CHEST WALL

The muscular, tendinous, and bony structures of the chest serve several functions. The chest wall must be rigid enough to protect the thoracic viscera and serve as a fixation point against which the muscles of the upper extremity and abdomen can work yet flexible enough to expand and contract with vigorous respirations.

With gentle respirations, the chest wall is a cylinder with the diaphragm as its piston. With inspiration, the diaphragm contracts, its dome is flattened, and, like a piston, it descends in the chest. This motion increases the volume of the thorax, and actively expands the lungs by drawing in air through the trachea. The lungs are very elastic and tend to collapse without outward forces keeping them expanded. With exhalation, the diaphragm relaxes, the elasticity of the lungs causes lung volume to decrease, and air is expelled. Ultimately, the tendency of the lung to collapse is countered by the outward force/rigidity of the chest wall. With vigorous respirations, the intercostal muscles, scalenes, and other accessory muscles of respiration elevate the ribs and increase the thoracic volume much more than usual. With vigorous respirations, the chest wall and diaphragm act in concert like a bellows increasing thoracic volume and then relaxing and allowing the elasticity of the lung to decrease thoracic volume.

The bony structures of the chest wall include 12 ribs, 12 thoracic vertebrae, and the sternum. All ribs articulate posteriorly with the transverse processes and vertebral bodies of their respective thoracic vertebrae and the vertebral body directly superior (Figure 1). Ribs 1 through 7 are called true ribs because they articulate anteriorly directly with the sternum through their own costal cartilage. Ribs 8, 9, and 10 are called false ribs because they articulate anteriorly to the costal cartilage of the rib above. This creates a construct of stairstepping costal cartilages, which ultimately articulates with the sternum and creates the costal arch or costal margin. Ribs 11 and 12 are called floating ribs because they do not articulate with any structure anteriorly (Figure 2). Rather, they attach to the abdominal wall musculature, primarily the internal oblique muscle.

Figure 1 Costovertebral junction. Lateral view showing two left ribs and three vertebrae. Note that ribs articulate with transverse process and body of one vertebrae and body of vertebrae above.

(Redrawn from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2005, figures 1.13–1.14, pp. 14–15.)

Figure 2 Bony chest wall. Anterior view.

(Redrawn from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figure 1.8, p. 9.)

Because ribs 1 through 10 are fixed anteriorly and posteriorly, they function much like a bucket handle (Figure 3A). When performing a tube thoracostomy, as you approach the sternum anteriorly and the transverse processes posteriorly, the size of the interspace becomes fixed and narrow. Laterally, away from these points of attachment, the ribs separate and the interspace opens. The widest portion of the interspaces can be found at the lateral apogee or “keystone” of the rib. Tube thoracostomies placed laterally will be easier to place through the interspace and more comfortable for the patient (Figure 3B). Also, when creating a thoracotomy, division of the intercostal muscles far anterior and posterior will create a larger working space without tearing the intercostal muscle or fracturing a rib with placement of the rib spreader. The skin need only be divided over the working space, not over the entire intercostal incision.

Figure 3 Bucket handle motion of ribs. Ribs are fixed anteriorly at the sternum and posteriorly at the vertebrae. The ribs will move like a “bucket handle.” The widest space between the ribs will be at the lateral apogee or “keystone.”

(Redrawn from Pearson FG, editor: Thoracic Surgery, 2nd ed. Philadelphia, Churchill Livingstone, 2002, figure 48-3, p. 1327.)

The sternum has three parts, the manubrium, the body, and the xiphoid process. The manubrium is thick and broad, articulating with the clavicle, first rib, and sharing the second rib articulation with the body of the sternum. The sternoclavicular articulation is the only bony articulation of the thorax to the shoulder girdle (see Figure 2). Understanding the angle of the clavicle, manubrium, and first rib is important in safe placement of central venous catheters into the subclavian vein. The subclavian vein and artery leave the arm and enter the thoracic inlet over the top of the first rib and under the clavicle. Once under the clavicle, a needle directed parallel to the clavicle and first rib will not enter the chest and cause a pneumothorax before finding the subclavian vein. A needle directed too steeply in its approach will quickly enter and exit the triangle where the subclavian vein is found, penetrate the intercostal space, and puncture the lung (Figure 4).

Figure 4 Central venous cannulation of subclavian vein. (A) The clavicle and rib cage form a triangle through which the subclavian vein courses. The vein runs roughly parallel to both the clavicle and the rib cage. (B) A needle, once passed under the clavicle, directed parallel to the rib cage and clavicle will have a far greater chance of finding the vein. A needle directed too steeply will enter and exit this triangle, penetrate the intercostal space, and puncture the lung.

(Redrawn from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figures 1.8, 6.29, pp. 9, 379.)

The second rib inserts into the sternomanubrial junction (angle of Louis). This can be easily palpated in most people as a horizontal ridge in the sternum or where the two planes that make up the sternum intersect (Figure 5). The interspace immediately below the angle of Louis is the second interspace. The angle of Louis serves as a landmark to rapidly locate the second rib and second interspace for placement of a catheter to decompress a tension pneumothorax or to place an anterior tube thoracostomy for an apical pneumothorax.

Figure 5 Sternum, lateral view. Angle of Louis can be palpated in the midline as a raised horizontal ridge or as the point where the plane of the manubrium and body intersect. The second rib articulates directly lateral to the angle of Louis.

(Redrawn from Gray’s Anatomy, 39th ed., figure 57.5, p. 954.)

The first rib is short, broad, flat, and arches sharply from posterior to anterior (Figure 6). The second rib is longer than but very similar to the first rib (Figure 7). The first slip of the serratus anterior muscle attaches to the second rib approximately one-third of the arc from posterior to anterior—this slip also attaches to the inferior aspect of the first rib. Posterior to this attachment, the scalenus posterior attaches to the second rib.

