Medical Health Encyclopedia

A primary malignant brain tumor is one that originates in the brain itself. Although primary brain tumors often shed cancerous cells to other sites in the central nervous system (the brain or spine), they rarely spread to other parts of the body.

Brain tumors are generally named and classified according to the following:

• the normal brain cells from which they originate, or
• the location in which the cancer develops.

The biologic diversity of these tumors, however, makes classification difficult, and some experts believe that more specific categories are needed.

Categories of Primary Glioma Brain Tumors by Cell Types

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About half of all primary brain tumors are known collectively as gliomas. They are cancerous forms of glial cells, which are the building-block cells of the connective, or supportive, tissue in the central nervous system. There are several glial cells types from which gliomas form and are named:

• Astrocytomas are primary brain tumors derived from astrocytes, which are star-shaped glial cells. Normal astrocytes provide nutrients, support, and insulation for nerve cells and are one of the primary neurologic cells in the body. The malignant astrocytomas called glioblastomas account for 23% of brain tumors and are the most common ones.
• Oligodendrogliomas develop from oligodendrocyte glial cells, which form the protective coatings around nerve cells. Although oligodendrogliomas were thought to represent about 5% of all gliomas, more recent evidence suggests they may comprise about 20% of gliomas. Pure oligodendrogliomas, however, are rare and in most cases they occur in mixed gliomas.
• Ependymomas are derived from ependymal cells, which line the ventricles (fluid-filled cavities) in the lower part of the brain and the central canal of the spinal cord. They constitute about 6% of all primary tumors in the central nervous system. About 30% of these tumors occur in the spinal cord.
• Mixed Gliomas contain a mixture of malignant gliomas. About half of these tumors contain cancerous oligodendrocytes and astrocytes.