Ictal Semiology Important for Electrode Implantation and Interpretation of Stereoelectroencephalography

Abstract

Scalp video-electroencephalography (video-EEG) monitoring should be analyzed thoroughly to preoperatively evaluate stereoelectroencephalography (SEEG). Formulating the working hypotheses for the epileptogenic zone (EZ) considering “anatomo-electroclinical correlations” is the most crucial step, which determines the placement of SEEG electrodes. If these hypotheses are insufficient, precise EZ identification may not be achieved during SEEG recording. In ictal semiology analysis, temporal and spatial patterns with reference to ictal EEG changes are emphasized. In frontal lobe epilepsy, seizures often begin with relatively widespread synchronous activity, and complex motor symptoms manifest within seconds. Due to the wide area involved and intense interhemispheric connectivity, a comprehensive evaluation is often required. Hypotheses are formulated on the basis of the motor symptoms and emotional manifestations that are related to the prefrontal cortices. In temporal lobe epilepsy, EEG onset often precedes clinical onset. Propagation from the EZ to locations within and outside of the temporal lobe is examined from both the EEG and semiological standpoint. The characteristics of contralateral versive seizures, contralateral tonic seizures, and frequent focal onset bilateral tonic-clonic seizures indicate a higher risk of temporo-perisylvian epilepsy. In parietal/occipital lobe epilepsy, despite that some symptoms result from activity in the immediate vicinity, stronger connectivity with other regions usually contributes to the generation of prominent ictal semiology. Hence, multilobar electrode placement is often useful in practice. For insular epilepsy, it is important to understand the anatomy, function, and networks between other regions. A semiological approach is one of the most important clues for electrode implantation and interpretation of SEEG.

Keywords

• ictal semiology
• stereoelectroencephalography
• anatomo-electroclinical correlations
• epileptogenic zone