Monofocal MEG in lesional TLE: does video EEG monitoring add crucial information?

Objective: Unilateral monofocal temporal magnetoencephalography (MEG) findings might determine epileptogenicity of a lesion in symptomatic epilepsy during presurgical evaluation. To evaluate the additive effect of video-electroencephalography (vEEG), monofocal temporal lobe MEG findings were compared to electrophysiological findings from vEEGs of patients with lesional epilepsy.

Methods: In 28 patients with drug-resistant lesional temporal lobe epilepsy (TLE), epileptogenicity of the lesion was determined by monofocal temporal MEG localisations. Findings for lesions of different aetiologies (20 mesial, 6 lateral, and 2 extended mesiolateral lesions) were compared to electrophysiological findings from long-term vEEG monitoring and validated by histology and postsurgical outcome (mean follow-up: 2 years (range 0.5-5)).

Results: The mean distance between a lesion and MEG localisation was 11mm (range 0-30mm). The distance to the lesion was on average 5mm (range 0-22mm) in patients with neocortical foci and on average 13mm (range 0-30mm) in patients with mesial foci. Predominant interictal and ictal vEEG findings were consistent with MEG findings in all patients, although they were sometimes distributed over multiple lobes and bilaterally pronounced on the side of the MEG findings. Postsurgical outcome of Engel 1 could be achieved in 82% (23 patients), and none of the patients had an outcome worse than Engel 2.

Conclusion: MEG localisations in lesional TLE are able to determine epileptogenicity of mesial and lateral temporal lobe lesions. MEG results are consistent with predominant electrophysiological findings from long-term vEEG. Future studies should assess the substitutability of vEEG by MEG in selected cases.