upper from lower liver segments. (Bottom) Transverse US of the right lobe of the liver inferiorly at the level of the gallbladder shows the inferior anterior segment of the right lobe of the liver (segment 5) and inferior posterior segment of the right lobe of the liver (segment 6). The demarcation between the 2 segments is created by drawing a plane vertically from the right hepatic vein. A vertically oriented plane at the level of the gallbladder and middle hepatic vein separates the right and left lobe of the liver.

Liver Abdomen

LIVER SEGMENTAL ANATOMY: TRANSVERSE LEFT LIVER (US)

Plane of left hepatic v.

Segment 4a

Segment 2

Plane of middle hepatic v. Segment 8 IVC

Segment 3

Plane of left hepatic v. and falciform l. Ligamentum venosum Segment 4b Plane of middle hepatic v. Segment 5

Caudate IVC Aorta

Segment 4b Portal v.

Segment 3 Falciform l.

IVC

Aorta

(Top) Transverse grayscale US of the left lobe of the liver at the level of the confluence of the hepatic veins and IVC shows the left hepatic vein separates the superior lateral segment of the left lobe of the liver (segment 2) from the superior medial segment of the left lobe of the liver (segment 4a). (Middle) Transverse grayscale US shows the left lobe of the liver at a level just inferior to the left portal vein. The caudate lobe of the liver (segment 1) abuts the ligamentum venosum, IVC, and left portal vein. The falciform ligament separates the inferior lateral segment of the left lobe of the liver (segment 3) from the inferior medial segment of the left lobe of the liver (segment 4b). (Bottom) Transverse grayscale US shows the inferior aspect of the left lobe of the liver at the level of the pancreas. The falciform ligament separates the inferior lateral segment of the left lobe of the liver (segment 3) from the medial inferior segment of the left lobe (segment 4b).

271

Abdomen

Biliary System

TERMINOLOGY Abbreviations • Extrahepatic biliary structures ○ Gallbladder (GB) ○ Cystic duct (CD) ○ Right hepatic (RH) and left hepatic (LH) ducts ○ Common hepatic duct (CHD) ○ Common bile duct (CBD)

Definitions • Proximal/distal biliary tree ○ Proximal refers to portion of biliary tree that is closer in proximity to liver and hepatocytes ○ Distal refers to caudal end closer to ampulla and bowel • Central/peripheral ○ Central refers to biliary ducts close to porta hepatis ○ Peripheral refers to higher-order branches of intrahepatic biliary tree extending into hepatic parenchyma

IMAGING ANATOMY Overview • Biliary ducts carry bile from liver to duodenum ○ Bile is produced continuously by liver, stored and concentrated by GB, and released intermittently by GB contraction in response to presence of fat in duodenum ○ Hepatocytes form bile → bile canaliculi → interlobular biliary ducts → collecting bile ducts → right and left hepatic ducts → CHD → CBD → intestines • Common bile duct ○ Forms in free edge of lesser omentum by union of CD and CHD ○ Length of duct: 5-15 cm, depending on point of junction of cystic and CHD ○ Descends posterior and medial to duodenum, lying on dorsal surface of pancreatic head ○ Joins with pancreatic duct to form hepaticopancreatic ampulla of Vater ○ Ampulla opens into duodenum through major duodenal (hepaticopancreatic) papilla ○ Distal CBDt is thickened into sphincter of Boyden and hepaticopancreatic segment is thickened into a sphincter of Oddi – Contraction of these sphincters prevents bile from entering duodenum; forces it to collect in GB – Relaxation of sphincters in response to parasympathetic stimulation and cholecystokinin (released by duodenum in response to fatty meal) • Vessels, nerves, and lymphatics ○ Arteries – Hepatic arteries supply intrahepatic ducts – Cystic artery supplies proximal common duct – RH artery supplies middle part of common duct – Gastroduodenal and pancreaticoduodenal arcade supply distal common duct – Cystic artery supplies GB (usually from RH artery; variable) ○ Veins – From intrahepatic ducts → hepatic veins 272

– From common duct → portal vein (in tributaries) – From GB directly into liver sinusoids, bypassing portal vein ○ Nerves – Sensory: Right phrenic nerve – Parasympathetic and sympathetic: Celiac ganglion and plexus; contraction of GB and relaxation of biliary sphincters is caused by parasympathetic stimulation, but more important stimulus is from hormone cholecystokinin ○ Lymphatics – Same course and name as arterial branches – Collect at celiac lymph nodes and node of omental foramen – Nodes draining GB are prominent in porta hepatis and around pancreatic head • Gallbladder ○ ~ 7-10 cm long, holds up to 50 mL of bile ○ Lies in shallow fossa on visceral surface of liver ○ Vertical plane through GB fossa and middle hepatic vein divides LH and RH lobes ○ May touch and indent duodenum ○ Fundus is covered with peritoneum and relatively mobile; body and neck attached to liver and covered by hepatic capsule ○ Fundus: Wide tip of GB, projects below liver edge (usually) ○ Body: Contacts liver, duodenum, and transverse colon ○ Neck: Narrowed, tapered, and tortuous; joins CD ○ CD: 3-4 cm long, connects GB to CHD; marked by spiral folds of Heister; helps to regulate bile flow to and from GB • Normal measurements ○ CBD/CHD – < 6-7 mm in patients without history of biliary disease in most studies – Controversy about dilatation related to previous cholecystectomy and old age ○ Intrahepatic ducts – Normal diameter of 1st and higher-order branches < 2 mm or < 40% of diameter of adjacent portal vein – 1st- (i.e., LH duct and RH duct) and 2nd-order branches are normally visualized – Visualization of 3rd and higher-order branches is often abnormal and indicates dilatation

ANATOMY IMAGING ISSUES Imaging Recommendations • Patient should fast for at least 4-6 hours prior to US examination to ensure GB is not contracted after meal, ideally fasting for 8-12 hours (overnight) • Complete assessment includes scanning liver, porta hepatis region, and pancreas in sagittal, transverse, and oblique views • Subcostal and right intercostal transverse views help align bile ducts and GB along imaging plane for optimal visualization • Usually structures are better assessed and imaged with patient in full-suspended inspiration and in left lateral oblique position

Biliary System

Imaging Approaches • Transabdominal USis ideal initial investigation for suspected biliary tree or GB pathology ○ Cystic nature of bile ducts and GB (especially if these are dilated) provides inherently high-contrast resolution ○ Acoustic window provided by liver and modern state-ofthe-art US technology provides good spatial resolution ○ Common indications of US for biliary and GB disease include – Right upper quadrant/epigastric pain – Abnormal liver function test or jaundice – Suspected gallstone disease – Pancreatitis ○ US plays key role in multimodality evaluation of complex biliary problems • Supplemented by various imaging modalities, including MR/MRCP and CT

Imaging Pitfalls • Common pitfalls in evaluation of GB ○ Posterior shadowing may arise from GB neck, Heister valves of CD, or adjacent gas-filled bowel loops – May mimic cholelithiasis – Scan after repositioning patient in prone or left lateral decubitus positions ○ Food material within gastric antrum/duodenum – Mimics GB filled with gallstones or GB containing milk of calcium – During real-time scanning, carefully evaluate peristaltic activity of involved bowel with oral administration of water • Common pitfalls in US evaluation of biliary tree ○ Redundancy, elongation, or folding of GB neck on itself – Mimics dilatation of CHD or proximal CBD – Avoided by scanning patient in full-suspended inspiration – Careful real-time scanning allows separate visualization of CHD/CBD medial to GB neck ○ Presence of gas-filled bowel loops adjacent to distal extrahepatic bile ducts – Obscure distal biliary tree and render detection of choledocholithiasis difficult – Scan with patient in decubitus positions or after oral intake of water ○ Gas/particulate material in adjacent duodenum and pancreatic calcification – Mimic choledocholithiasis within CBD

○ Presence of gas within biliary tree – May mimic choledocholithiasis, differentiated by presence of reverberation artifacts – Limits US detection of biliary calculus

Abdomen

• Harmonic imaging provides improved contrast between bile ducts and adjacent tissues, leading to improved visualization of bile ducts, luminal content, and wall • For imaging of gallstone disease, special maneuvers are recommended ○ Move patient from supine to left lateral decubitus position – Demonstrates mobility of gallstones – Gravitates small gallstones together to appreciate posterior acoustic shadowing ○ Set focal zone at level of posterior acoustic shadowing – Maximizes effect of posterior acoustic shadowing to confirm gallstone(s)

Key Concepts • Direct venous drainage of GB into liver bypasses portal venous system, often results in sparing of adjacent liver from generalized steatosis (fatty liver) • Nodal metastasis from GB carcinoma to peripancreatic nodes may simulate primary pancreatic tumor • Sonography: Optimal means of evaluating GB for stones and inflammation (acute cholecystitis); best done in fasting state (distends GB) • Intrahepatic bile ducts follow branching pattern of portal veins ○ Usually lie immediately anterior to portal vein branch; confluence of hepatic ducts just anterior to bifurcation of right and main portal veins

CLINICAL IMPLICATIONS Clinical Importance • In patients with obstructive jaundice, US plays key role ○ Differentiates biliary obstruction from liver parenchymal disease ○ Determines presence, level, and cause of biliary obstruction • Common variations of biliary arterial and ductal anatomy result in challenges to avoid injury at surgery ○ CD may run in common sheath with bile duct ○ Anomalous RH ducts may be severed at cholecystectomy • Close apposition of GB to duodenum can result in fistulous connection with chronic cholecystitis and erosion of gallstone into duodenum

Function & Dysfunction • Obstruction of CBD is common ○ Gallstones in distal bile duct ○ Carcinoma arising in pancreatic head or bile duct ○ Result is jaundice due to back up of bile salts into bloodstream

Embryologic Events • Abnormal embryological development of fetal ductal plate can lead to spectrum of liver and biliary abnormalities, including ○ Polycystic liver disease ○ Congenital hepatic fibrosis ○ Biliary hamartomas ○ Caroli disease ○ Choledochal cysts

273

Abdomen

Biliary System GALLBLADDER IN SITU

Right hepatic lobe

Left hepatic lobe

Extrahepatic bile duct Peritoneal reflection Gallbladder (body)

Gallbladder (fundus)

Proper hepatic a. Main portal v.

Lesser omentum (cut edge, anterior)

Duodenum Colon (hepatic flexure) Pancreas

Cystic duct Common hepatic duct Neck

Body

Fundus

Common bile duct Pancreatic duct Superior mesenteric a.

Ampulla Superior mesenteric vein

(Top) Graphic shows that the gallbladder is covered with peritoneum, except where it is attached to the liver. The extrahepatic bile duct, hepatic artery, and portal vein run in the lesser omentum. The fundus of the gallbladder extends beyond the anterior-inferior edge of the liver and can be in contact with the hepatic flexure of the colon. The body (main portion of the gallbladder) is in contact with the duodenum. (Bottom) The neck of the gallbladder narrows before entering the cystic duct, which is distinguished by its tortuous course and irregular lumen. The duct lumen is irregular due to redundant folds of mucosa, called the spiral folds of Heister, that are believed to regulate the rate of filling and emptying of the gallbladder. The cystic duct joins the hepatic duct to form the common bile duct, which passes behind the duodenum and through the pancreas to enter the duodenum.

274

Biliary System Abdomen

ANATOMIC VARIATIONS OF BILIARY TREE

Left hepatic duct Right hepatic duct

Accessory right hepatic (joining common hepatic duct)

Cystic duct Accessory left hepatic (joining common bile duct)

Accessory right hepatic (joining cystic duct)

Accessory right hepatic (joining common bile duct)

Conventional junction of cystic and common hepatic ducts Low insertion of cystic duct

Spiral course of cystic duct around common hepatic duct

Cystic and common bile ducts in common sheath

(Top) Graphic shows the conventional arrangement of the extrahepatic bile ducts, but variations are common (20% of population) and may lead to inadvertent ligation or injury at surgery (such as during cholecystectomy), where the cystic duct is clamped and transected. Most accessory ducts are on the right side and usually enter the common hepatic duct, but they may enter the cystic or common bile duct. Accessory left ducts enter the common bile duct. While referred to as accessory, these ducts are the sole drainage of bile from at least 1 hepatic segment. Ligation or laceration can lead to significant hepatic injury or bile peritonitis. (Bottom) The course and insertion of the cystic duct are highly variable, leading to difficulty in isolation and ligation at cholecystectomy. The cystic duct may be mistaken for the common hepatic or common bile duct.

275

Abdomen

Biliary System BILIARY TREE

Ducts to segment IV

Right anterior-cephalic ducts (segments V and VIII)

Right posterior-caudal ducts (segments VI and VII)

Ducts to segments II-III

Left hepatic duct Right hepatic duct

Common hepatic duct

Accessory pancreatic duct (of Santorini) Minor papilla

Hepatoduodenal papilla (major papilla)

Main pancreatic duct (of Wirsung)

Note the distribution of the larger intrahepatic bile ducts. The common bile duct usually joins with the pancreatic duct in a common channel or ampulla (of Vater) but may enter the major duodenal papilla separately. The distal bile duct has a sphincteric coat of smooth muscle, the choledochal sphincter (of Boyden), which regulates bile emptying into the duodenum. When contracted, this sphincter causes bile to flow retrograde into the gallbladder for storage. The common hepaticopancreatic ampulla may be surrounded by a smooth muscle sphincter (of Oddi).

276

Biliary System

Peritoneal reflection

Inflamed Rokitansky-Aschoff sinus

Abdomen

BILIARY TREE

Liver Aberrant bile duct (of Luschka)

Gallbladder neck glands

Gallbladder wall m. Gallbladder lumen

Cholelithiasis

Choledocholithiasis

(Top) The gallbladder body and neck are adherent to the liver and may be bridged by aberrant bile ducts (of Luschka). Mucous glands are found in the gallbladder neck. Rokitansky-Aschoff sinuses are pseudodiverticula that extend into the wall and may collect debris, becoming inflamed. (Bottom) Graphic demonstrates cholelithiasis (stones in the gallbladder) and choledocholithiasis (stones in the bile ducts). Gallstones are extremely common and may remain asymptomatic. Stones that become impacted, even temporarily, in the gallbladder neck may cause inflammation and distention of the gallbladder, clinically referred to as acute cholecystitis. Stones that pass through the cystic duct often cause biliary colic (spasms of right upper quadrant pain), as they often become trapped within the common bile duct, causing obstruction.

277

Abdomen

Biliary System RIGHT HEPATIC LOBE

Rectus m. Gallbladder

Right hepatic lobe Duodenum Middle hepatic v. Portal v.

Inferior vena cava Heart

Rectus musculature Right hepatic lobe

Portal triad

Portal triad

Gallbladder Right kidney Inferior vena cava

Aorta Psoas Spine

(Top) Subcostal, longitudinal ultrasound shows the right hepatic lobe and gallbladder with patient in the left lateral decubitus position. Ideally, a patient must fast for at least 4-6 hours to allow for adequate gallbladder distension. (Bottom) Subcostal, transverse ultrasound of the right hepatic lobe demonstrates its anatomical relationships with major vessels and the right kidney. The intrahepatic bile ducts are localized within the portal triads, which are visible by the prominent echogenic walls of the portal veins in these triads. The portal triad contains the portal vein, bile duct, and hepatic artery. Normally, the intrahepatic bile ducts and hepatic arteries are not readily visible unless they are dilated.

278

Biliary System Abdomen

LEFT HEPATIC LOBE

Right rectus m.

Portal triad Portal triad Left hepatic v.

Inferior vena cava

Rectus musculature

Portal triad Left hepatic v.

Inferior vena cava

Left hepatic lobe Portal triad

Gallbladder Portal v.

Heart

(Top) Subxiphoid, transverse grayscale ultrasound of the left hepatic lobe shows the left hepatic vein and several portal triads. The portal triads are identified by the prominent echogenic walls of the portal veins. The portal triad contains a portal vein, a bile duct, and a hepatic artery. The hepatic artery and bile duct are not readily visible unless they are dilated. (Bottom) Longitudinal ultrasound of the left hepatic lobe near the confluence of the left hepatic vein with the inferior vena cava is shown. Portal triads are recognizable by the prominent walls of the portal veins.

279

Abdomen

Biliary System GALLBLADDER

Right rectus m.

Right hepatic lobe Gallbladder Junctional fold

Common hepatic duct

Duodenum

Hepatic a. Main portal v.

Cystic duct

Left hepatic lobe

Gallbladder Stomach Inferior vena cava

Aorta Vertebral body

(Top) Subcostal, longitudinal grayscale ultrasound shows the gallbladder with patient in the left lateral decubitus position. The gallbladder is distended with bile, causing increased transmission of echoes. A patient must fast for at least 4-6 hours to allow for adequate gallbladder distension. (Bottom) Transverse ultrasound of a distended gallbladder in the left lateral decubitus position is shown. The gallbladder is best evaluated if the patient has fasted at least 4-6 hours, ideally 8-12 hours.

280

Biliary System Abdomen

COMMON BILE DUCT

Common bile duct Hepatic a. Main portal v.

Inferior vena cava

Head of pancreas

Body of pancreas Splenic v. Superior mesenteric a.

Common bile duct Left renal v. Aorta

Vertebral body

(Top) Subcostal, longitudinal oblique ultrasound shows the common bile duct and the portal vein in the hepatoduodenal ligament. The common bile duct is normally identified anterior to the portal vein. The distal common bile duct pierces the pancreatic head. Also demonstrated is the hepatic artery, which normally traverses between the portal vein and common bile duct. (Bottom) Transverse ultrasound at the level of the pancreas demonstrates the distal common bile duct as it pierces the pancreatic head. Overlying bowel gas may obscure this area; positioning the patient upright or in a left lateral decubitus position may help visualization.

281

Abdomen

Biliary System RIGHT INTRAHEPATIC DUCTS

Intrahepatic bile duct

Portal v. Intrahepatic bile duct Right hepatic lobe

Portal v. Inferior vena cava

Intrahepatic duct

Posterior branch of right portal v. Main portal v.

(Top) Transverse ultrasound through the right hepatic lobe in a patient with biliary obstruction demonstrates dilated right intrahepatic bile ducts. Normally, intrahepatic ducts are not readily visualized unless they are dilated. Parallel linear hypoechoic structures are not normally seen in the liver, and this may represent a dilated bile duct or dilated hepatic artery adjacent to the normally visualized portal venous structure in the portal triad. (Bottom) Transverse color Doppler ultrasound through the right hepatic lobe in a patient with biliary obstruction demonstrates dilated right intrahepatic bile ducts. Normally, intrahepatic ducts are not readily visualized unless they are dilated. Color Doppler ultrasound helps to determine whether the dilated structure is a dilated hepatic artery or dilated bile duct.

282

Biliary System

Portal venous branch

Abdomen

LEFT INTRAHEPATIC DUCTS

Left hepatic lobe

Intrahepatic duct

Inferior vena cava

Aorta

Left hepatic lobe Portal venous branch

Intrahepatic ducts

(Top) Transverse ultrasound through the left hepatic lobe in a patient with biliary obstruction demonstrates dilated left intrahepatic bile ducts. Normally, intrahepatic ducts are not readily visualized unless they are dilated. (Bottom) Transverse color Doppler ultrasound through the left hepatic lobe in a patient with biliary obstruction demonstrates dilated left intrahepatic bile ducts. Normally, intrahepatic ducts are not readily visualized unless they are dilated. Color Doppler ultrasound is helpful to determine whether the dilated structure is vascular or biliary, as dilated hepatic arteries can be mistaken for dilated bile ducts. The absence of flow allows one to determine that these are biliary in origin.

283

Abdomen

Spleen

GROSS ANATOMY Overview • Intraperitoneal lymphatic organ located posterior to stomach and intimately associated with retroperitoneum (pancreatic tail and left kidney) • Surrounded by peritoneum (except at hilum) and suspended by several ligaments ○ Gastrosplenic ligament – Left anterior margin of lesser sac – Connects spleen to greater curvature of stomach – Carries short gastrics and left gastroepiploic arteries and venous branches to spleen ○ Splenorenal ligament – Left posterior margin of lesser sac – Connects spleen to left kidney and pancreatic tail – Carries splenic artery and vein to splenic hilum ○ Splenocolic ligament: Between spleen and splenic flexure of colon ○ Splenophrenic ligament: Between spleen and inferior surface of diaphragm • Normal size is variable; no universal consensus ○ Generally, normal adult spleen considered 12 cm length x 7 cm width x 4 cm thickness – Length = longest diameter in longitudinal plane; width = longest transverse (anterior-posterior) diameter; thickness = maximal thickness in transverse plane at hilum ○ Splenic index (product of length, thickness, and width): Normally 120-480 cm³ • Functions ○ Manufactures lymphocytes, filters blood (removes damaged red blood cells and platelets) ○ Acts as blood reservoir: Can expand or contract in response to changes in blood volume • Histology ○ Soft organ with fibroelastic capsule and comprised of pulp – White pulp: Lymphoid nodules/tissue primarily surrounding vasculature – Red pulp: Sinusoidal spaces containing blood ○ Trabeculae: Extensions of capsule into parenchyma; carry arterial and venous branches ○ Splenic cords (plates of cells) lie between sinusoids; red pulp veins drain sinusoids • Vasculature ○ Splenic artery arises from celiac axis in > 90%; 8% directly from aorta – Often very tortuous ○ Splenic vein runs in groove along dorsal surface of pancreatic body and tail – Receives inferior mesenteric vein (IMV) – Combined splenic vein and IMV join superior mesenteric vein to form portal vein

IMAGING ANATOMY Overview • Homogeneous echogenicity ○ Echogenicity: Pancreas > spleen > liver > kidney ○ Radiating pattern of segmental arteries and veins 284

• Splenic artery ○ Low-resistance waveform; tortuosity of vessel results in turbulence and spectral broadening ○ Normal diameter: 4-8 mm; peak systolic velocity (PSV): 25-45 cm/sec • Splenic vein ○ Normal diameter: 5-10 mm; PSV: 9-18 cm/sec ○ Splenic vein at midline is useful landmark for locating pancreas – Pancreas lies anterior to splenic vein ○ Diameter increases between 50-100% from quiet respiration to deep inspiration; increase of < 20% suggests portal hypertension ○ Spectral Doppler waveform typically shows band-like flow profile with minimal respiratory fluctuations

ANATOMY IMAGING ISSUES Imaging Recommendations • Patient positioned supine or right decubitus position (left side up) with left arm raised • Place transducer parallel to ribs in 10th or 11th intercostal space at left midaxillary line, searching for best window ○ Due to rib angle, this results in oblique view, which by convention is called longitudinal or transverse (depending on transducer orientation) ○ Transverse US view of spleen does not correlate directly to axial CT view • End expiration may be helpful; lung base may obscure spleen in full inspiration • Spleen poorly accessed from posterior (obscured by left lung base), anterior, or subcostal approach (obscured by stomach and colon) • Assess splenic vein at hilum and midline for patency and flow direction • Can use spleen as acoustic window to visualize tail of pancreas

Key Concepts • Spleen has highly variable size and shape ○ Easily indented and displaced by masses and even loculated fluid collections

EMBRYOLOGY Practical Implications • Accessory spleen (splenunculus, splenule) ○ Found in 10-30% of population, and may be multiple ○ Usually small, near splenic hilum ○ Can enlarge and simulate mass, especially after splenectomy ○ Ectopic intrapancreatic splenule can mimic pancreatic tail mass; should not be > 3 cm from tail tip • Wandering spleen: Spleen may be on long mesentery ○ Found in any abdominopelvic location; risk of torsion • Asplenia and polysplenia (heterotaxy syndromes) ○ Rare congenital conditions of altered left/right orientation of organs ○ Associated with cardiovascular anomalies, intestinal malrotation, etc. • Splenosis: Peritoneal implantation of splenic tissue after traumatic splenic injury, can mimic polysplenia

Spleen Abdomen

LIGAMENTS AND VESSELS

Splenophrenic l. Stomach

Gastrosplenic l. Lesser omentum Spleen

Splenorenal l.

Root of transverse mesocolon Splenocolic l.

Left gastric a.

Splenic a.

Celiac axis Common hepatic a.

Splenic v. Portal v. Inferior mesenteric v.

Superior mesenteric v. Superior mesenteric a.

(Top) Graphic shows the liver is retracted upward and the stomach transected to reveal the pancreas and spleen. The spleen is affixed to surrounding organs by several ligamentous attachments. The gastrosplenic ligament connects the spleen to the greater curve of the stomach and transports the short gastrics and left gastroepiploic vessels. The splenorenal ligament connects the spleen to the left kidney and pancreatic tail and carries the splenic artery and vein into the spleen at the hilum. The splenocolic ligament extends to the splenic flexure of the colon and the splenophrenic ligament to the diaphragm. (Bottom) Coronal graphic with the mesenteric reflections removed to show the splenic vascular supply. The splenic artery arises from the celiac axis and is often quite tortuous. The splenic vein runs posterior to the body of the pancreas and receives the inferior mesenteric vein. It joins the superior mesenteric vein behind the neck of the pancreas to form the portal vein.

285

Abdomen

Spleen SPLENIC SHAPE Gastric impression

Stomach Renal impression

Prominent medial lobulation Kidney

Oblique and transversus abdominis mm.

Spleen Left kidney

Stomach

Large medial lobulation

Left kidney

(Top) Graphic shows the medial surface of the spleen and representative axial sections at 3 levels through the parenchyma. The spleen is of variable shape and size, even within the same individual, varying with states of nutrition and hydration. It is a soft organ that is easily indented by adjacent organs. The medial surface is often quite lobulated as it is interposed between the stomach and the kidney. (Middle) Longitudinal ultrasound shows the spleen conforming to the shape of the left kidney. In this plane, the spleen appears quite small. (Bottom) The oblique transverse plane in the same patient shows a large medial lobulation. Volume measurements are more accurate in determining the size of the spleen than any individual measurements, but even that has large individual variability.

286

Spleen Abdomen

SPLENIC SHAPE

White pulp

Splenic capsule Red pulp

Branching trabeculae

Spleen

Splenic artery in hilum

Pancreatic tail

Left hemidiaphragm

Left hemidiaphragm

Spleen

Tail of pancreas

(Top) Histologic section of a normal spleen viewed at low power shows white pulp and red pulp. A thin splenic capsule with slivers of branching trabeculae is also noted. The red pulp is "spongy" and compressible. (Middle) This longitudinal view of the spleen through the left flank shows the intimate relationship with the tail of the pancreas. In this case, the spleen was long (13.5 cm), but the splenic index and volume were normal. (Bottom) Oblique correlative multiplanar reconstruction CT of the spleen is shown. Note the extension of the pancreatic tail toward the splenic hilum. This allows the pancreatic tail to be visualized by ultrasound using the spleen as an acoustic window.

287

Abdomen

Spleen SPLENIC VESSELS

Left hepatic lobe

Pancreatic head Left renal v.

Inferior vena cava

Pancreatic body Splenic v.

Superior mesenteric artery

Aorta

Splenic v.

Superior mesenteric artery

Left renal v. Aorta

Left hepatic lobe Splenic a. Common hepatic a. Portal v.

Inferior vena cava

Splenic v. Celiac a. Abdominal aorta

288

(Top) Midline transverse anterior grayscale ultrasound of the splenic vein is shown. The splenic vein is located deep to the pancreatic body. Note the left renal vein course between the superior mesenteric artery and aorta. (Middle) Color Doppler ultrasound of the same area shows the normal direction of flow in the splenic vein toward the liver (hepatopetal). Note the change in color from red to blue, which is due to the position of the transducer, aligned at the midpoint of the vein. Using the information provided by the color bar, the red portion of the splenic vein is blood flowing toward the transducer (away from the spleen), and the blue is blood flowing away from the transducer (toward the the liver). (Bottom) Power Doppler ultrasound of the upper abdomen at midline shows the origin of the splenic artery from the celiac axis. The celiac artery branches into the splenic artery, common hepatic artery, and left gastric artery (not shown). After its takeoff, the splenic artery typically has a tortuous course. The branching of the celiac axis, as shown in this image, has been referred to as the seagull sign.

Spleen Abdomen

SPLENIC VESSELS

Splenic v.

Splenic a.

Segmental arterial branches

Splenic a.

Splenic v.

(Top) Longitudinal oblique color Doppler ultrasound demonstrates the branching of the splenic arteries and veins in the splenic hilum. (Middle) Spectral Doppler waveform ultrasound of the distal splenic artery at the splenic hilum is shown. Because of a tortuous course, flow in this vessel is typically turbulent. The splenic artery has a low-resistance waveform (ample flow throughout diastole). Normal peak systolic velocity for the splenic artery is 25-45 cm/sec. (Bottom) Spectral Doppler waveform ultrasound of the splenic vein at the hilum shows a typical band-like flow profile with minimal respiratory fluctuations; flow is directed away from the transducer (away from the spleen). Normal peak systolic velocity of the splenic vein is 9-18 cm/sec.

289

Abdomen

Spleen SPLENULE

Spleen

Splenule

Left kidney

Spleen

Splenule Splenic a. Accessory splenic vessels supplying splenule Splenic v.

Stomach

Splenic a.

Spleen

Accessory vessels supplying splenule

Splenic v. Pancreas

Splenule Left kidney

(Top) Transverse oblique intercostal ultrasound shows a splenule between the spleen and left kidney. Splenules should have the same echogenicity and echotexture as the spleen, though this may depend on the sonographic window. (Middle) Longitudinal oblique intercostal color Doppler ultrasound shows a splenule adjacent to the spleen tip. The identification of vascular supply from the splenic vessels may also aid in identification of a splenule. (Bottom) Correlative coronal CECT of the left upper quadrant demonstrates a splenule along the inferior tip of the spleen. Branch vessels from the splenic artery and vein supplying the splenule are visualized.

290

Spleen

Intercostal m.

Abdomen

SPLENOSIS AND HETEROTAXY

Splenosis Left kidney

Pancreatic tail

Superior pole of left kidney

Splenosis

Ascites Splenic cyst

Left-sided liver Right-sided spleen

(Top) Longitudinal oblique intercostal grayscale ultrasound through the left upper quadrant in a patient with prior splenectomy shows rounded, hypoechoic structures adjacent to the upper pole of the left kidney; this represents splenosis. (Middle) Correlative axial CECT through the left upper quadrant in a patient with prior splenic trauma and splenectomy shows residual splenosis. (Bottom) Transverse anterior ultrasound in the setting of heterotaxy with polysplenia demonstrates the relationship between the right-sided spleen and the left-sided liver. The classification of heterotaxy syndromes is complex; there is a spectrum ranging from classic asplenia to classic polysplenia. Heterotaxy with polysplenia (i.e., left double sidedness or left isomerism) may present with multiple spleens (resembling splenules) or a single spleen, as in this case.

291

Abdomen

Pancreas

GROSS ANATOMY Overview • Pancreas: Accessory digestive gland lying behind stomach in anterior pararenal space (APS) of retroperitoneum ○ Exocrine function: Pancreatic acinar cells secrete pancreatic juice → pancreatic duct → duodenum ○ Endocrine: Pancreatic islet cells (of Langerhans) secrete insulin, glucagon, and other polypeptides → portal venous system

Divisions • Head: Thickest part; lies to right of superior mesenteric artery and vein (SMA, SMV) ○ Attached to "C" loop of duodenum (2nd and 3rd parts) ○ Uncinate process: Head extension, posterior to SMV ○ Bile duct lies along posterior surface of head, joins with pancreatic duct (of Wirsung) to form hepatopancreatic ampulla (of Vater) ○ Main pancreatic and bile ducts empty into major papilla in 2nd portion of duodenum • Neck: Thinnest part; lies anterior to SMA, SMV ○ SMV joins splenic vein behind pancreatic neck to form portal vein • Body: Main part; lies to left of SMA, SMV ○ Splenic vein lies in groove on posterior surface of body ○ Anterior surface is covered with peritoneum forming back surface of omental bursa (lesser sac) • Tail: Lies between layers of splenorenal ligament in splenic hilum

Internal Structures • Pancreatic duct (of Wirsung) runs length of pancreas, turning inferiorly through head to join bile duct • Accessory pancreatic duct (of Santorini) opens into duodenum at minor duodenal papilla ○ Usually communicates with main pancreatic duct ○ Variations are common, including dominant accessory duct draining most pancreatic juice • Vessels, nerves, and lymphatics ○ Arteries to head mainly from gastroduodenal artery – Pancreaticoduodenal arcade of vessels around head also supplied by SMA branches ○ Arteries to body and tail from splenic artery ○ Veins are tributaries of SMV and splenic vein → portal vein ○ Autonomic nerves from celiac and superior mesenteric plexus – Parasympathetic stimulation of pancreatic secretion, but pancreatic juice secretion is mostly under hormonal control (secretin, from duodenum) ○ Lymphatics follow blood vessels – Collect in splenic, celiac, superior mesenteric and hepatic nodes

IMAGING ANATOMY Overview • Pancreas can be localized on ultrasound by ○ Typical parenchymal architecture: Homogeneously isoechoic/hyperechoic echo pattern when compared with overlying liver 292

○ Surrounding anatomical landmarks: Body anterior to splenic vein; neck anterior to SMA/SMV • Variations in reflectivity related to degree of fatty infiltration; uncinate process and posterior pancreatic head are relatively echo-poor in 25% of subjects (lack of intraparenchymal fat)

ANATOMY IMAGING ISSUES Imaging Recommendations • Use 2- to 5-MHz transducers, or up to 9 MHz for smaller patients • Techniques to combat overlying stomach and bowel gas include ○ Displacement of intervening bowel gas by gentle graded compression with transducer ○ Overnight fasting or fasting > 6-8 hours ○ Noneffervescent fluid can be given orally to fill gastric fundus – Scanning delayed for few minutes to allow fluid to settle – Patient can lie on left side to allow imaging of body and tail of pancreas – Patient can then be turned right to allow gastric fluid to flow to stomach antrum and duodenum, allowing imaging of head and uncinate process • CT is preferred imaging modality for imaging of pancreas • MRCP (± secretin) or ERCP useful for defining pancreatic duct

Imaging Pitfalls • Ultrasound examination of pancreas is often limited by overlying bowel gas

Key Concepts • Shape, size, and texture of pancreas are quite variable ○ Largest in young adults ○ Atrophy and fatty infiltration with age (> 70), obesity, diabetes, corticosteroids, Cushing disease ○ Pancreatic duct also becomes more prominent with age (normal < 3 mm diameter) ○ Focal bulge or mass effect is abnormal • Location behind lesser sac ○ Acute pancreatitis often results in lesser sac fluid (may mimic pseudocyst) • Pancreas lies in APS ○ Inflammation (from pancreatitis) easily spreads to duodenum and descending colon; also lie in APS ○ Inflammation easily spreads into mesentery and mesocolon; roots of these lie just ventral to pancreas • Obstruction of pancreatic duct ○ Relatively common result of chronic pancreatitis (fibrosis &/or stone occluding pancreatic duct), or pancreatic ductal carcinoma • Acute pancreatitis ○ Relatively common result of gallstone (lodged in hepatopancreatic ampulla causing bile to reflux into pancreas) or damage from alcohol abuse

Pancreas Abdomen

PANCREAS IN SITU

Stomach (cut & removed)

Spleen Superior (dorsal) pancreatic a. Gastroduodenal a. Splenic a.

Great pancreatic a. Posterior superior pancreaticoduodenal a. Anterior superior pancreaticoduodenal a.

Transverse colon

Duodenojejunal junction Base of transverse mesocolon

Duodenum

Superior mesenteric a. & v. Base of small bowel mesentery

Graphic shows the arterial supply to the body & tail of the pancreas through terminal branches of the splenic artery, which are variable in number and size. The 2 largest are usually the dorsal (superior) and great pancreatic arteries, which arise from the proximal and distal splenic artery, respectively. The arteries to the pancreatic head and duodenum come from the pancreaticoduodenal arcades that receive flow from the celiac and superior mesenteric arteries. The superior mesenteric vessels pass behind the neck of the pancreas and in front of the 3rd portion of the duodenum. The root of the transverse mesocolon and small bowel mesentery arise from the surface of the pancreas and transmit the blood vessels to the small bowel and transverse colon. The splenic vein runs along the dorsal surface of the pancreas. The splenic vessels and pancreatic tail insert into the splenic hilum.

293

Abdomen

Pancreas PANCREAS, TRANSVERSE VIEW

Body of pancreas

Tail of pancreas Head of pancreas Splenic v. Gallbladder Superior mesenteric a. Inferior vena cava

Aorta

Stomach (with fluid)

Body of pancreas Head of pancreas Inferior vena cava Aorta

Superior mesenteric a. Splenic v. Tail of pancreas

Left renal a.

Left lobe of liver Body of pancreas Head of pancreas

Superior mesenteric a.

Inferior vena cava

Tail of pancreas

Uncinate process Abdominal aorta

Splenic v. Left kidney

(Top) Transverse transabdominal grayscale ultrasound at the epigastrium is shown. Anatomically, the pancreatic axis from head to tail is directed superiorly and to the left. This lower transverse section demonstrates the bulk of the pancreatic head. (Middle) Transverse transabdominal grayscale ultrasound at the epigastrium is shown, slightly higher than the previous image. Note that the pancreatic body and tail have now come into view. (Bottom) Oblique transabdominal grayscale ultrasound at the epigastrium is shown. The transducer is tilted slightly cranially and laterally to the left to follow the pancreatic axis, thus imaging the pancreas in its entirety. The splenic vein courses along the posterior pancreas and provides an excellent landmark in locating the pancreas. The superior mesenteric artery is more posteriorly located and has a characteristic dot shape as it is imaged end-on.

294

Pancreas Abdomen

PANCREAS, TRANSVERSE VIEW, CT

Portal splenic confluence Common bile duct

Body of pancreas

Head of pancreas Tail of pancreas Inferior vena cava

Splenic v. Superior mesenteric a.

Right kidney

Aorta Left kidney

Head of pancreas

Neck of pancreas

Common bile duct Body of pancreas Portal splenic confluence

Splenic v.

Inferior vena cava Tail of pancreas Aorta Left kidney Right kidney

Gastroduodenal a. Head of pancreas Uncinate process Inferior vena cava

Spleen

Gastric antrum Body of pancreas Superior mesenteric a. Tail of pancreas

Right renal a. Aorta

Splenic v.

Left kidney

(Top) Correlative transverse CECT of the pancreas is shown at the level of the origin of the superior mesenteric artery. Note the common bile duct within the pancreatic head before it exits into the duodenum. (Middle) Correlative transverse CECT of the pancreas shows the course of the pancreatic tail, which goes posteriorly and forms close relations with the left kidney and spleen. (Bottom) Correlative oblique CECT follows the pancreatic axis and demonstrates its head, body, and tail. The splenic vein courses along the posterior pancreas, following its contour. The anteriorly located stomach may be distended with fluid and used as an acoustic window during ultrasound.

295

Abdomen

Pancreas PANCREATIC ARTERIAL ANATOMY

Celiac a.

Splenic a. Hepatic a.

Gastroduodenal a. Caudal pancreatic a. Anterior superior pancreaticoduodenal a. Posterior superior pancreaticoduodenal a.

Magna pancreatic a.

Dorsal pancreatic a.

Posterior inferior pancreaticoduodenal a. Transverse pancreatic a. Anterior inferior pancreaticoduodenal a. Superior mesenteric a.

Graphic demonstrates the arterial supply to the pancreas. The pancreatic head is primarily supplied by the anterior and posterior pancreaticoduodenal arcades, including anterior and posterior superior pancreaticoduodenal arteries arising from the gastroduodenal artery and anterior and posterior inferior pancreaticoduodenal arteries arising from the superior mesenteric artery (SMA). The blood supply to the body and tail segments is primarily via the splenic artery with the 2 biggest branches, including the dorsal pancreatic artery and the pancreatic great (magna) artery, which arise from proximal and midportions of the splenic artery, respectively.

296

Pancreas Abdomen

PANCREAS VASCULATURE, TRANSVERSE VIEW

Splenic v. Splenic a.

Inferior vena cava

Pancreatic body Superior mesenteric a. Left renal v.

Aorta

Splenic v. Splenic a. Left renal v. Inferior vena cava

Superior mesenteric a. Left renal v. Aorta

Superior mesenteric a. Inferior vena cava Splenic v. Aorta Left renal a.

(Top) Transverse subxiphoid grayscale ultrasound shows the left renal vein coursing posterior to the pancreatic body, superior mesenteric artery, and splenic vein. Two segments of the tortuous splenic artery are visible in cross section anteriorly. (Middle) Transverse color Doppler ultrasound is shown at the same level. There is a small amount of caudal tilt so that the SMA is blue, away from the transducer, and the IVC is mostly red, toward the transducer. The splenic and left renal veins on the right side of the image are toward the transducer (red) then switch to blue as they travel away from the transducer toward the SMV and IVC, respectively. Note the mixing in the IVC secondary to the left renal vein inflow. The splenic artery is tortuous and the 2 visible segments flow opposite directions. (Bottom) Transverse subxiphoid ultrasound in a different patient is shown using color power Doppler. This is more sensitive for detecting vascular flow but fails to provide information on flow direction, although some newer ultrasound machines support directional color power Doppler.

297

Abdomen

Pancreas PANCREAS, SAGITTAL VIEW

Right rectus m.

Gas within duodenum

Head of pancreas

Inferior vena cava Right psoas m.

Air within gastroduodenal region

Neck of pancreas Left lobe of liver

Superior mesenteric v.

Inferior vena cava

Neck of pancreas

Left lobe of liver Celiac trunk

Superior mesenteric v. Superior mesenteric a.

Abdominal aorta

(Top) Longitudinal transabdominal grayscale ultrasound at the epigastrium, right paramedian region, is shown. Note the relationship of the pancreatic head with the posteriorly located inferior vena cava. (Middle) Longitudinal transabdominal grayscale ultrasound at the epigastrium, right paramedian region, is shown continuing medially from the previous image. Note the superior mesenteric vein coming into view; this is a good landmark for locating the neck of the pancreas on sagittal ultrasound. (Bottom) Longitudinal transabdominal grayscale ultrasound at the epigastrium, right paramedian region, is shown slightly more medial to the previous image. The origin of the superior mesenteric artery arising from the abdominal aorta is brought into view. The SMA is also a useful marker for identifying the neck of the pancreas on sagittal ultrasound.

298

Pancreas

Left lobe of liver Superior mesenteric v.

Abdomen

PANCREAS, SAGITTAL VIEW

Neck of pancreas Splenic v.

Abdominal aorta Superior mesenteric a.

Stomach (with fluid)

Left adrenal gland

Body of pancreas Splenic v. Splenic a. Left renal v.

Left renal a.

Spleen Splenic a.

Tail of pancreas Splenic v.

Left kidney

(Top) Longitudinal oblique transabdominal grayscale ultrasound at the midline epigastrium is shown, revealing the SMA that has taken off from the abdominal aorta, its relationship with the splenic vein, and the anteriorly located pancreatic neck. The inferior mesenteric vein joins the splenic vein here. (Middle) Longitudinal transabdominal grayscale ultrasound at the epigastrium, left paramedian region, is shown by sweeping the transducer laterally from the top image. The body of the pancreas lies to the left of the SMA (not shown). The stomach lies superiorly and may be filled with fluid for use as an acoustic window. The splenic vein maintains its course behind the pancreas. (Bottom) Longitudinal transabdominal grayscale ultrasound at the epigastrium is shown, continuing the scan laterally from the middle image. The pancreatic tail is identified between the spleen and the left kidney.

299

Abdomen

Pancreas PANCREATIC DUCT VARIATIONS

Accessory duct (of Santorini) Minor papilla Major papilla Double accessory duct Main duct (of Wirsung)

Absence of accessory duct

Pancreas divisum (no communication between ducts)

Tortuous pancreatic duct

Double duct of Wirsung

Double crossing of ducts

Crossing of ducts

The accessory duct (of Santorini) originates with the dorsal pancreatic anlage, which is the larger bud from the embryologic foregut, comprising the pancreatic body and tail. The main duct (of Wirsung) originates with the ventral, smaller, anlage that develops into the pancreatic head and uncinate process. Usually, the main and accessory pancreatic ducts fuse, and the main duct becomes the primary conduit for drainage of secretions into the duodenum. The pancreatic duct courses through the center of the gland and is joined by tributaries that enter it at right angles. In the head, the duct turns caudally and dorsally and runs parallel to the common bile duct before joining it at the ampulla of Vater and entering the major papilla. The accessory duct usually enters the duodenum more proximally through the minor papilla.

300

Pancreas Abdomen

ANNULAR PANCREAS

Duodenum (dilated proximally)

Duct of Wirsung (pancreatic head)

Superior mesenteric v.

Annular pancreas

Superior mesenteric a. Aorta

Inferior vena cava

2nd segment of duodenum

Left lobe of liver

2nd segment of duodenum Superior mesenteric v.

Head of pancreas

(Top) Graphic shows annular pancreas in which there is abnormal rotation and fusion of the ventral and dorsal pancreatic anlage resulting in a circumferential mass of pancreatic tissue that encircles and narrows the duodenum. The duct draining the pancreatic head encircles the 2nd portion of the duodenum. This condition may remain asymptomatic or may result in obstruction of the duodenum, often in neonates. (Middle) Axial CECT shows the 2nd portion of duodenum completely encircled by pancreatic tissue, consistent with an annular pancreas. (Bottom) Transverse transabdominal grayscale ultrasound at the midline epigastrium, angled slightly caudally through the liver, shows the descending segment of the duodenum coursing through the pancreatic head in this patient with annular pancreas.

301

Abdomen

Kidneys

GROSS ANATOMY Overview • Kidneys are paired, bean-shaped, retroperitoneal organs ○ Function: – Removal of excess water, salts, and wastes of protein metabolism from blood – Regulation of water and electrolyte balance – Secretion of hormones which control blood pressure, bone and blood production

• •

Anatomic Relationships • Located in retroperitoneum, within perirenal space, surrounded by renal fascia (of Gerota) • Each adult kidney is ~ 9-14 cm in length, 5 cm in width, 3 cm in thickness • Both kidneys lie on quadratus lumborum muscles, lateral to psoas muscles, between T12-L3

•

Internal Structures • Kidneys are hollow centrally with renal sinus occupied by fat, renal pelvis, calyces, vessels, and nerves • Renal hilum: concavity where artery enters and vein and ureter leave renal sinus • Renal pelvis: Funnel-shaped expansion of upper end of ureter ○ Receives major calyces (infundibula) (2 or 3), each of which receives minor calyces (2-4) • Renal papilla: Pointed apex of renal pyramid of collecting tubules that excrete urine ○ Each papilla indents a minor calyx ○ 7-10 papilla per kidney • Renal cortex: Outer part, contains renal corpuscles (glomeruli, vessels), proximal portions of collecting tubules and loop of Henle • Renal medulla: Inner part, contains renal pyramids, distal parts of collecting tubules, and loops of Henle • Vessels, nerves, and lymphatics ○ Artery – Usually 1 for each kidney – Arise from aorta at about L1-L2 vertebral level ○ Vein – Usually 1 for each kidney – Lies in front of renal artery and renal pelvis ○ Nerves – Autonomic from renal and aorticorenal ganglia and plexus ○ Lymphatics – To lumbar (aortic and caval) nodes

IMAGING ANATOMY Overview • Well-defined retroperitoneal bean-shaped structures, which move with respiration

Internal Contents • Renal capsule ○ Normal kidneys are well-defined due to presence of renal capsule and are less reflective than surrounding fat • Renal cortex 302

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○ Renal cortex has reflectivity that is less than adjacent liver or spleen ○ If renal cortex brighter than normal liver (hyperechoic), high suspicion of renal parenchymal disease Medullary pyramids ○ Medullary pyramids are less reflective than renal cortex Corticomedullary differentiation ○ Margin between cortex and pyramids is usually welldefined in normal kidneys ○ Margin between cortex and pyramids may be lost in presence of generalized parenchymal inflammation or edema Renal sinus ○ Echogenic due to the fat that surrounds blood vessels and collecting systems ○ Outline of renal sinus is variable, from smooth to irregular ○ Renal sinus fat may increase in obesity, steroid use, and sinus lipomatosis ○ Renal sinus fat may decrease in cachectic patients and neonates ○ If sinus echoes are indistinct in noncachectic patient, tumor infiltration or edema should be considered Collecting system (renal pelvis and calyces) ○ Not usually visible in dehydrated patient ○ May be seen as physiological "splitting" of renal sinus echoes in patients with a full bladder undergoing diuresis ○ Physiological "splitting" of renal sinus echoes is common in pregnancy – Causes of dilatation of pelvicalyceal system include mechanical obstruction by enlarging uterus, hormonal factors, increased blood flow, and parenchymal hypertrophy – May occur as early as 12 weeks into pregnancy – Seen in up to 75% of right kidneys at 20 weeks into pregnancy, less common on left side, thought to be due to cushioning of ureter from gravid uterus by sigmoid colon – Obvious dilatation of pelvicalyceal system can be seen in 2/3 of patients at 36 weeks – Changes usually resolve within 48 hours after delivery ○ Possible obstruction can be excluded by performing post micturition images of collecting system and looking for ureteral jets in the bladder with color Doppler – AP diameter of renal pelvis in adults should be < 10 mm Renal arteries ○ Normal caliber 5-8 mm ○ 2/3 of kidneys are supplied by single renal artery arising from aorta ○ 1/3 of kidneys are supplied by 2 or more renal arteries arising from aorta – Main renal artery may be duplicated – Accessory renal arteries may arise from aorta superior or inferior to main renal artery – Accessory renal arteries may enter kidney either in hilum or at poles – Extrahilar accessory renal arteries may arise from ipsilateral renal artery, ipsilateral iliac artery, aorta, or retroperitoneal arteries ○ Spectral Doppler

Kidneys

Size • Bipolar length is found by rotating transducer around its vertical axis such that the longest craniocaudal length can be identified • Normal size between 10-15 cm • Volume measurements ○ May be more accurate, but is time consuming ○ 3D ellipsoidal formula can be used for volume estimation – Length x AP diameter x transverse diameter x 0.5 ○ Consistency and changes in volume over time more important

ANATOMY IMAGING ISSUES Imaging Recommendations • Right kidney ○ Liver used as acoustic window ○ Transducer placed in subcostal or intercostal position ○ Varying degree of respiration is useful ○ Raising patient's right side and scanning laterally/posterolaterally may be useful • Left kidney ○ More difficult to visualize due to bowel gas from small bowel and splenic flexure ○ Usually easier to search for left kidney using posterolateral approach with left side raised ○ Full right lateral decubitus with pillow under right flank and left arm extended above head may be useful in difficult cases

– Spleen can be used as acoustic window for imaging upper pole of left kidney • Posterior approach for both kidneys ○ Useful for interventional procedures such as renal biopsy, nephrostomy ○ Use bolster or pillow under the patient's abdomen to decrease lordosis ○ Image quality may be impaired by thick paraspinal muscles and ribs shadowing • Renal arteries ○ Origins best seen from midline anterior approach ○ Right renal artery can usually be followed from origin to kidney ○ Left renal artery often requires posterolateral coronal transducer scanning position for visualization • Renal veins ○ Best seen on transverse scan from anterior approach ○ May also be seen on coronal scan from posterolateral coronal

Abdomen

– Open systolic window, rapid systolic upstroke occasionally followed by secondary slower rise to peak systole with subsequent diastolic delay but persistent forward flow in diastole – Continuous diastolic flow is present due to low resistance in renal vascular bed – Low resistance flow pattern is also present in intrarenal branches – Normal peak systolic velocity (PSV) 75-125 cm/s, not more than 180 cm/s □ > 200 cm/s is abnormal – Resistive index (RI) is (peak systolic velocity - end diastolic velocity)/peak systolic velocity; normal < 0.7 – Pulsatility index (PI) is (peak systolic velocity - end diastole velocity)/mean velocity, normal < 1.8 • Renal veins ○ Normal caliber 4-9 mm ○ Formed from tributaries that coalesce at renal hilum ○ Right renal vein is relatively short and drains directly into IVC ○ Left renal vein receives left adrenal vein from above and left gonadal vein from below ○ Left renal vein crosses midline between aorta and superior mesenteric artery ○ Spectral Doppler – Normal PSV 18-33 cm/s – Spectral Doppler in right renal vein mirrors pulsatility in IVC – Spectral Doppler in left renal vein may show only slight variability of velocities consequent upon cardiac and respiratory activity

Key Concepts • Accessory renal vessels ○ Accurate diagnosis necessary when planning surgery (e.g., resection, transplantation) ○ Due to limitations of ultrasound, CT Arteriography, magnetic resonance angiography or digital subtraction angiography are more sensitive and accurate • Normal variants may mimic disease ○ Dromedary hump and hypertrophied column of Bertin may be mistaken for renal tumors • Congenital anomalies very common ○ Leading cause of renal failure in children ○ Early diagnosis important

EMBRYOLOGY Embryologic Events • Congenital structural anomalies include abnormal renal number, position, structure and vessels ○ Abnormal number: absence of one or both kidneys; supernumerary kidney ○ Abnormal position: pelvic kidney, crossed fused renal ectopia, malrotation, ptosis ○ Abnormal structure: – Duplication: results from lack of fusion and commonly produces an enlarged kidney with 2 separate hila and pelvicalyceal systems, these may join or continue as 2 ureters □ Ureters may be completely separate until they join the bladder or join proximal to the bladder □ "Duplex kidney": Bifid renal pelvis with single ureter – Hypertrophied column of Bertin (lobar dysmorphism; Fetal lobulation; Hilar lip – Pelviureteric junction obstruction ○ Often accompanied by anomalies of other systems ○ VATER acronym: Vertebral, anorectal, tracheoesophageal, radial ray, renal anomalies

303

Abdomen

Kidneys RENAL FASCIA AND PERIRENAL SPACE

Anterior renal fascia

Lateroconal fascia Psoas (major) m.

Posterior renal fascia

Quadratus lumborum m.

Latissimus dorsi m.

Erector spinae mm.

Liver

Adrenal gland Anterior renal fascia

Posterior renal fascia Hepatorenal fossa (Morison pouch) Peritoneum Iliac crest Transverse colon

(Top) The anterior and posterior layers of the renal fascia envelop the kidneys and adrenals along with the perirenal fat. Medial to the kidneys, the course of the renal fascia is variable (and controversial). The posterior layer usually fuses with the psoas or quadratus lumborum fascia. The perirenal spaces do not communicate across the abdominal midline. However, the renal and lateroconal fasciae are laminated structures that may be distended with fluid collections to form interfascial planes that do communicate across the midline and also inferiorly to the extraperitoneal pelvis. (Bottom) Sagittal section through the right kidney shows the renal fascia enveloping the kidney and adrenal gland. Inferiorly, the anterior and posterior renal fasciae come close together at about the level of the iliac crest. Note the adjacent peritoneal recesses.

304

Kidneys Abdomen

KIDNEYS IN SITU

Inferior phrenic vessels

Right adrenal v. Left inferior adrenal vessels Renal vv.

Left gonadal v. Right gonadal v.

Superior mesenteric a.

Gonadal aa.

Inferior mesenteric a.

Renal a. Renal v. Renal pelvis

Capsule (incised & peeled back)

(Top) The kidneys are retroperitoneal organs that lie lateral to the psoas, on the quadratus lumborum muscles. The oblique course of the psoas muscles results in the lower pole of the kidney lying lateral to the upper pole. The right kidney usually lies 1-2 cm lower than the left, due to inferior displacement by the liver. The adrenal glands lie above and medial to the kidneys, separated by a layer of fat and connective tissue. The peritoneum covers much of the anterior surface of the kidneys. The right kidney abuts the liver and the hepatic flexure of the colon and duodenum, while the left kidney is in close contact with the pancreas (tail), spleen, and splenic flexure. (Bottom) The fibrous capsule is stripped off with difficulty. Subcapsular hematomas do not spread far along the surface of the kidney, but compress the renal parenchyma, unlike most perirenal collections.

305

Abdomen

Kidneys RENAL ARTERY

Adrenal

Arcuate aa.

Interlobar aa. Cortical column (of Bertin)

Interlobular aa. Inferior adrenal a.

Superior segmental a.

Anterior superior segmental a.

Posterior segmental a.

Renal a.

Anterior inferior segmental a.

Inferior segmental a. Renal pyramid

Pelvic & ureteric branches

Renal papilla

Renal cortex

The kidney is usually supplied by a single renal artery, the 1st branch of which is the inferior adrenal artery. It then divides into 5 segmental arteries, only 1 of which (the posterior segmental artery) passes dorsal to the renal pelvis. The segmental arteries divide into the interlobar arteries that lie in the renal sinus fat. Each interlobar artery branches into 4-6 arcuate arteries that follow the convex outer margin of each renal pyramid. The arcuate arteries give rise to the interlobular arteries that lie within the renal cortex, including the cortical columns (of Bertin) that invaginate between the renal pyramids. The interlobular arteries supply the afferent arterioles to the glomeruli. The arterial supply to the kidney is vulnerable, as there are no effective anastomoses between the segmental branches, each of which supplies a wedge-shaped segment of parenchyma.

306

Kidneys Abdomen

RENAL ARTERY VARIANTS

Aberrant upper polar a.

Aberrant lower polar a.

Splenic v.

Inferior vena cava Anterior right renal a.

Superior mesenteric a. Aorta

Posterior right renal a. Vertebral body

Aorta

Superior right renal a. with pre-hilar branching

Superior mesenteric a.

Inferior right renal a.

Contrast in renal pelvis

(Top) Graphic depicts supernumerary renal arteries arising directly from the aorta. Some of these enter the kidney at locations other than the renal hilum, close to the renal poles. These "polar" or "extrahilar" arteries may be ligated or transected unintentionally during renal or other surgeries. These are sometimes referred to as "accessory" renal arteries, but each is an end artery and the sole arterial supply to a substantial portion of the renal parenchyma. (Middle) Transverse ultrasound shows 2 right renal arteries running posterior to the Inferior vena cava. (Bottom) Combined arterial/excretory phase CT in a potential renal donor shows 2 right renal arteries. Their origins are relatively far apart, which is a factor limiting the sensitivity of ultrasound for multiple renal arteries.

307

Abdomen

Kidneys RENAL VEIN VARIANTS

Supernumerary renal vv.

Right gonadal vessels

Conventional preaortic renal v.

Retroaortic renal v.

Pancreas IVC Aorta

Vertebral body

Left retroaortic renal v.

(Top) Persistence of the collar of veins on the right results in supernumerary right renal veins that encircle the renal pelvis. (Middle) Anomalies of the renal veins are less common than those of the arteries but are encountered in clinical practice and may have important implications. All anomalies are variations of the embryologic development and persistence of portions of the paired longitudinal channels, the subcardinal and supracardinal veins, which form a ladder-like collar around the aorta. Normally, only the anterior components persist, becoming the renal veins, which course anterior to the aorta. Persistence of the whole collar results in a circumaortic renal vein, which is depicted in this graphic. This anomaly is more common than an isolated retroaortic renal vein. (Bottom) Transverse oblique ultrasound shows an incidental retroaortic left renal vein.

308

Kidneys Abdomen

RENAL VEIN VARIANTS

Right renal a. Left renal a. Right renal v. IVC

Left renal v. running posterior to aorta

Left-sided inferior vena cava (empties into left renal v.)

Right renal a.

Retroperitoneal adenopathy Right IVC Left IVC

(Top) The left renal vein is retrocaval. (Middle) Persistence of the left supracardinal vein below the kidney results in a "duplicated" inferior vena cava. (Bottom) Incidental finding of a duplicated vena cava is shown in a patient with mixed germ cell tumor and retroperitoneal adenopathy.

309

Abdomen

Kidneys CT UROGRAM

Minor calyces 12th rib Major calyces Renal pyramids

Ureter

Renal pelvis

Urinary bladder

Right renal pelvis

Low-lying left kidney with malrotation

(Top) Volumetric multidetector CT can be viewed as a surface-rendered 3D image to simulate an excretory urogram. Postprocessing includes multiplanar reformation with window leveling, bone subtraction, and arbitrary color maps. Here, opacified urine is displayed as white. Less dense urine within the renal tubules in the pyramids and the diluted urine within the bladder are displayed as red. The CT scan was obtained in suspended inspiration, resulting in caudal displacement of the kidneys. In the supine position at quiet breathing, the upper poles of the kidneys usually lie in front of the 12th ribs. (Bottom) Coronal maximum-intensity projection obtained during a CT urogram shows a congenital low-lying left kidney. Both kidneys are malrotated with the renal pelves directed anteriorly.

310

Kidneys Abdomen

RIGHT KIDNEY, ANTERIOR ABDOMEN SCAN

Right lobe of liver

Renal vascular pedicle

Psoas m. Vertebral bodies

Oblique mm.

Right lobe of liver

Renal sinus

Medullary pyramid

Psoas m.

Right lobe of liver Medullary pyramids

Right psoas m.

Vertebral body

(Top) Longitudinal oblique grayscale ultrasound shows the right kidney using the liver as an acoustic window with the probe angled medially toward the renal hilum and vascular pedicle. (Middle) Longitudinal grayscale ultrasound shows the right kidney using the liver as an acoustic window. This approach usually provides excellent visualization of the right kidney and is useful for measuring bipolar renal length. (Bottom) Longitudinal oblique grayscale ultrasound of the right kidney using the liver as an acoustic window, obtained with more lateral angulation (when compared with the previous 2 images), cuts through the renal parenchyma on the lateral aspect of the right kidney. Note that the echogenic sinus is not demonstrated.

311

Abdomen

Kidneys RIGHT KIDNEY, CT CORRELATION

Right lobe of liver Right hemidiaphragm

Gallbladder Renal cortex Renal medullary pyramids

Right lobe of liver

Portal v. Right kidney with fetal lobulation Right main renal v.

Perinephric fat Right psoas m.

Right lobe of liver

Right hemidiaphragm

Right portal v.

Duodenum

Right kidney with fetal lobulations

(Top) Correlative longitudinal CT multiplanar reconstruction of the right kidney is shown. Real-time ultrasound can be performed in any plane; thin-slice CT is acquired in the axial plane and then reconstructed in other planes. These images have been reconstructed to mirror the planes used in ultrasound. CT is typically performed with intravenous contrast and acquired at different time points to image the renal vessels, cortex, medulla, and collecting system. (Middle) Correlative longitudinal oblique CT multiplanar reconstruction of the right kidney cutting through the right renal vein is shown. The plane of this image is angulated more medially when compared with the previous image. (Bottom) Correlative longitudinal oblique CT multiplanar reconstruction of the right kidney through the right portal vein is shown. This plane is angled more laterally when compared with the previous 2 images.

312

Kidneys Abdomen

RIGHT KIDNEY, ANTERIOR ABDOMEN SCAN

Rectus m.

Right lobe of liver

Gallbladder

Duodenum

Inferior vena cava Right kidney

Aorta

Psoas m.

Rectus m. Oblique mm. Right lobe of liver

Bowel Right renal v.

Right kidney

Subcutaneous fat Oblique mm.

Rectus m. Renal sinus Right kidney

Psoas m.

(Top) Transverse grayscale ultrasound of the upper pole of the right kidney is shown. (Middle) Transverse grayscale ultrasound of the mid pole of the right kidney shows the renal hilum with the renal vein. Note that the pelvicalyceal system within the renal sinus echoes is not usually visible unless dilated. (Bottom) Transverse grayscale ultrasound of the lower pole of the right kidney is shown. The renal parenchymal echogenicity is less than the adjacent liver or spleen. If the renal parenchyma is brighter than normal liver, renal parenchymal disease should be suspected.

313

Abdomen

Kidneys RIGHT KIDNEY, CT CORRELATION

Pancreas Hepatic a. Right portal v.

Inferior vena cava Right adrenal

Superior mesenteric a. Aorta Vertebral body Spinal canal

Right kidney

Right lobe of liver Inferior vena cava Right renal v. Right kidney

Left renal v. Right psoas m.

Inferior vena cava Superior mesenteric a. Ascending colon Right lobe of liver

Aorta Vertebral body

Right kidney

Right psoas m. Quadratus lumborum

(Top) 1st in a series of 3 correlative transverse CT images shows the right kidney from the upper pole to the lower pole. These are planes commonly used when performing ultrasound. This image shows the upper pole of the right kidney. (Middle) Transverse CT at the level of the mid pole of the right kidney shows the renal hilum with the renal vein. The right and left renal veins are opacified, but the vena cava is not yet opacified. (Bottom) Correlative transverse CT shows the lower pole of the right kidney. The psoas and quadratus lumborum are variable in thickness depending on patient gender and level of activity.

314

Kidneys Abdomen

RIGHT KIDNEY, POSTERIOR ABDOMEN SCAN Subcutaneous fat

Renal cortex

Latissimus dorsi m. Renal sinus echoes

Renal medullary pyramids

Subcutaneous fat

Quadratus lumborum m.

Renal v.

Renal cortex

Vena cava

Right renal cortex

Renal sinus

Quadratus lumborum m.

(Top) Longitudinal grayscale ultrasound of the right kidney, scanning from the posterior approach, shows normal medullary pyramids. This approach is useful for intervention, such as renal biopsy or percutaneous nephrostomy, as the kidney is just deep to skin and muscle. This approach is also a good way for standardizing renal length measurements in children. (Middle) Oblique scan through the longitudinal axis shows the right kidney with the patient prone. This approach may be problematic due to the presence of ribs. Deep inspiration may help to bring the kidney down from below the ribs. (Bottom) Longitudinal view shows the lateral right kidney from a posterior approach.

315

Abdomen

Kidneys RIGHT KIDNEY, POSTERIOR ABDOMEN SCAN

Rib shadowing

Right erector spinae m. Right psoas m.

Right kidney

Vertebral body

Right erector spinae m. Right quadratus lumborum Right psoas m.

Right kidney

Vertebral body Renal hilum

Right erector spinae m.

Right quadratus lumborum Right psoas m.

Subcutaneous fat Lower pole of right kidney

Vertebral body

(Top) Transverse grayscale ultrasound of the right kidney, scanning from the posterior approach, is shown. Scanning through the posterior approach is useful while performing interventional procedures, such as nephrostomy or renal biopsy. However, visualization/image quality may be impaired by thick paraspinal muscles and rib shadowing. This image shows the upper pole of the right kidney. (Middle) Transverse grayscale ultrasound from the posterior approach shows the mid pole of the right kidney. (Bottom) Transverse grayscale ultrasound from the posterior approach shows the lower pole of the right kidney.

316

Kidneys Abdomen

RIGHT MAIN RENAL ARTERY AND VEIN

Right lobe of liver

Right renal mid pole Right rectus abdominis m. Right renal a.

Right renal v.

Inferior vena cava Right renal a.

Gallbladder Right renal v.

Right renal a. Inferior vena cava Aorta

Continuous forward systolic flow

Right renal a.

Continuous forward diastolic flow

Right renal v.

Undulating renal venous waveform

(Top) Transverse color Doppler ultrasound shows the right renal hilum. Note that the right renal artery lies posterior to the renal vein and inferior vena cava. The renal artery normally measures 5-8 mm in caliber. (Middle) In this spectral Doppler waveform of the right renal artery, note the low-resistance renal waveform with continuous forward systolic and diastolic flow. Normal PSV ranges from 60140 cm/sec; not > 180 cm/sec. Normal resistivity index is < 0.7 and normal pulsatility index is < 1.8. Note the artifactual absence of color signal in the aorta and vena cava secondary to Doppler angle. (Bottom) Spectral Doppler waveform of the right renal vein is shown, which usually mirrors the pulsatility in the inferior vena cava. The renal vein normally measures 4-9 mm in caliber. Normal PSV ranges from 18-33 cm/sec.

317

Abdomen

Kidneys RIGHT INTRARENAL ARTERY AND VEIN

Intrarenal vv. Segmental renal aa, Renal cortex Main renal v.

Intrarenal renal a.

Segmental renal v. Continuous antegrade arterial flow Renal venous waveform with mild phasic variation

Segmental renal v. Arterial pulse included by Doppler gate Segmental renal v. spectral Doppler waveform with phasic variation

(Top) Longitudinal color Doppler ultrasound of the right kidney shows renal artery branches as red and renal vein branches as blue. However, as color Doppler colors can be changed by the operator, it is important to look at the color scale bar (not included). (Middle) In this spectral Doppler waveform of a right segmental renal artery branch, note the low-resistance arterial Doppler waveform with continuous diastolic flow, similar to that seen in the more proximal renal artery. The venous waveform shows minimal phasicity. (Bottom) In this spectral Doppler waveform of a right segmental renal vein branch, note the phasic variation in the renal vein, which can vary depending on systemic venous pressure and cardiac and fluid status.

318

Kidneys Abdomen

LEFT KIDNEY, POSTERIOR SCAN

Subcutaneous fat

Perinephric fat

Left latissimus dorsi m. Medullary pyramids Renal cortex

Renal sinus

Rib shadow

Renal cortex Medullary pyramids Renal v.

Latissimus dorsi Rib shadow

Renal vascular pedicle

(Top) Longitudinal grayscale ultrasound of the left kidney, scanning from the posterolateral approach, is shown. This approach avoids interference from bowel gas shadowing. However, the ribs and lung base may degrade the image. Deep inspiration can decrease artifact from ribs and lung base. Note the regular distribution of the renal medullary pyramids. (Middle) Longitudinal grayscale ultrasound shows the left kidney, scanning from the posterolateral approach, with the transducer angling more posteriorly when compared with the previous image. Note shadowing from rib degrading imaging of the upper pole. (Bottom) Longitudinal grayscale ultrasound shows the left kidney, scanning from the posterolateral approach, with the transducer angling more anteriorly when compared with the previous 2 images. The renal sinus is no longer in the field of view.

319

Abdomen

Kidneys LEFT KIDNEY, CT CORRELATION

Left renal v. Spleen

Renal hilum Left kidney Superior mesenteric v.

Left psoas m.

Left hemidiaphragm Aorta

Spleen

Left kidney

Vertebral bodies

Left psoas m.

Stomach Splenic a.

Superior mesenteric v.

Spleen

Left kidney

Superior mesenteric a.

Gas in descending colon Bowel loops

(Top) The 1st in a series of 3 correlative longitudinal oblique multiplanar reconstruction CT images of the left kidney, through planes commonly used when examining the patient with ultrasound, shows clear visualization of the kidney, renal pedicle, and surrounding structures. This makes multidetector row CT the imaging modality of choice (over ultrasound) for evaluation of renal vascular anatomy and pathology. (Middle) Correlative longitudinal oblique multiplanar reconstruction CT shows the left kidney in a plane more posterior to the previous image. (Bottom) Correlative longitudinal oblique multiplanar reconstruction CT shows the left kidney in a plane more anterior than the previous 2 images. Note that ultrasound has a much more limited field of view compared to CT using this approach.

320

Kidneys Abdomen

LEFT KIDNEY, POSTERIOR TO POSTEROLATERAL ABDOMEN SCAN

Shadowing from ribs

Upper pole of left kidney Spleen

Rib shadow

Left quadratus lumborum m. Left psoas m. Mid pole of left kidney Rib shadow

Lower pole of left kidney

Renal sinus echoes

Erector spinae mm. Left quadratus lumborum m. Left psoas m. Vertebral body

Aorta

(Top) Transverse ultrasound of the left upper kidney shows that ribs often interfere with good visualization of the upper kidney regardless of the approach. (Middle) Transverse grayscale ultrasound of the mid pole of the left kidney, using the posterior lateral approach, shows persistent degradation by rib shadows. Deep inspiration will move the kidney away from the lower ribs and improve image quality. (Bottom) Transverse ultrasound of the lower pole of the left kidney, using the posterior approach with the patient prone, decreases interference from ribs. There is a suitable window for nontargeted renal biopsy.

321

Abdomen

Kidneys LEFT KIDNEY, ANTERIOR TO ANTEROLATERAL TRANSVERSE SCAN

Shadowing from rib Costal cartilage Spleen Splenic vessels Left renal upper pole

Rib shadow

Spleen

Left kidney

Abdominal wall mm.

Renal cortex

Left psoas m.

Vertebral body

(Top) Transverse grayscale ultrasound shows the upper pole of the left kidney using the anterolateral approach. Note the proximity of the kidney to the spleen and the interfering rib shadows. (Middle) Transverse grayscale ultrasound shows the mid pole of the left kidney using the posterolateral approach. (Bottom) Transverse grayscale ultrasound shows the lower pole of the left kidney using the posterolateral approach.

322

Kidneys Abdomen

LEFT KIDNEY, ANTEROLATERAL APPROACH

Rib shadow

Left kidney

Costal cartilage Sinus echoes

Spleen

Rib shadow

Spleen Left kidney

Oblique abdominal mm.

Artifact from lung Medullary pyramids Left kidney

(Top) Longitudinal grayscale ultrasound shows the upper pole of the left kidney using the anterolateral approach. Note that the spleen may occasionally be used as an acoustic window for the left kidney. (Middle) Longitudinal ultrasound shows the left kidney using the anterolateral approach. (Bottom) Longitudinal grayscale ultrasound shows the left kidney using the anterolateral approach and angling posteriorly. The lung base causes reverberation artifact, which partially obscures the upper pole.

323

Abdomen

Kidneys LEFT KIDNEY, CT CORRELATION

Pancreatic tail

Stomach Colon

Left adrenal

Perinephric fat Left kidney Spleen

Splenic v.

Common bile duct Descending colon

Left renal v. Left kidney

Stomach

Descending colon Left kidney

Quadratus lumborum Left psoas m.

(Top) The 1st in a series of 3 correlative transverse CT images of the left kidney, through planes commonly used when examining the kidney, is shown using the anterior approach. Note the relationship of the spleen to the upper pole of the left kidney, allowing it to be used as an acoustic window, particularly in patients with splenomegaly. This transverse CT shows the upper pole of the left kidney. (Middle) Correlative transverse CT shows the mid pole of the left kidney at the level of the left renal vein. (Bottom) Correlative transverse CT shows the lower pole of the left kidney.

324

Kidneys Abdomen

LEFT MAIN RENAL ARTERY AND VEIN

Left lobe of liver

Splenic v./superior mesenteric v. confluence Superior mesenteric a.

Pancreas Bowel gas

Inferior vena cava

Left renal v.

Right renal a.

Left renal a.

Aorta

Left renal v. Left renal a.

Continuous forward arterial flow

Quadratus lumborum

Left renal v.

Psoas m.

Two renal aa.

(Top) Transverse ultrasound in the anterior midline shows that the left renal artery arises from the anterolateral aorta just around or below the level of the superior mesenteric artery. The normal caliber of the renal artery ranges from 5-8 mm. The left renal vein courses between the aorta and superior mesenteric artery. (Middle) Spectral Doppler waveform of the left renal artery is shown. The normal PSV in the artery ranges from 60-140 cm/sec with a normal resistive index < 0.7 and pulsatility index < 1.8. There is variability in venous velocity consequent upon cardiac and respiratory activity. The renal vein normally measures 4-9 mm in caliber with a PSV of 18-33 cm/sec. (Bottom) Transverse color Doppler waveform of the left renal hilum obtained from a posterior approach is shown. An anterior approach may not be feasible secondary to bowel gas. There are 2 left renal arteries anterior and posterior to the left renal vein.

325

Abdomen

Kidneys LEFT INTRARENAL ARTERY AND VEIN

Renal cortex

Color aliasing Intrarenal segmental aa. Main renal v.

Intrarenal renal a.

Low-resistance renal a. spectral Doppler waveform

Venous waveform

Renal Doppler indices

Segmental renal a. Renal a. spectral Doppler waveform with autotrace

(Top) Longitudinal color Doppler ultrasound of the left kidney shows renal artery branches as red and renal vein branches as blue. There is some color aliasing in the veins, shown as yellow. (Middle) In this spectral Doppler waveform of a left segmental renal artery, there is continuous flow throughout the cardiac cycle with a low- resistance pattern. The segmental renal vein shows mild phasicity. (Bottom) Spectral Doppler waveform of a left segmental renal artery in the transverse plane is shown. Doppler indices are normal: PSV of 37.3 cm/s, EDV of 13.9 cm/sec, and resistive index (RI) of 0.63.

326

Kidneys Abdomen

HYPERTROPHIED COLUMN OF BERTIN

Normal cortical column Renal pyramid Hypertrophied column of Bertin

Renal sinus

Hypertrophied column of Bertin

Renal cortex

Column of Bertin

(Top) Graphic depicts a hypertrophied column of Bertin, which is a rounded enlargement of the septal cortical tissue that separates the renal pyramids. This is normal tissue with the same imaging features as other parts of the renal cortex, but it may protrude into the renal sinus fat and may be mistaken for a renal mass. This generally tends to be more of a diagnostic dilemma on ultrasound relative to either CT or MR. (Middle) Longitudinal ultrasound of the right kidney shows an ovoid lesion, isoechoic to cortex, indenting the renal sinus. The patient was asymptomatic. (Bottom) Coronal CECT in the same patient shows that the column of Bertin enhances just like renal cortex. On the delayed phase, the column of Bertin remained isodense to cortex.

327

Abdomen

Kidneys RENAL DUPLICATION

Upper pole hydronephrosis Cortical tissue splitting renal pelvis

Upper pole ureter Lower pole ureter Non dilated lower pole ureter

Dilated tortuous upper pole ureter

Ureterocele

Renal sinus

Cortical tissue dividing renal sinus

Right renal a.

Right superior ureter

Left renal a.

Left superior ureter Left inferior ureter

Right inferior ureter

(Top) Graphic shows bilateral renal duplication. On the right, there are 2 ureters exiting the renal pelvis with fusion in the mid third. On the left, the duplication is complete with the ureter of the superior moiety inserting lower than normal and terminating in a ureterocele. The ureter of the lower pole moiety inserts superior to the upper pole moiety (Weigert-Meyer rule) and is prone to reflux. (Middle) Longitudinal ultrasound through the left kidney shows separation of the renal sinus echo by cortical tissue indicating duplication. (Bottom) Anterior volume-rendered CT angiogram of a potential renal donor is shown. There are duplicated ureters bilaterally, joining near the bladder.

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Kidneys

Superior renal aa.

Abdomen

HORSESHOE KIDNEY

Right kidney Left kidney

Inferior cortical fusion

Inferior renal aa.

Cortical bridge

Right kidney

Left kidney Aorta

Inferior vena cava

Vertebral body

Inferior mesenteric a. Fused lower poles Malrotated renal pelvis Right kidney Left kidney Inferior vena cava Aorta

(Top) Graphic depicts a horseshoe kidney with fusion of the lower poles in the midline. The midline bridge may consist of fibrous or renal tissue. Note the multiple renal arteries bilaterally with inferior arteries arising from the distal aorta or common iliac arteries. The inferior mesenteric artery (not shown) prevents further ascent of the midline bridge. (Middle) Transverse midline ultrasound shows a horseshoe kidney using an anterior approach. There is a bridge of cortical tissue between the 2 moieties. Because horseshoe kidneys are malrotated, pelvic dilation is not uncommon. (Bottom) Arterial phase CECT of a horseshoe kidney shows malrotation with anteriorly directed renal pelves. The inferior mesenteric artery prevents ascent of the kidneys.

329

Abdomen

Adrenal Glands

GROSS ANATOMY Overview • Adrenal (suprarenal) glands are part of both endocrine and nervous systems • Lie within perirenal space, bounded by perirenal (Gerota) fascia • Right adrenal is more apical in location ○ Lies anterolateral to right crus of diaphragm, medial to liver, posterior to inferior vena cava (IVC) ○ Often pyramidal in shape, inverted V shape on transverse section • Left adrenal is more caudal ○ Lies medial to upper pole of left kidney, lateral to left crus of diaphragm, posterior to splenic vein and pancreas ○ Often crescentic in shape, lambda, tricorn hat, or triangular on transverse section • Adrenal cortex ○ Derived from mesoderm ○ Has important endocrine functions ○ Secretes corticosteroids (cortisol, aldosterone) and androgens • Adrenal medulla ○ Derived from neural crest ○ Part of sympathetic nervous system ○ Chromaffin cells secrete catecholamines (mostly epinephrine) into bloodstream

Vessels, Nerves, and Lymphatics • Adrenal gland has very rich vascular and nervous connections • Arteries ○ Superior adrenal arteries: 6-8 from inferior phrenic arteries ○ Middle adrenal artery: 1 from abdominal aorta ○ Inferior adrenal artery: 1 from renal arteries • Veins ○ Right adrenal vein drains into IVC ○ Left adrenal vein drains into left renal vein (usually after joining left inferior phrenic vein) • Nerves ○ Extensive sympathetic connection to adrenal medulla ○ Presynaptic sympathetic fibers from paravertebral ganglia end directly on secretory cells of medulla • Lymphatics drain to lumbar (aortic and caval) nodes

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer: 2-5 MHz for adults ○ High-frequency (7.5- to 10.0-MHz) linear transducer may be used in neonates • Complex shape requires multiplanar evaluation • US may be used for initial screening and detection of adrenal lesions, followed by CT/MR for further characterization • Right adrenal gland ○ Intercostal transverse approach, using liver as acoustic window ○ Direct anterior abdomen scanning is limited by overlying bowel loops and depth to gland 330

• Left adrenal gland ○ Intercostal at midaxillary line, using spleen or left kidney as acoustic window ○ In pediatric subjects and thin adults, direct transabdominal US at epigastrium – Stomach may be distended with fluid to serve as acoustic window • US appearance ○ Relative to body size, adrenal glands are much larger and more easily identified in neonatal population – Also makes them more vulnerable to hemorrhage ○ Cortex is hypoechoic with hyperechoic medulla – Creates ice cream sandwich appearance ○ Adrenal glands often difficult to see and easily overlooked in adult patients (especially if obese), unless specifically targeted

CLINICAL IMPLICATIONS Clinical Importance • Rich blood supply reflects important endocrine function • Adrenal glands are designed to respond to stress (trauma, sepsis, surgery, etc.) by secreting cortisol and epinephrine ○ Overwhelming stress may result in adrenal hemorrhage, acute adrenal insufficiency (addisonian crisis) • Adrenal glands are common site for hematologic metastases (lung, breast, melanoma, etc.) • Adrenal cortex lesions ○ Adrenal adenomas – Very common (at least 2% of general population) but usually cause no symptoms – US appearance is nonspecific; best evaluated by CT and MR sequences that show lipid-rich mass ○ Cushing syndrome (excess cortisol) – Signs: Truncal obesity, hirsutism, hypertension, abdominal striae – Causes: Pituitary tumors (↑ ACTH), exogenous (steroids) > adrenal adenoma > carcinoma ○ Conn syndrome (excess aldosterone) – Signs: Hypertension, hypokalemic alkalosis – Causes: Adrenal adenomas > hyperplasia > carcinoma ○ Addison syndrome (adrenal insufficiency) – Signs: Hypotension, weight loss, altered pigmentation – Causes: Autoimmune > adrenal metastases > adrenal hemorrhage > adrenal infection ○ Myelolipoma – Benign tumor composed of mature adipose tissue and variable amount of hematopoietic elements – Echogenic on US • Adrenal medulla lesions ○ Neuroblastoma – Malignant tumor of sympathetic chain – Most common extracranial solid malignancy in children (median age at diagnosis: 15-17 months) – Location: Adrenal gland > retroperitoneum > posterior mediastinum ○ Pheochromocytoma – Tumor arising from chromaffin cells of adrenal medulla or extraadrenal paraganglia – Location: Adrenal gland (90%), sympathetic chain from neck to bladder (10%)

Adrenal Glands Abdomen

ADRENAL GLANDS

Inferior phrenic a.

Superior adrenal aa.

Right adrenal v. Middle adrenal a. Left inferior phrenic v. Inferior adrenal a.

Left adrenal v.

Left renal a. Left renal v.

Pancreas Splenic v. Right adrenal gland

Diaphragmatic crura

Left adrenal gland

Left kidney

(Top) The size of the adrenal glands is exaggerated in this illustration to facilitate demonstration of the vascular anatomy. The adrenal glands have a very rich vascular supply, reflecting their critical role in maintaining homeostasis and responding to stress. The superior adrenal arteries are short branches of the inferior phrenic arteries bilaterally. The middle adrenal arteries are short vessels arising from the aorta. The inferior adrenal arteries are branches of the renal arteries. The left adrenal vein drains into the left renal vein (usually after joining with the inferior phrenic vein), while the right adrenal vein drains directly into the inferior vena cava (IVC). (Bottom) Graphic shows the right adrenal gland lying above the right kidney, while the left adrenal gland lies partly in front of the upper pole of the left kidney. The left adrenal gland lies directly posterior to the splenic vein and body of pancreas and lateral to the left crus of the diaphragm. The right adrenal gland lies lateral to the crus, medial to the liver, and directly behind the IVC.

331

Abdomen

Adrenal Glands ADRENAL GLANDS, NEONATE

Adrenal gland

Fetal lobulation

Capsule Cortex

Medulla

Liver

Kidney Adrenal gland

(Top) Graphic shows the appearance of the adrenal gland and kidney in a fetus or neonate. The adrenal gland is much larger relative to the body size than in the adult, making it easier to see on US. The kidney has a lobulated appearance, reflecting the ongoing fusion of the individual renal lobes, each comprised of 1 renal pyramid and its associated renal cortex. This appearance can sometimes persist into adulthood. (Middle) The adrenal gland is essentially 2 organs in a single structure. The cortex is an endocrine gland, secreting primarily cortisol, aldosterone, and androgenic steroids. The adrenal medulla is part of the autonomic nervous system and secretes epinephrine and norepinephrine. (Bottom) A longitudinal US of the right adrenal gland in a neonate shows its folded, triangular morphology and relative large size when compared to the kidney.

332

Adrenal Glands

Ascites

Abdomen

ADRENAL GLANDS, NEONATE

Spleen Adrenal cortex Adrenal medulla

Aorta

Right lobe of liver Perinephric fat Right adrenal gland (medial limb)

Crus of right hemidiaphragm

Right lobe of liver

Right adrenal gland (lateral limb) Renal medullary pyramids

Crus of right hemidiaphragm

(Top) Transverse US of the left adrenal gland in a newborn shows the typical trilaminar, ice cream sandwich appearance with a hypoechoic cortex and hyperechoic medulla. (Middle) Longitudinal US of the right adrenal gland is shown using the liver as acoustic window. Using a high-frequency linear transducer better demonstrates the adrenal gland in neonates and infants; note the typical trilaminar appearance. (Bottom) Another image in the same patient with the transducer angulated slightly more laterally shows the lateral limb of the right adrenal gland. The crus of the right hemidiaphragm is seen posteriorly; it is more hypoechoic and lacks the adrenal glands trilaminar appearance.

333

Abdomen

Adrenal Glands ADRENAL GLANDS, ADULT

Pancreas Inferior vena cava Right adrenal gland

Splenic v. Left adrenal gland

Crus of diaphragm

Left kidney

Crus of diaphragm

Crus of diaphragm

Stomach Spleen

Right adrenal gland

Tail of pancreas Left adrenal gland

Colon Right kidney Left kidney

Left portal v. Right portal v. Inferior vena cava Right kidney Right adrenal gland

(Top) The right adrenal gland is usually suprarenal, touches the back of the IVC and lies lateral to the right crus and medial to the liver. The left adrenal gland lies medial to upper pole of left kidney, lateral to left crus of diaphragm, and posterior to splenic vein and pancreas. (Middle) This coronal view demonstrates the relation between the adrenals and adjacent organs. (Bottom) Axial US in a 19year-old woman shows the adrenal gland adjacent to the IVC. Note the trilaminar appearance is still seen in this young adult.

334

Adrenal Glands Abdomen

ADRENAL GLANDS, ADULT

Portal v. Right adrenal gland (anterior limb) Inferior vena cava

Right adrenal gland (posterior limb)

Aorta Crus of diaphragm

Spine

Inferior vena cava

Crus of hemidiaphragm

Lateral limb of right adrenal gland

Vertebral body Medial limb of right adrenal gland

Right kidney

Left lobe of liver

Splenic v.

Inferior vena cava Abdominal aorta

Tail of pancreas Left adrenal gland

Vertebral body Left kidney

(Top) Using the liver as an acoustic window, the right adrenal gland is particularly well seen in this thin adult. Two limbs are easily identified. (Middle) Zoomed transverse grayscale US shows the right adrenal gland. Note the medially located crus of the right hemidiaphragm, which may be mistaken for the gland. The crus is more hypoechoic, and its contour hugs the vertebral body. (Bottom) Subxiphoid transverse grayscale US performed at the epigastrium, level of the pancreatic body and tail, is shown. The left adrenal gland is seen as a lambda structure and surrounded by hyperechoic perirenal fat. It is anterior to the left kidney and to the left of the abdominal aorta. The adrenal gland can be easily missed if not specifically targeted.

335

Abdomen

Bowel

336

GROSS ANATOMY Divisions • Esophagus ○ Cervical and thoracic segments • Stomach ○ Hollow muscular organ between esophagus and small intestine ○ Location: Intraperitoneal, in left upper quadrant, bordered superiorly by left hemidiaphragm, posterolaterally by spleen, posteroinferiorly by pancreas – Greater omentum attached from greater curvature and drapes over small and large intestines – Lesser omentum attached from lesser curvature to porta hepatis, covers lesser sac ○ Function – Gastric acid production for breakdown of large molecules of food into smaller molecules in preparation for small intestinal absorption – Storage of food ○ Sections – Gastroesophageal junction/cardia, lower esophageal sphincter – Fundus and body: Delineated by horizontal plane passing through cardia – Antrum/pylorus: Lower section facilitating entry of gastric contents into duodenum ○ Curvatures – Greater curvature: Lateral wall of stomach – Lesser curvature: Medial wall of stomach ○ Rugae/internal ridges increase surface area for digestion ○ Arterial supply – Right and left gastric arteries supply lesser curvature – Right and left gastroepiploic arteries supply greater curvature – Short gastric artery supplies fundus ○ Venous drainage – Follow arteries and drain into portal vein and its tributaries • Small bowel ○ Between stomach and large intestine ○ ~ 4-7 meters in length ○ Centrally located in abdomen ○ Intraperitoneal, except for 2nd-4th portions of duodenum ○ Function: Further breakdown of food molecules from stomach with eventual absorption ○ Intraluminal extensions/folds valvulae conniventes increase surface area for absorption – Abundant in proximal small bowel, decrease in number in distal small bowel loops ○ Duodenum – C-shaped hollow tube connecting stomach with jejunum – Begins with duodenal bulb, ends in ligament of Treitz (duodenojejunal junction) – Arterial supply and venous drainage: Superior and inferior pancreaticoduodenal artery, pancreaticoduodenal veins ○ Jejunum

– – – – –

Connects duodenum with ileum ~ 2.5 meters in length Begins at ligament of Treitz Along with ileum, suspended by mesentery Arterial supply and venous drainage: Superior mesenteric artery and vein ○ Ileum – Connects jejunum with ascending colon – ~ 3.5 meters in length – Along with jejunum, suspended by mesentery – Arterial supply and venous drainage: Superior mesenteric artery and vein • Large bowel ○ Between small bowel and anus ○ ~ 1.5 meters in length ○ Peripherally located in abdomen – Cecum and appendix, transverse colon, and rectosigmoid intraperitoneal – Ascending colon, descending colon, and middle rectum retroperitoneal – Distal rectum extraperitoneal ○ Function: Absorption of remaining water, storage, and elimination of waste ○ Sections – Ascending colon: Located in right side of abdomen, includes cecum where appendix arises – Hepatic flexure: Turn of colon at liver – Transverse colon: Traverses upper abdomen – Splenic flexure: Turn of colon at spleen – Descending colon: Left side of abdomen – Sigmoid/rectum: At posterior pelvis ○ With taenia coli: 3 bands of smooth muscle just under serosa – Haustration: Sacculations in colon resulting from contraction of taenia coli – Epiploic appendages: Small fat accumulations on viscera ○ Arterial supply – Superior mesenteric artery supplies colon from appendix through splenic flexure – Ileocolic branch supplies cecum – Right colic branch supplies ascending colon – Middle colic branch supplies transverse colon – Inferior mesenteric artery supplies descending colon through rectum – Left colic branch supplies descending colon – Sigmoid branches supply sigmoid – Superior rectal artery supplies superior rectum – Middle and inferior rectum supplied by arteries of same name originating from internal iliac artery ○ Venous drainage – Superior and inferior mesenteric veins • Anus ○ External opening of rectum – Termination of gastrointestinal tract ○ With sphincters for controlling defecation ○ Internal anal sphincter – Thin ring of smooth muscle surrounding anal canal, deep to submucosa – Under involuntary control

Bowel

Histology • Bowel wall throughout GI tract has uniform general histology, comprised of 4 layers ○ Mucosa – Functions for absorption and secretion – Composed of epithelium and loose connective tissue – Lamina propria – Muscularis mucosa (deep layer of mucosa) ○ Submucosa – Consists of fibrous connective tissue – Contains Meissner plexus ○ Muscularis externa – Muscular layer responsible for peristalsis or propulsion of food through gut – Contains Auerbach plexus ○ Serosa – Epithelial lining continuous with peritoneum

•

•

•

IMAGING ANATOMY Overview • GI tract extends from mouth to anus • Esophagus, which is intrathoracic, is difficult to visualize with external ultrasound due to rib cage and air-containing lungs ○ Endoluminal ultrasound performed to assess mural pathology • Stomach to rectum lie within abdomen and pelvis • Stomach, 1st part of duodenum, jejunum, ileum, transverse colon, and sigmoid colon suspended within peritoneal cavity by peritoneal folds and are mobile • 2nd-4th part of duodenum, ascending colon, descending colon, and rectum typically extraperitoneal/retroperitoneal ○ Retroperitoneal structures have more fixed position and are easy to locate • Stomach located in left upper quadrant ○ Identified by presence of rugae/mural folds ○ Prominent muscular layer facilitates identification of pylorus • Small bowel loops are located centrally within abdomen ○ Abundant valvulae conniventes helps identify jejunal loops ○ Jejunalization of ileum seen in celiac disease to compensate for atrophy of folds in proximal small bowel ○ Contents of jejunal loops usually liquid and appear hypoechoic/anechoic • Cecum and colon identified by haustral pattern

•

○ Located peripherally in abdomen ○ Contain feces and gas ○ Haustra seen as prominent curvilinear echogenic arcs with posterior reverberation ○ Cecum identified by curvilinear arc of hyperechogenicity (representing feces and gas) in right lower quadrant blind ending caudally ○ Not uncommonly, cecum high lying and may be horizontally placed ○ Sigmoid colon variable length and mobile ○ Junction of left colon with sigmoid colon identified in left iliac fossa by tracing descending colon ○ Rectosigmoid junction has fixed position and is identified with full bladder, which acts as acoustic window Appendicular base normally located in right lower quadrant ○ Length and direction of tip vary ○ Retrocecal appendix and pelvic appendix can be difficult to locate transabdominally – Transvaginal ultrasound examination useful to identify pelvic appendix Normal measurements of bowel caliber ○ Small bowel < 3 cm ○ Large bowel – Cecum < 9 cm – Transverse colon < 6 cm Stratified appearance of bowel wall on histology is depicted by 5 distinct layers on ultrasound as alternating echogenic/sonolucent (hypoechoic) appearance (gut signature) ○ Interface of lumen and mucosa: Echogenic ○ Muscularis mucosa: Hypoechoic ○ Submucosa: Echogenic ○ Muscularis propria/externa: Hypoechoic ○ Serosa: Echogenic Normal bowel wall thickness < 3 mm

Abdomen

– Continuous with muscularis propria of rectum – Forms incomplete ring in females ○ External anal sphincter – Thick ring of skeletal muscle around internal anal sphincter – Under voluntary control – 3 parts from superior to inferior: Deep, superficial, and subcutaneous ○ Longitudinal muscle – Thin muscle between internal and external anal sphincters – Conjoined muscle from muscularis propria of rectum and levator ani

Bowel Motility • Bowel is hollow viscus and is constantly mobile due to peristalsis ○ Assessing direction of flow of contents often challenging ○ When visibility permits, direction of flow can be determined by following long segments of bowel in continuous fashion • Fixed points of bowel easy to assess with transabdominal ultrasound ○ Pylorus, "C loop" of duodenum, and ileocecal junction useful landmarks to assess direction of content flow • Different bowel pathologies have potential to alter normal gut motility • Real-time dynamic ultrasound provides useful information regarding bowel mobility, which can aid in diagnosis of underlying condition ○ Cine function useful to store dynamic images for review • Abnormal bowel identified as thickened or dilated segments ○ Thickened bowel demonstrates reduced peristalsis – Stands out among normally peristalsing loops of normal bowel

337

Abdomen

Bowel GASTROINTESTINAL TRACT IN SITU

Esophagus

Right hemidiaphragm

Aorta

Stomach

Transverse colon

Descending colon

Ascending colon

Small intestine

Cecum

Sigmoid Appendix Rectum

Graphic shows the gastrointestinal tract in situ. The liver and the greater omentum have been removed. Note the relatively central location of the small intestine compared with the peripherally located large intestine. Most of the bowel segments are intraperitoneal, apart from the 2nd-4th parts of the duodenum, the ascending and descending colon, and the middle 1/3 of the rectum, which are retroperitoneal. The distal 1/3 of the rectum is extraperitoneal.

338

Bowel Abdomen

STOMACH AND DUODENUM IN SITU

Liver (left lobe)

Falciform l.

Fundus Cardia

Gallbladder Body Duodenal bulb Gastroepiploic artery branches Pylorus Antrum Gastrocolic l. Transverse colon

Greater omentum

Hepatogastric l.

Left gastric a.

Hepatoduodenal l. Celiac a. Pyloric sphincter

Inner (oblique) m. layer Rugal folds

Outer (longitudinal) m. layer Middle (circular) m. layer

(Top) Graphic shows the stomach and proximal duodenum in situ. The liver and gallbladder have been retracted upward. Note that the lesser curvature and anterior wall of the stomach touch the underside of the liver, and the gallbladder abuts the duodenal bulb. The greater curvature is attached to the transverse colon by the gastrocolic ligament, which continues inferiorly as the greater omentum, covering most of the colon and small bowel. (Bottom) Graphic shows the lesser omentum extending from the stomach to the porta hepatis, divided into the broader and thinner hepatogastric ligament and the thicker hepatoduodenal ligament. The lesser omentum carries the portal vein, hepatic artery, common bile duct, and lymph nodes. The free edge of the lesser omentum forms the ventral margin of the epiploic foramen. Note the layers of gastric muscle; the middle circular layer is thickest.

339

Abdomen

Bowel DUODENUM

Hepatoduodenal l.

2nd portion of duodenum Transverse mesocolon Root of transverse mesocolon Pancreas

Transverse colon 3rd portion of duodenum

Jejunum

Superior mesenteric a. and v.

Root of small bowel mesentery

Hepatoduodenal l.

Pylorus

Common bile duct Major papilla (of Vater) Pancreatic duct

Proximal jejunum Superior mesenteric a.

Superior mesenteric v.

(Top) The duodenum is retroperitoneal, except for the bulb (1st part). The proximal jejunum is intraperitoneal. The hepatoduodenal ligament attaches the duodenum to the porta hepatis and contains the portal triad (bile duct, hepatic artery, portal vein). The root of the transverse mesocolon and mesentery both cross the duodenum. The 3rd portion of the duodenum crosses in front of the aorta and inferior vena cava (IVC) and behind the superior mesenteric vessels. The 2nd portion of the duodenum is attached to the pancreatic head and lies close to the hilum of the right kidney. (Bottom) Graphic shows the duodenal bulb suspended by the hepatoduodenal ligament. The duodenal-jejunal flexure is suspended by the ligament of Treitz, an extension of the right crus. The major pancreaticobiliary papilla enters the medial wall of the 2nd portion of the duodenum.

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Bowel Abdomen

SMALL INTESTINE

Celiac a.

Superior mesenteric a.

Ileocolic a.

Jejunal straight a. Jejunal arterial arcades

Ileal straight a.

Liver

Pancreas Stomach Superior mesenteric a. Duodenum (3rd part) Transverse colon Aorta

Greater omentum

Inferior vena cava Small bowel loops

(Top) Graphic shows the vascular supply of the entire small intestine from the superior mesenteric artery (SMA). The small bowel segments are displaced inferiorly. The SMA arises from the anterior abdominal aorta and gives off the inferior pancreaticoduodenal branch that supplies the duodenum and pancreas. Arising from the left side of the SMA are numerous branches to the jejunum and ileum. Jejunal arteries are generally larger and longer than those of the ileum. After a straight course, the arteries form multiple intercommunicating, curvilinear arcades. (Bottom) Graphic shows the sagittal section of the central abdomen, revealing the jejunum and ileum suspended in a radial pattern by the mesentery. Note the overlying greater omentum attached from the inferior portion of the stomach to drape the small bowel segments and transverse colon.

341

Abdomen

Bowel COLON, RECTUM, AND ANUS

Taenia coli Transverse colon

Splenic flexure Hepatic flexure

Superior mesenteric a.

Descending colon Ascending colon

Inferior mesenteric a.

Cecum

Appendix Rectum

Sigmoid

Taeniae coli

Sacrum Sigmoid mesocolon Rectosigmoid junction

Uterus

Rectouterine pouch (of Douglas) Rectum & rectal fascia

Bladder & vesical fascia

Levator ani muscle External anal sphincter

342

(Top) Graphic shows the colon in situ. The transverse colon has been retracted upward to demonstrate the arterial supply of the colon from the superior and inferior mesenteric arteries. The SMA supplies the colon from the appendix through the splenic flexure, and the inferior mesenteric artery (IMA) supplies the descending colon through the rectum. Note the band of smooth muscle (taenia coli) running along the length of the intestine, which terminates in the vermiform appendix; these result in sacculations/haustrations along the colon, giving it a segmented appearance. (Bottom) The sigmoid colon is on a mesentery, while the rectum is retroperitoneal. The anterior surface of the rectum has a peritoneal covering, which extends deep in the pelvis in women, forming the rectouterine pouch (of Douglas) as it is reflected along the posterior surface of the uterus. The rectum is narrowed as it passes through the pelvic diaphragm and then enters the anal canal with 3 levels of the anal sphincter (deep, superficial, and subcutaneous). The rectum has a continuous external longitudinal coat of muscle, unlike the colon with its discontinuous rows of taeniae.

Bowel Abdomen

STOMACH

Abdominal wall

Left hepatic v. Left lobe of liver Gastro esophageal junction Vertebral body

Stomach fundus

Abdominal wall Left lobe of liver

Aorta

Vertebral body

Collapsed body of stomach

Tail of pancreas

Subcutaneous adipose tissue Rectus muscle

Anterior wall of stomach Rugae

Posterior wall of stomach

(Top) Transverse oblique ultrasound at the epigastric region shows the gastroesophageal junction, which can be traced to the fundus of the stomach. Note the relationship to the adjacent structures. (Middle) Transverse oblique ultrasound through the left upper quadrant shows the collapsed stomach body with the rugal folds. Echogenic gas is seen between the rugae. The tail of the pancreas is seen posterior to the stomach, and the left lobe of the liver is anterior to the stomach. (Bottom) High-resolution transverse ultrasound through the epigastric region shows the gastric body tapering to the gastric antrum. Note the gastric folds (rugae). The stomach wall shows the gut signature.

343

Abdomen

Bowel GASTRODUODENAL REGION/DUODENUM

Subcutaneous adipose tissue Abdominal wall musculature Left lobe of liver

Pylorus

Duodenal bulb (D1) Pancreas Inferior vena cava Aorta

Abdominal wall

Gastric antrum

Superior mesenteric v. Uncinate process of pancreas D3

Superior mesenteric a. D3/D4 junction

D2/D3 junction Inferior vena cava

Aorta

Abdominal wall

D3

Inferior mesenteric a. origin Aorta

Inferior vena cava

(Top) Transverse oblique ultrasound through the epigastric region shows the pylorus with the hypoechoic prominent muscular wall leading to the duodenal bulb. (Middle) Transverse ultrasound through the upper abdomen shows the gastric antrum anteriorly compressed by the curvilinear probe and collapsed 3rd part of the duodenum (D3) posteriorly. The SMA and the superior mesenteric vein (SMV) are seen in the plane in between. The IVC and aorta are seen posterior to the D3. (Bottom) Axial midline high-resolution ultrasound through the upper abdomen shows fluid distended in the D3 located across, in the upper retroperitoneum. Note the aorta and IVC posterior to the D3. Gut signature is seen in the wall of the D3.

344

Bowel Abdomen

SMALL BOWEL

Rectus abdominis m.

Jejunal loops Valvulae conniventes

Rectus m.

Ileum Jejunum with valvulae conniventes

Right rectus m.

Anterior bowel wall Ileal segment Posterior bowel wall

Psoas m.

(Top) Transverse oblique ultrasound through the left flank shows jejunal loops with mucosal folds, valvulae conniventes. (Middle) Transverse ultrasound through the lower abdomen close to midline shows jejunal ileal transition from a segment with folds to a segment with no folds. (Bottom) Sagittal oblique ultrasound through the right lower quadrant shows a normal ileal segment. Note the lack of folds and a normal gut signature in the wall.

345

Abdomen

Bowel SMALL BOWEL AND LARGE BOWEL

Cecum Terminal ileum

Right iliopsoas complex

Right common iliac a.

Right common iliac v.

Cecum, anterior wall

Ileocecal junction

Terminal ileum

Cecum, posterior wall

Abdominal wall musculature

Jejunal loops Descending colon

Psoas m.

(Top) Transverse oblique ultrasound through the right iliac fossa (RIF) with graded compression shows a compressed, normal terminal ileum (between the abdominal wall musculature anteriorly and psoas muscle posteriorly) leading to the cecum. (Middle) Transverse high-resolution ultrasound through the RIF in the same patient shows the ileocecal junction and the ileocecal valve. (Bottom) Transverse ultrasound through the left iliac fossa shows a short-axis view of the descending colon with gut signature. Medial to the descending colon, normal jejunal loops can be seen with valvulae conniventes.

346

Bowel Abdomen

ILEOCECAL JUNCTION

Abdominal wall musculature Cecum Terminal ileum Iliacus m.

Psoas m.

Iliac blade

Abdominal wall musculature

Anterior lip of ileocecal junction Ileocecal junction Posterior lip of ileocecal junction

Ileocecal valve en face

(Top) Transverse ultrasound through the RIF shows the cecum, which is represented by curvilinear echogenicity with posterior reverberation. Note the terminal ileum compressed by the probe between the abdominal wall musculature and the iliopsoas complex posteriorly. (Middle) High-resolution transverse ultrasound through the RIF shows echogenic (fatty) lips of a normal ileocecal valve. (Bottom) Oblique right sagittal ultrasound through the RIF in the same patient shows the ileocecal junction end on.

347

Abdomen

Bowel APPENDIX Subcutaneous adipose tissue

Abdominal wall musculature

Appendix Tip of appendix Psoas m.

Abdominal wall

Tip of appendix Appendix

Appendix

(Top) Coronal oblique ultrasound through the RIF shows a long-axis normal appendix with a stratified mural appearance. Note the absence of periappendiceal inflammatory changes. (Middle) Transverse oblique ultrasound through the RIF shows a blind-ending tubular structure with a gut signature representing the long-axis view of a normal appendix. (Courtesy A. Law, MD.) (Bottom) Transverse oblique ultrasound through the RIF shows the short-axis view of a normal appendix with preservation of gut signature. Note the normal appearance of periappendicular fat. (Courtesy A. Law, MD.)

348

Bowel Abdomen

LARGE BOWEL

Abdominal wall musculature

Haustra of ascending colon

Abdominal wall Transverse colon

Posterior reverberation artifact from gas in transverse colon

Abdominal wall

Descending colon Outer muscular layer of colon Posterior reverberation artifact

(Top) Right sagittal ultrasound shows a normal ascending colon with curvilinear arcs of echogenicity from luminal gas/feces reflecting the normal haustra pattern. (Middle) Transverse ultrasound through the epigastric region close to the midline shows the normal haustral pattern of intraluminal gas/feces within the horizontally lying transverse colon. Note the posterior reverberation artifact from a gas-filled colon. (Bottom) Left sagittal ultrasound through the left side of the abdomen shows the descending colon represented by arcs of echogenicity with posterior reverberation artifacts due to gaseous contents of the colon. Note the normal haustral pattern. Images obtained with curvilinear probe or linear probe with virtual convex are better for orientation of anatomy within the peritoneal cavity.

349

Abdomen

Bowel LARGE BOWEL

Abdominal wall musculature

Long-axis view of collapsed descending colon

Abdominal wall Muscularis propria layer Compressed lumen

Submucosal layer Muscularis mucosa Compressed lumen Muscularis propria layer

Psoas m.

Loops of small bowel

Sigmoid colon Muscularis propria layer

Iliacus m. in pelvic wall

(Top) Left sagittal ultrasound shows the normal descending colon in a collapsed state and compressed by the ultrasound probe. Note the gut signature. This is an alternative appearance to the descending colon when it is collapsed and empty. (Middle) High-resolution left sagittal ultrasound obtained with a higher frequency linear probe from the same patient shows the collapsed descending colon with gut signature. The hypoechoic outer layer represents the muscularis propria layer. (Bottom) Transvaginal ultrasound shows the sigmoid colon and pelvic loops of small bowel. Note the hypertrophied outer muscularis propria layer of the sigmoid colon, seen in patients with irritable bowel syndrome and early diverticular disease.

350

Bowel Abdomen

RECTOSIGMOID REGION

Urinary bladder

Prostate gland Anterior wall of rectosigmoid

Bladder

Seminal vesicles Anterior wall of rectum

Bladder

Base of prostate gland Lower rectum Puborectalis

(Top) Midline sagittal ultrasound in a male patient shows the anterior wall of the rectosigmoid region and its relationship to the prostate gland anteriorly. (Middle) Transverse ultrasound through the pelvis in the same patient (with cystic fibrosis) shows the anterior wall of the rectosigmoid region and its relationship to the seminal vesicles anteriorly (note the small seminal vesicles seen here). (Bottom) Transverse ultrasound at a lower level in the same patient shows the lower rectum, pelvic floor, and anterior relationship to the prostate gland.

351

Abdomen

Abdominal Lymph Nodes

GROSS ANATOMY Overview • Major lymphatic vessels and nodal chains lie along major blood vessels (aorta, inferior vena cava, iliac) • Lymph nodes carry same name as vessel they accompany • Lymph from alimentary tract, liver, spleen, and pancreas passes along celiac, superior mesenteric chains to nodes ○ Efferent vessels from alimentary nodes form intestinal lymphatic trunks ○ Cisterna chyli (chyle cistern) – Formed by confluence of intestinal lymphatic trunks and right and left lumbar lymphatic trunks, which receive lymph from nonalimentary viscera, abdominal wall, and lower extremities – May be discrete sac or plexiform convergence • Thoracic duct: Inferior extent is chyle cistern at L1-L2 level ○ Formed by convergence of main lymphatic ducts of abdomen ○ Ascends through aortic hiatus in diaphragm to enter posterior mediastinum ○ Ends by entering junction of left subclavian and internal jugular veins • Lymphatic system drains surplus fluid from extracellular spaces and returns it to bloodstream ○ Important function in defense against infection, inflammation, and tumor via lymphoid tissue present in lymph nodes, gut wall, spleen, and thymus ○ Absorbs and transports dietary lipids from intestine to thoracic duct and bloodstream • Lymph nodes ○ Composed of cortex and medulla ○ Invested in fibrous capsule, which extends into nodal parenchyma to form trabeculae ○ Internal honeycomb structure filled with lymphocytes that collect and destroy pathogens ○ Hilum: In concave side, with artery and vein, surrounded by fat

Abdominopelvic Nodes • Preaortic nodes ○ Celiac nodes: Drainage from gastric nodes, hepatic nodes, and pancreaticosplenic nodes ○ Superior and inferior mesenteric nodes: Drainage from mesenteric nodes • Lateral aortic nodes ○ Drainage from kidneys, adrenal glands, ureter, posterior abdominal wall, testes and ovary, uterus, and fallopian tubes • Retroaortic nodes ○ Drainage from posterior abdominal wall • External iliac nodes ○ Primary drainage from inguinal nodes ○ Flow into common iliac nodes • Internal iliac nodes ○ Drainage from inferior pelvic viscera, deep perineum, and gluteal region ○ Flow into common iliac nodes • Common iliac nodes ○ Drainage from external iliac, internal iliac, and sacral nodes 352

○ Flow into lumbar (lateral aortic) chain of nodes • Superficial inguinal nodes ○ In superficial fascia parallel to inguinal ligament, along cephalad portion of greater saphenous vein ○ Receive lymphatic drainage from superficial lower extremity, superficial abdominal wall, and perineum ○ Flow into deep inguinal and external iliac nodes • Deep inguinal nodes ○ Along medial side of femoral vein, deep to fascia lata and inguinal ligament ○ Receive lymphatic drainage from superficial inguinal and popliteal nodes ○ Flow into external iliac nodes

IMAGING ANATOMY Overview • CT is test of choice for cancer staging • May be supplemented by PET/CT in select cancers • US may be useful in children or thin adults ○ Normal nodes are elliptical with echogenic fatty hilum and uniform hypoechoic cortex ○ Normal lymph nodes rarely detected on abdominal US • Normal diameter of lymph node varies depending on location ○ Short-axis diameter – Abdominopelvic < 10 mm – Hepatogastric ligament < 8 mm – Retrocrural < 6 mm

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer: 2-5 MHz or 5-9 MHz for thinner patients • Patient examined in supine position with < 4 hours of fasting to decrease bowel gas • Graded compression technique to clear overlying bowel loops

CLINICAL IMPLICATIONS Clinical Importance • Nodal enlargement is nonspecific, may be neoplastic, inflammatory, or reactive • Normal-sized lymph nodes may harbor metastatic malignancy • Node morphology is more specific for pathology ○ Abnormal nodes have replacement or loss of fatty hilum ○ Look for central necrosis, cystic change, or calcification • Lymphoma ○ Multiple enlarged hypoechoic or anechoic nodes • Metastatic lymphadenopathy ○ More echogenic and heterogeneous nodes compared to lymphomatous nodes • Infectious/reactive lymphadenopathy ○ Nonspecific sonographic features ○ May contain necrotic centers in mycobacterial infection

Abdominal Lymph Nodes Abdomen

RETROPERITONEAL LYMPH NODES

Celiac nodes Thoracic duct Superior mesenteric nodes Cisterna chyli

Lumbar trunks (of cisterna chyli)

Intestinal trunk (of cisternal chyli)

Right lumbar (retrocaval) nodes Lumbar (paraaortic) nodes Aortocaval nodes

Inferior mesenteric nodes

Common iliac nodes

External iliac nodes Internal iliac (hypogastric) nodes

Graphic shows that the major lymphatics and lymph nodes of the abdomen are located along and share the same name as the major blood vessels, such as the external iliac nodes, celiac, and superior mesenteric nodes. The paraaortic and paracaval nodes are also referred to as the lumbar nodes and receive afferents from the lower abdominal viscera, abdominal wall, and lower extremities; they are frequently involved in inflammatory and neoplastic processes. The lumbar trunks join with an intestinal trunk (at ~ the L1 level) to form the cisterna chyli, which may be a discrete sac or a plexiform convergence. The cisterna chyli and other major lymphatic trunks join to form the thoracic duct, which passes through the aortic hiatus to enter the mediastinum. After picking up additional lymphatic trunks within the thorax, the thoracic duct empties into the left subclavian or innominate vein.

353

Abdomen

Abdominal Lymph Nodes NONENLARGED NODES AND PATHOLOGIC NODES

Distal common bile duct Pancreatic tail

Splenic v. Small interaortocaval node

Left renal v.

Stomach Liver

Pancreas Portal v.

Peripancreatic lymph node

Lymphomatous nodes

Superior mesenteric a. Aorta

(Top) Transverse US at the level of the pancreas and splenic vein shows a small interaortocaval node. (Middle) Transverse US of the epigastric region shows an enlarged hypoechoic peripancreatic lymph node anterior to the portal vein in a patient with hepatitis C. Normal-sized lymph nodes are rarely seen in adult abdominal US. (Bottom) Transverse US of the upper midline abdomen in a patient with lymphoma shows multiple abnormal enlarged hypoechoic lymph nodes around the superior mesenteric artery.

354

Abdominal Lymph Nodes Abdomen

LYMPHANGIOGRAM

Left lumbar (paraaortic) nodes

Right lumbar (paracaval) nodes

Common iliac nodes

Common iliac nodes

External iliac nodes

(Top) This is the 1st of 3 images from a lymphangiogram. Iodinated oil is slowly infused into the lymphatics of the foot to produce opacification of the lymph channels and nodes. Note the subcentimeter (short-axis) diameter of these normal retroperitoneal lymph nodes. (Middle) Lymphatic channels and lymph nodes parallel the course of major blood vessels and share similar names, such as these common iliac nodes. (Bottom) With the availability of CT, MR, and PET/CT, lymphangiograms are rarely performed; however, they provide a unique depiction of the lymphatic system.

355

Abdomen

Aorta and Inferior Vena Cava

TERMINOLOGY Definitions • "Proximal" and "distal" in arterial and venous systems apply to position of arterial and venous segment in relation to heart (rather than direction of flow) • Aneurysm is focal increase in caliber of artery with diameter of dilated segment measuring at least 1.5x > adjacent unaffected segments

•

GROSS ANATOMY Overview • Abdominal aorta ○ Enters abdomen at T12 level, bifurcates at L4 ○ Level of origins of major branches: Celiac axis (T12), superior mesenteric artery (SMA) (L1), renal arteries (L1/2), inferior mesenteric artery (IMA) (L3), common iliac arteries (L4) • Inferior vena cava (ICV) ○ Blood from alimentary tract passes through portal venous system before entering IVC through hepatic veins ○ Begins at L5 level with union of common iliac veins ○ Leaves abdomen via IVC hiatus in diaphragm at T8 level ○ IVC tributaries correspond to paired visceral and parietal branches of aorta ○ IVC development has complex embryology – Various anomalies are common (up to 10% of population), especially at and below level of renal veins – All are variations of persistence/regression of embryologic sub- and supracardinal veins

•

•

IMAGING ANATOMY Overview • Not all branches of abdominal aorta and tributaries of IVC can be well seen on ultrasound examination • Major arterial branches of abdominal aorta seen on ultrasound ○ Celiac artery, common hepatic artery, splenic artery, SMA, IMA, renal arteries, common iliac arteries • Major venous tributaries draining into IVC ○ Common iliac veins, renal veins, hepatic veins

Internal Contents • Abdominal aorta ○ Normal peak systolic velocity (PSV): 60-110 cm/sec ○ Spectral Doppler waveform – Upper: Narrow, well-defined systolic complex with forward flow during diastole – Mid: Reduced diastolic flow – Distal: Absent diastolic flow, similar to lower limb arteries ○ Normal caliber: 15-25 mm – Upper: 22 mm above renal arteries – Middle: 18 mm below renal arteries – Lower: 15 mm above bifurcation ○ Best ultrasound imaging plane: Both transverse and longitudinal • Celiac axis 356

•

•

○ Normal PSV: 98-105 cm/sec ○ Spectral Doppler demonstrates low-resistance flow with high end-diastolic velocities ○ Flow velocity not dependent on food intake ○ Normal caliber: 6-10 mm ○ Best ultrasound imaging plane: Transverse plane: To show typical T-shaped bifurcation Common hepatic artery ○ Normal PSV: 70-120 cm/sec ○ Spectral Doppler shows low-resistance flow characteristics with large amount of continuous flow in diastole ○ Normal caliber: 4-10 mm ○ Best ultrasound imaging plane – Start transverse midline to follow common hepatic artery to right of T-shaped bifurcation from celiac axis – Gastroduodenal artery may be seen to arise from common hepatic artery along anterosuperior aspect of pancreas; thereafter, common hepatic artery becomes proper hepatic artery Splenic artery ○ Normal PSV: 70-110 cm/sec ○ Spectral Doppler shows typically turbulent flow due to tortuosity of vessel ○ Normal caliber: 4-8 mm ○ Best ultrasound imaging plane – Transverse midline approach: Shows proximal portion of artery well – Intercostal through spleen, using it as acoustic window: Useful for showing distal splenic artery around hilum SMA ○ Normal PSV: 97-142 cm/sec ○ Spectral Doppler demonstrates high-impedance flow with low diastolic velocities during fasting due to relative vasoconstriction ○ End-diastolic velocity increases after meal due to vasodilation of mesenteric branches – Typically 30-90 min after meals ○ Normal caliber: 5-8 mm ○ Best ultrasound imaging plane – Longitudinal midline approach: Best for evaluation of SMA blood flow – Transverse plane: Useful for identifying short anteriorly directed stump, shows dot-like appearance, surrounded by distinctive triangular mantle of fat IMA ○ Normal PSV: 93-189 cm/sec ○ Spectral Doppler demonstrates high-impedance flow with low diastolic velocities during fasting due to relative vasoconstriction ○ End-diastolic velocity increases after meal due to vasodilation of mesenteric branches ○ Normal caliber: 1-5 mm ○ Best imaging plane: Transverse plane following line of aorta – Origin of IMA arises from below origins of renal arteries and may be anterior or slightly to left of midline Renal arteries ○ Normal PSV: 60-140 cm/sec

Aorta and Inferior Vena Cava ○ Best imaging plane: Transverse anterior approach and oblique anterior approach along long axis of iliac veins • Renal veins ○ Normal PSV: 18-33 cm/sec ○ Right renal vein is relatively short and drains directly into IVC ○ Left renal vein runs slightly longer course – Receives left gonadal vein, usually courses anterior to aorta before joining IVC ○ Spectral Doppler of right renal vein mirrors pulsatility of IVC ○ Spectral Doppler of left renal vein may show only slight variability of flow velocities consequent upon cardiac and respiratory activity ○ Normal caliber: 4-9 mm ○ Best imaging plane: Transverse anterior approach • Hepatic veins ○ Normal PSV: 16-40 cm/sec ○ Spectral Doppler shows triphasic waveform due to transmitted cardiac activity ○ Best imaging plane: Transverse/oblique subcostal approach with cranial angulation

Abdomen

– Not > 180 cm/sec ○ Spectral Doppler demonstrates open systolic window, rapid systolic upstroke occasionally followed by secondary slower rise to peak systole with subsequent gradual diastolic decline but with persistent forward flow in diastole ○ Normal caliber: 5-8 mm ○ Best imaging plane – Transverse anterior midline approach: Best for identification of origins of renal arteries – Posterolateral approach using kidneys as acoustic window: Useful for visualization of distal portions of renal arteries • Common iliac arteries ○ Normal spectral Doppler shows characteristic triphasic waveform – Initial high-velocity peak forward-flow phase resulting from cardiac systole – Brief phase of reverse flow in early diastole – Low velocity forward flow in diastole ○ Normal caliber: 8-12 mm ○ Best imaging plane: Transverse anterior approach and oblique anterior approach along long axis of iliac arteries ○ Stenosis causing 1-19% diameter reduction – Triphasic waveform with minimal spectral waveform broadening – PSV increase < 30% relative to adjacent proximal segment; proximal and distal waveform remain normal ○ Stenosis causing 20-49% diameter reduction – Triphasic waveform usually maintained, though reverse flow component may be diminished – Spectral broadening is prominent with filling in of area under systolic peak – PSV 30-100% increase relative to adjacent proximal segment, proximal and distal segment remain normal ○ Stenosis causing 50-99% diameter reduction – Monophasic waveform with loss of reverse flow component, forward flow throughout cardiac cycle – Extensive spectral broadening – PSV > 100% increase relative to adjacent proximal segment – Distal waveform is monophasic with reduced systolic velocity ○ Occlusion – No flow on color or spectral Doppler – Preocclusive thump may be heard proximal to site of obstruction – Distal waveforms are monophasic with reduced systolic velocities • IVC ○ Normal PSV: 44-118 cm/sec ○ Spectral Doppler shows slow flow that varies with respiration and cardiac pulsation ○ Normal caliber: 5-29 mm during quiet inspiration ○ Best imaging plane: Both transverse and longitudinal • Common iliac veins ○ Spectral Doppler shows 5 normal characteristics – Spontaneous flow, phasic flow, flow ceases with Valsalva maneuver, flow augmentation with distal compression, unidirectional flow towards heart

ANATOMY IMAGING ISSUES Imaging Recommendations • Use 2- to 5-MHz transducer • Fasting for 12 hours is recommended to reduce interference by bowel gas ○ Imaging patient in morning after overnight fast is most convenient protocol ○ Satisfactory Doppler signal for aorta and IVC can be obtained in up to 90% of patients • Lateral decubitus position and graded compression to displace intervening bowel gas may be useful • Angle correction is crucial in spectral Doppler assessment • Detailed delineation of branches of aorta and IVC better assessed on CTA or MRA • Digital subtractive angiography usually reserved for when intervention may be required (e.g., embolization of mesenteric artery branches in GI bleed, renal artery stenting, etc.)

Imaging Pitfalls • Bowel gas, patient body habitus, and operator dependence are main factors contributing to suboptimal ultrasound examination of aorta and IVC

357

Abdomen

Aorta and Inferior Vena Cava AORTA

Inferior phrenic aa.

Esophageal branch

Celiac a. (trunk)

Superior adrenal aa. Inferior adrenal aa.

Middle adrenal a.

Superior mesenteric a.

Left renal a.

Gonadal aa. Lumbar a.

Inferior mesenteric a.

Common iliac a.

Middle sacral a. External iliac a. Internal iliac a.

Graphic shows the major arteries to the GI tract arise as unpaired vessels from the aortic midline plane and include the celiac, superior, and inferior mesenteric arteries. Branches to the urogenital and endocrine organs arise as paired vessels in the lateral plane and include the renal, adrenal, and gonadal (testicular or ovarian) arteries. The diaphragm and posterior abdominal wall are supplied by paired branches in the posterolateral plane, including the inferior phrenic and lumbar arteries (4 pairs, only 1 of which is labeled in this graphic). The anterior abdominal wall is supplied by the inferior epigastric and deep circumflex iliac arteries, both branches of the external iliac artery. The inferior epigastric artery turns superiorly to run in the rectus sheath where it anastomoses with the superior epigastric artery, a terminal branch of the internal mammary (thoracic) artery.

358

Aorta and Inferior Vena Cava Abdomen

CT ANGIOGRAM

Celiac a. Inferior vena cava

Left gastric a.

Splenic a.

Superior mesenteric a.

Renal vv.

Jejunal aa.

Ileocolic a. Inferior mesenteric a.

Right common iliac a.

Left common iliac a.

Left external iliac a.

Left internal iliac a.

Volume-rendered CT angiogram shows the aorta and some of its major abdominal branches. This image was obtained in the late arterial phase of imaging, resulting in some opacification of the renal veins and the suprarenal inferior vena cava (IVC). The infrarenal IVC is not yet opacified because the circulation to the lower abdominal organs and legs is neither as abundant nor rapid as it is to the kidneys.

359

Abdomen

Aorta and Inferior Vena Cava INFERIOR VENA CAVA

Inferior phrenic vv.

Hepatic vv.

Adrenal vv.

Renal vv.

Right gonadal v.

Ascending lumbar v.

Left gonadal (ovarian) v.

Ascending lumbar v.

Middle sacral v. External iliac v.

Internal iliac (hypogastric) v.

The IVC begins at the L5 level with the confluence of the common iliac veins, which are themselves the result of the confluence of the internal and external iliac veins. Note the ascending lumbar veins, which anastomose freely between the IVC, azygous and hemiazygos veins, and renal veins. These are an important pathway for collateral flow in the event of obstruction of the IVC or one of its major tributaries, and these veins play an important role in spread of tumor and infection from the pelvis and spine to the thorax, upper spine, and brain. The right renal vein rarely receives tributaries, while the left receives the gonadal, adrenal, and lumbar veins. The left adrenal vein also anastomoses with the inferior phrenic vein. The hepatic veins return blood from the liver as they join the IVC just below its hiatus in the diaphragm at ~ the T8 level.

360

Aorta and Inferior Vena Cava Abdomen

COMMON VARIATIONS OF INFERIOR VENA CAVA

Aorta Inferior vena cava

(Top) The first 2 of 4 graphics illustrating common variations of the IVC is shown. The labeled lines on the frontal graphics correspond to the levels of the axial sections. The left graphic shows transposition of the IVC in which the infrarenal portion of the IVC lies predominantly to the left side of the aorta. A more common anomaly is shown on the right graphic, a "duplication" of the IVC in which the left common iliac vein continues in a cephalad direction without crossing over to join the right iliac vein. Instead, it joins the left renal vein and then crosses over to the right. The suprarenal IVC has a conventional course and appearance. (Bottom) The left graphic shows a circumaortic left renal vein with the smaller, more cephalic vein passing in front of the aorta and the larger vein passing behind and caudal. The right graphic shows a completely retroaortic renal vein.

361

Abdomen

Aorta and Inferior Vena Cava PROXIMAL AORTA, SAGITTAL VIEW

Pancreas Superior mesenteric v. Superior mesenteric a. Left lobe of liver Celiac axis Abdominal aorta

Pancreas Superior mesenteric v. Superior mesenteric a. Left lobe of liver Celiac axis

Abdominal aorta

Proximal aorta

Well-defined narrow systolic complex

Forward flow during diastole

(Top) Longitudinal grayscale ultrasound of the proximal abdominal aorta shows the origins of the celiac axis and superior mesenteric artery. The origin of the celiac axis is usually seen at T12, while the origin of the superior mesenteric artery is usually seen at L1 immediately below the origin of the celiac axis on this view. The normal diameter of the abdominal aorta is 15-25 mm, and the average diameter of the proximal abdominal aorta above the renal arteries is around 22 mm. (Middle) Longitudinal color Doppler ultrasound of the proximal abdominal aorta shows the origins of the celiac axis and superior mesenteric artery. Apart from assessment of flow through the aorta, this is also a useful view for assessment of the flow in the superior mesenteric artery. (Bottom) Spectral Doppler ultrasound of the proximal aorta shows narrow, well-defined systolic complex with forward flow during diastole.

362

Aorta and Inferior Vena Cava Abdomen

MIDDLE AND DISTAL AORTA, SAGITTAL VIEW

Abdominal aorta Common iliac a.

Shadowing from lumbar transverse processes

Mid/distal aorta

Reduced diastolic flow compared with proximal aorta

(Top) Longitudinal grayscale ultrasound of the mid/distal abdominal aorta shows one of the common iliac arteries coming off the aortic bifurcation. The aortic bifurcation is usually seen at the L4 level. The average diameter of the mid portion of the abdominal aorta is around 18 mm below the renal arteries and 15 mm above the aortic bifurcation. (Middle) Color Doppler ultrasound of the mid/distal abdominal aorta shows one of the common iliac arteries coming off the aortic bifurcation. (Bottom) Spectral Doppler ultrasound of the mid/distal abdominal aorta shows reduced diastolic flow compared with the proximal aorta. The spectral Doppler waveform that is to be expected in the distal abdominal aorta usually shows absent diastolic flow, similar to that seen in the lower limb arteries.

363

Abdomen

Aorta and Inferior Vena Cava CELIAC AXIS

Left lobe of liver

Celiac axis Portal v. Aorta Inferior vena cava Vertebral body

Left lobe of liver

Celiac axis Portal v. Aorta Inferior vena cava

Vertebral body

Celiac axis

High end-diastolic velocities

(Top) Transverse grayscale ultrasound of the abdominal aorta at the level of the celiac axis via a midline approach is shown. The celiac axis is the 1st branch of the abdominal aorta seen arising anteriorly, usually at the level of T12. The normal caliber of the celiac axis is between 6-10 mm. Note the normal position of the IVC to the right of the abdominal aorta. (Middle) Transverse color Doppler ultrasound of the abdominal aorta at the level of the celiac axis via a midline approach is shown. As the celiac axis is perpendicular to the transducer, a small amount of cranial angulation was used to improve the color Doppler signal obtained. (Bottom) Spectral Doppler ultrasound of the celiac axis shows low-resistance flow with high end-diastolic velocities. Flow velocity in the celiac axis is not dependent on food intake, and the normal peak systolic velocity (PSV) ranges from 98-105 cm/sec.

364

Aorta and Inferior Vena Cava Abdomen

SPLENIC ARTERY

Left lobe of liver Splenic a. Portal v. Inferior vena cava

Celiac axis Aorta

Vertebral body

Left lobe of liver Portal v. Inferior vena cava

Splenic a. Aorta

Vertebral body

Splenic a.

(Top) Transverse grayscale ultrasound via a midline approach shows the origin of the splenic artery as it branches from the celiac axis and hooks to the left. This is usually the best view for visualizing the proximal portion of the splenic artery. The more distal splenic artery is tortuous in its course. An intercostal approach using the spleen as an acoustic window may be useful for showing the distal splenic artery around the hilum. The normal caliber of the splenic artery ranges from 4-8 mm. (Middle) Transverse color Doppler ultrasound via a midline approach shows flow within the proximal splenic artery. (Bottom) Spectral Doppler ultrasound of the proximal splenic artery shows typically turbulent flow due to tortuosity of the vessel. The normal PSV in the splenic artery ranges between 70110 cm/sec.

365

Abdomen

Aorta and Inferior Vena Cava COMMON HEPATIC ARTERY

Common hepatic a. Aorta

Vertebral body

Common hepatic a. Aorta

Vertebral body

Common hepatic a.

(Top) Transverse grayscale ultrasound via a midline approach shows the proximal portion of the common hepatic artery as it branches to the right off the T-shaped bifurcation of the celiac axis (not imaged). The normal diameter of the common hepatic artery ranges from 4-10 mm. (Middle) Color Doppler ultrasound shows flow within the proximal portion of the common hepatic artery. The gastroduodenal artery may be seen to arise from the common hepatic artery along the anterosuperior aspect of the pancreas; thereafter, the common hepatic artery becomes the proper hepatic artery. (Bottom) Spectral Doppler ultrasound of the common hepatic artery shows lowresistance flow characteristics with large amount of continuous flow in diastole. The normal PSV for the common hepatic artery ranges from 70-120 cm/sec.

366

Aorta and Inferior Vena Cava

Portal v.

Inferior vena cava

Abdomen

SUPERIOR MESENTERIC ARTERY

Splenic v. Superior mesenteric a. Left renal a. Aorta Vertebral body

Portal v. Splenic v. Superior mesenteric a. Inferior vena cava

Left renal a. Aorta

Superior mesenteric a.

High impedance flow with low diastolic velocities

(Top) Transverse grayscale ultrasound of the origin of the superior mesenteric artery seen arising anteriorly from the aorta is shown. The origin of the superior mesenteric artery is usually seen at L1 between the celiac axis (T12) and the renal arteries (L1/2). The normal caliber of the superior mesenteric artery ranges between 5-8 mm. (Middle) Transverse color Doppler ultrasound of the proximal superior mesenteric artery is shown. The transducer has been angled slightly cranially with the arterial blood coming toward the transducer shown in red and the venous blood going away from the transducer shown in blue. (Bottom) Spectral Doppler ultrasound of the proximal portion of the superior mesenteric artery is shown. High-impedance flow with low diastolic velocities is observed during fasting due to relative vasoconstriction. End-diastolic velocity increases after meals due to vasodilation of the mesenteric branches, typically within 30-90 min.

367

Abdomen

Aorta and Inferior Vena Cava RIGHT RENAL ARTERY

Left lobe of liver Portal v. Hepatic a. Inferior vena cava

Right renal a.

Superior mesenteric a. Aorta

Vertebral body

Right kidney

Left lobe of liver

Portal v. Superior mesenteric a. Hepatic a. Inferior vena cava

Right renal a.

Aorta

Vertebral body

Right kidney

Right renal a.

Secondary rise to peak systole Rapid systolic upstroke Persistent forward flow in diastole

(Top) Transverse grayscale ultrasound shows the proximal right renal artery as it branches from the aorta and courses behind the IVC. This midline anterior approach is usually the best for evaluating the origin of the renal arteries. The normal diameter of the renal arteries ranges from 5-8 mm. The renal arteries arise around the L1/2 level at or below the level of the superior mesenteric artery. (Middle) Transverse color Doppler ultrasound of the abdominal aorta shows the proximal right renal artery as it branches from the aorta and courses behind the IVC. (Bottom) Spectral Doppler ultrasound of the right renal artery shows an open systolic window, rapid systolic upstroke followed by a secondary slower rise to peak systole. There is a subsequent gradual decrease in flow but it remains persistently forward throughout diastole. The normal PSV ranges from 60-140 cm/sec but not more than 180 cm/sec.

368

Aorta and Inferior Vena Cava Abdomen

LEFT RENAL ARTERY

Head of pancreas Body of pancreas Aorta Inferior vena cava

Superior mesenteric a. Splenic v. Left renal a. Tail of pancreas

Inferior vena cava Aorta

Superior mesenteric a. Left renal a. Splenic v.

Left renal a.

Secondary slower rise to peak systole Rapid systolic upstroke

Persistent forward flow in diastole

(Top) Transverse grayscale ultrasound shows the proximal left renal artery as it branches from the aorta and courses posterior to the superior mesenteric artery and splenic vein. This midline anterior approach is usually the best for evaluating the origin of the renal arteries. The normal diameter of the renal arteries ranges from 5-8 mm. The renal arteries arise around the L1/2 level. (Middle) Power Doppler ultrasound shows flow in the proximal left renal artery as it branches from the aorta and courses posterior to the superior mesenteric artery and splenic vein. (Bottom) Spectral Doppler ultrasound of the left renal artery shows an open systolic window, rapid systolic upstroke followed by a secondary slower rise to peak systole with subsequent gradual decrease in velocity but persistent forward flow throughout diastole. The normal PSV ranges from 60-140 cm/sec but not more than 180 cm/sec.

369

Abdomen

Aorta and Inferior Vena Cava INFERIOR MESENTERIC ARTERY

Inferior mesenteric a. Inferior vena cava Aorta Vertebral body

Inferior mesenteric a. Inferior vena cava Aorta

Inferior mesenteric a.

Low diastolic velocities

(Top) Transverse grayscale ultrasound shows the distal abdominal aorta at the level of the origin of the inferior mesenteric artery. The inferior mesenteric artery arises from the anterior or left anterolateral aspect of the abdominal aorta at the L3 level. The transverse plane following the line of the aorta is the best imaging plane for identification of the origin of the inferior mesenteric artery. The normal caliber of the inferior mesenteric artery ranges from 1-4 mm. (Middle) Transverse power Doppler ultrasound shows flow in the proximal inferior mesenteric artery. (Bottom) Spectral Doppler ultrasound of the inferior mesenteric artery shows high-impedance flow with low diastolic velocities during fasting due to relative vasoconstriction. End-diastolic velocity increases after meal due to vasodilation of the mesenteric branches. Normal PSV ranges from 93-189 cm/sec.

370

Aorta and Inferior Vena Cava Abdomen

AORTIC BIFURCATION

Left common iliac a. Right common iliac a. Inferior vena cava

Right psoas m.

Vertebral body

Spinal canal

Left common iliac a. Right common iliac a. Inferior vena cava

Right psoas m.

Vertebral body

Spinal canal

Left common iliac a. Right common iliac a. Inferior vena cava

Right psoas m.

Vertebral body

Spinal canal

(Top) Transverse grayscale ultrasound of the aortic bifurcation shows the origins of the right and left common iliac arteries. The aortic bifurcation is usually seen at the L4 level. (Middle) Transverse color Doppler ultrasound shows flow in the origins of the right and left common iliac arteries. (Bottom) Transverse power Doppler ultrasound shows flow in the origins of the right and left common iliac arteries. Power Doppler is less angle dependent and demonstrates flow more readily, particularly in vascular structures that are close to a right angle with the transducer.

371

Abdomen

Aorta and Inferior Vena Cava RIGHT COMMON ILIAC ARTERY

Left common iliac a.

Vertebral body Right common iliac a. Inferior vena cava

Left common iliac a.

Vertebral body Right common iliac a. Inferior vena cava

Right common iliac a.

Initial high-velocity peak forward-flow phase Low-velocity forward flow in diastole Brief phase of reverse flow in early diastole

(Top) Oblique grayscale ultrasound shows the course of the right common iliac artery as it branches off the aortic bifurcation. The proximal common iliac artery is 1st identified on the transverse plane, and the transducer is then angulated along the long axis of the right common iliac artery. The normal diameter of the common iliac arteries ranges from 8-12 mm. (Middle) Oblique color Doppler ultrasound shows flow in the proximal right common iliac artery. (Bottom) Spectral Doppler ultrasound of the right common iliac artery shows a triphasic waveform. An initial high-velocity peak forward flow phase, resulting from cardiac systole, is followed by a brief phase of reversed flow in early diastole, and low-velocity forward flow in the remainder of diastole.

372

Aorta and Inferior Vena Cava Abdomen

LEFT COMMON ILIAC ARTERY

Inferior vena cava

Right common iliac a. Left common iliac a. Vertebral body

Inferior vena cava Right common iliac a.

Left common iliac a.

Vertebral body

Left common iliac a.

Initial high-velocity peak forward flow phase Low-velocity forward flow in diastole Brief phase of reverse flow in early diastole

(Top) Oblique grayscale ultrasound shows the course of the left common iliac artery as it branches off the aortic bifurcation. The proximal common iliac artery is 1st identified on the transverse plane, and the transducer is then angulated along the long axis of the left common iliac artery. The normal diameter of the common iliac arteries ranges from 8-12 mm. (Middle) Oblique color Doppler ultrasound shows flow in the proximal left common iliac artery. (Bottom) Spectral Doppler ultrasound of the left common iliac artery shows the characteristic triphasic waveform. An initial high-velocity peak forward flow phase, resulting from cardiac systole, is followed by a brief phase of reversed flow in early diastole, and low-velocity forward flow in the remainder of diastole.

373

Abdomen

Aorta and Inferior Vena Cava PROXIMAL INFERIOR VENA CAVA, SAGITTAL VIEW

Left lobe of liver

Middle hepatic v. Portal v. Inferior vena cava

Right renal a.

Left lobe of liver

Portal v. Middle hepatic v.

Right renal a.

Inferior vena cava

Proximal inferior vena cava

(Top) Longitudinal grayscale ultrasound of the epigastric region shows the proximal IVC. The normal caliber of the IVC ranges from 5-29 mm during quiet respiration with the diameter being larger in the proximal portion. The diameter increases by ~ 10% during deep inspiration. (Middle) Longitudinal color Doppler ultrasound of the epigastric region shows flow within the proximal IVC (shown in blue). (Bottom) Spectral Doppler ultrasound of the proximal IVC shows slow flow that varies with respiration and cardiac pulsation. The pulsatile Doppler flow pattern contributed by atrial pressure changes is more apparent in the proximal portion of the IVC. The normal PSV ranges from 48-115 cm/sec.

374

Aorta and Inferior Vena Cava Abdomen

MID INFERIOR VENA CAVA, SAGITTAL VIEW

Right rectus m. Bowel gas Middle 1/3 of inferior vena cava Vertebral body anterior edge Right psoas m. (partially imaged) Intervertebral discs

Right rectus m. Bowel gas Middle 1/3 of inferior vena cava

Right psoas m. (partially imaged)

Mid portion of inferior vena cava

(Top) Longitudinal grayscale ultrasound of the epigastric region shows the middle portion of the IVC lying to the right of the lumbar vertebrae. Therefore, the right psoas may be included in the image. The normal caliber of the IVC ranges from 5-29 mm during quiet respiration with the diameter being larger in the proximal portion. The diameter increases by ~ 10% during deep inspiration. (Middle) Longitudinal color Doppler ultrasound shows flow in the mid portion of the IVC. (Bottom) Spectral Doppler ultrasound of the mid portion of the IVC shows less pulsatility than that seen in the proximal IVC. This is due to the reduction in influence of the right atrium.

375

Abdomen

Aorta and Inferior Vena Cava DISTAL INFERIOR VENA CAVA, SAGITTAL VIEW Right rectus abdominis m. Bowel Distal inferior vena cava Anterior edge of vertebral body

Intervertebral discs

Right rectus abdominis m.

Distal inferior vena cava Anterior edge of vertebral body

Intervertebral discs

Distal inferior vena cava

(Top) Longitudinal grayscale ultrasound of the distal IVC below the level of the renal veins is shown. Left-sided IVC and other congenital anomalies are encountered in the IVC below the renal veins in ~ 10% of the population. The diameter of the distal IVC is normally smaller than that seen in the proximal IVC. Note that in this subject, the anterior border of the vertebral bodies and the intervertebral discs can be visualized. (Middle) Longitudinal color Doppler ultrasound shows flow in the distal IVC above the common iliac vein confluence. (Bottom) Spectral Doppler ultrasound of the distal IVC shows only variations from respiration with no influence from the right atrium, unlike that seen in the proximal IVC.

376

Aorta and Inferior Vena Cava Abdomen

PROXIMAL INFERIOR VENA CAVA, TRANSVERSE VIEW

Segment 4a Left hepatic v.

Right hemidiaphragm

Segment 2

Suprahepatic inferior vena cava

Segment 4a Middle hepatic v. Segment 8 Right hepatic v. Segment 7

Left hepatic v. Segment 2

Hepatic v. confluence

Right hemidiaphragm

Liver Portal v. Aorta Hepatic a. Inferior vena cava Vertebral body

Right kidney

(Top) Transverse grayscale ultrasound with cranial angulation shows the suprahepatic IVC proximal to the hepatic confluence. The IVC leaves the abdomen via the IVC hiatus in the diaphragm at the T8 level. (Middle) Transverse grayscale ultrasound shows the hepatic vein confluence. Cranial angulation is often required to produce this image and is a very useful view for designation of the segments of the liver. The middle hepatic vein defines the plane that separates the right and left lobe of the liver. The right hepatic vein defines the plane that separates the anterior and posterior segments of the right lobe. The left hepatic vein defines the plane that separates the medial and lateral segments of the left lobe. (Bottom) Transverse grayscale ultrasound shows the distal intrahepatic IVC at the level of the extrahepatic portal vein.

377

Abdomen

Aorta and Inferior Vena Cava LEFT HEPATIC VEIN

Middle hepatic v.

Right hepatic v.

Left hepatic v.

Hepatic v. confluence

Right hemidiaphragm

Middle hepatic v.

Right hepatic v.

Left hepatic v.

Hepatic v. confluence

Right hemidiaphragm

Left hepatic v.

(Top) Transverse grayscale ultrasound shows the left hepatic vein as it drains into the hepatic vein confluence. It may join the middle hepatic vein before joining the proximal IVC. The left hepatic vein runs between the medial and lateral segments of the left lobe and is frequently duplicated. (Middle) Transverse color Doppler ultrasound shows flow within the left hepatic vein. (Bottom) Spectral Doppler ultrasound of the left hepatic vein shows the normal chaotic pulsatile waveform, which results from a combination of phasic variation and transmission of right atrial pulsations to the vein. The normal PSV in hepatic veins ranges from 16-40 cm/sec.

378

Aorta and Inferior Vena Cava Abdomen

MIDDLE HEPATIC VEIN

Middle hepatic v. Left hepatic v.

Right hepatic v.

Middle hepatic v.

Right hepatic v.

Middle hepatic v.

(Top) Transverse grayscale ultrasound of the middle hepatic vein as it drains directly into the hepatic vein confluence is shown. The middle hepatic vein lies in a sagittal or parasagittal plane between the right and left lobes of the liver. (Middle) Color Doppler ultrasound shows flow within the middle hepatic vein. (Bottom) Spectral Doppler ultrasound of the middle hepatic vein shows the normal chaotic pulsatile waveform, which results from a combination of phasic variation and transmission of right atrial pulsations to the vein. The normal PSV in hepatic veins ranges from 16-40 cm/sec.

379

Abdomen

Aorta and Inferior Vena Cava RIGHT HEPATIC VEIN

Middle hepatic v. Left hepatic v.

Hepatic v. confluence Right hepatic v.

Right hemidiaphragm

Middle hepatic v. Left hepatic v.

Right hepatic v.

Hepatic v. confluence

Right hemidiaphragm

Right hepatic v.

