Abstracts

Rationale: Determining the site of ictal onset can be difficult in some patients with refractory partial epilepsy. MEG is a diagnostic tool with excellent spatial and temporal resolution that can provide non-invasive interictal localizing information not available from other testing methods. Recently we have shown (Elisevich 2011) that using MEG imaged coherence to localize brain networks can provide a better outcome for temporal lobe epilepsy surgery (77% for Engels Class Ia outcome) if this area of the brain is resected. In this study we further investigated the highly coherent areas to determine the direction of the network connections, as a region that sends information or receives information and whether this has any impact on the outcome. Methods: An archival review of twenty five presurgical MEG studies were included in this analysis, 17 (68%) female with a mean age at surgery of 30.6 years (S.D. =13.5, range from 8 to 64). The imaged coherence location classified as a sender or a receiver was determined by Granger causality analysis of the MEG imaged coherence solution from 10 min of spontaneous brain activity and compared to surgically resected brain areas outlined on each subject's magnetic resonance image (MRI). ILAE and Engel classifications outcome were assessed using nonparametric tests.Results: Pairwise comparisons of the patient groups for ILAE and Engel classifications showed significant differences in both outcomes for the receiver resected status (Table 1). Patients with any receiver resection had on average worse outcomes when compared to patients with no receiver resection. No significant differences were detected in both outcomes for the sender resected status (Table 2). The difference between patients with and without Phase II was significant for ILAE (with 2.21(s.d.=1.42) vs without 1.18 (s.d.=0.4), p=0.047) and showed a trend for Engel (with 1.64(s.d.=1.08) vs without 1.0 (s.d.=0), p=0.077). For both outcomes, patients with Phase II testing had on average worse outcomes than patients without Phase II testing. The presence or absence of MRI lesion did not make any significant differences in either outcome.Conclusions: Investigating the direction of information flow in the brain may provide additional information prior to surgical resection. Our study found that resection of high coherent areas that were receivers as opposed to senders ap-peared to result in worse outcome. This may be due to the nature of a receiving area in the brain being the re-gions where the epilepsy propagated to, as opposed to the location where the epilepsy initiated. We hypothesize that the epileptic network is very dynamic and highly plastic and therefore may be able to change the direction of information flow.