Oligodendroglioma is a primary brain tumor that grows from glial cells called oligodendrocytes, which normally make myelin—the “insulation” around nerve fibers. In the modern World Health Organization (WHO) system, the name must include two genetic features: an IDH mutation and a combined loss of two chromosome arms called 1p/19q codeletion. When both are present, the tumor is officially classified as “oligodendroglioma, IDH-mutant and 1p/19q-codeleted,” and it is graded as CNS WHO grade 2 (lower grade) or grade 3 (higher grade). This definition matters because these markers predict behavior, treatment response, and prognosis. PMC+2PMC+2
Oligodendroglioma is a slow-growing brain tumor that starts from cells called oligodendrocytes, which help insulate nerve fibers. Today, doctors define oligodendroglioma by two specific lab findings: the tumor must carry an IDH mutation and a combined 1p/19q codeletion (missing parts of chromosomes 1 and 19). Tumors that meet both rules are called “oligodendroglioma, IDH-mutant, 1p/19q-codeleted,” and are graded as CNS WHO grade 2 (lower grade) or grade 3 (anaplastic, faster-growing) based on how active the cells look under the microscope (more mitoses, microvascular proliferation, or necrosis suggests a higher grade). Common synonyms/older terms include: “oligodendroglial tumor,” “anaplastic oligodendroglioma,” and “1p/19q-codeleted diffuse glioma.” These tumors often occur in adults, frequently in the frontal lobe, and generally respond better to radiation and chemotherapy than similar astrocytoma-type gliomas. PMC+2Lippincott Journals+2
Under the microscope, pathologists may see classic patterns such as round cells with clear halos (often nicknamed a “fried-egg” look from fixation artifact), delicate branching “chicken-wire” blood vessels, and frequent calcification. Today, though, the diagnosis relies on the molecular definition above, not just appearance. PMC+1
Other names
You may also see: “oligodendroglioma, IDH-mutant, 1p/19q-codeleted” (WHO 2021 wording), “grade 2 oligodendroglioma,” or “grade 3 oligodendroglioma.” The older term “anaplastic oligodendroglioma” was used for higher grade tumors but is no longer preferred; we now say CNS WHO grade 3 oligodendroglioma. Historical phrases like “oligodendroglial tumor” appear in older reports but should be interpreted using the new molecular rules. PMC+1
Types
Two grades exist in adults:
Grade 2 oligodendroglioma. These grow relatively slowly. Many people first present with seizures. Surgery is the main first step; depending on residual tumor, age, and risk features, some people are monitored, while others receive radiotherapy and chemotherapy. Nature+1
Grade 3 oligodendroglioma. These are faster-growing and usually need multimodality care (surgery followed by radiotherapy and chemotherapy). For 1p/19q-codeleted tumors, adding PCV chemotherapy (procarbazine, lomustine/CCNU, vincristine) to radiotherapy gives major survival benefits in long-term trials. Nature+1
Causes
The exact cause is usually unknown for any one person. Below are well-supported contributors that help explain why these tumors arise or who is at higher risk. (Some are genetic changes inside the tumor that drive growth; others are rare external or inherited risk factors.)
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Early IDH mutation. A change in the IDH1/IDH2 gene is often one of the earliest steps toward forming this tumor and helps set its biology. PubMed+1
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1p/19q codeletion. The combined loss of chromosome arms 1p and 19q is a hallmark of oligodendroglioma and cooperates with IDH mutation to drive tumor behavior. PMC
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CIC gene alterations. Mutations in the CIC gene are frequent in these tumors and shape how the cancer grows. PubMed
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FUBP1 gene alterations. Loss-of-function changes in FUBP1 often occur with CIC mutations and contribute to tumor development. PubMed
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TERT promoter mutations. Changes near the telomerase gene are common in IDH-mutant, 1p/19q-codeleted tumors, helping cells maintain their chromosomes and keep dividing. Oxford Academic
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Epigenetic reprogramming (G-CIMP). IDH mutations rewire tumor DNA methylation patterns and metabolism, encouraging glioma formation. Oncotarget
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Prior high-dose ionizing radiation. Past therapeutic radiation to the head is a rare but established risk for later gliomas. PMC
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Rare inherited cancer syndromes. Conditions such as Li-Fraumeni, Lynch/Turcot, and neurofibromatosis type 1 increase the chance of gliomas (not specifically oligodendroglioma, but the overall glioma risk is higher). American Cancer Society+1
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Family history of glioma (uncommon). A small subset of adult gliomas shows familial clustering. PMC
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Adult age. Oligodendroglioma is uncommon in children and most often diagnosed in adults in their 30s–50s; biology likely reflects adult-type diffuse glioma pathways. American Brain Tumor Association
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Male sex (slight excess). Some series report a modest male predominance among adults with oligodendroglioma. American Brain Tumor Association
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Spontaneous DNA replication errors. Like many cancers, random DNA copying mistakes over time can lead to the driver mutations listed above. (General principle; reflected in population data on adult gliomas.) PMC
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Ongoing tumor evolution. Over years, low-grade tumors can acquire new alterations and progress to higher grade disease. Nature
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Tumor microenvironment and metabolism. IDH mutations produce 2-hydroxyglutarate, which affects cell metabolism and gene regulation to promote tumor survival. Oncotarget
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MGMT promoter methylation (modifier). This change does not “cause” the tumor but influences sensitivity to alkylating chemotherapy; it reflects the tumor’s epigenetic state. Nature
