Usefulness of Dynamic MR Imaging for the Evaluation of the Solitary Pulmonary Nodules Smaller than 15 mm: Differentiation between Benign and Malignant Nodules

PURPOSE: We wanted to evaluate the usefulness of dynamic magnetic resonance (MR) imaging for differentiating between benign and malignant solitary pulmonary nodules (SPNs). MATERIALS AND METHODS: Sixteen patients who had an undetermined SPN (<15 mm) upon chest computed tomography (8 males and 8 females; mean age: 55 years; age range: 40-76 years) underwent dynamic MR imaging. After the bolus injection of contrast material, the arterial (20-35 seconds), portal (45-60 seconds) and equilibrium (3-5 minutes) phase T1-weighted axial images were obtained with using a volumetric interpolated breath-hold examination. For discriminating the benign from malignant SPNs, the maximum relative enhancement ratio (MER) and the slope of the enhancement (SLE) were calculated and then they were statistically compared. With varying the threshold of the two indexes, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated. RESULTS: The mean MER of the malignant SPN group was significantly higher than that of the benign SPN group (malignant; 0.56+/-0.17, benign; 0.43+/-0.17). With 0.33 as the threshold of MER for distinguishing the malignant SPN group from the benign SPN group, the sensitivity, specificity, positive predictive value and negative predictive value were 100%, 70%, 50%, and 100%, respectively. The mean SLE for the benign SPN group was higher than that for the malignant SPN group (malignant; m= 0.008+/-0.006/sec, benign; m=0.013+/-0.008/sec). With 0.025 as the threshold of the SLE, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 100%, 60%, 62.5%, 100% and 69.2%, respectively. CONCLUSION: Dynamic MRI was useful for differentiating between benign and malignant SPNs. Moreover, MER and SLE might be good indexes for distinguishing benign SPNs from malignant SPNs.

Diagnostic Usefulness of MRI for Pulmonary Hamartoma: CT, MRI and Histopathologic Correlations

PURPOSE: To determine the diagnostic usefulness of MRI in pulmonary hamartoma, and the significant MRI features other than fat or characteristic calcification, both revealed by CT. MATERIALS AND METHODS: We prospectively studied chest MR images in five patients with pulmonary hamartoma. All underwent narrow-collimated CT scanning and conventional MRI, specimen MRI was available in three cases. Pulmonary nodular size, shape and margin and the presence of intratumoral fat density, calcification and a cleft-like structure were determined. At MRI, the presence and signal intensity (SI) of the cleft-like structure, including intratumoral cystic space and SI of the main portion of the tumor, were analyzed and compared with the findings of specimen MRI, and correlated with the histopathologic findings. In three cases, the typical enhancement pattern revealed by post-contrast MRI was also evaluated. RESULTS: Narrow-collimated CT scanning revealed fat density or popcorn-shape calcification in two cases and a cleft-like structure in one. The other two cases showed neither fat nor calcification. At MRI, however, all five cases showed a cleft-like structure, which was especially evident on T2WI. The detectability of this did not vary between conventional and specimen MRI. The cleft-like structure showed varying SI on T1, and T2WI correlated to variable mesenchymal component including with respiratory epithelial cells lining the cleft. Marginal rim enhancement was noted on all three post-contrast MR images, and correlated with the relatively rich vascularity of the tumor's marginal portion. An enhanced cleft-like structure was noted in two cases. CONCLUSION: The presence of a cleft-like structure, especially prominent on T2WI and with variable SI, is a useful MR finding for the diagnosis of pulmonary hamartoma, and marginal rim enhancement is an ancillary diagnostic MR finding. In particular, MRI is a useful diagnostic tool in cases where a simple pulmonary nodule demonstrates neither fat nor calcification.

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.