Oligodendrogliomas are a rare form of brain tumors. The brain is made up of many supporting cells that are called glial cells. Any tumor of these glial cells is called a glioma. Oligodendrogliomas are tumors that arise from a type of glial cell called oligodendrocytes. These cells are the specialized cells of the brain that produce the fatty covering of nerve cells (myelin).
Oligodendrogliomas can grow in different parts of the brain, but they are most commonly found in the frontal or temporal lobes of the cerebrum. The frontal lobes are responsible for cognitive thought processes (knowing, thinking, learning, and judging). The temporal lobes are responsible for coordination, speech, hearing, memory, and awareness of time.
There are two types of oligodendroglioma: the well-differentiated tumor, which grows relatively slowly and in a defined shape; and, the anaplastic oligodendroglioma, which grows much more rapidly and does not have a well-defined shape. Anaplastic oligodendrogliomas are much less common than well-differentiated oligodendrogliomas.
More common than either form of pure oligodendroglioma is the mixed glioma, or oligoastrocytoma. These mixed gliomas are a mixture of oligodendroglioma and astrocytoma . An astrocytoma is a tumor that arises from the astrocytes, specialized cells in the brain that regulate the chemical environment of the brain and help to form the blood-brain barrier.
Oligodendrogliomas and mixed gliomas account for approximately 4 to 5% of all primary brain tumors and 10% of all gliomas. A primary brain tumor is a tumor that begins in the brain, as opposed to a secondary (or metastatic) brain tumor, which originates in another organ and spreads (metastasizes) to the brain.
Oligodendromas occur in approximately nine in every one million people. Oligodendrogliomas can occur in people of any age, but most occur in middle-aged adults.
Oligodendrogliomas occur with equal frequency in members of all races and ethnic groups. There does not appear to be any relation of oligodendrogliomas to any geographic region. For unknown reasons, men are affected by oligodendrogliomas in higher numbers than women.
Causes and symptoms
The cause, or causes, of oligodendrogliomas are not known; however, most people with these types of tumors have some type of genetic mutation on chromosome 1, chromosome 19, or on both chromosomes 1 and 19. In early 2001, investigations were ongoing in an attempt to determine if these genetic factors, or other factors, cause oligodendrogliomas. Oligodendrogliomas are not contagious.
The symptoms of oligodenrogliomas are the result of increased pressure in the fluid within the skull (intracranial hypertension). These symptoms include:
- vision disturbances
- enlargement of the head
Oligodendrogliomas may also be accompanied by a weakness or paralysis on the side of the body opposite to the side of the brain where the tumor is located. When the tumor is located in a frontal lobe, the patient may experience gradual changes in mood and personality. When it is located in a temporal lobe, the patient may experience difficulty with speech, hearing, coordination, and memory.
The diagnosis of oligodendrogliomas begins in the doctor's office with a basic neurological examination. This examination involves:
- testing eye reflexes, eye movement, and pupil reactions
- testing hearing with a tuning fork or ticking watch
- reflex tests with a rubber hammer
- balance and coordination tests
- pin-prick and cotton ball tests for sense of touch
- sense of smell tests with various odors
- facial muscle tests (e.g., smiling, frowning, etc.)
- tongue movement and gag reflex tests
- head movement tests
- mental status tests (e.g., asking what year it is, who the President is, etc.)
- abstract thinking tests (e.g., asking for the meaning of a common saying, such as "every cloud has a silver lining.")
- memory tests (e.g., asking to have a list of objects repeated, asking for details of what a patient ate for dinner last night, etc.)
If the doctor suspects a brain tumor may be present, further diagnostic tests will be ordered. These tests are performed by a neurological specialist. Imaging tests that may be ordered include computed tomography (CT) and magnetic resonance imaging (MRI).Other tests may include a spinal tap, to examine the cerebrospinal fluid, and an electroencephalogram (EEG), which measures the electrical activity of the brain.
Treatment of any primary brain tumor, including oligodendrogliomas, is different from treating tumors in other parts of the body. Brain surgery requires much more precision than most other surgeries. Also, many medicinal drugs cannot cross the blood-brain barrier. Therefore, the therapies that are used to treat oligodendrogliomas, and the side effects of these therapies, are quite complex.
The most up-to-date treatment opportunities are available from experienced, multi-disciplinary medical professional teams made up of doctors, nurses, and technologists who specialize in cancer (oncology), neurology, medical imaging, drug or radiation therapy , and anesthesiology.
