An Unusual Cause of Thoracic Outlet Syndrome.

Thoracic outlet syndrome (TOS) is a condition arising from compression of the subclavian vessels and/or brachial plexus. Many factors or diseases may cause compression of the neurovascular bundle at the thoracic outlet. We describe the case of a 41-year-old woman with TOS who presented with vascular venous symptoms. Chest computed tomography (CT) scan showed a cystic mass at the level of cervico-thoracic junction, located between the left subclavian artery and vein, which appeared compressed. The cystic mass was removed through a cervical approach and it was found to be a cyst arising from the thoracic duct compressing and anteriorly dislocating the left subclavian vein. After surgery symptoms promptly disappeared.