What percentage of common bile duct (CBD) stones can be detected using ultrasound?

Ultrasound Detection Rate of Common Bile Duct Stones

Ultrasound has a sensitivity of approximately 73% (range 44-90%) for detecting common bile duct (CBD) stones, meaning it can identify only about three-quarters of CBD stones that are actually present. 1

Diagnostic Accuracy of Ultrasound for CBD Stones

• Ultrasound demonstrates a sensitivity of 73% (44-90%) and specificity of 91% (84-95%) for detecting CBD stones 1
• The positive post-test probability varies based on pre-test probability:
  • Low pre-test probability (9.5%): 45% positive post-test probability 1
  • Moderate pre-test probability (40.8%): 85% positive post-test probability 1
  • High pre-test probability (65.8%): 94% positive post-test probability 1

Factors Affecting Ultrasound Detection

• Direct visualization of CBD stones on ultrasound is a very strong predictor of choledocholithiasis 1, 2
• Small stones (less than 5mm) are more likely to be missed by ultrasound 3, 4
• CBD diameter alone is not sufficient to identify patients with CBD stones 1, 2
  • A CBD diameter >10mm is associated with 39% incidence of stones 1, 5
  • A CBD diameter <9.9mm is associated with only 14% incidence of stones 1, 5

Alternative Diagnostic Modalities

• When ultrasound is negative but clinical suspicion remains high, additional imaging is recommended 2, 4
• MRCP and EUS both demonstrate superior sensitivity compared to ultrasound:
  • EUS: 95-98.5% sensitivity 1, 4
  • MRCP: 93% sensitivity 1
• For small stones (<5mm) missed by ultrasound, EUS shows particularly high sensitivity 3, 4

Clinical Implications

• The American College of Radiology recommends documenting specific findings in ultrasound reports, including direct visualization of stones if present 2
• An "EUS-first" approach in patients with suspected CBD stones can reduce unnecessary ERCP procedures by approximately 40% 6
• Relying solely on ultrasound CBD diameter measurements may lead to missed diagnoses, as diameter alone has limited predictive value 1, 2
• In acute cholecystitis, ultrasound CBD diameter is not sufficient to identify patients at significant risk for CBD stones 5

Practical Approach

• For patients with suspected CBD stones and negative ultrasound:
  • If clinical suspicion is high, proceed with either MRCP or EUS 1, 4
  • EUS is particularly valuable for detecting small stones that may be missed by both ultrasound and MRCP 3, 4
• Direct visualization of stones on ultrasound is more valuable than indirect signs like CBD dilation 1, 2