Mapping degeneration of the visual system in long-term follow-up after childhood hemispherectomy – A series of four cases

Abstract

ObjectiveAlthough hemidisconnection surgery may eliminate or reduce seizure activity in patients with epilepsy, there are visual, cognitive and motor deficits which affect patients’ function post-operatively, with varying severity and according to pathology. Consequently, there is a need to map microstructural changes over long time periods and develop/apply methods that work with legacy data. MethodsIn this study, we applied the novel single shell 3-Tissue method to data from a cohort of 4 patients who were scanned 20-years following childhood hemidisconnection surgery and presented with variable clinical outcomes. We have successfully reconstructed tractography of the whole visual pathway from single shell diffusion data with reduced number of gradient directions. ResultsAll patients presented with degeneration of the visual system characterised by low fractional anisotropy and high mean diffusivity. There were no apparent microstructural differences between both optic nerves that could explain the different level of visual function across patients. However, we provide evidence suggesting an association between the level of visual function and DTI metrics within the remaining components of the visual system, particularly the optic tract, of the contralateral hemisphere post-surgery. SignificanceWe believe this study suggests that diffusion MRI can be used to monitor the integrity of the visual system following hemispherectomy and if extended to larger cohorts and a greater number of time-points, including pre-surgically, can provide a clearer picture of the natural history of visual system degeneration. This knowledge may in turn help to identify patients at greatest risk of poor visual outcomes that might benefit from rehabilitation therapies.