Left atrial septum thrombus masquerading as a myxoma in a patient with aortic stenosis in sinus rhythm.

A 77-year-old female underwent right and left heart catheterization, left ventriculography, and coronary arteriography for symptoms of severe exertional dyspnea with physical Žndings consistent with aortic stenosis. The electrocardiogram revealed normal sinus rhythm. The patient had no prior cardiac history, and in particular, no history of arrhythmia or arterial embolic events. At catheterization, the patient was found to have normal left ventricular systolic function but critical aortic stenosis with single vessel coronary artery disease. There was no mitral valve gradient, but the pulmonary capillary wedge pressure was 26 mmHg. Preoperative transthoracic echocardiography (TTE) conŽrmed critical aortic stenosis. The left atrium was mildly enlarged at 44 mm. Transesophageal echocardiography (TEE) was instituted during induction of anesthesia for intraoperative monitoring. Before the patient was placed on cardiopulmonary bypass, a mobile mass attached to the left atrial (LA) side of the fossa ovalis was visualized Žrst in the horizontal plane (Fig. 1) and then the vertical plane (Fig. 2). Based on the appearance by TEE, it was thought to be a myxoma, and then was surgically inspected and removed from the mid-portion of the fossa ovalis. Of note, there was no evidence of a patent foramen ovale either by TEE or by direct visual inspection of the atrial septum. By TTE and TEE, the patient had no evidence of any mitral valve abnormality; in particular, there was no evidence of rheumatic valve disease. In addition, spontaneous echo contrast was not visualized within the LA. Histopathological evaluation revealed the mass to be organized thrombus without any evidence of myxoma or other tumor histology. Postoperatively, a hematological evaluation was unremarkable. This atrial septal thrombus had TEE features usually associated with a myxoma. The mass was attached to the LA side of the fossa ovalis, had a heterogeneous appearance, and was mobile.1 In contradistinction to this, LA thrombus is found most often within the left atrial appendage (LAA) and is associated frequently with atrial Žbrillation or rheumatic mitral valve disease. Furthermore, thrombus within the LA or LAA is associated often with spontaneous echo contrast, a signiŽcantly enlarged LA, or a poor cardiac output. This patient had none of these. While certain features of a mass found within the LA may suggest its etiology, exceptions occur. Our case and a reported myxoma within the LAA are exemplary of such exceptions.