Rapid Review Gross and Developmental Anatomy, 3e (2010, Mosby) PDF

Rapid Review Gross and Developmental Anatomy Third Edition N. Anthony Moore, PhD Professor of Anatomy, University of Mississippi Medical Center, Jackson, Mississippi William A. Roy, PT, PhD Professor of Basic Sciences, Touro University Nevada, Henderson, Nevada Mosby Copyright 1600 John F....

Rapid Review Gross and Developmental Anatomy Third Edition N. Anthony Moore, PhD Professor of Anatomy, University of Mississippi Medical Center, Jackson, Mississippi William A. Roy, PT, PhD Professor of Basic Sciences, Touro University Nevada, Henderson, Nevada Mosby Copyright 1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899 RAPID REVIEW GROSS AND DEVELOPMENTAL ANATOMY, Third Edition Copyright © 2010, 2007, 2003 by Mosby, Inc., an affiliate of Elsevier Inc. ISBN-13: 978-0-323-07294-6 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. Permissions may be sought directly from Elsevier?s Rights Department: phone: (+1) 215 239 3804 (US) or (+44) 1865 843830 (UK); fax: (+44) 1865 853333; e-mail: [email protected]. You may also complete your request on- line via the Elsevier website at http://www.elsevier.com/permissions. Notice Knowledge and best practice in this field are constantly changing. As new research and experience broaden our knowledge, changes in practice, treatment and drug therapy may become necessary or appropriate. 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 the practitioner, relying on their own experience and knowledge of the patient, 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 assume any liability for any injury and/or damage to persons or property arising out or related to any use of the material contained in this book. Library of Congress Cataloging-in-Publication Data Moore, N. Anthony. Rapid review gross and developmental anatomy / N. Anthony Moore, William A. Roy.—3rd ed. p. ; cm.—(Rapid review series) Rev. ed. of: Gross and developmental anatomy / N. Anthony Moore, William A. Roy. 2nd ed. c2007. ISBN 978-0-323-07294-6 1. Human anatomy. 2. Human anatomy–Examinations, questions, etc. I. Roy, William A. II. Moore, N. Anthony Gross and developmental anatomy. III. Title. IV. Series: Rapid review series. [DNLM: 1. Anatomy–Outlines. QS 18.2 M823r 2011] QM23.2.M675 2011 612–dc22 2010002962 Acquisitions Editor: James Merritt Developmental Editor: Christine Abshire Publishing Services Manager: Hemamalini Rajendrababu Project Manager: Nayagi Athmanathan Design Direction: Steven Stave Printed in China Last digit is the print number: 9 8 7 6 5 4 3 2 1 Dedication To my friend and mentor Duane Haines for his unfailing support and counsel. —NAM To my postdoctoral mentors, Maurits Persson and the late Jan Langman, for their guidance and encouragement. —WAR Series Preface The First and Second Editions of the Rapid Review Series have received high critical acclaim from students studying for the United States Medical Licensing Examination (USMLE) Step 1 and consistently high ratings in First Aid for the USMLE Step 1. The new editions will continue to be invaluable resources for time-pressed students. As a result of reader feedback, we have improved upon an already successful formula. We have created a learning system, including a print and electronic package, that is easier to use and more concise than other review products on the market. Special features Book Outline format: Concise, high-yield subject matter is presented in a study-friendly format. High-yield margin notes: Key content that is most likely to appear on the exam is reinforced in the margin notes. Visual elements: Full-color figures are utilized to enhance your study and recognition of key concepts. Abundant two-color schematics and summary tables enhance your study experience. Two-color design: Colored text and headings make studying more efficient and pleasing. New! Online Study and Testing Tool A minimum of 350 USMLE Step 1–type MCQs: Clinically oriented, multiple-choice questions that mimic the current USMLE format, including high-yield images and complete rationales for all answer options. Online benefits: New review and testing tool delivered via the USMLE Consult platform, the most realistic USMLE review product on the market. Online feedback includes results analyzed to the subtopic level (discipline and organ system). Test mode: Create a test from a random mix of questions or by subject or keyword using the timed test mode. USMLE Consult simulates the actual test-taking experience using NBME's FRED interface, including style and level of difficulty of the questions and timing information. Detailed feedback and analysis shows your strengths and weaknesses and allows for more focused study. Practice mode: Create a test from randomized question sets or by subject or keyword for a dynamic study session. The practice mode features unlimited attempts at each question, instant feedback, complete rationales for all answer options, and a detailed progress report. Online access: Online access allows you to study from an Internet- enabled computer wherever and whenever it is convenient. This access is activated through registration on www.studentconsult.com with the pin code printed inside the front cover. Student Consult Full online access: You can access the complete text and illustrations of this book on www.studentconsult.com. Save content to your PDA: Through our unique Pocket Consult platform, you can clip selected text and illustrations and save them to your PDA for study on the fly! Free content: An interactive community center with a wealth of additional valuable resources is available. Preface to the Third Edition N. Anthony Moore, PhD , William A. Roy, PT, PhD The United States Medical Licensing Examination Step 1 incorporates the major themes and essential concepts of gross and developmental anatomy into relevant clinical vignettes. Rapid Review Gross and Developmental Anatomy is designed to help you review these themes and concepts while articulating their clinical relevance. High-yield margin notes recall topics of clinical significance that likely will be tested on Step 1. Clinical correlations appear in pink boxes directly within the outline to emphasize the clinical application of the preceding concept. Development and developmental defects are integrated into the outline. Netter images, diagnostic images, and simple line drawings facilitate recall of essential gross anatomy and development. Comprehensive tables summarize essential clinically oriented information. Web questions emulate the USMLE Step 1 format. Complete discussions of each answer and distractors facilitate your review. We hope that you will find this integrated approach helps you to prepare for your USMLE Step 1 examination. Good luck! Acknowledgment of Reviewers The publisher expresses sincere thanks to the medical students and faculty who provided many useful comments and suggestions for improving both the text and the questions in previous editions. Our publishing program will continue to benefit from the combined insight and experience provided by your reviews. For always encouraging us to focus on our target, the USMLE Step 1, we thank the following: Ellen K. Carlson, University of Iowa College of Medicine John D. Cowden, Yale University School of Medicine Mark D. Fisher, University of Virginia School of Medicine Charles E. Galaviz, University of Iowa College of Medicine Brian Harrison, University of Illinois Chicago School of Medicine Gregory L. Lacy, Tulane University School of Medicine Erica L. Magers, Michigan State University College of Human Medicine Mrugeshkumar K. Shah, MD, MPH, Harvard Medical School/Spaulding Rehabilitation Hospital Lara Wittine, University of Iowa College of Medicine Julie E. Zurakowski, Northeastern Ohio Universities College of Medicine Acknowledgments N. Anthony Moore, PhD , William A. Roy, PT, PhD The authors thank Edward Goljan, Series Editor, for constructive suggestions and some clinical correlations in this edition; Christine Abshire, Developmental Editor, for her hard work, attention to detail, and patience; and James Merritt, Senior Acquisitions Editor, for arranging the inclusion of color images from the Netter collection. This volume builds upon work done by the editors of earlier editions: Susan Kelly, Katie DeFrancesco, and Therese Grundl. Some of Matt Chansky’s original illustrations have been retained, and we appreciate the permission to include new figures from other Elsevier publications. We thank Duane Haines, Professor and Chairman of Anatomy, University of Mississippi Medical Center, for his encouragement and for creating an academic environment conducive to scholarly activity. I (WAR) also thank Mitchell Forman, Dean and Professor, and Ronald Hedger, Medical Director of Student Health Services and Associate Professor, Touro University Nevada College of Osteopathic Medicine, for helpful discussions and for patiently answering my questions about assorted diseases and injuries. Finally, we gratefully acknowledge the contributions of the many student physicians whose constructive criticisms, both formal and informal, have greatly increased this book’s value as preparation for the USMLE Step 1 and COMLEX Level 1. Table of Contents Instructions for online access Title Page Copyright Dedication Series Preface Preface to the Third Edition Acknowledgment of Reviewers Acknowledgments Chapter 1: The Back Chapter 2: The Thorax Chapter 3: The Abdomen Chapter 4: The Pelvis and the Perineum Chapter 5: The Lower Extremity Chapter 6: The Upper Extremity Chapter 7: The Neck Chapter 8: The Head Common Laboratory Values Index Chapter 1 The Back I. Typical Vertebra Body, vertebral arch, processes for muscular attachment and articulation with adjacent vertebrae, and vertebral foramen (Figure 1-1) A. The Body 1-1 Typical cervical vertebrae. A, Superior view of a typical cervical vertebra. B, Lateral view of articulated cervical vertebrae. (From Greene, W B: Netter’s Orthopaedics. Philadelphia, Saunders, 2006, Figure 13-4.) Anterior weightbearing cylinder B. Vertebral Arch 1. Overview  a. U-shaped component attached to posterior aspect of body b. Provides attachment for spinous, transverse, and articular processes 2. Pedicle has superior and inferior vertebral notches. 3. Lamina fuses in posterior midline with opposite lamina. C. Transverse Processes D. Articular Processes 1. Superior and inferior articular processes project from junction of pedicle and lamina separated by pars interarticularis 2. Form synovial zygapophysial (facet) joints with articular processes of adjacent vertebrae Zygapophysial joints are synovial joints that may develop osteoarthritis with age or trauma. E. Vertebral Foramen 1. Space enclosed by vertebral arch and body 2. Collectively form vertebral canal for spinal cord and meninges F. Intervertebral Foramina 1. Formed between inferior and superior vertebral notches in pedicles of adjacent vertebrae 2. Transmit spinal nerves and related blood vessels Compressing spinal nerve in intervertebral foramen may cause radiculopathy. Any space-occupying lesion in an intervertebral foramen may compress the spinal nerve or its roots and produce back pain that may radiate into an extremity. Motor nerve fibers may become involved, resulting in loss of strength. II. Vertebral Column Comprises 33 vertebrae in normal adult: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae A. Cervical Vertebrae (see Figure 1-1; Table 1-1) 1. Typical cervical vertebrae: C3-C6 a. Spinous processes allow neck extension because they are short. b. Articular processes with nearly horizontal facets allow relatively free movement in all directions at the expense of stability. c. Transverse foramen in each transverse process allows passage of vertebral artery and vein. TABLE 1-1 Features of Vertebrae The vertebral artery ascends transverse foramina of vertebrae C1-6. 