There are two main types of brain and spinal cord tumors:
- Tumors that start in the brain or spinal cord are called primary brain (or spinal cord) tumors.
- Tumors that start in another part of the body and then spread to the brain or spinal cord are called metastatic or secondary brain (or spinal cord) tumors.
In adults, metastatic tumors to the brain are actually more common than primary brain tumors, and they are treated differently. This information is about primary brain tumors.
Unlike cancers that start in other parts of the body, tumors that start in the brain or spinal cord rarely spread to distant organs. Even so, brain or spinal cord tumors are rarely considered benign (non-cancerous). They can still cause damage by growing and spreading into nearby areas, where they can destroy normal brain tissue. And unless they are completely removed or destroyed, most brain or spinal cord tumors will continue to grow and eventually be life-threatening.
How brain and spinal cord tumors are classified
Several factors are important when doctors are trying to figure out how best to treat a brain or spinal cord tumor and what the prognosis (outlook) is likely to be:
The type of tumor (based on the type of cell it starts in): Tumors can form in almost any type of tissue or cell in the brain or spinal cord. Some tumors have a mix of cell types. Different types of tumors tend to start in certain parts of the brain or spinal cord, and tend to grow in certain ways. (The most common types of brain and spinal cord tumors in adults are described below.)
The grade of the tumor: Some types of brain and spinal cord tumors are more likely to grow into nearby brain or spinal cord tissue (and to grow quickly) than are others. Brain and spinal cord tumors are typically divided into 4 grades (using Roman numerals I to IV), based largely on how the tumor cells look under a microscope:
- Lower grade (grade I or II) tumors tend to grow more slowly and are less likely to grow into (invade or infiltrate) nearby tissues.
- Higher grade (grade III or IV) tumors tend to grow quickly and are more likely to grow into nearby tissues. These tumors often require more intense treatment.
Gene changes in the tumor cells: Even for a specific type of brain tumor, the changes in the genes (DNA) of the tumor cells can be different. For example, many types of tumors are now divided based on whether the cells have mutations in one of the IDH genes (IDH1 or IDH2). For a specific type of tumor, those with IDH mutations tend to have a better outlook than those without a mutation. Other gene mutations can also be important for certain types of tumors.
The location of the tumor: Where the tumor is in the brain or spinal cord can affect what symptoms it causes, as well as which treatments might be best.
Gliomas are not a specific type of brain tumor. Glioma is a general term for tumors that start in glial cells. A number of tumors can be considered gliomas, including:
- Astrocytomas (which include glioblastomas)
About 3 out of 10 of all brain tumors are gliomas. Most fast-growing brain tumors are gliomas.
Astrocytomas are tumors that start in glial cells called astrocytes. About 2 out of 10 brain tumors are astrocytomas.
Most astrocytomas can spread widely throughout the brain and blend with the normal brain tissue, which can make them very hard to remove with surgery. Sometimes they spread along the cerebrospinal fluid (CSF) pathways. It is very rare for them to spread outside of the brain or spinal cord.
As with other types of brain tumors, astrocytomas are often grouped by grade.
Low-grade (grade I or II) astrocytomas tend to grow slowly. These include:
- Non-infiltrating (grade I) astrocytomas, which do not usually grow into nearby tissues and tend to have a good prognosis. Examples include pilocytic astrocytomas and subependymal giant cell astrocytomas (SEGAs). These are more common in children than in adults.
- Grade II astrocytomas, such as diffuse astrocytomasand pleomorphic xanthoastrocytomas (PXAs). These tumors tend to be slow growing, but they can grow into nearby areas, which can make them harder to remove with surgery. These tumors can become more aggressive and faster growing over time.
High-grade (grade III or IV) astrocytomas tend togrow quickly and spreadinto the surrounding normal brain tissue. These include:
- Anaplastic (grade III) astrocytomas
- Glioblastomas (grade IV), which are the fastest growing. These tumors make up more than half of all gliomas and are the most common malignant brain tumors in adults.
These tumors start in brain glial cells called oligodendrocytes. These are grade II tumors that tend to grow slowly, but most of them can grow into (infiltrate) nearby brain tissue and can't be removed completely by surgery. Oligodendrogliomas sometimes spread along the CSF pathways but rarely spread outside the brain or spinal cord. As with astrocytomas, they can become more aggressive over time. Very aggressive (grade III) forms of these tumors are known as anaplastic oligodendrogliomas. Only about 1% to 2% of brain tumors are oligodendrogliomas.
These tumors start in ependymal cells, and typically grow in the ventricles or spinal cord in adults. They can range from fairly low-grade (grade II) tumors to higher grade (grade III) tumors, which are called anaplastic ependymomas. Only about 2% of brain tumors are ependymomas.
