Brain Tumor: Diagnosis

Your doctor begins to make a diagnosis by taking your medical history. You are asked to describe your symptoms, how long you have had them, when they occur, if they seem to be brought on by something in particular, the order of their appearance, and if they seem to be getting worse. Following the question and answer phase of the diagnosis, your doctor will perform a basic neurological examination.

Imaging Studies

Scans take the place of conventional x-rays, which do not show tumors located behind the bones of the skull or spine. Different types of imaging devices are used to perform scans. The most common scans for diagnosis and follow-up are Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI). Both CTs and MRIs use computer graphics to create an image of the brain. An injection of a special contrast material ("dye") to make abnormal tissue more obvious is usually given before the scan. The contrast materials concentrate in diseased tissues in greater quantity than in healthy tissues. That concentration is due to the leakiness of blood vessels in and around brain tumors. Contrast materials highlight abnormalities such as tumors. Small tumors, tumors next to bone, brain stem tumors, low grade and metastatic tumors might be imaged better by the MRI than the CT. CT is more effective at showing calcification and bony erosion. Your doctor determines which scan/s to use, based upon your history and exam.

Normal CT	Normal MRI

CT Scan This scan combines an x-ray device with a computer. For some types of tumors, CT images are obtained both with and without contrast enhancement to provide important additional information. If contrast is used, it is usually injected after a few pictures are taken. The patient lies on a table that slides into a doughnut-shaped opening. The CT scanner circles the head so x-rays penetrate the brain from many directions. Absorption of the x-rays varies with the type of tissue penetrated. Thousands of thin cross-section readings are fed into the computer which transforms the information into a picture.

MRI Scan The MRI is a tunnel-shaped piece of equipment. Some pictures are taken prior to contrast injection. If contrast is to be used, it is injected prior to the completion of the scan. The patient lies on a table that slides into the tunnel. Inside the scanner, a magnetic field surrounds the head. A radio frequency pulse is introduced to the area. No x-rays are used. The magnetic field causes atoms in the brain to change direction. The radio frequency pulse causes another change of direction. When the pulse stops, the atoms relax and return to their original position. During relaxation, the atoms give off energy in differing amounts and at different intervals of time. Antennas pick up these signals and feed them into a computer which assembles a picture. Because different atoms have their own characteristic radio signals, the computer can distinguish between healthy and diseased tissue. Patients with cardiac monitors, pacemakers, or some types of surgical clips cannot undergo MRI scanning because of the magnetic fields. For those who are claustrophobic, sedation or "open" MRI scanners can be an option.

Other CT or MRI Based Scans Computer technology advances have made possible the development of new methods for using existing scanning equipment. These new methods provide advanced tools for diagnosis. Most of these new tools measure the rate of blood flow into the brain. A contrast dye is given to the patient by intravenous (IV) infusion. The scanner begins taking pictures as soon as the dye is given. Using computerized timing, a succession of rapid pictures can be imaged, tracing the path of blood flow into the brain and to the brain tumor. These techniques are also used to scan spinal cord tumors. These new methods are collectively called hemodynamic imaging. The information gathered can be converted into images or graphed into charts. Several different types of scanning equipment are used to produce these images: CT, MRI, PET, and SPECT.

Additional Tests

Lumbar puncture (Spinal tap): Lumbar puncture is used to obtain a sample of cerebrospinal fluid (CSF). This procedure is not frequently used in the diagnosis of brain tumors. The sample of CSF is examined in a laboratory to determine if tumor cells, infection, protein, or blood is present. This information is particularly helpful in diagnosing primary CNS lymphoma, a pineal region or meningeal tumor. After surgery, the presence of tumor cells in the CSF indicates tumor spread. That information is used for tumor staging and helps the doctor determine appropriate treatment choices. The CSF is also examined for the presence of known tumor markers, substances which indicate the presence of a tumor. Unfortunately, most primary brain tumors have no tumor markers. If they are present, tumor markers are helpful in the diagnosis and follow-up evaluation of germ cell and metastatic brain tumors only.

Myelogram: Lumbar puncture is used to inject a special dye before a myelogram. The patient is then tilted to allow the dye to mix with the spinal fluid. This test is used primarily to diagnose a spinal tumor and obtain pre-operative information for spinal tumor surgery. Spinal MRI has replaced myelography for many conditions.

Audiometry: This hearing test is useful in the diagnosis of a cerebellopontine angle tumor such as the acoustic neuroma.

Endocrine evaluation: Measurements of hormone levels in samples of blood and urine are used, along with scans, to diagnose a pituitary or hypothalamic tumor.

Perimetry: This technique measures the size of visual fields. The information obtained might be useful in diagnosing a tumor in the area of the optic chiasm, such as a pituitary tumor.