What is the recommended imaging for ruling out appendicitis in pediatric patients?

Pediatric Imaging for Suspected Appendicitis

For pediatric patients with suspected appendicitis, ultrasound should be used as the initial imaging modality, with MRI or CT reserved for cases where ultrasound results are equivocal or non-diagnostic and clinical suspicion persists. 1

Initial Imaging Approach

• Ultrasound should be the first-line imaging study in children with suspected appendicitis due to its lack of radiation exposure, wide availability, and good accuracy when results are definitive 1
• When ultrasound results are definitively positive or negative, the sensitivity approaches 99% and specificity is excellent 1
• The use of ultrasound as the primary imaging modality has led to sustained decreases in CT utilization (up to 70% reduction) without compromising diagnostic accuracy 2
• Ultrasound is operator-dependent and may yield equivocal results in approximately 25-30% of cases, particularly in obese patients or those early in the disease course 3

Ultrasound Criteria for Appendicitis

• Positive ultrasound findings for appendicitis include:
  • Maximum outer diameter ≥7 mm 4
  • Appendiceal wall thickness >1.7 mm 4
  • Presence of periappendiceal inflammatory changes 3
• Using these revised criteria can achieve sensitivity of 98.7% and specificity of 95.4%, correctly classifying 96.6% of cases 4
• Requiring the presence of periappendiceal inflammatory changes before interpreting a mildly distended appendix as positive can increase accuracy 3

Management of Equivocal Ultrasound Results

• When ultrasound results are equivocal or non-diagnostic and clinical suspicion persists, the next step should be either MRI or CT imaging rather than repeating ultrasound 1
• Factors that should prompt consideration of follow-up CT after equivocal ultrasound include:
  • Age >11 years 5
  • Leukocytosis >15,000 cells/ml 5
  • Secondary signs of appendicitis on initial ultrasound 5
• CT with IV contrast is usually appropriate for follow-up imaging, though CT without IV contrast may also be appropriate in certain situations 1
• MRI is a radiation-free alternative that should be considered, particularly in settings where it is readily available, though it may require sedation in young children 1

Pitfalls and Considerations

• Community hospitals are 4.4 times more likely to use CT as the initial imaging modality compared to children's hospitals, potentially exposing children to unnecessary radiation 6
• Ultrasound sensitivity may be lower when performed at community hospitals versus children's hospitals 6
• Girls are more likely to undergo both ultrasound and CT scans and have lower ultrasound sensitivity for appendicitis, requiring more careful evaluation 6
• Not requiring visualization of the normal appendix for exclusion of acute appendicitis can reduce the indeterminate study rate 3
• For low-risk patients with equivocal ultrasound, observation and reassessment may be appropriate before proceeding to CT imaging 5
• If there is strong clinical suspicion for appendicitis after equivocal imaging, exploratory laparoscopy or laparotomy may be considered if subsequent imaging would delay appropriate management 1

Institutional Approach

• Implementation of a standardized pathway using ultrasound as the initial imaging modality can achieve high adherence rates (approximately 90%) and maintain low negative appendectomy rates (approximately 2.4%) 2
• Such pathways have demonstrated sustained decreases in CT utilization over time without compromising diagnostic accuracy 2