Diffusion Tensor Imaging of Brain Plasticity After Occipital Lobectomy

Reorganization involving residual visual pathways with unilateral damage to the primary visual cortex was previously described. Using diffusion tensor imaging, we measured water diffusion-related changes in the optic radiation contralateral to occipital lobe ablation in children with intractable epilepsy. We studied 10 children who had undergone a resection of the unilateral occipital cortex and 13 control subjects. Diffusion tensor imaging was acquired using a 1.5 Tesla magnetic resonance scanner. Fiber bundles representing optic radiation were tracked. Diffusion parameters included mean fractional anisotropy, apparent diffusion coefficient, and diffusion parallel and perpendicular to the fiber tract. In the surgical group, fractional anisotropy values of optic radiation contralateral to the side of resection exhibited a significant positive partial correlation (r = 0.752, P = 0.019) with duration of time between surgery and diffusion tensor imaging acquisition, after controlling for age. The apparent diffusion coefficient and parallel diffusivity were higher in the surgical versus the control group, but did not differ among patients. After unilateral resection of the occipital lobe, the contralateral optic radiation undergoes significant changes in anisotropy. Such structural white-matter changes may represent an adaptive response because of unilateral occipital ablation, and may account for plasticity changes observed in functional magnetic resonance imaging.