Atypical presentation of lipomatous hypertrophy of the interatrial septum: a case report.

BACKGROUND: Lipomatous hypertrophy of the interatrial septum (LHIAS) is a common finding on transthoracic echocardiogram (TTE). Occasionally, the appearance of LHIAS is atypical and multimodality imaging is helpful to make the diagnosis. We present a case of atypical LHIAS to highlight the potential aetiologies for an interatrial septal mass and review features on multimodality imaging that help decrease uncertainty and establish a diagnosis. CASE
SUMMARY: A 64-year-old man with a history of hypertension, diabetes mellitus, and coronary artery disease with multiple percutaneous coronary interventions presented to the emergency room with chest pain. Transthoracic echocardiogram showed a homogenous echo-dense, intracardiac mass present within the interatrial septum. Computed tomography (CT) angiogram of the chest showed a homogenous mass similar in radiodensity to extracardiac and pericardial fat. Cardiac magnetic resonance (CMR) confirmed LHIAS by homogenous signal that was nulled on fat suppression images. DISCUSSION: This case highlights that while most LHIAS has the standard 'dumbbell' appearance on TTE, there are instances where it can appear more like an adherent mass prompting a wider differential. Unenhanced CT of the heart can be used to confirm LHIAS by the presence of low attenuation values for tissue. Alternatively, CMR can be used for tissue characterization and confirmation of LHIAS. Precontrast T2/T1-weighted CMR images with steady-state free precession show high signal intensity in the area of LHIAS and produce a black/hypointense boundary effect between fat and myocardium. A multimodality approach is crucial in arriving at the appropriate diagnosis using the tissue characterization capabilities of CT and CMR.

Learning points

Differential of interatrial masses commonly includes lipomatous hypertrophy of the interatrial septum, though it can present atypically.

Multimodality imaging aids in the differential diagnosis of an interatrial mass. Computed tomography and cardiac magnetic resonance imaging provide advanced tissue characterization abilities that help cinch the diagnosis.

Introduction

Lipomatous hypertrophy of the interatrial septum (LHIAS) is a common finding on transthoracic echocardiogram (TTE). Although TTE is typically sufficient for diagnosis of LHIAS through pattern recognition of the classic dumbbell-shaped morphology within the interatrial septum, occasionally the appearance of LHIAS is atypical and multimodality imaging is helpful to make the diagnosis. Computed tomography (CT) and cardiac magnetic resonance (CMR) imaging offer the additional benefit of tissue characterization. We present a case of atypical LHIAS to highlight the potential aetiologies for an interatrial septal mass and review features on multimodality imaging that help decrease uncertainty and establish a diagnosis.

Case presentation

A 64-year-old man with a history of hypertension, diabetes mellitus, and coronary artery disease with multiple percutaneous coronary interventions (PCI) of the left anterior descending artery and left circumflex arteries, most recently 2 weeks prior, presented to the emergency room with chest pain. On the day of admission, he noted the sudden onset of precordial chest pain associated with dyspnoea while ambulating consistent with his prior angina. This pain was initially relieved by nitroglycerine spray, but due to continued pain he presented to the emergency room. On arrival, his vital signs were notable for heart rate of 75 beats per minute, blood pressure of 167/72 mmHg, respiratory rate of 20 breaths per minute, and oxygen saturation of 98% on ambient air. His body mass index was 35 kg/m2. Physical examination was notable for regular rate and rhythm, clear lung sounds, and a jugular venous pressure of 9 cmH2O. Serial cardiac enzymes were normal (troponin T 0.02 ng/mL, normal 0–0.03 ng/mL), and an electrocardiogram showed sinus rhythm with right bundle branch block and lateral t-wave inversions, unchanged compared to prior. His medication list prior to hospitalization included aspirin 81 mg daily, clopidogrel 75 mg daily, atorvastatin 40 mg daily, metoprolol tartrate 25 mg twice daily, amlodipine 10 mg daily, ranolazine 500 mg twice daily, and furosemide 20 mg daily. A TTE was performed for further evaluation of his chest pain and to assess for regional wall motion abnormalities. The study showed a homogenous echo-dense, intracardiac mass present within or attached to the interatrial septum () measuring 4 cm × 4 cm. The mass was noted within the superior aspect of the interatrial septum and extended superiorly and posterior to the aortic root. Movement of the mass was synchronous with the atrial walls (). The right and left atrial and left ventricular size were normal with normal left ventricular wall thickness and function. Pulmonary artery pressure was unable to be measured due to the absence of tricuspid regurgitation. Although images from a prior TTE were not available, a report of a TTE performed 1 year prior made no mention of an interatrial mass.

Transthoracic echocardiogram showing a left atrial mass (arrows) associated with the interatrial septum. (A) Apical four-chamber view. (B) Zoomed in apical four-chamber view. (C) Apical three-chamber view.

The differential diagnosis for this mass includes an atrial myxoma, iatrogenic haematoma, invasive or metastatic tumour, lipoma, liposarcoma, and LHIAS. While the most common cause of interatrial septal thickening is LHIAS, an extensive differential diagnosis was considered because of the absence of the typical symmetrical ‘dumbbell’ shape. In the setting of a clinical history of severe chest pain after a PCI, we were concerned about a complication of the procedure including vascular trauma and haematoma. To further localize the mass and evaluate for tumour and iatrogenic haematoma, a CT angiogram of the chest was performed. There was no evidence of aortic dissection or haematoma and no extension of the mass outside of the cardiac structures. The homogenous mass seen on echocardiogram was similar in radiodensity to extracardiac and pericardial fat with Hounsfield units (HU) within the fat range (−64 HU). The mass extended from the interatrial septum to the posterior left and right atria and spared the fossa ovalis suggestive of LHIAS (, Supplementary material online, ). Contrast imaging using CT demonstrated no enhancement to suggest vascularity to the mass and a normal pericardium.