2. C1 (atlas) (Figure 1-2; see Table 1-1) a. Midline anterior tubercle on anterior arch and posterior tubercle on posterior arch b. Sulcus for vertebral artery on posterior arch on each side 3. C2 (axis) (Figure 1-3; see Table 1-1) 1-2 Atlas (C1) from superior view. (From Greene, W B: Netter’s Orthopaedics. Philadelphia, Saunders, 2006, Figure 13-4.) 1-3 Axis (C2) and atlantoaxial joints. A, Posterosuperior view of axis. B, Posterosuperior view of articulated atlas and axis. Posterior articular facet of dens is for articulation with transverse ligament of atlas at median atlantoaxial joint. C, Open mouth radiograph of atlantoaxial joints. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 17.) The dens (odontoid process) and body of the axis develop from separate ossification centers. The ossification centers may fail to fuse, and this anomaly must be distinguished from an odontoid fracture in patients with cervical trauma. The dens also may be congenitally absent. The dens may be congenitally absent or fail to fuse with the body of the axis. 4. C7  a. Called vertebra prominens because of its long spinous process, which helps in counting vertebrae. Vertebra prominens is helpful in counting vertebrae. b. Small transverse foramen does not contain vertebral artery. Dislocations without fracture occur only in cervical spine. Dislocations may cause cervical vertebra to move out of alignment because articular surfaces lie in nearly a horizontal plane and are less stable. Although the spinal cord may be compressed, it may escape severe injury because of the large vertebral canal. Nevertheless, all movement of patients suspected of having a neck injury should be minimized until the cervical spine is properly stabilized. Injury to the cervical spinal cord may not appear on a radiograph. Failure of segmentation of cervical vertebrae results in congenital fusion, causing Klippel-Feil syndrome, which is characterized by a short, stiff neck. Klippel-Feil syndrome is congenital fusion of cervical vertebrae.  B. Thoracic Vertebrae (Figure 1-4; see Table 1-1) Articular processes are oriented to favor lateral bending and rotation, although range of movement is limited by the rib cage, thin intervertebral discs, and overlapping spinous processes. 1. Typical thoracic vertebrae: T2-T9 a. Costal demifacets on the body articulate with the head of the corresponding rib and the inferior rib. b. Costal facet on transverse process articulates with tubercle of corresponding rib 2. T1 and T10-T12 a. Complete facet on the body articulates with the entire head of the corresponding rib. b. Inferior demifacet on body of T1 articulates with superior part of head of rib 2 1-4 Typical thoracic vertebra. A, Superior view. B, Lateral view. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 154.) Traumatic injury to the thoracic vertebrae may produce dislocation with fracture because articular facet joints are arranged vertically. An aortic aneurysm may cause left-sided erosion to bodies of T5-T8 as seen on a radiograph. An aneurysm of the descending thoracic aorta may erode bodies of vertebrae T5-8 on the left side. C. Lumbar Vertebrae (Figures 1-5 and 1-6; see Table 1-1) Articular processes with facets oriented to favor flexion and extension 1-5 Lumbar vertebrae. A, Superior view of a typical lumbar vertebra. B, Lateral view of articulated lumbar vertebrae. Intervertebral foramina transmit spinal nerves. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 155.) 1-6 A, Oblique radiograph of lumbar spine showing characteristic “Scottie dog” form (B). The appearance of a collar indicates a fracture of the pars interarticularis. Traumatic injury to lumbar vertebrae may produce dislocation with fracture because articular surfaces are arranged vertically. Stress fractures of the pars interarticularis occur frequently in lumbar vertebrae (spondylolysis), with the posterior part of the vertebral arch separating from the anterior part to cause back pain. It occurs commonly in L5 in adolescent athletes involved in sports that require repeated spinal hyperextension. The vertebral column is not misaligned in unilateral fractures, which show up in oblique lumbar radiographs as a collar on the neck of the “Scottie dog” (Figure 1-6). Spondylolysis is a fracture of pars interarticularis that may cause spondylolisthesis. In spondylolisthesis, a vertebral body is displaced forward on the vertebral body immediately below. It occurs frequently at the L5/S1 level and is often secondary to bilateral pars interarticularis fractures. Alignment of the vertebral column is compromised, and the cauda equina may be affected. Patients with spondylolisthesis may encounter difficulty during childbirth because of the resulting narrowed pelvic inlet. Spondylolisthesis may interfere with childbirth. Degenerative changes in the lumbar spine and ligamenta flava may cause narrowing of the spinal canal (spinal stenosis). The resulting compression of neural structures produces pain on walking or standing that is relieved by bending forward or sitting (neurogenic claudication). This differs from vascular claudication of the lower extremities that is relieved by standing still. Neurogenic claudication from lumbar spinal stenosis differs from vascular claudication in being unrelieved by standing still. D. Sacrum 1. Wedge-shaped bone formed by fusion of five sacral vertebrae 2. Articulates superiorly with L5 at lumbosacral joint and laterally with hip bones at sacroiliac joints 3. Four pairs of anterior sacral foramina for anterior rami and four pairs of posterior sacral foramina for posterior rami of spinal nerves S1-S4 4. Sacral canal contains dural sac down to lower border of S2. 5. Sacral hiatus in place of spine and laminae of S5 (and sometimes S4) with sacral cornua located laterally When administering caudal epidural anesthesia, sacral cornua are used as landmarks to locate the sacral hiatus. Sacral cornua are landmarks for caudal epidural anesthesia. E. Coccyx Triangular bone formed from fusion of four coccygeal vertebrae; often C1 is not fused. III. Joints and Ligaments of Vertebral Column A. Joints between Vertebrae 1. Intervertebral discs (Figure 1-7)  a. Fibrocartilaginous joints between bodies of adjacent vertebrae except C1/C2, sacrum, and coccyx 1-7 Ligaments connecting vertebrae. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 158.) There is no intervertebral disc between vertebrae C1/C2. b. Separated from each vertebral body by thin plate of hyaline cartilage c. Permit little movement between adjacent vertebrae but cumulatively allow considerable flexibility of column d. Function as shock absorbers (1) Anulus fibrosus  (a) Fibrocartilaginous portion of disc surrounding nucleus pulposus; thinner posteriorly (b) Firmly attached to anterior and posterior longitudinal ligaments (2) Nucleus pulposus (a) Incompressible gelatinous center of intervertebral disc located closer to its posterior surface (b) Produces shock-absorbing quality of disc (c) Loses water temporarily during daily activities and permanently with age as it gradually becomes replaced by fibrocartilage The nucleus pulposus loses water temporarily each day and permanently with age. Rupture of the nucleus pulposus through the anulus fibrosus causes a herniated intervertebral disc. Herniated discs usually occur in lumbar (L4/L5 or L5/S1) or cervical regions (C5/C6 or C6/C7) of individuals younger than age 50 and may impinge on spinal nerves or their roots. Herniations may follow degenerative changes in the anulus fibrosus or be caused by sudden compression of the nucleus pulposus. Herniated lumbar discs usually involve the nerve root descending to exit the intervertebral foramen inferior to the vertebra below (traversing root) rather than the nerve root leaving the vertebral canal at the level of the disc (exiting root) (Figure 1-8). 1-8 Herniated lumbar intervertebral disc. Herniation usually occurs posterolaterally and affects traversing root, not exiting root (i.e., herniation at L4-L5 affects L5 root, whereas herniation at L5-S1 affects S1 root). An intervertebral disc usually herniates posterolaterally just lateral to posterior longitudinal ligament. Intervertebral discs herniate most commonly at L4/L5 and L5/S1 and compress traversing nerve root. 2. Facet joints (zygapophysial/zygapophyseal joints) a. Synovial joints between superior and inferior articular facets of adjacent vertebrae b. Provide varying amounts of flexion, extension, rotation, or lateral bending depending on vertebral level Facet joints diseased by osteoarthritis (degenerative joint disease) border the intervertebral foramen, and osteophytes may impinge on an adjacent spinal nerve, causing severe pain. Lumbar zygapophysial joints may be denervated by surgical or percutaneous radiofrequency neurotomy (percutaneous rhizolysis) to relieve low back pain. Each joint is innervated by medial branches of two adjacent posterior rami, and both branches must be sectioned. Osteoarthritis is degenerative joint disease from aging or trauma. Osteophyte on zygapophysial joint may compress spinal nerve B. Ligaments Connecting Vertebrae (Table 1-2; see Figure 1-7) TABLE 1-2 Ligaments of Vertebral Column Ligament Attachment Comments Limits flexion of vertebral Connects tips of spinous Supraspinous column; expanded in cervical processes region as ligamentum nuchae Connects spinous Limits flexion of vertebral Interspinous processes of adjacent column vertebrae Limits extension of vertebral Attached to anterior Anterior column; supports anulus surface of vertebral bodies longitudinal fibrosus and may be strained or and intervertebral discs torn in whiplash Limits flexion of vertebral Attached to posterior column; supports anulus Posterior surface of vertebral bodies fibrosus and directs herniation longitudinal and intervertebral discs and of intervertebral disc lies within vertebral canal posterolaterally Paired ligament that Limits flexion of vertebral Ligamentum connects laminae of column; yellowish due to flavum adjacent vertebrae elastic tissue Because its presence reinforces the intervertebral disc in the posterior midline, the posterior longitudinal ligament reduces the incidence of disc herniations that may compress the spinal cord and cauda equina. The cervical spinal cord may be injured without x-ray evidence of vertebral damage. The cervical spinal cord may be injured by transient inward bulging of the ligamentum flavum during sudden forced hyperextension. A radiograph may not show vertebral damage. Whiplash (cervical extension sprain) is forceful hyperextension of the cervical spine that stretches the anterior longitudinal ligament and adjacent structures. Rear-end automobile collisions often cause whiplash, and symptoms include neck pain, headache, and pain and numbness radiating into the upper extremities. Rear-end automobile collision causes whiplash injury. C. Craniocervical Joints and Ligaments 1. Atlantooccipital joint (Figure 1-9) a. Paired synovial joint between occipital condyle and superior articular facet of atlas  b. Allows flexion/extension of head (nodding head “yes”) and some lateral flexion but no rotation c. Posterior atlantooccipital membrane penetrated by vertebral artery and suboccipital nerve 2. Atlantoaxial joint (see Figure 1-9) a. Paired lateral atlantoaxial joints and median atlantoaxial joint with dens held against anterior arch of atlas by transverse ligament of atlas b. Allows rotation of head (shaking head “no”) but not flexion, extension, or lateral bending 1-9 Internal craniocervical ligaments connecting skull and vertebral column. Atlas and axis are separately attached to skull base to ensure maximum stability. Strong transverse ligament of atlas (horizontal part of cruciate ligament) binds dens in place to protect posteriorly related spinal cord. