Abstract

Malignant rhabdoid tumor is a distinct renal tumor in pediatric age group and extremely rare in adults. It was originally described as a rhabdomyosarcomatoid variant of Wilms' tumor. But subsequent studies failed to confirm myogenous differentiation, so the rhabdoid tumor is now considered to be a distinct and unique disease type of highly malignant renal tumor, histogenetically unrelated to Wilms' tumor. However the histogenesis have not been clearly defined until now. We report a case of malignant rhabdoid tumor of the kidney in a 34-year-old man who represented with a left abdominal mass. Grossly, a large mass occupying most of the left kidney except for a part of upper pole was invading beyond renal capsule and the perirenal soft tissue. It measured 18x14 cm in dimension and was soft, lobulated and yellowish gray with large areas of hemorrhage and necroses. Microscopically, the tumor mass was composed of sheets of round or polygonal neoplastic cells growing in a solid pattern. These tumor cells were medium to large in size with ample cytoplasm containing recognizable eosinophilic inclusion and had an eccentrically located, large nucleus with one or a few prominent nucleoli. Mitotic figures were frequently observed. Ultrastructurally, the tumor cells contained whorled filamentous inclusions corresponding to vimentin, epithelial membrane antigen and cytokeratin in immunostaining.

• Keywords: Rhabdoid tumor;Wilms' tumor;Filamentous cytoplasmic inclusion;Renal sarcoma