Synopsis
Select biliary imaging by the exact unanswered question, disease probability and need for therapy, while avoiding diagnostic ERCP and delays to drainage in infected obstruction.
- Ultrasound is the initial structural test for suspected gallstone disease and is paired with liver blood tests.
- MRCP non-invasively maps ducts when ultrasound does not show a stone but duct dilatation or abnormal liver tests sustain suspicion.
- EUS can resolve small distal stones or ampullary lesions after inconclusive MRCP and may be paired with same-session ERCP in suitable services.
Key red flags
Shock or organ dysfunction with obstructive jaundice requires urgent drainage planning rather than completion of every diagnostic modality.
New severe pain, bleeding, fever or instability after ERCP raises concern for pancreatitis, perforation, haemorrhage or inadequate drainage.
Cholangitis, confirmed obstructing stones or malignant blockage creates a drainage or tissue-intervention question rather than a purely diagnostic one.
Reasoning priorities
Detect gallbladder stones, inflammation and duct dilatation.
Use with liver tests at the start of suspected gallstone disease. Operator, body habitus and bowel gas limit the distal duct and pancreas.
Worked reasoning
A stable 63-year-old with biliary pain has bilirubin 78 micromol/L, alkaline phosphatase 310 units/L and a 10 mm common bile duct on ultrasound, but no duct stone is seen and there is no fever, hypotension or organ dysfunction.
- Identify the unresolved common-duct-stone question from the dilated duct and abnormal liver tests, while confirming that the patient has no cholangitis requiring emergency drainage.
- Request MRCP according to the NICE sequence; it demonstrates a 6 mm distal common-bile-duct stone without a mass or intrahepatic obstruction.
- Refer for therapeutic ERCP, at which sphincterotomy and balloon extraction remove the stone and the completion cholangiogram shows free contrast drainage with no residual filling defect.
- Verify the observed response the next morning: pain has settled, bilirubin has fallen to 41 micromol/L and the patient remains afebrile, then arrange definitive gallbladder management.