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

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.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 mm/s and ADC2 reconstructed from b factors of 0 and 1000 mm/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.Quantitatively, differences in signal intensities on DW trace images with b factors of 650 and 1000 mm/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 mm/s for metastatic malignant thickening and 2.11±0.69×10 mm/s for benign thickening (P=0.045); ADC2 was 1.06±0.56×10 mm/s for metastatic malignant thickening and 1.56±0.71×10 mm/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.Despite fair sensitivity and specificity, DW imaging may serve as a complementary tool that improves the differential diagnosis of pleural thickening.