Lipomatous Hypertrophy of Interatrial Septum in Asssociation of Hypertrophic Cardiomyopathy: A Case Report

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1 Chin J Radiol 2002; 27: Lipomatous Hypertrophy of Interatrial Septum in Asssociation of Hypertrophic Cardiomyopathy: A Case Report WEI-YU WANG 1 YEUN-CHUNG CHANG 1 CHIEN-HUA HUANG 2 YIU-WAH LI 1 Departments of Medical Imaging 1 and Emergency Medicine 2, National Taiwan University Hospital (LHIS), usually found in echocardiography, is a rare non-neoplastic disease entity, which may cause arrhythmia or sudden death. We reported a case of LHIS associated with hypertrophic cardiomyopathy (HCM), which was suspected a hyperechoic intraatrial tumor in transthoracic echocardiography. Magnetic resonance (MR) imaging showed fat infiltration of the interatrial septum, indicating lipomatous hypertrophy in addition to hypertrophic myocardium. Combined HCM and LHIS were assumed incidental but had not been reported to our knowledge. Characteristic MR imaging of LHIS is an important supplement to echocardiography with ambiguous findings. Key words: Heart, lipomatous hypertrophy; cardiomyopathy; magnetic resonance; imaging; echocardiography Reprint requests to: Dr. Yeun-Chung Chang Department of Medical Imaging, National Taiwan University Hospital. No. 7, Chung-Shan South Road, Taipei 100, Taiwan, R.O.C. (LHIS) first described by Prior in 1964 is accumulation of adipose tissue cephalic and caudal to the fossa ovalis in the interatrial septum [1]. It was reported more commonly in mid-aged or seventh to eighth decade of life, because of increased age-associated epicardial fat deposition and life-threatening arrhythmia [2]. Associated hypertrophic cardiomyopathy (HCM) in patients of LHIS has not been reported to our knowledge. We report a case of HCM with suspected intratrial tumor due to ambiguious finding in transthoracic echocardiography. The diagnosis of LHIS has been established by using magnetic resonance (MR) imaging. CASE REPORT A 62 year-old woman, who had a history of hypertension and hyperlipidemia for more than ten years, was admitted to evaluate her chest tightness sensation. Neither cerebrovascular accident nor pulmonary embolism was noted. Regular heartbeat and grade III/VI systolic murmur were found. Transthoracic echocardiography revealed systolic anterior movement of the mitral valve, asymmetric septal hypertrophy, dilated left atrium, good contractility of left ventricle and increased pressure gradient (about 60 mmhg) at left ventricular outflow track. The findings were suggestive of HCM. An initial transthoracic echocardiography revealed a hyperechoic mass in right atrium. A hyperechogenic mass (2.1x1.7cm) over the interatrial septum was found by transesophageal echocardiography (Fig. 1). For differentiating a cardiac tumor and lipomatous hypertrophy of interatrial septum, she received cardiac magnetic resonance (MR) imaging. Spin-echo EKG-gated MR imaging (TR/TE, 779/16, slice thickness 5 mm) was performed in axial and coronal planes. An evenly distributed hyperintense

2 258 mass was noted along the atrial septum with sparing of the foramen ovale on spin-echo T1 weighted image (Fig. 2). LHIS was diagnosed. Characteristic findings of HCM were also noted in cardiac MR imaging. Afterwards, she received cardiac cathetization, which showed patent coronary artery and concentric myocardial hypertrophy. Under the impression of incidental association of LHIS in HCM, she received medication for hypertension and then follow-up in outpatient clinic. DISCUSSION Unlike intracardiac lipoma, LHIS showing increased fat deposition is not a true neoplasm. LHIS generally occurs anterior or superior to the fossa ovalis, and histologically is characterized by mature fat with varying quantity of fetal fat, inflammation and fibrosis, and entrapment of myocardial fibers with atypia cytologically [3]. It has been advocated to evaluate this disorder by computed tomography (CT), MR imaging, or echocardiography (Table 1). CT or MR can define the fatty nature within the interatrial septum and measure the thickness of the fatty tissue precisely [4]. The normal range of thickness of the interatrial fat is from 0 to 9.6mm anterior to fossa ovalis and from 0 to 9.9mm posterior to the fossa ovalis [5]. In our case, the thickness of the interatrial septum was about 2 cm, at both cephalic and caudal to the fossa ovalis (Figure 2). The diagnosis of LHIS can be made on the basis of marked thickening of the interatrial septum with sparing of the fossa ovalis. MR imaging on coronal plane can demonstrate the characteristic distribution and signal intensity of adipose tissue on the interatrial septum in LHIS without the limitation of appropriate window and depth resolution on echocardiography. LHIS has been reported to be associated with arrhythmias (Table 1) [1,6,7,8]. It has been assumed that fat infiltrating in the region of the conduction system can cause arrhythmias and sudden death [9]. The mechanism by which fatty infiltration results in arrhythmias and causes sudden death is unclear. It is assumed that localized fat of LHIS causes a delay in the intraventicular transmission of impulses, with the subsequent development of re-entrant ventricular arrhythmias [10]. Fatty infiltration of the heart is also more susceptible to rupture if acute myocardial infarction occurs [11]. Malignant transformation of cardiac lipomatous hypertrophy, though rarely encountered, can occur [12]. HCM causes obstruction of the outflow from left ventricle. The hypertrophy of myocardium results Figure 1. Transesophageal echocardiography showed hyperechoic mass at the atrial septum cephalad and caudal to fossa ovalis (arrow). RA, right atrium; LA, left atrium. Figure 2. Conventional spin echo (TR/TE:779/16) T1 weighted coronal image showed characteristic fatty infiltration of the interatrial septum with sparing of fossa ovalis (arrow). RA, right atrium; LA, left atrium. from mutation of the gene, which interferes with the organization and function within the myocytes showing myocyte disarray histologically [13]. There was no known correlation between HCM and LHIS. In this report, incidental association of these two conditions was considered (Table 1). Since no arrhythmias was found, conservative medical treatment for hypertension was undertaken. Since LHIS is not a true neoplasm, the role of surgical intervention remains controversial. The diagnosis of LHIS can be confidently made by transesophageal echocardiography, CT or MR imaging. Surgical incisional biopsy is unnecessary after the

