Computed tomography of renal oncocytoma

Renal oncocytoma is a relatively rare tumor that has an excellent prognosis and usually may be treated adequately by local resection. Preoperative differentiation from renal cell carcinoma, which requires radical nephrectomy, is thus of importance. The computed tomographic (CT) and pathologic features of three incidentally-detected renal oncocytomas were compared with those of six renal cell carcinomas of comparable size. Renal cell carcinoma appears on CT as a solid mass that generally has an indistinct interface with normal renal parenchyma, a lobulated contour, and a nonhomogeneous pattern of contrast enhancement. These features correlate with the pathologic findings of an irregular tumor margin and the frequent presence of tumor hemorrhage and necrosis. Oncocytoma, on the other hand, generally has a distinct margin, a smooth contour, and a homogeneous appearance on contrast-enhanced CT scans. These findings correlate with a smooth tumor margin and absence of tumor hemorrhage and necrosis on pathologic examination. These features are not pathognomonic of oncocytoma, as angiographic evidence suggests that renal cell carcinoma may show both distinct margination and a homogeneous blush in 6% of cases. However, their demonstration by CT should alert radiologists and surgeons to the possibility that a renal mass may be an oncocytoma. Such a presumptive diagnosis then can lead to a surgical approach that allows for renal-conserving surgery.