Giant coronary sinus aneurysm misdiagnosed as an extracardiac mediastinal tumor

Coronary sinus aneurysm is a rare heart anomaly. Herein, we report a rare case with giant coronary sinus aneurysm misdiagnosed as an extracardiac mediastinal tumor. The preoperative diagnostic imaging failed to diagnose the correct location of the tumor and a simple resection was planned. It turned out to be coronary sinus aneurysm intraoperatively and required cardiopulmonary bypass support for the resection.