Cochlear implantation in children with anomalous cochleovestibular anatomy

To evaluate outcomes after cochlear implantation in children with anomalous cochleovestibular anatomy, a review of radiological classification, surgical implantation, and outcome of 103 children with such anomalies was performed. The hypothesis was that children with anomalous cochleovestibular anatomy would have poorer outcomes and therefore be poorer candidates as a result of their diminished ability to interpolate and use auditory information delivered through a cochlear implant.

A series of studies was carried out to review the cochleovestibular anomalies among 298 children implanted over the decade ending in January 2002. Children were grouped based on cochleovestibular anatomy as follows: normal (n = 195), common cavity deformity (n = 8), hypoplastic cochlea (n = 16), incomplete partition (n = 42), and vestibular aqueduct enlargement (n = 37). Concomitant anomalies of the posterior labyrinth (n = 26) and internal auditory canal/cochlear canal (n = 11) were also identified. Findings at surgery, postoperative speech perception outcomes, and speech processor programmability were examined as a function of cochleovestibular anatomy.

A database containing demographics (age at implant, duration of implant use), audiological characteristics, pure-tone average, surgical findings (cerebrospinal fluid leak/perilymph leak, abnormal facial nerve anatomy), speech perception data (from two closed-set and three open-set tests), and data relating to speech processor programmability were used for analysis. Electrically evoked auditory brainstem response was measured in 94 of the children (2 cases of common cavity deformity, 7 of hypoplastic cochlea; 10 of incomplete partition; and 12 of vestibular aqueduct enlargement). Response morphological findings were assessed by visual inspection of the waveforms. Data were analyzed using analyses of variance with post hoc testing using the Bonferroni multiple-comparisons test. To further assess differences in outcomes between different categories of cochleovestibular anomalies, linear regression analyses were performed. The significance level was set at P < .05.

The use of high-resolution imaging techniques resulted in the detection of a cochleovestibular anomaly in 35% of implanted ears. Implantation was more challenging in 24% of the children as a result of abnormal middle ear anatomy (17.5%) or cerebrospinal fluid leak/perilymph leak (6.7%). There was no significant difference in speech perception scores in children with anomalous cochleae compared with children with normal cochleovestibular anatomy. Children with narrowing of the internal auditory canal/cochlear canal performed more poorly than all other groups. Children with common cavity deformity and hypoplastic cochlea had reduced dynamic range and increased incidence of facial simulation and were judged to be more difficult to program despite the fact that no fewer electrodes were inserted. Children with common cavity deformity and hypoplastic cochlea tended to require wider pulse widths more often than children in other groups, and these requirements were associated with abnormal morphological findings on evoked auditory brainstem response testing.

The authors have been continuing to assess the candidacy of each child applying for cochlear implantation individually, and the results of present study have suggested that the presence of anomalous cochleovestibular anatomy, with the exception of narrowing of the internal auditory canal/cochlear canal, should not play a significant role in candidacy assessment. Children with narrow internal auditory canal/cochlear canal should be carefully and individually considered. In children with anomalous cochleovestibular anatomy, the potentially increased difficulty in the establishment of optimal stimulation levels and the higher potential for surgical difficulty must be weighed in candidacy decisions but do not universally preclude successful implantation and a good outcome.