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 22.) Atlantooccipital joints: nodding head “yes.” Atlantoaxial joints: shaking head “no” Atlantoaxial dislocation or subluxation (partial dislocation) may injure the spinal cord and medulla. Subluxation can occur after rupture of the transverse ligament of the atlas caused by congenital weakness, trauma, or rheumatoid arthritis (Figure 1-10). A weak or absent transverse ligament occurs in 15% to 20% of Down syndrome patients. Subluxation due to rupture of the transverse ligament of the atlas may be apparent on a lateral x- ray only if the spine is flexed. 1-10 Lateral x-rays of the cervical spine in a rheumatoid arthritis patient with a ruptured transverse ligament of the atlas. A, Little space is apparent between the anterior arch of the atlas and the dens in neck extension (arrows). B, Increased space is seen between the anterior arch and dens in flexion (arrows). (From Mettler, F A: Essentials of Radiology, 2nd ed. Philadelphia, Saunders, 2004, Figure 8-9.) The transverse ligament of atlas may rupture in rheumatoid arthritis and Down syndrome patients. 3. Uncovertebral joints (of Luschka)  a. Jointlike structures that can develop postnatally in cervical spine between lips of bodies of adjacent vertebrae Osteophytes on uncovertebral joints may cause neck pain. b. Osteophyte formation here may cause neck pain. 4. Cruciate ligament (Table 1-3; see Figure 1-9) Consists of transverse ligament of atlas with superior and inferior extensions D. Curvatures of Vertebral Column TABLE 1-3 Craniocervical Ligaments Ligament Attachment Comments Continuation of posterior Covers dens and Tectorial longitudinal ligament from body of transverse ligament of membrane axis to anterior margin of foramen atlas posteriorly magnum Apical Extends from apex of dens to anterior ligament margin of foramen magnum Stout paired ligament connecting side Alar Limits rotation at of dens to medial aspect of occipital ligament atlantoaxial joints condyle Binds dens tightly Cruciate Expansion of transverse ligament of against anterior arch of ligament atlas atlas Normal adult vertebral column is concave anteriorly in thoracic and sacral regions, convex anteriorly in cervical and lumbar regions. 1. Normal curvatures (Figure 1-11) a. Primary curves (1) Concave anteriorly (same direction as fetal curvature) (2) Retained in thoracic and sacral regions of adult b. Secondary curves Become convex anteriorly in cervical and lumbar regions when infant begins to hold head up and to stand, respectively 2. Abnormal curvatures (Figure 1-12) a. Scoliosis (1) Any lateral curvature of spine (2) May be thoracic, lumbar, or thoracolumbar and is designated right or left according to convex side of major curve 1-11 Normal curvatures of vertebral column. A, Anterior view. B, Lateral view. 1-12 Abnormal curvatures of vertebral column. Scoliosis is a lateral curvature of the thoracolumbar spine. Scoliosis may be nonstructural and reversible (e.g., discrepancy in length of lower limbs) or structural and irreversible (e.g., idiopathic or neuropathic). Idiopathic right thoracic scoliosis in adolescent females is the most common form, and additional spinal curves that place the eyes in a horizontal plane may develop to compensate. A rib hump appears on the convex side during forward bending in structural scoliosis due to the posterior displacement of ribs from vertebral rotation. Congenital scoliosis may result from failure of one side of a vertebral body to form (hemivertebra) or asymmetric fusion of vertebrae. Idiopathic scoliosis in adolescent females is the most common form. b. Kyphosis Abnormal curvature that is convex posteriorly In osteoporosis, kyphosis of the thoracic spine may occur after compression fractures produce a wedge-shaped deformity of vertebral bodies. Although most common in postmenopausal women, kyphosis can occur in elderly men. An adolescent form of kyphosis (Scheuermann’s disease) results from disturbances in hyaline cartilage growth plates of thoracic vertebral bodies. Bracing may limit progression of the adolescent form. Kyphosis and scoliosis may occur together (kyphoscoliosis). Kyphosis is increased thoracic spine curvature that is common in postmenopausal women. c. Lordosis (1) Abnormal curvature that is convex anteriorly (2) Normal compensation of lumbar spine during pregnancy but may develop with obesity in both males and females Lordosis is increased anterior convexity of lumbar spine and is normal late in pregnancy. IV. The Development of the Vertebral Column (Figure 1-13) A. Origin from Somites 1. Mesenchymal cells from sclerotome of somites form condensations around the neural tube and notochord. 2. Condensation and proliferation of caudal half of one sclerotome join cranial half of next sclerotome to form a vertebral body 3. Anulus fibrosus of intervertebral disc is formed from mesenchymal cells of sclerotome that fill space between adjacent vertebral bodies as they form B. Contribution from Notochord Notochord persists within each intervertebral disc and undergoes mucoid degeneration to form nucleus pulposus. 1-13 Development of vertebral column. A, Caudal and cranial halves of adjacent sclerotomes fuse to form vertebral bodies (arrows). B, Note position of segmental neurovascular structures and myotomes relative to developing vertebral bodies. Intervertebral discs develop in middle of original sclerotomes. C, Muscles that develop from myotomes bridge intervertebral discs and move adjacent vertebrae. Vertebral bodies develop from the caudal half of one sclerotome and the cranial half of the succeeding sclerotome. The nucleus pulposus is a remnant of the embryonic notochord. V. Congenital Abnormalities of Vertebral Column and Spinal Cord (Figure 1-14) A. Spina Bifida Occulta 1. Results from vertebral arch failing to fuse in midline 2. Frequently occurs at L5 or S1 and may be marked by a tuft of hair and/or pigmented skin 3. Not associated with any neurological deficit 1-14 Transverse sections showing types of spina bifida. Each defect includes a failure of formation of the vertebral arch. A, Spina bifida occulta. B, Meningocele. C, Meningomyelocele. Spina bifida occulta is usually asymptomatic and detectable only by x-ray. B. Spina Bifida Cystica 1. Overview a. Protrusion of meninges and/or spinal cord through defect in vertebral arches b. Occurs in about 1:1000 births c. Often detected through high levels of alpha-fetoprotein in maternal serum or amniotic fluid d. May have reduced incidence with vitamin and folic acid supplements before conception and increased incidence with anticonvulsant valproic acid during week 4 Neural tube defects cause high alpha-fetoprotein levels in maternal serum and amniotic fluid. Neural tube defects may be preventable by folic acid supplements before and during pregnancy.  2. Spinal meningocele a. Protrusion of meninges through a defect in vertebral arches b. May be associated with neurological deficits 3. Meningomyelocele a. Protrusion of spinal cord and/or nerve roots in meningeal sac b. Causes neurological deficits that depend on level and extent of lesion If only nerve roots are involved in spina bifida with meningomyelocele, resultant paralysis is flaccid (lower motor neuron lesion), but spinal cord damage results in spastic paralysis (upper motor neuron lesion); mixed types of paralysis may occur. Hydrocephalus commonly develops due to herniation of the brainstem and cerebellar tonsils through the foramen magnum (Arnold-Chiari malformation). The exposed meninges and spinal cord are vulnerable to infection. Meningomyelocele is congenital protrusion of spinal cord and nerve roots through vertebral defect with neurological damage. VI. The Muscles of the Back A. Development of the Back Muscles (Figure 1-15) 1. Differentiating somites give rise to segmental myotomes; each myotome splits into the dorsal epimere and ventral hypomere. 2. Epimere gives rise to epaxial muscles, which are intrinsic back muscles innervated by the posterior rami of spinal nerves. 3. Hypomere gives rise to hypaxial muscles that are innervated by the anterior rami of spinal nerves.  4. Limb muscles that arise from hypomere migrate into limb buds and are therefore innervated by anterior rami of spinal nerves 5. Superficial muscles of back are actually muscles of upper limb that develop from limb bud mesoderm and migrate into back, carrying with them their nerve supply from anterior rami 1-15 Development of muscles of limb (A) and trunk (B). Intrinsic back muscles are derived from epimere and are innervated by posterior (dorsal) rami of spinal nerves. Muscles of limbs and of anterior and lateral body wall develop from hypomere and are supplied by anterior (ventral) rami. (From Netter, F H: The Netter Collection of Medical Illustrations, Vol. 8: Musculoskeletal System, Part 1: Anatomy, Physiology, and Metabolic Disorders. Philadelphia, Saunders Elsevier, 1987, p. 142, Section II, Plate 18.) Posterior rami innervate intrinsic back muscles. Anterior rami innervate all other muscles of trunk and extremities. B. Other Features 1. Triangle of auscultation  a. Bounded medially by trapezius, laterally by scapula and rhomboid major, and inferiorly by latissimus dorsi b. Allows lung sounds to be clearly heard at sixth intercostal space because no muscle intervenes between skin and rib cage when shoulders are pulled forward Triangle of auscultation allows posterior access to sixth intercostal space. 2. Thoracolumbar fascia a. Forms investing sleeve that encloses intrinsic back muscles by attaching anteriorly to transverse processes of lumbar vertebrae and posteriorly to spinous processes of lumbar and lower thoracic vertebrae b. Fuses with aponeuroses of internal abdominal oblique, transversus abdominis, and latissimus dorsi C. Suboccipital Region (Figure 1-16) 1. Suboccipital triangle Bounded medially by rectus capitis posterior major, inferiorly by obliquus capitis inferior, and laterally by obliquus capitis superior muscles 2. Arteries and nerves of suboccipital region a. Vertebral artery branches from subclavian, ascends through transverse foramina of vertebrae C1-C6, and runs transversely across posterior arch of atlas under posterior atlantooccipital membrane. b. Suboccipital nerve, posterior ramus of C1, passes between vertebral artery and posterior arch of atlas to supply suboccipital muscles c. Greater occipital nerve, posterior ramus of C2, emerges inferior to obliquus capitis inferior muscle and ascends to supply overlying muscles and scalp d. Third occipital nerve, posterior ramus of C3, supplies scalp over occiput 1-16 Relationships of the suboccipital triangle, posterior view. In the triangle, the vertebral artery lies on the posterior arch of the atlas and then pierces the atlantooccipital membrane to enter the foramen magnum. The suboccipital nerve (posterior ramus of C1) emerges between the posterior arch and the vertebral artery to supply suboccipital muscles. The greater occipital nerve (posterior ramus of C2) passes inferior to the obliquus capitis inferior muscle and pierces the semispinalis capitis muscle to supply the posterior scalp. Because of the course of the vertebral artery through transverse foramina of cervical vertebrae, individuals with atherosclerosis may become dizzy and experience other symptoms of brainstem ischemia when the neck is rotated. Atherosclerotic vertebral artery may result in brainstem ischemia during neck rotation. If the left subclavian artery or the brachiocephalic trunk is stenosed or occluded proximal to the origin of the vertebral artery, exercising the upper extremity may reverse blood flow through the vertebral and basilar arteries, causing subclavian steal syndrome. The transient neurologic symptoms are related to brainstem and posterior cerebral ischemia (e.g., dizziness, unsteadiness, visual changes). Subclavian steal syndrome is reversed blood flow through vertebral artery with upper extremity exertion. VII. The Meninges and the Spinal Cord A. Meninges (Figure 1-17) Three connective tissue membranes that enclose spinal cord within vertebral canal and are continuous with cranial meninges around brain 1-17 Transverse section through the vertebral column. Note that the dura mater and the arachnoid mater are not separated by space. The arachnoid mater is joined to the pia by thin trabeculae with intervening space filled by cerebrospinal fluid (CSF). The spinal cord is thus surrounded by and suspended in a fluid-filled space. Meninges are dura mater, arachnoid mater, and pia mater. 