for Brain Tumors
Doctors may utilize several tests to diagnose a brain tumor. The purpose for conducting diagnostic tests are to first, determine whether an abnormal growth is malignant (cancerous) or benign (non-cancerous), and second, if it is malignant, to determine what type of cancer it is, and how extensively it has spread, which is called the stage of the disease.
In addition to a complete neurological examination the following tests are used to evaluate the nervous system to determine whether any abnormalities exist. A typical neurologic exam involves testing of reflexes, sensation, muscle strength, eye and mouth movement, coordination, and alertness.
Computed Tomography (CT) Scan: A CT scan is a technique for imaging body tissues and organs, during which X-ray transmissions are converted to detailed images, using a computer to synthesize X-ray data. A CT scan is conducted with a large machine positioned outside the body that can rotate to capture detailed images of the organs and tissues inside the body.
Magnetic Resonance Imaging (MRI): MRI uses a magnetic field rather than X-rays, and can often distinguish more accurately between healthy and diseased tissue than a CT. An MRI gives a better picture of cancer located near bone than does CT, does not use radiation, and provides pictures from various angles that enable doctors to construct a three-dimensional image of the cancer.
Positron emission tomography (PET): Positron emission tomography scanning is an advanced technique for imaging body tissues and organs. One characteristic of living tissue is the metabolism of sugar. Prior to a PET scan, a substance containing a type of sugar attached to a radioactive isotope (a molecule that emits radiation) is injected into the patient’s vein. The cancer cells “take up” the sugar and attached isotope, which emits positively charged, low energy radiation (positrons) that create the production of gamma rays that can be detected by the PET machine to produce a picture. If no gamma rays are detected in the scanned area, it is unlikely that the mass in question contains living cancer cells.
Biopsy: When CT, MRI, or PET scans show evidence of abnormal brain tissue, a biopsy is often necessary to confirm the diagnosis. A biopsy involves removing a sample of the abnormal tissue for examination under a microscope. There are a variety of different types of biopsies and the method used to gain a tissue sample depends on the size and location of the suspected tumor.
- A typical biopsy is the surgical removal of a mass of abnormal cells.
- Fine needle aspiration involves guiding a thin needle into the tumor and gently sucking out cells for microscopic evaluation.
- A stereotactic biopsy utilizes a computer and a three-dimensional scan to direct the placement of the aspiration needle
Genomic or Biomarker Testing-Precision Cancer Medicine
The purpose of precision cancer medicine is to define the genomic alterations in the cancers DNA that are driving that specific cancer. Precision cancer medicine utilizes molecular diagnostic & genomic testing, including DNA sequencing, to identify cancer-driving abnormalities in a cancer’s genome. Once a genetic abnormality is identified, a specific targeted therapy can be designed to attack a specific mutation or other cancer-related change in the DNA programming of the cancer cells. Precision cancer medicine uses targeted drugs and immunotherapies engineered to directly attack the cancer cells with specific abnormalities, leaving normal cells largely unharmed.
By testing a cancer for specific unique biomarkers doctors can offer the most personalized treatment approach utilizing precision medicines.
Biomarkers most commonly looked at for brain tumors include:
- Oligodendroglioma – 1p and 19q co-deletion: is linked to more successful treatment, particularly with chemotherapy, and can be used to help plan treatment, especially for anaplastic oligodendroglioma.
- Mutations in the isocitrate dehydrogenase (IDH) gene: Found in about 70% to 80% of low-grade gliomas and some.higher-grade tumors this mutation is linked with a better prognosis in both low-grade and high-grade tumors.
- Methyl guanine methyl transferase (MGMT) gene: may help the doctor understand a patient’s prognosis and how well treatment will work.
To learn more about biopsies and stereotactic techniques, go to Surgery for Brain Tumors.
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. 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.
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, 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.
- 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.
- 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.
American Cancer Society. Cancer Facts & Figures 2017.