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Parapneumonic Pleural Effusions and Empyema Thoracis: Differential Diagnoses & Workup
Updated: Sep 17, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
Other Problems to Be Considered
Malignant pleural effusion
Tuberculous pleural effusion
Esophageal perforation (Boerhaave syndrome)
Drug-induced pleural effusion
Pleuritis secondary to systemic collagen-vascular diseases
Subdiaphragmatic abscess
Workup
Laboratory Studies
So specific laboratory studies suggest the presence of a parapneumonic effusion or empyema. However, the possibility of a parapneumonic effusion and empyema should be a consideration for every patient with pneumonia. The presence of pleural fluid may be suggested based on physical examination findings; however, small pleural effusions may not be detected during the physical examination. In this case, any significant effusion can be visualized using 2-view (ie, posteroanterior, lateral) chest radiography.
Sputum should be submitted for culture, especially if purulent. The infecting organism may be suggested based on Gram stain results. Mixed florae are often seen in anaerobic infections.
As with any infection, leukocytosis may be present (>12,000/µL); however, it should decrease with adequate antibiotic therapy. Persistent fever and leukocytosis despite adequate antibiotic therapy may signal a persistent focus of infection, such as a complicated parapneumonic effusion or empyema, with subsequent evaluation as outlined in the following sections. Diagnosing a complicated parapneumonic effusion and/or empyema is crucial for optimal management because a delay in drainage of the pleural fluid substantially increases morbidity.
Imaging Studies
- Chest radiography
- Lateral chest radiography usually demonstrates the presence of a significant amount of pleural fluid (see Media File 2).
Left lateral chest radiograph shows a large, left pleural effusion.
- If either of the diaphragms is not visible throughout its entire length, the posterior costophrenic angles are blunted, or a lateral meniscus is visible, obtain bilateral decubitus chest radiographs.
- Free pleural fluid is seen as a dense linear shadow layering between the chest wall and the lung parenchyma.
- Unchanging pleural-based linear densities, pleural-based masslike densities, or collections with obtuse angles suggest the presence of loculated fluid, especially if the differences in the fluid or the appearance between upright and lateral views are minimal.
- If the pleural fluid distance measures more than 10 mm from the chest wall, sufficient fluid is present to perform a diagnostic thoracentesis.
- Ultrasonography
- Ultrasonography can be used to localize fluid for a thoracentesis. Fluid appears dark or black on ultrasound images, and most bedside ultrasonography devices permit measurement of the depth of location from the chest wall.
- Complex fluid (purulent or viscous) may have more density or shadows within in the pleural fluid collection. Sometimes, fibrinous strands can be seen floating in the pleural fluid.
- Other structures such as the diaphragm or lung parenchyma can provide landmarks to assist in needle placement for thoracentesis.
- Loculated pleural effusions may be difficult to localize during physical examination, but they can usually be identified with ultrasonography.
- Ultrasonography can effectively distinguish loculated pleural fluid from an infiltrate. The latter may have air bronchograms visible, but the distinction may be difficult if dense consolidation is present. If a loculated pleural effusion is suspected, an ultrasonographic examination is recommended for diagnosis and marking the area for thoracentesis.
- CT scanning of the thorax
- CT scanning of the chest with contrast enhances the pleural surface and assists in delineating the pleural fluid loculations (see Media Files 4-5).
- Pleural enhancement can be seen in patients with active inflammation and severe pleuropulmonary infections, which provides another sign of the possibility of a complicated pleural effusion or empyema.
- CT scanning of the chest may also help detect airway or parenchymal abnormalities such as endobronchial obstruction or the presence of lung abscesses.
CT scan of thorax shows loculated pleural effusion on left and contrast enhancement of visceral pleura, indicating the etiology is likely an empyema.
Chest CT scan with intravenous contrast in a patient with mixed Staphylococcus milleri and anaerobic empyema following aspiration pneumonia, showing a thickened contrast-enhanced pleural rind, high-density pleural effusion, loculation, and septation. Thoracentesis yielded foul-smelling pus.
