Hemiazygos vein aneurysm mimicking an enlarged lymph node.

Idiopathic hemiazygos vein aneurysm is a rare lesion that can be difficult to diagnose. Here we report a case of asymptomatic idiopathic hemiazygos vein aneurysm (HAVA) that was incidentally discovered on chest computed tomography (CT) and mistaken for enlarged lymph nodes. The patient underwent thoracoscopic surgery for a biopsy, which confirmed that he had an idiopathic hemiazygos aneurysm. Delayed contrast-enhanced CT was performed after surgery, and it was confirmed that the hemiazygos vein aneurysm was connected to the adjacent vessel.