Posterior reversible encephalopathy syndrome
By Hyo-Jeong Lee, MD
Magnetic resonance imaging (MRI) and magnetic resonance angiography
(MRA) of the brain were performed with a GE Signa LX 1.5T MRI
scanner (GE Healthcare, Waukesha, WI). Contrast media (Magnevist,
gadopentetate dimeglumine, Berlex Laboratories, Montville, NJ) was
injected intravenously (0.1 mmol/kg body weight). The MRI showed
bilateral symmetric vasogenic edema mainly involving the
subcortical white matter in the parieto-occipital, posterior
temporal, and posterior frontal lobes (Figure 1). The MRA of the
vertebrobasilar system was unremarkable without any area of
stenosis or vasospasm (Figure 2).
Reversible posterior leukoencephalopathy syndrome is a
clinicoradiologic entity characterized by headaches, altered mental
status, seizures, and visual loss and is associated with white
matter vasogenic edema predominantly affecting the posterior
occipital and parietal lobes of the brain.1
been some controversy about what the proper term should be for this
entity because MRI has shown that lesions can occur in both gray
and white matter. Therefore, a new name, posterior reversible
Most cases of PRES occur with hypertension or
immunosuppression, but it can occur with many diverse clinical
Since PRES is often unsuspected by
clinicians, recognition of the characteristic imaging findings by
radiologists is key to diagnosing this syndrome and should prevent
deleterious work-ups or therapies.
The pathophysiology of PRES is under debate, but it is related
to disordered cerebral autoregulation. Two pathophysiologic
mechanisms have been proposed regarding cerebral
autoregulation-cerebral vasospasm, which results in cytotoxic
edema,4 and vasodilatation, which results in vasogenic
edema.5 The latter is more favored by most experimental
and clinical data.6,7 The pathophysiology of PRES also
implicates endothelial dysfunction, especially in cases without
severe hypertension, such as pre-eclampsia or cytotoxic
The most characteristic imaging pattern in PRES is the presence
of edema involving the white matter of the posterior portions of
both cerebral hemispheres, especially the parieto-occipital
regions, in a relatively symmetric pattern that spares the
calcarine and paramedian parts of the occipital lobes.1
However, other structures (such as the brain stem, cerebellum, and
frontal and temporal lobes) may also be involved, and although the
abnormality primarily affects the subcortical white matter, the
cortex and the basal ganglia may also be involved.8
Although they are rare, gyriform signal enhancement or parenchymal
hemorrhage can occur in complicated cases.9 Recently,
studies with diffusion-weighted sequences6 and
diffusion-tensor sequences7 have shown increased
apparent diffusion coefficients (ADCs) in the involved regions
accompanied by anisotropy loss, which suggests reversible vasogenic
edema as an underlying pathophysiology. Therefore, early diagnosis
and treatment is essential for the patients' prognosis.
Posterior reversible leukoencephalopathy syndrome is a
clinicoradiologic entity associated with hypertension,
immunosuppression, or many diverse clinical entities. Since PRES is
often unsuspected by clinicians, recognition of the characteristic
imaging findings by radiologists is key to diagnosing this syndrome
and should prevent deleterious work-ups or therapies.
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- Casey SO, Sampaio RC, Michel E, et al. Posterior reversible
encephalopathy syndrome: Utility of fluid-attenuated inversion
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entities mediated by vascular autoregulatory dysfunction.
- Lewis LK, Hinshaw DB Jr, Will AD, et al. CT and angiographic
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- Strandgaard S, Paulson OB. Cerebral autoregulation.
- Schwartz RB, Mulkern RV, Gudbjartsson H, Jolesz F.
Diffusion-weighted MR imaging in hypertensive encephalopathy: Clues
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- Mukherjee P, McKinstry RC. Reversible posterior
leukoencephalopathy syndrome: Evaluation with diffusion-tensor MR
imaging. Radiology. 2001;219:756-765.
- Lamy C, Oppenheim C, Meder JF, Mas JL. Neuroimaging in
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- Schwartz RB, Jones KM, Kalina P, et al. Hypertensive
encephalopathy: Findings on CT, MR imaging and SPECT imaging in 14
cases. AJRAm J Roentgenol. 1992;159:379-383.
Posterior reversible encephalopathy syndrome.
May 03, 2007