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: Surgery
Which is the most frequent cause for Budd chiari syndrome? 
Select and explain. 
A. Hepatic vein thrombosis, B. Poal vein thrombosis, C. Malignancy, D. Valves in hepatic veins
A: Hepatic vein thrombosis
Answer: A: Hepatic vein thrombosis 
Explanation: The Budd-Chiari syndrome results from the thrombosis of one or more major hepatic veins and is characterized by hepatomegaly ascites, and abdominal pain. All hypercoagulable states cause an increased risk of Budd chain's syndrome. Hepatic vein thrombosis is associated with myeloproliferative disorders (especially polycythemia vera), pregnancy, the postpaum state, the use of OCPs, paroxysmal nocturnal hemoglobinuria, and intra-abdominal cancers, paicularly hepatocellular carcinoma.