Pleural effusion associated with pulmonary embolization.

Pulmonary embolization should be considered as a possible cause of any pleural effusion of unknown etiology. This disorder may be the one that is most commonly overlooked in the work-up of patients with pleural effusions. Although para-embolic effusions have classically been considered to be bloody exudates with a predominance of polymorphonuclear leukocytes, many such effusions have none of these characteristics. Up to 25 per cent may be transudates and the RBC count exceeds 100,000 per mm3 in fewer than 20 per cent of such effusions. The WBC may range from less than 100 to more than 50,000 cells per mm3. Characteristics of these effusions are so variable that no diagnostic patterns can be said to occur. Paraembolic effusions usually begin to resolve within a few days after institution of anticoagulant therapy, although those that are associated with parenchymal infiltrates may resolve more slowly. Unless complications occur (which are rare), pulmonary embolism with associated pleural effusion is treated no differently than is pulmonary embolism without effusion.