Brain and Central Nervous System (CNS) Tumors
Brain tumors can be gliomas (thought to grow from glial cells or glial precursor cells) or non-gliomas. As a group, gliomas are one of the most common types of brain tumor. Brain tumors can also be primary or secondary. Primary brain tumors start in the brain, while secondary tumors are cancerous tumors that began in another part of the body and spread (metastacized) to the brain. In adults, secondary brain tumors are much more common than primary tumors. A low-grade primary tumor generally grows slowly, but it can turn into a faster-growing high-grade tumor.
Although primary tumors rarely spread outside the brain, they can spread throughout the brain and spinal cord tissue. Even non-cancerous (benign) tumors can destroy normal brain tissue as they grow and cause serious harm. For this reason, doctors usually speak of “brain tumors” rather than “brain cancers.”
Forms of brain and CNS tumors – Gilomas
Doctors are moving toward using tumor genetics to better classify gliomas. Currently, the types of gliomas include:
Astrocytoma is the most common type of glioma. Astrocytoma cells look like glial cells called astrocytes that are found in the cerebrum or cerebellum.
Oligodendroglioma tumor cells look like glial cells called oligodendrocytes, which make myelin.
Ependymoma tumor cells commonly form where cerebral spinal fluid (CSF) is made and stored. In adults, they occur more often in the spine, while in children they tend to occur in the cerebellum. Ependymoma can block the normal flow of CSF and lead to a condition called hydrocephalus. Children with hydrocephalus often complain of headaches, nausea, vomiting, blurred vision, and difficulty walking.
Brain stem glioma begins in the glial cells in the brain stem. In children, brain stem glioma tends to occur between the ages of 5 and 10 years old. This type of tumor is typically very aggressive, growing and spreading quickly. A small percentage of brain stem tumors, called focal tumors, are very localized and often less aggressive.
Forms of brain and CNS tumors – Non-Gilomas
Non-Gilomas tumors include:
Meningioma is the most common primary brain tumor. It begins in the meninges and is usually non-cancerous. Meningioma can cause serious symptoms if it grows and presses on the brain or spinal cord or grows into the brain tissue.
Pineal gland and pituitary gland tumors start in the pineal gland and pituitary gland.
Primary CNS lymphoma is a rare and very aggressive form of lymphoma, a cancer that begins in the lymphatic system. Primary CNS lymphoma starts in the brain and can spread to the spinal fluid and eyes.
Medulloblastoma is thought to start from a specific type of cell (cerebellar granule progenitor cells) in the cerebellum. It is most common in children and is usually cancerous, often spreading throughout the CNS.
Craniopharyngioma is a benign CNS tumor that begins near the pituitary gland located near the base of the brain. These tumors are rare.
Schwannoma is a rare, usually non-cancerous tumor that begins in the nerve sheath, or the lining of the nerves. It may often occur in a nerve in the inner ear (the vestibular nerve), which helps control balance.
Risk factors for brain and central nervous system tumors
Age — Brain tumors are more common in children and older adults, although people can develop a brain tumor at any age.
Gender — Men are more likely than women to develop a brain tumor, but some types of brain tumors (like meningioma) are more common in women.
Family History — About 5 percent of brain tumors may be linked to hereditary genetic factors or conditions. These include Li-Fraumeni syndrome, neurofibromatosis, nevoid basal cell carcinoma syndrome, tuberous sclerosis, Turcot syndrome, and von Hippel-Lindau disease. Scientists have also found “clusters” of brain tumors within some families without a link to these known hereditary conditions. Studies are trying to find a cause for these clusters.
Exposure to infections, viruses, and allergies — Infection with the Epstein-Barr virus (EBV) increases the risk of CNS lymphoma. In other research, high levels of a common virus called cytomegalovirus (CMV) have been found in brain tumor tissue. Conversely, studies have shown that patients with a history of allergies or skin conditions have a lower risk of glioma.
Race and Ethnicity — In the United States, white people are more likely to develop gliomas but less likely to develop meningioma than African Americans. People from northern Europe are more than twice as likely to develop a brain tumor as people in Japan.
Radiation Exposure — Radiation-induced brain tumors are rare; most are caused by radiation to the head given to treat other cancers. They occur most often in people who received radiation to the brain as children as part of their treatment for leukemia. Brain tumors usually develop around 10 to 15 years after the radiation. The possible risk from exposure to imaging tests that use much lower levels of radiation, such as X-rays or CT scans, is not definitively known.
Head Injury and Seizures — Some studies have shown a link between head trauma and meningioma, but not between head trauma and glioma. A history of seizures has also been linked with brain tumors. However, a brain tumor can cause seizures, so it is not known if seizures increase the risk of brain tumors, if seizures occur because of the tumor, or if anti-seizure medication increases the risk.
Weakened Immune System — People with weakened immune systems have an increased risk of developing CNS lymphomas.
