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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


  • Surgical resection has been performed but is usually not required


  • 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