Results show the evidence is insufficient to make a reliable decision. The relative effectiveness of surgical resection compared to biopsy for people with malignant glioma (high-grade) is unknown.For high-grade gliomas, a 2003 meta-analysis compared radiotherapy with radiotherapy and chemotherapy. It showed a small but clear improvement from using chemotherapy with radiotherapy. A 2019 meta-analysis suggested that for people with less aggressive gliomas, radiotherapy may increase the risk of long term neurocognitive side effects. Whilst, evidence is uncertain on whether there are long term neurocognitive side effects associated with chemoradiotherapy.Temozolomide is effective for treating Glioblastoma Multiforme (GBM) compared to radiotherapy alone. A 2013 meta-analysis showed that Temozolomide prolongs survival and delays progression, but is associated with an increase in side effects such as blood complications, fatigue, and  infection. For people with recurrent GBM, when comparing temozolomide with chemotherapy, there may be an improvement in the time-to-progression and the persons quality of life, but no improvement in overall survival, with temozolomide treatment. Evidence suggests that for people with recurrent high-grade gliomas who have not had chemotherapy before, there are similar survival and time-to-progression outcomes between treatment with temozolomide or the chemotherapy multidrug known as PCV (procarvazine, lomustine and vincristine).A mutational analysis of 23 initial low-grade gliomas and recurrent tumors from the same patients has challenged the benefits and usage of Temozolomide. The study showed that when lower-grade brain tumors of patients are removed and patients are further treated with Temozolomide, 6 out of 10 times the recurrent tumors were more aggressive and acquired alternative and more mutations.
Oligodendrogliomas: oligodendrocytes
Brainstem glioma: develop in the brain stem
Optic nerve glioma: develop in or around the optic nerve
Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia

By grade
Gliomas are further categorized according to their grade, which is determined by pathologic evaluation of the tumor. The neuropathological evaluation and diagnostics of brain tumor specimens is performed according to WHO Classification of Tumours of the Central Nervous System. Biologically benign gliomas [WHO grade I] are comparatively low risk and can be removed surgically depending on their location 
Low-grade gliomas [WHO grade II] are well-differentiated (not anaplastic);  these tend to exhibit  benign tendencies and portend a better prognosis for the patient. However, they have a uniform rate of recurrence and increase in grade over time so should be classified as malignant. High-grade [WHO grades III–IV] gliomas are undifferentiated or anaplastic; these are malignant and carry a worse prognosis.Of numerous grading systems in use, the most common is the World Health Organization (WHO) grading system for astrocytoma, under which tumors are graded from I (least advanced disease—best prognosis) to IV (most advanced disease—worst prognosis). By location
Gliomas can be classified according to whether they are above or below a membrane in the brain called the tentorium. The tentorium separates the cerebrum (above) from the cerebellum (below). The supratentorial is above the tentorium, in the cerebrum, and mostly found in adults (70%). The infratentorial is below the tentorium, in the cerebellum, and mostly found in children (70%). The pontine tumors are located in the pons of the brainstem.