Extrahepatic Causes

Although possibly declining in frequency, extrahepatic portal venous obstruction, caused by a congenital thrombotic or atretic process, is an important cause of noncirrhotic portal hypertension, especially in developing countries but certainly not confined there (Sarin & Agarwal, 2002). Septic or traumatic umbilical vein injury from omphalitis and/or catherization accounts for some cases, but most cases are idiopathic or represent a congenital malformation of the portal venous system. Portal vein stenosis or thrombosis may also occur in the context of portal vein anastomoses in liver transplantation. In the congenital form, the portal vein is transformed into a cavernoma, resulting in portal hypertension and esophagogastic varices. Importantly, from a treatment standpoint, splenic vein or more extensive portal system involvement results in somewhat different hemodynamics, with an extensive collateral circulation involving a preponderance of gastric varices (Shah et al, 2003) and sometimes ectopic varices involving paracholecystic, paracholedochal, and pancreatoduodenal veins. Esophageal bleeding, or sometimes gastric variceal bleeding, is thus the most important consequence, although the presence of naturally occurring shunts may reduce the risk over time, usually by the second decade of life. Besides variceal bleeding, which is the commonest presentation, hypersplenism is common, and anemia, easy bruising from thrombocytopenia, and abdominal pain may be presenting features. Some patients may develop symptomatic portal biliary obstruction. Growth retardation from malabsorption as a result of failure of the enteropancreatic and enterohepatic circulation is not uncommon. Overt encephalopathy as a result of shunting appears uncommon, but subclinical signs may occur, including disturbed neurocognitive function, particularly attention and short-term memory problems (Mack et al, 2006). Although the liver may appear normal, reversible decompensation may be seen after an acute variceal hemorrhage, and functional compromise may develop over the long term.

Intrahepatic Causes

Portal hypertension may result from a range of presinusoidal, sinusoidal, and postsinusoidal causes of increased portal bed resistance within the liver. Presinusoidal conditions, such as congenital hepatic fibrosis, do not result in impaired liver function. Congenital hepatic fibrosis is a developmental disorder that belongs to the family of hepatic ductal plate malformations and is characterized histologically by a variable degree of periportal fibrosis and irregularly shaped proliferating bile ducts (Summerfield et al, 1986). Liver biopsy is highly specific for the diagnosis. In most patients, the first manifestations of the disease are signs or symptoms related to portal hypertension, especially splenomegaly and varices, often with spontaneous gastrointestinal (GI) bleeding that occurs from early childhood and sometimes even into adulthood.

Increased sinusoidal resistance and portal hypertension occur almost invariably in cirrhosis in children. In children, common causes include forms of infant cholestasis, such as biliary atresia, as well as a range of metabolic disorders, infections, toxins, and vascular and nutritional diseases. Cirrhosis is a chronic, diffuse disease characterized by irreversible widespread hepatic fibrosis with regenerative nodule formation (see Chapter 6, Chapter 70A, Chapter 70B ). The prominent fibrous tissue contains vascular anastomoses, which cause hemodynamic alterations and portosystemic shunting. This diffuse pathology superimposed on the primary liver disease often obscures the nature of the original insult. The major pathophysiologic consequences are the result of impaired hepatic function and portal hypertension. Progression to cirrhosis and its complications in pediatric liver diseases is highly variable and represents an important consideration in management, particularly when considering surgical options that may compromise later outcomes. In some conditions, such as neonatal extrahepatic biliary atresia, the development of cirrhosis can be extraordinarily rapid, occurring by 12 to 16 weeks of age with liver failure as early as 24 weeks of age. Early diagnosis and surgical treatment by hepatoportoenterostomy improves outcome, but in most cases, liver transplant becomes the only available treatment option. Other disorders, such as cystic fibrosis–associated focal biliary cirrhosis, can be compatible with normal liver function for many years, presenting with signs of portal hypertension in the second decade of life.

Postsinusoidal intrahepatic conditions, such as venoocclusive disease, are rare in children and usually occur only in the context of chemotherapy for childhood cancers (Gharib et al, 2006) or occasionally related to toxin ingestion, such as from eating poisonous mushrooms. However, posthepatic portal hypertension is a significant condition in children (see Box 71.1). Obstruction to hepatic venous outflow, such as from hepatic vein anastomotic stenosis, can occur after liver transplantation, with Budd-Chiari syndrome, or as a result of cardiac lesions that cause an increase in right atrial pressure and/or chronic systemic venous hypertension. Acute Budd-Chiari syndrome is rare in children; although it may occur with some thrombophilic disorders, it is usually idiopathic and is not associated with the causes seen in adults, such as myeloproliferative disorders. A cavopulmonary or atriopulmonary shunt, known as a Fontan procedure, allows life-saving systemic-pulmonary blood flow in single-ventricle syndromes in neonates but results in chronic systemic venous hypertension (pressures may be >20 mm Hg) and eventually to portal hypertension (Narkewicz et al, 2003).