Radiologic work up of suspected biliary tree obstruction
US: US is the screening examination of choice for suspected biliary ductal disease. Doppler can readily differentiate biliary ducts from vasculature in the portal triad. A CBD diameter larger than 6 mm is more sensitive than dilated intrahepatic ducts in assessing early or partial biliary obstruction; however, the extrahepatic ductal diameter may increase with age, following cholecystectomy or previous resolved obstruction. Normal intrahepatic ducts are smaller than 2 mm in diameter and less than 40% of the diameter of the adjacent PV. With intrahepatic ductal dilatation (> 2 mm), tubular, low-echogenicity structures are seen to parallel the PVs, producing the “too many tubes” sign.
MDCT and MRI/MRCP: Once biliary disease is detected, MDCT or MRI are more efficacious in depicting the degree, site, and cause of obstruction because bowel gas commonly obscures US visualization of the distal CBD. MDCT and MRI/MRCP also provide more complete delineation of the entire CBD, especially with the use of coronal imaging.
ERCP or percutaneous transhepatic cholangiography: These imaging methods provide a more detailed evaluation than US, MDCT, or MRI/MRCP, but both modalities are invasive.