Indeterminate CT reporting of adult acute appendicitis: radiologist versus lexicon-based diagnostic certainty

Abstract Objectives To evaluate report indeterminacy, diagnostic performance, and agreement with final diagnosis in CT performed for suspected adult acute appendicitis (AA), comparing original radiologist reports, adjudicated impressions, and certainty derived from structured lexicon-based schemes. We also aimed to identify factors associated with indeterminate reporting. Materials and methods A total of 983 consecutive CT reports between August 2021 and July 2025 were reviewed. Diagnostic certainty was categorized from original radiology reports (negative, indeterminate, positive), with indeterminate cases adjudicated by two radiologists. Two objective lexicon-based schemes were applied using extracted CT findings (appendiceal diameter (6-mm and 7-mm cutoffs), wall thickening, wall hyperenhancement, and periappendiceal fat stranding) to generate four certainty categories (negative, possible, probable, positive). Surgical, pathological, and clinical outcomes served as reference standards. Results Acute appendicitis was confirmed in 393 patients (40%). Indeterminate reporting occurred in 15.5% of original reports, 12% of adjudicated reports, and 27.9–46.1% of lexicon-based schemes. Across all approaches, AA prevalence increased consistently with higher diagnostic certainty. Adjudicated reports demonstrated the highest diagnostic performance (sensitivity 85.2–98.7%, specificity 85.9–97.1%, accuracy 91.0–92.4%) and excellent agreement with final diagnosis (kappa = 0.819–0.838). Several CT features were independently associated with indeterminate reporting. Conclusions Radiologist-adjudicated impressions conveyed diagnostic certainty more effectively than original reports and lexicon-based schemes, with lower indeterminacy and stronger agreement with the final diagnosis. These findings underscore the practical importance of careful wording and judicious use of indeterminate categories when communicating CT findings for suspected adult AA. Critical relevance statement Careful wording of CT impressions, grounded in radiologists’ integrated judgment, can reduce diagnostic ambiguity and potentially improve clinical decision-making, supporting standardized languages to express diagnostic certainty in suspected adult acute appendicitis. Key Points CT reports for suspected appendicitis vary in wording, leading to indeterminate impressions, potentially affecting diagnostic performance and agreement with final diagnosis. Adjudicated radiologist impressions reduced indeterminate reports and achieved higher accuracy and agreement with final diagnosis than original reports or lexicon-based schemes.