Abstracts

Rationale: Rates of seizure freedom following surgery for patients with medically refractory neocortical epilepsy are relatively low in comparison to patients with temporal lobe epilepsy.  One reason for surgical failure may be sparring unrecognized epileptogenic brain.  Methods: In a prior retrospective study we found that in a cohort of 46 patients with neocortical epilepsy, resection of brain sites generating early ictal phase locked HFOs in the high gamma band correlated with good seizure outcome (Engel I/II). In this study, we performed a subgroup analysis and compared brain regions generating early ictal phase locked high gamma to the seizure onset zone in patients with poor seizure outcomes. Results: We found that in half (7/14) of the patients with poor seizure outcomes, the clinically defined seizure onset zone was completely resected. In this subgroup of 7 patients, 4 had brain sites generating early ictal phase locked high gamma surgically spared, whereas in two other patients the seizures lacked ictal phase locked high gamma sites entirely. In another subgroup of patients with good seizure outcomes, despite incomplete resection of the seizure onset zone,  a proportionally larger proportion of early ictal phase locked high gamma sites were resected.  Conclusions: These results suggest that seizure outcomes may be improved in patients with medically refractory neocortical epilepsy by incorporating the location of early ictal phase locked high gamma in to the resection margins, or increasing intracranial electrode coverage to detect these sites.