Conceptual overview                                   124   Diaphragm                                            156
     ...
 3   
                         Thorax




Drake_ch03_main.indd 3        8/25/2008 4:10:13 PM
Thorax



              Conceptual overview
              GENERAL	DESCRIPTION
              The thorax is an irregularly s...
Conceptual overview •  component parts                     3
            ■    a left and a right pleural cavity, each surr...
Thorax

                                           Superior articular process               Superior costal facet



     ...
Conceptual overview •  component parts                     3
                                                             ...
Thorax

                 As the diaphragm contracts, the height of the domes              Each pleural cavity is completel...
Conceptual overview •  Relationship to other regions                             3
                                       ...
Thorax

                                                                              num to supply anterior aspects of th...
Conceptual overview •  Key features                       3
                                                A

           ...
Thorax

                                                                                left upper limb, and part of the l...
Conceptual overview •  Key features                     3
            ■     the thoracic aorta, which is in the posterior ...
Thorax

                          B                                                                                       ...
Conceptual overview •  Key features                        3



                    Paravertebral
                 sympath...
Thorax



                                                           C3

                                                 ...
Regional anatomy •  Pectoral region              3


            Regional anatomy
            The cylindrical thorax consi...
Thorax

                                                                              Internal thoracic artery

          ...
Regional anatomy •  Pectoral region                    3
               In the clinic

               Breast cancer       ...
Thorax

                                                                                                  Subclavius
     ...
Regional anatomy •  Thoracic wall                           3
                                              Anterior
     ...
Thorax

                 Not all vertebrae articulate with ribs in the same fashion                    of its own rib—in o...
Regional anatomy •  Thoracic wall            3
               A typical rib consists of a curved shaft with anterior and  ...
Thorax

              vertebra TI and therefore has only one articular surface.             Articular site                ...
Regional anatomy •  Thoracic wall                3
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T O R A X D R A K E

