Cochlear Nerve Aplasia and Hypoplasia: Predictors of Cochlear Implant Success

Abstract

Objective To identify factors predicting performance outcomes following cochlear implantation in patients with cochlear nerve aplasia or hypoplasia. Data Sources Individual patient data extracted from published case series and reports. Review Methods The MEDLINE database, Cochrane Library, Embase, Web of Science, and Google Scholar were queried for "cochlear implant" in conjunction with "aplasia" or "hypoplasia" between 1985 and 2015. Eighteen studies were included describing 97 subjects with individual postimplant auditory data. Postimplant performance was categorized as follows: level 1, nonstimulation/minimal detection; level 2, improved detection; level 3, closed-set speech perception; or level 4, open-set speech perception. The subjects achieving speech perception (levels 3 and 4) were descriptively compared with those who did not. Results Subjects with a hypoplastic cochlear nerve on magnetic resonance imaging had higher reported rates of achieving speech perception than those with an aplastic nerve. Subjects with syndromic medical comorbidities had higher reported rates of nonstimulation than nonsyndromic subjects. The data showed that some children with an aplastic cochlear nerve or those with partial electrode insertion could obtain levels of speech discrimination. Reporting of patient characteristics and auditory outcomes was extremely variable across studies. Conclusion As previously shown, cochlear implant in patients with cochlear nerve aplasia or hypoplasia can provide meaningful hearing for select patients. The current study suggests that presence of a cochlear nerve on magnetic resonance imaging and lack of comorbid medical syndrome are associated with better auditory outcomes in such patients. Future efforts to report individual data in a consistent manner may allow better determination of predictive factors.

A Predictive Model for Cochlear Implant Outcome in Children with Cochlear Nerve Deficiency

“…Although the speech performance with CI was known to be unrelated to the remaining number of spiral ganglion cells 37 , patients with CND showed a poorer outcome of CI than those with normal sized cochlear nerve. Furthermore, speech performance was poor in those with cochlear nerve aplasia 14,16,18 or lower grades of IAC 16,19 nerves; this means that the amount of cochlear nerve fibers was less than normal sized cochlear nerve. Therefore, the amount of cochlear nerve fiber might be related to the outcome of CI in patients with CND, and the quantitative evaluation of cochlear nerve might be helpful to predict the speech performance after CI.…”

“…Several factors related to the CI outcome in patients with CND have been reported. Speech performance or aided threshold with CI was relatively poor when patients showed cochlear nerve aplasia 14,16,18 , low grades of IAC nerve 16,19 , narrow bony cochlear nerve canal 20 , no response to the intracochlear electrically evoked auditory brain stem response (EABR) 21 , or smaller diameter of vestibulocochlear nerve (VCN) than FN at the cerebellopontine angle (CPA) 21,22 . These factors were helpful for predicting whether the CI outcome would be good.…”

Appropriate Imaging Modality for the Etiologic Diagnosis of Congenital Single-Sided Deafness in Children

“…Recently, CI in SSD pediatric patients with proven intact CN has been implicated regarding significant audiological and subjective benefits, even after critical period for brain plasticity [33]. On the other hand, children with CND demonstrated reduced response to electrical stimuli compared with those with intact CN, implying abnormalities of CN on MRI are associated with poor auditory outcomes in such patients [34,35]. A recent case-series study showed that the benefits are restricted by speech intelligibility or perception ability during a follow-up of at least one year after surgery in all children with CND, with a caution of its limited effectiveness and uncertain cost-benefit [36].…”

Cochlear Nerve Canal Stenosis: Association With MYH14 and MYH9 Genes

“…This may be explained by the presence of cochlear nerve fibers traveling along the other nerves, such as the vestibular nerves, in the internal auditory canal. 12 Congenital hearing loss may arise secondary to perinatal infections or genetic mutations. The most common nonsyndromic genetic cause of congenital hearing loss is a mutation in GJB2 or GJB6, which encode for gap junction (connexin) proteins in the inner ear.…”