Bone Conduction ABR Masking in Infants

[Seb]

What is the anatomical reason for not masking bone conduction in infants / newborns at lower levels if the sound can travel from one petrous bone to the other through the skull base without crossing any sutures?

There should be a need to mask any BC!







(Admin Note: this post and the following were split from another thread to its own separate thread)

[Guy]

Seb, implied in your comment is "if the sound can travel without attenuation from one petrous bone to the other through the skull base without crossing any sutures".
Can it?

Yes, it would be wonderful to know the exact physics of the sound/vibration transmission mechanism but on a pragmatic note, what is important is the minimum inter-aural attenuation for the transducer being used.

The inter-aural attenuation of neonates is known to be typically 20-30dB (for BC clicks). For that reason NHSP will be revising its advice on the level to test by BC without masking: if clear ABRs are recorded at 20dBnHL in a <3/12 baby then masking is unnecessary since that stimulus will be below 0dBnHL on the non-test ear. Obviously this is not true for older patients and I agree with Seb's conservative approach when appropriate.

What we don't have (and desperately need) is IA data for supra-aural phones, inserts and BC versus age and frequency in the first 2 years of life. Anyone fancy doing a PhD?

Seb, if there is real data behind your comment then let's have it.

[Seb]

Unfortunately I have no hard data or anything.
People I challenged on this could not provide any convincing evidence why we do not need masking.

David Stapells team presented at IERASG about BC ABR and I asked them, but the assumption was that it is the incomplete closure of skull sutures, however this can not be it as the skull base is one bone without sutures.

So having a PhD on this would be great work and possibly help understanding some more of strange audiometric presentations.
The Pseudo-conductive hearing loss in Meniere patients and those with enlarged vestibular aqueduct is another mystery.

[Guy]

Is there a suture between the temporal bone and skull base?
I entirely agree that the model of incomplete fusion of skull sutures is probably just speculation and that we need someone to provide some hard data on this. Nevertheless, it does appear that, for whatever reason, newborns do have an additional inter-aural attenuation which is a boon in testing, reducing the need for masking and the levels of noise needed. But how quickly does this effect reduce with age and how does it vary with frequency?

You mention Pseudo-conductive hearing loss in Meniere patients. I was once told that this was because of the raised endolymphatic pressure increases the stiffness at the oval window, attenuating movement of the stapes and thus creating an air-bone gap. That's probably just speculation too but since then I have seen some "mixed" losses in classic Meniere patients.

[Mona Dokla]

what about the frequency of stimulation clicks differ from tone bursts (I have never used them)??
I think literature also mentions comparing the ipsi and contra responses as a way to differentiate if you are not doing masking
and the output of the bone vibrator itself as a transducer?? I know it has is much distorted above 1.5 or 2 KHz
what about the force of application??
A good paper or early evoked potentials the ASHA guidlines
I have done some cases on the old amplaid MMK10 and MK12 but failed to get response with newer equipment any ideas??

[Guy]

Mona Dokla, you raise a lot of issues there so let's try to keep this thread simple and going in a straight line.

This thread is about inter-aural attenuation in infants.
The more general subject of cross-hearing of BC in infants is a wider topic and I suggest you start a new thread, where I'll be happy to contribute. I have answers to all the issues you mention.