Posterior Reversible Encephalopathy Syndrome, Pres

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Posterior reversible encephalopathy syndrome

Posterior reversible encephalopathy syndrome (PRES) is a neurotoxic state that occurs secondary to the inability of posterior circulation to autoregulate in response to acute changes in blood pressure. Hyperperfusion with resultant disruption of the blood brain barrier results in vasogenic oedema, but not infarction, most commonly in the parieto-occipital regions.

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PRES is also known as hypertensive encephalopathy or reversible posterior leukoencephalopathy .

The term PRES can be a misnomer as the syndrome can involve or extend beyond the posterior cerebrum. Furthermore, although most cases involve a resolution of changes with the treatment of the precipitating cause and clinical recovery some patients can progress to develop permanent cerebral injury and be left with residual neurological defects.

It should not be confused with chronic hypertensive encephalopathy. also known as hypertensive microangiopathy, which results in microhemorrhages in the basal ganglia, pons and cerebellum.

Clinical presentation

Patients present with a headache, seizures, encephalopathy and/or visual disturbance.


Various clinical settings can precipitate the syndrome. The mechanism is not well understood but is thought to be related to the altered integrity of the blood brain barrier. Two main theories have been proposed:

high blood pressure: leads to loss of self-regulation, hyperperfusion with endothelial damage and vasogenic oedema

endothelial dysfunction: leads to vasoconstriction and hypoperfusion resulting in cerebral ischaemia and subsequent vasogenic oedema

Hypertension is not present or does not reach the upper limits to self-regulation (150-160 mmHg) in 25% of patients.


Radiographic features

Most commonly there is vasogenic oedema within the occipital and parietal regions (

95% of cases), perhaps relating to the posterior cerebral artery supply. The oedema is usually symmetrical. Despite being termed posterior, PRES can be found in a non-posterior distribution, mainly in watershed areas, including within the frontal, inferior temporal, cerebellar and brainstem regions 2. Both cortical and subcortical locations are affected.

There are three main imaging patterns:

holohemispheric at watershed zones

superior frontal sulcus

parieto-occipital dominance

Other uncommon patterns of PRES in <5% include: purely unilateral, or "central" (brainstem or basal ganglia lacking cortical or subcortical white matter involvement).

Parenchymal infarctions and haemorrhage are associated with PRES in respectively 10-25% and 15% of cases.

The presence of contrast enhancement, no matters the pattern or how avid, does not portend the clinical outcome.


The affected regions, as outlined above, are hypoattenuating.


Signal characteristics of affected areas include:

T1: hypointense in affected regions

T1 C+ (Gd): patchy variable enhancement. It can be seen in

35% of patients, whether leptomeningeal or cortical pattern.

T2: hyperintense in affected regions

DWI: usually normal

ADC: signal increased in affected regions due to increased diffusion

GRE: may show hypointense signal in cases of haemorrhage

SWI: may show microhemorrhages in up to 50%

Differential diagnosis

General imaging differential considerations include:


1. Foocharoen C, Tiamkao S, Srinakarin J et-al. Reversible posterior leukoencephalopathy caused by azathioprine in systemic lupus erythematosus. J Med Assoc Thai. 2006;89 (7): 1029-32. Pubmed citation

2. Bartynski WS, Boardman JF. Distinct imaging patterns and lesion distribution in posterior reversible encephalopathy syndrome. AJNR Am J Neuroradiol. 2007;28 (7): 1320-7. doi:10.3174/ajnr. A0549 - Pubmed citation

3. Bartynski WS. Posterior reversible encephalopathy syndrome, part 1: fundamental imaging and clinical features. AJNR Am J Neuroradiol. 2008;29 (6): 1036-42. doi:10.3174/ajnr. A0928 - Pubmed citation

4. Bartynski WS. Posterior reversible encephalopathy syndrome, part 2: controversies surrounding pathophysiology of vasogenic edema. AJNR Am J Neuroradiol. 2008;29 (6): 1043-9. doi:10.3174/ajnr. A0929 - Pubmed citation

5. Bartynski WS, Tan HP, Boardman JF et-al. Posterior reversible encephalopathy syndrome after solid organ transplantation. AJNR Am J Neuroradiol. 2008;29 (5): 924-30. doi:10.3174/ajnr. A0960 - Pubmed citation

6. Fugate JE, Claassen DO, Cloft HJ et-al. Posterior reversible encephalopathy syndrome: associated clinical and radiologic findings. Mayo Clin. Proc. 2010;85 (5): 427-32. doi:10.4065/mcp.2009.0590 - Free text at pubmed - Pubmed citation

7. McKinney AM, Short J, Truwit CL, McKinney ZJ, Kozak OS, SantaCruz KS, Teksam M. Posterior reversible encephalopathy syndrome: incidence of atypical regions of involvement and imaging findings. AJR Am J Roentgenol. 2007 Oct;189(4):904-12. www. ncbi. nlm. nih. gov/pubmed/17885064

8. McKinney AM, Sarikaya B, Gustafson C, Truwit CL. Detection of microhemorrhage in posterior reversible encephalopathy syndrome using susceptibility-weighted imaging. AJNR Am J Neuroradiol. 2012 May;33(5):896-903. http://www. ncbi. nlm. nih. gov/pubmed/22241378

9. McKinney AM, Jagadeesan BD, Truwit CL. Central-variant posterior reversible encephalopathy syndrome: brainstem or basal ganglia involvement lacking cortical or subcortical cerebral edema. AJR Am J Roentgenol. 2013 Sep;201(3):631-8. http://www. ncbi. nlm. nih. gov/pubmed/23971457

10. Karia SJ, Rykken JB, McKinney ZJ, Zhang L, McKinney AM. Utility and Significance of Gadolinium-Based Contrast Enhancement in Posterior Reversible Encephalopathy Syndrome. AJNR Am J Neuroradiol. 2015 Nov 12. http://www. ncbi. nlm. nih. gov/pubmed/26564441

Article Information

Synonyms or Alternate Spellings:

Posterior reversible encephalopathy syndrome (PRES)


Hypertensive encephalopathy


Reversible posterior leukoencephalopathy syndrome

Reversible posterior cerebral edema syndrome

Hyperperfusion encephalopathy

Occipito-parietal encephalopathy

Reversible leukoencephalopathy

Acute hypertensive encephalopathy

Reversible posterior cerebral oedema syndrome

Cases and Figures

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Imaging Differential Diagnosis

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