Abstracts

Rationale: Propagation of epileptic spikes may have an important role in the pathophysiology of epilepsy. We previously investigated that frontotemporal spike propagation is equally represented by intracranial electroencephalography (IEEG) and magnetoencephalography (AES 2009). However, structural basis underlying spike propagation has been unclear. The purpose of this study is to explore the method of investigating propagation pathway, and we specifically focus on the uncinate fasciculus identified by diffusion tensor imaging (DTI) tractography and propagation time of frontotemporal spikes represented by IEEG in patients with temporal lobe epilepsy.Methods: Nine patients (male:3, female:5, age: 9-21) with temporal lobe epilepsy were retrospectively studied. All patients had magnetic resonance imaging (MRI) and IEEG monitoring as a part of presurgical evaluation. MRI was acquired by using a high-resolution 3T scanner, including magnetization-prepared rapid acquisition gradient-echo (MPRAGE, TE=3.37ms, TR=2000ms, flip angle=9 , voxel size=1mm x1mm x 1mm) and DTI (60 gradient directions, 10 non-diffusion weighted acquisition, b-value= 700, TE=82ms, TR=7850ms, flip angle=90 , voxel size=2mm x 2mm x 2mm). IEEG was recorded with a digital EEG system at a sampling rate of 512Hz and was digitally low-pass filtered at 30Hz for analysis. Two active spiking electrodes were determined in each ipsilateral anterior temporal and inferior frontal cortex. We selected 50 interictal spikes in each patient and obtained the propagation time by averaging the maximum time difference of each spike between anterior temporal and inferior frontal peaks at the electrodes described above. We used Diffusion Toolkit and TrackVis software (www.trackvis.org) to reconstruct and visualize each patient's DTI tractography pathways, using an interpolated streamline algorithm. After calculating all possible fiber pathways in the whole brain, we deployed region of interests (ROIs) in the ipsilateral anterior temporal and the anterior floor of the external capsule. The ROIs were determined and placed based on the tractography atlas provided by Catani and de Shotten (2008), and tractography pathways between two ROIs were considered to identify the uncinate fasciculus. The mean fractional anisotropy (FA) values were obtained from the identified uncinate fasciculus. We compared the propagation time and FA values in each patient.Results: The propagation time of the whole patients ranged from 29.4 to 44.3ms (mean 36.9ms). The FA values obtained from the selected tracks ranged from 0.31 to 0.46 (mean 0.41). There was a tendency that the patients with longer propagation time showed lower FA values. Correlation coefficient (R) between the propagation time and FA values was 0.42.Conclusions: The results may suggest that the propagation time in frontotemporal spikes may be correlated with FA values of uncinate fasciculus, and encourage further investigation in a larger patient group. This study also demonstrates that combining DTI and neurophysiological methods may provide useful information for investigating spike propagation.