Many types of tumors start in the brain and spinal cord (central nervous system or CNS). If you have one of these tumors, your symptoms, outlook for survival (prognosis), and treatment depend on your age, the tumor type, and the precise location of the tumor within the CNS.

To help you understand the anatomy, we’ll begin with an introduction to the main parts of the brain and spinal cord. Your prognosis and treatment also depend on the type of cells the cancer developed from, so we’ll discuss the main types of brain and spinal cord cells and the names of the cancers that they form.

CNS tumors of adults and children often form in different areas and from different cell types, so they may have a different prognosis and treatments. This document refers only to tumors of adults. For tumors of children, see the American Cancer Society document, “Brain and Spinal Cord Tumors in Children.” 

The brain is the center of thought, memory, and emotion, as well as a control site for many body processes . The spinal cord and special nerves in the head called cranial nerves carry and receive 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 very hard bones of the skull. Likewise, the spinal cord is protected by the bones of the vertebral column. The brain and spinal cord are surrounded and cushioned by a special fluid called cerebrospinal fluid. Cerebrospinal fluid is produced in cavities within the brain called ventricles. The ventricles, as well as the spaces around the brain and spinal cord, are filled with cerebrospinal fluid.

Parts of the Brain and Spinal Cord

 The main areas of the brain include the cerebral hemispheres, basal ganglia, cerebellum, and brain stem. Each of these parts has a special purpose. Tumors of different parts of the CNS disrupt different functions and cause different symptoms. These symptoms are not specific for brain tumors and may be caused by any disease that damages that particular location within the brain. Also, tumors in different areas of the CNS may be treated differently and have a different prognosis (outlook for survival).

The cerebral hemispheres control reasoning, thought, emotion, and language. They also direct muscle movements and receive sensory information, such as vision, hearing, touch, and pain sensation. The symptoms caused by a tumor of a cerebral hemisphere depend on the part of the hemisphere in which the tumor arises. A tumor in the motor area would cause weakness of a part of the body. A tumor in the frontal lobe, which accounts in part for personality, could cause personality changes. Depending on the site, there could also be changes in vision, hearing, and sensation. Tumors anywhere in this region could cause seizures. The character of the seizures (loss of consciousness, shaking movements, or sensations) depend on the location of the tumor.

The basal ganglia help control our muscle movements. Tumors or other problems in this part of the brain typically cause weakness, but in rare circumstances chorea (abnormal movements) or athetosis (abnormal positioning) can occur.

The cerebellum controls coordination of movement. Tumors of the cerebellum cause lack of coordination in walking, difficulty with fine movements of arms and legs, and changes in rhythm of speech.

The brain stem contains bundles of very long nerves that carry signals controlling muscles and sensation or feeling. In addition, most cranial nerves start in the brain stem. Cranial nerves have an important role in the senses of smell, vision, hearing, and taste and in controlling muscles of the face, tongue, and neck. Special centers in the brain stem control breathing, beating of the heart, and wakefulness. Tumors in this critical area of the brain may cause weakness, stiff muscles, or problems with sensation, hearing, facial movement, and swallowing. Double vision is a common early symptom of brain stem tumors, as is lack of coordination in walking. Because the brain stem is so essential, it is usually impossible to completely remove tumors from the brain stem with surgery.

The spinal cord, like the brain stem, contains bundles of very long nerves that carry signals controlling muscles, sensation or feeling, and bladder and bowel control. Spinal cord tumors may cause weakness, paralysis, or numbness. Although the spinal cord of an adult is about 18-inches long, it is less than 1-inch wide. Because the spinal cord is so narrow, tumors arising within it usually cause symptoms involving both sides of the body (for example, weakness or numbness in both legs). This distinguishes them from tumors of the brain, which usually cause symptoms affecting only one side of the body. Moreover, most tumors of the spinal cord arise below the neck after nerves to the arms have branched off the spinal cord, so only leg function is affected.

