Differentiation of Benign and Malignant Solitary Pulmonary Nodules: Value of Contrast-Enhanced Dynamic MRImaging

PURPOSE: To evaluate the usefulness of contrast-enhanced dynamic MR imaging for differentiation of benign andmalignant solitary pulmonary nodules (SPNs). MATERIALS AND METHODS: Twenty-three patients with histologically orradiologically provened SPNs smaller than 40mm (14 benign, 9 malignant) underwent MR examination using the breathhold fast multiplanar spoiled gradient echo (FMPSPGR) technique. Pre-enhancement MR examination wasfollowed by serial scans obtained at one-minute intervals, beginning one-minute after the onset of bolus injectionof paramagnetic contrast agent for a total of five scans. Signal intensities of SPNs were measured from pre- andpost-contrast enhanced MR images and peak percentage increase in signal intensity (p%SI) was calculated. Meanpercentage increase in signal intensity (m%SI) was also calculated and the time-m%SI curve was plotted. The enhancement patterns of SPNs were classified as homogeneous, peripheral rim-like, inhomogeneous, or no (orminimal) enhancement. We compared differences in p%SI, the pattern of the time-m%SI curve, and the pattern ofenhancement between benign and malignant SPNs. RESULTS: On dynamic MR images, alignant SPNs (n=9) showed asignificantly higher p%SI than benign SPNs (n=14) (malignant: mean 120.6, range 81.8-171.6; benign: mean 29.5,range 3.7-78.9) (p < 0.0001). With 80 p%SI as the threshold for malignancy-positive, both sensitivity andspecificity were 100%. The m%SI of malignant SPNs rapidly increased at one minute after enhancement and decreasedgradually thereafter, whereas that of benign SPNs increased more slowly to form a plateau. Eighty-nine percent(8/9) of malignant SPNs showed homogeneous enhancement. In contrast, among benign SPNs, peripheral rim-likeenhancement and no (or minimal) enhancement occurred in the same proportion of cases: 50% (7/14). CONCLUSION:The superb demonstration of different enhancement characteristics obtained using dynamic contrast-enhanced MRimaging is useful to discriminate malignant from benign SPNs.