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The first sign of pathology is usually stenosis (narrowing) of the subclavian artery. The stenosis may spontaneously recede following a surgical procedure called thoracic outlet decompression. If the artery continues to be compressed, causing long standing inflammation, the artery may become fibrotic (tissue takes on fibrous quality). This could result in the formation of emboli, ranging from mild to severe. Ischemic (lack of oxygen) events occur usually due to distal emboli (in the arm or hand) or proximal (close to the thoracic outlet) arterial thrombosis (e.g., absent pulses, gangrene, symptoms of Raynaud's phenomenon)

Venous Thoracic Outlet Syndrome

Vascular TOS which involves the subclavian vein is also known as Paget-Schroetter Syndrome. It can be caused by thrombosis (formation of a clot attached to the wall of the vein) or it could be of a nonthrombotic origin.

There are two types of venous thoracic outlet syndrome:

• Primary Venous TOS

  This is caused by a congenital narrowing of space in the part of the thoracic outlet where the subclavian vein passes through and may be caused by:

  • an anomalous first rib
  • long transverse process of the cervical spine
  • cervical ribs
  • hypertrophic (overgrown) scalene muscle which may develop in athletes whose muscles hypertrophy (enlarge from heavy lifting) and may cause compression of the subclavian vein.

• Secondary Venous TOS

  This is caused by stenosis or thrombosis for known reasons, (e.g. a central line catheter inserted into the subclavian vein for treatment or placement of a pacemaker). The wall of the subclavian vein may be damaged during:

  • placement of a central line catheter
  • the infusion of medications
  • incorrect catheter placement.

Venous TOS typically occurs in young men. When it is related to overexertion, patients usually experience pain, swelling and/or cyanosis. Veins in the neck, shoulder, or front of the chest may be distended and the symptoms will intensify with increased activity of the involved arm.

Some patients develop Paget-Schroetter Syndrome which is a condition where a thrombus (clot) develops in the subclavian vein (beneath the collarbone) which results in pain, swelling, blue discoloration, and congestion of the arm. It is most commonly caused by compression of the vein between the collarbone and the first rib, and is considered one of the venous manifestations of thoracic outlet syndrome. It can be caused by primary (congenital anomaly) or secondary TOS and is associated with strenuous activity or unusual positioning of the arm. Approximately 15% of patients with subclavian vein thrombosis demonstrate some degree of occlusion (blockage) in the unaffected arm. A minority of patients spontaneously form collateral veins around the point of occlusion or the obstruction resolves. In the remainder of patients, immediate treatment is necessary.

Neurovascular Thoracic Outlet Syndrome

Neurovascular TOS usually follows trauma or injury. The most common type of trauma involves a fracture of the clavicle (collar bone) which may also cause secondary injury to the nerves and blood vessels within the thoracic outlet. Traumatic TOS usually develops on the same side where the injury occurred. The most frequent symptom is pain in the neck/shoulder area which may be accompanied by weakness and/or numbness in the arm/hand.