Abstracts

Rationale: Treatment-resistant frontal lobe epilepsy in children is a challenging condition and favorable outcomes after surgery less common compared to temporal lobe epilepsy. Prior studies have shown that the greatest predictor for long term seizure freedom is complete resection of the seizure onset zone. Even in children with discrete lesions, the epileptogenic zone may extend beyond the borders of the lesion as seen on MRI. Therefore, we often perform a multistage procedure in children with frontal lobe epilepsy at our institution. This includes invasive monitoring for localization of the epileptic focus, resection of the seizure onset zone, and, in selected cases, post-resection extraoperative video-EEG monitoring with invasive electrodes. The efficacy for this post-resection implantation has not been studied. The aim of this study is to report the experience with post-resection monitoring.Methods: We retrospectively reviewed the charts of 28 patients who underwent 30 frontal lobe epilepsy surgeries and had post-resection invasive monitoring. Patient demographics, clinical seizures characteristics, invasive EEG characteristics, MR and histopathological findings as well as Engel outcomes at 1 year and at last follow up were reviewed.Results: The mean duration of follow up was 48.9 months (range 12 to 109 months). Neuropathological exam showed 16 patients with tuberous sclerosis complex (TSC), 6 focal cortical dysplasia (FCD), 4 gliosis, 1 ganglioglioma, 1 desmoplastic neuroepithelial tumor (DNET). In 21 of the 28 cases (75%) who had post-resection invasive monitoring, information was obtained that led to additional resection (re-resection; RR). Sixty one percent of the cases (17/28) had an Engel score of I at 1 year of follow up, but after a mean follow-up of 48.9 months, the Engel I outcome decreased to 43% (12/28). Twelve of the 21 patients (57%) who underwent RR had an Engel I outcome at 1 year. Five of 7 patients (71%) without reresection (NRR) had an Engel I outcome at 1 year. Long term Engel I outcome in the RR group was 48% (10/21), whereas in the NRR it decreased to 29% (2/7). Diffuse seizure onsets seen on invasive EEG recordings during the initial stage of monitoring was correlated with worse seizure-free outcome. No mortality, no infection, no unexpected neurologic deficit occurred.Conclusions: Re-resection after post-resection monitoring may have a positive long term effect on outcome. Our overall results by the modified Engel scale were in the range of previous studies, and we had no mortality, no infections, and no major morbidity. The striking finding in our study was that patients who underwent RR appeared to have a more durable surgical response. Short term outcome was more favorable in the NRR group, but on the long term outcome was more favorable in the RR group. This raises the possibility that RR after monitoring may increase the likelihood of a long term seizure-free outcome in selected cases, because a more complete resection of the epileptogenic zone is achieved. This may be especially useful in patients with TSC and FCD; in which the pathology can be more diffuse.