The effect of catecholamines on the glucose uptake in brown adipose tissue demonstrated by ¹⁸F-FDG PET/CT in a patient with adrenal pheochromocytoma

Excerpt

A 50-year-old man had the diagnosis of right adrenal pheochromocytoma made by computed tomography (CT) scan together with the evidence of raised plasma catecholamine and urinary catecholamine metabolite levels. A positron emission tomography (PET)/CT study with ¹⁸F-fluorodeoxyglucose (FDG) demonstrated intense, bilateral, and symmetric uptake in brown adipose tissue (BAT) in the neck, supraclavicular, axillary, mediastinal, paravertebral, and perinephric regions and also in the right adrenal gland (a, arrows). Histologic examination of the excised tumor demonstrated a typical presentation of pheochromocytoma. Five days after the surgery, another PET/CT scan showed no uptake in BAT. A slight uptake was seen in the right adrenal bed which was attributed to an inflammatory process (b, arrow). Symmetrically increased ¹⁸F-FDG uptake occurring in areas of fat of the neck, supraclavicular, paravertebral, mediastinal, and perinephric regions has been described with ¹⁸F-FDG PET/CT [1]. Brown fat has the ability to increase its blood flow with norepinephrine stimulation and is rich in adrenergic innervation [2]. Glucose uptake increases when the BAT sympathetic nervous system is activated [3, 4]. Although BAT is more prominent in newborns and diminishes with age, it may persist into adulthood as an adaptive change for cold-induced thermogenesis. The presence of generalized activity of brown fat was demonstrated by biochemical analysis on the BAT obtained at laparotomy from subjects with high circulating noradrenaline concentrations in the presence of pheochromocytoma [5]. The striking change in ¹⁸F-FDG PET pattern before and after the excision of the pheochromocytoma confirms the findings based on histopathologic investigations about the activation of BAT metabolism by excessive circulating catecholamines released by the tumor [5]. …