Diagnosis: Cholelithiasis with a dilated common bile duct (CBD), and intrahepatic ductal dilatation.
Discussion: Anatomically, the intrahepatic ducts form in the liver and form the common hepatic duct (CHD) in the porta hepatis. The CHD combines with the cystic duct to form the CBD. No distinction is typically made between the CHD and CBD; some experts go on to divide the CBD into a proximal, mid, and distal portion. Most do not. Measurements are made from inner wall to inner wall. A normal CBD is <6mm in diameter, while 6-8 mm is considered equivocal, and >8mm is dilated. I use the formula of adding 1mm for every decade of life (60yo=6mm). That said, after a cholecystectomy, the CBD may commonly dilate to as much as 1cm in diameter.
The intrahepatic ducts are more difficult to evaluate due to small diameter (<1mm in the periphery); they should always be <50% the size of the adjacent portal vessel Dilated intrahepatic biliary ducts may show a classic “shotgun” appearance; “too many tubes”; “antler signs”. Look for a stone in the CBD, though with the understanding that U/S only has a sensitivity of 15-55% for detection of CBD stones.
In this patient, cholelithiasis and a markedly dilated CBD were both noted on U/S. A CBD stone was suspected clinically, but not visible on U/S. She went on to have an MRCP, which showed multiple stones in the main bile duct. Biliary cannulation, sphincterotomy, and stone extraction were performed. The patient subsequently had a laparsoscopic cholecystectomy.