  1. 1. Conceptual overview 124 Diaphragm 156 Venous drainage 160 General description 124 Innervation 160 Functions 125 Movements of the thoracic wall and Breathing 125 diaphragm during breathing 160 Protection of vital organs 125 Pleural cavities 160 Conduit 125 Pleura 160 Component parts 125 Lungs 165 Thoracic wall 125 Mediastinum 178 Superior thoracic aperture 126 Middle mediastinum 178 Inferior thoracic aperture 126 Superior mediastinum 206 Diaphragm 127 Posterior mediastinum 217 Mediastinum 127 Anterior mediastinum 225 Pleural cavities 127 Relationship to other regions 130 Neck 130 Surface anatomy 226 Upper limb 130 Abdomen 131 Thorax surface anatomy 226 Breast 131 How to count ribs 226 Key features 132 Surface anatomy of the breast in women 227 Vertebral level TIV/V 132 Visualizing structures at the TIV/V Venous shunts from left to right 132 vertebral level 228 Segmental neurovascular supply of Visualizing structures in the superior thoracic wall 132 mediastinum 228 Sympathetic system 135 Visualizing the margins of the heart 228 Flexible wall and inferior thoracic aperture 135 Where to listen for heart sounds 229 Innervation of the diaphragm 137 Visualizing the pleural cavities and lungs, pleural recesses, and lung lobes and fissures 229 Regional anatomy 139 Where to listen for lung sounds 230 Pectoral region 139 Breast 139 Clinical cases 235 Venous drainage 139 Muscles of the pectoral region 141 Thoracic wall 142 Skeletal framework 142 Intercostal spaces 149 Drake_ch03_main.indd 2 8/25/2008 4:10:06 PM
  2. 2.  3    Thorax Drake_ch03_main.indd 3 8/25/2008 4:10:13 PM
  3. 3. Thorax Conceptual overview GENERAL DESCRIPTION The thorax is an irregularly shaped cylinder with a narrow The musculoskeletal wall of the thorax is flexible and opening (superior thoracic aperture) superiorly and a rela­ consists of segmentally arranged vertebrae, ribs, muscles, tively large opening (inferior thoracic aperture) inferiorly and the sternum. (Fig. 3.1). The superior thoracic aperture is open, allowing The thoracic cavity enclosed by the thoracic wall continuity with the neck; the inferior thoracic aperture is and the diaphragm is subdivided into three major closed by the diaphragm. compartments: Superior thoracic aperture Vertebral column Mediastinum Right pleural cavity Left pleural cavity Rib I Manubrium of sternum Sternal angle Body of sternum Ribs Xiphoid process Diaphragm Inferior thoracic aperture Fig. 3.1 Thoracic wall and cavity. 3- Drake_ch03_main.indd 4 8/25/2008 4:10:18 PM
  4. 4. Conceptual overview •  component parts 3 ■ a left and a right pleural cavity, each surrounding a The esophagus, vagus nerves, and thoracic duct pass lung; through the mediastinum as they course between the ■ the mediastinum. abdomen and neck. The phrenic nerves, which originate in the neck, also The mediastinum is a thick, flexible soft tissue partition pass through the mediastinum to penetrate and supply the oriented longitudinally in a median sagittal position. It diaphragm. contains the heart, esophagus, trachea, major nerves, and Other structures such as the trachea, thoracic aorta, major systemic blood vessels. and superior vena cava course within the mediastinum en The pleural cavities are completely separated from each route to and from major visceral organs in the thorax. other by the mediastinum. Therefore, abnormal events in one pleural cavity do not necessarily affect the other cavity. This also means that the mediastinum can be entered sur­ COMPONENT PARTS gically without opening the pleural cavities. Another important feature of the pleural cavities is that Thoracic wall they extend above the level of rib I. The apex of each lung The thoracic wall consists of skeletal elements and actually extends into the root of the neck. As a conse­ muscles (Fig. 3.1): quence, abnormal events in the root of the neck can involve the adjacent pleura and lung, and events in the adjacent ■ posteriorly, it is made up of twelve thoracic vertebrae pleura and lung can involve the root of the neck. and their intervening intervertebral discs; ■ laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the FUNCTIONS intercostal spaces between adjacent ribs, move the ribs and provide support for the intercostal spaces; Breathing ■ anteriorly, the wall is made up of the sternum, which One of the most important functions of the thorax is breath­ consists of the manubrium of sternum, body of sternum, ing. The thorax not only contains the lungs but also pro­ and xiphoid process. vides the machinery necessary—the diaphragm, thoracic wall, and the ribs—for effectively moving air into and out The manubrium of sternum, angled posteriorly on the of the lungs. body of sternum at the manubriosternal joint, forms the Up and down movements of the diaphragm and changes sternal angle, which is a major surface landmark used in the lateral and anterior dimensions of the thoracic wall, by clinicians in performing physical examinations of the caused by movements of the ribs, alter the volume of the thorax. thoracic cavity and are key elements in breathing. The anterior (distal) end of each rib is composed of costal cartilage, which contributes to the mobility and elasticity of the wall. Protection of vital organs All ribs articulate with thoracic vertebrae posteriorly. The thorax houses and protects the heart, lungs, and Most ribs (from rib II to IX) have three articulations great vessels. Because of the domed shape of the diaphragm, with the vertebral column. The head of each rib articulates the thoracic wall also offers protection to some important with the body of its own vertebra and with the body of the abdominal viscera. vertebra above (Fig. 3.2). As these ribs curve posteriorly, Much of the liver lies under the right dome of the dia­ each also articulates with the transverse process of its phragm, and the stomach and spleen lie under the left. The vertebra. posterior aspects of the superior poles of the kidneys lie on Anteriorly, the costal cartilages of ribs I to VII articulate the diaphragm and are anterior to rib XII, on the right, and with the sternum. to ribs XI and XII, on the left. The costal cartilages of ribs VIII to X articulate with the inferior margins of the costal cartilages above them. Ribs XI and XII are called floating ribs because they do not Conduit articulate with other ribs, costal cartilages, or the sternum. The mediastinum acts as a conduit for structures that pass Their costal cartilages are small, only covering their tips. completely through the thorax from one body region to The skeletal framework of the thoracic wall provides another and for structures that connect organs in the extensive attachment sites for muscles of the neck, thorax to other body regions. abdomen, back, and upper limbs. 3- Drake_ch03_main.indd 5 8/25/2008 4:10:18 PM
