You are in: eMedicine Specialties > Radiology > CHEST EmpyemaArticle Last Updated: Aug 14, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Marc Tobler, MD, Staff Physician, Department of Diagnostic Radiology, Scott and White Memorial Hospital and Clinic Marc Tobler is a member of the following medical societies: American Medical Association Coauthor(s): J Michael Holbert, MD, Associate Professor, Department of Radiology, Scott and White Memorial Hospital and Clinic Editors: Judith K Amorosa, MD, FACR, Clinical Professor and Program Director, Department of Radiology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School; Consulting Staff, Department of Radiology, Robert Wood Johnson University Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; W Richard Webb, MD, Chief of Thoracic Imaging, Professor, Department of Radiology, University of California at San Francisco; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Barry H Gross, MD, Professor, Department of Radiology, University of Michigan Medical School; Professor, University of Michigan Cancer Center Author and Editor Disclosure Synonyms and related keywords: organizing effusion, complicated effusion, loculated effusion, pleural pus, intrapleural pus, pleural-space infection INTRODUCTIONSection 2 of 12
  BackgroundEmpyema 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:
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. PathophysiologyThe 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:
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.FrequencyUnited StatesOne 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. InternationalOverall, 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
RaceRace statistics for pleural-space infection or empyema are not known. SexThe 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. AgeAge statistics for pleural-space infection are not known. AnatomyThe 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.Clinical DetailsAs 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 ExaminationStandard 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 TechniquesTwo-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. DIFFERENTIALSSection 3 of 12
Effusion, Pleural Mesothelioma, Malignant RADIOGRAPHSection 4 of 12
FindingsFree-flowing pleural fluid collects in the dependent portion of the pleural space. On 2-view chest radiographs, pleural fluid obscures the costophrenic angle (see Image 1). Approximately 75 mL of fluid is required to blunt the posterior costophrenic angle on a lateral chest radiograph. Almost 200 mL of fluid is required to blunt the lateral costophrenic angles on frontal radiographs. If loculations have formed, fluid opacity may be seen in a nondependent area. The D configuration of loculated fluid bulging out from the chest wall is a classically described but infrequently observed finding. Although supine or semierect radiographs do not show pleural effusion as well as upright 2-view chest radiographs do, an ill patient is often unable to stand. A unilateral free-flowing effusion results in increased hazy opacity on the side of the affected hemithorax. If a pleural effusion is suspected, bilateral decubitus views are recommended. When an effusion is identified, the width of the layering fluid may be measured. If the width of the fluid is <10 mm, the effusion may be managed medically and followed up with serial radiographs. However, if the effusion is wider than 10 mm, thoracentesis or catheter drainage should be performed, if clinically indicated. CT or ultrasonographic guidance is best for placing a pleural catheter for drainage. Degree of ConfidenceWhen 2-view chest radiographs are used to detect pleural fluid, the sensitivity is 67% and the specificity is 70%. Decubitus views increase the degree of confidence. However, decubitus views are often skipped, and instead, the patient undergoes a CT examination. False Positives/NegativesEmpyema is not diagnosed strictly on the basis of traditional radiographic findings. Further imaging with CT and confirmation of pleural infection with thoracentesis are usually required to diagnose empyema. CT SCANSection 5 of 12
FindingsCT is the imaging study of choice for evaluating possible empyema. Depending on the expected clinical management, patients can undergo imaging with or without intravenously administered contrast material. If tapping of a clinically significant pleural effusion is clinically indicated, no intravenous contrast medium is necessary to evaluate for the presence and location of pleural fluid. The typical empyema is lenticular. Nonenhanced CT scans can demonstrate atypical pleural effusions along the mediastinum, thickened pleurae, loculations in the fissures, septa, or gas bubbles in the pleural space (see Image 2). Gas bubbles in the pleural space strongly suggest an empyema in the proper clinical context (ie, in the absence of recent thoracentesis). Lung windows can demonstrate pneumonia adjacent to the abnormal pleural collection. Soft-tissue windows can demonstrate a cause for the empyema, such as esophageal rupture or mediastinal surgery. With most empyemas, enhanced chest CT scans demonstrate the split-pleura sign (see Image 3). This