This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
What is the most common cause for Budd chiari syndrome : 
Select and explain. 
A. Right ventricular failure, B. PNH, C. Valve in hepatic veins, D. Polycythemia vera
D: Polycythemia vera
Answer: D: Polycythemia vera 
Explanation: Answer is D (Polycythemia vera): Amongst the options provided Polycythemia vera is the commonest cause of Budd chiary syndrome. Budd chiari syndrome includes acute, subacute or chronic occlusion of hepatic vein most commonly caused by hepatic vein thrombosis. Hepatic vein thrombosis is associated with in decreasing order of frequency: - Polycythemia vera Q - Pregnancy - Postpaum state - Use of oral contraceptives - Paroxysmal nocturnal hemoglobinuria (PNH) Q - lntraabdominal cancers, paicularly hepatocellular carcinoma