(Top) Transverse grayscale ultrasound of the right hepatic vein as it enters the hepatic vein confluence is shown. The right hepatic vein runs in a coronal plane between the anterior and posterior segments of the right lobe of the liver and may be absent in 6% of the population. (Middle) Transverse color Doppler ultrasound shows flow in the right hepatic vein. Note that the mid portion of the vein is perpendicular to the transducer thereby creating an area of lack of signal in the mid portion of the vein. (Bottom) Spectral Doppler ultrasound of the right hepatic vein shows the normal chaotic pulsatile waveform, which results from a combination of phasic variation and transmission of right atrial pulsations to the vein. The normal PSV in hepatic veins ranges from 16-40 cm/sec.

380

Aorta and Inferior Vena Cava

Right lobe of liver Portal v.

Abdomen

RIGHT RENAL VEIN

Inferior vena cava

Hepatic v. Vertebral body Right kidney

Right renal v.

Superior mesenteric a. Inferior vena cava Right renal v.

Abdominal aorta Left renal v.

Vertebral body

Right renal v.

(Top) Transverse grayscale ultrasound shows the right renal vein utilizing the liver as an acoustic window. This is usually the best approach for imaging the proximal right renal vein. The right renal vein is relatively short and drains directly into the IVC. The normal caliber of the right renal vein is between 4-9 mm. (Middle) Transverse color Doppler ultrasound shows flow in the right renal vein. The image is obtained with slight cranial angulation so that flow toward the transducer is registered as red (right renal vein, aorta, superior mesenteric artery, left renal vein) and flow away from the transducer in the IVC is registered as blue. (Bottom) Spectral Doppler ultrasound of the right renal vein mirroring the pulsatility in the IVC is shown. The normal PSV ranges from 18-33 cm/sec.

381

Abdomen

Aorta and Inferior Vena Cava LEFT RENAL VEIN

Left renal v. Left kidney Vertebral body

Splenic v. Aorta

Portal v. Inferior vena cava

Left renal v. Vertebral body

Left renal v.

(Top) Transverse grayscale ultrasound of the left renal vein via the anterior approach is shown. This approach may be affected by intervening bowel loops. The left renal vein has a longer course to the IVC compared with the right renal vein. The normal caliber of the left renal vein is between 4-9 mm. (Middle) Transverse color Doppler ultrasound with slight cranial angulation shows flow in the left renal vein in red. Flow toward the transducer is shown in red (aorta, splenic vein) and flow away from the transducer is shown in blue (IVC, portal vein). Note that the left renal vein usually courses anterior to the aorta before entering the IVC. (Bottom) Spectral Doppler of the left renal vein shows slight variability of flow velocities consequent upon cardiac and respiratory activity.

382

Aorta and Inferior Vena Cava Abdomen

COMMON ILIAC VEINS

Right common iliac a. Right common iliac v. Left common iliac a. Vertebral body

Left common iliac v.

Right common iliac a. Right common iliac v. Left common iliac a. Vertebral body

Left common iliac v.

Left common iliac v.

(Top) Transverse grayscale ultrasound shows the common iliac veins just below where they converge to form the IVC. Note at this level the common iliac arteries are located anterior to the common iliac veins. Examination of the common iliac veins with ultrasound is often limited by intervening bowel loops and the patient's body habitus. (Middle) Transverse color Doppler ultrasound of the proximal common iliac veins below the origin of the IVC shows flow in the common iliac veins in blue and flow in the common iliac arteries in red. (Bottom) Spectral Doppler ultrasound of the left common iliac vein is shown. The normal spectral Doppler of the common iliac veins has 5 characteristics: Spontaneous flow, phasic flow, flow ceases with Valsalva maneuver, flow augmentation with distal compression, and unidirectional flow toward the heart.

383

Abdomen

Aorta and Inferior Vena Cava AORTIC ANEURYSM AND DISSECTION

Abdominal aorta

Thrombus

Thrombus Patent lumen of abdominal aortic aneurysm

Abdominal aorta Intimal flap

(Top) Oblique transabdominal grayscale ultrasound shows a distal abdominal aortic aneurysm with no involvement of the bifurcation. A vessel is considered aneurysmal when it is dilated 1.5x or more compared to normal adjacent segments. The abdominal aorta is considered to be dilated when its caliber exceeds 3 cm. (Middle) Transverse color Doppler ultrasound shows an abdominal aortic aneurysm with circumferential mural thrombus in the lumen of an aortic aneurysm. (Bottom) Longitudinal grayscale ultrasound shows dissection of the abdominal aorta with an echogenic intimal flap. Dissection in the abdominal aorta is more commonly seen as an extension of a dissection of the thoracic aorta rather than a localized event in the abdominal aorta.

384

Aorta and Inferior Vena Cava

Inferior vena cava

Abdomen

INFERIOR VENA CAVA OBSTRUCTION

Thrombus

Cystic tumor

Vertebral body Compressed IVC

Liver

Middle hepatic v.

Echogenic tongue of thrombus in inferior vena cava

(Top) Longitudinal color Doppler ultrasound shows thrombosis within the IVC. Tumors such as renal cell carcinoma and hepatocellular carcinoma have a propensity to invade venous structures and are both causes of tumor thrombus extension into the IVC. Note the color Doppler flow within the thrombus, suggesting it is a tumor thrombus rather than a bland stasis/occlusive thrombus. (Middle) Transverse transabdominal grayscale ultrasound shows a large complex cystic tumor compressing the IVC. (Bottom) Longitudinal grayscale ultrasound shows an echogenic "tongue" of thrombus extending from the iliac veins into the partially patent IVC. This patient is at high risk of pulmonary embolism.

385

Abdomen

Peritoneal Cavity

TERMINOLOGY Definitions • Peritoneal cavity: Potential space in abdomen between visceral and parietal peritoneum, usually containing only small amount of peritoneal fluid (for lubrication) • Abdominal cavity: Not synonymous with peritoneal cavity ○ Contains all of abdominal viscera (intra- and retroperitoneal) ○ Limited by abdominal wall muscles, diaphragm, and (arbitrarily) pelvic brim

GROSS ANATOMY Divisions • Greater sac of peritoneal cavity • Lesser sac (omental bursa) ○ Communicates with greater sac via epiploic foramen (of Winslow) ○ Bounded anteriorly by caudate lobe, stomach, and greater omentum – Posteriorly by pancreas, left adrenal, and kidney – On left by splenorenal and gastrosplenic ligaments – On right by epiploic foramen and lesser omentum

Compartments • Supramesocolic space ○ Divided into right and left supramesocolic spaces, which are separated by falciform ligament – Right supramesocolic space: Composed of right subphrenic space, right subhepatic space, and lesser sac – Left supramesocolic space: Divided into left perihepatic spaces (anterior and posterior) and left subphrenic (anterior perigastric and posterior perisplenic) • Inframesocolic compartment ○ Divided into right inframesocolic space, left inframesocolic space, paracolic gutters, and pelvic cavity ○ Pelvic cavity is most dependent part of peritoneal cavity in erect and supine positions

Peritoneum • Thin serous membrane consisting of single layer of squamous epithelium (mesothelium) ○ Parietal peritoneum lines abdominal wall ○ Visceral peritoneum (serosa) lines abdominal organs

Mesentery • Double layer of peritoneum that encloses organ and connects it to abdominal wall • Covered on both sides by mesothelium and has core of loose connective tissue containing fat, lymph nodes, blood vessels, and nerves passing to and from viscera • Most mobile parts of intestine have mesentery, while ascending and descending colon are considered retroperitoneal (covered only by peritoneum on anterior surface) • Root of mesentery is its attachment to posterior abdominal wall • Root of small bowel mesentery is ~ 15 cm and passes from left side of L2 vertebra downward and to right 386

○ Contains superior mesenteric vessels, nerves, and lymphatics • Transverse mesocolon crosses almost horizontally in front of pancreas, duodenum, and right kidney

Omentum • Multilayered fold of peritoneum that extends from stomach to adjacent organs • Lesser omentum joins lesser curve of stomach and proximal duodenum to liver ○ Hepatogastric and hepatoduodenal ligament components contain common bile duct, hepatic and gastric vessels, and portal vein • Greater omentum ○ 4-layered fold of peritoneum hanging from greater curve of stomach like apron, covering transverse colon and much of small intestine – Contains variable amounts of fat and abundant lymph nodes – Mobile and can fill gaps between viscera – Acts as barrier to generalized spread of intraperitoneal infection or tumor

Ligaments • All double-layered folds of peritoneum, other than mesentery and omentum, are peritoneal ligaments • Connect 1 viscus to another (e.g., splenorenal ligament) or viscus to abdominal wall (e.g., falciform ligament) • Contain blood vessels or remnants of fetal vessels

Folds • Reflections of peritoneum with defined borders, often lifting peritoneum off abdominal wall (e.g., median umbilical fold covers urachus and extends from dome of urinary bladder to umbilicus)

Peritoneal Recesses • Dependent pouches formed by peritoneal reflections • Many have eponyms [e.g., Morison pouch for posterior subhepatic (hepatorenal) recess; pouch of Douglas for rectouterine recess]

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer: Typically 2-5 MHz for abdominal survey and deep recesses, up to 9 MHz for thinner patients • High-frequency linear transducer 8-15 MHz may be used to evaluate anterior abdominal wall and parietal peritoneum • Patient examined supine with additional decubitus positions to determine if fluid collection is free or loculated • Peritoneal cavity and its various mesenteries and recesses are usually not apparent on imaging studies unless distended or outlined by intraperitoneal fluid or air

Peritoneal Cavity Abdomen

PERITONEAL CAVITY

Liver (caudate lobe) Lesser omentum

Lesser sac

Stomach

Pancreas Superior mesenteric a.

Duodenum (3rd portion)

Gastrocolic l.

Transverse mesocolon

Transverse colon

Greater omentum

Small bowel mesentery

Graphic of a sagittal section of the abdomen shows the peritoneal cavity artificially distended to show anatomy. Note the margins of the lesser sac in this plane, including the caudate lobe of the liver, stomach, gastrocolic ligament anteriorly and pancreas posteriorly. The hepatogastric ligament is part of the lesser omentum and carries the hepatic artery and portal vein to the liver. The mesenteries are multilayered folds of the peritoneum that enclose a layer of fat and convey blood vessels, nerves, and lymphatics to the intraperitoneal abdominal viscera. The greater omentum is a 4-layered fold of the peritoneum that extends down from the stomach, covering much of the colon and small intestine. The layers are generally fused together caudal to the transverse colon. The gastrocolic ligament is part of the greater omentum.

387

Abdomen

Peritoneal Cavity PERITONEAL DIVISIONS AND COMPARTMENTS

Greater peritoneal cavity Lesser omentum

Gastrosplenic l. Lesser sac (omental bursa) Splenorenal l.

Transverse colon

Greater omentum

Small bowel mesentery

Descending colon Ascending colon Left paracolic gutter

(Top) The borders of the lesser sac (omental bursa) include the lesser omentum, which contains the common bile duct and hepatic and gastric vessels. The left border includes the gastrosplenic ligament (with short gastric vessels) and the splenorenal ligament (with splenic vessels). (Bottom) The paracolic gutters are formed by reflections of the peritoneum covering the ascending and descending colon and the lateral abdominal wall. Note the innumerable potential peritoneal recesses lying between the bowel loops and their mesenteric leaves. The greater omentum covers much of the bowel like an apron.

388

Peritoneal Cavity Abdomen

PERITONEAL DIVISIONS AND COMPARTMENTS

Hepatogastric l. Hepatoduodenal l. Epiploic foramen (of Winslow)

Greater omentum

Left triangular l. Gastrophrenic l. Coronary l. of liver

Root of transverse mesocolon

Phrenicocolic l. Root of transverse mesocolon Left paracolic gutter

Right paracolic gutter

Site of descending colon

Site of ascending colon Root of small bowel mesentery

Root of sigmoid mesocolon

(Top) In this graphic, the liver has been retracted upward. The lesser omentum is comprised of the hepatoduodenal and hepatogastric ligaments. It forms part of the anterior wall of the lesser sac and contains the common bile duct, hepatic and gastric vessels, and portal vein. The aorta and celiac artery can be seen through the lesser omentum, as they lie just posterior to the lesser sac. (Bottom) Frontal view of the abdomen, with all of the intraperitoneal organs removed, shows that the root of the transverse mesocolon divides the peritoneal cavity into supramesocolic and inframesocolic spaces that communicate only along the paracolic gutters. The coronary and triangular ligaments suspend the liver from the diaphragm. The superior mesenteric vessels traverse the small bowel mesentery, whose root crosses obliquely from the upper left to the lower right posterior abdominal wall.

389

Abdomen

Peritoneal Cavity RIGHT SUPRAMESOCOLIC SPACE

Fluid in right subphrenic space

Cirrhotic liver Atelectatic right lung

Right hemidiaphragm Right pleural effusion

Fluid in anterior subhepatic space

Cirrhotic liver (right lobe)

Gallbladder

Fluid in Morison pouch

Right kidney

Fluid in right anterior subhepatic space Visceral peritoneum Right lobe of liver (cirrhotic with nodular contour) Fluid in Morison pouch

Parietal peritoneum Right kidney

(Top) Intercostal oblique grayscale ultrasound (in a patient with cirrhosis) shows the dome of the right lobe of the liver and moderate fluid in the right subphrenic region extending anterior to the liver. The fluid is separated from the right-sided pleural effusion by the right diaphragmatic leaf. (Middle) Subcostal oblique transverse ultrasound of the right upper quadrant shows fluid in the right anterior subhepatic space and in the hepatorenal space. The ascites are secondary to hepatic cirrhosis, and the gallbladder is physiologically distended. (Bottom) Longitudinal transabdominal grayscale ultrasound shows fluid in the right posterior subhepatic space, also known as the Morison pouch, and hepatorenal fossa. This space is continuous with the right anterior subhepatic space and right paracolic gutter.

390

Peritoneal Cavity Abdomen

RIGHT SUPRAMESOCOLIC SPACE: LESSER SAC

Liver

Stomach Pancreas

Lesser sac loculated collection (with artifactual echoes)

Superior mesenteric a. Splenic v. Abdominal aorta

Left lobe of liver

Stomach with fluid Fluid in lesser sac Fluid in lesser sac Splenic v. Aorta

Left lobe of liver transplant Pancreas Right subphrenic space

Left anterior perihepatic space Lesser sac fluid Colon

Anasarca

Tip of spleen

Hepatorenal fossa fluid Posterior perisplenic space Perisplenic collaterals

(Top) Subxiphoid transverse grayscale ultrasound shows a fluid collection in the lesser sac, which extends to the left, behind the stomach and anterior to the pancreas. The lesser sac is part of the right supramesocolic space and communicates with the rest of the peritoneal cavity through the epiploic foramen (of Winslow). (Middle) Subxiphoid transverse color Doppler ultrasound of the same patient shows moderate fluid in the lesser sac posterior to the stomach. The splenic vein was dilated in this patient with portal hypertension status post liver transplant. (Bottom) Axial CECT of the same patient shows fluid in the lesser sac and peritoneal cavity as well as diffuse anasarca.

391

Abdomen

Peritoneal Cavity LEFT SUPRAMESOCOLIC SPACE

Falciform l.

Fluid in supramesocolic space Left portal v. Caudate lobe Inferior vena cava Vertebral body

Fluid in left subphrenic space

Left hemidiaphragm

Spleen

Left kidney

Left pleural effusion

Perisplenic fluid Left lobe of liver Lesser sac fluid

Septation

Splenorenal l. Inferior spleen

(Top) Subxiphoid transverse grayscale ultrasound shows fluid anterior to the left lobe of the liver that is localized to the left posterior subhepatic space. Incidental calculi are seen within a dilated intrahepatic biliary duct. (Middle) Longitudinal grayscale ultrasound of the left upper quadrant shows a small amount of perisplenic fluid extending under the left hemidiaphragm. The left subphrenic space is separated from the right subphrenic space by the falciform ligament. (Bottom) Transverse grayscale ultrasound of the left upper quadrant reveals fluid in the perisplenic space and lesser sac.

392

Peritoneal Cavity Abdomen

INFRAMESOCOLIC SPACE

Fluid in inframesocolic space

Small bowel loops with intraluminal air and fluid

Ascites

Small bowel

Urinary bladder Urinary bladder wall

Fluid in rectovesical pouch

Rectum

Fluid in pelvic cavity Bowel Urinary bladder with Foley catheter Vesicouterine pouch Fluid in rectouterine space/pouch of Douglas

Uterus

(Top) Transverse transabdominal ultrasound of the central abdomen reveals moderate to large ascites with floating small bowel loops. The left inframesocolic space is larger compared to the right and communicates directly with the pelvic cavity. (Middle) Longitudinal ultrasound of the midline suprapubic region in a male patient demonstrates intraperitoneal fluid between bowel loops and extending into the dependent rectovesical pouch. There is a distended urinary bladder. (Bottom) Longitudinal grayscale ultrasound of the female pelvis shows free fluid. The uterus divides the pelvic cavity into the vesicouterine and rectouterine (pouch of Douglas) spaces. In this case, the vesicouterine space contains minimal fluid.

393

Abdomen

Abdominal Wall

TERMINOLOGY Definitions • Abdomen: Region between diaphragm and pelvis

GROSS ANATOMY Anatomic Boundaries of Anterior Abdominal Wall • Superiorly: Xiphoid process and costal cartilages of 7th-10th ribs • Inferiorly: Iliac crest, iliac spine, inguinal ligament, and pubis • Inguinal ligament is inferior edge of aponeurosis of external oblique muscle

Muscles of Anterior Abdominal Wall • Consist of 3 flat muscles (external oblique, internal oblique, and transverse abdominal), and 1 strap-like muscle (rectus) • Combination of muscles and aponeuroses (sheet-like tendons) act as corset to confine and protect abdominal viscera • Linea alba is fibrous raphe stretching from xiphoid to pubis ○ Forms central anterior attachment for abdominal wall muscles ○ Formed by interlacing fibers of aponeuroses of oblique and transverse abdominal muscles ○ Rectus sheath also formed by these aponeuroses as they surround rectus muscle • Linea semilunaris is vertical fibrous band at lateral edge of rectus sheath bilaterally ○ Aponeuroses of internal and transversus abdominis join in linea semilunaris before forming rectus sheath • External oblique muscle ○ Largest and most superficial of 3 flat abdominal muscles ○ Origin: External surfaces of ribs 5-12 ○ Insertion: Linea alba, iliac crest, pubis via broad aponeurosis • Internal oblique muscle ○ Middle of 3 flat abdominal muscles ○ Runs at right angles to external oblique ○ Origin: Posterior layer of thoracolumbar fascia, iliac crest, and inguinal ligament ○ Insertion: Ribs 10-12 posteriorly, linea alba via broad aponeurosis, pubis • Transversus abdominis (transversalis) muscle ○ Innermost of 3 flat abdominal muscles ○ Origin: Lowest 6 costal cartilages, thoracolumbar fascia, iliac crest, inguinal ligament ○ Insertion: Linea alba via broad aponeurosis, pubis • Rectus abdominis muscle ○ Origin: Pubic symphysis and pubic crest ○ Insertion: Xiphoid process and costal cartilages 5-7 ○ Rectus sheath: Strong, fibrous compartment that envelops each rectus muscle – Contains superior and inferior epigastric vessels • Actions of anterior abdominal wall muscles ○ Support and protect abdominal viscera ○ Help flex and twist trunk, maintain posture ○ Increase intraabdominal pressure for defecation, micturition, and childbirth ○ Stabilize pelvis during walking, sitting up • Transversalis fascia 394

○ Lies deep to abdominal wall muscles and lines entire abdominal wall ○ Separated from parietal peritoneum by layer of extraperitoneal fat

Muscles of Posterior Abdominal Wall • Consist of psoas (major and minor), iliacus, and quadratus lumborum • Psoas: Long, thick, fusiform muscle lying lateral to vertebral column ○ Origin: Transverse processes and bodies of vertebrae T12-L5 ○ Insertion: Lesser trochanter of femur (passing behind inguinal ligament) ○ Action: Flexes thigh at hip joint; bends vertebral column laterally • Iliacus: Large triangular sheet of muscle lying along lateral side of psoas ○ Origin: Superior part of iliac fossa ○ Insertion: Lesser trochanter of femur (after joining with psoas tendon) ○ Action: "Iliopsoas muscle" flexes thigh • Quadratus lumborum: Thick sheet of muscle lying adjacent to transverse processes of lumbar vertebrae ○ Invested by lumbodorsal fascia ○ Origin: Iliac crest and transverse processes of lumbar vertebrae ○ Insertion: 12th rib ○ Actions: Stabilizes position of thorax and pelvis during respiration, walking; bends trunk to side

Paraspinal Muscles • Also called erector spinae muscles ○ Invested by lumbodorsal fascia • Composed of 3 columns ○ Iliocistalis: Lateral ○ Longissimus: Intermediate ○ Spinalis: Medial • Origins: Sacrum, ilium, and spines of lumbar and 11th-12th thoracic vertebrae • Insertions: Ribs and vertebrae with additional muscle slips joining columns at successively higher levels • Action: Extends vertebral column

ANATOMY IMAGING ISSUES Imaging Recommendations • High-frequency (5-12 MHz) linear transducer for anterior abdominal wall and paraspinal muscles • 3-5 MHz for posterior abdominal wall muscles • Supine position for examination of anterior and lateral abdominal wall ○ Image during Valsalva maneuver and in standing position to increase abdominal pressure and elicit hernias  ○ Prone position for ultrasound of paraspinal muscles • Compare with contralateral side to check for symmetry

Abdominal Wall Abdomen

ANTERIOR ABDOMINAL WALL

Linea alba Rectus m. External oblique m.

Tendinous inscription

Internal oblique m.

Aponeuroses & rectus sheath

Umbilicus

Linea semilunaris Anterior layer of rectus sheath

Inguinal l.

Graphic shows the aponeuroses of the internal and external oblique and transverse abdominal muscles are 2-layered and interweave with each other, covering the rectus muscle, constituting the rectus sheath and linea alba. About midway between the umbilicus and symphysis, at the arcuate line, the posterior rectus sheath ends (arcuate line), and the transversalis fascia is the only structure between the rectus muscle and parietal peritoneum.

395

Abdomen

Abdominal Wall POSTERIOR ABDOMINAL WALL

Central t. (of diaphragm) Median arcuate l. arches

Esophagus Right crus of diaphragm

Medial arcuate l. Oblique & transverse mm. Lateral arcuate l. Right crus of diaphragm Left crus of diaphragm Quadratus lumborum m. Psoas minor m.

Anterior longitudinal l.

Psoas major m.

Iliacus m. Piriformis m. Levator ani m. Inguinal l. Rectum Urethra

Insertion of iliopsoas m.

Graphic shows the lumbar vertebrae are covered and attached by the anterior longitudinal ligament and the diaphragmatic crura are closely attached to it, as are the origins of the psoas muscles, which also arise from the transverse processes. The iliacus muscle arises from the iliac fossa of the pelvis and inserts into the tendon of the psoas major, constituting the iliopsoas muscle, which inserts onto the lesser trochanter. The quadratus lumborum arises from the iliac crest and inserts onto the 12th rib and transverse processes of the lumbar vertebrae. The diaphragmatic and transverse abdominal fibers interlace. The psoas and quadratus lumborum pass behind the diaphragm under medial and lateral arcuate ligaments.

396

Abdominal Wall Abdomen

MUSCLES OF BACK IN SITU

Spinous process Spinalis thoracis m.

Longissimus thoracis m.

Iliocostalis m.

Transversus abdominis (m. and t.)

Serratus posterior inferior m.

Internal oblique m.

External oblique m.

Iliac crest

Graphic shows the paraspinal muscles and muscles of the back. The latissimus dorsi muscles are not included. The erector spinae have thick, tendinous origins from the sacral, iliac crests, the lumbar, and 11th to 12th thoracic spinous processes. Superiorly, the muscle becomes fleshy, and in the upper lumbar region subdivides to become the iliocostalis, longissimus, and spinalis muscles (from lateral to medial), tapering as they insert into the vertebrae and ribs. The erector muscles flank the spinous processes and span the length of the posterior thorax and abdomen. They are responsible for extension of the vertebral column.

397

Abdomen

Abdominal Wall ANTERIOR ABDOMINAL WALL

Subcutaneous fat

Rectus sheath Right rectus abdominis m.

Left rectus abdominis m. Linea alba

Peritoneum Bowel

Subcutaneous fat

Rectus abdominis m.

Deep inferior epigastric a. and v. Bowel gas

Perforator branch of deep inferior epigastric a. Subcutaneous fat Rectus abdominis m.

Deep inferior epigastric a.

(Top) Transverse grayscale ultrasound of the midline anterior abdominal wall shows the paired rectus abdominis muscles separated by the linea alba. The rectus abdominis muscles are comparable in echogenicity and thickness. The surrounding rectus sheath is seen as a fine, thin, echogenic structure around the muscles. (Middle) Transverse power Doppler ultrasound of a rectus abdominis muscle in the lower abdomen shows the deep inferior epigastric artery and vein. Branches of the superior epigastric artery that arise in the upper abdomen anastomose with branches of the inferior epigastric artery at the umbilicus. (Bottom) Longitudinal color Doppler ultrasound shows a perforating branch of the deep inferior epigastric artery extending into the rectus muscle. These perforators are important for breast reconstruction with abdominal wall flaps.

398

Abdominal Wall Abdomen

ANTEROLATERAL ABDOMINAL WALL

Subcutaneous fat Right external oblique Right internal oblique m. Right transverse abdominal m.

Right rectus abdominis Linea alba Gas within bowel loops

Right linea semilunaris

Skin Right external oblique m. Right internal oblique m.

Right rectus abdominis m. Linea semilunaris

Right transverse abdominal m. Gas within bowel loops

Skin

Linea alba

Linea semilunaris Subcutaneous fat

Right rectus abdominis m.

Right external oblique m. Right internal oblique m.

Bowel loops

Right transversus abdominis m.

Right lobe of liver Right kidney

(Top) Transverse extended FOV grayscale ultrasound shows the relationship of the medially located rectus abdominis and the laterally located oblique and transverse abdominal muscles. Medially, the external and internal oblique and the transversus abdominal muscles form aponeuroses that comprise the rectus sheath, with the muscles thinning at the linea semilunaris. The linea alba is thin in the lower abdomen. (Middle) Transverse grayscale ultrasound at the right anterolateral abdominal wall shows the relationship of the lateral abdominal wall muscles in better detail. Note the oblique and transverse abdominal muscles taper medially as they become aponeuroses. (Bottom) Correlative axial CECT illustrates the muscles of the abdominal wall. The rectus abdominis muscle in the anterior abdominal wall is shown, along with the oblique and transverse abdominal muscles in the anterolateral abdominal wall and their aponeuroses.

399

Abdomen

Abdominal Wall POSTERIOR ABDOMINAL WALL

Subcutaneous fat

Right psoas m.

Right oblique mm.

Right kidney

Vertebrae

Subcutaneous fat Right rectus abdominis m. Bowel Inferior vena cava Right oblique mm.

Right vertebral body

Right psoas m. Right kidney Quadratus lumborum Right erector spinae m.

Bowel Inferior vena cava

Right oblique mm.

Vertebral body

Right quadratus lumborum m.

Right psoas m.

Right erector spinae

(Top) Longitudinal oblique grayscale ultrasound through the lower right abdomen shows the right psoas muscle, which originates from the lumbar spine and inserts into the proximal femur. (Middle) Transverse grayscale ultrasound of right mid abdomen using the kidney as an acoustic window is shown. The kidney is anterior and lateral to the psoas and anterior to the quadratus lumborum. The psoas runs along the paravertebral region in its entire abdominal course. The quadratus lumborum originates from the iliolumbar ligament and iliac crest to insert into the last rib and lumbar transverse processes. It is easily identified as the muscle on which the kidney rests. (Bottom) Transverse grayscale ultrasound of the right upper abdomen, continuing the scan inferiorly, shows the relationship of the posterior abdominal wall muscles are maintained.

400

Abdominal Wall Abdomen

POSTERIOR ABDOMINAL WALL, CT CORRELATION

Spleen Right lobe of liver Right psoas m. Right kidney

Ascending colon

Left kidney Left psoas m. Lumbar vertebral body

Right rectus abdominis m.

Right oblique and transverse mm. Right lobe of liver Right kidney

Right psoas m.

Right rib Right quadratus lumborum m. Right erector spinae m.

Right lobe of liver Right kidney

Right psoas m.

Right quadratus lumborum m. Right erector spinae m.

(Top) Correlative coronal CECT shows the paralumbar location of the psoas muscles and their medial location relative to the kidneys. The psoas muscles originate from the lumbar and 12th thoracic vertebral bodies and their transverse processes and run past the pelvic brim, where they course inferolaterally to be joined by the iliacus muscle. (Middle) Correlative axial CECT better illustrates the anatomic relationships of the kidney with the posterior abdominal wall muscles. The kidney is lateral to the psoas muscle and rests upon the quadratus lumborum muscle. The erector spinae muscles are immediately posterior to the quadratus lumborum, and the 2 muscles are invested by the lumbodorsal fascia. (Bottom) Correlative axial CECT at the level of the inferior pole of the right kidney is shown. The psoas muscle and quadratus lumborum muscles, seen in their midsections, are now thicker.

401

Abdomen

Abdominal Wall POSTERIOR ABDOMINAL WALL

Right rectus m. Bowel

Right external oblique m. Right internal oblique m. Right transversus abdominis

Inferior vena cava Right psoas m.

Vertebral body Right quadratus lumborum m. Transverse process

Right rectus m. Linea semilunaris Bowel gas

Right external oblique m.

Right psoas m.

Right internal oblique m. Right transversus abdominis m. Right iliac crest Right iliacus m.

Right rectus abdominis m.

Shadowing from bowel gas Tendon of psoas m. Right oblique mm. Right iliopsoas m.

Right external iliac a.

Right iliac crest

Right external iliac v.

(Top) Transverse grayscale ultrasound in the lower abdominal region shows the right psoas muscle, composed of the psoas minor, which rests upon the psoas major. The 2 muscles cannot be separated clearly on ultrasound. Because of their depth, the paraspinal muscles cannot be demonstrated in detail. (Middle) Transverse grayscale ultrasound of the right lower abdomen, continued from the previous image, shows that the distal psoas muscle has diminished in size. It rests on the medial portion of the iliacus muscle; the latter is a flat muscle that fills the iliac fossa. Both continue inferiorly together. (Bottom) Distally, the fibers from the iliacus muscle converge and insert into the lateral side of the psoas muscle to form the iliopsoas muscle. Common iliac vessels can be seen medially.

402

Abdominal Wall Abdomen

POSTERIOR ABDOMINAL WALL, CT CORRELATION

Right rectus abdominis m.

Right external oblique m. Right internal oblique m. Right transverse abdominal m.

Right psoas m.

Right quadratus lumborum m. Right erector spinae m.

Right psoas m.

Right external iliac a. Right iliac blade

Right external iliac v.

Right iliacus mm.

Right gluteus mm.

Right external iliac a.

Right sacroiliac joint

Right external iliac v.

Right iliopsoas m. Right iliac blade Internal iliac vessels Right gluteus mm. Left piriformis m.

(Top) Correlative axial CECT below the kidneys shows the quadratus lumborum muscle is more laterally located and the psoas muscle is directly anterior to the erector spinae muscle. (Middle) Axial correlative CECT shows the psoas muscle has begun its dorsolateral course and is now anterior to the iliacus muscle. The iliacus muscle is easily identified as a flat muscle filling the iliac fossa, arising from the upper 2/3 of the iliac fossa, inner lip of the iliac crest, anterior sacroiliac and the iliolumbar ligaments, and base of the sacrum. (Bottom) Correlative axial CECT shows the psoas and iliacus muscles have converged and are now indistinguishable from one another. The resultant iliopsoas muscle passes beneath the inguinal ligament and becomes tendinous as it inserts into the lesser trochanter of the femur.

403

Abdomen

Abdominal Wall PARASPINAL MUSCLES

Subcutaneous fat Spinous process Skin Left erector spinae m. Left kidney

Right erector spinae m. Right kidney

Subcutaneous fat

Left longissimus thoracis and iliocostalis mm. Left quadratus lumborum m.

Left kidney

Vertebral body Psoas m.

Aorta

Right rectus abdominis m.

Right lobe of liver Right kidney Lumbar vertebra

Left psoas m. Left quadratus lumborum m.

Spinous process

Left erector spinae m.

(Top) Transverse extended FOV grayscale ultrasound of the back (with the patient prone) shows the erector spinae muscles flanking the spinous process. They are invested by the lumbodorsal fascia, which also invests the anteriorly located quadratus lumborum muscle. The kidneys are partially demonstrated. (Middle) Transverse oblique grayscale ultrasound shows the left erector spinae muscle (with the patient prone). The 3 columns (iliocostalis, longissimus, and spinalis muscles, from lateral to medial) comprising the erector spinae are not clearly separated from one another on ultrasound. They are identified collectively as a thick, fleshy muscle lateral to the spinous process. (Bottom) Correlative axial CECT of the paraspinal muscles at the level of the kidneys shows the erector spinae muscles originate from a broad and thick tendon, which originates from the sacrum and iliac crest, lumbar, and 11th and 12th thoracic spinous processes.

404

Abdominal Wall

Subcutaneous fat

Abdomen

MR

Linea alba

Right rectus m. Right linea semilunaris

Aorta

Right external oblique m. Right internal oblique m.

Inferior vena cava

Right transversus abdominis m. Right quadratus lumborum

Right erector spinae mm.

Linea alba Linea semilunaris Right external oblique m. Right internal oblique m. Right transversus abdominis m. Right psoas m.

Aorta Inferior vena cava

Right quadratus lumborum m.

Right erector spinae m.

Linea alba Subcutaneous fat Right rectus m.

Deep inferior epigastric vessels

Right iliopsoas m. Right external iliac a. and v.

Right gluteal mm.

(Top) Axial T2 HASTE MR in an older patient with muscle atrophy shows fat in between the individual muscles of the anterior and posterior abdominal wall. (Middle) Axial T2 HASTE MR in a younger male patient shows more bulky abdominal wall musculature with little intermuscular fat. (Bottom) Axial T1 MR at a lower level shows the iliopsoas as 1 muscle bundle.

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SECTION 5

Pelvis

Iliac Arteries and Veins Ureters and Bladder Prostate and Seminal Vesicles Testes and Scrotum Penis and Urethra Uterus Cervix Vagina Ovaries Pelvic Floor

408 424 434 446 458 468 482 488 494 504

Pelvis

Iliac Arteries and Veins

GROSS ANATOMY Arteries • Abdominal aorta ○ Testicular and ovarian arteries originate below renal arteries ○ Median (middle) sacral artery is small, unpaired branch from posterior aspect of distal aorta ○ Divides into common iliac arteries at L4-5 • Common iliac arteries ○ Run anterior to iliac veins and inferior vena cava ○ Usually no major branches – Rarely, gives off aberrant iliolumbar or accessory renal arteries ○ ~ 4 cm long • External iliac artery ○ No major branches ○ Exits pelvis beneath inguinal ligament ○ Larger than internal iliac artery ○ Inferior epigastric (medial) and deep iliac circumflex (lateral) arteries demarcate junction between external iliac and common femoral arteries • Internal iliac (hypogastric) artery ○ Principal vascular supply of pelvic organs ○ Divides into anterior and posterior trunk – Anterior trunk to pelvic viscera – Posterior trunk to pelvic musculature • Anterior trunk of internal iliac artery ○ Branching pattern quite variable ○ Umbilical artery – Only pelvic segment remains patent after birth – Remainder becomes fibrous medial umbilical ligament ○ Obturator artery – Exits pelvis through obturator canal to supply medial thigh muscles ○ Superior vesicle artery – Supplies bladder and distal ureter – Gives off branch to ductus deferens in males ○ Inferior vesicle artery (male) – May arise from middle rectal artery – Supplies prostate, seminal vesicles, and lower ureters ○ Uterine artery (female) – Passes over ureter at level of cervix ("water under the bridge") – Anastomoses with vaginal and ovarian arteries ○ Vaginal artery (female) ○ Middle rectal artery runs above pelvic floor and anastomoses with superior and inferior rectal arteries to supply rectum – Also anastomoses with inferior vesicle artery ○ Internal pudendal artery – Supplies external genitalia (penis, clitoris) and rectum ○ Inferior gluteal (sciatic) artery – Largest and terminal branch of anterior division of hypogastric artery – Supplies muscles of pelvic floor, thigh, buttocks and sciatic nerve • Posterior division of internal iliac artery ○ Iliolumbar artery

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– Ascends laterally to supply iliacus, psoas, and quadratus lumborum muscles ○ Lateral sacral artery – Runs medially toward sacral foramina to anastomose with middle sacral artery ○ Superior gluteal artery – Largest and terminal branch of posterior division – Supplies piriformis and gluteal muscles

Veins • External iliac vein ○ Upward continuation of femoral vein at level of inguinal ligament ○ Receives inferior epigastric, deep iliac circumflex, and pubic veins • Internal iliac vein begins near upper part of greater sciatic foramen ○ Gluteal, internal pudendal and obturator veins have origins outside pelvis ○ Pelvic viscera drain into multiple, deep pelvic venous plexuses – These drain into veins, which roughly parallel pelvic arteries • Right gonadal vein drains into IVC, left gonadal vein drains into left renal vein • Common iliac vein is formed by union of external and internal iliac veins ○ Unites with contralateral side to form IVC

IMAGING ANATOMY Overview • CT angiography (CTA) and MR angiography (MRA) are imaging modalities of choice to evaluate pelvic vessels ○ Ultrasound is limited to demonstrating common iliac, external iliac, and proximal internal iliac vessels

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer: 2-5 MHz • Patient examined in supine position ○ Place transducer lateral to rectus muscles, angulating medially • Fasting for 4 hours may help decrease overlying bowel gas

Imaging Pitfalls • Pelvic vessels are usually obscured by overlying bowel gas

CLINICAL IMPLICATIONS Clinical Importance • Abdominal aortic aneurysms may extend to involve iliac arteries • Rich, complex collateral circulation helps ensure delivery of blood to pelvic organs and lower limbs in event of proximal obstruction • Patients with deep venous thrombosis of lower limbs may have involvement of iliac veins

Iliac Arteries and Veins Pelvis

ILIAC ARTERIES AND VEINS IN SITU

Superior mesenteric a.

Ovarian (gonadal) a. Abdominal aorta Inferior vena cava Inferior mesenteric a. Ureter

Common iliac a.

Middle sacral a. Iliolumbar a. Fallopian tube

Ovarian a.

Internal iliac a. Anterior trunk of internal iliac a. External iliac a. Lateral sacral a.

Uterine a. Deep iliac circumflex a.

Medial umbilical l.

Frontal graphic shows the abdominal aorta, inferior vena cava, and the iliac vessels in a female. The inferior mesenteric artery is the smallest of the anterior mesenteric branches of the aorta and continues in the pelvis as the superior rectal artery. The paired ovarian arteries arise from the aorta below the renal arteries and pass inferiorly on the posterior abdominal wall to enter the pelvis. The ureters cross anterior to the bifurcation of the common iliac arteries on their way to the urinary bladder. The common iliac artery divides into the external iliac artery, which supplies the lower extremity and the internal iliac (hypogastric) artery, which supplies the pelvis. The internal iliac artery divides into an anterior trunk for the pelvic viscera and a posterior trunk for the muscles of the pelvis.

409

Pelvis

Iliac Arteries and Veins COMMON ILIAC ARTERY AND BRANCHES

Abdominal aorta

Common iliac a.

Iliolumbar a. Internal iliac a. External iliac a. Anterior division of internal iliac a.

Lumbosacral n. trunk Posterior division of internal iliac a. S1 nerve root Superior gluteal a.

Obturator a.

Lateral sacral a.

Umbilical a. Medial umbilical l.

Superior vesicle aa. Inferior vesicle a.

Inferior gluteal a.

Middle rectal a.

Internal pudendal a.

Uterine a.

Graphic shows the pelvic arteries and their relation to the sacral nerves. The superior gluteal artery passes posteriorly and runs between the lumbosacral trunk and the anterior ramus of the S1 nerve, whereas the inferior gluteal artery usually runs between the S1-2 or S2-3 nerve roots to leave the pelvis through the inferior part of the greater sciatic foramen. Only the proximal portion of the umbilical arteries remains patent after birth, while the distal portion obliterates forming the medial umbilical ligaments. Arteries to the deep pelvic viscera include the superior and inferior vesicle, uterine, middle rectal, and internal pudendal. The individual branching pattern is quite variable.

410

Iliac Arteries and Veins Pelvis

ILIAC VEINS IN SITU

Left renal v.

Right ovarian v. Left ovarian v. Inferior vena cava Ureter

Median sacral v. Iliolumbar v. External iliac v. Internal iliac v. Lateral sacral v. Round l.

Uterine v. Inguinal l.

Middle rectal v.

Superior vesicle v.

Common femoral v.

Graphic of the veins of the pelvis is shown. The left ovarian vein drains into the left renal vein, whereas the right ovarian vein drains directly into the inferior vena cava. Multiple intercommunicating pelvic venous plexuses (rectal, vesicle, prostatic, uterine, and vaginal) drain mainly to the internal iliac veins. There is a communication between the pelvic veins and the intraspinal epidural plexus of veins through the sacral venous plexus.

411

Pelvis

Iliac Arteries and Veins AORTIC BIFURCATION

Left common iliac a. Distal abdominal aorta

Right common iliac a.

Left common iliac a. Artifacts from bowel peristalsis Distal abdominal aorta

Right common iliac a.

Left common iliac a. Artifacts from bowel peristalsis

Distal abdominal aorta

Right common iliac a.

Artifacts from bowel peristalsis

(Top) Coronal grayscale ultrasound shows the bifurcation of the distal aorta into the common iliac arteries. This occurs at the level of the L4 vertebra and corresponds to the umbilicus, serving as a useful landmark for transducer placement for common iliac artery insonation. (Middle) Coronal color Doppler ultrasound demonstrates color flow in the distal aorta and bifurcation. The right common iliac artery assumes a blue color (as opposed to the red color of the distal aorta and right common iliac artery) owing to its flow direction. Peristalsis of adjacent bowel segments also demonstrates color on color Doppler ultrasound, rendering artifacts. (Bottom) Coronal power Doppler is more sensitive than color Doppler in demonstrating blood flow without providing information on flow direction. There is also significant increase in image artifacts from peristalsis.

412

Iliac Arteries and Veins Pelvis

COMMON ILIAC ARTERY

Left common iliac a. Distal abdominal aorta

Distal abdominal aorta

Right common iliac a.

Left common iliac a. Right common iliac a.

Distal abdominal aorta

Left common iliac a.

(Top) Coronal transabdominal grayscale ultrasound is shown, angulating the transducer to demonstrate the course of the left common iliac artery. The common iliac artery is about 5 cm long with diameters of 1.3 cm (females) and 1.5 cm (males). (Middle) Coronal transabdominal color Doppler of the left common iliac artery (shown in red) with consistent intense color indicating uniform mean flow velocity is shown. This is a useful plane for examining abdominal aortic aneurysms when there is extension into the common iliac arteries. (Bottom) Transabdominal color pulsed Doppler ultrasound of the left common iliac artery shows peak systolic velocity of 129 cm/sec, within the normal range of 80-187 cm/sec. Note normal triphasic spectral waveform.

413

Pelvis

Iliac Arteries and Veins INTERNAL ILIAC ARTERY

External iliac a. Common iliac a.

Internal iliac a.

External iliac a.

Common iliac a.

Internal iliac a.

External iliac a. Common iliac a.

Internal iliac a.

(Top) Oblique transabdominal grayscale ultrasound of the distal common iliac artery demonstrates its bifurcation into the external iliac and internal iliac arteries. The internal iliac artery has a smaller caliber compared to the external iliac artery and courses more posteriorly. The internal iliac artery divides into 2 trunks, which are usually too deep to be demonstrated on ultrasound. (Middle) Longitudinal transabdominal color Doppler ultrasound shows intense red color in the distal common iliac and external iliac arteries, suggesting uniform mean velocity in the arterial segments. The branches of the internal iliac artery (shown in blue) supply the wall and viscera of the pelvis, including the reproductive organs. (Bottom) Pulsed Doppler ultrasound shows the internal iliac artery, which is usually investigated in graft kidneys and some cases of erectile dysfunction.

414

Iliac Arteries and Veins Pelvis

EXTERNAL ILIAC ARTERY

External iliac a. External iliac v.

Artifacts from bowel peristalsis External iliac a. External iliac v.

High velocity forward flow in systole

Reversal of flow in early diastole

Low-velocity forward flow in diastole

(Top) Longitudinal transabdominal grayscale ultrasound shows the external iliac artery, usually easily demonstrated owing to its superficial location and absence of overlying bowel gas. Normal diameters are up to 11 mm in females and 12 mm in males. (Middle) Longitudinal transabdominal color Doppler ultrasound shows the relationship of the external iliac artery (shown in red) with the external iliac vein (shown in blue), which is located posteriorly. The 2 vessels run along the same course as they enter the thigh. (Bottom) Pulsed Doppler ultrasound of the external iliac artery is shown; the waveform resembles those from lower extremity arteries. Note high-velocity forward flow during systole and low-velocity forward flow during diastole. There is an intervening short reversal of flow in early diastole due to peripheral resistance. Peak systolic velocity of 129 cm/sec is within the normal range (< 140 cm/sec).

415

Pelvis

Iliac Arteries and Veins ILIAC VESSELS, TRANSVERSE

Left rectus m.

Abdominal aorta Inferior vena cava

Vertebral body

Right common iliac a. Left common iliac a. Inferior vena cava

Vertebral body

Left common iliac a. Right common iliac a. Right common iliac v.

Left common iliac v. Vertebral body

(Top) Transverse transabdominal color Doppler ultrasound at the supraumbilical level shows the distal aorta (shown in red) and inferior vena cava (shown in blue), both of which have not yet bifurcated. The inferior vena cava is to the right of the abdominal aorta; a leftsided inferior vena cava is rarely encountered (0.2-0.5%) and may be associated with other vascular anomalies such as circumaortic or retroaortic renal vein. (Middle) Transverse transabdominal color Doppler ultrasound at the infraumbilical level is shown. The distal aorta has bifurcated into the paired common iliac arteries at the level of L4, occurring more proximally than the formation of the inferior vena cava. (Bottom) Transverse transabdominal color Doppler ultrasound continued from the above image. The paired common iliac veins (in blue) are now identified, which run posterior to their arterial counterparts (in red).

416

Iliac Arteries and Veins Pelvis

ILIAC VESSELS, CT

Inferior mesenteric a. Abdominal aorta Inferior vena cava

Aortic bifurcation Inferior mesenteric a. Inferior vena cava Lumbar a. L4 vertebral body

Inferior mesenteric a. Right common iliac a.

Right common iliac v.

Left common iliac a. Left common iliac v. L5 vertebral body

(Top) First of 3 axial CECT images of the pelvic vessels is shown. The abdominal aorta rests on the vertebral body; its distal portion gives off the inferior mesenteric artery, the smallest of the mesenteric arteries. The inferior vena cava is identified to the right of the abdominal aorta and spine. (Middle) The aorta bifurcates at the level of L4 into the 2 common iliac arteries. Despite its diminutive caliber, the lumbar artery is identified on CT. (Bottom) The common iliac arteries usually give off no visceral branches. They may, however, give origin to accessory renal arteries. At this lower level, the termination of the common iliac veins are identified just before forming into the inferior vena cava. The left common iliac vein is longer than the right as it traverses the spine to form the IVC, which is located in the right paraspinal region.

417

Pelvis

Iliac Arteries and Veins ILIAC VESSELS, TRANSVERSE

Right external iliac a. Right internal iliac a.

Right common iliac v. Vertebral body

Right rectus abdominis m. Right external iliac a. Right external iliac v. Right internal iliac v.

External iliac a. Right iliopsoas m. External iliac v. Iliac crest

(Top) Transverse transabdominal color Doppler ultrasound shows dichotomous branching of the right common iliac artery into the larger caliber external iliac artery (red) and smaller caliber internal iliac artery (red). The common iliac vein (blue) maintains its posterior location in relation to the 2 arteries. (Middle) Transverse transabdominal color Doppler ultrasound, continued more inferiorly in the same patient demonstrates the right external iliac vein (blue) and smaller internal iliac vein (blue). The right external iliac artery (red) is identified anterior to its venous counterpart. (Bottom) Transverse color Doppler ultrasound at the right iliac fossa is shown. The right external iliac artery (red) and vein (blue) course medial to the psoas major/iliopsoas muscle and maintain their relationship until they exit the pelvis beneath the inguinal ligament. Note the larger diameter of the vein compared to the artery.

418

Iliac Arteries and Veins

Right external iliac a. Right internal iliac a.

Pelvis

ILIAC VESSELS, CT

Left external iliac a. Left internal iliac a. Left common iliac v.

Right common iliac v. Iliolumbar a.

Inferior epigastric a.

Right external iliac a.

Right external iliac v. Right internal iliac v.

Left external iliac a.

Left internal iliac a. Anterior division, internal iliac a. Posterior division, internal iliac a.

Inferior epigastric a.

Right external iliac a. Right external iliac v.

Left external iliac a. Left external iliac v.

Anterior division internal iliac a.

Superior gluteal a.

(Top) First of 3 axial CECTs of the pelvic vessels is shown. The common iliac arteries bifurcate more proximal to the formation of the common iliac veins. The iliolumbar artery, usually a branch of the posterior trunk of the internal iliac artery, arises in this subject from the main internal iliac artery. CT is the imaging modality of choice in the examination of smaller pelvic vessels. (Middle) The internal iliac artery divides into an anterior and posterior trunk. The anterior trunk mainly supplies the pelvic viscera, whereas the posterior trunk supplies the pelvic musculature. Note their deep location relative to the external iliac vessels, which limits ultrasound examination of internal iliac vessel branches and tributaries. (Bottom) The external iliac artery and vein continue in an anterolateral direction as they course out of the pelvis and into the thigh.

419

Pelvis

Iliac Arteries and Veins COMMON ILIAC VEIN

Common iliac a. External iliac v. Common iliac v.

Internal iliac v.

External iliac a. External iliac v. Common iliac v. Internal iliac a. Internal iliac v.

External iliac v. Common iliac v.

Internal iliac v.

(Top) Longitudinal transabdominal grayscale ultrasound shows the external and internal iliac veins converging to form the common iliac vein. (Middle) Longitudinal transabdominal color Doppler ultrasound provides information on the direction of blood flow in the pelvic vessels, facilitating identification and differentiation of the veins from arteries. The external iliac vein (shown in blue) is a largecaliber vessel seen posterior to its arterial counterpart (shown in multicolor). Note its uniform intensity in color flow. The internal iliac vein (shown in red) is smaller in diameter and directed inferomedially. (Bottom) Pulsed Doppler ultrasound of the common iliac vein shows uniform velocity with mild phasic changes associated with respiration.

420

Iliac Arteries and Veins Pelvis

INTERNAL ILIAC VEIN

Common iliac a. External iliac v. Common iliac v.

Internal iliac v.

External iliac v. Common iliac v. Internal iliac a.

Internal iliac v.

Common iliac v.

External iliac v. Internal iliac a.

(Top) Longitudinal transabdominal grayscale ultrasound shows the external and internal iliac veins converging to become the common iliac vein. The internal iliac vein drains various veins from outside the pelvis, the sacrum, and from the venous plexuses connected to pelvic viscera. (Middle) Longitudinal transabdominal color Doppler ultrasound shows a short segment of the internal iliac vein (shown in red) draining into the common iliac vein (shown in blue). Owing to its depth, the internal iliac vein cannot be identified on ultrasound in its entirety. (Bottom) Pulsed Doppler ultrasound of the internal iliac vein shows continuous venous flow and uniform velocity devoid of phasic changes and unaffected by respiration.

421

Pelvis

Iliac Arteries and Veins EXTERNAL ILIAC VEIN

External iliac a. External iliac v. Internal iliac a. Internal iliac v.

Urinary bladder

External iliac a. External iliac v.

Urinary bladder

External iliac v.

External iliac a.

(Top) Longitudinal transabdominal grayscale ultrasound at the lower abdomen is shown. The external iliac vein runs parallel and posterior to the external iliac artery. The 2 vessels are readily identified owing to their superficial location. The transducer is angulated medially, and the urinary bladder is included in the image. (Middle) Longitudinal transabdominal color Doppler ultrasound shows different flow directions in the external iliac artery (shown in red) and vein (shown in blue). The artery is anterior to the vein, and the 2 vessels run beneath the inguinal ligament to enter the thigh. Owing to its superficial location, the external iliac vein is easily examined during ultrasound investigation for deep venous thrombosis in the lower limbs. (Bottom) Pulsed Doppler ultrasound of the external iliac vein is shown. Normal spectral waveform shows continuous flow and exaggerated phasic changes from deep inspiration/expiration.

422

Iliac Arteries and Veins Pelvis

ATHEROSCLEROTIC DISEASE

Thrombus

Distal abdominal aorta Left common iliac a.

Right common iliac a.

Stenotic segment

Distal abdominal aorta

Left common iliac a.

Stenotic segment

(Top) Longitudinal color Doppler ultrasound shows a moderate amount of mural thrombus in the infrarenal aorta (shown in blue) just above the bifurcation, causing narrowing of the lumen. The thrombus extends into the left common iliac artery. (Middle) Oblique color Doppler ultrasound shows the common iliac artery with a > 50% diameter reduction. High-velocity turbulent flow is seen as "aliasing" artifact on color Doppler imaging at the stenotic segment. (Bottom) Corresponding oblique pulsed color Doppler ultrasound shows spectral Doppler trace at the common iliac artery stenosis with characteristic high-velocity bidirectional waveform.

423

Pelvis

Ureters and Bladder

GROSS ANATOMY Ureters • Muscular tubes (25-30 cm long) that carry urine from kidneys to bladder • Course ○ In abdomen, retroperitoneal location – Proximal ureters lie in perirenal space – Mid ureters lie over psoas muscles slightly medial to tips of L2-L5 transverse process ○ In pelvis, lie anterior to sacroiliac joints crossing common iliac artery bifurcation near pelvic brim – Lie anterior to internal iliac vessels and course along pelvic sidewall – At level of ischial spines, ureters curve anteromedially to enter bladder at level of seminal vesicles (men) or cervix (women) ○ Ureterovesical junction (UVJ): Ureters pass obliquely through muscular wall of bladder for ~ 2 cm – Creates valve effect with bladder distension, preventing vesicoureteral reflux (VUR) • 3 points of physiological narrowing ○ Ureteropelvic junction ○ Pelvic brim (crossing over common iliac artery) ○ UVJ • Vessels, nerves, and lymphatics ○ Arterial branches are numerous and variable, arising from aorta and renal, gonadal, internal iliac, vesicle, and rectal arteries ○ Venous branches and lymphatics follow arteries with similar names ○ Innervation – Autonomic from adjacent sympathetic and parasympathetic plexuses □ Responsible for ureteral peristalsis – Also carry pain (stretch) receptors □ Stone in abdominal ureter perceived as back and flank pain □ Stone in pelvic ureter may project to scrotum or labia ○ Lymphatics to external and internal iliac nodes (pelvic ureter), aortocaval nodes (abdomen)

Bladder • Hollow, distensible viscus with strong, muscular wall and normal adult capacity of 300-600 mL of urine • Lies in extraperitoneal (retroperitoneal) pelvis • Peritoneum covers dome of bladder ○ Reflections of peritoneum form deep recesses in pelvic peritoneal cavity ○ Rectovesical pouch (between rectum and bladder) is most dependent recess in men (and in women following hysterectomy) ○ Vesicouterine pouch (between bladder and uterus) and rectouterine pouch of Douglas (between rectum and uterus) – Rectouterine pouch most dependent in women • Bladder is surrounded by extraperitoneal fat and loose connective tissue ○ Perivesical space (contains bladder and urachus) 424

○ Prevesical or retropubic space (of Retzius) between bladder and symphysis pubis – Communicates superiorly with infrarenal retroperitoneal compartment – Communicates posteriorly with presacral space ○ Spaces can expand to contain large amounts of fluid (as in extraperitoneal rupture of bladder and hemorrhage from pelvic fractures) • Bladder wall composed mostly of detrusor muscle ○ Trigone of bladder: Triangular structure at base of bladder with apices marked by 2 ureteral orifices and internal urethral orifice • Vessels, nerves, and lymphatics ○ Arteries from internal iliac – Superior vesicle arteries and other branches of internal iliac arteries in both sexes ○ Venous drainage – Men: Vesicle and prostatic venous plexuses → internal iliac and internal vertebral veins – Women: Vesicle and uterovaginal plexuses → internal iliac vein ○ Autonomic innervation – Parasympathetic from pelvic splanchnic and inferior hypogastric nerves (causes contraction of detrusor muscle and relaxation of internal urethral sphincter to permit emptying of bladder) – Sensory fibers follow parasympathetic nerves

IMAGING ANATOMY Overview • Normal ureters are small in caliber (2-8 mm) and are difficult to appreciate on ultrasound • Fluid-distended urinary bladder is anechoic with posterior acoustic enhancement • Urinary bladder changes in shape and position depending on intraluminal volume of urine ○ In its nondistended state, urinary bladder is retropubic in location, lying anterior to uterus in females and rectum in males ○ In markedly distended state, urinary bladder may occupy abdominopelvic area ○ Urinary bladder wall changes in thickness depending on state of distension of urinary bladder and is normally 3-5 mm in thickness

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer: Curvilinear 2-5 MHz • Ureters ○ Ureters are normally not seen on ultrasound unless they are dilated; when dilated, overlying bowel gas may still limit ureteral evaluation in transabdominal approach – Proximal dilated ureters may be well seen using kidney as window in coronal oblique plane – Middle portion of dilated ureter may be identified in pediatric patients or thin adults using transabdominal approach – Dilated terminal ureter/UVJ are seen best along posterolateral aspect of urinary bladder on transverse view

Ureters and Bladder

Imaging Pitfalls • Reverberation artifacts are commonly encountered behind anterior wall of urinary bladder ○ Appear as regularly spaced lines at increasing depth as result of repeated reflection of ultrasound signals between highly reflective interfaces close to transducer ○ May be reduced or avoided by changing scanning angle or by moving transducer or using spacer • Underdistended bladder may give false impression of wall thickening and limits intraluminal assessment ○ Have patient drink water and rescan with better distention • Large midline ovarian or pelvic cystic mass may simulate bladder on transabdominal ultrasound ○ Attention to normal bladder shape, rescanning after voiding to confirm empty bladder, or transvaginal imaging is helpful to differentiate

CLINICAL IMPLICATIONS

Pelvis

□ Can also be evaluated by endovaginal sonography in women ○ Ureteral caliber may slightly increase as result of overfilled urinary bladder – Distended bladder may cause ureteral and pelvicalyceal dilation and rescanning post void is beneficial to exclude obstruction ○ Color Doppler – Assess normal ureteral jets at and helps exclude complete ureteral obstruction – Look for twinkle artifact from obstructing stone • Bladder ○ Recommend fluid intake prior to examination to ensure optimal distension of urinary bladder – In fully distended state, urinary bladder is easily visualized using transabdominal approach ○ Examine patient in supine position with transabdominal suprapubic approach – Perform scanning in sagittal and transverse planes – Patient may be placed in decubitus position to determine mobility and differentiated intravesical masses from debris or stones – With poor distention, caudal transducer angulation is needed to visualize urinary bladder in its retropubic location ○ Nature of cystic structure in pelvis may be ascertained by asking patient to void or by inserting Foley catheter ○ Transvaginal ultrasound may be used in women for evaluation of suspect bladder neck lesions, UVJ stone, or ureterocele ○ Advantages of ultrasound – Radiation-free, real-time assessment with high spatial resolution of bladder and bladder wall – Real-time assessment of intraluminal masses in bladder for mobility and vascularity – Real-time imaging guidance for bladder intervention, e.g., placement of percutaneous suprapubic catheters – Real-time assessment of ureteral jets using color Doppler imaging; particularly useful in pregnant patients with dilated collecting system

Clinical Importance • Ureters are at high risk of inadvertent injury during abdominal or gynecological surgery due to close proximity to uterine (in uterosacral ligament) and gonadal arteries (at pelvic brim) • Ectopic ureter ○ Usually (80%) associated with complete ureteral duplication; more common in females ○ In complete duplication, upper moiety inserts ectopically inferiorly and distally to lower moiety (Weigert-Meyer rule) and can be associated with ureterocele – Ureterocele may cause obstruction of upper pole moiety; also distorts UVJ of normally inserting lower pole moiety causing predisposition to VUR ○ Ectopic ureteral insertion in females can occur in urethra or vagina, leading to urinary incontinence • Ureterocele ○ Cystic dilation of intramural portion of ureter bulging into bladder – Orthotopic: Normal insertion of single ureter – Ectopic: Inserts below trigone, mostly in duplicated system • Ureteral duplication ○ Bifid ureter drains duplex kidney, but ureters unite before entering bladder • Urachal anomalies ○ Patent fetal urachus forms conduit between umbilicus and bladder ○ Urachus is normally obliterated to form median umbilical ligament ○ May persist as cyst, diverticulum, or rarely, fistula ○ Risk of infection or carcinoma (adenocarcinoma) • Bladder diverticula are common ○ Congenital: Hutch diverticulum (near UVJ) ○ Acquired (usually due to chronic bladder outlet obstruction), associated with trabeculated bladder wall ○ Can lead to infection, stones, tumor • Trauma ○ Extraperitoneal bladder rupture – Urine and blood distend prevesical space (Retzius) – Urine often tracks posteriorly into presacral space, superiorly into retroperitoneal abdomen – High association with pelvic fractures ○ Intraperitoneal bladder rupture – Urine flows up paracolic gutters into peritoneal recesses and surrounds bowel – Bladder ruptures along dome, which is in contact with intraperitoneal space – Usually caused by blunt trauma to overdistended bladder

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Pelvis

Ureters and Bladder URETERS AND URINARY BLADDER IN SITU

Ureteric branch from renal a. Superior mesenteric a.

Gonadal (ovarian) aa. Left ureter

Right ureter

Inferior mesenteric a.

Psoas m.

External iliac a. & v. Internal iliac a.

Rectum Uterus

Uterine a.

Ureteric branch from inferior vesicle a.

Vaginal a.

Superior vesicle a.

Median l.

Urinary bladder

The ureters receive numerous and highly variable arterial branches from the aorta and the renal, gonadal, and internal iliac arteries. These vessels are short and can be easily ruptured by retraction of the ureter during surgical procedures. The arterial supply to the bladder is also quite variable. Both genders receive supply from the superior vesicle arteries and from various branches of the internal iliac arteries. Branches to the prostate and seminal vesicles (men) also send branches to the inferior bladder wall. In women, branches to the vagina send arteries to the base of the bladder. Note how the ureters deviate anteriorly as they cross the external (or common) iliac vessels and pelvic brim. This may constitute a point of relative narrowing where the passage of ureteral calculi (stones) may be impeded. In the abdomen, the ureters course along the psoas muscles.

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Ureters and Bladder Pelvis

URINARY BLADDER IN SITU, MALE

Peritoneum Detrusor m. Urinary bladder

Rectovesical pouch

Space of Retzius

Seminal vesicle

Public symphysis

Rectum

Prostate Urogenital diaphragm

Supravesical space

Vas deferens

Trigone Perivesical space Obturator internus m. Levator ani m.

Prostatic urethra Urogenital diaphragm Penile urethra

Corpus spongiosum Corpus spongiosum

(Top) Graphic of a sagittal section of the male bladder shows that it rests on the prostate, which separates it from the muscular pelvic floor. The bladder wall is muscular, strong, and very distensible. In males, the urinary bladder is directly anterior to the rectum, and the rectovesical pouch is the deepest point in the pelvis. (Bottom) A coronal section of the male bladder shows the anatomic relationships of the bladder with its surrounding structures. The trigone is a triangle formed by the ureteral orifices and urethral outlet. The ureters enter the bladder through an oblique anteromedial course that helps to prevent urinary reflux into the ureters.

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Pelvis

Ureters and Bladder URINARY BLADDER IN SITU, FEMALE

Uterus

Peritoneum

Detrusor m.

Space of Retzius

Rectum Rectouterine pouch of Douglas

Vesicouterine pouch Vagina

Pubic symphysis

Fundus (dome) of bladder

Peritoneum Body of bladder Left ureteral orifice Perivesical space

Trigone Vesical fascia Tendinous arch of pelvic fascia

Obturator internus m. Levator ani m.

Urogenital diaphragm Urethra

Vagina

(Top) Sagittal graphic shows a nondistended bladder in a female. When decompressed, the bladder wall can appear quite thick and can erroneously be interpreted as abnormal. The dome of the bladder is covered with peritoneum. The bladder is surrounded by a layer of loose fat and connective tissue (the prevesical space of Retzius and perivesical spaces) that communicate superiorly with the retroperitoneum. Note the vagina/uterus in the female pelvis, which intervenes between the urinary bladder and rectum. (Bottom) A frontal (coronal) section of the female bladder shows that it rests almost directly on the muscular floor of the pelvis. The dome of the bladder is covered with peritoneum. The trigone is the distinct triangular base of the bladder whose apices are formed by the ureteral and urethral orifices.

428

Ureters and Bladder Pelvis

URETERS

Kidney L2 vertebral body

Renal pelvis

Ureter

Urinary bladder

Abdominal musculature

Liver

Ureter Kidney

Renal pelvis

Vertebral body

Dilated calyces

Dilated ureter

Dilated ureter

Twinkle artifact from stone

(Top) Volume-rendered 3D reformatted image from a CT urogram shows the normal course of the ureters overlying L3-L5 transverse process. (Middle) The ureter is identified in this very thin teenage girl by scanning through the right flank and using the liver as an acoustic window. Even in thin patients, the ureter is usually not seen secondary to overlying bowel gas. (Bottom) This composite image shows an obstructing midureteral stone just above the pelvic rim. The pelvic rim, along with the ureteropelvic and ureterovesical junctions, are areas of narrowing and are the most likely locations for a stone to lodge. Even if you can't seen the entire ureter, specifically target these areas on your scan when evaluating for an obstructing stone.

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Pelvis

Ureters and Bladder URETERS

Liver

Dilated calyx Dilated ureter Vertebral bodies Dilated renal pelvis

Normal left ureteral jet

Right ureterovesical junction stone causing twinkling artifact with absent ureteral jet

Mild hydronephrosis

Significant urothelial thickening

(Top) Longitudinal transabdominal grayscale ultrasound of the right kidney shows a dilated pelvicalyceal system and proximal ureter. The ureter is normally not visible on ultrasound unless it is dilated, as seen here. (Middle) Oblique color Doppler ultrasound of the suprapubic region in the same patient shows a calculus at the right ureterovesical junction causing twinkling artifact with an absent ureteral jet. A normal left ureteric jet is seen. (Bottom) Longitudinal transabdominal ultrasound of the left kidney shows significant urothelial thickening of the pelvicalyceal system and proximal ureter in this patient with known extramedullary hematopoiesis.

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Ureters and Bladder Pelvis

BLADDER

Bladder lumen

Bladder wall

Uterus

Reverberation artifact

Enlarged prostate Trabeculations

Trabeculations

Right ureteral jet Left ureteral

(Top) Transverse transabdominal grayscale ultrasound shows a distended bladder with a smooth wall. The transducer must be angled caudally to image the urinary bladder, especially when it is not well distended and assumes a retropubic location. (Middle) Transverse ultrasound of the bladder shows wall thickening and trabeculations in this patient with benign prostatic hypertrophy and chronic bladder outlet obstruction. Note the reverberation artifact, which compromises evaluation of the anterior bladder wall. (Bottom) Transverse color Doppler image at the level of the ureteral orifices shows bilateral, symmetric, ureteral jets. Always evaluate for the presence of ureteral jets when evaluating for obstruction.

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Pelvis

Ureters and Bladder URINARY BLADDER

Internal echoes

Layering echogenic debris

Urinary bladder wall

Urinary bladder

Diverticulum

Prostate Prostatic urethra

Diverticulum neck

Urine jet at diverticulum neck

Bladder diverticula

(Top) Transverse transabdominal ultrasound of the bladder shows floating internal echoes with layering echogenic debris in this patient with cystitis. This could be confused with wall thickening, and the patient should be put in a decubitus position to document debris movement. (Middle) Graphic shows a diverticulum arising from the lateral urinary bladder wall with herniation of the mucosa and submucosa through the muscular wall. (Bottom) Transverse oblique transabdominal color Doppler ultrasound through the bladder shows 2 well-distended bladder diverticula along the left posterolateral bladder. A urine jet is identified in one of the diverticular necks.

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Ureters and Bladder Pelvis

WEIGERT-MEYER RULE

Orthotopic ureter with ureterocele

Orthotopic ureter

Dilated ectopic ureter and ureterocele

Bladder

Ureterocele

Dilated right distal ureter

Nondilated lower pole collecting system

Dilated upper pole collecting system (moiety)

(Top) Graphic illustrates an orthotopic ureterocele in a single ureter system (left, upper) and an ectopic ureterocele in a duplicated ureter system (right, lower). Note the hydroureter accompanying the ectopic ureterocele. The ectopic ureterocele inserts inferior and medial to the normally inserting ureter (Weigert-Meyer rule). (Middle) Longitudinal oblique transabdominal grayscale ultrasound at the suprapubic region shows a dilated ureter seen terminating in a ureterocele; the patient had complete duplication of the collecting system. (Bottom) Longitudinal transabdominal grayscale ultrasound through the right kidney in the same patient shows a dilated, obstructed upper pole moiety with a decompressed inferior moiety. The lower pole moiety is at risk for reflux and may also be dilated.

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Pelvis

Prostate and Seminal Vesicles

GROSS ANATOMY Prostate • Walnut-sized gland beneath bladder and in front of rectum ○ Normal prostate in young male ~ 3 cm length x 4 cm width x 2 cm depth ○ Normal weight ~ 20-30 grams • Inverted conical shape ○ Base: Superior portion, continuous with bladder neck ○ Apex: Inferior portion, continuous with striated sphincter • Capsule: Composed of condensed fibromuscular band, not true capsule ○ Does not completely envelop prostate: Absent at base and not clearly defined at apex ○ Capsular components are inseparable from prostatic stroma and periprostatic connective tissue • Posteriorly, Denonvilliers fascia (thin layer of connective tissue) separates prostate and seminal vesicles from rectum • Laterally, prostate is cradled by pubococcygeal portion of levator ani • Toward apex, puboprostatic ligaments extend anteriorly to affix prostate to pubic bone ○ Apex is continuous with striated external urethral sphincter • Ejaculatory ducts form at junction of vas deferens and seminal vesicles and enter prostate base • Prostatic urethra ○ Verumontanum (a.k.a. colliculus seminalis) – Midway between base and apex where urethra makes ~ 35° bend anteriorly □ Openings of prostatic utricle and ejaculatory ducts – Divides prostatic urethra into proximal (preprostatic) and distal (prostatic) segments ○ Preprostatic sphincter: Thickened circular smooth muscle in proximal segment (a.k.a. involuntary internal urethral sphincter, periurethral zone) – Thought to function during ejaculation to prevent retrograde flow of seminal fluid – May also have resting tone, which maintains closure of preprostatic urethra, thereby aiding urinary continence – Contains small periurethral glands completely enclosed in sphincter □ Although these glands constitute < 1% of glandular prostate, they can contribute significantly to prostatic volume as one site of origin of benign prostatic hyperplasia (BPH) ○ Urethral crest: Narrow longitudinal ridge on midline posterior wall – Multiple small openings draining prostatic ducts ○ Prostatic utricle: Small, superoposteriorly directed vestigial blind pouch with opening in verumontanum, ~ 6 mm long – Müllerian remnant (homologous with uterus and vagina) • Neurovascular bundles (NVB) ○ Lie posterolaterally to prostate ○ Carry nerves and vascular supply to corpora cavernosa • Vascular supply

○ Most commonly, arterial supply from inferior vesical artery – Often divides into 2 main branches: Urethral arteries and capsular artery □ Urethral arteries supply periurethral glands and transition zone (TZ) → main supply for BPH □ Bulk of capsular artery runs posterolaterally with cavernous nerves in NVB and ends at pelvic diaphragm ○ Venous drainage via periprostatic plexus; receives blood from dorsal vein of penis; drains into internal iliac veins • Nerve supply: Pelvic plexuses arising from S2-4 (parasympathetic) and L1-2 (sympathetic) fibers • Lymphatic drainage chiefly to obturator and internal iliac nodes; small portion may initially pass through presacral group or, less commonly, external iliac nodes

Lobar Anatomy (Lowsley) • Based on studies on human fetal prostate; distinct lobes do not exist in prepubertal and normal adult prostate • Lobes: Anterior, median, posterior, and 2 lateral ○ Currently used in context of BPH – Lateral lobes: Hyperplasia of glands in TZ – Median lobe: Hyperplasia of periurethral glands in preprostatic sphincter or TZ and may project into bladder • Largely replaced by zonal anatomy

Zonal Anatomy (McNeal) • Prostate is histologically composed of ~ 70% glandular and 30% nonglandular elements • 2 nonglandular elements: Prostatic urethra and anterior fibromuscular stroma (AFMS) ○ AFMS is contiguous with bladder muscle and external urethral sphincter, up to 1/3 of prostatic mass ○ AFMS runs anteriorly from bladder neck to striated urinary sphincter • Peripheral zone (PZ): ~ 70% glandular tissue, covers posterolateral aspects of gland ○ Surrounds central zone (CZ) and prostatic (distal) urethra ○ Ducts drain into prostatic sinuses along urethra ○ ~ 70-75% prostatic adenocarcinomas arise in this zone • CZ: ~ 25% glandular tissue; cone-shaped zone around ejaculatory ducts with widest portion making majority of prostatic base ○ Only 1-5% prostate adenocarcinoma originate in this zone; mainly involved by secondary invasion • TZ: ~ 5-10% glandular tissue, 2 separate lobules surround preprostatic urethra (urethra proximal to verumontanum) ○ 1 site of origin of BPH, along with periurethral glands ○ ~ 20-25% of prostate adenocarcinoma arise in this zone • Periurethral glands in preprostatic sphincter: < 1% glandular tissue, a site of origin of BPH • Prostate pseudocapsule ("surgical capsule") ○ Visible boundary between TZ and PZ representing compressed tissue ○ Frequently, calcified corpora amylacea (laminated bodies formed of secretions and degenerate cells) highlight plane between PZ and TZ

Seminal Vesicles and Ejaculatory Ducts • Seminal vesicles

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Prostate and Seminal Vesicles

IMAGING ANATOMY Ultrasound • Prostate ○ Transabdominal ultrasound can assess size but transrectal ultrasound (TRUS) required for detailed assessment ○ Normal TZ is typically uniformly more echogenic than inner gland ○ Inner gland (TZ and CZ) is often distinguishable from PZ – Heterogeneous TZ in BPH ○ TRUS is mainstay of many image-guided prostate interventions – Prostate biopsy: Either abnormal digital rectal exam or elevated prostate-specific antigen (PSA) – Brachytherapy, cryotherapy, high-intensity focused ultrasonography (HIFU), and BPH evaluation • Prostate volume measurement ○ Prolate ellipse volume for 3 unequal axes: Width x height x length x 0.523 ○ 1 cc of prostate tissue ~ 1 g; prostate weighs ~ 20 g in young men ○ Prostatic enlargement when gland is > 40 g • Seminal vesicles and vasa deferentia ○ Cystic appearance on TRUS, should be symmetric

MR • Best modality for evaluating extracapsular spread and staging of prostatic carcinoma • T1WI: Homogeneous intermediate signal intensity ○ Often best sequence for NVB, which are at 5- and 7o'clock positions • T2WI: Depicts zonal anatomy ○ AFMS is low signal intensity ○ PZ is high signal intensity, ≥ periprostatic fat ○ PZ is surrounded by thin, low signal true capsule ○ CZ and TZ are similar T2 signal intensity, < PZ ○ Seminal vesicles are bright, similar to other fluid containing structures • Tumors are low signal on T2WI, bright on diffusion weighted imaging, and show faster, stronger enhancement and rapid washout on dynamic contrast enhancement

○ 7-10 MHz rectal transducer (end-firing or transverse panoramic) ○ 3.5-6 MHz curved linear transducer for transabdominal ultrasound ○ Perform in at least 2 orthogonal planes (axial and sagittal) • Patient position ○ TRUS: Left lateral decubitus with flexed hips and knees or in lithotomy position ○ Transabdominal ultrasound: Supine, using urinary bladder as acoustic window (transvesical) – Fluid intake to ensure bladder distension

Pelvis

○ Sac-like structures superolateral to prostate, lateral outpouchings of vas deferens ○ Secrete fructose-rich fluid (energy source for sperm) ○ Arterial supply: Vesiculodeferential artery (branch of superior vesical artery) – May have additional supply from inferior vesical artery ○ Venous drainage into pelvic venous plexus ○ Lymphatic drainage into external and internal iliac nodes • Ejaculatory ducts ○ Located on either side of midline ○ Formed by union of seminal vesicle duct and vas deferens ○ Start at base of prostate and run forward and downward through gland in CZ

Imaging Pitfalls • Abnormal vascularity on power Doppler ultrasound may be seen in hypertrophy, inflammation, and cancer ○ Useful for directing biopsy • Transabdominal ultrasound of prostate is limited to evaluation of prostate size

Transrectal Biopsy of Prostate • Most transrectal transducers have needle guidance system • Periprostatic block with local anesthesia injected along NVB; may also use anesthetic gel and intraprostatic injection of local anesthetic • Complications ○ Common: Hematuria, hematochezia, and hematospermia ○ Other: Acute prostatitis, UTI, sepsis

CLINICAL IMPLICATIONS Function • Main function is to add nutritional secretions to sperm to form semen during ejaculation • Also plays role in controlling flow of urine; prostate muscle fibers are under control of involuntary nervous system and contract to slow and stop urine

Zonal Distribution of Prostatic Disease • Prostate adenocarcinomas ○ 75% in PZ – Up to 80% of prostatic cancers in PZ are hypoechoic ○ 20% in TZ ○ 5% in CZ • BPH: Nodular stromal and epithelial hyperplasia in periurethral (preprostatic) glands and TZ ○ Compresses CZ and PZ ○ Can cause bladder outlet obstruction from urethral compression &/or increased smooth muscle tone along bladder neck, prostate, and urethra

Spread of Prostate Carcinoma • Signs of extraprostatic extension of prostatic carcinoma ○ Asymmetry of NVB ○ Obliteration of rectoprostatic angle ○ Irregular bulge in prostatic contour

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer 435

Pelvis

Prostate and Seminal Vesicles PROSTATE

Urinary bladder Seminal vesicle

Ejaculatory duct Prostate Prostatic urethra

Membranous urethra

Rectovesical septum (Denonvilliers fascia) Urogenital diaphragm Bulbourethral (Cowper) gland and duct

Urethral crest Prostatic sinus Prostatic ducts Ejaculatory duct orifice

Verumontanum Utricle orifice

Bulbourethral (Cowper) gland

(Top) Graphic illustrates the relationship between the prostate and the male pelvic organs. The prostate surrounds the upper part of the urethra (prostatic urethra). The base of the prostate is continuous with the bladder neck, and its apex is continuous with external sphincter. The posterior surface is separated from the rectum by the rectovesical septum (Denonvilliers fascia). (Bottom) Graphic shows the topography of the posterior wall of the prostatic urethra. The urethral crest is a mucosal elevation along the posterior wall with the verumontanum being a mound-like elevation in the midportion of the crest. The utricle opens midline onto the verumontanum with the ejaculatory ducts opening on either side. The prostatic ducts are clustered around the verumontanum and open into the prostatic sinuses, which are depressions along the sides of the urethral crest.

436

Prostate and Seminal Vesicles Pelvis

VAS DEFERENS AND SEMINAL VESICLES

Ureter Vas deferens

Seminal vesicle

Seminal vesicle duct

Prostate

Corpus spongiosum Vas deferens

Epididymis

Bladder

Ureter

Vas deferens

Seminal vesicle (cut surface)

Seminal vesicle duct Ejaculatory duct

Prostate

(Top) This lateral view shows the position of the prostate deep in the pelvis. The vas deferens leaves the scrotum as a component of the spermatic cord, which courses through the inguinal canal into the pelvis. (Bottom) Posterior view of the prostate gland and seminal vesicles is shown. The cut surface of the seminal vesicle shows its highly convoluted fold pattern. The vas deferens crosses superior to the ureterovesical junction and continues along the posterior surface of the urinary bladder medial to the seminal vesicle. In the base of the prostate, it is directed forward and joined at an acute angle by the duct of the seminal vesicle to form the ejaculatory duct. The ejaculatory ducts course anteriorly and downward through the prostate to slit-like openings on either side of the orifice of the prostatic utricle.

437

Pelvis

Prostate and Seminal Vesicles ZONAL ANATOMY OF THE PROSTATE

Anterior fibromuscular stroma Central zone

Pseudocapsule Peripheral zone

Urethra

Transition zone

Peripheral zone Ejaculatory ducts

Anterior fibromuscular stroma Urethra

Peripheral zone

Graphic depiction of the prostate with axial drawings of the zonal anatomy at 3 different levels is shown. The transition zone (TZ) (in blue) is anterolateral to the verumontanum. The central zone (CZ) (in orange) surrounds the ejaculatory ducts and encloses the periurethral glands and the TZ. It is conical in shape and extends downward to about the level of the verumontanum. The peripheral zone (PZ) (in green) surrounds the posterior aspect of the CZ in the upper 1/2 of the gland, and it surrounds the urethra in the lower half, below the verumontanum. The prostatic pseudocapsule is a visible boundary between the CZ and PZ. The anterior fibromuscular stroma (in yellow) covers the anterior part of the gland and is thicker superiorly and thins inferiorly in the prostatic apex.

438

Prostate and Seminal Vesicles

Seminal vesicles

Pelvis

ZONAL ANATOMY OF THE PROSTATE

Urinary bladder

Central zone

Ejaculatory duct

Transition zone

Anterior fibromuscular stroma

Peripheral zone

Urinary bladder Proximal prostatic urethra

Central zone Periurethral glands

Preprostatic sphincter

Transition zone Peripheral zone

Distal prostatic urethra

Verumontanum

(Top) Graphic illustrates the zonal anatomy of the prostate in the sagittal plane. The CZ surrounds the proximal urethra posterosuperiorly, enclosing both the periurethral glands and the TZ. It forms most of the prostatic base. The PZ surrounds both the CZ and the distal prostatic urethra. (Bottom) The proximal 1/2 of the prostatic urethra is surrounded by preprostatic sphincter, which extends inferiorly to the level of the verumontanum and encloses the periurethral glands. The preprostatic sphincter is thought to function during ejaculation to prevent retrograde flow and may also contribute to resting tone. The TZ is a downward extension of the periurethral glands around the verumontanum. Periurethral glands are < 1% of the normal prostate but are one of the sites of origin for benign prostatic hyperplasia (BPH) and can enlarge significantly.

439

Pelvis

Prostate and Seminal Vesicles NORMAL PROSTATE AND BENIGN PROSTATIC HYPERPLASIA

Vas deferens Seminal vesicle

Central zone (in orange) Urethra Transition zone (in blue)

Peripheral zone (in green)

Vas deferens Seminal vesicle Compressed central zone (in orange)

Hypertrophied transition zone (in blue)

Compressed urethra

Peripheral zone (in green)

(Top) First of 2 graphics comparing zonal anatomy in a young man to an older man with BPH is shown. The TZ in young men is small in size, comprising 5% of the volume of the glandular tissue of the prostate. It surrounds the anterolateral aspect of the urethra at the level of verumontanum in a horseshoe fashion. (Bottom) With the development of BPH, there is enlargement of the TZ. This causes enlargement of the prostate and compression of the CZ and PZ. BPH mainly involves the TZ, though other zones may also be involved. The enlarged TZ causes compression of the prostatic urethra, the primary reason for development of urinary obstructive symptoms in patients with BPH.

440

Prostate and Seminal Vesicles Pelvis

GROSS IMAGES, PROSTATE Vas deferens

Seminal vesicle

Base of gland

Seminal vesicle

Urethra

Apex of gland

Probe in urethra

Vas deferens Seminal vesicle

Ejaculatory duct

Prostatic urethra

35° urethral angulation

Anterior fibromuscular stroma

Transition zone

Urethra Verumontanum

Peripheral zone

(Top) Anterior-superior view of a resected prostate shows the urethra at the base. Paired bilateral seminal vesicles are attached to the posterior aspect of the base, lateral to the tubular vas deferens. (From DP: Genitourinary.) (Middle) These different views of the prostate depict the course of the prostatic urethra (yellow), which has a 35° anterior angulation halfway between base and apex, at the level of the verumontanum; this divides the prostatic urethra into proximal and distal segments. The ejaculatory ducts (blue) have a straighter course from the base of the seminal vesicles to the verumontanum. (From DP: Genitourinary.) (Bottom) This cross section of the prostate at the level of the verumontanum shows the PZ, which has a more spongy appearance, surrounding the hypertrophied, nodular TZ. (From DP: Genitourinary.)

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Pelvis

Prostate and Seminal Vesicles VARYING DEGREES OF BENIGN PROSTATIC HYPERPLASIA

Transition zone Pseudocapsule Peripheral zone Neurovascular bundle

Rectum

Transition zone Transition zone Urethra Peripheral zone Neurovascular bundles

Transition zone Urethra Peripheral zone

Peripheral zone Neurovascular bundles

Transition zone

Pseudocapsule Peripheral zone

Neurovascular bundle

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(Top) Axial T2 MR shows nodular enlargement of the TZ, a typical appearance of BPH. The PZ is high signal intensity. There is a prominent low-signal pseudocapsule between the TZ and PZ. (Middle) Transverse TRUS at the level of the midprostate shows the 2 lobes of the TZ on either side of the urethra. The more homogeneous PZ is along the posterolateral aspects of the prostate. The neurovascular bundles course through the retroprostatic fat at the 5- and 7-o'clock positions but are usually not identified as discrete structures. Note the periurethral calcifications. (Bottom) Transverse TRUS of the midprostate gland demonstrates an enlarged TZ in a patient with BPH. The pseudocapsule separates the TZ from the PZ. Frequently, the pseudocapsule will be outlined by calcifications, which represent calcified corpora amylacea (laminated bodies formed by secretions and degenerate cells). The pseudocapsule is also referred to as the surgical capsule, as it is a landmark for transurethral resection of the prostate (TURP). Modern medical treatments for symptomatic BPH has made TURP procedures much less common than in the past.

Prostate and Seminal Vesicles Pelvis

VARYING DEGREES OF BENIGN PROSTATIC HYPERPLASIA

Transition zone

Urethra Pseudocapsule Peripheral zone

Postvoid residual

Median lobe Enlarged prostate

Urethra Nodular hypertrophy of transition zone Nodular hypertrophy of transition zone

Urethra Peripheral zone

Peripheral zone

(Top) Transverse TRUS of the midprostate in a different patient with BPH shows heterogeneous enlargement of the 2 lobes of the TZ, which flank the urethra. Tiny cystic spaces within the TZ represent cystic BPH nodules vs. retention cysts, which are often indistinguishable by imaging. The more hyperechoic PZ is being compressed along the posterolateral aspects of the prostate. (Middle) This longitudinal transabdominal postvoid image shows a markedly enlarged prostate with a hypertrophied median lobe projecting into the bladder. The median represents hyperplasia of the periurethral glands and is common with BPH. It typically projects cephalad into the bladder and can be associated with significant urinary retention. There is a large postvoid residual in this case. (Bottom) Consecutive cross sections of a prostate gland with BPH show marked nodular enlargement of the TZ. It is compressing the prostatic urethra, which was the cause of the patient's bladder-obstructive symptoms. The PZ is compressed and attenuated by the hyperplastic TZ. (From DP: Genitourinary.)

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Pelvis

Prostate and Seminal Vesicles SAGITTAL PROSTATE

Seminal vesicle

Bladder neck Proximal prostatic urethra

Peripheral zone

Anterior fibromuscular stroma Distal prostatic urethra

Urogenital diaphragm

Central zone Bladder neck

Seminal vesicle Ejaculatory duct

Prostatic urethra

Peripheral zone Verumontanum

Rectal mucosa

Seminal vesicle

Transition zone

Ejaculatory duct Peripheral zone

(Top) Sagittal T2 MR shows the bladder neck and proximal prostatic urethra, which has a posterior course. It makes a 35° anterior angulation at the level of the verumontanum. (Middle) Sagittal TRUS in a patient without significant BPH shows the course of the proximal prostatic urethra anterior to the CZ. The ejaculatory ducts start at the base of the prostate and run forward and downward through the CZ. They terminate at the verumontanum on either side of the utricle orifice. The verumontanum is the boundary between the proximal and distal segments of the prostatic urethra. (Bottom) Parasagittal TRUS shows the ejaculatory duct emerging after fusion of the vas deferens and seminal vesicle, entering the prostate base. The ejaculatory ducts are surrounded by the CZ, which is not readily distinguishable on TRUS especially in the setting of BPH. Calcifications are seen within the more anterior TZ. The PZ runs along the posterolateral aspect of the prostate.

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Prostate and Seminal Vesicles Pelvis

SEMINAL VESICLES AND VAS DEFERENS

Urinary bladder

Vas deferens

Seminal vesicle Seminal vesicle

Rectum

Bladder Vas deferens

Vas deferens Seminal vesicles

Seminal vesicles

Bladder Vas deferens Seminal vesicles

Vas deferens Seminal vesicles

(Top) Axial T2 MR shows the seminal vesicles between the urinary bladder and the rectum. The low-signal walls of the vas deferens should not be confused with tumor extension from prostate carcinoma. (Middle) Transverse TRUS at the level of the seminal vesicles shows bilateral seminal vesicles and the vas deferens. (Bottom) Transverse TRUS shows the vas deferens converging with the seminal vesicles. Their union will form the ejaculatory ducts, which enter the prostate base and course within the prostate enclosed within the CZ. The ejaculatory ducts empty into the urethra at the verumontanum.

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Pelvis

Testes and Scrotum

GROSS ANATOMY Testis • Densely packed seminiferous tubules separated by thin fibrous septa ○ 200-300 lobules in adult testis ○ Each has 400-600 seminiferous tubules ○ Total length of seminiferous tubules 300-980 meters • Seminiferous tubules converge posteriorly to form larger ducts (tubuli recti) ○ Drain into rete testis at testicular hilum • Rete testis converges posteriorly to form 15-20 efferent ductules ○ Penetrate posterior tunica albuginea at mediastinum to form head of epididymis • Tunica albuginea forms thick fibrous capsule around testis • Mediastinum testis is thickened area of tunica albuginea where ducts, nerves, and vessels enter and exit testis • Testicular appendage (appendix testis) ○ Small, nodular protuberance from surface of testis ○ Remnant of müllerian system

Epididymis • Crescent-shaped structure running along posterior border of testis • Efferent ductules form head (globus major) ○ Unite to form single, long, highly convoluted tubule in body of epididymis • Tubule continues inferiorly to form epididymal tail (globus minor) ○ Attached to lower pole of testis by loose areolar tissue • Tubule emerges at acute angle from tail as vas deferens (a.k.a. ductus deferens) ○ Continues cephalad within spermatic cord ○ Eventually merges with duct of seminal vesicle to form ejaculatory duct • Epididymal appendage (appendix epididymis) ○ Small nodular protuberance from surface of epididymis ○ Remnant of wolffian system

Spermatic Cord • Contains vas deferens, nerves, lymphatics, and connective tissue • Begins at internal (deep) inguinal ring and exits through external (superficial) inguinal ring into scrotum • Arteries ○ Testicular artery – Branch of aorta – Primary blood supply to testis ○ Deferential artery – Branch of inferior or superior vesicle artery – Arterial supply to vas deferens ○ Cremasteric artery – Branch of inferior epigastric artery – Supplies muscular components of cord and skin • Venous drainage ○ Pampiniform plexus – Interconnected network of small veins – Merges to form testicular vein – Left testicular vein drains to left renal vein – Right testicular vein drains to inferior vena cava 446

• Lymphatic drainage ○ Testis follows venous drainage – Right side drains to interaortocaval chain – Left side drains to left paraaortic nodes near renal hilum ○ Epididymis may also drain to external iliac nodes ○ Scrotal skin drains to inguinal nodes

EMBRYOLOGY Testis • Testis develop from genital ridges, which extend from T6S2 in embryo • Composed of 3 cell lines ○ Germ cells – Form in wall of yolk sac and migrate along hindgut to genital ridges – Form spermatogenic cells in mature testes ○ Sertoli cells – Supporting network for developing spermatozoa – Form tight junctions (blood-testis barrier) – Secrete müllerian-inhibiting factor □ Causes paramesonephric (müllerian) ducts to regress □ Embryologic remnant may remain as appendix testis ○ Leydig cells – Principal source of testosterone production – Lies within interstitium – Causes differentiation of mesonephric duct (wolffian) ducts □ Each duct forms epididymis, vas deferens, seminal vesicle, ejaculatory duct □ Embryologic remnant may remain as appendix epididymis • Scrotum derived from labioscrotal folds ○ Folds swell under influence of testosterone to form twin scrotal sacs – Point of fusion is median raphe, which extends from anus, along perineum, to ventral surface of penis ○ Processus vaginalis, sock-like evagination of peritoneum, elongates through abdominal wall into twin sacs – Aids in descent of testes, along with gubernaculum (ligamentous cord extending from testis to labioscrotal fold) – Results in component layers of adult scrotum • Testicular descent ○ Between 7-12th week of gestation, testes descend into pelvis – Remain near internal inguinal ring until 7th month, when they begin descent through inguinal canal into twin scrotal sacs – Testes remain retroperitoneal throughout descent – Testes intimately associated with posterior wall of processus vaginalis ○ Component layers of spermatic cord and scrotum form during descent through abdominal wall – Transversalis fascia → internal spermatic fascia

Testes and Scrotum

ANATOMY-BASED IMAGING ISSUES Imaging Recommendations • Palpate scrotal contents and take history prior to US examination • High-frequency (10- to 15-MHz) linear transducer • Patient in supine position ○ Penis positioned on anterior abdominal wall ○ Towel draped over thighs to elevate scrotum ○ Additional positions with patient upright or with patient performing Valsalva maneuver – Important for evaluation of inguinal hernia or varicocele

IMAGING ANATOMY

CLINICAL IMPLICATIONS

Pelvis

□ Transversus abdominis muscle is discontinuous inferiorly and does not contribute to formation of scrotum – Internal oblique muscle → cremasteric muscle and fascia – External oblique muscle → external spermatic fascia – Dartos muscle and fascia embedded in loose areolar tissue below skin ○ Processus vaginalis closes and forms tunica vaginalis – Mesothelial-lined sac around anterior and lateral sides of testis – Visceral layer of tunica vaginalis blends imperceptibly with tunica albuginea

Hydrocele • Fluid between visceral and parietal layers of tunica vaginalis • Small amount of fluid is normal • Larger hydroceles may be either congenital (patent processus vaginalis) or acquired

Cryptorchidism • Failure of testes to descend completely into scrotum • Most lie near external inguinal ring • Associated with decreased fertility and testicular carcinoma ○ Risk of carcinoma is increased for both testes, even if other side is normally descended

Varicocele • Idiopathic or secondary to abdominal mass ○ Idiopathic more common on left • Vessel diameter > 3 mm abnormal

Dilated Rete Testes • Clusters of dilated tubules in mediastinum testis ○ Do not confuse with mass • Empty into epididymis • Often associated with epididymal cysts

Scrotal Calculi • Free-floating calcifications within tunica vaginalis • May result from torsion of appendix testis or epididymis

Sonographic Anatomy

Torsion

• Testes ○ Ovoid, homogeneous, medium-level, granular echotexture ○ Mediastinum testis may appear as prominent echogenic line emanating from posterior testis ○ Blood flow – Testicular artery pierces tunica albuginea and arborizes over periphery of testis – Multiple, radially arranged vessels travel along septa – May have prominent transmediastinal artery – Tunica vasculosa: Vascular plexus in periphery of testis, beneath tunica albuginea – Low-velocity, low-resistance waveform on Doppler imaging with continuous forward flow in diastole • Epididymis ○ Isoechoic to slightly hyperechoic compared with testis ○ Best seen in longitudinal plane ○ Head has rounded or triangular configuration ○ Head 10-12 mm, body and tail often difficult to visualize – May be helpful to follow course of epididymis in transverse plane if difficult to visualize in longitudinal plane • Spermatic cord ○ Scan along course of inguinal canal – May be difficult to differentiate from surrounding soft tissues ○ Slow flow in pampiniform plexus may make identification on color Doppler difficult – Use provocative maneuvers (Valsalva, standing), especially when looking for varicocele

• Occurs most commonly when tunica vaginalis completely surrounds testis and epididymis ○ Testis is suspended from spermatic cord (like bell clapper) rather than being anchored posteriorly • Normal grayscale appearance with early torsion ○ Becomes heterogeneous and enlarged with infarction • Color and spectral Doppler required for diagnosis ○ Some flow may be seen even if torsed but will be decreased compared to normal side ○ Venous flow compromised 1st, then diastolic flow, and finally systolic flow • Look in inguinal canal for twist in spermatic cord (whirlpool sign)

Testicular Carcinoma • Most common malignancy in young men ○ 95% are germ cell tumors – Seminoma (most common pure tumor), embryonal, yolk sac tumor, choriocarcinoma, teratoma – Mixed germ cell tumor (components of 2 or more cell lines) most common overall ○ Remainder of primary tumors are sex cord (Sertoli cells) or stromal (Leydig cells) ○ Lymphoma, leukemia, and metastases more common in older men • Most metastasize via lymphatics in predictable fashion ○ Right-sided 1st echelon nodes: Interaortocaval chain at 2nd vertebral body ○ Left-sided 1st echelon nodes: Left paraaortic nodes in area bounded by renal vein, aorta, ureter, and inferior mesenteric artery 447

Pelvis

Testes and Scrotum TESTIS AND EPIDIDYMIS

Pampiniform plexus

Testicular a. Head of epididymis

Vas deferens Efferent ductules

Deferential a. Rete testis

Mediastinum testis Body of epididymis

Seminiferous tubules Cremasteric a.

Tunica albuginea

Tail of epididymis

Septa

Graphic shows the testis is composed of densely packed seminiferous tubules, which are separated by thin fibrous septa. These tubules converge posteriorly, eventually draining into the rete testis. The rete testis continues to converge to form the efferent ductules, which pierce through the tunica albuginea at the mediastinum testis and form the head of the epididymis. Within the epididymis these tubules unite to form a single, highly convoluted tubule in the body, which finally emerges from the tail as the vas deferens. In addition to the vas deferens, other components of the spermatic cord include the testicular artery, deferential artery, cremasteric artery, pampiniform plexus, lymphatics, and nerves.

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Testes and Scrotum Pelvis

EPIDIDYMIS AND SCROTAL WALL LAYERS IN SITU

Ureter

Seminal vesicle Vas deferens Prostate

Corpus spongiosum

Head of epididymis

Tail of epididymis

External oblique m.

Transversalis fascia (level of internal inguinal ring) Transversus abdominis

Internal oblique m. External oblique fascia Superficial (external) inguinal ring External spermatic fascia

Cremasteric m.

(Top) Graphic shows that the tail of the epididymis is loosely attached to the lower pole of the testis by areolar tissue. The vas deferens (also referred to as the ductus deferens) emerges from the tail at an acute angle and continues cephalad as part of the spermatic cord. After passing through the inguinal canal, the vas deferens courses posteriorly to unite with the duct of the seminal vesicle to form the ejaculatory duct. These narrow ducts have thick, muscular walls composed of smooth muscle, which reflexly contract during ejaculation and propel sperm forward. (Bottom) The muscle layers of the pelvic wall have been separated to show the spermatic cord as it passes through the inguinal canal. The cremasteric muscle is derived from the internal oblique muscle, while the external spermatic fascia is formed by the fascia of the external oblique muscle.

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Pelvis

Testes and Scrotum SCROTAL DEVELOPMENT

Peritoneum Transversalis fascia Transversus abdominis m.

Processus vaginalis

Internal oblique m. External oblique m.

Labioscrotal fold Gubernaculum

Peritoneum Transversalis fascia Internal oblique m. External oblique m.

Processus vaginalis

Gubernaculum

Peritoneum Transversalis fascia Internal oblique m. External oblique m.

Internal spermatic fascia (pink) Tunica vaginalis Cremasteric m. and fascia (green)

External spermatic fascia (blue) Dartos m. and fascia (yellow) Skin

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(Top) The processus vaginalis is a sock-like evagination of the peritoneum, which elongates caudally through the abdominal wall. It forms just anterior to the developing testes and, along with the gubernaculum (a ligamentous cord extending from the testis to the labioscrotal fold), aids in their descent. (Middle) As the processus vaginalis evaginates, it becomes ensheathed by fascial extensions of the abdominal wall, which ultimately form the layers of the scrotum and spermatic cord. The transversus abdominis muscle is discontinuous inferiorly and does not contribute to the formation of the scrotum. (Bottom) The abdominal wall derivative layers of the scrotum are as follows: Transversalis fascia → internal spermatic fascia, internal oblique muscle → cremasteric muscle and fascia, external oblique muscle → external spermatic fascia. The dartos muscle is embedded in the loose areolar tissue and is closely associated with the skin. The various layers of the scrotum cannot usually be discerned with imaging. The superior portion of the processus vaginalis closes and forms an isolated mesothelial-lined sac, the tunica vaginalis.

Testes and Scrotum Pelvis

SCROTUM AND TESTES Scrotal wall (spermatic fascia with cremasteric m.)

Right testis Left testis

Scrotal septum (median raphae)

Mediastinum testis

Scrotal wall (fascial layers with cremasteric m.)

Area of external inguinal ring

Testis

Spermatic cord

(Top) Transverse grayscale ultrasound shows both testes. This is a useful approach for comparing the appearance of the testes, which should have similar, homogeneous, medium-level, granular echotexture. (Middle) Longitudinal ultrasound shows the ovoid shape. The tunica albuginea may form an echogenic linear band where it invaginates at the mediastinum testis. The mediastinum testis has a craniocaudal linear course and is where the efferent ductules, vessels, and lymphatics pierce through the capsule. (Bottom) Longitudinal scan at the superior pole of the testis shows the spermatic cord as it is entering the inguinal canal. It is important to look at the spermatic cord for a twist (whirlpool sign) in cases of suspected torsion.

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Pelvis

Testes and Scrotum TUNICA VAGINALIS, ALBUGINEA, AND VASCULOSA

Tunica vaginalis

Hydrocele

Parietal layer of tunica albuginea

Visceral layer of tunica albuginea

Testis

Visceral layer of tunica albuginea

Parietal layer of tunica albuginea

Tunica vasculosa

(Top) Sagittal grayscale ultrasound of the left scrotum shows the outermost serous membrane covering the testis and epididymis, the tunica vaginalis. There is small fluid within the tunica vaginalis (hydrocele). (Middle) Transverse grayscale ultrasound of the right testis shows 2 thin echogenic layers covering the testis, representing the parietal and visceral layers of tunica albuginea, which is the fibrous covering of the testis. (Bottom) Sagittal color Doppler ultrasound shows the vascular plexus (tunica vasculosa) along the outermost layer of the testis, just beneath the tunica albuginea.

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Testes and Scrotum Pelvis

SCROTAL DOPPLER Median raphae

Mediastinum testis

Intratesticular vessels

Transmediastinal a.

Tunica vasculosa

(Top) Transverse color Doppler ultrasound shows normal symmetric blood flow in the testes. It is important to compare flow between testes to determine if the symptomatic side has increased or decreased flow when compared to the asymptomatic side. (Middle) Longitudinal color Doppler ultrasound shows prominent, radially arranged vessels within the testis. (Bottom) Color Doppler ultrasound shows a prominent transmediastinal artery with pulsed Doppler showing normal low-resistance arterial flow. Also shown is the tunica vasculosa, a vascular plexus that runs beneath the tunica albuginea.

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Pelvis

Testes and Scrotum SCROTAL DOPPLER

Intratesticular a.

Normal low-resistance wave form

Cremasteric a.

Epididymal a.

Epididymis

Right testis Vessels in pampiniform plexus

(Top) Sagittal color Doppler ultrasound of a normal left testis shows normal blood flow with a normal spectral waveform of an intratesticular artery. The artery should have a low-resistance waveform and the resistive index (RI) should be between 0.48-0.75 (mean RI: 0.62). (Middle) Two color Doppler ultrasounds show the epididymal arterial supply. The upper image demonstrates the normal cremasteric artery with a low-flow, high-resistance pattern. The lower image shows the normal epididymal artery, a branch of the testicular artery with a low-resistance waveform. (Bottom) Transverse power Doppler ultrasound shows flow within the pampiniform plexus of the spermatic cord. If looking for a varicocele, it is important to use provocative maneuvers, including Valsalva and scanning in the standing position, to distend the veins.

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Testes and Scrotum Pelvis

EPIDIDYMIS

Epididymal head Epididymal tail Epididymal body Testis

Epididymal head

Epididymal body

Mediastinum testis

Epididymal body Epididymal head

Hydrocele

Inflamed epididymal head

Inflamed epididymal body

(Top) Longitudinal ultrasound shows both the epididymal head (globus major) and tail (globus minor). The epididymal head measures ~ 10-12 mm and is iso- to slightly hyperechoic compared to the testis. The body and tail are often more difficult to visualize and may be slightly less echogenic than the head. (Middle) This composite image shows the normal epididymal head and body. The body may be difficult to visualize from an anterior scanning plane (above), but by moving the transducer more posteriorly (below), it is often better visualized. (Bottom) This composite image of a longitudinal grayscale ultrasound (above) and a color Doppler ultrasound (below) in a patient with acute epididymitis shows enlargement and hyperemia of both the epididymal head and body.

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Pelvis

Testes and Scrotum RETE TESTIS AND TUBULAR ECTASIA

Tunica albuginea

Rete testis Mediastinum testis

Dilated rete testis

Testis

Tubular ectasia

Epididymal body

(Top) Transverse grayscale ultrasound of the normal testis shows diffuse low-level internal echoes in the parenchyma, an echogenic mediastinum testis, and the striated pattern of the rete testis as it converges to the mediastinum. The testis is covered with 2 thin, echogenic layers of tunica albuginea. (Middle) Transverse ultrasound of the the right testis shows tubular ectasia of the rete testis. Tubular ectasia is located posteriorly by the mediastinum and is frequently bilateral. It may give an impression of a mass, but careful scanning shows the "mass" is actually a series of dilated tubules. (Bottom) Sagittal grayscale ultrasound of the epididymis demonstrates tubular ectasia within the epididymis.

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Testes and Scrotum Pelvis

TESTICULAR AND EPIDIDYMAL APPENDAGES Spermatic cord

Epididymal head Epididymal body Appendix epididymis

Appendix testis

Epididymal tail

Testis

Scrotal skin, m., and fascial layers

Hydrocele

Appendix testis Testis Epididymis

Scrotal skin, m., and fascial layers

Appendix epididymis Testis Epididymis Tunica albuginea Hydrocele

(Top) Gross specimen shows the the testis, epididymis, and spermatic cord. Two embryologic remnants form small appendages from the testis and epididymis. (Middle) Ultrasound of the testis in a patient with a hydrocele shows a small, nodular protuberance from the surface of the testis. This is the appendix testis, which is a remnant of the müllerian system. (Bottom) Longitudinal ultrasound of the upper testis and epididymis shows a small "tag" of tissue projecting from the epididymis. This is an appendix epididymis, which is a remnant of the wolffian system. Both the appendix testis and appendix epididymis are usually not visible sonographically unless there is a hydrocele. They are usually of no clinical significance; however, they can torse and be a cause of scrotal pain.

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Pelvis

Penis and Urethra

IMAGING ANATOMY Penis • Composed of 3 cylindrical shafts ○ 2 corpora cavernosa: Main erectile bodies – On dorsal surface of penis – Diverge at root of penis (crura) and are invested by ischiocavernosus muscles – Chambers traversed by numerous trabeculae, creating sinusoidal spaces – Multiple fenestrations between corpora, creating multiple anastomotic channels ○ 1 corpus spongiosum: Contains urethra – On ventral surface, in groove created by corpora cavernosa – Becomes penile bulb (urethral bulb) at root and is invested by bulbospongiosus muscle – Forms glans penis distally – Also erectile tissue but of far less importance • Tunica albuginea forms capsule around each corpora ○ Thinner around spongiosum than cavernosa • All 3 corpora surrounded by deep fascia (Buck fascia) and superficial fascia (Colles fascia) • Suspensory ligament of penis (part of fundiform ligament) is inferior extension of abdominal rectus sheath • Main arterial supply from internal pudendal artery ○ Cavernosal artery runs within center of each corpus cavernosum – Gives off helicine arteries, which fill trabecular spaces – Primary source of blood for erectile tissue ○ Paired dorsal penile arteries run between tunica albuginea of corpora cavernosa and Buck fascia – Supplies glans penis and skin ○ Multiple anastomoses between cavernosal and dorsal penile arteries • Venous drainage of corpora cavernosa ○ Emissary veins in corpora pierce through tunica albuginea → circumflex veins → deep dorsal vein of penis → retropubic venous plexus ○ Superficial dorsal vein drains skin and glans penis • Primary innervation from terminal branches of internal pudendal nerve

Normal Erectile Function • Neurologically mediated response eliciting smooth muscle relaxation of cavernosal arteries, helicine arteries, and cavernosal sinusoids • Blood flows from helicine arteries into sinusoidal spaces • Sinusoids distend, eventually compressing emissary veins against rigid tunica albuginea ○ Venous compression prevents egress of blood from corpora, which maintains erection

Urethra • Posterior urethra (prostatic, membranous) and anterior urethra (bulbous and penile) • Prostatic urethra: Traverses prostate ○ Verumontanum is 1-cm ovoid mound along ureteral crest (smooth muscle ridge on posterior wall) ○ Prostatic utricle, prostatic ducts, and ejaculatory ducts enter in this segment 458

• Membranous urethra: Short course through urogenital diaphragm (level of external urethral sphincter) ○ Contains bulbourethral glands (Cowper glands) • Bulbous urethra: Below urogenital diaphragm to suspensory ligament of penis at penoscrotal junction • Penile urethra: Pendulous portion, distal to suspensory ligament • Both penile and bulbous urethra lined by mucosal urethral glands (glands of Littre) • 2 points of fixations: Urogenital diaphragm (membranous urethra) and penoscrotal junction

ANATOMY IMAGING ISSUES Imaging Recommendations • Transducer: High-frequency (7.5- to 10-MHz) linear transducer • Patient is supine with penis lying on anterior abdominal wall • Transducer placed on ventral side of penis ○ Corpus spongiosum easily compressed so use ample gel and gentle pressure • For erectile dysfunction studies, vasodilating agent is injected into dorsal 2/3 of shaft • Cavernosal artery evaluation ○ In flaccid state, there is little diastolic flow ○ At onset of erection, there is dilatation with increase in both systolic and diastolic flow ○ At maximum erection, venous drainage is blocked – Waveform changes to high resistance with reversal of diastolic flow – Peak systolic velocity > 30 cm/sec – Cavernosal artery diameter increase > 75% • Urethra ○ Imaging of anterior urethra is optimal with distension – Gel may be injected retrograde or patient may be asked to void during scan ○ Posterior urethra is best imaged by transrectal ultrasound of prostate

CLINICAL IMPLICATIONS Erectile Dysfunction • Complex and often multifactorial including vascular, neurogenic, and psychologic factors • Arteriogenic impotence effects inflow ○ Usually internal pudendal and penile arteries ○ Blockage may be as high as distal aorta (Leriche syndrome) • Venogenic impotence effects outflow ○ Ineffective venoocclusion with continuous outflow of blood from sinusoids

Trauma • Need to carefully evaluate tunica albuginea in suspected penile fracture • Membranous urethra most commonly injured with pelvic trauma and fractures • Bulbous urethra most often from straddle injury

Peyronie Disease • Plaque formation on tunica albuginea • Painful erections with shortening and curvature of penis

Penis and Urethra Pelvis

PENIS AND PERINEUM

Corpora cavernosa

Glans penis

Corpus spongiosum

Buck fascia

Bulbospongiosus muscle

Ischiocavernosus muscle

Inferior ischiopubic ramus

Penile (urethral) bulb

Perineal fascia

Levator ani muscle

Deep transverse perineal muscle Cowper gland

Perineal body

At the root of the penis, the corpora split into a triradiate form. The crura of the corpora cavernosa diverge and each crus is invested by an ischiocavernosus muscle. The corpus spongiosum remains midline and is invested by the bulbospongiosus muscle. It widens at its attachment to the urogenital diaphragm and is called the penile or urethral bulb. The root of the penis is firmly anchored between the urogenital diaphragm above and Colles fascia below (cut away to show perineal muscles). Additional supports include fascial attachments to the medial surface of the pubic rami and and pubic symphysis.

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Pelvis

Penis and Urethra PENIS AND URETHRA

Trigone

Verumontanum

Urethral crest

Urogenital diaphragm

Cowper gland

Penile bulb (root of corpus spongiosum) Crus of corpus cavernosum

Trabeculae

Cavernosal artery Helicine arteries

Glands of Littre

Fossa navicularis

Prepuce

Graphic shows the posterior wall of the urethra from the bladder base to the fossa navicularis. The verumontanum is the most prominent portion of the urethral crest. The prostatic utricle (an embryologic remnant of the müllerian system) enters in the center of the verumontanum, along with the ejaculatory ducts, which are just distal on either side. Cowper glands are within the urogenital diaphragm, but their ducts course distally ~ 2 cm to enter the bulbous urethra. Multiple, small, mucosal glands (glands of Littre) line the mucosa of the anterior urethra. The corpora cavernosa are the primary erectile bodies. They are traversed by numerous trabeculae, creating sinusoidal spaces. The cavernosal artery runs within the center of each corpus cavernosum and gives rise to the helicine arteries, which flow into the sinusoids.

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Penis and Urethra Pelvis

PENIS AND URETHRA

Pubic symphysis Seminal vesicle Suspensory ligament of penis Cowper (bulbourethral) gland

Urogenital diaphragm Corpus cavernosum

Cowper duct

Bulbospongiosus muscle Corpus spongiosum Glans penis

Fossa navicularis

Skin

Superficial fascia

Superficial dorsal v. Dorsal penile aa.

Buck fascia Deep dorsal v. Circumflex vv. Helicine aa. Emissary vv. Cavernosal a. Corpus cavernosum

Tunica albuginea Corpus spongiosum Urethra

(Top) Sagittal midline graphic shows the course of the urethra. The anterior urethra runs within the corpus spongiosum. The external (pendulous) portion of the penis begins below the pubic symphysis at the penoscrotal junction. It is fixed at this position by the suspensory ligament of the penis, which is part of the fundiform ligament, an inferior extension of the rectus sheath. (Bottom) Cross section of the penis viewed from above shows the 3 corpora, each of which is invested by a tunica albuginea. The 3 corpora are surrounded by Buck fascia. The cavernosal arteries run within the corpora cavernosa and give rise to the helicine arteries, which fill the sinusoids. Normal drainage is via the emissary veins → circumflex veins → deep dorsal vein of penis. With an erection, the emissary veins are compressed against the strong tunica albuginea, occluding venous drainage. The dorsal penile arteries and deep dorsal vein run beneath the Buck fascia. The penile arteries supply the glans and skin, but there are significant anastomoses between both the arterial and venous systems.

461

Pelvis

Penis and Urethra NORMAL ERECTILE FUNCTION

Corpora cavernosa Cavernosal a. Cavernosal a. Tunica albuginea and Buck fascia

Corpus spongiosum

Deep dorsal vessels Helicine aa.

Cavernosal a. Helicine aa.

Cavernosal a.

Circumflex vessel

Corpus cavernosum Corpus cavernosum

Corpus spongiosum

(Top) The 1st of 3 cross-sectional ultrasounds of the penis showing the changing appearance during a normal erection is shown. The paired corpora cavernosa are the primary erectile bodies. They are composed of a complex network of trabeculae, which create the sinusoids and give a sponge-like appearance on ultrasound. Each corpus is surrounded by a tough tunica albuginea, which appears as a thin echogenic line. Buck fascia, which surrounds all 3 corpora, is intimately associated with the tunica and cannot be distinguished as a separate structure. (Middle) Color Doppler ultrasound at the onset of an erection shows arterial inflow. There is dilation of the cavernosal and helicine arteries as they begin to fill the sinusoidal spaces. (Bottom) With continued arterial inflow and compressed venous outflow, the corpora become maximally distended and rigid.

462

Penis and Urethra Pelvis

NORMAL ERECTILE FUNCTION

Diastolic flow

Peak systolic velocity

End diastolic flow

Peak systolic velocity

Reversed diastolic flow

(Top) The 1st of 3 Doppler tracings showing the changing flow patterns during a normal erection is shown. In the flaccid state, there is little to no diastolic flow. (Middle) At onset of erection, there is vasodilation of the cavernosal and helicine arteries (increased inflow) and smooth muscle relaxation within the sinusoids (decreased resistance). This causes a marked increase in both the peak systolic velocity (PSV) and end diastolic flow. (Bottom) In the fully erect state, the emissary veins are compressed against the rigid tunica albuginea, preventing outflow of blood. This dramatically increases the arterial resistance resulting in absent or reversed diastolic flow. A PSV > 30 cm/sec is considered normal, while < 25 cm/sec is strong evidence of arteriogenic impotence (25-30 borderline). Venogenic impotence is due to failure of draining vein occlusion. The Doppler tracing would show continuous forward flow in diastole.

463

Pelvis

Penis and Urethra NORMAL ERECTILE FUNCTION

Cavernosal a.

Corpora cavernosa Cavernosal a.

Cavernosal a.

Corpora cavernosa Cavernosal septum

Cavernosal a.

Deep dorsal v. of penis

Cavernosal a.

464

(Top) The 1st of 3 longitudinal ultrasounds show the corpora cavernosa. In the flaccid state, the cavernosal arteries are tortuous and therefore can only be intermittently visualized in the longitudinal plane. (Middle) In the erect state, the cavernosal arteries assume a straighter course and can be easily imaged. Magnified views of the cavernosal artery should be obtained to measure vessel diameter. Most measure < 1 mm in the flaccid state. The diameter should increase by 75% with an erection. Failure to increase in size, coupled with an abnormal Doppler waveform, is strong evidence of arteriogenic impotence. Despite the fact that each corpora is sheathed within its own tunica albuginea, there is significant communication across the septum between the 2 corpora cavernosa. Therefore, when performing a study, only 1 corpus cavernosum needs to be injected with the vasodilating agent. (Bottom) Color Doppler shows flow in both the cavernosal artery and deep dorsal vein of the penis. As an erection starts to wane, or in venogenic impotence, significant flow is seen in the draining vein.

Penis and Urethra Pelvis

MR Corpora cavernosa Corpus spongiosum

Crura of corpora cavernosa

Penile bulb

Ischiocavernosus muscle

Ischium Rectum

Prostate

Corpora cavernosa (crura)

Corpus spongiosum (penile bulb)

Superficial fascia

Deep dorsal v.

Tunica albuginea and Buck fascia Cavernosal arteries in corpora cavernosa Corpus spongiosum

(Top) Axial T2 MR of the pelvis shows the shaft and root of the penis. Upon entering the pelvis, the 3 corpora are each invested within a muscle layer. The ischiocavernosus muscles surround the crura of the corpora cavernosa, and the bulbospongiosus muscle surrounds the root of the corpus spongiosum. These muscles are innervated by the perineal nerves and assist in erection, ejaculation, and the sensation of orgasm. (Middle) Coronal STIR MR at the level of the prostate shows all 3 corpora at the same level. The corpora cavernosa crura diminish in size as they continue to diverge and attach to the inferior ischiopubic rami. The corpus spongiosum remains midline and enlarges to form the penile bulb (a.k.a. the urethral bulb). (Bottom) T2 MR cross section of the penis shows the low-signal tunica albuginea surrounding each of the corpora (more prominent around the cavernosa). Buck fascia cannot be separated from the tunica albuginea.

465

Pelvis

Penis and Urethra URETHRA

Urinary bladder

Prostatic urethra

Bulbous urethra

Membranous urethra Penile urethra

Penile urethra

Bulbous urethra Pubic symphysis (unossified) Membranous urethra Urinary bladder

Prostatic urethra Prostate

Urethra

Corpora spongiosum

466

Corpora cavernosum

(Top) Graphic shows the urethra's 2 major divisions: Anterior and posterior urethra, each with two parts. The posterior urethra is composed of the prostatic and membranous portions, and the anterior urethra is composed of the bulbous and penile portions. The prostatic urethra begins at the bladder base and extends to the apex of the prostatic gland. The membranous urethra traverses the urogenital diaphragm. It is the shortest portion of the urethra but the area most vulnerable to injury. The bulbous urethra extends from the bottom of the urogenital diaphragm to the suspensory ligament of the penis. The penile urethra is distal to the suspensory ligament and travels through the pendulous portion of the penis. It widens into the fossa navicularis at the distal glans. (Middle) Longitudinal transpelvic/perineal ultrasound of a male neonate shows the urethral segments. (Bottom) Longitudinal scan shows the penis positioned on the anterior abdominal wall and scanned on the ventral side. The urethra is identified within the substance of the corpora spongiosum. One of the paired corpora cavernosa, which is more hypoechoic relative to the spongiosum, is shown.

Penis and Urethra Pelvis

PEYRONIE DISEASE Corpora cavernosa

Calcified plaques

Calcified plaques

Corpus cavernosum

Calcified plaques

Glans penis

(Top) The 1st of 3 images in a patient with Peyronie disease shows a cross-sectional ultrasound of the calcified plaques within the tunica albuginea of the corpora cavernosa. (Middle) Longitudinal ultrasound of 1 corpus cavernosum shows densely calcified plaques with significant posterior shadowing. (Bottom) Lateral radiograph of the penis shows not only the calcified plaques, but also shortening and upward curvature of the penis. Peyronie disease is an incompletely understood inflammatory process with fibroblastic proliferation and calcification involving the tunica albuginea. It manifests as pain and deformity with erection. The penis may shrink in size with disease progression.

467

Pelvis

Uterus

GROSS ANATOMY Overview • Anatomical divisions ○ Body (corpus): Upper 2/3 of uterus – Fundus: Superior to ostia of fallopian tubes ○ Cervix: Lower 1/3 of uterus – Isthmus: Junction of body and cervix • Parametrium: Outer layer, part of visceral peritoneum • Myometrium: Smooth muscle that forms main bulk of uterus • Endometrium: Inner layer ○ Stratum functionalis (inner): Thicker, varies with cyclical changes ○ Stratum basalis (outer): Thin, does not change

○ Progesterone induces secretion of glycogen, mucus, and other substances • Menstrual phase ○ Sloughing of functionalis layer

Uterine Variations With Age • Neonatal: Prominent size secondary to effects of residual maternal hormone stimulation • Infantile: Corpus < cervix (1:2) • Prepubertal: Corpus = cervix (1:1) • Reproductive: Corpus > cervix (2:1) ○ 7.5-9.0 cm (length) ○ 4.5-6.0 cm (breadth) ○ 2.5-4.0 cm (thickness) • Postmenopausal: Overall reduction in size, similar to prepubertal uterus

Anatomic Relationships • Extraperitoneal location in midline of true pelvis • Uterine position ○ Flexion is axis of uterine body relative to cervix ○ Version is axis of cervix relative to vagina ○ Anteversion with anteflexion is most common • Peritoneum extends over bladder dome anteriorly and rectum posteriorly ○ Vesicouterine pouch (anterior cul-de-sac): Anterior recess between uterus and bladder ○ Rectouterine pouch of Douglas (posterior cul-de-sac): Posterior recess between vaginal fornix and rectum; most dependent portion of peritoneum in female pelvis • Supporting ligaments ○ Broad ligaments: Double layer of peritoneum – Extends laterally to pelvic wall and forms supporting mesentery for uterus ○ Round ligaments: Arise from uterine cornu – Course anteriorly, through inguinal canal to insert on labia majora ○ Uterosacral ligaments (posteriorly), cardinal ligaments (laterally), and vesicouterine ligaments (anteriorly) form from connective tissue thickening of broad ligament by cervix • Fallopian tubes connect uterus to peritoneal cavity ○ 4 segments: Interstitial, isthmus, ampulla, infundibulum • Arteries: Dual blood supply ○ Uterine artery (UA) arises from internal iliac artery, anastomoses with ovarian artery ○ Arcuate arteries arise from UAs; seen in outer 1/3 of myometrium ○ Radial arteries arise from arcuate arteries and penetrate vertically into myometrium ○ Basal and spiral arteries arise from radial arteries to supply stratum basalis and stratum functionalis • Venous drainage mirrors arteries ○ Parametrial venous network prior to drainage into uterine or ovarian veins

Endometrial Variations With Menstrual Cycle • Proliferative phase (follicular phase of ovary) ○ End of menstrual phase to ovulation (~ 14 days) ○ Estrogen induces proliferation of functionalis layer • Secretory phase (luteal phase of ovary) ○ Ovulation to beginning of menstrual phase 468

IMAGING ANATOMY Myometrium • Inner layer (junctional zone): Thin and hypoechoic, < 12 mm • Middle layer: Thick, homogeneously echogenic • Outer layer: Thin, hypoechoic layer peripheral to arcuate vessels

Endometrium • Proliferative phase ○ Early: Thin, single echogenic line ○ Progressive hypoechoic thickening (4-8 mm), classic trilaminar appearance • Secretory phase ○ Increased echogenicity and thickening up to 16 mm • Menstrual phase ○ Early: Cystic areas within echogenic endometrium indicating endometrial breakdown ○ Progressive heterogeneity with mixed cystic (blood) and hyperechoic (clot or sloughed endometrium) regions

ANATOMY IMAGING ISSUES Imaging Recommendations • Sonohysterography to evaluate endometrial pathology • 3D ultrasound additive in many cases, particularly müllerian duct anomalies and intrauterine device evaluation

EMBRYOLOGY Embryologic Events • Organogenesis phase: Uterus formed from paired paramesonephric (müllerian) ducts • Fusion phase: Paired ducts fuse in midline to form uterus and upper vagina ○ Unfused portions remain as fallopian tubes • Resorption phase: Resorption of uterine septum

Practical Implications • Müllerian duct anomalies occur during 1 of 3 phases of formation ○ Organogenesis: Uterine agenesis, hypoplasia, unicornuate ○ Fusion: Didelphys, bicornuate ○ Resorption: Septate, arcuate

Uterus Pelvis

UTERUS

Proper ovarian l. Suspensory l. of ovary Fallopian tube

Mesosalpinx Ovary Broad l. Ureter

Uterosacral l.

Interstitial (intramural) portion of fallopian tube Fallopian tube

Endometrium Internal os

Inner and outer layers of myometrium Round l.

Endocervical canal

Anterior cul-de-sac

External os Bladder

(Top) Illustration shows the posterior aspect of the uterus and ovaries with the other tissues removed. The ovary is suspended from the pelvic side wall by the suspensory ligament of the ovary and from the uterus by the proper ovarian ligament. These ligaments separate the mesosalpinx above from the broad ligament below. (Bottom) The uterus is composed of a glandular endometrium and muscular myometrium. The smooth muscle within the inner portion of the myometrium is more compacted and relatively hypovascular.

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Pelvis

Uterus VASCULAR SUPPLY

Right ureter

Inferior mesenteric a. Common iliac a.

Ovarian a. Middle sacral a. Internal iliac a. Anterior trunk of internal iliac a. Anastomoses between uterine and ovarian aa.

Obturator a. Lateral sacral a.

Uterine a.

Medial umbilical l. Uterine a. Middle rectal a.

Superior and inferior vesicle aa.

Fallopian tube

Ovary Fallopian a. Ovarian a. Endometrium Uterine a.

Ureter

Spiral a.

Cervix

Basal a.

Vaginal a. Vagina

Radial a. Arcuate a.

Bladder

(Top) Frontal graphic shows the arterial supply to the pelvis. The uterus has a dual blood supply with contributions from both the uterine and ovarian arteries. The ovarian artery originates from the aorta, and the uterine artery is a branch off the anterior trunk of the internal iliac artery. (Bottom) Graphic shows the uterine vasculature. The descending segment of the uterine artery, after branching off from the internal iliac artery, runs medially toward the cervix. The ascending segment ascends laterally along the uterine wall to meet the ovarian and fallopian arteries. The transverse segments cross the cardinal ligament and anastomose extensively with each other to form the arcuate arteries, which give rise to the radial arteries penetrating the myometrium vertically. The arteries then branch into spiral and basal arteries in the functional and basal layers of the endometrium respectively.

470

Uterus Pelvis

VASCULAR SUPPLY Ovarian v.

Ovarian venous plexus

Radial vv.

Uterine v.

Arcuate vv.

External iliac v.

Internal iliac a.

External iliac a.

Descending segment of uterine a. Posterior branch of internal iliac a. Anterior branch of internal iliac a.

Arcuate a. Fluid in endometrial cavity Uterine a.

(Top) This graphic shows the venous drainage from of the uterus, which follows the arterial system. There is venous drainage via both the uterine and ovarian veins. (Middle) Longitudinal transabdominal color Doppler ultrasound shows the uterine artery arising from the anterior branch of the internal iliac artery, which is near the level of the uterine cervix. The uterine artery can also be assessed with transvaginal ultrasound by locating it lateral to the cervix. (Bottom) Color Doppler ultrasound in a patient who has just undergone a dilatation and curettage for a failed 1st trimester pregnancy is shown. There is very prominent flow in the arcuate arteries, which run in the outer 1/3 of the myometrium.

471

Pelvis

Uterus CUL-DE-SACS AND LIGAMENTS

Bladder dome Round l. Mesosalpinx

Broad l. Ureter Uterine a. in cardinal l. Suspensory l. of ovary Uterosacral l.

Posterior cul-de-sac

Suspensory l. of ovary

Uterus

Posterior vagina fornix

Bladder

Posterior cul-de-sac Anterior vaginal fornix

Space of Retzius Vagina

(Top) Uterus viewed in situ from above and behind shows its positioning and major ligaments. The uterus is covered by a sheet of peritoneum, creating a double layer (the broad ligament), which sweeps laterally to attach to the pelvic wall. Areas of thickening at its base are the cardinal ligaments, which attach to the lateral pelvic wall, and the uterosacral ligaments, which attach to the sacrum. The uterosacral ligaments form the lateral borders of the posterior cul-de-sac (rectouterine pouch or pouch of Douglas). The round ligaments arise from the cornu of the uterus and course anteriorly to pass through the inguinal canal and insert on the labia majora. They offer little support for the uterus. (Bottom) Sagittal graphic of the female pelvis shows the bladder, uterus, and rectum, all of which are extraperitoneal. Note the posterior vaginal fornix extends more cephalad than the anterior vaginal fornix, and the posterior cul-de-sac is the most dependent portion of the peritoneal cavity.

472

Uterus Pelvis

3D UTERUS

Localizer, axial plane Localizer, sagittal plane

Uterine fundus

Localizer, coronal plane

Endometrium

Fundus

Cornua

Right arm of IUD in myometrium Endometrium

Body of IUD

Slice levels

Submucosal fibroid

Endometrium

(Top) This set of images shows a 3D data set of a normal uterus. A dedicated 3D ultrasound probe provides automated acquisition of a volume data set. This data is displayed in 3 simultaneous orthogonal planes. A central localizer point on each image allows the operator to know the precise location in all 3 planes and manipulate the image to the optimal projection. In the coronal image, the entire endometrial and fundal contours are displayed. This has particular utility in evaluating müllerian duct anomalies. (Middle) 3D images are also helpful for showing intrauterine uterine device (IUD) position. In this case, the right arm of the IUD is projecting into the myometrium. (Bottom) 3D data sets can be manipulated and sliced through like a CT or MR. This shows a set of 6 slices through a submucosal fibroid, which is projecting into the endometrial cavity. The lines on the localizer image on top correspond to slices below (the yellow line indicates the level of the image in the yellow box).

473

Pelvis

Uterus NORMAL SAGITTAL IMAGES OF UTERUS

Bladder

Body Fundus

Vagina Isthmus

Endometrium Myometrium Cervix Parametrium Rectouterine pouch of Douglas

Anterior vaginal fornix Central line of endometrium Inner functional layer of endometrium Basal layer of endometrium

Arcuate aa. and vv.

Cervical canal Inner zone of myometrium Middle zone of myometrium Outer zone of myometrium

Endometrium

(Top) Longitudinal TA ultrasound shows a normal anteverted uterus. Version refers to the angle the cervix makes with the vagina. In this case, the cervix is angled anteriorly, and the uterus continues in a straight line with the cervix. This is the most common position found in the female pelvis. (Middle) Longitudinal TV ultrasound obtained in the secretory phase demonstrates different zones. The smooth muscle within the inner zone of the myometrium is more compact, making it more hypoechoic (subendometrial halo). The majority of myometrium is homogeneously echogenic with the outer zone being less echogenic. (Bottom) Longitudinal transvaginal scan obtained in the early proliferative phase shows prominent arcuate arteries and veins, which run in the outer 1/3 of the myometrium. These may become calcified following menopause.

474

Uterus Pelvis

NORMAL VARIATIONS, UTERINE POSITION

Endometrium Uterine fundus Folding of anterior uterine wall Vaginal mucosa Cervix

Endometrium

Cervix

Folding of posterior uterine wall

Uterine fundus

Endometrium Orientation of vagina Orientation of cervix Uterine fundus

(Top) Longitudinal TA ultrasound of an anteverted, anteflexed uterus shows the uterine cervix is angled forward with respect to the vagina, and the uterine body is angled forward with respect to the cervix. Version refers to the angle of the cervix relative to the vagina. Flexion refers to the angle of the uterine body relative to the cervix, i.e., the uterus and the cervix are not in a straight line. (Middle) Uterine retroflexion is shown. This is an anteverted uterus with exaggerated retroflexion in which the uterus resembles a boxing glove. Folding of the posterior uterine wall may be confused with an intramural fibroid. (Bottom) Uterine retroversion is shown. The orientation of the uterus and cervix is posterior with respect to the vagina. Retroversion frequently limits transabdominal evaluation of the uterus, as seen here.

475

Pelvis

Uterus UTERINE VARIATIONS WITH AGE

Vagina Uterine body Cervix

Uterine body

Cervix

Uterine body Cervix

(Top) Longitudinal TA ultrasound shows an immediate neonatal uterus (day 2). The uterus is prominent with a bulbous cervix and a rudimentary body. The endometrium is seen as a thin, echogenic line, which may be due to stimulation by the residual maternal hormones. (Middle) Longitudinal TA ultrasound shows a prepubertal uterus in a 8-year-old patient. The uterus demonstrates a tubular appearance with the length of the cervix nearly double that of the uterine body. (Bottom) Longitudinal TA ultrasound shows an early pubertal uterus in a 12-years-old patient. The body length of the uterus approximates the cervical length with the endometrium, changing in appearance and thickness during the menstrual cycle. At this time, the uterine body grows dramatically until it reaches the adult size.

476

Uterus Pelvis

UTERINE VARIATIONS WITH AGE

Uterine body Cervix

Uterine body Cervix

Vagina

Uterine body

Cervix

(Top) Longitudinal TA ultrasound shows a nulliparous uterus. The normal adult uterus should attain a pear-shaped or hourglass appearance with the length of the uterine body double that of the cervix. The size of a nulliparous uterus is usually smaller than that of a parous uterus. (Middle) Longitudinal TA ultrasound shows an early postmenopausal uterus, which is atrophic with prominent reduction in body size relative to the cervix. (Bottom) Longitudinal TA ultrasound shows a later postmenopausal uterus. Note that the cervix: body ratio is similar to that of a prepubertal uterus.

477

Pelvis

Uterus CYCLIC CHANGES OF ENDOMETRIUM

Endometrium, early proliferative phase

Endocervical canal Central endometrium line

Functional layer of endometrium

Arcuate vessels

Central endometrium line

Stratum basalis

Stratum functionale

(Top) Longitudinal TA ultrasound shows endometrium in the postmenstrual or early proliferative phase. Note the endometrium is thin and echogenic. (Middle) Longitudinal TA ultrasound of the endometrium during mid proliferative phase shows the endometrium progressively thickened and slightly more echogenic. (Bottom) Longitudinal TA ultrasound of endometrium in the periovulatory phase shows thickening of the stratum functionalis with an echogenic central line and a layered, trilaminar appearance.

478

Uterus Pelvis

CYCLIC CHANGES OF ENDOMETRIUM

Endometrium, early secretory phase

Endometrium, secretory phase

Shedding endometrium, onset of menstruation Trace fluid in canal

(Top) Longitudinal TV scan shows the endometrium during the early secretory phase. The endometrium becomes progressively thickened and more echogenic with loss of the trilaminar appearance. These are cyclic endometrial changes in a neutral uterus. (Middle) Longitudinal TV ultrasound in the late secretory phase shows the endometrium is uniformly thickened and echogenic. The normal maximal endometrial thickness should not exceed 1.6 cm, through transmission can sometimes be visualized secondary to the mucus-filled glands. (Bottom) Longitudinal TV ultrasound shows a thickened endometrium just prior to menstruation. Echogenicity has decreased and is more heterogeneous than in the secretory phase. A small amount of fluid can be seen within the endometrial cavity.

479

Pelvis

Uterus INTRAUTERINE ARTERIES

Internal iliac aa.

Cervix

Uterine aa.

Arcuate vv.

Descending trunk of uterine a. Arcuate aa.

Basalis layer of endometrium Radial aa. Spiral aa.

Functional layer of endometrium (stratum functionalis)

(Top) Transverse TA color Doppler ultrasound shows descending branches of both uterine arteries running medially at the level of the cervix. Care must be taken not to confuse these with the iliac arteries, which lie more laterally. (Middle) Longitudinal TA color Doppler ultrasound shows the arcuate arteries and veins located at the periphery of the uterus. The arcuate arteries commonly calcify with advancing age. (Bottom) Longitudinal TV color Doppler ultrasound shows arcuate arteries branching into radial arteries, which run vertically in the myometrium. These in turn give rise to the basal and spiral arteries, which supply the basal and functional layers of the endometrium, respectively. The spiral arteries penetrate deep into the stratum functionalis of the endometrium, which sheds during menstruation.

480

Uterus Pelvis

FALLOPIAN TUBES Isthmus Interstitial (intramural) portion of tube Ampulla Mucosal folds Infundibulum Fimbriae

Hydrosalpinx

Mucosal folds

(Top) A graphic of the right fallopian tube shows the 4 segments, including the interstitial (intramural) portion, isthmus, ampulla, and infundibulum, which is ringed by the fimbriae. (Middle) First of 2 transvaginal ultrasound images of a left-sided hydrosalpinx is shown. During real-time scanning, it is important to try to elongate the tube, as in this image. This allows differentiation from a cystic ovarian mass. (Bottom) In the cross-sectional plane, a hydrosalpinx will often display a cogwheel appearance. The mucosal folds of the fallopian tube project into the lumen. As the hydrosalpinx becomes more chronic, these folds will become thick and nodular.

481

Pelvis

Cervix

GROSS ANATOMY Overview • Begins at inferior narrowing of uterus (isthmus) ○ Supravaginal portion: Endocervix ○ Vaginal portion: Ectocervix • Endocervical canal: Spindle-shaped cavity communicates with uterine body and vagina • Internal os: Opening into uterine cavity • External os: Opening into vagina • Largely fibrous stroma with high proportion of elastic fibers interwoven with smooth muscle • Endocervical canal lined by mucus-secreting columnar epithelium ○ Epithelium in series of small, V-shaped folds (plicae palmatae) • Ectocervix lined by stratified squamous epithelium • Squamocolumnar junction near external os but exact position variable • Nabothian cysts are commonly seen ○ Represent obstructed mucus-secreting glands • Entire cervix is extraperitoneal ○ Anterior: Peritoneum reflects over dome of bladder above level of internal os ○ Posterior: Peritoneum extends along posterior vaginal fornix, creating rectouterine pouch of Douglas (cul-desac) • Arteries, veins, nerves, and lymphatics ○ Arterial supply – Descending branch of uterine artery from internal iliac artery ○ Venous drainage – To uterine vein and drains into internal iliac vein ○ Lymphatics – Drain into internal and external iliac lymph nodes ○ Innervation – Sympathetic and parasympathetic nerves from branches of inferior hypogastric plexuses • Variations with pregnancy ○ Nulliparous: Circular external os, arterial waveform shows high resistivity index (RI) ○ During pregnancy: Changes become apparent by ~ 6 weeks of gestation – Softened and enlarged cervix due to engorgement with blood with decreased RI of uterine artery – Hypertrophy of mucosa of cervical canal: Increased echogenicity of mucosal layer – Increased secretion of mucous glands: Increased volume of mucus ± mucus plug in cervical canal ○ Parous: Larger vaginal part of cervix, external os opens out transversely with anterior and posterior lips • Variations with age: Cervix grows less with age than uterus ○ Neonatal: Adult configuration due to residual maternal hormonal stimulation ○ Infantile: Cervix predominant with cervix:corpus length ratio ~ 2:1 ○ Prepubertal: Cervix:corpus length ratio ~ 1:1 ○ Reproductive: Uterus predominant, cervix:corpus length ratio ≥ 1:2 ○ Postmenopausal: Overall reduction in size

482

Anatomy Relationships • Anterior ○ Supravaginal cervix: Superior aspect of posterior bladder wall ○ Vaginal cervix: Anterior fornix of vagina • Posterior ○ Supravaginal cervix: Rectouterine pouch of Douglas ○ Vaginal cervix: Posterior fornix of vagina • Lateral ○ Supravaginal cervix: Bilateral ureters ○ Vaginal cervix: Lateral fornices of vagina • Ligamentous support: Condensations of pelvic fascia attached to cervix and vaginal vault ○ Transverse cervical (cardinal) ligaments – Fibromuscular condensations of pelvic fascia – Pass to cervix and upper vagina from lateral walls of pelvis ○ Pubocervical ligaments – 2 firm bands of connective tissue – Extend from posterior surface of pubis, position on either side of neck of bladder and then attach to anterior aspect of cervix ○ Sacrocervical ligaments – Fibromuscular condensations – Attach posterior aspect of cervix and upper vagina from lower end of sacrum – Form 2 ridges, 1 on either side of rectouterine pouch of Douglas

IMAGING ANATOMY Ultrasound • Transabdominal scan ○ Mucus within endocervical canal usually creates echogenic interface ○ In periovulatory phase, cervical mucus becomes hypoechoic due to high fluid content ○ Mucosal layer: Echogenic – Thickness and echogenicity shows cyclical changes similar to endometrium ○ Submucosal layer: Hypoechoic ○ Cervical stroma: Intermediate to echogenic • Transvaginal scan ○ Angle of insonation should be optimized for best visualization ○ Imaging may be improved with withdrawal of probe into mid vagina

MR • Important in local staging of cervical cancer • Uniform intermediate signal on T1WI • Zonal anatomy on T2WI ○ Endocervical canal: High signal ○ Cervical stroma: Predominately low signal, contiguous with junctional zone ○ Outer layer of smooth muscle (variably present): Intermediate signal ○ Parametrium: Variable signal intensity – Cardinal ligament and associated venous plexuses high signal – Sacrocervical ligament low signal

Cervix Pelvis

GRAPHICS OF CERVIX ANATOMY

Endometrial canal

Internal os Endocervix

Endocervical canal Posterior fornix of vagina

Vesicouterine pouch Ectocervix

External os Anterior fornix of vagina Vaginal canal

Bladder

Prevesical space (space of Retzius)

Paravesical space Vesicocervical/vesicovaginal space Cardinal l. Rectovaginal space Uterosacral l. Pararectal space

Presacral space

(Top) Median sagittal graphic shows the cervix, which begins at the isthmus, the inferior narrowing portion of the uterus. It has a supravaginal portion (endocervix) and a vaginal portion (ectocervix), which divides the vagina into shallow anterior fornix, deep posterior, and lateral fornices. (Bottom) Graphic shows the female pelvic ligaments and spaces at the cervical/vaginal junction. The ligaments are visceral ligaments, which are composed of specialized endopelvic fascia and contain vessels, nerves, and lymphatics. Some of the main supporting ligaments for the uterus are attached to the cervix, which are cardinal and uterosacral ligaments. The spaces are largely filled with loose connective tissue and are used as dissection planes during surgery.

483

Pelvis

Cervix TRANSVAGINAL ULTRASOUND OF CERVIX

External os Internal os

Free fluid in cervical canal

Vaginal fornix

Cervical stroma

Submucosal layer

Internal os

Nabothian cysts

Mid cervical canal with thin mucosal layers

External os

Submucosal layers Free fluid in rectovaginal pouch (Douglas)

(Top) Sagittal transvaginal ultrasound of the cervix shows hypoechoic fluid present in the endocervical canal. The endocervical canal is rich in mucus-secreting glands. The mucus secreted is usually slightly echogenic but becomes hypoechoic during periovulatory phase. As the transducer abuts the anterior lip of the cervix, the posterior wall of the vaginal fornix can be seen to cover the external os and extend along the posterior lip of the cervix. (Middle) Transverse transvaginal ultrasound of the cervix at the lower endocervical canal shows a typical appearance with an echogenic mucosal layer, a hypoechoic band of the submucosal layer, and intermediate echogenic stroma. The submucosal layer is filled with mucus-secreting glands leading to its hypoechoic appearance. (Bottom) Longitudinal transvaginal ultrasound shows the transducer abutting the anterior lip of the external os. The submucosal layer is thickened with typical low echogenicity.

484

Cervix Pelvis

TRANSVAGINAL ULTRASOUND OF CERVIX

Cervical stroma Nabothian cysts Thin mucosal layer Submucosal layers

Thickened mucosa

Acoustic shadows from edges

Cervical stroma Submucosal layers

Nabothian cyst

Posterior acoustic enhancement

Uterine vv.

(Top) Longitudinal transvaginal ultrasound of cervix shows 2 small nabothian cysts adjacent to the internal os. Nabothian cyst is a common sonographic finding in the cervix and is usually anechoic but sometimes can contain internal debris. It is generally of no clinical significance. (Middle) Transverse transabdominal ultrasound at the level of the cervix of a nonpregnant uterus commonly shows thickened mucosal layers. Note that during the menstrual cycle, the thickness and echogenicity of the mucosal layer undergoes changes as the endometrium does. When thickened, it typically casts shadowing from its edges. (Bottom) Transverse transvaginal ultrasound of the cervix at the mid endocervical canal shows the echogenic mucosal layers and thickened submucosal layers. A simple nabothian cyst is present with minimal posterior acoustic enhancement. The submucosal layer is filled with mucus-secreting glands leading to its hypoechoic appearance and posterior acoustic enhancement.

485

Pelvis

Cervix TRANSABDOMINAL ULTRASOUND OF CERVIX

Urinary bladder

External os

Right lateral vaginal fornix

Ectocervix

Left lateral vaginal fornix

Urinary bladder

Cervical stroma Submucosal layer Mucosa layer of cervix

Endocervical canal Shadowing from edges of mucosal layer

Urinary bladder

Internal os

Lower uterine wall

(Top) Transverse transabdominal ultrasound shows the ectocervix at the level of external os. The lateral vaginal fornices are seen as relatively hypoechoic areas on each side of the ectocervix. (Middle) Transverse transabdominal ultrasound of the mid endocervix shows the mildly thickened and echogenic mucosal layer. Note that during the menstrual cycle, the thickness and echogenicity of the mucosal layer undergoes changes as the endometrium does. When thickened, it typically casts shadowing from its edges. (Bottom) Transverse transabdominal ultrasound shows the upper cervix at the level of the internal os, which opens into the uterine cavity. Identification of the internal os is clinically significant in pregnancy for placental site localization.