Factors with uncertain, controversial, or unproven effects on brain tumor risk
Electromagnetic Fields — Most studies show no link between exposure to electromagnetic fields, such as energy from power lines or from cell phone use, to an increased risk of developing a brain tumor in adults. However, there is conflicting information regarding risk in children. For that reason, the World Health Organization (WHO) recommends limiting cell phone use and promotes the use of a hands-free headset for both adults and children.
N-nitroso Compounds — Some studies suggest that dietary N-nitroso compounds may raise the risk of both childhood and adult brain tumors. Dietary N-nitroso compounds are formed in the body from nitrites or nitrates found in some cured meats, cigarette smoke, and cosmetics. However, additional research is necessary before a definitive link can be established.
Chemical Exposures — Exposure to solvents, pesticides, oil products, rubber, or vinyl chloride may increase the risk of developing a brain tumor. These chemicals were linked to an increased risk of brain tumors in some studies but not in others.
Symptoms of brain and central nervous system tumors
Many brain and CNS tumor symptoms may be due to other causes. Likewise, the brain controls numerous functions, including hormone production, so tumors can also cause symptoms not listed here.
Tumors in any part of the brain might increase the pressure inside the skull (known as intracranial pressure). This pressure can result from tumor growth, swelling in the brain, or the blocked flow of cerebrospinal fluid. General symptoms resulting from this increased pressure can include:
Headache — Headaches that tend to get worse over time are a common symptom of brain tumors, occurring in about half of patients.
Crossed eyes or blurred vision
Personality or behavior changes
Seizures — As many as half of people with brain tumors will have seizures at some point. However, fewer than 1 in 10 first seizures are caused by brain tumors.
Drowsiness or coma
Symptoms in children can also include:
Loss of appetite
Drop in intellectual and/or physical abilities — and poor school performance
Increased head size — sometimes along with bulging of the soft spots of the skull (fontanelles)
Tumors and their symptoms
Brain and spinal cord tumors often cause problems with the specific functions of the region in which they develop.
Cerebrum (governing movement or sensation)
- Weakness or numbness of part of the body, often on just one side
Cerebrum (governing language)
- Problems with speech or with understanding words
- Thinking, personality, and language
Cerebrum (back) or around the pituitary gland, the optic nerve, or certain other cranial nerves
- Vision problems
- Trouble walking
- Trouble with precise movements of hands, arms, feet, and legs
- Problems swallowing or synchronizing eye movements
- Changes in speech rhythm
- Hearing loss (in one or both ears)
- Balance problems
- Weakness of some facial muscles
- Facial numbness or pain
- Trouble swallowing
- Weakness or lack of coordination in the arms and/or legs (usually on both sides of the body)
- Bladder or bowel problems.
How are brain and central nervous system tumors treated with radiation?
External-beam radiation therapy can be directed at a brain tumor in the following ways:
Three-dimensional conformal radiation therapy (3D-CRT) first creates a 3-dimensional model of the tumor and surrounding healthy tissue on a computer, using images from CT and MRI scans. This model is used to aim radiation beams directly at the tumor, sparing the healthy tissue.
Intensity modulated radiation therapy (IMRT) is a type of 3D-CRT that can more directly target a tumor. Radiation beams are broken up into smaller beams and the intensity of each of these smaller beams can be changed. IMRT can deliver higher doses of radiation to the tumor while giving less to the surrounding healthy tissue.
Proton therapy uses protons rather than X-rays. At high energy, protons can destroy tumor cells. Proton beam therapy is typically used for tumors when less radiation is needed because of the location. This includes tumors that have grown into nearby bone, such as the base of skull, and those near the optic nerve.
Stereotactic radiosurgery delivers a single, high dose of radiation directly to the tumor and not healthy tissue. It works best for a tumor that is only in one area of the brain and certain non-cancerous tumors. It can also be used when a person has more than one metastatic brain tumor. Stereotactic radiosurgery equipment includes a modified linear accelerator, which creates high-energy radiation by using electricity to form a stream of fast-moving subatomic particles; a gamma knife, which concentrates highly focused beams of gamma radiation on the tumor; and a cyber knife, a robotic device that guides radiation to the tumor.
Fractionated stereotactic radiation therapy delivers small daily doses (fractions) over several weeks, in contrast to the one-day radiosurgery. This technique is used for tumors located close to sensitive structures, such as the optic nerves or brain stem.
Conventional radiation therapy can be used for whole brain and spinal cord radiation therapy (craniospinal radiation) if the tumor has spread along the covering of the spinal cord (meninges) or into the surrounding cerebrospinal fluid. Some tumors such as ependymomas and medulloblastomas are more likely to spread this way.
Brachytherapy (internal radiation therapy) differs from external beam radiation therapy because a radiation source is placed directly into or near the tumor. The radiation travels a very short distance, so it affects only the tumor. This technique is most often used along with external radiation. It provides a high dose of radiation at the tumor site, while the external radiation treats nearby areas with a lower dose.
More extensive information about brain, central nervous system, and other cancers may be found at these sites:
American Cancer Society: Cancer.org
American Society of Clinical Oncology: Cancer.net
National Cancer Institute: Cancer.gov