Cervical ribs, abnormalities of the scalenus anticus muscle, proximity of the clavicle to the first rib, or abnormal insertion of the pectoralis minor muscle may compress the subclavian artery, subclavian vein (see below), and brachial plexus as these structures pass from the thorax to the arm.> Depending on the structures affected, thoracic outlet compression syndrome may be divided into arterial, venous, and neurogenic forms.> Patients with neurogenic thoracic outlet compression may develop shoulder and arm pain, weakness, and paresthesias.> Patients with arterial compression may experience claudication, Raynaud's phenomenon, and even ischemic tissue loss and gangrene.> Venous compression may cause thrombosis of the subclavian and axillary veins; this is often associated with effort and referred to as Paget-Schroetter syndrome.> Examination of the patient with thoracic outlet compression syndrome is often normal unless provocative maneuvers..."">