What is the most common cause of thoracic outlet syndrome?

• A. Fracture of the first rib
• B. Clavicular dislocation
• C. Pancoast tumor
• D. Anomalous cervical rib

Answer: (D)

Compression at the thoracic outlet is often caused by space-occupying anatomical anomalies near the outlet. An anomalous cervical rib, a supernumerary rib arising from the seventh cervical vertebra, is a common congenital cause that narrows the outlet and can press on the lower trunk of the brachial plexus or the subclavian vessels, leading to thoracic outlet syndrome.

Traumatic events like fracture of the first rib or clavicular dislocation can cause TOS, but they’re not the typical or most frequent culprits. A Pancoast tumor can produce similar symptoms by invading the outlet region, yet it’s a less common cause overall compared with a cervical rib.