chapter 2 thoracic wall and pleurae.pdf

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5/24/2014 Print: Chapter 2. Thoracic Wall and Pleurae

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Tuffier 1914 Used omentum to maintain lung collapse after thoracoplasty

Robinson 1915 Described open dra inage and partia l obliteration of empyema cavity using latissimus dors i muscle

Lilienthal 1922 Reported use o f chest tubes in postope ra tive management fo llowing thoracic surge ry

Sauerbruch 1925 Furthe red deve lopment o f parave rte bral tho ra copla sty

U.S. Army EmpyemaCommission (headed byGraham)

1925 Recommended closed versus open drainage in early onset of empyema

Gudger 1926 Collected 31 cases of live fish in air and food passages

Semb 1934 Added extrafascial apicolysis to thoracoplasty

Eloesser 1935 Described technique of open dra inage us ing U-shaped skin flap (Eloesser flap) as a tube less one-way va lve. This involvedremoving a segment of rib over empyema cavity and suturing skin flap to pleura. Upon completion, he sewed remainingedges of skin together.

Bigger 1937 Performed thoracotomy to resect pulmonary blebs

Sattler 1937 Treated spontaneous pneumothorax using thoracoscope

Alexander 1937 Introduced three-stage thoracoplasty involving resection of posterior segments of ribs, leaving periosteum intact

Churchill 1941 Used gauze abrasion of pleura to treat pneumothorax

Gaens ler 1956 Des cribed parie ta l pleure ctomy fo r pre vention of recurrent pneumotho rax

Clagett and Geraci 1963 Described open window thoracostomy to manage postpneumonectomy empyema.

Re-established open-drainage as a viable method of empyema treatment.

Deslauriers 1980 Advocated axillary thoracotomy, bleb resection, and apical pleurectomy for recurrent pneumothorax

Hansell and Strickland 1989 Described use of CT for finding extent of disease and pleural involvement

History table compiled by David A. McClusky III and John E. Skandalakis.

References

Beauchamp G. Spontaneous pneumothorax and pneumomediastinum. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds).Thoracic Surgery. New York: Churchill Livingstone, 1995, pp. 1037-1038.

Braimbridge MV. The history of thoracoscopic surgery. Ann Thorac Surg 1993;56:610-614.

Clerf LH. Historical aspe cts of foreign bodies in the air and food passages . South Med J 1975;68:1449-1454.

Deslauriers J. Empyema and bronchopleural fistula. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds). Thoracic Surgery. NewYork: Churchill Livingstone, 1995, pp. 1017-1018.

Deslauriers J, Carrier G, Beauchamp G. Diagnostic procedures. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds). ThoracicSurgery. New York: Churchill Livingstone, 1995, pp. 987-988.

Deslauriers J, Jacques LF. Thoracoplasty. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC, (eds). Thoracic Surgery. New York:Churchill Livingstone, 1995, pp. 1140-1141.

Deslauriers J, Mehran RJ, Jacques LF. Therapeutic thoracoscopy. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds). ThoracicSurgery. New York: Churchill Livingstone, 1995, p. 1149.

Deslauriers J, Perrault LP. Fibrothorax and decortication. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds). Thoracic SurgeryNew York: Churchill Livingstone, 1995, pp. 1107-1108.

Grgoire J, Deslauriers J. Closed drainage and suction systems. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds). ThoracicSurgery. New York: Churchill Livingstone, 1995, pp. 1121-1122.

Hansell DM, Strickland B. High-resolution computed tomography in pulmonary cystic fibrosis. Br J Radiol 1989;62:1-5.

Jacques LF, Deslauriers J. Open drainage. In: Pearson FG, Deslauriers J, Hiebert CA, McKneally MF, Ginsberg RJ, Urschel HC (eds). Thoracic Surgery. New York:Churchill Livingstone, 1995, p. 1136.

Naef AP. Pionee rs on the road to thoracic surgery. Thorac Cardiovasc Surg 1991;101:377-384.

Roussos C (ed). The Thorax: Part A: Physiology (2nd ed). New York: Marcel Dekker, 1995, p. xvi.

Zimmerman LM, Veith IM. Ferdinand Sauerbruch and the explosive expans ion of thoracic surgery. In: Zimmerman LM, Veith IM. Great Ideas in the History ofSurgery (2nd ed). New York: Dover, 1967, pp. 536-547.

EMBRYOGENESIS

Normal Development

Thoracic Wall

The small costal processes of the primitive thoracic vertebrae develop extensions that form the ribs (Fig. 2-1A). In the fifth week, the costal processesof the vertebrae in the thoracic region begin to elongate. The costovertebral joints form and separate the ribs from the vertebrae late in the sixth week

Fig. 2-1.


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A,Development of ribs. B,Development of sternum. (Modified from Larsen WJ. Human Embryology. New York: Churchill Livingstone, 1993; with permission.)

Initially, the future ribs are cartilaginous. Around the ninth week of embryonic life, ossification begins. The head and tubercle of each rib will hostsecondary centers of ossification. Complete bony formation is accomplished at 20-25 years of age.

The sternum has a peculiar genesis. Its primordium is, most likely, of mesodermal origin. At the end of the sixth week, paired mesenchymalcondensations (Fig. 2-1B) form within the ventral body wall. Presternal pieces and a pair of lateral parallel bars fuse into a single cartilage. These sterna

bars quickly fuse together at their cranial ends. The lateral edges of the sternal bars connect with the distal ends of the growing ribs. The sternal barsthen "zipper" together in a craniocaudal direction.

As early as 60 days, ossification centers appear within the sternum; these are responsible for the genesis of the manubrium and the sternebrae (Fig. 2-

1B). The xiphoid process does not ossify until birth.3

The intercostal muscles arise from the hypomere portion of myotomes (Fig. 2-2) in the thoracic region. Tendons and internal connective tissue of thesemuscles apparently arise from somatopleuric lateral plate mesoderm.

Fig. 2-2.


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Differentiation of myotomes and establishment of primordia of chief muscle groups o f abdomen. Left:Transverse section through thoracic region of 5-weekembryo. Dorsal portion of body wa ll musculature (epimere) and ventral portion (hypomere) innervated by dorsal primary ramus and ventral primary ramus,respectively. Right:Similar section to left,at later stage of development. Hypomere has formed three s eparate muscle layers and ventral longitudinal muscle.(Modified from Sadler TW. Langman's Medical Embryology (8th ed). Philadelphia: Lippincott Williams & Wilkins, 2000; with permission.)

Mesoderm of the lateral thoracic wall forms the three muscle layers of the thoracic wall; these are differentiated by week 7. The inner layer consists ofthe subcostalis, innermost intercostal, and transverse thoracic muscles. The middle layer consists of the internal intercostal muscles. The externalintercostal muscles form the outer layer.

Remember

The ribs perhaps develop from the thoracic sclerotomes.

The sternum and the costa l cartilages perhaps develop from the somatopleuric mesenchyme.

The intercostal muscles perhaps develop from the ventrolateral border of the epithelial plate of the somites.

Pleurae and Pleural Cavity

The pleurae are derived from the primitive coelom. The coelom is formed by the division of the right and left lateral mesoderm into splanchnic and

somatic layers. Therefore, two large cavities are formed. Later, these cavities will be separated into four smaller cavities (pericardial, peritoneal, andtwo pleural) by the embryologic entities responsible for the genesis of the diaphragm. These entities are the septum transversum, pairedpleuropericardial folds, and pleuroperitoneal folds.

Around the fourth week, the laryngotracheal groove (respiratory diverticulum) appears from the floor of the pharynx as the anlage of the lowerrespiratory tract. The most cranial portion forms the larynx from which the trachea extends caudally. In the fifth week, the two lung buds start to growinto the right and left pleural canals. The pleural spaces welcome the expanded lungs. The splanchnic mesoderm becomes the covering of thebronchopulmonary tree (visceral pleura). The somatic mesoderm forms the parietal pleura.

The pleurae are thin, serous, mesothelial membranes. The parietal pleura covers the thoracic wall, mediastinum, diaphragm, and cupola. The reflectionsof the mediastinal pleura cover the surface of the lungs and extend within the pulmonary fissures (visceral pleura). Between the parietal and visceralpleurae is a potential space containing minimal fluid to lubricate the pleural surfaces and facilitate the slide of the pleurae.

Remember

The embryologic formation of the pleural cavity is necessary to permit the normal physiologic action of the lungs.

The parietal part o f the pleurae develops from the coelomic epithelium of the somatopleure (somatic mesode rm).

The visceral part of the pleurae develops from the splanchnic mesenchyme (mesoderm covering the lungs).

Congenital Anomalies

Thoracic Wall

STERNUM

Congenital anomalies of the sternum include:

Depression (pectus excavatum or funnel chest) (Figs. 2-3A and 2-3B)

Protrusion (pectus carinatum or pigeon breast) (Figs. 2-3)

Mixed deformities (Fig. 2-3F)

Absence deformities (Figs. 2-4A and 2-4C)

Fusion/nonunion deformities (Fig. 2-4B)

Fig. 2-3.


