Basic Science for the MRCS 4th Edition PDF

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Access to the eBook is limited to the first individual who redeems the PIN, located on the inside cover of this book, at studentconsult.inkling.com and may not be transferred to another party by resale, lending, or other means. 2020_ME WWW.BOOKBAZ.IR BASIC SCIENCE MRCS FOR THE A revision guide for surgical trainees This page intentionally left blank WWW.BOOKBAZ.IR BASIC SCIENCE MRCS FOR THE A revision guide for surgical trainees FOURTH EDITION Michael S. Delbridge MBChB (Hons) MD FRCS (Vascular) Consultant Vascular and Endovascular Surgeon Norfolk and Norwich University Hospital, Norwich, UK Wissam Al-Jundi MBBS MSc MEd MBA FRCS (Vascular) Consultant Vascular and Endovascular Surgeon Norfolk and Norwich University Hospital, Norwich, UK Honorary Senior Lecturer, University of East Anglia, Norwich, UK 3 © 2023, Elsevier Limited. All rights reserved. First edition 2006 Second edition 2012 Third edition 2018 The right of Michael S. Delbridge and Wissam Al-Jundi to be identified as authors of this work has been asserted by them in accordance with the Copyright, Designs and Patents Act 1988. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds or experiments described herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made. To the fullest extent of the law, no responsibility is assumed by Elsevier, authors, editors or con- tributors for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.  WWW.BOOKBAZ.IR  CONTENTS Preface vi Acknowledgements vii I ANATOMY 1 The Thorax 2 2 The Abdomen, Pelvis and Perineum 20 3 The Upper Limb and Breast 62 4 The Lower Limb 80 5 The Head, Neck and Spine 106 6 The Nervous System 145 II PHYSIOLOGY 7 General Physiology 171 8 Respiratory System 186 9 Cardiovascular System 204 10 Gastrointestinal System 214 11 Urinary System 232 12 Endocrine System 240 13 Nervous and Locomotor Systems 259 III PATHOLOGY 14 Cellular Injury 279 15 Disorders of Growth, Morphogenesis and Differentiation 297 16 Inflammation 305 17 Thrombosis, Embolism and Infarction 311 18 Neoplasia 317 19 Immunology 330 20 Haemopoietic and Lymphoreticular System 342 21 Basic Microbiology 360 22 System-Specific Pathology 386 IV APPENDIX OSCE Scenario Answers 431 Index 490 v AR P C EKFA N OCW E LEDGE The authors are grateful to the publishers, Elsevier, for the sample answers provided in an appendix at the back of invitation to produce a fourth edition of Basic Science for the book. More than 20 new OSCE scenarios have been the MRCS. added to this edition. In addition, to accompany this edi- The book is a concise revision guide to the core basic tion there is an online question bank within the Student sciences which comprise the essential knowledge for those Consult eBook comprising over 200 Single Best Answer entering surgical training. It is a basic requirement that questions (SBAs) based on each chapter in the book. The every surgical trainee has a thorough understanding of the reader can access the section from the Table of Contents basic principles of anatomy, physiology and pathology irre- in the eBook. spective of which speciality within surgery they intend to No book of this length could hope to be comprehensive pursue as a career. It is equally important that they under- and we have therefore concentrated on the topics that tend stand the clinical application of the basic sciences. This to be recurring examination themes. As with previous edi- revision guide has been written with this in mind, using a tions, this book has been written primarily as a means of bullet-point style which we hope will make it easier for the rapid revision for the surgical trainee. However, it should reader to revise the essential facts. also prove useful for those in higher surgical training, as Much has changed both in the undergraduate curricu- well as for the surgically inclined, well-motivated medi- lum and in the post-graduate examination system since cal student. We hope that this fourth edition will provide the first edition was published 16 years ago. In this fourth a simple and straightforward approach to the basic science edition, the chapters have been updated where appropri- that underpins surgical training. ate and sections expanded to cover topics which are par- ticularly relevant to examinations. As most examinations are Objective Structured Clinical Examinations (OSCEs), Michael S. Delbridge each chapter has OSCE scenario questions at the end with Wissam Al-Jundi vi WWW.BOOKBAZ.IR  ACKNOWLED GEMENTS ACKNOWLED GE We are extremely grateful to the publishers, Elsevier, and in particular to Alexandra Mortimer, Content Strategist, for her support and help with this project. We are also grateful to the following colleagues at the Sheffield Teaching Hospitals NHS Foundation Trust who provided help, advice and criticism: Dr Paul Zadik, Consultant Microbiologist; Dr TC Darton, NIHR Academic Clinical Research Fellow, Infectious Diseases and Medical Microbiology; Mr BM Shrestha, Consultant General and Transplant Surgeon. We would also like to thank our consultant radiologist colleagues, who provided images: Dr Matthew Bull, Dr Peter Brown, Dr James Hampton, Dr Robert Cooper and Dr Rebecca Denoronha. Mr Raftery would like to thank his secretary, Mrs Denise Smith, for the long hours and hard work she has put in typing and re-typing the manuscript, and Anne Raftery for collating and organizing the whole manuscript into its final format. The task could not have been completed without them. The figures in this book come from a variety of sources, and many are reproduced from other pub- lications, with permission, as follows: Fig. 3.9 from the University of Michigan Medical School, with kind permission of Thomas R. Gest, PhD Figs 13.10A, 13.10B and 13.11 from Crossman & Neary (2000) Neuroanatomy: An Illustrated Colour Text, 2nd edn. Churchill Livingstone, Edinburgh Figs 3.11 and 4.14, and Tables 6.1 and 6.3 from Easterbrook (1999) Basic Medical Sciences for MRCP Part 1, 2nd edn. Churchill Livingstone, Edinburgh Fig. 9.1 from Hoffman & Cranefield (1960) Electrophysiology of the Heart. McGraw-Hill, New York (now public domain) Figs 4.20, 4.24, 5.25, 6.5 and 6.6 from Jacob (2002) Atlas of Human Anatomy. Churchill Livingstone, Edinburgh Figs 8.1, 8.12B, 8.12C, 10.3, 10.4, 10.5, 10.6, 10.7, 11.1, 11.3, 13.1, 13.5 and 13.6 from McGeown (2002) Physiology, 2nd edn. Churchill Livingstone, Edinburgh Figs 8.3 and 8.4 from Pocock & Richards (2004) Human Physiology: The Basis of Medicine, 2nd edn. Oxford University Press, Oxford Figs 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.11, 1.13, 1.14, 2.1, 2.2, 2.3, 2.4, 2.7, 2.8, 2.9, 2.10, 2.12, 2.13, 2.14, 2.17, 2.18, 2.19, 2.20, 2.21, 2.22, 2.23, 2.24, 2.25, 2.27, 2.28, 2.29, 2.30, 2.31, 2.32, 5.1, 5.2, 5.7, 5.8, 5.16, 5.17, 6.1, 6.2, 6.3, 6.4, 6.7, 6.8, 6.9, 6.10, 6.11, 6.12, 6.13, 6.15, 8.2, 8.6, 8.10, 8.12A, 9.2, 9.4, 9.6, 11.4, 12.1, 12.4, 13.8, 19.2, 20.1, 20.2, 20.3, 21.1, 22.1, 22.2 and 22.3 from Raftery (ed) (2000) Applied Basic Science for Basic Surgical Training. Churchill Livingstone, Edinburgh Fig. 17.2 and A.3 (Q&A) from Pretorius & Solomon (2011) Radiology Secrets Plus, 3rd edn. Elsevier, Philadelphia Figs 5.35, 6.14, 22.2 & A.5 (Q&A), 22.3 & A.6 (Q&A) and 22.5 & A.7 (Q&A) from Raftery, Delbridge & Wagstaff (2011) Pocketbook of Surgery, 4th edn. Churchill Livingstone, Edinburgh Figs 1.10, 3.1, 3.2, 3.3, 3.4, 3.8, 3.12, 4.1, 4.2, 4.3, 4.4, 4.6, 4.7, 4.8, 4.9, 4.11, 4.12, 4.13, 4.15, 4.16, 5.3, 5.4, 5.5, 5.9, 5.10, 5.11, 5.13, 5.14, 5.21, 5.22, 5.24, 5.26, 5.27, 5.28, 5.29, 5.30, 5.31 and 6.16 from Rogers (1992) Textbook of Anatomy. Churchill Livingstone, Edinburgh Fig. 13.4 from Stevens & Lowe (2000) Pathology, 2nd edn. Mosby, Edinburgh Figs 15.1 and 15.2, and Boxes 15.1 and 15.2 from Underwood (ed) (2004) General and Systematic Pathology, 4th edn. Churchill Livingstone, Edinburgh vii This page intentionally left blank WWW.BOOKBAZ.IR  SECTION I Anatomy 1. The Thorax, 2 2. The Abdomen, Pelvis and Perineum, 20 3. The Upper Limb and Breast, 62 4. The Lower Limb, 80 5. The Head, Neck and Spine, 106 6. The Nervous System, 145 1  1 The Thorax DEVELOPMENT An interventricular septum develops from the apex up towards the endocardial cushions. Heart and Great Vessels In the atrium a partition, the septum primum, Heart (Fig. 1.1) grows down to fuse with the endocardial cushions. Paired endothelial tubes fuse to become the primitive Before fusion is complete, a hole appears in the upper heart tube. part of the septum primum that is called the foramen Primitive heart tube develops in the pericardial cavity secundum. and divides into five regions: A second incomplete membrane, the septum secundum, sinus venosus then develops to the right of the septum primum but is atrium never complete. It has a free lower edge that extends low ventricle enough for it to overlap the foramen secundum in the bulbus cordis septum primum and eventually close it. truncus arteriosus. The two overlapping defects in the septa form the valve- Heart tube elongates in pericardial cavity becoming like foramen ovale. U-shaped and then S-shaped. The septum secundum acts as a valvelike structure, Sinus venosus becomes incorporated into the atrium. allowing blood to go straight from the right to the left Bulbus cordis becomes incorporated into the ventricle. side of the heart in the fetus. Boundary tissue between the primitive single atrial cav- At birth, where there is an increased blood flow through ity and single ventricle grows out as dorsal and ventral the lungs and a rise in left atrial pressure, the septum endocardial cushions. primum is pushed across to close the foramen ovale. The endocardial cushions meet in the midline, dividing The septum primum and septum secundum usually the common atrioventricular (AV) orifice into a right fuse, obliterating the foramen ovale and leaving a small (tricuspid) and left (mitral) orifice. residual dimple (the fossa ovalis). Truncus arteriosus SVC Aortic Bulbus arch cordis Pulmonary veins Pulmonary trunk Ventricle Right atrium Left Atrium ventricle IVC Sinus venosus Left atrium Right ventricle Primitive heart tube Fig. 1.1 The development of the heart. IVC, Inferior vena cava; SVC, superior vena cava. 2 WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 3 The sinus venosus joins the atria, becoming the two side. On the right, the fifth and sixth arches disappear to venae cavae on the right and the four pulmonary veins leave the nerve hooked round the fourth, i.e. subclavian on the left. artery. On the left it remains hooked round the sixth arch (ligamentum arteriosum in the adult). Great Vessels (Fig. 1.2) Truncus arteriosus gives off six pairs of arches. Fetal Circulation (Fig. 1.3) These curve round the pharynx to join the dorsal aortae, Oxygenated blood travels from the placenta along the which fuse distally into the descending aorta. umbilical vein. First and second arches disappear completely. Most blood bypasses the liver in the ductus venosus, Third arch remains as carotid artery. joining the inferior vena cava (IVC) and then travelling Fourth arch becomes subclavian artery on the right to the right atrium. and aortic arch on the left (giving off the left subclavian Most of the blood passes through the foramen ovale artery). into the left atrium so that oxygenated blood can enter Fifth arch disappears. the aorta. Sixth arch (ventral part) becomes right and left pul- The remainder goes through the right ventricle with monary arteries with a connection to dorsal aorta dis- returning systemic venous blood into the pulmonary appearing on the right, but continuing as the ductus trunk. arteriosus on the left connecting with the aortic arch. In the fetus the unexpanded lungs present high resis- The above developmental anatomy explains the differ- tance to flow so that blood in the pulmonary trunk ent positions of the recurrent laryngeal nerves on each tends to pass down the low-resistance ductus arteriosus into the aorta. Right and left Blood returns to the placenta via the umbilical arteries recurrent laryngeal (branches of the internal iliac arteries). Vagus Vagus At birth, when the baby breathes, the left atrial pressure nerves nerve nerve Aortic rises, pushing the septum primum against the septum arch secundum and closing the foramen ovale. Blood flow through the pulmonary artery increases and I Carotid becomes poorly oxygenated as it now receives systemic venous blood. II Pulmonary vascular resistance is abruptly lowered as lungs inflate and the ductus arteriosus is obliterated over the next few hours to days. III Ligation of the umbilical cord causes thrombosis of the umbilical artery, vein and ductus venosus. Right Left subclavian subclavian artery Congenital Anomalies IV Malposition Arch of Dextrocardia: mirror image of normal anatomy. aorta V Situs inversus: inversion of all viscera. VI Left-to-Right Shunt Pulmonary trunk Atrial septal defect (ASD) Ductus Fusion between the septum primum and septum secun- arteriosus dum usually takes place about 3 months after birth. May be incomplete in 10% of the population. If the septum secundum is too short to cover the foramen secundum in the septum primum and ASD persists after the primum and septum secundum are pressed together at birth, this results in an ostium secundum defect, which allows shunting of blood from the left to the right atrium. ASD may also result if the septum primum fails to fuse Fig. 1.2 The development of the aortic arches. with the endocardial cushions. 4 SECTION I Anatomy Aortic arch Ductus arteriosus SVC Septum secundum Foramen ovale Pulmonary trunk Septum primum IVC Liver Abdominal Ductus aorta venosus Umbilical vein Umbilical cord Common iliac artery Umbilical Placenta arteries arising from the internal iliac arteries Fig. 1.3 The fetal circulation. IVC, Inferior vena cava; SVC, superior vena cava. This is an ostium primum defect lying immediately Eisenmenger’s syndrome above the AV boundary and may be associated with a Pulmonary hypertension may cause reversed flow ventricular septal defect (VSD). (right-to-left shunting). Ventricular septal defect This is due to an increased pulmonary flow resulting This is the most common abnormality. from either ASD, VSD or PDA. Small defects occurring in the muscular part of the sep- When cyanosis occurs as a result of this mechanism it is tum may close. known as Eisenmenger’s syndrome. Larger ones occurring in the membranous part of the septum just below the aortic valves may require repair. Right-to-Left Shunt (Cyanotic) Patent ductus arteriosus (PDA) Fallot’s tetralogy The ductus may fail to close