Brown adipose tissue demonstrating intense FDG uptake in a patient with mediastinal pheochromocytoma.

We present an interesting case with a central mediastinal pheochromocytoma showing intense F-18 fluorodeoxyglucose (FDG) uptake in tumor and systemic brown adipose tissue (BAT) mimicking metastases. The findings of hypertension and high plasma catecholamine concentration suggested the presence of pheochromocytoma. Mediastinal tumor showed intense FDG uptake and faint uptake of I-131 metaiodobenzylguanidine. Intense FDG uptake was demonstrated in cervical, paravertebral, mediastinal, and perirenal regions. Positron emission tomography and computed tomography (PET/CT) revealed uptake in a fat density area suggesting that the FDG uptake had occurred in BAT. The mediastinal tumor was resected along with an adhesion to the left atrial wall and pathologically confirmed as pheochromocytoma. The plasma catecholamine concentration and blood pressure then reverted to normal. The FDG uptake in BAT disappeared after tumor resection.