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Postgraduate Education Corner: CHEST IMAGING FOR CLINICIANS: REVIEW |

Diagnostic Utility and Clinical Application of Imaging for Pleural Space Infections FREE TO VIEW

John E. Heffner, MD, FCCP; Jeffrey S. Klein, MD, FCCP; Christopher Hampson, MD
Author and Funding Information

From the Department of Medical Education (Dr Heffner), Providence Portland Medical Center, Oregon Health and Science Center, Portland, OR; and the Department of Thoracic Radiology (Drs Klein and Hampson), Fletcher Allen Health Care, University of Vermont College of Medicine, Burlington, VT.

Correspondence to: John E. Heffner, MD, FCCP, Providence Portland Medical Center, 5050 NE Hoyt St, Suite 540, Portland, OR 97213; e-mail: John_heffner@mac.com


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(2):467-479. doi:10.1378/chest.08-3002
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Timely diagnosis of pleural space infections and rapid initiation of effective pleural drainage for those patients with complicated parapneumonic effusions or empyema represent keystone principles for managing patients with pneumonia. Advances in chest imaging provide opportunities to detect parapneumonic effusions with high sensitivity in patients hospitalized for pneumonia and to guide interventional therapy. Standard radiographs retain their primary role for screening patients with pneumonia for the presence of an effusion to determine the need for thoracentesis. Ultrasonography and CT scanning, however, have greater sensitivity for fluid detection and provide additional information for determining the extent and nature of pleural infection. MRI and PET scan can image pleural disease, but their role in managing parapneumonic effusions is not yet clearly defined. Effective application of chest images for patients at risk for pleural infection, however, requires a comprehensive understanding of the unique features of each modality and relative value. This review presents the diagnostic usefulness and clinical application of chest imaging studies for evaluating and managing pleural space infections in patients hospitalized for pneumonia.

Figures in this Article

Because of the considerable morbidity and mortality of empyema, all patients hospitalized with pneumonia should undergo a careful evaluation to identify the presence of a parapneumonic effusion and determine whether pleural fluid needs to be drained.1 Thoracic imaging represents an important component of this evaluation.1,2 Recent advances in imaging techniques have revolutionized the management of pleural infections by improving the detection of infected fluid and guiding and monitoring therapeutic interventions. The present review compares the diagnostic usefulness of imaging modalities and how they can contribute to management decisions for patients with pneumonia complicated by parapneumonic effusions.

In health, imaging studies cannot visualize the pleural space against the diaphragm and chest wall3 because pleural membranes are only 0.2 to 0.4 mm thick and physiologic volumes (4 to 18 mL)4 of pleural fluid form a thin 5- to 10- μ m layer.5 The invaginations of visceral pleura composing the interlobar and accessory fissures appear as linear or curvilinear lines. Interlobar loculated fluid may simulate parenchymal or intrapleural neoplasms (pseudotumors) (Fig 1). The peripheral pleural surfaces adjacent to the chest wall include the costal pleurae that compose the majority of the pleural surface in contact with the ribs, the mediastinal pleurae, and the diaphragmatic pleurae situated medially and inferiorly, respectively. What may appear to represent costal pleural membranes on CT images is actually a combination of visceral and parietal pleurae, physiologic pleural fluid, fascia, and the innermost intercostal muscles (Fig 1C).

Figure Jump LinkFigure 1. The frontal radiograph (A) shows right-sided subpulmonic and loculated lateral pleural effusion and a pseudotumor in the medial, mid-lung field. The lateral projection (B) localizes the pseudotumor to the upper major fissure. The pseudotumor appears more rounded than the usual lenticular appearance. A contrast-enhanced chest CT slice (C) confirms the pseudotumor to be a loculated pleural effusion within the major fissure (arrow), with additional lateral and posterior locules. The CT scan does not visualize costal pleural membranes in the left hemithorax; what appear to be pleural membranes (arrowheads) actually represent a combination of visceral and parietal pleurae, physiologic pleural fluid, fascia, and the innermost intercostal muscles.Grahic Jump Location

Standard chest radiographs survey the entire pleural space, underlying lung, mediastinum, chest wall, and spine for potential causes and complications of the pleural process. The presence of a lung cavity situated medial to pleural fluid collections, for instance, identifies a lung abscess (Fig 2).

Figure Jump LinkFigure 2. Frontal chest radiograph that demonstrates an air-fluid level within rounded density (arrow) that suggested a lung abscess in a patient with multiloculated empyema involving the right apex and paramediastinal pleurae. Contrast-enhanced CT scan (B) through the lower thorax showed fluid collections in the major fissure (F) and posteriorly with a cavitary abscess in the right lower lobe (arrow). The hilum is poorly defined on the frontal radiograph because of a paramediastinal fluid collection confirmed by CT scan (CT image not shown).Grahic Jump Location

The radiographic appearance of infected pleural fluid collections depends on the volume and viscosity of pleural fluid, the patient ' s position, and presence of pleural loculations. Of special note are difficulties of detecting and assessing subpulmonic effusions (Fig 3),6 nondependent loculations that simulate masses or airspace densities on frontal projections (Fig 4), loculated collections along mediastinal pleural reflections (Fig 5), and effusions on portable radiographs (Figs 5-7).

Figure Jump LinkFigure 3. Frontal (A) and lateral (B) radiographs demonstrate a subpulmonic effusion with apparent elevation of the right diaphragm with a laterally displaced apex (arrow in A). In B, note the sloping interface (white arrows) between the effusion (*) and the middle lobe anterior to the major fissure (solid arrow). This appearance results from the oblique interface between the subpulmonic effusion and the middle lobe anterior to the major fissure, as the lung-fluid interface fails to create a sharp tangent to the lateral x-ray beam and therefore is not evident radiographically.Grahic Jump Location
Figure Jump LinkFigure 4. Frontal radiograph (A) of a patient with multilocular empyema demonstrating obscuration of the left hemidiaphragm by lung consolidation and pleural fluid and an ill-defined density in the medial, midlung field (arrow). The lateral view (B) demonstrates a nondependent loculated empyema (arrows) with the “ d-sign.” Grahic Jump Location
Figure Jump LinkFigure 5. Supine portable radiograph (A) in a patient with large posterior bilateral pleural effusions that demonstrates increased density over both lung fields. The CT scan (B) shows the large effusions layering posteriorly. Passive atelectasis of the left and right lung (arrows) is demonstrated in this contrast-enhanced study. The homogeneity of the atelectatic lung on all sections excludes lung necrosis or abscess There is no evidence of parietal pleural thickening or enhancement on this CT level.Grahic Jump Location
Figure Jump LinkFigure 6. Portable radiograph (A) of a large left pleural effusion in a patient with mediastinal lymphoma (note mediastinal widening and obscuration of aortic arch) that demonstrates crescentic fluid density (arrow) over the lung apex. A contrast-enhanced CT scan (B) shows the left pleural effusion with the enhancing atelectatic left lung sharply delineated from the effusion.Grahic Jump Location
Figure Jump LinkFigure 7. Frontal radiograph of a patient with a pleural effusion that collects within an incomplete right major fissure, which creates a perihilar lucency outlined peripherally by a circumscribed concave opacity.Grahic Jump Location

For ultrasonographic chest examination, a narrow footprint linear or sector transducer is typically used. A high-frequency linear transducer (5-7.5 MHz) provides high-resolution intercostal scanning, but is limited in penetration for patients with thick chest walls and does not provide a large field of view for visualization of the pleural space and underlying lung.7 For most patients, a convex or sector transducer of intermediate frequency (3-4 MHz) provides the best compromise between near-field resolution of the lung-pleura interface, a wider evaluation of large effusions, and assessment of the parietal pleura and lung parenchyma.8-10

Normal pleural membranes are too thin to be visualized even by high-resolution ultrasonography. The interface between the normal visceral pleura and underlying lung produces the “ pleural stripe ” which is a thin echogenic line projecting internal to the ribs (Fig 8). It moves craniocaudally with respiration on ultrasonograph.7 Another ultrasonography finding in normal patients is the comet-tail artifact, which is seen deep to the pleural stripe and results from subpleural interlobular septae in normally aerated lung at its interface with the pleural surface. In patients with underlying consolidation or atelectasis of the lung, particularly in the presence of pleural effusion, the visceral pleura is visible as an echogenic line thinner than the previously mentioned pleural interface. Focal pleural masses associated with an effusion are readily seen and biopsied with ultrasonography guidance.11,12 Ultrasonography allows characterization of pleural fluid collections with septations and loculations being better appreciated than on CT scan, but pleural thickening and the extent of pleural disease throughout the thorax are more difficult to assess.

