Abstracts

Rationale: Localization of the epileptogenic focus from noninvasive measurements would greatly aid in the presurgical planning in patients with partial seizure disorders. In the absence of lesions visible on neuroimaging studies, identification of the epileptogenic cortex is made through the analysis of electrophysiological data obtained during ictal activity from prolonged intracranial recordings. The development of a noninvasive means to identify the seizure onset zone (SOZ) would thus play an important role in patients with extra-temporal lobe epilepsy. In the present study, we have developed a noninvasive cortical imaging method to estimate cortical potentials from the scalp-recorded EEG, and have examined its applicability to image epileptiform activity in patients with medically intractable epilepsy. Methods: Ten pediatric patients (3M/7F, ages 4-16) with intractable partial epilepsy were studied using a protocol approved by the Institute Review Boards of the University of Minnesota and the University of Chicago. Each patient had multiple (6 to 14) interictal spikes (IIS) subjected to the cortical potential imaging (CPI) analysis. Realistic geometry inhomogeneous boundary element head models were built using each individual’s MRI. CPI analysis was performed on the IIS, and extrema in the estimated CPI images were compared with SOZ as determined from the ictal ECoG recordings. Results: In the group of patients studied, the CPI results identified the epileptogenic foci which were confirmed by neurosurgical resection. Among the ten patients studied, five were seizure free and five had substantial reduction in seizure. Ictal ECoG recordings revealed that 8 patients exhibited a single epileptogenic focus while 2 patients had two foci. In each patient, the CPI results revealed an area of activity overlapping with the SOZ as identified by ictal ECoG. The distance from the extreme of the CPI images at the peak of IIS to the nearest intracranial electrode associated with the onset of the ictal activity was evaluated for each patient and this averaged distance was 4.6 mm. Conclusions: In the present study, we have developed and validated a novel CPI technique in a group of 10 pediatric epilepsy patients. The CPI analysis was successfully performed in a number of interictal spikes in patients whose ictal ECoG recordings revealed epileptogenic foci in the temporal, fontal and parietal lobes. The quantitative comparison of the foci as estimated from the scalp EEG with the SOZ determined from ictal ECoG showed a high degree of consistency between the CPI results and ictal ECoG results. These promising results demonstrate the potential for noninvasive localization of the epileptogenic focus from interictal scalp EEG recordings. The present results may have a significant impact on the presurgical planning in pediatric patients with intractable epilepsy by dramatically reducing or eliminating the use of intracranial recording.