Medullomyoblastoma.

A case of medullomyoblastoma, arising in the cerebellar vermis of a five-year-old boy, is presented. The light and electron microscopic features of the tumor are described and compared to other published cases. Within typical medulloblastoma areas light microscopy revealed signs of neuroblastic differentiation thus indicating its neuroepithelial origin. No signs of glial differentiation were found. Myogenic tumor component formed irregular, distinctly separated islands although some intermingling of two cell types was observed at the borders between the two zones. Within the myogenic tumor component, electron microscopy revealed rhabdomyoblastic elements in different stages of differentiation, frequently forming small groups encompassed by the same basement membrane. No indication of a common host cell for two cell lines was observed. No mesenchymal elements other than muscle, and no indication of possible teratoid origin of this tumor were observed. Considering histogenesis of muscle elements within this neuroepithelial tumor, the origin from multipotential neural-crest-derived ectomesenchymal cells seems the most appropriate one.