My child failed his/her newborn hearing screening (part 3)

We have now talked about the anatomy of the ear and the tests.  Now let’s discuss what a failed hearing screening means and what will usually follow.  In general, there are 2 types of hearing loss: sensorineural and conductive.  If you refer back to part 1 of the series, conductive hearing loss occurs when there is a break in the conduction of sound between the outside world and the end of the stapes or 3^rd hearing bone.  The second type of hearing loss is sensorineural, or nerve related.  This can occur within the cochlea or anywhere along the path of the cochlear/auditory nerve and remainder of the pathways from the cochlea to the brain. 

Conductive hearing loss is easy to understand.   Something is blocking the sound from getting into the inner ear.  There things that cause a conductive hearing loss which result in a failed newborn hearing screening.  The most common of these is fluid in the ear canal or middle ear.  The middle ear space is filled with fluid in general up until delivery.  As the baby is delivered, the movement through the birth canal helps push the fluid out of the middle ear space.  When this does not happen effectively, fluid can remain in the middle ear space and cause a conductive hearing loss and a failed newborn screening.  This usually goes away after a short time, but it can persist for 4-6 months and may necessitate a procedure to drain the fluid from the ears. 

A second cause of conductive hearing loss is a malformation of the ear canal called congenital aural atresia.  This differs from a malformation of the pinna or external ear called microtia.  Both can cause difficulties with hearing but an isolated microtia does not usually cause enough hearing loss to result in a failed hearing screening.  When the ear canal has not developed, sound is unable to be conducted down it, thereby causing a conductive hearing loss and a failed newborn screening.  It may occur with or without a microtia.  This should be evident on physical examination.  Other causes of conductive hearing loss resulting in a failed newborn screening include fixation of the hearing bones, poor development of the hearing bones, and a disconnection between 1 or more of the hearing bones.

Sensorineural hearing loss can also cause a failed newborn screening.  The conductive apparatus may be fully developed and normal but if the sound pressure wave is not converted into electrical signal, sensorineural hearing loss will result.  The number of causes of sensorineural hearing loss is vast.  There can be infectious reasons like cytomegalovirus (CMV), herpes simplex virus (HSV), meningitis or congenital syphilis.  There can be congenital malformations of the cochlea or balance system.  There can be an error in the development of the cochlear/auditory nerve called auditory neuropathy.  There can be impaired blood flow to the nerve or cochlea which causes the structure to have impaired function.  Prematurity and jaundice are also risk factors for sensorineural hearing loss. 

After a failed hearing screening, your child will require follow-up with an audiologist, and, if another failed screening occurs, then with a pediatric otolaryngologist (ENT doctor).  The second test is usually more thorough than the first and usually is done when the baby is napping.  Sometimes this limits the amount of testing that can be done, especially if the baby is waking up during the examination.  Follow-up is very important as the earlier we are able to intervene, the less impact there will be on speech and language development should that be your desired mode of communication for your child.  For more information about hearing loss and the services we offer, visit our website: www.childrenentdocs.com

My child failed his/her hearing screening (part 2)

Now that we have reviewed how sound makes its way from the outside world into the brain, today we are going to discuss the different types of tests which make up a newborn hearing screen.  The newborn hearing screening program was setup as an early intervention program in an attempt to identify children with early onset hearing loss and facilitate early treatment.  Children with even mild hearing loss can have significant delays in their speech and language development. 

There are 2 main tests which are currently used to perform a newborn hearing screening.  The first test is called otoacoustic emissions, or OAEs.  This test checks the hearing pathway from the outside world to the cochlea.  It does not test cochlear/auditory nerve integrity or any of the pathways from the nerve to the brain.    In order to have a normal OAE test, the hair cells of the cochlea must be present and healthy.  They actually produce a very slight sound, which we cannot routinely hear, in response to a sound administered to the ear through a very small probe.  Therefore the sound administered by the probe must be funneled to the eardrum, vibrate the eardrum, vibrate the hearing bones, and vibrate the membranes of the cochlea to vibrate these hair cells, which, in turn, produce a sound.  The probe that produces the initial stimulus sound is able to detect the sound produced by the hair cells, or the otoacoustic emission. 

