Dynamic CT of solitary pulmonary nodules: comparison of contrast medium distribution characteristic of malignant and benign lesions

To prospectively assess the role of the dynamic contrast-enhanced CT enhancement characteristics in distinguishing malignant form of benign solitary pulmonary nodules. The study included 87 patients (59 men, 28 women; median age, 59 years) with 87 solitary pulmonary nodules. In all cases, dynamic CT images were obtained before and 20, 30, 45, 60, 75, 90, 120 s, 3, 5, 9, 12, 15 and 20 min after injection of contrast medium. Peak enhancement attenuation value, net enhancement attenuation value, the slope of enhancement, enhancement ratio, outflow of contrast medium (washout), washout ratio and the slope of washout ratio were assessed. Statistical analyses were performed with the Mann-Whitney test, chi(2) test, and receiver-operating characteristic curves. There were 52 malignant and 35 benign nodules. There were no significant differences in net enhancement value, enhancement ratio and the slope of enhancement ratio between malignant and benign nodules (P > 0.05). Malignant nodules showed smaller outflow of contrast medium than did benign nodules. With 12.4HU or lower washout as a cutoff value, the sensitivity and specificity for malignancy were 52.5 and 65.0 %, respectively. With 18.9 % or lower washout ratio as a cutoff value, sensitivity and specificity for malignancy were 60.0 and 75.0 %, respectively. With 0.0180 %/s or lower slope of washout ratio as a cutoff value, sensitivity and specificity for malignancy were 60.0 and 80.0 %, respectively. Dynamic contrast-enhanced CT is helpful in differentiating malignant from benign solitary pulmonary nodules. Smaller washout of contrast enhancement is a predictor that a lesion is malignant.