Portal Hypertension

Portal hypertension occurs when blood flow through the liver is obstructed.

The liver serves many purposes within the body from making carbohydrates, proteins, and fats to synthesizing bile to help digest food. Because of this, the liver requires a significant blood supply. As opposed to other organs in the body, the majority of this blood supply (75%) comes from the venous system through the portal system. Blood vessels from the stomach, small intestine, pancreas, and spleen converge and form the portal vein delivering nutrients and chemical building blocks to the liver. Once in the liver, the portal vein and hepatic artery (which accounts for 25% of the liver's blood supply) come together to form sinusoids, spaces where the blood is filtered. From there, blood makes its way to the vena cava, the largest vein in the body to return to the heart.

Portal hypertension describes elevated pressure within the portal system, including the portal vein and the tributary veins that drain into it. The pressure within the portal system is not normally measured and is not an issue except if an illness or disease occurs that makes it difficult for blood to flow through the liver tissue. This damming effect increases pressure within the portal venous system and causes potential problems with liver function. It is the onset of symptoms associated with liver disease that might cause the health care professional to look for the presence of portal hypertension.

Portal hypertension occurs when there is an obstruction of blood flow through the liver, and pressure rises within the portal vein. This obstruction can be intrahepatic (intra=within +hepatic=liver), pre-hepatic (pre=before), or post-hepatic (post=after).

Intrahepatic causes of portal hypertension

Intrahepatic causes of portal hypertension include cirrhosis and hepatic fibrosis or scarring. A wide variety of illnesses are implicated as the cause of portal hypertension. Examples include the following:

• Alcohol abuse,
• Hepatitis B and C infections,
• Fatty liver (NASH, non-alcoholic steatohepatitis),
• Wilson's disease, an abnormality of copper metabolism,
• Hemochromatosis (iron overload), excess iron buildup
• Cystic fibrosis
• Primary sclerosing cholangitis, a hardening of the bile ducts
• Biliary atresia poorly formed bile ducts
• Parasite infections such as schistosomiasis

Pre-hepatic causes of portal hypertension

• Portal vein thrombosis or blood clots within the portal vein
• Congenital portal vein atresia or failure of the portal vein to develop

Post-hepatic causes of portal hypertension

Post-hepatic causes are due to obstruction of blood flow from the liver to the heart and can include:

• Hepatic vein thrombosis
• Inferior vena cava thrombosis
• Restrictive pericarditis, where the lining of the heart stiffens and does not allow the heart to relax and expand when the blood returns to it. Causes may include tuberculosis, fungal infections, tumors, connective tissue disorders (for example, scleroderma), and complications from radiation therapy.

When blood cannot easily flow through the liver architecture (from the portal vein to sinusoids to the hepatic vein to the vena cava), it tries to bypass the portal system, using the systemic venous system to return to the heart. Symptoms of portal hypertension are due to the complications of decreased blood flow through the liver, and from increased pressure within the veins where blood is shunted.

• Varices describe enlarged veins. Blood, meant for the portal system, is diverted to and gathers in other veins as it makes its way to the heart. These varices can occur in the esophagus, stomach, around the umbilicus, and in the anus and rectum.
• Esophageal and gastric varices are at risk for life-threatening bleeding and can have signs and symptoms with vomiting blood and blood in the stool. Melena describes a black, tarry stool that is the result of upper gastrointestinal bleeding.
• Ascites describe abnormal fluid collection within the peritoneum (the sac that contains the intestines within the abdominal cavity) and are due to a combination of factors, including increased pressure in the portal system and decrease protein in the body. The liver produces the body's protein; portal hypertension and the underlying liver disease decrease its ability to function.
• Hepatic encephalopathy is another complication of liver disease, causing confusion and lethargy due to the buildup of waste products and the inability of the liver to adequately filter them.
• Splenomegaly or enlargement of the spleen. Because of portal hypertension, blood backs up, and this also can trap the components of blood (red blood cells, white blood cells, and platelets) within the spleen causing anemia and thrombocytopenia (low platelet count in the bloodstream).
• Decreased white blood cell counts increase the risk of general infection. Spontaneous bacterial peritonitis is an infection within the peritoneal sac within the abdomen and is seen as a consequence of long-standing portal hypertension.

Portal hypertension usually is diagnosed well after the process has begun in the body, and only after a complication occurs. When a patient develops ascites or has gastrointestinal bleeding, the healthcare professional will look for potential causes, including portal hypertension.

Once the diagnosis is a possibility, it can be confirmed by the following:

• Blood tests
• X-rays
• CT or MRI
• Endoscopy

Pressures within the portal vein are not routinely measured except in specific situations (see TIPS procedure).

Treatment for portal hypertension is often directed at preventing complications. This includes treating the underlying cause and avoidance of alcohol. Because of the risk of further liver damage, over-the-counter medications that contain acetaminophen (Tylenol, Panadol, for example) should also be avoided.

• Dietary restrictions include limiting salt to prevent further ascites fluid accumulation. Protein may also be restricted since increased protein load can overwhelm the liver's ability to synthesize it and may lead to hepatic encephalopathy.
• Medications such as beta-blockers and nitroglycerin may be appropriate to decrease pressure within the portal system. Lactulose may be prescribed as a treatment for hepatic encephalopathy.
• Endoscopy may be required to band or tie off varices in the esophagus to prevent catastrophic and life-threatening bleeding.

A TIPS procedure (transjugular intrahepatic portosystemic shunt) may be an option to decrease the pressure within the portal system. An interventional radiologist attempts to place a tube that connects the portal vein with the hepatic vein. This may decrease the pressure within the liver and may also reduce pressure within the veins of the stomach and esophagus, hopefully decreasing the risk of bleeding.

If portal hypertension and liver dysfunction become bad enough, liver transplantation may be necessary.

The complications of portal hypertension are the complications of liver failure. These include gastrointestinal bleeding from varices, ascites, and hepatic encephalopathy. Splenomegaly can also cause anemia, low white blood cell counts, and low platelet counts.

Some liver diseases due to inborn errors of metabolism like copper and iron cannot be prevented. The same can be said with congenital anatomy problems. However, when liver disease is due to alcohol and drug abuse, prevention is a real possibility. Chronic alcoholism can lead to cirrhosis and portal hypertension. IV drug abuse can be the cause of hepatitis B and C, resulting in cirrhosis.

Portal hypertension is a complication of underlying liver disease. It is a disease that can be controlled but requires patients to be compliant with dietary restrictions and abstain from alcohol and drugs. Survival rates can be quite high as long as some liver function is maintained. The worse the liver function, the worse the prognosis.