Portal hypertension is a pathologic condition characterized by an excessive increase in the pressure within the portal vein or one of its branches. Typical portal vein pressure is 5 to 10 millimeters of mercury (abbreviated mmHg). When the pressure exceeds 5 mmHg above inferior vena cava pressure, it is characterized as portal hypertension. The portal vein carries nutrient rich blood from the digestive system to the liver. Normally, the veins come from the stomach, intestine, spleen, and pancreas. They merge into the portal vein, which then branches into smaller vessels and travels through the liver. If the vessels in the liver are blocked, it is hard for the blood to flow causing high pressure in the portal system. When the pressure becomes too high, the blood backs up and finds other ways to flow back to the heart, which causes large varices (swollen or knotted bodily vessels, usually veins) to develop across the esophagus and stomach to bypass the blockage. Because of this bypass, substances (such as toxins) that are normally removed from the blood by the liver can pass into the general circulation. The varices become fragile and can bleed easily, sometimes seriously and occasionally with fatal results. Portal hypertension often causes the spleen to enlarge (splenomegaly) because the pressure interferes with blood flow from the spleen into the portal blood vessels. Pressure in the portal blood vessels may cause fluid from the surface of the liver and intestine to leak into the abdominal cavity producing a condition called ascites (an accumulation of serous fluid in the peritoneal cavity, causing abdominal swelling).
Sonographically speaking, portal hypertension can be separated into presinusoidal and interhepatic. Presinusoidal venous hypertension often occurs in a patient with normal liver function when the portal vein and its branches are compressed before they enter the liver. Presinusoidal portal hypertension can be further divided into extrahepatic and intrahepatic forms. Extrahepatic presinusoidal portal hypertension can be caused by either thrombosis (formation of blood clots) of the portal veins or of the splenic veins. The causes of portal vein thrombosis in adults include trauma, sepsis (blood or tissue infection), hepatocellular carcinoma (cancer of the liver cells), pancreatic carcinoma (cancer of the pancreas), pancreatitis (inflammation of the pancreas), portacaval shunts (shunt between the portal vein and inferior vena cava), splenectomy (removal of the spleen), and hypercoagulable states (excessive blood clotting). This form of portal hypertension should be suspected in any patient that has a normal liver biopsy and any of the clinical signs of portal hypertension (ascites, splenomegaly, and varices). The intrahepatic presinusoidal portal hypertension is caused by primary biliary cirrhosis, congenital hepatic fibrosis, toxic substances, and schistosomiasis, all of which are diseases (or results of diseases), affecting the portal zones of the liver.
The other type of portal hypertension, interhepatic, is almost always caused by cirrhosis, accounting for more than 90% of all cases of portal hypertension in the Western Hemisphere. Cirrhosis results from the healing of a liver injury caused by hepatitis, alcohol abuse, or other causes of liver damage. Cirrhosis is a chronic progressive liver disease characterized by the replacement of healthy cells with scar tissue. The scar tissue blocks the flow of blood through the liver and slows its processing functions because it is dense enough that it increases the resistance to portal venous blood flow and obstructs hepatic venous outflow, causing portal hypertension. Another liver disease that produces portal hypertension in the same fashion is diffuse metastatic liver disease.
Altogether, the most common cause of portal hypertension is cirrhosis. Thrombosis is another main cause of portal hypertension but...
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