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Tumor Categories
Glioma
A diffuse brain tumor arising from glial cells. Genetic testing shapes both the diagnosis and what follows surgery.
MEMORIAL GÖZTEPEBrain Tumor Surgery
Glioma is a general term for tumors that arise from the brain's glial cells, the supportive tissue that surrounds and nourishes neurons. Several distinct tumor types fall under this umbrella, each with its own behavior and outlook. This page covers the diffuse gliomas that present as WHO Grade 2 or Grade 3 tumors: IDH-mutant astrocytomas and IDH-mutant, 1p/19q-codeleted oligodendrogliomas. These typically affect younger adults, often in their 20s to 40s, and are different from glioblastoma (IDH-wild type, Grade 4) and from pilocytic astrocytoma (WHO Grade 1), which are covered on their own pages.
These tumors infiltrate the surrounding brain tissue diffusely, often spreading along white matter tracts without a clear border separating tumor from normal brain. That's part of what makes a complete cure difficult even when imaging shows no visible tumor left behind. Since the WHO's 2021 classification update, a diffuse glioma is defined as much by its molecular profile as by how it looks under the microscope: two tumors that appear identical to a pathologist can carry very different outlooks depending on their genetic makeup.
Grade 3 tumors behave more aggressively and sit closer to glioblastoma in their clinical course than Grade 2 tumors do, and even within Grade 2 and Grade 3, molecular testing has as much influence on prognosis and treatment as the grade itself.
Unlike glioblastoma, where headaches often dominate, the most common first symptom of a diffuse glioma is a seizure, since these tumors frequently sit close to the cortex. Other symptoms depend on the tumor's location.
MRI is the starting point, typically supplemented with advanced sequences that help characterize the tumor before surgery: MR spectroscopy, perfusion imaging, DTI tractography to map white matter pathways, and functional MRI to localize speech and motor areas when the tumor sits near them. A definitive diagnosis requires tissue: the pathology and molecular testing of tissue obtained at surgery. IDH mutation status is required to confirm the diagnosis, 1p/19q co-deletion distinguishes oligodendroglioma from astrocytoma, MGMT methylation status helps predict chemotherapy response, and CDKN2A/B deletion status can upgrade the tumor's grade regardless of how it looks under the microscope.
Surgery is the standard first step for a diffuse glioma. The goal is maximal safe resection, guided by neuronavigation, intraoperative ultrasound, and continuous neuromonitoring; when the tumor sits near eloquent areas such as speech or motor cortex, awake craniotomy with cortical and subcortical mapping is used to protect function while removing as much tumor as safely possible. In select cases, this extends to a supratotal resection, going beyond the visible tumor margin into functionally confirmed safe tissue, which has been shown to reduce recurrence and delay malignant transformation.
Some lesions look suspicious on imaging but aren't clearly diagnostic, or sit in a location too deep or too risky for safe resection. In these less common situations, a stereotactic biopsy may be used to obtain tissue for diagnosis; it isn't a therapeutic procedure in itself, but it confirms what the tumor is and guides everything that follows.
What follows surgery depends on the molecular and pathological findings, and is decided through a multidisciplinary discussion involving neurosurgery, neuro-oncology, and radiation oncology. Some Grade 2 tumors with favorable molecular features are followed with observation alone after surgery. Grade 3 tumors, or Grade 2 tumors with less favorable molecular findings, are generally treated with radiotherapy, chemotherapy, or both.
Because these tumors can transform to a higher grade over time, lifelong regular MRI follow-up is essential and should never be discontinued, even years after surgery when the patient feels well.
Explore how the decision is made for glioma, and what a typical treatment course looks like.
MRI, often with spectroscopy, perfusion, and DTI tractography, defines the tumor and its relationship to functional pathways.
The tumor's proximity to speech, motor, and other functional areas determines how surgery is planned. Tap a profile to see more.
Regular MRI continues indefinitely, since these tumors can transform to a higher grade over time even after a good initial response.
Imaging (including functional MRI and DTI tractography when the tumor sits near eloquent areas), labs, anesthesia clearance, and surgical planning.
Maximal safe resection is carried out with neuronavigation, intraoperative ultrasound, and continuous neuromonitoring; awake craniotomy with mapping is used when the tumor is near eloquent cortex. An early MRI is obtained that same night to confirm the extent of resection. Larger tumors or cases with significant brain swelling may warrant a night of ICU observation afterward for close monitoring.
Neurological exam, pain control, and gradual mobilization under close observation.
Patients with a stable neurological exam are discharged with instructions.
Pathology is typically back within about a week; the fuller molecular workup (IDH status, 1p/19q co-deletion, MGMT methylation, CDKN2A/B) may take a few more weeks. The multidisciplinary team then finalizes whether observation or radiotherapy/chemotherapy follows.
Follow-up MRI continues at regular intervals indefinitely, since these tumors can transform to a higher grade over time.
Shown for a typical, uncomplicated case. Individual treatment course may vary.