Portal Hypertension: Symptoms, Signs, and Diagnosis
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Most clinical consequences of portal hypertension can be attributed to the development of portosystemic collateral vessels to return splanchnic blood to the heart. These vessels may form at several sites in the gut circulation. The most important are esophageal varices, formed by gross dilation of esophageal submucosal veins. These vessels carry blood from the coronary veins of the portal system into the azygos-hemiazygos veins. Other collateral sites include the umbilical vein into the omphalomesenteric vein. This occasionally results in striking dilation and prominence of the collateral vessels on the anterior abdominal wall with centrifugal radiation outward from the umbilicus, a pattern known as caput medusae. Rarely, a venous hum may be heard over such dilated veins (Cruveilhier’s sign). Other sites of collateral formation include the retroperitoneal cavity, splenorenal veins between the left kidney and the spleen, and vessels between the rectal and inferior mesenteric circulations. The latter results in large dilated, inferior rectal veins, often mistaken as gross hemorrhoids. Rarely, collaterals can develop in atypical sites (eg, duodenum, colon, or vagina). Portopulmonary collaterals have also been described.
These collateral vessels result in shunting of portal blood into the systemic circulation, causing high systemic concentrations of several hormones and substances normally extracted by the liver. The pathogenesis of hepatic or portosystemic encephalopathy is often ascribed to a failure of the liver to degrade a putative metabolic toxin produced in the gut.
Since cirrhosis is the dominant cause of portal hypertension in the West, presentation will be that of cirrhosis with decompensation, or directly attributable to portal hypertension. This includes GI bleeding, ascites and edema, encephalopathy, or nonspecific constitutional symptoms (eg, fatigue, lethargy, anorexia).
Radiologic investigations may provide clues to the presence of portal hypertension. A plain x-ray of the abdomen may show a ground-glass appearance due to ascites and an enlarged spleen. US of the abdomen may show ascites, abnormal density and texture of the liver, and occasionally dilated portal veins and collaterals, if they are large. Doppler US can determine blood flow, patency, and caliber of the portal vein. Esophageal varices may be recognized as a tortuous, worm-like appearance of the mucosa on a barium swallow, but are best directly visualized during endoscopy. Radionuclide liver scan often shows a patchy uptake in the liver associated with increased bone marrow and splenic uptake. CT scans of the abdomen can identify dilation of the portal vein and often collateral vessels (eg, the azygos vein). Venography, either indirectly (venous phase of a celiac axis angiogram especially with subtraction techniques) or directly (splenic venography or transhepatic portography), visualizes the portal system to identify venous occlusion and collateral flow.
Portal pressure can be measured by several methods. A thin needle may be introduced percutaneously directly into the hepatic parenchyma. Similarly, a thin needle may be introduced percutaneously into the spleen to measure splenic pulp pressure, an accurate reflection of splenic vein pressure. The latter technique also offers the advantage of enabling injection of contrast material into the splenic venous system, providing a splenoportogram. Another approach involves fluoroscopic guidance of a thin (Chiba) needle percutaneously and then transhepatically into a portal vein branch. Alternatively, a small-bore cannula can be introduced percutaneously or at laparotomy into the umbilical vein and, thus, into the omphalomesenteric vein, since this system becomes prominent in portal hypertension. A drawback common to all of these foregoing procedures is the lack of an internal zero reference, the zero value being estimated level of the right atrium. In addition, piercing hepatic or splenic parenchyma entails a small but significant risk of bleeding (1 to 3%). Probably the best technique involves catheterization of the hepatic vein through either a jugular or femoral vein approach. Wedging of the catheter in a small hepatic vein branch results in a pressure that closely approximates the portal pressure in most causes of liver disease. When the catheter tip lies free in the hepatic vein, this free hepatic vein pressure normally should be 1 to 4 mm Hg less than the wedged hepatic pressure. The difference between the wedge and free hepatic venous pressures, also known as the hepatic venous pressure gradient, portohepatic gradient, or corrected sinusoidal pressure, represents the contribution of the hepatic sinusoids to portal pressure.
Classification:
Portal hypertension has been subclassified traditionally according to the presumed site of resistance. Presinusoidal hypertension can be either intra- or prehepatic: Prehepatic (extrahepatic) causes include portal and splenic vein thromboses. Intrahepatic presinusoidal hypertension occurs in schistosomiasis, myelofibrosis and leukemic liver infiltration, idiopathic portal fibrosis, nodular regenerative hyperplasia, and granulomatous diseases (eg, sarcoidosis and early stages of primary biliary cirrhosis). In all cases of presinusoidal hypertension, the directly measured portal venous pressure will greatly exceed the hepatic venous pressure gradient, which should be normal or near normal. The presinusoidal block prevents transmission of the elevated portal pressure to the wedged hepatic vein. The overwhelming basis for sinusoidal and postsinusoidal portal hypertension is cirrhosis, particularly that due to alcohol. Postsinusoidal hypertension can again be divided into intrahepatic and posthepatic. Posthepatic causes include chronic heart failure, constrictive pericarditis, and obstruction of the hepatic venous outflow tract by membranous webs in the inferior vena cava. Intrahepatic postsinusoidal causes of portal hypertension include occlusive disease of the small veins and venules (veno-occlusive disease) and occlusions in large hepatic veins (Budd-Chiari syndrome). All cases of sinusoidal and postsinusoidal portal hypertension are associated with hepatic venous pressure gradients, which are about equal to the directly measured portal venous pressures. The resistance to flow extends from the hepatic venous system to the portal vein.
This traditional classification is somewhat arbitrary, since the actual site of resistance in many conditions is unclear. In practical terms, almost all presinusoidal conditions are associated with relatively well-preserved liver function, whereas the sinusoidal and postsinusoidal conditions generally have cirrhosis or otherwise deranged function. Therefore, bleeding or surgery is generally better tolerated by the patient with presinusoidal hypertension.
