Unlikely cause of primary upper limb venous thrombosis.

Primary upper limb venous thrombosis is a rare disease usually caused by external compression of the proximal deep upper limb veins from aberrant musculoskeletal anatomy such as cervical ribs, abnormal tendon insertions and hypertrophy of the anterior scalene or subclavius muscles. We present an unusual case of primary upper limb thrombosis caused by compression of the brachiocephalic vein from a sternoclavicular ganglion cyst. This case illustrates the importance of considering a wide differential when searching for a cause of primary upper limb venous thrombosis.