Brain tumors are masses of abnormal cells that have grown out of control. In most other parts of the body, it is very important to distinguish between benign (non-cancerous) tumors and malignant (cancerous) ones. Benign tumors in other parts of the body are almost never life threatening. The main reason cancers are so dangerous is because they can spread throughout the body. Most brain cancers can spread through the brain tissue but rarely spread to other areas of the body. Even so-called "benign" tumors can, as they grow, compress normal brain tissue, causing damage that is often disabling and sometimes fatal. For this reason, doctors usually speak of "brain tumors" rather than "brain cancers." The major differences are how readily they spread through the rest of the central nervous system and whether they can be removed and not come back.

Brain and spinal cord tumors are different in adults and children. They often form in different places, develop from different cell types, and may have a different treatment and prognosis (outlook). This document refers only to children's tumors. Brain and spinal cord tumors in adults are discussed in a separate American Cancer Society document.

To understand brain and spinal cord tumors, it helps to know about the normal structure and function of the central nervous system.

The central nervous system

The central nervous system (CNS) is the medical name for the brain and spinal cord.

The brain is the center of thought, feeling, memory, speech, vision, hearing, movement, and much more. The spinal cord and special nerves in the head called cranial nerves carry messages between the brain and the rest of the body. These messages tell our muscles how to move, transmit information gathered by our senses, and help coordinate our internal organs. The brain is located within and protected by the skull. Likewise, the spinal cord is protected by the bones (vertebrae) of the spinal column.

The brain and spinal cord are surrounded and cushioned by a special fluid, called cerebrospinal fluid (CSF). Cerebrospinal fluid is made by the choroid plexus, which is located in cavities within the brain called ventricles. The ventricles, as well as the spaces around the brain and spinal cord, are filled with CSF.

Parts of the brain and spinal cord

The brain and spinal cord are the 2 main parts of the central nervous system.

The main areas of the brain include the cerebrum, cerebellum, and brain stem. Each of these parts has a special purpose.

Cerebrum: The cerebrum, which is made up of 2 hemispheres (halves), controls reasoning, thought, emotion, and language. It is also responsible for your planned muscle movements (throwing a ball, walking, chewing, etc.) and for taking in sensory information such as vision, hearing, smell, touch, and pain.

The symptoms caused by a tumor in a cerebral hemisphere depend on the part of the hemisphere in which the tumor develops. Common symptoms include:

• seizures
• trouble speaking
• a change of mood such as depression
• a change in personality
• weakness or paralysis of part of the body
• changes in vision, hearing, or sensation

Cerebellum: The cerebellum controls coordination of movement. Tumors of the cerebellum can cause problems with coordination in walking, trouble with fine movements of arms and legs, impairment of synchronized eye movements, and changes in rhythm of speech.

Brain stem: The brain stem has bundles of very long nerve fibers that carry signals controlling muscles and sensation or feeling between the cerebrum and the rest of the body. In addition, most cranial nerves (which carry signals directly between the brain and the face, eyes, tongue, and mouth) start in the brain stem. Special centers in the brain stem also control breathing and the beating of the heart.

Tumors in this critical area of the brain may cause weakness, stiff muscles, or problems with sensation, hearing, facial movement, or swallowing. Double vision is a common early symptom of brain stem tumors, as are problems with coordination in walking. Because tumors of the brain stem often intermingle with normal nerve cells and the brain stem is so essential for life, it may not be possible to surgically remove these tumors.

Spinal cord: The spinal cord, like the brain stem, has bundles of very long nerve fibers that carry signals that control muscles, sensation or feeling, and bladder and bowel control. Spinal cord tumors may cause weakness, paralysis, or numbness. Because the spinal cord is such a narrow structure, tumors that develop there usually cause symptoms on both sides of the body (for example, weakness or numbness of both legs). This is different from tumors of the brain, which usually affect only one side of the body. Moreover, most tumors of the spinal cord develop below the neck after the nerves to the arms have branched off the spinal cord, so that only lower body functions -- bowel, bladder, or leg movement or sensation -- are affected.

