AQP4 and Posterior Leukoencephalopathy Syndrome: On the basis of all these findings, we believe that the vasogenic edema in PRES was reduced with mannitol treatment, which increased the hyperosmotic stress and opened the blood–brain barrier; meanwhile, upregulation of AQP4 expression secondary to the increased osmotic pressure resulted in cytotoxic edema in the astrocytes in SCC (RESLES).