Figure 6 Right first rib.

(Adapted from Gray’s Anatomy, 20th ed., plate 124.)

Figure 7 Right second rib.

(Adapted from Gray’s Anatomy, 20th ed., plate 125.)

When performing a thoracotomy, counting ribs can identify the correct interspace. Once the latissimus dorsi muscle has been divided and the serratus anterior muscle divided or swept anterior, the scapula is elevated. Thin fibrous attachments hold the undersurface of the scapula to the chest wall. A hand placed deep to the scapula, posterior near the spine, and apically can palpate ribs. The first rib is identified by its conspicuously broad and flat contour. Inferior to this, the second rib can be identified by the attachment of the scalenus posterior muscle. This muscle body is palpable by sweeping the finger from posterior to anterior along the second rib (Figure 8). Less distinct will be the third rib, which seems to “turn the corner” from the apex of the chest to the lateral chest wall (Figure 9). In a lateral decubitus position, the tip of the scapula overlies the sixth interspace. In a male, the nipple overlies the fourth interspace.

Figure 8 Counting ribs. Once the rib cage is visualized, the scapula is elevated, and a hand placed posterior and superior to palpate and count ribs. Note that the first rib is broad, short, and flat; the second rib has the insertion of the scalenus posterior; and the third rib “turns the corner” from apex to lateral chest wall.

Figure 9 Third rib “turns the corner.” Anteroposterior chest radiograph illustrating how the rib cage forms a loose box with the third rib at a corner. Arrows denote third rib.

MUSCLES OF THE CHEST WALL

Integral to safe thoracentesis, placement of a tube thoracostomy, or a thoracotomy, is understanding the layers of the chest wall and the anatomy of the interspace.

The paired pectoralis major muscles cover the majority of the anterior chest wall. The pectoralis major muscle originates from the clavicle and anterior aspects of ribs 1 through 6 inserting on the proximal humerus. Its origin from the chest wall is broad and an anterior thoracotomy will divide or separate its fibers. Inferiorly, the rectus abdominus muscle inserts onto the costal cartilages of ribs 5 through 7 and the xiphoid process. Lateral to this, the muscle fibers of the external oblique insert onto ribs 5 through 12. The external oblique muscle interdigitates with the serratus anterior muscle as it inserts on ribs 1 through 8 (Figure 10). Most thoracotomies do not traverse the interspaces guarded by the rectus abdominus and external oblique. These muscles will be encountered with thoracoabdominal incisions crossing the costal margin.

Figure 10 Muscles of thorax: left lateral view.

(Adapted from Gray’s Anatomy, 20th ed., plate 392.)

Laterally and posteriorly, two musculo-fascial layers guard the ribs. The more superficial layer contains the latissimus dorsi muscle laterally. Posteriorly, at the ausculatory triangle, or posterior border of the latissimus dorsi, this layer becomes a thin but tough layer of fascia, which more posteriorly envelopes the trapezius muscle. The second musculo-fascial layer contains the serratus anterior muscle laterally, becoming a broader sheet of thin but tough fibrous tissue posteriorly and then becoming the rhomboid major muscle then the rhomboid minor muscle posteriorly and superiorly (Figure 11). A tube thoracostomy will traverse these muscle layers to reach the ribs and interspaces. Knowing where you are in these layers allows precious time to be saved in traversing them and getting to where you need to be to complete the procedure.

Figure 11 Muscles of the thorax. (A) Superficial layer containing latissimus dorsi m. and trapezius m. (B) Deep layer containing serratus anterior m., rhomboid major m., and rhomboid minor m.

(Redrawn from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figures 4.47, 4.48, 6.13, pp. 233, 234, 367.)

A typical tube thoracostomy is placed in the fifth interspace at the anterior axillary line. The muscle bodies traversed are thinner here. From superficial to deep, the surgeon will separate skin, subcutaneous fat, the latissimus dorsi/trapezius musculo-fascial layer, and then the serratus anterior musculo-fascial layer. At this depth, the shiny surface of the periosteum of the ribs and the oblique fibers of the external intercostal muscle can be seen. As discussed later, tube thoracostomies are performed over the superior aspect of the rib. It is much easier to locate the superior aspect of the rib when you do not have intervening layers of muscle and fascia.

A thoracotomy can be fashioned to divide or spare these muscles as needed in order to gain access to the rib cage. A full thoracotomy will divide the latissimus dorsi laterally and the trapezius posteriorly. The incision sweeps from horizontal across the lateral chest to vertical and parallel to the spine posteriorly (Figure 12). Deep to this layer, the serratus anterior can be swept anterior or divided. Posteriorly, the fascial layer coming off the serratus anterior is divided and then the rhomboid major and rhomboid minor muscles are divided. The innervation of the trapezius muscle and rhomboid muscles runs from medial to lateral. The more muscle body that is left medially, the more muscle function will be retained. Enough muscle needs to be left attached to the scapula to allow suture repair of the muscle, and the muscle should not be stripped from the scapula. The posterior and vertical aspect of this incision where the trapezius and rhomboids are divided is done to elevate the scapula off the chest wall, to access the interspaces underneath.

Figure 12 Full posterolateral thoracotomy.

(Redrawn from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, Figs. 4.47, 4.48, 6.13, pp. 233, 234, 367.)

