A radiological study of cerebral white matter lesions in patients with dementia using diffusion-weighted MR imaging

We investigated the changes in water diffusion in the cerebral white matter and the corpus callosum in 12 patients with Binswanger's disease (BD), and 19 patients with Alzheimer's Disease (AD), including 12 without (AD-) and 7 with periventricular hyperintensity (PVH) lesions (AD+), using diffusion-weighted magnetic resonance imaging (MRI). Apparent diffusion coefficients (ADCs) in the anterior and posterior white matter were significantly higher in patients with BD and AD than in 12 age-matched controls. The ADCs were significantly higher in AD (+) than in AD (-) patients. Anisotropic ratios (ARs), defined as diffusion restricted perpendicular to the direction of the nerve fibers, were significantly higher in BD and AD (+) patients, and even in AD (-) patients, than in the controls. ARs in the anterior white matter were significantly higher in BD than in AD (+), while in the posterior white matter the ratios were significantly higher in AD (+) rather than BD patients. The ADCs and ARs in the genu of the corpus callosum were significantly higher in patients with BD and AD (+) compared to the control subjects, while ADCs and ARs in the splenium were significantly higher in patients with AD (+) and AD (-) than in those with BD. These results suggest that mild myelin loss occurs in AD patients even in apparently normal white matter and in the splenium of the corpus callosum. A definite loss of myelin and axons, including incomplete infarction, occurs preferentially in anterior white matter in BD, while in posterior white matter in AD (+), as seen on T2-weighted images as PVH. Studies with diffusion-weighted MRI may allow the characterization of different pathological processes and enable the demonstration of underlying white matter lesion in patients with dementia that cannot be visualized by conventional MRI. (author)