Hearing and Facial Nerve Preservation Following Gross-Total Resection of a Koos Grade IV Vestibular Schwannoma Through the Retrosigmoid Approach: Surgical Video

Introduction: Hearing preservation in patients with large Koos grade IV vestibular schwannomas remains one of the greatest challenges in skull base surgery because of the close anatomical relationship of these tumors with the cochlear nerve, facial nerve, brainstem, and cerebellar structures. Tumor size, nerve displacement, vascular compromise, and manipulation during dissection may all influence postoperative auditory function. In carefully selected patients with preserved serviceable hearing, however, a hearing-preservation strategy may be considered. Appropriate surgical planning, meticulous microsurgical technique, preservation of the arachnoid planes, and continuous intraoperative neurophysiological monitoring are essential to maximize the chances of complete tumor removal while maintaining neurological function. Case Report: A 26-year-old man presented with a large left-sided Koos grade IV vestibular schwannoma extending into the cerebellopontine angle, with preserved serviceable hearing preoperatively. Considering the patient’s young age, functional hearing status, and tumor characteristics, microsurgical resection was performed through a retrosigmoid approach with the patient in the park-bench position. Continuous neurophysiological monitoring was used throughout the procedure to assess facial and cochlear nerve function. After adequate exposure of the cerebellopontine angle, the tumor capsule was identified and progressive intracapsular debulking was performed to reduce tumor volume and minimize traction on surrounding neural structures. Subsequent extracapsular microsurgical dissection was carried out along the tumor–arachnoid interface, with particular attention to preservation of the facial and cochlear nerves. The facial nerve was identified and meticulously dissected from the tumor capsule, while the cochlear nerve was preserved by limiting traction, avoiding unnecessary manipulation, and maintaining the integrity of the surrounding vascular and arachnoid planes. Gross-total tumor resection was achieved without loss of anatomical continuity of either nerve. Results: Postoperatively, the patient maintained serviceable hearing and demonstrated normal facial nerve function, corresponding to House-Brackmann grade I. No new neurological deficits were observed. Postoperative imaging confirmed complete tumor removal, with satisfactory decompression of the cerebellopontine angle. Conclusion: The retrosigmoid approach is a very good surgical option for selected patients with large Koos grade IV vestibular schwannomas and preoperative serviceable hearing. Although hearing preservation in large tumors is technically demanding, careful intracapsular debulking, meticulous extracapsular dissection, preservation of the arachnoid and vascular planes, and continuous neurophysiological monitoring can contribute to favorable functional outcomes. This case demonstrates that gross-total resection may be achieved while preserving both serviceable hearing and normal facial nerve function, providing an optimal balance between oncological control and neurological preservation in appropriately selected patients.