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 loss
Conductive 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.
Sensorineural hearing loss
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 potential causes of sensorineural hearing loss is vast. There can be infectious reasons like cytomegalovirus (CMV), herpes simplex virus (HSV), meningitis or congenital syphilis. Congenital malformations of the cochlea or balance system could be responsible. Also, errors in the development of the cochlear/auditory nerve called auditory neuropathy can cause such issues to arise. Impaired blood flow to the nerve or cochlea may cause the structure to have impaired function. Prematurity and jaundice are also risk factors for sensorineural hearing loss.
What happens after a failed hearing screening?
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 us at: Pediatric Audiology & Hearing Services