Convergence of Stereotactic Surgery and Epilepsy

Abstract

Because successful resective epilepsy surgery relies on accurate preoperative localization of the epileptogenic zone (EZ), presurgical evaluation is necessary to obtain the widest and most accurate spectrum of information from clinical, anatomic, and neurophysiological aspects, with the ultimate goal of performing an individualized resection for each patient.1-3 Noninvasive studies are successful in identifying and anatomically delineating the EZ in approximately 70% of the patients who are operated on at the Cleveland Clinic Epilepsy Center (unpublished data). Consequently, a formulation of a clear anatomo-electro-clinical (AEC) hypothesis may not be possible in the remaining 30% of patients, or an AEC hypothesis is partially generated but the exact location of the epileptogenic area within a specific neuronal network, its extent, or its overlap with functional (eloquent) cortex remains unclear. In these clinical scenarios, when the noninvasive data are insufficient to define the EZ, extraoperative invasive monitoring may be indicated. The stereoelectroencephalography (SEEG) is one of the extraoperative invasive methods that can be applied in patients with medically refractory focal epilepsy to anatomically define the EZ and the possible related functional cortical areas. SEEG: HISTORICAL PERSPECTIVE AND PRINCIPLES Human cerebral stereotaxis was conceptualized and initiated in 1947 by Spiegel and Wycis,4 and its use in recording from deep brain structures has been reported since 1950. Since then, stereotactic placement of intracerebral electrodes has gained progressive popularity and was reported for the first time in the evaluation of temporal lobe epilepsy in the early 1960s by Crandall and colleagues.5,6 Meanwhile, in the neurosurgical unit of the Saint Anne Hospital in Paris, stereotactic investigations of epileptic patients with intracerebral electrodes were inspired by a new, innovative concept: Epileptic seizures were regarded as a dynamic process, with a spatial-temporal, often multidirectional organization best defined as a 3-dimensional arrangement. This method was originally called SEEG.7,8 The SEEG method was originally developed by Jean Talairach and Jean Bancaud during the 1950s and has been used mostly in France and Italy as the method of choice for invasive mapping in refractory focal epilepsy.9-19 In France, after the development of the stereotactic techniques and frames, which were applied initially for abnormal movement disorder surgery, Jean Talairach focused most of his attention to the field of epilepsy, along with Jean Bancaud, who joined him in 1952. The new methodology created by both physicians led them to depart very quickly from an approach limited to the mapping of the superficial cortical areas, as did Wilder Penfield and colleagues at Montreal Neurological Institute. Posteriorly, the development of specific surgical tools, adapted to a new stereotactic frame designed by Talairach and colleagues, directed the Saint Anne investigators to propose the functional exploration of the brain by depth electrodes, allowing the study of both superficial and deep cortical areas. The debut of SEEG was on May 3, 1957, with the first implantation of intracerebral electrodes for epilepsy in Saint Anne Hospital. By departing from the current methods of invasive monitoring, such implantations have allowed the exploration of the activity of different brain structures and recording of the patient’s spontaneous seizures, something that Penfield’s method of investigation failed to achieve. The principle of SEEG methodology remains similar to the principles originally described by Bancaud and Talairach, which are based on AEC correlations with the main aim of conceptualizing the 3-dimensional spatial-temporal organization of the epileptic discharge within the brain.9,10,14-18,20-26 The implantation strategy is individualized, with electrode placement based on a preimplantation hypothesis that takes into consideration t