Specific Imaging Findings

Posterior Reversible Encephalopathy Syndrome (PRES) usually shows characteristic bilateral, predominantly symmetric, patchy areas of hyperintense T2 signal in the subcortical regions of the parietal and occipital lobes. Cortex may also be involved, while mass effect is absent to minimal. In addition to the primary parietal- occipital pattern, patchy bilateral T2 hyperintensities are also found in holohemispheric and superior frontal patterns, and may be present in the cerebellum, basal ganglia, and brainstem. There is characteristically increased diffusion on ADC maps corresponding to vasogenic edema, while contrast enhancement is absent to minimal, usually leptomeningeal. Hemorrhage, either subarachnoid or parenchymal, is associated with vasogenic edema in a minority of patients. Areas of reduced diffusion are found in some cases, likely representing infarction. More prominent cases of PRES are visible on CT as ill-defined foci of subcortical low attenuation. Vascular studies commonly show evidence of vasculopathy with irregular and beaded appearance of distal intracranial arteries, which is, similar to other imaging findings, typically reversible. Findings on perfusion studies can span from decreased to increased cerebral blood flow, which may depend on the timing, underlying etiology, and brain area.

Pertinent Clinical Information

The most common presentations include headache, altered mentation, nausea, and visual disturbances. Symptoms may develop acutely or over several days and may lead to generalized seizures and coma. Various conditions place patients at risk of PRES, the most common are pre-eclampsia/eclampsia, hypertensive crisis, following transplantation, autoimmune diseases, infection/sepsis/shock, and after cancer chemotherapy.