Current State of Knowledge Regarding Cochlear Implantation in Children With Single-Sided Deafness

The present collection of articles represents data from 174 children with single-sided deafness (SSD) who have received cochlear implants (CIs) in their deaf ear, which, combined with their acoustically hearing ear (SSD + CI), provides bilateral hearing. The significance of this collection is that it provides the most comprehensive view of knowledge to date from leading CI centers spanning around the globe. Together, the intent of all groups reporting here has been to provide children with SSD bilateral hearing to avoid potentially irreversible effects of unilateral deprivation during sensitive periods in development (Gordon et al. 2015; Gordon & Kral 2019) and to mitigate the clear effects of SSD in childhood on cognition, language, and balance (van Wieringen et al. 2019; Lieu et al. 2020; McSweeny et al. 2021). The CI provides the only present solution to stimulate the deaf ear in these children but, as shown in this collection, outcomes remain mixed. This might reflect differences in candidacy criteria, CI devices and related programming, consistency of CI use, etiology of SSD, and other personal factors, including family education and support. This collection of studies expands the present state of knowledge, demonstrating that the CI supports the development of hearing from the deaf ear while also showing that the added benefit of bilateral hearing is restricted to particular hearing configurations and may be linked to early implantation. These factors might explain, in part, why the CI may not be used as frequently in some children with SSD as compared with other cohorts of children using CIs. An article by a group from KULeuven (Arras et al. 2025) reports outcomes from 20 children who met strict candidacy criteria for CI (prelingual onset and <3 yr of age) compared with an age-matched group of 17 children with prelingual SSD who did not receive a CI and a group of 33 children with normal hearing (NH). These data follow important findings in the same cohort of language skills on par with children who have NH (Arras et al. 2021). Like the language findings, the present report shows deficits in cognition, speech perception in noise, sound localization, and balance in children with untreated SSD. The SSD + CI group shows small improvements in measures of cognition, speech perception in noise, and sound localization. However, in the cognitive measures, the benefits are not enough to reduce the significant differences relative to the NH group. Also important are findings that higher maternal education positively affect outcomes across groups, and that balance was better in children with older siblings and poorer in children with congenital cytomegalovirus (cCMV), as previously reported (Cushing et al. 2019; Cejas et al. n.d.). The cCMV group was mostly in the SSD + CI group. A second article comes from a group at the World Hearing Center, Institute of Physiology and Pathology of Hearing (Obycka et al. 2025). This study reports on a relatively large cohort of 99 children with SSD receiving CIs (SSD + CI). Onset of SSD ranged from congenital/perinatal (n = 58) to acquired (n = 41) and the duration of SSD before CI was longer than in the other studies (mean ~5 yr). Common etiologies of SSD were cCMV and inner ear pathology in the congenital/perinatal group versus sudden onset (perhaps idiopathic) in the acquired SSD group. Datalogging showed good device use (mean ~8 hr) with most children using the CI for >4 hr/d. Benefits of the CI were shown for speech perception in particular conditions in noise (collocated with speech: SoNo; and when speech was on the side of the deaf ear and noise on the side of the good ear: SdNg). Sound localization also improved with the CI on and the benefits were larger in the children with acquired SSD. A third study is from a group in Israel who researched a tailored rehabilitation protocol that addresses the unique needs of the population of children with SSD + (Adi-Besaid et al. 2025) CI. Auditory training was conducted in 33 children with SSD by audio streaming sounds directly to the CI. Outcome measures included speech perception results, cortical auditory evoked potentials, parental questionnaire scores, and datalogging information. The study outcomes support the feasibility and efficacy of the protocol, which may serve as a guideline for clinicians involved in the rehabilitation of this population. A fourth study is by an Australian group whose findings demonstrate the practical challenges of CI use over several years of follow-up in a group of 22 children who received CIs quite quickly after either early onset (<5 yr of age, n = 16) or late (5+ yr of age) (Weng et al. 2025). Device use was highly variable with only 7 of the 22 children using the CI for >4 hr/d and this rate was the same in children with early versus late onset of SSD. There were no significant effects (either benefits or detriments) of CI on language, localization, or co-located speech perception in noise. The authors suggest a possible trend for slightly better outcomes when the delay to the CI is reduced to under 12 mo. Two articles from the group at the Hospital for Sick Children (Bartels et al. 2025; Gao et al. 2025) report on a large cohort of children with SSD + CI who received their CI quickly after early (n = 51) or late onset (n = 19) SSD. Comparisons were made with children listening bimodally with a CI in one ear and a hearing aid in the other in preschoolers (age ≤5 yr) and school-aged children (age >5 yr). Etiology was most often due to cCMV in the SSD group and genetic hearing loss was more common in children with hearing loss in the nonimplanted ear. Datalogging showed variable CI use in both cohorts (70 children with SSD and 40 children with mild-moderate hearing loss in the nonimplanted ear) but significantly lower daily use in the SSD group (mean ~6 h in SSD versus ~7 hr with bimodal) (Gao et al. 2025). Long-term follow-up included the COVID-19 pandemic period of school closures and shutdowns. Device use increased over the years in preschool children and remained stable in school-aged children. Analyses of use relative to CI activation revealed declines over time in the SSD group which were most clear in the school-aged group. School-aged children in all groups experienced declines in exposure to speech through their CIs during the pandemic which improved postpandemic in proportion to daily CI use. Speech perception testing in 43 children with SSD–CI and 143 children using bimodal devices at the Hospital for Sick Children (Bartels et al. 2025) quantified the significant speech perception impairments. Children with asymmetric hearing loss have using their acoustic hearing ear alone in noise. Speech perception abilities were clear with the CI alone in quiet and were similar regardless of degree of residual hearing in the non-implanted ear. Asymmetries between the two ears were largest for the children with SSD and for children with longer hearing in the deaf ear (later onset of deafness). The addition of the CI provided benefits for speech perception in noise in all groups, but these benefits were smallest in children with SSD. In sum, CIs are being increasingly provided to children with SSD across the world with the goal of supporting their hearing needs and reducing their challenges listening in difficult situations by providing access to sound in both ears. The data presented in this special collection of Ear and Hearing suggest that measurable outcomes as a result of providing a CI in children with SSD will depend on the duration of normal acoustic hearing before the onset of unilateral deafness, and how quickly implantation can occur after the onset of deafness. This delay is closely related to when the hearing loss is identified. The high prevalence of cCMV in all cohorts of children with early-onset SSD reported here thus supports efforts to add cCMV testing to universal neonatal hearing screening programs (Gantt et al. 2016; Dunn et al. 2025). Deficits due to SSD during development are shown in this collection of articles for speech perception, language, cognition, and balance, confirming prior reports in children with unilateral hearing loss (Lieu 2004; Fitzpatrick et al. 2017; Lieu et al. 2020; McSweeny et al. 2021). The most important benefit of CI in children with SSD shown here is the stimulation of the deaf ear and subsequent development of speech perception for sounds presented to that ear, consistent with early reports (Rahne & Plontke 2016; Ramos Macías et al. 2019; Lee et al. 2020; Arras et al. 2021; Benchetrit et al. 2021; Deep et al. 2021; Rauch et al. 2021; Gordon et al. 20239202122232425). This could potentially support speech perception in noise, language acquisition, and cognitive development. On the other hand, spatial hearing benefits are modest at best and variability in consistent device use, particularly as children age, suggest that benefits of CI in some children with SSD may insufficient relative to negative aspects of CI use. ACKNOWLEDGMENTS This independently conducted and peer-reviewed study was able to be distributed with open access through sponsorship by Cochlear Corp.

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