  5. 5. Thorax Superior articular process Superior costal facet Costal facet of transverse process Sternum Inferior articular Intervertebral disc process Vertebral body Inferior costal facet Rib V Costal cartilage Fig. 3.2 Joints between ribs and vertebrae. A number of these muscles attach to ribs and function between the neck and head and the thorax pass more verti­ as accessory respiratory muscles; some of them also stabi­ cally through the superior thoracic aperture. lize the position of the first and last ribs. Inferior thoracic aperture The inferior thoracic aperture is large and expand­ Superior thoracic aperture able. Bone, cartilage, and ligaments form its margin Completely surrounded by skeletal elements, the superior (Fig. 3.4A). thoracic aperture consists of the body of vertebra TI pos­ The inferior thoracic aperture is closed by the dia­ teriorly, the medial margin of rib I on each side, and the phragm, and structures passing between the abdomen and manubrium anteriorly. thorax pierce or pass posteriorly to the diaphragm. The superior margin of the manubrium is in approxi­ Skeletal elements of the inferior thoracic aperture are: mately the same horizontal plane as the intervertebral disc between vertebrae TII and TIII. ■ the body of vertebra TXII posteriorly; The first ribs slope inferiorly from their posterior articu­ ■ rib XII and the distal end of rib XI posterolaterally; lation with vertebra TI to their anterior attachment to the ■ the distal cartilaginous ends of ribs VII to X, which unite manubrium. Consequently, the plane of the superior tho­ to form the costal margin anterolaterally; and racic aperture is at an oblique angle, facing somewhat ■ the xiphoid process anteriorly. anteriorly. At the superior thoracic aperture, the superior aspects The joint between the costal margin and sternum lies of the pleural cavities, which surround the lungs, lie on roughly in the same horizontal plane as the intervertebral either side of the entrance to the mediastinum (Fig. disc between vertebrae TIX and TX. In other words, the post­ 3.3). erior margin of the inferior thoracic aperture is inferior to Structures that pass between the upper limb and thorax the anterior margin. 3- pass over rib I and the superior part of the pleural cavity as When viewed anteriorly, the inferior thoracic aperture they enter and leave the mediastinum. Structures that pass is tilted superiorly. Drake_ch03_main.indd 6 8/25/2008 4:10:20 PM
  6. 6. Conceptual overview •  component parts 3 Esophagus Common carotid artery Vertebra TI Trachea Superior thoracic aperture Rib I Internal jugular vein Apex of right lung Subclavian artery and vein Manubrium of sternum Rib II Fig. 3.3 Superior thoracic aperture. A B Right dome Central tendon Xiphoid process Inferior thoracic Left dome aperture Distal cartilaginous ends of ribs VII to X; costal margins Esophageal hiatus Rib XI Rib XII Aortic hiatus Vertebra TXII Fig. 3.4 A. Inferior thoracic aperture. B. Diaphragm. Diaphragm Because of the oblique angle of the inferior thoracic The musculotendinous diaphragm seals the inferior tho­ aperture, the posterior attachment of the diaphragm is racic aperture (Fig. 3.4B). inferior to the anterior attachment. Generally, muscle fibers of the diaphragm arise radially, The diaphragm is not flat; rather, it “balloons” superi­ from the margins of the inferior thoracic aperture, and orly, on both the right and left sides, to form domes. The 3- converge into a large central tendon. right dome is higher than the left, reaching as far as rib V. Drake_ch03_main.indd 7 8/25/2008 4:10:24 PM
  7. 7. Thorax As the diaphragm contracts, the height of the domes Each pleural cavity is completely lined by a mesothe­ decreases and the volume of the thorax increases. lial membrane called the pleura. The esophagus and inferior vena cava penetrate the dia­ During development, the lungs grow out of the medias­ phragm; the aorta passes posterior to the diaphragm. tinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura. Mediastinum Each lung remains attached to the mediastinum by a The mediastinum is a thick midline partition that extends root formed by the airway, pulmonary blood vessels, lym­ from the sternum anteriorly to the thoracic vertebrae phatic tissues, and nerves. posteriorly, and from the superior thoracic aperture to the The pleura lining the walls of the cavity is the parietal inferior thoracic aperture. pleura, whereas that reflected from the mediastinum at the A horizontal plane passing through the sternal angle roots and onto the surfaces of the lungs is the visceral and the intervertebral disc between vertebrae TIV and pleura. Only a potential space normally exists between the TV separates the mediastinum into superior and inferior visceral pleura covering lung and the parietal pleura lining parts (Fig. 3.5). The inferior part is further subdivided by the wall of the thoracic cavity. the pericardium, which encloses the pericardial cavity sur­ The lung does not completely fill the potential space rounding the heart. The pericardium and heart constitute of the pleural cavity, resulting in recesses, which do not the middle mediastinum. contain lung and are important for accommodating The anterior mediastinum lies between the sternum changes in lung volume during breathing. The costodia­ and the pericardium; the posterior mediastinum lies be­ phragmatic recess, which is the largest and clinically most tween the pericardium and thoracic vertebrae. important recess, lies inferiorly between the thoracic wall and diaphragm. Pleural cavities The two pleural cavities are situated on either side of the mediastinum (Fig. 3.6). Sternal angle Rib I I Superior mediastinum IV V Anterior mediastinum Middle mediastinum Posterior mediastinum Inferior mediastinum X Diaphragm XII Fig. 3.5 Subdivisions of the mediastinum. 3- Drake_ch03_main.indd 8 8/25/2008 4:10:25 PM
  8. 8. Conceptual overview •  Relationship to other regions 3 Apex of right lung Trachea Left pleural cavity Right main bronchus Parietal pleura Visceral pleura Mediastinum Costodiaphragmatic recess Diaphragm Superior thoracic aperture Rib I Fig. 3.6 Pleural cavities. Esophagus Scapula Brachial plexus Axillary inlet RELATIONSHIP TO OTHER REGIONS Neck The superior thoracic aperture opens directly into the root of the neck (Fig. 3.7). The superior aspect of each pleural cavity extends approximately 2–3 cm above rib I and the costal cartilage into the neck. Between these pleural extensions, major visceral structures pass between the neck and superior mediastinum. In the midline, the trachea lies immediately Subclavian Trachea Coracoid artery and vein process anterior to the esophagus. Major blood vessels and nerves Clavicle pass in and out of the thorax at the superior thoracic aper­ Fig. 3.7 Superior thoracic aperture and axillary inlet. ture anteriorly and laterally to these structures. 3- Drake_ch03_main.indd 9 8/25/2008 4:10:29 PM
