Quantitative Assessment of Diffusion Abnormalities in Posterior Reversible Encephalopathy Syndrome
James M. Provenzalea,
Jeffrey R. Petrellaa,
Luiz Celso H. Cruz Jra,
Jimmie C. Wonga,
Stefan Engeltera and
Daniel P. Barboriaka
a From the Department of Radiology (J.M.P., J.R.P., J.C.W., S.E., D.P.B.), Duke University Medical Center, Durham, North Carolina; Clinica de Diagnostico por Imagem—CDPI (L.C.H.C.), Barrashopping, Rio de Janeiro, Brazil; and the Department of Neurology (S.E.), University Hospital Basel, Petersgraben 4, Basel, Switzerland.
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FIG 1. MR imaging of a 32-year-old woman with PRES resulting from severe hypertension. Most severe degree of elevation of ADC values is seen in posterior WM despite relatively diffuse distribution of hyperintense regions on T2-weighted images.
A, Axial T2-weighted MR image at 2800/90 (TR/TE) shows diffuse areas of hyperintense signal. Note diffuse anterior WM involvement in addition to moderately prominent posterior WM involvement.
B, Isotropic DW image at 12,000/101 (inversion recovery pulse for cerebrospinal fluid suppression, 2200 ms; b value, 1000 s/mm2) shows very mild, diffuse increase in SI in posterior WM regions (possibly reflecting T2 prolongation effects) but no discrete abnormalities within the regions of hyperintense signal seen in A.
C, ADC map shows areas of hyperintense SI (arrowheads), consistent with vasogenic edema, within abnormal regions found in A. Mean ratio of ADC values within abnormal regions to values within normal WM (ADCL/ADCN) was 1.74. Note that the lesions having elevated ADC values are not seen as hypointense regions on the DW image shown in A due to balance of T2 prolongation effects and diffusibility effects (T2 washout). Because a cerebrospinal fluid suppression pulse was used for the DW imaging pulse sequence, cerebrospinal fluid appears hypointense on the ADC maps.
D, ADC map using a threshold of  3 SD (above mean ADC of normal WM) superimposed on axial T2-weighted image (seen in A) shows that nearly entire region of hyperintense signal seen in A has ADC values above this threshold. Regions of highest degree of ADC value elevation are designated by yellow or light green color.
E, ADC map with threshold of 10 SD (above mean ADC of normal WM) superimposed on axial T2-weighted image shows that area of ADC values above this threshold is much greater in posterior WM. This is the case even though hyperintense lesions in A are relatively equally distributed between anterior and posterior WM.
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FIG 2. Region of vasogenic edema appearing much smaller on DW image than on T2-weighted images and ADC map in a 28-year-old woman with PRES resulting from severe hypertension. This case shows that lesions with decreased SI on DW images have higher ADC values than lesions that have normal SI on such images. As a result, the contribution of T2 effects in these lesions is not sufficient to cancel the decreased SI caused by elevation of ADC values, and T2 washout does not occur.
A, Axial T2-weighted MR image at 2700/90 (TR/TE) shows areas of hyperintense signal that are much more prominent within posterior WM regions.
B, Isotropic DW MR image at 12,000/101 (inversion recovery pulse for cerebrospinal fluid suppression, 2200 ms; b value, 1000 s/mm2) shows a region of decreased SI consistent with vasogenic edema in left parietal lobe (curved arrow). Note that the overall extent of abnormal SI seen in B is much less than that seen in A. A small region of increased SI is seen in the right parietooccipital WM, possibly a result of T2 prolongation effects.
C, ADC map shows areas of hyperintense signal, consistent with vasogenic edema, that closely correlate with abnormal regions found in A. Mean ratio of ADC values within the left parietal abnormal region to values within normal WM (ADCL/ADCN) was 2.51, and the mean ratio in regions that were abnormal on the ADC map but appeared normal on DW image seen in B was 1.81. Because water diffusibility within the region of abnormal SI seen on the DW image is greater than that in other regions (as measured by the higher ADC), T2 washout does not occur.
D, ADC map with threshold of 3 SD (above mean ADC of normal WM) superimposed on axial T2-weighted image (shown in A) shows that essentially all hyperintense regions in A have ADC values above this threshold. Regions of highest degree of ADC value elevation are designated by red or orange color and are more severely elevated than those seen in figure 1D.
E, ADC map with threshold of 10 SD (above mean ADC of normal WM) superimposed on axial T2-weighted image shows that only posterior WM regions have ADC values above this threshold and, therefore, severity of degree of ADC elevation is greatest in posterior WM.
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