Lipomatous hypertrophy of the interatrial septum is an exaggerated growth of normal fat existing within the septum and is not a true tumor. Rather, it is a developmental disorder caused by expansion of adipose tissue trapped in the interatrial septum during embryogenesis. The septal hypertrophy may be as large as 2 cm in thickness and is seen primarily in older patients and in those who are obese.
It has been suggested that this disorder is associated with the presence of coronary artery disease in proportion to the degree of atrial septal thickness (possibly true in this case although the patient is a vasculopath).
Lipomatous hypertrophy of the interatrial septum is indistinguishable from lipoma except that the former occurs in the atrial septum with a typical distribution (generally sparing the fossa ovalis). In the absence of symptoms of atrial arrhythmias, heart block, or rare vena caval obstruction, they do not require resection.