What scan is used to diagnose cholecystitis?

Ultrasound is the First-Line Imaging for Diagnosing Cholecystitis

Ultrasound should be used as the initial imaging modality for diagnosing suspected cholecystitis due to its excellent diagnostic accuracy, wide availability, lack of radiation exposure, and ability to evaluate gallbladder morphology. 1, 2

Diagnostic Approach for Cholecystitis

First-Line Imaging: Ultrasound

• Ultrasound has 88% sensitivity and 80% specificity for acute cholecystitis, with 96% accuracy for detection of gallstones 1
• Key ultrasound findings to evaluate include:
  • Presence or absence of gallstones
  • Gallbladder wall thickness (>3mm is abnormal)
  • Sonographic Murphy sign (pain when pressing on the gallbladder)
  • Pericholecystic fluid
  • Common bile duct diameter measurement 1, 3
• Ultrasound is preferred over other imaging modalities due to shorter examination time, no radiation exposure, and ability to evaluate gallbladder morphology 3, 1
• Despite being operator-dependent and potentially limited in obese patients, ultrasound remains the first-choice imaging test 3, 4

Second-Line Imaging (If Ultrasound is Equivocal/Non-diagnostic)

• CT with IV contrast is recommended as the next imaging step if ultrasound is inconclusive and clinical suspicion persists 3
• CT can detect features of acute cholecystitis such as:
  • Gallbladder wall thickening
  • Pericholecystic inflammation
  • Gas formation
  • Hemorrhage 3
  • Adjacent liver parenchymal hyperemia (only visible with IV contrast) 3
• CT is particularly valuable for detecting complications of cholecystitis (emphysematous, gangrenous, perforated) 5, 6
• CT may have higher sensitivity than ultrasound in certain clinical scenarios (92% vs 79% in one study) 7

Third-Line Imaging (If Both Ultrasound and CT are Inconclusive)

• If both ultrasound and CT are equivocal and clinical suspicion remains high, either:
  • MRI/MRCP (Magnetic Resonance Cholangiopancreatography) or
  • HIDA scan (Hepatobiliary Iminodiacetic Acid scan) should be performed 3
• HIDA scan has the highest sensitivity (97%) and specificity (90%) for acute cholecystitis but requires several hours of fasting before the test 3, 1
• MRI/MRCP provides better visualization of surrounding structures and faster results but is more costly than HIDA 3

Special Populations

Pregnant Patients

• For pregnant patients with suspected cholecystitis, either ultrasound or MRI should be used as the initial imaging modality to avoid radiation exposure 3, 1
• No clear recommendation exists favoring one over the other in pregnancy 3

Children

• Although evidence is limited due to the uncommon nature of cholecystitis in children, the same imaging pathway as adults is reasonable 3
• Ultrasound should be the first-line imaging to minimize radiation exposure 3

Potential Pitfalls and Limitations

• Ultrasound sensitivity decreases with time between imaging and surgery, falling below 50% after 140 days 4
• Ultrasound may miss approximately 25% of acute cholecystitis cases and over 50% of chronic cholecystitis cases 4
• CT has limited sensitivity (approximately 75%) for detecting gallstones compared to ultrasound (87%) 3
• Relying solely on sonographic Murphy sign is not recommended due to its relatively low specificity 1
• Technical limitations such as bowel gas or body habitus may affect ultrasound diagnostic accuracy 8

Conclusion

For suspected cholecystitis, a systematic imaging approach should begin with ultrasound, followed by CT with IV contrast if ultrasound is inconclusive, and then MRI/MRCP or HIDA scan if both initial tests are equivocal and clinical suspicion remains high.