Lipomatous Hypertrophy of the Interatrial Septum

General Considerations

• Less rare than originally thought
• Benign accumulation of unencapsulated collection of brown fat in interatrial septum
• Hyperplasia more than hypertrophy of fat cells
• Associated with older age and obesity

Clinical Findings

• Asymptomatic in most
• Atrial arrhythmias

Imaging Findings

• Imaging modalities include transthoracic or transesophageal echo, CT or MRI
• The latter allow for tissue characterization and are more accurate in assessing extent of lesion
• CT
  • Non-enhancing, dumbbell-shaped mass of fat density
• Confined to interatrial septum
• Spares fossa ovalis producing dumbbell shape
• Cephalad portion thicker than caudal portion of mass
• MRI
• Homogenous, bilobed high signal mass
• Associated with mediastinal lipomatosis

Differential Diagnosis

• Myxoma
• Rhabdomyoma
• Fibroma
• Lipomas
  • Very rare, well-encapsulated but may be the same entity as lipomatous hypertrophy

Treatment

• Surgical resection has been performed but is usually not required

Complications

• Can cause right atrial obstruction
• Supraventricular arrhythmias
• Unexpected cardiac death

Lipomatous Hypertrophy of the Interatrial Septum. Axial, contrast-enhanced, CT scans through the heart demonstrate a fatty mass in the interatrial septum (blue and red arrows) which has a dumbbell shape to it (blue arrow). sparing the fossa ovalis.
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Lipomatous Hypertrophy of the Interatrial Septum: An Overview. O'Connor, S;  Recavarren, R; Nichols, L and Parwani, A. Archives of Pathology & Laboratory Medicine. March 2006

CT appearance of lipomatous hypertrophy of the interatrial septum. Meaney, J; Kazerooni, E; Jamadar D and Korobkin, M. American Journal of Roentgenology, Vol 168, 1081-108