In arterial TOS, which vessel is most commonly affected?

• A. Brachial plexus
• B. Subclavian artery
• C. Subclavian vein
• D. Axillary artery

Answer: (B)

In arterial TOS, the problem is compression of the artery as it passes through the thoracic outlet. The subclavian artery is the vessel most commonly involved because it runs right through that tight space beneath the clavicle and over the first rib, making it susceptible to compression from an extra cervical rib, scalene muscle crowding, or other anatomic variations. This compression can produce ischemic symptoms in the upper limb, such as diminished pulses, coldness, and claudication, and may lead to aneurysm or embolization if prolonged. The brachial plexus is the structure typically affected in neurogenic TOS, not arterial TOS; the subclavian vein is more commonly implicated in venous TOS, and the axillary artery is not the usual site of primary compression in arterial TOS.