Abstracts

Rationale: Localization and surgical treatment of neocortical epilepsy can be challenging. This difficulty is compounded further in the absence of radiographic abnormality. We reviewed our experience with the surgical localization and treatment of neocortical epilepsy.Methods: A retrospective review of our epilepsy database over a nine year period identified all patients with suspected neocortical epilepsy that underwent surgical management. For patients that subsequently underwent resection radiographic findings, suspected zone of seizure onset, and operative complications were reviewed. Pre and post-operative seizure frequencies were analyzed for this entire group, which was then separated into patients with and without radiographic lesions for further comparison.Results: During a nine year period, fifty-two patients with suspected neocortical epilepsy underwent monitoring with either depth electrodes (n=22), subdural grid electrodes (n=23) or both (n= 7). Twenty-six (50%) underwent subsequent resection. Of the 26 patients undergoing resection, 25 required subdural grid, 6 required depth electrodes and one patient had intraoperative corticography only. Thirteen cases were “lesional” and 13 were “non-lesional”. Lesions consisted of atrophy/gliosis in 10 cases and cortical migration defect in 3 cases. There were 5 complications (9%) related to invasive electrode placement and no deaths or permanent morbidities. Mean follow-up was 39.5 months. Mean pre and post-operative seizure frequencies (fig 1) were significantly improved in all groups (p< 0.05). Mean percentage reduction in seizure frequency was 82% for the entire group, 74% in the “lesional” group, and 89% in the “non-lesional” group. Fifty-four percent of “lesional” patients were seizure-free (Engel Class I) at last follow-up compared with 38% of “non-lesional” patients. Eighty percent of all patients in this study had at least an 80% reduction in seizure frequency. Magnetoencephalography(MEG) was performed in all 26 patients, but no correlation between MEG localization and seizure outcome could be defined. Conclusions: Localization of neocortical epilepsy remains difficult. When neocortical seizures can be localized with invasive monitoring, most patients experience a significant improvement in seizure frequency following neocortical resection. Engel class I outcomes are more common in patients with lesions but overall seizure reduction is greater in patient without radiographic lesions. Localization of neocortical epilepsy remains difficult and emphasizes the need for better pre-surgical localization techniques.