What is a brain tumor?

The brain--a soft, spongy mass of nerve and supportive tissue--sits inside the skull. The base of the brain is connected to the spinal cord. Brain tumors are tumors that grow in the brain. A tumor is an abnormal growth caused by cells reproducing themselves in an uncontrolled manner.

A benign brain tumor consists of benign (harmless) cells and has distinct boundaries. Surgery alone may cure this type of tumor

A malignant brain tumor is life-threatening. It may be malignant because it consists of cancer cells, or it may be called malignant because of its location. In other words, a brain tumor composed of benign cells--but located in a vital area--is still considered malignant. A malignant brain tumor made up of cancerous cells may spread or seed (metastasize) to otherlocations in the brain or spinal cord. It can invade and destroy healthy tissue so it cannot function properly. Malignant tumors grow the way a plant does, with "roots" invading various tissues. Or, they can shed cells that travel to distant parts of the brain. Some cancerous tumors, however, remain localized. Malignant brain tumors seldom metastasize outside the brain and spinal cord.

The bones of the skull hide brain tumors. The doctor can not feel or see them during a routine examination. Scans produce pictures that suggest a particular type of tumor. Only a sample of tumor examined under a microscope can provide an exact diagnosis . If this type of examination is not possible, an educated assumption is made based on available test results.

Primary brain tumors occur in people of all ages. Metastatic brain tumors are much more common in adults. Accurate statistics for the frequency and outcome of brain tumors are not available. It is estimated These statistics are based on the 1989 United States population of 249,000,000 people, and an incidence rate of 8.2 per 100,000 for primary brain tumors, and an incidence rate of 8.3 per 100,000 for metastatic brain tumorsthat in the United States in 1990, there were 20,500 new cases of primary brain tumor . New cases of metastatic brain tumor diagnosed in 1990 were estimated to be at least 20,700. The combined estimate of 41,200 new cases of brain tumor included both benign and malignant brain tumors.

Naming Tumors

Tumor names depend on where the tumor originated, its pattern of growth, and whether it is cancerous or not. The following are some general names of tumors:

  • ADENOMA A usually benign tumor arising from a gland; for example, pituitary adenoma.
  • BLASTOMA A malignant tumor whose cells have undeveloped(embryonic) characteristics; for example, medulloblastoma or glioblastoma multiforme.
  • CARCINOMA A malignant tumor that arises from skin or the lining of the digestive, respiratory,and urogenital systems; for example, lung cancer (small cell carcinoma) or colon cancer (adenocarcinoma).
  • SARCOMA A malignant tumor that arises from connective tissue, blood vessels, or the lymphsystem; for example, osteosarcoma.
  • GLIOMA The general name for a tumor that arises from the supportive tissue of the brain; forexample, astrocytoma or oligodendroglioma. It may be benign or malignant.

How are brain tumors diagnosed?

The diagnosis of a brain tumor begins in the doctor's office. The doctor begins by asking the patient a number of questions to get a complete history of the symptoms. Then he or she will do a basic neurological examination. Neurological specialists perform several diagnostic tests for brain tumors. These include:

  • SCANS - Scans are done in place of conventional x-rays, which are not able to show tumors behind bone. Different types of imaging devices are used to perform brain scans. The most commonly used devices for both diagnosis and follow-up are the Computerized Axial Tomographer (CT or CAT) and the Magnetic Resonance Imager (MRI). Positron Emission Tomography (PET) is also available, but it tends to be used more for research than for routine diagnosis.
  • CT or CAT - This machine combines an x-ray device and computer. Before the CT scan begins, the person being examined is given an injection of a special dye (contrast) material. This dye helps make any abnormal tissue more evident. Then the patient lies on a table that slides into a doughnut-shaped opening.While the patient lies very still, the CT scanner circles the head, and x-rays penetrate the brain.Absorption of the x-rays varies with the type of tissue penetrated. A ring of detectors measures theamount of rays remaining after their path through the brain. Thousands of thin cross section readings are fed into the computer which then transforms the data into a picture.
  • MRI - The MRI is a tunnel-shaped piece of equipment. The person being examined lies on a table that slides into the tunnel. Inside the scanner, a magnetic field surrounds the patient's head while radio energy is beamed to the area. No x-rays are used. The magnetic field causes atoms in the brain to change direction. The radio waves cause another change of direction. When the beam stops, the atoms relax and return to their original position. During relaxation, the atoms give off signals in differing amounts and at different intervals of time. Antennas pick up these signals and feed them into a computer which assembles a picture. Because different atoms have their own characteristic radio signals, the computer can distinguish between healthy and diseased tissue. A contrast material (Gadolinium) may be used with the MRI. Because the MRI ignores bone which can obstruct CT images, this device provides clearer pictures of tumors located near bone. The MRI can also produce a wider variety of image angles. The MRI can detect edema but has difficulty distinguishing edema from tumor. Some tumors have calcification, which the MRI cannot detect. MRI imaging takes longer than a CT scan, and it is very noisy. Patients with cardiac monitors, pacemakers, or surgical clips cannot take an MRI because of the magnetic fields.
  • PET - In a PET scan, a low-dose radionuclide produced by a cyclotron (an atom smashing radiation unit) is coupled to a chemical such as glucose (a sugar) and injected into the patient. The PET scanner rotates around the patient's head, detecting the rays emitted by the radioactive sugar. Highly malignant tumors consume glucose at a higher rate than normal brain. Measurements of brain activity (determined by concentrations of the glucose) feed into a computer, which produces a color-coded moving picture or a gray scale image of the brain as it converts food (glucose) into energy. The use of PET is limited because cyclotrons are scarce.
  • RN - A radionuclide (RN) scan uses short-lived radioactive material injected into a vein in the arm. The scanner moves back and forth over the patient's head, plotting a chart. The chart shows the various concentrations of the injected material in the brain. The contrast materials used with CT or MRI scanners concentrate in diseased tissue in larger quantity than in healthy tissue. The radioactive materials used with RN scanners also concentrate in diseased tissue. In all three cases, the concentration is due to the leakiness of blood vessels in and around brain tumors. The concentration of contrast materials or radioactive drug outlines abnormalities such as tumors. A neuroradiologist interprets the computer images produced by the CT, MRI, PET, and RN scans. The pictures help establish a tentative diagnosis. Scans do not show a specific type of tumor. Only examination of an actual sample of tumor tissue can provide an exact diagnosis.
  • ELECTROENCEPHALOGRAM - An EEG is used to record electrical activity of the brain, particularly of the cerebral hemispheres, using electrodes attached to the scalp.
  • BIOPSY - A biopsy is a surgical procedure used to remove a small amount of tumor tissue. The neurosurgeon then submits samples of the tumor tissue to a neuropathologist for analysis. An accurate diagnosis is then possible. For those areas not easily reached via an open biopsy, a surgeon can, through a small hole made in the skull, use stereotaxic instrumentation to obtain a "closed" biopsy. Stereotaxic instrumentation allows the surgeon to precisely position a biopsy probe in three-dimensional space to allow access almost anywhere in the brain. In most instances, therefore, it is possible to obtain tissue for diagnosis, if it is desired. When biopsy is not performed, diagnosis relies solely on scan test results and their interpretation.

