What is the workup for a small right pleural effusion?

Diagnostic Workup for Small Right Pleural Effusion

The initial workup for a small right pleural effusion should begin with a chest radiograph followed by thoracic ultrasound to confirm the effusion, with subsequent CT chest with IV contrast if the etiology remains unclear after initial assessment. 1

Initial Imaging Approach

• Chest radiography is the first-line imaging modality, capable of detecting >75 mL of fluid on lateral view and >175 mL on frontal view 1
• Thoracic ultrasound should follow as it can detect smaller effusions (>20 mL) and provides real-time assessment of the effusion's characteristics 1
• CT chest with IV contrast is recommended when the etiology remains unclear after initial assessment, as it is considered the reference standard for imaging pleural effusions and can detect as little as 10 mL of fluid 1

Laboratory Evaluation

• Thoracentesis should be performed for new and unexplained pleural effusions to distinguish between transudate and exudate using Light's criteria 2, 3
• For exudative effusions, pleural fluid should be analyzed for:
  • Cell count and differential 2
  • pH (values <7.2 suggest infection, rheumatoid arthritis, malignancy, or esophageal rupture) 2
  • Glucose (levels <3.3 mmol/L suggest empyema, rheumatoid disease, tuberculosis, malignancy) 2
  • Amylase (elevated in pancreatitis, esophageal rupture, or malignancy) 2
  • Microbiological studies including cultures 3
  • Cytology for malignant cells 3

Diagnostic Algorithm Based on Clinical Context

If Recent Pneumonia is Present:

• Consider parapneumonic effusion or empyema 1
• CT chest with IV contrast is recommended, ideally with images acquired 60 seconds after contrast administration to optimize pleural visualization 1
• Look for specific CT findings: pleural enhancement (84% sensitivity), pleural thickening (68% sensitivity), loculation (52% sensitivity), and extrapleural fat changes 1

If Malignancy is Suspected:

• CT chest with IV contrast is recommended for suspected malignant pleural effusion 1
• Pleural fluid cytology should be performed, which identifies malignant cells in approximately 60% of malignant effusions 2
• If cytology is negative but suspicion remains high, consider pleural biopsy 1, 3

If Tuberculosis is Suspected:

• Pleural fluid analysis for acid-fast bacilli (positive in only 10-20% of cases) 1
• Pleural fluid culture (positive in 25-50% of cases) 1
• Pleural biopsy for histology and culture improves diagnostic yield to about 90% 1
• Consider measuring adenosine deaminase (ADA) levels in pleural fluid 1

If Pulmonary Embolism is Suspected:

• No specific pleural fluid characteristics distinguish PE-related effusions 1
• Maintain high clinical suspicion as small effusions are present in up to 40% of PE cases 1
• 80% of PE-related effusions are exudates and 80% are bloodstained 1

Special Considerations

• Small right-sided effusions may be incidental findings and require clinical correlation 1
• Parapneumonic effusions <2.5 cm in anteroposterior dimension can often be managed without thoracentesis 1
• Misclassification of cardiac and liver transudates as exudates occurs in 25-30% of cases; serum-effusion albumin gradient >1.2 g/dL can help reclassify an effusion as a transudate when heart failure is suspected 2
• NT-proBNP levels >1500 μg/mL in serum or pleural fluid can accurately diagnose heart failure-related effusions 2

Common Pitfalls to Avoid

• Failing to consider common causes: heart failure, malignancy, pneumonia, and pulmonary embolism are the most frequent etiologies 4
• Neglecting to obtain thoracic ultrasound before thoracentesis, which improves safety and diagnostic yield 1
• Overlooking drug-induced pleural effusions, particularly with newer medications like tyrosine kinase inhibitors 1
• Inadequate follow-up of small effusions, as some conditions (like benign asbestos pleural effusion) require prolonged monitoring 1