Multislice CT illuminates cholangiocarcinoma cases

Cholangiocarcinoma is an adenocarcinoma that arises from the intra- and extrahepatic bile duct epithelium. It is a relatively common liver cancer, the second most prevalent after hepatocellular carcinoma.

The exact cause of cholangiocarcinoma is unknown and most cases occur sporadically. Some biliary diseases are known to be risk factors. These include intrahepatic stone disease, choledochal cyst, Caroli disease, and primary sclerosing cholangitis.¹ Cholangiocarcinomas tend to grow slowly and to infiltrate duct walls, dissecting along tissue planes. Tumors may extend locally into the liver, porta hepatis, and regional lymph nodes of the celiac and pancreaticoduodenal chains.

Cholangiocarcinoma may arise at any portion of the bile duct epithelium, from terminal ductules (canals of Hering) to the ampulla of Vater, as well as the peribiliary glands. Intrahepatic cholangiocarcinoma is subdivided into peripheral or hilar disease (Klatskin tumor), on the basis of its site of origin.²

Perihilar tumors occur where the right and left hepatic ducts bifurcate, and are the most common type of cholangiocarcinoma. Intrahepatic tumors (located peripheral to the secondary confluence) are the least common. Extrahepatic tumors are located from the upper border of the pancreas to the ampulla. The tumor is located distal to the cystic duct takeoff, leading to augmentation of the gallbladder (Figure 1).

Three types of cholangiocarcinoma have traditionally been regarded as distinct disease entities clinically, therapeutically, and radiologically. This classification scheme is controversial, though.

The Liver Cancer Group of Japan proposed a classification scheme for primary liver cancer that divided intrahepatic cholangiocarcinoma into three types based on macroscopic appearance: exophytic or mass-forming, periductal infiltrating, and intraductal or polypoid.³ Most—but not all—intrahepatic peripheral cholangiocarcinomas are mass-forming.

Periductal infiltrating growth is typically observed in the hilar and extrahepatic areas. Intraductal intrahepatic cholangiocarcinoma is morphologically similar to papillary cholangiocarcinoma of the large bile duct in the hepatic hilum and extrahepatic area. This type of malignancy is characterized by superficial mucosal spreading and is associated with a better prognosis than other types of cholangiocarcinoma.⁴

A ROLE FOR CT

Many different multislice CT protocols can be used in the diagnosis of cholangiocarcinoma. We use a combination of oral contrast (750 to 1000 mL) and intravenous contrast (120 to 150 mL, delivered at 3 to 5 mL/sec). Imaging is performed at 120 kVp with a tube current of 200 to 250 mA in the late arterial phase after IV contrast administration (40 sec), the venous phase (60 to 70 sec), and the parenchymal phase (five to 10 min). Collimation is 1.25 to 2.5 mm for arterial imaging, and 2.5 to 5 mm when visualizing venous anatomy.

Contrast-enhanced CT can detect intrahepatic bile duct tumors, the level of biliary obstruction, and the presence of liver atrophy with good sensitivity. CT may also visualize nodal metastasis.⁵ A triple-phase spiral CT scan will detect all cholangiocarcinomas that are greater than 1 cm in diameter.^6,7

Dynamic CT can establish resectability in only about 60% of patients. Dynamic CT may still, however, provide more information on resectability than MRI. ⁸ Both imaging methods are similarly capable of showing tumor enhancement and biliary ductal dilatation, though the relationship of the tumor to vessels and surrounding organs is evaluated more easily using CT.

COMMON SIGNS

The appearance of cholangiocarcinoma on MSCT depends on biological behavior. This varies according to the tumor's location, size at the time of diagnosis, and macroscopic growth type, as described above.⁴

Mass-forming cholangiocarcinoma. This kind of macroscopic growth is the most common among intrahepatic cholangiocarcinomas. Masses are generally large, lobulated, and well-defined, but they can also be irregular. The mass is typically hypodense on MSCT with stippled or punctate hyperattenuating foci within the tumor (Figure 2).