Adrenal incidentalomas are common findings necessitating extensive laboratory work-up and repetitive radiological examinations. Positron emission tomography (PET) using ¹¹C-labeled metomidate (MTO) has previously been described as a tool for specific adrenocortical imaging.

Objective: We evaluated 212 MTO-PET examinations in 173 patients to identify its role in the management of adrenal tumors.

Design: Seventy-five histopathological examinations from 73 patients were retrospectively analyzed.

Setting: All examinations were performed at a referral center.

Patients: Patients who were operated or biopsied due to adrenal tumors had histopathological diagnoses as: adrenocortical adenoma (n = 26), adrenocortical cancer (ACC; n = 13), adrenocortical hyperplasia (n = 8), pheocromocytoma (n = 6), metastasis (n = 3) and tumors of non-adrenal origin (n = 19).

Main Outcome Measures: Statistical analyses and findings while scrutinizing images. The hypothesis that MTO-PET is of value in the management of adrenal tumors, especially incidentaloma, was stated before data collection.

Results: Sensitivity was 0.89 and specificity 0.96 for MTO-PET in proving adrenocortical origin of the lesions. Pheocromocytomas, metastases to the adrenal gland and non-adrenal masses were all MTO-negative. PET measurements using standardized uptake values (SUV) in pathological adrenocortical tissue could differentiate lesions larger than 1-1.5 cm from normal adrenocortical tissue.

SUV was higher in aldosterone hypersecreting adenomas and the SUV ratio between tumor and the contralateral gland was significantly higher in all hormonally hypersecreting adenomas as well as in ACC.

Conclusion: MTO-PET is a specific and sensitive method for diagnosing adrenocortical tumors. MTO-PET is useful in the imaging work-up of adrenal incidentalomas and may be beneficial for the examination of patients with primary aldosteronism or ACC.