Figure Jump LinkFigure 8. Sonogram of a normal patient shows a thin echogenic interface between the normal visceral pleura and underlying lung deep to the ribs that produces the normal pleural stripe (arrows).Grahic Jump Location

Ultrasonography is more sensitive (5 mL fluid detectable) than decubitus radiography.13-18 Pleural effusions typically appear as triangular anechoic collections immediately above the diaphragm (Fig 9) that change shape with respiration and outline the underlying echogenic, airless posterior costophrenic sulcus. Portable chest ultrasonograph examination is particularly useful to detect and quantify pleural fluid collections in supine critically ill patients.19

Figure Jump LinkFigure 9. The frontal radiograph (A) suggests a right parapneumonic effusion, which is confirmed by sonographic evidence (B) of a characteristic triangular anechoic fluid collection immediately above the diaphragm. Eff = effusion; L = lung; Li = liver.Grahic Jump Location

Chest ultrasonography can also suggest the nature of fluid collections. Four typical internal echogenicity patterns of pleural effusion on sonography have been described: (1) homogeneously anechoic (Fig 10A), (2) complex nonseptated with internal echogenic foci (Fig 10B), (3) complex septated (Fig 10C), and (4) homogeneously echogenic (Fig 10D).20 Although transudative pleural effusions are typically anechoic, as many as 55% of proven transudative pleural effusions will have a complex nonseptated appearance.21 Conversely, although most complicated parapneumonic effusions and empyemas contain internal echoes or appear entirely echogenic, up to 27% of exudative effusions are anechoic.20

Figure Jump LinkFigure 10. Sonographic appearance of parapneumonic effusions with the patterns of homogeneously anechoic (asterisk denotes fluid) (A), complex nonseptated with internal echogenic foci (B), complex septated (C), and homogeneously echogenic (D). Most complicated parapneumonic effusions and empyemas have internal echoes or appear entirely echogenic. “ L ” denotes lung and curved arrow identifies the diaphragm.Grahic Jump Location

Uniformly echogenic collections typically contain blood or debris and almost invariably indicate the presence of an empyema in patients who appear clinically infected.22 Large, discrete, primary loculations of pleural fluid establish the presence of visceral to parietal pleural adhesions and suggest empyema in appropriate settings.23 Evidence by ultrasonography of secondary loculations or septations within pleural fluid collections (honeycomb appearance) has no diagnostic value.

Multidetector CT scan allows acquisition of contiguous 1- to 3-mm sections through the chest during one breath hold and provides high-resolution imaging of the pleura with multiplanar coronal and sagittal reconstructions that assist the evaluation of complex pleural abnormalities adjacent to lung, mediastinal, and chest wall lesions (Fig 11).24 Intravenous contrast allows differentiation of pleural membranes from parenchymal processes for patients with empyema and associated pulmonary infections or neoplasms.7 Obtaining images 20 to 60 s after contrast infusion allows the best visualization of pulmonary vasculature and separation of lung from pleural abnormalities.7

Figure Jump LinkFigure 11. Pyopneumothorax due to bronchopleural fistula complicating lung abscess. (A) Upright chest radiograph shows a large right hydropneumothorax with small air-fluid level in consolidated right mid lung (arrow). (B) Contrast-enhanced CT shows a cavity with air-fluid level (white arrow) reflecting an abscess within the consolidated middle lobe. There is a large right hydropneumothorax with thickening and enhancement of the parietal pleura (black arrow). (C) Sagittal reformatted image through the middle lobe abscess shows a large bronchopleural fistula (white arrows) extending posterosuperiorly from the abscess cavity to the posterior hydropneumothorax. Purulent material was recovered at surgery.Grahic Jump Location

CT scan cannot visualize normal pleura against the chest wall because pleural membranes blend in with endothoracic fascia and intercostal muscles.3 In the paravertebral regions, a thin line representing the pleural layers and pleural space may be visible because the innermost intercostal muscle is absent in this region. The interlobar and accessory fissures are visible in cross section as curvilinear opacities on thin-section axial, sagittal, and coronal reformatted images. Visualization of a thin layer of tissue along the internal margin of the inner cortices of the ribs is abnormal and indicates the presence of pleural thickening or effusion. An exception to this rule exists along the right and left parasternal portions of the costal pleural surfaces, where the transversus thoracis muscles are seen as symmetric thin soft-tissue densities, and along the lower posterior costal pleural surface, where the subcostalis muscles are variably seen as thin linear opacities internal to the lower posterior ribs. These densities are easily distinguished from pleural thickening (Fig 12).

Figure Jump LinkFigure 12. A patient with two chest tubes in the right hemithorax that drain a parapneumonic effusion. There is asymmetric thickening of the right posterolateral chest wall and expansion of the extrapleural fat (black straight arrow) due to edema, findings commonly observed with empyemas. A small amount of pleural fluid remains posteriorly (curved arrow). The left hemithorax demonstrates the normal appearance of the inner cortices of the ribs wherein no tissue can be visualized adjacent to the lung (arrowhead). In contrast, the finding of even a thin layer of tissue along the inner rib cortices establishes pleural thickening or effusion (white arrow).Grahic Jump Location

Chest CT scan is more sensitive than chest radiography for detecting small pleural effusions.7 Because CT scan provides an unimpeded view of the entire pleural surface, the underlying lung parenchyma, and the adjacent mediastinum and chest wall, it is the ideal modality for determining the extent of pleural infection and the nature of fluid collections.

The signs of pleural fluid on CT scan parallel those observed on conventional radiography. Small, free-flowing effusions appear as meniscoid collections of water attenuation along the posterior pleural surfaces. Small effusions form a sharp interface with the lower lobe. Large effusions cause passive atelectasis of adjacent lung and produce on non-contrasted studies an irregular interface with aerated lung. With contrast, the atelectatic lung undergoes enhancement and becomes sharply delineated from the effusion (Fig 6B). As effusions increase in volume, they extend farther cranially up the posterior pleural surface, eventually extending over the lung apex. They also extend along the lateral margins of the lung and into interlobar fissures. Large effusions produce extensive passive atelectasis of the lung and often produce contralateral shift of the heart and mediastinum.

Loculated effusions appear as lenticular masses of fluid attenuation, most often situated in the dependent portions of the costal pleural space along the lower posterior pleural surface. Medially situated fluid collections adjacent to the mediastinum are easily delineated on CT scan. Loculated fluid collections within the major or minor fissures produce pseudotumors, which can simulate underlying lung cancer or abscess on standard radiographs (Fig 1C).5

The attenuation of pleural fluid collections provides some diagnostic information but does not allow definite distinction between infected and uninfected effusions. Most infected pleural fluid collections have attenuation similar to water (ie, 0 Hounsfield units), whereas collections with high protein content and bloody effusions may have attenuations of soft tissue (ie, 30-50 Hounsfield units) (Fig 13). The detection of air in the pleural space, in the absence of recent thoracentesis, chest tube placement, or surgical intervention, almost invariably indicates pleural infection, most often a necrotizing pneumonia or abscess with rupture into the pleural space. Spontaneous or posttraumatic rupture of the esophagus or central airways can likewise produce a hydropneumothorax. The detection of small air bubbles within a pleural collection is specific for an infected pleural fluid collection.

