Objective:

To evaluate the clinical impact of a newly established magnetoencephalography (MEG) laboratory on surgical decision-making in patients undergoing epilepsy evaluation.

Background:

MEG is a noninvasive modality to assist in localizing epileptic focus and functional areas. Our institution recently established a MEG laboratory to support presurgical evaluation of patients with drug-resistant epilepsy.

Design/Methods:

The first 100 sequential MEG studies performed at our lab were reviewed. 21 were excluded due to Minnesota law limiting retrospective review. Diagnostic yield and impact on surgical planning were analyzed, focusing on interictal and ictal findings, concordance with scalp electroencephalography (EEG) findings, and influence on stereotactic EEG (sEEG) planning.

Results:

79 MEG recordings were conducted in 74 unique patients. All but 3 were part of surgical epilepsy evaluations. Interictal abnormalities were identified in 61 patients (82%). Three had no interictal findings but had recorded seizures on initial MEG. Three without abnormalities on initial study underwent repeat MEG; one had interictal findings on a second, and one had a recorded seizure on a third study. Of those with interictal findings, 51 (69%) were concordant with seizure onset localization from scalp EEG, while 10 suggested alternative localizations. MEG findings influenced surgical evaluation, often by providing sub-lobar localization to inform sEEG. Seventeen patients underwent sEEG for further localization; all had MEG findings targeted by sEEG electrodes. For 8 (47%) patients, the sEEG-defined seizure onset zone included the MEG-defined area of interest. For the remaining 9, the MEG-defined area of interest correlated with interictal discharges or was seen to be an area of propagation of habitual seizures.

Conclusions:

In most patients referred for MEG in a newly established laboratory, the study identified epilepsy-related discharges helpful for pre-surgical evaluation, especially in refining sEEG studies. In approximately 1 of 7 cases, MEG provided unexpected information beyond phase 1 evaluations.