Mediastinal Hibernoma on Fluorine-18 Fluorodeoxyglucose (18F-FDG) Positron-Emission Tomography/Computed Tomography (PET/CT): A Case Report and Literature Review.

Hibernomas are infrequent brown adipose tissue tumors that can mimic various other soft tissue tumors, both malignant and benign, and multiple imaging modalities are usually used in the diagnostic approach. We present the case of a 30-year-old female patient who was initially diagnosed with a mediastinal hibernoma through complete excisional biopsy in 2022 and underwent surgical resection at that time. She required a second surgical intervention in 2024 due to recurrence and is now being evaluated for a second recurrence using fluorine-18 fluorodeoxyglucose positron-emission tomography/computed tomography (18F-FDG PET/CT), reporting an extensive polylobulated mediastinal tumor intercalating normometabolic and discretely hypermetabolic zones. Hibernomas consist of a combination of brown adipose tissue and normal adult adipose tissue. The brown adipose tissue has a higher glucose metabolism, leading to increased 18F-FDG uptake and significant radiotracer accumulation. A multidisciplinary approach is important. The use of 18F-FDG PET/CT is valuable in hibernoma evaluation, as it can detect increased metabolism compared to other tissues. This provides additional information that can complement other imaging studies. However, it is important to interpret these results carefully, as they can raise concerns for false-positive metastasis. Given the infrequent nature and somewhat difficult diagnosis, there is yet much to learn about hibernomas.