Introduction
Background
Empyema is inflammatory fluid and debris in the pleural space. It results from an untreated pleural-space infection that progresses from free-flowing pleural fluid to a complex collection in the pleural space.
Empyema most commonly occurs in the setting of bacterial pneumonia. About 20-60% of all cases of pneumonia are associated with parapneumonic effusion. With appropriate antibiotic therapy, parapneumonic effusions most often resolve without complications, and they are of little clinical significance. However, some effusions do not resolve; these are called complicated effusions. The resulting infection and inflammatory response can proceed until adhesive bands form. The infected fluid becomes loculated pus in the pleural space.
Empyema may also result from causes other than bacterial pneumonia. Any process that introduces pathogens into the pleural space can lead to an empyema. Some of these other causes are the following:
- Thoracic trauma (About 1-5% of cases of thoracic trauma lead to an empyema.)
- Rupture of a lung abscess into the pleural space
- Extension of a non–pleural-based infection (eg, mediastinitis, abdominal infection)
- Esophageal tear
- Iatrogenic introduction at the time of thoracic surgery
- An indwelling catheter that is a nidus for infection
Mortality related to empyema is associated with respiratory failure and systemic sepsis, which occurs when the immune response and antibiotics are inadequate to control the infection.
Drainage is performed to remove the collection and to improve outcomes. The proper intervention depends on the severity of the disease and ranges from minimally invasive catheter drainage to open surgical decortication. Early intervention decreases the mortality rate associated with empyema. Prompt diagnosis, treatment, and proper management of empyema are crucial.
Pathophysiology
The secretion of fluid into the pleural space is normally in equilibrium with drainage by the subpleural lymphatics. The pleural lymphatic system can drain almost 500 mL/d. When the volume of pleural fluid exceeds the ability of the lymphatics to drain it, an effusion begins to form.
Parapneumonic effusions are the most common causes of empyema. Pneumonia triggers an inflammatory response. Inflammation near the pleura increases permeability of the mesothelial cells, the outermost monolayer of cells on the pleura. Mesothelial cells thus affected have increased permeability to albumin and other proteins. This is why pleural effusions due to infection are rich in protein.
Chemical mediators of the inflammatory process stimulate the mesothelial cells to release chemokines, which recruit other inflammatory cells to the area. Mesothelial cells play an important role in attracting neutrophils to the pleural space. Under normal conditions, neutrophils are not found in pleural fluid. They are found only in the pleural space when they are recruited as part of the inflammatory process. Neutrophils, mononuclear phagocytes, and lymphocytes amplify the inflammatory response and release mediators to attract additional inflammatory cells to the pleural space.
The formation of an empyema has 3 stages:
- Exudative stage: Protein-rich pleural fluid remains free flowing. The number of neutrophils is rapidly increasing. Glucose and pH levels are normal. Drainage of the effusion and appropriate antimicrobial therapy are normally sufficient for treatment.
- Fibrinolytic stage: Viscosity of the pleural fluid increases. Coagulation factors are activated, and fibroblastic activity begins coating the pleural membrane with an adhesive meshwork. Glucose and pH levels are lower than normal.
- Organizing stage: Loculations form. Fibroblastic activity causes adherence to the visceral and parietal pleura. This activity may progress with the formation of pleural peels in which the pleural layers are indistinguishable. Pus, which is a protein-rich fluid with inflammatory cells and debris, is present in the pleural space. Surgical intervention is often required at this stage.
Simple parapneumonic effusions resolve with treatment of the underlying disease. The lymphatics drain the effusion, and the mesothelial layer returns to normal. A parapneumonic effusion is considered complicated if the effusion does not resolve with antibiotic therapy. Complicated effusions progress to empyema if they are not drained.
In rare cases, an infected pleural collection can extend through the pleural space into the chest wall; this condition is called empyema necessitatis. A fluctuant mass can be palpable, and, if the empyema is left untreated, the infection can extend to the surface and drain spontaneously. This is considered a pleurocutaneous fistula.Frequency
United States
One million pleural-space infections occur each year in the United States.
In a review of several published case series, Strange and Sahn analyzed the causes of pleural infections. They identified parapneumonic effusions as the origins of 70% of pleural infections.1
About 5-10% of simple parapneumonic effusions become complicated effusions.
As many as 5% of patients with thoracic trauma develop an empyema.
International
Overall, the international incidence of pleural-space infection or empyema is not known. However, 4000 pleural-space infections occur each year in the United Kingdom.
Mortality/Morbidity
- The table below shows radiographic predictors of mortality and rates in a series of patients with clinical pneumonia.2
Open table in new window
* Bilateral effusions due to congestive heart failure were not excluded from this analysis.Effusion Mortality Rate, % 7 Day 30 Day None 1.3 4 Unilateral 2.5 5.9 Bilateral* 10 28
- In the United Kingdom, the mortality rate due to frank empyema is 20%.
- Comorbid conditions increase mortality due to pleural-space infection. In elderly and chronically debilitated patients, reported mortality rates are 25-75%.
Race
Race statistics for pleural-space infection or empyema are not known.
