Astrocytomas are the most common glioma, accounting for about half of all primary brain and spinal cord tumors. Astrocytomas develop from star-shaped glial cells called astrocytes, part of the supportive tissue of the brain. They may occur in many parts of the brain, but most commonly in the cerebrum. They occur less commonly in the spinal cord. People of all ages can develop astrocytomas, but they are more prevalent in adults, particularly middle-aged men. Astrocytomas in the base of the brain are more prevalent in children or younger people and account for the majority of children’s brain tumors. In children, most of these tumors are considered low-grade, while in adults most are high-grade.
There are different types of astrocytomas, and these lesions are classified into several categories according to their appearance under a microscope. This classification is important because, the appearance of an astrocytoma will often predict its behavior and, therefore, a patient's prognosis.
Classification of Astrocytomas
Astrocytomas are generally classified (graded) into one of three types: Low grade astrocytomas, anaplastic astrocytomas and glioblastomas. Low grade astrocytomas account for 10 percent of astrocytomas. These tumors are typically slow growing and may not require specific treatment at the time of diagnosis. Many patients with low grade astrocytomas live for prolonged periods of time after their diagnosis. However, these tumors often advance into the higher grades and more rapidly growing forms of brain gliomas. Anaplastic astrocytomas and glioblastomas are the most aggressive and, unfortunately, the most common astrocytomas. Glioblastomas are fast growing astrocytomas that contain areas of dead tumor cells. In adults, glioblastoma occurs most often in the cerebrum, especially in the frontal and temporal lobes of the brain.
Symptoms vary depending on the location of the brain tumor, but may include any of the following:
- Persistent headaches
- Double or blurred vision
- Loss of appetite
- Changes in mood and personality
- Changes in ability to think and learn
- New seizures
- Speech difficulty of gradual onset
In early stages, children may experience headaches, nausea, vomiting, blurred or double vision, dizziness, and changes in coordination.
Sophisticated imaging techniques can pinpoint brain tumors. Diagnostic tools include computed tomography (CT or CAT scan) and magnetic resonance imaging (MRI). Intraoperative MRI is also used during surgery to guide tissue biopsies and tumor removal. Magnetic resonance spectroscopy (MRS) is used to examine the tumor's chemical profile and determine the nature of the lesions seen on the MRI. Positron emission tomography (PET scan) can help detect recurring brain tumors.
Treatment options include surgery, radiation, radiosurgery, and chemotherapy. The main goal of surgery is to remove as much of the tumor as possible without injuring brain tissue needed for neurological function (such as the ability to speak, walk, motor skills, etc.). However, high-grade tumors often have tentacle-like structures that invade surrounding tissues, making it more difficult to remove the entire tumor. If the tumor cannot be completely removed, surgery can still reduce or control tumor size. In most cases, surgeons open the skull through a craniotomy to best access the tumor site. The goal of radiation therapy is to selectively kill tumor cells while leaving normal brain tissue unharmed. In standard external beam radiation therapy, multiple treatments of standard-dose "fractions" of radiation are applied to the brain. Each treatment induces damage to both healthy and normal tissue. By the time the next treatment is given, most of the normal cells have repaired the damage, but the tumor tissue has not. This process is repeated for a total of 10 to 30 treatments, depending on the type of tumor. This additional treatment provides some patients with improved outcomes and longer survival rates.
Radiosurgery is a treatment method that uses computerized calculations to focus radiation at the site of the tumor while minimizing the radiation dose to the surrounding brain. Radiosurgery may be an adjunct to other treatments, or it may represent the primary treatment technique for some tumors
Patients undergoing chemotherapy are administered special drugs designed to kill tumor cells. Although chemotherapy may improve overall survival in patients with the most malignant primary brain tumors, it does so in only about 20 percent of patients. Chemotherapy is often used in young children instead of radiation, as radiation may have negative effects on the developing brain. The decision to prescribe this treatment is based on a patient’s overall health, type of tumor, and extent of the cancer. Before considering chemotherapy, you should discuss it with your doctor, as there are many side effects.
Because traditional treatment modalities are unlikely to result in a prolonged remission of malignant astrocytomas, researchers are presently investigating a number of promising new treatments including gene therapy, highly focused radiation therapy, immunotherapy and novel chemotherapies. A number of new treatments are being made available on an investigational basis at centers specializing in brain tumor therapies.
Copyright, the American Association of Neurological Surgeons, August 2005.