False-positive findings on 18F-FDG PET/CT:: Differentiation of hibernoma and malignant fatty tumor on the basis of fluctuating standardized uptake values

OBJECTIVE. Hibernoma is a benign tumor of brown fat that has imaging features similar to those of malignant fat-containing soft-tissue tumors. Hibernoma is metabolically active on F-18-FDG PET/CT, and its presence can lead to false-positive interpretations. We present three cases in which fatty lesions with increased radiotracer uptake identified on FDG PET/CT turned out to be hibernomas. The standardized uptake values of the lesions were similar to those reported in the literature for liposarcoma. However, all three patients had variable standardized uptake values over time. CONCLUSION. Variation in standardized uptake values over time is an imaging characteristic that may be helpful for differentiating hibernoma and malignant fatty tumor.