486

Cervix Pelvis

CHANGES OF CERVIX DURING PREGNANCY

Nabothian cyst

Diastolic notch

Uterine aa.

Mucus plug

Acoustic shadows from edges

(Top) Transverse transvaginal ultrasound shows spectral waveform of the uterine artery at the lateral margin of a nonpregnant cervix. There is typical high-resistance flow with a diastolic notch. In normal women, the Doppler waveform usually demonstrates a highresistance pattern except in late secretory phase. (Middle) As softening of the cervix due to engorgement with blood becomes apparent by 6 weeks after conception, the changes can be reflected in the uterine artery with high-velocity, low-resistance flow seen on this transabdominal spectral Doppler examination. (Bottom) Transverse transabdominal ultrasound shows the typical thick and echogenic mucus plug in a pregnant cervix casting dense shadows from its edges.

487

Pelvis

Vagina

TERMINOLOGY Abbreviations • Vaginal artery (VA), uterine artery (UA)

GROSS ANATOMY Overview • Muscular tube formed by smooth muscle and elastic connective fibers • Serves as excretory duct for uterus, female organ for copulation, and part of birth canal • Extends up and back from vestibule of external genitalia to surround cervix of uterus • Has anterior and posterior walls, normally in apposition, with longer posterior wall • Superiorly, cervix projects downward and backward into vagina and divides vagina into shallow anterior, deep posterior, and lateral fornices • Upper 1/2 of vagina lies above pelvic floor, lower 1/2 lies within perineum • Lined with stratified squamous epithelium • Inner mucosal surface of wall form rugae when collapsed • Thin mucosal fold called hymen surrounds entrance to vaginal orifice • Outer surface (adventitial coat) is thin fibrous layer continuous with surrounding endopelvic fascia • Vasculature ○ Arterial supply – VA: Can branch directly from internal iliac artery (anterior trunk) or sometimes from inferior vesical artery or UA – Vaginal branches of UA – Branches of VA and UA anastomose to form 2 median longitudinal vessels: Azygos arteries, 1 in front and 1 behind vagina ○ Venous drainage – Form venous plexus around vagina – Eventually drains to internal iliac veins • Variations with age ○ Menarche: 7-10 cm long ○ Postmenopausal: Shrinks in length and diameter; fornices virtually disappear

488

○ Lower 1/3: Perineal body

IMAGING ANATOMY Ultrasound • Transabdominal US with distended bladder is standard imaging technique ○ Caudal angulation on both longitudinal and transverse scans ○ Commonly found at/near sagittal midline of pelvis ○ Length and wall thickness vary in response to bladder and rectal filling ○ Combined thickness of anterior and posterior vaginal walls should not exceed 1 cm for transabdominal scan with distended bladder ○ Characteristic appearance of 3 parallel lines – Highly echogenic mucosa centrally, may be difficult to visualize if stretched by distended bladder – Moderately hypoechoic muscular walls • Transperineal US with nondistended bladder for assessment of uterine prolapse or for difficult cases ○ Vagina, especially vaginal canal, is less well-defined

EMBRYOLOGY Embryologic Events • Uterus and upper vagina are formed from paired müllerian (paramesonephric) ducts • Paired ducts meet in midline and fuse, forming uterovaginal canal • Lower vagina is formed from urogenital sinus

CLINICAL IMPLICATIONS Uterine Prolapse • Ligamentous support of pelvic organs may be damaged or become lax, leading to uterine prolapse or prolapse of vaginal walls • Cystocele: Sagging of bladder with bulging of anterior vaginal wall • Rectocele: Sagging of ampulla of rectum with bulging of posterior vaginal wall • Best to be investigated by transperineal US supplemented with 3D

Anatomic Relationships

Müllerian Duct Anomalies

• Anterior ○ Superior: Bladder base ○ Inferior: Urethra • Posterior ○ Upper 1/3: Rectouterine pouch of Douglas ○ Middle 1/3: Ampulla of rectum ○ Lower 1/3: Perineal body • Lateral ○ Upper 1/3: Ureters ○ Middle 1/3: Levator ani and pelvic fascia ○ Lower 1/3: Bulb of vestibule, urogenital diaphragm, and bulbospongiosus muscles • Ligamentous supports ○ Upper 1/3: Levator ani muscles, transverse cervical (cardinal), pubocervical, and sacrocervical ligaments ○ Middle 1/3: Urogenital diaphragm

• Failure of müllerian duct development ± fusion • Vagina most commonly affected in uterus didelphys (class III anomaly); vaginal septum seen in ~ 75% of cases

Pelvic Abscess • Common site: Rectouterine pouch of Douglas • Feasible for transvaginal US-guided drainage of pelvic abscess without doing major operation

Persistent Sexual Arousal Syndrome • Persistent sexual arousal during sleep in postmenopausal women • VA blood flow as 1 diagnostic aid • VA normally shows high-resistance flow • During sexual arousal, increased blood flow to VA with lowresistance spectral waveform

Vagina Pelvis

VAGINA IN SITU AND ARTERIAL SUPPLY

Ovary

Fallopian tube Uterus

Broad l. Round l. of uterus

Vagina

Obturator vessels and n.

Obturator internus m. Levator ani m.

Vestibule

Deep transverse perineal m. and fascia

Internal iliac a. (anterior trunk)

Uterine a. Descending trunk of uterine a. Vaginal a. Inferior vesical a. Superior vesical a. Occluded umbilical a.

(Top) Coronal view shows the pelvic floor at the level of the vagina. The levator ani muscles form the pelvic floor through which the urethra, vagina, and rectum pass and are the main support for the pelvic organs. The deep transverse perineal muscle and fascia, along with the urethral sphincter, form the urogenital diaphragm, which is the main support of the lower vagina. (Bottom) Frontal graphic shows the iliac vessels. The internal iliac artery divides into an anterior trunk and posterior trunk. The vaginal artery (VA) can branch off directly from the anterior trunk of the internal iliac artery or sometimes from the inferior vesical artery or uterine artery (UA). The arterial supply of the vagina includes the VA and vaginal branch of the descending trunk of UA.

489

Pelvis

Vagina VAGINAL IMAGING BY VARIOUS TECHNIQUES Urinary bladder Urethra

Muscular walls of vagina Mucosal layer of vagina

Cervix Rectum

Muscular walls of vagina

Vaginal canal Urinary bladder

Cervix, external os Cervix

Distal vagina Anal canal Urethra Rectovaginal fascia Urinary bladder

Vaginal wall

(Top) Transabdominal midline sagittal US of the vagina shows characteristic triple-line echoes, i.e., hypoechoic muscular walls interfaced by echogenic mucosa. When looking for the vagina using transabdominal US, it is best to view with a distended bladder, starting at the midline near the cervical level and tilting the transducer further caudally. (Middle) Longitudinal transvaginal US of the vagina again shows the characteristic triple-line echo pattern. Using transvaginal US, gradually withdraw the high-frequency vaginal transducer so as to outline the vaginal canal. (Bottom) Transperineal sagittal US shows the vagina sandwiched between the urethra anteriorly and the rectum posteriorly. Note that the vaginal canal is barely visible in the absence of intraluminal acoustic jelly or fluid.

490

Vagina Pelvis

TRANSVERSE US OF VAGINA

Urinary bladder

Vagina

Urethra

Anal canal

Levator ani mm.

Urinary bladder

Urethra

Vagina

Rectum

Levator ani mm.

Urinary bladder

Ureteric orifices

Vagina Obturator internus m. Rectal gas with shadowing

Iliococcygeus mm.

(Top) Transverse transabdominal US shows the mid to lower vagina at the level of anal canal. For transabdominal US of the vagina, caudal angulation of the US probe is needed on both longitudinal and transverse scans. Note that the vaginal canal is better demonstrated on transabdominal US because the angle of insonation is more favorable, approaching a right angle. (Middle) Transverse transabdominal US of the mid vagina shows the levator ani muscles adjacent to the posterolateral aspect of the vagina. (Bottom) The upper vagina is shown at the level of the ureteric orifices. The ureters run lateral to the lateral fornices of the vagina, cross anteriorly, and then enter into the posterior wall of the bladder. This is a useful plane for investigation of the ureteric jets.

491

Pelvis

Vagina COLOR DOPPLER US OF VAGINAL ARTERY

Urinary bladder

Azygos a.

Vaginal canal

Rectum

Symphysis pubis

Vaginal canal Vaginal a. Vesicovaginal fascia

Periurethral aa. Urethra

Urinary bladder

Vaginal a.

Rectal canal Periurethral aa.

Vagina Vesicovaginal fascia

Urethra

Rectovaginal fascia

Bladder

(Top) Longitudinal transabdominal color Doppler US of the vagina shows the longitudinally running azygos artery, which arises from the anastomosis of vaginal branches of the UA and branches of the VA. (Middle) Longitudinal transvaginal color Doppler US shows the highly vascularized vagina with multiple small branches of the VA running along the vesicovaginal fascia. (Bottom) Transperineal sagittal color Doppler US shows a tortuous branch of the VA running along the vesicovaginal fascia in the vagina.

492

Vagina Pelvis

SPECTRAL WAVEFORM OF VAGINAL ARTERY

Azygos a.

Periurethral a. Vaginal a.

Periurethral a.

Vaginal a.

(Top) Transabdominal spectral Doppler US of the azygos artery shows a low-resistance flow during mid cycle. The findings are most probably due to the influence of cyclical/hormonal change. (Middle) Spectral waveform of VA by transvaginal scan shows highresistance flow, which is the most common pattern in normal females. (Bottom) Spectral Doppler US shows the VA by transperineal scan. The typical high-flow resistance in the VA may decrease during sexual arousal, cyclically or related to hormonal changes. This phenomenon is useful for investigation and management of sexual dysfunction in postmenopausal women.

493

Pelvis

Ovaries

GROSS ANATOMY Overview • Ovaries located in true pelvis, although exact position variable ○ Only pelvic organ entirely inside peritoneal sac ○ Laxity in ligaments allows some mobility ○ Location affected by parity, bladder filling, ovarian size, and uterine size/position ○ Located within ovarian fossa in nulliparous women – Lateral pelvic sidewall below bifurcation of common iliac vessels – Anterior to ureter – Posterior to broad ligament ○ Position more variable in parous women – Pregnancy displaces ovaries, seldom return to same spot • Fallopian tube drapes over much of surface ○ Partially covered by fimbriated end • Composed of medulla and cortex ○ Vessels enter and exit ovary through medulla ○ Cortex contains follicles in varying stages of development ○ Surface covered by specialized peritoneum called germinal epithelium • Ligamentous supports ○ Suspensory ligament of ovary (infundibulopelvic ligament) – Attaches ovary to lateral pelvic wall – Contains ovarian vessels and lymphatics – Positions ovary in craniocaudal orientation ○ Mesovarium – Attaches ovary to broad ligament (posterior) – Transmits nerves and vessels to ovary ○ Proper ovarian ligament (utero-ovarian ligament) – Continuation of round ligament – Fibromuscular band extending from ovary to uterine cornu ○ Mesosalpinx – Extends between fallopian tube and proper ovarian ligament ○ Broad ligament – Below proper ovarian ligament • Arterial supply: Dual blood supply ○ Ovarian artery is branch of aorta, arises at L1/L2 level – Descends to pelvis and enters suspensory ligament – Continues through mesovarium to ovarian hilum – Anastomoses with uterine artery • Drainage via pampiniform plexus into ovarian veins ○ Right ovarian vein drains to inferior vena cava ○ Left ovarian vein drains to left renal vein • Lymphatic drainage follows venous drainage to preaortic lymph nodes at L1 and L2 levels

Physiology • ~ 400,000 follicles present at birth, but only 0.1% (400) mature to ovulation • Variations in menstrual cycle ○ Follicular phase (days 0-14) – Several follicles begin to develop 494

– By days 8-12, dominant follicle develops, while remainder start to regress ○ Ovulation (day 14) – Dominant follicle, typically 2.0-2.5 cm, ruptures and releases ovum ○ Luteal phase (days 14-28) – Luteinizing hormone induces formation of corpus luteum from ruptured follicle – If fertilization occurs, corpus luteum maintains and enlarges to corpus luteum cyst of pregnancy

Variations With Age • At birth: Large ovaries ± follicles due to influence of maternal hormones • Childhood: Volume < 1 cm³, follicles < 2-mm diameter • Above 8 year old: ≥ 6 follicles of > 4-mm diameter • Adult, reproductive age: Mean volume ~ 10 ± 6 cm³, max 22 cm³ • Postmenopausal: Mean ~ 2-6 cm³, max 8 cm³ and may contain few follicle-like structures

IMAGING ANATOMY Ultrasound • Scan between uterus and pelvic sidewall ○ Ovaries often seen adjacent to internal iliac vessels • Medulla mildly hyperechoic compared to hypoechoic cortex • Dominant follicle around time of ovulation ○ Cumulus oophorus: Nodule or cyst along margin of dominant follicle represents mature ovum • Corpus luteum may have thick, echogenic ring ○ Doppler: Vascular wall or "ring" ○ Hemorrhage common • Echogenic foci common ○ Nonshadowing, 1-3 mm ○ Represent specular reflectors from walls of tiny unresolved cysts or small vessels in medulla • Doppler: Low-velocity, low-resistance arterial waveform • Volume (0.523 x length x width x height) more accurate than individual measurements

ANATOMY IMAGING ISSUES Imaging Recommendations • Transabdominal (TA) US with full bladder is good for overview of pelvic organs ○ Detects ovaries and masses superior to uterus that may be missed by transvaginal (TV) US • TV US is excellent in assessing detail of ovaries and characterizing lesions compared to TA US ○ Lesions higher in pelvis can be missed because of limited field of view • Postmenopausal ovaries can be difficult to detect because of atrophy, paucity of follicles and surrounding bowel

Ovaries

Mesosalpinx

Pelvis

LIGAMENTOUS SUPPORT AND ANATOMY OF OVARY

Suspensory l. of ovary (infundibulopelvic l.) Ovarian a. and v.

Mesovarium Fallopian tube Proper ovarian l. Ovary

Broad l.

Ureter

Suspensory l. of ovary

External iliac vessels Fallopian tube

Ureter Ovary Uterus

Urinary bladder

Rectum

Proper ovarian l. Round l.

Uterine fundus Fallopian tube Stitch

Mesovarium Fallopian tube Broad l.

Uterosacral ll. Right ovary

Left ovary Cul-de-sac Suspensory l. of ovary Rectum

(Top) Posterior view of the ligamentous attachment of the ovary is shown. The ovary is attached to the pelvic sidewall by the suspensory ligament (infundibulopelvic ligament) of the ovary, which transmits the ovarian artery and vein. These vessels enter the ovary through the mesovarium, a specialized ligamentous attachment between the ovary and broad ligament. The ovary is attached to the uterus by the proper ovarian ligament, which divides the mesosalpinx above from the broad ligament below. (Middle) Sagittal graphic of the female pelvis shows the location of the ovary, which lies in the ovarian fossa, the area below the iliac bifurcation, posterior to the external iliac vessels, and anterior to the ureter. (Bottom) Photograph during laparoscopy viewing the uterine fundus from above demonstrates the ligamentous structures of the ovary and uterus.

495

Pelvis

Ovaries NORMAL OVARY, VARIATIONS WITH AGE

Fallopian tube/broad l.

Fallopian tube/broad l.

Right ovary Uterus

Dominant follicle Ovary Solid parenchyma

Bladder

Uterus Right ovary Immature follicles

(Top) Transverse TA ultrasound at the level of the uterine fundus in a 23-year-old woman shows the right ovary in the typical position of the ovarian fossa. The fallopian tube and broad ligament can sometimes be seen as a band of tissue connecting the ovary to the uterine horn. Ovarian ligaments can be lax making ovarian position quite variable from above the fundus to the posterior rectouterine pouch of Douglas. (Middle) Transverse TA ultrasound of the ovary in a neonate is shown. The size of the ovary is enlarged with a dominant follicle related to stimulation from residual maternal gonadotrophins. Visible follicles may persist until 9 months of age or longer. (Bottom) Longitudinal TA ultrasound of the ovary of a 5-month-old girl is shown. The ovary is slightly prominent due to stimulation from maternal hormones. The ovary is small (total volume of 1.7 cc) with immature follicles of variable size (usually < 0.9 cm). The size of the ovaries change very little in the first 6 years of life.

496

Ovaries Pelvis

NORMAL OVARY, VARIATIONS WITH AGE Transvaginal transducer

Immature follicles

Bowel gas

Immature follicles

Ovarian stroma

Developing follicle

Broad l. Cysts Right ovary Uterus

Iliac v.

Bowel

(Top) Transverse TV ultrasound of the right ovary in a 18-year-old woman shows an oval ovary with immature follicles. This image also demonstrates the superior resolution of TV ultrasound, from the ability to bring the ovary to the near field, as well as the higher frequencies used. (Middle) Transverse TV ultrasound of an adult ovary is shown. There are multiple developing follicles of variable size around the echogenic ovarian stroma (medulla) where the ovarian vessels and lymphatics enter and exit. Ovulation usually occurs when the follicle enlarges to be between 2.0 and 2.5 cm. (Bottom) TV ultrasound in a 74-year-old postmenopausal woman demonstrates atrophic right ovary containing tiny cysts. Normal ovaries are variably detected in the postmenopausal woman because of their small size, lack of follicles, and surrounding bowel loops.

497

Pelvis

Ovaries COLOR DOPPLER IMAGING OF OVARIAN ARTERY

Uterus Broad l. Ovarian branch of uterine a.

Right ovary

Ovarian vessels

Intrastromal ovarian a.

(Top) Transverse TV ultrasound shows the ovarian branch of the uterine artery running in the broad ligament. It begins at the uterine horn and goes to the ovary through the proper ovarian ligament/mesovarium anastomosing with the ovarian artery. (Middle) Transverse TV ultrasound of the left ovary demonstrates involuting corpus luteum (calipers). The ovarian vessels are seen entering the ovary from the suspensory ligament of the ovary. (Bottom) Longitudinal color Doppler TV ultrasound shows an intrastromal ovarian artery running in the ovarian medulla. Note the ovarian vascularity will progressively increase after menstruation and approach a maximum in the luteal phase.

498

Ovaries Pelvis

SPECTRAL WAVEFORM OF OVARIAN ARTERY

Ovarian a.

Cortical arteriole of ovarian a. Ovary

Intrastromal ovarian a.

(Top) Transverse spectral Doppler TA ultrasound shows a normal ovarian artery with a high-resistance flow pattern suggestive of an inactive state of the ovary. (Middle) Transverse spectral Doppler TA ultrasound shows the waveform of the cortical arteriole of the ovarian artery. (Bottom) Transverse spectral Doppler TV ultrasound of the intrastromal ovarian artery as a continuation of the straight cortical arteriole shows a typical low-resistance, low-velocity waveform during the luteal phase.

499

Pelvis

Ovaries CYCLIC CHANGES OF OVARY

Developing follicles Cumulus oophorus Corpus albicans

Corpus luteum

Dominant follicle

Mature follicles

(Top) During the follicular phase of the menstrual cycle, several follicles begin to develop, but by days 8-12, a dominant follicle has formed, and the remainder begin to regress. On day 14, the follicle ruptures, and the egg is released. After ovulation, a corpus luteum forms, and if fertilization does not occur, the corpus luteum degenerates into a corpus albicans. (Middle) Longitudinal TV ultrasound of the ovary at the early follicular phase is shown. Note the developing follicles of variable size at the periphery of the ovary. (Bottom) TV ultrasound shows a dominant follicle developed in the late follicular phase days before ovulation. This should not be confused for a pathologic cyst.

500

Ovaries Pelvis

CYCLIC CHANGES OF OVARY

Mature follicle Cumulus oophorus

Recently ruptured follicle

Regressing corpus luteum

Immature follicles

(Top) Transverse TV color Doppler ultrasound of the ovary demonstrates a large mature follicle with a small cyst on its wall representing a cumulus oophorus. The size of a mature follicle can reach up to 25 mm before ovulation. (Middle) Longitudinal TV color Doppler ultrasound of the ovary shows a dominant follicle immediately after its rupture at ovulation. Note the partially collapsed wall resulting from loss of part of the liquor folliculi and the hypoechoic internal contents representing blood. (Bottom) Transverse TV ultrasound of the ovary shows a regressing corpus luteum with typical hypoechoic, thick, crenulated wall, and echogenic internal contents representing blood.

501

Pelvis

Ovaries CYCLIC CHANGES OF INTRAOVARIAN ARTERY

Ovarian v. Ovarian a. Ovarian hilum and intraovarian a.

Developing follicles

Internal iliac a. Internal iliac v.

Corpus luteum A. around wall of corpus luteum

Corpus luteum

(Top) Color Doppler TA ultrasound shows an inactive ovary. The ovary demonstrates a hilar artery surrounded by small developing follicles in the early follicular phase. Note the nondominant ovary may show a similar appearance as an inactive ovary. (Middle) Longitudinal TV ultrasound of the ovary in the early luteal phase is shown. A corpus luteum with low-level internal echoes is seen following ovulation. The wall of the corpus luteum usually displays the most intense color pattern. (Bottom) Transverse TV ultrasound in midluteal phase is shown. The ovary shows a regressing corpus luteum with typical peripheral color Doppler vascularity.

502

Ovaries Pelvis

CYCLIC CHANGES OF INTRAOVARIAN ARTERY

Early diastolic notch Peak systole

End diastole

Immediate postovulatory ruptured follicle

Corpus luteum

(Top) Transverse spectral Doppler TA ultrasound of the ovarian artery is shown. The ovarian artery blood flow shows a high-resistance flow pattern with low end-diastolic velocity and an early diastolic notch. This notch indicates initial resistance to forward flow through the ovarian parenchyma. The flow resistance is at its maximum during the first 8 days of the cycle. (Middle) Spectral Doppler TV ultrasound of the intraovarian artery in early luteal phase is shown. The ovarian artery has a low-resistance flow, which reaches the lowest level in early luteal phase. At this time, the intraovarian vascularity is easily detectable. (Bottom) Spectral Doppler of TA ultrasound of the intraovarian artery in midluteal phase is shown. The ovarian arterial flow is of medium resistance, and the flow resistance will gradually increase through to the regenerative phase.

503

Pelvis

Pelvic Floor

GROSS ANATOMY Functional Anatomy • Classic 3-compartment approach ○ Anterior: Includes urinary bladder, urethra, and urethral support system ○ Middle: Includes vagina (anterior and posterior wall) and uterocervical support ○ Posterior: Contains rectum and supporting structures • Active (pelvic floor muscles) and passive (pelvic bones, supportive connective tissue) conceptual approach • Multilayered system approach: Considers passive and active components of pelvic floor as integrated multilayer system, organized from cranial to caudal ○ 1st layer: Endopelvic fascia ○ 2nd layer: Pelvic diaphragm ○ 3rd layer: Urogenital diaphragm ○ 4th layer: Superficial external genital muscles • Functional supporting systems approach: New, more function-based classification of pelvic floor support system ○ Urethral support system: Structures that maintain urinary continence ○ Vaginal support system: Supporting elements that prevent prolapse ○ Maintenance of anal continence: Supporting elements and anal sphincter complex

Ligaments & Fascia

• Osseous structures: 2 iliac bones, sacrum and coccyx ○ Pubic bones meet in midline at pubic symphysis ○ Pelvis is divided into 2 parts by pelvic brim – False pelvis above forms part of abdominal cavity – True pelvis below pelvic brim • Walls ○ Anterior wall formed by posterior surfaces of bodies of pubic bone, symphysis pubis (SP), and pubic rami ○ Posterior wall formed by coccyx and sacrum, piriformis muscles, and their covering parietal pelvic fascia ○ Lateral wall formed by Ilium, ischium, and obturator internus muscle and fascia • Supporting ligaments: Sacrotuberous and sacrospinous

• Complex network of connective tissue • Ligaments: Forms well-defined layer composed of specialized aggregation of connective tissue ○ Arcus tendineus levator ani (ATLA): Condensation of obturator fascia – Major attachment site of levator ani muscles ○ Arcus tendineus fascia pelvis (ATFP) – Provides lateral anchoring sites for anterior vaginal wall that underlies and supports urethra • Endopelvic fascia: Forms diffuse layer of less well-defined connective tissue beneath parietal peritoneum ○ Important for passive support of visceral organs and pelvic floor • Vaginal support: Can be divided into 3 levels ○ Level I (suspension): Upper portion of vagina adjacent to cervix – Suspended from above by relatively long connective tissue fibers of upper paracolpium ○ Level II (attachment): Midportion of vagina – Attaches vaginal wall more directly to ATFP ○ Level III (fusion): From introitus to 2-3 cm above hymenal ring – Near introitus, vagina is fused laterally to levator ani – Posteriorly, attached to perineal body – Anteriorly, blends with urethra • Urethral support: Urethral ligaments, level III endopelvic fascia, and puborectalis muscle

Pelvic Diaphragm

Urogenital Diaphragm & Perineum

• Formed by coccygeus and levator ani muscles ○ Acts as shelf to support pelvic organs • Coccygeus muscle ○ Broad musculotendinous structure forming posterior part of pelvic diaphragm • Levator ani muscle: Divided anatomically into 3 components (differentiated according to origin and direction of fiber bundles) ○ Puborectalis muscle – Arises from superior and inferior pubic rami – Unites with contralateral puborectalis muscle posterior to rectum, forming sling – Does not insert onto any skeletal structure ○ Pubococcygeus muscle – Arises from back of pubic bone and anterior part of obturator fascia – Inserts onto lateral aspect of coccyx ○ Iliococcygeus muscle

• Cavity of pelvis is divided by pelvic diaphragm into main pelvic cavity above and perineum below • Urogenital diaphragm: Fibromuscular layer directly below pelvic diaphragm ○ Spans anterior pelvic outlet and is attached to pubic bones ○ Crossed by urethra and vagina (continuous sheet in males) • Perineal body: Fascial condensation posterior to vagina ○ Insertion site of perineal muscle and external anal sphincter • Perineum is divided into anterior and posterior parts by line drawn across ischial tuberosities ○ Anterior: Urogenital triangle ○ Posterior: Anal triangle • Superficial external genital muscles include superficial transverse perineal, bulbospongiosus, and ischiocavernosus

Bony Pelvis & Walls

504

– Arises from fascia overlying obturator internus – Inserts onto lateral aspect of coccyx, overlapping with fibers of pubococcygeus muscle in staggered arrangement ○ Levator ani muscle group works at rest and during stress to counteract intraabdominal pressure and support pelvic organs • Urogenital hiatus: Opening within levator ani muscle through which urethra, vagina, and rectum pass (and through which prolapse occurs) ○ Bounded ventrally by pubic bones and laterally by puborectalis muscle

Pelvic Floor

Overview • SP: Appears as echogenic structure with highly reflective surface anterior to urethra ○ On Valsalva maneuver, inferior margin of SP serves as line of reference for maximal bladder descent, uterovaginal prolapse, and rectocele • Lower urinary tract ○ Bladder neck and urethra form funnel ○ Urethra: Multilayer; cylindrical; posterior to SP – Central: Mucosa/submucosa; hypoechoic – Concentric: Muscular lissosphincter; echogenic – Outer: Striated rhabdosphincter ○ Periurethral artery – Identified in urethral mucosa parallel to lumen – Resistivity index (RI): Postmenopausal > premenopausal • Anterior vaginal septum: Hypoechoic vesicovaginal fascia between urethra and vagina • Vagina: Posterior to urethra ○ Longitudinal: Hypoechoic structure; poorly defined lumen unless outlined by air, fluid, or jelly ○ Transverse: Visualized as H-shaped hypoechoic structure ○ Vaginal artery: High RI; ↓ during sexual arousal • Posterior vaginal septum: Perineal body and rectovesical fascia ○ Perineal body: Fibrous and muscular tissue between anus and lower vagina ○ Rectovesical fascia: Hypoechoic fascia between rectum and mid vagina • Anus ○ Mucosa: Thin hypoechoic innermost layer ○ Submucosa: Echogenic layer ○ Internal anal sphincter: Concentric hypoechoic ring surrounding central mucosa ○ External anal sphincter: Hyperechoic ring encircling internal anal sphincter • Levator ani muscle: 3 components ○ Puborectalis: Hyperechoic sling around anorectal junction ○ Pubococcygeus: Runs from pubic bone posteriorly towards coccyx ○ Iliococcygeus: Lies posterolaterally between ischial spine and coccyx; usually small

ANATOMY IMAGING ISSUES Imaging Recommendations • Bladder neck position and motility can reliably be assessed by transperineal US • Parting of labia necessary to improve image quality • Bladder filling required depending on applications • Stool and gas may interfere with exam; consider prior enema for better diagnostic accuracy

Imaging Approaches • Performed with patient in dorsal lithotomy with hips flexed or slightly abducted or in standing position • 3.5- to 7-MHz curvilinear transducer is commonly used; higher frequency for superficial structures

• 3D US advantages: Produces 3 orthogonal planes and allows sequential assessment • Urethra ○ Midsagittal scan most useful projection ○ Different pelvic floor maneuvers key for detecting functional abnormalities – Resting, straining by Valsalva maneuver, contracting by withholding maneuver used to demonstrate bladder neck mobility ○ Retrovesical angle between proximal urethra and trigone is useful to assess bladder neck descent • Anorectal canal ○ Axial scan: Most useful projection ○ Anal sphincter complex is best evaluated with 3D transperineal US; transrectal scan for mucosa and wall

Pelvis

IMAGING ANATOMY

CLINICAL APPLICATIONS Normal Function • Pelvic organs lie between high abdominal pressure and low atmospheric pressure • Muscles give active support of pelvic floor; ligaments give passive support to hold pelvic organs in place • When pelvic muscles function properly, pelvic floor is closed ○ Ligaments and fasciae are under no tension ○ Fasciae simply act to stabilize pelvic organs in their position above levator ani muscle

Abnormal Function • When pelvic muscles relax or are damaged, ligaments are put under strain ○ If damaged pelvic floor muscles cannot close levator hiatus, connective tissues must support pelvic organs for extended periods ○ Connective tissue will eventually fail to hold vagina and other pelvic organs in place • Stress urinary incontinence ○ Funneling of internal urethral meatus on Valsalva or at rest is suggestive of incontinence ○ Retrovesical angle > 160° on Valsalva is often associated with funneling ○ Bladder neck descent > 2.5 cm on Valsalva is strongly associated with urodynamic stress incontinence ○ Color Doppler US may demonstrate urine leakage through urethra on Valsalva maneuver • Fecal incontinence ○ Largely due to anal sphincter musculature damage during vaginal delivery ○ Anal sphincter defects are best diagnosed with 3D transperineal US • Prolapse ○ Anterior compartments (cystocele) better demonstrated than posterior compartment (rectocele) ○ Lateral defects of endopelvic fascia well-demonstrated by 3D transperineal US • Postoperative assessment ○ Status of bladder neck after colposuspension ○ Demonstration of fascial and synthetic slings; bulking agents

505

Pelvis

Pelvic Floor BONES AND LIGAMENTS

Anterior superior iliac spine

False pelvis

Anterior inferior iliac spine Arcuate line Iliopubic eminence

Sciatic notch True pelvis

Obturator canal Pubic bone

Inguinal l.

Greater sciatic foramen Sacrospinous l. Obturator canal Lesser sciatic foramen Obturator membrane Sacrotuberous l.

Symphysis pubis Inferior pubic ramus

Pubic tubercle

Ischial ramus

Femoral head

Ischium Sacrospinous l. Ischial spine Iliac bone

Sacroiliac joint

Sacrum

(Top) 3D CT reconstruction of the female pelvis viewed from the medial surface. The arcuate line is a bony prominence, which courses from the sacral promontory anteriorly toward the iliopubic eminence. The false pelvis is above the arcuate line, while the true pelvis is below it. (Middle) 3D CT reconstruction with graphic enhancement of the ligaments shows a medial view of the pelvic sidewall. The sacrospinous ligament extends between the sacrum and ischial spine. The sacrotuberous ligament extends from the lateral part of sacrum, coccyx, and posterior inferior iliac spine to insert on the ischial tuberosity. The greater sciatic foramen is above the sacrospinous ligament and the lesser sciatic foramen is below it. (Bottom) 3D CT reconstruction shows the pelvic outlet viewed from below and graphically enhanced to show the sacrospinous ligament. The pelvic outlet is formed by the ischiopubic rami, ischial spines, inferior symphysis pubis, sacrospinous ligaments, and coccyx.

506

Pelvic Floor Pelvis

PELVIC DIAPHRAGM

Symphysis pubis

Urethra Vagina

Puborectalis m. Pubococcygeus m.

Rectum Iliococcygeus m. Ischial tuberosity Coccygeus Piriformis

Sacrum

Iliac bone

Obturator internus m.

Piriformis m.

Obturator canal Arcus tendineus levator ani Ischial spine Iliococcygeus m. Pubococcygeus m.

Coccygeus m. Rectum

Urogenital diaphragm Urethra

External anal sphincter

Vagina

(Top) Female pelvic diaphragm, superior view, shows the passage of urethra, vagina, and rectum through the pubococcygeus muscle. (Bottom) The true pelvis is bowl-shaped; therefore, the designation of walls is somewhat arbitrary. The lateral wall of the true pelvis is formed by part of the ilium and ischium below the pelvic inlet, the obturator internus muscle and its covering membrane, and the sacrotuberous and sacrospinous ligaments. The pelvic floor is formed by the pelvic diaphragm (coccygeus and levator ani muscles and fascia). The levator ani is composed of 3 separate muscles: Pubococcygeus, iliococcygeus, and puborectalis. The levator ani is attached to the pubic bones anteriorly, the ischial spines laterally, and to the arcus tendineus levator ani (thickening in the obturator fascia) between the bony attachments. The pelvic diaphragm separates the pelvic cavity from the perineum.

507

Pelvis

Pelvic Floor UROGENITAL DIAPHRAGM

Round l. of uterus

Obturator vessels and n. Vagina Obturator internus m.

Levator ani (Iliococcygeus m.)

Urogenital diaphragm

Superior fascial layer of urogenital diaphragm Deep transverse perineal m. Inferior fascial layer of urogenital diaphragm

Arcuate l. Deep dorsal v. of clitoris

Urethra

Vagina

Superficial transverse perineal m. Perineal body

(Top) Coronal graphic of the pelvic floor shows the urogenital (UG) diaphragm. The UG diaphragm is the fibromuscular layer directly below the pelvic diaphragm (levator ani muscles). It is a trilaminar structure with the deep transverse perineal muscle sandwiched between superior and inferior fascial layers. It is part of the perineum, which is located below the levator ani and includes the external genitalia. (Bottom) Graphic shows the inferior view of the UG diaphragm. It is triangular in shape and attaches laterally to the pubic bones. At the most anterior (ventral) aspect of the perineal membrane (covering fascia), the base of the arcuate ligament is separated from the anterior border of the UG diaphragm by an opening for the deep dorsal vein of the clitoris. Both the urethra and vagina pass through the UG diaphragm.

508

Pelvic Floor Pelvis

PERINEUM

Clitoris

Ischiocavernosus m.

Bulb of vestibule Perineal membrane/fascia

Bulbospongiosus m. Deep transverse perineal m.

Greater vestibular (Bartholin) gland Levator ani m.

Superficial transverse perineal m. Perineal body

External anal sphincter Anus Sacrotuberous l. Anococcygeal l.

Gluteus maximus m. Tip of coccyx

Symphysis pubis Urethra Vagina

Puborectalis m.

Pubococcygeus m. Rectum Ischium

Sacrotuberous l.

Obturator internus m.

Iliococcygeus m.

Sacrospinous l.

(Top) The perineum is a diamond-shaped region bordered by the 2 ischiopubic rami and the 2 sacrotuberous ligaments. A horizontal line, along the superficial transverse perineal muscle, connecting the 2 ischial tuberosities divides the perineum into the anterior UG triangle (blue in inset) and the posterior anal triangle (green in inset). The perineal body lies at the midpoint of this line, just anterior to the anal canal and provides attachment for muscles and ligaments that support the perineum. (Bottom) A deeper dissection, with the superficial external genital muscles removed, shows the muscles of the levator ani (puborectalis, pubococcygeus, and iliococcygeus).

509

Pelvis

Pelvic Floor VAGINA AND SUPPORTING STRUCTURES Median umbilical l. Medial umbilical l. Urinary bladder Vesical fascia

Cervix

Arcus tendineus levator ani Arcus tendineus fascia pelvis

Cardinal l.

Rectum

Uterosacral l.

Level I: Suspension

Vagina (uterus removed) Level II: Attachment Arcus tendineus levator ani Arcus tendineus fascia pelvis

Level III: Fusion

Urogenital diaphragm

(Top) Endopelvic fascia, a complex network of connective tissue, forms a continuous adventitial layer covering the pelvic diaphragm and viscera. Ligaments are a more well-defined aggregate of connective tissue. (Middle) This schematic diagram (uterus removed) shows the type of support the vagina (purple) receives at various levels. In level I (suspension), the paracolpium suspends the vagina from the lateral pelvic walls. In level II (attachment), the vagina is attached to the arcus tendineus fasciae pelvis and the superior fascia of levator ani. In level III (fusion), the vagina, near the introitus, is fused laterally to the levator ani. (Bottom) Lateral schematic of the 3 levels of endopelvic fascia support. Level I, the upper 2-3 cm, gives support to the upper vagina and uterus. Level II supports the midportion of the vagina and bladder. Level III is the distal 2-3 cm. At this level, there is no intervening paracolpium, and the anterior vaginal wall is fused with the lower posterior urethra. Level III provides urethral and vesical neck support.

510

Pelvic Floor Pelvis

URETHRA AND SUPPORTING STRUCTURES Bladder Uterus Upper sphincter portion of external urethral sphincter

External urethral meatus Vaginal wall Compressor urethrae

Urethrovaginal sphincter

Peritoneum

Perivesical space (with pudendal venous plexus) Obturator internus m.

Levator ani m. Urogenital diaphragm Crus of clitoris and ischiocavernosus m.

Trigone

Arcus tendineus fascia pelvis Urethra End of round l.

Bulb of vestibule and bulbospongiosus m. Vaginal introitus

Superficial trigonal m. Deep trigone m. Trigonal ring Pubovesical m. Longitudinal smooth m.

Detrusor m. Trigonal plate

Circular smooth m. Striated urogenital sphincter m.

Longitudinal subepithelial vascular plexus Submucosal vaginal smooth m. Vaginal mucosa

Nonkeratinizing squamous epithelium

(Top) Graphic shows the external urethral sphincter. It has 2 different components, an upper circumferential sphincteric portion, and 2 lower, arch-like muscular bands (compressor urethrae and urethrovaginal sphincter). (Middle) Coronal graphic shows the bladder rests on the muscular floor of the pelvis and is supported by the endopelvic fascia suspended between the arcus tendineus fascia pelvis. The urethra passes through the UG (opening in the levator ani) and then through the UG diaphragm. (Bottom) Midsagittal section of the urethra shows its histologic complexity. The lamina propria is rich in collagen and elastic components, and has an extensive vascular plexus that functions in maintaining urinary continence by coapting and creating a seal. This is surrounded by 2 layers of smooth muscle, an inner longitudinal and outer circular layer. The urethra undergoes marked histologic and morphologic changes with aging. Striated muscle decreases and is replaced by connective tissue. The vascular plexus is also affected by decreased estrogen levels. All of these changes can adversely affect continence.

511

Pelvis

Pelvic Floor PASSIVE AND ACTIVE COMPONENTS OF PELVIC SUPPORT

Cervical ring Uterosacral ll. (USLs)

Arcus tendineus fascia pelvis Pubocervical fascia Suburethral l. Posterior anal plate (anococcygeal l.) Perineal membrane

Rectovaginal fascia

Pubocervical fascia Pubourethral l. Perineal body

Pubococcygeus m. Levator plate

Urogenital diaphragm

Longitudinal m. of anus

Puborectalis m.

Perineal body

External anal sphincter

(Top) This series of 2 graphics illustrates the passive and active conceptual approach to the pelvic floor. Passive components include the bony pelvis and supportive connective tissue. The supportive connective tissue is either in the form of a diffuse ill-defined layer (the endopelvic fascia), or as well-defined specialized aggregations of connective tissue (ligaments). The 3 endopelvic fascial levels include level I (upper vagina adjacent to the cervix), level II (midportion of the vagina), and level III (from the introitus to 2-3 cm above the hymenal ring). (Bottom) Graphic shows the main active component of pelvic support system, the levator ani muscle. The levator ani muscle is a wide sheet of muscle whose main components are the puborectalis muscle, which forms a sling around the junction of the rectum and anal canal, the pubococcygeus muscle, which passes posteriorly to insert into the anococcygeal body, and the iliococcygeus muscle, whose fibers fuse to form the levator plate and insert on coccyx.

512

Pelvic Floor Pelvis

PASSIVE AND ACTIVE COMPONENTS OF PELVIC SUPPORT

Uterosacral ll.

Arcus tendineus fascia pelvis

Suburethral l. Pubocervical fascia Perineal membrane Levator plate Anococcygeal l. Pubococcygeus m. Rectovaginal fascia Urogenital diaphragm Puborectalis m. Pubourethral l. Longitudinal m. of anus

Urethra

External anal sphincter

Perineal body

Graphic of the pelvis illustrates the multilayered system approach that considers the passive and active components of pelvic floor as an integrated multilayer system. From cranial to caudal, the pelvic support system consists of endopelvic fascia, pelvic diaphragm, perineum, and the external genital muscles. The muscles (levator ani) give active support to the pelvic floor, whereas the ligaments give passive support holding organs in place. When the levator ani is functioning properly, the pelvic floor is closed and the ligaments and fasciae are under no tension. When the musculature is damaged and cannot close the levator hiatus, ligaments are put under strain and will eventually fail resulting in pelvic organ prolapse.

513

Pelvis

Pelvic Floor RECTUM, ANAL CANAL, AND SPHINCTER COMPLEX

Intraperitoneal rectum

Extraperitoneal rectum

Anococcygeal l.

Levator ani

Anal sphincter complex

Perineal body

Rectum

Puborectalis m.

Anal sphincter m. complex

(Top) The rectum is formed from the terminal portion of the colon. It begins at the level of the 3rd sacral segment and ends at the anus. Anatomically, it is divided into 2 sections: The rectum proper (10-12 cm in length), and the anal canal (3-4 cm in length). The intraperitoneal portion is related anteriorly to the upper vagina and uterus. The extraperitoneal rectum is related anteriorly to the posterior vaginal wall and rectovaginal septum. The inferior rectum has no mesentery but is enveloped in fat and is bordered by the mesorectal fascia (mesorectum). The anal sphincter envelops the anal canal and is composed of several cylindrical layers. (Bottom) The ampullary portion of the rectum rests on the pelvic diaphragm; at this level, it turns ~ 90° posteriorly. The anal sphincter is tilted anteriorly in the sagittal plane. The puborectalis muscle is schematically shown forming a sling around the rectum; it is responsible for creating the anal rectal angle. The anal canal is fixed posteriorly to the sacrum by the presacral fascia (fascia of Waldeyer).

514

Pelvic Floor Pelvis

RECTUM, ANAL CANAL, AND SPHINCTER COMPLEX

Rectum Puborectalis

Deep external anal sphincter Coccyx Perineal body Anococcygeal body Superficial external anal sphincter

Anal canal

Subcutaneous external anal sphincter

Anus

Outer longitudinal m. layer

Inner circular m. layer Iliococcygeus m.

Anal cushion Puborectalis m.

Internal anal sphincter

Superficial external anal sphincter

External anal sphincter m. complex

(Top) This schematic diagram shows the arrangement of the puborectalis muscle and the external anal sphincter (EAS) complex. The superficial EAS attaches to the perineal and anococcygeal bodies. (Bottom) The internal anal sphincter (IAS) is a continuation of the circular muscle layer of the muscularis propria of the rectum. The EAS is composed of multiple components and constitutes the outer and inferior part of the anal sphincter complex. The lowermost part of the anal canal is surrounded by the superficial external anal sphincter.

515

Pelvis

Pelvic Floor TRANSPERINEAL ULTRASOUND ANATOMY

Urethra Vagina Rectovaginal fascia

Levator ani mm. Anus

Anal canal Anorectal muscularis Vagina Urethra Rectovaginal fascia Symphysis pubis

Vesicovaginal fascia

Bladder

Perineal body

Anal canal Puborectalis m. Symphysis pubis

Vagina Rectovaginal fascia

Urethra Vesicovaginal fascia Bladder

(Top) 3D volume US (axial plane) shows the relationship of the urethra, vagina, and anus. The urethra is seen imbedding in the anterior wall of the vagina while the anus is separated from the vagina by the rectovaginal fascia. (Middle) Midsagittal scan of the anterior triangle shows the urethra and vagina. The urethra is seen as a hypoechoic tubular structure immediately posterior to the symphysis pubis and is separated from the vagina by the vesicovaginal fascia. (Bottom) Midsagittal scan in the same woman as previous image, but tilted more posteriorly to show the vaginal septum, is shown. The perineal body is seen as the distal attachment between the vagina and the anus, whereas the rectovaginal fascia is depicted as a hypoechoic lining separating the mid vagina from the rectum. Note the hyperechogenicity of the puborectalis muscle is similar to that of the symphysis pubis.

516

Pelvic Floor Pelvis

TRANSPERINEAL ULTRASOUND ANATOMY

Distal urethra Symphysis pubis Anorectal canal Urethra

Rectovaginal fascia Vagina

Bladder

Vesicovaginal fascia

Pubic rami

Lateral vaginal walls Urethra

Bladder

Pubic ramus Distal urethra

Vagina Superficial transverse perineal mm. Perineal body External anal sphincter Anus Levator ani mm. (puborectalis) (Top) Midsagittal plane of 3D transperineal US shows the relationship between the urethra, vagina, and anorectal canal. Note the vaginal canal is barely visible unless it is outlined by fluid or acoustic jelly. (Middle) Corresponding coronal plane shows the urethra and bladder. Note the lateral walls of the vagina appear as slightly hypoechoic areas on either side of the urethra. (Bottom) Corresponding axial plane at the level just caudal to the symphysis pubis shows the distal urethra "resting" on the vagina. The anus is supported by a muscle complex formed by the superficial transverse perineal muscles, which insert into the perineal body and external anal sphincter. Note the hyperechoic puborectalis forms a "sling" around the anus.

517

Pelvis

Pelvic Floor HIGH-RESOLUTION 3D US OF URETHRA

Subcutaneous perineal layer

Urethral orifice

Vesicovaginal fascia Vagina

Symphysis pubis

Rectovaginal fascia

Posterior urethral wall Anterior urethral wall Urethral canal Bladder

Urethral compressor mm.

Urethral sphincter m. Urethral orifice

Lateral walls of vagina Urethra

Symphysis pubis

Anterior urethral wall Vesicovaginal fascia Urethral canal Posterior urethral wall

Lateral walls of vagina

(Top) Midsagittal scan of the urethra using a high-resolution 12 MHz linear 3D transducer is shown. With this technology, the muscular wall of the urethra can be clearly depicted, and measurement of the urethral wall thickness is feasible. (Middle) Corresponding coronal plane shows the urethral orifice in cross section. The urethral orifice is encircled by the echogenic urethral sphincter muscle and arched over by the urethral compressor muscles. (Bottom) Corresponding axial plane shows the urethra in cross section. Although the wall thickness of urethral wall is discernible, differentiation of different layers of the urethra is generally not feasible with the standard transperineal technique.

518

Pelvic Floor Pelvis

MEASUREMENT OF BLADDER NECK DESCENT Level of inferior edge of symphysis pubis

Symphysis pubis Bladder neck-symphyseal distance Retrovesical angle

Level of bladder neck

Bladder

Level of inferior edge of symphysis pubis

Bladder neck-symphyseal distance at rest Retrovesical angle at rest Anterior

Posterior

Level of bladder neck

Level of inferior edge of symphysis pubis

Bladder neck-symphyseal distance on Valsalva Retrovesical angle on Valsalva Level of bladder neck Anterior

Posterior

(Top) Midsagittal plane of the lower urinary tract demonstrates measurements of bladder neck-symphyseal distance (BSD) and retrovesical angle (RVA) used in the evaluation of bladder neck descent as a cause of urinary stress incontinence. BSD is the distance between the inferior edge of the SP and bladder neck. RVA is the angle between proximal urethra and trigone. A significant change of BSD and RVA between resting and Valsalva maneuver reflects severe bladder neck descent. (Middle) Bladder neck position at rest is shown. The RVA measured at rest normally ranges between 90-120°. (Bottom) Change of bladder neck position on Valsalva maneuver. The proximal urethra demonstrates a posteroinferior rotational descent that shortens the BSD and widens the RVA. A shortening of BSD > 2.5 cm or a widening of RVA > 160° is indicative of significant bladder descent.

519

Pelvis

Pelvic Floor STRESS URINARY INCONTINENCE: INTRINSIC SPHINCTERIC DEFICIENCY

Urinary bladder

Bladder neck

Urethra

Bladder neck

Urethra

Bladder neck

Urethra

Bladder filling

Cough

Cough

No change in detrusor pressure Urine leak

Transperineal ultrasound evaluation of a patient with urinary incontinence shows a sagittal view of the urine-filled bladder, bladder neck, and symphysis pubis. Images at rest revealed intrinsic malfunction of the urethral sphincter characterized by an open vesical neck. During straining and withholding (active contraction of the pelvic floor), the bladder neck was persistently open with funneling, without the expected narrowing during withholding. The patient had urine leakage throughout the exam. Subtracted cystometrogram shows a stable bladder with no rise in detrusor pressure during filling. When a cough is elicited, there is a sharp, isolated pressure spike on the intravesical and intraabdominal tracings, but there are no spikes on the subtracted detrusor tracing. The presence of leakage occurring with coughing confirms that this is stress urinary incontinence due to ineffective urethral closure rather than detrusor overactivity.

520

Pelvic Floor Pelvis

URGE URINARY INCONTINENCE: DETRUSOR INSTABILITY

Urinary bladder

Bladder neck

Urethral wall

Bladder neck

Bladder neck

Urine leakage

Cough

Cough

No change in detrusor pressure

Increased detrusor pressure without increased abdominal pressure Urine leak

Transperineal evaluation of a patient with urinary incontinence shows a sagittal view of the urine-filled bladder, bladder neck, and symphysis pubis. Note the relatively high position of the bladder neck. The bladder neck does not descend and remains above the inferior margin of the pubis symphysis during maximum straining. During the examination, there was a sudden descent and opening of the bladder neck accompanied by passage of urine, which the patient was unable to stop. Subtracted cystometrogram shows detrusor instability. There is a normal sharp spike in vesical and abdominal pressures during coughing with the subtracted detrusor pressure remaining stable. However, there was a spontaneous increase in detrusor pressure without an increase in the abdominal pressure, indicating that the pressure originated from the detrusor muscle. These findings are consistent with urge urinary incontinence related to detrusor muscle instability.

521

Pelvis

Pelvic Floor COLOR DOPPLER US, URETHRA AND VAGINA

Periurethral aa.

Urethra Vaginal aa.

Vesicovaginal fascia

Vagina

Bladder

Intramuscular urethral a.

Muscular wall of urethra

Urethral canal

Vaginal a.

Periurethral aa.

Vesicovaginal fascia

Bladder

(Top) Midsagittal color Doppler US of the urethra shows 2 periurethral arteries near the mucosa of the urethra and numerous vessels in the vagina. Care must be taken not to confuse vaginal arteries with periurethral arteries. (Middle) High-resolution color Doppler US (midsagittal scan) of the urethra shows a small artery running in the muscular layer of the urethra. Note urethral vascularity is influenced by hormonal changes during the menstrual cycle, pregnancy, and post menopause. It is higher in premenopausal women than those in menopause. (Bottom) Midsagittal color Doppler US of the vaginal artery, which is in the vicinity of the periurethral arteries and is easily confused with them. Special attention should be paid to differentiate vaginal and periurethral arteries. These are separated by the vesicovaginal fascia.

522

Pelvic Floor Pelvis

SPECTRAL DOPPLER US, URETHRA AND VAGINA

Periurethral a.

Intramuscular urethral a.

Vaginal a.

(Top) Midsagittal spectral Doppler scan of the periurethral artery shows normal, low-resistance blood flow. It has been suggested that decrease in periurethral vascularity is related to stress incontinence in postmenopausal women. (Middle) Doppler waveform of intramuscular urethral artery demonstrates high-flow resistance with absent diastolic velocity in this artery. (Bottom) Doppler waveform of the vaginal artery demonstrates high-resistance blood flow with a low diastolic velocity component. Flow resistance may be lowered during the state of sexual arousal.

523

Pelvis

Pelvic Floor AXIAL TRANSPERINEAL US, ANAL CANAL

Subcutaneous external anal sphincter Mucosa/submucosa Internal anal sphincter

Mucosa/submucosa Superficial external anal sphincter

Internal anal sphincter

Mucosa/submucosa Deep external anal sphincter Internal anal sphincter Conjoined longitudinal m.

(Top) 3D ultrasound evaluation of the anal orifice is shown. The echogenic mucosa/submucosa of the anus is surrounded by 2 concentric rings. The inner hypoechoic ring represents the IAS and the outer hyperechoic ring denotes the subcutaneous EAS. (Middle) In the midanal anal canal, the IAS appears as a hypoechoic ring that is asymmetrical in thickness. With advancing age, IAS may lose its uniform thickness and echogenicity. (Bottom) In the high anal canal, the conjoined longitudinal muscle is identified as a moderately echogenic band between the IAS and EAS. However, it is not always distinguishable from the EAS along the entire anal canal.

524

Pelvic Floor Pelvis

3D VOLUME RENDERED US, VAGINA

Urethra

Lower vaginal walls

Puborectalis m.

Vaginal canal Puborectalis m. Anal canal

Urethra Mid vaginal walls Vaginal canal Rectovaginal fascia Anal canal

Urethra

Vaginal canal Upper vaginal walls Rectum

(Top) 3D volume rendered axial scan of the lower vagina at the level of the symphysis pubis shows the vagina "sandwiched" between the urethra and the anus. The vaginal canal is enhanced by acoustic jelly and air bubbles trapped within it following transvaginal scan. It resembles a widened letter "V." (Middle) At a higher lever in the mid vagina, it appears as a "cradle" partially invaginating the urethra in its anterior wall. The vaginal canal changes its shape from "V" to "U." (Bottom) In its upper portion, the vagina appears flattened and loses its anterolateral extensions. The vaginal canal becomes an echogenic straight line.

525

Pelvis

Pelvic Floor 3D VOLUME RENDERED US, PELVIC FLOOR

Artifact, urethra out of field

Vagina

Levator ani m.

Anus Internal anal sphincter Superficial external anal sphincter

Artifact, urethra out of field Anovaginal septum Perineal body Superficial transverse perineal mm. Puborectalis Levator ani m. Internal anal sphincter

Anorectal canal Deep external anal sphincter

Distal urethra

Vagina Puborectalis mm. Rectovaginal septum Perineal body Anal canal (oblique) Internal anal sphincter External anal sphincter

(Top) Axial scan of the mid anal canal is shown. The superficial EAS is seen as an incomplete ring with absent anterior portion. It is a frequent finding either due to a natural gap in normal females or sphincter rupture in multiparous women. (Middle) Axial scan of the anorectal junction and the perineal body is shown. The deep EAS is seen to be integral with the puborectalis, which forms a "sling" around the anorectal junction. The EAS and transverse perineal muscles meet in the perineal body, which provides fundamental support to all musculoligamentous components of the pelvis. (Bottom) Axial scan of the puborectalis muscle in the anterior triangle is shown. The muscles are seen as 2 echogenic linear structures running alongside the lower vagina and urethra that are projected on an end-on view.

526

Pelvic Floor Pelvis

3D VOLUME RENDERED US, PELVIC FLOOR Symphysis pubis Paravaginal support

Distal urethra Lower vagina

Pubococcygeus Superficial external anal sphincter Conjoined longitudinal m.

Anus Internal anal sphincter

Mid urethra

Mid vagina

Pubococcygeus m.

Oblique anus Internal anal sphincter

Proximal urethra

Mid vagina Pubococcygeus mm. Rectal muscular layer Lower rectum

Rectal mucosal layer

(Top) Axial plane of the paravaginal support is shown. It is seen as the pubovaginal attachment lateral to the urethra. Identification of the paravaginal support is important because disruption of this structure during vaginal delivery may be related to anterior vaginal prolapse and stress urinary incontinence. (Middle) Axial scan of the pubococcygeus in the anterior triangle is shown. The echogenic muscle arises from the pubic bone and runs posteriorly towards the ischial spine. It also crosses the midline to form rectal and vaginal hiatus. (Bottom) Axial scan of the distal rectum is shown. The rectal wall shows 2 distinct layers: The innermost echogenic mucosa and outermost hypoechoic muscular layer, which is a continuation of the IAS and conjoined longitudinal muscle.

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SECTION 6

Upper Extremity

Sternoclavicular and Acromioclavicular Joints Shoulder Axilla Arm Arm Vessels Elbow Forearm Forearm Vessels Wrist Hand Hand Vessels Thumb Fingers Brachial Plexus Radial Nerve Median Nerve Ulnar Nerve

530 536 554 562 570 578 598 606 614 628 640 646 656 668 676 684 694

Upper Extremity

Sternoclavicular and Acromioclavicular Joints

TERMINOLOGY Abbreviations • Sternoclavicular joint (SCJ) • Acromioclavicular joint (ACJ)

GROSS ANATOMY Sternoclavicular Joint • Between medial end of clavicle & manubrium ○ Synovial sellar-type (saddle) joint ○ Medial end of clavicle = large & bulbous ○ Much larger than manubrial concavity ○ < 1/2 of medial clavicle articulates with manubrium – Stability through capsuloligamentous structures • Intraarticular disc ○ Attached to joint capsule anteriorly & posteriorly ○ Complete or incomplete ± perforations ○ Thickest posterosuperiorly (3 mm) • Ligaments of SCJ ○ Capsular ligaments – Cover anterosuperior & posterior aspects of SCJ – Prevent upward displacement of medial clavicle, which may be caused by downward force on shoulder – Anterior stronger than posterior portion ○ Interclavicular ligament – Connects superomedial aspect of clavicle to capsular ligaments & upper manubrium – Covers anterosuperior & posterior aspects of joint – Prevents excessive upward motion of clavicle ○ Costoclavicular ligaments – Unite inferior surface medial end clavicle to upper surface of 1st rib – Anterior fibers arise from anteromedial surface of 1st rib & resist upward motion – Posterior fibers arise lateral to anterior fibers & resist downward motion • Muscle attachments to medial clavicle & sternum ○ Pectoralis major from anterior aspect medial 2/3 of clavicle (clavicular head) ○ Sternocleidomastoid from posterior surface medial 1/3 of clavicle (clavicular head) ○ Sternohyoid & sternothyroid muscles separate great vessels from SCJ

Acromioclavicular Joint • Synovial joint between lateral end of clavicle & medial end of acromion ○ Articular surface of clavicle oriented posterolaterally whereas articular surface of acromion oriented anteromedially – Angle of inclination between opposing articular surfaces varies with clavicle overriding acromion (50%), vertical orientation between acromion & clavicle (25%), clavicle underriding acromion (5%), & mixed pattern (20%) – Maximum width of normal joint on ultrasound = 5 mm if < 35 years & < 4.4 mm if > 35 years – Maximum thickness of capsule from bony surface = 2.7 mm if < 35 years & < 3.6 mm if > 35 years • Intraarticular disc 530

○ Undergoes rapid degeneration beginning in 2nd decade → marked degeneration of disc by 4th decade • Ligaments of ACJ ○ Superior AC ligament – Stronger & thicker (2.0-5.5 mm) than thin or absent inferior AC ligament – Inserts along lateral clavicle (8 mm) & medial acromion (10 mm) ○ Coracoclavicular ligaments – Conoid & trapezoid ligaments – Vary significantly in length & width – Conoid ligament located posteromedially – Inserts to conoid tubercle, which is located where middle 1/3 of clavicle curves into lateral 1/3 of clavicle – Mainly prevents upward movement of clavicle – Trapezoid ligament located anterolaterally – Inserts to trapezoid ridge, which runs along inferior surface, of lateral 1/3 of clavicle – Mainly prevents lateral compression of clavicle against acromion ○ Muscle attachments to lateral clavicle – Deltoid attached to anterior surface lateral 1/3 of clavicle – Trapezius attached to posterior surface lateral 1/3 of clavicle

ANATOMY IMAGING ISSUES Imaging Recommendations • High-resolution linear transducer • Align transducer transversely along SCJ or ACJ • ACJ laxity can be assessed by pulling down on arm while observing change in joint width on ultrasound ○ Compare with contralateral side • Main clinical presentation of SCJ is painless lump ○ Mild degrees of capsular thickening readily apparent clinically since joint is just beneath skin surface – Clinical swelling often due to relative forward positioning of apparently swollen SCJ due to axial rotation of upper trunk – Occasionally due to mild capsular swelling ± mild subluxation secondary to SC osteoarthritis ○ Main clinical presentation of ACJ is pain due to osteoarthritis, ACJ impingement, inflammatory arthropathy, & subluxation/dislocation

Imaging Pitfalls • SCJ or ACJ ○ Normally, step-off between medial clavicle & manubrium &, to lesser degree, between lateral clavicle & acromion ○ Should not be interpreted as subluxation ○ Acromion normally elevates from rest position during arm adduction ○ ACJ index = ACJ width of uninjured side/ACJ width of injured side = 1.0 normally ○ Determine whether – ACJ not subluxed (similar to opposite side): Grade 1 – ACJ partially subluxed (clavicle subluxed < 50% depth of ACJ): Grade 2 – ACJ severely subluxed or dislocated (clavicle subluxed > 50% depth of ACJ): Grade 3

Sternoclavicular and Acromioclavicular Joints

Interclavicular l. 1st rib Anterior sternoclavicular l.

Upper Extremity

TRANSVERSE US, STERNOCLAVICULAR JOINT

Clavicle Articular disc 1st costal cartilage

Costoclavicular l. Manubrium sternum

Medial end of clavicle

Sternoclavicular joint

Manubrium, sternum

Interclavicular l.

Medial end of clavicle

Interclavicular l. Joint capsule Manubrium, sternum

(Top) Graphic shows the anterior aspect of the sternoclavicular joint. Note the joint capsule, articular disc, and interclavicular ligament. (Middle) Transverse grayscale ultrasound shows the anterosuperior aspect of the sternoclavicular joint. The medial clavicle is much larger than the articulating surface of the manubrium. The thin interclavicular ligament is closely applied to the superior aspect of manubrium, and its connection with the medial ends of both clavicles is depicted. (Bottom) Transverse grayscale ultrasound shows the superior aspect of the sternoclavicular joint. The costoclavicular ligament prevents upward movement of the medial clavicle when the lateral clavicle or shoulder is depressed.

531

Upper Extremity

Sternoclavicular and Acromioclavicular Joints LONGITUDINAL US, STERNOCLAVICULAR JOINT

Pectoralis major m.

Costoclavicular l. Medial end of clavicle 1st rib

Sternocleidomastoid m., sternal end Sternum Sternocleidomastoid m., sternal insertion Sternohyoid, sternothyroid t.

Subclavian a.

Sternocleidomastoid, clavicular insertion

Medial end of clavicle

Sternocleidomastoid m. Subclavian v. Subclavian a.

(Top) Longitudinal grayscale US shows sternoclavicular joint. Costoclavicular ligament prevents upward movement of the medial clavicle when the shoulder is depressed. Pectoralis major muscle arises from the medial 1/2 of the anterior surface of the clavicle, as well as from the sternum, upper costal cartilages, and upper part of external oblique aponeurosis. (Middle) Longitudinal grayscale US shows the sternoclavicular joint region. Sternocleidomastoid is attached to the upper surface of the medial end of the clavicle, as well as the upper anterior surface of the manubrium. Sternohyoid and sternothyroid are attached to the posterior aspect of the sternum, as well as the clavicle and 1st costal cartilage. (Bottom) Longitudinal grayscale US shows the sternoclavicular joint. Great vessels lie posterior to the sternoclavicular joint and may get injured in posterior dislocation. All tendinous attachments should be assessed if dislocation is present as they may also be injured.

532

Sternoclavicular and Acromioclavicular Joints

Superior acromioclavicular l. Inferior acromioclavicular l. Coracoacromial l. Coracoclavicular l., trapezoid component Coracohumeral l.

Clavicle, distal

Upper Extremity

US, ACROMIOCLAVICULAR JOINT

Coracoclavicular l., conoid band

Coracoid process

Transverse humeral l. Biceps t., long head

Subscapularis m.

Biceps t., short head Latissimus dorsi m.

Teres major m.

Lateral end of clavicle Coracoclavicular l., trapezoid component Coracoid process

Deltoid m. Coracoacromial l. Coracoid process Acromion Supraspinatus m. Humeral head

(Top) Anterior graphic shows the shoulder in superficial dissection. (Middle) Longitudinal grayscale ultrasound shows the acromioclavicular joint region. The coracoclavicular ligament is demonstrated but is not as clearly depicted on US as it is on MR exam. These ligaments prevent upward and lateral movement of the clavicle. (Bottom) Transverse grayscale ultrasound of the acromioclavicular joint region shows the coracoacromial ligament. The supraspinatus tendon and intervening bursa can impinge against the coracoacromial ligament during arm abduction.

533

Upper Extremity

Sternoclavicular and Acromioclavicular Joints TRANSVERSE US, ACROMIOCLAVICULAR JOINT

Superior acromioclavicular l.

Clavicle

Acromion Anterior capsule

Superior acromioclavicular l.

Clavicle

Joint capsule Acromion

Superior acromioclavicular l. Clavicle

Joint capsule Acromion

(Top) Transverse grayscale ultrasound shows the anterior aspect of the acromioclavicular joint. The joint capsule of the acromioclavicular joint is thin with a strong supporting superior acromioclavicular ligament. (Middle) Transverse grayscale ultrasound shows the anterosuperior acromioclavicular joint. Separation of the clavicle and acromion can be readily appreciated. Note how opposing bone margins are not vertically aligned. (Bottom) Transverse grayscale ultrasound shows the superior aspect of the acromioclavicular joint. In this image, the clavicle slightly overrides the acromion. This is a normal configuration.

534

Sternoclavicular and Acromioclavicular Joints

Superior acromioclavicular l.

Upper Extremity

TRANSVERSE US, ACROMIOCLAVICULAR JOINT

Acromion Joint capsule Clavicle

Superior acromioclavicular l.

Joint capsule Acromion Clavicle

Joint capsule Acromion

Clavicle

(Top) Transverse grayscale ultrasound shows the anterosuperior aspect of the acromioclavicular joint with the arm positioned by the side of the body. Note that the clavicle slightly overrides the acromion. (Middle) Transverse grayscale ultrasound shows the acromioclavicular joint with the arm in abducted position. The acromion is now level with the lateral aspect of the clavicle. Note how the joint capsule bulges superiorly and the opposing bones are approximated with the arm abducted. (Bottom) Transverse grayscale ultrasound shows the acromioclavicular joint with the arm in an adducted position. The acromion is now depressed relative to this lateral end of the clavicle.

535

Upper Extremity

Shoulder

536

IMAGING ANATOMY Overview • Rotator cuff ○ Consists of supraspinatus, infraspinatus, teres minor, subscapularis muscles, and tendons ○ Cuff tendons blend with shoulder joint capsule ○ Supraspinatus and infraspinatus tendons are inseparable at insertion ○ Anterior 2.25 cm of tendon comprises supraspinatus tendon insertional area • Supraspinatus muscle ○ Origin: Supraspinatus fossa of scapula ○ Insertion: Superior facet (horizontal orientation) and anterior portion of middle facet of greater tuberosity – Broad insertional area ○ Nerve supply: Suprascapular nerve ○ Blood supply: Suprascapular artery and circumflex scapular branches of subscapular artery ○ Action: Abduction of humerus ○ Muscle consists of 2 distinct portions – Anterior portion is larger, fusiform in shape, has dominant tendon, and is more likely to tear – Posterior portion is flat and has terminal tendon ○ Most commonly injured rotator cuff tendon • Infraspinatus muscle ○ Origin: Infraspinatus fossa of scapula ○ Insertion: Mid to posterior aspects of middle facet of greater tuberosity; centrally positioned within tendon ○ Nerve supply: Suprascapular nerve, distal fibers ○ Blood supply: Suprascapular artery and circumflex scapular branches of subscapular artery ○ Action: External rotation of humerus and resists posterior subluxation • Teres minor muscle ○ Origin: Lateral scapular border, middle 1/2 ○ Insertion: Inferior facet (vertical orientation) of greater tuberosity ○ Nerve supply: Axillary nerve ○ Blood supply: Posterior circumflex humeral artery and circumflex scapular branches of subscapular artery ○ Action: External rotation of humerus ○ Least commonly injured rotator cuff tendon • Subscapularis muscle ○ Origin: Subscapular fossa of scapula ○ Insertion: Lesser tuberosity and up to 40% may insert at surgical neck ○ Some fibers cross over to lateral lip of bicipital groove, reinforcing and blending with transverse ligament ○ Nerve supply: Subscapular nerve, upper and lower ○ Blood supply: Subscapularis artery ○ Action: Internal rotation of humerus, also adduction, extension, depression, and flexion ○ 4-6 tendon slips converge into main tendon; multipennate morphology increases strength • Rotator cuff tendon blood supply ○ Derived from adjacent muscle, bone, and bursae ○ Normal hypovascular regions in tendons – Termed critical zone: ~ 1 cm proximal to insertion – Vulnerable to degeneration and calcific deposition

•

•

•

•

•

– However, insertional area is more prone to tearing than critical zone Biceps tendon, long head ○ Origin: Superior glenoid labrum (biceps anchor) – Portions may attach to supraglenoid tubercle, anterosuperior labrum, posterosuperior labrum, and coracoid base ○ Runs along superior aspect of shoulder to bicipital groove ○ Action: Stabilizes and depresses humeral head ○ Anatomic variants: Anomalous intra- and extraarticular origins from rotator cuff and joint capsule ○ Tendon sheath communicates with glenohumeral joint and normally contains small amount of fluid Subacromial-subdeltoid fat plane ○ Subacromial and subdeltoid portions – ± subcoracoid extension in some patients ○ Fat plane is superficial to bursa ○ May be interrupted or absent in normal patients ○ Attached along free border of coracoacromial ligament and deep surface of deltoid muscle, and humeral neck Rotator cuff interval ○ Space between supraspinatus and subscapularis tendon through which biceps tendon passes ○ Borders of rotator cuff interval – Triangular-shaped space – Reflections of glenohumeral ligament and coracohumeral ligament form biceps reflection pulley – Biceps reflection pulley stabilizes biceps tendon within rotator cuff interval – Superior border: Leading edge of supraspinatus – Inferior border: Superior aspect of subscapularis tendon – Lateral border: Long head of biceps tendon and bicipital groove – Medial border: Base of coracoid process ○ Contents of rotator interval – Long head of biceps tendon; biceps reflection pulley Coracoacromial ligament ○ Forms coracoacromial arch along with acromion and coracoid process – Reinforces inferior aspect of acromioclavicular joint ○ Extends from distal coracoid to subacromial area ○ Broad insertion to undersurface acromion – Ligament is thicker at acromion (normal thickness < 2.5 mm) and may be associated with spurs Glenoid labrum ○ Triangular-shaped rim of fibrocartilage, which extends around periphery of glenoid

ANATOMY IMAGING ISSUES Imaging Approaches • Tendons best seen when on stretch ○ High-resolution linear transducer ○ Long-axis (longitudinal) & transverse view of each tendon ○ Each part of tendon needs to be examined; anisotropy prevents all parts of curved rotator cuff tendons from being seen at same time ○ Need to realign ("toggle") probe to see different parts of tendons

Shoulder

•

•

•

•

•

Imaging Sweet Spots • Look for tears particularly at anterior leading edge of supraspinatus tendon ○ Unexplained bursal fluid is good secondary sign of rotator cuff tear • Bursal fluid is often best seen with arm in neutral position or ↓ internal rotation (hand in back pocket)

•

Imaging Pitfalls • Anisotropy ○ Echoes are optimally reflected when transducer is parallel to tendon fibers ○ Rotator cuff tendons are prone to anisotropy due to curved course ○ If transducer is not at right angles to tendon, it will appear either isoechoic or hypoechoic to muscle – May simulate tendinosis or partial tear • Tendon edges

•

○ Interfaces of tendons with adjacent structures may simulate tears ○ All pathology should be confirmed in 2 planes Rotator cuff cable ○ Thick band of fibers running perpendicular to supraspinatus tendon ○ Located on deeper aspect of tendon just proximal to insertional area ○ May reinforce critical zone supraspinatus fibers ○ Cable thicker in young subjects but more easily seen in elderly subjects due to supraspinatus tendinosis ○ Can simulate tendinosis or partial-thickness tear Tendinous interspace at rotator cuff interval ○ Interspace between leading (anterior) edge of supraspinatus and long head of biceps tendon may simulate tear ○ Overcome by recognizing ovoid or rounded shape of biceps tendon ○ Rotator cuff interval best seen with external rotation Focal thinning at supraspinatus-infraspinatus junction ○ Mild diffuse thinning of supraspinatus and infraspinatus tendon junction is normal finding ○ Should not be mistaken for tendon attenuation or partial-thickness tear Musculotendinous junction ○ Supraspinatus tendon – Hypoechoic muscle extending along superficial aspect of tendon may simulate subacromial-subdeltoid bursal distension – Interdigitating tendons of anterior and posterior portions may simulate tendinosis or tear ○ Infraspinatus tendon – Muscle fibers surrounding centrally positioned tendon may be confused with tear ○ Subscapularis tendon – 4-6 tendon slips converging into main tendon may simulate tendinosis Fibrocartilaginous insertion ○ Thin layer of fibrocartilage exists between tendon and bone at insertional area ○ Steeper tendon insertion = thicker fibrocartilaginous layer ○ This thin hypoechoic layer of fibrocartilage may simulate avulsive tear Subacromial-subdeltoid fat plane ○ Fat plane lies mainly superficial to bursa and deep to deltoid muscle ○ Normal bursa is very thin ○ Thickness of echogenic fat plane is variable among patients though usually similar from side to side ○ May be wrongly interpreted as bursal fluid – Look for intrabursal fluid ± hyperemia (latter is feature of inflammatory arthropathy) Fluid in biceps tendon sheath ○ Communicates with glenohumeral joint ○ Small amount of fluid is normal – Do not misinterpret as long head of biceps tenosynovitis ○ ↑ fluid in biceps tendon sheath usually reflects ↑ fluid in glenohumeral joint

Upper Extremity

• Supraspinatus tendon ○ Arm extended and internally rotated behind lumbar region (Crass position) – If too painful, hand in behind hip ("back pocket") with elbow close to body (modified Crass position) • Infraspinatus and teres minor tendons ○ Arm flexed and internally rotated with hand placed on contralateral shoulder ○ Teres minor tendon located posteroinferior to infraspinatus tendon • Subscapularis tendon: Arm neutral and externally rotated • Long head of biceps tendon ○ Arm neutral and externally rotated ○ Vary degree of external rotation for optimal view of biceps tendon ○ Check for tendon subluxation • Subacromial-subdeltoid bursa ○ Stretching tendons may squeeze fluid from area of bursa under inspection ○ Examine in all positions and also in neutral position ○ Fluid collects preferentially just lateral to acromion and proximal humerus and near coracoacromial ligament • Coracoid process and coracoacromial ligament ○ Neutral position • Acromioclavicular joint ○ Neutral position ○ Can pull down on arm to assess joint laxity • Glenohumeral joint ○ Neutral position ○ Best seen from posterior aspect of joint ○ Passive movement of arm during scanning can help in identifying posterior glenoid labrum • Spinoglenoid notch ○ Neutral position just medial to glenohumeral joint • Supraspinatus and infraspinatus muscles ○ Neutral position with hands resting on thigh ○ Examine thickest part of muscles from behind (in coronal and sagittal planes) ○ ↓ muscle bulk, ↑ echogenicity, and ↓ visibility of central tendon are signs of atrophy with fatty replacement – Compare muscle echogenicity to that of trapezius or deltoid muscle

537

Upper Extremity

Shoulder MUSCLES AND LIGAMENTS

Coracoacromial l. Supraspinatus m. Deltoid m.

Superior transverse scapular l.

Supraspinatus t. Biceps t., long head

Transverse l.

Coracoid process

Biceps t., short head

Subscapularis m.

Latissimus dorsi t. Teres major m. Biceps m., long head

Superior scapular transverse l.

Supraspinatus m.

Acromion process Deltoid m. Supraspinatus t. Infraspinatus t.

Infraspinatus m. Teres minor t.

Teres minor m.

Posterior circumflex humeral a. and axillary n.

Teres major m. Triceps m. and t., lateral head Latissimus dorsi m. Deep brachial a. Triceps m. and t., long head

Radial n.

(Top) Anterior graphic of the shoulder illustrates the rotator cuff and adjacent structures. The rotator cuff consists of supraspinatus, infraspinatus, teres minor, and subscapularis muscles and tendons. The biceps tendon courses the rotator cuff interval between the supraspinatus and subscapularis tendons, then descends along the bicipital groove, which is covered by the transverse ligament. (Bottom) Posterior graphic of the shoulder illustrates the rotator cuff and adjacent structures. The infraspinatus and teres muscles and tendons form the posterior wall of the rotator cuff. Inferior to the teres minor muscle and superior to the teres major is the axillary nerve and posterior circumflex humeral vessels running through the quadrilateral space.

538

Shoulder

Suprascapular n. in suprascapular notch Supraspinatus m.

Acromion process

Upper Extremity

DEEP STRUCTURES

Superior transverse scapular l. Supraspinatus t. Suprascapular n., infraspinatus branch in spinoglenoid notch

Infraspinatus t. Joint capsule

Infraspinatus m. Teres minor m. Deltoid m.

Teres major m.

Triceps m. and t., lateral head

Triceps m. and t., long head Latissimus dorsi m.

Capsular l.

Acromioclavicular joint

Supraspinatus t. Supraspinatus m. Subdeltoid bursa

Deltoid m.

Synovial membrane

Glenoid labrum

Glenoid cavity of scapula

Axillary recess

(Top) Deep scapulohumeral dissection shows the course of the suprascapular nerve. The nerve enters the supraspinous fossa through the suprascapular notch, below the superior transverse scapular ligament. The nerve then passes beneath the supraspinatus and curves around the lateral border of the spine of the scapula to enter the infraspinous fossa. (Bottom) Graphic shows the coronal section through the midportion of the shoulder joint. Note the subacromial-subdeltoid bursa is situated in the space between the deltoid, acromion, acromioclavicular joint, distal clavicle superiorly, and the supraspinatus tendon and muscle inferiorly. There is no direct communication between the bursa and glenohumeral joint unless there is full-thickness tear of the supraspinatus tendon. The bursa is the main pain-producing structure around the shoulder. The wide expanse of the subacromial-subdeltoid bursa enables one to understand why shoulder symptoms are poorly localized. Patients often complain of generalized shoulder pain.

539

Upper Extremity

Shoulder SAGITTAL NORMAL LABRUM

Supraspinatus t.

Deltoid m.

Labrum, 12-o'clock position Infraspinatus t.

Labrum, 9-o'clock position Glenoid fossa

Coracohumeral l.

Biceps t.

Superior glenohumeral l.

Subscapularis t. Middle glenohumeral l.

Teres minor m. and t. Labrum, 3-o'clock position

Inferior glenohumeral ligament complex, posterior band

Inferior glenohumeral l. complex, anterior band Labrum, 6-o'clock position

Inferior glenohumeral ligament complex, axillary pouch

Subscapularis m.

Sagittal graphic shows the glenoid fossa. The labrum lines the edge of the glenoid, increasing the circumference and depth of the shoulder joint. The labrum plays an important role in stabilization of the shoulder joint. At the inferior aspect of the glenoid, the labrum is barely discernible. The superior, middle, and inferior glenohumeral ligaments are distinctive thickenings of the anterior shoulder capsule and cannot be seen as separate structures on ultrasound examination.

540

Shoulder Upper Extremity

LONGITUDINAL US, SUPRASPINATUS INSERTIONAL AREA

Deltoid m. Greater tuberosity Subdeltoid peribursal fat Insertional area Supraspinatus t. Articular cartilage Humeral head

Deltoid m. Greater tuberosity

Subdeltoid peribursal fat Supraspinatus t. Articular cartilage Humeral head

Deltoid m. Sharpey fibers at insertional site Greater tuberosity

Subdeltoid peribursal fat Supraspinatus t. Humeral head

(Top) Longitudinal grayscale US shows the anterior fibers of the supraspinatus tendon insertional area. The supraspinatus tendon inserts over a wide area (footprint) on the anterior aspect of the greater tuberosity. Many tears of the supraspinatus tendon involve avulsion of the tendon from its insertional site. (Middle) Longitudinal grayscale US shows the supraspinatus tendon midfibers. There is often a thin hypoechoic line at the insertional area. This represents Sharpey fibers and fibrocartilage. (Bottom) Longitudinal grayscale US shows the supraspinatus tendon posterior fibers. The anterior, middle, and posterior fibers should be evaluated in turn.

541

Upper Extremity

Shoulder TRANSVERSE US, SUPRASPINATUS INSERTIONAL AREA

Deltoid m. Greater tuberosity Subdeltoid peribursal fat Insertional area, lateral fibers Supraspinatus t.

Humeral head

Deltoid m. Greater tuberosity Insertional area, midfibers Subdeltoid peribursal fat Supraspinatus t. Humeral head

Deltoid m.

Greater tuberosity Subdeltoid peribursal fat

Insertional area, medial fibers

Supraspinatus t.

Humeral head

(Top) Transverse grayscale US shows the supraspinatus tendon insertional area. Angulation and slight movement of the transducer will allow visualization of the lateral, middle, and medial fibers, respectively. The leading anterior edge of the supraspinatus is a common site of tear (rim rent tear). (Middle) Transverse grayscale US shows the supraspinatus tendon at the insertional area of midfibers. The fibrillar echotexture of the supraspinatus tendon can be seen but is prone to anisotropy. (Bottom) Transverse grayscale US shows the supraspinatus midfibers insertional area. Subdeltoid peribursal fat is variable in depth. The normal bursa cannot be depicted. It is seen only when distended with fluid or thickened due to synovitis.

542

Shoulder Upper Extremity

TRANSVERSE AND LONGITUDINAL US, SUPRASPINATUS

Deltoid m. Subdeltoid peribursal fat Supraspinatus t.

Acromion

Insertional area Humeral head

Deltoid m. Subdeltoid peribursal fat Supraspinatus t. Articular cartilage Humeral head

Deltoid m. Subdeltoid peribursal fat Supraspinatus t. Humeral head

Musculotendinous junction Articular cartilage Glenoid

(Top) Transverse grayscale US shows the supraspinatus tendon just medial to the insertional area. The critical zone is located just medial to the insertional area. This is a relatively hypovascular area. It is prone to calcific tendinosis and tears, though most tears tend to occur at the insertional site. (Middle) Transverse grayscale US shows the supraspinatus medial to the insertional area. The fibrillar pattern of the supraspinatus tendon is prone to anisotropy. With tendinosis, the fibrillar pattern is disrupted. The tendon becomes more hypoechoic and thickened. (Bottom) Longitudinal grayscale US shows the supraspinatus tendon at a slightly more medial aspect. Tears of the musculotendinous junction are relatively uncommon.

543

Upper Extremity

Shoulder GRAPHIC AND TRANSVERSE US, ROTATOR CUFF INTERVAL

Acromion

Coracohumeral l. Supraspinatus t.

Biceps t., long head

Capsule

Synovium

Infraspinatus t.

Subscapularis t.

Deltoid m. Subdeltoid peribursal fat Biceps t. Subscapularis t. Supraspinatus t.

Humeral head

(Top) Graphic shows the relationship of the coracohumeral ligament to the rotator cuff tendons. The coracohumeral ligament is not a true ligament but a folded portion of the glenohumeral capsule that extends from the coracoid process to the humerus. The undersurface is lined by synovium. Portions of the coracohumeral ligament pass superficial and deep to the supraspinatus tendon. The coracohumeral ligament attaches to the superior border of the subscapularis tendon as well as to the greater tuberosity. (Bottom) Transverse grayscale US shows the shoulder at the rotator cuff interval. The rotator cuff interval represents the space between the leading anterior edge of the supraspinatus tendon and the adjacent superior edge of the subscapularis. It contains the biceps tendon. This should not be mistaken for a tear of the anterior aspect of the supraspinatus tendon. Patients with adhesive capsulitis may show increased hypoechogenicity and hyperemia of the rotator cuff interval as a result of inflammatory fibrovascular soft tissue overgrowth.

544

Shoulder Upper Extremity

TRANSVERSE US, BICEPS TENDON

Deltoid m. Biceps t.

Subdeltoid peribursal fat

Humeral head Upper end of bicipital groove

Deltoid m. Transverse l. Lateral lip of bicipital groove

Subscapularis t.

Biceps t. Bicipital groove

Humeral head Medial lip of bicipital groove

Deltoid m. Transverse l. Lateral lip of bicipital groove

Subscapularis m. Humeral head

Biceps t.

Medial lip of bicipital groove

(Top) Transverse grayscale US at the proximal aspect of the biceps tendon is shown. The bicipital groove forms a fibroosseous tunnel for the biceps tendon. The normal biceps tendon has an ovoid configuration. With tendinosis, the tendon becomes larger and more rounded in appearance. (Middle) Transverse grayscale US shows the biceps tendon. The biceps tendon is held in position by the transverse ligament. The subscapularis tendon inserts into the lesser tuberosity, which forms the medial lip of the bicipital groove. The biceps tendon may sublux medially from the groove and may be associated with subscapularis tendon injury. (Bottom) Transverse grayscale US shows relations of the biceps tendon. The transverse ligament is not a distinct entity but consists of a fibrous expansion of both the pectoralis major tendon and subscapularis tendon inserting into the lateral lip of the bicipital groove.

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Upper Extremity

Shoulder LONGITUDINAL US, BICEPS TENDON

Subcutaneous fat Deltoid m. Biceps t. entering shoulder joint

Humeral head

Subcutaneous fat Deltoid m.

Biceps t. Humeral head

Subcutaneous fat Deltoid m.

Biceps t. Humeral shaft

(Top) Longitudinal grayscale US shows the uppermost section of the biceps tendon. The intraarticular portion of the biceps long head tendon cannot be fully depicted on longitudinal imaging. On longitudinal section, the biceps tendon seems to expand at its upper end as it becomes more ovoid in contour. This location is also the most common site of biceps tendinosis, which also manifests as enlargement of the biceps tendon. (Middle) Longitudinal grayscale US shows the upper section of the biceps tendon. A small amount of fluid in the biceps tendon sheath, which is continuous with the glenohumeral joint, is normal and should not be mistaken for tenosynovitis. No fluid is depicted in this image. (Bottom) Longitudinal grayscale US shows the lower aspect of the biceps tendon. Most incomplete tears of the biceps tendons are longitudinal in orientation and are best depicted on transverse imaging.

546

Shoulder Upper Extremity

LONGITUDINAL US, SUBSCAPULARIS

Deltoid m. Subscapularis t. Biceps t. Medial lip of bicipital groove Lateral lip of bicipital groove

Deltoid m.

Humeral head

Subscapularis t.

Deltoid m.

Subscapularis t. Coracoid process Humeral head

(Top) Longitudinal grayscale US shows the subscapularis insertion. The subscapularis inserts into the medial lip of the bicipital groove but has a fibrous expansion traversing the biceps tendon through which it also gains attachment to the lateral lip of the bicipital groove. (Middle) Longitudinal grayscale US shows the subscapularis insertional area. Complete tears of the subscapularis are uncommon and usually follow a severe traumatic event. Partial tears are more common and usually involve the superior edge of the tendon. (Bottom) Longitudinal grayscale US shows the subscapularis tendon. The subscapularis moves beneath the coracoid process during internal-external rotation. Impingement may potentially occur at this location (subcoracoid impingement).

547

Upper Extremity

Shoulder TRANSVERSE US, SUBSCAPULARIS TENDON

Deltoid m.

Subscapularis t. Subdeltoid peribursal fat Humeral head

Deltoid m. Subdeltoid peribursal fat

Subscapularis t. (midfibers)

Humeral head

Deltoid m.

Subscapularis t. (lateral fibers)

Humeral head

(Top) Transverse grayscale US shows the subscapularis tendon midfibers. As they converge toward the insertion, fiber bundles of the multipennate subscapularis tendon give the tendon a mixed echogenic appearance. This is normal and should not be mistaken for tendinosis. (Middle) Transverse grayscale US shows the subscapularis at the level of midfibers. (Bottom) Transverse grayscale US shows the subscapularis tendon. Tears of the subscapularis tendon usually occur just proximal to the insertional area. These tears may involve the fascial covering of the biceps tendon, facilitating biceps tendon dislocation.

548

Shoulder

Infraspinatus t.

Upper Extremity

LONGITUDINAL AND TRANSVERSE US, INFRASPINATUS

Deltoid m. Subdeltoid peribursal fat

Humeral head

Insertional area of infraspinatus Greater tuberosity

Subdeltoid peribursal fat Deltoid m. Musculotendinous junction in infraspinatus m.

Infraspinatus t. Humeral head

Articular cartilage

Deltoid m. Subdeltoid peribursal fat Infraspinatus t. Insertional area Humeral head

(Top) Longitudinal grayscale US shows the infraspinatus tendon insertional area. The infraspinatus tendon is less commonly torn than the supraspinatus tendon. Most tears are avulsive-type tears involving the insertional area. (Middle) Longitudinal grayscale US shows the infraspinatus musculotendinous junction. The muscle fibers interdigitate with the tendon at the musculotendinous junction and should not be mistaken for tears/tendinosis. (Bottom) Transverse grayscale US shows the infraspinatus insertional area. All tears of the rotator cuff tendons should be confirmed in both planes (transverse and longitudinal).

549

Upper Extremity

Shoulder LONGITUDINAL AND TRANSVERSE US, TERES MINOR

Deltoid m.

Teres minor musculotendinous junction

Insertional area of teres minor

Deltoid m.

Articular cartilage

Teres minor t.

Insertional area of teres minor Humeral head

Latissimus dorsi m. Teres minor m.

Infraspinatus m. Scapula

(Top) Longitudinal grayscale US shows the teres minor muscle insertional area. The teres minor muscle is usually not torn in isolation, but it may be torn in massive rotator cuff tears. It is a small muscle and tendon seen at the posteroinferior edge of the infraspinatus tendon. (Middle) Longitudinal grayscale US shows the teres minor insertional area. (Bottom) Transverse grayscale US shows the teres minor. The teres minor muscle is best depicted on longitudinal imaging at the inferior aspect of the infraspinatus tendon. Isolated atrophy of the teres minor muscle can occur in quadrilateral space syndrome due to compression of the axillary nerve (part of the deltoid muscle may also be affected).

550

Shoulder

Superior and inferior acromioclavicular l.

Upper Extremity

SHOULDER JOINT AND POSTERIOR ASPECT

Clavicle Acromion Coracoacromial l. Coracohumeral l.

Superior transverse scapular l.

Superior glenohumeral l.

Greater tuberosity Lesser tuberosity Bicipital groove

Proximal humerus

Supraspinatus m. Scapular spine

Middle glenohumeral l. Inferior glenohumeral l. complex

Scapula

Acromion process Supraspinatus t. Infraspinatus t.

Infraspinatus m. Teres minor m.

Teres minor t. Deltoid m.

Teres major m. Triceps m. and t., lateral head

Latissimus dorsi m.

Triceps m. and t., long head

(Top) Anterior graphic illustrates the right shoulder in deep dissection. The muscles have been removed. (Bottom) Posterior graphic illustrates the shoulder. Superficial scapulohumeral dissection demonstrates the musculature.

551

Upper Extremity

Shoulder LONGITUDINAL US, POSTERIOR ASPECT

Trapezius m. Central t. of supraspinatus m. Spine of scapula

Supraspinatus m. Scapula

Deltoid m. Central t. of infraspinatus m.

Infraspinatus m. Spine of scapula

Deltoid m.

Acromion

Subdeltoid peribursal fat

Supraspinatus t. Humeral head

(Top) Longitudinal grayscale US shows the posterior shoulder at the supraspinatus muscle. Muscle atrophy is common in rotator cuff pathology. Ultrasound is almost as sensitive as MR in depiction of muscle atrophy. Atrophy is seen as a reduction in muscle bulk with increase in muscle echogenicity. As a result, the central tendon is less readily seen. (Middle) Longitudinal grayscale US shows the shoulder on posterior view. Infraspinatus muscle atrophy usually accompanies supraspinatus muscle atrophy to a lesser or greater degree. Similar to the supraspinatus muscle, muscle bulk is reduced and becomes more echogenic with the central tendon becoming less easy to see. (Bottom) Longitudinal grayscale US shows the supraspinatus tendon. The supraspinatus tendon slides below the acromion during abduction. This relationship may be seen from either the anterior or posterior aspect of the shoulder. Dynamic imaging may reveal impingement of the supraspinatus against the acromion during abduction.

552

Shoulder

Deltoid m.

Upper Extremity

LONGITUDINAL AND TRANSVERSE US, POSTERIOR GLENOID LABRUM AND GLENOHUMERAL JOINT

Humeral head Infraspinatus m. Joint capsule Posterior glenoid labrum Glenoid Glenohumeral joint

Deltoid m. Acromion Coracoacromial l.

Coracoid process Musculotendinous junction of supraspinatus m.

Deltoid m. Subscapularis t. Humeral head

Coracoid process

(Top) Longitudinal grayscale US shows the posterior shoulder. The glenohumeral joint is most easily seen from the posterior aspect. This is a good site for US-guided joint injection. Joint effusions are also best seen in this area. (Middle) Longitudinal grayscale US shows the coracoacromial ligament. The coracoacromial ligament extends from the coracoid process to the anteroinferior margin of the acromion. Impingement of the supraspinatus tendon and the overlying subacromial-subdeltoid bursa may occur during shoulder abduction. (Bottom) Transverse grayscale US shows the coracoid process. The coracoid process is close to the humeral head and intervening subscapularis. Occasionally, the coracohumeral distance is reduced and subcoracoid impingement may potentially occur.

553

Upper Extremity

Axilla

TERMINOLOGY Definitions • Fat-filled space between upper limb and thoracic wall

IMAGING ANATOMY Extent • Axilla is shaped like pyramid with top layers shaved off • Consists of apex, base, and 4 walls ○ Apex – Bounded by scapula, 1st rib, and mid 1/3 of clavicle – Arm communicates with posterior triangle of neck via apex of axilla ○ Anterior wall – Composed of pectoralis major and minor muscles ○ Posterior wall – Composed of teres major, latissimus dorsi, and subscapularis muscles ○ Medial wall – Composed of serratus anterior, upper ribs, and intercostal spaces ○ Lateral wall – Medial and lateral lips of bicipital groove into which anterior and posterior walls are inserted ○ Base – Composed of axillary fascia, subcutaneous fat, and skin • Contents of axilla ○ Axillary artery and vein ○ Cords and branches of brachial plexus ○ Coracobrachialis and biceps muscles ○ Lymph nodes and vessels ○ Fat • Axillary artery ○ Continuation of subclavian artery ○ Lies on posterior wall of axilla ○ Surrounded by cords and branches of brachial plexus ○ Vein lies medial to artery ○ Arterial branches – Superior thoracic artery – Acromiothoracic artery – Lateral thoracic artery – Subscapular artery – Anterior and posterior circumflex humeral arteries • Axillary vein ○ Continuation of brachial vein – Tributaries correspond to branches of axillary artery and also cephalic vein • Brachial plexus ○ Cord and terminal branches of brachial plexus pass through axilla ○ 3 cords: Lateral, medial, and posterior ○ Lateral cord gives rise to – Lateral pectoral nerve – Musculocutaneous nerve: Pierces coracobrachialis to descend down arm between biceps and brachialis muscles – Contributes to median nerve ○ Medial cord gives rise to

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– Medial pectoral nerve – Ulnar nerve – Contributes to median nerve – Medial cutaneous nerves of arm and forearm ○ Posterior cord gives rise to – Subscapular nerve – Thoracodorsal nerve – Axillary nerve, which passes through quadrilateral space posteriorly around surgical neck of humerus, accompanied by posterior circumflex humeral artery – Radial nerve

Anatomy Relationships • Quadrilateral space ○ Superior border: Teres minor muscle ○ Inferior border: Teres major muscle ○ Lateral border: Surgical neck of humerus ○ Medial border: Long head of triceps muscle ○ Contents: Axillary nerve and posterior circumflex humeral artery – Axillary nerve supplies teres minor muscle, deltoid muscle, posterolateral cutaneous region of shoulder and upper arm • Triangular space ○ Located medial to quadrilateral space ○ Superior border: Teres minor muscle ○ Inferior border: Teres major muscle ○ Lateral border: Long head of triceps muscle ○ Contents: Circumflex scapular artery – Branch of subscapular artery supplying infraspinatus fossa

ANATOMY IMAGING ISSUES Key Concepts • Quadrilateral space syndrome = neurovascular compression syndrome due to compression of axillary nerve or posterior humeral circumflex artery in quadrilateral space ○ Can have complications that are purely neurologic, purely vascular, or both ○ Effects – Point tenderness of quadrilateral space – Poorly localized shoulder pain ± paresthesia radiating top lateral arm – Symptoms aggravated by abduction and external rotation of arm – Teres minor ± deltoid atrophy – Intermittent, ischemic-type pain ○ Due to – Humeral fracture – Fibrous bands secondary to trauma – Muscle hypertrophy ± fibrotic bands seen in throwing athletes, tennis players, or volleyball players – Paralabral cysts: Most common cause of mass in this region, high associations with labral tears – Glenohumeral joint dislocation – Extreme or prolonged abduction of arm during sleep

Axilla

Acromion process

Upper Extremity

MUSCLES

Supraspinatus m. Scapular spine

Supraspinatus t. Infraspinatus t.

Infraspinatus m.

Teres minor t.

Teres minor m. Quadrilateral space

Deltoid m.

Triangular space Triceps m. and t., lateral head Teres major m. Latissimus dorsi m.

Supraspinatus m. Superior transverse scapular l.

Suprascapular notch Suprascapular a. and n.

Triceps m. and t., long head

Acromion process Deltoid m. Supraspinatus t. Infraspinatus t. Joint capsule Posterior circumflex humeral a. and axillary n.

Spinoglenoid notch Suprascapular a., infraspinatus branch

Deep brachial a. Radial n.

Infraspinatus m.

Triceps m. and t., lateral head

Teres minor m. Teres major m.

Triceps m. and t., long head

Latissimus dorsi m.

(Top) Posterior graphic shows the shoulder. Superficial scapulohumeral dissection shows the location of the quadrilateral space and triangular space (each outlined in green). The quadrilateral space transmits the axillary nerve and the posterior circumflex humeral artery, while the much less important triangular space transmits the scapular circumflex vessels. (Bottom) Graphic of the deep scapulohumeral dissection shows the major neurovascular structures, including those in the quadrilateral space.

555

Upper Extremity

Axilla DEEPER STRUCTURES Suprascapular n. in suprascapular notch Supraspinatus m.

Acromion process

Superior transverse scapular l. Supraspinatus t. Suprascapular n., infraspinatus branch, in spinoglenoid notch

Infraspinatus t. Joint capsule

Infraspinatus m. Teres minor m. Deltoid m.

Teres major m.

Triceps m. and t., lateral head

Triceps m. and t., long head Latissimus dorsi m.

Deltoid m., anterior belly

Cephalic v. Pectoralis major m.

Biceps t., long head

Pectoralis minor m. Coracobrachialis and biceps m., short head

Deltoid m., middle belly Humeral head

Axillary neurovascular bundle Anterior labrum

Glenoid Posterior labrum Suprascapular n. branch and vessels

Subscapularis m.

Infraspinatus m. Deltoid m., posterior belly

(Top) Graphic of deep scapulohumeral dissection shows the course of the suprascapular nerve. (Bottom) Axial graphic shows the location of the suprascapular artery, nerve, and vein branches just below the level of the spinoglenoid notch. The suprascapular nerve is a mixed motor and sensory nerve. It arises from the anterior rami of the C5 and C6 roots. It passes deep to the superior transverse scapular ligament of the suprascapular notch. It then passes deep to the inferior transverse scapular ligament of the spinoglenoid notch. It supplies the supraspinatus and the infraspinatus muscles with sensory fibers to the acromioclavicular joint and the glenohumeral joint capsules.

556

Axilla

Brachial plexus trunks

C5

Anterior and posterior divisions

C6

Brachial plexus cords

Upper Extremity

RELATIONSHIP OF NEUROVASCULAR STRUCTURES

Dorsal scapular n. C7

C8 T1 Median n. Long thoracic n. Axillary a. Radial n. Ulnar n. Medial cutaneous n. of arm

Pectoralis minor

Axillary v.

Humeral neck

Trunk of axillary n.

Cutaneous branches

Deltoid m. Long and lateral head of triceps

Nerve to teres minor

Anterior and posterior branches

Upper lateral cutaneous n. of arm

Pseudoganglion

(Top) Graphic shows relations of the brachial plexus in the axilla. The brachial plexus arises from the anterior rami of the C5, C6, C7, C8, and T1 nerves. They 1st unite to form the superior, middle, and inferior trunks. The trunks then divide and reunite to form the lateral, posterior, and middle cords. Beyond the lateral margin of the pectoralis minor muscle, they continue as the terminal branches of the plexus (axillary, musculocutaneous, radial, medial, and ulnar nerves). (Bottom) Graphic shows a section through the upper arm with the axillary nerve and its branches.

557

Upper Extremity

Axilla TRANSVERSE US, AXILLA

Pectoralis major m. Brachial plexus cords Coracobrachialis m.

Pectoralis minor m.

Axillary v.

Lymph node

Axillary a.

Pectoralis major m. Brachial plexus cords Axillary v.

Axillary a.

Median n. Brachial vv.

Ulnar n. Biceps m., short head Coracobrachialis m. Humeral shaft

Radial n. Teres major m.

Brachial a.

(Top) Transverse grayscale ultrasound shows the proximal axilla with the arm abducted. The contents of the axilla are inspected with the arm fully abducted. (Middle) Transverse grayscale ultrasound shows the midportion of the axilla. The axillary artery and vein pass through the axilla surrounded by the cords of the brachial plexus. The cords (medial, lateral, and posterior) are named relative to their position alongside the axillary artery. Lymph nodes with variably fatty hila are commonly seen in the axilla around the neurovascular bundle. (Bottom) Transverse grayscale ultrasound shows the distal aspect of the axilla.

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Axilla

Pectoralis major m.

Upper Extremity

TRANSVERSE US, ANTERIOR AXILLARY WALL

Pectoralis minor m. Coracobrachialis Subscapularis

Brachial plexus cords Axillary v.

Axillary a.

Pectoralis major m.

Pectoralis minor m. Coracobrachialis m.

Brachial plexus cords Axillary a.

Subscapularis m. Axillary v.

Pectoralis major m.

Pectoralis minor m. Coracobrachialis m.

Teres major m.

Brachial plexus branches

Axillary a. Axillary v.

(Top) Transverse grayscale ultrasound shows the proximal anterior wall of the axilla. The anterior wall of the axilla can be examined with the arm by the side. (Middle) Transverse grayscale ultrasound shows the midsection of the anterior wall of the axilla. The anterior wall of the axilla is formed by the pectoralis major and pectoralis minor muscles. (Bottom) Transverse grayscale ultrasound shows the distal anterior wall of axilla.

559

Upper Extremity

Axilla TRANSVERSE US, QUADRILATERAL SPACE

Triceps m., long head Latissimus dorsi m. Teres minor m. Humeral shaft Teres major m. Axillary n. in quadrilateral space

Triceps m., long head Latissimus dorsi

Teres minor m. Humeral shaft Teres major m. Axillary n. in quadrilateral space Posterior circumflex humeral a.

Triceps m., long head

Latissimus dorsi m. Teres minor m.

Humerus

Posterior circumflex humeral a.

Teres major m.

(Top) Transverse grayscale ultrasound of the arm shows the anterior aspect of the quadrilateral space (quadrangular space) with the arm abducted. This space contains the axillary nerve and posterior circumflex humeral vessels. (Middle) Transverse grayscale ultrasound shows the quadrilateral space with the arm adducted. The contents of the space are more easily seen with the arm adducted. (Bottom) Transverse grayscale ultrasound in the more posterior position of the arm shows the posterior circumflex humeral artery posterior to the quadrilateral space.

560

Axilla Upper Extremity

TRANSVERSE US, POSTERIOR AXILLARY WALL

Deltoid m. Infraspinatus m. Scapula Humerus

Deltoid m.

Teres minor m. Humeral shaft

Teres major m. Scapula

Artifact due to posterior axillary fold

Triceps m., long head

Latissimus dorsi m.

Teres major m.

(Top) Transverse grayscale ultrasound shows the upper aspect of the posterior axillary wall. (Middle) Transverse grayscale ultrasound shows the middle aspect of the posterior wall of the axilla. The posterior wall of the axilla is composed of the teres major, latissimus dorsi, and subscapularis muscles. (Bottom) Transverse grayscale ultrasound shows the lowermost aspect of the axilla.

561

Upper Extremity

Arm

IMAGING ANATOMY Overview • Muscles of upper arm are divided into anterior and posterior compartments

Anatomy Relationships • Anterior compartment of arm ○ Coracobrachialis muscle – Origin: Coracoid process tip, in common with and medial to short head biceps tendon – Insertion: Medial surface of humeral midshaft, between brachialis and triceps muscle origins – Nerve supply: Musculocutaneous nerve, perforates muscle – Blood supply: Brachial artery, muscular branches – Action: Flexes and adducts shoulder, supports humeral head in glenoid ○ Biceps muscle, short head – Origin: Coracoid process tip, in common with and lateral to coracobrachialis tendon – Insertion: Radial tuberosity after joining long head – Nerve supply: Musculocutaneous nerve – Blood supply: Brachial artery, muscular branches – Action: Flexes elbow and shoulder, supinates forearm ○ Biceps muscle, long head – Origin: Predominantly supraglenoid tubercle; also superior glenoid labrum and coracoid base – Insertion: Radial tuberosity after joining with short head – Tendon runs along bicipital groove, which is covered by transverse ligament – Transverse ligament spans proximal end of bicipital groove and comprises deeper layer formed from subscapularis tendon fibers and superficial fibrous layer in continuity with supraspinatus tendon and coracohumeral ligament – Nerve supply: Musculocutaneous nerve – Blood supply: Brachial artery, muscular branches – Action: Flexes elbow, supinates forearm – Variants, biceps muscle: 3rd head in 10% arising at upper medial aspect of brachialis muscle; 4th head can arise from lateral humerus, bicipital groove, or greater tuberosity ○ Brachialis muscle – Origin: Distal 1/2 of anterior humeral shaft and 2 intermuscular septa – Insertion: Tuberosity of ulna and anterior surface of coronoid process – Nerve supply: Musculocutaneous nerve plus branch of radial nerve – Blood supply: Brachial artery, muscular branches, and recurrent radial artery – Action: Flexes forearm – Covers anterior aspect of elbow joint • Posterior compartment of arm ○ Triceps muscle, long head – Origin: Infraglenoid tubercle of scapula – Insertion: Proximal olecranon and deep fascia of arm after joining with lateral and medial heads – Nerve supply: Radial nerve

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– Blood supply: Deep brachial artery branches – Action: Elbow extension, adducts humerus when arm is extended ○ Triceps muscle, lateral head – Origin: Posterior and lateral humeral shaft, lateral intermuscular septum – Insertion: Proximal olecranon and deep fascia of arm after joining with long and medial heads – Nerve supply: Radial nerve – Blood supply: Deep brachial artery branches – Action: Elbow extension ○ Triceps muscle, medial head – Origin: Posterior humeral shaft from teres major insertion to near trochlea, medial intermuscular septum – Insertion: Proximal olecranon and deep fascia of arm after joining with lateral and long heads – Nerve supply: Radial and branches of ulnar nerve – Blood supply: Deep brachial artery branches – Action: Elbow extension ○ Anconeus muscle – Origin: Lateral epicondyle of humerus – Insertion: Lateral cortex of olecranon and posterior 1/4 of ulna – Nerve supply: Radial nerve – Blood supply: Deep brachial artery branch – Action: Assists elbow extension, abducts ulna • Fascia ○ Brachial fascia – Continuous with fascia covering deltoid and pectoralis major – Varies in thickness; thin over biceps and thick over triceps muscles – Lateral intermuscular septum from lower aspect of greater tuberosity to lateral epicondyle – Medial intermuscular septum from lower aspect of lesser tuberosity to medial epicondyle – Perforated by ulnar nerve, superior ulnar collateral artery, and posterior branch of inferior ulnar collateral artery – Provides traction on deep fascia of forearm ○ Bicipital fascia – a.k.a. lacertus fibrosus – Arises from medial side of distal biceps tendon at level of elbow joint – Passes superficial to brachial artery – Continuous with deep fascia of forearm

ANATOMY IMAGING ISSUES Imaging Recommendations • Examine with arm extended in supine and prone positions • Transverse plane most helpful to delineate borders of anterior and posterior compartments and relationship to neurovascular structures

Imaging Pitfalls • Muscle may appear echogenic, simulating fatty replacement or edema when beam not aligned parallel to muscle fibers

Arm

Acromion Coracoid process Transverse l. Anterior circumflex humeral a.

Coracobrachialis

Upper Extremity

ARM

Musculocutaneous n. Circumflex scapular a. Subscapularis m. Teres major m.

Biceps m., short head Latissimus dorsi Biceps m., long head

Brachial a. Lateral antebrachial cutaneous n. Biceps t.

Brachioradialis

Median n. Pronator teres Flexor carpi radialis m.

Pectoralis major m. Cephalic v. Pectoralis major t. Biceps m., long head Coracobrachialis m.

Biceps m., short head Musculocutaneous n. Medial antebrachial n. Basilic v. Median n.

Humerus Deltoid m. Latissimus dorsi t. Triceps m., lateral head Teres major m.

Brachial v. Ulnar n. Deep brachial a. Medial brachial cutaneous n. Brachial a. Radial n.

Triceps m., long head

Brachial v.

(Top) Anterior graphic of the arm is shown. The short head of the biceps originates from the coracoid process tip, in common with the coracobrachialis tendon. The long head of the biceps tendon originates from the biceps labral complex at the supraglenoid tubercle and extends along the rotator cuff interval and bicipital groove of humerus to join with the short head and form the biceps muscle. The brachialis muscle originates from the distal 1/2 of the anterior humeral shaft. The transverse ligament spans the proximal bicipital groove from medial to lateral lip. Anatomical studies suggest that the transverse ligament is formed from fibers of the subscapularis tendon as well as a more superficial discrete fibrous band. (Bottom) Graphic shows the upper humeral level. Note that the coracobrachialis muscle is lying deep to the biceps muscle. In the posterior compartment, the lateral head and long heads of the triceps muscles can be seen at this level. All the neurovascular bundles are lying on the medial side of the upper arm.

563

Upper Extremity

Arm AXIAL, ARM

Median n. Biceps m. Cephalic v.

Musculocutaneous n. Brachialis m. Humerus Radial collateral a. Posterior antebrachial cutaneous n.

Brachial v. Brachial a. Medial antebrachial cutaneous n. Medial brachial cutaneous n. Basilic v. Brachial v. Ulnar n. Superior ulnar collateral a.

Triceps m., medial head

Radial n. Middle collateral a.

Triceps m., long head

Triceps m., lateral head

Cephalic v. Biceps m. Lateral antebrachial cutaneous n. Brachialis m. Radial n. Brachioradialis m. Extensor carpi radialis longus m. Posterior antebrachial cutaneous n.

Brachial v. Brachial a. Medial antebrachial cutaneous n. Median n. Basilic v. Brachial v. Ulnar n. Humerus

Triceps m. Triceps t.

(Top) Axial graphic shows the right arm at the midhumeral level. The posterior compartment of the arm consists of 3 heads of triceps muscle, and the medial head of the triceps can be delineated in this level. In the anterior compartment, the brachialis can be delineated at this midarm level. (Bottom) Axial section shows the distal humeral level. The deep brachial artery and radial nerve course along the posterolateral humerus reaching the anterolateral aspect of the humerus at this level. The median nerve is lying within the intermuscular septum. The biceps muscle is thinning anteriorly, and the triceps tendon appears.

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Arm

Median n. Subcutaneous tissue

Upper Extremity

TRANSVERSE US, ANTEROMEDIAL ASPECT

Long head of biceps m.

Brachial v.

Ulnar n. Radial n.

Musculocutaneous n.

Brachial a. Triceps m.

Coracobrachialis m. Humeral shaft

Musculocutaneous n. Brachial a.

Brachialis m. Ulnar n. Musculocutaneous n. Triceps m. Humeral shaft

Brachial a. Median n. Brachialis m. Brachial v.

Brachialis m.

Medial antebrachial cutaneous n.

Triceps m.

Humeral shaft

(Top) Transverse grayscale ultrasound shows the anteromedial aspect of the upper arm. The terminal branches of the brachial plexus (namely, the median nerve, ulnar nerve, and radial nerve) all lie around the brachial vein and artery. They can be recognized by their position relative to the brachial artery, the radial nerve lying deep, median nerve laterally, and ulnar nerve medially. (Middle) Transverse grayscale ultrasound shows the anteromedial aspect of the midarm. Compression of the median or ulnar nerve is uncommon in the midarm. The neurovascular bundle helps define the separation of the anterior and posterior compartments of the arm medially. (Bottom) Transverse grayscale ultrasound shows the anteromedial aspect of the distal arm. In the distal arm, the median nerve alone is closely associated with the brachial neurovascular bundle.

565

Upper Extremity

Arm TRANSVERSE US, ANTERIOR ASPECT

Subcutaneous tissue Long head of biceps m.

Short head of biceps m. Musculocutaneous n. Coracobrachialis m. Humeral shaft

Long head of biceps m. Brachial v. Short head of biceps m. Musculocutaneous n. Brachialis m.

Coracobrachialis m.

Humeral shaft

Long head of biceps m.

Short head of biceps m. Brachialis m. Musculocutaneous n.

Brachialis m.

Humeral shaft

(Top) Transverse grayscale ultrasound shows the proximal 1/3 of the arm. The anatomy of the upper arm is quite straightforward. The arm muscles are divided into 2 compartments. The anterior compartment is composed of the biceps, brachialis, and coracobrachialis muscles. The biceps muscle is midline, the brachialis muscle is midline and lateral, and the coracobrachialis muscle is midline and medial. (Middle) Transverse grayscale ultrasound shows the mid 1/3 of the anterior arm. Most of the neurovascular bundles in the arm lie anteromedially. (Bottom) Transverse grayscale ultrasound shows the distal 1/3 of the anterior arm. The musculocutaneous nerve is the main critical neurovascular structure of the anterior arm lying between the biceps, coracobrachialis, and brachialis muscles.

566

Arm

Subcutaneous tissue

Deltoid m.

Upper Extremity

TRANSVERSE US, ANTEROLATERAL ASPECT

Long head of biceps m.

Humeral shaft Coracobrachialis m.

Subcutaneous tissue Long head of biceps m. Short head of biceps m. Brachialis m.

Humeral shaft

Subcutaneous tissue

Brachioradialis m.

Long head of biceps m. Short head of biceps m. Brachialis m. Lateral supracondylar portion of humerus

(Top) Transverse grayscale ultrasound shows the anterolateral aspect of the proximal arm. This is an area prone to injury during contact sports. Fortunately, there is no neurovascular bundle in the area that would be exposed to injury. (Middle) Transverse grayscale ultrasound shows the anterolateral section of the midarm. Both the biceps muscle and brachialis muscle may be prone to overuse muscle injury if too vigorous exercise is undertaken. The biceps muscle may appear echogenic if the transducer is aligned at an angle to the transverse plane. (Bottom) Transverse grayscale ultrasound shows the anterolateral aspect of the distal arm. Both heads of the biceps converge to form the distal biceps tendon just proximal to the antecubital fossa.

567

Upper Extremity

Arm POSTERIOR ARM

Acromion Deltoid m. Supraspinatus m. Greater tuberosity of humerus Infraspinatus m.

Teres minor m.

Teres major m.

Posterior circumflex humeral a. and axillary n.

Radial collateral a. Radial n. Triceps m., long head

Latissimus dorsi m. Triceps m., lateral head

Triceps t.

Medial intermuscular septum

Brachioradialis m. Anconeus m.

Flexor carpi ulnaris m.

Posterior antebrachial cutaneous n.

Graphic shows the superficial dissection of the posterior arm. Note that the quadrilateral space is an anatomic space bounded by the long head of the triceps, teres minor and teres major muscles, and cortex of the humerus. Axillary nerve and posterior circumflex humeral artery are within the space. Any narrowing of this space will cause quadrilateral space syndrome.

568

Arm

Triceps m., lateral head

Humeral shaft

Upper Extremity

TRANSVERSE US, POSTERIOR ASPECT

Triceps m., medial head

Radial n.

Triceps m. Radial n. in spiral groove Triceps m.

Profunda brachii a.

Humeral shaft

Triceps m. Radial n.

Profunda brachii a.

Humeral shaft Brachialis m.

(Top) Transverse grayscale ultrasound shows the posterior upper arm. The triceps muscle occupies nearly the whole of the posterior upper arm. The radial nerve supplies the triceps and supinator muscles. (Middle) Transverse grayscale ultrasound shows the posterior midarm. The radial nerve runs in the spiral groove on the posterior aspect of the midarm. At this level, it is prone to injury from humeral shaft fractures, fibrosis, or fibrotic bands following trauma or extrinsic compression. (Bottom) Transverse grayscale ultrasound shows the posterior aspect of the distal arm. The radial nerve pierces the lateral intermuscular septum just proximal to the lateral epicondyle. It then runs between the brachialis and brachioradialis muscles and passes anterior to the lateral epicondyle. The nerve may be compressed by the lateral intermuscular septum.

569

Upper Extremity

Arm Vessels

GROSS ANATOMY Arteries

Imaging Recommendations

• • • • •

• Venous examination ○ Examination of upper limb veins is normally performed with patient supine and arm abducted to about 90° ○ Use of high-frequency linear transducer (5-10 MHz) is recommended – Determination of compressibility – Flow pattern: Normal venous waveform ○ Augmentation of flow is obtained by manual compression of forearm or upper arm – Alternatively, patient clenches fist to increase venous flow – Flow can also be augmented by deep inspiration • Arterial examination ○ In patients with possible arterial compression syndromes, arteries are examined in various positions of shoulder abduction so that any compression may be accentuated

Brachial artery Continuation of axillary artery Extends from lower border of teres major to neck of radius Accompanies median nerve Branches of brachial artery in arm ○ Superior ulnar collateral arises medially, descends with ulnar nerve posterior to medial epicondyle, and then forms anastomosis with branches of ulnar artery ○ Inferior ulnar collateral arises distal to superior ulnar collateral artery, descends anterior to medial epicondyle, and then forms anastomosis with branches of ulnar artery ○ Profunda brachii: Main branch of brachial artery – Arises just distal to teres major, accompanies radial nerve, and passes backwards in spiral groove on posterior surface of humerus – Gives off another branch, which passes upward and anastomoses with arteries around shoulder joint – Gives 2 lower medial branches, which descend to elbow joint on its medial side and take part in anterior and posterior anastomosis around elbow joint • Brachial artery lies superficial in its course in arm • Covered by bicipital aponeurosis at elbow where it may be compressed against medial surface of humerus • Brachial artery divides at neck of radius into radial artery and ulnar artery ○ High takeoff of radial artery from brachial artery is common anatomical variant ○ Radial artery passes inferiorly and laterally, lying on tendon of biceps brachii ○ Ulnar artery passes down and medially, deep to pronator teres ○ Within antecubital fossa, radial and ulnar arteries give off recurrent branches to elbow joint

Veins • Categorized as superficial and deep venous system ○ Veins of upper limb are variable in number and position • Brachial vein ○ Forms deep venous system ○ Singular or paired, continue into axillary vein ○ Accompanied by brachial artery and nerves of upper limb • Cephalic vein ○ Lies anterolaterally in superficial fascia of antecubital fossa and gives off medial cubital vein, which joins basilic vein ○ Runs in deltopectoral groove before piercing clavipectoral fascia to drain into axillary vein • Basilic vein ○ Passes upward on medial side of forearm, receiving anterior and posterior tributaries, and then passes to anteromedial aspect of elbow where it receives medial cubital vein ○ Continues on medial aspect of biceps brachii until it pierces deep fascia to run cranially, medial to brachial artery ○ Joins brachial vein and becomes axillary vein at lower border of teres major 570

ANATOMY IMAGING ISSUES

Imaging Pitfalls • Clavicle can produce mirror artifact of subclavian vessels • Brachial vein duplication is common • Due to proximity, arm venous flow is affected by respiration ○ Deep inspiration will augment flow • Angle of insonation should not be > 60° as this will reduce sensitivity of Doppler and color flow signals • Color signal scale should match flow velocity • Doppler gate should be located at center of artery or vein as this is site of peak flow velocity • Arteriography: Gold standard for assessment of accuracy of arterial Doppler ultrasound with respect to stenoses or occlusion ○ Other methods of visualizing arterial tree are computed tomography angiography and magnetic resonance angiography

CLINICAL IMPLICATIONS Clinical Importance • Brachial artery may be used for access in angiography, either by high brachial approach or in antecubital fossa, where it lies medial to biceps tendon and lateral to median nerve • Spontaneous thrombosis of axillary vein occasionally occurs following excessive movements of arm at shoulder joint • Diagnosis of exclusion of deep vein thrombosis in upper or lower limb; spontaneous or related to indwelling catheters • Vein mapping prior to bypass grafts • Localization of veins for venous access and cannulation

Arm Vessels

Transverse cervical a. Suprascapular a. Dorsal scapular a. Acromial branch, thoracoacromial a. Axillary a. Clavicular branch, thoracoacromial a. Posterior circumflex humeral a. Anterior circumflex humeral a.

Ascending branch, deep brachial a. Brachial a. Deep brachial a.

Inferior thyroid a. Thyrocervical trunk

Upper Extremity

ARTERIES

Vertebral a. Internal thoracic a. Subclavian a. Superior thoracic a. Thoracoacromial a. Pectoral branch, thoracoacromial a. Deltoid branch, thoracoacromial a. Circumflex scapular a. Lateral thoracic a. Thoracodorsal a.

Dorsal scapular a. Suprascapular a.

Thoracoacromial a., acromial branch Acromial plexus

Suprascapular a., infraspinatus branch

Axillary a. Dorsal scapular a. anastomoses with intercostal aa.

Anterior circumflex humeral a.

Posterior circumflex humeral a. Brachial a. Circumflex scapular a. Deep brachial a.

(Top) Anterior graphic shows arterial supply to the shoulder. The shoulder is predominantly supplied by the anterior and posterior circumflex humeral, suprascapular, and circumflex scapular arteries. (Bottom) Posterior graphic shows arterial supply to the shoulder. Extensive collateral blood vessels include anastomoses with intercostal arteries.

571

Upper Extremity

Arm Vessels AXIAL, RIGHT ARM ARTERIES AND VEINS

Cephalic v.

Coracobrachialis m. Median n. Basilic v. Brachial v. Deep brachial a. Brachial a. Brachial v. Teres major m.

Cephalic v.

Brachial v. Brachial a. Basilic v. Brachial v.

Radial collateral a.

Superior ulnar collateral a.

Radial n. Medial collateral a.

Cephalic v.

Radial n.

Brachial v. Brachial a. Median n. Basilic v. Brachial v. Ulnar n.

(Top) Axial graphic shows the upper right arm. The brachial artery is a continuation of the axillary artery and accompanies the median nerve. The deep brachial artery (profunda brachii artery) is the main branch of brachial artery and accompanies the radial nerve. The basilic vein lies medially and the cephalic vein anterolaterally. (Middle) Axial graphic shows the right arm at the midhumeral level. Note that the profunda brachii artery accompanies the radial nerve and passes backward in spiral groove of humeral shaft before dividing into medial and radial collateral arteries. Superior ulnar collateral artery arises from the brachial artery and descends with the ulnar nerve. (Bottom) Axial graphic shows the right arm at the distal humeral level. Note how the median nerve is on the medial side of the brachial artery at this level.

572

Arm Vessels

Brachial a.

Biceps m. Coracobrachialis m. Humeral shaft

Upper Extremity

TRANSVERSE US, PROXIMAL ARM

Basilic v. Brachial v. Triceps m.

Basilic v. Brachial v. Brachial a. Brachial v. Biceps m.

Ulnar n. Brachial v.

Coracobrachialis m.

Radial n.

Brachial v. Brachial a. Basilic v. Musculocutaneous n. Brachial vv.

Triceps m. Humeral shaft

(Top) Transverse grayscale ultrasound shows the vessels of the proximal arm. The basilic vein lies deep to the investing fascia in the arm. The veins are highly variable in location and are surrounded by nerves; hence, ultrasound guidance is helpful when cannulating the veins of the arm. (Middle) Transverse grayscale ultrasound shows the vessels of the midarm. The basilic vein is formed on the ulnar side of the wrist and is joined by the median cubital vein (from cephalic vein at the elbow). In some cases, the brachial artery may bifurcate in the midarm or higher. (Bottom) Transverse grayscale ultrasound shows the vessels of the distal arm. The brachial artery can be seen clinically as a pulsatile vessel in "locomotor brachialis," i.e., in arteriosclerosis.

573

Upper Extremity

Arm Vessels COLOR DOPPLER, BRACHIAL ARTERY

Brachial vv. Basilic v.

Brachial a. Humeral shaft

Triceps m.

Biceps brachii m.

Brachial a.

Brachialis m.

Doppler gate in center of brachial a.

Spectral trace of brachial a.

(Top) Transverse color Doppler ultrasound shows the brachial artery. Note the accompanying paired brachial veins. (Middle) Longitudinal color Doppler ultrasound shows the brachial artery. The normal diameter of the brachial artery at the antecubital fossa ranges from 5.5-6.0 mm. (Bottom) Longitudinal color Doppler spectral analysis ultrasound shows the brachial artery. Normal triphasic flow pattern of the large arteries is seen, compared to the biphasic flow of more distal arteries, but changes in temperature or even maneuvers, such as fist clenching, may dramatically change the characteristics of upper extremity waveforms, especially in and near the hands. Peak systolic velocity of the brachial artery ranges from 50-100 cm/sec (average 57 cm/sec); end diastolic velocity 7-12 cm/sec and a pulsatility index around 5 is considered normal.

574

Arm Vessels Upper Extremity

LONGITUDINAL COLOR DOPPLER, BRACHIAL VEIN

Brachial v.

Brachialis m.

Humeral shaft

Brachial v.

Brachialis m. Humeral shaft

Brachial v.

Doppler gate in brachial v.

Spectral flow in brachial v.

(Top) Longitudinal grayscale ultrasound shows the brachial vein. Normal brachial vein in the upper arm measures around 2.5-2.7 mm. The venous system of the upper limb is categorized as a superficial and deep system. Brachial vein constitutes the deep venous system. Brachial veins can be paired or singular. (Middle) Longitudinal color Doppler ultrasound shows the brachial vein. The ulnar and radial veins collect blood from the deep palmar arch and run in pairs alongside the corresponding arteries. They unite slightly above the elbow joint and flow into the brachial veins, which may be either paired or singular. (Bottom) Spectral Doppler ultrasound shows the flow pattern in the brachial vein. The flow is intermittent due to respiration. Examinations using proximal compression are not clinically relevant. Distal compression, which produces augmentation sounds, helps locate the veins.

575

Upper Extremity

Arm Vessels LONGITUDINAL US, DYNAMIC

Brachial v.

Humeral shaft

Brachialis m.

Brachial v.

Doppler gate in brachial v.

Spectral flow in brachial v.

Doppler gate in brachial v.

Normal venous pattern

Spectral flow of brachial v.

On augmentation

(Top) Longitudinal color Doppler ultrasound shows the brachial vein. Using Doppler mode, phasic flow during normal respiration is observed. (Middle) Spectral Doppler ultrasound shows the flow pattern in the brachial vein. In the upper extremities, including the subclavian vein, the behavior of venous flow during respiration is the opposite of what it is in the lower body region. During inspiration, pressure in the thorax decreases, and the venous blood flows toward the heart. During expiration, the thoracic pressure increases and the flow decreases, or even ceases, during deep respiration. (Bottom) Spectral Doppler ultrasound shows the phenomenon of augmentation, demonstrating the patency of the veins. It involves squeezing of the distal arm muscles (causing motion artifacts from movement), which will increase venous flow. Deep inspiration will have the same effect.

576

Arm Vessels

Cephalic v.

Upper Extremity

TRANSVERSE AND LONGITUDINAL US, CEPHALIC VEIN

Biceps m. Brachialis m.

Humeral shaft

Cephalic v.

Arm mm.

Cephalic v.

Biceps brachii m.

Brachialis m. Humeral shaft

(Top) Transverse grayscale ultrasound at the proximal arm shows the cephalic vein. The normal diameter of the cephalic vein just above the elbow measures 2.5-2.9 mm. (Middle) Longitudinal grayscale ultrasound at the proximal arm shows the cephalic vein. The most important veins of the arm are the cephalic vein and basilic veins. The superficial cephalic vein unites the deep-seated brachial and axillary veins. Assessment of valvular insufficiency has no clinical role in the upper limb vessels. (Bottom) Longitudinal color Doppler ultrasound in the distal arm shows the cephalic vein. Color flow duplex sonography allows ready assessment of the important upper arm veins (the paired brachial veins, cephalic veins, and basilic veins). Continuous color intensity makes it possible to exclude thromboses.

577

Upper Extremity

Elbow

GROSS ANATOMY Joint Capsule Attachments • Posterior ○ Proximally attaches to humerus proximal to olecranon fossa and capitellum; distally attaches to proximal ulna • Anterior ○ Proximally attaches to humerus proximal to coronoid and radial fossae; distally attaches to coronoid process and annular ligament • Anterior and posterior elbow fat pads are intracapsular but extrasynovial • Capsule of elbow is weakest anteriorly; it is strengthened on both sides by ligaments • Synovial recesses ○ Olecranon recesses – Largest; superior, medial, and lateral around olecranon process ○ Anterior humeral recess – Proximal to coronoid fossa ○ Annular recess – Surrounds radial neck ○ Ulnar collateral ligament recess – Deep to ligament ○ Radial collateral ligament recess – Deep to ligament ○ Capsule of elbow is weakest anteriorly – Capsule is strengthened on both sides by collateral ligaments

Ligaments • Ulnar collateral ligament ○ Extends from distal aspect of medial epicondyle to coronoid and olecranon portions of ulna ○ Separated from overlying common flexor tendon by thin layer of fat ○ 3 bands: Anterior, posterior, and transverse – Anterior band: Most important; cord-like, 4-6 mm thick, taut in extension, extends from medial epicondyle to coronoid process (sublime tubercle); divided into superficial and deep layers – Posterior band: Less important; fan-like and thinner, taut in flexion, extends from medial epicondyle to olecranon – Transverse band: Functionally unimportant; forms base of triangle between anterior and posterior bands • Radial collateral ligament ○ Triangular in shape ○ Apex on lateral epicondyle → blends distally with annular ligament ○ Lies deep to common extensor tendon ○ Provides origin for superficial head of supinator muscle • Annular ligament ○ Attached to anterior and posterior aspects of radial notch of ulna forming collar around radial head – Anterior attachment becomes taut in supination – Posterior attachment becomes taut in extreme pronation – Provides origin for superficial head of supinator muscle 578

Tendons • Triceps tendon ○ 3 heads combine to insert onto olecranon process ○ Medial fibers insert exactly on medial margin of olecranon ○ Lateral fibers may fan out as lateral cubital retinaculum to connect with ulna and antebrachial fascia • Biceps tendon ○ Flat tendon forms ~ 7 cm proximal to elbow joint ○ Twists 90° as it passes deep so that anterior surface faces laterally – Expands close to attachment into radial tuberosity; attachment area is ~ 3 cm² ○ Short and long heads have separate adjoined attachments ○ Also attaches to bicipital aponeurosis – Bicipital aponeurosis completely encircles ulnar forearm flexor muscles – Merges with investing fascia of forearm – May be important in stabilizing distal aspect of biceps tendon • Common extensor tendon ○ Arises from lateral epicondyle ○ Superficial to radial collateral ligament ○ Composed of extensor-supinator group – Extensor carpi radialis brevis, extensor carpi radialis longus, extensor digiti minimi, extensor digitorum communis • Common flexor tendon ○ Arises from medial epicondyle ○ Superficial to ulnar collateral ligament ○ Composed of flexor-pronator group – Flexor carpi radialis, flexor carpi ulnaris, flexor digitorum superficialis, pronator teres, palmaris longus

Bursae • Subtendinous olecranon bursa ○ Between triceps tendon and olecranon • Subcutaneous olecranon bursa ○ Between skin and olecranon process • Bicipitoradial bursa ○ Between biceps tendon and radial tuberosity • Radioulnar bursa ○ Between extensor digitorum and radiohumeral joint

ANATOMY IMAGING ISSUES Imaging Recommendations • • • • • •

High-frequency linear transducer Large amount of gel for superficial structures Examination is usually tailored to site of symptoms Lateral elbow is best seen with elbow fully or slightly flexed Medial elbow is best seen with elbow extended Distal biceps tendon is best seen with forearm in full supination • Distal biceps tendon insertion is best seen from posterior part of elbow with forearm fully pronated and elbow flexed with transducer aligned transversely over radial tuberosity • Effusion will displace fat pads away from bone

Elbow Upper Extremity

CORONAL ELBOW

Medial epicondyle of humerus Lateral epicondyle of humerus Common extensor t. Common flexor t. Radial collateral l.

Radial head

Ulnar collateral l.

Proximal radioulnar joint Ulnar coronoid Annular l.

Coronal section through the level of the epicondyles shows the collateral ligaments deep to the common tendon groups. Although the radial collateral ligament is shown, the section is too anterior to show most of the ulnar collateral ligament, which originates just posterior to the radial collateral ligament.

579

Upper Extremity

Elbow PROXIMAL ELBOW CROSS SECTION

Basilic v. Brachial a. Median n.

Biceps m. Cephalic v.

Brachialis m. Brachioradialis m. Pronator teres m. Radial n. Ulnar n.

Triceps m. and t.

Extensor carpi radialis longus m. Anterior fat pad Distal humerus Posterior fat pad

Median n.

Brachial a.

Biceps t. Basilic v. Pronator teres m. Common flexor t. Medial epicondyle Ulnar n. Ulnar recurrent a.

Cephalic v.

Brachialis m. Brachioradialis m. Radial n. Extensor carpi radialis longus m.

Cubital retinaculum Lateral epicondyle Triceps m. and t. Olecranon process

(Top) Axial graphic shows the supracondylar region of the humerus. The anterior and posterior fat pads are seen in the coronoid and olecranon fossae, respectively. The brachialis muscle accounts for the bulk of the anterior compartment of the distal arm. (Bottom) Axial graphic shows the epicondylar region of the distal humerus. The triceps muscle thins as its tendon attaches to the olecranon. The ulnar nerve and posterior ulnar recurrent artery are held in the cubital tunnel by the cubital retinaculum (formed from the ligament of Osborne and the fascia of flexor carpi ulnaris tendon).

580

Elbow

Cephalic v. Brachial a.

Upper Extremity

MID ELBOW CROSS SECTION

Biceps aponeurosis

Median n. Biceps t. Pronator teres m. Radial n. Common flexor t. Ulnar n.

Brachioradialis m. Brachialis m.

Flexor carpi ulnaris m. Ulnar collateral l. Triceps m. and t.

Extensor carpi radialis longus m. Common extensor t. Radial collateral l. Olecranon process

Brachial a. Median n. Pronator teres m.

Brachialis m. and t. Flexor digitorum superficialis m. Flexor carpi ulnaris m. Ulnar n. Posterior ulnar recurrent a. Flexor digitorum profundus m. Ulna Radial notch of ulna

Radial n.

Brachioradialis m.

Radial head Extensor carpi radialis brevis and longus mm. Annular l. Extensor digitorum m.

Lateral ulnar collateral l. Anconeus m.

(Top) Axial graphic immediately proximal to the elbow joint is shown. The common extensor tendon overlies the radial collateral ligament and may be difficult to distinguish at this level. The ulnar nerve has exited the cubital tunnel and is entering the flexor carpi ulnaris. (Bottom) Axial graphic at the level of the proximal radioulnar joint is shown. The articulating surfaces of the proximal radioulnar joint are well seen with the radial head being held in the radial notch of the ulna by the annular ligament. The lateral ulnar collateral ligament blends with the posterior aspect of the annular ligament.

581

Upper Extremity

Elbow DISTAL ELBOW CROSS SECTION

Brachial a.

Median n.

Palmaris longus m.

Pronator teres m.

Biceps t. Radial n., superficial and deep branch Brachioradialis m.

Flexor digitorum superficialis m.

Extensor carpi radialis longus m.

Flexor carpi ulnaris m.

Extensor carpi radialis brevis m.

Ulnar n. Flexor digitorum profundus m.

Supinator m. Extensor digitorum m.

Ulna

Extensor carpi ulnaris m. Anconeus m.

Flexor digitorum superficialis m.

Palmaris longus m.

Flexor carpi radialis m.

Pronator teres m.

Radial a. Median n. Flexor digitorum profundus m. Ulnar a.

Radial n., superficial branch Radius Supinator m.

Ulna Anconeus m. Extensor carpi ulnaris m. Extensor digitorum m.

Extensor carpi radialis longus m. Extensor carpi radialis brevis m. Posterior interosseous n.

(Top) Graphic shows the axial elbow at a level immediately above the radial tuberosity. The brachialis tendon inserts on the ulnar tuberosity, and the biceps tendon approaches its insertion on the radial tuberosity, which is more distal than the brachialis insertion. (Bottom) At the level of the proximal forearm, the muscles are starting to align themselves into the anterior (flexor) compartment and the posterior (extensor) compartment.

582

Elbow

Biceps t.

Upper Extremity

LONGITUDINAL US, ANTERIOR ELBOW

Brachialis m.

Humeral capitellum

Anterior fat pad Distal shaft of humerus

Biceps t.

Humeral capitellum

Brachialis m. Radius

Articular cartilage

Subcutaneous tissue Biceps t. Radial head Supinator m.

Humeral capitellum

Radial shaft

(Top) Longitudinal grayscale ultrasound shows the biceps tendon proximal to the elbow. Most biceps tendon tears occur near the shoulder. Tears of the distal end of the biceps tendon are uncommon and mostly occur when unexpected force is applied to the bent arm. (Middle) Longitudinal grayscale ultrasound shows the biceps tendon at the elbow. With a torn biceps tendon, a bulge in the arm ("Popeye" muscle) may appear. (Bottom) Longitudinal grayscale ultrasound shows the biceps tendon just distal to the elbow. The biceps tendon flattens and rotates 90° as it approaches the insertion into the posterior aspect of the radial tuberosity. The distal biceps tendon is best visualized on longitudinal section with the forearm fully supinated. To see the insertional area of distal biceps tendon, fully pronate the forearm and flex the elbow with transducer placed posteriorly over the radial tuberosity.

583

Upper Extremity

Elbow TRANSVERSE US, ANTERIOR ELBOW

Biceps t. Brachial a.

Brachioradialis m. Radial n.

Brachialis m. Humeral capitellum

Humeral trochlea

Cephalic v.

Brachioradialis m.

Brachial a. Brachialis m.

Radial n. Humeral capitellum Anterior coronoid recess

Humeral trochlea

Median n. Cephalic v.

Brachioradialis m. Radial head

Brachialis m.

Brachialis m. Humeral capitellum

(Top) Transverse grayscale ultrasound shows the proximal end of the antecubital fossa. Flexion and extension occur at the humeroulnar articulation, while pronation and supination involve pronation of the radius around the ulna. (Middle) Transverse grayscale ultrasound shows the midportion of the antecubital fossa. The median cubital vein unites the cephalic vein with the basilic vein. It is often used for venipuncture and venous access. It lies superficial to the bicipital aponeurosis. (Bottom) Transverse grayscale ultrasound shows the distal aspect of the antecubital fossa. The elbow joint is supplied by arteries from the profunda brachii, brachial arteries, and recurrent branches of the radial and ulnar arteries.

584

Elbow

Cephalic v.

Upper Extremity

TRANSVERSE US, ANTECUBITAL FOSSA

Biceps t. Brachioradialis m. Brachialis m.

Distal shaft of humerus

Biceps t. Brachioradialis m. Radial n. Radial recurrent a. Extensor carpi radialis longus m. Humeral capitellum

Medial antecubital v. Brachialis m. Humeral trochlea

Biceps t. Brachioradialis m. Radial recurrent a. Radial n. Extensor carpi radialis longus m.

Brachial v. Brachialis m.

Radial head

(Top) Transverse grayscale ultrasound shows the anterior elbow and proximal antecubital fossa. The antecubital fossa or cubital fossa is the area anterior to the elbow joint. (Middle) Transverse grayscale ultrasound shows the antecubital fossa at the midportion. The antecubital fossa contains the radial nerve, biceps brachii tendon, brachial artery, and median nerve from lateral to medial orientation. (Bottom) Transverse grayscale ultrasound shows the distal antecubital fossa. The bicipital aponeurosis forms the roof of the antecubital fossa. The superficial veins of the elbow lie above the bicipital aponeurosis.

585

Upper Extremity

Elbow TRANSVERSE US, BICEPS TENDON

Antecubital v. Biceps t. Brachioradialis m. Radial v.

Brachialis m.

Radial n.

Radial recurrent a.

Brachioradialis m.

Pronator teres m. Radial a. Extensor carpi radialis longus m.

Ulnar a.

Biceps t.

Supinator m.

Anconeus m.

Supinator m.

Ulna

Biceps t. insertion Radial tuberosity

(Top) Transverse grayscale ultrasound shows the biceps tendon at the upper antecubital fossa. The biceps tendon forms a few centimeters above the elbow joint. (Middle) Transverse grayscale ultrasound shows the biceps tendon at the midcubital fossa. The biceps tendon dips deeply and rotates as it passes to its insertion. The distal aspect of the biceps tendon and the insertion is difficult to see on ultrasound of the anterior surface of the elbow. Maximum supination will increase its visibility. (Bottom) Transverse grayscale ultrasound shows the biceps tendon insertional area. The insertional area of the biceps tendon is best seen with the elbow flexed and the wrist fully pronated. This positions the radial tuberosity posteriorly, allowing the insertional area to be viewed from the posterior aspect as shown here.

586

Elbow Upper Extremity

TRANSVERSE AND LONGITUDINAL US, ANTEROLATERAL ELBOW

Radial n. Brachioradialis m. Brachialis m. Extensor carpi radialis longus m.

Lateral epicondyle

Brachioradialis m. Radial n. Brachialis m. Extensor carpi radialis longus m.

Biceps m. Articular cartilage Brachialis m. Brachioradialis m. Fat pad

Pronator teres m. Radial head Capitellum of humerus

(Top) Transverse grayscale ultrasound shows the proximal anterolateral aspect of the elbow. The radial nerve is located on the anterolateral aspect of the elbow. It can be readily identified deep to the brachioradialis muscle. (Middle) Transverse grayscale ultrasound shows the midsection of the anterolateral elbow. The radial nerve passes anterior to the epicondyle deep to the brachioradialis muscle. (Bottom) Longitudinal grayscale ultrasound shows the anterolateral aspect of the elbow. The fat pads are intracapsular but extrasynovial. The synovial space lies deep to the fat pad on the bone surface. Distension of the fat pads allows these to become visible radiographically in elbow joint effusions.

587

Upper Extremity

Elbow LATERAL ELBOW

Brachialis m. Biceps m.

Common extensor t. origin

Extensor carpi radialis longus m. Anconeus m.

Extensor carpi radialis brevis Extensor digitorum and minimi mm.

Extensor carpi ulnaris m.

Side view of the lateral aspect of the elbow shows the extensor-supinator group and its common extensor tendon origin attaching to the lateral epicondyle and supracondylar aspect of the humerus. The common extensor tendon origin is composed of the extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris. The extensor digitorum origin and extensor carpi radialis brevis are very closely aligned in this section.

588

Elbow

Common extensor t. origin Common extensor tt. Radial head

Upper Extremity

LONGITUDINAL US, COMMON EXTENSOR ORIGIN

Radiohumeral joint Lateral epicondyle Radial collateral l. Humeral capitellum

Common extensor tt. Anular l. Supinator m. Radial head

Radial collateral l. Common extensor t. origin

Common extensor tt. Supinator m. Humeral capitellum Radial head

Radial collateral l.

(Top) Longitudinal grayscale US at the common extensor tendon origin is shown. Common extensor tendon origin has a broad attachment on the posteroinferior aspect of the lateral epicondyle. Tendon fibers cannot be separated into individual components at or near the insertion. Fibers from extensor digitorum make up most of the superficial portion, while fibers from extensor carpi radialis brevis make up most of the deep fibers. Contribution from extensor carpi ulnaris and extensor digiti minimi is only small. (Middle) Longitudinal grayscale US at common extensor tendon origin with the wrist in neutral position is shown. The radial collateral ligament is less distinct than the ulnar collateral ligament. It runs from the inferior aspect of the lateral epicondyle to gain attachment to the annular ligament. (Bottom) Longitudinal grayscale US at common extensor tendon origin with the wrist in extension is shown. Wrist extension slightly straightens extensor tendons, and dynamic movement during US can help separate movable tendons from fixed radial collateral ligament.

589

Upper Extremity

Elbow TRANSVERSE US, COMMON EXTENSOR TENDONS Common extensor origin

Extensor carpi radialis longus Lateral epicondyle

Extensor carpi radialis longus m. Common extensor tt. Extensor carpi radialis brevis m.

Humeral capitellum

Extensor carpi radialis longus m. Extensor carpi radialis brevis m. Humeral capitellum

(Top) Transverse grayscale ultrasound shows the common extensor origin. The common extensor tendon gains broad insertion onto the posterior aspect of the lateral epicondyle. (Middle) Transverse grayscale ultrasound shows the common extensor origin just distal to its attachment. The tendons begin to diverge just distal to the attachment though they are not yet separate. (Bottom) Transverse grayscale ultrasound shows the common extensor tendons even more distal to the above section. The individual components of the common tendon origin begin to be seen near the elbow joint.

590

Elbow

Common extensor t. origin

Upper Extremity

TRANSVERSE AND LONGITUDINAL US, LATERAL ELBOW

Anconeus m. Extensor digitorum, slip Lateral epicondyle

Brachioradialis m.

Common extensor origin Extensor carpi ulnaris t.

Articular cartilage Anconeus m. Extensor digitorum m. Radial head

Ulna

Pronator teres m.

Articular cartilage

Brachialis m. Humeral capitellum

Annular l. Radial head

(Top) Transverse grayscale ultrasound shows the common extensor tendon origin. The tendon caliber is often better appreciated on transverse, rather than on longitudinal, imaging. (Middle) Transverse grayscale ultrasound shows the common extensor tendons at the level of the radial head. The extensor tendons that originate from the common tendon origin can be traced distally, allowing them to be seen as separate tendons (extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and extensor carpi radialis brevis). (Bottom) Longitudinal grayscale ultrasound shows the common extensor tendon origin. The caliber of the common extensor tendon origin can be best appreciated on transverse imaging.

591

Upper Extremity

Elbow TRANSVERSE AND LONGITUDINAL US, ANTEROMEDIAL ELBOW

Median n. Pronator teres m. Brachial a. Medial epicondyle Brachialis m. Articular cartilage

Humeral trochlea

Pronator teres m. Brachialis m.

