AJR 2004; 182:598-600
© American Roentgen Ray Society
MRI of Atypical Lipomatous Hypertrophy of the Interatrial Septum
Servet Tatli1,
Patrick Thomas O'Gara2,
Jarvis Lambert3,
Raymond Kwong4,
John Gerald Byrne5 and
E. Kent Yucel1
1 Department of Radiology, Brigham and Women's Hospital, Harvard Medical School,
75 Francis St., Boston, MA 02115.
2 Department of Medicine, Cardiovascular Division, Brigham and Women's Hospital,
Harvard Medical School, Boston, MA 02115.
3 Department of Cardiology, Charlton Memorial Hospital, 363 Highland Ave., Fall
River, MA 02720.
4 Department of Cardiology, Brigham and Women's Hospital, Harvard Medical
School, Boston, MA 02115.
5 Department of Cardiac Surgery, Brigham and Women's Hospital, Harvard Medical
School, Boston, MA 02115.
Received January 9, 2003;
accepted after revision July 23, 2003.
Address correspondence to S. Tatli
(statli{at}partners.org).
Introduction
Lipomatous hypertrophy of the interatrial septum is a well-described
abnormality characterized by excessive deposition of nonencapsulated adipose
tissue. The classic finding is a homogeneous, bilobed configuration of the
interatrial septum with sparing of the fossa ovalis. We present the MRI
findings of lipomatous hypertrophy of the interatrial septum with atypical
features, including the extent, signal intensity, and contrast enhancement of
the infiltrated myocardium.
Case Report
A 45-year-old man was found to have abnormal findings on an ECG obtained
for routine preoperative testing, characterized by marked biatrial enlargement
and incomplete right bundle branch block. He also provided a several-year
history of rapid, sustained palpitations and was referred for successful
radiofrequency ablation of atrioventricular nodal reentrant tachycardia. After
receiving the diagnosis of squamous cell carcinoma of the floor of the mouth,
the patient underwent CT of the chest that suggested an infiltrative right
atrial mass. Subsequently, he was referred to our institution for MRI of the
heart. His medical history included an occipital scalp lipoma. Until recently,
he had smoked two packs of cigarettes per day.
MRI was performed with a 1.5-T superconducting magnet (Signa, General
Electric Medical Systems, Milwaukee, WI) using a cardiac surface coil, ECG
gating, and breath-holding. Multiphase, gradient-echo, steady-state free
precession images were obtained in axial, short-, and long-axis planes (TR/TE,
4.09/1.64; views per segment, 16). Double inversion recovery axial images were
used for bright-fat imaging (TR = 2 R-R intervals) and repeated with fat
saturation. T1-weighted fast spin-echo axial images were obtained with fat
saturation before and immediately after administration of 0.2 mmol/kg
gadopentetate dimeglumine. A frequency-selective fat-saturation technique was
used for fat saturation.
All images revealed diffuse and nodular thickening of the entire right
atrial wall in addition to a bilobed mass in the interatrial septum (Figs.
1A and
1B). The fossa ovalis was
spared. The abnormality was circumferential and nodular with a maximal
thickness of 3.2 cm. The thickening involved the wall of the right atrial
appendage (Fig. 1C). Extension
of the mural thickening to the inferior portion of the superior vena cava gave
evidence of lumen narrowing (Fig.
1D). The free wall of the right ventricle was also thickened with
extensive fatty infiltration, especially in the basal and mid portions
(Fig. 1A).
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Fig. 1A. —45-year-old man with history of palpitations. Axial MR image
obtained with double inversion recovery technique (TR/TE, 2,069/38) shows
diffuse thickening of free walls of right atrium (solid white arrows)
and right ventricle (black arrow). Note interatrial septal mass
(open arrow). Thickened right atrial wall, which exhibits slightly
more intense signal than normal myocardium, is less intense in signal than
pericardial and posterior mediastinal fat or fat-infiltrated right ventricular
wall.
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Fig. 1B. —45-year-old man with history of palpitations. Axial MR image
obtained with double inversion recovery technique and fat saturation reveals
saturation of abnormal myocardium in lateral and posterior walls of right
atrium (open white arrows) and in free wall of right ventricle
(open black arrow). Note lack of saturation in anterior portion of
right atrial wall (solid white arrow).
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Fig. 1C. —45-year-old man with history of palpitations. Axial MR image
obtained with double inversion recovery technique and fat saturation shows
thickened wall of right appendage (arrow). Note lack of saturation
anteriorly.
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Fig. 1D. —45-year-old man with history of palpitations. Axial MR image
obtained with double inversion recovery technique shows circumferential
thickening of wall of superior vena cava (arrow). Note partial
obstruction.
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On double inversion recovery images, the thickened right atrial wall showed
homogeneous, slightly increased signal intensity compared with that of normal
myocardium. The degree of the signal intensity of the thickened myocardium was
substantially less than that of the pericardial, posterior mediastinal, and
subcutaneous fat (Fig. 1A). The
fat-saturated images showed saturation in the interatrial septum and lateral
and posterior aspects of the right atrium and the free wall of the right
ventricle, indicating the presence of fat. However, no saturation was noted in
the thickened anterior and superior aspects of the right atrium (Figs.
1B and
1E). Gadolinium-enhanced images
showed enhancement of the nonsaturated components of the mass and some of the
fat-infiltrated regions (Fig.
1F). The infiltrated walls of the right atrium were hypokinetic on
cine images. The wall motion was normal in the left and right ventricles
including the thickened portions of the right ventricle.
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Fig. 1E. —45-year-old man with history of palpitations. T1-weighted
axial MR image (1,000/20; flip angle, 90°) obtained with fat saturation
shows thickened right atrial wall (arrow). Note lack of saturation
anteriorly.
