Hepatobiliary disease is listed in the differential diagnosis of patients presenting to the emergency department with abdominal pain. Patients with right upper quadrant (RUQ) pain associated with fever, nausea, vomiting, and/or jaundice may have hepatobiliary disease as the cause and a bedside biliary ultrasound will assist in making this diagnosis.

Sonographic evaluation of the biliary system is a core emergency ultrasound application according to the 2008 American College of Emergency Physicians Policy on Emergency Ultrasound.

Clinical Indications for Performing a Biliary Ultrasound

The main indication for biliary emergency ultrasound is rapid identification of sonographic markers of acute cholecystitis.

Performing a Biliary Ultrasound

Anatomic landmarks and considerations. The liver is an intraperitoneal structure located in the RUQ of the abdomen. The liver is bordered superiorly by the diaphragm, inferomedially by the duodenum and head of the pancreas, and inferiorly by the gallbladder, hepatic flexure and ascending colon, and the superior pole of the right kidney. The gallbladder lies on the inferior surface of the liver between the right and left lobe of the liver. It is bordered inferiorly by the hepatic flexure and transverse colon and medially by the duodenum.

The liver has a characteristic sonographic appearance and serves as an echo-friendly window for imaging the gallbladder. The gallbladder appears as a cystic oval-shaped organ whose wall may contain normal anatomic variants such as folds, septations, and – when located at the fundus – a Phrygian cap. The main lobar fissure (MLF) appears to connect the gallbladder on long axis view to the portal vein and altogether gives a characteristic “exclamation point” appearance. The median hepatic vein divides the liver into right and left lobes and runs with the MLF. The hepatic artery and common bile duct (CBD) lie anterior to the portal vein, and the three together make the portal triad.

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.

A dependent layer of variable nonshadowing echogenicity in the gallbladder is characteristic of sludge, which often contains stones (Figure 4).

Attempts also should be made to evaluate the presence of a sonographic Murphy’s sign – tenderness to direct palpation over the gallbladder with the ultrasound probe. The sonographic Murphy’s sign is a useful but imperfect sign with an overall accuracy of 87.2%, sensitivity of 63%, specificity of 93.6%, positive predictive value of 72.5%, and negative predictive value of 90.5%.

The presence of pericholecystic fluid should also be noted. This appears as an anechoic stripe of fluid along the dependent surface or in the gallbladder wall.

Gallbladder wall thickening occurs in the normal postprandial state as well as in a variety of disease entities, including cirrhosis, hypoalbuminemia, congestive heart failure, HIV disease, pancreatitis, and renal failure.

Acalculous cholecystitis is a rare disease but should be considered when the gallbladder is enlarged; the patient appears toxic and has certain underlying medical conditions such as diabetes.

Biliary duct obstruction. Biliary duct obstruction caused by stones, pancreatic pathology (e.g. mass), or stricture is detected measuring a CBD larger than 6-7 mm. Sonographically, the CBD appears as an anechoic tubular structure in the main portal triad, anterior to and following the course of the main portal vein (Figure 5).

Variants and mimics. Several normal anatomic variants may be noted. Indentations may produce septations of the lumen and can be mistaken for gallstones (Figure 6). Shadowing does not usually occur with septations. A fold of the gallbladder fundus is termed a Phrygian cap.

Biliary polyps can be mistaken for gallstones but may be distinguished from stones because they do not move with a change in positioning (Figure 7).

Hepatic cysts also can be mistaken for the gallbladder. Hepatic cysts have sharp margins, no internal echoes, and increased posterior acoustic enhancement.

Pearls and Pitfalls

Some final pearls and pitfalls include the following:

• The gallbladder is a mobile organ; remember to change patient positioning and/or probe placement to find the organ of interest.
• Distinguish gallstones from polyps and septations or folds by always scanning through the whole organ and in both longitudinal and transverse planes.
• During the biliary exam, use color Doppler to help distinguish nonvascular from vascular structures.
• Ultrasound findings must be interpreted in the context of the clinical presentation; findings suggestive of acute cholecystitis (e.g., gallstone or thickened wall) may be present in patients in a nondiseased state.
• The common bile duct can be dilated in the absence of pathology in older patients and postcholecystectomy patients.
• Measure the anterior wall of the gallbladder. The posterior wall may appear artificially thickened because of acoustic enhancement or artifact from bowel gas.

Conclusion

Bedside biliary ultrasound to evaluate for acute cholecystitis can be accurately performed by emergency physicians. Bedside ultrasound should always be used in the context of the clinical scenario.

References

1. American College of Emergency Physicians Policy Statement on Emergency Ultrasound Guidelines. October 2008.
2. Cooperberg PL, Gibney RG. Imaging of the gallbladder. Radiology 1987;163(3);605-13.
3. Kendall JL, Shimp RJ. Performance and interpretation of focused right upper quadrant ultrasound by emergency physicians. J. Emerg. Med. 2001;21(1):7-13.
4. Ralls PW, Colletti PM, Lapin SA, Chandrasoma P, Boswell WD Jr, Ngo C, Radin DR, Halls JM. Real-time sonography in suspected acute cholecystitis: Prospective evaluation of primary and secondary signs. Radiology 1985;155(3):767-71.
5. Ralls PW, Halls J, Stewart LA, Quinn, MF, Morris UK, Boswell W. Prospective evaluation of the sonographic Murphy’s sign in suspected acute cholecystitis. J. Clin. Ultrasound 2005;10(3):113-5.
6. Theodoro D. Hepatobiliary. In: Ma OJ, Mateer JR, and Blaivas M, eds. Emergency Ultrasound. McGraw-Hill, 2007, pp. 177-86.