[Melanotic medulloblastoma. Ultrastructural and histochemical study of a case].

A electron microscopic and immunohistochemical study of a Melanotic medulloblastoma is reported. The cerebellar tumor was located in the vermis of a 6-year-old boy, dead 11 months after diagnosis. The tumor consisted of medulloblastoma-like areas with focal differentiation and pseudoepithelial structures pigmented with melanin. Electron microscopy showed melanosomes and tight junctions in pigmented areas. On immunohistochemistry, the cytoplasm of melanotic cells were positive to S-100 protein and the differentiated glial cells to GFAP. The tumor histogenesis, its relationship with other pigmented tumors of the CNS and their low frequency is commented on.