Diagnostic Accuracy of Imaging Modalities for Choledocholithiasis
Statement B is most correct: The sensitivity of EUS is similar to that of ERCP for detecting choledocholithiasis.
Evidence Supporting Statement B
EUS demonstrates diagnostic accuracy comparable to ERCP, with both modalities achieving sensitivities of 95-97% for detecting common bile duct stones 1, 2. Multiple prospective studies confirm that EUS sensitivity ranges from 89-97%, while ERCP achieves 92-97% sensitivity, with no statistically significant difference between the two modalities 3, 4, 5, 2.
The American Society for Gastrointestinal Endoscopy recognizes EUS as equivalent to MRCP for detecting common bile duct abnormalities, with both achieving sensitivities of 93-95% and specificities of 96-97% 1, 6. In experienced endoscopic units, EUS may be used instead of MRCP for detection of bile duct stones and other lesions causing extrahepatic obstruction 1.
Why the Other Statements Are Incorrect
Statement A: Transabdominal Ultrasonography Sensitivity
Transabdominal ultrasound has poor sensitivity for choledocholithiasis, ranging from 50-63%, well below the claimed >80% 5, 7. While US has high specificity (95%) 5, its low sensitivity makes it inadequate as a standalone diagnostic test for CBD stones 1. US is appropriately used as first-line imaging to assess for biliary dilatation and gallstones, but additional testing is required when choledocholithiasis is suspected 1.
Statement C: MRI/MRCP Sensitivity
MRCP demonstrates high sensitivity of 77-93% for detecting choledocholithiasis, far exceeding the claimed <50% 1, 6. The ACR Appropriateness Criteria report MRCP sensitivity ranging from 77-88% with specificity between 50-72% compared to ERCP as the reference standard 1. MRCP is more sensitive than CT or transabdominal US for detection of ductal calculi 1.
Statement D: Multidetector CT Utility
Multidetector CT is useful for detecting both bile duct strictures and stones, contrary to the statement 1. After the advent of MDCT with improved spatial resolution (as low as 0.6-mm slice thickness), sensitivity for biliary obstruction improved to >90% 1. MDCT can determine both the site and cause of biliary obstruction more accurately than US, with sensitivity of 74-96% and specificity of 90-94% 1.
Clinical Implications
When moderate-risk patients require confirmatory imaging for suspected choledocholithiasis, the choice between MRCP and EUS should be based on local expertise and availability, as both achieve comparable diagnostic accuracy 1, 6. EUS offers the advantage of being safer than diagnostic ERCP (no complications versus 1-2% complication rate) while maintaining equivalent accuracy 1, 4, 2.
A critical pitfall is performing unnecessary diagnostic ERCP when EUS or MRCP could provide equivalent diagnostic information without the 1-2% complication rate (increasing to 10% with sphincterotomy) 1, 6. ERCP should be reserved for therapeutic intervention when stones are confirmed or for high-risk patients where immediate treatment is anticipated 1, 6.