Gliomas arise in nervous system cells known as glial cells, or neuroglia. There are several types of brain and nervous system cancers that fall into this category.
Astrocytomas: Astrocytomas are gliomas that begin in connective cells called astrocytes, because of their star-like shape, and they account for about half of all brain tumors in adults. The severely malignant form of astrocytoma, glioblastoma multiforme, accounts for 30 percent of all brain tumors in middle-aged adults and is the most common brain tumor in this age group. Astrocytomas may also grow near structures at the center of the brain, such as the optic nerve, a nearby nervous tissue structure called the optic chiasm, and the brain stem. Brain stem astrocytomas are rare in adults but relatively common in children. Because of the vital function of the brain stem, these tumors cannot be removed surgically.
Low-grade astrocytomas: These include juvenile pilocytic astrocytomas, which occur mainly in children, subendymal giant cell astrocytomas and astrocytomas. Median survival of patients with low-grade astrocytomas is six to eight years.
Mid-grade astrocytomas: These are more malignant astrocytomas. They include anaplastic astrocytomas and gemistocytic astrocytoma. The average survival for a person with anaplastic astrocytoma is three years.
High-grade astrocytomas: These include glioblastoma multiforme and gliosarcoma. Average survival with glioblastoma multiforme is 12 to 18 months.
Oligodendrogliomal Tumors: These tumors begin in brain cells called oligodendrocytes that produce myelin, a substance that covers and protects nerve cells. They represent 5 to 15 percent of intracranial gliomas, and are most common in people in their 40s and 50s. They are broken into two categories: oligodendrogliomas, which are not malignant; and anaplastic oligodendroglioma, which is malignant. They mainly appear in the white matter of the cerebral hemispheres.
Ependymal Tumors: These tumors begin in the tissue lining the ventricles, hollow spaces within the brain through which cerebrospinal fluid circulates. Ependymal tumors may block normal drainage of cerebrospinal fluid, causing water to collect in the brain. This condition is called hydrocephalus, and can be relieved by placing a tube called a shunt in the brain to drain the fluid.
These tumors rarely spread beyond this area, and are usually curable with surgery. They account for 2 to 6 percent of gliomas and are most common in children and adolescents. Benign ependymal tumors include myxopapillary ependymoma and papillary ependymoma. They are more common than the malignant type, which is called anaplastic ependymoma.
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