Thoracic outlet syndrome: a common sequela of neck injuries. This course explains the compression of the subclavian vein against the subclavius tendon found in patients with an abnormally anterior insertion of the anterior scalene muscle. The subclavian vein is bound by the anterior scalene muscle laterally, the costoclavicular ligament medially, the subclavius tendon cranially, and first rib caudally ( Fig. 3 ). It then exits through the costoclavicular space as the axillary vein. It then travels anterior to the anterior scalene muscle (outside of the technical scalene triangle) and continues in parallel to the artery with the anterior scalene muscle separating the two structures. On either side, the vein ascends superiorly with the subclavian artery into the neck. The left subclavian vein also receives chyle from the thoracic duct drainage. The subclavian veins provide the venous drainage of the upper extremities. In the thoracic outlet, the subclavian artery occasionally penetrates the anterior scalene muscle and rarely may pass entirely anterior to it. Anomalies of the distal subclavian artery are rare, although anomalies of the aortic arch frequently encompass the origin of the either artery. The left subclavian artery develops from the left seventh intersegmental artery, whereas the right subclavian artery arises from the fourth aortic arch, right dorsal aorta, and right seventh intersegmental artery. Because of the close proximity of the clavicle, first rib, and anterior and middle scalene muscles, the costoclavicular space is the most frequent site of arterial compression. Each subclavian artery ascends superiorly into the neck before arching laterally and traveling posterior to the anterior scalene muscle through the scalene triangle and exiting the thoracic outlet via the costoclavicular space (above the first rib, below the clavicle) to become the axillary artery. The left subclavian artery branches directly from the aorta, whereas the right subclavian artery arises from the brachiocephalic artery. The subclavian arteries are the primary blood supply to the upper extremities. A thorough understanding of this anatomy and embryology is therefore critical to the understanding of TOS. Much of this aberrancy is explained by the embryologic origins of the structures that comprise the thoracic outlet. Such anatomy predisposes patients to compression of the neurovascular bundle and development of clinical TOS. Reprinted with permission from the Journal of the American College of Surgeons, formerly Surgery Gynecology & Obstetrics.)Īberrant anatomy is common in the thoracic outlet. Surgical treatment for symptoms produced by cervical ribs and the scalenus anticus muscle. It is subdivided into three areas: the scalene triangle above the clavicle, the costoclavicular space or cervicoaxillary canal between the clavicle and first rib, and the subcoracoid or pectoralis minor space below the clavicle, ( Fig. 1 ). It is bounded by the clavicle anteriorly, the first thoracic rib posteriorly, the insertion of the pectoralis minor muscle onto the coracoid process of the humerus laterally, and the sternum medially. The thoracic outlet is defined as the space in the lower neck between the thorax and axilla through which the subclavian vein, subclavian artery, and brachial plexus travel from their central origins to their peripheral termini. The scalene muscles may have significant variability, including several anomalies associated with thoracic outlet syndrome. Anomalous first ribs originate from T1 and may fuse to the second rib, whereas cervical ribs arise from cervical vertebral bodies (usually C7). The first rib normally develops from the T1 costal process to the manubrium. The brachial plexus is composed of C5-T1 nerve roots, trunks, divisions, cords, and branches, and variability in development may influence anomalies of the surrounding structures. The subclavian artery and brachial plexus travel together through the costoclavicular space posterior to the anterior scalene muscle, whereas the subclavian vein travels anterior to the anterior scalene muscle.
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