Endoscopic Ultrasonography and Intraductal Ultrasonography in the Diagnosis of the Biliary Tract Diseases

We outline the present status of endoscopic ultrasonography (EUS) and intraductal ultrasonography (IDUS) in the diagnosis of biliary tract lesions. An echoendoscope, whichis equipped with a high-frequency probe (7. 5 to 20 MHz) at its end, has recently become essential for high-qualityimaging and diagnosis of pancreatobiliary diseases. A thin ultrasound probe, which is a catheter equipped with a high-frequency probe (7. 5 to 30 MHz), can provide a precise echogram from the intraluminal (gastrointestinal) or intraductal (from pancreatobiliary duct) aspect. The role of EUS in gallbladder lesions is for the precise investigation of gallbladder polyps and wall thickening, negative cholecystogram by ERCP, and for the staging of gallbladder carcinomas. The indications of EUS and IDUS for bile duct lesions include the diagnosis of small residual commonbile duct stones after endoscopic extraction, differential diagnosis of biliary strictures, the diagnosis ofpancreatobiliary maljunction, and the staging of biliary duct carcinomas. EUS and IDUS are clinically useful in the differential diagnosis of enlargement of papilla of Vater andthe staging of periampullary carcinomas. Recent advances in imaging techniques and refinements of the EUS procedure such as the electric radial echoendoscope, contrast-enhanced EUS or IDUS, three-dimensional EUS or IDUS, and endoscopic elastography have become available for clinical use. These modalities are expected to improve the existing diagnostic accuracy of EUS for biliary tract lesions.