OAEs are a good screening test, but have several important limitations.  First, if there is a blockage of the ear canal, whether from ear wax, fluid or vernix, or a developmental malformation of the ear canal, the OAEs will be absent.  Similarly, and abnormality in the ear or eardrum that blocks the conduction of sound will impair OAEs.  That is because the sound cannot be conducted to the inner ear effectively to vibrate the hair cells.  Secondly, one may have a perfectly intact cochlea with normal hair cells and have a profound hearing loss due to a break in the pathway from the cochlea to the brain, an example of which is auditory neuropathy where there is abnormal development of the cochlear/auditory nerve.

The second test is called automated auditory brainstem response testing, or AABR.  This is a newer test which actually checks the integrity of the entire pathway of hearing, including the area beyond the cochlea up to the brain.  During this test, there is a probe which is placed into the ear which administers a broad-band click stimulus at a consistent level.  This device then measures, with probes that are placed on the head, the passing of that sound from the probe, through the ear, into the cochlear/auditory nerve and into the pathway from the brainstem to the brain.  This test is very good at ruling out children who do not have hearing loss and ruling in children who do.  Each ear is measured independently as in the other test.

While this test evaluates the more of the hearing pathway, it, too, has some limitations.  First, this test is a pass/fail test.  There is no interpretation possible.  Therefore a failed test must be followed up with a formal auditory brainstem response (ABR) test.  Second, the click stimulus is not frequency specific.  It generally tests from 1000 to 4000 Hz which are the frequencies thought to be most important for speech and language, but there is much more to our hearing range than is tested with a click stimulus.  Finally, as with the OAE test, the AABR depends on the conduction of the administered sound into the inner ear and hearing pathway.  Therefore any abnormality in the outer or middle ear could compromise the result of this test.

Given the relative strengths and weaknesses of these tests, many institutions are using a combination of tests for newborn hearing screening.  Now that we have discussed these tests and what they measure, in part 3 of our series we will discuss how we deal with a failed newborn hearing screening and what follow-up is involved.

My child failed his/her hearing screening! (Part 1)

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Amid all of the excitement of a newborn child, there are several tests that are run shortly after birth while your baby is in the newborn nursery that are mandated by the state.  One of those tests is a hearing screen which checks to see if the most basic parts of the hearing mechanism are intact.  We are going to discuss the newborn hearing screening, how it works, what the results mean, and what should be done in follow-up of an abnormal test in a 3-part posting.  Please be sure to check back for the second and third parts to follow shortly.

To understand the hearing screening test, we should first talk about how sound gets from the outside world into the brain.  There are many important pieces which are needed in order to hear sound.  Sound is actually a pressure wave.  That wave gets funneled into the ear canal by the ear which you see on the side of the head, or pinna/auricle.  Once in the ear canal that wave is transmitted down to the ear drum, which it vibrates.  The eardrum is connected to 3 of the tiniest bones in the body: the malleus, incus and stapes (or hammer, anvil and stirrup bones).  When the sound wave hits the eardrum, the eardrum vibrates, and, as a result, the 3 hearing bones vibrate as well.  The 3^rd hearing bone (stapes) is connected to the inner ear and transmits that wave into the inner ear. 

Here is where all of the magic happens.  The sound wave that is transmitted into the inner ear, or cochlea, vibrates delicate membranes that are within the body of the cochlea.  There are cells along those membranes which respond to different frequencies of vibration.  When that frequency of sound is present, those cells, called hair cells, activate and change that mechanical wave into an electrical signal.  This electrical signal is then collected by the cochlear, or auditory, nerve which then takes that information into the brainstem and relays it all the way to the temporal lobe of the brain where that signal is perceived as sound.

For a basic animation to understand this process, please visit: http://www.youtube.com/watch?v=tkPj4IGbmQQ

In the next part of this series, we will discuss the types of newborn hearing screening tests and what type of information these tests gives us as ear, nose, and throat doctors.

Thank you very much for reading our blog!  Please check back again for parts 2 and 3 of this series.