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Varieties of chest deformities (in cross section). Aand B,Depress ion deformities. Cand D,Protrusion deformities. E,Bilateral protrusion. F,Chondromanubrialprotrusion w ith gladiolar depress ion. (Modified from Sanger PW, Taylor Fredrick H, Robicsek F. Deformities of the anterior wa ll of the ches t. Surg Gynec Obstet1963;116:515-522; with permission.)

Fig. 2-4.


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Sternal problems, shown in increasing severity from Ato C. A,Absence o f sternal elements w ith separation of manubrium from the remainder of s ternum. B,Failure of sternal fusion. In this patient the ste rnum and ribs appear to have ceased their normal medial migration at about the sixth week of development andto have o ssified in that position. Skin was intact over bony defect. C,Absence of entire ste rnum. Defect was covered by skin, fat, and se rosa. A ventral

diaphragmatic hernia opened into pericardial cavity, so that pericardial diaphragmatic and sternal de fects required repair. (A,modified from Martin LW,Helsworth JA. The management of congenital deformities of the sternum. JAMA 1962;179:82-84. B,modified from Maier HC, Bortone F. Complete failure ofsternal fusion with herniation of pericardium. J Thorac Surg 1949;18:851-859; with permission.)

Sadler4stated that abnormalities of rib morphogenesis and growth are the most likely causes for sternal abnormalities such as pectus excavatum andpectus carinatum.

Wu et al.5advocated minimally invasive correction of pectus excavatum.

Robicsek6notes that repair of pectus carinatum involves positional correction, shortening of the sternum, and maintenance of the corrected position byaction of the rectus abdominis and pectoralis muscles.

Wada and Ade7reported positive results with sternal turnover (orthotopic bone transplantation in reverse position).

Ravitch and Steichen8classified sternal defects into 3 categories:

Sternal cleft without associated anomalies

Upper ste rnal cleft

Lower ste rnal cleft

Entire sternum as a cleft

Ectopia cordis (usually a malformed heart outside the chest wa ll)

Cantrell's pentalogy with the following anomalies:

Cleft or absence of the distal sternum

Ventral diaphragmatic defect (crescentic)

Omphalocele or midline ventral abdominal defect

Apical pericardial defect communicating with the peritoneal cavity

Cardiac defects

Two cases of neonatal surgical treatment of bifid sternum by Dmini et al.9confirmed that the bifid sternum should be repaired early in life when thethorax is compliant and the primary closure is generally safe and relatively easy.

RIBS

Rib abnormalities include:

Complete absence


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Microthorax (thoracic dystrophy)

Absence o f costal cartilage

Incomplete fusion of cartilage and rib (resulting in their separation)

We quote from Hannam et al.10:

Rib abnormalities detected in the neonatal period are usually thought to be part of a skeletal disorder. There are, however, many causes whichinclude metabolic bone disease, infec tion and trauma. Rib abnormalities are also found in general disorders such as chromosomal abnormalities orhypothyroidism.

Other anomalies inc lude a combination of deformities of the sternum and ribs.

When anomalies of the anterior thoracic wall exist, several other defects are often associated:

Scoliosis11

Craniofacial hemangioma and omphalocele12

Ventricular septal defect13

Poland's syndrome is characterized by:

Absence of costal cartilages and a portion of the third, or third and fourth, ribs

Absence of nipple or breast with hypoplasia

Absence of subcutaneous fat

Absence of axillary hair

Absence of pectoralis minor muscle

Absence o f costosternal pa rt of pectoralis major muscle

Slovis et al.14reported that hepatic pulmonary fusion in neonates should be suspected in instances of apparent diaphragmatic hernia characterized bymediastinal shift toward the hypoplastic lung or when the mediastinum does not shift away from the mass.

It is not within the scope of this chapter to present embryogenesis or congenital defects in detail. For such information, we refer the reader to

Embryology for Surgeons.15

Pleurae

There appear to be no congenital anomalies of the pleurae that are of importance. The occasional continuity between the pericardium and the leftpleura causes no clinical problems, but is an interesting condition.

SURGICAL ANATOMY

Thoracic Wall

Surface Anatomy

The surface anatomy of the thoracic wall can be more clearly appreciated and remembered by separate descriptions of the anterior area, anterior lateraarea, posterior area, and posterior lateral area.

ANTERIOR AREA

Skin:Nipple is typically located in the fourth intercostal space

Bones:Sternum, clavicle, cartilages and ribs, lower margin of rib cage

Muscles:Pec toralis major, pec toralis minor

ANTERIOR LATERAL AREA

Bones:Ribs

Muscles:Serratus anterior, upper slips of origin of the external abdominal oblique

POSTERIOR AREA

Bones:Scapula, thoracic spine

Muscles:T rapezius, levator scapulae, rhomboideus major and minor, t eres major, lat issimus dorsi, serratus posterior (superior and inferior), intrinsic

muscles of the s ine


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The "triangle of auscultation" (Fig. 2-5) is the area between the medial border of the scapula, the lateral border of the trapezius, and the upper borderof the latissimus dorsi. The rhomboideus major forms the floor of the triangle. There is, effectively, relatively little tissue between the skin and the ribcage, making it a good site for auscultation. If the patient protracts (adducts) the scapula, the triangle increases in size, making it easier to listen tolung sounds with the stethoscope.

Fig. 2-5.

Superficial muscles of back and "triangle of auscultation." Trapezius muscle divided and reflected on left side to show underlying structures. (Modified fromGrant JCB. An Atlas of Anatomy. Baltimore: Williams & Wilkins, 1956; with permission.)

POSTERIOR LATERAL AREA

Bones:Ribs

Muscles:Serratus anterior, latissimus dorsi

Skeleton

STERNUM

Topography

The sternum (Fig. 2-6) is a flat bone formed from three parts: the manubrium, the body or gladiolus, and the xiphoid process. These three parts arenamed according to their supposed resemblance to the handle, shaft, and point of the Roman short sword.


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Fig. 2-6.

The sternum. A,Ventral view. B,Dorsal view. (Modified from Anson BJ (ed). Morris' Human Anatomy (12th ed). New York: McGraw-Hill, 1966; with permission.)

Manubrium.The manubrium is somewhat wedge-shaped. It is broader above than below, narrowing sharply toward its articulation with the body of the

sternum. The upper end of the manubrium is characterized by a large central concavity, the jugular notch (Fig. 2-6). Two superolateral notches forarticulation with the clavicles form the right and left sternoclavicular joints.

The lateral borders of the manubrium have two facets, one upper and one lower. The upper facet is for the articulation of the first costal cartilage (asynchondrosis), just inferior to the sternoclavicular joints. The lower facet (which is situated between the lateral borders of the lower manubrium andthe first sternebra) is for the articulation of the second costal cartilage (forming a synovial joint).

The articulation of the manubrium and the first sternebra is notable for the palpable ridge produced by the angulation occurring there. This is called thesternal angle (or angle of Louis or angle of Ludwig) (Figs. 2-6, 2-7). The slight hingelike nature of this articulation allows movement at the joint duringrespiration. The angle of Louis corresponds roughly to the level of the intervertebral disk between vertebrae T4 and T5, or the body of T5.

Fig. 2-7.


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Vertebral and visceral relations of sternum. (Modified from Frick H, Kummer B, Putz R. Wolf-Heidegger's Atlas of Human Anatomy (4th ed). New York: Karger,1990; with permission.)

The angle of Louis (sternal angle) is a very important anatomic landmark for the following reasons:

It is a point from which to count the ribs (Fig. 2-8).


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Thorax (dorsal aspect). (Modified from Frick H, Kummer B, Putz R. Wolf-Heidegger's Atlas of Human Anatomy (4th ed). New York: Karger, 1990; with permission.)

Occasionally, the twelfth rib is absent. In some cases, adjacent ribs may be fused, or they may be bifid. Supernumerary ribs are not rare. A cervical rib

associated with the seventh cervical vertebra occurs in about 1 percent of cases;16lumbar ribs are seen less commonly. Hollinshead16notes furtherthat symptoms occur in only 10 percent of persons having a cervical rib, and that such ribs appear about twice as often in females as in males.

Typical Ribs

Pairs 3-9 of the 12 pairs of ribs are known as "typical" ribs. A typical rib (Fig. 2-10) is composed of the following parts: head, neck, tubercle, and shaft.

Fig. 2-10.

"Typical" rib. Surface features of left seventh rib (inferior view). (Modified from Anson BJ (ed). Morris' Human Anatomy (12th ed). New York: McGraw-Hill, 1966;with permission.)

