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Diffusion-weighted Magnetic Resonance Imaging in the Differential Diagnosis of Benign and Metastatic Malignant Pleural Thickening

Purpose: Imaging plays a critical role not only in detection but also in characterization of pleural thickening as benign or malignant. The aim of the study was to investigate the value of diffusion-weighted (DW) imaging in the differential diagnosis of benign and metastatic malignant pleural thickening. Materials and Methods: Thirty-four patients with 64 pleural foci of nodular thickening (47 metastatic malignant and 17 benign) were included in this prospective study. DW imaging was performed using a breath-hold single-shot spin-echo echo-planar sequence. Two different apparent diffusion coefficient (ADC1,2) maps were obtained with different b factors (ADC1 reconstructed from b factors of 0 and 650 mm2/s and ADC2 reconstructed from b factors of 0 and 1000 mm2/s), and ADCs were calculated. Quantitatively, ADCs were compared between the groups, and the optimal cutoff value was found by using receiver operating characteristic curve analysis. Results: Quantitatively, differences in signal intensities on DW trace images with b factors of 650 and 1000 mm2/s were not statistically significant. The ADC1 and ADC2 of the metastatic malignant thickening were significantly lower than those of benign ones [mean ADC1 was 1.37±0.65×10−3 mm2/s for metastatic malignant thickening and 2.11±0.69×10−3 mm2/s for benign thickening (P=0.045); ADC2 was 1.06±0.56×10−3 mm2/s for metastatic malignant thickening and 1.56±0.71×10−3 mm2/s for benign thickening (P=0.038)]. However, because of the ADC overlap between malignant and benign disease, a sufficiently discriminative cutoff value could not be defined by the receiver operating characteristic curve analysis. Conclusion: Despite fair sensitivity and specificity, DW imaging may serve as a complementary tool that improves the differential diagnosis of pleural thickening.