Imaging and clinicopathological features of a high-SUV hibernoma mimicking liposarcoma on PET/CT, MRI, and CT: A case report.

Hibernomas are rare benign tumors of brown adipose tissue that can demonstrate remarkably high fluorodeoxyglucose (FDG) avidity on positron emission tomography/computed tomography (PET/CT), often mimicking malignant sarcomas and leading to unnecessary aggressive management. A 65-year-old woman with peripheral arterial disease underwent CT angiography that incidentally revealed a large (9 × 8.5 cm) mixed-density lipomatous mass in the proximal left thigh. MRI confirmed a well-encapsulated lesion with signal intensity consistent with fat on T1-weighted imaging, strikingly prominent internal vascular channels, and a feeding vascular pedicle. PET/CT demonstrated intense hypermetabolism with a maximum standardized uptake value (SUVmax) of 34.8-among the highest reported for hibernoma-and a central photopenic area corresponding to vascular spaces. Core biopsy suggested hibernoma (positive for S100 and CD10, negative for MDM2), creating significant radiological-pathological discordance given the aggressive imaging appearance. Multidisciplinary tumor board review recommended marginal excision, which confirmed a completely resected hibernoma; the patient remained recurrence-free at 12-month follow-up. Hibernoma should be considered in the differential diagnosis of any FDG-avid lipomatous soft tissue mass, particularly when imaging shows prominent internal vascularity and absence of thickened fibrous septa. An SUVmax exceeding 30 does not exclude benignity, and recognizing these characteristic findings can improve diagnostic accuracy and help avoid unnecessary aggressive treatment.