British Journal of Radiology (2003) 76, 427-428
© 2003 British Institute of Radiology
doi: 10.1259/bjr/61128761
An unusual cause of tachycardia
G Klafkowski, MBCB, DMRD, FRCR1,
N Newall, MBBS, MRCP2 and
C Sampson, FRCS, FRCR, FACC1
Department of 1 Radiology and 2 Cardiology, The Cardiothoracic Centre, University of Liverpool NHS Trust, Liverpool, UK
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Introduction
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A 55-year-old female presented to our tertiary referral cardiology centre with sudden onset regular tachycardia of greater than 3 h duration. She had experienced previous similar episodes over the preceding 10 years each with sudden onset and termination without associated syncope, dyspnoea or chest pain. Past medical history included hypertension, atypical chest pain with left bundle branch block and breast carcinoma for which she had a lumpectomy in 1987. Exercise testing in 1998 was unremarkable. The patient smoked 20 cigarettes per day.
On examination the pulse was 120 regular and the blood pressure 170/100 mmHg. The patient had central obesity: body mass index=32. No other cardiovascular abnormalities were detected. 12 lead ECG demonstrated atrial tachycardia of 120/min with left bundle branch block which spontaneously fell to 60/min without a change in the P or QRS morphology.
Transoesophageal echocardiography was performed and demonstrated normal left ventricular systolic function and a normally functioning bicuspid aortic valve. The upper two-thirds of the interatrial septum and to a lesser extent the free wall of the right ventricle were thickened and echo bright (Figure 1
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Figure 1. Four chamber mid oesophageal transoesophageal echocardiography demonstrating a thickened echogenic interatrial septum and incidental bicuspid aortic valve.
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Appearances suggested fatty tissue, but further imaging was required to confirm this. Furthermore, due to the previous history of a breast neoplasm, the exclusion of metastatic deposits was required. Therefore, a quad spiral multislice CT (Somaton Plus 4 Vol Zoom, Siemens Medical Systems, Erlangen, Germany) and MRI characterization of the presumed benign fat infiltration was performed (Figures 2 and 3).
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Figure 2. Contrast enhanced axial 5 mm quad spiral, demonstrating low density thickening of the atrial septum.
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Figure 3. T1W spin echo axial image demontrating the classic dumbbell shaped high signal intensity thickening of the atrial septum.
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What is the possible diagnosis?
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Answer
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Although lipomatous hypertrophy of the atrial septum (LHAS) was suspected on the basis of the echocardiography in this patient, a further complicating factor was the past medical history of a breast carcinoma.
On CT the superior and middle parts of the atrial septum were markedly enlarged and of low density consistent with fat. There was thickening of the pericardium retrosternally over the free wall of the right ventricle, thought to be due to pericardial fat rather than fatty infiltration. The left atrium was noted to be distorted by the atrial septal mass (Figure 2
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Further non-invasive tissue characterization with MRI also confirmed the adipose content of the atrial septum. The axial T1W spin echo image (Figure 3) showed the atrial septum to be of high signal intensity and a confident diagnosis of lipomatous hypertrophy of the atrial septum was made.
LHAS, which is an uncommon benign proliferation of unencapsulated fat cells in the interatrial septum with sparing of the fossa ovalis, has a quoted incidence at autopsy of approximately 1% [1]. Although most patients are asymptomatic it can be associated with supraventricular tachyarrythmias due to infiltration of the conduction system and rarely it may present with the signs and symptoms of superior vena cava obstruction [2].
Although echocardiography is well suited as a screening method for cardiac masses [3], fat cannot easily be differentiated from myxomas or other tumours on the basis of hyper-reflectivity. However, characteristic appearances on CT and MRI obviates the need for biopsy.
Meaney et al [4] analysed the CT findings of LHAS and concluded that the dumbbell shaped mass of fat attenuation within the atrial septum was highly characteristic.
The normal atrial septum on MRI is thin with a signal intensity similar to that of muscle on standard spin echo pulse sequences. In LHAS the fat is of increased signal on T1W images compared with muscle. Atrial myxoma and thrombi are rarely and atypically of increased signal on T1W spin echo and inversion recovery fat suppressed sequences can be employed in such circumstances for problem solving.
CT further supplemented with MRI in our case demonstrated the characteristic, non-enhacing, lobular interatrial thickening of fat density and signal, respectively. Thus, the need for biopsy as a means of diagnosis was avoided.
Although this appears to be a rare finding and is rarely reported in the UK population, it is related to obesity and with this becoming an increasing problem the incidence of its occurrence may increase. Therefore, it is important for radiologists to recognize and be aware of the characteristic appearances on cross-sectional imaging.
Received for publication December 18, 2001.
Accepted for publication January 14, 2002.
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References
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- Reyes CV, Jablokow VR. Lipomatous hypertrophy of the cardiac inter atrial septum: a report of 38 cases and review of the literature. Am J Clin Pathol 1979;72:785–8.[Medline]
- Tschirkov A, Stegaru B. Lipomatous hypertrophy of interatrial septum presenting as recurring pericardial effuion and mistaken for constrictive pericarditis. Thorac cardiovasc Surgeon 1997;27:400–3.
- Wann SL, Sampson C, Liu Y. Cardiac and paracardiac masses. Echocardiography 1998;15:139–46.[Medline]
- Meaney JFM, Kazerooni EA, Jamadar EA, Korobkin. CT appearance of lipomatous hypertrophy of the interatrial septum. AJR Am J Roentgenol 1997;168:1081–4.[Abstract/Free Full Text]
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