Brain tumors are the second most common malignancy in children under the age of 15 years. Most are very malignant, but a great many are neverthelesss curable.
Medulloblastoma is a very aggressive tumor starting in the fourth ventricle of the brain, which is located next to the brain stem in the back of the brain. Most patients are under the age of ten, but it does occasionally occur in adults. Symptoms usually include headaches, balance difficulties, and sometimes double vision. The symptoms are usually caused by blockage of the fluid pathways in the brain by the tumor.
Treatment includes surgery, radiation therapy, and chemotherapy. Surgery is used to relieve the obstruction to fluid flow and to remove as much of the tumor as possible, but no patients are cured with surgery alone because all medulloblastomas will spread to other areas in the brain if not treated adequately. To prevent this, radiation therapy is given to all sites of fluid circulation. This is called craniospinal irradiation and involves treating the entire brain as well as the sac that surrounds the spinal cord all the way to its farthest extent in the pelvis. Long-term effects of this treatment may occur, but there is no evidence that patients can be cured without it.
Chemotherapy is now used in most patients to allow use of a lower dose of radiation to the brain and spine, and the cure rate appears to be better with chemotherapy. Studies to date show an advantage to giving most of the chemotherapy after the radiation instead of before.
Brain Stem Gliomas
This variant of glioma occurs in a specific site, the brain stem. The brain stem controls a number of unconscious activities such as heart rate, breathing, and others. It also serves as a conduit for nerves to the spinal cord. Because of the vital nature of the brain stem, tumors in this area cause a great many symptoms, including double vision, paralysis or weakness of the arms and legs, balance difficulties and facial paralysis on one side, or deviation of the tongue to one side.
It is often too dangerous to perform a biopsy of these tumors, but the diagnosis is usually clear on an MR scan (magnetic resonance imaging, MRI). A CT scan (computed tomography), however, is not always adequate to show the exact extent of the tumor.
Brain stem gliomas can be high-grade or low-grade. The slowly growing low-grade lesions are treated with radiation therapy, often successfully. Patients with high-grade lesions fare less well, and many experimental protocols involving chemotherapy and radiation therapy are being tried to in an effort to improve their prognosis.
Pineal tumors are a group of different types of malignancies arising in the region of the pineal gland, which is located slightly behind the center of the brain, just above the brain stem. Types include germ cell tumors (germinomas and others), pineoblastomas, and pineocytomas.
Germinomas, the most common type, usually occur in teenagers. They are very curable with radiation therapy alone or a combination of radiation therapy and chemotherapy. Surgery is used to provide a diagnosis and relieve obstructions.
The other germ cell tumors are more difficult to cure, but combinations of radiation therapy and chemotherapy are becoming more successful. Pineoblastomas usually arise in young children and are very malignant, and are usually treated with chemotherapy and radiation therapy. Pineocytomas can be slow-growing or more aggressive, and can occur in children as well as adults. They are usually treated with surgery, if possible, and radiation therapy.
Radiation therapy techniques for all these tumors often include craniospinal irradiation in addition to treatment of the primary tumor itself.
Optic Nerve Glioma
These tumors arise in one of the optic nerves or in the junction of the optic nerves, the optic chiasm. They are usually slow-growing and low-grade but can be more aggressive at times. Some physicians believe in observation if the tumor is only in one optic nerve. If progression occurs, then surgery is often performed. Radiation therapy and chemotherapy are alternatives to surgery, since both are effective and can sometimes preserve the patient’s vision.
If the tumor involves the chiasm, then surgery is not an option because total removal will cause total blindness. Radiation therapy is used for older children, with chemotherapy usually given first in younger patients, saving radiation therapy for the case of disease progression. Chemotherapy can sometimes cure the tumor, and in other cases is useful in allowing the child to grow, which decreases the long-term effects of radiation.
Gliomas outside the brain stem and optic nerves do occur in children, and treatment is similar to that given adults, though chemotherapy is probably more effective in children. There are also a large number of very rare tumors in children which are beyond the scope of this brief review.