Diagnosis

Doctors use many tests to diagnose a brain tumor, determine the type of brain tumor, and learn 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 (called a biopsy) or 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 is the result of spread from another type of cancer in the body. Your doctor may consider these factors when choosing a diagnostic test:

• Age and medical condition
  
  
• The type of tumor suspected
  
  
• Severity of symptoms
  
  
• Previous test results

Most brain tumors are not diagnosed until after symptoms appear. The oncologist (a doctor who specializes in cancer) or the neuro-oncologist (a doctor who specializes in diagnosing and treating brain tumors) 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 order the following tests be done 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. Individual diagnostic tests are described below.

Imaging tests. 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 gain more information about a tumor while a patient is undergoing treatment or if there is a recurrence (the tumor comes back after treatment).

Once an imaging scan shows a tumor is present, the primary way of determining the type of brain tumor is the results of the tissue sampling tests (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 brain tumors 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. Types of MRIs include:

  Intravenous (IV) gadolinium-enhanced MRI is typically used to aid in the diagnosis of 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 is another series of pictures using the dye.

  A spinal MRI may be used in diagnosing 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 perform certain tasks that result in detectable changes in the brain and can be seen on the fMRI image. This test is often used in surgical planning, so the surgeon can avoid damaging the functional area of the brain while removing the tumor.
  
  

• MRS. Magnetic resonance spectroscopy (MRS) is a test using MRI that provides information on the chemical composition of the brain. It has shown usefulness in distinguishing dead (necrotic) tissue caused by previous radiation treatments from 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. Sometimes, a contrast medium (a special dye) is injected into a patient’s vein to provide better detail, particularly if the patient is not able to undergo 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 and absorbed by the organs or tissues being studied. This substance gives off energy that is detected by a scanner, which produces the images. This energy is mostly detectable when the cellular content of the tissue is actively dividing, such as in malignant tumors.
  
  
• 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 (a special dye) is injected into the main arteries of the patient’s head.
  
  
• 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 order a myelogram to look for metastases. A myelogram uses a dye injected into the CSF that surrounds the spinal cord. The dye shows up on x-ray and can outline the spinal cord to help the doctor look for tumors.

Tissue sampling/biopsy/surgical removal of a tumor. As explained above, imaging is 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 cancer 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 after the entire tumor is removed surgically or as a separate procedure (if surgical removal of the tumor is not possible due to its location or the medical condition of the patient.)

Neurological, vision, and hearing tests. These tests help determine the suspected tumor’s effects on the brain’s functioning. An eye examination can detect changes to the optic nerve.

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 conducted 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.

Tumor markers/laboratory tests. Laboratory tests can detect tumor markers (also called biomarkers), which 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 determine the presence of a brain tumor before symptoms begin.

Lumbar puncture (spinal tap). A lumbar puncture is a procedure in which a doctor takes 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.

Electroencephalography (EEG). An EEG is a noninvasive test in which electrodes are attached to a person's scalp to measure electrical activity of the brain.

Evoked potentials. Evoked potentials involve the use of electrodes to measure the electrical activity of nerves and can often detect acoustic schwannoma, a benign brain tumor. This test can be used as a guide during surgical removal of a tumor that is growing around important nerves.

Learn more about what to expect when having common tests, procedures, and scans.

Find out more about common terms used during a diagnosis of cancer.