Unusual Pattern of Brown Fat Uptake on ¹⁸ F-FDG PET/CT in a Case of Malignant Phaeochromocytoma

Phaeochromocytoma is a rare catecholamine-secreting tumour arising from chromaffin cells of the adrenal medulla. Some case reports describe an association between phaeochromocytoma-induced catecholamine excess and Brown adipose tissue (BAT) accumulation, presenting as a pseudotumour. BAT receives innervation from the noradrenergic sympathetic nervous system, which, through a regulatory mechanism, stimulates hypertrophy and hyperplasia of adipocytes and trans differentiation of white to brown adipocytes. We hereby demonstrate a case of malignant phaeochromocytoma arising from the right adrenal gland with skeletal and lung metastases, along with diffuse brown adipose tissue confounding the interpretation of the disease extent on ¹⁸ F fluorodeoxyglucose positron emission tomography/ computed tomography ( ¹⁸ F FDG PET/CT).