Single-sided sensorineural deafness (SSSD) is the presence of sensorineural hearing loss in one ear and satisfactory or near-satisfactory hearing in the other ear. 1 Population studies have demonstrated that 3% of school-age children and up to 14% of adolescents have SSSD when case ascertainment includes low-frequency or high-frequency unilateral loss. 2 Delay in diagnosing and managing SSSD can have a detrimental effect on integration of binaural information in children. The reduced interaural time difference and interaural level difference signals in children with SSSD leads to inability to localize sounds and lowered speech intelligibility in noisy backgrounds. 3
Although children with SSSD can experience academic difficulties because of listening and language difficulties, there is still no consensus on the advantages of early management of these children. This leads to some countries not including them in their national health target disorder. 4 The management options include regular monitoring, conventional behind-the-ear hearing aids, Contralateral Routing of Signal (CROS ) hearing aids, osseo-integrated bone anchored implants, and cochlear implants.
Different factors have been proposed as a cause of SSSD with cochlear dysplasia and enlarged vestibular aqueduct syndrome responsible for more than half of the cases. There are no identifiable genes responsible for SSSD, but in utero and postnatal infections, neonatal intensive care unit (NICU), craniofacial abnormalities and several syndromes are also suggested as potential risk factors for SSSD. 5
With no consensus on the best management modality of children with SSSD, this project aims to determine the use and benefit of hearing aids in children with SSSD in Oxfordshire over the last 18 years and which device is most commonly used.
All children with sensorineural hearing loss in one ear and normal hearing in the other ear who live in Oxfordshire were included in the study. They all had hearing tested in the form of visual reinforcement audiometry (VRA) or single-ear audiometry and tympanometry in addition to MRI IAM and cochlea.
Data were collected from patient electronic record. The degree of hearing loss, any anatomical abnormality and the management have been identified and verified with telephone consultation with the parents. The parents were also asked if their children were offered amplification device during the consultation, trial of these devices, and the reason for rejection. All children included in this study and their parents were given free choice whether to use amplification or not.
There are 35 cases with sensorineural hearing loss ranging from mild to profound in one ear and normal hearing in the other ear. Most of the children have severe or severe-to-profound sensorineural hearing loss (SNHL) (29 cases [82.8%]), two cases (5.7%) have moderate-to-severe SNHL, while four cases (11.4%) have mild or moderate SNHL.
In 25 children (71.4%) there was no identified underlying cause for the hearing loss. In five cases the cochlear nerve was absent or hypoplastic; in two cases congenital CMV was deemed the cause; two cases were admitted to the neonatal ICU due to prematurity; and one patient was admitted after head trauma (Table 1).
All children had investigation with visual reinforcement audiometry (VRA) or single-ear audiometry and tympanometry. Imaging in the form of MRI IAM and cochlea has been done for all children. MRI was normal in 30 cases (85.71%) with 4 patients showing absent cochlear nerve and 1 case with hypoplastic nerve.
The majority of the children did not experience hearing difficulties without hearing aids. Their parents reported that their school achievement and social interaction with their peers were satisfactory without amplification. In our study, 77% of children with SSSD did not use a hearing aid, while eight children (23%) used different types of hearing devices.
An offer of amplification was documented in 74% of the children in the group although it is likely many of the others were verbally offered the option of aids. Some children were deemed inappropriate for amplification because of cochlear nerve absence or the child was too young to try a hearing aid. Eleven children tried different modalities of hearing aids, with BTE devices tried by six children, CROS tried by five children, bone conduction devices tried in two children (Table 2). Two children tried two different modalities of hearing aids.
Children who tried hearing aids and found them useful were mainly between the age of 10 to 14 years old. Most of these children used CROS (five cases) followed by BAHA (two cases) and then BTE (one case) (Table 3). No children had cochlear implants for SSSD in this study because cochlear implants are not funded in the UK for SSSD. Patient who used CROS or BAHA have severe or severe-to-profound SNHL while the patient who used a BTE device has mild-to-moderate SNHL.
