A 24-year-old woman with postprandial abdominal pain characteristic of biliary colic undergoes imaging. What is the best initial diagnostic study?

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

Answer: (A)

Abdominal ultrasound is the best initial study because it directly and efficiently looks for gallstones and assesses the gallbladder and biliary tree without radiation. In biliary colic, pain arises from transient cystic duct obstruction by stones, and ultrasound can detect these stones with high sensitivity. It can also show gallbladder wall thickening or pericholecystic fluid if inflammation is present, helping to distinguish uncomplicated biliary disease from more serious conditions.

CT scans are less reliable for detecting gallstones (many stones are radiolucent) and expose the patient to radiation, making them less ideal as a first test. Magnetic resonance imaging of the abdomen provides excellent soft-tissue detail but is more costly, less accessible, and not needed initially when ultrasound can diagnose gallstones or biliary pathology. Magnetic resonance cholangiopancreatography is particularly useful for evaluating the biliary ducts and detecting CBD stones when there is a high suspicion after initial testing, but it’s not the first-line study.