Tracking posttraumatic hemianopia.

Hemianopia after traumatic brain injury is not infrequent and results from retro-chiasmatic lesions. Differentiating optic pathway lesions can be challenging with classic imaging. Advanced imaging techniques as an investigational tool for posttraumatic hemianopia are discussed and their pitfalls highlighted through an illustrative case study. In a patient with posttraumatic hemianopia, MRI at 8 weeks and 2 years after trauma were analyzed. Diffusion tensor imaging (DTI) and morphometric analysis of the primary visual cortex (V1) were performed. Optical coherence tomography (OCT) was performed 2 years after trauma. DTI at 8 weeks showed a decrease in fractional anisotropy (FA) of the left optic tract together with a decrease in FA in the right optic tract and optic radiation. At 2 years, an isolated decrease of the left optic tract FA values was noticed together with signs of Wallerian degeneration on classic MR imaging. OCT showed thinning of the retina congruent with the visual field deficit. While DTI abnormalities were also present in the early scan, they were more diffuse and also encompassed functionally intact structures. Results of advanced imaging techniques need to be interpreted with caution and can vary according to the timing of imaging due to Wallerian degeneration.