Left atrial septal pouch thrombus assessed on three-dimensional transoesophageal echocardiography

The left atrial septal pouch (LASP) is an anatomical entity that came to the attention of the medical community in 2010 when Krishnan and Salazar described it as a possible source of embolism. It is formed by the caudal fusion of the area of overlap of the septum primum and the septum secundum. The potential for thrombus formation inside this pouch remains debatable. A 59-year-old man was admitted to our institution for cardiac failure. The patient was known to have an ischaemic dilated cardiomyopathy with a left ventricular ejection fraction of 20% and elevated filling pressures. He presented a relapse of paroxysmal atrial fibrillation. The transoesophageal echocardiogram showed the presence of a thrombus arising from a typical LASP. Spontaneous contrast was noted in the left atrium and the left atrial appendage, but no thrombus in any other LA location. The patient received anticoagulation therapy. A month later, the echocardiogram showed a LASP totally free of any echoes. There were no signs of systemic embolism. A cranial and abdominal CT scan ruled out major embolism.