About half of all brain tumors that start in the brain are gliomas. They usually occur in the lobes of the upper part of the brain, but they can also grow in other areas, especially near the optic nerve, brain stem and the cerebellum (particularly in children).
Gliomas are tumors that contain a variety of cell types, and the distribution of the cell types varies with each tumor. The most common type of gliomas are astrocytomas. They develop from abnormal, star-shaped cells. Astrocytomas are graded on a scale of 1 to 4, grade 4 being the most malignant. The types and grades of these tumors are:
- Well differentiated (low-grade or grade I and II) astrocytomas. These tumors contain cells that are less malignant than higher grade tumors. They grow slowly and can sometimes be completely removed by surgery. However, even well differentiated astrocytomas can be difficult to reach via surgery. If they are truly inaccessible, they can be life threatening.
- Anaplastic (grade III) astrocytomas. They grow more rapidly than the low-grade type, and contain cells that have malignant traits. Recommended treatment is surgery followed by radiation and chemotherapy.
- Glioblastoma multiforme (high grade or grade IV) astrocytomas. These tumors grow rapidly, invade nearby tissue and contain cells that are very malignant. Glioblastoma multiforme are among the most common and devastating primary brain tumors in adults. They are usually treated with surgery followed by radiation therapy. Chemotherapy may be used after radiation.
Mixed gliomas contain more than one type of glial cell, usually astrocytes and other glial cell types like oligodendroglial cells. Treatment focuses on the most malignant cell type found within the tumor. They may be classified under anaplastic oligodendrogliomas or be called mixed gliomas, depending on the relative cell types seen by the pathologist.
Brain Stem Gliomas
Named for their location rather than for the cells they contain, brain stem gliomas are most common in children and young adults. Surgery is not usually an option to treat these types of tumors because of their location in vital or critical areas. Radiation therapy sometimes helps to reduce symptoms and improve survival by slowing the tumor's growth.
Optic Nerve Gliomas
Also named for their location, these tumors are found on the optic nerve and are particularly common in individuals who have neurofibromatosis. Treatment may include surgery, radiation or chemotherapy. Some of these tumors can be very slow growing and best managed by observation alone.
A neurologic evaluation should be done if a patient has slowly increasing signs of mental dysfunction, new seizures, persistent headaches or evidence that there is pressure inside the skull, such as vomiting or swelling or protrusion of the blind spot at the back of the eye.
A neurologist (a doctor who has received special additional training in the diagnosis and treatment of disorders of the brain, spinal cord and nerves) performs a complete examination, which may include a magnetic resonance imaging (MRI) scan, a computed tomography (CT or CAT) scan or a chest X-ray to determine if the tumor has spread from another part of the body. An MRI usually finds low-grade astrocytomas earlier than CT. Cerebral angiography is rarely used to diagnose a brain tumor, but it may be done before surgery.
Depending on the patient's symptoms, specialized tests may be done, including tests of the field of vision, the sharpness of vision and hearing. If the results of other tests are not conclusive, an examination of the fluid that surrounds the brain and spinal cord may be done, although it is usually unnecessary.
Treatment of a brain tumor depends on the nature of the tumor, how rapidly it is growing, what symptoms it causing and where it is located. Often several treatment approaches are used. Surgery is usually done to make a diagnosis and to improve symptoms, and it may be enough to cure benign tumors.
Radiation therapy is required to treat gliomas. Radiation therapy may also be beneficial in the short-term for tumors that have spread from other parts of the body. Chemotherapy also benefits some patients with such tumors.
Low-grade gliomas (astrocytoma and oligodendroglioma, for example) should be removed surgically if possible, followed by radiation therapy. The timing of radiation therapy is debatable because early may be better therapeutically, but the brain can be exposed to radiation damage earlier than necessary.