RESUMO
Fused positron emission tomography-computed tomography (PET/CT) technology has enabled the determination that nonmalignant fluorodeoxyglucose (FDG) uptake is observed in brown adipose tissue (BAT). FDG uptake in BAT is a known potential source of false-positive interpretations for PET. The typical locations of BAT include neck, supraclavicular area, mediastinum, and paravertebral intercostal spaces. Examples of atypical locations for BAT include posterior neck, left paratracheal area, axillae, perirenal area, and retrocrural area. We report PET/CT findings in a young male patient with malignant retroperitoneal extra-adrenal pheochromocytoma, who demonstrated FDG uptake in BAT at multiple locations including mesenteric BAT. We also propose catecholamine-secreting pheochromocytoma as a possible cause of BAT activation in our case.