Direct imaging with high-density electroencephalography (EEG) may localize seizure onset zone prior to surgery in patients with focal epilepsy, according to study results published in Neurology.

Identifying the epileptogenic zone is crucial prior to surgical intervention for focal epilepsy and in recent years, EEG has become an important modality to guide surgical interventions. The objective of the current study was to assess the role of EEG recordings and source localization analyses in localizing seizure onset zone prior to surgical planning in patients with focal epilepsy.

The study included 39 adult patients (51.28% women; mean age, 17.87 years) with partial seizures who underwent pre-surgical evaluation with high-density long-term EEG monitoring at Mayo Clinic, Rochester, MN, between 2007 and 2017. Patients underwent either surgical resection or invasive intracranial EEG monitoring. Study researchers used a new method for directly imaging seizure sources and interictal spikes from high density EEGs, and confirmed it for seizure onset zone localization assessed with intracranial EEG findings and surgical resection volume.

There were a total of 138 seizures included in the study. The sub-lobar concordance rate between EEG seizure onset zone results and clinical findings was 94.87%. The difference was more significant in patients with greater than 1 interictal epileptic discharge cluster as ictal source imaging indicated a concordance rate of 87.5%.


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The mean localization error, calculated as the average distance from the estimated source to the closest intracranial seizure onset zone electrode, was about 1.35 cm in patients with concordant results. For patients following successful surgery, the average distance from the estimated source to the boundary of the resected volume was 0.74 cm.

The interictal study included at least 10 hours of recordings for each patient. The concordance rate was 78.4% when study researchers used the dominant interictal epileptic discharge cluster for source imaging. The difference was more significant in patients with greater than 1 interictal epileptic discharge cluster as the interictal source imaging showed a concordance rate of 56.2%.

The study had several limitations, including limiting participants to patients with focal epilepsy, the use of high quality magnetic resonance imaging, and the use of high-density EEG.

“The present study demonstrates the clinical applicability and merits of a noninvasive electrophysiological seizure imaging approach, which is currently missing in clinical routine, but may become an important component of the pre-surgical evaluation routine for epilepsy treatment,” concluded the study researchers.

Reference

Ye S, Yang L, Lu Y, et al. Contribution of ictal source imaging for localizing seizure onset zone in patients with focal epilepsy patients. Neurology. Published online October 23, 2020. doi:10.1212/WNL.0000000000011109