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Here we report 3 cases of renal oncocytoma with a dominating small cell component 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 initially thought to be a malignant tumor by the referring pathologists. In all 3 cases minor areas of the tumors, which were identical to the classical renal oncocytomas were found. The small cell areas were arranged in a characteristic organoid pattern different from all the known types of the renal benign and malignant tumors. We summarize all morphologic, immunohistochemical, and ultrastructural features of this unusual oncocytoma variant with regard to its differential diagnosis. Int J Surg Pathol 9(3):215-222, 2001
Key words: renal oncocytoma, small cell variant, kidney.
Renal oncocytoma (RO) is a distinctive benign tumor comprising approximately 4% of all kidney neoplasms, usually presenting as a unilateral solitary tumor with the average size of 5 cm. The occurrence is higher in men, with the peak incidence in the seventh decade of life 11-31. In general, RO may show a broad spectrum of appearances, the most common being the alveolar, tubular, or cystic arrangement 141. The polygonal tumor cells are typically uniform with abundant granular eosinophilic cytoplasm packed with mitochondria to the virtual exclusion of other organelles. Besides the classic oncocytes, RO may contain oncocytic cells with pyknotic nuclei and small cells with a high nuclear/cytoplasmic ratio and dense hyperchromatic nuclei (so-called oncoblasts). In spite of several observations describing the existence of the small (so-called oncoblastic) cells in renal oncocytomas [4-81, we are not aware of any published RO case composed predominantly of small cells.
Here we describe morphologic, immunohistochemical, and ultrastructural features of 3 unusual RO with a dominating small cell component arising in adult women. We consider the presence of extensive areas of small cells in RO a rather unusual, potentially confusing feature demanding enlarging of the differential diagnosis of this benign tumor entity.
Materials and Methods
The 3 unusual cases were identified among 134 renal oncocytomas in routine diagnostic and consultation files of the authors. Tissues for light microscopy were fixed in 4% formaldehyde and embedded in paraffin by...