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Fig. 1F. —45-year-old man with history of palpitations.
Gadolinium-enhanced T1-weighted axial MR image (1,000/20; flip angle, 90°)
obtained with fat saturation shows enhancement of thickened anterior right
atrial wall (arrow). Signal intensity of this region increased 90% in
comparison to that seen in unenhanced image.
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Because of these atypical features, malignancy such as liposarcoma could
not be excluded. After catheterization revealed normal coronary arteries, the
patient underwent right anterolateral thoracotomy and wedge biopsy of the
right atrial wall from two different regions. During thoracotomy, the mass
appeared solid and involved the right atrial wall, encompassing most of the
lateral wall. It extended cephalad to the proximal superior vena cava.
Palpation and visual inspection revealed thickening and fatty infiltration of
the free wall of the right ventricle. The pathologic analysis revealed
lipomatous hypertrophy of the right atrial wall with moderate to severe
myocyte hypertrophy and vascular medial hypertrophy
(Fig. 1G).
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Fig. 1G. —45-year-old man with history of palpitations. High-power
photograph of myocardial biopsy specimen from right atrium shows abundant
adipocytes (white arrows) with moderate to severe myocyte hypertrophy
(black arrows). (H and E, x100)
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Discussion
Lipomatous hypertrophy of the interatrial septum is an abnormality
characterized by the excessive deposition of fatty tissue in the cardiac
interatrial septum. Pathologically, the lesion consists of a nonencapsulated
mass of adipose tissue with entrapped and hypertrophied myocytes
[1]. The absence of
encapsulated fat cells together with the presence of fetal fat cells and
hypertrophied myocytes distinguish it from lipoma
[1]. Typically, these fatty
masses of the interatrial septum extend from the coronary sinus to the level
of the aortic root with sparing of the fossa ovalis, resulting in a dumbbell
configuration [2].
The clinical significance of lipomatous hypertrophy of the interatrial
septum has been debated. In most of the affected patients, it represents an
incidental echocardiographic finding that requires no intervention. On rare
occasions, this finding may be associated with atrial arrhythmias, obstructive
symptoms, or even sudden death
[1,
2]. Antemortem diagnosis is now
made with increasing frequency by a variety of noninvasive techniques
including echocardiography, CT, and MRI
[1]. The transthoracic and
transesophageal echocardiographic appearances of lipomatous hypertrophy of the
interatrial septum are well documented. The diagnosis is based on the classic
morphology of the thickened, bilobed interatrial septum
[3]. On CT, lipomatous
hypertrophy of the interatrial septum is shown as a dumbbell-shaped mass of
fat attenuation in the interatrial septum
[2].
MRI diagnosis of lipomatous hypertrophy of the interatrial septum is
straightforward in classic cases, and this entity is characterized by a
bilobar interatrial septal thickening revealing homogeneous high signal
intensity similar to that of subcutaneous fat tissue
[4]. The exclusively fatty
nature of such masses can be seen on fat-suppressed imaging
[2].
However, lipomatous hypertrophy may not be confined to just the interatrial
septum. Rarely, the process may be diffuse, and the free wall of the right
atrium may be partially or completely infiltrated by adipose tissue
[3]. The fatty infiltration may
extend into the free wall of the left atrium
[5]. The free wall of the right
ventricle and interventricular septum may also be involved
[6]. The fatty mass may extend
superiorly and encase the superior vena cava with, in rare instances,
obstruction to right atrial inflow
[4]. Lipomatous hypertrophy of
the interatrial septum might appear as a rounded, circumscribed fatty mass
that may be large and occupy the right atrium
[7].
The signal intensity of the lipomatous hypertrophy has been described as
homogeneous, similar to pericardial and subcutaneous fat. In our patient, the
signal intensity was lower than pericardial and other mediastinal fat and
nearly isointense to normal myocardium in contradistinction to previously
published cases. The fat-suppressed images were helpful to reveal fatty
content. However, some areas in the infiltrated myocardium did not suppress
with fat saturation. These nonfatty areas showed some enhancement with
contrast administration. In light of the pathology result, the solid-looking
areas in the fatty infiltrated myocardium represent entrapped and atypically
hypertrophied myocytes. The enlarged, hypertrophied myocytes generally seen in
lipomatous hypertrophy of the interatrial septum may result in atypical
appearance [1].
The number of cases of lipomatous hypertrophy of the interatrial septum
reported by MRI is limited. Thus, any variation from the "classic"
appearance may, in fact, represent part of the "normal" spectrum.
In addition, MRI has inherent limitations. The anterior aspect of the heart
may appear brighter than the posterior aspect because of the proximity to the
cardiac surface coil, which may cause signal differences compared with the
posterior aspect. Incomplete fat suppression may also be seen with current
fat-suppression techniques.
In summary, MRI offers a highly sensitive, thorough, and noninvasive method
for the diagnosis of lipomatous hypertrophy of the interatrial septum, which
may rarely present with extensive infiltration far beyond the interatrial
septum. MRI may show inhomogeneous or low signal intensity that may not be
isointense with pericardial fat. In addition, there may be areas that do not
suppress with fat saturation and that show enhancement with gadopentetate
dimeglumine, mimicking malignant infiltration.
These unusual presentations of lipomatous hypertrophy of the interatrial
septum can cause diagnostic uncertainty and prompt biopsy or excision.
Radiologists should be aware of these atypical presentations. Lipomatous
hypertrophy of the interatrial septum must be included in the differential
diagnosis of any fat-containing right atrial neoplasm regardless of its extent
and signal characteristics.
Acknowledgments
We thank Joel M. Henderson, Department of Pathology, Brigham and Women's
Hospital, for providing a photograph of the pathology specimen.
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Introduction
Case Report