  9. 9. Thorax num to supply anterior aspects of the thoracic wall. Those Upper limb branches associated mainly with the second to fourth An axillary inlet, or gateway to the upper limb, lies on intercostal spaces also supply the anteromedial parts of each side of the superior thoracic aperture. These two axil­ each breast. lary inlets and the superior thoracic aperture communi­ Lymphatic vessels from the medial part of the breast cate superiorly with the root of the neck (Fig. 3.7). accompany the perforating arteries and drain into the Each axillary inlet is formed by: parasternal nodes on the deep surface of the thoracic wall: ■ the superior margin of the scapula posteriorly; ■ the clavicle anteriorly; and ■ vessels and lymphatics associated with lateral parts ■ the lateral margin of rib I medially. of the breast emerge from or drain into the axillary region of the upper limb; The apex of each triangular inlet is directed laterally ■ lateral and anterior branches of the fourth to sixth inter­ and is formed by the medial margin of the coracoid process, costal nerves carry general sensation from the skin of which extends anteriorly from the superior margin of the the breast. scapula. The base of the axillary inlet’s triangular opening is the lateral margin of rib I. KEY FEATURES Large blood vessels passing between the axillary inlet and superior thoracic aperture do so by passing over Vertebral level TIV/V rib I. When working with patients, physicians use vertebral Proximal parts of the brachial plexus also pass between levels to determine the position of important anatomical the neck and upper limb by passing through the axillary structures within body regions. inlet. Inferior vena cava Abdomen Esophagus The diaphragm separates the thorax from the abdomen. Caval opening Aorta Structures that pass between the thorax and abdomen (vertebral level TVIII) Central tendon either penetrate the diaphragm or pass posteriorly to it of diaphragm (Fig. 3.8): ■ the inferior vena cava pierces the central tendon of the diaphragm to enter the right side of the mediasti­ num near vertebral level TVIII; ■ the esophagus penetrates the muscular part of the diaphragm to leave the mediastinum and enter the abdomen just to the left of the midline at vertebral level TX; ■ the aorta passes posteriorly to the diaphragm at the midline at vertebral level TXII; ■ numerous other structures that pass between the thorax and abdomen pass through or posterior to the diaphragm. Breast LI Esophageal hiatus The breasts, consisting of secretory glands, superficial Aortic hiatus (vertebral level TX) fascia, and overlying skin, are in the pectoral region on (vertebral level TXII) each side of the anterior thoracic wall (Fig. 3.9). Branches from the internal thoracic arteries and veins Fig. 3.8 Major structures passing between abdomen and thorax. 3-10 perforate the anterior chest wall on each side of the ster­ Drake_ch03_main.indd 10 8/25/2008 4:10:31 PM
  10. 10. Conceptual overview •  Key features 3 A Axillary process Axillary lymph nodes B Internal thoracic artery Pectoralis major Second, third, and fourth perforating branches of internal thoracic artery Parasternal lymph nodes Lactiferous sinuses Fourth thoracic intercostal nerve Lactiferous ducts Secretory glands Lymphatic vessel Deep (pectoral) fascia Fig. 3.9 Right breast. Superior mediastinum Trachea Aortic arch Rib II Sternal angle The horizontal plane passing through the disc that sepa­ TIV rates thoracic vertebrae TIV and TV is one of the most sig­ nificant planes in the body (Fig. 3.10) because it: ■ passes through the sternal angle anteriorly, marking the position of the anterior articulation of the costal TV cartilage of rib II with the sternum. The sternal angle is used to find the position of rib II as a reference for count­ ing ribs (because of the overlying clavicle, rib I is not palpable); ■ separates the superior mediastinum from the inferior mediastinum and marks the position of the superior limit of the pericardium; ■ marks where the arch of the aorta begins and ends; Inferior mediastinum ■ passes through the site where the superior vena cava penetrates the pericardium to enter the heart; ■ is the level at which the trachea bifurcates into right and left main bronchi; and ■ marks the superior limit of the pulmonary trunk. Fig. 3.10 Vertebral level TIV/V. 3-11 Drake_ch03_main.indd 11 8/25/2008 4:10:36 PM
  11. 11. Thorax left upper limb, and part of the left thoracic wall into the Venous shunts from left to right superior vena cava. The right atrium is the chamber of the heart that receives The hemiazygos and accessory hemiazygos veins deoxygenated blood returning from the body. It lies on the drain posterior and lateral parts of the left thoracic wall, right side of the midline, and the two major veins, the supe­ pass immediately anterior to the bodies of thoracic ver­ rior and inferior venae cavae, that drain into it are also tebrae, and flow into the azygos vein on the right side, located on the right side of the body. This means that, to which ultimately connects with the superior vena get to the right side of the body, all blood coming from the cava. left side has to cross the midline. This left­to­right shunting is carried out by a number of important and, in some cases, Segmental neurovascular supply very large, veins, several of which are in the thorax (Fig. 3.11). of thoracic wall In adults, the left brachiocephalic vein crosses the The arrangement of vessels and nerves that supply the midline immediately posterior to the manubrium and thoracic wall reflects the segmental organization of the delivers blood from the left side of the head and neck, the wall. Arteries to the wall arise from two sources: Left internal jugular vein Left brachiocephalic vein Superior vena cava Intercostal vein Right atrium Accessory hemiazygos vein Azygos vein Hemiazygos vein Inferior vena cava 3-12 Fig. 3.11 Left-to-right venous shunts. Drake_ch03_main.indd 12 8/25/2008 4:10:38 PM
