What is the recommended initial imaging modality for suspected pneumothorax (collapsed lung)?

Imaging for Pneumothorax: Diagnostic Approach

The initial imaging modality of choice for suspected pneumothorax should be lung ultrasound due to its superior sensitivity (79-85.7%) compared to chest radiography (31.8-71.4%) and excellent specificity (95-100%). 1

Initial Diagnostic Algorithm

1. First-line imaging: Lung ultrasound

   • Advantages:
     • Higher sensitivity (78.6%) compared to chest X-ray (39.8%) 2
     • Excellent specificity (98.4%) 2
     • Can be performed at bedside during resuscitation 1
     • Avoids patient transport and radiation exposure 3
   • Diagnostic criteria:
     • Absence of lung sliding, B-lines, and lung pulse
     • Presence of lung point (pathognomonic for pneumothorax) 1

2. Second-line imaging: Posteroanterior (PA) and lateral chest radiography

   • Indicated when:
     • Ultrasound expertise is unavailable
     • Documentation purposes
     • Monitoring known pneumothorax over time 1
   • Technical considerations:
     • PA and lateral views have significantly greater sensitivity (83.9%) than single-view AP radiographs (67.3%) 4
     • Use upright positioning when possible 4
     • Lateral decubitus radiograph is superior to erect or supine radiograph when findings on PA radiograph are unclear 4

3. Third-line imaging: CT scan

   • Indicated when:
     • Ultrasound and X-ray findings are equivocal
     • Evaluation of underlying lung pathology is needed
     • Differentiation from bullous lung disease is required 4, 1
     • Precise measurement is needed for research purposes 1

Size Assessment

• Pneumothorax size classification:

  • Small: visible rim <2 cm between lung margin and chest wall
  • Large: visible rim >2 cm between lung margin and chest wall 4

• Ultrasound assessment:

  • Lung point detection can differentiate between small and large pneumothorax
  • Mapping technique can determine physical limits of pneumothorax on chest wall 1

Special Considerations

• Primary vs. Secondary Pneumothorax:

  • Even small pneumothoraces may have significant implications in secondary pneumothorax (with underlying lung disease) 4
  • Lateral or lateral decubitus radiographs are valuable in suspected secondary pneumothoraces with unclear PA findings 4

• Symptomatic Patients:

  • Breathless patients should not be left without intervention regardless of pneumothorax size on imaging 4
  • Clinical symptoms in secondary pneumothoraces are often more severe than those in primary pneumothoraces 4

• Bullous Lung Disease:

  • CT scanning will differentiate emphysematous bullae from pneumothoraces in patients with severe bullous lung disease 4
  • This distinction prevents unnecessary and potentially dangerous aspiration 4

Common Pitfalls and Limitations

• Chest Radiography Limitations:

  • Underestimates pneumothorax size 4
  • Lower sensitivity, especially in supine patients 1
  • Most missed pneumothoraces occur in patients with coexistent lower lobe consolidation 4

• Ultrasound Limitations:

  • False positives can occur due to lung bullae, contusions, and adhesions 1
  • Technical limitations with subcutaneous emphysema, severe obesity, or extensive chest wall injuries 1

• CT Scan Limitations:

  • Resource-intensive
  • Requires patient transport
  • Higher radiation exposure
  • More time and cost 1

By following this evidence-based approach to pneumothorax imaging, clinicians can achieve faster diagnosis, reduce radiation exposure, and improve patient outcomes through prompt and appropriate management.