Epilepsy Fellow UT Southwestern Medical Center Dallas, Texas
Rationale: Temporal lobe epilepsy (TLE) responds well to surgical treatment, although up to 45% of patients experience seizure relapse after resection. Among the reasons explaining surgical failures, it could be relapse on the contralateral mesial temporal lobe, extratemporal lobe epilepsy mimicking TLE or temporal plus epilepsy. In our study we investigate the utility of a standard stereoelectrodes (SE) placement template for localization of the epileptogenic zone in patients with presumable TLE. Methods: We included patients with one of the preimplantation hypotheses suggesting temporal lobe epilepsy, who underwent stereo-EEG (SEEG) evaluation at our institution and had 12 SE placed to the sixteen brain regions (additional SE could be placed according to the hypothesis). This allows us to explore limbic and paralimbic network by mesial SE contacts sampling the anterior and posterior hippocampus, amygdala, entorhinal cortex, precuneus, anterior and posterior insula, orbitofrontal cortex, anterior and posterior cingulate, fusiform gyrus, and contralateral hippocampus; lateral SE contacts sample temporal, frontal, parietal and contralateral temporal neocortex. Patients who underwent previous temporal lobectomy were excluded. Neuroimaging and results of ictal onset localization with SEEG were analyzed. Results: Twenty-four out of 179 SEEG subjects met inclusion criteria. Among the 16 brain regions included in the analysis. only the anterior and posterior cingulate, precuneus, lateral parietal and contralateral temporal neocortex were not involved in the seizure onset in our patient cohort. Eight out of 24 patients had unilateral mesial temporal onset, 5 - bilateral mesial temporal, 3 - unilateral lateral temporal, 1 - unilateral mesial and lateral temporal, 2 - unilateral mesial and lateral temporal, and extratemporal, 1 - unilateral extratemporal, 3 - unilateral lateral temporal and extratemporal, 1 - bilateral involving lateral temporal and extratemporal cortex in one hemisphere, and contralateral hippocampus. Four patients had an MRI lesion related to the ictal onset (2 mesial, 2 lateral temporal). Nine patients had brain lesion(s) not related to ictal onset (3 temporal, 3 extratemporal, 3 - temporal and extratemporal). Seventeen out of 24 patients had post-SEEG resection with mean follow up duration of 10 (range 2-21) months, out of which 12/17 have Engel class I outcome, 2/17 - Engel class II, 2/17 - Engel class III, and 1/17 - Engel class IV. In patients with Engel class III and IV outcomes the ictal onset involved posterior and anterior insula, and orbitofrontal cortex. Conclusions: Our study demonstrates involvement of certain ‘high-yield’ regions at ictal onset in patients with presumed TLE. Larger studies are needed to create guidelines for effective exploration of medically refractory TLE with SEEG in order to improve surgical outcomes. Funding: Please list any funding that was received in support of this abstract.: None.
