End-to-End Hypoglossal-Facial Anastomosis Following Anatomically Preserved but Functionally Irreversible Facial Nerve Injury After Resection of a Koos Grade IV Vestibular Schwannoma in a Patient with Neurofibromatosis Type 2: Surgical video.

Introduction: Facial nerve dysfunction remains one of the most relevant complications following vestibular schwannoma surgery, particularly in large tumors involving the cerebellopontine angle. Even when the nerve is anatomically preserved, postoperative function may be severely impaired because of traction, ischemia, thermal injury, or axonal damage during microsurgical dissection. In patients with persistent complete paralysis and no evidence of spontaneous recovery, facial reanimation procedures may be required. Hypoglossal-facial anastomosis remains a well-established reconstructive technique capable of restoring meaningful facial movement, symmetry, and quality of life in appropriately selected patients. Case Report: A 23-year-old woman with neurofibromatosis Type 2 (NF2), previous resection of a right-sided vestibular schwannoma at another institution, and non-serviceable hearing bilaterally presented with a large left-sided Koos grade IV vestibular schwannoma occupying the cerebellopontine angle. Gross-total tumor resection was achieved through a retrosigmoid approach with the patient in the park-bench position. The facial nerve was anatomically identified and preserved throughout microsurgical dissection. However, intraoperative neurophysiological monitoring demonstrated an approximately 90% reduction in facial motor evoked potential amplitude after tumor removal, suggesting severe functional impairment despite preserved anatomical continuity. Postoperatively, the patient developed severe facial paralysis. Serial clinical evaluations demonstrated no meaningful neurological recovery over the following months. At eight months after tumor resection, electroneuromyography confirmed complete facial nerve paralysis and severe denervation, supporting the diagnosis of irreversible functional injury. Considering the prolonged absence of spontaneous recovery and electrophysiological findings, surgical facial reanimation was indicated. An end-to-end hypoglossal–facial anastomosis was subsequently performed, providing a new motor source to the denervated facial musculature. Postoperative evolution was favorable. Results: Five months after the reconstructive procedure, facial function improved from House-Brackmann grade V to House-Brackmann grade II, with substantial recovery of facial symmetry and voluntary movement. Importantly, the patient reported no clinically significant tongue hemiatrophy, dysarthria, swallowing dysfunction, or other relevant hypoglossal nerve morbidity. Conclusion: Anatomical preservation of the facial nerve during resection of large Koos grade IV vestibular schwannomas does not necessarily ensure functional recovery. Severe intraoperative deterioration of facial motor responses may indicate substantial neural injury even when nerve continuity is maintained. In patients with persistent complete paralysis and electrophysiological evidence of irreversible denervation, end-to-end hypoglossal–facial anastomosis is a reliable reconstructive option capable of providing meaningful facial reanimation with acceptable donor nerve morbidity. Early recognition of irreversible facial nerve injury, serial clinical and electrophysiological assessment, and timely reconstructive surgery are essential for optimizing facial symmetry, motor recovery, and long-term functional outcomes.