Pleural Effusion

Definition and Clinical FeaturesTop

Pleural effusion results from an imbalance between fluid formation and resorption within the pleural space. It may be transudative or exudative. Pleural effusion may be asymptomatic or manifest with dyspnea, trepopnea (dyspnea sensed while lying in one lateral position but not the other), orthopnea, cough, or chest pain, depending the on underlying conditions and degree of fluid accumulation. Signs of pleural effusion and differential diagnosis: see Table 1 in Respiratory Sounds. Diagnosis is based on results of imaging studies (chest radiographs, computed tomography [CT], ultrasonography) and analyses of pleural fluid. Also see Thoracentesis.

DiagnosisTop

If history and physical examination are suggestive of pleural effusion (decreased breath sound with dullness on percussion and reduced vocal and tactile fremitus), further investigations are required to confirm the diagnosis. Posteroanterior chest radiography should be performed in the assessment of pleural effusion. Pleural effusions ≥200 mL normally exhibit an abnormal opacity with decreased lung volume on chest radiographs, but effusions of as little as 50 mL can cause blunting of the costophrenic angle. Ultrasonography is the gold standard investigation to diagnose a pleural effusion. It detects fibrin and septations within the pleural space with greater sensitivity than CT. It also increases the success rate of thoracentesis while minimizing procedure-related complications. Chest CT with contrast is useful in the evaluation of exudative pleural effusions, providing additional findings that may be suggestive of a malignant effusion, mesothelioma, complications of lung infection (parapneumonic effusion, empyema), and vascular or lymphatic obstruction.

Pleural fluid analysis is critical in characterizing the type of pleural effusion and guiding further investigations. Pleural effusion may appear serous, serosanguinous, bloody, purulent, or milky. Some presentations are associated with specific conditions, such as putrid purulent fluid in anaerobic empyema, milky fluid in chylothorax or pseudochylothorax, and bile-stained fluid in biliary-pleural fistula. Results of pleural fluid analysis are used to categorize pleural effusion as transudative and exudative using Light’s criteria (Table 1), which are highly sensitive for an exudative process (sensitivity, 98%; specificity, 83%). Pleural fluid differential cell counts are helpful in the differential diagnosis but not disease specific (Table 2). Neutrophil-predominant effusions are associated with acute processes, while effusion related to malignancy, tuberculosis, and cardiac failure are commonly lymphocytic. However, any long-standing pleural effusion over time tends to become populated by lymphocytes. Fluid cytology should be done in all patients with exudative effusions to evaluate for malignancy. Gram stain and culture should be considered for a newly diagnosed effusion. It should be noted that while some pleural effusions are always exudative (eg, tuberculosis), misclassification of transudates from hepatic and cardiac sources as exudates is relatively frequent and can appear in up to 30% of cases.

TablesTop