Medulloblastoma with cartilaginous differentiation.

We describe the histologic, immunocytochemical, and electron microscopic features of a medulloblastoma containing cartilage that occurred in the left cerebellar hemisphere of a 57-year-old man. By light microscopy, highly cellular areas of the tumor typical of medulloblastoma showed evidence of both glial and neuroblastic differentiation. The tumor also contained foci of mature and immature cartilage. Transitions were observed between the cartilaginous foci and the more densely cellular regions of the tumor. No frankly teratomatous features or mesenchymal components other than cartilage were present. We postulate that the production of cartilage within this neoplasm most likely resulted from the metaplastic transformation of preexisting mesenchymal elements within the tumor or from multipotential neural crest-derived ectomesenchymal cells. Alternatively, the cartilage could have been produced directly by the neuroectodermal cells themselves, possibly related to a capacity for the latter to produce a chondroid ground substance.