Primary sclerosing cholangitis (PSC) is an uncommon disease of unknown etiology seen primarily in young or middle-aged males (2/3 of patients are < 45 years old). The disease is characterized by inflammation and fibrosis of the intra and extrahepatic bile ducts with diffuse stricture formation. In about 20% of cases, the extrahepatic ducts are normal and the changes are confined to the intrahepatic and proximal extrahepatic ducts only. There is a high association (70% of cases) with inflammatory bowel disease, particularly ulcerative colitis. PSC may appear before or after the onset of IBD or even years after colectomy. There is also an increased incidence of cholangiocarcinoma in patients with PSC.
The onset of PSC is insidious, with fatigue, pruritus and elevated LFT's initially. Intermittent bouts of cholangitis and jaundice occur as the strictures progress. The obliterative biliary fibrosis leads ultimately to cirrhosis and liver failure. There is no effective medical treatment; the strictures and stones may be managed with surgery or with percutaneous or endoscopic balloon dilatation and stenting.
Imaging plays a central role in the diagnosis and management of PSC. Direct cholangiography with PTC or ERCP is necessary to confirm the diagnosis, assess severity of disease and look for the complications of stones or tumor. Because the intrahepatic ducts are not uniformly dilated, ERCP may more easily visualize the ducts. MRCP has been shown to evaluate the intrahepatic ducts as well or better than ERCP and is noninvasive. In most cases, the cholangiographic features are characteristic. The bile ducts are markedly irregular with multiple short segment strictures and intermittent areas of dilatation resulting in a "beaded" appearance. Small diverticular-like outpouchings are seen in approximately 25% of patients. Obliteration of the peripheral intrahepatic ducts results in a "pruned" pattern.
The main differential diagnosis is the diffuse form of cholangiocarcinoma, which can be indistinguishable on cholangiography. Malignant degeneration is usually associated with clinical deterioration and is suspected on cholangiography when one or more polypoid masses of 1 cm or more are seen. Other suggestive changes of malignancy include marked dilatation of ducts or ductal segments and marked progression of stricture formation or ductal dilatation on serial studies. Primary biliary cirrhosis (PBC) may simulate the cholangiograhic picture of PSC but involves only the intrahepatic ducts. Secondary cholangitis from post-op stricture or CBD stone should not be a diagnostic dilemma. Changes resembling PSC may be seen after hepatic artery chemotherapy or with the polymicrobial cholangitis seen with AIDS.
US and CT may be more helpful in the diagnosis of more advanced disease. US has limitations in detecting PSC early since the periductal fibrosis prevents the ducts from dilating. Areas of focal dilatation and the relatively echogenic fibrosis of the duct wall may be seen on sonography. CT shows areas of focal, discontinuous, mild dilatation of the intrahepatic ducts without associated mass. This pattern is not seen in other causes of biliary obstruction such as tumor or stone and is highly suggestive of sclerosing cholangitis. Duct wall thickening may be seen and may show enhancement with contrast administration.
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