Methodology of "in vivo" anatomical study and stereo-electroencephalographic exploration in brain surgery for epilepsy.

Stereotactic implantation of deep SEEG electrodes performed as a prelude to surgery in some patients with drug-resistant focal epilepsy requires previous "in vivo" identification and localization of the cortical and subcortical structures to be explored, visualized "semi-directly" "or directly" by neuroradiological imaging techniques. Stereoscopic stereotactic teleangiography is a safety factor in transcutaneous electrode implantation and biopsies, but it also localizes the cortical sulci in a "semi-direct" manner by identifying vascular segments deeply buried in this sulci, which constitute their lamina vascularis. Although RMI greatly contributes to the study of the pallium, visualizing fragments of sulci and gyri does not necessarily mean that these structures can be identified with certainty, notably on the convexity of the brain. To solve this problem, RMI sections are enlarged by a photographic process, then combined with the images obtained from neuroradiological stereotaxis by means of anatomical landmarks that are common to both types of documents, using the bicommissural reference systems, bicallosal l/nl or vascular segments. This enables the angiographic laminae vascularis, which define the sulci in a "semi-direct" manner, to be used a kind of "Ariadne's clew" to identify cortical structures on RMI sections. In percutaneous stereotactic electrode implantation, the choice of the trajectories results from a compromise between the need to reach the desired anatomical structures, identified and localized within the stereotactic space, and the necessity to avoid the blood vessels displayed by stereoangiography. In some cases, the accuracy of anatomical definition can be verified during the SEEG study and/or by the evoked potential technique. Once the electrodes have been removed, their traces can be identified in a control RMI examination which constitutes a further verification.