A brain tumor is an abnormal growth of tissue, either malignant (cancerous) or benign (noncancerous), in the brain. Each year, more than 17,000 brain tumors are diagnosed in the United States.
Benign brain tumors
A benign brain tumor is composed of slow-growing noncancerous cells that never spread (by local extension or any other means) beyond the site where they originate. Common benign tumors are meningiomas, acoustic neuromas, pituitary gland tumors, craniopharyngiomas, germinomas, pinealomas, and hemangioblastomas. Even though a tumor is benign it may still be dangerous because, depending on its location, it may be inoperable and/or affect one or more brain functions.
Benign brain tumors have clearly defined borders, can often be removed completely, especially if they are on the brain's surface, and are unlikely to recur. Benign brain tumors do not infiltrate nearby tissues but as they continue to grow can cause severe pain, permanent brain damage, and death. Benign brain tumors sometimes become malignant.
Malignant brain tumors
A brain tumor is considered malignant if it contains cancer cells. Unlike other tumors, these spread by local extension and rarely metastasize beyond the brain. About half of all brain tumors are malignant.
Malignant brain tumors do not have distinct borders. They tend to grow rapidly, increase intracranial pressure, and metastasize to other parts of the brain or spinal cord. It is highly unusual for malignant brain tumors to spread beyond the central nervous system (CNS).
Primary brain tumors
Primary brain tumors originate in the brain. They represent about 1% of all cancers and 2.5% of all cancer deaths.
Metastatic or secondary brain tumors
Most brain tumors do not originate in the brain; they are metastases from other primary cancer sites. Approximately 25% of all cancer patients develop secondary or metastatic brain tumors when cancer cells spread from another part of the body. Secondary brain tumors are most apt to occur in patients who have melanoma, breast, colon, kidney, or lung cancer. Brain metastases can develop on any part of the brain or spinal cord.
Patient demographics
Primary brain tumors may develop at any age, but are most common in children between the ages of three and 12, and in adults aged 40–70. Primary brain cancer is the second-most common cause of cancer death between birth and the age of 34, and the third-most common cause of cancer death in men aged 35–54. Primary tumors of the brain and central nervous system are associated with AIDS in some patients.
Naming and grading brain tumors
A brain tumor's name describes its origin, how it grows, and the cell type it contains. A tumor in an adult is also graded or staged according to the extent or degree to which it is malignant; how rapidly it is growing, and how likely it is to invade other tissues; and how closely its cells resemble normal cells. (The less normal a tumor cell appears, the faster it is likely to grow.)
Low-grade tumors usually have well-defined borders. Some low-grade brain tumors form or are encapsulated (enclosed) in cysts. Low-grade brain tumors grow slowly, if at all. They may spread throughout the brain, but rarely metastasize to other parts of the body.
Mid- and high-grade tumors grow more rapidly than low-grade tumors; these tumors usually infiltrate healthy tissue. Their growth pattern makes it difficult to remove the entire tumor, and they recur more often than low-grade tumors.
A single brain tumor can contain several different types of cells. The tumor's grade is determined by the highest-grade (most malignant) cell detected under a microscope, even if most of the cells in the tumor are less malignant. An infiltrating tumor is a tumor of any grade that grows into surrounding tissue.
Types of brain tumors
Glioblastomas, also known as gliomas, are the most prevalent primary brain tumors. They arise from glial tissue, which supports and nourishes cells that send messages from the brain to other parts of the body. Gliomas can be either malignant or benign. Astrocytomas, ependymomas, and mixed glioblastomas are three of the most common types.
ASTROCYTOMAS. Named for their star-shaped cells and the tumor's radiating tentacles, astrocytomas can develop on any part of the brain or spinal cord. Noninfiltrating astrocytomas grow slowly, and rarely spread to nearby tissue. Mild-to-moderately anaplastic (malignant) astrocytomas with well-differentiated borders grow more quickly, and tend to infiltrate surrounding tissues. These are grade I and II astrocytomas.
Anaplastic, or grade III astrocytomas, look more abnormal and grow more rapidly than noninfiltrating or mild-to-moderately anaplastic tumors. Grade IV astrocytomas are also called glioblastoma multiforme (GBM) tumors. Accounting for 30% of all primary brain tumors, GBMs are the most common brain tumors in middle-aged adults. GBMs are also the most malignant of all brain tumors. Because they contain a greater mixture of cells than any other brain tumor, they are the most difficult to treat.
