Reversible posterior leukoencephalopathy syndrome: Evaluation with diffusion-tensor MR imaging

PURPOSE: To characterize the changes in brain water diffusion caused by rev ersible posterior leukoencephalopathy syndrome (RPLS). MATERIALS AND METHODS: Twelve patients with the clinical features and conve ntional magnetic resonance (MR) imaging findings of RPLS underwent diffusio n-tensor echo-planar MR imaging. The isotropic diffusion coefficient ((D) o ver bar) and diffusion anisotropy (A(sigma)) were measured in posterior reg ions of diffusion abnormality and in anterior areas of normal-appearing bra in. RESULTS: Across all 12 subjects, the mean (D) over bar of (1.09 +/- 0.13 [S D]) x 10(-3) mm(2)/sec in affected posterior regions was 26% greater than i ts value of (0.87 +/- 0.07) x 10-3 in normal-appearing anterior regions. Th e mean A, of 0.15 +/- 0.03 in mm posterior regions was 35% less than its va lue of 0.23 +/- 0.02 in anterior regions (t(11) = 9.58; P <.001). There was a significant inverse correlation between <(D)over bar> and A(sigma) in po sterior regions (r = -0.67; P < .018) but not in anterior regions (r = -0.1 2; P -.719). A follow-up study performed in one patient after resolution of symptoms documented reversal of elevated isotropic diffusion and at least partial recovery of anisotropy loss. CONCLUSION: The increased magnitude of brain water diffusion characteristic of RPLS is accompanied by reduced A(sigma). The magnitudes of these two ef fects are correlated and may be reversible. These observations support the proposal that vasogenic edema due to cerebrovascular autoregulatory dysfunc tion is the underlying pathophysiologic mechanism in uncomplicated RPLS.