Incidental pulmonary embolism and the value of CT pulmonary angiography follow-up versus expert review

OBJECTIVES: Evaluate the prevalence of true-positive and false-positive incidental PE diagnoses and the impact of expert review on diagnostic accuracy. METHODS: This single-centre retrospective study included consecutive contrast-enhanced thoracic CT examinations without dedicated PE protocols which reported iPE over an 18-month period (2022-2024). Electronic health records were reviewed to identify requests to confirm PE based on previous non-dedicated studies. Studies identifying iPE were graded from 1 (most certain) to 5 by original report diagnostic certainty and compared between PE-positive and PE-negative subgroups using Fisher's exact test. Identified imaging received retrospective expert review to calculate expert agreement with CTPA, where CTPA had been performed, using Cohen's Kappa. RESULTS: 260/25 214 (1%) CTs reported iPE (mean age 73±12 years; 51% women). 25% (n = 65/260) underwent confirmatory CTPA. Patients receiving CTPA had lower initial iPE diagnostic certainty (median 3 versus 1, p < 0.01) and 52% (n = 34/65) were PE-positive on CTPA. Patients with false-positive diagnoses had reduced diagnostic certainty on non-dedicated studies compared to those with a true-positive diagnosis (median 3 versus 2, p < 0.001). Agreement between the expert review of the iPE scan and the ground-truth CTPA diagnosis had κ of 0.96. CONCLUSIONS: Expert review could be an effective tool to reduce CTPA requirement in cases of intermediate (grade 3) iPE diagnostic certainty. ADVANCES IN KNOWLEDGE: Low-certainty incidental pulmonary embolism diagnoses on initial non-dedicated CT are more likely to be false-positives according to CTPA findings or expert thoracic radiologist review. Expert review of initial CT may therefore reduce excessive imaging and avoid treating false-positive cases.