after birth. Fallot’s tetralogy consists of: This should be surgically corrected because it causes VSD increased load on the left ventricle and pulmonary stenosed pulmonary outflow track hypertension. a wide aorta which overrides the right and left In open surgery to close a patent ductus, care must be ventricles taken to avoid the left recurrent laryngeal nerve. right ventricular hypertrophy. WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 5 Because there is a right-to-left shunt across the VSD Clinical Points there is usually cyanosis at an early stage. Different types of congenital diaphragmatic hernias occur, The degree of cyanosis depends mainly on the severity depending on which section has failed to close. of the pulmonary outflow obstruction. Posterolateral hernia through the foramen of Bochdalek (the pleuroperitoneal membrane)—more common on Other congenital anomalies the left. Coarctation of the aorta A hernia through a deficiency of the whole central tendon. Caused by abnormality of obliterative process, which A hernia through the foramen of Morgagni anteriorly normally occludes ductus arteriosus. between xiphoid and costal origins. Hypertension in upper part of body with weak, delayed A hernia through a congenitally large oesophageal hiatus. femoral pulses. Extensive collaterals develop to try and bring blood THORACIC CAGE from upper to lower part of body. Enlarged intercostal arteries cause notching of the infe- The thoracic cage is formed by: rior borders of the rib seen on chest X-ray. vertebral column behind Abnormalities of valves ribs and intercostal spaces on either side Any valve may be imperfectly formed. sternum and costal cartilages in front. May cause stenosis or complete occlusion. Pulmonary and aortic valves are more frequently Ribs affected than mitral and tricuspid. There are 12 pairs. Ribs 1–7 connect via their costal cartilages with the ster- The Diaphragm (Fig. 1.4) num. These are ‘true’ ribs articulating directly with the The diaphragm develops from the fusion of four parts: sternum. 1. septum transversum (the fibrous central tendon) Ribs 8–10 articulate with their costal cartilages, each 2. the mesentery of the foregut (the area adjacent with the rib above. These are ‘false’ ribs as they do not to the vertebral column becomes the crura and median articulate directly with the sternum. part) Ribs 11 and 12 are free anteriorly. These are ‘floating 3. ingrowth from the body wall ribs’ as they have no anterior articulation. 4. the pleuroperitoneal membrane (a small dorsal part). A typical rib comprises: These close the primitive communications between a head with two articular facets for articulation with pleura and peritoneal cavities. the corresponding vertebra and the vertebra above Right pleuroperitoneal membrane Foregut (oesophageal) mesentery Body wall contribution Left pleuroperitoneal membrane Oesophagus Septum transversum Fig. 1.4 The development of the diaphragm. 6 SECTION I Anatomy a neck giving attachment to the costotransverse Coarctation of the Aorta ligament Collateral vessels develop between vessels above and a tubercle with a smooth facet for articulation below the block. with the transverse process of the corresponding The superior intercostal artery, derived from the costo- vertebra cervical trunk of the subclavian artery, supplies blood to a shaft flattened from side to side possessing an angle the intercostal arteries of the aorta, bypassing the nar- which marks the lateral limit of attachment of erec- rowed aorta. tor spinae. The shaft possesses a groove on its lower As a consequence, the intercostal vessels dilate and surface, the subcostal groove, in which the vessels become more tortuous because of increased flow erod- and nerves lie. ing the lower border of the ribs, giving rise to notching which can be seen on X-ray. Atypical ribs First rib Cervical Ribs Shortest, flattest and most curved. Incidence of 1:200. Flattened from above downwards. May be bilateral in 1:500. Bears a prominent tubercle on the inner border of its Rib may be complete, articulating with the transverse upper surface for insertion of scalenus anterior. process of the seventh cervical vertebra behind and the In front of the scalene tubercle the subclavian vein first rib in front. crosses the rib. Occasionally a cervical rib may have a free distal extrem- Behind the scalene tubercle is the subclavian groove ity or may be only represented by a fibrous band. where the subclavian artery and lowest trunk of the bra- Cervical ribs may cause vascular or neurological chial plexus are related to the rib. symptoms. The neck of the first rib is crossed by (medial to lateral): Vascular consequences include poststenotic dilata- sympathetic trunk; superior intercostal artery; and T1 tion of the subclavian artery, causing local turbulence, to the brachial plexus. thrombosis and possibility of distal emboli. First digitation of serratus anterior attaches to outer Subclavian aneurysm may also arise. edge. Pressure on vein may result in subclavian vein Suprapleural membrane (Sibson’s fascia) is attached to thrombosis. inner border. Pressure on the lower trunk of the brachial plexus may Second rib result in paraesthesia of dermatomal distribution of Less curved than first. C8/T1 together with wasting of small muscles of hands Twice as long. (myotome T1). Tenth rib Only one articular facet on head. Costal Cartilages Eleventh and twelfth ribs Upper seven connect ribs to sternum. Short. 8, 9 and 10 connect ribs to cartilage immediately above. No tubercles. Composed of hyaline cartilage and add resilience to tho- Only single facet on head. racic cage, protecting it from more frequent fractures. Eleventh rib has shallow subcostal groove. Calcify with age; irregular areas of calcification seen on Twelfth rib has no subcostal groove and no angle. chest X-ray. Clinical Points Sternum Rib Fractures The sternum consists of three parts: May damage underlying or related structures. manubrium Fracture of any rib may lead to trauma to lung and body development of pneumothorax. xiphoid. Fracture of left lower ribs (ninth, tenth and eleventh) may traumatize the spleen. Manubrium Fracture of right lower ribs may traumatize the right Approximately triangular in shape. lobe of the liver. Articulates with medial end of clavicle. Rib fractures may also traumatize related intercostal First costal cartilage and upper part of second articulate vessels leading to haemothorax. with manubrium. WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 7 Articulates with body of sternum at manubriosternal joint (angle of Louis). Relations Anterior boundary of superior mediastinum. Lowest part is related to arch of aorta. Upper part is related to left brachiocephalic vein; left brachiocephalic artery; left common carotid artery; left subclavian artery. Vein Laterally it is related to the lungs and pleura. Artery External Nerve Body intercostal Innermost Composed of four pieces (sternebrae). Internal intercostal Lateral margins are notched to receive most of the sec- intercostal ond and third to seventh costal cartilages. Relations On the right side of the median plane, the body is related to the right pleura and the thin anterior border of the right lung, which intervenes between it and the pericardium. On the left side of the median plane, the