Postoperative axonal changes in the contralateral hemisphere in children with medically refractory epilepsy: A longitudinal diffusion tensor imaging connectome analysis.

To determine brain plasticity changes due to resective epilepsy surgery in children, we performed a longitudinal connectome analysis on the pattern of axonal connectivity in the contralateral hemisphere. Pre- and postoperative diffusion tensor imaging (DTI) data were acquired from 35 children with intractable focal epilepsy. A total of 54 brain regions of interest (ROIs) were generated in the hemisphere contralateral to the resection. Within a 54 × 54 connectivity matrix, a pairwise connectivity score was calculated for each connection between two ROIs, based on the DTI fiber streamline number in each connection. A permuted Spearman's ρ-rank analysis was used to identify specific inter-regional connections showing a significant association between the postoperative change of connectivity score and clinical variables. Nineteen connections in the contralateral hemisphere showed postoperative increases in the strength of connectivity. Postoperative increase in connectivity between insular-inferior frontal operculum regions as well as that between superior frontal orbital and mid frontal orbital regions were both significantly associated with a larger surgical resection volume (ρ > +0.40) and a younger patient age (ρ > -0.34). These increases were more robust in patients with frontal resection and in those achieving seizure freedom. Neuropsychological evaluation on subsets of patients revealed that such increases in connectivity were associated with preserved or improved cognitive functions such as visual memory and planning. Resective epilepsy surgery may lead to increased contralateral axonal connectivity in children with focal epilepsy. Our data lead to a hypothesis that such increased connectivity may be an imaging marker of postoperative brain plasticity to compensate for cognitive function. Hum Brain Mapp 37:3946-3956, 2016.