Purpose: To determine the accuracy of computed tomography (CT) in enabling differentiation of pleural exudates from transudates.
Materials and methods: Eighty consecutive patients (86 effusions) underwent contrast-enhanced CT. Thoracentesis was performed to measure pleural and serum total protein and lactate dehydrogenase (LDH) values. Effusions were classified as exudates with accepted criteria. CT scans were evaluated for the presence and appearance of parietal pleural and extrapleural fat thickening.
Results: Fifty-nine effusions were exudates and 27 were transudates. Thirty-six of the 59 exudates (61%) were associated with parietal pleural thickening. All cases of empyema and 56% of the parapneumonic exudative effusions had pleural thickening. The specificity of this finding in diagnosing the presence of an exudate is 96%.
Conclusion: Parietal pleural thickening at contrast-enhanced CT almost always indicates the presence of a pleural exudate. A pleural exudate in the absence of pleural thickening occurs most frequently in patients with malignancy or uncomplicated parapneumonic effusion.