What are adult brain and spinal cord tumors?
Brain and spinal cord 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) and malignant (cancerous) tumors. Benign tumors in other parts of the body do not grow into nearby tissues or spread to distant areas, so they are almost never life threatening. One of the main reasons cancers are so dangerous is because they can spread throughout the body.
Although brain tumors rarely spread to other parts of the body, most of them can spread through the brain tissue. Even so-called benign tumors can, as they grow, destroy and 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 main concerns with brain and spinal cord tumors are how readily they spread through the rest of the brain or spinal cord 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 areas, develop from different cell types, and may have a different outlook and treatment.
This document refers only to adult tumors. Brain and spinal cord tumors in children are discussed in a separate 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 help 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 the functions of our internal organs.
The brain is 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 liquid, called cerebrospinal fluid (CSF). Cerebrospinal fluid is made by the choroid plexus, which is located in spaces within the brain called ventricles. The ventricles and the spaces around the brain and spinal cord are filled with CSF.
Parts of the brain and spinal cord
The main areas of the brain include the cerebrum, cerebellum, and brain stem. Each of these parts has a special function.
Cerebrum: The cerebrum is the large, outer part of the brain. It has 2 hemispheres (halves) and controls reasoning, thought, emotion, and language. It is also responsible for planned (voluntary) muscle movements (throwing a ball, walking, chewing, etc.) and for taking in and interpreting sensory information such as vision, hearing, smell, touch, and pain.
The symptoms caused by a tumor in a cerebral hemisphere depend on where the tumor starts. Common symptoms include:
- 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 other sensations
Basal ganglia: The basal ganglia are structures deeper within the brain that help control our muscle movements. Tumors or other problems in this part of the brain typically cause weakness, but in rare cases can cause tremor or other involuntary movements.
Cerebellum: The cerebellum lies under the cerebrum at the back part of the brain. It helps coordinate movement. Tumors of the cerebellum can cause problems with coordination in walking, trouble with fine movements of arms and legs, problems swallowing or synchronizing eye movements, and changes in rhythm of speech.
Brain stem: The brain stem is the lower part of the brain that connects to the spinal cord. It contains bundles of very long nerve fibers that carry signals controlling muscles and sensation or feeling between the cerebrum and the rest the body. Special centers in the brain stem also help control breathing and the beating of the heart. Also, most cranial nerves (which carry signals directly between the brain and the face, eyes, tongue, mouth, and some other areas) start in the brain stem.
Tumors in this critical area of the brain may cause weakness, stiff muscles, or problems with sensation, eye movement, hearing, facial movement, or swallowing. Double vision is a common early symptom of brain stem tumors, as are problems with coordination in walking. Because the brain stem is a small area that is so essential for life, it may not be possible to surgically remove tumors in this area.
Spinal cord: The spinal cord, like the brain stem, contains bundles of very long nerve fibers that carry signals controlling 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 within it usually cause symptoms on both sides of the body (for example, weakness or numbness of both legs). This is different from brain tumors, which usually affect only one side of the body.
The nerves that reach the arms begin in the spinal cord at the level of the neck (cervical spine). Nerves that branch off the spinal cord to the legs, bowel, and bladder arise in the back (thoracic and lumbar spine). Tumors of the spinal cord in the neck can cause symptoms in the arms and legs, as well as affect bowel and bladder function. Spinal cord tumors below the neck may only affect the legs and bowel and bladder function.
Cranial nerves: The cranial nerves extend directly out of the base of the brain (as opposed to coming out of the spinal cord). Tumors starting in cranial nerves may cause vision problems, trouble swallowing, hearing loss in one or both ears, or facial paralysis, numbness, or pain.
Types of cells and body tissues in the brain and spinal cord
The brain and spinal cord have many kinds of tissues and cells, which can develop into different types of tumors. People with these tumors can have different prognoses (outlooks) and may be treated differently.
Neurons (nerve cells): These are the most important cells in the brain. They transmit chemical and electric signals that determine thought, memory, emotion, speech, muscle movement, and just about everything else that the brain and spinal cord do. Neurons send these signals through their nerve fibers (axons). Axons in the brain tend to be short, while those in the spinal cord can be as long as several feet.
Unlike many other types of cells that can grow and divide to repair damage from injury or disease, neurons in the brain and spinal cord largely stop dividing about a year after birth (with a few exceptions). Neurons do not usually form tumors, but they are often 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. These tumors are sometimes referred to as gliomas.
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 a glial cell.
- 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 fatty substance that surrounds and insulates the nerve cell axons of the brain and spinal cord. This helps neurons send electric signals through the 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 CSF flows. Tumors starting in these cells are called ependymomas.
- Microglia are the immune (infection fighting) cells of the central nervous system.
Neuroectodermal cells: These are very early forms of nervous system cells that are probably involved in brain cell development. They are found throughout the brain, although they are not often seen in the adult central nervous system. The most common tumors that come from these cells develop in the cerebellum and are called medulloblastomas.
Meninges: These are layers of tissue that line and protect the brain and spinal cord. CSF travels through spaces formed by the meninges. The most common tumors that start in these tissues 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.
Pituitary gland and hypothalamus: The pituitary is a small gland at the base of the brain. It is connected to a part of the brain called the hypothalamus. 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. As a result, a person may have low levels of one or more hormones after treatment and may need to take hormones to correct any deficiencies.
Pineal gland: The pineal gland is not strictly part of the brain. It is, in fact, a small endocrine gland that sits between the cerebral hemispheres. It makes melatonin, a hormone that regulates sleep, in response to changes in light.
Blood-brain barrier: The inner lining of the small blood vessels (capillaries) in the brain and spinal cord creates a very selective barrier between the blood and the tissues of the central nervous system. This barrier normally helps maintain the brain’s metabolic balance and 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.
Last Medical Review: 10/09/2012
Last Revised: 02/06/2013