Abstracts

RATIONALE: To examine the relationship of magnetic source imaging (MSI) - defined interictal activity to the epileptogenic focus as defined by chronic electocorticography (ECoG). METHODS: Fourteen patients underwent both MSI and ECoG with subdural grids, strips and depth electrodes. The relationship of the two modalities was analyzed using coregistration in a three-dimensional imaging space. RESULTS: Three patients had extratemporal loci, nine temporal, and two frontotemporal. Two MSI studies were non-diagnostic (14%). Five (36%)MSI-defined foci were 'concordant' with the epileptogenic foci identified by ECoG, whereas seven (50%) were 'discordant'. Four of 5 'concordant' patients underwent resections: 2 (50%) have experienced a good to excellent outcome (Engel I or II), and 2 a poor outcome (Engel III or IV) at last follow-up. Five of 7 'discordant' patients have been resected: all have experienced good to excellent seizure control. One of the two patients with a non-diagnostic MSI has been resected with an Engel IIA outcome. CONCLUSIONS: Although this is a limited series, the value of interictal MSI has been modest, and in only one patient did MSI significantly alter electrode placement and surgical outcome. This experience suggests that while MSI can provide useful adjunct information, invasive monitoring remains the gold standard for defining the epileptogenic focus in patients with intractable epilepsy.