Figure Jump LinkFigure 13. CT image of a patient with a subpleural lung abscess (upper short arrow) and an adjacent region (lower short arrow) of either loculated pleural fluid of high attenuation or pleural thickening. Additional high-attenuation pleural fluid or thickening is seen posteriorly (long arrow).Grahic Jump Location

Conditions that thicken the pleura render them visible on CT scan. Parietal pleural thickening almost always indicates the presence of a pleural exudate, although this finding is not specific for infection.25 Even without contrast, thickening of the parietal pleura in a patient with pleural infection is easily detected by CT scan. Pleural infection typically produces smooth, uniform pleural thickening almost always limited to the costal and diaphragmatic pleural surfaces. The detection of mediastinal pleural thickening or nodules along thickened parietal pleural surfaces on CT scan suggests pleural malignancy. Although thickening of the parietal pleura underlying the ribs is relatively specific for an exudative pleural effusion, patients with transudative effusions and preexisting underlying pleural fibrosis or pleural malignancy will also demonstrate this finding. In patients with infected pleural fluid collections, the identification of a thickened, enhancing rim of parietal and visceral pleura surrounding a loculated pleural fluid collection on contrast-enhanced CT scan (split pleura sign) (Fig 14) is reliable evidence of empyema.25

Figure Jump LinkFigure 14. A CT image of a patient with empyema demonstrating enhancing rims of parietal and visceral pleurae (short arrows) surrounding a loculated pleural fluid collection (split pleura sign). Note the hypertrophied extrapleural fat (long arrows) due to the chronic thickening and retraction of the pleural layers, which are commonly associated with empyemas.Grahic Jump Location

Increased attenuation of extrapleural fat and thickening of the fat layer ≥ 3 mm is seen in 60% of empyemas.25,26 Patients with transudates have normal-appearing extrapleural tissue.26 Although similar extrapleural changes are noted in 27% of patients with malignant pleural processes, the majority of such patients have a complicating pleural infection or a history of prior pleurodesis.27

CT scan evaluates the underlying lung, adjacent chest wall including ribs and spine, the diaphragm, and the subphrenic space. Pneumonia, lung abscess, or obstructing malignancy are readily evident on contrast-enhanced studies. In patients with fibrinopurulent pleural infections, the underlying lung often shows multiple alternating outpouchings and indentations due to fibrin strands that produce intrapleural adhesions. Septations within an infected effusion are less readily imaged as compared with ultrasonography.28 Pleural-based lung abscesses may be difficult to distinguish from loculated empyemas. On CT scan, lung abscesses tend to be round rather than lenticular in shape like empyemas and also have thick, irregular walls and do not displace adjacent lung.29

If ineffectively treated, empyemas can progress to a fibrothorax with pleural peels that appear as uniform smooth thickenings of the pleurae with hypertrophy of the extrapleural fat and reduced volume of the affected hemothorax with narrowing of the intercostal spaces and shift of the mediastinum to the affected side. Chest CT scan cannot predict the likelihood that pleural thickening during the fibrinopurulent phase of pleural infections will progress to fibrothorax.30

MRI plays a limited role in evaluating suspected pleural infections. The ability of MRI to provide a global view of the pleural space in axial, sagittal, and coronal planes without ionizing radiation suggests possible advantages. Chest MRI provides similar accuracy as CT scan in differentiating loculated pleural effusions from underlying lung. But difficulties in performing motion-free high-quality MRI studies for seriously ill patients and the superior spatial resolution of multidetector CT scan in evaluating the underlying lung have limited the application of MRI for evaluating the pleural space. Its use is limited to assessing patients with known pleural infection who have suspected spinal or rib involvement.

Chest imaging with positron emission tomography using 2-[18F]-fluoro-2-deoxy-glucose (FDG-PET) has a limited role for evaluating pleural infections. It may contribute in special circumstances when more conventional techniques cannot discriminate between pleural infections and malignancies (see later discussion) because FDG-PET scan may demonstrate different uptake characteristics in pleural membranes in these two conditions.31,32

As reviewed in the previous sections, existing chest imaging provides information about the presence, nature, and extent of pleural infection. Application of various modalities to individual patients, however, requires an understanding of the comparative value of each modality in addressing specific clinical questions faced in managing pneumonia. The following sections review evidence that assists clinicians in applying chest imaging studies and interpreting their results when evaluating suspected pleural infections.

Detection of Pleural Effusions in Patients at Risk

Standard chest radiographs remain the initial study to screen patients with pneumonia for pleural fluid.7 Free-flowing or loculated moderate-to-large effusions may present obvious evidence of pleural fluid and justify in most circumstances proceeding to image-guided thoracentesis. Lower lung zone lung consolidation may obscure radiographic evidence of pleural fluid and require additional imaging studies. Decubitus views represent the traditional follow-up study when standard radiographs cannot exclude pleural fluid.33 Chest ultrasonography has replaced decubitus views because it is fast, effective, more sensitive,13-18,34 and portable.35

The utility of portable ultrasonography for detecting effusions has been demonstrated in the ED13 and in the ICU.22,36 Also, Tu and coworkers22 demonstrated in critically ill patients that the ultrasonographic features of pleural fluid predict the probability of pleural infection and need for diagnostic thoracentesis. Patients with anechoic or complex nonseptated and relatively nonhyperechoic fluid had low risk for empyema and thoracentesis could be deferred, whereas patients with complex septated, homogenously echogenic, or complex nonseptated and relatively hyperechoic patterns required immediate thoracentesis.

Chest CT scan is not used routinely as the initial imaging study for detecting pleural fluid. Exceptions include patients suspected of having fluid loculated in interlobar fissures or paramediastinal locations beyond the range of ultrasonography detection. Also, in centers with ready access to CT scanning on an urgent basis, contrast-enhanced CT scan may be the preferred initial imaging study rather than ultrasonography if the standard radiograph demonstrates pulmonary parenchymal lesions suggestive of cancer, septic emboli, or cavitation. Additionally, chest CT scan can better distinguish between a loculated empyema or subpleural lung abscess.

Imaging for Guiding Thoracentesis

Experts have deemed thoracentesis guided by chest percussion and auscultation as safe and feasible if standard radiographs demonstrate large effusions or if small effusions layer to a depth of > 1 cm on decubitus views.37 These approaches, however, have a pneumothorax rate of 10% to 39%38-42 and a 12% to 15% rate for a dry tap.43 Thoracentesis guided by ultrasonography decreases complications38,40,41 and improves fluid collection rates.43-45 Diacon and coworkers46 demonstrated the superiority of US as compared with standard radiographs combined with the physical examination to identify appropriate needle insertion sites. Ultrasonography is rapidly emerging as a standard of care in guiding thoracentesis for parapneumonic effusions, especially in the critical care setting.22,36 For guiding thoracentesis, chest CT scan is reserved for patients with pleural fluid loculations in locations that do not allow safe access by ultrasonographic guidance.47

Using Imaging Studies for Selecting Therapeutic Interventions

Pleural space infections that progress to empyema are categorized in three phases: exudative, fibrinopurulent, and organized.1 Each phase has management implications, with more advanced phases requiring increasingly invasive drainage interventions. Ideally, findings from imaging studies would assist clinicians in identifying the phase of empyema formation and selecting patients for initial chest tube drainage, fibrinolytic therapy, thoracoscopy, or thoracotomy.

