VWF and thrombotic thrombocytopenic purpura: Thrombotic microangiopathies may result from four types of lesions: ultra-large von Willebrand factor (UL-VWF)-platelet thrombi, as in thrombotic thrombocytopenic purpura (TTP); fibrin-platelet thrombi, as exemplified by disseminated intravascular coagulopathy (DIC) and catastrophic antiphospholipid syndrome; inflammatory or proliferative microangiopathy accompanied by variable fibrin thrombi, as in hemolytic uremic syndrome (HUS); and intravascular clusters of cancer cells.4