Abstracts

Rationale: The success of epilepsy surgery heavily depends on accurately identifying the epileptogenic zone. Even when the condition is surgically remediable, the success rate of focal cortical dysplasia (FCD) does not exceed 60%. Moreover, diverse patterns and rapid propagation of ictal activity limit the accuracy of presurgical evaluations. This study aims to explore the critical sources of EEG and their time series values during the ictal period in FCD.

Methods: EEG data were extracted from a cohort of patients who underwent resective surgery between January 1998 and August 2023. Among these patients, 165 were pathologically confirmed to have FCD, with a minimum follow-up duration of one year after surgery. Ictal EEGs were available only in 43 patients among 100 were seizure-free following surgery. Among those, five patients each with frontal lobe epilepsy (FLE) and temporal lobe epilepsy (TLE) were selected for this pilot analysis. Initial 10-second segments of ictal EEG, were divided into one-second intervals. The preprocessing included applying a bandpass filter (1 to 30 Hz) to eliminate high-frequency artifacts and direct current components, as well as artifact rejection through independent component analysis. Independent components with a residual variance exceeding 20% were also excluded. Each dipole source was ranked and analyzed according to onset pattern and resection regions.

Results: 'Correct localization (CL)' was defined as cases where at least one of the top three most frequent ictal dipole sources was included in the resected area. Analyzing whole sessions, all patients were classified as CL except one with TLE, who had a rhythmic spike-and-wave onset pattern. The other patients have rhythmic sinusoidal waves. For the dynamic course of the dipole source, the 10-second epoch was divided into three sessions: early (1-3 sec), middle (4-7 sec), and late (8-10 sec). Two FLE and one TLE were CL during all three sessions. In TLE, three patients showed an early dominant CL pattern. In FLE, two patients showed a late dominant pattern, but none showed an early pattern. Overall, the frequent sources in the middle session corresponded to the resection area in all patients except one, without a significant source found.

Conclusions: The study successfully identified and ranked EEG source regions for each patient, except for one with TLE, highlighting the top three regions in the initial 10-second period for their potential clinical significance. The findings suggest that the middle (4-7 sec) ictal phase contains valuable information that can aid in the diagnosis and surgical planning for epilepsy patients. Preliminary results could enhance the understanding of the epileptic network within the brain. Furthermore, the study has the potential to improve the localization of the epileptogenic zone and enhance surgical outcomes.


Funding: Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, Republic of Korea (RS-2023-00265638)