Abstracts

Rationale: Foramen ovale (FO) electroencephalography (EEG) have been shown useful to localize epileptogenic foci after inconclusive noninvasive investigations in patients with suspected mesial temporal lobe epilepsy (MTLE). However, previous studies have not investigated the utility of this technique in nonlesional mesial temporal lobe epilepsy which is more challenging and most often multifocal. Our goal was to assess if FO EEG recordings are diagnostic in nonlesional cases and to assess the surgical outcome in this group. Methods: We retrospectively studied all patients over 18 years old with possible MTLE but inconclusive scalp EEG recordings who underwent FO EEG between January 1 2004  and  January 31 2017. We collected data on age, sex, lesional status (evidence of mesiotemporal sclerosis based on MRI and/or PET brain findings), whether FO EEG was diagnostic (could localize the epileptogenic focus confidently and delineate the surgical plan), if surgery was performed or not, and surgery outcome (Engel class I-IV). Categorical variables were compared using Fishers exact test and continuous variables were compared using Wilcoxon rank sum test. Results: 86 patients (43 male, 43 female) met inclusion criteria. In 58 cases (67.4%) FO was diagnostic and in 28 cases it was not. There were 68 lesional and 18 non lesional cases. FO EEG recording was diagnostic in 72.1% of lesional cases versus 50% of nonlesional cases which did not reach statistical significance (p=0.094; Fishers exact test). 46 cases underwent some type of surgery (anterior temporal lobectomy (ATL), other resection, vagal nerve stimulator (VNS), or responsive neurostimulation (RNS)). 25 lesional  (36.8%) and 5 nonlesional (27.8%) patients underwent ATL. There was no significant difference in surgical outcome between these two groups (table 1). Conclusions: This study shows that FO EEG provides a useful minimally invasive diagnostic tool to localize the MTLE epileptogenic focus regardless of the presence of anatomic/functional lesion on the brain imaging. Future studies with higher number of nonlesional cases who had FO EEG studies and ATL based on FO EEG results are needed to better assess the accuracy of FO EEG in localizing the epileptogenic zone. Funding: N/A