1. Dura mater a. Tough, fibrous outer layer that forms a closed sac around brain and spinal cord, ending inferiorly at S2 vertebra b. Continuous with meningeal layer of dura inside skull but separated from walls of vertebral canal by epidural space Adult spinal cord ends at vertebra L1/L2 but dural sac ends at S2 c. Follows spinal nerve roots and is continuous with epineurium of spinal nerve 2. Arachnoid mater a. Delicate intermediate layer applied to inner surface of dura mater b. Sends fine arachnoid trabeculae across subarachnoid space to pia mater 3. Pia mater Fine vascular layer inseparable from surface of spinal cord Meningitis is characterized by severe headache, fever, and stiff neck. Viral meningitis is usually benign and self-limiting. Meningitis is inflammation of meninges usually due to self-limiting viral or life-threatening bacterial infection. Bacterial meningitis is serious and may be fatal, even with treatment. Diagnosis is confirmed by analyzing cerebrospinal fluid from lumbar puncture. Flexion of the neck of a supine patient will stretch inflamed meninges, producing characteristic pain and possibly eliciting involuntary hip and knee flexion (Brudzinski’s sign) that minimizes tension on meninges. Kernig’s sign is similar pain elicited by raising one lower limb while the knee is kept fully extended (straight leg raise). Pain can be relieved by flexing the knee and reducing tension on the meninges. Pneumococcal meningitis is the most common and most serious form of bacterial meningitis in adults. Bacterial meningitis is diagnosed by analysis of CSF collected by lumbar puncture. B. Features Related to Meninges (see Figure 1-17) 1. Epidural space a. Lies between dural sac and walls of vertebral canal b. Contains epidural fat and internal vertebral venous plexus 2. Subdural space a. Artifact of pathology and not a true space b. Formed by physical separation of dura mater from arachnoid mater by hemorrhage (subdural hematoma) or CSF collection (subdural hygroma) Subdural space is pathological artifact created by collection of blood or CSF 3. Subarachnoid space a. Lies between arachnoid mater and pia mater and extends inferiorly to S2 vertebra b. Contains cerebrospinal fluid that protects spinal cord and removes catabolites from neuronal activity c. Below spinal cord forms lumbar cistern, which contains cauda equina Lumbar puncture should not be performed in patient with intracranial mass When performing a lumbar puncture, the needle enters the subarachnoid space to extract cerebrospinal fluid (spinal tap) or to inject anesthetic (spinal block) or contrast material (Figure 1-18). The needle is usually inserted between L3/L4 or L4/L5. Remember that the spinal cord may end as low as L3 in adults and does end at L3 in infants. Before the procedure, the patient should be examined for signs of increased intracranial pressure (e.g., papilledema) because cerebellar tonsils may herniate through the foramen magnum due to a space-occupying mass. 1-18 Sagittal section of the vertebral canal illustrating needle placement for epidural anesthesia and lumbar puncture. To reach the subarachnoid space, the needle must successively penetrate the skin, fascia, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura, and arachnoid mater. Lumbar puncture is usually performed between vertebrae L3/L4 or L4/L5. In epidural anesthesia, the needle is placed into the epidural space to inject anesthetic around roots of the lower lumbar and sacral spinal nerves without entering the subarachnoid space (see Figure 1-18). Epidural anesthesia: injection into epidural space. Spinal block: injection into subarachnoid space 4. Denticulate ligaments a. Flattened fibrous bands of pia mater from sides of spinal cord between posterior and anterior nerve rootlets b. Have toothlike projections that pierce arachnoid mater to anchor spinal cord to dura 5. Filum terminale a. Threadlike inferior extension of pia mater from conus medullaris surrounded by cauda equina in lumbar cistern b. Penetrates arachnoid mater and dura mater to become enclosed by filum of dura, which attaches to coccyx Denticulate ligaments and filum terminale of pia mater anchor the spinal cord in subarachnoid space.  6. Vertebral venous plexus (Figure 1-19) a. Interconnecting system of valveless veins from coccyx to skull that allows blood flow in either direction b. Anastomoses with segmental veins at all levels and with dural venous sinuses of cranial cavity (1) Internal vertebral venous plexus lies in epidural space around dural sac (2) External vertebral venous plexus surrounds outside of vertebral column 1-19 Internal vertebral venous plexus in epidural space and external vertebral plexus surrounding vertebral column communicate and drain to inferior and superior venae cavae. Internal plexus also communicates superiorly with dural venous sinuses of cranial cavity. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 173.) The vertebral venous plexus provides a pathway for tumor cells to metastasize from pelvic, abdominal, and thoracic viscera to vertebrae, spinal cord, and brain. Prostate, lung, and breast cancer can spread to the brain via the plexus. Infections of the skin of the back may also spread to dural venous sinuses of the cranial cavity via the plexus. Vertebral venous plexus is pathway for cancer cell metastasis from pelvic, abdominal, and thoracic regions C. Spinal Cord 1. Continuous above with medulla oblongata of brainstem and ends below near superior border of vertebra L2 in adults, but range is T12-L3 2. Tapers at inferior end to conus medullaris 3. Cervical enlargement is related to brachial plexus and innervation of upper extremity, and lumbosacral enlargement is related to lumbosacral plexus and innervation of lower extremity 4. Blood supply (Figure 1-20) a. Spinal arteries Comprise one anterior spinal artery and paired posterior spinal arteries, which arise from vertebral arteries or posterior inferior cerebellar arteries 1-20 Anastomoses of anterior segmental medullary arteries with anterior spinal artery. Connections occur with vertebral, ascending cervical, deep cervical, posterior intercostal, and lumbar arteries. Great anterior segmental medullary artery helps supply lower ⅔ of spinal cord. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 171.) Anterior and posterior spinal arteries depend on blood flow from segmental arteries. b. Segmental arteries (1) Arise from vertebral, ascending cervical, deep cervical, posterior intercostal, and lumbar segmental arteries and travel through intervertebral foramina (2) Supply blood directly to spinal nerves, nerve roots, and adjacent areas of spinal cord (radicular arteries) (3) Supplement blood to spinal cord through anastomoses with anterior and posterior spinal arteries (segmental medullary arteries) One segmental artery of special importance is the great anterior segmental medullary artery arising from a lower intercostal or upper lumbar artery. It may supply as much as the inferior two-thirds of the spinal cord, and its occlusion can cause paraplegia, sensory loss below the level of injury, and incontinence. The vessel may be injured during repair of aortic aneurysms, and it may be affected by a tumor involving the posterior thoracic or abdominal wall. A severe drop in systemic blood pressure may have the same result as occlusion. Loss of flow through the great anterior segmental medullary artery may cause paraplegia and sensory loss.  5. Spinal nerves (Figures 1-21 to 1-23) a. Comprise 31 pairs of nerves—8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal—attached to corresponding spinal cord segment b. Numbered according to vertebra above except in cervical region 1-21 Typical thoracic spinal nerve. Note gray and white rami communicantes connecting spinal nerve to sympathetic chain ganglion. Anterior ramus of thoracic spinal nerve becomes intercostal nerve. Cutaneous branches of anterior and posterior rami supply the dermatome innervated by that spinal cord segment. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 180.) 1-22 General somatic efferent (light red) and general somatic afferent (dark red) components of spinal nerve. 1-23 General visceral efferent (light red) and general visceral afferent (dark red) components of spinal nerve. Spinal nerves are numbered according to vertebra above except in cervical region.  c. Formed by union of posterior root and anterior root and divide into posterior and anterior rami (1) Posterior root (dorsal root) Contains axons of afferent neuron cell bodies located in the posterior root ganglion that carry sensory information from muscle, bone, joints, and skin. Strip of skin it supplies is a dermatome (see Figure 3-8). A ganglion is a collection of nerve cell bodies outside the central nervous system. A dermatome is a strip of skin innervated by a pair of spinal nerves. (2) Anterior root (ventral root) (a) Contains axons of efferent neuron cell bodies located in anterior horn gray matter of spinal cord that innervate skeletal muscle (b) At T1-L2 level contains axons of visceral efferent (preganglionic sympathetic) neuron cell bodies located in intermediolateral cell column of spinal cord that innervate cardiac muscle, smooth muscle, and glands Only T1-L2 anterior nerve roots contain preganglionic sympathetic fibers. (3) Posterior ramus Supplies intrinsic back muscles and overlying skin (4) Anterior ramus Supplies muscles and skin of anterolateral neck and trunk and all muscles and skin of upper and lower extremities  (5) Functional components of spinal nerves (see Figures 1-22 and 1-23; Table 1-4) TABLE 1-4 Functional Components of Spinal Nerves A typical spinal nerve contains GSA, GVA, GSE, and GVE fibers. (6) Somatic nerve plexuses (a) Formed by mixing nerve fibers from anterior rami (b) Supply nerves to upper extremity (brachial plexus) and lower extremity (lumbosacral plexus) (c) Allow nerve fibers from several spinal cord segments to be distributed in one peripheral nerve (d) Mean that dermatomal pattern does not correspond to cutaneous distribution of peripheral nerves Somatic nerve plexuses: cervical C1-C4, brachial C5-T1, lumbar L1-L4, sacral L4-S3 D. Development of Spinal Cord (Figures 1-24 and 1-25) 1. Neural tube formation (neurulation)  a. Neural plate (neuroectoderm) is induced by the notochord and prechordal plate. b. Developing neural tube initially remains open at the cranial and caudal neuropores. c. Brain develops from rostral swellings of neural tube after closure of cranial neuropore 1-24 Transverse sections through embryos during successive stages of neural tube formation. A and B, Notochord induces ectoderm to form neural plate with a central neural groove and elevated lateral neural folds. C, Neural folds fuse in midline to form a hollow neural tube. D, Neural crest ectoderm separates from neural tube and surface ectoderm and begins to migrate, forming spinal posterior root ganglia and other structures. 