Cranial nerves: Tumors may also develop in the cranial nerves, which are nerves that extend directly out of the base of the brain (as opposed to coming out of the spinal cord). The most common cranial nerve tumors in children are optic gliomas, which are tumors of the optic nerve (the large nerve that runs from the brain to the eye) that cause vision problems. Tumors starting in other cranial nerves may cause trouble swallowing, hearing loss in one or both ears, facial paralysis, or facial numbness or pain.

Peripheral nervous system: The peripheral nervous system consists of the parts of the nervous system other than the brain and spinal cord (which make up the central nervous system). Tumors that start in the nerves of the peripheral nervous system generally cause pain, weakness, and/or loss of sensation in the area served by that nerve.

Types of cells and body tissues in the brain and spinal cord

The brain and spinal cord contain different kinds of tissues and cells,which means different types of tumors can develop. These tumors can have varying outlooks for survival and may be treated differently.

Neurons (nerve cells): These are the most important cells within the brain. They send signals through their nerve fibers (axons). These may be very short (in the brain) or 2 to 3 feet long (in the spinal cord). Electric signals carried by neurons determine thought, memory, emotion, speech, muscle movement, and just about everything else that the brain and spinal cord do. Unlike many other types of cells that can grow and divide to repair damage from injury or disease, neurons stop dividing about a year after birth (with a few exceptions). Neurons do not usually form tumors, but they can be damaged by tumors that start nearby.

Glial cells: Glial cells are the supporting cells of the brain. Most brain and spinal cord tumors develop from glial cells. They are sometimes referred to as a group called gliomas. Normal glial cells grow and divide very slowly. They continue to increase in number until a child is about 5 years of age. At this time, the brain reaches its maximum size and will be the same size until late in adulthood, when it may shrink some.

There are 3 types of glial cells -- astrocytes, oligodendrocytes, and ependymal cells. A fourth cell type called microglia is part of the immune system and is not truly glial in origin.

• Astrocytes help support and nourish neurons. When the brain is injured, astrocytes form scar tissue that helps repair the damage. The main tumors starting in these cells are called astrocytomas or glioblastomas.

• Oligodendrocytes make myelin, a substance that surrounds and insulates axons of the brain and spinal cord. This allows oligodendrocytes to help neurons transmit electric signals through axons. Tumors starting in these cells are called oligodendrogliomas.

• Ependymal cells line the ventricles (fluid-filled areas) within the central part of the brain and form part of the pathway through which cerebrospinal fluid travels. Tumors starting in these cells are called ependymomas.

• Microglia are the immune (infection fighting) cells of the central nervous system.

Neuroectodermal cells: These are primitive cells that are probably the remains of embryonic cells. They are found throughout the brain. The most common tumor that comes from these cells is the medulloblastoma, which arises in the cerebellum from forerunners of nerve cells called granule cells.

Meninges: These are tissues that line the brain and spinal cord. The meninges help form the spaces through which CSF travels. The most common tumors that start in these cells are called meningiomas.

Choroid plexus: The choroid plexus is the area of the brain within the ventricles that makes CSF, which nourishes and protects the brain. Choroid plexus papillomas and carcinomas arise from this site.

Pituitary gland and hypothalamus: The pituitary is a small gland found at the base of the brain. The hypothalamus is the part of the brain to which the pituitary gland is connected. Both help regulate the activity of several other glands. For example, they control the amount of thyroid hormone made by the thyroid gland, the production and release of milk by the breasts, and the amount of male or female hormones made by the testicles or ovaries. They also make growth hormone, which stimulates body growth, and vasopressin, which regulates water balance by the kidneys.

The growth of tumors in or near the pituitary or hypothalamus, as well as surgery and/or radiation therapy in this area, can interfere with these functions. Consequently, a child may have low levels of one or more hormones and may need hormone treatments to correct any hormone deficiency.

Pineal gland: The pineal gland is not strictly part of the brain. It is, in fact, an endocrine gland that sits between the cerebral hemispheres. Its main function is probably to make melatonin, a hormone that regulates sleep, in response to changes in light.

Blood-brain barrier: Unlike the case with most other organs, the small blood vessels (capillaries) in the brain and spinal cord have a protective inner lining that serves as a very selective barrier between the blood and the tissues of the central nervous system. This normally keeps harmful toxins from getting into the brain. Unfortunately, it also keeps out most chemotherapy drugs that are used to kill cancer cells, which in some cases limits their usefulness.