Sex
The male-to-female ratio is 1.8:1. No definite cause for the increased rate in men has been described. Men with pneumonia may seek treatment at a late stage of infection, when antibiotics are insufficient.
Age
Age statistics for pleural-space infection are not known.
Anatomy
The thoracic cavity encompasses 2 pleural cavities and the mediastinum. The mediastinum contains the heart, the esophagus, the trachea, the great vessels, and other structures. The left and right pleural cavities are lateral to the mediastinum and contain the lungs and their associated structures. A pleural sac surrounds each lung. The pleura is a continuous layer of mesothelial cells and submesothelial matrix that covers the chest wall and lungs.
The parietal pleura lines the wall of the pleural cavity. Connective tissue attaches it to the internal thoracic wall and the superior surface of the diaphragm. During respiration, the parietal pleura moves with diaphragmatic contraction and with expansion of the chest wall. The parietal pleura is continuous with the visceral pleura at the hilum, where structures enter and leave the lung.
The visceral pleura envelops the lung and is attached to the lung by connective tissue. Reflections of the visceral pleura line the lobes of the lungs and are visualized as pulmonary fissures on chest radiographs. The visceral pleural is normally near the parietal pleura as the lung expands to fill the potential pleural space.
The pleural space contains a minimal amount of fluid (approximately 5 mL in a typical 70-kg individual). Pleural fluid decreases friction between surfaces. Subpleural lymphatics drain excessive pleural fluid.Presentation
As many as 70% of all empyemas are due to complications of pneumonia. In the setting of pneumonia, empyema may be associated with several symptoms. Patients may report having chills, high-grade fever, sweating, poor appetite, malaise, and cough. Pleurisy and dyspnea may be symptoms in some patients. Pleurisy and dyspnea do not depend on the size of the effusion. If an effusion of sufficient size is present, physical findings may include dullness to percussion and absent breath sounds.
Before the modern era of antibiotics, most effusions and empyemas were related to Streptococcus pneumoniae pneumonia. Pneumococcal infections normally respond to antibiotic therapy. These are less frequently associated with pleural-space infections today than they were before. Staphylococcal species and anaerobic pathogens are now the most common microorganisms associated with empyema. Because half of staphylococcal effusions progress to empyema, early drainage may be indicated if this organism is isolated. The reemergence of tuberculosis may increase the association of Mycobacterium infection with empyema.
Most parapneumonic effusions resolve with appropriate and timely antibiotic therapy. However, other effusions can progress to an empyema if drainage is not promptly performed. Interventions are uncomfortable, and complications can occur.
See Intervention for more information about treatments.
Preferred Examination
Standard 2-view chest radiography remains the first study for evaluating effusion or empyema. If an effusion is present, bilateral decubitus imaging is indicated for further characterization. These examinations are informative and cost-effective.
Ultrasonography may show small volumes of pleural fluid, and it may provide information about viscosity. Ultrasonography may also quickly demonstrate septa in the pleural fluid collection.
Chest CT provides the most information. CT imaging depicts fluid, loculation, and thickening of the pleural membranes. CT and ultrasonography are also used in the placement of drainage catheters.
Limitations of Techniques
Two-view chest radiographs and decubitus views are not always obtainable in the intensive care unit. Radiographs are often limited to bedside supine or semierect anteroposterior views in very ill patients. A small fluid collection in the subpulmonic recess may be present but not detected on radiographs. Ultrasonography may demonstrate septa in the pleural fluid, but it poorly demonstrates the thickness of the pleura.
Patient Education: For excellent patient education resources, visit eMedicine's Pneumonia Center. Also, see eMedicine's patient education article Bacterial Pneumonia.
Differential Diagnoses
More on Empyema |
 Overview: Empyema |
| Imaging: Empyema |
| Follow-up: Empyema |
| Multimedia: Empyema |
| References |
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References
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Light RW. Clinical practice. Pleural effusion. N Engl J Med. Jun 20 2002;346(25):1971-7. [Medline].
Light RW. The management of parapneumonic effusions and empyema. Curr Opin Pulm Med. Jul 1998;4(4):227-9. [Medline].
Lim TK. Management of parapneumonic pleural effusion. Curr Opin Pulm Med. Jul 2001;7(4):193-7. [Medline].
Ploton C, Freydiere AM, Benito Y, Bendridi N, Mazzocchi C, Bellon G. Streptococcus pneumoniae thoracic empyema in children: rapid diagnosis by using the Binax NOW immunochromatographic membrane test in pleural fluids. Pathol Biol (Paris). Oct-Nov 2006;54(8-9):498-501. [Medline].
Sahn SA. Use of fibrinolytic agents in the management of complicated parapneumonic effusions and empyemas. Thorax. Aug 1998;53 Suppl 2:S65-72. [Medline].
Temes RT, Follis F, Kessler RM, et al. Intrapleural fibrinolytics in management of empyema thoracis. Chest. Jul 1996;110(1):102-6. [Medline].
Further Reading
Keywords
organizing effusion, complicated effusion, loculated effusion, pleural pus, intrapleural pus, pleural-space infection
