Diagnostic Accuracy of Ultrasonography for Common Bile Duct Stones
Ultrasonography (USG) can diagnose approximately 73% of patients with common bile duct (CBD) stones, with sensitivity ranging from 32% to 100% and specificity of 91%. 1
Diagnostic Performance of USG for CBD Stones
- Transabdominal ultrasound has variable sensitivity for detecting CBD stones, with a summary sensitivity of 73% (95% CI 44% to 90%) according to meta-analysis data 1
- Specificity of USG for CBD stones is consistently high, ranging from 77% to 97% with a summary specificity of 91% (95% CI 84% to 95%) 1
- The visualization of a stone in the CBD at transabdominal US is considered a predictor of CBD stones in patients with acute calculous cholecystitis, though this evidence is of very low quality 1
- The diagnostic accuracy of USG is limited by several factors including operator experience, patient body habitus, and overlying bowel gas 1, 2
Limitations of USG in CBD Stone Detection
- CBD stones are not detected with the same sensitivity as gallbladder calculi, with reported sensitivities for CBD stone detection on USG ranging from 22.5% to 75% 1
- The subhepatic common duct may not be visible on USG due to overlying bowel gas, further limiting detection capability 1
- In obese patients, USG has significant limitations due to body habitus affecting visualization of the biliary tree 2
- An increased diameter of CBD on USG is an indirect sign of stone presence but is not sufficient on its own to identify patients with CBD stones 1
Factors Affecting USG Accuracy
- Sensitivity of CBD stone detection can be increased to between 70% to 86% by combining tissue harmonic imaging with findings of elevated bilirubin, patient age >55 years, and CBD dilatation between 6 to 10 mm 1
- CBD diameter alone is not a reliable predictor - a study found that CBD diameter larger than 10 mm was associated with only 39% incidence of CBD stones, while diameter smaller than 9.9 mm was associated with CBD stones in 14% of cases 1, 3
- Stone size affects detection rates, with smaller stones (<4mm) being more likely to be missed on USG 4, 5
Alternative Diagnostic Approaches
- For patients with intermediate risk of CBD stones (10-50%), second-level examination is recommended, either preoperatively with endoscopic ultrasound (EUS) or magnetic resonance cholangiopancreatography (MRCP), or intraoperatively with laparoscopic US or intraoperative cholangiography 1, 2
- EUS has higher sensitivity (95-98.5%) compared to MRCP (55-93%) for detecting CBD stones, particularly small ones or those impacted at the distal CBD or papillary region 5, 6, 7
- Linear EUS has shown 93% sensitivity and 93% specificity for CBD stones in patients with high suspicion 7
- The negative predictive value of EUS for CBD stones is 95.4%, suggesting that patients with normal EUS findings have a low risk of needing ERCP in a 1-year period 6
Risk Stratification for CBD Stones
- The American Society of Gastrointestinal Endoscopy and the Society of American Gastrointestinal Endoscopic Surgeons recommend risk stratification of CBD stones into low risk (<10%), moderate risk (10-50%), and high risk (>50%) 1
- Patients with low risk should undergo surgery without further investigation; those with moderate risk should have second-level examination; and those with high risk should undergo preoperative diagnostic and therapeutic ERCP 1
- The World Society of Emergency Surgery recommends performing liver function tests and abdominal US in all patients with acute calculous cholecystitis to assess the risk for CBD stones 1
In summary, while USG is recommended as the initial imaging test for suspected CBD stones due to its wide availability and lack of invasiveness, its sensitivity is limited to approximately 73%. For patients with intermediate or high probability of CBD stones, additional imaging modalities such as MRCP or EUS should be considered to improve diagnostic accuracy.