Abstracts

Rationale: In mesial temporal lobe epilepsy (MTLE), the functional deficit zone was frequently observed outside the temporal lobe, most likely due to epileptic bombardment through the cortico-cortical network form the epileptic focus. It is, however, not exactly known whether epileptic discharges just hitch-hike the normal network or impair the network itself to generate the extratemporal functional deficit zone. By combining FDG-PET and probabilistic diffusion tractography, we investigated the integrity of the white matter pathway connecting the focus to the extratemporal functional deficit zone.Methods: We recruited 18 MTLE patients (8 right, 10 left) and age-matched 18 healthy control subjects. These patients were diagnosed as MTLE by seizure semiology, EEG and MRI. Diffusion MRI (Trio Scanner, Siemens) and [18F]-fluorodeoxyglucose PET (FDG-PET: Advance PET scanner,GE) were performed in both groups. Functional deficit zone or hypometabolic region was identified in the MTLE group by group comparison in the MNI standard space using SPM8 software. To delineate the seizure propagation tract (SPT), the seed region of interest (ROI) was set at the hypometabolic temporal region that comprises the focus and the target ROI at the extra-temporal hypometabolic region in each individual patient. The corresponding tract was drawn in the control subjects by coregistering these ROIs from the MNI standard brain onto the individual brain. The corticospinal tract (CST) was employed as a control that was not related with seizure propagation. In the control group, the hemisphere of the tractography (right or left) was carefully controlled to the MTLE group. Probabilistic diffusion tractography was employed to trace these tracts using FSL software v.416. FA values of tracts were submitted to repeated measure ANOVA, with the tract (SPT vs. CST) as a within-subject factor and with the group (MTLE vs. control) as a between-subject factor.Results: Compared with the control group, glucose hypometabolism was observed not only in the medial and basal temporal area but also in the ventrolateral and basal frontal area in the hemisphere ipsilateral to the focus in the MTLE group. SPT ran through the uncinate fasciculus, the extreme capsule and the fornix to reach the frontal hypometabolic region. The MTLE group showed lower FA value than the control group both in SPT and CST in the hemisphere ipisilateral to the focus. Significant interaction was observed between the two groups with FA of SPT more decreased than FA of CST in the MTLE group.Conclusions: In MTLE patients, integrity of the white matter tracts connecting the focus to the remote frontal functional deficit zone was more impaired than the control tract (CST). It is likely that epileptic bombardments impaired the whole network involved in generation of the remote functional deficit zone.