Brain tumor is a noncancerous (benign) or cancerous (malignant) growth in the brain. It may originate in the brain or have spread (metastasized) to the brain from another part of the body.
Brain tumors are slightly more common among men than women. Only meningiomas, which are noncancerous, are more common among women. Brain tumors usually develop during early or middle adulthood but may develop at any age. They are becoming more common among older people.
Brain tumors—whether cancerous or not—can cause serious problems because the skull is rigid, providing no room for the tumor to expand. Also, tumors may develop near parts of the brain that control vital functions and cause problems.
There are two main types of brain tumors:
Brain metastases are about 10 times more common than primary tumors. Over 80% of people with brain metastases have more than one metastasis.
Noncancerous tumors are named for the specific cells or tissues in which they originate. For example, hemangioblastomas originate in blood vessels (“hema” refers to blood vessels, and hemangioblasts are the cells that develop into blood vessel tissue). Some noncancerous tumors originate in cells of the embryo (embryonic cells), early in the development of the fetus. Such tumors may be present at birth.
The most common type of primary cancerous brain tumor is a glioma, which has several subtypes. Gliomas account for 65% of all primary brain tumors. However, most cancerous brain tumors are secondary—metastases from cancer that started in another part of the body.
Metastases may grow in a single part of the brain or in several different parts. Many types of cancer—including breast cancer, lung cancer, cancers of the digestive tract, malignant melanoma, leukemia, and lymphoma—can spread to the brain. Lymphomas of the brain are common among people who have AIDS and, for unknown reasons, are becoming more common among people who have a normal immune system.
Brain tumors can cause problems in the following ways:
Symptoms occur whether a brain tumor is noncancerous or cancerous. Noncancerous tumors grow slowly and may become quite large before causing symptoms.
A brain tumor can cause many different symptoms, and symptoms may occur suddenly or develop gradually. Which symptoms develop first and how they develop depend on the tumor's size, growth rate, and location. In some parts of the brain, even a small tumor can have devastating effects. In other parts of the brain, tumors can grow relatively large before any symptoms appear. As the tumor grows, it pushes and stretches but usually does not destroy nerve tissue, which can compensate for these changes very well. Thus, symptoms may not develop at first.
Many symptoms result from increased pressure within the skull:
Headache is the most common and often the first symptom. However, most headaches are not caused by brain tumors. A headache due to a brain tumor usually recurs more and more often as time passes. It eventually becomes constant, without relief. It is often worse when people lie down. The headache may awaken people from sleep. A gradually growing tumor causes a headache that typically is worse when people first awaken. If headaches with these characteristics start in people who have not had headaches before, a brain tumor may be the cause.
Often, increased pressure within the skull also causes mental function to deteriorate and mood to worsen. The personality may change. For example, people may become withdrawn, moody, and, often, inefficient at work. They may feel drowsy, confused, and unable to think. Such symptoms are often more apparent to family members and co-workers than to the affected person. Depression and anxiety, especially if either develops suddenly, may be an early symptom of a brain tumor. People may behave bizarrely. They may become uninhibited or behave in ways they never have before. In older people, certain brain tumors cause symptoms that may be mistaken for those of dementia.
Later, as the pressure within the skull increases, nausea, vomiting, lethargy, increased drowsiness, intermittent fever, and even coma may occur. Vision may blur suddenly when people change positions.
Depending on which area of the brain is affected, a tumor can do any of the following:
For example, a pituitary tumor may press on the nearby optic nerves (2nd cranial nerves), which are involved in vision, and thus impair peripheral vision. Any of the above symptoms suggests a serious disorder and requires immediate medical attention.
Other common symptoms of a brain tumor include vertigo, loss of balance, and incoordination. Some brain tumors, usually primary tumors, cause seizures.
If a tumor blocks the flow of cerebrospinal fluid through the spaces within the brain (ventricles), fluid may accumulate in the ventricles, causing them to enlarge (a condition called hydrocephalus). As a result, pressure within the skull increases. In addition to other symptoms of increased pressure, hydrocephalus makes turning the eyes upward difficult. In infants and very young children, the head enlarges.
If the pressure within the skull is greatly increased, the brain may be pushed downward because the skull cannot expand. Herniation of the brain may result. Two common types are
People with metastases to the brain may also have symptoms related to the original cancer. For example, if the cancer originated in the lungs, people may cough up bloody mucus. With metastases, weight loss is common.
Symptoms worsen over time unless the tumor is treated. With treatment, particularly for benign tumors, some people completely recover. For others, life span is shortened, sometimes greatly. The outcome depends on the type and location of the tumor.
COMMON SYMPTOMS OF SOME BRAIN TUMORS
Gliomas include astrocytomas, oligodendrogliomas, medulloblastomas, and ependymomas. Astrocytomas are the most common glioma.
Some astrocytomas and oligodendrogliomas grow slowly and may initially cause only seizures. Others (anaplastic astrocytomas and anaplastic oligodendrogliomas) grow fast and are cancerous. They can cause various symptoms of brain dysfunction. Astrocytomas tend to develop in young people. They can become more aggressive (often after about 5 years) and are then called glioblastomas. Glioblastomas tend to develop during middle or old age. Glioblastoma multiforme, the most aggressive type of astrocytoma, grows so fast that it increases pressure in the brain, causing headaches and slowed thinking. If the pressure becomes high enough, drowsiness, then coma, may result.
