Abstracts

RATIONALE: Using MEG imaging techniques, the location of primary epileptic foci are assumed to be identical to the locations of interictal spike events [1]. The validity of this assumption was investigated. During routine MEG recordings of a presurgical patient with epilepsy both interictal spike activity and a complex partial seizure were recorded with a whole head neuromagnetometer,(4D Neuroimaging Magnes 2500). METHODS: Whole cortex images of neuronal activity were generated using 2DII imaging [2] applied to both the interictal activity data and the MEG data at the onset of the seizure event. In addition, Equivalent current dipole(ECD) source localization was performed and compared to the corresponding 2DII whole brain images. RESULTS: Both the 2DII and ECD techniques localized the primary site of seizure activity to a single location on the border of previously resected cortex. The sites of interictal activity differed from the primary ictal focus by an average of 2.2 cm. However,based on the 2DII whole braine images of cortical activity, the interictal spike locations were within the extended region involved in the complete seizure event. CONCLUSIONS: These results suggest that interitcal spike activity can be used to locate cortex involved in seizeure events but not necessarily the seizure initiation site. Further, these results indicate that for this patient the primary initiation site is much less active than cortex involved in interictal activity. However, it is possible that some or all of the interictal spike locations,identified by MEG, may be additional seizure initiation sites. Thus the question of whether interictal spikes should be used as the basis for determining the area of cortex that is to be resected is unresolved. 1. Ebersole JS, Elepisy 38 (suppl 4) S1-S5 (1997). 2. Moran JE, Tepley N., Two Dimensional Inverse Imaging (2DII) of Current Sources in Magnetoencephalography, Brain Topography, Vol. 12, No. 3,2000