  12. 12. Conceptual overview •  Key features 3 ■ the thoracic aorta, which is in the posterior mediasti­ (the anterior rami of thoracic spinal nerves), which inner­ num; and vate the wall, related parietal pleura, and associated skin. ■ a pair of vessels, the internal thoracic arteries, which The position of these nerves and vessels relative to the ribs run along the deep aspect of the anterior thoracic wall must be considered when passing objects, such as chest on either side of the sternum. tubes, through the thoracic wall. Dermatomes of the thorax generally reflect the segmen­ Posterior and anterior intercostal vessels branch seg­ tal organization of the thoracic spinal nerves (Fig. 3.12B). mentally from these arteries and pass laterally around The exception occurs, anteriorly and superiorly, with the the wall, mainly along the inferior margin of each rib (Fig. first thoracic dermatome, which is located mostly in the 3.12A). Running with these vessels are intercostal nerves upper limb, and not on the trunk. A Left common carotid artery Right subclavian artery Internal thoracic arteries Arch of aorta Lateral cutaneous branch Posterior intercostal artery Anterior intercostal artery Anterior cutaneous branch Intercostal nerve Fig. 3.12 A. Segmental neurovascular supply of thoracic wall. 3-13 Drake_ch03_main.indd 13 8/25/2008 4:10:41 PM
  13. 13. Thorax B C Supraclavicular nerves T2 T2 T3 T3 T4 T4 T5 Xiphoid process T5 T2 T6 T6 T7 T7 T8 Costal margin T8 T1 T9 T9 T10 Umbilicus T10 T11 T11 Anterior superior iliac spine T12 T12 Inguinal ligament Pubic tubercles Fig. 3.12, cont’d B. Anterior view of thoracic dermatomes associated with thoracic spinal nerves. C. Lateral view of dermatomes associated with thoracic spinal nerves. The anterosuperior region of the trunk receives branches allow movement, and because of the shape and orientation from the anterior ramus of C4 via supraclavicular branches of the ribs (Fig. 3.14). of the cervical plexus. A rib’s posterior attachment is superior to its anterior The highest thoracic dermatome on the anterior chest attachment. Therefore, when a rib is elevated, it moves the wall is T2, which also extends into the upper limb. In the anterior thoracic wall forward relative to the posterior midline, skin over the xiphoid process is innervated by T6. wall, which is fixed. In addition, the middle part of each rib Dermatomes of T7 to T12 follow the contour of the ribs is inferior to its two ends, so that when this region of the onto the anterior abdominal wall (Fig. 3.12C). rib is elevated, it expands the thoracic wall laterally. Finally, because the diaphragm is muscular, it changes the volume of the thorax in the vertical direction. Sympathetic system Changes in the anterior, lateral, and vertical dimen­ All preganglionic nerve fibers of the sympathetic system sions of the thoracic cavity are important for are carried out of the spinal cord in spinal nerves T1 to L2 breathing. (Fig. 3.13). This means that sympathetic fibers found any­ where in the body ultimately emerge from the spinal cord as components of these spinal nerves. Preganglionic sym­ Innervation of the diaphragm pathetic fibers destined for the head are carried out of the The diaphragm is innervated by two phrenic nerves that spinal cord in spinal nerve T1. originate, one on each side, as branches of the cervical plexus in the neck (Fig. 3.15). They arise from the anterior Flexible wall and inferior rami of cervical nerves C3, C4, and C5, with the major contribution coming from C4. thoracic aperture The phrenic nerves pass vertically through the neck, The thoracic wall is expandable because most ribs articu­ the superior thoracic aperture, and the mediastinum 3-1 late with other components of the wall by true joints that to supply motor innervation to the entire diaphragm, Drake_ch03_main.indd 14 8/25/2008 4:10:42 PM
  14. 14. Conceptual overview •  Key features 3 Paravertebral sympathetic trunk Gray ramus Spinal cord communicans T1 Spinal nerve Spinal cord Spinal nerve Thoracic sympathetic ganglion Sympathetic trunk White ramus communicans L2 Elevation of lateral aspect Sternum moves forward of ribs in inspiration in inspiration because of rib elevation Fig. 3.13 Sympathetic trunks. including the crura (muscular extensions that attach the diaphragm to the upper lumbar vertebrae). In the medias­ tinum, the phrenic nerves pass anteriorly to the roots of the lungs. The tissues that initially give rise to the diaphragm are in an anterior position on the embryological disc before the head fold develops, which explains the cervical origin of the nerves that innervate the diaphragm. In other words, the tissue that gives rise to the diaphragm originates superior to the ultimate location of the Diaphragm descends to diaphragm. increase thoracic capacity in inspiration Spinal cord injuries below the level of the origin of the phrenic nerve do not affect movement of the Fig. 3.14 Flexible thoracic wall and inferior thoracic aperture. diaphragm. 3-1 Drake_ch03_main.indd 15 8/25/2008 4:10:45 PM
  15. 15. Thorax C3 C4 C5 Right phrenic nerve Left phrenic nerve Pericardial branch of phrenic nerve Pericardium Diaphragm Fig. 3.15 Innervation of the diaphragm. 3-1 Drake_ch03_main.indd 16 8/25/2008 4:10:49 PM
  16. 16. Regional anatomy •  Pectoral region 3 Regional anatomy The cylindrical thorax consists of: regions, this condenses to form well­defined ligaments, the suspensory ligaments of breast, which are continu­ ■ a wall; ous with the dermis of the skin and support the breast. ■ two pleural cavities; Carcinoma of the breast creates tension on these ligaments, ■ the lungs; and causing pitting of the skin. ■ the mediastinum. In nonlactating women, the predominant component of the breasts is fat, while glandular tissue is more abundant The thorax houses the heart and lungs, acts as a conduit in lactating women. for structures passing between the neck and the abdomen, The breast lies on deep fascia related to the pectoralis and plays a principal role in breathing. In addition, the major muscle and other surrounding muscles. A layer of thoracic wall protects the heart and lungs and provides loose connective tissue (the retromammary space) sepa­ support for the upper limbs. Muscles anchored to the rates the breast from the deep fascia and provides some anterior thoracic wall provide some of this support, and degree of movement over underlying structures. together with their associated connective tissues, nerves, The base, or attached surface, of each breast extends and vessels, and the overlying skin and superficial fascia, vertically from ribs II to VI, and transversely from the define the pectoral region. sternum to as far laterally as the midaxillary line. It is important for clinicians to remember when evaluat­ ing the breast for pathology that the upper lateral region PECTORAL REGION of the breast can project around the lateral margin of the pectoralis major muscle and into the axilla. This axillary The pectoral region is external to the anterior thoracic wall process (axillary tail) may perforate deep fascia and extend and anchors the upper limb to the trunk. It consists of: as far superiorly as the apex of the axilla. ■ a superficial compartment containing skin, superficial Arterial supply fascia, and breasts; and The breast is related to the thoracic wall and to structures ■ a deep compartment containing muscles and associ­ associated with the upper limb; therefore, vascular supply ated structures. and drainage can occur by multiple routes (Fig. 3.16): Nerves, vessels, and lymphatics in the superficial com­ ■ laterally, vessels from the axillary artery—superior tho­ partment emerge from the thoracic wall, the axilla, and the racic, thoraco­acromial, lateral thoracic, and subscap­ neck. ular arteries; ■ medially, branches from the internal thoracic artery; ■ the second to fourth intercostal arteries via branches Breast that perforate the thoracic wall and overlying The breasts consist of mammary glands and associated muscle. skin and connective tissues. The mammary glands are modified sweat glands in the superficial fascia anterior to the pectoral muscles and the anterior thoracic wall Venous drainage (Fig. 3.16). Veins draining the breast parallel the arteries and ulti­ The mammary glands consist of a series of ducts and mately drain into the axillary, internal thoracic, and inter­ associated secretory lobules. These converge to form 15 to costal veins. 