Tumors may also arise from cranial nerves or peripheral nerves. The most common cranial nerve tumor, the acoustic neuroma, arises from the acoustic or hearing nerve and causes loss of hearing in one ear. Tumors arising from other cranial nerves may cause vision loss (optic nerve), facial paralysis (facial nerve) or facial pain (trigeminal nerve). Tumors arising in the peripheral nervous system generally cause numbness or pain in the area where that nerve goes, as well as weakness of muscles controlled by that nerve.

Types of Cells and Tissues in the Brain and Spinal Cord

The brain consists of different kinds of tissues and cells. This is important to understand because different types of tumors can start in these different cell and tissue types. These tumors vary in prognosis and the ways they are treated. For most other parts of the body, we try to distinguish tumors that are benign (do not spread to other sites) from those that are malignant (likely to spread). This is less important in brain and spinal cord tumors. That’s because these tumors grow in such a vital area of the body that they can cause severe damage even if they don’t spread elsewhere. Still, some tumors can be defined as more “malignant” because they grow rapidly and spread within the brain.

Neurons:

• Astrocytes: This type of glial cell helps support and nourish neurons. When the brain is injured, astrocytes form scar tissue that helps repair the damage.

• Oligodendrocytes: These cells make myelin. Myelin forms a layer that surrounds and insulates axons of the brain and spinal cord. In this way, oligodendrocytes help neurons transmit electric signals through axons.

• Ependymal cells: These cells line the ventricles within the central part of the brain and spinal cord that provide the pathway through which cerebrospinal fluid travels.

• Microglia: The microglia that represent 10% to 20% of the total population of glial cells in the brain are the immune cells of the CNS.

Tumors that start in other organs, such as the lung or breast, and then spread to the brain are called metastatic or secondary brain tumors, and those that start in the brain are called primary brain tumors. Most brain tumors come from cancers that started somewhere else in the body and spread, or metastasized, to the brain. Primary brain tumors can start in any of the different types of tissues or cells within the brain or spinal cord. Some tumors contain a mixture of cell types. This is an important point because metastatic and primary brain tumors are usually treated differently.

Metastatic tumors to the brain are more common than primary brain tumors. Unlike other cancers, tumors arising within the brain or spinal cord rarely metastasize to distant organs. They cause damage because they spread locally and destroy normal brain tissue in the place where they arise. This document is only about primary brain and spinal cord tumors, not those that have spread from elsewhere in the body.

With a few exceptions, tumors of the brain or spinal cord are never benign (noncancerous). Unless it is possible to completely remove brain or spinal cord tumors, they will continue to grow and eventually (sometimes after many years) lead to death.

Meningioma: Strictly speaking, meningiomas are not brain tumors because they arise from the meninges, the layers of tissue that surround the outer part of the brain and spinal cord. Meningiomas cause symptoms by pressing on the brain or spinal cord. Meningiomas are quite common; they account for about 25% of primary brain tumors and the majority of spinal cord tumors. They are the most common brain tumor in adults. Their incidence rate increases with age, being highest in people in their 70s and 80s. They are almost twice as common in women. Occasionally these occur in families, mostly those with a syndrome of multiple benign tumors of nerve tissue called von Recklinghausen disease. Another risk factor for meningiomas is cranial radiation, particularly in young individuals.

Most meningiomas (about 85%) are benign and can be cured by surgery. Some meningiomas, however, are located dangerously close to vital structures within the brain and cannot be cured by surgery alone. A small number of meningiomas are malignant and may come back many times after surgery or, rarely, even spread to other parts of the body.

Astrocytoma: Most tumors that arise within the brain itself start in brain cells called astrocytes. These tumors are called astrocytomas. About 35% of brain tumors are astrocytomas. Most astrocytomas cannot be cured because they spread widely throughout the surrounding normal brain tissue. Sometimes astrocytomas spread along the cerebrospinal fluid pathways. With only rare exceptions, astrocytomas, however, do not spread outside of the brain or spinal cord.

