Venous thoracic outlet syndrome in a patient with an aberrant subclavius posticus muscle: a case report.

Venous thoracic outlet syndrome is typically caused by extrinsic compression of the subclavian or axillary vein within the thoracic outlet. Although several anatomical abnormalities have been implicated in its pathogenesis, isolated venous compression associated with the subclavius posticus muscle has not previously been reported. We present the case of a 40-year-old male who developed deep vein thrombosis of the left upper limb following repetitive overhead activity. Duplex ultrasonography demonstrated axillary vein thrombus, and further imaging, comprising computed tomography angiography and magnetic resonance imaging, identified an aberrant muscular structure extending from the first rib to the superior border of the scapula, consistent with the appearance of the subclavius posticus muscle compressing the subclavian vein. The patient was treated conservatively with anticoagulants and individualized physical therapy. Upon final follow-up, complete recanalization of the thrombus and absence of any symptoms were recorded. This case suggests that subclavius posticus muscle may be among the possible compression sites, and its potential presence should be considered in patients with unexplained deep vein thrombosis of the upper limb.