Diagnostic ultrasound ( PDFDrive )

CHAPTER 6 The Biliary Tree and Gallbladder 173
Migration of stones from the gallbladder into the CBD
constitutes secondary choledocholithiasis. Whereas primary
choledocholithiasis is relatively rare outside endemic regions
(East Asia), secondary choledocholithiasis is quite common,
representing the worldwide distribution of gallstone disease. Bile
duct stones are found in 8% to 18% of patients with symptomatic
gallstones. 21
Intrahepatic Stones
Harmonic and compound imaging have improved the ability to
ind small stones within the intrahepatic bile ducts, especially
with dilated ducts. Visualization of small intrahepatic stones is
quite diicult on MRCP and other biliary imaging modalities;
because of the intrinsic high contrast of stones on ultrasound,
it is oten the irst modality to detect intrahepatic stones.
he appearance of stones depends on their size and texture
(Fig. 6.10, Video 6.2). Most stones are highly echogenic with
posterior acoustic shadowing, although small (<5 mm) or sot
pigment stones (especially in the patient with recurrent pyogenic
cholangitis) may not show shadowing. When the afected ducts
are illed with stones, the individual stones may not be appreciated;
instead, a bright, echogenic linear structure with posterior shadowing
is seen. Stones should always be suspected if discrete or linear
echogenicities with or without shadowing are seen in the region
of the portal triads, paralleling the course of the portal veins within
the liver. Harmonic imaging improves both the contrast resolution
and the detection of the acoustic shadow and is therefore recommended
for routine assessment of the biliary tree. 22
Common Bile Duct Stones
he majority of stones in the CBD are in the distal duct close
to or at the ampulla of Vater. herefore sonographic evaluation
should include assessment of the entire duct, focusing on the
periampullary region. Unfortunately, this region is oten the most
A
B
C
D
FIG. 6.10 Choledocholithiasis. (A) Intrahepatic stones. Small stones (arrow) are seen in the right lobe causing acoustic shadowing. Note the
dilated duct proximal to the larger stone. (B) Multiple stone clusters (arrowheads) in the left lobe appearing as echogenic linear structures with
shadowing. Both patients (in A and B) had cystic ibrosis. (C) and (D) Common bile duct (CBD) stones. (C) Small stone (arrow) may not show
shadowing. (D) Distal stone (arrow) with posterior acoustic shadowing. See also Videos 6.2 and 6.3.