How does a focal white matter lesion affect neighboring white matter integrity? How does a focal lesion affect other parts of the fiber itself? Would trans-synaptic effect be evident? What is the directionality of this effect – anterograde or retrograde? And, will the effect depends on the pathophysiology of the damage – a demyelinative lesion or axonal loss? Being a well-defined system, the visual pathways make a fine model for assessing these questions.
We use Diffusion Tensor Imaging (DTI) and fiber tractography for tracking white matter and investigating its structural integrity. Comparing cohorts of patients and control subjects, we evaluate the outcome of localized white matter damage on the entire visual pathway.
In a recent study on patients following an optic neuritis attack, we showed that a localized optic nerve demyelinative damage affected the integrity of the continuing optic tract. This is in accordance with a process of Wallerian degeneration. However, no damage to consecutive optic radiation was found, opposing trans-synaptic anterograde degeneration. Furthermore, lesions along the optic radiations did not affect white matter integrity along the optic tract, opposing retrograde degeneration (Raz et al., AAN abstract 2013).