The American College of Chest Physicians clinical practice guideline for empyema management recommends initial imaging findings for guiding therapeutic decisions.1 Large effusions that occupy greater than 50% of the hemithorax, the presence of pleural loculations, and signs of pleural thickening are stated to indicate a poor prognosis with medical management and require surgical drainage.1 Unfortunately, limited evidence exists to support these recommendations.

The standard radiograph provides minimal information for guiding therapeutic interventions. The presence of intrapleural air-fluid levels indicative of a bronchopleural fistula establishes a need for surgery. Otherwise, the size, location, or distribution of pleural fluid on standard radiographs has limited therapeutic implications.

Expert opinion advises that demonstration of loculations and pleural thickening by CT scan or ultrasonography identifies patients with late-stage empyemas who will fail chest tube drainage and require fibrinolytic therapy or surgical interventions.48 Studies have conflicted, however, in supporting this impression. For determining success of image-guided chest tube drainage, Akhan and coworkers47 reported that the presence of nonloculated anechoic collections without septae on ultrasonograph had a high likelihood of successful treatment with image-guided catheter drainage. Otherwise, no other ultrasonography findings were associated with chest tube success or failure. Another study examined all patients with ultrasonography before image-guided catheter drainage and noted success rates of 92% with anechoic effusions, 81% with complex nonseptated effusions, and 63% with complex septated effusions.49 In contrast, Keeling and coworkers50 found no relationship between ultrasonography or CT scan appearances of the pleural space and the phase of empyema or efficacy of small-bore chest tube drainage. In the absence of appropriately designed blinded prospective studies, it remains unclear whether scan CT scan or ultrasonography findings predict outcome of image-guided chest tube drainage. Despite the absence of data, Chen and coworkers51 noted that evidence of sonographic septae indicated that clinicians would be more likely to proceed to intrapleural fibrinolytic therapy (63.8% vs 38.8%) or surgical intervention (24.3% vs 7.5%) in an unblinded study.

Regarding the ability of imaging studies to predict the success or failure of fibrinolytic therapy, Gervais and colleagues52 reported that CT scan features of number of loculations, degree of pleural thickening (range 1-15 mm), or pleural heterogeneity did not predict ultimate outcome for patients treated with intrapleural recombinant tissue plasminogen activator. Similarly, Levinson and Pennington53 noted no differences in outcomes between patients with single or multiple loculations treated with intrapleural urokinase or recombinant tissue plasminogen activator.

For selecting patients for initial video-assisted thoracoscopic surgery (VATS) vs proceeding directly to thoracotomy, CT scan and ultrasonography provide only general guidance. Among patients with empyema taken to VATS, 30% were under-staged by preoperative CT scanning and subsequently required drainage by thoracotomy.54 Similarly, Roberts55 demonstrated that CT scan did not identify patients who failed VATS and required conversion to thoracotomy. Evidence on CT scan of mediastinitis, severe tissue trauma, bronchopleural fistula, esophageal perforation, or other serious intrathoracic lesions may indicate a need for thoracotomy.54 Because multiloculated empyema can be treated by medical thoracoscopy as well as VATS,56 preoperative CT scanning assists patient selection for VATS only by detecting loculations beyond the reach of the medical thoracoscope or demonstrating definite evidence of fibrothorax. Most surgeons, however, recommend a preoperative CT scan before taking patients to VATS or thoracotomy.57

Although chest CT scan and ultrasonography may provide some guidance for selecting a therapeutic approach, their accuracies should not be overestimated. Prognostication from the results of imaging studies is difficult because multiple clinical factors, such as duration of illness, severity of illness, comorbid conditions, and operability, often determine the response to therapy and clinical course.2,58 Up to 70% of patients admitted with pneumonia and parapneumonic effusions have serious associated conditions.58-60 The clinical approach is as much driven by these factors as by the imaging appearance of the pleural space.

Imaging for Guiding Chest Tube Placement and Fibrinolytic Therapy

The success of chest tube drainage with or without fibrinolytic therapy depends on accurately placing the catheter into dependent regions of free-flowing or loculated effusions. Imaging by fluoroscopy, ultrasonography, or CT scan has been used for placement of small-bore catheters with good clinical results.47,50,52,61-65 Many centers use real-time ultrasonography imaging as their primary modality for placing catheters,49,66 although some interventional radiologists insert catheters without real-time imaging if the standard radiograph shows a large free-flowing effusion or if a recent CT scan or ultrasonograph is available.52 Advantages of real-time imaging include the ability to determine the need for multiple pigtail catheters during the procedure.47

Chest CT scan for catheter guidance is preferred when effusions are loculated and no safe access route can be identified by ultrasonography47 and when coexisting parenchymal lesions require imaging during catheter insertion.25-27,67 It is not the primary imaging modality for guiding catheter insertion, however, because of its cost, radiation exposure, and the need to transport patients.

Chest CT scan and ultrasonography have usefulness for directing drainage by thoracoscopy and thoracotomy. For medical thoracoscopy, it is advisable to select a site by ultrasonography for insertion of the trocar where loculated pleural fluid collections are the largest and a position distant from the diaphragm, which may be elevated.48 Most surgeons who perform drainage by VATS or thoracotomy perform a preoperative CT scan to determine the extent of pleural fluid collection to guide initial inspection of the pleural space.

Imaging for Monitoring Adequacy of Drainage

No outcome studies exist to guide the selection of post-drainage image studies to ensure adequacy of drainage and to time periodic imaging assessments efficiently. Depending on the location and nature of the initial pleural effusion at the time of drainage, periodic standard radiographs, ultrasonography studies, or repeat CT scans may be indicated. Standard radiographs are most useful for patients with free-flowing effusions that appear to drain well after catheter insertion with evidence on a postprocedure radiograph that complete drainage has occurred. For patients with more complicated pleural effusions with loculations, follow-up real-time ultrasonography provides opportunities to reposition the chest catheter, insert additional catheters if residual fluid appears unlikely to drain, and perform thoracentesis for loculations distant from the chest catheter.47 Chest CT scan may be necessary for patients with loculated effusions in interlobar fissures or adjacent to the mediastinum.53

Judgment is necessary for determining when to initiate additional drainage interventions when follow-up imaging identifies residual pleural fluid after catheter insertion. Levinson and coworkers47 recommend observing residual fluid collections less than 3 to 4 cm in diameter or containing less than 50 to 75 mL. Additional drainage procedures were recommended for larger fluid collections. Clinical signs of ongoing infection or sepsis, however, should also determine the need for additional efforts to drain residual fluid.