A thoracotomy can be extended anterior, dividing the pectoralis major muscle overlying the interspace of interest. The sternum can be split transversely, and a thoracotomy continued on the contralateral side. This is termed a “clam shell” thoracotomy. The left and right mammary artery will be found 1 cm lateral to and on either side of the sternum, deep to the ribs and intercostal muscles, but superficial to the pleura. These vessels can be cauterized if speed is needed, but are prone to spasm and late bleeding, and should be sought and ligated when possible.

INTERCOSTAL SPACE

Each intercostal space from superficial to deep, has two layers of muscle; an artery, a vein, and a nerve; and a diminutive inner layer of muscle. The external intercostal muscles run obliquely with fibers in the same orientation as the external oblique muscle of the abdomen (fingers in pockets). Deep are the internal intercostal muscles running in the opposite direction. The intercostal artery, vein, and nerve run along the inferior aspect of each rib, occasionally running underneath a ledge in the costal groove. To avoid injury to these three structures, tube thoracostomies and thoracotomies are directed over the superior aspect of each rib or through the middle of the interspace, but not the inferior aspect of the rib (Figure 13). The innermost intercostal muscles are located deep to the neurovascular bundle and run in the same direction as the internal intercostal muscles. While mentioned in anatomy texts, surgically, the innermost intercostal muscles do not need to be considered separately from the internal intercostal muscle (Figure 14). The intercostal arteries originate as segmental branches off the descending aorta. The intercostal space, including the underlying pleura, can be harvested as a posteriorly based pedicled muscle flap (Figure 15). This flap is useful for reinforcing bronchial or esophageal repairs.

Figure 13 Technique for tube thoracostomy. Tubes placed emergently for trauma are placed along the anterior axillary line, fourth or fifth interspace. The intercostal space is entered on the superior aspect of the rib. Finger palpation confirms entrance into the pleural cavity and avoids inadvertent subscapular or intraabdominal placement of tubes as well as injury to adhesed lung.

(From Moore FA, Moore EE: Trauma resuscitation. In Wilmore DN, Brennan MF, Harken AH, et al., eds. Care of the Surgical Patient. New York, Scientific American, 1989.)

Figure 14 Intercostal space in cross-section. Note main intercostal bundle along the inferior aspect of the rib. The collateral nerve and artery, while present, are diminutive.

(Adapted from Crafts RC: A Textbook of Human Anatomy, 3rd ed., New York, John Wiley & Sons, 1985.)

Figure 15 (A) Intercostal muscle flap. Based on intercostal artery with pedicle posterior. (B) Transverse view of this flap.

The internal mammary artery originates from the subclavian arteries bilaterally, and descends on the inside of the chest wall, approximately 1 cm lateral to the sternum bilaterally (Figure 16).

Figure 16 Internal mammary arteries as viewed from inside the chest.

(From Pearson FG, editor: Thoracic Surgery, 2nd ed. Philadelphia, Churchill Livingstone, 2002, figure 48-8, p. 1330.)

PLEURAL SPACE

Normally the lung is coupled to the chest wall by the vacuum, which exists between the visceral and parietal pleura. With penetration of the chest wall air is allowed into the pleural space from the outside or more commonly, penetration of the lung allows air to escape from air spaces within the lung (alveoli, bronchioles, bronchi) into the pleural space. The coupling of the visceral and parietal pleura is broken and the potential space, which is the pleural space, becomes a real space. The elasticity of the lung causes it to collapse and a pneumothorax is formed. The pleural space extends superiorly to where it rises above the circumference of the first rib to inferiorly where the diaphragm inserts on the costal margin and the 12th rib. Lung may or may not be present between the diaphragm and ribs in the lower most recesses of the pleural space. Anterior to the pericardium and posterior to the sternum, the two pleural cavities can abut but rarely communicate.

DIAPHRAGM

The diaphragm is the movable dome-shaped partition between the thoracic and abdominal cavities. With full exhalation, the dome of the diaphragm can rise to the level of the fourth interspace anteriorly (nipple level). With full inhalation, the diaphragm flattens, bringing the thoracic cavity down to the level of the costal margin anteriorly and the 12th rib posteriorly. The muscle fibers of the diaphragm originate from the sternum, the ribs, and the vertebral column. All three groups insert on a tough, fibrinous central tendon. Fibers of the sternal portion are short, arising as small slips from the back of the xiphoid process. Laterally on either side of the xiphoid, fibers originate from the inner surface of the lower six costal cartilages (costal margin). Posteriorly, fibers originate from a thick band arching over the quadratus lumborum (lateral arcuate ligament) and the psoas major (medial arcuate ligament). The paired lateral arcuate ligaments extend from the tip and lower margin of the 12th ribs and arch over the quadratus lumborum muscle to the transverse processes of L1. The paired medial arcuate ligaments complete the journey, arching over the psoas major from the tip of the transverse process of the first lumbar vertebrae to the tendinous portion of each diaphragmatic crus (Figure 17).

Figure 17 Diaphragm as viewed from the abdomen. The diaphragm originates bilaterally from the xiphoid process, costal margin, lateral arcuate ligament, and medial arcuate ligament, and inserts into the central tendon. The left and right crus originate from the lumbar vertebral bodies and insert into the central tendon.

(Adapted from Langley LL, Telford IR, Christensen JB: Dynamic Anatomy and Physiology, 5th ed., New York, McGraw-Hill, 1980.)

The posterior medial portion of the diaphragm is composed of two crura—an anatomic right crus originating from the upper three lumbar vertebral bodies and an anatomic left crus originating from the upper two lumbar vertebral bodies. Anterior to the aorta, the medial margins of the two crura form a poorly defined arch called the median arcuate ligament. Anterior to this arch, either the anatomic right crus (64%) or the anatomic left crus (2%) or both (34%) form the esophageal hiatus. While anatomists name the crura left or right by their origin from the left or right side of the vertebral bodies, surgeons name the crura left or right by their relationship to the esophagus. In the abdomen, visualization of the esophagus and division of the crus running to the left of the esophagus will expose the distal thoracic aorta above the level of the celiac artery and renal arteries. A clamp can be applied here to obtain vascular control. Alternatively, a retractor wrapped with a laparotomy pad can be used in this position to occlude the aorta by compressing it against the posteriorly located vertebral body (Figure 18).

