Vasogenic oedema in the parieto-occipital subcortical white matter in a patient with severe hypertension, eclampsia, renal failure or immunosuppression — recognise the pattern, the atypical variants and the complications (haemorrhage, restricted diffusion).
Orient first
- Failure of cerebral autoregulation causes vasogenic (not cytotoxic) oedema, typically symmetric and posterior.
- Patterns: dominant parieto-occipital, holohemispheric watershed, superior frontal sulcus; atypical: brainstem, cerebellum, basal ganglia.
- Most is reversible if the cause is treated; restricted diffusion and haemorrhage mark worse outcome.
Acquire the study
- Axial FLAIR, DWI with ADC map, SWI/gradient echo and post-contrast T1.
The manoeuvre
- FLAIR: symmetric subcortical and cortical hyperintensity in the parieto-occipital lobes; name the pattern.
- DWI/ADC: high ADC (vasogenic) — areas of low ADC indicate infarction.
- SWI: microhaemorrhages or sulcal haemorrhage.
- Post-contrast T1: patchy leptomeningeal or cortical enhancement in some.
What confirms it
- Symmetric vasogenic oedema in a typical distribution in a patient with a recognised trigger, improving on follow-up.
What licenses you to exclude it
- A normal MRI with FLAIR and DWI excludes PRES at the time of imaging.
The classic misread
- Calling PRES bilateral posterior circulation infarcts — infarcts restrict on DWI and follow vascular territories.