Abstracts

Rationale: Recently the concept of human epilepsy as a disorder of large neural networks has been proposed [1]. Positron Emission Tomography (PET) has played a major role in the development of the network hypothesis of human epilepsy [1]. Recent study demonstrated that the topography of the glucose-hypometabolism may be related to brain areas which produces the clinically ictal onset and contributes spread. The Temporal Spread Image (TSI) method using spatial filter from the magnetoencephalography (MEG) data was demonstrated to be useful to evaluate and visualize the temporal evolution of epileptic activities [2]. The aim of this study is to evaluate dynamic propagation of epileptic activities noninvasively by TSI of MEG data and to compare the neurophysiological propagation with PET hypometabolic areas.Methods: We studied seven patients with medically intractable mesial temporal lobe epilepsy (MTLE) retrospectively. All had interictal MEG and six had FDG-PET for presurgical evaluation. After noise reduction, Equivalent Current Dipole (ECD) and TSI analysis were performed. TSI showed the brain areas where epileptic activities propagated repeatedly. Brain regions showing hypometabolism was determined by contrasting PET to that of healthy volunteers.Results: In six of the seven patients, TSI epileptic activities propagated outside the temporal lobe. The propagation patterns of interictal epileptic activities varied across the patients, but certain features were delineated as follows: interictal activities originated from the temporal focus and propagated to the ipsilateral frontal lobe, especially fronto-orbital and inferior frontal regions. PET data from two patients showed hypometabolic regions in the ipsilateral fronto-orbital and inferior frontal regions which were overlapped with the propagation areas of interictal activities depicted by TSI (Figure shows the propagation pattern and hypometabolic regions in a patient. Color scale represents the average time from the peak of MEG spikes when the epileptic activities at each voxel reached the predetermined threshold. Hypometabolic regions are shown by magenta color in the right panel. )Conclusions: In this study electrophysiological evidence of propagation of epileptic activity was combined to metabolic evidence to reveal the pathophysiology in the hypometabolic areas outside the epileptic focus. Frequent propagation of epileptic activities to the ipsilateral frontal lobe may have caused metabolic disturbances in those areas as part of epileptic networks in MTLE. 1.Spencer, S.S., Neural networks in human epilepsy: evidence of and implications for treatment. Epilepsia, 2002. 43(3): p. 219-227. 2.Matsuhashi, M., et al. Temporal Spread Image to delineate MEG spike foci in epilepsy patients. in Complex Medical Engineering (CME), 2012 ICME International Conference on. 2012. IEEE..