sign can also be seen in chronic pleural effusions. Enhanced CT scans also depict parietal pleural thickening in most cases of empyema. Empyema necessitatis occurs when the pleural infection extends beyond the thoracic cavity into the chest wall (see Image 5). Although CT signs can be diagnostic of empyema, a pleural tap is indicated for culturing and sensitivity analysis. Degree of ConfidenceIf no interventional procedure has been performed, gas bubbles in a pleural fluid collection are virtually diagnostic of an empyema. Enhancing pleura and thickened parietal pleura are also strongly associated with empyema. In a study of empyema, pleural enhancement was seen in every case, and pleural thickening was seen in 92%.3 False Positives/NegativesAn enhancing pleura sign can be present in chronic pleural effusion and metastatic disease. Without gas bubbles in a pleural fluid collection or an enhancing pleura sign, the diagnosis of infection in pleural fluid depends on a high level of clinical suspicion confirmed with findings from thoracentesis. Although pleural thickening is present in empyemas, it can also be seen in other diseases, such as chronic effusion or asbestos exposure. A pleural exudate without pleural thickening most likely represents malignancy or uncomplicated pleural effusion.MRISection 6 of 12
FindingsMRI is rarely used to image pleural effusion and empyema. It may be useful for evaluating thickening of the pleural membrane when the administration of contrast material is contraindicated. Degree of ConfidenceThe degree of confidence in the diagnosis of empyema is moderate. False Positives/NegativesMRI is not routinely used to diagnose empyema. ULTRASOUNDSection 7 of 12
FindingsUltrasonography is an important adjunct in defining the characteristics of a pleural effusion. It may be used to detect small effusions. Ultrasonography also provides information about fluid viscosity, the presence of septa, and the free-flowing or loculated nature of the effusion. Degree of ConfidenceLoculated effusions suggest empyema in the proper clinical context, but the diagnosis must be confirmed with thoracentesis. False Positives/NegativesThe diagnosis of empyema is not based solely on ultrasonographic results. NUCLEAR MEDICINESection 8 of 12
FindingsNuclear medicine scans are not used in the routine workup for effusion and empyema. Effusions may be seen on ventilation and perfusion scans. Diffusely decreased unilateral intensity on both ventilation and perfusion studies may suggest a layering effusion. Degree of ConfidenceNuclear medicine tests are not used as diagnostic studies for empyema. ANGIOGRAPHYSection 9 of 12
FindingsAngiography does not have a role in the management of empyema. The interventional radiologist may need to perform thoracentesis with imaging guidance, and an indwelling catheter may be needed. INTERVENTIONSection 10 of 12
The main clinical decision is determining the appropriate time to drain the empyema. Appropriate imaging may help the clinician in choosing and timing intervention. Choosing the appropriate time to perform drainage is a difficult clinical decision. In 2000, the American College of Chest Physicians reviewed the literature and issued a consensus statement on the medical and surgical treatment of parapneumonic effusions. In the setting of a parapneumonic effusion, the following findings suggest a moderate or high risk for a poor outcome: large, free-flowing effusion (at least half of a hemithorax); loculated effusion or effusion with thickened parietal pleura; positive cultures or Gram stains; pleural pus; and pH < 7.20. When these findings are present, drainage is recommended. Light's criteria define transudative and exudative effusions. Other investigators have tried to clarify when an exudative effusion should be drained. Laboratory indications for consideration of drainage are the following:
Thoracentesis Ultrasonography or CT guidance is often used to improve the success of a thoracentesis. Single thoracentesis and a course of antibiotics may be effective at the earliest stages of empyema formation. If the effusion recurs, placement of a chest tube or small-bore catheter for continuous drainage is the next step. The placement of a small-bore catheter (thin-walled, 8-16F catheter) is also often accomplished under ultrasonographic or CT guidance. The small-bore catheter is often more comfortable for the patient than the traditional thoracostomy tube. Surgical interventions In the past, a few loculations in an empyema often indicated the need for surgical intervention because the loculations did not drain well. Fibrinolytics increase the success rate of catheter drainage by decreasing the viscosity of the effusion and by dissolving some adhesions. Fibrinolytic therapy has reduced the need for surgery. Surgical intervention is still required for effusions with multiple loculations that are difficult to drain and for effusions that have not responded to catheter drainage. Empyema at the organizing stage requires surgical intervention. Surgical interventions may include the following:
Medical/Legal Pitfalls
MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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