O3302: Staged Ultrasound with MRI: The Most Cost-Effective Imaging Strategy for Pediatric Appendicitis

Background: The optimal imaging strategy in pediatric appendicitis remains unclear. While ultrasound is generally recommended as the first-line imaging technique, its diagnostic accuracy is inferior to computed tomography (CT) and magnetic resonance imaging (MRI). However, CT exposes children to ionizing radiation, increasing lifetime cancer risk, and MRI is associated with higher costs, and is not universally accessible. The objective of this study was to estimate the cost-effectiveness of diagnostic strategies for acute appendicitis in children.

Methods: A Markov model of the natural history of acute appendicitis was created to examine the cost-effectiveness of four approaches to diagnosing acute appendicitis in children: 1) CT alone, 2) MRI alone, 3) US followed by CT, if inconclusive, 4) US followed by MRI, if inconclusive. The model had a lifetime time horizon over annual cycles. The model accounted for increased lifetime risk of cancer from radiation exposure from CT. Costs were estimated from a societal perspective and included direct medical costs and indirect patient costs. The effectiveness measure was quality adjusted life-years (QALY). Both costs and QALYs were discounted at a rate of 3%. Costs, utilities, and transition probabilities were obtained from the best available recent literature. Cost-effectiveness was estimated from the incremental cost-effectiveness ratio (ICER) with an assumed willingness-to-pay (WTP) threshold of $100,000 per additional QALY.

Results: In the base case, the most cost-effective strategy was US followed by MRI, if US was inconclusive, which had an expected cost of $14,249 and 59.732 QALYs (Table 1). This strategy dominated the other three strategies. In sensitivity analyses, this result was robust to alternative assumptions about the prevalence of acute appendicitis and the prevalence of perforated appendicitis. The model was somewhat sensitive to alternative assumptions about inconclusive rates for the diagnostic techniques and the cost of MRI but remained cost-effective under plausible ranges.

Conclusion: A staged approach using US first, followed by MRI if inconclusive, is the most cost-effective strategy for diagnosing pediatric appendicitis, balancing accuracy, safety, and resource utilization. Efforts to improve MRI accessibility and increase skill in MRI interpretation could enhance implementation.