Patients with pleural effusions most often report dyspnea, cough, or respirophasic chest pain. Symptoms are more common in patients with existing cardiopulmonary disease. Small pleural effusions are less likely to be symptomatic than larger effusions. Physical findings are usually absent in small effusions. Larger effusions may present with dullness to percussion and diminished or absent breath sounds over the effusion. Compressive atelectasis may cause bronchial breath sounds and egophony just above the effusion. A massive effusion with increased intrapleural pressure may cause contralateral shift of the trachea and bulging of the intercostal spaces. A pleural friction rub indicates pulmonary infarction or pleuritis.
The gross appearance of pleural fluid helps identify several types of pleural effusion. Grossly purulent fluid signifies empyema. Milky white pleural fluid should be centrifuged. A clear supernatant above a pellet of white cells indicates empyema, whereas a persistently turbid supernatant suggests a chylous effusion; analysis of this supernatant reveals chylomicrons and a high triglyceride level (greater than 100 mg/dL [1 mmol/L]), often from disruption of the thoracic duct. Hemorrhagic pleural effusion is a mixture of blood and pleural fluid. Ten thousand red cells per microliter create blood-tinged pleural fluid; 100,000 red cells/mcL create grossly bloody pleural fluid. Hemothorax is the presence of gross blood in the pleural space, usually following chest trauma or instrumentation. It is defined as a ratio of pleural fluid hematocrit to peripheral blood hematocrit greater than 0.5.
Pleural fluid samples should be sent for measurement of protein, glucose, and LD in addition to total and differential white blood cell counts. Chemistry determinations are used to classify effusions as transudates or exudates. This classification is important because the differential diagnosis and subsequent evaluation for each entity is vastly different (Table 9–25). A pleural exudate is an effusion that has one or more of the following laboratory features: (1) ratio of pleural fluid protein to serum protein greater than 0.5; (2) ratio of pleural fluid LD to serum LD greater than 0.6; (3) pleural fluid LD greater than two-thirds the upper limit of normal serum LD. Pleural transudates occur in the setting of normal capillary integrity and demonstrate none of the laboratory features of exudates. A transudate suggests the absence of local pleural disease; characteristic laboratory findings include a glucose equal to serum glucose, pH between 7.40 and 7.55, and fewer than 1000 white blood cells/mcL (1.0 × 109/L) with a predominance of mononuclear cells.
Heart failure accounts for 90% of transudates. Bacterial pneumonia and cancer are the most common causes of exudative effusion. Other causes of exudates with characteristic laboratory findings are summarized in Table 9–26.
Table 9–26.Characteristics of important exudative pleural effusions. ||Download (.pdf) Table 9–26. Characteristics of important exudative pleural effusions.
|Etiology or Type of Effusion ||Gross Appearance ||White Blood Cell Count (cells/mcL) ||Red Blood Cell Count (cells/mcL) ||Glucose ||Comments |
|Malignancy ||Turbid to bloody; occasionally serous ||1000–100,000 M ||100 to several hundred thousand ||Equal to serum levels; < 60 mg/dL in 15% of cases ||Eosinophilia uncommon; positive results on cytologic examination |
|Uncomplicated parapneumonic ||Clear to turbid ||5000–25,000 P ||< 5000 ||Equal to serum levels ||Tube thoracostomy unnecessary |
|Empyema ||Turbid to purulent ||25,000–100,000 P ||< 5000 ||Less than serum levels; often very low ||Drainage necessary; putrid odor suggests anaerobic infection |
|Tuberculosis ||Serous to serosanguineous ||5000–10,000 M ||< 10,000 ||Equal to serum levels; occasionally < 60 mg/dL ||Protein > 4.0 g/dL (may exceed 5 g/dL); frequently lymphocyte predominant (> 50%); eosinophils (> 10%) or mesothelial cells (> 5%) make diagnosis unlikely; see text for additional diagnostic tests |
|Rheumatoid ||Turbid; greenish yellow ||1000–20,000 M or P ||< 1000 ||< 40 mg/dL ||Secondary empyema common; high LD, low complement, high rheumatoid factor, cholesterol crystals are characteristic |
|Pulmonary infarction ||Serous to grossly bloody ||1000–50,000 M or P ||100 to > 100,000 ||Equal to serum levels ||Variable findings; no pathognomonic features |
|Esophageal rupture ||Turbid to purulent; red-brown ||< 5000 to > 50,000 P ||1000–10,000 ||Usually low ||High amylase level (salivary origin); pneumothorax in 25% of cases; effusion usually on left side; pH < 6.0 strongly suggests diagnosis |
|Pancreatitis ||Turbid to serosanguineous ||1000–50,000 P ||1000–10,000 ||Equal to serum levels ||Usually left-sided; high amylase level |
Pleural fluid pH is useful in the assessment of parapneumonic effusions. A pH less than 7.30 suggests the need for drainage of the pleural space. An elevated amylase level in pleural fluid suggests pancreatitis, pancreatic pseudocyst, adenocarcinoma of the lung or pancreas, or esophageal rupture.
