Idiopathic saccular azygos vein aneurysm.

We present a case of asymptomatic saccular aneurysm of the azygos vein. This abnormality is exceedingly rare. Dynamic computed tomography revealed strong enhancement of the mass, suggesting a vascular structure, which was very important for preoperative diagnosis. It is unclear whether the mass should be resected if the preoperative diagnosis has been made and the mass is not so large.