Glioma is the general term for all tumors that arise from glial cells. Glial cells perform a variety of functions across the nervous system, including providing support to the neurons. Just as there are many types of glial cells, there are many types of gliomas.
Overview of Gliomas
The broad category of glioma accounts for 26.5% of all brain tumors, and primarily occur in the frontal, temporal, parietal, and occipital lobes of the brain.1
While imaging studies (including CT scans and MRIs) can characterize the size, location, and spread of a glioma, surgical biopsy may be required to further classify certain glioma subtypes. Each glioma subtype can have very different symptoms and does not occur equally--some are much more rare than others. Accordingly, treatment options and patient outcomes also vary by glioma subtype.
- Astrocytomas grow from glial cells called astrocytes.
- Oligodendrogliomas grow from glial cells called oligodendrocytes
- Ependymomas grow from glial cells called ependymal cells
- Oligoastrocytomas (also called mixed gliomas) contain a mix of astrocytes and oligodendrocytes
- Mixed neuronal-glial tumors contain a mix of neurons and glial cells.
Tumors that grow from astrocytes are called astrocytomas (which includes glioblastomas). Normally, astrocytes are responsible for a variety of functions throughout the nervous system, including providing nutrients to neurons, maintaining the blood-brain barrier, and modulating neurotransmission (how neurons communicate with each other).
Astrocytomas can be further classified into more specific subtypes based on its grade, location, how the cells look under a microscope (its histological characteristics), and the specific mutations it has (its genetic characteristics):
- Pilocytic astrocytoma (grade I)
- Subependymal giant cell astrocytoma (grade I)
- Diffuse astrocytoma (grade II)
- Pleomorphic xanthoastrocytoma (grades II-III)
- Anaplastic astrocytoma (grade III)
- Glioblastoma (grade IV)
- Brainstem glioma (grades I-IV)
- Diffuse midline glioma (grade IV)
Tumors that grow from oligodendrocytes are called oligodendrogliomas. Normally, oligodendrocytes are the cells that wrap around and provide support to nerve fibers in the brain.
Oligodendrogliomas are relatively uncommon tumors that primarily occur in adults. Depending on the location of the tumor, symptoms may include seizure, headaches, weakness on one side of the body, or speech problems.
Tumors that grow from ependymal cells are called ependymomas. Ependymal cells normally line the fluid-filled cavities (called ventricles) in the brain, in addition to the fluid-filled central canal of the spinal cord.
Ventricles are filled with cerebrospinal fluid (CSF), which helps cushion the brain from trauma. When ependymomas develop, they often interfere with the flow of CSF within the brain, causing a buildup of CSF and an increase in pressure. This condition, also called hydrocephalus, is often associated with headaches (or a rapidly increasing head size in infants) and is often the first symptom.
Ependymomas are relatively rare tumors that primarily occur in children.
- Ostrom, Q.T., et al., CBTRUS Statistical Report: Primary brain and other central nervous system tumors diagnosed in the United States in 2010-2014. Neuro Oncol, 2017. 19(suppl_5): p. v1-v88.
This content was reviewed by UCSF Neuro-oncology Fellow, Sarah Lapointe MD.