Superimposed intraoperative neuromonitoring for epidermoid cyst: Two-dimensional operative video

Background: Intraoperative neuromonitoring (IONM) is critical for preserving cranial nerve function during cerebellopontine angle (CPA) tumor surgery, particularly when multiple cranial nerves are involved. We report a case of an epidermoid cyst resection in which IONM waveforms were projected in real time onto the surgical microscope display. Case Description: A 36-year-old woman presented with the left facial spasm and numbness. Magnetic resonance imaging (MRI) revealed a left CPA lesion extending from the medulla to the midbrain, compressing the brainstem and involving cranial nerves III-XII. The tumor was removed through a lateral suboccipital approach with the patient in the park-bench position. A microscope was integrated with the neuromonitoring system. Auditory brainstem responses were used for hearing monitoring, while continuous transcranial facial motor-evoked potentials and intermittent electrical stimulation assessed facial, trigeminal, and lower cranial nerves. Real-time waveform projection onto the microscope allowed immediate recognition of signal changes during dissection. The tumor was completely removed while preserving cranial nerves III-V, VII-VIII, and lower cranial nerves. No intraoperative deterioration in waveform amplitude occurred. Postoperative MRI confirmed complete removal, and histopathology diagnosed. Facial spasm and numbness resolved without hearing loss. The patient was discharged with a modified Rankin scale score of 0 and remained symptom-free and recurrence-free at one year. Conclusion: Real-time IONM projection facilitated intraoperative communication and may contribute to safe, complete resection with cranial nerve preservation. Ethics committee approval was obtained, and the patient provided written informed consent for participation, surgical video, and publication.