A brain tumor is any intracranial tumor created by abnormal and uncontrolled cell
division, normally either in the brain itself (neurons, glial cells (astrocytes,
oligodendrocytes, ependymal cells), lymphatic tissue, blood vessels), in the
cranial nerves (myelin-producing Schwann cells), in the brain envelopes (meninges),
skull, pituitary and pineal gland, or spread from cancers primarily located
in other organs (metastatic tumors). Primary (true) brain tumors are commonly
located in the posterior cranial fossa in children and in the anterior two-thirds
of the cerebral hemispheres in adults, although they can affect any part of
the brain. In the United States in the year 2005, it was estimated that there
were 43,800 new cases of brain tumors (Central Brain Tumor Registry of the United
States, Primary Brain Tumors in the United States, Statistical Report, 2005
- 2006), which accounted for 1.4 percent of all cancers, 2.4 percent of all cancer
deaths, and 20–25 percent of pediatric cancers.Ultimately, it is estimated
that there are 13,000 deaths/year as a result of brain tumors.
Tumors
occurring in the brain include: astrocytoma, pilocytic astrocytoma, dysembryoplastic
neuroepithelial tumor, oligodendrogliomas, ependymoma, glioblastoma multiforme,
mixed gliomas, oligoastrocytomas, medulloblastoma, retinoblastoma, neuroblastoma,
germinoma and teratoma.
Most primary brain tumors originate
from glia (gliomas) such as astrocytes (astrocytomas), oligodendrocytes (oligodendrogliomas),
or ependymal cells (ependymoma). There are also mixed forms,
with both an astrocytic and an oligodendroglial cell component. These are called
mixed gliomas or oligoastrocytomas. Plus, mixed glio-neuronal tumors (tumors
displaying a neuronal, as well as a glial component, e.g. gangliogliomas, disembryoplastic
neuroepithelial tumors) and tumors originating from neuronal cells
(e.g. gangliocytoma, central gangliocytoma) can also be encountered.
Other
varieties of primary brain tumors include: primitive neuroectodermal
tumors (PNET, e.g. medulloblastoma, medulloepithelioma, neuroblastoma, retinoblastoma,
ependymoblastoma), tumors of the pineal parenchyma (e.g. pineocytoma, pineoblastoma),
ependymal cell tumors, choroid plexus tumors, neuroepithelial tumors
of uncertain origin (e.g. gliomatosis cerebri, astroblastoma), etc.
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