Abstracts

Rationale: There is considerable interest in understanding and predicting outcome to epilepsy surgery in patients with medically refractory epilepsy. We studied the relationship between infraslow network structure observed in the presurgical magnetoencephalogram (MEG) and surgical outcome.  Methods: We selected 31 medically refractory epilepsy patients who underwent presurgical MEG scans and subsequent intracranial EEG (icEEG) monitoring and epilepsy surgery. MEG was acquired in 10-minute segments for approximately one hour of recording. We estimated the average magnitude-squared coherence (MSC) below 0.15 Hz of traditional EEG/MEG frequency band power time-series for all sensor pairs to quantify infraslow envelope correlation for each of these epochs. We segmented sensors into seizure onset area (SOA), which included sensors overlying the lobe of seizure onset, and non-SOA, which included all other lobes. Surgical outcomes were determined at 1-year and 2-years post-surgery using Engel classification. We grouped patients as being either: (1) Engel Class I or (2) Class II or higher, and determined how presurgical infraslow envelope MSC varied with surgical outcome. Results: At 1-year post surgery, 17 patients were classified as Engel Class I, while 12 patients were Class I at 2-years post-surgery. Five patients were lost to follow up between 1 and 2 years post-surgery. The infraslow envelope MSC was decreased in SOA compared to non-SOA in all frequency bands. Interestingly, average infraslow envelope MSC was increased significantly in all frequency bands in both SOA and non-SOA for the patients who experienced poorer surgical outcomes (p < 0.01).  Conclusions: Mean infraslow envelope MSC in both SOA and non-SOA is lower in patients who experienced better outcome to surgery as compared to those who had poor outcome. This observation may have value for prospectively predicting neurosurgical outcome non-invasively using MEG.  Funding: No funding