SURGICAL ANATOMY
A detailed knowledge of surgical anatomy is of major importance in the practice of thoracic surgery. The following descriptions only summarize the basic anatomic information that every thoracic surgeon and chest physician must know.
Chest Wall
The bony thorax includes the sternum, 12 pairs of ribs and costal cartilages, and 12 thoracic vertebrae.
Ribs
Ribs form bony arches that curve downward from back to front.
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Accordingly, ribs are two interspaces lower anteriorly than posteriorly.
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The point of greatest change in the curvature of a rib is called the angle of the rib.
Typical ribs (3–9) are composed of a head, neck, and shaft.
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The head (enlarged posterior portion) articulates with the corresponding thoracic vertebra and the vertebra immediately above (costovertebral joint).
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The neck connects the head to the shaft. At this junction, there is a tubercle that articulates with the transverse process of the corresponding vertebra (costotransverse joint).
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The intercostal vessels and nerve run in the costal groove on the inferomedial surface of the rib ( Fig. 8-1 ).
Figure 8-1
Cross-sectional diagram of the chest wall demonstrating the anatomic relationship of the intercostal space, rib neurovascular bundle, and accessory vessels. Observe that a chest tube inserted above the superior border of the rib will avoid trauma to the main neurovascular bundle.
Rights were not granted to include this figure in electronic media. Please refer to the printed book.
(From McFadden PM, Jones JW. Tube thoracostomy: anatomical considerations, overview of complications, and a proposed technique to avoid complications. Milit Med 1985;150:681-685.)
The ribs are true, false, and floating.
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True ribs (1–7) articulate directly with the sternum and manubrium by way of their own costal cartilages.
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False ribs (8–10) articulate with the cartilage of the rib above, not the sternum directly.
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Floating ribs (11–12) end freely into the muscles of the anterior abdominal wall.
Sternum
The sternum is a flat bone that consists of three parts: manubrium, body, and xyphoid process.
Manubrium
The manubrium is the most superior part of the sternum.
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The suprasternal notch is located in the midline superiorly.
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Laterally, three paired notches articulate with the clavicles, first, and second costal cartilages.
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The manubrium articulates with the body of the sternum at the sternal angle.
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The sternal angle is located at vertebral level 4 to 5 and is a useful anatomic landmark because it marks the level of the insertion of the second costal cartilages.
The Body of the Sternum and Xyphoid Process
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Laterally, six paired notches articulate with costal cartilages 2 to 7.
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The xyphoid process articulates with the body at vertebral level 10 to 11.
Muscles
Major muscles of the chest wall include the pectoralis major, latissimus dorsi, serratus anterior, and trapezius muscles ( Fig. 8-2 ). These muscles cover large portions of the chest wall and thus are frequently involved by thoracic incisions, which may affect postoperative pain, breathing mechanics, and upper limb function. These muscles may be useful clinically in the reconstruction of major soft tissue defects of the chest wall and the management of intrathoracic surgical complications such as infected pleural spaces.
Pectoralis Major
Insertions:
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Clavicular head: medial half of the clavicle.
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Sternocostal head: anterior surface of the sternum, costal cartilages 1–6, and external oblique aponeurosis.
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Lateral lip of the intertubercular groove of the humerus.
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Innervation: medial and lateral pectoral nerves.
Function: depresses the shoulder, adducts and medially rotates the arm, elevates the upper ribs during forced inspiration.
The pectoralis major is a large fan-shaped muscle which can be useful for covering soft tissue defects of the chest wall and for obliterating complicated pleural spaces.
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It can be harvested as either a muscle flap or a myocutaneous flap based on the thoracoacromial vessels. The fifth rib may be harvested with the muscle in cases where skeletal support is required. It can also be used as a turn over flap based on internal mammary perforator vessels.
Latissimus Dorsi
Insertions: spines of the lower six thoracic vertebrae, thoracolumbar fascia, iliac crests, as well as the lower 3 to 4 ribs. Superiorly, the floor of the intertubercular groove of the humerus.
Innervation: Thoracodorsal nerve.
Function: Powerful adductor and extensor of the arm.
The latissimus dorsi is useful for the reconstruction of full-thickness chest wall defects anteriorly and laterally and can also be used intrathoracically.
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It can be harvested as either a muscle flap or a myocutaneous flap based on the thoracodorsal artery (a branch of the subscapular artery) or as a reverse flap based on multiple paraspinous perforators (from the posterior intercostal vessels).
Serratus Anterior
Insertion: Arises from the external surfaces of first 8-9 ribs and inserts over the anterior surface of the medial border of the scapula.
