Brain and Central Nervous System Tumors

views updated

Brain and central nervous system tumors

Definition

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 in 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 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 metastasize, 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.

Demographics

In 2008, the American Cancer Society (ACS) estimated 21,810 new cases of malignant tumors of the brain or spinal cord would be diagnosed in adults and children in the United States. The ACS projected that 13,070 would die from malignant CNS tumors. This type of cancer represents 1.3% of all cancers and 2.2%of all cancer-related deaths among adults and children. The incidence of primary malignant brain tumors has been increasing in the United States especially among the elderly. Metastatic brain and central nervous system tumors are much more common than primary brain and CNS tumors, occurring about 10 times more frequently. About 20 to 40 percent of all patients diagnosed with a type of systemic cancer develop brain metastases at some point during the course of their illness.

Causes and symptoms

Most brain and CNS cancers occur for no apparent reason; therefore, most cancers of this type cannot be prevented.

Frequently observed signs of a brain tumor are the following:

headaches, which occur in about 50% of patients
an ataxic, or stumbling, gait
nausea and vomiting
lack of coordination
unusual drowsiness
weakness or loss of feelings in the arms and legs
changes in personality or memory
changes in speech
changes in vision or abnormal eye movements
seizures

Diagnosis

Typically, diagnosis of CNS tumor is made by a physician who does a complete physical examination, including a family history and neurological examination. Computerized tomography (CT) scans, magnetic resonance imaging (MRI) scans, skull x rays, brain scans, angiograms, or myelograms are among the means of visualizing the brain or spinal cord to search for tumors. A biopsy, when some of the tissue of the tumor is removed and examined, is typically the only way to definitively diagnosis brain cancer. However, sometimes the tumor is located in an area of the brain that makes biopsy impossible or too dangerous. In those situations diagnosis may be confirmed by the appearance of the tumor on MRI or positron emission tomography (PET) scan.

Types of brain and CNS 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 have the following variations:

Astrocytomasare named for the star-shaped, small cells that they are comprised of. Children may develop these in their brain stem, cerebrum, or cerebellum, whereas 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.
Ependymomasoccur 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.

QUESTIONS TO ASK YOUR DOCTOR

What type of brain tumor do I have?
What treatments are available for this type?
What side effects can I expect from the treatments?
Am I a candidate for a clinical trial?
What is my prognosis?

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 hypothalamus, 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.

KEY TERMS

Angiogram —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.

Brain scan —A general term that can include CT scans, MRIs, seldom-used radionuclide scanning (use of radioactive isotopes), or ultrasounds.

Computerized tomography (CT) scan —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.

Treatment

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. Treatment may prolong survival, but most malignant primary brain tumors are not curable.

Clinical trials

As of 2008, there were over 160 clinical trials in progress related to brain and CNS tumors. Information about current clinical trials is available through the National Cancer Institute in the National Institutes of Health.

Prognosis

Important factors that affect prognosis are:

cell type of the tumor
aggressiveness of the tumor cells, or how quickly they are growing and dividing
patient's age, survival rates drop as age increases
degree of damage and disability the tumor has already caused
size and location of the tumor and whether it has spread to other parts of the brain or spinal cord

Prevention

There is no known cause for most primary brain cancers. Therefore, there are no known methods to prevent brain tumors, as of 2008.

Caregiver concerns

Many patients diagnosed and treated for brain and CNS cancers suffer from symptoms that dramatically affect their quality of life. These symptoms may include impaired cognition (memory, judgment, thought processes), impaired physical mobility, alterations in bowel and urinary elimination, and other major changes. The patient may also be at high risk for seizure activity.