An epicardial mesothelial cyst attached to the ascending aorta

An epicardial mesothelial cyst, which can be defined as a mesothelial cyst attached to the epicardium surrounding the heart and the great vessels inside the pericardial sac, is a rare condition. We herein report a case of epicardial cyst, which was attached to the ascending aorta. The patient was a 76-year-old male who underwent coronary artery bypass surgery, and the cyst was found incidentally. It was approximately 5 cm in diameter, and histological examination confirmed mesothelial cell origin. The ascending aorta has not previously been reported as the origin of an epicardial mesothelial cyst. This case gives new insight into the embryology of these cysts.