upper two pieces are related to the pleura and left lung; the lower two pieces are related directly to the pericardium. Fig. 1.5 An intercostal space. A needle passed into Xiphoid the chest immediately above a rib will avoid the neu- Small and cartilaginous well into adult life. rovascular bundle. May become prominent if patient loses weight. Clinical Points The neurovascular bundle lies between the internal and Sternal puncture is used to obtain bone marrow from the innermost intercostal. the body of the sternum; one should be aware of the The neurovascular bundle consists of (from above posterior relations! down): the vein, artery and nerve; the vein lying directly The sternum is split for access to the heart and occasion- in the groove on the undersurface of the corresponding ally a retrosternal goitre, thymus or ectopic parathyroid rib. tissue. The xiphoid may become more prominent when a Clinical Points patient loses weight (naturally or due to disease). The Insertion of a chest drain should be close to the upper patient may present in clinic because they have noticed border of the rib below the intercostal space to avoid the a lump, which was previously covered in fat. neurovascular bundle. Irritation of the intercostal nerves (anterior primary Intercostal Spaces (Fig. 1.5) rami of the thoracic nerves) may give rise to pain A typical intercostal space contains three muscles com- referred to the front of the chest wall or abdomen in the parable to those of the abdominal wall. region of the termination of the nerves. External intercostal muscle: passes downwards and forwards from the rib above to the rib below; deficient TRACHEA (Fig. 1.6) in front where it is replaced by the anterior intercostal membrane. Extends from lower border of cricoid cartilage (level Internal intercostal muscle: passes downwards and of the sixth cervical vertebra) to termination into two backwards; deficient behind where it is replaced by the main bronchi (level of fifth thoracic vertebra)—11 cm posterior intercostal membrane. long. Innermost intercostal muscle: may cover more than one Composed of fibroelastic tissue and is prevented from intercostal space. collapsing by a series of U-shaped cartilaginous rings, 8 SECTION I Anatomy Right main bronchus Left main bronchus Right upper lobe bronchus Left upper lobe bronchus Carina Right middle Left lower lobe bronchus lobe bronchus Apical segmental bronchus of lower lobe Right lower lobe bronchus Fig. 1.6 The trachea and bronchi. open posteriorly, the ends being connected by smooth BRONCHI (Fig. 1.6) muscle (trachealis). Lined by columnar ciliated epithelium containing The trachea terminates at the level of the sternal angle, numerous goblet cells. dividing into right and left bronchi. Right main bronchus: Relations wider, shorter and more vertical than left In the Neck approximately 2.5 cm long Anteriorly: isthmus of thyroid gland over second to passes downwards and laterally behind ascending fourth tracheal rings, inferior thyroid veins, sternohy- aorta and superior vena cava (SVC) to enter hilum of oid, sternothyroid. lung Laterally: lobes of thyroid gland, carotid sheath. azygos vein arches over it from behind to enter Posteriorly: oesophagus, recurrent laryngeal nerves in SVC the groove between the trachea and oesophagus. pulmonary artery lies first below and then anterior to it In the Thorax gives off upper lobe bronchus before entering lung Anteriorly: brachiocephalic artery and left common divides into bronchi to middle and inferior lobes carotid artery, left brachiocephalic vein, thymus. within the lung. Posteriorly: oesophagus, recurrent laryngeal nerves. Left main bronchus: Right side: vagus nerve, azygos vein, pleura. approximately 5 cm long Left side: aortic arch, left common carotid artery, left passes downwards and laterally below arch of aorta, subclavian vein, left recurrent laryngeal nerve, pleura. in front of oesophagus and descending aorta WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 9 gives off no branches until it enters hilum of lung, Each has a blunt apex extending above the sternal end of where it divides into bronchi to upper and lower lobes the first rib. pulmonary artery lies at first anterior to, and then Each has a concave base related to the diaphragm. above, the bronchus. Each has a convex parietal surface related to the ribs. Each has a concave mediastinal surface related to the Clinical Points pericardium. The trachea may be displaced or compressed by patho- Each has a thin anterior border overlapping the pericar- logical enlargement of adjacent structures, e.g. thyroid, dium and deficient on the left at the cardiac notch. arch of aorta. Each has a hilum where the bronchi and vessels pass to The trachea may be displaced if the mediastinum is and from the root. pushed across, e.g. by tension pneumothorax displacing Each has a rounded posterior border that occupies the it to the opposite side. groove by the side of the vertebrae. Calcification of tracheal rings may occur in the elderly and be visible on X-ray. Right Lung Because the right main bronchus is wider and more ver- Slightly larger than the left. tical, foreign bodies are more likely to be aspirated into Divided into three lobes—upper, middle and lower—by this bronchus. the oblique and horizontal fissures. Distortion and widening of the carina (angle between the main bronchi), seen at bronchoscopy, usually indi- Left Lung cates enlargement of the tracheobronchial lymph nodes Has only an oblique fissure and therefore only two lobes. at the bifurcation by carcinoma. The anterior border has a notch produced by the heart (cardiac notch). Anatomy of Tracheostomy The equivalent of the middle lobe of the right lung in the Either a vertical or cosmetic transverse skin incision left lung is the lingula, which lies between the cardiac may be employed. notch and oblique fissure. A vertical incision is made downwards from the cricoid cartilage passing between the anterior jugular veins. Roots of the Lungs A transverse cosmetic skin crease incision may be used Comprise the principal bronchus, the pulmonary artery, placed halfway between the cricoid cartilage and supra- the two pulmonary veins, the bronchial arteries and sternal notch. veins, pulmonary plexuses of nerves, lymph vessels, The incision goes through the skin and superficial fascia bronchopulmonary lymph nodes. (in the transverse incision, platysma will be located in Chief structures composing the root of each lung are the lateral part of the incision). arranged in a similar manner from before backwards on The pretracheal fascia is split longitudinally. both sides, i.e. the upper of the two pulmonary veins in Bleeding may be encountered from the anterior rela- front; pulmonary artery in the middle; bronchus behind. tions at this point, namely anastomosis between ante- Arrangement differs from above downwards on the two rior jugular veins across the midline, inferior thyroid sides: veins, thyroidea ima artery (when present). right side from above downwards: upper lobe bron- In the young child, the brachiocephalic artery, the left chus, pulmonary artery, right principal bronchus, brachiocephalic vein and the thymus may be apparent lower pulmonary vein in the lower part of the wound. left side: pulmonary artery, bronchus, lower pulmo- After splitting