Abstracts

RATIONALE: Despite the success in treating medically refractory temporal lobe epilepsy (TLE) in patients with mesial temporal sclerosis (MTS), there is less enthusiasm for operating on non-MTS TLE patients because of poorer reported surgical outcomes and higher risk of neuropsychological sequelae. METHODS: To better define outcome and prognostic variables in non-MTS TLE, we prospectively followed all patients with medically intractable seizures of mesial temporal lobe origin, without evidence of either a mass lesion or developmental abnormality, who were operated on over a five year period. All operations were performed in a tailored fashion. The extent of hippocampal resection was guided by intraoperative electrocorticography (ECoG), with the resection extending to just beyond the most posterior contact of the hippocampal strip that had epileptiform activity. RESULTS: Of 143 operated patients, 44 had no focal neuronal loss in any of the CA subfields on blinded pathological review (non-MTS patients). The average age of seizure onset in this subgroup was 17 years (range 2-42), with age at operation of 35 years (range 11-59). There were 19 right and 25 left-sided TLE resections, with hippocampal resection varying from 10mm to 45mm. With mean follow up of 29 months (range 18-61), 27/44 patients were seizure free, with similar results in both the smaller (< 25mm, n=10) and larger hippocampal resection groups. A history of viral encephalitis and residual hippocampal epileptiform activity on post-resection ECoG recording were significantly associated with a worse outcome. Seven of eight patients with self-reported worsening of memory function postoperatively had larger hippocampal resections. CONCLUSIONS: More than 60% of non-MTS TLE patients are seizure free following resective epilepsy surgery, comparing very favorably with continued medical therapy or vagal nerve stimulation. Most patients who complain of new memory deficits postoperatively had larger hippocampal resections. Whether ECoG guided limitation of hippocampal resection can improve memory preservation without compromising outcome in non-MTS TLE patients needs to be studied in randomized prospective fashion.