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Doctors use many tests to diagnose a brain tumor, find out the type of brain tumor, and rarely, find out if it has metastasized (spread). Some tests may also determine which treatments may be the most effective. For most types of tumors, taking a sample of the tumor tissue, either by biopsy (see below) or by removing the entire tumor, is the only way to make a definitive diagnosis of a brain tumor. If this is not possible, the doctor may suggest other tests that will help make a diagnosis. Imaging tests may be used to help determine whether the tumor is a primary brain tumor or if it is another type of cancer from elsewhere in the body that has spread to the brain. Your doctor may consider these factors when choosing a diagnostic test:
- Age and medical condition
- Type of tumor suspected
- Severity of symptoms
- Previous test results
Most brain tumors are not diagnosed until after symptoms appear. Often a brain tumor is initially diagnosed by an internist (a doctor who specializes in treating adults) or a neurologist (a doctor who specializes in problems with the brain and central nervous system).
To learn more about the brain tumor, an oncologist (a doctor who specializes in cancer) or neuro-oncologist (a doctor who specializes in treating a brain tumor) can use the patient's symptoms as clues to the location of the tumor. In addition to asking the patient for a detailed medical history and doing a physical examination, the doctor may recommend the tests described below to determine the presence, and perhaps the type or grade, of a brain tumor. Based on the combined results of the different tests, the doctor will recommend treatment options.
The most effective and common tool for diagnosing a brain tumor is the use of a magnetic resonance imaging (MRI) scan, although computed tomography (CT or CAT) scans are also used. A positron emission tomography (PET) scan is generally used to find out more about a tumor while a patient is being treated or if there is a recurrence (the tumor comes back after treatment).
Once an imaging scan shows that there is a tumor in the brain, the most common way to determine the type of brain tumor is to look at the results from a sample of tissue (called a pathology report or laboratory test results) after a biopsy or surgery (see below).
Each imaging test can provide specific information, but they must be combined with the results of the patient history, physical examination, and neurologic and other tests. The most common imaging tests used for diagnosing a brain tumor include:
MRI. An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRIs may create more detailed pictures than CT scans (see below) and are the preferred method of diagnosing a brain tumor. The MRI may be of the brain, spinal cord, or both, depending on the type of tumor suspected and the likelihood that it will spread in the CNS. There are different types of MRI, and the results of a neuro-examination, done by the internist or neurologist, helps determine which type of MRI to use.
- Intravenous (IV) gadolinium-enhanced MRI is typically used to help diagnose a brain tumor. This is when a patient first has a regular MRI, and afterwards is given a contrast (a special type of dye called gadolinium) through an IV; a second MRI is then done to get another series of pictures using the dye.
- A spinal MRI may be used to diagnose a tumor on or near the spine.
- A functional MRI (fMRI) provides information about the location of specific areas of the brain that are responsible for muscle movement and speech. During the fMRI examination, the patient is asked to do certain tasks that cause changes in the brain and can be seen on the fMRI image. This test is often used to plan surgery, so the surgeon can avoid damaging the functional parts of the brain while removing the tumor.
- Magnetic resonance spectroscopy (MRS) is a test using MRI that provides information on the chemical composition of the brain. It can help tell the difference between dead (necrotic) tissue caused by previous radiation treatments and new tumor cells in the brain.
CT scan. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. A CT scan can help find bleeding and enlargement of the fluid-filled spaces in the brain, called ventricles. Changes to bone in the skull can also be seen on a CT scan. Sometimes, a contrast medium (a special dye) is injected into a patient's vein to provide better detail, particularly if the patient cannot have an MRI (such as if the person has a pacemaker).
PET scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient's body. This substance is absorbed mainly by organs and tissues that use the most energy. Because a tumor tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.
Cerebral arteriogram (also called cerebral angiogram). A cerebral arteriogram is an x-ray, or series of x-rays, of the head that shows the arteries in the brain. X-rays are taken after a contrast medium is injected into the main arteries of the patient's head.
Lumbar puncture (spinal tap). A lumbar puncture is a procedure in which a doctor uses a needle to take a sample of CSF to look for tumor cells, blood, or tumor markers. Typically an anesthetic is given to numb the patient's lower back before the procedure.
Myelogram. Because some specific types of brain tumors can spread to the spinal fluid, other parts of the brain, or the spinal cord, the doctor may recommend a myelogram to look for areas where the tumor may have spread. A myelogram uses a dye injected into the CSF that surrounds the spinal cord. The dye shows up on an x-ray and can outline the spinal cord to help the doctor look for a tumor. This is rarely done; a lumbar puncture (see above) is more common.
Tissue sampling/biopsy/surgical removal of a tumor
As explained above,imaging tests are useful, but a sample of the tumor's tissue is typically needed for the final diagnosis.A biopsy is the removal of a small amount of tissue for examination under a microscope and is the only definitive way a brain tumor diagnosis can be made. The sample removed from the biopsy is analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease). A biopsy can be done as part of surgery to remove the entire tumor or as a separate procedure (if surgical removal of the tumor is not possible because of its location or the health of the patient.)
Molecular testing of the tumor
Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors, such as tumor markers, unique to the tumor. Tumor markers (also called biomarkers) are substances found in higher than normal amounts in the blood, urine, spinal fluid, plasma or other bodily fluids of people with certain types of cancer. Researchers are examining biomarkers to find ways to diagnose a brain tumor before symptoms begin. Results of these tests may help decide whether your treatment options include a type of treatment called targeted therapy (see Treatment).
Neurological, vision, and hearing tests
These tests help determine if a tumor is affecting how the brain functions. An eye examination can detect changes to the optic nerve.
This consists of a detailed assessment of all major functions of the brain, such as storage and retrieval of memory, expressive and receptive language abilities, calculation, dexterity, and the overall well-being of the patient. These tests are done by a licensed clinical neuropsychologist, who will write a formal report to be used for comparison with future assessments or to identify specific problems that can be helped through treatment.
An EEG is a noninvasive test in which electrodes are attached to the outside of a person's head to measure electrical activity of the brain. It is used to monitor for possible seizures (see Symptoms).
Evoked potentials involve the use of electrodes to measure the electrical activity of nerves and can often detect acoustic schwannoma, a noncancerous brain tumor. This test can be used as a guide during surgical removal of a tumor that is growing around important nerves.
Find more about what to expect when having common tests, procedures, and scans.
After these diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is a tumor, these results also help the doctor describe the tumor; this is called staging. Learn more about the first steps to take after diagnosis.