Glioma is a broad category of brain and spinal cord tumors that come from glial cells, brain cells that can develop into tumors.
The symptoms, prognosis, and treatment of a malignant glioma depend on the person’s age, the exact type of tumor, and the location of the tumor within the brain. These tumors tend to grow and infiltrate into the normal brain tissue, which makes surgical removal very difficult -- or sometimes impossible -- and complicates treatment.
These brain tumors are often diagnosed in the 4th through 6th decade of life, depending on the type of glioma. Low-grade versions of gliomas can occur in children. Brain tumors are slightly more likely to occur in males.
Prior radiation to the brain is a risk factor for malignant gliomas. Some genetic disorders also increase the risk of development of these tumors in children but rarely in adults.
There are no lifestyle risk factors associated with malignant gliomas. This includes alcohol, cigarette smoking, or cell phone use.
Are There Different Types of Gliomas?
While many of benign brain tumors are gliomas, almost 80% of malignant brain tumors are gliomas.
Gliomas are named based on the specific type of glioma, or brain cell, affected. According to the American Cancer Society, there are three types of gliomas, including astrocytomas, oligodendrogliomas, and ependymomas. (A fourth type of glioma, contains more than one type of cell so is not a true glioma.)
Ependymomas make up less than 2% to 3% of all brain tumors but up to 10% of all brain tumors in children. These tumors come from the ependymal cells and because they do not spread into the normal brain tissue, some ependymomas can be cured by surgery. They rarely spread outside the brain. But they do have a high risk of local recurrence and thus are considered malignant.
Astrocytomas make up almost 50% of all brain tumors and start in brain cells called astrocytes. Most of these brain tumors cannot be cured because they spread all through the normal brain tissue. Astrocytomas are usually classified as low grade, intermediate grade, or high grade, depending on criteria used by a doctor examining the biopsy under a microscope. Tumors that are low grade grow the slowest. Intermediate-grade astrocytomas grow at a moderate rate, while the highest grade, called glioblastomas, the most common adult malignant brain tumor, are fast growing.
Oligodendrogliomas are tumors that spread in a similar manner to astrocytomas. Some of these tumors may be slow growing but still spread into nearby tissue. Sometimes they can be cured. A higher grade anaplastic oligodendroglioma grows and spreads more quickly and usually can’t be cured.