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.