A case of inverted left atrial appendage mimicking a tumor.

We report a rare case of an inverted left atrial appendage without prior cardiac surgery. A left atrial mass was incidentally found during routine echocardiography in a 19-year-old man with mitral valve prolapse. Echocardiography revealed a hyperechoic mass in the left atrium, and a neoplastic lesion could not be excluded. On magnetic resonance imaging (MRI), this mass consisted of fat tissue that showed continuation to epicardial fat, indicating an inverted left atrial appendage mimicking a tumor in the left atrium. When a mass in the left atrium is observed on echocardiography, there are several differential diagnoses, including thrombus, vegetation, and intra-atrial neoplasms such as myxomas. Recently, several studies reported cases with inverted left atrial appendages mimicking tumors in patients after cardiac operations. We present a case of inverted left atrial appendage without any prior cardiac surgery. Cardiac MRI was highly useful to obtain the final diagnosis of inverted left atrial appendage.