Introduction
Background
Portal hypertension may be defined as a portal pressure gradient of 12 mm Hg or greater and is often associated with varices and ascites. Many conditions are associated with portal hypertension, of which cirrhosis is the most common cause (see Causes).
The portal vein drains blood from the small and large intestines, stomach, spleen, pancreas, and gallbladder. The superior mesenteric vein and the splenic vein unite behind the neck of the pancreas to form the portal vein. The portal trunk divides into 2 lobar veins. The right branch drains the cystic vein, and the left branch receives the umbilical and paraumbilical veins that enlarge to form umbilical varices in portal hypertension. The coronary vein, which runs along the lesser curvature of the stomach, receives distal esophageal veins, which also enlarge in portal hypertension.
Pathophysiology
Two important factors exist in the pathophysiology of portal hypertension, vascular resistance and blood flow. Ohm law is V = IR, where V is voltage, I is current, and R is resistance. This can be applied to vascular flow, ie, P = FR, where P is the pressure gradient through the portal venous system, F is the volume of blood flowing through the system, and R is the resistance to flow. Changes in either F or R affect the pressure. In most types of portal hypertension, both the blood flow and the resistance to blood flow are altered.
Increase in vascular resistance
The initial factor in the pathophysiology of portal hypertension is the increase in vascular resistance to the portal blood flow. Poiseuille law, which can be applied to portal vascular resistance, states that R = 8 h L/p r4, where h is the viscosity of blood, L is the length of the blood vessel, and r is the radius of the blood vessel. The viscosity of the blood is related to the hematocrit (HCT). The lengths of the blood vessels in the portal vasculature are relatively constant.
Thus, changes in portal vascular resistance are determined primarily by blood vessel radius. Because portal vascular resistance is indirectly proportional to the fourth power of the vessel radius, small decreases in the vessel radius cause large increases in portal vascular resistance and, therefore, in portal blood pressure (P = F8 h L/p r4, where P is portal pressure and F is portal blood flow).
Liver disease is responsible for a decrease in portal vascular radius, producing a dramatic increase in portal vascular resistance. In cirrhosis, the increase occurs at the hepatic microcirculation (sinusoidal portal hypertension). Increased hepatic vascular resistance in cirrhosis is not only a mechanical consequence of the hepatic architectural disorder, but a dynamic component also exists due to the active contraction of myofibroblasts, activated stellate cells, and vascular smooth-muscle cells of the intrahepatic veins.
Endogenous factors and pharmacological agents that modify the dynamic component include those that increase hepatic vascular resistance and those that decrease hepatic vascular resistance. Factors that increase hepatic vascular resistance include endothelin, alpha-adrenergic stimulus, and angiotensin II. Factors that decrease hepatic vascular resistance include nitric oxide, prostacyclin, and vasodilating drugs (eg, organic nitrates, adrenolytics, calcium channel blockers).
Increase in portal blood flow
The second factor that contributes to the pathogenesis of portal hypertension is the increase in blood flow in the portal veins, which is established through splanchnic arteriolar vasodilatation caused by an excessive release of endogenous vasodilators (eg, endothelial, neural, humoral). The increase in portal blood flow aggravates the increase in portal pressure and contributes to why portal hypertension exists despite the formation of an extensive network of portosystemic collaterals that may divert as much as 80% of portal blood flow.
Manifestations of splanchnic vasodilatation include increased cardiac output, arterial hypotension, and hypervolemia. This explains the rationale for treating portal hypertension with a low-sodium diet and diuretics to attenuate the hyperkinetic state.
Frequency
United States
Incidence is not known.
International
Incidence is not known.
Mortality/Morbidity
Variceal hemorrhage is the most common complication associated with portal hypertension. Almost 90% of patients with cirrhosis develop varices, and approximately 30% of varices bleed. The first episode of variceal hemorrhage is estimated to carry a mortality rate of 30-50%.
Clinical
History
The medical history from a patient with portal hypertension should be directed towards determining the cause of portal hypertension and, secondarily, the presence of the complications of portal hypertension.
