Indications and limits of stereoelectroencephalography (SEEG)

Epilepsy surgery is now an accepted treatment to achieve seizure control in carefully selected patients, both children and adults, suffering from drug-resistant focal epilepsy. Although surgical strategies can often be defined on the basis of non-invasive diagnostic procedures, and despite the recent advances in this field, an increasing number of more complex cases requires invasive EEG (iEEG) to provide precise information on the localization of the epileptogenic zone (EZ), its relationships with eloquent cortex (EC), and the feasibility of a tailored surgical resection. Stereoelectroencephalography (SEEG) is one of the iEEG techniques currently used in the presurgical work-up, and it is well-distinguished from other invasive techniques, such as subdural grids and strips. SEEG depth electrodes enable exploration of deeply located structures and lesions, and of buried cortex, which are not easily assessable by subdural or other iEEG methods. Simultaneous recording of SEEG signals from deep and superficial brain structures allows, when the position of each electrode is precisely determined, delineation of a three-dimensional, spatial and temporal organization of epileptic activities. In the following chapter we discuss some specific indications (temporal or extra-temporal, lesional or non-lesional epilepsies) as well as the limits of the SEEG technique, with respect to some epileptological issues during presurgical evaluation.