Anaplastic oligodendroglioma is a grade 3 (faster-growing) brain tumor that starts from cells called oligodendrocytes, which help make the insulation (myelin) around brain nerve fibers. Today, doctors define this tumor by its molecular “fingerprint”: the tumor must carry an IDH gene mutation (IDH1 or IDH2) and a combined loss of two chromosome arms called 1p/19q codeletion. When a tumor has both of these changes and looks like an oligodendroglioma under the microscope, and the tissue shows high-grade features (e.g., brisk mitoses and/or microvascular proliferation), it is called oligodendroglioma, IDH-mutant and 1p/19q-codeleted, CNS WHO grade 3—the current name for what used to be called “anaplastic oligodendroglioma.” College of American Pathologists+3PMC+3PMC+3
Compared with other adult-type diffuse gliomas, oligodendrogliomas are uncommon and typically affect adults in their 30s–50s, often in the frontal lobe. They frequently present with seizures and other focal brain symptoms. NCBI+2PMC+2
Other names
Oligodendroglioma, IDH-mutant and 1p/19q-codeleted, CNS WHO grade 3 (current preferred term). PMC
Anaplastic oligodendroglioma (older term; still common in clinical notes, but “anaplastic” is no longer the official label). College of American Pathologists+1
High-grade oligodendroglioma (informal description meaning grade 3). NCBI
Types
Oligodendrogliomas are grouped by WHO 2021 as adult-type diffuse gliomas and split by grade and molecular features:
CNS WHO grade 2 – slower-growing oligodendroglioma (IDH-mutant, 1p/19q-codeleted).
CNS WHO grade 3 – faster-growing oligodendroglioma (IDH-mutant, 1p/19q-codeleted) with higher mitotic activity and often microvascular proliferation; this corresponds to the historical term anaplastic oligodendroglioma. PMC+2PMC+2
(Notes: “Anaplastic” is now avoided in formal naming, but many clinicians still use it to mean grade 3. Some grade-3 tumors may also show microvascular proliferation and even necrosis; these findings correlate with more aggressive behavior.) NCBI+1
Causes & risk factors
Strictly speaking, the exact “cause” is unknown for most people. Instead, doctors talk about drivers and risk associations—changes inside tumor cells and a few conditions that raise the chance of a glioma. Here are 20 important ones, each in plain language:
IDH1 or IDH2 mutation (driver event). An early DNA change that rewires cell metabolism and helps start a glioma; it’s required for this diagnosis. PMC
1p/19q codeletion (defining event). Loss of genetic material on the short arm of chromosome 1 and long arm of 19; together with IDH mutation, it defines oligodendroglioma. PMC
TERT promoter mutation. Very common (>80–90%) in IDH-mutant, 1p/19q-codeleted tumors; supports continuous cell division by activating telomerase. PMC+1
CIC gene mutation. A frequent alteration in codeleted tumors that influences cell growth programs. PMC+1
FUBP1 gene mutation. Another recurrent tumor-suppressor alteration associated with oligodendroglioma biology. PMC+1
NOTCH pathway changes (e.g., NOTCH1). Reported in subsets of oligodendroglioma and may affect cell signaling. Wiley Online Library
PI3K/AKT/mTOR pathway alterations (e.g., PIK3CA/PTEN). Less common drivers that can promote growth signaling. (Summarized across genomic series.) Wiley Online Library
CDKN2A/2B homozygous deletion. A poor-prognosis event found in some grade-3 tumors; it disables key cell-cycle brakes. Department of Pathology
Retained ATRX (and low p53) pattern. Not a risk itself but a characteristic of oligodendroglioma compared with astrocytoma (which often loses ATRX); helps pathologists confirm the tumor type. SpringerLink
Prior cranial irradiation. Rarely, past brain radiation can increase later glioma risk. (Association reported for diffuse gliomas.) Cleveland Clinic
Hereditary cancer syndromes (Li-Fraumeni). TP53-related syndrome increases overall glioma risk (not specific to oligodendroglioma). (General neuro-oncology consensus.) PMC
Mismatch repair syndromes (Lynch/Turcot). Raise glioma risk in some families; not specific but recognized. (General guideline discussions.) Nature
Somatic IDH mosaicism disorders (Ollier/Maffucci). Rare disorders with early IDH changes; linked to higher glioma risk. SpringerLink
Age (adult peak 35–50+). Oligodendrogliomas occur mostly in adults; grade-3 skew slightly older than grade-2. PMC+1
Male sex (slight excess). Many series report a modest male predominance. PMC+1
Frontal/temporal lobe location predisposition. Not a “cause,” but these lobes are the common sites where tumors arise. PMC
Telomere biology shifts (TERT-p). The telomerase changes that maintain chromosome ends facilitate long-term tumor growth. PMC
Epigenetic profile (DNA methylation class). Oligodendrogliomas form a distinct methylation class; this profile reflects underlying biology that favors this tumor type. SpringerLink
CIC/FUBP1 haploinsufficiency from 1p/19q loss. The whole-arm codeletion may “dose-reduce” these genes and contribute to tumor development. BioMed Central
General unknown environmental factors. For most patients, no clear outside trigger is found; research continues. (Consensus across reviews.) PMC
Common symptoms
Seizures. Very common first sign, especially with frontal lobe tumors; abnormal electrical activity causes convulsions or brief spells. PMC
Headache. Can come from pressure effects or swelling around the tumor. Cleveland Clinic
Nausea/vomiting. Often accompanies raised intracranial pressure (ICP). Cleveland Clinic
Personality or behavior change. Frontal lobe involvement may cause apathy, disinhibition, or irritability. Columbia Neurosurgery in New York City
Speech or language problems. Tumors in dominant frontal/temporal regions can produce word-finding trouble or aphasia. Columbia Neurosurgery in New York City
