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Ultrasound Med Biol. 2008 Mar;34(3):362-9. Epub 2007 Nov 8.

Sonographic appearances in transudative pleural effusions: not always an anechoic pattern.

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Division of Pulmonary and Critical Care Medicine, Department of Medicine, China Medical University Hospital, Taichung, Taiwan.


Pleural effusion patterns in sonographic appearances can be subclassified as anechoic, complex nonseptated, complex septated and homogeneously echogenic. Previous studies have suggested that transudates are usually anechoic; however, in daily practice we find frequently that heterogeneous echogenic material is present in transudative pleural effusions. This clinical study was to re-evaluate the sonographic appearances of transudative pleural effusions. A total of 127 patients with transudative pleural effusion that met Light's criteria ([1] a pleural fluid-serum protein ratio of <0.5, [2] a pleural fluid-serum lactate dehydrogenase [(LDH] ratio of <0.6 and [3] a pleural fluid LDH of less than two thirds of the upper limit of normal for serum LDH) and clinical presentations were enrolled. Results showed that transudative pleural effusions had the following sonographic appearances: an anechoic pattern in 45% (57/127) and a complex nonseptated pattern in 55% (70/127). There was no complex septated or homogenously echogenic pattern. In conclusion, sonographic presentations in transudative pleural effusions are not always in an anechoic pattern. If an afebrile patient without infectious symptoms/signs has bilateral pleural effusion compatible with transudate of Light's criteria, treat the underlying problems and ignore the complex nonseptated sonographic appearance. (E-mail:

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