Abstracts

Rationale: Seizure outcomes after extra-temporal lobe epilepsy (ETLE) surgery are less favorable than with temporal lobectomy, but the reasons for surgical failure are incompletely understood. While others have studied predictors of seizure freedom in ETLE surgery, few have performed in-depth examination of seizure recurrences to identify possible reasons for failure. Methods: We reviewed 107 resections for drug-resistant ETLE surgery performed at our institution between 1998 and 2011. We performed quantitative analysis of seizure outcome predictors, as well as detailed qualitative review of failed surgical cases - including relevant post-operative diagnostic studies - to provide insight into the source of recurrent seizures. Results: Of 107 ETLE resections, 64 (60%) resulted in freedom from disabling seizures (Engel I outcome). Mean (± SEM) patient age was 17.9 ± 1.3 years, mean follow-up was 4.3 years (range, 1-17), and 59% of patients were male. Less favorable (Engel II-IV) seizure outcome was predicted by a higher frequency (≥4/day) of seizures before surgery (OR: 0.32; 95% CI: 0.14 - 0.78), and by a history of generalized tonic-clonic seizures (OR: 0.37; 95% CI: 0.15 - 0.95). Among 32 surgical failures examined, 24 (75%) were related to "extent of resection," with residual epileptic focus at the resection margins, while 8 (25%) involved "location of resection," with an additional epileptogenic zone distant from the resection (Figure 1). Other factors commonly associated with failure were also identified. Of 16 patients who then received reoperation after seizure recurrence, 10 (63%) achieved seizure freedom. Conclusions: Insufficient extent of resection is a common reason for recurrent seizures after ETLE surgery, although some patients harbor an additional epileptic focus. Accurate delineation of the entire epileptogenic zone is a critical goal, but some patients who fail surgery may be candidates for reoperation.