Atypical Brown Fat Distribution in Young Males Demonstrated on PET/CT

The development of PET/CT has led to the recognition that metabolically active fat, referred to as "brown fat," can accumulate FDG and represents a possible source of false-positive scans in oncology patients. Numerous reports have described the typical appearance of brown fat, which most commonly presents as neck and paravertebral uptake in young female patients. Other described sites of uptake include the mediastinum and retroperitoneum. We present examples of 2 cases of atypical diffuse brown fat uptake seen in the subcutaneous fat of the thighs, abdomen, and pelvis. Both of these patients were young men and did not show uptake in the typical supraclavicular and neck fat. Although rare in our experience, knowledge of this condition may prevent misinterpretation of this finding as an infiltrative condition of the skin, such as lymphoma.