Neuropathology in patients with multiple surgeries for medically intractable epilepsy

Outcomes following surgery for chronic epilepsy are generally good; however, seizures persist/recur following initial surgery in some patients. We hypothesize that in patients who require multiple surgeries for intractable epilepsy, an identifiable pathologic substrate can be found in the subsequent surgical specimen, which accounts for the recurrent seizures. We retrospectively studied 102 patients (56 females) with medically intractable epilepsy who have had at least 2 surgeries more than 60 days apart from 1990-2010. Patient age at time of 1st surgery ranged from 3 months-60 years (mean 18.1 years). Mean duration of seizures prior to 1st surgery was 9.7 years. Time between the 1st and 2nd surgeries ranged from 0.28-15.3 years (mean 4.3 years). The most common pathologies at initial resection included focal cortical dysplasia (45%), tumor (19%), hippocampal sclerosis (16%), and non-specific changes (13%); 10% of patients had multiple significant pathologies. Of the 89 patients that had a significant initial surgical finding, 74 (83.1%) had a significant pathology at 2nd surgery; the same pathology was identified in 49 (66.2%) of these cases. The most commonly identified pathologies at 2nd surgery included remote infarcts (likely postoperative) (N = 51) and focal cortical dysplasia (N = 29). Three out of the 13 patients with initially non-specific findings had a significant finding at 2nd surgery, excluding postoperative infarct. Follow-up after last surgery ranged from 0.5-190 months (mean 48 months); 83% of patients were on anti-convulsive medication and 57% were seizure-free at last known follow-up. In the majority of cases of recurrent epilepsy with at least 2 surgeries (84%), pathologic findings accounting for seizures were found at the 2nd surgery. In most cases with significant initial pathology, a similar pathology was present at 2nd surgery (55%). Post-operative contusional damage may account for persistent seizures following initial surgery in a subset of patients.