Chulalongkorn Medical Journal


Background : Pleural effusion is one of the most frequent findings of thoracicabnormality, detected by computed tomography (CT). Differentiationbetween exudative from transudative effusions is crucial for diagnosisof various pathologies.Objective : To determine the accuracy of computed tomography in enablingdifferentiation of pleural exudates from transudates.Setting : King Chulalongkorn Memorial Hospital.Research design : A retrospective study.Patients : Patients who had pleural effusions and underwent CT of thorax andthoracentesis within 14 days of each other from March 2005 to August2007 were recruited.Methods : We analyzed 41 pleural effusions in 41 patients. Effusions wereclassified as transudates or exudates using laboratory markers basedon Light’s criteria. All CT scans were reviewed for the mean CTattenuation values and distribution of an effusion, the presence andappearance of pleural thickening, thickening and increased attenuationof extrapleural fat.Results : Thirty-four effusions were exudates, and 7 were transudates.The optimal threshold value was determined to be 11.75 HU fordifferentiation of pleural exudates. The mean attenuation value ofexudates (14.8 ± 5.8 HU) was higher than transudates (10.7 ± 5.1HU), but there was no detected significant difference (p = 0.09).Loculation of pleural effusion was found in 52.9% of exudates, with53% sensitivity, 100 % specificity and 61% accuracy. Pleural thickeningswere found in 61.8% of exudates and in 14.3% of transudates, with62% sensitivity, 86% specificity and 66% accuracy. Extrapleural fatwas thickened in 29.4% of exudates, and 64.7% of transudates.The attenuation of extrapleural fat was increased in 64.7% of exudatesand 28.6% of transudates. None of transudates had loculated effusion,nodular pleural thickening nor thickening of extrapleural fat.The sensitivity, specificity and accuracy of extrapleural fat thickeningwere 29%, 100% and 41%; and of increased attenuation of extrapleuralfat were 65%, 71% and 66%, respectively.Conclusion : Loculation of pleural effusion, nodular pleural thickening and thickeningof extrapleural fat at contrast-enhanced CT are highly suggestive ofthe presence of pleural exudates. CT attenuation values of exudatesare higher than transudates, but there were no clinical value indifferentiating exudates from transudates.


Faculty of Medicine, Chulalongkorn University

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