Types of brain and spinal cord tumors in children

Tumors can form in any type of tissue or cell in the brain or spinal cord. Some tumors have a mixture of cell types.

Unlike other cancerous tumors, tumors arising within the brain or spinal cord rarely spread (metastasize) to distant organs. They cause damage because they spread locally and destroy normal tissue where they arise.

Tumors in different areas of the central nervous system may be treated differently and have a different prognosis (outlook for survival).

Gliomas

Gliomas are not a specific type of cancer. Glioma is a general term for a group of tumors that start in glial cells. A number of tumors can be considered gliomas, including glioblastoma multiforme, anaplastic astrocytoma, astrocytoma, oligodendroglioma, ependymoma, brain stem glioma, optic glioma, and choroid plexus tumors. Most brain and spinal cord tumors in children are gliomas.

Astrocytomas: Most tumors that develop within the brain itself start in brain cells called astrocytes, a kind of glial cell. These tumors are called astrocytomas. About half of all childhood brain tumors are astrocytomas. When these tumors occur in the brain stem, they are referred to as brain stem gliomas.

Most astrocytomas can spread widely throughout, and intermingle with, the normal brain tissue, which can make them very hard to remove by surgery. Sometimes they spread along the cerebrospinal fluid pathways. It is very rare for them to spread outside of the brain or spinal cord.

Astrocytomas are classified as low grade, intermediate grade, or high grade, based on how the cells look under the microscope.

• Low-grade astrocytomas are the slowest growing and the most common type of astrocytoma in children.

• Intermediate-grade astrocytomas, or anaplastic astrocytomas, grow at a moderate rate.

• The highest-grade astrocytoma, known as glioblastoma multiforme (or just glioblastoma), is the fastest growing.

There are some special types of astrocytomas that tend to have a good prognosis.

• Juvenile pilocytic astrocytomas most commonly occur in the cerebellum but also occur in the optic nerve, hypothalamus, brain stem, or other areas.

• Subependymal giant cell astrocytomas occur in the ventricles and are almost always linked with tuberous sclerosis (an inherited condition which may also cause epilepsy, mental retardation, and tumors of the skin and kidneys).

• Optic gliomas are low-grade astrocytomas of childhood that start in the optic nerve. They are often linked with an inherited condition called neurofibromatosis type 1. These tumors can sometimes be treated successfully by surgery. At other times radiation therapy or chemotherapy may be required. These tumors are rarely lethal but may cause substantial visual loss and injury to nearby brain tissue.

Oligodendrogliomas: These tumors start in brain glial cells called oligodendrocytes. Like astrocytomas, most of these can spread or infiltrate into nearby brain tissue and cannot be completely removed by surgery. Oligodendrogliomas may spread along the cerebrospinal fluid pathways but rarely spread outside the brain or spinal cord.

Ependymomas: Almost 10% of brain tumors in children are ependymomas. These tumors arise from the ependymal cells that line the ventricles or central canal of the spinal cord. They can range from fairly low-grade (less aggressive) tumors to higher grade ones, which are called anaplastic ependymomas.

Ependymomas may block the flow of cerebrospinal fluid out of the ventricles, causing the ventricles to become very large -- a condition called hydrocephalus. Unlike astrocytomas and oligodendrogliomas, ependymomas usually do not spread into or infiltrate normal brain tissue. As a result, some (but not all) ependymomas can be removed and cured by surgery. Spinal cord ependymomas have the greatest chance of being cured. Ependymomas may spread along the cerebrospinal fluid pathways but do not spread outside the brain or spinal cord.

Choroid plexus tumors: These rare tumors arise in the choroid plexus within the ventricles of the brain. Most are benign (choroid plexus papillomas) and cured by surgery. However, some are malignant (choroid plexus carcinomas).

Primitive neuroectodermal tumors (PNETs)

These tumors start in primitive (immature) cells of the central nervous system. About 1 out of 4 brain tumors in children are of this type. They are rare in adults. Primitive neuroectodermal tumors tend to grow fast and frequently spread throughout the cerebrospinal fluid pathways. These tumors sometimes have different names depending on where they occur.

Medulloblastomas: PNETs that start in the cerebellum are called medulloblastomas. About 15% of childhood brain tumors are medulloblastomas. These tumors can often be treated effectively and tend to have a better prognosis than PNETs in other parts of the brain. They are treated with surgery and radiation therapy, sometimes with added chemotherapy.

