Malignant rhabdoid tumor of the kidney--a case report.

Malignant rhabdoid tumor is a distinct renal tumor in children. It had been regarded as a rhabdomyosarcomatoid variant of Wilms' tumor, but it is now thought as a separate entity. We report a case of malignant rhabdoid tumor of the kidney in a 26-month-old girl who presented with a left abdominal mass. Grossly, a large mass in the lower pole of the left kidney was well encapsulated and measured 4 x 4 x 3.5cm. On cross section, it was soft and yellowish white and showed multifocal necroses. The mass was mainly located in the medial medullary portion and compressed the renal pelvis laterally. Microscopically, the tumor masses were hypercellular and anaplastic without definite blastematous elements. In larger portion, the tumor cells had abundant eosinophilic cytoplasm and hyaline globules. In addition to the classic "rhabdoid" feature, alveolar, sclerosing, and lymphomatous patterns were seen. Ultrastructurally, tumor cells with abundant cytoplasm contained tangles of intermediate filament corresponding to vimentin in immunostaining.