What is parapneumonic effusion?

Parapneumonic Effusion

A parapneumonic effusion is a pleural fluid collection that occurs in association with an underlying pneumonia, representing the early stage in a continuum of pleural infection that progresses through exudative, fibropurulent, and organizational stages. 1

Definition and Pathophysiology

Parapneumonic effusions are part of the spectrum of pleural infections associated with pneumonia:

• They occur in approximately 40% of patients with pneumonia 1
• The incidence in children is about 3.3 per 100,000, with higher frequency in winter and spring 1
• They occur most frequently with bacterial pneumonia, present in 50% of cases due to typical bacteria including S. pneumoniae, S. pyogenes, and S. aureus 2
• Less commonly seen in viral (10%) and Mycoplasma pneumoniae (20%) infections 2

Clinical Presentation

Patients with parapneumonic effusion typically present with:

• Classic symptoms of pneumonia: cough, dyspnea, fever, and malaise 1
• Pleuritic chest pain 1
• Physical examination findings:
  • Decreased chest expansion on affected side
  • Dullness to percussion
  • Reduced or absent breath sounds 1
  • SpO₂ <92% indicating severe disease 1

In children specifically, prolonged fever, chest pain, and abdominal pain have all been associated with parapneumonic effusion 2.

Diagnosis

Imaging

1. Chest radiography - First-line imaging modality 1

   • May show obliteration of costophrenic angle and meniscus sign
   • Lateral decubitus views help confirm presence of pleural fluid 2

2. Ultrasound - Preferred for further evaluation 2, 1

   • Confirms presence of pleural fluid
   • Estimates size of effusion
   • Differentiates free from loculated fluid
   • Detects septations
   • Safer than CT in children (no radiation) 2

3. CT scan - Reserved for diagnostic difficulties 1

   • Shows "split pleura sign" in empyema
   • Pleural thickening seen in 86-100% of empyemas

Pleural Fluid Analysis

All parapneumonic effusions should be aspirated for diagnostic purposes 3. Analysis may show:

• Frank pus (empyema)
• Positive culture
• Low pH (<7.20 in complicated effusions)
• High LDH
• Low glucose levels (<60 mg/dl in complicated effusions) 1, 3

Classification

Parapneumonic effusions are classified based on progression:

1. Uncomplicated (simple) parapneumonic effusion

   • Early exudative phase
   • pH >7.20
   • Glucose >60 mg/dl
   • No loculations
   • Small to moderate size 4

2. Complicated parapneumonic effusion

   • Fibropurulent phase
   • pH <7.20
   • Glucose <60 mg/dl
   • Positive Gram stain or culture
   • Loculations present 3, 4

3. Empyema

   • Organizational phase
   • Presence of pus in pleural space
   • Advanced stage of pleural infection 1

Management

Management depends on the classification of the effusion and the degree of respiratory compromise:

Size-Based Management 2

• Small effusions (<10 mm rim of fluid on lateral decubitus or less than one-fourth of hemithorax opacified)

  • Usually respond to antibiotics alone
  • Rarely require drainage

• Moderate to large effusions (more than half of hemithorax opacified)

  • More likely to cause respiratory compromise
  • Often benefit from drainage (66% of large effusions require drainage)

Treatment Approach

1. Antibiotics

   • Required for all parapneumonic effusions 1
   • Options include:
     • Second-generation cephalosporins or aminopenicillins with beta-lactamase inhibitors
     • Addition of metronidazole for anaerobic coverage
     • Clindamycin as an alternative single agent
   • Avoid aminoglycosides (poor penetration into pleural space) 1

2. Drainage indications 3, 4

   • Any effusion that meets at least one criterion:
     • Size ≥1/2 of hemithorax
     • Loculations present
     • pH <7.20 or glucose <60 mg/dl
     • Positive Gram stain or culture
     • Purulent appearance (empyema)

3. Drainage methods

   • Therapeutic thoracentesis
   • Tube thoracostomy (chest tube)
   • Small-caliber chest tubes with ultrasound or CT guidance
   • Initial drainage limited to 10 ml/kg to avoid re-expansion pulmonary edema 1

4. Fibrinolytic therapy

   • Consider for loculated collections 1
   • Urokinase administered twice daily for 3 days
   • Dosage: 40,000 units in 40 ml saline for children ≥10 kg; 10,000 units in 10 ml saline for children <10 kg 1
   • Effectiveness remains controversial 3

5. Surgical intervention

   • Video-assisted thoracoscopic surgery (VATS)
   • Thoracotomy with decortication
   • Indicated when drainage methods fail 4

Prognosis

The prognosis in children with parapneumonic effusions is generally excellent:

• Most make complete recovery with normal lung function
• Chest radiographs return to normal in 60-83% by 3 months, over 90% by 6 months 1
• Potential complications (rare in children):
  • Bronchopleural fistula
  • Lung abscess
  • Empyema necessitatis
  • Thrombocytosis
  • Secondary scoliosis (usually transient) 1

Common Pitfalls to Avoid

1. Failing to consider parapneumonic effusion in patients with pneumonia who aren't improving
2. Relying on clinical features alone to determine need for drainage
3. Delaying drainage when indicated
4. Not obtaining pleural fluid analysis when indicated 1
5. Not recognizing that patients should demonstrate clinical improvement within 48-72 hours of appropriate therapy 2