You are in: eMedicine Specialties > Radiology > CHEST Effusion, PleuralArticle Last Updated: Aug 10, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Omar Lababede, MD, Consulting Staff, Department of Regional Diagnostic Radiology, Cleveland Clinic Foundation Omar Lababede is a member of the following medical societies: American College of Radiology and Radiological Society of North America 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; Kavita Garg, MD, Professor, Department of Radiology, University of Colorado Health Sciences Center Author and Editor Disclosure Synonyms and related keywords: increased pleural fluid, hydrothorax, hemothorax, pyothorax, chylothorax INTRODUCTIONSection 2 of 12
  BackgroundMany benign and malignant diseases can cause pleural effusion. The characteristics of the fluid depend on the underlying pathophysiologic mechanism. The fluid can be transudate, nonpurulent exudate, pus, blood, or chyle. Imaging studies are valuable in detecting and managing pleural effusions but not in accurately characterizing the biochemical nature of the fluid. PathophysiologyA small amount of fluid is normally present in the pleural space. The parietal pleura continuously produce the fluid, which is absorbed by the visceral pleura and by the lymphatics of the parietal pleura. The hydrostatic, colloid osmotic, and tissue pressures affect circulation of the fluid. Alteration of 1 or more of these factors causes abnormal accumulation of fluid in the pleural space and is the primary mechanism of transudative effusions. For instance, increased hydrostatic pressure and decreased osmotic pressure cause effusions in congestive heart failure (CHF) and nephrotic syndrome, respectively. In addition to alteration in the circulation of pleural fluid, injury to the pleura or subpleural lung parenchyma can cause increased vascular permeability and a shift of fluid from the pulmonary interstitium. This mechanism is primarily seen in exudative effusions, such as effusion associated with pneumonia and infarction. In certain cases, such as traumatic hemothorax or postsurgical chylothorax, the fluid accumulates from leaking damaged vessels or lymphatic ducts. Because peritoneal and pleural spaces communicate through defects in the diaphragm in some patients, peritoneal fluid crosses the diaphragm due to the negative pressure in the pleural cavity. Hepatic hydrothorax and pleural effusion secondary to gynecologic malignancies with ascites are 2 examples of this mechanism. FrequencyUnited StatesBecause pleural effusion is a manifestation of a wide spectrum of diseases rather than a primary entity, its exact incidence is not known. In addition, pleural effusion can be an intermittent phenomenon in some case, such as in CHF. An estimated 1 million patients develop pleural effusion each year. Most pleural effusions are secondary to CHF, malignancy, pneumonia, or pulmonary emboli. Approximately 72% of patients with CHF were found to have effusion at autopsy. Parapneumonic effusions develop in 36-66% of hospitalized patients with bacterial pneumonia. The incidence of effusion is lower in fungal and viral lung infections than in bacterial infection (2-9% in Coccidioides immitis infection and 7-19% in viral pneumonia). About 10-50% of patients with pulmonary embolism develop pleural effusion. The incidence of the effusion varies from approximately 90-100% after coronary bypass or heart and/or lung transplantation to 16-37% in systemic lupus erythematosus, 4-20% in acute pancreatitis, and 5% in rheumatoid arthritis. InternationalIn 1 international epidemiologic study of pleural effusion in a well-defined region of central Bohemia, the incidence was 0.32%. Extrapolated to the entire population of the former Czechoslovakia, this rate represents 48,000 cases annually. Mortality/MorbidityMorbidity and mortality are primarily related to the underlying disease.
