Partial thrombosis of an idiopathic azygos vein aneurysm.

Aneurysms of the azygos vein are often asymptomatic, detected on a chest radiograph simulating paratracheal mass. When the aneurysm is totally thrombosed, it is impossible to distinguish it from another cause of mediastinal mass. A case is presented in which partial thrombosis of the aneurysm and communication with the superior vena cava led to a diagnosis on angiography and CT.