Lipomatous hypertrophy of the interatrial septum is a pathologic, not an anatomic diagnosis

Lipomatous hypertrophy of the interatrial septum (LHIS), a fatty tumor, is usually diagnosed on both echo and CT/MRI imaging. Cases of LHIS located outside of the interatrial septum are extremely rare and rarer still are these cases large enough to cause symptoms. The clinical literature demonstrates a misunderstanding that fatty tumors outside the intra-atrial area represent lipomas. However, pathologic understanding of these fatty tumors is clear and is based on microscopic findings.

The tumor was removed by diving the base of attachment at the left ventricular apex via a median sternotomy on cardiopulmonary bypass.

The patient made an uneventful recovery and remains well at 6 months postoperatively.

On rare occasions, LHIS can arise from outside the interatrial septum. An LHIS can be differentiated from a lipoma by the presence of entrapped cardiac myocytes in LHIS, making it a pathological, rather than an anatomic, diagnosis.