Innervation: long thoracic nerve (C5–7), which courses on the anterior surface of the muscle in the midaxillary line.
Function: Applies the scapula to the chest wall. Allows elevation and abduction of the arm. Paralysis of the serratus anterior is characterized by winging of the scapula.
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It may be harvested as a muscle flap based on the lateral thoracic artery (a branch of the thoracodorsal artery). It may also be used as a composite flap of muscle, rib and skin, or together with the latissimus dorsi based on the thoracodorsal artery.
Trapezius
Insertions: Occiput at superior nuchal line, ligamentum nuchae of neck, spinous processes of vertebrae C7–T12, spine of scapula, acromion, and lateral third of clavicle.
Innervation: Spinal accessory nerve and fibers from C3 to 4. The spinal accessory nerve is vulnerable to injury in the posterior triangle of the neck, where it may be very superficial.
Function: stabilizes the shoulder; elevates, depresses and rotates the scapula; and participates in entire the range of scapulohumeral movements.
Intercostal Space
Main site of surgical access to the chest (thoracentesis, thoracostomy, thoracotomy) (see Fig. 8-1 ).
Because of the position of the intercostal vessels and nerves in the costal groove, they are vulnerable to injury by an incision along the inferior border of the rib, which may cause hemorrhage and prolonged neuralgia.
Intercostal Muscles
Three layers of intercostal muscles span the intercostal space. They are attached to the periosteum of the rib above and the rib below.
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Fibers of the external intercosal muscle run obliquely forward and downward from the rib tubercle to the costal cartilage.
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Fibers of the inner intercostal muscles run obliquely backward and downward from the sternum to the angle of the rib. These fibers run at right angle from the external intercostal.
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The innermost intercostal muscles are present only at the midportion of the intercostal spaces. They may be absent superiorly. Muscle fibers run backward and downward. Along with the subcostal and transversus thoracic muscles they form the most internal muscular layer.
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The neurovascular bundle is located between the inner and innermost intercostal muscle layers.
Intercostal Arteries
The first and second posterior intercostal arteries arise from the superior intercostal arteries (branches of the subclavian artery). The other posterior intercostal arteries arise directly from the thoracic aorta.
Branches
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A posterior branch supplies the spinal cord and soft tissues of the back.
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An anterior branch runs in the costal groove. At the midaxillary line, a lateral cutaneous branch perforates the intercostal space to supply the skin.
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A collateral branch arises near the angle of the rib and travels anteriorly along the superior border of the rib below.
Anterior Intercostal Arteries
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Branches of the internal thoracic artery superiorly, and of the musculophrenic arteries inferiorly.
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They give off two segmental arteries in each space.
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One courses above (in the costal groove) and the other along the upper border of the rib below, anastomosing with branches of the posterior arteries.
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The subcostal artery (below rib 12) has a similar course but no collaterals.
Intercostal Veins
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Follow the same course as the arteries and are mostly tributaries of the azygos and hemiazygos venous systems.
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The posterior intercostal vein of the first intercostal space may be a tributary of the brachiocephalic, vertebral, or superior costal veins.
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The superior intercostal vein drains the second, third, and fourth intercostal veins, and is a tributary of the azygos vein on the right and innominate vein on the left.
Intercostal Nerves
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Provide the sensory innervation to the entire chest wall (1–8), and upper portion of the epigastrium (9). Anesthesia and paralysis are seldom produced by the section of only one nerve because of the considerable overlap in innervation that exists between adjacent nerves.
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Spinal nerves T 3 to T 6 have the most common pattern and are thus considered typical nerves. While exiting the intervertebral foramen, each spinal nerve divides into a ventral and a dorsal ramus. The ventral ramus communicates with the sympathetic chain via rami communicators and beyond this point, it becomes the intercostal nerve.
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In the costal groove, the intercostal nerve lie first inferior to the intercostal artery.
DIAPHRAGM
The diaphragm is a two-dome–shaped musculotendinous structure separating the thorax from the abdomen. Each half of the muscle inserts into a central (costal part) tendon.
Insertions: Lumbar vertebrae (L1–3) (crurae), lower six ribs and costal cartilages, xyphoid process.
Innervation: Phrenic nerves.
Function: The diaphragm is the most important respiratory muscle. Its contraction lowers the position of its central tendons, elevates the ribs, and widens the thoracic cavity.
