Which type of thoracic outlet syndrome is most common?

• A. Venous
• B. Arterial
• C. Mixed
• D. Neurogenic

Answer: (D)

Neurogenic thoracic outlet syndrome is most common because the brachial plexus nerves are the structures most frequently compressed as they pass through the thoracic outlet. The space between the clavicle, first rib, and surrounding muscles (like the scalene group and, in some positions, under the pectoralis minor) is relatively small and easily narrowed by posture, muscle bulk, or repetitive arm use. When the nerves are compressed, people usually notice sensory and motor symptoms in the arm and hand—numbness, tingling, weakness, and fatigue with use—which is why this type is seen most often in clinic.

In contrast, venous and arterial thoracic outlet syndromes involve compression of the subclavian vessels and present with vascular signs such as arm swelling and heaviness (venous) or ischemic changes, pallor, and diminished pulses (arterial). These vascular forms are much less common than neurogenic TOS. The mixed category exists but is far less frequently diagnosed than neurogenic TOS.