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 (ROIs) 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 non-functional adenomas. Normal adrenal cortex was suppressed after dexamethasone (p<0.05) but tumour SUV was not significantly decreased after suppression in either PA or non-functional 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 ubable to increase the tumour-to-normal-adrenal ratio to further facilitate detection of small adenomas in PA as an alternative to adrenal venous sampling.
