Abstracts

Rationale: Increasing evidence has suggested that repeated seizures may reconfigure long range connections between neuronal populations in different parts of the brain. Surgical intervention may affect the trajectory of this reconfiguration in contralateral hemisphere as well. This study applies whole brain connectome analysis for children who underwent epilepsy surgery in order to investigate the potential effect of epilepsy surgery and seizure outcome on the pattern of axonal plasticity in the contralateral hemisphere.Methods: Pre-/post-operative DTI data were acquired from 25 children with focal epilepsy (age: 9.2±5.2 y.o., 15 boys, 9/4 left/right temporal, 2/5 left/right frontal, 2/3 left/right fronto-temporal foci) using a 3T MRI scanner at b=1000 s/mm2 and 55 encoding directions. The average intervals between pre-/post-surgical MRI and surgery were 2.7 and 7.1 months, respectively. The seizure outcome was assessed at least 1 year after surgery according to Engel's category, seizure-free (SF, n=18) and non-seizure-free (non-SF) group (II-IV, n=7). For each DTI, an independent component analysis with ball and stick model was applied for whole brain tractography. A total of 58 cortical regions of interest in contralateral hemisphere were generated to construct a 58×58 connectivity matrix in which the elements quantify the pair-wise connectivity scores (i.e., fiber numbers connecting any two given cortical regions normalized by total volume of two regions). A two-way mixed ANOVA with between-subject 'random' factor (non-SF vs. SF) and within-subject 'fixed' factor (pre vs. post) was performed for each score in order to identify specific connections showing a significant group-by-treatment interaction.Results: The non-SF group showed six pair-wise contralateral connections whose scores were normal before surgery and significantly increased after surgery (Figure 1, Temporal pole mid-Temporal mid: F=7.97 p=0.009, Temporal pole mid-Rolandic operculum: F=8.68, p=0.007, Temporal pole mid-Temporal pole sup: F=5.99, p=0.020, Temporal sup-Temporal inf: F=8.96, p=0.006, Frontal inf triangularis-Caudate: F=7.37, p=0.012, Insula-Putamen: F=8.49, p=0.008). Resection volume was significantly correlated with post-operative score in Temporal pole mid-Temporal pole sup connectivity (R=0.46, p=0.023). In the SF group, there was only one connection (Figure 1, Frontal inf-Parietal inf) showing significant change (decreased in post-operative score, F=12.35, p=0.002).Conclusions: Post-operative seizures were associated with increased connectivity, most pronounced in the temporal pole region of the contralateral hemisphere. Further prospective studies are warranted to determine if such increased connectivity serves as an imaging marker predicting recurrent seizures after focal cortical resection. The functional correlates of this network reorganization will need to be clarified.