Idiopathic saccular aneurysm of the azygos vein.

Idiopathic saccular aneurysm of the azygos vein is a rare condition. We report the case of a 52-year-old man with saccular aneurysm of the azygos vein who underwent surgical resection. Preoperative dynamic computed tomography revealed strong and rapid enhancement of the chest mass. Magnetic resonance imaging showed a thoracic tumor with low signal intensity on the T1-weighted image and coexistence of low and high signal intensity on the T2-weighted image. Intraoperative findings showed cystic dilatation of the azygos vein. Although an accurate preoperative diagnosis of saccular azygos vein aneurysm is difficult, especially differential diagnosis between this anomaly and mediastinal tumors, a markedly enhanced mass shown by dynamic computed tomography was useful for the preoperative diagnosis of this anomaly.