Lipomatous Hypertrophy of Interatrial Septum

Figure: Axial chest CT image (non cardiac-gating) shows a fatty mass (arrows) in the interatrial septum with a "dumbbell shape" sparing the fossa ovalis (double-headed arrow). The mass extends to the wall of the superior vena cava.

Facts

• Excessive deposition of fat in the interatrial septum of unknown etiology
• Not common, incidence about 1% in autopsy, 2% on CT and up to 8% on echocardiography
• In most cases, they are incidental. However, they may cause arrhythmias

CT Appearance

• Fatty mass with thickness >/= 20 mm, sharp margin, no enhancement
• Spares fossa ovalis, resulting in a "dumbbell" shape on axial images
• Fat can extend to the level of coronary sinus and to the aortic root

Imaging Differential Diagnoses

• Atrial myxoma: this tumor arises from fossa ovalis and is usually pedunculated
• Cardiac lipoma: encapsulated, true neoplasm in younger patients

Reference:

Heyer CM, Kagel T, Lemburg SP, Bauer TT, Nicolas V. Lipomatous hypertrophy of the interatrial septum: A prospective study of incidence, imaging findings, and clinical symptoms. Chest 2003; 124:2068-2073.