Axillary Fossa

AXILLARY FOSSA, fossa (cavi) axillaris, axillary or subaxillary depression. Cavum axillare is well-defined even with intact coverings. It is situated between the thoracic wall, the upper extremity, and those parts that directly transition from the thoracic wall to the upper extremity, forming a depression in this area. Thus, the walls of the subaxillary fossa include: posteriorly—the scapula with its covering muscles, including m. latissimus dorsi and teres major; anteriorly—the clavicle and two pectoral muscles; internally—m. serratus ant.; externally, the anterior and posterior walls of the fossa converge to form an angle, closed by the humerus and m. coracobrachialis. The lower free borders of m. latissimi dorsi and m. pectoralis majoris bound the inferior opening of the subaxillary fossa, which is covered by fascia and skin with hair. The superior opening of the fossa is located between the clavicle (with the subclavian muscle) anteriorly and the first rib posteriorly, and leads to the neck. The pectoral fascia (fascia pectoralis) extends to the A. fossa as fascia fossae axillaris. The latter connects with the coracoclavicular costal fascia (fasc. coraco-clavi-costalis), being denser above and called fasc. coraco-costalis. The area cavum axillare presents great practical interest topographically, as here lie the main vascular and nerve trunks for the upper extremity and lymph glands; the latter also for the breast. When cutting through the skin, subcutaneous fatty tissue and fascia, one encounters a packet of numerous lymph nodes densely adhered to the fascia, collecting lymph from the upper extremity and from the suprapubic part of the corresponding side of the trunk, especially from the mammary gland. Of interest to surgeons is the presence of loose connective tissue surrounding the organs of the axillary fossa: this tissue continues into the space between the scapula and thoracic cage. The lymph nodes, especially those collecting lymph from the mammary gland (important for surgeons), are located closer to the inner wall of the fossa and, mainly, along the axillary vein, while the blood vessels themselves run closer to the outer wall. As the axillary fossa narrows upward, its organs lie closer together. Proceeding deeper (with the arm abducted), beyond the fascial aponeurosis, one encounters: a) the axillary vein, b) the medial cutaneous and ulnar nerves, c) the axillary artery, d) the median nerve, e) the coracobrachialis muscle (m. coracobrachialis), f) the shoulder joint capsule. The relative position of the vessels in the axillary fossa is as follows: in its depth (corresponding to trigonum clavipector.) the vein is located medial to the corresponding artery. But with strong blood filling, it advances over the anterior surface of the artery, partially covering it. Injury to vena axillaris is dangerous due to the possibility of air embolism. Into it open vv. acromio-thoracicae, cephalica and a collateral trunk of v. axillaris. The terminal and still connected branches of the brachial plexus are located behind and lateral to the axillary artery. Nervus thoracicus anter. crosses the anterior surface of the artery, while n. thorac. post. crosses the posterior. These two nerves form an anastomotic loop that surrounds the vein at the site of entry of v. acromio-thoracica. In the area corresponding to trigonum pectorale, the vein deviates from the artery, displaced in part by plexus brachialis. The three trunks of the latter are arranged here as follows: posteriorly—fascic. post., laterally—the lateral root of n. medianus, medially—the medial root of the same nerve, crossing the artery. In the area corresponding anteriorly to trigonum subpectorale, the relationships are simpler. Here n. musculocutaneus enters the muscular canal; n. medianus lies adjacent to the artery, located superficial to it. Somewhat lower pass n. ulnaris and n. cutaneus brachii medialis, and finally, even more superficially—the vein. A. axillaris gives off 6-7 branches in the area of the axillary fossa, namely: a. thoracica superior, a. thoraco-acromialis, a. thoracica longa, a. subscapularis, aa. circumflexae humeri ant. et post. The topographic relationships of n. medianus are very variable and therefore controversial. With the arm hanging down along the body, the vessels and nerves are arranged in the sagittal plane; n. medianus lies more superficially than the artery and approaches the midline more closely. With the arm abducted, n. medianus is located closer to m. coracobrachialis than to the artery. Besides injury to vessels and nerves, in the area of the axillary fossa, frequent metastases of cancerous neoplasms into the lymph nodes of A. v. from the affected mammary gland (in women) and less commonly in cancer of the lip and lower jaw are of practical interest. Lymphoma malignum descending from regio supraclavicularis is also encountered here. Multiple, very persistent abscesses and phlegmonas are also common here. For disease of the apocrine glands of A. v.—see Apocrine glands, a. Sopov-Yaroshevich.