3-DIMENSIONAL LOCALIZATION OF INTERICTAL EPILEPTIFORM ACTIVITY WITH DIPOLE ANALYSIS - COMPARISON WITH INTRACRANIAL RECORDINGS AND SPECT FINDINGS

Seventeen patients with therapy-resistant partial epilepsy were studie d in order to compare the localization of the epileptic focus provided by three-dimensional dipole analysis of scalp interictal epileptiform EEG activity to the localization of the ictal pacemaker zone obtained by intracranial recordings. The results were also compared with regio nal abnormalities in interictal Tc-99m-hexamethylpropylenenamine oxime single-photon emission computed tomography (SPECT). Dipole analysis w as performed using a well-known commercial computer program based on a three-shell model. For 12 of the 17 patients, the dipoles for all the individual spikes were located in the same area, in two cases, two se parate locations were found, and in three cases the dipoles were scatt ered over a large area. In 8 of the 12 patients with a single dipole l ocation, intracranial ictal recordings revealed a seizure initiation z one corresponding to the dipole location. In another two cases, intrao perative corticography confirmed the dipole findings. In the two remai ning patients, the intracranial recordings revealed a different patter n of seizure initiation than had been anticipated from the dipole anal ysis. In one of the two patients with two dipole locations, intracrani al recordings revealed a seizure initiation zone corresponding to one of the two dipole location sites, whereas in the other patient the sei zure onset pattern was more complex. In two of the three patients with widely scattered dipole areas, seizure onset was complex, whereas in the third patient a localized seizure onset was found. In 10 of the 12 patients with a single dipole location site, there was good correlati on between this site and regions of low flow in the interictal SPECT m easurements. In both patients with two dipole areas, there was a low f low area corresponding to at least one of the dipole localizations. In two of the three patients with widespread dipoles, there were major S PECT low-flow areas, whereas in the third patient interictal SPECT was normal. Although our investigations so far are tentative, we think th e results indicate that dipole analysis of interictal epileptiform EEG activity may become a useful supplementary method for the localizatio n of the epileptogenic region in patients who are under consideration for surgical therapy, especially ff combined with SPECT or other indep endent localizing techniques.