Figure 18 Cross-clamping of distal descending thoracic aorta from abdomen. (A) Left crus divided and thoracic aorta found deep. (B) Lateral view, aorta occluded by compression against vertebral body.

The phrenic nerve and twigs from the lower intercostal nerves innervate the diaphragm. The phrenic nerve originates primarily from the C4 nerve root, but receives innervation from C3 and C5 (C3, C4, and C5 keep the body alive). In the neck, the phrenic nerve originates lateral to the scalenus anterior muscle and descends from lateral to medial on the superficial surface of this muscle, deep to the sternocleidomastoid muscle. It enters the thoracic inlet and is found on the medial aspect of the mediastinum just deep to the pleura bilaterally. Superiorly, it is very anterior in the chest and vulnerable to injury, especially with a median sternotomy and dissection of the great vessels where it is often not readily visible in the wound, but very close to the dissection. On the left, it descends outside the pericardium, deep to the pleura, passing over the arch of the aorta, anterior to the hilum of the lung, and anterior to the inferior pulmonary ligament. As it nears the diaphragm, it is often invested in a veil of pericardial fat, hanging like a curtain between the pericardium and the diaphragm. The nerve reaches the diaphragm just lateral to the left border of the heart and in a plane slightly more anterior than the right phrenic nerve (see Figure 33). The right phrenic nerve descends along the right lateral border of the superior vena cava, passes anterior to the hilum of the lung, and anterior to the inferior pulmonary ligament. It is also invested in a veil of pericardial fat as it approaches the diaphragm. The right phrenic nerve enters the diaphragm just lateral to the inferior vena cava (see Figure 32).

Figure 33 Hilum of left lung. Dotted line marks incision for pericardial window.

(Adapted from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figure 1.44, p. 44.)

Figure 32 Hilum of right lung. Dotted line marks incision for pericardial window from right chest.

(Redrawn from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figure 1.43, p. 40.)

Both left and right phrenic nerves immediately trifurcate into three muscular branches after entering the hemi-diaphragm. One is directed anterior-medially toward the sternum, one anterior-laterally, and a third posteriorly. The posterior branch bifurcates into a branch directed toward the 12th rib and one toward the crus. Safe incisions in the diaphragm are fashioned to avoid cutting major branches of the phrenic nerve (Figure 19). A peripheral and circumferential incision will avoid all but distal twigs of the phrenic nerve. Radial incision can be placed but must be done with care to avoid major branches of the phrenic nerve.

Figure 19 Diaphragmatic incisions and branches of the phrenic nerve. Incisions are fashioned to avoid denervating large portions of the diaphragm.

(From Meredino KA, Johnson RS, Skinner HH, et al: The intradiaphragmatic distribution of the phrenic nerve with particular reference to the placement of diaphragmatic incisions and controlled segmental paralysis. Surgery 39:189, 1956.)

Because the primary innervation of the diaphragm, the phrenic nerve, enters centrally and spreads centrifugally, the diaphragm can be transposed to higher or lower origins from the thoracic cage while maintaining its innervation. This is occasionally required in repair of a diaphragmatic rupture when surface area of the diaphragm is lost or the chest wall has lost its rigidity and can no longer subserve its cylinder function. Care should be taken to maintain a dome shape to the diaphragm. A diaphragm that is flattened at rest will pull the walls of the thorax closer together when contracting. With contraction, instead of increasing intrathoracic volume, the diaphragm will now decrease intrathoracic volume and become a muscle of expiration (Figure 20).

Figure 20 A hemidiaphragm that is flattened when relaxed, when contracting draws the rib cage in and causes expiration, not inspiration.

PERICARDIUM

The pericardial space is considerably smaller than the pleural space and a small increase in the volume of fluid in this space can have a dramatic impact on cardiac function. The parietal pericardium is a thick, fibrous sac with an inner serosal surface containing the heart, the proximal ascending aorta, the distal superior vena cava, the distal inferior vena cava, the pulmonary trunk and bifurcation, proximal left and right main pulmonary arteries, and a short segment of all four distal pulmonary veins. From this description, it can be visualized that all vessels flowing into and out of the heart have short segments contained in the pericardial sac (Figure 21). It is also these vascular structures, which fix the heart in the pericardial sac. If the heart is allowed to rotate, these structures will be twisted or kinked, impeding blood flow. Because they are the lowest pressure conduits, the superior vena cava and inferior vena cava are the most vulnerable to kinking and impedance of flow. With decreased blood flow into the heart, there is decreased blood flow out of the heart, and systemic blood pressure falls. This is the physiology of hypotension associated with tension pneumothorax and with cardiac herniation.

Figure 21 Pericardial sac, posterior and lateral aspects. Anterior pericardial sac has been removed. Heart has been removed.

(Adapted from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figure 1.61, p. 55.)

There are two sinuses behind the heart. The oblique pericardial sinus is a cul-de-sac behind the heart bounded by pericardial attachments to the inferior vena cava and the four pulmonary veins. Because of the oblique sinus, with a median sternotomy, a hand can be placed around the apex of the heart and the apex gently elevated into the wound. This allows visualization of the lateral and posterior walls of the left ventricle, including the vascular distribution of the diagonal, circumflex, and obtuse marginal coronary arteries. This maneuver is generally poorly tolerated without opening the right pericardium vertically, parallel to the phrenic nerve. This allows the right heart to fall into the right pleural space and maintain filling as the heart is lifted. In addition, severe Trendelenburg and an apically placed suction retraction device will aid exposure and improve hemodynamics. Internal defibrillating paddles should be open and ready prior to performing this maneuver, as ventricular fibrillation is not uncommon.

