Localization of the epileptic focus during methohexital-induced anesthesia

A short anesthesia was provided by methohexital for painless percutaneous removal of subdural electrodes in 27 patients with medically intractable, complex partial seizures who had undergone invasive preoperative evaluation. Electrocorticographic(ECoG) recordings performed before and during the narcosis were submitted to visual (n = 27) and computerized (n = 3) analysis to obtain additional information about the location of the epileptic focus (or foci). The following observations were made: focal epileptiform potentials were induced in 24 of 27 patients (89%); (b) in 20 of these 24, the induced spikes appeared amid or were followed by isoelectric or subdelta activity. These spikes were characterized by high amplitude as well as rhythmic and synchronized appearance over a circumscribed focal area (or areas) known to be spontaneously epileptogenic. This phenomenon, termed spike-burst-suppression (SBS) pattern, allowed identification of the primary epileptic focus in many patients with temporal lobe epilepsy. Furthermore, it indicated a good outcome of epilepsy surgery. Computerized analysis of the induced synchronized spikes (n = 3) allowed further delineation of the primary site of epileptogenicity and quantitative comparison of multiple epileptic generators. ECoG recording during deep methohexital-induced narcosis is a valuable tool for lateralization and delineation of the primary epileptogenic focus.