• Brain Tumor Overview

    One way to classify a brain tumor is by the location from which it originates. Tumors that begin growing in the brain are known as primary brain tumors. Tumors that begin growing elsewhere in the body and then spread to the brain are referred to as metastatic, or secondary, brain tumors.

    Metastatic brain tumors are far more common than primary brain tumors. According to the American Brain Tumor Association, of the 190,000+ Americans diagnosed with a brain tumor each year, slightly more than 40,000 have primary tumors, while the remaining 150,000 have metastatic tumors.

    Primary Brain Tumors

    There are more than 120 different types of brain tumors, each of which is classified as either benign (low-grade) or malignant (high-grade). Cells from high-grade tumors look more abnormal and generally grow faster than cells from low-grade tumors. Neuropathologists are the specialists who examine brain tumors under a microscope to determine the tumor grade, based on the cells' appearance. Brain tumors range from grade I (low-grade) to IV (high-grade).

    Common Characteristics

    Typically, the following is true for each type of brain tumor:

    Benign (low-grade)


    Malignant (high-grade)

    • Do not contain cancer cells; however, in very rare cases, can become malignant
    • Contain cancer cells
    • Slow-growing
    • Grow rapidly
    • Have clearly defined borders or edges
    • Multiply and invade surrounding healthy brain tissue
    • Look like normal brain cells
    • Have an abnormal appearance when compared to normal brain cells
    • Have the potential to be life-threatening due to pressure on the brain because the skull cannot expand to accommodate a growing tumor
    • Often life-threatening
    • Can be surgically removed and rarely grow back
    • Even when surgically removed, often grow back

    The Naming of Primary Brain Tumors

    Primary brain tumors are named according to the type of cells or part of the brain from which they originate. The most common primary brain tumors are gliomas. Gliomas arise from glial cells, or the supportive and connective cells of the central nervous system that surround neurons and provide support for, and insulation between, them. The main types of gliomas include the following:

    • Astrocytoma: Tumor that arises from star-shaped glial cells called astrocytes. In adults, astrocytomas begin most commonly in the cerebrum, or the largest and uppermost portion of the brain, which is responsible for all thought, judgment, memory and association. Specialized names for astrocytomas include anaplastic astrocytomas (grade III) and glioblastoma multiforme (grade IV).
    • Oligodendroglioma: Rare tumor arising from the cells that produce the fatty substance (myelin) that covers and protects nerves. Oligodendrogliomas usually begin in the cerebrum, grow slowly and typically do not spread to surrounding brain tissue. They are most common in middle-aged adults.
    • Brainstem glioma: Tumor that begins in the lowest part of the brain and is most often diagnosed in young children and middle-aged adults.
    • Ependymoma: Tumor that arises from the cells that line the ventricles (central canal) of the spinal cord. Ependymomas are most commonly found in children and young adults.

    Some types of brain tumors do not begin in glial cells. The most common of these tumors include the following:

    • Meningioma: Tumor that arises in the meninges, or three-layer connective tissue membrane that covers the brain and spinal cord. Meningiomas are the most common type of benign (low-grade) brain tumor and tend to grow slowly.
    • Pituitary tumor: Tumor that arises from epithelial cells of the pituitary gland (located at the base of the brain) and can cause endocrine dysfunction.
    • Medulloblastoma: Tumor that usually arises in the cerebellum, or the portion of the brain that is located in the back of the head, between the cerebrum and brainstem, and controls balance and other complex motor functions. Medulloblastomas are the most common brain tumors in children. They are sometimes called primitive neuroectodermal tumors (PNET).
    • Schwannoma: Tumor arising from a Schwann cell, or a cell that lines the nerve in the inner ear that controls balance and hearing. Schwannomas are also called acoustic neuromas. They occur most often in adults.
    • Craniopharyngioma: Tumor that grows at the base of the brain, near the pituitary gland, and is found most commonly in children.
    • Germ cell tumor of the brain: Tumor that arises from a germ cell, or a reproductive cell that has traveled to the brain. Most germ cell tumors that arise in the brain affect people under the age of 30. A germinoma is the most common type of germ cell tumor of the brain.
    • Pineal region tumor: Rare brain tumor that arises on or near the pineal gland, which is located between the cerebrum and the cerebellum.

    Metastatic Brain Tumors

    Metastatic brain tumors (secondary brain tumors) start as cancer cells in another part of the body and metastasize, or spread, to the brain through the blood stream. The most common types of tumors that spread to the brain are lung, breast, colon and kidney cancers, as well as malignant melanoma (skin cancer). According to the Brain Tumor Society, brain metastases are the most common complication of cancer, occurring in 20 to 40 percent of all oncology patients.

    The above information was adapted from the National Cancer Institute's (NCI's) Web site.

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