RADIOLOGY: HEPATOBILIARY: Case# 32874: BREAST CA METS, BILIARY OBSTRUCTION., CHOLECYSTITIS. 64 year old white female with breast carcinoma, S/P left side radical mastectomy in 1986. The patient has recently had a history of biliary obstruction by tumor and a stent placed. There is a moderate amount of air in the biliary tree, mostly in the left hepatic lobe. Biliary stent is seen unchanged in position extending from the right hepatic duct into the duodenum. Since the previous exam, the gallbladder has gotten progressively larger with more prominent irregular wall thickening. Pericholecystic fluid is present and surrounding soft tissue inflammatory changes are seen which extend inferiorly to the hepatic flexure. Multiple small air bubbles are now seen within the gallbladder lumen and there appears to be discontinuity of the wall inferiorly. Perihepatic fluid is present which may communicate with the pericholecystic fluid. Small amount of free fluid is seen within the abdomen and pelvis in the parasplenic area, left pericolic gutter and pelvis. The stomach is distended and the duodenum is narrowed. The major causes of biliary obstruction are gallstones, tumor, stricture, and pancreatitis. The demonstration of dilated bile ducts is a key factor in diagnosing biliary obstruction via CT examination. Proximal to the point of obstruction, the biliary tree dilates, while bile ducts distal to the obstruction point remain normal or are reduced in size. CT findings will be falsely negative in the diagnosis of biliary obstruction if the biliary tree is prevented from dilating due to cirrhosis, cholangitis, or periductal fibrosis. CT findings of biliary obstruction include multiple branching, tubular, round or oval low density structures representing dilated intrahepatic biliary ducts course toward the porta hepatis; dilation of the common duct in the porta hepatis seen as tubular or oval fluid density structure greater than 7mm in diameter; enlargement of the common duct in the hepatoduodenal ligament (Mickeys right ear) to greater than 7mm in diameter; dilation of the common duct in the pancreatic head seen as a round fluid density structure larger than 7mm; and enlargement of the gallbladder to greater than 5cm in diameter, when the obstruction is distal to the cystic duct. CT is approximately 95% accurate in determining the presence, level, and cause of biliary obstruction.