The head of the rib has an articular area that is divided by an interarticular crest into a superior facet and a larger inferior facet. The superior facetarticulates with the inferior part of the next higher vertebra. The lower facet articulates with the superior facet of the body of the vertebra with whichthe rib is similarly numbered; these are the vertebrocostal joints. The interarticular crest is attached by ligamentous fibers to the interveningintervertebral disk.

The neck of the rib is approximately 2.5 cm long. The neck is the relatively flattened part of the rib between the head and the tubercle.

The tubercle (Figs. 2-10 and 2-11) is a prominence on the posterior surface of the rib at the junction of the neck and body. The tubercle has anarticular and a non-articular component. The articular part of the tubercle has a small oval facet that articulates with t he facet on the t ip of the


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transverse process of the vertebra with which the rib is numerically associated, forming a costotransverse joint. A synovial capsule reinforced by

radiating ligaments covers the articulations.

Fig. 2-11.

General features and topographic anatomy of left first and second ribs. (Modified from Anson BJ (ed). Morris' Human Anatomy (12th ed). New York: McGraw-Hill,1966; with permission.)

The shaft of the rib is typically flat and thin. It has an average length of about 6 cm, measured from the tubercle to the angle. This distance getsprogressively longer from the second to the seventh rib, thereafter decreasing again. The location of the angle is indicated by a roughened site ofattachment for the iliocostalis muscle on the posterior surface of the rib. Fractures from indirect violence usually occur in the middle ribs, just in front othe angle.

The internal surface of the rib is characterized by the costal groove, which contains the intercostal neurovascular bundle. Dorsally, the groove is seenas a feature of the inferior border of the rib. At the angle of the rib, the groove becomes deeper and more of a feature of the inner surface of the rib.

The curvature of the shaft after its dorsolateral extension is forward, lateral, and downward. Along this pathway, the shaft is twisted partially so thatthe outer surface faces laterally and upward. From the third to the seventh costal cartilages, there is a gradual increase in length, a decrease indiameter, and a medial tapering as the cartilages ascend from the ribs to attachment with the sternum (Fig. 2-8). The thoracic cavity has a kidney-shaped appearance in cross section, due to the curvatures of the shafts and the manner of their articulations ventrally with the sternum.

In contrast to the orientation of the ribs in the adult, the ribs of the newborn are oriented in a nearly horizontal plane, so that little excursion of the ribstakes place in respiration; hence, the diaphragmatic excursions and abdominal wall movements provide the principal mechanical forces for respiration inthe baby (for more information, see the sec tion on pediatric diaphragm in the "Diaphragm" chapter).

Non-Typical Ribs

The first, second, tenth, eleventh, and twelfth of the 12 pairs of ribs have individual characteristics that are somewhat different from pairs 3-9.

First Rib.In comparison with the other ribs, the first rib is very short, flat, broad, and markedly curved (Fig. 2-11). Its two surfaces face cranially andcaudally; it has an internal and an external border. Its head has one facet for its articulation with the first thoracic vertebra. Its orientation isdownward and forward from its vertebral to its sternal end. The angle of the first rib coincides with its very prominent tubercle.

There are two shallow grooves near the midpoint of the cranial or superior surface of the first rib. The grooves are separated by a slight, roughenedelevation on the medial side of the rib (the scalene tubercle) for the insertion of the anterior scalene muscle (Fig. 2-11). The more anterior of the

grooves is related to the passage of the subclavian vein (Fig. 2-12). The groove posterior to the scalene tubercle indicates the course of the subclaviaartery and, behind it, the lower trunk of the brachial plexus.

Fig. 2-12.


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Thoracic outlet. A,Relations of neurovascular elements w ith anterior scalene present. B,Anterior scalene muscle removed to expose subclavian artery andbrachial plexus. (Modified from Edwards EA, Malone PD, Collins JJ Jr. Operative Anatomy of the Thorax. Philadelphia: Lea & Febiger, 1972; with permission.)

Posterior to the subclavian arterial groove is a rather broad area for insertion of the scalenus medius muscle; usually the area is poorly marked. At thelateral border of the rib, just posterior to the groove for the subclavian artery, is the site of origin of the first digitation of the serratus anterior muscle.The sternal end of the first rib is quite thick; it provides origin for the subclavius muscle (Fig. 2-12A).

Second Rib.The second rib (Fig. 2-11) is almost double the length of the first rib. It is markedly curved, but not twisted, so that the isolated rib tendsto lie flat upon a plane surface. The facets of its head articulate with adjacent facets on the bodies of the first and second thoracic vertebrae.

The special characteristic of the second rib is a roughened tuberosity on its lateral border for part of the first digitation of the serratus anterior muscle,in addition to the second digitation of origin. Fusion of the first rib to the second is possible, with the union taking place at the tubercle.

Tenth Rib.The tenth rib may be very much like a typical rib, but in most cases the articular surface of its head has only one facet. The tenth ribarticulates with the body of the tenth thoracic vertebra by this facet.

Eleventh and Twelfth Ribs.The heads of the eleventh and twelfth ribs have only one facet. They have almost no angle or costal groove. These ribs donot always have tubercles. The lengths of the eleventh and twelfth ribs are variable, but the twelfth rib is smaller.

Occasionally, a lumbar rib may be present and may articulate with the first lumbar vertebra. In some cases, the eighth rib may be attached to thesternum on both sides or on one side only. We have seen this peculiar phenomenon only once.

Spain et al.17found twelfth rib resection to be a useful approach for draining subphrenic abscesses.


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Internal thoracic and intercostal vessels; ventral view of thoracic wall. (Modified from Grant JCB. An Atlas of Anatomy (5th ed). Baltimore: Williams & Wilkins,1962; with permission.)

The anterior scalene muscle arises from the anterior tubercles of the transverse processes of C3-C6. This muscle inserts upon the scalene tubercle ofthe first rib (Fig. 2-12), ventral to the groove for the subclavian artery.

The middle scalene muscle (Fig. 2-14) is the largest of the scalenes. It arises from the posterior tubercles of C1 or C2-C7, and inserts upon the first rib,dorsal to the groove for the subclavian artery.

The posterior scalene muscle also arises from the posterior tubercles of transverse processes C4-C6. It descends to insert upon the second rib.

The subclavian artery (Fig. 2-14) and the brachial plexus are related to the middle of the upper surface of the shaft of the first rib. They are locatedbehind the scalene tubercle in the very narrow, triangular, potential space between the anterior scalene muscle and the middle scalene muscle. Thesubclavian artery often rests directly upon the first rib, with the lower trunk of the brachial plexus between the artery and the surface of the middlescalene muscle.

In some individuals, the first thoracic spinal nerve and even part of the lower trunk of the plexus (Fig. 2-15) can be situated between the artery andthe rib. Then the pressure of the subclavian artery prevents easy passage of anesthesia around the nerves. This is presumed to be associated with theoccasional difficulty of adequately infiltrating and anesthetizing the C8 and T1 spinal nerve roots.

Fig. 2-15.

Thoracic outlet. Relations of subclavian artery and brachial plexus to scalene muscles and first rib.

A cervical rib arising from the transverse process of the seventh cervical vertebra occurs in 1 or 2 percent of people, either unilaterally or bilaterally.18

This occurrence can be associated with compression of the subclavian artery or brachial plexus. The rib may be represented simply by an epiphysisarticulating with C7; more commonly, however, it is formed of a head, neck, and tubercle. These entities extend laterally into the posterior cervical

triangle. Here, the rib may terminate freely or find attachment elsewhere. According to Healey and Hodge,18attachment can be to the upper surface othe first rib. In such cases, the subclavian artery and plexus must cross the rib element, thereby readily leading to compression of these structures.

The scalenus minimus muscle (Fig. 2-16) or dense connective tissue bands occur more often than the cervical rib. They often pass between the

subclavian arter and the brachial lexus or between elements of the lexus. It is reasonable to assume that such bands ma have a constrict ive


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effect upon the large neurovascular structures passing through the small interscalene space.

Fig. 2-16.

Scalenus minimus muscle. In this case it s eparates inferior trunk o f brachial plexus from remainder of tha t plexus (not show n) and subclavian a rtery. (Modifiedfrom Hollinshead W H. Anatomy for Surgeons (3rd ed), Volume I The Head and Neck. Philadelphia: Harper & Row, 1982; with permission.)

The subclavian vein, together with the phrenic nerve, lies deep to the prevertebral fascia. It is located on the anterior surface of the anterior scalenemuscle, and anterior to the tubercle of the first rib (Fig. 2-11). The subclavian vein lies superficial to and a little below the corresponding artery.

Remember

A needle inserted beneath the clavicle will reach the subclavian (or axillary) vein. The subclavian vein is located deep to the clavicle and anterior to the anterioscalene muscle. The route for percutaneous subclavian catheterization is infraclavicular, approximately 2 cm lateral to the junction of the clavicle and first rib.

External trauma or an indwe lling catheter w ithin the subclavian vein can produce thrombosis. Roy et al.19reported primary subclavian vein thrombosis withpulmonary embolism secondary to repetitive action of the upper extremity.

