11C-metomidate positron emission tomography after dexamethasone suppression for detection of small adrenocortical adenomas in primary aldosteronism.

PURPOSE: To evaluate whether dexamethasone suppression treatment can improve (11) C-metomidate positron emission tomography (MTO-PET) detection of small adrenocortical adenomas in primary aldosteronism (PA).

MATERIALS AND METHODS: Eleven patients with proven PA and two patients with non-hyperfunctioning adrenocortical incidentalomas and small adrenocortical tumours observed on CT underwent MTO-PET before and 3 days after administration of oral dexamethasone suppression treatment. Small "hot-spot" regions of interest comprising 4 pixels (SUVhs) and 1 pixel (SUVmax) were placed in the tumour area with the highest radioactivity concentration and their respective standardised uptake values (SUV) were recorded.

RESULTS: All tumours were detected and categorised as adrenocortical by MTO-PET. SUVhs as well as SUVmax were higher in PA compared to nonfunctional adenomas. Normal adrenal cortex was suppressed after dexamethasone (p < 0.05), but tumour SUV was not significantly decreased after suppression in either PA or nonfunctional tumours (p > 0.05). However, these changes caused no significant increase in the tumour-to-normal adrenal ratio (p > 0.05).

CONCLUSION: MTO-PET is a highly sensitive method for detecting and categorising even small adrenocortical tumours in PA. In this series, dexamethasone-suppressed MTO-PET was unable to increase the tumour-to-normal adrenal ratio to further facilitate detection of small adenomas in PA as an alternative to adrenal venous sampling.