Technical Advancements in Hearing Preservation in Vestibular Schwannoma Surgery

Introduction and Goals: Preservation of auditory function remains a major challenge in skull base surgery, despite improved monitoring machinery and online waveform analysis. To counteract negative factors such as slow and deformed delivery of monitoring information, this study was designed to evaluate the benefit from a combined application of conventional brainstem responses and additional near-field techniques.

Methods: Patients underwent retrosigmoid tumor resection with motor cranial and auditory nerve monitoring consisting of conventional auditory brainstem recording (ABR) and additional near-field recording by a ball electrode placed for an extratympanic electrocochleography (ECochG) or at the eighth nerve entry zone (D-ABR). The presence of ABR components I, III, and V as well as deformation were evaluated and correlated with pre- and postsurgical auditory function by Gardner Robertson (GR) classification. Three types of electrodes, surgical steel, platinum, and gold electrodes were used.

Results: In 180 vestibular schwannoma operations, analysis of standard ABR and nearfield recordings could be performed. Hearing preservation was achieved in 79 patients (44%), with GR Class I in 18 and GR II in 29 patients. Preoperative hearing classes showed a positive correlation with the ABR, D-ABR, and ECochG classes at the start of surgery.

End-surgical ECochG was less reliable than ABR/D-ABR in predicting postoperative hearing quality, with 20% of patients with postoperative deafness and preserved cochlea potential in ECochG. Both nearfield techniques provided significantly larger amplitudes and clearer waveforms. Analysis of ABR and ECochG classes identified a strong positive correlation (p < 0.01, Kendall-Tau-b pre-op 0.835, post-op 0.734) especially for formations with preserved wave V (p < 0.01 Kendall-Tau-b pre-op 0.741, post-op 1.000); here, both methods behaved almost in a linear correlation. In some large tumors covering the whole brainstem, nearfield recording did not yield reproducible results or could be placed only at a mid-stage of surgery. The technique of placement and adaptation during the surgical procedure as well as the quality of registration will be illustrated by case presentations.

Discussion and Conclusion: Both nearfield techniques are helpful in gaining faster and larger auditory responses, but may lead to a slight increase in false positive results. The special support of this method lies in the online information during microsurgical procedures enabling a highly flexible and fast adaptation of the surgical steps. With regard to the microsurgical placement as well as the interpretation, some training is needed for the surgical and the monitoring team. The monitoring team needs to get acquainted with characteristic wave morphologies of both nearfield techniques.

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Artikel online veröffentlicht:
07. Februar 2025