Malignant teratoid/rhabdoid tumour: long-term survival.

became symptomatic in October 1998 with right hand weakness and cessation of new words with progression of right sided weakness and decreased sensation over the next month. The computed tomography (CT) and magnetic resonance imaging (MRI) scans demonstrated a large, deep, left frontal periventricular enhancing mass with several cystic areas. A left frontoparietal craniotomy was performed and the tumour was grossly resected. The pathological diagnosis was AT/RT. Grossly, the tumour was composed of firm, pink-tan hemorrhagic tissue. Sections showed a densely cellular, infiltrating neoplasm with areas of necrosis (some calcified), fascicular and focal sheets of collagen, and a variable, often prominent reticulin network. There was no endothelial proliferation. Light microscopy with hematoxylin and eosin stain (Figure 1) revealed a varied tumour appearance predominantly composed of larger tumour cells, with randomly dispersed nests of small undifferentiated cells close to the interface of tumour and normal brain tissue. The larger cells had several growth patterns: some were loosely arranged bior multi-polar cells forming cords and acinar structures against a faintly basophilic mucinous background, some were elongated cells arranged in coarse follicles or other compact bundles, while others were arranged in sheets or nests with prominent, sometimes glassy eosinophilic and cytoplasmic inclusions and eccentric nuclei (rhabdoid cells). Larger cells had nuclei with vesicular chromatin and prominent nucleoli, and smaller cells had hyperchromatic nuclei. Mitoses were focally numerous with some atypical in form, and cytoplasmic glycogen was inconspicuous. Immunohistochemical studies revealed widespread staining for epithelial membrane antigen (EMA), vimentin (Figure 2), glial fibrillary acid protein (GFAP), groups of cells with membranous patterns of staining for CD99, regional staining for neuron-specific enolase (NSE), scattered staining for transthyretin, and rare staining for actin, cytokeratin, and synaptophysin. The tumour was positive for chromosome 22 monosomy. Electron microscopy showed polygonal cells arranged in ill-defined acini that formed inconspicuous, sometimes entwined short microvillus processes. Variable numbers of intermediate filaments were identified and some cells showed a rudimentary basal lamina. Desmosomes were not seen, and there was no evidence of neural differentiation. Post operative CT and MRI showed no definite residual tumour, however, the patient had residual right hemiparesis. The infant commenced a course of chemotherapy consisting of: Vincristine (0.05 mg/kg IV), Etoposide (1.5 mg/kg/day IV x 5