Temporal lobe epilepsy in patients with nonlesional MRI and normal memory: an SEEG study

Abstract

OBJECT Temporal lobe epilepsy (TLE) in the absence of MRI abnormalities and memory deficits is often presumed to have an extramesial or even extratemporal source. In this paper the authors report the results of a comprehensive stereoelectroencephalography (SEEG) analysis in patients with TLE with normal MRI images and memory scores. METHODS Eighteen patients with medically refractory epilepsy who also had unremarkable MR images and normal verbal and visual memory scores on neuropsychological testing were included in the study. All patients had seizure semiology and video electroencephalography (EEG) findings suggestive of TLE. 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 observed in the mesial temporal structures in 17 patients (94%) and in the temporal tip in 6 (33%). Seizure onset was exclusively from mesial structures in 13 (72%), exclusively from lateral temporal cortex and/or temporal tip structures in 2 (11%), 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 with a postoperative follow-up observation period of at least 1 year. CONCLUSIONS This study demonstrates 3 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 video EEG and semiology are consistent with focal TLE.

Method of invasive monitoring in epilepsy surgery and seizure freedom and morbidity: A systematic review

“…There were 12 studies that reported on epilepsy duration, with no significant difference between SEEG patients (mean = 126.8 months ± 65.0, median = 121.8) and SDE patients (mean = 62.4 months ± 51.1, median = 51.4; Table ). Among the SEEG patients, the etiology was identified as a temporal epileptogenic focus in 42.2% of patients, tumor in 6.7% of patients, FCD1 in 39.2% of patients, FCD2 in 10.7% of patients, and lesional in 41.5% of patients .…”

Seizure outcomes of temporal lobe epilepsy surgery in patients with normal MRI and without specific histopathology

“…A possible explanation might be that patients with TLE and N-MRI constitute a very heterogeneous group. In fact, some of them may be truly non-lesional (N-HP), while others may have different histopathological findings as demonstrated in several studies [14, 22, 29, 33, 34]. Due to different ratios of histopathological substrates in each study, the seizure outcomes between various reports are difficult to compare.…”

Prognostic factors for seizure outcome in patients with MRI-negative temporal lobe epilepsy: A meta-analysis and systematic review

“…Anterior temporal lobectomy (ATL) and amygdalohippocampectomy (SAH) are commonly used among these centers; neocortectomy was also used for lateral TLE [15,17], especially for dominant temporal lobe [15]; multiple hippocampal transection was applied for mesial TLE in a report from Cleveland [22]. Seizure outcome after surgery was not significantly different between an independent mesial and lateral epileptic focus among patients with MRI-negative TLE (61.3% vs. 53.3%, OR = 1.39, 95% CI = 0.61-3.20, p = 0.43, I 2 = 8%) (Fig.…”

“…Several studies have attempted to identify the prognostic factors for seizure-free outcome after surgery in MRI-negative TLE patients, including age, epilepsy duration, pathology, and fluorodeoxyglucose positron emission tomography (FDG-PET), single photon emission computer tomography (SPECT), scalp electroencephalogram (EEG), and intraoperative EEG results [2,5,[7][8][9][11][12][13][14][15][16][17][18][19][20][21][22][23]. However, further investigation is required due to the shortage of cases and the inconsistent and occasionally contradictory findings.…”