Brain Tumor: Diagnosis

Approved by the Cancer.Net Editorial Board, 11/2017

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, a brain tumor and learn the type of brain tumor. They also do tests to learn if it has spread to another part of the body from where it started. This is called metastasis and is rare for a brain tumor. Doctors may also do tests to learn which treatments could work best.

For most types of tumors, taking a sample of the possible tumor is the only sure way for the doctor to know whether an area of the body has a tumor. This may be done in a procedure called a biopsy or by removing part or all of the tumor with surgery. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If this is not possible, the doctor may suggest other tests that will help make a diagnosis.

Imaging tests can help doctors find out if the tumor is a primary brain tumor or if it is cancer that has spread to the brain from elsewhere in the body. Imaging tests show pictures of the inside of the body. Your doctor may consider these factors when choosing a diagnostic test:

  • The type of tumor suspected

  • Your signs and symptoms

  • Your age and medical condition

  • The results of earlier medical tests

Most brain tumors are not diagnosed until after symptoms appear. Often a brain tumor is initially diagnosed by an internist or a neurologist. An internist is a doctor who specializes in treating adults. A neurologist is a doctor who specializes in problems with the brain and central nervous system.

In addition to asking the patient for a detailed medical history and doing a physical examination, the doctor may recommend the tests described below. These tests are to help find out the presence, and perhaps the type or grade, of a brain tumor.

In general, diagnosing a brain tumor usually begins with magnetic resonance imaging (MRI). Once MRI 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 after a biopsy or surgery. These tests and procedures are described below in more detail.

  • MRI. An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can be used to measure the tumor’s size. A special dye called a contrast medium is given before the scan to create a clearer picture. This dye can be injected into a patient’s vein or given as a pill to swallow. MRIs create more detailed pictures than CT scans (see below) and are the preferred way to diagnose 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. 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 create a clearer picture of a brain tumor. This is when a patient first has a regular MRI, and afterwards is given a special type of contrast medium called gadolinium through an IV. Then, a second MRI is 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 used to help 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 tissue caused by previous radiation treatments and new tumor cells in the brain.

  • Tissue sampling/biopsy/surgical removal of a tumor. A sample of the tumor’s tissue is usually 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 can be diagnosed. A pathologist then analyzes the sample(s). A pathologist is 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 surgery may be done as a separate procedure if completely removing the tumor is not possible because of its location or a patient’s health.

Your health care team may also recommend other tests to help make a diagnosis or find out how well treatment is working. Not all tests listed below will be used for every person.

  • CT scan. A CT scan creates a 3-dimensional picture of the inside of the body using x-rays taken from different angles. A computer 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, and it can be used to measure a tumor’s size. A CT scan may also be used if the patient cannot have an MRI, such as if the person has a pacemaker for his or her heart. Sometimes, a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill to swallow.
  • Positron emission tomography (PET) or PET-CT scan. A PET scan is used at first to find out more about a tumor while a patient is receiving treatment. It may also be used if the tumor comes back after treatment. A PET scan is usually combined with a CT scan (see above), called a PET-CT scan. However, you may hear your doctor refer to this procedure just as a PET scan. A PET scan is a way to create pictures of organs and tissues inside the body using various substances, such as sugars or proteins. A small amount of a radioactive substance is injected into the patient’s body. This substance is taken up by cells that are actively dividing. Because tumor cells are more likely to be actively dividing, they absorb more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.
  • Cerebral arteriogram, also called a 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 or spinal tap. A lumbar puncture is a procedure in which a doctor uses a needle to take a sample of cerebrospinal fluid (CSF) to look for tumor cells, blood, or tumor markers. Tumor markers or 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. Typically, a local anesthetic is given to numb the patient’s lower back before the procedure.
  • Myelogram. The doctor may recommend a myelogram to find out if the tumor has spread to the spinal fluid, other parts of the brain, or the spinal cord. 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.
  • 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. Some biomarkers may help doctors determine a patient’s prognosis, which is the chance of recovery (see Grades and Prognostic Factors). Researchers are examining biomarkers to find ways to diagnose a brain tumor before symptoms begin. Ultimately, results of these tests may help decide whether your treatment options include a type of treatment called targeted therapy (see Treatment Options). The markers most commonly looked at for brain tumors include:
    • For oligodendroglioma, the loss of the p-arm of chromosome 1 and the loss of the q-arm of chromosome 19. This is called a 1p/19q co-deletion. It is linked to more successful treatment, particularly with chemotherapy. It can be used to help plan treatment, especially for anaplastic oligodendroglioma.

    • Mutations in the isocitrate dehydrogenase (IDH) gene which is found in about 70% to 80% of low-grade gliomas in adults. Higher-grade tumors can also have IDH gene mutations, which suggests that these tumors started as lower-grade tumors that became a higher grade. This mutation is linked with a better prognosis in both low-grade and high-grade tumors.

    • In glioblastoma, whether a gene called methyl guanine methyl transferase (MGMT) is changed can help the doctor understand a patient’s prognosis and how well treatment will work. Its role in determining the benefit of treatment is being tested in clinical trials.

  • 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, as well as changes to a person’s field of vision.

  • Neurocognitive assessment. 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. This specialist will write a formal report to compare with future assessments or identify specific problems that can be helped through treatment.

  • Electroencephalography (EEG). 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 and Signs).

  • Evoked potentials. 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 when removing a tumor that is growing around important nerves.

Test results

After diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is a brain tumor, additional tests will be done to learn more about the tumor. The results help the doctor describe the tumor and plan treatment.

The next section in this guide is Grades and Prognostic Factors. It explains the system doctors use to describe a brain tumor. You may use the menu to choose a different section to read in this guide.