The correlation of magnetoencephalography to intracranial EEG in localizing the epileptogenic zone: A study of the surgical resection outcome

Objectives: To evaluate the agreement between magnetoencephalography (MEG) and intracranial electroencephalography (ICEEG) results, to determine the characteristics that lead to concordance, and to assess how these factors relate to favorable epilepsy surgery outcome. Materials: This retrospective study reviewed 50 patients who had positive MEG findings and ICEEG recordings between 2008 and 2010. The anatomical concordance between MEG and ICEEG recordings, the features of the MEG focus, and the relationship between the MEG focus and the surgically resected regions were correlated with the epilepsy surgery outcome. Results: Thirty-six of the 50 patients with positive MEG and ICEEG findings underwent epilepsy surgery, and 27 (75%) of the patients had an anatomical concordance of MEG/ICEEG. Among the patients with concordant MEG/ICEEG, the seizure free outcome rate was significantly higher compared to the discordant group [18/27 (66.7%) patients concordant vs. 1/9 (11.1%) patients discordant (p < 0.006)]. Nineteen (53%) of the 36 patients had complete resection when the MEG focus overlapped with the resection area, and 15 (79%) of these 19 patients became seizure-free following surgery (p < 0.001); 17 (47%) of the 36 patients had an MEG focus that was not completely resected (the MEG foci of 7 patients partially overlapped the resection areas, and 10 patients had MEG foci that were in a different area from the resection area), and 13/17 (76.5%) patients had seizure recurrences (p < 0.001). Conclusions: Both the anatomical concordance of MEG/ICEEG and the complete resection of the MEG foci significantly increased the chance of seizure-free outcomes following epilepsy surgery.