2.1 Classification and Generalities
It would be more correct to call them intracranial tumors. Some of them originate from brain tissue and cells, others from vessels, from meninges, from cranial bones, from the glandular cells of the pituitary and from the cranial nerves. They have the common characteristic to grow in a rather rigid box, the skull, thus compressing the healthy brain tissue.
The first distinction is between intraxial tumors, i.e. those that grow from brain cells or from cells inside the brain tissue, and extraxial tumors, i.e. all the other ones.

Intraxial tumors
· Gliomas, which are subdivided in astrocytomas, oligodendrogliomas, ependymomas and glioblastomas.
· Neurocytomas, Gangliogliomas
· Lymphomas
· Pinealomas
· Hemangioblastomas
· Medulloblastomas
· Papillomas
· Lipomas

Extraxial tumors are those that originate from meninges, skull, nerves, pituitary and so on, but that grow inside the skull.
· Meningiomas
· Neurinomas
· Pituitary Adenomas
· Craniopharyngiomas
· Epidermoids
· Angiomas
· Chordomas, Chondromas and Chondrosarcomas
· Osteomas
· Metastases, i.e. all those intracranial secondary locations of tumors originating in other parts of the body: lung, breast, gastrointestinal and genitourinary tracts and skin (melanoma).

The same kind of tumors may be found in the other parts of the CNS: spine and spinal cord. Spinal tumors may also be classified anatomically:
·Extradural spinal tumors: those of the bone and spine ligaments (metastases, chordomas, osteomas).
·Intradural extramedullary tumors: those located between the dura and the spinal cord (mainly meningiomas, neurinomas).
·Intramedullary tumors: those growing inside the cord (gliomas, lipomas, ependymomas, hemangioblastomas).