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

Background and Aim: 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.
Methods: The tumor was removed by diving the base of attachment at the left ventricular apex via a median sternotomy on cardiopulmonary bypass.
Results: The patient made an uneventful recovery and remains well at 6 months postoperatively.
Conclusions: 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.
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