Intraoperative Transcranial Motor-Evoked Potential Monitoring During Head and Neck Surgeries: A Case of Cervical Vagus Nerve Schwannoma With Laryngeal Paralysis.

Abstract

Intraoperative transcranial motor-evoked potential (TcMEP) monitoring can effectively prevent neurological complications by enabling the evaluation of neurological deficits in all pathways from the motor cortex to the periphery. However, studies regarding its applicability in head and neck surgery are insufficient. This case report discusses a patient who was intraoperatively diagnosed with a right cervical vagus nerve schwannoma previously at another hospital. The patient then developed right laryngeal paralysis after the surgery without neuromonitoring. No significant recovery of the paralysis was observed, and after eight months of being referred to our institution, the patient opted for surgical retreatment following tumor growth and accompanying symptoms such as cervical swelling and discomfort. The patient was examined to evaluate the nerve damage in his previous surgery TcMEP monitoring as well as direct stimulation (DS). The right vagus nerve (RVN) showed no response on TcMEP monitoring throughout the surgery despite a significant response to DS at the tumor site. These findings suggest that the RVN had been damaged medial to the tumor site, and the damage occurred because of traction and ischemia during the previous surgery. Thus, contrary to our belief, medial nerve damage may be present even when local and peripheral nerve preservation is observed through peripheral neuromonitoring. This suggests that DS alone during neuromonitoring in head and neck surgery is insufficient. A multimodal evaluation approach, including TcMEP monitoring, is effective in not only preventing neurological complications but also in evaluating neurological deficits in all pathways from the motor cortex to the periphery.