Congenital giant aneurysm of the left innominate vein: is surgical treatment required?

Congenital aneurysms of the thoracic venous system are rare. In particular, innominate venous aneurysms are extremely rare. We describe a 16-year-old girl whose chest x-ray suggested a mediastinal tumor. Three-dimensional contrast-enhancement magnetic resonance venography showed a giant sacciform aneurysm of the left innominate vein and dilatation of the right innominate vein. The patient was asymptomatic, and there were no significant physical findings. Therefore, the patient is being followed without surgical treatment.