From a surgical point of view, one can consider that the clavicles provide an extrathoracic contribution to the superior thoracic aperture ventrally andanterolaterally. The superior thoracic aperture is approximately 5 cm in anteroposterior diameter from the manubrium to T1; it is about 10 cm in width(rib to rib).

The superior aperture can be subdivided into two lateral areas (right and left) and a medial area. The lateral areas are for the passage of the apex ofthe lung and pleura (cupola) and the neurovascular apparatus of the upper extremities. In the medial area are vessels of the head and neck, as well asseveral of the organs forming the midline viscera.

Thoracic Outlet Syndrome

Perhaps the best-known pathological clinical problem of the superior thoracic aperture is thoracic outlet syndrome. There is much controversy regardingits nature and treatment. The usual picture is that of compression of neural and vascular entities. This compression is ascribed, variably, to themusculature, connective tissue, deviated ribs, or atypical ribs in the superior aperture of the thorax.

There is confusion in the literature about the definition of the thoracic outlet. We agree with Ranney, 20and present his 1996 summary of findings as a

definition:

The diagnosis of thoracic outlet syndrome (TOS) is intrinsically difficult, and the literature about it is full of confusing terminology. Symptoms mayarise due to compression of neural and/or vascular elements in one or more of three different locations. A number of tests were developed duringthe early part of this century, and a variety of syndromes have been described that relate to these tests, all of which are now considered to besubtypes of the thoracic outlet syndrome. Yet anatomists and clinicians fail to agree on even the definition of the thoracic outlet. It is proposedthat anatomists not use the term thoracic inlet as a synonym for the superior thoracic aperture, nor thoracic outlet for the inferior thoracicaperture. What many clinicians call the thoracic outlet should be called the scalene triangle by both anatomists and clinicians, divisible into alower portion to be called the thoracic outlet (for subclavian vessels and nerve roots C8 and T1) and an upper portion, the cervical outlet (fornerve roots C5, C6, and normally C7). What is currently called thoracic outlet syndrome should be renamed the cervicoaxillary syndrome (CAS),divisible into three subtypes: thoracic outlet, costoclavicular, and pectoralis minor syndromes. Compression of the upper roots of the brachialplexus between the anterior and middle scalene muscles should be recognized as cervical outlet syndrome, and all terms containing the wordscalenus should be discarded.

An in-depth discussion of terminology relating to the thoracic outlet and thoracic outlet syndrome may be found in Skandalakis and Mirilas. 21

Several surgical procedures have been reported. For decompression of the neurovascular apparatus of the upper extremities, removal of the first rib

from within the thorax was advocated by Mansberger and Linberg.22Brodsky and Gol23removed the medial part of the first rib by an anterior

infraclavicular approach. Roos24advocated the removal of the first rib through the axilla. Edwards25advised removal of a cervical rib through a

supraclavicular scalene approach. Lindgren and Oksala26advised conservative treatment, then surgery only if the conservative approach failed.

INFERIOR THORACIC APERTURE


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Accor ing to ORa i y, t e in erior t orac ic aperture is oun e y t e 12t t orac ic verte ra, t e 12t pair o ri s, t e ree e ges o t e ower 6pairs of costal cartilages, and the xiphisternal joint; the outlet is large and uneven in outline. For all practical purposes and from a surgical standpoint,the inferior thoracic aperture is closed by the diaphragm.

Muscles

EXTRINSIC MUSCLES OF THE THORACIC WALL

Several groups of muscles are related to the wall of the thorax: muscles of the upper extremities, the back, and the abdominal wall. From a surgicalstandpoint, we present here muscles of the anterior thoracic wall and muscles of the posterior thoracic wall. The abdominal wall muscles will bedescribed in the chapter on the abdominal wall and hernias.

Anterior Thoracic Wall

The extrinsic muscles of the anterior thoracic wall are the pectoralis major (Fig. 2-17), the pectoralis minor, the subclavius, and the serratus anterior.

Fig. 2-17.

Musculature of anterior body wall. Superficial and deep muscles. (Modified from Frick H, Kummer B, Putz R. Wolf-Heidegger's Atlas of Human Anatomy (4th ed).New York: Karger, 1990; with permission.)

Pectoralis Major Muscle.The pectoralis major muscle (Fig. 2-17) originates from the medial third or half of the clavicle, the sternum, the costalcartilages of the upper six ribs, and the anterior lamina of the rectus sheath. It inserts into the lateral lip of the bicipital groove of the humerus.

The innervation of the pectoralis major, in general, is from the lateral and medial pectoral nerves. More specifically, the lateral pectoral nerve (C5, C6,C7), after arising from the lateral cord of the brachial plexus, quickly divides into an upper and lower branch. The upper branch passes close to the deepsurface of the clavicle, pierces the clavipectoral fascia, and enters the clavicular head of the pectoralis major. Should the lateral pectoral nerve or theupper branch suffer injury, the clavicular head undergoes atrophy, with resultant severe cosmetic deformity.

The lower branch of the lateral pectoral nerve joins the medial pectoral nerve in a nerve loop (ansa) ventral to the axillary artery, just distal to theorigin of the thoracoacromial artery. From this loop arise multiple small branches which enter the pectoralis minor and supply it. Two or three branches


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continue through the pectoralis minor to supply the sternal and costal parts of the pectoralis major. The medial pectoral nerve (C8, T1) originates from

the medial cord of the brachial plexus.

The tendinous insertion of the pectoralis major is such that the clavicular fibers pass more superficially and insert more distally on the humerus than dothe sternocostal and abdominal portions. The clavicular head, therefore, assists in flexion of the arm at the shoulder. The remainder of the pectoralismajor acts strongly to adduct the arm. It also plays a role in medial rotation of the arm against resistance. The muscle can assist in a major way inforced respiration, elevating the upper ribs if the shoulder girdle is fixed.

Pectoralis Minor Muscle.The pectoralis minor muscle (Fig. 2-17) lies deep to the pectoralis major. It originates from the upper border and externalsurface of the third (variably, also from the second rib) to fifth ribs. Its insertion is upon the coracoid process of the scapula.

As noted above, the pectoralis minor receives its nerve supply from both the medial and lateral pectoral nerves. The pectoralis minor assists in

protraction of the scapula and in downward rotation of the lateral angle of the scapula. It can also elevate the upper ribs in forced inspiration.

Subclavius Muscle.The subclavius (Fig. 2-11) is a relatively short, somewhat cylindrical muscle which takes origin medially from the first rib and itscartilage. It passes laterally beneath the clavicle to insert into a groove on the deep surface of its middle third. The subclavius is innervated by a smallbranch (C5, C6) from the upper trunk of the brachial plexus. This muscle assists in stabilizing the clavicle in shoulder movements, drawing the clavicleforward and downward.

Serratus Anterior Muscle.The serratus anterior (Fig. 2-17) arises from the upper eight or nine ribs, with digitations taking origin near the anterior axillaryline. As a unit, the serratus anterior is a flat muscle. It is closely applied to the lateral chest wall between the ribs and the scapula. The muscle insertsalong the deep surface of the medial border of the scapula.

The first digitation, arising from the upper two ribs, inserts upon the ventral side of the superior angle of the scapula. The next two digitations spreadout along the medial border of the scapula. The lower five or six digitations converge upon the ventral surface of the inferior angle.

The serratus anterior receives its nerve supply from the long thoracic nerve (C5, C6, C7). The long thoracic nerve arises from the roots of the brachialplexus and passes along the external surface of the muscle, near the midaxillary line.

The serratus anterior protracts the scapula. The muscle draws the scapula forward in such a way that it is referred to, variably, as the fencer's muscleand the boxer's muscle. By its various parts, the serratus anterior can assist in rotation of the scapula either upward or downward. The muscle can actto draw the ribs outward in forced inspiration.

In paralysis of the serratus anterior, the lower angle of the scapula juts outward, a phenomenon known as "scapular winging," the appearance of whichis intensified if the patient pushes against a resisting object.

Posterior Thoracic Wall

The muscles of the posterior thoracic wall (Fig. 2-5) are the trapezius, latissimus dorsi, rhomboideus major and minor, levator scapulae, serratusposterior superior, serratus posterior inferior, and levatores costarum (the rhomboids and the levator scapulae are muscles of the upper limb, which neednot be described here).

Trapezius Muscle.The trapezius muscle (Fig. 2-5, Fig. 2-17) originates from the superior nuchal line of the occipital bone, the ligamentum nuchae, thespine of C7, and all spines of the thoracic vertebrae and the intervening supraspinous ligaments. The insertion is upon the spine and the acromionprocess of the scapula and the lateral one-third of the clavicle. The innervation of the trapezius is principally by the spinal accessory nerve (cranial

nerve XI) with participation, probably proprioceptive, of cervical nerves C3 and C4.

