Diagnosis

If a person has symptoms that suggest a brain tumor, the doctor may perform one or more of the following procedures:

• Physical exam-The doctor checks general signs of health.

• Neurologic exam-The doctor checks for alertness, muscle strength, coordination, reflexes, and response to pain. The doctor also examines the eyes to look for swelling caused by a tumor pressing on the nerve that connects the eye and brain.

• CT scan-An x-ray machine linked to a computer takes a series of detailed pictures of the head. The patient may receive an injection of a special dye so the brain shows up clearly in the pictures. The pictures can show tumors in the brain.

• MRI-A powerful magnet linked to a computer makes detailed pictures of areas inside the body. These pictures are viewed on a monitor and can also be printed. Sometimes a special dye is injected to help show differences in the tissues of the brain. The pictures can show a tumor or other problem in the brain.

The doctor may ask for other tests:

• Angiogram-Dye injected into the bloodstream flows into the blood vessels in the brain to make them show up on an x-ray. If a tumor is present, the doctor may be able to see it on the x-ray.

• Skull x-ray-Some types of brain tumors cause calcium deposits in the brain or changes in the bones of the skull. With an x-ray, the doctor can check for these changes.

• Spinal tap-The doctor may remove a sample of cerebrospinal fluid (the fluid that fills the spaces in and around the brain and spinal cord). This procedure is performed with local anesthesia. The doctor uses a long, thin needle to remove fluid from the spinal column. A spinal tap takes about 30 minutes. The patient must lie flat for several hours afterward to keep from getting a headache. A laboratory checks the fluid for cancer cells or other signs of problems.

• Myelogram-This is an x-ray of the spine. A spinal tap is performed to inject a special dye into the cerebrospinal fluid. The patient is tilted to allow the dye to mix with the fluid. This test helps the doctor detect a tumor in the spinal cord.

• Biopsy-The removal of tissue to look for tumor cells is called a biopsy. A pathologist looks at the cells under a microscope to check for abnormal cells. A biopsy can show cancer, tissue changes that may lead to cancer, and other conditions. A biopsy is the only sure way to diagnose a brain tumor.

  Surgeons can obtain tissue to look for tumor cells in three ways:

  • Needle biopsy-The surgeon makes a small incision in the scalp and drills a small hole into the skull. This is called a burr hole. The doctor passes a needle through the burr hole and removes a sample of tissue from the brain tumor.

  • Stereotactic biopsy-An imaging device, such as CT or MRI, guides the needle through the burr hole to the location of the tumor. The surgeon withdraws a sample of tissue with the needle.

  • Biopsy at the same time as treatment-Sometimes the surgeon takes a tissue sample when the patient has surgery to remove the tumor.

Sometimes a biopsy is not possible. If the tumor is in the brain stem or certain other areas, the surgeon may not be able to remove tissue from the tumor without damaging normal brain tissue. The doctor uses MRI, CT, or other imaging tests instead.

When a brain tumor is suspected, the first test a doctor gives is a traditional neurological examination. This exam is divided into several components each focusing on a different part of the nervous system.  It evaluates eye movement, eye reflexes, and pupillary reactions, reflexes, hearing, sensation, movement, balance, and coordination. The neurological exam also includes a mental status exam, a series of questions designed to test cognitive ability, memory, and abstract thinking. 

In addition, the physician often orders additional specialized tests to come to a diagnosis. These techniques have dramatically improved the diagnosis of brain tumors in recent years and have replaced older tests, such as conventional X-rays, which do not show tumors located inside the skull or spine, and cerebral angiography.      

CT Scan (Computed Tomography Imaging) 

Computed Tomography, often called a "CT" or "CAT" scan, uses special X-ray equipment, which obtains images from different angles, and a computer that assembles them to create a detailed cross-sectional picture of the body's tissues. These pictures are called "slices." These slices provide more detailed information on brain tumors than conventional X-ray films.     

The CT scan is a painless, patient-friendly exam that requires no special preparation. The machine is large and square shaped with a patient-sized opening in the center. The patient lies still on a table which slides the patient in and out of the opening.  Within the machine, an x-ray tube moves around the patient's body to produce images - this causes a clicking and whirring noise. Depending on the number of images needed, a CT scan of the head and brain can take from 2 to 45 minutes. Sometimes an injection of dye, or contrast material, is injected prior to the scan to make abnormal tissue more obvious. Since contrast material concentrates more highly in diseased than in healthy tissue, it highlights abnormalities such as brain tumors. 

