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.
Malignant rhabdoid tumor (MRT) is a rare and highly aggressive neoplasm of infancy and childhood. Although it was originally described and most frequently reported in the kidney, it may occur in various extra-renal sites such as the liver, thymus, and soft tissue. In the last decade primary central nervous system (CNS) MRTs have been reported in both the supra- and infratentorial compartments. Patients with CNS MRT were generally below the age of two and reports in adults are extremely rare. This is a case of primary cerebellar MRT in a 24-year-old woman, who had presented with intermittent headache, vocal cord palsy, and cerebellar dysfunctions such as abnormal finger to nose test and tandem gait. By magnetic resonance imaging scan, a well-enhancing solid mass was demonstrated at the posterior fossa filling the 4th ventricle, which extended into the medulla and cervical cord via the foramen of Magendie. Histologically, the monotonous polygonal tumor cells were arranged in diffuse sheet with occasional hemorrhagic necrosis. The nuclei were vesicular and eccentrically located due to eosinophilic, PAS-positive, intracytoplasmic inclusions with prominent nucleoli. They were diffusely or focally immunoreactive for vimentin, neurofilament, cytokeratin, GFAP, synaptophysin, and smooth muscle actin, while epithelial membrane antigen and desmin were negative.
Ultrastructurally, the polyhedral tumor cells were densely packed with primitive intercellular junctions. Scanty fibrillar intermediate filaments were intermingled with cellular organelles. Postoperatively, craniospinal irradiation and systemic chemotherapy have been done and she has been free of tumor recurrence during the 13 months' follow-up periods.
Malignant rhabdoid tumor is a distinct renal tumor in the pediatric age group. It was originally described as a rhabdomyosarcomatoid variant of Wilms tumor. However, subsequent studies failed to confirm myogenous differentiation, so it is now considered to be a distinct and unique type of highly malignant tumor, histogenetically unrelated. Although extrarenal forms of this tumor are rare, several examples have been described in other sites, especially the liver, prostate, paravertebral area, urinary bladder and soft tissue. We experienced a case of malignant rhabdiod tumor located in the intraabdominal cavity in a 10 month-old boy. Smear of peritoneal fluid showed round, polygonal and irregular shaped cells with large nuclei, ample cytoplasm containing Jight pink "to purple cytoplasmic inclusions, and one or a few prominent nucleoli.
Immunocytochemistry revealed positivity to cytokeratin, epithelial membrane antigen and vimentin, and negativity to desmin and neuron-specific enolase. These distinct cytologic appearance and immunophenotypes were most consistent with a diagnosis of extrarenal malignant rhabdoid tumor. The cytoplasmic inclusions were correlated with eosinophilic inclusions seen in histologic section and electron microscopy confirmed this interpretation, showing filamentous aggregations in the cytoplasms of the tumor cells.