Inverted left atrial appendage presenting as a large left atrial mass.

Inverted left atrial appendage (ILAA) is a rare phenomenon. We describe a patient with mitral stenosis who presented with a homogenous mass in the left atrium, mimicking a large thrombus. The patient was sent to surgery and no thrombus was found; intraoperative examination by the surgeon revealed an ILAA. We briefly discuss the main features of this entity and also some aspects of the differential diagnosis.