[Diffusion anisotropy in cerebral white matter lesion]

Diffusion MRI studies were performed on 14 patients with diffuse high-signal lesions of the cerebral white matter on T2-weighted MR images. There were two patients with adrenoleukodystrophy, four with dentato-rubro-pallido-luysian atrophy, three with familial spastic paraplegia, two with myotonic dystrophy and three with dementia of unknown origin. In addition, a patient with of Sanfilippo disease and one of the three patients who exhibited dementia of unknown origin were also found to be low-signal in the cerebral cortex T2-weighted MR images. In every case except the last two, diffusion-weighted MR images yielded significantly higher apparent diffusion coefficients perpendicular to nerve fibers in the frontal white matter and the corpus callosum than in the normal controls. The lesions displayed increased diffusion anisotropy, calculated as the ratio of the diffusion coefficient perpendicular to the nerve fibers to the diffusion coefficient parallel to the nerve fibers, i.e., diffusion anisotropy was lost in the white matter, suggesting a demyelinating process in the lesion. In the last two cases, on the other hand, the diffusion coefficient and diffusion anisotropy were within normal range. The white matter lesions in these cases were thought to represent degeneration secondary to the cortical involvement. Thus, it was confirmed that diffusion-weighted MR images, unlike T2-weighted MR images, were confirmed to allow differentiation between at least two types of white matter lesions.