The diaphragm three most important openings are
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The aortic hiatus. It contains the aorta, azygos vein and thoracic duct. It is limited by the body of T12 posteriorly, the diaphragmatic crura laterally, and median arcuate ligament anteriorly.
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The esophageal hiatus. It contains the esophagus, vagus nerves, and branches of the left gastric artery. It is located anterior to the aorta at T10, where the fibers from the right crux of the diaphragm form a sling around the lower esophagus.
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The caval hiatus. It contains the inferior vena cava and is located posteriorly to the right of the midline at T8.
MEDIASTINUM
Trachea and Main Bronchi
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The trachea is a semirigid structure running from the cricoid cartilage to the carina; it measures 10 to 12 cm and is supported anteriorly by 16 to 20 horseshoe-shaped cartilaginous rings ( Figs. 8-4 and 8-5 ).
Figure 8-4
The lobes and segments of the lung. Right upper segments: 1, apical; 2, anterior; 3, posterior. Right middle segments: 4, lateral; 5, medial. Right lower lobe segments: 6, superior; 7, medial basal; 8, anterior basal; 9, lateral basal; 10, posterior basal. Left upper lobe segments: 1 + 3, apical posterior; 2, anterior; 4, superior lingular; 5, inferior lingular. Left lower lobe segments: 6, superior; 7 + 8, anteromedial basal; 9, lateral basal; 10, posterior basal.
(Courtesy of Dr. Thomas W. Rice.)
Figure 8-5
Right pulmonary hilum.
(Reprinted from Deslauriers J, Mehran R. Handbook of perioperative care in thoracic surgery. Philadelphia: Elsevier; 2005. p. 196.)
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Its posterior membranous portion is apposed against the esophagus.
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The tracheal lumen is lined by a columnar and ciliated epithelium. A submucosal layer of connective tissue contains mucous glands.
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The trachea divides into right and left main-stem bronchi at the carina, located at T5.
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The left main stem bronchus is longer and originates at a sharper angle than the right. It measures approximately 5 to 6 cm.
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The right main stem bronchus is shorter, wider, and more vertical than the left. Thus, the right lung is particularly vulnerable to aspiration of foreign bodies or digestive secretions.
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A rich network of lymphatics accompanies the bronchi and bronchial vessels.
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These lymphatics are important pathways in the spread of bronchogenic carcinoma, and their involvement by cancer has important therapeutic and prognostic implications.
Great Vessels
Systemic Arteries
The Aortic Arch
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Begins at the level of the sternal angle ( Fig. 8-6 )
Figure 8-6
Left pulmonary hilum.
(Reprinted from Deslauriers J, Mehran R. Handbook of perioperative care in thoracic surgery. Philadelphia: Elsevier; 2005. p. 195.)
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It arches superiorly and to the left, passing in front of the trachea and then to the left of the trachea and esophagus.
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The arch runs posteriorly behind the root of the left lung.
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It becomes the descending thoracic aorta at the level of the second sternocostal joint (T4).
The Brachiocephalic (Innominate) Trunk
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It arises from the aortic arch behind the manubrium slightly to the left of the midline.
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It ascends superolaterally on the anterior surface of the trachea and branches into the common carotid and right subclavian arteries at the level of the sternoclavicular joint.
The Left Common Carotid Artery
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Arises from the aortic arch posterolaterally to the innominate artery.
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It ascends first anterior and then to the left of the trachea. It courses posteriorly to the sternoclavicular joint and into the neck.
The Left Subclavian Artery
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It arises from the posterior part of the aortic arch; as ascending, it lies agains the left lung and pleura laterally. It passes into the neck behind the the sternoclavicular joint posterolateral to the carotid artery.
Pulmonary Arteries
The Main Pulmonary Artery
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Originates in the right ventricle, runs in a posterior direction, and divides into right and left pulmonary arteries behind the aortic arch.
The Right Pulmonary Artery
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Crosses between the carina and ascending aortic arch and posteriorly superior vena cava anteriorly to reach the hilum of the right lung.
The Left Pulmonary Artery
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It is shorter and attached to the underside of the aortic arch by the ligamentum arteriosum. It reaches the hilum of the left lung, just above the left main bronchus.
Systemic Veins
The Brachiocephalic (Innominate) Veins
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They arise posterior to the medial part of the clavicles by the union of the internal jugular and subclavian veins.
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Each brachiocephalic (innominate) vein drains the corresponding internal thoracic, vertebral, inferior thyroid and superior intercostal veins. The right brachiocephalic vein descends vertically, whereas the left crosses the superior mediastinum obliquely in front of the branches of the aortic arch.
