Electrically evoked auditory responses: A classification for brainstem implant placement in Neurofibromatosis Type 2

Objective: In auditory brainstem implant (ABI) surgery, array placement may be optimized by electro-physiological information of adequate brainstem activation gained from electrically evoked auditory brainstem responses (EABR). This study aims 1) to characterize in detail the EABR from ABI implantation, 2) to introduce an EABR Classification Scheme, and 3) to analyze data for their correlation with individual patients' findings.Methods: Out of a continuous series of 54 patients who received an ABI between 2005 and 2019, 23 Neurofibromatosis Type 2 patients with complete documentation of 154 recordings were selected for off-line analysis and for development and evaluation of a new EABR Classification Scheme comprising Class A: three vertex positive peaks, Class B:two peaks, Class C: a combination of one peak and a second melted double peak, Class D: one sole vertex positive peak and Class E: no peaks.Results: All 23 subjects showed EABR at final ABI position and experienced auditory sensations at first activation. The most frequent morphology consisted of two peaks, Classes B and C. Identified mean laten-cies were for P1 0.42 ms (+/- 0.095), P2 1.42 ms (+/- 0.244) and P3 2.41 ms (+/- 0.329). Peak latencies correlated positively with tumor extensions (p < 0.005).Conclusions: This study provides clear instructions on optimal EABR performance and evaluation.Significance: The new EABR Classification Scheme relies on a fast online identification of vertex positive peaks at the estimated post-artifact phase. The variability in EABR morphology provides an individual snapshot of the actual structural and functional status of the brainstem.(c) 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study provides a new EABR Classification Scheme for ABI surgery based on the analysis of EABR data. The findings show that all 23 subjects had EABR at the final ABI position and experienced auditory sensations at first activation. The most common EABR morphology consisted of two peaks, Classes B and C.