Diffusion MR imaging of posterior reversible encephalopathy syndrome: diagnostic and prognostic values

ABSTRACT

The purpose of this study was to evaluate the role of diffusion magnetic resonance [MR] imaging in diagnosis of patients with posterior reversible encephalopathy syndrome [PRES] and to demonstrate to how extent can apparent diffusion coefficient [ADC] maps be of value in quantitative assessment of severity of the lesion and predicting the conversion to infarction which can affect patient management and outcome. Eleven patients with PRES were examined with isotropic diffusion weighted imaging [DWI]. Quantitative assessment of the severity of the lesion was done by measurement of ADC of the lesion and of normal white matter and obtaining the degree of elevation of ADC values. These were compared with T2/DWI signal intensity score in each lesion. All patients were followed up by MR examination after medical treatment using the same parameters and the lesions were assessed for changes in signal intensity on T2/FLAIR images, DWI and ADC values. T2/FLAIR signal abnormalities were always present in the posterior white matter. Grey matter [of the posterior and anterior circulation structures] were involved in 6 out of 11 patients. White matter of anterior circulation structures were involved in 3 out of 11 patients. ADC values in areas of abnormal T2/FLAIR signal were high. Higher T2/DW score was seen in patients with a poor outcome than in patients who recovered. In 3 out of 11 patients, areas of high DWI signal intensity were seen with ADC values that were paradoxically normal. Follow-up images in two patients showed progression to infarction in pseudonormalized ADC map regions. Although vasogenic edema in PRES involves the posterior circulation territories, anterior circulation structures are also frequently involved. The extent of combined T2 and DWI signal changes and degree of ADC value elevation were correlated with patient outcome. Developement of ischemic infraction was seen in lesions with high DWI signal intensity and pseudonormalized ADC values. This may represent the earliest sign of nonreversibility as severe vasogenic edema progresses to cytotoxic edema