EPENDYMOMAS. Also called ependymal tumors, ependymomas account for 9% of all gliomas, 5% of all intracranial tumors, and are the most common brain tumors in children and adolescents. They begin in the ependymal cells that line the central canal of the spinal cord and the ventricles of the brain, where cerebrospinal fluid (CSF) is manufactured.
Ependymomas are often benign, have well-differentiated borders, resemble normal cells, and grow very slowly. The cells of anaplastic ependymomas look abnormal and grow more rapidly than the cells of benign tumors.
MIXED GLIOMAS. These heterogeneous tumors contain elements of astrocytomas, ependymomas, and/or oligodendrogliomas. These rare tumors usually occur in middle-aged adults, grow slowly, and do not usually spread beyond the part of the brain where they originate. Mixed gliomas follow the patterns of growth related to the highest-grade cells they contain.
Nonglial brain tumors
MEDULLOBLASTOMAS. Scientists once thought medulloblastomas (MDLs) developed from glial cells. These fast-growing malignant tumors are now believed to originate in embryonal cells not normally present in the body after birth. They are sometimes called primitive neurodectal tumors (PNET).
MDL tumors are most common in children and are found more often in males than females; only 30% occur in adults. MDL tumors usually originate in the cerebellum and often metastasize to other parts of the brain via cerebrospinal fluid. They rarely metastasize beyond the brain and spinal cord.
MENINGIOMAS. Meningiomas, which represent more than 20% of all primary brain tumors, originate in the meninges (the membranes that cover the brain and spinal cord). These tumors are usually benign and most often occur in women aged 30–50 years old. Meningiomas grow so slowly that the brain can sometimes become accustomed to their presence. Meningiomas compress brain tissue rather than invade it, and may grow to be quite large before any symptoms appear.
ACOUSTIC NEUROMA. These benign tumors, also known as vestibular schwannomas, are named for the cells in which they orginate. In this case, the tumor is named for the Schwann cells, which produce myelin, the material that sheaths all nerves. Acoustic neuromas are usually found on the auditory nerve, which controls hearing. They are twice as common in women as in men, and are most often diagnosed in patients between the ages 30–60.
Acoustic neuromas grow very slowly, and many patients adapt to the hearing loss balance problems, and tinnitus that are the tumors' earliest symptoms. As the tumor progresses, it can press on the nerves that control movement and sensation in the face, and cause headaches and facial numbness or tingling. The patient may have trouble walking, swallowing, or controlling eye movements, and the sense of taste can be affected. An acoustic neuroma that grows large enough to press on the brainstem can be deadly.
CHILDHOOD BRAIN TUMORS.Brain tumors that occur in children are treated differently than those found in adults because they usually appear in different parts of the brain, cause different symptoms, and require different treatment because of the patient's age and stage of development. They also often have a better prognosis than adult tumors.
Brain tumors are rare in children—only about 2,200 are diagnosed in the United States each year. Children under seven are most likely to be afflicted, with boys affected more often than girls. Headaches, nausea, vomiting, difficulty walking, vision problems, and changes in schoolwork are the chief symptoms.
Unlike adult tumors, childhood brain tumors are identified primarily by their location, either supratentorial (above the tentorium, the membrane that separates the brain from the cerebellum) or infratentorial (below the tentorium). Astrocytomas and ependymomas are common supratentorial tumors. Infratentorial tumors include medulloblastomas, astrocytomas, and ependymomas.
Causes and symptoms
The causes of primary brain tumors are unknown, but people who work with vinyl chlorides, polycyclic hydrocarbons, nitrosoureas, and certain pesticides have a greater-than-average risk of developing them. There is no evidence that head injury causes brain tumors, but researchers are trying to determine the relationship, if any, between brain tumors and viruses, genetic susceptibilities, and long-term exposure to electromagnetic fields.
Although brain tumor symptoms resemble those of many other illnesses, the presence of a brain tumor may be suspected in patients who have persistent headaches with vomiting or convulsions; progressive deterioration of sight, speech, hearing, touch; or deterioration in the ability to use an arm, hand, foot, or leg. Symptoms often do not appear until the tumor grows large enough to dis-place, damage, or destroy delicate brain tissue.
Diagnosis
When a patient experiences one or more of the above symptoms, a primary care physician will perform a focused physical examination, take a detailed medical history, and conduct a basic neurologic examination to evaluate:
balance and coordination
abstract thinking and memory
eye movements
hearing, touch, and sense of smell
reflexes
control of facial muscles and movements of the head and tongue
awareness
If the results of these examinations suggest a patient may have a brain tumor, the patient is referred to a neurologist or neurosurgeon, who will recommend any or all of several diagnostic tests:
electroencephalography (EEG) to measure the electrical activity in the brain when seizures are suspected
angiography can outline a tumor and the blood vessels that lead to it
a lumbar puncture (spinal tap) to see if spinal column pressure has increased and if the spinal fluid contains tumor cells
Interpreting these images and results enables the physicians to determine whether a tumor is present, but biopsy (microscopic examination of tumor tissue) is the only way to identify its cell type.
