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# Gallbladder and bile ducts: ultrasound, CT and MRCP

- Finding

Ultrasound is the first look at the gallbladder and bile ducts; MRCP maps the ducts without a tube; ERCP is kept for treatment.

Updated Nov 13, 2026

## Key points

- Ultrasound first: shadowing mobile stones, thick wall, fluid and a positive sonographic Murphy sign mean acute cholecystitis.
- HIDA: a gallbladder that never fills means a blocked cystic duct.
- MRCP to look at the ducts; ERCP to treat them.
- Central branching gas is pneumobilia; peripheral gas is portal venous gas.

## What it is

Ultrasound is the first test for right upper quadrant pain and for jaundice: it is quick, cheap, uses no radiation and is very good at seeing gallstones, the signs of acute cholecystitis and whether the bile ducts are dilated. Cholescintigraphy (a HIDA scan) is the most sensitive test for acute cholecystitis when ultrasound is unclear: if the tracer never fills the gallbladder, the cystic duct is blocked. CT is weaker for stones, many of which look like bile, but is better for complications, other causes of pain and tumours. Magnetic resonance cholangiopancreatography (MRCP) shows the bile and pancreatic ducts without radiation or a scope and is the non-invasive test for a stone in the common bile duct. Endoscopic retrograde cholangiopancreatography (ERCP) fills the ducts with contrast through a scope in the duodenum; because it carries risks, above all pancreatitis, it is used to treat (remove stones, place stents, drain an infected duct) rather than just to look.

## What it looks like

- Gallstone on ultrasound: a bright, mobile focus inside the gallbladder with a clean posterior acoustic shadow; it moves when the patient turns.
- Sludge: low-level echoes that layer and move, without a shadow. A gallbladder packed with stones shows the wall-echo-shadow (WES) sign.
- Acute cholecystitis: stones plus wall thickening (over about 3 mm), pericholecystic fluid, a distended gallbladder and a stone stuck in the neck.
- Sonographic Murphy sign: maximal tenderness when the probe presses directly over the gallbladder.
- Biliary obstruction: a common bile duct wider than about 6 mm (it widens a little with age and after cholecystectomy) and dilated ducts inside the liver.
- Gas in the gallbladder wall (emphysematous cholecystitis) or a torn, irregular wall (gangrene, perforation) are emergencies.

## Why it looks that way

- Stones reflect almost all the sound and block it, which casts the shadow; sludge reflects weakly and lets sound through.
- A blocked cystic duct traps bile, so the gallbladder swells and its wall becomes oedematous and inflamed.
- Bile cannot drain past a stone or tumour, so the ducts above it widen; the level of the dilatation points to the level of the block.

| Study | Best for | Limits |
| --- | --- | --- |
| Ultrasound | Stones, cholecystitis, dilated ducts; first test | Distal duct often hidden by bowel gas |
| HIDA scan (cholescintigraphy) | Acute cholecystitis when ultrasound is unclear | Slow; does not show stones themselves |
| CT with IV contrast | Complications, pancreatitis, tumours, other causes | Misses many stones; radiation |
| MRCP | Duct stones and strictures without radiation | Longer study; implants and claustrophobia |
| ERCP | Treatment: stone removal, stents, drainage | Invasive; post-ERCP pancreatitis, bleeding, perforation |

## Differential and pitfalls

- Gallstones are common and often incidental: they must match the pain and the findings before they are blamed.
- A normal CT does not exclude gallstones; ultrasound is the test for stones.
- Gas in the bile ducts (pneumobilia) gathers centrally near the hilum; portal venous gas reaches the periphery of the liver and is more ominous.
- Painless jaundice with a palpable, non-tender gallbladder (Courvoisier sign) suggests a tumour of the pancreatic head or distal duct: CT, not ERCP, first.
- A stone in the gallbladder neck or cystic duct that compresses the common hepatic duct (Mirizzi syndrome) can mimic a duct stone.

