An estimated 300,000 to 500,000 patients develop a pleural effusion secondary to pulmonary embolism each year in the United States. The pleural effusions due to pulmonary embolism are usually small. They occupy less than one third of the hemithorax in 90% and are frequently manifest only as blunting of the costophrenic angle. The pleural fluid with pulmonary embolism is almost always an exudate. When pulmonary embolism is considered a diagnostic possibility, the clinical probability of pulmonary embolism should be assessed. If the probability is low, measurement of D-dimers is useful. If the D-dimer test is negative, the diagnosis is virtually excluded. If the D-dimer test is positive or if there is a high clinical probability of pulmonary embolism, the best test to assess the possibility of pulmonary embolism is probably the computed tomographic angiogram (CTA). Patients who have a high probability of pulmonary embolism should be anticoagulated while the definitive test is being performed. The presence of a pleural effusion does not alter the standard treatment for pulmonary embolism. The two complications of pleural effusions in patients with pulmonary embolism are hemothorax and pleural infection. If the pleural effusion increases in size while a patient is being treated for pulmonary embolism, a diagnostic thoracentesis should be performed to rule out these complications.
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