Malignant oligodendroglioma is a rare brain tumor that grows from special support cells in the nervous system. Though the diagnosis can be unsettling, these tumors are among the most treatable types of brain cancers, and many patients respond well to modern approaches that combine surgery, radiation, and medication.
Understanding Malignant Oligodendroglioma
Malignant oligodendroglioma, also called grade 3 or anaplastic oligodendroglioma, is a fast-growing tumor that develops in the brain or, in very rare cases, in the spinal cord. Unlike lower-grade versions of this tumor, the malignant form is more aggressive and requires prompt treatment. The tumor grows from cells called oligodendrocytes, which are special support cells in the nervous system. These cells normally wrap around nerve fibers to form a protective coating called myelin, which helps signals travel quickly through the brain.[1]
The word “oligodendrocyte” comes from Greek and describes the way these cells look: they have a small body with tree-like branches that extend outward. When something goes wrong with these cells and they start growing uncontrollably, a tumor forms. What makes this tumor malignant is that it spreads to nearby brain tissue more quickly than low-grade versions and can cause more damage in a shorter time. Because the tumor affects the brain, which controls everything from movement to memory, its location and size determine what symptoms appear and how serious they become.[1]
These tumors belong to a larger family called gliomas, which are tumors that grow from glial cells—the general term for support cells in the nervous system. Oligodendrogliomas make up between 5% and 15% of all gliomas, and only about 3% to 4% of all brain tumors are oligodendrogliomas. When doctors talk about malignant oligodendroglioma, they are referring to grade 3 tumors, which are more dangerous than grade 2 tumors that grow slowly.[1][4]
How Common Is Malignant Oligodendroglioma?
Malignant oligodendroglioma is relatively uncommon. In the United States, approximately 14,950 people are currently living with oligodendroglioma of any grade. Only about 1.2% of all primary brain tumors are oligodendrogliomas. Worldwide, healthcare providers diagnose just under 24,000 people with oligodendroglioma each year. Most of these tumors are the slower-growing grade 2 type, making malignant grade 3 oligodendrogliomas even rarer.[1][2][6]
These tumors can develop at any age, but they are most commonly diagnosed in adults between the ages of 35 and 50. Some sources point to the 40 to 50 age range as the most typical time for diagnosis. Malignant oligodendrogliomas happen more often in men than in women, and they are most common in non-Hispanic white people. They are rare in children, though they can occasionally occur in younger patients.[1][6][11]
Because these tumors are so rare, many patients find themselves navigating unfamiliar medical territory. The good news is that oligodendrogliomas, even the malignant ones, generally respond better to treatment than many other types of brain tumors. This means that despite their aggressive nature, the outlook is often more hopeful than with other malignant brain cancers.[4]
What Causes Malignant Oligodendroglioma?
Malignant oligodendroglioma happens because of specific changes in the DNA inside brain cells. By definition, all oligodendrogliomas—whether grade 2 or grade 3—have two particular genetic changes. The first is called a 1p/19q co-deletion, which means that parts of two chromosomes (the structures that carry genetic information) are missing. Specifically, the short arm of chromosome 1 and the long arm of chromosome 19 are lost. The second genetic change is a mutation in a gene called IDH (isocitrate dehydrogenase), which is an enzyme found in cells.[1][6]
These genetic changes are not inherited from parents in most cases. Instead, they happen randomly during a person’s lifetime. Scientists don’t fully understand why these mutations occur. For most people with oligodendroglioma, there is no clear reason why their cells developed these abnormal changes. It’s simply a matter of unfortunate chance, where copying errors happened when cells were dividing and reproducing.[1]
However, there are a few known risk factors. Exposure to radiation has been linked to a higher chance of developing oligodendrogliomas. Additionally, certain rare gene changes that can be passed down through families may increase the risk, though this is uncommon. Only about 5% of brain tumors have a genetic component that runs in families. For the vast majority of patients, the tumor develops without any family history or known environmental trigger.[6]
Where Do These Tumors Grow?
