Posterior Reversible Encephalopathy Syndrome: Imperative to Define

Posterior reversible encephalopathy syndrome (PRES) (also termed reversible posterior leukoencephalopathy syndrome) represents an entity with an underlying pathophysiological mechanism suggested to be vasogenic edema.¹ Burrus and colleagues² reported up to 48% PRES in patients with thrombotic thrombocytopenic purpura (TTP) and acute brain abnormalities. We agree that diffusion-weighted imaging and apparent diffusion coefficient mapping are indispensible to differentiation of vasogenic edema from cytotoxic edema in PRES. However, we have some concern regarding their definition of PRES.