Presentation
Right upper limb weakness in patient with known multiple sclerosis
Patient Data
T2 weighted images reveal two well-defined oval shaped hyperintense plaques seen at left forceps minor region consistent with demyelinating plaques and responsible for patient's symptomatology.
Fractional anisotropy map which combines water molecular diffusion with direction. White matter fibers appear bright as the water molecules diffuse relatively freely but only in certain directions (anisotrophy) while grey matter appears dark as their water molecules diffuse similarly, but not constrained to a specific direction (isotropy). At the site of the plaque the diffusion becomes isotrophic denoting white matter destruction at this point.
Anatomical color map identifies dominant white matter diffusion direction superimposed on T2 WI which delineates the anatomy. ROIs are put at the site of the plaque, near normal appearing white matter and abnormal appearing white matter with FA and ADC calculated. At the site of the plaque FA is markedly reduced and ADC is elevated compared to other ROIs. This indicates increase water molecular diffusivity at plaque site.
Tractography of the forceps minor fibers and fronto-occipital fasciculus reveals white matter disruption at the site of the plaque.
Case Discussion
Demyelinating plaques, as seen in multiple sclerosis, cause destruction of white matter fibers which is manifested on diffusion tensor imaging (DTI) as increased diffusivity of water molecules. This can be demonstrated by comparing fractional anisotropy (FA) and ADC values at the plaque site, normal appearing white matter (which may be affected but to less degree) and far normal appearing white matter. Tractography can illustrate the affected white matter tract.
FA and ADC values can be used to assess progress on follow-up.
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