Purpose:

The purpose of the study was to evaluate the potential role of PET with the adrenocortical-specific tracer ¹¹C-metomidate in the characterization of incidentally found adrenal cortical lesions and in adrenocortical carcinomas.

Methods:

PET with ¹¹C-metomidate was performed in 15 patients with unilateral adrenal mass confirmed by CT (incidentalomas) and in 9 additional patients with adrenocortical cancer. All incidentalomas subsequently underwent surgery, except 2 subjected to biopsy only. These lesions were histopathologically examined and diagnosed as adrenal cortical adenoma (n = 6; 3 nonfunctioning), adrenocortical carcinoma (n = 2) and nodular hyperplasia (n = 1). The remaining were non-cortical lesions including 1 pheochromocytoma, 1 myelolipoma, 2 adrenal cysts, and 2 metastases.

Results:

All lesions, except 1, with an adrenocortical origin were easily identified due to exceedingly high uptake of ¹¹C-metomidate, whereas the non-cortical lesions showed very low uptake. The 1 false negative was a cancer that at surgery was found to be extensively necrotic. High uptake was also seen in normal adrenal glands. The tracer uptake kinetics indicated trapping of the tracer in the cortical lesions. For quantitative evaluation of tracer binding in individual lesions, the simple SUV concept was found to be equally accurate as more elaborate kinetic analyses.

Conclusion:

The patients presented and altogether over 40 PET investigations have demonstrated ¹¹C-metomidate to be an attractive tracer for the characterization of adrenal masses with the ability to discriminate lesions of adrenal cortical origin from non-cortical lesions. Additionally the method allows the assessment of metastases from adrenocortical cancers, and the very high contrast has allowed partial whole-body examinations.