01Principles and purposeThe professional or clinical skill and the decisions it supports.
Modality selection is a reasoning task, not a ladder that every patient climbs. Begin by writing the question: gallbladder stones, acute gallbladder inflammation, duct obstruction, a small distal stone, a malignant level of obstruction, or a need to drain. Combine prior probability from symptoms and liver tests with what the last study could actually see. A technically limited ultrasound is not equivalent to a normal high-quality examination.
Ultrasound is accessible and radiation free, displaying gallstones, gallbladder wall changes and duct calibre, though bowel gas obscures the distal duct. MRCP surveys intrahepatic and extrahepatic ducts without endoscopy and helps plan intervention. EUS places high-frequency imaging next to the distal duct and pancreas, improving detection of small stones or ampullary lesions, but needs sedation and expertise. Neither MRCP nor diagnostic EUS decompresses an infected system; therapeutic EUS-guided biliary drainage is a specialist rescue technique outside this diagnostic sequence.
ERCP should enter the pathway with a therapeutic objective. Consent includes post-ERCP pancreatitis, bleeding after sphincter intervention, perforation, cholangitis and sedation-related harm, plus the possibility of failure. In severe cholangitis the question may be how to achieve drainage fastest; complete stone extraction can be staged. After any procedure, document whether the duct is cleared, whether a stent remains, and exactly who owns exchange, removal and definitive gallbladder treatment.
Key points
- 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.
- ERCP is chosen when drainage, extraction, sphincter therapy, sampling or stenting is anticipated; it carries pancreatitis, bleeding, infection and perforation risks.
- CT answers different questions, including alternative abdominal diagnoses, complications and some tumours, but is relatively insensitive for many cholesterol stones.
- The safest sequence changes in cholangitis: therapeutic access becomes urgent and diagnostic purity becomes secondary to decompression.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Typical biliary pain asks whether stones are present and whether the gallbladder shows inflammatory change; ultrasound usually answers this efficiently.
Jaundice, abnormal liver tests or duct dilatation raises a common-duct question even when ultrasound cannot see the stone.
Fluctuating cholestasis with negative MRCP may justify EUS because the ampulla and small distal stones are assessed at close range.
Cholangitis, confirmed obstructing stones or malignant blockage creates a drainage or tissue-intervention question rather than a purely diagnostic one.
A new syndrome after ERCP must be investigated on its own merits and not dismissed as expected procedural discomfort.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Ultrasound - Why
- Detect gallbladder stones, inflammation and duct dilatation.
- Interpretation and limitations
- Use with liver tests at the start of suspected gallstone disease. Operator, body habitus and bowel gas limit the distal duct and pancreas.
- 02
MRCP - Why
- Map bile and pancreatic ducts without cannulation.
- Interpretation and limitations
- Useful when ultrasound is negative for a duct stone but biochemical or calibre abnormalities persist; small stones and motion can still cause false negatives.
- 03
Endoscopic ultrasound - Why
- Look closely for tiny distal stones and ampullary or pancreatic lesions.
- Interpretation and limitations
- Highly informative after equivocal MRCP, but requires endoscopic expertise and sedation and does not itself clear the duct.
- 04
ERCP - Why
- Perform bile-duct therapy and selected sampling.
- Interpretation and limitations
- Specify extraction, sphincter intervention, stenting or drainage. Its complications make a vague diagnostic request inappropriate when non-invasive tests suffice.
- 05
Contrast CT - Why
- Assess alternative diagnoses, tumour, perforation or pancreatitis complications.
- Interpretation and limitations
- CT provides wide anatomical coverage but may miss radiolucent cholesterol stones; its role depends on the extra-biliary question and renal risk.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked case: choose MRCPResolve a demonstrated intermediate duct riskA 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.+
- 1Identify 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.
- 2Request MRCP according to the NICE sequence; it demonstrates a 6 mm distal common-bile-duct stone without a mass or intrahepatic obstruction.
- 3Refer 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.
- 4Verify 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.
02Worked case: choose ERCPTreat, do not merely imageA febrile jaundiced patient is hypotensive and ultrasound shows a dilated duct.+
- 1Recognise cholangitis and start resuscitation, cultures and antibiotics.
- 2Contact the therapeutic endoscopy team for urgent drainage with a defined goal of decompression.
- 3Use percutaneous or operative drainage when endoscopic access is unavailable or unsuccessful.
- 4Reassess perfusion, urine output, bilirubin and inflammatory markers after intervention to verify source control.
03Worked case: consider EUSInvestigate a hidden distal stoneA patient has recurrent transient jaundice, negative MRCP and persisting clinical suspicion of choledocholithiasis.+
- 1Review the quality and timing of prior imaging and exclude non-obstructive cholestasis.
- 2Choose EUS when detection of a small distal stone or ampullary lesion would lead directly to therapy.
- 3Avoid ERCP if probability remains too low to justify procedural harm.
- 4Communicate the result and next action to the patient and the responsible biliary team.
05Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- Record the exact clinical question on every request so the report can address the decision.
- Track liver-test trajectory while awaiting imaging because rising obstruction changes urgency.
- After EUS or ERCP, monitor sedation recovery and new pain, fever, bleeding or cardiorespiratory change.
- Document duct clearance, residual stones, stent type and planned removal or exchange date.
- Audit failed cannulation and post-ERCP adverse events as service-quality outcomes, not unavoidable background noise.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Normal ultrasound is conditional
It can exclude visible gallbladder stones more confidently than tiny distal duct stones hidden by gas.
MRCP maps before intervention
Non-invasive duct anatomy can prevent unnecessary cannulation and help the endoscopist or surgeon plan access.
EUS narrows uncertainty
Its greatest value is often between a non-diagnostic scan and an invasive therapeutic decision.
Drainage may be enough initially
During severe cholangitis, a short decompression procedure can be safer than prolonged attempts at complete clearance.
07Common pitfallsFrequent interpretation and management errors.
- 01
Ordering all four modalities sequentially without specifying what each will change.
- 02
Using diagnostic ERCP because it is available when MRCP or EUS could answer the question.
- 03
Waiting for MRCP while a patient with septic shock has convincing obstructed infection.
- 04
Omitting the follow-up plan for a temporary biliary stent.