Small-cell variant of renal oncocytoma with dominating solid growth pattern: a potential diagnostic pitfall

We report a rare case of renal oncocytoma with a predominant small-cell component, accounting for about 80% of the entire tumour. The unusual extensive solid growth pattern of the tumour may represent a potential diagnostic pitfall. Although the possibility that a renal oncocytoma is composed exclusively of small cells does exist, the present case, along with the three previously reported in the literature [2], suggests that a thorough tissue sampling and careful identification of typical oncocytes, even if as a minor cellular population of the tumour, is the diagnostic key of the small-cell variant of oncocytoma. In addition, the present case, providing evidence that such a rare variant may have a dominating solid growth pattern, widens the morphological spectrum of renal oncocytoma, preventing a potential misdiagnosis of malignancy.