Weakness (one side). Involvement of motor pathways leads to loss of strength, clumsiness, or slower movements. Stroke Manual
Numbness or tingling. Sensory cortex or white-matter pathway involvement can cause altered sensation. Stroke Manual
Vision loss or field cuts. Occipital or optic-pathway involvement can reduce visual fields; papilledema can blur vision if ICP is high. Merck Manuals
Double vision. Elevated ICP can cause sixth-nerve palsy and eye movement problems. EyeWiki
Balance or coordination problems. Cerebellar or fronto-parietal pathway involvement affects gait and fine movements. Stroke Manual
Cognitive slowing and memory issues. Diffuse network disruption leads to slower thinking or forgetfulness. Neurology at Washington University
Fatigue and sleep disturbance. Seizures, medications, and tumor burden commonly cause tiredness. (Clinical experience summarized in reviews.) Cancer.gov
Mood or anxiety symptoms. Brain network changes and uncertainty about illness can drive anxiety or depression. (Patient-facing resources concur.) National Brain Tumor Society
Smell/taste changes. If the tumor involves orbitofrontal or temporal networks. Columbia Neurosurgery in New York City
Papilledema (optic disc swelling). A sign of raised ICP seen on eye exam; may cause transient vision dimming. Cleveland Clinic+1
Diagnostic tests
A) Physical examination
Complete neurologic exam. Checks mental status, cranial nerves, strength, reflexes, sensation, coordination, and gait to localize the problem. Abnormalities point clinicians to where the tumor might be. NCBI
General physical and vitals. Identifies systemic clues (e.g., blood pressure elevations with headache from ICP) and fitness for procedures. (Standard practice sources.) Hopkins Medicine
Eye (fundus) exam. Looks for papilledema, which supports raised intracranial pressure from a mass; urgent if present. Cleveland Clinic+1
Bedside visual field testing. Confrontation fields can reveal missing portions of vision from occipital or optic-radiation involvement. (Neuro exam references.) NCBI
B) Manual bedside tests
Pronator drift. A simple arm-holding test that picks up subtle weakness from motor-pathway lesions. meded.ucsd.edu
Romberg test. Checks balance using vision, proprioception, and cerebellar input—instability may reflect sensory or cerebellar pathway issues. meded.ucsd.edu
Finger-to-nose / heel-to-shin. Coordination maneuvers that detect cerebellar or connection problems caused by tumor infiltration. Neurology at Washington University
Brief cognitive screening (e.g., orientation, memory, language). Quick bedside checks help detect cortical dysfunction from frontal/temporal lesions. NCBI
C) Laboratory & pathological tests
Surgical biopsy / resection for histology (H&E). Confirms a diffuse glioma with oligodendroglial features (uniform cells, “chicken-wire” vasculature) and grade-3 activity such as brisk mitoses; microvascular proliferation and necrosis can be seen in higher-grade behavior. NCBI+1
IDH1 R132H immunohistochemistry (IHC). A fast screen for the common IDH1 mutation; highly reliable, with sequencing used when negative/equivocal. BioMed Central+1
1p/19q codeletion testing (FISH/NGS/LOH). Essential to prove oligodendroglioma; required along with IDH mutation to make the diagnosis. PMC
ATRX and p53 IHC. Oligodendrogliomas typically retain ATRX and have lower p53 expression than astrocytomas; this pattern supports the diagnosis. Lippincott Journals
TERT promoter mutation testing. Very common in codeleted oligodendroglioma; helps round out the molecular profile and may carry prognostic value. PMC
MGMT promoter methylation (pyrosequencing/MSP). Often methylated; relevant to prognosis and therapy sensitivity in diffuse gliomas. PMC
Ki-67 (MIB-1) proliferative index. Estimates how quickly tumor cells are dividing; tends to be higher in grade-3 disease. (Pathology reviews.) Department of Pathology
(Advanced profiling often includes DNA methylation class—a genome-wide signature that can resolve difficult cases and, in some settings, can even “establish” the oligodendroglioma class when concordant.) SpringerLink
D) Electro-diagnostic tests
EEG (electroencephalogram). Records brain waves to evaluate seizures common in oligodendroglioma; useful to classify spells and guide anti-seizure therapy, though not tumor-specific. (Standard neuro-oncology practice.) NCBI
Evoked potentials (VEP, SSEP) when relevant. Measure pathway conduction (vision or somatosensory). They’re most useful for surgical planning/monitoring to protect function near eloquent cortex. NCBI+1
Intraoperative neurophysiologic monitoring (SSEPs/MEPs/VEPs). During tumor removal, live monitoring helps surgeons avoid injury to motor, sensory, or visual pathways. PMC+1
E) Imaging tests
MRI brain with and without contrast (gold standard imaging). Shows tumor location, size, and spread along white matter; grade-3 lesions may enhance and often sit in the frontal lobe. PMC
CT head. Useful quickly and for calcifications, which are common in oligodendroglioma. Radiopaedia
MR perfusion (rCBV). Measures tumor blood volume; higher values suggest higher grade and more vascular tumor tissue. J Pathol Transl Med
MR spectroscopy. Looks at brain chemicals; oligodendrogliomas often show high choline (cell turnover) and low N-acetylaspartate (NAA) (neuronal marker). (Imaging reviews.) PMC
Diffusion-weighted MRI. Helps assess cellularity and tumor heterogeneity (lower ADC can suggest higher cellular density). PMC
Amino-acid PET (e.g., FET-PET) when available. Can help distinguish treatment change vs. progression and refine target areas; increasingly used with MRI. SpringerLink
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Last Updated: September 16, 2025.