Although binaural hearing has several benefits, such as sound localization, discrimination of the signal from the surrounding noise, and improved differentiation of the sound sources from their reflection 6 most children in our study did not gain additive benefit from using different types of hearing aids. Most parents of children who rejected amplification reported that their children did not gain benefit or tolerate using the hearing aids and their school performance and social interaction was satisfactory without amplification.
The cause of SSSD in our study was not identified in most of the cases. This is also consistent with Dahl et al. in 2013 who reported no cause in 44.4% of cases. 7 Cochlear nerve absence was the most common identifiable cause in our series which is also consistent with Laury et al. who identified 8 cases (73%) of cochlear nerve deficiency out of 11 cases with identifiable cause of SSSD. 8
All children included in the study had MRI scan of the internal auditory meatus (IAM) and cochlea to identify the cause of the SSSD. MRI was favored over CT which according to Sang-Yeon Lee et al. as it is more accurate than CT in identifying cochlear nerve abnormalities. 9 All children were also screened for CMV as a potential cause. Paul et al. recommended MRI IAM and CMV screen in all cases of unilateral hearing loss. 10
The decision to provide children with SSSD with a hearing aid or not was based on the degree of hearing loss and the age of presentation. In our study, 23% (8 out of 35) were fitted with a hearing aid and they continued to use it. This is less than 37% (40 of 108) reported in a study done by Fitzpatrick et al. in Canada in 2017 2 and Bagatto et al. in 2016 who reported 44% of 115 received a hearing aid. 11 This could be attributed to the improved awareness of the condition and the improved techniques of helping these children manage life at school and home.
The most commonly used device to amplify hearing in these children was CROS at 14.2% (5 of 35). This is consistent with Fogels et al. who found that CROS was the preferred intervention in 8 out of 15 participants (53%) with unilateral SNHL over BAHA and remote microphone. 12 CROS hearing aid provide a noninvasive approach to convey sound arriving from the non-hearing ear. It reroutes the sound of interest from the affected ear to the better-hearing ear by means of a microphone placed behind the deaf side to collect sounds then transmit it wirelessly to a receiver inserted in the better-hearing ear. The main advantage of rerouting of the signal is that it reduces the head shadow effect by improving the signal to noise ratio. The downside of this modality is the need to wear a receiver in the normal-hearing ear which can interfere with the natural acoustics of the ear, potentially disrupting gain of some sounds or altering the monaural pinna cues that patients with SSSD become dependent on to aid with directional hearing and the filtering of sounds. CROS hearing aid also do not provide binaural hearing which means that unmasking of speech in the presence of interfering noise and localization are not improved. 13
Bone anchored implants preserve monoaural sound cues by avoiding the need to occlude the normal-hearing ear. Sounds are transmitted from the deafened ear to the normal-hearing ear transcranially. A drawback of these devices is the loss of signal intensity when the sounds travel across the skull especially in the high-frequency cues. BAHA devices also do not improve sound localization because the ability to localize sounds relies on the ability to differentiate between the interaural time and intensity and incorporate this information through the central nervous system. 14
The determination of hearing aids’ benefit was based on children’s hearing in the school and home environments which was subjectively reported by the children themselves and their parents’ observations. This could be a confounding factor, as children may report that they are not gaining any benefit from the hearing aid because they do not want to wear the device or are ashamed of wearing it. Further, the parents’ attitude towards hearing aids may affect their children’s use of the device (i.e., if the parents are not keen for their children to use the hearing aids they are unlikely to persist with them).
Despite several papers highlighting the importance of amplification in children with SSSD, we found that most of children in Oxfordshire, who tried or did not try hearing aids, reported satisfactory hearing with acceptable hearing in school and social interaction with their peers based on what their parents reported during telephone consultations. With schools offering hearing support for these children and one-on-one classes, the school performance of these children was satisfactory. Children who discontinued using hearing aids after a period of trying it reported that these devices did not add to their hearing or they caused discomfort. However, children who used hearing aid found CROS aids to be the most useful.
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