Résumé
Malignant rhabdoid tumor of the kidney(MRTK), an uncommon renal tumor found in children, is one of the most lethal neoplasms of early life. It was first recognized during a review of the first National Wilms' Tumor Study(NWTS) as an extremely aggressive neoplasm whose appearance often mimicks those of skeletal muscle tumors, but without histological, immunohistochemical, and ultrastructural markers of rhabdomyogenesis. Herein we present two cases of malignant rhabdoid tumor of the kidney, one occurring in a 6-month-old male baby, and the other in a 123-month-old girl. They presented a huge tender mass on the left upper quadrant of the abdomen. Microscopically, each case was very cellular and composed of sheets of round or polygonal cells with ample cytoplasm often containing eosinophilic filamentous inclusions and round vesicular nuclei with prominent nucleoli. Case 1 showed lymphomatoid pattern, but case 2 showed foci of several variant patterns associated with classic appearances. The tumor cells showed a strong reactivity for vimentin in both cases. Unusually, case 2 showed focal reactivity for epithelial membrane antigen(EMA), muscle specific actin, and smooth muscle actin. Ultrastructural study confirmed the presence of whorled bundles of intermediate filaments in paranuclear position, and a prominent nucleolus.