A glioma is a type of tumor that starts in the brain or spine. It is called a glioma because it arises from glial cells. The most common site of gliomas is the brain.
Symptoms of gliomas depend on which part of the central nervous system is affected. A brain glioma can cause headaches, nausea and vomiting, seizures, and cranial nerve disorders as a result of increased intracranial pressure. A glioma of the optic nerve can cause visual loss. Spinal cord gliomas can cause pain, weakness, or numbness in the extremities. Gliomas do not metastasize by the bloodstream, but they can spread via the cerebrospinal fluid and cause "drop metastases" to the spinal cord.
High-grade gliomas are highly-vascular tumors and have a tendency to infiltrate. They have extensive areas of necrosis and hypoxia. Often tumor growth causes a breakdown of the blood-brain barrier in the vicinity of the tumor. As a rule, high-grade gliomas almost always grow back even after complete surgical excision.
On the other hand, low-grade gliomas grow slowly, often over many years, and can be followed without treatment unless they grow and cause symptoms.
Gliomas cannot be cured. The prognosis for patients with high-grade gliomas is generally poor, and is especially so for older patients. Of 10,000 Americans diagnosed each year with malignant gliomas, about half are alive 1 year after diagnosis, and 25% after two years. Those with anaplastic astrocytoma survive about three years. Glioblastoma multiforme has a worse prognosis with less than 12 month survival after diagnosis.
Gliomas are classified by cell type, by grade, and by location.
By type of cell
Gliomas are named according to the specific type of cell they most closely resemble. The main types of gliomas are:
- Ependymomas — ependymal cells
- Astrocytomas — astrocytes - Glioblastoma multiforme is the most common astrocytoma.
- Oligodendrogliomas — oligodendrocytes
- Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia.
Gliomas are further categorized according to their grade, which is determined by pathologic evaluation of the tumor.
- Low-grade gliomas are well-differentiated (not anaplastic); these are benign and portend a better prognosis for the patient.
- High-grade gliomas are undifferentiated or anaplastic; these are malignant and carry a worse prognosis.
Of numerous grading systems in use, the most common is the World Health Organization (WHO) grading system for astrocytoma.
Gliomas can be classified according to whether they are above or below a membrane in the brain called the tentorium. The tentorium separates the cerebrum, above, from the cerebellum, below.
- supratentorial: Above the tentorium, in the cerebrum, mostly in adults (70%). Senator Edward M. Kennedy’s brain tumor, for example was supratentorial, in the parietal area in the upper part of the left side of his brain, above the ear.
- infratentorial: Below the tentorium, in the cerebellum, mostly in children (70%)
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