Clots commonly result from the following: Thrombotic conditions (eg, protein C or S deficiency, antiphospholipid syndrome, antithrombin III deficiency, factor V Leiden mutation, pregnancy, oral contraceptive use) Hematologic disorders (eg, myeloproliferative disorders such as polycythemia and paroxysmal nocturnal hemoglobinopathy) Inflammatory bowel disease Connective tissue disorders Trauma Infection (eg, hydatid cyst, amebiasis) Tumor invasion of the hepatic vein (eg, hepatocellular carcinoma or renal cell carcinoma) Sometimes Budd-Chiari syndrome begins during pregnancy and unmasks a previously asymptomatic hypercoagulability disorder.