[Lipomatous Hypertrophy of the Interatrial Septum Preoperatively Misdiagnosed as Right Atrial Lipoma]

A 73-year-old man with a right atrial tumor and a distal aortic arch aneurysm was scheduled for tumor resection and total arch replacement (TAR). Although the tumor was diagnosed as an intraatrial lipoma preoperatively, it could not be differentiated from an infiltrating lipoma on the basis of intraoperative pathological examination. We decided to completely excise the tumor. However, we found intraoperatively that the tumor was contiguous with the epicardial fat tissue of the heart, strongly suggesting a lipomatous hypertrophy of the interatrial septum (LHIS). Thus, we discontinued the resection, reconstructed the atrial septum and right atrial wall, and performed TAR with a frozen elephant trunk technique. Although the patient required temporary continuous hemodiafiltration because of his preoperative renal dysfunction, he was discharged 30 days postoperatively. If LHIS was the preoperative diagnosis, only an incisional biopsy was needed for diagnosing this case. However, LHIS is quite rare in Japan. Therefore, awareness of the disease and meticulous analysis of preoperative heart imaging are important to avoid an unnecessary surgery.