[Utility of Presurgical Evaluation Using Stereoelectroencephalography(SEEG)]

Precise localization of the "epileptogenic zone(EZ)" is the goal of presurgical investigations in patients with drug-resistant focal epilepsy. Intracranial electroencephalography recordings are required when noninvasive evaluation results are not consistent. Although subdural grid electrodes(SDG)have been widely used in Japan, stereoelectroencephalography(SEEG)has been recently introduced. The principle of SEEG is based on anatomo-electro-clinical correlations to investigate surgical hypotheses that are primarily driven by the analysis of seizure semiology as well as other noninvasive investigations. The most important element of the SEEG methodology is to formulate preimplantation electrode trajectories considering the anatomo-electro-clinical correlations of epileptic seizures. If the preimplantation hypotheses are insufficient or incorrect, SEEG recordings will not identify the EZ. A detailed analysis of seizure semiology with respect to anatomo-electro-clinical correlates, particularly including various deep structures, such as the insular, operculum, and cingulate cortex, forms the basis of the implantation strategy for SEEG. The strategy of implantation is not to map the lobes/lobules but the epileptic networks, which usually involve multiple lobes, indicating that the theory of SEEG is completely different from that of SDG. Herein, we introduce the basics of SEEG, especially presurgical evaluations, with a representative case presentation.