Incidental Bilateral Renal Oncocytoma in a Patient with Metastatic Carcinoma of Unknown Primary: a Pitfall on 18F-FDG PET/CT

Bilateral renal masses are uncommon but can raise a strong suspicion of primary or secondary malignancy, especially during the initial work-up of an oncology patient. Renal oncocytomas are benign renal tumors that are commonly discovered incidentally on diagnostic imaging with a small percentage occurring bilaterally. Although ¹⁸F-FDG uptake in renal oncocytomas has been described, a case of a bilateral ¹⁸F-FDG-avid renal oncocytoma has not been previously reported in the literature. A variety of malignant causes of bilateral ¹⁸F-FDG positive renal masses are known, however it is important to include this benign etiology in the differential diagnosis. We report an unusual case of an incidental bilateral renal oncocytoma evaluated with contrast enhanced CT and ¹⁸F-FDG PET/CT.