Gliomas are malignancies of the glial cells of the central nervous system. These cells are important for myelination of neuronal axons (oligodendrocytes) or for nutritional supply of neurones (astrocytes). Glial cells have a limited life span and a small pool of stem cells exist. Glial cells fall into several broad categories:
- Astrocytes are the most numerous (five times more astrocytes than neurones), and serve numerous roles in the support of the neurons and oligodendrocytes.
- Oligodendrocytes are smaller and form myelin sheaths around neuronal axons
- Ependymal cells line the CSF spaces and facilitate transport of nutrients from the CSF to the underlying neurons and glial cells
Microglia are differentiated monocytes that exist in the CSF. They are not truly glial cells.
The WHO divides glial tumours based on the cell of origin; this is mixed in some circumstances.