Approximately 40-45% of patients who are hospitalized for pneumonia develop a parapneumonic effusion 3.
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.
Plain radiograph / CT
Similar findings to a simple pleural effusion 1:
- usually small volume
- normal meniscus sign
- no loculation (very rarely can be loculated)
- "split pleura sign" is not typical and more specific for empyema
- empyema: , ~7.5-10 % of patients with parapneumonic pneumonia 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.
- 1. Webb WR, Higgins CB. Thoracic Imaging. Lippincott Williams & Wilkins. (2010) ISBN:1605479764. Read it at Google Books - Find it at Amazon
- 2. Kraus GJ. The split pleura sign. Radiology. 2007;243 (1): 297-8. doi:10.1148/radiol.2431041658 - Pubmed citation
- 3. Sahn SA. Diagnosis and management of parapneumonic effusions and empyema. Clin. Infect. Dis. 2007;45 (11): 1480-6. doi:10.1086/522996 - Pubmed citation
- 4. B.K. Moffett, T.S. Panchabhai, E. Anaya, R. Nakamatsu, F.W. Arnold, P. Peyrani, T. Wiemken, J. Guardiola, J.A. Ramirez. Computed tomography measurements of parapneumonic effusion indicative of thoracentesis. (2011) European Respiratory Journal. 38 (6): 1406. doi:10.1183/09031936.00004511 - Pubmed
- 5. Jessica Kurian, Terry L. Levin, Bokyung K. Han, Benjamin H. Taragin, Samuel Weinstein. Comparison of Ultrasound and CT in the Evaluation of Pneumonia Complicated by Parapneumonic Effusion in Children. (2012) American Journal of Roentgenology. doi:10.2214/AJR.09.2791