Mixed ependymoma-astrocytoma (subependymoma?) of the cerebral cortex.

Tumors of mixed glial origin may present as low-grade neoplasms with distinct cell populations or as polymorphic malignant gliomas. Such cell populations are usually appropriate to the location of the tumor. A mixed tumor, with a cell population inappropriate to tumor location, is presented to discuss theories of glial differentiation and cellular heterogeneity. This mixed ependymoma-astrocytoma of the parietal cortex, ultrastructurally similar to subependymoma but anatomically separate from the subependymal cell matrix or ventricular surface, gives evidence for neoplastic differentiation into ependymal and astrocytic cell lines. This supports the idea of a common progenitor cell, the ependymoglia or tanycyte, in human cerebral cortex.