Abstracts

To determine whether the size of the epileptogenic zone derived from chronic ECoG predicts post-resection seizure outcome.
We retrospectively analyzed the topographic ictal onset pattern in 15 epilepsy patients (age [gt]17 years) who underwent subdural recording to localize electrographic ictal onset. The number of contiguous electrode contacts (center-to-center inter-electrode distance = 10 mm) involved at ictal onset was tabulated, as well as lobar localization and any associated structural lesion. Surgical resection was tailored according to ECoG results. The degree of post-operative seizure control was graded according to Engel classification. For 6 patients long-term ([gt]5 years) outcome data were available. The remaining 9 patients have been followed for 5 to 24 months (short-term) following resection.
An average of 4 seizures per patient were analyzed. As expected if fewer electrodes were involved in ECoG ictal onset, there was a greater chance for a favorable post-operative outcome, usually Engel Class I (seizure-free). In general, it appeared that ictal onsets encompassing 7 or more ECoG electrode contacts were most often associated with an Engel Class IV outcome (no worthwhile improvement). There was no significant difference in these results in comparing short- versus long-term follow-up.
A small epileptogenic focus on ECoG results in better post-operative seizure outcome. This could be because larger foci have greater involvement of hyperexcitable subcortical networks rather than just a limited cortical mantle of epileptogenicity. A further implication of this study is that if broad regions of ictal onset are discovered on chronic ECoG multiple subpial transactions or vagus nerve stimulation may offer equal or better treatment efficacy versus surgical extirpation of the entire ECoG focus.