20 lactiferous ducts, which open independently onto the nipple. The nipple is surrounded by a circular pigmented Innervation area of skin termed the areola. Innervation of the breast is via anterior and lateral cutane­ A well­developed, connective tissue stroma surrounds ous branches of the second to sixth intercostal nerves. The the ducts and lobules of the mammary gland. In certain nipple is innervated by the fourth intercostal nerve. 3-1 Drake_ch03_main.indd 17 8/25/2008 4:10:49 PM
  17. 17. Thorax Internal thoracic artery Pectoral branch of thoracoacromial artery Pectoralis major muscle Apical axillary nodes Central axillary nodes Secretory lobules Lateral thoracic artery Suspensory ligaments Lateral axillary nodes Lactiferous ducts Pectoral axillary nodes Lactiferous sinuses Axillary process Retromammary space Parasternal nodes Lymphatic and venous drainage passes from lateral and superior part of the breast into axilla Mammary branches of Areola internal thoracic artery Lymphatic and venous drainage passes from medial part Secretory of the breast parasternally lobules Lymphatic and venous drainage passes from inferior part of the breast into the abdomen Fig. 3.16 Breasts. Lymphatic drainage Axillary nodes drain into the subclavian trunks, para­ Lymphatic drainage of the breast is as follows: sternal nodes drain into the bronchomediastinal trunks, and intercostal nodes drain either into the thoracic duct or ■ approximately 75% is via lymphatic vessels that drain into the bronchomediastinal trunks. laterally and superiorly into axillary nodes (Fig. 3.16); ■ most of the remaining drainage is into parasternal nodes deep to the anterior thoracic wall and associated with the internal thoracic artery; and Breast in men ■ some drainage may occur via lymphatic vessels that The breast in men is rudimentary and consists only of follow the lateral branches of posterior intercostal small ducts, often composed of cords of cells, that normally arteries and connect with intercostal nodes situated do not extend beyond the areola. Breast cancer can occur 3-1 near the heads and necks of ribs. in men. Drake_ch03_main.indd 18 8/25/2008 4:10:53 PM
  18. 18. Regional anatomy •  Pectoral region 3 In the clinic Breast cancer Further imaging may include bone scanning using Breast cancer is one of the most common radioactive isotopes, which are avidly taken up by the malignancies in women. In the early stages, curative tumor metastases in bone. treatment may include surgery, radiotherapy, and Lymph drainage of the breast is complex. Lymph chemotherapy. vessels pass to axillary, supraclavicular, parasternal, and Breast cancer develops in the cells of the acini, abdominal lymph nodes, as well as the opposite breast. lactiferous ducts, and lobules of the breast. Tumor Containment of nodal metastatic breast cancer is growth and spread depends on the exact cellular site of therefore potentially difficult because it can spread origin of the cancer. These factors affect the response to through many lymph node groups. surgery, chemotherapy, and radiotherapy. Breast tumors Subcutaneous lymphatic obstruction and tumor spread via the lymphatics and veins, or by direct growth pull on connective tissue ligaments in the breast invasion. resulting in the appearance of an orange peel texture When a patient has a lump in the breast, a diagnosis of (peau d’orange) on the surface of the breast. Further breast cancer is confirmed by a biopsy and histological subcutaneous spread can induce a rare manifestation of evaluation. Once confirmed, the clinician must attempt to breast cancer that produces a hard, woody texture to the stage the tumor. skin (cancer en cuirasse). Staging the tumor means defining the: A mastectomy (surgical removal of the breast) involves excision of the breast tissue to the pectoralis major muscle ■ size of the primary tumor; and fascia. Within the axilla the breast tissue must be ■ exact site of the primary tumor; removed from the medial axillary wall. Closely applied to ■ number and sites of lymph node spread; and the medial axillary wall is the long thoracic nerve. Damage ■ organs to which the tumor may have spread. to this nerve can result in paralysis of the serratus anterior Computed tomography (CT) scanning of the body may muscle producing a characteristic “winged” scapula. It is be carried out to look for any spread to the lungs also possible to damage the nerve to the latissimus dorsi (pulmonary metastases), liver (hepatic metastases), or muscle, and this may affect extension, medial rotation, bone (bony metastases). and adduction of the humerus. Muscles of the pectoral region Pectoralis major adducts, flexes, and medially rotates Each pectoral region contains the pectoralis major, pecto­ the arm. ralis minor, and subclavius muscles (Fig. 3.17 and Table 3.1). All originate from the anterior thoracic wall and Subclavius and pectoralis minor insert into bones of the upper limb. The subclavius and pectoralis minor muscles underlie pectoralis major: Pectoralis major The pectoralis major muscle is the largest and most ■ subclavius is small and passes laterally from the ante­ superficial of the pectoral region muscles. It directly rior and medial part of rib I to the inferior surface of the underlies the breast and is separated from it by deep fascia clavicle; and the loose connective tissue of the retromammary ■ pectoralis minor passes from the anterior surfaces of space. ribs III to V to the coracoid process of the scapula. Pectoralis major has a broad origin that includes the anterior surfaces of the medial half of the clavicle, the Both subclavius and pectoralis minor pull the tip of the sternum, and related costal cartilages. The muscle shoulder inferiorly. fibers converge to form a flat tendon, which inserts A continuous layer of deep fascia, clavipectoral fascia, into the lateral lip of the intertubercular sulcus of the encloses subclavius and pectoralis minor and attaches to humerus. the clavicle above and to the floor of the axilla below. 3-1 Drake_ch03_main.indd 19 8/25/2008 4:10:53 PM