Humeral trochlea

Humeral shaft Coronoid fossa

Ulnar coronoid

Pronator teres Brachialis m. Humeral trochlea Ulnar coronoid

(Top) Transverse grayscale ultrasound shows the anteromedial aspect of elbow. The pronator teres has 2 heads: 1 from the common flexor origin (medial epicondyle) and supracondylar region and 1 from the medial side of the coronoid process. The median nerve lies deep to the pronator teres and may be trapped between these 2 heads as it enters the forearm. (Middle) Longitudinal grayscale ultrasound shows the anteromedial aspect of the elbow. Centrally at the junction of the distal humerus between the coronoid fossa anteriorly and the olecranon fossa posteriorly, the humerus is very thin and potentially simulating a bone defect. (Bottom) Longitudinal grayscale ultrasound shows the anteromedial aspect of the elbow. The brachialis muscle is closely applied to the anterior aspect of the elbow joint as it descends to its insertion on the ulnar tuberosity and the coronoid process of the ulna.

592

Elbow Upper Extremity

FLEXOR ASPECT

Pronator teres (anterior) and flexor carpi radialis m. Palmaris longus m. Brachialis t.

Biceps t.

Flexor digitorum superficialis m. Flexor carpi ulnaris m.

Posterior band of ulnar collateral l.

Transverse band of ulnar collateral l.

Biceps aponeurosis

Side view of the medial aspect of the elbow shows the flexor-pronator group and its common flexor tendons attaching to the medial epicondyle. The anterior band of the ulnar collateral ligament is deep to the common flexor tendons. The biceps aponeurosis blends with the anterior aspect of the common flexor muscle mass. The flexor digitorum profundus (not shown) arises from the proximal and midulna, posterior and deep to the flexor carpi ulnaris. It does not act on the elbow and is not part of the flexor-pronator group.

593

Upper Extremity

Elbow LIGAMENTS AROUND ELBOW

Posterior band Anterior band Transverse band

Annular l. Radial collateral l. Ulnar collateral l. Lateral ulnar collateral l. Accessory lateral collateral l.

Oblique cord

Common flexor t.

Olecranon

Ulnar n. Cubital retinaculum Posterior ulnar recurrent a.

Triceps m. and t.

(Top) Side view of the medial aspect of the elbow shows the 3 components of the ulnar collateral ligament: Anterior, posterior, and transverse band. (Middle) Anterior view of the elbow shows the radial collateral ligament complex, which is composed of the radial collateral ligament (provides varus stability), lateral ulnar collateral ligament (provides posterolateral stability), annular ligament (holds radial head against radial notch of the ulna), and accessory lateral collateral ligament (reinforces annular ligament). The oblique cord is part of the proximal radioulnar joint. (Bottom) Axial graphic shows the cubital tunnel. The ulnar nerve may be compressed within the cubital tunnel (cubital tunnel syndrome) by a mass, posttraumatic osseous deformity, or aneurysm of the recurrent ulnar artery. The ulnar nerve may also sublux out of the cubital tunnel leading to a low-grade traumatic neuritis and symptoms of carpal tunnel syndrome.

594

Elbow

Common flexor t. origin

Upper Extremity

LONGITUDINAL US, COMMON FLEXOR ORIGIN

Common flexor tt. Coronoid process Trochlea

Medial epicondyle

Ulnar collateral l.

Common flexor tendon origin Flexor tendons

Coronoid process

Medial epicondyle Ulnar collateral ligament

Trochlea

Anterior band of ulnar collateral l.

Coronoid process

Common flexor tt.

Trochlea

Medial epicondyle

(Top) Longitudinal grayscale ultrasound shows the common flexor tendon origin. These tendons (pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor carpi ulnaris) are inseparable at or close to the origin. (Middle) Longitudinal grayscale ultrasound shows the ulnar collateral ligament. The ulnar collateral ligament runs from the medial epicondyle to the coronoid process. The ulnar collateral ligament lies just deep to the flexor tendons and may be injured along with these tendons. (Bottom) Longitudinal grayscale ultrasound shows the ulnar collateral ligament anterior band. The anterior band (medial epicondylesublime tubercle) is the strongest component of the ulnar collateral ligament.

595

Upper Extremity

Elbow TRANSVERSE US, COMMON FLEXOR ORIGIN Common flexor t. origin

Flexor carpi ulnaris m., ulnar head Pronator teres m. Medial epicondyle

Common flexor t. origin

Humeral trochlea Pronator teres m.

Palmaris longus t.

Flexor digitorum superficialis m. Flexor carpi ulnaris m. Ulna

Pronator teres m.

Flexor digitorum profundus m. Ulnar n.

(Top) Transverse grayscale ultrasound shows the common flexor tendon origin. Tendinosis of the common flexor tendon is termed golfer's elbow or medial epicondylitis. Yet most people who get this injury are involved in other sports, particularly tennis. (Middle) Transverse grayscale ultrasound shows the common flexor tendons just distal to the elbow. The different components of the common flexor tendons can be seen by following the tendon distally and proximally. (Bottom) Transverse grayscale ultrasound shows the forearm more distal to the common flexor origin.

596

Elbow

Triceps m.

Upper Extremity

TRANSVERSE US, POSTERIOR ELBOW

Triceps t. Triceps m.

Ulnar n.

Lateral epicondyle, humerus Medial epicondyle, humerus Posterior fat pad

Triceps m. insertion

Anconeus m.

Ulnar n. Flexor carpi ulnaris t., ulnar head

Lateral epicondyle Olecranon

Medial epicondyle

Anconeus m.

Extensor carpi ulnaris m. Anular l. Radial head

Olecranon

Interosseus a. and v.

(Top) Transverse grayscale ultrasound shows the posterior elbow. There are 3 fat pads in the elbow: 2 anterior fat pads (radial and coronoid fossa) and 1 posterior fat pad (olecranon fossa). The synovium extends from the articular surface of the humerus and lines these fossae, i.e., it lies deep to the fat pads, which are enclosed by the elbow capsule. The fat pads therefore are intraarticular but extrasynovial. Fluid distension of the synovial cavity elevates the fat pads. (Middle) Transverse grayscale ultrasound shows the elbow at the level of the olecranon. The anconeus is a small muscle on the posterior aspect of the elbow that extends from the lateral epicondyle to the olecranon. (Bottom) Transverse grayscale ultrasound shows the proximal radioulnar joint. The annular ligament is attached to the anterior and posterior margins of the radial notch of the ulna.

597

Upper Extremity

Forearm

IMAGING ANATOMY Flexors • Deep flexor group ○ Flexor digitorum profundus – Origin: Proximal ulna – Insertion: Index, middle, ring, and little finger distal phalangeal bases ○ Flexor pollicis longus – Origin: Radius, interosseous membrane, coronoid process – Insertion: Thumb distal phalangeal base ○ Pronator quadratus – Origin: Medial distal volar ulna – Insertion: Lateral distal dorsal radius • Superficial ○ Flexor carpi radialis (FCR) – Origin: Medial epicondyle/common flexor tendon – Insertion: 2nd metacarpal (MC) base; slip to 3rd MC base ○ Palmaris longus (PL) – Origin: Medial epicondyle/common flexor tendon – Insertion: Volar distal flexor retinaculum and palmar aponeurosis ○ Flexor carpi ulnaris (FCU) – Origin: Medial epicondyle (humeral head) and medial proximal ulna (ulnar head) – Insertion: Pisiform ○ Flexor digitorum superficialis – Origin: Medial epicondyle and ulnar coronoid process (humeroulnar head); volar proximal radius (radial head) – Insertion: Middle phalanges index, middle, ring, and little fingers

Extensors • Deep ○ Abductor pollicis longus (APL) – Origin: Dorsal lateral ulna, dorsal midradius – Insertion: 1st MC radial base ○ Extensor pollicis brevis (EPB) – Origin: Dorsal midradius – Insertion: Thumb proximal phalangeal base ○ Extensor pollicis longus (EPL) – Origin: Dorsal midulna – Insertion: Thumb distal phalanx base – Variant: Fused with EPB ○ Extensor indicis – Origin: Dorsal midulna and interosseous membrane – Insertion: Extensor hood of index finger • Superficial ○ Extensor carpi radialis longus (ECRL) – Origin: Lateral epicondyle/common extensor tendon – Insertion: Dorsal radial 2nd MC ○ Extensor carpi radialis brevis (ECRB) – Origin: Lateral epicondyle/common extensor tendon – Insertion: Dorsal radial 3rd MC ○ Extensor digitorum (ED) – Origin: Lateral epicondyle/common extensor tendon 598

– Insertion: Middle and distal phalanges of index, middle, ring, little fingers ○ Extensor digiti minimi (EDM) – Origin: Lateral epicondyle/common extensor tendon – Insertion: Extensor hood of little finger proximal phalanx with slip to ring finger ○ Extensor carpi ulnaris (ECU) – Origin: Common extensor tendon and dorsal ulna – Insertion: Dorsal ulnar 5th MC base

Anomalous Muscles • May present as soft tissue mass ○ May create neural compression • Accessory PL ○ Superficial to FD tendons, medial to FCR • ED manus brevis ○ Arises from distal radius or dorsal radiocarpal ligament ○ Inserts on 2nd MC ○ May be tender or present as mass • Extensor carpi radialis intermedius ○ Arises from humerus or as accessory slip from ECRB or ECRL ○ Inserts on 2nd &/or 3rd MC • Extensor carpi radialis accessory ○ Arises from humerus or ECRL ○ Inserts on 1st MC bone, abductor pollicis brevis (APB), or 1st dorsal interosseous muscle

ANATOMY IMAGING ISSUES Imaging Pitfalls • Many variations of flexor and extensor muscles and tendons • EPB may be absent or fused with EPL • PL absent in 10%; short tendon with extended muscle belly may compress median nerve • Multiple tendon slips can mimic longitudinal tendon tears (e.g., APL) • Small amount of fluid common in tendon sheath (e.g., ECRB, ECRL, ECU)

Imaging Issues • APL and EPB intersect ECRB and ECRL just proximal to extensor retinaculum; may impinge at musculotendinous intersection ("intersection syndrome") • Sites of radial nerve entrapment in forearm ○ Posterior interosseous nerve within radial tunnel under arcade of Frohse ○ Posterior interosseous nerve between deep and superficial heads of supinator muscle ○ Superficial radial nerve between brachioradialis and ECRL in mid- to distal forearm • Sites of ulnar nerve entrapment in forearm ○ Cubital tunnel ○ Beyond cubital tunnel, it passes between humeral and ulnar origins of FCU muscle • Sites of medial nerve entrapment in forearm ○ Between heads of pronator teres

Forearm

Brachialis m.

Upper Extremity

COMMON EXTENSOR TENDON

Biceps m.

Common extensor t.

Extensor carpi radialis longus m.

Anconeus m.

Extensor digitorum and minimi mm.

Extensor carpi ulnaris m.

Extensor carpi radialis brevis

Graphic of a side view of the lateral aspect of the elbow shows the extensor-supinator group and its common extensor tendon origin attached to the lateral epicondyle and supracondylar aspect of the humerus. The common extensor tendon origin is composed of the extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris.

599

Upper Extremity

Forearm TRANSVERSE US, ANTERIOR FOREARM

Radial a. and v. Flexor carpi radialis m. Brachioradialis m. Extensor carpi radialis longus m.

Extensor carpi radialis brevis m.

Radial n. Flexor digitorum superficialis m. Radius Median n.

Supinator m.

Flexor carpi radialis m. Palmaris longus m. Brachioradialis m.

Flexor digitorum superficialis m.

Extensor carpi radialis brevis m. Flexor digitorum superficialis m.

Median n. Flexor digitorum profundus m.

Radius Flexor pollicis longus m.

Anterior interosseous neurovascular bundle

Interosseous membrane

Ulna

Radial a. and v. Flexor carpi radialis m. Flexor digitorum superficialis m. Flexor pollicis longus m. Radius Interosseous membrane

Median n. Flexor digitorum profundus m. Pronator quadratus m. Ulna

(Top) Transverse grayscale ultrasound shows the anterior aspect of the proximal 1/3 of the forearm. The anterior aspect of the forearm consists of 5 flexor muscles: 3 superficial and 2 deep. (Middle) Transverse grayscale ultrasound shows the anterior aspect of the midforearm. The 3 superficial flexor muscles are, from ulnar to radial aspect, the flexor carpi ulnaris, flexor digitorum superficialis, and flexor carpi radialis. The 2 deep flexor muscles are flexor digitorum profundus and flexor pollicis longus. (Bottom) Transverse grayscale ultrasound shows the anterior aspect distal 1/3 of the forearm. The pronator quadratus is an easily recognized muscle that helps to pronate the forearm.

600

Forearm

Flexor carpi radialis m. Flexor digitorum superficialis m.

Upper Extremity

TRANSVERSE US, ANTEROMEDIAL FOREARM

Pronator teres m. Brachioradialis m. Median n. Palmaris longus m. Flexor digitorum profundus m.

Flexor carpi ulnaris m.

Radius Ulna

Flexor digitorum superficialis m. Pronator teres m. Flexor carpi ulnaris m. Median n. Flexor digitorum profundus m. Radius Interosseous membrane

Ulna

Ulnar a.

Flexor digitorum superficialis m. Median n. Flexor digitorum profundus m. Flexor carpi ulnaris m. Pronator quadratus m. Flexor pollicis longus m.

Ulna Interosseous membrane

Radius

(Top) Transverse grayscale ultrasound shows the anteromedial aspect of the proximal 1/3 of the forearm. The main flexors of the wrist are contained along the anterior and anteromedial aspect of the forearm. These are divided into 2 groups: Superficial and deep. (Middle) Transverse grayscale ultrasound shows the anteromedial aspect of the middle 1/3 of the forearm. The superficial group consists of the flexor carpi ulnaris, the flexor digitorum superficialis, and the flexor carpi radialis. The deep group consists of the flexor digitorum profundus and the flexor pollicis longus. (Bottom) Transverse grayscale ultrasound shows the anteromedial aspect of the distal 1/3 of the forearm. The ulnar nerve lies deep to the flexor carpi ulnaris, while the median nerve lies between the flexor digitorum superficialis and flexor digitorum profundus muscles.

601

Upper Extremity

Forearm TRANSVERSE US, ANTEROLATERAL FOREARM

Extensor carpi radialis longus m.

Extensor carpi radialis brevis m.

Supinator m.

Extensor carpi radialis brevis m.

Radius

Brachioradialis m.

Radial n. Radius

Brachioradialis m.

Pronator teres m.

Extensor digitorum m. Flexor digitorum superficialis m.

Extensor carpi radialis brevis t. Subcutaneous branch of radial n. Tendon of brachioradialis Flexor carpi radialis m. Radial a. Extensor pollicis longus t. Median n. Flexor digitorum superficialis m.

Flexor digitorum profundus m.

Flexor pollicis longus m.

(Top) Transverse grayscale ultrasound shows the anterolateral proximal 1/3 of the forearm. The anterolateral aspect of the forearm comprises 4 extensor muscles running along the course of the radius. (Middle) Transverse grayscale ultrasound shows the anterolateral aspect of the middle 1/3 of the forearm. The anterolateral group comprises the extensor carpi radialis brevis, extensor carpi radialis longus, brachioradialis, and the pronator teres. (Bottom) Transverse grayscale ultrasound shows the anterolateral aspect of the distal 1/3 of the forearm.

602

Forearm Upper Extremity

ANTERIOR FOREARM, ARTERIES AND NERVES

Brachialis m.

Musculocutaneous n.

Biceps m. and t.

Brachial a.

Median n. Radial n.

Common flexor t.

Brachioradialis m. Pronator teres Radial n., deep branch

Radial n., superficial branch

Biceps aponeurosis

Anterior interosseus n. Radial a. Ulnar a.

Median n.

Extensor mm.

Pronator teres m.

Graphic of the anterior view of the cubital fossa shows the median nerve and brachial artery passing underneath the biceps aponeurosis. The anterior interosseus nerve arises from the median nerve as the median nerve passes between the 2 heads of the pronator teres muscle. The radial nerve, deep to the brachioradialis muscle, is seen dividing into the superficial and deep branches.

603

Upper Extremity

Forearm COMMON FLEXOR TENDON

Pronator teres and flexor carpi radialis m. Brachialis t.

Palmaris longus m. Flexor digitorum superficialis m.

Biceps t. Flexor capri ulnaris m.

Posterior band of ulnar collateral l.

Transverse band of ulnar collateral l.

Biceps aponeurosis

Graphic of the side view of the medial aspect of the elbow shows the flexor-pronator group and the common flexor tendon origin attaching to the medial epicondyle. The anterior band of the ulnar collateral ligament is deep to the common flexor tendon. The biceps aponeurosis blends with the anterior aspect of the common flexor muscle mass. The flexor digitorum profundus arises from the proximal ulna, posterior and deep to the flexor carpi ulnaris. It does not act on the elbow and is not part of the flexor-pronator group.

604

Forearm

Extensor carpi ulnaris m. Posterior interosseus n. Extensor digiti minimi m.

Upper Extremity

TRANSVERSE US, POSTERIOR ASPECT

Extensor digitorum m.

Extensor carpi radialis brevis m. Supinator m. Radial n., deep branch

Ulna Extensor pollicis longus m. Radius

Abductor pollicis longus m.

Extensor carpi ulnaris m. Extensor digiti minimi m. Extensor digitorum m. Radius

Ulna

Abductor pollicis longus m. Extensor indicis m. Interosseus membrane Extensor pollicis longus m. Extensor pollicis brevis m.

Extensor digiti minimi m. Extensor carpi radialis t. Radius Ulna Extensor digitorum t. Extensor carpi ulnaris m. Extensor pollicis brevis m. Extensor indicis m. Extensor pollicis longus m.

(Top) Transverse grayscale ultrasound shows the posterior aspect of the proximal 1/3 of the forearm. The posterior aspect of the forearm contains the extensor muscles. They are contained in 2 groups: Superficial and deep. (Middle) Transverse grayscale ultrasound shows the posterior aspect of the middle 1/3 of the forearm. The superficial group comprises (ulnar to radial) the extensor carpi ulnaris, extensor digiti minimi, and extensor digitorum. The deep group comprises the extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus. (Bottom) Transverse grayscale ultrasound shows the posterior aspect of the distal 1/3 of the forearm.

605

Upper Extremity

Forearm Vessels

GROSS ANATOMY Arteries • Brachial artery ○ Continuation of axillary artery ○ Located in cubital fossa, medial to biceps tendon and deep to biceps aponeurosis ○ Accompanies median nerve ○ Gives off 2 medial branches, which descend toward elbow joint on medial side of brachial artery and contribute to anterior and posterior anastomosis around elbow ○ Brachial artery divides into radial artery and ulnar artery in cubital fossa • Radial artery ○ Medial to distal biceps tendon ○ Covered by brachioradialis muscle ○ Distally, leaves forearm and moves laterally, crossing floor of anatomical snuffbox ○ Terminates in deep palmar arch of hand ○ Branches – Radial recurrent artery: Runs proximally along lateral side of elbow to form anastomosis with branches of deep brachial artery – Muscular branches to lateral side of forearm – Distal anastomotic branches: Palmar carpal arch, superficial palmar arch, and dorsal carpal arch • Ulnar artery ○ Proximally deep to pronator teres ○ Distally lies on flexor digitorum profundus and lateral to ulnar nerve ○ Anterior and posterior ulnar recurrent arteries form anastomosis around medial side of elbow with branches of brachial artery ○ Branches – Common interosseus artery: Arises in distal aspect of cubital fossa, 2 cm below origin of ulnar artery from brachial artery – Anterior interosseus artery: Runs distally on interosseus membrane and ends in dorsal carpal arch; reaches posterior compartment by means of perforating branches; terminates at wrist joint after piercing interosseus membrane; supplies deep muscles of forearm – Posterior interosseus artery: Enters posterior compartment proximal to interosseus membrane, between supinator and abductor pollicis longus, and supplies posterior muscles – Muscular branches to medial side of forearm – Distal anastomotic branches: Palmar carpal arch, dorsal carpal arch

Veins • Veins of upper limb are variable in number and position ○ In hand, there are 2 sets of veins: Deep and superficial – Deep veins follow arteries traveling as paired venae comitantes; radial, ulnar, and brachial veins ○ Superficial veins of hand and forearm are drained by cephalic and basilic veins • Cephalic vein

606

○ Begins on lateral aspect of wrist by draining blood from venous plexus on dorsum of hand – Ascends along lateral side of forearm and upper arm in superficial fascia – As vein drains cranially, it receives tributaries from anterior and posterior aspects of forearm – Cephalic vein lies laterally in superficial fascia of antecubital fossa and gives off median cubital vein – Median vein of forearm flows into medial cubital vein • Basilic vein ○ Begins on medial side of wrist and drains medial part of venous plexus on dorsum of hand ○ Basilic vein passes upward on medial side of forearm, receiving anterior and posterior tributaries ○ Passes to anteromedial aspect of elbow where it receives median cubital vein

ANATOMY IMAGING ISSUES Imaging Recommendations • Venous examination ○ Examination of upper limb veins is normally performed with patient supine and arm abducted to ~ 90° ○ Use of high-frequency linear transducer (5-10 MHz) is recommended – Determination of compressibility and flow pattern is normally performed – Phasicity with respiration noted ○ Augmentation of flow is obtained by manual compression of forearm ○ Alternatively, augmentation can be achieved by asking patient to clench fist • Arterial examination ○ In patients with possible arterial compression syndromes, arteries are examined in various degrees of abduction so that any compression may be accentuated ○ If angle of insonation is > 60°, Doppler and color sensitivity ↓ ○ Keep Doppler gate in center of lumen for peak flow velocity ○ Match color signal scale with flow velocity

Imaging Pitfalls • Gold standard for assessment of accuracy of arterial Doppler ultrasound is usually arteriography

CLINICAL IMPLICATIONS Clinical Importance • Brachial artery in antecubital fossa may be used for arterial access for angiography • High takeoff of radial artery from brachial artery is common anatomical variant ○ On arterial Doppler studies, if either radial or ulnar artery is difficult to trace distally from elbow, then artery should be sought at wrist and followed proximally • Hemodialysis arteriovenous fistulae are generally constructed by joining cephalic veins to radial artery at wrist

Forearm Vessels Upper Extremity

FOREARM ARTERIES

Brachial a.

Deep branch of brachial a. Superior ulnar collateral a.

Inferior ulnar collateral a.

Interosseus recurrent a.

Posterior ulnar recurrent a.

Radial recurrent a. Anterior ulnar recurrent a.

Common interosseus a.

Posterior interosseus a.

Radial a.

Anterior interosseus a.

Ulnar a.

Graphic shows the brachial artery, the major artery of the arm. It divides into the radial and ulnar arteries in the proximal forearm.

607

Upper Extremity

Forearm Vessels TRANSVERSE US, PROXIMAL FOREARM

Brachioradialis m. Antecubital v. Pronator teres m. Median n. Extensor carpi radialis longus m. Extensor carpi radialis brevis m. Radial n., superficial branch

Brachial a. Basilic v. Radius

Supinator m.

Brachioradialis m. Radial a. Pronator teres m. Extensor carpi radialis longus m. Radial n., subcutaneous branch Extensor carpi radialis brevis m. Radius

Flexor digitorum superficialis m. Median n. Ulnar a. Supinator m.

Brachioradialis m. Cephalic v. Radial v. Radial a. Median n. Extensor carpi radialis brevis m.

Ulnar a. Ulnar v.

Supinator m.

(Top) Transverse grayscale ultrasound shows forearm vessels at the volar aspect of the proximal forearm. The brachial artery divides into the radial and ulnar arteries in the proximal arm. The forearm veins are very variable in number and appearance. Both main veins should be assessed when investigating deep vein thrombosis. (Middle) Transverse grayscale ultrasound shows radial vessels on the volar aspect of proximal forearm just distal to bifurcation of the brachial artery. (Bottom) Transverse grayscale ultrasound shows radial vessels on the volar aspect of midforearm. The superficial branch of the radial nerve roughly follows the radial artery, while the ulnar nerve closely follows the ulnar artery.

608

Forearm Vessels

Radial vv.

Upper Extremity

TRANSVERSE US, RADIAL ARTERY

Cephalic v. Radial n., superficial branch Extensor carpi radialis longus m.

Pronator teres m.

Flexor carpi radialis m. Radial a. Flexor digitorum superficialis m.

Radius

Ulnar vv. Flexor digitorum superficialis m.

Flexor carpi ulnaris m. Ulnar n. Median n.

Ulnar a. Flexor digitorum profundus m.

Flexor carpi radialis m. Flexor digitorum superficialis m. Radial v. Radial a. Cephalic v.

Median n. Flexor digitorum profundus m.

Radius Pronator quadratus m. Flexor pollicis longus m.

(Top) Transverse grayscale ultrasound shows the radial artery on the volar aspect of the midforearm. The radial artery serves as a landmark to divide the anterior (flexor) and posterior (extensor) compartments of the forearm. (Middle) Transverse grayscale ultrasound shows the ulnar artery on the volar aspect of the midforearm. The ulnar artery is more variable in position than the radial artery. It may arise more proximal in the arm region. When the ulnar artery arises proximally, it often has an aberrant course and may lie superficial to the flexor muscles in the forearm. (Bottom) Transverse grayscale ultrasound shows the radial artery on the volar aspect of distal forearm. The radial artery is sometimes used instead of the long saphenous vein in coronary artery surgery. The caliber of the artery can be checked prior to surgery by ultrasound.

609

Upper Extremity

Forearm Vessels TRANSVERSE AND LONGITUDINAL US, ULNAR ARTERY Flexor digitorum superficialis m. Flexor carpi ulnaris m. Ulnar a. Ulnar n. Flexor digitorum profundus m. Pronator quadratus m.

Ulnar vv. Ulna

Ulnar a.

Ulna

Doppler gate in ulnar a.

(Top) Transverse grayscale ultrasound shows the ulnar artery on the volar aspect of the distal forearm. The Allen test is performed clinically to check dual arterial supply to the hand prior to radial artery cannulation or excision. (Middle) Longitudinal color Doppler ultrasound shows the ulnar artery on the volar aspect of distal forearm. Flow velocity and direction is denoted by the color signal. The normal diameter of the ulnar artery (1.9-2.2 mm) is measured near the wrist. (Bottom) Longitudinal spectral Doppler analysis of the ulnar artery on the volar aspect of the distal forearm is shown. The spectral gate is placed in the middle of the arterial lumen. Normal unidirectional flow is present with a systolic peak and good diastolic flow. The peak systolic velocity of the ulnar artery ranges between 40-90 cm/sec, while end-diastolic velocity ranges between 5-12 cm/sec. Pulsatility index is variable, ranging 3.9-5.0.

610

Forearm Vessels

Radial a.

Upper Extremity

ARTERIES AT DISTAL FOREARM AND HAND

Doppler gate in radial a.

Spectral trace, radial a.

Ulnar a., superficial palmar arch Ulnar a., deep palmar arch

Radial a.

Ulnar a.

Radial a.

(Top) Longitudinal color Doppler ultrasound shows the radial artery on the volar aspect of the distal forearm just proximal to the wrist. The normal diameter of the radial artery just proximal to the wrist ranges 2.2-2.8 mm. (Middle) Spectral analysis shows the radial artery just proximal to the wrist. Spectral analysis is best performed with the artery visualized longitudinally rather then transversely. The normal angle corrected peak systolic velocity of the radial artery ranges 40-90 cm/sec, the end diastolic velocity ranges 5-10 cm/sec, and pulsatility index is variable, ranging 3.9-5.0. (Bottom) Graphic shows the distal aspect of the radial and ulnar arteries in the forearm and their terminal course in the wrist and hand to form the superficial and deep palmar arterial arches.

611

Upper Extremity

Forearm Vessels VENOUS SYSTEM, ANTERIOR

Cephalic v.

Accessory cephalic v.

Basilic v.

Intermediate (median) basilic v.

Intermediate (median) cephalic v.

Cephalic v.

Basilic v.

Accessory cephalic v.

Intermediate (median) antebrachial v.

Perforating vv.

Radial v.

Intercapitular vv.

Palmar digital vv.

Graphic shows the superficial venous system of the forearm. The most important collecting vein of the forearm and arm is the cephalic vein. The cephalic vein proceeds from the radial margin of the dorsal venous network of the hand and follows a course diagonally above the radial margin of the forearm to the cubital fossa. From there, it continues laterally in the distal arm, moving anteromedially in the upper arm to enter the axillary vein just below the clavicle. It contains 6-10 valves. The ulnar and radial veins collect blood from the deep palmar arch and course in pairs alongside the corresponding arteries. Blood is continuously shunted from these superficial veins in the subcutaneous tissue to deep veins via the perforating veins. Although the upper extremities have many communicating veins, they have no clinical significance and are therefore not specifically named and located.

612

Forearm Vessels Upper Extremity

VENOUS SYSTEM, POSTERIOR

Accessory cephalic v.

Superficial vv. of forearm

Cephalic v. Basilic v.

Cephalic v. Basilic v.

Dorsal metacarpal vv. Dorsal venous arch

Intercapitular vv.

Dorsal digital vv.

Graphic shows the posterior view of the superficial venous system of the forearm. The basilic vein starts from the ulnar margin of the dorsal venous plexus and travels onward to the bend of the elbow, where it is joined by the cephalic vein. It contains 4-8 valves. There are 2 additional small branches that pass superficially on the volar side of the forearm, the median antebrachial vein and the median cubital vein, which flow into the cephalic vein and the basilic vein somewhat above the bend of the elbow. Although the upper extremities have many communicating veins, they have no clinical significance and are therefore not specifically named and located.

613

Upper Extremity

Wrist

TERMINOLOGY Definitions • Articulation complex comprising distal radioulnar, radiocarpal, ulnocarpal, pisotriquetral, midcarpal, and carpometacarpal joints

IMAGING ANATOMY Osseous Structures • Distal radius: Lister tubercle on dorsal surface • Distal ulna: Ulnar variance refers to length of ulnar head relative to distal radius: Ulnar minus or ulnar plus • Proximal carpal row: Scaphoid, lunate, triquetrum, pisiform ○ Scaphoid: Proximal and distal pole separated by waist – Tuberosity = volar prominence of distal pole ○ Lunate: 1/2 moon-shaped ○ Triquetrum: Triangular-shaped ○ Pisiform: Pea-shaped, sesamoid-type bone to which flexor carpi ulnaris attaches and continues distally as pisohamate and pisometacarpal ligaments • Distal carpal row: Trapezium, trapezoid, capitate, hamate ○ Trapezium: Saddle-shaped bone linking carpus and thumb ○ Trapezoid: Wedge-shaped bone ○ Capitate: Head (proximal), neck (midportion), and body (bulky distal portion) ○ Hamate: Hook (hamulus) arises from palmar surface

Retinacula

• Extrinsic (on palmar or volar aspects of wrist) or intrinsic (between carpal bones) • Major wrist stabilizers: Volar ligaments • Extrinsic ligaments ○ Palmar: Radioscaphocapitate, radiolunotriquetral, radioscapholunate, ulnotriquetral, ulnolunate, scaphotriquetral ○ Dorsal: Scaphotriquetral, radiotriquetral, ulnotriquetral, radial collateral • Intrinsic ligaments ○ Proximal interosseous: Scapholunate, lunotriquetral ○ Distal interosseous: Trapeziotrapezoid, trapeziocapitate, capitohamate

• Flexor retinaculum ○ Also called transverse carpal ligament: Attached to pisiform and hook of hamate, scaphoid, and trapezium • Extensor retinaculum ○ Attaches to ulnar styloid process, triquetrum, and pisiform medially; crosses obliquely to attach to Lister tubercle and radial styloid process laterally – Sends septa to radius, creating 6 compartments for extensor tendons ○ Compartment contents – 1st: Abductor pollicis longus and extensor pollicis brevis – 2nd: Extensor carpi radialis longus and brevis – 3rd: Extensor pollicis longus – 4th: Extensor digitorum and extensor indicis – 5th: Extensor digiti minimi – 6th: Extensor carpi ulnaris

Muscles and Tendons

Anatomic Spaces

• Flexors, deep ○ Flexor digitorum profundus: Originated from ulna; inserted to index, middle, ring, and little finger distal phalangeal bases ○ Flexor pollicis longus: Originated from radius, interosseous membrane, and coronoid process of ulna; inserted to distal phalangeal base of thumb • Flexors, superficial ○ Flexor carpi radialis: Originated from medial epicondyle; inserted to 2nd metacarpal base ○ Palmaris longus: Originated from medial epicondyle; inserted to palmar aponeurosis ○ Flexor carpi ulnaris: Originated from medial epicondyle and medial olecranon/proximal ulna; inserted to pisiform ○ Flexor digitorum superficialis: Originated from medial epicondyle and coronoid process of ulna and anterior radius; inserted to middle phalangeal bases of digits 2-5

• Carpal tunnel ○ Margins: Carpal bones (dorsal margin); flexor retinaculum (volar margin); pisiform and hook of hamate (ulnar margin); scaphoid and trapezium (radial margin); radiocarpal joint (proximal margin); and metacarpal base (distal margin) – Contents: Flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, median nerve • Guyon canal ○ Margins: Fascial extension from flexor retinaculum, volar carpal ligament (volar margin), pisiform and flexor carpi ulnaris (ulnar margin), flexor retinaculum (radial and dorsal margins) – Contents: Ulnar artery and vein, ulnar nerve

Ligaments

614

• Extensors, deep ○ Abductor pollicis longus: Originated from ulna; inserted to radial aspect 1st metacarpal base ○ Extensor pollicis brevis: Originated from radius; inserted to proximal phalangeal base of thumb ○ Extensor pollicis longus: Originated from midulna; inserted to distal phalangeal base of thumb ○ Extensor indicis: Originated from midulna; joins ulnar side of extensor digitorum tendon inserting into 2nd digit extensor hood • Extensors, superficial ○ Extensor carpi radialis longus: Originated from lateral supracondylar ridge of humerus; inserted to dorsal radial 2nd metacarpal base ○ Extensor carpi radialis brevis: Originated from lateral humeral epicondyle; inserted to dorsal radial 3rd metacarpal base ○ Extensor digitorum: Originated from lateral humeral epicondyle; inserted to distal phalangeal bases of digits of 2-5 ○ Extensor digiti minimi: Originated from lateral humeral epicondyle; inserted to extensor hood of little finger ○ Extensor carpi ulnaris: Originated from lateral humeral epicondyle; inserted to 5th metacarpal base

Wrist Upper Extremity

CARPAL BONES AND WRIST COMPARTMENTS

Capitate 1st metacarpal Hamate Pisiform

Triquetrum

Trapezoid 1st carpometacarpal joint Trapezium Scaphoid

Lunate

Radial styloid process

Ulna

Distal radioulnar joint

Common carpometacarpal compartment

1st carpometacarpal compartment

Midcarpal compartment Pisotriquetral compartment Radiocarpal compartment

Distal radioulnar compartment

(Top) Graphic shows the bones of the wrist joint. (Bottom) Graphic shows the 5 different wrist compartments. Distal radioulnar compartment is separated from the radiocarpal compartment by the triangular fibrocartilage complex. Pisotriquetral compartment is separated from the radiocarpal compartment in 20%. Midcarpal compartment is separated from the radiocarpal compartment by the scapholunate and lunotriquetral ligaments and typically communicates with the carpometacarpal joints. First carpometacarpal compartment is separated from the common carpometacarpal compartment by the trapeziometacarpal ligament.

615

Upper Extremity

Wrist DORSAL TENDONS AND TENDON SHEATHS

Extensor carpi radialis brevis t.

Extensor digitorum t.

Extensor carpi radialis longus t. Extensor indicis t. Extensor pollicis longus t.

Extensor carpi ulnaris t. Extensor digiti minimi t.

Abductor pollicis longus t.

Extensor pollicis brevis t.

Extensor retinaculum

Compartment 1: Abductor pollicis longus, extensor pollicis brevis Compartment 3: Extensor pollicis longus

Compartment 6: Extensor carpi ulnaris Compartment 5: Extensor digiti minimi Compartment 4: Extensor digitorum, extensor indicis

Compartment 2: Extensor carpi radialis longus, Extensor carpi radialis brevis

(Top) Dorsal extensor tendons pass deep to the extensor retinaculum, separated into 6 compartments by fibrous attachments of the retinaculum to underlying bone. Compartment contents include abductor pollicis longus and extensor pollicis brevis, extensor carpi radialis longus and brevis, extensor pollicis longus, extensor digitorum and extensor indicis, extensor digiti minimi, and extensor carpi ulnaris. (Bottom) Separate tendon sheaths enclose the dorsal extensor tendons in compartments 1-6 individually.

616

Wrist

Extensor digitorum t. slips

Extensor pollicis longus t.

Extensor digiti minimi t.

Extensor carpi radialis brevis t.

Extensor carpi ulnaris t.

Extensor carpi radialis longus t.

Upper Extremity

TENDONS: RELATIONS TO DORSAL AND VOLAR WRIST

Extensor indicis t. Extensor pollicis brevis t.

Flexor digitorum profundus t. Ulnar n. Flexor carpi ulnaris

Abductor pollicis longus t.

Flexor pollicis longus t. Flexor carpi radialis t. Median n.

Flexor digitorum superficialis t.

Extensor digitorum t. slips Extensor digiti minimi t.

Palmaris longus t.

Extensor pollicis longus t.

Extensor carpi radialis brevis and longus t.

Extensor carpi ulnaris t. Abductor pollicis longus t. Extensor indicis t. Flexor digitorum t.

Extensor pollicis brevis t. Flexor pollicis longus t.

Abductor digiti minimi t. Flexor carpi radialis t. Ulnar n.

Volar carpal l.

Median n. Flexor retinaculum

(Top) Graphic representation shows tendons in the proximal wrist. Extensor tendons are deep to the extensor retinaculum, whereas flexor tendons are proximal to the flexor retinaculum at this level in the wrist. (Bottom) Midcarpal tunnel is shown. Median nerve is slightly flattened as it passes deep to the flexor retinaculum and remains superficial to the flexor pollicis longus. Ulnar nerve, artery, and veins lie lateral to the pisiform and may divide near the pisiform into deep and superficial branches.

617

Upper Extremity

Wrist TRANSVERSE US, RADIAL ASPECT

Cephalic v. 1st compartment tt. 2nd compartment tt. Distal end of radius

Extensor pollicis brevis t.

Abductor pollicis t. Radius

Extensor pollicis brevis t. Abductor pollicis longus t.

Cephalic v. Scaphoid

Radial artery, superficial and deep branch Radial vv.

(Top) Transverse grayscale US shows the 1st extensor compartment proximal to the distal radius. The 1st compartment contains the extensor pollicis brevis and the larger abductor pollicis longus tendons. The 1st compartment tendons run obliquely over 2nd compartment tendons a few centimeters proximal to the wrist. Pain may occur at this intersection (intersection syndrome). (Middle) Transverse grayscale US shows the 1st extensor compartment at the distal radius. Extensor pollicis brevis extends to the base of the proximal phalanx of the thumb, whereas abductor pollicis longus inserts onto the base of the 1st metacarpal bone. They form the radial aspect of the anatomical snuff box. These tendons are swollen in patients with de Quervain disease. (Bottom) Transverse grayscale US shows the 1st extensor compartment at the level of the scaphoid. Dorsal branch of the radial artery passes deep to the tendons of the 1st extensor compartment to enter the dorsum of the hand.

618

Wrist

Extensor carpi radialis brevis t.

Upper Extremity

TRANSVERSE US, DORSAL WRIST

Extensor pollicis longus t. Cephalic v. Lister tubercle

Extensor carpi radialis longus t. Radius

Extensor pollicis longus t.

Extensor carpi radialis brevis t.

Radius

Extensor carpi radialis brevis t.

Extensor carpi radialis longus t. Scaphoid

Extensor pollicis longus t.

(Top) Transverse grayscale US shows the 2nd and 3rd extensor compartments at the distal radius level. The 2nd extensor compartment comprises the extensor carpi radialis longus and extensor carpi radialis brevis. Extensor carpi radialis longus inserts into the base of the index finger metacarpal, whereas the extensor carpi radialis brevis inserts into the middle finger metacarpal. The 2nd compartment is separated from the 3rd compartment, containing the extensor pollicis longus, by the Lister tubercle. (Middle) Transverse grayscale US shows the 2nd and 3rd extensor compartments at the distal radius level. The 2nd compartment forms the dorsal aspect of the anatomical snuff box. (Bottom) Transverse grayscale US shows the 2nd extensor compartment at the scaphoid level. The extensor pollicis longus tendon hooks around the Lister tubercle and crosses superficial to the 1st compartment tendons as it runs toward its insertion on the base of the distal phalanx of the thumb. It is prone to rupture in inflammatory arthropathies and distal radial fractures.

619

Upper Extremity

Wrist TRANSVERSE US, EXTENSOR DIGITORUM Extensor retinaculum Extensor digitorum t. Extensor pollicis longus t. Lister tubercle Ulna Extensor digiti minimi t.

Radius

Extensor retinaculum Extensor digitorum t. Extensor digiti minimi t.

Scaphoid Lunate

Extensor retinaculum

Extensor digitorum tt. Scapholunate l. (dorsal component) Lunate

Scaphoid

(Top) Transverse grayscale US shows the 4th extensor compartment at the distal radius. The 4th extensor compartment contains the 4 extensor digitorum tendons and the extensor indicis tendon, which lies radial to the extensor digitorum tendons. The extensor digiti minimi has a separate compartment. (Middle) Transverse grayscale US shows the 4th extensor compartment at the level of the proximal carpal row. The extensor retinaculum is a thickened continuation of the antebrachial fascia. It is attached to the anterior aspect of the distal radius, styloid process of the ulna, and the triquetral and pisiform bones. (Bottom) Transverse grayscale US shows the 4th extensor compartment at the level of the proximal carpal row. The extensor retinaculum holds the extensor tendons in place. Because it is closely applied to the extensor tendons, with anisotropy, it may appear hypoechoic and be confused with tenosynovitis.

620

Wrist Upper Extremity

TRANSVERSE US, EXTENSOR CARPI ULNARIS

Extensor carpi ulnaris t.

Ulna

Extensor digiti minimi t.

Radius

Extensor carpi ulnaris t. Articular disc Extensor digiti minimi t. Radius

Extensor carpi ulnaris t. Hamate

Capitate

(Top) Transverse grayscale US shows the 5th and 6th extensor compartments. The 5th compartment contains the extensor digiti minimi tendon. This tendon is joined by the extensor digitorum tendon to the little finger just proximal to the metacarpophalangeal joint. The 6th compartment contains the extensor carpi ulnaris tendon, which runs in a groove in the distal ulna. Its position in the groove will change with pronation and supination. (Middle) Transverse grayscale US shows the 5th and 6th extensor compartments. The extensor carpi ulnaris tendon often has a midline irregular hypoechoic line within its substance close to the insertion. This should not be mistaken for a longitudinal tear. (Bottom) Transverse grayscale US at insertion of the extensor carpi ulnaris tendon is shown. The extensor carpi ulnaris tendon widens as it passes the lunate bone on its way to insert into the base of the 5th metacarpal.

621

Upper Extremity

Wrist VOLAR WRIST

Hypothenar eminence

Thenar eminence

Flexor retinaculum Extensor pollicis brevis t. Flexor digitorum profundus tt. Abductor pollicis longus t. Flexor digitorum superficialis tt. Flexor carpi radialis t. Flexor carpi ulnaris t. Flexor pollicis longus m. and t. Pronator quadratus m.

Flexor pollicis longus t. Opponens digiti minimi m.

Flexor digiti minimi brevis m.

Flexor pollicis brevis m. Abductor pollicis brevis m. Flexor retinaculum

Abductor digiti minimi m.

Flexor digitorum superficialis tt.

Extensor pollicis brevis t.

Abductor pollicis longus t.

Flexor digitorum profundus tt. Flexor pollicis longus t. Pronator quadratus m.

Flexor carpi ulnaris t.

Flexor carpi radialis t.

(Top) Graphic shows tendons and retinaculum of the volar wrist. The flexor retinaculum spans the palmar arch, attaching to the tubercle of the scaphoid, pisiform, hook of hamate, and ridge of the trapezium. The thenar eminence musculature includes abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, and adductor pollicis. The hypothenar eminence musculature includes palmaris brevis, adductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi. (Bottom) Volar muscles and tendons are displayed with their relation to the flexor retinaculum. Note the muscles of thenar and hypothenar eminences arise from the retinaculum itself. The flexor digitorum and flexor pollicis longus tendons pass deep to the retinaculum. On the radial side, the retinaculum splits to accommodate the flexor carpi radialis tendon.

622

Wrist

Flexor carpi radialis t. Palmaris longus t. Radial a.

Upper Extremity

TRANSVERSE US, VOLAR WRIST

Flexor digitorum superficialis m. Flexor pollicis longus t.

Flexor digitorum profundus m.

Median n. Radius

Pronator quadratus m. Anterior interosseous a., v., and n.

Ulna Interosseous membrane

Flexor carpi radialis t. Median n.

Scaphoid

Flexor tt. Triquetrum Lunate

Flexor retinaculum Flexor carpi radialis t. Scaphoid Flexor tt. Ulnar a., v., and n. Extrinsic carpal l. Capitate

Pisiform Median n.

(Top) Transverse grayscale US shows the volar aspect of the distal forearm just proximal to the wrist. In addition to the tendons that pass through the carpal tunnel, the flexor carpi ulnaris, flexor carpi radialis, and palmaris longus tendons also traverse the wrist joint. (Middle) Transverse grayscale US shows the volar aspect of the wrist just proximal to the carpal tunnel. The 4 tendons of flexor digitorum superficialis, 4 tendons of flexor digitorum profundus, and flexor pollicis longus tendons pass through the carpal tunnel. The median nerve dips deeply as it enters the carpal tunnel. (Bottom) Transverse grayscale US shows the volar aspect of the wrist at the tunnel inlet. The inlet (and outlet) of the carpal tunnel can be best recognized by identifying the proximal and distal margins of the flexor retinaculum. In evaluating carpal tunnel syndrome, the caliber of the nerve should be measured proximal to the tunnel, at the tunnel inlet, and at the tunnel outlet.

623

Upper Extremity

Wrist US, VOLAR WRIST Opponens pollicis m. Ulnar a. Ulnar n. and v. Flexor retinaculum Trapezium

Median n. Flexor tt.

Abductor pollicis brevis m.

Capitate

Abductor pollicis brevis m. Flexor retinaculum Hook of hamate Median n. Opponens pollicis m.

Flexor tt.

Trapezium Base of 3rd metacarpal

Capitate

Abductor pollicis brevis m. Ulnar a. Branch of median n. Flexor tt. Flexor pollicis longus t. Opponens pollicis m. Flexor pollicis brevis m. Metacarpal of index finger

Adductor pollicis m. Metacarpal of ring finger

Metacarpal of 3rd finger

(Top) Transverse grayscale US shows the volar aspect at midcarpal tunnel. The median nerve lies in the carpal tunnel just deep to the retinaculum. You may need to use anisotropy to clearly identify the margins of the median nerve separate from the adjacent flexor tendons. (Middle) Transverse grayscale US shows the volar aspect of the wrist at the tunnel outlet. The tunnel outlet is considered to be the narrowest part of the carpal tunnel. (Bottom) Transverse grayscale ultrasound shows the volar aspect of the wrist just beyond the tunnel outlet. The median nerve divides into its terminal branches just beyond the tunnel outlet.

624

Wrist Upper Extremity

US, SCAPHOID

Flexor carpi radialis t. Distal part of scaphoid Waist of scaphoid

Radius Joint Proximal part of scaphoid

Articular cartilage Radial a. Trapezium

Radius Scaphoid

Articular cartilage

Trapezium

Radial a.

Scaphoid

(Top) Grayscale US longitudinal to the palmar aspect of the scaphoid bone is shown. US is a useful means of diagnosing a scaphoid fracture. Angulation of the transducer along the long axis of the scaphoid allows the palmar cortical outline to be appreciated. (Middle) Grayscale US longitudinal to dorsal aspect of the scaphoid bone is shown. There is often mild cortical irregularity of the scaphoid surface, particularly on the dorsal side. The absence of surrounding edema, hematoma, periosteal thickening, and cortical discontinuity allows one to differentiate this normal appearance from a fracture. (Bottom) Grayscale US transverse to dorsal aspect of the scaphoid bone is shown.

625

Upper Extremity

Wrist GRAPHICS AND US, TRIANGULAR FIBROCARTILAGE

Ulnar collateral l.

Extensor carpi ulnaris Ulnar styloid process

Extensor carpi ulnaris t.

Ulnocarpal l. Dorsal radioulnar l.

Dorsal radioulnar l. Articular disc

Volar radioulnar l.

Extensor carpi ulnaris t. Triquetrum

Ulnar head

Articular disc (fibrocartilage)

Articular cartilage

626

(Top) Graphic shows supporting structures of the triangular fibrocartilage complex. The ulnocarpal ligaments and the volar radioulnar ligament are on the volar side. At the ulnar border, there is the ulnar collateral ligament. On the dorsal surface, there is the extensor carpi ulnaris tendon and its subsheath as well as the dorsal radioulnar ligament. (Middle) Graphic depicts the axial view of the articular disc of triangular fibrocartilage complex. The articular disc is inseparable from supporting dorsal and volar radioulnar ligaments. The disc is widest at its radial attachment. Central tears are more common, while peripheral tears, being better vascularized, have the capacity to heal. (Bottom) Longitudinal grayscale US shows the ulnar aspect of triangular fibrocartilage complex. The fibrocartilaginous articular disc is of different echotexture to hypoechoic hyaline cartilage. US is not as sensitive at depicting triangular fibrocartilage complex tears as MR. The extensor carpi ulnaris tendon provides an acoustic window though which to see the articular disc of the triangular fibrocartilage complex.

Wrist Upper Extremity

VOLAR AND DORSAL LIGAMENTS

Carpometacarpal ll.

Trapeziocapitate l. Capitohamate l.

Scaphotrapezium-trapezoid l.

Triquetrocapitate l. Ulnotriquetral l. Lunotriquetral l., volar portion

Ulnocapitate l. Ulnolunate l Volar radioulnar l.

Interligamentous sulcus Radial collateral l. Radioscaphocapitate l. Long radiolunate l. Radioscapholunate l. Short radiolunate l.

Carpometacarpal ll.

Trapeziotrapezoid l.

Dorsal intercarpal l.

Capitohamate l. Triquetrohamate l.

Dorsal scaphotriquetral l.

Dorsal radiocarpal l.

Dorsal radioulnar l.

(Top) Graphic shows volar intrinsic and extrinsic ligaments. The extrinsic ligaments connect the bones of the forearm (radius and ulna) and those of the carpus. The intrinsic ligaments connect carpal bones to carpal bones. (Bottom) Dorsal ligaments stabilize and restrict motion but are less critical to the stability of the wrist structures than the volar ligaments. On the volar aspect of the wrist, there is a triangular area of weakness (called the space of Poirier) between the lunate and capitate, which is not covered by any ligaments.

627

Upper Extremity

Hand

EXTRINSIC FLEXOR MUSCLES: DIGITS 2-5 Flexor Digitorum Superficialis

Lumbricals

• Origin: Common flexor tendon origin (medial humeral epicondyle) & midradius • Insertion: Volar plate proximal interphalangeal (IP) joints & bases of middle phalanges digits 2-5 • Innervation: Median nerve • Superficialis tendons split at bases of proximal phalanges into 2 tendon slips ○ Slips pass around flexor digitorum profundus (FDP) tendon before inserting into middle phalangeal bases ○ Flexor digitorum superficialis (FDS) forms "tunnel" for FDP • Flexes metacarpophalangeal joints (aided by lumbricals & interossei) & proximal IP joints

• Numbered 1-4 from radial to ulnar • Origin: Radial aspect FDP tendon index to little fingers • Insertion: Radial aspect extensor tendon expansion index to little fingers • Innervation: Most radial 2 lumbricals by median nerve, most ulnar 2 lumbricals by ulnar nerve • Actions: Flex metacarpophalangeal joints & extend IP joints

Flexor Digitorum Profundus • Origin: Proximal 1/2 of radius & interosseus membrane • Insertion: Volar plates, distal IP joints, & bases of distal phalanges of digits 2-5 • Innervation: Ulnar & median nerves • Flexes distal IP joints & proximal IP, metacarpophalangeal (aided by lumbricals & interossei) joints of digits 2-5

INTRINSIC MUSCLES: HYPOTHENAR AREA Hypothenar Eminence • Mirror image of thenar eminence • Muscles (superficial to deep): Abductor digiti minimi (ADM), flexor digiti minimi (FDM), opponens digiti minimi (ODM) ○ Origin: ADM from pisiform; FDM & ODM from flexor retinaculum & hook of hamate ○ Insertion: ADM & FDM → conjoint insertion ulnar aspect base of proximal phalanx little finger – ODM to proximal 2/3 metacarpal shaft little finger ○ Innervation: All by ulnar nerve

INTRINSIC MUSCLES: THENAR AREA Thenar Eminence • Muscles: Abductor pollicis brevis (APB), flexor pollicis brevis (FPB), opponens pollicis (OP) ○ Origin: Flexor retinaculum & tubercle of trapezium ○ Insertion: APB, FPB conjoint insertion at base of proximal phalanx radial aspect – OP to volar aspect 1st metacarpal shaft • Innervation: All by median nerve except FPB, which has also partially supplied by ulnar nerve

Adductor Pollicis Muscle • Oblique (proximal) & transverse (distal) heads • Origin: Capitate, trapezoid, 2nd & 3rd metacarpals • Insertion: Ulnar aspect base of proximal phalanx of thumb, IP joint, volar plate of thumb ○ Also contributes fibers to extensor hood of thumb, which forms adductor aponeurosis • Innervation: Ulnar nerve • Actions: Adducts thumb toward 3rd digit & aids extension of IP joint • Separated from thenar muscles by fascial plane & innervated by ulnar rather than median nerve 628

INTRINSIC MUSCLES: PALMAR AREA

Palmar Interossei • Numbered 1-3 from radial to ulnar • Origin: Mesial palmar aspect diaphyses of 2nd, 4th, & 5th metacarpals • Insertion: Mesial lateral bands & mesial aspect bases of proximal phalanges of same digit as origin • Innervation: Ulnar nerve • Actions: Adduct digits & assist lumbricals with flexion of metacarpophalangeal joints & extension of IP joints of digits 2, 4, & 5

Dorsal Interossei • • • • •

Numbered 1-4 from radial to ulnar Origin: FDP tendons just distal to carpal tunnel Insertion: Radial lateral bands of digits 2-5 Innervation: Ulnar nerve Actions: Extends IP joints 2-5 & abducts digits 2-5

TENDONS Tendon Sheaths • Common flexor sheath (a.k.a. ulnar bursa) ○ Contains FDS & FDP tendons ○ Begins just proximal to carpal tunnel ○ Ends just beyond carpal tunnel for digits 2-4 ○ Encloses 5th digit flexor tendons over entire course to distal IP joint • Flexor pollicis longus tendon sheath (a.k.a. radial bursa) ○ Encloses flexor pollicis longus tendon from just proximal to carpal tunnel to tendon insertion at base of distal phalanx thumb ○ ± communication with ulnar bursa at level of carpal tunnel in ~ 50% of normal population – Potential route for spread of infection • Individual flexor digital sheaths (digits 2-4) ○ Encloses flexor tendons from level of metacarpal necks to bases of distal phalanges

Extensor Expansion (or Extensor Hood) • Expansions of extensor digitorum, extensor indicis, & extensor digiti minimi tendons on dorsum of fingers ○ Help prevent lateral translation of tendon • 3 bands of extensor expansion ○ Single, wide middle band passes over dorsum of proximal phalanx & proximal 1/2 of middle phalanx ○ 2 cord-like lateral bands extend from proximal phalanx to distal phalanx – Lumbricals, palmar & dorsal interossei insert into these lateral bands

Hand Upper Extremity

PALMAR ASPECT

A5 pulley Common digital tendon sheath

C3 pulley A4 pulley

FDP tendon

C2 pulley A3 pulley

C1 pulley FDS tendon

A2 pulley A1 pulley

Deep transverse metacarpal ligament Ulnar bursa (common flexor sheath) Flexor digiti minimi muscle Abductor digiti minimi muscle

A2 pulley Oblique pulley Av pulley A1 pulley Radial bursa (flexor pollicis longus tendon sheath) Adductor pollicis m.

Flexor retinaculum Flexor tendons

Abductor pollicis brevis m. Opponens digiti minimi m.

Pulley system for the 3rd-5th digits is identical to that demonstrated for the 2nd digit. Common digital sheath of the 4th digit is removed to show the relationship of flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons. Deep transverse metacarpal ligaments connect the volar plates (not shown) of digits 2-5. Although there is overlap of the radial and ulnar bursae in this image, these structures normally do not invariably communicate. The radial and ulnar bursae may communicate as a normal variation in ~ 50% of the population. Similarly, any 1 or more of the common digital sheaths may communicate with the ulnar bursa in up to 10% of the normal population. These different bursal communications are important as they provide routes for more extensive spread of infection.

629

Upper Extremity

Hand LUMBRICAL AND INTEROSSEI MUSCLES

Lumbrical t. becoming portion of lateral band

2nd lumbrical m. 4th lumbrical m. 1st lumbrical m. 3rd lumbrical m.

FDP tt.

Lateral band

Extensor hood

Dorsal interossei m.

(Top) Lumbricals originate from the FDP tendons as shown. Note how the 1st and 2nd lumbricals arise only from tendons to the 2nd and 3rd digits, respectively (unipennate), whereas the 3rd and 4th lumbrical arise from the tendons to both the 3rd and 4th and the 4th and 5th digits, respectively (bipennate). (Bottom) Graphic of the dorsal surface of the extensor mechanism of the hand and digits 2-5 demonstrates the complex relationship of the various fiber bands. As in imaging, distinction of individual fiber bands is often difficult and must be inferred by knowledge of where the structure "should" be with respect to more easily identifiable structures (such as bones and joints).

630

Hand Upper Extremity

PALMAR INTEROSSEI

Some fibers contribute to adjacent lateral band

Some fibers insert at base of adjacent proximal phalanx

3rd palmar interosseus m.

1st palmar interosseus m.

2nd palmar interosseus m.

Palmar interossei insert at both bases of adjacent proximal phalanges as well as adjacent lateral bands. The 2nd and 3rd palmar interossei contribute to the radial lateral bands of the 4th and 5th digits, respectively, whereas the 1st palmar interosseus contributes to the ulnar lateral band of the 2nd digit.

631

Upper Extremity

Hand TRANSVERSE US, PALM

Abductor pollicis brevis m. Palmar aponeurosis Ulnar a. Palmaris brevis m. Opponens brevis m. Flexor pollicis brevis m. Adductor pollicis brevis m. Median n.

Flexor digiti minimi brevis m. Opponens digiti minimi m. 5th metacarpal FDS m.

2nd metacarpal FDP m. 3rd metacarpal

4th metacarpal

Median n., superficial branches Ulnar artery Ulnar n., superficial branch Flexor tendon to index finger Adductor pollicis m. Lumbrical m.

Opponens digiti minimi m. Flexor t. to little finger Flexor t. to ring finger

2nd metacarpal

4th metacarpal

Flexor t. to middle finger

3rd metacarpal

FDS m.

Lumbrical m.

FDP m.

Interosseus mm.

4th metacarpal

Second metacarpal

3rd metacarpal

(Top) Transverse grayscale ultrasound shows the proximal aspect of the palm. The palmar aponeurosis is thin and difficult to demonstrate in the mid- to distal palm especially. (Middle) Transverse grayscale ultrasound shows the midportion of the palm. Beneath the aponeurosis lies the flexor tendons, the lumbrical muscles, the muscles of the thenar and hypothenar eminences, and, most deeply, the interossei. There are 3 palmar interossei and 4 dorsal interossei muscles. (Bottom) Transverse grayscale ultrasound shows the distal portion of the palm.

632

Hand Upper Extremity

THENAR-HYPOTHENAR EMINENCE

Transverse head of adductor pollicis m.

Flexor digiti minimi m.

Opponens digiti minimi m.

Flexor retinaculum (roof of carpal tunnel)

Osseus insertion of adductor pollicis m. Oblique head of adductor pollicis m.

Flexor pollicis brevis m.

Opponens pollicis m.

Graphic shows the thenar and hypothenar muscles of the hand. Strictly speaking, the adductor pollicis is not one of the thenar group of muscles since it has a separate fascia and separate nerve supply.

633

Upper Extremity

Hand TRANSVERSE US, THENAR EMINENCE

Abductor pollicis brevis m. Opponens pollicis m. Flexor pollicis longus t. 1st metacarpal

Adductor pollicis m. Deep palmar a.

Flexor pollicis brevis m.

Abductor pollicis brevis m. Opponens pollicis m. Flexor pollicis longus t. 1st metacarpal Flexor pollicis brevis m. Dorsal interossei m.

Adductor pollicis m.

2nd metacarpal Deep palmar a.

Abductor pollicis brevis m. Flexor pollicis longus m. Adductor pollicis m. Opponens pollicis m. Flexor pollicis brevis m. 1st metacarpal

2nd metacarpal Dorsal interosseus muscle

Princeps pollicis a.

(Top) Transverse grayscale ultrasound shows the proximal aspect of the thenar eminence. The thenar eminence comprises 4 muscles: Abductor, opponens, flexor, and adductor pollicis from above downward. The adductor muscle is, strictly speaking, not part of the thenar eminence since it is separated by a fascial layer and has a separate innervation. (Middle) Transverse grayscale ultrasound shows the midportion of the thenar eminence. The flexor pollicis longus tendon is easily recognized as an echogenic tendon alongside the flexor pollicis brevis, deep to the opponens pollicis and superficial to the adductor pollicis muscle. (Bottom) Transverse grayscale ultrasound shows the distal portion of the thenar eminence.

634

Hand

Abductor pollicis m. Opponens pollicis m.

Upper Extremity

LONGITUDINAL US, THENAR EMINENCE

Flexor pollicis brevis m.

1st metacarpal

Abductor pollicis brevis m. Opponens pollicis m.

Flexor pollicis brevis m. Flexor pollicis longus t. Princeps pollicis a.

Adductor pollicis m. 2nd metacarpal

Dorsal interosseus m.

Opponens pollicis m. 1st metacarpal Flexor pollicis longus t. Flexor pollicis brevis m. Deep palmar arch

2nd metacarpal Adductor pollicis m.

Dorsal interosseus m.

(Top) Longitudinal grayscale ultrasound shows the proximal aspect of the thenar eminence. Use the mnemonic ABOF to remember the muscles of the thenar eminence. (Middle) Longitudinal grayscale ultrasound shows midthenar eminence. The abductor pollicis brevis, opponens pollicis, and flexor pollicis brevis (ABOF) lie superficial to deep in that order. (Bottom) Longitudinal grayscale ultrasound shows the distal aspect of the thenar eminence. The flexor pollicis longus tendon passes through the more distal aspect of the thenar eminence.

635

Upper Extremity

Hand TRANSVERSE US, HYPOTHENAR EMINENCE

Ulnar a. Ulnar n., superficial branch Ulnar n., deep branch Abductor digiti minimi m. Hook of hamate

Hamate

Ulnar n., superficial branch

Flexor digiti minimi brevis m. Ulnar a.

Opponens digiti minimi brevis m.

Palmaris brevis m. Base of 5th metacarpal

Superficial palmar arch Ulnar n., superficial branch Abductor digiti minimi m. Flexor digiti minimi brevis m. Ulnar a. Lumbrical m.

Opponens digiti minimi m. 5th metacarpal

Palmar interossei m. Dorsal interossei m.

(Top) Transverse grayscale ultrasound shows the proximal 1/3 of the hypothenar eminence. The hypothenar eminence along with the other muscles of the hand, except for the thenar, are supplied by the ulnar nerve. (Middle) Transverse grayscale ultrasound shows the middle 1/3 of the hypothenar eminence. Hypothenar muscle atrophy can occur with injury to the deep branch of the ulnar nerve just distal to Guyon canal. (Bottom) Transverse grayscale ultrasound shows the distal 1/3 of the hypothenar eminence. The order of muscles in the hypothenar eminence is different from the thenar eminence with abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi from superficial to deep.

636

Hand Upper Extremity

DORSAL ASPECT OF HAND

Terminal t.

Triangular l.

Central slip of EDC t.

Lateral band contribution to central slip

Conjoined t.

EDC contribution to conjoined t. Lateral band Extensor hood

Junctura tendinum

3rd lumbrical

PIP joint capsule

Sagittal band

4th dorsal interosseus

Abductor digiti minimi m. Extensor indicis t. EDC t. to 5th digit EDC tendon to 2nd digit Extensor digiti minimi t. Extensor pollicis brevis t.

Abductor pollicis longus t. Extensor pollicis longus t.

Extensor carpi ulnaris t.

Extensor retinaculum

4th EDC t. contribution to 5th EDC t.

Extensor mechanism composite shows different components of the extensor mechanism on different digits. With the exception of the extensor indicis, extensor digiti minimi, abductor digiti minimi, and 4th extensor digitorum communis (EDC) tendon contribution to the 5th EDC tendon, any structure on any of the 2nd-5th digits can be extrapolated to any and all of the other 2nd-5th digits. Note that the 2nd extensor retinaculum compartment and its contents (extensor carpi radialis longus and brevis tendons) are not included in this graphic. Although the abductor pollicis longus tendon travels in the 1st compartment of the extensor retinaculum, its insertion (not shown) is actually on the radial aspect of the volar surface of the base of the 1st metacarpal.

637

Upper Extremity

Hand DORSAL INTEROSSEI

Contributions to lateral bands

1st dorsal interosseus m. 4th dorsal interosseus m. 2nd dorsal interosseus m.

3rd dorsal interosseus m.

Tendons of the dorsal interossei muscle (along with tendons of the palmar interossei and tendons of the lumbricals) help form lateral bands. Note how each interosseus muscle only contributes fibers to the mesial-most adjacent lateral band. The dorsal interossei do not contribute any lateral band fibers to the 1st or 5th digits.

638

Hand

Extensor retinaculum Extensor tt.

Upper Extremity

TRANSVERSE US, DORSUM HAND

Dorsal radiocarpal l. Triquetrum Lunate

Scaphoid Scapholunate l.-dorsal component

Extensor tt.

Joint Hamate

Loose areolar tissue Capitate

Extensor digitorum tt. 3rd metacarpal

4th metacarpal 2nd metacarpal Dorsal interosseus mm.

(Top) Transverse grayscale ultrasound shows the proximal aspect of the dorsum hand. The tissues on the dorsum hand are less tightly bound than the tissues on the palmar aspect of the hand, and this part of the hand tends to swell much more with inflammatory or edematous processes. (Middle) Transverse grayscale ultrasound shows the mid aspect of the dorsum of hand. Loose areolar tissue separates the extensor tendons from the metacarpal bones. The extensor tendons do not have a complete tendon sheath from the level of the extensor retinaculum to the insertion. (Bottom) Transverse grayscale ultrasound shows the distal aspect of the dorsal hand. There are 4 dorsal interossei, 1 for each metacarpal interspace.

639

Upper Extremity

Hand Vessels

TERMINOLOGY Abbreviations • • • • •

Abductor pollicis longus (APL) Extensor pollicis longus (EPL) Extensor pollicis brevis (EPB) Flexor retinaculum (FR) Pronator quadratus (PQ)

GROSS ANATOMY

640

– Located deep to palmar aponeurosis but superficial to long flexor tendons and digital nerves – Common palmar digital arteries arise from superficial palmar arch – Run distally on surface of 2nd, 3rd, and 4th lumbrical muscles – Near metacarpophalangeal joints, each common palmar digital artery divides into 2 proper digital arteries – Run in subcutaneous fat of digits (lateral aspects)

Arteries

Veins

• Radial artery ○ Terminal branch of brachial artery ○ Located superficial to PQ, then continues dorsally around radial styloid process, then passes deep to APL and EPB, across anatomic snuffbox and deep to EPL ○ Branches of radial artery – Superficial palmar branch continues distally superficial to FR through thenar eminence to anastomose with ulnar artery as superficial palmar arch ○ Deep palmar arch is continuation of radial artery in hand – Main radial artery continues dorsally at radial styloid across anatomic snuffbox deep to EPB and APL – Passes over dorsal aspect of scaphoid bone – Passes between heads of 1st dorsal interosseus muscle to enter palm, joins ulnar artery to form deep palmar arch – Deep palmar arch is located at level of metacarpal bases 1 cm proximal to superficial palmar arch – Lies deep to long flexor tendons and superficial to interossei – Deep branch of ulnar nerve lies on convexity of deep palmar arch – Princeps pollicis artery, radial artery of index finger, and palmar metacarpal arteries arise from deep palmar arch • Ulnar artery ○ Terminal branch of brachial artery ○ Located superficial to PQ, then runs between flexor carpi ulnaris and flexor digitorum superficialis tendons ○ Branches of ulnar artery ○ Common interosseus artery branches in forearm divide into anterior and posterior interosseus arteries – Anterior interosseus artery travels distally; at proximal PQ, gives small branch that pierces membrane, enters dorsal forearm, and anastomoses with posterior interosseus artery – Median artery (branch of anterior interosseus artery) arises in forearm and may persist accompanying median nerve into carpal tunnel, contributing to superficial palmar arch – Posterior interosseus artery travels distally between deep and superficial extensors to anastomose with anterior interosseus artery ○ Superficial palmar arch is continuation of ulnar artery in hand – Located along line extended in arch across palm from thumb web space – Similar to metacarpal shaft level ~ 1 cm distal to deep palmar arch

• Dorsal venous network of hand and network formed by dorsal metacarpal veins ○ Found on dorsum of hand ○ Unite to form cephalic vein (radial side of wrist) and basilic vein (ulnar side of wrist) – Basilic and cephalic veins travel proximally in superficial tissues – Both veins unite at antecubital fossa via median cubital vein – Continues proximally as cephalic vein until it joins brachial vein in axilla to form axillary vein ○ Layout of superficial veins in hand and forearm is highly variable • Causes of deep venous thrombosis in upper limb extremity are different from that of lower limb ○ Related to intravenous cannulations, infusions, radiotherapy, effort-induced thrombosis, and malignant obstruction

IMAGING ANATOMY Overview • Extensive volar and dorsal anastomoses typically exist

ANATOMY IMAGING ISSUES Imaging Recommendations • Assessment of caliber of small arteries of hand best performed by digital subtraction angiography as they are close to limit of resolution by ultrasound ○ For example, when investigating suspected Raynaud disease or Buerger disease

Imaging Pitfalls • Vessel visualization on standard imaging is limited ○ Radial and ulnar artery: 2-3 mm, typically visualized ○ Vascular arches: 1 mm, inconsistently visualized ○ Multiple branches and anastomoses, < 1 mm, rarely visualized • Entry points of nutrient vessels into bone should not be mistaken for erosions • If angle of insonation of ultrasound beam is at or near 90° to vessel, Doppler and color sensitivity will ↓ • Optimize gate size for small-caliber arteries and position at center of arterial lumen to detect peak flow velocity

Hand Vessels Upper Extremity

HAND VASCULATURE

Deep palmar arch, radial a. Dorsal metacarpal a. Dorsal venous plexus tributary Dorsal carpal arch, radial branch Radial a.

Dorsal carpal arch, ulnar branch

Cephalic v. Basilic v.

Posterior interosseous a.

Dorsal metacarpal a. Dorsal metacarpal a.

Superficial palmar arch, ulnar branch 5th dorsal metacarpal a. Deep palmar arch, ulnar branch

Superficial palmar arch, radial branch Deep palmar arch, radial branch

Radial a.

Cephalic v. Palmar carpal arch, ulnar branch Basilic v. Anterior interosseous a.

Palmar carpal arch, radial branch Median a. Radial a.

Ulnar a.

(Top) Vasculature of the dorsal wrist is shown. The dorsal carpal arch supplies the distal radius, distal carpal row, and lateral proximal carpal row. The venous plexus drains into 2 main venous systems, the cephalic and basilic, with multiple anastomotic communications. (Bottom) Vasculature of the volar wrist is shown. Three major arterial arches are contributed to by the radial, ulnar, and interosseous arteries: Palmar (volar) carpal, deep, and superficial palmar arches. A dorsal venous plexus drains into the cephalic and basilic veins.

641

Upper Extremity

Hand Vessels TRANSVERSE US, WRIST AND PALM

Ulnar n. Flexor carpi ulnaris m. Ulnar artery and vv.

Pisiform

Flexor retinaculum Carpal tunnel

Ulnar a. Ulnar n., superficial branch

Ulnar vv.

Ulnar n., deep branch

Flexor retinaculum Hook of hamate Carpal tunnel

Superficial palmar branch of radial a. Ulnar a., superficial branch Common palmar digital a.

Flexor digitorum t.

Ulnar n., deep branch

Opponens pollicis m. Flexor digitorum t.

(Top) Transverse grayscale ultrasound shows the ulnar artery at the level of the pisiform bone within Guyon canal. The ulnar artery at the wrist lies on the radial side of the pisiform. Between the ulnar artery and the pisiform lies the ulnar nerve. The ulnar artery divides either within or just beyond the Guyon canal. (Middle) Transverse grayscale ultrasound shows the ulnar artery at the level of the hook of hamate. Here, it is prone to compression injury (hypothenar hammer syndrome), which may damage its walls leading to either thrombosis, occlusion, or aneurysms. It is usually the superficial branch of the ulnar artery that is most prone to hypothenar hammer syndrome. (Bottom) Transverse grayscale ultrasound shows the ulnar artery at the level of the midpalm. The superficial branch of the ulnar artery contributes to the superficial palmar arch.

642

Hand Vessels

Abductor pollicis longus t. Extensor pollicis brevis t.

Upper Extremity

TRANSVERSE US, DORSAL ASPECT

Cephalic v. Styloid process of radius Radial v. Radial a.

Abductor pollicis t. Extensor pollicis brevis t. Cephalic v.

Radial a.

Radial v. Styloid process of radius

Cephalic v. Trapezium

Radial v.

Radial a. Scaphoid

(Top) Transverse grayscale ultrasound shows the radial artery just proximal to the wrist. The radial artery runs a superficial course parallel with the shaft of the radius in the distal forearm. At the wrist, it lies alongside the 1st extensor compartment, comprising abductor pollicis and extensor pollicis brevis tendons. (Middle) Transverse grayscale ultrasound shows the radial artery at the wrist joint level. The radial artery runs deep to the 1st extensor compartment tendons. Just before it winds around the wrist, it gives off the superficial palmar branch, which helps form the superficial palmar arch. (Bottom) Transverse grayscale ultrasound shows the radial artery at the dorsum of the hand. The deep branch of the radial artery runs on the dorsal surface of the scaphoid and trapezium bones and then passes deep between the oblique and transverse heads of the adductor pollicis muscle to enter the palm to form the deep palmar arch along with the deep branch of the ulnar artery.

643

Upper Extremity

Hand Vessels TRANSVERSE US, PALMAR ASPECT Flexor digitorum superficialis t. Flexor digitorum profundus t. Common palmar digital a. Common palmar digital a. Digital branch of median n.

Palmar interossei m. Metacarpal shaft

Lumbrical m.

Flexor digitorum superficialis t. Digital a. Digital v. Proximal phalanx Flexor digitorum profundus t.

Digital v. Flexor tt. Digital a. Digital v.

Middle phalanx

Digital a.

(Top) Transverse grayscale ultrasound shows the vessels of the midpalm at the midmetacarpal shaft level. The common palmar digital arteries arise from the superficial palmar arch and divide at the finger bases into proper digital arteries. Each finger has 4 (2 volar, 2 dorsal) proper digital arteries. (Middle) Transverse grayscale ultrasound shows the digital vessels at the proximal phalanx level. The palmar digital arteries lie dorsal to the digital nerves. The palmar digital arteries are usually bigger than the dorsal digital arteries. Ulnopalmar arteries are twice as big as the radiopalmar arteries (1.8 mm vs. 1.1 mm). Peak systolic velocity in hand arteries is variable, ranging 30-70 cm/sec. (Bottom) Transverse grayscale ultrasound shows vessels at the middle phalanx level. The veins of the fingers and the hand are variable in number and location. Dorsal veins are of variable size, ranging 1.0-1.5 mm.

644

Hand Vessels

Proper digital aa.

Upper Extremity

HAND ARTERIES

Common proper digital aa.

Deep palmar arch Superficial palmar arch Radialis indicis a. Princeps pollicis a. Ulnar artery contribution to deep palmar arch Radial artery contribution to superficial palmar arch

Ulnar a.

Ulnar n., superficial branch

Radial a.

Median n., muscular branches Flexor retinaculum

Ulnar n., deep branch Volar carpal l.

Ulnar a.

Median n., palmar cutaneous branch

Radial a., palmar cutaneous branch

Median n.

Radial a.

(Top) Graphic shows the hand arteries. After giving off its contribution to the superficial palmar arch, the radial artery travels around the radial aspect of the wrist to the dorsum of the hand where it travels deep in the anatomic snuffbox. It then dives into the 1st interspace between the heads of the 1st dorsal interosseus muscle as well as between the transverse and oblique heads of the adductor pollicis muscle before forming the deep palmar arch. (Bottom) Graphic shows the relationship of the nerves and arteries to the volar carpal ligament (superficial fibers of flexor retinaculum that form the roof of Guyon canal) and flexor retinaculum (which forms the roof of the carpal tunnel). The ulnar nerve (and accompanying artery) pass deep to the volar ligament before branching into the deep and superficial branches.

645

Upper Extremity

Thumb

TERMINOLOGY Abbreviations • • • • • • • •

Abductor pollicis brevis (APB) Extensor pollicis longus (EPL) Extensor pollicis brevis (EPB) Flexor pollicis longus (FPL) Flexor pollicis brevis (FPB) Metacarpophalangeal (MCP) Opponens pollicis (OP) Adductor pollicis (AP)

Tendon Pulley System • More variable than finger tendon pulley system • In addition to standard A1 and A2 pulleys, have oblique and variable annular pulleys (Av) • A1 pulley: At MCP joint level • Av pulley: Along proximal 1/2 of proximal phalanx, variable in position, runs either obliquely or transversely across proximal phalanx • Oblique pulley: Runs obliquely just proximal to A2 pulley • A2 pulley: At interphalangeal joint level

IMAGING ANATOMY GROSS ANATOMY Muscles • Thenar muscle ○ Composed of 4 muscles – APB – FPB – OP – AP ○ Origin: All originate from flexor retinaculum and tubercle of trapezium – APB also originates from tubercle of scaphoid ○ Insertion: APB and FPB share combined insertion at base of proximal phalanx radial aspect – OP inserts onto volar aspect 1st metacarpal ○ AP is often grouped with thenar muscles but is anatomically distinct from them – AP is separated from thenar muscles by fascial plane and innervated by ulnar nerve rather than median nerve • Extensor muscles ○ EPL – Origin: Midulna and interosseus membrane – Insertion: Dorsal aspect base of distal phalanx of thumb – Extends both MCP and interphalangeal joints of thumb ○ EPB – Origin: Distal radius and interosseus membrane – Insertion: Dorsal aspect base of proximal phalanx of thumb – Extends MCP joint of thumb • FPL ○ Origin: Midradius and interosseus membrane ○ Insertion: Base of distal phalanx of thumb ○ Flexes MCP and interphalangeal joints of thumb ○ FPL tendon sheath (a.k.a. radial bursa) – Encompasses FPL tendon from just proximal to carpal tunnel to its insertion (distal phalanx of thumb) – Radial bursa occasionally communicates with ulnar bursa (common flexor sheath) at level of carpal tunnel • Extensor expansion ○ Formed by fibers from AP on ulnar side and APB on radial side ○ Aids extension of interphalangeal joint ○ AP contribution to extensor expansion is a.k.a. adductor aponeurosis

646

Overview • On dorsal transverse imaging, extensor expansions are seen as thin, regular, hypoechoic bands arising from edges of extensor tendon • On palmar transverse imaging, annular pulleys are seen as thin, ring-shaped structures covering flexor tendons and inserting in palmar plate

ANATOMY IMAGING ISSUES Imaging Recommendations • Thenar muscles can be identified reliably on ultrasound ○ All thenar muscles can be identified by placing transducer in orthograde position, parallel to direction of muscle fibers • Extensor and flexor tendons of thumb bear similar ultrasound features to other flexor and extensor tendons of hand

CLINICAL IMPLICATIONS Clinical Importance • Radial bursa may communicate with ulnar bursa at level of carpal tunnel, allowing spread of infection • Ulnar collateral ligament of MCP joint of thumb is especially prone to tearing in forced abduction and extension ○ Referred to as gamekeeper's thumb or skier's thumb ○ If ulnar collateral ligament is torn, position of its proximal free end with respect to adductor aponeurosis is of importance – If proximal portion is displaced superficial to adductor aponeurosis, it is referred to as Stener lesion, and surgery is usually required – Stener lesion: Interposition of adductor aponeurosis between proximally retracted torn ulnar collateral ligament and distal portion – If proximal portion remains deep to adductor aponeurosis, conservative management may suffice • A1 pulley implicated in pathogenesis of trigger thumb ○ Normal thickness of A1 pulley < 0.5 mm ○ In trigger thumb, A1 pulley is thickened to ~ 1 mm or greater ○ ± restricted movement of FPL tendon under A1 pulley during passive flexion on real-time US imaging

Thumb

Common digital tendon sheath

Upper Extremity

DEEP DISSECTION OF HAND

A5 pulley C3 pulley A4 pulley

Flexor digitorum profundus t.

C2 pulley A3 pulley

C1 pulley Flexor digitorum superficialis t.

A2 pulley A1 pulley

Deep transverse metacarpal l. Ulnar bursa (common flexor sheath) Flexor digiti minimi m.

A2 pulley Oblique pulley Av pulley A1 pulley

Abductor digiti minimi m. Radial bursa (flexor pollicis longus t. sheath) Flexor retinaculum Adductor pollicis m.

Flexor tt.

Abductor pollicis brevis m. Opponens digiti minimi m.

Graphic shows the pulley system of the 2nd digit. The pulley system for 3rd-5th digits, which are identical to that demonstrated for 2nd digit, are removed in this graphic. The common digital sheath of the 4th digit is removed to show the relationship of the flexor digitorum superficialis and flexor digitorum profundus tendons. Deep transverse metacarpal ligaments connect volar plates (not shown) of digits 2-5. Although there is overlap of radial and ulnar bursae in this image, these structures normally do not communicate. It is, however, important to know that radial and ulnar bursae may communicate as a normal variation in a small percentage of population. Similarly, 1 or more of common digital sheaths may communicate with radial bursa in up to 10% of the normal population. These normal variant bursal communications are important as they can provide routes for more extensive spread of infection.

647

Upper Extremity

Thumb US, CARPOMETACARPAL JOINT Opponens pollicis m. Abductor pollicis brevis m.

Trapezium 1st metacarpal

Joint space

Abductor pollicis brevis m. Opponens pollicis m. 1st carpometacarpal joint Trapezium 1st metacarpal

Extensor pollicis longus m.

1st metacarpal

Trapezium

Dorsal interossei

(Top) Longitudinal grayscale ultrasound shows the palmar aspect of the carpometacarpal joint with radial deviation of the thumb. The carpometacarpal joint of the thumb is by far the most mobile of the carpometacarpal joints. It is best viewed by radially deviating the thumb. (Middle) Longitudinal grayscale ultrasound shows the palmar aspect of the carpometacarpal joint of the thumb. Because of its mobility, the carpometacarpal joint of the thumb is the only carpometacarpal joint prone to osteoarthritis. This gives rise to deep pain in the thenar eminence. (Bottom) Longitudinal grayscale ultrasound shows the dorsal aspect of the carpometacarpal joint of the thumb. The large dorsal component of the 1st metacarpal base relative to the articulating surface on the trapezium leads to a normal step-off on the dorsal aspect of this joint.

648

Thumb

Opponens pollicis m. Radial sesamoid bone

Upper Extremity

US, METACARPOPHALANGEAL JOINT

Proximal phalanx Head of 1st metacarpal

Adductor pollicis m. Shaft of 1st metacarpal

Princeps pollicis a.

Flexor pollicis longus t.

Head of 1st metacarpal

Base of proximal phalanx

Volar plate

Opponens pollicis m. Ulnar sesamoid of metacarpophalangeal joint

(Top) Longitudinal grayscale ultrasound shows the metacarpophalangeal joint of the thumb. The collateral ligament complex makes up most of the lateral aspects of the metacarpophalangeal and interphalangeal joint capsules. The ulnar collateral ligament of the 1st metacarpophalangeal joint is especially prone to tearing during forced abduction and extension. Such an injury is commonly referred to as gamekeeper's thumb or skier's thumb. (Middle) Longitudinal grayscale ultrasound shows the metacarpophalangeal joint of the thumb. The volar plate constitutes the majority of the volar aspect of the joint capsule of the metacarpophalangeal joint. The volar plate may be avulsed with forced extension. (Bottom) Transverse grayscale ultrasound shows the 1st metacarpophalangeal joint. The metacarpal head is usually involved in erosions before the proximal phalanx. The metacarpophalangeal joint is an area prone to erosions in inflammatory arthritis.

649

Upper Extremity

Thumb ULNAR COLLATERAL LIGAMENT, THUMB

Proximal phalanx 1st metacarpal head Ulnar collateral l.

Adductor aponeurosis

1st metacarpal head

Proximal phalanx

Ulnar collateral l.

Adductor pollicis m. Ulnar collateral l.

Metacarpal head

Ulnar sesamoid at metacarpophalangeal joint

(Top) Longitudinal grayscale ultrasound along the palmar aspect of the ulnar collateral ligament of the thumb is shown. The ulnar collateral ligament of the metacarpophalangeal joint is commonly injured by forced abduction of the thumb. Avulsion normally occurs at the distal (i.e., proximal phalangeal) attachment. (Middle) Longitudinal grayscale ultrasound shows the ulnar collateral ligament at the midportion. The adductor pollicis aponeurosis overlies the ulnar collateral ligament. The thin adductor aponeurosis is attached to the medial side of the proximal phalanx base and the ulnar sesamoid bone. If the torn ulnar collateral ligament displaces above the adductor aponeurosis (Stener lesion), this is an indication for operative repair. (Bottom) Transverse grayscale ultrasound shows the metacarpophalangeal joint of the thumb. This shows the normal thick ulnar collateral ligament in transverse section.

650

Thumb

A1 pulley

Upper Extremity

TRANSVERSE US PALMAR ASPECT, THUMB

Flexor pollicis brevis t. 1st metacarpal head Flexor pollicis longus t.

Radial sesamoid

Flexor pollicis longus 1st metacarpal head Adductor pollicis m. Metacarpophalangeal joint Ulnar sesamoid

2 distal slips of flexor pollicis longus t.

Distal phalanx Princeps pollicis a. and v. Joint recess

(Top) Transverse grayscale ultrasound along the flexor aspect of the thumb at the metacarpal head level is shown. The flexor pollicis brevis inserts into the radial sesamoid and the base of the proximal phalanx. The flexor pollicis longus inserts into the base of the distal phalanx. (Middle) Transverse grayscale ultrasound along the flexor aspect of the thumb at the metacarpophalangeal joint level is shown. The flexor pollicis longus tendon passes over the ulnar sesamoid bone of the metacarpophalangeal joint. (Bottom) Transverse grayscale ultrasound along the flexor aspect of the thumb at the interphalangeal joint level is shown. The flexor pollicis longus tendon is held in position primarily by the A1 pulley at the metacarpophalangeal joint and the A2 pulley at the interphalangeal joint. The flexor pollicis longus tendon may divide into 2 slips at its insertion.

651

Upper Extremity

Thumb EXTENSOR ASPECT, THUMB

Extensor pollicis longus t. 1st metacarpal Joint recess Proximal phalanx

Extensor pollicis longus t. Proximal phalanx Joint recess Nail base

Interphalangeal joint

Distal phalanx

Dorsal digital vessels

Dorsal digital vessels

Proximal phalanx

Extensor pollicis longus t.

(Top) Longitudinal grayscale ultrasound along the extensor aspect of the thumb at the metacarpophalangeal joint level is shown. The extensor pollicis longus tendon thins as it merges with the extensor expansion on the dorsum of the thumb. (Middle) Longitudinal grayscale ultrasound along the extensor aspect of the thumb at the interphalangeal joint level is shown. The extensor pollicis longus tendon inserts into the distal phalanx. (Bottom) Transverse grayscale ultrasound along the extensor aspect of the thumb at the proximal phalanx level is shown. The thin extensor expansion of the extensor pollicis longus is visible.

652

Thumb

Abductor pollicis brevis m. Opponens pollicis m.

Upper Extremity

TRANSVERSE US, THENAR EMINENCE

Flexor pollicis brevis m. Adductor pollicis m. Flexor pollicis longus t. 1st metacarpal Deep palmar arch a.

Abductor pollicis brevis m. Opponens pollicis m. Flexor pollicis longus t. Flexor pollicis brevis m. Adductor pollicis m. 1st metacarpal

2nd metacarpal

Dorsal interosseus m. Deep palmar arch a.

Abductor pollicis brevis m. Opponens pollicis m. 1st metacarpal Flexor pollicis brevis m. Princeps pollicis a.

2nd metacarpal

Dorsal interosseus m.

(Top) Transverse grayscale ultrasound along the proximal aspect of the thenar eminence is shown. The thenar eminence is composed of 4 muscles: The abductor, opponens, flexor, and adductor pollicis from superficial to deep. The adductor muscle is, strictly speaking, not part of the thenar eminence since it is separated by a fascial layer and has a separate innervation. (Middle) Transverse grayscale ultrasound shows the midportion of the thenar eminence. The flexor pollicis longus tendon is easily recognized as an echogenic tendon alongside the flexor pollicis brevis, deep to the opponens pollicis and superficial to the adductor pollicis muscle. (Bottom) Transverse grayscale ultrasound shows the distal portion of the thenar eminence.

653

Upper Extremity

Thumb LONGITUDINAL US, THENAR EMINENCE

Abductor pollicis brevis m. Opponens pollicis m. Flexor pollicis brevis m.

1st metacarpal

Abductor pollicis brevis m. Opponens pollicis m.

Flexor pollicis brevis m. Flexor pollicis longus t.

Adductor pollicis m. Princeps pollicis a.

Dorsal interosseus m.

2nd metacarpal

Opponens pollicis m. Flexor pollicis brevis m.

Flexor pollicis longus t. 1st metacarpal Deep palmar arch a.

2nd metacarpal

Dorsal interosseus m. Adductor pollicis m.

(Top) Longitudinal grayscale ultrasound along the proximal aspect of thenar eminence is shown. ABOF, a mnemonic to remember the muscles of the thenar eminence, stands for abductor pollicis brevis, opponens pollicis, and flexor pollicis brevis, which lie superficial to deep in that order. (Middle) Longitudinal grayscale ultrasound shows the midthenar eminence. The abductor pollicis brevis and flexor pollicis brevis share a combined insertion at the lateral base of the proximal phalanx of the 1st digit. (Bottom) Longitudinal grayscale ultrasound along the ulnar aspect of the thenar eminence is shown. Although often grouped with the thenar muscles due to proximity, the adductor pollicis is distinct from them, as it is separated from the thenar muscles by a fascial plane and innervated by the ulnar nerve as opposed to the median nerve.

654

Thumb

Extensor tendon with tendon expansion

Upper Extremity

GRAPHICS, STENER LESION

Adductor aponeurosis

1st metacarpal

Proximal phalanx

Flexor t. with pulley Adductor pollicis m.

Reflected adductor t. aponeurosis

Reflected adductor tendon aponeurosis

Ulnar collateral l.

Retracted torn ulnar collateral l.

Graphic shows the ulnar aspect of the metacarpophalangeal joint of the thumb. On the top image, the adductor tendon aponeurosis attaches to the extensor expansion on the dorsum of the thumb. The middle image shows a reflected adductor aponeurosis with the ulnar collateral ligament beneath. When a complete tear of the ulnar collateral ligament occurs, shown in the bottom image, the proximal end of the ligament may be retracted back over the adductor aponeurosis. This is referred to as a Stener lesion and does require surgical intervention.

655

Upper Extremity

Fingers

TERMINOLOGY Abbreviations • • • •

Extensor digitorum communis (EDC) Extensor digiti minimi (EDM) Interphalangeal (IP) joint Metacarpophalangeal joint (MCP) joint

GROSS ANATOMY

656

○ Numbered 1-4 from radial to ulnar ○ Origin: FDP tendons, just distal to carpal tunnel ○ Insertion: Radial lateral bands of digits 2-5 – Extend IP and flex MCP joints of digits 2-5 • Dorsal interossei ○ Numbered 1-4 from radial to ulnar ○ Origin: Dorsolateral metacarpal diaphyses ○ Insertion: Adjacent lateral bands of digits 2-4 – Extend 2nd-5th IP joints and abduct digits 2-5

Muscles

Tendon Pulley System

• Flexor aspect ○ Flexor digitorum superficialis – Origin: Common flexor tendon origin and midradius – Insertion: Volar plates of proximal IP joints and bases of middle phalanges digits 2-5 – Superficialis tendon is superficial to profundus tendon in palm until it divides at level of proximal 1/3 of proximal phalanx – 2 slips of superficialis tendon pass around profundus tendon and reunite deep to profundus tendon prior to insertion – Flexes both MCP joints, aided by lumbricals and interossei and proximal IP joints of digits 2-5 ○ Flexor digitorum profundus (FDP) – Origin: Proximal radius, midradius, and interosseus membrane – Profundus tendon passes through divided superficialis tendon to insert at base of distal phalanx – Insertion: Volar plates of distal IP joints and bases of distal phalanges digits 2-5 – Flexes distal and proximal IP joints as well as MCP joints aided by lumbricals and interossei • Palmar interossei ○ Denoted 1-3 from radial to ulnar ○ Origin: Mesial palmar diaphyses of 2nd, 4th, and 5th metacarpals ○ Insertion: Mesial lateral bands and proximal phalanges have same base as digit of origin ○ Adducts digits and assists lumbricals with flexion MCP and extension IP joints in digits 2, 4, and 5 • Extensor aspect ○ EDC – Origin: Common extensor tendon origin (lateral humeral epicondyle) – Insertion: As central slip at bases of middle phalanges and proximal IP joint capsule – Separate EDC tendon to 5th digit tendon is present in 50% of general population ○ Extensor indicis – Origin: Posterior ulna, distal ulna, and interosseus membrane – Insertion: Blends with 2nd digit EDC tendon and extensor hood ○ EDM – Origin: Common extensor tendon origin (lateral humeral epicondyle) – Insertion: 2 tendons of EDM fuse with one another and with 5th digit EDC tendon prior to insertion at base of proximal phalanx 5th digit • Lumbricals

• Annular pulley ○ Retinaculum that retain flexor tendons at 5 points = annular pulleys ○ Prevent tendon bowstringing during finger flexion ○ Odd-numbered pulleys at oval parts (i.e., joints) ○ Even-numbered pulleys at elegant waists (i.e., shafts) ○ A2 and A4 are functionally most important pulleys to prevent bowstringing – A1: MCP joint and base of proximal phalanx – A2: Middle and distal 3rds of proximal phalanx – A3: Proximal IP joint – A4: Midshaft of middle phalanx – A5: Distal IP joint ○ Also cruciform pulleys, C1-C3 • Extensor expansion ○ Begins just proximal to MCP joints and terminates just proximal to proximal IP joint ○ Dorsal expansion of fibers oriented perpendicular to long axis of extensor tendons ○ Fibers of extensor expansion interdigitate with EDC tendons to prevent lateral translation

Tendon Sheaths • 2nd-4th flexor synovial sheaths extend from metacarpal neck to bases of distal phalanges • Different for 5th digit flexor tendons, which are covered by synovial sheath over their entire course (to level of distal IP joint)

ANATOMY IMAGING ISSUES Imaging Approaches • Extensor tendons in digits often seen best on longitudinal imaging • Pulleys are seen as focal hypoechoic thickening overlying tendon sheath ○ As pulleys are widened at base, thickness of pulleys should be measured at 10 or 2 o'clock positions ○ Do not misdiagnose as tendon sheath thickening ○ A1 and A2 pulley can be depicted in most cases ○ Injury inferred by bowstringing of flexor tendons ○ Compare with normal fingers

CLINICAL IMPLICATIONS Clinical Importance • Digital sheaths may connect to ulnar bursa in up to 10% of population, providing route for spread of infection from digits 2-4 to common flexor sheath and vice versa • Pulley injury inferred by bowstringing of flexor tendons

Fingers

Common digital tendon sheath

Upper Extremity

TENDON SHEATHS

A5 pulley C3 pulley A4 pulley

Flexor digitorum profundus t.

C2 pulley A3 pulley

C1 pulley Flexor digitorum superficialis t.

A2 pulley A1 pulley

Deep transverse metacarpal l. Ulnar bursa (common flexor sheath) Flexor digiti minimi

A2 pulley Oblique pulley Av pulley A1 pulley

Abductor digiti minimi

Flexor retinaculum

Radial bursa (flexor pollicis longus tendon sheath) Adductor pollicis m.

Flexor tt.

Abductor pollicis brevis m.

Opponens digiti minimi m.

Graphic of pulley system on the palmar side of the 3rd-5th digits is identical to that demonstrated for the 2nd digit. The common digital sheath of the 4th digit is removed to show the relationship of the flexor digitorum superficialis and flexor digitorum profundus tendons. Deep transverse metacarpal ligaments connect the volar plates (not shown) of digits 2-5. Although there is overlap of the radial and ulnar bursae in this image, these structures normally do not communicate. It is, however, important to know that the radial and ulnar bursae may communicate as a normal variation in a small percentage of the population. Similarly, any one or more of the digital sheaths may communicate with the radial bursa in up to 10% of the normal population. These normal variant bursal communications are important as they can provide routes for more extensive spread of infection.

657

Upper Extremity

Fingers LIGAMENTS AND PULLEYS

Terminal t.

Triangular l.

Central slip of extensor digitorum communis t. Extensor digitorum communis contribution to conjoined t. Extensor hood

Junctura tendinum

3rd lumbrical m.

Lateral band contribution to central slip

Conjoined t.

Lateral band Proximal interphalangeal joint capsule Sagittal band

4th dorsal interosseus m.

Abductor digiti minimi m. Extensor indicis t.

Extensor digitorum communis t. to 2nd digit Extensor pollicis brevis t.

Extensor digitorum communis t. to 5th digit Extensor digiti minimi t.

Extensor carpi ulnaris t. Abductor pollicis longus t. Extensor pollicis longus t.

Extensor retinaculum

4th extensor digitorum communis t. contribution to 5th extensor digitorum communis t.

Graphic of the dorsum hand and finger extensor mechanism shows different components of the extensor mechanism on different digits. With the exception of the extensor indicis, extensor digiti minimi, abductor digiti minimi, and 4th extensor digitorum communis tendon contribution to the 5th extensor digitorum communis tendon, any structure on any of the 2nd-5th digits can be extrapolated to any and all of the other 2nd-5th digits. Note that the 2nd extensor retinaculum compartment and its contents (extensor carpi radialis longus and brevis tendons) are not included in this graphic. Although the abductor pollicis longus tendon travels in the 1st compartment of the extensor retinaculum, its insertion (not shown) is actually on the radial aspect of the volar surface of the base of the 1st metacarpal.

658

Fingers Upper Extremity

GRAPHIC AND LONGITUDINAL US, METACARPOPHALANGEAL JOINT

Sagittal band Extensor digitorum communis t. Proximal phalanx Main collateral l.

Accessory collateral l.

Extent of articular cartilage of proximal phalanx

Metacarpal

Flexor digitorum t. A1 pulley

Extent of articular cartilage of metacarpal head

Membranous portion of volar plate Thick portion of volar plate

A1 pulley

Volar plate

Flexor t. Joint capsule

Proximal phalanx Articular cartilage Metacarpophalangeal joint

Metacarpal shaft Metacarpal head

(Top) Surface and cut-section graphics show the metacarpophalangeal (MCP) joint. The collateral ligament complex is composed of 2 separate fiber bands. The main collateral ligament inserts on the base of the adjacent phalanx. The accessory collateral ligament inserts on the volar plate. The volar plate is thick distally and thin and redundant proximally. With the exception of the sagittal band (present only at MCP joints), anatomy in this graphic is duplicated in all MCP and interphalangeal (IP) joints in the hand. (Bottom) Longitudinal grayscale US shows the middle finger at the MCP joint.

659

Upper Extremity

Fingers LONGITUDINAL US

Flexor tt. Articular cartilage Metacarpal head

Adductor pollicis m. Metacarpal shaft

A1 pulley Volar plate Flexor tt. Adductor pollicis m. Joint

Metacarpal shaft

Metacarpal head Joint capsule

A2 pulley

Flexor tt. Proximal phalanx

(Top) Longitudinal grayscale US shows the finger at the metacarpal shaft level. From the base of the metacarpals (carpal tunnel outlet) to the neck of the metacarpals, the flexor tendons of the 2nd-4th fingers (i.e., index, middle, and ring fingers) are devoid of flexor tendon sheaths. A normal flexor tendon sheath cannot be seen on ultrasound and can only be seen when it is distended. Do not confuse the flexor tendon pulleys with tendon sheath thickening. (Middle) Longitudinal grayscale US shows fingers at the MCP joint level. MCP joints are narrowed dorsally and flare in the volar direction, increasing contact with the proximal phalanx as the joint is flexed. The capsule of the MCP joint extends from the metacarpal neck level to the base of proximal phalangeal joint. (Bottom) Longitudinal grayscale US shows the A2 pulley of the middle finger at the proximal phalanx.

660

Fingers

Volar plate

Upper Extremity

LONGITUDINAL US

Flexor t. Middle phalanx Proximal phalanx Joint capsule

A4 pulley Flexor t. Distal interphalangeal joint Middle phalanx shaft Proximal interphalangeal joint

Insertion of flexor t. Pulp space Terminal phalanx Joint capsule Distal interphalangeal joint

(Top) Longitudinal grayscale US shows the proximal IP joint of the middle finger. The volar plate is a fibrocartilaginous thickening on the volar aspect of the MCP joint and proximal IP joints. At the proximal IP joint, it is firmly attached to the base of the middle phalanx and has a thinner insertion onto the distal end of the proximal phalanx. It may become avulsed during hyperextension injuries often associated with a small avulsion fracture. There is an inability to fully extend and flex the joint, a condition that usually improves with time unless the joint is locked. (Middle) Longitudinal grayscale US shows the middle finger at the middle phalanx. The A4 pulley prevents bowstringing of flexor tendons at the middle phalanx. (Bottom) Longitudinal grayscale US shows the distal IP joint of middle finger. An avulsion of the flexor tendon from the distal phalangeal base is usually accompanied by a small avulsion fracture.

661

Upper Extremity

Fingers TRANSVERSE US Flexor digitorum superficialis t. Digital a. Flexor digitorum profundus t. Lumbrical mm. Adductor pollicis m.

Palmar interosseus m.

Palmar interosseus m. Dorsal interosseus m. Metacarpal

A1 pulley

Flexor digitorum superficialis m. Flexor digitorum profundus m. Subtendinous areolar tissue

Metacarpal head

Flexor digitorum superficialis t.

Digital a. Flexor digitorum profundus t.

Proximal phalanx

(Top) Transverse grayscale US shows the middle finger at the metacarpal shaft. There are 4 lumbrical muscles in the hand. These are unusual muscles in that they do not originate from the skeleton but instead originate from the flexor digitorum tendons and insert into the extensor expansions. (Middle) Transverse grayscale US shows the middle finger at the metacarpal head. This image is of the A1 pulley level. The A1 pulley extends from the metacarpal head to the proximal phalanx base. It is seen as a thin hypoechoic to hyperechoic rim (depending on the beam angulation) around the flexor tendons. It broadens considerably at the base, which cannot be clearly depicted. (Bottom) Transverse grayscale US shows the middle finger at the proximal phalanx. The flexor digitorum superficialis tendon splits just proximal to the insertion, enabling the flexor digitorum profundus tendon to push through the gap.

662

Fingers

A2 pulley

Upper Extremity

TRANSVERSE US

Flexor digitorum profundus t. Digital artery Flexor digitorum superficialis t. Shaft of proximal phalanx

Flexor digitorum superficialis t.

Flexor digitorum profundus t. Capsule Head of proximal phalanx Digital a.

Flexor digitorum superficialis t. Flexor digitorum profundus t. Digital a.

Proximal end of middle phalanx

(Top) Transverse grayscale US shows the middle finger shaft of the proximal phalanx. Do not confuse thickening of the A2 pulley with tendon sheath thickening. (Middle) Transverse grayscale US shows the middle finger proximal phalangeal head region just distal to the A2 pulley. The small slips of the flexor digitorum superficialis tendon descend on either side of the flexor digitorum profundus tendon to insert onto the volar aspect of the base of the middle phalanx. (Bottom) Transverse grayscale US shows the middle finger at the proximal end of the middle phalanx. The insertions of the slips of the flexor digitorum superficialis are small. As such, particularly in the presence of edema, it may be difficult to confirm isolated avulsion of 1 slip on US. In this situation, the flexor digitorum superficialis tendon will not be retracted.

663

Upper Extremity

Fingers TRANSVERSE US AND GRAPHIC

Flexor digitorum profundus t.

Subtendinous areolar tissue

A4 pulley

Middle phalanx

A5 pulley

Terminal phalanx

Flexor digitorum profundus t.

Flexor t. sheaths of fingers

Flexor t. sheath of thumb

Ulnar bursa

(Top) Transverse grayscale US shows the middle finger at the shaft of the middle phalanx. Do not confuse the subtendinous connective tissue as part of the tendon. (Middle) Transverse grayscale US shows the middle finger at the base of the distal phalanx. The flexor digitorum profundus tendon gains broad attachment to the base of the distal phalanx and is supported by the A5 pulley just proximal to the insertion. (Bottom) Graphic shows the tendon sheaths of the fingers (blue). Digital sheaths may connect to the ulnar bursa (green) in up to 10% of the population, providing a route for the spread of infection from digits 2-4 to the common flexor sheath and vice versa.

664

Fingers

Extensor digitorum t.

Upper Extremity

LONGITUDINAL US, EXTENSOR ASPECT

Proximal interphalangeal joint

Proximal phalanx

Extensor digitorum t. Middle phalanx

Proximal interphalangeal joint

Extensor digitorum t. Nail Nail bed Distal phalanx Extensor digitorum tendon insertional area Distal interphalangeal joint

Middle phalanx

(Top) Longitudinal grayscale US shows the dorsal aspect of the proximal phalanx. The extensor expansion on the dorsum of the fingers is thin and flat and does not have a synovial sheath. (Middle) Longitudinal grayscale US shows the dorsal aspect of the middle phalanx. No pulleys are present on the extensor aspect of the fingers. The extensor expansion (or hood) are attached to the phalanges and the lateral bands. (Bottom) Longitudinal grayscale US shows the dorsal aspect of the distal phalanx. The extensor digitorum is attached to the base of the distal phalanx. This is a common site of avulsion, often with a small avulsion fracture.

665

Upper Extremity

Fingers TRANSVERSE US, EXTENSOR ASPECT Extensor digitorum t.

Digital a. Dorsal interosseus m.

Dorsal interosseus

Metacarpal head

Extensor digitorum t.

Extensor expansion Digital a. and v.

Joint capsule

Metacarpal head

Extensor hood

Extensor digitorum t. slip

Proximal phalanx Digital a.

(Top) Transverse grayscale US shows the metacarpal head/neck region of the extensor aspect of the fingers. The extensor tendons of the hand do not have a complete synovial sheath. They are covered by thin paratenon. The tendons have an ovoid configuration. (Middle) Transverse grayscale US shows the extensor aspect of the fingers at the metacarpal head region. At the proximal phalanx extending over the middle phalanx, the extensor tendons spread out and connect to the extensor expansion or hood. (Bottom) Transverse grayscale US shows the extensor aspect of the fingers at the proximal phalanx level. With expansion of the extensor tendon, it becomes very thin such that the normal tendon is difficult to illustrate on the dorsum of the fingers. If injured, the tendon swells and is usually more readily seen.

666

Fingers

Extensor t.

Upper Extremity

AXIAL FINGER AND HAND DERMATOMES

Extensor expansion

Lumbrical m. Interosseus m. Phalanx

Digital n.

Flexor digitorum superficialis t.

Digital aa. and vv.

Flexor digitorum profundus t.

Collateral ll.

C8 dermatome

C7 dermatome

C6 dermatome

T1 dermatome C8 dermatome

C5 dermatome

(Top) Graphic shows the transverse section of a finger depicting the relationships of the digital nerve, vessels, and tendons to the phalanx. On the dorsal aspect, the extensor expansion interdigitate with the extensor digitorum communis tendons to prevent lateral translation. On the palmar side, the collateral ligaments extend from the palmar aponeurosis in the palm to fuse with the fibrous digital sheaths. Other thickenings of the fibrous digital sheaths form annular pulleys and cruciform bands. The common digital artery and the accompanying nerve intervene between the lumbrical muscle and the tendons. (Bottom) Dermatomes of the hand and wrist correlated to corresponding cervical or thoracic nerves. It is necessary for a physician to test the integrity of spinal cord segment C5 to T1 in the upper limb. Usually, physicians will test the C6 to C8 dermatomes in the hand, i.e., the thumb represents C6 dermatome, the middle finger tip represents C7 dermatome, and the little finger represents C8 dermatome.

667

Upper Extremity

Brachial Plexus

GROSS ANATOMY Overview • Brachial plexus is major neural supply to upper limbs ○ Formed from C5-T1 roots combining to form 3 trunks, 6 divisions, 3 cords, and 5 motor/sensory terminal branches (classic description) – 5 motor/sensory terminal branches are ulnar, median, musculocutaneous, axillary, and radial nerves ○ In reality, up to 30 variations on this classic pattern exist with no predominant pattern – Cannot rely on having definite number of trunks, divisions, or cords at any particular location

Ultrasound Anatomy • 5 specific areas should be assessed to ensure complete evaluation ○ Extraforaminal, intrascalene supraclavicular, infraclavicular, and axillary areas • Extraforaminal area (5 roots) ○ Single large fascicle arising from spinal cord levels C5 to T1 ○ Divides and recombines along length of brachial plexus ○ Epineurium is thin proximally and becomes thicker more distally along brachial plexus • Intrascalene area (5 roots → 3 trunks) ○ Posterior to clavicular head of sternocleidomastoid muscle between scalenus anterior muscle anteromedially and scalenus medius muscle posterolaterally ○ Roots are present in superior interscalene area proximally ○ C5 and T1 roots are more difficult to see due to their deep location ○ Roots unite to form trunks in inferior interscalene area distally – Upper (C5-6), middle (C7), lower (C8, T1) trunks – Average cross-sectional area of these trunks is 0.07 cm² (upper), 0.09 cm² (middle), and 0.09 cm² (lower) – Upper and middle trunks are cephalad and posterior to subclavian artery – Upper (C5-6) trunk or part of it may run through or anterior to anterior scalene muscle – Lower trunk is posterior to subclavian artery and can be more difficult to see because of its depth – Deep cervical artery runs posteriorly between middle and lower trunks – Minor nerves arising directly from trunks: Suprascapular nerve and nerve to subclavius muscle ○ Brachial plexus enters supraclavicular fossa by emerging between scalenus anterior and medius muscles • Supraclavicular area (6 divisions) ○ Trunk divides into anterior and posterior divisions in supraclavicular fossa ○ Lie superoposterior and lateral to subclavian artery ("bunch of grapes") ○ Anterior divisions innervate anterior (flexor) muscles ○ Posterior divisions innervate posterior (extensor) muscles ○ Transverse cervical artery runs laterally in this region, usually below divisions of brachial plexus 668

• Infraclavicular area (3 cords) ○ Passageway between supraclavicular fossa and apex of axilla ○ About 3 cm inferomedial to coracoid process, cords position themselves lateral, medial, and posterior to axillary artery ○ Lateral cord innervates anterior (flexor) muscles ○ Medial cord innervates anterior (flexor) muscles ○ Posterior cord innervates posterior (extensor) muscles – Posterior cord is most difficult to see as it lies posterior to brachial artery ○ Cords tend to be more hyperechoic than hypoechoic trunks or divisions as brachial plexus contains increasing number of fascicles and more connective tissue distally ○ Overlying cords is pectoralis major muscle medially, pectoralis minor muscle laterally, while serratus anterior covers chest wall medially • Axillary area (5 terminal branches) ○ Pyramidal space beneath glenohumeral joint ○ Lateral cord → median nerve and musculocutaneous nerve (C5-6) ○ Medial cord → median nerve and ulnar nerve (C8-T1) ○ Posterior cord → axillary nerve (C5-6), radial nerve (C5T1), thoracodorsal nerve (C6-8) as well as upper (C6-7) and lower (C5-6) subscapular nerves ○ Both lateral and medial cords contribute to median nerve ○ Nerves are arranged around axillary artery with ulnar nerve at 2-3 o'clock, radial nerve at 5-6 o'clock, and median nerve at 10-11 o'clock ○ Median, ulnar, and radial nerves are enclosed within sheath separate from musculocutaneous nerve ○ In most cases, musculocutaneous nerve branches early from lateral cord – Musculocutaneous nerve is easily seen by moving probe over medial bicipital groove proximally where nerve is seen between coracobrachialis and biceps muscles – Musculocutaneous nerve then descends along lateral side of arm between biceps and brachialis muscles

ANATOMY IMAGING ISSUES Imaging Approaches • Ultrasound is most efficient way of seeing brachial plexus as perineural fat allows good visualization of nerves • Best to evaluate brachial plexus on transverse scanning though roots; also well seen on longitudinal scanning • Routinely evaluate each of 5 designated areas • Color Doppler imaging helps distinguish brachial plexus from vascular structures • Infraclavicular portion of brachial plexus is least well seen on ultrasound ○ It is covered by pectoralis muscle and lies relatively deep at ~ 4 cm from skin surface

Brachial Plexus Upper Extremity

BRACHIAL PLEXUS

C5 Upper trunk Middle trunk

C6 C7 C8

Lower trunk

T1

Trunks Divisions Medial cord Posterior cord Lateral cord Musculocutaneous n. Axillary n. Median n. Radial n. Ulnar n.

(Top) Coronal graphic of the cervical spine and supraclavicular brachial plexus demonstrates the cervical ventral primary rami combining to form the brachial plexus. The C1-C7 roots exit above the same numbered pedicle, C8 exits above the T1 pedicle, and more caudal roots exit below their numbered pedicle. The trunks are visualized on ultrasound mainly in the intrascalene area. (Bottom) Coronal graphic of the brachial plexus demonstrates the more distal plexus elements extending into the axilla. The trunks recombine into posterior and anterior divisions that form the cords. The posterior cord forms the radial and axillary nerves. The medial cord forms the ulnar nerve, while the lateral cord forms the musculocutaneous nerve. The median nerve is formed from branches of both the lateral and medial cords.

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Upper Extremity

Brachial Plexus BRACHIAL PLEXUS AND PERIPHERAL NERVES

Ulnar n.

Radial n.

Median n. Humerus Radial n. Ulnar n. Brachialis m. Median n. Musculocutaneous n. Biceps m.

Deep branch of radial n.

Anterior interosseous n.

Ulna Ulnar n. Radius

Superficial branch of radial n.

Median n.

This graphic shows 3 of the 5 terminal branches of the brachial plexus (median, radial, and ulnar nerves), as they course down the arm. The other 2 terminal branches are the musculocutaneous and axillary nerves. The axillary nerve innervates the teres minor and deltoid muscles, while the musculocutaneous nerve passes through the coracobrachialis muscle and descends between the biceps and brachialis muscles.

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Brachial Plexus Upper Extremity

CORONAL AND SAGITTAL T1 MR

Roots

Trunks Divisions Cords

Peripheral n.

Scalenus medius m. Roots/trunks brachial plexus Scalenus anterior m. Subclavian a.

Subclavian v. Clavicle

Clavicle

Divisions/cords of brachial plexus Subclavian a. Subclavian v.

(Top) Oblique coronal T1WI MR with large field of view shows the normal brachial plexus. The divisions and cords run alongside the subclavian artery. The approximate locations of the roots, trunks, divisions, cords, and peripheral nerves are shown. (Middle) Sagittal T1WI MR shows the hypoechoic roots/trunks of the brachial plexus in the intrascalene area between the scalenus anterior and medius muscles. The scalenus anterior muscle separates the subclavian artery from the subclavian vein. (Bottom) A more lateral sagittal T1WI MR shows the infraclavicular region (costocervical space) with the hypointense divisions/cords of the brachial plexus located dorsocephalad to the subclavian artery.

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Upper Extremity

Brachial Plexus TRANSVERSE AND LONGITUDINAL ULTRASOUND Subcutaneous fat Sternocleidomastoid m.

Scalenus anterior m. Lymph node Emerging root/rami of brachial plexus Transverse process of cervical vertebra Transverse process of cervical vertebra

Thickened brachial plexus trunks

Sternocleidomastoid m. Scalenus anterior m. Thickened brachial plexus elements Scalenus medius m.

Internal jugular v.

(Top) Longitudinal grayscale ultrasound of the posterior triangle of the neck shows the root and trunk of the brachial plexus, which appears as a thin, tubular, hypoechoic structure related superficially to the scalenus anterior muscle and deeply to the cervical vertebrae. (Middle) Longitudinal grayscale ultrasound of right posterior triangle/supraclavicular fossa confirms the elongated linear, hypoechoic, thickened elements of the brachial plexus. The patient had past history of neck irradiation for metastatic neck nodes, and the nerve thickening is likely secondary to postradiation change. (Bottom) Transverse grayscale ultrasound of right lower posterior triangle/supraclavicular fossa shows round smooth hypoechoic nodules between the scalenus anterior and medius muscles. The anatomical location suggests the possibility of thickened brachial plexus elements.

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Brachial Plexus

Sternocleidomastoid m.

Upper Extremity

TRANSVERSE AND LONGITUDINAL ULTRASOUND

Scalene anterior m.

Scalene medius m.

Carotid a. Brachial plexus roots

Sternocleidomastoid m.

Scalenus anterior m.

C5 nerve root

Scalenus anterior m.

Brachial plexus nerve roots Scalenus medius m.

(Top) Transverse ultrasound of the anterolateral lower neck shows the hypoechoic roots of the brachial plexus as they exit the neural foramina and move to the intrascalene area. (Middle) Longitudinal ultrasound shows the longitudinal section of the hypoechoic C5 nerve root as it emerges from the exit of the foraminal area and descends to the intrascalene area. (Bottom) Transverse ultrasound at the entry into the intrascalene area shows 5 hypoechoic roots of the brachial plexus between the scalenus anterior and medius muscles. The hypoechoic roots are clearly seen against the adjacent hyperechoic intermuscular fat.

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Upper Extremity

Brachial Plexus MR AND ULTRASOUND

Scalenus anterior Upper trunk (C5 + C6) C5 C6

Scalenus medius

C7 C8

1st rib T1 transverse process Semispinalis mm.

C4 vertebral body C5 vertebral body Upper trunk Middle trunk Lower trunk

C6 vertebral body C7 vertebral body T1 vertebral body

Divisions

Scalenus medius m. Roots and trunks of brachial plexus

Sternocleidomastoid m. Scalenus anterior m.

(Top) Axial STIR MR at the C7/T1 level depicts the linear alignment of the C5 through C8 ventral primary rami. C5 and C6 are closely approximated and form the left upper trunk. (Middle) Reformatted oblique coronal T2WI MR of the brachial plexus shows that the trunks and divisions of the brachial plexus continue from cervical nerve roots to the axilla. (Bottom) Transverse ultrasound at the exit from the intrascalene area shows 5 hypoechoic roots and trunks of the brachial plexus between the scalenus anterior and medius muscles. The roots and trunks of the brachial plexus are readily seen between the scalene muscles, but there is considerable variability in their appearance due to the inherent variability in the brachial plexus regarding the formation of the individual trunks, divisions, and cords.

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Brachial Plexus

Divisions of brachial plexus

Upper Extremity

TRANSVERSE ULTRASOUND

Subclavian a. 1st rib

Pleura

Clavicle Subclavian v. Pectoralis major m. Cords of brachial plexus

Median n. Axillary a. Biceps m. Ulnar n. Radial n. Teres major m.

(Top) Transverse ultrasound at supraclavicular area shows hypoechoic divisions of the brachial plexus located dorsocranial to the subclavian artery akin to a "cluster of grapes." In a small percentage of subjects, some of the divisions may lie caudal to the subclavian artery. (Middle) Transverse ultrasound at the infraclavicular area shows hypoechoic cords of the brachial plexus located dorsocaudal to the subclavian artery. More medially, the cords are covered by the pectoralis major muscle, while more laterally, they are covered also by the pectoralis minor muscle. (Bottom) Transverse ultrasound at the upper axillary region shows the axillary artery surrounded by the median, ulnar, and radial nerves. The position of these nerves can vary with regard to the axillary artery, so each nerve should be traced distally to confirm its identity.

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Upper Extremity

Radial Nerve

TERMINOLOGY Abbreviations

Imaging Recommendations

• • • • • • •

• Use high-frequency (at least ≥ 7.5-MHz) transducer • Radial nerve is best identified at lateral aspect of distal arm where it runs deep to brachialis ○ Identified deep to triceps in spiral groove midhumeral level ○ Or in proximal aspect arm medially – Lies just deep to brachial artery • Assess shape, size, echotexture, and integrity of nerve ○ Trace medium-sized branches by following their course as they branch from parent nerve • Examination of nerves along transverse plane is preferable to longitudinal scanning as it allows easier, continuous following of nerves throughout limb

Extensor digitorum (ED) Extensor carpi radialis brevis (ECRB) Extensor digiti minimi (EDM) Extensor carpi ulnaris (ECU) Extensor pollicis longus (EPL) Abductor pollicis longus (APL) Extensor indicis (EI)

GROSS ANATOMY Arm • Radial nerve is largest branch of posterior cord of brachial plexus ○ Receives contributions from cervical roots C5-C8 ○ Contains motor and sensory components that supply muscles of extensor compartments of arm, forearm, and hand • Lies between coracobrachialis and teres major muscles and then between bellies of medial and lateral head of triceps • Runs deep to triceps in spiral groove and then deep to brachioradialis • ~ 10 cm proximal to lateral epicondyle of humerus, radial nerve penetrates lateral intermuscular septum to enter anterior space of upper arm • Just anterior to lateral epicondyle, nerve bifurcates into sensory (superficial branch of radial nerve) and motor (deep branch of radial nerve and posterior interosseous nerve) components

Forearm • Branches of radial nerve ○ Divides at level of lateral epicondyle ○ Superficial – Purely sensory – Direct continuation of radial nerve – Courses distally, deep to brachioradialis, to posterior compartment distal forearm and then to dorsal wrist – Divides into lateral branch (supplies radial wrist and thumb skin) and medial branch (supplies mid and ulnar wrist skin) – Dorsal digital nerves supply ulnar thumb, index, middle, and radial ring fingers ○ Deep – Purely motor – Enters supinator, then exits distally and runs posteriorly as posterior interosseous nerve – Supplies ECRB, supinator, ED, EDM, ECU, EPL, APL, and EL

Hand: Branches of Radial Nerve • Not usually seen on routine imaging • No motor innervation in hand • Sensory: Dorsal surface from radiocarpal joint to just distal to proximal interphalangeal joints for digits 1-3 and radial 1/2 of 4th digit ○ Gives terminal branches to supply skin of lateral 2/3 dorsum of wrist and hand and lateral 2.5 digits

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ANATOMY IMAGING ISSUES

Imaging Approaches • Ultrasound ○ Nerve echotexture – Transverse: Uniformly dispersed hypoechoic dots (nerve fascicles) separated by hyperechoic epineurium – Longitudinal: Parallel hypoechoic tracts of uniform caliber – Overall gain control and focus settings optimized for adequate visualization of nerve

Imaging Pitfalls • Smaller nerves and nerve branches (1-2 mm) are difficult to identify, and their location may only be inferred by adjacent vessels • Anisotropy artifacts may affect scanning, especially in short axis; tilting transducer during scanning helps to achieve best view • Structural compression is easier to appreciate than functional compression

CLINICAL IMPLICATIONS Clinical Importance • Sites of potential entrapment of radial nerve ○ Lateral to long head of triceps due to fibrous arch ○ Spiral groove between medial and lateral heads of triceps muscle due to fibrous arch, fractures, tourniquet ○ Between brachialis and brachioradialis muscles at antecubital fossa due to muscle (body builders) ○ Posterior interosseous nerve by arcade of Frohse (superficial proximal margin of supinator) or recurrent radial artery (leash of Henry) crossing just proximal to arcade ○ Posterior interosseous nerve between deep and superficial heads of supinator muscle (supinator syndrome) ○ Superficial radial nerve between brachioradialis and extensor carpi radialis longus in mid to distal forearm (Wartenberg syndrome)

Radial Nerve Upper Extremity

RADIAL NERVE

Posterior cord

Axillary n.

Radial n. n. to triceps m. n. to anconeus

Supinator

Lower lateral cutaneous n. of arm

Posterior interosseus n.

Superficial terminal branch of radial n.

Graphic shows the course and distribution of the radial nerve. The radial nerve arises from the posterior cord of the brachial plexus (C5C8, T1). It spirals posterolaterally around the humerus with the deep brachial artery located anterolateral between the brachialis and the brachioradialis. It gives off the posterior cutaneous nerve of the forearm, which passes posterior to the lateral condyle and supplies the posterior forearm. It divides into deep and superficial branches at the lateral epicondyle. The deep branch is purely motor and pierces the supinator muscle and winds around the lateral aspect of the radial neck. The superficial branch is purely sensory and is located in the anterolateral aspect of the forearm, superficial to the supinator and pronator teres muscles.

677

Upper Extremity

Radial Nerve POSTERIOR ARM

Acromion Supraspinatus m. Deltoid m.

Infraspinatus m. Teres minor m.

Greater tuberosity of humerus Posterior circumflex humeral a. and axillary n.

Teres major m.

Radial n. Latissimus dorsi m.

Middle collateral a.

Radial collateral a.

Triceps m., long head

Radial n. course in spiral groove

Medial intermuscular septum

Brachioradialis m.

Anconeus m.

Flexor carpi ulnaris m. Posterior antebrachial cutaneous n.

Graphic shows the course of the radial nerve in the posterior aspect of the arm. The radial nerve spirals posterolaterally around the humerus with the deep brachial artery. It gives off the posterior cutaneous nerve of the forearm, which passes posterior to the lateral condyle and supplies the posterior forearm. It is located anterolaterally, between the brachialis and brachioradialis, where it supplies the triceps, anconeus, brachioradialis, and the lateral portion of the brachialis.

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Radial Nerve

Median n. Biceps brachii m.

Upper Extremity

TRANSVERSE US, ARM

Deltoid m. Coracobrachialis m. Ulnar n. Humeral shaft

Brachial v. Triceps m. Radial n.

Triceps m.

Radial n. Triceps m.

Profunda brachii a. Brachialis m.

Humeral shaft

Triceps m.

Profunda brachii v. Radial n. Humeral shaft

Profunda brachii a.

(Top) Transverse grayscale ultrasound shows the radial nerve in the proximal 1/3 of the arm. The radial nerve is a continuation of the posterior cord of the brachial plexus. It supplies the triceps and the supinator. In the proximal arm, it lies deep to the brachial artery and vein. (Middle) Transverse grayscale ultrasound shows the radial nerve at the mid 1/3 of the arm. The radial nerve may be injured as it passes around the posterior aspect of the mid to distal 1/3 of the humeral shaft. This injury may occur at the time of fracture, during fracture manipulation or fixation, or as a result of postoperative fibrosis. (Bottom) Transverse grayscale ultrasound shows the radial nerve at the mid 1/3 of the arm (coned view). The radial nerve is accompanied in the spiral groove by the profunda brachii artery and vein.

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Upper Extremity

Radial Nerve TRANSVERSE US, SPIRAL GROOVE

Triceps m. Radial n. Humeral shaft Profunda brachii vessels

Brachialis m. Triceps m. Profunda brachii vessels Radial n. Humeral shaft

Profunda brachii a. Brachioradialis m.

Radial n.

Triceps m. Brachialis m. Humeral shaft

(Top) Transverse grayscale ultrasound shows the radial nerve in the midpart of the spiral groove (coned view). The surgeon must be aware of the site of the radial nerve when performing fixation of the humerus, as the fixator screws or plate may potentially damage the radial nerve. (Middle) Transverse grayscale ultrasound shows the radial nerve in the distal aspect of the spiral groove in the midhumerus region. (Bottom) Transverse grayscale ultrasound shows the radial nerve on the volar aspect of the distal 1/3 of the arm. The radial nerve passes from the posterior to the anterior compartment by piercing the lateral intermuscular septum. Compression of the radial nerve at the lateral intermuscular septum may occur. The radial nerve may be compressed between the brachioradialis and brachialis muscles in very muscular individuals.

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Radial Nerve

Brachioradialis m.

Upper Extremity

TRANSVERSE US, POSTERIOR FOREARM

Radial n., superficial branch Radial n., deep branch m. Extensor carpi radialis longus m.

Radial recurrent a. Brachialis m. Radial head

Supinator m. Extensor carpi radialis brevis m.

Brachioradialis m. Radial n., superficial branch Radial n., deep branch

Pronator teres m.

Extensor carpi radialis longus m. Radial recurrent a. Extensor carpi radialis brevis m. Supinator m. Radius

Brachioradialis m.

Extensor carpi radialis longus m.

Radial a. Radial n., superficial branch Pronator teres m.

Extensor carpi radialis brevis m. Radius Supinator m.

(Top) Transverse grayscale ultrasound shows the radial nerve course in the proximal forearm. The radial nerve passes in front of the lateral epicondyle. It can be readily identified deep to the brachioradialis muscle. It divides into superficial and deep branches in the region of the radial head. The radial nerve is prone to compression between the radial head and the supinator muscle (radial tunnel syndrome). (Middle) Transverse grayscale ultrasound shows the radial nerve at the proximal forearm. The superficial branch of the radial nerve continues to descend in the forearm deep to the brachioradialis muscle. The deep branch pierces the supinator muscle, after which it is known as the posterior interosseus nerve. (Bottom) Transverse grayscale ultrasound shows the radial nerve in the midforearm. The deep branch of the radial nerve may be compressed as it passes through the supinator muscle (arcade of Frohse).

681

Upper Extremity

Radial Nerve TRANSVERSE US, FOREARM

Extensor digiti minimi m. Extensor digitorum m. Radial n. deep branch Extensor carpi radialis brevis m. Radial recurrent a. Radius

Extensor pollicis longus m. Ulna

Radial n., superficial branch Flexor carpi radialis m. Brachioradialis Extensor carpi radialis longs m.

Flexor digitorum superficialis m.

Radius

Brachioradialis m.

Flexor digitorum superficialis m. Flexor digitorum profundus m. Radial n., superficial branch

Radial shaft

Extensor carpi radialis longus t. Interosseus membrane

(Top) Transverse grayscale ultrasound shows the deep branch of the radial nerve on the volar aspect of the distal forearm. (Middle) Transverse grayscale ultrasound shows the superficial branch of the radial nerve on the volar aspect of the distal forearm. About 8 cm proximal to the radial styloid, the superficial branch of the radial nerve emerges from underneath the brachioradialis muscle to lie between the brachioradialis and the extensor carpi radialis longus tendons. It may be compressed in this location (Wartenberg syndrome). (Bottom) Transverse grayscale ultrasound shows the superficial branch of the radial nerve on the radial side of distal forearm close to the wrist. It now lies close to the skin.

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Radial Nerve Upper Extremity

ELBOW AND WRIST

Biceps brachii m.

Radial n.

Arcade of Frohse Biceps t. Radial n., deep branch

Bicipital aponeurosis Supinator m. Radial n., superficial branch

Ulnar n., dorsal digital branches

Ulnar n. Radial n., dorsal digital branches

Ulnar n., dorsal branch

Radial n., posterior interosseus branch Radial n., posterior cutaneous n.

Radial n., superficial branch

(Top) Graphic shows the radial nerve course at the anterolateral aspect of the elbow. The deep branch of the radial nerve is potentially prone to impingement at the superficial proximal margin of the supinator muscle (arcade of Frohse) resulting in posterior interosseus nerve syndrome. (Bottom) Graphic shows the nerves of the dorsal wrist. The radial nerve branches in the forearm with the superficial, posterior cutaneous, and posterior interosseus branches supplying the wrist and hand. The ulnar nerve provides branches to both the dorsal and volar wrist.

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Upper Extremity

Median Nerve

TERMINOLOGY Abbreviations

Imaging Recommendations

• • • • • •

• Examination of nerve in transverse plane is preferable to longitudinal scanning since it allows nerve to be followed continuously throughout limb • Use proximal and distal borders of retinaculum as markers of carpal tunnel

Flexor digitorum profundus (FDP) Flexor digitorum superficialis (FDS) Flexor carpi ulnaris (FCU) Flexor pollicis longus (FPL) Pronator quadratus (PQ) Palmaris longus (PL)

GROSS ANATOMY Arm: Median Nerve • Arises from both medial and lateral cords of brachial plexus (C6-C8, T1) • Lies medial to brachial artery and vein • Located deep to biceps aponeurosis in cubital fossa • Gives articular branches to elbow joint • Supplies pronator teres, PQ, and flexors of anterior compartment forearm (except FCU and medial 1/2 of FDP, which are supplied by ulnar nerve)

Forearm: Median Nerve and Branches • Enters forearm by passing between heads of pronator teres; located in forearm between FDP and FDS ○ Courses distally and attached to deep surface of FDS by fascial sheath ○ Anterior interosseus nerve – Arises from median nerve at level of pronator teres – Located in forearm anterior to interosseus membrane, between FPL and FDP • At wrist, median nerve emerges from lateral side of FDS, becomes more superficial, and runs deep to PL tendon toward carpal tunnel ○ Supplies FPL, PQ, and lateral 1/2 of FDP

Wrist and Hand: Median Nerve and Branches • Median nerve lies along axis of ring finger, i.e., to ulnar side of midline • Lies deep to antebrachial fascia and PL before dipping deeply to enter carpal tunnel • At distal radioulnar joint: Nerve is rounded, deep to PL, medial and superficial to FCR and FPL, and lateral and superficial to FDS • Carpal tunnel is fibroosseous tunnel located immediately distal to volar wrist crease ○ Formed by carpal bones and flexor retinaculum (transverse carpal ligament) ○ Flexor retinaculum attaches to pisiform, hook of hamate, scaphoid, and trapezium ○ 9 structures pass through carpal tunnel – 4 FDS tendons, 4 FDP tendons, FPL tendon, and median nerve – Median nerve is located superficially in carpal tunnel just deep to retinaculum ○ Tunnel outlet is narrowest part of carpal tunnel • Branches ○ Motor to thenar and 1st and 2nd lumbrical muscles ○ Sensory to radial 1/2 of palm, radial 3.5 digits – Palmar cutaneous branch typically arises proximal to carpal tunnel ○ Median nerve divides just distal to carpal tunnel 684

ANATOMY IMAGING ISSUES

Imaging Approaches • Ultrasound ○ Use high-frequency 12- to 17-MHz transducer

Imaging Pitfalls • Median nerve may be bifid ○ If quantifying size of nerve, both components should be measured and summated • Angle transducer at right angles to nerve as angulation will ↑ nerve caliber ○ May need to make use of anisotropy to best differentiate nerve from tendons in carpal tunnel • Avoid too much transducer pressure as this will ↓ nerve caliber and ↑ flattening • Median nerve may be difficult to see at tunnel outlet in subjects with thick palmar skin

CLINICAL IMPLICATIONS Clinical Importance • Normal cross-sectional area of median nerve ranges from 3.9-9.0 mm² ○ Mean fascicular diameter ranges from 0.3-0.5 mm ○ Nerve thickening is considered if size changes beyond above-mentioned limits (e.g., > 10 mm² cross-sectional area) ○ Larger median nerve = greater the likelihood of carpal tunnel syndrome • Potential sites of median nerve compression ○ Deep to ligament of Struthers – Ligament between medial epicondyle and anomalous bony spur arising from distal humeral diaphysis (present in 1% population) – May compress median nerve or brachial artery or both ○ Between brachialis and bicipital aponeurosis – Bicipital aponeurosis = medial fascial expansion of biceps tendon that extends superficial to brachial artery and median nerve and merges with investing fascia forearm ○ Between heads of pronator teres – Either median nerve or anterior interosseus nerve may be compressed ○ Carpal tunnel syndrome – Pain, paresthesia, numbness due to compression of nerve in carpal tunnel – Most common compressive neuropathy – Nerve swollen proximal to inlet ± at inlet ± at outlet ± distal to outlet – Do not use opposite side as comparative standard as subclinical compression common

Median Nerve

Lateral cord of brachial plexus

Upper Extremity

MEDIAN NERVE

Medial cord of brachial plexus

Musculocutaneous n.

Median nerve in arm

Biceps brachii m. Lateral cutaneous nerve of forearm Pronator teres Lateral cutaneous n. of forearm Bicipital aponeurosis Anterior interosseus n.

Median nerve in forearm Nerves to thenar mm.

Digital branches of median n.

Graphic shows the course and distribution of the median and musculocutaneous nerves. The median nerve arises from the medial and lateral cords of the brachial plexus (C6-C8, T1). It travels together with other nerves of the arm. In the elbow, it is located deep to the biceps aponeurosis, enters the forearm by passing between the heads of the pronator teres, and is located in the forearm between the flexor digitorum superficialis and profundus muscles. The musculocutaneous nerve arises from the lateral cord of brachial plexus (C5, C6, C7). It lies between the brachialis and biceps brachii muscles and supplies both of them. It then becomes superficial at the elbow and continues laterally as the lateral cutaneous nerve of the forearm, which innervates the skin of the lateral side of the forearm.

685

Upper Extremity

Median Nerve CUBITAL FOSSA

Brachial a.

Median n. Biceps m.

Biceps t.

Common flexor t. Radial n. Common flexor m. mass

Anterior interosseus n.

Median n.

Bicipital aponeurosis

Median n.

Pronator teres, humeral head

Anterior interosseus n.

Biceps aponeurosis

(Top) Graphic of the anterior view of the cubital fossa shows the median nerve and brachial artery passing underneath the biceps aponeurosis. The anterior interosseus nerve arises from the median nerve as the median nerve passes between 2 heads of the pronator teres muscle. (Bottom) The median nerve may be entrapped between 2 heads of the pronator teres muscle or by the overlying biceps aponeurosis. The median nerve gives rise to the articular branches to the elbow joint. It supplies the pronator teres, pronator quadratus, and flexors of the anterior compartment of the forearm (except the flexor carpi ulnaris and medial 1/2 of the flexor digitorum profundus, which are supplied by the ulnar nerve).

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Median Nerve Upper Extremity

TRANSVERSE US

Biceps brachii m. Median n. Brachial v. Brachial a.

Ulnar n.

Coracobrachialis m. Radial n.

Biceps brachii m. Brachial v. Median n.

Ulnar n.

Brachioradialis m. Triceps m. Brachial a. Humeral shaft

Basilic v. Median n. Biceps brachii m.

Brachial a. and v. Triceps m.

Brachialis m. Humeral shaft

(Top) Transverse grayscale ultrasound shows the median nerve at the proximal arm. The median nerve arises from the lateral and medial cords of the brachial plexus. In the proximal arm, it lies just lateral to the brachial vein and artery. (Middle) Transverse grayscale ultrasound shows the median nerve at the midarm. Little happens to the median nerve in the upper to midarm. It gives off no branches and is not prone to compression by normal structures. (Bottom) Transverse grayscale ultrasound shows the median nerve of the distal arm. The median nerve passes over the brachial artery and vein from lateral to medial. There is occasionally a ligament (of Struthers) in the distal arm with a bony spur attached to the humerus ~ 5 cm proximal to the medial epicondyle. The pronator teres gains additional attachment from this ligament. The median nerve may be compressed deep to this ligament.

687

Upper Extremity

Median Nerve TRANSVERSE US

Brachial a.

Cephalic v. Brachialis m.

Pronator teres m. Median n. Humeral trochlea Articular cartilage

Humeral capitellum

Bicipital aponeurosis Median n. Cephalic v.

Pronator teres m.

Brachial a. Brachialis m.

Cephalic v.

Pronator teres m. Median n. Brachioradialis m. Brachialis m.

Biceps t. Brachialis m.

Articular cartilage Radial head

(Top) Transverse grayscale ultrasound shows the median nerve at the distal arm. The median nerve travels deep to the bicipital aponeurosis. A fascial aponeurosis (a.k.a. lacertus fibrosis) arises from the biceps musculotendinous junction and inserts into the antebrachial fascia. The median nerve may be compressed deep to this fascia. (Middle) Transverse grayscale ultrasound shows the median nerve at the elbow region. (Bottom) Transverse grayscale ultrasound shows the median nerve at the proximal forearm. The median nerve is also prone to compression between the 2 heads of the pronator teres muscle (i.e., common flexor origin head and coronoid process head). The median nerve branches as it passes through these heads (giving rise to the anterior interosseus nerve) and may be compressed at this location (pronator teres syndrome). Pain in forearm or hand occurs with either prolonged forearm pronation or recurrent pronation and supination of forearm.

688

Median Nerve

Flexor digitorum superficialis m.

Upper Extremity

TRANSVERSE US

Brachioradialis m. Radial n., superficial branch Extensor carpi radialis brevis m. Radius Supinator m.

Median n. Flexor digitorum profundus m. Anterior interosseus n. Anterior interosseus vessels Ulna

Palmaris longus m. Radial n., superficial branch Flexor digitorum superficialis m. Flexor pollicis longus m. Radius

Anterior interosseus neurovascular bundle

Median n. Flexor digitorum profundus m.

Palmaris longus t. Flexor carpi radialis m. Radial a. and v. Flexor pollicis longus m. Flexor digitorum superficialis m. Median n. Flexor digitorum profundus m. Radius Anterior interosseus neurovascular bundle

Ulna Pronator quadratus m.

(Top) Transverse grayscale ultrasound shows the median nerve at the proximal forearm. The anterior interosseus nerve supplies all the muscles of the anterior compartment of the forearm except the ulnar 1/2 of the flexor digitorum profundus muscle. It may be injured with fracture of the radial shaft. (Middle) Transverse grayscale ultrasound shows the median nerve at the midforearm. The median nerve is clearly identified in the middistal forearm as it travels between the flexor digitorum superficialis and profundus muscles. (Bottom) Transverse grayscale ultrasound shows the median nerve at the distal forearm.

689

Upper Extremity

Median Nerve TRANSVERSE US: WRIST Flexor carpi radialis t. Palmaris longus t. Flexor digitorum superficialis m. Flexor carpi ulnaris m. Median n. Radial a. and v.

Flexor digitorum profundus t. Pronator quadratus m.

Flexor pollicis longus m.

Flexor carpi radialis t. Palmaris longus t. Flexor digitorum superficialis m. Flexor carpi ulnaris m. Flexor digitorum profundus m. Radial a. Flexor pollicis longus m. Radius Median n.

Pronator quadratus m. Anterior interosseus neurovascular bundle Ulna

Flexor carpi radialis m. Palmaris longus t. Flexor digitorum superficialis m. Median n. Flexor digitorum profundus m. Radial a. and v. Radius Flexor pollicis longus m.

(Top) Transverse grayscale ultrasound shows the median nerve in the distal forearm. (Middle) Transverse grayscale ultrasound shows the median nerve just proximal to the wrist. The median nerve gives off the palmar cutaneous branch in the distal forearm. This branch innervates the skin on the palm of the hand. (Bottom) Transverse grayscale ultrasound shows the median nerve just proximal to the carpal tunnel; the median nerve ascends from a deeper position (between the flexor digitorum profundus and superficialis) to lie just deep to palmaris longus tendon. Enlargement of the median nerve in patients with carpal tunnel syndrome may present clinically as a mass-like lesion in this area. In suspected carpal tunnel syndrome, the caliber of the nerve should be measured at this location.

690

Median Nerve Upper Extremity

TRANSVERSE US, CARPAL TUNNEL

Flexor retinaculum

Median n. Flexor digitorum superficialis t. Scaphoid Lunate

Pisiform Flexor digitorum profundus t. Triquetrum Extrinsic carpal l.

Palmaris longus t. Flexor pollicis longus t. Flexor carpi radialis t. Median n. Scaphoid

Ulnar n. Ulnar a. Hamate

Capitate

Abductor pollicis brevis m. Opponens pollicis m. Trapezium

Trapezoid Median n. Flexor digitorum superficialis t.

Hook of hamate Flexor digitorum profundus t. Capitate

(Top) Transverse grayscale ultrasound shows the median nerve at the carpal tunnel inlet. The best way to identify the carpal tunnel is to identify the leading and trailing edges of the flexor retinaculum. The median nerve dips deep to the retinaculum. The cross-sectional area should be measured at this location in suspected carpal tunnel syndrome. (Middle) Transverse grayscale ultrasound shows the median nerve at the midcarpal tunnel. The median nerve lies just deep to the retinaculum. It is variable in shape and changes with flexor tendon movement. (Bottom) Transverse grayscale ultrasound shows the median nerve at the carpal tunnel outlet. The cross-sectional area of the median nerve should also be measured at this location in patients with suspected carpal tunnel syndrome. This is the narrowest part of the carpal tunnel.

691

Upper Extremity

Median Nerve TRANSVERSE AND LONGITUDINAL US Opponens pollicis m. Abductor pollicis brevis m. Palmar aponeurosis Ulnar a. Opponens digiti minimi Branches of median n. Flexor pollicis longus t.

Flexor digitorum profundus t. Flexor digitorum superficialis t. Adductor pollicis m. Flexor pollicis brevis m.

Flexor retinaculum

Median n. Flexor tt. Radius

Capitate

Lunate

Flexor digitorum superficialis

Median n.

Flexor digitorum profundus

(Top) Transverse grayscale ultrasound shows the median nerve just beyond the carpal tunnel outlet. The median nerve fairly consistently divides into its digital branches just beyond the tunnel outlet. This makes it difficult to get consistent results for nerve caliber at this location. (Middle) Longitudinal grayscale ultrasound shows the median nerve in the carpal tunnel. (Bottom) Longitudinal grayscale ultrasound shows the median nerve in the distal forearm.

692

Median Nerve Upper Extremity

PALMAR NERVES

Digital branches

Abductor digiti minimi fibers forming lateral band Adductor pollicis m.

Common insertion site for abductor and flexor digiti minimi

Recurrent branches of median n.

Flexor digiti minimi m. Abductor digiti minimi m.

Pisohamate ligament (roof of Guyon canal)

Flexor retinaculum (roof of carpal tunnel)

Abductor pollicis brevis m.

Median n.

Ulnar n.

The median nerve travels deep to the flexor retinaculum (within the carpal tunnel). The ulnar nerve travels superficial to the flexor retinaculum and deep to the pisohamate ligament (within the Guyon canal). Both are prone to compression syndromes within these fibroosseous tunnels. Motor supply of the median nerve is to the thenar muscles (via the recurrent branch) and the 1st and 2nd lumbricals. The ulnar nerve motor supply is to all intrinsic muscles of the hand not supplied by the median nerve. Muscle atrophy should prompt an evaluation of the supplying nerve.

