Parapneumonic effusions refer to an exudative pleural effusion associated with pneumonia.
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Epidemiology
Approximately 40-45% of patients who are hospitalized for pneumonia develop a parapneumonic effusion 3.
Pathology
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 3.
Radiographic features
Plain radiograph / CT
Similar findings to a simple pleural effusion 1:
usually small volume
normal meniscus sign
dependent
no loculation (very rarely can be loculated)
"split pleura sign" is not typical and more specific for empyema
some authors suggest a depth of less than 30 mm being an additional supportive feature more suggestive of a parapneumonic effusion verses an empyema when other factors are also taken into account 6.
Complications
empyema: , ~7.5-10 % of patients with parapneumonic effusions progress to a fibrinopurulent stage such as empyema 3-4
Treatment and prognosis
Parapneumonic effusions often resolve with the treatment of underlying pneumonia. Some authors suggest effusions with depth measurements of <2.5 cm able to be conservatively managed without thoracentesis 4.
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