Magnetoencephalographic source imaging improves localization of the epileptogenic zone in multimodal imaging evaluation

OBJECTIVE: To assess the added diagnostic value of magnetoencephalographic source imaging (MSI) beyond conventional magnetic resonance imaging (MRI) and fluorodeoxyglucose-positron emission tomography (FDG-PET) in localizing the epileptogenic zone, with stereo-electroencephalography (SEEG) and surgical resection serving as reference standards. METHODS: Among 101 patients prospectively enrolled with drug-resistant focal epilepsy in the EPIMAGE study to assess the diagnostic yield of non-invasive multimodal imaging (MSI, MRI, FDG-PET), those undergoing SEEG and/or surgery were analyzed to compare imaging with SEEG seizure-onset zone (SOZ) or resection zone. We employed binomial generalized linear mixed models (GLMMs) to evaluate the detection accuracy of MRI, PET, and MSI, individually and in combination, for identifying the SEEG-defined SOZ and resection zones. We further assessed the spatial concordance between imaging abnormalities and these reference standards. RESULTS: Using SEEG as reference, MSI identified additional SOZ regions beyond MRI in 55.6% of patients, beyond PET in 29.6%, and beyond combined MRI + PET in 33.3%. When the resection zone served as reference, MSI added new localizing value beyond MRI in 55.6% of patients, beyond PET in 29.6%, and beyond MRI + PET in 33.3%. GLMM analysis revealed that bimodal combinations improved detection rates (MRI + PET: 73.7%; MRI + MSI: 81.3%; PET+MSI: 79.8%). The trimodal combination (MRI + PET+MSI) achieved the highest detection probability at 85.3%, significantly higher than MRI, PET, or MSI alone (p = .003, p = .008, and p = .008, respectively). MSI significantly enhanced SOZ detection when added to either MRI (p = .01) or PET (p = .05). SIGNIFICANCE: MSI adds significant localizing value to the presurgical workup of focal epilepsy by expanding the detection of the epileptogenic network beyond the limits of structural MRI and metabolic PET. The primary clinical benefit of MSI lies in its ability to identify additional seizure-onset regions in complex cases, without increasing false-positive localizations. These findings demonstrate that a multimodal approach incorporating MSI optimizes surgical planning by increasing the probability of capturing the full extent of the epileptogenic zone.