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The brachiocephalic veins unite at the inferior border of the first costal cartilage to form the superior vena cava.
The Superior Vena Cava And Azygos System
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The superior vena cava (SVC) drains all venous blood from above the diaphragm except that from the heart and lungs.
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It lies anterolateral to the trachea and posterolateral to the ascending aorta, and enters the right atrium at the level of the third costal cartilage.
The azygos and hemiazygos veins are located on either side of the vertebral column, and drain the back and the thoracic and abdominal walls. Their anatomy is variable. They assume particular importance in cases of SVC obstruction where they provide important collateral pathways.
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The azygos vein arises from the right ascending lumbar vein. It drains blood from the right posterior intercostal veins. It travels close to the right side of the inferior 8 thoracic vertebrae. It arches anteriorly just above the hilum of the right lung and drains into the superior vena cava.
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The hemiazygos vein arises from the left ascending lumbar vein. It drains the lower left posterior intercostal veins and ascends on the vertebral bodies posterolateral to the descending aorta. At T8, it crosses to the right behind the aorta, thoracic duct, and esophagus, and joins the azygos vein.
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The accessory hemiazygos vein descends on the left side of vertebrae T5 to T8. It receives tributaries from the fourth to eighth intercostal veins and sometimes the left bronchial veins. It crosses to the right at T7 or T8 behind the aorta and thoracic duct to join the azygos vein.
Nerves
Phrenic Nerves
The paired phrenic nerves originate from C3 to 5. Although supplying mainly motor fibers to the diaphragm, some of their fibers are sensory (see Figs. 8-5 and 8-6 ).
In the neck the phrenic nerves course over the scalenus anterior muscle from lateral to medial.
The right phrenic nerve enters the chest between the subclavian artery and the origin of the right brachiocephalic vein. It crosses the internal thoracic artery at the thoracic inlet, runs along the right side of the the right brachiocephalic vein and SVC, and over the pericardium anterior to the hilum of the lung all the way to the diaphragm.
The left phrenic nerve enters the chest between the subclavian artery and the left brachiocephalic vein; it crosses the internal thoracic artery and descends between the left subclavian and common carotid arteries, crosses over the aortic arch anterior to the left vagus. It continues its course over the pericardium anterior to the hilum and all the way to the diaphragm.
Vagus Nerves
The right vagus nerve enters the thorax anterior to the right subclavian artery. It courses behind the right brachiocephalic vein and SVC and then posteroinferiorly on the right side of the trachea. The pulmonary plexus arises from the vagus nerve behind the lung hilum. The vagus then courses over the esophagus where it branches into a periesophageal plexus.
The left vagus nerve descends posterolateral to the left common carotid artery. It diverges posteriorly at the level of the aortic arch, where it lies deep to the superior intercostal vein. Distally, its course mirrors that on the right side.
The recurrent laryngeal nerves are important branches of the vagi that innervate the larynx. They may be vulnerable to injury during surgical procedures in the neck and chest.
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The right recurrent laryngeal nerve loops posteriorly around the right subclavian artery and ascends to the larynx in the tracheoesophageal groove.
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The left recurrent laryngeal nerve arises at the level of the aortopulmonary window. It arches posteriorly around the aortic arch lateral to the ligamentum arteriosum, and ascends to the larynx in the tracheoesophageal groove.
Sympathetic Nerves
The sympathetic chain is located in the paravertebral gutter.
The stellate ganglion (lower cervical ganglion) is located at the superior border of the first rib. Traumatic injury or destruction by a malignant process causes ipsilateral Horner’s syndrome (ptosis, myosis, anhydrosis of the face).
The greater splanchnic nerve is formed by branches of sympathetic ganglia to 10. It courses inferiorly over thoracic vertebral bodies, medial to the sympathetic trunk and lateral to the azygos/hemiazygos veins. It pierces the diaphragm and courses to the celiac ganglion.
Esophagus
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The esophagus is a muscular tube extending from the pharynx cartilage to the cardia, and averaging 25 to 30 cm in length (see Figs. 8-2 and 8-5 ).
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It has cervical, thoracic, and abdominal segments.
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Striated muscle present in the wall of the proximal esophagus is progressively replaced by smooth muscle fibers distally.
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The esophagus is fixed to the diaphragm (phrenoesophageal membrane) and back of the cricoid cartilage. Otherwise, it is loosely attached to surrounding structures.
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Within the mediastinum, the esophagus is located posterior to the trachea and left main bronchus, posterior to the pericardium, and to the right of the descending aorta.
Thoracic Duct
