ERCP and Endoscopic Ultrasound Indications
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Direct answer
ERCP, or endoscopic retrograde cholangiopancreatography, is an endoscopic procedure used mainly to treat biliary and pancreatic duct obstruction. Endoscopic ultrasound uses an echo-endoscope to image and sample the pancreas, bile duct wall and regional lymph nodes. ERCP is therapeutic for stones, cholangitis and malignant obstruction, whereas EUS is the most useful test for staging pancreatic tumours and sampling masses. Post-ERCP pancreatitis is the most common complication.
What you must remember
- Bile duct stones: ERCP with sphincterotomy and stone extraction is the standard therapeutic route for choledocholithiasis.
- Acute cholangitis: urgent biliary drainage by ERCP is needed once the patient is resuscitated and on antibiotics.
- Malignant obstruction: ERCP can place biliary or pancreatic stents for palliation or preoperative drainage, with brushings for cytology.
- EUS staging: highly accurate for local staging of pancreatic head tumours and small lesions, including regional nodes.
- EUS-guided sampling: fine needle aspiration or biopsy of pancreatic masses and suspicious nodes is a key EUS indication.
- MRCP: a non-invasive test that is the first choice when biliary or duct disease is suspected but intervention is not yet planned.
- Post-ERCP pancreatitis: the commonest complication, reduced by rectal indomethacin and pancreatic duct stenting in high-risk patients, with fluid hydration.
- Other ERCP complications: bleeding after sphincterotomy, perforation and cholangitis.
Matching the clinical question to the right test
The choice depends on the probability of a stone and on whether treatment is needed at the same sitting. Each row answers a question that the exam commonly frames as a stem.
| Clinical question | First choice | Why |
|---|---|---|
| Probable bile duct stone with cholangitis | ERCP | Stones can be extracted and the duct drained at the same sitting |
| Intermediate probability of bile duct stone | MRCP or EUS | Neither carries the risks of ERCP, and ERCP follows only if a stone is confirmed |
| Pancreatic head mass needing staging | EUS with fine needle aspiration | Assesses the tumour, adjacent vessels and nodes, and samples tissue |
| Malignant biliary stricture | ERCP with stent | Relieves obstruction and allows brushings for cytology |
| Recurrent pancreatitis without stones | MRCP or EUS first | Defines duct anatomy and finds microlithiasis, pancreas divisum or a small mass before any ERCP |
Diagnostic ERCP alone is now avoided, because MRCP or EUS can answer the diagnostic question without ERCP's complication risk. ERCP is reserved for patients in whom a therapeutic intervention is needed in the same session.
Where the exam tries to catch you
The exam tests whether you choose the least invasive test that answers the question.
- Trap: ordering diagnostic ERCP for every suspected stone Correct: MRCP or EUS is first for intermediate probability, and ERCP is kept for when treatment is needed.
- Trap: treating post-ERCP abdominal pain as a bleed alone Correct: pancreatitis is the commonest complication, so amylase or lipase and the pain pattern are assessed first.
- Trap: assuming a normal liver function test excludes a bile duct stone Correct: small stones can coexist with normal bilirubin, so imaging is needed when suspicion remains.
Frequently asked questions
Which investigation should precede ERCP for suspected bile duct stones?
MRCP or EUS is usually performed first when the probability of bile duct stones is intermediate, since neither carries the risks of ERCP. ERCP is reserved for high-probability cases that need immediate extraction or drainage.
What is the most common complication of ERCP?
Post-ERCP pancreatitis is the most common complication of ERCP, presenting with epigastric pain and raised pancreatic enzymes after the procedure. Rectal indomethacin and pancreatic duct stenting reduce its risk in high-risk patients.
Why is EUS preferred for staging pancreatic cancer?
EUS shows the pancreatic parenchyma, tumour margins, adjacent vessels and regional lymph nodes at high resolution. It also allows fine needle aspiration of suspicious nodes or masses, which is why it is valued for locoregional staging before resection.
When is ERCP indicated in acute cholangitis?
ERCP is indicated urgently in acute cholangitis once the patient is resuscitated and on antibiotics, to decompress the obstructed bile duct. Early biliary drainage is the key treatment, and the timing depends on the severity grade of the cholangitis.