The most important action of the trapezius muscle is rotation of the scapula, so that the glenoid fossa is either elevated (as in abduction of theshoulder) or depressed. The muscle also elevates the shoulder or retracts the scapula.

NOTE:We have presented the trapezius muscle because of its location at the posterior aspect of the thorax; it does not participate in any movementsof the ribs.

Latissimus Dorsi Muscle.The latissimus dorsi muscle (Fig. 2-5, Fig. 2-17) originates principally from the posterior layer of the thoracolumbar fascia. In abroad aponeurosis, it attaches to the spines of the lower thoracic vertebrae, the lumbar vertebrae, the sacrum, and the supraspinous ligaments. Inaddition, the muscle arises more laterally from the iliac crests and lower three or four ribs. A small bundle usually arises from the inferior angle of thescapula.

The latissimus dorsi muscle twists upon itself as it passes medial to the humerus in such fashion that its lower edge inserts more cranially, then caudallyinto the floor of the intertubercular groove of the humerus.

The thoracodorsal (or middle subscapular) nerve provides motor supply to the latissimus dorsi muscle. The nerve is a branch of the posterior cord of thebrachial plexus with fibers from C6, C7, and C8.

The latissimus dorsi muscle adducts, extends, and medially rotates the humerus. It figures significantly in such actions as performing chin-ups, walkingwith crutches, and swimming. It assists in extending the spine and tilting the pelvis. It can play a role in coughing, sneezing, and deep inspiration.

Serratus Posterior Muscles

Superior.The posterior superior serratus muscle originates from the ligamentum nuchae and the spinous processes of the C7 to T3 vertebrae. Itdescends laterally and inserts upon the upper borders of the first three ribs (occasionally the first five). Innervation is from the ventral rami of the firstthree to five intercostal nerves. The task of the posterior superior serratus muscle is to elevate the upper ribs in inspiration.

Inferior. The posterior inferior serratus muscle arises from the spinous processes of vertebrae T11 to L2 by way of a common aponeurotic origin withthe latissimus dorsi in the thoracolumbar fascia. The slips of this muscle pass upward and laterally to insert upon the lower three or four ribs. Innervatiois from the ventral rami of the segmental spinal nerves. The serratus posterior inferior muscle draws the lower ribs downward and outward in inspiration,counteracting the inward pull of the diaphragm.


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Levatores Costarum Muscles.The levatores costarum are thin, flat muscles that arise from the transverse processes of vertebrae C7 to T11. Eachmuscle passes inferolaterally, inserting upon the outer surface of the rib one or two levels below. They are innervated by the segmental ventral primary

rami. These muscles assist in elevating the ribs in inspiration. According to Gardner et al., 28the levatores costarum belong physiologically to theintercostals.

INTRINSIC MUSCLES OF THE THORACIC WALL

The 12 pairs of ribs have 11 intercostal spaces which are wider anteriorly and above. Located within the intercostal spaces are the intrinsic thoracicmuscles and the intercostal arteries, veins, and nerves.

The intrinsic muscles (also known as the intercostal muscles) (Fig. 2-14) are arranged in three layers: external, middle, and internal. From a surgicalstandpoint, the muscles are known as the external, internal, and innermost.

External Intercostal Muscle

The external intercostal muscle layer is homologous with the external abdominal oblique muscle of the abdominal wall. The external intercostal musclesbegin posteriorly at the tubercle of the rib and extend to the rib junctions with the costal cartilages. They arise from the lower margin of each rib anddescend inferomedially to insert upon the upper border of the next rib below. Beginning at the costochondral junctions and extending to the lateralborder of the sternum, the external intercostal muscle layer becomes aponeurotic and is replaced by the anterior intercostal membrane.

Because of its downward and medial direction on the front of the chest wall, the external intercostal muscle (like the external abdominal oblique) can bethought of as a "hands-in-the-front-pockets" muscle in orientation. Some authors say that the action of the external intercostals is to elevate the ribsin inspiration; yet they are also active in expiration. It is likely that their principal function is that of maintaining the tension of the intercostal spaces.

Internal Intercostal Muscle

The middle layer of musculature is the internal intercostal muscle (Fig. 2-18). It begins at the lateral border of the sternum and continues as a musclelayer to the angle of the rib. It is replaced by an aponeurotic layer, the posterior intercostal membrane, at the angle of the rib. The internal intercostal

muscle arises from the lower margin of the intercostal groove and descends to the upper border of the succeeding rib.

Fig. 2-18.


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Anterior thoracic wall. Relations o f vascular and lymphatic structures (dorsal view). Transversus thoracis muscle removed on left side to illustrate vesse ls moreclearly.

The internal intercostal is considered to be homologous with the internal abdominal oblique muscle of the abdominal wall. This is due to the downwardand lateral, or posterior, orientation of its muscle bundles from origin to insertion. It is a "hands-in-the-back-pockets" muscle. Like the externalintercostal muscle, the internal intercostal is active both in inspiration and expiration, although some authors associate it principally with expiration.

Innermost Intercostal Muscle

The innermost intercostal muscle layer is homologous with the transversus abdominis muscle. It consists of three subsets or groups of muscles.

The first subgroup is the transversus thoracis (sternocostalis) muscle (Fig. 2-18). It takes origin from the lower third of the body or lower two

sternebrae of the sternum, from the xiphoid process, and from the third to the sixth costal cartilages at the sternum. The transversus thoracis muscleinserts into the lower borders and inner surfaces of the cartilages of ribs 3-6. In orientation, the muscle ascends in a lateral direction from origin toinsertion. The transversus thoracis muscle draws the ribs downward in expiration.

The second part of the innermost intercostal muscle layer is that which in some respects is most similar to the other intercostal layers. This layer ismost distinct as an entity in intercostal spaces beginning near the anterior axillary line and extending to the region of the angle of the rib. These fiberstake origin from the upper margin of the intercostal groove. They descend laterally to the upper margin of the next rib, their bundles passing parallelwith the internal intercostal. The intercostal nerve, artery, and vein course between the internal intercostal muscle and the innermost intercostalmuscle. This layer is often deficient in the upper four or five intercostal spaces.

The subcostalis muscle (Fig. 2-19) is thought of as the third representative of the innermost muscle layer of the thoracic wall. It is best seen in theposterior part of the thoracic cavity, beginning at the rib angles. These muscle bundles run parallel with the internal intercostal layer. They arise fromthe inner surface of one rib, and pass inferomedially to insert on the inner surface of a rib two or three levels below.

Fig. 2-19.


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Anterior intercostal arteries

Pe ricardiacophrenic artery

Mediastinal twigs to connective tissue and lymph nodes

Thymus branch to the thymus or its remnants and lymph nodes

Sternal branches

Pericardial branches

Occasionally, a bronchial or tracheal artery can arise from the internal thoracic artery. A lateral costal (lateral internal thoracic) branch is present inabout one-fourth of cases, usually limited to the upper four (or so) rib levels, descending obliquely some distance lateral to the parasternal line.

The pericardiacophrenic artery courses obliquely downward and slightly posteriorly between the pleura and the pericardium. This artery accompanies thephrenic nerve toward the diaphragm until it anastomoses with an ascending branch from the superior phrenic artery.

Perforating arterial branches at the upper six intercostal spaces pass through the intercostal musculature and pectoralis major, helping to supply themand the overlying superficial fascia and skin. The second to fourth perforating branches are of significance in supplying the tissues of the breast; ingeneral they descend laterally toward the areola.

Rigaud et al.31advised continued use of the internal thoracic artery for aorto-coronary bypasses, despite the partial and temporary devascularization othe sternum and the possibility of infections.

Pietrasik et al.32studied the number, size, and manner of origin of the branches of the internal thoracic arteries, with a view to the widespreadpopularity of harvesting of the internal thoracic artery for coronary arterial bypass. Advantages to the use of the internal thoracic artery rather than

saphenous vein bypass are well known, yet postoperative infections in general, mediastinitis, and ischemia of the lower sternum are recognized asserious risks in using the artery for bypass, especially when both internal thoracic arteries are used.

In the study by Pietrasik et al.32solitary sternal, perforating, mediastinal, and intercostal branches of the internal thoracic artery represented about82% of vessels originating from the internal thoracic; common trunks for two or more branches were seen in addition to the singular vessels, accountingfor the remainder of branches. The authors concluded that all branches should be ligated as close as possible to their origins to create anatomicpathways for retrograde flow to protect the blood supply of the sternum to reduce postoperative morbidity. These thoughts are amplified furtherhereafter in the presentation of the anatomy of the anterior and posterior intercostal arteries and their anastomoses.

Lachman and Satyapal33described a trifurcation of the internal thoracic artery. The first two branches are the well known musculophrenic and superiorepigastric arteries. The authors call this third branch the xiphoid branch. It was present in 61.3% of 62 cadavers. They found that the xiphoid branchcontributes to the supply of the lower sternal region.

