Sensitivity and specificity of seizure-onset zone estimation by ictal magnetoencephalography

Purpose: Ictal video–electroencephalography (EEG) is commonly used to establish ictal onset‐zone location. Recently software development has enabled systematic studies of ictal magnetoencephalography (MEG). In this article, we evaluate the ability of ictal MEG signals to localize the seizure‐onset zone. Methods: Twenty‐six patients underwent ictal MEG and epilepsy surgery. Prediction of seizure‐onset zone by ictal and interictal MEG was retrospectively compared with ictal‐onset area found by intracranial EEG in 12 patients. The specificity and sensitivity of the prediction were calculated at hemisphere‐lobe (HL) and at hemisphere‐lobe‐surface (HLS) levels. Key Findings: The sensitivity of ictal MEG source localization was 0.958 on HL and 0.706 on HLS levels, and its specificity was 0.900 on HL and 0.731 on HLS levels. The interictal MEG dipole cluster, defined as >10 dipoles on one lobar surface, had sensitivity of 0.400 and specificity of 0.769. Ictal MEG was equally sensitive and specific on dorsolateral and nondorsolateral neocortical surfaces up to a depth of 4 cm from the scalp. Significance: Sources of ictal‐onset MEG signals and interictal dipole clusters are essentially equally specific in estimation of the ictal‐onset zone on lobar surface resolution, but ictal MEG is more sensitive. On the lobe resolution, ictal MEG estimates ictal‐onset zone with high sensitivity and specificity.