Can choledocolithiasis (gallstones in the common bile duct) be detected on ultrasound?

Detection of Choledocholithiasis on Ultrasound

Choledocholithiasis can be detected on ultrasound, but with limited sensitivity (73%) compared to other imaging modalities, making it unreliable as a standalone test for excluding common bile duct stones. 1

Diagnostic Accuracy of Ultrasound for Choledocholithiasis

Transabdominal ultrasound is the recommended first-line imaging modality for suspected biliary obstruction, but its performance for detecting common bile duct stones has important limitations:

• Sensitivity: 73% (95% CI: 44% to 90%)
• Specificity: 91% (95% CI: 84% to 95%) 1
• Direct visualization of stones in the common bile duct on ultrasound is considered a very strong predictor of choledocholithiasis 1

The diagnostic accuracy of ultrasound varies significantly based on pre-test probability:

• With low pre-test probability (9.5%): positive post-test probability is 45%, negative post-test probability is 3%
• With high pre-test probability (65.8%): positive post-test probability is 94%, negative post-test probability is 37% 1

Comparison with Other Imaging Modalities

Ultrasound is significantly less sensitive than other available modalities:

Modality	Sensitivity	Specificity	Notes
Ultrasound	73%	91%	First-line test, widely available [1]
MRCP	93%	96%	Non-invasive, no radiation [1,2]
EUS	95%	97%	Highly accurate, more invasive [1,3,4]
CT	Lower	Lower	Less sensitive than MRCP/EUS for stones [1]

Clinical Approach to Suspected Choledocholithiasis

When choledocholithiasis is suspected:

1. Start with ultrasound and liver function tests as initial screening 1

   • Look for direct visualization of CBD stones
   • Check for dilated bile ducts (>6mm with gallbladder in situ)
   • Assess for gallbladder stones and wall thickening

2. Risk stratification based on findings 1:

   • High risk: CBD stone visible on ultrasound or ascending cholangitis
   • Moderate risk: CBD diameter >6mm, total bilirubin >1.8 mg/dl, abnormal liver tests, age >55 years, or gallstone pancreatitis
   • Low risk: No predictors present

3. Next steps based on risk level:

   • High risk: Proceed to ERCP for diagnosis and treatment 1
   • Moderate risk: Second-level investigation with MRCP, EUS, intraoperative cholangiography (IOC), or laparoscopic ultrasound (LUS) 1
   • Low risk: No further biliary imaging needed 1

Important Caveats and Pitfalls

• Normal ultrasound does not exclude choledocholithiasis - up to 37% of patients with high pre-test probability and negative ultrasound may still have CBD stones 1
• Small stones (<5mm) are frequently missed on ultrasound 5, 6
• Patient factors affecting visualization include obesity, bowel gas, and anatomic variations
• Operator dependence significantly impacts diagnostic accuracy
• False positives can occur due to pneumobilia, blood clots, or tumor debris

Clinical Bottom Line

While ultrasound is an appropriate first-line imaging test for suspected choledocholithiasis due to its wide availability, safety, and low cost, its limited sensitivity means that negative results should not be used to exclude common bile duct stones when clinical suspicion is moderate to high. In these cases, additional imaging with MRCP or EUS is warranted to avoid missing clinically significant stones that could lead to complications such as cholangitis, pancreatitis, or biliary obstruction 1, 2.