- Determining the cause of portal hypertension involves the following:
- History of jaundice
- History of blood transfusions, intravenous drug use (hepatitis B and C)
- Pruritus
- Family history of hereditary liver disease (hemochromatosis, Wilson disease)
- History of alcohol abuse
- Determining the presence of the complications of portal hypertension involves the following:
- Hematemesis or melena (gastroesophageal variceal bleeding or bleeding from portal gastropathy)
- Mental status changes such as lethargy, increased irritability, and altered sleep patterns (presence of portosystemic encephalopathy)
- Increasing abdominal girth (ascites formation)
- Abdominal pain and fever (spontaneous bacterial peritonitis [SBP], which also presents without symptoms)
- Hematochezia (bleeding from portal colopathy)
Physical
- Signs of portosystemic collateral formation include the following:
- Dilated veins in the anterior abdominal wall (umbilical epigastric vein shunts)
- Venous pattern on the flanks (portal-parietal peritoneal shunting)
- Caput medusa (tortuous collaterals around the umbilicus)
- Rectal hemorrhoids
- Ascites - Shifting dullness and fluid wave (if significant amount of ascitic fluid is present)
- Paraumbilical hernia
- Signs of liver disease include the following:
- Ascites
- Jaundice
- Spider angiomas
- Palmar erythema
- Asterixis
- Testicular atrophy
- Gynecomastia
- Dupuytren contracture
- Muscle wasting
- Splenomegaly
- Signs of hyperdynamic circulatory state include the following:
- Bounding pulses
- Warm, well-perfused extremities
- Arterial hypotension
Causes
Causes of increased resistance to flow are described as follows:- Prehepatic
- Portal vein thrombosis
- Splenic vein thrombosis
- Congenital atresia or stenosis of portal vein
- Extrinsic compression (tumors)
- Splanchnic arteriovenous fistula
- Intrahepatic, predominantly presinusoidal
- Schistosomiasis (early stage)
- Primary biliary cirrhosis (early stage)
- Idiopathic portal hypertension (early stage)
- Nodular regenerative hyperplasia: Pathogenesis probably is obliterative venopathy. The presence of nodules that press on the portal system also has been postulated to play a role, although nodularity is present in most cases without clinical evidence of portal hypertension.
- Myeloproliferative diseases: These act by direct infiltration by malignant cells.
- Polycystic disease
- Hepatic metastasis
- Granulomatous diseases (sarcoidosis, tuberculosis): Clinical liver dysfunction is rare in sarcoidosis. Portal hypertension is an unusual, although well-recognized manifestation of hepatic sarcoidosis. Sarcoid granulomas frequently localize in the portal areas, resulting in injury to the portal veins.
- Intrahepatic, predominantly sinusoidal and/or postsinusoidal
- Hepatic cirrhosis
- Acute alcoholic hepatitis
- Schistosomiasis (advanced stage)
- Primary biliary cirrhosis (advanced stage)
- Idiopathic portal hypertension (advanced stage)
- Acute and fulminant hepatitis
- Congenital hepatic fibrosis
- Vitamin A toxicity: Noncirrhotic portal fibrosis is observed with various toxic injuries, and one of these includes vitamin A toxicity. This probably is due to vascular injury. Excessive doses of vitamin A taken for months or years can lead to chronic hepatic disease. Intake of doses ranging from as small as 3-fold the recommended daily dose continued for years to doses as high as 20-fold the approved dose in a few months can lead to hepatic disease. The pericellular fibrosis characteristic of vitamin A toxicity may lead to portal hypertension.
- Peliosis hepatitis
- Venoocclusive disease
- Budd-Chiari syndrome
- Posthepatic
- Inferior vena cava (IVC) obstruction
- Right heart failure
- Constrictive pericarditis
- Tricuspid regurgitation
- Budd-Chiari syndrome
- Arterial-portal venous fistula
- Increased portal blood flow
- Increased splenic flow
More on Portal Hypertension |
 Overview: Portal Hypertension |
| Differential Diagnoses & Workup: Portal Hypertension |
| Treatment & Medication: Portal Hypertension |
| Follow-up: Portal Hypertension |
| References |
| Next Page » |
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Further Reading
Keywords
cirrhosis, variceal hemorrhage, ascites, portal vein
