Preoperative CT detection of appendiceal neoplasms in suspected acute appendicitis using a simple diameter-and-fecalith criterion: multicenter derivation and validation.

OBJECTIVES

Appendiceal neoplasms (ANs) may mimic acute appendicitis (AA), making preoperative recognition difficult in emergency settings. We aimed to derive and externally validate a simple non-contrast CT criterion combining appendiceal diameter and fecalith obstruction status for differentiating AN from AA.

METHODS

This multicenter retrospective case-control study included adults who underwent appendectomy at four tertiary hospitals from January 2013 to June 2025. Histopathology after centralized re-review served as the reference standard. In the derivation cohort, receiver operating characteristic analysis was used to determine the optimal cutoff for maximum appendiceal diameter. A locked criterion of significantly enlarged appendiceal diameter (SEAD) without fecalith obstruction was then applied unchanged to the validation cohorts and reader-based validation subsets. Its diagnostic performance was also compared with that of the original CT reports.

RESULTS

The final analytic cohort included 292 patients with ANs and 876 controls with AA. A cutoff of 12.48 mm defined SEAD. In the derivation cohort, SEAD without fecalith obstruction yielded an AUC of 0.76 (95% CI, 0.71-0.80), with 64.1% sensitivity and 87.0% specificity. In Center 2, the AUC was 0.82 (95% CI, 0.77-0.87), and in the pooled Centers 3 and 4 cohort it was 0.73 (95% CI, 0.66-0.81), without significant differences versus the derivation cohort (p = 0.051 and p = 0.598). Reader-based AUCs were 0.80, 0.76, and 0.72, without significant between-reader differences (all p > 0.05). Compared with original CT reports, the criterion substantially improved preoperative AN detection across cohorts (all p < 0.001).

CONCLUSIONS

A predefined non-contrast CT criterion of SEAD without fecalith obstruction may facilitate preoperative identification of AN in patients with presumed AA.