PURPOSE:To evaluate the diagnostic accuracy of diffusion-weighted magnetic resonance (MR) imaging performed within 6 hours of the onset of stroke symptoms. MATERIALS AND METHODS:The authors reviewed the patient records and images from all patients hospitalized in a 10-month period in whom diffusion-weighted imaging was performed within 6 hours of the onset of strokelike symptoms (n = 22). Analyses included comparison of the initial interpretation of the diffusion-weighted images with the final clinical diagnosis; blinded reviews of computed tomographic (CT) scans and conventional and diffusion-weighted images; and determination of lesion contrast-to-noise ratios (CNRs). RESULTS:Diffusion-weighted images indicated stroke in 14 patients, all of whom had a final diagnosis of acute stroke. Diffusion-weighted images were negative in eight patients, all of whom had a final clinical diagnosis other than stroke (100% sensitivity, 100% specificity, chi 2 = 23.00, P < .0001). Blinded reviews yielded 100% sensitivity and 86% specificity for diffusion-weighted MR imaging (chi 2 = 15.43, P < .0005); 18% sensitivity and 100% specificity for conventional MR imaging (chi 2 = 2.85, P > .2); and 45% sensitivity and 100% specificity for CT (chi 2 = 4.40, P > .10). Lesion percentage CNRs were 77% for diffusion-weighted imaging, 5.5% for CT, 9.8% for T2-weighted MR imaging, and 3.1% for proton-density-weighted MR imaging (P < .002 for diffusion-weighted imaging vs others). CONCLUSION:Diffusion-weighted MR imaging is highly accurate for diagnosing stroke within 6 hours of symptom onset and is superior to CT and conventional MR imaging.

Objective: Standard MRI confirms the diagnosis of posterior leukoencephalopathy syndrome (PLES), recently associated with an increasing number of medical conditions. In PLES, T2-weighted MRI demonstrates hyperintensity spreading out from posterior brain regions; the pathophysiology remains mysterious. In the acute setting, diffusion-weighted imaging (DWI), but not standard MR imaging, can distinguish ischemic injury from those conditions known to cause vasogenic brain edema. DWI is potentially valuable in understanding the pathophysiology of PLES and in diagnosing patients who do not have previously known risk factors. Methods: Serial CT and MRI studies (including DWI, apparent diffusion coefficient [ADC] maps, and, in one instance, perfusion-weighted imaging) were performed in three female patients with a neurologic syndrome consistent with PLES while hospitalized for treatment of other conditions. Results: None of the patients had previously described risk factors for PLES; all had only mild elevations in blood pressure. MRI showed large, abnormal, T2 hyperintense regions in the posterior cerebrum with corresponding hyperintensity on ADC maps-signal characteristics predominantly consistent with vasogenic edema. There were also smaller patchy posterior cortical regions with decreased ADC and bright DWI consistent with infarction in one, and dramatic conversion of a large region to an ischemic pattern in another. Conclusions: ADC maps and DWI can successfully differentiate PLES from early cerebral ischemia, thus playing a pivotal role in treatment decisions. PLES is associated with a wider variety of conditions than has been previously reported and is not always reversible. Hyperintense DWI signal in patients with the syndrome likely marks a tissue stage of permanent brain injury.