Malignant oligodendrogliomas most often develop in the front part of the brain, in an area called the frontal lobe. They can also form in the temporal lobes, which are located on the sides of the brain above the ears. However, these tumors can appear anywhere in the largest part of the brain, called the cerebrum, which extends from the top of the head almost to the neck and takes up most of the space inside the skull.[5][12]
These tumors are commonly found in both the white matter (the inner part of the brain where nerve fibers run) and the cortex (the wrinkly outer surface of the brain). Because they often affect the cortex, which controls many abilities we use every day like vision, language, and muscle control, they frequently cause noticeable symptoms. The frontal lobe is responsible for tasks like voluntary movement, speech, reasoning, and personality. The temporal lobe handles hearing, memory, and language. Depending on where the tumor grows, it will affect different functions.[6][13]
Although rare, oligodendrogliomas can also form in the spinal cord. They can spread to other areas of the brain or spinal cord through the fluid that surrounds these structures, called cerebrospinal fluid (CSF), though this is uncommon. They rarely spread outside the brain and spinal cord to other organs in the body.[1][6]
What Symptoms Should You Watch For?
The symptoms of malignant oligodendroglioma depend on where the tumor is located and how large it has grown. Many oligodendrogliomas grow slowly at first, meaning they can be present for years before causing noticeable problems. Sometimes they are discovered accidentally when a person gets a brain scan for another reason, like a head injury or severe headaches. But when a low-grade tumor transforms into a malignant one, or when a malignant tumor develops from the start, symptoms tend to appear more quickly.[3][8]
The most common symptom is a seizure. Up to 80% of people with oligodendroglioma experience a seizure at some point, and for many, it is the first sign that something is wrong. A seizure happens when the tumor irritates the brain tissue around it, causing abnormal electrical activity. This can lead to sudden uncontrolled movements, loss of consciousness, or strange sensations. Around 60% of people have a seizure before they are even diagnosed with the tumor.[1][5][6]
Headaches are another frequent symptom. These headaches may be different from regular headaches—they might be persistent, worse in the morning, or accompanied by other symptoms like nausea or vomiting. Because the tumor takes up space inside the skull, it can increase pressure inside the brain, leading to these uncomfortable sensations.[3][6]
Besides seizures and headaches, malignant oligodendrogliomas can cause what doctors call focal symptoms. These are symptoms that point to a problem in a specific area of the brain. They might include muscle weakness or paralysis, especially on one side of the body or face; trouble speaking or understanding what others are saying (a condition called aphasia); vision problems such as blurred vision, double vision, or loss of part of the visual field; hearing loss; numbness or tingling; memory problems; difficulty thinking or concentrating; changes in personality or behavior; and problems with balance or movement.[1][6][8]
Tumors in the frontal lobe may cause noticeable changes in personality or behavior, along with weakness on one side of the body. Temporal lobe tumors sometimes cause fewer obvious symptoms, but when they do, seizures and language difficulties are common. Each person’s experience is different because the symptoms depend entirely on which part of the brain is affected.[5][13]
How Is Malignant Oligodendroglioma Diagnosed?
Diagnosing malignant oligodendroglioma involves several steps. The process usually begins when a person experiences symptoms like seizures or headaches and visits a doctor. The doctor will first perform a neurological exam, which checks vision, hearing, balance, coordination, strength, and reflexes. Problems in any of these areas can give clues about where in the brain a problem might be located.[10]
The next step is imaging tests, which create pictures of the inside of the brain. The most common test is an MRI (magnetic resonance imaging), which uses magnets and radio waves to produce detailed images. MRIs can show where the tumor is, how large it is, and what it looks like. Oligodendrogliomas often appear on an MRI as a single tumor with well-defined borders. They may have some swelling around them and sometimes show up more brightly when a special dye called contrast is used. A CT scan (computed tomography), which uses X-rays to create images, may also be used and can reveal calcium deposits inside the tumor, which are common in oligodendrogliomas.[6][10]
However, imaging alone cannot confirm the diagnosis. To know for certain that a tumor is a malignant oligodendroglioma, doctors need to examine a sample of the tumor tissue under a microscope. This sample is usually obtained during surgery to remove the tumor, though sometimes a separate procedure called a biopsy is performed just to collect tissue. During a biopsy, a surgeon makes a small opening in the skull and removes a piece of the tumor using a needle or other tool.[10]
Once the tissue sample is obtained, it goes to a laboratory where a specialist called a neuropathologist examines it. Under the microscope, oligodendroglioma cells often have a distinctive appearance that doctors describe as looking like “fried eggs.” The tumor also typically has a “chicken wire” pattern of blood vessels. But the microscope exam is only part of the diagnosis. The tissue must also undergo special genetic tests called biomarker testing.[4][8]
Biomarker testing looks for the specific genetic changes that define oligodendroglioma: the 1p/19q co-deletion and the IDH mutation. Only tumors with both of these changes can be diagnosed as oligodendroglioma. If these genetic markers are not found, the tumor may be classified differently. The presence of these markers is also important because it helps predict how well the tumor will respond to treatment. Tumors with the 1p/19q co-deletion tend to be more sensitive to chemotherapy and radiation.[6][8]
Based on how the cells look under the microscope and the genetic test results, the tumor is assigned a grade. Grade 3 tumors, or malignant oligodendrogliomas, look more abnormal and grow more quickly than grade 2 tumors. The grading system helps doctors decide on the best treatment plan.[6][11]
Can Malignant Oligodendroglioma Be Prevented?
