Dipole-source analysis in a realistic head model in patients with focal epilepsy

Purpose: By the use of three different head models in EEG dipole analysis, we tried to model the origin of interictal and ictal epileptic activity as precisely as possible. Further, as a control, a second evaluation was made by an independent group to control for interindividual reliability of the d ipole source analysis. With the realistic head model (CURRY) considering co rtex, skull, and skin segmentation, the spike source was located. Methods: In five patients with mesial temporal epileptogenesis, confirmed b y successful epilepsy surgery, the spike source was close to the hippocampu s, with a mean distance of the dipole source from the hippocampus of 13.6 m m (range, 9-17.2 mm). In one case the ictal EEG also could be analyzed and resulted in a dipole-source localization comparable to the interictal sourc e. Results: In both head models using either pure cortex segmentation only or a concentric three-shell model, the dipole source was systematically disloc ated in a more superior position. Data analysis by a second group with inde pendently chosen EEG samples and identical individual head model resulted i n deviations of <5.3 mm. Data analysis using independently selected spikes and independently segmented head models resulted in deviations less than or equal to 16.7 mm. Conclusions: In four cases of extratemporal epileptogenesis, the origin of interictal epileptiform discharges was localized to the suspected primary e pileptogenic zone.