Posterior reversible encephalopathy syndrome: the endothelial hypotheses.

Posterior reversible encephalopathy syndrome (PRES) is characterised by headache, visual disorders, seizures, altered mentation, consciousness disturbances and focal neurological signs. Initially described in patients with pre and eclampsia, severe hypertension, posterior reversible encephalopathy syndrome can occur in other clinical conditions such as infection, sepsis, shock, cancer chemotherapy, autoimmune diseases and hypercalcemia. Pathogenesis of brain lesions in PRES is not full understood and two opposite theories have been proposed. Both models are based on the central role of hypertension. According to the first theory, hypertension could cause a breakdown of the autoregulatory system in cerebral circulation, leading to brain edema. The second theory suggests that hypertension causes activation of autoregulatory system, which finally results in a vasoconstriction of brain vessels with hypoperfusion, ischemia and subsequent fluid leakage. However a large number of patients, with PRES, doesn't show hypertension. We here describe the hypothesis of the crucial role of endothelial dysfunction and activation in PRES pathogenesis. Our hypothesis offers a common pathogenetic mechanism in which every PRES-related condition can be set. In our model, the activation of immune system and the consequent endothelial activation start a molecular cascade which finally causes the production of molecules which alter the normal homeostasis of blood-brain barrier. This alteration consists in a weakening of brain vessel tight junctions, which allows fluid leakage and edema. In this scenario, hypertension would be an epiphenomenon of the underlying mechanism and not the cause and, for this reason, it can be present or not in PRES.