Sixteen years of cochlear implant surgery in cochleovestibular malformation and cochlear nerve deficiency: Insights from northern Malaysia.

Abstract

Introduction: Congenital sensorineural hearing loss associated with cochleovestibular malformations (CVM) and/or cochlear nerve deficiency (CND) presents distinct surgical and audiological challenges. Patients with CVM face elevated risks of intraoperative cerebrospinal fluid (CSF) gushers and aberrant facial nerve courses, while those with CND have historically been viewed as poor candidates for cochlear implantation (CI) due to concerns regarding neural sufficiency. This study aims to bridge this gap by evaluating the surgical safety and audiological outcomes of CI in a focused cohort of patients with CVM and CND at a tertiary referral centre in northern Malaysia.

Materials and methods: A retrospective cohort study was conducted on 20 cases with CVM and/or CND performed between January 2009 and December 2024 at Hospital Sultanah Bahiyah, Kedah, Malaysia. The study population included patients with radiologically confirmed CVM classified according to the Sennaroglu classification and CND. Surgical outcomes, including the incidence of CSF gushers, were analysed by Fisher's exact test following stratification into high-risk and low-risk gusher group. Primary audiological outcomes were assessed using the aided average pure tone audiometry (PTA), analysed longitudinally using a linear mixed-effects model. Secondary functional audiological outcomes were evaluated by comparing pre-implantation and 12-month post-implantation Categories of Auditory Performance-II (CAP-II) scores using the Wilcoxon signed-rank test.

Results: The cohort was predominantly prelingual (90.0%). Surgical analysis revealed a shift in technique over the 16- year period, moving from cochleostomy to round window insertion. Intraoperative CSF gushers were encountered in 12 of 20 ears (60%). We found no statistically significant difference in the incidence of gushers between the "high risk" group (enlarged vestibular aqueduct and incomplete partition type II) and to the "low risk" group (p=0.559). There were no incidences of facial nerve injury. In terms of audiology outcome, the linear mixed-effects model revealed a highly significant improvement in aided PTA over time for all ears (p<0.001). Crucially, comparing CND versus non- CND ears revealed no statistically significant difference in outcomes, with both groups following a parallel trajectory of auditory improvement. Functional analysis confirmed that these gains translated into real-world benefits, with CAP-II scores improving significantly from a median of 2.0 preoperatively to 4.5 at 12 months (p=0.003).

Conclusion: Cochlear implantation is a safe and effective intervention for children with CVM and/or CND. Our findings indicate that the risk of intraoperative CSF gushers extends beyond specific high-risk groups, underscoring the need for broad surgical readiness across the spectrum of malformations. The audiological outcomes observed, irrespective of the presence of CND, support the expansion of CI candidacy to this challenging population, provided there is requisite surgical expertise and thorough family counselling.