Sudden Loss of Motor-Evoked Potentials (MEPs) During the Resection of A Nondominant Insular Glioma: Case Report and Management Review.

A 43-year-old man was admitted into the emergency room at our hospital after presenting with a tonic-clonic seizure. MRI showed a right-side operculo-insular tumor. This was treated by performing a craniotomy under general anesthesia with intraoperative monitoring. Tumor resection was started by exploring the temporal and frontal opercula without problems. However, during the resection of the insular compartment, a sudden loss of MEPs was observed. Surgery was stopped immediately, and all the relevant anesthetic parameters, vital signs, anesthetic drugs were reviewed. No retractors had been used at that time, so vasospasm was suspected as the underlying cause of the signal change. An ICG bolus injection confirmed vasospasm in one of the M2 branches running over the insula. A direct vessel massage was performed yet resulted in no apparent improvement in the appearance of the vessel when ICG was injected. Therefore, repeated massage with nimodipine was performed, which resulted in the resolution of the vasospasm. MEPs progressively recovered to base line levels, and surgery could then be finished without further incident. During the postoperative recovery period, no focal deficit was identified, and the postoperative MRI showed a planned subtotal resection without apparent ischemia. The goal of this report is to review the potential causes of such a loss of intraoperative MEPs and its best management in order to prevent postoperative motor deficit and to manage the situation should it occur.