Incidental Malignancies in the Emergency Department: Missed Diagnoses, Radiological Difficulty, and a Risk-Based Framework for Follow-Up

Background: Incidental malignancies on emergency department (ED) CT may go unrecognized, risking delayed diagnosis. We investigated their prevalence, recognition rate, and follow-up risk stratification. Methods: We retrospectively reviewed 15,347 CT reports from a tertiary ED (April 2016–March 2019). To determine whether missed diagnoses reflected inherent radiological difficulty or situational factors, ten board-certified emergency physicians completed a standardized 18-case interpretation test under off-duty conditions. Results: Incidental malignancies were identified in 25 patients (0.16%); lung carcinoma was most common (28%). Of 25 patients, 16 (64%) had malignancy recognized at the initial ED visit; 9 (36%) were missed. One discharged new patient without scheduled follow-up represented the highest-risk group for loss to follow-up. Diagnostic accuracy ranged from 0/10 to 9/10 (Cochran’s Q test, p < 0.001). Cases 1, 4, and 7 were unidentified by all evaluators (p = 0.002 vs. Case 16, McNemar test with Bonferroni correction). No significant inter-physician difference was observed (p = 0.73, Friedman test). Conclusions: Incidental malignancies occurred in 0.16% of ED CT examinations, with 36% missed at initial presentation. Missed diagnoses reflected inherent radiological difficulty and systemic factors rather than individual expertise. Discharged new patients without scheduled follow-up represent the highest-risk group, underscoring the need for systems-based interventions.