Monday 22 August 2011

Posterior Reversible Encephalopathy MRI

Syn: PRES, Reversible Posterior Leukoencephalopathy, Hypertensive encephalopathy.
Has typical imaging findings as in this case.
Axial FLAIR images of Brain show bilateral patchy parieto occipital cortical T2 hyper intensities. (has predilection for parieto occipital cortex, may extend to adjacent frontal and temporal lobes, cranial portions of cerebellum, parts of basal ganglia and vary rarely brain stem; involvement is bilateral but asymmetrical)

Absence to restricted diffusion on Dw images is characteristic (implies to a reversible vasogenic odema; in rare and advanced cases patchy high signals on diffusion may indicate irreversible infarction and low signal intensity hemosiderin staining on T2*GRE  indicate hemorrhage and are known )

Normal MR Venogram is very typical of posterior reversible encephalopathy.

Closest DDs: 
1st Posterior Circulation Arterial Stroke which show restricted diffusion.
2nd CVT, Thrombosed superior sagittal sinus is expected on MR Venogram.

The signal abnormality in PRES results from abnormal cerebro vascular auto regulation due to multiple aetiologies most common being hypertension and typically reverses on normalization of blood pressure. Other uncommon causes are ecclampsia preeclampsia, uremic encephalopathy and drug toxicity.
The most common clinical picture is post partum female with seizures / eclapsia / high blood pressure. Less commonly young male with hypertension. Some patient particularly children reported even with normal Blood pressure.

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