A conductive hearing loss, which occurs in the outer and/or middle ear, refers to a disruption or blockage of the sound waves (vibrations) before they reach the inner ear. Sound waves travel through the air into the ear canal and then are transmitted further by the vibration of the middle ear bones. The conduction of sound waves can be disrupted by wax buildup in the ear canal, the absence of an outer ear, a hole in the eardrum, or the presence of fluid in the middle ear.
Conductive hearing loss can be temporary or permanent. Earwax and ear infections can cause temporary hearing loss that can be medically treated. Ear infections may require prescription medication from an ENT doctor or pediatrician, and pressure equalization (PE) tubes may be recommended for chronic ear infections. A hole in the eardrum usually heals itself but may require repair with surgery. Many conductive hearing losses can be treated, and in many cases, eliminated with medication or surgery.
Sometimes the conductive hearing loss occurs because the bony or soft tissues of the outer ear have not fully developed. This is a congenital deformity called microtia, and there are four “grades” of microtia to reflect how much of the outer ear is developed. This does not allow enough sound to the eardrum for the middle and inner ear to detect sound. Sometimes the outer ear can be reconstructed to allow for normal hearing, but if there are other structural problems in the middle ear or with the facial bones, a surgeon may recommend not attempting the procedure. Microtia is often accompanied by atresia, which is the absence or closure of the external ear canal.
The malformation of the middle ear bones of the ear (incus, stapes, and malleus) may be affected including the narrowing of the ear canal, known as canal stenosis. These three small bones in the middle ear may be fused, or stuck together so that they cannot carry the sound from the eardrum to the cochlea. Consult your ENT doctor regarding medical treatment for these types of hearing loss.
A sensorineural hearing loss involves damage to the nerve cells of the inner ear, the auditory nerve or the hearing center of the brain. It can range from mild to profound, and most children with this type of hearing loss will have some degree of residual hearing. The child may be able to learn to use this residual hearing, with or without hearing aids, to be able to hear speech and/or environmental sounds. It is considered permanent because nerve cells are not able to grow back or be replaced like other types of cells in our body. It cannot be treated medically, which can cause frustration and anxiety for some parents.
Sometimes there is a malformation in the inner ear because the cochlea did not fully develop before birth. The two most common malformations are Mondini Malformation and Enlarged Vestibular Aqueduct Syndrome (EVAS). Mondini Malformation causes the cochlea to develop with fewer turns in the spiral than is typical. EVAS develops from an enlargement in one or more of bony canals that are part of the vestibular and the hearing systems. Frequently, with cochlear malformations, there is only minimal hearing loss at birth. As the child ages, their hearing loss can progress, so discuss with your ENT doctor the steps you can take to minimize the risk of additional hearing loss.
A mixed hearing loss is a combination of conductive and sensorineural hearing losses. Many parents are surprised to learn their child still has a hearing impairment even after treatment to correct the conductive part of the hearing loss, such as fluid in the ear. Depending on which type of loss is more severe, a little or a lot of hearing may be restored by correcting the cause of the conductive loss. A sensorineural hearing loss can go undetected once a conductive loss has been treated, so tests which can detect underlying sensorineural hearing problems should also be administered. A child with a sensorineural loss who later develops a conductive hearing loss should be actively treated. The potential benefit from hearing aids can be lost due to an additional complication from a conductive loss, temporary or permanent.
Auditory Neuropathy (AN) is a type of hearing loss where the cochlea appears to be functioning normally, but sound cannot travel to the hearing center of the brain because the auditory nerve is not working properly. This condition is sometimes referred to as Auditory Dyssynchrony because it is a disorder of the timing of the auditory nerve. Often auditory neuropathy and auditory dyssynchrony are combined into one diagnosis (AN/AD). According to Linda J. Hood, Ph.D., with the Louisiana State University Health Sciences Center, children with AN sometimes can hear sounds but cannot understand what those sounds mean. Sometimes children with AN hear better on different days, with no obvious reason for the difference. Even those who can discriminate words in a quiet environment, cannot use their residual hearing in noise.
AN is difficult to diagnose and requires that an audiologist test the function of the cochlea with an otoacoustic emissions test, and also test the inner ear function using an auditory brainstem response. Doctors don’t know the exact cause of this type of hearing loss, but there seems to be an increased risk for children who have a brother or sister with AN or babies who were born premature or had severe jaundice.
A unilateral hearing loss (UHL) is defined as a loss of hearing in one ear and hearing within normal limits in the other ear. This is sometimes referred to as single-sided deafness (SSD). Hearing levels from mild to profound in one ear are considered a unilateral loss. Parents may be told that a unilateral hearing loss is not a big deal because children with unilateral loss usually can learn spoken language on par with typically hearing peers. However, speech and language development will depend on the child’s level of hearing, the listening environment in the home and their exposure to language.
Localizing sound and listening in noisy environments can be difficult to impossible, depending on the level of hearing in the affected ear. A child whose poorer hearing ear is facing a speaker can appear rude and non-responsive to the speaker and following conversations that involve multiple speakers is very difficult. Group work activities that involve several students, sometimes all speaking at once, can leave a student with a unilateral hearing loss out of the conversation.
Accommodations are critical to ensure a child with unilateral hearing loss can be successful. Young children can be taught self-advocacy skills to help them recognize the best position from which they can hear a speaker clearly and how to ask for clarification of missed information. Children with unilateral hearing loss should be monitored by a pediatric audiologist on a regular basis. Hearing protection should be worn in very loud situations to ensure residual hearing remains stable in one or both ears.