Preoperative Inflammatory Markers and Sonographic Free Peritoneal Fluid in Relation to Histopathologically Confirmed Appendiceal Perforation in Children: A Retrospective Cohort Study

Background/Objectives: Distinguishing perforated from non-perforated appendicitis preoperatively is difficult, and routine scores diagnose appendicitis rather than grade severity. We examined whether two inflammatory markers and one sonographic sign, combined in a model, discriminate between perforated and non-perforated appendicitis, and how this compares with a bedside score. Methods: Retrospective single-center cohort of 142 children aged 3–17 years undergoing initially attempted laparoscopic appendectomy (October 2022–December 2023). Log-transformed neutrophil-to-lymphocyte ratio (NLR) and C-reactive protein (CRP) were prespecified; sonographic free peritoneal fluid was selected from four signs using the outcome, and reported in-sample performance is an upper bound. Predictors were fitted by Firth penalized logistic regression with bootstrap validation. Results: Perforation occurred in 27 patients (19.0%). All three were independent predictors (odds ratios: CRP 2.583, NLR 3.045, free peritoneal fluid 3.638). The area under the curve was 0.900 (0.890 optimism-corrected). At the Youden-optimal threshold, sensitivity was 96.3% and negative predictive value 98.9%. The Pediatric Appendicitis Score reached 0.855 (difference not significant, p = 0.375); at matched sensitivity its specificity was 38.9% versus 74.8%. Conclusions: The model’s potential value lies in excluding perforation rather than establishing it, and applies after the decision to operate has been taken, informing antibiotic selection, operative urgency and family counselling rather than the indication for surgery. Overall discrimination did not differ significantly from the Pediatric Appendicitis Score, the advantage lying in the operating point rather than in the area under the curve. These findings are hypothesis-generating and require external validation.