Biliary malignancies: multi-slice CT or MRI?
© International Cancer Imaging Society 2003
Accepted: 5 November 2002
Published: 5 May 2015
Cholangiocarcinoma is the most common malignant bile duct and the second most common primary malignant tumor in the liver. It can be classified as intrahepatic (peripheral) or extrahepatic. Extrahepatic cholangiocarcinoma originate most often from the main hepatic duct and confluence (referred to as Klatskin tumor). The patients usually present with jaundice because of biliary obstruction. Prognosis of hilar cholangiocarcinoma is poor, because most tumors are not resectable at the time of diagnosis. Surgical exploration should only be undertaken when there is potential for curative resection shown by imaging.
ERCP (endoscopic retrograde cholangio-pancreatography) demonstration of Klatskin tumors is often incomplete due to incomplete ductal filling. MR imaging and helical CT are the methods of choice in the diagnosis and staging of hilar cholangiocarcinoma. MR cholangiography, in conjunction with MR imaging and MRA, provides information on tumor size, bile duct involvement, and vascular compromise, and thus resectability of the tumor. Multi-phasic contrast-enhanced thin-section helical CT may show Klatskin tumors with a sensitivity of up to 100%. Tumors are better seen on arterial-dominant phase than on portal venous phase scans (sensitivity, 100% vs. 86%). However, single-slice CT is not accurate for assessing resectability (accuracy, 60%), because proximal tumor extent is largely underestimated. Preliminary experience with multi-slice CT indicates that the extent of bile duct involvement may be better displayed due to multi-planar imaging capabilities. Curved planar reconstruction of multi-slice CT data sets along the portal vein and the bile ducts reveals tumor involvement.
Intrahepatic cholangiocarcinoma have a non-specific imaging appearance. Because of abundant fibrous stroma, they exhibit little contrast enhancement during CT or MR imaging scanning in the early phase with delayed accumulation of contrast material. Although not pathognomonic, the presence of bile duct dilatation within the tumor and retraction of the liver capsule adjacent to the tumor are suggestive of the diagnosis.
In conclusion, the role of contrast-enhanced MR imaging with MR cholangiography and multi-slice CT in the detection and preoperative staging of cholangiocarcinoma is emphasised.
Classification of bile duct malignancies
Biliary duct tumors are uncommon, with cholangiocarcinoma being by far the most common. Cholangiocarcinoma arise from any portion of the intrahepatic or extrahepatic bile duct epithelium. Accordingly, they are classified as intrahepatic (peripheral) cholangiocarcinoma or extrahepatic cholangiocarcinoma. They usually become clinically apparent because of progressive biliary obstruction. Intrahepatic cholangiocarcinoma are the second most common primary malignancy of the liver. Extrahepatic cholangiocarcinomata originate most often from the main hepatic duct and confluence (often referred to as Klatskin tumor). Rarely, extrahepatic cholangiocarcinoma originate from the distal common bile duct, and which are then virtually indistinguishable from pancreatic tumors by imaging.
Hilar cholangiocarcinoma (Klatskin tumors) are categorised according to the Bismuth classification: a type I tumor involves the main hepatic duct below the bifurcation; a type II tumor affects the main hepatic duct bifurcation; a type III tumor involves segmental ducts beyond the primary hepatic duct bifurcation in one liver lobe (type IIIa: right lobe, type IIIb: left lobe); type IV tumors involve segmental ducts in both liver lobes. Prognosis of hilar cholangiocarcinoma is poor, with few of the tumors being resectable at the time of diagnosis. Thus, surgical exploration should only be undertaken when there is potential for curative resection shown by imaging.
Intrahepatic (peripheral) cholangiocarcinoma
Peripheral cholangiocarcinoma is a primary adenocarcinoma of the liver arising from the epithelium of the small bile ducts. Histopathologically, the diagnosis is difficult to differentiate from metastatic adenocarcinoma. Macroscopically, intrahepatic cholangiocarcinomata are classified as mass-forming type, periductal-infiltrating type, and intraductal-growth type. Intrahepatic cholangiocarcinoma have a non-specific imaging appearance. Because of the presence of abundant fibrous stroma, these tumors most often show little contrast enhancement at CT or MR imaging scanning in the early phase, but delayed accumulation of contrast material. Although non-specific signs, the presence of bile duct dilatation within the tumor and retraction of the liver capsule adjacent to the tumor are suggestive of the diagnosis.
In conclusion, detection and accurate staging of Klatskin tumors is improved by multi-phasic helical CT scanning and MR imaging. Curved planar reconstructions from multi-slice CT data sets with thin collimation may further improve our ability to diagnose vascular involvement. MR cholangiography, in conjunction with contrast-enhanced MR imaging, provides 3D images of the biliary tracts that facilitate planning of surgery or guide palliative drainage.
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