Tailored Auditory Implantation in Inner Ear Malformations: A Long-Term Prospective Study Integrating Imaging and Functional Outcomes.

INTRODUCTION

This study aimed to evaluate long-term auditory outcomes in patients with inner ear malformations (IEMs) treated with cochlear or auditory brainstem implants (CI/ABI) and assess the influence of anatomical subtype, electrode design, insertion depth, and genetic/syndromic background on hearing performance over a 10-year follow-up.

METHODS

We conducted a prospective cohort study including patients with radiologically confirmed IEMs and bilateral severe-to-profound hearing loss, all of whom underwent implantation and completed at least 10 years of follow-up. Outcomes were assessed using pure-tone average (PTA) and speech recognition scores (SRSs) at defined intervals. Additional analyses explored the influence of electrode array design, insertion depth, genetic and syndromic diagnosis, and intraoperative complications.

RESULTS

Eighty-two patients were included in the study, of whom 71 (86.58%) received a CI, while the remaining 11 patients (13.41%) were treated with an ABI. After a 10-year follow-up, the mean PTA gain with CI was 64.56 ± 14.52 dB, and mean SRS improved by 56.88 ± 25.32%. On the other hand, patients treated with ABI presented a gain of 45.00 ± 18.22 and 32.62 ± 10.67% dB, respectively. Enlarged vestibular aqueduct had the highest 10-year SRS (80.04%), whereas cochlear nerve agenesis, Michel deformity, and cochlear hypoplasia type I had the lowest (23.72%, 24.00%, and 26.50%, respectively). The mean insertion depth was 19.66 ± 3.74 mm and showed a non-significant correlation with final SRS (r = 0.243, p = 0.084). The presence of residual auditory brainstem responses was significantly associated with better pre-implant PTA (p = 0.041) and higher SRS at 10 years (p = 0.034). Finally, having a syndromic condition was not significantly associated with the risk of a worse SRS at 10 years post-implantation (p = 0.091), nor with poorer auditory outcomes measured in PTA prior to surgery (p = 0.315).

CONCLUSION

Auditory outcomes in IEMs are modulated by malformation subtype, neural status, and electrode design. A stratified, anatomy-guided approach is essential, especially when considering perimodiolar arrays. Delayed gains in some subtypes underscore the value of long-term follow-up, and integrating imaging and genetic data may enhance personalized implant strategies.