Medulloblastomas and ependymomas usually develop below the cerebellum (the part of the brain that coordinates the body's movements). Medulloblastomas develop mainly in children and young adults. Ependymomas, which are uncommon, develop mainly in children.
Symptoms vary depending on the tumor's location.
Meningiomas are among the most common brain tumors. They are usually noncancerous but may recur after they are removed. They occur more often in women and usually appear in people aged 40 to 60, but they can begin growing during childhood or later life. These tumors do not directly invade the brain but may compress the brain or cranial nerves, block the absorption of cerebrospinal fluid, or do both.
Symptoms depend on where the tumor develops. They may include weakness or numbness, seizures, an impaired sense of smell, changes in vision, and impaired mental function. In older people, a meningioma may cause dementia.
Pineal tumors usually develop during childhood and often cause early puberty. They can block the drainage of cerebrospinal fluid around the brain, leading to hydrocephalus.
The most common type of pineal tumor is a germ cell tumor. Symptoms include the inability to look up and drooping eyelids.
Pituitary Gland Tumors
The pituitary gland, located at the base of the skull, controls much of the body's endocrine system. Tumors of the pituitary gland (pituitary adenomas) are usually noncancerous. They may secrete abnormally large amounts of pituitary hormones or block production of hormones. When large amounts of hormones are secreted, effects vary depending on which hormone is involved.
Pituitary gland tumors can block hormone production by destroying the tissues in the pituitary gland that secrete hormones, eventually resulting in insufficient levels of these hormones in the body. Headaches commonly occur. If the tumor enlarges, peripheral vision in both eyes is lost.
Doctors consider the possibility of a brain tumor in people who have had a seizure for the first time or who have characteristic symptoms. Although doctors can often detect brain dysfunction during an examination, other procedures are needed to diagnose a brain tumor.
Magnetic resonance imaging (MRI) is the best test for identifying brain tumors. Computed tomography (CT) is a good alternative. It can identify most brain tumors. Before these tests, a substance that makes the tumor easier to see (a contrast agent for MRI or a radiopaque dye for CT) is injected into a vein. These tests can show the tumor's size and exact position in great detail. When a brain tumor is detected, more diagnostic procedures are done to determine the particular kind.
Sometimes a spinal tap is done to obtain cerebrospinal fluid for examination under a microscope. This procedure is done when doctors suspect that the tumor has invaded the layers of tissues that cover the brain (meninges). Such tumors may block the absorption of cerebrospinal fluid. A spinal tap may also help when the diagnosis or the type of tumor is unclear. Cerebrospinal fluid may contain cancer cells. However, a spinal tap cannot be done in people who have a large tumor that is increasing pressure within the skull. In these people, removing cerebrospinal fluid during a spinal tap may cause the tumor to move, resulting in herniation of the brain.
Specialized tests can sometimes help with the diagnosis. For example, blood and cerebrospinal fluid may also be tested to check for substances secreted by tumors (called tumor markers) and for gene abnormalities that are characteristic of certain tumors. Identifying certain gene abnormalities can help predict which treatments will be most effective.
A biopsy of the tumor (removal of a sample of the tumor for examination under a microscope) is sometimes needed to identify the type of tumor, including whether it is cancerous. A biopsy may be done during surgery in which all or part of the tumor is removed. If a tumor is difficult to reach, a stereotactic biopsy may be done. For this procedure, a frame is attached to the skull. The frame provides reference points that can be identified on an MRI or a CT scan. These reference points enable doctors to guide the biopsy needle precisely into the tumor.
Treatment of a brain tumor depends on its location and type. When possible, the tumor is removed surgically in a procedure called craniotomy (which involves opening the skull). Some brain tumors can be removed with little or no damage to the brain. However, many grow in an area that makes removal by traditional surgery difficult or impossible without destroying essential structures.
Traditional surgery sometimes causes brain damage that can lead to symptoms such as partial paralysis, changes in sensation, weakness, and impaired mental function. Nevertheless, removing a tumor—whether cancerous or noncancerous—is essential if its growth threatens important brain structures. Even when a cure is impossible, surgery may be useful to reduce the tumor's size, relieve symptoms, and help doctors determine whether other treatments, such as radiation therapy or chemotherapy, are warranted.
Surgical removal is often safe and cures the person. However, very small tumors and tumors in older people may be left in place as long as they are not causing symptoms. Sometimes radiation therapy is given after surgery to destroy any remaining tumor cells.
Radiosurgery is effective in treating noncancerous tumors such as meningiomas and acoustic neuromas. Therefore, radiosurgery is often used instead of traditional surgery for these tumors. Radiosurgery directs highly focused beams of radiation precisely at the tumor. It does not involve an incision. To focus the radiation more precisely, doctors often use stereotactic techniques, which sometimes involve attaching a frame to the head to provide reference points.
