Abstract
<jats:p>After focal seizures, many patients have surgical lesions that must be addressed (e.g., high-grade tumors, high-risk vascular malformations, cerebral abscesses, etc.). Furthermore, epilepsy surgery evaluation is indicated for patients with drug-resistant epilepsy (DRE), as epilepsy surgery is more effective than medications in controlling focal seizures in patients with DRE. Patients with DRE undergo comprehensive testing called a phase 1 evaluation to localize the epileptogenic zone, which is the smallest region of the brain, which if removed or destroyed, would render seizure freedom. Most of the phase 1 evaluation is noninvasive, though curative intent treatment with epilepsy surgery requires invasive measures such as surgically implanted phase 2 monitoring electrodes, resection, disconnection, or ablation. Epilepsy surgery and intracranial surgery carry risks, as with all neurosurgical procedures. The clinical neurophysiologist can detect and monitor changes in a patient’s motor, sensory, speech, and special sense neurons through intraoperative neuromonitoring (IONM). IONM includes electrical stimulation mapping (ESM), which allows identification and monitoring of eloquent cortices and subcortical tracts that should be preserved during surgery by applying intraoperative current to those structures. Furthermore, IONM with electrocorticography (ECoG) during surgery utilizing ESM detects spontaneous or iatrogenic seizures, which are treated to reduce the risks of brain injury and surgical complications. IONM makes epilepsy surgery and other neurosurgical procedures safer, reducing post operative deficits (POD) (e.g., weakness, numbness, aphasia, etc.). This chapter serves as a primer for providers and patients regarding IONM in epilepsy surgery and other neurosurgical procedures to make surgery as safe as possible.</jats:p>