Growth-adjusted reference values for the main pulmonary artery-to-ascending aorta ratio derived from clinically indicated chest CT in children.

objectivesTo establish growth-adjusted reference values for the main pulmonary artery-to-ascending aorta (MPA/AA) ratio in children on clinically indicated chest CT and to explore their external hemodynamic applicability in an independent right heart catheterization (RHC) cohort. MATERIALS AND

methodsThis retrospective multicenter study included a modeling cohort of 1306 children younger than 18 years from two pediatric centers and an independent RHC cohort of 175 children. Children in the modeling cohort underwent clinically indicated chest CT for conditions not expected to directly alter pulmonary arterial morphology after predefined exclusions. MPA and AA diameters were measured using a standardized axial method. Age-adjusted reference values were derived from generalized additive models for location, scale, and shape. In the RHC cohort, the primary binary analysis included 169 children older than 3 months and assessed whether reference values were associated with mPAP-defined pressure elevation.

resultsIn the modeling cohort, the median age was 6.4 years, and the median MPA/AA ratio was 1.12. The ratio was highest in early life, declined with growth, and stabilized in later childhood. The primary model was an age-based, sex-adjusted unified model. In the analyzable RHC cohort, age-adjusted MPA/AA values were associated with invasive hemodynamic status, with an area under the curve (AUC) of 0.881 (95% confidence interval, 0.830-0.932).

conclusionThe pediatric MPA/AA ratio is growth-dependent and should be interpreted against age-adjusted reference values rather than a fixed raw threshold. On clinically indicated CT, this approach may support more consistent interpretation while remaining complementary to invasive hemodynamic assessment. KEY POINTS: Question How should the pediatric main pulmonary artery-to-ascending aorta ratio be interpreted on CT when growth-related variation limits the use of fixed reference standards? Findings In 1306 children, the main pulmonary artery-to-ascending aorta ratio declined with growth, and age-adjusted values remained associated with invasively defined pulmonary arterial pressure elevation. Clinical relevance Age-adjusted reference values provide a developmental context for pediatric main pulmonary artery-to-ascending aorta measurements on clinically indicated CT and support decisions on further hemodynamic evaluation.