What is the etiology, clinical features, diagnosis, and management of parapneumonic effusion?

Parapneumonic Effusion: Etiology, Clinical Features, Diagnosis, and Management

Etiology

Parapneumonic effusions occur most frequently with bacterial pneumonia, affecting 2-12% of children with community-acquired pneumonia and up to 50% of cases caused by typical bacteria including S. pneumoniae, S. pyogenes, and S. aureus. 1

• In previously well children, effusions are usually secondary to acute bacterial pneumonia, with S. pneumoniae being the predominant pathogen 1
• M. pneumoniae causes effusions in up to 20% of cases, and viral pneumonias in 10%, though these rarely require intervention 1
• The pathophysiology follows three progressive stages: exudative (clear fluid, low WBC, normal glucose), fibropurulent (fibrin deposition with septation/loculation), and organizational (pleural peel formation) 2, 3

Clinical Features

Key clinical features include prolonged fever despite antibiotic therapy, chest pain, and abdominal pain—all strongly associated with parapneumonic effusion. 1, 2

• Physical examination reveals dullness to percussion, diminished breath sounds, and altered quality of breath sounds/transmitted speech over the effusion 1
• Patients are typically more unwell than those with simple pneumonia, presenting with persistent high fever despite appropriate antibiotics 4
• Pleuritic chest pain is common, and patients may lie on the affected side to splint the hemithorax 4
• Unilateral decreased chest expansion and possibly scoliosis may be observed 4

Diagnosis

Chest radiography with lateral decubitus views should confirm the presence of pleural fluid; if uncertainty exists, chest ultrasound is preferred over CT due to lack of ionizing radiation. 1, 2

Imaging Approach:

• Look for obliteration of the costophrenic angle or meniscus sign of fluid ascending the lateral chest wall on chest radiograph 4
• Ultrasound must be used to confirm pleural fluid presence, assess for loculations, and guide any thoracentesis or drain placement 2, 4
• If patient remains febrile or unwell 48 hours after admission, parapneumonic effusion must be actively excluded through repeat chest radiography 4

Pleural Fluid Analysis:

• Gram stain and bacterial culture should be performed whenever pleural fluid is obtained (positive in up to 49% of cases, though most report <25%) 1
• All non-purulent, possibly infected effusions require pleural fluid pH assessment 2
• PCR and antigen testing increase pathogen detection (42-80% of samples) and are useful for management 1
• WBC count with differential helps differentiate bacterial from mycobacterial, fungal, or malignancy etiologies 1

Classification (British Thoracic Society):

• Simple parapneumonic effusion: pH >7.2, LDH <1000 IU/L, glucose >2.2 mmol/L, negative culture—resolves with antibiotics alone 2
• Complicated parapneumonic effusion: pH <7.2, LDH >1000 IU/L, may have positive culture—requires chest tube drainage 2
• Empyema: frank pus, WBC >50,000/μL, may have positive culture—requires chest tube drainage 2

Management

The size of the effusion and the child's degree of respiratory compromise are the two most important factors determining management. 1

Size-Based Algorithm:

Small effusions (<10mm rim on lateral decubitus or <1/4 hemithorax):

• Treat with antibiotics alone without drainage 1, 4
• All small effusions in one series recovered uneventfully without requiring drainage 1

Moderate effusions (1/4 to 1/2 hemithorax):

• In absence of mediastinal shift, only 27% required drainage 1
• Majority can be managed successfully without pleural drainage 1
• Monitor closely; only 1 child required readmission for drainage in one series 1

Large effusions (>1/2 hemithorax):

• 66% ultimately required pleural drainage 1
• Drain any effusion meeting at least one criterion: loculations present, pH <7.2, glucose <60 mg/dl, positive Gram stain/culture, or purulent appearance 2, 4

Drainage Methods:

• Frankly purulent or turbid/cloudy pleural fluid on sampling mandates prompt chest tube drainage 2
• Image-guided catheter placement is safe and highly effective in select patients 5
• Intrapleural fibrinolytic agents remain controversial but may have a role in early complicated, loculated effusions 6, 7
• Surgical options (VATS or thoracotomy) are reserved for failed medical management 5, 6

Antibiotic Therapy:

• Complicated infections with effusions/empyema may require therapy for >10 days 1
• Some experts treat appropriately drained effusion 7-10 days after fever resolution, others recommend up to 4-6 weeks 1
• Clinical improvement should occur within 48-72 hours; if not, further investigation is required 1

Follow-Up:

• Children should be followed until complete recovery and chest radiograph returns to near normal 1
• Prognosis in children is usually very good with complete recovery and normal lung function 4
• Secondary scoliosis is common but transient; no specific treatment required but resolution must be confirmed 1