Abstracts

Rationale: The absence of lesion in magnetic resonance imaging (MRI) presents several challenges in the presurgical evaluation and the surgical treatment of drug-resistant epilepsy. If visualization of the epileptic focus is possible, it will help to determine the resection margin and improve the prognosis of the patient. Therefore, we studied the accuracy of visualization of seizure focus using electrical source imaging (ESI) and its effect on postoperative outcome. Methods: We retrospectively reviewed medical records of operated MRI-negative intractable epilepsy patients in our center from 2010 through 2016. All the patients included in the analysis underwent video electroencephalography (EEG) monitoring, high-resolution MRI, 18-fluorodeoxyglucose positron emission tomography (18-FDG-PET) scan, and intracranial EEG monitoring. 13 patients successfully underwent ictal single-photon emission computed tomography (SPECT). For ESI, CURRY 8 program was used to compute ESI following the visual identification of interictal spikes. Outcomes were determined using Engel’s classification at six months after the surgery. Results: Among 21 operated MRI-negative intractable epilepsy patients, 17 patients (men 9, 52.9%, mean age 30.1 ± 8.8 years) had sufficient data for the ESI analysis. The onset of age was 14.6 ± 8.0 years. Intracranial EEG monitoring determined seizure focus in the temporal area (n=5), the extratemporal area (n=9), and both temporal and extratemporal area (n=3). Eleven patients (65%) showed a favorable outcome corresponding to Engle's classification I and II. ESI correctly localized the epileptic focus within the resected area in 13 of 17 patients. Among 13 patients, nine (69%) had favorable postoperative outcomes. Among the four incorrectly localized patients, two (50%) had unfavorable post-surgical outcomes. The accuracy of ESI in predicting surgical outcome was 64.7%. The accuracy of FDG-PET and ictal SPECT was 41.1% and 61.5%, respectively. Conclusions: Despite significant advances in anatomic and functional cerebral imaging, MRI-negative epilepsy still represents the most challenging scenario for presurgical evaluation and eventually, surgical treatment. This study demonstrated that the localization accuracy of ESI (64.7%) was not significantly different from ictal SPECT (61.5%) but slightly superior to the Brain FDG PET scan (41.1%). ESI is a relative simple evaluation method to identify the epileptogenic zone in MRI-negaitve epilepsy patients, improving prognosis of the patients. Funding: No funding