Agreement Between Intraoperative Findings and Histopathological Diagnosis and Their Association with Postoperative Outcomes in Acute Appendicitis

Background/Objectives: Intraoperative assessment guides the immediate postoperative management of acute appendicitis, whereas histopathological confirmation becomes available only after key clinical decisions have been made. This study evaluated the agreement between intraoperative and histopathological grading of acute appendicitis and compared their associations with postoperative outcomes, particularly length of hospital stay (LOS) and duration of antibiotic therapy. Methods: This retrospective single-center study included pediatric and adult patients who underwent appendectomy for suspected acute appendicitis at the University Hospital of Split between 1 January 2020 and 31 December 2025. After exclusion criteria were applied, 2279 patients were included. Agreement between intraoperative and histopathological classifications was assessed using Cohen’s kappa and weighted kappa. Associations with postoperative outcomes were examined using Kendall’s tau correlation, bootstrap comparison between age groups, Kruskal–Wallis testing with Bonferroni-adjusted post hoc analyses, adjusted negative binomial regression for length of hospital stay, zero-inflated negative binomial regression for total antibiotic duration, and Firth penalized logistic regression for binary outcomes. Results: Overall concordance between intraoperative and histopathological grading was 74.0%. Agreement was moderate by unweighted Cohen’s kappa (0.539) and substantial by weighted kappa (0.643), with intraoperative grading more often overestimating than underestimating histopathological severity. Intraoperative severity showed stronger correlations than histopathological severity with LOS (τ = 0.347 vs. 0.207) and total duration of antibiotic therapy (τ = 0.331 vs. 0.224). Both outcomes showed a non-linear pattern, with patients with a negative appendix having a longer hospital stay and greater antibiotic exposure than those with phlegmonous appendicitis, while advanced disease was associated with the greatest treatment burden. Thirty-day readmission was uncommon and not associated with severity. Conclusions: Agreement between intraoperative and histopathological grading was moderate to substantial. Intraoperative grading showed stronger associations with immediate postoperative outcomes than histopathological grading, reflecting its role as the primary driver of clinical decision-making in the immediate postoperative period. These findings do not diminish the diagnostic value of histopathological examination, which remains essential for confirmation and detection of unexpected pathology.