DIFFUSION-WEIGHTED MR-IMAGING IN HYPERTENSIVE ENCEPHALOPATHY - CLUES TO PATHOGENESIS

PURPOSE: Hypertensive encephalopathy, a complex of cerebral disorders, including headache, seizures, visual disturbances, and other neurolog ic manifestations, is associated with a variety of conditions in which blood pressure rises acutely. It has been ascribed to either exuberan t vasospasm with ischemia/infarction or breakthrough of autoregulation with interstitial edema. Diffusion-weighted MR imaging may be used to determine whether the edema in hypertensive encephalopathy is cytotox ic or vasogenic in origin. METHODS: Diffusion-weighted imaging was per formed using the double line scan diffusion imaging technique on a 1.5 -T MR system. Seven patients with hypertensive encephalopathy were ima ged within 1 day of the onset of their symptoms. Apparent diffusion co efficient maps as well as low and high b-factor images were acquired. The two-tailed paired Student's t-test was used to compare the apparen t diffusion coefficients in edematous brain regions with those of norm al white matter. RESULTS: In all cases the apparent diffusion coeffici ent maps of the patients with hypertensive encephalopathy showed incre ased signal in regions corresponding to increased T2 signal on standar d T2-weighted (low b-factor) images. Quantitative apparent diffusion c oefficients in regions of abnormal T2 signal were 1.36 +/- 0.14 mu m(2 )/ms, compared with 0.80 +/- 0.05 mu m(2)/ms in normal white matter. D iffusion-weighted (high b-factor) T2-weighted images did not show abno rmal signal. CONCLUSION: Diffusion-weighted MR imaging shows that the edema in hypertensive encephalopathy is of vasogenic origin and does n ot represent ischemia or infarction, This finding may have therapeutic implications.