89 - Intracranial Monitoring with Subdural Grids and Strips

Abstract

Subdural grid and strip electrodes have long played an important role in the presurgical evaluation for epilepsy surgery. Patients requiring intracranial electroencephalographic (EEG) monitoring for both seizure localization and functional mapping are good candidates for subdural electrode implantation. More recently, subdural electrodes have been used to directly record the epileptiform discharges in a chronically ambulatory setting as a component of a neuromodulatory device used to treat epilepsy. The main goal of any intracranial EEG monitoring is to evaluate both the irritative and ictal onset zones so as to best estimate the region comprising the epileptogenic zone. Compared with the scalp electroencephalogram (EEG), the intracranial EEG has the ability to record a broad range of frequencies with greater spatiotemporal resolution. Currently there are a number of neurophysiologic intracranial EEG biomarkers whose aim is to assess epileptogenicity, allowing further differentiation of epileptic from normal brain regions. The implantation of any intracranial electrodes as a part of an epilepsy presurgical evaluation requires an initial working hypothesis of the epileptogenic zone based on noninvasive data that include seizure semiology, imaging, nuclear medicine studies, magnetoencephalography, and neuropsychological assessments. Although subdural electrodes can be associated with some complications, such as cerebrospinal fluid leakage or infection, their use is relatively safe and the data accrued may yield additional information to guide epilepsy surgery.