What are the different types of brain tumors?

Classification is the grouping of tumors on the basis of their characteristics. Each tumor is then given a unique name. Several different brain tumor classification systems are now in use. The following is an alphabetical list of the most common brain tumors. Included in the list are alternate names commonly in use

  • Acoustic Neuroma (Neurilemmoma, Schwannoma, Neurinoma)
  • Adenoma ( Pituitary Adenoma)
  • Astrocytoma
  • Brain Stem Glioma
  • Chordoma
  • Choroid Plexus Papilloma
  • CNS Lymphoma (Primary Malignant Lymphoma)
  • Cysts (Dermoid Cyst, Epidermoid Cysts)
  • Craniopharyngioma
  • Ependymoma
  • Gangliocytoma (Ganglioneuroma)
  • Ganglioglioma
  • Glioblastoma Multiforme (GBM)
  • Glioma
  • Hemangioblastoma
  • Lymphoma
  • Medulloblastoma (MDL)
  • Meningioma
  • Mixed Glioma
  • Neurofibromatosis (von Recklinghausen's Disease)
  • Oligodendroglioma
  • Optic Nerve Glioma
  • Pituitary Adenoma
  • PNET (Primitive Neuroectodermal T umor)
  • Tuberous Sclerosis (Bourneville's Disease)

How are brain tumors treated?

Treatment of a brain tumor is different from treatment of tumors in other parts of the body. First, brain surgery requires far more precision and highly sophisticated instruments. Second, the brain itself prevents many therapeutic drugs from entering it. Third, both the therapies used to treat brain tumors and side effects of these therapies are quite complicated. Experienced, multi-disciplinary medical professional teams offer the most up-to-date treatment opportunities. The brain tumor specialist recommends one or several treatment methods based on information from the various diagnostic tests. Treatment modalities include surgery, radiation therapy, chemotherapy, immunotherapy, or a combination of these treatments.

Surgery is the treatment of choice for accessible brain tumors. Accessible tumors are those which can be surgically removed without causing severe neurological damage. Tumors located in gray matter or deep within the brain may be inaccessible. The goal of surgery is to remove all visible tumor. Many benign tumors are treated only by surgery. Most malignant tumors require additional treatment. Malignant tumors lack distinct borders. They often invade nearby normal brain tissue. Tumor cells may also spread throughout the brain and spine by way of the cerebrospinal fluid. But, even partial tumor removal is beneficial.

Biopsy alone is performed when the tumor is inoperable or when surgery must be delayed. Biopsy is the removal of a small quantity of tumor for microscopic examination to determine an exact diagnosis. Needle biopsy uses a narrow, hollow needle. A small hole (called a burr hole) is drilled in the skull and the needle passes through the hole under CT guidance (stereotaxic biopsy). Tumor tissue is removed from the core of the needle. Stereotaxic biopsy is more exact than free-hand biopsy, and is considered by many practitioners to be safer. This technique is usually available at major medical centers.

Resection of a Tumor. If the tumor is accessible and the patient's general health is good, resection is the treatment of choice. The goal of surgery is to remove as much tumor as possible. The most commonly performed surgery for removal of a brain tumor is a craniotomy. The neurosurgeon makes an incision into the scalp. Removal of a piece of bone exposes the area of brain over the tumor. Location and removal of the tumor then takes place. After resection and bone replacement, the skin is sewn together. Sometimes, replacing the bone is not necessary. For example, the muscles in the back of the head are very strong and can protect the brain by themselves. The neurosurgeon has a wide choice of tools to use in removing brain tumors. Commonly used tools are the surgical laser, ultrasonic aspirator, and operating microscope. Other tools include evoked potentials, ultrasound imaging, and stereotactic apparatus. Usually, all of these surgical tools are available at major medical institutions. The tools used for surgical removal depend on the type of tumor and its location.

This text is prepared on the basis of "A PRIMER OF BRAIN TUMORS, A Patient's Reference Manual", Fifth Edition,American Brain Tumor Association, http://neurosurgery.mgh.harvard.edu/abta/primer.htm

Last update: 06.19.95

Northeast Parallel Arhitectures Center, Syracuse University