## Next step

- Right upper quadrant pain: ultrasound first; add a HIDA scan if acute cholecystitis is suspected and ultrasound is inconclusive.
- Jaundice or cholestatic liver tests: ultrasound to see if the ducts are dilated, then MRCP or CT depending on the suspected cause.
- Suspected common bile duct stone without cholangitis: MRCP (or endoscopic ultrasound where available) before deciding on ERCP.
- Fever, jaundice and pain (cholangitis), especially with hypotension or confusion: resuscitate and call gastroenterology and surgery for urgent ERCP drainage.
- Gas in the wall, a perforated gallbladder or portal venous gas: call the surgeon and the radiologist now.

## Test yourself

Think of the answer, then tap the question to see it.

## What distinguishes a gallstone from sludge on ultrasound?

A stone is a bright mobile focus with a clean acoustic shadow; sludge gives layering low-level echoes without a shadow.

## What is the sonographic Murphy sign?

Maximal tenderness when the ultrasound probe presses directly over the gallbladder; it supports acute cholecystitis.

## Why is ERCP not used just to look for a common bile duct stone?

It is invasive and can cause pancreatitis, bleeding or perforation; MRCP shows the ducts without those risks, so ERCP is kept for treatment.

## What does a HIDA scan show in acute cholecystitis?

The tracer goes into the liver, ducts and bowel but never fills the gallbladder, because the cystic duct is blocked.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/radiology/gallbladder-and-bile-ducts-ultrasound-ct-and-mrcp/)

## Elsewhere in DurgiPedia

- [Murphy sign](https://durgical.com/en/clinical-exam/murphy-sign/)
- [Jaundice: prehepatic, hepatic and posthepatic](https://durgical.com/en/clinical-exam/jaundice-prehepatic-hepatic-and-posthepatic/)
- [Courvoisier sign](https://durgical.com/en/clinical-exam/courvoisier-sign/)

## Connections

## Related 6

- [Which abdominal study to order, by complaint](https://durgical.com/en/radiology/which-abdominal-study-to-order-by-complaint/)
- [Ultrasound: echogenicity, probes, Doppler and artefacts](https://durgical.com/en/radiology/ultrasound-echogenicity-probes-doppler-and-artefacts/)
- [Imaging in pancreatitis: when and what](https://durgical.com/en/radiology/imaging-in-pancreatitis-when-and-what/)
- [Calcifications on the abdominal X-ray: stones and vessels](https://durgical.com/en/radiology/calcifications-on-the-abdominal-x-ray-stones-and-vessels/)
- [CT of the acute abdomen: what to look for](https://durgical.com/en/radiology/ct-of-the-acute-abdomen-what-to-look-for/)
- [Nuclear medicine and PET: how they work](https://durgical.com/en/radiology/nuclear-medicine-and-pet-how-they-work/)

## Related conditions 5

- [Gallstones (cholelithiasis)](https://durgical.com/en/conditions/gallstones/)
- [Acute cholecystitis](https://durgical.com/en/conditions/acute-cholecystitis/)
- [Choledocholithiasis](https://durgical.com/en/conditions/choledocholithiasis/)
- [Acute cholangitis](https://durgical.com/en/conditions/acute-cholangitis/)
- [Pancreatic cancer](https://durgical.com/en/conditions/pancreatic-cancer/)

[← All of radiology](https://durgical.com/en/radiology/)

Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: [Acute Cholecystitis](https://www.ncbi.nlm.nih.gov/books/NBK459171/) (StatPearls (NCBI Bookshelf), 2025); [Gallstones (Cholelithiasis)](https://www.ncbi.nlm.nih.gov/books/NBK459370/) (StatPearls (NCBI Bookshelf), 2026); [Endoscopic Retrograde Cholangiopancreatography](https://www.ncbi.nlm.nih.gov/books/NBK493160/) (StatPearls (NCBI Bookshelf), 2025).

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Source: https://durgical.com/en/radiology/gallbladder-and-bile-ducts-ultrasound-ct-and-mrcp/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/radiology/gallbladder-and-bile-ducts-ultrasound-ct-and-mrcp/