A glioma is a type of tumor that starts in the brain or spine. It is called a glioma because it arises from glial cells. The most common site of gliomas is the brain.

Gliomas are classified by cell type, by grade, and by location.

By type of cell

Gliomas are named according to the specific type of cell they most closely resemble. 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.
[edit]By grade

Gliomas are further categorized according to their grade, which is determined by pathologic evaluation of the tumor.

Low-grade gliomas are well-differentiated (not anaplastic); these are benign and portend a better prognosis for the patient.
High-grade 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.

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.
supratentorial: Above the tentorium, in the cerebrum, mostly in adults (70%). Senator Edward M. Kennedy’s brain tumor, for example was supratentorial, in the parietal area in the upper part of the left side of his brain, above the ear.
infratentorial: Below the tentorium, in the cerebellum, mostly in children (70%)
Pontine: Located in the pons of the brainstem; The brain stem has three parts (Pons, midbrain and the medulla). The Pons controls critical functions such as breathing making surgery extremely dangerous.


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