In general terms, astrocytomas are classified, or graded, as low grade, intermediate grade, or high grade. Their grade is based on examining a biopsy specimen (sample of the tumor) under the microscope. The pathologist (a doctor specializing in diagnosis of diseases by laboratory tests) examining an astrocytoma will look for the following:

• how closely cells are packed together within the tumor
• how abnormal the cells are
• how many of the cells are dividing or multiplying
• whether abnormal blood vessels are growing within the tumor
• whether some of the cancer cells have broken down or died on their own

Low-grade astrocytomas are the slowest growing. Intermediate-grade astrocytomas, or anaplastic astrocytomas, grow at a moderate rate. The highest-grade astrocytomas, glioblastomas, are the fastest growing. These make up about two-thirds of all astrocytomas and are the most common malignant brain tumors of adults

Some special types of astrocytomas tend to have a particularly good prognosis. These are called noninfiltrating astrocytomas (for example, juvenile pilocytic astrocytomas).

Oligodendrogliomas: These tumors start in brain cells called oligodendrocytes. They spread or infiltrate in a manner similar to astrocytomas and, in most cases, cannot be completely removed by surgery. Oligodendrogliomas sometimes spread along the cerebrospinal fluid pathways but rarely spread outside the brain or spinal cord. Only about 4% of brain tumors are oligodendrogliomas.

Ependymomas: About 2% of brain tumors are ependymomas. These tumors arise from the ependymal cells, which line the ventricles. Ependymomas may block the exit of cerebrospinal fluid from the ventricles, causing the ventricles to become very large – a condition called hydrocephalus. Unlike astrocytomas and oligodendrogliomas, ependymomas characteristically do not spread or infiltrate into normal brain tissue. As a result, some but not all ependymomas can be completely removed and cured by surgery. Spinal cord ependymomas have the greatest chance of surgical cure. Ependymomas may spread along the cerebrospinal fluid pathways but do not spread outside the brain or spinal cord.

Gliomas: This is not a specific type of cancer. Glioma is a general category that includes astrocytomas, oligodendrogliomas, and ependymomas. About 42% of all brain tumors, including benign ones, are gliomas. Counting only malignant tumors, 77% are gliomas. They are uncommon in children, but their incidence rate goes up with age and peaks in the age group from 75 to 84.

Medulloblastomas: Tumors arising from the neurons are rare. Medulloblastomas are tumors that develop from neurons of the cerebellum. They are fast-growing tumors, but they can be treated and are often cured by radiation therapy. Medulloblastomas occur most commonly in children and often spread throughout the cerebrospinal fluid pathways. They are discussed in the American Cancer Scoiety document "Brain and Spinal Cord Tumors in Children."

Ganglioglioma: A tumor containing both neurons and glial cells is called a ganglioglioma. These are very uncommon and have a high rate of cure by surgery alone or surgery combined with radiation therapy.

Schwannoma (neurilemoma): Schwannomas start in Schwann cells, which are a part of cranial nerves and other nerves. These are usually benign tumors that often form near the cerebellum and in the cranial nerve responsible for hearing and balance. These make up about 7% of all CNS tumors.

Chordoma: These tumors start in the bone at the back of the skull or at the lower end of the spine. These tumors are not from the central nervous system. Typically they come back many times over 10 to 20 years, causing progressive injury to the adjacent central nervous system. They usually do not spread to other organs.

Lymphoma: Lymphomas start in lymphocytes (the main cell type of the immune system). Many of these occur in people infected with HIV, the virus that causes AIDS. Because of new treatments for AIDS, brain lymphomas have become less common. Also, in the past, lymphomas of the brain have been thought of as highly malignant, usually leading to death within approximately 1 year. Recent advances in chemotherapy, however, have dramatically changed the prognosis of people with these cancers. For more information, see the American Cancer Society document "Non-Hodgkin Lymphoma in Adults."