the pretracheal fascia and retracting the nary vein. strap muscles, the isthmus of the thyroid will be encoun- Visceral and parietal pleura meet as a sleeve surround- tered and may be either retracted upwards or divided ing the structures passing to and from the lung. This between clamps to expose the cartilages of the trachea. sleeve hangs down inferiorly at the pulmonary liga- An opening is then made in the trachea to admit the ment. It allows for expansion of the pulmonary veins tracheostomy tube. with increased blood flow. THE LUNGS BRONCHOPULMONARY SEGMENTS (Fig. 1.7) Conical in shape. Each lobar bronchus divides to supply the broncho­ Conform to shape of pleural cavities. pulmonary segments of the lung. 10 SECTION I Anatomy 1 2 3 1 1 2 2 3 3 6 6 5 6 4 4 5 5 7 10 8 10 9 8 9 7 8 10 9 A Lateral Medial 1 1 2 1 3 2 3 2 3 6 6 4 6 4 5 4 8 10 8 5 10 5 9 8 9 8 10 B 9 Lateral Medial Fig. 1.7 Bronchi and bronchopulmonary segments for the lungs. Divisions of the main bronchi in the centre, with corresponding pulmonary segments on the surfaces. (A) Right lung upper lobe: 1 = apical, 2 = posterior, 3 = anterior; middle lobe, 4 = lateral, 5 = medial; lower lobe, 6 = apical, 7 = medial basal (cardiac), 8 = ante- rior basal, 9 = lateral basal, 10 = posterior basal. (B) Left lung upper lobe: 1, 2 = apicoposterior, 3 = anterior; lingula (middle lobe), 4 = superior, 5 = inferior; lower lobe, 6 = apical, 8 = anterior basal, 9 = lateral basal, 10 = posterior basal. There are 10 bronchopulmonary segments for each Blood Supply lung. Pulmonary trunk arises from the right ventricle. Each is supplied by a segmental bronchus, artery and Directed upwards in front of the ascending aorta. vein. Passes upwards and backwards on the left of the ascend- There is no communication with adjacent segments. ing aorta to reach concavity of the aortic arch. It is possible to remove an individual segment without Divides in front of the left main bronchus into right and interfering with the function of adjacent segments. left branches. There is little bleeding or alveolar air leak from the raw lung surface if excision takes place accurately along the Right Pulmonary Artery boundaries (marked by intersegmental veins). Passes in front of oesophagus to the root of the right Each segment is wedge-shaped with the apex at the lung behind the ascending aorta and SVC. hilum and the base at the lung surface. At the root of the lung it lies in front of and between the Each segment takes its name from that of the supplying right main bronchus and its upper lobe branch. segmental bronchus. Divides into three branches, one for each lobe. WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 11 Left Pulmonary Artery Lungs Connected at its origin with the arch of the aorta via the Apex of the lung follows the line of cervical pleura. ligamentum arteriosum. Anterior border of the right lung corresponds to the Runs in front of the left main bronchus and descending right mediastinal pleura. aorta. Anterior border of the left lung has a distinct notch (car- Left recurrent laryngeal nerve loops below the aortic diac notch), which passes behind the fifth and sixth cos- arch in contact with the ligamentum arteriosum. tal cartilages. The lower border of the lung (midway between inspira- Bronchial Arteries tion and expiration) crosses: Supply the air passages. sixth rib in the midclavicular line Branches of the descending aorta. eighth rib in the midaxillary line tenth rib at the lateral border of erector spinae. The oblique fissure is represented by the medial border PLEURA of the scapula with the arm fully elevated (abducted) or Each pleural cavity is composed of a thin serous mem- by a line drawn from 2.5 cm lateral to the fifth thoracic brane invaginated by the lung. vertebrae to the sixth costal cartilage, about 4 cm from The visceral pleura is intimately related to the lung sur- the midline. face and is continuous with the parietal layer over the The horizontal fissure of the right lung passes horizon- root of the lung. tally and medially from the oblique fissure at the level of The parietal layer is applied to the inner aspect of the the fourth costal cartilage. chest wall, diaphragm and mediastinum. Below the root of the lung the pleura forms a loose fold Clinical Points known as the pulmonary ligament, which allows for dis- The pleura rises above the clavicle into the neck. It may tension of the pulmonary vein. be injured by a stab wound, the surgeon’s knife or inser- The lungs conform to the shape of the pleural cavities tion of a subclavian or internal jugular line. but do not occupy the full cavity as this would not allow A needle passing through the left fourth and fifth inter- expansion as in full inspiration. costal spaces immediately lateral to the sternal edge will The two pleural cavities are totally separate from one enter the pericardium without traversing the pleura. another. The pleura descends below the medial extremity of the twelfth rib and therefore may be inadvertently opened Surface Anatomy of Pleura and Lungs in the loin approach to the kidney or adrenal gland. Pleura Cervical pleura extends above the sternal end of the Nerve Supply of Pleura first rib. Receives nerve supply from structures to which it is It follows a curved line drawn from the sternoclavi­cular attached. joint to the junction of the inner third and the outer Visceral pleura obtains an autonomic supply from the two-thirds of the clavicle, the apex arising 2.5 cm above branches of the vagus nerve supplying the lung and is the clavicle. sensitive only to stretching. Line of pleural reflection passes behind the sternocla- Parietal pleura receives somatic innervation from the vicular joint on each side to meet in the midline at the intercostal nerves. angle of Louis (second costal cartilage level). Diaphragmatic pleura is supplied by the phrenic nerve. The right pleural edge passes vertically down to the level Parietal pleura and diaphragmatic pleura are therefore of the sixth costal cartilage and crosses: sensitive to pain. eighth rib in midclavicular line tenth rib in midaxillary line Clinical Points twelfth rib at the lateral border of erector spinae. Pain from the parietal pleura of the chest wall may be Left pleural edge arches laterally at the fourth costal car- referred via the intercostal nerves to the abdomen, e.g. tilage and descends lateral to the border of the sternum right lower lobar pneumonia may irritate the parietal whence it follows a path similar to the right. pleura and refer pain to the right lower abdomen, mim- Medial end of the fourth and fifth left intercostal spaces icking acute appendicitis; irritation of the diaphragmatic are therefore not covered by pleura. pleura may refer pain to the tip of the shoulder [irritat- The pleura descends below the twelfth rib at its medial ing the phrenic nerve (C3, 4, 5) and referring pain to the extremity. dermatomal distribution of C4 at the shoulder tip]. 