[Renal oncocytoma. Fundamental radiologic manifestations and enhancement patterns in tri-phase helical CT]

Oncocytoma is a relatively uncommon benign kidney tumor. To date, it has been impossible to differentiate this tumor from renal cell carcinoma radiologically, although few articles report on the use of tri-phase CT in this tumor. We describe the triphasic CT findings in these tumors and evaluate whether some characteristics, although not sufficient to ensure the diagnosis, can suggest the possibility of oncocytoma. In some cases, this may lead to a different approach to the management of patients.

We describe the tri-phase CT findings in 10 cases of oncocytoma in eight patients (one case was bilateral and multifocal). The diagnosis was made after histological examination of surgical specimens in all cases.

All the tumors were found incidentally at ultrasound examination prior to CT study. Tumors all had well-defined borders, and their size ranged from 3 to 15 cm, with a mean diameter of 5.2 cm. One patient had bilateral tumors (2 right and 1 left). All but one of the tumors had a star-shaped scar inside, with a marked lobular pattern in one case. All tumors showed avid uptake, with mean enhancement of 120 HU in the arterial phase and 116 HU in the venous phase. All patients evolved favorably with no post-surgical relapse.

Although oncocytoma cannot be differentiated from renal cell carcinoma with certainty, the possibility of oncocytoma should be suggested in the case of small tumors with a central scar, without necrosis or infiltration, and an enhancement pattern as described here. Regardless of the size of the tumor, lobular morphology should also suggest this possibility.