Suspected tuberculous pleural effusion should be evaluated by thoracentesis with culture along with pleural biopsy, since pleural fluid culture positivity for M tuberculosis is low (less than 23–58% of cases). Closed pleural biopsy reveals granulomatous inflammation in approximately 60% of patients, and culture of three pleural biopsy specimens combined with histologic examination of a pleural biopsy for granulomas yields a diagnosis in up to 90% of patients. Tests for pleural fluid adenosine deaminase (approximately 90% sensitivity and specificity for pleural tuberculosis at levels greater than 70 units/L) and interferon-gamma (89% sensitivity, 97% specificity in a meta-analysis) can be extremely helpful diagnostic aids, particularly in making decisions to pursue invasive testing in complex patients.
Between 40% and 80% of exudative pleural effusions are malignant, while over 90% of malignant pleural effusions are exudative. Almost any form of cancer may cause effusions, but the most common causes are lung cancer (one-third of cases) and breast cancer. In 5–10% of malignant pleural effusions, no primary tumor is identified.
Pleural fluid specimens should be sent for cytologic examination in all cases of exudative effusions in patients suspected of harboring an underlying malignancy. The diagnostic yield depends on the nature and extent of the underlying malignancy. Sensitivity is between 50% and 65%. A negative cytologic examination in a patient with a high prior probability of malignancy should be followed by one repeat thoracentesis. If that examination is negative, thoracoscopy is preferred to closed pleural biopsy. The sensitivity of thoracoscopy is 92–96%.
The term paramalignant pleural effusion refers to an effusion in a patient with cancer when repeated attempts to identify tumor cells in the pleura or pleural fluid are nondiagnostic but when there is a presumptive relation to the underlying malignancy. For example, superior vena cava syndrome with elevated systemic venous pressures causing a transudative effusion would be “paramalignant.”
The lung is less dense than water and floats on pleural fluid that accumulates in dependent regions. Subpulmonary fluid may appear as lateral displacement of the apex of the diaphragm with an abrupt slope to the costophrenic sulcus or a greater than 2-cm separation between the gastric air bubble and the lung. On a standard upright chest radiograph (Figure 9–8), approximately 75–100 mL of pleural fluid must accumulate in the posterior costophrenic sulcus to be visible on the lateral view, and 175–200 mL must be present in the lateral costophrenic sulcus to be visible on the frontal view. Chest CT scans may identify as little as 10 mL of fluid. At least 1 cm of fluid on the decubitus view is necessary to permit blind thoracentesis. Ultrasonography increases the safety of thoracentesis and should be incorporated routinely by trained users.
Left pleural effusion. Frontal chest radiograph showing a meniscus-shaped density at the left costophrenic angle sulcus indicative of a moderate-sized pleural effusion. (Reproduced, with permission, from Lechner AJ, Matuschak GM, Brink DS. Respiratory: An Integrated Approach to Disease. McGraw-Hill, 2012.)
Pleural fluid may become trapped (loculated) by pleural adhesions, thereby forming unusual collections along the lateral chest wall or within lung fissures (eFigure 9–29). Round or oval fluid collections in fissures that resemble intraparenchymal masses are called pseudotumors. Massive pleural effusion causing opacification of an entire hemithorax is most commonly caused by cancer but may be seen in tuberculosis and other diseases.
A: Pleural effusion. The lateral border of the right hemithorax shows evidence of a loculated pleural effusion. To determine whether this effusion is indeed loculated, a decubitus film must be obtained. B: The decubitus view demonstrates that the fluid is not loculated.