MSI, FDG-PET, and ictal SPECT each have clinical value in predicting seizure-free surgical outcome in epilepsy surgery candidates who typically require ICEEG.

Objective-Intracranial electroencephalography (ICEEG) with chronically implanted electrodes is a costly invasive diagnostic procedure that remains necessary for a large proportion of patients who undergo evaluation for epilepsy surgery. This study was designed to evaluate whether magnetic source imaging (MSI), a non-invasive test based on magnetoencephalography source localization, can supplement ICEEG by affecting electrode placement to improve sampling of the seizure onset zone(s).Methods-Of 298 consecutive epilepsy surgery candidates (between 2001-2006) 160 cases were prospectively enrolled on the basis of insufficient localization from seizure monitoring and MRI results. Prior to presenting MSI results, decisions were made as to whether to proceed with ICEEG, and if so, where to place electrodes such that the hypothetical seizure onset zone would be sampled. MSI results were then provided with allowance of changes to the original plan.Results-MSI indicated additional electrode coverage in 18 of 77 (23%) ICEEG cases. In 39% percent (95% CI: 16.4, 61.4) seizure onset ICEEG patterns involved the additional electrodes indicated by MSI. Sixty-two patients underwent surgical resection based on ICEEG recording of seizures. Highly localized MSI was significantly associated with seizure-free outcome (mean=3.4 years, minimum > 1 year) for the entire surgical population (n=62).Interpretation-MSI spike localization increases the chance that the seizure onset zone is sampled when patients undergo ICEEG for presurgical epilepsy evaluations. The clinical impact of this effect--improving diagnostic yield of ICEEG--should be considered in surgery candidates

Conclusively positive MSI has a high predictive value for seizures localized with ICEEG. Diagnostic gain may be achieved with addition of either PET or ictal SPECT to MSI. Diagnostic values for imaging tests are lower than "true values" because of the limitations of ICEEG as a gold standard.