  19. 19. Thorax Subclavius Lateral pectoral nerve Pectoralis major Thoracoacromial artery Pectoralis minor Medial pectoral nerve Lateral thoracic artery Clavipectoral fascia Fig. 3.17 Muscles and fascia of the pectoral region. Table 3.1 Muscles of the pectoral region Muscle Origin Insertion Innervation Function Pectoralis major Medial half of clavicle and anterior surface of Lateral lip of Medial and Adduction, medial rotation, and sternum, first seven costal cartilages, intertubercular lateral pectoral flexion of the humerus at the aponeurosis of external oblique sulcus of humerus nerves shoulder joint Subclavius Rib I at junction between rib and costal Groove on inferior Nerve to Pulls clavicle medially to stabilize cartilage surface of middle subclavius sternoclavicular joint third of clavicle Pectoralis minor Anterior surfaces of the third, fourth and Coracoid process of Medial pectoral Depresses tip of shoulder; fifth ribs, and deep fascia overlying the scapula nerves protracts scapula related intercostal spaces The muscles of the pectoral region form the anterior pectoral region and the axilla pass through the clavipec­ wall of the axilla, a region between the upper limb and toral fascia between subclavius and pectoralis minor or the neck through which all major structures pass. pass under the inferior margins of pectoralis major and Nerves, vessels, and lymphatics that pass between the minor. 3-20 Drake_ch03_main.indd 20 8/25/2008 4:10:57 PM
  20. 20. Regional anatomy •  Thoracic wall 3 Anterior Superior articular process Facet for articulation Superior Vertebral body with tubercle of rib Superior demifacet Vertebral Posterior Anterior foramen Pedicle Inferior Spinous process Lamina Facet for articulation Transverse process Inferior articular process Demifacets for articulation with tubercle of rib with head of ribs Posterior Superior view Superolateral view Fig. 3.18 Typical thoracic vertebra. THORACIC WALL (Fig. 3.18). The vertebral foramen is generally circular and the laminae are broad and overlap with those of the The thoracic wall is segmental in design and composed of vertebra below. The superior articular processes are skeletal elements and muscles. It extends between: flat, with their articular surfaces facing almost directly pos­ teriorly, while the inferior articular processes project ■ the superior thoracic aperture bordered by vertebra TI, from the laminae and their articular facets face anteriorly. rib I, and the manubrium of sternum; and The transverse processes are club shaped and project ■ the inferior thoracic aperture bordered by vertebra posterolaterally. TXII, rib XII, the end of rib XI, the costal margin, and the xiphoid process of sternum. Articulation with ribs A typical thoracic vertebra has three sites on each side for Skeletal framework articulation with ribs. The skeletal elements of the thoracic wall consist of tho­ racic vertebrae, intervertebral discs, ribs, and sternum. ■ Two demifacets (i.e., partial facets) are located on the Thoracic vertebrae superior and inferior aspects of the body for articulation There are twelve thoracic vertebrae, each of which is with corresponding sites on the heads of adjacent ribs. characterized by articulations with ribs. The superior costal facet articulates with part of the head of its own rib, and the inferior costal facet artic­ A typical thoracic vertebra ulates with part of the head of the rib below. A typical thoracic vertebra has a heart­shaped vertebral ■ An oval facet (transverse costal facet) at the end of body, with roughly equal dimensions in the transverse the transverse process articulates with the tubercle of and anteroposterior directions, and a long spinous process its own rib. 3-21 Drake_ch03_main.indd 21 8/25/2008 4:10:59 PM
  21. 21. Thorax Not all vertebrae articulate with ribs in the same fashion of its own rib—in other words, the head of rib I does not (Fig. 3.19): articulate with vertebra CVII; ■ similarly, vertebra TX (and often TIX) articulates only ■ the superior costal facets on the body of vertebra TI are with its own ribs and therefore lacks inferior demifacets complete and articulate with a single facet on the head on the body; ■ vertebrae TXI and TXII articulate only with the heads of their own ribs—they lack transverse costal facets and have only a single complete facet on each side of their bodies. Vertebra TI Ribs There are twelve pairs of ribs, each terminating anteriorly in a costal cartilage (Fig. 3.20). Although all ribs articulate with the vertebral column, only the costal cartilages of the upper seven ribs, known as true ribs, articulate directly with the sternum. The remaining five pairs of ribs are false ribs: Superior costal facet for head of rib I ■ the costal cartilages of ribs VIII to X articulate anteri­ orly with the costal cartilages of the ribs above; ■ ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs. Vertebra TX True ribs I–VII Intercostal space Costal cartilage Single complete costal facet for head of rib X Vertebra TXI False ribs VIII–XII Floating ribs No costal facet on transverse process Costal margin Fig. 3.19 Typical thoracic vertebrae. Fig. 3.20 Ribs. 3-22 Drake_ch03_main.indd 22 8/25/2008 4:11:03 PM
  22. 22. Regional anatomy •  Thoracic wall 3 A typical rib consists of a curved shaft with anterior and The shaft is generally thin and flat with internal and posterior ends (Fig. 3.21). The anterior end is continuous external surfaces. with its costal cartilage. The posterior end articulates with The superior margin is smooth and rounded, whereas the vertebral column and is characterized by a head, neck, the inferior margin is sharp. The shaft bends forward just and tubercle. laterally to the tubercle at a site termed the angle. It also The head is somewhat expanded and typically presents has a gentle twist around its longitudinal axis so that the two articular surfaces separated by a crest. The smaller internal surface of the anterior part of the shaft faces some­ superior surface articulates with the inferior costal facet on what superiorly relative to the posterior part. The inferior the body of the vertebra above, whereas the larger inferior margin of the internal surface is marked by a distinct facet articulates with the superior costal facet of its own costal groove. vertebra. The neck is a short flat region of bone that separates the head from the tubercle. Distinct features of upper and The tubercle projects posteriorly from the junction of lower ribs the neck with the shaft and consists of two regions, an The upper and lower ribs have distinct features (Fig. articular part and a nonarticular part: 3.22). ■ the articular part is medial and has an oval facet for Rib I articulation with a corresponding facet on the trans­ Rib I is flat in the horizontal plane and has broad superior verse process of the associated vertebra; and inferior surfaces. From its articulation with vertebra ■ the raised nonarticular part is roughened by ligament TI, it slopes inferiorly to its attachment to the manubrium attachments. of sternum. The head articulates only with the body of Rib I Head Neck Tubercle A Posterior Tubercle Angle Head Neck Internal surface Scalene tubercle Costal groove Grooves Costal cartilage External surface Anterior Costal B Neck cartilage Tubercle Crest Rib XII Non-articular surface Articular facets Articular facet Fig. 3.21 A typical rib. A. Anterior view. B. Posterior view of proximal end of rib. Fig. 3.22 Atypical ribs. 3-23 Drake_ch03_main.indd 23 8/25/2008 4:11:05 PM
