F173. Seizure risk from intraoperative motor evoked potential stimulation

Abstract

Introduction Intraoperative Neurophysiologic Monitoring (IONM) tests the function of the brain and spine to help prevent new neurological deficits during surgery. IONM modalities can include electroencephalography (EEG) and motor evoked potentials (MEPs). MEPs involve high-intensity electrical stimulation to the scalp (transcranial) or brain (direct cortical) to test responses through the motor pathways. Transcranial stimulation can provoke a seizure, and previous studies have estimated that risk to be 0.8%. Methods 1175 adult IONM cases, in 605 females and 570 males, between July 1, 2015 and June 30, 2016 were retrospectively examined. There were 394 craniotomies, 178 interventional neuroradiology procedures, 509 spinal, 5 trans-nasal, 71 vascular, 1 neck, and 18 peripheral nerve cases with patients 18 to 95 years old. Seizures were identified through EEG, clinical observation of movement, and electronic medical chart review. Results Only two (0.170%) intraoperative seizures occurred. Electrographic seizure and clinical movement were observed in both. One was during an awake craniotomy with direct cortical stimulation for the resection of a left temporal metastasis. The other was a craniotomy for brainstem tumor resection under general anesthesia with transcranial MEPs. Although 98 cases (8.340%) involved a patient with one or more pre-operative seizures, usually from a new brain lesion, 0% of these patients experienced intraoperative seizures. Out of 14 awake craniotomy cases, only one (7.143%) had an intraoperative seizure. Conclusion The rate of intraoperative seizures in cases involving IONM is very low; and in this review, lower than previously published data. Having a seizure prior to surgery does not seem to confer added risk when using MEPs.