Which imaging modality is second-line but excellent for identifying stones in the biliary tract in suspected choledocholithiasis?

• A. Abdominal radiograph
• B. Magnetic resonance cholangiopancreatography
• C. Magnetic resonance imaging of the abdomen
• D. Ultrasound

Answer: (B)

When choledocholithiasis is suspected, the goal is to noninvasively visualize the biliary tree to detect stones. An abdominal ultrasound is often done first because it can show gallstones and ductal dilation, but it may miss stones within the common bile duct. Magnetic resonance cholangiopancreatography provides a noninvasive, highly sensitive and specific view of the biliary and pancreatic ducts without needing contrast, making it superb for identifying stones in the biliary tract. It also helps map anatomy and plan next steps, such as ERCP if stone extraction is needed. While MRCP excels at detection, it does not treat stones, which is where ERCP comes in for intervention. Other options, like a plain abdominal radiograph, are not reliable for most biliary stones, and a general MRI of the abdomen is less focused on the ductal system than MRCP.