693

Upper Extremity

Ulnar Nerve

GROSS ANATOMY Arm: Ulnar Nerve • Arises from medial cord of brachial plexus (C8, T1) • Located posteromedially, deep to triceps muscles in distal arm • Cubital tunnel: Fibroosseous tunnel formed by medial epicondyle, olecranon, & cubital retinaculum (Osborne fascia) ○ Cubital tunnel syndrome – Pain, weakness, & numbness in 4th & 5th fingers due to compression of ulnar nerve in cubital tunnel • May sublux anterior to medial epicondyle in 15% of normal elbows during flexion • Anconeus epitrochlearis muscle runs on same course at cubital retinaculum, i.e., lies between cubital retinaculum & ulnar nerve ○ From medial cortex of olecranon to medial epicondyle ○ Present in 11% of normal subjects, bilateral in 25% ○ Can contribute to cubital tunnel syndrome ○ When anconeus epitrochlearis muscle is not present, it may be replaced by band of tissue called epitrochleoanconeus ligament

Forearm: Ulnar Nerve & Branches • Passes behind medial epicondyle, enters forearm between humeral & ulnar heads of flexor carpi ulnaris (FCU) • Courses distally between FCU & flexor digitorum profundus (FDP) ○ Supplies FCU, medial 1/2 of FDP • Palmar cutaneous branch ○ Arises midforearm & supplies skin on ulnar 1/2 of palm • Dorsal cutaneous branch ○ Arises distal forearm & supplies skin on ulnar side of dorsum hand • Distally, becomes superficial & passes into wrist superficial to flexor retinaculum

Hand: Ulnar Nerve & Branches • In Guyon canal, ulnar nerve lies radial to pisiform & at ulnar & dorsal aspect of ulnar artery • Enters Guyon canal; small, triangular-shaped fibroosseous tunnel ○ Floor = flexor retinaculum; ulnar wall = pisiform & hook of hamate; roof = fascia continuous with flexor retinaculum (superficial palmar ligament) ○ Contains ulnar artery & ulnar nerve ○ Nerve lies between ulnar artery & pisiform or hook of hamate ○ Divides at distal tunnel into superficial sensory branch & deep motor branch – Superficial branch; sensory to ulnar side of palm, little finger, & ulnar 1/2 of ring finger – Deep branch lying medial to hook of hamate where prone to injury; motor to hypothenar muscles, all interossei, 3rd & 4th lumbricals, & adductor pollicis

ANATOMY IMAGING ISSUES Imaging Recommendations • Knowledge of nerve location & anatomic relationships is essential for sonographic identification 694

• Examination of nerves in transverse plane is preferable to longitudinal plane as it allows nerves to be followed continuously throughout limb

Imaging Approaches • Ultrasound ○ Use of high-frequency 12- to 17-MHz transducer ○ Nerve echogenicity – Transverse scan: Irregularly dispersed hypoechoic dots, due to nerve fascicles separated by hyperechoic epineurium – Longitudinal scan: Parallel hypoechoic tracts of uniform caliber – Gain control & focus settings should be optimized for adequate visualization

Imaging Pitfalls • Smaller nerves & nerve branches (1-2 mm) are difficult to identify, & their location may only be inferred by adjacent vessels • Anisotropy artifacts may affect scanning, especially in short axis ○ Tilting transducer during scanning helps to achieve best view • Fixed structural causes of nerve compression are more easy to identify than functional structural compression • Ulnar nerve normally swells to mild degree in cubital tunnel though not as much as in cubital tunnel syndrome

CLINICAL IMPLICATIONS Clinical Importance • Direct sonographic visualization of nerves can reveal focal abnormality or injury, differentiate from extraneural tumor, & show extent of lesion & relationship to adjacent structures & vessels • Ulnar nerve prone to compression in cubital tunnel, between humeral & ulnar origins of FCU, & in Guyon canal ○ Cubital tunnel syndrome = compression of nerve in cubital tunnel – Mostly idiopathic without structural cause being found – Nerve swelling in cubital tunnel – Measure nerve caliber proximal to, within, & distal to cubital tunnel – Compare with opposite side ○ Guyon canal compression is often structural – Due to ganglion cyst at Guyon canal from pisotriquetral joint, fracture hook of hamate, or nerve sheath tumor – Other causes are occupational neuritis, ulnar artery aneurysm, anomalous muscle, lipoma, laceration, or giant cell tumor of tendon sheath • Dislocation of ulnar nerve over medial epicondyle can be observed on ultrasound during elbow flexion ○ ± dislocation of medial triceps muscle belly ○ Repeated dislocation of ulnar nerve may lead to ulnar neuritis, functional impairment, & symptoms of cubital tunnel syndrome

Ulnar Nerve Upper Extremity

ULNAR NERVE

C8 ventral rami

T1 ventral rami

Medial cord of brachial plexus

Ulnar n. in arm

Ulnar n. in forearm Flexor carpi ulnaris m.

Deep branch of ulnar n.

Palmar branch of ulnar n.

Nerves to hypothenar eminence

Digital branches of ulnar n.

Graphic shows the course of the ulnar nerve. The ulnar nerve arises from the medial cord of the brachial plexus (C8, T1). It is located posteromedially, deep to the triceps muscles in the distal arm, where it passes posterior to medial epicondyle in the cubital tunnel (cubital syndrome due to compression of ulnar nerve in cubital tunnel). The ulnar nerve may sublux anterior to the medial epicondyle in ~ 15% of normal people, usually during flexion. The ulnar nerve passes behind the medial epicondyle, entering the forearm between the humeral and ulnar heads of flexor carpi ulnaris. The ulnar nerve then courses distally between flexor carpi ulnaris and the flexor digitorum profundus muscles, supplying the flexor carpi ulnaris muscle and medial 1/2 of the flexor digitorum profundus muscle.

695

Upper Extremity

Ulnar Nerve CUBITAL TUNNEL

Ulnar n.

Anconeus epitrochlearis m.

Common flexor origin

Cubital retinaculum (l. of Osborne) Flexor carpi ulnaris Ulnar nerve in forearm

Common flexor t.

Olecranon

Ulnar n.

Cubital retinaculum Triceps m. and t. Posterior ulnar recurrent a.

(Top) Medial graphic shows the cubital tunnel. The anconeus epitrochlearis is an inconstant accessory muscle that lies superficial to the ulnar nerve and may compress the nerve against the medial epicondyle. (Bottom) Axial graphic shows the cubital tunnel. The ulnar nerve may be compressed within the cubital tunnel (cubital tunnel syndrome) by a mass, synovitis, posttraumatic osseous deformity, or aneurysm of the recurrent ulnar artery. The ulnar nerve may sublux out of the cubital tunnel aided by the adjacent medial head of the triceps. Recurrent subluxation, which can be found in ~ 15% of asymptomatic subjects, can lead to ulnar neuritis, which can produce similar symptoms to ulnar nerve compression.

696

Ulnar Nerve

Biceps brachii m.

Upper Extremity

TRANSVERSE US, ARM

Median n. Coracobrachialis m. Radial n.

Brachial v. Ulnar n.

Brachial a.

Subcutaneous tissue

Ulnar n.

Brachial v.

Triceps m., long & short head

Ulnar n.

Brachial v.

Triceps m.

Humeral shaft

(Top) Transverse grayscale ultrasound shows the ulnar nerve at the proximal arm. The ulnar nerve arises from the medial cord of the brachial plexus and lies just medial to the brachial vein. (Middle) Transverse grayscale ultrasound shows the ulnar nerve at the midarm. The ulnar nerve pierces the medial intermuscular septum in the midarm where it may be potentially compressed. The ulnar nerve gives off no branch in the arm. (Bottom) Transverse grayscale ultrasound shows the ulnar nerve in the distal arm. The ulnar nerve runs distally on the surface of the triceps muscle to reach the area between the olecranon and the medial epicondyle, i.e., the cubital tunnel.

697

Upper Extremity

Ulnar Nerve TRANSVERSE US, CUBITAL TUNNEL

Ulnar n. Triceps m.

Medial epicondyle Pronator teres m.

Triceps m. Accompanying v. and a.

Medial epicondyle Ulnar n.

Olecranon process of ulna

Flexor carpi ulnaris m., humeral head

Flexor carpi ulnaris m., ulnar head

Ulnar n. Humerus

(Top) Transverse grayscale ultrasound shows the ulnar nerve just proximal to the cubital tunnel. The cubital tunnel is the most common site of ulnar neuropathy. Neuropathy may take the form of compression from the overlying retinaculum or fibrous bands, bony impingement and tumors, subluxation of the ulnar nerve over the medial epicondyle, or direct injury. (Middle) Transverse grayscale ultrasound shows the ulnar nerve at the cubital tunnel. The cubital tunnel retinaculum (formed from an extension of investing fascia of the flexor carpi ulnaris and ligament of Osborne) forms the roof of the cubital tunnel. The retinaculum is 4 mm wide and difficult to depict on ultrasound. The floor and wall of cubital tunnel are formed by containing bones, elbow capsule, and the medial collateral ligament. The ulnar nerve normally enlarges slightly within the cubital tunnel. (Bottom) Transverse grayscale ultrasound shows the ulnar nerve just beyond the cubital tunnel.

698

Ulnar Nerve

Flexor digitorum superficialis m.

Upper Extremity

TRANSVERSE US, FOREARM

Flexor carpi ulnaris m. Ulnar n. Pronator teres m.

Flexor carpi ulnaris m. Ulna

Flexor carpi ulnaris m.

Ulnar n. Flexor digitorum superficialis m.

Flexor digitorum profundus m.

Flexor carpi ulnaris m.

Flexor digitorum superficialis m.

Ulnar n.

Ulnar a. Flexor digitorum profundus m.

(Top) Transverse grayscale ultrasound shows the ulnar nerve just beyond the cubital tunnel, where the ulnar nerve passes between the 2 heads (humeral and ulnar) of the flexor carpi ulnaris tendon. This is a potential site of compression. (Middle) Transverse grayscale ultrasound shows the ulnar nerve in the midforearm. The ulnar nerve pierces the intermuscular septum, dividing the flexor and extensor compartments of the forearm to descend in the flexor compartment between flexor carpi ulnaris and flexor digitorum profundus muscles. (Bottom) Transverse grayscale ultrasound shows the ulnar nerve in the distal forearm. The ulnar nerve is joined on its radial side by the ulnar artery in the distal forearm, and the 2 structures travel to the wrist, deep to the flexor carpi ulnaris muscle.

699

Upper Extremity

Ulnar Nerve TRANSVERSE AND LONGITUDINAL US, WRIST AND FOREARM

Flexor carpi ulnaris m. Ulnar a. Ulnar n. Pronator quadratus m. Flexor digitorum superficialis m.

Ulna

Flexor digitorum profundus m.

Ulnar a. Flexor carpi ulnaris t. Ulnar n. Flexor digitorum profundus m. Flexor digitorum superficialis t.

Flexor carpi ulnaris m.

Ulnar n.

Flexor digitorum profundus m.

(Top) Transverse grayscale ultrasound shows the ulnar nerve at the distal forearm. The ulnar nerve can be identified by 1st visualizing the ulnar artery and then identifying the nerve just ulnar to the artery. (Middle) Transverse grayscale ultrasound shows the ulnar nerve just proximal to the wrist. At this location, the ulnar nerve is prone to injury from dog bite, penetrating injury, and nonaccidental selfinjury. (Bottom) Longitudinal grayscale ultrasound shows the ulnar nerve at the distal 1/3 of the forearm. Note the fibrillar pattern of the nerve with a mixed hypoechoic and hyperechoic pattern due to hypoechoic nerve fascicles separated by hyperechoic epineurium.

700

Ulnar Nerve

Flexor carpi ulnaris t.

Upper Extremity

TRANSVERSE US, GUYON CANAL

Antebrachial fascia

Flexor digitorum superficialis t. Flexor digitorum profundus t.

Ulnar n. Ulnar a. and v.

Flexor carpi ulnaris t. Ulnar a. Ulnar n. Flexor digitorum superficialis tt.

Pisiform (proximal end)

Flexor digitorum profundus tt. Triquetrum Lunate

Flexor carpi ulnaris t. Ulnar a. Ulnar n. Flexor digitorum superficialis tt. Pisiform (midportion) Flexor retinaculum Flexor digitorum profundus tt.

(Top) Transverse grayscale ultrasound shows the ulnar nerve just proximal to the Guyon canal. (Middle) Transverse grayscale ultrasound shows the ulnar nerve at the proximal end of the Guyon canal. Guyon canal is the 2nd most common site of ulnar neuropathy. (Bottom) Transverse grayscale ultrasound shows the ulnar nerve at the proximal end of the Guyon canal. Ganglia arising from the pisiform-triquetral articulation are the most common cause of ulnar nerve compression in the Guyon canal.

701

Upper Extremity

Ulnar Nerve TRANSVERSE US, DISTAL TO GUYON CANAL

Ulnar n., superficial branch

Ulnar a. Digital a. Ulnar n., deep branch Flexor retinaculum Hook of hamate

Ulnar n., superficial branch

Ulnar a. Hook of hamate

Slip of palmaris brevis Ulnar n., deep branch

Abductor digiti minimi m. Palmaris brevis m.

Flexor digiti minimi brevis m. Opponens digiti minimi m.

Ulnar n., superficial branch

5th metacarpal Ulnar n., deep branch

(Top) Transverse grayscale ultrasound shows the ulnar nerve at the distal end of Guyon canal, where the ulnar nerve divides into superficial and deep branches. These pass close to the top of (superficial branch) and side of (deep branch) the hook of hamate. (Middle) Transverse grayscale ultrasound shows the ulnar nerve at the distal end of the hook of hamate level. Hook of hamate fractures (common in golfers and baseball players) and repeated blunt trauma ("handle bar" palsy) may injure the ulnar nerve as it passes by the hook of hamate. The ulnar artery can be injured at this location as well (hypothenar hammer syndrome). (Bottom) Transverse grayscale ultrasound shows the ulnar nerve at the base of the hypothenar muscles. The superficial branch of the ulnar nerve stays superficial to supply the skin, while the deep branch stays deep to supply the hypothenar muscles and the 3rd and 4th lumbrical muscles.

702

Ulnar Nerve

C5 spinal n. Dorsal scapular n. Suprascapular n. Lateral cord of brachial plexus

Upper Extremity

PROXIMAL AND DISTAL ULNAR NERVE

C6 spinal n. C7 spinal n. C8 spinal n. T1 spinal n.

Posterior cord of brachial plexus Medial cord of brachial plexus Axillary n. Musculocutaneous n.

Long thoracic n.

Medial and lateral pectoral nn.

Radial n. Median n. Ulnar n.

Ulnar n., palmar digital branches

Ulnar n., superficial branch

Median n. Ulnar n., palmar cutaneous branch

Ulnar n.

(Top) Anterior graphic shows the ulnar nerve arising from the medial cord of the brachial plexus. (Bottom) Ulnar nerve supplies the ulnar wrist and hand. In addition to the branches shown, a dorsal branch of the ulnar nerve passes between the flexor carpi ulnaris and ulna about 5 cm proximal to the wrist to supply the dorsal ulnar wrist and the little finger. Deep and superficial branches supply motor and sensory branches to the hypothenar eminence.

703

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SECTION 7

Lower Extremity

Gluteal Muscles Groin Hip Thigh Muscles Femoral Vessels and Nerves Knee Leg Muscles Leg Vessels Leg Nerves Ankle Tarsus Foot Vessels Metatarsals and Toes

706 716 726 736 748 762 780 792 810 814 832 846 852

Lower Extremity

Gluteal Muscles

TERMINOLOGY Abbreviations • • • •

Origin (O) Insertion (I) Nerve supply (N) Function (F)

IMAGING ANATOMY Gluteal Muscles • Components: Gluteus maximus, gluteus medius, gluteus minimus, tensor fascia lata, piriformis, obturator internus and externus, superior and inferior gemellus, quadratus femoris • Common Fs: Hip abduction, external rotation • Inferior gemellus ○ O: Ischial tuberosity ○ I: Piriformis fossa ○ N: Nerve to quadratus femoris muscle ○ F: Hip external rotation, weak abduction • Superior gemellus ○ O: Ischial spine ○ I: Piriformis fossa ○ N: Nerve to obturator internus muscle ○ F: Hip external rotation, weak abduction • Gluteus maximus ○ O: Posterior gluteal line (ilium), posterior sacrum and coccyx, sacrotuberous ligament ○ I: Iliotibial tract, gluteal tuberosity ○ N: Inferior gluteal ○ F: Hip extension, abduction, and external rotation • Gluteus medius ○ O: Between anterior and posterior gluteal lines (ilium) ○ I: Lateral and posterosuperior facets of greater trochanter ○ N: Superior gluteal ○ F: Hip abduction and internal rotation • Gluteus minimus ○ O: External ilium between anterior and inferior gluteal lines ○ I: Anterior facet of greater trochanter ○ N: Superior gluteal ○ F: Hip abduction and internal rotation • Obturator internus ○ O: Internal surface of obturator foramen and membrane ○ I: Piriformis fossa (joins with gemelli tendons) ○ N: L5, S1, S2 ○ F: Hip external rotation, weak abduction • Obturator externus ○ O: Edge of obturator foramen and obturator membrane ○ I: Posterior aspect of femur in trochanteric fossa ○ N: Obturator nerve ○ F: Lateral rotation of hip • Piriformis ○ O: Anterior sacrum, sacrotuberous ligament ○ I: Greater trochanter (may fuse with obturator internus and gemellus muscles) ○ N: S1, S2 ○ F: Hip external rotation, assists abduction 706

• Tensor fascia lata ○ O: External lip anterior iliac crest, external anterior superior iliac spine ○ I: Iliotibial tract ○ N: Superior gluteal ○ F: Hip flexion, abduction, and weak internal rotation • Quadratus femoris ○ O: Lateral ischial tuberosity ○ I: Quadrate line, intertrochanteric crest of femur ○ N: L4, L5, S1 ○ F: Strong hip external rotation

Rotator Cuff of Hip • Gluteus medius and minimus tendons, trochanteric bursa, subgluteus medius and minimus bursae

Bursa • Trochanteric ○ Greater trochanter and gluteus maximus muscle • Ischiogluteal ○ Ischial tuberosity and gluteus maximus muscle • Subgluteus medius ○ Greater trochanter and gluteus medius • Subgluteus minimus ○ Greater trochanter and gluteus minimus muscle • Gluteofemoral ○ Iliotibial tract and vastus lateralis muscle • Obturator internus ○ Muscle and ischium • Obturator externus ○ Synovial protrusion beneath inferior border

Piriformis Fossa • Between posterior femoral neck and posterior medial surface of greater trochanter • Insertion site for piriformis, superior and inferior gemelli, obturator internus

Ischial Tuberosity • Covered by gluteus maximus muscle when hip extended, uncovered in hip flexion • Origin of hamstrings and adductor magnus muscles

Sacroiliac Joint • Anterior synovial joint • Posterior syndesmosis: Tuberosities of sacrum and ilium • F: Primarily weight transfer from axial to appendicular skeleton ○ Limited gliding and rotation • Widening anteriorly can occur without instability • Posterior widening indicates instability • Sacroiliac ligaments ○ Interosseous sacroiliac: Within syndesmotic joint – Between tuberosities of ilium and sacrum – Oriented superiorly and laterally – Weight transferred to sacrum; sacrum displaced inferiorly; force transmitted to ligaments; ligaments pull ilii inward and compress sacrum and interlocking surfaces of sacroiliac joints – Extremely strong ○ Anterior sacroiliac: Weak ligaments – Mainly anterior joint capsule

Gluteal Muscles

Posterior Sacroiliac Ligaments of Pelvis • Primary stabilizers of pelvis ○ Little contribution from anterior structures • Resist rotational forces and vertical shear • Sacrotuberous: Superior and inferior posterior iliac spines, sacrum, and coccyx to ischial tuberosity • Sacrospinous: Lateral sacrum and coccyx to ischial spine • Iliolumbar: Tip of L5 transverse process to iliac crest • Sacroiliac ligaments: Interosseous, long and short dorsal

Greater Sciatic Foramen • Greater sciatic notch converted to foramen by sacrospinous ligament • Contents: Nerves, vessels, piriformis muscle • Passageway from pelvis to thigh ○ Structures identified as exiting pelvis above or below piriformis muscle – Above: Superior gluteal artery, vein, and nerve – Below: Pudendal nerve; internal pudendal artery and vein; nerve to obturator internus; sciatic nerve; inferior gluteal artery, vein, and nerve; posterior cutaneous nerve of thigh; nerve to quadratus femoris muscle ○ Relationship of structures – Most medial: Pudendal nerve – Most lateral: Sciatic nerve – Nerve to quadratus femoris muscle deep to sciatic nerve • Inferior gluteal artery ○ Larger terminal branch of anterior division internal iliac artery ○ Passes between S1 and S2 or S2 and S3 ○ Exits pelvis inferior to piriformis muscle ○ Posteromedial to sciatic nerve ○ Prenatally continuous with popliteal artery; remnant is artery to sciatic nerve ○ Supplies gluteus maximus, obturator internus, quadratus femoris, superior hamstrings muscles ○ Inferior gluteal vein travels with artery, drains into internal iliac vein • Inferior gluteal nerve ○ Branch of sacral plexus ○ Exits pelvis inferior to piriformis muscle ○ Posterior to sciatic nerve • Superior gluteal artery ○ Continuation of posterior division of internal iliac artery ○ Passes between lumbosacral trunk and S1 ○ Exits pelvis superior to piriformis muscle ○ Superficial branch supplies gluteus maximus muscle ○ Deep branch supplies gluteus medius and minimus, tensor fascia lata muscles ○ Superior gluteal vein travels with artery, drains into internal iliac vein • Superior gluteal nerve ○ Branch of sacral plexus

○ Exits pelvis superior to piriformis muscle • Sciatic nerve ○ Exits pelvis inferior to piriformis muscle ○ Most lateral structure • Pudendal nerve and internal pudendal vessels ○ Exit inferior to piriformis muscle ○ Nerve most medial structure • Nerve to obturator internus muscle ○ Exits pelvis inferior to piriformis muscle

Lower Extremity

○ Posterior sacroiliac: Posterior fibers interosseous ligament – Short dorsal sacroiliac: Horizontal; lateral sacral crest S1 and S2 to posterior iliac crest – Long dorsal sacroiliac: Vertical oblique; posterior superior iliac spine to lateral sacral crest S3, S4

Lesser Sciatic Foramen • Lesser sciatic notch converted to foramen by intersection (crossing) with sacrotuberous and sacrospinous ligaments • Contents ○ Pudendal nerve and internal pudendal vessels – Pass over sacrospinous ligament – Exit buttock, enter perineum ○ Obturator internus muscle

ANATOMY IMAGING ISSUES Imaging Recommendations • US ○ Subcutaneous fat in gluteal region can be thick and mistaken for muscle ○ Look for investing fascia and fiber orientation to identify muscle layer ○ Anisotropy gives gluteal muscles varying echogenicity due to different orientation of fibers – Allows clear distinction between muscles – Lesions may be better demonstrated/detected by scans along and across muscle fibers to make lesion more conspicuous ○ Iliac crest, greater trochanter, and ischial tuberosity are important bony landmarks for orientation ○ Use of panoramic (extended field of view) images will help referring clinicians to understand location of lesion – Panoramic images should be performed in standard anatomical planes to help interpretation – Landmarks, especially osseous (e.g., iliac crest, sacrum, ischial tuberosity), also help interpretation of panoramic image – Panoramic images do not provide accurate measurements – Wide lesions are best assessed using dual screen/multiple contiguous images for summated linear measurement • MR ○ Diagnose masses, anatomic anomalies, other causes of nerve compression ○ Preferred modality for sacroiliitis • CT ○ Mainly used for assessing bone and joint (sacroiliac) abnormalities

Imaging Pitfalls • Lower frequency transducers (5 MHz or below) should be used initially in examination to exclude deep-seated lesions

707

Lower Extremity

Gluteal Muscles GLUTEAL MUSCLES

Tensor fascia lata m. Gluteus medius m. Gluteus maximus m.

Gracilis m. Adductor magnus m. Semimembranosus m. Semitendinosus m.

Iliotibial tract

Biceps femoris m.

Tensor fascia lata m. Posterior sacroiliac l.

Gluteus medius m.

Piriformis m. Superior gemellus m. Sacrotuberous l.

Greater trochanter Iliotibial tract Obturator internus m.

Gracilis m. Inferior gemellus m. Quadratus femoris m. Adductor magnus m.

(Top) The gluteus muscles from anterior to posterior and deep to superficial are the gluteus minimus, medius, and maximus. These muscles form the bulk of the gluteal region. The gluteus maximus, in particular, covers most of the deep gluteal structures. (Bottom) After removing the gluteus maximus, the deep muscles are visible: Piriformis, superior gemellus, obturator internus, inferior gemellus, and quadratus femoris. These all function as external rotators of the thigh. Note the piriformis muscle, which exits via the greater sciatic foramen, and the obturator internus muscle via the lesser sciatic foramen.

708

Gluteal Muscles Lower Extremity

SCIATIC NERVE AND GLUTEAL REGION OVERVIEW

Tensor fascia lata m. Gluteus medius m. Gluteus maximus m. Piriformis m. Superior gemellus m. Obturator internus m. Sciatic n.

Iliotibial tract Inferior gemellus m.

Gracilis m.

Quadratus femoris m.

Adductor magnus m. Semimembranosus m. Semitendinosus m.

Biceps femoris m.

Serratus posterior Erector spinae m.

Ischial tuberosity Gemelli m.

Transverse processes Iliac crest

Gluteus maximus m.

Gluteus medius m.

(Top) The deep external rotators of the hip share an intimate relationship with the sciatic nerve, which emerges between the piriformis and superior gemellus muscles and then between the gluteus maximus and the rest of the deep external rotators. More distally, the sciatic nerve is covered by the biceps femoris muscle. (Bottom) Sagittal panoramic view shows the medial aspect of the gluteal region. The iliac crest separates the back muscles from the glutei. At this level, the gluteus maximus muscle forms the main muscle bulk. Inferiorly, the gluteus maximus runs across the surface of the ischial tuberosity in this extended (hip joint) position. Coverage is lost (gluteus maximus moves superiorly) when the hip joint is flexed and the ischial tuberosity is exposed.

709

Lower Extremity

Gluteal Muscles GLUTEAL REGION OVERVIEW

Gluteus maximus m.

Iliac crest

Gluteus medius m.

Greater trochanter

Femoral head

Gluteus minimus m.

Iliotibial tract Oblique abdominal m.

Greater trochanter

Iliac crest

Gluteus maximus m. Gluteus medius m. Gluteus minimus m.

(Top) Oblique sagittal panoramic view shows the lateral 1/2 of the gluteal region. The close relationship between the gluteus minimus muscle and the posterior aspect of the hip joint can be appreciated here. In this region, all 3 gluteal muscles are present and can be distinguished by their different echogenicity. The gluteus maximus muscle fibers are running ~ horizontally along the scan plane and, being most superficial, produce the highest echogenicity. The gluteus medius is running obliquely (lateral inferiorly) and thus shows short echogenic fibers. The gluteus minimus runs obliquely and almost horizontally toward the anterior facet of the greater trochanter. It is the deepest gluteal muscle and usually appears hypoechoic. (Bottom) Coronal panoramic view shows the gluteus medius and minimus muscles and their insertion on the greater trochanter. The iliotibial tract runs on the surface of the greater trochanter.

710

Gluteal Muscles

Gluteus maximus m.

Lower Extremity

SAGITTAL GLUTEAL REGION

Gluteus medius m. Gluteus minimus m. Quadratus femoris m. Piriformis m. Gemelli m.

Gluteus maximus m.

Gluteus medius m. Gluteus minimus m.

Ischium

Greater trochanter

Femoral neck

Gluteus maximus m. Gluteus medius m.

Greater trochanter superior facet Gluteus medius t. insertion

Gluteus minimus m. Proximal femur Ilium

(Top) Oblique sagittal scan in the lateral 1/2 of the gluteal region shows the 3 gluteal muscles and their relationship with the deeper, small external rotators: Piriformis, superior and inferior gemellus, and quadratus femoris muscles. (Middle) Further laterally, the femoral neck can be seen under the gluteus minimus. Again, the different echogenicity and echotexture of the 3 gluteal muscles can be appreciated. (Bottom) Further laterally, the gluteus medius tendon fibers insert onto the lateral and posterosuperior facets of the greater trochanter. The gluteus minimus tendon runs anteriorly under the gluteus medius to insert on the anterior facet of greater trochanter.

711

Lower Extremity

Gluteal Muscles TRANSVERSE GLUTEAL REGION

Gluteus maximus m.

Gluteus maximus m.

Gluteus medius m.

Gluteus medius m.

Gluteus minimus m.

Gluteus minimus m. Sacroiliac joint Posterior sacral foramen

Lateral cortex of ilium

Sacral median crest

Gluteus maximus m. Gluteus medius m. Posterior sacral foramen Sacroiliac joint

Gluteus minimus m.

Ilium

Gluteus maximus m. Gluteus medius m.

Ilium

(Top) Transverse panoramic scan shows the dorsal surface of the sacrum. This is the medial origin of the gluteus maximus muscle. Deep to this muscle, the gluteus medius and gluteus minimus muscles can be seen originating from the iliac surface. (Middle) Transverse panoramic view shows the right gluteal region. The 3 gluteal muscles show their signature difference in echogenicity and echotexture even in the horizontal plane. (Bottom) Transverse focused view of the medial gluteal region shows the fiber orientation of the different muscles. Those of the gluteus maximus are longer as they run roughly horizontally compared to those of the gluteus medius. This orderly fiber pattern is helpful in detecting intra- and intermuscular lesions in the gluteal region (orderly fiber alignment tends to be disrupted in disease).

712

Gluteal Muscles Lower Extremity

ISCHIAL REGION

Gluteus maximus m. Greater trochanter superior surface Sacrotuberous l.

Greater trochanter medial surface

Ischial tuberosity Quadratus femoris m.

Femoral neck posterior cortex

Gluteus maximus m. Iliac crest Posterior inferior iliac spine

Sciatic n.

Piriformis m. Adductor magnus m. Sciatic n. Greater sciatic foramen Ischial tuberosity

Hamstrings originating from ischial tuberosity

Gluteus maximus m. Piriformis m. Quadratus femoris m. Greater sciatic foramen Sciatic n. Ischium posterior cortex

Inferior gemellus m. Obturator internus t. Superior gemellus m.

(Top) Transverse panoramic view shows the ischial region. The gluteus maximus forms most of the bulk at this lower gluteal level. Deep to this, small external rotators of the hip can be seen (in this scan, the quadratus femoris muscle). (Middle) Sagittal panoramic scan is seen from the lower iliac bone to below the ischial tuberosity. The greater sciatic foramen is demonstrated in this scan. The piriformis and sciatic nerve exit the pelvis via this foramen and run inferolaterally, the former to insert on the greater tuberosity and the latter inferiorly to supply the leg. (Bottom) Sagittal view shows the greater sciatic foramen using the ischial tuberosity as a landmark. The sciatic nerve and its relationship with the small external rotators of the hip is shown here. The sciatic nerve emerges between the piriformis and superior gemellus muscles after exiting the pelvis through the greater sciatic foramen.

713

Lower Extremity

Gluteal Muscles TRANSVERSE ISCHIAL REGION

Gluteus maximus m.

Lesser sciatic foramen

Sciatic n.

Obturator internus t. Posterior wall acetabulum Hip joint capsule Hip joint

Femoral head posterior cortex

Greater trochanter Ischial tuberosity Inferior gluteal a.

Sciatic n. Medial surface of greater trochanter Inferior gemellus m.

Femoral neck posterior cortex

Gluteus maximus m. Hamstring origin Sciatic n.

Quadratus femoris m.

Quadrate tubercle of posterior cortex of femur

Lessor trochanter

Iliopsoas t.

(Top) Series of 3 transverse scans show the inferomedial aspect of the gluteal region. This image shows the obturator internus tendon exiting the lesser sciatic foramen, running laterally toward the lower aspect of the hip joint. The sciatic nerve runs superficial to this tendon. (Middle) Slightly inferiorly, this image shows the inferior gemellus muscle arising from the ischial tuberosity, running laterally over the neck of the femur and inserting at the piriformis fossa on the medial surface of the greater trochanter. The sciatic nerve runs superficial to this muscle. (Bottom) Further inferiorly, this image shows the quadratus femoris muscle arising from the lateral border of the ischial tuberosity and running laterally to insert on the quadrate tubercle of the femur. The sciatic nerve also runs superficial to this tendon.

714

Gluteal Muscles

Semitendinosus t. Semimembranosus t. Ischial tuberosity

Lower Extremity

ISCHIAL TUBEROSITY

Sciatic n. Quadratus femoris m. Inferior gluteal v. Biceps femoris t.

Gluteus maximus m.

Biceps femoris t. Ischial tuberosity

Gluteus maximus m. Semitendinosus t. Semimembranosus t.

Ischial tuberosity

(Top) Transverse scan shows the ischial tuberosity. The biceps femoris tendon originates lateral to the semimembranosus and semitendinosus tendons. The sciatic nerve and inferior gluteal vessels run just lateral to the ischial tuberosity. Inflammation in this region (e.g., ischiogluteal bursitis) may cause irritation of the sciatic nerve. More importantly, aspiration or injection to treat ischiogluteal bursitis should be performed with image guidance to avoid damaging the sciatic nerve. (Middle) Sagittal scan of the lateral aspect of the ischial tuberosity shows the origin of the biceps femoris tendon. (Bottom) Sagittal scan more medially on the ischial tuberosity shows the insertion of the semitendinosus and semimembranosus tendons. The semitendinosus muscle originates and runs for most of its course on the dorsal surface of the semimembranosus tendon.

715

Lower Extremity

Groin

TERMINOLOGY Abbreviations • Origin (O), insertion (I)

Definitions • Junctional region between thigh and trunk

IMAGING ANATOMY Overview • Incorporates lower abdominal wall, inguinal canal, femoral triangle, and femoral adductor muscles

Osseous Anatomy • Pubic bone ○ Pubic tubercle: Small protuberance, lateral border pubic crest – Attachment: Inguinal ligament ○ Superior and inferior rami: Extend from pubis ○ Pecten: Ridge, posterior aspect superior pubis – O of pectineus muscle – I of conjoint tendon (internal oblique and transverse abdominis) ○ Pubic crest: Superior surface, anterior aspect pubic body – O of rectus abdominis muscle – I of transversus abdominis and external oblique muscles ○ Pubic symphysis: Cartilaginous joint between pubic bodies ○ Superior pubic ligament: Laterally extends to pubic tubercles

Anterior Abdominal Wall • Abdominal wall muscles ○ Rectus abdominis: Paired midline muscles – O: Superior pubic ramus, pubic crest – I: Xiphoid process, costal cartilages 5-7 ○ Linea alba: Aponeurotic junction of rectus femoris, transverse abdominis, and internal and external oblique muscles ○ External oblique: Most superficial – O: Ribs 5-12 – I: Pubic crest, anterior iliac crest, linea alba – Lower border of aponeurosis contributes to inguinal ligament ○ Internal oblique: Between external oblique, transversus abdominis – O: Lateral inguinal ligament, iliac crest, thoracolumbar fascia – I: Pecten (conjoined tendon), pubic crest, inferior aspect of ribs 10-12, linea alba – O anterior to deep inguinal ring – I lateral to rectus abdominis muscle, posterior and medial to superficial inguinal ring – Arches over inguinal canal, forming roof ○ Transversus abdominis: Deepest – O: Iliac crest, posterior aspect of lateral inguinal ligament, thoracolumbar fascia – I: Pubic crest, pecten (conjoined tendon), linea alba – Remains posterior to inguinal canal 716

Inguinal Ligament • Thickening inferior border of external oblique aponeurosis • Attachments: Anterior superior iliac spine and pubic tubercle • Separates lower extremity from pelvis • Fascia lata attaches to inferior border • Subinguinal space: Deep to inguinal ligament ○ Passageway for femoral vessels and nerve, iliopsoas muscle into femoral triangle ○ External iliac vessels become femoral vessels upon entering this space

Inguinal Canal • Entrance: Deep inguinal ring ○ Located midinguinal ligament ○ Opening of evaginated transversalis fascia through which spermatic cord/round ligament pass • Exit: Superficial inguinal ring ○ Division of external oblique aponeurosis lateral to pubic tubercle • Contents: Ilioinguinal nerve; male: Spermatic cord; female: Round ligament; associated vessels ○ Covered by evaginated transversalis fascia

Adductor Musculature • Adductor longus muscle: Thin tendon arises from medial superior pubic ramus ○ Overlies O of gracilis, adductor brevis, and magnus muscles • Gracilis muscle: O from anterior aspect of symphysis pubis and medial aspect of inferior pubic ramus ○ O medial to adductor brevis muscle, deep to adductor longus muscle

Groin Nodes • 2 groups of groin lymph nodes • Superficial inguinal nodes ○ Lie in subcutaneous tissues below inguinal ligament and alongside great saphenous vein ○ Subdivided into 3 groups of lymph nodes – Inferior group are located distal to saphenous opening and receive drainage from lower limb – Superolateral group are located lateral to saphenous opening and receive drainage from lateral buttock and lower anterior abdominal wall regions – Superomedial group are located medial to saphenous opening and receive drainage from perineum and external genitalia • Deep inguinal nodes ○ 3-5 nodes located in femoral triangle just medial to femoral vein ○ Cloquet node is most proximal of deep inguinal lymph nodes located just below inguinal ligament

ANATOMY IMAGING ISSUES Imaging Recommendations • Usual imaging pathway for assessing groin pathology is radiography followed by ultrasound • If this does not provide necessary information, MR is next best investigation for most groin pathology

Groin Lower Extremity

GROIN

Iliacus m.

Psoas m. Femoral n.

Femoral canal/Cloquet node

Common femoral a. Femoral sheath Common femoral v.

Inguinal l. Symphysis pubis Pubic tubercle

Greater saphenous v.

Saphenous opening Lymphatics

Iliacus m. Femoral n.

Psoas m. Femoral canal/Cloquet node

Common femoral a. Common femoral v.

Inguinal l. Symphysis pubis

Tensor fascia lata m.

Pubic tubercle Pectineus m.

Rectus femoris m. Apex femoral triangle

Sartorius m. (cut away)

Adductor longus m.

Gracilis m.

(Top) The boundaries of the femoral triangle can be remembered by the mnemonic SAIL for sartorius, adductor longus, and inguinal ligament. The contents of the femoral triangle from lateral to medial (remembered by the mnemonic NAVeL) are the femoral nerve, femoral artery and vein, and lymphatics. The nerve lies superficial to the iliopsoas muscle. The fascia lata encases the structures of the thigh. The femoral sheath is the fascial covering over the proximal vessels. At the cut away proximal boundary, note the septa dividing the sheath into compartments. The femoral canal is the medial compartment. (Bottom) Femoral triangle is shown after removal of the fascia lata, sartorius muscle, and the vessels. The apex of the triangle is at the crossing of the sartorius and adductor longus muscles. The pectineus, adductor longus, and iliopsoas muscles form the floor of the triangle.

717

Lower Extremity

Groin GROIN MUSCLES

Psoas major m. Iliacus m. Anterior superior iliac spine

Tensor fascia lata m.

Pectineus Adductor longus m.

Sartorius m.

Rectus femoris m.

Adductor brevis m.

Gracilis m.

Iliotibial tract

Vastus lateralis m.

Psoas major m. Iliacus m. Anterior superior iliac spine

Pectineus Adductor longus m. Femoral neck

Adductor brevis m.

Vastus intermedius m.

Vastus medialis m. Vastus lateralis m.

(Top) Superficial muscles of the groin are shown. The most lateral muscle is the sartorius; its oblique course is easily appreciated. The psoas major and iliacus muscle exit from the pelvis toward the lesser trochanter. On the medial side, the most medial muscle is the gracilis. The adductor brevis muscle is deep to the adductor longus and pectineus muscles. (Bottom) After removing the superficial layer of muscles, the floor of the femoral triangle is better appreciated. The iliopsoas muscle dives deeply to its trochanteric insertion. The adductors fan out laterally from their pubic origin and constitute the major medial component at a midthigh level. The adductor magnus is in a deeper and more posterior position.

718

Groin

Inferior epigastric vessels

Lower Extremity

GROIN OVERVIEW

Internal oblique m. Sartorius m. Tensor fascia lata m.

Rectus abdominis m.

Gluteus medius m. Iliopsoas m. Origin of rectus femoris m.

Bowel gas External iliac vessels

Anterior inferior iliac spine

Sartorius m. Iliopsoas m. Gluteus medius m.

Pubic tubercle Pectineus m. Common femoral v.

Rectus femoris m.

Common femoral a. Femoral n.

Adductor longus m. Great saphenous v. Femoral n. Sartorius m. Rectus femoris m. Tensor fascia lata m. Vastus lateralis m.

Adductor brevis m. Adductor magnus m. Obturator externus m. Pectineus m.

Iliopsoas m.

Common femoral v. Superficial and profunda femoral aa.

(Top) Series of transverse panoramic scans show the groin. At this higher level, the lateral components of the groin include the sartorius and iliopsoas muscles and at the medial boundary, the rectus abdominis muscle. At this level, where most structures are above the inguinal ligament, there is bowel (containing gas, which produces shadowing artifact). At this level, vessels are named external iliac vessels. (Middle) At a lower level, through the pubic bone, the vessels have moved superficially after passing under the inguinal ligament and now become the common femoral vessels. Bowel is not normally present at this level; instead, the pectineus muscle and superior pubic ramus form the floor. (Bottom) Further inferiorly, the adductor muscles become the major medial component. Femoral vessels divide into superficial and profunda branches.

719

Lower Extremity

Groin MIDLINE GROIN

Rectus abdominis m. Transverse abdominis m. External oblique m. Adductor longus m. Adductor brevis m. Obturator externus m.

Internal oblique m. Inguinal l. Adductor magnus m. (ischiocondylar) Gracilis m. Adductor magnus m. (adductor)

Rectus sheath

Rectus abdominis m. Superior pubic l. Body of pubic bone Pubic symphysis

Rectus abdominis m. Bowel gas with posterior shadow

Anterior surface of pubic bone Superior surface of pubic bone

(Top) Anterior view shows the anterior pelvis and the associated muscle attachments. A number of muscles take origin or insert onto the anterior aspect of the pelvis. These muscles aid in movement and stabilization of the trunk as well as movement and stabilization of the leg and form the medial components of the groin. (Middle) Transverse scan at the superior aspect shows pubic symphysis. The superior pubic ligament runs horizontally across the symphysis, deep to the rectus abdominis muscle origin. (Bottom) Sagittal image shows the lower rectus abdominis originating from the superior surface of the pubic bone (pubic crest). Deep to the rectus abdominis muscle is the peritoneal cavity and bowel. Bowel gas produces posterior shadowing artifact, which obscures deeper structures.

720

Groin Lower Extremity

MEDIAL GROIN

Inguinal l.

Pectineus m. Body of pubic bone

Adductor brevis m.

Adductor longus m. Body of pubic bone Adductor brevis m. Inferior pubic ramus Adductor magnus m.

Adductor longus m.

Adductor brevis m.

Gracilis m.

Adductor magnus m.

(Top) Series of (oblique) transverse scans through the adductor muscles is shown. Superiorly, the pectineus muscle originates from the pectineal line (which is a ridge on the superior ramus of the pubic bone) and runs laterally to insert on the pectineal line of the proximal femur. The pectineal line of the proximal femur lies between the lesser trochanter and the linea aspera. The pectineus muscle runs lateral to the adductor longus muscle and superficial to the adductor brevis muscle. (Middle) Slightly inferiorly and scanning more obliquely, the adductor longus, brevis, and magnus can be seen originating from the pubic body and inferior ramus. Scanning this region requires thigh abduction and balancing the transducer head on the bony landmark. From here, individual muscles can be traced inferolaterally. Note that the scout image is a graphic in this sagittal plane. (Bottom) Oblique transverse scan of adductors using a medial approach is shown. Adductor longus and gracilis muscles form the superficial layer; adductor brevis and magnus muscles run deeper. All muscles run inferolaterally to their femoral insertions.

721

Lower Extremity

Groin CENTRAL GROIN, FEMORAL TRIANGLE

Femoral n.

Common femoral v. Iliopsoas m. Common femoral a.

Pubic bone

Superficial epigastric a. Common femoral a. Common femoral v.

Femoral canal Femoral n. Pectineus m. Iliopsoas m. Pubic bone Femoral head anterior cortex

Inguinal lymph node (superficial chain)

Common femoral a. Common femoral v. Iliopsoas m. Pectineus m. Femoral head anterior cortex Pubic bone

(Top) Series of transverse scans through the femoral triangle is shown. Above the inguinal ligament, the femoral nerve, artery, and vein run medial to the iliopsoas tendon. The pubic bone acts as a hard support for the iliopsoas and pectineus muscular floor. (Middle) Slightly inferiorly, below the inguinal ligament, the femoral triangle commences. The mnemonic for the contents is NAVeL, standing for femoral nerve, common femoral artery, common femoral vein, and lymph nodes (within femoral canal). The pectineus muscle forms the floor of femoral triangle. This floor is supported by the pubic bone and hip joint. (Bottom) In addition to lymph nodes in the femoral canal, lymph nodes are frequently seen superficially (the superficial inguinal chain) in the subcutaneous tissue.

722

Groin

Great saphenous v. Lymph node

Lower Extremity

CENTRAL GROIN, FEMORAL TRIANGLE

Superficial epigastric a. Femoral n. Common femoral a. Common femoral v.

Adductor longus m. Medial circumflex femoral v.

Sartorius m.

Vastus medialis m. Profunda femoral a.

Adductor longus m. Superficial femoral a. Superficial femoral v.

Profunda femoral v. Adductor magnus m.

Sartorius m. Vastus medialis m. Superficial femoral v.

Adductor longus m. Superficial femoral a.

Adductor magnus m. Profunda femoral v.

(Top) Further inferiorly and still within the femoral triangle, the great saphenous vein perforates the anterior wall of the femoral sheath to enter the femoral vein. Also, the floor changes from the pectineus to adductor longus muscle with no bony support. (Middle) Transverse scan is shown at the apex of the femoral triangle, defined as where the sartorius muscle becomes the roof of the femoral triangle. Just before exiting the femoral triangle, the femoral vessels divide into superficial and profunda branches. (Bottom) Transverse scan shows the adductor canal. Distal to the femoral triangle, the superficial femoral vessels continue within a muscular conduit, the adductor canal. The groin muscles (the adductor longus and magnus muscles) form the medial wall and floor of this canal.

723

Lower Extremity

Groin LATERAL GROIN, ANTERIOR SUPERIOR ILIAC SPINE

Internal oblique m.

Latissimus dorsi m.

External oblique m. Tensor fascia lata m. Inguinal l. Sartorius m. Rectus femoris m. Iliofemoral l. Pectineus m. Adductor longus m. Gracilis m. Adductor brevis m. Obturator externus m.

Gluteus maximus m. Gluteus medius m. Piriformis m. Gluteus minimus m. Quadratus femoris m. Superior gemellus m. Inferior gemellus m. Semimembranosus m. Long head, biceps femoris m. Semitendinosus m. Adductor magnus m. Inguinal l.

Sartorius m. Anterior superior iliac spine Iliopsoas m.

Inguinal l. Anterior superior iliac spine Gluteus medius m. Gluteus minimus m.

Iliacus m.

(Top) Muscle and ligament attachments to the external surface of the pelvis are shown. Note the relatively small origin of the tendon of the adductor longus muscle. The adductor brevis muscle is just deep to the longus muscle. The origin of the gracilis muscle is lateral to the adductor brevis muscle. The adductor magnus muscle has a broad origin with its posterior fibers in close proximity to the hamstring tendon origins. (Middle) Oblique sagittal scan of the anterior superior iliac spine shows the origin of the sartorius muscle (longest muscle in the body). This slender muscle runs inferomedially over the iliopsoas muscle, covers the adductor canal, and inserts at the proximal tibia as part of the pes anserinus. (Bottom) Coronal scan of the anterior superior iliac spine shows division of muscle groups by this bone. Gluteal muscles lie lateral and hip flexors medial. The inguinal ligament originates here and runs inferomedially to the pubic tubercle.

724

Groin Lower Extremity

ACROSS GROIN, INGUINAL LIGAMENT

Anterior superior iliac spine Sartorius m. Inguinal l. Rectus femoris m.

Iliopsoas m. Hip joint capsule

Hip joint Anterior cortex of femoral head

Femoral neck

Common femoral a. Common femoral v. Iliopsoas m.

Pubic tubercle Inguinal l.

Pectineus m.

Anterior cortex of superior pubic ramus

Internal oblique m. Inguinal l.

Femoral n. Common femoral a.

Lymph node

Iliopsoas m. Common femoral v.

Inferior epigastric a. and v.

(Top) Oblique transverse scan of the upper groin shows the inguinal ligament attachment on the anterior superior iliac spine with the sartorius muscle originating immediately inferior. The inguinal ligament runs inferomedially and covers the iliopsoas muscle. (Middle) Oblique transverse scan along the medial aspect of the inguinal ligament is shown. Medially, the inguinal ligament forms the roof of the femoral canal (covering the femoral vessels and nerve). It then runs over the pectineus muscle to insert on the pubic tubercle. (Bottom) Superficially focused oblique transverse scan over the upper femoral triangle shows the inguinal ligament forming its roof. Inferior epigastric vessels branch out from the femoral vessels and run superomedially. Clinically, the inferior epigastric vessels define the lateral boundary of direct inguinal hernias. Inguinal hernias that emerge lateral to the inferior epigastric vessels are considered indirect.

725

Lower Extremity

Hip

IMAGING ANATOMY Overview • Ball and socket joint with wide range of motion 2nd only to glenohumeral joint

Acetabulum • • • •

Formed by pubis, ilium, ischium Oriented anterior, inferior, lateral Covers > 50% femoral head Anterior and posterior rims: Osseous margins of acetabulum • Medial wall: Quadrilateral plate ilium

Femoral Head • 2/3 of sphere • Covered by articular cartilage ○ Cartilage thickest superiorly ○ Cartilage thins at head/neck junction

Labrum • • • • •

Fibrocartilage lip deepens acetabular rim Joins transverse ligament at margins of acetabular notch Thickest posteriorly and superiorly Widest anteriorly and superiorly Vascular supply: Branches of obturator, superior, and inferior gluteal arteries ○ Mainly capsular surface • Shape ○ Triangular in 66-94% ○ Variants: Rounded/blunt or absent ○ Absent labra: Constellation absent anterior labrum and small remnant superiorly – In 10-14% asymptomatic individuals • Function ○ Protect cartilage: Distributes forces by maintaining synovial fluid layer between articular surfaces ○ Prevents lateral translation femoral head • Labral tear ○ Frequently has associated paralabral ganglion/cyst ○ Easier to detect in presence of joint effusion/arthrographic contrast ○ More common anterosuperiorly and anteriorly

Joint Capsule • 2 layers: Internal synovial and external fibrous (not usually separable on imaging) ○ External layer forms capsular ligaments • Attachments ○ Acetabulum – Base of labrum anteriorly and posteriorly – Several millimeters above labrum superiorly ○ Femur – Anterior: Intertrochanteric line – Posterior: Proximal to intertrochanteric crest – Anterior attachment more lateral than posterior attachment ○ Perilabral recess: Between labrum and capsule – Smaller anteriorly and posteriorly – Larger superiorly 726

Vascular Supply • Branches of medial and lateral circumflex femoral, deep division of superior gluteal, inferior gluteal arteries, artery of ligamentum teres (branch of obturator artery)

Innervation • Branches from nerve to rectus femoris, nerve to quadratus femoris, anterior division obturator nerve, accessory obturator nerve, superior gluteal nerve

Major Adjacent Structures • Greater trochanter ○ Insertion – Gluteus minimus and medius muscles – Gluteus minimus to anterior facet – Gluteus medius to lateral and posterosuperior facets ○ Separated from overlying iliotibial tract by thin trochanteric bursa (normally barely perceptible on imaging) • Lesser trochanter ○ Insertion – Iliopsoas muscle • Anterior inferior iliac spine ○ Origin – Rectus femoris muscle • Iliopsoas muscle ○ Run inferomedially across anterior surface of hip joint • Femoral vessels ○ Separated from hip joint by iliopsoas muscle

Neonatal Hip • High success rate in treatment of developmental dysplasia demands early imaging diagnosis (with ultrasound) • Established measurements of bony and cartilaginous components for comparison with normal reference • Main measurements reflect depth of acetabulum and acetabular coverage of femoral head

ANATOMY IMAGING ISSUES Imaging Recommendations • Radiographs for assessing osseous alignment • Ultrasound for joint effusion and surrounding soft tissue ○ Also used for real-time guided procedures: Hip joint or abscess aspiration/biopsy; intraarticular contrast injection ○ Ideal in neonates for suspected developmental hip dysplasia • MR arthrography preferred to assess intraarticular structures

Imaging Sweet Spots • Small joint effusions are best detected on ultrasound by hypoechoic thickening/layer over anterior surface of femoral neck ○ Best site for aspiration/injection • Paralabral ganglion cysts should alert physician to presence of labral tear

Imaging Pitfalls • Synovial proliferation usually shows no evidence of vascularity on color Doppler scanning and is therefore difficult to distinguish from effusion

Hip

Femoral n. Iliopsoas bursa

Femoral a.

Lower Extremity

AXIAL & SAGITTAL HIP SECTIONS

Femoral v. Anterior rim of acetabulum Anterior column of acetabulum

Longitudinal capsular ll. Zona orbicularis

Ligamentum teres Medial wall of acetabulum Posterior rim of acetabulum

Greater trochanter Posterior column of acetabulum Ischial spine

Internal pudendal v. and a.

Ilium

Anterior column of acetabulum

Anterior labrum Femoral head

Posterior column of acetabulum Articular cartilage Posterior labrum

Ischial tuberosity

(Top) Axial graphic representation shows the hip joint. The iliopsoas bursa is closely approximated to the joint anteriorly. The ligamentum teres is seen in profile as a flattened structure. The 2 layers of the external capsule, the more superficial longitudinal fibers and deep circular fibers, are visible. (Bottom) Sagittal representation of the hip joint nicely demonstrates the inverted Y of the acetabulum. The ilium is the stem, and the limbs are the anterior and posterior acetabular columns.

727

Lower Extremity

Hip CORONAL HIP SECTION & LIGAMENTS

Superior labrum

Iliofemoral l. Zona orbicularis Subgluteus medius bursa

Pulvinar Ligamentum teres Transverse l.

Trochanteric bursa

Anterior superior iliac spine

Anterior inferior iliac spine

Iliofemoral l. Pubofemoral l. Ischiofemoral l. Greater trochanter

Intertrochanteric line Lesser trochanter

(Top) This coronal image demonstrates many of the important structures of the hip joint. The longitudinally oriented fibers of the ligaments of the external joint capsule and the deeper circularly oriented fibers of the zona orbicularis are visible. Note the long axis of the ligamentum teres and its insertion onto the transverse ligament. The pulvinar fills the acetabular fossa. (Bottom) Anterior ligaments are shown. The longitudinal spiral of the iliofemoral and pubofemoral ligaments is well seen with attachments to the anterior inferior iliac spine and pubic aspect of the obturator foramen, respectively. The ischiofemoral ligament wraps over the superior aspect of the femoral neck to attach to the anterior femoral neck.

728

Hip Lower Extremity

HIP OVERVIEW

Femoral n. Sartorius m. Pectineus m. Tensor fascia lata m. Superior public ramus Rectus femoris m. Iliopsoas m. and t. Hip joint capsule and femoral head cartilage Anterior femoral head cortex

Common femoral v. Common femoral a. Anterior acetabular rim

Sartorius m. Anterior inferior iliac spine Long head of rectus femoris m.

Iliopsoas m.

Anterior surface of acetabulum

Neck of femur

Acetabular labrum

Cortex of head of femur

Anterior hip joint capsule

(Top) Transverse panoramic scan shows the femoral head. Medially and superiorly, the femoral head is covered by bony acetabulum and not visible with ultrasound. Laterally, the hip joint lies deep to the iliopsoas muscle and femoral triangle. Further laterally, the hip joint is associated with the gluteal muscles. (Bottom) Oblique sagittal scan shows hip joint and anterior inferior iliac spine. The acetabular labrum, which is thickest and widest anteriorly, can be seen between the acetabular rim and joint capsule. Small joint effusions are 1st detected not over the femoral head, but over the femoral neck as a hypoechoic layer. The femoral neck's relatively safe access makes it a suitable site for guided aspiration/injection.

729

Lower Extremity

Hip ACETABULUM

Iliopsoas m. and t.

Bony acetabulum

Zona orbicularis

Anterior acetabular labrum Femoral head

Femoral n. Common femoral a. Common femoral v.

Iliopsoas m. and t.

Pectineus m.

Anterior hip joint capsule Anterior acetabular rim Anterior cortex of femoral head

Common femoral a.

Acetabular labrum Femoral head cortex Iliopsoas t. Femoral neck cortex Minimal hypoechoic layer of joint fluid/synovium

(Top) Oblique sagittal scan along the axis of the femoral neck shows the triangular cross section of anterior acetabular labrum. Joint effusion/contrast tends to allow better delineation of its contour and lesions. (Middle) Transverse scan is shown at the level of the hip joint. Anterior femoral cortex/cartilage, hip joint capsule, and acetabular rim are well visualized. The contents of the femoral triangle are separated from the hip joint by the iliopsoas muscle and tendon, which explains why paralabral cysts may tract along the iliopsoas muscle. (Bottom) Effusions are 1st detected not over the femoral head but over the femoral neck as an increase in the normally minimal hypoechoic layer of joint fluid and synovium. This is also the safest site for joint injections (intraarticular contrast or medication).

730

Hip

Sartorius m. Common femoral a.

Lower Extremity

ILIOPSOAS INSERTION

Psoas m. Iliacus m.

Rectus femoris m. Common femoral v.

Iliofemoral l. Obturator externus m.

Lesser trochanter

Intertrochanteric line

Adductor longus m. Common femoral v. Pectineus m.

Adductor brevis m.

Iliopsoas t. Adductor magnus m.

Lesser trochanter Femoral neck anterior cortex

Superficial femoral a. Femoral n. Rectus femoris m. Profunda femoral a. Pectineus m. Psoas m. Iliacus m.

Common femoral v.

Obturator externus m.

Anterior surface of femur Lesser trochanter

(Top) Oblique sagittal scan along the course of the iliopsoas muscle is shown. Resolution is reduced due to depth of structures, which may be partially improved by externally rotating the hip to bring deep structures closer to the surface. (Middle) Oblique sagittal scan is shown slightly more distal. Insertion of iliopsoas tendon is at the lesser trochanter, which may be avulsed in injury. Notice the close relationship between these structures and the adductor compartment. (Bottom) Transverse scan shows distal iliopsoas tendon just before insertion. A functional division is present between the hip flexor (iliopsoas) and hip adductors. This is also the apex level of the femoral triangle where superficial and profunda vessels bifurcate.

731

Lower Extremity

Hip ANTERIOR INFERIOR ILIAC SPINE Sartorius m.

Tensor fascia lata m.

Iliopsoas m.

Gluteus minimus m. Anterior inferior iliac spine

Sartorius m.

Tensor fascia lata m.

Iliopsoas m.

Gluteus minimus m. Long head of rectus femoris m.

Hip joint

Sartorius m. Iliopsoas m.

Anterior inferior iliac spine

Hip joint capsule

Anterior acetabular labrum Cartilage of anterior femoral head

(Top) Transverse scan through the anterior inferior iliac spine is shown. The rectus femoris muscle, together with the sartorius muscle (which originates from anterior superior iliac spine) and the iliopsoas muscle (which originates from iliac fossa and lumbar transverse processes), cross the hip joint and form the hip flexors. (Middle) Transverse scan more inferior shows the long head of the rectus femoris muscle running deep to the sartorius muscle and lateral to the iliopsoas muscle. Note that the rectus muscle is the only quadriceps muscle that crosses the hip joint and thus acts as both hip flexor and knee extensor. (Bottom) Oblique scan along the sartorius muscle at hip joint level shows it to be roughly parallel with the iliopsoas muscle. The rectus femoris lies in a more lateral plane.

732

Hip

Gluteus medius m.

Lower Extremity

GREATER TROCHANTER

Gluteus minimus t. Superior surface of greater trochanter Gluteus medius t.

Iliotibial tract

Lateral surface of greater trochanter Cortex of femoral shaft

Vastus lateralis m.

Iliotibial tract Gluteal fascia Gluteus maximus m. Gluteus minimus t. Superior surface of greater trochanter

Vastus lateralis m. Gluteus medius t.

Iliotibial tract Gluteus medius t. Gluteal fascia Gluteus maximus m. Vastus lateralis m. Superior surface of greater trochanter

(Top) Coronal panoramic scan shows the greater trochanter. The gluteus minimus and medius tendons insert on the anterior, lateral, and superoposterior facets of the greater tuberosity. The iliotibial tract originates from the anterior aspect of the iliac crest (as the tensor fascia lata muscle) and runs inferiorly, passing superficial to the lateral surface of the greater trochanter. (Middle) Transverse scan through the anterior facet of the greater trochanter shows insertion of the gluteus minimus tendon. The gluteus medius tendon and iliotibial tract pass superficial to this. (Bottom) Transverse scan of the lateral facet of the greater trochanter shows the insertion of the gluteus medius tendon. The iliotibial tract is closest to the trochanter at this point and may be irritated, resulting in the formation of bursitis (trochanteric bursitis).

733

Lower Extremity

Hip PEDIATRIC HIP

Gluteus medius

Unossified greater trochanter Femoral shaft cortex Gluteus minimus Acetabular labrum

Femoral head

Acetabular roof Part of triradiate cartilage

Gluteus medius

Unossified greater trochanter

Gluteus minimus Acetabular roof Femoral head Part of triradiate cartilage

Gluteus medius

Gluteus minimus Acetabular roof Femoral head Part of triradiate cartilage

(Top) Coronal scan shows the hip of a 1-month-old neonate with the hip in extension. The femoral head and the greater trochanter are purely cartilaginous. This allows ultrasound transmission and thus visualization of the acetabular fossa. (Middle) Coronal scan shows the hip of a 1-month-old neonate with the hip in flexion, which produces an axial section of the femoral head. The femoral head should appear round in this section. Both the femoral head and the greater trochanter are purely cartilaginous, allowing ultrasound transmission and thus better visualization of the depth of the acetabular fossa. (Bottom) Transverse scan of the femoral head with hip in extension also shows the central position of a normal femoral head on the triradiate cartilage (golf ball on tee appearance).

734

Hip Lower Extremity

PEDIATRIC HIP

Labrum

Iliac cortex

β angle

Promontory

α angle

Acetabular roof

Line a

Gluteus medius Gluteus minimus

Acetabular labrum

Femoral shaft cortex Ossification in femoral head

Acetabular roof Part of triradiate cartilage

(Top) Three lines are drawn on the standard coronal image of the pediatric hip: (A) Along the straight contour of the iliac cortex, (B) from promontory along the acetabular roof to describe the α angle, and (C) from promontory to the tip of the labrum for β angle. Normal ranges are α angle > 60° and β angle < 55°. Measurements outside of these ranges are suggestive of developmental hip dysplasia. (Middle) The proportion of the femoral head contained within the acetabulum is calculated by dividing the depth (d) of femoral head below line a by the diameter of the femoral head (D). In normal subjects, > 50% of the femoral head should be below line a. (Bottom) Coronal scan shows the hip of a 4-month-old child with the hip in extension. The center of the femoral head has begun to ossify, showing up as an echogenic focus with posterior acoustic shadowing.

735

Lower Extremity

Thigh Muscles

TERMINOLOGY Abbreviations • Function (F), insertion (I), origin (O)

IMAGING ANATOMY Compartment Anatomy • Compartmental anatomy is different from functional groupings • Thigh divided into anterior, medial, and posterior compartments ○ Anterior compartment: Iliotibial tract, tensor fascia lata muscle, quadriceps muscles, sartorius muscle ○ Medial compartment: Gracilis muscle, adductor muscles ○ Posterior compartment: Hamstring muscles, short head of biceps femoris muscle, sciatic nerve • Additional muscles at junction pelvis/thigh ○ Pectineus, iliopsoas, obturator externus, lateral femoral muscles • Extensions from fascia lata divide compartments ○ Medial intermuscular septum: Anterior/medial ○ Lateral intermuscular septum: Anterior/lateral ○ Thin fascia separates medial, posterior compartments • Clinical note: Compartment anatomy critical to tumor staging and biopsy planning ○ Cross-compartment extension of tumor, contamination by biopsy requires change from limb salvage to amputation

Medial Femoral Muscles • Anterior division: Adductor brevis and longus, gracilis muscles • Posterior division: Adductor portion adductor magnus muscle • Common function: Hip adduction; assist hip flexion, internal rotation (except obturator externus muscle) • Adductor brevis ○ O: Inferior pubic ramus ○ I: Inferior 2/3 pectineal line, superior 1/2 medial lip of linea aspera • Adductor longus ○ O: Pubic body inferior to crest ○ I: Medial lip of linea aspera • Adductor magnus: 2 separate muscles with different innervations and functions ○ Adductor portion – O: Ischiopubic ramus – I: Gluteal tuberosity, medial lip linea aspera, medial supracondylar line ○ Adductor hiatus between 2 divisions of muscle in distal thigh • Gracilis ○ O: Inferior pubic ramus, symphysis pubis ○ I: Medial proximal tibia (pes anserine) ○ F: Also assists knee flexion • Obturator externus ○ O: External margins of obturator foramen membrane ○ I: Piriformis fossa ○ F: Hip external rotation only • Pectineus 736

○ ○ ○ ○

O: Superior pubic ramus, pecten I: Pectineal line femur Femoral nerve ± accessory obturator nerve Unclear pre- or postaxial muscle

Anterior Femoral Muscles • Common function: Knee extension (except sartorius) • Rectus femoris ○ O: Straight head = anterior inferior iliac spine; reflected head = groove above acetabulum ○ I: Superior patella, tibial tuberosity ○ F: Also hip flexion ○ Crosses 2 joints • Sartorius: Tailor's muscle ○ O: Anterior superior iliac spine, notch below ○ I: Proximal medial tibia (pes anserine) ○ F: Hip flexion, abduction, external rotation; knee flexion ○ Crosses 2 joints ○ Longest muscle in body ○ Separate fascial covering • Vastus lateralis ○ O: Superior intertrochanteric line femur, anterior and inferior greater trochanter, gluteal tuberosity, lateral lip of linea aspera, lateral intermuscular septum ○ I: Lateral tibial condyle (lateral patellar retinaculum) superolateral patella (quadriceps tendon) ○ Largest quadriceps muscle • Vastus medialis ○ O: Entire medial lip of linea aspera, inferior intertrochanteric line, medial intermuscular septum ○ I: Tendon of rectus femoris muscle, superomedial patella (quadriceps tendon), medial condyle tibia (medial patellar retinaculum) • Vastus intermedius ○ O: Anterior and lateral femoral shaft, inferior lateral lip of linea aspera, lateral intermuscular septum ○ I: Blends along deep aspect rectus femoris, vastus medialis, vastus lateralis muscles • Quadriceps femoris: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius muscles ○ Common tendon of insertion onto superior, lateral, medial patella

Posterior Femoral Muscles • Common functions: Hip extension, knee flexion • Biceps femoris ○ Long head O: Ischial tuberosity (inferior, medial) – Common tendon with semitendinosus muscle ○ Short head O: Lateral lip of linea aspera femur, lateral supracondylar line, lateral intermuscular septum – Postaxial muscle – Not part of hamstring muscles ○ I: Fibular head, lateral condyle tibia ○ F: Also external rotation flexed knee • Semimembranosus ○ O: Ischial tuberosity (superior, lateral) ○ I: Posterior medial condyle tibia, popliteal fascia – Some fibers extend to form oblique popliteal ligament ○ F: Also internal rotation flexed knee ○ Membranous in upper thigh

Thigh Muscles

Lateral Femoral (Gluteal) Muscles • Iliotibial tract/band: Lateral thickening fascia lata ○ O: Tubercle iliac crest ○ I: Lateral condyle tibia ○ Insertion site tensor fascia lata muscle, portion of gluteus maximus muscle

Hip Flexors • Iliopsoas I: Lesser trochanter ○ Iliacus – O: Iliac crest, iliac fossa, sacral ala, sacroiliac joint capsule – Femoral nerve ○ Psoas major – O: Lateral vertebral body and intervertebral discs T12L5, all lumbar transverse processes – L1, L2, L3 ○ Psoas minor – O: Lateral vertebral body T12, L1, and T12-L1 intervertebral disc – L1, L2 • Sartorius and pectineus

Femoral Triangle • Anterior wall: Inguinal ligament • Posterior wall: Adductor longus and pectineus muscles (medial), iliopsoas muscle (lateral) • Medial border: Adductor longus muscle • Lateral border: Sartorius muscle • Apex: Crossing of adductor longus and sartorius muscles • Contents: Femoral nerve and branches, femoral vessels, lymph node ( node of Cloquet), femoral sheath ○ Structures lateral to medial at entrance – Mneumonic is NAVeL: Nerve, artery, vein, lymphatics • Femoral artery/vein relationships ○ Entrance: Artery lateral ○ Apex: Artery anterior • Femoral nerve branches within triangle ○ Saphenous nerve and nerve to vastus medialis are only branches to exit triangle • Femoral sheath: Transversalis fascia covers vessels proximally

○ 3 compartments – Lateral: Artery – Middle: Vein – Medial: Lymph node (femoral canal) • Femoral canal: Medial compartment femoral sheath ○ Anterior border: Inguinal ligament ○ Posterior border: Pubic bone ○ Medial border: Lacunar ligament ○ Lateral border: Femoral vein ○ Entrance: Femoral ring – Anterior border: Medial inguinal ligament – Posterior border: Superior pubic ramus – Medial border: Lacunar ligament – Lateral border: Septum between femoral canal and femoral vein – Open to peritoneal cavity ○ Contents: Lymphatic vessels and nodes (node of Cloquet), fat, connective tissue – Groin nodes divided into superficial and deep groups – Superficial nodes are situated around superficial veins – Deep nodes lie medial to femoral vein – Node of Cloquet in most medial of deep group; located medial to femoral vein at femoral triangle ○ Clinical note: Femoral hernia – Lateral and inferior to pubic tubercle – Travels femoral ring to femoral canal to saphenous opening to subcutaneous tissue

Lower Extremity

• Semitendinosus ○ O: Ischial tuberosity (inferior, medial) – Common tendon of long head biceps femoris muscle ○ I: Medial proximal tibia (pes anserine) ○ F: Internal rotation flexed knee ○ Entirely tendinous in distal thigh • Ischiocondylar portion of adductor magnus ○ O: Ischial tuberosity ○ I: Adductor tubercle ○ Medial-most aspect adductor magnus muscle • Hamstrings: Long head biceps femoris, semimembranous, semitendinosus, ischiocondylar portion adductor magnus muscles ○ Does not include short head biceps femoris muscle • Pes anserine ○ Common aponeurosis for insertion gracilis, semitendinosus, sartorius tendons ○ Pes anserine bursa between tendons and tibia

Adductor (Subsartorial or Hunter) Canal • Fascial passageway for vessels midthigh ○ Boundaries are fascial surfaces of adjacent muscles • Anteromedial border: Sartorius muscle • Anterolateral border: Vastus medialis muscle • Posterior border: Adductor longus and magnus muscles • Entrance: Apex femoral triangle • Exit: Adductor hiatus ○ Gap adductor magnus muscle between adductor portion and ischiocondylar portion of distal thigh • Vessel passageway from thigh to popliteal fossa • Contents: Femoral artery and vein, saphenous nerve ○ Nerve initially anterior to artery then medial ○ Artery anterior to vein ○ Descending geniculate artery arises in canal

ANATOMY IMAGING ISSUES Imaging Recommendations • US: Highest combined spatial and contrast resolution of different imaging modalities ○ Excellent for detecting and characterizing small lesions or fine anatomy, e.g., small nerve sheath tumors, internal vascularity of lesions, etc. ○ Real-time interrogation allows evaluation of muscle and tendon movement during dynamic maneuvers, e.g., for snapping hips, nerve impingement, etc. ○ Limited by depth of penetration • CT: Best for evaluating osseous integrity ○ Soft tissue assessment inferior to US and MR • MR: Highest contrast resolution especially when using fluidsensitive or contrast-enhanced sequences ○ Most sensitive modality to detect tissue edema 737

Lower Extremity

Thigh Muscles ANTERIOR THIGH

Iliacus m. Psoas m. Anterior superior iliac spine Tensor fascia lata m. Sartorius m.

Pectineus m. Adductor brevis m.

Iliotibial band

Adductor longus m. Gracilis m.

Rectus femoris m. Vastus lateralis m. Vastus medialis m.

Lateral patellar retinaculum

Medial patellar retinaculum Pes anserine t.

Iliacus m. Psoas m.

Lesser trochanter

Pectineus m. Adductor brevis m. Adductor longus m.

Iliotibial band Vastus intermedius m. Vastus lateralis m. Vastus medialis m.

Lateral patellar retinaculum

Medial patellar retinaculum Pes anserine t.

(Top) Superficial muscles of the anterior thigh are shown. The oblique course of the sartorius muscle is easily appreciated. The adductor brevis muscle is deep to the adductor longus and pectineus muscles. The most medial muscle is the gracilis. The vastus lateralis and medialis muscles continue to their insertions as the lateral and medial patellar retinacula, respectively. (Bottom) Deep muscles of the anterior thigh are shown. The vastus intermedius muscle is deep to the rectus femoris muscle. The vastus intermedius muscle tendon blends with the rectus femoris tendon along its deep surface. The iliopsoas muscle dives deep after crossing over the pelvic brim. With removal of the sartorius muscle, a little more of the adductor brevis muscle is visible. The pes anserine tendons, the gracilis, sartorius, and semitendinosus have a conjoined insertion into the proximal medial tibia.

738

Thigh Muscles

Sartorius m.

Lower Extremity

OVERVIEW, ANTERIOR THIGH

Rectus femoris m. Tensor fascia lata m.

Adductor longus m. Vastus lateralis m.

Superficial vessels Adductor brevis m.

Gluteus maximus m. Profunda femoral v. & a. Anterior femoral cortex Vastus medialis m.

Rectus femoris m.

Vastus lateralis m.

Anterior femoral cortex

Vastus medialis m.

Vastus intermedius m.

(Top) Transverse panoramic view shows the anterior compartment of the upper thigh. The anterior compartment is composed of the quadriceps muscle, tensor fascia lata/iliotibial tract, and sartorius muscle. Medially, it is bordered by the femoral neurovascular bundle and adductor muscles. Laterally, it is bordered by the gluteal and hamstring muscles. (Bottom) In the lower thigh, the rectus femoris is much reduced in size and will continue inferiorly as the quadriceps tendon. The rest of the quadriceps continue as bulky muscles down to the suprapatellar level. They contribute directly to the quadriceps femoris tendon. The major neurovascular bundle has moved to the posterior compartment, and the only anterior compartment vessels are branches of the profunda femoris artery and vein.

739

Lower Extremity

Thigh Muscles ANTERIOR COMPARTMENT, CENTRAL

Vastus lateralis m. Lateral circumflex femoral vessels Vastus intermedius m.

Common femoral v. Rectus femoris m. Pectineus m.

Anterior femoral cortex

Vastus lateralis m. Vastus medialis m. Vastus intermedius m.

Rectus femoris m.

Anterior femoral cortex

Vastus lateralis m.

Vastus medialis m.

Contributing fibers to quadriceps t. Vastus intermedius m.

Rectus femoris t.

Anterior femoral cortex

(Top) Series of 3 transverse scans shows the central part of the anterior compartment. At the proximal level, the dominant (in terms of bulk) quadriceps muscle is the rectus femoris muscle. It is easily identified by its central position; it is lateral to the femoral neurovascular bundle (the femoral triangle). The lateral circumflex artery is important because together with the medial circumflex, its posterior counterpart, they supply the head of the femur. (Middle) Transverse scan is shown through the midthigh. The vastus medialis and intermedius have originated, and at this level, all 4 quadriceps muscles can be seen. (Bottom) Transverse scan shows the distal thigh above the level of the suprapatellar pouch. The rectus femoris has become a central tendon, which receives contributions from the vasti muscles.

740

Thigh Muscles

Vastus lateralis m.

Perforating vessel from profunda femoris

Lower Extremity

ANTERIOR COMPARTMENT, LATERAL

Lateral intermuscular septum

Gluteus maximus m. Lateral femoral cortex

Vastus lateralis m.

Long head of biceps femoris m.

Lateral intermuscular septum

Short head of biceps femoris m.

Vastus intermedius m.

Perforating v. from profunda femoris

Lateral femoral cortex

Sciatic n.

Linea aspera of posterior femoral cortex

Vastus lateralis m. Long head of biceps femoris m.

Short head of biceps femoris m. Lateral intermuscular septum Common peroneal n.

Vastus intermedius m.

Tibial n. Lateral femoral cortex

Popliteal a. Popliteal v.

(Top) Series of transverse scans through the lateral aspect of the thigh is shown. Proximally, the vastus lateralis muscle is dominant and borders with the gluteus maximus muscle (which inserts onto the posterior surface of the femur). The lateral intermuscular septum separates anterior from posterior compartments laterally and also acts as conduit for vessels. (Middle) Further inferiorly, the vastus lateralis borders the biceps femoris. The linea aspera is a distinct protrusion from the posterior femoral shaft where many muscles originate and insert, including the lateral intermuscular septum. On ultrasound, it is consistently seen and therefore serves as a useful bony landmark. (Bottom) At the superior popliteal level, the vastus lateralis muscle becomes less bulky (the reverse occurs with the vastus intermedius muscle), as does the bordering long head of the biceps muscle. The sciatic nerve divides into tibial and common peroneal branches.

741

Lower Extremity

Thigh Muscles MEDIAL AND POSTERIOR THIGH

Iliac crest Anterior superior iliac spine

Ischial spine

Iliacus m. Sacrospinous l. Psoas m.

Sacrotuberous l.

Obturator membrane Gluteus maximus m. Adductor longus m. Gracilis m.

Adductor magnus m.

Rectus femoris m. Sartorius m. Semimembranosus m. Vastus medialis m. Semitendinosus m.

Medial patellar retinaculum Pes anserine

Gluteus minimus m. Gluteus medius m. Piriformis m. Superior gemellus m. Obturator internus m. Inferior gemellus m. Sacrotuberous l.

Adductor magnus m.

Quadratus femoris m.

Vastus lateralis m.

Gracilis m. Ischiocondylar portion, adductor magnus m.

Short head, biceps femoris m.

Adductor hiatus

Gracilis t.

(Top) Medial muscles of the thigh are shown. The gracilis muscle has a thin profile when viewed from the front; however, when viewed from the side, it is quite broad. The semimembranosus muscle runs along the deep surface of the semitendinous muscle and inserts onto the tibia posterior to the pes anserine tendons. Its insertion is hidden on this image. The iliopsoas muscle courses over the pelvic brim on its course to the lesser trochanter. (Bottom) Deep muscles of the posterior thigh are shown. With removal of the hamstring muscles, the expansive adductor magnus muscle is visible. The separation of its 2 heads in the distal thigh forms the adductor hiatus.

742

Thigh Muscles

Sartorius m.

Lower Extremity

OVERVIEW, MEDIAL THIGH

Rectus femoris m.

Vastus medialis & intermedius m. Femoral shaft

Great saphenous v.

Femoral n. Adductor longus m. Common femoral v. Gracilis m. Common femoral a.

Adductor brevis m.

Adductor magnus m.

Vastus medialis

Great saphenous v. Medial femoral cortex

Sartorius m.

Gracilis m.

Semimembranosus

(Top) Transverse panoramic view shows the medial compartment at the upper thigh level. At this level, all 3 adductor muscles can be seen, together with the gracilis muscle. This compartment is bordered anteriorly by the femoral triangle, which continues inferiorly as the adductor canal. Posteriorly, the medial compartment is bordered by the semimembranosus muscle. (Bottom) Transverse panoramic scan shows the medial aspect of the lower thigh. At this level, the adductor muscles have inserted superiorly; therefore, the medial compartment is much smaller and composed mainly of the gracilis muscle. The adductor hiatus, which is above this level, provides an entrance for the femoral vessels into the popliteal fossa.

743

Lower Extremity

Thigh Muscles MEDIAL THIGH, ADDUCTOR CANAL Sartorius m. Superficial femoral a.

Adductor longus m. Vastus medialis m.

Superficial femoral v.

Profunda femoral a. Profunda femoral v. Adductor magnus m.

Sartorius m.

Adductor longus m. Vastus medialis m.

Profunda femoral v.

Superficial femoral a. Superficial femoral v. Adductor magnus m.

Sartorius m.

Adductor magnus m. Vastus medialis m.

Superficial femoral a. Superficial femoral v.

Semimembranosus m.

(Top) Transverse scan shows the anterior part of the medial thigh. Above the adductor canal, the apex of the femoral triangle contains bifurcation of the common femoral vessels. The profunda will run deep to supply the thigh muscles and femur. The superficial femoral vessels continue into the adductor canal. (Middle) Transverse scan more inferiorly shows that the superficial femoral vessels are now under the cover of the sartorius muscle, indicating that they are in the adductor canal. (Bottom) Transverse scan shows the medial aspect of the midthigh. The common adductor canal continues medially and more deeply. At this level, the medial wall of the adductor canal changes from the adductor longus muscle to the adductor part of the adductor magnus muscle.

744

Thigh Muscles

Great saphenous v.

Vastus medialis m.

Lower Extremity

MEDIAL THIGH

Adductor magnus m. ischiocondylar part

Gracilis m. Superficial femoral a. Superficial femoral v.

Adductor magnus m. adductor part

Gracilis m.

Vastus medialis m. Semimembranosus m. Sartorius

Adductor magnus m. ischiocondylar part

Lateral femoral cortex

Gracilis m. Adductor longus m. Adductor brevis m.

Adductor magnus m.

Common femoral v. Medial femoral cortex

(Top) Transverse scan using an anteromedial approach is shown. At this level, the superficial femoral vessels enter the popliteal fossa via the adductor hiatus, which is a gap in the adductor magnus muscle, between the adductor and ischiocondylar parts before their insertions (on the medial supracondylar line and adductor tubercle, respectively). (Middle) More inferiorly, only the gracilis muscle and the ischiocondylar part of the adductor magnus (acting like a hamstring) are left in the medial compartment. This space is encroached on by the vastus medialis muscle anteriorly and semimembranosus muscle posteriorly. (Bottom) Using a medial approach (from the inner thigh), the deeper muscles can be demonstrated. The adductor longus and brevis muscle plus the gracilis muscle form an anterior division, while the bulky adductor magnus muscle forms the posterior division.

745

Lower Extremity

Thigh Muscles OVERVIEW, POSTERIOR

Semimembranosus m. Semitendinosus m. Sciatic n. Biceps femoris m.

Gracilis m. Vastus lateralis m. Adductor magnus m.

Lateral intermuscular septum

Posterior femoral cortex

Semitendinosus m. Biceps femoris m. Lateral intermuscular septum Semimembranosus m. Gracilis m. Vastus lateralis m. Sartorius m. Vastus intermedius m. Vastus medialis m.

Posterior femoral cortex

(Top) Transverse panoramic scan shows the posterior compartment at the upper thigh level. At this level, the hamstring muscles form a small proportion of the posterior muscle bulk. The main contributions come from adductors (the medial compartment) and vastus lateralis (the anterior compartment). The sciatic nerve runs under the cover of the biceps femoris muscle. (Bottom) Transverse panoramic scan shows the posterior aspect of the distal thigh. At this more inferior level, the hamstrings form a much larger proportion of the posterior muscle bulk. In particular, the semimembranosus becomes the dominant muscle on the posteromedial side, as most of the adductors have inserted onto the femur above this level.

746

Thigh Muscles

Long head of biceps femoris m. Semitendinosus m.

Lower Extremity

POSTERIOR THIGH

Semimembranosus t. Sciatic n. Posteromedial intermuscular septum

Adductor magnus m. Posteromedial femoral cortex Adductor longus m.

Long head of biceps femoris m. Semitendinosus m.

Semimembranosus m.

Posteromedial intermuscular septum

Sciatic n. Short head of biceps femoris m. Vastus lateralis m.

Adductor magnus m.

Linea aspera Posteromedial femoral cortex

Long head of biceps femoris m. Semitendinosus m. Semimembranosus m.

Adductor magnus m. Posteromedial intermuscular septum

Short head of biceps femoris m. Vastus lateralis m. Linea aspera

Popliteal v. & a. Vastus medialis m.

Posteromedial femoral cortex

(Top) Series of 3 transverse scans shows the central portion of the posterior thigh. After their origin from the ischial tuberosity, the semitendinosus and semimembranosus muscles run on the medial side, and the biceps femoris muscle runs on the lateral side. The sciatic nerve is under the cover of the biceps femoris for most of its way to the popliteal fossa. (Middle) At the midthigh level, the hamstrings are bulkier and the adductors smaller. The 2 groups are divided by the posteromedial intermuscular septum. (Bottom) Further inferiorly, the popliteal vessels enter via the adductor hiatus into the popliteal fossa. The superior aspect of the popliteal fossa is lined by the semimembranosus and semitendinosus muscle medially and the biceps femoris laterally.

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Lower Extremity

Femoral Vessels and Nerves

IMAGING ANATOMY Femoral Vessels • Enter thigh deep to inguinal ligament, midpoint between anterior superior iliac spine and symphysis pubis ○ Change from external iliac vessels to common femoral vessels • Upper thigh: Vessels within femoral triangle ○ Enter: Artery lateral to vein ○ Exit: Artery anterior • Midthigh: Vessels within adductor canal ○ Enter: Artery anterior to vein ○ Exit: Artery anterior • Distal thigh: Exit adductor canal via adductor hiatus, enter popliteal fossa • Common femoral arterybranches ○ Superficial epigastric, superficial circumflex iliac, superficial external pudendal arise anteriorly ○ Deep external pudendal arises medially – May branch from medial circumflex femoral ○ Divides into superficial and deep branches ○ Superficial femoral artery – Branch: Descending genicular ○ Deep femoral (profunda femoris) – Arises laterally in femoral triangle – Dives between pectineus and adductor longus muscles – Medial to femur, deep to adductor longus muscle – Branches in femoral triangle: Medial circumflex femoral (main supply femoral head and neck), lateral circumflex femoral, muscular branches – Branches in adductor canal: 3 perforating branches, descending genicular – Terminal branch: 4th perforating artery • Femoral vein: Travels with artery ○ Tributaries: Lateral circumflex femoral vein, deep femoral vein and its associated perforating veins, descending genicular, lateral circumflex femoral, medial circumflex femoral, deep external pudendal, greater saphenous veins ○ Greater saphenous vein – Longest vein in body – Toes to saphenous opening (fascia lata) – Tributaries: Accessory saphenous, superficial epigastric, superficial circumflex femoral, superficial external pudendal veins

Femoral Nerve • • • • •

Nerve contributions from L2, L3, L4, L5 Largest branch of lumbar plexus Exits plexus at lower psoas muscle Travels in groove between psoas and iliacus muscles Exits pelvis beneath inguinal ligament, lateral to femoral vessels, enters femoral triangle • Multiple branches in femoral triangle ○ Muscular branches: To pectineus, sartorius, rectus femoris, vastus lateralis, vastus medialis, vastus intermedius muscles ○ Cutaneous nerves: Anterior femoral cutaneous, saphenous – Saphenous nerve exits triangle, enters adductor canal 748

○ Articular branches hip and knee

Sciatic Nerve • Nerve contributions from: L4, L5, S1, S2, S3 levels • Largest nerve in body • 2 nerves in 1 sheath ○ Tibial nerve (medial) and common peroneal nerve (lateral) ○ Separate in popliteal fossa • Course ○ Exits pelvis inferior to piriformis muscle – Anomalous relationship in 10% ○ Deep to gluteus maximus muscle, more inferiorly deep to biceps femoris muscle – Crosses over superior gemellus, obturator internus, inferior gemellus, quadratus femoris, adductor magnus muscles – Midway between ischial tuberosity and greater trochanter in transverse plane ○ Runs deep to long head of biceps femoris muscle after exiting gluteal region • Branches arising in thigh: Articular to hip, nerves to hamstring muscles • Supply ○ In thigh: Biceps femoris, semitendinosus, semimembranosus, ischiocondylar portion of adductor magnus muscle • Tibial nerve: Larger division of sciatic nerve ○ Supplies posterior femoral muscles except short head biceps femoris muscle • Common peroneal nerve ○ Oblique lateral course with biceps femoris muscle ○ Supplies short head biceps femoris muscle

ANATOMY IMAGING ISSUES Imaging Recommendations • Ultrasound is unique in that it assesses both morphology and functional response of vessels ○ Complete examination should include interrogation with color Doppler ○ In cases with stenosis, reflux, or reverse flow, spectral Doppler helpful to demonstrate waveform and document flow velocity ○ Dynamic maneuvers, such as transducer compression, breath holding, Valsalva, and calf augmentation are helpful to assess patency of veins on color and spectral Doppler ○ Intravenous contrast is not necessary • High spatial resolution makes ultrasound suitable for assessing superficial nerves ○ Disruption of parallel continuity of nerve bundles suggests pathology ○ Transducer angulation may need to be changed to avoid anisotropy

Femoral Vessels and Nerves

Common iliac a. Deep circumflex iliac a.

Internal iliac a. Obturator a.

Lower Extremity

THIGH ARTERIES

Inferior epigastric a. Superficial epigastric a. Superficial circumflex iliac a.

External pudendal a. Common femoral a. Medial femoral circumflex a.

Lateral circumflex femoral a. Muscular branches Profunda femoral a. Superficial femoral a. Perforating vessels Descending branch lateral circumflex femoral a.

Popliteal a. Descending genicular a.

Superior medial genicular a. Superior lateral genicular a. Inferior lateral genicular a.

Inferior medial genicular a.

Superior gluteal a. Inferior gluteal a.

Medial circumflex femoral a.

Ascending and descending branches medial circumflex

Muscular branches Perforating a. Superficial femoral a. Descending genicular a.

Descending branch lateral circumflex femoral a.

Popliteal a. Superior medial genicular a.

Inferior medial genicular a.

Superior lateral genicular a.

Inferior lateral genicular a.

(Top) Anterior view shows the external iliac, femoral, and popliteal arteries and their branches. (Bottom) Posterior view shows the femoral and popliteal arteries and the superior and inferior gluteal arteries of the greater sciatic notch. All of the main arteries and veins can be readily evaluated with ultrasound. CT angiography or MR angiography are the best investigations to provide an imaging roadmap of the main arteries in the lower limb, and these investigations have replaced standard angiography in this respect. Standard DSA is still the best investigation to demonstrate the smaller arteries of the lower limb (such as those around of the feet or around the hip).

749

Lower Extremity

Femoral Vessels and Nerves THIGH VEINS

Common iliac v. Deep circumflex iliac v. Internal iliac v. Common femoral v.

Inferior epigastric v. Obturator v.

Medial circumflex femoral v.

Greater saphenous v. Lateral circumflex femoral v.

Perforating v.

Deep femoral v. Superficial femoral v.

Popliteal v.

Superior gluteal v. Obturator v.

Superficial femoral v.

Inferior gluteal v.

Deep femoral v.

Perforating v.

Popliteal v.

(Top) Anterior view shows the veins of the thigh. The veins typically follow the arterial tree. The main venous drainage is the superficial femoral vein, which is actually a deep venous structure. Note the entrance of the greater saphenous vein into the femoral vein; the saphenous venous system has no accompanying artery. (Bottom) Posterior view shows the veins of the thigh and buttocks. The veins generally follow the arterial tree, although more variability is seen within the venous system.

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Femoral Vessels and Nerves Lower Extremity

THIGH NERVES

Inguinal l. Femoral n. Pectineus m. Sartorius m. Saphenous n. Apex femoral triangle Adductor longus m.

Piriformis m. Obturator internus m.

Gemelli m. Quadratus femoris m. Sciatic n.

Biceps femoris m.

Common peroneal n. Tibial n.

(Top) Femoral nerve is shown. After emerging from the groove between the psoas and iliacus muscles, the nerve passes under the inguinal ligament to enter the femoral triangle. It immediately branches into muscular, cutaneous, and articular nerves. The only nerve to pass through the femoral triangle into the adductor canal is the saphenous nerve. (Bottom) The sciatic nerve enters the lower extremity by passing under the inferior border of the piriformis muscle. The sciatic nerve passes posterior to the external rotator muscles and then courses deep to the biceps femoris muscle. It separates into the tibial and common peroneal nerves in the distal thigh. The tibial nerve bisects the popliteal fossa. The common peroneal nerve follows the biceps femoris muscle around the fibular head.

751

Lower Extremity

Femoral Vessels and Nerves LONGITUDINAL THIGH VESSELS

Subcutaneous fat

Superficial femoral a. Common femoral a. Profunda femoris a. Iliopsoas m.

Femoral head

Sartorius m. Superficial femoral a. Superficial femoral v. Venous valve leaflets Adductor longus m.

Echogenic signal representing sluggish flow

Profunda femoral a.

Semimembranosus m. Tibial n. Popliteal v. Popliteal a.

Popliteal surface of femur

(Top) Sagittal scan shows the common femoral artery and its bifurcation into the superficial femoral artery and the profunda femoral artery. The superficial femoral artery continues into the femoral triangle and adductor canal before ending at the adductor hiatus to become the popliteal artery. The profunda femoris artery supplies the muscles of the thigh. (Middle) Sagittal scan shows the upper adductor canal. The superficial femoral vessels are covered by the sartorius muscle. The high spatial resolution of ultrasound allows venous valves and sluggish flow to be visualized (the latter as increased echogenicity). (Bottom) Sagittal scan shows the popliteal vessels using a posterior approach. Note the reversed relationship between the vessels: The vein now lies more superficially than the artery.

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Femoral Vessels and Nerves Lower Extremity

TRANSVERSE THIGH VESSELS

Superficial circumflex a. Femoral n. Common femoral a.

Inguinal l. Common femoral v. Pectineus m.

Iliopsoas m.

Anterior pubic cortex

Superficial femoral a.

Sartorius m. Femoral n. Superficial femoral v. Vastus medialis m.

Adductor longus m. Adductor magnus m.

Femoral cortex

Tibial n. Semimembranosus m. Popliteal v. Popliteal a. Biceps femoris m.

Posterior surface of femoral epicondylar region

(Top) Transverse scan shows the common femoral vessels emerging from under the inguinal ligament. The femoral nerve lies lateral to the common femoral artery. The iliopsoas muscle and pectineus muscle form the floor. (Middle) Transverse scan shows the lower aspect of the femoral triangle. The sartorius begins to cover the femoral vessels. The vastus medialis and the adductor longus muscles form the side walls of the femoral triangle. More inferiorly, the common femoral vessels bifurcate into the superficial and profunda branches. (Bottom) Transverse scan shows the posterior thigh at the upper level of the popliteal fossa. After passing through the adductor hiatus, the superficial femoral vessels enter the popliteal fossa. The hamstring muscles form the side walls of this fossa.

753

Lower Extremity

Femoral Vessels and Nerves COLOR DOPPLER THIGH ARTERY Subcutaneous fat

Superficial femoral a. Common femoral a. Iliopsoas m.

Profunda femoral a.

Superficial femoral a. Sartorius m. Superficial femoral v.

Adductor longus m.

Semimembranosus m.

Tibial n. Popliteal v. Popliteal a. Popliteal surface of femur

(Top) Sagittal color Doppler scan shows the common femoral bifurcation. Color, representing flow, should fill the entire lumen with appropriate scan settings (as seen in this image). (Middle) Sagittal color Doppler scan shows the superficial femoral vessels in the upper adductor canal. The color of flow is direction dependent (the Doppler effect) and here demonstrates the opposite direction of flow between the artery (red, away from the trunk) and vein (blue, toward the trunk). Again, the color should fill the entire lumen (red superficial to blue). (Bottom) Sagittal color Doppler scan shows the popliteal vessels using a posterior approach. The vein now lies superficial to the artery (blue superficial to red).

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Femoral Vessels and Nerves

Superficial femoral a.

Lower Extremity

SPECTRAL DOPPLER THIGH ARTERIES

Common femoral a. Profunda femoral a.

Triphasic Doppler waveform

Superficial femoral a. Superficial femoral v.

Triphasic Doppler waveform

Popliteal a. Quantitative parameters of Doppler waveform

Triphasic Doppler waveform

(Top) Spectral Doppler trace at the common femoral artery is shown. The typical waveform for an artery should be triphasic: Forward sharp upstroke of forward flow (systolic), then reverse flow (early diastolic), and finally slow forward flow (late diastolic), as seen in this trace. (Middle) Spectral Doppler trace performed at the superficial femoral artery shows a similar waveform and slight decrease in the peak systolic flow. In general, as one moves further away from the heart, the peak velocity decreases. (Bottom) The typical arterial waveform is again seen in a spectral Doppler trace of the popliteal artery.

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Lower Extremity

Femoral Vessels and Nerves SAPHENOFEMORAL JUNCTION

Great saphenous v. Common femoral v. Valve leaflets at saphenofemoral junction Circumflex vessels Iliopsoas m.

Closure valve leaflets on Valsalva maneuver

Distended common femoral v. Circumflex vessels Iliopsoas m.

Superficial epigastric a. Saphenofemoral junction Pectineus m. Superficial femoral a.

Common femoral v.

Iliopsoas m.

(Top) Sagittal scan at the confluence of the great saphenous vein with the common femoral vein is shown. On this image, the valve at the saphenofemoral junction is open to allow blood from the great saphenous vein to drain into the common femoral vein. (Middle) Sagittal color Doppler scan shows the saphenofemoral junction during a Valsalva maneuver. The increased abdominal pressure is transmitted in the common femoral vein. This closes the valve at the saphenofemoral junction to prevent reflux into the great saphenous vein and also distends the common femoral vein (seen here as an increase in caliber). The lack of color flow across the valve indicates that the valve is competent. (Bottom) Transverse scan shows the saphenofemoral junction. The great saphenous vein penetrates the femoral sheath to enter the common femoral vein.

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Femoral Vessels and Nerves

Saphenofemoral junction

Lower Extremity

DOPPLER SAPHENOUS VEIN

Common femoral v.

Iliopsoas m.

Great saphenous v. Closure of valve leaflets at saphenofemoral junction Common femoral v.

Venous Doppler waveform with phasic changes

Valsalva maneuver applied

Sartorius m. Great saphenous v. Adductor longus m.

(Top) Sagittal color Doppler scan shows the saphenofemoral junction. The color flow in both the great saphenous vein and the common femoral vein is toward the trunk. (Middle) Spectral Doppler trace of the great saphenous vein before and during a Valsalva maneuver is shown. The normal venous Doppler spectrum is biphasic due to respiratory variations. Applying a Valsalva maneuver, the valve closes abruptly at the saphenofemoral junction and stops flow in the great saphenous vein, which is seen as a zero-flow velocity on the trace. (Bottom) Oblique coronal color Doppler scan of the great saphenous vein in the medial thigh shows blood flow toward the trunk (correct direction).

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Lower Extremity

Femoral Vessels and Nerves THIGH VEIN Common femoral a.

Superficial femoral v. Valve inside superficial femoral v. Common femoral v. Profunda femoral v.

Iliopsoas m.

Superficial femoral a. Superficial femoral v.

Venous Doppler waveform with phasic changes

Popliteal v.

Popliteal a.

Venous Doppler waveform with phasic changes (Top) Sagittal scan shows the confluence of the common femoral vein. The common femoral vein is formed by its main tributaries: The superficial femoral vein and the profunda femoral vein (both accompanying the course of the arteries of the same name). (Middle) Spectral Doppler trace shows the superficial femoral vein. The normal venous Doppler waveform is biphasic and varies with the phase of respiration. The flow velocity is also much slower than that in the artery. (Bottom) Spectral Doppler trace of the popliteal vein shows a similar venous waveform with respiratory phasic changes.

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Femoral Vessels and Nerves

Inguinal l.

Lower Extremity

FEMORAL VEIN: COMPRESSION

Inguinal l. Common femoral a. Common femoral v.

Common femoral v. (partially compressible) Common femoral a.

Iliopsoas m.

Sartorius m. Superficial femoral a. Superficial femoral v. Superficial femoral a. Vastus medialis m. Superficial femoral v. (completely compressed) Adductor longus m.

Popliteal v. (completely compressed)

Popliteal v. Popliteal a.

Biceps femoris m. Popliteal a.

Popliteal surface of femur Popliteal surface of femur

(Top) Without and with compression split screen transverse scan shows the common femoral vessels. The left 1/2 of the image is obtained by applying normal gentle transducer pressure; the right 1/2 is scanned with firm compression. Patent veins are normally compressible with firm transducer pressure, with the exception demonstrated here due to the inguinal ligament. This is not a sign of venous thrombosis. (Middle) Without and with compression split screen transverse scan in the adductor canal shows the normal compressible superficial femoral vein. With firm pressure, the superficial artery is distorted, but the lumen is not obliterated. (Bottom) Without and with compression split screen transverse scan of the popliteal vessels shows the same response: Obliterated venous lumen and distorted arterial lumen.

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Lower Extremity

Femoral Vessels and Nerves SCIATIC NERVE

Gluteus maximus m. Greater sciatic foramen Posterior femoral cortex Sciatic n. Biceps femoris m. Adductor magnus m.

Gluteus maximus m. Piriformis m. Quadratus femoris m. Greater sciatic foramen Sciatic n.

Inferior gemellus m. Obturator internus t. Superior gemellus m. Ischium posterior cortex

Long head of biceps femoris m. Sciatic n. Adductor magnus m.

(Top) Longitudinal panoramic view of the sciatic nerve shows its course after it has exited the greater sciatic foramen. It runs distally deep to the gluteus maximus and then deep to the biceps femoris to the popliteal fossa. (Middle) Sagittal scan shows the greater sciatic foramen using the ischial tuberosity as a landmark. The sciatic nerve and its relationship with the small external rotators of the hip is shown here. The sciatic nerve emerges between the piriformis and superior gemellus muscles after passing through the greater sciatic foramen. (Bottom) This longitudinal view of the sciatic nerve demonstrates the parallel and uniform hypoechoic tracts (representing nerve bundles). Any disruption of the uniformity or parallel course should be considered abnormal.

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Femoral Vessels and Nerves

Inferior gluteal a.

Lower Extremity

TRANSVERSE SCIATIC NERVE

Ischial tuberosity Sciatic n.

Greater trochanter

Inferior gemellus m. Medial surface greater trochanter Gluteus maximus m. Femoral neck posterior cortex

Long head of biceps femoris m.

Semimembranosus t. Sciatic n.

Adductor magnus m.

Semimembranosus m. Sciatic n.

Adductor magnus m.

Long head of biceps femoris m.

Linea aspera of posterior femoral cortex

(Top) Transverse scans at 3 different levels show the sciatic nerve. The sciatic nerve, after it has exited the greater sciatic foramen, passes superficial to the small external rotators of the hip joint (obturator internus, superior and inferior gemelli, and quadratus femoris). The inferior gluteal artery lies medial to the nerve. (Middle) At the upper thigh level, the sciatic nerve is covered by the long head of the biceps femoris muscle and is relatively superficial. The high spatial resolution of ultrasound allows individual nerve bundles to be identified as black dots in a bright matrix of epineurium. (Bottom) The same relationship with the long head of biceps femoris muscle continues inferiorly down the thigh until the sciatic nerve divides into the peroneal nerves.

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Lower Extremity

Knee

TERMINOLOGY Abbreviations • Origin (O), insertion (I), function (F)

GROSS ANATOMY Overview • Largest and most complex joint ○ Hinge joint throughout its greatest range of motion ○ Bones do not interlock; stability is maintained by ligaments, tendons, capsule, and menisci • Motion of knee and relationship of osseous structures ○ In full flexion – Posterior surfaces of femoral condyles articulate with posterior tibial condyles – Lateral facet of patella is in contact with lateral femoral condyle – Supporting ligaments are not taut, and rotation of leg is allowed ○ During motion of extension – Patella slides upward on femur, engaging with femoral trochlea – Femoral condyles roll forward on tibial condyles and menisci – Lateral femoral condyle is shorter anteroposteriorly than medial and reaches full extension earlier – Medial tibial condyle continues to slide after lateral stops, rotates slightly laterally on femur and medial meniscus ("screwing it home") – This tightens cruciate ligaments turning knee into rigid pattern ○ Initiating flexion from fully extended knee – Requires slight medial rotation of tibia, produced by popliteus muscle – "Unlocks" joint, allowing remainder of motion to take place • Muscles acting on knee joint ○ Extensors: 4 parts of quadriceps femoris – I: Patella – F: Acts together for hip flexion and knee extension ○ Rectus femoris – O: Anterior inferior iliac spine ○ Vastus medialis – O: Medial shaft of femur ○ Vastus intermedius – O: Anterior shaft of femur ○ Vastus lateralis – O: Lateral shaft of femur ○ Biceps femoris – O: Ischial tuberosity – I: Fibular head and tibia – F: Crosses both hip and knee joints, extending hip and flexing knee ○ Flexors ○ Popliteus – O: Arises as tendon from popliteal groove at lateral femoral condyle – I: Posterior surface tibia – F: Flexes knee and medially rotates tibia at beginning of flexion

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○ Sartorius – O: Anterior superior iliac spine – I: Anteromedial tibia – F: Flexes both hip and knee joints, rotating thigh laterally ○ Gracilis – O: Pubis – I: Anteromedial tibia – F: Adducts thigh, flexes knee, and rotates flexed leg medially ○ Semitendinosus – O: Ischial tuberosity – I: Anteromedial tibia – F: Extends hip, flexes knee, medially rotates flexed leg ○ Semimembranosus – O: Ischial tuberosity – I: Posterior medial condyle tibia – F: Extends hip, flexes knee, medially rotates flexed knee

IMAGING ANATOMY Osseous Anatomy • Distal femur ○ Distal femoral metaphysis flares into medial and lateral epicondyles ○ Medial femoral condyle larger than lateral ○ Anteriorly, trochlear groove accommodates patella and is generally V-shaped • Proximal tibia ○ Gerdy tubercle anterolateral just distal to joint ○ Tibial tubercle (apophysis) anterior and slightly lateral, several cm distal to joint • Proximal fibula ○ Posterolateral relative to tibia ○ Fibular styloid process • Tibiofibular joint ○ True synovial joint; subject to any arthritic process ○ Connects to knee joint in 20% • Patella ○ Triangular sesamoid ○ Wider at base superiorly than at apex inferiorly ○ Nonarticular outer surface may develop prominent enthesopathy where quadriceps tendon insertion blends into origin of inferior patellar tendon ○ Bipartite (multipartite) patella: Always upper outer quadrant; osseous fragments may not appear to "match," but cartilage is continuous over defect

Articular Capsule • Highly complex, noncontiguous structure • Contributions from multiple muscles, tendons, and ligaments

Extensor Mechanism • Quadriceps ○ Composed of rectus femoris: Vastus lateralis, medialis, and intermedius muscles ○ Quadriceps tendon inserts on anterior surface of patella ○ Patellar tendon is mainly composed of rectus femoris fibers that course over patella

Knee

Fat Pads • Suprapatellar: Anterior and posterior to suprapatellar bursa • Infrapatellar (Hoffa fat pad): Inferior to patella and between patellar ligament and anterior knee joint • Posterior: Around joint margin extending into intercondylar region

Medial Supporting Structures • Superficial (layer 1) ○ Pes anserinus: Anteromedial tibial insertion – Sartorius embedded in crural fascia – Gracilis immediately deep to sartorius – Semitendinosus immediately deep to gracilis • Middle (layer 2) ○ Superficial medial collateral ligament (longitudinal and oblique components) – Origin: Medial epicondyle; runs slightly anteromedially to insert on tibia 5 cm distal to joint line – Anteriorly, longitudinal component fascia blends with layer 1 – Posteriorly, oblique component blends with layer 3 as posterior oblique ligament • Deep (layer 3) ○ Capsular layers [sometimes termed deep fibers of medial collateral ligament (MCL)] at midportion of knee – Meniscofemoral ligament: From outer superior aspect of body of meniscus to either superficial MCL or femur – Meniscotibial (coronary) ligament: From outer inferior aspect of body of meniscus to tibia just distal to joint line ○ More posteriorly, superficial MCL blends with capsular layers MCL ○ Posterior oblique ligament arises from superficial MCL – Blends with posteromedial meniscus – Receives fibers from semimembranosus tendon – Envelops posterior aspect of femoral condyle, termed oblique popliteal ligament

Lateral Supporting Structures • Superficial (layer 1) ○ Iliotibial band anteriorly, inserting on Gerdy tubercle ○ Superficial portion biceps femoris posterolaterally, inserting on fibular styloid • Middle (layer 2) ○ Quadriceps retinaculum anteriorly ○ Posteriorly, 2 ligamentous thickenings, which originate from lateral patella – Proximal: Terminates at lateral intermuscular septum on femur – Distal: Terminates at femoral insertion of posterolateral capsule and lateral head of gastrocnemius • Deep (layer 3): Several thickenings in lateral part of capsule function as discrete structures ○ Lateral (fibular) collateral ligament originates from lateral femoral epicondyle, extends posterolaterally to insert on lateral fibular head

○ Arcuate ligament originates from styloid process of fibular head, interdigitates with popliteus, and inserts into posterior capsule near oblique popliteal ligament ○ Several other small and inconstant structures are located posterolaterally, which are difficult to differentiate by imaging

Lower Extremity

○ Patellar tendon runs from inferior pole of patellar to tibial tuberosity ○ Fibers of vastus lateralis and medialis contribute to lateral and medial retinacula, respectively

Internal Structures • Menisci ○ Cushion, lubricate, and stabilize knee ○ Fibrocartilage ○ Only peripheral portion visualized by ultrasound ○ Medial attached to capsule throughout extent of knee ○ Lateral attached to capsule at anterior horn and far posteriorly, but by fascicles to popliteus at body and posterior horn • Cruciate ligaments ○ Major stabilizing structures to anteroposterior motion • Cruciate ligaments and central portions of menisci are not well visualized by ultrasound

Synovial Recesses of Knee Joint • Suprapatellar, medial patellar, lateral patellar • Increase in synovial fluid 1st accumulates in either medial or lateral recess and then suprapatellar recess • Small amount of fluid in knee joint is normal but should not get more than small amount • Synovial proliferation can also be best assessed at medial and lateral recesses • Baker cyst is distension of gastrocnemiussemimembraneous bursa • Slit-like opening occasionally connects knee joint to Baker cyst • Synovial fluid can be expressed from knee joint into Baker cyst if this interconnection is present

ANATOMY IMAGING ISSUES Imaging Approaches • Ultrasound ○ Good for assessing extracapsular structures and their abnormalities but unable to satisfactorily interrogate internal structures of knee ○ Given size and complexity of this joint, ultrasound examination needs to be compartmentalized to area of complaint – e.g., posterior examination for popliteal mass, lateral examination for suspected iliotibial band syndrome, etc. ○ In acutely inflamed joint, ultrasound is most effective as screening tool for effusion, allowing image-guided aspiration concurrently ○ Ultrasound is ideal for assessing extraarticular abnormalities, e.g., tendinosis, ligament disruptions, bursitis, masses, etc. ○ For structures containing fibers, e.g., ligaments and tendons, longitudinal scans tend to be more helpful both in confirming course of structure and assessing integrity – For this reason, knee should be flexed during examination of anterior knee – Flexion tenses most tendinous and ligamentous structures and accentuates straight course of its fibers 763

Lower Extremity

Knee EXTENSOR MECHANISM

Rectus femoris t. Vastus lateralis & medialis t. Vastus intermedius t.

Anterior suprapatellar (quadriceps) fat pad Suprapatellar bursa Posterior suprapatellar (prefemoral) fat pad

Infrapatellar (Hoffa) fat pad Patellar t.

Patella Posterior cruciate l. Synovium covering posterior cruciate l.

Lateral femoral condyle

Medial gastrocnemius Gracilis and semitendinosus t.

Sartorius m. Semimembranosus t.

Anterior cruciate l. Synovium covering anterior cruciate l. Biceps femoris m. Lateral gastrocnemius m.

Superficial fascia (crura)

Posterior capsule

Popliteal vessels

(Top) Graphic shows trilaminar configuration of the quadriceps tendon. The superficial portion is the rectus femoris, the middle portion is the aponeurosis of the vastus medialis and lateralis, and the deep portion is the vastus intermedius tendon. (Bottom) Graphic shows the relationships of the posterior capsule and overlying structures. The most superficial layer is the crural fascia, which envelops the sartorius and otherwise confines all of the structures. The posterior capsule (white) is continuous with the synovium (pink thin line) both posteromedially and posterolaterally. Superficial to the capsule are the plantaris and gastrocnemius muscles, hamstring muscle and tendons, and the popliteal vessels.

764

Knee Lower Extremity

EXTENSOR MECHANISM

Vastus medialis m.

Rectus femoris m.

Trochlear surface of femur Posterior suprapatellar fat pad

Quadriceps t.

Suprapatellar bursa

Anterior suprapatellar fat pad Anterior surface of patella

Infrapatellar (Hoffa) fat pad Patellar t.

Tibial condyle

Tibial tuberosity

Sagittal panoramic scan of the anterior knee shows the main components of the extensor mechanism: Quadriceps muscle and tendon, patella, and patellar tendon. The scan performed here is with the knee in extension. More focused views of individual components of the anterior knee can be performed with the knee in flexion (with a pillow to support the popliteal region). Flexion increases the tension of the extensor mechanism, thus straightening the tendons. This will help highlight abnormalities in terms of tendon alignment and continuity. However, the amount of suprapatellar fluid may be decreased (due to displacement) in flexion, and assessment of the suprapatellar region in extension may be more sensitive in this respect.

765

Lower Extremity

Knee EXTENSOR MECHANISM

Vastus intermedius m.

Upper pole of patella Anterior suprapatellar fat pad

Quadriceps t. Small amount of fluid in suprapatellar pouch Femur Posterior suprapatellar fat pad

Vastus medialis m.

Suprapatellar fat pad Quadriceps t. Hyaline cartilage

Medial surface of trochlear groove

Lateral surface of trochlear groove

Subcutaneous fat

Quadriceps tendon fibers on patellar surface Patella

(Top) Sagittal scan shows the quadriceps tendon. The quadriceps tendon is the direct continuation of the rectus femoris with contributions medially and laterally from the vastus medialis and the vastus lateralis, respectively, and posteriorly from vastus intermedius. The tendon inserts on the superoanterior surface of the patella. In this scan, the suprapatellar pouch can be seen. It may normally contain a small amount of fluid (several millimeters thick). (Middle) Transverse scan shows quadriceps tendon with the knee flexed. The central position of the quadriceps tendon can be appreciated here, receiving contributions from the vastus muscles. The articular cartilage of the trochlear groove can also be seen with the patella out of the way during flexion. (Bottom) Transverse scan of the anterior surface of the patella shows tendon fibers inserting or running on the patellar surface.

766

Knee

Patella

Patellar t.

Lower Extremity

EXTENSOR MECHANISM

Tibial tuberosity

Tibial condyle

Infrapatellar (Hoffa) fat pad

Subcutaneous fat Patellar t.

Fibers from rectus femoris t. Lower pole of patella Infrapatellar (Hoffa) fat pad

Tibial tuberosity

Patellar t. Infrapatellar (Hoffa) fat pad

Infrapatellar bursa

Tibial condyle

(Top) Sagittal panoramic view shows the patellar tendon. Most of the fibers of the tendon are continuations of quadriceps tendon fibers. (Middle) Focused sagittal view of the apex of the patella shows quadriceps fibers running on the anterior surface of the patella, continuing distally as the patellar tendon. For this reason, many consider the patella a sesamoid bone. Also seen here are fibers originating from the apex of the patella itself. (Bottom) Focused sagittal scan shows the tibial tuberosity. The distal fibers of the patellar tendon are separated from the anterior surface of the tibial condyle by the infrapatellar bursa. A small amount of fluid (2-3 mm thick) may be normally present in this bursa.

767

Lower Extremity

Knee EXTENSOR MECHANISM

Medial patellar retinaculum Patellar dorsal surface

Subcutaneous fat

Patellar t.

Infrapatellar (Hoffa) fat pad

Tibial tuberosity Patellar t.

(Top) Series of 3 transverse scans through the patellar tendon is shown. Proximally, fibers from the quadriceps tendon continue over the anterior patellar surface to contribute to the patellar tendon. On both sides, fibers from the medial and lateral patellar retinaculum also insert onto the patella and blend with the patellar tendon fibers. (Middle) At the midsubstance of the patellar tendon, the tendon assumes a flattened appearance. The fibers within the tendon can be seen as tiny hyperechoic dots. A disruption to the uniformity of these dots or a change in thickness (focal or general) of the patellar tendon suggests tendinosis. (Bottom) More inferiorly, a transverse scan shows the patellar tendon inserting onto the tibial tuberosity. The patellar tendon paratenon is seen as thin echogenic line on the anterior surface and side walls of the tendon. It becomes thickened in patellar paratenonitis. This is an infrequently encountered condition.

768

Knee Lower Extremity

EXTENSOR MECHANISM

Lateral patellar retinaculum Anterior surface of patella

Articular cartilage of lateral surface of the trochlear groove

Anterior surface of patella

Medial articular facet of patella

Medial femoral condylar cartilage Inferior medial geniculate a.

Lateral articular facet of patella

Medial patellar retinaculum Articular cartilage of medial trochlear surface

Medial tibial condyle Patellar retinaculum

(Top) Transverse scan at the lateral margin of the patella shows the articulation between the lateral patella and the lateral surface of the trochlear groove. This articular plane is steeper (closer to sagittal) than the medial side for mechanical advantage. As a result of the obliquity of the course of the patellar tendon with respect to the tibial axis, the patella is prone to lateral dislocation or subluxation. The steeper lateral articular plane helps prevents this. (Middle) Transverse scan at the medial margin of the patella shows the articulation between the patella and the medial surface of the trochlear groove showing the patellar retinaculum as a thick structure. (Bottom) Sagittal color Doppler scan of the medial infrapatellar region shows the patellar retinaculum inserting onto the tibia. At this level, the retinaculum has fanned out, becoming much thinner.

769

Lower Extremity

Knee MEDIAL KNEE Posterior cruciate l. Medial femoral condyle Meniscofemoral l. Superficial fibers medial collateral l. Medial collateral bursa (variable) Fat between superficial & deep medial collateral fibers

Body medial meniscus

Meniscotibial (coronary) l.

Semimembranosus m. Gastrocnemius t. Retrocondylar bursa Medial femoral condyle Posterior capsule Sub-gastrocnemius bursa Posterior oblique l. Posterior horn medial meniscus Semimembranosus t. Posterior capsule Deep & superficial semimembranosus bursae

Vastus medialis m. Vastus medialis obliquus m. Sartorius m. Medial patellofemoral l.

Gracilis t. Semitendinosus t.

Inferior patellar t. Medial patellotibial l.

(Top) Coronal graphic at midjoint shows superficial fibers extending from adductor tubercle to ~ 5 cm below the joint line. Deep fibers are shorter. The meniscotibial (coronary) ligament extends from the meniscus to the tibia adjacent to the joint line & the meniscofemoral ligament extends from the meniscus to the femur or superficial medial collateral ligament (MCL). (Middle) Sagittal graphic shows the far medial portion of posterior capsule. Superiorly, the capsule attaches to the cortex of the posterior femoral condyle and fuses with fibers of the medial gastrocnemius. (Bottom) Graphic shows the anteromedial attachment of pes anserinus tendons. The sartorius is the most anterior and superficial. The gracilis inserts directly adjacent and deep to the sartorius, and the semitendinosus inserts directly posterior and inferior to the gracilis. These tendons and their crural fascia comprise the superficial layer of the medial capsuloligamentous complex.

770

Knee

Superficial fibers of medial collateral l. Meniscofemoral l. Medial femoral condyle

Posterior oblique l.

Lower Extremity

MEDIAL KNEE

Cortex of medial tibial condyle Meniscotibial l. Body of medial meniscus

Adductor tubercle Superficial fibers of medial collateral l.

Medial surface of medial femoral condyle

Gracilis t.

Medial head of gastrocnemius m. Cartilage of medial femoral condyle Posterior cortex of medial tibial plateau Posterior horn of medial meniscus Medial tibial condyle

Semimembranosus t.

(Top) Coronal scan shows the medial joint line. The medial collateral ligament is composed of 2 layers: Superficial and deep. The superficial fibers run from the medial femoral condyle to the tibial condyle 5 cm below the joint line. The deep layer consists of the meniscofemoral (femoral condyle to body of meniscus) and meniscotibial (body of meniscus to tibia just distal to joint line). (Middle) Transverse scan shows the medial condylar region. The superficial fibers of the medial collateral ligament arise just distal to the adductor tubercle. The popliteal oblique ligament arises adjacent to this and runs posterior to the posterior joint capsule. (Bottom) Sagittal scan shows the posteromedial joint line. The semimembranosus tendon inserts onto the posterior surface of the medial tibial condyle, just below the joint margin. Only the outer part of the meniscus is visible.

771

Lower Extremity

Knee LATERAL KNEE

Posterior cruciate l. Popliteus t.

Popliteal hiatus Posterior horn and root of lateral meniscus

Posterior horn and root medial meniscus

Biceps femoris t.

Superior fascicle, popliteomeniscal portion

Lateral gastrocnemius m. & t.

Superior fascicle, meniscocapsular portion (popliteomeniscal l.)

Posterior capsule

Posterior horn of lateral meniscus Inferior fascicle (popliteomeniscal l.)

Popliteus t. Popliteal hiatus Popliteofibular l. Posterolateral corner fibers contributing to posterolateral capsule

(Top) Coronal graphic shows the roots of the posterior horns of both the medial and lateral menisci. The popliteus tendon courses through the hiatus adjacent to the body/posterior horn of the lateral meniscus. (Bottom) Sagittal graphic of lateral part of posterior capsule shows that it is intimately attached to the lateral gastrocnemius muscle. The popliteus tendon is intraarticular but extrasynovial and is attached to the capsule. Fibers from the posterolateral corner and arcuate ligament originating from the fibular head contribute to the lateral portion of the posterior capsule.

772

Knee Lower Extremity

LATERAL KNEE

Iliotibial tract

Gerdy tubercle Lateral femoral condyle Lateral inferior geniculate a.

Lateral tibial condyle

Patellar t.

Iliotibial tract Lateral femoral condyle Lateral patellar retinaculum

Iliotibial tract

Patellar t.

Gerdy tubercle

(Top) Oblique sagittal scan shows the lateral aspect of the joint line using Gerdy tubercle as a landmark. The iliotibial tract is shown here, passing over the edge of the lateral femoral condyle [where it is subject to impingement (iliotibial tract syndrome)] before inserting on the Gerdy tubercle on the anterior surface of the lateral tibial condyle. (Middle) Transverse scan of the anterolateral knee at the level of the femoral condyle shows that the iliotibial tract and the patellar tendon are connected by fibers of the lateral patellar retinaculum. (Bottom) More inferiorly, the 2 tendons have moved closer to each other. This transverse scan shows insertion of the iliotibial tract onto the Gerdy tubercle. The patellar tendon is also approaching its tibial insertion.

773

Lower Extremity

Knee LATERAL KNEE

Popliteal t.

Groove for popliteal t.

Bicipital t.

Posterior horn of lateral meniscus Lateral tibial condylar cortex

Fibular collateral l.

Lateral cortex of fibular head

Biceps femoris m.

Lateral femoral condylar cortex

Inferior lateral genicular vessels Lateral tibial condyle Posterior horn of lateral meniscus Fibular collateral l. Groove containing popliteal t.

Biceps femoris t.

Fibular insertion of fibular collateral l.

Apex of fibular head Popliteal t. Fibular collateral l.

Proximal tibiofibular joint Lateral tibial condyle

(Top) Coronal panoramic scan shows the lateral collateral complex. The biceps femoris muscle is the dominant muscle on this side of the knee. It runs from the ischial tuberosity laterally and inferiorly to insert onto the lateral aspect of the head of the fibula. (Middle) Coronal scan of the lateral femoral condyle shows the insertion of the fibular collateral ligament. Just under this insertion is the groove for the popliteal tendon. The fibular collateral ligament is cord-like compared to the superficial component of the lateral collateral ligament, which is a flatter strap. (Bottom) The fibular collateral ligament inserts onto the lateral wall of the head of the fibula. The tendon of the biceps femoris inserts at and around the apex of the fibular head.

774

Knee Lower Extremity

POSTERIOR KNEE

Semitendinosus m. Biceps femoris m.

Semimembranosus m.

Posterior cutaneous nerve of thigh

Gracilis m.

Saphenous n.

Tibial n.

Nerve to medial gastrocnemius Sartorius t. Common peroneal n. Great saphenous v. Nerve to lateral gastrocnemius, soleus Saphenous n.

Sural n.

Peroneal communicating n.

Small saphenous v.

Medial head gastrocnemius m.

Lateral head gastrocnemius m.

Graphic shows the superficial posterior muscles and nerves. The popliteal fossa is a diamond-shaped fossa bordered superiorly by the hamstring muscles and inferiorly by the head of the gastrocnemius muscle. Superiorly, the medial margin is represented by the semimembranosus and semitendinosus muscles, and laterally by the biceps femoris muscle. Inferiorly, the medial and lateral borders are the medial and lateral heads of the gastrocnemius muscle. This fossa contains the popliteal vessels, the sciatic nerve, and its branches. Note that the common peroneal nerve is part of the deeper nerve system, but it travels more superficially, following the posterior biceps femoris muscle and tendon until it wraps around the fibular neck.

775

Lower Extremity

Knee POSTERIOR KNEE

Semitendinosus m.

Biceps femoris m. long head Gracilis m. Semimembranosus m.

Tibial n.

Biceps femoris m. short head

Lateral head of gastrocnemius m. Plantaris m.

Medial head of gastrocnemius m.

Popliteal v.

Popliteal a.

(Top) Panoramic transverse scan of the posterior knee shows the upper popliteal fossa. At this level, the hamstring muscles form the superior boundaries (medial and lateral) of the popliteal fossa. The semimembranosus and semitendinosus muscles form the medial margin, while the biceps femoris muscle forms the lateral margin. (Bottom) Panoramic view of the posterior knee shows the lower aspect of the popliteal fossa. At this level, the boundaries of the popliteal fossa are the heads of the gastrocnemius muscle, the lateral head of gastrocnemius being the lateral margin and the medial head the medial margin. The popliteal vessels are a continuation of the superficial femoral vessels after they have emerged through the adductor hiatus.

776

Knee Lower Extremity

POSTERIOR KNEE

Biceps femoris t.

Biceps femoris m. Plantaris m.

Lateral head of gastrocnemius m.

Posterior cortex of lateral femoral condyle

Lateral femoral condylar cartilage

Lateral femoral condyle

Lateral head of gastrocnemius m.

Fabella

Lateral head of gastrocnemius m.

Lateral femoral condyle Cartilage on lateral femoral condyle

Plantaris m.

Inferior medial geniculate a. Lateral tibial condyle

(Top) Sagittal scan shows the lateral femoral condyle. The plantaris muscle originates slightly more superior and medial to the lateral head of the gastrocnemius. The plantaris runs inferomedially across the thigh to lie on the medial side of the Achilles tendon. More superficially, the bicipital tendon runs laterally toward its fibular head insertion. (Middle) A more lateral sagittal view shows the sesamoid bone within the lateral head of the gastrocnemius muscle, the fabella. (Bottom) A more inferior oblique scan shows both the plantaris and lateral heads of the gastrocnemius muscle running over the posterior surface of the knee joint. Further distally, the plantaris muscle becomes a thin tendon and is difficult to discern until it reaches the medial side of the Achilles tendon in the distal calf.

777

Lower Extremity

Knee POSTERIOR KNEE

Plantaris m. Lateral head of gastrocnemius m. Sciatic n. Medial head of gastrocnemius m. Lateral femoral condylar cartilage Medial femoral condylar cartilage Popliteal v. Intercondylar groove

Popliteal a.

Biceps femoris m.

Lateral head of gastrocnemius m. Popliteal m.

Popliteal t.

Lateral femoral condyle

Biceps femoris m.

Fibular collateral l.

Lateral femoral condyle Popliteal groove

Lateral tibial condyle

Popliteal t.

(Top) Transverse scan shows the posterolateral aspect of the knee joint at the level of the inferior popliteal fossa. The sciatic nerve is the largest nerve in the body. In cross section, nerve fibrils are seen as hypoechoic dots separated by hyperechoic perineurium. (Middle) Scanning more laterally and inferiorly, the popliteal muscle and its tendon can be demonstrated. The popliteal tendon originates from the proximal posterior tibial surface and runs superolaterally under the lateral head of the gastrocnemius muscle to insert onto the lateral cortex of the lateral femoral condyle. (Bottom) Coronal scan shows the popliteal groove on the lateral femoral condyle and the popliteal tendon entering this groove as it heads toward its insertion.

778

Knee

Semitendinosus t.

Lower Extremity

POSTERIOR KNEE

Semimembranosus t.

Popliteal a. Articular cartilage of medial femoral condyle

Medial head of gastrocnemius m.

Intercondylar notch

Semitendinosus t. Gracilis t. Semimembranosus t. Sartorius m.

Acoustic shadow from femoral shaft

Gracilis t. Semitendinosus t.

Insertion site Tibial cortex

(Top) Transverse scan shows the posteromedial knee at the level of the femoral condyles. The semimembranosus tendon can be seen running medial to the medial head of the gastrocnemius muscle and deep to the semitendinosus tendon. The semimembranosus tendon will continue inferiorly to its posterior tibial insertion, whereas the semitendinosus will be joined by others to insert on the anteromedial surface of the tibia. (Middle) More superiorly, transverse scan of the posteromedial aspect of the supracondylar region shows the medial tendons and muscles. Three of these, the sartorius, gracilis, and semitendinosus, will continue together inferiorly and insert adjacent to each other as the pes anserine on the anteromedial aspect of the proximal tibial shaft. (Bottom) Oblique transverse scan along the course of the pes anserine tendons shows their insertion on the anteromedial tibial cortex.

779

Lower Extremity

Leg Muscles

GROSS ANATOMY Osseous Anatomy • Tibia ○ Proximal tibiofibular joint – Head of fibula and lateral condyle tibia joined by synovial-lined fibrous capsule – May communicate with knee joint (10%) – Posterolaterally located – Synovial joint, so can be affected by any synovial inflammatory process ○ Anterolateral tibia: Origin of anterior muscles of leg ○ Anterior border (shin): Sharp ridge running from tibial tuberosity proximally to anterior margin of medial malleolus ○ Medial tibial surface – Wide and flat – Proximally, covered by pes anserinus – Remainder is subcutaneous ○ Medial border of tibia: Saphenous nerve and great saphenous vein run along it ○ Posterior tibia: Origin of deep posterior muscles of leg ○ Lateral border of tibia: Ridge for attachment of interosseous membrane ○ Medial malleolus: 2 colliculi, anterior longer than posterior ○ Distal tibiofibular joint – Fibula articulates with tibia at fibular notch; joined by interosseous ligament – Strengthened by anterior and posterior tibiofibular ligaments – Posterolaterally located • Fibula ○ Anterior fibula – Origin of lateral muscles of leg ○ Medial fibula – Origin of deep posterior muscles of leg ○ Posterolateral fibula – Origin of posterior muscles of leg ○ Lateral malleolus: 1 cm longer than medial malleolus

Interosseous Membrane • Stretches across interval between tibia and fibula • Greatly extends surface for origin of muscles • Strong, oblique fibers run downward and laterally from tibia to fibula • In upper part, below lateral condyle of tibia, there is opening for passage of anterior tibial vessels • Distally, opening allows passage of perforating branch of peroneal artery • Tibialis posterior and flexor hallucis longus take partial origin from back of membrane • Tibialis anterior, long extensors of toes, and peroneus tertius take partial origin from front of membrane

Muscles of Leg • Compartments separated by deep fascia, which give partial origin to several muscles • Posterior compartment: Superficial muscles ○ Gastrocnemius 780

– Origin: Medial from posterior femoral metaphysis; lateral from posterior edge of lateral epicondyle – Heads separated from posterior capsule by bursa – 2 heads unite to form main bulk of muscle – Join in thin aponeurotic tendon near midleg – Joins soleus aponeurosis to form Achilles tendon; concave in cross section; musculotendinous junction is 5 cm above calcaneal insertion – Nerve supply: Tibial nerve – Action: Plantar flexor of ankle and flexor of knee ○ Plantaris – Origin: Superior and medial to lateral head of gastrocnemius origin, as well as from oblique popliteal ligament – Continues deep to lateral head of gastrocnemius – Myotendinous junction at level of origin of soleus (muscle is 5-10 cm long) – Tendon then lies between medial head gastrocnemius and soleus – Follows medial side of Achilles to insert either anteromedially on Achilles or on calcaneus – Plantaris absent in 7-10% of general population – Nerve supply: Tibial nerve – Action: Acts with gastrocnemius ○ Soleus – Origin: Extensive, from back of fibular head and upper 1/3 of posterior surface of shaft of fibula, from soleal line and middle 1/3 of medial border of tibia, and from tendinous arch joining these across popliteal vessels – Flat, thick, powerful muscle that ends in strong tendon – Joins with tendon of gastrocnemius to form Achilles tendon – Nerve supply: Tibial nerve – Action: Stabilizes ankle in standing, plantarflexes ankle – Accessory soleus: Rare variant, arises from anterior surface of soleus or from fibula and soleal line of tibia; inserts into Achilles or onto calcaneus anteromedially to Achilles; presents as mass • Posterior compartment: Deep muscles ○ Popliteus – Origin: Tendon from popliteal groove of lateral femoral condyle – Passes through popliteal hiatus posteriorly and medially, pierces posterior capsule of knee – Muscle fibers directed medially and downward to insert on posterior surface of tibia above soleal line – Nerve supply: Tibial nerve – Action: Flexes knee and medially rotates tibia with respect to femur at onset of flexion (unlocking extension "screwing home" mechanism) ○ Tibialis posterior – Origin: Interosseous membrane and adjoining parts of posterior surfaces of tibia and fibula – Superior end bifid; anterior tibial vessels pass forward between 2 attachments – Distally it inclines medially, under flexor digitorum longus – Grooves and curves around medial malleolus – Nerve supply: Tibial nerve – Action: Plantarflexes and inverts foot

Leg Muscles – Origin: Upper 1/2 of lateral surface of tibia and interosseous membrane – Tendon originates in distal 1/3; passes deep to retinaculum – Nerve supply: Deep peroneal and recurrent genicular – Action: Dorsiflexor and invertor of foot ○ Extensor digitorum longus – Origin: From upper 3/4 of anterior surface fibula – Descends behind extensor retinacula to ankle – Nerve supply: Deep peroneal – Action: Extends interphalangeal and metatarsophalangeal joints of lateral 4 toes, dorsiflexes foot ○ Peroneus tertius – Small, not always present – Origin: Continuous with extensor digitorum longus, arising from distal 1/4 of anterior surface of fibula and interosseous membrane – Inserts into dorsal surface at base of 5th metatarsal – Nerve supply: Deep peroneal – Action: Dorsiflexes ankle and everts foot ○ Extensor hallucis – Thin muscle hidden between tibialis anterior and extensor digitorum longus – Origin: Middle 1/2 of anterior surface of fibula and interosseous membrane – Tendon passes deep to retinacula to great toe – Nerve supply: Deep peroneal – Action: Extends phalanges of great toe and dorsiflexes foot

Lower Extremity

○ Flexor digitorum longus – Origin: Posterior surface of tibia, below popliteus, and medial to vertical ridge – Crosses superficial to distal part of tibialis posterior – Tendon grooves lower end of tibia lateral to that of tibialis posterior, passes around medial malleolus to foot – Nerve supply: Tibial nerve – Action: Flexes interphalangeal and metatarsophalangeal joints of lateral 4 toes; plantarflexes and inverts foot ○ Flexor hallucis longus – Origin: Posterior surface of fibula, below origin of soleus – Passes medially, descends down posterior to midtibia – Associated with os trigonum posterior to talus – Tendon occupies deep groove on posterior surface of talus, passes around medial malleolus, under sustentaculum tali, to great toe – Nerve supply: Tibial nerves – Action: Flexes interphalangeal and metatarsophalangeal joints of great toe; plantarflexes foot • Lateral compartment ○ Peroneals separated from extensors by anterior intermuscular septum and from posterior muscles by posterior septum ○ Peroneus longus – Origin: Upper 2/3 lateral surface of fibula and intermuscular septa and adjacent muscular fascia – Becomes tendinous few cm above lateral malleolus – Curves forward behind lateral malleolus, posterior to peroneus brevis – Nerve supply: Superficial peroneal – Action: Everts foot and secondarily plantarflexes foot ○ Peroneus brevis – Origin: Lower 2/3 lateral surface of fibula and intermuscular septa and adjacent muscular fascia – Muscle is medial to peroneus longus at origin but overlaps peroneus longus in middle 1/3 – Tendon curves forward behind lateral malleolus, in front of peroneus longus tendon – Nerve supply: Superficial peroneal – Action: Everts foot and secondarily plantarflexes foot ○ Synovial sheath for peroneals begins 5 cm above tip of lateral malleolus and envelops both tendons; divides into 2 sheaths at level of calcaneus ○ Peroneus quartus – Accessory muscle with prevalence of 10% – Originates from distal leg, frequently from peroneal muscles, with variable insertion sites at foot – At level of malleolus, located medial or posterior to both peroneal tendons ○ Peroneus digiti minimi – Accessory with prevalence of 15-36% – Extends from peroneus brevis muscle around medial malleolus to foot – Tiny tendinous slip • Anterior compartment ○ Tibialis anterior

ANATOMY IMAGING ISSUES Imaging Recommendations • US ○ Owing to its smaller size, compared to thigh (less depth to penetrate), leg muscles and vessels are well demonstrated by ultrasound throughout their course ○ Relationship of different structures in posterior compartment tends to change along their courses – If in doubt, start from ankle level and trace structures proximally

Imaging Sweet Spots • Deep structures of posterior compartment, such as peroneal vessels and tibialis posterior muscle, may be difficult to visualize in very muscular patients ○ Structures can be interrogated by scanning anteriorly through anterior compartment and gap between tibia and fibula • One of most common reasons to image calf is for suspected muscle tear ○ Most common site of muscle tear is at distal myofascial junction of medial belly of gastrocnemius ○ Look carefully for preservation of arrowhead appearance of myofascial junction at this location ○ With plantaris tendon tear, this junction is intact, and there is more extensive hemorrhage deep to medial belly of gastrocnemius

781

Lower Extremity

Leg Muscles ANTEROLATERAL LEG

Rectus femoris m. Vastus lateralis m.

Sartorius t. Vastus medialis m. Quadriceps t.

Lateral retinaculum

Medial retinaculum

Inferior patellar t.

Peroneus longus m.

Medial gastrocnemius m.

Anteromedial bare area tibia

Extensor digitorum longus m.

Extensor hallucis longus m.

Extensor digitorum longus t.

Tibialis anterior m.

Tibialis anterior t.

Extensor hallucis longus t.

Graphic shows the anterior leg muscles. Note that nearly the entire anteromedial tibia is bare of muscle. Thus, it is poorly vascularized, resulting in slow fracture healing. The tibialis anterior has an extensive origin from both tibia and interosseous membrane and is the most substantial muscle of the anterior compartment. The extensor digitorum longus originates from the fibula. The extensor hallucis longus originates between the 2, from the fibula and the interosseous membrane. These 3 muscles retain the same orientation as they become tendinous anterior to the ankle. The mnemonic "Tom, Harry, & Dick" applies to the tendon order, from medial to lateral (tibialis anterior, extensor hallucis longus, extensor digitorum).

782

Leg Muscles

Tibialis anterior m. Anterior intermuscular septum

Lower Extremity

PANORAMIC ANTEROLATERAL LEG

Anterior tibial a.

Peroneus longus m. Deep peroneal n. Posterior intermuscular septum Superficial peroneal n.

Lateral tibial cortex Interosseous membrane Extensor digitorum longus m.

Lateral head of gastrocnemius m. Soleus m. Peroneal v.

Anterior tibial v. Lateral fibular cortex Peroneal a.

Tibialis anterior t. Extensor hallucis longus m. Anterior tibial v. & a. Extensor digitorum longus m. Lateral fibular cortex Deep peroneal n.

Lateral tibial cortex Peroneus longus m. Peroneus brevis m.

Peroneal vessels

Flexor hallucis longus m.

Lesser saphenous v.

(Top) Transverse panoramic view shows the anterior and lateral compartments of the upper leg. The crural compartments are divided by the tibia and the 2 intermuscular septa (anterior and posterior) into the anterior (extensor), lateral (peroneal), and posterior (flexor) compartments. The intermuscular septum separates the anterior from the posterior compartments. (Bottom) Transverse panoramic view shows the anterior and lateral compartments of the inferior leg. All muscles are smaller in caliber compared to those seen superiorly. An interosseous gap is still present between the tibia and fibula, but ultrasound interrogation through this gap is no longer possible and the interosseous membrane cannot be demonstrated.

783

Lower Extremity

Leg Muscles ANTERIOR COMPARTMENT Extensor digitorum longus m. Extensor hallucis longus m. Tibialis anterior m. Lateral tibial cortex Anterior tibial a. & branches Lateral fibular cortex Anterior tibial v. Popliteal a.

Tibialis posterior m.

Expected region of tibial n. Popliteal v.

Extensor digitorum longus m. Extensor hallucis longus m. Tibialis anterior m. Lateral tibial cortex Deep peroneal n. Anterior tibial v./a./v. Lateral fibular cortex Tibialis posterior m. Peroneal v./a./v.

Interosseous membrane

Tibial n. Posterior tibial v./a./v. Extensor digitorum longus m. Extensor hallucis longus m. Tibialis anterior m.

Peroneus longus m.

Lateral tibial cortex

Deep peroneal n. Interosseous membrane Anterior tibial v./a./v. Peroneal v./a./v.

Tibialis posterior m.

Flexor hallucis longus m.

(Top) Transverse color Doppler scan shows the anterior compartment at the upper leg level slightly below the proximal tibiofibular joint. At this level (above the superior margin of the interosseous membrane), the anterior tibial artery and vein (branches of the popliteal artery and vein) run anteriorly to supply the anterior compartment. (Middle) Transverse scan shows the anterior compartment at a slightly lower level. The tibialis anterior, extensor hallucis longus, and extensor digitorum longus muscles form the muscular component of this compartment. The deep peroneal nerve has penetrated laterally to supply this compartment. The anterior tibial vessels run on the surface of the interosseous membrane. (Bottom) Transverse scan more inferiorly shows a decrease in size of the extensor muscles and gradual migration of nerve and vessels more medially and superficially.

784

Leg Muscles

Tibialis anterior m.

Anterior tibial v.

Lower Extremity

ANTERIOR COMPARTMENT

Tibialis posterior m.

Anterior tibial a.

Soleus m.

Tibialis anterior m./t./m. Anterior tibial a. Interosseous membrane Tibialis posterior m. Peroneal v. Soleus m.

Tibialis posterior m.

Tibialis anterior m.

Peroneal a. and v.

Soleus m.

(Top) Sagittal scan shows the anterior compartment at the upper leg level. The anterior tibial vessels pass above the superior margin of the interosseous membrane to enter the anterior compartment and supply the extensor muscles. (Middle) Sagittal scan of the anterior and posterior compartments at the midleg level shows that the interosseous gap between the tibia and fibula can be used as a window to interrogate the deep posterior structures. (Bottom) Sagittal scan shows the anterior compartment at a lower level. Within the posterior compartment, the peroneal vessels run anteriorly and just below the inferior margin of the interosseous membrane.

785

Lower Extremity

Leg Muscles LATERAL COMPARTMENT Soleus m. Peroneus longus m. Superficial peroneal n. Extensor digitorum longus m.

Peroneal v./a./v.

Deep peroneal n. Anterior tibial v./a./v. Tibialis anterior m.

Tibial n. Lateral fibular cortex

Interosseous membrane Tibialis posterior m. Posterior tibial cortex

Soleus m. Peroneus longus m. Peroneus brevis m. Anterior intermuscular septum Extensor digitorum longus m. Posterior intermuscular septum Anterior tibial v./a./v. Lateral fibular cortex

Tibialis anterior m. Interosseous membrane Lateral tibial cortex

Sural n. Short saphenous v.

Peroneus longus t. Lateral fibular cortex Peroneus brevis m. Flexor hallucis longus m. Peroneal a. Peroneal v.

(Top) Transverse scan shows the lateral compartment at a high level. At this level, only the peroneus longus muscle has originated and is the only muscle occupying this compartment. The superficial peroneal nerve lies on the posterior surface of the peroneus longus muscle. The deep peroneal nerve has already entered the anterior compartment after curving around the fibular neck (above this scan level). (Middle) Transverse scan at the midleg level shows that the peroneus brevis muscle has now originated and resides anterior and deep to the peroneus longus muscle. More inferiorly, the peroneus longus muscle will become smaller and turn into a tendon while the peroneus brevis will still have muscle fibers down to the level of the ankle joint. (Bottom) Transverse scan shows the level of the lateral malleolus. The peroneal tendons will run posterior to the lateral malleolus and curve around its tip to run toward the lateral foot.

786

Leg Muscles Lower Extremity

LATERAL COMPARTMENT

Common peroneal n. Peroneus longus m. Lateral fibular cortex

Peroneus brevis m.

Peroneus longus m.

Flexor hallucis longus m.

Posterior intermuscular septum Peroneal a. Peroneal v.

Tibialis posterior

Peroneus longus t.

Peroneus brevis m. Peroneal v. Flexor hallucis longus m.

Peroneal a.

Posterolateral cortex of tibia

(Top) Coronal scan shows the lateral compartment at the level of the fibular neck. The common peroneal nerve runs together with the biceps femoris tendon, then curves anteriorly around the neck of fibula to enter the lateral and then the anterior compartments. (Middle) Coronal scan of the lateral compartment at the midleg level shows the transition between the peroneus longus and peroneus brevis muscles. These are separated from the posterior compartment by the posterior intermuscular septum. (Bottom) Coronal scan further inferiorly shows that the peroneus longus muscle is now only a tendon, compared to the muscular peroneus brevis. Similarly, in the posterior compartment, the flexor hallucis longus muscle is the only muscle at this level, as the others have also become tendons.

787

Lower Extremity

Leg Muscles LATERAL LEG

Rectus femoris m. Biceps femoris m. Vastus lateralis m.

Iliotibial tract Quadriceps t.

Lateral retinaculum Biceps femoris t. inserting on fibular head Inferior patellar t.

Tibialis anterior m.

Lateral gastrocnemius m.

Soleus m.

Extensor digitorum longus m.

Peroneus longus m. & t.

Peroneus brevis m. Tibialis anterior t. Pre-Achilles fat pad Extensor hallucis longus t. Extensor digitorum longus t.

Achilles t.

Graphic of the lateral leg shows the anterior compartment (extensors), lateral compartment (peroneals), and superficial muscles of the posterior compartment. Of the ankle tendons, tendinosis most commonly affects the Achilles tendon, the posterior tibialis tendon, and the peroneal tendons. The tibialis anterior tendon is also affected, though less commonly. As the peroneus brevis lies closest to the bone, it is more prone to trauma particularly in the retromalleolar region. Typically, this tear consists of a longitudinal split in which the overlying peroneus longus tendon pushes into the peroneus brevis tendon, splitting it into 2 sections. One may then see 3 rather than 2 tendons behind the lateral malleolus. Another reason to see 3 tendons behind the lateral malleolus is when there is a quartus tendon present.

788

Leg Muscles Lower Extremity

POSTERIOR LEG

Semitendinosus m. Biceps femoris m. Semimembranosus m. & t. Plantaris m. Sartorius t. Gracilis t.

Lateral gastrocnemius m.

Medial gastrocnemius m.

Soleus m.

Plantaris t.

Achilles t.

Posterior view shows superficial muscles and tendons of the leg. The gastrocnemius muscles are bulky in the proximal 1/2 of the leg and taper to an aponeurosis, which blends with the soleus more distally to become the Achilles tendon. The plantaris muscle is superficial only at its origin from the lateral femoral metaphysis, just medial to the origin of the lateral head of gastrocnemius. The muscle extends only a few centimeters before becoming tendinous, extending distally between the soleus and medial gastrocnemius. Eventually, the plantaris tendon merges with the medial side of the Achilles or inserts on the calcaneus, medial to the Achilles insertion.

