Fig. 16.30 Hepaticcirculatorydisorders.Formsandclinicalmanifestationsofcompromisedhepaticbloodflow.
Fig. 16.31 Liverinfarct.Athrombusislodgedinaperipheralbranchofthehepaticartery(arrow)andcompressestheadjacentportalvein;thedistalhepatictissueispale,withahemorrhagicmargin.
Blockage of the extrahepatic portal vein may cause only vague symptoms or may be a catastrophic and potentially lethal event; most cases fall somewhere in between. Occlusive disease of the portal vein or its major radicles typically produces abdominal pain and other manifestations of portal hypertension, principally esophageal varices that are prone to rupture. Ascites is not common (because the block is presinusoidal), but, when present, is often massive and intractable.
Extrahepatic portal vein obstruction may be idiopathic (approximately one-third of cases) or may arise from a number of conditions. Some of the most common settings for development of extrahepatic portal vein obstruction include the following:
Cirrhosis, which is associated with portal vein thrombosis in 25% of patients, some of whom have other risk factors as well
Hypercoagulable states, including myeloproliferative neoplasms such as polycythemia vera (Chapter 12), inherited thrombophilias such as factor V Leiden (Chapter 4), and miscellaneous hypercoagulable conditions such as paroxysmal nocturnal hemoglobinuria and antiphospholipid antibody syndrome
Inflammatory processes involving the splenic vein or portal vein, such as pancreatitis and intraabdominal sepsis
Trauma, surgical or otherwise
Obstruction of intrahepatic portal vein radicles may be caused by acute thrombosis. The thrombosis does not cause ischemic infarction but instead results in a sharply demarcated area of red-blue discoloration called infarct of Zahn. There is no necrosis, only severe hepatocellular atrophy and marked congestion of distended sinusoids. The most common cause of small portal vein branch obstruction is schistosomiasis; the eggs of the parasites lodge in and obstruct the smallest portal vein branches. The other disorders producing this pattern of injury are now collectively referred to as obliterative portal venopathy, which often presents as noncirrhotic portal hypertension. Causes of obliterative portal venopathy are not well understood. It occurs in both untreated and treated HIV disease, and may in some instances be a complication of anti-retroviral therapy.
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The most common intrahepatic cause of blood flow obstruction is cirrhosis, as discussed earlier. In addition, physical occlusion of the sinusoids occurs in sickle cell disease, disseminated intravascular coagulation, eclampsia, and intrasinusoidal metastasis of solid tumors. If severe and unabated, all of these disorders may produce sufficient obstruction of blood flow to cause massive necrosis of hepatocytes and fulminant hepatic failure.
Occlusive events can occur in any caliber of hepatic vein branches. If it occurs in the smallest intrahepatic branches, it produces sinusoidal obstruction syndrome (formally known as veno-occlusive disease). A rare, but well-known cause of this syndrome is consumption of pyrrolizidine alkaloid– containing Jamaican bush tea, but it now occurs primarily following allogeneic hematopoietic stem cell transplantation, usually within the first 3 weeks, or in cancer patients receiving chemotherapy, in whom it can have as high as 30% mortality.