Renal Oncocytoma with Intracytoplasmic Lumina: A Case Report with Ultrastructural Findings of "Oncoblasts"

Abstract

The authors present a case of renal oncocytoma with numerous intracytoplasmic lumina in a 45-year-old woman, with an emphasis on the ultrastructural findings of so-called oncoblasts. The tumor was located in the upper pole of the left kidney, measuring about 3.3 cm in diameter. Histologically, it was composed of solid nests or acinar growths of so-called oncocytic tumor cells with numerous intracytoplasmic lumina and scattered foci of so-called oncoblasts. The luminal surface was positive for Halés colloidal iron stain. A very small number of glycogen-containing cells were found scattered in a few nests. Immunohistochemically, tumor cells were positive for cytokeratin and epithelial membrane antigen, but negative for vimentin and carcinoembryonic antigen. The Ki-67 labeling index was 1.2%. All of the Ki-67-positive cells were oncocytes. So-called oncoblasts were negative for Ki-67. Ultrastructural examination revealed that the predominant tumor cells had cytoplasm packed with round mitochondria and the mitochodria had lamellar long cristae. So-called oncoblasts showed scant cytoplasm with a moderate numberof small mitochondria. Someof themshowed pyknosis which can be regarded as mitochondrial involution. The authors believe that so-called oncoblasts are damaged or involuted oncocytes rather than precursors of oncocytes.

• Intracytoplamic Lumina Kidney Neoplasms Oncoblast Oncocytoma Ultrastructural Findings