Definition of Brain tumor - adults:

A primary brain tumor is a group (mass) of abnormal cells that start in the brain. This article focuses on primary brain tumors in adults.

See also:

• Brain tumor - metastatic (cancer that has spread to the brain)
• Brain tumor - children

Causes, incidence, and risk factors:

Primary brain tumors include any tumor that starts in the brain. Tumors may be confined to a small area, invasive (spread to nearby areas), benign (not cancerous), or malignant (cancerous).

Tumors can directly destroy brain cells. They can also indirectly damage cells by producing inflammation, compressing other parts of the brain as the tumor grows, causing swelling in the brain, and increasing pressure within the skull.

Brain tumors are classified depending on the exact site of the tumor, the type of tissue involved, benign or malignant tendencies of the tumor, and other factors. Primary brain tumors can arise from the brain cells, the meninges (membranes around the brain), nerves, or glands.

The cause of primary brain tumors is unknown. This is because they are rare, there are many types, and there are many possible risk factors that could play a role. Exposure to some types of radiation, head injuries, and hormone replacement therapy may be risk factors, as well as many others. The risk of using cell phones is hotly debated.

Some inherited conditions increase the risk of brain tumors, including neurofibromatosis, Von Hippel-Lindau syndrome, Li-Fraumeni syndrome, and Turcot syndrome.

Tumors may occur at any age, but many specific tumors have a particular age group in which they are most common. In adults, gliomas and meningiomas are most common.

SPECIFIC TUMOR TYPES

• Astrocytic tumors include astrocytomas (less malignant), anaplastic astrocytomas, and glioblastomas (most malignant). Astrocytomas can progress over time more malignant forms, including glioblastoma.
• Oligodendroglial tumors also can vary from low grade to very malignant. Some primary brain tumors are composed of both astrocytic and oligodendrocytic tumors. These are called mixed gliomas.
• Glioblastomas are the most aggressive type of primary brain tumor. These may or may not arise from a prior lower grade primary brain tumor.

Meningiomas are another type of brain tumor. These tumors:

• Occur most commonly between the ages of 40 - 70
• Much more common in women.
• While 90% are benign, they still may cause devastating complications and death due to their size or location. Some are cancerous and aggressive.

Other primary brain tumors in adults are rare and include ependymomas, craniopharyngiomas, pituitary tumors, primary lymphoma of the brain, pineal gland tumors, and primary germ cell tumors of the brain.