Clinical DetailsThe pleuritic chest pain associated with pleural irritation is localized, sharp, and severe. It is exacerbated by deep inspiration or coughing. The development of effusion may relieve the pleuritic pain. The mass effect associated with large pleural effusions can cause dyspnea. In cases of associated lung pathology, small effusions can cause dyspnea. The clinical history may help in limiting the differential diagnosis of the underlying etiology. Small effusions might not be detectable on physical examination. Large effusions produce dependent, diminished breath sounds and dullness to percussion. Signs of an underlying process, such as pneumonia or CHF, can be detected on physical examination. Preferred ExaminationDifferent imaging modalities can be used to diagnose and manage pleural disease. Findings on chest radiographs frequently confirm the presence of pleural effusion. Lateral decubitus projections enhance the sensitivity of conventional radiography. Depending on the clinical context, ultrasonography or CT can be used to confirm a pleural effusion, especially in cases of loculated pleural effusion, complete opacification of hemithorax, or associated lung parenchymal abnormalities. Ultrasonography and CT are more accurate than chest radiography in identifying the underlying etiology. Both modalities can depict small effusions not visualized radiographically. Ultrasonography and CT are also used to guide interventional procedures to manage pleural effusions. MRI is sometimes used to evaluate questionable CT findings. MRI has been reported to be more sensitive than CT in differentiating benign from malignant causes of effusion. Limitations of TechniquesRadiographic studies may not help in differentiating parenchymal processes from pleural processes. In addition, chest radiography is limited in evaluating the underlying etiology, as in differentiating benign disease from malignant pleural disease. DIFFERENTIALSSection 3 of 12
Other Problems to Be ConsideredElevated hemidiaphragm and/or herniation on a chest radiograph
RADIOGRAPHSection 4 of 12
FindingsTypical pleural effusionMany factors influence the radiographic findings of pleural effusion, including the nature of the fluid (free vs loculated), the amount of fluid, the patient's position, the radiographic projection, and the presence of underlying lung abnormalities. In the absence of clinically significant lung parenchymal changes, free pleural fluid tends to accumulate in the most dependent portion of the chest because of a difference in density compared with the air-filled lung. The pressure of the fluid causes atelectasis of the adjacent (dependent) lung tissue. Lung elasticity tends to preserve the shape of the collapsed lung. As a consequence, the lung collapses from the periphery toward the hilum, with a higher degree of collapse in the dependent portion of the lung. These factors force some of the fluid to rise against gravity and surround the dependent portion of the lung. The fluid-lung interface is curved, but the upper limits of the fluid remain horizontal. The relation between orientation of the x-ray beam and the fluid surface affects the radiographic appearance of the effusion. Upright frontal view A small amount of effusion accumulates in a subpulmonic location, causing slight elevation of the hemidiaphragm. As the fluid increases, the fluid starts to spill over into the most dependent costophrenic (CP) sulci. Small effusions may not be visualized on frontal views because of the orientation of the diaphragm, since the posterior CP sulcus is inferior to the lateral CP sulcus. Fluid accumulating posteriorly can be seen on the lateral view before it becomes visible on the frontal view. When the fluid is slightly above the level of the upper portion of the diaphragm, blunting of the lateral CP angle is seen. This is the earliest sign of pleural effusion on the frontal view. A minimal amount of fluid (approximately 175 mL) is required to produce detectable blunting. As much as 500 mL of pleural fluid can be present without apparent changes on the frontal view. A large free pleural effusion appears as a dependent opacity with lateral upward sloping of a meniscus-shaped contour. The diaphragmatic contour is partially or completely obliterated, depending on the amount of the fluid (silhouette sign). Differences in the depth to which the x-ray beam traverses the fluid produce the contour of the meniscus. Although the true upper limit of the fluid is horizontal, only the lateral aspect of the fluid is visible as the meniscal apex. (The apex of the meniscus can be slightly lower than the actual upper limit.) Because the fluid is laterally tangential to the x-ray beam, the depth of fluid penetration increases and consequently increases attenuation of the radiation. The depth of the fluid penetrated anteriorly and posteriorly is small, especially in the upper portion of the effusion. The attenuation is not sufficient to produce a shadow on the radiograph. A very large pleural effusion appears as an opaque hemithorax with a mediastinal shift to the contralateral side. The mediastinal shift can be less prominent or even absent in the presence of underlying lung pathology (eg, atelectasis) or contralateral hemithorax abnormality. Upright lateral view A small amount of effusion accumulates in a subpulmonary location, causing slight elevation of the ipsilateral hemidiaphragm. As the fluid increases, the amount of fluid spills over into the most dependent (posterior) CP sulci. Small effusions appear as a dependent opacity with posterior upward sloping of a meniscus-shaped