Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most common form of medically refractory focal epilepsy treated with surgery and roughly half of patients may continue to have seizures after surgery. Why TLE is resistant to surgery in certain patients is not known. Understanding the mechanisms of surgical failure may reveal ways to improve outcomes of epilepsy surgery. Methods: Seizure outcomes and predictors were reviewed for 118 patients who underwent a standardized anteromedial temporal resection (AMTR), without extratemporal resections, by a single surgeon at a comprehensive epilepsy center over 16 years. Intracranial EEG (iEEG) recordings from simultaneous neocortical grids/strips and depth electrodes were analyzed visually for seizure spread. Fast beta power activity was projected onto reconstructions of patients’ brain MRI to visualize spread patterns. Results: Cumulative probability of continuous Engel class-I seizure freedom since surgery was 65.6% at post-operative year 10 and beyond, with 92% of recurrences in post-operative years 1 - 3. Multivariable statistical analyses found selection for iEEG study to be the most reliable predictor seizure recurrence (P=0.001). In patients studied with iEEG, rapid seizure spread in <10 seconds correlated significantly with recurrence (P<0.01). Looking at the first 10 seconds of seizures, fast beta power activity in the lateral temporal cortex, outside resective margins, was significantly greater in patients whose seizures recurred (P<0.05). Conclusions: Seizure-spread on iEEG suggest rapid spread to lateral temporal foci outside resective margins plays a role in surgically refractory TLE. Seizure-control after epilepsy surgery might be improved by investigating areas of early spread as candidates for resection or neuromodulation. Funding: HHMI-CURE Med Fellowship supporting John P. Andrews