Primary malignant rhabdoid tumours of the central nervous system: an immunohistochemical and ultrastructural study.

Three cases of primary rhabdoid tumour of the CNS (RT-CNS) are presented. In case 1 a hemispheric tumour developed in a 10.5 months old girl, who survived for 6 months after incomplete resection, radio- and polychemotherapy. Case 2 was a 4 years and 8 months old boy with a large IIIrd ventricle tumour, who died of leptomeningeal tumour dissemination 7 months after diagnosis despite radiotherapy. In case 3 a pineal mass occurring in a 14 month old female was radioresistant and totally exstirpated. The child died due to tumour recurrence two months later. Autopsy examination revealed widespread leptomeningeal dissemination. All three cases fulfilled light and electron microscopic criteria of RT-CNS including abundant eosinophilic cytoplasm, vesicular nuclei with large nucleoli and conspicuous anti-vimentin positive filaments. Extensive immunohistochemical studies showed expression of epithelial (EMA, KL1), macrophage (alpha-1 antichymotrypsin), neuro-ectodermal (GFAP, NSE, beta-tubulin III) and myogenic markers (desmin, actin). Different stress proteins (alpha-B crystallin, HSP70) were also expressed. Tumour cells showed a proliferation (MIB1) index of 28.4% (case 1) and 33.4% (case 2). From our study it can be concluded that RT-CNS reveals significant immuno-morphological heterogeneity thus supporting the view that it is not a specific pathological entity but merely a phenotypic appearance of different neoplasms, some of which are linked to primitive neuro-ectodermal tumours.