Extinction of Lipomatous Hypertrophy of the Interatrial Septum FDG Uptake With Propranolol Premedication

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 ¹⁸F-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 ¹⁸F-FDG uptake. Final characterization was made thanks to ¹⁸F-FDG PET with β-blocker premedication, avoiding an invasive procedure.

FIGURE 1: We present the case of a 65-year-old woman, obese, with subacute general condition’s alteration, referred for characterization of a suspect interatrial lesion. CT with IV contrast media and cardiac MR (CMR) described a fatty oval pericardial lesion of the right atrium, with infiltrative component, presenting pejorative criteria with heterogeneous contrast enhancement on CMR. ¹⁸F-FDG PET was performed to characterize this lesion. Because of its localization, an extended fasting protocol was required to shut down physiological myocardial carbohydrate metabolism. Hybrid PET/CT axial view (A) found a fatty oval lesion (density: −69 HU, B) measuring more than 2 cm diameter (orange arrow), with significant radiotracer uptake (SUV_max-bw: 5.8, C). Because of radiological and epidemiological characteristics and lack of other lesions on PET, lipomatous hypertrophy of the interatrial septum (LHIS) was proposed, but the hypermetabolic character remained suspect. Thus, to distinguish LHIS from neoplasia, a second ¹⁸F-FDG PET was performed still with extended fasting protocol and propranolol premedication (40 mg 2 hours before injection). On this second scan, no significant uptake was found in the lesion (A, axial hybrid PET/CT; B, axial CT; C, axial PET). This suggested the existence of brown adipose tissue (BAT) initially activated, ruling out malignancy. No other treatment had been prescribed or modified, particularly no anti-inflammatory treatment. Notice that the atypical characteristics shown by the first CT were not found on the noninjected CT associated with PET, with this time typical LHIS aspect. LHIS is a rare benign lesion, mainly composed by adipocytes, forming an interatrial septum’s tumor.¹ Statistical association has already been shown with obesity, elderly, and women patients.² Generally, diagnosis is made by CT and CMR; however, biopsy for histological analysis can be needed, but it remains a heavy and invasive procedure.³ In PET imaging, it has already been described that LHIS can have ¹⁸F-FDG uptake, sometimes intensely.^4,5 This might be due to active BAT,⁶ but other potential mechanisms of uptake might have been identified.⁷ When active, this fat is avid for ¹⁸F-FDG, with uptake on PET images influenced by various factors.⁸ BAT is well known on ¹⁸F-FDG PET/CT, more frequently seen in the cervicothoracic region; β-blockers are often used to rest BAT and reduce ¹⁸F-FDG uptake, avoiding false-positive PET examinations.^9,10 Although BAT has been previously described in LHIS, to our knowledge, this is the first article reporting uptake extinction using β-blockers premedication with ¹⁸F-FDG PET imaging. This also allowed us to show that here LHIS uptake was related to activate BAT more than by potential inflammation, or cardiomyocyte existence.⁷ LHIS characterization is an important issue, particularly in oncological settings, where it can clearly modify disease’s staging, increasing false-positives numbers.^{11 18}F-FDG PET/CT with β-blocker premedication finally appears as a relevant tool for characterization of LHIS, even when CT and CMR are lacking, thus making it possible to avoid biopsy.