DOI:10.2214/AJR.06.0996
AJR 2007; 188:W550-W553
© American Roentgen Ray Society
Cardiac Septal Aneurysm Mimicking Pseudomass: Appearance on ECG-Gated Cardiac MRI and MDCT
Jonathan D. Dodd1,2,
Suzanne L. Aquino1,
Godtfred Holmvang3,
Ricardo C. Cury1,2,
Udo Hoffmann1,2,
Thomas J. Brady1,2 and
Suhny Abbara1,2
1 Department of Radiology, Massachusetts General Hospital and Harvard Medical
School, 55 Fruit St., Boston, MA 02114.
2 Cardiac CT/MRI/PET Program, Department of Radiology, Massachusetts General
Hospital and Harvard Medical School, Boston, MA.
3 Division of Cardiology, Massachusetts General Hospital and Harvard Medical
School, Boston, MA.
Received July 30, 2006;
accepted after revision October 11, 2006.
Address correspondence to J. D. Dodd
(jddodd{at}partners.org).
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Abstract
OBJECTIVE. Cardiac septal aneurysms in adults are diagnosed when the
interatrial or interventricular septal membrane deviates more than 10–15
mm to either side in the cardiac chamber. Routine non-ECG-gated chest CT does
not have sufficient temporal and spatial resolution for adequate
characterization of such an entity. We report the imaging findings of cardiac
septal aneurysms depicted in two patients with ECG-gated cardiac MRI and in a
third with ECG-gated cardiac 64-MDCT. Each aneurysm was initially believed to
be a cardiac tumor on the basis of the appearance on non-ECG-gated chest CT or
MRI.
CONCLUSION. Nonopacified blood can fill a cardiac septal aneurysm
and mimic a pseudomass. It is important that radiologists recognize such an
entity on chest CT and MRI because of the association with intracardiac
shunting and stroke and to avoid misdiagnosis of an aneurysm as a cardiac
tumor.
Keywords: aneurysm • cardiopulmonary imaging • CT • CT technique • heart • MRI
Introduction
Cardiac septal aneurysm in adults is an uncommon but well-recognized
abnormality defined by a cardiac septum deviating more than 10–15 mm to
either side in the cardiac chamber
[1]. The size of the base of
the aneurysm is important and must be more than 15 mm but not involve the
entire septum. The prevalence of cardiac septal aneurysm is 0.2–3% in
the general population [2].
Variation in the reported prevalence is related to the method of diagnosis
(autopsy, transthoracic echocardiography, or transesophageal
echocardiography), variable size criteria (> 5 mm in children, 6–15
mm in adults), and the population studied (general cardiac patients,
cardiothoracic surgical patients, and patients who have had a stroke). The
clinical significance of these aneurysms lies in associated intracardiac
shunting, usually through a patent foramen ovale or, less commonly, an atrial
septal defect. Such shunts can be a source of paradoxic embolism and stroke
[3]. A systematic review
[4] of patients with
cryptogenic stroke revealed an annual stroke rate of 3.8% among patients with
interatrial septal aneurysm and patent foramen ovale compared with 1.05% among
those without these anomalies.
Cardiac septal aneurysm is traditionally imaged with echocardiography. With
the increasing use of ECG-gated cardiac MRI and MDCT for noninvasive cardiac
imaging, previously undetected structures are becoming evaluable
[5]. We describe three patients
with imaging findings initially interpreted as atrial masses on routine chest
CT in two cases (Figs. 1A and
2A) and on suboptimally gated
cardiac MRI in a third patient (Figs.
3A and
3B).
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Fig. 1A —88-year-old man with history of penile carcinoma. See also
Figure S1C, cine loop, in supplemental data. Nongated routine
contrast-enhanced axial chest CT scan shows smooth mass (arrow)
suspected of being left atrial tumor.
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Fig. 2A —74-year-old man with bladder cancer. See also Figure S2C,
cine loop, in supplemental data. Staging nongated contrast-enhanced chest CT
scan shows mass (arrow) suspected of being tumor in left atrium.
