Right Upper Quadrant Ultrasound is the First-Line Imaging for Suspected Acute Cholecystitis in the Emergency Department
Right upper quadrant ultrasound should be performed as the initial imaging study for any ED patient with suspected acute cholecystitis, regardless of the clinical presentation. 1, 2
Primary Rationale for Ultrasound as First-Line
The American College of Radiology designates RUQ ultrasound as the imaging of choice despite cholescintigraphy having superior diagnostic accuracy (sensitivity 96-97% vs 75.7-88% for ultrasound) 1, 2. This recommendation is based on several practical advantages:
- Rapid study completion allows for faster clinical decision-making in the ED setting 1
- Morphologic evaluation provides comprehensive assessment of gallbladder wall edema, pericholecystic fluid, and gallbladder distention 1
- Gallstone detection with 96% accuracy, which is superior to CT 1, 3
- Evaluation of alternative diagnoses including assessment of intrahepatic and extrahepatic bile ducts, liver pathology, and other RUQ pathology 1, 4
- Bedside availability in many EDs with sensitivity of 89.58% and specificity of 96.59% when performed by emergency physicians 5
Algorithmic Approach to Imaging
Step 1: Initial RUQ Ultrasound
Perform RUQ ultrasound looking for:
- Gallstones (96% accuracy) 1, 3
- Gallbladder wall thickening >5mm 6
- Pericholecystic fluid 6
- Sonographic Murphy sign 6
- Impacted stone in the gallbladder neck 6
Step 2: If Ultrasound is Negative or Equivocal
Proceed to cholescintigraphy (HIDA scan) if clinical suspicion remains high, as it has sensitivity of 96-97% and specificity of 90% for acute cholecystitis 1, 2. The HIDA scan demonstrates cystic duct obstruction through gallbladder non-visualization, which is the pathophysiologic hallmark of acute cholecystitis 1.
Step 3: If Complications are Suspected
Order CT with IV contrast when clinical presentation suggests:
- Emphysematous cholecystitis 1, 2
- Gallbladder perforation 1, 2
- Gangrenous cholecystitis 1, 2
- Hemorrhagic cholecystitis 1, 2
CT has a negative predictive value approaching 90% and superior ability to detect complications compared to ultrasound 1.
Critical Limitations and Pitfalls
Ultrasound Limitations
- Critically ill patients present a significant challenge, as gallbladder abnormalities are common in the absence of true acute cholecystitis 1, 2
- Post-pain medication administration invalidates the reliability of a negative sonographic Murphy sign 3
- Elderly, diabetic, or immunocompromised patients may lack typical sonographic findings despite severe disease 3
Common Diagnostic Errors to Avoid
- Do not rely on sonographic Murphy sign alone, as it has a positive likelihood ratio of only 2.8 and relatively low specificity 3
- Do not skip ultrasound and proceed directly to HIDA scan, even though HIDA has better sensitivity—ultrasound provides essential morphologic information and identifies alternative diagnoses 1, 2
- Do not use CT as first-line imaging unless complications are suspected, as it is less sensitive for gallstones (60% vs 87% for ultrasound) 7
Evidence Reconciliation
While one study suggested CT may be more sensitive than ultrasound for acute cholecystitis diagnosis (92% vs 79%) 7, this contradicts guideline recommendations. The ACR guidelines appropriately prioritize ultrasound first because CT patients in that study were atypical presentations without classic signs of cholecystitis—exactly the population where ultrasound should be followed by additional imaging if negative 1, 7. The algorithmic approach of ultrasound first, then HIDA or CT based on clinical context, remains the standard of care. 1, 2