Cancerous brain tumors
Usually, a combination of surgery, radiation therapy, and chemotherapy is used. As much of the tumor as can be removed safely is removed, and then radiation therapy is begun. Radiation therapy is given over a course of several weeks. Radiosurgery is used when traditional surgery cannot be, especially for the treatment of metastases.
For very aggressive tumors, chemotherapy is given with radiation therapy. Radiation therapy plus chemotherapy rarely cures but may shrink a tumor enough to keep it under control for many months or even years.
After radiation therapy, ongoing chemotherapy is used to treat some types of cancerous brain tumors. Chemotherapy appears to be particularly effective in treating anaplastic oligodendrogliomas.
Increased pressure within the skull
This extremely serious condition requires immediate medical attention. If people are in a coma or have difficulty breathing, herniation may be the cause. To help such people breathe, doctors insert a plastic tube through the nose or mouth into the windpipe (trachea) and attach it to a ventilator (a procedure called endotracheal intubation). This procedure also helps reduce pressure within the skull until other treatments can be given. Drugs such as mannitol and corticosteroids are usually given by injection to reduce the pressure and prevent herniation. They reduce swelling around the tumor. Within days or sometimes hours, corticosteroids can often restore functions lost because of the tumor and can relieve headache, even if the tumor is large.
If the tumor is blocking the flow of cerebrospinal fluid through the spaces within the brain, a device may be used to drain the cerebrospinal fluid and thus reduce the risk of herniation. The device consists of a small tube (catheter) connected to a gauge that measures the pressure within the skull. The tube is inserted through a tiny opening drilled in the skull. A local anesthetic (usually plus a sedative) or a general anesthetic may be used. The tube is removed or converted to a permanent drain (shunt) after a few days. During this time, doctors surgically remove all or part of the tumor or use radiosurgery or radiation therapy to reduce the size of the tumor and thus relieve the blockage.
Treatment depends largely on where the cancer originated. Radiation therapy directed at the metastases in the brain is often used. Surgical removal may benefit people who have only a single metastasis. Sometimes radiosurgery is used.
People with cancerous brain tumors have a limited life expectancy and are likely to become unable to make decisions about medical care. Consequently, establishing advance directives is advisable. Advance directives can help a doctor determine what kind of care people want if they become unable to make decisions about medical care.
Many cancer centers, especially those with hospice facilities, provide counseling and home health services.
UNDERSTANDING TUMOR TREATMENT
Craniotomy: After part of the scalp is shaved, an incision is made through the skin. A high-speed drill and a special saw are used to remove a small piece of bone above the tumor. The tumor is located and removed using one of the following:
Lasers and ultrasound devices are used to remove tumors that would be difficult to cut out. Usually, the bone is then replaced, and the incision stitched closed.
Stereotactic techniques: These techniques are ways to localize tumors very precisely. Computers are used to produce a three-dimensional image. The three-dimensional image can be obtained by attaching a light-weight metal imaging frame with a series of rods to the person's skull. A local anesthetic is given to numb the area, and the pins are attached to the skull, piercing the skin. A computed tomography (CT) scan shows the rods as dots, providing reference points, which help locate the tumor. Other devices do not involve attaching a frame and may be used instead. Stereotactic techniques can be used to locate a site for biopsy, to locate tumors during surgery, or to determine where to insert implants or a laser to destroy tumor cells.
Radiosurgery: Radiosurgery is not really surgery because no incision is required. Focused radiation is used to destroy a tumor. Several machines, including a gamma knife and a linear accelerator, can produce this type of radiation.
When a gamma knife is used, an imaging frame is attached to the person's skull. The person lies on a sliding bed, and a large helmet with holes in it is placed over the frame. The head of the bed is then slid into a globe that contains radioactive cobalt. Radiation passes through the holes in the helmet and is aimed precisely at the tumor.
A linear accelerator circles the head of the person, who lies on a sliding bed. The linear accelerator rotates around the person and aims radiation precisely at the tumor from different angles.
Implants: Occasionally, after a tumor is removed and before the skull and incision are closed, wafers soaked with a chemotherapy drug may be placed in the space where the tumor was. As the wafers gradually dissolve, they release the drug to destroy any remaining cancer cells.
A thin tube (catheter) may be inserted through an incision and used to place radioactive implants directly into the tumor. The implants may be removed after a few days or months or may be left in place. Unlike people who have externally applied radiation therapy, people who have radioactive implants are radioactive for a time (that is, they give off radiation). They thus need to take precautions as advised by their doctor. After this procedure, surgery may be necessary to remove dead cancer cells.
Shunts: If a tumor causes pressure within the skull to increase, a shunt may be surgically placed. A shunt is a thin piece of tubing that is inserted into one of the spaces of the brain (ventricles) or sometimes into the space around the spinal cord that contains cerebrospinal fluid (subarachnoid space). The other end of the tubing is threaded under the skin from the head or back usually into the abdomen. Excess cerebrospinal fluid is drained from the brain into the abdomen, where it is absorbed. The shunt contains a one-way valve that opens when there is too much fluid in the brain. Shunts may be temporary (until the tumor is removed) or permanent.