Imaging for surgeons
Each test answers a different question. Knowing what it cannot show matters as much as knowing what it can.
Reviewed against its sources on 25 October 2026.
- Ultrasound first, always; a normal duct on ultrasound does not rule out a duct stone.
- CT is for doubt and complications; for acute cholecystitis it matches ultrasound and is the next test when ultrasound is equivocal.
- MRCP or endoscopic ultrasound decides who needs ERCP; HIDA is the most accurate test when ultrasound and CT leave doubt.
01Ultrasound: the first test
- Every patient with suspected gallstone disease has an ultrasound first. It is cheap and fast, uses no radiation, and finds gallbladder stones well.
- It is a weak test for acute cholecystitis and a poor test for duct stones. A normal duct on ultrasound does not rule out a stone in it.
- Read the report against the patient. A thick wall, fluid or a “positive Murphy’s” means little on its own.
| In the report | What it tells you | Watch out for |
|---|---|---|
| Stones: mobile, shadowing | Gallstone disease is likely the cause | A stone impacted in the neck does not move; it may be the cause of cholecystitis |
| Wall thickening, pericholecystic fluid, distension | Support acute cholecystitis with the right clinical picture | The wall is also thick in heart failure, cirrhosis, ascites, low albumin and hepatitis |
| Sonographic Murphy’s sign | Tenderness over the gallbladder under the probe | Lost after opiates, and in the elderly or diabetic patient |
| Gas in the wall or lumen, a broken wall, a collection | Emphysematous, gangrenous or perforated gallbladder: a harder operation | Plan for a senior surgeon and a bail-out |
| Common bile duct diameter | Dilated duct raises the chance of a duct stone | Write the number in the notes; it decides the next test with the liver tests |
| Polyp: size, stalk, wall | Size and shape decide follow-up or surgery | See gallbladder polyps |
| Focal or irregular wall thickening, a mass, liver invasion | Possible gallbladder cancer | Cross-sectional imaging and a hepatobiliary opinion before any operation |
- Look at the images, or ask the radiologist, when the report will change what you do.
- Combine the duct diameter with the liver tests to grade the risk of a duct stone. See when to image the duct.
- Repeat the scan when the picture changes: a patient with colic who becomes septic needs a new look. Expert opinion
- Treat a normal duct on ultrasound as proof there is no stone.
- Call a thick wall cholecystitis in a patient with heart failure or cirrhosis without other signs.
- Operate on an ultrasound report you have not checked against the clinical picture. Expert opinion
Sources
Acute cholecystitis: Kiewiet et al., Radiology 2012;264:708-720, meta-analysis of 57 studies. Ultrasound sensitivity 81 percent (95% CI 75 to 87), specificity 83 percent (74 to 89); the authors note a wide margin of error. Systematic review Duct stones: Gurusamy et al., Cochrane 2015. Ultrasound sensitivity 0.73 (95% CI 0.44 to 0.90), specificity 0.91 (0.84 to 0.95). In one study of 262 people, bilirubin above about 1.3 mg/dL had a sensitivity of 0.84 and specificity of 0.91. The authors warn that many people have duct stones despite a negative ultrasound or normal liver tests. Systematic review The causes of a thick wall other than cholecystitis are standard radiological teaching.
02CT: for doubt and for complications
- CT is not a gallstone test. Many stones have the same density as bile and do not show.
- It earns its place when the diagnosis is in doubt, when the gallbladder may be gangrenous, perforated or emphysematous, when cancer is suspected, and after an operation that is not going well.
- For acute cholecystitis itself, CT performs about as well as ultrasound in a 2024 meta-analysis, and 2024 IDSA guidance suggests CT as the next test when the ultrasound is equivocal and suspicion persists. Ultrasound stays the first test.
Before the operation
Another diagnosis is possible: perforated ulcer, pancreatitis, appendicitis, a colonic or renal cause. The gallbladder may be gangrenous (a wall that does not enhance), emphysematous (gas in the wall) or perforated (a defect and a collection). A mass or liver invasion is suspected.
