Abstracts

Rationale: The goal of epilepsy surgery is to cure epilepsy by removing or disconnecting the epileptogenic zone while preserving normal brain. Seizure freedom correlates with an identifiable lesion on MRI, and the extent of resection/disconnection. 3 Tesla (3T) iMRI-is a promising tool to confirm complete resection/disconnection. However, a large proportion of epileptogenic pathologies in children, such as focal cortical dysplasia, are poorly defined on imaging. The utility of iMRI in regard to such cases should be questioned.Methods: Over the past five years, we have used 3T-iMRI-based neuronavigation for pediatric epilepsy surgery. We conducted a retrospective chart and imaging review of all such cases with at least 2 year follow-up. Based on their pre-operative definition on imaging we stratified all cases into three categories: well defined cases (WDCs), poorly defined cases (PDCs), and diffuse hemispheric cases (DHCs). The primary outcome measures assessed were (1) degree of complete seizure freedom and (2) Engel Outcome Classification at 2-year follow-up.Results: Forty-five cases met our inclusion criteria, including 26 PDCs, 10 DHCs, and 9 WDCs. The iMRI neuronavigation suite was used in all 45 surgeries. An iMRI was performed to confirm complete resection/disconnection in 40/45 (88.9%) cases overall, including all PDCs and all DHCs, and 21/26 (80.7%) PDCs. Second look surgery based on iMRI findings, was performed in 11/46 (23.9%) surgeries overall, including 8/26 (30.8%) PDCs, 2/9 (22.2%) WDCs, and 1/10 (10%) DHCs. Complete resection was achieved in 7/9 (77.8%) WDCs, and complete disconnection was achieved in 10/10 (100%) DHCs. iMRI assisted in achieving complete resection in 1/2 (50.0%) second look surgeries for WDCs, and in achieving complete disconnection the single DHC in which a second look surgery after iMRI was performed. By definition, the concept of complete resection is not applicable to PDCs. Complete seizure freedom (Engel Class Ia) was achieved in 9/9 (100%) of the WDCs, and in 9/10 (90%) of the DHCs, but in only 12/26 (46.2%) of PDCs. Within the PDCs, outcome was particularly poor for cases of focal cortical dysplasia with only 7/15 (46.7%) achieving seizure freedom, and the other 6/15 (40.0%) achieving no benefit from surgery (Engel class IVb outcome).Conclusions: For WDCs and DHCs, epilepsy surgery outcomes achieved with iMRI-based neuronavigation compare favourably with historic controls. However, this technology appears to be less beneficial for PDCs, such as focal cortical dysplasia. Further work, to better localize the extent of the epileptogic zone, is needed to improve epilepsy outcomes for these most challenging cases.