The Accuracy of Chest Computed Tomography Findings in Differentiation of Exudative from Transudative Pleural Effusion

Aim: There is a controversy in the usefulness of computed tomography (CT) in differentiating transudate or exudates. The aim of this study is to evaluate the utility of CT in characterizing pleural effusions. Material and Method: We evaluated 100 patients with pleural effusions who underwent chest CT and diagnostic thoracentesis. Effusions were classified as exudates or transudative on the basis of Light's criteria. CTs were reviewed by two radiologists to determine the mean Hounsfield unit value of an effusion and other CT features including loculation and pleural thickening. Results: Pleural fluid was exudative in 58 patients and transudative in 42 patients. Exudative effusion significantly had higher mean attenuation values (8.1 +/- 5.69 vs. 3.53 +/- 4.23 HU; p< 0.001), higher loculation (91.4% vs. 64.3%; p= 0.002) and higher pleural thickening (50.9% vs. 19.5%; p= 0.002) than transudative effusion. Sensitivity and specificity in differentiating exudative from transudative effusion was 74.46% and 62.5% for attenuation value of > 4.5 HU, 66.25% and 75.00% for loculation, and 78.38% and 54.10% for pleural thickening. Discussion: Attenuation value and loculation had relatively good sensitivity and specificity in comparison to other features and could better differentiate between effusions. However, in comparison to thoracentesis, CT scan is not a more reliable method to evaluate the nature of the effusion and would be useful only in cases with contraindications of thoracentesis.