Primary hyperaldosteronism – a new trick for an old Conn — ASN Events
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Primary hyperaldosteronism – a new trick for an old Conn (#49)

Mark Gurnell 1
  1. Wellcome Trust-MRC Institute of Metabolic Science & University of Cambridge School of Clinical Medicine, Addenbrooke’s Hospital, Cambridge, UK

Adrenal vein sampling (AVS) presents a considerable hurdle between diagnosis of primary hyperaldosteronism (PHA) and potential curative surgery. Metomidate (MTO), a potent inhibitor of the steroidogenic enzymes CYP11B1 and CYP11B2, can be C11H3-labelled as a positron emission tomography (PET) tracer (11C-MTO).

In a non-inferiority study, comparing 11C-MTO PET-CT with AVS, 39 patients with PHA and five with non-functioning adrenal adenomas (incidentalomas – AI) were pre-treated with dexamethasone (0.5 mg qds for 72h) prior to PET-CT. In 25 patients with PHA and AVS lateralization to the side of an adenoma, SUVmax over tumour (mean ± SEM) of 21.7 ± 1.6 was greater than over normal adrenal, 13.8 ± 0.6 (P<0.00003); this difference was absent in 10 patients without lateralization on AVS (P=0.28) and in four of five AI. On receiver-operator characteristics analysis, an SUVmax ratio of 1.25:1 provided a specificity of 87% [95% confidence interval (69, 104)] and sensitivity of 76% (59, 93); in tumours with absolute SUVmax values greater than 17, the specificity rose to 100%. 11C-MTO PET-CT also visualised subcentimetre adenomas and distinguished hot from cold adenomas within a gland.

In a follow-up study of 17 patients with unsuccessful or equivocal AVS, a confident diagnosis of unilateral (n=10) or bilateral (n=7) PHA was made using a SUVmax tumour:normal ratio of 1.25:1. Eight of the patients with unilateral PHA have subsequently undergone adrenalectomy, which reversed the aldosterone-to-renin ratio in all cases. Importantly, in several patients with small adenomas that were initially ‘missed’ on cross-sectional imaging, 11C-MTO PET-CT clearly demonstrated increased tracer uptake corresponding to the site of a small aldosterone-producing adenoma (APA) as confirmed at adrenalectomy. 

11C-MTO PET-CT therefore offers a sensitive and specific non-invasive alternative to AVS in the management of PHA. Initial findings suggest that it may offer particular advantages to visualise small APAs, and differentiate functional tumours from AI.   

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