Posterior reversible encephalopathy syndrome (PRES), also known as hypertensive encephalopathy, is a neurotoxic state that occurs secondary to the inability of posterior circulation to auto-regulate 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.
It should not be confused with chronic hypertensive encephalopathy, also know as hypertensive microangiopathy, which results in microhemorrhages in the basal ganglia, pons and cerebellum.
Patients present with headache, seizures, encephalopathy and/or visual disturbance.
The syndrome can be precipitated by various clinical settings. The mechanism is not well understood but is thought to be related to 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.
- severe hypertension
- haemolytic uraemic syndrome (HUS)
- thrombocytopaenic thromboic purpura (TTP)
- systemic lupus erythematosus (SLE)
- drug toxicity
- bone marrow or stem cell transplantation
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
Parenchymal infarctions and hemorrhage are associated with PRES in respectively 10-25% and 15% of cases.
- affected regions as outlined above are hypoattenuating
Signal characteristics of affected regions include:
- T1: hypo intense in affected region(s)
- C+: patchy variable enhancement
- T2: hyperintense in affected region(s)
- DWI: usually normal
- ADC: signal increased in affected regions due to increased diffusion
- GRE: may show hypointense signal in cases of haemorrhage
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
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Posterior reversible encephalopathy syndrome (PRES)||✓|
|Reversible posterior leukoencephalopathy syndrome||✓|
|Reversible posterior cerebral edema syndrome||✓|
|Acute hypertensive encephalopathy||✓|
|Reversible posterior cerebral oedema syndrome||✗|