Unilateral hearing loss in children is perplexing. On one hand, it would seem as though the condition would not have a major impact on communication development, as the children at least possess one ear with normal hearing.
However, we have known for many years that children with unilateral hearing loss are more likely to experience academic challenges than their peers with normal hearing in both ears ( Pediatrics 1984;74:206-216http://pediatrics.aappublications.org/content/74/2/206.abstract; Lang Sp Hear Serv Schools 1988;19:201-210http://lshss.pubs.asha.org/article.aspx?articleid=1777812).
More recent research suggests that children with unilateral hearing loss may also experience differences in speech and language development compared with children who have normal bilateral hearing ( Pediatrics 2010; 125:e1348-e1355http://pediatrics.aappublications.org/content/125/6/e1348.full).
Despite the evidence that children with unilateral hearing loss may be at risk, making decisions about amplification and monitoring outcomes can be difficult.
Data to suggest what type of amplification to use, at which age to initiate amplification, and how to measure audiological outcomes in children with unilateral hearing loss is limited compared with the evidence base for children who have bilateral hearing loss.
CONVENTIONAL VS CONTRALATERAL
One factor that can help audiologists determine the appropriate management approach for children with unilateral hearing loss is the degree of loss in the impaired ear.
In cases of mild-to-moderate unilateral hearing loss, a conventional hearing aid may provide audibility to the impaired ear and increase the potential for use of binaural cues to localize sound and listen in background noise.
For children with severe, profound, or complete unilateral hearing loss, also referred to as single-sided deafness, the likelihood of providing a high-quality amplified signal is small.
Even if some audibility can be restored through conventional hearing aids, the sound quality difference between the normal ear and impaired ear may be bothersome. In such cases, providing contralateral routing of sound (CROS) to the normal hearing ear may be an option.
Many different device configurations have been used to attempt to route sound from the impaired side of the head to the opposite ear in cases of profound or complete unilateral hearing loss.
One option that has had mixed success in our clinic is a CROS hearing aid. On the ear with hearing loss, the child wears a microphone that routes sound to an amplifier and receiver on the ear with normal hearing, which typically is coupled to an earmold for retention purposes.
CROS amplification also can be achieved using bone-conduction devices, including bone-conduction hearing aids and auditory osseointegrated device processors coupled to a soft headband.
In older children and adolescents with single-sided deafness, a bone-anchored implant may be an option for coupling the osseointegrated device processor. These devices route sound from the opposite ear to the normal cochlea via bone conduction.
AVAILABILITY OF BINAURAL CUES
The availability of binaural cues makes for an important difference between providing amplification to the impaired ear and using a CROS approach for routing sound to the opposite ear.
When amplification is provided to the impaired ear, the signal may not be equivalent to that of the normal ear, but stimulation of the two ears is occurring. With CROS methods, the signals for both ears are being routed to a single ear.
While these statements might seem overly simplistic, this distinction has important implications for choosing an option and setting realistic expectations of the benefits that might be observed, which are likely to be different across the two approaches.
In cases of unilateral hearing loss, providing amplification to the impaired ear should be the default option. Not only does amplification increase the likelihood that binaural cues will be available to the child, but it also may maintain auditory stimulation for the impaired ear.
Stimulation with a hearing aid may be important if late-onset hearing loss occurs in the normal ear or if cochlear implantation becomes an option in children with profound unilateral hearing loss.
On the other hand, the main benefit of routing signals to the ear with normal hearing is increased awareness of sounds in the high frequencies from the impaired side, since frequencies above 1,500 to 2,000 Hz from the side of the impaired ear may not be audible due to the head–shadow effect.
Since the separation between aided and unaided conditions with CROS configurations is subtle, clinical measures of aided speech recognition may not yield significant differences, even with background noise.
For example, the Parents’ Evaluation of Aural/Oral Performance of Children questionnaire ( J Am Acad Audiol 2007; 18:220-235http://www.ncbi.nlm.nih.gov/pubmed/17479615), which is typically used in this young patient population, may not be sensitive to the changes that are observed with CROS devices and unilateral hearing loss.
Other questionnaires, such as the Speech, Spatial, and Qualities of Hearing Scale (SSQ; Int J Audiol 2004;43:85-99http://informahealthcare.com/doi/abs/10.1080/14992020400050014), may contain specific items that inquire about binaural and spatial listening, but some questions may not be applicable until children are school-age or adolescents.
Management of unilateral hearing loss in children can be difficult due to a wide range of potential options and emerging evidence on audiological outcomes.
Binaural input and auditory stimulation should be prioritized to support development whenever residual hearing allows. If residual hearing is not available, CROS can be used to provide audibility of signals from the side of the child's impaired ear.
Future research will help determine the most effective options for handling unilateral hearing loss in children. New methods for the management of profound unilateral hearing loss and single-sided deafness, including cochlear implantation, may greatly alter how we approach these cases.