000 Pleural Effusion

What is it:
- Pleural effusion refers to:
  - The accumulation of excess fluid in the pleural cavity,
  - resulting from an imbalance in fluid production and absorption.
- It may present as:
  - Transudative effusion (caused by systemic factors like increased hydrostatic pressure or decreased oncotic pressure).
  - Exudative effusion (caused by local factors such as inflammation, infection, or malignancy).
Etymology:
- Derived from the Greek word pleura (side or rib) and the Latin word effusio (to pour out), describing fluid accumulation in the pleural space.
AKA:
- Fluid in the pleural space, Pleural fluid accumulation.
How does it appear on each relevant imaging modality:
- Chest X-ray:
  - Classification of effusions:
    - Mild effusion: Blunting of the costophrenic angle; corresponds to fluid volumes of 200–300 mL.
    - Moderate effusion: Extends up to the hemithorax but spares the apices; corresponds to volumes of 500–1,000 mL.
    - Large effusion: Fills the entire hemithorax with mediastinal shift away from the effusion; corresponds to volumes >1,000 mL.
  - Supine view:
    - Veiling opacity: Diffuse increased density over the affected hemithorax caused by layering of fluid, often obscuring normal lung markings.
- Chest CT:
  - Classification of effusions (volumetric):
    - Mild effusion: Small fluid collections limited to the posterior costophrenic sulcus.
    - Moderate effusion: Fluid extends along the lateral pleural space but does not occupy the entire hemithorax.
    - Large effusion: Fluid occupies most or all of the pleural cavity with significant mediastinal shift.
  - Shape:
    - Free (non-loculated): Fluid layers in dependent portions of the pleural cavity.
    - Loculated: Encapsulated fluid collections within the pleural cavity;
      - Often visible with thickened pleura.
      - May demonstrate the split pleura sign: separation of visceral and parietal pleura due to inflammation or exudative processes.
  - Associated compressive atelectasis:
    - Seen as passive collapse of adjacent lung tissue caused by large effusions exerting pressure on the lung.
- Ultrasound:
  - Hypoechoic or anechoic fluid collection in the pleural space.
  - Can identify septations or loculations, especially in exudative effusions.
These findings reflect:
- Systemic factors (transudative effusion):
  - Congestive heart failure (most common cause).
  - Cirrhosis (hepatic hydrothorax).
  - Nephrotic syndrome (low oncotic pressure).
- Local factors (exudative effusion):
  - Infection:
    - Parapneumonic effusion: Occurs adjacent to bacterial pneumonia; can progress to complicated effusion or empyema if untreated.
    - Tuberculosis.
  - Inflammation:
    - Rheumatoid arthritis or lupus pleuritis.
  - Neoplasm:
    - Primary lung cancer or metastatic disease.
  - Trauma:
    - Hemothorax or chylothorax.
Differential diagnosis:
- Transudative causes:
  - Congestive heart failure.
  - Hypoalbuminemia (e.g., cirrhosis, nephrotic syndrome).
  - Constrictive pericarditis.
- Exudative causes:
  - Parapneumonic effusion or empyema.
  - Malignancy (e.g., mesothelioma, metastatic cancer).
  - Tuberculosis.
  - Connective tissue diseases (e.g., rheumatoid arthritis, lupus).
- Special types:
  - Hemothorax: Blood in the pleural space.
  - Chylothorax: Milky lymphatic fluid, often due to thoracic duct injury.
Recommendations:
- Perform thoracic ultrasound for bedside evaluation and to guide thoracentesis.
- Analyze pleural fluid via thoracentesis to classify effusion as transudative or exudative (Light’s criteria).
- Use Chest CT to assess loculations, pleural thickening, associated compressive atelectasis, and lung abnormalities.
- Treat underlying causes (e.g., diuretics for heart failure, antibiotics for infection).
- Monitor parapneumonic effusions closely to identify progression to empyema, which may require chest tube drainage.
Key points and pearls:
- Transudative effusions are typically bilateral and associated with systemic conditions like heart failure or cirrhosis.
- Exudative effusions often require further evaluation for infection, malignancy, or inflammatory diseases.
- Loculated effusions may show the split pleura sign and require advanced imaging or interventions for diagnosis and drainage.
- Large effusions may cause compressive atelectasis, leading to dyspnea.
- Parapneumonic effusions adjacent to pneumonia should be treated promptly to prevent progression to empyema.