Endocrine Abstracts

Introduction: Prior studies have demonstrated that individuals with phaeochromocytoma and paranganglioma may manifest activation of Brown Adipose Tissue (BAT) as a result of excess catecholamines secretion^1–2. In this case series, we describe two cases featuring patients with phaeochromocytoma who exhibited increased uptake of BAT on ^18-FDG-PET/CT scans.

Case 1: A 74-year-old woman was referred to the Endocrinology department with a 7 cm right adrenal mass detected on CT imaging performed for the investigation of weight loss. Medical history included hypertension requiring three antihypertensives, type 2 diabetes and migraine. Blood work revealed elevated plasma normetanephrines, >25 000 pmol/l (0-1180), metanephrines, >16 000 pmol/l (0-510), and 3-methoxytyramine, 623 pmol/l (0-180). She subsequently had MRI Adrenal which showed 7 cm right adrenal mass and MIBG SPECT/CT which showed intensely MIBG-avid right adrenal mass. ^18-FDG-PET/CT arranged prior to the metanephrine results being available showed mild uptake in the right adrenal mass and intense uptake localising in thoracic paravertebral and perinephric fat indicative of BAT activation. Elective open right-sided adrenalectomy was performed, confirming a pheochromocytoma with Phaeochromocytoma Adrenal Scaled Score (PASS) of 7/20. Postoperatively, plasma metanephrines normalised and ^18-FDG-PET/CT showed a normalisation of perinephric FDG distribution and no FDG-avid disease.

Case 2: A 56-year-old woman was referred to Endocrinology department due to a 9 cm right retroperitoneal mass which was suspected to arise from right adrenal gland for investigation of recurrent vomiting. Medical history included hypertension and she reported having recurrent palpitations and anxiety. Blood work revealed elevated plasma normetanephrines >25 000 pmol/l (0-1180), metanephrines 1854 pmol/l (0-510) and 3-methoxytyramine, 731 pmol/l (0-180). Further investigations included MRI Adrenal, which identified well-circumscribed, peripherally enhancing 9 cm mass on right adrenal gland. She subsequently had ^18-FDG-PET/CT which showed partially cystic/necrotic right adrenal mass with intense FDG uptake in its solid component, with BAT uptake was observed in cervical, subclavicular and paraspinal stations. Subsequently, she had elective right-sided open adrenalectomy with histology confirmed phaeochromocytoma with PASS score of 11/20. Postoperatively, plasma metanephrines normalized and repeat CT TAP 6 months later showed no evidence of recurrence.

Discussions: Norepinephrine-induced beta-adrenoceptor activation in patients with phaeochromocytoma and paraganglioma may lead to brown fat activation, which is associated with increased energy wasting and cachexia². In case 1, this manifested in weight loss and marked BAT activation on ^18-FDG-PET-CT, both of which were reversed following removal of the phaeochromocytoma.

References: 1. doi:10.1210/jc.2015-3205.

2. doi.org/10.1210/clinem/dgz314