Differentiating Complicated Acute Appendicitis From Non-complicated Acute Appendicitis Based on Ultrasound Characteristics

AIM: This study aimed to identify key ultrasound (US) characteristics that differentiate complicated acute appendicitis (CAA) from non-complicated acute appendicitis (NCAA) and to develop and validate a US-based predictive model for preoperative diagnosis. METHODS: A retrospective analysis was conducted on 178 patients with surgically confirmed acute appendicitis between June 2022 and May 2025. All patients underwent a standardized preoperative US examination. Clinical and sonographic variables were compared between the CAA (n = 63) and NCAA (n = 115) groups. Least Absolute Shrinkage and Selection Operator (LASSO) regression was used for variable selection, followed by multivariable logistic regression to construct a predictive model. Model performance was evaluated using the area under the receiver operating characteristic curve (AUC), calibration plots, and decision curve analysis (DCA). RESULTS: Compared to the NCAA group, the CAA group had significantly older age, longer symptom duration, higher white blood cell (WBC), and higher neutrophil percentage (NE%) (p < 0.05). Significant US-based predictors included greater appendiceal outer diameter (AOD), increased periappendiceal inflammatory fat thickness (PIFT), and higher incidences of periappendiceal fluid collection (PAFC), marginal indistinctness (MI), and altered bowel peristalsis (ABP). The final model identified eight independent predictors: age, symptom duration, WBC, NE%, PIFT, PAFC, MI, and ABP. The nomogram showed excellent discrimination (AUC = 0.890), good calibration (Hosmer–Lemeshow test, p = 0.108), and sustained performance during internal validation (AUC = 0.902). DCA confirmed high clinical utility. CONCLUSIONS: The proposed US-based nomogram provides an accurate, non-invasive tool for preoperative differentiation of CAA from NCAA, potentially aiding in risk stratification and treatment decision-making.