Other Tests
While no diagnostic laboratory tests are available for a parapneumonic effusion, serum total protein and lactic dehydrogenase (LDH) levels should be obtained to help characterize whether the pleural fluid is an exudate or transudate. The ratio of pleural fluid/serum protein and LDH is used to distinguish between these two entities.
Procedures
Thoracentesis is recommended when the suspected parapneumonic pleural effusion is greater than or equal to 10 mm thick on a lateral decubitus chest radiograph.7 See Media File 3.
A right lateral decubitus chest radiograph shows a free-flowing pleural effusion, which should be sampled with thoracentesis for pH determination, Gram stain, and culture.
Pleural fluid appearance may vary from a clear yellow liquid to an opaque turbid fluid to grossly purulent thick, viscous, foul-smelling pus. Foul-smelling fluid indicates an anaerobic infection.
- Pleural fluid studies
- Blood cell count (WBC count) and differential: Results generally are not diagnostic, but most transudates are associated with a WBC counts of less than 1000 cells/µL and empyemas are exudates, with WBC counts generally greater than 50,000 cells/µL.
- Pleural fluid total protein, LDH, and glucose (corresponding serum protein and LDH): Exudates are defined by pleural/serum total protein ratio of greater than 0.5 and a pleural/serum LDH ratio of greater than 0.6 or a pleural fluid LDH value greater than two thirds the upper limit of normal. One criterion is sufficient to classify fluid as an exudate.
- Pleural fluid pH (iced blood gas syringe): Values of less than 7.20 are suggestive of a complicated pleural effusion.
- Other laboratories suggestive of complicated pleural effusion or empyema: These include (1) an LDH value of greater than 1000 U/L and a glucose level of less than 40 mg/d of (2) a pH of less than 7.00 and a glucose level of less than 40 mg/dL.
- Microbiology (Gram stain, bacterial culture): Acid-fast bacilli and fungal infections may cause pleural effusions or empyema, but theses organisms are more difficult to culture from pleural fluid.
Histologic Findings
Multiple granulocytes would be seen on histologic examination, but no specific pattern is recognized. Necrotic debris may be present. Bacteria are seen in the pleural fluid in severe infections.
Staging
The following classification and treatment scheme has been used to characterize parapneumonic effusions and empyema.
- Category 1 (parapneumonic effusion)
- Minimal free-flowing fluid, smaller than 10 mm on decubitus films
- Culture, Gram stain, and pH unknown
- No thoracentesis needed; treatment with antibiotics alone
- Category 2 (uncomplicated parapneumonic effusion)
- Larger than 10 mm fluid and less than half the hemithorax on decubitus films
- Gram stain and culture negative
- pH higher than 7.20
- Treatment with antibiotics alone
- Category 3 (complicated parapneumonic effusion)
- Large free-flowing effusion, more than half the hemithorax
- pH lower than 7.20, LDH level greater than 1000 U/L and glucose level greater than 40 mg/dL
- Gram stain or culture positive
- Treatment with tube thoracostomy and antibiotics
- Multiloculated effusions may require multiple tubes
- Thrombolytics may help resolution
- Category 4 (empyema)
- Large free-flowing effusion, greater than equal to half the hemithorax
- Loculated effusion or effusion with thickened pleura
- Gross pus on aspiration
- Treatment with tube thoracostomy
- Thrombolytics may help resolution
- May require decortication
More on Parapneumonic Pleural Effusions and Empyema Thoracis |
| Overview: Parapneumonic Pleural Effusions and Empyema Thoracis |
 Differential Diagnoses & Workup: Parapneumonic Pleural Effusions and Empyema Thoracis |
| Treatment & Medication: Parapneumonic Pleural Effusions and Empyema Thoracis |
| Follow-up: Parapneumonic Pleural Effusions and Empyema Thoracis |
| Multimedia: Parapneumonic Pleural Effusions and Empyema Thoracis |
| References |
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References
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Further Reading
Keywords
empyema thoracis, pleural effusions, pleural effusion, parapneumonic pleural effusion, pleuropulmonary empyema, complicated parapneumonic pleural effusion, uncomplicated parapneumonic effusion, thoracic empyema, thoracoplasty, decortication, pneumonia, parapneumonic effusion, esophageal perforation, trauma, surgical procedure on pleural space, septicemia