Anterior Intercostal Arteries. The anterior intercostal branches arise from the internal thoracic in the upper six intercostal spaces (Figs. 2-14, 2-20)supplemented by a variably small branch of the axillary artery, the superior (supreme) thoracic artery. The superior thoracic artery usually supplies the

upper one or two intercostal spaces, although we have seen instances in which its distribution was more extensive, particularly when the lateralthoracic branch of the axillary artery was unusually diminutive in size. There are two branches in each space, one superior and one inferior, althoughthese two branches can arise from a common stem. The upper branch is usually, although not always, the larger of the two. Therefore paracentesis,incisions, or other entry to the intercostal space near the sternum should be placed in the middle of the space rather than over the upper border of arib, as would typically be done in more lateral parts of the thoracic wall.

Fig. 2-20.


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Relations of intercostal neural and vascular structures at sternum. (Modified from Edwards EA, Malone PD, Collins JJ Jr. Operative Anatomy of the Thorax.Philadelphia: Lea & Febiger, 1972; with permission.)

Occasionally with medial sternotomy or other related approaches to the sternum for coronary bypass, the blood supply of the sternum is violated.

Rigaud et al.31presented a precise systematization of the vascularization of the sternum:

It is based on the internal thoracic artery and its collaterals, which form multiple anastomoses. This anatomic basis provides an understanding ofthe problems of the devascularisation (partial and temporary) and the infections that may occur following the use of one or both internal thoracicarteries during coronary bypass operations.

The upper anterior intercostal artery in an interspace anastomoses with the posterior intercostal artery and the lower intercostal artery. Its collateralbranch (also participating in the collateral circulation) anastomoses with the collateral branch of the posterior intercostal artery.

The musculophrenic artery (passing behind the costal diaphragmatic attachments) (Fig. 2-21) perforates the diaphragm behind the 8th costal cartilage.It ends in the vicinity of the 10th intercostal space. The artery anastomoses with the last two intercostals, as well as with the deep circumflex iliacartery. From it, one or two anterior intercostal arteries arise for the 7th, 8th, and 9th interspaces. The diaphragm and muscles of the anterior abdominawall are supplied partially by the musculophrenic artery.

Fig. 2-21.

Collateral arterial channels in aortic coarctation. (Modified from Edwards EA, Malone PD, Collins JJ Jr. Operative Anatomy of the Thorax. Philadelphia: Lea &Febiger, 1972; with permission.)

Following its origin from the internal thoracic artery, the superior epigastric artery (Fig. 2-18) passes between the sternal and costal slips of origin ofthe diaphragm, lateral to the xiphoid process. It enters the rectus sheath between the rectus abdominis muscle and the posterior lamina of the sheath,thereafter quickly entering the substance of the muscle.

The superior epigastric artery anastomoses with the inferior epigastric artery within the substance of the rectus (Fig. 2-18); these anastomoses are noalways visible grossly. This anastomotic pathway provides the only real communication between the vasculature of the upper and lower extremities. Thesuperior epigastric artery supplies the diaphragm and the proximal anterior abdominal wall.


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Costocervical T runk.The costocervical trunk springs from the second part of the subclavian artery on the right, but on the left it springs from the first

part.

Highest (Supreme) Intercostal Artery.The highest (supreme) posterior intercostal artery (Figs. 2-12, 2-13) is a branch of the costocervical trunk,which arises from the second part of the subclavian artery, deep to the anterior scalene muscle. The other usual branch of the costocervical trunk isthe profunda cervicalis artery, which ascends in the neck, behind the transverse processes of the cervical vertebrae. The highest intercostal arteryarises between the first thoracic nerve laterally and the sympathetic trunk (cervicothoracic ganglion) medially.

The highest intercostal artery (Fig. 2-22) descends between the pleura and the ventral surface of the necks of the first and second ribs, giving origin tothe first and second posterior intercostal arteries, and anastomosing with the third posterior intercostal artery. The longitudinal anastomosing vesselthat joins the highest intercostal and third posterior intercostal represents the vestige of the cranial part of the embryonic right dorsal aorta.

Fig. 2-22.

Origins and courses of intercostal arteries. (Modified from Edwards EA, Malone PD, Collins JJ Jr. Operative Anatomy of the Thorax. Philadelphia: Lea & Febiger,

1972; with permission.)

Thoracic Aorta

Posterior Intercostal Arteries.The first two posterior intercostal arteries (highest [supreme] intercostal and the profunda cervicalis) arise from a branchof the costocervical trunk; the 3rd through the 11th and the subcostal artery arise from the aorta (Fig. 2-22).

The posterior part of the descending thoracic aorta produces the 3rd through the 11th posterior intercostal arteries (Fig. 2-23) and the subcostalartery. As we mentioned above, the first two posterior intercostals spring from the highest intercostal. The third posterior intercostal arteries ascend

from the beginning of the descending thoracic aorta to reach their respective intercostal space. En route, the right third posterior intercostal regularlyprovides a branch to the esophagus and gives off the right bronchial artery.

Fig. 2-23.


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Visceral and parietal branches of an intercostal a rtery. (Modified from Edwards EA, Malone PD, Collins JJ Jr. Operative Anatomy of the Thorax. Philadelphia: Lea& Febiger, 1972; w ith permission.)

Remember

Because the aorta lies upon the left side of the vertebral column, the right posterior intercostal arteries are necessarily longer than those of the left

side. The pathway of the right posterior intercostals is as follows:

In front of the thoracic vertebrae

Behind the esophagus

Behind the tho racic duct

Behind the azygos vein

Behind the pleura

The pathway of the left poste rior intercostals is:

Behind the hemiazygos or accessory hemiazygos

Behind the pleura

The origin of the posterior intercostal arteries (Fig. 2-24) is such that in their initial course posteriorly they must ascend across the intercostal spacetoward the lower border of the rib. They are, therefore, inferior to both their counterpart vein and intercostal nerve. After crossing the intercostalnerve, they attain their position with the vein above, and the intercostal nerve below.

Fig. 2-24.

Relations of intercostal vessels and their branches in posterior ends of intercostal spaces . (Modified from Edwards EA, Malone PD, Collins JJ Jr. OperativeAnatomy of the Thorax. Philadelphia: Lea & Febiger, 1972; with permission.)

As it begins to cross the intercostal space, each posterior intercostal artery provides origin for a dorsal branch (Fig. 2-24) which passes directly

-


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. . - ,continues dorsally to supply the overlying body wall.

The spinal arteries are of great importance in collateral supply to the spinal cord; thus, injury to one of the posterior intercostal arteries proximal to itsdorsal branch can result in ischemia of the spinal cord. The largest and most significant of such spinal arteries usually arises from one of the lower leftposterior intercostal arteries, especially the left ninth thoracic posterior intercostal, the "great radicular artery of Adamkiewicz." Often this is the onlysource of anterior spinal arterial supply to the cord below the level of T10.

The posterior intercostal arteries reach the intercostal groove near the angle of the rib. Soon thereafter, they give origin to their small collateral branchwhich descends to the upper border of the next lower rib. A cutaneous branch also arises, near the midaxillary line. It passes externally between theribs, in company with a similar branch of the intercostal nerve. Passing forward, the intercostal vein, artery, and nerve pass between the internal andthe innermost intercostal muscles.

In general, the posterior intercostals anastomose with the anterior intercostals. However, the 10th and 11th posterior intercostals anastomose withinthe abdominal wall with arteries arising from the superior epigastric, subcostal, and lumbar arteries. Branches of these arteries supply the muscles andskin of the back, and participate in the arterial supply of the spermatic cord. Other small branches participate in the arterial blood supply to the breast.

Subcostal Arteries.The subcostal arteries arise on each side under the twelfth ribs. They lie anterior to the twelfth thoracic vertebra. The subcostalarteries are posterior to the azygos vein (the left is posterior to the hemiazygos vein), thoracic duct, pleura, and diaphragm.

Each subcostal artery enters the posterior abdominal wall in company with the twelfth thoracic nerve. The pathway is lateral to the medial arcuateligament (lumbocostal arch), between the kidney anteriorly and the quadratus lumborum posteriorly. After penetrating the transversus abdominisaponeurosis, the subcostal artery passes forward between the transversus abdominis and internal oblique. It anastomoses with the superior epigastric,lower posterior intercostal, and lumbar arteries.

Axillary Artery

Superior (Supreme) Thoracic Artery.The axillary artery is topographically divided into three parts by its relation to the pectoralis minor muscle. The firspart of the artery is that proximal to the pectoralis minor, the second part lies deep to the muscle, and the third part is that which proceeds distallyfrom under the cover of the muscle. One branch, the superior (supreme) thoracic artery arises from the first part of the axillary artery; two branches

arise from the second part; and three branches arise from the third part of the artery. The latter vessels are not described here.

