WS1.8. Invasive Monitoring: Understanding the Chronological Occurrence of Seizure Semiology

Abstract

The percentage of patients considered for epilepsy surgery in need for invasive evaluation ranges 30% and 40% in tertiary epilepsy centers (Kovac et al., 2017). It will become unavoidable when mapping epileptogenic zone for the patients with “MRI-negative” study and when mapping eloquent cortex for the patients subject to functional deficit following resection surgery. Invasive evaluation includes various type of intracranial electrodes, such as stereotactically implanted intracerebral (depth) electrodes (SEEG), subdural electrodes (SD-EEG) and intraoperative electrocorticography (ECoG). Stereoelectroencephalography (SEEG) was designed and developed by Talairach and Bancaud in France in 1960s. It is an invasive method of exploration for drug-resistant focal epilepsies, offering the advantage of a tridimensional and temporally precise study of the epileptic discharges (Isnard et al., 2018). Differently from SD-EEG in part, it does not need craniotomy. The basic principle of Bancaud and Talairach’s approach to epilepsy surgery was to study the seizures themselves, through what they named the “anatomo-electro-clinical correlations” (Kahane, 2006). A group of selective cases, studied with assistance of SEEG for refractory focal epilepsies, will be presented in the workshop to illustrate significance of the anatomo-electro-clinical correlation approach. All the cases had motor seizures which generated respectively from allocortical and isocortical subdivisions of the frontal, temporal and parietal lobes. The different systems of hierarchical organization activated during seizures gave rise to the chronology of semiology dissimilarly. It is more likely for the complex motor behaviors (i.e. automatism) to occur if the motor seizures generate from phylogenetically older or less differentiated cerebral cortex (i.e. histologically defined allocortex). On the other hand, the more phylogenetically recent or the more differentiated cortex (i.e. histologically defined isocortex), from which the motor seizures generate, the more likely the simple motor (i.e. tonic or tonic-clonic) signs develop. This is to imply that meaningful categorization of motor seizures in terms of semiology is possible and correlates with anatomic organization along a histological differentiation, in keeping with current hypotheses of hierarchical organization in the human brain.