Auditory Brain Stem Testing (ABR)
Auditory brainstem response (ABR) audiometry is a non-invasive electrophysiologic test of auditory pathway and brainstem function in response to auditory click stimuli. It is also known as brainstem evoked response (BSER) testing. The ABR is a clinical screening tool used in the evaluation of the auditory pathway for pathology between the cochlear and the brainstem. Acoustic neuroma (vestibular schwannoma), benign tumors of the 8th cranial nerve, larger than one cm, are frequently associated with delayed ABR responses. The ABR may be recommended if the following symptoms or audiological results are present: asymmetrical or unilateral sensorineural hearing loss, unilateral tinnitus (ringing or ear noises in one ear), poor word discrimination for the degree of hearing loss (particularly unilateral), and a feeling of fullness or distortion in one ear when hearing is normal. If the ABR is abnormal, then an MRI of the inner ear will be recommended to definitively rule out a tumor. Although the ABR has a greater than 90% sensitivity to 8th cranial nerve tumors larger than one cm, its sensitivity for very small tumors is not as high. If there is concern about a small tumor, an MRI may still be recommended in symptomatic patients with normal ABR results.
What to Expect:
Electrodes will be placed on the forehead and behind both ears after scrubbing your skin with a mildly abrasive liquid. Foam earplugs will be inserted in the right and left ears. During the test you will hear moderately loud high-frequency click sounds for several minutes in each ear. We will record the electrical responses of the auditory nerve that runs from your ear to your brain. The electrical responses from your ear and auditory brain waves (auditory pathway) will be picked up by the electrodes. You will be asked to relax in a comfortably reclining chair and the lights will be turned off; you may even fall asleep if you like, since this electrodiagnostic test does not require voluntary responses.
The ABR waveforms are then reconstituted with computer software for analysis and review by your audiologist and physician.