contour. The opacity obliterates the underlying portion of the diaphragmatic contour (silhouette sign). Large free pleural effusion appears as a dependent opacity with a meniscus-shaped contour. The highest points of the meniscus are anteriorly and posteriorly located at approximately the same level. The ipsilateral diaphragmatic contour is obliterated (silhouette sign). Variation in the depth of fluid traversed by the x-ray beam produces the contour of the meniscus. As noted, the actual upper limit of the fluid is horizontal. The anterior and posterior aspects are visible as the meniscal apices because the fluid is tangential to the x-ray beam, with increased depth of fluid penetration and attenuation. The depth of the penetrated fluid laterally is too small to produce a shadow on the radiograph, especially in the upper portion of the effusion. A very large pleural effusion produces generalized increased opacity with obliteration of the underlying hemidiaphragm. Only 1 diaphragm on the lateral view may be a clue to a large pleural effusion. Supine frontal view The normal supine view does not exclude the presence of effusion. This view is the least sensitive for detecting pleural effusions. A somewhat large amount of fluid is required to produce detectable radiographic findings, especially in bilateral effusions. In 1 study, a minimal volume of 175 mL was required to produce notable change on the supine radiograph. The fluid accumulates in the posterior aspect of the hemithorax. The lung fluid interface is mostly in a plane perpendicular or oblique (not tangential) to the orientation of the x-ray beam. Subsequently, the effusion initially causes generalized hazy homogeneous opacity with ill-defined margins. The opacity first projects over the lower lung zones. With further fluid accumulation, the opacity of the entire hemithorax increases, and obliteration of the diaphragm becomes obvious. Depending on the amount of the fluid and the degree of the lung collapse, lung markings (eg, vessels) can be seen through this opacity. This finding helps in differentiating opacity secondary to effusion from one caused by lung parenchymal abnormalities, such as atelectasis or airspace disease. The absence of an air bronchogram also helps in differentiation. Well-defined ipsilateral apical opacity (apical capping) is often produced, especially with large effusions. This opacity is believed to be secondary to small capacity of the lung at the apex with the extension of the fluid lateral and superior to the lung tissue. Blunting of the CP angles (meniscus sign), which can be seen in more than 50% of large effusions, is attributed to accumulation of fluid about the level of the lateral CP sulcus. Lateral decubitus view A lateral decubitus view obtained with a horizontal x-ray beam is the most sensitive radiographic projection for detecting an effusion. A small amount of fluid (10-25 mL) can be depicted on this projection. The layering fluid can easily be detected as a dependent, sharply defined, linear opacity separating the lung from the parietal pleural and chest wall. The parietal pleura–chest wall margin can be identified as a line connecting the inner apices of the curvature of the ribs. In some patients, especially obese patients, the parietal pleura is slightly medial to this line because of subpleural fat. This appearance is easily appreciated because it is bilateral on frontal examination and because it persists on the nondependent hemithorax of the contralateral decubitus image. Atypical pleural effusionLarge subpulmonary effusion Although a small effusion may accumulate first in a subpulmonary location, accumulated fluids usually spill into the posterior CP sulcus. A large subpulmonary effusion can be considered an atypical effusion. Unilateral subpulmonary effusion is more common on the right side. On upright frontal and lateral views, subpulmonary effusion presents as an elevated diaphragm (pseudodiaphragmatic contour). Additional findings, which can help in suggesting the presence of effusion, include the following:
Loculated pleural effusion An atypical distribution of pleural fluid can be also caused by loculation secondary to adhesions or by lung parenchymal changes that alter the recoil characteristics of the lung. The second mechanism can occur in atelectasis. Loculation secondary to adhesions is usually secondary to an infected or hemorrhagic effusion. Loculated effusions produce peripheral soft-tissue opacity with smooth obtuse tapering margins when seen tangentially. Loculated effusion in the pulmonary fissures appears as a well-defined elliptical opacity with pointed margins. Degree of ConfidenceUpright chest radiography is highly sensitive in detecting pleural effusion. Lateral decubitus projections are the most sensitive radiographic images for detecting free pleural effusion. Even large loculated or atypical effusions may demonstrate substantial gravitational movement to suggest their nature. False Positives/NegativesPleural thickening and/or fibrothorax and subpleural fat may mimic a small pleural effusion. Subpulmonic effusion is sometimes hard to differentiate from an elevated hemidiaphragm. Small pleural effusions can be difficult to detect radiographically. In addition, lung parenchymal abnormalities may obscure large effusions. CT SCANSection 5 of 12