12 SECTION I Anatomy Inferior vena cava Right phrenic nerve Left phrenic nerve Central tendon Oesophagus Left crus of the diaphragm Right crus of the diaphragm Aorta Quadratus lumborum Psoas major Fig. 1.8 The inferior aspect of the diaphragm. THE DIAPHRAGM (Fig. 1.8) aortic (strictly speaking the aortic ‘opening’ is not in Dome-shaped septum separating the thorax from the the diaphragm, but lies behind it): lies at the level of abdomen. T12; it transmits the abdominal aorta, the thoracic Composed of a peripheral muscular part and a central duct and often the azygos vein tendon. oesophageal: lies in the right crus of the diaphragm at Muscular part arises from crura, arcuate ligaments, ribs the level of T10. Transmits oesophagus, vagus nerves and sternum. and branches of the left gastric artery and vein Right crus arises from the front of the bodies of the first IVC opening: lies at T8 level in the central tendon three lumbar vertebrae and the intervening interverte- of the diaphragm. Transmits IVC and right phrenic bral discs. nerve. Left crus arises from the first and second lumbar verte- Greater and lesser splanchnic nerves pierce the crura. brae and the intervening disc. Sympathetic chain passes behind the medial arcuate The lateral arcuate ligament is a condensation of the fas- ligament lying on psoas major. cia over quadratus lumborum. The medial arcuate ligament is a condensation of the Nerve Supply fascia of psoas major. Phrenic nerve (C3, 4, 5): the phrenic nerve is the sole The medial borders of the medial arcuate ligament join motor nerve supply to the diaphragm. The sensory anteriorly over the aorta as the median arcuate ligament. innervation of the central tendon of the diaphragm The costal part is attached to the inner aspect of the is via the phrenic nerve but the periphery of the dia- lower six ribs. phragm is supplied by the lower six intercostal nerves. The sternal portion arises as two small slips from the Irritation of the diaphragm (e.g. in peritonitis or pleu- back of the xiphoid process. risy) results in referred pain to the cutaneous area of The central tendon is trefoil in shape and receives supply, i.e. the shoulder tip via C4 dermatome. insertion of muscular fibres. Above, it fuses with the Damage to the nerve (e.g. in the neck) leads to paralysis pericardium. of the diaphragm. Clinical examination reveals dullness There are three main openings in the diaphragm: to percussion at the base on the affected side and absent WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 13 breath sounds. This is due to the diaphragm being Inspiration elevated as seen on chest X-ray. Paradoxical movement Quiet inspiration is a combination of thoracic and of the diaphragm occurs on respiration. abdominal respiration. Forced inspiration (e.g. asthma) brings into action the ANATOMY OF RESPIRATION accessory muscles of respiration, i.e. sternocleidomas- toid, scalenes, pectoralis major, pectoralis minor, serra- Thoracic breathing: movements of rib cage. tus anterior. Abdominal breathing: contraction of diaphragm. Expiration Thoracic Breathing Elastic recoil of lung tissue and chest wall. ‘Pump handle’ action of ribs. Anterior ends of ribs are Forced expiration (e.g. coughing and trumpet playing) raised and, as these are below the posterior end, this requires use of muscles, i.e. rectus abdominis, external and increases the anteroposterior diameter of the thorax. internal obliques, transversus abdominis, latissimus dorsi. ‘Bucket handle’ action of ribs. Ribs 4–7 are raised. As the centre of these ribs is normally below the anterior and THE HEART (Fig. 1.9) posterior ends, the transverse diameter of the chest is increased when they move upwards. Roughly conical in shape, lying obliquely in the middle mediastinum. Abdominal Breathing Attached at its base to the great vessels, otherwise lies Muscular fibres of the diaphragm contract and the cen- free in pericardial sac. tral tendon descends, increasing the vertical diameter of Base directed upwards, backwards, to the right. the thorax. Apex directed downwards, forwards, to the left. As the central tendon descends it is arrested by the liver. Consists of four chambers: right and left atria, right and The central tendon is now fixed and acts as the origin for left ventricles. muscle fibres, which now elevate the lower six ribs. Viewed from the front it has three surfaces and three Combination of thoracic and abdominal breathing borders. increases all diameters of the thorax. Three surfaces: The negative intrapleural pressure is increased and the anterior: right atrium, right ventricle and narrow lung expands. strip of left ventricle, auricle of left atrium Arch of aorta Pulmonary trunk Superior vena cava Pulmonary trunk Left pulmonary artery Right pulmonary Auricle of left atrium veins Right coronary artery Right atrium Left ventricle Left atrium Coronary sinus Small cardiac vein Right ventricle Posterior Middle cardiac vein Anterior descending (interventricular) branch interventricular of left coronary artery artery A and great cardiac vein B Fig. 1.9 The heart and great vessels in (A) anterior and (B) posterior view. 14 SECTION I Anatomy posterior (base): left ventricle, left atrium with four Left Ventricle pulmonary veins entering it Longer and more conical than right with thicker wall inferior (diaphragmatic surface): right atrium with (three times thicker). IVC entering it and lower part of ventricles. Communicates with atrium via mitral valve. Three borders: Connects with aorta via aortic valve. right: right atrium with IVC and SVC Mitral valve has two cusps: anterior (larger) and inferior: right ventricle and apex of left ventricle posterior. left: left ventricle, auricle of left atrium. Chordae tendineae run from the ventricular surfaces of Chambers of Heart cusps to papillary muscles. Aortic valve is stronger than pulmonary valve. Has three Right Atrium cusps—anterior, right and left posterior—each having a Receives blood from IVC, SVC, coronary sinus, anterior central nodule in its free edge and a sinus or dilatation cardiac vein. in the aortic wall alongside each cusp. Crista terminalis runs between cavae–muscular ridge, The mouths of the right and left coronary arteries are separating smooth-walled posterior part of atrium seen opening into the anterior and left posterior aortic (derived from sinus venosus) from rougher area (due to sinuses, respectively. pectinate muscles) derived from true atrium. The fossa ovalis (the site of the fetal foramen ovale) is an Fibrous Skeleton of the Heart oval depression on the interatrial septum. The AV orifice is bound together by a figure-of-eight conjoined fibrous ring. Right Ventricle Acts as a fibrous skeleton for attachment of valves and Thicker-walled than atrium. muscles of atria and ventricles. Communicates with atrium via tricuspid valve. Helps to maintain shape and position of heart. Connects with pulmonary artery via pulmonary valve. Tricuspid valve has three cusps: septal, anterior, posterior. Conducting System Atrial surface of valve is smooth but ventricular surfaces Sinoatrial (SA) node situated in right atrial wall at upper have fibrous cords, the chordae tendineae, which attach end of crista terminalis (SA node = pacemaker of heart). them to papillary muscles on the ventricular wall. They From SA node, cardiac impulse spreads to reach AV prevent eversion of the cusps in the atrium during ven- node. tricular contraction. AV node lies in interatrial septum immediately above Moderator band is a muscle bundle crossing from the opening of coronary sinus. interventricular septum to the anterior wall of the heart. Cardiac impulse is conducted to ventricles via AV Moderator band may prevent