Treatment
Patients with brain tumors are treated by multidisciplinary teams of highly skilled specialists whose decisions are based on test results; tumor size, position, and growth pattern; the patient's history and current medical status; and the patient's wishes.
Surgery
Surgery is the treatment of choice for accessible brain tumors that can be removed without causing serious neurological damage. A craniotomy, the procedure performed most often, allow surgeons to remove as much of the tumor as possible and send a specimen to the laboratory for microscopic analysis. The operation also creates an entry channel for chemotherapy drugs and forms of radiation that are implanted in the brain.
Prior to surgery, patients are often given corticosteroids and other medications to reduce swelling of brain tissue and anticonvulsants to prevent or control seizures. Preoperative radiation treatments may also be administered to reduce tumor size.
Patients whose benign brain tumors can be completely removed may not require any additional postoperative treatment, however, periodic physical and neurologic examinations and CT or MRI scans are usually recommended to determine whether the tumor has returned. Surgeons cannot be absolutely sure that every bit of an infiltrating or metastasizing tumor has been removed and microscopic growth may still exist, so radiation and chemotherapy are used to eradicate malignant cells that may have escaped the scalpel.
If a tumor cannot be completely removed, debulking (removing a major portion of it) can alleviate symptoms, enhance the sense of well-being, and increase the effectiveness of other treatments.
Radiation therapy
External radiotherapy is generally delivered on an outpatient basis, and directs radiation to the tumor and the area around it. Implant radiation therapy involves placing radioactive material into channels made in the brain. Left in place permanently, or for a short time, these radioactive pellets, sometimes called seeds, release measured doses of radiation each day. Patients are usually hospitalized for observation during the several days the pellets are most active. Immediate family are encouraged to keep a distance or use protective gear, in some instances, during this period.
Stereoactic radiosurgery involves fitting the patient with a frame to stabilize the head, using imaging techniques to determine the exact location of tumor cells, and using a sophisticated instrument called a gamma knife to administer radiation precisely to that point.
Chemotherapy
One or more anticancer drugs may be taken by mouth or injected into a blood vessel, muscle, or the cerebrospinal fluid to kill malignant cells. Chemotherapy may be used in combination with radiation and surgery as part of initial treatment, or used alone to treat tumors that recur in the same place or in another part of the body. When a young child has a brain tumor, chemotherapy is often used to eliminate or delay the need for radiation.
Other treatments
If a brain tumor cannot be eradicated, treatment is designed to make the patient as comfortable as possible and preserve as much neurologic function as possible. The patient's physician may prescribe analgesics to relieve pain, anticancer drugs to limit tumor growth, anti-convulsants to control seizures, and steroids to reduce swelling of brain tissue.
Potential therapies
Researchers are exploring ways to empower chemotherapy drugs to penetrate the blood-brain barrier (which protects the CNS by separating the brain from blood circulating throughout the body), and attack cancer cells that have infiltrated tissue inside it. The goal is to target these drugs to certain types of cells or cell-growth mediators, keeping healthy brain tissue unaffected.
Researchers also are investigating:
less-invasive surgical procedures
methods of incorporating chemotherapy drugs into tumor cells to reduce the need for radiation
laboratory techniques that enable physicians to select the chemotherapy drugs most likely to kill particular types of tumors
gene therapy in which genetically engineered material is transported to tumor cells by viruses that infect tumor cells and convert them to normal cells, stop their growth, or kill them
Alternative therapies have not been demonstrated to cure brain tumors and should never be substituted for conventional therapy. However, complementary therapies (used with, not instead of, standard treatments) may help some patients cope with the stress of illness and side effects of their treatment. Among these are biofeedback training, massage, meditation, and botanical and homeopathic treatments.
Biofeedback can teach patients to influence and control heart rate, muscle tension, and other stress-related body functions. Some patients claim that guided imagery (visualization) helps them feel healthier and more in control of their disease.
Massage, meditation, guided imagery, and reflexology help some patients relax; while yoga is said to soothe the body, spirit, and mind while reducing the other effects of stress. Hydrotherapy uses ice, liquid, and steam to improve circulation and relieve pain. Body work and therapeutic touch may help relieve pain and other symptoms.
