Identification of unilateral aldosterone-producing (Conn's) adenomas has traditionally required lateralization by the invasive and technically difficult procedure of adrenal vein sampling (AVS). ¹¹C-metomidate, a potent inhibitor of adrenal steroidogenic enzymes, is a positron emission tomography (PET) radiotracer that is selectively accumulated by Conn's adenomas.

The objective of the study was to compare the sensitivity and specificity of ¹¹C-metomidate PET-computed tomography (CT) against the current gold standard of AVS.

The design of the study was within-patient comparison of diagnostic techniques.

The study was conducted at a single center-university teaching hospital.

Thirty-nine patients with primary hyperaldosteronism (PHA) and five with nonfunctioning adenomas (incidentalomas) participated in the study.

The first six PHA patients were studied on three occasions to determine whether steroid pretreatment reduced ¹¹C-metomidate uptake by normal adrenal. Subsequent patients received dexamethasone for 3 d prior to injection of ¹¹C-metomidate 150–500 MBq.

Maximum standardized uptake values (SUV_max) over regions of interest determined from 35–45 min after injection were measured.

Dexamethasone increased tumor to normal adrenal SUV_max ratio by 25.6 ± 5.0% (P < 0.01). PET-CT visualized subcentimeter adenomas and distinguished hot from cold adenomas within a gland. In 25 patients with PHA and AVS lateralization to the side of an adenoma, SUV_max over tumor (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 incidentalomas. On receiver-operator characteristics analysis, an SUV_max ratio of 1.25:1 provided a specificity of 87% [95% confidence interval (69, 104)] and sensitivity of 76% (59, 93); in tumors with SUV_max greater than 17, the specificity rose to 100%.

¹¹C-metomidate PET-CT is a sensitive and specific noninvasive alternative to AVS in the management of PHA.