Diffuse 18F-fluoro-2-deoxy-D-glucose uptake of brown adipose tissue in pheochromocytoma due to increased sympathetic nervous system activity

A pheochromocytoma is a tumor of chromaffin cells that originates from either the adrenal medulla or extra-adrenal sympathetic tissues. The diagnosis of pheochromocytoma is based on elevated concentrations of plasma and urinary catecholamines or their metabolites. In most patients, the anatomic localization of the tumor is determined with computed tomography or magnetic resonance imaging. However, metaiodobenzylguanidine-scintigraphy or positron emission tomography (PET) can also easily identify the foci of neuroendocrine tumors. We diagnosed a patient with pheochromocytoma and high urinary norepinephrine levels, whose PET images revealed diffuse 18F-fluoro-2-deoxy-D-glucose (18FDG) accumulation in the shoulder, lower neck, and perivertebral area. The regions of 18FDG uptake corresponded to the location of human brown adipose tissue (BAT), which is minimally active in adults. It is thought that excessive sympathetic stimulation by high circulating catecholamine concentrations augmented the metabolic activity and tracer uptake in the BAT. This uptake in the BAT was normalized after surgical resectionope