Abstract
Objective: Accurate estimation of the epileptogenic zone (EZ) is essential for favorable outcomes in epilepsy surgery. Conventional ictal electrocorticography (ECoG) onset is generally used to detect the EZ but is insufficient in achieving seizure-free outcomes. By contrast, high-frequency oscillations (HFOs) could be useful markers of the EZ. Hence, we aimed to detect the EZ using interictal spikes and investigated whether the onset area of interictal spike-related HFOs was within the EZ.Methods: The EZ is considered to be included in the resection area among patients with seizure-free outcomes after surgery. Using a complex demodulation technique, we developed a method to determine the onset channels of interictal spike-related ripples (HFOs of 80–200 Hz) and investigated whether they are within the resection area.Results: We retrospectively examined 12 serial patients who achieved seizure-free status after focal resection surgery. Using the method that we developed, we determined the onset channels of interictal spike-related ripples and found that for all 12 patients, they were among the resection channels. The onset frequencies of ripples were in the range of 80–150 Hz. However, the ictal onset channels (evaluated based on ictal ECoG patterns) and ripple onset channels coincided in only 3 of 12 patients.Conclusions: Determining the onset area of interictal spike-related ripples could facilitate EZ estimation. This simple method that utilizes interictal ECoG may aid in preoperative evaluation and improve epilepsy surgery outcomes.
Highlights
The epileptogenic zone (EZ) is characterized by excessive synchronization at seizure onset [1]
Between July 2011 and June 2014, we retrospectively identified patients with medically intractable epilepsy who underwent intracranial EEG monitoring and focal resective surgery within the Tohoku University Hospital Comprehensive Epilepsy Program who met the following inclusion criteria: resective surgery performed after intracranial EEG monitoring, with available postsurgical seizure outcome after 2 years, without seizure recurrence for 2 years after surgery, without previous brain surgery, and with a spike observed in the intracranial EEG
Patients who did not become seizure-free after epilepsy surgery were excluded from this study because it was presumed that the EZ was not fully included within the implanted intracranial electrodes
Summary
The epileptogenic zone (EZ) is characterized by excessive synchronization at seizure onset [1]. It is generally located within the resection region following surgery and has seizure freedom [2, 3]. The identification of the EZ, including the seizure onset zone (SOZ) [4], and the complete resection thereof are essential for improving epilepsy seizure outcomes. The area with the earliest ictal electrocorticography (ECoG) change is currently used to detect the SOZ [5]. Resection of the EZ identified based on ictal ECoG patterns leads to a seizure-free outcome in only about 60% of patients who undergo epilepsy surgery [6, 7].
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