Objective: To determine the prevalence of lipomatous hypertrophy of the interatrial septum (LHIS) on CT and its metabolic pattern on 18F fluorodeoxyglucose (FDG)-positron emission tomography (PET).
Method and materials: Eight hundred two CT PET scans were reviewed. Patients were included if the interatrial septum was > or = 1 cm and excluded if there was evidence of malignancy in the adjacent lung, hilum, or mediastinum. CT scans were fused with PET scans, and the mean standardized uptake value (SUV) was calculated over the LHIS, chest wall (CW) fat, and mediastinal blood pool. CT scans were reviewed for presence of excessive fat in the mediastinum, pericardial, peridiaphragmatic, peritoneal, and retroperitoneal regions and for the presence of emphysema. Medical records were reviewed for body mass index (BMI) and history of arrhythmia.
Results: Twenty-three of 802 patients (2.8%) had LHIS on CT (9 women and 14 men); average age was 75.6 years (range, 58 to 95 years). Average BMI of 17 patients (+/- SD) was 31 +/- 4.9 (range, 22.1 to 39.9). Mean CT values were as follows: thickening of LHIS, 1.47 +/- 0.35 cm (range, 1.07 to 2.25 cm); LHIS, - 79.6 + 24.5 Hounsfield unit (HU) [range, - 11 to - 121 HU]. LHIS was dumbbell shaped in 18 patients. Mean SUVs were as follows: LHIS, 1.84 +/- 0.10 (range, 0.48 to 3.48); CW fat, 0.36 + 0.37 (range, 0.04 to 1.98); blood pool, 1.74 + 0.51 (range, 0.25 to 2.71). The SUV of LHIS was greater than the SUV of CW wall fat in all patients (p < 0.0001). There was significant correlation between SUV and thickness of the LHIS on CT (p < 0.0001, r = 0.883). Those with dumbbell-shaped LHIS (p < 0.003) and presence of emphysema (p < 0.0377) had greater LHIS mean SUV.
Conclusion: The SUV of LHIS was greater than the SUV of CW fat in all patients. LHIS with greater thickness or dumbbell shape had greater FDG uptake. These findings on CT and PET are important to recognize in order to avoid false-positive FDG-PET interpretations.