Utility of Superimposed Intraoperative Neuromonitoring for Cerebellopontine Angle Tumor Surgery: A Retrospective Study of 22 Patients

Purpose Conventional workflows often prevent surgeons from directly viewing intraoperative neuromonitoring (IONM) signals, potentially delaying communication between surgeons and neurophysiologists. This study evaluated the clinical utility of overlaying real-time IONM waveforms on an operating microscope display during cerebellopontine angle (CPA) tumor surgery, focusing on cranial nerve sparing and intraoperative decision-making. Methods We retrospectively analyzed 22 consecutive patients who underwent CPA tumor resection using a microscope-integrated IONM waveform display system. Facial nerve monitoring included transcranial facial motor-evoked potentials (Tc-fMEPs) from the orbicularis oculi and orbicularis oris muscles, continuous facial nerve monitoring, and occasional electrical stimulation. IONM waveforms were transmitted directly to the microscope display through a digital video integration pathway, enabling the surgeon to monitor neurophysiological changes without diverting attention from the surgical field. Clinical outcomes, extent of resection, intraoperative waveform changes, and postoperative cranial nerve function were evaluated. Results Gross total resection, near-total resection, subtotal resection, and partial resection were achieved in one (5%), six (27%), four (18%), and 11 patients (50%), with a mean removal rate of 83%, respectively. One patient with a 50% decrease in Tc-fMEP developed House–Brackmann grade III facial nerve paralysis postoperatively, which resolved at 6 months. Transient trochlear nerve paralysis and transient dysphagia occurred in one patient each and resolved. One patient without usable hearing preoperatively had postoperative hearing loss; hearing was preserved in the remaining patients. No patient had permanent deterioration in facial nerve function, and no other permanent cranial nerve dysfunction was observed. Conclusion Overlaying IONM waveforms on the surgical microscope display improves real-time functional assessment during CPA tumor surgery, supports cranial nerve preservation, and reduces communication errors with monitoring personnel. Furthermore, displaying the monitoring screen on the surgical video enabled accurate recording.