Floating left atrial mass in a patient with mitral stenosis.

Mobile masses within the left atrial cavity are commonly caused by organized thrombi or left atrial myxoma. The use of transesophageal echocardiography has provided means for differentiation between the 2 conditions. We report a case of a left atrial mass in a female patient who presented with mitral stenosis and atrial fibrillation, and was diagnosed by transthoracic echocardiography (TTE). The mass appeared freely mobile but did not prolapse between the mitral leaflets due to the tightly stenosed valve orifice. In the presence of mitral stenosis, atrial fibrillation and dilated left atrium, the appearance of the mass was in keeping with mobile thrombus. Consequently, the patient was referred for surgical treatment and the mass removed through left atriotomy. Microscopic examination revealed a highly organized thrombus. We conclude that TTE is still a reliable tool in the diagnosis of large mobile atrial thrombi; TEE is needed when differentiation from atrial myxoma is difficult.