Special Circumstances
Empyema Necessitans:

If left untreated, chronic empyemas may progress to empyema necessitans, which develop when intrapleural suppuration dissects into the chest wall.47,47,47 Common pathogens include TB, Actinomycosis, and Nocardia, although this complication can also occur with mixed anaerobic species.68 Patients classically present with a painful chest wall mass typically between the second and sixth intercostal spaces.69 Empyema necessitans can also present as fistula tracts into the bronchi, esophagus, breast, diaphragm, retroperitoneum, and groin.69 Chest CT scan provides the most sensitive technique for detecting empyema necessitans and characterizing the extent of chest wall and adjacent structure invasion.69,70

Coexisting Malignancies or Extrapulmonary Infections:

Empyemas may occur in association with lung cancer, endobronchial metastases, and primary pleural malignancies. Endobronchial lung cancer and cancers metastatic to bronchi may cause postobstructive pneumonia with secondary empyema. In such settings, loculated empyemas may obscure radiographic evidence of the underlying malignancy. Patients with chronic empyemas, most notably tuberculous empyemas, can develop pyothorax-associated lymphoma (PAL), which is a body cavity primary lymphoma.71,72 Most of these tumors are non-Hodgkin lymphomas, which have been reported in 2.2% of patients with chronic empyemas in Japan.73

The standard chest radiograph has poor sensitivity for detecting malignancies because mediastinal lymphadenopathy, pleural thickening, cavitary lung lesions, and airway obstruction may result from the underlying lung and pleural infection. Chest ultrasonography may identify evidence of focal pleural masses and guide needle biopsy.11,12 Ultrasonography has advantages over chest CT scan in imaging the pleura overlying the diaphragms with the ability to guide successful biopsy of pleural nodules as small as 0.5 cm.12

Chest CT scan provides the most global information for detecting coexisting malignancies. CT scans may detect obstructing airway tumors and evidence of lung and pleural masses. Chest CT scan is also helpful in patients at risk for PAL. Evidence of increased opacity in the pleural space compared with the rest of the empyema cavity, soft tissue bulging, reduced sharpness of the fat planes in the chest wall, destruction of bone near the empyema, extensive medial deviation of calcified pleurae, and new onset of an air-fluid level in an empyema cavity have high sensitivity but low specificity for PAL.74,75 A single case report suggests that FDG-PET scan allows early detection of local recurrence of PAL in patients who responded to chemotherapy.76

Small studies suggest that FDG-PET scan can assist the discrimination of pleural infection from malignancy. In one study of 98 patients, only two of 12 patients with parapneumonic effusions had moderate or intense FDG uptake as compared with 52 of the 54 patients with cancer.31 Larger studies are needed, however, to establish the value of PET scan in this setting.

Chest CT scan or MRI may also demonstrate evidence of coexisting osteomyelitis of the vertebral column or rib with demonstration of bone destruction, periosteal reaction, or disc space destruction. An intraabdominal origin of pleural infection is demonstrated by CT scan detection of subphrenic fluid collections.

Modern imaging modalities have advanced the diagnosis and management of pleural infections. Standard radiographs remain the initial screening examination for most patients at risk, but ultrasonography and CT scan have emerged as important techniques, each with its unique value and application. The uniqueness of each patient who presents with pleural infection requires a clear understanding of the relative value of existing modalities in different settings. Unfortunately, the evidence base for the operating characteristics of imaging in pleural infections remains insufficient for developing high-grade clinical recommendations.

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

FDG-PET

2-[18F]-fluoro-2-deoxy-glucose positron emission tomography

PAL

pyothorax-associated lymphoma

VATS

video-assisted thoracoscopic surgery

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Davies CW, Gleeson FV, Davies RJ. Pleural Diseases Group Standards of Care Committee British Thoracic Society BTS guidelines for the management of pleural infection. Thorax. 2003;58suppl 2:ii18-ii28
 
Im JG, Webb WR, Rosen A, Gamsu G. Costal pleura: appearances at high-resolution CT. Radiology. 1989;1711:125-131
 
Noppen M, De Waele M, Li R, et al. Volume and cellular content of normal pleural fluid in humans examined by pleural lavage. Am J Respir Crit Care Med. 2000;1623 pt 1:1023-1026
 
Henschke CI, Davis SD, Romano PM, Yankelevitz DF. Pleural effusions: pathogenesis, radiologic evaluation, and therapy. J Thorac Imaging. 1989;41:49-60. [CrossRef]
 
Schwarz MI, Marmorstein BL. A new radiologic sign of subpulmonic effusion. Chest. 1975;672:176-178. [CrossRef]
 
Evans AL, Gleeson FV. Radiology in pleural disease: state of the art. Respirology. 2004;93:300-312. [CrossRef]
 
Wernecke K. Sonographic features of pleural disease. AJR Am J Roentgenol. 1997;1684:1061-1066
 
McLoud TC, Flower CDR. Imaging the pleura: sonography, CT, and MR imaging. AJR Am J Roentgenol. 1991;1566:1145-1153
 
Beckh S, B ölcskei PL, Lessnau KD. Real-time chest ultrasonography: a comprehensive review for the pulmonologist. Chest. 2002;1225:1759-1773. [CrossRef]
 
Chang DB, Yang PC, Luh KT, Kuo SH, Yu CJ. Ultrasound-guided pleural biopsy with Tru-Cut needle. Chest. 1991;1005:1328-1333. [CrossRef]
 
Adams RF, Gleeson FV. Percutaneous image-guided cutting-needle biopsy of the pleura in the presence of a suspected malignant effusion. Radiology. 2001;2192:510-514
 
Tayal VS, Nicks BA, Norton HJ. Emergency ultrasound evaluation of symptomatic nontraumatic pleural effusions. Am J Emerg Med. 2006;247:782-786. [CrossRef]
 
Mathis G. Thoraxsonography — Part I: Chest wall and pleura. Ultrasound Med Biol. 1997;238:1131-1139. [CrossRef]
 
Kocijancic I, Vidmar K, Ivanovi-Herceg Z. Chest sonography versus lateral decubitus radiography in the diagnosis of small pleural effusions. J Clin Ultrasound. 2003;312:69-74. [CrossRef]
 
Feller-Kopman D. Therapeutic thoracentesis: the role of ultrasound and pleural manometry. Curr Opin Pulm Med. 2007;134:312-318. [CrossRef]
 
Vignon P, Chastagner C, Berkane V, et al. Quantitative assessment of pleural effusion in critically ill patients by means of ultrasonography. Crit Care Med. 2005;338:1757-1763. [CrossRef]
 
Balik M, Plasil P, Waldauf P, et al. Ultrasound estimation of volume of pleural fluid in mechanically ventilated patients. Intensive Care Med. 2006;322:318-321. [CrossRef]
 
Lichtenstein DA, Menu Y. A bedside ultrasound sign ruling out pneumothorax in the critically ill. Lung sliding. Chest. 1995;1085:1345-1348. [CrossRef]
 
Yang P-C, Luh K-T, Chang D-B, et al. Value of sonography in determining the nature of pleural effusion: analysis of 320 cases. AJR Am J Roentgenol. 1992;1591:29-33
 
Chen HJ, Tu CY, Ling SJ, et al. Sonographic appearances in transudative pleural effusions: not always an anechoic pattern. Ultrasound Med Biol. 2008;343:362-369. [CrossRef]
 
Tu CY, Hsu WH, Hsia TC, et al. Pleural effusions in febrile medical ICU patients: chest ultrasound study. Chest. 2004;1264:1274-1280. [CrossRef]
 
Lomas DJ, Padley SG, Flower CDR. The sonographic appearances of pleural fluid. Br J Radiol. 1993;66787:619-624. [CrossRef]
 
Ravenel JG, McAdams HP. Multiplanar and three-dimensional imaging of the thorax. Radiol Clin North Am. 2003;413:475-489. [CrossRef]
 
Aquino SL, Webb WR, Gushiken BJ. Pleural exudates and transudates: diagnosis with contrast-enhanced CT. Radiology. 1994;1923:803-808
 
Takasugi JE, Godwin JD, Teefey SA. The extrapleural fat in empyema: CT appearance. Br J Radiol. 1991;64763:580-583. [CrossRef]
 
Waite RJ, Carbonneau RJ, Balikian JP, Umali CB, Pezzella AT, Nash G. Parietal pleural changes in empyema: appearances at CT. Radiology. 1990;1751:145-150
 
Kearney SE, Davies CW, Davies RJ, Gleeson FV. Computed tomography and ultrasound in parapneumonic effusions and empyema. Clin Radiol. 2000;557:542-547. [CrossRef]
 
Stark DD, Federle MP, Goodman PC, Podrasky AE, Webb WR. Differentiating lung abscess and empyema: radiography and computed tomography. AJR Am J Roentgenol. 1983;1411:163-167
 
