Brain tumor is any intracranial tumor consisting of abnormal and uncontrollably dividing cells, which are commonly found within the brain tissue (neurons, astrocytes, oligodendrocytes, ependimalnye cells, lymphatic tissue, blood vessels) in the tissues of the cranial nerves (myelin-producing Schwann cells) in the meninges, bones, skull, pituitary and pineal gland, or spreading of the tumors, which is primarily localized in other organs (metastatic tumors). Primary (true) brain tumors are usually localized in the posterior cranial fossa in children and in the anterior two thirds of the cerebral hemispheres in adults, although they can affect any of the brain. Currently there are about 120 types of brain tumors. Brain tumors is relatively rare - about 1,5% among all types of tumors. In Russia in 2002, there were 5320 new cases of brain tumors, which accounted for 36% more than the v1993 year. The prevalence of brain tumors in Russia is 3.7 per 100 000 population. Thus, approximately 13,000 deaths per year occur due to brain tumors. 

Classification of tumors. 

By origin all brain tumors can be divided into primary and secondary

Primary tumor 
The main types of tumors in this group: astrocytoma, pilocytic astrocytoma, dizembrioplastichesky neuroepithelial tumor, oligodendrogliomas, ependymoma, glioblastoma multiforme, mixed gliomas, oligoastrotsitomy, medulloblastoma, retinoblastoma, meningiomas, pituitary tumors, tumors of the pineal gland (pinealomy) and neurinomas of the auditory nerve. 

Most primary tumors derived from neuroglia (gliomas), astrocytes (astrocytomas), oligodendrocytes (oligodendrogliomas), or ependimalnyh cells (ependymoma). Also, there are mixed forms containing astrocytes and oligodendroglialny components.These tumors are called mixed-cell or oligoastrotsitomami. In addition, can be found mixed glio-neural tumors, containing the elements of glial cells and neurons, such gangliogliomy, dizembrioplastichesky neuroepithelial tumor, and tumor, occurring only from the neurons (gangliotsitoma, central gangliotsitoma). 

In terms of histological structure of astrocytomas, oligodendrogliomas and oligoastrotsitomy may be benign or malignant. Glioblastoma multiforme is the most aggressive variant of malignant gliomas. On the opposite side of the spectrum of tumors located pilocytic astrocytoma - the most benign flows astrocytic tumor. Most of them are localized in the posterior cranial fossa in children and adolescents and characterized clinically favorable course and prognosis. 

Another example of primary intracranial tumors is a primary lymphoma of the brain, which is a non-Hodgkin's lymphoma and is most common in at immunodeficiencies, such as AIDS. Unlike other tumors, primary brain tumors rarely metastasize, and in the case of metastatic spread to the bones of the skull and spinal canal, or through the bloodstream to other organs. 
The secondary (metastatic) tumors. 

Secondary brain tumors originate from malignant primary tumors at other sites (metastasis). The incidence of secondary tumors is higher than the primary. Most of brain metastases in the lung, skin (malignant melanoma), kidney (hypernephroma), breast and colon. These tumor cells enter the brain via the bloodstream.