Differentiation Between Transudative and Exudative Pleural Effusions by Diffusion Weighted Magnetic Resonance Imaging

Pleural effusion could develop in very different pathological conditions. It is important to characterize pleural effusion and to identify its etiology. Different radiological methods, such as ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI) are used for the diagnosis of pleural effusion. To assess the ability of diffusion weighted imaging and apparent diffusion coefficient (ADC) maps to differentiate transudative effusions (TEs) from exudative effusions (EEs). This prospective observational, single center study was performed on 100 consecutive patients who had pleural fluid detected by chest X-ray, US, or CT and were referred for MRI. Afterwards diffusion-weighted MRI (DW-MRI) was obtained using a multislice, single shot, respiratory triggered spin echo, echo planar imaging sequence. Pleural effusions obtained with thoracentesis were classified into TEs or EEs according to the clinical criteria established by clinical, pathologic findings and Light's criteria. Analysis of MRI was interpreted by one radiologist specialist who was blinded to clinical findings and according to the clinical criteria established by Light. The ADCs of EEs were significantly lower than those of the TEs. The difference between the mean ADC values of TEs and EEs was significant (P < 0.01). The optimum cutoff point for ADC values was 3.51 × 10-3 mm2/s, with a sensitivity of 90.4% and a specificity of 78%. We conclude that ADC value is a noninvasive, reliable, and reproducible imaging parameter that may help to assess and characterize pleural effusion.