Endocrine Abstracts

Although adrenal vein sampling (AVS) remains the gold-standard for distinguishing unilateral and bilateral disease in primary hyperaldosteronism (PHA), it is technically demanding and not always feasible. Metomidate (MTO), a potent inhibitor of CYP11B1 and CYP11B2, can be C¹¹H₃-labelled as a PET tracer (¹¹C-MTO), and we have previously shown it to be an alternative to AVS for localising unilateral aldosterone-producing adenomas (APAs) (Burton et al. JCEM 2012).

Here, we report a case series in which ¹¹C-MTO PET–CT was superior to AVS in specific settings:

i) AVS technically unsuccessful with failure to cannulate both adrenal veins: ¹¹C-MTO PET–CT accurately localised a unilateral lesion in 12 of 19 cases, with bilateral disease confirmed in 7. Ten of the patients with unilateral PHA have subsequently undergone adrenalectomy, which corrected PHA with normalisation of the aldosterone-to-renin ratio (ARR) in all cases. 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 APA as confirmed at adrenalectomy.

ii) Technically adequate AVS, but without lateralisation: in a subgroup of patients with successful bilateral adrenal vein cannulation, but in whom AVS did not meet criteria for lateralisation, ¹¹C-MTO PET–CT showed focal tracer uptake corresponding to a nodule on cross-sectional imaging; six patients have subsequently undergone adrenalectomy, with correction of PHA and normalisation of ARR.

iii) AVS not possible (unable to safely withdraw spironolactone): in patients with refractory severe hypertension, controlled only with spironolactone, ¹¹C-MTO PET–CT successfully localised an APA and facilitated surgery, resulting in correction of PHA (and ARR), with requirement for fewer/no antihypertensive agents post-surgery.

Finally, where multiple nodules co-exist within a single or both glands, ¹¹C-MTO PET–CT often accurately identifies the causative tumour (confirmed by cell culture and genotyping). We speculate this may facilitate non-surgical targeted nodule-specific ablation or selective surgical adenomectomy.