Thrombus Attached to the Left Atrial Septal Pouch Assessed on 3-Dimensional Transesophageal Echocardiography

ecently, left atrial septal pouch (LASP), a kangaroo pouch-like structure on the left atrial side of the interatrial septum, has gained significant interest as a new anatomical entity with a potential for cardioembolic stroke.1 A 52-year-old man with a longstanding history of cardiac murmur was admitted to the municipal hospital with a 1-week history of progressive dyspnea. Electrocardiogram showed normal sinus rhythm and possible left ventricular hypertrophy. Chest X-ray showed cardiomegaly, pulmonary congestion and bilateral pleural effusion. Transthoracic echocardiography indicated severe aortic stenosis (AS) probably due to bicuspid aortic valve and severely depressed left ventricular function (left ventricular ejection fraction: 25%). He was transferred to University Hospital of Occupational and Environmental Health as a definite surgical candidate for aortic valve replacement after the stabilization of heart failure symptoms. He had not taken anticoagulants. Transesophageal echocardiography (TEE) showed that he had severe AS with the anteroposterior type of bicuspid aortic valve. Although the left atrium was severely dilated with a mild degree of spontaneous echo contrast, there was no thrombus in the left atrial appendage. A small mobile mass was incidentally found to be attached on the inter-atrial septum, where fusion between the septum primum and septum secundum is limited to the