Effects of unilateral cortical resection of the visual cortex on bilateral human white matter

Children with unilateral resections of ventral occipito-temporal cortex do not necessarily evince visual perceptual impairments, even when category-selective regions are resected. We aim to elucidate the extent to which bilateral cortical white matter is affected by the focal resection in search of possible explanations for the apparent behavioral competence. In order to uncover both local and broader resection-induced changes, we analyzed tractography data from eight children with unilateral cortical resections and 15 age-matched controls using two complementary approaches. First, we used a deterministic fiber tracking algorithm to define the two major white matter pathways in the visual cortex that connect the occipital and temporal lobes: the inferior longitudinal and inferior fronto-occipital fasciculi. We then compared the microstructural indices of the tracts in the patients to the controls, and found that group differences were restricted to the ipsilesional hemisphere in the patients. Single-subject analyses showed further that these differences were evident only in the site of the resection. Second, we characterized the connectivity of the contralesional hemisphere’s occipito-temporal cortex using network analysis and found that, consistent with the normal microstructural indices of the contralesional fasciculi, there were no changes to the contralesional networks in patients with resections to their left visual cortex. Interestingly, while the integrity of specific tracts was intact, we found altered network properties in two patients with resections to their right visual cortex. Our results suggest first, that in cases of cortical resection during childhood, the microstructural damage to white matter is specific to the site of the resection without anterograde degeneration of the tracts; second, that hemispheric lateralization might be key to differential changes to the contralesional network organization; and last, that a unilateral network of regions with intact structural connectivity might be sufficient to subserve normal visual perception. Abbreviations AD axial diffusivity DNET dysembryoplastic neuroepithelial tumor FA fractional anisotropy IFOF inferior fronto-occipital fasciculus ILF inferior longitudinal fasciculus LH left hemisphere RD radial diffusivity RH right hemisphere ROI region of interest VOTC ventral occipito-temporal cortex