A case of cerebellar neuroectomesenchymoma in an infant.

This case report concerns a congenital cerebellar tumor in an infant. The tumor consisted of small, immature lymphocyte-like cells, medium-sized, rhabdoid cell-like cells, and large, polymorphic gemistocytic astrocyte-like cells, which were admixed in motley form on a background of neuronal matrix and dural and collagen fibrous tissues. Immunohistochemical studies revealed that the cytoplasm of rhabdoid cells had conspicuous structures, resembling weakly eosinophilic homogeneously amorphous inclusion bodies, and that the strongly eosinophilic cytoplasm, seen abundantly in the gemistocytic astrocyte-like cells, was a mixture of components that were positive for glial fibrillary acidic protein (GFAP) and vimentin and of components positive for myoglobin. Because of the simultaneous expression of both, neuroectodermal and mesenchymal characteristics the reported tumor was not a mixed tumor of independent neuroectodermal and mesenchymal tumor components, but a very rare neuroectomesenchymoma derived from immature cells with pluripotential differentiating capabilities.