Oligodendroglioma

Types and Grades of Oligodendroglioma

Oligodendroglioma is unusual among brain tumors in that its definition is entirely molecular. Two findings must both be present: a mutation in IDH1 or IDH2, and co-deletion of chromosome arms 1p and 19q. A tumor that looks like an oligodendroglioma under the microscope but lacks either finding is classified as something else and is treated differently. Within that single defined tumor type, there are two grades:

Symptoms

Because these tumors grow slowly, the brain adapts as they expand, and seizures are often the only sign for a long time — sometimes months before the tumor is found. Most patients with an oligodendroglioma have had at least one seizure by the time of diagnosis. Other symptoms depend on location. Because these tumors favor the frontal lobes, changes in personality, motivation, attention, or word-finding are common and are easy to attribute to stress or mood before an MRI is obtained. Headaches, weakness, and vision changes can also occur.

The pace of symptoms varies with the tumor’s grade and location. Grade 2 tumors may change little over years, while grade 3 tumors can produce symptoms that progress over weeks to months. Seizure control is often an additional treatment goal. Removing as much tumor as possible improves seizure control in a substantial proportion of patients, and this is one of the reasons surgery is recommended even for a slow-growing tumor.

Diagnosis

Imaging

Evaluation begins with a neurological examination and MRI of the brain with and without contrast. Oligodendrogliomas have a fairly characteristic appearance: they favor the frontal lobes, tend to involve the cortex rather than sitting purely in deep white matter, and often have a heterogeneous, somewhat blurred border. Calcification within the tumor is common and is best seen on CT. None of these features is diagnostic on its own, and imaging cannot substitute for tissue — but together they often tell the team what to expect before surgery.

Molecular Testing

Because these tumors are defined by their molecular features, tissue obtained at biopsy or surgery is essential. A neuropathologist examines the tissue and testing is performed for IDH mutation and for 1p/19q co-deletion using chromosomal microarray or next-generation sequencing.

These molecular results are now part of the formal diagnosis of oligodendroglioma and the final integrated pathology combines the microscopic appearance, the molecular findings, and WHO grade. Supporting findings typically include a TERT promoter mutation, retained ATRX, and mutations in CIC or FUBP1, which together reinforce the diagnosis. National guidelines treat this molecular workup as part of the initial evaluation of all diffuse gliomas.

Planning for Surgery

Because these tumors so often sit in the frontal lobes and involve cortex, functional MRI and diffusion tensor tractography are frequently obtained before surgery to map language, motor, and executive networks and the fiber tracts connecting them. These studies are loaded into the intraoperative navigation system and, when the tumor is close to language territory, confirmed during surgery by direct stimulation.

Treatment

Maximal Safe Surgery

Treatment begins with maximal safe surgical resection, which removes as much tumor as possible and provides the tissue needed for molecular diagnosis. Extent of resection matters more here than the tumor’s slow growth might suggest: more complete removal is associated with longer time to progression and with better seizure control, and in a disease often measured in decades, that difference compounds. The operation is therefore planned around what can be removed safely rather than around what appears most urgent on the scan.

At Atlantic Brain and Spine, oligodendrogliomas near language or motor territory are approached with a combination of techniques. Frameless stereotactic navigation merges the preoperative MRI, functional MRI, and tractography into a three-dimensional map used throughout the case. Awake craniotomy with direct cortical and subcortical stimulation allows language, motor, and cognitive pathways to be identified and tested in real time while the tumor is removed — a technique that matters particularly for these tumors, given how often they involve the frontal lobe in patients who are young, working, and neurologically intact at diagnosis. Continuous intraoperative neurophysiologic monitoring tracks these pathways when surgery is performed under general anesthesia.

What Happens After Surgery?

Radiation, Chemotherapy & Targeted Therapy

Oligodendrogliomas differ from most other gliomas. Two large randomized trials followed patients for more than a decade and found that adding PCV chemotherapy — a three-drug combination — to radiation roughly doubled median survival in 1p/19q co-deleted tumors. No other diffuse glioma has results of that magnitude. Temozolomide is often substituted for PCV, though its long-term evidence in these tumors is less established.

Vorasidenib, an oral IDH inhibitor approved in 2024, is an additional option for eligible patients with residual or recurrent grade 2 disease and can delay the need for radiation and chemotherapy.