Figures 18-20. (18) Involvement of the main portal vein. Sagittal gray-scale US scan shows an infiltrative mass in the common bile duct. A nodular component (arrowheads) is seen invading the main portal vein (pv). An indwelling stent is also visible (arrow). (19) Hepatic artery encasement. Subcostal oblique gray-scale US scan through the porta hepatis shows incomplete encasement of the hepatic artery (*) by a mass in the ductal confluence (arrowheads). The hepatic artery is incompletely circumscribed by tumor tissue; there is an intact tissue plane between the artery and the adjacent portal vein (pv). (20) Involvement of the right portal vein. Subcostal oblique gray-scale US scan through the porta hepatis shows an abrupt narrowing (arrow) with complete obliteration of the right portal vein (rpv) secondary to an isoechoic infiltrating Klatskin tumor (m). A biliary stent appears as two parallel echogenic lines within the tumor.