An ABR, or auditory brainstem response test, tells you something much different than an audiogram. An audiogram simply tells you if you have hearing loss, but it doesn't tell you whether this is due to a problem in the cochlea or with the hearing nerve. The ABR measures the response of the hearing nerve to stimulus at several points (five, if I remember correctly) along its length. It used to be that ABR tests were relied upon more heavily to determine if an AN was present, the assumption being that impaired response meant a tumor must be degrading the nerve's function. But some people can have an AN without the ABR showing degraded response; those people usually have well-preserved hearing despite their AN. So now an MRI is the gold standard for diagnosis.
So why then is an ABR still used? The way Dr. Derald Brackmann (world renowned neurosurgeon at House Ear Clinic) explained it to me is that by seeing how many points along the hearing nerve are compromised and how badly (i.e., by measuring the amplitude, or strength, of the response), one can reach a conclusion as to how likely hearing can be preserved with surgical resection of the tumor. When Dr. Brackmann looked at my lousy ABR results, he concluded that surgery would surely leave me deaf on my AN side -- even with using the retrosigmoid approach, which is often used in an attempt to preserve hearing when a middle fossa approach isn't feasible. That is why he recommended I have radiation treatments instead of surgery (the chances of hearing preservation were higher for me with radiation, due to the size and location of my tumor).
It's a good thing to have an ABR and have a doctor look at the results who knows its value as a predictor of treatment outcome vis-a-vis hearing preservation (some doctors merely look at it as an outdated and inaccurate method for determining if someone has an AN). Be involved in your test results. Ask what the practical ramifications of the results mean. By doing so, you will be better able to make an informed decision as to which treatment is best for you and avoid the regret of learning too late (after treatment) that another approach might have left you with more function or had some other positive benefit.
Best wishes,
TW