Some patients and practitioners incorporate botanical therapies, homeopathic treatment, traditional Chinese medicine treatments, changes in diet, and use of dietary supplements as complementary therapies.
Before, during and after treatment, nurses and allied health professionals should inform and educate patients and families about the risks and complications of any planned diagnostic test, intervention or treatment. It is important to realize that in order for informed consent to be valid, the surgeon or other physician must be the one to offer initial information on the pros and cons of therapies. Patients and families should be taught about some of the common side effects of treatment including weight loss, malnutrition, increased risk of infection, pain, fatigue, and depression.
Occupational therapists can teach patients and families new ways to approach daily tasks. Physical therapists, physical therapy assistants, and speech therapists can help patients who have difficulty keeping their balance, expressing their thoughts, speaking, or swallowing. Children may need special tutors and counseling before and after returning to school. For patients who have incurable brain tumors, hospice care can provide a supportive environment and specially trained health professionals to help patients manage pain and remain comfortable, whether at home or in a treatment facility.
Prognosis
The patient's prognosis depends on the location of the tumor and its cell type. A patient whose tumor is discovered early and removed completely may make a full recovery, but the surgery itself may harm or destroy normal brain tissue. This can result in additional problems, such as seizures, weakness, personality changes, or thought, speech, and coordination difficulties. Although these postoperative problems may initially be more severe than the symptoms produced by the tumor, they usually diminish or disappear over time.
Consequences of radiation therapy
Cells killed by radiation can cluster in the brain, resembling tumors. These dead-cell clusters can cause headaches, seizures, and memory loss. Children treated with radiation may lose some of their eyesight and develop learning problems. Radiation damage to the pituitary gland can hinder normal growth and development.
Consequences of chemotherapy
Some anticancer drugs may cause kidney damage and other temporary or permanent dysfunction, such as tingling in the fingers and ringing in the ears.
Inoperable tumors
Brain tumors that cannot be removed may cause irreversible brain damage and death.
Prevention
Since the causes of primary brain tumors have not been determined conclusively, there is no known way to prevent them. The best way to prevent secondary or metastatic brain tumors is to reduce risk factors such as:
poor nutrition and a low-fiber diet; since these contribute to development of intestinal cancers
excessive alcohol consumption, which is associated with liver cancer
excessive exposure to the sun, which can cause melanoma
KEY TERMS
Central nervous system (CNS)—The division of the nervous system that consists of the brain and spinal cord.
Cerebrospinal fluid (CSF)—Clear lymph-like liquid that fills brain cavities and protects the brain and spinal cord.
Craniotomy—Surgical procedure in which part of the skull is removed (then replaced) to allow access to the brain.
Gamma knife—High-dose radiation treatment for intracranial tumors.
Intracranial—Located within or on the surface of the brain; within the cranium (skull).
Malignant—A cancerous or life-threatening tumor.
Melanoma—A particularly deadly type of skin cancer that develops in the melanocytes, or skin-pigmenting cells.
Metastasis—Spread of disease, particularly cancer, from one part of the body to another.
BOOKS
Cicala, Roger S. The Brain Disorders Sourcebook. Lowell House, 1999.
Kleihues, P., and Webster K. Cavanee, eds. "Pathology and Genetics of Tumours of the Nervous System." In World Health Organization Classification of Tumours. 2nd edition. Oxford University Press, 2000.
Murphy, Gerald P., et al. American Cancer Society Textbook of Clinical Oncology. 2nd edition. Atlanta, GA: The American Cancer Society, Inc., 1995.
PERIODICALS
Moulignier, Antoine, et al. "Cerebral Glial Tumors and Human Immunodeficiency Virus-1 Infection: More Than a Coincidental Association." Cancer 74, no. 2 (July 15,1994): 686-87.
ORGANIZATIONS
American Brain Tumor Association. 2770 River Road, Des Plaines, IL 60018. (847) 827-9918. <http:/www.abta.org>.
Brain Tumor Foundation for Children, Inc. 2231 Perimeter Park Drive, Suite 9, Atlanta, GA 30341. (404) 454-5554.
Brain Tumor Information Services. Box 405, Room J341, University of Chicago Hospitals, 5841 S. Maryland Avenue, Chicago, IL 60637. (312) 684-1400.
MedHelp International. 6300 N. Wickham, Suite 130, Box 188, Melbourne, FL 32940. (407) 253-9048. <http://www.medhlp.netusa.net>.
Kelly, Patrick J. "Brain Tumors: Their Symptoms, Therapy, and Future Cure." New York University, Department of Neurosurgery. <http://mcns10.med.nyu.edu/intro/treatment.html> (June 28, 2001).