FindingsFree pleural effusion presents as a crescent-shaped attenuating area in the dependent portion of the hemithorax. The lung-effusion interface has an upward concave configuration due to the recoil tendency of the lung. Because most CT examinations are performed in the supine position, the fluid starts to accumulate posteriorly in the CP sulcus. With a large effusion, the fluid extends into the apical and anterior aspects of the chest. The fluid can sometimes extend into the fissure. In the prone or lateral position, the fluid shifts to the most dependent aspect of the pleural cavity. This shift confirms the free nature of the effusion. Loculated effusion is characterized by an absence of a shift with a change in position. In addition, loculated fluids are more elliptical than others and can be found in nondependent locations. The pleural effusion usually has near-water attenuation, but its attenuation can be higher than that of water. The attenuation value of the fluid is unreliable in differentiating transudative from exudative effusions. Hemothorax is associated with increased attenuation. Heterogeneous attenuation with increased dependent attenuation can be seen in hemothorax. A fluid-hematocrit level can also be seen in hemothorax. Decreased attenuation (less than that of water) is sometimes present in chylothorax. The high protein content of the chylothorax may decrease the effect of the lower attenuation fat. However, fat attenuation on CT does not always indicate chylous effusion. The less commonly seen pseudochyle (chyliform pleural effusion) can manifest as a fat-fluid or fat-calcium level. The chyliform pleural effusion, which is caused by degenerating red and white blood cells in the pleural fluid, is associated with long-standing effusions, especially tuberculous empyema. The presence of pleural thickening and enhancement suggests underlying inflammation, infection, or neoplasm. The absence of pleural thickening and enhancement is usually seen in transudative effusion. However, pleural thickening and enhancement can also be absent in effusions of early infection or metastasis. Nodular pleural thickening on chest radiography or CT indicates a malignant pleural effusion. Degree of ConfidenceCT scan is sensitive in detecting pleural effusion; however, a small effusion is sometimes hard to differentiate from pleural thickening. Contrast enhancement is helpful in separating an effusion from an adjacent lung process (airspace disease or atelectasis). Unlike pleural fluid, lung tissue enhances with the administration of contrast material. CT is superior to plain radiography in evaluating the presence of loculated effusion or effusions with associated lung disease. CT is also more helpful than plain radiography in evaluating the underlying etiology of effusion. False Positives/NegativesExtrapleural fat and fat in the inferior aspect of a fissure may mimic the appearance of pleural effusion. The low attenuation of fat and the symmetry help in differentiating extrapleural fat from effusion. Pleural effusion may simulate ascites in cases of a small effusion in the posterior CP sulcus, a large effusion with inversion of the diaphragmatic convexity, and lower-lobe compressive atelectasis producing a pseudodiaphragm. Careful analysis of the sequential images (especially with scrolling on picture archiving and communications system workstations) and use of multiplanar reconstruction often helps in determining whether effusion, ascites, or both are present. Four signs assist in differentiating effusion from ascites (see the Table below). All of these signs should be considered in each case because they can be misleading when used individually. Summary of distinguishing CT findings
MRISection 6 of 12
FindingsMRI can help in evaluating the etiology of the pleural effusion. Nodularity and/or irregularity of the pleural contour, circumferential pleural thickening, mediastinal pleural involvement, and infiltration of the chest wall and/or diaphragm are suggestive of a malignant cause both on CT and MRI. MRI signal intensity has recently been suggested to be a valuable tool for differentiating malignant from benign pleural disease. Malignant pleural lesions are typically enhancing on contrast-enhanced T1-weighted images and hyperintense on proton density– and T2-weighted images. A pleural lesion with low signal intensity on images obtained with a long repetition time is a reliable and predictive sign of benign disease. Pleural calcification likely indicates a benign cause. The signal intensity of the pleural fluids depends on their biochemical characteristics. In most cases of nonhemorrhagic or nonchylous effusions, the fluids have high signal intensity on T2-weighted images and low signal intensity on T1-weighted images. Degree of ConfidenceThe combination of MRI signal intensity and morphologic features is more useful than, and superior to, CT in differentiating malignant from benign pleural disease. ULTRASOUNDSection 7 of 12
FindingsIn healthy individuals, the visceral can be hard to differentiate from the parietal pleura by using a 3.5-MHz curvilinear transducer. However, these structures can be differentiated by using high-frequency linear transducers. The visceral and parietal pleura slide over each other on real-time examination. Immediately medial to the visceral pleura, the air-filled lung appears as an echogenic structure, and visualization of the deep lung parenchyma is limited. The typical appearance of the pleural effusion is an anechoic layer between the visceral pleura and the parietal pleura. The shape of the effusion may vary with respiration and position. The sonographic characteristics of pleural effusion depend on the etiology and type of fluid, as well as on the chronicity of the collection. The sonographic appearance of the effusion is not correlated with its biochemical characteristics. The classic