Figure 23b. Choledocholithiasis in a 46-year-old man who presented with right flank pain. (a) Initial unenhanced helical CT scan shows mild intrahepatic biliary ductal dilatation (arrow). No obstructing ureteral stone was found. (b) Unenhanced CT scan obtained slightly caudad to a shows high attenuation within the duct (arrow). Findings at endoscopic retrograde cholangiopancreatography helped confirm the presence of choledocholithiasis.