Prepared by Dr. Pavni Patel and Dr. Charles S. White at the
Department of Radiology, University of Maryland School of
Medicine, Baltimore, MD.
A 46-year-old diabetic woman fell from a standing height. The
next day she presented to the Emergency Department with lower back
pain. On physical examination she had signs of a peripheral
neuropathy. A CT scan of the lumbar spine revealed degenerative
changes in the spine and excluded a fracture. A CT scan of the
abdomen and pelvis was also performed to assess for any injury. CT
images of the lower chest and heart are shown (A, B, C).
Lipomatous hypertrophy of the interatrial septum
An incidental abnormality is evident in the CT of the lower
chest. CT images demonstrate a smoothly marginated, fat-containing
dumbbell-shaped mass in the region of interatrial septum with
relative sparing in the region of fossa ovalis (images A, B, C).
There is an extension of mass along the lateral wall of the right
atrium and a convex bulge of the septum into the left atrium.
Superiorly, the mass appears to be in contact with the superior
vena cava; however, no definite invasion is present. Inferiorly the
mass extends to the level of coronary sinus.
Lipomatous hypertrophy of the interatrial septum (LHAS) is a
benign entity characterized by fat accumulation in the interatrial
septum of the heart. Although it is frequently asymptomatic and
found incidentally on echocardiography, cases of lipomatous
hypertrophy are reported to be associated with atrial arrhythmias.
There may also be an association between LHAS and obesity. Excision
is performed only in those cases in which superior vena caval
obstruction necessitates surgical removal.
Embryologically, LHAS is thought to be due to the mesenchymal
cells becoming trapped with the interatrial septum and developing
into adipocytes later in life.
CT shows a non-enhancing, homogenous, smooth, well-marginated
mass of fat density confined to the atrial septum. LHAS can vary in
size from a few cm to a large mass. In a study by Meaney et al,
the average dimensions were 7 cm for cranio-caudal extent, 4.5 cm
along the interatrial septum, and 2.7 cm perpendicular to the
septum. CT is also useful in determining the extent of the
infiltration of the mass into the right atrium and differentiating
it from other cardiac lesions. MR imaging is an excellent
noninvasive method, since it can distinguish tissue composition and
document any caval obstruction. On T1-weighted MR images, LHAS is
seen as a high signal intensity structure in the interatrial septum
projecting into the right atrium. On fat-suppressed MR images, LHAS
exhibits signal suppression similar to the subcutaneous fat.
Cardiac lipoma is an important differential of LHAS; however, it
is typically an encapsulated fat density in a subendocardial and
subpericardial location and occurs in a younger age group. Cardiac
myxoma, the most common primary cardiac tumor, has the same signal
intensity as adjacent myocardium on both T1- and T2-weighted images
and should not be mistaken for LHAS. Liposarcoma is a rare
malignant cardiac tumor, which shows fat density sometimes admixed
with soft tissue. However, no cases of liposarcoma have been
reported in the region of interatrial septum.
Angiosarcoma, the most common primary malignant cardiac tumor in
adults, usually arises from the right atrial free wall and often
spares the atrial septum. Rhabdomyosarcoma is the most common
cardiac malignancy in infants and children. The tumor is often
multi-focal, arises from the myocardium, and may involve cardiac
valves and invade the pericardium. MR imaging is useful in
differentiating this entity from LHAS because rhabdomyosarcoma
appears isointense compared to the myocardium. Leiomyosarcomas are
masses that arise from the wall of atrium but they have a more
irregular and lobulated appearance than LHAS. They are also more
invasive and may be seen as multiple filling defects in the
pulmonary veins suggesting invasion.