Resection of an azygos vein aneurysm that formed a thrombus during a 6-year follow-up period.

We report a resection of an azygos vein aneurysm that formed a thrombus during a 6-year follow-up period. An azygos vein aneurysm is commonly detected as an asymptomatic mediastinal mass. A thrombus could suddenly form without enlarging the aneurysm. Therefore we suggest that even asymptomatic azygos vein aneurysms causing blood stagnation should be resected before they can form a thrombus and cause a pulmonary embolism.