The epileptogenic zone: general principles.

Sir Victor Horsley, a British neurosurgeon, pioneered epilepsy surgery and, in 1886, published the reports of successful cortical resections that resulted in a significant reduction in epileptic seizures in three patients (Horsley, 1886). At that time, V. Horsley assisted by J.H. Jackson (epileptologist) and D. Ferrier (neurophysiologist), identified the region to be resected by the location of either a structural lesion and/or the area of cortex which, on stimulation, reproduced the initial symptoms of the clinical seizure. As J.H. Jackson indicated, they hoped that surgery would result in “cutting out the discharging lesion” that they believed was “the very local cause of the fits”. In other words, in the 19 century, the so-called “discharging lesion”, defined by the location of the macroscopic cortical lesion and/or clinical ictal semiology, was equivalent to the epileptogenic zone of modern epileptology. In 1929, H. Berger (Berger, 1929) published the first report of EEG recordings in humans, and in 1934 O. Foerster (Foerster and Altenburger 1934) reported the first electrocorticogram. However, the extent of the “epileptogenic zone” was defined almost exclusively by the limits of the macroscopical cortical lesion until the early 1950s. At that time, Bailey and Gibbs (Bailey and Gibbs 1951) and Penfield and Jasper (Penfield and Jasper 1954) also used complementary interictal scalp EEG and interictal corticography to establish the limits of the epileptogenic zone. For the next 10-20 years these techniques remained the essential armamentarium used to define the epileptogenic zone, even if researchers realized the limitations and lack of precision intrinsic to the interictal epileptiform activity as an index of the epileptogenic zone. A new breakthrough was the introduction of the stereo-electroencephalography (SEEG) by Jean Talairach and Jean Bancaud that revolutionized our concept of the epileptogenic zone (Bancaud et al. 1962a, Bancaud and Chauvel 1987, Buser et al. 1973, Talairach and Bancaud 1973, Talairach and Bancaud 1974). The French investigators assumed that “stereoencephalographie” would actually provide the ideal methodology to define, with extreme precision, what they defined as the epileptogenic zone. Since the pioneer work of Talaraich and Bancaud in the 1960s, extensive surgical experience and the emergence of new, powerful diagnostic techniques have led to the redefinition of the epileptogenic zone, clearly distinctive from that originally described by Talairach and Bancaud (Lüders et al. 1993). The approach of this definition was significantly more abstract and allowed the inclusion of modern diagnostic techniques and possible future technological advances. For example, the epileptogenic zone in Talaraich and Bancaud definition was determined by the results of the stereo-EEG evaluation and therefore was primarily an ictal EEG concept. On the other hand, the modern/ practical “epileptogenic zone” is deCorrespondence: H.O. Lüders Epilepsy Center, Cleveland Clinic Foundation, Cleveland, OH USA Epileptic Disord 2006; 8 (Suppl. 2): S1-9