789

Lower Extremity

Leg Muscles PANORAMIC POSTERIOR LEG

Soleus m. Medial head of gastrocnemius Lateral head of gastrocnemius

Flexor hallucis longus m. Peroneus longus Extensor digitorum longus

Popliteal vessels

Posterior fibular cortex

Posterior tibial cortex

Posterior cortex of medial tibial condyle

Medial head of gastrocnemius Soleus m. Posterior cortex of tibia

Posterior tibial v. Tibialis posterior m.

Posterior tubercle of calcaneus

Achilles t.

(Top) Transverse panoramic scan shows the posterior compartment at the level of the midleg. The medial head of the gastrocnemius muscle is larger than the lateral head throughout its course. From this midcalf level downward, the soleus muscle will assume relatively more bulk as the gastrocnemius turns tendinous. (Bottom) Sagittal panoramic scan shows the posterior compartment. The gastrocnemius is muscular down to ~ the level of the midcalf. Below this level, it forms the Achilles tendon, receiving contributions from the soleus muscle. For the deep layer, the tibialis posterior muscle lies on the surface of the tibial shaft and interosseous membrane.

790

Leg Muscles

Medial and lateral heads of gastrocnemius

Lower Extremity

TRANSVERSE POSTERIOR LEG

Gastrocnemial v. Soleus m. Tibial n. Posterior tibial a. Popliteus m. Posterior tibial cortex

Tibialis posterior m. Posterior fibular cortex Peroneal a. Posterior tibial v. Anterior compartment

Medial and lateral heads of gastrocnemius

Soleus m. Posterior fibular cortex Flexor hallucis longus

Expected position of peroneal vessels

Expected position of posterior tibial vessels Flexor digitorum longus m. Tibialis posterior m. Posterior tibial cortex

Gastrocnemius aponeurosis Soleus m.

Tibial n.

Soleal v. Posterior fibular cortex

Tibial a. Flexor digitorum longus m.

Posterior tibial cortex

Flexor hallucis longus m. Tibialis posterior m.

Interosseous membrane

(Top) Transverse scan is seen through the posterior compartment at the upper-calf level. For this compartment, the superficial layer consists of the gastrocnemius, plantaris, and soleus muscles. The deep layer consists of the popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles. (Middle) Transverse scan shows the midcalf level. The tibial vessels have bifurcated into their peroneal and posterior tibial branches, which delineates a separation between the tibialis posterior and flexor digitorum longus from the rest of the calf muscles. Given the thickness of the gastrocnemius and soleus muscle, these deep muscles may be better seen using the anterior compartment as a window. (Bottom) Further inferiorly, the gastrocnemius has become a thin aponeurosis and together with the tendon from the soleus muscle will form the Achilles tendon.

791

Lower Extremity

Leg Vessels

792

GROSS ANATOMY Arteries • Popliteal artery ○ Begins as continuation of superficial femoral artery after it has passed through adductor hiatus (inferior end of adductor canal) ○ Runs through fat of popliteal fossa ○ Relationships – Deep to artery: Femoral shaft, knee joint capsule, popliteus fascia – Superficial to artery: Semimembranosus and gastrocnemius muscles – Relation to popliteal vein is variable □ Artery lies just deep to vein in 40% □ Deep and medial to vein in 43% □ Deep and lateral to vein in 9% □ Just medial or lateral to vein in 8% ○ Gives off 4 named geniculate branches around knee – Superior medial and lateral geniculate arteries – Inferior medial and lateral geniculate arteries ○ Ends at distal border of popliteus muscle and divides into 2 branches – Anterior tibial artery – Posterior tibial artery (may be referred to as tibioperoneal trunk until branch point of peroneal artery) • Anterior tibial artery ○ Smaller of 2 terminal branches of popliteal artery ○ Origin in back of leg, at distal border of popliteus muscle ○ Passes through upper part of interosseous membrane ○ Straight course down front of leg to become dorsalis pedis artery ○ Runs on anterior surface of interosseous membrane, deep to extensor muscles ○ Muscular branches along length ○ Malleolar branches ramify over malleoli – Lateral branch anastomoses with perforating branch of peroneal artery • Posterior tibial artery ○ Larger of 2 terminal branches of popliteal artery ○ Main blood supply to foot ○ Passes downward and slightly medially along with tibial nerve ○ Terminates in space between medial malleolus and calcaneus ○ Within calf, artery runs just deep to transverse intermuscular septum ○ Divides into lateral and medial plantar arteries in tarsal tunnel behind medial malleolus ○ Branches – Circumflex fibular (may arise from anterior tibial), □ Runs laterally around neck of fibula – Nutrient artery to tibia – Muscular branches • Peroneal artery ○ Largest branch of posterior tibial artery ○ Runs obliquely downward and laterally beneath soleus muscle to fibula ○ Descends deep to flexor hallucis longus

Veins • Deep leg veins ○ Paired venae comitantes follow arteries of same name – Anterior, posterior, and peroneal veins ○ Popliteal vein – Runs superficial to artery – Usually begins at inferior border of popliteus muscle from anterior and posterior tibial veins – Crosses from medial to lateral side of popliteal artery as it runs in popliteal fossa – Ends at adductor hiatus by becoming superficial femoral vein – Also receives small saphenous vein in popliteal fossa • Superficial leg veins ○ Great saphenous vein – Longest vein in human body – Begins at medial border of foot and ascends anterior to medial malleolus – Passes obliquely upward and backward across medial surface of distal 1/3 of tibia – Passes vertically upward along medial border of tibia and over posterior border medial femoral epicondyle – Courses anteriorly along thigh – Passes through saphenous opening in fascia lata to join common femoral vein ○ Small saphenous vein – Extends behind lateral malleolus, ascends lateral to Achilles tendon – At midline of calf, in lower popliteal region, pierces popliteal fascia, and terminates in popliteal vein

ANATOMY IMAGING ISSUES Imaging Recommendations • Examination of lower limb vessels requires use of morphological and functional techniques ○ Morphology: Documentation of areas of stenosis or occlusion, sites of venous valves, aberrant branches, aneurysm formation, etc. ○ Functional: Combination of color and spectral Doppler examination • Arteries ○ Require use of spectral Doppler scanning to show their phasicity; normal wave form is triphasic – Sharp forward flow upstroke (systolic phase) – Small reverse flow (early diastolic phase) – Final smaller forward flow (late diastolic phase) • Veins ○ Require use of dynamic maneuvers – Compression: Normal vein should compress with transducer pressure (thrombus will not compress) – Augmentation: To increase venous return (to demonstrate venous flow and patency) by manually squeezing calf or by gently moving toes □ Frequently required to demonstrate flow in deep calf veins (which normally show no color Doppler flow) – Valsalva: To increase abdominal pressure and accentuate reverse flow and incompetent venous valves

Leg Vessels

Adductor hiatus

Lower Extremity

LEG ARTERIES, POSTERIOR

Adductor magnus m.

Superior medial geniculate a.

Superior lateral geniculate a.

Popliteal a.

Inferior lateral geniculate a. Inferior medial geniculate a.

Popliteus m. Anterior tibial a. Posterior tibial a. Tibialis posterior m.

Popliteal a.

Biceps femoris t.

Popliteal m. Soleus m. Tibialis posterior m.

Anterior tibial a. Peroneal a.

Posterior tibial a. & branches

Flexor digitorum longus t. Flexor hallucis longus t. Tibialis posterior t. Achilles t.

(Top) Graphic shows the the popliteal artery, from the hiatus in adductor magnus proximally to the lower border of popliteus distally. At this point, the popliteal artery bifurcates into anterior and posterior tibial arteries. The anterior tibial is the smaller branch that extends through a slit in tibialis posterior muscle and on through the interosseous membrane to descend along the interosseous membrane down the anterior compartment. There are 4 named geniculate branches, a superior and inferior both medially and laterally. (Bottom) The posterior tibial artery passes downward and slightly medially adjacent to the tibial nerve to end in the space between the medial malleolus and calcaneus. The largest branch of the posterior tibial artery is the peroneal artery, which runs obliquely downward and laterally beneath the soleus muscle to the fibula.

793

Lower Extremity

Leg Vessels LEG ARTERIES, ANTERIOR AND ANKLE

Iliotibial tract Fibular head Peroneus longus m.

Inferior patellar t. Anterior recurrent tibial a. Interosseous membrane

Peroneus tunnel

Anterior tibial a.

Perforating branch peroneal a.

Peroneus longus t.

Extensor retinaculum

Dorsalis pedis a. Lateral tarsal a.

Soleus m.

Superior extensor retinaculum

Achilles t. Posterior tibial a.

Dorsalis pedis a.

Flexor retinaculum Medial plantar a.

Lateral plantar a.

(Top) Graphic of the anterior leg shows the anterior tibial artery perforating the interosseous septum proximally and descending along this membrane down the front of leg to terminate as the dorsalis pedis. Distally, one sees a perforating branch of the peroneal artery, which in a variant situation may provide the major blood supply to the dorsum of the foot. (Bottom) Graphic of the medial aspect of the ankle shows the distal portion of both the posterior and anterior tibial arteries. The posterior tibial artery passes between the medial malleolus and calcaneus, and divides into the lateral and medial plantar arteries. The dorsal pedis artery is a direct continuation of the anterior tibial artery and supplies the dorsum of the foot.

794

Leg Vessels Lower Extremity

LEG VEINS

Popliteal v. Anterior tibial v.

Peroneal v.

Posterior tibial v.

Great saphenous v.

Great saphenous v. Small saphenous v.

(Top) This graphic shows the deep veins of the leg, which follow their accompanying artery of the same name and are often paired. (Bottom) This graphic shows the superficial leg veins. The great saphenous vein is the longest vein in the human body. It begins in the dorsomedial area of the foot. It passes obliquely upward over the posterior medial femoral epicondyle, then anteriorly across the thigh to finally join with the common femoral vein. The small saphenous vein drains from the lateral malleolus, up the posterior calf to join with the popliteal vein in the popliteal fossa.

795

Lower Extremity

Leg Vessels POPLITEAL VESSELS

Medial head of gastrocnemius m. Popliteal v. Popliteal a.

Soleus m.

Medial head of gastrocnemius m.

Popliteal v. Soleus m. Popliteal a.

Lateral head of gastrocnemius m. Medial head of gastrocnemius m. Tibia

Popliteal v.

Popliteal a.

Popliteus m.

(Top) Sagittal scan shows the lower part of the popliteal vessels. The popliteal vessels are continuations of the superficial femoral vessels after they have exited the adductor canal through the adductor hiatus. The popliteal vein lies superficial to the popliteal artery, a reverse of the relationship between the superficial femoral vein and artery. The popliteal vessels pass inferolaterally through the fat of the popliteal fossa. (Middle) Sagittal color Doppler scan of the popliteal vessels shows complete color filling of the lumina (excluding luminal thrombus) and normal flow direction: Toward the trunk (blue) for the vein and away from the trunk (red) for the artery. (Bottom) Transverse scan shows the lower part of the popliteal vessels. The popliteal vein runs superficial to the popliteal artery and usually bifurcates at the inferior margin of the popliteus muscle.

796

Leg Vessels

Gastrocnemius v.

Lower Extremity

POPLITEAL VESSEL BIFURCATION

Medial head of gastrocnemius m. Short saphenous v. Lateral head of gastrocnemius m. Posterior tibial v. Posterior tibial a.

Peroneal v.

Tibia Fibula

Soleus m.

Posterior tibial a.

Soleal v. Peroneal a.

Posterior tibial v.

Peroneal v.

Soleus m. Medial head of gastrocnemius m. Posterior tibial v. Posterior tibial a.

Posterior tibial a. Peroneal a.

Peroneal v. Peroneal a.

Fibula

(Top) Transverse scan below the bifurcation of the popliteal artery is shown. The popliteal artery bifurcates into the anterior and posterior tibial arteries. The posterior tibial artery is the larger of the 2 terminal branches of the popliteal artery and passes inferiorly for a short distance before giving out its largest branch, the peroneal artery. (Middle) Transverse color Doppler scan shows the posterior compartment vessels of the proximal calf. Color flow highlights the paired venae comitantes nature of the posterior tibial and peroneal veins, lying on both sides of the corresponding artery. (Bottom) Transverse scan at the midproximal calf scanning from the medial side is shown. The lumina of the peroneal and tibial veins can be compressed by firm transducer pressure (right 1/2 of image), indicating the lack of thrombus.

797

Lower Extremity

Leg Vessels TRANSVERSE POSTERIOR TIBIAL VESSELS Tibia Transverse intermuscular septum Medial head of gastrocnemius m.

Posterior tibial a.

Posterior tibial v. Tibialis posterior m.

Soleus m. Flexor digitorum longus m. Peroneal a.

Peroneal v. Fibula

Posterior tibial a.

Soleus m.

Tibia

Posterior tibial v.

Flexor digitorum longus m. Tibialis posterior m. Peroneal v. Peroneal a. Fibula

Tibia Posterior tibial a.

Flexor digitorum longus m. Flexor hallucis longus m. Posterior tibial v.

Fibula

(Top) Three transverse scans show the posterior tibial vessels using a medial scanning approach. Superiorly, the posterior tibial vessels give off their main branches, the common peroneal vessels. The posterior tibial artery lies just deep to the transverse intermuscular septum while the peroneal arteries are deep to the flexor digitorum muscle. (Middle) At the midcalf level, the posterior tibial vessels no longer line up side by side (3 in a line). Anatomical variations occur, as seen here with 3 posterior tibial veins accompanying 1 artery. The peroneal vessels continue their deeper course, running on the surface of the tibialis posterior, which separates them from the anterior leg compartment. (Bottom) Further inferiorly, the posterior tibial vessels emerge superficially as they prepare to enter the tarsal tunnel behind the medial malleolus.

798

Leg Vessels

Soleus m.

Lower Extremity

LONGITUDINAL POSTERIOR TIBIAL VESSELS

Posterior tibial v.

Posterior tibial a. Tibial n. Tibialis posterior m.

Posterior tibial v.

Soleus m. Posterior tibial a.

Tibial n. Tibialis posterior m.

Posterior tibial a. Tibial n. Posterior tibial v. Flexor hallucis longus m.

(Top) Oblique coronal scan shows the posterior tibial vessels using a medial approach. The posterior tibial artery is accompanied by paired venae comitantes (posterior tibial veins) and the tibial nerve. They run deep to the transverse intermuscular septum of the leg. (Middle) Color Doppler scan shows the posterior tibial vessels. Notice the marked difference in caliber between the artery and the veins, all of which show normal, complete color filling and normal direction of flow. (Bottom) Further inferiorly, oblique coronal scan of the lower calf shows the distal part of the posterior tibial vessels running superficial to the flexor hallucis muscle and getting ready to curve under the medial malleolus. The posterior tibial vessels and tibial nerve run in the tarsal tunnel together with the tendon flexors of the foot.

799

Lower Extremity

Leg Vessels TRANSVERSE PERONEAL VESSELS Lateral head of gastrocnemius m. Soleus m. Fibula Flexor hallucis longus m.

Peroneal a. Peroneal v. Soleal v. Posterior tibial v.

Tibial posterior m. Posterior tibial a.

Soleus m.

Fibula

Peroneal a. Peroneal v.

Posterior tibial v.

Posterior tibial a.

Tibia

Peroneus longus m.

Fibula

Flexor hallucis longus m.

Peroneal v. Peroneal a. Tibia

(Top) Three transverse scans of the calf using a lateral scanning approach are shown. The peroneal artery is a branch of the posterior tibial artery. It runs obliquely toward the fibula and then runs along the medial surface of the fibula distally, sandwiched between the flexor hallucis longus muscle and tibialis posterior muscle. (Middle) More distally, the relationship between the peroneal vessels and the fibula and flexor muscles remains the same. Nutrient vessels branch out to supply the fibula and the adjacent muscles. (Bottom) Most distally, the peroneal artery runs behind the tibiofibular syndesmosis before dividing into lateral calcaneal branches, which run over the lateral and posterior surfaces of the calcaneum.

800

Leg Vessels

Lateral head of gastrocnemius m.

Lower Extremity

LONGITUDINAL PERONEAL VESSELS

Soleus m. Peroneal a. Peroneal v.

Tibialis posterior m.

Soleus m.

Flexor hallucis longus m.

Peroneal v. Peroneal a. Tibialis posterior m.

Soleus m.

Flexor hallucis longus m. Peroneal v. Tibialis posterior m. Peroneal a.

(Top) Oblique coronal scan shows the peroneal vessels using a lateral approach. The peroneal artery, like the posterior tibial, is also accompanied by venae comitantes (peroneal veins). The difference is that there is no peroneal nerve to accompany the vessels. The peroneal nerve runs in the lateral leg compartment after curving around the neck of the fibula. (Middle) More inferiorly, oblique coronal scan shows the peroneus vessels lie deep to the flexor hallucis longus and soleus muscles while running superficial to the tibialis posterior muscle. (Bottom) Further inferiorly, the peroneal vessels are much smaller in caliber after giving out many branches. They pass posterior to the tibiofibular syndesmosis.

801

Lower Extremity

Leg Vessels TRANSVERSE ANTERIOR TIBIAL VESSELS Extensor digitorum longus m.

Lateral tibial cortex Tibialis anterior m. Anterior tibial v. Fibula Anterior tibial a.

Peroneal v.

Tibialis posterior m. Peroneal a. Posterior tibial a.

Posterior tibial v.

Extensor digitorum longus m. Tibialis anterior m.

Anterior tibial v.

Lateral tibial cortex

Fibula Anterior tibial a. Peroneal a. Peroneal v.

Tibialis posterior m.

Extensor digitorum and hallucis longus m. Tibialis anterior m. Anterior tibial v./a./v.

Fibula Peroneal v.

Lateral tibial cortex

Peroneal a.

Tibialis posterior m.

(Top) Three transverse scans show the anterior tibial vessels using an anterior scanning approach. The anterior tibial vessels are the smaller terminal branches of the popliteal vessels (smaller compared to the posterior tibial vessels at the bifurcation). After its origin, the anterior tibial vessels run anterior through the interosseous membrane and then pass inferiorly on the anterior surface of this membrane. (Middle) At midleg level, the anterior tibial vessels continue to run in a deep position on the surface of the interosseous membrane. Through the window between the tibia and fibula, the peroneal vessels and tibialis posterior muscle are seen. (Bottom) In the most distal part of the leg, the anterior tibial vessels move medially to lie on the surface of the tibia. At this level, the peroneal artery branches run anteriorly to penetrate the interosseous membrane.

802

Leg Vessels

Tibialis anterior m.

Lower Extremity

LONGITUDINAL ANTERIOR TIBIAL VESSELS

Anterior tibial v. Anterior tibial a.

Interosseous membrane

Popliteal a. Posterior tibial vessels Tibialis posterior m.

Tibialis anterior m.

Anterior tibial a. Tibialis posterior m.

Peroneal v. and a. Flexor hallucis longus m.

Tibialis anterior m.

Anterior tibial v. Anterior tibial a.

Flexor hallucis longus m.

(Top) Oblique sagittal color Doppler scan shows the anterior tibial vessels as they bifurcate from the popliteal vessels. The anterior tibial vessels run anteriorly to penetrate the interosseous membrane into the anterior compartment. (Middle) Sagittal scan shows the anterior tibial artery in the midleg level. The anterior tibial artery runs deep within the anterior compartment and on the surface of the interosseous membrane, being covered by the tibialis anterior muscle. (Bottom) Sagittal color Doppler scan shows the lower aspect of the anterior tibial vessels. The vessels begin to run more superficially, and in the foot, the anterior tibial artery continues as the dorsalis pedis artery.

803

Lower Extremity

Leg Vessels SPECTRAL DOPPLER OF LEG ARTERIES Soleus m.

Posterior tibial a.

Posterior tibial v.

Triphasic Doppler waveform

Soleus m.

Peroneal a. Peroneal v. Triphasic Doppler waveform

Tibialis anterior m.

Anterior tibial a. Tibialis posterior m.

Triphasic Doppler waveform

(Top) Spectral Doppler scan of the posterior tibial artery demonstrates the typical triphasic pattern seen in normal arteries. Loss of the reverse flow in the diastolic phase is termed a biphasic pattern and is suggestive of stenosis proximal to the point of interrogation. With proximal stenosis, the peak flow velocity is also decreased. (Middle) Similarly, the peroneal artery shows a triphasic waveform on spectral Doppler. (Bottom) Oblique coronal spectral Doppler scan of the anterior tibial artery in the upper calf level also shows a normal triphasic pattern. Abnormal increase in reverse flow (negative flow in early diastolic phase) suggests increased distal resistance from stenosis.

804

Leg Vessels

Soleus m.

Posterior tibial v.

Posterior tibial a.

Augmentation applied

Augmented flow

Lower Extremity

SPECTRAL DOPPLER OF LEG VEINS

Soleus m. Flexor hallucis longus m. Peroneal v.

Augmentation applied

Augmented flow

Tibialis anterior m.

Anterior tibial v. Tibialis posterior m.

Slow spontaneous flow Augmentation applied

Augmented flow

(Top) Oblique coronal spectral Doppler scan of the posterior tibial vein shows absence of spontaneous flow at rest (left 1/2 of the spectral trace). After augmentation (squeezing calf muscles distal to transducer), a surge of blood flow toward the trunk (negative values) can be demonstrated and indicates luminal patency. (Middle) Oblique coronal spectral Doppler scan of the peroneal vein before and after augmentation shows a similar sudden surge of blood flow. (Bottom) Oblique coronal spectral Doppler scan of the anterior tibial vein demonstrates slow spontaneous flow at rest. After augmentation, a sustained surge of flow is demonstrated.

805

Lower Extremity

Leg Vessels SOLEAL VEINS

Soleal v.

Soleus m.

Tibialis posterior m.

Gastrocnemius m.

Soleal v. draining into posterior tibial v.

Soleal v.

Posterior tibial v. Posterior tibial a.

Posterior tibial v./a./v. Gastrocnemius m. Compressed soleal v. Soleal v. Soleus m. Peroneal v. and a. Fibula

(Top) Oblique sagittal color Doppler scan shows the posterior compartment in the midcalf level. The soleal vein shows complete color filling of its lumen indicating the absence of thrombus. Soleal veins are the most common veins to develop thrombosis and should be assessed when scanning for deep venous thrombosis. (Middle) Oblique sagittal scan of the posterior compartment shows the soleal vein running proximally and joining the posterior tibial vein. This pathway allows a soleal vein thrombus to extend into the posterior tibial vein and propagate proximally. (Bottom) Dual transverse images show the posterior compartment using a medial approach, before (left image) and during (right image) firm transducer compression. The soleal veins are completely compressed by transducer pressure, indicating an absence of thrombus.

806

Leg Vessels Lower Extremity

GASTROCNEMIUS VEINS

Gastrocnemius m. Gastrocnemius v.

Soleus m.

Gastrocnemius v.

Popliteal v.

Soleus m.

Gastrocnemius m.

Gastrocnemius m.

Gastrocnemius v. Compressed gastrocnemius v. Soleus m.

Soleus m.

(Top) Oblique sagittal color Doppler scan shows the posterior leg compartment. The gastrocnemius vein shows complete color filling, indicating absence of thrombus. The gastrocnemius veins are the 2nd most common site for venous thrombosis. (Middle) Oblique sagittal scan of the posterior compartment of the upper calf shows the gastrocnemius vein joining the popliteal vein, allowing a gastrocnemius vein thrombus to extend proximally to the popliteal vein. (Bottom) Dual transverse images show gastrocnemius veins before (left image) and during (right image) compression. The gastrocnemius veins are completely compressed during compression, indicating an absence of thrombus. Compression is regarded as the most reliable technique to rule out venous thrombosis.

807

Lower Extremity

Leg Vessels SMALL SAPHENOUS VEIN

Saphenopopliteal junction

Small saphenous v.

Popliteal v.

Investing fascia

Small saphenous v.

Gastrocnemius m.

Soleus m.

(Top) Sagittal scan shows central popliteal fossa. The small saphenous vein running from the lateral surface of the calf turns medially and penetrates the popliteal fascia to drain into the popliteal vein. Varicose veins arise as a result of reflux and stasis due to incompetent valves. Varicose veins on the lateral side of the calf suggest an incompetent small saphenous system. (Middle) Sagittal color Doppler scan shows the central popliteal fossa with augmentation. Flow toward the popliteal vein (red) is demonstrated at the saphenopopliteal junction. Reverse flow into the small saphenous vein would suggest valvular incompetence. (Bottom) Transverse scan shows the posterior surface of the upper calf. The small saphenous vein is sandwiched between 2 layers of investing fascia. Minimal probe pressure is required to avoid inadvertent compression of the small saphenous vein.

808

Leg Vessels

Investing fascia

Lower Extremity

GREAT SAPHENOUS VEINS

Small saphenous v.

Gastrocnemius m. Soleus m.

Subcutaneous tissue Great saphenous v. Investing fascia separating superficial and deep calf Flexor digitorum longus m. Perforator

Soleus m. Posterior tibial v.

Great saphenous v.

Flexor digitorum longus m. Competent perforator Posterior tibial v. and a. Soleus m.

(Top) Sagittal color Doppler scan shows upper midcalf with augmentation. The complete filling of the venous lumen of the small saphenous vein is demonstrated, indicating the absence of a superficial vein thrombus. If flow toward the trunk is demonstrated, valvular incompetence can be excluded. (Middle) Transverse scan shows the medial aspect of the lower 1/3 of the calf. A perforator arising from the great saphenous vein is seen penetrating through the investing fascia to join the posterior tibial vein. (Bottom) Transverse color Doppler scan shows the medial aspect of the lower 1/3 of the calf. With augmentation, color filling of the perforator lumen is demonstrated in the perforator between the great saphenous vein and the posterior tibial vein, indicating patency of vessel. If flow toward the posterior tibial vein can be documented on Doppler study, incompetence can be excluded.

809

Lower Extremity

Leg Nerves

GROSS ANATOMY Sciatic Nerve • Actually 2 nerves (common peroneal and tibial) bound together

Common Peroneal Nerve • Smaller of 2 terminal divisions of sciatic nerve • Arises from dorsal divisions of sacral plexus (L4, L5, S1, S2) • Separates from tibial nerve midthigh, at superior angle of popliteal fossa, runs downward laterally along medial border of biceps femoris muscle and tendon • Leaves popliteal fossa by crossing plantaris and lateral head of gastrocnemius, passes posterior and superficial to head of fibula • Curves anteriorly over posterior aspect of head of fibula • Winds around lateral surface of fibular neck ○ Location at fibular head/neck puts peroneal nerve at risk in several clinical situations – Fibular neck fracture may result in foot drop – Realignment during correction of chronic knee valgus deformity may stretch nerve • Ends between lateral side of neck of fibula and peroneus longus by dividing into 3 terminal branches ○ Recurrent articular branch – To proximal tibiofibular joint – Occasionally acts as conduit for intraneural transmission of ganglion arising from joint ○ Deep peroneal nerve – Arises on lateral side of neck of fibula, under peroneus longus – Pierces anterior intermuscular septum and extensor digitorum longus to enter anterior compartment – Extends down to ankle between tibialis anterior and long extensors – Near ankle, crossed by extensor hallucis and passes to ankle midway between malleoli – Muscular branches to anterior compartment and articular branch to ankle joint – Deep peroneal nerve crosses over to lateral side of dorsalis pedis artery at ankle joint – Medial and lateral terminal branches to dorsum of foot – Medial is main terminal branch and travels distally just medial to dorsalis pedis artery ○ Superficial peroneal nerve – Descends in substance of peroneus longus until it reaches peroneus brevis – Passes obliquely over anterior border of brevis and descends in groove between peroneus brevis and extensor digitorum longus – In distal 1/3 of leg, pierces deep fascia and divides into medial and lateral sensory branches to foot

Tibial Nerve • Arises from ventral surface of sacral plexus • Runs roughly along central axis of popliteal fossa • Descends under fascial septum, which separates deep and superficial posterior muscle compartments • In upper 2/3, lies on fascia of tibialis posterior and on flexor digitorum longus 810

• In lower 1/3, located midway between Achilles tendon and medial border of tibia • Crosses posterior surfaces of tibia and ankle joint • Posterior tibial vessels run with it, crossing in front of it from lateral to medial side • At ankle, under flexor retinaculum, divides into lateral and medial plantar nerves ○ 1st branch of lateral plantar nerve is inferior calcaneal nerve (Baxter nerve) – Since this nerve supplies calcaneal periosteum, neuritis of this nerve can simulate plantar fasciitis ○ Medial plantar nerve can become compressed between navicular tuberosity and abductor hallucis muscle belly (jogger's foot)

Saphenous Nerve • Longest branch of femoral nerve, arising 2 cm below inguinal ligament and descending via adductor canal • Passes posterior to sartorius, descends posteromedial to knee where it pierces deep fascia • In leg, accompanies great saphenous vein

Sural Nerve • Purely sensory nerve that arises in popliteal fossa from tibial nerve • Descends between 2 heads of gastrocnemius • Pierces deep fascia midway between knee and ankle • Courses superficial and posterior to peroneal tendons • Accompanies small saphenous vein to lateral border of foot

ANATOMY IMAGING ISSUES Imaging Approaches • Ultrasound ○ Use high-frequency transducers to assess nerves ○ Neural signature on ultrasound – Short axis: Uniformly dispersed hypoechoic dots (nerve fascicles) separated by hyperechoic epineurium – Long axis: Parallel hypoechoic tracts of uniform caliber – Overall gain control and focus settings may have to be optimized for ultrasound to demonstrate nerve well – Anisotropy artifact may affect scanning, especially in short axis; tilting transducer during scanning helps achieve best view – Distortion of this uniform appearance suggests pathology ○ Trace medium-sized nerves by following their course as they branch from their parent ○ Small (1- to 2-mm) nerves are difficult to identify and location may only be inferred by adjacent vessels • MR ○ Also suffers from inability to detect small nerves ○ Use of superficial small field of view coils may improve resolution

Leg Nerves

Popliteal a. Tibial n. Popliteal m. Tibialis posterior m.

Biceps femoris t. Common peroneal n.

Lower Extremity

GRAPHICS, ANTERIOR AND POSTERIOR LEG NERVES

Anterior tibial a. Soleus m. Peroneal a.

Posterior tibial a. and branches

Tibial n. and muscular branches

Flexor digitorum longus t. Flexor hallucis longus t. Tibialis posterior t. Achilles t.

Common peroneal n. Fibular head Peroneus longus m.

Iliotibial tract Inferior patellar t. Anterior recurrent tibial n. and a. Interosseous membrane

Peroneus tunnel

Anterior tibial a. Superficial peroneal n. Deep peroneal n.

Perforating branch peroneal a. Extensor retinaculum Medial and lateral terminal branches deep peroneal n. Dorsalis pedis a. Peroneus longus t.

Lateral tarsal a.

(Top) Graphic shows posterior leg nerves and arteries. The sciatic nerve divides into common peroneal and tibial branches. The common peroneal nerve then follows the biceps femoris around the lateral fibular neck. The tibial nerve descends between the deep and superficial posterior leg muscles, paralleling the posterior tibial artery. (Bottom) Graphic of the anterior leg shows the common peroneal nerve extending through the peroneal tunnel (between the peroneus longus tendon and the fibular neck), branching into deep and superficial components. Both have muscular branches along their length; the deep peroneal nerve parallels the anterior tibial artery and terminates in the medial and lateral branches to the dorsum of the foot and ankle, respectively.

811

Lower Extremity

Leg Nerves TIBIAL NERVE

Tibial n.

Lateral head of gastrocnemius m. Medial head of gastrocnemius m. Lateral femoral condyle Popliteal a.

Posterior tibial cortex Medial head of gastrocnemius

Tibial n. Posterior tibial v. (left)/a. (central)/v. (right)

Soleus m.

Tibialis posterior m. Peroneal v.

Posterior fibular cortex

Medial talar tubercle Flexor hallucis longus t.

Posterior tibial cortex Tibial n.

(Top) Transverse scan shows the lower aspect of the popliteal fossa. The tibial nerve demonstrates the typical neural signature of small black dots within a bright matrix. It lies superficial to the popliteal artery. (Middle) Further inferiorly, at the level of the midcalf, the tibial nerve is deep to the soleus muscle and lies lateral to the posterior tibial vessels. Notice that even at this depth the neural signature is still visible. (Bottom) Sagittal scan shows the posterior aspect of the medial ankle. The longitudinal neural signature of the tibial nerve is well shown here with parallel hypoechoic tracts, which are roughly uniform in size. Contrast this to the more densely packed appearance of tendons.

812

Leg Nerves Lower Extremity

PERONEAL NERVE

Peroneus longus m. Soleus m. Common peroneal n.

Tibialis anterior m.

Lateral fibular cortex Anterior tibial vessels

Peroneus longus m. Fibular head

Common peroneal n.

Fibular neck

Peroneus longus m. Extensor hallucis longus m. Deep peroneal n. Extensor digitorum longus m. Anterior fibular cortex Anterior tibial vessels

Lateral tibial cortex

(Top) Transverse scan of the head of fibula shows the common peroneal nerve running along the posteromedial aspect of the peroneus longus muscle. Superior to this, the nerve is covered by the biceps femoris muscle and tendon. (Middle) Coronal scan of the fibular neck shows the common peroneal nerve passing deep to the peroneus longus muscle. The nerve will then enter the anterior compartment. (Bottom) Transverse scan shows the anterior compartment at the midleg level. The deep peroneal nerve runs anterior to the anterior tibial vessels deep in this compartment.

813

Lower Extremity

Ankle

GROSS ANATOMY Osseous Anatomy • Ankle (talocrural) joint ○ Tibia, fibula, and talus form synovial joint ○ Supported by lateral and medial collateral ligaments ○ Mainly uniaxial hinge joint, dorsiflexion, plantar flexion, also dynamic shift of axis of rotation during dorsiflexion and plantar flexion • Distal tibiofibular joint ○ Fibrous joint ○ Supported by syndesmotic ligaments ○ Synovial recess from ankle joint extends into joint ○ May have articular cartilage far distally ○ Minimal stretch ("give") during dorsiflexion: Allows increase in malleolar gap and slight fibular lateral rotation

Ligaments • 3 sets bind ankle: Distal tibiofibular syndesmotic complex, lateral collateral ligaments, and deltoid ligaments • 4 tibiofibular syndesmotic ligaments ○ Anterior and posterior tibiofibular ligaments – Extend obliquely between anterior and posterior tibial and fibular tubercles, respectively – Distal anterior tibiofibular ligament: Bassett ligament ○ Inferior transverse ligament: Distal part of posterior tibiofibular ligament ○ Interosseous ligament: Distal thickening of syndesmotic membrane • 3 lateral collateral ligaments ○ Anterior talofibular ligament – Originates 1 cm proximal to lateral malleolar tip; inserts on talar neck – Stabilizes talus against anterior displacement, internal rotation, and inversion – Weakest, 1st to tear ○ Calcaneofibular ligament – Originates from lateral malleolar tip; inserts on calcaneal trochlear eminence – Deep to peroneal tendons – Lateral restraint of subtalar joint, often tears with anterior talofibular ligament ○ Posterior talofibular ligament – Extends from lateral malleolar fossa to lateral talar tubercle – Strongest, rarely tears • Deltoid ligament (medial collateral ligament) ○ Fan-shaped, originates from anterior, apex, and posterior medial malleolus; inserts on talus, sustentaculum tali, spring ligament, and navicular ○ Deep: Posterior and anterior tibiotalar bands ○ Superficial: Tibiocalcaneal, tibiospring, tibionavicular, and posterior tibiotalar (variable) bands • Spring ligament (plantar calcaneonavicular ligament) ○ Binds calcaneus to navicular, 3 components – Superomedial = origin: Sustentaculum tali; insertion: Superomedial navicular, tibiospring band of deltoid – Medioplantar oblique = origin: Calcaneal coronoid fossa; insertion: Plantar navicular 814

– Inferoplantar longitudinal = origin: Coronoid fossa; insertion: Navicular beak

Retinacula • Focal thickening of deep fascia • Prevents bowstringing, binds tendons down • Superior extensor retinaculum ○ Few cm above ankle joint ○ Attaches to anterior fibula laterally, tibia medially ○ Proximally continues with fascia cruris ○ Distally attaches to inferior extensor retinaculum ○ Binds down anterior compartment muscles • Inferior extensor retinaculum ○ At ankle joint, Y-shaped, stem laterally, proximal and distal bands medially ○ Stem attaches laterally to upper calcaneus – Loops around extensor tendons – Roots extend into sinus tarsi ○ Proximal medial band has deep and superficial layers, loops around extensor hallucis longus tendon and occasionally tibialis anterior tendon ○ Distal medial band superficial to extensor hallucis longus and tibialis anterior tendons – Attaches to plantar aponeurosis ○ Dorsalis pedis vessels, deep peroneal nerve: Deep to all layers of inferior extensor retinaculum • Flexor retinaculum ○ Attaches to medial malleolus ○ Proximally continuous with deep fascia of leg ○ Distally continuous with plantar aponeurosis ○ Abductor hallucis partly attached to it ○ Binds deep flexor tendons to tibial and calcaneal grooves ○ Lateral border of tarsal tunnel • Superior peroneal retinaculum ○ Origin: Lateral malleolus, insertions vary, most commonly to deep fascia of leg and calcaneus ○ Binds peroneal tendons into retrofibular groove • Inferior peroneal retinaculum ○ Continuous with inferior extensor retinaculum ○ Inserts on lateral calcaneus, peroneal tubercle (trochlea) ○ Binds peroneus brevis, peroneus longus tendons to calcaneus

Tendons • Anterior (extensor) compartment ○ Tibialis anterior tendon – Most medial and largest tendon in anterior compartment – Inserts on medial cuneiform, base of 1st metatarsal – Dorsiflexes ankle, inverts foot, tightens plantar aponeurosis – Supports medial longitudinal arch during walking ○ Extensor hallucis longus tendon – Inserts on dorsal base of 1st distal phalanx – Extends 1st phalanges, dorsiflexes foot ○ Extensor digitorum longus tendon – Divides into 4 slips on dorsum of foot – Slips receive tendinous contributions from extensor digitorum brevis, lumbricals, and interosseous muscles

Ankle

•

•

•

– Inserts on navicular tuberosity, cuneiforms, sustentaculum tali, bases of 2nd-4th metatarsals – Main invertor of foot, aids in plantar flexion – Supports medial longitudinal arch ○ Flexor digitorum longus tendon – Lateral to tibialis posterior tendon in tibial groove – Crosses flexor hallucis longus tendon at knot of Henry (where there is also exchange of tendon fibers at this crossing of 2 tendons) – Divides into 4 slips, which give origin to lumbricals – Slips pass through openings in corresponding tendons of flexor digitorum brevis – Slips insert on bases of 2nd-5th distal phalanges – Flexes distal phalanges, assists in plantar flexion of ankle – When foot on ground: Maintains pads of toes on ground – When foot off ground: Plantar flexes 2nd-5th phalanges, aids in maintaining longitudinal arches ○ Flexor hallucis longus tendon – Passes 3 fibroosseous tunnels: (1) Between medial and lateral talar tubercles, (2) under sustentaculum tali, and (3) between 1st medial and lateral sesamoids – Crosses and sends slip to flexor digitorum longus at knot of Henry – Inserts on base of 1st distal phalanx – When foot on ground: Maintains pad of 1st toe on ground – When foot off ground: Plantar flexes 1st phalanges, aids in maintaining medial longitudinal arch – Weak plantar flexor of ankle – Innervated by tibial nerve

Lower Extremity

•

– Each slip divides into 3: Central slip inserts on dorsal base of middle phalanx and 2 collateral slips, which reunite and insert on bases of 2nd-5th distal phalanges – Dorsiflexes ankle, extends toes, tightens plantar aponeurosis ○ Peroneus tertius tendon – Typically part of extensor digitorum longus tendon – Inserts on dorsal base of 5th metatarsal Lateral compartment ○ Peroneus longus tendon – Posterolateral to peroneus brevis tendon in retrofibular groove, deep to superior peroneal retinaculum – Proximally has common tendon sheath with peroneus brevis – Separates tendon sheath at sole of foot – Descends inferior to peroneal tubercle, deep to inferior peroneal retinaculum – Curves in cuboid groove deep to long plantar ligament – Inserts on plantar base of 1st metatarsal, medial cuneiform – Plantarflexes ankle, everts foot, supports longitudinal and transverse arches during walking – Os peroneum is in ~ 20% of individuals ○ Peroneus brevis tendon – Anteromedial to peroneus longus tendon in retrofibular groove, deep to superior peroneal retinaculum – Descends superior to peroneal tubercle of calcaneus, deep to inferior peroneal retinaculum – Inserts into base of 5th metatarsal – Everts foot, limits foot inversion Superficial posterior compartment ○ Achilles tendon – Largest and strongest tendon in body – Commonest tendon to rupture – Conjoint tendon of medial and lateral gastrocnemius and soleus muscles – ~ 15 cm long – Lacks tendon sheath partially enclosed by paratenon – Inserts into posterior calcaneal tuberosity – Crescent-shaped insertion with medial and lateral projections – Retrocalcaneal bursa between distal tendon and calcaneal tuberosity – Main plantar flexor of ankle, foot – Midsection of Achilles tendon is supplied by peroneal artery – Proximal and distal portions supplied by posterior tibial artery Plantaris tendon ○ Vestigial, slender tendon, medial to Achilles tendon ○ Inserts on or medial to Achilles tendon Deep posterior (flexor) compartment ○ Tibialis posterior tendon – Crosses flexor digitorum longus tendon above ankle joint to become most posteromedial tendon – Shares tibial groove with flexor digitorum longus tendon

ANATOMY IMAGING ISSUES Imaging Recommendations • Ultrasound ○ Use ultrasound to assess tendon and ligamentous abnormalities aside from masses around ankle joint ○ Ligaments and tendons need to be assessed in both long and short axis ○ Since most structures run obliquely and tendons make acute turns around joint, clear understanding of their relationships and associated bony landmarks is helpful • CT ○ Best for bony anatomy ○ Superior to MR for detecting small avulsion fragments • MR of ankle and hindfoot ○ Axials optimal for ankle tendons, ligaments ○ Coronals useful for bones, cartilage, ankle, and sinus tarsi ligaments ○ Sagittals optimal for Achilles tendon, bones, cartilage, sinus tarsi ligaments

815

Lower Extremity

Ankle ANTERIOR ANKLE

Superior extensor retinaculum Deep peroneal nerve Lateral branch, deep peroneal nerve Inferior extensor retinaculum

Extensor digitorum brevis m.

Medial branch, deep peroneal nerve Extensor hallucis brevis m.

Tibialis anterior t.

Extensor digitorum longus t.

Superior extensor retinaculum Proximal limb, inferior extensor retinaculum

Stem, inferior extensor retinaculum

Distal limb, inferior extensor retinaculum

Extensor hallucis longus t.

(Top) The deep peroneal nerve travels deep to the extensor retinacula in the anterior tarsal tunnel and gives a lateral motor branch to the extensor digitorum brevis muscle. The medial branch continues dorsal to the talonavicular joint, middle cuneiform, and in between 1st and 2nd metatarsal to provide mostly sensory, but some motor, supply to the 1st web space. (Bottom) The peroneus tertius and tibialis anterior tendon insert proximally on the base of the 5th metatarsal and on the medial cuneiform and 1st metatarsal, respectively. The rest of the extensor tendons continue distally toward their insertion sites on the digits. The extensor tendons are held in place by the superior and inferior extensor retinacula.

816

Ankle

Tibialis anterior t. Superior extensor retinaculum

Lower Extremity

ANTERIOR ANKLE

Extensor digitorum longus t. Extensor hallucis longus t. Peroneus tertius m. Extensor hallucis longus m.

Deep peroneal nerve Anterior tibial v./a./v.

Anterior tibial cortex

Tibialis anterior t. Inferior extensor retinaculum

Peroneus tertius m. Extensor hallucis longus t. and m. Fibular cortex Anterior tibiofibular l.

Deep peroneal nerve Anterior tibial v./a./v.

Extensor digitorum longus t. Anterior tibial cortex

Tibialis anterior t. Extensor digitorum longus t. Peroneus tertius m. and t. Anterior lateral corner of talar dome

Extensor hallucis longus t. and m.

Dorsalis pedis v./a./v. Deep peroneal nerve

(Top) Anterior transverse color Doppler scan above level of the ankle joint is shown. The basic relationship of the main structures of the anterior ankle hold true here and down through the ankle joint. From medial to lateral, the structures are: Tibialis anterior, extensor hallucis longus, nerve and vessels, and extensor digitorum longus (mnemonic: Tom, Harry, and Dick). (Middle) Transverse scan of the ankle joint at the level of the anterior talofibular ligament is shown. The anterior talofibular ligament, like most ankle ligaments, runs an oblique course and therefore may appear irregular or interrupted on a straight axial scan. This can be corrected by scanning obliquely along the long axis of the ligament. (Bottom) Transverse scan more inferiorly shows the asymmetrical soft tissue thickness anterior to the talus (thicker medially) due to different orientation axes of talus and foot.

817

Lower Extremity

Ankle ANTERIOR ANKLE

Tibialis anterior t.

Navicular Anterior cortex of distal tibia

Talonavicular joint Head of talus

Ankle joint Talar dome

Neck of talus

Extensor hallucis longus t. and m.

Navicular Talonavicular joint Anterior cortex of distal tibia

Head of talus

Ankle joint Talar dome

Neck of talus

Dorsalis pedis a. Accompanying v. Anterior cortex of tibia Talar dome

Navicular

Head of talus Neck of talus

(Top) Longitudinal scan of the lateral aspect of the ankle shows the course of the tibialis anterior tendon. A thin hypoechoic synovial layer can be seen enveloping the tendon. (Middle) Slightly more laterally, sagittal scan shows the extensor hallucis longus tendon and muscle, the latter distinguishing it from the tibialis anterior tendon. (Bottom) Further laterally, the dorsalis pedis artery and the accompanying vein(s) come into view. At this point, the subcutaneous tissue is thinnest, a result of the transverse arch of the midfoot with the apex roughly coinciding with the site of this artery. This creates a shallow bony backing for palpating the artery.

818

Ankle Lower Extremity

MEDIAL ANKLE

Achilles t.

Posterior tibial nerve Tibialis anterior t. Extensor hallucis longus t.

Medial calcaneal nerve

Medial plantar nerve Inferior calcaneal nerve Flexor hallucis longus t.

Lateral plantar nerve

Interosseous membrane Tibia

Fibula

Talus Posterior tibiotalar, deep deltoid l.

Talofibular l. Interosseous talocalcaneal l. Sinus tarsi

Tibiocalcaneal, superficial deltoid l. Tibialis posterior t.

Peroneus brevis t.

Abductor hallucis m.

Peroneus longus t.

Quadratus plantae m.

Abductor digiti minimi m.

Flexor digitorum brevis m.

(Top) Tarsal tunnel is seen accommodating the posterior tibial neurovascular bundle. The medial calcaneal nerve supplies the skin of the medial heel. The medial plantar nerve supplies the flexor hallucis brevis, abductor hallucis, flexor digitorum brevis, and 1st lumbrical. It carries sensation from the medial 2/3 of the plantar foot. The lateral plantar nerve supplies all other plantar muscles, including 2nd-4th lumbricals and all interossei, plus sensation from lateral 1/3 of mid and forefoot. (Bottom) Illustration of coronal section through the tibia, fibula, talus, and calcaneum shows the ankle ligaments. On the medial side, the medial malleolus is connected via the deep and superficial deltoid ligaments to the medial tarsal bones. The tibialis posterior tendon passes over the deltoid ligament as it curves below the medial malleolus. The talocalcaneal interosseous ligament, which has at least 4 discrete components, maintains apposition of the talus and calcaneus during hindfoot eversion and inversion.

819

Lower Extremity

Ankle MEDIAL ANKLE Flexor retinaculum

Tibialis posterior t. Posteromedial angle of distal tibia Flexor digitorum longus m. and t.

Tibial nerve Posterior tibial a. Posterior tibial v. Flexor hallucis longus t. and m.

Flexor retinaculum

Tibialis posterior t. Posteromedial surface of medial malleolus Flexor digitorum longus m. and t.

Tibial nerve Posterior tibial a. Posterior tibial v. Flexor hallucis longus t. and m.

Posterior tibial v. and a.

Tibial nerve Posterior surface of medial malleolus Tibialis posterior t. Posterior aspect of ankle joint

Flexor hallucis longus t. Medial tubercle of posterior talus

Flexor digitorum longus and synovial fluid

(Top) Transverse color Doppler scan shows the posterior aspect of the distal tibia just above the medial malleolus. This area is held down by the flexor retinaculum and termed the tarsal tunnel. Within this tunnel are tibialis posterior, flexor digitorum longus, vessels and nerve, and flexor hallucis longus (mnemonic: Tom, Dick, and Harry). (Middle) Corresponding grayscale transverse scan just above the medial malleolus is shown. Image is less grainy without simultaneous color Doppler interrogation, and the nerve fibers (hypoechoic dots) give the typical neural signature. (Bottom) At the level of the talus, the tibial nerve moves anteriorly to run deep to the posterior tibial vessels and superficial to the flexor hallucis longus tendon. The flexor hallucis longus tendon runs in a groove on the posterior surface of the talus.

820

Ankle

Posterior tibial vessels Tibialis posterior t.

Lower Extremity

MEDIAL ANKLE

Spring l. Flexor digitorum longus t. Sustentaculum talus Flexor hallucis longus t. Medial and lateral plantar nerves

Posterior tibial a. and v.

Medial malleolus Tibialis posterior t. Deltoid l. Tibial nerve Flexor digitorum longus t.

Flexor hallucis longus t.

Talus Sustentaculum tali of calcaneus

Medial navicular cortex Tibialis posterior t. Talonavicular joint

Neck of talus Head of talus

(Top) More inferiorly, oblique transverse scan through the sustentaculum tali of the calcaneus shows that the mnemonic of Tom, Dick, and Harry still holds (tibialis posterior anteriorly and flexor hallucis longus posteriorly). The flexor hallucis longus tendon now runs in a groove behind the sustentaculum tali. (Middle) Coronal scan shows the tarsal tunnel. All structures within the tunnel curve around the medial malleolus to run forward to the midfoot. The tibialis posterior tendon runs on the surface of the deltoid ligament, flexor digitorum longus on the talus, and flexor hallucis longus on the calcaneus under the sustentaculum tali. (Bottom) Transverse image shows the long axis of the tibialis posterior tendon inserting onto the medial pole of the navicular. This insertion is sometimes accompanied by an accessory navicular bone, which may take on different shapes.

821

Lower Extremity

Ankle MEDIAL AND POSTERIOR LIGAMENTS

Tibia

Anterior tibiotalar, superficial deltoid Talus

Tibiospring, superficial deltoid Tibiocalcaneal band, superficial deltoid

Dorsal talonavicular l. Posterior tibiotalar, superficial deltoid Navicular

Posterior tibiotalar, deep deltoid

Tibionavicular band, superficial deltoid Superomedial, spring l. Short plantar l.

Calcaneus

Long plantar l.

Interosseous membrane Tibia

Posterior tibiotalar, deep deltoid

Fibula

Posterior tibiofibular l. Inferior transverse l.

Tibiocalcaneal, superficial deltoid Posterior talofibular l. Talus Calcaneofibular l.

Calcaneus

(Top) Medial view shows the ankle. The deltoid ligament is the major supporter of the ankle. It has many variable components, but a commonly accepted division includes the deep anterior and posterior tibiotalar and superficial anterior and posterior tibiotalar, tibiocalcaneal, and tibiospring and tibionavicular bands. Note that the superficial deltoid is band-like, and distinction between its various components relies on the sites of insertion. (Bottom) Posterior view shows the ankle. The tibiofibular ligaments are obliquely oriented and their fibular origin is above the fibular fossa. The inferior transverse ligament, which is the inferior aspect of the posterior tibiofibular ligament, extends distal to the tibial posterior surface.

822

Ankle

Tibialis posterior t. Medial malleolus

Lower Extremity

DELTOID LIGAMENT

Posterior tibiotalar part of deltoid l. Flexor digitorum longus t.

Talus

Flexor digitorum longus t. Tibialis posterior t. Medial malleolus Deltoid ligament deep layer Deltoid ligament superficial layer

Sustentaculum tali

Talus

Tibialis posterior t.

Medial malleolus Flexor digitorum longus t. Deltoid ligament deep layer Deltoid ligament superficial layer Medial talar cortex

Spring l. Anterior talocalcaneal joint

(Top) Coronal image is seen through the posterior (posterior tibiotalar) portion of deltoid ligament, which runs from the medial malleolus to the talus. The tibialis posterior and flexor digitorum longus tendons run superficial to this ligament. (Middle) Coronal image through a more anterior portion of the deltoid ligament is shown. The superficial layer (tibiocalcaneal) runs from the malleolus to the sustentaculum tali, the deep component (posterior tibiotalar) to the talus. (Bottom) Coronal image is seen through the midportion of the deltoid ligament. The superficial layer (tibiospring) runs from the malleolus to the spring ligament, the deep component to the talus.

823

Lower Extremity

Ankle DELTOID LIGAMENT

Tibialis posterior t.

Medial malleolus Anterior tibionavicular l.

Navicular Talonavicular joint Talus

Medial malleolus Anterior tibiotalar l.

Talar neck

Tibialis posterior t.

Deltoid l. deep and superficial layers Medial talar cortex

(Top) Coronal image is seen through the anterior portion of deltoid ligament; a superficial layer (talonavicular) runs from the malleolus to the navicular. (Middle) Oblique sagittal image is seen through the most anterior portion of the deltoid ligament; fibers (anterior tibiotalar) run from the malleolus to the talar neck. From front to back, these superficial and deep components of the deltoid create a strong restraint against ankle eversion. (Bottom) Transverse scan through the medial wall of the talus shows deep and superficial components of the deltoid ligament. The tibialis posterior tendon runs superficial to this ligament.

824

Ankle

Tibia Fibula

Interosseous membrane

Lower Extremity

LATERAL ANKLE

Anterior tibiofibular l. Posterior tibiofibular l. Dorsal talonavicular l. Anterior talofibular l. Posterior talofibular l.

Navicular Bifurcate l.

Calcaneofibular l. Cervical l. Cuboid Calcaneus Dorsal calcaneocuboid l. Talocalcaneal interosseous l. Long plantar l.

Fibula Tibia Fibula Peroneus longus t.

Fibrocartilaginous ridge Peroneus brevis t. Peroneus longus t.

Peroneus brevis

Superior peroneal retinaculum

Achilles t.

Peroneus brevis t. Superior peroneal retinaculum Cuboid Calcaneus 5th metatarsal Inferior peroneal retinaculum

(Top) Lateral view shows the ankle. Two groups of lateral ligaments support the ankle: (1) The syndesmotic ligaments, including the anterior tibiofibular, posterior tibiofibular, and syndesmotic ligaments, and (2) the lateral collateral ligaments, including the anterior talofibular, posterior talofibular, and calcaneofibular ligaments. Other ligaments that bind the lateral hindfoot include the talocalcaneal interosseous ligament and cervical ligament in the sinus tarsi. Note the bifurcate ligament, which extends from the calcaneus to the navicular and cuboid. (Bottom) Peroneal retinacula is shown. The superior peroneal retinaculum holds the peroneal tendons in the retrofibular groove. The retinaculum has variable insertions but typically inserts on deep fascia of the leg and on the calcaneus. The inferior peroneal retinaculum holds the peroneal tendons against the calcaneus.

825

Lower Extremity

Ankle LATERAL ANKLE

Peroneus longus t.

Lesser saphenous v. tributaries Flexor hallucis longus m.

Peroneus brevis t. Peroneus brevis m. Fibula Peroneal v./a./v.

Tibia

Superior peroneal retinaculum

Lateral malleolus Peroneus longus t. Lesser saphenous v. tributaries

Peroneus brevis t. Peroneus brevis m. Peroneal v./a./v.

Lateral calcaneal cortex

Superior peroneal retinaculum Synovial sheath Lateral calcaneal cortex Peroneus longus t. Peroneus brevis t.

Calcaneal fibular l. Posterior aspect of lateral malleolus

(Top) Transverse scan of the posterior aspect of the distal fibula shows the distal peroneal muscles. The peroneus longus tendon runs anterior to the peroneus brevis. The latter is easily identified by its muscle component, which continues to just above the tip of the lateral malleolus. (Middle) Transverse scan is shown at the level just above the tip of the lateral malleolus. The peroneal tendons are now held down by the superior peroneal retinaculum, which prevents tendon subluxation (bowstringing). There is still a residual component of the peroneus brevis muscle. (Bottom) Oblique coronal scan of the posterior aspect of the lateral malleolus shows the longitudinal course of the peroneal tendons. Both tendons run inferior onto the lateral surface of the calcaneus, passing over the calcaneal fibular ligament on the way.

826

Ankle

Peroneus longus t.

Lower Extremity

LATERAL ANKLE

Inferior peroneal retinaculum Cuboid

Calcaneal fibular l.

Lateral calcaneal cortex

Peroneus brevis t. Inferior peroneal retinaculum

Tributaries of lesser saphenous v. Peroneal trochlea

Peroneus longus t. Lateral cortex of calcaneus

Peroneus longus t. Cuboid

Base of 5th metatarsal Peroneus brevis t.

Groove for peroneus longus t.

(Top) Oblique transverse scan shows the lateral aspect of the calcaneus along the course of the peroneus longus tendon. Close to the anterior end of the calcaneus, the peroneus longus turns medially and inferiorly to enter the plantar region. (Middle) Coronal scan of the lateral surface of the calcaneus shows the peroneal tendons held down by the inferior peroneal retinaculum but partially separated by peroneal tubercle, a protuberance on the lateral calcaneal cortex. The peroneus brevis tendon lies more superior than the peroneus longus tendon at this level. (Bottom) Transverse scan of the lateral aspect of the foot shows insertion of the peroneus brevis tendon onto the base of the 5th metatarsal bone. Also shown here is the peroneus longus tendon turning inferiorly on the surface of the cuboid into a groove solely for this tendon to enter the plantar aspect of the foot.

827

Lower Extremity

Ankle FIBULAR LIGAMENTS

Lateral malleolus Anterior talofibular l.

Extensor digitorum brevis m.

Neck of talus

Ankle joint recess with fluid

Lesser saphenous v. Lateral malleolus Peroneus longus t. Peroneus brevis t.

Lateral calcaneal cortex

Calcaneofibular l.

Lateral malleolus posterior cortex Peroneus longus t.

Peroneus brevis t.

Flexor hallucis longus m.

Lateral tubercle of talus Posterior recess of ankle joint

Posterior talofibular l.

(Top) Oblique transverse scan shows the lateral ankle along the course of the anterior talofibular ligament. An anterolateral ankle joint recess exists deep to this ligament, making it a good area to look for small effusions. The lateral fibers of the extensor digitorum brevis muscle run on the surface of this ligament. (Middle) Oblique coronal scan along the long axis of the calcaneofibular ligament is shown. The peroneal tendons can be seen curving under the lateral malleolus and running partly on the surface of this ligament. (Bottom) Transverse scan of the posterior aspect of the lateral malleolus shows the posterior talofibular ligament. Deep to this ligament is the posterior recess of the ankle joint.

828

Ankle Lower Extremity

POSTERIOR ANKLE PANORAMA

Soleus m. Flexor hallucis longus m.

Tibia

Posterior margin of talar dome

Lateral tubercle of talus

Inferior extent of soleal musculotendinous junction Achilles t.

Recess from posterior subtalar joint

Middle facet of posterior calcaneus Achilles t. insertion

Sagittal panoramic view shows the posterior ankle. The dominant structure in the posterior ankle is the Achilles tendon, the largest tendon in the body. This runs craniocaudally just under the skin and is well demonstrated by ultrasound. The ankle should be in dorsiflexion to tighten this tendon during examination so that the organization of its fibers and continuity can be assessed. More superiorly, its contributing muscles, the soleus and gastrocnemius, can be traced. Deep to the Achilles tendon is the flexor hallucis longus muscle. An accessory soleus muscle may be seen inferomedial to the Achilles tendon. It occurs in 30% of the normal population and may be symptomatic in athletes with low-grade pain and stiffness after exercise.

829

Lower Extremity

Ankle ACHILLES TENDON, LONGITUDINAL

Achilles t. Soleus m. Retrocalcaneal fat Flexor hallucis longus m.

Achilles t. Soleus m.

Retrocalcaneal fat

Flexor hallucis longus m.

Achilles t. Retrocalcaneal bursa

Central facet of calcaneal tuberosity

(Top) Sagittal scan of the lower posterior leg shows the musculotendinous junction between the soleus muscle and the Achilles tendon. These structures join at an angle with a crisp border. A disruption of this sharp transition (usually due to hemorrhage and rupture of inserting muscle fibers) is suggestive of injury to the musculotendinous junction. (Middle) Color Doppler scan of the same region shows the rich blood supply to this region and the cause for extensive bruising in tendon damage at this site. (Bottom) Sagittal scan more distally shows the insertion of Achilles tendon onto the middle facet of the posterior calcaneal surface. The retrocalcaneal bursa separates the Achilles tendon from the superior facet of the posterior calcaneal surface. This bursa usually contains a tiny amount of fluid detectable on ultrasound.

830

Ankle

Achilles t.

Lower Extremity

ACHILLES TENDON, AXIAL

Soleus m.

Retrocalcaneal fat

Achilles t.

Achilles t.

Retrocalcaneal bursa

Calcaneal tuberosity

(Top) Series of transverse scans through the Achilles tendon is shown. At a superior level, the soleus muscle can be seen deep to the Achilles tendon. The Achilles tendon begins superiorly as a continuation of the gastrocnemius aponeurosis, which then joins with the soleus tendon to form the Achilles tendon. At the level of this scan, the tendon is crescent-shaped to accommodate the soleus muscle. (Middle) Transverse scan shows the Achilles tendon at its midportion. The tendon now assumes an oval shape. The fibrils within the tendon produce a coarsely dotted appearance. Focal hypoechogenicity or change in shape of this tendon should suggest tear/rupture or tendinosis. (Bottom) At a lower level before its insertion onto the calcaneal tuberosity, the Achilles tendon becomes flattened. A small amount of fluid is frequently seen in the retrocalcaneal bursa deep to the tendon.

831

Lower Extremity

Tarsus

TERMINOLOGY Definitions • 3 major divisions ○ Hindfoot: Calcaneus and talus ○ Midfoot: Navicular, cuneiforms, and cuboid ○ Forefoot: Metatarsals and phalanges • 2 columns ○ Medial column: Talus, navicular, cuneiforms 1-3, digits 13 ○ Lateral column: Calcaneus, cuboid, digits 4 and 5 • Some authors use 2 columns in hind and midfoot as above but divide forefoot into 3 columns ○ Medial column: 1st toe ○ Middle column: 2nd-4th toes ○ Lateral column: 5th toe

IMAGING ANATOMY Overview • Alignment of foot can only be assessed on weight-bearing radiographs

Arches of Foot • Foot is arched from posterior to anterior and from medial to lateral • Transverse arch of foot ○ Cuneiform bones form keystone of arch due to triangular shape ○ Major supporting structures of transverse arch – Spring ligament – Lisfranc ligament and intermetatarsal ligaments – Intertarsal ligaments • Longitudinal arch of foot ○ From posterior process calcaneus to metatarsal heads ○ Medial side is higher than lateral ○ Apex of arch is at navicular and cuneiforms ○ Metatarsals slant downward from apex of arch to metatarsophalangeal (MTP) joint – This is called inclination angle – Inclination angle decreases from 20° at 1st to 5° at 5th metatarsal ○ Major supporting structures of longitudinal arch – Plantar fascia – Long and short plantar ligaments – Spring ligament – Posterior tibial tendon, peroneus longus tendon • Radiographic assessment of normal longitudinal arch ○ Evaluate talometatarsal alignment – Normal: Axis of talus continues along axis of 1st metatarsal – Pes planus: Axis of talus points below axis of 1st metacarpal, due to flattened arch – Pes cavus: Axis of talus points above axis of 1st metacarpal, due to exaggerated arch

Distribution of Weight Bearing • 50% of weight is borne on subtalar joint and calcaneus • Remainder is transmitted via arch anteriorly to MTP joints, greatest weight on 1st toe 832

Bony Anatomy • Cuboid bone ○ Roughly cuboidal shape ○ 1 ossification center: Ossifies between 9th fetal month and 6 months of age ○ Articulates with calcaneus, navicular, 3rd cuneiform, and 4th and 5th metatarsals, rarely head of talus – Dorsal ligaments (calcaneocuboid, cubonavicular, cuneocuboid, cubometatarsal) strengthen each of these articulations – Short and long plantar ligaments attach to plantar surface ○ Sulcus at lateral margin, under which passes peroneus longus tendon ○ 5th metatarsal base extends beyond lateral margin • Navicular bone ○ Curved shape, concave proximally and convex distally ○ 1 ossification center: Ossifies in 3rd year of life ○ Articulates with talus, cuboid, cuneiforms – Dorsal ligaments strengthen each of these articulations – Single facet proximally for articulation with head of talus – 3 facets distally for cuneiform articulations – 1 facet laterally for articulation with cuboid – Connected to anterior process of calcaneus by bifurcate ligament – Connected to sustentaculum tali by spring ligament ○ Large median eminence for attachment of posterior tibial tendon is located more plantar than main body of navicular • Cuneiform bones ○ Wedge-shaped, with base of wedge at dorsal surface of 2nd and 3rd cuneiforms, dorsomedial surface 1st cuneiform ○ In combination, form arch ○ 1st cuneiform (medial cuneiform) – Articulates with navicular, 2nd cuneiform, 1st metatarsal – 1 or 2 ossifications centers: Ossify in 2nd year of life ○ 2nd cuneiform (middle or intermediate cuneiform) – Articulates with navicular, 1st and 3rd cuneiforms, 2nd metatarsal – Smallest of cuneiforms – 1 ossification center: Ossifies in 3rd year of life ○ 3rd cuneiform (lateral cuneiform) – Articulates with navicular, 2nd cuneiform, cuboid, 3rd metatarsal • Metatarsal bones ○ 2 ossifications centers: Shaft ossifies in 9th prenatal week, epiphysis in 3rd-4th years of life – 1st metatarsal has epiphysis at proximal end, others at distal end ○ 2nd-5th metatarsals have articulations at bases with adjacent metatarsals ○ 1st metatarsal – Largest of metatarsals – Articulates with 1st cuneiform, 1st proximal phalanx, sesamoids of metatarsal head – Variable articulation with 2nd metatarsal base

Tarsus

Musculature • Plantar muscles: 4 muscle layers, numbered from superficial to deep ○ 1st layer: Abductor hallucis, flexor digitorum brevis, abductor digiti minimi ○ 2nd layer: Quadratus plantae (flexor accessorius), flexor digitorum and hallucis longus tendons, lumbricals ○ 3rd layer: Flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis, tibialis posterior tendon ○ 4th layer: Plantar interossei (3), dorsal interossei (4) ○ Peroneus longus tendon courses across all layers, from superficial plantar laterally to deep plantar medially • Dorsal muscles: 2 muscle layers ○ Superficial layer: Tibialis anterior tendon, extensor hallucis longus tendon, extensor digitorum longus tendon, peroneus tertius tendon ○ Deep layer: Extensor hallucis brevis, extensor digitorum brevis ○ In forefoot, long and short extensors run side by side in single layer

Compartments • Plantar compartments: 4 plantar compartments are located deep to plantar fascia ○ Divided by fascial layers ○ Lateral and medial intermuscular septa determine major compartment divisions ○ Medial plantar compartment – Contains abductor hallucis, flexor hallucis longus, and flexor hallucis brevis tendons ○ Central plantar compartment – Superficial subcompartment: Contains flexor digitorum brevis, distal portion of flexor digitorum longus tendons – Intermediary subcompartment: Contains proximal plantar portion of flexor digitorum longus tendon, quadratus plantae, lumbricals – Deep subcompartment: Limited to forefoot, contains adductor hallucis ○ Lateral plantar compartment – Contains abductor and flexor digiti minimi ○ Interosseous compartment – Contains plantar and dorsal interosseous muscles • Dorsal compartment

○ Superficial layer: Extrinsic extensor tendons ○ Deep layer: Intrinsic extensor muscles

Major Ligaments • Plantar fascia (aponeurosis): 3 portions extend from tuberosity of calcaneus to transverse metatarsal ligaments of toes ○ Medial band: Thin structure superficial to abductor hallucis muscle ○ Central band: Thick, strong structure superficial to flexor digitorum brevis – Divides into separate bands to each toe; these are linked by transverse bands – Distally sends septa superficially into subcutaneous fat and deep to MTP joints ○ Lateral band: Thin structure superficial to abductor digiti minimi ○ Medial and lateral bands sometimes terminate at level of midmetatarsals • Long plantar ligament ○ Originates at calcaneal tuberosity, inserts at cuboid and bases of 2nd-4th metatarsals ○ Forms retinaculum for peroneus longus tendon as it courses medially on plantar aspect of foot • Short plantar (plantar calcaneocuboid) ligament ○ Deep to long ligament, inserts more proximally on cuboid • Plantar calcaneocuboid (spring) ligament ○ Originates on sustentaculum tali, inserts on plantar aspect navicular • Bifurcate ligament: Originates on anterior process of calcaneus dorsally, inserts on navicular and cuboid • Lisfranc ligament: Originates at 1st cuneiform, inserts at base of 2nd metatarsal • Intermetatarsal ligaments: Dorsal and plantar ligaments between 2nd-5th metatarsal bases • Transverse metatarsal ligaments: Superficial and deep ligaments between metatarsal heads

Lower Extremity

○ 2nd-3rd metatarsals – Articulate with respective cuneiforms and proximal phalanges – 2nd metatarsal base recessed relative to 1st and usually 3rd ○ 4th-5th metatarsals – Articulate with cuboid and respective proximal phalanges – Styloid process of 5th metatarsal extends lateral to cuboid • Phalanges ○ 1st toe is biphalangeal, other toes are triphalangeal ○ 5th toe sometimes has failure of segmentation of middle and distal phalanges ○ 2 ossification centers: Shaft ossifies 9th-15th prenatal weeks, epiphysis 2nd-8th years

Nerves • Tibial nerve divides into medial and lateral plantar branches at level of tarsal tunnel ○ Medial plantar nerve – Between 1st and 2nd muscle layers, accompanies medial plantar artery – Motor branches: Abductor hallucis, flexor digitorum and hallucis brevis, 1st lumbrical – Plantar digital nerves to 1st-3rd toes, medial aspect of 4th toe ○ Lateral plantar nerve: Has deep and superficial divisions – Motor branches: Flexor digiti minimi brevis, lumbricals, interossei, adductor hallucis – Superficial lateral plantar nerve: Between 1st and 2nd muscle layers – Plantar digital nerves to 5th toe, lateral aspect of 4th toe – Deep lateral plantar nerve: Between 3rd and 4th muscle layers; accompanies lateral plantar artery • Deep peroneal nerve: Extends along dorsum of foot, between tibialis anterior and extensor hallucis longus ○ Motor branch: Extensor digitorum brevis 833

Lower Extremity

Tarsus • Superficial peroneal nerve: Divides into medial and lateral branches at dorsum of foot ○ Sensory branches to dorsal foot • Sural nerve: Lateral, superficial branch of tibial nerve ○ Extends along lateral margin of foot ○ Sensory branches to lateral foot

Arteries • Posterior tibial artery divides into medial and lateral plantar arteries at level of tarsal tunnel ○ Plantar arteries accompany medial and deep lateral plantar nerves • Peroneal artery accompanies superficial peroneal nerve down anterolateral aspect of ankle ○ May join or replace posterior tibial artery • Anterior tibial artery continues into foot as dorsalis pedis artery, deep to extensor retinaculum ○ Divides into multiple branches in midfoot, forming arcade

Bursae • Extensor digitorum brevis: Between muscle and 2nd cuneiform and metatarsal bases • Extensor hallucis longus: Between tendon and 1st cuneiform and metatarsal bases • Abductor digiti minimi: Between muscle and tuberosity of 5th metatarsal • MTP joints: Dorsally between metatarsal heads and medial to 1st metatarsal head

ANATOMY IMAGING ISSUES Imaging Recommendations • Radiographs ○ Weight bearing, when possible ○ Standard views: Anteroposterior (dorsoplantar), lateral, oblique • US ○ Offers highest spatial resolution for muscle and tendons ○ Particularly useful given limited depth of most soft tissue structures in foot ○ As result of transverse arch of foot, interrogation should be performed separately for medial and lateral sides for best visualization ○ Due to complex soft tissue anatomy, panoramic (extended field of view) images provide better depiction of location and extent of lesion and course of different structures ○ Dorsal foot structures tend to be very superficial and thin (tendons) or compressible (vessels) – To better visualize these structures, minimal compression and thick layer of coupling gel may help • CT ○ Multidetector 1-mm images with sagittal and coronal reformations ○ 3D reconstructions often useful for analyzing relationship between bones and bone fragments • MR ○ Better images obtained when field of view is limited to area of concern, not entire foot ○ Demonstration of bone marrow edema aside from soft tissue lesions 834

Imaging Sweet Spots • Tendon movement can be easily demonstrated with US by moving the bone onto which it inserts ○ Helps with confirming tendon location and also with establishing tendon integrity • Tarsal ligaments are usually seen as hypoechoic thickenings on cortices and between bones ○ Orientation of transducer along long axis makes ligament stand out and easier to identify

Imaging Pitfalls • Alignment can only be reliably assessed on weight-bearing radiographs

CLINICAL IMPLICATIONS Foot Motion • Supination: Elevation of medial arch of foot ○ Combination of inversion and adduction • Pronation: Depression of medial arch of foot ○ Combination of eversion and abduction • Complex motions at multiple joints ○ Chopart (calcaneocuboid and talonavicular) joint – These 2 joints move together on oblique axis to produce compound motions – Pronation-abduction-extension to supinationadduction-flexion ○ Tarsometatarsal joints – Dorsiflexion and plantar flexion – 2nd and 3rd tarsometatarsal joints relatively immobile – Slight abduction of 1st tarsometatarsal joint ○ MTP joints – Dorsiflexion and plantar flexion – Abduction and adduction at 1st MTP joint

Alignment • Normal weight bearing and gait depend on normal foot alignment • Evaluated initially with anteroposterior and lateral weightbearing radiographs

Malalignment • Forefoot adductus: Medial angulation of metatarsals from axis of hindfoot • Forefoot varus: Inversion of metatarsals resulting in shift of weight bearing to 5th metatarsal from 1st metatarsal • Metatarsus primus varus: Medial deviation of 1st metatarsal axis relative to 2nd • Hallux valgus (hallux abductus): Lateral deviation of 1st proximal phalanx relative to axis of 1st metatarsal ○ Valgus refers to angular deformity in vertical plane, where apex points medially ○ Abductus refers to angular deformity in horizontal plane, where apex points medially ○ Hallux valgus is misnomer, but it remains term commonly used for hallux abductus

Tarsus Lower Extremity

DORSAL FOOT

Superior extensor retinaculum Deep peroneal n. Lateral branch, deep peroneal n. Inferior extensor retinaculum

Extensor digitorum brevis m.

Medial branch, deep peroneal n. Extensor hallucis brevis m.

Bifurcate l. Dorsal talonavicular l. Cuneiform-cuboid l.

Dorsal tarsometatarsal l.

Dorsal Lisfranc l. Dorsal intermetatarsal l.

Transverse metatarsal l.

(Top) The deep peroneal nerve travels deep to the extensor retinacula, in the anterior tarsal tunnel, and gives a lateral motor branch to the extensor digitorum brevis muscle. The medial branch continues dorsal to the talonavicular joint, middle cuneiform, and in between the 1st and 2nd metatarsals to provide mostly sensory, but some motor, supply to the 1st web space. (Bottom) Graphic of the dorsal ligaments shows dense ligaments between the tarsal bones and between tarsals and metatarsals. Ligaments are generally named for the bones they bridge. Exceptions are the bifurcate ligament, which extends from the anterior process of the calcaneus to the cuboid and the navicular, and the dorsal Lisfranc ligament, from the 1st cuneiform to the 2nd metatarsal.

835

Lower Extremity

Tarsus DORSAL FOOT

Dorsalis pedis a.

Extensor hallucis longus t.

Tibialis anterior t. Dorsal v. Extensor digitorum longus t. Dorsal talonavicular l. Extensor digitorum brevis m.

Anterolateral calcaneal cortex

Anteromedial talar head Anterolateral talar head surface

Interosseous talocalcaneal l.

Extensor digitorum longus t. Dorsalis pedis a. Extensor hallucis longus t.

Tibialis anterior t. Extensor digitorum brevis m.

Anterolateral calcaneal cortex

Anteromedial navicular surface Dorsal talonavicular l. Anterolateral navicular surface

Bifurcate l.

(Top) Coronal panoramic US shows the dorsal foot at the talocalcaneus level. The foot can be divided into 2 columns: The medial column (talus, navicular, and cuneiforms) and lateral column (calcaneus and cuboid) form the anteromedial and anterolateral surfaces of the transverse midfoot arch. The dorsalis pedis artery runs at the apex of this arch. (Bottom) Coronal panoramic US shows the dorsal foot through the navicular-calcaneal level. The transverse arch of the dorsal foot creates 2 surfaces: Anteromedial and anterolateral, over which extensor tendons and small muscles lie. More focal examination of these structures requires scanning along each surface separately. Panoramic scans give an overview of anatomy. However, high-resolution imaging of the site of interest provides more details, and both should be performed as complementary techniques.

836

Tarsus

Inferior extensor retinaculum Extensor hallucis longus t.

Lower Extremity

DORSAL FOOT

Dorsalis pedis a. Extensor digitorum brevis m. Dorsal vessels Tibialis anterior t. Anteromedial surface of talar head

Superficial vessels Inferior extensor retinaculum Extensor hallucis longus t. Dorsalis pedis a. and v. Extensor digitorum brevis m. Anteromedial surface of navicular

Dorsal venous arch Tibialis anterior t.

Dorsal venous arch Extensor hallucis longus t.

Extensor digitorum brevis m. Dorsalis pedis a.

Tibialis anterior t. Medial cuneiform

Intermediate cuneiform

(Top) Series of 3 coronal scans shows the dorsal medial surface of the foot. At this most proximal level, the talus is the underlying bone. The extensor hallucis can be seen partially covering the dorsalis pedis artery. More medially, the tibialis anterior tendon can be found. (Middle) At a midtarsal level, this coronal US shows the anteromedial surface of the navicular. The tibialis anterior tendon begins to turn acutely medially to curve around to the medial edge of the foot, eventually inserting on the medial cuneiform. As seen here, the use of light pressure and copious amounts of gel will allow visualization of small superficial veins, which are numerous on the dorsum of the foot. (Bottom) Coronal color Doppler US shows the level of the cuneiforms. The intimate relationship between the dorsalis pedis artery and the extensor hallucis longus tendon continues.

837

Lower Extremity

Tarsus DORSAL FOOT Peroneus tertius t. Extensor digitorum longus t. (5, 4, 3, 2)

Dorsalis pedis a. Calcaneus Lateral tarsal a.

Extensor digitorum brevis m. Lateral surface of talus

Peroneus tertius t. Extensor digitorum longus t.

Extensor digitorum brevis m.

Cuboid

Extensor hallucis brevis m. Navicular surface

Dorsal cuboidonavicular l.

Extensor digitorum longus t. (5 and 4) Extensor digitorum longus t. (3 and 2)

Peroneus tertius t. Cuboid

Extensor hallucis brevis m. Lateral cuneiform

Extensor digitorum brevis m.

(Top) Series of 3 coronal scans is shown over the dorsal lateral surface of the tarsus. At this proximal level, the lateral surface of the calcaneus and the talus are the underlying bones. The extensor digitorum longus tendons are close to each other and share a common synovial sheath. The extensor digitorum brevis muscle lies deep to the longus tendons. The lateral tarsal artery runs deeper and is a branch of the dorsalis pedis artery. (Middle) At the level of the midtarsus, the extensor digitorum longus tendons for individual toes begin to spread out and also flatten (the latter making them just discernible on ultrasound). At this level, the extensor hallucis brevis muscle can also be seen. (Bottom) At a more distal level, the extensor digitorum brevis muscle and the extensor hallucis brevis muscle are much thinner and will turn into tendons distally.

838

Tarsus

Medial tarsal a. Medial tarsal v. Talus Navicular

Lower Extremity

DORSAL FOOT

Tibialis anterior t.

Medial cuneiform

Extensor hallucis longus t.

Dorsal v. Intermediate cuneiform Navicular

Extensor digitorum brevis m. Extensor digitorum longus t.

Extensor digitorum brevis t. Lateral tarsal a. Cuboid Calcaneus

Navicular

(Top) Series of sagittal scans is shown through the tarsus. Medially, the tibialis anterior is seen running over the medial tarsal vessels (branch of dorsalis pedis) to insert on the medial and inferior surfaces of the base of the medial cuneiform. (Middle) Slightly laterally, the extensor hallucis longus tendon runs toward the big toe, passing over the intermediate cuneiform bone. (Bottom) More laterally, the extensor digitorum longus tendon and the extensor digitorum brevis muscle come into view. They lie on the surface of the calcaneus with the lateral tarsal artery coursing between the muscle and bone. The gradual tapering of the extensor digitorum brevis muscle distally can be appreciated here.

839

Lower Extremity

Tarsus PLANTAR MUSCLES, SUPERFICIAL LAYERS

Flexor digitorum longus t. Flexor digitorum brevis insertions, 4th toe

Flexor t. sheath

Flexor t. sheath Abductor hallucis insertion Medial sesamoid, 1st toe Flexor hallucis longus t.

Flexor digitorum brevis, individual digital t. slips Abductor hallucis m. Abductor digiti minimi m. Flexor digitorum brevis m.

Flexor digitorum longus t. insertions Flexor t. sheath, 5th toe

Flexor hallucis longus t.

Lumbrical m.

Flexor hallucis brevis m., lateral head

Flexor digiti minimi m.

Flexor hallucis brevis m., medial head Flexor digitorum longus, individual t. slips Flexor digitorum longus t.

Quadratus plantae m.

Flexor hallucis longus t.

(Top) Graphic shows the superficial layer of the plantar foot muscles: Abductor digiti minimi, flexor digitorum brevis, and abductor hallucis. The deep muscles are partially visible deep to the superficial layer. The flexor digitorum brevis tendons split in each digit (4th digit labeled), attaching at lateral aspects of the middle phalangeal bases. The flexor tendon sheaths hold the flexor mechanism in close proximity to the phalanges. (Bottom) Graphic shows the 2nd layer of plantar muscles. The interesting arrangement of interactions between flexors is well seen: Quadratus plantae inserting on flexor digitorum longus tendon and lumbricals arising from individual flexor digitorum longus tendon slips. In the toes, the flexor tendons are contained within fibrous tendon sheaths.

840

Tarsus Lower Extremity

PLANTAR FOOT MUSCLES, DEEP LAYERS

Lateral sesamoid, 1st toe

Adductor hallucis m., transverse head Adductor hallucis m., oblique head

Flexor digiti minimi m.

Long plantar l.

Medial sesamoid, 1st toe Flexor hallucis brevis m., lateral head Flexor hallucis brevis m., medial head Flexor hallucis longus t.

Tibialis posterior t. Spring l.

1st plantar interosseous m.

1st dorsal interosseous m.

2nd dorsal interosseous m. 2nd plantar interosseous m.

3rd dorsal interosseous m.

3rd plantar interosseous m. 4th dorsal interosseous m.

Long plantar l. Spring l.

(Top) Graphic shows the 3rd layer of plantar muscles. This layer contains the flexor hallucis brevis and flexor digiti minimi as well as the adductor hallucis muscle. The oblique head of the adductor hallucis is thick and broad, whereas the transverse head is thin. (Bottom) Graphic shows the 4th layer of plantar muscles, the interosseous muscles. There are 4 dorsal interossei. They have bipennate origins from 2 adjacent metatarsals. There are 3 plantar interossei. The 1st plantar interosseous muscle originates from the medial side of the 3rd metatarsal and inserts on the medial side of the 3rd proximal phalanx. The 2nd and 3rd plantar interossei originate on the medial sides of the 4th and 5th metatarsals, respectively, and insert on the medial side of the corresponding proximal phalanx.

841

Lower Extremity

Tarsus PLANTAR APONEUROSIS Plantar fat pad Central plantar aponeurosis

Adductor digiti minimi m.

Abductor hallucis m. Medial process of calcaneus

Lateral process of calcaneus

Plantar fat pad

Flexor digitorum brevis m. Central band of plantar aponeurosis

Lateral process of calcaneus

Central band of plantar aponeurosis

Lateral process of calcaneus Flexor digitorum brevis m. Anterior tubercle of calcaneus Quadratus plantae m.

Flexor digitorum longus t. 2nd metatarsal Middle cuneiform Navicular

(Top) Transverse US of the calcaneus shows the origin of the plantar aponeurosis. The plantar aponeurosis fascia consists of 3 parts: Strong, thick central band over the flexor digitorum brevis muscle; lateral band over the abductor digiti muscle; and thin medial band over the abductor hallucis muscle. (Middle) Sagittal US shows the origin of the central band of the plantar aponeurosis. This arises from the medial process of the calcaneus and runs anteriorly deep to the plantar subcutaneous fat. (Bottom) Sagittal panoramic US shows the central band of plantar aponeurosis. The central is the thickest and most easily identified component of the plantar aponeurosis. Deep to this are the flexor digitorum brevis and quadratus plantae muscles, which form the bulk of the central tarsal plantar compartment.

842

Tarsus Lower Extremity

SAGITTAL FOOT OVERVIEW

Flexor digitorum longus t.

Medial band of plantar aponeurosis Medial process of calcaneus Abductor hallucis m. Quadratus plantae m.

Sesamoid bone Head of 1st metatarsal Flexor hallucis longus t. Flexor hallucis brevis m. Lumbrical m.

Navicular Middle cuneiform

Base of 1st metatarsal

Peroneus longus t.

Base of 2nd metatarsal

Central band of plantar aponeurosis Medial process of calcaneus Flexor digitorum brevis m. Flexor digitorum longus t. Quadratus plantae m. Navicular Lateral cuneiform

Head of 3rd metatarsal Adductor hallucis m., oblique head Body of 3rd metatarsal Flexor digitorum longus t. Base of 3rd metatarsal

Peroneus longus t.

Lateral band of plantar aponeurosis Lateral process of calcaneus Abductor digiti minimi m.

Head of 5th metatarsal Flexor digitorum longus t. Flexor digiti minimi brevis

Cuboid tuberosity Peroneus longus t.

Body of 5th metacarpal Cuboid

(Top) Series of 3 panoramic sagittal scans is shown through the plantar aspect of the foot. This scan shows the content of the medial compartment: The abductor hallucis muscle, flexor hallucis longus tendon, and flexor hallucis brevis muscle, together with smaller structures. (Middle) In the central plantar compartment, the contents can be divided into layers. Superficially, there is the flexor digitorum brevis muscle and the flexor digitorum longus tendon. Deep to this layer are the quadratus plantae muscle, oblique head of the adductor hallucis muscle, and the lumbricals. (Bottom) A scan through the lateral compartment shows the abductor digiti minimi muscle and the flexor digiti minimi muscle.

843

Lower Extremity

Tarsus MEDIAL TARSUS

Medial band of plantar aponeurosis

Medial plantar n. Medial plantar a. Flexor digitorum brevis m.

Medial plantar v. Abductor hallucis m.

Quadratus plantae m. Lateral plantar v.

Lateral plantar n. Lateral plantar a.

Calcaneus

Abductor hallucis m.

Flexor digitorum brevis m.

Tibialis posterior t. Navicular

Flexor hallucis longus t. Quadratus plantae m. Long plantar l.

Medial plantar a. Medial plantar n. Medial plantar v. Flexor digitorum longus t.

Cuboid

Abductor hallucis m. Flexor digitorum brevis m.

Medial cuneiform Flexor hallucis longus t.

Quadratus plantae m.

Flexor digitorum longus t.

Intermediate cuneiform

(Top) Series of 3 coronal scans is shown through the medial 1/2 of the plantar aspect of the foot. At this proximal level, the 2 main muscles (flexor digitorum brevis and quadratus plantae) of the central compartment can be seen lying superficial to the calcaneus. The medial compartment muscle (abductor hallucis) can also be seen medially. (Middle) At the level of the midtarsus, the knot of Henry can be seen. This is where tendons of the flexor digitorum longus and flexor hallucis longus tendons cross and exchange fibers. The medial plantar neurovascular bundle lies in close proximity to this. (Bottom) More distally, the flexor hallucis longus and digitorum longus tendons separate and head toward their respective insertions.

844

Tarsus

Central band of plantar aponeurosis

Lower Extremity

LATERAL TARSUS

Lateral band of plantar aponeurosis Flexor digitorum brevis m. Abductor digiti minimi m. Peroneus longus t. Calcaneus

Lateral plantar n. Lateral plantar a. Lateral plantar v.

Flexor digiti minimi brevis m. Abductor digiti minimi m. Lateral plantar neurovascular bundle Flexor digitorum brevis m. 5th metatarsal base

Quadratus plantae m.

Peroneus longus t. Cuboid

Lateral cuneiform

Flexor digiti minimi brevis m. Lateral plantar neurovascular bundle Flexor digitorum brevis m. 5th metatarsal base

Quadratus plantae m.

Peroneus longus t.

4th metatarsal base

(Top) Series of 3 coronal scans is shown through the lateral 1/2 of the plantar aspect of the foot. The lateral compartment (abductor digiti minimi) and 1/2 of the central compartment can be seen here, separated by the lateral plantar neurovascular bundle. The calcaneus forms the bony support of all structures at this level. (Middle) At the level of the midtarsus, the separation between the lateral and the central compartment by the neurovascular bundle continues. Within the lateral compartment, the abductor digiti minimi muscle moves laterally to give way to the other component of the lateral compartment, the flexor digiti minimi brevis muscle. (Bottom) Most distally, the abductor digiti minimi muscle runs on the lateral border, and only the flexor digiti minimi brevis muscle is seen on the plantar aspect of the foot.

845

Lower Extremity

Foot Vessels

846

IMAGING ANATOMY Arteries • Dorsalis pedis artery ○ Dorsal artery of foot ○ Direct continuation of anterior tibial artery, changing name at ankle joint ○ Course and relations – Crosses superficial to talocrural articular capsule, talus, navicular, and intermediate cuneiform bones – Passes deep to inferior extensor retinaculum and distal to extensor hallucis brevis – Lies lateral to extensor hallucis longus tendon – Passes to proximal end of intermetatarsal space and curves deeply to enter sole between heads of 1st dorsal interosseous muscle – Forms part of plantar arch ○ Main branches – Medial and lateral tarsal arteries: Arise at level of navicular bone – Lateral tarsal artery runs under extensor digitorum brevis – 2 or 3 medial tarsal arteries run on medial surface of tarsus ○ Arcuate artery: Arises at medial cuneiform level and runs laterally over metatarsal bases, deep to extensor tendons; gives off branches to metatarsals and toes ○ 1st dorsal metatarsal artery: Arises just before dorsalis pedis dives deep into sole • Posterior tibial artery ○ Continuation of calf vessel by same name, branch of popliteal artery ○ Runs in tarsal tunnel behind and below medial malleolus accompanied by tibial nerve ○ Divides into terminal branches (medial and plantar arteries) in tarsal tunnel ○ Medial plantar artery is smaller – Runs in medial aspect of foot medial to medial plantar nerve – Then deep to abductor hallucis and flexor digitorum brevis muscles ○ Lateral plantar artery is much larger than medial – Runs in lateral aspect of foot lateral to lateral plantar nerve – Then deep to abductor hallucis muscle and distally between flexor digitorum brevis and quadratus plantae muscles – Distally runs between flexor digitorum brevis and abductor digiti minimi, then between base of 1st and 2nd metatarsals, and finally joins dorsalis pedis to form plantar arch • Plantar arch ○ Arterial arch at level of metatarsals ○ Formed by dorsalis pedis and lateral plantar arteries ○ Gives off branches to metatarsals and toes • Peroneal artery ○ Accompanies superficial peroneal nerve down anterolateral aspect of ankle and sends off perforating branch that joins communicating branch from anterior tibial artery ○ May join or replace posterior tibial artery

Veins • Superficial veins ○ Great saphenous vein – Arises from medial part of dorsal venous arch of foot – Runs subcutaneously over muscles and tendons to pass anterior to medial malleolus – Passes superiorly on medial aspect of calf and thigh to join common femoral vein at femoral triangle ○ Small saphenous vein – Arises from lateral part of dorsal venous arch – Runs subcutaneously over muscles and tendons to pass posterior to lateral malleolus – Passes superiorly on lateral and posterior side of calf to join popliteal vein in popliteal fossa • Deep veins ○ Plantar venous arch: Receives venous drainage from dorsal and plantar aspects of toes and metatarsals ○ Medial and lateral plantar veins: Arise from plantar venous arch to accompany same named arteries ○ Communication exists with great and small saphenous veins ○ Medial and lateral plantar veins form posterior tibial veins in tarsal tunnel and run proximally to calf, accompanying posterior tibial artery

ANATOMY IMAGING ISSUES Imaging Recommendations • US ○ Provides greatest amount of information on vasculature of foot of different imaging modalities available ○ Morphology and functional status of vessels can be assessed ○ Color Doppler scans allow assessment for vessel occlusion and thrombosis ○ Spectral Doppler scans allow quantitative and semiquantitative documentation of flow velocity, resistance, waveform, etc. ○ Augmentation of foot veins usually only requires small degrees of flexion/extension of toes to produce enough venous flow for detection (unlike need to squeeze muscles in calf)

Imaging Pitfalls • Superficial veins are easily compressed even with lightest transducer pressure ○ Thick layer of coupling gel helps act as spacer between transducer and skin to minimize pressure and allows for better visualization of vessels

Foot Vessels Lower Extremity

DORSAL AND PLANTAR ARTERIES AND NERVES

1st toe dorsal digital nn.

Dorsal metatarsal aa. Arcuate a. Sural n. Lateral tarsal a. Lateral malleolar a. Superficial peroneal n., lateral branch

Superficial peroneal n., medial branch Dorsalis pedis a. Anterior tibial a. Deep peroneal n.

Dorsal metatarsal aa.

Plantar digital nn. Plantar digital nn. Lateral plantar n., deep branch

Plantar arch

Lateral plantar a. Medial plantar a. Lateral plantar n., superficial branch

Medial plantar n.

Lateral plantar n.

(Top) Graphic shows arteries and nerves at the dorsal aspect of the foot. The deep peroneal nerve accompanies the anterior tibial artery. The superficial peroneal nerve divides into medial and lateral branches in distal 1/3 of leg. Anterior tibial artery is called dorsalis pedis in foot. It terminates in arcuate artery, which communicates with plantar arterial arch, and in digital vessels. (Bottom) Graphic shows arteries and nerve at the plantar aspect of the foot. The posterior tibial nerve and artery divide into medial and lateral plantar branches. These divide further into digital branches to the medial and lateral aspects of each toe. The plantar arch sends vessels dorsally as well as to the plantar aspect of the toes.

847

Lower Extremity

Foot Vessels DORSALIS PEDIS ARTERY Extensor hallucis longus t. Dorsal venous arch

Dorsalis pedis a. Talar dome

Talus

Dorsalis pedis a.

Medial cuneiform Navicular

Triphasic Doppler waveform

Extensor digitorum brevis

Extensor hallucis longus t. Dorsalis pedis a. Intermediate cuneiform

Accompanying v.

Lateral tarsal a. Medial cuneiform

(Top) Sagittal scan shows the dorsum of the foot. The dorsalis pedis artery runs at the anterior aspect of the transverse arch formed by the tarsal bones. It is a continuation of the anterior tibial artery and runs lateral to the extensor hallucis longus tendon. (Middle) Sagittal spectral Doppler scan of the dorsalis pedis artery shows the typical triphasic artery flow. (Bottom) Coronal color Doppler scan shows the dorsum of the foot at the level of the cuneiform. The dorsalis pedis artery gives rise to medial and lateral tarsal arteries at the level of the navicular. The dorsalis pedis artery remains lateral to the extensor hallucis longus tendon even at this distal level.

848

Foot Vessels

Extensor digitorum longus t.

Lower Extremity

METATARSAL AND DIGITAL ARTERIES

Dorsal metatarsal a.

Dorsal interosseous m. Plantar interosseous m.

Dorsal metatarsal aa. Dorsal interosseous m. Plantar interosseous m.

2nd, 3rd, and 4th metatarsals Plantar metatarsal aa.

Extensor digitorum longus t.

Proximal phalanx of 3rd toe Dorsal digital a.

Proximal phalanx of 2nd toe

Plantar digital a.

(Top) Sagittal color Doppler shows the 2nd interosseous space. The arcuate artery gives rise to dorsal metatarsal arteries that run in the interosseous spaces to supply the metatarsals and toes. The 2 layers of interosseous muscles can be appreciated here. (Middle) Transverse color Doppler scan shows the metatarsal bodies. Both the dorsal and plantar interosseous muscles can be seen between the bones. The dorsal and plantar metatarsal arteries are also demonstrable by the use of color Doppler. The plantar metatarsal arteries arise from the plantar arch. (Bottom) Coronal color Doppler scan shows the 2nd web space. The dorsal and plantar metatarsal arteries continue distally as the digital arteries, which will divide further to run on the sides of the phalanges.

849

Lower Extremity

Foot Vessels PLANTAR ARTERIES

Medial plantar a. Abductor hallucis m. Lateral plantar vv.

Medial plantar n. Lateral plantar n.

Lateral plantar a.

Quadratus plantae m. Calcaneus

Abductor hallucis m.

Medial plantar a. Quadratus plantae m.

Triphasic Doppler waveform

Abductor hallucis longus m.

Medial plantar a. Quadratus plantae m.

Calcaneus

(Top) Coronal scan shows the medial plantar compartment. The tibial nerve has divided into the medial and lateral plantar nerves, and, similarly, the posterior tibial vessels have divided into medial and lateral plantar vessels. Note that this is a scan of the left foot and the lateral side is on the right of the image. (Middle) Spectral Doppler scan of the medial plantar artery shows a typical triphasic arterial waveform. (Bottom) Oblique sagittal color Doppler scan of the medial compartment shows the medial plantar artery running between the abductor hallucis muscle and the quadratus plantae muscle.

850

Foot Vessels

Plantar digital aa.

Lower Extremity

PLANTAR ARTERIES

Flexor digitorum brevis t. Flexor digitorum longus t.

Proximal phalanx of 3rd toe

Proximal phalanx of 2nd toe

Dorsal venous arch

Extensor digitorum longus tt.

3rd metatarsal

2nd metatarsal

Dorsal interosseous m.

Dorsal metatarsal vv.

Extensor digitorum longus tt.

Dorsal interosseous m. 3rd metatarsal 4th metatarsal

(Top) Coronal color Doppler scan shows the plantar aspect of the toes. The digital arteries can be seen on both sides of the phalanges as they travel more distally. (Middle) Coronal scan shows the dorsum of the foot at the metatarsal level. Minimal pressure was used during this scan to prevent compression of the superficial (subcutaneous) veins. Here, the transversely running dorsal venous arch is demonstrated. The extensor tendons and the interossei run deep to this arch. (Bottom) More distally, a coronal scan of the dorsum of the foot shows the tributaries of the dorsal venous arch, the dorsal metatarsal veins.

851

Lower Extremity

Metatarsals and Toes

IMAGING ANATOMY Overview • In normal weight-bearing stance, all metatarsal heads are at same level and all are weight bearing ○ Metatarsophalangeal (MTP) joints are slightly extended in standing position • Each MTP joint is separate synovial cavity

Metatarsal Bones • 1st metatarsal ○ Largest metatarsal ○ Articulates with 1st cuneiform, 1st proximal phalanx, sesamoids ○ Medially receives attachments from tibialis anterior tendon, plantar side receives peroneus longus tendon ○ Origin of medial head of 1st dorsal interosseous muscle on its lateral surface • 2nd-4th metatarsals ○ Gradually smaller and shorter moving laterally ○ Receive interosseous muscle on medial and lateral sides • 5th metatarsal ○ Insertion of peroneus tertius and brevis

Phalanges • Distal phalanx is insertion site for tendons from flexor and extensor digitorum longus • Middle phalanx is insertion site for tendons from flexor and extensor digitorum brevis • 2nd-4th proximal phalanges are attachments of interosseous muscles on both sides and lumbricals on medial side

1st Metatarsophalangeal Joint • Dorsiflexion of toe important in push-off phase of gait • Metatarsal head has 2 concave facets at plantar surface, 1 for each sesamoid, separated by ridge (crista) • Distal articular surface of metatarsal head may be flat, rounded, or have central prominence • Base of proximal phalanx has concave contour • Sesamoids ○ Either sesamoid may be unipartite or bipartite ○ Medial sesamoid in medial head flexor hallucis brevis and abductor hallucis ○ Lateral sesamoid in lateral head flexor hallucis brevis and adductor hallucis and deep metatarsal ligament ○ Medial and lateral sesamoids joined by intersesamoid ligament – Intersesamoid ligament is floor of canal in which flexor hallucis longus tendon runs ○ Both are embedded in plantar plate of joint ○ Sesamophalangeal apparatus – Sesamoids fixed in position relative to 1st proximal phalanx, move relative to 1st metatarsal – Therefore, displaced laterally in hallux valgus • Plantar plate ○ Fibrocartilaginous plantar capsular thickening extending from metatarsal neck to base of proximal phalanx ○ Incorporates sesamoids

852

Lateral Metatarsophalangeal Joints • Convex articular surface of metatarsal head articulates with concave articular surface of proximal phalangeal base • Plantar aspect of metatarsal head has rounded contour • Dorsal aspect of metatarsal head is smaller than plantar aspect ○ Has concave or notched contour along medial and lateral margins • Sesamoids variably present, most commonly at 5th toe • Phalangeal apparatus is combination of plantar plate and proximal phalanx • Plantar plate ○ Fibrocartilaginous plantar capsular thickening extending from metatarsal neck to base of proximal phalanx ○ Attached to deep transverse metatarsal ligament, plantar fascia and flexor tendon sheath, medial and lateral collateral ligaments ○ Instability may mimic Morton neuroma

ANATOMY IMAGING ISSUES Imaging Recommendations • Ultrasound ○ Good for assessing tendon integrity and joint alignment – Tendon integrity recognized by morphology (continuity of tendon and densely packed appearance of tendon fibers) and by behavior during passive movement – Joints can also be assessed dynamically during flexion and extension ○ Limited use in assessing for global bony alignment

CLINICAL IMPLICATIONS Clinical Importance • Instability of MTP joints results in pain and deformity of forefoot

Stability of 1st Metatarsophalangeal Joint • Collateral ligaments • Flexor and extensor hallucis brevis muscles • Flexor and extensor hallucis longus have smaller contribution to stability

Stability of Lateral Metatarsophalangeal Joints • Collateral ligaments • Plantar plate ○ Rupture of plantar plate results in dorsal subluxation of MTP joint and hammer toe deformity

Short 1st Metatarsal (Morton Foot) • Normal variant but increases stress on 2nd metatarsal • Predisposes to osteonecrosis of 2nd metatarsal head (Freiberg infraction)

Metatarsals and Toes Lower Extremity

1ST METATARSAL HEAD SECTION AND TOES

Intersesamoid l.

Adductor hallucis m. Lateral (fibular) sesamoid

Median crest (crista) of metatarsal

Medial (tibial) sesamoid Flexor hallucis longus t.

Flexor digitorum brevis t. Plantar plate

Adductor hallucis, transverse head

Adductor hallucis, oblique head

Flexor hallucis brevis m., medial and lateral heads

Adductor hallucis m.

(Top) Coronal (perpendicular to long axis of metatarsal bone) graphic shows sesamoid bone located on the plantar surface of the 1st metatarsal head, separated by the median crest of the metatarsal bone. The sesamoids are united by the intersesamoid ligament. The intersesamoid ligament forms the floor of the groove between the sesamoids; the flexor hallucis longus tendon runs along this groove. (Bottom) Axial graphic shows muscle attachments to sesamoids of the 1st metatarsophalangeal joint. Abductor hallucis and medial head of flexor hallucis brevis attach to medial sesamoid. Lateral head of flexor hallucis brevis and adductor hallucis attach to the lateral sesamoid.

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Lower Extremity

Metatarsals and Toes DORSUM METATARSAL Extensor digitorum brevis tt. for 2nd and 3rd metatarsals Extensor hallucis brevis t. Extensor hallucis longus t.

5th metatarsal 1st metatarsal Dorsal interossei mm.

Dorsal venous arch

Medial cuneiform Base of metatarsal

Extensor hallucis longus t. Shaft of metatarsal

Dorsal venous arch

Extensor hallucis longus t. Shaft of 1st metatarsal

Head of 1st metatarsal Neck of 1st metatarsal

(Top) Coronal panoramic scan shows the dorsal surface of the bodies of the metatarsals. The dorsal interosseous muscles lie between the bodies of the metatarsals. Their action is to abduct the toes. The plantar interosseous muscles act to adduct the toes. The extensor digitorum longus and extensor hallucis longus tendons receive assistance from their brevis tendons, which are deeper and approach from a lateral aspect. (Middle) Sagittal scan shows the dorsum of the big toe at the level of the tarsometatarsal joint. The extensor hallucis longus tendon is in close proximity to the bones around the joint. Note the densely packed and parallel echogenic tendon fibers. (Bottom) Sagittal scan shows the head of the 1st metatarsal. The extensor hallucis longus tendon is separated from the neck and most of the body of the metatarsal by fat.

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Metatarsals and Toes

Subcutaneous tissue

Flexor hallucis longus t.

Head of 1st metatarsal

Flexor hallucis brevis m.

Shaft of 1st metatarsal

Lower Extremity

PLANTAR METATARSAL

Subcutaneous tissue

Flexor hallucis longus t. Head of 1st metatarsal

Proximal phalanx of big toe Metatarsophalangeal joint

Plantar plate

Lateral head of flexor hallucis brevis m.

Tendon insertion of lateral head of flexor hallucis brevis Sesamoid bone

Shaft of 1st metatarsal Head of 1st metatarsal

(Top) Sagittal scan shows the plantar aspect of the head of the 1st metatarsal. The flexor hallucis longus muscle originates in the calf, while the brevis muscle arises from the cuboid and lateral cuneiform bones and tendon of the tibialis posterior. (Middle) Sagittal scan shows the center of the 1st metatarsophalangeal joint. The flexor hallucis longus tendon passes over the plantar plate of this joint to reach its insertion at the distal phalanx. (Bottom) Oblique sagittal scan shows the 1st metatarsophalangeal joint just lateral to the center. The flexor hallucis brevis tendons insert onto both sides of the base of the proximal phalanx via 2 tendons. Each tendon contains a sesamoid bone. Sesamoid bones may be bipartite as seen here, especially for the medial sesamoid.

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Lower Extremity

Metatarsals and Toes TRANSVERSE METATARSALS Flexor hallucis longus t.

Abductor hallucis m. Base of 1st metatarsal Flexor digitorum brevis m. Flexor hallucis brevis m.

Bases of 2nd, 3rd, and 4th metatarsals

Flexor digitorum longus tt.

3rd metatarsal base 2nd metatarsal base Flexor digitorum brevis tt.

Flexor hallucis longus t.

Medial slip of flexor hallucis brevis t. Common plantar digital a.

2nd metatarsal Sesamoid bone in lateral head of flexor hallucis brevis t.

Sesamoid bone in medial head of flexor hallucis brevis t. Head of 1st metatarsal, partially obscured by sesamoid

(Top) Transverse scan shows the plantar aspect of the bases of the medial metatarsals. The abductor hallucis muscle is superficial to the 1st and 2nd metatarsals. The base of the 1st metatarsal is uniquely large compared to the rest of the metatarsals and is easily identifiable. The flexor hallucis longus tendon runs superficial to the brevis muscle. (Middle) Transverse scan shows the plantar surface of the base of the 2nd and 3rd metatarsals. The base of the metatarsals form an arch with plantar concavity. The flexor digitorum longus tendons run centrally on the plantar surfaces of the metatarsals. (Bottom) Transverse scan shows the plantar surface of the 1st metatarsal. The flexor hallucis longus runs between the 2 sesamoid bones on the plantar aspect of the 1st metatarsal. The sesamoids adhere to the medial and lateral heads of the flexor hallucis brevis tendons.

856

Metatarsals and Toes

Superficial vv. Flexor hallucis longus t.

Head of 1st metatarsal Metatarsophalangeal joint

Flexor digitorum longus and brevis tt.

Proximal phalanx Middle phalanx

Lower Extremity

TOE, PLANTAR AND DORSUM

Proximal phalanx

Insertion of flexor digitorum longus t.

Distal phalanx Distal interphalangeal joint

Nail Coupling gel as acoustic window

Extensor digitorum longus t. Proximal phalanx of big toe

Nail bed Distal phalanx of big toe

Superficial vv.

(Top) Sagittal scan shows the plantar surface of the 1st tarsometatarsal joint. The flexor hallucis tendon runs close to the plantar surface of the phalanges and inserts at the base of the distal phalanx. (Middle) Sagittal scan shows the plantar surface of the 2nd toe. The flexor digitorum longus tendon inserts centrally at the base of the distal phalanx. The flexor digitorum brevis inserts on the sides of the base of the middle phalanx. Passive flexion of only the distal interphalangeal joint allows isolated evaluation of the tendon's movement (and integrity) of the flexor digitorum longus tendon. (Bottom) Sagittal color Doppler scan shows the dorsal surface of the distal phalanx of the big toe. The extensor digitorum longus tendon inserts on the dorsal surface of the base of the distal phalanx. The nail bed has a rich vascular supply as demonstrated by the color flow.

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SECTION 8

Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester Embryology and Anatomy of Brain Embryology and Anatomy of Spine Embryology and Anatomy of Face and Neck Embryology and Anatomy of Chest Embryology and Anatomy of Cardiovascular System Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract Embryology and Anatomy of Genitourinary Tract

860 872 888 894 906 914 924 934

Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester

TERMINOLOGY Definitions • 1st trimester covers time from 1st day of last menstrual period to end of 13th postmenstrual week

EMBRYOLOGY Embryologic Events • 1st trimester includes ○ Ovulation ○ Fertilization ○ Cleavage ○ Implantation ○ Embryonic development ○ Organogenesis ○ Placental development ○ Umbilical cord development

Ovulation • Primordial follicles → 5-12 primary follicles per cycle • All but 1 degenerate, leaving single dominant follicle • Pituitary gonadotrophin surge → ovulation → oocyte extruded onto ovarian surface • Oocyte surrounded by tough zona pellucida as well as layers of cumulus cells • Fimbria sweep oocyte into fallopian tube • Remaining "empty" follicle becomes corpus luteum, producing estrogen and progesterone

Fertilization • • • •

Occurs in fallopian tube Oocyte can be fertilized for ~ 24 hours Sperm penetrates oocyte, cell membranes fuse → zygote Spermatozoon and oocyte nuclei become male and female pronuclei • Nuclear membranes disappear, chromosomes replicate in preparation for zygote cleavage

Cleavage • Zygote → 2 cells → 4 cells → 8 cells → morula → blastocyst • Several cell divisions result in smaller parts called blastomeres • At 8-cell stage, compaction occurs with some cells → inner cell mass or embryoblast, some cells → peripheral trophoblast ○ Inner cell mass/embryoblast = embryonic pole of blastocyst • 16-32 blastomeres = morula • Morula absorbs fluid → central cavity called blastocoele within blastocyst

Implantation • Blastocyst "hatches" from zona pellucida • "Naked" blastocyst then interacts directly with maternal endometrium • Trophoblast cells give rise to membranes and placenta, not embryo proper ○ Trophoblast cells at embryonic pole → syncytiotrophoblast, which burrows into endometrial lining ○ Remaining trophoblast cells become cytotrophoblast 860

• Maternal endometrial cells differentiate into decidual cells in response to ○ Progesterone secreted by corpus luteum ○ β human chorionic gonadotrophin produced by syncytiotrophoblast

Embryonic Development • Bilaminar embryonic disc forms when embryoblast splits into epiblast and hypoblast • Hypoblast = primitive endoderm ○ Hypoblast cells migrate around cavity of blastocyst to create primary yolk sac ○ Hypoblast + primary yolk sac give rise to extraembryonic mesoderm (loosely associated cells filling blastocyst cavity around primary yolk sac) ○ 2nd wave of migrating hypoblast cells create secondary yolk sac, which displaces primary yolk sac ○ Extraembryonic mesoderm splits into 2 layers, creating chorionic cavity (extraembryonic coelom) ○ Chorionic cavity separates embryo/amnion/yolk sac from chorion (outer wall of blastocyst) • Epiblast contributes to embryo and gives rise to amnion ○ Fluid collects between epiblast and overlying trophoblast → cavity ○ Layer of epiblast differentiates into amniotic membrane separating new cavity from cytotrophoblast • Trilaminar disc ○ Develops by process of gastrulation, which moves cells to new locations with resulting induction ○ 3 primary germ layers = ectoderm, mesoderm, endoderm ○ Body axes also determined by gastrulation • Disc elongates and folds → series of tubular structures → major organ systems • Ectoderm → neural plate → neural tube + neural crest cells ○ Neural tube → brain and spinal cord ○ Neural crest cells migrate from neural tube → many differing structures and cell types • Mesoderm ○ Head mesoderm → muscles of face, jaw, and throat ○ Notochordal process ○ Cardiogenic mesoderm ○ Somites → most of axial skeleton ○ Intermediate mesoderm → genitourinary system ○ Lateral plate mesoderm → abdominal wall and gut walls • Endoderm ○ Foregut, midgut, hindgut (oropharyngeal membrane → mouth)

Organogenesis • Central nervous system ○ Arises from neural folds → neural tube + neural crest – Cranial/rostral 2/3 of neural tube → brain – Caudal 1/3 of neural tube → spinal cord, nerves – Neural crest → peripheral nerves, autonomic nervous system • Cardiovascular system ○ Arises from cardiac tube → heart and great vessels ○ Cardiogenic precursors form 1° heart field at cranial end of embryo

Embryology and Anatomy of 1st Trimester

•

•

•

Placental Development • Chorionic sac initially covered in villi, atrophy of those adjacent to uterine cavity → chorion laeve • In villi adjacent to implantation site, burrowing syncytiotrophoblast develops trophoblastic lacunae ○ Adjacent maternal capillaries expand → maternal sinusoids, anastomose with trophoblastic lacunae ○ Budding/proliferation of cytotrophoblast into syncytiotrophoblast and maternal lacunae → mature tertiary villi ○ Tertiary villi contain fully differentiated blood vessels for gas exchange in chorion frondosum • Chorion frondosum + decidua basalis = placenta

• Embryo initially connected to chorion by connecting stalk, which arises from extraembryonic mesoderm ○ Allantois (endodermal hindgut diverticulum) arises as outpouching of yolk sac ○ Allantois and allantoic vessels extend into connecting stalk (become umbilical vessels) • Embryonic growth and folding result in blind-ended foregut and hindgut tubes with midgut open to yolk sac ○ As body wall forms by lateral folding and midgut becomes tubular, yolk sac is "pinched off" ○ Narrow elongated neck of yolk sac = vitelline duct, which connects yolk sac to closing midgut tube • As embryo enlarges and folds, amniotic cavity expands to encompass embryo completely except at umbilical ring ○ Connecting stalk, allantois, vitelline duct become incorporated as umbilical cord ○ Amnion continues to enlarge and forms tubular covering over incorporated cord elements → dense epithelial covering • Progressive cord elongation and coiling occur with embryonic/fetal growth and movement

Obstetrics and Developmental Anatomy

•

○ Lateral endocardial tubes brought together by embryonic folding → primitive heart tube ○ Looping, remodeling, septation of primitive heart tube → definitive 4-chamber heart ○ Conotruncus = primitive outflow tract that splits → ventricular outflow tracts Respiratory system ○ Foregut → respiratory diverticulum → 1° bronchial buds → 3 right + 2 left 2° bronchial buds → terminal bronchioles → respiratory bronchioles → primitive alveoli Gastrointestinal system ○ Early embryonic folding → endodermal tube → foregut, midgut, hindgut ○ Foregut (blind ending at oropharyngeal membrane) → esophagus, stomach, proximal duodenum – Liver, gallbladder, cystic duct, and pancreas arise from duodenal diverticula ○ Midgut (initially open to yolk sac) → distal duodenum to proximal 2/3 transverse colon – Future ileum elongates rapidly → 1° intestinal loop, which herniates into base of umbilical cord rotating 90° – During retraction into peritoneal cavity, additional 180° rotation secures normal bowl orientation with cecum right, duodenojejunal flexure left ○ Hindgut (blind ending at cloacal membrane) → distal 1/3 transverse colon to rectum – Terminal expansion of primitive hindgut tube → cloaca – Urorectal septum divides cloaca into urogenital sinus + dorsal anorectal canal Genitourinary system ○ Intermediate mesoderm → pronephros, mesonephros, metanephros – Mesonephros → rudimentary kidneys connected to cloaca by mesonephric ducts – Mesonephric ducts → ureteral bud → collecting system – Ureteral bud connection to metanephric blastema → induction of nephron formation ○ Bladder arises from cloaca and allantois ○ Bladder separated from rectum by urogenital sinus Musculoskeletal system ○ Upper and lower extremities develop from individual limb buds

ANATOMY IMAGING ISSUES Questions • Developmental milestones (in weeks post last menstrual period) ○ Gestational sac (intradecidual sac sign) usually visible by 4.0-4.5 weeks ○ Yolk sac usually visible by 5.0-5.5 weeks ○ Distinct embryo with cardiac activity usually visible by 6.06.5 weeks • Developmental milestones based on mean sac diameter (MSD) ○ Embryo should be visible if MSD > 25 mm endovaginal (EV) scan • Embryo of > 7 mm in length must have cardiac activity ○ If embryo seen within visible amnion, cardiac activity should be present (expanded amnion sign) • Gestational age assessment most accurate in 1st trimester ○ Biological variations take effect after 13 weeks • Determination of chorionicity best done in multiple pregnancies ○ Most important factor in prognosis • Is there evidence of increased risk for aneuploidy ○ 11- to 13-week scan can be used to adjust a priori risk of aneuploidy, determine need for invasive testing • Is anatomy normal ○ Organogenesis is complete by end of 13th week ○ Use EV sonography for best resolution • 1st trimester is time of complex cell multiplication and differentiation ○ Great potential for error if normal processes are not clearly understood

Umbilical Cord Development • Embryonic disc lies between amnion and yolk sac 861

Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester OVULATION AND FERTILIZATION

Dominant follicle

Primordial follicles

Corpus albicans

Oocyte surrounded by cumulus cells

Corpus luteum

2-cell stage

Zygote surrounded by zona pellucida

Spermatozoa penetrates oocyte for fertilization

4-cell stage 8-cell stage Morula (composed of blastomeres)

Blastocele cavity within blastocyst

"Naked" blastocyst

Oocyte swept into tube by fimbria

Oocyte extruded from ovary

(Top) During the follicular phase of the menstrual cycle, several follicles begin to develop; 1 becomes dominant, and eventually, a mature oocyte is extruded from the ovarian surface at the time of ovulation. The remaining follicle becomes the corpus luteum, which produces progesterone and helps to maintain the early pregnancy until the placenta is formed. If fertilization does not occur, the corpus luteum degenerates into a corpus albicans. (Bottom) The oocyte is swept into the fallopian tube where it is fertilized. The fertilized ovum divides repeatedly during passage along the tube so that by the time it reaches the endometrial cavity, a blastocyst has formed. The blastocyst "hatches" from the zona pellucida and implants into the maternal endometrium.

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Embryology and Anatomy of 1st Trimester

Decidual lining

Uterine cavity

Hypoblast Embryoblast Epiblast

Cytotrophoblast

Extraembryonic mesoderm splits to form chorionic cavity

Obstetrics and Developmental Anatomy

CLEAVAGE AND IMPLANTATION

Syncytiotrophoblast

Primary yolk sac Syncytiotrophoblast Bilaminar embryo

Chorionic cavity

Amniotic cavity

Cytotrophoblast

Secondary yolk sac

Amniotic cavity Involuting primary yolk sac

Bilaminar embryo

Chorionic cavity

Syncytiotrophoblast Maternal sinusoid

(Top) While the dividing zygote is still in the fallopian tube (8-cell stage), cells differentiate into embryoblast and trophoblast. Syncytiotrophoblast interacts with the endometrium to form the placenta; the remainder is the cytotrophoblast. Embryoblast cells will give rise to the embryo, amnion, and yolk sac. (Middle) The embryoblast splits into 2 layers: Epiblast and hypoblast. The hypoblast gives rise to the primary and secondary yolk sacs and extraembryonic mesoderm. The latter splits, forming the chorionic cavity. The epiblast gives rise to the embryo and the amnion. (Bottom) As the primary yolk sac involutes, the secondary yolk sac develops. It is the secondary yolk sac that is visible sonographically; however, by convention, it is usually referred to as simply the yolk sac on ultrasound images. The chorionic cavity enlarges. The embryo is still a bilaminar disc.

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Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester INTRADECIDUAL SAC SIGN

Myometrium Intradecidual sac Endometrial cavity

Decidualized endometrium

Intradecidual sac

Myometrium

Endometrial cavity

Myometrium Intradecidual sac

Intracavitary blood Endometrial cavity

Primary yolk sac Intradecidual sac Endometrial cavity

(Top) The graphic illustrates the earliest sonographic manifestation of the embryological development. The gestational sac has burrowed into the decidualized endometrium, creating an asymmetrically placed echogenic ring with a lucent center. This was initially described as the intradecidual sac sign (IDSS). It is not always visible in early pregnancy, and it is subject to considerable interobserver variability. (Middle) The intradecidual gestational sac is an echogenic ring eccentric to the line created by apposition of the endometrial surfaces. Currently, recommended terms for such an observation are intrauterine sac-like structure or probable intrauterine pregnancy. (Bottom) In this example of IDSS, bleeding has resulted in accumulation of blood in the endometrial cavity. Again, note the eccentric location of the 4-mm diameter sac. In the lower image, a tiny circular structure within the gestational sac is likely the primary yolk sac, which can be seen with high-resolution modern transducers.

864

Embryology and Anatomy of 1st Trimester

Yolk sac

Decidua basalis

Embryo

Decidua capsularis

Chorionic cavity Uterine cavity

Obstetrics and Developmental Anatomy

DOUBLE DECIDUAL SAC SIGN

Decidua parietalis

Decidua basalis

Decidua capsularis Chorionic cavity

Decidua parietalis

Decidua basalis

Embryo Yolk sac

Decidua capsularis Decidua parietalis

(Top) This graphic illustrates the double decidual sac sign (DDSS). This is seen when the enlarging gestational sac protrudes from the site of implantation and starts to expand into the uterine cavity, exerting mass effect on the opposite uterine wall. The decidua covering the expanding sac is decidua capsularis, that which is being pushed ahead of the expanding sac is the decidua parietalis. The decidua basalis is where the sac is adherent to the uterine wall and marks the site where the placenta will develop. Internal structures may be seen on transvaginal scans. (Middle) The decidual layers are easily seen on this transvaginal scan. The concentric rings created by the decidua capsularis and parietalis create the DDSS. This finding is characterized as a probable intrauterine pregnancy. (Bottom) In this example, the embryo and yolk sac are visible in addition to the DDSS; this indicates a definite intrauterine pregnancy. It would also be a pregnancy of uncertain viability if there were no cardiac activity in an embryo < 7 mm in length.

865

Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester EMBRYONIC DEVELOPMENT: 6 WEEKS Uterine cavity

Amnion Chorionic cavity Embryo Connecting stalk Chorionic villi Yolk sac (secondary)

Myometrium

Trilaminar embryo

Chorion

Myometrium

Embryo Yolk sac

Chorion

(Top) The graphic illustrates normal early development. The embryo is intimately associated with the yolk sac so that the amnion and yolk sac appear as a double bleb with the embryo sandwiched between them. The embryo is within the amniotic sac; both the embryo and yolk sac are inside the chorionic sac. (Middle) Vaginal ultrasound at 5 weeks, 5 days from last menstrual period shows a 2-mm embryo. There are 3 linear echoes that resemble an Oreo cookie. The process of gastrulation results in cellular movement with creation of the 3 primary germ layers: The endoderm, mesoderm, and ectoderm. Despite the tiny size of this embryo, cardiac activity was visible in real time. (Bottom) Vaginal ultrasound shows the embryo immediately adjacent to the yolk sac. The amnion is not yet visible. At this gestational age, the abdominal wall is still open, and the midgut is in continuity with the yolk sac. After the abdominal wall closes, the "discarded" yolk sac is compressed between the expanding amnion and the chorion.

866

Embryology and Anatomy of 1st Trimester

Chorion laeve Chorionic cavity Embryo Vitelline duct

Amnion Connecting stalk

Yolk sac

Obstetrics and Developmental Anatomy

EMBRYONIC DEVELOPMENT: 7-8 WEEKS

Chorionic villi in chorion frondosum

Myometrium

Chorion

Amnion

Yolk sac Embryo

Chorion Crown end of embryo

Limb bud Yolk sac Rump end of embryo

(Top) Curvature and folding of the embryo result in closure of the abdominal wall and pinching off of the yolk sac. The elongated neck forms the vitelline duct. Eventually, the yolk sac separates from the embryo, dropping into the chorionic cavity. At the same time, it becomes clear which end of the embryo is which, and limb buds start to form. The chorion adjacent to the uterine cavity is now completely smooth. Chorionic villi in the developing placenta become more complex in structure. (Middle) Vaginal ultrasound at 7 weeks, 4 days from last menstrual period shows the yolk sac is separate from the embryo. It lies outside the amnion, which is now expanded enough to be just visible as it surrounds the embryo. Remember that the yolk sac will always be outside the amnion; the embryo lies inside the amniotic sac. (Bottom) 3D surface-rendered ultrasound shows the yolk sac separate from the embryo, which now has an elongated configuration with defined cranial or crown and pelvic or rump ends. The crown rump-length is measured to confirm menstrual dating.

867

Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester EMBRYONIC DEVELOPMENT: 8-9 WEEKS

Chorion laeve Embryo

Lower extremity limb bud Amnion Connecting stalk

Yolk sac Vitelline duct

Amnion

Cranium Upper extremity limb bud

Umbilical cord

Lower extremity limb bud

Yolk sac Chorion

Chorion laeve

Edge of amnion Rhombencephalon

Chorion

Yolk sac

Thickened chorionic villi in developing placenta

(Top) The graphic illustrates continued embryonic development; the limb buds are evident, the head has grown dramatically, and the embryo is assuming a recognizable human form. The umbilical cord forms as a result of fusion of the vitelline duct, allantois, and connecting stalk. Once formed, it elongates rapidly until the embryo is suspended within the enlarging amniotic sac. Cord elongation allows for free mobility of the developing fetus. (Middle) 3D surface-rendered ultrasound of an 8-week embryo shows the short limb buds and the relatively thick umbilical cord. The crown end is assuming a more recognizable head shape, and the embryo is curling into the typical fetal position. (Bottom) Another 3D ultrasound in the sagittal plane shows the rhombencephalic vesicle in the cranial part of the embryo. This fluid-filled space is a precursor of the 4th ventricle and should not be confused with a pathological intracranial cyst.

868

Embryology and Anatomy of 1st Trimester

Chorion laeve Amnion Bowel herniated into base of cord

Yolk sac now separated from embryo Chorionic villi in developing placenta

Obstetrics and Developmental Anatomy

EMBRYONIC DEVELOPMENT: 10-13 WEEKS

Cranium

Upper extremities

Crown rump length

Cord insertion site Lower extremity

Placenta Ossified cranium Nasal bone Thalamus Lower extremity Liver

Diaphragm Vertebral column

Midbrain Intracranial translucency

Amnion Myometrium

(Top) Toward the end of the 1st trimester, the amnion fills the chorionic cavity. The membranes do not "fuse" until 14-16 weeks. The placenta continues to grow, and the chorionic villi develop an increasingly complex branching pattern. (Middle) 3D surface-rendered ultrasound at 10 weeks shows increasingly recognizable fetal anatomy with a well-developed cranium and extremities. The abdominal wall cord insertion site is quite broad due to the physiologic herniation of bowel into its base. This occurs as the peritoneal cavity is too small to accommodate the rapidly growing bowel at this gestational age. (Bottom) Sagittal transabdominal ultrasound at 12 weeks, 6 days from last menstrual period shows recognizable anatomic features. Organogenesis is completed by the end of the 13th week. Growth and maturation of the various organ systems occurs during the remainder of gestation.

869

Obstetrics and Developmental Anatomy

Embryology and Anatomy of 1st Trimester ABDOMINAL WALL AND GI TRACT

Liver

Aorta

Gut tube herniates into base of umbilical cord rotating 90°

Hindgut

Stomach

Gut tube rotates additional 180° as it returns to peritoneal cavity

Chorion

Bowel loops in base of umbilical cord

Torso

Umbilical cord Chorionic cavity (extraembryonic coelomic space)

Cranium

Upper extremity

Coiled umbilical cord

Cord insertion site; bowel herniation has resolved Lower extremities

(Top) The graphic illustrates herniation of bowel into the base of the cord in the 1st trimester. This happens as the gut tube elongates before there is adequate room to accommodate it in the peritoneal cavity. The gut undergoes a 90° counterclockwise rotation as it herniates and an additional 180° rotation as it is retracted into the peritoneal cavity. Only the gut herniates; liver is never normally seen at the base of the cord. (Middle) Vaginal ultrasound at 10 weeks, 3 days shows echogenic bowel at the base of the umbilical cord. This is normal at this gestational age and should not be misinterpreted as a bowel-containing omphalocele. (Bottom) 3D surface-rendered ultrasound of a 12-week fetus shows a normal abdominal wall contour. The cord insertion is normal, and there is no residual bowel herniation. Three of the extremities are seen, the cranial contour is normal, and the cord is already coiled.

870

Embryology and Anatomy of 1st Trimester

Inferior vena cava Ductus venosus

Portal v. Umbilical v.

Umbilical cord

Obstetrics and Developmental Anatomy

UMBILICAL CORD DEVELOPMENT

Bowel herniated into base of cord

Chorionic cavity (extraembryonic coelomic space) Cranium Coiled umbilical cord

Amniotic cavity Yolk sac

Amnion

Myometrium

Chorion

Amnion

Umbilical aa.

Umbilical v.

Umbilical cord cyst

(Top) The graphic illustrates fetal circulation in which oxygenated blood from the placenta returns to the fetus via the umbilical vein. The umbilical vein courses through the left lobe of the liver to the left portal vein, across the ductus venosus into the inferior vena cava. The umbilical cord also contains 2 arteries that arise from the internal iliac arteries. (Middle) At 10 weeks, there is some residual herniation of bowel into the base of the cord. The embryo is freely suspended within the amniotic sac by the cord, which already shows evidence of coiling. The yolk sac will be obliterated as the amnion apposes to the chorion. (Bottom) Color Doppler ultrasound shows a small umbilical cord cyst as an avascular area adjacent to the cord vessels. As a 1st-trimester finding, this is usually of no significance; the cysts form at 8-9 weeks and usually resolve by ~ 12 weeks.

871

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain

TERMINOLOGY Definitions • Rostral: Cranial (i.e., toward head end of embryo) • Caudal: Tail (i.e., toward sacral end of embryo)

MAJOR EMBRYOLOGIC EVENTS Neurulation • Ectodermal cells give rise to dorsal, midline neural plate ○ Neural folds develop then fuse → neural tube + neural crest • Neural tube → brain, spinal cord • Neural crest → peripheral nerves, autonomic nervous system • Errors in neurulation ○ Anencephaly ○ Cephalocele ○ Myelomeningocele ○ Chiari 2: Abnormal neurulation of hindbrain

Neuronal Proliferation • Begins in rhombencephalon; neuroepithelial proliferation → neurons, glial cells, ependymal cells ○ Neurons "born" in ventricular zone (around central lumen) are called young neurons – Migrate peripherally to form mantle zone (i.e., gray matter precursor) – Axons extending peripherally to mantle zone establish marginal zone (i.e., white matter precursors) – White matter is outside, gray matter is inside ○ Glioblast cells → astrocytes, oligodendrocytes – Provide metabolic/structural support to neurons ○ Ependymal cells line ventricles/spinal canal – Produce cerebrospinal fluid • Errors in neuronal proliferation ○ Holoprosencephaly ○ Agenesis of corpus callosum ○ Pituitary maldevelopment ○ Dandy-Walker malformation ○ Rhombencephalosynapsis

Histogenesis • Process of proliferation, migration, differentiation → development of mature cerebral cortex • Unique difference between cerebral hemisphere neuroepithelium and that of other parts of neural tube ○ Made up of several layers (6 in dominant neocortex) ○ Inside-out arrangement of gray/white matter – Unlike rest of CNS, cerebral hemispheres have white matter inside and gray matter outside – Mechanism poorly understood • Specialized neurogenesis in cerebellum → gray matter of cerebellar cortex/deep cerebellar nuclei • Errors in histogenesis ○ Abnormal histogenesis of periaqueductal gray matter is 1 cause of aqueduct stenosis

Neuronal Migration • Peak activity at 11-15 weeks ○ Majority of neurons in correct location by 24 weeks ○ Migration continues up to 35 weeks 872

• Newly proliferated cells migrate along predetermined pathways of radial glial fibers → organized cortical layering ○ Inside-out pattern of 6 layers with newest arrivals "outside" those that migrated earlier ○ Process governed by multiple genes, circulating factors • Errors in migration ○ Microcephaly ○ Megalencephaly ○ Heterotopia ○ Cortical dysplasia ○ Lissencephaly: Arrested neuronal migration ○ Phakomatoses

Myelination • Can be detected as early as 20 weeks • Occurs in orderly, predictable manner ○ Caudal → cranial, deep → superficial, posterior → anterior • Continues into adulthood

Operculization • Development of insular cortex and infolding of sylvian fissures • During weeks 11-28 • Errors in operculization ○ Defective speech and language processing

Gyral and Sulcal Development • Occurs earlier in vivo than can be detected by current imaging modalities ○ 4- to 6-week time lag before structures become visible by imaging • Gestational age by which sulcus/fissure should always be seen ○ Callosal: US 14 weeks, MR 22 weeks ○ Sylvian: US 18 weeks, MR 24 weeks ○ Parietooccipital: US 18 weeks, MR 22-23 weeks ○ Calcarine: US 18 weeks, MR 22-23 weeks • Continues through end of 35th week

CEREBRUM, CEREBELLUM, AND VENTRICLES Cerebral Hemispheres • Notochord development ○ Bilaminar germ disc evolves into trilaminar germ disc with ectoderm, mesoderm, endoderm ○ Mesoderm forms midline, hollow, central tube: Notochordal process ○ Notochordal process evolves into solid notochord ○ Notochord + mesoderm induce formation of neural plate ○ Neural plate grows in length and width until day 21 when neurulation begins • Formation of neural tube (primary neurulation) ○ Neural plate folds elevate, forming trough (neural groove) between them ○ Neural folds fuse → neural tube – Neural crest cells (derived from neuroectoderm) split from neural tube as it fuses ○ Neural tube temporarily open at both ends; openings are called neuropores – Rostral 2/3 of neural tube → brain – Caudal 1/3 of neural tube → spinal cord, nerves

Embryology and Anatomy of Brain

•

•

•

•

Cerebellum • Thickening of alar plate of rhombencephalon → rhombic lips • Rhombic lips → cerebellar hemispheres by intense neuronal proliferation • Rhombic lips fuse → cerebellar commissures in roof of 4th ventricle • Cerebellar hemispheric fusion starts cranially, forming flocculi of hemispheres and nodulus of vermis in 9th week ○ Proliferation and fusion continue caudally until complete by 15th week • Flocculonodular fissure separates flocculi of hemispheres and nodulus of vermis

• Foramina of Monro connect lateral ventricle to 3rd ventricle • Aqueduct of Sylvius connects 3rd-4th ventricles ○ Develops from cavity of mesencephalon • Vessels from diencephalon and myelencephalon invade ventricular walls → choroid plexus • 4th ventricle roof ○ Highly complex area ○ Ridge of developing choroid plexus divides roof → anterior and posterior membranous areas – Anterior superior part incorporated into choroid plexus – Posterior inferior persists, midline cavitation → foramen of Magendie

IMAGING ISSUES

Obstetrics and Developmental Anatomy

•

○ Bidirectional closure begins at occipitocervical level – Rostral/cranial neuropore closes at day 24 – Caudal/sacral neuropore closes at day 25 Primary vesicles form by middle of 4th week ○ Prosencephalon (forebrain) ○ Mesencephalon (midbrain) ○ Rhombencephalon (hindbrain) Secondary vesicles form during 5th week ○ Prosencephalon → anterior telencephalon + posterior diencephalon – Diencephalon → hypothalamus, thalamus, posterior pituitary, eyes – Telencephalon → cerebral hemispheres (by sagittal cleavage), basal ganglia ○ Rhombencephalon → anterior metencephalon + posterior myelencephalon – Metencephalon → pons + cerebellum – Myelencephalon → medulla oblongata Tube elongates at same times as vesicles form; flexures develop at specific locations ○ Midbrain (mesencephalic) flexure ○ Cervical flexure at junction of brainstem with spinal cord ○ Pontine flexure develops between midbrain and cervical flexures Cerebral hemispheres formed by 11th week ○ Arise as lateral outpouchings of telencephalon ○ Grow rapidly to cover diencephalon, mesencephalon Cerebral hemispheres connected by lamina terminalis ("zip" of cranial neuropore closure) ○ Thickening of lamina terminalis at rostral end → lamina reuniens + massa commissuralis – Lamina reuniens → anterior commissure – Massa commissuralis → corpus callosum, hippocampal commissure – Hippocampal commissure merges with splenium of corpus callosum ○ Corpus callosum should be complete by 20 weeks – Composed of 4 parts; from front to back, these are rostrum, genu, body, splenium

Protocol Advice • US ○ Use highest resolution transducer possible ○ 3D volume acquisition allows manipulation of dataset to "create" true orthogonal image planes ○ Use color Doppler to evaluate course of marker vessels • MR ○ Use fast sequences with single slice rather than volume acquisition ○ Diffusion tensor imaging can be performed for tractography ○ T2WI for global anatomy ○ T1WI for blood, fat, myelination

Imaging Pitfalls • Normal structures mistaken for pathology ○ Yolk sac confused with cephalocele ○ Rhombencephalic vesicle confused with posterior fossa cyst ○ Corner of ventricular atrium mistaken for choroid plexus cyst ○ Fornices mistaken for cavum septi pellucidi • Subtle lesions that may be missed if normal development not understood ○ Absent cavum septi pellucidi ○ Heterotopia ○ Lissencephaly ○ Cortical dysplasia • Posterior fossa ○ Rotation of vermis may be mistaken for vermian dysgenesis ○ Rhombencephalosynapsis may be confused with cerebellar hypoplasia

Ventricles • Cavities within brain vesicles → ventricles during weeks 4-12 ○ Lateral ventricles develop as diverticula from telencephalic primitive ventricle ○ 3rd ventricle develops from cavity of diencephalon ○ 4th ventricle develops from cavity of rhombencephalon 873

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain 1ST TRIMESTER EMBRYO

Cranial neuropore

Somites

Closing neural tube

Caudal neuropore

Yolk sac

Prosencephalon Optic vesicle

Body stalk

Mesencephalon

Embryo Rhombencephalon

Amnion

Amniotic cavity

Umbilical cord

Embryo rump end

Embryo crown end

(Top) The neural tube closes in a bidirectional manner. The cranial neuropore closes at day 24, while the caudal neuropore closes at day 25. (Middle) A series of vesicles develop at the same time the head end of the embryo enlarges and the flat embryonic disc becomes curved in profile and tubular in cross section. These are the precursors to the adult brain. The prosencephalon (green) gives rise to the forebrain, the mesencephalon (purple) to the midbrain, and the rhombencephalon (light blue) to the hindbrain. (Bottom) Surfacerendered 3D US of a 7-week embryo shows the external contour with a recognizable head end. The abdominal wall has closed, the yolk sac has detached, and the umbilical cord has formed. The torso is relatively small, the limb buds have not yet developed, but neural tube has already developed the precursors to the forebrain, midbrain, and hindbrain.

874

Embryology and Anatomy of Brain

Amnion Chorionic frondosum (developing placenta)

Embryonic rump

Prosencephalon Mesencephalon Rhombencephalon

Obstetrics and Developmental Anatomy

1ST TRIMESTER EMBRYO

Telencephalon Diencephalon

Mesencephalon Metencephalon

Myelencephalon

Telencephalon and diencephalon

Mesencephalon Metencephalon and myelencephalon

(Top) This is a vaginal US of an 8-week, 2-day embryo in which the primitive brain vesicles are visible. This is a normal finding with highresolution modern equipment and should not be mistaken for holoprosencephaly or other brain malformation. (Middle) With further embryonic growth, the prosencephalon gives rise to secondary vesicles known as the telencephalon and diencephalon. The mesencephalon elongates, while the rhombencephalon gives rise to the secondary vesicles, metencephalon, and myelencephalon. At this point, several flexures develop in the neural tube so that it adapts to the contour of the developing cranium. (Bottom) Another midline sagittal scan of a slightly older embryo, this time 9 weeks, 6 days, shows further neural tube growth with development of multiple flexures in the lengthening tube so that it adapts to the contour of the developing cranium. Again, it is important to recognize that this is normal for gestational age.

875

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain 1ST TRIMESTER FETUS

Frontal lobes

Choroid plexus

Occipital lobes Ossified cranium

Choroid plexus

Nasal bone Thalamus Midbrain

Maxilla Mandible Brainstem

Intracranial translucency

Choroid plexus of 4th ventricle

Falx cerebri

Right frontal lobe

Right eye

Left frontal lobe

Left eye Oral cavity

Right upper extremity Left upper extremity

(Top) At 12 weeks, the choroid plexus fills most of the ventricular cavity, and the brain parenchyma is thin and smooth. The echogenicity and shape of the choroid plexus on an axial US image gives rise to the butterfly sign in which the choroid forms the butterfly wings. This confirms 2 cerebral hemispheres. (Middle) Sagittal abdominal US at 13 weeks shows a normal thalamus, midbrain, and brainstem. The intracranial translucency (the future 4th ventricle) is seen between the brainstem and the choroid plexus of the 4th ventricle. Intracranial translucency assessment may be used for early detection of open neural tube defects. (Bottom) Transabdominal US at 13 weeks, 1 day shows clear separation of the cerebral hemispheres by the falx cerebri. The ocular globes are visible within the bony orbits, and the oral cavity is visible between the bright echoes of the maxilla and mandible.

876

Embryology and Anatomy of Brain

Parietooccipital fissure indentation

Interhemispheric fissure Lateral ventricle

Sylvian fissure indentation

Width of lateral ventricle

Obstetrics and Developmental Anatomy

2ND TRIMESTER FETUS

Choroid plexus

Corpus callosum Thalamus

Midbrain Primary vermian fissure

Pons Fastigial point of vermis

Interhemispheric fissure

Occipital lobe Occipital horn of lateral ventricle

Cerebellar vermis Cisterna magna

Choroid plexus Calcarine fissure indentation Tentorium cerebelli

Cerebellar hemispheres

(Top) At 18 weeks, the cerebral mantle is quite smooth with just the earliest "thumb print" indentation for the sylvian fissure and a tiny indentation at the site of the developing parietooccipital fissure. The latter marks the anatomic location at which the width of the lateral ventricle should be measured. (Middle) Sagittal transabdominal US at 20 weeks shows normal midline structures very well. Although not a standard image in a 2nd-trimester scan, this is as easy to obtain as a profile view of the face. (Bottom) Coronal image in a 22-week fetus shows another nonstandard, but easily obtainable, view of the fetal brain. Turning the transducer 90° from the standard axial images provides another way to assess symmetry of the hemispheres, ventricles, and the cortical mantle. The cisterna magna cannot be measured in this plane as it is artificially deepened by the extension into the foramen magnum.

877

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain CAVUM SEPTI PELLUCIDI

Septi pellucidi (walls of cavum) Cavum septi pellucidi

Falx cerebri Cingulate gyrus

Corpus callosum Frontal horn of lateral ventricle Cavum septi pellucidi Sylvian fissure

Cavum septi pellucidi Interhemispheric fissure Frontal horn of lateral ventricle

3rd ventricle echo Thalamus Smooth immature cortex

Sylvian fissure

Fornices

Interhemispheric fissure

Cerebellar hemisphere Cerebellar vermis Cerebellar hemisphere

Sylvian fissure

(Top) Coronal graphic (with axial insert) illustrates the cavum septi pellucidi, which is a marker for normal midline brain development. (Middle) The cavum should be demonstrated on all routine obstetric scans between 18 and ~ 37 weeks. It is a box-shaped, anechoic space in the midline between the frontal horns of the lateral ventricles. It can also be seen on coronal views obtained transabdominally or transvaginally. (Bottom) A pitfall for the unwary is to confuse the normal fornices with the cavum. The fornices may be normal in a fetus with an absent cavum. They are seen just inferior (toward the skull base) to the normal location of the cavum. They form a series of parallel, black and white lines around the intact midline. The cavum is a box-shaped structure that interrupts the midline echo.

878

Embryology and Anatomy of Brain

Cavum septi pellucidi

Interhemispheric fissure

Thalamus

3rd ventricle echo

Frontal horn Insular cortex

Obstetrics and Developmental Anatomy

SYLVIAN FISSURE

Sylvian fissure

Cisterna magna

Cavum septi pellucidi

Interhemispheric fissure

Cerebellum

Sylvian fissure

Insular cortex Cavum septi pellucidi Parietooccipital sulcus Cingulate gyrus Interhemispheric fissure

Cingulate sulcus Frontal operculum

Lateral ventricle Glomus of choroid plexus Parietal operculum

Sylvian fissure

(Top) The sylvian fissure is one of the easiest cortical indentations to see in the fetus. In this 19-week fetus, the sylvian fissure is seen as a shallow groove on the surface of the brain; it creates obtuse angles with the insular cortex. The cortical mantle is quite smooth at this gestational age. As the brain grows, the sylvian fissure deepens and the cortical mantle becomes convoluted. (Middle) As the brain grows and the surface becomes more convoluted, the sylvian fissure deepens and becomes square in profile, like an open box. This is a 25-week, 3-day gestation. (Bottom) In this fetus, at 28-weeks gestation, the process of operculization results in the sylvian fissure "closing." The floor of the box is the insular cortex, and the lid of the box is composed of the frontal and temporoparietal opercula. The sylvian fissure separates the parietal lobe superiorly from the temporal lobe inferiorly. The surface of the brain is becoming more convoluted with visible parietooccipital sulcus, cingulate sulcus, and shallow surface gyri.

879

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain TELENCEPHALON: CEREBRAL HEMISPHERES

Insular cortex

Central sulcus

Frontal lobe

Sylvian fissure (box-shaped, uncovered) Occipital lobe Temporal lobe Cerebellum Medulla oblongata

Precentral gyrus

Central sulcus Postcentral gyrus

Precentral sulcus Postcentral sulcus

Sylvian fissure (closed, operculization complete) Cerebellum Medulla oblongata

Interhemispheric fissure Parietal operculum

Corpus callosum Frontal horn Cavum septi pellucidi

Sylvian fissure 3rd ventricle Temporal operculum

Insular cortex

Temporal lobe

External auditory meatus Semicircular canals

(Top) With advancing gestational age, the forebrain enlarges dramatically in comparison to the mid- and hindbrain. The telencephalon and diencephalon arise from the prosencephalon; between them, they give rise to most of the supratentorial brain. This graphic illustrates the relative proportions of the brain arising from the prosencephalon (green), metencephalon (yellow), and myelencephalon (light blue). The mesencephalic, midbrain structures are not visible. (Middle) With advancing gestational age, multiple secondary and tertiary gyri develop and the number and complexity of the cerebellar folia increases. (Bottom) Coronal T2WI in the 3rd trimester shows the appearance of a mature brain with well-developed surface sulci and gyri and operculized sylvian fissures.

