<prompt> Commonest cause of Budd Chiary syndrome is:Valve in the IVCHepatocellular carcinomaParoxysmal nocturnal hemoglobinuriaRenal cell carcinoma  <response>: Answer is C Paroxysmal nocturnal hemoglobinuria: The most common cause of hepatic vein thrombosis from the list mentioned in Harrison is Paroxysmal nocturnal hemoglobinuria, and hence is the answer of choice here. 