Unfortunately, there is no known way to prevent malignant oligodendroglioma. Because the genetic changes that cause these tumors happen randomly and are not inherited in most cases, there are no specific lifestyle changes, diets, or behaviors that have been proven to reduce the risk. The only known risk factor that can be controlled is exposure to radiation. People who have received radiation therapy to the head as treatment for another condition may have a slightly higher risk of developing brain tumors later in life, but this accounts for only a small number of cases.[6][11]
Because oligodendrogliomas are so rare and develop without warning, regular screening tests are not recommended for the general population. Unlike some cancers that can be detected early through routine screening (like mammograms for breast cancer or colonoscopies for colon cancer), there is no standard screening test for brain tumors in people without symptoms. The best approach is to be aware of symptoms and seek medical attention promptly if unusual neurological symptoms develop, especially seizures, persistent headaches, or sudden changes in thinking or behavior.[1]
For individuals with a family history of brain tumors or certain rare genetic conditions, genetic counseling may be recommended to assess risk. However, this applies to only a very small percentage of people, and most oligodendrogliomas occur in individuals with no family history at all.[6]
What Happens Inside the Brain with This Tumor?
To understand the pathophysiology of malignant oligodendroglioma—how it disrupts normal body functions—it helps to know what normally happens in the brain. The brain is made up of billions of nerve cells called neurons, which send electrical signals to communicate with each other and control everything from breathing to thinking. Supporting these neurons are glial cells, which include oligodendrocytes. These support cells maintain the environment around neurons, provide nutrients, remove waste, and form the myelin coating that insulates nerve fibers.[1]
In malignant oligodendroglioma, the oligodendrocytes or their precursor cells start growing out of control due to the genetic mutations described earlier. Instead of performing their normal supportive functions, these cells multiply rapidly and form a mass. As the tumor grows, it takes up space inside the skull, which is a rigid structure that cannot expand. This leads to increased pressure on the surrounding brain tissue, a condition called increased intracranial pressure. This pressure can cause headaches, nausea, and vomiting.[3]
The tumor also invades and damages healthy brain tissue. Malignant oligodendrogliomas are particularly invasive, meaning they spread into nearby areas of the brain rather than staying in one clearly defined spot. As they invade, they disrupt the normal connections between neurons and interfere with the brain’s ability to perform its functions. For example, if the tumor invades an area that controls movement, it can cause weakness or paralysis. If it affects areas involved in language, it can cause difficulty speaking or understanding speech.[1][6]
The tumor cells also irritate the surrounding brain tissue, which can trigger seizures. Seizures happen when groups of neurons fire abnormally and all at once, creating a sudden surge of electrical activity. Because oligodendrogliomas often grow in the cortex, where many critical functions are located, seizures are a very common symptom.[1]
Additionally, the tumor can interfere with blood flow in the brain. It may cause swelling (called edema) around the tumor, which further increases pressure and damages tissue. In some cases, the tumor can block the normal flow of cerebrospinal fluid, the liquid that cushions the brain and spinal cord, leading to a buildup of fluid and additional pressure.[6]
On a molecular level, the genetic changes in oligodendroglioma cells—the 1p/19q co-deletion and IDH mutation—affect how the cells grow and respond to signals. The IDH mutation, in particular, changes the way cells process energy and can lead to the accumulation of abnormal substances that promote tumor growth. Understanding these molecular changes has helped scientists develop more targeted treatments.[6]