An auxiliary 18F-FDG uptake pattern clarifying equivocal adrenal gland mass after dual-tracer imaging with 123I-mIBG SPECT/CT and 18F-FDG PET/CT.

Pheochromocytomas are rare catecholamine-producing neuroendocrine tumors arising from the adrenal medulla. Several studies have reported activation of brown adipose tissue (BAT) in up to 30% of patients with pheochromocytoma. Brown adipose tissue is characterized by abundant mitochondria to provide heat generation rather than energy storage. Pheochromocytoma seems to act on BAT via two parallel mechanisms. These include the trans-differentiation of white to brown adipocyte as well as the hypertrophy of existing brown adipocytes and increased glucose uptake by noradrenergic (β-AR) sympathetic nervous system stimulation.