COMMENTARY

Portal Vein Thrombosis: Early Recognition Key to Improved Outcomes

Rowen K. Zetterman, MD

Disclosures

August 18, 2016

In This Article

Assessing the Risk for Portal Vein Thrombosis

Portal vein blood flow accounts for 75% of total hepatic blood flow, with the hepatic artery accounting for the remainder. As a result, portal vein occlusion may have significant consequences for liver function.

Portal vein thrombosis (PVT) is defined by partial or complete thrombosis of the main, right, or left portal vein, by extension of thrombus into the intrahepatic portal vein branches or the splenic and/or superior mesenteric vein. PVT may be acute, after recent formation of thrombus, or chronic, with cavernous transformation of the portal vein identified as multiple venous channels along it permit portal circulation to liver flow. However, cavernous transformation may not allow all mesenteric and splenic venous flow to reach the liver, resulting in esophagogastric varices and other signs of portal hypertension.

PVT can be classified as (1) thrombosis of the portal vein only, distal to the splenic and superior mesenteric vein confluence; (2) thrombosis of the portal vein that extends into the superior mesenteric vein; (3) thrombosis of the portal vein, superior mesenteric vein, and splenic vein associated with large collaterals; or (4) thrombosis of the portal vein, superior mesenteric vein, and splenic vein associated with fine collaterals.[1]

The risk for PVT is approximately 1% in the general population,[2] though the cause is not always apparent. In an autopsy series, only 14% of patients had an identifiable association.[2] Of these, 28% had cirrhosis, 23% had primary liver or gallbladder cancer, 44% had secondary hepatobiliary cancer, 3% had a myeloproliferative disorder, and 10% had evidence of an intra-abdominal infection or inflammation. Approximately 11% of patients with cirrhosis will develop PVT, of which 40% of cases will be asymptomatic.[3] Some may exhibit worsening portal hypertension, abdominal pain, or intestinal injury as presenting symptoms.

The risk for PVT in cirrhosis increases as hepatic fibrosis worsens[4] and may be present in 25%-40% of patients with end-stage liver disease.[5] In a retrospective analysis of patients with viral-induced cirrhosis, 40% eventually developed PVT over 8-10 years of follow-up.[6] Nonocclusive thrombus may be an incidental finding in patients with cirrhosis who are being screened for hepatocellular carcinoma. Patients with cirrhosis from nonalcoholic fatty liver disease may have an even greater risk for PVT,[7] raising the question of whether nonalcoholic steatohepatitis might be a prothrombotic state.

Thrombosis in patients with cirrhosis may be due to many factors, including reduced or stagnant blood flow and reduced levels of circulating anticoagulants (ie, protein C, protein S, and antithrombin III) as cirrhosis worsens. Sequential ultrasounds may identify changing flow velocity in the portal vein, with reduction of overall flow a consequence of worsening portal hypertension and the development of large collateral vessels.[8]

Hepatocellular carcinoma is also a risk for PVT and may be present in as many as 35% of cases of PVT.[2,3,9] Metastatic carcinoma is also associated with vascular invasion, adding to the risk.

Clotting disorders increase the risk for PVT in patients without cirrhosis or carcinoma of the liver. Myeloproliferative disorders, including paroxysmal nocturnal hemoglobinuria,[10] are frequent associations.[11] Factor V Leiden, prothrombin G20210A mutation, anticardiolipin antibodies, and circulating lupus anticoagulant can also result in thrombosis.[6] In addition, deficiencies of protein C, protein S, and antithrombin III,[12] and occurrence with pregnancy and oral contraceptive use,[10] have been reported.

Other conditions identified with the development of PVT include endothelial injury of the portal vein after splenectomy or creation of surgical shunts, as well as local inflammatory diseases, such as pancreatitis or cholecystitis. Pylephlebitis—the development of an infected portal vein thrombus associated with intra-abdominal infections, such as diverticulitis and appendicitis—may present with fever and bacteremia, and carries an increased mortality of 11%.[13]

Pathophysiology

PVT is associated with conditions that reduce portal vein flow, create a hypercoagulable state, or produce endothelial injury of the portal vein.[5,14] Local factors that restrict portal vein flow account for approximately 21% of cases of thrombosis.[14] Progressive cirrhosis with worsening intrahepatic fibrosis leading to increased intrahepatic resistance to portal vein flow, coupled with portal venous collaterals flowing away from portal circulation, in turn results in stagnant flow in the portal vein.[15] Occlusion of hepatic veins (Budd-Chiari syndrome) can also result in stagnant portal vein flow, as does extravascular compression of the portal vein from enlarged lymph nodes, carcinoma, or extension of intravascular tumor.

A hypercoagulable state from circulating procoagulants or thrombophilia may be a primary cause of PVT or a contributing factor in conjunction with other associations.[16] Portal vein endothelial injury also increases the risk for thrombosis[5,14] associated with intra-abdominal inflammation or infection, acute cholecystitis, hepatic abscess, umbilical vein catheter placement, or the backflow of sclerosants into the portal vein used for elimination of esophagogastric varices.[3] Cavernous transformation of the portal vein may develop from chronic portal vein occlusion due to congenital venous abnormalities, omphalitis, umbilical vein catheter placement, abdominal sepsis, neonatal abdominal surgery, and prothrombotic disorders. It is often observed in children but is also seen in adults.

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