Commonest cause of Budd Chiary syndrome is:
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.
Valve in the IVC
Hepatocellular carcinoma
Paroxysmal nocturnal hemoglobinuria
Renal cell carcinoma