Whole head magnetoencephalography: Detection of epileptic discharges on bilateral hemisphere

In four patients with intractable complex partial seizures, interictal epileptic discharges, i.e., epileptic spikes and wave complex, were measured using a newly developed helmet shaped whole head magnetoencephalography (MEG) system with scalp and sphenoidal EEG. Three dimensional MR images were obtained in each patient with MEG coordinate system. Current sources of interictal discharges were estimated using a single or a two dipole model within the best fit sphere for each subject's head. Position and orientation of the dipoles were superimposed on MRI. We observed bilateral two dipole patterns in two cases. These dipolar patterns overlap each other across the midline. A two dipole model estimated 'spike' or 'wave' dipoles in bilateral neocortices, unilateral neocortex and contralateral mesial temporal structure, or bilateral mesial temporal structures. In the other 2 cases, single dipole pattern appeared on unilateral hemisphere only; these spike or wave dipoles were estimated within one lobe. The whole head MEG system is useful to localize multifocal epileptic discharges, as well as to evaluate signal propagation between bilateral hemispheres.