Pineoblastomas: Primitive neuroectodermal tumors are called pineoblastomas when they occur in the pineal gland. The outlook for pineoblastomas is not as favorable as for medulloblastomas.

Craniopharyngiomas

This type of slow-growing tumor grows above the pituitary gland but below the brain itself. It may compress the pituitary gland and the hypothalamus, causing hormonal problems. Most craniopharyngiomas are very close to the optic nerve, making them hard to remove surgically because of possibly damaging the child's vision. Some are cured by surgery; others require radiation therapy, either alone or combined with surgery.

Mixed glial and neuronal tumors

Certain tumors that occur in children and young adults (and rarely in older adults) seem to have both glial and neuronal cell components. They tend to have a fairly good prognosis.

• Pleomorphic xanthoastrocytoma and dysembryoplastic neuroepithelial tumors appear malignant under the microscope, but these tumors are relatively benign and most are cured by surgery alone.

• Ganglioglioma is a type of tumor that has both mature neurons and glial cells. Most can be cured by surgery alone or surgery combined with radiation therapy.

Schwannomas (neurilemomas)

This type of tumor starts in Schwann cells that surround and insulate cranial nerves and other nerves. Schwannomas are usually benign tumors. They often form near the cerebellum in the cranial nerve responsible for hearing and balance, in which case they are called acoustic neuromas. They may also arise from spinal nerves after the point where they have left the spinal cord. When this is the case, they can compress the spinal cord, causing weakness, sensory loss, and bowel and bladder problems.

These tumors are rare in children. When present in this age group, particularly if there is more than one, they might suggest an inherited tumor syndrome such as neurofibromatosis.

Other tumors that can start in or near the brain

Meningiomas: These tumors arise from the meninges, the tissues that surround the outer part of the brain and spinal cord. Meningiomas cause symptoms by pressing on the brain or spinal cord. They are much less common in children than in adults.

Meningiomas are benign and are usually cured by surgery. Some, however, are located dangerously close to vital structures in the brain and cannot be cured by surgery.

Meningiosarcomas are rare but very malignant (cancerous) tumors of the meninges that may come back many times after surgery or, rarely, spread to other parts of the body.

Chordomas: These tumors start in the bone at the base of the skull or at the lower end of the spinal column. Chordomas may come back many times over a period of 10 to 20 years, causing progressive neurologic damage and deterioration. They usually do not spread or metastasize to other organs.

Germ cell tumors: Germ cell tumors develop from germ cells that normally form eggs in women and sperm in men. During normal embryonic and fetal development, germ cells migrate to the ovaries or testicles and develop into eggs or sperm cells. Sometimes, however, a few germ cells may not migrate properly and end up in abnormal locations such as the brain. They may then develop into germ cell tumors similar to those that can form in the ovaries or testicles.

Germ cell tumors of the nervous system usually occur in children, most often in the pineal gland or above the pituitary gland. Germ cell tumors can sometimes be diagnosed without a biopsy by measuring certain chemicals in the cerebrospinal fluid or blood.

The most common germ cell tumor of the nervous system is the germinoma, which can be cured by radiation therapy and possibly chemotherapy in almost all cases. Other tumors that originate in germ cells, such as choriocarcinoma or yolk sac tumors are rarely cured by surgery. Both radiation therapy and chemotherapy are used in their treatment, although in some cases this may not control the tumor completely.

Neuroblastomas: This type of nerve cell tumor is the third most common cancer in children. Neuroblastomas rarely develop in the brain or spinal cord; most develop from nerve cells inside the abdomen or chest. This type of cancer is most commonly diagnosed during early infancy. For more information, see the separate American Cancer Society document, Neuroblastoma.

Cancers that spread to the brain from other sites

Sometimes brain tumors are found not to have started in the brain but rather to have spread (metastasized) from some other part of the body. Tumors that start in other organs and then spread to the brain are called metastatic brain tumors (as opposed to primary brain tumors, which start in the brain). This is important because metastatic and primary brain tumors are usually treated differently.

In children, metastatic tumors to the brain are much less common than primary brain tumors. This document only covers primary brain tumors.