Thoracic Outlet Syndrome: Four Structures Causing Nerve Compression

Thoracic Outlet Syndrome: Anatomical Sites of Neurovascular Compression

Thoracic outlet syndrome (TOS) arises from compression of the brachial plexus, subclavian artery, or subclavian vein in the thoracic outlet. Four key anatomical structures can cause this compression:

1. Cervical Rib

An accessory rib originating from the seventh cervical vertebra (C7). Present in ~0.5–1% of the population. It narrows the costoclavicular space, compressing the brachial plexus (lower trunk) and subclavian vessels.

2. Scalene Muscles (Anterior and Middle)

Hypertrophy, spasm, or anomalous insertion of the scalene muscles narrows the interscalene triangle, compressing the brachial plexus and subclavian artery. Common in repetitive overhead activities.

3. Pectoralis Minor

Tightness or hypertrophy of the pectoralis minor compresses the neurovascular bundle against the coracoid process in the retropectoralis space (especially with arm abduction/extension).

4. Costoclavicular Ligament (Costoclavicular Syndrome)

Thickening, fibrosis, or congenital anomaly of the ligament connecting the first rib to the clavicle narrows the costoclavicular space, compressing the subclavian vein and artery and lower brachial plexus.

Clinical Relevance

Accurate identification of the compression site guides targeted treatment: physical therapy (scalene/pec minor stretching, postural correction), botulinum toxin injections, or surgical decompression (first rib resection, scalenectomy, pectoralis minor release).