[Contribution of the stereo-EEG to the definition of an epileptic focus]

For epilepsy, surgical success rates rely on the validity of the spatial definition of the epileptogenic focus. Clinical seizure characteristics and interictal and ictal EEG patterns have been the traditional means of localization. Electrocorticography and stereo-electroencephalography are sometimes used. With stereo-EEG, the topographic determination of an epileptogenic zone depends above all on the study of the anatomo-electro-clinical correlations evidenced during the seizures themselves. Interictal abnormalities, infra-clinical discharges, stimulations also help to evaluate the topography of the focus. Because surgical success is increased neither with stereo-EEG nor with EEG, the procedure remains controversial. But stereo-EEG allows the selection of 36% more patients for surgery by defining otherwise unidentifiable single epileptogenic foci (Spencer). Furthermore, the use of stereo-EEG in seizure disorders of extra-temporal origin is a real diagnostic benefit.