1-25 Neural tube formation at beginning of week 4, dorsal view. A, Neural folds have begun to fuse in the future neck region. B, Fusion is complete except at cranial and caudal neuropores. The notochord and the prechordal plate induce the neural plate to form the neural tube. d. Spinal cord develops from caudal neural tube on closure of caudal neuropore Myeloschisis (rachischisis) is an open spinal cord caused by failure of the caudal neuropore to close at the end of week 4. Severe neurological deficits are produced, and infection is likely. Failure of the cranial neuropore to close on day 25 results in anencephaly. Failure of cranial neuropore closure: anencephaly. Failure of caudal neuropore closure: myeloschisis 2. Neural crest a. Arises from junction of neural tube and surface ectoderm b. Forms dorsal root ganglia, autonomic ganglia, and adrenal medulla Sensory ganglia, autonomic ganglia, and adrenal medulla develop from the neural crest. VIII. The Autonomic Nervous System (Visceral Nervous System) The autonomic nervous system innervates smooth muscle, cardiac muscle, and glands. A. Overview 1. Divided into sympathetic and parasympathetic nervous systems 2. Involuntary, generally acting below consciousness to help maintain homeostasis 3. Consists of two neurons in series: preganglionic neuron with cell body in central nervous system and postganglionic neuron with cell body in peripheral autonomic ganglion The sympathetic and parasympathetic nervous systems have preganglionic and postganglionic neurons connecting the CNS and effector. The sympathetic nervous system is the thoracolumbar system because preganglionic neuron cell bodies are found only in T1-L2 spinal cord segments. B. Sympathetic Nervous System Controls the response to stress (i.e., fight-or-flight response) 1. Preganglionic sympathetic neuron (see Figure 1-23) a. Cell bodies located only in T1-L2 spinal cord segments b. Axon may synapse on postganglionic neuron cell body in sympathetic chain ganglion at level of entrance into sympathetic trunk or may ascend or descend in sympathetic chain before synapsing in another ganglion  c. Axon may pass into splanchnic nerve to reach abdominal prevertebral ganglion to synapse Postganglionic sympathetic neuron cell bodies are located in paravertebral or prevertebral ganglia. 2. Postganglionic sympathetic neuron (see Figure 1-23) a. Cell body in paravertebral (sympathetic chain) or prevertebral ganglion b. Axon leaves paravertebral ganglion through gray ramus communicans to join spinal nerve or through visceral branch to join visceral plexus c. Axon leaves prevertebral ganglion to join visceral plexus 3. Sympathetic trunk (sympathetic chain) a. Paired string like structure lying on bodies of vertebrae from base of skull to coccyx b. Sympathetic (paravertebral) ganglia formed by aggregations of postganglionic neuron cell bodies are swellings on the sympathetic trunk. 4. Gray ramus communicans a. Connects sympathetic ganglion to its corresponding spinal nerve b. Carries postganglionic sympathetic fibers that end on sweat glands, vascular smooth muscle, or arrector pili muscles of skin 5. White ramus communicans a. Connects each paravertebral ganglion from T1 to L2 levels to corresponding spinal nerve b. Carries preganglionic sympathetic fibers to sympathetic trunk for distribution to entire body, including head c. Contains preganglionic sympathetic fibers and visceral afferent fibers White communicating rami connect to only spinal nerves T1-L2, but gray rami connect to all spinal nerves. C. Parasympathetic Nervous System 1. Overview a. Mediates vegetative functions b. Innervates visceral structures only and is not distributed to body wall or extremities c. Innervates erectile tissue of genitalia and coronary arteries but no other blood vessels Parasympathetic nerve fibers aren’t present in body walls or extremities. 2. Preganglionic parasympathetic neuron a. Cell body in nucleus of brainstem or in sacral parasympathetic nucleus of spinal cord segments S2-S4 The parasympathetic nervous system is the craniosacral system because preganglionic neuron cell bodies are located only in the brainstem or the sacral spinal cord. b. Carried in cranial nerves III, VII, IX, or X or spinal nerves S2-4 3. Postganglionic parasympathetic neuron  Cell body in peripheral autonomic ganglion (terminal ganglion) lying close to or within wall of organ to be innervated Postganglionic parasympathetic neurons are located in the terminal ganglia near or in the organ innervated. D. General Visceral Afferent Fibers 1. Accompany sympathetic and parasympathetic fibers and form afferent limb of autonomic reflex arcs 2. Follow sympathetic and parasympathetic nerve fibers to central nervous system except for cranial nerve III (oculomotor) 3. Traverse white, not gray, ramus communicans 4. Accompanying sympathetic nerve fibers in visceral branches (e.g., cardiac or splanchnic nerves) carry pain from visceral organs to spinal cord between segments T1 and L2 GVA fibers accompanying sympathetic fibers carry pain from thoracic and abdominal viscera. Chapter 2 The Thorax I. The Thoracic Wall A. The Thoracic Skeleton 1. Ribs (Figure 2-1, A) a. Overview (1) True ribs: ribs 1-7 connected to sternum by costal cartilages 2-1 Thoracic skeleton and typical rib. A, Anterior view of thoracic skeleton showing relationships of ribs and costal cartilages to sternum. B, Posterior view of a typical rib. It consists of a head, neck, and body with a tubercle located at the junction of neck and body. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plates 185 and 186.) Ribs 1-7: true ribs. 8-12: false ribs. 11-12: floating ribs (2) False ribs: ribs 8-12 with costal cartilages that do not reach sternum; cartilages of ribs 8-10 join cartilage immediately superior (3) Floating ribs: ribs 11 and 12, which have a free anterior end b. Typical ribs: ribs 3-9 (1) Head articulates with body of corresponding vertebra and vertebra superior. (2) Tubercle articulates with transverse process of corresponding vertebra. (3) Body or shaft is twisted about its long axis, turning sharply forward at angle. A fracture of the well-protected rib 1 suggests severe chest trauma. Ribs 1 and 2 (protected by the clavicle) and ribs 11 and 12 are seldom fractured. In adults, a typical rib usually fractures near the angle, the point of greatest curvature. In a severe crush injury on one side, multiple ribs may fracture in two places. Fractured segments (flail chest) are sucked in during inspiration and pushed out during expiration, producing paradoxical respiratory movements. Associated pulmonary contusions contribute to respiratory insufficiency. The more flexible ribs and costal cartilages of children mean that blunt trauma may injure thoracic organs without fracturing ribs, masking the seriousness of the injury. Thoracic and abdominal organ trauma may occur in children without rib fracture. Paradoxical respiratory movements occur in flail chest. A segment of rib can be excised to gain access to the thoracic cavity (thoracotomy) by longitudinally splitting the periosteum. Osteogenic cells of the periosteum regenerate bone to fill the defect. c. Atypical ribs: ribs 1, 2, 10-12 Ribs 1 and 10-12 articulate with only one vertebra each. d. Cervical rib Elongated transverse process of C7, often attached to first thoracic rib by a fibrous band In thoracic outlet syndrome, the subclavian artery or inferior trunk of the brachial plexus is stretched or compressed between the anterior and middle scalene muscles, often when the arm is hanging at the side. It produces numbness and tingling in the extremity, simulating a cervical disc problem. Thoracic outlet syndrome may be due to a cervical rib, hypertrophied scalene muscles, or an anomalous fibrous band. A cervical rib may cause thoracic outlet syndrome. 2. Sternum (Figure 2-1, A)  a. Manubrium (1) Easily palpable jugular (suprasternal) notch on superior border at root of neck (2) Articulates with clavicle, first costal cartilage, superior part of second costal cartilage, and body of sternum b. Body (1) Articulates with manubrium, second through seventh costal cartilages, and xiphoid process (2) Has marrow cavity used for bone marrow biopsy Xiphisternal joint marks inferior border of heart and superior border of liver. A traumatic sternal fracture requires evaluation for heart injury. c. Xiphoid process (1) May be bifid or perforated (2) Can be palpated in infrasternal angle at T10 vertebral level The sternum is split in the midline (sternotomy) and the two halves retracted for surgery on the heart (e.g., coronary bypass surgery) or other thoracic organs. The halves are wired back together. Defective ossification may result in a lack of fusion of the right and left halves of the sternum, producing a sternal cleft. A congenital perforation in the body (sternal foramen) may be mistaken for a bullet wound. A caving in of the sternum and costal cartilages during development (pectus excavatum or funnel chest) may impair cardiac and respiratory function. It is the most common congenital abnormality of the chest wall and usually is apparent at birth but may not become pronounced until puberty. A congenital protrusion of the sternum and costal cartilages (pectus carinatum or pigeon chest) may occur alone or as part of syndrome, sometimes impairing respiration and decreasing endurance. Pectus excavatum: funnel chest. Pectus carinatum: pigeon chest Pectus excavatum is the most common congenital defect of the thoracic wall. 3. Joints of thoracic wall (Table 2-1) TABLE 2-1 Joints of Thoracic Wall Joint Articulating Structures Comments Sternal angle marks Manubrium with body of Manubriosternal level of second sternum costal cartilage Head of rib with body of Ribs 1 and 10- Costovertebral corresponding vertebra and 12 articulate with Joints of head of vertebra above Tubercle of rib only one vertebra rib Costotransverse with transverse process of Not present with corresponding vertebra ribs 11-12 Costochondral Rib with costal cartilage Costal cartilages 1-7 with Sternocostal sternum Sternal angle marks level of second costal cartilages, which is useful in counting ribs. The sternal angle is a landmark for physical diagnosis because it is a convenient starting place for counting ribs. It is also useful because it indicates the level of a horizontal plane marking the bifurcation of the trachea, the beginning and end of the arch of the aorta, and the division into superior and inferior mediastinum. Sternal angle marks level of tracheal bifurcation and inferior boundary of aortic arch. B. The Muscles of the Thoracic Wall (Figure 2-2) 2-2 Typical intercostal space. The neurovascular bundle lies between the internal intercostal and the innermost intercostal muscles near the superior border of the intercostal space. Paralysis of the intercostal muscles results in intercostal tissues being sucked in during inspiration and ballooning out during expiration. C. The Intercostal Space (see