Suspected cancer: stage with CT (and MRI as needed) before any operation
After the operation
Pain, fever, ileus or a rising CRP after a cholecystectomy: CT shows a collection, free fluid, bleeding or a bowel injury. It does not show the bile ducts well; magnetic resonance cholangiopancreatography (MRCP) does.
A collection after cholecystectomy is bile until proved otherwise. See bile leak
In pancreatitis
Contrast CT is for diagnostic doubt on admission and for the patient who is not improving. Early CT rarely changes treatment and can understate necrosis. Expert opinion
Source
Kiewiet et al., Radiology 2012: only one study of CT met the inclusion criteria (sensitivity 94 percent, specificity 59 percent), so in 2012 the authors judged CT “insufficiently evaluated” for acute cholecystitis. Systematic review The 2024 meta-analysis of 64 studies, five of them head to head, found CT sensitivity 83.9 percent (95% CI 78.4 to 88.2) and specificity 94 percent (82 to 98) against 79.0 and 93.6 percent for ultrasound in the same patients, with the two tests agreeing in 82 percent of cases; a second test ordered after the first changed management in 4 to 8 percent (de Oliveira et al., Eur Radiol 2024). Systematic review The IDSA 2024 guideline suggests ultrasound as the first test and CT as the next test when the ultrasound is equivocal or non-diagnostic and clinical suspicion persists, with HIDA or MRI after both (all conditional, very low to low certainty) (IDSA 2024, Clin Infect Dis). Guideline The other uses listed above are standard practice. Expert opinion
03MRCP and endoscopic ultrasound for duct stones
- Both are accurate. Use one of them for the patient at intermediate risk of a duct stone, so that endoscopic retrograde cholangiopancreatography (ERCP) is kept for treatment and not used to make the diagnosis.
- MRCP needs no endoscope and no sedation, and it also shows the duct anatomy. It misses some stones under about 5 mm.
- Endoscopic ultrasound finds small stones better, and an ERCP can follow in the same session, but it needs an endoscopist and sedation.
- Choose by local access: MRCP is the usual test in the UK and India; endoscopic ultrasound where it is quick to get. Expert opinion
- Look at the MRCP for anatomy as well as stones: a low or parallel cystic duct, an aberrant right posterior sectoral duct. Expert opinion
- Use MRCP to map the ducts after a suspected injury. See bile duct injury.
- Treat a normal MRCP as excluding a small stone when the liver tests keep rising.
- Use the MRCP as a road map in place of the Critical View of Safety. Anatomy on a scan does not replace identification in the operation. Expert opinion
- Send a patient with cholangitis for MRCP first. Drainage comes first. See treatment of cholangitis.
Sources
Giljaca et al., Cochrane 2015: endoscopic ultrasound sensitivity 0.95 (95% CI 0.91 to 0.97), specificity 0.97 (0.94 to 0.99); MRCP sensitivity 0.93 (0.87 to 0.96), specificity 0.96 (0.90 to 0.98). Both tests had high accuracy; the authors asked readers to interpret the results with caution because the studies were of poor quality. Systematic review Risk groups for duct stones: Buxbaum et al., ASGE guideline 2019. Guideline
04HIDA scan (cholescintigraphy)
- A radioactive tracer is taken up by the liver and excreted in bile. If the gallbladder does not fill, the cystic duct is blocked, which in the right patient means acute cholecystitis.
- It is the most accurate single test for acute cholecystitis, but it takes hours, needs a nuclear medicine department and is not available everywhere.
- Use it when ultrasound, and usually CT, have left the diagnosis open and the decision to operate depends on the answer. IDSA 2024 places it after CT.
Useful for
Suspected acute cholecystitis that ultrasound, and usually CT, have left in doubt. Suspected acalculous cholecystitis (see acalculous cholecystitis). Showing that bile is leaking after a cholecystectomy, though not exactly where.