  23. 23. Thorax vertebra TI and therefore has only one articular surface. Articular site Jugular notch Like other ribs, the tubercle has a facet for articulation with for clavicle the transverse process. The superior surface of the rib is Manubrium of sternum characterized by a distinct tubercle, the scalene tubercle, which separates two smooth grooves that cross the rib approximately midway along the shaft. The anterior Attachment Sternal angle site for rib I (manubriosternal groove is caused by the subclavian vein, and the posterior joint) groove is caused by the subclavian artery. Anterior and posterior to these grooves, the shaft is roughened by Articular muscle and ligament attachments. demifacets for rib II Rib II Rib II, like rib I, is flat but twice as long. It articulates with the vertebral column in a way typical of most ribs. Transverse ridges Rib X The head of rib X has a single facet for articulation with its own vertebra. Articular facets for ribs III –VI Body of Ribs XI and XII sternum Ribs XI and XII articulate only with the bodies of their own vertebrae and have no tubercles or necks. Both ribs are short, have little curve, and are pointed anteriorly. Articular facets Sternum for rib VII Xiphoid The adult sternum consists of three major elements: the process broad and superiorly positioned manubrium of sternum, the narrow and longitudinally oriented body of sternum, Fig. 3.23 Sternum. and the small and inferiorly positioned xiphoid process (Fig. 3.23). Manubrium of sternum The manubrium of sternum forms part of the bony framework of the neck and the thorax. The lateral margins of the body of the sternum have The superior surface of the manubrium is expanded articular facets for costal cartilages. Superiorly, each lateral laterally and bears a distinct and palpable notch, the margin has a demifacet for articulation with the inferior jugular notch (suprasternal notch), in the midline. aspect of the second costal cartilage. Inferior to this demi­ On either side of this notch is a large oval fossa for articu­ facet are four facets for articulation with the costal carti­ lation with the clavicle. Immediately inferior to this fossa, lages of ribs III to VI. on each lateral surface of the manubrium, is a facet for At the inferior end of the body of the sternum is a demi­ the attachment of the first costal cartilage. At the lower facet for articulation with the upper demifacet on the end of the lateral border is a demifacet for articulation seventh costal cartilage. The inferior end of the body of the with the upper half of the anterior end of the second sternum is attached to the xiphoid process. costal cartilage. Xiphoid process Body of the sternum The xiphoid process is the smallest part of the sternum. The body of the sternum is flat. Its shape is variable: it may be wide, thin, pointed, bifid, The anterior surface of the body of the sternum is often curved, or perforated. It begins as a cartilaginous struc­ marked by transverse ridges that represent lines of fusion ture, which becomes ossified in the adult. On each side of between the segmental elements called sternebrae, from its upper lateral margin is a demifacet for articulation with 3-2 which this part of the sternum arises embryologically. the inferior end of the seventh costal cartilage. Drake_ch03_main.indd 24 8/25/2008 4:11:07 PM
  24. 24. Regional anatomy •  Thoracic wall 3 intervertebral disc and separates the two articular surfaces Joints on the head of the rib. The two synovial compartments and Costovertebral joints the intervening ligament are surrounded by a single joint A typical rib articulates with: capsule attached to the outer margins of the combined articular surfaces of the head and vertebral column. ■ the bodies of adjacent vertebrae, forming a joint with the head of the rib; and Costotransverse joints ■ the transverse process of its related vertebra, forming a Costotransverse joints are synovial joints between the costotransverse joint (Fig. 3.24). tubercle of a rib and the transverse process of the related vertebra (Fig. 3.24). The capsule surrounding each joint is Together, the costovertebral joints and related liga­ thin. The joint is stabilized by two strong extracapsular liga­ ments allow the necks of the ribs either to rotate around ments that span the space between the transverse process their longitudinal axes, which occurs mainly in the upper and the rib on the medial and lateral sides of the joint: ribs, or to ascend and descend relative to the vertebral column, which occurs mainly in the lower ribs. The com­ ■ the costotransverse ligament is medial to the joint bined movements of all of the ribs on the vertebral column and attaches the neck of the rib to the transverse are essential for altering the volume of the thoracic cavity process; during breathing. ■ the lateral costotransverse ligament is lateral to the joint and attaches the tip of the transverse process to Joint with head of rib the roughened nonarticular part of the tubercle of The two facets on the head of the rib articulate with the the rib. superior facet on the body of its own vertebra and with the inferior facet on the body of the vertebra above. This joint A third ligament, the superior costotransverse liga- is divided into two synovial compartments by an intra­ ment, attaches the superior surface of the neck of the rib articular ligament, which attaches the crest to the adjacent to the transverse process of the vertebra above. Vertebra Joint capsule Superior Rib costotransverse ligament Disc Intra-articular ligament Vertebra Joint cavities Costotransverse ligament Lateral costotransverse ligament Joint with vertebral body Costotransverse joint Fig. 3.24 Costovertebral joints. 3-2 Drake_ch03_main.indd 25 8/25/2008 4:11:10 PM

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