Etiology

Portal hypertension can result from obstruction to portal blood flow anywhere along the course of the portal venous system. The various disorders associated with portal hypertension are outlined in Table 359-1. Portal hypertension can occur as a result of prehepatic, intrahepatic, or posthepatic obstruction to the flow of portal blood.

Extrahepatic portal vein obstruction is an important cause of portal hypertension in childhood. The obstruction can occur at any level of the portal vein. Umbilical infection (omphalitis) with or without a history of catheterization of the umbilical vein may be causal in neonates. The infection can potentially spread from the umbilical vein to the left branch of the portal vein and eventually to the main portal venous channel. Intra-abdominal infections, including acute appendicitis and primary peritonitis, can be causal in older children. Portal vein thrombosis has also been associated with neonatal dehydration and systemic infection. In older children, inflammatory bowel disease can be associated with a hypercoagulable state and portal venous obstruction. Thrombosis of the portal vein has also occurred in association with biliary tract infections and primary sclerosing cholangitis. Portal vein thrombosis is associated with hypercoagulable states such as deficiencies of factor V Leiden, protein C, or protein S. The portal vein can be replaced by a fibrous remnant or contain an organized thrombus. Rare developmental anomalies producing extrahepatic portal hypertension include agenesis, atresia, or stenosis of the portal vein. Obstruction by a web or diaphragm can also occur. At least half of reported cases have no defined cause.

Uncommonly, presinusoidal hypertension can be caused by increased flow through the portal system as a result of a congenital or acquired arteriovenous fistula.

The intrahepatic causes of portal hypertension are numerous. Obstruction to flow can occur on the basis of a presinusoidal process, including acute and chronic hepatitis, congenital hepatic fibrosis, and schistosomiasis. Portal infiltration with malignant cells or granulomas can also contribute. An idiopathic form of portal hypertension characterized by splenomegaly, hypersplenism, and portal hypertension without occlusion of portal or splenic veins and with no obvious disease in the liver has been described. In some patients, noncirrhotic portal fibrosis has been observed.

Cirrhosis is the predominant cause of portal hypertension and is related to obstruction of blood flow through the portal vein. The numerous causes of cirrhosis include recognized disorders such as biliary atresia, autoimmune hepatitis, chronic viral hepatitis, and metabolic liver disease such as α₁-antitrypsin deficiency, Wilson disease, glycogen storage disease type IV, hereditary fructose intolerance, and cystic fibrosis.

Postsinusoidal causes of portal hypertension are also observed in childhood. The Budd-Chiari syndrome occurs with obstruction to hepatic veins anywhere between the efferent hepatic veins and the entry of the inferior vena cava into the right atrium. In most cases, no specific cause can be found, but thrombosis can occur from inherited and acquired hypercoagulable states (antithrombin III deficiency, protein C or S deficiency, factor V Leiden or prothrombin mutations, paroxysmal nocturnal hemoglobinemia, pregnancy, oral contraceptives) and can complicate hepatic or metastatic neoplasms, collagen vascular disease, infection, and trauma. Additional causes of the Budd-Chiari syndrome include Behçet syndrome, inflammatory bowel disease, aspergillosis, dacarbazine therapy, and inferior vena cava webs. Sinusoidal obstruction syndrome (veno-occlusive disease) is the most common cause of hepatic vein obstruction in children. In this disorder, occlusion of the centrilobular venules or sublobular hepatic veins occurs. The disorder occurs after total body irradiation with or without cytotoxic drug therapy that is commonly used before bone marrow transplantation. The disease has also occurred after ingestion of herbal remedies containing the pyrrolizidine alkaloids, which are sometimes taken as medicinal teas.

Pathophysiology

The primary hemodynamic abnormality in portal hypertension is increased resistance to portal blood flow. This is the case whether the resistance to portal flow has an intrahepatic cause such as cirrhosis or is due to portal vein obstruction. Portosystemic shunting should decompress the portal system and thus significantly lower portal pressures. Despite the development of significant collaterals deviating portal blood into systemic veins, portal hypertension is maintained by an overall increase in portal venous flow and thus maintenance of portal hypertension. A hyperdynamic circulation is achieved by tachycardia, an increase in cardiac output, and decreased systemic vascular resistance. Splanchnic dilatation also occurs. Overall, the increase in portal flow likely contributes to an increase in variceal transmural pressure. The increase in portal blood flow is related to the contribution of hepatic and collateral flow; the actual portal blood flow reaching the liver is reduced. It is also likely that hepatocellular dysfunction and portosystemic shunting lead to the generation of various humoral factors that cause vasodilatation and an increase in plasma volume.

Stay updated, free articles. Join our Telegram channel

Join