The superior thoracic artery arises from the deep side of the axillary artery; that is, the surface of the axillary artery which is closer to the thoracicwall. Its specific site of origin is usually just slightly distal to the passage of the axillary artery beneath the clavicle. Here, the artery is related to thefirst intercostal space, the external intercostal muscle, the upper part of the serratus anterior, the long thoracic nerve, and elements of the brachialplexus.

From its origin, the superior thoracic artery courses medially behind the axillary vein to the musculature of the first intercostal space. There, it givesbranches to the pectoralis major and minor, the intercostal musculature of the upper one or two spaces, and enters into anastomoses with the internalthoracic artery and the intercostal arteries in the upper one or two intercostal spaces. The superior thoracic artery may arise from the thoracoacromialartery or an aberrant branch of the subscapular artery, or it may be absent, its region of distribution supplied by other vessels in the region. It may beof larger size, and its distribution more extensive if the lateral thoracic artery is small.

Collateral Arterial Circulation

According to Edwards et al.34in cases of coarctation of the aorta distal to the ligamentum arteriosum (developmental ductus arteriosus), extensive

collateral circulation can develop to fill the descending thoracic aorta. Blood is carried from the subclavian arteries by way of the internal thoracicarteries, and then by their anterior intercostal branches. Collateral flow thereby fills the posterior intercostal arteries and the descending thoracic aorta(Fig. 2-21). Flow through this pathway can be so rich as to result in marked, radiographically visible "notching" of the ribs from the bounding of theenlarged intercostal arteries against them. Potential anastomotic flow can occur also by way of the superior epigastrics and inferior epigastrics to theiliac branches of the abdominal aorta.

VEINS

Internal Thoracic, Posterior Intercostal, and Subcostal Veins

NOTE:The adjectives "highest," "superior," and "supreme" are used almost interchangeably from one source to another, although often to describe

obviously different vessels. Nomina Anatomica35used only the term "superior," without designation as to its application. In our discussion, we wouldunderstand "supreme" or "highest" as being most understandably synonymous, whereas "superior" might not necessarily mean the uppermost vessel.

The anterior intercostal veins form the internal thoracic veins (Fig. 2-20) by uniting close to the third costal cartilage. The internal thoracic veinsascend to join the left and right brachiocephalic veins (or, rarely, the superior vena cava on the right side).

The lower left posterior intercostal vein drains into the hemiazygos vein (Fig. 2-19), which ordinarily crosses the vertebral column at about the level ofT8 or T7 to join the azygos vein. The left supreme posterior intercostal vein, draining the first interspace, usually joins the brachiocephalic vein,although this is quite variable.

The second through fourth or fifth posterior intercostal veins on the left empty into the left superior intercostal vein, a tributary to the leftbrachiocephalic vein. The intermediate posterior intercostal veins typically join to form the accessory hemiazygos vein (Fig. 2-19), a vein of highlyvariable size. The accessory hemiazygos terminates by draining with the hemiazygos into the azygos vein.

As it passes to the left brachiocephalic vein, the left superior intercostal vein passes to the left of the aortic arch. Because of its proximity to the aorticarch, when the left superior intercostal vein is of significant size it can appear radiologically as a nipplelike expansion of the aortic profile. Thisoccasionally leads to a false diagnosis of aortic aneurysm.

The right first posterior intercostal vein (right supreme intercostal) is also variable in its termination, draining to the brachiocephalic, right subclavian,etc. The right second, third, and fourth intercostal veins drain into the right superior intercostal vein, which then drains into the azygos. The rightsubcostal vein, together with the right ascending lumbar vein, forms the azygos vein. The left subcostal vein joins the left ascending lumbar vein toform the hemiazygos vein.


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Remember

Behind the sternoclavicular joints the internal jugular and subclavian veins of the two sides unite to form the right and left brachiocephalic (innominate)veins.

Azygos System

A complete presentation of the azygos system (azygos, hemiazygos, and accessory hemiazygos veins) is practically impossible. As described in Gardne

Gray-O'Rahilly Anatomy,27"the azygos system is so variable that no short account of it can include the variations."

We have seen so many variations in the dissecting lab that we do not know which one is the most common. Figure 2-25, based on information from the

38th edition of Gray's Anatomy,36shows the course of the azygos system that Gray'scalls "perhaps the commonest."

Fig. 2-25.

A frequent (perhaps the most common) course followed by intrathoracic azygos, hemiazygos, and accessory hemiazygos veins. Outlines of the root o f the rightlung and descending tho racic aorta are shown in w hite. (After Williams PL (ed). Gray's Anatomy, 38th Ed. New York: Churchill Livingstone, 1995.)

We agree with Gabella37that "schemata are usually misleading"; however, we present Figure 2-26 to give the student one representation of thiscomplicated, unorthodox, and highly atypical system.

Fig. 2-26.


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A,Main connections of azygos , caval, and vertebral systems of veins. B,Main veins of tho rax. Interrupted lineto coronary sinus indicates course of a leftsuperior vena cava (a rare anomaly). (Modified from O'Rahilly R. Gardner-Gray-O'Rahilly Anatomy (5th ed). Philadelphia: WB Saunders, 1986; with permission.)

Azygos Vein.The azygos vein (Fig. 2-26B) may originate from the posterior wall of the inferior vena cava (IVC) just above the renal veins andterminates in the superior vena cava (SVC). Its ascent is along the right anterior aspect of the thoracic vertebrae. Rarely, however, it originates below

the renal veins.On its pathway up, the azygos accepts the right ascending lumbar, right subcostal, and all the right intercostal veins except the first intercostal, whichdrains directly into the SVC.

The upward pathway of the azygos vein is related to the right side of the aorta; it arches above the root of the right lung and ends in the SVC. Theright greater splanchnic nerve is located to its lateral side. At its left lateral side are the esophagus, right vagus, and trachea.

Hemiazygos Vein.The hemiazygos vein (Fig. 2-26B) is formed by the union of the left ascending lumbar and left subcostal veins. In most cases it isconnected to the left renal vein. On its pathway up it accepts the 3 lower posterior intercostal veins and empties into the azygos vein (Fig. 2-19).

Accessory Hemiazygos Vein.Grzybiak et al.38consider the accessory hemiazygos (Fig. 2-26B) to be the most variable of the azygos veins. In mostcases it receives the 4th through 8th posterior intercostal veins, and occasionally the left bronchial veins. At the area of T7-T8 it empties into theazygos vein or may, with the hemiazygos, form a common trunk that empties into the azygos vein.

zbek et al.39reported multiple variations of the azygos venous system, such as absence of the hemiazygos, with unification of the posterior 8th, 9th,

and 10th intercostal veins draining by a common channel to the azygos vein.

For another presentation on the azygos system, please see the chapter on the mediastinum.

Collateral Venous Circulation

Collateral venous circulation may be accomplished by connections of the azygos, hemiazygos, and intercostal veins, the inferior and superior venacavae, and the vertebral system of veins. Additionally, there are rich channels in the superficial tissues, such as those interconnected by thethoracoepigastric tributary to the axillary vein above and the femoral vein below.

LYMPHATICS

The thoracic lymph nodes are anatomically divided into two groups: parietal and visceral. The parietal group consists of parasternal, diaphragmatic, andintercostal nodes.

Parietal parasternal (internal thoracic) lymph nodes (Figs. 2-18, 2-20, 2-27) are small in size and few in number. They are located along the internalthoracic vessels, approximately 0.5 to 1.5 cm from the lateral sternal line at the upper four or five intercostal spaces, in the thin areolar tissue underthe endothoracic fascia. There are one, two, or three on each side. Findings of several investigations are presented in Table 2-3.

Table 2-3. Thoracic Lymphatics: Internal Mammary Nodes

Author Y ear Avg Total #

LNs per

Subject

Location in Interspaces Between Costal Cartilages

Stibbe 1918 8.5 Four on one side, five on other: one in each of 3 upper interspaces & 6th space; extra one in one of the upper spaces on oneof the sides

Soerensen 1931 7 Average of 3.5 minute nodes on each side

Ju * 6.2 Most in the upper 3 spaces, infrequently in lower spaces

Putti 1953 7.7 Most in upper 3, some in lower spaces

Aro &Abro

1954 16.2 An average of 8.9 nodes on right side, 7.3 on left. In some subjects, retromandibular nodes between right and left lymphatictrunks at level of 1st intercostal space. An average of 6.6 nodes were seen when the retromandibular nodes were present.


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Unpublished research reported by Haagensen (referenced below)

Data from:

Bland KI, Copeland EM III. The Breas t, 2nd Ed. Philadelphia: WB Saunders, 1998, pp. 33-34.

Haagensen CD. Diseases of the Breast, 3rd Ed. Philadelphia: WB Saunders, 1986, pp. 36-39.

Fig. 2-27.

Retromanubrial nodes . (Modified from Haagensen CD. Diseases o f the Breast (3rd ed). Philadelphia: Saunders, 1986; with permission.)