Figure 2-2) VAN = intercostal Vein, Artery, and Nerve from superior to inferior in intercostal space. To block an intercostal nerve, the needle is inserted near the inferior border of the rib superior to the intercostal space. In contrast, to enter the pleural cavity to aspirate fluid or to perform a biopsy, the needle is inserted near the superior border of the rib inferior to the intercostal space. To enter the pleural cavity, a needle is inserted at the superior border of the lower rib bounding the intercostal space. D. Intercostal Nerves and Blood Vessels 1. Intercostal nerves (see Figure 1-21) a. Overview (1) Anterior rami of first 11 spinal nerves in intercostal spaces (2) Lie between internal and innermost intercostal muscles Cardiac pain is often referred to the medial side of the left arm because the T1 and T2 dermatomes continue there from the thoracic wall. Communication of the intercostobrachial nerve (T2) with the medial brachial cutaneous nerve (C8, T1) is one pathway for referred pain. Cardiac pain is often referred to the medial side of the left arm. Herpes zoster (shingles) of an intercostal nerve produces vesicular eruptions and burning pain in the affected dermatome. Reactivation of the varicella-zoster virus follows a period of dormancy within the posterior root ganglion from years to decades after chicken pox. Elderly and immunocompromised individuals are particularly susceptible. Some patients experience severe residual pain for months or even years (postherpetic neuralgia). Contact with the shingles rash can cause chicken pox in a child who has never had it. Shingles lesions follow a dermatomal pattern. b. First intercostal nerve is short because most of anterior ramus of T1 joins anterior ramus of C8 to form lower trunk of brachial plexus c. Intercostobrachial nerve is lateral cutaneous branch of second intercostal nerve (T2) d. Subcostal nerve is anterior ramus of T12 spinal nerve and lies immediately below rib 12  e. Thoracoabdominal nerves are seventh to eleventh intercostal nerves, which leave intercostal space anteriorly to supply the anterolateral abdominal wall. The T4 dermatome lies at the level of the nipple. The T10 dermatome lies at the level of the umbilicus. Disease of the thoracic wall (e.g., in lower costal parietal pleura) may cause abdominal pain and tenderness and rigidity of abdominal muscles because the thoracoabdominal nerves continue into the anterior abdominal wall. 2. Intercostal blood vessels Include 11 pairs of posterior intercostal arteries and veins and one pair of subcostal arteries and veins (see Section IX) E. The Breast 1. Overview a. Mammary gland embedded in superficial fascia with fat and secretory activity contributing to size and contour b. Overlies ribs 2-6 in young adult female; rudimentary in male and prepubertal female c. Pigmented, projecting nipple surrounded by circular, pigmented areola. In males and young females, nipple lies over fourth intercostal space d. Supported by suspensory ligaments that attach to overlying skin e. Separated from deep fascia over pectoralis major (pectoral fascia) by retromammary space, which allows movement on chest wall 2. Mammary gland  a. Has 15-20 lobes, each drained by a single corresponding lactiferous duct that opens on nipple b. Lactiferous sinus, expansion for each lactiferous duct deep to nipple, serves as milk reservoir during lactation c. May extend into axilla as axillary tail The mammary gland usually extends into the axilla as an axillary tail. 3. Blood supply and innervation of breast a. Supplied by mammary branches of internal thoracic, intercostal, and lateral thoracic arteries b. Veins are tributaries of internal thoracic, intercostal, and lateral thoracic veins. c. Innervation is by intercostal nerves T2-T6. 4. Lymphatic drainage of breast a. Facilitates metastasis of breast cancer b. 75% of lymph passes to axillary lymph nodes but also may pass to lymph nodes near clavicle or lymph nodes draining upper abdominal wall. c. From medial quadrants is to parasternal nodes along internal thoracic artery or across midline to opposite breast Seventy-five percent of the lymph from the breast drains to the axillary lymph nodes, particularly the pectoral group. Radiographic examination of the breast by mammographic screening is used for early detection of small, nonpalpable breast carcinomas and is recommended annually for women over 40 or with a family history. BRCA1 and BRCA2 tumor suppressor gene mutations are responsible for most hereditary breast cancers, although these account for only about 7% of breast cancers. BRCA1 and BRCA2 gene mutations cause most hereditary breast cancer. Breast cancer may result in dimpling of the skin and retraction of the nipple caused by fibrosis and shortening of the suspensory ligaments or involvement of the ductal system. The skin may look like an orange peel (peau d’orange) because lymphatics are obstructed by the tumor. The breast may become fixed to the chest wall after the tumor invades the retromammary space, which is evident when the pectoralis major is contracted with the hand pressed against the hip. The incidence of breast cancer in males is only 1% that of females, but often it is not diagnosed until extensive metastases have occurred. Males with Klinefelter syndrome (47, XXY) frequently exhibit gynecomastia and have an increased incidence of breast cancer. Dimpling and an orange peel appearance of the skin and nipple retraction are signs of breast cancer. Klinefelter syndrome males have an increased incidence of breast cancer. Although less common than metastasis through lymphatics, cancer can spread from the breast through the venous system to the vertebral column, spinal cord, and brain through the posterior intercostal veins to the vertebral venous plexuses, and then superiorly to the dural venous sinuses of the cranial cavity. Surgical removal of a breast carcinoma may involve only the tumor and adjacent tissue (lumpectomy), removal of the breast and axillary lymph nodes (modified radical mastectomy), or rarely the breast along with the axillary contents and pectoralis muscles (radical mastectomy). Surgery is often augmented by chemotherapy and/or radiation. During a radical mastectomy, the long thoracic nerve, which lies on the superficial surface of the serratus anterior muscle, is vulnerable. Paralysis of the serratus anterior prevents abduction of the arm above 90 degrees and causes a winged scapula. The thoracodorsal nerve also may be injured. Breast cancer can metastasize through the venous system to the vertebral column, spinal cord, and brain. II. Pleura (Figures 2-3 to 2-5) A. Overview 1. Thin serous sac around each lung enclosing pleural cavity, which is potential space empty except for thin layer of serous fluid 2. Consists of visceral pleura adherent to lung surface and parietal pleura adherent to chest wall, diaphragm, and mediastinal structures (mainly fibrous pericardium) B. Pleural Reflections (see Figure 2-5) C. Cupula is cervical pleura extending above the first rib. D. Pleural recesses contain no lung tissue during quiet respiration but fill with lung tissue during deep inspiration.  1. Costodiaphragmatic recess is the lowest part of the pleural cavity and may accumulate abnormal pleural fluid. 2. Costomediastinal recess 2-3 Transverse (axial) section through the superior mediastinum. Because structures within the mediastinum are closely packed, any space-occupying or invasive lesion may compromise their functions. 2-4 Axial CT near same level as Figure 2-3. Brachiocephalic trunk = 1; left common carotid artery = 2; left subclavian artery = 3; right brachiocephalic vein = 4; left brachiocephalic vein = 5; trachea = 6; esophagus = 7; spinal cord = 8. (From Weir, J, Abrahams, P: Imaging Atlas of Human Anatomy, 3rd ed. London, Mosby Ltd., 2003, p 92, b.) 2-5 Surface projections of lungs and pleurae. Numbers, ribs. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 196.) Pneumothorax is air in the pleural cavity, resulting in collapse of the lung. Pneumothorax is air in the pleural cavity that results in partial or total collapse of the lung. The parietal pleura may be punctured and the lung accidentally deflated (open pneumothorax) during a posterior approach to the kidney near rib 12, liver biopsy, nerve block of the stellate ganglion or brachial plexus at the root of the neck, or intravenous line insertion into the subclavian vein. Pleural effusion is fluid in the pleural cavity from any of multiple causes, including infection, cancer, or congestive heart failure. Thoracentesis is surgical removal of fluid from the pleural cavity. A needle or incision over a lower intercostal space in the midaxillary line penetrates the skin, superficial fascia, serratus anterior, intercostal muscles, endothoracic fascia, and parietal pleura. The long thoracic nerve may be injured. To enter pleural cavity in midaxillary line the needle penetrates skin, fascia, serratus anterior, intercostal muscles, endothoracic fascia, and parietal pleura. Parietal pleura injury is painful due to somatic afferent innervation, but visceral pleura is not painful due to visceral afferent innervation. Pleuritis (pleurisy) involving only visceral pleura may not be painful because innervation is from visceral afferent nerves. However, on inspiration a sharp pain in the chest wall is felt in pleuritis involving parietal pleura because innervation is from somatic nerves. Roughening of the pleura results in a pleural friction rub heard with a stethoscope, and pleural adhesions may develop between inflamed visceral and parietal pleurae. Pain in the thorax, abdomen, or shoulder on deep inspiration suggests a pleural origin. Shoulder pain can be referred from irritated diaphragmatic pleura. Pleural pain related to pneumonia or cancer of the lower lobe may be referred to the anterior abdominal wall. Pleuritis may cause chest pain and pleural friction rub. III. Trachea and Bronchi (Figure 2-6) A. Trachea 1. Begins as continuation of larynx and ends by dividing into two main (primary) bronchi at level of sternal angle 2. Contains carina, posterior process of last tracheal cartilage that internally marks bifurcation of trachea as seen with bronchoscope 3. See Figures 2-3 and 2-4 for relationships in superior mediastinum. 2-6 Trachea and bronchi, anterior view. The right lung has 10 segmental (tertiary) bronchi, and the left lung has 8-10. During bronchoscopy, the carina is a critical landmark, and a deviation in its position may indicate metastasis of lung cancer to the tracheobronchial lymph nodes at the bifurcation of the trachea. Insertion of an endotracheal tube during surgery or in emergency situations protects air flow to and from the lungs. Insertion too deeply may result in only one lung being ventilated, possibly causing pneumothorax and the other main bronchus being obstructed to cause atelectasis (see VI.A.3. following). Inadvertent insertion into the esophagus may result in aspiration of stomach contents and aspiration pneumonia. Distorted carina on bronchoscopy often indicates metastatic lung cancer. The trachea may be compressed by an enlarged thyroid gland or by an aortic arch aneurysm. B. Right Main Bronchus 1. Crossed superiorly by arch of azygos vein, passing to superior vena cava 2. Aspirated objects will more likely enter wider, more vertical right main bronchus. An aspirated object or an endotracheal tube that is inserted too far is likely to enter the right main bronchus. C. Left Main Bronchus Passes inferior to arch of aorta and anterior to esophagus D. Eparterial Bronchus Another name for right upper lobe bronchus because it arises above level of pulmonary artery IV. Lungs (Figure 2-7) A. Overview 1. One main bronchus, one pulmonary artery, and two pulmonary veins divide within the substance of each lung. 2. Surfaces are diaphragmatic, costal, and mediastinal. 