P. Tournoux’s research while affiliated with Policlinico Universitario Agostino Gemelli and other places

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.

M.R.I. allows us to visualise cortical sulci and convolutions. But visualisation doesn't mean precise and reliable identification, because there is individual variability in these structures and because of the presence of 'plis de passage', and secondary and tertiary sulci. G. Szikla has demonstrated the possibility of defining indirectly the topography of cortical sulci by means of Tele-Stereotactic-Stereoscopic Angiography. Indeed, Three-Dimensional Angiography permits one to identify deep vascular segments (laminae vascularis) buried in the sulcal walls of the invaginated cortex, thereby indicating the shape, the depth and the direction of a given sulcus. We propose a procedure utilising these same laminae vascularis as a means for directly identifying sulci and convolutions visible on MRI images. This method needs magnification of MRI images which are matched against stereotactic films using ventricular (bicommisural line) and/or vascular landmarks. We think that this procedure, in spite of some factors of errors, provides better anatomical knowledge and constitutes real progress in comparison with the previous stereotactic neuroradiological study.

Modern neurosurgical concepts call for not only "seeing" but also for "localizing" structures in three-dimensional space in relationship to each other. Hence there is a need for a reference system. This book aims to put this notion into practice by means of anatomical and MRI sections with the same stereotaxic orientation. The purpose is to display the fundamental distribution of structures in three-dimensional space and their spatial evolution within the brain as a whole, while facilitating their identification; to make comparative studies of cortico-subcortical lesions possible on a basis of an equivalent reference system; to exploit the anatomo-functional data such as those furnished by SEEG in epilepsy and to enable the localization of special regions such as the SMA in three-dimensional space; and to apply the anatomical correlations of this reference system to neurophysiological investigations lacking sufficient anatomical back-up (including PET scan).