Budd-Chiari syndrome is a rare disorder characterized by obstruction of the veins of the liver that carry the blood flow from the liver. When the blood flow out of the liver is impeded, blood backs up in the liver, causing it to enlarge (hepatomegaly). The spleen may also enlarge (splenomegaly). This backup of blood increases blood pressure in the portal vein, which carries blood to the liver from the intestines (portal hypertension), and result in dilated, twisted veins in the esophagus (esophageal varices). Portal hypertension, leads to fluid accumulating in the abdomen (called ascites). The clot may extend to also block the inferior vena cava (the large vein that carries blood from the lower parts of the body to the heart). Varicose veins in the abdomen near the skin's surface may develop and become visible. In some cases, scarring of the liver (cirrhosis) occurs. Other symptoms may include fatigue, abdominal pain, nausea, jaundice and bleeding in the esophagus. The severity of the disorder varies from case to case, depending on the site and number of affected veins. It most often occurs in patients which have a disorder that makes blood more likely to clot, such as those who are pregnant or who have a tumor, a chronic inflammatory disease, a clotting disorder, an infection, or a myeloproliferative disorder. In about one third of the cases, the cause of Budd-Chiari syndrome is unknown.