Neff CC, vanSonnenberg E, Lawson DW, Patton AS. CT follow-up of empyemas: pleural peels resolve after percutaneous catheter drainage. Radiology. 1990;1761:195-197
 
Duysinx BC, Larock MP, Nguyen D, et al. 18F-FDG PET imaging in assessing exudative pleural effusions. Nucl Med Commun. 2006;2712:971-976. [CrossRef]
 
Toaff JS, Metser U, Gottfried M, et al. Differentiation between malignant and benign pleural effusion in patients with extra-pleural primary malignancies: assessment with positron emission tomography-computed tomography. Invest Radiol. 2005;404:204-209. [CrossRef]
 
Light RW. Parapneumonic effusions and empyema. Proc Am Thorac Soc. 2006;31:75-80. [CrossRef]
 
Eibenberger KL, Dock WI, Ammann ME, Dorffner R, Hörmann MF, Grabenwöger F. Quantification of pleural effusions: sonography versus radiography. Radiology. 1994;1913:681-684
 
Mayo PH, Doelken P. Pleural ultrasonography. Clin Chest Med. 2006;272:215-227. [CrossRef]
 
Nicolaou S, Talsky A, Khashoggi K, Venu V. Ultrasound-guided interventional radiology in critical care. Crit Care Med. 2007;355 suppl:S186-S197. [CrossRef]
 
Light RW. Pleural Disease. 2007; Philadelphia Lippincott Williams & Wilkins
 
Grogan DR, Irwin RS, Channick R, et al. Complications associated with thoracentesis. A prospective, randomized study comparing three different methods. Arch Intern Med. 1990;1504:873-877. [CrossRef]
 
Mayo PH, Goltz HR, Tafreshi M, Doelken P. Safety of ultrasound-guided thoracentesis in patients receiving mechanical ventilation. Chest. 2004;1253:1059-1062. [CrossRef]
 
Jones PW, Moyers JP, Rogers JT, Rodriguez RM, Lee YC, Light RW. Ultrasound-guided thoracentesis: is it a safer method? Chest. 2003;1232:418-423. [CrossRef]
 
Raptopoulos V, Davis LM, Lee G, Umali C, Lew R, Irwin RS. Factors affecting the development of pneumothorax associated with thoracentesis. AJR Am J Roentgenol. 1991;1565:917-920
 
Lichtenstein D, Hulot JS, Rabiller A, Tostivint I, Mezière G. Feasibility and safety of ultrasound-aided thoracentesis in mechanically ventilated patients. Intensive Care Med. 1999;259:955-958. [CrossRef]
 
Kohan JM, Poe RH, Israel RH, et al. Value of chest ultrasonography versus decubitus roentgenography for thoracentesis. Am Rev Respir Dis. 1986;1336:1124-1126
 
Hirsch JH, Rogers JV, Mack LA. Real-time sonography of pleural opacities. AJR Am J Roentgenol. 1981;1362:297-301
 
Weingardt JP, Guico RR, Nemcek AA Jr, Li YP, Chiu ST. Ultrasound findings following failed, clinically directed thoracenteses. J Clin Ultrasound. 1994;227:419-426. [CrossRef]
 
Diacon AH, Brutsche MH, Solèr M. Accuracy of pleural puncture sites: a prospective comparison of clinical examination with ultrasound. Chest. 2003;1232:436-441. [CrossRef]
 
Akhan O, Ozkan O, Akinci D, Hassan A, Ozmen M. Image-guided catheter drainage of infected pleural effusions. Diagn Interv Radiol. 2007;134:204-209
 
Tassi GF, Davies RJ, Noppen M. Advanced techniques in medical thoracoscopy. Eur Respir J. 2006;285:1051-1059. [CrossRef]
 
Shankar S, Gulati M, Kang M, Gupta S, Suri S. Image-guided percutaneous drainage of thoracic empyema: can sonography predict the outcome? Eur Radiol. 2000;103:495-499. [CrossRef]
 
Keeling AN, Leong S, Logan PM, Lee MJ. Empyema and effusion: outcome of image-guided small-bore catheter drainage. Cardiovasc Intervent Radiol. 2008;311:135-141. [CrossRef]
 
Chen KY, Liaw YS, Wang HC, Luh KT, Yang PC. Sonographic septation: a useful prognostic indicator of acute thoracic empyema. J Ultrasound Med. 2000;1912:837-843
 
Gervais DA, Levis DA, Hahn PF, Uppot RN, Arellano RS, Mueller PR. Adjunctive intrapleural tissue plasminogen activator administered via chest tubes placed with imaging guidance: effectiveness and risk for hemorrhage. Radiology. 2008;2463:956-963. [CrossRef]
 
Levinson GM, Pennington DW. Intrapleural fibrinolytics combined with image-guided chest tube drainage for pleural infection. Mayo Clin Proc. 2007;824:407-413. [CrossRef]
 
Potaris K, Mihos P, Gakidis I, Chatziantoniou C. Video-thoracoscopic and open surgical management of thoracic empyema. Surg Infect (Larchmt). 2007;85:511-517. [CrossRef]
 
Roberts JR. Minimally invasive surgery in the treatment of empyema: intraoperative decision making. Ann Thorac Surg. 2003;761:225-230. [CrossRef]
 
Brutsche MH, Tassi GF, Györik S, et al. Treatment of sonographically stratified multiloculated thoracic empyema by medical thoracoscopy. Chest. 2005;1285:3303-3309. [CrossRef]
 
Silen ML, Naunheim KS. Thoracoscopic approach to the management of empyema thoracis. Indications and results. Chest Surg Clin N Am. 1996;63:491-499
 
Alfageme I, Muñoz F, Peña N, Umbría S. Empyema of the thorax in adults. Etiology, microbiologic findings, and management. Chest. 1993;1033:839-843. [CrossRef]
 
Ferguson AD, Prescott RJ, Selkon JB, Watson D, Swinburn CR. The clinical course and management of thoracic empyema. QJM. 1996;894:285-289. [CrossRef]
 
Chapman SJ, Davies RJ. Recent advances in parapneumonic effusion and empyema. Curr Opin Pulm Med. 2004;104:299-304. [CrossRef]
 
Ulmer JL, Choplin RH, Reed JC. Image-guided catheter drainage of the infected pleural space. J Thorac Imaging. 1991;64:65-73. [CrossRef]
 
Klein JS, Schultz S, Heffner JE. Interventional radiology of the chest: image-guided percutaneous drainage of pleural effusions, lung abscess, and pneumothorax. AJR Am J Roentgenol. 1995;1643:581-588
 
Rosenberg ER. Ultrasound in the assessment of pleural densities. Chest. 1983;843:283-285. [CrossRef]
 
Westcott JL. Percutaneous catheter drainage of pleural effusion and empyema. AJR Am J Roentgenol. 1985;1446:1189-1193
 
Merriam MA, Cronan JJ, Dorfman GS, et al. Radiographically guided percutaneous catheter drainage of pleural fluid collections. AJR Am J Roentgenol. 1988;1516:1113-1116
 
vanSonnenberg E, Nakamoto SK, Mueller PR, et al. CT- and ultrasound-guided catheter drainage of empyemas after chest-tube failure. Radiology. 1984;1512:349-353
 
Balfour-Lynn IM, Abrahamson E, Cohen G, et al. Paediatric Pleural Diseases Subcommittee of the BTS Standards of Care Committee BTS guidelines for the management of pleural infection in children. Thorax. 2005;60suppl 1:i1-i21. [CrossRef]
 
Ahmed SI, Gripaldo RE, Alao OA. Empyema necessitans in the setting of pneumonia and parapneumonic effusion. Am J Med Sci. 2007;3332:106-108. [CrossRef]
 
