Abstracts

Rationale: Although intracranial electroencephalography (ICEEG) continues to be widely used in the surgical evaluation of refractory epilepsy, there remain inherent limitations associated with sufficient sampling for accurate seizure localization. Therefore, magnetoencephalography (MEG) provides a promising, non-invasive alternative. Both prospective and retrospective studies have shown the yield of seizure localization are comparable between ICEEG and MEG. Nevertheless, further investigation is required with larger sample sizes to fully determine the clinical utility and reliability of MEG evaluation prior to surgical intervention in comparison to ICEEG. Methods: A retrospective chart review was completed investigating 50 epilepsy patients who underwent intracranial EEG and had preoperative MEG between the years 2010 and 2017_. The MEG report was reviewed for those patients where epileptiform discharges were localized. The suspected seizure localization based upon MEG reports was then compared with expected seizure focus based on intracranial EEG monitoring. Single equivalent current dipole modeling was used to estimate source localization from the observed magnetic fields (at a single latency in the early phase of single spontaneous discharges with temporally and spatially stable magnetic flux patterns). Comparative statistical analysis was then completed to determine the correlation between seizure localization as predicted by ICEEG and MEG. Results: 50 patients (M: F 28:22), Age: 44±2 years, Onset age: 5 years .) with intractable partial epilepsy underwent IEEG/SEEG placement for localizing the EZ/SOZ. SOZ ranged between - mesial temporal/amygdala-hippocampus (N=24), mesial frontal (N=5), cingulate (N=2), perisylvian/insular (N=6), lateral frontal (N=13). The concordance between MEG detected spike, and icEEG detected SOZ was maximum between lateral temporal, perisylvian, intermediate for lateral frontal and mesial temporal and least with mesial frontal.  Conclusions: Magnetoencephalography provides a non-invasive technique for the localization of seizure focus in patients with medically refractory epilepsy prior to surgical intervention. An increasing number of studies have compared MEG with intracranial EEG monitoring for seizure focus, with promising results for the use of MEG. The results of our study show the benefit of MEG in surgical planning. Funding: This study was supported by NSF grant OIA 1632891