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Abstract: Lipomatous hypertrophy of the interatrial septum is a rare lesion of the heart. CT and cardiac MR are often sufficient to determine the benign lipomatous nature of the tumor and can avoid the need for histological confirmation. Lipomatous hypertrophy of the interatrial septum contains variable amounts of brown adipose tissue, resulting in different degrees of 18 F-FDG uptake in PET. We report the case of a patient with an interatrial lesion suspected of malignancy, discovered on CT and failing cardiac MR, with initial 18 F-FDG uptake. Final characterization was made thanks to 18 F-FDG PET with β-blocker premedication, avoiding an invasive procedure., Competing Interests: Conflicts of interest and sources of funding: none declared., (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc.)

Abstract: Lipomatous hypertrophy of the interatrial septum (LHIS) is a benign anomaly with low prevalence. Lipomatous hypertrophy of the interatrial septum is asymptomatic in most of the cases and rarely leads to atrial arrhythmias, obstructive flow symptoms, or sudden death. It is mostly diagnosed as an incidental finding in cross-sectional imaging and echocardiography, and increased 18F-FDG uptake on LHIS has been described. We present a case of repeated increased 18F-PSMA uptake in LHIS. Although very rare, familiarity with the typical features and prevalence of LHIS in PET/CT can avoid misinterpretation for metastatic disease., Competing Interests: Conflicts of interest and sources of funding: none declared., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Lipomatous hypertrophy of the interatrial septum (LHIS) may be associated with arrhythmias or sudden death. Increased fluorine-18 fluorodeoxyglucose (FDG) uptake in LHIS is occasionally found on positron emission tomography, and has been attributed to metabolically active brown adipose tissue (BAT) contained within LHIS. We report a case of a patient suggesting that neither of the 2 currently known mechanisms of glucose uptake by BAT is responsible for FDG uptake in LHIS, unless a mechanism of BAT activation exists that has not been previously described. This study also suggests that FDG uptake is unlikely to be due to cardiomyocytes contained within LHIS. Inflammation is a potential mechanism, although further investigation is needed.