"Primitive neuroectodermal tumor.
The most useful pathologic classification for brain tumors is based on embryonic derivation and histologic cell of origin. Tumors are further classified by grading the degree of malignancy within a particular tumor type. This grading is useful in astrocytoma and ependymoma. Criteria that are useful microscopically in grading the degree of malignancy include:
1. Cellular pleomorphism
2. Mitotic index
3. Anaplasia and necrosis
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