General principles of pre-surgical evaluation

Abstract

To estimate where the epileptogenic zone is and what its boundaries are, epileptologists have been using different diagnostic tools of increasing complexity and technical difficulty. This includes careful analyses of seizure semiology, electrophysiological studies (noninvasive and invasive), anatomical neuroimaging, and functional neuroimaging. These diagnostic methods have led to the definition of several cortical zones (symptomatogenic zone, irritative and ictal onset zones, epileptogenic lesion, and functional deficit zone), each one of which is a more or less precise index of the epileptogenic zone. During modern presurgical evaluation of patients with intractable epilepsy, an attempt is made to locate and define the boundaries of these five zones. In the ideal surgical candidate, all five zones will show a high degree of overlap and the resection can be performed with a high likelihood of seizure freedom. However, in most patients the different cortical areas are somewhat discordant in location or extent and, in the final decision about surgery, the relative significance of each one of these areas (based on the information presented below) must be weighted carefully.