To discern the level (intraor extrahepatic) as well as the cause (benign or malignant) of biliary obstruction, other criteria such as luminal content (concretion, sludge, solid masses), thickening of bile duct wall and compression by neighboring pathological structures are of great importance.1

Diameter (Fig. 3.1, Fig. 3.2)

●Barely visible interlobar branches

●Right/left hepatic duct: 1–2 mm

●Hilar common hepatic duct: 1–2 mm/ detection limit

●Prepancreatic CBD: 3–7(9) mm

Shape

●Slender interlobar segment/close to the hepatic duct confluence

●Hepatic duct confluence not or barely visualized

●Slender hilar segment

●Slender/slightly ectatic prepancreatic segment

●Intrapancreatic segment not or barely visualized

Both the other vessels of the hepatic triad, the trunks and branches of the portal vein and the hepatic artery, can be considered mandatory and highly reliable sonographic landmarks accompanying the intrahepatic and extrahepatic biliary tree.

Intrahepatic biliary tree. Ultrasound visualization of the intrahepatic biliary tree (Fig. 3.2, Fig. 3.3) is facilitated by the fact that the regular vascular branching of the hepatic triad (“vascular architecture”) at all levels results in multiple, ever-smaller branches running parallel to the surface of the probe, which makes for optimum detection. The best resolution of detail, almost resembling that of a magnifying glass, is seen in the portal vein branches (up to the intralobular level), followed by the small branches of the bile ducts. Normally, only the large intrahepatic branches of the hepatic artery can be seen (with color-flow Doppler scanning even more peripheral branches may be

visualized especially in typical cirrhotic arterial hyperperfusion).

Extrahepatic biliary tree ( 3.1). The hilar/ prepancreatic course of the extrahepatic biliary tree is also well defined in terms of ultrasound anatomy by the vascular triads originating here. The portal vein always runs posterior to the more slender common duct (see Fig. 3.1,

Fig. 3.2c, Fig. 3.4, Fig. 3.5a,b). The relationship of the portal vein with the hepatic artery and its variant extrahepatic hilar branches is somewhat more complex (Fig. 3.5c,d). The hepatic artery always enters the porta hepatis from the left4 ( 3.1e–g) and therefore initially lies to the left of the common duct; it (or its main right branch) then crosses behind the common duct. Thus, it courses anterior to the portal vein and posterior to the common duct ( 3.1a–c, Fig. 3.2c), and in scans of the porta hepatis ( 3.1e–g) it appears as a round tubular crosssection. Infrequently—only in about 5%—this

cross-section of the hepatic artery may progress into its intrahepatic course anterior to the common duct (Fig. 3.5a,b).5 Owing to the pressure of the adjacent pancreatic parenchyma, the intrapancreatic segment of the CBD is almost impossible to visualize; it is best seen in sections orthogonal to its anatomical course ( 3.1h).

Clinical Notes

The structures of the porta hepatis are best imaged with the patient in the left lateral decubitus position and inhaling deeply: this moves the liver caudad and to the left, thereby providing an excellent “sono-opti- cal” window. Occasionally intercostal planes are necessary in relative diaphragmatic elevation. Planes that capture the structures of the porta hepatis parallel to their longitudinal axis are preferable. As a