Pneumatocele

Pneumatoceles are air-filled cystic structures that commonly appear in the lungs following infection, trauma, or mechanical ventilation. These lesions are often incidental findings on chest imaging, meaning they are not the cause of your symptoms. This article will discuss the causes, imaging appearance and mimics of pneumatoceles.

Imaging Characteristics of Pneumatocele

Pneumatocele is diagnosed through imaging, with chest X-ray and CT scans being the most useful modalities. These lesions appear as thin-walled, air-filled cysts that can range from a few millimeters to several centimeters in size. Unlike other cystic lung diseases, pneumatoceles do not have thickened walls or solid components unless complicated by secondary infection or hemorrhage.

Chest X-Ray Findings of Pneumatocele

Chest X-rays are often the first imaging modality used to detect pneumatocele. The typical findings include:

Round or oval air-filled cavities:  These lesions are usually well-defined and may appear solitary or multiple.

Thin walls: Unlike lung abscesses, pneumatoceles have thin, non-enhancing walls.

Location in affected lung segments: In infectious causes, they often develop in regions previously affected by pneumonia.

Shifting size: Size may change over time, especially in ventilated patients, due to dynamic air trapping.

CT Scan Features of Pneumatocele

CT imaging provides a more detailed evaluation of pneumatocele, allowing differentiation from other lung lesions such as bullae, cysts, and abscesses. Key findings include:

Well-demarcated, air-filled lesions with smooth margins.

No significant wall thickening unless superimposed infection is present.

Multiple lesions in post-infectious cases.

Compression of adjacent lung tissue, especially in larger pneumatocele.

Associated findings such as consolidation, ground-glass opacities, or pleural effusion.

Ultrasound in Pneumatocele Diagnosis

Ultrasound can be useful in pediatric cases where radiation exposure is a concern. While not the primary imaging modality, lung ultrasound may demonstrate an anechoic (air-filled) structure with surrounding lung consolidation in cases of infected pneumatocele.

Common Causes of Pneumatocele on Imaging

Pneumatocele can result from various conditions, each with distinct imaging patterns. Recognizing the underlying cause is important for accurate diagnosis and management.

Infectious Pneumatocele

Infections are the most common cause of pneumatocele, especially in children. Imaging may show:

Post-pneumonic pneumatoceles: Typically seen in bacterial pneumonia, particularly with Staphylococcus aureus, Streptococcus pneumoniae, and Klebsiella pneumoniae.

Multiple pneumatoceles in one lobe: can be seen with staphylococcal pneumonia.

Coexisting consolidation and pleural effusion: Suggests an ongoing infectious process.

In my practice, I often encounter pneumatocele as a residual finding in patients recovering from severe pneumonia.  These pnematoceles can be monitored with imaging over time.

Traumatic Pneumatocele

Blunt or penetrating chest trauma can lead to pneumatoceles due to alveolar rupture. On imaging, these lesions may present as:

Solitary, well-defined air cavities in regions of lung contusion.

Surrounding hemorrhage or consolidation, depending on injury severity.

Air-fluid levels if secondary infection or hematoma formation occurs.

Ventilator-Induced Pneumatocele

Patients on mechanical ventilation, particularly those with neonatal respiratory distress syndrome (RDS) or acute respiratory distress syndrome (ARDS), are at risk of developing pneumatocele due to high airway pressures. Imaging findings include:

Bilateral, irregular air-filled cysts in ventilated lung regions.

Association with bronchopulmonary dysplasia (BPD) in neonates.

Progression or resolution depending on ventilation adjustments.

Differentiating Pneumatocele from Other Cystic Lung Lesions

Pneumatoceles must be distinguished from other air-filled lung lesions to avoid misdiagnosis. CT imaging plays an important role in differentiation.

Pneumatocele vs. Pulmonary Bullae

Pneumatoceles are transient and usually post-infectious, while bullae are chronic and associated with emphysema.

Bullae have very thin, imperceptible walls, whereas pneumatoceles may have slightly thicker walls.

Pneumatocele vs. Lung Abscess

Pneumatocele walls are thin and non-enhancing, while abscesses have thick, enhancing walls with a necrotic center.

Air-fluid levels are more common in abscesses due to liquefied debris.

Pneumatocele vs. Congenital Pulmonary Airway Malformation (CPAM)

CPAM is usually diagnosed in infancy and has multiple cystic components, whereas pneumatoceles arise after infection or trauma.

CPAM lesions do not resolve spontaneously, unlike pneumatocele.

When to Follow Up on Pneumatocele

While many pneumatocele cases resolve on their own, follow-up imaging may be needed in certain scenarios:

Persistent pneumatocele beyond six months- To rule out chronic lung disease.

Increasing size over time- Suggests air trapping or secondary infection.

Development of thick walls or air-fluid levels- Indicates possible abscess formation.

Conclusion

Pneumatoceles are thin walled cysts that are most commonly seen after infection, trauma, or mechanical ventilation. Chest X-ray and CT are the primary imaging tests for diagnosis, distinguishing them from other cystic lung lesions. While most pneumatoceles resolve without treatment, radiologists must monitor for complications such as infection. Accurate interpretation of imaging findings plays an important role in guiding clinical management.

References

1.https://www.ncbi.nlm.nih.gov/books/NBK556146/

2.https://www.jtcvs.org/article/S0022-5223(03)00367-2/fulltext

3.https://radiopaedia.org/articles/pneumatocele-1?lang=us