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Fig. 3A —57-year-old man with squamous cell carcinoma of skin
secondary to immunosuppressive therapy. See also Figure S3D, cine loop, in
supplemental data. Double-inversion T1-weighted fast spin-echo short-axis MR
image shows apparent high-signal-intensity nodular mass (arrow)
arising from region of tricuspid annulus.
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Fig. 3B —57-year-old man with squamous cell carcinoma of skin
secondary to immunosuppressive therapy. See also Figure S3D, cine loop, in
supplemental data. Proton-density fast spin-echo four-chamber MR image shows
apparent mass (arrow) in region of tricuspid annulus. Slight blurring
of heart borders is evident with motion artifact secondary to suboptimal
gating.
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Subjects and Methods
Two patients underwent CT of the chest, abdomen, and pelvis as part of
annual surveillance or staging (Table
1). Chest CT was performed with a 16-MDCT system (LightSpeed 16,
GE Healthcare) at 2.5-mm slice thickness, no slice overlap, 140 kVp at 350
mAs, and 65 mL of iodinated contrast medium ([iopamidol] Isovue 370, Bracco
Diagnostics) injected at 2 mL/s after an empiric delay of 35 seconds in a
single-infusion protocol followed by a saline chaser of 30 mL. The third
patient underwent cardiac MRI for evaluation of an arrhythmogenic myocardial
focus.
At our institution, cardiac MRI includes cine images obtained with
steady-state free precession technique (TR/TE, 3.5/1.4; matrix size, 192
x 192; field of view, 34 x 34 cm; slice thickness, 8 mm) obtained
in two-chamber, four-chamber, and short-axis planes followed by fast spin-echo
sequences in a plane through the abnormality in question. Cardiac MDCT
(SOMATOM Sensation 64, Siemens Medical Solutions) with retrospective ECG
gating was performed at a slice thickness of 0.75 mm, slice overlap of 0.5 mm,
120 kVp at 850 mAs, and 90 mL of iodinated contrast medium (Isovue 370)
injected at 6 mL/s in a single-infusion contrast bolus protocol followed by a
40-mL saline chaser. A timing bolus with the region of interest placed on the
ascending aorta was used to determine scanning delay. Multiphasic
reconstructions at 10% intervals of the R-R interval were used to obtain cine
loops through systole and diastole, as described in previous studies
[6] (Figs. S1C, S2C, and
S3D).
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Fig. 1B —88-year-old man with history of penile carcinoma. See also
Figure S1C, cine loop, in supplemental data. Cardiac bright-blood steady-state
free precession MR image in four-chamber view shows thin membrane
(arrow) consistent with interatrial septal aneurysm filled with
nonopacified blood and corresponding exactly to pseudomass seen on nongated
chest CT.
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Fig. 2B —74-year-old man with bladder cancer. See also Figure S2C,
cine loop, in supplemental data. Cardiac MR image obtained with steady-state
free precession sequences shows thin membrane (arrow) consistent with
interatrial septum filled with blood and bowing 12 mm into left atrium.
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Fig. 3C —57-year-old man with squamous cell carcinoma of skin
secondary to immunosuppressive therapy. See also Figure S3D, cine loop, in
supplemental data. Cardiac-gated MDCT scan shows membranous interventricular
septal aneurysm (arrow) protruding 15 mm into right ventricular
outflow tract. Finding was confirmed on transthoracic echocardiography.
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Results
ECG-gated cardiac MRI of two patients (Figs.
1B and
2B) and cardiac 64-MDCT of the
third patient (Fig. 3C) showed
that in each case the mass represented nonopacified blood filling a cardiac
septal aneurysm.
Discussion
Interatrial and ventricular septal aneurysms in adults are defined by
bowing of the septum more than 10–15 mm to either side
[1]. Most of these aneurysms
are thought to be congenital, although some are caused by increased atrial or
ventricular pressure or develop postoperatively. The clinical relevance of
these abnormalities lies in the presence of an interchamber shunt, which for
interatrial septal aneurysm is most commonly a patent foramen ovale, although
atrial septal defect has been described. Such shunts may be present in as many
as 50% of patients with interatrial septal aneurysm
[7]. Membranous
interventricular septal aneurysms are most commonly associated with a
left-to-right shunt. They also have been associated with thromboembolism, and
some may become large enough to obstruct the right ventricular outflow tract
[8–11].