Kono SA, Nauser TD. Contemporary empyema necessitatis. Am J Med. 2007;1204:303-305. [CrossRef]
 
Bouros D, Tzouvelekis A, Antoniou KM, Heffner JE. Intrapleural fibrinolytic therapy for pleural infection. Pulm Pharmacol Ther. 2007;206:616-626. [CrossRef]
 
Aozasa K. Pyothorax-associated lymphoma. J Clin Exp Hematop. 2006;461:5-10. [CrossRef]
 
Aozasa K, Takakuwa T, Nakatsuka S. Pyothorax-associated lymphoma: a lymphoma developing in chronic inflammation. Adv Anat Pathol. 2005;126:324-331. [CrossRef]
 
Iuchi K, Aozasa K, Yamamoto S, et al. Non-Hodgkin's lymphoma of the pleural cavity developing from long-standing pyothorax. Summary of clinical and pathological findings in thirty-seven cases. Jpn J Clin Oncol. 1989;193:249-257
 
Minami M, Kawauchi N, Yoshikawa K, et al. Malignancy associated with chronic empyema: radiologic assessment. Radiology. 1991;1782:417-423
 
Oh JK, Ahn MI, Kim CH, et al. The value of F-18 FDG-PET/CT in diagnosis of chronic empyema-associated malignancy. Clin Radiol. 2008;6310:1177-1180. [CrossRef]
 
Asakura H, Togami T, Mitani M, et al. Usefulness of FDG-PET imaging for the radiotherapy treatment planning of pyothorax-associated lymphoma. Ann Nucl Med. 2005;198:725-728. [CrossRef]
 

Figures

Figure Jump LinkFigure 1. The frontal radiograph (A) shows right-sided subpulmonic and loculated lateral pleural effusion and a pseudotumor in the medial, mid-lung field. The lateral projection (B) localizes the pseudotumor to the upper major fissure. The pseudotumor appears more rounded than the usual lenticular appearance. A contrast-enhanced chest CT slice (C) confirms the pseudotumor to be a loculated pleural effusion within the major fissure (arrow), with additional lateral and posterior locules. The CT scan does not visualize costal pleural membranes in the left hemithorax; what appear to be pleural membranes (arrowheads) actually represent a combination of visceral and parietal pleurae, physiologic pleural fluid, fascia, and the innermost intercostal muscles.Grahic Jump Location
Figure Jump LinkFigure 2. Frontal chest radiograph that demonstrates an air-fluid level within rounded density (arrow) that suggested a lung abscess in a patient with multiloculated empyema involving the right apex and paramediastinal pleurae. Contrast-enhanced CT scan (B) through the lower thorax showed fluid collections in the major fissure (F) and posteriorly with a cavitary abscess in the right lower lobe (arrow). The hilum is poorly defined on the frontal radiograph because of a paramediastinal fluid collection confirmed by CT scan (CT image not shown).Grahic Jump Location
Figure Jump LinkFigure 3. Frontal (A) and lateral (B) radiographs demonstrate a subpulmonic effusion with apparent elevation of the right diaphragm with a laterally displaced apex (arrow in A). In B, note the sloping interface (white arrows) between the effusion (*) and the middle lobe anterior to the major fissure (solid arrow). This appearance results from the oblique interface between the subpulmonic effusion and the middle lobe anterior to the major fissure, as the lung-fluid interface fails to create a sharp tangent to the lateral x-ray beam and therefore is not evident radiographically.Grahic Jump Location
Figure Jump LinkFigure 4. Frontal radiograph (A) of a patient with multilocular empyema demonstrating obscuration of the left hemidiaphragm by lung consolidation and pleural fluid and an ill-defined density in the medial, midlung field (arrow). The lateral view (B) demonstrates a nondependent loculated empyema (arrows) with the “ d-sign.” Grahic Jump Location
Figure Jump LinkFigure 5. Supine portable radiograph (A) in a patient with large posterior bilateral pleural effusions that demonstrates increased density over both lung fields. The CT scan (B) shows the large effusions layering posteriorly. Passive atelectasis of the left and right lung (arrows) is demonstrated in this contrast-enhanced study. The homogeneity of the atelectatic lung on all sections excludes lung necrosis or abscess There is no evidence of parietal pleural thickening or enhancement on this CT level.Grahic Jump Location
Figure Jump LinkFigure 6. Portable radiograph (A) of a large left pleural effusion in a patient with mediastinal lymphoma (note mediastinal widening and obscuration of aortic arch) that demonstrates crescentic fluid density (arrow) over the lung apex. A contrast-enhanced CT scan (B) shows the left pleural effusion with the enhancing atelectatic left lung sharply delineated from the effusion.Grahic Jump Location
Figure Jump LinkFigure 7. Frontal radiograph of a patient with a pleural effusion that collects within an incomplete right major fissure, which creates a perihilar lucency outlined peripherally by a circumscribed concave opacity.Grahic Jump Location
Figure Jump LinkFigure 8. Sonogram of a normal patient shows a thin echogenic interface between the normal visceral pleura and underlying lung deep to the ribs that produces the normal pleural stripe (arrows).Grahic Jump Location
Figure Jump LinkFigure 9. The frontal radiograph (A) suggests a right parapneumonic effusion, which is confirmed by sonographic evidence (B) of a characteristic triangular anechoic fluid collection immediately above the diaphragm. Eff = effusion; L = lung; Li = liver.Grahic Jump Location
Figure Jump LinkFigure 10. Sonographic appearance of parapneumonic effusions with the patterns of homogeneously anechoic (asterisk denotes fluid) (A), complex nonseptated with internal echogenic foci (B), complex septated (C), and homogeneously echogenic (D). Most complicated parapneumonic effusions and empyemas have internal echoes or appear entirely echogenic. “ L ” denotes lung and curved arrow identifies the diaphragm.Grahic Jump Location
Figure Jump LinkFigure 11. Pyopneumothorax due to bronchopleural fistula complicating lung abscess. (A) Upright chest radiograph shows a large right hydropneumothorax with small air-fluid level in consolidated right mid lung (arrow). (B) Contrast-enhanced CT shows a cavity with air-fluid level (white arrow) reflecting an abscess within the consolidated middle lobe. There is a large right hydropneumothorax with thickening and enhancement of the parietal pleura (black arrow). (C) Sagittal reformatted image through the middle lobe abscess shows a large bronchopleural fistula (white arrows) extending posterosuperiorly from the abscess cavity to the posterior hydropneumothorax. Purulent material was recovered at surgery.Grahic Jump Location
Figure Jump LinkFigure 12. A patient with two chest tubes in the right hemithorax that drain a parapneumonic effusion. There is asymmetric thickening of the right posterolateral chest wall and expansion of the extrapleural fat (black straight arrow) due to edema, findings commonly observed with empyemas. A small amount of pleural fluid remains posteriorly (curved arrow). The left hemithorax demonstrates the normal appearance of the inner cortices of the ribs wherein no tissue can be visualized adjacent to the lung (arrowhead). In contrast, the finding of even a thin layer of tissue along the inner rib cortices establishes pleural thickening or effusion (white arrow).Grahic Jump Location
Figure Jump LinkFigure 13. CT image of a patient with a subpleural lung abscess (upper short arrow) and an adjacent region (lower short arrow) of either loculated pleural fluid of high attenuation or pleural thickening. Additional high-attenuation pleural fluid or thickening is seen posteriorly (long arrow).Grahic Jump Location
Figure Jump LinkFigure 14. A CT image of a patient with empyema demonstrating enhancing rims of parietal and visceral pleurae (short arrows) surrounding a loculated pleural fluid collection (split pleura sign). Note the hypertrophied extrapleural fat (long arrows) due to the chronic thickening and retraction of the pleural layers, which are commonly associated with empyemas.Grahic Jump Location

