Recurrence of a functional adrenocortical oncocytoma of borderline malignant potential showing high FDG uptake on 18F-FDG PET/CT.

Adrenocortical oncocytoma is a very rare tumor, which is not malignant and nonfunctioning in most cases. We report a case of a 53-year-old male with a 9.8 cm sized hyperfunctioning, well-encapsulated adrenal mass, which exhibited by high FDG uptake on a PET/CT scan. The patient had complained of symptoms of Cushing's syndrome for 4 months. Laparoscopic adrenalectomy was performed and the mass was pathologically confirmed as adrenocortical oncocytoma of uncertain malignant potential. Four years after surgery, the tumor recurred with distant metastases, which was proven by subsequent biopsy. 18F-FDG PET/CT also showed hypermetabolism in the recurred tumor and multiple metastatic lesions. Adrenocortical oncocytoma of borderline malignant potential with high FDG uptake may require long-term follow-up with clinical, hormonal, and imaging evaluations.