Use of trans-tympanic electrically evoked auditory brainstem responses (TT-EABR) in decision making of cochlear implants in hypoplastic auditory nerve cases

INTRODUCTION: Cochlear Nerve Deficiency, particularly Hypoplastic Auditory Nerve (HAN), creates uncertainty regarding Cochlear Implant (CI) outcomes. This study evaluated the utility of Transtympanic Electrically Evoked Auditory Brainstem Response (TT-EABR) in managing HAN cases. METHODS: Twenty-two children with MRI-confirmed HAN were assessed using TT-EABR to guide ear selection for CI vs Auditory Brainstem Implantation (ABI) candidacy. Consequently, 13 children received CIs (HAN -CI group). Their auditory and speech outcomes -measured via CAP, SIR, and MAIS/IT-MAIS at baseline and 12 months post-implantation (with Auditory-Verbal Therapy) -were compared against an age-matched control group of 13 children with normal auditory nerves. RESULTS: The HAN -CI group demonstrated significant improvements from baseline to 12 months in CAP (p=0.001), SIR (p=0.005), and MAIS/IT-MAIS (p=0.001) scores. Remarkably, no statistically significant differences were found between the HAN and control groups for CAP (p=0.93), SIR (p=0.70), and MAIS/IT-MAIS (p=0.97). Favorable outcomes correlated with Kumar-Dutt Type A and B TT-EABR responses, with Type A yielding the best results. DISCUSSION & CONCLUSION: While historical data associates HAN with poor outcomes, this study highlights that precise preoperative TT-EABR assessment and ear selection can lead to outcomes comparable to non-anomalous cases. TT-EABR is a pivotal prognostic tool, crucial for ear selection and managing parental expectations. Preoperative TT-EABR is essential for tailored clinical management and successful CI intervention in selected HAN cases.