anechoic effusion is particularly observed in transudates. In a study of 320 patients with effusion, transudates were anechoic, whereas anechoic effusions were either transudates or exudates. Associated thickening of the pleura and parenchymal lesions in the lung indicated an exudate. The echogenic pleural fluid can be seen in hemorrhagic effusion or empyema. Septa can be present, especially in exudates. Exudates may appear anechoic, complex, or echogenic. Septated, complex, or echogenic effusions are usually seen in exudative effusion. Malignant effusions are more commonly anechoic than echogenic. The presence of adhesions in inflammatory effusions may prevent the lung from moving (sliding) over the effusion. Color Doppler ultrasonography can help in differentiating small effusions from pleural thickening by demonstrating the fluid-color sign (ie, presence of color signal in the fluid collection). The sign is positive in pleural effusions because of the transmitted respiratory and cardiac movements. The sign has a reported sensitivity of 89.2% and a specificity of 100% in identifying small effusions. Several methods can be used to estimate the volume of an effusion by means of sonography. Sonographic evidence of a pleural nodule indicates malignant effusion. Degree of ConfidenceUltrasonography is primarily used to confirm an effusion in a patient with abnormal chest radiographs and to guide interventional procedures (eg, thoracentesis, biopsy, placement of chest drains). Ultrasonography is helpful in characterizing pleural effusions and in differentiating pleural effusions and pleural thickening. It is also useful in evaluating some underlying causes of effusion. NUCLEAR MEDICINESection 8 of 12
FindingsNo well-established clinical indications have been defined for nuclear imaging studies in the workup of pleural effusion. In a recent study, fluorodeoxyglucose (FDG) positron emission tomography (PET) of pleural effusions was used to evaluate non–small-cell lung cancer in 22 patients. Pleural activity greater than the background mediastinal activity was considered to be positive for malignant effusion. FDG PET was 95% sensitive, 67% specific, and 92% accurate. The authors concluded that increased pleural FDG uptake usually indicated pleural metastases. FDG-PET was subsequently suggested to improve staging in patients with non–small-cell lung cancer and a pleural effusion. However, because of the small number of benign effusions in the study, the relevance of negative findings was considered uncertain. Sometimes, pleural effusion is an incidental finding in a study performed for another reason. Pleural effusion produces defects on both ventilation and perfusion lung scans. Malignant effusions can cause increased activity in the involved hemithorax on technetium-99m methylene diphosphonate (MDP) bone scans. ANGIOGRAPHYSection 9 of 12
FindingsAngiography is not used to evaluate the presence of effusion. On pulmonary angiograms, extrapulmonary defects can suggest a large pleural effusion. INTERVENTIONSection 10 of 12
The advent of ultrasonography and CT and the advances in drainage catheter design and interventional techniques have made imaging-guided management of intrathoracic collections a safe and effective alternative to traditional surgical therapy. Ultrasonography or CT can be used to guide thoracocentesis or catheter drainage of effusions. Thoracocentesis is primarily performed under sonographic rather than CT guidance. The use of image guidance improves the safety of the procedure and reduces the rate of complications. The small catheters are also associated with a complication rate lower than that associated with thoracotomy tubes. The management of pleural effusion depends on the underlying disease. For instance, in patients with parapneumonic effusion, the clinical approaches for drainage and the appropriate drainage methods may vary. In addition to treating the underlying pneumonia with antibiotics, management of parapneumonic effusions may include therapeutic thoracentesis, tube thoracostomy, tube thoracostomy with fibrinolytics, video-assisted thoracoscopic surgery (VATS) with postprocedural tube thoracostomy, and surgery (including thoracotomy with or without decortication and rib resection). In patients at low risk for a poor outcome, drainage may not be required. In most patients at high risk for a poor outcome, therapeutic thoracentesis or tube thoracostomy alone may not be sufficient. Fibrinolytics, VATS, and surgery are helpful in treating patients at high risk. These procedures are associated with the lowest mortality rates and need for second interventions. However, the relative values of each of these procedures are not well established. In malignant effusion, management is palliative. Treatment options include thoracentesis, tube thoracostomy, chemical pleurodesis, and thoracoscopic poudrage. In a study of 32 patients with a known primary malignancy and a symptomatic malignant pleural effusion, 72% had a complete response to thoracostomy with a small-bore catheter and talc pleurodesis. Percutaneous thoracocentesis is reportedly most successful in effusions that are sonographically anechoic, complex, or complex with movable septa, as compared with echogenic or complex effusions with fixed septa. However, in a recent study, no correlation was found between the sonographic appearance of the effusion and the success of percutaneous chest drainage. The success rate of radiologically guided drainage procedures is 72-88%. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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