The transverse pericardial sinus allows a finger or clamp to be placed along the right side of the ascending aorta, behind the aorta and pulmonary trunk, and be visualized to the left of the pulmonary trunk and superior to the left superior pulmonary vein in the vicinity of the left atrial appendage (see Figure 21).

The pericardium can be drained through a median sternotomy, left or right thoracotomy, subxiphoid approach, or laparotomy. From a left or right thoracotomy, an incision is made anterior or posterior to and parallel to the phrenic nerve. From the left chest the left ventricle and from the right chest the right atrium will be encountered in the pericardial space behind these incisions (Figure 22).

Figure 22 Approaches to a pericardial window. The pericardium can be opened from (A) left thoracotomy, (B) right thoracotomy, (C) median sternotomy, (D) subxiphoid, or (E) abdominal approach.

(Adapted from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figure 1.49.)

From a laparotomy, a modification of the subxiphoid approach can be used to enter the pericardium. Alternatively, the central portion of the diaphragm makes up the inferior fibrous parietal pericardial sac. An incision in the diaphragm in this location will enter the pericardial sac, visualizing the inferior wall of the heart.

Subxiphoid Space

The subxiphoid space is a favored access to the pericardium for diagnosis and treatment of pericardial effusions. Both the linea alba and the diaphragm attach to the xiphoid. The peritoneum on the diaphragm is continuous with the peritoneum on the deep surface of the posterior fasciae of the anterior abdominal wall. An incision from above the xiphoid process to 4 cm below will pass through skin, fat, and linea alba. Incising the linea alba will reveal the xiphoid superiorly and the peritoneum inferiorly. The diaphragmatic attachments to the xiphoid can be divided flush with the xiphoid and the xiphoid resected to the level of the sternal body/costal margin. A large vein is routinely encountered at the angle between the xiphoid, costal margin, and sternal body. Posterior retraction of the diaphragm and superior retraction of the sternum will reveal the pericardial reflection on the diaphragm. Incising the pericardium will enter the pericardial space. The acute margin of the right ventricle will be visible through this incision (Figure 23). Since this incision is at the corner where two perpendicular planes meet, fluid can be aspirated in two directions. First, straight posterior, parallel to the diaphragm, along the inferior border of the heart, and second, superior, parallel to the sternal body, anterior to the anterior surface of the heart (Figure 24).

Figure 23 Subxiphoid space.

Figure 24 Subxiphoid pericardial window.

HEART

The heart occupies the central and left portion of the thorax and is the primary content of the middle mediastinum. It is bounded on all sides by the parietal pericardium. Outside this pericardium, it is bounded anteriorly by the sternum and posteriorly by the esophagus, vertebral column and descending aorta. On the right, mediastinal pleura and lung are present with the phrenic nerve running just anterior to the hilum of the lung. On the left, the same structures are present but the phrenic nerve runs more anteriorly. Extra care is required to protect this nerve when the heart is approached from the left.

Body Surface Markings for Heart

The surface projection of the superior border of the heart is a line joining a point 2 cm lateral to the sternum in the left second intercostal space to a point just to the right of the sternum in the same space. This marks the line of the main pulmonary arteries. The right border extends inferiorly to the sixth costal cartilage adjacent to the sternum. This is formed by the right atrium. The inferior border extends from the right sixth costal cartilage to the point of maximum cardiac impulse, which is usually in the left fifth intercostal space just medial to the mid-clavicular line. The right ventricle forms the inferior border. The left border extends superiorly to the second intercostal space 2 cm lateral to the sternal edge. The left ventricle forms the left border (Figure 25).

Figure 25 Surface projections of heart and lungs.

(Adapted from Gray’s Anatomy, 20th ed., plates 1216, 1218.)

External Features

The heart consists of four chambers divided by three grooves. The atrioventricular groove contains the coronary sinus, which is the largest vein of the heart and lies posteriorly opening into the right atrium. The interatrial groove is covered anteriorly by the ascending aorta and the main pulmonary artery. The interatrial groove is visible to the right of the heart as a fatty line between the superior vena cava and right superior pulmonary vein. The interventricular groove runs anteriorly toward the apex and contains the great cardiac vein. Posteriorly, it continues along the inferior surface of the heart toward the right margin and contains the middle cardiac vein. The heart has five surfaces, anterior, posterior, inferior, and a right and left. The anterior surface is formed primarily by the right ventricle and the right atrium, and is therefore at risk from any frontal injury. Two-thirds of the right atrium and ventricle face anteriorly. The posterior surface or the base of the heart is formed by the left and right atria. The two pulmonary veins on either side, inferior and superior, open into the left atrium at this posterior location. The superior and inferior vena cava open into the right atrium. The posterior surface of the heart is related to the sixth through the ninth thoracic vertebrae being separated from them only by the pericardium, right pulmonary veins, esophagus, and aorta (from right to left). One-third of the right ventricle and two-thirds of the left ventricle form the inferior or diaphragmatic surface of the heart. This part of the heart is in contact with the central portion of the diaphragm. The right atrium and the right ventricle form the right surface of the heart. They are related to the pericardium, the right lung, and the right phrenic nerve just anterior to the hilum. The left ventricle and the left atrium form the left surface. They are related to the same structures as on the right but the phrenic nerve runs across the middle of the surface (Figure 26).

