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 detects only about three-quarters of CBD stones that are actually present. 1

Diagnostic Performance 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 detection rate varies significantly based on pre-test probability:
  • With low pre-test probability (9.5%): positive post-test probability 45% (31-60%)
  • With moderate pre-test probability (40.8%): positive post-test probability 85% (75-91%)
  • With high pre-test probability (65.8%): positive post-test probability 94% (89-97%) 1

Factors Affecting Ultrasound Detection of CBD Stones

• Stone size is a critical factor - smaller stones (<5mm) are more likely to be missed by ultrasound 2
• Direct visualization of CBD stones on ultrasound is a very strong predictor of choledocholithiasis when seen 1
• CBD diameter alone is not a reliable indicator of stones:
  • Diameter >10mm is associated with 39% incidence of CBD stones
  • Diameter <9.9mm is associated with only 14% incidence of CBD stones 1, 3

Comparison with Other Imaging Modalities

• Endoscopic ultrasound (EUS) has superior sensitivity (95-100%) compared to ultrasound (73%) for CBD stone detection 2, 4, 5
• Magnetic resonance cholangiopancreatography (MRCP) has better sensitivity (88-93%) than conventional ultrasound 1, 2
• When ultrasound is negative but clinical suspicion remains high, additional imaging is recommended:
  • EUS is particularly valuable for detecting small stones missed by other modalities 4, 5, 6
  • MRCP is less invasive than EUS and has comparable accuracy for larger stones 1

Clinical Implications and Pitfalls

• Relying solely on ultrasound for excluding CBD stones can lead to missed diagnoses, particularly with small stones 3, 2, 4
• Ultrasound findings should be interpreted in conjunction with clinical and laboratory parameters 1
• Common pitfalls include:
  • Misinterpreting increased CBD diameter as definitive evidence of stones, especially in elderly patients where normal diameter may be larger 3, 7
  • Failing to recognize that normal liver biochemical tests have a high negative predictive value (97%) but abnormal tests have a low positive predictive value (15%) for CBD stones 1

Recommended Diagnostic Approach

• For patients with suspected CBD stones, ultrasound should be performed as an initial imaging test along with liver biochemical tests 1
• When ultrasound is negative but clinical suspicion remains:
  • For intermediate or high probability: proceed to MRCP or EUS 1, 4
  • For high probability with negative CT: EUS-first approach is recommended to avoid unnecessary ERCP 5, 6
• Direct visualization of CBD stones on ultrasound is highly specific and warrants therapeutic intervention 1, 3