Deafness/Hearing Impairment/Need Help in Understanding Test Results for SNHL
QUESTION: Hello Dr. Reiter,
My 8 year old son has Congenital Sensorineural Unilateral Hearing Loss (profound)in his right ear. He is very normal in all aspects. We have got OAE and ABR done at 5 months,as well as CT scan at 8 months.
The results of the tests are :
OAE - No response in right ear, passed in left ear
BAER - No response in right ear
Tympanogram - normal
Bone conduction Testing - No response
ASSR - Right ear 1000 Hz >90 dB,2000 Hz > 100 dB,4000 Hz > 100 dB
CT of Temporal bones (without contrast) -
- bony inner ear structures are symmetric & normal.
- Ossification of both Temporal bones is normal
- Ossicles normal
So here are my questions :
1. How did the ENT reach the "diagnosis" that something is wrong with his cochlea?
2. Is there a way of knowing chochlear pathology or auditory nerve pathology.
3. Since his Auditory nerve does not get stimulated, would that lead to nerve atrophy? What happens to the nerve that is not "used"?
PLEASE help me understand. I have been trying to get answer as to where is the 'disconnect' in my son's ear, since last 7 years.
THANK YOU for your patience in going through my long email.
ANSWER: Dear SJ,
I hope I can answer your questions to your satisfaction.
1- Your ENT or his audiologist did the correct tests to determining that a damaged cochlea is one of the sites responsible for your son's hearing loss. However, I do not see how auditory nerve damage cannot be entirely ruled out.
By way of explanation:
1- OAEs measure the response of the Cochlea's Outer Hair Cells. The fact that OAEs were absent means that the cochlea was not functioning normally. It could happen that if there is middle ear fluid it will block the reading of the OAE test, thus confounding the diagnosis. However, in your son's case his Tympanometry test was normal-- which tends to rule out Middle Ear fluid.
Therefore, the absent OAE results may represent a dysfunctional cochlea.
2- If your son's profound sensorineural hearing loss was due entirely to auditory nerve failure, then OAEs would still be robust. This is another finding that supports the diagnosis of a cochlear hearing loss.
3- ASSR astsess the neural synchrony of the inner hair cells and auditory nerve fibers. However the starting point is the stimulation of the cochlear hair cells. If they are profoundly impaired there will be no ASSR, or there may be a response at profound levels as is the case with your son. The fact that there was an ASSR at 90 - 100 nHl in the impaired ear indicates that the auditory nerve is responding OK when the auditory stimuli are loud enough that the damaged cochlea can process them.
4- The findings that radiological findings were normal indicates that the cochlear pathology is not related to bony cochlear malformations, but is likely to be damage or lack of development of the membranous portions of the cochlea, e.g. hair cells, etc.
5- Bone conduction assess the integrity of the cochlea and 8th nerve directly, by bypassing the outer and middle ear. Absence of Bone conduction responses means that there is a Sensori-neural problem underlying the hearing loss.
6- You question is "with a profound sensorineural hearing loss in one ear, does the auditory nerve atrophy?" This is a very good question. I think the answer is found in congenitally deaf individuals who elect to receive a cochlear implant in their adult years. The implant is usually successful, yet its success depends entirely upon having an intact auditory nerve to carry the electric signal to the brainstem. In these many successful cases the auditory nerve has survived for many years without atrophy despite the lack of cochlear stimulation. Therefore the answer to your question is no; the auditory nerve does not usually deteriorate when the cochlea does not function. There is literature as recently as 2012 which backs this up-- see: Patterns of Neural Degeneration in the Human Cochlea and Auditory Nerve-- by
J.B. Nadol Jr : 2012, of Otolayngology, Head & Neck Surgery.
If I can be of further help please write.
All the best,
---------- FOLLOW-UP ----------
QUESTION: Dear Dr. Reiter,
THANK YOU so very much for a very clear answer that a layperson like me can understand easily.
My followup questions (if you may please answer) are :
Would Electronystagmography test help in ruling out the nerve damage?
Would MRI help in anyway?
When you say "The implant is usually successful, yet its success depends entirely upon having an intact auditory nerve to carry the electric signal to the brainstem."
If we don't know for sure that my son's auditory nerve is intact how would a hearing aid that uses bone conduction be useful? Or the HA would use the "good" ear? I am thinking about something like SoundBite.
Dr. Reiter, you have no idea how helpful your answer has been to me. When my son asks - mom what is wrong with my ear? I can give an answer now because things are much clearer.
You have my heartfelt THANKS...
MRI can visualize the auditory nerve--just to ascertain that it is intact; however it will not show whether it is functional. The fact that your son can hear at extremely high levels is proof that the 8th nerve is in fact intact and functional. The usual scenario in cases of SNHL is that the cochlea is impaired. If your interest is in determining whether there is something impinging on the 8th nerve which may be not be safe to have growing, then an MRI would be in place. However 1) your son has had a CT scan which showed the Internal auditory meati to be symmetrical and normal. Anything impinging on the 8th nerve would probably show up on CT scan of the temporal bone.... 2)the kind of thing I am describing normally takes many years to grow, and is rarely if ever congenital. In my humble opinion, your son's congenital hearing loss involves primarily, if not exclusively the cochlea.
Regarding helping your son to hear on the "deaf" side, there are options. The preferred option in my opinion is a bone conduction hearing aid. This hearing aid would be worn on the "deaf" side. Bone conduction sends the signal to both cochleas, so the "working" cochlea will receive a clear auditory signal, speech, etc., even when the person speaking is on the "deaf" side. In other words, the signal will vibrate the entire skull including both cochleas. Obviously only the working cochlea will process the information, but your son will then be able to hear from each side without having to turn his head, etc. In addition, even though sound from the right side and left side will be heard by only one cochlea, your son will know where the sound is coming from because the sound quality will be slightly different when coming from the bone conduction hearing aid versus his good ear.
If this idea appeals to you, look up in google the term "Baha" by Cochlear Corporation. This is an ideal option for "one-sided" deafness. My own patients have been pleased with the results of this device. As you mentioned "sound byte" is another option and works on the same principle.
I hope this helps to answer your questions.
Levi A. Reiter, Ph.D.