Patient positioning. Patient positioning is the key to performing biliary emergency ultrasound. Five positions may be considered: supine, left-lateral decubitus, semi-erect, upright, or prone. Begin by placing the patient in the supine position. As the diaphragm descends with inspiration, the liver and associated structures move inferiorly toward or beyond the costal margin, pushing the gallbladder into view. Other positions can be helpful when visualization of the gallbladder is difficult or to confirm movement of a gallstone.

Scanning the Biliary System

A low-frequency (e.g., 3.5-5 MHz) curvilinear or phased-array probe should be used to scan the liver and biliary tree. Four probe placements can be considered when locating the gallbladder: subcostal, epigastrium, intercostal, flank.

With the patient in the supine position, the probe can be placed subcostally in the midclavicular line with the probe marker directed toward the patient’s head. Some operators place the probe in the epigastrium and point the probe marker toward the patient’s right shoulder. Alternatively, the probe can be placed in the right anterior axillary line over the lower rib spaces for an intercostal position. Finally, consider placing the probe in the right flank/Morison’s pouch area to locate the gallbladder.

Rotate the probe marker into a more oblique position as necessary to locate the gallbladder. If any confusion exists in distinguishing the gallbladder from a vascular structure such as the inferior vena cava, color-flow Doppler mode is a useful adjunct (Figures 1 and 2).

The gallbladder should be imaged in two planes, longitudinal and transverse (long axis and short axis), with caliper measurements made of the anterior gallbladder wall and the common bile duct. The anterior gallbladder wall should measure less than 3 mm. Measuring the posterior gallbladder wall may suggest a falsely thickened wall because of posterior enhancement artifact.

The “exclamation point” of the gallbladder, MLF, and portal vein should be located to aid in the identification of the CBD, which lies anterior to the portal vein. The CBD should be

measured from inner wall to inner wall and is normally less than 6-7 mm. The CBD dilates with age and in postoperative states.

Identifying Biliary Pathology

Acute cholecystitis. In the patient with RUQ pain, the sonographic findings suggestive of acute cholecystitis that should be noted are:

• Gallstones or sludge.
• Sonographic Murphy’s sign.
• Pericholecystic fluid.
• Gallbladder wall thickening (more than 3 mm).
• Common bile duct dilation (more than 6-7 mm).
• Enlarged gallbladder (more than 10 cm × 5 cm).

The presence of gallstones is the primary sonographic criterion for the diagnosis of acute cholecystitis. Gallstones can be present in the setting of acute biliary disease or found incidentally. A gallstone appears as a mobile, hyperechoic focus within the gallbladder, casting an anechoic shadow (Figure 3). Gallstones typically lie in the most dependent region, moving when the patient is repositioned. Smaller gallstones, especially less than 3 mm, may not cast a shadow. A stone in the neck of the gallbladder may cause distention of the organ, which normally measures approximately 10 cm × 5 cm. When the gallbladder is entirely filled with stones, a wall echo shadow (WES) sign is seen, which consists of an anterior echogenic line within the near wall of the gallbladder, an anechoic stripe representing bile, a hyperechoic line representing stones, and a posterior acoustic shadow.