880

Embryology and Anatomy of Brain

Parietal lobe

Corpus callosum

Frontal horn of lateral ventricle Head of caudate nucleus Sylvian fissure Thalamus

Cavum septi pellucidi Fornices 3rd ventricle echo

Temporal lobe

Obstetrics and Developmental Anatomy

CORPUS CALLOSUM, CINGULATE GYRUS

Cavum septi pellucidi

Genu of corpus callosum

Postcentral gyrus

Frontal horn of lateral ventricle

Cental sulcus Precentral gyrus

Body of corpus callosum Genu of corpus callosum

Cingulate gyrus

Rostrum of corpus callosum 3rd ventricle

Splenium of corpus callosum

Midbrain Cerebellar vermis Pons 4th ventricle Medulla oblongata

(Top) Vaginal US allows for exquisite anatomical assessment of the fetal brain. At 21 weeks, the corpus callosum is visible, forming the roof of the cavum septi pellucidi, which sits between the frontal horns of the lateral ventricles, above the 3rd ventricle. The cingulate gyrus has not yet developed. (Middle) Even though the corpus callosum is best seen on direct sagittal view, the genu can be identified on the standard axial image obtained at the level of the cavum septi pellucidi. The genu of the corpus callosum forms the curved part of the "anchor complex" in the normal anterior brain. The stem of the anchor is created by the interhemispheric fissure. This fetus is at 28weeks of gestation. (Bottom) If the fetus is in cephalic presentation, transvaginal US in the 3rd trimester produces exquisite images of normal brain anatomy. In this image, the cingulate gyrus is seen running parallel to the body of the corpus callosum, which is seen in its entirety.

881

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain CORPUS CALLOSUM, CINGULATE GYRUS

Cingulate gyrus Corpus callosum Frontal horn of lateral ventricle Cavum septi pellucidi "Open" sylvian fissure

Corpus callosum

Septi pellucidi (walls of cavum)

Interhemispheric fissure Cingulate sulcus Cingulate gyrus Cavum septi pellucidi

Frontal horn of lateral ventricle Insular cortex at base of "closed" sylvian fissure Temporal lobe

Tentorium cerebelli

Cerebellum Corpus callosum

Cingulate gyrus Cingulate gyrus

Pons Midbrain

Torcular

(Top) A complete neuroanatomic survey requires multiplanar imaging. In this coronal image at 24-weeks gestation, the brain surface is still relatively smooth, but the corpus callosum and cingulate gyrus are well seen. (Middle) Later in the 3rd trimester (this is a 31-week fetus), the ventricles appear relatively small compared to scans at 20 and 24 weeks. The corpus callosum is thicker and easier to see. The cingulate gyrus and sulcus are well developed. Note that operculization of the sylvian fissure is also complete in this fetus. (Bottom) MR was performed to evaluate focal dilation of the occipital horn and confirmed occipital lobe cortical dysplasia. This midline sagittal MR shows the normal curved corpus callosum with the cingulate gyrus wrapped around it. In agenesis of the corpus callosum, the cingulate gyrus does not form, and the medial surface gyri are oriented in a sunburst pattern called stenogyria.

882

Embryology and Anatomy of Brain

Parietooccipital sulcus

Interhemispheric fissure Lateral ventricle

Choroid plexus

Obstetrics and Developmental Anatomy

PARIETOOCCIPITAL SULCUS

Surface undulations

Cavum septi pellucidi

Parietooccipital sulcus

Interhemispheric fissure Lateral ventricle Precentral gyrus

Central sulcus

Postcentral gyrus

Superior sagittal sinus Central sulcus

Lateral ventricle Parietooccipital sulci Postcentral gyrus Central sulcus Interhemispheric fissure

Precentral gyrus Precentral sulcus

(Top) High axial US at 25-weeks, 3-days gestational age shows a well-developed parietooccipital sulcus. The surface of the brain is starting to develop some undulations as the convexity sulci begin to form. (Middle) By 28 weeks, the parietooccipital sulcus is well established, the surface of the brain has more pronounced undulations, and there are now some named convexity sulci and gyri visible. (Bottom) At 30 weeks, the parietooccipital sulcus is clearly visible on MR. The convexity sulci are more established with clear visibility of the central sulcus and adjacent gyri.

883

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain CALCARINE SULCUS

Tentorium

Calcarine sulci Falx cerebri Cerebellar hemisphere Occipital lobe

Occipital horn of lateral ventricle

Central sulcus Corpus callosum

Postcentral gyrus Parietooccipital sulcus

Calcarine sulcus

Torcular Herophili Cerebellar hemisphere

Cingulate gyrus Corpus callosum

Parietooccipital sulcus

3rd ventricle Midbrain

Calcarine sulcus

Pons Cisterna magna

4th ventricle

(Top) The calcarine sulcus develops on the medial surface of the occipital lobe branching from the parietooccipital sulcus. It is best seen on the coronal plane since the US beam is then perpendicular to the plane of the sulcus. In this composite image, note how smooth the medial occipital cortex is at 20 weeks. By 28 weeks, the calcarine sulcus is easily visible in the same fetus. (Middle) Sagittal MR nicely shows the orientation of the calcarine sulcus as a branch of the parietooccipital sulcus. (Bottom) At 37 weeks, the convexity sulci are well established. Note the relative decrease in the cerebrospinal fluid volume over the surface of the brain. This is normal, as is the relative decrease in size of the ventricular system compared to the size of the brain.

884

Embryology and Anatomy of Brain

Lateral ventricle Choroid plexus

Surface gyri

Obstetrics and Developmental Anatomy

CONVEXITY SULCI AND GYRI

Interhemispheric fissure Parietal lobe Convexity gyri

Closed sylvian fissure

Temporal lobe

Convexity sulci

Cingulate gyrus

Ocular globe Temporal horn of lateral ventricle

Calcarine sulcus

Cerebellar hemisphere

Middle ear

(Top) "Zoomed" view of an axial US in the 3rd trimester shows numerous convexity sulci and gyri in the far field. There is usually loss of detail in the near field due to reverberation of the beam at the ossified skull vault. It is important to examine the brain from multiple directions as well as in multiple planes if there is any concern for structural malformation. (Middle) Coronal US in the 3rd trimester in a fetus with osteogenesis imperfecta type III shows how an underossified skull vault allows for beautiful images of the brain. This is described as the brain too-well-seen sign. (Bottom) Parasagittal MR late in the 3rd trimester shows well-developed sulci and gyri over the convexity of the brain.

885

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Brain POSTERIOR FOSSA Thalamus Cerebellar hemisphere 3rd ventricle echo

Fornices

Cisterna magna

Sylvian fissure Cerebellar hemisphere

Cisterna magna Echogenic vermis

Choroid plexus in temporal horn of lateral ventricle Developing cerebellar folia

Temporal lobe with mature gyri

Vermis

Falx cerebelli

(Top) The posterior fossa structures are evaluated on an axial oblique view. For measurement of the nuchal fold and cisterna magna depth, the cavum septi pellucidi is used as a landmark to confirm the appropriate obliquity. This image is slightly underangled, so it includes the fornices. At 18 weeks, the hemispheres are round with relatively simple architecture. The vermis is visible between the hemispheres but does not differ markedly in echogenicity from them. (Middle) With advancing gestational age, the echogenicity of the vermis increases in relation to that of the hemispheres. The cerebellar folia become visible as bright, echogenic lines around the margin of the hemispheres. (Bottom) In the late 3rd trimester, the vermis is plainly seen. Note the increasing complexity of the temporal lobe gyri. The cisterna magna is stable in size throughout gestation. It should always measure < 10 mm from the posterior surface of the vermis to the inner table of the occipital bone.

886

Embryology and Anatomy of Brain

Corpus callosum

Cavum septi pellucidi Thalamus Primary fissure Midbrain

Pons

Medulla oblongata

Fastigial point

Obstetrics and Developmental Anatomy

POSTERIOR FOSSA

Cisterna magna

Massa intermedia Straight sinus 3rd ventricle Aqueduct of Sylvius

Pons

Primary fissure

Fastigial point

Cerebellar tonsil Foramen magnum

Cingulate gyrus

Cavum septi pellucidi

Culmen Primary fissure

3rd ventricle Aqueduct of Sylvius Lingula

Pons Nodulus

Straight sinus

Mega cisterna magna Fastigial point

(Top) This is a transabdominal scan of a 3rd-trimester fetus in breech presentation. Use of the metopic suture allows acquisition of a very nice sagittal image with superb detail of the posterior fossa structures. (Middle) This sagittal graphic illustrates normal anatomy and landmarks in the cerebellar vermis. The primary fissure divides the vermis into an anterior lobe (lingula, central, and culmen lobules) and a posterior lobe (declive, folium, tuber, pyramis, and uvula). The nodulus is referred to as the flocculonodular lobe. (Bottom) MR in a fetus with Gorlin syndrome (done at 37 weeks to exclude an oral cavity mass) shows normal vermian anatomy and location with a mega cisterna magna. Note the complexity of the convexity sulci as well as those on the medial surface of the brain at this gestational age.

887

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Spine

SPINAL CORD DEVELOPMENT Early Embryologic Events • 3rd week: Bilaminar germ disc evolves into trilaminar germ disc • Trilaminar germ disc ○ Ectoderm: Part of amniotic cavity ○ Mesoderm: Forms midline hollow central tube (notochordal process) – Extends along long axis of embryonic disc ○ Endoderm: Part of yolk sac cavity • Day 18: Notochord and remainder of intraembryonic mesoderm induce development of neural plate ○ Neural plate grows in length and width until day 21, when neurulation begins ○ Neural plate gives rise to most of central nervous system • Day 21: Hollow tube (notochordal process) evolves into solid cord (notochord)

Neurulation • Primary: Formation of cephalic spine to level of conus • Secondary: Formation of spine caudal to level of conus

Primary Neurulation • Occurs between days 18-28 ○ Formation of neural tube – Neural plate folds and elevates, forming trough (neural groove) – Fusion of resultant neural folds – Before complete fusion, neuroectoderm cells give rise to neural crest cells – Neural crest cells will later migrate to various parts of body and contribute to variety of tissues □ Autonomic nervous system, adrenal medulla, tissues of head and neck ○ Neural tube open at both ends temporarily – Communicates freely with amniotic fluid – Cranial and caudal openings of neural tube are called neuropores • Simultaneously, somites paramedian to notochord differentiate to form sclerotome cells ○ Precursors to vertebral column • Day 22-23 (4 weeks): Neural tube closure begins at occipitocervical level ○ Closure extends bidirectionally ○ Neural canal: Hollow center of neural tube later becomes – Ventricular system of brain – Central canal of spinal cord • Day 24: Complete cranial neuropore closure is achieved ○ Cranial end of neural tube will become brain • Day 26: Caudal neuropore closure ○ Caudal end of neural tube will become spinal cord • Closed neural tube is required for normal development of neural arch

Dysjunction • Final phase of primary neurulation • Neural tube separates from overlying ectoderm • Premature dysjunction

888

○ Perineural mesenchyme can access neural groove and ependymal lining → differentiates into fat ○ Prevents complete neural tube closure ○ May result in lipomatous malformation spectrum – Intradural lipoma – Lipomyelomeningocele: Subcutaneous fatty mass contiguous with neural placode/lipoma through posterior dysraphism □ Lipomyelomeningocele accounts for 20-56% of occult spinal dysraphism – Tethered cord may result □ Lipomatous malformation prevents normal ascent of cord as vertebral column elongates • Nondysjunction ○ Failure of dysjunction to occur ○ Ectodermal-neuroectodermal tract forms → prevents mesenchymal migration ○ Results in focal or widespread spinal dysraphism and open neural tube defects – Myelomeningocele: Open neural tube defect with meningocele and neural elements – Myelocystocele: Enlarged central spinal cord canal (inner cyst) protrudes through osseous dysraphic defect into dilated subarachnoid space (outer cyst) – Dorsal dermal sinus: Midline/paramedian stratified squamous epithelial-lined sinus tract • At end of primary neurulation, spine is formed from cephalic end of embryo through level of conus

Secondary Neurulation • Formation of spine caudal to level of conus • Days 28-48: Caudal neural tube forms via process referred to as secondary neurulation or canalization ○ Below or distal to posterior neuropore, undifferentiated cells form primitive streak or caudal cell mass – Once caudal neuropore closes, neural tissue is laid down as neural cord ○ Rostral neural tube extends into caudal eminence ○ Caudal cell mass forms vacuoles that fuse to form distal neural tube – Day 48: Transient ventriculus terminalis appears in future conus – These cells eventually form conus medullaris, cauda equina, and filum terminale • Terminal cord undergoes retrogressive differentiation ○ Occurs over ensuing gestational period and into early postnatal period • Secondary neurulation is less precise and leads to wide range of malformations ○ Tethered cord – Most common lesion in caudal cell mass dysplasia spectrum – Low-lying cord with thickened filum terminale ○ Caudal regression – Type 1: Foreshortened terminal vertebral column with high conus termination; severe associated anomalies – Type 2: Low-lying tethered cord with milder associated anomalies – Associated anomalies: Renal hypoplasia, pulmonary hypoplasia, anorectal malformations

Embryology and Anatomy of Spine

VERTEBRAL BODY DEVELOPMENT Cartilaginous Stage • Week 4: Notochord induces surrounding paraxial mesoderm derived from primitive streak ○ Forms paired somite blocks: Myotomes and sclerotomes ○ Myotomes form paraspinous muscles and skin covering ○ Sclerotomes divide into medial and lateral formations – Form vertebral body, intervertebral disc, meninges, spinal ligaments (medial), and posterior spinal elements (lateral) – Migrate from somites and surround adjacent neural tube and notochord – Ventral portion of sclerotome surrounds notochord and forms rudiment of vertebral body – Dorsal portion of sclerotome surrounds neural tube, forms precursors to neural arch, and condenses to produce spinous processes – Notochord will degenerate and involute where it is surrounded by vertebral body – Notochordal remnant between vertebra expands to form nucleus pulposus of intervertebral discs

○ Failure of notochord induction leads to incomplete division of neural plate → neurenteric cyst or diastematomyelia • Week 6: Cartilaginous stage of vertebral development occurs when chondrification centers appear ○ Chondrification centers appear in each mesenchymal vertebral body ○ 2 centers in each mesenchymal vertebral body fuse at end of embryonic period – Forms cartilaginous centrum ○ At same time, centers of vertebral arches fuse with each other and with centrum of vertebral body ○ Spinous and transverse processes develop from extensions of chondrification centers of vertebral arch

Ossification Stage

Obstetrics and Developmental Anatomy

– Associated spinal anomalies: Open dysraphism, segmentation and fusion anomalies, split cord malformations ○ Terminal myelocystocele – Hydromyelic cord terminating in skin-covered myelocystocele – Anorectal and visceral anomalies result in high morbidity ○ Anterior sacral meningocele – Large meningocele traversing enlarged sacral foramen produces presacral cystic mass ○ Sacrococcygeal teratoma – Primitive streak incompletely regresses and leaves caudal remnant – Occurs due to residual totipotent cell rests (Hensen node) → 3 cell layers with varying proportions of mature and immature elements • Spinal cord ascent ○ At 12-weeks gestational age, spinal cord extends entire length of developing spinal column ○ Vertebral column and dura elongate disproportionately compared to spinal cord – Conus medullaris ascends relative to vertebrae; filum terminale elongates ○ Nerve roots exit at levels of their respective foramen ○ Nerve roots then grow longer to accommodate this relative ascension of spinal cord – Forms cauda equina (sheath of nerve roots inferior to conus) • Conus should be at or above L3-L4 after 18-weeks gestation ○ This process extends into postnatal period – By 2 months of age, conus is located at adult level □ Final position is near L1-L2 interspace – Conus below L2 after 1st month of life, in term infant, is probably abnormal □ Needs evaluation for tethered cord

• Vertebral ossification begins during embryonic period and ends by age 25 • Vertebral body centrum forms from fusion of ventral and dorsal primary ossification center • At end of embryonic period, there are 3 primary ossification centers for each vertebra, including ○ Centrum ○ Each 1/2 of vertebral arch • Week 8: Ossification is visible ○ Ossification begins in lower thoracic and upper lumbar regions ○ Ossification progresses both cranial and caudal • Week 13: 3 ossification centers present in vertebrae C1-L3 • At birth, each vertebra consists of 3 bony parts connected by cartilage

Anomalies of Vertebral Formation and Segmentation • Abnormal vertebrae may replace normal vertebrae or be supernumerary • Failure of vertebral formation (total or partial) ○ Degree and location of vertebral formation failure predicts morphology – Unilateral chondral center defect and failure of ossification → hemivertebrae • Failure of vertebral segmentation ○ Block vertebrae with posterior elements fusion • More severe segmentation and fusion defect → increased incidence of concurrent malformations ○ Neuraxis anomalies: Tethered cord, abnormal alignment (kyphosis, scoliosis), dysraphism ○ Visceral organ anomalies

FAILURE OF NEURAL TUBE CLOSURE Clinical Implications • Failure of any part of neural tube to close disrupts development of nervous system and disrupts induction of overlying vertebral arches • Timing of event is such that other systems are also impacted ○ Look for associated visceral and anorectal malformations • Look for consequences of abnormal innervation ○ Abnormal lower extremity positioning

889

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Spine NEURAL TUBE EMBRYOLOGY

Neural groove Cutaneous ectoderm Neural plate

Neural crest cells Neural ectoderm Notochord Migration of neural crest cells

Primary neurulation

Fusion of neural folds Cranial neuropore

Notochord

Neural tube closure at occipitocervical region Cutaneous ectoderm Neural crest

Notochord

Center of neural tube

Cutaneous ectoderm

Neural crest Neural tube separates from ectoderm

Notochord

(Top) On day 18, the notochord and intraembryonic mesoderm induce development of the neural plate. The neural plate will grow in length and width until day 21, when primary neurulation begins. The neural plate folds and resultant neural folds fuse. (Bottom) Neural tube closure begins at 4 weeks at the occipitocervical region. The hollow center of the neural tube will become the central canal of the spinal cord and ventricular system of the brain. During primary neurulation, the neural tube separates from the overlying ectoderm in a process called dysjunction. Early dysjunction results in perineural mesenchyme access to the neural groove, which differentiates into fat (intradural lipoma); it may also prevent closure of the neural tube (lipomyelomeningocele). If dysjunction fails to occur, a spectrum of open neural defects results.

890

Embryology and Anatomy of Spine

Neural grove Cranial neuropore (unclosed cranial end) Neural fold

Body ectoderm

Obstetrics and Developmental Anatomy

NEURAL TUBE EMBRYOLOGY

Somites Neural tube closed and complete

Neural tube complete

Caudal neuropore (unclosed caudal end)

Neural tube Neural crest

Somite Sclerotome

Aorta and inferior vena cava

Notochord Dorsal mesentery

Embryo showing level of section

Caudal eminence (site of secondary neurulation)

Gut tube

Coelomic cavity

(Top) Graphic of neural tube closure as viewed from above is shown. At either end, there is an opening, the cranial and caudal neuropore, which are open to the amniotic fluid at this stage. The cranial neuropore closes by day 24 and will become the brain. The caudal end closes by day 26. (Bottom) Cross section of an embryo shows the neural tube, which has formed dorsal to the notochord. The neural tube will form the spinal cord, while the notochord largely degenerates with remnants contributing to the intervertebral discs. Neural crest cells migrate throughout the body and give rise to diverse tissues, including ganglia of the autonomic nervous system, adrenal medulla, and tissues of the head and neck. Somites form from the mesoderm and form multiple tissues. The medial somite is the sclerotome, which will form the vertebral column. Secondary neurulation begins at he caudal eminence and forms the conus medullaris, cauda equina, and filum terminale of the spinal cord.

891

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Spine FETAL SPINE

Ossified centrum of vertebral body Pedicle Transverse process Lamina Cartilaginous spinous process S1 ossification center Neural arch ossification center

Cartilaginous coccyx

Kidney Iliac crest Gluteal mm.

Intervertebral disc

Cartilaginous portion of vertebral body

Ossified portion of vertebral body (centrum)

Unossified sacrum and coccyx

Ossification centers S1 and S2

Unossified coccyx

Ossification centers S1-S4

(Top) Axial graphic shows the normal ossification centers within the developing vertebrae. The vertebral body and neural arch primary ossification centers (beige) are forming within the cartilaginous (blue) vertebral axis. Coronal graphic illustrates the normal appearance of the sacral ossification centers and cartilage. The sacrum and coccyx are the last portions of the vertebral column to ossify. (Middle) Coronal ultrasound of the lumbar spine at 22 weeks shows the ossification center (centrum) within the vertebral body; the remainder of the vertebral body is cartilaginous. (Bottom) Sagittal transabdominal ultrasound at 19.5 weeks (top) shows normal ossification and alignment of the lumbar spine. The coccyx and sacrum are unossified, which is an expected finding. At 22 weeks (bottom), there has been more complete ossification. Ossification should be complete by 25 weeks.

892

Embryology and Anatomy of Spine

Sagittal plane

Axial plane Laminae

Coronal plane

Scapula Transverse process Rib Vertebral body

Obstetrics and Developmental Anatomy

FETAL SPINE

Pedicles

Spinous processes

Conus medullaris

Cauda equina Central canal

Spinous processes Spinal cord Nerve roots Conus medullaris Central canal

Spinal cord Paraspinous musculature

Ossified portion of L1 vertebral body

L1 vertebral body L3-L4 intervertebral disc

Cartilaginous portion of vertebral body

L4-L5 disc

Cerebrospinal fluid

(Top) 3D ultrasound is ideal for evaluating the spine as all 3 planes can be evaluated with 1 acquisition. A 3D bone algorithm renders a skeletal view. (Middle) Sagittal graphic shows the normal appearance of the lumbar spinal column, conus medullaris, cauda equina, and central spinal canal. A correlative sagittal ultrasound of a fetal spine shows the normal hypoechoic appearance of the cord with a hyperechoic central canal. The lumbar portion of the spinal cord widens slightly compared to the thoracic portion. The normal cord ascends during gestation and should be at or above L3-L4 after 18 weeks and L1-L2 by 2 months of age. (Bottom) Sagittal T2 fetal MR (left) and newborn MR (right) show the neural axis. The ossified portion of the vertebral bodies is hypointense with hyperintense intervertebral discs. The spinal cord is surrounded by high-signal CSF. MR is an excellent tool for evaluating spinal dysraphism or cord abnormalities suspected on ultrasound.

893

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Face and Neck

GENERAL CONCEPTS Branchial Arches • Form during 4th and 5th weeks of embryonic development • 4 branchial arches appear as bars of mesenchymal tissue • Branchial arches are separated by clefts ○ Branchial grooves • Branchial arch and groove composition ○ External ectoderm ○ Internal endoderm ○ Central mesoderm ○ Migratory neural crest cells

Swellings Form on Branchial Arches • Prominences • Placodes ○ Migrate and fuse to form face • Failed migration and fusion leads to common facial anomalies

Lymphatics • • • •

Initial separate paired lymphatics Fuse with venous system Drain head, neck, upper limbs Failure to form or fuse leads to lymphatic disorders

NOSE, LIPS, AND PALATE Frontonasal Prominence • Anterior cranial bulge of tissue • Contains forebrain

Nasal Placodes • Develop on frontonasal prominence (FNP) ○ 5th week of embryonic life • Bilateral, oval-shaped thickenings • Eventually evaginate ○ Form nasal pits

Medial + Lateral Nasal Prominences • Develop on FNP ○ 6th week of embryonic life • Mesenchyme proliferation of nasal margins ○ Horseshoe-shaped elevations • Deepening of nasal pit forms nasal sacs ○ Nasal sacs grow dorsal and superior ○ Initial separation between oral and nasal cavity ○ Primitive choanae forms posterior to primary palate – Rupture of oronasal membrane • Medial nasal prominences merge ○ Fusion of midline medial prominence ○ Form intermaxillary segment – Becomes philtrum of lip

Maxillary Prominences • 5th-8th week of embryonic life • Start as paired swellings lateral to primitive mouth ○ Enlarge and grow rapidly toward midline • Fuse with lateral nasal prominences ○ Lateral margins of philtrum – Just below nostrils 894

Palate • 6th-12th week of embryonic life • Forms from 2 primordia • Primary palate ○ Innermost part of intermaxillary segment – From medial nasal prominence ○ Wedge-shaped segment ○ Eventual small section of adult hard palate – Anterior maxilla to incisor foramen – Includes incisor teeth • Secondary palate ○ Primordia of most of hard palate and soft palate ○ Develops from maxillary prominences – Lateral palatine shelves ○ Palatine shelves grow toward midline and superiorly – Over developing tongue ○ Lateral palate shelves fuse – Medially with each other – Anteriorly with primary palate – Superiorly with nasal septum ○ Neural crest cells concurrently ossify palate – Posterior portion is without bone (soft palate)

MANDIBLE AND EARS Mandible • 4th-8th week of embryonic life • Jaw is 1st part of face to form • Paired mandibular prominences ○ Caudal boundary of primitive mouth ○ Fuse medially by end of 4th week • Part of Meckel cartilage migrates ○ Forms incus and malleus of middle ear

Ears • • • •

4th-8th week of embryonic life Inner ear arises from hindbrain Middle ear arises from 1st pharyngeal pouch External ear from 1st branchial groove ○ Inferior and dorsal to mandibular prominence – Early ears are located in upper part of future neck – Migrate lateral and superior as mandible develops ○ Auricle from 6 swellings (hillocks)

EYES Lens Placode • Forms on FNP during 3rd week • Induced by optic vesicles ○ From forebrain ○ Becomes lens vesicle and final lens of eye • Forms optic cups ○ Large at first, then invaginate

Orbits • From mesenchyme that encircles optic vesicle ○ Neural crest cells • Walls of orbit from 7 skull bones ○ Superiorly: Frontal bone ○ Inferiorly: Maxilla, zygomatic ○ Medially: Frontal, lacrimal, maxilla

Embryology and Anatomy of Face and Neck

LYMPHATICS Lymph Sacs • Begin to develop at end of 5th week ○ 2 weeks after cardiovascular system • Develop alongside vessels • Lymph sacs form from fusion/dilatation of adjacent mesenchymal spaces • 6 primary lymph sacs ○ Paired jugular lymph sacs – Subclavian and internal jugular vein junction – Drain head, neck, thorax, upper extremities ○ Cisterna chyli – Lymph sac below diaphragm – Along posterior abdominal wall ○ Retroperitoneal (mesenteric) lymph sac – Root of mesentery – Posterior abdominal wall, anterior to cisterna chyli ○ Paired iliac lymph sacs – Junction of iliac and posterior cardinal veins – Drain abdominal wall, pelvis, lower extremity – Join cisterna chyli • Lymph sacs eventually become groups of lymph nodes ○ Exception is superior cisternal chyli • Lymphatic vessels grow out from lymph sacs and make connections with venous system

Thoracic Duct • 2 channels connect jugular sacs with cisterna chyli ○ Right and left thoracic ducts • Anastomosis and attrition occurs between paired ducts • Final thoracic duct anatomy ○ Superior part from left duct ○ Central part from anastomosis ○ Caudal part from right duct • Variations of thoracic duct anatomy common

EMBRYOLOGY OF COMMON ANOMALIES Cleft Lip and Palate • Isolated cleft lip ○ Involves lip ± primary palate – Incisive foramen is boundary of primary and secondary palate – Secondary palate intact ○ Maxillary prominence fails to unite with nasal prominence – Results in persistent labial groove ○ Rare cases – Median isolated cleft lip – Bilateral isolated cleft lip • Cleft palate ± cleft lip ○ Failure of lateral palatine processes fusion – Nonunion with each other – Nonunion with nasal septum – Most often involves lip and primary and secondary palate ○ Isolated cleft palate (intact lip and primary palate) – Posterior to incisive foramen

• Rare facial clefts ○ Median cleft of mandible ○ Lateral or transverse facial cleft (from mouth toward ear) ○ Oblique facial cleft (upper lip to medial margin of orbit)

Eye Anomalies • Hypertelorism and hypotelorism ○ Optic migration follows forebrain migration – Holoprosencephaly: Hypotelorism, cyclopia ○ Associated with craniofacial dysostosis – Hypertelorism • Absent or small eye/orbit ○ Failure of optic vesicle or lens placode to form

Hypognathia • Insufficient 1st branchial arch ○ From poor neural crest cell migration • Syndromes ○ Pierre Robin syndrome – Hypoplasia of mandible – Cleft palate + ear anomalies ○ Treacher Collins syndrome – Mandibulofacial dysostosis – Eye and ear anomalies

Obstetrics and Developmental Anatomy

○ Lateral: Zygomatic, frontal

Ear Anomalies • Low-set ears ○ Ear migration follows mandible development – Small chin associated with low-set ears • Abnormal hillock development ○ Auricular appendages (tags) ○ Ear duplication ○ Anotia (absent ear), microtia (small ear)

Nose and Mouth Anomalies • Congenital microstomia (small mouth) ○ Excessive merging of mesenchymal masses • Absent nose ○ Paired nasal placodes do not form • Single nostril ○ Only 1 nasal placode forms • Bifid nose ○ Medial nasal prominences do not merge completely

Lymphangioma • Dilated primitive lymphatic channels ○ Diffuse congenital lymphedema ○ Focal cystic mass • Cystic hygroma ○ Failed jugular sac leads to venous connection ○ Primary fluid collection in dorsal and lateral neck – Multiseptated fluid ○ Associated with hydrops fetalis and aneuploidy – Turner syndrome most common – Trisomy 21 is 2nd most common • Body lymphangioma ○ Sites – Axillary (most common) – Intraperitoneal, retroperitoneal – Extremities ○ Often large, infiltrative cystic mass 895

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Face and Neck EMBRYOLOGY OF FACE AND PALATE

Nasal pit on nasal plate Frontonasal prominence

Stomodeum (primitive oral cavity)

Maxillary prominence Mandibular prominence

2nd pharyngeal arch

Nasal pit

Medial nasal process

Nasolacrimal groove Lateral nasal process Eye Maxillary prominence Mandibular prominence

Nostril

Primary palate

Upper lip

Secondary palate (palatine shelf)

(Top) Graphic shows a coronal view of a 5-week embryo. The face forms from 5 primordia that appear in the 4th week (frontonasal prominence, 2 maxillary prominences, and 2 mandibular prominences). By the 5th week, the mandibular prominences have fused. Nasal pits form on a pair of ectodermal thickenings, the nasal plates. (Middle) Graphic shows a coronal view of a 6-week embryo. Invagination of the nasal pits has occurred. Medial nasal processes will fuse to form an intermaxillary process and, subsequently, the upper lip philtrum. In addition, the maxillary prominences will fuse with the intermaxillary process to form an intact upper lip. (Bottom) Graphic shows an axial view of the palate at 7-8 weeks. The primary palate arises dorsally from the intermaxillary process, and the secondary palate originates from the maxillary prominence. Complete fusion occurs by the 10th week.

896

Embryology and Anatomy of Face and Neck

Lateral nasal process

Medial nasal process Maxillary prominence

Eye (lens vesicle) 6 auricular hillocks

Obstetrics and Developmental Anatomy

EMBRYOLOGY OF FACE AND EAR

1st branchial groove

Frontonasal prominence primordia

Maxillary prominence primordia

Eyelids

Auricle

Mandibular prominence primordia

Helix Medial epicanthus of eye

Tragus Lobule

Intermaxillary segment fusion forms philtrum of upper lip

(Top) Graphic of a 5-week embryo profile shows the lateral and medial nasal processes, not yet fused with the maxillary prominence. Arising from the 1st and 2nd pharyngeal arches, the auricular hillocks of the external ear flank the 1st branchial groove. (Middle) Graphic of a 10-week embryo profile shows the development of eyelids and the external ear. The ear position is medial and low at this time. As the mandible grows, the ear migrates superiorly. (Bottom) Graphic of a 14-week fetus profile shows that the philtrum of the lip has formed from fusion between the paired medial nasal processes. The philtrum and maxillary prominences have also fused. The ear is now at its final location with the top of the helix at the same level as the medial epicanthus of the eye.

897

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Face and Neck EYES Nasal bones

Lens

Orbit

Superior orbit

Lens

Lens Nasal bone

Central hyaloid a.

Eye lens

Midbrain pons

(Top) Transvaginal axial ultrasound through the orbits of a 12-week fetus shows paired nasal bones and normal-sized orbits. The lens of the eye can be seen even at this early gestational age. (Middle) Coronal transvaginal ultrasound of a 13-week fetus shows the frontal bones and nasal bones contributing to the superior and medial borders of the bony orbit. The eyes and lens are once again seen very well. (Bottom) Axial ultrasound through the eyes in an early 2nd-trimester fetus shows the normal central hyaloid artery, which is located within the hyaloid canal. This artery supplies nutrients to the developing lens and is a normal finding at this time, usually regressing during the 3rd trimester.

898

Embryology and Anatomy of Face and Neck

Lens

Interocular distance

Binocular distance

Orbital diameter

Obstetrics and Developmental Anatomy

EYES

Medial epicanthus

Open eyelids

(Top) Axial T2WI MR of a late 2nd-trimester fetus shows the orbits. MR or ultrasound can be used to measure the globe diameter, interocular distance, and binocular distance. The lens of the eye is low signal on MR. (Middle) 3D ultrasound of a 3rd-trimester fetal face shows the eyes, nose, and lips. The interocular distance and the medial epicanthus of the eyes are seen well. (Bottom) 3D ultrasound of a fetal profile shows open eyes. In the 3rd trimester, it is common to see the eyes open and close. In addition, globe movement is also commonly seen with real-time imaging.

899

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Face and Neck NOSE

Nasal bone Tip of nose skin Frontal bone Maxilla

Mandible

Paired frontal bones

Nasal bones Frontal process of maxilla

Frontal process of maxilla

Palate Mandible

Medial epicanthus of eye

Top and bottom of ear helix

(Top) Sagittal ultrasound of a 12-week fetus shows a normal nasal bone. The echogenic nasal bone is as bright as the frontal bone, and it is seen separately from the nasal skin. (Middle) 3D ultrasound with skeletal reconstruction of a 13-week fetus shows the retronasal triangle view comprised of the paired nasal bones superiorly, the frontal process of the maxilla laterally, and the inferior primary palate. (Bottom) 3D ultrasound profile view that includes the nose, eye, and ear shows normal relationships. The top of the helix should be at the same height as the medial epicanthus of the eye.

900

Embryology and Anatomy of Face and Neck

Nostrils

Upper lip

Lower lip

Obstetrics and Developmental Anatomy

LIPS AND PALATE

Nares

Philtrum

Secondary palate Fluid in hypopharynx

Tongue

(Top) Coronal ultrasound through the nose and lips shows the nostrils and intact upper lip. This view is considered standard for anatomy scans. (Middle) 3D ultrasound with soft tissue reconstruction shows the normal rounded nares of the nose and the intact philtrum of the upper lip. (Bottom) T2WI MR of a 30-week fetus shows an intact secondary palate. A sliver of high-signal fluid in the mouth, superior to the tongue, provides excellent contrast, allowing for visualization of the palate. The fluid-filled hypopharynx is also seen extending down to the upper trachea.

901

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Face and Neck SKULL AND FACIAL BONES

Chondrocranium

Viscerocranium

Membranous neurocranium

Chondrocranium

Membranous viscerocranium Pharyngeal arches

Occipital bone Frontal bone Sphenoid Nasal bone Zygomatic arch Maxilla Mandible

Squama of occipital bone Squama of temporal bone Styloid process

(Top) Graphic shows the cartilaginous skeleton of the embryonic head. Purple represents the developing chondrocranium; blue represents the developing viscerocranium of the pharyngeal arches. The chondrocranium arises from the notochord and is the forerunner of the skull base. The viscerocranium, derived from the pharyngeal arches, gives rise to the facial bones. (Middle) The chondrocranium and portions of pharyngeal arches ossify as the membranous neurocranium (protective case around the brain) and the membranous viscerocranium develop. (Bottom) The final development of cranial bones from chondrocranium, pharyngeal arches, membranous viscerocranium, and membranous neurocranium is shown.

902

Embryology and Anatomy of Face and Neck

Coronal suture

Parietal bone

Frontal bone

Sphenoidal fontanelle

Squamosal suture

Zygomatic bone

Obstetrics and Developmental Anatomy

SKULL AND SUTURES

Metopic suture Nasal bone

Maxilla Zygomatic or malar bone

Mandibular symphysis

Anterior fontanelle

Metopic suture

(Top) 3D ultrasound of an 18-week fetus profile shows normal skull and suture anatomy. (Middle) Coronal 3D ultrasound with skeletal reconstruction of a 20-week fetus shows normal skull bones and sutures. (Bottom) 3D ultrasound of an early 3rd-trimester fetus shows the anterior fontanelle and metopic suture.

903

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Face and Neck LYMPHATIC SYSTEM EMBRYOLOGY

Jugular lymph sacs

Right and left thoracic ducts

Retroperitoneal lymph sac Cisterna chyli

Iliac lymph sacs

Right and left internal jugular vv.

Jugular lymphatic drainage sites

Subclavian v.

Superior vena cava

Thoracic duct Right and left thoracic ducts Cisterna chyli

Cisterna chyli

(Top) Graphic of a 6- to 7-week embryo shows lymph sacs that collect lymph fluid before venous connections are established. Lower extremity and body lymph fluid drain into external and internal iliac veins. (Bottom) Graphic of the lymphatic system at 7 weeks (left) and 17 weeks (right) shows that, originally, there are paired thoracic ducts. In most embryos, the caudal left and cranial right ducts atrophy, resulting in a thoracic duct that crosses the midline. Upper body lymphatic drainage occurs mostly at the venous connection near the jugular-subclavian vein junction.

904

Embryology and Anatomy of Face and Neck

Distended lymphatic sacs Distended lymphatic sacs

Obstetrics and Developmental Anatomy

CYSTIC HYGROMA

Increased nuchal translucency

Septations

Front of head

Arm Dorsal neck cystic hygroma

Front of body

Legs

(Top) Graphic of cystic hygroma shows massively distended jugular lymph sacs secondary to failure of establishment of venous connections at the jugular drainage site. (Middle) Sagittal ultrasound of a 12-week fetus shows cystic hygroma. The nuchal translucency is markedly increased and contains septations. (Bottom) 3D ultrasound of a 13-week fetus shows posterior neck cystic hygroma. This fetus was found to have Turner syndrome.

905

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Chest

GENERAL CONCEPTS Overview of Lung Development • Larynx and trachea ○ Origin of primitive larynx from laryngotracheal groove ○ Separation of primitive trachea from foregut and developing esophagus • Bronchi ○ Tracheal bud branches into 2 primitive bronchial buds ○ Bronchial buds are precursors of bilateral main bronchi • Lungs ○ Sequential branching of primitive bronchi ○ Formation of distinct pulmonary lobes ○ Formation of distinct pulmonary segments • Distal airways and lung parenchyma ○ Interaction of endodermal and mesodermal elements allow normal lung development ○ Continued branching of primitive airways ○ Progressive vascularization of surrounding mesenchyme ○ Development of alveolar-capillary interface ○ Postnatal airway development and maturation • Pleural development ○ Developing lungs protrude into coelomic cavity ○ Separation of pleural and pericardial cavities ○ Pleural investment of lungs within bilateral hemithoraces • 5 developmental stages ○ Embryonic stage ○ Pseudoglandular stage ○ Canalicular stage ○ Saccular stage ○ Alveolar stage

EMBRYONIC STAGE (26 DAYS TO 6 WEEKS) Laryngotracheal Groove • Develops 26-28 days after fertilization • Arises caudal to primitive pharynx and 4th pair of pharyngeal pouches • Longitudinal growth

Primary Bronchial Buds and Branches • Branching of primitive tracheal bud into right and left branches (5th week after fertilization) ○ Right bronchial bud: Larger and vertically oriented ○ Left bronchial bud: Smaller and horizontally oriented • Branching of primary bronchial buds into 2 primitive lobar bronchi ○ Right superior lobar bronchus → right upper lobe bronchus ○ Right inferior lobar bronchus → primitive bronchus intermedius – Right middle lobe bronchus – Right lower lobe bronchus ○ Left superior lobar bronchus → left upper lobe bronchus ○ Left inferior lobar bronchus → left lower lobe bronchus • Branching of primitive lobar bronchi into primitive segmental bronchi

PSEUDOGLANDULAR STAGE (6-16 WEEKS) Important Events • Formation of all major airway elements ○ Bronchial development complete to level of terminal bronchioles • All bronchopulmonary segments formed by 7 weeks after fertilization

Microscopic Morphology • Gland-like appearance of lung • Formation of tracheobronchial cartilages, mucus glands, and cilia by 13 weeks after fertilization • Primitive airways lined by endodermal-derived columnar epithelium • Primitive airways surrounded by mesodermal-derived mesenchymal tissue • Absent alveolar-capillary interface

Physiologic Implications • Respiration not possible • No possibility of extrauterine survival

Respiratory Diverticulum or Lung Bud • Develops 4 weeks after fertilization • Pouch-like outgrowth from caudal aspect of laryngotracheal groove • Caudal growth • Invested in mesodermal-derived splanchnic mesenchyme

Tracheal Bud • Globular enlargement of distal lung bud • Caudal growth from primordial pharynx • Proximal communication with foregut through primordial laryngeal inlet

Tracheoesophageal Septum • Longitudinal tracheoesophageal folds form on either side of developing tracheal bud • Medial growth of bilateral tracheoesophageal folds • Formation of tracheoesophageal septum from midline fusion of tracheoesophageal folds • Separation of primitive trachea from developing esophagus

CANALICULAR STAGE (16-28 WEEKS) Important Events • Continued vascularization of lung • Continued development of primitive airways ○ Terminal bronchioles give rise to 2 or more respiratory bronchioles ○ Respiratory bronchioles give rise to 3-6 alveolar ducts ○ Development of small number of terminal saccules • Lamellar inclusions within type 2 pneumocytes in terminal saccules with potential for surfactant production

Microscopic Morphology • • • •

Continued enlargement of primitive airway lumina Continued thinning of airway epithelium Epithelial differentiation into type 1 and type 2 cells Airways separated by reduced but significant mesenchymal tissue

Physiologic Implications • Limited surfactant production

906

Embryology and Anatomy of Chest

SACCULAR STAGE (28-36 WEEKS) Important Events • Development of increasing numbers of terminal saccules • Establishment of primitive alveolar-capillary interface • Increased potential for surfactant production

Microscopic Morphology • • • •

Continued airway differentiation Continued thinning of airway epithelium Some capillaries abut and bulge into developing alveoli Terminal sacs begin to approach morphology of adult alveoli

Physiologic Implications • Respiration with adequate gas exchange is possible • Survival of premature neonates with appropriate life support

ALVEOLAR STAGE (36 WEEKS TO 8 YEARS) Important Events • Continued development of distal airways with primordial alveoli forming along respiratory bronchioles and terminal saccules • Development of thin alveolar-capillary membrane • Postnatal lung development ○ 24 million terminal sacs and alveoli present at birth compared to 300 million in adult lungs ○ 5x increase of alveolar numbers within 1st year of life ○ Formation of 95% of adult alveoli by 8 years of age

Microscopic Morphology • Continued thinning of epithelial lining of terminal sacs • Formation of primordial alveoli • Adjacent capillaries bulge into terminal saccules

Circulatory Requirements • Circulation affects pulmonary development ○ Pulmonary arterial development along developing airways ○ Vasculogenesis within primitive mesenchyme to form capillary network ○ Pulmonary vein and lymphatic development along segmental boundaries • Right-sided obstructive lesions decrease pulmonary blood flow with subsequent poor lung development

Diaphragm Development • Complex embryonic origin with 4 embryologic structures ○ Septum transversum: Forms most of central tendon ○ Pleuroperitoneal membranes: Bulk of diaphragm muscle, innervated by phrenic nerve ○ Paraxial mesoderm of body wall: Outer rim of diaphragmatic muscle ○ Esophageal mesenchyme: Condenses to form diaphragmatic crura

Thymus • Arises from 3rd pharyngeal pouch • Between 4th-7th week, thymic primordia migrate to chest ○ Posterior to sternum in superior mediastinum ○ Fuse to form bilobed gland • Once formed, lymphocytes infiltrate gland • Large and highly active in perinatal period ○ Continues to grow until puberty and then involutes in adulthood • May be confused with chest mass ○ Look for thy-box to confirm it is thymus – Thymus is flanked by internal mammary arteries, branches of subclavian arteries – Color Doppler of superior mediastinum, at level of 3vessel view, shows thymus between internal mammary arteries creating box appearance

NEONATAL LUNG

Physiologic Implications

1st Breath

• Presence of nearly mature alveolar-capillary interface • Adequate surfactant production • Respiration possible without external support

• Diaphragmatic contraction • Pulmonary vascular changes ○ Fluid-filled lungs result in high-resistance pulmonary circulation – Small portion of cardiac output goes to lungs prior to birth ○ Pulmonary expansion with 1st breath – Vasodilatation – Increased pulmonary blood flow – Clearance of fetal lung fluid via lymphatics and capillaries • Role of surfactant ○ Alveolar expansion results in surfactant discharge by type 2 pneumocytes ○ Decreased surface tension of remaining intraalveolar fluid ○ Increased surfactant activity with decreased surface area ○ Prevention of alveolar collapse during expiration

OTHER DEVELOPMENTAL REQUIREMENTS Volume Requirements • Adequate intrathoracic volume required for normal pulmonary development • Intrathoracic masses (especially diaphragmatic hernia) and chest wall abnormalities (e.g., skeletal dysplasias) restrict space for lung growth

Amniotic Fluid Requirements • Amniotic fluid and fetal breathing required for normal lung development • Oligohydramnios has severe adverse effect on lung development ○ Fetal compression causes decreased space for lung growth ○ Restriction of breathing movements with efflux of lung fluid into amniotic space

Obstetrics and Developmental Anatomy

• Respiration is possible in late canalicular stage • Possibility of neonatal survival with intensive care and appropriate life support

907

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Chest LUNG DEVELOPMENT

Primordial heart

Tracheal bud (4-5 weeks)

Primitive lung (5-6 weeks)

Branchial arches

Respiratory diverticulum (4 weeks)

Foregut-derived esophagus

Primitive mesenchyme Plane of section Tracheoesophageal fold Tracheal bud

Tracheal bud Primitive airway epithelium

Foregut

Plane of section

Primitive esophagus Midline fusion of tracheoesophageal folds Primitive trachea

Primary bronchial buds

Foregut

(Top) Graphic shows the development of the primitive lung. The respiratory diverticulum arises from the laryngotracheal groove near the primordial esophagus caudal to the 4th pharyngeal pouches. The sequential evolution of the respiratory diverticulum to the tracheal bud and the primitive lung is shown. Note the close relationship of the developing tracheobronchial tree and lungs to the primitive esophagus. (Middle) Graphic shows the tracheal bud, a ventral outpouching of the foregut surrounded by mesodermal-derived mesenchyme and lined by endodermal-derived epithelium. The axial plane of section (right) shows communication between the tracheal bud and the foregut. The formation of bilateral longitudinal tracheoesophageal folds is shown. (Bottom) Graphic shows vertical development of the primary bronchial buds. The tracheoesophageal folds fuse in the midline to separate the trachea from the esophagus.

908

Embryology and Anatomy of Chest

Endodermal-derived epithelium

Mesodermal-derived mesenchyme

Primary bronchial buds

Foregut

Obstetrics and Developmental Anatomy

LUNG DEVELOPMENT

Left superior bronchial bud Right superior bronchial bud

Right inferior bronchial bud

Left inferior bronchial bud

Primitive mesenchyme Foregut

Right superior bronchial bud: Right upper lobe bronchus Right inferior bronchial bud: Bronchus intermedius

Primitive mesenchyme

Left superior bronchial bud: Left upper lobe bronchus Left inferior bronchial bud: Left lower lobe bronchus

Foregut

(Top) Graphic shows the development and morphology of the bronchial buds as they invaginate into the primitive mesenchyme. The bronchial buds are the precursors of the main bronchi. Note that the right bronchial bud is vertically oriented, and the left follows a more horizontal course. (Middle) Graphic shows the tracheobronchial tree at 28 days of gestation as the right and left bronchial buds begin to divide. The developing tracheobronchial tree is surrounded by primitive mesenchyme. (Bottom) Graphic shows the developing tracheobronchial tree at 42 days of gestation with continued elongation and branching of the bronchial buds to form rudimentary lobar bronchi. Further growth and branching of the distal primitive airway forms rudimentary segmental bronchi. The rudimentary bronchus intermedius gives rise to primitive right middle and right lower lobe bronchi.

909

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Chest LUNG DEVELOPMENT

Right upper lobe

Left upper lobe

Right middle lobe

Right lower lobe

Left lower lobe

Trachea

Left upper lobe bronchial branches Right upper lobe bronchial branches

Right middle lobe bronchial branches Left lower lobe bronchial branches Right lower lobe bronchial branches

Mesenchymal connective tissue

Airway epithelium

Capillaries

Developing airway

(Top) Graphic shows tracheobronchial development at 56 days of gestation with continued branching of the primitive airways and rudimentary lung lobes. (Middle) Graphic shows tracheobronchial development at ~ 10 weeks of gestation. Note the airway differentiation into the rudimentary lobar bronchial branches (shown in different colors) and segmental bronchial branches. Note that the green and red bronchial branches represent different portions of the primitive left upper lobe. Recognizable lung lobes are present. The interaction between the primitive tracheobronchial tree and the surrounding primitive mesenchyme induces the development of lung parenchyma. (Bottom) Graphic shows the primitive airway in the pseudoglandular stage of development (6-16 weeks). The airways are blind-ending tubules. There is no alveolar-capillary interface as connective tissue separates the thick-walled primitive airway from the pulmonary capillaries. Respiration is not possible.

910

Embryology and Anatomy of Chest

Mesenchymal connective tissue

Airway epithelium

Capillaries

Developing airway

Obstetrics and Developmental Anatomy

LUNG DEVELOPMENT

Mesenchymal connective tissue

Airway epithelium

Developing airway

Capillaries

Mesenchymal connective tissue

Airway epithelium

Developing airway Capillaries

(Top) Graphic of the canalicular stage of development (16-28 weeks) shows the airway lumen has enlarged, and the epithelium has thinned. There is an increased number of vessels within the primitive mesenchyme, some of which abut the airway wall. Respiration is possible at the end of this stage of lung development, but these infants require intensive care for survival. (Middle) Graphic of the saccular stage of lung development (28-36 weeks) shows the airway lumen continuing to enlarge. More numerous capillaries abut the wall, and some bulge into the lumen. Respiration is possible, and many infants born at this stage of pulmonary development survive with proper medical management and support. (Bottom) Graphic of the alveolar stage of pulmonary development (36 weeks to 8 years) shows continued airway enlargement with less surrounding connective tissue. The airway epithelium is thin, and many capillaries bulge into the airway lumen establishing mature alveolar-capillary interfaces. Airway development continues after birth and into childhood.

911

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Chest FETAL LUNGS

Liver

Diaphragm

Right lung Descending thoracic aorta Left lung

Liver Ribs

Diaphragm Lung

Trachea Right mainstem bronchus Right lung

Liver

Left mainstem bronchus Left lung

Stomach Small bowel

(Top) Coronal ultrasound of a 3rd trimester fetus shows the lungs are homogeneous in echotexture and hyperechoic when compared to the liver. In the 1st trimester, the lungs and liver are similar in echogenicity, but the lungs become more hyperechoic as alveolar development progresses, creating more acoustic interfaces. (Middle) Sagittal ultrasound of the fetal chest shows the diaphragm, which is a thin, hypoechoic, muscular band. The diaphragm is best evaluated in this projection to ensure it has been seen in its entirety. (Bottom) Coronal T2WI MR of the chest shows the relatively high signal intensity lungs compared to the low signal intensity liver. Fluidfilled structures, including the trachea, bronchi, stomach, and small bowel, are all very high signal and easily distinguished on T2weighted sequences.

912

Embryology and Anatomy of Chest

Thymus

Liver Lung Diaphragm Posterior ribs

Obstetrics and Developmental Anatomy

FETAL THYMUS

Thy-box Right internal mammary a. and v. Left internal mammary a. Thymus

Thymus

Lung

Lung

Spinal canal

(Top) Sagittal ultrasound of the fetal chest in the 3rd trimester shows the fetal thymus. It is hypoechoic when compared to the lungs and has a slightly reticular appearance. The thymus is often quite prominent in a fetus and should not be confused with a lung or mediastinal mass. (Middle) Axial color Doppler of the superior mediastinum at the top of the outflow tracts shows the thy-box. The internal mammary arteries, branches of the subclavian arteries, flank the thymus, creating a box appearance. Thymic measurements can be taken if there is a suspicion for hypoplasia, as in 22q11 deletion syndrome. (Bottom) Axial T2WI MR at ~ the same level shows the thymus is hypointense when compared to the lungs.

913

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Cardiovascular System

EMBRYOLOGY OVERVIEW Heart Fields • Heart formed from 2 fields; primary and secondary heart fields • Primary heart field (cardiac crescent) ○ Patterned at 16-18 days and is dependent on normal signals that establish laterality ○ Cardiac progenitor cells from splanchnic mesoderm ○ Angiogenic cell clusters create endocardial tubes ○ Body folding brings tubes ventral and midline ○ Tubes fuse in midline to create primitive heart tube • Secondary heart field ○ Contributes to cardiac development at 22-28 days ○ Cardiac progenitor cells in pharyngeal mesoderm help develop arterial/venous poles of heart tube – Outflow tract, right ventricle (RV), atria – Contribute to myocardium, smooth muscle ○ Signaling critical in differentiation, elongation, and looping

Primitive Heart Tube • Composed of endothelial cells surrounded by myoepicardial mantle, cardiac jelly • From caudal → cranial (or venous → arterial) pole ○ Sinus venosus, primitive atria, primitive ventricle, bulbus cordis, truncus arteriosus – Aortic arch vessels sprout from arterial pole – Truncus arteriosus divides into ascending aorta, pulmonary artery (PA) • Heart tube begins contracting around 4th week • Effective circulation in 5th week

Looping • Differential gene expression controlling sidedness detected as early as cardiogenic field stage • Differential growth causes heart tube to fold into U shape ○ Creates typical heart shape by 28 days • Venous pole remains anchored dorsally • Atria migrate cephalad • Arterial end bends rightward and ventral

Septation • Occurs from 30- to 40-days gestation • Atria ○ Septum primum grows down from above to meet endocardial cushions – Fusion with endocardial cushions closes ostium primum – Apoptosis in center of septum primum creates ostium secundum ○ Septum secundum grows to right of septum primum ○ Septum secundum fenestrates to create foramen ovale • Atrioventricular canal ○ Initially directed toward primitive ventricle [developing left ventricle (LV)] ○ By 5th week, bulboventricular flange divides ventricles equally ○ Anterior, posterior, and lateral endocardial cushions grow inward – Cells derived from endocardium or neural crest 914

○ Endocardial cushion fusion creates mitral valves (MVs)/tricuspid valves (TVs), separates atria from ventricles • Ventricles ○ Separated by muscular septum; grows as ventricles grow downward ○ Membranous septum extends from inferior endocardial cushions ○ Outflow septum extends from outflow tract cushions in bulbus cordis • Great arteries ○ Swellings in conus and truncus create endocardial ridges ○ Endocardial ridges grow to separate great arteries in 7th week ○ Spiraling of great arteries results from – Inferior/superior orientation of truncal ridges – Left/right orientation of conal ridges – Secondary heart field directs neural crest cells through signaling pathways

ARTERIAL EMBRYOLOGY Aortic Arches • Paired dorsal aortae develop in mesenchyme on either side of notochord ○ Notochord is primitive axis of developing body • Heart tube rotates into chest as cranial end of embryo bends • Dorsal aortae follow in loop → 1st aortic arch • Series of other arches develop and regress → adult arterial anatomy ○ 6 paired arches are blood supply for pharyngeal arches, connect to ipsilateral dorsal aorta – Right dorsal aorta, 1st, 2nd, and 5th arches regress – 3rd arches → internal carotid arteries ○ Left 4th arch → aortic arch ○ Right 4th arch → right subclavian artery ○ Left 6th arch → ductus arteriosus, left PA ○ Right 6th arch → right PA • Paired dorsal aortae fuse from 4th thoracic to 4th lumbar vertebrae → single midline aorta

Conotruncus • Conotruncus constitutes outflow tract of primitive heart tube • Endocardial ridge growth separates truncus arteriosus into ascending aorta and PA ○ Same process creates aortic and pulmonary valves • Aortic valve typically rightward of and posterior to pulmonary valve • Initially 2 subarterial coni ○ Subpulmonary conus persists ○ Subaortic conus resorbs – Fibrous continuity between aortic and MVs – Aorta "anchored" into LV □ Gooseneck deformity in atrioventricular canal due to lack of septal-aortic continuity

Pulmonary Artery • Anterior and to left of aortic root

Embryology and Anatomy of Cardiovascular System

VENOUS EMBRYOLOGY Sinus Venosus • Has right and left horns • Each horn receives vitelline, umbilical, and cardinal veins • With differential growth, sinus entrance shifts rightward into developing right atrium (RA)

Systemic Vein Development • Right anterior cardinal vein → superior vena cava (SVC) • Left anterior cardinal vein involutes, left sinus venosus horn → coronary sinus ○ Persistent left anterior cardinal vein results in left SVC • Vitelline veins drain yolk sac, develop into hepatic/portal venous system • Left umbilical vein (UV) drains through ductus venosus to return oxygenated placental blood to fetal heart • Right UV involutes • UV also enters liver via portal sinus ○ Obliterated UV becomes ligamentum teres

CARDIAC ANATOMY Segmental Nomenclature • Each segment of heart is identified based on morphology • Cardiac anatomic description is based on segments, relative locations, how connected

Normal Chamber/Vessel Morphology • RA identified by limbic bands of fossa ovalis, large pyramidal appendage with pectinate muscles that extend outside appendage, and crista terminalis ○ Fetal marker for RA is systemic venous connection • Left atrium (LA): Identified by finger-like appendage, pectinate muscles confined to appendage, no crista terminalis ○ Fetal marker for LA is pulmonary venous connection • RV is heavily trabeculated with moderator band ○ TV belongs to RV – More apically placed than MV, has septal and free wall attachments ○ Fetal marker for RV is moderator band • LV is smooth walled with fine apical trabeculations ○ MV belongs to LV, only has free wall attachment ○ Fetal marker for LV is smooth internal contour/absence of moderator band • PA should come off RV, branches early into ductus arteriosus, left and right branches • Aorta should come off LV, head and neck vessels come off apex of arch ○ Continues to descending aorta, which connects with ductus arteriosus right after isthmus

CIRCULATION Fetoplacental • Arteries move blood away from heart ○ Aorta takes blood to brain and body ○ Umbilical arteries (internal iliac branches) carry deoxygenated blood away from heart to placenta – Become medial umbilical ligaments in adults ○ MPA takes blood from RV to body via ductus arteriosus – Only small volume circulates through lungs in fetal life (no gas exchange) • Veins take blood to heart ○ UV brings oxygenated blood back to heart, from placenta – Oxygenated blood preferentially crosses foramen ovale to left heart to be directed to brain ○ Inferior vena cava (IVC) brings deoxygenated blood from body to RA ○ SVC brings deoxygenated blood from head to RA • Distribution of cardiac output is very different in fetus compared to adult ○ Ductus arteriosus connects MPA to descending aorta – Allows oxygenated blood in RV to bypass lungs and be directed to body □ Becomes ligamentum arteriosum in adults ○ Fetal combined cardiac output (CCO) is 55% RV, 45% LV – ~ 40% CCO → body via ductus arteriosus – ~ 15% CCO → lungs via branch PAs – ~ 30% CCO → brain via ascending aorta – ~ 10% CCO → body via aortic arch/isthmus and descending aorta – ~ 3% CCO → heart via coronaries arteries • Streaming optimizes delivery of oxygenated blood to head ○ Oxygenated UV blood enters RA via ductus venosus and IVC – Jet streams preferentially across foramen ovale to LA, LV – Blood with highest oxygen content perfuses brain, heart ○ Deoxygenated systemic venous blood drains to RA via SVC, IVC – Jet streams preferentially into RV

Obstetrics and Developmental Anatomy

• In fetus, main PA (MPA) trifurcates into ductus arteriosus and right and left PAs • In adults, MPA bifurcates into right and left branches as it leaves pericardium ○ Atrophic ductus arteriosus becomes ligamentum arteriosum

Neonatal • Onset of breathing increased oxygen in lungs, PAs dilate in response ○ Decreased pulmonary arterial resistance • Low-resistance arterial connection to placenta removed when cord clamped ○ Increased systemic arterial resistance • End result is decreased flow across ductus arteriosus, increased flow in MPA ○ Ductus arteriosus closes • Pulmonary veins bring oxygenated blood from lungs to LA • Increased LA pressure closes foramen ovale flap

915

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Cardiovascular System PRIMITIVE HEART TUBE

Fusion of limbs of primary cardiac crescent

Primary cardiac crescent

Secondary heart field Embryonic disc

Primordium of outflow tract and right ventricle

Primordium of left ventricle

Right and left sinus horns

Outlet end of primitive heart tube

Ventricular loop

Sinus horns (will be incorporated into atrial chamber precursors)

(Top) Cells destined to form the heart derive from mesoderm, forming the primary cardiac crescent at the cranial border of the embryo. The secondary heart field lying contiguous with, but medial to, the primary cardiac crescent populates the outflow tract and primordium of the right ventricle. As the embryo elongates and folds, the limbs of the crescent come together in the midline and fuse, creating the heart tube (which moves into the thorax). (Bottom) As the straight heart tube elongates, it rotates and folds on itself due to differential growth in a standard D loop, moving the ventricles to the right and left sides. The proximal, venous pole remains anchored dorsal and will become part of the atria, while the arterial pole bends rightward and ventral and will become the outflow tract.

916

Embryology and Anatomy of Cardiovascular System

Outflow tract Sinus horns will incorporate into right atrium

Developing right ventricle (outlet)

Obstetrics and Developmental Anatomy

4-CHAMBER HEART

Developing left ventricle (inlet)

Atrial chambers (ballooned from primitive atrium, cells from tertiary heart field)

Right ventricle and outflow tract (from secondary heart field)

Left ventricle (from primary heart field)

(Top) Cellular growth leads to both the looping and development of the definitive cardiac chambers. The right and left ventricles are shown as well as the eventual right atrium and great vessels. (Bottom) Graphic shows a schematic of the early 4-chamber heart. The left ventricle is derived from the primary heart field (red), the right ventricle, and outflows from the secondary heart field (blue). The tertiary field (orange) contributes to formation of the atria and provides cellular components to the ventricles.

917

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Cardiovascular System VENTRICLES

Moderator band Right ventricle Tricuspid valve Right atrium Foramen ovale

Left ventricle

Mitral valve

Left atrium

Right atrium

Atria septum

Tricuspid valve Left atrium Flap of foramen ovale Descending aorta

Moderator band Right ventricle Ventricular septum

Left ventricle Mitral valve

(Top) Four-chamber view in the 2nd trimester provides excellent anatomic detail, given that the heart is about the size of a dime and is beating at 130-160 beats per minute. Note the moderator band in the trabeculated right ventricle; this can be used to identify the morphologic right ventricle, which should always be the anterior ventricle. (Bottom) This is a more zoomed-in 4-chamber view using the ultrasound machine's cardiac setting, which creates more contrast to bring out the fine details of the cardiac structures. Note that the flap of the foramen ovale is in the left atrium, which signifies right-to-left flow with the oxygenated stream of blood from the umbilical vein and ductus venosus crossing to the left to provide oxygenated blood to the brain.

918

Embryology and Anatomy of Cardiovascular System

Tricuspid valve Right ventricular outflow tract Ventricular septum Left ventricle

Obstetrics and Developmental Anatomy

VENTRICULOARTERIAL CONNECTIONS

Left ventricle Membranous septum Left ventricular outflow tract Ascending aorta

Mitral valve

Left atrium

Main pulmonary a. Aortic valve Branch pulmonary a. Ductus arteriosus

(Top) A short-axis view through the ventricles is not a standard view in OB ultrasound but is an important component of fetal echocardiography as it allows side-by side assessment of ventricular size and function in real time. The tricuspid valve is seen in cross section in the center of the right ventricular cavity. (Middle) The left ventricular outflow tract view is the best view to evaluate the membranous ventricular septum. A defect in this area may simply be an isolated perimembranous ventricular septal defect but may also be found in association with right ventricular outflow tract or conotruncal lesions, such as tetralogy of Fallot or double outlet right ventricle. (Bottom) This is the standard right ventricular outflow tract view, which is a short-axis view at the level of the aortic valve. It allows one to lay out the main pulmonary artery and the ductus arteriosus as it runs posteriorly, toward the spine, to join the descending aorta.

919

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Cardiovascular System VENOATRIAL CONNECTIONS

Right atrium Right ventricle Foramen ovale Foramen ovale flap Left atrium

Left ventricle

Descending aorta

Right atrium Right pulmonary v. Atrial septum

Left atrium Left pulmonary v.

Right atrium Superior vena cava

Fetal spine

Hepatic v.

Inferior vena cava

(Top) Abnormal 4-chamber view in a monochorionic twin with ischemic cardiomyopathy following the demise of the co-twin illustrates that the atria and ventricles may be symmetric even when abnormal. The atria are enlarged due to atrioventricular valve regurgitation. The regurgitation is secondary to myocardial ischemia and impaired ventricular contraction. (Middle) Image shows a right-sided pulmonary vein that drains across the midline to the left atrium as well as a left-sided pulmonary vein draining into the left atrium. Note the right vein is blue, so the probe is anterior and to the right of the fetus. (Bottom) This is the bicaval view demonstrating systemic venous return to the right atrium. Note the hepatic vein confluence with the inferior vena cava (IVC). In azygous continuation of the IVC, the hepatic veins may drain directly to the right atrium, but they are small and should not be mistaken for the IVC. In azygous continuation of the IVC, the enlarged azygous vein is seen as 2nd vessels posterior to the heart on the 4-chamber view.

920

Embryology and Anatomy of Cardiovascular System

"Normal" superior vena cava

Right atrium

Left superior vena cava

Coronary sinus

Obstetrics and Developmental Anatomy

ANATOMIC VARIANT: LEFT SUPERIOR VENA CAVA

Left superior vena cava Right atrium

Coronary sinus

Ventricular septum

Dilated coronary sinus Descending aorta Atrial septum Tricuspid valve

(Top) Graphic illustrates the anatomic variant of a persistent left superior vena cava (SVC). This occurs when the left anterior cardinal vein fails to involute. The left SVC drains into the right atrium via the coronary sinus, which is enlarged due to the increased volume of blood entering it. Enlargement of the coronary sinus is visible on the 4-chamber heart view. (Middle) Sagittal view of the left SVC draining to a dilated coronary sinus and into the right atrium is shown. Be careful to check for anomalous pulmonary venous return to the coronary sinus, another important cause of dilation of this structure. (Bottom) Four-chamber view with a dilated coronary sinus (*) is shown. This finding is suspicious for a persistent left SVC.

921

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Cardiovascular System FETAL CIRCULATION

Transverse aortic arch

Ductus arteriosus Right pulmonary a.

Left pulmonary a.

Foramen ovale

Ductus venosus Left portal v.

Umbilical v.

Descending aorta

Inferior vena cava

Placenta

Umbilical aa.

In the fetus, blood is oxygenated by the placenta and returns to the heart via the umbilical vein. This highly oxygenated blood (red) shunts through the ductus venosus and streams across the foramen ovale to the left side of the heart, supplying the head. Deoxygenated blood (blue) returns to the right atrium via the SVC and IVC. This blood preferentially flows to the right ventricle, which pumps a small amount to the pulmonary arteries but the majority is shunted across the ductus arteriosus to the descending aorta.

922

Embryology and Anatomy of Cardiovascular System

Main pulmonary a.

Transverse aortic arch

Ligamentum arteriosum

Superior vena cava Pulmonary vv.

Left atrium

Obstetrics and Developmental Anatomy

POSTNATAL CIRCULATION

Right atrium Left ventricle Right ventricle Ligamentum venosum Inferior vena cava

Ligamentum teres Descending aorta Portal v.

Medial umbilical ll.

Internal iliac a.

In adult circulation, blood is oxygenated in the lungs and returns to the left heart via the pulmonary veins. The left heart pumps to the body via the aorta and its branches. Deoxygenated blood returns via the SVC and IVC to the right side of the heart, which pumps deoxygenated blood to the lungs for gas exchange. The umbilical arteries become the medial umbilical ligaments, the umbilical vein becomes the ligamentum teres, and the ductus arteriosus becomes the ligamentum arteriosum.

923

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract

EARLY EMBRYOLOGIC EVENTS 2nd Week: 8-14 Days Post Conception • Rule of 2s ○ Embryoblast splits into 2 layers: Epiblast and hypoblast ○ Trophoblast gives rise to 2 tissues: Cytotrophoblast and syncytiotrophoblast ○ Blastocyst cavity is remodeled twice: Primary and secondary yolk sac ○ 2 novel cavities appear: Amnion and chorion ○ Extraembryonic mesoderm splits into 2 layers lining chorionic cavity: Somatic and splanchnic mesoderm

3rd Week: 15-21 Days Post Conception • Bilaminar disk → trilaminar disk (gastrulation begins) • Gastrulation: Process of forming 3 primary germ layers ○ Ectoderm → epidermis, retina, central and peripheral nervous systems, other ○ Mesoderm → smooth muscle, connective tissue, vessels, most of cardiovascular system, blood cells, bone marrow, skeleton, striated muscles, reproductive and excretory organs ○ Endoderm → epithelial linings of respiratory passages and GI tract, including glands opening into GI tract and glandular cells of liver and pancreas • Endoderm and ectoderm separated by mesoderm in all areas of gut with 2 exceptions ○ Areas of mesodermal deficiency: Oropharyngeal membrane (future oropharyngeal cavity) and cloacal membrane (future area of urethra and anus) • Allantois appears as diverticulum from caudal yolk sac on day 16 and extends into connecting stalk ○ Involved in development of bladder in humans and early blood formation ○ Becomes urachus as bladder enlarges ○ Blood vessels of allantois become umbilical arteries and veins

4th Week: 22-28 Days Post Conception • Rapid growth results in folding of embryo ○ 4 folds: Cranial, caudal, 2 lateral • Folding causes yolk stalk to narrow, bringing it in close proximity to body stalk • Umbilical ring surrounds both yolk and body stalks • Allantois contained within body stalk • Lateral edges of trilaminar disk fold ventrally to form body wall, moving toward yolk stalk and body stalk

5th Week: 29-35 Days Post Conception • Viscera develop in mesentery of caudal part of foregut • Fetal stomach is suspended by 2 mesogastria, and rotation of stomach begins ○ Dorsal mesogastrium: Site for developing spleen, bodytail of pancreas ○ Ventral mesogastrium: Site for developing liver, bile ducts, head of pancreas – Dorsal part of ventral mesogastrium becomes lesser omentum – Lesser omentum includes gastrohepatic ligament and hepatoduodenal ligament • Foregut: Caudal to liver bud forms esophagus, stomach, and proximal duodenum 924

• Midgut: From liver bud to 2/3 of transverse colon; opens into yolk sac ○ Gut tube begins to lengthen → primary intestinal loop (attached to yolk sac via yolk/vitelline duct) ○ Axis of loop is superior mesenteric artery (SMA) ○ Yolk duct and connecting stalk begin to merge • Hindgut: Gives rise to distal 1/3 of transverse colon, descending colon, sigmoid, rectum, and upper anal canal ○ Endoderm of hindgut also forms internal lining of bladder and urethra ○ Caudal end of hindgut terminates in endodermally lined cloaca – Cloaca includes base of allantois ○ Shelf of mesodermal tissue, urorectal septum, sits between hindgut and base of allantois

6th-7th Weeks: 36-49 Days Post Conception • Merging of yolk stalk and body stalk to form umbilical cord is complete ○ Yolk stalk atrophies: Failure to regress completely → Meckel diverticulum, blind outpouching from distal ileum • Physiologic herniation ○ Length of midgut increases, volume of gut is greater than body can accommodate → herniation into base of umbilical cord ○ Rotates 90° counterclockwise around axis of SMA (as viewed from front of embryo) ○ Folds grow out from urorectal septum to partition cloacal membrane and divide cloaca into rectum and urogenital sinus – Cloacal membrane is divided into anal membrane and urogenital membrane

8th Week: 50-58 Days Post Conception • Fusion of urorectal septum, lateral mesodermal folds, and cloacal membrane to form perineal body, partition between GI and urogenital systems • Cloacal membrane ruptures by beginning of 8th week, creating anal opening for hindgut and ventral opening for urogenital sinus

9th Week • Abdominal cavity has enlarged sufficiently to accommodate intestines, which begin to migrate back into abdomen

10th Week • Upon return of intestines into abdominal cavity, rotation proceeds additional 180° for total of 270°

ABDOMINAL VESSELS Arteries • Major fetal arteries course anteriorly through dorsal mesenteries from aorta to supply gut and intramesenteric viscera • Omphalomesenteric arteries supply yolk sac, then gradually fuse to form arteries in dorsal mesentery of gut ○ Celiac artery supplies foregut, superior mesenteric artery supplies midgut, inferior mesenteric artery supplies hindgut

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract

• Umbilical vein ○ Carries oxygenated blood from placenta to fetus (major source of blood flow to liver) ○ Enters liver through ventral part of ventral mesentery (falciform ligament in adults) ○ Obliterated umbilical vein → ligamentum teres • Vitelline veins ○ Paired vessels that carry blood from yolk sac to fetus in 1st few weeks of gestation ○ Give rise to venous plexus within liver – Precursor to hepatic and portal veins and sinusoids ○ Proximal extrahepatic veins → portal venous system – Carries blood (and nutrients) from gut to liver ○ Proximal vitelline veins → hepatic vein precursors – Carry blood from liver to heart via inferior vena cava (IVC) • Ductus venosus ○ Derived from left umbilical vein (after right vein has atrophied) ○ Bypasses liver to carry umbilical vein blood to IVC and heart ○ In neonate, atrophies to become ligamentum venosum • Portal sinus ○ In fetus, diverts some oxygenated blood from umbilical vein to liver parenchyma

ABDOMINAL ORGANS

• Rotates counterclockwise and attaches to right side of diaphragm at bare area • Rotation of liver results in right peritoneal space extending leftward, posterior to stomach ○ Becomes lesser sac (omental bursa)

Spleen • Develops within dorsal mesogastrium, which elongates to form gastrosplenic ligament ○ Carries short gastric vessels and forms left anterior wall of lesser sac (omental bursa) ○ Elongated caudal parts of gastrosplenic ligament hang down (drape-like) from stomach – Forms greater omentum and gastrocolic ligament ○ Greater omentum and gastrocolic ligament carry gastroomental vessels

Obstetrics and Developmental Anatomy

Veins

Pancreas • Develops within dorsal part of dorsal mesentery ○ Leaves only short splenorenal ligament – Carries splenic vessels and tail of pancreas – Forms left posterior wall of lesser sac • Pancreas becomes retroperitoneal organ

Peritoneal Spaces • Ventral mesentery resorbs to allow communication between right and left peritoneal cavity in adults • Variations in complex rotation, fusion, and growth of mesenteric viscera result in common variations in peritoneal and retroperitoneal spaces in adults

Abdominal Viscera • Alimentary tube ○ Foregut (esophagus, stomach, duodenum) ○ Midgut (small intestine, colon up to splenic flexure) ○ Hindgut (descending and sigmoid colon, rectum) • Intramesenteric viscera develop from diverticula of ventral or dorsal foregut • Supporting mesentery

SELECTED DEFECTS IN DEVELOPMENT Omphalocele • Lack of continuous folding results in failure of closure of umbilical ring vs. failure of resolution of physiologic herniation of gut • Pathogenetic mechanism may differ depending upon which organs are prolapsed

Small and Large Intestine

Gastroschisis

• Duodenum ○ In fetus, is intraperitoneal, has mesoduodenum – Ventral pancreas also lies in mesoduodenum ○ Becomes retroperitoneal organ when ascending mesocolon fuses to posterior abdominal wall, "trapping" duodenum and pancreas in retroperitoneum • Small intestine ○ Develops within dorsal mesentery, which elongates and persists into adulthood as small bowel mesentery • Large intestine (colon) ○ Develops as straight tube within dorsal mesentery • Ascending and descending colon usually lose their mesentery and become retroperitoneal structures in adult ○ Common variant: Ascending colon that is mobile due to persistent mesocolon (predisposes to twist and obstruct, "cecal volvulus")

• Likely involves more than 1 pathogenetic mechanism • Failure of right lateral abdominal fold, resulting in body stalk and yolk stalk not merging to form umbilical cord vs. focal weakness at juncture of right lateral fold and umbilical cord, permitting intestines to be extruded

Pentalogy of Cantrell • Abnormality of mesodermal development of cephalic fold at ~ 14-18 days post conception

Liver • Arises from ventral bud of foregut • Rapid growth is main factor in distortion of peritoneal spaces and mesentery

925

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract 18-DAY EMBRYO

Yolk sac

Body stalk Primitive heart Amniotic cavity

Plane for cross-sectional image #2

Midgut

Plane for cross-sectional image #1

Yolk sac

Extraembryonic coelom Splanchnic mesoderm Midgut Dorsal mesentery Amniotic cavity

Somatic mesoderm Aorta

Neural tube

Ventral mesentery Abdominal cavity (right division) Splanchnic mesoderm Amniotic cavity

Abdominal cavity (left division) Midgut Dorsal mesentery Aorta Neural tube

(Top) Lateral illustration shows an 18-day embryo. The roof of the yolk sac becomes incorporated in the form of a tube as part of the primitive gut. The cranial end of the tube becomes the foregut and the caudal end becomes the hindgut. (Middle) Cross-sectional illustration along plane #1 (indicated on the lateral image) shows that the midgut has a wide communication with the yolk sac at this phase. (Bottom) Cross-sectional illustration more distally along plane #2 (indicated on the lateral image) shows that the gut is suspended by the ventral and dorsal mesenteries.

926

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract

Yolk sac

Allantois (in connecting stalk)

Hindgut Aorta Amniotic cavity

Plane for cross-sectional image #2

Extraembryonic coelom

Heart Pharynx Lung bud Stomach Hepatic diverticulum

Obstetrics and Developmental Anatomy

4-WEEK EMBRYO

Plane for cross-sectional image #1

Yolk sac Amniotic cavity

Ventral mesentery Hepatic diverticulum

Abdominal cavity (right division) Dorsal pancreas

Neural tube

Amniotic cavity

Duodenum Visceral peritoneum and dorsal mesentery Parietal peritoneum Aorta

Persistent edge of ventral mesentery

Abdominal cavity Midgut Dorsal mesentery Aorta

Parietal peritoneum Visceral peritoneum

Neural tube

(Top) Lateral illustration shows a 4-week embryo. The pharynx and lung bud arise from the foregut, along with the stomach. The allantois connects the body stalk to the hindgut. The yolk sac communicates broadly with the primitive gut. Errors in development include communication between the foregut branches, such as a tracheoesophageal fistula. (Middle) Cross-sectional illustration along plane #1 (indicated on the lateral image) shows that the liver arises from a ventral bud of the foregut, while the pancreas arises from the dorsal mesentery. (Bottom) Cross-sectional illustration along plane #2 (indicated on the lateral image) shows that the ventral mesentery begins to disintegrate to allow communication between right and left sides of the abdominal cavity.

927

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract BOWEL ROTATION Ventral mesogastrium (lesser omentum) Esophagus Spleen Liver

Gallbladder

Body stalk Yolk stalk

Stomach Celiac a. Dorsal pancreas Ventral pancreas Superior mesenteric a. Dorsal mesentery of midgut Inferior mesenteric a.

Allantois Cloaca

Lesser omentum

Liver

Stomach Spleen Dorsal mesogastrium (bulging leftward)

Falciform l. Gallbladder Primary gut loop

Dorsal pancreas Ventral pancreas (within mesoduodenum)

Yolk stalk Allantois Cecum

Superior mesenteric a. (within dorsal mesentery) Inferior mesenteric a. (within mesocolon)

Hindgut

Diaphragm

Aorta Lesser omentum

Liver

Spleen

Pancreas Cecum (rotating counterclockwise above small intestine)

Superior mesenteric a. (in dorsal mesentery)

Urinary bladder

Inferior mesenteric a. (in mesocolon)

Genital tubercle Urogenital sinus

Urorectal septum

Anus

Rectum

(Top) The primary gut begins to elongate along with its dorsal mesentery. The hepatic diverticulum gives rise to the biliary tree and ventral pancreas. The arterial supply to the gut is already defined: Celiac artery (foregut), superior mesenteric artery (midgut), and inferior mesenteric artery (hindgut). (Middle) The liver expands within the ventral mesentery, which later disintegrates, leaving only the falciform ligament and the lesser omentum. The primary gut elongates and herniates out into the umbilical cord. (Bottom) The liver continues its rapid enlargement. Only the caudal part of the ventral mesentery remains (falciform ligament). The dorsal mesogastrium elongates, forming the left and caudal portions of the lesser sac. The gut continues to elongate and rotates counterclockwise (as viewed from the front) around the superior mesenteric artery within the dorsal mesentery. The urogenital sinus has separated from the rectum and anus. Common developmental errors include midgut malrotation, omphalocele, and imperforate anus.

928

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract

Stomach Falciform l.

Arrow (passing into lesser sac)

Pancreas (within dorsal mesogastrium)

Umbilical v. Greater omentum (growing caudally) Transverse colon

Obstetrics and Developmental Anatomy

BOWEL ROTATION

Small intestine

Liver Spleen

Cecum (continuing to rotate after returning to abdomen last)

Descending colon (against dorsal abdominal wall) Small intestine (elongating and coiling)

Yolk stalk (involuting) Umbilical cord

Liver

Stomach Transverse mesocolon

Duodenum (retroperitoneal)

Descending colon Duodenojejunal flexure Descending mesocolon

Terminal ileum Cecum (in final position after rotation)

Root of sigmoid mesocolon

Appendix Root of small bowel mesentery

(Top) The umbilical vein enters the liver along the caudal (free) edge of the falciform ligament. The leaves of the greater omentum elongate to the left and caudally, expanding the lesser sac and covering the transverse colon and small intestine. (Middle) At 10 weeks post conception (12 weeks by last menstrual period), the small intestine has returned to the abdomen. The yolk stalk, which connected the yolk sac to the primitive gut, is disintegrating. The cecum is the last part to return and continues to rotate in a counterclockwise direction until reaching the right lower quadrant. Errors in development include persistence of a part of the yolk stalk (Meckel diverticulum) and errors of bowel rotation. (Bottom) By 4- to 5-months gestation, the ascending and descending colon are fixed in a retroperitoneal location by fusion of their mesocolons to the posterior abdominal wall. The small bowel and transverse and sigmoid colon remain intraperitoneal, suspended by their respective mesenteries.

929

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract MOUTH AND ANUS FORMATION

Nasomedial prominence

Forebrain prominence

Nasolateral prominence Nasal pit Maxillary prominence Oropharyngeal membrane beginning to disintegrate Mandibular prominence Pharyngeal arch Cardiac prominence

Allantois Developing urorectal septum Future urinary bladder Hindgut

Cloacal membrane

Urinary bladder

Cloaca

Hindgut

Urogenital sinus Ruptured urogenital membrane Rectum Perineal body Ruptured anal membrane

(Top) The endoderm and ectoderm are separated by mesoderm in all areas of the gut except for the oropharyngeal and cloacal membranes. These are areas of mesodermal deficiency, which upon disintegrating became the oropharyngeal cavity and area of the urethra and anus, respectively. This graphic shows the beginning of disintegration of the oropharyngeal membrane in the 4th week. The stomodeum, or primitive mouth, is the result. (Middle) During the 6th to 7th weeks, a mesodermal shelf called the urorectal septum begins to grow between the hindgut and allantois, toward the cloacal membrane. It fuses with the cloacal membrane, dividing it into the anal and urogenital membranes, and forms the perineal body. (Bottom) By the end of the 8th week, the anal membrane ruptures, allowing access from the hindgut to the exterior of the body. The urethra forms within the urogenital sinus.

930

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract

Sinus venosus

Vitelline vv (proximal) Developing liver

Intrahepatic plexus of vitelline vv

Right umbilical v.

Left umbilical v

Obstetrics and Developmental Anatomy

LIVER, PORTAL, AND HEPATIC VEINS

Vitelline vv (distal)

Involuting portion of left umbilical v. Left umbilical v. branch

Hepatic v. plexus

Involuting right umbilical v. Distal vitelline vv.

Umbilical v.

Inferior vena cava Right hepatic v.

Left hepatic v.

Portal venous branches Main portal v.

Ductus venosus Portal sinus Umbilical v.

Umbilical cord

(Top) The vitelline veins return blood from the yolk sac and branch within the liver to form the hepatic sinusoids and venous system. They unite again to form the proximal vitelline veins, which join with the (initially) paired umbilical veins to enter the sinus venosus of the heart. (Middle) All of the right and much of the left umbilical veins atrophy. The left umbilical vein sends a large branch to the liver, which anastomoses with the plexus derived from the vitelline veins. The extrahepatic (distal) vitelline veins form the precursors to the portal venous system. (Bottom) The portal sinus diverts some oxygenated blood to the liver. The proximal parts of the vitelline veins have become the hepatic veins, returning blood from the liver to the heart. The distal parts have developed into the portal venous system, returning blood from the gut to the liver sinusoids.

931

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract FETAL ABDOMEN MR IMAGING

Diaphragm

Renal aa. Spleen

Liver Right kidney Ascending colon

Left kidney Aorta

Iliac aa.

Lung

Amniotic fluid

Diaphragm Left lobe of liver Right lobe of liver Duodenum

Stomach Small bowel

Bladder Placenta

Liver Sigmoid colon Descending colon

Rectum Iliac crest

(Top) Coronal T2WI MR through the level of the kidneys shows a portion of the ascending colon, which has a low to intermediate signal intensity, blending into the surrounding soft tissues. Both the liver & spleen are very low in signal intensity & are easily identified. (Middle) More anteriorly, the liver crosses the midline & is the main contributor to the abdominal circumference measurement. The lungs are higher in signal intensity. Fluid-filled structures, including the bladder, stomach, & small bowel, are very high signal intensity. Because of its excellent contrast resolution, MR is ideally suited for evaluating the contents of a diaphragmatic hernia. (Bottom) While T2WI MR is the primary sequence in evaluating most fetal anatomy, T1WI is particularly helpful for evaluating the colon as meconium is high in signal intensity & is obvious on this sequence. Also note the higher signal of the liver parenchyma on T1WI compared to T2WI. In addition to evaluating the colon, T1WI is valuable for evaluating for blood products, which are often high in in signal intensity.

932

Embryology and Anatomy of Abdominal Wall and Gastrointestinal Tract

Ribs

Diaphragm

Heart (short axis view) Lung

Liver Umbilical vein at ductus venosus

Stomach

Gallbladder

Obstetrics and Developmental Anatomy

FETAL ABDOMEN ULTRASOUND

Small bowel

Spinal lamina Lung base Lung base Liver

Spleen Stomach

Transverse colon Liver Gallbladder

Colonic haustra

Umbilical vein Lung

Liver

Lumbar spine

Rectum Transverse colon Bladder Anal dimple Rectum Labia

(Top) Coronal ultrasound in a 20-week fetus shows the anatomy of the upper abdomen. (Middle) Subtle differences in echogenicity allow the identification of the various organs, as shown in this composite image of a 3rd-trimester fetus. The upper oblique axial image shows the lungs are mildly hyperechoic compared to the liver and spleen. Changes in echotexture often provide clues regarding any pathologic process in a given organ. The lower image is an oblique coronal US of the transverse colon. US can show detailed anatomy, such as the colonic haustra. (Bottom) Anorectal malformations are a complex group of anomalies that require a complete evaluation of the colon down to the anus. Sagittal T1WI MR (left) shows normal rectal tapering. Following the colon on ultrasound (top right) is somewhat more difficult, but the anal dimple image (bottom right) of the perineum should be performed in any case of suspected anorectal malformation. It has a classic doughnut or target appearance with a thick, hypoechoic sphincter and hyperechoic mucosa.

933

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Genitourinary Tract

DEVELOPMENT OF URINARY TRACT Kidney Formation • Stages of development similar to those found in more primitive animals (e.g., invertebrates, amphibians) ○ Reflects evolutionary history • 3 successive nephric structures of increasing advanced design: Pronephroi, mesonephroi, metanephroi [pronephros, mesonephros, metanephros (singular form)] ○ Structures develop and regress in craniocaudal sequence • Nonfunctional, primitive nephrotomes develop in cervical region ○ Vestige of pronephroi, which form primitive kidney in lower vertebrates ○ Regress by 4th week and are replaced by mesonephroi • Mesonephroi are elongated, functional primitive kidneys, which develop from upper thoracic to 3rd lumbar level • Mesonephric (wolffian) ducts 1st appear at 24 days dorsolateral to mesonephroi in thoracic region ○ Grow caudally and fuse with ventrolateral wall of bladder ○ Mesonephric ducts connect to, and drain urine from, mesonephric tubules • After 10 weeks, mesonephric tubules cease to function and regress ○ Mesonephric ducts also regress in females but persist in males to form part of genital tract • Ureteric bud (also called metanephric diverticulum) sprouts from distal mesonephric duct ○ Induces sacral mesoderm (metanephric blastema) to develop into metanephroi, definitive kidneys ○ Ureteric bud and metanephric blastema exert reciprocal inductive effects on each other – Ureteric bud induces metanephric blastema to form nephrons – In turn, metanephric blastema induces ureteric bud to bifurcate into developing calyces • Anomalies resulting in failure of ureteric bud to interact appropriately with metanephric blastema ○ Renal agenesis – Failure of ureteric bud to come into contact with metanephric blastema ○ Multicystic dysplastic kidney (proposed mechanisms) – Ureteric bud does not appropriately signal metanephros, leading to abnormal collecting duct development with loss of nephrons, stromal expansion, and cyst formation – Very early ureter obstruction leads to dysplasia (metanephric tissue does not form nephrons)

Renal Ascent • Initially, kidneys (metanephroi) lie close together low in pelvis with renal hila facing anteriorly • Mechanism for "ascent" to final retroperitoneal flank position is not completely understood, but caudal embryonic growth is likely major contributing factor • Blood supply changes as kidneys successively "recruit" arterial blood supply from iliac arteries and aorta ○ New, more superior arterial branches form as inferior branches involute • With ascent, renal pelves rotate medially ~ 90° 934

• Ascent complete by 9 weeks when kidneys come into contact with adrenal glands • Anomalies related to abnormal "ascent" ○ Renal ectopia – Kidney usually low in position with abnormal rotation ○ Crossed fused ectopia and other fusion abnormalities – Fusion of metanephroi prior to ascent leads to various appearances ○ Horseshoe kidney – Inferior poles of 2 metanephroi fuse – Become "stuck" under inferior mesenteric artery ○ Accessory renal arteries – Persistence of normally transient renal arteries during ascent

Bladder • Cloaca (Latin for sewer) is common chamber with early communication between urinary, gastrointestinal, and reproductive tracts ○ Divided by urorectal septum into urogenital sinus anteriorly and anorectum posteriorly – Both structures open through perineum upon rupture of cloacal membrane • Urogenital sinus has 3 major components ○ Allantois is cephalad portion – Extends from bladder to connecting stalk of yolk sac – Intraabdominal portion involutes to become urachus; in adult, this is median umbilical ligament ○ Middle vesicular portion becomes urinary bladder ○ Caudal portion forms lower vagina in females and penile urethra in males • Distal portions of mesonephric ducts and attached ureteric ducts become incorporated into posterior bladder ○ During this process, ureters are incorporated superiorly in trigone ○ Orifices of mesonephric ducts move inferomedially and enter prostatic urethra, forming ejaculatory ducts

DEVELOPMENT OF ADRENAL GLANDS Cortex and Medulla • Cortex and medulla derive from 2 different tissues ○ Cortex – Forms from mesoderm – 3 zones: Glomerulosa, fasciculata, and reticularis – Only glomerulosa and fasciculata present at birth – Reticularis not recognizable until 3rd year of life ○ Medulla – Forms from neural crest cells derived from sympathetic ganglion • Fetal adrenal glands 10-20x larger than adult adrenal glands relative to body size ○ May be mistaken for fetal kidneys, especially early in pregnancy – May potentially miss renal agenesis before oligohydramnios has developed ○ Large size is from adrenal cortex – Rapidly become smaller as cortex regresses in 1st year of life

Embryology and Anatomy of Genitourinary Tract

Mesonephric (Wolffian) Ducts • Persist in males to form part of genital tract ○ Epididymis ○ Vas deferens ○ Seminal vesicles ○ Ejaculatory ducts

Testes • Form from genital ridges, which extend from T6-S2 in embryo • Composed of 3 cell lines, which form primitive sex cord ○ Germ cells ○ Sertoli cells ○ Leydig cells • Germ cells ○ Form in wall of yolk sac and migrate along hindgut to genital ridges ○ Form spermatogenic cells in mature testes • Sertoli cells ○ Secrete müllerian inhibiting factor – Causes paramesonephric (müllerian) ducts to regress ○ In adult, form supporting network for developing spermatozoa – Form tight junctions (blood-testis barrier) • Leydig cells ○ Principal source of testosterone production ○ Lie within interstitium ○ Cause differentiation of mesonephric (wolffian) ducts into male genital tract

Scrotum • Derived from labioscrotal folds ○ Folds swell under influence of testosterone to form twin scrotal sacs – Point of fusion is median raphe □ Extends from anus, along perineum to ventral surface of penis ○ Processus vaginalis, sock-like evagination of peritoneum, elongates through abdominal wall into twin sacs – Forms anterior to developing testes – Aids in descent of testes, along with gubernaculum (ligamentous cord extending from testis to labioscrotal fold)

Testicular Descent • Between 7th-12th week of gestation, testes descend into pelvis ○ Testes are retroperitoneal throughout their descent and are intimately associated with posterior wall of processus vaginalis ○ Remain near internal inguinal ring until 7th month, when they begin descent through inguinal canal into twin scrotal sacs • Component layers of spermatic cord and scrotum formed during descent through abdominal wall ○ Transversalis fascia → internal spermatic fascia ○ Internal oblique muscle → cremasteric muscle and fascia ○ External oblique muscle → external spermatic fascia

○ Dartos muscle and fascia embedded in loose areolar tissue below skin ○ Processus vaginalis closes and forms tunica vaginalis • Cryptorchidism results from incomplete descent

Prostate • In 10th week, endodermal evaginations bud from prostatic portion of urethra and develop into prostatic cords • Under increasing levels of testosterone, these cords develop into glandular acini • Rest of gland forms from surrounding mesenchyme, which differentiates into stroma and smooth muscle

DEVELOPMENT OF FEMALE GENITAL TRACT Ovaries • Male and female gonadal development identical through 7th week • In absence of testis determining factor from Y chromosome, ovaries will develop • Primitive sex cords degenerate and mesothelium of genital ridges form secondary sex cords • Secondary sex cords invest primordial germ cells to form follicle cells ○ Germ cells undergo 1st meiotic division but further development arrested until puberty • Like testis, ovaries also descend with help from gubernaculum

Obstetrics and Developmental Anatomy

DEVELOPMENT OF MALE GENITAL TRACT

Uterus • Formed from paired paramesonephric (müllerian) ducts • Paramesonephric ducts form lateral to mesonephric ducts ○ Join with urogenital sinus medial to mesonephric ducts ○ In absence of Y chromosome, paramesonephric ducts will continue to develop and form uterus • These paired paramesonephric ducts fuse in midline ○ Fusion forms uterovaginal canal, becoming uterus and upper vagina ○ Unfused portions remain as fallopian tubes • Lower vagina formed from urogenital sinus • Failure of müllerian duct development &/or fusion leads to spectrum of congenital uterine anomalies ○ Class I: Agenesis or hypoplasia ○ Class II: Unicornuate uterus – Single uterine horn, may have accessory rudimentary horn ○ Class III: Uterus didelphys – 2 separate, noncommunicating horns ○ Class IV: Bicornuate uterus – Concave or heart-shaped external uterine contour ○ Class V: Septate uterus – Normal external contour • Müllerian duct anomalies and renal anomalies are commonly associated ○ If fetal renal anomaly is seen, consider performing postnatal pelvic ultrasound ○ Uterus is often well seen in immediate neonatal period

935

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Genitourinary Tract KIDNEY DEVELOPMENT

Cervical nephrotomes (pronephroi)

Mesonephroi

Metanephric blastema

Gut

Bowman capsule Mesonephric tubule Mesonephric duct

Aorta Glomeruli

Neural tube

Mesonephric tubules Allantois

Cloaca Ureteric bud

Mesonephric duct Metanephros

(Top) Three sets of nephric structures develop in human embryos. They form and regress in a craniocaudal progression. The pronephroi are transitory and nonfunctional. The mesonephroi also degenerate, although the distal mesonephric duct will persist in males and form part of the genital tract. (Middle) Cross section of the embryo shows the mesonephroi. By the 4th fetal week, the mesonephric tubules and duct are formed. Branched vessels from the aorta reach the blind ends of the tubules to form glomeruli. Although these achieve an excretory function in the human embryo, they degenerate as the metanephroi form. (Bottom) The 3rd, and definitive, kidney is formed when the ureteric bud induces the metanephric blastema to form the metanephros.

936

Embryology and Anatomy of Genitourinary Tract

Yolk stalk Mesonephros Allantois Hindgut

Obstetrics and Developmental Anatomy

BLADDER DEVELOPMENT

Urorectal septum

Mesonephric duct Tailgut

Cloaca Ureteric bud

Allantois Kidney Urinary bladder (vesicular portion of urogenital sinus) Ureter Genital tubercle

Mesonephric duct

Caudal urogenital sinus Rectum

(Top) The cloaca is a common chamber with early communication between the urinary, gastrointestinal, and reproductive tracts. Between 4-6 weeks, the urorectal septum will separate the urogenital sinus anteriorly from the rectum posteriorly. (Bottom) The largest vesicular portion of the urogenital sinus forms the bladder. It is in direct continuity with the allantois superiorly. The allantois will eventually involute to form the urachus. The caudal portion of the urogenital sinus will form the lower portion of the vagina in females and the penile urethra in males. The ureteric buds are incorporated into the posterior bladder, forming the upper portion of the trigone, while the mesonephric ducts migrate inferomedially and will ultimately insert into the prostatic urethra as the ejaculatory ducts.

937

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Genitourinary Tract RENAL ASCENT Umbilical v.

Umbilical artery

Iliac artery Kidney

Umbilical a.

Iliac a. Kidney Aorta

Aorta

Iliac a.

Iliac a.

Kidney

Kidney

Bladder

New, developing renal aa.

Involuting renal a. Involuting renal a.

(Top) Graphic looking down from above shows the kidneys low in the fetal pelvis. The definitive kidneys form from specialized sacral mesoderm called the metanephric blastema. Please note that while the umbilical vein carries oxygenated blood, for this set of graphics, veins will be depicted in blue and arteries in red. (Middle) The kidneys are located close together and may even be in direct continuity, leading to various anomalies of fusion. The kidneys face forward with the renal pelves directed anteriorly. When initially formed, the arterial supply is from the iliac arteries. (Bottom) With ascent, the more inferior renal arteries regress, while more superior ones are recruited.

938

Embryology and Anatomy of Genitourinary Tract

Fetal lobulation

Obstetrics and Developmental Anatomy

RENAL ASCENT

Ureter

Bladder

Normal adrenal gland

Adrenal gland in renal fossa

(Top) Normally, each kidney will be left with a single main renal artery. Accessory renal arteries, a common anatomic variant, are from failure of involution of transient arteries during ascent. The fetal kidneys have a distinct lobular contour (fetal lobulation), reflecting the developmental process between the ureteric bud forming the calyces and the metanephric blastema forming the nephrons. (Bottom) Aberration in the development and ascent of the kidneys causes an array of anomalies. Renal developmental variants include unilateral renal agenesis (A), pelvic kidney (B), crossed fused renal ectopia (C), and horseshoe kidney (D). Errors of formation, fusion, and ascent lead to these anomalies.

939

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Genitourinary Tract FEMALE GENITAL TRACT

Allantois Paramesonephric (müllerian) ducts Urinary bladder (vesicular portion of urogenital sinus)

Caudal urogenital sinus

Unfused portion of paramesonephric ducts Allantois Metanephros (developing kidney) Bladder

Genital tubercle

Uterovaginal canal (fused paramesonephric ducts)

Urogenital sinus

Urachus

Bladder

Kidney

Fallopian tube Uterus

Urethra

Upper vagina from paramesonephric ducts Lower vagina from urogenital sinus

Clitoris

(Top) The fallopian tubes, uterus, and upper vagina form from the paired paramesonephric (müllerian) ducts, which develop on either side of the midline lateral to the mesonephric ducts (the mesonephric ducts regress in a female fetus). (Middle) The paramesonephric ducts must meet in the midline and fuse to form the uterus and upper portion of the vagina (uterovaginal canal). The unfused portions will form the fallopian tubes. The development of the kidney (metanephros) is closely related to uterine development, and coexistent renal and müllerian duct anomalies are common. (Bottom) The distal portion of the vagina (shown in yellow) is formed from the caudal urogenital sinus, which splits to form the urethra anteriorly and the vagina posteriorly. The allantois involutes to form the urachus.

940

Embryology and Anatomy of Genitourinary Tract

Allantois

Metanephros

Urinary bladder (vesicular portion of urogenital sinus) Ureter Genital tubercle

Mesonephric duct

Caudal urogenital sinus

Obstetrics and Developmental Anatomy

MALE GENITAL TRACT

Kidney Urachus

Bladder Seminal vesicle Prostate

Vas deferens

Penis Penile urethra

Peritoneum Transversalis fascia Transversus abdominis m.

Processus vaginalis

Internal oblique m. External oblique m. Testis

Labioscrotal fold Gubernaculum

(Top) The mesospheric ducts (only 1 shown) persist in a male and will form the epididymides, vas deferens, seminal vesicles, and ejaculatory ducts. (Middle) The caudal urogenital sinus forms the penile urethra. The allantois involutes and forms the urachus. The prostate forms from endodermal evaginations of the prostatic portion of the urethra and surrounding mesenchyme. (Bottom) The processus vaginalis is a sock-like evagination of the peritoneum, which elongates caudally through the abdominal wall. It forms just anterior to the developing testes and, along with the gubernaculum (a ligamentous cord extending from the testis to the labioscrotal fold), aids in their descent. As the processus vaginalis evaginates, it becomes ensheathed by fascial extensions of the abdominal wall, which ultimately form the layers of the scrotum and spermatic cord.

941

Obstetrics and Developmental Anatomy

Embryology and Anatomy of Genitourinary Tract URINARY TRACT, US Spinal lamina Renal pyramid

Paraspinous mm. Left kidney

Renal pelvis Small bowel Liver

Vertebral body with shadowing

Liver Adrenal gland

Aorta

Liver

Renal cortex Renal pyramid

Adrenal medulla Adrenal cortex Kidney

Aorta Main left renal artery Right kidney

Intrarenal branches

Iliac arteries

(Top) This axial ultrasound is through the renal fossa with the spine at the 12 o'clock position. This is the best position to measure the renal pelvis diameter. (Middle) This is a composite image of an axial ultrasound of the right fetal adrenal gland (top) and sagittal ultrasound of the adrenal gland of a newborn (bottom). The fetal adrenal gland is 10-20x larger than the adult adrenal gland relative to body size. It is often quite prominent on fetal imaging and is recognized by its ice cream sandwich appearance with a hyperechoic medulla and hypoechoic cortex. It typically is folded and angular in shape with a Y or tricorn hat configuration. (Bottom) Color Doppler ultrasound shows normal renal vasculature.

942

Embryology and Anatomy of Genitourinary Tract

Scrotum and testes Right leg Left leg Gallbladder Liver

Small bowel Spleen

Right kidney Left kidney

Obstetrics and Developmental Anatomy

URINARY TRACT, MR

Paraspinous mm. Spinal canal

Lungs Humeral head Placenta Aorta

Diaphragm Left adrenal

Right adrenal Liver

Corticomedullary differentiation

Right kidney

Spinal canal

Placenta twin A

Eye

Heart Lung Head twin B Diaphragm Adrenal gland Renal pelvis

Liver

Placenta twin B

Kidney

(Top) Axial T2 MR through the abdomen, at the level of the kidneys, in a 30-week fetus shows normal anatomy. The kidneys are well seen and are higher in signal than the liver, spleen, or muscles. (Middle) Coronal T2 MR through the renal fossa shows the fetal adrenals, which are lower in signal compared to the kidneys. Normal corticomedullary differentiation is particularly well seen on the left kidney; also note the slightly "bumpy" contour (fetal lobulations). (Bottom) This image is a sagittal MR of twin A of a dichorionic twin gestation (note 2 placentas). The renal pelvis contains urine and is high signal intensity on T2-weighted imaging. Note the folded, tricorn shape of the adrenal gland.

943

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INDEX

A

A wave, 258, 261, 264 A1 pulley, 629, 647, 651, 657, 659, 660, 662 A2 pulley, 629, 647, 657, 660, 663 A3 pulley, 629, 647, 657 A4 pulley, 629, 647, 657, 661, 664 A5 pulley, 629, 647, 657, 664 Abdomen - adrenal glands, 330–335 - biliary system, 272–283 - bowel, 336–351 - kidneys, 302–329 - liver, 248–271 - lymph nodes, 352–355 - pancreas, 292–301 - peritoneal cavity, 386–393 - spleen, 284–291 - wall, 394–405 Abdominal aorta, 225, 227, 288, 294, 298, 299, 335, 391, 409, 410, 416, 417 Abdominal cavity - 4-week embryo, 927 - 18-day embryo, 926 Abdominal lymph nodes, 352–355 - lymphangiogram, 355 - nonenlarged, 354 - pathologic, 354 - retroperitoneal, 353 Abdominal musculature, 259, 429 Abdominal wall, 343, 344, 348, 349, 350, 394–405, 870 - anatomy, 924–933 - anterior, 394, 395, 398 - anterolateral, 399 - back muscles, in situ, 397 - embryology, 924–933 - musculature, 322, 344, 345, 346, 347, 348, 349 - paraspinal muscles, 394, 404 - posterior, 394, 396, 400, 402 CT correlation, 401, 403 Abdominopelvic nodes, 352 Abductor digiti minimi muscle, 622, 629, 636, 637, 647, 657, 658, 693, 702, 819, 840, 843, 845 Abductor hallucis muscle, 819, 840, 842, 843, 844, 850, 856 - insertion, 840 Abductor pollicis brevis muscle, 622, 624, 629, 632, 634, 635, 647, 648, 653, 654, 657, 691–692, 693 Abductor pollicis longus muscle, 598, 605, 616, 617, 618, 622, 643, 658

Abductor pollicis muscle, 635, 643 Aberrant bile duct (of Luschka), 277 Aberrant lower polar artery, 307 Aberrant upper polar artery, 307 Abscess, 123, 129 - cavity gas within, 123 with pus, 128 - gas locule within, 128 - pelvic. See Pelvic abscess. Accessory cephalic vein, 612, 613 Accessory collateral ligament, 659 Accessory duct - double, 300 - of Santorini, 300 Accessory lateral collateral ligament, 594 Accessory meningeal artery, 52 Accessory nerve, 131, 165 Acetabular labrum, 729–730, 734–735 Acetabulum, 730 - anterior, 727 - bony, 730 - medial wall, 727 - posterior, 727 - roof, 734–735 Achilles tendon, 788–790, 793, 794, 811, 815, 819, 825, 829, 830–831 Acoustic shadow, 213 Acromial plexus, 571 Acromioclavicular joint, 229, 530–535, 539 - US, 533 transverse, 534, 535 Acromion, 533, 534, 535, 543, 544, 551, 552, 553, 563, 568, 678 Acromion process, 538, 539, 551, 555, 556 Addison syndrome, 330 Adductor aponeurosis, 650, 655 Adductor brevis muscle, 719–721, 724, 731, 738–739, 743, 745 Adductor digiti minimi muscle, 842 Adductor hallucis muscle, 853 - oblique head, 841, 843, 853 - transverse head, 841, 853 Adductor hiatus, 793 Adductor longus muscle, 719–721, 723–724, 738–739, 742–745, 747, 751, 752, 753 Adductor magnus muscle, 708–709, 713, 719–721, 723, 724, 753, 793 Adductor pollicis brevis muscle, 632 Adductor pollicis muscle, 624, 628, 629, 632, 634, 635, 647, 649, 651, 653, 654, 655, 657, 660, 662, 692, 693 - oblique head, 633 i

INDEX - osseus insertion, 633 - transverse head, 633 Adrenal adenomas, 330 Adrenal artery, 306 - inferior, 306, 331 - middle, 330, 331 - superior, 331 Adrenal capsule, 332 Adrenal cortex, 330, 332, 333, 942 - lesions, 330 Adrenal glands, 251, 304, 330–335, 939, 942, 943 - adult, 334, 335 - development, 934 - fetal, 934 - graphics, 331 - left, 299, 324, 330, 331, 334, 335 - neonate, 332, 333 - right, 314, 330, 331, 333, 334, 335 lateral limb of, 335 medial limb of, 335 - US, 330 - vessels, nerves, and lymphatics, 330 Adrenal medulla, 330, 332, 333, 942 - lesions, 330 Adrenal vein, 303 - left, 331 - right, 305, 331 Adrenal vessels, inferior, left, 305 Airways, 219 - developing, 910, 911 - distal, 906 - epithelium, 910, 911 Alar fascia, 113 Alimentary tube, 925 Allantois, 924, 928, 930, 934, 936, 937, 940, 941 - 4-week embryo, 927 Ambient cistern, 17, 27 Amnion, 866, 867, 868, 869, 871, 874, 875 - edge of, 868 Amniotic cavity, 863, 871, 874 - 4-week embryo, 927 - 18-day embryo, 926 Amniotic fluid, 932 Ampulla, 274, 481 Anal canal, 491, 514, 515, 516, 525, 526 - axial transperineal US, 524 Anal continence, maintenance of, 504 Anal cushion, 515 Anal dimple, 933 Anal membrane, ruptured, 930 Anal sphincter muscle complex, 514 Anasarca, 391 Anconeus epitrochlearis muscle, 696 Anconeus muscle, 562, 568, 581, 582, 586, 588, 591, 597, 599 - nerve to, 677, 678 Aneuploidy, cystic hygroma associated, 895 Angular gyrus, 10 Angular vein, 43 Ankle, 814–831 - Achilles tendon, 830–831 ii

- anterior, 816–818 - deltoid ligament, 823–824 - fibular ligaments, 828 - lateral, 825–827 - medial, 819–821 - medial and posterior ligaments, 822 - posterior, 829 Ankle joint, 814, 818 - posterior aspect of, 820 - posterior recess of, 828 - recess with fluid, 828 Annular ligament, 578, 589, 597 Annular pulley, 656 Anococcygeal body, 515 Anococcygeal ligament, 509, 512, 513, 514 Anorectal canal, 517, 526 Anorectal muscularis, 516 Anorectum, 934 Anovaginal septum, 526 Antebrachial fascia, 701 Antebrachial vein, intermediate, 612 Antecubital fossa, 585 Antecubital vein, 586, 608 - medial, 585 Anterior axillary wall, transverse US, 559 Anterior belly digastric muscle, 201 Anterior capsule, 534 Anterior-cephalic ducts, right, 276 Anterior cerebral artery, 32, 33, 34, 50, 52, 53, 54–57, 59, 72 - cortical branch, 35 - horizontal, 54 - splenial branch, 54 - vertical, 54 Anterior cerebral vein, 50, 70, 71, 72, 73 Anterior cervical space, 88, 119 Anterior chamber of eyeball, 42, 49 Anterior choroidal artery, 52, 53 Anterior circumflex artery, 563 - humeral, 571 Anterior clinoid, 14 Anterior commissure, 11, 152, 155 Anterior communicating artery, 34, 50, 54, 55, 57, 59 Anterior coronoid recess, 584 Anterior cruciate ligament, 764 Anterior cul-de-sac, 468, 469 Anterior fat pad, 580, 583 Anterior fibromuscular stroma, 438, 439, 441, 444 Anterior fontanelle, 4, 5, 27, 29, 903 Anterior inferior cerebellar artery, 32, 50 Anterior inferior iliac spine, 506, 719, 728–729, 732 Anterior inferior pancreaticoduodenal artery, 296 Anterior inferior segmental artery, 306 Anterior intercostal vessels, 222 Anterior interosseous artery, 607, 623, 641 Anterior interosseous nerve, 600, 623, 670, 685–686, 690 Anterior interosseous neurovascular bundle, 600, 689–690 Anterior interosseous vein, 623 Anterior interosseous vessels, 689 Anterior jugular vein, 121, 139, 146, 161, 167, 191, 193, 211

INDEX Anterior labrum, 556, 727 Anterior longitudinal ligament, 79, 396 Anterior mammary fascia, 240 Anterior pleural reflection, 221 Anterior recurrent tibial artery, 794, 811 Anterior recurrent tibial nerve, 811 Anterior renal fascia, 304 Anterior sacral meningocele, 889 Anterior scalene muscle, 120, 192, 210, 212, 215, 223 Anterior spinal artery, 66, 76 Anterior spinal ligament, 77 Anterior sternoclavicular ligament, 531 Anterior strap muscles, 119 Anterior subhepatic space, fluid, 390 Anterior superior iliac spine, 506, 728, 738, 742 Anterior superior pancreaticoduodenal artery, 293 Anterior superior segmental artery, 306 Anterior suprapatellar fat pads, 764–766 Anterior talocalcaneal joint, 823 Anterior talofibular ligament, 814, 825, 828 Anterior temporal artery, 58, 62 Anterior thalamostriate artery, 35 Anterior tibial artery, 783–785, 792, 793, 794, 802, 803, 804, 811, 817, 847 Anterior tibial cortex, 817 Anterior tibial vein, 783–785, 795, 802, 803, 805, 817 Anterior tibial vessels - longitudinal, 803 - transverse, 802 Anterior tibiofibular ligament, 814, 817, 825 Anterior tibionavicular ligament, 824 Anterior tibiotalar ligament, 824 Anterior ulnar recurrent artery, 607 Anterior urethral wall, 518 Anterior uterine wall, folding, 475 Anterior vaginal fornix, 472, 474 Anterior vaginal septum, 505 Anterolateral calcaneal cortex, 836 Anterolateral fontanelle, 4, 5 Anteromedial navicular surface, 836 Antrum, 339 Anus, 336–337, 342, 505, 509, 515, 516, 517, 526, 527, 928 - formation, 930 - longitudinal muscle of, 512, 513 Aorta, 256, 259, 271, 278, 280, 281, 283, 288, 294, 295, 297, 301, 307, 308, 313, 314, 317, 320, 321, 325, 329, 333, 335, 338, 341, 343, 344, 354, 391, 404, 405, 870, 891, 915, 932, 936, 938, 942, 943 - 4-week embryo, 927 - 18-day embryo, 926 - abdominal, 225, 227, 288, 294, 391, 409, 410, 416, 417 - ascending, 919 - bifurcation, 412, 417 - descending, 918, 920, 921, 922, 923 Aortic arch, 172, 209 - proximal, 172 - transverse, 922, 923 Aortic hiatus, 224 Aortic valve, 919 Aortocaval nodes, 353

Apical pleural, 210, 211, 212, 215 Appendix, 338, 342, 348, 929 - tip, 348 Appendix epididymis, 457 Appendix testis, 457 Aqueduct of Sylvius, 873, 887 Arachnoid, 76 Arcuate arteries, 306, 470, 471, 474, 480, 847 Arcuate ligament, 508 - lateral, 224, 225 - medial, 224, 225 - median, 224, 225, 227 Arcuate line, 506 Arcuate veins, 471, 474, 480 Arcuate vessels, 478 Arcus tendineus fascia pelvis, 510, 511, 512, 513 Arcus tendineus levator ani, 507, 510 Areolar skin, 242 Areolar tissue - loose, 639 - subtendinous, 662, 664 Arm, 562–569, 905 - anterior aspect, 566 - anterolateral aspect, 567 - anteromedial aspect, 565 - axial, 564 - posterior aspect, 568, 569 - vessels, 570–577 Arnold nerve, 164 Arterial pulse, included by Doppler gate, 318 Arteries, 408 - abdominal, 924 - aortic, 914 - embryology, 914 - fetoplacental circulation, 915 - pulmonary, 914–915 - umbilical, 915 Arteriogenic impotence, 458 Articular cartilage, 541, 543, 549, 550, 583, 587, 591, 592, 625, 626, 659, 660, 688, 727 Articular disc, 531, 620, 626 Aryepiglottic folds, 115, 121, 150, 151, 153, 155, 157, 175 Arytenoid, 121, 133, 167 - vocal process, 152 Arytenoid cartilage, 150, 153, 154, 155, 157 Ascending aorta, 172 Ascending colon, 314, 338, 342, 388, 401 - site, 389 Ascending pharyngeal artery, 170, 173 Ascites, 291, 333, 393 Asplenia, 284 Asterion, 4, 5 Atherosclerotic disease, 423 Atherosclerotic plaque, 180, 181 Atlas, anterior arch of, 97 Atlas loop, V3 segment, 62 Atria, septation, 914 Atria septum, 918, 920 Atrial chambers, 917 Atrioventricular canal, septation, 914 iii

INDEX Atrium, 9, 12 - left, 915, 918, 919, 920, 923 - right, 259, 915, 918, 920, 921, 923 Auricle, 897 Auricular branch, 164 Av pulley, 629, 647, 657 Axilla, 554–561 - apex, 209 - deeper structures, 556 - muscles, 555 - neurovascular structures, 557 - transverse US, 558 Axillary artery, 209, 214, 239, 557, 558, 559, 571, 675 Axillary lymph nodes, 235, 245 Axillary nerve, 538, 555, 557, 568, 669, 677–678 - quadrilateral space, 560 Axillary neurovascular bundle, 556 Axillary nodes - level I, 238 - level II, 238 - level III, 238 Axillary recess, 539 Axillary vein, 209, 214, 239, 557, 558, 559 - left, 238 Axillary wall, transverse US - anterior, 560 - posterior, 561 Azygos artery, 492, 493 Azygos vein, 224, 225

B

Back muscles, in situ, 397 Bare area, 250 Bartholin gland, 509 Basal arteries, 470 Basal ganglia, 8 Basal vein, 71, 72, 73 - of Rosenthal, 50, 70, 71 Basilar artery, 28, 32, 33, 34, 62, 184 - proximal, 67 Basilar venous plexus, 70 Basilic vein, 563, 564, 570, 572, 573, 574, 580, 606, 608, 612, 613, 641, 687 - intermediate (median), 612 Basion, 75, 78 Benign prostatic hyperplasia, 434, 440 - varying degrees, 442–443 Bertin, column of - cortical, 306 normal, 327 - hypertrophied, 327 Biceps aponeurosis, 581, 593, 603, 604 Biceps brachii muscle, 563, 564, 574, 577, 599, 603, 604, 670, 675, 679, 683, 685, 686, 687 - long head, 556, 562, 563, 565, 566, 567, 724 - short head, 556, 558, 562, 563, 566, 567

iv

Biceps femoris muscle, 708–709, 751, 764, 774 - long head, 741, 747 - short head, 741–742, 747 Biceps femoris tendon, 715, 772, 793, 811 Biceps muscle, 573, 577, 580, 587, 588 Biceps tendon, 540, 544, 545, 546, 547, 578, 580, 581, 582, 583, 584, 593 - insertion, 586 - long head, 533, 536, 538, 544 - longitudinal US, 546 - sheath, 537 - short head, 533, 538 - transverse US, 545, 586 Bicipital aponeurosis, 685–686, 688 Bicipital fascia, 562 Bicipital groove, 545, 547, 551 Bicornuate uterus, 935 Bifurcate ligament, 825, 835, 836 Bilaminar embryo, 863 Bile duct, 249 - common, 252, 263, 272, 274, 281, 295 cystic and, common sheath, 275 Biliary system, 272–283 - gallbladder, 272 - variations of biliary tree, 275 Biliary tree, 276, 277 - biliary system variations of, 275 Bladder, 437, 445, 470, 472, 474, 483, 492, 496, 511, 516, 517, 518, 519, 522, 932, 933, 934, 938, 939, 940, 941 - development, 937 - urinary, 310 Bladder diverticula, 432 Bladder dome, 472 Bladder fascia, 342 Bladder filling, 520 Bladder lumen, 431 Bladder neck, 444, 520, 521 - descent, measurement of, 519 - level of, 519 Bladder neck-symphyseal distance, 519 Bladder wall, 431, 432 - trabeculations, 431 Blastema, metanephric, 934 Blastocyst - blastocele cavity within, 862 - "naked," 862 Body, gallbladder, 274 Body stalk, 874, 928 - 18-day embryo, 926 Bones - facial, 902 - nasal, 898, 900, 902, 903 - pelvic floor, 506 Bony orbital socket, 47 Bowel, 313, 336–351, 393, 398, 400, 402, 497 - gas, 325, 398, 402, 497 shadowing, 402 - herniated into base of cord, 869 - large, 336, 346, 349, 350 - loops, 320, 399 in base of umbilical cord, 870

INDEX - motility, 337 - small, 336, 344, 346, 393 loops, 341, 350, 393 mesentery, 293, 340, 387, 388 - wall anterior, 345 posterior, 345 Bowel peristalsis artifacts, 412, 415 Bowman capsule, 936 BPH. See Benign prostatic hyperplasia. Brachial artery, 558, 563, 564, 565, 570, 571, 572, 573, 580, 581, 582, 584, 592, 606, 607, 608, 686, 687–688, 697 - color Doppler, 574 - deep branch of, 607 Brachial fascia, 562 Brachial nerve, 573 Brachial plexus, 124, 125, 165, 209, 213, 668–675 - branches, 239, 559 - cords, 557, 558, 559, 671, 675 - divisions, 671, 675 - elements, 91, 126, 132, 212, 214, 215 - lateral cord, 685, 703 - medial cord, 685, 703 - posterior cord, 703 - root, 127, 131, 671, 672, 673, 674 - schwannoma, 129 - trunk, 133, 557, 671, 672, 674 Brachial vein, 558, 563, 564, 565, 566, 570, 572, 573, 574, 575, 576, 679, 687, 697 Brachialis muscle, 562, 564, 565, 566, 567, 569, 574, 575, 576, 577, 580, 581, 583, 584, 585, 586, 587, 588, 591, 592, 599, 603, 670, 681, 687–688 Brachialis tendon, 604 Brachiocephalic artery, 137, 171, 172, 182, 183, 185, 191, 211 Brachiocephalic trunk, 223 Brachiocephalic vein, 128, 129, 191, 193, 194, 195, 196, 197 - right, 125 Brachioradialis muscle, 563, 564, 567, 568, 580, 581, 582, 584, 585, 586, 587, 591, 600, 601, 602, 603, 608, 678, 680, 681–682, 687–689 Brachioradialis tendon, 602 Brain, 8–37 - anterior cerebral artery, 54–57 - axial US through temporal bone, 27 - choroid plexus, 9 - coronal T1 MR, 15, 17, 19 - coronal US via anterior fontanelle, 14, 16, 18 - embryology and anatomy of, 872–887 - intracranial veins and sinuses, 70–73 - middle cerebral artery, 58–61 - midline color Doppler, 33 - posterior cerebral artery, 62–65 - premature infant, 24 - sagittal T1 MR, 21, 23 - sagittal US via anterior fontanelle, 20, 22, 26 - scalp and calvarial vault, 4–7 - standard US planes via anterior fontanelle, 13

- subarachnoid spaces/cisterns, 9 - transcranial Doppler, 50–73 - vascular anatomy of, 32 - ventricular system, 8–9 - vertebrobasilar system, 66–69 Brainstem, 8, 10, 17, 876 Branchial arches, 894, 908 - swellings, 894 Branchial cleft cyst, 2nd, 116, 117 Branchial groove, 1st, 897 Branching trabeculae, 287 Breast, 234–245 - axillary lymph nodes, 235, 245 - duct orifices, 234 - ductal system, 234 - ducts, 243 - innervation, 234 - interlobular stromal fibrous tissue, 235 - lactation-related changes, 244 - lobe/segment, 234, 237 - lymph node, 235 - lymphatic drainage, 235 - lymphatics and lymph nodes, 235 - major ducts, 234 - neurovascular supply, 239 - parenchymal variation, 240, 241 - tanner stages of development, 236 phase I, 236 phase II, 236 phase III, 236 phase IV, 236 phase V, 236 - terminal ductal lobular unit, 237 - tissue, developing, 236 - vascular supply, 234–235 - zonal anatomy, 234 Broad ligament, 469, 472, 489, 495, 496, 497, 498 Bronchi, 906 Bronchial branches, 906, 910 Bronchial buds - left inferior, 909 - left superior, 909 - primary, 906, 909 - right inferior, 909 - right superior, 909 Bronchus, mainstem, 912 Buccal fat space, 111 Buccal mucosa interface, 110 Buccinator muscle, 95, 107, 110, 111 Buccinator node, 200 Buck fascia, 458, 459, 461, 462, 465 Bulbospongiosus muscle, 458, 461, 509, 511 Bulbourethral (Cowper) gland, 436 Bulbous urethra, 466

C C1 - anterior arch of, 75, 78 v

INDEX - nerve, 75 - posterior arch of, 78 - pulley, 629, 647, 657 - transverse foramen, 185 C2 - body of, 75, 78, 109 - odontoid process of, 75, 78 - pulley, 629, 647, 657 - spinous process of, 78 - transverse foramen, L-shaped, 185 C3 pulley, 629, 647, 657 C4, vertebral body, 674 C5, 669, 674 - dermatome, 667 - nerve root, 673 - spinous process, 75 - vertebral body, 75, 674 C6, 669, 674 - dermatome, 667 - transverse process/foramen, 185 - vertebral body, 674 C7, 669, 674 - dermatome, 667 - vertebral body, 674 C8, 669, 674 - dermatome, 667 - nerve, 75 - ventral rami, 695 Calcaneal cortex - anterolateral, 836 - lateral, 826, 827, 828 Calcaneal fibular ligament, 826, 827 Calcaneal nerve - inferior, 819 - medial, 819 Calcaneal tuberosity, 831 - central facet of, 830 Calcaneocuboid ligament, dorsal, 825 Calcaneofibular ligament, 814, 822, 825, 828 Calcaneus, 822, 825, 838, 839, 844, 845, 850 - anterior tubercle of, 842 - lateral cortex of, 827 - lateral process of, 842, 843 - medial process of, 842, 843 - posterior, middle facet of, 829 - sustentaculum tali of, 821 Calcarine artery, 62 Calcarine fissure, indentation, 877 Calcarine sulcus, 11, 19, 884, 885 Calcification - within adenoma, 147 - artifact, 162 Calcified plaques, 467 Calculus, 102 Callosal sulcus - above corpus callosum, 20 - genu of, 21 Callosomarginal artery, 32, 33, 54, 55, 57, 62 Calvarial unit, 4–7 Calyces - dilated, 429, 430 vi

- major, 310 - minor, 310 Capillaries, 910, 911 Capitate, 615, 620, 623, 624, 639, 691 Capitohamate ligament, 627 Capsular ligaments, 530, 539 - longitudinal, 727 Capsule, 332, 544 Cardia, 339 Cardiac crescent, primary, 916 Cardiac prominence, 930 Cardinal ligament, 483, 510 Cardiovascular system, embryology and anatomy, 914–923 Carotid arteries, 170–183, 673 - common, 170, 171, 172, 173, 174, 182–183 - external, 170, 171, 173, 174, 175, 176, 177, 178–179 - graphics, 171 - grayscale and Doppler ultrasound, 180–181 - internal, 173, 174, 175, 176–177, 178, 179, 180, 181 Carotid bifurcation, 112, 113, 116, 117, 174–175 Carotid body paraganglioma, 116, 117 Carotid bulb, 167, 174, 175, 177, 179, 181 - internal carotid artery, 171, 173 - spectral Doppler waveform, 175 Carotid sheath, 88, 165 Carotid space, 88, 107, 113, 115, 131, 159 Carotid triangle. See Upper cervical level. Carpal arch - dorsal, 641 - palmar radial branch, 641 ulnar branch, 641 Carpal bones, 615 Carpal ligament, volar, 617, 645 Carpal tunnel, 642 - roof, 633 Carpometacarpal compartment - 1st, 615 - common, 615 Carpometacarpal joint, 648 - 1st, 615, 648 Carpometacarpal ligament, 627 Cartilaginous spinous process, 892 Cartilaginous tracheal ring, 210 Cauda equina, 77, 80, 888, 889, 893 Caudal cell mass, 888 Caudal eminence, 891 Caudal neuropore, 888, 891 Caudal pancreatic artery, 296 Caudal regression, 888–889 Caudate, 16, 17, 24 - head, 15, 21 Caudate lobe, 257, 271, 392 Caudate nucleus, 14, 20, 35 - head of, 881 Caudothalamic groove, 20, 21, 24 Cavernosal artery, 458, 460, 461, 462, 464 - corpora cavernosa, 465 Cavernosal septum, 464 Cavernous internal carotid artery, 43

INDEX Cavernous sinus, 43, 70, 191 Cavum septi pellucidi, 9, 16, 24, 30, 878, 879, 880, 881, 882, 883, 887 Cavum velum interpositum, 9, 30, 31 Cavum vergae, 9, 30 Cecum, 338, 342, 346, 928, 929 - anterior wall, 346 - posterior wall, 346 Celiac artery, 253, 259, 288, 296, 339, 341, 924, 928 Celiac axis, 285 Celiac nodes, 353 Celiac trunk, 253, 298 Central canal, 893 Central endometrium line, 478 Central group, 238 Central gyrus, 881, 882 Central hyaloid artery, 898 Central intranodal vessels, 205 Central retinal artery, 44 Central retinal vein, 44 Central spinal canal, 75 Central sulcus, 10, 11, 20, 21, 23, 880, 883, 884 Central tendon, 225 - left leaf of, 225 - right leaf of, 225 Centrum, 889, 892 - ossified, 892 Centrum semiovale, 14, 15 Cephalic vein, 556, 563, 564, 570, 572, 577, 606, 608, 609, 612, 613, 618, 619, 641, 643, 688 - accessory, 612, 613 - intermediate, 612 Cerebellar artery - inferior, 50 - superior, 50 Cerebellar folia, 29 - developing, 886 Cerebellar hemispheres, 16, 17, 19, 21, 23, 25, 28, 29, 877, 878, 884, 885, 886 Cerebellar peduncles, 29 Cerebellar tonsil, 75, 887 Cerebellar vermis, 17, 25, 27, 877, 878, 881 Cerebellum, 8, 10, 20, 24, 28, 97, 873, 879, 880, 882 - great horizontal fissure, 66 Cerebral aqueduct, 12, 21, 28 Cerebral arteries, 35 Cerebral cortex, 6, 7 Cerebral hemispheres, 6 - coronal T1 MR, 15, 17, 19 - coronal US, via anterior fontanelle, 14, 16, 18 - sagittal T1 MR, 21, 23 - sagittal US via anterior fontanelle, 20, 22, 26 Cerebral peduncle, 27 Cerebral sinuses, 36–37 Cerebral sulcus, 6 Cerebral veins, 36–37 - anterior, 50, 70, 71, 72, 73 - middle deep, 50, 70 superficial, 50, 70 Cervical artery, transverse, 571

Cervical canal, 474, 484 Cervical cord, 78 Cervical esophagus, 118, 126, 137, 152, 182 Cervical fascia, 105 Cervical internal carotid artery, 170 Cervical ligament, 825 Cervical lymph nodes, 198–205 - axial CECT, 201 - graphics, 199–200 - normal, 203 - pathology, 204–205 - power Doppler US and pathology, 203 - transverse and longitudinal US and pathology, 202 Cervical nerve root - 5th, 212 exiting, 212 transverse process, 212 - 6th, 212 exiting, 212 transverse process, 212 - 7th, 212 exiting, 212 transverse process, 212 Cervical plexus branches, 239 Cervical ring, 512 Cervical space - anterior, 119 - posterior, 113, 115, 121 Cervical spine, 75, 78 Cervical stroma, 484, 485, 486 Cervical trachea, 91 Cervical vertebra, 140, 162, 177, 179, 181, 183 - transverse process, 114, 120, 132, 166, 169, 186, 187, 188, 192, 672 Cervical vertebral bodies, 141, 186, 187 Cervicomedullary junction, 75, 78 Cervix, 468, 470, 474, 475, 476, 477, 480, 482–487, 490, 510 - changes of, during pregnancy, 487 - graphics, 483 - mucosa layer, 486 - mucus plug, 487 - orientation, 475 - submucosal layer, 484, 485, 486 - transabdominal ultrasound, 486 - transvaginal ultrasound, 484, 485 Chaotic peripheral intranodal vessels, 205 Chest - anatomy, 906–913 - embryology, 906–913 Chest wall, 228–233, 240, 242, 243 - intercostal spaces, 228, 229 - MR, 231 - muscles, 219, 228, 230 - serratus anterior, 228 - skeletal structures, 228 - subcutaneous tissue, 219 - vessels and nerves, 228 Choledocholithiasis, 277 Cholelithiasis, 277 Chondrification centers, 889 vii

INDEX Chondrocranium, 902 Chorion, 866, 867, 868, 870, 871 Chorion frondosum, chorionic villi in, 867 Chorion laeve, 867, 868, 869 Chorionic cavity, 863, 865, 866, 867, 870, 871 - extraembryonic mesoderm splits to form, 863 Chorionic frondosum, 875 Chorionic villi, 866 - in chorion frondosum, 867 - in developing placenta, 869 - thickened, in developing placenta, 868 Choroid, 25, 44 - glomus of, 26 Choroid plexus, 9, 876, 877, 883, 885 - 4th ventricle, 876 - atrium, 22 - foramen of Monro, 16 - glomus, 17, 19, 879 - lateral ventricle in atrium, 23 in temporal horn, 23 - roof of 3rd ventricle, 16 - temporal horn of lateral ventricle, 886 Choroidal arteries, 44, 62 Choroidal fissure, 16, 17 Cingulate gyrus, 11, 15, 16, 19, 20, 21, 32, 33, 54, 878, 879, 881–882, 884, 885, 887 Cingulate sulcus, 11, 14, 20, 21, 32, 33, 54, 879, 882 Circle of Willis, 33 Circular smooth muscle, 511 Circulation, 915 - fetal, 922 - fetoplacental, 915 - neonatal, 915 - postnatal, 923 Circumflex femoral artery - descending branch lateral, 749 - lateral, 749 - medial, 749 Circumflex femoral vessels, lateral, 740 Circumflex humeral artery - anterior, 571 - posterior, 568, 571 Circumflex iliac artery - deep, 749 - superficial, 750 Circumflex scapular artery, 563, 571 Circumflex veins, 461 Circumflex vessel, 462 Cirrhotic liver (right lobe), 390 - nodular contour, 390 Cisterna chyli, 353, 895, 904 Cisterna magna, 11, 20, 25, 28, 29, 30, 877, 879, 884, 886, 887 Cisternal segment, 164 Clavicle, 125, 128, 129, 131, 193, 195, 196, 197, 216, 217, 531, 534, 535, 551, 671, 675 - acoustic shadow, 213, 215 - anterior cortex, 211 - distal, 533 - lateral end, 533 viii

- left, 229 - medial end, 531, 532 - sternal end, 210 Cleavage, 860, 863 Cleft lip and palate, 895 Clitoris, 509, 940 - deep dorsal vein of, 508 Clivus, 97, 109 Cloaca, 924, 928, 930, 934, 936, 937 Cloacal membrane, 930 Coccygeus muscle, 504, 507 Coccyx, 81, 515 - cartilaginous, 892 - unossified, 892 Coelom, extraembryonic - 4-week embryo, 927 - 18-day embryo, 926 Coelomic cavity, 891 Collateral artery - medial, 572 - middle, 564, 678 - radial, 564, 568, 572 - ulnar inferior, 607 superior, 572, 607 Collateral branches, 229 Collateral bursa, medial, 770 Collateral ligament, 667 - accessory, 659 - lateral accessory, 594 ulnar, 594 - main, 659 - medial, 770–771 - radial, 578, 579, 581, 589, 594 - ulnar, 578, 579, 581, 594, 595 Collecting system (renal pelvis and calyces), 302 - dilated upper pole, 433 - nondilated lower pole, 433 Colles fascia, 458 Colliculus seminalis. See Verumontanum. Colon, 324, 334, 342, 391, 925 - ascending, 338, 342, 388, 401, 925, 932 haustra, 349 site, 389 - descending, 324, 338, 342, 346, 349, 388, 925, 929, 932 collapsed, long-axis view, 350 gas in, 320 - hepatic flexure, 274 - outer muscular layer of, 349 - sigmoid, 350, 932 - transverse, 293, 338, 339, 340, 341, 342, 348, 387, 388, 929, 933 posterior reverberation artifact from gas, 348 root, 388 Colonic haustra, 933 Color aliasing, 326 Column of Bertin - cortical, 306 - hypertrophied, 327

INDEX Common bile duct, 252, 263, 324, 340 - distal, 354 Common carotid artery, 43, 90, 109, 114, 115, 118, 119, 120, 121, 122, 123, 125, 126, 127, 128, 129, 133, 134, 137, 138, 139, 141, 142, 145, 146, 147, 149, 161, 163, 165, 166, 167, 168, 170, 171, 172, 173, 174, 182–183, 185, 186, 192, 193, 195, 197, 202, 203, 204, 210, 211 - right, 122 - spectral Doppler waveform, 183 Common digital tendon sheath, 629, 647, 657 Common extensor tendon, 578, 579, 581 - graphic, 599 - longitudinal US, 589 - origin, 589–590 - transverse US, 590 Common femoral artery, 719, 722–723, 729–731, 743 Common femoral vein, 411, 719, 722–723, 729–731, 740, 743, 745 - right, 416 Common flexor sheath, 628, 629 Common flexor tendon, 578, 579, 580, 581, 594, 686, 696 - longitudinal US, 595 - origin, 595–596, 596 - transverse US, 596 Common hepatic artery, 249, 285 Common hepatic duct, 274, 276, 280 Common iliac artery, 346, 409, 413, 414, 420, 421, 470 - branches, 410 - left, 412, 416, 417, 423 - right, 412, 416, 417, 423 Common iliac nodes, 353, 355 Common iliac vein, 346, 420, 421, 750 - left, 416, 419 - right, 417, 418, 419 Common interosseous artery, 607, 640 Common palmar digital artery, 644 Common peroneal nerve, 741, 751, 787, 810, 811 Common plantar digital artery, 856 Common proper digital artery, 645 Complete flow reversal, 189 Compressed lumen, 350 Compressor urethrae, 511 Concha, 95 Congenital microstomia, 895 Conjoined longitudinal muscle, 524, 527 Conn syndrome, 330 Connecting stalk, 866, 867, 868 Conotruncus, 914 Contiguous nerve, 129 Continuous antegrade arterial flow, 318 Continuous forward diastolic flow, 317 Continuous forward systolic flow, 317 - arterial, 325 Contralateral anterior cerebral artery, 56, 60 Contralateral posterior cerebral artery, 55 Conus, 77 - 18-weeks gestation, 889 Conus elasticus, 153 Conus medullaris, 77, 80, 81, 82, 888, 893 Cooper ligaments, 234, 241 Coracoacromial ligament, 533, 536, 538, 551, 553

Coracobrachialis muscle, 214, 556, 558, 559, 562, 563, 565, 566, 567, 572, 679, 697 Coracoclavicular ligaments, 530, 533 Coracohumeral ligament, 533, 540, 544, 551 Coracoid process, 533, 538, 547, 553, 563 Cornea, 42 Corniculate cartilage, 150 Cornua, 473 Corona radiata, 19 Coronal suture, 4, 5, 27, 29, 903 Coronary ligament, 250, 251 - liver, 389 Coronary sinus, 921 - dilated, 921 Coronoid, ulnar, 579, 592 Coronoid fossa, 592 Coronoid process, 595 Coronoid recess, anterior, 584 Corpora cavernosa, 458, 459, 462, 464, 465, 466, 467 - cavernosal arteries, 465 - crura of, 465 - crus of, 460 Corpora spongiosum, 466 Corpus, 468 Corpus albicans, 500, 862 Corpus callosum, 8, 24, 30, 32, 33, 37, 873, 877, 878, 880, 881–882, 884, 887 - body, 16, 17, 26, 881 - callosal sulcus above, 20 - genu, 11, 14, 15, 20, 21, 881 - rostrum, 881 - splenium, 11, 18, 19, 21, 26, 31, 881 Corpus cavernosum, 461, 462, 467 Corpus luteum, 500, 502, 503, 862 - regressing, 501 Corpus spongiosum, 427, 437, 449, 458, 459, 461, 462, 465 Cortex, 245, 934 Cortical bridge, 329 Cortical gyrus, 22 Cortical hypertrophy, 202 Cortical sulcus, 14, 22, 25 Cortical tissue - dividing renal sinus, 328 - splitting renal pelvis, 328 Cortical vein, in subarachnoid space, 6, 7 Corticomedullary differentiation, 302, 943 Costal cartilage, 225, 229, 230, 322, 323 - 1st, 531 - 3rd, 233 - 4th, 233 rib, 232 - 5th, 222, 232 - 6th, 222, 232 - 7th, 222 Costal margin, 229 Costal pleura, 220, 221, 225 Costocervical trunk, 137, 171 Costochondral junction, 209, 229 Costoclavicular ligament, 530, 531, 532 ix

INDEX Costoclavicular space, 208, 213 - subclavian artery, 216, 217 Costodiaphragmatic recess, 218, 220 - anterior, 221 Costomediastinal recess, 225 Costophrenic angle, right, 227 Costophrenic recess, right, slip of lung in, 227 Coupling gel filling supraclavicular fossa, 211 Cowper duct, 461 Cowper gland, 459, 460, 461 Cranial neuropore, 888, 890, 891 Craniofacial dysostosis, hypertelorism associated, 895 Cranium, 868, 869, 870, 871 - ossified, 869, 876 Cremasteric artery, 448, 454 Cremasteric muscle, 449, 450 Cricoid cartilage, 87, 119, 121, 141, 150, 152, 153, 155, 156, 157, 159, 162 - plane, 199, 200 Cricopharyngeus muscle, 159, 162 Cricothyroid joint, 152 Cricothyroid membrane, 152, 153 Cricothyroid muscle, 159 Cricothyroid space, 152 Crossed fused ectopia, 934 Crown rump length, 869 Cruciate ligament - anterior, 764 - posterior, 764, 770, 772 Crus - of clitoris, 511 - right, 225 Cryptorchidism, 447, 935 Cubital retinaculum, 580, 594, 696 Cubital tunnel, 698 Cuboid, 825, 827, 832, 838, 839, 843, 844, 845 Cuboid tuberosity, 843 Cuboidonavicular ligament, dorsal, 838 Cul-de-sac, 495 Culmen, 887 Cumulus cells, oocyte surrounded by, 862 Cumulus oophorus, 500, 501 Cuneiform, 832 - intermediate, 837, 839, 844, 848 - lateral, 838, 843, 845 - medial, 837, 839, 844, 848, 854 - middle, 842, 843 Cuneiform-cuboid ligament, 835 Cursor line, 227 Cushing syndrome, 330 Cutaneous branches - anterior, 239 - lateral, 239 Cutaneous nerve - antebrachial lateral, 563, 564 medial, 563, 564, 565 posterior, 564, 568 - antebrachial, posterior, 678 - brachial, medial, 564 - lateral, 677, 685 x

- posterior, 683 Cyclopia, 895 Cyst, 241 - ovarian, 497 Cystic artery, 253, 254 Cystic duct, 252, 274, 275, 280 - low insertion of, 275 - spiral course of, around common hepatic duct, 275 Cystic hygroma, 895, 905 Cytotrophoblast, 863

D

D wave, 258, 261, 264 Danger space, 88, 113, 119 Dartos muscle, 450 Decidua basalis, 865 Decidua capsularis, 865 Decidua parietalis, 865 Decidual lining, 863 Deep brachial artery, 538, 555 Deep cervical fascia, 165 - deep layer, 119, 131 - middle layer, 119, 145 - superficial layer, 119, 131 Deep circumflex iliac artery, 749 Deep circumflex iliac vein, 750 Deep deltoid ligament, posterior tibiotalar, 819, 822 Deep dorsal vein, 461, 465 - of penis, 464 Deep dorsal vessels, 462 Deep external anal sphincter, 515, 524, 526 Deep facial vein, 43, 190 Deep femoral vein, 750 Deep iliac circumflex artery, 409 Deep inferior epigastric artery, 398 - perforator branch, 398 Deep inferior epigastric vessels, 405 Deep leg veins, 792 Deep middle cerebral vein, 70 Deep palmar arch, 611, 635, 640, 641, 645, 653, 654 Deep palmar artery, 634 Deep peroneal nerve, 783–784, 786, 810, 811, 816, 817, 833, 835, 847 - lateral branch, 816, 835 - medial and lateral terminal branches, 811 - medial branch, 816, 835 Deep transverse metacarpal ligament, 629, 647, 657 Deep transverse perineal muscle, 459, 489, 508, 509 Deep trigone muscle, 511 Deep vascular plexi, superficial, 5 Deferential artery, 448 Delphian node, 198 Deltoid ligament, 814, 821 - ankle, 823–824 - deep, 819, 822, 823, 824 - posterior tibiotalar part of, 823 - superficial, 819, 822, 823, 824

INDEX Deltoid muscle, 533, 538, 539, 540, 541, 542, 543, 544, 545, 546, 547, 548, 549, 550, 551, 552, 553, 555, 556, 557, 561, 563, 567, 568, 678–679 Denonvilliers fascia, 434, 436 Denticulate ligament, 76 Dermis, 4, 5 Descending aorta, 172 Descending colon, 324, 338, 342, 346, 349, 388 - collapsed, long-axis view, 350 - site, 389 Descending genicular artery, 749 Detrusor instability, 521 Detrusor muscle, 427, 428, 511 Diaphragm, 224–227, 250, 259, 260, 261, 265, 270, 869, 912, 913, 928, 932, 933, 943 - central tendon, 224, 396 right leaf of, 226 - costal part of muscular component of, 226 - crura, 224, 331 - crus, 334, 335 left, 225, 227 right, 225, 227 - development, 907 - at full expiration, 227 - at full inspiration, 227 - hiatus, 224 - intersection between cursor line and, 227 - left crus, 396 - movement, 227 - muscular components, 224 costal part, 226 - pleura, 220, 225 - right crus, 396 - urogenital, 436, 444 Diaphragmatic crus, 260 Diastematomyelia, 889 Diastole - low-velocity forward flow, 415 - reversal of flow, 415 Diastolic flow, 463 Diastolic notch, 487 Diencephalon, 875 Digastric muscle - anterior belly, 89, 94, 95, 96, 97, 99, 100, 102, 103 - posterior belly, 88, 89, 100, 101, 102, 105, 106, 107, 108, 111, 112, 113, 114 Digital artery, 644, 662, 663, 666, 667, 702, 849 - dorsal, 849 - palmar, common, 644 - plantar, 849, 851 - proper, 645 Digital nerve, 667 - dorsal, 1st toe, 847 - plantar, 847 Digital tendon sheath, common, 629, 647, 657 Digital vein, 644, 666, 667 - dorsal, 613 - palmar, 612 Digital vessels, dorsal, 652 Dilated intraglandular ducts, 102 Dilated vein, 244