Diaphragmatic (phrenic) nodes (Fig. 2-27) are discussed in the chapter on the diaphragm.

Intercostal lymph nodes (Fig. 2-19) consist of one or two lymph nodes close to the head of each rib, at the posterior aspect of all intercostal spaces.

Visceral lymph nodes are related to the intrathoracic anatomic entities (pulmonary nodes in the roots and hila, paratracheal nodes, and mediastinalnodes). We describe the visceral lymph nodes in the chapters on the individual organs.

It should be mentioned here, though, that some of the lymphatic drainage of the thorax is to the thoracic duct; other major pathways terminate in theright bronchomediastinal trunk. The right bronchomediastinal trunk may join the right lymph duct; more often, however, it appears to drain separatelyinto the beginning of the right brachiocephalic vein. Remember that the right lymphatic duct (Fig. 2-18), which receives the right jugular and rightsubclavian trunks, usually passes to the junction of the right internal jugular and right subclavian veins.

Irrespective of the specific vessels whether right bronchomediastinal or right lymph duct the lymph from the right side of the head and neck, rightupper extremity, right hemithorax, and right lung appear to drain to the region of junction of the right internal jugular and right subclavian veins. Animalstudies have demonstrated that lymph from the lower two-thirds of the left lung also drains to the right lymphatic drainage system.

The American Thoracic Society, in an effort to present in toto the lymph nodes of the thoracic cavity, presented a lymph node map which we reproducehere as Table 2-4.

Table 2-4. American Thoracic Society Lymph Node Map of Thoracic Cavity

Nodal

Stations

Definitions/Nodal Staging

1 R/L Supraclavicular

Supraclavicular or scalene nodes (always N3)

2 R/L Right/left upper paratracheal nodes

Nodes to the right/left of the midline of the trachea, betw een apex of the lung and the superior margin of aortic arch (N2 if ipsilateral to tumorotherwise N3)

4 R Right lower paratracheal nodes

Nodes to the right of the midline of the trachea, between superior margin of aortic arch and supe rior margin of azygos vein (N2 if ipsilateral tumorotherwise N3)

4 L Left lower paratracheal nodes

Nodes to the left of the midline of the trachea be tween the top of the aortic arch and the level of the carina, medial to the ligamentum arteriosum(N2 if ipsilateral tumor otherwise N3)

5 Aortopulmonary nodes

-


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-pulmonary artery (N2 if ipsilateral tumor otherwise N3)

6 Anterior mediastinal nodes

Nodes anterior to the as cending aorta or the innominate artery (N2 if ipsilateral tumor otherwise N3)

7 Subcarinal nodes

Nodes arising caudal to the carina of the trachea but not associated w ith the lower lobe bronchi or arteries within the lung (always N2)

8 Paraesophageal nodes

Nodes surrounding the esophagus dorsal to the posterior wall of the trachea, includes nodes relating to the descending aorta + nodes within theright or left pulmonary ligament (N2 if ipsilateral tumor otherwise N3)

10 R Right tracheo/bronchial nodes

Nodes to the right of the midline of the trachea, from the level of the cephalic border of the azygos vein to the origin of the right upper lobebronchus (N1 if ipsilateral tumor otherwise N3)

10 L Left tracheo/bronchial nodes

Nodes to the left of the midline of the trachea be tween the carina and the left upper lobe bronchus, medial to the ligamentum arteriosum (N2 ifipsilateral tumor otherw ise N3)

11 R/L Intrapulmonary nodes

Nodes lying within the lung distal to the upper lobe bronchus (N1 if ipsilateral tumor otherw ise N3)

14 Superior diaphragmatic nodes

Nodes adjacent to the pe ricardium within 2 cm of the d iaphragm (N2 if ipsilateral tumor otherw ise N3)

Source:As modified by Murray JG, Breatnach . The American Thoracic Society Lymph Node Map: a CT demonstration. Eur J Radiol 17:61-68, 1993; withpermission.

Lymph node biopsy routes are shown in Table 2-5.

Table 2-5. Lymph Node Biopsy Routes

Method of Sampling Nodal Stations

Mediastinoscopy 2R, 4R, 4L, 10R

2L nodes adjacent to trachea

7 nodes in ante rior subcarinal area

Transbronchial needle aspiration Same nodal groups as mediastinoscopy, but 7 nodes more easily accessible

10L and 11 nodes can also be reached

Anterior parasternal thoracotomy 5, 6 and 2L nodes anterior to great vessels

Percutaneous needle biopsy Under CT guidance, potentially can reach all nodal groups

Source:Glazer HS, Aronberg DJ, Sagel SS, Friedman PJ. CT demonstration of calcified mediastinal lymph nodes: a guide to the new ATS classification. AJR 147: 17-25, 1986; with pe rmission.

Innervation

Twelve in number, the thoracic spinal nerves are mixed. They arise from the spinal cord by two roots: sensory (dorsal) and motor (ventral). A spinalganglion is on each dorsal root where the root begins its passage through the intervertebral foramen. At that site, the dorsal and ventral roots are heldtogether closely by their meningeal coverings. The roots unite at the intervertebral foramen, producing a spinal nerve trunk that is subdivided into fourbranches: meningeal branch, dorsal primary ramus, ventral primary ramus, and rami communicantes.

The meningeal branch arises quickly from the spinal nerve trunk. It reenters the foramen to innervate the meninges and the vertebral column.Thereafter, the nerve trunk quickly divides into its two principal branches.

The dorsal primary ramus (Fig. 2-28) provides skeletal motor, sympathetic motor, and sensory and other afferent fibers for the muscles and the skin ofthe back.

Fig. 2-28.


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Anatomy of intercostal space: relations and branches of intercostal nerves and vesse ls. Nerves shown on left; arteries shown on right. (Modified from AgurAMR. Grant's Atlas of Anatomy (9th Ed). Baltimore: Williams & Wilkins, 1991; with permission.)

The ventral primary ramus (Fig. 2-28) in the thorax is responsible for the formation of the intercostal nerves. However, the first thoracic spinal nervepasses upward to cross the upper border of the first rib, joining the eighth cervical nerve to form the lower trunk of the brachial plexus. The twelfththoracic spinal nerve, being a subcostal nerve, gives origin to a branch that participates in the formation of the lumbar plexus. The last five spinalnerves extend medially and downward to supply the abdominal wall.

The anterior and lateral cutaneous nerves (Fig. 2-28) also belong to the ventral primary ramus. The anterior cutaneous branch emerges at the

parasternal line and divides into medial and lateral rami for the subcutaneous fat and skin. The lateral cutaneous branch leaves the intercostal space atthe midaxillary line, and divides again into anterior and posterior rami.

Remember

The lateral cutaneous branch of the second thoracic nerve extends to the brachium for the innervation of the skin in this area (upper and medial).

White and gray rami communicantes leave the ventral primary ramus and pass forward to reach the ganglia of the sympathetic chain. The white ramicommunicantes comprise myelinated preganglionic sympathetic fibers and general visceral afferent fibers. The gray rami communicantes arepostganglionic unmyelinated fibers that travel from the sympathetic ganglia to the ventral primary ramus. These fibers course into the dorsal and ventraprimary rami, and are then distributed to the body wall. The first two lumbar nerves also have white rami communicantes. Together with the thoracicnerves, they form the thoracolumbar sympathetic outflow.

In Summary

The first intercostal space receives sensory supp ly by way of the supraclavicular nerves C3 and C4 from the cervical plexus.

The thoracic wall is supplied by T2-T6.

The abdominal wall above the umbilicus is supplied by T7-T9.

The umbilical region is supplied by T10.


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Two-thirds of the upper infraumbilical area is supplied by T10-T12.

Pleurae

Structural Characteristics

Each pleura and its subdivisions has several characteristics. The diaphragmatic part of the parietal pleura is attached firmly to the diaphragm; strippingis therefore impossible. A similar situation can exist between the pericardium and the mediastinal pleura. The costal pleura can be stripped with ease:sometimes it can be stripped along with the underlying endothoracic fascia, and sometimes these two layers can be dissected from the inner chest wall

Occasionally, the parietal pleura is thick and heavily fixed to the visceral pleura of the lungs. When that occurs, expansion and aeration of thepulmonary parenchyma is minimal. The procedure to free the lung and remove the pleura is called decorticat ion; it is explained under "AnatomicComplications."

At the hilum of the lung, the parietal pleura (Fig. 2-29) becomes continuous with the visceral pleura. Characteristically, the cuff of pleura projects

around the pulmonary root, but is redundant. It hangs down like a bishop's sleeve and forms the pulmonary ligament. We agree with Last 40that this isnot a true ligament, but a space that welcomes the descending lung root when the diaphragm descends.

Fig. 2-29.

Pleurae and pleural cavity. (Modified from Agur AMR. Grant's Atlas of Anatomy (9th Ed). Baltimore: Williams & Wilkins, 1991; with permissi

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