DEFINITION, ANATOMY, AND PATHOPHYSIOLOGY
Venous thoracic outlet syndrome (vTOS) is a condition characterized by thrombosis of the axillo-subclavian vein due primarily to extrinsic compression of the structures of the thoracic outlet as the vein drains into the chest. This results in arm swelling and pain, often with bluish and purplish discoloration. Acute primary axillo-subclavian vein thrombosis was first defined in the late 1800s1,2 and bears the eponym Paget–Schroetter Syndrome.
The anatomic structures that compress the axillo-subclavian vein at the thoracic outlet include the subclavius muscle, the first rib, the anterior scalene muscle, and the costoclavicular ligament (Halstead ligament; Fig. 146-1A). The other components of the thoracic outlet that pertain to the arterial and neurogenic variants of thoracic outlet syndrome are discussed in Chapters 143 and 144. The subclavius muscle originates on the undersurface of the clavicle and extends medially to insert upon the cartilaginous portion of the first rib. The muscle lies on the anterior-superior surface of the axillo-subclavian vein. The anterior scalene muscle extends from the transverse processes of the third through sixth cervical vertebrae, to insert upon the scalene tubercle on the superior aspect of the first rib. The anterior scalene muscle and its tubercle lie posterior to the axillo-subclavian vein. The first rib lies on the inferior aspect of the axillo-subclavian vein. The subclavius muscle is responsible for depressing the clavicle with downward shoulder movements. The anterior scalene muscle similarly assists in depressing the clavicle while the shoulder is moved downward. The costoclavicular ligament lies medial to the subclavius muscle and unites the clavicle with the cartilaginous portion of the first rib. The costoclavicular ligament may be abnormally laterally inserted upon the first rib in vTOS and may contribute to the pathology.3
A. In the relaxed normal position, the subclavian vein runs between the subclavius muscle tendon, the costoclavicular ligament, and the anterior scalene muscle and first rib. B. Under tension, the vein is severely compressed between the subclavius muscle tendon and costoclavicular ligament antero-superiorly and the anterior scalene muscle tendon and the first rib postero-inferiorly.
With overhead activities of the arms, especially those requiring downward shoulder motions, the axillo-subclavian vein is forcefully compressed between the subclavius muscle and costoclavicular ligament antero-superiorly and the first rib and anterior scalene muscle posteriorly (Fig. 146-1B). Over time, chronic repetitive overhead arm motions cause repetitive cycles of compression and relaxation of the axillo-subclavian vein, resulting in endothelial cell injury and intermittent episodes of venous stasis. Perivenous fibrosis with narrowing of the axillo-subclavian vein ensues. Additionally, hypertrophy and fibrosis occur, especially of the subclavius and anterior scalene muscles and the anterior scalene tubercle on the first rib. Patients often develop collateral venous drainage, which becomes visible on physical examination. If left unchecked, the fibrosis becomes so severe that the collateral venous drainage ...