overdistension of ventri- bundle (of His). cle. Conducts right branch of the AV bundle to anterior AV bundle passes through fibrous skeleton of heart to wall of ventricle. membranous part of interventricular septum, where it Infundibulum is the outflow tract of the ventricle. divides into right and left branch. Directed upwards and to the right towards the pulmo- Left AV bundle is larger and both run under endocar- nary trunk. dium to activate all parts of the ventricular muscle. Pulmonary orifices guarded by the pulmonary valve Papillary muscles contract first and then wall and consisting of three semilunar cusps. septum in a rapid sequence from apex towards outflow tract, both ventricles contracting together. Left Atrium AV bundle is normally the only pathway through which Smaller than the right. impulse can reach ventricles. Consists of principal cavity and auricle. Auricle extends forwards and to the right, overlapping Blood Supply of Heart (see Fig. 1.9) the commencement of the pulmonary trunk. Right Coronary Artery Four pulmonary veins open into the cavity (two from Arises from anterior aortic sinus. each lung: superior and inferior). Passes to the right of the pulmonary trunk between it Shallow depression on septal surface corresponds to and the auricle. fossa ovalis of right atrium. Runs along the AV groove around the inferior border of Largely smooth-walled, except for ridges in the auricle the heart and anastomoses with the left coronary artery owing to underlying pectinate muscles. at the posterior interventricular groove. WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 15 Branches include: Coronary sinus: marginal branch along the lower border of the heart main venous drainage posterior interventricular (posterior descending) lies in posterior AV groove branch, which runs forward in the inferior interven- opens into the right atrium just to the left of the tricular groove to anastomose near the apex with the mouth of the IVC. corresponding branch of the left coronary artery. Tributaries of coronary sinus: great cardiac vein: ascends in anterior interventricu- Left Coronary Artery lar groove next to anterior interventricular artery Arises from the left posterior aortic sinus. middle cardiac vein: drains posterior and inferior Larger than the right coronary artery. surfaces of heart and lies next to the posterior inter- Main stem varies in length (4–10 mm). ventricular artery Passes behind and then to the left of the pulmonary trunk. small cardiac vein: accompanies marginal artery and Reaches the left part of the AV groove. drains into termination of coronary sinus. Initially lies under cover of the left auricle where it divides into two equally sized branches. Nerve Supply of Heart Branches: Sympathetic (cardioaccelerator). anterior interventricular (left anterior descending): Vagus (cardioinhibitor). runs down to the apex in the anterior interventricular groove supplying the wall of the ventricles, to anasto- Clinical Point mose with the posterior interventricular artery Cardiac pain is experienced not only in the chest but is circumflex: continues round the left side of the heart referred down the inner side of the left arm and up to in the AV groove to anastomose with the terminal the neck and jaw. Cardiac pain is referred to areas of the branches of the right coronary artery. body surface which send sensory impulses to the same Occlusion of the left coronary artery will lead to rapid level of the spinal cord that receives cardiac sensation. demise. The sensory fibres from the heart travel through the cardiac plexus, sympathetic chain and up to the dorsal Variations root ganglia of T1–4. Excitation of spinothalamic tract Left coronary and circumflex arteries may be larger and cells in the upper thoracic segments contribute to the longer than usual and give off the posterior intraven- anginal pain experienced in the chest and inner aspect tricular artery before anastomosing with the right coro- of the arm via dermatomes T1–4. Cardiac vagal afferent nary artery, which is smaller than usual (known as ‘left fibres synapse in the nucleus of the tractus solitarius of dominance’; occurs in 10% of population). the medulla and then descend to excite upper cervical Right and left coronary arteries may have equal contri- spinothalamic tract cells. This innervation contributes bution to posterior interventricular artery (known as to the angina pain experienced in the area of the neck codominance; occurs in 10% of population). and jaw. Left main stem may divide into three branches. The third lies between the anterior interventricular and cir- PERICARDIUM cumflex arteries and may be large, supplying the lateral wall of the left ventricle. Fibrous In just under 60% of the population the SA node is sup- Heart and roots of the great vessels are contained within plied by the right coronary artery, while in just under the conical fibrous pericardium. 40% it is supplied by the circumflex artery. In 3% it has Apex: fuses with adventitia of great vessels about 5 cm a dual supply. from the heart. The AV node is supplied by the right coronary artery in Base: fuses with central tendon of the diaphragm. 90% and the circumflex in 10%. Relations Venous Drainage (see Fig. 1.9) Anterior sternum: third to sixth costal cartilages, Venae cordis minimae: tiny veins draining directly into thymus, anterior edges of lungs and pleura. the chambers of the heart. Posterior: oesophagus, descending aorta, T5–8 vertebrae. Anterior cardiac veins: small, open directly into the Lateral: roots of lung, phrenic nerves, mediastinal right atrium. pleura. 16 SECTION I Anatomy Serous Surface Anatomy of Heart The fibrous pericardium is lined by a parietal layer of Superior: line from second left costal cartilage 1.2 cm serous pericardium. from sternal edge to third right costal cartilage, 1.2 cm The parietal layer is reflected to cover the heart and roots from sternal edge. of great vessels to become continuous with visceral layer Inferior: line from the sixth right costal cartilage 1.2 cm of serous pericardium. from sternal edge to fifth left intercostal space, 9 cm from midline (i.e. position of apex beat). Oblique and Transverse Sinuses (Fig. 1.10) Left border: curved line joining second left costal car- At the pericardial reflections, veins are surrounded by one tilage 1.2 cm from sternal edge to fifth left intercostal sleeve of pericardium and arteries by another. space, 9 cm from midline. Right border: curved line joining third right costal Transverse Sinus cartilage 1.2 cm from sternal edge to sixth right costal Lies between the aorta and pulmonary trunk in front, cartilage, 1.2 cm from sternal edge. and the SVC and left atrium behind. Oblique Sinus MEDIASTINUM (Fig. 1.11) Bounded by the pulmonary veins. The space between the two pleural cavities is called the Forms a recess between pericardium and left atrium. mediastinum. It is divided into: superior mediastinum Clinical Points anterior mediastinum Fibrous pericardium can stretch gradually if there is middle mediastinum gradual enlargement of the heart. posterior mediastinum. Sudden increase in pericardial contents as in sudden bleeds: stretching does not occur and cardiac function Superior Mediastinum is embarrassed (cardiac tamponade). Boundaries are: anterior: manubrium sterni posterior: first four thoracic vertebrae above: continues up to root of neck Superior vena cava Aorta below: continues with inferior mediastinum at level of horizontal line drawn through angle of Louis. Pulmonary trunk Tranverse sinus 1 Right 2 pulmonary Left pulmonary Superior veins veins 3 mediastinum Angle of 4 Louis 5 Anterior mediastinum 6 7 Posterior mediastinum 8 Inferior vena cava Oblique sinus 9 Fig. 1.10 The posterior surface of the pericardial 10 cavity after removal of the heart. The reflection of Middle 11 Diaphragm the pericardium around the great vessels is shown. mediastinum 12 (From Rogers AW. Textbook of Anatomy. Churchill Livingstone, Edinburgh, 1992, with permission.) Fig. 1.11 The divisions of the mediastinum. WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 17 Contents: Contents: lower end of trachea heart oesophagus great vessels thoracic duct phrenic nerves aortic arch pericardiophrenic vessels. innominate artery part of carotid and subclavian arteries Posterior Mediastinum innominate veins Boundaries are: upper part of SVC anterior: pericardium, roots of lungs, diaphragm phrenic and vagus nerves below left recurrent laryngeal nerves posterior: vertebral column from lower border of fourth cardiac nerves to twelfth vertebrae lymph nodes above: horizontal plane drawn through the angle of remnants of thymus gland. Louis below: diaphragm. Anterior Mediastinum Contents: Boundaries are: descending thoracic aorta anterior: sternum oesophagus posterior: pericardium. vagus and splanchnic nerves Contents: azygos vein part of the thymus gland in children hemiazygos vein anterior mediastinal lymph nodes. thoracic duct mediastinal lymph nodes. Middle Mediastinum Fig. 1.12 shows some of the structures in the anterior, Boundaries are: middle and posterior mediastinum. anterior: anterior mediastinum posterior: posterior mediastinum. Body of sternum Thymic residue in anterior mediastinal fat Pulmonary trunk Ascending aorta Left pulmonary artery Superior vena cava Descending aorta Azygos vein Scapula Subscapularis Infraspinatus Oesophagus Body of T5 vertebra Trachea Fig. 1.12 Contrast CT at the level of the fifth thoracic vertebra showing some of the structures in the anterior, middle and posterior mediastinum. 18 SECTION I Anatomy Left common carotid artery Oesophagus Oesophagus Left subclavian artery Trachea Sympathetic chain Right vagus nerve Left vagus nerve Arch of aorta Superior vena cava Recurrent laryngeal nerve Right phrenic Left phrenic nerve nerve Descending thoracic aorta Azygos vein Fig. 1.14 The mediastinum seen from the right side. Fig. 1.13 The mediastinum seen from the left side. T4, which is an important landmark. The following occur The Mediastinal Surfaces (Figs. 1.13 and 1.14) at T4: Because of the arrangements of structures in the mediasti- commencement and termination of aortic arch num, it appears differently when viewed from left and right bifurcation of trachea sides. junction of superior and inferior mediastinum second costosternal joint The Angle of Louis confluence of azygos vein with superior vena cava The angle of Louis (manubriosternal junction) is an impor- thoracic duct runs from right to left tant anatomical landmark. It corresponds to the plane of ligamentum arteriosum lies on this plane. OSCE SCENARIOS OSCE Scenario 1.1 OSCE Scenario 1.2 A 19-year-old male is admitted with a right-sided spon- A 35-year-old male sustains a crushing upper abdominal taneous pneumothorax. He has a past history of a treated injury in a road traffic accident. On admission to A&E he coarctation of the aorta. He requires a chest drain. has a tachycardia of 120 and a systolic blood pressure of 1. Describe the anatomy of a typical intercostal space. 90 mmHg. He is complaining of abdominal and bilateral 2. Why is this knowledge important in your technique of shoulder tip pain. Urgent CT scan reveals liver and splenic insertion of an intercostal drain? trauma as well as a ruptured left hemidiaphragm. 3. What is the ‘triangle of safety’ when inserting a chest 1. Describe the three origins of the muscular part of the drain? diaphragm. 4. Explain the anatomical basis for notching of the lower 2. At what vertebral levels do the oesophagus and the IVC border of a rib seen on a chest X-ray of a patient with pass through the diaphragm? coarctation of the aorta. 3. What is the nerve supply of the diaphragm? WWW.BOOKBAZ.IR  CHAPTER 1 The Thorax 19 4. Explain why in some cases irritation of the diaphragm 1. Describe the surface anatomy of the heart. may result in referred pain to the shoulder while in oth- 2. Why does cardiac tamponade result in drop in the blood ers it may result in referred pain to the abdomen. pressure and clinical shock? 3. Describe how you would treat a cardiac tamponade. OSCE Scenario 1.3 A 60-year-old female undergoes a right open nephrec- OSCE Scenario 1.5 tomy via a loin approach through the bed of the twelfth An 18-month-old girl developed sudden-onset bouts of rib. A postoperative chest X-ray shows a small right cough and wheezes. A bowl of peanuts was found nearby pneumothorax. while she was playing unwitnessed. She was rushed to A&E 1. Describe the surface anatomy of the pleura. and found to be conscious but distressed, tachypnoeic and 2. Why has this patient developed a right pneumothorax? wheezy. A chest X-ray revealed a collapsed lung. 3. At which other site, other than surgery on the thorax, 1. In which main bronchus a foreign body is more likely to may surgery or trauma result in a pneumothorax? be dislodged and why? 2. In relation to the surface anatomy, where does the tra- OSCE Scenario 1.4 chea commence and terminate? A 22-year-old male is brought to A&E with a penetrating 3. Describe briefly how you would treat the patient. injury in the left third intercostal space, anterior to the mid- axillary line. His blood pressure is 80/40, pulse rate 140 Answers in Appendix pages 431–433 beats/min and has muffled hear sounds and distended neck veins. A diagnosis of cardiac tamponade is established. Please check your eBook at https://studentconsult.inkling.com/ for more self-assessment questions. See inside cover for registration details.  2 The Abdomen, Pelvis and Perineum DEVELOPMENT Development of the Gut The gut develops from a primitive endodermal tube. It is divided into three parts: foregut: extends to the entry of the bile duct into the duodenum (supplied by the coeliac axis) midgut: extends to distal transverse colon (supplied by superior mesenteric artery) hindgut: extends to ectodermal part of anal canal (sup- plied by inferior mesenteric artery). A B Foregut Starts to divide into the oesophagus and the laryngotra- Fig. 2.1 Types of oesophageal atresia. (A) Oeso­ cheal tube during the 4th week. pha­ geal atresia with distal tracheo-oesophageal If it fails to do so correctly, there may be pure oesopha- fistula—most common type, with an incidence of geal atresia (8% of cases), or atresia associated with 80%. (B) Isolated oesophageal atresia—second com­ tracheo-oesophageal fistula (the commonest, 80% of monest, with an incidence of about 8%. cases), the fistula being between the lower end of the trachea and the distal oesophagus (Fig. 2.1). artery, bringing the third and fourth parts of the duode- Distal to the oesophagus, the foregut dilates to form the num across to the left of the midl