3. Root of lung consists of structures passing between the lung and mediastinum, and the hilum is the region where structures enter or leave the lung. 4. Pulmonary ligament is a double-layered vertical fold of pleura extending inferiorly from hilum to base. 2-7 Medial views of right (top) and left (bottom) lungs. Oblique and horizontal fissures divide the right lung into three lobes while an oblique fissure divides the left lung into two lobes. The lingula of the left lung corresponds to the middle lobe of the right lung. The pulmonary ligament is a double layer of pleura inferior to the hilum. Adjacent structures produce contact impressions in embalmed lungs. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 199.) A tumor of the apex of the lung (Pancoast tumor) may involve the sympathetic chain and interrupt sympathetic innervation to the head, producing Horner syndrome (ipsilateral anhidrosis, miosis, ptosis, and vasodilation). The tumor also may involve the inferior roots of the brachial plexus, producing upper-extremity symptoms. An apical lung tumor (Pancoast tumor) may cause Horner syndrome. B. Right Lung 1. Divided into upper, middle, and lower lobes by oblique and horizontal fissures; horizontal fissure is at level of fourth rib and costal cartilage 2. Shorter than left because of higher right dome of diaphragm 3. Contains three lobar (secondary) and 10 segmental (tertiary) bronchi 4. See Figure 2-7 for relationships at hilum. C. Left Lung 1. Divided into upper and lower lobes at oblique fissure 2. Includes cardiac notch that lies over heart and pericardium anteriorly (see Figure 2-5); lingula forms inferior margin of cardiac notch and corresponds to middle lobe of right lung 3. Two lobar and 8-10 segmental bronchi 4. See Figure 2-7 for relationships at hilum. The cardiac notch allows a needle to enter the pericardium and heart through the left fifth intercostal space without damaging the lung and pleura. D. Bronchopulmonary Segments (see Figure 2-6) 1. Pyramidal regions of lung supplied by one segmental (tertiary) bronchus and its accompanying segmental branch of pulmonary artery 2. Drained in part by intersegmental veins used as surgical landmarks 3. Usually number 10 in right lung and 8-10 in left, depending on fusion of segments Bronchopulmonary segments are independent functional and surgical units. Patient position determines the location of inhaled foreign objects. Gravity moves foreign material to different bronchopulmonary segments of the right lung depending on the patient’s position (Figure 2-8). In a standing or sitting patient, the posterobasal segment is involved; in the supine patient, the superior segment of the lower lobe; in the right-sided recumbent position, the middle lobe or posterior segment of the right upper lobe. The arrangement of segments also means that a patient can be optimally positioned for postural drainage of an infected bronchopulmonary segment aided by percussion of the chest wall over the segment. 2-8 Bronchopulmonary segments of right lung where foreign material lodges depending on patient position. Standing or sitting: posterobasal segment. Supine position: superior segment of lower lobe. Right-sided recumbent: right middle lobe or posterior segment of right upper lobe. (From Goljan, E F: Rapid Review Pathology, 3rd ed. Philadelphia, Mosby Elsevier, 2010, Box 16-1.) Because bronchi and arteries of adjacent bronchopulmonary segments do not communicate, a segment can be resected without compromising the surrounding lung. Intersegmental tributaries of pulmonary veins are landmarks for segmentectomies. Intersegmental veins are surgical landmarks for segmentectomies. E. Blood Vessels of Lungs 1. Pulmonary arteries carry deoxygenated blood from right ventricle to lungs  a. Left pulmonary artery attached to aortic arch by ligamentum arteriosum, the remnant of the fetal ductus arteriosus b. Right pulmonary artery crosses under arch of aorta to reach hilum of right lung Pulmonary arteries carry deoxygenated blood to the lungs; pulmonary veins return the oxygenated blood to the heart. 2. Pulmonary veins carry oxygenated blood from lungs to the left atrium. Lung cancer may metastasize to the brain through the arterial system when cancer cells enter the pulmonary veins and are returned to the left side of the heart. From the aorta, cancer cells pass through the common and internal carotid arteries or the subclavian and vertebral arteries. 3. Bronchial arteries a. Supply oxygenated blood to bronchial tree and visceral pleura b. Number two on the left, arising from descending thoracic aorta, but only one on the right, often branching from third right posterior intercostal artery Bronchial arteries supply oxygenated blood to lung tissues. 4. Bronchial veins Lung cancer may metastasize to the spinal cord and brain through the venous system if cancer cells enter a bronchial vein and pass to the azygos system. Cancer cells may then pass to the vertebral venous plexuses and ascend to the dural venous sinuses in the cranial cavity. F. Lymphatic Drainage of Lungs 1. Superficial lymphatic plexus lies just beneath visceral pleura and drains toward hilum 2. Deep lymphatic plexus follows bronchial tree to hilum and includes peribronchial pulmonary nodes lying within substance of lung 3. Bronchopulmonary nodes at root of lung receive drainage from both superficial and deep plexuses. 4. Tracheobronchial nodes at tracheal bifurcation receive lymph from bronchopulmonary nodes. 5. Right and left bronchomediastinal lymph trunks drain tracheobronchial nodes and eventually reach a venous angle, either directly or through right lymphatic duct and thoracic duct, respectively Left and right venous angles formed at the union of internal jugular and subclavian veins. The upper lobe of the left lung has lymphatic drainage to the left bronchiomediastinal trunk, but the lower lobe of the left lung has lymphatic drainage mainly to the right bronchomediastinal lymph trunk. Lung cancer cells can metastasize through arteries, veins, or lymphatic vessels. G. Nerve Supply of Lungs 1. Pulmonary plexuses contain sympathetic, parasympathetic, and visceral afferent fibers derived from the deep cardiac plexus. 2. Parasympathetic fibers come from vagus nerves and produce bronchial constriction and mucus secretion. 3. Sympathetic fibers are postganglionic fibers from upper five thoracic sympathetic ganglia; they relax bronchial smooth muscle and constrict pulmonary vessels. 4. Visceral afferent fibers from vagus nerves a. Sensitive to stretch and participate in reflex control of respiration b. End in bronchial mucosa and participate in cough reflex V. Development of Respiratory System and Related Defects A. Development of Trachea and Bronchi 1. Laryngotracheal (respiratory) diverticulum forms during week 4 in floor of pharynx. 2. Tracheoesophageal septum separates developing larynx and trachea from pharynx and esophagus 3. Lung buds develop in week 5 at caudal end of laryngotracheal tube, growing into splanchnic mesoderm surrounding foregut to give rise to primary, secondary, and tertiary bronchi by week 6 Esophageal atresia results in polyhydramnios. A congenital tracheoesophageal fistula is an abnormal communication between the trachea and distal esophagus usually associated with esophageal atresia (blind-ending esophagus) (Figure 2-9). The resulting regurgitation and aspiration of swallowed milk (and possible reflux of gastric contents into lungs) cause pneumonia. Because esophageal atresia prevents the fetus from swallowing and absorbing amniotic fluid in the small intestine, the condition is often accompanied by excess amniotic fluid (polyhydramnios). An acquired tracheoesophageal fistula may result from malignancy, infection, or trauma. 2-9 Tracheoesophageal fistula and esophageal atresia. Tracheoesophageal fistula with esophageal atresia causes pneumonia. B. Development of Lung 1. Pseudoglandular period a. Comprises weeks 5-16 when conducting system is formed as far as terminal bronchiole b. Birth during this period is incompatible with life. 2. Canalicular period a. Comprises weeks 16-26 when terminal bronchioles give rise to respiratory bronchioles, each of which divides into alveolar ducts, and respiratory vasculature forms b. Some terminal sacs (primitive alveoli) develop toward end of period, so some infants born late in canalicular period may survive with intensive care Some infants born at 22-25 weeks survive with intensive care but often suffer lifelong disability. 3. Terminal sac period Comprises week 26-birth when more terminal sacs develop and pulmonary surfactant is produced by type II alveolar cells (pneumocytes) Pulmonary surfactant produced by type II alveolar cells reduces surface tension to prevent alveolar collapse. 4. Alveolar period Comprises week 32 of gestation through age of 8 years when alveoli form and mature; boundary between terminal sac and alveolar period open to interpretation Surfactant reduces surface tension to allow inflation of alveoli. Neonatal respiratory distress syndrome (hyaline membrane disease) results from deficient surfactant production by type II alveolar cells in premature infants. Glucocorticoid treatment in at-risk pregnancies speeds up lung development and surfactant production. Treatment with artificial surfactant reduces neonatal mortality. Maternal glucocorticoid treatment may prevent neonatal respiratory distress syndrome. VI. Respiration and Respiratory Diaphragm A. Respiration Serous fluid adhesion between visceral and parietal pleura links volume of lungs with movements of diaphragm and thoracic wall and facilitates respiration 1. Inspiration increases volume of thoracic cavity and lungs to create a negative intrathoracic pressure that draws air into lungs a. Quiet inspiration Involves contraction of diaphragm, pulling it downward to increase vertical dimension of thorax The diaphragm is the primary muscle of inspiration. b. Forced inspiration (1) External intercostal muscles contract, elevating ribs and carrying sternum upward and forward, and increase anteroposterior and lateral diameters of thorax (2) Recruits accessory muscles of respiration to assist elevating ribs, further increasing depth of inspiration Patient with dyspnea may lean on upper extremities to allow accessory muscles to aid in respiration. 2. Expiration decreases volume of thorax and lungs to create a positive intrathoracic pressure that forces air from lungs  a. Quiet expiration is passive process largely caused by elastic recoil of lungs and relaxation of diaphragm b. Forced expiration is active process involving contraction of anterior abdominal wall muscles, which depress ribs and sternum and increase intraabdominal pressure, and internal intercostal muscles 3. Accessory muscles of respiration Include head and neck muscles and upper limb muscles attached to rib cage or sternum In spontaneous pneumothorax, air enters the pleural cavity because of rupture of a bleb on a diseased lung. It occurs commonly in tall, slender males under 40 who smoke and Marfan syndrome patients. Spontaneous pneumothorax occurs in tall, slender male smokers under 40. Tension pneumothorax is a life-threatening condition in which air enters the pleural cavity during inspiration due to a penetrating wound but cannot exit during expiration. Air pressure increases on the affected side, and the mediastinum shifts away, compressing the contralateral lung and compromising venous return to the heart (Figure 2-10). Bedside ultrasonography often replaces chest radiographs for diagnosis. The patient complains of chest pain and dyspnea. Jugular venous distention and a tracheal shift develop as the pressure increases. 