Tables

References

Colice GL, Curtis A, Deslauriers J, et al. Medical and surgical treatment of parapneumonic effusions: an evidence-based guideline. Chest. 2000;1184:1158-1171. [CrossRef]
 
Davies CW, Gleeson FV, Davies RJ. Pleural Diseases Group Standards of Care Committee British Thoracic Society BTS guidelines for the management of pleural infection. Thorax. 2003;58suppl 2:ii18-ii28
 
Im JG, Webb WR, Rosen A, Gamsu G. Costal pleura: appearances at high-resolution CT. Radiology. 1989;1711:125-131
 
Noppen M, De Waele M, Li R, et al. Volume and cellular content of normal pleural fluid in humans examined by pleural lavage. Am J Respir Crit Care Med. 2000;1623 pt 1:1023-1026
 
Henschke CI, Davis SD, Romano PM, Yankelevitz DF. Pleural effusions: pathogenesis, radiologic evaluation, and therapy. J Thorac Imaging. 1989;41:49-60. [CrossRef]
 
Schwarz MI, Marmorstein BL. A new radiologic sign of subpulmonic effusion. Chest. 1975;672:176-178. [CrossRef]
 
Evans AL, Gleeson FV. Radiology in pleural disease: state of the art. Respirology. 2004;93:300-312. [CrossRef]
 
Wernecke K. Sonographic features of pleural disease. AJR Am J Roentgenol. 1997;1684:1061-1066
 
McLoud TC, Flower CDR. Imaging the pleura: sonography, CT, and MR imaging. AJR Am J Roentgenol. 1991;1566:1145-1153
 
Beckh S, B ölcskei PL, Lessnau KD. Real-time chest ultrasonography: a comprehensive review for the pulmonologist. Chest. 2002;1225:1759-1773. [CrossRef]
 
Chang DB, Yang PC, Luh KT, Kuo SH, Yu CJ. Ultrasound-guided pleural biopsy with Tru-Cut needle. Chest. 1991;1005:1328-1333. [CrossRef]
 
Adams RF, Gleeson FV. Percutaneous image-guided cutting-needle biopsy of the pleura in the presence of a suspected malignant effusion. Radiology. 2001;2192:510-514
 
Tayal VS, Nicks BA, Norton HJ. Emergency ultrasound evaluation of symptomatic nontraumatic pleural effusions. Am J Emerg Med. 2006;247:782-786. [CrossRef]
 
Mathis G. Thoraxsonography — Part I: Chest wall and pleura. Ultrasound Med Biol. 1997;238:1131-1139. [CrossRef]
 
Kocijancic I, Vidmar K, Ivanovi-Herceg Z. Chest sonography versus lateral decubitus radiography in the diagnosis of small pleural effusions. J Clin Ultrasound. 2003;312:69-74. [CrossRef]
 
Feller-Kopman D. Therapeutic thoracentesis: the role of ultrasound and pleural manometry. Curr Opin Pulm Med. 2007;134:312-318. [CrossRef]
 
Vignon P, Chastagner C, Berkane V, et al. Quantitative assessment of pleural effusion in critically ill patients by means of ultrasonography. Crit Care Med. 2005;338:1757-1763. [CrossRef]
 
Balik M, Plasil P, Waldauf P, et al. Ultrasound estimation of volume of pleural fluid in mechanically ventilated patients. Intensive Care Med. 2006;322:318-321. [CrossRef]
 
Lichtenstein DA, Menu Y. A bedside ultrasound sign ruling out pneumothorax in the critically ill. Lung sliding. Chest. 1995;1085:1345-1348. [CrossRef]
 
Yang P-C, Luh K-T, Chang D-B, et al. Value of sonography in determining the nature of pleural effusion: analysis of 320 cases. AJR Am J Roentgenol. 1992;1591:29-33
 
Chen HJ, Tu CY, Ling SJ, et al. Sonographic appearances in transudative pleural effusions: not always an anechoic pattern. Ultrasound Med Biol. 2008;343:362-369. [CrossRef]
 
Tu CY, Hsu WH, Hsia TC, et al. Pleural effusions in febrile medical ICU patients: chest ultrasound study. Chest. 2004;1264:1274-1280. [CrossRef]
 
Lomas DJ, Padley SG, Flower CDR. The sonographic appearances of pleural fluid. Br J Radiol. 1993;66787:619-624. [CrossRef]
 
Ravenel JG, McAdams HP. Multiplanar and three-dimensional imaging of the thorax. Radiol Clin North Am. 2003;413:475-489. [CrossRef]
 
Aquino SL, Webb WR, Gushiken BJ. Pleural exudates and transudates: diagnosis with contrast-enhanced CT. Radiology. 1994;1923:803-808
 
Takasugi JE, Godwin JD, Teefey SA. The extrapleural fat in empyema: CT appearance. Br J Radiol. 1991;64763:580-583. [CrossRef]
 
Waite RJ, Carbonneau RJ, Balikian JP, Umali CB, Pezzella AT, Nash G. Parietal pleural changes in empyema: appearances at CT. Radiology. 1990;1751:145-150
 
Kearney SE, Davies CW, Davies RJ, Gleeson FV. Computed tomography and ultrasound in parapneumonic effusions and empyema. Clin Radiol. 2000;557:542-547. [CrossRef]
 
Stark DD, Federle MP, Goodman PC, Podrasky AE, Webb WR. Differentiating lung abscess and empyema: radiography and computed tomography. AJR Am J Roentgenol. 1983;1411:163-167
 
Neff CC, vanSonnenberg E, Lawson DW, Patton AS. CT follow-up of empyemas: pleural peels resolve after percutaneous catheter drainage. Radiology. 1990;1761:195-197
 
Duysinx BC, Larock MP, Nguyen D, et al. 18F-FDG PET imaging in assessing exudative pleural effusions. Nucl Med Commun. 2006;2712:971-976. [CrossRef]
 
Toaff JS, Metser U, Gottfried M, et al. Differentiation between malignant and benign pleural effusion in patients with extra-pleural primary malignancies: assessment with positron emission tomography-computed tomography. Invest Radiol. 2005;404:204-209. [CrossRef]
 
Light RW. Parapneumonic effusions and empyema. Proc Am Thorac Soc. 2006;31:75-80. [CrossRef]
 
Eibenberger KL, Dock WI, Ammann ME, Dorffner R, Hörmann MF, Grabenwöger F. Quantification of pleural effusions: sonography versus radiography. Radiology. 1994;1913:681-684
 
Mayo PH, Doelken P. Pleural ultrasonography. Clin Chest Med. 2006;272:215-227. [CrossRef]
 
Nicolaou S, Talsky A, Khashoggi K, Venu V. Ultrasound-guided interventional radiology in critical care. Crit Care Med. 2007;355 suppl:S186-S197. [CrossRef]
 
Light RW. Pleural Disease. 2007; Philadelphia Lippincott Williams & Wilkins
 
Grogan DR, Irwin RS, Channick R, et al. Complications associated with thoracentesis. A prospective, randomized study comparing three different methods. Arch Intern Med. 1990;1504:873-877. [CrossRef]
 
Mayo PH, Goltz HR, Tafreshi M, Doelken P. Safety of ultrasound-guided thoracentesis in patients receiving mechanical ventilation. Chest. 2004;1253:1059-1062. [CrossRef]
 
Jones PW, Moyers JP, Rogers JT, Rodriguez RM, Lee YC, Light RW. Ultrasound-guided thoracentesis: is it a safer method? Chest. 2003;1232:418-423. [CrossRef]
 
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