Diagnostic Ultrasound - Abdomen and Pelvis

Approach to Biliary Sonography
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Diagnoses: Biliary System
Imaging Anatomy
The gallbladder is a fluid-filled, pear-shaped sac that lies in the
vertical plane between the right and left hepatic lobes. The
fundus is the most distal and distensible portion. The fundus is
more mobile than the body and neck, which are attached to
the liver. The neck drains into the cystic duct. The gallbladder
is in contact with the duodenum, the posterior aspect of the
liver, and the proximal transverse colon. The distended lumen
is filled with anechoic bile. The wall is uniformly thin, typically
1-2 mm. When physiologically distended after fasting, the
gallbladder can measure up to 5 x 5 x 10 cm. A fatty meal
produces gallbladder emptying and apparent wall thickening.
Intrahepatic bile ducts drain toward the porta hepatis as the
right and left hepatic ducts. These converge to form the
common hepatic duct at the bifurcation of right and left
portal veins. The cystic duct joins the common hepatic duct to
form the common bile duct. The common bile duct runs
through the pancreatic head and joins the pancreatic duct
before draining into the duodenum at the major duodenal
papilla. The normal common bile duct measures < 6 mm.
Anatomy-Based Imaging Issues
The bile-filled, distended gallbladder is easily and ideally
evaluated with ultrasound. It is intimately related to the liver
and is included during imaging of the liver. The gallbladder is
located in the plane lying along the middle hepatic vein and
interlobar fissure. If the gallbladder is contracted, look
carefully along that plane in the transverse plane.
Due to their small caliber, the cystic duct and the second and
third order intrahepatic ducts are only seen if dilated. The
common hepatic duct is routinely visualized at the porta
hepatis, but the common bile duct may be obscured by gastric
or duodenal gas as it courses inferiorly toward the ampulla.
After cholecystectomy, the common bile duct caliber may be
slightly increased. There is debate as to whether biliary ductal
caliber increases with age.
Pathologic Issues
The gallbladder and biliary tree are affected by a wide range
of acute and chronic inflammatory conditions and benign and
malignant neoplasms. The most common pathology is
gallstone disease and its complications, such as acute and
chronic cholecystitis. These are among the most common
indications for ultrasound of the abdomen.
Imaging Protocols
Prior to elective right upper quadrant ultrasound, patients
should fast for 6-8 hours. Tube feeds should be withheld for
the same length of time; however, in an emergency,
ultrasound can be performed in the non-fasted state and can
still be diagnostic. Fasting is not necessary after
cholecystectomy but may still improve diagnostic ability by
reducing gas obscuring the common bile duct and pancreas.
Studies are performed with a curved array transducer at
frequencies between 1-5 MHz for most adults and as high as 9
MHz in thin adults. Focal zone placement should be optimized
to the lesion of interest, especially with gallstones. Use of
harmonic techniques improves evaluation of the gallbladder
lumen and increases tissue contrast with fewer artifacts.
Compound imaging techniques are used to decrease speckle
and increase lesion conspicuity.
Gallbladder
The gallbladder is evaluated in multiple planes and patient
positions. The approach should include subcostal and
intercostal windows with static images obtained in multiple
longitudinal, transverse, and oblique planes. Patients are
imaged in the supine position but the left lateral decubitus
position is essential to ensure that small stones located in the
gallbladder neck are not missed. Additionally, patient
movement demonstrates mobility of intraluminal lesions and
differentiates stones from polypoid mural lesions. Other
useful positions include right lateral decubitus, semi-erect,
erect, and prone. If the patient is immobile, elevation of the
head of the bed or stretcher is an inferior substitute for
decubitus or prone positioning. Deep inspiration can improve
visualization of the gallbladder and determine the presence of
the sonographic Murphy sign.
Gallbladder assessment includes evaluation of the wall for
thickness and integrity, gallbladder volume, and intraluminal
contents. Assessment of the sonographic Murphy sign is
essential. Adjacent structures are also assessed.
Bile Ducts
Evaluation of the biliary tree is a key component of the study.
The intrahepatic ducts, left and right hepatic ducts are
evaluated during evaluation of the liver. The common hepatic
duct is measured at the porta hepatis, anterior to the main
portal vein with the proper hepatic artery in cross section.
Decubitus positioning and deep inspiration can improve
visualization. The bile duct should be followed distally through
the head of the pancreas. A low insertion of the cystic duct is
an important variant that should be conveyed to the surgeon
considering surgery. Gastric or duodenal gas may obscure the
distal common bile duct. Maneuvers such as turning the
patient to their right side or having the patient drink water
may allow a diagnostic study.
Color Doppler is used to identify and to confirm patency of
vessels and differentiate vessels from intra- and extrahepatic
dilated bile ducts. Color Doppler is helpful to evaluate
potential masses and gallbladder or bile duct wall thickening.
Color Doppler twinkling artifact can confirm stones or
adenomyomatosis. Spectral Doppler is used to determine
flow dynamics and direction.
Clinical Implications
Ruling Out Gallstones
In the majority of patients, gallstones are easy to diagnose by
demonstrating mobile echogenic intraluminal lesions with
acoustic shadowing. Shadowing from gallstones can be
variable but can be enhanced with harmonic imaging. Falsenegatives
include small nonshadowing stones mistaken for
sludge or small stones hidden in the gallbladder neck with the
patient supine. Other pitfalls include a contracted gallbladder
packed with stones, misinterpreted as duodenum or a nondistended/non-visualized
gallbladder. The contracted stone
filled gallbladder can be diagnosed if the wall-echo-shadow
(WES) sign is present. Suspected porcelain gallbladder is
optimally confirmed with CT with a careful search for
associated mass. Emphysematous cholecystitis or gas in the
gallbladder from reflux can be difficult to evaluate with
ultrasound, often requiring CT.
Intraluminal lesions to be differentiated from gallstones
include sludge and polyps. Gallstones can be differentiated
from polyps by demonstrating mobility, although rare stones
may be embedded in the wall. Sludge is common in