Evaluation of the Sensitivity and Specificity of ¹¹C-Metomidate Positron Emission Tomography (PET)-CT for Lateralizing Aldosterone Secretion by Conn's Adenomas

Context:

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.

Objective:

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.

Design:

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

Setting:

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

Patients:

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

Intervention(s):

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.

Main Outcome Measure(s):

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

Results:

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%.

Conclusions:

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