Diagnostic ultrasound ( PDFDrive )

174 PART II Abdominal and Pelvic Sonography
diicult area to visualize because it may be hidden by bowel gas,
making detection of distal CBD stones diicult. Maneuvers to
improve assessment include the following:
• Changes in patient position. he CBD may be examined
in supine, let lateral decubitus, and standing positions.
he change in the relative position of adjacent organs and
bowel gas may allow improved visualization of the distal
duct.
• Choice of sonographic window. he subcostal view is most
useful for the assessment of the porta hepatis and proximal
CBD. An epigastric view is best for the distal CBD.
• Use of compression sonography. Physically compressing the
epigastrium may collapse the supericial bowel and displace
the bowel gas that is blocking the view.
• Detailed assessment of the distal CBD. he distal intrapancreatic
CBD is oten best visualized with the probe focused
on the pancreatic head in the transverse plane. Once the
dilated CBD is identiied, a slight rocking of the transducer
to just “peek” at the point of caliber change will oten allow
a glimpse of a stone impacted in the distal duct, which is
otherwise hidden from sonographic view. Similarly, a sagittal
view focused on the pancreatic head should show the dilated
CBD on the dorsal aspect of the head. Again, slight manipulation
of the transducer, focusing on the point of caliber change,
is best to see a solitary stone impacted in the distal duct. If
the gallbladder is distended, it may be used as an acoustic
window through which the distal CBD and ampulla may be
visible.
he classic appearance of CBD stones is a rounded echogenic
lesion with posterior acoustic shadowing (see Fig. 6.10, Video
6.3). Importantly, no luid rim will be seen around an impacted
distal CBD stone because it is compressed against the duct wall.
he lateral margins of the stone are therefore not seen, decreasing
the conspicuity of the stone, versus a stone seen in the gallbladder
or proximal duct, where it is likely to be surrounded by bile.
Small stones may lack good acoustic shadows and appear only
as a reproducible bright, linear echogenicity, either straight or
curved. Awareness of this subtle appearance of CBD stones
deinitely improves their detection.
Pitfalls in the diagnosis of choledocholithiasis include blood
clot (hemobilia), papillary tumors, and occasionally biliary
sludge; none of these will shadow. Surgical clips in the porta
hepatis, mostly from previous cholecystectomy, appear as linear
echogenic foci with shadowing. 23 he short length, the relatively
high degree of echogenicity, the lack of ductal dilation, and the
absence of the gallbladder should allow diferentiation of surgical
clips from stones.
Mirizzi Syndrome
Mirizzi syndrome is a clinical syndrome of jaundice with pain
and fever resulting from obstruction of the CHD caused by a
stone impacted in the cystic duct. It occurs most oten when the
cystic duct and CHD run a parallel course. he stone is oten
impacted in the distal cystic duct, and the accompanying inlammation
and edema result in the obstruction of the adjacent CHD.
he obstruction of the cystic duct causes recurrent bouts of
FIG. 6.11 Mirizzi Syndrome. Mirizzi syndrome in a patient with
abdominal pain and jaundice. Sagittal sonogram shows a dilated common
bile duct obstructed by a large stone impacted in the distal cystic duct.
This appearance may be mistaken for a common bile duct stone. There
is thickening of the wall of the cystic duct (arrow).
cholecystitis, and the impacted stone may erode into the CHD,
resulting in a cholecystocholedochal istula and biliary obstruction.
24 Identiication of the istula complication (called Mirizzi
type II) is important because the treatment requires surgical
repair of the istula. Acute cholecystitis, cholangitis, and even
pancreatitis may occur. 25
Mirizzi syndrome should be considered on sonography when
biliary obstruction with dilation of the biliary ducts to the CHD
level is seen with acute or chronic cholecystitis. hus the gallbladder
has features of acute cholecystitis but may or may not
be distended. 2 A stone impacted in the cystic duct with surrounding
edema at the level of the obstruction is conirmatory
(Fig. 6.11).
Hemobilia
Iatrogenic biliary trauma, mostly caused by percutaneous biliary
procedures or liver biopsies, accounts for approximately 65%
of all causes of hemobilia. Other causes include cholangitis
or cholecystitis (10%), vascular malformations or aneurysms
(7%), abdominal trauma (6%), and malignancies, especially
hepatocellular carcinoma and cholangiocarcinoma (7%). 26
Pain, gastrointestinal bleeding, and biochemical jaundice are
the usual complaints at presentation. Apart from the blood loss,
which occasionally is severe, complications are rare and include
cholecystitis, cholangitis, and pancreatitis.
he appearance of blood within the biliary tree is similar to
blood clots encountered elsewhere (Fig. 6.12). Most oten, the
clot is echogenic or of mixed echogenicity, and retractile, conforming
to the shape of the duct. Occasionally, hemobilia may appear
tubular with a central hypoechoic area. Acute hemorrhage will
appear as luid with low-level internal echoes. Blood clots may
be mobile. Extension into the gallbladder is common. he clinical
history is oten essential to the diagnosis.