What does a whole body abdomen CT (Computed Tomography) scan show with a gallstone?

CT Appearance of Gallstones on Abdominal Imaging

CT abdomen has approximately 75% sensitivity for detecting gallstones because up to 80% of gallstones are noncalcified and appear isodense to bile, making them invisible on CT imaging. 1, 2

What Gallstones Look Like on CT

Calcified Gallstones (20% of cases)

• Appear as bright white (hyperdense) structures within the gallbladder or bile ducts 1
• CT can detect partially or completely calcified biliary calculi with high confidence 1
• These stones are easily visible and create clear contrast against surrounding bile and soft tissue 3

Noncalcified Gallstones (80% of cases)

• Most gallstones are composed of cholesterol or bilirubinate and do NOT show up on CT 1, 2
• These stones are isodense (same density) as bile, rendering them essentially invisible 2
• This is the primary limitation of CT for gallstone detection 1, 2

Secondary Signs of Gallstone Disease on CT

When the stone itself is not visible, CT may show indirect evidence:

Biliary Obstruction

• Dilated intrahepatic and/or extrahepatic bile ducts (contrast-enhanced CT has 74-96% sensitivity for detecting biliary obstruction) 1, 2
• The common bile duct may appear enlarged (>6-10 mm) 1

Gallbladder Wall Changes

• Thickened gallbladder wall (>3 mm) suggesting chronic cholecystitis 3
• Pericholecystic fluid or inflammatory changes (best seen with IV contrast) 2

Complications

• Gallbladder hydrops (distended, fluid-filled gallbladder) 3
• Secondary liver abscesses 3
• Emphysematous cholecystitis (gas in the gallbladder wall) 2

Why CT is NOT First-Line for Gallstone Detection

Ultrasound is the recommended initial imaging modality with 96% accuracy for gallstone detection, compared to CT's 75% sensitivity. 1, 2

Key Limitations of CT

• Misses 80% of noncalcified stones 1, 2
• Exposes patients to radiation 2
• More expensive than ultrasound 2
• Less sensitive than ultrasound for detecting gallbladder stones 1

When CT is Appropriate

If CT is performed for gallstone evaluation, always use IV contrast because it allows detection of:

• Wall enhancement indicating acute cholecystitis 2
• Peribiliary enhancement suggesting cholangitis 4
• Complications such as perforation or abscess 2
• Alternative diagnoses causing right upper quadrant pain 2

Single-phase post-contrast CT is sufficient; adding a noncontrast phase provides minimal additional diagnostic value. 2

Clinical Algorithm

For Suspected Gallstones

1. Start with ultrasound (96% accuracy, no radiation, lower cost) 1, 2
2. If ultrasound shows dilated bile ducts or is equivocal, proceed to MRCP (85-100% sensitivity for bile duct stones) 5, 4
3. Reserve CT with contrast for suspected complications (cholangitis, perforation, alternative diagnoses) 1, 2

Common Pitfall to Avoid

Do not rely on CT to rule out gallstones—a negative CT does not exclude gallstone disease because most stones are radiolucent. 1, 2 If clinical suspicion remains high despite negative CT, proceed to ultrasound or MRCP. 5, 4