Abstracts

Rationale: Temporal lobe epilepsy in the absence of MRI abnormalities and memory deficits is often presumed to have an extramesial or even extratemporal source. We report the results of widespread SEEG analysis in patients with temporal lobe epilepsy with normal MRI images and memory scores. Methods: Eighteen patients with medically refractory epilepsy who also had unremarkable MRI scans and normal verbal and visual memory scores on formal neuropsychological testing were included in the study. All patients had seizure semiology and video-EEG findings consistent with temporal lobe epilepsy. A standardized SEEG investigation was performed for each patient with electrodes implanted into the mesial and lateral temporal lobe, temporal tip, posterior temporal neocortex, orbitomesiobasal frontal lobe, posterior cingulate gyrus, and insula. This information was used to plan subsequent surgical management. Results: Interictal SEEG abnormalities were seen in the mesial temporal structures in 17 patients (94%) and in the lateral temporal neocortex in 6 (33%). Seizure onset was exclusively from mesial structures in 13 (72%), exclusively from neocortical structures in 2 (12%), and independently from mesial and neocortical foci in 3 (17%). No seizure activity was observed arising from any extratemporal location. All patients underwent surgical intervention targeting the temporal lobe and tailored to the SEEG findings, and all experienced significant improvement in seizure frequency at least one year postoperatively. Conclusions: Our study demonstrates three important findings: (1) normal memory does not preclude mesial temporal seizure onset, (2) onset of seizures exclusively from mesial temporal structures without early neocortical involvement is common even in the absence of memory deficits, and (3) extratemporal seizure onset is rare when vEEG and semiology are consistent with focal temporal lobe epilepsy.