BACKGROUND. Differentiation of primary lung cancers and pulmonary metastases may present a diagnostic dilemma given overlapping CT findings. OBJECTIVE. The purpose of this study was to compare the utility of ringlike peripheral increased iodine concentration and conventional findings for differentiating primary lung cancers from pulmonary metastases on dual-energy CT (DECT). METHODS. This retrospective study included 93 patients (64 men, 29 women; median age, 70 years) who underwent resection of a primary lung cancer (n = 68) or pulmonary metastasis (n = 25) corresponding to a solid lesion on preoperative contrast-enhanced DECT performed between April 2020 and March 2021. Venous phase 120-keV single-energy images, equilibrium phase 66-keV virtual monoenergetic images, and iodine concentration maps were reconstructed. Two radiologists independently assessed lesions for spiculated margins, air bronchograms, rim enhancement, and thin ringlike peripheral high iodine concentration; differences were resolved by consensus. Inter-reader agreement and diagnostic performance were assessed. Multivariable logistic regression analysis incorporated additional patient and lesion characteristics. RESULTS. Interobserver agreement, expressed as kappa, was 0.26 for spiculated margins, 0.60 for air bronchograms, 0.56 for rim enhancement, and 0.80 for ringlike peripheral high iodine concentration. Pulmonary metastases, compared with primary lung cancers, exhibited significantly higher frequency of ringlike peripheral high iodine concentration (52% vs 19%; p = .004) but no significant difference in frequency of spiculated margins (49% vs 32%; p = .17), air bronchograms (36% vs 51%; p = .24), or rim enhancement (4% vs 4%; p > .99). Sensitivity and specificity for diagnosing pulmonary metastasis were 68% and 49% for absence of spiculated margins, 64% and 51% for absence of air bronchograms, 4% and 96% for presence of rim enhancement, and 52% and 81% for presence of ringlike peripheral high iodine concentration. In multivariable analysis including smoking history, lesion diameter, multiple resected lesions, and ringlike peripheral high iodine concentration, the only independent significant predictor of pulmonary metastasis was ringlike peripheral high iodine concentration (OR, 7.81 [95% CI, 2.28-29.60); p = .001). CONCLUSION. Ringlike peripheral high iodine concentration had excellent interobserver agreement and high specificity (albeit poor sensitivity) for differentiating pulmonary metastasis from primary lung cancer and was independently predictive of pulmonary metastasis. CLINICAL IMPACT. Ringlike peripheral high iodine concentration could help guide management of patients with known cancer and an indeterminate solitary nodule.
Keywords: contrast media; dual-energy CT; lung cancer.