Thoracic outlet syndrome (TOS) is a combination of pain, numbness, tingling, weakness or coldness in the upper extremity caused by pressure on the blood vessels and/or the nerves in the thoracic outlet. Possible causes of compression are an extra first rib, an old fracture of the clavicle, a broad insertion of the musculus scalenus anterior on the clavicle or the wedge formed by the coracoid process and the tendon of the musculus pectoralis minor, which reduces the space of the outlet between the rib cage (thorax) and the collar bone (clavicle) through which the main blood vessels and nerves pass from the neck and thorax into the arm. These factors can cause an impingement of the vascular and neural structures during abduction of the arm.
The symptoms can mimic many other conditions, such as a herniated disk in the spine neck, carpal tunnel syndrome, and even bursitis of the shoulder.
Investigations should include chest radiography to rule out cervical ribs or other bone anomalies.
Conventional angiography is usually performed when surgical intervention is considered in order to confirm the extrinsic compression of the artery.
MR angiography is a non-invasive approach and doesn't require ionising radiation or iodinated contrast material administration. It allows a good evaluation of the subclavian artery in both adducted and abducted positions of the arm.