Posterior reversible encephalopathy syndrome (PRES) (also known as hypertensive encephalopathy) is a neurotoxic statethat 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 no infarction, most commonly in the parieto-occipital regions.
It should not be confused with chronic hypertensive encephalopathy (aka hypertensive microangiopathy) which results in microhemorrhages in the basal ganglia, pons and cerebellum.
Soft-tissue rim sign – helpful in distinguishing a ureteric stone from a phlebolith on CT imaging. Ureteric stones appear as a calcific density with a surrounding rim of soft tissue representing the oedematous ureteric wall (red arrow). Phleboliths on the other hand usually have imperceptible walls and therefore they appear to be surrounded by fat (green arrow). Occasionally phleboliths have a tail of remnant parent vein associated with one edge known as the comet-tail sign.
