Pleural Effusion and Its Causes

Study Notes

Pleural effusion occurs when over 200 ml of fluid accumulates in the pleural space.
Typically, the fluid is seen as a unilateral blunting of the costophrenic angle on a chest X-ray.
Pleural effusion may appear with homogeneous density and a meniscus-shaped margin (meniscus sign) on a chest X-ray.
Large effusions can displace structures from the abdomen to the thorax.

Transudative effusions result from increased hydrostatic pressure or decreased oncotic pressure.

Hypoalbuminemia, or low serum albumin, can cause decreased oncotic pressure. Causes include:
- Nephrotic syndrome
- Liver disease
- Malnutrition

Common causes include:
- Congestive heart failure
- Cirrhosis
- Nephrotic syndrome
- Hypothyroidism

Empyema is an accumulation of pus in the pleural cavity.
- Etiology
  - Most common cause is pneumonia.
  - Less common causes include:
    - Infected hemothorax
    - Ruptured lung abscess
    - Esophageal tear
    - Thoracic trauma
- Classification
  - Stage I (exudative): Accumulation of fluid and pus.
  - Stage II (fibrinopurulent): Aggregation of fibrin deposits that form septations and pockets within the pleural cavity.
  - Stage III (organizing): Formation of thick fibrous peel on the pleural surface that restricts lung movement.
- Clinical features:
  - Fever
  - Chills
  - Cough
  - Chest discomfort
- Diagnosis:
  - Chest X-ray:
    - Opacity with:
      - Meniscus sign
      - Lenticular shape
      - Diffuse consolidation of adjacent lung
  - Ultrasound: Heterogeneous fluid collection
  - Chest CT: Distinctive appearance of empyema fluid
  - Pleural fluid analysis:
    - Exudative effusion:
      - Grossly purulent appearance
      - Positive Gram stain and bacterial culture
      - pH < 7.2
      - Low glucose (< 30-60 mg/dL)
Loculated pleural collection: A localized area of fluid accumulation within the pleural space.