In neurogenic thoracic outlet syndrome, which structure is primarily compressed?

• A. Subclavian artery
• B. Brachial plexus
• C. Axillary nerve
• D. Phrenic nerve

Answer: (B)

Neurogenic thoracic outlet syndrome primarily involves compression of the brachial plexus as it passes through the thoracic outlet. Because the plexus carries both sensory and motor fibers to the upper limb, compression produces neurological symptoms such as numbness, tingling, and weakness in the arm and hand, often with elevation or overhead use. The common entrapment sites are the scalene interval (between the anterior and middle scalene muscles) and the costoclavicular space, where the plexus lies close to the first rib and clavicle. Other forms of thoracic outlet syndrome involve the subclavian vessels (arterial or venous), which lead to vascular signs rather than nerve-type symptoms. The axillary nerve and phrenic nerve are not the primary structures affected in this condition.