Drilling technique of the internal auditory canal in vestibular schwannoma surgery assisted by neuronavigated autofocus microscope

Background: The wide anatomical variability of temporal bone structures makes the application of neuronavigation particularly useful. This technical note outlines an IAC drilling technique performed with the assistance of a neuronavigated autofocus microscope to enhance intraoperative anatomical orientation, facilitate tailored bone removal and prevent injuries at the intraosseous petrous structures. Method: From January 2023 to January 2024, twenty-one out of thirty-six patients with vestibular schwannoma underwent a retrosigmoid transmeatal approach with IAC drilling assisted by the neuronavigated autofocus microscope. The technique employed the autofocus function of the surgical microscope as an active navigation pointer, with real-time trajectory feedback display through the heads-up display. This setup enables continuous intraoperative adaptation of the drilling path to individual anatomical landmarks. Results: Postoperative high-resolution CT imaging confirmed preservation of critical intraosseous structures in all but one case, which showed limited endolymphatic duct violation. No injuries to the posterior semicircular canal, common crus, or jugular bulb were observed. Complete tumour resection was achieved in all patients. The technique has enabled different drilling angles and trajectories tailored to individual patient anatomy. Conclusions: The IAC drilling, performed under the assistance of a neuronavigation-integrated autofocus microscope, provides a tailored anatomy-guided approach. This technique facilitates individualized exposure of the intrameatal tumour component while supporting the preservation of critical intraosseous petrous structures. By continuously adapting the drilling trajectory to the patient’s specific anatomy, it enables a controlled removal of the IAC posterior wall and may contribute to reducing the risk of unintended structural injury.