A systematic review on MEG and its use in the presurgical evaluation of localization-related epilepsy

Magnetoencephalography (MEG), also referred to as magnetic source imaging (MSI) when combined with structural imaging, provides a new, noninvasive tool for epilepsy localization. In contrast to EEG, the magnetic fields generated by electrical discharges are minimally affected by intervening tissue layers. The purpose of this study was to determine the effectiveness of MEG/MSI in the presurgical evaluation of localization-related epilepsies by means of a systematic review.

We searched MEDLINE, the Cochrane library, and EMBASE between 1987 and 2006 for English articles. References of reviews and book chapters were searched. In addition, we contacted experts in MEG and epilepsy. Studies including a minimum of four patients with at least 6 months follow-up after surgery were reviewed. In each study, surgical outcome (seizure freedom) was correlated with the concordance of MEG source localization and resection area.

The literature search generated 192 articles. Twenty-eight papers satisfied the inclusion criteria. Eleven of the 28 articles were excluded due to an inability to determine the concordance between the MEG epileptic focus and the resected area based on the published data. Analysis of the 17 remaining studies allowed us to obtain sensitivity (range: 0.20-1.0) values for all articles, and specificity (0.06-1.00) values, positive likelihood ratios (0.67-2.0) and negative likelihood ratios (0.40-2.13) for some articles.

There is insufficient evidence in the current literature to support the relationship between the use of MEG in surgical planning and seizure-free outcome after epilepsy surgery. Additional studies are needed.