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Possible occupational/environmental exposures (uncertain). Studies have explored links to pesticides, petroleum, and synthetic rubber, but evidence is limited and inconsistent; only high-dose radiation is firmly established. American Cancer Society
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Absence of ATRX/p53 pathway alterations. In oligodendroglioma, ATRX is typically retained and p53 low—this pattern helps distinguish it from astrocytoma and signifies a different causal route. PMC
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Frontal lobe predilection (presentation link, not cause). Many tumors arise in the frontal lobes, influencing symptom patterns like seizures and behavior change. PMC
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Calcification biology. These tumors often calcify; while not a cause, it is a biologic feature that reflects their slow-growing nature and helps on CT scans. PMC
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Overall: multistep, multifactorial path. Most cases reflect a combination of early IDH mutation plus 1p/19q codeletion, then additional changes (e.g., CIC/FUBP1, TERT promoter), not a single lifestyle trigger. PMC+2PubMed+2
Common symptoms
Seizures. The most common first sign. Many people have a seizure before diagnosis because the tumor irritates the brain’s cortex. PMC+1
Headache. Pressure from the mass or swelling can cause headaches that are new or changing over time. NCCN
Speech or language trouble. If the tumor sits in language areas (often left side), people may have trouble finding words or understanding speech. NCCN
Weakness or clumsiness. Tumors near motor pathways can cause one-sided weakness or difficulty with fine movements. NCCN
Numbness or tingling. Sensory pathways can be affected, causing odd feelings on one side of the body. NCCN
Personality or behavior change. Frontal lobe tumors may lead to apathy, impulsivity, or reduced judgment noticed by family. PMC
Memory and attention problems. Thinking can slow and short-term memory can worsen, especially with frontal or temporal lobe involvement. NCCN
Balance and coordination problems. If pathways for balance are involved, people may feel unsteady or stagger. NCCN
Vision changes. Blurred vision, field cuts, or double vision can appear if visual pathways are compressed. NCCN
Nausea and vomiting. Increased pressure inside the skull can trigger these symptoms, especially in the morning. NCCN
Fatigue. Chronic tiredness is common from the tumor, seizures, and medications. NCCN
Word-finding pauses. Subtle language pauses can be an early clue in low-grade disease. NCCN
Irritability or mood change. Emotional shifts may reflect frontal/temporal lobe effects. PMC
Difficulty multitasking. Complex tasks may become harder as executive functions are affected. NCCN
Worsening over months to years. Lower-grade tumors often evolve slowly, so symptoms can creep up gradually. Nature
Diagnostic tests
A) Physical examination
General neurologic exam. A clinician checks alertness, orientation, strength, sensation, reflexes, and coordination to map which brain areas may be affected. Nature
Cranial nerve exam. Eye movements, facial strength/sensation, hearing, and swallowing are tested to see if specific pathways are involved. Nature
Gait and posture assessment. Walking pattern, tandem gait, and posture can reveal balance/cerebellar or frontal lobe issues. Nature
Visual field testing at bedside. Confrontation testing screens for blind-spot patterns from occipital or parietal involvement. Nature
Funduscopic exam (when indicated). Looking at the optic nerves may show papilledema from raised intracranial pressure. Nature
B) Manual (bedside) tests
Mini-Mental State Exam (MMSE) or MoCA. Short paper-and-pencil screens for attention, memory, language, and executive function that tumors often impair. Nature
Pronator drift. With arms outstretched, downward drift of one arm suggests subtle weakness from a frontal lesion. Nature
Finger-to-nose and heel-to-shin. These coordination tasks detect cerebellar or sensorimotor pathway problems. Nature
Romberg test. Standing with feet together and eyes closed tests proprioception and balance; sway may point to sensory or cerebellar involvement. Nature
Confrontational naming and fluency tests. Simple bedside word-finding tasks help localize language network involvement. Nature
C) Laboratory & pathological tests
Surgical biopsy or resection with histology. Tissue shows oligodendroglial cytology and characteristic vascular patterns and calcifications; however, molecular markers define the entity. PMC+1
IDH1/IDH2 testing. Immunohistochemistry for IDH1-R132H and/or DNA sequencing confirms the required IDH mutation. PMC
1p/19q codeletion testing. FISH, PCR-LOH, or NGS demonstrates combined 1p/19q loss, the other required criterion for diagnosis. PMC
ATRX and p53 immunostains. In oligodendroglioma, ATRX is typically retained and p53 expression is usually low—supporting the 1p/19q-codeleted pathway and helping distinguish from astrocytoma. PMC
MGMT promoter methylation. This epigenetic test predicts sensitivity to alkylating chemotherapy and is often assessed to guide treatment. Nature
D) Electrodiagnostic tests
EEG (electroencephalogram). Records brain waves to evaluate seizures, which are very common in oligodendroglioma; helps classify seizure type and guide antiseizure therapy. PMC
Intraoperative neurophysiologic monitoring (when used). Somatosensory and motor evoked potentials help surgeons protect critical pathways during tumor removal. Nature
E) Imaging tests
MRI of the brain with and without contrast (core test). MRI best defines the tumor’s size, location, and effects on nearby tissue. Many oligodendrogliomas are cortico-subcortical (often frontal lobe). Advanced MRI (perfusion and spectroscopy) can add information. PMC
CT head (especially helpful for calcification). CT readily shows calcifications, which are common and can raise suspicion for oligodendroglioma before biopsy. PMC
Functional mapping MRI / awake mapping in select cases. For tumors near language or motor cortex, pre-op functional imaging and awake mapping aim to maximize safe tumor removal while preserving function. Nature
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The article is written by Team RxHarun and reviewed by the Rx Editorial Board Members
Last Updated: September 16, 2025.
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