USMLE® Step 1 style questions USMLE
A 75-year-old man comes to the emergency room because of jaundice, light-colored stools, and unintentional weight loss. He denies abdominal pain or irregularity of bowel function, but has felt a bulging lump in his right upper quadrant (RUQ). A RUQ ultrasound does not show any abnormalities but a non-contrast abdominal CT shows dilated biliary ducts throughout the liver parenchyma. The hepatic ducts, gallbladder, cystic duct, and common biliary duct all appear normal. Which of the following is the most likely diagnosis?