Percutaneous transhepatic cholangiography consists of inserting a cannula into one of the intrahepatic bile ducts through a long biopsy needle and injecting x-ray contrast material directly into the duct. This procedure outlines the biliary duct system and both confirms biliary tract obstruction by demonstrating a dilated duct system and pinpoints the location of the obstruction. The technique is not easy and requires considerable experience; more than 25% of attempts fail (most often in patients with intrahepatic obstruction due to liver cell damage). There is a definite risk (although very small) of producing bile peritonitis, which occasionally has been fatal. Preparation for surgical intervention should be made in advance in case this complication does develop.