Figure 26 Heart. (A) Anterior. (B) Posterior.

(Adapted from Gray’s Anatomy, 39th ed., plate 970, and figure 60.2.)

Coronary Arteries and Veins

Right and left coronary arteries arise from the ascending aorta. The right coronary artery supplies the right atrium, the right ventricle, the posterior one-third of the interventricular septum and the inferior portion of the septum. The left coronary artery supplies the left atrium, the left ventricle and the anterior two-thirds of the interventricular septum. Collateral circulation in the heart is minimal therefore occlusion of a coronary artery results in a specific area of myocardial infarction and dysfunction (Figure 27).

Figure 27 Coronary arteries. LCA, Left coronary artery; LAD, left anterior descending; LCx, left circumflex; D, diagonal branch of LAD; OM, obtuse marginal branch of LCx; RCA, right coronary artery; AM, acute marginal branch of right coronary artery; PDA, posterior descending coronary artery; AVNA, AV nodal artery.

The named coronary arteries travel just under the epicardium, superficial to the myocardium. Lacerations close to a coronary artery, but not including the artery, can be repaired with unpledgeted horizontal mattress sutures of Halsted. Alternatively, pledgeted horizontal mattress sutures may also be used, placed under the coronary bed, effectively repairing the myocardium but not occluding the coronary artery (Figure 28). Care should be taken in placing and tying the suture so as not to kink the coronary by incorporating too much myocardium. If the left anterior descending artery is the adjacent vessel being avoided, it is possible with this suture to occlude a major septal perforator diving deep to the vessel.

Figure 28 Repair of a cardiac laceration near a coronary artery.

The venous system of the heart is centered on the coronary sinus, which receives the tributaries from the different areas of the heart and drains into the posterior aspect of the right atrium just superior to the tricuspid valve (see Figure 26B).

Conduction System

The sinoatrial node is the pacemaker of the heart and is located just to the right and anterior to the opening of the superior vena cava. The impulses are transmitted to the atrioventricular node through the wall of the atrium. The atrioventricular node is situated in the posteroinferior portion of the interatrial septum just superior to the opening of the coronary sinus. From here the impulses travel through the bundle of His (atrioventricular bundle) along the posterosuperior edge of the muscular interventricular septum to the right and left bundle branches. These run through the interventricular septum to the papillary muscles in the left and right ventricle and then form a subendocardial network (Purkinje fibers) (Figure 29).

Figure 29 Cardiac conduction system.

(Adapted from Gray’s Anatomy, 20th ed., plate 501.)

Internal Features of Heart Chambers

The right atrium has a smooth-walled posterior aspect onto which the vena cava and the coronary sinus open. Anteriorly, the wall is trabeculated muscle. Posteromedially is the interatrial septum with a depression called the fossa ovalis, which marks the previous foramen ovale or communication between the atria that existed in utero. Anteroinferiorly is the orifice of the tricuspid valve opening into the right ventricle.

The right ventricle is triangular in shape and muscular with an inflow area from the tricuspid valve and an outflow area, which is smooth leading to the pulmonary valve.

The ventricular wall gives rise to three (anterior, posterior, septal) conical projections of the papillary muscles. Tendinous structures arise from the apex of each of these to attach to cusps of the tricuspid valve. Injury to any portion of the valve apparatus can give rise to incompetence of the valve. Placed medially and obliquely is the interventricular septum separating the two ventricles.

The left atrium is quadrangular in shape and has smooth walls. The left atrial appendage projects to the left and is the only portion of the atrium that can be seen anteriorly. The openings of the veins lie posteriorly on the left and right. The interatrial septum lies to the right and slopes posteriorly making the left atrium lie behind the right atrium. The mitral valve orifice lies in the anteroinferior part of the atrium (Figure 30).

Figure 30 Left and right heart chamber anatomy.

(Adapted from Gray’s Anatomy, 20th ed., plate 498.)

The left ventricle is muscular and has an inflow area from the mitral orifice and an outflow area to the aortic root. The ventricular wall gives rise to anterior and posterior papillary muscles that have chordae tendineae that attach to the anterior and posterior mitral valve leaflets (cusps). The anterior leaflet separates the inflow of the mitral valve orifice from the outflow of the aortic root. The aortic orifice is therefore positioned anterior to the mitral orifice. The interventricular septum is present to the right and anteriorly (see Figure 30).

ANATOMY OF PULMONARY ARTERY/SWAN-GANZ CATHETER PLACEMENT

A pulmonary artery catheter is usually introduced via the subclavian or internal jugular vein but the femoral vein can also be used. The catheter passes through these veins into the superior or inferior vena cava and then into the right atrium. The flow of blood carries the tip through the tricuspid valve orifice into the right ventricle and then through the right ventricular outflow tract and the pulmonary valve into the main pulmonary artery. Due to the orientation of the right main pulmonary artery to the pulmonary trunk the catheter tends to pass to the right preferentially and lodge in the distal pulmonary artery.

Occasionally the catheter may pass into the inferior vena cava or the coronary sinus while traversing the right atrium. Entry into the coronary sinus can be recognized by loss of right atrial tracing soon after it appears. Persistence of this tracing after considerable length of the catheter has been introduced suggests coiling within the atrium or passage into the inferior vena cava.

