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Gliomas are named according to the specific type of cell they share histological features with, but not necessarily originate from. The main types of gliomas are:
Ependymomas — ependymal cells.
Astrocytomas — astrocytes (glioblastoma multiforme is the most common astrocytoma).
Oligodendrogliomas — oligodendrocytes.
Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia.
Gliomas are further categorized according to their grade, which is determined by pathologic evaluation of the tumor.
Low-grade gliomas [WHO grade II] are well-differentiated (not anaplastic); these are NOT benign but still portend a better prognosis for the patient.
High-grade [WHO grade 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).