Approximately 40% of patients who are hospitalized for pneumonia develop a parapneumonic effusion .
Fluid leaks into the pleural space due to increased permeability of the visceral pleura adjacent to the infected lung. Bacterial pneumonia is a more common cause of parapneumonic effusions than viral pneumonia .
Plain radiograph / CT
Similar findings to a simple pleural effusion :
- usually small volume
- normal meniscus sign
- no loculation
- "split pleura sign" is not typical and more specific for empyema
Treatment and prognosis
Parapneumonic effusions often resolve with the treatment of underlying pneumonia. However, ~7.5% of patients with parapneumonic pneumonia progress to a fibrinopurulent stage such as empyema .