Merck Manual

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Overview of Brain Tumors


Steven A. Goldman

, MD, PhD, University of Rochester Medical Center;

Nimish A. Mohile

, MD, University of Rochester Medical Center

Last full review/revision Sep 2018| Content last modified Sep 2018
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A 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.

  • Symptoms may include headaches, personality changes (such as suddenly becoming depressed, anxious, or uninhibited), loss of balance, trouble concentrating, seizures, and incoordination.

  • Imaging tests can often detect brain tumors, but sometimes a biopsy of the tumor is needed.

  • Treatment may involve surgery, radiation therapy, chemotherapy, or a combination.

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, if tumors develop near parts of the brain that control vital functions, they may cause problems, such as weakness, difficulty walking, loss of balance, partial or complete loss of vision, difficulty understanding or using language, and problems with memory.

Brain tumors can cause problems in the following ways:

  • By directly invading and destroying brain tissue

  • By directly putting pressure on nearby tissue

  • By increasing pressure within the skull (intracranial pressure) because the tumor takes up space and the skull can not expand to accommodate it

  • By causing fluids to accumulate in the brain

  • By blocking normal circulation of cerebrospinal fluid through the spaces within the brain

  • By causing bleeding

Classification of Brain Tumors

There are two main types of brain tumors:

  • Primary: These tumors originate in the cells within or next to the brain. They may be cancerous or noncancerous.

  • Secondary: These tumors are metastases. That is, they originate in another part of the body and spread to the brain. Thus, they are always cancerous.

Primary tumors

Primary tumors include

Gliomas account for 65% of all primary brain tumors.

Did You Know...

  • Tumors that spread (metastasize) to the brain from elsewhere in the body are about 10 times more common than tumors that start in the brain.

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.

Secondary tumors

Brain metastases are about 10 times more common than primary tumors. Over 80% of people with brain metastases have more than one metastasis.

Metastases from other parts of the body may grow in a single part of the brain or in several different parts. Many types of cancer can spread to the brain. They include

Lymphomas of the brain are becoming more common among people who have a weakened immune system (such as those who have AIDS), among older people and, for unknown reasons, among people who have a normal immune system.


Some Tumors That Originate in or Near the Brain*

Type of Tumor


Cancer Status

Percentage of All Primary Brain Tumors

People Affected

Astrocytoma (a type of glioma)

Cells of the tissue that supports nerve cells (glial cells)

Cancerous or noncancerous (some initially noncancerous astrocytomas become cancerous)

(See note.)

Children and adults


Cells of the embryo (embryonic cells) that develop into the spinal cord

Noncancerous but invasive

Less than 1%

Children and adults

May be present at birth


Embryonic cells from the pituitary gland

Mostly noncancerous

Less than 1%

Children and adults

May be present at birth

Dermoid cysts and epidermoid tumors

Embryonic cells of the skin


Less than 1%

Children and adults

Dermoid cysts: May be present at birth


Cells of the tissue that lines the spaces within the brain (ventricles)

Mostly noncancerous

About 2–3% (almost 10% of brain tumors in children)


Uncommon in adults

Germ cell tumors (including germinomas)

Embryonic cells near the pineal gland

Cancerous or noncancerous



Germinomas: May be present at birth

Glioblastoma (a type of glioma)

Immature glial cells (called progenitor cells)


About 15%



Embryonic cells that develop into blood vessels



Children and adults


Embryonic cells of the cerebellum


Almost 20% of childhood brain tumors

Children and, rarely, adults


Cells of the layers of tissue covering the brain (meninges)

Noncancerous but may recur

About 35%


Oligodendroglioma (a type of glioma)

Cells (called oligodendrocytes) that wrap around nerve fibers in the brain, forming the myelin sheath, and the cells from which they originate

Cancerous but slow-growing (ultimately often becoming anaplastic oligodendroglioma)


Children and adults

Pineal gland tumors

Cells of the pineal gland or nearby tissues

Noncancerous or cancerous

Less than 1%


Pituitary adenoma

Cells of the pituitary gland



Children and adults

Primitive neuroectodermal tumor

Immature cells lining the spaces within the brain (ventricles)

Usually noncancerous but sometimes becomes cancerous

Less than 1%

Children and young adults


Immature cells lining the spaces within the brain

Usually noncancerous but sometimes becomes cancerous

Less than 1%

Children and young adults

The percentage of all primary brain tumors is given unless noted otherwise.

