Diagnostic ultrasound ( PDFDrive )

CHAPTER 6 The Biliary Tree and Gallbladder 167
extrahepatic and, along with the CHD, form the hilar or central
portion of the biliary tree at the porta hepatis. his is the most
common location for cholangiocarcinoma. he normal diameter
of the irst-order and higher-order branches of the CHD has
been suggested to be 2 mm or less, and no more than 40% of
the diameter of the adjacent portal vein. 2
he most common biliary branching pattern occurs in 56%
to 58% of the population 3,4 (Figs. 6.2 and 6.3). On the right side,
the right hepatic duct forms from the right anterior and right
posterior branches, draining the anterior (segments 5 and 8)
and posterior (segments 6 and 7) segments of the right lobe,
respectively. On the let side, segment 2 and 3 branches join to
the let of the falciform ligament to form the let hepatic duct.
his duct becomes extrahepatic in location as it extends to the
right of the falciform ligament, where it is joined by ducts of
segments 4 and 1.
he key to understanding the common normal variants of
biliary branching lies in the variability of the site of insertion of
the right posterior duct (RPD) (segments 6 and 7). he RPD
oten extends centrally toward the porta hepatis in a cranial
direction. It passes superior and posterior to the right anterior
duct (RAD) and then turns caudally, joining the RAD to form
the short right hepatic duct (see Fig. 6.2). hree other common
sites of insertion of the RPD account for the majority of the
biliary anatomic variations. If the RPD extends more to the
let than usual, it can join the junction of the right and let
hepatic ducts (“trifurcation pattern”; ≈8% of normal variants)
or the let hepatic duct (≈13%) (Fig. 6.4). If the RPD extends in
a caudal-medial direction instead, it can join the CHD or common
bile duct (CBD) directly (≈5%). Anomalous drainage of various
segmental hepatic ducts directly into the CHDs is less common.
he normal caliber of the CHD/CBD in patients without
history of biliary disease is up to 6 mm in most studies 5 (see
Fig. 6.1). Controversy surrounds whether there is a normal
widening of the duct with increasing age. 6 Similarly, studies
on an association between cholecystectomy and a large-caliber
CBD are inconclusive. Although diameters of up to 10 mm have
been recorded in an asymptomatic normal population, the great
majority of the diameters are under 7 mm. herefore a ductal
diameter of 7 mm or greater should prompt further investigations,
such as correlation with serum levels of cholestatic liver
enzymes.
A B C D
FIG. 6.2 Common Variants of Bile Duct Branching. Right posterior duct (RPD) is in red. (A) RPD joins the right anterior duct in 56% to 58%
of the population. (B) Trifurcation pattern, 8%. (C) RPD joins the left hepatic duct, 13%. (D) RPD joins the common hepatic or common bile duct
directly, 5%.
A
B
FIG. 6.3 Typical Ductal Branching Order. Intrahepatic biliary tree is dilated because of an obstructed common bile duct (not shown). (A) and
(B) Subcostal oblique views foreshorten the right (R) and left (L) hepatic ducts. RA, Right anterior duct; RP, right posterior duct; 2, segment 2 duct;
3, segment 3 duct; 4, segment 4 duct.