What type of ultrasound should be ordered to rule out cholecystitis?

Ultrasound for Ruling Out Cholecystitis

Abdominal ultrasound (US) is the recommended initial imaging modality for ruling out cholecystitis due to its high accuracy, wide availability, non-invasive nature, and lack of radiation exposure. 1, 2

Rationale for Abdominal Ultrasound

• First-line imaging test for suspected cholecystitis according to multiple guidelines including the American College of Radiology (ACR) Appropriateness Criteria 1
• Diagnostic performance:
  • Sensitivity: 81-88%
  • Specificity: 80-83%
  • Accuracy: 70-79% 1, 3
• Advantages over other imaging modalities:
  • No radiation exposure
  • Cost-effective
  • Widely available
  • Shorter study time
  • Can evaluate alternative diagnoses 1, 2

Key Ultrasound Findings in Cholecystitis

When ordering an abdominal ultrasound to rule out cholecystitis, the following findings should be evaluated:

• Primary findings:

  • Presence of gallstones (96% accuracy for detection) 1
  • Gallbladder wall thickening
  • Pericholecystic fluid
  • Sonographic Murphy sign (tenderness directly over the gallbladder) 1, 4

• Additional findings to request assessment for:

  • Dilated gallbladder
  • Tensile fundus sign (bulging fundus)
  • Wall hyperemia (can be quantified by cystic artery velocities)
  • Mucosal ischemic changes
  • Pericholecystic inflammation 4

When Ultrasound Is Not Definitive

If the initial ultrasound is inconclusive:

1. Hepatobiliary Iminodiacetic Acid (HIDA) scan should be considered as the next step

   • Higher sensitivity (97%) and specificity (90%) than ultrasound 1
   • Gold standard diagnostic test when ultrasound is equivocal 3

2. CT with IV contrast may be considered as a second-line investigation

   • Useful for evaluating complications or alternative diagnoses
   • Can help guide surgical planning 1, 2

3. Magnetic Resonance Cholangiopancreatography (MRCP)

   • Sensitivity of 85% and specificity of 81% for cholecystitis
   • Useful for visualizing hepatic and biliary abnormalities not characterized on ultrasound 1, 2

Important Considerations

• The sonographic Murphy sign has relatively low specificity and its absence is unreliable if the patient has received pain medication prior to imaging 1, 4
• Ultrasound has limitations in critically ill patients where gallbladder abnormalities are common even in the absence of acute cholecystitis 1
• Early diagnosis is crucial to prevent complications such as cholangitis, pancreatitis, or gallbladder perforation 2
• Complicated cholecystitis (emphysematous, hemorrhagic, gangrenous, or perforated) may present similarly to uncomplicated disease but requires prompt surgical intervention 1, 5

Clinical Caveat

Intensivists and critical care providers should not personally perform ultrasound primarily for the diagnosis of acute cholecystitis, as there is insufficient evidence supporting this practice 1. The examination should be performed by qualified radiologists or sonographers for definitive diagnosis.