False results
The gallbladder may not fill without cholecystitis after a long fast, on parenteral nutrition, in severe illness and in liver disease. A patient who has just eaten may fill slowly. Expert opinion
Gallbladder ejection fraction
Used for suspected functional gallbladder pain without stones. The evidence that a low ejection fraction predicts relief after cholecystectomy is weak. Contested
Source
Kiewiet et al., Radiology 2012: cholescintigraphy sensitivity 96 percent (95% CI 94 to 97), specificity 90 percent (86 to 93); MRI 85 and 81 percent. “Cholescintigraphy has the highest diagnostic accuracy of all imaging modalities in detection of acute cholecystitis.” Systematic review
05Cholangiograms: on the table and after
- An intra-operative cholangiogram is only as safe as its reading. Read it in a fixed order before anything is divided: technique, both hepatic systems, cystic duct and junction, common duct, flow into the duodenum.
- A missing right hepatic system, a cut-off with no filling above it, or contrast outside the ducts is an injury until proved otherwise. Stop.
- After the operation, a cholangiogram comes from MRCP, ERCP or a percutaneous route. Each answers a different question.
The step-by-step reading is on the indocyanine green (ICG) page: how to read an intra-operative cholangiogram. Routine or selective use is covered under routine or selective cholangiography.
| After the operation | Best for | Limits |
|---|---|---|
| MRCP | Mapping the ducts: a stone, a stricture, a transection, the level of an injury | Shows no leak unless contrast is used; no treatment |
| ERCP | Leak from the cystic stump or a duct of Luschka, a retained stone: diagnosis and stent or clearance at once | Shows nothing above a complete transection or clip on the common duct |
| Percutaneous cholangiogram | The ducts above a complete block, with drainage at the same time | Hard with undilated ducts; for specialist units |
Source
A correct cholangiogram shows the anatomy, filling of the right and left hepatic ducts and flow into the duodenum without filling defects (Hope et al., SAGES clinical spotlight review on intra-operative cholangiography). Guideline The table of post-operative tests is standard hepatobiliary practice. Expert opinion
06Which test, when
| The question | First test | Then |
|---|---|---|
| Is it gallstones? | Ultrasound | Repeat or endoscopic ultrasound if the story is typical and the scan is normal |
| Is it acute cholecystitis? | Ultrasound with the Tokyo criteria | Equivocal and suspicion persists: CT next (IDSA 2024), which also shows another diagnosis or a complication. Still unclear: HIDA or MRI. Where HIDA is quick to get, some units go to it straight after the ultrasound because it is the most accurate single test (Kiewiet 2012); both routes are reasonable |
| Is there a duct stone? Intermediate risk | MRCP or endoscopic ultrasound | ERCP only to treat; or cholangiography and duct exploration at the operation |
| Is there a duct stone? High risk | ERCP before surgery, or cholangiography and exploration at surgery | See bile duct exploration |
| Fever, jaundice and pain | Bloods, cultures, ultrasound | Drainage by grade; MRCP only once the patient is safe. See cholangitis |
| Jaundice or pain after cholecystectomy | Liver tests, ultrasound or CT | MRCP to map; ERCP to treat a stone or leak; refer early if the duct may be injured |
| A mass or focal thickening | CT (and MRI) | Hepatobiliary opinion before any operation. See gallbladder cancer |
| Pancreatitis not improving after 2 to 3 days | Contrast CT | MRCP or endoscopic ultrasound if a duct stone is still suspected |
This table is a summary of the pages linked from it and of standard practice. The acute cholecystitis row follows the IDSA 2024 sequence (ultrasound, then CT, then HIDA or MRI; all conditional recommendations) and notes the HIDA-first alternative that rests on its accuracy in the 2012 meta-analysis. Local access often decides between equally good tests. Guideline Expert opinion
07What examiners ask
- The ultrasound shows a 7 mm duct and no stone; the bilirubin is 2.3 mg/dL. Does the patient have a duct stone, and what next?
- Why is CT a poor test for gallstones, and when do you ask for one?
- MRCP or endoscopic ultrasound: how do you choose?
- What is a HIDA scan, and when would it change your decision?
- Read this cholangiogram aloud. What would make you stop?
Test yourself further: Practise questions on Imaging for surgeons in the Exam zone.