There are primary and secondary brain tumors. Tumors that begin in brain tissue are known as primary tumors. Secondary tumors are when cancer spreads from another site to the brain, which is called metastasis. Brain tumors are classified by the type of tissue in which they begin. The most common brain tumors are gliomas.

Types of gliomas:

• Astrocytomas arise from small, star-shaped cells called astrocytes. They may grow anywhere in the brain or spinal cord. In adults, astrocytomas most often arise in the cerebrum. In children, they occur in the brain stem, the cerebrum and the cerebellum. A grade III astrocytoma is sometimes called anaplastic astrocytoma. A grade IV astrocytoma is usually called glioblastoma multiforme.
• Brain stem gliomas occur in the lowest, stem-like part of the brain. The brain stem controls many vital functions. Tumors in this area generally cannot be removed. Most brain stem gliomas are high-grade astrocytomas.
• Ependymomas usually develop in the lining of the ventricles. They also may occur in the spinal cord. Although these can develop at any age, they are most common in childhood and adolescence.
• Oligodendrogliomas arise in the cells that produce myelin, the fatty covering that protects nerves. These tumors usually arise in the cerebrum. They grow slowly and usually do not spread into surrounding brain tissue. Oligodendrogliomas are rare. They occur most often in middle-aged adults but have been found in people of all ages.

There are other types of brain tumors that do not begin in glial tissue. Some of the most common are:

• Medulloblastomas were once thought to develop from glial cells. However, recent research suggests that these tumors develop from primitive nerve cells that normally do not remain in the body after birth. For this reason, medulloblastomas are sometimes called primitive neuroectodermal tumors (PNET). Most medulloblastomas arise in the cerebellum; however, they may occur in other areas as well. These tumors occur most often in children and are more common in boys than in girls.
• Meningiomas grow from the meninges. They are usually benign. Because these tumors grow very slowly, the brain may be able to adjust to their presence; meningiomas often grow quite large before they cause symptoms. They occur most often in women between 30 and 50 years of age.
• Schwannomas are benign tumors that begin in Schwann cells, which produce the myelin that protects the acoustic nerve (the nerve of hearing). Acoustic neuromas are a type of schwannoma. They occur mainly in adults. These tumors affect women twice as often as men.
• Craniopharyngiomas develop in the region of the pituitary gland near the hypothalamus. They are usually benign; however, they are sometimes considered malignant because they can press on or damage the hypothalamus and affect vital functions. These tumors occur most often in children and adolescents.
• Germ cell tumors arise from primitive sex cells, or germ cells. The most frequent type of germ cell in the brain is the germinoma.
• Pineal region tumors occur in or around the pineal gland, a tiny organ near the center of the brain. The tumor can be slow growing (pineocytoma) or fast growing (pineoblastoma). The pineal region is very difficult to reach, and these tumors often cannot be removed.