Presurgical evaluation: Current role of invasive EEG

Our purpose was to review the current role of invasive and semi-invasive EE G in the presurgical evaluation of candidates for epilepsy surgery. The use of stereotactically implanted intracranial depth (stereo-EEG), subdural st rip and grid, and foramen ovale electrodes, as well as intraoperative elect rocorticography and electrical brain stimulation ("functional mapping") at the Epilepsy Center University Hospital Zurich, from 1984 to 1998, is analy zed. Advantages and disadvantages of the various intracranial EEG technique s are critically discussed. Out of 422 selective amygdalohippocampectomies performed in Zurich, 54% had non-invasive, 32% had semi-invasive, and 14% h ad invasive presurgical EEG evaluation. Because patients currently referred to our center increasingly present with a complex history of disease, i.e. , constitute so-called "difficult cases", there is trend to combine several invasive and semi-invasive, pre- and intraoperative neurophysiological tec hniques.