2-10 PA chest x-ray of tension pneumothorax showing collapsed left lung (white arrows), radiolucent air-filled pleural cavity, and flattened left hemidiaphragm. Mediastinal contents have been pushed to the right (black arrows). (From Mettler, F A: Essentials of Radiology, 2nd ed. Philadelphia, Saunders, 2004, Figure 3-72.) Tension pneumothorax may fatally compromise cardiopulmonary function. Emphysema is destruction of the walls of airspaces distal to the terminal bronchioles. Because airspaces are consequently enlarged, surface area for gas exchange is reduced. Elastic tissue is destroyed, impairing expiration and requiring participation of accessory muscles of expiration. Asthma is a variable obstruction of the airway caused by spasmodic contraction of smooth muscle in the bronchial tree, mucosal edema, and mucus plugging. Dyspnea, wheezing, coughing, and chest tightness are characteristic. Precipitating factors include ozone, inhalation of allergens, respiratory tract infections, emotions, exercise, and some drugs (e.g., aspirin). Atelectasis is collapse of lung tissue from obstruction of airflow (e.g., by tumor, mucus, or aspirated body) and is a frequent postoperative complication because the patient cannot cough thick mucus loose from the bronchial lumen. The left main bronchus may be obstructed by an endotracheal tube inserted into the right main bronchus (Figure 2-11). Unlike tension pneumothorax, lung collapse in atelectasis results in mediastinal shift toward the affected side. 2-11 Atelectasis of left lung due to obstruction of left main bronchus by endotracheal tube (arrows) inserted too far and entering right main bronchus. Opacity increases as air is resorbed. Lung collapse results in mediastinal shift toward affected side. (From Mettler, F A: Essentials of Radiology, 2nd ed. Philadelphia, Saunders, 2004, Figure 3-23.) Mediastinum shifts toward affected lung in atelectasis but away from affected lung in tension pneumothorax Bronchiectasis is a pathologic condition involving chronic dilatation of portions of the bronchial tree that may be caused by prolonged atelectasis or respiratory infection. It is common in cystic fibrosis patients. Saddle embolus may fatally block pulmonary trunk bifurcation. Fat embolism syndrome 1-3 days following long bone fracture or orthopedic surgery is acute respiratory failure, CNS dysfunction, and petechiae. A pulmonary embolus usually originates in deep veins of the lower extremity (usually the femoral vein). It may pass through the right side of the heart and lodge in a pulmonary artery. The clot may cause sudden death if it lodges at the bifurcation of the pulmonary trunk (saddle thrombus). Pulmonary emboli can arise from other sources, including the fatty marrow of a long bone following fracture or orthopedic surgery. These fat emboli are usually clinically silent but may cause fat embolism syndrome 1-3 days later with pulmonary insufficiency, neurologic symptoms, anemia, thrombocytopenia, and petechiae. Amniotic fluid embolism is an uncommon, but potentially fatal, complication of labor and the immediate postpartum period. Thoracocentesis through lower intercostal space risks injury to diaphragm and liver on right and to diaphragm and spleen on left B. Respiratory Diaphragm (Figure 2-12) 1. Overview a. Includes right dome that arches superiorly to fifth rib and left dome that arches to fifth intercostal space b. Receives motor and sensory innervation from phrenic nerves except for peripheral part with sensory supply from lower intercostal nerves 2-12 Respiratory diaphragm, inferior view. Openings allow the passage of the inferior vena cava (T8), esophagus (T10), and aorta (T12). Right crus splits to form esophageal hiatus. Phrenic nerves supply motor innervation and sensory innervation to all but peripheral part, which receives sensory supply from lower intercostal nerves. Inferior phrenic arteries contribute to blood supply. (From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 195.) Phrenic nerves (C3,4,5) innervate the respiratory diaphragm. 2. Other features (Table 2-2) TABLE 2-2 Features of Respiratory Diaphragm Attachments or Feature Comments Location Receives insertions of Central Cloverleaf-shaped central sternal, costal, and tendon aponeurotic part lumbar parts Median Unites crura across arcuate midline anterior to aorta ligament Medial Body to transverse arcuate Arches over psoas major process of L1 ligament Lateral Transverse process of arcuate Arches over quadratus lumborum L1 to rib 12 ligament Bodies of vertebrae L1- Right crus Larger and longer than left crus 3 Bodies of vertebrae L1- Left crus 2 Opening Vena caval Through central tendon Transmits inferior vena cava and hiatus at T8 vertebral level right phrenic nerve Through right crus at Transmits esophagus, vagal trunks, Esophageal T10 level; left of and esophageal branches of left hiatus midline gastric vessels Posterior to diaphragm so Between crura behind movements don’t affect aortic Aortic hiatus median arcuate flow; transmits aorta, thoracic ligament at T12 level duct, maybe azygos vein Diaphragm openings: vena caval T8; esophageal T10; aortic T12 Diaphragm movements don’t affect aortic blood flow because aortic hiatus is posterior to the diaphragm. Chronic, intractable hiccups sometimes are treated by crushing one phrenic nerve. A lesion of one phrenic nerve produces hemiparalysis of the diaphragm unless the lesion is proximal to union with an accessory phrenic nerve. On radiographs, paralysis is apparent by the diaphragm’s paradoxical movement (i.e., diaphragm is elevated during inspiration by abdominal viscera). Paralyzed hemidiaphragm rises during inspiration on radiograph. Because the diaphragm domes superiorly, upper abdominal organs are enclosed by the thoracic rib cage. Therefore, fractures of the lower ribs may damage not only the diaphragm but also the liver, right kidney, spleen, or left kidney. Fracture of lower right ribs may injure liver, and fracture of lower left ribs may injure spleen  3. Development of respiratory diaphragm occurs by incorporation of derivatives from the following four embryonic structures (Figure 2-13). a. Septum transversum (1) Lies in cervical region in week 4, adjacent to third, fourth, and fifth cervical somites, which accounts for innervation of diaphragm by phrenic nerves (C3,4,5) (2) Descends into thoracic region between developing heart and liver due to differential growth (3) Gives rise to central tendon and to myoblasts that migrate into pleuroperitoneal membranes and esophageal mesentery 2-13 Progressive development (A and B) of the respiratory diaphragm, transverse section viewed from below. Septum transversum, pleuroperitoneal membranes and esophageal mesentery, and body wall mesoderm form the diaphragm. Diaphragm origins: septum transversum, pleuroperitoneal membranes, esophageal mesentery, and body wall mesoderm  b. Pleuroperitoneal membranes (1) Mesodermal tissue of posterior body wall that closes pericardioperitoneal canals by fusing with septum transversum and dorsal mesentery of esophagus (2) Partition pleural cavity from peritoneal cavity Intraembryonic body cavity divided into pericardial, pleural, and peritoneal cavities by pleuropericardial and pleuroperitoneal membranes c. Esophageal mesentery (1) Forms middle of diaphragm posteriorly (2) Invaded by myoblasts that give rise to crura of diaphragm d. Body wall mesoderm Forms peripheral part of diaphragm as a result of excavation by developing lungs and pleural cavities Congenital diaphragmatic hernia: failure of pleuroperitoneal membrane to close pericardioperitoneal canal A congenital diaphragmatic hernia, the most common congenital malformation of the diaphragm, results from developmental failure of the pleuroperitoneal membrane in week 6, usually posterolaterally on the left side (foramen of Bochdalek). Abdominal viscera then herniate into the thorax and compress the thoracic viscera; consequently, often fatal pulmonary hypoplasia occurs. Congenital diaphragmatic hernia may cause fatal lung hypoplasia. VII. Mediastinum (Figure 2-14) A. Overview 1. Median partition of tissue lying between paired pleural sacs that contains all thoracic organs except lungs 2. Divided into superior and inferior mediastinum to assist clinical localizations; inferior mediastinum is subdivided into anterior, middle, and posterior mediastinum 2-14 Mediastinum, sagittal view. Horizontal plane at the sternal angle divides the superior and inferior mediastinum. The inferior mediastinum is subdivided by limits of the pericardium into middle, anterior, and posterior mediastinum. Mediastinum is a median mass of tissue between pulmonary cavities. B. Subdivisions of mediastinum (Table 2-3) TABLE 2-3 Subdivisions of Mediastinum A goiter is prevented from expanding superiorly by the insertions of the sternothyroid muscles; therefore, it may extend inferiorly as a retrosternal goiter, possibly compressing the trachea and causing dyspnea. Less commonly the esophagus or superior vena cava is compressed. In resecting a parathyroid adenoma, it is important to remember that the inferior parathyroid glands may be found in the superior mediastinum because they migrate with the thymus during development. Fatal mediastinitis may result from the spread of a neck infection. Infection that causes mediastinitis may travel a pathway of loose connective tissue (e.g., retropharyngeal space) from the neck to the mediastinum. Because a child’s neck is relatively short, the left brachiocephalic vein may be superior to the jugular notch, where it is at risk during a tracheostomy. Child’s left brachiocephalic vein may lie superior to the jugular notch in the root of the neck. VIII. Pericardium and Heart A. Pericardium 1. Overview a. Sac that encloses heart, proximal segments of great arteries, and terminal segments of great veins b. Consists of outer fibrous layer and inner serous sac 2. Fibrous pericardium a. Tough, indistensible, fibrous external layer b. Fused inferiorly with central tendon of diaphragm 3. Serous pericardium Closed sac that covers heart as visceral layer and inner surface of fibrous pericardium as parietal layer 4. Pericardial cavity Potential space normally empty except for a small amount of lubricating fluid that allows heart to move freely as it beats 5. Pericardial sinuses  Formed by reflection of visceral layer of serous pericardium onto parietal layer at roots of great vessels entering and leaving heart a. Oblique pericardial sinus is blind pocket dorsal to left atrium formed by pericardial reflections surrounding pulmonary veins and venae cavae. b. Transverse pericardial sinus (1) Passageway between right and left sides of pericardial cavity anterior to superior vena cava, posterior to ascending aorta and pulmonary trunk, and superior to pulmonary veins and left atrium (2) Critical to cardiothoracic surgeon who must identify and clamp great vessels Transverse pericardial sinus allows clamping of great vessels for cardiopulmonary bypass during cardiac surgery. Cardiac tamponade is life-threatening rapid fluid accumulation within the pericardial cavity. Cardiac tamponade is a potentially fatal compression of the heart caused by rapid accumulation of fluids within the pericardial cavity, which compromises venous return. Tamponade may be caused by blood (hemopericardium) or