Background: Malignant pleural effusions are classically exudative, though occasionally they can be transudative. We attempted to determine the prevalence of transudative malignant pleural effusions and to describe their clinical and radiographic characteristics.
Methods: We studied the medical records of 215 patients with malignant pleural effusion, which contained complete data on pleural fluid analysis for 171 of them.
Results: Eight cases of transudative malignant effusion were found. Seven of these eight patients had a concomitant disorder known to cause transudative pleural effusion. One patient had fluid overload due to renal failure, and another had been admitted earlier with congestive heart failure. Two patients had definite evidence of deep venous thrombosis, allowing us to postulate pulmonary embolism as a factor contributing to transudation. Three patients had CT evidence of superior vena cava obstruction. Only one patient had no known associations with causes of transudative effusion.
Conclusion: Malignant pleural effusions were transudative in 5% of our patients. In all except one patient, some evidence suggested the concomitant presence of a transudative state.