Are the Echogenicities on Intraductal Ultrasonography Really Biliary Microlithiasis?

Background Intraductal ultrasonography (IDUS) is a useful procedure for diagnosing microlithiasis in the bile duct but it is not easy to differentiate between tiny echogenicity and real microlithiasis. We compared the echogenicity seen on IDUS and the findings of bile microscopy (BM) of bile that was collected in the common bile duct (CBD) to determine whether the echogenicity seen on IDUS is real microlithiasis. Methods This prospective study involved a total of 30 patients who experienced biliary pain ( n = 11), acute cholecystitis ( n = 11) or indeterminate pancreatitis ( n = 8) without a filling defect or obstruction in the bile duct. IDUS was performed during endoscopic retrograde cholangiopancreatography (ERCP), followed by bile aspiration for BM. Endoscopic sphincterotomy (EST) was performed if definite echogenic materials were observed on IDUS. Results Of the 30 patients, 23 (77%) had echogenic materials visible in the CBD on IDUS. Of these 23 patients, 13 (57%) were found to have biliary crystals by BM. The size of the echogenic materials was the only significant factor associated with BM positivity. Using the receiver operating curve, the optimal size of the echogenicity to differentiate real microlithiasis was 1.4 mm. Conclusions Optimal concordance between IDUS and BM was observed when the size of the microlithiasis was greater than 1.4 mm; under these conditions the sensitivity and specificity were 71% and 75%, respectively. This information may be useful when deciding whether to perform endoscopic sphincterotomy.