These tumors arise in the cerebral hemispheres of adults, where they appear as well-circumscribed gelatinous grey masses. There are sheets of monotonous cells 4025 with uniform central nuclei, surrounded by a clear halo of cytoplasm. There is a delicate network of capillaries, and many contain foci of calcification. This is the most frequently calcified glioma 4035 - a useful diagnostic sign on radiographs. These are slow growing tumors with a favorable prognosis.
Anaplastic variants are more aggressive.
Medulloblastoma A primitive, undifferentiated embryonal tumor derived from neuroepithelial stem cells. They typically arise in the cerebellum 4036 usually in the midline vermis in young children. However, in older patients they may arise laterally in the cerebellar hemispheres. Typically, they spread rapidly into the leptomeninges, and then dissseminate through the CSF to the spinal cord - seeding along the subarachnoid space and involving the ependymal surfaces. Microscopically, they are cellular neoplasms composed of ribbons and sheets of small round cells 4038 with hyperchromatic nuclei and scant cytoplasm.