Pneumatocoele

Pneumatocoeles are intrapulmonary air-filled cystic spaces that can have a variety of sizes and appearances. They may contain air-fluid levels and are usually the result of ventilator-inducted lung injury in neonates or post-pneumonic. They should not be mistaken for a cavitating lung mass

Although pneumatoceles are seen in all age groups, they are most frequently encountered in infancy 1

The majority of pneumatocoeles occur as a result of pneumonia (post pneumotic pneumatocoele). The causative agents include:

  • Staphylococcus aureus (most common)
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Escherichia coli
  • group A streptococci
  • Klebsiella pneumoniae
  • adenovirus
  • primary pulmonary tuberculosis

In addition to infection, pneumatococele are also seen in a number of other settings including:

  • trauma - usually blunt trauma
  • positive pressure ventilation, especially in preterm neonates 4
  • hydrocarbon ingestion

Three main theories have been put forward to explain the formation of pneumatocoeles 1:

  1. Pulmonary overinflation caused by transient bronchial/bronchiolar obstruction and a ball-valve effect.
  2. Drainage of necrotic lung parenchyma with subsequent enlargement secondary to a ball-valve effect.
  3. Focal collections of air within the pulmonary interstitium following inflammation and necrosis of airway wall and fistula formation with the pleura.

Pneumatocoeles are typically asymptomatic and, if secondary to pneumonia, remain visible after septic symptoms have resolved 1. Occasionally pneumatoceles become large enough to compress adjacent lung and the mediastinum enough to cause respiratory or cardiovascular symptoms. 

Secondary infection may occur resulting in features of chest septis. 

When mature, pneumatoceles appear as thin walled cystic spaces within the lung parenchyma, containing air. However, it is important to remember that as they usually occur in the setting of infection, their appearance may vary, depending on the stage at which they are imaged. 

They tend to appear within the first week of infection and have usually resolved by week six.

If they are imaged during formation, they may have surrounding consolidation and be difficult to distinguish from abscess. Some features make the diagnosis of a pneumatocoele more likely than abscess 1:

  • smooth inner margins
  • contain little if any fluid
  • wall (if visible) is thin and regular
  • persist despite absence of symtpoms

Post-pneumonic pneumatocoeles tend to spontaneously resolve providing the infection is adequately treated with antibiotics.  Surgical intervention is only required if the pneumatocoele causes symptoms because of mass-effect or if it ruptures into the pleural space resulting in pneumothorax.

Complications
  • a rupture of a pneumatocoele may cause pneumothorax 3
  • secondary infection - secondarily infected pneumatocele 5

The differential is generally that of cavitating lung masses and other air containing lung lesions. 

In an older patient, the differential diagnosis for a cavitating lung lesion include:

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Article Information

rID: 15516
System: Chest
Section: Gamuts
Synonyms or Alternate Spellings:
  • Pneumatocoeles
  • Pneumatocele
  • Pneumatoceles

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