Astrocytomas, ependymomas, glioblastoma multiforme, medulloblastomas, and oligodendrogliomas are gliomas, which account for 65% of all primary brain tumors.


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

  • Deterioration in mental function

  • Problems due to pressure on specific structures in or near the brain, such as the nerve to the eye (optic nerve)

Headache is the most common and often the first symptom. However, some people with brain tumors do not get headaches, and 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 is often worse when people lie down. The headache may be most intense when people awaken from sleep, then lessen later in the day. 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 (see page Dysfunction by Location), a tumor can do any of the following:

  • Cause an arm, a leg, or one side of the body to become weak or paralyzed

  • Impair the ability to feel heat, cold, pressure, a light touch, or sharp objects

  • Make people unable to express or understand language

  • Increase or decrease the pulse and breathing rates if the tumor compresses the brain stem

  • Reduce alertness

  • Impair the ability to hear, smell, or see (causing such symptoms as double vision and loss of vision)

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

  • Transtentorial herniation: The upper part of the brain (cerebrum) is forced through the narrow opening (the tentorial notch) in the relatively rigid tissue that separates the cerebrum from the lower parts of the brain (cerebellum and brain stem). In people with this type of herniation, consciousness is reduced. The side of the body opposite the tumor may be paralyzed.

  • Tonsillar herniation: A tumor that originates in the lower part of the brain pushes the lowest part of the cerebellum (cerebellar tonsils) through the opening at the base of the skull (foramen magnum). As a result, the brain stem, which controls breathing, heart rate, and blood pressure, is compressed and malfunctions. If not diagnosed and treated immediately, a tonsillar herniation rapidly results in coma and death.

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.

Viewing the Brain

Viewing the Brain


  • Magnetic resonance imaging or computed tomography

  • Sometimes a spinal tap

  • Sometimes biopsy

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 contrast agent 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 (lumbar puncture) 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.


  • Surgery, radiation therapy, chemotherapy, or a combination

  • Sometimes drugs to reduce pressure within the skull

Treatment of a brain tumor depends on its location and type.

Specific treatments for brain tumors

Treatments for brain tumors include the following:

  • Craniotomy (brain surgery)

  • Radiosurgery

  • Implants

  • Shunts

  • Stereotactic techniques

Craniotomy (surgical removal of the tumor) is done when possible. This procedure involves opening the skull. Some brain tumors can be removed with little or no damage to the brain. However, many grow in areas that make removal by traditional surgery difficult or impossible without destroying essential structures.

For this procedure, part of the scalp is shaved. Then, 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:

  • A scalpel may be used to cut out the tumor.

  • A laser may be used to vaporize the tumor.

  • A device that emits ultrasound waves may be used to break the tumor apart, so that the pieces can be suctioned out (aspirated).

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.

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.

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 are occasionally inserted into the brain.

One type of implant consists of wafers soaked with a chemotherapy drug, After a tumor is removed and before the skull and incision are closed, these wafers 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.

Another type is radioactive. Radioactive implants, are placed directly into the tumor through a thin tube (catheter) is inserted through an incision. 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 may be surgically placed if a tumor causes pressure within the skull to increase. 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 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.

Stereotactic 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. In a similar procedure, a plastic frame is used, and magnetic resonance imaging (MRI) is used to show where the tumor is.

Techniques that do not involve attaching a frame may be used instead. For examples, special markers can be taped to the skull to provide reference points. The location of these markers is entered into a computer that contains images of the brain tumor.

Stereotactic techniques can be used to

  • Locate a site for biopsy

  • Locate tumors during surgery

  • Determine where to insert implants or a laser to destroy tumor cells

Stereotactic techniques can also be used to help with diagnosis.

Noncancerous tumors

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 developing. 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 before radiation therapy may benefit people who have only a single metastasis. Sometimes radiosurgery is used.

End-of-life issues

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. Treatment that focuses on relieving symptoms as fully as possible (palliative care), rather than curing the person, may be more appropriate.

Many cancer centers, especially those with hospice facilities, provide counseling and home health services.

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