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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.

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).

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

Common Characteristics Table
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

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 (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.

Frequently Asked Questions (FAQs)

The brain contains three main structures: the cerebrum, cerebellum and brainstem.

Cerebrum

The cerebrum is the largest area of the brain. It is divided into two halves referred to as the right and left hemispheres. The right hemisphere controls the left side of the body, and vice versa. Each hemisphere is composed of four sections-called lobes-as follows:

Cerebrum Table
Description/Location Responsibilities
Frontal lobe Front portion of the cerebral hemisphere; located behind the forehead
  • Emotional control center
  • Home to our personality
  • Motor function control
  • Involvement in problem solving, memory, judgment and language
Parietal lobe Upper central portion of the cerebral hemisphere; located behind the frontal lobe
  • Sensation and perception
  • Integration of sensory input, primarily with the visual system
  • Assistance with making calculations, reading and writing
Occipital lobe Back portion of the cerebral hemisphere; located beneath the parietal lobe and behind the temporal lobe
  • Vision control
Temporal lobe Lower portion of the cerebral hemisphere; located beneath the frontal and parietal lobes
  • Hearing
  • Language comprehension (left temporal lobe)
  • Long-term memory
  • Smell

Cerebellum

The cerebellum is the second largest part of the brain. It is located at the back of the head, between the cerebrum and the brainstem. The cerebellum is responsible for coordinating muscle groups for smooth and steady movements (e.g., balance for walking and standing) and controlling other complex motor functions.

Brainstem

The brainstem is located at the base of the brain and connects the cerebrum with the spinal cord. It provides the major route by which the upper portions of the brain send information to, and receive information from, the spinal cord and peripheral nerves. The brainstem is where the majority of the cranial nerves-including those that control hearing, vision, sense of smell and balance-are located. In addition, it contains conduction pathways going from the spinal cord to the brain that transmit messages related to movement and the senses. The brainstem also controls involuntary functions (e.g., breathing, heartbeat, sleep/wake cycle).

The three main parts of the brainstem are the midbrain, pons and medulla oblongata. The midbrain is a short, narrow segment located toward the front of the brainstem and is involved with functions such as vision, hearing, eye movement, and voluntary motor function. The pons-which is Latin for bridge-“bridges” the portion of the central nervous system between the midbrain and medulla oblongata. It is in the pons that nerve cells cross from one side of the brain to control the opposite side of the body. The medulla oblongata is located at the lowest part of the brainstem. In addition to controlling essential life functions such as respiration, heart rate and blood flow, the medulla oblongata is also involved with sound localization (the listener’s ability to identify the origin of a detected sound) and function control of coughing, sneezing, swallowing, blinking, vomiting and the sucking reflex.

CT (computed tomography) scan uses an X-ray machine linked to a computer to take a series of detailed pictures of the head to reveal any tumors present in the brain. MRI (magnetic resonance imaging) uses magnetism, radio waves and a computer to produce detailed images of the brain. With both CT and MRI, the patient may receive an injection of a special dye to make abnormal brain tissue easier to identify in the pictures.

Generally speaking, CT is used more frequently than MRI because it is more widely available, is less expensive and can be used on patients who cannot undergo MRI-including those with cardiac monitors or pacemakers, permanent surgical clips, or any metal fragments within their body-due to potential problems that may be caused by the magnetic fields. Compared to CT, however, MRI offers the following advantages:

  • Does not use radiation to produce images
  • Has higher accuracy in distinguishing between healthy and diseased tissue
  • Provides pictures from different angles, allowing physicians to develop 3-D images
  • Produces better pictures of tumors located close to bone

Two practitioners talking man light blue shirt woman lab coat blue screen images behind themPrimary brain tumors arise in brain tissue, whereas metastatic, or 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).

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.

Following a biopsy or tumor resection, a neuropathologist will examine a brain tumor under a microscope to determine the tumor grade, based on the cells’ appearance. Cells from high-grade tumors look more abnormal and generally grow faster than cells from low-grade tumors. Brain tumors range from grade I (low-grade) to IV (high-grade). The tumor grade helps guide physicians in determining the optimal treatment for each patient (e.g., level and intensity of treatment required).

Brain tumors are cancerous in some cases, but not all. Malignant (high-grade) brain tumors contain cancer cells, but benign (low-grade) brain tumors do not. In very rare cases, some benign brain tumors later develop into cancer.

Two of the most common forms of brain cancer are metastatic brain tumors (cancers that have spread to brain tissue from elsewhere in the body) and glioblastoma multiforme, or GBM (the most aggressive form of gliomas-primary brain tumors arising from glial cells in the brain).

Generally speaking, a benign tumor or condition is not harmful. However, that is not the case with anything growing in the brain, including benign tumors. There is a confined space within the skull, meaning it cannot expand to accommodate a growing tumor. Therefore, as they grow, benign brain tumors have the potential to become life threatening due to pressure on the brain. Fortunately, benign tumors generally grow slowly and rarely grow back after being surgically removed. Depending on the location and size of the tumor, however, benign brain tumors can sometimes be difficult to treat.

When a tumor is referred to as “stable,” it means that the tumor cells are in a phase in which they have stopped growing or multiplying. Such stability may be temporary or permanent. When the tumor has actually been destroyed, and the area it occupied in the brain is composed only of dead tissue (necrosis), no new growth will occur. However, if tumor cells remain, it is possible that they will begin growing again at a later date.

Recurrent tumors are those that grow back after being surgically removed or stabilized. They can be either benign or malignant, although the latter is more common.

Recurrent brain tumors often appear in the same area where the original tumor developed, but they may also develop in another part of the brain or spinal cord. It is impossible to predict whether or not a tumor will recur, and therefore, routine follow-ups (e.g., MRIs) are a necessity for all brain tumor patients.