Characteristics and Selection of Intracranial Electrodes for the Exploration of Epileptogenic Zone

Abstract

  The precise delineation of the “epileptogenic zone” is crucial for resective epilepsy surgery. No single examination is adequate for delineating the zone partly, because it is included within the resected area in patients with a favorable postoperative seizure outcome. Preoperative estimation of the epileptogenic zone is conducted using a multidisciplinary approach. This diagnostic approach includes examinations, such as magnetic resonance imaging, fluorodeoxyglucose positron emission tomography, magnetoencephalography, and video-electroencephalographic monitoring with scalp or intracranial electrodes. Among these, intracranial electrode recording is an important method for precisely estimating the epileptogenic zone. In Japan, subdural grid electrodes have been used to examine epileptogenic zone and functional cortices following the clinical standards established in the United States during the 20th century. Stereotactic implantation of multiple depth electrodes (stereotactic electroencephalography : SEEG) is gaining popularity because it is less invasive and enables the exploration of deep structures. However, the concept of SEEG is quite different from that of subdural grids in terms of planning, procedure, interpretation of results, and subsequent resection strategy. Therefore, a thorough understanding of the characteristics of these two types of electrodes is needed to select the appropriate modality for each patient.