Ictal electrical source imaging for localizing the epileptogenic zone in drug-resistant epilepsy: A retrospective study

Purpose

This study aims to analyze the clinical utility of electrical source imaging (ESI) of ictal rhythms in epilepsy surgery.

Methods

Medical records of 42 patients who underwent resective epilepsy surgery at Asan Medical Center (2000–2021) were reviewed. All patients underwent long-term video-EEG monitoring. EEG data were analyzed for ictal onset, rhythm patterns, and dominant frequency. Ictal ESI (IC-ESI) findings were compared with 18-fluorodeoxyglucose positron emission tomography (18-FDG-PET), ictal single-photon emission computed tomography (SPECT), and intracranial EEG to assess concordance, with surgical outcomes in Engel classification.

Results

Among 223 analyzed seizures, the overall localization accuracy of IC-ESI was 48.0 % (95 % CI: 41.5–54.5 %). Localization to the deep temporal region showed significantly higher accuracy (64.7 %, 95 % CI: 54.1–74.0 %) and sensitivity (86.4 %, 95 % CI: 75.5–93.0 %) than those outside this region (accuracy: 35.2 %, 95 % CI: 27.4–43.9 %; sensitivity: 17.4 %, 95 % CI: 11.0–26.7 %; p < 0.001 for both). At the patient level, IC-ESI demonstrated a 59.5 % accuracy (95 % CI: 44.5–73.0 %) and 76.7 % sensitivity (95 % CI: 59.1–88.2 %). Accuracy differences between IC-ESI and 18-FDG-PET and ictal SPECT were not significant (p = 0.15). Dye injection within 15.5 s of ictal EEG onset was associated with concordant SPECT and IC-ESI findings (p = 0.03). IC-ESI accuracy was independent of MRI (p = 0.60) or intracranial EEG findings (p = 0.18; 95 % CI: 0.02–1.94).

Conclusion

IC-ESI achieves accuracy comparable to that of ictal SPECT and 18-FDG-PET, supporting its reliability for identifying epileptogenic zones, particularly in temporal lobe epilepsy. Despite challenges in detecting ictal rhythms, IC-ESI adds clinical value to presurgical evaluations.