[1 of the variants of Wilms' tumor]

A peculiar variant of Wilms' tumor was studied. Out of 77 cases of nephroblastoma 2 observations were selected in which the tumor consisted of loosely arranged oval and polygonal cells with clear nuclei. Occasional formed tubules were found in the tumor. The cells had anastomosing processes, few organoids, microfibrils. A nonepithelial nature of the tumor is assumed. A trend for primary metastasis of the tumor into bones was observed. Because of the difficulties and rare occurrence of such tumors, their histology and differential criteria are presented at the light and ultrastructural levels. Indication of this variant in the diagnosis may also suggest the possibility of metastatic affection of the skeleton.