Traditional instruction on pulmonary artery catheter placement includes orienting the coil of the catheter such that it enters the atrium from the SVC and is directed toward the tricuspid valve. The coil of the catheter is oriented on a coronal plane with the tricuspid valve perceived to be a hole in a sagittal plane (Figure 31A). The tricuspid valve, however, truly exists on a plane rotated 40–50 degrees off the sagittal plane (Figure 31B). In a patient lying supine, blood flows from a right posterior position in the right atrium, through the tricuspid valve diagonally anterior and to the left. The coil of the catheter should therefore have its tip directed 40–50 degrees toward the ceiling rather than straight toward the left wall. The right ventricular outflow tract, however, is in the sagittal plane. Once the pressure tracing indicates the tip of the catheter is in the right ventricle, it should be rotated counterclockwise such that the coil is directed toward the left wall.

Figure 31 Placement of pulmonary artery catheter. (A) Traditional placement of coil is directed toward the wall to the patient’s left on a coronal plane, perceiving the tricuspid valve as an opening on a sagittal plane. (B) Tricuspid valve is actually an opening on a plane 40–50 degrees off the sagittal plane, and correct orientation will direct the catheter 40–50 degrees more toward the ceiling.

HILUM OF LUNG

The hilum of the lung is the point where the airway and pulmonary artery enter the lung and the pulmonary veins leave. It represents a fixed point where the relatively mobile lung is tethered to the mediastinum. The reflection of the visceral onto parietal pleura occurs at the hilum, adding additional support.

Much thoracic surgery is done through exposures retracting the lung anterior or posterior or looking directly at the anterior or posterior surface of the hilum. Bilaterally, the respective phrenic nerves run anterior to the hilum. On the right (Figure 32), the esophagus, vagus nerve, thoracic duct, and azygous veins are posterior. On the left (Figure 33), the descending aorta, esophagus, and vagus nerve are posterior.

Right Hilum

The inferior pulmonary ligament is a reflection of the visceral pleura of the medial aspect of the right lower lobe. This ligament attaches the lung to the mediastinum. Dividing this ligament will bring the right lower lobe into view for inspection or repair through a standard fifth interspace thoracotomy. The ligament should be divided as close to the lung as possible without injuring lung parenchyma to avoid injury to the underlying thoracic duct, esophagus, and vagus nerve. The superior most aspect of the inferior pulmonary ligament is the inferior pulmonary vein. This can be visualized as a reflection of the pericardium into the lung. A lymph node will often guard the inferior pulmonary vein at the top of this ligament.

At the superior aspect of the right hilum is the azygous vein coursing posterior to anterior to join the backside of the superior vena cava. Deep to the azygous vein the trachea bifurcates. Traveling under or medial to the azygous vein is anteriorly the right main stem bronchus and posteriorly the esophagus. The right main pulmonary artery enters the right chest underneath the superior vena cava just inferior to the azygous vein and anterior to the trachea and right mainstem bronchus. The right main pulmonary artery travels further than the left main pulmonary artery before reaching the pleural space and before branching. After entering the right chest, the pulmonary artery takes an abrupt turn inferior into the deepest part of the horizontal and oblique fissures. It gives off branches to the right upper lobe, right middle lobe, and right lower lobe, respectively. It should be remembered that the pulmonary artery branches distally into the lung like a deciduous tree. Larger vessels will be found close to the hilum and in the horizontal and oblique fissures. Progressively smaller vessels will be found as you approach the outer surface of the lung (Figure 34). The first branch of the right main pulmonary artery goes to the right upper lobe. This branch may come off the pulmonary artery very proximal and course under the superior vena cava separate from the main pulmonary artery. This branch is often located just anterior to the right upper lobe bronchus, and just inferior to the azygous vein as it arches over the hilum. In this location, it is very susceptible to iatrogenic traction injury by too vigorously pulling the lung inferior.

Figure 34 Generic bronchopulmonary segment.

(From Pearson FG, editor: Thoracic Surgery, 2nd ed. Philadelphia, Churchill Livingstone, 2002, figure 20-1, p. 428.)

Proximal vascular control of the right pulmonary artery can be obtained as it courses under the superior vena cava either by encircling the vessel with a vessel loop, careful vascular clamping (Figure 35), or if needed, applying a nonselective clamp across the entire hilum (Figure 36). A nonselective clamp is sometimes referred to as “dirty” clamping because the immediate need is control of hemorrhage and structures other than the offending vessel may initially be included in the clamp.

Figure 35 Clamping the right main pulmonary artery as it courses under the superior vena cava.

Figure 36 “Dirty” clamping of the left or right pulmonary hilum.

(From Pearson FG, editor: Thoracic Surgery, 2nd ed. Philadelphia, Churchill Livingstone, 2002, figure 68-3, p. 1837.)

From the right chest or a median sternotomy, the superior vena cava and inferior vena cava can be clamped. This is termed inflow occlusion and will cause cardiac standstill that can be tolerated no more than 3–5 minutes. In desperate circumstances, this allows time and visualization to obtain vascular control of a large hemorrhage such as from a main or branch pulmonary artery. Once the hemorrhage is contained, blood should be allowed to return to the heart before performing a definitive repair. Cardioversion will be necessary if the heart has fibrillated and should be anticipated.

The remaining vascular structure making up the hilum of the right lung is the superior pulmonary vein. This vein is seen anteriorly, sending a superior branch to the upper lobe, which crosses anterior to the pulmonary artery traveling in the horizontal fissure and variable branches to the right middle lobe.

The right mainstem bronchus can be visualized on the posterior superior right hilum. It bifurcates from the carina and travels underneath the azygous vein. While visualizing the bronchus from the posterior hilum, the delicate membranous airway is seen, with the bases of the arching bronchial cartilages visible and palpable on either side.