Diploic space, 4, 5, 6 Displaced hilar vascularity, 135, 205 Distal abdominal aorta, 412, 413 Distal airways, 906 Distal ductal branch, 237 Distal interphalangeal joint, 661, 665, 857 Distal pericallosal artery, 32 Distal phalanx, 651, 652, 665, 857 - of big toe, 857 Distal radioulnar compartment, 615 Distal radioulnar joint, 615 Distal splenic artery, 289 Distal tibia - anterior cortex of, 818 - posteromedial angle of, 820 Distal tibiofibular joint, 814 Distal ureter, dilated right, 433 Distal urethra, 517, 526, 527 Distal vagina, 490 Diverticulum, 432 Dominant follicle, 862 Dorsal calcaneocuboid ligament, 825 Dorsal carpal arch, 641 Dorsal cuboidonavicular ligament, 838 Dorsal dermal sinus, 888 Dorsal digital artery, 849 Dorsal digital nerve, 1st toe, 847 Dorsal digital vein, 613 Dorsal digital vessels, 652 Dorsal horn, 76 Dorsal intercarpal ligament, 627 Dorsal intermetatarsal ligament, 835 Dorsal interosseous muscle, 628, 630, 634, 635, 636, 638, 639, 648, 653, 654, 656, 662, 666, 849, 851, 854 - 1st, 638, 841 - 2nd, 638, 841 - 3rd, 638, 841 - 4th, 637, 638, 658, 841 Dorsal Lisfranc ligament, 835 Dorsal median sulcus, 76 Dorsal mesentery, 891, 925 - 18-day embryo, 926 Dorsal metacarpal artery, 641 Dorsal metacarpal vein, 613 Dorsal metatarsal artery, 847, 849 Dorsal metatarsal vein, 851 Dorsal nerve root, 76, 80 Dorsal pancreatic artery, 296 Dorsal penile arteries, 461 - paired, 458 Dorsal radiocarpal ligament, 627, 639 Dorsal radioulnar ligament, 626, 627 Dorsal scaphotriquetral ligament, 627 Dorsal scapular artery, 571 Dorsal scapular nerve, 130, 557 Dorsal talonavicular ligament, 825, 835, 836 Dorsal tarsometatarsal ligament, 835 Dorsal vein, 836, 839 Dorsal venous arch, 613, 837, 848, 851, 854 Dorsal venous plexus, 641 Dorsal vessels, 837 xi

INDEX Dorsalis pedis artery, 794, 811, 817, 818, 836, 837, 838, 846, 847, 848 Dorsalis pedis vein, 817, 837 Dorsum hand, 639 Double decidual sac sign, 865 Duct orifices, 237 Ducts, 240, 242, 243 - breast, 243 - crossing, 300 - normal, 241 - to segment IV, 276 - to segments II-III, 276 - of Wirsung, 300, 301 Ductus arteriosus, 915, 919, 922 Ductus venosus, 871, 922, 925, 931 - umbilical vein, 933 Duodenal bulb, 339, 344 Duodenojejunal flexure, 929 Duodenojejunal junction, 293 Duodenum, 274, 278, 280, 293, 301, 312, 313, 336, 340, 344, 925, 929, 932 - 2nd portion, 340, 344 - 2nd segment of, 301 - 3rd portion, 340, 341, 344, 387 - 4-week embryo, 927 - 4th portion, 344 - gas within, 298 - in situ, 339 Dura mater, 76, 77, 80 Dural nerve root sleeve, 76, 79 Dysjunction, 888

E

Ears, 894 - anomalies, 895 - embryology, 897 - low-set, 895 Echogenic complex, 79, 80 Echogenic hilum - normal jugular lymph node, 202 - preserved, 202 Ectocervix, 482, 483, 486 Ectoderm, 888, 924 - body, 891 - cutaneous, 890 - neural, 890 Ectopic ureter, 425, 433 Efferent ductules, 448 Ejaculatory ducts, 434–435, 436, 437, 438, 439, 441, 444 Elbow, 578–597 - anterior, 583–584 - anterolateral, 587 - anteromedial, 592 - common extensor origin, 589 tendons, 590 - common flexor origin, 596 xii

- coronal, 579 - distal, 582 - flexor aspect, 593 - lateral, 588, 591 - ligaments around, 594 - mid, 581 - posterior, 597 - proximal, 580 Embryo, 865, 866, 867, 868, 874 - 1st trimester, 874–875 - crown end, 867, 874 - rump end, 867, 874 - trilaminar, 866 - yolk sac separation from, 869 Embryoblast, 863 Embryology and anatomy, of brain, 872–887 Embryonic development, 860 - 6 weeks, 866 - 7-8 weeks, 867 - 8-9 weeks, 868 - 10-13 weeks, 869 Embryonic disc, 916 Embryonic rump, 875 Emissary veins, 461 Empyema, 223 End diastole, 263 End diastolic flow, 463 Endocardial cushions, 914 Endocardial ridges, 914 Endocardial tubes, 914 Endocervical canal, 469, 478, 482, 486 Endocervix, 482, 483 Endoderm, 888, 924 Endometrial canal, 483 Endometrial cavity, 864 - fluid, 471 Endometrium, 468, 469, 470, 473, 474, 475 - basal layer, 474, 480 - central line, 474 - cyclic changes, 478, 479 - decidualized, 864 - early proliferative phase, 478 - early secretory phase, 479 - functional layer, 478, 480 - inner functional layer, 474 - secretory phase, 479 - shedding, 479 Endopelvic fascia, 504 Endothoracic fascia, 229, 230 Epiblast, 863 Epicondyle, humerus - lateral, 579, 580, 587, 589, 590, 591, 597 - medial, 579, 580, 592, 595, 596, 597, 698 Epicranial aponeurosis, 5 Epicranial tissue, 4 Epidermis, 4, 5 Epidermoid cyst, 97 Epididymal appendage, 457 Epididymal artery, 454 Epididymis, 437, 446, 449, 454, 455, 457 - appendix, 457

INDEX - body, 448, 455, 456, 457 - head, 448, 449, 455, 457 - tail, 448, 449, 457 Epidural fat, 76, 79 Epidural hematoma, 82 Epigastric artery - deep inferior, 398 perforator branch, 398 - inferior, 419 - superficial, 749 Epigastric vessels, deep inferior, 398, 405 Epiglottis, 97, 115, 143, 150, 153, 155, 157, 162 - fixed portion, 151 - free edge, 151, 153 - free margin, 153 Epiploic foramen (of Winslow), 389 Epitrochlearis muscle, 696 Erectile dysfunction, 458 Erectile function, 458, 462, 463, 464 Erector spinae muscles, 230, 304, 321, 709 - left, 404 - right, 400, 401, 403, 404, 405 Esophageal hiatus, 224, 225 Esophageal lumen, 160 - air, 163 - nasogastric tube, 163 Esophageal mesenchyme, 907 Esophageal tumor, 163 Esophagus, 90, 121, 127, 138, 139, 140, 141, 145, 146, 147, 158–163, 167, 193, 195, 209, 225, 336, 338, 396, 928 - axial CECT, 161 - cervical, 158, 159 - CT, 162 - foregut-derived, 908 - graphics, 159 - longitudinal ultrasound, 162 - pathology, 163 - primitive, 908 - transverse ultrasound, 160 Ethmoid air cells, 97 Extensor carpi radialis brevis muscle, 581, 582, 588, 590, 598, 599, 600, 602, 605, 608, 616, 617, 619, 681–682, 689 Extensor carpi radialis longus muscle, 564, 580, 581, 582, 585, 586, 587, 588, 590, 598, 599, 600, 602, 605, 608, 609, 616, 617, 619, 681 - tendon, 682 Extensor carpi ulnaris muscle, 582, 588, 597, 598, 599, 605, 616, 617, 621, 626, 637, 658 Extensor digiti minimi muscle, 598, 599, 605, 616, 617, 620, 621, 682 Extensor digitorum brevis muscle, 816, 828, 835, 836, 837, 838, 839, 848 - tendon, 839 Extensor digitorum communis muscle, 637, 656, 658, 659 Extensor digitorum longus muscle, 782–785, 787, 802 - tendon, 814–815, 816, 817, 836, 838, 839, 849, 851, 857 Extensor digitorum minimi muscle, 656, 658

Extensor digitorum muscle, 581, 582, 588, 598, 599, 602, 605, 616, 620, 639, 665, 666, 682 - slip, 591 - tendon slips, 617 Extensor expansion, 646, 656, 666, 667 Extensor hallucis brevis muscle, 816, 835, 838 - tendon, 854 Extensor hallucis longus muscle, 782–784, 788, 817, 818 - tendon, 814, 816, 817, 818, 819, 836, 837, 839, 848, 854 Extensor hood, 630, 637, 658, 666 Extensor indicis muscle, 605, 616, 617, 637, 656, 658 Extensor muscle, 646 Extensor pollicis brevis muscle, 598, 605, 616, 617, 618, 622, 643, 646, 658 Extensor pollicis longus muscle, 598, 602, 605, 616, 617, 619, 620, 637, 646, 648, 652, 682 Extensor retinaculum, 616, 620, 637, 639, 658, 794, 811 - inferior, 814, 816, 817, 835, 837 - superior, 814, 816, 817, 835 Extensor tendon, 639, 655, 667 - common, 578, 579, 581 graphic, 599 longitudinal US, 589 origin, 589–590 transverse US, 590 External anal sphincter, 342, 507, 509, 512, 513, 517, 526 - muscle complex, 515 External auditory meatus, 105, 880 External carotid artery, 43, 90, 105, 106, 107, 108, 111, 112, 113, 114, 115, 116, 117, 137, 167, 170, 171, 173, 174, 175, 176, 177, 178–179, 187, 201 - branches, 114, 116, 117, 174, 176, 177, 178 - spectral Doppler waveform, 179 External iliac artery, 409, 410, 414, 415, 418, 420, 422, 426, 471 - left, 419 - right, 402, 403, 405, 418, 419 External iliac nodes, 353, 355 External iliac vein, 411, 415, 418, 420, 421, 422, 426, 471 - left, 419 - right, 402, 403, 405, 418, 419 External iliac vessels, 495 External intercostal membrane, 233 External intercostal muscle, 229, 230 External jugular vein, 101, 115, 121, 127, 131, 133, 167, 175, 177, 179, 190, 191, 193, 194, 195, 196 - tributaries, 132 External oblique fascia, 449 External oblique muscle, 222, 232, 395, 397, 449, 450, 720, 724, 935, 941 - right, 399, 402, 403, 405 External os, 469, 482, 483, 484, 486, 490 External pudendal artery, 749 External spermatic fascia, 449, 450 External urethral meatus, 511 External urethral sphincter, upper sphincter portion of, 511 Extracranial branches, in head and neck, 164 Extracranial internal carotid artery, 43 xiii

INDEX Extracranial segment, 164 Extraembryonic mesoderm, splitting to form chorionic cavity, 863 Extrahepatic bile duct, 274 Extralobular terminal duct, 237 Extraosseous (V1) artery segment, 184, 185 Extraperitoneal rectum, 514 Extraspinal (V3) artery segment, 184, 185 Extrinsic carpal ligament, 623 Extrinsic flexor muscles, 628 Eyelids, 42, 897, 899 - upperlid, 41 Eyes, 14, 15, 24, 53, 894–895, 896, 897, 898, 943 - anomalies, 895 - left, 876 - medial epicanthus, 897, 899, 900 - right, 876

F Face - anatomy, 894–905 - bones, 902 - embryology, 894–905 common anomalies, 895 - lymphatics, 894, 895 Facet joint, 230 Facial artery, 89, 100, 101, 102, 103, 170, 171, 173, 175, 177, 178, 179 Facial clefts, 895 Facial nerve - buccal branches, 105 - cervical branch, 105 - intraparotid, 105, 107 - main trunk, 105 - mandibular branch, 105 - temporal branches, 105 - zygomatic branches, 105 Facial vein, 43, 90, 95, 101, 102, 103, 114, 115, 117, 190 - angular branch, 191 - common, 191 Falciform ligament, 248, 250, 251, 256, 259, 269, 270, 271, 339, 392, 925, 928, 929 Fallopian arteries, 470 Fallopian tube, 409, 468, 469, 470, 481, 489, 495, 496 - interstitial (intramural) portion of, 469 Fallopian tubes, 935, 940 False pelvis, 506 False ribs, 229 Falx, 15, 16, 18 - cerebri, 17, 19 Falx cerebelli, 886 Falx cerebri, 14, 56, 70, 876, 878, 884 Fascia, investing, 808, 809 - separating superficial and deep calf, 809 Fasciculata, 934 Fastigial point, 887 - of vermis, 877 xiv

Fat, 130, 240, 241, 242 Fat-filled buccal space, 110 Fat lobule, 241 Fat pad, 587 - anterior, 580, 583 - posterior, 580, 597 Fatty hilum, effaced, 245 Fecal incontinence, 505 Femoral artery, 727 - common, 719, 722–723, 729–731, 743, 749, 752, 753 - profunda, 723, 731, 739, 741, 744 - superficial, 731, 744, 745 Femoral condylar cartilage, medial, 769, 777 Femoral condyle - lateral, 764, 769, 773, 777–778 - medial, 769–771, 779 Femoral cortex - anterior, 739–741 - lateral, 741, 745 - medial, 743, 745 - posterior, 746 - posteromedial, 747 Femoral head, 506, 710, 727, 730, 734, 752 - anterior cortex, 722 - cartilage, 732 anterior, 732 - posterior cortex, 710 Femoral neck, 714, 730–731 - posterior cortex, 714 Femoral nerve, 719, 722, 725, 727, 729–731, 743, 751, 753 Femoral shaft, 743 - cortex of, 733–734 Femoral triangle, apex, 751 Femoral vein, 727 - common, 719, 722–723, 729–731, 740, 743, 745 - compression, 759 - medial circumflex, 723 - profunda, 723, 739, 744 - superficial, 744–745 Femoral vessels, 748–761 - circumflex, lateral, 740 Femur, 766 - anterior surface, 731 - cortex, 714 - popliteal surface, 752 - trochlear surface, 765 Fertilization, 860, 862 Fetal lobulation, 332 Fetoplacental circulation, 915 Fetus - 1st trimester, 876 - 2nd trimester, 877 Fibrocartilaginous ridge, 825 Fibroglandular tissue, 240, 241, 242, 243, 244 Fibrous bands, 240 Fibrous tissue, 236, 240 Fibula, 797, 798, 800, 802, 806, 819, 822, 825, 826 Fibular cortex, 817 - lateral, 783–784, 786 - posterior, 812

INDEX Fibular head, 794, 811 Fibular ligaments, ankle, 828 Fibular sesamoid, 853 Filum terminale, 77, 80, 81, 888 Fimbriae, 481 Fingers, 656–667 - axial, 667 - extensor aspect, 665–666 - fingers, 657 - graphic, 664 - ligaments, 658 - longitudinal US, 660–661 - metacarpophalangeal joint, 659 - pulleys, 658 - transverse US, 662–664 1st trimester, embryology and anatomy, 860–871 Flash artifact, 32 Flexion, 468 Flexor carpi radialis muscle, 563, 598, 600, 601, 602, 604, 609, 617, 622, 623, 625, 682, 689–690 Flexor carpi ulnaris muscle, 568, 581, 582, 583, 596, 597, 610, 617, 622, 642, 678, 690, 695–696, 698–701 Flexor digital tendon sheath, 628 Flexor digiti minimi brevis muscle, 622, 632, 636, 702, 843, 845 Flexor digiti minimi muscle, 629, 633, 647, 657, 693, 840, 841 Flexor digitorum brevis muscle, 819, 840, 842, 843, 844, 845, 856 - individual digital tendon slips, 840 - insertions, 840 - tendon, 851, 853, 856, 857 Flexor digitorum longus muscle, 798, 809, 820, 843 - individual tendon slips, 840 - synovial fluid and, 820 Flexor digitorum longus tendon, 793, 811, 815, 820, 821, 823, 840, 842, 843, 844, 851, 856, 857 - insertions, 840, 857 Flexor digitorum muscle, 642, 659 Flexor digitorum profundus muscle, 581, 582, 596, 598, 600, 601, 602, 609, 610, 617, 622, 623, 628, 632, 644, 647, 656, 662, 663, 664, 667, 689–692, 699–701 Flexor digitorum superficialis muscle, 581, 582, 593, 596, 598, 600, 601, 602, 604, 608, 610, 617, 622, 623, 628, 632, 644, 647, 656, 657, 662, 663, 667, 682, 689–691, 699–701 - tendon, 629 Flexor hallucis brevis muscle, 855, 856 - lateral head, 840, 841, 853, 855 tendon insertion of, 855 - medial head, 840, 841, 853 Flexor hallucis brevis tendon, 843 - medial slip, 856 - sesamoid bone lateral head, 856 medial head, 856 Flexor hallucis longus muscle, 783–784, 786–787, 790–791, 798, 799, 800, 801, 803, 805, 820, 826, 828, 829, 830

Flexor hallucis longus tendon, 793, 811, 812, 819, 820, 821, 840, 841, 843, 844, 853, 855, 856, 857 Flexor pollicis brevis muscle, 622, 624, 632, 633, 634, 635, 651, 653, 654, 692 Flexor pollicis longus muscle, 598, 600, 601, 602, 609, 617, 622, 623, 624, 646, 649, 651, 653, 654, 689–692 - tendon, 629, 634, 635 Flexor retinaculum, 617, 622, 623, 624, 629, 633, 642, 647, 657, 691–692, 693, 701–702, 794, 814, 820 Flexor tendon, 623, 624, 629, 632, 647, 655, 657, 659, 660, 661, 664, 692 - common, 578, 579, 580, 581, 594, 686 longitudinal US, 595 origin, 595–596 transverse US, 596 Flexor tendon sheath, 840 Flow reversal, in separation zone, 175 Folds, 386 Foley catheter, urinary bladder with, 393 Follicle - dominant, 862 - primordial, 862 Follicular phase, 494 Fontanelle, 4 - anterior, 4, 903 - anterolateral, 4 - mastoid, 4 - posterior, 4 - posterolateral, 4 - sphenoidal, 903 Foot - dorsal, 835–839 - plantar muscles deep layers, 841 superficial layers, 840 - sagittal, 843 - vessels, 846–851 Foramen cecum, 143 Foramen lacerum, 109 Foramen magnum, 78, 185, 887 Foramen ovale, 52, 918, 920, 922 - flap, 918, 920 Foramen rotundum, 52 Foraminal (V2) artery segment, 184, 185 Forearm, 598–605 - anterior, 600, 603 - anterolateral, 602 - anteromedial, 601 - arteries, 607 - common flexor tendon, 604 - distal, 611 - posterior, 605 - proximal, 608 - venous system, 612–613 - vessels, 606–613 Forebrain prominence, 930 Foregut, 908, 909, 924 Fornices, 878, 881, 886 Fornix, 11, 20, 21, 31 Fossa, posterior, 886–887 Fossa navicularis, 460, 461 xv

INDEX 4th ventricle, 12, 20, 21, 26, 28, 29, 37 Frontal bone, 900, 902, 903 - paired, 900 Frontal gyrus, superior, 14 Frontal horn, 12, 14, 15, 879, 880 Frontal lobe, 8, 14, 16, 20, 21, 56, 876, 880 - left, 876 - right, 876 Frontal operculum, 879 Frontonasal prominences, 894, 896 - primordia, 895 Frontonasal suture, 5 Frontopolar artery, 55 - branches, 54 Fundus, 274, 339, 473, 474 - of bladder, 428 Fused lower poles, 329 Fused synchondrosis, 78

G Galen, vein of, 32, 36, 37, 70, 71 Gallbladder, 226, 250, 252, 270, 272, 274, 278, 279, 280, 294, 312, 313, 317, 339, 390, 928, 933, 943 - fundus, 265 - lumen, 265, 277 - neck glands, 277 - in situ, 274 - wall, 265 fold, 265 - wall muscle, 277 Gastric antrum, 295, 344 Gastric artery, left, 253, 254, 255, 285, 339 Gastric impression - liver, 250 - spleen, 286 Gastric pylorus, 227 Gastrocnemial vein, 791 Gastrocnemius muscle, 806, 807, 808, 809 - aponeurosis, 791 - lateral head, 775, 790–791, 796, 797, 800, 801, 812 - medial head, 771, 775–776, 790–791, 796, 797, 798, 812 - nerve to medial, 775 Gastrocnemius tendon, 770 Gastrocnemius vein, 797, 807 Gastrocolic ligament, 339, 387, 925 Gastroduodenal artery, 253, 254, 255, 293, 295, 296 Gastroduodenal region, 344 - air within, 298 Gastroepiploic artery, 339 - right, 253 Gastroesophageal junction, 342 Gastrointestinal tract, 870 - abdominal organs, 925 - abdominal vessels, 924–925 - anatomy, 924–933 - bowel rotation, 928–929 xvi

- defects in development, 925 - embryology, 924–933 2nd week: 8-14 days post conception, 924 3rd week: 15-21 days post conception, 924 4th week: 22-28 days post conception, 924, 927 5th week: 29-35 days post conception, 924 6th-7th weeks: 36-49 days post conception, 924 8th week: 50-58 days post conception, 924 9th week, 924 10th week, 924 18-day embryo, 926 rule of 2s, 924 - mouth and anus formation, 930 - in situ, 338 Gastroomental vessels, 925 Gastrophrenic ligament, 389 Gastroschisis, 925 Gastrosplenic ligament, 284, 285, 388, 925 Gastrulation, 924 Gemellus muscle, 751 - inferior, 708–709, 714, 742 - superior, 708–709, 742 Geniculate artery - lateral, inferior, 773 - medial, inferior, 777 Genioglossus muscle, 89, 93, 94, 95, 96, 97, 101 Geniohyoid muscle, 89, 93, 94, 95, 96, 97 Genital tract development - female, 935, 940 - male, 935, 941 Genital tubercle, 928, 937, 940, 941 Genitourinary tract, embryology and anatomy, 934–943 Germ cells, 935 Glands of Littre, 460 Glandular elements, 240, 241 Glans penis, 458, 459, 461, 467 Glenohumeral joint, 229, 553 Glenoid, 543, 553, 556 Glenoid fossa, 540 Glenoid labrum, 536, 539 Globe, 40, 47, 48 Glomeruli, 936 Glomerulosa, 934 Glossoepiglottic fold, 151 Glossopharyngeal nerve, 93, 165 Glottic larynx, 150, 152 Gluteal fascia, 733 Gluteal muscle, 81, 706–715, 892 - graphics, 708–709 - ischial region, 713 - ischial tuberosity, 715 - overview, 710 - right, 405 - sagittal gluteal region, 711 - transverse, 712, 714 Gluteal vein, inferior, 715 Gluteus maximus muscle, 509, 708–715, 724, 733, 739, 741–742 Gluteus medius muscle, 708–712, 719, 724, 733–735, 742 Gluteus minimus muscle, 724, 742 Gluteus minimus tendon, 732–734

INDEX Gluteus muscles, right, 403 Gonadal arteries, 305, 426 Gonadal vein - left, 305 - right, 305 Gonadal vessels, right, 308 Gracilis muscle, 708–709, 717–718, 720–721, 724, 738, 742–743, 745–746, 764, 775, 776 - tendon, 770–771, 779 Gray matter, 76 Great arteries, septation, 914 Great pancreatic artery, 293 Great saphenous vein, 743, 745, 792, 795, 809, 846 Greater omentum, 339, 341, 387, 388, 389, 925, 929 Greater peritoneal cavity, 388 Greater saphenous vein, 717, 719, 723, 750 Greater sciatic foramen, 506, 713 Greater trochanter, 708, 710–711, 727–728, 733 - lateral surface, 733 - medial surface, 713–714 - superior surface, 713, 733 - unossified, 734 Greater tuberosity, 541, 542, 549, 551 Greater vestibular gland, 509 Groin, 716–725 - across, 725 - central, 722–723 - graphics, 717–718 - lateral, 724 - medial, 721 - middle, 720 - overview, 719 Gubernaculum, 450, 935, 941 Gut, 936 Gut tube, 870, 891 Guyon canal, 701 Gyrus, 8 - central, 881, 882 - cingulate, 878, 879, 881–882, 884, 885, 887 - convexity, 885 - development, 872 - mature, temporal lobe with, 886 - postcentral, 880, 881, 882, 884 - precentral, 880, 881, 883 Gyrus rectus, 15, 54

H Hair follicle, 5 Hamate, 615, 620, 636, 639, 691 - hook of, 624, 636, 642, 702 Hamstrings, originating from ischial tuberosity, 713 Hand, 628–639 - arteries, 611, 645 - deep dissection, 647 - dermatomes, 667 - dorsal aspect, 637, 643 - dorsal interossei, 638 - dorsum, 639

- hypothenar eminence, 636 - interossei muscles, 630 - lumbrical muscles, 630 - palm, 632, 642 - palmar aspect, 629, 644 - palmar muscles, 631 - thenar eminence, 634–635 - thenar-hypothenar eminence, 633 - vessels, 640–645 Hard palate, 95, 97 Head and neck - carotid arteries, 170–183 - cervical lymph nodes, 198–205 - front, 905 - larynx and hypopharynx, 150–157 - lower cervical level and supraclavicular fossa, 124–129 - midcervical level, 118–123 - neck veins, 190–197 - parathyroid glands, 144–149 - posterior triangle, 130–135 - thyroid gland, 136–143 - trachea and esophagus, 158–163 - upper cervical level, 112–117 - vagus nerve, 164–169 - vertebral artery, 184–189 Heart, 219, 259, 264, 278, 279, 933, 943 - 4-chamber, 917 - 4-week embryo, 927 - anatomy, 915 - normal chamber/vessel morphology, 915 - primitive, 18-day embryo, 926 - primordial, 908 - segmental nomenclature, 915 Heart field, 914 - primary, 914 - secondary, 914, 916 Heart tube, primitive, 914, 916 - outlet end, 916 Helicine arteries, 458, 460, 461, 462 Helix, 897, 900 Hemidiaphragm - crus of, 335 - left, 287, 320, 392 thoracic surface, 226 - right, 227, 312, 338, 390 crus of, 333 posterior aspect of, 227 Hemivertebrae, 889 Hepatic artery, 259, 263, 280, 281, 296, 314 - accessory left, 254 - anatomy, 253 - common, 249, 253, 254, 255, 285, 288 - "conventional" right and left, 254 - left, 252, 253, 254, 255 - proper, 252, 253, 254, 255, 274 - right, 249, 252, 253, 254, 255, 263 - variants, 254, 255 Hepatic diverticulum - 4-week embryo, 927

xvii

INDEX Hepatic duct - common, 252, 274, 276, 280 conventional junction of cystic and, 275 - left, 252, 275, 276 accessory, 275 - right, 252, 275, 276 accessory, 275 Hepatic flexure, 342 Hepatic lobe - left, 274, 279, 280, 283, 288 - right, 274, 278, 280, 282 Hepatic vein, 248, 249, 920, 931 - branch, 249, 262, 265 - confluence of, 248, 270, 271 - left, 252, 256, 258, 259, 260, 261, 264, 270, 279, 931 plane, 268, 269, 271 - middle, 249, 252, 256, 257, 258, 260, 261, 264, 278 plane, 268, 269, 270, 271 - plexus, 931 - precursors, 925 - right, 252, 256, 257, 258, 260, 261, 931 branch, 260 plane, 268, 269, 270 Hepatoduodenal ligament, 339, 340, 389 Hepatoduodenal papilla, 276 Hepatogastric ligament, 339, 389 Hepatorenal fossa, 304 Hepatorenal fossa fluid, 391 Herniation, physiologic, 924 Heterotaxy, 291 High internal jugular lymph nodes, 87, 200, 201 High spinal accessory lymph nodes, 87, 200 Hilar blood vessels, 242 Hilar fat, 245 Hilar vascularity - displaced, 205 - within normal lymph node, 203 Hillocks - abnormal development, 895 - auricular, 897 Hindgut, 870, 924, 928, 930 - 4-week embryo, 927 Hip, 726–735 - acetabulum, 730 - joint capsule, 732 - minimal hypoechoic layer of joint fluid/synovium, 730 - overview, 729 - pediatric, 734–735 Histogenesis, brain, 872 Hoffa fat pad, 764–765, 767–768 Holoprosencephaly, 895 Hook of hamate, 624, 636, 642, 691, 702 Horizontal (A1) anterior communicating artery segment, 34 Horseshoe kidney, 329, 934 Humeral artery, circumflex - anterior, 571 - posterior, 571 Humeral head, 533, 541, 542, 543, 544, 545, 546, 547, 548, 549, 550, 552, 553, 556, 943 Humeral neck, 557 xviii

Humeral shaft, 546, 558, 560, 561, 563, 566, 567, 569, 573, 574, 575, 576 Humerus, 560, 561, 563, 564, 670, 698 - capitellum, 583, 584, 585, 587, 589, 590, 591, 688 - distal, 580 - greater tuberosity, 568, 678 - head, 686, 698 - lateral epicondyle, 579, 580, 587, 589, 590, 591, 597 - lateral supracondylar portion, 567 - medial epicondyle, 579, 580, 592, 595, 596, 597, 698 - shaft, 679–680, 687, 697, 698 - trochlea, 584, 585, 592, 596, 688 Hyaline cartilage, 766 Hydrocele, 447, 452, 455, 457 Hydronephrosis - mild, 430 - upper pole, 328 Hydrops fetalis, cystic hygroma associated, 895 Hydrosalpinx, 481 Hygroma, cystic, 895, 905 Hyoepiglottic ligament, 151, 153 Hyoglossus muscle, 89, 93, 100, 101 Hyoid bone, 87, 97, 113, 115, 119, 125, 143, 151, 153, 156, 157, 159, 162, 175, 179, 187 - plane, 199 Hyperechoic ossification center, 81 Hypertelorism, 895 Hypoblast, 863 Hypoechoic cartilaginous portion, 81 Hypoglossal nerve, 93, 165 Hypoglossus muscle, 95 Hypognathia, 895 Hypopharynx, 97, 137, 150, 155, 162, 175, 177. See also Larynx and hypopharynx. - fluid, 901 - postcricoid, 152 Hypotelorism, 895 Hypothenar eminence, 622 - hand, 628, 636 - nerve to, 695

I Ileal segment, 345 Ileal straight artery, 341 Ileocecal junction, 346, 347 - anterior lip, 347 - posterior lip, 347 Ileocolic artery, 141 Ileum, 336, 345 - terminal, 346, 347, 929 Iliac arteries and veins, 408–423, 932, 938, 942 - common, 749 - in situ, 409, 411 Iliac blade, 347 - right, 403 Iliac bone, 506, 507

INDEX Iliac crest, 304, 397, 418, 709–710, 742, 892, 932 - right, 402 Iliac lymph sacs, 895, 904 Iliac muscle, right, 402 Iliac spine, 727 - inferior anterior, 728–729, 732 posterior, 713 - superior, anterior, 728, 738, 742 Iliac vein, 497 - common, 750 Iliac vessels - CT, 417, 419 - external, 719 - transverse, 416, 418 Iliacus muscle, 347, 396, 717–718, 724, 731, 738, 742 - pelvic wall, 350 - right, 403 Iliococcygeus muscle, 491, 504, 507, 508, 509, 515 Iliocostalis muscle, 397, 404 Iliofemoral ligament, 724, 728, 731 Iliolumbar artery, 409, 410, 419 Iliolumbar vein, 411 Iliopsoas complex, right, 346 Iliopsoas muscle, 719, 722, 724, 725, 752, 753 - bursa, 727 - insertion, 396, 731 - right, 402, 403, 405, 418 Iliopubic eminence, 506 Iliotibial band, 738 Iliotibial tract, 708–711, 733, 794, 811 Ilium, 711–713, 727 Implantation, 860, 863 Incomplete minor fissure, 220 Inferior acromioclavicular ligament, 533 Inferior adrenal vessels, left, 305 Inferior alveolar artery, 173 Inferior alveolar nerve, 99, 101 Inferior calcaneal nerve, 819 Inferior cerebellar artery, 70 Inferior cortical fusion, 329 Inferior epigastric artery, 419, 725, 749 Inferior epigastric vein, 725 Inferior epigastric vessels, 719 Inferior extensor retinaculum, 814, 816, 817, 835, 837 - distal limb, 816 - proximal limb, 816 - stem, 816 Inferior frontal gyrus, 10, 15, 17, 23 Inferior frontal lobe, 20 Inferior frontal sulcus, 15 Inferior gemellus muscle, 708–709, 714, 724, 742 Inferior glenohumeral ligament complex, 540, 551 Inferior gluteal artery, 410, 749 Inferior gluteal vein, 715 Inferior hemispheric branches, 66 Inferior iliac spine - anterior, 506, 728–729, 732 - posterior, 713 Inferior ischiopubic ramus, 459 Inferior lateral genicular artery, 749

Inferior lateral geniculate artery, 793 Inferior liver margin, 265 Inferior medial geniculate artery, 749, 777, 793 Inferior mesenteric artery, 305, 329, 342, 344, 409, 417, 426, 470, 924, 928 Inferior mesenteric nodes, 353 Inferior nasal concha, 97 Inferior nasal turbinate, 95 Inferior oblique muscle, 39, 41, 111 Inferior occipital gyrus, 19 Inferior ophthalmic vein, 43, 46, 191 Inferior parathyroid glands, 144, 145 Inferior parietal lobule, 10 Inferior patellar tendon, 770, 782, 794, 811 Inferior peroneal retinaculum, 814, 825, 827 Inferior petrosal sinus, 70 Inferior pharyngeal constrictor muscle, 159 Inferior phrenic artery, 255, 331 Inferior phrenic vessels, 305 Inferior pubic ramus, 506 Inferior rectus muscle, 39, 41 Inferior sagittal sinus, 36, 70 Inferior temporal gyrus, 10, 17, 23 Inferior thyroid arteries, 127, 136, 137, 138, 139, 140, 141, 145, 167, 571 Inferior thyroid vein, 137, 139, 141, 145 Inferior transverse ligament, 814, 822 Inferior ulnar collateral artery, 607 Inferior ureter - left, 328 - right, 328 Inferior vena cava (IVC), 21, 225, 226, 227, 250, 251, 252, 256, 257, 258, 260, 262, 263, 264, 271, 278, 279, 280, 282, 283, 288, 294, 295, 297, 298, 301, 307, 308, 309, 313, 314, 317, 325, 329, 334, 335, 341, 344, 392, 400, 402, 405, 409, 411, 416, 417, 871, 891, 920, 922, 923, 931 - foramen, 225 - left, 309 - left-sided, 309 - right, 309 - sulcus for, 251 Inferior vermian, 66 Inferior vesicle artery, 470, 489 - ureteric branch, 426 Inferolateral trunk, 52 Inflamed Rokitansky-Aschoff sinus, 277 Infrahyoid strap muscle, 121, 133, 139, 167, 193 Infrahyoid thyroglossal duct cyst, 143 Inframesocolic space, 393 Infraorbital artery, 173 Infraorbital node, 200 Infrapatellar bursa, 767 Infrapatellar fat pad, 764–765, 767–768 Infraspinatus muscle, 231, 536, 538, 539, 549, 550, 551, 552, 553, 555, 556, 561, 568, 678 Infraspinatus tendon, 539, 540, 544, 549, 551, 555, 556 Infundibular recess, 12 Infundibulum, 481

xix

INDEX Inguinal ligament, 395, 396, 411, 506, 717, 718, 720, 721, 724, 725, 751, 753 Inguinal ring, superficial (external), 449, 451 Inner circular muscle layer, 515 Inner muscle layer, oblique, 339 Inner table, 4, 5, 6, 7 Innermost intercostal muscle, 229, 230, 232, 233 Insula, 8, 14, 17, 24, 25, 27 Insular cortex, 879, 880 Intercapitular vein, 612, 613 Intercarpal ligament, dorsal, 627 Intercavernous sinuses, 70 Interclavicular ligament, 530, 531 Intercostal artery, 229, 230 - anterior, 233 - collateral branch of, 233 - perforators, 239 Intercostal muscles, 222, 225, 232, 233, 240, 291 - external, 229, 230, 232 - innermost, 229, 230 - internal, 222, 229, 232, 233 Intercostal nerve, 229, 230 Intercostal neurovascular bundles, 231 Intercostal spaces, 222, 232, 233 Intercostal vein, 229, 230 - anterior, 233 - collateral branch of, 233 Intercostal vessels, anterior, 222 Intercostal window, 222 Interhemispheric fissure, 14, 15, 18, 19, 27, 34, 54, 72, 877, 878, 879, 882, 883, 885 Interligamentous sulcus, 627 Interlobar arteries, 306 Interlobular fibrous stroma, 241 Intermediate antebrachial vein, 612 Intermediate basilic vein, 612 Intermediate cephalic vein, 612 Intermediate cuneiform, 837, 839, 844, 848 Intermetatarsal ligament, dorsal, 835 Intermuscular fat plane, 91, 132 Intermuscular septum - anterior, 783 - lateral, 741, 746 - medial, 568, 678 - posterior, 783, 786–787 - posteromedial, 747 - transverse, 798 Internal anal sphincter, 515, 524, 526, 527 Internal capsule, 14, 15 Internal carotid artery, 34, 43, 50, 52–53, 58, 90, 107, 109, 111, 114, 115, 116, 117, 137, 161, 165, 167, 173, 174, 175, 176–177, 178, 179, 180, 181, 187, 201 - bifurcation, 34 - carotid bulb, 171, 173, 174 - cavernous (C4) segment, 52 - cavernous portion of, 97 - cervical, 112, 113, 170 - clinoid (C5) segment, 52, 53 - communicating (C7) segment, 52, 59, 63 - contralateral, 60, 64 - horizontal (C2) segment, 52 xx

- lacerum (C3) segment, 52 - ophthalmic (C6) segment, 52 - spectral Doppler waveform, 177 - stenotic segment, 180 - supraclinoid, 62 - vertical (C2) segment, 52 Internal cerebral veins, 31, 36, 70 Internal echoes, 432 Internal iliac artery, 414, 420, 421, 422, 426, 470, 480, 489, 502, 749, 923 - anterior division, 409, 410, 419 - left, 419 - posterior division, 410, 419 - right, 418, 419 Internal iliac (hypogastric) nodes, 353 Internal iliac vein, 411, 420, 421, 422, 471, 502, 750 - right, 418, 419 Internal iliac vessel, 403 Internal intercostal muscle, 222, 229, 233 Internal jugular nodal group (II-IV), 199 Internal jugular vein, 90, 91, 101, 107, 111, 112, 113, 114, 115, 116, 117, 118, 120, 121, 122, 123, 125, 126, 127, 128, 129, 133, 138, 139, 141, 146, 147, 160, 161, 165, 166, 167, 168, 169, 171, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 187, 190, 191, 192, 193, 194, 195, 196, 197, 201, 202, 203, 204, 209, 210, 211, 223, 672 - phasic venous waveform of, 193 - proximal, valve in, 126 - right, 122 - thrombosed, 197 - tumor thrombus, 122 Internal mammary artery, 137, 171 Internal mammary chain, 238 Internal mammary lymph nodes, 235 Internal maxillary artery, 52 Internal oblique muscle, 395, 397, 449, 450, 719, 935, 941 - right, 399, 402, 403, 405 Internal os, 469, 482, 483, 484, 486 Internal pudendal artery, 410, 727 Internal pudendal vein, 727 Internal spermatic fascia, 450 Internal thoracic artery, 211, 223, 230, 233, 571 Internal thoracic vein, 233, 239 Internal thyroid artery, 161 Interossei muscles, 630, 632, 667 - anterior, 670 - dorsal, 628, 630, 634, 635, 636, 638, 639, 648, 653, 654, 656, 662, 666, 849, 851, 854 1st, 638, 841 2nd, 638, 841 3rd, 638, 841 4th, 637, 638, 841 - palmar, 628, 631, 636, 644, 656, 662 1st, 631 2nd, 631 3rd, 631 - plantar, 849 1st, 841 2nd, 841 3rd, 841

INDEX - posterior, 641 Interosseous artery, 597 - anterior, 607, 623, 641 - common, 607, 640 - posterior, 607 - recurrent, 607 Interosseous ligament, 814 - talocalcaneal, 819 Interosseous membrane, 600, 601, 623, 783–786, 791, 794, 803, 811, 819, 822, 825 Interosseous nerve - anterior, 600, 623, 685–686, 690 - posterior, 582, 605, 677 Interosseous neurovascular bundle, anterior, 600, 689–690 Interosseous recurrent artery, 607 Interosseous talocalcaneal ligament, 836 Interosseous vein, 597 - anterior, 623 Interosseous vessels, anterior, 689 Interpeduncular cistern, 11, 27 Interphalangeal joint, 652 - distal, 661, 665, 857 - proximal, 637, 658, 661, 665 Interscalene triangle, 208, 212 Intersesamoid ligament, 853 Interspinous ligament, 75, 79 Intertrochanteric line, 728, 731 Intervertebral disc, 79, 101, 121, 892 Intestinal trunk (of cisternal chyli), 353 Intraarticular disc, 530 Intraaxial segment, 164 Intracavitary blood, 864 Intracranial translucency, 869, 876 Intracranial veins, 51, 70–73 Intradecidual sac sign, 864 Intradural/intracranial (V4) segment, 184, 185 Intradural lipoma, 888 Intrahepatic ducts, 282, 283 - left, 283 - right, 282 Intralobular acini (alveoli), 237 Intralobular stroma, 237 Intralobular terminal duct, 237 Intramammary lymph nodes, 235, 238 Intramuscular urethral artery, 522, 523 Intranodal cystic necrosis, 128, 204 Intranodal necrosis, 204, 205 Intraovarian artery, 502 - cyclic changes of, 502, 503 Intraparotid duct, 108 Intraperitoneal rectum, 514 Intrarenal artery - left, 326 - right, 318 Intrarenal branches, 942 Intrarenal segmental arteries, 326 Intrarenal vein, 318 - left, 326 - right, 318 Intratesticular artery, 454

Intratesticular vessels, 453 Intratumoral vascularity, 117, 169 Intratumoral vessels, 49 Intrauterine arteries, 480 Intrauterine device (IUD), 473 Intrinsic muscles, 154, 156 - hypothenar area, 628 - palmar area, 628 - thenar area, 628 Intrinsic sphincteric deficiency, 520 Intrinsic tongue muscles, 93 Investing fascia, 133 Ipsilateral anterior cerebral artery, 55, 56, 60 Ipsilateral middle cerebral artery, 55, 60 Ipsilateral posterior cerebral artery, 55, 63 Iris, 42, 47 Ischial ramus, 506 Ischial spine, 506, 507 Ischial tuberosity, 507, 709, 713–714, 715, 727 Ischiocavernosus muscles, 458, 459, 465, 509, 511 Ischiofemoral ligament, 728 Ischiopubic ramus, inferior, 459 Ischium, 465, 506, 509, 711, 713 Isthmus, 474, 481

J Jejunal arterial arcades, 341 Jejunal loops, 345, 346 Jejunal straight arteries, 341 Jejunum, 336, 340 Joint capsule, 531, 534, 535, 539, 553, 555, 556, 659, 660, 661, 666 Joint recess, 651, 652 Joint space, 648 Jugular lymph node, metastatic, 163 Jugular lymph sacs, 904 - internal, 904 - paired, 895 Jugular vein, 70 Jugulodigastric lymph node, 87, 90, 112, 114, 115, 116, 117, 174, 176, 177, 178 - echogenic hilus in, 116 - hilar vascularity of, 117 Jugulodigastric node, 101, 198, 199, 200, 201 Junctional fold, 280 Junctura tendinum, 637, 658

K

Kidneys, 286, 302–329, 332, 429, 892, 937, 938, 941, 942, 943 - ascent, 934, 938–939 - CT urogram, 310 - development, 936 - duplex, 303 xxi

INDEX -

fascia, 304 formation, 934 horseshoe, 329 hypertrophied column of Bertin, 327 left, 286, 290, 291, 294, 295, 299, 320, 322, 323, 324, 329, 331, 334, 335, 392, 401, 404, 932 anterior to anterolateral transverse scan, 322 anterolateral approach, 323 CT correlation, 320, 324 low-lying, 310 lower pole of, 321 mid pole of, 321 posterior scan, 319 posterior to posterolateral abdomen scan, 321 superior pole of, 291 upper pole of, 321 - perirenal space, 304 - right, 265, 270, 278, 295, 313, 314, 316, 329, 334, 335, 390, 399, 400, 401, 404, 932 anterior abdomen scan, 311, 313 CT correlation, 312, 314 with fetal lobulation, 312 lower pole of, 316 posterior abdomen scan, 315, 316 - in situ, 305 Knee, 762–779 - extensor mechanism, 764–769 - lateral, 772–774 - medial, 770–771 - posterior, 775–779

L L2 vertebral body, 429 L4 vertebral body, 417 L5 vertebral body, 417 Labia, 933 Labial groove, persistent, 895 Labioscrotal fold, 450, 941 Labrum, 540 - acetabular, 729–730, 734–735 - anterior, 727 - posterior, 727 - superior, 728 Lacrimal artery, 43, 45 Lacrimal gland, 40, 43 Lactiferous sinus, 234, 237 Lambdoid suture, 4, 5, 27, 29 Laminae, 79, 80, 892, 893 Large bowel, 336, 346, 349, 350 Large intestine, 925 Large medial lobulation, 286 Laryngeal cartilages, 150 Laryngeal ventricle, 150, 153, 157 Laryngotracheal groove, 906 Larynx and hypopharynx, 141, 150–157, 162, 906 - axial CECT, 155 - graphics, 151–153 xxii

- longitudinal ultrasound, 156 - sagittal and coronal reformatted NECT, 157 - transverse ultrasound, 154 Lateral antebrachial cutaneous nerve, 563, 564 Lateral arcuate ligament, 224, 396 Lateral band, 630, 637, 638, 658, 693 Lateral breast innervation, 234 Lateral calcaneal cortex, 826, 828 Lateral circumflex femoral artery, 749 Lateral circumflex femoral vein, 750 Lateral circumflex femoral vessels, 740 Lateral cord, 669 Lateral cuneiform, 838, 843, 845 Lateral cutaneous nerve, 677 - of forearm, 685 Lateral epicondyle, 579, 580, 587, 589, 590, 591, 597 Lateral femoral condyle, 764, 769, 773, 777–778, 812 Lateral femoral cortex, 741, 745 Lateral fibular cortex, 783–784, 786 Lateral gastrocnemius muscle, 764, 772 - nerve to, 775 Lateral inferior geniculate artery, 773 Lateral intermuscular septum, 741, 746 Lateral malleolar artery, 847 Lateral malleolus, 826, 828 - posterior cortex, 828 Lateral mass, 193 Lateral mesencephalic vein, 71 Lateral orbital wall, 40 Lateral orbitofrontal artery, 59 Lateral patellar retinaculum, 738, 769, 773 Lateral pectoral nerve, 703 Lateral plantar artery, 794, 844, 845, 847, 850 Lateral plantar nerve, 819, 833, 844, 845, 850 - deep branch, 847 - superficial branch, 847 Lateral plantar neurovascular bundle, 845 Lateral plantar vein, 844, 845, 846, 850 Lateral posterior choroidal artery, 66 Lateral rectus muscle, 39, 40, 41, 48, 49 Lateral sacral artery, 409, 410, 470 Lateral sacral vein, 411 Lateral segment (left lobe), 251 Lateral sesamoid, 841, 853 Lateral tarsal artery, 811, 838, 839, 847, 848 Lateral thoracic artery, 571 Lateral tibial cortex, 783–784, 786, 802 Lateral ulnar collateral ligament, 594 Lateral ventricle, 16, 17, 21, 31, 873, 877, 879, 883, 885 - body, 12, 16, 19, 20, 22 - frontal horn, 20, 878, 881, 882 - occipital horn, 877, 884 - temporal horn, 885, 886 - width, 877 Lateroconal fascia, 304 Latissimus dorsi muscle, 230, 231, 304, 315, 319, 533, 539, 550, 551, 555, 556, 560, 561, 563, 568, 678 - left, 319 - tendon, 538 Left anterior cerebral artery, 55 Left atrium, 915

INDEX Left hepatic vein, 342 Left lateral vaginal fornix, 486 Left lobe lateral segment, 257 Left major fissure, 220, 221 Left ovary, 495 Leg muscles, 780–791 - anterior compartment, 784–785 - anterolateral leg, 782–783 - lateral compartment, 786–787 - lateral leg, 788 - posterior, 789–791 Legs, 905 - arteries, 804 anterior, 794 posterior, 793 - nerves, 810–812 - veins, 795, 805 - vessels, 792–809 Lens, 42, 47, 49 - eyes, 898, 899 - vesicle, 897 Lenticulostriate artery, 58 Leriche syndrome, 458 Lesser omentum, 251, 274, 285, 387, 388, 928 Lesser sac (omental bursa), 387, 388, 391, 925 - fluid, 392 Lesser saphenous vein, 783, 828 - tributaries of, 826, 827 Lesser sciatic foramen, 506 Lesser trochanter, 728, 731, 738 Lesser tuberosity, 551 Levator ani muscle, 342, 396, 427, 428, 459, 489, 491, 504, 505, 508, 509, 511, 514, 516, 517, 526 Levator palpebrae superioris muscle, 39, 41 Levator plate, 512, 513 Levator scapulae muscle, 91, 115, 121, 132, 133, 135, 175, 177 Leydig cells, 935 Ligaments, 386 - pelvic floor, 506 Ligamentum arteriosum, 915, 923 Ligamentum flavum, 79 Ligamentum nuchae, 75 Ligamentum teres, 248, 250, 727, 923, 925 Ligamentum venosum, 248, 251, 256, 257, 271, 923 - fissure for, 250, 269 Limb bud, 867 - lower extremity, 868 - upper extremity, 868 Limbic system, 8 Linea alba, 395, 398, 399, 405 Linea semilunaris, 395, 399, 402, 405 - right, 399, 405 Lingual artery, 89, 93, 94, 95, 170, 173, 179 Lingual follicles, 97 Lingual nerve, 93 Lingual septum, 101, 111 Lingula, 887 Lipoma, intradural, 888 Lipomyelomeningocele, 888

Lips, 894, 901 - lower, 901 - upper, 896, 901 Lisfranc ligament, dorsal, 835 Lister tubercle, 619, 620 Liver, 223, 227, 248–271, 277, 304, 332, 341, 354, 391, 429, 430, 869, 870, 912, 913, 925, 928, 929, 931, 932, 933, 942, 943 - attachments and relations, 251 - capsule, 265 - caudate lobe, 248, 387 - coronary ligament, 389 - left lateral, 259 - left lobe, 227, 248, 325, 339, 343, 344, 391, 392, 932 longitudinal, 259 - left-sided, 291 - lobe of left, 294, 298, 299, 301, 335 right, 333 - longitudinal, 264 - other views of, 265 - right lobe, 226, 227, 248, 251, 261, 265, 311, 312, 313, 314, 317, 399, 401, 404, 932 - segment 1, 253, 266, 268, 269 - segment 2, 253, 258, 266, 268, 271 - segment 3, 253, 256, 266, 268, 269, 271 - segment 4, 253 - segment 4a, 266, 268, 270, 271 - segment 4b, 256, 266, 268, 269, 270, 271 - segment 5, 253, 266, 269, 270, 271 - segment 6, 253, 266, 268, 269, 270 - segment 7, 253, 258, 266, 268, 270 - segment 8, 253, 258, 266, 268, 270, 271 - segmental anatomy, 266, 268, 269 - transverse left lobe, 256, 271 right lobe, 260, 270 - vessels and bile ducts, 252 - visceral surface, 250 Lobule, 237, 897 Long plantar ligament, 822, 825, 841, 844 Long radiolunate ligament, 627 Long thoracic nerve, 239, 557, 703 Longissimus thoracis muscle, 397, 404 Longitudinal capsular ligament, 727 Longitudinal esophageal muscle, 159 Longitudinal peroneal vessels, 801 Longitudinal smooth muscle, 511 Longitudinal subepithelial vascular plexus, 511 Longitudinal tibial vessels - anterior, 803 - posterior, 799 Longus capitis muscle, 97, 152 Longus coli muscle, 90, 91, 101, 109, 114, 115, 121, 126, 133, 138, 139, 140, 141, 161, 186, 187, 193 Looping, 914 Loose areolar tissue, 639 Low internal jugular lymph nodes, 87 Low-set ears, 895 Low spinal accessory lymph nodes, 87, 200 xxiii

INDEX Lower cervical level and supraclavicular fossa, 124–129 - axial CECT, 127 - CECT, 129 - graphics, 125 - longitudinal ultrasound, 128 - pathology, 128–129 - power Doppler ultrasound, 127 - transverse ultrasound, 126 Lower extremity, 869, 870 - ankle, 814–831 - foot vessels, 846–851 - knee, 762–779 - leg nerves, 810–812 - leg vessels, 792–809 - limb bud, 868 - metatarsals, 852–857 - tarsus, 832–845 - toes, 852–857 Lower internal jugular nodes, 198, 200 Lower rectum, 527 Lower urinary tract, 505 Lower uterine wall, 486 Lower vagina, 527 Lower vaginal walls, 525 Lumbar artery, 417 Lumbar nodes - left, 353 - right, 353, 355 Lumbar spine, 933 Lumbar trunks (of cisterna chyli), 353 Lumbosacral nerve trunk, 410 Lumbrical muscle, 628, 630, 632, 636, 644, 656, 662, 667, 840, 843 - 1st, 630 - 2nd, 630 - 3rd, 630, 637, 658 - 4th, 630 Lunate, 615, 620, 623, 639, 691–692, 701 Lung bud, 906 - 4-week embryo, 927 Lung interface, 210, 211, 212, 215 Lungs, 219, 229, 913, 932, 933, 943 - artifact from, 323 - base, 933 - caudal extent of, 219, 220, 221 - development, 906, 908–911 alveolar stage, 907, 911 amniotic fluid requirements, 907 canalicular stage, 906–907, 911 circulatory requirements, 907 embryonic stage, 906 pseudoglandular stage, 906 saccular stage, 907, 911 volume requirements, 907 - fetal, 912 - left, 912 - lobes, 910 - neonatal, 907 - parenchyma, 906 - primitive, 908 xxiv

- right, 912 atelectatic, 390 Lunotriquetral ligament, volar portion, 627 Luschka, paired foramina of, 12 Luteal phase, 494 Lymph nodes, 101, 102, 103, 109, 118, 120, 166, 202, 203, 238, 558, 672 - abnormal level II, 245 - cortex, 242 - fatty hilum, 242 - hilar vascularity in, 166 - intraparotid, 105, 108 - jugulodigastric, 109 - lymphomatous, 204, 205 - matted tuberculous, 204 - metastatic, 122, 123, 204, 205 - posterior triangle, 115, 134, 186, 187 - submandibular, 115 - thickened cortex, 245 - transverse cervical chain, 124 - tuberculous, 135 Lymph sacs, 895 - cisterna chyli, 895, 904 - distended, 905 - iliac, 895, 904 - jugular, 904 internal, 904 paired, 895 - retroperitoneal (mesenteric), 895, 904 Lymphangiogram, 355 Lymphangioma, 895 - body, 895 Lymphatic drainage, 136, 235 Lymphatic malformation, 135 Lymphatics, 717 - embryology, 904 - face and neck, 894, 895 Lymphomatous lymph node, 204, 205 Lymphomatous nodes, 354 Lymphovascular malformation, 135

M

Magendie, foramen of, 12 Magna pancreatic artery, 296 Main collateral ligament, 659 Main duct, 237 Major papilla (of Vater), 300, 340 Malar bone, 903 Malar node, 200 Malleolar artery, lateral, 847 Malleolus - lateral, 826, 828 - medial, 820, 821, 823, 824 Malrotated renal pelvis, 329 Mammary arteries - lateral, 235, 239 - left internal, 913 - medial, 235, 239

INDEX - right internal, 913 Mammary fascia, anterior, 240 Mammary vein, right internal, 913 Mammary zone, 234 Mandible, 96, 97, 103, 109, 110, 876, 894, 900, 902 - alveolar process, 95 - angle, 100, 102 - body, 95, 101, 109 - mylohyoid ridge, 99 - ramus, 89, 106, 107, 108, 110, 111 Mandibular node, 200 Mandibular prominences, 896, 930 - primordia, 897 Mandibular symphysis, 903 Manubrium, 195, 209 Manubrium sternum, 531 Massa intermedia, 12, 887 Masseter muscle, 99, 101, 105, 106, 107, 110, 111 Masticator space, 88, 93, 99, 105, 107, 113 Mastoid fontanelle, 4, 5, 27, 29 Mastoid node, 199, 200 Mastoid process, 89, 106 - tip, 110 Mastoid tip, 105, 131 Maternal sinusoid, 863 Matted tuberculous lymph nodes, 204 Maxilla, 95, 876, 900, 902, 903 - frontal process, 900 - zygoma, 47 Maxillary (internal maxillary) artery, 170, 173 Maxillary prominences, 894, 896, 897, 930 - isolated cleft lip, 895 - primordia, 897 Maxillary sinus, 95 Meatus, 95 Meckel cave, 109 Meckel diverticulum, 924 Medial and lateral nasal prominences, 894 Medial antebrachial cutaneous nerve, 563, 564, 565 Medial antecubital vein, 585 Medial arcuate ligament, 224, 225 Medial brachial cutaneous nerve, 564 Medial breast innervation, 234 Medial calcaneal nerve, 819 Medial circumflex femoral vein, 723 Medial collateral artery, 572 Medial collateral bursa, 770 Medial collateral ligament, 770–771 Medial cord, 669 Medial cuneiform, 837, 839, 844, 848, 854 Medial cutaneous nerve, 557 Medial epicondyle, 579, 580, 592, 595, 596, 597, 698 Medial femoral circumflex artery, 749 Medial femoral circumflex vein, 750 Medial femoral condylar cartilage, 769, 777 Medial femoral condyle, 769–771, 779 Medial femoral cortex, 743, 745 Medial frontal gyrus, 11 Medial gastrocnemius muscle, 764, 782, 789 - nerve to, 775 Medial geniculate artery, inferior, 777

Medial intermuscular septum, 568, 678 Medial malleolus, 820, 821, 823, 824 Medial meniscus, 770–772 Medial navicular cortex, 821 Medial orbital wall, 40 Medial patellar retinaculum, 738, 742 Medial patellofemoral ligament, 770 Medial pectoral nerve, 703 Medial plantar artery, 794, 844, 847, 850 Medial plantar nerve, 819, 833, 844, 847, 850 Medial plantar vein, 844, 846 Medial posterior choroidal artery, 66 Medial pterygoid muscle, 101, 111 Medial rectus muscle, 15, 39, 40, 41, 48, 49 Medial retinaculum, 782 Medial segment (left lobe), 251 Medial sesamoid, 840, 841, 853 Medial talar tubercle, 812 Medial tarsal artery, 839 Medial tarsal vein, 839 Medial tibial condyle, 769, 771 Medial tibial plateau, 771 Medial umbilical ligament, 409, 410, 470, 510 Median arcuate ligament, 225, 227, 396 Median artery, 641 Median ligament, 426 Median nerve, 557, 558, 563, 564, 565, 572, 580, 581, 582, 584, 592, 600, 601, 602, 603, 608, 609, 617, 623, 624, 632, 645, 669, 670, 675, 684–693, 690 - carpal tunnel, 691 - digital branch, 644, 685, 693 - longitudinal US, 692 - muscular branch, 645 - palmar cutaneous branch, 645 - palmar nerve, 693 - recurrent branches, 693 - superficial branches, 632 - transverse US, 684–689 Median raphe, 935 Median sacral vein, 411 Median umbilical ligament, 510, 934 Mediastinum testis, 448, 451, 453, 455, 456 Medulla, 8, 20, 21, 26, 28, 30, 934 Medulla oblongata, 97, 880, 881, 887 Medullary pyramids, 302, 311, 319, 323 - renal, 333 Mega cisterna magna, 887 Membranous neurocranium, 902 Membranous septum, 919 Membranous urethra, 436, 466 Membranous viscerocranium, 902 Mendosal suture, 5 Meningocele, anterior sacral, 889 Meningohypophyseal trunk, 52 Meniscofemoral ligament, 770–771 Meniscotibial ligament, 770–771 Meniscus - lateral, 772, 774 - medial, 770–772 Menstrual cycle, endometrial variations, 468 Mental foramen, 101 xxv

INDEX Mentalis muscle, 101 Mesencephalon, 8, 28, 56, 60, 63, 64, 67, 71, 72, 874, 875 Mesenchymal connective tissue, 911 Mesenchyme, primitive, 908, 909 Mesenteric artery - inferior, 329 - superior, 254, 255, 259, 274, 281, 285, 288, 293, 294, 295, 296, 297, 298, 299, 301, 305, 307, 314, 320, 325 Mesenteric (retroperitoneal) lymph sac, 895, 904 Mesenteric vein - inferior, 285 - superior, 274, 285, 293, 298, 299, 301, 320 Mesentery, 386 - dorsal 4-week embryo, 927 18-day embryo, 926 - small bowel, 293, 387 - ventral 4-week embryo, 927 18-day embryo, 926 persistent edge, 927 Mesocolon - descending, 929 - sigmoid, 342 root, 389, 929 - transverse, 340, 387 root, 285, 389 Mesoderm, 888, 924 - somatic, 18-day embryo, 926 - splanchnic, 18-day embryo, 926 Mesogastrium - dorsal, 924 - ventral, 924, 928 Mesonephric tubules, 936 Mesonephric (Wolffian) ducts, 934, 935, 936, 937, 941 Mesonephroi, 934, 936 Mesosalpinx, 469, 472, 494, 495 Mesovarium, 494, 495 Metacarpal, 659, 662 - 1st, 615, 634, 635, 648, 649, 652, 653, 654, 655 - 2nd, 624, 632, 635, 639, 653, 654 - 3rd, 624, 632, 639 base, 624 - 4th, 624, 632, 639 - 5th, 632, 636, 702 Metacarpal artery, dorsal, 641 Metacarpal base, 5th, 636 Metacarpal body, 5th, 843 Metacarpal head, 650, 659, 660, 662, 666 - 1st, 650, 651 Metacarpal ligament, deep transverse, 629, 647, 657 Metacarpal shaft, 644, 659, 660 Metacarpal vein, dorsal, 613 Metacarpophalangeal joint, 649, 651, 659 - ulnar sesamoid of, 649, 650 Metanephric blastema, 934, 936 Metanephroi, 934 Metanephros, 936, 937, 940, 941 Metastasis, 163 Metastatic lymph nodes, 122, 123, 204, 205 xxvi

Metatarsal, 832–833, 852–857 - 1st, 854 - 2nd, 842, 849, 851 extensor digitorum brevis tendon, 854 - 3rd, 849, 851 extensor digitorum brevis tendon, 854 - 4th, 849, 851 - 5th, 825, 827, 854 - dorsum, 854 - median crest (crista) of, 853 - plantar, 855 - shaft, 854 - transverse, 856 Metatarsal artery, 849 - dorsal, 847, 849 - plantar, 849 Metatarsal base, 854 - 1st, 843, 856 - 2nd, 843, 856 - 3rd, 843, 856 - 4th, 845, 856 - 5th, 845 Metatarsal body, 3rd, 842 Metatarsal head - 1st, 843, 853, 854, 855, 856, 857 - 3rd, 843 - 5th, 843 Metatarsal ligament, transverse, 835 Metatarsal neck, 1st, 854 Metatarsal shaft, 1st, 854, 855 Metatarsal vein, dorsal, 851 Metatarsophalangeal joint, 855, 857 - 1st, 852 - lateral, 852 Metencephalon, 875 Metopic suture, 5, 903 Microstomia, congenital, 895 Mid cervical canal, with thin mucosal layers, 484 Mid internal jugular nodes, 198, 200 Midbrain, 8, 20, 21, 26, 27, 28, 30, 869, 876, 877, 881, 882, 884, 887 Midbrain pons, 898 Midcarpal compartment, 615 Midcervical level, 118–123 - axial CECT, 121 - graphics, 119 - transverse color ultrasound, 123 - transverse Doppler ultrasound, 123 - transverse grayscale ultrasound, 122, 123 - transverse ultrasound, 120 Middle adrenal artery, 330, 331 Middle cerebral artery, 34, 35, 50, 52, 53, 55, 57, 58–61, 63, 71, 72, 73 - bifurcation, 58 - contralateral, 63 - cortical (M4) segment, 58 - horizontal (M1) segment, 58, 59, 60, 61, 64 - insular (M2) segment, 58, 59, 60, 61, 64 - opercular (M3) segment, 58 Middle cerebral vein - deep, 50, 70

INDEX - superficial, 50, 70 Middle collateral artery, 564, 678 Middle cranial fossa, 14, 15 Middle cuneiform, 842, 843 Middle ear, 885 Middle frontal gyrus, 10, 15, 23 Middle glenohumeral ligament, 540, 551 Middle internal jugular lymph nodes, 87 Middle meatus, 97 Middle meningeal artery, 52, 173 Middle muscle layer, circular, 339 Middle occipital gyrus, 19 Middle phalanx, 644, 661, 663, 664, 665, 857 Middle rectal artery, 410, 470 Middle rectal vein, 411 Middle sacral artery, 409, 470 Middle temporal gyrus, 10, 17, 23 Midgut, 924 - 4-week embryo, 927 - 18-day embryo, 926 - dorsal mesentery, 928 Minor papilla, 276, 300 Mitral valve, 918, 919 Moderator band, 915, 918 Molar tooth, 95 Monro, foramen of, 12, 16, 17 Morison pouch, fluid, 390 Morula, 862 Mouth - anomalies, 895 - formation, 930 Mucosa, 524 Mucosal folds, 481 Mucus plug, 487 Müllerian duct anomalies, 488 Müllerian inhibiting factor, 935 Multicystic dysplastic kidney, 934 Multifidus muscle, 133 Muscular component - lumbar part of, 225 - sternal part of, 225 Muscular floor, 130 Muscularis mucosa, 350 Muscularis propria layer, 350 Musculocutaneous nerve, 563, 564, 565, 566, 573, 603, 669, 670, 685 Musculotendinous junction, 543 Myelencephalon, 875 Myelination, 872 Myelocystocele, 888 - terminal, 889 Myelolipoma, 330 Myelomeningocele, 888 Mylohyoid cleft, 101, 103 Mylohyoid muscle, 89, 93, 94, 95, 96, 97, 99, 100, 101, 102 Mylohyoid ridge, of mandible, 99 Myometrium, 468, 474, 864, 866, 867, 869, 871 - inner and outer layer, 469 - inner zone, 474 - IUD, 473 - middle zone, 474

- outer zone, 474 Myotomes, 889

N

Nabothian cysts, 484, 485, 487 Nail, 665, 857 Nail base, 652 Nail bed, 665, 857 Nares, 901 Nasal bone, 869, 876, 902, 903 Nasal pit, 896, 930 Nasal placodes, 894 Nasal plate, nasal pit on, 896 Nasal process - lateral, 896, 897 - medial, 896, 897 Nasal septum, 95, 97 Nasofrontal vein, 43 Nasolacrimal groove, 896 Nasolateral prominence, 930 Nasomedial prominence, 930 Navicular bone, 818, 822, 824, 825, 832, 839, 842, 843, 844, 848 - anteromedial surface of, 837 - cortex, medial, 821 - surface, 838 anteromedial, 836 Near occlusive segment, 188 Neck, 86–91, 274 - anatomy, 894–905 - embryology, 894–905 common anomalies, 895 - lymphatics, 894, 895 - parotid region, 104–111 - submandibular region, 98–103 Neck veins, 190–197 - CECT color and power Doppler ultrasound, 197 spectral Doppler ultrasound, 193, 195 - graphics, 191 - grayscale and color Doppler ultrasound, 192, 194 - longitudinal and transverse ultrasound, 196 Neonatal circulation, 915 Nephrotomes, 934 - cervical, 936 Nerve roots, 79, 82, 889, 893 Neural arch, ossification center, 892 Neural canal, 888 Neural crest, 890, 891 Neural crest cells, 888, 890 - migration, 890 Neural folds, 891 - fusion, 890 Neural groove, 888, 890, 891 Neural plate, 888, 890 Neural tube, 872–873, 936 - 4-week embryo, 927 - 18-day embryo, 926 xxvii

INDEX - center, 890 - closure, 874, 888 failure, 889 at occipitocervical region, 890 - complete, 891 - embryology, 890–891 - formation, 888 Neurenteric cyst, 889 Neuroblastoma, 330 Neurocranium, membranous, 902 Neuronal migration, 872 Neuronal proliferation, 872 Neuropores, 888 - caudal, 874, 888, 891 - cranial, 874, 888, 890, 891 Neurovascular bundles, 434, 442 - anterior interosseous, 600, 689–690 - lateral plantar, 845 Neurulation, 872, 888 - primary, 888, 890 - secondary, 888 malformations, 888–889 Nipple, 236, 242, 243 - intramammary node, 242 Nipple-areolar complex innervation, 234 Nodulus, 887 Nondysjunction, 888 Nonkeratinizing squamous epithelium, 511 Normal jugular lymph node, echogenic hilum, 202 Normal lymph node, 100 Normal venous waveform, 195 Nose, 47, 894, 900 - absent, 895 - anomalies, 895 - bifid, 895 - tip, skin, 900 Nostril, 896, 901 - single, 895 Notochord, 888, 890, 891 - cartilaginous stage, 889 - development, 872 - induction, failure, 889 Notochordal process, 888 Notochordal remnant, 889 NVB. See Neurovascular bundles.

O Obex, 12 Oblique, external, 222 Oblique abdominal muscle, 286, 323, 710 Oblique anus, 527 Oblique cord, 594 Oblique ligament, posterior, 770–771 Oblique muscles, 311, 313, 396 - right, 400, 401, 402 Oblique pulley, 629, 647, 657

xxviii

Obstetrics and developmental anatomy, embryology and anatomy - 1st trimester, 860–871 - abdominal wall and gastrointestinal tract, 924–933 - brain, 872–887 - cardiovascular system, 914–923 - chest, 906–913 - face and neck, 894–905 - genitourinary tract, 934–943 - spine, 888–893 Obturator artery, 410, 470, 749 Obturator canal, 506, 507 Obturator externus muscle, 719–720, 724, 731 Obturator internus muscle, 427, 428, 489, 491, 507, 508, 509, 511, 708–709, 751 Obturator membrane, 506 Obturator nerve, 508 Obturator tendon, 713–714 Obturator vein, 750 Obturator vessels, 489, 508 Occipital artery, 170, 173 Occipital bone, 902 - squama, 902 Occipital horns, 12, 17, 22, 30 Occipital lobe, 8, 18, 19, 20, 21, 24, 27, 29, 876, 877, 880, 884 Occipital node, 199, 200 Occipital pole, 10 Occipital sinus, 36, 70 Occipitotemporal gyrus, 17 Occluded umbilical artery, 489 Ocular globe, 885 Ocular melanoma, 49 Oculomotor nerve, 34, 62 Odontoid process, anterior arch, 97 Olecranon, 594, 597, 696 Olecranon process, 580, 581, 698 Olfactory nerve, 34, 54 Omental bursa, 925 Omentum, 386 - greater, 387, 388, 389 - lesser, 251, 387, 388 Omohyoid muscle, 87, 118, 119, 131, 138, 182, 212 - inferior belly, 124, 131 - superior belly, 90 Omohyoid node, 198 Omphalocele, 925 Omphalomesenteric arteries, 924 Oocyte - extruded from ovary, 862 - surrounded by cumulus cells, 862 - swept into tube by fimbria, 862 Opercula, 24 Operculization, 872 Operculum, frontal, 879 Ophthalmic artery, 39, 40, 43, 45 Opisthion, 75, 78 Opponens brevis muscle, 632 Opponens digiti minimi brevis muscle, 636 Opponens digiti minimi muscle, 622, 629, 632, 633, 636, 647, 657, 692, 693, 702

INDEX Opponens pollicis muscle, 624, 633, 634, 635, 642, 648, 649, 653, 654, 691–692 Optic chiasm, 39, 70 Optic nerve, 15, 34, 39, 40, 41, 43, 44, 45, 47, 54 - meningioma, 48 Optic nerve-sheath complex, 39 Optic recess, 12 Optic tract, 39 Optic vesicle, 874 Oral cavity, 876 - primitive, 896 Oral mucosal space/surface, 93, 95, 99 Orbicularis oculi muscle, 42 Orbit, 38–49 - extraocular muscles, 40–41 Orbital roof, 14, 15 Orbitofrontal artery, 54, 58 Orbits, 894–895, 898 - absent or small, 895 - superior, 898 Organogenesis, 860–861 Oropharyngeal membrane, 930 Oropharyngeal mucosal space/surface, 99 Oropharynx, 97, 111 Osseous structures, pelvic floor, 504 Ossification center, 892 - neural arch, 892 Ostium primum, 914 Ostium secundum, 914 Outer longitudinal muscle layer, 515 Outer muscle layer, longitudinal, 339 Outer table, 4, 5, 6, 7 Outflow tract, 917 Ovarian artery, 409, 470, 495, 499, 502 - cortical arteriole of, 499 - intrastromal, 498, 499 - spectral waveform of, 499 Ovarian follicles - developing, 497, 500, 502 - dominant, 496, 500 - immature, 496, 497, 501 - immediate postovulatory ruptured, 503 - mature, 500, 501 - ruptured, 501 Ovarian hilum, 502 Ovarian ligament, proper, 495 Ovarian stroma, 497 Ovarian vein, 471, 495, 502 - left, 411 - right, 411 Ovarian venous plexus, 471 Ovarian vessels, 498 Ovaries, 469, 470, 489, 494–503, 935 - color Doppler imaging, 498 - cyclic changes, 500, 501 - ligamentous support and anatomy, 495 - oocyte extruded, 862 - suspensory ligament, 469, 472 - variations with age, 494, 496, 497 Ovulation, 494, 860, 862

P

Palate, 894, 900, 901 - embryology, 896 - primary, 894, 896 - secondary, 894, 896, 901 Palatine shelf, 896 Palm, 632 Palmar aponeurosis, 632, 692 Palmar arch - deep, 611, 635, 640, 641, 645, 653, 654 - superficial, 611, 636, 640, 645 Palmar artery, deep, 634 Palmar carpal arch - radial branch, 641 - ulnar branch, 641 Palmar digital artery, common, 644 Palmar digital vein, 612 Palmar interossei muscle, 628, 631, 636, 644, 656, 662 - 1st, 631 - 2nd, 631 - 3rd, 631 Palmaris brevis muscle, 632, 702 Palmaris longus muscle, 582, 593, 596, 598, 600, 601, 604, 689 - tendon, 689–691 Pampiniform plexus, 448 - vessels, 454 Pancreas, 256, 274, 290, 292–301, 308, 314, 325, 331, 334, 340, 341, 344, 354, 387, 391, 925, 928, 929 - annular, 301 - body, 281, 288, 294, 295, 299 - dorsal, 925, 928 - head, 281, 294, 295, 298, 301 - neck, 295, 298, 299 - sagittal view, 298, 299 - in situ, 293 - tail, 287, 294, 295, 299, 334, 335, 343 - transverse view, 294 CT, 295 - uncinate process, 344 - vasculature, transverse view, 297 - ventral, 928 Pancreas divisum, 300 Pancreatic artery, 296 - anatomy, 296 Pancreatic body, 297 Pancreatic duct, 274, 340 - accessory (of Santorini), 276 - main (of Wirsung), 276 - variations, 300 Pancreatic head, 288 Pancreatic tail, 291, 324, 354 Pancreaticoduodenal artery, anterior superior, 296 Pancreatitis, acute, 292 Papillary thyroid carcinoma, 122 Paracolic gutter - left, 388, 389 xxix

INDEX - right, 389 Paraglottic space, 121, 151, 153, 154, 155, 156, 157 Parahippocampal gyrus, 11 Paramesonephric (Müllerian) ducts, 935, 940 Parametrium, 468, 474 Parapharyngeal space, 88, 105, 107, 109, 111, 113 Pararectal space, 483 Paraspinal component, 131 Paraspinal muscles, 121, 131, 394, 404 Paraspinous muscle, 893, 942, 943 Parasternal lymph node, 230 Parathyroid glands, 144–149, 159, 165 - adenoma, 147–149 - graphics, 145 - normal, 146 Paratracheal lymph node, 145, 159 Paratracheal node, 165 Paravaginal support, 527 Paravesical space, 483 Parietal bone, 903 Parietal lobe, 8, 18, 19, 20, 21, 881, 885 Parietal operculum, 25, 879, 880 Parietal peritoneum, 390 Parietal pleura, 218, 220, 221, 229 - thick and enhancing, 223 Parietooccipital artery, 62 Parietooccipital fissure, indentation, 877 Parietooccipital sulcus, 11, 21, 24, 879, 883, 884 Parotid duct, 105, 107 - course of, 111 Parotid gland, 87, 89, 105, 106, 107, 108, 109, 110, 111, 113 - tail, 102 Parotid nodes, 199, 200, 201 Parotid region, 104–111 Parotid space, 88, 107, 113 Patella, 764, 766–767 - anterior surface, 765, 769 - dorsal surface, 768 - lateral articular facet, 769 - lower pole, 767 - medial articular, 769 - upper pole, 766 Patellar retinaculum, 769 - lateral, 738, 769, 773 - medial, 738, 742, 768–769 Patellar tendon, 764–765, 767, 768 - inferior, 770, 782 Patellofemoral ligament, medial, 770 Patellotibial ligament, 770 Peak systolic velocity, 463 Pectineus muscle, 719, 721–722, 724–725, 731, 738, 740, 751, 753 Pectoral group, 238 Pectoral nerve, 703 Pectoralis major muscle, 213, 214, 215, 222, 228, 230, 231, 232, 233, 241, 245, 532, 556, 558, 559, 563, 675 Pectoralis minor muscle, 213, 214, 215, 222, 228, 230, 231, 238, 245, 556, 557, 558, 559 Pedicles, 892, 893 Pelvic & ureteric branches, 306 xxx

Pelvic abscess, 488 Pelvic cavity, fluid, 393 Pelvic diaphragm, 504, 507 Pelvic fascia, tendinous arch, 428 Pelvic floor, 504–527 - 3D volume rendered US, 526, 527 Pelvic support, passive and active components of, 512, 513 Pelvis - cervix, 482–487 - iliac arteries and veins, 408–423 - ovaries, 494–503 - penis and urethra, 458–467 - prostate, seminal vesicles, 434–445 - testes and scrotum, 446–457 - ureters and bladder, 424–433 - vagina, 488–493 Penile bulb, 458, 459, 460, 465 Penile urethra, 427, 466, 941 Penis, 458–467, 941 - MR of, 465 - suspensory ligament of, 461 Pentalogy of Cantrell, 925 Perforating branch peroneal artery, 794 Perforating vein, 612 Perforator, 809 - competent, 809 Pericallosal artery, 32, 33, 54, 55, 57, 62 Pericallosal cistern, 11 Pericardial sac, 225 Pericranium, 4, 5 Perihepatic space - left anterior, 391 - posterior, 391 Perineal body, 459, 504, 508, 509, 512, 513, 514, 515, 516, 517, 526, 930 Perineal fascia, 459 Perineal membrane, 509, 512, 513 Perinephric fat, 312, 319, 324, 333 Perineum, 459, 504, 509 Periosteum, calvarium, 6 Peripancreatic lymph node, 354 Peripheral nerves, 670, 671 Peripheral/subcapsular intranodal vascularity, 123 Perirenal fat, 304 Perisplenic collaterals, 391 Perisplenic fluid, 392 Peritoneal cavity, 386–393 - divisions and compartments, 386, 388–389 Peritoneal recesses, 386 Peritoneal reflection, 274, 277 Peritoneal space, 925 - right, 925 Peritoneum, 304, 386, 398, 427, 428, 450, 511, 941 - parietal, 927 - visceral, 927 Periurethral artery, 492, 493, 505, 522, 523 Periurethral glands, 439 Periventricular halo, 18 Perivertebral space, 88, 131 - paraspinal component, 113

INDEX - prevertebral component, 113 Perivesical space, 427, 428, 511 Peroneal artery, 783–787, 792, 793, 797, 798, 800, 801, 802, 803, 804, 806, 811, 826, 846 - perforating branch, 811 Peroneal nerve - common, 741, 751, 787 - deep, 783–784, 786 - superficial, 783, 786 Peroneal retinaculum - inferior, 825 - superior, 814, 825, 826 Peroneal trochlea, 827 Peroneal vein, 783–787, 795, 797, 798, 800, 801, 802, 803, 804, 805, 806, 812, 826 Peroneal vessels, 783, 791 - longitudinal, 801 - transverse, 800 Peroneus brevis muscle, 783, 786–788, 825, 826 Peroneus brevis tendon, 815, 819, 825, 826, 827, 828 Peroneus longus muscle, 782, 783, 784, 786, 787, 788, 790, 794, 800, 811 Peroneus longus tendon, 786–787, 794, 811, 815, 819, 825, 826, 827, 828, 843, 845 - groove for, 827 Peroneus tertius muscle, 817 Peroneus tertius tendon, 815, 817, 838 Peroneus tunnel, 794, 811 Persistent sexual arousal syndrome, 488 Pes anserine, 738, 742 Petrosal fissure, 28 Petrous bone, 53 Petrous internal carotid artery, 43 Peyronie disease, 458, 467 Phalanges, 833, 852 Phalanx, 667 - distal, 651, 652, 665, 857 - middle, 644, 661, 663, 664, 665, 857 - proximal, 644, 649, 650, 652, 655, 659, 660, 661, 662, 663, 666, 857 2nd toe, 849, 851 3rd toe, 849, 851 of big toe, 855, 857 - terminal, 661, 664 Pharyngeal arches, 902, 914, 930 - 2nd, 896 Pharyngeal branches, 164 Pharyngeal constrictor muscle, 111, 121, 151, 152 Pharyngeal mucosal space/surface, 88, 113 Pharyngeal wall, posterior, 121 Pharyngoepiglottic fold, 151 Pharynx, 4-week embryo, 927 Pheochromocytoma, 330 Philtrum, 897, 901 Phrenic artery, inferior, 331 Phrenic nerve, 125, 224 - left, 224 - right, 224 Phrenic vein, inferior, left, 331 Phrenic vessels, inferior, 305 Phrenicocolic ligament, 389

Pia mater, 76 Pierre Robin syndrome, 895 Pineal body, 71 Pineal recess, 12 Piriform fossa, 97 Piriform sinus, 187 Piriformis muscle, 396, 507, 708–709, 711, 713, 751 - left, 403 Pisiform, 615, 623, 642, 691, 701 Pisohamate ligament, 693 Pisotriquetral compartment, 615 Pituitary gland, 97 Pituitary infundibulum, 34, 39, 54 Placenta, 869, 922, 932, 943 - development, 861 chorionic villi in, 869 thickened chorionic villi in, 868 Placodes, 894 - lens, 894 - nasal, 894 Plantar aponeurosis, 833 - central band, 842, 843, 845 - lateral band, 843, 845 - medial band, 843, 844 Plantar arch, 846, 847 Plantar artery, 850–851 - lateral, 844, 845, 847, 850 - medial, 794, 844, 847, 850 Plantar digital artery, 849, 851 Plantar digital nerve, 847 Plantar fat pad, 842 Plantar interosseous muscle, 849 - 1st, 841 - 2nd, 841 - 3rd, 841 Plantar ligament - long, 822, 841, 844 - short, 822 Plantar metatarsal artery, 849 Plantar muscles - deep layers, 841 - superficial layers, 840 Plantar nerve - lateral, 821, 833, 844, 845 - medial, 819, 821, 833, 844, 847, 850 Plantar neurovascular bundle, lateral, 845 Plantar plate, 852, 853, 855 Plantar vein - lateral, 844, 845, 846, 850 - medial, 844, 846 Plantar venous arch, 846 Plantaris tendon, 815 Platysma muscle, 89, 94, 95, 96, 99, 100, 101, 102, 106, 114, 115, 116, 119, 120, 121, 133, 146, 167, 177, 202, 203 Pleura, 218–223, 675 - anterior lung interface, 232, 233 - caudal extent, 219 - development, 906 - intercostal window, 222 - lung interface, 232 xxxi

INDEX - spaces, 218, 219–220 graphic, 221 - thickening, 218 Pleura/lung interface - at apex, 223 - visceral, reflective surface of, 222 Pleural effusion, 218 - left, 392 - right, 390 Pleural reflection, 220 Pleuroperitoneal membranes, 907 Pole ureter - lower, 328 non dilated, 328 - upper, 328 dilated tortuous, 328 Polysplenia, 284 Pons, 8, 20, 26, 28, 30, 877, 881, 882, 884, 887 Pontine perforating branches, 62 Popliteal artery, 741, 747, 749, 752, 753, 784, 792, 793, 796, 803, 808, 811, 812 Popliteal muscle, 793, 811 Popliteal vein, 741, 747, 750, 752, 753, 783, 792, 795, 796, 807, 808 Popliteal vessels, 764, 776, 778, 796 - bifurcation, 797 Popliteus muscle, 793, 796 Porta hepatis, 250, 263 Portal sinus, 925, 931 Portal splenic confluence, 295 Portal triad, 248, 278, 279 Portal vein, 226, 227, 248–250, 256, 259, 271, 278, 279, 282, 285, 288, 312, 335, 354, 871, 923, 931 - anterior branch right, 260 - anterior right branch, 260 - appearing intermittently on, 227 - branches, 256, 265, 931 - left, 252, 256, 257, 259, 264, 268, 334, 392, 922 spectral tracing of, 257 - main, 252, 262, 263, 264, 274, 280, 281, 282 spectral tracing, 262 - middle, 257 - right, 252, 257, 260, 262, 269, 312, 314, 334 anterior, 261 posterior branch, 260, 282 Portal venous branch, 283 Portal venous system, 925 Post cricoid region, 150 Postcentral gyrus, 10, 23, 880, 881, 882, 884 Postcentral sulcus, 10, 880 Postcricoid hypopharynx, 152 Posterior acoustic enhancement, 110, 143, 485 Posterior acoustic shadowing, 222, 232 Posterior anal plate, 512 Posterior antebrachial cutaneous nerve, 564, 568 Posterior auricular artery, 170, 173 Posterior auricular nerve, 105 Posterior axillary wall, transverse US, 561 Posterior calcaneus, middle facet of, 829 Posterior capsule, 764, 770, 772 Posterior-caudal ducts, right, 276 xxxii

Posterior cerebellar artery, 34 Posterior cerebral artery, 32, 50, 54, 57, 59, 60, 62, 63, 64, 65, 72 - ambient (P2) segment, 62, 63, 64, 67, 71, 73 - calcarine (P4) segment, 62 - contralateral, 63 - precommunicating (P1) segment, 62, 64 - quadrigeminal (P3) segment, 62, 64, 67, 71 - splenial branch, 54 Posterior cervical space, 88, 113, 115, 121, 131 - nodes, 198 Posterior chamber of eyeball, 49 Posterior circumflex humeral artery, 538, 555, 560, 568, 571 Posterior commissure, 155 Posterior communicating artery, 34, 52, 53, 60, 62, 63, 64, 65 Posterior cord, 669 Posterior costodiaphragmatic recess, 221 Posterior cricoarytenoid muscle, 152 Posterior cruciate ligament, 764, 770, 772 Posterior cul-de-sac, 468, 472 Posterior dural margin, 79 Posterior fat pad, 580, 597 Posterior femoral cortex, 741, 746 Posterior fibular cortex, 790–791, 812 Posterior fontanelle, 4, 5, 26, 29 Posterior fossa, 28, 886–887 - via mastoid approach, 29 Posterior glenoid labrum, 553 Posterior hypopharyngeal wall, 150, 151, 152, 155, 157 Posterior inferior cerebellar artery, 32, 50 - anterior medullary segment, 66 - caudal loop, 66 - supratonsillar segment, 66 Posterior inferior pancreaticoduodenal artery, 296 Posterior interosseous artery, 607, 641 Posterior interosseous nerve, 582, 605, 677 Posterior labrum, 556, 727 Posterior longitudinal ligament, 79 Posterior meningeal artery, 66 Posterior oblique ligament, 770–771 Posterior pharyngeal wall, 121 Posterior pleural reflection, 221 Posterior renal fascia, 304 Posterior reverberation artifact, 349 Posterior sacral foramen, 712 Posterior scalene muscle, 127, 213 Posterior segmental artery, 306 Posterior spinal ligament, 77 Posterior subtalar joint, recess from, 829 Posterior superior pancreaticoduodenal artery, 293, 296 Posterior suprapatellar fat pad, 764–765 Posterior talofibular ligament, 814, 825, 828 Posterior temporal artery, 62 Posterior thalamostriate artery, 35 Posterior tibial artery, 791, 792, 793, 794, 797, 798, 799, 800, 802, 804, 805, 806, 809, 812, 820, 821, 846 - branches and, 793, 811 Posterior tibial cortex, 790–791, 812 Posterior tibial nerve, 819

INDEX Posterior tibial vein, 791, 795, 797, 798, 799, 800, 802, 804, 805, 806, 809, 812, 820, 821 - soleal vein draining into, 806 Posterior tibial vessels, 803, 821 - longitudinal, 799 - transverse, 798 Posterior tibiofibular ligament, 814, 825 Posterior triangle, 130–135 - axial MR, 133 - graphics, 131 - lymph nodes, 186, 187 - pathology, 134–135 - transverse ultrasound, 132 Posterior ulnar recurrent artery, 581, 594, 607, 696 Posterior urethral wall, 518 Posterior uterine wall, folding, 475 Posterior vagina fornix, 472 Posterior vaginal septum, 505 Posterolateral fontanelle, 4, 5, 27, 29 Posteromedial femoral cortex, 747 Posteromedial intermuscular septum, 747 Pre-epiglottic space, 115 Preaxillary brachial plexus, 130 Precentral gyrus, 10, 23, 880, 881, 883 Precentral sulcus, 10, 880, 883 Precommunicating (P1) posterior cerebral artery segment, 34 Precuneus, 11 Preepiglottic space, 150, 151, 153, 154, 155, 156, 157 Prefemoral fat pad, 764–765 Prefrontal artery, 59 Premammary fat, 244 Premammary zone, 234 - fat, 240 Premature dysjunction, 888 Premedullary cistern, 11, 21 Prepontine cistern, 11, 21 Preprostatic sphincter, 434, 439 Prepuce, 460 Presacral space, 483 Preserved echogenic hilum, 202 Prevertebral component, 131 Prevertebral muscles, 115, 127, 139, 161, 167 Prevesical space, 483 Primary fissure, 887 Primary gut loop, 928 Primary palate, 894, 896 - isolated cleft lip, 895 Primary vermian fissure, 877 Primary yolk sac, 863, 864 - involuting, 863 Primitive airway epithelium, 908 Primitive streak, 888 Primordial follicles, 862 Princeps pollicis artery, 634, 645, 649, 651, 653, 654 Princeps pollicis vein, 651 Processus vaginalis, 450, 935, 941 Profunda brachii artery, 569, 570, 679–680 Profunda brachii vessels, 679–680 Profunda femoral artery, 723, 731, 739, 741, 744, 749, 752

Profunda femoral vein, 723, 739, 744 Profunda femoris artery, 752 Prolapse, pelvic floor, 505 Prominences, 894 - cardiac, 930 - forebrain, 930 - frontonasal, 894, 896 primordia, 895 - mandibular, 896, 930 primordia, 897 - maxillary, 894, 896, 897, 930 isolated cleft lip, 895 primordia, 897 - medial and lateral nasal, 894 - nasolateral, 930 - nasomedial, 930 Prominent intraglandular vessels, 103 Prominent medial lobulation, 286 Pronator quadratus muscle, 598, 600, 601, 609, 610, 622, 623, 689–690, 700 Pronator teres muscle, 563, 580, 581, 582, 586, 587, 591, 592, 593, 596, 608, 609, 681, 685–686, 688, 698–699 Pronephroi, 934, 936 Proper digital artery, 645 Proper hepatic artery, 274 Proper ovarian ligament, 469, 495 Prosencephalon, 874, 875 Prostate, 427, 432, 434–445, 449, 465, 466, 935, 941 - central zone, 438, 439, 440, 444 - enlarged, 431, 443 - gross images, 441 - lobar anatomy, 434 - normal, 440 - peripheral zone, 434, 438, 439, 440, 441, 442, 443, 444 - sagittal, 444 - seminal vesicles, 434–445 - transition zone, 438, 439, 440, 441, 442, 443, 444 - zonal anatomy, 434, 438–439 Prostate gland, 351 Prostate pseudocapsule, 434, 438, 442, 443 Prostatic ducts, 436 Prostatic sinus, 436 Prostatic urethra, 427, 436, 439, 441, 444, 458, 466 Prostatic utricle, 434 Proximal humerus, 551 Proximal interphalangeal joint, 637, 658, 661, 665 Proximal jejunum, 340 Proximal phalanx, 644, 649, 650, 652, 655, 659, 660, 661, 662, 663, 666, 857 - 2nd toe, 849, 851 - 3rd toe, 849, 851 - of big toe, 855, 857 Proximal radioulnar joint, 579 Proximal urethra, 527 Pseudoganglion, 557 Pseudothrombus, 196 Psoas muscle, 225, 278, 304, 311, 313, 325, 345, 346, 347, 348, 350, 400, 426, 731, 738, 742 - left, 320, 321, 322, 324, 400, 404 - major, 396 - minor, 396 xxxiii

INDEX - right, 298, 311, 312, 314, 316, 400, 401, 402, 403, 405 - tendon, 402 Pterion, 4, 5 Pterygoid muscle, 99, 107 Pterygoid plexus, 43, 190 Pterygoid venous plexus, 191 Pterygopalatine fossa, 173 Puberocervical fascia, 513 Pubic bone, 506 Pubic cortex, anterior, 753 Pubic ramus, 517 - superior, 729 Pubic symphysis, 427, 428, 461 - unossified, 466 Pubic tubercle, 506 Pubocervical fascia, 512 Pubocervical ligaments, 482 Pubococcygeus muscle, 504, 507, 509, 512, 513, 527 Pubofemoral ligament, 728 Puborectalis muscle, 351, 504, 507, 509, 512, 513, 514, 515, 516, 525, 526 Pubourethral ligament, 512, 513 Pubovesical muscle, 511 Pudendal artery, internal, 727 Pudendal vein, internal, 727 Pulmonary artery, 914–915, 919, 922, 923 Pulmonary vein, 920, 923 Pulp space, 661 Pulvinar, 728 Pupil, 42, 47 Pyloric sphincter, 339 Pylorus, 339, 340, 344 Pyramidal lobe, 136, 142 Pyriform fossa, 115 Pyriform sinus, 150, 151, 155, 157 Pyriform sinus apex, 152

Q Quadrangular membrane, 153 Quadratus femoris muscle, 708–709, 711, 713–714, 751 Quadratus lumborum muscle, 225, 304, 314, 315, 324, 325, 396, 400 - left, 321, 404 - right, 316, 400, 401, 402, 403, 405 Quadratus plantae muscle, 819, 840, 842, 843, 844, 845, 850 Quadriceps fat pad, 764–766 Quadriceps tendon, 740, 765–766, 782, 788 Quadrigeminal cistern, 11, 16, 17, 28 Quadrilateral space, 554, 555 - transverse US, 560

xxxiv

R

Radial artery, 470, 582, 586, 600, 603, 606, 607, 608, 611, 625, 640, 641, 643, 645, 689–690 - contribution to superficial palmar arch, 645 - deep branch, 618 - palmar cutaneous branch, 645 - subcutaneous branch, 602 - superficial branch, 618 - superficial palmar branch, 642 - transverse US, 609 Radial bursa, 629, 647, 657 Radial collateral artery, 564, 568, 572 Radial collateral ligament, 578, 579, 581, 589, 594, 627 Radial collateral nerve, 678 Radial head, 579, 581, 583, 584, 585, 587, 589, 591, 597, 688 Radial nerve, 538, 555, 557, 558, 564, 565, 569, 572, 573, 580, 581, 582, 584, 585, 586, 587, 600, 602, 603, 605, 608, 609, 669, 670, 675, 676–683, 679, 680, 682, 683, 703 - deep branch, 681–683 - superficial branch, 670, 681–683, 689 - superficial terminal, 677 Radial notch, 581 Radial recurrent artery, 585, 586, 607, 681–682 Radial sesamoid, 649, 651 Radial shaft, 583 Radial styloid process, 615 Radial tuberosity, 586 Radial vein, 471, 586, 600, 608, 609, 612, 618, 643, 689–690 Radialis indicis artery, 645 Radiocarpal compartment, 615 Radiocarpal ligament, dorsal, 627, 639 Radiohumeral joint, 589 Radiolunate ligament, 627 Radioscaphocapitate ligament, 627 Radioscapholunate ligament, 627 Radioulnar compartment, distal, 615 Radioulnar joint - distal, 615 - proximal, 579 Radioulnar ligament - dorsal, 626, 627 - volar, 626, 627 Radius, 582, 583, 600, 601, 602, 605, 608, 609, 618, 619, 620, 623, 625, 670, 682, 689–690, 692 - styloid process, 643 Ramus of mandible, 106, 107, 108, 110, 111 Ranula, 96 Reactive nodes, 134 Rectal canal, 492 Rectal fascia, 342 Rectal mucosa, 444 Rectal mucosal layer, 527 Rectal muscular layer, 527 Rectosigmoid junction, 342

INDEX Rectosigmoid region, 351 - anterior wall, 351 Rectouterine pouch of Douglas, 342, 428, 468, 474 - fluid, 393 Rectovaginal fascia, 490, 492, 512, 513, 516, 517, 518, 525 Rectovaginal pouch, free fluid, 484 Rectovaginal septum, 526 Rectovaginal space, 483 Rectovesical pouch, 427 - fluid, 393 Rectovesical septum, 436 Rectum, 393, 396, 426, 427, 428, 442, 445, 465, 490, 491, 492, 495, 507, 509, 510, 514, 515, 525, 928, 930, 932, 933, 937 - anterior wall, 351 - fascia, 342 - lower, 342, 351 - muscle, 345, 402 Rectus abdominis muscle, 256, 257, 278, 279, 313, 343, 345, 395, 398, 719–720, 724 - left, 258, 398, 416 - right, 258, 279, 280, 298, 317, 398, 399, 400, 401, 402, 403, 404, 405, 418 Rectus femoris muscle, 719, 724, 725, 729, 731, 738–740, 742–743, 765, 782, 788 - long head of, 729 Rectus femoris tendon, 764, 767 Rectus sheath - anterior layer, 395 - aponeuroses, 395 Recurrent artery - radial, 585, 586 - ulnar, 580 Recurrent interosseous artery, 607 Recurrent laryngeal nerve, 119, 125, 145, 147, 152, 159, 164, 165 - right, 137 Recurrent radial artery, 607 Recurrent tibial artery, anterior, 794, 811 Recurrent tibial nerve, anterior, 811 Recurrent ulnar artery - anterior, 607 - posterior, 607 Red pulp, 287 Reflected adductor tendon aponeurosis, 655 Renal agenesis, 934 Renal artery, 302–303, 305, 306, 932, 938, 942 - accessory, 934 - inferior, 329 - intrarenal, 318, 326 - involuting, 938 - left, 256, 297, 299, 309, 325, 328, 331 main, 325 running posterior to aorta, 309 - low-resistance, 326 - right, 309, 317, 325, 328 anterior, 307 inferior, 307 posterior, 307

superior, with pre-hilar branching, 307 - segmental, 318, 326 - spectral Doppler waveform with autotrace, 326 - superior, 329 - two, 325 - ureteric branch, 426 - variants, 307, 309 Renal cortex, 306, 312, 315, 318, 319, 322, 326, 327, 942 - right, 315 Renal Doppler indices, 326 Renal duplication, 328 Renal ectopia, 934 Renal fascia, 304 - anterior, 304 Renal hilum, 316, 320 Renal impression - right, 250 - spleen, 286 Renal medullary pyramid, 312, 315 Renal mid pole, right, 317 Renal papilla, 306 Renal parenchyma, 305, 311, 313 Renal pelvis, 305, 310, 429, 942, 943 - contrast in, 307 - dilated, 430 - right, 310 Renal pyramid, 306, 310, 327, 942 Renal sinus, 302, 311, 313, 315, 319, 327, 328 - echoes, 315, 321 - fat, 306, 327 Renal upper pole, left, 322 Renal vascular pedicle, 311, 319 Renal vein, 303, 305, 315, 319 - conventional preaortic, 308 - left, 281, 288, 297, 299, 314, 320, 324, 325, 331, 354, 411 main, 325 - main, 326 - retroaortic, 308 - right, 309, 313, 314, 317 main, 312, 317, 318 - segmental, 318 spectral Doppler waveform with phasic variation, 318 - supernumerary, 308 - variants, 308 Renal venous waveform, with mild phasic variation, 318 Respiratory diverticulum, 906, 908 Rete testes, 447, 448, 456 Reticularis, 934 Retina, 40, 44 Retrobulbar fat, 40 Retrocalcaneal bursa, 830, 831 Retrocalcaneal fat, 830, 831 Retrocondylar bursa, 770 Retromammary fat, 241, 244 Retromammary zone, 234 - fat in, 240 Retromandibular vein, 43, 89, 102, 103, 105, 106, 107, 108, 109, 111, 115, 190 Retropectoralis minor space, 208, 214 Retroperitoneal adenopathy, 309 xxxv

INDEX Retroperitoneal lymph nodes, 353 Retroperitoneal (mesenteric) lymph sac, 895, 904 Retropharyngeal nodes, 199 Retropharyngeal space, 88, 113, 119, 159, 162 Retrovesical angle, 519 Retrozygomatic node, 200 Retzius, space, 424, 427, 428 Reverberation artifacts, 425, 431 Reversed diastolic flow, 463 Rhombencephalon, 868, 874, 875 Rhomboid muscle, 230, 231 Ribs, 219, 225, 228, 229, 232, 233, 236, 240, 241, 244, 893, 912, 933 - 1st, 133, 209, 531, 532, 674, 675 - 3rd, 222 - 4th, 222 anterior cortex, 232 - 8th, anterior cortex, 232 - 9th, anterior cortex, 232 - 12th, 310 - posterior, 913 - right, 401 - shadow, 316, 319, 321, 322, 323 - true, 229 Right anterior cerebral artery, 55 Right anterior inferior cerebral artery, 62 Right atrium, 915 Right erector spinae muscle, 316 Right lateral vaginal fornix, 486 Right major fissure, 220 Right ovary, 495, 496, 497, 498 Right posterior inferior cerebral artery, 62 Right subclavian artery, 141 Right ureter, 470 Ring down artifact, 227 Rootlets, 75 Rosenthal, basal vein of, 36, 70, 71 Rotator cuff, 536 - cable, 537 - interval, 536, 537, 544 - tendon blood supply, 536 Rotter nodes, 238 Round ligament, 411, 469, 472, 495, 511 - of uterus, 489, 508 Rounded morphology lymph node, 245 Rugae, 343 Rugal folds, 339

S S wave, 258, 261, 264 S1 nerve root, 410 Sacral artery - lateral, 409 - middle, 409 Sacral foramen, posterior, 712 Sacral median crest, 712 Sacral meningocele, anterior, 889 xxxvi

Sacral vein - lateral, 411 - median, 411 Sacrocervical ligaments, 482 Sacrococcygeal teratoma, 889 Sacroiliac joint, 506, 712 - right, 403 Sacrospinous ligament, 506, 509 Sacrotuberous ligament, 506, 509, 708, 713 Sacrum, 81, 342, 506, 507 - unossified, 892 Sagittal band, 637, 658, 659 Sagittal sinus, superior, 6 Sagittal suture, 4, 5 Saphenofemoral junction, 756 Saphenopopliteal junction, 808 Saphenous nerve, 810 Saphenous vein - Doppler, 757 - greater, 717, 719, 723, 743, 745 - lesser, 783 - short, 786 Sappey plexus, 238 Sartorius muscle, 719, 723, 724, 725, 729, 731–732, 738–739, 742–745, 751, 752, 764, 770 Sartorius tendon, 775 Scalenus anterior muscle, 90, 91, 114, 115, 116, 120, 124, 125, 126, 127, 132, 133, 139, 146, 161, 166, 167, 193, 223, 671, 672, 673, 674 Scalenus medius muscle, 91, 126, 132, 133, 146, 167, 193, 212, 671, 673, 674 Scalenus posterior muscle, 133, 212 Scalp, 4–7 - graphics, 5 - US and T2WI MR, 6–7 Scaphoid, 615, 618, 619, 620, 623, 625, 639, 643, 691 Scapholunate ligament, 620, 639 Scaphotrapezium-trapezoid ligament, 627 Scaphotriquetral ligament, dorsal, 627 Scapula, 230, 231, 550, 551, 552, 561, 893 - glenoid cavity of, 539 Scapular artery - circumflex, 571 - dorsal, 571 Scapular group, 238 Scapular spine, 551, 552, 555 Sciatic foramen - greater, 713 - lesser, 714 Sciatic nerve, 709, 713, 741, 746–747, 751, 760, 810 - transverse, 761 Sciatic notch, 506 SCJ. See Sternoclavicular joint. Sclera, 42, 44 Sclerotomes, 889, 891 Scrotal calculi, 447 Scrotal development, 450 Scrotal Doppler, 453–454 Scrotal septum, 451 Scrotal skin, 457

INDEX Scrotal wall, 451 - layers, in situ, 449 Scrotum, 446–457, 935, 943 Sebaceous gland, 4, 5 Secondary palate, 894, 896, 901 Secondary sex cords, 935 Secondary yolk sac, 863, 866 Segmental arterial branches, 289 Sella turcica, 14, 55 Semicircular canals, 880 Semimembranosus bursae, 770 Semimembranosus muscle, 724, 752, 753, 770, 775–776 Semimembranosus tendon, 708–709, 715, 764, 770 Seminal vesicles, 351, 427, 434–445, 449, 461, 941 Seminiferous tubules, 448 Semispinalis capitis muscle, 91, 115, 121, 132, 133 Semispinalis cervicis muscle, 115, 121, 132, 133 Semispinalis muscle, 132, 133, 674 Semitendinosus muscle, 708–709, 724, 747, 765–766 Semitendinosus tendon, 764, 770, 779 Septa, 448 Septal vein, 70 Septate uterus, 935 Septation, 135, 392, 914 Septi pellucidi, 878, 882 Septum, membranous, 919 Septum pellucidum, 11 Septum primum, 914 Septum secundum, 914 Septum transversum, 907 Serratus anterior muscle, 230, 231 Serratus posterior inferior muscle, 397 Serratus posterior muscle, 709 Sertoli cells, 935 Sesamoid, 843, 855 - lateral, 841, 853 - medial, 840, 841, 853 - radial, 649, 651 - ulnar, 649, 650, 651 Short plantar ligament, 822 Short posterior ciliary arteries, 43 Short radiolunate ligament, 627 Short saphenous vein, 786, 797 Shoulder, 536–553 - biceps tendon, 545, 546 - deep structures, 539 - glenohumeral joint, 553 - infraspinatus, 549 - ligaments, 538 - muscles, 538 - posterior aspect, 551, 552 - posterior glenoid labrum, 553 - rotator cuff interval, 544 - sagittal normal labrum, 540 - subscapularis, 547, 548 - supraspinatus, 541, 542, 543 - teres minor, 550 Sigmoid, 338, 342 - colon, 350, 932 - mesocolon, 342 root, 389, 929

Sigmoid sinus, 36, 70 Sinus confluence, 32, 36, 70 Sinus echoes, 323 Sinus horns, 916, 917 Sinus tarsi, 819 Sinus venosus, 915, 931 Sinusoid, maternal, 863 Sinusoidal space, within venous vascular malformation, 197 Skin, 229, 230, 232, 399, 404 Skull, 902, 903 Skull base segment, 164 Small bowel, 336, 344, 346, 393, 912, 932, 933, 942, 943 - loops, 341, 350, 393 - mesentery, 293, 340, 387, 388 root, 389 Small cortical branch, 60 Small diastolic flow reversal, 189 Small interaortocaval node, 354 Small intestine, 338, 341, 925, 929 Small saphenous vein, 792, 795, 808, 809, 846 Smooth immature cortex, 878 Soft palate, 97, 111 Soft tissue, thickening, 128 Soleal musculotendinous junction, inferior extent of, 829 Soleal veins, 797, 800, 806 Soleus muscle, 783, 785–786, 788–791, 793, 794, 796, 797, 798, 799, 800, 801, 804, 805, 806, 807, 808, 809, 811, 812, 829, 830 Solid parenchyma, 496 Somatic mesoderm, 18-day embryo, 926 Somites, 874, 891 Space of Retzius, 472, 483 Spectral Doppler waveform, in carotid bulb, 175 Spermatic cord, 446, 451, 457 Spermatic fascia - external, 449, 450 - internal, 450 Spermatozoa, penetration to oocyte for fertilization, 862 Sphenoid, 53, 55, 902 - sinus, 97 Sphenoidal fontanelle, 903 Sphenopalatine artery, 173 Sphenoparietal sinus, 53, 70 Sphincter complex, 514, 515 Spinal accessory lymph node chain, 130, 131, 198 Spinal accessory nerve, 130 Spinal accessory nodes, 200, 201 - group (VA-VB), 199 Spinal canal, 76, 314, 913, 943 Spinal cord, 74–83, 97, 231, 893 - ascent, 889 - cervical, 28 - development, 888–889 Spinal ganglion, 75, 76 Spinal lamina, 933, 942 Spinal nerve, 703 Spinalis thoracis muscle, 397 Spine, 225, 256, 278, 335 - embryology and anatomy, 888–893 - fetal, 892–893, 920 xxxvii

INDEX Spinoglenoid notch, 555, 556 Spinous process, 79, 397, 404, 893 Spiral arteries, 470 Splanchnic mesoderm, 914 - 18-day embryo, 926 Spleen, 227, 284–291, 293, 299, 320, 321, 322, 323, 333, 334, 392, 401, 925, 928, 929, 932, 933, 943 - accessory, 284 - inferior, 392 - ligaments and vessels, 285 - medial surface, 226 - right-sided, 291 - shape, 286, 287 - superolateral surface, 226 - tip, 391 - US, 284 - vessels, 288, 289 Splenial artery, 62 Splenic artery, 253, 255, 284, 285, 288, 289, 290, 293, 296, 297, 299, 320 - hilum, 287 Splenic capsule, 287 Splenic cyst, 291 Splenic flexure, 342 Splenic vein, 256, 281, 284, 285, 288, 289, 290, 294, 295, 297, 299, 307, 324, 331, 334, 335, 354, 391 Splenic vein/superior mesenteric vein confluence, 325 Splenic vessels, 322, 925 Splenius capitis muscle, 111, 133 Splenocolic ligament, 285 Splenophrenic ligament, 285 Splenorenal ligament, 284, 285, 388, 392, 925 Splenosis, 284, 291 Splenule, 290 - accessory splenic vessels supplying, 290 Split cord, 82 "Split pleura" encloses fluid collection, 223 Spring ligament, 814, 821, 823, 841 - superomedial, 822 Squamosal suture, 903 Stener lesion, 655 Stenotic segment, 423 Sternal angle, 229 Sternal cortex, 233 Sternal notch, 211, 229 - fat, 210 Sternoclavicular joint, 229, 530–535 - longitudinal US, 532 - transverse US, 531 Sternocleidomastoid muscle, 87, 90, 91, 101, 106, 107, 109, 111, 114, 115, 116, 117, 120, 121, 122, 123, 126, 127, 128, 129, 131, 132, 133, 135, 138, 139, 140, 146, 147, 160, 161, 166, 167, 168, 169, 174, 175, 176, 177, 178, 179, 180, 182, 183, 186, 187, 192, 193, 194, 195, 196, 201, 202, 203, 204, 210, 211, 212, 223, 532, 672, 673, 674 - anterior portion, 140 - clavicular head, 161 - pseudotumor, 134

xxxviii

- sternal head, 161, 211 insertion, 211 Sternohyoid muscle, 90, 91, 120, 126, 127, 133, 138, 140, 146, 160, 161, 182, 192, 210, 211, 532 Sternothyroid muscle, 90, 91, 120, 126, 127, 133, 138, 139, 140, 146, 160, 161, 182, 192, 210, 211 Sternum, 222, 228, 230, 231, 531 - body, 209, 229 - manubrium, 229 Stomach, 259, 280, 285, 286, 290, 293, 294, 299, 320, 324, 334, 336, 338, 341, 342, 354, 387, 391, 870, 912, 928, 929, 932, 933 - 4-week embryo, 927 - anterior wall, 343 - collapsed body, 343 - with food content, 227 - fundus, 343 - posterior wall, 343 - in situ, 339 Stomodeum, 896 Straight gyrus, 15 Straight sinus, 32, 36, 37, 70, 887 Strap muscles, 138, 141, 142, 146, 148, 154, 155, 156, 160, 161, 162, 167, 168 Stratum basalis, 478 Stratum functionalis, 478, 480 Stress urinary incontinence, 505, 520 Striated urogenital sphincter muscle, 511 Styloid process, 105, 902 Stylopharyngeus muscle, 111 Subacromial-subdeltoid fat plane, 536, 537 Subaponeurotic areolar tissue, 5 Subaponeurotic tissue, 4 - fibroadipose, 4 Subarachnoid space, 5, 36, 76, 79, 80 Subcapsular/peripheral nodal vascularity, 205 Subclavian artery, 124, 125, 137, 161, 171, 172, 182, 183, 185, 209, 210, 211, 212, 213, 215, 223, 239, 532, 571, 671, 675 - branch of, 194 - costoclavicular space, 216, 217 - right, 141 Subclavian vein, 125, 126, 127, 128, 129, 190, 191, 193, 194, 195, 196, 197, 209, 213, 215, 216, 223, 239, 531, 671, 904 - tributary of, 194 Subclavian vessels, branches of, 195 Subclavicular group, 238 Subclavius muscle, 213, 215, 217 Subcutaneous adipose tissue, 343, 344, 348 Subcutaneous external anal sphincter, 515, 524 Subcutaneous fat, 222, 223, 229, 230, 232, 245, 256, 313, 315, 316, 319, 398, 399, 400, 404, 405, 546, 672 Subcutaneous fibroadipose tissue, 5 Subcutaneous perineal layer, 518

INDEX Subcutaneous tissue, 89, 90, 91, 94, 95, 96, 100, 101, 102, 106, 108, 109, 110, 111, 114, 116, 117, 120, 126, 127, 128, 132, 133, 138, 140, 154, 156, 160, 161, 162, 166, 174, 176, 177, 178, 182, 186, 194, 196, 202, 203, 565, 566, 567, 583, 698, 809, 855 - thickening, 123, 128, 135 Subdeltoid bursa, 539 Subdeltoid peribursal fat, 541, 542, 543, 544, 545, 548, 549, 552 Subdural space, 76 Subglottic larynx, 150, 152 Subgluteus medius, bursa, 728 Subhepatic space - anterior, fluid, 390 - right, 391 Sublingual gland, 89, 93, 94, 95, 96, 97 Sublingual region, 92–97 Sublingual space, 93, 96, 99 Submandibular duct, 93, 101 Submandibular gland, 89, 90, 95, 99, 100, 101, 102, 103, 113, 114, 115, 116, 117, 167, 175, 176, 177, 178, 179, 201 Submandibular nodes, 87, 95, 99, 115, 198, 199, 200, 201 Submandibular region, 98–103 Submandibular space, 88, 93, 99, 113 Submental lymph node, 87 Submental node, 198, 199, 200, 201 Submental region, 92–97 Submucosa, 524 Submucosal fibroid, 473 Submucosal layer, 350 Submucosal vaginal smooth muscle, 511 Suboccipital fissure, 28 Subscapular nerve, 703 Subscapularis muscle, 230, 231, 533, 536, 538, 540, 545, 552, 556, 559, 563 Subscapularis tendon, 540, 544, 545, 547, 548, 553 - transverse US, 548 Subtalar joint, posterior, recess from, 829 Subtendinous areolar tissue, 662, 664 Suburethral ligament, 512, 513 Sulcus, 8 - calcarine, 884 - central, 880, 883, 884 - cingulate, 879, 882 - convexity, 885 - development, 872 - parietooccipital, 879, 883, 884 - postcentral, 880 - precentral, 880, 883 Superficial circumflex artery, 752 Superficial cortical vein, 36 Superficial deltoid ligament - anterior tibiotalar, 822 - posterior tibiotalar, 822 - tibiocalcaneal band, 819, 822 - tibionavicular band, 822 - tibiospring, 822 Superficial dorsal vein, 461 Superficial epigastric artery, 722–723, 749

Superficial external anal sphincter, 515, 524, 526, 527 Superficial external genital muscles, 504 Superficial (external) inguinal ring, 449, 451 Superficial fascia, 461, 465, 764 Superficial femoral artery, 731, 744, 745, 749, 752 Superficial femoral vein, 744–745, 750, 752 Superficial leg veins, 792 Superficial middle cerebral vein, 70 Superficial palmar arch, 611, 636, 640, 645 Superficial peroneal nerve, 783, 786, 810, 811, 834 - lateral branch, 847 - medial branch, 847 Superficial temporal artery, 170, 173 Superficial transverse perineal muscle, 508, 509, 517, 526 Superficial trigonal muscle, 511 Superficial vessels, 837 Superior acromioclavicular ligament, 533, 534, 535, 551 Superior adrenal arteries, 330, 331 Superior alveolar artery, 173 Superior breast innervation, 234 Superior cerebellar artery, 34, 37, 50, 62, 66 Superior cerebellar cistern, 11, 21, 28 Superior cerebral artery, 32 Superior (dorsal) pancreatic artery, 293 Superior extensor retinaculum, 794, 814, 816, 817, 835 Superior frontal gyrus, 10, 15, 23 Superior frontal sulcus, 10, 15 Superior gemellus muscle, 708–709, 724, 742 Superior glenohumeral ligament, 540, 551 Superior gluteal artery, 410, 419, 749 Superior hemispheric branches, 66 Superior iliac spine, anterior, 506, 728, 738, 742 Superior labrum, 728 Superior laryngeal nerve, 153, 164 Superior lateral geniculate artery, 749, 793 Superior longitudinal muscle, 97 Superior medial geniculate artery, 749, 793 Superior mediastinal nodes, 87, 198, 199, 200 Superior mediastinum, 141 Superior mesenteric artery, 285, 288, 340, 341, 342, 344, 354, 387, 391, 409, 426, 924, 928 Superior mesenteric nodes, 353 Superior mesenteric vein, 274, 285, 340, 344 Superior oblique muscle, 39, 41 Superior ophthalmic vein, 41, 43, 46, 191 Superior parathyroid gland, 137, 144, 145 Superior parietal lobule, 10, 19 Superior peroneal retinaculum, 814, 825, 826 Superior petrosal sinus, 70, 191 Superior pubic ligament, 720 Superior pubic ramus, 729 Superior rectus muscle, 39, 41, 47 - levator palpebrae superioris complex, 41 Superior sagittal sinus, 6, 19, 32, 36, 70, 883 Superior scapular transverse ligament, 538 Superior segmental artery, 306 Superior segmental vein, 320 Superior tarsus, 42 Superior temporal gyrus, 17, 23 Superior thoracic aperture, 210–211 Superior thoracic artery, 571 xxxix

INDEX Superior thyroid artery, 121, 136, 137, 140, 145, 170, 171, 173, 175, 178, 179 Superior transverse scapular ligament, 538, 539, 551, 555, 556 Superior ulnar collateral artery, 564, 572, 607 Superior ureter - left, 328 - right, 328 Superior vena cava, 191, 904, 920, 923 - left, 921 - normal, 921 Superior vermian artery, 66 Superior vesicle arteries, 410, 470, 489 - ureteric branch, 426 Superior vesicle vein, 411 Supinator muscle, 582, 583, 586, 589, 600, 602, 605, 608, 681, 683, 689 Supporting ligaments, 468 Supraclavicular fossa, 133 Supraclavicular lymph node, metastatic, 128 Supraclavicular nodes, 238 Supraclinoid internal carotid artery, 54 Supraclinoid internal cerebral artery, 58 Supraglottic larynx, 150, 151 - gas in, 114, 120, 178, 202 Suprahyoid anterior triangle. See Upper cervical level. Suprahyoid thyroglossal duct cyst, 143 Supramarginal gyrus, 10 Supramesocolic space - left, 392 - right, 390 lesser sac, 391 Supraorbital artery, 43 Suprapatellar bursa, 764–765 Suprapatellar fat pad, 764–766 Suprapineal recess, 12 Suprascapular artery, 555, 571 Suprascapular nerve, 539, 555, 556 Suprascapular notch, 555 Suprasellar cistern, 11 Supraspinatus muscle, 533, 536, 538, 539, 551, 552, 553, 555, 556, 568, 678 Supraspinatus tendon, 538, 539, 540, 541, 542, 543, 544, 551, 552, 555, 556 Supraspinous ligament, 79 Supratrochlear vein, 43 Supravesical space, 427 Sural nerve, 786, 810, 834, 847 Surface gyri, 885 Surface undulations, 883 Surfactant, 907 Suspensory ligament, 458 - of ovary, 469, 495 - of penis, 461 Sustentaculum talus, 821, 823 Sutures, 903 - coronal, 903 - metopic, 903 - squamosal, 903 Sweat gland, 5 xl

Sylvian fissure, 10, 14, 15, 16, 17, 19, 22, 23, 25, 58, 878, 879, 880, 881, 886 - "closed," 882, 885 - at different ages, 25 - indentation, 877 - "open," 882 Sympathetic chain, 165 Sympathetic trunk, 119 Symphysis, mandibular, 903 Symphysis pubis, 492, 506, 507, 509, 516, 517, 518, 519, 527 - level of inferior edge of, 519 Syncytiotrophoblast, 863 Synovial membrane, 539 Synovial sheath, 826 Synovium, 544 Systole, forward flow, 415 Systolic deceleration, 189 Systolic peak, 263

T T1, 669 - transverse process, 674 - ventral rami, 695 - vertebral body, 674 T1 dermatome, 667 T1 nerve, 75 T1 vertebral body, 209 T12, vertebral body, cortex of, 227 Taeniae coli, 342 Tailgut, 937 Talocalcaneal interosseous ligament, 825 Talocalcaneal joint, anterior, 823 Talocalcaneal ligament, interosseous, 819 Talofibular ligament, 819 - anterior, 814, 825, 828 - posterior, 814, 825, 828 Talonavicular joint, 818, 821, 824 Talonavicular ligament, dorsal, 822, 825, 835, 836 Talus, 819, 821, 822, 823, 824, 839, 848 - dome, 817, 818, 829, 848 - head, 818, 821, 836, 837 - lateral surface, 838 - lateral tubercle, 828, 829 - medial cortex, 823, 824 - medial tubercle, 812 - neck, 818, 821, 824, 828 - posterior, 820 Tarsal artery - lateral, 794, 838, 839, 847, 848 - medial, 839 Tarsal vein, medial, 839 Tarsometatarsal ligament, dorsal, 835 Tarsus, 832–845 - dorsal foot, 835–839 - lateral, 845 - medial, 844

INDEX - plantar aponeurosis, 842 - plantar foot muscles deep layers, 841 superficial layers, 840 - sagittal foot, 843 Telencephalon, 875, 880 Temporal bone, 27 - squama, 902 Temporal horn, 12, 17 - tips, 24 Temporal lobe, 8, 14, 15, 16, 17, 20, 21, 22, 24, 27, 880, 881, 882, 885 - with mature gyri, 886 Temporal operculum, 25, 880 Temporosquamosal suture, 5, 27, 29 Tendinous inscription, 395 Tendinous interspace, 537 Tendon - conjoined, 637, 658 - hand, 628 Tendon pulley system, 646 - fingers, 656 Tendon sheaths - fingers, 656, 657 - hand, 628 - wrist, 616 Tensor fascia lata muscle, 708–709, 719, 724, 729, 732, 738–739 Tentorial fissure, 28 Tentorium, 884 Tentorium cerebelli, 16, 17, 19, 21, 25, 877, 882 Teratoma, sacrococcygeal, 889 Teres major muscle, 230, 231, 533, 538, 539, 551, 555, 556, 558, 559, 560, 561, 563, 568, 572, 675, 678 Teres minor muscle, 231, 536, 538, 539, 540, 550, 551, 555, 556, 560, 568, 678 - nerve to, 557 Teres minor musculotendinous junction, 550 Teres minor tendon, 538, 540, 550, 551 Terminal duct, 234 Terminal ductal lobular unit (TDLU), 234, 237 Terminal ileum, 346, 929 Terminal myelocystocele, 889 Terminal phalanx, 661, 664 Terminal tendon, 637, 658 Testes, 446–457, 935, 941, 943 - appendix, 457 - descent, 935 - left, 451 - right, 451, 454 Testicular appendage, 457 Testicular artery, 448 Testicular carcinoma, 447 Tethered cord, 888 Thalamostriate vein, 70 Thalamus, 8, 16, 17, 20, 21, 22, 24, 25, 26, 27, 28, 31, 35, 869, 876, 877, 878, 879, 881, 886, 887 Thenar eminence - hand, 628, 634–635 - thumb, 653–654 - wrist, 622

Thenar-hypothenar eminence, 633 Thenar muscle, 646 - nerve to, 685 Thickened mucosa, 485 Thickened node cortex, 245 Thickened pleura, 223 Thigh - arteries, 749 color Doppler, 754 spectral Doppler, 755 - longitudinal vessels, 752 - muscle, 736–747 anterior, 738–741 medial, 742–745 posterior, 742, 746–747 - nerves, 753 - transverse vessels, 750 - veins, 750, 758 3rd ventricle, 12, 16, 17, 20, 21, 25, 27, 30 - roof of, 31 Thoracic aorta, descending, 912 Thoracic artery - internal, 230, 571 - lateral, 239, 571 - superior, 571 Thoracic cavity, 227 Thoracic duct, 353, 895, 904 Thoracic great vessels, 219 Thoracic muscle, transverse, 230 Thoracic nerve, 703 Thoracic outlet, 208–217 - costoclavicular space, 213 - dynamic interrogation, 215 - graphics, 209 - interscalene triangle, 212 - lateral boarder, 209 - posterior boarder, 209 - retropectoralis minor space, 214 - spectral Doppler interrogation, 216–217 - superior thoracic aperture, 210–211 Thoracic spine, 79 Thoracic vein, lateral, 239 Thoracoacromial artery, 214, 571 - pectoral branch, 214 Thoracodorsal artery, 571 Thorax - breast, 234–245 - chest wall, 228–233 - diaphragm, 224–227 - pleura, 218–223 - thoracic outlet, 208–217 Thrombus, 423 Thumb, 646–655 - carpometacarpal joint, 648 - extensor aspect, 652 - metacarpophalangeal joint, 649 - palmar aspect, 651 - Stener lesion, 655 - thenar eminence, 653–654 - ulnar collateral ligament, 650 Thy-box, 913 xli

INDEX Thymus, 907, 913 - fetal, 913 Thyroarytenoid gap, 152, 155 Thyroarytenoid muscle, 152, 153 Thyrocervical trunk, 125, 137, 171, 571 Thyroglossal duct cyst, 143 - infrahyoid, 143 - suprahyoid, 143 Thyrohyoid ligament, 156 Thyrohyoid membrane, 153, 159 Thyroid, isthmus of, 91 Thyroid artery - inferior, 127 - superior, 121 Thyroid capsule, 138, 148 Thyroid carcinoma, 122 Thyroid cartilage, 87, 97, 121, 125, 141, 143, 150, 151, 152, 153, 155, 156, 157, 159, 162, 167 - anterior lamina, 153 - inferior cornu, 152, 153 - isthmus, 156 - superior cornu, 153 Thyroid gland, 90, 91, 119, 121, 123, 125, 127, 136–143, 145, 147, 148, 149, 152, 157, 159, 182 - axial CECT, 139 - graphics, 137 - inferior pole, 140 - lobe, 126, 127, 129, 133, 134, 138, 139, 141, 142, 143, 146, 147, 160, 161, 162, 163, 166, 167, 182, 183, 192, 193, 195, 197 - longitudinal ultrasound, 140–141 - lower pole, 138, 168 - superior pole, 120, 140 - transverse ultrasound, 138 Thyroid isthmus, 138, 139, 142, 145, 147, 160, 161 Thyroid lamina, 120, 133, 154 Thyroid nodules, 148 Thyroid notch, 153, 155 Thyroid tissue, normal, 163 Thyroidea ima, 137 Tibia, 796, 797, 798, 800, 819, 822, 825, 826, 829 - anterior cortex, 817 - anteromedial bare area, 782 - distal, 818, 820 - posterior cortex, 790 Tibial artery - anterior, 792, 793, 794, 802, 803, 804, 811, 817, 847 - posterior, 792, 793, 794, 797, 798, 799, 800, 802, 804, 805, 806, 809, 820, 821, 846 branches and, 793 - recurrent, anterior, 794, 811 Tibial condyle, 765, 767 - lateral, 773 - medial, 769, 771 Tibial cortex, posterior, 812 Tibial nerve, 741, 751, 752, 753, 784, 786, 791, 799, 810, 811, 812, 820 - muscular branches, 811 - posterior, 819 - recurrent, anterior, 811 Tibial plateau, medial, 771 xlii

Tibial posterior muscle, 800 Tibial sesamoid, 853 Tibial tuberosity, 765, 767–768 Tibial vein - anterior, 795, 802, 803, 805, 817 - posterior, 795, 797, 798, 799, 800, 802, 804, 805, 806, 809, 820, 821 soleal vein draining into, 806 Tibial vessels - anterior, transverse, 802 - longitudinal anterior, 803 posterior, 799 - posterior, 803, 821 transverse, 798 Tibialis anterior muscle, 783–786, 802, 803, 804, 805 Tibialis anterior tendon, 783, 788, 814, 816, 817, 818, 819, 836, 837, 839 Tibialis posterior muscle, 784–786, 790, 791, 793, 798, 799, 801, 802, 803, 804, 805, 806, 811, 812 Tibialis posterior tendon, 793, 811, 815, 819, 820, 821, 823, 824, 841, 844 Tibiocalcaneal band, 822 Tibiofibular ligament - anterior, 814, 817, 825 - posterior, 814, 822, 825 Tibionavicular ligament, anterior, 824 Tibiotalar ligament, anterior, 824 Tip of coccyx, 509 Toes, 852–857 Tongue, 111, 901 - base, 115 - intrinsic muscle, 95, 111 - median raphe, 95 - root, 93, 99 Tonsil, cerebellar, 887 Torcular, 882 Torcular Herophili, 36, 884 Torsion, 447 Torso, 870 Tortuous pancreatic duct, 300 Trabeculae, 460 Trachea, 121, 125, 127, 128, 134, 138, 139, 141, 142, 145, 146, 147, 149, 158–163, 167, 183, 193, 195, 209, 210, 906, 910, 912 - axial CECT, 161 - cervical, 158 - CT, 162 - graphics, 159 - longitudinal ultrasound, 162 - lumen, 210 - pathology, 163 - primitive, 908 - transverse ultrasound, 160 Tracheal air artifact, 162 Tracheal bud, 906, 908 Tracheal cartilages, 158 Tracheal ring, 97, 133, 138, 139, 162 - 1st, 153, 159, 162 - 2nd, 162 - 3rd, 162

INDEX - 4th, 162 - cartilage, 160 - cartilaginous, 210 Tracheoesophageal folds, 907 - midline fusion, 907 Tracheoesophageal groove, 139, 145, 146, 158, 159, 161, 165 Tracheoesophageal septum, 906 Tragus, 897 Transcranial Doppler, 50–73 Translucency, intracranial, 869, 876 Transmediastinal artery, 453 Transperineal ultrasound anatomy, pelvic floor, 516, 517 Transversalis fascia, 449, 450, 935, 941 Transverse abdominis muscle, 720 Transverse anterior tibial vessels, 802 Transverse aortic arch, 922, 923 Transverse cervical artery, 125, 130, 571 Transverse cervical (cardinal) ligaments, 482 Transverse cervical chain lymph nodes, 124 Transverse cervical nodes, 199 Transverse cervical vein, 130 Transverse colon, 293, 304, 338, 339, 340, 341, 342, 348, 387, 388, 929, 933 - base, 293 - posterior reverberation artifact from gas, 348 - root, 388 Transverse humeral ligament, 533 Transverse ligament, 538, 545, 563, 728 Transverse mesocolon, 340, 387, 929 - root, 285, 389 Transverse metatarsal ligament, 835 Transverse muscle, 396 Transverse pancreatic artery, 296 Transverse process, 114, 121, 126, 133, 134, 177, 193, 402, 709, 892, 893 - cervical vertebra, 114, 120, 132, 166, 169, 186, 187, 188, 192 Transverse sinus, 36, 37, 70 Transverse spinous process, 230 Transversus abdominis muscle, 286, 397, 449, 450, 941 - right, 399, 400, 403, 405 - tendon, 397 Transversus thoracis muscle, 222 Trapeziocapitate ligament, 627 Trapeziotrapezoid ligament, 627 Trapezium, 615, 624, 625, 643, 648, 691 Trapezius muscle, 87, 124, 125, 131, 132, 133, 213, 230, 231, 552 Trapezoid, 615, 691 Trauma, 458 Treacher Collins syndrome, 895 Triangular fibrocartilage, 626 Triangular ligament, 251, 637, 658 - left, 250, 251, 389 - right, 250, 251 Triangular space, 554, 555

Triceps muscle, 564, 565, 568, 569, 573, 574, 679–680, 687, 696, 697–698 - lateral head, 538, 539, 551, 555, 556, 557, 562, 563, 564, 568, 569 - long head, 538, 539, 551, 555, 556, 557, 560, 561, 562, 563, 564, 568, 678, 697 - medial head, 562, 564, 569 - nerve to, 677 - short head, 697 Triceps tendon, 578, 580, 581, 594, 597 - insertion, 597 - lateral head, 538, 539, 551 - long head, 538, 539, 551 Tricolor carotid sheath, 131 Tricuspid valve, 918, 919, 921 Trigeminal nerve, 34 Trigonal ring, 511 Trigone, 9, 54, 427, 428, 460, 511 Trilaminar embryo, 866 Trilaminar germ disc, 888 Triphasic waveform, 216 Triquetrocapitate ligament, 627 Triquetrohamate ligament, 627 Triquetrum, 615, 623, 626, 639, 691, 701 Triradiate cartilage, 734–735 Trochanter - greater, 708, 710–711, 727–728, 733 lateral surface, 733 superior surface, 733 unossified, 734 - lesser, 728, 731, 738 Trochanteric bursa, 728 Trochlea, 39, 595 Trochlear groove, 766, 769 Troisier node, 198 True pelvis, 506 Tuberculous lymph node, 135 Tubular ectasia, 456 Tumor thrombus, vascularity within, 123 Tunica albuginea, 448, 452, 456, 457, 458, 461, 462, 465 Tunica vaginalis, 450, 452 Tunica vasculosa, 452, 453 Twinkle artifact, stone, 425, 429, 430

U

Ulna, 600, 601, 605, 610, 615, 620, 621, 623, 670, 682, 689–690, 700 - head, 626, 698 - styloid process, 626 Ulnar artery, 582, 586, 603, 606, 607, 608, 609, 611, 623, 624, 632, 636, 640, 641, 642, 645, 691–692, 699–702 - contribution to deep palmar arch, 645 - superficial branch, 642 - transverse and longitudinal US, 610 Ulnar bursa, 629, 647, 657, 664 Ulnar collateral artery - inferior, 607 xliii

INDEX - superior, 564, 572, 607 Ulnar collateral ligament, 578, 579, 581, 594, 595, 626, 655 - anterior band, 595 - lateral, 594 - posterior band, 593, 604 - retracted torn, 655 - thumb, 650 - transverse band, 593, 604 Ulnar coronoid, 579, 592 Ulnar nerve, 557, 558, 564, 565, 572, 573, 580, 581, 582, 594, 596, 597, 610, 617, 623, 624, 642, 669, 670, 675, 679, 687, 691, 693, 694–703 - in arm, 695, 697 - in cubital tunnel, 698 - deep branch, 636, 642, 645, 695, 702 - digital branches of, 695 - distal to Guyon canal, 702 - in forearm, 695–696, 699–700 - graphics, 695–696, 703 - in Guyon canal, 701 - palmar branch of, 695, 703 - superficial branch, 632, 636, 642, 645, 702–703 - transverse US, 697–702 - in wrist, 700 Ulnar recurrent artery, 580 - anterior, 607 - posterior, 581, 594, 607, 696 Ulnar sesamoid, 649, 650, 651 Ulnar vein, 608, 609, 610, 623, 624, 642, 701 Ulnocapitate ligament, 627 Ulnocarpal ligament, 626 Ulnolunate ligament, 627 Ulnotriquetral ligament, 627 Umbilical artery, 410, 871, 915, 922, 938 Umbilical cord, 868, 874, 931 - base bowel herniated into, 869, 871 bowel loops in, 870 - coiled, 870, 871 - cyst, 871 - development, 860, 871 - insertion site, 869, 870 Umbilical ligaments, medial, 923 Umbilical ring, 924 Umbilical veins, 871, 915, 922, 925, 929, 931, 933, 938 - at ductus venosus, 933 - left, 931 - right, 931 involuting, 931 Umbilicus, 395 Uncinate process, 294, 295 Uncus, 11 Undulating renal venous waveform, 317 Unicornuate uterus, 935 Upper cervical level, 112–117 - axial CECT, 115 - graphics, 113 - power Doppler ultrasound, 117 - transverse ultrasound, 114, 116 xliv

Upper extremity, 869, 870 - arm, 562–569 - axilla, 554–561 - elbow, 578–597 - fingers, 656–667 - forearm, 598–605 - hand, 628–639 - left, 876 - limb bud, 868 - right, 876 - shoulder, 536–553 - sternoclavicular and acromioclavicular joints, 530–535 - wrist, 614–627 Upper internal jugular nodes, 198 Upper lateral cutaneous nerve, of arm, 557 Upper vaginal walls, 525 Urachus, 940, 941 Ureter, 310, 411, 437, 449, 469, 470, 472, 495, 937, 939, 941 - right, 470 Ureteral jet - normal left, 430 - right, 431 Ureteral orifice, left, 428 Ureteric bud, 934, 936, 937 Ureteric orifices, 491 Ureterocele, 328, 425, 433 Ureterovesical junction, 424, 430 Ureters and bladder, 424–433 - in situ, 426 - Weigert-meyer rule, 433 Urethra, 396, 428, 438, 440, 441, 442, 443, 458–467, 490, 491, 492, 505, 507, 508, 509, 511, 513, 516, 517, 518, 520, 522, 525, 940 - artifact, 526 - color Doppler US, 522 - high-resolution 3D US, 518 - muscular wall, 522 - prostatic, 432 - spectral Doppler US, 523 - supporting structures, 511 Urethral bulb, 459 Urethral canal, 518, 522 Urethral compressor muscle, 518 Urethral crest, 434, 436, 460 Urethral orifice, 518 Urethral sphincter muscle, 518 Urethral support system, 504 Urethral wall, 521 Urethrovaginal sphincter, 511 Urge urinary incontinence, 521 Urinary bladder, 351, 393, 422, 426, 429, 432, 436, 439, 445, 466, 486, 490, 491, 492, 495, 510, 520, 521, 928, 930, 937, 940, 941 - future, 930 - in situ female, 428 male, 427 Urinary tract, 942 - development, 934 Urine jet, diverticulum neck, 432

INDEX Urine leakage, 521 Urogenital diaphragm, 427, 428, 436, 444, 460, 461, 504, 507, 508, 510, 511, 512, 513 - inferior fascial layer, 508 - superior fascial layer, 508 Urogenital hiatus, 504 Urogenital membrane, ruptured, 930 Urogenital sinus, 928, 930, 934, 940 - caudal, 934, 940, 941 Urorectal septum, 924, 928, 930, 934, 937 Uterine artery, 409, 410, 426, 470, 471, 480, 487, 488, 489 - cardinal ligament, 472 - descending segment, 471 - descending trunk, 480, 489 - ovarian branch, 498 Uterine body, 476 Uterine cavity, 863, 865, 866 Uterine fundus, 473, 475, 495 Uterine prolapse, 488 Uterine vein, 411, 471, 485 Uterine wall, folding of - anterior, 475 - posterior, 475 Uterosacral ligament, 469, 472, 483, 495, 510, 512, 513 Uterovaginal canal, 935, 940 Uterus, 342, 393, 409, 426, 428, 431, 468–481, 489, 495, 496, 497, 498, 511, 935, 940 - 3D, 473 - arteries, 468 - bicornuate, 935 - body, 477 - ligaments, 472 - normal sagittal images, 474 - round ligament of, 489 - septate, 935 - unicornuate, 935 - variations with age, 476, 477 position, 475 - vascular supply, 470, 471 Uterus didelphys, 935 Utricle orifice, 436

V

Vagal schwannoma, 168, 169 Vagina, 428, 470, 472, 474, 476, 477, 488–493, 505, 507, 508, 509, 516, 517, 518, 522, 526 - 3D volume rendered US, 525 - anterior fornix, 483 - arterial supply, 489 - color Doppler US, 522 - imaging, by various techniques, 490 - lateral walls, 518 - mucosal layer, 490 - muscular walls, 490 - orientation, 475

- posterior fornix, 483 - in situ, 489 - spectral Doppler US, 523 - and supporting structures, 510 - transverse US, 491 Vaginal artery, 426, 488, 489, 492, 493, 522, 523 - color Doppler US of, 492 - spectral waveform of, 493 Vaginal canal, 490, 492, 525 Vaginal fornix, 484 - left lateral, 486 - right lateral, 486 Vaginal introitus, 511 Vaginal mucosa, 475, 511 Vaginal support system, 504 Vaginal wall, 490, 511 Vagus nerve, 90, 112, 113, 114, 115, 118, 119, 125, 137, 145, 164–169, 192 - axial and coronal CECT, 167 - graphics, 165 - pathology, 168–169 - thickened, 168, 169 - transverse, power Doppler, and longitudinal ultrasounds, 166 - trunk, 165 Vallecula, 115, 151, 157, 187 Valve, 194 Valvulae conniventes, 345 - jejunum, 345 Varicocele, 447 Vas deferens, 427, 437, 440, 441, 445, 448, 449, 941 Vascularity, within tumor thrombus, 123 Vastus intermedius muscle, 738, 739, 740, 741, 746, 766 Vastus intermedius tendon, 764 Vastus lateralis muscle, 719, 733, 738–742, 746–747, 764, 782, 788 Vastus medialis muscle, 723, 738–740, 742–747, 765–766, 770, 782 Vastus medialis obliquus muscle, 770 Vein of Galen, 32 Veins, 408 - abdominal, 925 - development, systemic, 915 - embryology, 915 - fetoplacental circulation, 915 Velum interpositum, cistern of, 11 Vena cava, 315 Vena caval foramen, 224, 226 Venoatrial connections, 920 Venogenic impotence, 458 Venous arch - dorsal, 613, 837, 848, 851, 854 - plantar, 846 Venous drainage, 136 - breast, 235 - corpora cavernosa, 458 Venous lake, 5 Venous plexus, dorsal, 641 Venous valve leaflets, 752 Venous vascular malformation, 196 xlv

INDEX Venous waveform, 217, 326 - normal, 195 Ventral horn, 76 Ventral median fissure, 76 Ventral mesentery, 925 - 4-week embryo, 927 - 18-day embryo, 926 - persistent edge, 927 Ventral nerve roots, 76, 80 Ventricles, 918 - 3rd, 873, 880, 881, 884, 887 - 4th, 873, 881, 884 - developing, 917 - lateral, 873, 877, 879, 883, 885 frontal horn, 878, 881, 882 occipital horn, 877, 884 temporal horn, 885, 886 width, 877 - left, 918, 919, 920, 923 - right, 918, 920, 923 - septation, 914 Ventricular loop, 916 Ventricular septum, 919, 921 Ventriculoarterial connections, 919 Vermis, 16, 19, 20, 26, 28, 29, 30, 37, 886 - cerebellar, 877, 878, 881 - echogenic, 886 - fastigial point of, 877 Version, 468 Vertebrae, 400 Vertebral arch, fusion, 889 Vertebral artery, 32, 101, 115, 121, 137, 139, 161, 167, 168, 171, 172, 175, 177, 179, 183, 184–189, 211, 571 - axial and coronal CECT, spectral Doppler ultrasound, 187 - extraspinal (V3) segment (atlas loop), 66, 68 - graphic and volume-rendered CTA, 185 - grayscale and Doppler ultrasound, 188–189 - intradural (V4) segment, 66, 67, 69 - transverse, longitudinal grayscale and color Doppler, 186 - V1 segment, 184 - V2 segment, 184 - V3 segment, 184 - V4 segment, 184 Vertebral body, 115, 121, 133, 139, 146, 161, 177, 193, 230, 280, 281, 307, 308, 311, 314, 316, 320, 321, 322, 329, 335, 342, 392, 400, 402, 404, 416, 418, 429, 430, 893, 942 - cartilaginous portion, 892 - development, 889 cartilaginous stage, 889 ossification stage, 889 - formation and segmentation anomalies, 889 failure, 889 - lumbar, 401, 404 - ossified centrum, 892 - ossified portion, 892 - right, 400 - T1, 133 xlvi

Vertebral column, 74–83, 869 Vertebral lamina, 133 Vertebral transverse process, 91 Vertebral vein, 69, 115, 167, 186 Vertebral venous plexus, 190 Vertebral vessel, 90 Vertebrobasilar system, 50, 66–69 Verumontanum, 434, 436, 439, 441, 444, 460 Vesical fascia, 342, 428, 510 Vesicocervical space, 483 Vesicouterine pouch, 393, 428, 468, 483 Vesicovaginal fascia, 492, 516, 517, 518, 522 Vesicovaginal space, 483 Vestibule, 489 - bulb of, 509, 511 Vidian artery, 52 Virchow node, 198, 199 Visceral peritoneum, 390 Visceral pleura, 218, 220, 221, 229 - thick and enhancing, 223 Visceral space, 88, 159 - nodes, 87, 198, 199, 200 Viscerocranium, 902 - membranous, 902 Vitelline duct, 867, 868 Vitelline veins, 925, 931 - distal, 931 - intrahepatic plexus of, 931 Vitreous body, 40 Vocal cord, 121, 133, 152, 167 - false, 153, 154, 155, 157 - true, 153, 154, 155, 157 Vocal ligament, 152, 153 Vocal process, 152, 155 Vocalis muscle, 152, 153 Volar carpal ligament, 617, 645 Volar plate, 649, 659, 660, 661 Volar radioulnar ligament, 626, 627

W Wandering spleen, 284 Weigert-Meyer rule, 433 White matter, 8, 18 White pulp, 287 Willis, circle of, 33 Wrist, 614–627, 642 - carpal bones, 615 - compartments, 615 - dorsal, 619 - extensor carpi ulnaris, 621 - extensor digitorum, 620 - ligaments, 627 - radial aspect, 618 - scaphoid, 625 - tendon sheaths, 616 - tendons dorsal, 616 relations to dorsal and volar wrist, 617

INDEX - triangular fibrocartilage, 626 - volar, 622–624

X

Xiphoid process, 209, 225, 229

Y Yolk sac, 865, 866, 867, 868, 871, 874 - 4-week embryo, 927 - 18-day embryo, 926 - primary, 863, 864 - secondary, 863, 866 - separation from embryo, 869 Yolk stalk, 928, 929, 937

Z

Zona orbicularis, 727–728, 730 Zygoma of maxilla, 47 Zygomatic arch, 95, 902 Zygomatic bone, 903 Zygomaticus muscle, 111 Zygote, surrounded by zona pellucida, 862

xlvii