Computed tomography four-chamber view. Interatrial septum measures 42.1 mm × 20.9 mm in height and width, respectively (A). Attenuation of the mass is measured at −64 HU which is similar to pericardial (−88 HU) and extracardiac (−97 HU) fat (B).

Although the attenuation on CT was similar to fat, the mass was not completely visualized. For further evaluation of the mass and chest pain, the patient was referred for CMR imaging without the stress protocol. Cardiac magnetic resonance imaging was performed on a 1.5-T scanner and confirmed LHIAS by homogenous signal that was nulled on fat suppression images (, Supplementary material online, Video S1). Although T1 weighted spin echo with and without fat suppression is more widely used in this situation, we used gradient echo technique here due to the benefit of shorter imaging times.

Cardiac magnetic resonance imaging showing lipomatous hypertrophy of the interatrial septum as evidenced by loss of signal on T-1 weighted gradient echo technique fat saturation images (A) compared to non-fat saturation images (B) and no abnormal enhancement on perfusion imaging (C). (A) Fat saturation pre-contrast four-chamber view of interatrial septum. (B) Non-fat saturation four-chamber view of interatrial septum. (C) Perfusion imaging four-chamber view of interatrial septum.

Cardiac magnetic resonance and TTE demonstrated normal ventricular function. Ultimately, the patient’s chest pain was determined to be of non-cardiac origin and he was discharged from the hospital in stable condition with recommendations for repeat imaging with TTE and/or CMR every 6 months to 1 year to monitor for interval progression.

Discussion

Lipomatous hypertrophy of the interatrial septum is a common finding seen on echocardiography with an incidence reported to be 1–8% of the general population. It is more commonly seen in women and in the elderly and is associated with obesity, steroid use, and emphysema. Histologic examination shows adipocyte hyperplasia and fat infiltration of the myocardial fibres differentiating it from a lipoma which has solely adipocytes. Lipomas account for ∼10% of cardiac neoplasms and are discrete collections of adipocytes that are normally extramyocardial and present as a defined rounded mass., While similar in tissue characterization to lipomas, LHIAS on TTE respects the boundaries of the atrial septum and typically spares the fossa ovalis. On transoesophageal echocardiogram, LHIAS appears as an echo-dense, globular thickening of the interatrial septum best seen on the bicaval view. This case highlights that while most LHIAS has the standard ‘dumbbell’ appearance on TTE, there are instances where it can appear more like an adherent mass prompting a wider differential. Unenhanced CT of the heart can be used to confirm LHIAS by the presence of low attenuation values for tissue (−80 to −120 HU) in the area of the interatrial septum. Alternatively, CMR can be used for tissue characterization and confirmation of LHIAS. Precontrast T2/T1 weighted cine CMR images with steady-state free precession show high signal intensity in the area of LHIAS and produces a black/hypointense boundary effect between fat and myocardium. A fat suppression protocol can also be used to confirm LHIAS. In light of the atypical appearance of the echo-dense mass seen on TTE in this patient, a multimodality approach was used to narrow the differential diagnosis and arrive at the final determination of LHIAS. Lipomatous hypertrophy of the interatrial septum is a benign condition in most cases. Rarely, if severe interatrial hypertrophy is present, patients may develop obstruction of right atrial filling, shortness of breath, and/or heart failure symptoms. Lipomatous hypertrophy of the interatrial septum may coexist with other intracardiac malignancies, which would dictate any necessary interventions.

Conclusion

This case highlights the differential diagnosis of an interatrial septal mass. Lipomatous hypertrophy of the interatrial septum may have atypical appearances and present with a variety of morphologic features. A multimodality imaging approach in these cases is crucial in arriving at the appropriate diagnosis using the tissue characterization capabilities of CT and CMR.

Lead author biography

Dipika J. Gopal is a third-year cardiology fellow at the University of Pennsylvania in Philadelphia, Pennsylvania, with an interest in Preventive Cardiology and non-invasive imaging. She also has a passion for medical education and plans to pursue a career as a physician-educator.

Supplementary material

Supplementary material is available at European Heart Journal - Case Reports online.

Click here for additional data file.

Hospital Day 1
0100	Patient arrived in emergency department
0700	Patient was seen by general cardiology consult
0700	Transthoracic echocardiogram (TTE) completed The TTE showed a homogenous, echo-dense, intracardiac mass present within or attached to the superior aspect of the interatrial septum measuring 4 cm × 4 cm. Movement of the mass was synchronous with the atrial walls.
1130	Computed tomography (CT) angiography of the heart completed The CT showed a homogenous mass similar in radiodensity to extracardiac and pericardial fat with Hounsfield units within the fat range. The mass extended from the interatrial septum to the posterior left and right atria and spared the fossa ovalis.
1600	Cardiac magnetic resonance (CMR) imaging performed The CMR showed a homogenous mass that was nulled on fat suppression images consistent with fat.
Hospital Day 2
1200	Patient discharged