Ependymomas are more likely to spread along the cerebrospinal fluid (CSF) pathways than other gliomas but do not spread outside the brain or spinal cord. These tumors may block the flow of CSF from the ventricles, causing the ventricles to become very large – a condition called hydrocephalus.
Some (but not all) ependymomas can be removed completely and cured by surgery. But because they can spread along ependymal surfaces and CSF pathways, treating them can sometimes be difficult. Spinal cord ependymomas have the greatest chance of being cured with surgery, but treatment can cause side effects related to nerve damage.
Meningiomas begin in the meninges, the layers of tissue that surround the outer part of the brain and spinal cord. Meningiomas account for about 1 out of 3 primary brain and spinal cord tumors. They are the most common primary brain tumors in adults (although strictly speaking, they are not actually brain tumors).
The risk of these tumors increases with age. They occur about twice as often in women. Sometimes these tumors run in families, especially in those with neurofibromatosis, a syndrome in which people develop many benign tumors of nerve tissue.
Meningiomas are often assigned a grade, based on how the cells look under the microscope.
- Grade I (benign) meningiomas have cells that look the most like normal cells. These are the most common type of meningioma. Most of these tumors can be cured by surgery, but some grow very close to vital structures in the brain or cranial nerves and cannot be cured by surgery alone.
- Grade II (atypical or invasive) meningiomas usually have cells that look slightly more abnormal. They can grow directly into nearby brain tissue and bone and are more likely to come back (recur) after surgery.
- Grade III (anaplastic or malignant) meningiomas have cells that look the most abnormal. These are the least common type of meningiomas. They tend to grow quickly, can grow into nearby brain tissue and bone, and are the most likely to come back after treatment. Some may even spread to other parts of the body.
Medulloblastomas develop from neuroectodermal cells (early forms of nerve cells) in the cerebellum. They are fast-growing (grade IV) tumors and often spread throughout the CSF pathways, but they can be treated by surgery, radiation therapy, and chemotherapy.
Medulloblastomas occur much more often in children than in adults. They are part of a class of tumors called embryonal tumors that can also start in other parts of the central nervous system. For more information on these tumors, see Brain and Spinal Cord Tumors in Children.
Gangliogliomas contain both neurons and glial cells. These tumors are very uncommon in adults. They are typically slow growing (grade I) tumorsand can usually be cured by surgery alone or surgery combined with radiation therapy.
Schwannomas develop from Schwann cells, which surround and insulate cranial nerves and other nerves. They make up about 8% of all CNS tumors.
Schwannomas are almost always benign (grade I) tumors. They can arise from any cranial nerve. When they form on the cranial nerve responsible for hearing and balance near the cerebellum, they are called vestibular schwannomas or acoustic neuromas. They can also start on spinal nerves after the point where they have left the spinal cord. When this happens, they can press on the spinal cord, causing weakness, sensory loss, and bowel and bladder problems.
These slow-growing (grade I) tumors start above the pituitary gland but below the brain itself. They may press on the pituitary gland and the hypothalamus, causing hormone problems. Because they start very close to the optic nerves, they can also cause vision problems. Their tendency to stick to these important structures can make them hard to remove completely without damaging vision or hormone balance. Craniopharyngiomas are more common in children, but they are sometimes seen in adults.
Other tumors that can start in or near the brain
These rare tumors start in the bone at the base of the skull or at the lower end of the spine. Chordomas don’t start in the central nervous system, but they can injure the nearby brain or spinal cord by pressing on it.
These tumors are treated with surgery if possible, often followed by radiation therapy, but they tend to come back in the same area after treatment, causing more damage. They usually do not spread to other organs. For more information on chordomas, see Bone Cancer.
Lymphomas are cancers that start in white blood cells called lymphocytes (one of the main cell types of the immune system). Most lymphomas start in other parts of the body, but some start in the CNS, and are called primary CNS lymphomas.
These lymphomas are more common in people with immune system problems, such as those infected with HIV, the virus that causes AIDS. Because of new treatments for AIDS, primary CNS lymphomas have become less common in recent years. They account for about 2% of primary brain tumors.
These lymphomas often grow quickly and can be hard to treat. Recent advances in chemotherapy, however, have improved the outlook for people with these cancers. For more information on primary CNS lymphomas (including treatment), see Non-Hodgkin Lymphoma.
Tumors that start in the pituitary gland are almost always benign (non-cancerous). But they can still cause problems if they grow large enough to press on nearby structures or if they make too much of any kind of hormone. For more information, see Pituitary Tumors.