LUNG ANATOMY

The right lung has three lobes, the right upper, right middle, and right lower. The left lung has two lobes, the left upper and left lower. The lingula of the left upper lobe is analogous to the middle lobe on the right. Fissures of the lung are usually present, but variably complete. On the right, the horizontal fissure, usually incomplete, divides the right upper lobe from the right middle lobe. The horizontal fissure joins the oblique fissure posteriorly. The oblique fissure divides the right upper lobe from the superior segment of the right lower lobe and the right middle lobe from the right lower lobe. The right lower lobe rests on the diaphragm posteriorly. The right middle lobe will often rest on the diaphragm anteriorly and is mistaken for the right lower lobe in this position. On the left, the oblique fissure divides the left upper lobe from the left lower lobe. The left lower lobe rests on the diaphragm posteriorly. The lingula of the left upper lobe can extend down to the diaphragm anteriorly.

Figure 37 shows the lung segments. Pulmonary arteries and the airway will enter the middle of their respective lung segment and bifurcate toward the periphery. Pulmonary veins travel in the border zones between lung segments and along the walls of the horizontal and oblique fissures (see Figure 34).

Figure 37 Segmental anatomy of the lung.

(From Pearson FG, editor: Thoracic Surgery, 2nd ed. Philadelphia, Churchill Livingstone, 2002, figure 20-2, p. 428.)

AORTA, TRACHEA, ESOPHAGUS, AND THORACIC DUCT

Posterior to the heart, outside the pericardium, several tubular structures travel parallel to each other. They are the aorta, trachea, esophagus, and thoracic duct (Figure 38).

Figure 38 Aorta, trachea, esophagus, and thoracic duct.

(Adapted from Grant’s Atlas of Anatomy, 11th ed., Philadelphia, Lippincott Williams & Wilkins, 2004, figure 1.78, p. 68.)

TRACHEA

The trachea begins in the neck at the cricoid cartilage, enters the thorax anterior to the esophagus and posterior to the great vessels, including posterior to the arch and ascending aorta and the pulmonary arteries. Distally, near the carina, the arch of the aorta crosses to the left of the trachea. The trachea bifurcates into the right and left mainstem bronchi at the carina. The carina is at the level of the angle of Louis anteriorly and T4/T5 posteriorly. The average adult trachea is 11 cm in length and varies according to the height of the person. In a young person, hyperextension of the neck can bring 50% of the trachea out of the chest and into the neck. Conversely, in a kyphotic elderly patient, the cricoid cartilage can be at the level of the sternal notch. In the neck, the trachea is anterior and subcutaneous. As it enters the chest, it travels obliquely posterior to the posterior mediastinum. The shortest distance from a point to a line is a perpendicular from that line, intersecting the point. If the trachea is a line, obliquely posterior, the shortest distance from a point on the skin to the trachea will be in a trajectory slightly superior. Visualizing this relationship aids in tracheostomy and cricothyroidotomy incisions (Figure 39). The trachea is composed anteriorly of cartilaginous arches with fibrous tissue in between. The posterior wall of the trachea is membranous. The blood supply to the trachea is segmental, superiorly primarily from the inferior thyroidal arteries and inferiorly from the bronchial arteries. The subclavian artery, highest intercostal artery, internal thoracic arteries, and innominate artery also supply it. These vessels also supply the esophagus. The blood supply enters the trachea laterally at 3 and 9 o’clock.

Figure 39 Trachea travels diagonally posterior as it leaves the neck and enters the chest. The shortest distance between a point and a line is perpendicular to that line through the point.

ESOPHAGUS

The esophagus travels through the posterior mediastinum anterior to the vertebral bodies, to the right of the descending aorta, and to the left of the azygous vein (see Figure 38). Its blood supply is from segmental branches of the descending aorta, draining into intercostal veins. Above the level of the carina, the esophagus is posterior to the trachea and immediately abuts the membranous trachea. Above the level of the ligamentum arteriosum, the recurrent laryngeal nerve travels in the left tracheoesophageal groove. Above the level of the right brachiocephalic artery the right recurrent laryngeal nerve travels in the right tracheoesophageal groove. Below the carina, the esophagus directly abuts the posterior pericardium. To its left and right from superior to inferior are the superior pulmonary veins, the inferior pulmonary veins, and the inferior pulmonary ligaments. The esophagus enters the diaphragm through the esophageal hiatus at the level of T10 or T11. The area to the left and right of the esophagus at and below the inferior pulmonary ligament and before entering the diaphragm represents an anatomic weak spot. The wall of the esophagus is not buttressed by other firm mediastinal structures and is exposed to the negative pressure of the pleural space. It is for this reason that increased intraesophageal pressure causing a perforation of the esophagus most commonly occurs here (Boerhaave’s syndrome).

THORACIC DUCT

The thoracic duct originates from the cisterna chyli (Figure 40). The cisterna chyli is located in the abdomen, at the level of the celiac axis, anterior to the vertebral body and to the right of the aorta. The thoracic duct travels superiorly, entering the thorax through the aortic hiatus of the diaphragm. It ascends in the posterior mediastinum between the aorta and the azygous vein. Above the arch of the aorta, it travels posterior to the esophagus, arches behind the internal jugular vein to join the venous system at the junction of the internal jugular vein and subclavian vein. The thoracic duct is thin walled and often invisible to the naked eye if not distended with lymph. Injury to the duct is visible as a pooling of lymph in the vicinity of the leak. Fat delivered to the small bowel will within 10–20 minutes turn this lymph milky white, enhancing visualization. Ligation of the thoracic duct is accomplished by ligating all fatty material and lymphatics bounded by four walls, consisting of the azygous vein, the parietal pleura, the esophagus, and the aorta below the level of the suspected leak.

Figure 40 Thoracic duct.

(From Pearson FG, editor: Thoracic Surgery, 2nd ed. Philadelphia, Churchill Livingstone, 2002, figure 20.7, p. 431.)