To our knowledge, the appearance of cardiac septal aneurysms mimicking
cardiac masses on nongated CT of the chest has not been previously described.
In our series, two patients with underlying primary carcinoma underwent
cardiac-gated MRI because routine chest CT findings suggested a mass in the
left atrium. The principal reason for such appearances relates to the fact
that routine chest CT is typically performed with a single-infusion contrast
bolus protocol. In two cases in this series, despite the use of a saline
chaser, nonopacified blood in the right atrium filled an interatrial septal
aneurysm and caused the appearance of a pseudomass. For patients with routine
chest CT scans showing a possible atrial pseudomass, we now perform
echocardiography for further evaluation. If the findings do not allow optimal
evaluation, cardiac-gated MRI or CT is performed. For cardiac-gated CT, a
dual-phase infusion protocol with a second, more diluted (half contrast, half
saline solution) contrast bolus immediately after the first results in better
contrast opacification of the right atrium.
Cardiac MRI is currently the reference standard noninvasive imaging test
for the depiction of cardiac masses because of its superior temporal
resolution (50 ms) and tissue characterization. Although several sequences can
be used, cine steady-state free precession sequences provide high spatial and
temporal resolution throughout the cardiac cycle and are particularly useful
for evaluating mobile structures within the heart. In each of our patients,
the interatrial septal aneurysms were clearly depicted on the four-chamber
view, which provided the best imaging plane for evaluation of the cardiac
septa. Poor ECG signal acquisition in the third case, however, resulted in
poor image quality. In this patient, the diagnosis of membranous
interventricular septal aneurysm was readily apparent on cardiac 64-MDCT.
Developments in cardiac vector-gating techniques have markedly improved
ECG-gated signal acquisition in cardiac MRI and might have proved beneficial
in imaging of this patient.
Cardiac septal aneurysms mimicking cardiac masses have been detected with
echocardiography [12].
Recognition of such an entity with cardiac CT and MRI is important to avoid
confusion with tumors and unnecessary additional investigation. In our
patients, the cardiac septal aneurysms most closely mimicked atrial myxoma and
metastatic lesions. Atrial myxoma, the most common primary cardiac tumor of
the left atrium, usually has a characteristic pedicular attachment to the
interatrial septum. This feature further enhances its similarity to
interatrial septal aneurysm. Metastatic lesions are most commonly located in
the right atrium, are 20–40 times more common than primary cardiac
malignant tumors, and usually have a broad base and infiltrative appearance
involving the atrial wall. Metastatic lesions usually show low signal
intensity on T1-weighted images and high signal intensity on T2-weighted
images and typically enhance after contrast administration. The membranous
interventricular septal aneurysm in our patient had a remarkably similar
appearance. Slow blood flow within the aneurysm caused high signal intensity
on T2-weighted sequences, and contrast material filling the aneurysm mimicked
enhancement.
The case of our third patient illustrates a limitation of ECG-gated cardiac
MRI: The magnetic field can have an electroconductive effect on ECG signal.
Any moving conductive substance within a magnetic field develops its own
inducible electrical signal, which can interfere with the ECG signal and cause
suboptimal gating. Because it has no electroconductive effects on ECG signal
acquisition, CT sometimes gives better image quality with less motion
artifact. The current spatial and temporal resolution of 64-MDCT of the heart
is approximately 0.4 x 0.4 x 0.4 mm voxel size and 165 ms. As a
result, thin intracardiac structures, such as septal membranes, can be
visualized. Further technologic developments, such as the improved temporal
resolution of dual-source CT (85 ms), are likely to increase the use of
ECG-gated cardiac CT in the evaluation of intracardiac abnormalities such as
cardiac masses [13,
14].
Cardiac septal aneurysms can mimic cardiac masses on nongated chest CT. In
such cases, echocardiography should provide clarification. When
echocardiographic evaluation is suboptimal, cardiac MRI and CT are useful
alternatives and provide excellent depiction of cardiac septal aneurysms. It
is important for radiologists to recognize such entities because of their
association with intracardiac shunting and thromboembolic complications and to
avoid misdiagnosis of an aneurysm as a cardiac tumor.
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Abstract
Introduction
