After patients have received routine auditory tests that show loss of hearing and speech discrimination (hearing sound but not understanding what is being said), the hearing care provider may perform an auditory brainstem response test (ABR, BAER or BSER). This test provides information on the passage of sound information along the path from the ear to the brain. The results may indicate that the acoustic nerve is not functioning optimally. If there is an abnormality in the ABR test, a detailed imaging test such as a CT (also called CAT) Scan or MRI is typically ordered.
A CT (CAT) Scan stands for Computerized (Axial) Tomography. The CT scanning device takes x-rays from many different angles and uses a computer to assemble them into a series of cross sections or ‘slices’ to provide a detailed look at the inside of the body. The CT Scan is painless but sometimes makes patients uncomfortable because they feel closed in during the time in which they are within the scanning device. The CT Scan has proven to be effective in locating acoustic neuromas, although small tumors that are still confined to the internal auditory canal may not show up on standard CT Scans. To assist in providing the clearest possible scan, for some brain scans, the patient may be given an injection of ‘contrast medium’ dye before the scan begins to make the images clearer.
MRI stands for Magnetic Resonance Imaging. An MRI Scan is a radiology technique that uses magnetism, radio waves, and advanced computer technology to produce images of body structures. The images and resolution produced by MRI are very detailed and can detect tiny changes of structures within the body. In the case of diagnosis for acoustic neuroma, gadolinium, a contrast agent, is used to increase the accuracy of the images. Gadolinium enhances the tumor, making it easier to see. An MRI scan is a painless scan that has the advantage of avoiding x-ray radiation exposure.