Clinical usefulness of ultrasonographic evaluation of common bile duct (CBD) size in cholecystectomized patients with suspected obstructive biliary pathology

Introduction: While the direct visualization by ultrasonography (US) of the cause of biliary flow impairment is often difficult, the diameter of CBD is easily obtainable. There are controversies as to what diameter of CBD on US should be regarded as abnormal in cholecystectomized patients.

Aim: Evaluation of US measurement of CBD size (the clinically optimal cut-off value) in post-cholecystectomy patients, suspected for impaired biliary flow.

Material and methods: 795 post-cholecystectomy patients suspected for impaired biliary flow [657 women (83%); mean age 60.5; range 19-94 years], evaluated in years 1990-2005. CBD size was measured in antero-posterior transverse and left semilateral positions. The reference diagnostic method in every case was ERCP, completed by endoscopic sphincterotomy in 588 (74% of cases). Calculations of diagnostic sensitivity, specificity, NPV, PPV, likelihood ratios (LR+/–) and accuracy were used to find out the optimal cut-off value for CBD size.

Results: The most common pathology on ERCP was biliary lithiasis (500 cases), followed by benign CBD stricture combined with biliary lithiasis (14 cases), benign CBD stricture alone (5 cases) and malignant stricture alone
(2 cases). In 274 cases no biliary pathology was found. There was a correlation between CBD diameter and choledocholithiasis (Z=–11,7 p=0.0001, Mann-Whitney U test). The best cut-off (the best diagnostic accuracy of 75% with sensitivity of 76% and specificity of 72%) was found for CBD size equal to or greater than 9 mm. NPV was 100% for CBD diameter less than 5 mm. PPV was 95% for CBD greater than 16 mm and PPV was 100% for CBD diameter greater than 22 mm.

Conclusions: In cholecystectomized patients the best sonographic discriminator between present and absent biliary pathology is CBD size ł9 mm, but the clinical utility of this finding is far from expectations.