3 259 Table 1. In vivo diagnostic modality and associated abnormality in lipomatous hypertrophy of the interatrial septum Authors Diagnostic modality Associated abnormality Study References Tschirkov. A et al Surgery Pericardial effusion Case report. Thoracic and Cardiovascular Surgeon 27(6): 400-3, 1979 Isner et al CT Arrhythmias Case report. Circulation 66(2): 470-3, 1982 Silverman et al TTE & CT Case report American Journal of Cardiology 54(8): ,1984 Levine et al CT & MR Case report Journal of the American College of Cardiology 7(3): , 1986 Fisher et al MR Case report Journal of Computed Tomography 12(4): 267-9, 1998 Case report Journal of the American Society of Echocardiography 1(6): 450-4,1988. Beau et al TTE Long-term total parenteral nutrition Original report Journal of Parenteral & Enteral Nutrition 15(6): ,1991 Bhattacharjee et al Surgery Ischemic heart disease Case report British Heart Journal. 65(1): 49-50,1991 Smith et al Surgery Coronary artery disease Case report Journal of Clinical Anesthesia 5(1): Arrhythmias 73-5, 1993 Zeebregts et al Surgery Ischemic heart disease, premature Case report European Journal of Cardio-Thoracic ventricular contractions Surgery 11(4): 785-7, 1997 Mortele et al MR Foot numbness Case report Journal of Magnetic Resonance Imaging 8(5): , 1998 Dotti et al.1998 TTE Cerebrotendinous xanthomatosis Original report Journal of Neurology 245(11): 723-6,1998 Noma et al TTE & MR Case report Circulation 100(6): 684,1999 Wang et al MR Hypertrophic cardiomyopathy Case report CT, Computed Tomography; MR, Magnetic Resonance; TTE, Trans-thoracic echocardiography; TEE, Trans-esophageal echocardiography diagnosis has been made. The major risk of LHIS is arrhythmias and sudden death. In non-arrhythmic patient, surgical intervention may be not beneficial and is still controversial [14]. MR imaging is excellent in evaluating and diagnosing LHIS with multiplanar capability and tissue characterization. Though characteristic findings of echocardiography has been reported, limitations of echocardiography, including depth resolution, small field of view, and confusing nature of hyperechogeniety, may cause difficulty of making a correct diagnosis of LHIS. MR imaging overcomes technically difficult location for transthoracic and transesophageal echocardiography and avoids the possible partial volume artifact on CT imaging. It also provides excellent characterization of the fatty tissues by T1-weighted image and fat saturation techniques. MR imaging is an important supplementary evaluation for patients with inconclusive echocardiography. REFERENCES 1. Prior JT. Lipomatous hypertrophy of cardiac interatrial septum: a lesion resembling hibernoma, lipoblastomatosis and infiltrating lipoma. Arch Pathol 1964; 78: Reyes CV. Jablokow VR. Lipomatous hypertrophy of the cardiac interatrial septum. A report of 38 cases and review of the literature. Am J Clin Pathol 1979; 72: Gay JD. Clinical and Morphologic features of lipomatous hypertrophy of the interatrial septum. Am J Foren Pathol 1996; 17: Isner, JM, Swan CS II, Mikus P, Carter BL: Lipomatous hypertrophy of the interatrial septum: in vivo diagnosis. Circulation 1982; 66: Broderick LS, Conces DJ Jr, Tarver RD. CT evaluation of normal interatrial fat thickness. J Comput Assist Tomogr 1996; 20: Page DL. Lipomatous hypertrophy of the cardiac interatrial septum: its development and probable clinical significance. Human Pathol 1970; 1: Hutter AM, Page DL. Atrial arrhythmias and lipomatous hypertrophy of the cardiac interatrial septum. Am Heart J 1971; 82: Shirani J, Roberts WC. Clinical, electrocardiographic and morphologic features of massive fatty deposits ( lipomatous hypertrophy ) in the atrial septum. J Am Coll Cardiol 1983; 1: Bharati S, Lev M. Cardiac coduction system involvement in sudden death of obese young people. Am Heart J 1996; 129: Pantonowitz L. Fat infiltration in the heart. Heart 2001; 85: Roberts WC, Roberts JD. The floating heart or the heart too fat to sink: analysis of 55 necropsy patients. Am J Cardiol 1983; 52: Castleman B, Mcneely BU. Case records of the Massachusetts General Hospital (case ). Liposarcoma of the interatrial septum and both atria. N Engl J Med 1971; 285:

4 McAllister HA, Fenoglio JJ Jr. Tumors of the cardiovascular system, 2nd Series Fasc 15. Washington, DC: Armed Forces Institute of Pathology 1978: Zeebregts CJ, Hensens AG, Timmermans J, Pruszczynski Ms, Lacquet LK. Lipomatous hypertrophy of the interatrial septum: indication of surgery? Eur J Cardiol Thorac Surg. 1997; 11:

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