     The injection of contrast material may cause some discomfort, and contrast agents contain iodine, which causes allergic reactions in some individuals. If you have had an allergic reaction to iodine or contrast material in the past, be sure to share this information with the technologist, nurse or radiologist.  Although the amount of radiation in CT scanner is kept to a minimum, it is also important to inform your doctor if you are, or think you may be, pregnant. 

MRI Scan (Magnetic Resonance Imaging) 

Unlike conventional X-rays and CT scans, MRI does not use radiation. Instead, radio waves and a strong magnetic field are used to produce clear and detailed pictures of internal organs. The radio waves are directed at protons, the nuclei of hydrogen atoms. In the setting of a strong magnetic field, the protons become excited and then relaxed, emitting radio signals, which are then computer-processed to form an image. Since protons are most abundant in the hydrogen atoms of water, an MRI image shows differences in the water content in various body tissues. For example, different types of tissue within the same organ, such as the white and gray matter of the brain, can be distinguished. Small tumors, tumors next to bone, brain stem tumors, and low grade or metastatic tumors are often best imaged by MRI.  

The conventional MRI is a large piece of equipment - a closed cylindrical magnet which has an opening for the patient. Once inside the patient must lie absolutely still. MRI causes no pain, but the feeling of being closed-in can cause anxiety reactions, especially for people who are claustrophobic. This is a common reason for stopping an examination before it is completed. Fortunately, newer "open air" MRIs offer the opportunity to scan these patients.  

Patients are placed on a sliding table and a radio antenna, called a surface coil, is positioned around in the area to be scanned. The radiologist or technologist leaves the room while the MRI sequences are performed, but the patient can communicate with them via intercom.  Many MRI centers allow patients to have someone stay in the room with them. If contrast material is used, there may be some discomfort at the injection site. 

No special preparation is needed for an MRI, but it's important to know that the strong magnetic field will pull any implanted metal objects in the body. The MRI staff will ask about this; for example, do you have a prosthetic hip, pacemaker, or any metal plates, pins or surgical staples or wire?  MRI is generally avoided during the first 12 weeks of pregnancy.  

     There are also new scanning methods called hemodynamic imaging, which measure the rate of blood flow in the brain. Contrast dye is intravenously administered and the scanner starts taking a rapid succession of images - this traces the path of blood flow into the brain and brain tumor.  MRI Angiography (MRA)  uses MRI scans to outline blood vessels in the brain by following blood flow.  Angiography is used to plan the surgical removal of a tumor suspected to have a large blood supply or one located in a part of the brain with dense blood vessels.  Functional MRI or Fast MRI  produces MRI images in a faster sequence than conventional MRI. This technique allows the tumor's use of oxygen to be determined and is helpful in distinguishing between tumor and edema. The speedy production of images makes this technique useful for mapping specific areas of the brain during surgery.  The images of  Magnetic Resonance Spectroscopy, or  MRS, depicts patterns of activity, rather than shape, and are helpful in diagnosing particular tumors and differentiating between radiation necrosis and tumor recurrence. 

PET Scan (Positron Emission Topography) 

     A PET scan provides a picture of brain activity, rather than structure, by measuring levels of injected glucose (sugar) labeled with a radioactive tracer. After a low-dose of radioactive glucose is injected, a scanner rotates around the patient's head and detects the amount of radioactivity in different parts of the brain. Different degrees of brightness and color represent different types of tissue or organ function. For example, cancerous tissue uses more glucose than healthy tissue, and consequently, appears brighter when scanned. A PET scan is not regularly used for diagnosing tumors, but is used with other scans to determine the grade of the tumor or distinguish between necrosis and scar tissue. 

 The PET scanner has an opening  in the middle and looks like a large doughnut. Patients are injected with the radioactive substance approximately 30 to 60 minutes before the scan. During this time, they are asked to rest quietly and remain still. The scan takes 30 to 45 minutes. Other than the discomfort of an injection, the radioactive substance will not cause any feeling. Like other scanning devices, being enclosed can make some patients feel claustrophobic.   

 The radioactive tracer required for the PET has a very low radiation exposure and is short-lived.  Although the exposure is low, it is important to notify the radiologist if there is a chance that you are pregnant. This scan is useful in that it allows physicians to detect alterations in body function that might indicate disease before changes can be seen in other types of scans. The drawback is that PET requires complex and expensive equipment that is only available in major medical centers. It can also give misleading results if a patient's chemical balances are abnormal, such as in patients with diabetes. PET scans are more valuable when used in a larger diagnostic work-up in which they are compared with other imaging studies, such as CT and MRI scans.