Like all other parts of the body, the brain and central nervous system are made up of cells that ordinarily grow and divide to create new cells as needed. This is usually an orderly process; but when cells lose their ability to grow normally or to die off naturally, they divide too often and produce tumors that are made up of these extra cells.
Description
The brain and spinal cord together comprise what is known as the central nervous system (CNS). Like all
tumors in the body, CNS tumors are either benign or malignant. Benign tumors are called non-cancerous because they have precise borders, are not invasive, and the cells that make up the growth are similar to other normal cells and grow relatively slowly. However, benign CNS tumors can press on a specific region of the spinal cord or brain and, thereby, cause symptoms. However, when such a benign tumor develops in an area that interferes with essential nervous system functioning, it is treated as malignant.
Malignant, or cancerous, tumors of the central nervous system are likely to be fast-growing, are invasive into surrounding healthy tissue, and the cells are very different from normal cells. These tumors can create a life-threatening situation by stopping vital functions of the brain. Some cancerous CNS tumors do not put out roots nor do they grow rapidly. These tumors are described as being encapsulated.
Another way that brain and central nervous system tumors are classified is by site of origin. Those that actually develop in the brain or spinal cord are called primary CNS tumors. Metastasis to the brain or spinal cord is, for the most part, a one-way street, meaning these tumors almost never metastasize to other areas in the body. The tumors that develop elsewhere in the body and metasta-size, or spread, to the central nervous system are considered to be secondary CNS tumors. Such metastatic cells do not resemble other CNS cells. Instead, they have the same appearance as the cancer cells at the original cancer site elsewhere in the body.
Frequently observed signs of a brain tumor are the following:
Approximately 1 1/2% of all diagnosed cancers are CNS cancers, and they account for about 2 1/2% of all cancer deaths. The American Cancer Society (ACS) estimates that in 2001 17, 200 malignant tumors of the brain or spinal cord will be diagnosed in adults and children in the United States. Of those people diagnosed, ACS projects that 13, 100 will die from malignant CNS tumors.
General categories of treatment methods for CNS tumors include surgery, radiation therapy, and chemotherapy, with surgery being the single most commonly used therapy. Steroids are usually given prior to treatment to decrease swelling, and anti-convulsant drugs may be given to prevent seizures.
Types of cancers
Primary brain tumors are also classified by their site of origin. Gliomas, occurring in the glial, or supportive tissues around the brain, are the most common. Gliomas are further broken down into the following variations:
Astrocytomas are named for the star-shaped, small cells that they are comprised of. Children may develop these in their brain stem, cerebrum, or cerebellum, while adults commonly develop them in the cerebrum.
Brain-stem gliomas are usually astrocytomas that originate in the bottom, stem-like portion of the brain. Because this area controls many essential bodily functions, such tumors often cannot be removed.
Ependymomas occur in the linings of the four brain ventricles, or chambers, or along the spinal cord. These are more common in children.
Oligodendrogliomas are very rare and, when seen, are usually found in middle-aged adults. They grow slowly and ordinarily do not invade surrounding brain or spinal cord tissue. They originate in the cells responsible for the manufacture of myelin, a fatty covering for nerve tissue.
Other CNS tumors do not originate in glial tissue. Among these are:
Medulloblastomas, tumors of the cerebellum, are most common in male children. Studies have shown these to originate in primitive nerve cells that normally would have disappeared soon after birth.
Meningiomas are usually benign. They develop in the meninges, or brain linings, and grow very slowly. Because of this slow growth, they may go undetected for years. Meningiomas are more common in women between the ages of 30 and 50.
Schwannomas are also benign tumors, specific to the myelin-producing cells (Schwann cells) for the acoustic, or hearing, nerve. These, too, are more common in women than men.
Craniopharyngiomas are usually benign, but because of their location near the pituitary gland and hypothalmus, they can easily affect vital functions and are therefore treated as if malignant. They occur more frequently in children and teenagers.
Germinomas, or germ cell tumors, develop from primitive sex cells called germ cells.
Pineal-region tumors originate in the area near the pineal gland, a small central brain gland that secretes melatonin, a brain chemical. These can be either fast-growing pineoblastoma, or slow-growing pineocytoma.
Resources
BOOKS
Clayman, Charles, M.D. The American Medical Association
Home Medical Encyclopedia. New York: Random House, 1989.
Diamond, John W., MD, Cowden, W. Lee, M.D., and Burton Goldberg. An Alternative Medicine Definitive Guide to Cancer. Tiburon, CA: Future Medicine Publishing, Inc., 1997.
—A diagnostic test that makes it possible for blood vessels to be seen on film by filling them with a contrast substance or dye that appears on x rays.
Anti-convulsant drugs
—A group of medications used in the treatment of seizures.
—The combined use of a computer and x rays that are passed through the body to produce clear, cross-sectional images.
Magnetic resonance imaging (MRI)
—An imaging technique that produces good cross-sectional images without x rays or other radiation sources.
Myelogram
—X-ray examination of the spinal cord after injection of a contrast substance or dye that shows up on x rays.
Neurological exam
—A physical examination that focuses on the patient's nerves, reflexes, motor and sensory functions, and muscle strength and tone.
Seizures
—Sudden, uncontrolled electrical activity in the brain resulting in characteristic twitching, or spastic, movements that may be accompanied by loss of consciousness.
Steroids
—A group of drugs that are similar to the hormones produced by the cortex of the adrenal gland.
Ventricles of the brain
—The four fluid-filled chambers, or cavities, found in the two cerebral hemispheres of the brain, at the center of the brain, and between the brain stem and cerebellum, and linked by channels, or ducts, allowing cerebral fluid to circulate through them.
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