What is a renal oncocytoma, and what are its CT and MRI features?
A renal oncocytoma is a benign renal neoplasm that occurs more commonly in men than in women, most commonly in the seventh decade of life. On CT and MRI, it appears as a solid enhancing well-circumscribed renal mass that is indistinguishable from RCC. A central stellate scar may be seen in ≈33% of cases with delayed phase enhancement, and hemorrhage is rare. Segmental enhancement inversion has been reported to be a fairly specific feature of renal oncocytomas, where one portion of a renal mass has avid enhancement during the corticomedullary phase and becomes less enhancing during the nephrographic phase, and another portion of a renal mass has low enhancement during the corticomedullary phase and becomes more enhancing during the nephrographic phase. No regional lymphadenopathy and no distant metastatic disease is seen with renal oncocytomas.