Benign hormone-secreting adenoma within a larger adrenocortical mass showing intensely increased activity on 18F-FDG PET/CT.

Adrenal adenomas usually show 18F-FDG activity less than that of the liver parenchyma. However, lipid-poor and hormone-secreting adenomas have been reported to show mild 18F-FDG avidity. We report on a 51-year-old female with clinical symptoms of hypercortisolemia and a large right adrenal mass detected on CT. Post-contrast CT images showed an enhancing focus in the lower pole of the mass, with corresponding markedly increased activity on 18F-FDG PET/CT. Right adrenalectomy was performed and histology revealed a benign adenoma, indicating that functioning benign adenomas can show intensely increased metabolic activity on 18F-FDG mimicking malignancy.