What imaging is recommended for suspected gallstones (cholelithiasis)?

Imaging for Gallstones: Ultrasound as First-Line Diagnostic Tool

Abdominal ultrasound should be the initial imaging modality for suspected gallstones due to its high accuracy, wide availability, lack of radiation exposure, and cost-effectiveness. 1

Diagnostic Approach for Gallstones

First-Line Imaging

• Abdominal Ultrasound
  • Accuracy of 96% for detection of gallstones 1
  • Highly specific for cholelithiasis
  • Non-invasive with no radiation exposure
  • Cost-effective and widely available
  • Can differentiate gallstones from gallbladder sludge, polyps, or masses 1

When Initial Ultrasound is Equivocal/Non-Diagnostic

If the initial ultrasound is inconclusive but clinical suspicion remains high:

1. CT with IV contrast should be obtained as subsequent imaging 1

   • More sensitive than ultrasound for diagnosing acute cholecystitis (92% vs 79%) 2
   • Less sensitive than ultrasound for identifying gallstones (60% vs 87%) 2

2. If both ultrasound and CT are inconclusive:

   • MRI/MRCP or HIDA scan should be considered 1
   • HIDA scan has high sensitivity (97%) and specificity (90%) for detecting acute cholecystitis 1

Special Populations

Pregnant Patients

• Ultrasound or MRI can be used as initial diagnostic imaging modality 1
• No clear recommendation for one over the other due to limited evidence 1
• Avoid CT due to radiation exposure

Children

• Follow adult imaging pathway, starting with ultrasound 1
• Ultrasound is particularly advantageous due to lack of radiation exposure

Key Ultrasound Findings in Gallstone Disease

• Visualization of echogenic foci with acoustic shadowing (gallstones)
• Gallbladder wall thickening (>3mm) may indicate inflammation
• Sonographic Murphy's sign (92.2% positive predictive value for acute cholecystitis) 3
• Pericholecystic fluid (may indicate inflammation)

Pitfalls and Limitations

• Ultrasound is operator-dependent 4
• May miss small stones (<5mm) in the common bile duct 1
• Sensitivity for common bile duct stones ranges from 22.5% to 75% 1
• Bowel gas may obscure visualization of the subhepatic common duct 1
• False positives can occur with polyps, sludge, and other conditions causing wall thickening 3

Diagnostic Algorithm

1. Start with abdominal ultrasound for all patients with suspected gallstones
2. If ultrasound is positive for gallstones → diagnosis confirmed
3. If ultrasound is negative but clinical suspicion remains high:
   • Consider CT with IV contrast
   • If CT is negative but suspicion remains → proceed to MRI/MRCP or HIDA scan
4. For suspected common bile duct stones with normal ultrasound:
   • Consider MRCP or endoscopic ultrasound 1, 4

Ultrasound remains the cornerstone of gallstone diagnosis with excellent accuracy, safety profile, and accessibility, making it the optimal first-line imaging modality for suspected gallstones.