Clinical staging, treatments, and prognosis
Oligodendrogliomas and other primary brain tumors are diagnosed, or staged, in grades of severity from I to IV. Grade I tumors have cells that are not malignant and are nearly normal in appearance. Grade II tumors have cells that appear to be slightly abnormal. Grade III tumors have cells that are malignant and clearly abnormal. Grade IV, the most severe type of brain tumors, contain fast-spreading and abnormal cells. Well-defined oligodendrogliomas are generally stage I or stage II tumors. Anaplastic oligodenrogliomas are generally stage III or stage IV tumors.
The standard treatment for all grades of oligodendrogliomas is surgery to remove the tumor completely. This surgery is generally aided by an image guidance system that allows the surgeon to determine the most efficient route to location of the tumor. Approximately half of oligodendroglioma patients gain relief of the increased intracranial pressure after complete removal of their tumors. The other half require a spinal fluid shunt to allow drainage of the excess fluid.
In some instances of oligodendroglioma, the tumor is inoperable or cannot be completely removed. Patients with inoperable oligodendrogliomas are generally treated with radiation therapies. Oligodendrogliomas are among the only brain tumors that can be successfully treated with a type of chemotherapy called PCV (Procarbazine , CCNU or lomustine , and Vincristine ). Chemotherapy is usually used only in cases of recurrent anaplastic oligodendrogliomas.
For patients with well-defined oligodendrogliomas, median survival exceeds 10 years. For patients with anaplastic dendrogliomas, median survival ranges from two to five years.
Alternative and complementary therapies
For oligodendrogliomas, there are no effective alternative treatments—treatments used instead of conventional treatments like surgery or chemotherapy.
Coping with cancer treatment
Most patients who undergo brain surgery to remove their tumors can resume their normal activities within a few days of the operation.
There were 47 clinical trials underway, in early 2001, aimed at the treatment of oligodendrogliomas. More information on these trials, including contact information, may be found by conducting a clinical trial search at the web site of the National Cancer Institute, CancerNet <http://cancernet.nci.nih.gov/trialsrch.shtml>.
Because the cause or causes of oligodenrogliomas are not known, there are no known preventions.
Repeat surgery may be necessary for oligodendrogliomas because these tumors sometimes redevelop.
Careful monitoring by the medical team will be required. Also, if the tumor is located in the dominant hemisphere of the patient's brain, any treatment, especially surgery, requires special consideration and care not to disrupt the personality or other higher brain functions of the patient.
See Also Brain/Central nervous system tumors
Kaye, Andrew H. and Edward R. Laws (eds). Brain Tumors: An Encyclopedic Approach. New York: Churchill Living stone, 1995.
The Brain Tumor Society. 124 Watertown Street, Suite 3-H. Watertown, MA 02472. 617-924-9997. Fax 617-924-9998. <http://www.tbts.org/>.
"Understanding Oligodendrogliomas: Information on Diagnosis, Treatment, Radiotherapy, Surgery and Chemotherapy."<http://www.bacup.org.uk/info/oligodendroglioma.htm>. 15 April 2001. 27 June 2001.
Paul A. Johnson, Ed.M.
—A form of oligodendroglioma that does not have a well-defined shape and grows very rapidly and aggressively.
—A type of brain tumor that arises from the astrocytes, specialized brain cells that regulate the chemical environment of the brain and form the blood-brain barrier. These types of tumors are often mixed with oligodendrogliomas to form oligoastrocytomas.
—The two lobes of the cerebrum of the brain that are responsible for cognitive thought processes (knowing, thinking, learning, and judging).
—Any tumor that arises from the supporting cells in the brain called glial cells.
—A higher-than-normal pressure of the fluid in the skull.
—A type of brain tumor that is a mixture of oligodendroglioma and astrocytoma. This is also called a mixed glioma.
Spinal fluid shunt
—A small tube that is surgically implanted to allow excess spinal fluid to drain directly into the abdominal cavity.
—The two lobes of the cerebrum of the brain that are responsible for coordination, speech, hearing, memory, and awareness of time.
—A tumor that grows relatively slowly and in a well-defined shape.
QUESTIONS TO ASK THE DOCTOR
- Which type of oligodendroglioma do I have?
- Is my tumor operable?
- What is the likelihood of my type of oligodendroglioma coming back?
- How often should I seek follow-up examinations?