What it means if your child fails his/her newborn hearing screening part 2
In our previous post, we discussed the newborn hearing screening. Now let’s discuss what a failed hearing screening means and what will usually follow. In general, there are two types of hearing loss: sensorineural and conductive. 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 3rd 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 lossConductive hearing loss is easy to understand: something is blocking the sound from getting into the inner ear. There are several things that can cause conductive hearing loss which results 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, which 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 one or more of the hearing bones.