Renal oncocytoma with vascular and perinephric fat invasion.

Renal oncocytoma is a benign epithelial neoplasm typically composed of large cells with granular eosinophilic cytoplasm. Although rare, histologically worrisome features such as vascular and perinephric fat invasion have been reported. Of the 159 renal oncocytomas resected at our institution, 20 (12.6%) had vascular and/or perinephric fat invasion. Microscopically, 10 oncocytomas had perinephric fat invasion, 7 had vascular invasion and 3 had both vascular and perinephric fat invasion. Grossly, perinephric fat invasion was visible in three cases and tumour was identified within the branches of the renal vein in two cases. Tumours occurred in 14 men and 6 women (M:F = 2.3:1). The mean age at diagnosis was 64.5 years (range, 33-88 years). A total of 11 cases had radical nephrectomies while 9 cases had partial nephrectomies. There was no evidence of disease recurrence, metastasis or death due to tumour after a mean follow up of 25.6 months (range, 2-103 months). The presence of vascular and perinephric fat invasion in renal oncocytoma though worrisome, does not alter the benign course of the tumour.