Small cell variant of renal oncocytoma - A rare and misleading type of benign renal tumor

Here we report 3 cases of renal oncocytoma with a dominating small cell com ponent arising in adult women. These 3 cases of small cell variant of renal oncocytoma were found among 134 cases of oncocytomas of the kidney in the routine and consultation files of the authors. Two of 3 cases were initiall y thought to be a malignant tumor by the referring pathologists. In all 3 c ases minor areas of the tumors, which were identical to the classical renal oncocytomas were found. The small cell areas were arranged in a characteri stic organoid pattern different front all the known types of the renal beni gn and malignant tumors. We summarize all morphologic, immunohistochemical, and Ultrastructural features of this unusual oncocytoma variant with regar d to its differential diagnosis.